United States Office of Water and SW 176C.2
Environmental Protection Waste Management October 1979
Agency Washington, D.C. 20460
Solid Waste
&EPA European Refuse-Fired
Energy Systems
Evaluation of Design Practices
Volume 2
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Prepublioation issue for EPA libraries
and State Solid Waste Management Agencies
EUROPEAN REFUSE-FIRED ENERGY SYSTEMS
Evaluation of Design Practices
Volume 2
This report (SW-176C.2) describes work performed
for the Office of Solid Waste under contract no. 68-01-4376
and is reproduced as received from the contractor.
The findings should "be attributed to the contractor
and not to the Office of Solid Waste.
Copies will be available from the
National Technical Information Service
U.S. Department of Commerce
Springfield, VA 2216T
U.S. ENVIRONMENTAL PROTECTION AGENCY
1979
U.S. Environmental Prct^ct:on AC«T.:V
nc,;:Dn V, L- t
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This report was prepared by Battelle Columbus Laboratories, under contract
no. 68-01-4376.
Publication does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of commercial products constitute endorsement by the U.S. Government.
An environment protection publication (SW-176C.2) in the solid waste
management series.
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PREFACE
These documents are a two volume evaluation of European refuse -
fired energy systems design practices, which is a condensation and
analysis of trip reports describing visits in 1977 to fifteen (15)
European refuse fired steam and hot water generators. Interspersed
are Garments about another fifteen (15) plants for which official trip
reports were not prepared, i.e., a total of thirty (30) resource recovery
plants were visited. In addition, visits to five (5) federal environmental
protection agencies have provided additional insight to solid waste
management trends, legislation and perspectives on resource recovery
technologies.
The material in the reports describing the visits to the fifteen
(15) plants has been reviewed by the European system vendors and their
respective American licensees. The two volume evaluation report has
also been reviewed, but the comments of the various reviewers has not
been incorporated in the text. Rather, their comments are presented
in toto in the appendix to Volume II.
Battelle Columbus Laboratories maintains ultimate responsibility
for report content. The opinions set forth in this report are those
of the Battelle staff members and are not to be considered EPA policy.
There may be sane minor errors and certainly differences of opinion
in the report, but these do not take away from the usefullness of the
document.
The intent of the report is to provide decision making information.
The reader is thus cautioned against believing that there is enough
information to design a system. Some proprietary information has
been deleted at the request of vendors. While the contents are detailed,
they represent only the tip of the iceberg of knowledge necessary to
develop a reliable, economical and environmentally beneficial system.
The selection of particular plants to visit was made by Battelle,
the American licensees, the European grate manufacturers, and EPA.
Purposely, the sampling is skewed to the "better" plants that are models
of what the parties would like to develop in America. Some plants were
selected because many features evolved at the plant. Others were
chosen because of strong American interest in co-disposal of refuse
and sewage sludge.
The two volumes plus the trip reports for the 15 European plants
are available through the National Technical Information Source,
Springfield, Virginia, 22161. Of the 17 volumes, only the Executive
Summary has been prepared for wide distribution.
111
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ACKNOWLEDGEMENTS
The project owes much of its success to the many European vendors,
plant personnel, city officials, and European environmental protection agency
staff who opened up so fully to the visiting Battelle team. It is an
established fact that Europe is far advanced over America in commercialization
of the refuse-fired, steam- and hot-water generation tecnnology. This fact and
the accompanying pride of accomplishment are likely causes for the excellent
cooperation we received and outpouring of valuable information from visited
European professionals. Frankly, the amount of information freely provided has
amazed and challenged these researchers. The authors hope that we have been
able to summarize accurately the data provided.
Our appreciation is also extended to the EPA staff of David
Sussman--Pro j ect Officer, Steve Levy — Program Manager, and to Steve
Lingle—Chief of Technology and Markets Branch.
The detailed listing of the many names, organizations and addresses
is to be found in Part II. Each person and organization should realize that
they have contributed to the advancement of solid waste management in America.
IV
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ORGANIZATION OF REPORT
The report consists of twenty three chapters in two volumes.
Chapter A, The Executive Summary and Chapter B, The Inventory of Waste
to Energy Systems are being published by the Office of Solid Waste
for wide distribution. The Executive Summary and Inventory are also
included in the tv» volume set, which is available through NTIS.
Volume I contains information relating to the implementation of
the systems, whereas \folume II contains technical information about
the units themselves. The paragraphs in the Executive Summary follow
the same format.
v
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INTRODUCTION
Background
Since 189'
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Objective
The general objective of the project was to gather information about
European waste-to-energy practice and to interpret this experience as it may be
comnercially practicable in the U.S. The subobjectives are listed as follows:
1. Report on actual technical, economic, environmental, and social
experience in application of the European technologies of (1)
integrated water tube wall furnace/boiler and (2) refractory wall
furnace/waste heat boiler.
2. Aid American decision makers and engineers in utilization of the
successful experience of their European counterparts.
3. Describe in a technical manner how successful operations are
achieved and how unsuccessful operations are avoided.
4. Prepare Report — "Evaluation of European Refuse-Fired Energy
Systems Design Practices".
5. Prepare 15 Trip Reports describing systems visited.
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The geographic scope as clearly indicated in the title is Europe.
However, there will be frequent references to systems in America and comments
about other countries. For example, Japan has the greatest number of
refuse-fired energy generating units (^3) of any country in the world; with an
installed capacity of 27,000 tons per day.
Several solid waste management topics are discussed. Some are beyond
the original contract scope but are presented to give the reader a better
perspective of the total picture. The refuse to energy systems are as follows:
Water-tube wall furnace/integrated boiler
Refractory wall furnace/waste heat boiler
Vertical shaft pyrolysis
Other type
include:
Refuse transfer stations
Hazardous waste transfer stations
Landfilling
Composting
Rendering
Pathological incineration
Waste water treatment
Environmental, Energy and Industrial Parks.
The chronological scope begins in 1876 when the first refuse to
electricity system was built in Hamburg, West Germany.
The scope of processing capacity described ranges from the 120 tonne
(132 ton) per day single line facility at Werdenberg-Liechtenstein to the large
1,630 tonne (1,793 ton) per day four line system at Paris: Issy-les-Moulineaux.
The energy uses scope includes use of hot air, hot water, superheated water,
steam, superheated steam and electricity.
Vlll
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CONTENTS
DISCLAIMER i
DIGEST AND MAJOR CONCLUSIONS ii
PREFACE iii
ACKNOWLEDGEMENTS iv
ORGANIZATION v
INTRODUCTION vi
OBJECTIVE vii
SCOPE viii
TABLE OF CONTENTS ix
LIST OF TABLES xvii
LIST OF FIGURES xviv
A. EXECUTIVE SUMMARY AND CONCLUSIONS A-1
Executive Summary A-1
Development of the Refuse Fired Energy Generator Technology. ... A-1
Description of Communities Visited A-3
Locations Visited A-3
Collection Areas and Jurisdictions A-5
Terrain, Natural and Manmade Boundaries, Neighborhoods A-5
Population A-5
Separable Waste Streams A-5
Household, Commercial and Light Industrial Refuse A-10
Bulky and Large Industrial Wastes A-10
Wastewater and Sewage Sludge A-10
Source Separation A-10
Front-End Separation A-12
Waste Oils and Solvents A-12
Industrial Chemicals and Hazardous Wastes A-13
Animal Waste A-13
Street Sweepings A-13
Construction, Demolition Debris, and Ash A-13
Junk Automobiles A-14
Refuse Collection and Transfer Stations A-14
Household Containers A-14
Collecting Organization A-14
Collection Costs A-14
Assessment Methods A-15
Vehicles A-15
Collecting Times A-15
Homeowner Deliveries to Refuse Burning Plant A-15
Industrial and Bulky Waste Collection Activity Affecting
Resource Recovery A-15
Transfer Stations A-16
Composition of Refuse A-16
Physical Composition of Refuse A-16
ix
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CONTENTS (Continued)
Moisture Content A-16
Heating Value of Refuse A-16
Definitions and Calculations A-16
General Comments on Refuse Heating Values A-18
Refuse Generation and Burning Rates Per Person A-18
Total Operating System A-23
Energy Utilization A-23
District Heating (D.H.) A-25
District Cooling A-28
Underground Distribution , A-28
Relation of Refuse as a Fuel in the Long Term Community Plan for
Community Electrical Power, District Heating and Cooling . . . A-28
Energy Marketing and Standby Capacity A-32
Economics and Finance A-36
Capital Investment Costs A-36
Initial Capital Investment Cost per Daily Ton A-39
Expenses A-^2
Revenues A-46
Net Disposal Costs or Tipping Fees A-50
Personnel Categories A-53
Education, Training and Experience A-53
Finance A-53
System Ovnership and Governing Patterns A-53
Refuse Handling A-54
Weighing of Refuse Received A-51*
Tipping Floor, Pit and Crane A-51*
Pit Doors A-56
Crane A-56
Bulky Waste: Size Reduction A-57
Hoppers and Feeders A-57
Grates and Primary Air A-57
Grate Life A-58
Grate Materials A-58
Grate Action A-58
Grate Functions A-63
Ash Handling and Recovery A-66
Ash Exit from Grate, Quenching and Removal from the Furnace. . . A-66
Ram for Residue Removal (Martin) A-68
Submerged Conveyor A-68
Spray Quench with Conveyor A-68
Furnace Wall A-68
Furnace Requirements A-68
Secondary (Overfire Air) A-70
Principles of Overfire Jets A-70
Boilers A-71
Overall Boiler Design A-71
Boiler Tube and Wall-Clening Methods A-75
Steam Condensers A-75
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CONTENTS (Continued)
Supplementary Firing of Fuel Oil, Waste Oil and Solvents A-?8
Co-Disposal of Sewage Sludge and Refuse A-83
Air Pollution Control Equipment A-83
Particulates A-83
Precipitator Maintenance A-87
Gases A-8?
Measured Gaseous Emissions . A-88
Gaseous Emissions Limits A-88
Trends in Emissions Control A-88
Start-Up and Shut-Down Procedures A-88
Conclusions A-88
World Wide Inventory of Waste-to-Energy Systems A-90
Communities and Sites Visited A-91
Separable Waste Streams A-91
Collections and Transfer Stations A-92
Composition of Refuse A-92
Heating Value of Refuse A-92
Refuse Generation and Burning Rates Per Person A-93
Development of Visited Systems A-93
Total Operating System A-95
Organization and Personnel A-96
Economics. . , A-96
Capital Investment A-96
Expenses, Revenues and Net Disposal Costs A-97
Refuse Handling A-98
Hoppers and Feeders A-99
Grates and Primary Air A-99
Furnace Wall A-100
Secondary (Overfire) Air A-100
Boilers A-101
Start-Up and Shut-Down A-103
Supplementary Firing and Co-Firing of Fuel Oil, Waste Oil,
Solvents and Coal A-104
Air Pollution Control A-104
B. WORLDWIDE INVENTORY OF WASTE-TO-ENERGY SYSTEMS B-1
Exclusions B-1
Number and Tonnage Capacity B-1
Energy Use Patterns B-3
Furnace Size Distribution B-9
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CONTENTS (Continued)
C. DESCRIPTION OF COMMUNITIES VISITED C-1
General Comments about About the Communities C-1
Collection Areas and Jusisdictions C-1
Terrain, Natural and Manmade Boundaries, Neighborhoods .... C-1
Population C-1
Specific Comments About the Communities C-5
Werdenberg-Liechtenstein through Copenhagen West C-5-25
D. SEPARABLE WASTE STREAMS D-1
General Comments D-1
Household, Commercial and Light Industrial Refuse D-1
Bulky and Large Industrial Wastes D-1
Wastewater and Sewage Sludge D-4
Source Separation D-4
Front-End Separation 0-4
Waste Oils and Solvents D-9
Industrial Chemicals and Hazardous Wastes D-9
Animal Waste D-9
Street Sweepings D-12
Construction, Demolition Debris, and Ash D-12
Junk Automobiles D-16
Interrelation of Waste Streams D-16
E. REFUSE COLLECTION AND TRANSFER STATIONS E-1
General Comments on Collection E-1
Household Containers E-1
Collecting Organization E-1
Collection Costs E-1
Assessment Methods E-5
Vehicles E-5
Collecting Times E-5
Homeowner Deliveries E-5
Collection Activity Affecting Resource Recovery E-5
Transfer Stations E-8
Specific System Comments on Collection E-8
Werdenberg-Liechtenstein through Copenhagen West E-8-16
F. COMPOSITION OF REFUSE F-1
Physical Composition of Refuse F-1
Moisture Content F-1
Chemical, Elemental and Molecular Composition of Refuse F-1
G. HEATING VALUE OF REFUSE G-1
Definitions and Calculations .... G-1
General Comments on Refuse Heating Values . . . G-3
xti
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CONTENTS (Continued)
Specific Comments on Systems' Heating Values G-3
Werdenberg-Liechtenstein through Copenhagen West G-3-10
H. REFUSE GENERATION AND BURNING RATES PER PERSON H-1
I. DEVELOPMENT OF THE REFUSE FIRED ENERGY GENERATION TECHNOLOGY
AND DEVELOPMENT OF VISITED SYSTEMS 1-1
DEVELOPMENT OF THE REFUSE FIRED ENERGY GENERATOR TECHNOLOGY
(1896 to 1982) 1-2
General Comments About Development of Visited Systems 1-3
Motivations and Decision Making 1-3
Main Purpose - Waste Disposal? or Energy Production 1-4
Stated Reasons for Development of Refuse Fired Energy Systems.1-4
Unstated Reasons 1-13
Specific Comments About Development of Visited Systems .... 1-14
Werdenberg-Liechtenstein through Copenhagen West . . . M . . 1-14-29
J. TOTAL OPERATING SYSTEM J-1
General Comments J-1
Total Operations at Visited Systems J-1
Baden-Brugg through Copenhagen West J-1-36
K. ENERGY UTILIZATION K-1
General Comments K-1
District Heating (D.H.) K-5
District Cooling (Not Observed in Europe) K-7
Underground Distribution K-15
Community Electrical Power District Heating and Cooling
Development K-15
Energy Utilization - Specific System Comments K-32
Werdenberg-Liechtenstein through Copenhagen West ....... K-32-76
L. ECONOMICS L-1
General Comments About the Capital Investment Costs L-1
Initial Capital Investment Cost Per Daily Ton L-1
Specific Comments About the Visited Systems' Capital Invest-
ment Werdenberg-Liechtenstein through Copenhagen West. . . . L-8-18
General Comments About Expenses L-18
Economies of Scale L-24
General Comments About Revenues L-27
Sale of Energy L-27
Sludge Drying Credit L-31
Sale of Scrap Iron and Road Ash L-31
Interest on Reserves L-31
Net Disposal Cost or Tipping Fee L-31
Specific Comments About Expenses and Revenues L-34
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CONTENTS (Continued)
Werdenberg-Liechtenstein through Copenhagen West L-34-72
M. ORGANIZATION AND PERSONNEL M-1
System Ownership and Governing Patterns M-1
Personnel Categories M-1
Education, Training and Experience M-5
Organization and Personnel at Visited Systems M-5
Werdenberg-Liechtenstein through Copenhagen West M-5-27
N. and 0. Chapters are reserved
VOLUME II
P. REFUSE HANDLING P-1
Weighing of Refuse Received-General Comment P-1
Derails on Specific Weighing Systems P-1
Werdenberg, Liechtenstein through Copenhagen West P-1-8
Tipping Floor, Pit and Crane General Comments P-10
Pit Doors P-10
Pit or Bunker P-12
Crane P-12
Plant Details on Receiving Storing and Feeding Refuse P-12
Werdenberg-Liechtenstein through Copenhagen West P-12-51
Q. GRATES AND PRIMARY AIR Q-1
General Comments Q-1
Grate Functions Q-1
Grate Life Q-5
Grate Materials Q-5
Grate Action Q-5
Specific Vendor Grates Q-8
Von Roll Grate Q-8
Kunstler Grate Q-12
Martin Grate Q-15
Widmer & Ernst Grate Q-17
VKW (Duesseldorf Grate or Walzenrost) Q-17
Bruun & Sorensen Grate Q-22
Volund Grate Q-2^4
R. ASH R-1
Ash Exit from Grate, Quenching and Removal from the Furnace. . R-1
Clinker Discharge Roll (Martin) R-3
Ram for Residue Removal (Martin) R-3
xiv
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CONTENTS (Continued)
Flyash Ash Handling (Martin and Others) R-6
Submerged Conveyor (Old Widmer and Ernst and Old Volund). . . . R-6
Additional Ram-Type Dischargers R-6
Spray Quench with Conveyor R-6
Ash Handling in the Plant, General Comments R-12
Ash Recovery, General Comments R-12
Ash Handling and Recovery at Specific Plants R-15
Werdenberg-Liechtenstein to Copenhagen West R-15-^2
Road Test Procedures R-51
Parking Lot and Road Test Results R-51
S. FURNACE WALL • . S-1
General Comments S-1
Furnace Requirements S-1
Werdenberg-Liechtenstein through Copenhagen West S-3-^8
T. SECONDARY (OVERFIRE) AIR T-1
General Comments T-1
Principles of Overfire Jets T-1
Werdenberg-Leichtenstein through Copenhagen West T-2-20
U. BOILERS U-1
What is a Boiler? U-1
Definition of Boiler Terms U-3
Summary of Boiler-Furnaces U-5
Overall Boiler Design U-5
General Boiler Designs U-6
Comments About Specific Boilers U-8
Werdenberg-Liechtenstein through Copenhagen West U-8-83
Metal Wastage (Corrosion and Erosion) of Boiler Tubes U-85
Experience with Fossil Fuels U-85
Experience with Refuse as Fuel U-85
Oxidation-Reduction Reactions U-85
Effect of Soot Blowing U-86
A Proposed Corrosion Mechanism U-86
Reasons for Minimal Tube Corrosion U-88
Steam Condensers U-90
Werdenberg-Liechtenstein through Gothenburg:Savenas U-90-9M
Steam-to-Refuse Ratio U-94
V. SUPPLEMENTARY FIRING OF FUEL OIL, WASTE OIL AND SOLVENTS V-1
Oil and Waste Oil Co-Firing - General Comments V-1
Oil and Waste Oil Co-Firing - Specific Comments V-3
Werdenberg-Lechtenstein through Copenhagen West V-3-10
xv
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CONTENTS (Continued)
W. CO-DISPOSAL OF SEWAGE SLUDGE AND REFUSE W-1
Co-Disposal, General Comments W-1
Co-Disposal, Comments About Specific Systems W-1
Krefeld through Copenhagen West W-1-25
X. AIR POLLUTION CONTROL X-1
Development of Emission Controls X-1
Particulates X-1
Precipitator Maintenance X-1
Gases X-1
Measured Gaseous Emissions X-3
Gaseous Emission Limits X-3
Trends in Emissions Control X-6
Specific Comments about Air Pollution Control at Plants Visited. X-6
Werdenberg-Liechtenstein through Copenhagen West X-6-34
Stack Sampling Methods X-31*
Y. START-UP AND SHUT-DOWN PROCEDURES Y-1
General Comments Y-1
Specific System Comments Y-2
Z. APPENDIX Z-1
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LIST OF TABLES
VOLUME I
Table A-1. Summary Data on the 15 Surveyed Plants Visited by Battelle
for the U.S. EPA Project on Waste-to-Energy. . . A-U
Table A-1a. Summary Data on the 15 Surveyed Plants Visited by Battelle
for the U.S. EPA Project on Waste-to-Energy A-6
Table A-2. Minor Visits (15) - Date, Location, Manufacture, Reasons
and, Comments Related to Battelle's Brief Visit to 15
Other Waste-to-Energy Facilities A-7
Table A-3. Description of 19 Offices Visited by Battelle While on Tour
of European Waste-to-Energy Facilities A-8
Table A-U. Collection Areas, Radius, Jurisdictions and Population . . . A-9
Table A-5. Separable Waste Streams Identifiable Within the Grates of
Refuse-Fired Energy Plants A-11
Table A-6. Composition of Municipal Solid Waste in Switzerland, USA,
and Britain A-17
Table A-7. Refuse Lower Heating Values: Assumption for Plant Design and
Actual A-20
Table A-8. Energy Values of Selected Refuse Components (Dry) A-21
Table A-9. European Average Refuse Generation and Burning Rates Per
Person (1976-1977 Period) A-22
Table A-10. Three Steps of Energy Form and Use at Visited European
Plants A-2U
Table A-11. Key Energy Functions of 15 Visited Systems A-25
Table A-12. Internal Uses and Losses of Refuse Derived Energy A-26
Table A-13. Attractiveness of District Heating as a Function of Density
of Energy Use(a) A-29
Table A-1U. Favorable Demand Aspects of District Heating and Cooling
Systems in the U.S.A A-30
Table A-15a. Summary of Capital Investment A-37
Table A-15b. Summary of Capital Investment (Continued) A-38
Table A-16. Exchange Rates for Six European Countries, (National Monetary
Unit Per U.S. Dollar) 1948 to February, 1978(a) A-^1
Table A-17. Summary of Expenses for 15 European Refuse to
Energy Systems A-43
Table A-18. Summary of Revenues from 15 European Refuse to Energy
Plants (U.S. 1976 $ Per Ton) A-U7
Table A-19. Gross Summary of Revenue From European Refuse-Fired Energy
Plants A-M8
Table A-20. Refuse Pit Storage Volume, Dimensions and Capacities .... A-55
Plants A-U7
Table A-21. Design Pressure of Primary Air System at Plants
Visited A-59
Table A-22. Grate Bar Replacement A-60
Table A-23. Grate Dimensions A-61
Table A-24. Grate Burning Rates A-62
Table A-25. Refuse Burning Manufacturing and Representatives A-65
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LIST OF TABLES (Continued)
Table A-26. Summary of Ash Handling and Recovery Methods, A-67
Table A-27. Secondary Air Systems , A-72
Table A-28. Data Regarding Cleaning of Heat-Transfer Surfaces in
Visited Refuse-Fired Steam and Hot-Water Generators . . . A-76
Table A-29. Methods Used to Clean Tubes and Walls of European Refuse-
Fired Energy Plants A-77
Table A-30. Boiler Furnace Design Conditions A-79
Table A-31. Boiler Release Rates A-80
Table A-32. Comparison of Energy Recovery A-8l
Table A-33- Use of Supplementary Fuels at 16 European Refuse Fired
Energy Plants A-82
Table A-34. Systems for Co-Disposal of Refuse and Sewage Sludge
Location, Manufacturer, Volume, and Process A-84
Table A-35. Characteristics of Electrostatic Precipitators A-85
Table A-36. Measured Gaseous Emission Rates at European RFSG A-86
Table A-37. Emission Limits, mg/Nm^ A-89
Table B-1. Summary of World-Wide Inventory Waste-to-Energy Systems
(1986 - 1983) B-2
Table B-2. Pounds of Municipal Waste Converted to Energy Per Person
Per Day by Country Capacity when Plants were Surveyed in
1977 B-1
Table B-3. U.S.A. Waste-to-Energy Systems Operatinng (Tonnes/Day). . . B-6
Table B-^. The World's Uses of Energy Produced by Municipal* Waste-
to-Energy Commercially Operating or Large Demonstration
Systems B-7
Table B-5. Number of Furnaces by Capacity and Country (Currently
Operating and Planned Expansion to 1982). , B-10
Table B-6. Battelle Inventory of Worldwide Waste-to-Energy Systems . . B-11
Table C-1. Collection Area and Radius , C-2
Table C-2. Terrain, Natural Boundaries, Highways, Neighborhoods. . . . C-3
Table C-3. Population of Visited Areas C-4
Table D-1. Waste Streams Treated Independently from the Main Refuse
Burning Waste Stream , D-2
Table E-1. Household Refuse Containers E-2
Table E-2. Refuse Collection E-3
Table E-3. Collection Costs and Assessment Method. . E-4
Table E-H. Collecting Times , E-7
Table F-1. Moisture Percentages in Refuse Combusted in Visited European
Refuse-to-Energy Plants F-2
Table F-2. Composition of Municipal Solid Waste in Switzerland, USA,
and Britian F-3
Table F-3. Composition of Municipal Waste at Hamburg: Stellinger-Moor. F-4
Table F-4. Refuse Composition at Thun, 1975 F-5
Table F-5. Approximate Composition of Municipal Solid Waste in Zurich
Switzerland F-6
Table F-6. Average Chemical Composition of Municipal Solid Waste in
Zurich Switzerland F-7
Table F-7. West Incinerator of Copenhagen Refuse Analysis F-8
xviii
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LIST OF TABLES (Continued)
Table G-1. Hydrogen Content and Calorific Values of Four Fuels. . . . G-2
Table G-2. Refuse Lower Heating Values: Assumption for Plant Design
and Actual G-5
Table G-3. Energy Values of Selected Refuse components (Dry) G-6
Table G-4. Heating Values for Mixed Municipal Refuse in Refuse Power
Plants G-9
Table H-1. Quoted Refuse Burning Rate on a 7-Day Basis (Does Not Include
Alternate Disposal Means H-2
Table H-2. European Average Refuse Generation and Burning Rates Per
Person (1976-1977 Period) H-3
Table 1-1. Stated Reasons Associated With Each Unit 1-5
Table 1-2. Rank Order Listing of Reasons Mentioned for Deciding to
Construct a Refuse to Steam or Hot Water Plant 1-9
Table 1-3. Matrix of Stated Reasons for Development of Refuse Fired
Energy Systems 1-10
Table J-1. Energy Generation Rates at Baden-Brugg for 1975 and 1976
(From Plant Statistical Statement) J-2
Table J-2. Baden-Brugg Weekly Operating Summary May 2 to July 4, 1976 J-3
Table J-3. Dusseldorf Waste-Burning Facility-Operating Results - 1976 J-5
Table J-4. Availability of Issy's Total System J-8
Table J-5. Gross Operating Figures for December 1976 and The Complete
Years 1976 and 1975 for Hamburg: Stellinger-Moor .... J-9
Table J-6. Detailed Operating Statistics for November 4, 1976 Boiler
Number 1 at Hamburg: Stellinger-Moor J-11
Table J-7. Detailed Operatinng Statistics for April 2, 1977 Boiler
Number 1 at Hamburg: Stellinger-Moor J-12
Table J-8. Comparison of Zurich-Hagenholz Incinerator Performance, 1974
Table J-9. Report of Operations 197^ and 1976 J-11
Table J-10. Refuse Burning Summary, The Hague, 1976 (Compared to 1975) J-20
Table J-11. The Hague Plant Annual Operating Results Over Seven Year
Period (Furnace 4 Began Operation Early 1974) J-21
Table J-12. Summary for 1976 of Refuse-Sludge Burning Plant Operation
at Dieppe. Tabulation Prepared by Plant Operators,
Thermical-Inor, in Fulfillment of Their Operating Contract
with the City J-23
Table J-13. Dieppe Wastewater Plant Summary for 1976. Tabulation
Prepared by Thermical-Inor, in Fulfillment of Their
Operating Contract With the City J-24
Table J-14. Annual Refuse Incinerator Operating Results for Dieppe
1972 -1976 J-25
Table J-15. 1976 Operating Results for Gothenburg: Savenas Plant . . . J-26
Table J-16. Gothenburg Savanas Annual Results 1974-1976 J-27
Table J-17. Operating Data for the Uppsala Energy System for 1975 and
1975 J-28
xlx
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LIST OF TABLES (Continued)
K-5
K-9
K-11
K-13
K-1H
Table K-1. Three Steps of Energy Form and Use at Visited European
Plants ,
Table K-2. Key Energy Functions of 15 Visited Systems ,
Table K-3. Heat Utilization From German Refuse Power Plants Start-up
During the 1960-1975 Period K-4
Table K-4. Internal Uses and Losses of Refuse Derived Energy
Table K-5. Attractiveness of District Heating as a Function of Density
of Energy Use
Table K-6. Specific Heat and Energy Numbers of Different Types of
Swedish Buildings
Table K-7. Favorable Demand Aspects of District Heating and Cooling
Systems in the U.S.A
Table K-8. Report on Operations Nashville Thermal Transfer Corporation
for the Twelve-Month Period Ending May 31, 1978
Table K-9. Steam Production, Losses, Sale and Availability K-U5
Table K-10. History of Electrical Production, Sales, Purchases and
Internal Consumption K-47
Table K-11. C.P.C.U. District Heating Uses, Production Capacity,
Climatological Conditions and Annual Actual Steam
Production
Table K-12. C.P.C.U. District Heating Network-Facts
Table K-13. C.P.C.U. Percent Distribution of Customers
Table K-14. Hamburg: Stellinger-Moor Total Operating Figures K-51*
Table K-15. Energy Produced by Savenas Plant in 1976 K-68
Table K-16. Typical Autumn Month Operation Data for Uppsala Heat Power
Company, October 1977
Table L-1. Summary of Capital Investment
Table L-2. Exchange Rates for Six European Countries-
Table L-3. Status of construction Expenditures - Wuppertal - as of
December 31, 1975
Table L-l». Capital Investment Cost (1969) for Units #1 and #2 and Other
Buildings at Zurich: Hagenholz L-14
Table L-5. Capital Investment Costs (1972) for Unit #3 and the Water
Deaeration Tanks and Room at Zurich: Hagenholz
Table L-6. Assets and Liabilities of Copenhagen: Amager as of March
31, 1976
Table L-7. Capital Cost (Assets and Liabilities) at Copenhagen: West
(Fiscal Year 1975-1976)
Table L-8. Detailed Expenses for 15 European Refuse to Energy Systems
(U.S. 1976 $ Per Ton)
Table L-9. Summary of Expenses for 15 European Refuse to Energy Systems
(U.S. 1976 $ Per Ton) L-23
Table L-10. Detailed Revenues of 15 European Refuse to Energy Plants
(U.S. 1976 $ Per Ton) L-28
K-49
K-50
K-51
K-72
L-2
L-5
L-11
L-15
L-19
L-20
L-21
-------
LIST OF TABLES (Continued)
Page
Table L-11. Summary of Revenues From 15 European Refuse to Energy Plants
(U.S. 1976 $ Per Ton) L-29
Table L-12. Gross Summary of Revenue from European REfuse Fired Energy
Plants L-27
Table L-13. Operations Results at Werdenberg-Liechtenstein for 1976. . . L-35
Table L-1U. Revenue Estimate for 1977 at Werdenberg L-36
Table L-15. Operating Results for 1976 at Baden-Brugg L-15
Table L-16. Costs of the Waste Burning Facility at Duesseldorf, 1975 . . L-39
Table L-17. Duesseldorf Revenues from Sale of Steam, Baled Scrap Steel
and Processed Ash in 1975 L-MO
Table L-18. Operating Results for Paris: Issy During 1976 L-42
Table L-19. Operating Results for 1976 at Hamburg: Stellinger-Moor and
Hamburg: Borsigstrasse Plants (MVA I + II) L-46
Table L-20. Annual 1976 Operating, Maintenance, Interest, and Other
Costs for Zurich: Hagenholz Units #1, #2, and #3 L-48
Table L-21. Annual 1976 Revenues for Zurich: Hagenholz Units #1, #2,
and #3 L-50
Table L-22. Operations Results for 1976 at The Hague L-52
Table L-23. Annual Invoice Billings From the Contract Operator Thermal-
INOR to the Dieppe Community for Operations and Maintenance
(1976 Results) L-54
Table L-2U. Operating Results for 1976 at Gothenberg L-55
Table L-25. Operations Results at Uppsala for 1976 Expenses and 1975
Revenues L-57
Table L-26. Operating Budget for Horsens Plant, 1977-1978 L-60
Table L-27. Annual Costs and Revenues at Copenhagen: Amager L-6l
Table L-28. Operations Results at Copenhagen: Amager (Refuse to Energy
and Landfill) Plant, Transfer Station L-62
Table L-29. Operations Results at Copenhagen: West (Vest) for 1975-1976. L-63
Table L-30. Modes of Finance for European Refuse-Energy Plants L-65
Table L-31. Financial Structure of 15 European Refuse-Fired Energy
Plants L-66
Table L-32. Financial Structure of 15 European Refuse-Fired Energy
Plants L-67
Table L-33. Financial Structure of 15 European Refuse-Fired Energy
Plants L-68
xxi
-------
LIST OF TABLES (Continued)
Table M-1. Ownership/Governing Patterns
Table M-2. Personnel Category Listing for Refuse Fired Energy Plants.
Table M-3. Outside Contracted Services Frequently Used
Table M-lJ. Staff Organizatioon at Stadtwerke Duesseldorf Waste-to-
Energy Plant
Table N. and 0. Chapters are reserved
Page
. M-2
M-3
M-6
M-10
VOLUME II
Table P-1. Refuse Pit Storage Volume, Dimensions and Capacties. ... P-13
Table Q-1. Refuse Burning Manufacturers and Representatives Q-3
Table Q-2. Grate Dimensions and Burning Rates Q-4
Table Q-3. Design Pressure of Primary Air System at Plants Visted . . Q-3
Table Q--4. Grate Bar Replacement Q-7
Table R-1. Summary of Ash Handling and Recovery Methods R-2
Table R-2. Disposition of Bottom Ash, Scrap Metal and Fly Ash at
Paris: Issy R-23
Table R-3. Population, Refuse and Ash in and Around Zurich R-24
Table R-U. Analytical Values of Trace Elements in the Percolate . . . R-55
Table R-5. Element Composition of Soil and Cinders (All Analyses made
on Dry Material) R-57
Table R-6. Comparison of Analyses of Percolate from Depot 1 in
Vestskoven and Percolate, Drain Water, and Surface Run-
Off from Parking Lot in Ballerup R-58
Table S-1. Wall Tube Thickness Measurements of Screen Tubes at the
Rear of the Radiation First Pass at Hamburg:Stellinger-
Moor S-31
Table S-2. Wall Tube Thickness Measurements of Screen Tubes at the
Rear of the Radiation First Pass at HamburgrStellinger-
Moor S-33
Table S-3. Boiler Furnace Design Conditions S-47
Table T-1. Secondary Air Systems T-3
Table T-2. Primary, Secondary, Flue Gas and Recirculation Fan
Parameters at Copenhagen:Amager T-23
Table U-1. Composition of Sicromal Steel Used for Shielding Tubes
from Hot Corrosive Gases U-23
Table U-1a. Flue Gas Temperatures, CO Levels, and Steam Flow Rates
Recorded on June 9, 1977 at Zurich: Hangeholz Unit #3 • U-28
xxii
-------
LIST OF TABLES (Continued)
Table U-2. Superheater Tube-Materials Used U-51
Table U-3. Comparison of Energy Recovery U-77
Table U-4. Methods used to Clean Tubes and Walls of European Refuse-
Fired Energy Plants U-78
Table U-5. Comparison of Energy Recovery U-97
Table V-1. Use of Supplementary Fuels at 16 European Refuse Fired
Energy Plants V-2
Table W-1. Co-Disposal of Refuse and Sewage Sludge Location, System
Vendor and American Licensee W-2
Table W-2. Co-Disposal Unit Operation Moisture Conditions W-3
Table W-3. Sludge Drying Mill Design Conditions for Waste of Three (3)
Lower Heating Values W-10
Table W-4. Results of Calculation by Krings of Heat Balance for Dieppe
Plant W-16
Table W-5. Approximate composition and Lower Heat Value of Some
Typical Raw Sewage Sludges According to Eberhardt. ... W-17
Table W-6. Summary for 1976 of Refuse-Sludge Burning Plant Operation
at Dieppe W-20
Table W-7. Dieppe Wastewater Plant Summary for 1976 W-21
Table W-8. Annual Refuse Incinerator Operating Results for Dieppe -
1972-1976 W-22
Table X-1. Characteristics of Electrostatic Precipitators X-2
Table X-2. Measured Gaseous Emission Rates at European RFSG X-4
Table X-3. Emission Limits, mg/Nm3 X-5
Table X-4. Results of Two Performance Tests by TUV on a Precipitator
at the Duesseldorf Refuse Plant X-9
Table X-5. Precipitator Design Characteristics at Wuppertal X-12
Table X-6. Characteristics of the Two Krefeld Precipitators X-15
Table X-7. Paris-Issy Air Pollution Test Results X-18
Table X-8. Performance Test Data on Precipitator No. 2 Serving Furnace
No. 4 X-27
Table X-9. Results of Gaseous Emission Measurements from Original
Three Furnaces at Uppsala (April 23, 1974) X-28
xxxii
-------
LIST OF FIGURES
VOLUME I
Figure A-l. Annual Average Lower Heating Vaules for Berne, Stockholm,
Frankfurt, The Hague and Duesseldorf and Range of Value
for Other Cities A-19
Figure A-2. Connected and Specific Capacities in Europe A-27
Figure A-3. Steam Distribution and Return Condensate Pipes at
Werdenberg A-31
Figure A-4. Steam Distribution and Return Condensate Pipes at Paris. . A-31
Figure A-5. Hot Water Pipes at Werdenberg A-31
Figure A-6. Hot Water Pipes at Uppsala A-31
Figure A-7. Total Energy Plan Built up in Five Stages A-33
Figure A-8. Heat Load Duration Curve and Load-Split. Heat Only Package
Boilers Used (1) for Peaking, (2) When There is not Enough
Refuse Supply or (3) When Energy Demand is too Low . . . A-31*
Figure A-9. Heat Produced by Each Unit for the Optimum Case in the
Long Range Plan for District Heating Supply in the
Stockholm Area Using Oil, Refuse and Nuclear Power . . . A-35
Figure A-10. Capital Cost Per Daily Ton Capacity A-UO
Figure A-ll. Total Annual Expenses Versus Annual Tonnage A--44
Figure A-12. Net Disposal Cost or Tipping Fee at 13 European Refuse
Fired Energy Plants , A-49
Figure A-13. Basic Types of Grates for Mass Burning of Refuse A-6U
Figure A-14. Dacha Type Superheater and Boiler Convection Arrangement
for Proposed Stapelfeld Plant at Hamburg A-74
Figure B-l. Pounds of Waste Processed in Refuse-Fired Energy Generators
Per Capita Per Day in Selected Countries B-5
Figure C-1. Refuse Generation Showing the Service Areas in the Canton of
of St. Gallen and in Liechtenstein C-6
Figure C-2. Profile of Plant Surrounded by Mountains C-7
Figure C-3. View of Baden-Brugg 200 Tonne Per Day Plant From the
Adjacent Sewage Treatment Plant Property C-8
Figure C-4. Area in Aargau Canton Served by Duesseldorf Plant C-10
Figure C-5. Waste Collection Area Served by Duesseldorf Plant C-11
Figure C-6. Region Served by Wuppertal MVA C-12
Figure C-7. Krefeld Waste Processing Facility; Wastewater Treatment
Plant on Left, Refuse and Sewage-Sludge-Burning Plant
on Right C-13
Figure C-8. Waste Generation Area and Treatment Plants for the Paris,
France Plants that Treat Urban Waste C-15
Figure C-9. Location of Stellinger Moor Plant C-16
xxiv
-------
LIST OF FIGURES (Continued)
Figure C-10. The Hague Plant Situated Near the Center of The Hague
The Four Chimneys in the Background Serve the 200 MW
Oil-Fired Municipal Power Plant C-18
Figure C-11. Collection Area for Gothenburg Waste Handling System
Total Area Served is About 1000 km2 C-20
Figure C-12. Map of Aera Served by Horsens Refuse-Burning, Sludge-Drying
and District-Heating Plant C-22
Figure C-13. Aerial View of Horsens Refuse-Burning Plant, Sludge-
Drying and District-Heating Plant C-23
Figure C-14. Copenhagen: Amager Plant Located on Canal C-24
Figure C-15. Detailed Map Showing Location of West Plant at the
Intersection of Two Major Highways C-26
Figure C-16. Map of Copenhagen, South and East Metropolitan Area
Served by the Amager Plant C-27
Figure C-17. Map of Greater Copenhagen Area Showing the Location of
the West (Vest) Refuse Fired Steam Generator, The
Hillerod Transfer Station, Volund Headquarters, Etc . C-28
Figure D-1. Transfer Station Under Construction at Amager D-3
Figure D-2. Source Separation Recycling Station at Copenhagen:
West D-5
Figure D-3. White Goods, Bicycles, Etc., Reclamation at the
Hague (Battelle Photo) D-6
Figure D-4. Front End Separation of Cooper-Rich Motors and Tires in
Scrap Dealer's Area at the Hague (Battelle Photo) . . D-7
Figure D-5. Crushing White Goods After Motor Removal in Scrap
Area at the Hague (Battelle Photo) D-8
Figure D-6. Ferrous Material Bin in Corner of Tipping Floor at
Uppsala (Battelle Photo) D-10
Figure D-7. Industrial Chemical and Hazardous Waste Collection Center
at Horsens D-11
Figure D-8. Horizontal Ventilation Air Pipe From Rendering Plant to
Zurich :Hagenholz Plant D-13
Figure D-9. Street Sweeping Truck Off-Loading at The Hague D-14
Figure D-10. Front and Back End Materials Separation at The Hague. . D-15
Figure D-11. Automobile Junk Yard Next to Refuse Burning Plant at
Horsens D-17
Figure D-12. Waste Streams and Their Treatment Options in Copenhagen
and Its Western Suburbs D-18
xxv
-------
LIST OF FIGURES (Continued)
Figure E-1. Transfer Vehicle. The cylinderical Chamber Holds About
50m3 (1,675 ft3) Compressed at the Transfer Station
by a Factor of About 3.3 to 1 E-6
Figure E-2. Public Relations Cartoon of Oscar (of Sesame Street)
Encouraging People to Put All Trash in the Containers . E-11
Figure E-3. Cross Section and Plan View of Transfer Station E-14
Figure G-1. Annual Average Lower Heating Values for Berne, Stockholm,
Frankfurt, The Hague and Duesseldorf and Range of
Values for Other Cities G-4
Figure G-2. Shredder and Shear Layout at Duesseldorf G-7
Figure 1-1. Artist Sketch of the 1904 Refuse Fired Steam and Electricity
Electricity Generator as Manufactured by
Horsfall-Destructor Co. at Its Location
Location on Josefstrasse in Zurich 1-20
Figure 1-2. First Volund System Built at Gentofte in 1932 and
Decommissioned 40 Years Later in 1973 1-28
Figure J-1. Steam Production, Flue Gas Temperatures, and C02 Levels
(Weekly Average) During the 4000 Hour Operating Cycle
Between Cleaning at Zurich: Hagenholz Unit #3 J-17
Figure J-2. Steam Production, Flue Gas Temperatures, and C02 Levels
(Weekly Average) During the 4000 Hour Operating Cycle
Between Cleaning at Zurich: Hagenholz Unit #3 J-18
Figure J-3- Arrangement of Components of Bolanderna Incinerator Plant . J-31
Figure J-4. Total (Three Lines) Operation Hours Per Month J-32
Figure J-5. Taken From an Article Written By Gabriel S. Pinto in April
1976, that Discusses Basic Design of the Total Operating
System at Copenhagen: West J-34
Figure K-1. Connected ans Specific Capacities in Europe K-6
Figure K-2. Schematic Showing How a Central District Heating System
Compares in Efficiency With Individual Home Heating
Systems K-8
Figure K-3. Building HVAC System Survey K-10
Figure K-4. Maximum Hourly Heat Demand Average Monthly Heat Demand. . . K-12
xxvi
-------
LIST OF FIGURES (Continued)
Figure K-5a. Steam Distribution and Return Condensate Pipes at
Werdenberg K-16
Figure K-5b. Steam Distribution and Return Condensate Pipes at Paris . K-16
Figure K-5c. Hot Water Pipes at Werdenberg K-16
Figure K-5d. Hot Water Pipes at Uppsala K-16
Figure K-6. Conventional Hot Water Distribution Pipes K-17
Figure K-7a. Concrete Culvert K-18
Figure K-7b. Plastic Pipe Culvert K-18
Figure K-7c. Asbestos Cememt Pipe Culvert K-18
Figure K-7d. Copper Pipe Culvert K-18
Figure K-8. Design of the Trench When the Pipe is Insulated With
Mineral Wool K-19
Figure K-9. Design of the Trench When the Pipe is Insulated With Wirsbo-
Pur (Polyethylene Pipe) K-19
Figure K-10. Wirsbo-Pex Polyethylene Pipe and Wirsbo-Per Insulation Pre-
fabricated Parts at a Junction Box K-19
Figure K-11. Several Figures of the Aquawarm System of Polyethylene
Encased Copper Pipe K-20
Figure K-12. Asphalt Concrete Coated District Heating Pipe by
TK-ISOBIT K-21
Figure K-13. Total Energy Plan Built Up in Three Stages K-23
Figure K-11. Staged Development of District Heating in Sodertalje. . . K-24
Figure K-15. Annual Capital Investment of the City of Sodertalje
Energy Authority K-25
Figure K-16. Two Schemes Showing How Customer Systems Can Be Converted
to Hot Water District Heating K-26
Figure K-17. Portable Oil-Fired District Heating Sub Station K-27
Figure K-18. Portable Oil-Fired Fire-Tube Boiler K-27
Figure K-19. Original and permanent Standby Oil-Fired District Heating
Boiler Building K-28
Figure K-20. Heat Load Duration Curve and Load-Splie. Heat Only Package
boileer Used (1) for Peaking, (2) When There is not Enough
Refuse Supply or (3) When Energy Demand is Too Low. . . K-29
Figure K-21. Schematics of Simple Power Station and a Cogeneration
Electricity and District Heating System K-30
Figure K-22. Useful Energy and Losses of Simple Power Generation
Compared with Cogeneration K-30
Figure K-23. Fuel Economy in Condensing Plant and Combined Plant . . . K-31
xxvn
-------
LIST OF FIGURES (Continued)
Page
Figure K-24. Heat Produced by Each Unit for the Optimum Case in the
Long Range Plan for District Heating Supply in the
Stockholm Area Using Oil, Refuse and Nuclear Power. . . . K-33
Figure K-25. Werdenberg Steam and Hot-Water Distribution System
(Courtesy Widmer & Ernst, Alberti-Fonsar) K-34
Figure K-26. Standby Oil-Fired Package Boiler at Werdenberg K-35
Figure K-27. Back Pressure Turbine at Werdenberg K-35
Figure K-28. Steam Distribution Trench at Werdenberg K-36
Figure K-29. Two Views of Air-Cooled Condenser at Werdenberg K-37
Figure K-30. Cascade Type Water Heater on Left, Feedwater Tank and Steam
Lines on Right at Werdenberg K-39
Figure K-31• Insulation, Installation and map of Hot Water Electrical
Systems K-40
Figure K-32. Schematic Diagram of Baden-Brugg Thermal and Electrical
Systems K-41
Figure K-33. Steam and Return Condensate Lines Connecting Duesseldor's
Refuse-Fired Steam Generator and the Coal-Fired Electrical
Power Plant K-43
Figure K-3^. Steam Distribution and Return Condensate Pipes of C.P.C.U.
in Paris K-52
Figure K-35. Steam Produced TIRU (Solid Waste Fueled) and by C.P.C.U.
(Fossiled Fueled) in Paris K-53
Figure K-36. Diagrams Thermal and of Electrical Systems at Stellinger-
Moor K-56
Figure K-37. Electrical Power Generation Room K-58
Figure K-38. Steam and Boiler Feedwater Flow Pattern External to the
Zurich: Hagenholz Boiler K-58
Figure K-39. Tonne Steam Produced Per Tonne of Refuse Consumed (1976
Average was 2.41) K-59
Figure K-40. KWH Electrical Sales Per Tonne of Refuse Consumed K-59
Figure K-41. 1976 Heat Deliver to Kanton and Rendering Plant and Steam
to EWZ From Zurich: Hagenholz K-61
Figure K-42. Kanton District Heating System (5.3 km Long) Using 260 C
(500 F) Steam at Zurich, Switzerland K-62
Figure K-43. Entrance to Walk-Through District Heating Tunnel at Zurich:
Hagenholz K-63
Figure K-44. Cross-Section Schematic of Pipes in the District Heating
Supply and Return Tunnel at Zurich: Hagenholz K-64
xxvxii
-------
LIST OF FIGURES (Continued)
Page
Figure K-45. 1976 Energy Delivery (Warmeabgabe) to the Railroad
Station, the KZW and EWZ K-65
Figure K-46. Monthly Trend for 1976 of Heat Production and Utilization
in Gothenburg (Courtesy GRAAB). ...... K-69
Figure K-M7. Schematic of Uppsala Heating System (Courtesy Uppsala
Kraftvarme AB) K-71
Figure K-U8. Installation of Hot Water Distribution Piping (Courtesy
Uppsala Kraftvarmewerke AB) K-73
Figure K-49. Copenhagen: Amager's Refuse Fired Energy Plant in the
Foreground and the Oil Fired Plant in the Background. . K-75
Figure K-50. Insulated Hot Water Pipes Leaving Boiler at Amager. . . . K-77
Figure K-51. Pumps to Send Hot Water to the Power Plant Which Sends the
Hot Water to the District Heating Network at Amager . . K-77
Figure K-52. Map of District Heating Network of Amager Island K-77
Figure K-53. Energy Delivery to the District Heating Network K-78
Figure K-51*. Map Showing District Heating Customers K-80
Figure K-56. District Heating Pipe Tunnel at Copenhagen: West .... K-82
Figure L-1. Reasons for 10-Fold Increase in Capital Investment Costs
Over 10 Years for European Refuse Fired Energy Systems. L-4
Figure L-2. Comparison of European, American and Co-Disposal Systems. L-7
Figure L-3. Total Annual Expenses Versus Annual Tonnage L-25
Figure L-H. Expenses Per Tonnage (U.S. $ Per Ton) Versus Annual Tonnes
(1976 Exchange Rate) L-26
Figure L-5. Net Disposal Cost for Tipping Fee at 13 European Refuse-Fired
Energy Plants L-30
Figures L-6.
and L-7. Unit Prices for Electricity and Steam in Paris TIRU . . . L-44
Figure L-8. Revenue and.Expense Components for the Four TIRU Plants . L-45
Figure L-9. Costs of Zurich Cleansing Department Since 1928 L-^9
Figure L-10. Past and Predicted Trend of Net Operating Cost of Refuse
Burning Plant After Credit is Taken for the Value of
Heating Recovered L-58
Figure M-1. Organization Chart for Operation of Werdenberg Plant. . . M-8
Figure M-2. Wuppertal Organization Chart M-12
Figure M-3. Organization Chart of TIRU in Paris M-14
Figure M-4. Organization Chart for Hamburg: Stellinger-Moor M-15
Figure M-5. Organization Chart for Municipal Functions in the City of
Zurich: Switzerland M-16
XXIX
-------
LIST OF FIGURES (Continued)
Figure M-6. Organization Chart for Waste Collection and Disposal in
Zurich, Switzerland M-17
Figure M-7. Total Personnel (Collecting and Disposal) Working for
ABFUHRWESEN: The City of Zurich M-19
Figure M-8. Control Room at Savenas Plant M-22
Figure M-9. Management Structure of Copenhagen:Amager M-24
Figure M-10. Annual General Meeting Participants M-25
VOLUME II
Figure P-1. Layout of Flingern Refuse Power Plant at Duesseldorf. . . P-3
Figure P-2. Map of Wuppertal Plant P-4
Figure P-3. Two Partial Views of the Receiving Area at the Issy Plant
Showing the Scale House at the Unloading Platform . . . P-5
Figure P-*». Top View of Savenas Waste-to-Energy Plant Showing Traffic
Pattern, Weigh Stations and Distinctive Square 4-FLue
Chimney. Only three Flues in Use. Chimney Equipped with
Two-passenger Elevator at Gothenburg P-7
Figure P-5a. Scale House and Two Scales P-9
Figure P-5b. Plastic Card P-9
Figure P-5c. Monitor in Control Room of Truck Scale P-9
Figure P-5d. Digital Readout in Scale House P-9
Figure P-5e. Ramp to Tipping FLoor P-9
Figure P-5f• Tipping Floor P-9
Figure P-5g. Arrangement Permitting Good Crane View P-9
Figure P-6. Residences Viewed Through Truck Entrance at Deauville
Plant (Battelle Photograph) P-11
Figure P-7. Overall Section Inside the Werdenberg Plant (Courtesy
Widmer & Ernst-Alterti-Fonsar) P-14
Figure P-8. Truck Delivering Haste to the Pit at Baden-Brugg The
Pit Doors are Hydraucially Opened (Courtesy Region
of Baden-Brugg) P-16
Figure P-9. Crane Operator, Cranes and Graabs above Pit (Courtesy
Region of Baden-Brugg) P-17
Figure P-10. Main Storage Pit. There are two Crane Operators Operating
Pulpit for one is at Upper Left at Duesseldorf (Courtesy
Vereinigte Kesselwerke AG) P-18
xxx
-------
LIST OF FIGURES (Continued)
Figure P-11. New Polyp Bucket Being Prepared for Installation P-19
Figure P-12. Cross-Section of Boiler Systems, 1-3 The Hague P-24
Figure P-13- Crane Operator's Cabin at the Hague Plant with Empty
Furnace Hopper and a Portion of the Floor Plate of the
Vibrating Feeder in the Foreground P-25
Figure P-14. Mirror above a Furnace Hopper to Enable Crane Operator to
Determine when the Hopper Needs to be Replenished -
The Hague Plant P-26
Figure P-15. Polyp Bucket Dropping a Charge of Municipal Refuse into a
Furnace Hopper at the Hague Plant P-27
Figure P-16. Transfer Truck in Unloading Position at the Gothenburg
Savenas Plant P-29
Figure P-17. Refuse Pit with 2 of the 14 Doors Open to Receive Refuse '
at the Gothenburg Savenas Plant P-30
Figure P-18. Truck Entrance Ramp to Uppsala. This was Added in 1971 to
Enable Operation with a Much Deeper Bunker Which More Than
Doubled Refuse Storage Capacity P-32
Figure P-19. Photo Shows Polyp Grab with Heavy Concentration of
Plastic Waste from the Separate Commercial and Light
Industrial Waste Pit at Horsens P-33
Figure P-20a. Von Roll Shear Opening at Zurich P-34
Figure P-20b. Scissors-Type Hydraulicly Driven Shear Adjacent to
Hopper H P-34
Figure P-21. Elevation and Plan Views of Von Roll Shear P-36
Figure P-22. Furnace/Boiler Cross-Sectional View of the Zurich:
Hagenholz Unit #3 13 Martin's Double Feeder P-40
Figure P-23. Water Cooled Arch Connecting Feed Chute to Combustion
Chamber at Baden-Brugg P-42
Figure P-24. Cross Section of One of Boilers No. 1-4 P-43
Figure P-25. Arrangement of Uppsala Plant P-49
Figure P-26. Empty Feed Hopper Showing Line of Flame Beneath Double
Flap Doors at Uppsala P-50
Figure P-27. Warped Feed Chute at Copenhagen: West P-52
Figure Q-1. Basic Types of Grates for Mass Burning of Refuse. There
are Available Many Variations of These Basic Types. . . Q-2
Figure Q-2. Von Roll Reciprocating Step Grate in Refractory Walled
Furnace Q-9
xxxi
-------
LIST OF FIGURES (Continued)
Figure Q-3- Two Steps of Von Roll Grate Using Reciprocatig
Forward-Feed Design Q-10
Figure Q-4. Arrangement and Drive of Grate Blades in Original Von
Roll Grate Q-11
Figure Q-5. Kunstler Grate and Air-Cooled Wall Plates Applied to an
Incinerator Q-13
Figure Q-5a. Diagrammatic View of Application of a 3-Step Kunstler &
Koch Grate to 3-Pass Boiler Q-14
Figure Q-6. Martin Three Run Grate System Q-16
Figure Q-7. Side View of the Martin Grate Q-18
Figure Q-8. Refuse Tumbling Action of Martin Grate Q-19
Figure Q-9. An Example of the Alberti Fonsar Step Grate System
Assembled at the Factory Q-20
Figure Q-10. Six Drum Walzenrost (Roller Grate); also Commonly Known
as the Duesseldorf Grate. Note the Cast Iron Wiper Seals
Between Adjacent Rolls Which Prevent Large Pieces of
Refuse From Falling Out of the Furnace Q-21
Figure Q-11. Sketches of Grate Action Q-23
Figure Q-12. Bruun and Sorensen Cast Alloy Grate Bars. The Older Bar
is Shown Below the Newer, Wider Bar is Above Q-25
Figure Q-13. Volund's Lengthwise Placed Section of Grate Q-26
Figure Q-1U. Volund's Movable Sections Hydraulically Driven by a
Transverse Driving Shaft Connected to the Individual
Sections by Pendulum Driving Bars Q-27
Figure Q-15. One of the Earliest Volund Patents Q-28
Figure R-1. Martin Ash Discharger R-U
Figure R-2. Martin Ash Discharger Dumping Into Vibrating Conveyor at
Paris: Issy R-5
Figure R-3. Cross Section of Baden-Brugg Plant . .• R-7
Figure R-4. Discharge End of Residue Conveyor at AARAU, Switzerland
Showing Electric Truck for Removing Loaded Hopper. . . R-8
Figure R-5. Residue Removal Sump and Oscillating Ram at Bottom of Plant
at Trimmis, Switzerland , R-9
Figure R-6. Portion of Proposed Stapelfeld Plant at Hamburg Showing
Refuse Removal Sump and Oscillating Ram at S Which Dis-
charges to Either of 2 Trough Conveyors, C R-10
xxxn
-------
LIST_OF FIGURES (Continued)
Figure R-7. Widmer & Ernst Quench Tank and Residue Removal Drive
Mechanism at Oberthurgan, Switzerland R-11
Figure R-8. Furnace Bottom Ash Chute Discharging Into Ash Vibrating Steel
Conveyor at Uppsala R-13
Figure R-9. Alternative Designs for Flow of Refuse and Ash R-11
Figure R-10. Plan of Duesseldorf Waste-to-Energy Plant R-16
Figure R-11. Inclined Conveyors Removing Baled Scrap at Duesseldorf. . R-17
Figure R-12. Close-up of Baled Steel Scrap at Duesseldorf R-18
Figure R-13- Visitors Discussing Fine Ash Residue Uses Near Storage Area
at Duesseldorf R-19
Figure R-14. Wuppertal Plant Showing, in Top Portion, the Air-Cooled
Steam Condenser Housing at Rear of Plant and Below the
Privately-Operated Residue Processing Plant R-21
Figure R-15. Rear View Showing Ash Conveyor From the RFSG Plant to the
Ash Recovery Facility at Paris: Issy R-22
Figure R-16. Truck Dumping Unprocessed AHS (For Two-Week Stabilization
Prior to Processing) at Zurich: Hagenholz R-26
Figure R-17. Signed Stumps, Tirs, Paper Rolls, Etc., Remaining After
Ash Processing at Zurich: Hagenholz R-27
Figure R-18. Front End Loader Dumping Ash into Begining of Ash
Processing System (Hopper, Vibrating Conveyor and
Rubber Belt Conveyor) at Zurich: Hagenholz R-28
Figure R-19. Workman Removing Jammed material from Vibrating Conveyor
Near End of Coarse Ferrous Line at Zurich: Hagenholz . . R-29
Figure R-20. Medium Ferrous Scrap from the Ash Recovery Process at
Zurich: Hagenholz R-30
Figure R-21. Coarse Ferrous Scrap from the Ash Recovery Process at
Zurich: Hagenholz R-31
Figure R-22. Mountain Pile of Processed ASH (1/4" and less) for Road
Building at Zurich Hagenholz R-32
Figure R-23. Experiment Road Patch to Test Heavy Metal Leaching of
Processed Ash Use R-33
Figure R-21. Sketch of the Hague Plant Highlighting the Bottom Ash Pit
and the Flyash Slurry Tank (Before ash recovery was
installed) R-35
Figure R-25. Bottom Ash Pit and Fly Ash Slurry Tank at the Hague. . . . R-36
xxxiii
-------
LIST OF FIGURES (Continued)
Figure R-26. Conveyors and Magnetically Separated Scrap and Pile of
Sized Residue Accumulated by New Resource Recovery
System Adjacent to the Hague Plant (Battelle
Photograph) R-37
Figure R-27. Ash Being Discharged from Furnace onto Vibrating Steel
Conveyor at Uppsala R-39
Figure R-28. Vibrating Steel Conveyor Dumping Bottom and Fly Ash into
Container at Uppsala (Battelle Photograph) R-^O
Figure R-29. Elevator for Ash Containers in Pit one Level Lower than Ash
Conveyor at Uppsala , R-41
Figure R-30a. Rubber Ash Conveyor at Copenhagen: Amager . R-43
Figure R-30b. Ferrous Separation from Ash at Copenhagen: Amager .... R-43
Figure R-31. Skip Hoist Dumping Incinerator Ash (Slag) at Copenhagen:
West '. R-M
Figure R-32. Ash Handling and Processing at Copenhagen: West R-46
Figure R-33- Ash Recovery at Copenhagen: West R-47
Figure R-34. Vibrating Machinery for Ash Processing at Copenhagen:
West R-48
Figure R-35. Ferrous Magnetic Belt for Ash Recovery Processing at
Copenhagen: West , R-49
Figure R-36. Mountain of Processed Ash Residue Awaiting use for
Roadbuilding or Cinder Block Manufacture at
Copenhagen: West R-50
Figure R-37. The variation Interval for the 16mm Fraction of Graded
Cinders Before (solid line) and after (dotted line)
Compacting by Field Tests R-52
Figure S-1. Annual Average Lower Heating Values for Berne, Stockholm,
Frankfurt, The Hague and Duesseldorf and Range of Values
for Other Cities S-2
Figure S-2. Partially Water-Cooled and Air-Cooled Furnace at
Werdenberg-Liechtenstein S-4
Figure S-2a. Diagram of Application of Kunstler Sidewall Blocks. . . . S-6
Figure S-3. Cross Section of Baden-Brugg Plant S-8
Figure S-4. HR. B. Lochliger, Assistant Plant Manager, Holding Steel
Reinforcing Coil for Tube-Covering Molded Refractory. . S-9
Figure S-5. Cross Section of One of Boilers No. 1-4 S-11
xxxiv
-------
LIST OF FIGURES (Continued)
Figure S-6. Diagram of Location of Guiding Wall at Top of Furnace
Outlet Showing Effect on Oxygen Distribution in Gases . S-13
Figure S-7. Cross Section of Boiler No. 5 with Roller Grate "System
Duesseldorf" S-15
Figure S-8. Schematic Cross Section of the Paris-Issy-Les Moulineaux
Plant S-19
Figure S-9. Issy Alumina Blocks Surrounding Boiler Surrounding Boiler
Tubes S-21
Figure S-10. Plastic Silicon Carbide Surrounding Boiler Tubes S-21
Figure S-11. Issy Metal Wastage Zones and Areas of Corrective
Shielding S-22
Figure S-12. Issy New Second Pass Deflector Baffle to Protect Third
Pass Superheater S-24
Figure S-13. Metal Wastage of Water Headers Above the Hot Section of
the Grate at Hamburg :Stellinger-Moor S-26
Figure S-14. October 1976 Additions of Refractory to Hamburg
Stellinger-Moor Furnace #1 S-27
Figure S-15. May 1977 Additions of Caps onto Studs and Refractory to
Hamburg:Stellinger-Moor S-29
Figure S-16. Furnace/Boiler Cross-Sectional View of the Zurich:
Hagenholz Unit #3 S-3^
Figure S-17. First Pass Walls Covered with Silicon Carbide Over
Welded Studs: Shows Rejection of Slag from Walls of
Zurich: Hagenholz S-36
Figure S-18. Perforated Air-Cooled Refractory Wall Blocks by Didier
as Installed by Von Roll at the Solingen Plant,
West Germany S-39
Figure S-19. Construction Photograph Showing Air Supply Chambers for
the Refractory Wall Blocks Shown in Figure S-18 . . . . S-39
Figure S-20. Lower Portion of First Pass Showing 18 Original Sidewall
Jets, Now Abandoned, Rear Nose Formed of Refractory
Covered Bent Tubes, and Manifolds for New Front and
Rearwall Secondary Air Jets Aimed Downward about
30 Degrees S-41
xxxv
-------
LIST OF FIGURES (Continued)
Figure T-1. Schematic View of Werden-Liechtenstein Waste-to-Energy
Plant T-H
Figure T-2. Sketch of Air Flows to Furnace T-5
Figure T-3- Widmer & Ernst Photo of Man Applying Kunstler Air-Cooled
Wall Blocks at Plant in Trimmis Switzerland T-7
Figure T-4. Fifteen Secondary Air Jets of Revised System in the
Baden-Brugg Rear Wall T-8
Figure T-5. Proposed Revision of Sidewalls Incorporating Air-Cooled
Cast Iron, Kunstler Blocks T-10
Figure T-6. Anonymous Furnace Where Secondary Overfire Air is Very
Little or Totally Lacking T-13
Figure T-7. Highly Turbulent Air at Hamburg:Stellinger-Moor Resulting
from Very High Secondary Air Pressure T-14
Figure T-8. Nearly Clear View Across First Pass at Hagenholz Unit #3
After Secondary Overfire is Injected at High Pressure. T-16
Figure T-9 . Exterior View of Tubes for Secondary Air Jets on Side of
Unit #4 at The Hague. Ten Jets are Spaced Horizontally
and Two are Located Along a Slanting Vertical Line at
Left. Note Springloaded Cap on Each Tube to Facilitate
Inspection and Cleaning T-18
Figure T-10. Lower Portion of First Pass Showing 18 Original Sidewall
Jets, Now Abandoned, Rear Nose Formed of Refractory
Covered Bent Tubes, and Manifolds for New Front and
Rearwall Secondary Air Jets Aimed Downward About 30
Degrees T-19
Figure T-11. Six Dilution Sidewall Secondary Overfire Air Jets at
Copenhagen:Amager T-20
Figure U-1. Graphical Definition of Overall Steam Generation Plant
and the Specific Combination of Components Called the
Boiler U-2
Figure U-2. Dacha Type Superheater and Boiler Convection Arrangement
for Proposed Staplefeld Plant at Hamburg. U-7
Figure U-3. Section through Werdenberg-Liechtenstein Waste-to-Energy
Plant U-9
Figure U-4. Cross Section of Baden-Brugg Plant U-11
Figure U-5. Cross Section of One of Boilers No. 1-H U-13
xxxvi
-------
LIST OF FIGURES (Continued)
Figure U-6.
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
U-Y.
U-8.
U-9.
U-10.
U-11.
U-11a
U-12.
U-13.
Figure U-15.
Figure U-16.
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
U-17.
U-18.
U-19.
U-20.
U-21.
13-22.
U-23.
U-24.
Figure U-25.
Cross Section of Boiler No. 5 with Roller Grate "System
Duesseldorf"
Cross-Section of Wuppertal Plant
Issy-Les-Moulineaux Incinerator Plant Near Paris,
France
Large Boilers at Ivry Built for TIRU M Years after
Issy
Cross Section of Stellinger-Moor Plant Started up at
Hamburg in 1970
Furnace/Boiler Cross Section of Unit No. 3 at
Zurich:Hagenholz
Boiler Tube Sections Layout at Zurich:Hagenholz. . . .
Comparative Cross-Sections of the Two Boiler-Furnace
Systems at the Hague Plant
Cross-Section of Boiler Systems, 1-3 The Hague
Comparative Cross Sectins of Dieppe and Deauville
Refuse-Burning Plants
Cross Section of Nominal 900 Tonne Per Day. Refuse
Fired Steam-to-Hot Water Heating Plant at Savenas,
Gothenburg
Cross Section of Furnace No. 4 and Boiler No. 3 at
Uppsala
Arrangement of Uppsala Plant
Schematic of Original Horsens Plant with Water Spray
Cooling Tower
Engineering Drawing of Copenhagen: Amager
Moscow Plant Showing Four-Pass Water Wall Waste Heat
Boiler Separate from the Furnace
Half Shields for Clamping on Superheater Leading Face
at Baden Brugg
Hard Coating on Bends of Superheater Tubes to be
Installed in the Second Pass of Boiler No. 5 . . . .
Baden-Brugg Ruptured First Row Superheater Tube . . .
Wuppertal Plant Showing Superheater Located in
Second Pass Away from Furnace Flame
Issy Shields for Bottoms of Superheater Tubes ....
U-14
U-16
U-17
U-19
U-20
U-25
U-27
U-29
U-31
U-32
U-37
U-39
U-40
U-M2
U-43
U-52
U-53
U-55
U-60
U-62
xxxvii,
-------
LIST OF FIGURES (Continued)
Figure U-26.
Figure U-27.
Figure U-28.
Figure U-29.
Figure U-30.
Figure U-31.
Figure U-32.
Figure U-33.
Figure U-31*.
Figure U-35.
Figure U-36.
Figure 0-37.
Figure U-38.
Figure U-39.
Figure V-1.
Figure V-2.
Figure V-3.
Issy Old and New Superheater Spacing U-63
Superheater Tube Arrangements at Issy and Hagenholz . . U-63
Superheater Flue Gas and Steam Temperature and Flow
Patterns at Zurich: Hagenholz U-65
Superheater Flue Gas and Steam Temperature and Flow
Patterns at the New Zurich: Josefstrasse Plant and at
the Yokohama, Japan Martin Plant U-66
Three Superheater Bundles at Hamburg: Stellinger-
Moor U-69
Flow Defection Caused by Angle Iron Shields on First
Row of Superheater Tubes U-70
Method of Welding Curved 50 mm Shields on First Row
of Superheater Tubes U-71
Water-Tube Wall Portion of Boilers in Units 1-3, The
Hague, Showing Suspended Platten-Type Superheater at
Top of Radiation Pass, Screen Tubes at Outlet from
Radiation Pass, Screen Tubes at Outlet from Radiation
Pass, Sinuous Tube Convection-Type Superheater at Top
of Second Water-Tube Walled Pass, Boiler Convection
Sections, Economizer, and Tubular Air Heaters .... U-71*
Cross-Section of the No. 4 Boiler Furnace System
at the Hague Plant , U-75
Shot Pellet Cleaning Feed System at Uppsala U-84
Two Views of Air-Cooled Condenser at Werdemburg. . . . U-91
Underside View of Wuppertal Plant Highlighting the
Air-Cooled Steam Condensers and the Stack U-93
Sloping Air-Cooled Steam Condenser Tubes at Zurich:
Hagenholz U-95
Louvers Below Inverted V-Shaped Air-Cooled Steam
Condensers at Gothenburg: Savenas U-96
Oil Burner on Side of and Toward Rear of E^urnace for
Firing of Waste Oil at Baden-Brugg. . V-4
Cologne, West Germany Hospital Waste Incinerator with
Sidewall Oil Burner V-5
Schematic of the Process of Waste Oil Firing V-6
XXXVlll
-------
LIST OF FIGURES (Continued)
Page
Figure V-4. Krefeld Waste-to-Energy Facility: Plan View V-8
Figure V-5. Waste Oil and Solvent Receiving, Processing and Mixing
Layout at Zurich:Hagenholz V-11
Figure W-1. Krefeld Waste Processing Facility; Wastewater Treat-
ment Plant on Left, Refuse-and Sewage-Sludge-Burning
Plant on Right W-4
Figure W-2. Map of the Krefeld Refuse Burning and Wastewater
Plants W-5
Figure W-3. Krefeld Sludge-Processing and Burning Systems W-6
Figure W-4. Cross-Sectional View of Krefeld Plant W-7
Figure W-5. Calculated Drying Mill Conditions as a Function of
Sludge Drying Rate W-9
Figure W-6. Calculated Dust Load of the Flue Gas as a Function of
the Amount of Ash on the Grate W-11
Figure W-7. Top of Two Luwa Sludge Dryers at Dieppe W-13
Figure W-8. Cutaway Drawings Showing Principle of Luwa Dryer . . . W-14
Figure W-9. Plot by Eberhardt of Relation of Combustible and
Ash Content of Dry Sewage Sludge to Its Lower Heat
Value W-18
Figure W-10. Krings Results of Test in 1973 at Dieppe on the
Effect of Type of Sludge and Sludge Feed Rate on the
Efficiency of the'Luwa Thin-Film Dryer W-19
Figure W-11. Diagram of Horsens Refuse-Burning and Sludge-Drying
Plant W-11
Figure W-12. Co-Disposal of Refuse and Sewage Sludge at Ingolstadt,
West Germany W-26
Figure W-13. Overhead Plan for the Environmental Park at Biel,
Switzerland W-28
Figure W-14. Aerial Photo of Environmental Park at Biel,
Switzerland W-28
Figure W-15. Original Dano Kilns for Compost Initiation at Biel,
Switzerland W-29
Figure W-16. Aeration Turning by Pivot Bridge Final Composter at
Biel, Switzerland W-29
Figure W-17. Pig Feed made from Digested Sewage Sludge and Refuse. W-30
Figure W-18. Bricolari Compost Storage Yard (4-5 weeks) with Pig
Feed Buildings in Background at Biel, Switzerland . . W-18
xxxix
-------
LIST OF FIGURES (Continued)
Figure X-1. Sample Data Cards as Used in Plant Data System at
Duesseldorf X-11
Figure X-2. Downward View from the Wuppertal Plant Showing the
Nearby Country Club and Swimming Pool X-13
Figure X-3- Supply and Wastewater Systems at Krefeld X-16
Figure X-4. Replaceable Cast Alloy Steel Vane which Imparts Spin to
the Gases Entering Each Collection Tube of the Prat
Multiple Cyclone Dust Collector X-23
Figure X-5. Deauville Refuse-Sludge Cofiring Plant X-24
Figure X-6. Arrangement of components of Bolander Incinerator
Plant at Uppsala X-26
Figure X-7. Electrostatic Precipitators Retrofitted for Units
#1 and #2 Outside at Uppsala « • X-29
Figure X-8. Ducts leading to Base of Ten Flue Chimeny at Uppsala. X-30
Figure X-9. Looking out the Windows Taken from Under the
Electrostatic Precipitators at Copenhagen: West. . . X-32
Figure X-10. Diagram of Equipment for Measurement of Dust
Loading and Moisture Content of a Gas X-35
Figure X-11. Appartus for Isokinetic Determination of the Dust
Content of Flowing Gases (VDI Konmission Reinhaltung
Der Luft) X-36
Figure Y-1. Sample Data Cards Used in Plant Data System at
Duesseldorf Y-3
xxxx
-------
p-1
REFUSE HANDLING
Weighing of Refuse Received-General Comment
The amount of refuse handled is a major plant descriptor. Hence
considerable attention is usually given to measuring the amount of waste
received. Many of the plants visited used automatic recording of loaded
truck weight as it arrived at the plant. Many truck driver's especially in
Scandinavia, carried a coded identification card to be inserted into the
card slot at the scale at the time of weighing. Previously established
truck tare weights are recorded in the data processing equipment. The net
weight delivered was immediately displayed in the weigh-master's booth,
printed on the plant daily record and added to the monthly invoice which is
sent to each of the private haulers or surrounding communities.
Many of the plants have experienced early difficulty with failure
of the electronic system at the scales. In most cases these initial
problems have been cleared up by the scale manufacturer. However, the
electrical system usually requires frequent maintenance. A few large plants
use 2 scales for redundancy and to handle peak loads without causing long
lines of waiting trucks. One plant uses a separate scale to weigh the
residue from the furnaces. Most scales are recalibrated once every year or
two.
At very small plants the scale operation is observed and
controlled by the crane operator who sits at plant control board. In such
instances the main control room is located in such a way that the busy
operator can view the trucks discharging to the pit. In some cases he also
observes furnace condition by means of closed-circuit television.
In the larger plants the weighing operation is controlled by 1 or
2 scale operators who also direct the truck traffic through amplified voice
instructions and sometimes by means of red and green signal lights.
At most plants it is the duty of the scale operator to detect
bulky items and to instruct-the driver to deposit them in a separate
collection place.
Details on Specific Weighing Systems
Werdenberg, Switzerland
At Werdenberg, community and industrial wastes are delivered 5
days per week by eight regular trucks plus a few private ones. Incoming
trucks are weighed on an 80-ton semi-automatic weigh scale which is
operated by a plant worker who devotes about 1/4 time to weighing. The
scale operator controls receipts from the rear of the control room which is
on the second floor of the building. The weights, total and tare, are
printed by an electro-mechanical recorder with digital readout. The scale
is inspected, calibrated and serviced once per year. It is expected to last
more than 20 years.
Baden-Brugg
Both public and private trucks deliver refuse to the Baden-Brugg
plant 5 days per week. They are weighed on a Toledo scale which prints
-------
P-2
total, tare and net weights on a card. The scale is inspected the waste oil
totaled 172 tons for the year.
Duesseldorf
Six to 7,000 tonnes of refuse is delivered ot the pit per week by
700 to 800 public and private trucks between 7:00 a.m. to 2:00 p.m., 5 days
per week. On a 7-day week basis, hospital and hotes wastes are received.
Figure P-1 shows the plant property which is located in a
concentrated industrial area well inside the city. The weigh scale is to
the right of the figure. Two scales are provided--one on each side of the
scale building—so that two trucks can be weighed simultaneously. The
scales were built by Scheuck of Darmstadt. Normally there is one scale
operator. At peak times, there are two. Peak times are from 8:30 a.m. to
10:30 a.m., 12:00 p.m., and 2:30 p.m. to 3:00 p.m.
The scale reading and tare are punched automatically on data
cards. Also, an automatic typewriter logs the readings.
The scale service has been good with little maintenance.
Calibrations are made every 3 years. The scale data-recorder has caused
much difficulty. The electrical system requires repair 10 times per year.
When the scale operator observes bulky waste in a truck, he
directs it to either the shredder or the shear.
Wuppertal
This new plant is not yet up to full capacity. Incoming trucks are
weighed on 1 of 2 scales. Figure P-2 shows the plant arrangement. It is
located on a steep hillside and the roadways are nearly all on a grade,
hence the need for an entrance ramp close to the north wall of the tipping
floor and a turning apron for a 180 degree turn to enter the tipping floor.
The scales were reliable for the first 3 months of plant operation. Then
the electronic sysstem malfunctioned. It was still causing some difficulty
at the time of the visit, May 1977, 16 months after partial operation began.
Paris; Issy-les-Moulineaux
The weighing station at Issy is located centrally on the edge of
the tipping floor as shown in the 2 views in Figure P-3. That elevated
location is only 6.5 m (21.3 ft) above the nearby River Seine. The single
mechanical scale has good accuracy and is officially calibrated annually by
the government. It has posed no unusual maintenance problems.
Zurich
At the Hagenholz plant there is one scale which has performed very
well. It is calibrated once a year. Two men are asigned to the scale room.
One of when monitors driver cleanup of any spillage on the tipping floor.
Originally the refuse weight actually charged to the furnace hoppers was
also measured by means of a load cell on the cranes. But when that device
failed it was not repaired because the management feels that the energy
produced is the best measure of plant performance, not how much refuse is
processed.
-------
P-3
1. Entrance and Exit
2. Administration Building, Work Shop, Offices
3. Vehicle Turning Area
4. Bulky Waste Shear
5. Tipping Area
6. Refuse Storage Bunker with Charge Cranes
and Feed Hoppers
7. Boiler House, Boilers »? 1—6
8. Weight Scales
9, Steam and Condensate Lines Connecting to
Flingern Power Plant
10. Control Room
11. Information Center
12. Ash Processing Building
13. Loading Hoppers for Processed Ash
14. Scrap Baling Presses
15. Exhaust Fans and Stack
16. Excess Ash Storage Bunker
17. RG Type Silencers
18. Parking Lot
19. Sportsfield — Area for Future Plant Expansion
20. Fuel Oil Tank
21. Circulation Pumps
22. Feed Tank
23. Settling Tanks
24. Lime Storage Silos
25. Neutralization Tank
26. Electrostatic Precipitators
27. Bulky Waste Shredder
28. Overhead Conveyor
FIGURE P-l. LAYOUT OF FLINGERN REFUSE POWER PLANT AT DUESSELDORF
-------
P-4
1. Weigh station
2. Conference room
3. Machine shop and electrostatic precipitator
4. Boiler room
5. Refuse bunker
6. Tipping floor and bulky waste shear
7. Entrance ramp
8. Turning apron
9. Chimney
10. Air-cooled condenser
FIGURE P-2. MAP OF WUPPERTAL PLANT
-------
P-5
Scale House
^
®^^-S%^
^jgf~'^rr" -^.'."*T C&jJE-ft^^^'-aig ^-^-^ i ''J~, 'V^vS^-'-^''''!; ^r'i'rfam 'jnti* i'Tlr'*t-r-"*- ' Tii
FIGURE P-3. TWO PARTIAL VIEWS OF THE RECEIVING AREA AT THE ISSY PLANT
SHOWING THE SCALE HOUSE AT THE UNLOADING PLATFORM.
-------
P-6
Hamburg
At the Stellinger-Moor plant in Hamburg the scale house is located
near the plant entrance and the administration building. The plant
originally purchased an inexpensive under capacity scale that caused much
trouble. A mechanical level is used and the ensuing electrical resistance
is measured. Many improvements have been made to this semi-automatic
Essmann Scale manufactured in Hamburg.
Today, the weight indication almost never fails. However, the
electric printer is available only 60 percent of the time.
Several notable attitudes have developed in response to the
weighing problems. The local plant operations have about given up the truck
scale and, instead, depend on the more reliable load cell on the crane. The
truck scale is still used for weighing the burned residue removed from the
plant.
The Hague
The weigh station is not operated by The Hague plant. Instead, it
is operated by the municipal waste collection department. In 1976, the
weigh station was relocated and modernized. It is situated between two
scales, one for city trucks, one for private vehicles. The scale operator
regulates traffic flow by means of a manually controlled red-green signal
light on the approach to the scale house. Private trucks weigh in and then
out. City trucks weigh in by insertion of a coded magnetic card into a slot
at the scale which identifies the truck and causes immediate machine
recording of the loaded weight, known tare weight. Automatic subtraction
calculates the net weight delivered.
When the scale operator observes non-combustible bulky waste, such
as steel appliances being delivered, he directs the driver to unload the
objects in a walled-in yard near the new waste processing facility for
later processing, reclamation and disposal.
Dieppe and Deauville
A single scale near the plant entrance enables the scale operator
to weigh all entering trucks. At the Dieppe plant the scale room is in the
separate administration building. At Deauville the scale house is at the
site entrance and about 60 m (200 ft) from the main plant building which
also houses administration.
Gothenberg
All refuse is weighed at the entrance to the Savenas plant area
shown in Figure P-H. The weighing procedure is automated whenever possible.
Most suppliers use customer cards and need no service therefore.
The weighing plant is equipped with four electronic weighing
machines and a data recording system. Besides supplying continuous
information to operational management, the system also enables automatic
debiting and invoicing to be carried out. In addition, statistical
information is received. Traffic inside the area and the emptying bay is
-------
P-7
FIGURE P-4. TOP VIEW OF SAVENAS WASTE-TO-ENERGY PLANT SHOWING TRAFFIC
PATTERN, WEIGH STATIONS AND DISTINCTIVE SQUARE 4-FLUE
CHIMNEY. ONLY THREE FLUES IN USE. CHIMENY EQUIPPED WITH
TWO-PASSENGER ELEVATOR AT GOTHENBURG (Courtesy GRAAB)
1. Entrance gate - monitored by television.
2. Classification lanes for large and small trucks.
3. Weigh station.
4. Traffic control area.
5. Entrance ramp.
6. Entrance to enclosed tipping hall.
7. Bunker doors.
8. Exit door.
9. Exit lanes.
10. Exit weight station.
11. Automatic exit gate.
12. Cafeteria (open 9 am to 2 pm).
13. Washroom
14. Parking
15. Traffic control room
-------
P-8
monitored by a traffic controller stationed in the ceiling control room at
the rear of the emptying bay or tipping floor. In low traffic periods,
monitoring can be transferred to the central plant control room by use of
closed circuit television and electronic signals. After emptying, the
vehicles again pass the weighing room where tare weighing is carried out on
certain vehicles and where any cash is paid.
The weighing equipment and data system have required little
servicing, an estimated down-time of once per year. The scale is of Swedish
make, by Stathmos. The data system is by General Automation Co. of Anaheim,
California, U.S.A.
Uppsala
Arriving trucks are weighed, their weight and tare being recorded
by means of plastic identification cards issued to the truck dirvers. The
scale is sensitive to 20 Kg (MM Ib). A few trucks are weighed by manual
peration of the scale. Some difficulty was encountered at first (1961)
because of weather effects on the recording system which was installed by
Stathmos-Lindell.
Horsens
The 10-tonne weighing scale is located inside the tipping hall,
adjacent to the pit and within view of the control-room operator who is
also the crane operator and scale operator. The scale is calibrated once
per year by the manufacturer. Only the trucks delivering industrial waste
are weighed and pay a fee. All others, unweighed, dump free. For the
collection and disposal service each household pays a tax. Occasionally
truck-loads of sacked residential waste are weighed for a week or so to
obtain data from which the residential input can be estimated.
CopenhagentAmager and West Plants
At each Copenhagen plant arriving trucks proceed to one of the two
load cell type of 50 tonne (55 ton) scales manufactured by Philips of
Holland shown in Figure P-5a. Drivers produce their universal plastic cards
that identify the vehicle owner, etc. This information, along with the
gross weight, is fed into the computer, where the tare weight, mailing
address, etc. are stored.
Occasionally the plastic cards jam, break, or become lost. In this
event, the driver would have to get out of the truck and spend several
minutes in the scale house filling out a form. The cards were replaced on
an as-needed basis. They have changed the system so that every 6 months all
of the plastic cards are changed at once.
At the time of the visit in October, 1977, a particular card would
work at Amager, West, and the Hillerod transfer station. An identical
Philips system was under consideration for the Roskilde Volund plant as
well. In theory, the system could be used throughout Denmark to the
advantage of all.
Revelant information is displayed on digital readout devices. The
single operator can process 120 vehicles per hour if both scales are used
simultaneously. The scales can be used automatically at night when the
-------
P-9
FIGURE P-5a. SCALE
HOUSE AND TWO SCALES
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FIGURE P-5b. PLASTIC CARD
FIGURE P-5d. DIGITAL READOUT IN SCALE HOUSE
FIGURE P-5e. RAMP TO
TIPPING FLOOR
FIGURE P-5f. TIPPING
FLOOR
FIGURE P-5g. TIP
ARRANGEMENT PERMITTING
GOOD CRANE VIEW
-------
P-10
scale house is unmanned. Opening the plant gate and weighing the vehicles
can be controlled from inside the plant at the main control room with use
of television cameras shown in Figure P-5c.
Tipping Floor, Pit and Crane
General Comments
The universal European practice for receiving, storing and feeding
the solid waste to the funaces is the ancient pit arid crane system. To most
newcomers to the field this method appears incredibly archaic. However it
has so far defied efforts to supplant it with modern conveying equipment.
The major barrier to change is the heterogeneity of MSW and its strong
tendency to pack and densify when stored. Until economically reliable means
are developed to homogenize MSW this status will probably continue.
At most of the plants visited the tipping floor is indoors. Figure
P-5f shows the large tipping floor at Copenhagen. At the smaller plants and
even the large plants at The Hague and Issy-les-Monlineaux at Paris, the
trucks tip while outdoors or are only partially shielded from the weather
when actually discharging into the pit.
In all cases, indoors or outdoors, the discharge openings into the
pit are covered by power-operated doors. Thus pit odor is kept inside by
fresh combustion air flowing through the open doors under the action of the
combustion air blowers. In most cases the blowers take the air from
filtered air intakes near the top of the pit. Thus air flow is always in
and in no case was the odor of refuse detected outside the plants nor in
the neighborhood. Figure P-6 is a photo at Deauville of nearly apartments
viewed through the open doorway to the tipping floor. At that plant, in
addition to the powered exterior door, each of the 4 pit doors is also
covered, when not in use, by a powered door.
In most plants the entrance and agress of the trucks to the
tipping area i? controlled by the scale operator, with a workman on the
tipping floor controlling the opening and closing of the pit doors. In a
few cases the hydraulically lifted doors are operated by the truck driver.
Usually the drivers are expected to clean up any spilled refuse
before they leave and, in general, the tipping floors were free of debris,
but not always. The attitude of management toward housekeeping standards
was variable and resulted in a very few messy tipping floors. One plant,
Wuppertal, made daily use of a large mobile washer and sweeper to keep the
tipping floor and adjacent ramps exceptionally clear.
Pit Doors
The most commonly used powered pit door is the multi-hinged door
as at Gothenborg, Sweden. A distinct disadvantage of this type is that if
several such doors happen to be open at once at a busy time the lifted
doors hide much of the pit from the view of the crane operator who is
situated directly above the doors. Also such doors projecting into the
crane area are very vulnerable to accidental collision with the crane
bucket. For these reasons at the new Zurich: Josefstrasse plant will use
the more expensive guillotine door when it opens in 1979.
-------
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P-12
Pit or Bunker
Table P-1 shows the dimensions and capacity of the storage pits at
the plants visited. The floor of most pits is below grade. Because of
water-table or excavation problems, a few are at grade, in which case the
tipping floor is elevated and is reached by a sloping sometimes helical,
ramp. Most pit walls are reinforced concrete.
The predominant design philosophy provides a maximum pit storage
capacity of H to 5 days' operations. Since all of the larger plants usually
schedule units to be down for maintenance, the actual storage capacity
provides for 5 or 6 days of normal plant operation.
Pit fires are usually controlled by sprinkler systems and water
guns controlled by the crane operator. For extremely dry, industrial waste
at The Hague, there is a separate pit in which water sprays operate most of
the time to reduce the heat value of the refuse as fired. This prevents
fires and also avoids overheating of the boilers which were designed
originally for wet MSW. See Heat Value of Refuse.
Crane
The larger plants have 2 cranes which provide redundancy. The
almost universal comment was the the crane operator is the most important
worker in the plant. A skilled operator will divert troublesome bulky items
to avoid problems in the furnace and will mix segregated, highly
combustible wastes in the pit so as to avoid excessive heat release in the
furnace. Also his skill is very important in extending the life of the
crane cables which can become kinked and twisted in the process of
retreiving batches of waste from the pit.
In most small plants the crane operator performs from a
glass-walled podium at one side of the control room positioned so as to
provide a view of the tipping area, pit and furnace hoppers. In the larger
plants the separate podium is situated high in the wall above the pit often
the podium has dual controls and is lavishly equipped above the pit. In no
case did the crane operator ride the crane.
Plant Details on Receiving
Storing and Feeding Refuse
Werdenberg
Figure P-7 shows the tipping floor, hinged door in open position
and pit and crane at the small Werdenberg-Liechtenstein plant in eastern
Switzerland.
The main plant pit is 1300 m3 (1690 yd3) when filled level with
the tipping floor. It is 20m long, 8.5m deep and 7.5m wide (65.6 ft by
27.9 ft by 24.6 ft). It is estimated to hold 800 tonnes (854 tons) at a
compressed and settled density of 0.383 tonnes/m3 (645 lb/yd3). If fire
breaks out in the pit it can be controlled by overhead sprinklers.
There are 2 Von Roll bridge cranes of 5 tonne capacity but only
one is needed. A clamshell type of bucket on each crane can lift 1/2 to 1
tonne at a grab. The weight of a bucket load can be determined from the
current consumed by the cable motor when the bucket is being lifted at a
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P-15
constant rate of speed. The corresponding weight can be read by the crane
operator sitting in the control room.
There were problems due to inexperience during startup. If the
crane cables were not kept in tension they would jump the pulleys on the
bucket. With careful operation the cables last 2 months. With unskilled
operation they last 2 weeks. About 2 hours are required to repair broken
cables.
The plant control room also contains the crane operator's perch
high on one side of the pit. The room is air conditioned. The crane is
semi-automatic in that after the bucket is loaded the crane liftsand
positions it over the furnace hopper.
Baden-Brugg
Figure P-8 shows a truck delivering at Baden-Brugg. There are 6
doors. Five are closed. The scale operator can direct truck drivers to
alternate tipping bays by the red and green lights above the truck entrance.
The refuse pit storage capacity when level-full is 2600m3 (3400
yd3). Assuming a stored refuse density of 0.383 tonne/m3 (645 Ib/yd3) its
storage volume would be 995 tonnes (1095 tons), or about a 4.5-day fuel
supply at capactiy operation. The pit is 23.4m (76.7 ft) long, 14.1m (45.3
ft) deep and 8.4m (27.6 ft wide). Fires in the pit can be controlled by
means of overhead sprinklers.
The pit is equipped with 2 cranes built by Mars-Uto of 5-tonne
capacity each. Each is equipped with a 2m3 (2.6 yd3) polyp orange-peel type
of grab. The weight of each crane load can be observed by the crane
operator on a digital read-out actuated by a strain gage on the crane
cable. The operator, whose pulpit is at the end of the pit, records this
weight reading manually. Figure P-9 shows the operator and two crane grabs.
An automatic crane stop is provided so that if the crane
approaches an open delivery door on the side of the pit the crane is
prevented from striking and damaging the open door.
Duesseldorf
Figure P-10 shows the main bunker at this large 5-furnace plant
which has a storage capacity of 10,500 m3 (13,734 yd3). At a compressed and
settled density of 645 Ib/yd3 (0.383 tonnes/m3), this represents a storage
volume of (4022 tons), about 3 days' supply. Fire control is by means of
six nozzles at the operator's level plus a spray system.
There are three Schiess cranes (now part of Demag), 120 tonnes
(132 tons) each. One crane is stored as a spare on a track in a loft above
the boiler room. Also, the crane can be quickly rolled onto this storage
track for repairs. One of the two crane operator's posts can be seen on the
left in Figure P-10. Both cranes operate during the day, one at night.
Each crane bucket is the polyp type with a capacity of 4 m3 (141
ft 3). Figure P-11 shows a new bucket in preparation for installation.
For boiler tests, the crane motor electrical input was calibrated
in terms of weight lifted. During the tests, this current was recorded
continuously. In routine operation, the crane operator records the number
of bucket loads charged to each furnace per shift. From this, an
approximate average furnace load is calculated.
-------
P-16
FIGURE P-8. TRUCK DELIVERING WASTE TO THE PIT AT BADEN-BRUGG,
THE PIT DOORS ARE HYDRAUCIALLY OPENED.
(Courtesy Region of Baden-Brugg)
-------
FIGURE P-9. CRANE OPERATOR, CRANES AND GRAABS ABOVE PIT
(Courtesy Region of Baden-Brugg)
-------
P-17
I
FIGURE P-10.
MAIN STORAGE PIT. THERE ARE TWO CRANE OPERATORS
OPERATING PULPIT FOR ONE IS AT UPPER LEFT AT
DUESSELDORF, (Courtesy Vereinigte Kesselwerke AG)
-------
P-18
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P-19
Wuppertal
The refuse pit has a level-full capacity of 10,000 m3 (13,078
yd3). At a compressed and settled density of 6*J5 Ib/yd3 (0.383 tonnes/m3),
this represents a maximum storage volume 6894 tonnes (7583 tonnes/m3),
about 6 days' supply based on three-unit operation with one unit held as
spare, 5 days at full plant capacity.
There are two Ridinger cranes (no longer being manufactured) of
10 tonnes each. There are two control cab locations, one on either wall of
the pit. But only one cab and one crane are now in use; hence, there is one
operator per shift plus a reserve operator.
The polyp-type crane buckets lift approximately 6 m3 (7.8 yd3).
Replacement polyps will have a capacity of 7 m3 (9.2 yd3).
The crane operator can remotely control one of two water nozzles
from each control cab for supression of pit fires. These have not been
needed to date.
To provide an approximate measure of refuse fired, there are four
pressure transducers on the bucket with digital readout and recording in
the cab. The totals are tabulated for each shift.
After the crane operator loads a bucket and selects a desired
hopper, the crane travel to a position above that hopper is automatic but
the operator must then press the unloading button.
The polyp is serviced once per month. The crane cables are
rotated every 3 months and they last 6 months.
Paris:Issy
At the Issy-les-Monlineaux plant, nine (9) doors open to the 7000
m3 (9,160 yd3) pit that holds 2,700 tonnes (2,950 tons) when level. When
refuse is stacked above the tipping floor level, 5,000 tonnes (5,500 tons)
can be stored. Therefore, 3 to 4-daysf waste can be stored.
There occasionally is spontaneous combustion when 2 to 3 days
supply accumulate the pit. Another source of fires is sparks from
construction welding to repair the crane or bucket and torch cutting to
destroy large bulky refuse.
For small fires, the truck-tipping floor mounted hoses are
sufficient. The local fire department is called out for large fires.
The traveling bridge cranes are inspected each morning. Ten
electrical contracts must be maintained. Repairmen can replace contacts
until too many have failed. It is the welding of these contacts that
produced sparks causing several pit fires. Then the entire assembly must be
replaced.
"If future designers wish to avoid downtime" plant officials
recommended "they should consider two independent bridges where each has
individual circuits and are on different elevations."
The polyp bucket has two kinds of cable. One U-shaped strand
lifts and lowers while the other U-shaped strand opens and closes the
bucket. The cables last anywhere from 2 days to 1 month.
Cables are inspected every Friday to avoid calling in repairmen
over the weekend. Even this does not insure failsafe weekends. If a cable
is fraying or has kinks near the bucket, the cable is shortened by the
-------
P-20
operatins staff, not maintenance. Four people often spend 3-1 hours
repairing the opening-closing cable. Two people can repair the lifting and
lowering cable in 1-1/2 hours.
The crane is equipped with a Bourdon dynamometer to measure
weight. This load cell measures current in amperes, in the static position,
just above the hopper and immediately before discharging. The crane has a
capacity of 10 tonnes. The buckets are 5m3 (6.5 yds3) and can carry up to
3.5 tonnes (3.9 tons).
Zurich
The refuse pit at Hagenholz holds about 5,000 m3 (6H50 yds3) or
1920 tonnes (2100 tons) when filled to the level of the tipping floor
assuming a density of 0.383 tonnes/m3 (6^5 Ib/yd3). When three or four
doors are closed refuse can be piled up to 9,000 m3 (11,770 yds3). During
our visit, material was so piled up that the closed doors were bowed
outward.
There are fire hoses above the pit to fight small fires. Once,
since 1969, they did have to call the fire department.
The two three-tonne (3«3 ton) cranes manufactured by Haushahn of
Stuttgart are double bridge. The crane operator in the traveling cab is
often faced with difficulty in judging the type of waste available (for
calorific value and bulky items) because of the obstructed view of the
opened, bended knee door that extends out into the refuse pit. As a result,
the new plant at Josefstrasse will have vertically rising guillotine doors.
Existing Hagenholz
New Josefstrasse
Josefstrasse will have the semi-automatic crane feature that
accurately places the bucket over the hopper. (The Hagenholz system is
manually operated only). Hagenholz uses the less expensive clam shell
buckets. However, at Josefstrasse, polyps will be used. The clam shell,
while large in volume capacity does not compact well and is itself very
heavy. The polyp, however, is lighter, and can compact more. This results
in a bigger refuse load lifted per lift. The crane capacity at Hagenholz is
38.7 tonnes (42.6 tons) per hour while at Josefstrasse it will be M4 tonnes
(47.4 tons) per hour.
The load cell on the crane failed and has intentionally not been
repaired as stated by one official:
-------
P-22
However, there are occasional automatic recording functions that fail and
recordings must be made manually.
An unusual item in the pit area is the special closet for humans
that can be quickly attached to the crane and lowered into the pit. On
separate occasions, a truck driver and a pit floor controller were pushed
into the pit by backing-up trucks. The men were rescued from the pit with
this closet.
In a discussion of polyp versus clam shell advantages, the Martin
representative noted a perference for the more expensive polyp in large
plants. The clam shell compressing density is about 300 kg/m3 (500
pounds/yd3) compared to about 480 kg/m3 (800 pounds/yd3) with the polyp.
The Hague
This plant is unusual in that it has two bunkers: a large one of
about 10,000 m3 (13080 yd3) capacity (level full) for community refuse
which, with 4 of the hinged lift type doors closed, can be piled up to
about 16,000 m3 (20,930 yd3) plus a smaller one for private haulers which
often receives mainly bulky refuse. The tendency for the privately
delivered refuse in the smaller bunker to be very dry and highly
combustible is so great that water sprays located high on the bunker wall
are turned on much of the time to keep that waste dampened.
Figure P-12 shows a cross section of the Hague plant with one pit
door hinged outward into the bunker.
If four of the main bunker doors are closed, the estimated
storage capacity is about 6100 tonnes (6700 tons) at a packed density of
0.383 tonnes/m3 (645 Ib/yd3) supply for three furnaces.
Figure P-13 shows one of the two crane control rooms high on the
outside of the main bunker wall controlling one of the two cranes. Usually
only one crane operates at a time. The other smaller bunker is served by
one crane controlled by an operator riding the crane in a cab. Each of the
main cranes, made by Heema of Holland, is of nine tonne capacity carrying a
polyp-type bucket of 4 m3 each. Fire control in the main bunker is by both
fire hose and fixed water spray. To obtain a measure of firing rate, the
operators record the number of buckets charged to each furnace per hour.
Figure P-14 shows a slanted mirror located above one of the
furnace hoppers which enables the crane operator ot observe when a hopper
needs fuel. Figure 15 shows a polyp discharging to a hopper.
Where the scale operator observes non-combustible bulky wste,
such as steel appliances being delivered, he directs the driver to unload
the objects in a walled-in yard near the new waste processing facility for
later processing and relcamation and disposal.
Dieppe-Deauville
The Dieppe plant pit has a capacity when level full at 750 m3
(980 yd3). Above the pit is a single 4.25 tonne (4.7 ton) crane, built by
Reel, carrying a 1.5 m3 (2 yd3) clam shell bucket. The Deauville pit
capacity is 700 m3 (920 yd3). At both the Dieppe and Deauville plants, the
crane is controlled from the control room, a common feature to minimize
manpower needs at small plants in Europe.
-------
P-21
Hamburg
"We don't care how much refuse we are burning. Our concern is how
much steam we are producing. Hagenholz is an energy plant and not
primarily a refuse disposal plant. If we repair the load cells,
people may begin paying too much attention to refuse burning and
not enough to energy production."
At the Stellinger-Moor plant the pit is 54m (177 ft) long, 16m
(52 ft) deep and 12m (40 ft) wide. When refuse is stacked above the tipping
floor level, 350 tonnes (3850 tons) can be stored providing 3 to 4 days'
supply. Level storage is about 2500 tonnes (2750 tons).
The cab is centered between and slightly above the two hoppers as
shown below.
Bunker
H ]
/ \
Crane
Control
Room
H
The location of hoppers for two future units is shown.
The hinged metal doors open inward over the pit. Because of the
door the crane operator has difficulty seeing what is coming into the pit
as it is falling in. He needs to observe this to better determine how the
waste should be mixed. Often, but not in Hamburg, this obstacle is overcome
by having the crane control room located on the sides of the refuse pit.
The traveling crane at Hamburg was manufactured'by FA. Lavis.
Formerly, the crane cables had to be replaced every 3 weeks.
Often, the bucket will settle in the pit at a 30 degree to 45 degree angle
instead of flat. This causes the cable to catch in between the claw and
bucket. Strand breaking can then occur. In other cases, the operator may
let the cable unwind, causing the cable to kink, come out of the trolley,
or snag in some way thus leading to a breakage.
One of the plant employees (perhaps motivated by the pay
incentive program of "more steam means more pay") came up with the idea of
built-in guide shields. This has improved the situation and 3 months
(instead of 3 weeks) in the average cable life.
The polyp has lasted longer than expected and was replaced after
4 years. Now, the plant has a new Landers polyp in storage that is only
one-half the weight of the existing polyp. This will be used eventually to
replace the second polyp.
The plant staff relies more on the crane scales than the truck
scales. Four load cells are mounted on the crane. Readings are automaticaly
recorded in the main and the crane control rooms when the polyp is hovering
over the hopper. They have no problems with the load cells themselves.
-------
P-23
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P-24
FIGURE P-13.
CRANE OPERATOR'S CABIN AT THE HAGUE PLANT WITH EMPTY FURNACE
HOPPER AND A PORTION OF THE FLOOR PLATE OF THE VIBRATING
FEEDER IN THE FOREGROUND (Battelle Photograph)
-------
P-25
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P-27
At Deauville, it has been found that lack of a spare crane is a
distinct disadvantage when crane repairs were needed during the summer
period, when maximum operation is needed. At Dieppe, the crane cables
needed replacement after 1 year due to numerous startup problems in
learning to operate the crane in such a way as to minimize cable damage.
The new cables, made by Casar especially for the Dieppe plant, are
automatically lubricated and are formed of thick wires inside and finer
ones outside which are wound alternately in opposite directions to avoid
twisting.
At Dieppe, the crane lifts a load and automatically positions the
bucket above one or another system of the two furnace hoppers. At
Deauville, a similar automatic control system has been temporarily
by-passed because the bucket damaged a railing near the hoppers. Also at
Deauville, the winter load is so light that several days are required to
accumulate enough refuse to support one furnace operation. Thus, some
refuse is stored so long that fermentation begins in the pit. The resultant
vapors generated are corrosive when they condense on the electrical control
contacts. This has caused control failures.
The lightweight cellular concrete pit walls at Dieppe are
reinforced by steel columns to withstand occasional impact from the loaded
bucket.
At Dieppe, there are five temperature sensors at door height,
above the pit to detect pit fires. Small pit fires are handled by using the
clam shell bucket to lift the burning material into one of the furnace
hoppers. Larger fires are controlled by internal or external (city)
fire-fighting equipment. When a temperature sensor detects a temperature
rise, it actuates a recording which announces, "There is a fire in the pit".
Gothenburg
Figure P-16 shows a transfer truck backing toward an open pit
door to which the driver has been directed by signal lights. The tipping
floor control room is in the ceiling as shown at the upper right of the
photo.
The pit extends 9 m below the tipping floor. It holds
approximately 6,000 m3 (7,843 yd3). By closing half of the 14 bunker doors
and piling the waste high against the opposite wall, the storage capacity
can be doubled to 12,000 JB? (15,690 yd3). At a packed density of 645 Ib/yd3
(0.383 tonnes/m3) the maximum storage is 4600 tonnes.
The pit is served by two bridge cranes built by Kone with
capacities of 7.2 and 4.8 tonnes. Each has a polyp-type bucket of 6 m3 (7.8
yd3) capacity.
Figure P-17 shows the pit with two of the 14 doors open to
receive waste. The two crane operators can be seen in the glass walled
podium in the upper right. Beneath them is a platform supporting a
high-pressure water cannon which can inject water at 1 m3/sec for control
of pit fires. Because of a dangerous fire when two drums of solvent were
cut open in a shear, new foam nozzles have been added at the pit sides
which can cover the pit with foam 1 m deep in 10 minutes.
The weight of refuse in each bucket load is read from two
calibrated watt meters on the cranes with digital readout in the crane
podium and readout and recording in the control room. The total weights are
-------
P-28
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P-29
FIGURE P-17.
REFUSE PIT WITH 2 OF THE 14 DOORS OPEN TO
RECEIVE REFUSE AT THE GOTHENBURG SAVENAS PLANT
(Battelle Photograph)
-------
P-30
checked frequently against the truck scale totals. The watt-meter weights
are claimed to be accurate within 5kg (11 Ib).
Consideration is being given to an unusual energy recovery
scheme: the crane cables would be braked electrically when lowering a load
to the feed hopper. The staff estimates that this could generate enough
electricity to earn 2,000 S.Kr. ($400) per month, which could pay for the
system in 10 years.
To reduce crane cable wear,the cable drums have been enlarged to
24 times the wire diameter and wire size has been increased from 23 to 27
mm (0.9 to 1.1 in).
Uppsala
The maximum refuse storage volume of the present Uppsala pit is
2400 m3h (3140 yd3). At a packed density of 645 Ib/yd3 (0.383 tonnesAn3)
this provides for 920 tonnes, or about a 2 1/2 day supply at fill plant
rating.
Figure P-18 shows the exterior ramp which was added to the
Uppsala plant in 1971 to enable operation with a deeper bunker for greater
storage capacity.
Horsens
The control room operator at Horsens also operates the crane and
weighing platform which is adjacent to the pit. The operator has full view
of all of this area through a large window overlooking the pit which is 9 m
(30 ft) deep and has a total volume of 950 m3 (1240 yd3). It can hold about
360 tonnes a 3-day supply. It is divided into two equal volumes, each 7.7
by 7.2 m (25 by 23.5 ft). In this way,the industrial and residential wastes
can be separated. This enables the operator to mix them in appropriate
proportions as he operates the crane to fill the single furnace hopper. See
Figure P-19. The industrial pit is nearest the operator as it requires
close scrutiny to enable the operator to control the mixture fired.
Provisions for Bulky Refuse
Many plants have shears to reduce the size of bulky combustible
refuse such as furniture. The shear is usually fed by the crane and
discharges to the pit. However, a shear is one more item for maintenance
and a few plants have discontinued using their shear.
Figures P-20a and P-20b show a common type of shear made by Van
Roll. The specification for a typical shear of this type is as follows:
Max. throughput per hour up to 200 cu.yards/150 m3
(depending on the bulky waste,
and the way of feeding)
Size of feed opening 118" x 134" / 3 m x 3,*» m
Max. capacity of the
shear in open position 10 cu.yards / 8 m3
Width between the
shear beams 12" / 310 mm
Power of driving motor 45 kW
Average power
-------
P-31
FIGURE P-18.
TRUCK ENTRANCE RAMP TO UPPSALA. THIS WAS ADDED IN
1971 TO ENABLE OPERATION WITH A MUCH DEEPER BUNKER
WHICH MORE THAN DOUBLED REFUSE STORAGE CAPACITY
(Battelle Photograph)
-------
P-32
FIGURE P-19. PHOTO SHOWS POLYP GRAB WITH HEAVY
CONCENTRATION OF PLASTIC WASTE FROM
THE SEPARATE COMMERCIAL AND LIGHT
INDUSTRIAL WASTE PIT AT HORSENS
(Courtesy of Bruun and Sorensen)
-------
P-33.
FIGURE P-20a. VON ROLL SHEAR OPENING AT
ZURICH: HAGENHOLZ
(Courtesy City of Zurich)
If.-.!*-!! SKI* , -V
mi
FIGURE P-20b. SCISSORS-TYPE HYDRAUCIALLY
DRIVEN SHEAR ADJACENT TO
HOPPER H (Courtesy of
Bruun and Sorensen)
-------
P-34
consumption approx. 35 kW
Max. pressure in the
hydraulic system 2850 p.s.i. / 200 bar
Total weight of unit 62 tons
Cooling water 1000 liters/hour, of pure
quality; static head at
entrance to cooler minimum
5 metres, maximum 10 metres
Average time for one
working step approx. 50 sec.
The bulky waste shears (see Figure P-21 ) operate like multiple
sissors, cutting and crushing the bulky refuse between its shear beams.
Seven fixed and six moveable shear beams are connected at their lower end
through shaft and bearings. Each beam is equipped with double edge blades
of highly wear-resistant allow steel which can easily be turned once and
reused. The moving beams are arranged in two groups of three, each group
being opened and closed by a hydraulic working cylinder,,
The sheared material falls through the spaces between the fixed
and shear beams and down into the pit. The crane operator must then
carefully distribute this usually higher calorific waste over the entire
pit.
The unit operates either fully or semi-automatically, with
remote-control by the crane operator. Control can otherwise be exercised at
the main control panel installed near the hydraulic power unit. A preset
pressure switch set at a force of 75 tonnes (120 bars) provided in the
hydraulic circuit and combined with a back-up pressure relief valve, limits
the maximum thrust exerted by the hydraulic rams. When the limit is
reached, the forward thrust stops and the six moveable shears retract so
that more refuse can fall into the V-shaped hopper. Thus, the unit is
protected against damage when the shearing resistance should grow too high.
A distinct advantage of the Von Roll scissors shear is that it
can operate automatically without an attendent. Compared with the many
problems of size reduction equipment (jamming, explosions, fires, breakage,
wear, etc.), this shear has excellent operating results in most of the
visited plants.
Details of Bulky Refuse Handling Methods
Werdenberg-Liechtenstein
At Werdenberg there is no provision for procesing bulky waste.
Instead, the crane operator is instructed to crush bulky items, up to 2m by
2m, (6.5 by 6.5 ft) in the pit by dropping the 3-ton grapple on the object.
Large metal objects are lifted out and set aside for recycling which, in
1976, totalled 172 tonnes.
Baden-Brugg
Originally the Baden-Brugg plant was equipped with a Hazemag
hammermill shredder adjacent to the refuse pit to break up bulky refuse.
However, in 1972 owing to the need to replace the shredder bars and re-weld
-------
P-35
7965
FIGURE P-21. ELEVATION AND PLAN VIEWS OF VON ROLL SHEAR
-------
P-36
the hammers every 3 months, the receipt of bulky wastes was limited to a
maximum size of one meter. The homeowner is required to break up any
objects larger than one meter on a side or to send large metal objects
directly to a scrap dealer. The shredder is now operated only occasionally
to assure that its working parts are kept inoperable condition.
Duesseldorf
A 15 tonne/hr shear is available at one end of the pit area at
Duesseldorf to cut up bulky wastes. See previous Figure P-1. Since May,
1973, a 15 tonne/hr shredder located in a separate building has been used
to shred bulky wastes. When the scale operator observes bulky waste in a
truck, he directs it to either the shredder or the shear. The standard
refuse container in Duesseldorf takes up to 0.6 m (2 ft) pieces. Larger
pieces must be cut or broken by the homeowner.
The Lindenmann shear is a hydraulically driven knife and bar
machine usually operated 3 to 4 hours per day. At times of heavy use, the
operator is assisted by a scale operator. The shear produces pieces about
0.6 m by 0.5 m (2 ft by 1.6 ft). Rubber tires are usually cut to 0.25 m
square (0.8 ft). Shear load is indicated by the current input to the
hydraulic-driven motor. Shear stroke can be manually adjusted by the
operator. Operating time is recorded. Shear blades are turned over every 3
months and are replaced once per year. The ram of the shear is replaced
every 10 years. The hydraulic seals must be replaced five times per year.
The Lindemann shredder was added in May, 1973. Duesseldorf is the
headquarters for Lindemann. It is a horizontal-shaft, belt-driven machine
which operates about 6 hours per day. No one is permitted in the shredder
building during operation owing to explosion hazards. The size of pieces
produced is relatively large—0.3 m by 0.5 m (1 ft by 1.6 ft)—although
rubber tires may pass through essentially intact. The output is conveyed to
the main plant pit by a belt conveyor. Maintenance on the shredder is
minor. The management attributes this to the relatively large size of the
product. The first set of shredder hammers lasted 11,000 hours during which
UO.OOO tonnes (4U,000 tons) were shredded. The second set lasted 3,000
hours.
Much more difficulty has been experienced with the feed and
output conveyors for the shredded refuse. The oil mist lubrication for the
conveyor has been ineffective.
Wuppertal
When the scale operator at Wuppertal observes bulk refuse in a
truck, the driver is instructed to deliver it to a Lindemann shear adjacent
to the pit. This shear operates from 7:00 a.m. to 4:00 p.m. With no storage
location for bulky wastes, trucks must, at times, wait until the shear is
free. A new storage bunker is planned. There are 2 shear operators, one of
whom does cleaning and maintenance work on the shear from 2:00 p.m. to 1:00
p.m.
The nominal capacity of the shear is 1 tonne or 20 m^/hr or
approximately 150 m^/hr (200 yd^/hr) of normal bulky refuse. From the
shear, the cut refuse flows by gravity into the pit.
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P-37
Paris-Issy-les-Moulineaux
Bulky wastes (stoves, bedsprings, etc.) are not normally sent to
the Issy plant. The plant can accept almost any size material that can get
into a traditional garbage truck. Industrial waste generators sign a
contract where they agree not to deliver bulky liquid and other hazardous
waste to the TIRU plants. Several times per year, special bulky waste
collections are held.
However, if bulky wastes are taken to Issy, the scale operator
can order the driver to offload onto an open area and thus the oversized
pieces never enter the pit. The Martin hopper, feed chutes, grate, and ash
handling systems can, however, accomodate very large objects, but the
eventual bottleneck is often the ash discharger.
One amazing example was a fully assembled Fenwick forklift truck
that was found inside the furnace on the grate. Because it could not pass
through the ash handling system, it was removed after first being torch cut.
Also, other undesirable objects do enter the pit and may require
the following actions:
(1) If in the pit, pull large objects up to small platform next
to and at the level of the hopper. Using welding torch cut
the object into smaller pieces. Drop pieces into the hopper
for normal processing.
(2) Using the crane bucket, use hooks and rope to pull the
bucket back to the truck tipping door.
(3) Use long rakes and hooks for dislodging in the hot furnace.
(4) Use shorter rakes and hooks at the end of the ash
discharger.
(5) Assess penalties against the waste generator.
(6) If the waste generator continues to send undesirable
material to the plant, cancel his disposal privilege for
2-3 months.
Unfortunately, the pit area is not designed for a crane to simply
pick up the bulky or hazardous object for setting aside on the floor or
into a truck container. Martin engineers recommended that such provisions
be made at future plants.
Zurich-Hagenholz
A scissor shear, manufactured by Von Roll operates from 6 a.m. to
8 p.m. five days per week at Hagenholz. This unit operated 2,931 hours in
1971* and 2,809 hours in 1976. Normally this type of shear does not need an
operator in residence because it is in motion all the time. It can process
one to ten tonnes per hour.
In contrast to many other size reduction methods, the Von Roll
Hagenholz unit has been almost 100 percent reliable. Routine inspections
are conducted and repairs made three (3) times per year and the expected
life is at least 20 years.
The knives are completely changed every 16 months. But during
that period, the edges are rotated four (4) times, i.e., once every four
(4) months.
Once per week, the knives are cleaned. Bed springs and large
tires can be a problem and may need to be extracted with a long hook.
-------
P-38
Originally, the shear was not strong enough and was later
reinforced. There will be no shear at the new Josefstrasse plant because
the chute will be larger, i.e. 1.5 x 6 m (5 x 20 feet).
Hamburg
The Stellinger-Moor plant does not have a shear or shredder
because the management feels that the bulky waste problem is so minor that
capital and maintenance costs are unjustified.
The Hague
The original plant design for The Hague included a 15 tonne/hr
Von Roll shear. This shear received bulky waste form the small bunker which
receives primarily bulky waste from private haulers. However, owing the
light construction of this early shear design, much maintenance was
required. Also, some explosions were experienced within the shear.
Accordingly, in 1970 the use of the shear was discontinued and the crane
operators are instructed to try to smash bulky objects in the bunker by
dropping the crane bucket on them. Also, there is a holding pit which is
positioned to receive either sheared material or smaller bulk refuse that
can be by-passed over the shear. From that pit, the operators of the main
bunker cranes can lift refuse directly to the furnace hoppers or it can be
deposited in the main bunker for mixing with conventional refuse. This
complex arrangement requires good judgement and skill on the part of the
crane operators to assure a well-mixed and reasonably sized supply of
refuse to the four furnaces.
Gothenburg
When the crane operator at Gothenburg's Savenas plant observes
oversize waste being delivered, he can lift it to one of two Von Roll Model
13/310 shears situated between two of the furnace feed hoppers to have it
cut to smaller size. The cut pieces fall from the shears into the refuse
pit. The rated shear capacity is 120 tonnes/hr each.
Uppsala
At Uppsala a Von Roll scissors type shear, operated by the crane
operator, has the capacity to reduce 4m (13 ft) bulky refuse to 0.3 m (1
ft) pieces.
Horsens
Bulky waste is now sent directly to the Horsens landfill which
has a shredder. However, plans have been made to install a shear estimated
to cost 500,000 D.Kr. ($83,333). An alternate being considered is a double
screw size reduction device licensed by Norba and built by Volund. One such
installation at Horsholm is said to have provided good service for about 10
years.
-------
P-39
Copenhagen-Amager and West Plants
The Amager plant has no provision for bulky waste because the
adjacent transfer station screens out all bulky items. But at the West
plant the scale operator directs drivers with bulky wastes to either of the
two Lindenmann "Lomal 10" shears. The second shear was added in 1975. About
MO-50 percent of the refuse input is processed through the shears.
Previously, bicycles, tubs, furniture, etc, had been jamming in the refuse
hopper, chute, and ash discharge operations. The current rule to drivers is
that all garbage collection trucks and transfer truck-trailers disgorge
directly into the refuse pit. Equally as firm is the rule that all other
trucks (especially detachable container loads) must discharge to the
Lindeman shears.
The shears are adjacent to the pits. They are rated at 80 mVhr.
Operation is intermittent and only on the day shift when the operator is
present. The drive is hydraulic.
The maintenance record has been excellent. Blades are replaced
usually after one or two years. With the rule that all miscellaneous truck
loads must go to the shear, several problems have arisen. For example the
hear is sometimes difficult to operate when overloaded with small-sized and
wet refuse such as a truck load of grass clippings.
These shears cost 2.5 to 3.5 million D.Kr. ($450,000 to 600,000)
each.
Hoppers and Feeders
An integral feature of the pit-and-crane system is that each
furnace receives its waste from a hopper and chute which are fed
intermittently by the crane bucket. This intermittent batch feeding is
converted to nearly uniform flow to the furnace-grate by 2 factors:
1. Short-term storage capacity of the hopper and chute
2. Action of a reciprocating or vibrating feeder which moves
the refuse from the chute to the grate.
Figure P-22 shows a diagram of the feeder arrangement at
Zurich-Hagenholz. The feeder serves a multiple purpose. In addition to
supplying fuel to the furnace its action in moving*packed refuse away from
the bottom of the chute permits the crane operator to keep the chute packed
full. This packed mass served to prevent burn-back from the furnace into
the chute and hopper.
At times the crane operator may be so busy with multiple problems
of receipts, mixing and charging that some chutes may inadvertently become
emptied. If so, burn-back into the feed chute can occur. Accordingly many
chutes are equipped with gates or dampers that can be closed to prevent
flames from flowing upward through the chute and hopper. Some newer chutes
are equipped with radioactive level indicators which provide indication in
the control room and crane pulpit when the refuse level is low.
Because of the potential for burn-back causing overheating of the
feed chute, some chutes are water cooled or refractory lined.
-------
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-------
P-41
Werdenberg-Liechtenstein
At the small Werdenberg plant, the single furnace hopper is 4m by
Mm (13.1 ft by 13.1 ft) and the feed chute is 2.5m by 1.5m (8.2ft by 4.9
ft). The chute is insulated but uncooled. The lower portion of the chute
near the furnace is low alloy steel to reduce deterioration from high
temperature. An insulated cover can be placed over the hopper top to stop
burnback, if it occurs, by preventing air or gas flow. (See the previous
Figure P-7)
The single-level, ram-type, inclined feeder is hydraulically
driven by a Vickers drive. It feeds intermittently about 12 strokes per
hour which is about half the frequency of the reciprocating grate sections.
The feed is manually controlled from the control room. A spare hydraulic
drive is available. No repairs have been needed in 3 years.
Baden-Brugg
At Baden-Brugg, with two 120 tonne per day furnaces, the top of
each furnace hopper is Urn (13.1 ft) square and the feed chute is 2.5m by
1.5m (8.2 ft by 1.9 ft). The chute is not cooled nor insulated. If burnback
into the hopper occurs it can be stopped by means of hinged insulated cover
placed over the hopper. When large objects jam the chutes a heavy wood ram
held by the crane grab is used to force the object downward.
A single level, hydraulically-driven ram feeder made by Hydro
feeds the refuse inward every 1.5 minutes. The length of stroke is 600mm (2
ft). The speed of the motion is fixed. If something prevents the ram from
withdrawing from the furnace an alarm sounds. Reliability has been
essentially 100 percent. There is no feeder redundancy. After 7 years
operation the cyclinder on the drive has recently been replaced. The piston
guide is lubricated once per month.
Initially the feeder piston seal leaked. That defect was
corrected. The feeder plate was changed from cast iron to steel because
early in the operation, heavy objects falling from the feed chute broke the
feeder plate.
The Baden-Brugg furances begin with a water cooled arch
connecting the feed chute exit to the top of the furnace entrance. This
minimizes burnback. (See Figure 24)
Duesseldorf
Figure P-23 shows the original hopper, chute and feeder at
Duesseldorf. Some modification of the original 5 m by 5 m (16.3 ft by 16.3
ft) hoppers has been required to prevent bridging in the pyramidal hopper.
The remedy was to raise one side of the sloping hopper wall so that less
material could crowd downward into the feed chute. This crowding caused the
bridging. Also, the feed chute, 3 m by 1.8 m (10 ft by 5.9 ft), was
changed, tapered outward from top to bottom at the rate of 150 mm (5.9 in)
in 5 m (16.3 ft) to relieve the tendency to jam in the chute. In 1975 the
height of the opening where the refuse is pushed from the bottom of the
chute into the furnace, was reduced somewhat on three of the boilers to
prevent burnback. Also water cooling was added to the lower 2.5 m (8 ft) on
some of the feed chutes. On those chutes, which are not water cooled,
-------
P-42
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-------
P-43
FIGURE P-24. CROSS SECTION OF ONE OF BOILERS NO. 1-4 (Courtesy of
Stadtreinungs und Fuhramt Duesseldorf)
1. Refuse hopper
2. Refuse feeder and roller
Srate "system Duesseldorf"
3. Ignition burner
4. Heavy oil burner (both sides)
5. Economizer
6. Steam drun
7. Radiant water-tube-wall boiler
8. Boiler convection section
9. First and second stage super-
heater
10. High-temperature superheater
11. Steam discharge
12. Exhaust gas duct to electro-
static precipitator
13. Ash sift ings removal
l^t. Wet residue conveyor
15. Residue removal to processing
plant
-------
P-44
turnback during shutdown is prevented by use of guillotine doors covering
the opening between furnace and chute.
Four of the reciprocating refuse feeders are mechanically driven
and one drive is hydraulic. They feed horizontally under the automatic
control of boiler steam flow but are limited by furnace temperature and
excess oxygen. If temperature is too high or oxygen is too low, feed rate
is reduced. The reciprocating feeder plate is water cooled. The forward
feeding stroke is faster than the return stroke. Operators prefer the four
mechanically driven feeders because they require less maintenance than the
hydraulic drive. Also, any hydraulic fluid leakage constitutes a fire
hazard. The feeders used were developed at this plant.
Wuppertal
The top of the four furnace hoppers at Wuppertal are each 5 by 5
(16.3 by 16.3 ft) square. Water cooling of the chutes is available but is
used only when the temperature becomes to high. A lifting type of damper
can close off the chute if burnback occurs.
Each stoker has an automatic hydraulic ram-driven feeder which
can be controlled from the control room. Normally it strokes 15 times per
hour. The length of stroke can be varied from 20 to 50 cm (5 to 12 in) by
adjustment at the feeder. So far the feeders have had no problems. On some
occasions, during initial operation, there was back-burning in the chute
caused by loosely packed wood waste which allowed the flames to move upward
in the chute. The solution has been for the crane operator to mix the
refuse and to charge the hoppers in such a way that the chutes are kept
packed full. Repeatedly, here it was emphasized that the most important
worker in the plant is the crane operator.
Krefeld
The top opening of the two hoppers at Krefeld is 4.5 m (14.8 ft)
square. The water-cooled feed chute is 1.8 m by 2.85 m (5.9 by 9.4 ft). A
hydraulically operated damper in the upper part of the chute can be closed
in case of burnback.
The stroke frequency of a hydraulic ram feeder can be controlled
from the main control room. The frequency of the ram can be adjusted
between five and fifty strokes per hour. Normal speed is 15 per hour.
Paris; Issy-les-Moulineaux
The hopper opening at Issy is 6.25 m (20.67 feet) by 9.8 m (32.34
feet). The hopper tapers off to the chute having dimensions of 1.438 m (4.7
feet) by 6.25 m (20.5 feet). Normally, the hopper is kept empty while the
feed chute is full. The chute has a water cooled jacket. There is also a
horizontal water-cooled cut off gate to minimize burnback. Finally, there
is a water-cooled cut off gate to minimize burnback. Finally, there is a
water-cooled arch connecting the top of the feed opening to the combustion
chamber.
Not typical of most Martin plants, Issy plant experiences
frequent burnback during startup — about 90 percent of the time. Burnback
n shutdown is not quite as frequent. In Martin's newer Zurich plant, steam
-------
P-45
nozzles at the rear and bottom of the chute propel the refuse out onto the
grate, thus minimizing burnback while the chute is being cleared or filled.
The chute has one access door for maintenance access during
outage of the incinerator.
Of the four Issy furnace feeding systems, one is hydraulic 15 bar
(220 psia) and three are electro-mechanically driven. Plant officials value
the systems as about equal. Martin officials admitted their initial
skepticism regarding hydraulic feeders as proposed by TIRU. However,
Martin now normally recommends the hydraulic feeders. A key feature is that
the hydraulic system responds better to a jamming object without breaking.
A mechanical system will more easily break. The main problem with the
hydraulic system is oil loss with accompanying potential fire hazard.
Each of the three runs per furnace has two feeder mechanisms; an
upper and a lower ram or pusher. The furnace feeder total width is 6.3 m
(20.67 feet),i.e., 3 x 2.10 m. The depth is 4 m (13.2 feet). The cross
section of the fuel entry in to the furnace is 8.82 m^ (95 ft^) having
dimensions of 6.3 x 1.4 m (20.6? x 4.6 feet).
Each pusher is provided at its front end with heat-resisting
chromium steel alloy bars 12 mm thick at its rear end with a 10 mm thick
steel plate, which is reinforced to withstand the impact of refuse falling
from the hopper. Each pusher is supported at its front end by sliding
noses, and at its rear end by roller bearings on each side and guided by a
vertical roller bearing. Each pusher is operated by a hydraulic cylinder.
The control of the feeding device is over a range of more than 1
to 10. The control equipment is mounted in the hydraulic control cabinet
together with the control equipment of the grate. The feeder control is of
the auto-manual type where the manual operation may be controlled locally
or from the control room.
In some recent systems the refuse level within the chute at the
minimum allowable level can be measured by a radioactive device and
indicated in the crane operating cab and in the main control room.
Hamburg
Each hopper openig at Stellinger-Moor is 5.9 m (19.3 ft) by 6.3m
(20.7 ft). The hopper tapers to the chute which is 1.5 m (4.9 ft) by 4.9 m
(16 ft). Normally, the hopper is kept empty while the feed chute is full.
The chute has a watercooled jacket to reduce the effect of burnback.
As the average refuse heating value has risen, there have been
more burnback instances as ignition occurs closer to the chute. To reduce
the ignitability of the refuse, water was sprayed directly onto the refuse
in the hopper. Burnback was substantially reduced to once every week or
two.
Now most of the burnback comes from large voids in the chute due
to a bulky desk or cabinet. Also, an iron bar may jam the feeder, causing
normal refuse to burn but preventing new refuse from entering the
combustion chamber. When asked if a shredder might alleviate the problem of
chute-feeder jamming, the response was that "two million DM ($800,000) was
too high a price to pay for solving such a minor problem". Repairs to a
shredder or a shear might be even more expensive than repairs for
occasional shutdowns of the feeder.
-------
P-46
Each of the two grate runs per furnace has two feeder mechanisms:
an upper and a lower ram or pusher. The furnace feeder total width is 4.2
m (13.8 ft), ie., 2 x 2.10 m. The depth is 4 m (13.1 feet). The cross
section of the fuel entry into the furnace is 8.82 m2 (91.90 ft2) having
dimensions of 6.3 x 1.4 m (20.6? x 4.6 feet).
Each pusher is provided at its front end with heat-resisting
chromium steel alloy bars 12 mm thick and at its rear end with a 10 mm
thick steel plate, which is reinforced to withstand the impact of refuse
falling from the hopper. Each pusher is supported at its front end by
sliding noses, and at its rear end by roller bearings on each side and
guided by a vertical roller bearing. Each pusher is operated by a hydraulic
cylinder.
The control of the feeding device is over a range of more than 1
to 10. The furnace feed rate can thus be set at between 20 and 40 tonnes
(22 and 44 tons) per hour. Martin's analog computer controls exact feed
rate based on instantaneous temperature readings taken at the top of the
first pass.
There have been some hydrualic feed system problems with sticking
valves at the pumping station. Nevertheless, the plant operators emphasized
their preference for "hydraulic only" systems over mechanical drive
systems. As one operator stated, "we may have minor problems with the
hydraulics, but a mechanical system would actually break if jammed".
In future systems, Martin often recommends a system where the
refuse level within the chute at the minimum allowable level can be
indicated by means of a radioactive device communicating to the crane
operating cab and the main control room.
Zurich
At the Hagenholz plant, Unit No. 3» the hopper dimensions are
5.517 m (18 ft) by 7.056 m (23 ft).
The hopper tapers to the feed chute that is 1.5 m (4.9 ft) by
5,486 m (18 ft). The chute is surrounded by a water jacket.
Burnback has only occured once in four (4) years in Martin's #3
unit. While not certain, operators suspect that superheater tubes might
have become plugged to a point where the furnace became positive
pressurized. Another reason might be that the I.D. fan was not functioning
properly. For whatever reason, pressure likely built up and fire eventually
backed up the chute.
An explanation was made for the excessive burnback experience at
Paris: Issy - les - Moulineau. Issy has a very high chute. As a result, an
induced draft pulls the flame back up the chute in 90 percent of all
start-ups. Hagenholz is fortunate to have a stubby chute and wide enough
spaces between boiler tubes.
Unit #3 has three (3) grate runs. Each run has upper and lower
Martin feeders with the following specifications. Stoke frequency is a
function of steam temperature, steam pressure, and temperature entering the
electrostatic precipitator. The feeder characteristics are:
-------
P-47
Stroke (maximum)
Stroke (normal)
Frequency (strokes/minute)
Upper
600 mm
180 mm
2 to 5
Lower
1000 mm
300 mm
2 to 5
The feeders are hydraulically driven. Preventive maintenance
helps achieve reliability of almost 100 percent. On one occasion, a waste
container of acetone spilled into the chute, leaked out of the chute and
onto the rubber hydraulic lines. The acetone entering the furnace caught
fire which transmitted to the rubber tubes outside the chute. The tubes
were replaced with flexible steel hoses.
The feeders are controlled by the Martin "black box".
Zurich officials are pleased with the hopper and feeder
performance and Martin will use the same design at the new Josefstrasse.
The Hague
Figure P-13 shows a cross-section of boiler/furnaces 1-3 which
were built in 1967. Each of the four furnace hoppers has a top opening of 5
by 3.7 m (16.4 by 12.1 ft). Immediately beneath the hopper is a large
vibrating feeder which feeds into a water-cooled chute about 3.4 by 1 m (11
by 3.3 ft). The feeder, made by Schenck of Darmstad, West Germany, is
vibrated by rotating eccentric weights automatically controlled by a
radioactive chute-level indicator made by endress and Hauser. The
radio-active source is Cesium 37 with an intensity of 75 milliroentgens.
Burnback in the chute never occurs on start-up or shut-down, only
if the chute jams, preventing full flow or refuse. A flap damper can be
used to seal off the top of the chute in case of burnback. Jamming in a
hopper can be released by the force of a railroad tie dropped in by the
crane bucket. The vibrating feeders have been trouble-free for nearly ten
years. It is expected that the steel floor-plate of the feeders will need
replacement after about 12 years of service.
Dieppe and Deauville
The hoppers at both of these plants are similar, 2 m by 4 m (6.5
by 13 ft) at top and at the base of the chute, the dimensions are 1.6 m by
1.2 m (5.2 by 4 ft), with the juncture between hopper and chute sealed by a
flap damper to prevent burnback. This method of feeding and sealing is
impractical for much larger plants were Von Roll uses a vibrating feeder to
feed from the chute to the furnace. At both plants, the chute is water
jacketed but a thermocouple in the jacket at Deauville indicates that water
flow to the jacket for cooling is seldom needed. Some wet-type corrosion
was visible on the jackets.
A sloping reciprocating type of feeder in the furnace feeds the
main burning grate. There is no combuston air supplied to the feeder.
Gothenburg
The top of the three furnace feed hoppers is 3.5 by 2.4 m (11.5
by 8.1 ft) each. At the hopper bottom is a sloping vibrating table built by
Schenk and having an amplitude of 8 mm (0.3 in). The feeders are controlled
-------
P-48
by radioactive level indicators in the water-cooled feed chutes. The
indicators use Cesium 136 and were made by Endres and Hauser of Lorrach,
Germany.
The vibrating feeder has been satisfactory. The chief engineer
pointed out that the use of a vibrating feeder to feed the vertical chute
1.2 by 3-4 m (4 by 11 ft) requires about a 3 m (10 ft) height of refuse in
the chute to assure a tight air seal and avoid burnbacks in the chute. If a
hydraulic ram feeder was used just above the grate to maintain a seal, most
of the 10-meter chute height could be eliminated, thus reducing overall
building height by about 10 meters. However, the tall chute does provide a
simple, easily managed seal that has effectively minimized burnback.
Uppsala
Figure P-25 shows Furnace No. 4 the Brunn and Sorensen
installation at Uppsala. The vertical outwardly tapered steel chute feeds
directly onto the sloping grate without assistance by any feed mechanism
except the feeding action of the grate itself. For the first three furnaces
built by Kockum-Landsverk (not a part of Volund), the feed chutes are not
provided with dampers to control burnback. Instead, the height of the
gravity-packed refuse in the chute is depended upon as a seal. However,
with furnace No. 4 installed in 1970, the confinement of the existing roof
structure and the height of the top of the Brunn and Sorensen grate imposed
an upper limit on the length of the feed chute. Thus, to control burnback
in the chute, a double flap damper was installed. The operators have had no
problem with burnback.
Figure P-26 shows a view into the empty hopper where a thin line
of flame is visible between the mating halves of the flap damper.
Horsens
The top opening of the single hopper at Horsens is 4.2 by 4.8 m
(13.8 by 15.7 ft), and it is 2.1 m high (6.8 ft). The refuse flows by
gravity from the hopper into a refractory-lined feed chute 1.11 m high (3.6
ft) and 1 by 1.6 m (3.28 by 5.2 ft) at the top, tapering out to 1.6 by 2 m
(5.2 by 6.5 ft) at the bottom. Burnback can be arrested by the cast iron
flap damper in the chute.
The poured refractory lining of the chute is 50 mm (2 in) thick,
held in place by welding anchor rods.
At the bottom of the chute, the refuse is fed on to the sloping
grate by a similarly sloping hydraulic feeder designed by Bruun and
Sorensen and built by Monsund. The feed ram has a maximum stroke of 2.5 m
(8.2 ft) and a capacity of 5 tonnes/hour. Variable feed is provided by
timer which can be adjusted by the operator from 0 to 1 stroke/minute. The
only problem with the feeder has been oil leakage.
Copenhagen: Amager and West
At the Amager and West plants the hopper dimensions at the top
are 6 m (19.7 ft) by 6 m (19.7 ft). At the hopper bottom, the dimensions
are 2.3 m (7.5 ft) by 1.15 m (3.8 ft). Its height is 6 m (19.7 ft). The
-------
P-49
1. Crane and Bucket
2. Refuse Bunker
3. Crane Operator's Station
4. Furnace
5. Afterburner Chamber
6. Steam Boiler
7. Electrostatic Precipitator
8. Induced Draft Fan
9. Primary Air Zones
10. Residue Conveyor
11. Waste Oil Tank
FIGURE P-25. ARRANGEMENT OF UPPSALA PLANT
(Courtesy Bruun and Sorenson)
-------
P-50
W
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§
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-------
P-51
walls are made from 8 mm (0.3 in) carbon steel. Sometimes Volund installs a
concrete hopper instead of steel. Concrete is cheaper and reduces noise.
The filling chute has a slightly larger width dimension than the
hopper: 2.7 m (8.9 ft) by 1.15 m (3.8 ft). It too is made of 8 mm (0.3 in)
steel.
To prevent burnback a swivel gate or damper is located in the
chute. It is opened when refuse falls on it and closed when no refuse is
above it. The damper's dimensions are 2.58 m (8.5 ft) by 1.26 m (U.1 ft)
and is 10 mm (0.39 in) thick.
Amager and Volund officials do not believe that a water-cooled
chute is necessary. Volund typically installs chutes with only refractory
lining. Except for flowing material, the hopper should always be empty.
There should be no refuse above this kind of damper to interfere with its
closing. With proper crane operator training and performance, burnback can
be minimized. Officials believe that water cooled jackets, besides being
unnecessary, increase costs of operation and maintenance.
Originally at West the damper (swivel gate) on Units 1, 2, and 3
was located 2 m (6 feet) below the hopper/chute interface. Severe burnback
and metal warpage resulted. The 12 mm (0.5 inch) support ribs warped in
addition to the walls themselves. Figure P-27 shows the effects. The plant
successfully reduced serious burnback by raising the damper level to only
0.5 m (1.5 ft) below the hopper/chute interface. West Units 1-3 are
equipped with special pneumatic air hammers that can be used to dislodge
jammed feed hoppers or chutes.
In planning Unit 4 (which began operation five years later), the
designers also specified that refractory brick should be extended
internally up to the hopper/chute interface. Even with this, there has been
some burnback.
Another cause of burnback in the early years was that the crane
operators would put too much refuse in. Except for flowing material, the
hopper should always be empty. There should be no refuse above this kind of
damper to interfere with its closing. Persuasion and practice rectified
this problem. Unless radioactive monitoring is used, the crane operator
should view the hopper/chute interface if designed as West is designed.
-------
P-52
FIGURE P-27. WARPED FEED CHUTE AT COPENHAGEN: WEST
-------
Q-l
GRATES AND PRIMARY AIR
General Comments
The grates used in the early stages of mass burning of refuse were
adapted from coal burning practices, the principal change being to provide
much more fuel-bed agitation. This was needed because refuse is so
heterogeneous that discontinuities and gaps are always present and new ones
can form as the refuse burns. Agitation of the bed is the means used to
shuffle, tumble, or resettle the burning fuel so as to fill the gaps and
make it more uniform for better distribution of primary air and of burning.
Three basic grate systems are used as shown in Figure Q-l. There
are many other variations of these three types.
This report concentrates on European refuse burning to energy
systems. All systems visited have been mass-burning grate systems. To our
knowledge there was only one system in Europe (Birmingham, England) burning
refuse in suspension in contrast to U.S. developments. For the benefit
of American decision makers, both mass-burning and suspension systems are
listed in Table Q-1. This table includes a listing of independently
developed refuse burning systems, their home country and their American
representative "Refuse burning" refers to "combustion" or incineration"
where combustion products after a few seconds are I^O, C02, S02, etc. There
is no attempt to present manufacturers of pyrolysis or other developmental
resource recovery processes, i.e. this is not a full list of resource
recovery manufacturers. Also excluded are the many manufacturers of small
modular package incinerator-heat exchangers. The table includes present and
past manufacturers with heat recovery.
Manufacturers of only incinerators (without boilers to cool
combustion gases prior to gas cleaning) are not included in the listing.
Grate Functions
The three primary functions of grates are:
• Support the burning refuse
• Move and agitate the burning refuse
• Distribute the primary air.
There is a wide range of differing design philosophies aimed at
achieving these three functions. While all the grates observed do
accomplish these primary functions, they do so at varying levels of grate
maintenance required and with varying success in achieving uniform
combustion.
Table Q-2 compares the grate design characteristics for the plants
visited. The grate burning capacities range from 24.6 down to 3.33 tonnes
(27 to 3.7 tons) per hour, a unit size range of 7.^ to 1. And the burning
rates range from 560 down to 175 kg/m2/hr (11M.6 to 35.8 Ib/ft2/hr), a
range in rates of 3-2 to 1.
If all other factors are equal, the higher the grate burning rate,
the more effective and efficient the grate will be. However, the effect of
the prate on the combustion in the boiler furnace is of critical importance
to boiler-furnace life and efficiency. It appears that one popular design
philosophy is to use moderate burning rates and large boiler furnaces to
provide reasonable heat recovery efficiency while minimizing maintenance.
-------
Q-2
Reciprocating Grate
Reverse Acting Grate
Roller Grate
FIGURE Q-l. BASIC TYPES OF GRATES FOR MASS BURNING OF REFUSE.
THERE ARE AVAILABLE MANY VARIATIONS OF THESE
BASIC TYPES (FROM EBERHARDT-PROCEEDINGS 1966 NATIONAL
INCINERATOR CONFERENCE, ASME, NEW YORK, p 124-143)
-------
Q-3
TABLE Q-l. REFUSE BURNING MANUFACTURERS AND REPRESENTATIVES
(Traveling Grate and Suspension Firing)
International Technology
Country
Representative in the U.S.A.
Alberti-Fonsar
Babcock Wilcox (BW)
Bruun & Sorensen
Carbonisation Enterorise
et £eramique (CEC)
Claudius Peters
Combustion Engineering (CE)
De Bartolomeus
Destructor
Detroit Stoker
Dominion Bridge
Esslingen
Flynn & Emrich
Foster Wheeler
Heenan
K K K
Kunstler Koch
Keller-Peukert
Koc hum-Land s verk
Italy (Milan)
U.S.A. (North Canton, Ohio)
Denmark (Aarhus)
France
West Germany (Hamburg)
U.S.A. (Windsor, Conn.)
Italy (Milan)
Sweden
U.S.A. (Monroe, Mich.)
Canada
West Germany
U.S.A. (Baltimore, Md.)
U.S.A. (Livingston, N.J.)
United Kingdom
Widmer & Ernst (Swiss Co.)
Babcock Wilcox
looking for repre.
Combustion Engineering
Detroit Stoker
Flynn & Emrich
Foster Wheeler
Switzerland (Zurich)
West Germany (Leverkeusen)
West Germany
fohlenscheidungs-Gesellschaft(KSG) West Germany
Kraus-Maffei West Germany
Lambian-SHG West Germany (Kassel Bettenhausen)
Lokomo Finland
Lurgi West Germany (Frankfort)
Martin West Germany (Munich)
Nichols U.S.A.
Plibrico U.S.A. (Worcester, Mass.)
Riley Stoker U.S.A. (Chicago, II.)
Stein France
Steinmueller West Germany (Hamburg)
Widmer & Ernst
Grumman Ecosystems
Universal Oil Products
Nichols Research & Engineering
Plibrico
Riley Stoker
Widmer & Ernst (Swiss Co.)
Takuma
Venien
Vereinigte Kesselverke (VKW)
Volund
Von Roll
Widmer & Ernst
Burn Industries
Japan (Osaka)
France
West Germany (Duesseldorf)
Denmark (Copenhagen)
Switzerland (Zurich)
Switzerland (Wettingen)
U.S.A. (Erie, Pa.)
Inactive representative in CA.
Grumman Ecosystams (total
systen'i
Wheelabrator - Frye
Widmer & Ernst
2urn Industries
NOTE: 1. The above systems are combuston oriented.
2. Small modular package incinerator - heat exchanger manufacturers are not included.
3. Pyrolysis and other developmental resource recovery systems are not included.
4. The above systems have been installed with energy recovery.
* International Incinerators, Inc. of Atlants ' i the license until the mid 197C's uhen
As of 19T8, iCas'e ".tanacerer.t ".
as assur.ed me license.
-------
Q-4
TABLE Q_2. GRATE DIMENSIONS AND BURNING RATES
Separate Fatal 1*1
T«ar Ho. of Mfg. of Grata Crate **t«d
Trlo Started Boiler* Crates Crate Dimension* Section™ Hun* R«fua« KMX D«aign Design Crat«
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-------
Q-6
TABLE Q-3. DESIGN PRESSURE OF PRIMARY
AIR SYSTEM AT PLANTS VISITED
Primary Air
Plant
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Werdenberg-Liechtensteln
Baden-Brugg
Duesseldorf
Wuppertal
Krefeld
Paris rlssy
Hamburg : Stellinger-Moor
Zurich :Hagenholz
The Hague
Dieppe (and Deauville)
Gothenburg
Uppsala
Horsens
Copenhagen : Amager
Copenhagen :West
mmH 0
170
280
180
240
140
300
410
530
580
370
150
400
-
200
230
230
in.H20
6.7
11
7
4.5
5.5
11.8
16.1
21
23
14.4
5.9
15.7
-
7.9
9.0
9.0
Pressure
kPa.
1.67
2.74
1.74
2.37
1.37
2.94
4.00
5.23
5.72
3.585
1.471
3.91
-
1.97
2.24
2.24
-------
Q-7
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-------
Q-8
All grates observed provide agitation of the burning mass. This
is in recognition of the need to do two things:
• Continually expose fresh surfaces to ignition and air flow
• Keep filling in voids that form rapidly when zones of
lightweight highly combustible material burn out. This leaves
voids through which primary air can bypass the bed unless
such holes are promptly filled by rearrangement of the
heterogeneous mass.
Even the older traveling grate which provides no fuel bed
agitation was installed as a multiple series of stepped traveling grates so
that as the burning refuse tumbled from one grate down to the next, there
was momentary agitation and rearrangement of the bed.
Specific Vendor Grates
Von Roll Grate
Figure Q-2 shows in more detail the standard Von Roll sloping,
reciprocating grate installed as two steps in a large furnace. The original
Von Roll grate, which is still in use in many of the larger Von Roll
plants, involves the alternating forward motion of adjacent grate "plates".
This naturally caused wear by the abrasive action of ash and clinker
particles sifting between the plates as they slide relative to each other.
As a result, the air gaps between the grate plates at The Hague plant,
originally 3 mm (0.12 in) increased in nearly 10 years to, in some cases,
^0 mm (1.6 in). This impaired control of the distribution of primary air
and, at times, the air-flow resistance through portions of the grate and
fuel bed is so low that the air pressure below the grate becomes less than
atmospheric. However, there has been little grate repair work done in
nearly 10 years of operation except for annual renewal of the sliding
plates attached to the bottom of the grate bars.
For smaller furnaces (that is, 5 tonnes per hour or less), Von
Roll began 15 years ago to install the improved grate composed of alternate
fixed and moving rows in which each entire moving row of grate plates moved
forward and backward together, thus eliminating the relative motion and
grinding action between adjacent grate blocks. There is still a wearing
action then due to the relative motion of each moving row on the stationary
row beneath it, but the air gap there is kept minimal by the gravitational
force holding each upper row tightly against the next row below. Von Roll
is now applying this grate, as shown in Figure Q-3, to all new furnaces
regardless of size.
Drying Grate. In the early Von Roll plants, there was first a
large drying grate because it was anticipated that often the refuse would
be very wet. Also, directly above the drying grate there often was a
gas-burning chamber so that hot flue gas could be forced directly downward
against wet refuse on the drying grate. However, today's refuse has not
been as wet as in earlier years. Accordingly, the gas burning chamber is
now unused or eliminated, and the size of the drying grate has been reduced.
Burnout Grate. Figure Q-H illustrates another feature of the early Von
Roll grate, the use of grate knives which are raised intermittently to lift and
-------
Q-9
FIGURE Q-2.
VON ROLL RECIPROCATING STEP GRATE IN REFRACTORY
WALLED FURNACE (COURTESY VON ROLL, LTD.)
Circa: 1975-Present.
-------
Q-10
FIGURE Q-3. TWO STEPS OF VON ROLL GRATE USING RECIPROCATING
FORWARD-FEED DESIGN. (Courtesy of Von Roll)
-------
Q-ll
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FIGURE 0-4. ARRANGEMENT AND DRIVE OF GRATE BLADES IN
ORIGINAL VON ROLL GRATE (FROM R. TANNER,
SONDERDRUCK aus SCHWEIZERISCHEN BAUZEITUNG,
83 JAHRGANG, HEFT 16, 1965)
(1) Grate Blades Raised
(2) Grate Blades Lowered
(3) Cylinder for Pneumatic Drive
(4) Solenoid Control Valve
(5) Control Box
(6) Limit Switch
Circa: 1948-1965
-------
Q-12
agitate the fuel bed at the last stages of burnout. Tanner * described the
philosophy of these blades in 1965. Tests have shown:
"... burnout on ordinary grates is poor for the two following
reasons:
(1) At the end of combustion, the clinker is covered with a
layer of ash which hampers the access of oxygen to the
remaining fuel.
(2) Depending on the original composition of the refuse,
there is a tendency to form lumps ranging in size from
a fist to a football, which burn up on the surface
while remaining completely unchanged inside.
Both these effects can be avoided by means of grate blades
arranged on the last grate or the last grate portion. In a cycle
that is adjustable, they beat against the clinker layer from
below, knocking the ash from the clinker and splitting up any
refuse lumps. This ensures a satisfactory burnout of the clinker.
From the angle of design, the grate blades have the advantage that
they fit freely into the grate and do not prejudice any widening
of the latter."
Grate Steps. As illustrated in Figure Q-3, the Von Roll system
features one or more steps between grates to rearrange the fuel bed as it
tumbles downward from an upper to a lower grate. Because of the "opening
up" of unburned combustible surfaces as this tumbling action occurs, this
point in the furnace is one of intense burning. To provide enough air at
this point, in some plants, air is being admitted through the wall of the
step to assure ample oxygen supply for the increased combustion rate.
Grate Zones. Primary air under the grate is supplied to a number
of separate air zones, usually six or seven, with 'a manually set damper
controlling the flow to each zone. An automatically controlled damper
controls the total primary air supply.
Kunstler Grate
At The Hague, one furnace, after about 55,000 hours of operation,
will shortly be converted to use a Kunstler grate manufactured by K&K
Ofenbau AC, Zurich, This type of grate, shown in Figure Q-5,which is from
the Basel, Switzerland plant, similar to the improved Von Roll grate,
consists of horizontal rows of grate blocks which are moved forward in
unison, thus eliminating relative motion between adjacent blocks. At the
same time, the Kunstler air wall system is to be installed at The Hague in
the walls near the grate. This will be discussed later under "Furnace Wall".
A new form of reciprocating grate, not seen at any of the 15
plants visited, is the new Kunstler grate shown diagramatically in Figure
0-5. Instead of sloping downward, the three sets of grates slope slightly
upward. The design intent apparently is to prolong the retention of burning
waste in each section before it is tumbled downward over the step to the
next lower grate section.
*Tanner, R., "The Development of the Von Roll Refuse Incineration System,"
Sonderdruck aus Schweizerischen Bauzeitung, 83 Jahrgang, Heft 16 (1965).
-------
Q-13
FIGURE Q-5. KUNSTLER GRATE AND AIR-COOLED WALL PLATES
APPLIED TO AN INCINERATOR (COURTESY K&K
A.G. ZURICH)
-------
q-14
FIGURE Q-5a.
DIAGRAMMATIC VIEW OF APPLICATION
OF A 3-STEP KUNSTLER & KOCH GRATE
TO 3-PASS BOILER.
(Courtesy Kunstler & Koch)
-------
Q-15
Martin Grate
The Martin "Reverse Reciprocating" stoker grate, shown in Figure
Q-6, is inclined downward at an angle of 26 degrees from the feed end
towards the clinker discharge end. It is comprised of alternately fixed and
moving steps of grate bars. The activated steps move slowly counter to the
downhill refuse movement.
In this manner, the fuel bed is constantly agitated, rotated, and
again leveled out. The glowing mass is pushed back from the main burning
area towards the front or feeding end of the grate. The different phases of
combustion, i.e., drying, volatilization, ignition, and burnout, thus take
place at the same time in close contact with one another. Freshly fed
refuse is dried out and ignited from below by the burning fuel maintained
at the grate front end.
The grate bars are made of a heat resisting cast steel alloy of 16
to 18 percent chromium. Air entering the grate bars passes through the
serpentine channels in the underside of the bar before passing through the
air slot (less than 2 mm wide) between adjacent bars into the fuel bed.
Grate Zones. The grate bars are designed and assembled so that no
more than 2 percent of the grate area Js open for air flow. Thus, with
separate air flow control in each of the five to seven air plenums and with
the many small air holes, the primary air pressure drop can be kept at a
very high level for maximum control of air-fuel ratio and relatively
uniform distribution of air through the area of each grate zone.
The undergrate air is admitted to each zone through damper
openings of different sizes in accordance with air supply requirements over
the whole grate surface. The opening angle of these dampers is selected by
a central controller and is proportioned to the desired heat release. Each
section of grate with its air plenum and siftings hoppers are supported by
a structural steel system of ample strength to carry all of its parts and a
refuse bed of 500 kg/m2 unit weight. Grates and supports are sufficiently
strong to withstand the impact of freely falling refuse from the top of the
feed hopper and bulks of slag from the furnace walls, respectively.
The burned out residue travels slowly down the grate under
constant agitation. After reaching the grate end, a slowly rotating
clinker roll seizes the residue and dumps it into the quench pit. The
gentle grate action reduces dust and charred paper generation from the fire
bed. This helps reduce dust carried through the boiler and into the
precipitator. The grate action also minimizes the formation of excessive
hot spots and excessive clinker buildup and helps to produce a residue
having about 3 percent unburned carbon. Side faces of the bars are
machined to achieve even, uniform widths of air gaps between adjacent bars
and are arranged to prevent spreading or bunching of individual bars. At
the sides of the grate sections, self-compensating expansion blocks prevent
binding of the grate bars due to heat expansion. This helps to maintain a
constant air gap and ensures that the openings for combustion air are
limited to approximately 2 percent of the grate area surface. The air
openings in the Martin grate bar design are fixed at the front of the bar
so that the combur-tion air spreads over the whole underside of the firebed,
-------
Q-16
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Q-17
regardless of any dense objects in the bed. Figure Q-7 shovjs that some of
the bars have a pyramid head fixed on top to break up clinkers.
At the upper and lower -end of each stroking movement, the adjacent
bars in all grate steps will move, by mechanical action, a distance of
about 20 mm to each other. This movement prevents blockage of the air gaps
by fine ash. Figure Q-8 shows a side view of a Martin grate.
The operator has much flexibillity in grate control because the
grate strokes can be varied from seven to 80 strokes per hour.
A significant point in the design philosophy of the Martin grate
has been expressed by Stabenou:*
"Drop-off ledges to cause agitation of the burning bed should
be avoided, as they can cause a high percentage of dust to be
released into the furnace gas stream, and may also result in
undesirable slag buildup on the grate which, in turn, may restrict
the proper air flow to the fuel."
Widmer & Ernst (Alberti-Fonsar) Grate
The Alberti-Fonsar stepped grate is in seven sections on an
average fuel bed slope of about 2H degrees. It is fabricated in Italy by
the Fonderie e'Officine di Saronne S.p.A. using a grate material which is
25 to 30 percent, chromium, 4 percent nickel, with some manganese and
silicon. Figure Q-9 shows that the grate is made up of steps which
alternately are fixed and reciprocating. The reciprocating parts have a
maximum stroke of 380 mm (15 in) with the normal stroke being 350 mm (14
in) which occurs about once every 2 minutes. As the upper step moves
forward, it tends to tumble the burning refuse downward to the next step,
thus providing gentle agitation. Grate temperature can be monitored by the
control room operator from indicators connected to three thermocouples
located under the grate, near the middle of the grate surface, and on a
fixed grate section.
The grate sections are guaranteed for 16 months. The manufacturer
expects the grate to last 5 to 10 years.
The air supply to the grate is delivered to three zones under the
grate. The flow to each zone can be controlled from the control room by
means of butterfly valves where the operator has an indication of zone air
pressure and valve position.
V.'idmer and Ernst, as a turnkey contractor, uses the Alberti-Fonsar
grate for systems under 200 tonnes, (220 tons) per day. For larger systems,
such as their 400 tonne (440 ton) per day in each unit at the new plant at
Hamburg:Stapelfeld, they use the Steinmueller grate that is manufactured in
Hamburg.
VKW (Duesseldorf Grate or Walzenrost)
Figure Q-10 shows the essential characteristic of the "walzenrost"
(roller grate) which was developed in 1961 at the Flingern Power Plant in
Duesseldorf, using a four-roller pilot grate which has since been
dismantled. It is manufactured by the Vereinigte Kesselwerke in Duesseldorf
and is generally known as the "Duesseldorf Grate". It provides a sloping
fuel bed as do most European mass-burning grates for refuse. But instead of
using oscillating or reciprocating grate bars to agitate the burning
^Stabenow, G., "Problems with High Temperaure Incinerator Gases in the
Superheater Area," Proc, ASME Conference on Present Status and Research
Needs of Energy from Waste, Hueston Woods, Ohio, Sept. 1976, ASME,
New York, NY 10017
-------
Q-18
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Q-20
FIGURE Q-9. AN EXAMPLE OF THE ALBERTI FONSAR STEP GRATE SYSTEM ASSEMBLED AT THE
FACTORY, COURTESY OF WIDMER + ERNST (ALBERTI-FONSAR)
-------
Q-21
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-------
Q-22
material and to move the incombustible residues down the slope, the
walzenrost moves the bed by slow rotation of the 1.5 m (H.92 ft) diameter
drums which are formed of cast iron grate sections. Thus, there is
opportunity for a slow tumbling action of the refuse which helps to keep
the fibrous mass loose, thus allowing for more uniform distribution of
primary air throughout the bed.
The drums rotate at an adjustable speed of about 3 to 6
revolutions per hour. Instead of being continuously exposed to the hot fuel
bed, each grate bar rotates through a cool zone about half of the time.
Thus, for minor repairs to the grates, the temperature on the underside of
the grate is low enough to enable workmen to repair it while it is
operating.
Each grate roll is formed of 10 sections, each of which contains
CO curved grate bars. The bars at each side which rub against the air seal
plates are cast of chrome-nickel alloy to resist abrasion. Out of a total
of 600 bars per roll, 12 are cast alloy. Early plants had seven rolls each,
but in later designs there are six rolls per furnace.
The gap between adjacent rolls is filled by a cast iron wiper bar.
This bar is strong enough to shear off refuse that may become attached to
the grate. The only grate bar maintenance that is normally required is
replacement of the first roll if scrap containing considerable magnesium is
charged. In one case, 20,000 dry cells containing magnesium damaged a first
roll so that replacement was necessary. Usually the grate rolls have
operated 30,000 hours without major repairs.
The wiper seals are repaired three times a year. Normal wear of
the seal gradually widens the gap which allows larger and larger pieces of
refuse to fall through. A screw conveyor removes such residue from
underneath the grate.
The hollow steel roller shafts are usually never replaced.
Asbestos air seals at each end of the shaft require replacement every 5 or
5 years.
Each roller constitutes a separate supply zone for primary air.
The air enters the interior of the roll from both ends and flows through
the many small gaps between the interlocking grate bars. The amount of air
flow through each roll can be adjusted.
As the burning refuse moves down the slope, the rotative speed of
each successive roll is reduced so as to keep the fuel bed thickness
approximately uniform.
This is an extremely rugged type of grate. The first roll is
subject occasionally to severe impact from heavy objects being fed in by
the feed rarr. and then dropping 1.8 m (5.9 ft) to the first roll. Little
damage has occurred as a result of such impacts.
Bruun 8- So^ensen Grate
Figure Q-11a shows the oscillating type of rocking grate used by
Bruun anH Sorensen. As shown in the lower three sketches of the figure, the
grate sections oscillate rotationally in a coordinated rocking motion such
that the burning refuse is induced to cascade downward along the 30-degree
sloping grate in a wave-like motion, thus slowly agitating the fuel bed so
as to prevent compaction, voids, and consequent irregularity in air flow.
The notion of each grate section is controlled by an adjustable timer.
-------
Q-23
INCINERATOR
SYSTEM
FIGURE Q-ll SKETCHES OF GRATE ACTION
(COURTESY OF BRUNN & SORENSEN)
-------
Q-24
The moving part of the grate is formed of three sections with six
horizontal shafts in each section. The grate bars are fixed to the shafts.
Figure Q-11b shows two typical grate bars which are 0.5 m (1.6 ft) long.
The lower bar in the figure is 50 mm (2 in) wide. The upper one is a new
design of bar which is 100 mm (^ in) wide. Recent experiences at Horsens,
Denmark with a test section of the newer bar revealed that fine ash is less
likely to adhere in the interstices between, the bars; hence, less cleaning
is required to maintain the gaps free for uniform air flow. New bars have
been installed in all of the first grate section, and it is planned to
change also the other two grate sections. The new and old bars are cast by
a Swedish affiliate of Bruun & Sorensen using an alloy of 23 percent
chromium, 1.5 percent silicon, 0.2 percent nickel, and 0.25 percent
molybdenum. They are guaranteed for 10,000 hours.
Volund Grate
The sloping grate used by Volund is built up of fixed and movable
sections. Mr. E. Balch, formerly Volund's Chief Engineer, described the
grate as follows:
"This grate construction is built up of several grate
sections, each separated by a vertical grate transition bar. The
ratio of size between the individual grate sections and grate
transitions is determined by the composition of the refuse.
Figure Q-12 and Q-13 show the individual grate section is
built up of lengthwise-placed sections of 180 to 300 mm wide laid
up with an inclination of 18-15 degrees. Every other of these
sections are fixed and every other are movable, and each section
is built up of a through grate bar, which is welded up, on which a
number of grate blocks of specially alloyed cast iron are fitted,
which are in turn filled up with loose grate bars of cast iron.
Figure 0-1^4. The movable sections are driven hy'draulically by
a transverse driving shaft placed under the grate, which is
connected to the individual sections by pendulum driving bars.
From a neutral position, the movement in forwards stroke is slowly
raising, forward going, and then lowering and backwards going. In
the backwards stroke, the movement is slowly lowering and
backwards going and then raising and forwards going.
Along the side of grate sections, which are built into the
wall of the furnace, there are a number of side sealing beams,
which through building in springs give the grate sections a
transverse flexible assembling.
Figure 0-15. The first grate section acts as a feeding and
predrying grate and apart from the last part of the transition
bar, it is covered with grate plates. Ignition and the first part
of the combustion takes place at the first transition and on the
second grate. The final combustion and burnout takes place on the
third grate, and calcining and cooling of the clinkers begin at
the last part of the third grate and continue on the subsequent
clinke^ chute.
The layer of refuse is 300 to 500 mm (12 to 20 in). The
movable nrate sections give a lifting, moving, and turning
-------
Q-25
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Q-28
Oct. 1, 1935. A. CHRISTENSEN 2,015,842
FURNACE WITH GRATE FOR COMBUSTION OF REFUSE OF ANY KIND
Filed Nov. 5, 1932
INVENTOR
A AGE
FIGURE Q-15. ONE OF THE EARLIEST VOLUND PATENTS
-------
Q-29
movement in the lower half of the layer so that the combustion
air, which in a regulated way is supplied from below, can get to
all parts of the layer. At the transition bars, there is a
supplementary turning, mixing, and air supply."
Volund supplies furnaces with either three or four separate
grates. Following these grates is the rotary kiln in which the burning is
completed.
Each furnace has two operating hydraulic pumps. At some
installations, an additional hydraulic pump is used as a standby. Each
pump's capacity is 4? liters/minute (12.^ gallons/minute). Each pump has a
15 Hp motor. The resultant pressure is 1,160 pounds/in^ (8,000 kPa). The
plant has one 600-liter (160-gallon) hydraulic oil storage tank.
Each of the first three grates has five hydraulic cylinders with
cylinder bases of 80 mm (31 in) and stokes of 130 mm (59 in). The stroke
frequency is three strokes per minute.
Having three grates means that there are two steps. The height
between Drying Grate I and Grate II is 1 m (3.3 ft). Between Grate II and
Final Grate II, the height is 2 m (6.5 ft).
-------
R-l
ASH
This section on ash is divided into five parts as follows:
• Ash Exit from Grate, Quenching Removal From the Furnace
• Ash Handling in the Plant, General Comments
• Ash Recovery, General Comments
• Ash Handling Recovery at Specific Plants
For purposes of this discussion and design of refuse energy
plants, there are five kinds of ash, residue or slag that need to be
defined:
• Ash, Residue, Slag are general terms loosely used to name the
solid waste product after combustion. This is referred to
as residues in America and slag in Europe. It may contain
bottom ash, grate siftings and or flyash
• Bottom Ash is the solid waste falling off the grate end and
into the chute
• Grate Siftings are the relatively small particles and dust
falling under the grate normally through the spaces where the
primary underfire air rises
• Fly Ash is the solid waste material that falls from boiler
tubes and electrostatic precipitator either naturally or when
blown off by soot blowers
• Processed Ash is the sorted nonferrous aggregate of stone,
dirt, glass, etc. usually less that 1.5 cm (0.6 inch) ready
for use as road aggregate or cinder block, etc.
Table R-1 summarizes ash handling and recovery options exercised
at the 15 visited plants. Generally speaking ash handling is somewhat more
advanced in Europe over the U.S.A. Ash recovery, however, is practiced much
more in Europe than in this country. Of the 15 plants, 9 have ash recovery.
Ash Exit from Grate, Quenching and Removal
from the Furnace
All systems arrange for the moving grate to discharge the hot,
unburned residue into a water sump, quench tank or a spray chamber from
which it is removed by a variety of methods. The residue, usually
containing less than 3 percent combustible, is a highly variable material
both in size and composition. Quenching is necessary because if the glowing
residue were removed from the plant in its high temperature condition the
dust and odors emitted from the hot surface would frequently be a nuisance.
Usually the residue is continuously removed from the tank. During
that movement it is partially dewatered or drained by a drag conveyor or
some form of hydraulically-driven ram or pusher. The wet residue then is
discharged to a holding pit, movable bins or trucks for transport to a
processing plant or to a landfill.
The quench container is the sink for the boiler blowdown water and
other dirty water at most plants. Often this result in no wastewater
(except for sanitary waste water) leaving the plant except in ash trucks.
If scrubbers are not used, zero wastewater discharge can be a reasonable
challenge for designers. This is the reason that this report does not have
a chapter devoted to water pollution control in most systems there is
no real water pollution.
-------
R-2
TABLE R-l. SUMMARY OF ASH HANDLING AND
RECOVERY METHODS
In Plant Ash Handling
• Reciprocating Push Room
• Vibrating Conveyor
• Steel Slat Conveyor
• Rubber Conveyor
• Skip Hoist
• Detachable Container
• Ash Pit
• Ash Floor with Wheeled Front End Loader
*
Quench Method
• Bottom of Chute Has Water
• Water Pit
• Trough
• Ash Bunker is Wet
Ash Recovery
• Enclosed Building Recovery
• Outdoor Recovery
• Distant Recovery
• No Recovery at Plant
Recovery Operation Ownership
• Plant Itself
• Private Contractor, Receiver and
Processor
Separable Ash Components
• Ferrous Fines (caps, lids, nails)
• Ferrous Coarse (cans)
• Ferrous All Sizes
• Ferrous Bulky (bicycles, barrels)
• Ferrous Baled
• Road Aggregate
• Bulky Non Ferrous (stumps, tires,
paper rolls)
• Medium and Coarse Non Ferrous (2"
stones , bones)
• Land Reclamation Material
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R-3
Clinker Discharge Roll (Martin)
A full-width variable-speed residue discharge roll is fitted at
the end of the grate to regulate the depth of refuse bed on the grate and
to control the rate of residue discharge. The grate speed can be adjusted
to suite the nature of refuse so that optimum mixing of the fuel layer can
be obtained for fluctuations in load and composition.
The clinker roll is of heavy construction with replaceable cast
iron segments. The material is designed to resist heavy abrasion and the
temperature likely to be encountered at this point of the grate.
Ram for Residue Removal (Martin)
The simplest and most compact reside removal system uses a
curved-bottom tank which is cleared by a slowly reciprocating pusher.
Figure R-1 shows the schematic of the Martin ash discharger which uses that
system. As the submerged residue is pushed upward toward the left by the
ram it has time to drain off excess water before it drops into the pit,
buggy, truck or other container. The discharge channel is tapered outward
in the direction of motion to prevent packing and jamming. Figure R-2 shows
the Martin unit discharging ash at Issy.
The following paragraphs are abstractions from Martin literature.
A chute is provided at the end of the grate to direct burned-out
residue to the ash discharger. The bottom end is submerged in the water
contained in the ash discharger quench trough to ensure a gas seal and to
prevent ingress of cold air to the incinerator. The chute is lined with
steel plates bolted to form an abrasion resistant surface and it is
fabricated in thick plate adequately stiffened. An access door is included
in the lower section of the chute to facilitate access above the water
level in the ash discharger trough.
The Martin Ash Discharger receives the slag from the grate as well
as the siftings from the different sections of the grate and the fly ash
from the two boiler pass hoppers. The water bath forms an air-tight seal.
The whole slag and ash discharging equipment is able to handle the largest
pieces delivered by the discharging chute.
The inside cross sectional dimensional are 2 x 1 m (6.6 x 3.25
feet). The discharge rate can be as high as 6.3 tonnes (7 tons) per hour.
Water replacement for the relatively small water quenching bath is
limited to the water evaporated and carried away with the clinker. This
explains the very low water consumption rate of about 100 liters/1000 kg of
refuse. The water content in the slag and ash is about 15 percent. There is
no water flowing through the discharger and no polluted water effluent.
Under the discharger mouth, slightly inclined grids of 400 mm mesh
are provided through which clinker falls onto a vibrating conveyor whereas
bulky objects (bicycles, tires, stumps, barrels, etc.) are held back by the
grid and may easily be removed by the personnel and dumped into carts or
containers standing by.
The replaceable wearing plates are of 12 mm and 15 mm thickness.
All parts are designed to withstand wear and tear during the operation
period of at least 8000 hours.
-------
R-4
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R-6
The drive of the ash discharger is protected by an overload sensor
and the discharging capacity is controlled by an infinitely variable speed
regulator in the hydraulic distribution cabinet. The forming of excessive
vapor is avoided. The ash discharge has a grate valve at the bottom of the
trough for evacuation and maintenance purposes. The trough itself is
constructed of steel plates with thickness of 10 mm and suitably reinforced.
Flysh Ash Handling (Martin and Others)
The coarse fly ash collected in the hoppers under the boiler
passes is conveyed to the ash discharger via screws. On the other hand, the
fine ash collected in the electrostatic precipitator is not fed into the
ash discharger but rather into fly ash silos. The purpose is to avoid
fouling of the ferrous scrap which is extracted from the refuse clinker.
The fly ash collected in these silos is moistened by conditioning screws
and discharged onto the clinker in the clinker pit.
Submerged Conveyor (Old Widmer and Ernst and Old Volund)
Figure R-3 shows another common type of submerged drag conveyor
which slowly lifts the residue upward along a sloping channel so that it
has time to drain.
Figure R-4 shows the discharge end of a similar conveyor at Aarau,
Switzerland. An electric truck is used to remove the filled hopper. Note
that the conveyor housing is reinforced concrete to resist the corrosive
attack of the acids which accumulate the quench water. As explained in the
next section, the acid condition is caused because the flyash containing
sulfates and chlorides is also inserted into the bottom ash processing
system. Designers of future bottom ash handling systems could probably
worry less about corrosion if the flyash were handled elsewhere in a dry
dusty form.
A system not too unlike this has caused serious problems at
Copenhagen: Amager. The fines become enmeshed in the rollers and bearings
and sometimes the fines build up so much that the systems must be shut down
and the conveyor system cleaned.
Additional Ram-Type Dischargers
Since the early Widmer and Ernst plants were built a much simpler
design of oscillating ram type of residue system has been used in their
newer plants. Figure R-5 shows one form of this method applied to the small
refractory-walled, non-energy recovery plant at Trimmis, Switzerland. A
similar system will be used by Widmer and Ernst at the proposed Stapelfeld
Plant at Hamburg which is shown in Figure R-6. Figure R-7 is a photograph
of a similar device on a small Widmer and Ernst plant at Oberthurgau,
Switerland.
Spray Quench with Conveyor
An alternate system which avoids some corrosion problems of the
quench tank is the use of a water spray to quench the residue as it falls
off the end of the grate. The moisture pickup of the residue is much less
-------
R-7
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R-8
FIGURE R-4 DISCHARGE END OF RESIDUE CONVEYOR AT AARAU,
SWITZERLAND SHOWING ELECTRIC TRUCK FOR REMOVING
LOADED HOPPER (Courtesy of Widmer & Ernst)
-------
R-9
FIGURE R-5. RESIDUE REMOVAL SUMP AND OSCILLATING RAM AT BOTTOM
OF PLANT AT TRIMMIS, SWITZERLAND. (Courtesy of Widmer
and Ernst)
-------
R-10
FIGURE R-6 . PORTION OF PROPOSED STAPELFELD PLANT AT
HAMBURG SHOWING RESIDUE REMOVAL SUMP AND
OSCILLATING RAM AT S WHICH DISCHARGES TO
EITHER OF 2 TROUGH CONVEYORS, C (COURTESY
WIDMER & ERNST).
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R-12
with this system although it is more difficult to cool large, red hot
clinkers than by submersion. From the spray quench the cooled residue falls
into a belt or trough conveyor. Figure R-8 shows such a system built by
Bruun and Sorenson at Uppsala, Sweden.
Ash Handling In the Plant, General Comments
The plant ash handling flow is usually (1) parallel (2) reverse or
(3) perpendicular to the flow of refuse.
The parallel flow system (Figure R-9a) keeps the flow of refuse
and ash generally forward and downward until reaching the pit at the far
end of the plant. The reverse flow system (Figure R-9b) , however, sends
the ash back under the furnace back towards the refuse pit. At the VKW
plants at Wuppertal and Krefeld, the refuse pit is next to the ash pit.
Thirdly, the perpendicular flow system (Figure R-9c) redirects the
ash to the side of the plant. Usually all active furnaces disgorge their
residue onto the same active conveyor. Most plants have two conveyors with
a diverter to control flow. Redundency is necessary so that one conveyor
pin break does not require shutting down all lines in the plant.
Ash Recovery, General Comments
Of the 15 plants studied, 9 have some form of ash recovery. Of
these 9, two recover it in an enclosed building, six outdoors at the rear
of the plant and one has distant outdoor recovery. Ash recovery is more
likely to be performed at large plants near large metropolitan areas.
Of the 9 operations, four are run by the refuse burning plant
owners. However, in five central European operations, private enterprise is
active.
Ferrous scrap for remelting and sized aggregate ash for
roadbuilding are the items of value from refuse combustion ash. Only in one
case, was mention made of yanking obvious copper out for recycling.
There were no attempts to recover glass or aluminum in post
processing operations at any of the 30 plants visited. The reason for
ignoring glass and aluminum is both technical and economical. Glass and
aluminum may fuse to or may be fused upon at the high combustion
temperatures. Some of the aluminum may even vaporize into aluminum oxide.
Based on research done in Switzerland and Sweden there is definite
road ash potential from processed ash. A normal refuse fired steam
generator is a segregator of acids and bases. Normally the sulfur and
chlorine rise and exit as gas. However, much goes into sulfate and ferrous
chloride as deposits on tubes and into collectable flyash particulate
matter.
What remains in the bottom ash is quite basic. A bottom ash will
likely have a pH of 9 to 12 depending on refuse input composition. The
basic nature causes the heavy metals to remain insoluble and relatively
harmless to the environment. It is to be concluded that spreading basic
bottom ash over an acidic soil to neutralize the resultant soil is not a
good idea. Instead, the basic ash should be kept together as in a road base.
-------
R-13
I -
FIGURE R-8. FURNACE BOTTOM ASH CHUTE DISCHARGING INTO ASH VIBRATING
STEEL CONVEYOR AT UPPSALA (Battelle Photograph)
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R-14
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R-15
Ash Handling and Recovery at Specific Plants
Werdenberg-Liechtenstein
Moist bottom and fly ash are dumped into a detachable container
that is taken to a nearby hillside landfill. The tipping charge is about
$.50 per ton. There is no attempt at any form of ash recovery.
Baden-Brugg
As at Werdenberg, the residue falls into a detachable container
which is taken to a landfill.
Dusseldorf
A private operator processes ash at Duesseldorf inside a large
building addition to the main refuse plant (See Figure R-10). The many
conveyors, hoppers, magnets, sieves, etc., produce three separable
products: (1) ferrous material, (2) road aggregate and (3) miscellaneous
nonusable material for landfilling.
Figure R-11 shows two inclined conveyors removing baled scrap from
the processing plant. Figure R-12 is a close-up of the baled scrap which,
sold in 1975 for an average of 107.52 DM per tonne ($37/ton).
Figure R-13 pictures Mr. Thoemen, in lab coat answering questions
of the visiting team while standing in the sized residue storage area. This
fine gravel residue was sold in 1975 for an average price of 1.01 DM/tonne
($0.39/ton). The affiliated company sells a portion of the residue for 9
DM/tonne ($3.44/ton).
Because of refuse combustion and ash recovery, landfilling costs
as a percent of total solid waste management costs (collection, transport,
incineration and landfill costs) were only 143,375 DM ($54,682) for all of
Duesseldorf in 1975. Landfilling was thus 0.43 percent of total solid waste
management costs.
In 1975, 114,278 tonnes of raw ash were processed to obtain
105,092 tonnes of road ash, 5,986 tonnes of baled ferrous scrap. The
remaining 3,192 was landfilled.
A later plant report describing 1976 results show the following:
Wet Residue
Fine Ash for Roadbuilding 78,706.30 Tonnes
Discarded in Landfill 19,650.28 Tonnes
Total Residue 98,356.58 Tonnes
Total Residue Shipped 97,641.58 Tonnes
Storage (Net Increase in Stock) 935.00 Tonnes
Residue Analysis
Water 18.89 Percent
Combustible 5.03 Percent
Scrap Iron
Total 8,492.42 Tonnes
Bulky Scrap (non-baled white goods, etc.) 531.51 Tonnes
-------
R-16
Shredder
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and Office-
Residue „£-
Processin:
Steam Line to
Flingern Power
Plant and Condensate
-Return Line, 700 m
Total Area: 30,831 sq. meters
Buildings: 7,000 sq. meters
Streets: 15,831 sq. meters
Trees, 8,000 sq. meters
Shrubbery, Grass
FIGURE R-10. PLAN OF DUESSELDORF WASTE-TO-ENERGY PLANT
(COURTESY STADTWERKE DUESSELDORF)
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R-20
Wuppertal
Residue exits the furnace room basement and enters the long ash
quench pit located under the boiler. The wet solids are removed by a
drag-chain conveyor to the ash bunker. From there a crane lifts the residue
to trucks which deliver them to a private processing firm immediately below
the plant. Part of this operation is shown in Figure R-14. The private
operator pays DM 1.50 per tonne ($0.60/ton) of residue. In this outdoor
cleaning and sizing operation, the residue is upgraded to a useful raw
material which apparently is in much demand.
Krefeld
The ash is removed to a privately operated ash recovery area.
Aggregate is prepared and often barged away as far as the Netherlands.
Paris;Issy
Being an older system, ash recovery systems are not as extensive
at Issy as at several other facilities. Figure R-15 shows the ash conveyor
going to a ash recovery structure. Ferrous metals are removed and sold as
scrap. The volume of scrap and other related numbers are shown in Table
R-2. In 1976, of the 522,40*1 tonnes burned, 154,017 tonnes of ash or 29.4
percent were landfilled. Hence we conclude that at Issy, ash recovery is
not extensively practiced.
Hamburg; Stellinger-Moor
The Hamburg plant uses the Martin system. In Hamburg, the
Heidemann Company has a contract with S-M to process and remove all ash.
Mr. Siegfried Heidemann was stockpiling most of the production and
waiting for the price of this material to rise. Mr. Arndt, the plant
manager, pointed out that Hamburg's sea level position provides many
markets for the ash material. Much of this plant's ash is shipped to
Scandinavia and East Germany. Heidemann sells the raw residue for 4.50 DM
($1.80) per tonne. He sells the processed road material for about 12 - 15
DM ($4.80 - $6.00) per tonne. Scrap iron prices vary widely and no figure
was given.
Three Heidemann men are needed during the day to run the equipment.
The following mass balance accounting was provided assuming 1000
refuse input tonnes:
C, H, 0 etc. rising through the chimney 640 tonnes
Scrap iron (large pieces collected in RFSG) 10 tonnes
Scrap iron (mediums and fines) 65 tonnes
Road material, including flyash (?) 250 tonnes
Residue to landfill (stumps, tires, large paper rolls) 35 tonnes
Total refuse input tonnes 1000 tonnes
Twice a week, a truck takes singed tree stumps, tires, etc. to the
landfill.
-------
R-21
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Zurich; Hagenholz
Zurich: Hagenholz uses the Martin ash handling system described
under Paris: Issy.
Fly Ash. To prevent blowing dust from fly ash, it needs to be
wetted. While this is most difficult in the summer, wetting is almost
impossible in the winter due to freezing. As a result, the screw conveyors
transport all fly ash to the ash discharger where it is inserted 1 m (3
feet) above the water level. Some dust is recycled through the
furnace/boiler/ESP but that is no real problem. The fly ash is later
recycled for roadbuilding.
Ash Recovery. Ash recovery is very advanced at Hagenholz. Credit
for this accomplishment is to be shared among several parties that have
funded and guided the research and development. The entire program is
outlined in an excellent 50-page report written by Professor R. Hirt, a
professor of forest engineering at the Technical University in Zurich. His
publication is titled, "Die Verwendung von Kehvichtschlacke als Baustoff
fuer den Strassenban", dated October, 1975. The German title translated is
"Use of Processed Incinerator Ash for Road Building". The report is
available through Mr. Hirt.
The analysis mentions many Swiss cities. Data for the City of
Zurich in 1974 are presented in Table R-3.
TABLE R-3 POPULATION, REFUSE AND ASH IN AND AROUND ZURICH
Population
Refuse (generated, burned?)
Refuse per person (kg basis)
Refuse per person (pounds basis)
Refuse per person (365 days basis)
Ash generated by incinerators*
Ash per person (kg basis)
Ash per person (pounds basis)
Ash per person (365 days basis)
Ash as percentage of Refuse
City of Zurich Metroplitan Area
Zurich (14 Cities)
421,650 2,314,100 people
216,000 812,285 tonnes/year
512 351 kg/person/year
1,126 772 pounds/person/year
3.08 2.12 pounds/per day
61,800 271,260 tonnes/year
147 117 kg/person/year
323 257 pounds/person/year
0.88 0.70 pounds/person/day
28.6 33.4 tonnes/tonnes
*Josefstrasse and Hagenholz both in 1974.
-------
R-25
The ash disposal procedure is shown in Figures R-16 through R-23 and is
outlined below.
Figures
R-16 Truck takes ash from plant and dumps on storage pile.
Ash stays in pile for 2 weeks.
R-17 Front end loader has deposited bulky non-burning items
(logs, tires, etc.) in bulky waste pile.
R-18 Front end loader takes ash from pile and dumps into
first hopper.
R-19 Worker needs to remove wires and other jamming objects
from the hoppers, conveyors, and vibration equipment.
R-20 Ferrous fines are separated.
R-21 Coarse ferrous is separated. (Some larger ferrous is
separated where the ash discharger dumps into the in-
cineration plant's ash vibrator.
R-22 Nonferrous small material less than 1 cm (.39 in.) is
stockpiled for later use as road bed subsurface material.
R-23 A test patch is shown.
The ash residue (slag), when removed from the ash bunker, is
stored in a pile for two months for these several reasons:
o moisture reduction
o stop fires
o chemical reactions desired
-heat of hydration of free lime
-water and calcium carbonate
These exothermic reactions result in an internal temperature of
80 C (176 F). The bottom ash and flyash combined residue has a pH of 11 or
12. Interestingly, the dirty water removed during the semiannual boiler
cleaning to remove flyash deposits has a pH of 2 or 3 despite use of an
alkaline cleaning agent. Incinerators segregate acids and bases. Flyash
removed from the precipitators is always basic.
In 1976, the actual following figures were reported:
Quantity of solid waste burned 218,3^2 tonnes 100.0 percent
Quantity of raw ash generated 56,271 tonnes 25.8 percent
Quantity of metal recovered 6,49^ tonnes 3 to 5 percent
The following are percentage ranges for output from the ash recovery
process:
Roadbuilding material 80 percent
Ferrous metals 8-9 percent
Non-ferrous mediums re-
turned to furnace 3-5 percent
Stumps and tires sent
to landfill 3-5 percent
-------
R-26
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-------
R-34
Except for uncaptured participates and gases, the only materials
not recycled are the tree stumps and tires. This amounts to 3 to 5 percent
of ash; and ash is 25.8 percent of the total waste input. This means that
there is a 98.75 to 99.25 percent volume reduction, which greatly reduces
the necessary landfill requirements.
The copper,when conveniently seen and removable, is manually
removed and sold is as scrap. Aluminum is recycled indefinitely until
oxidized.
In 197^, before the recession, ferrous incinerator scrap sold for
30-90 S.Fr. ($12-35) per tonne depending on market conditions. In 1977, the
price ranged from 30-55 S.Fr. ($15-17) per tonne F.O.B. Zurich. Note the
singular effect of the exchange rate and the devaluing American dollar. For
example: 30 S.Fr. in 1974 equals about $12 while the 1977 conversion of 30
S.Fr. is about $15.
The roadbuilding ash (or slag as most Europeans call it) sells for
10 percent under the competitive price for gravel. Mr. Hirt believes that
the long term price is bound to rise substantially as gravel pits become
scarce. The 197^ price of S.Fr. 12 S.Fr. had fallen to 6 S.Fr. in 1977 due
to the recession.
There is a new plan to mix the material as aggregate with cement
to serve the Zurich and Wintertur areas.
Most of the processed ash is used for secondary roads.Because the
material can also be used as road base for paved roads, several tests have
been conducted. Tubes made of PVC, cement, zinc, rubber, etc. have been
inbedded in the processed ash to determine corrosion effects.
Three people, not employees of Abfuhrwesen, operate the facility
for a joint venture owned by the Bless and the Muldenzentrale
companies. They can operate in rain and freezing weather due to the
exothermic reactions.
The Hague
The ash handling process at The Hague is noteworthy due to
separate treatment of bottom and flyash. Figure R-2M shows the total plant
arrangement. Bottom ash that has been water sprayed at the furnace exit is
conveyed to the first pit. Flyash is slurried as it leaves the
electrostatic precipitator hopper. The flyash slurry is piped to the second
bunker.
Clam shell buckets as shown in Figure R-25 remove the ash from the
tanks and drop it onto a large mesh grate set at an inclined angle. The
larger material rolls down to a detachable container. The smaller material
falls through onto a conveyor belt that is the beginning of an ash
separation plant.
Until very recently, the quenched furnace residue and wet flyash
have been hauled by rail to the Rijswijk landfill without any processing
for resource recovery. However, in August 1977 the processing equipment
shown in Figure R-26 was installed adjacent to the plant by a private
company which evidently hopes to benefit from ash recovery. The
magnetically separated steel scrap piled in the foreground is to be sent to
a steel plant. The conical pile of sized cinders in the back ground will be
used for fill and road building. This processing plant is too new to have
produced any data on its costs and revenues.
-------
R-35
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R-36
FIGURE R-25. BOTTOM ASH PIT AND FLY ASH SLURRY TANK AT THE HAGUE
-------
R-37
-------
R-38
Ash at Dieppe is taken to an area on the same property where it is
dumped. Since the property is not located in residential area, there are
few complaints.
Gothenburg
The new Tagene landfill which receives the residue has a clay base
from which drainage (leachate) is collected and piped to the local
wastewater treatment plant. When the system was planned, there were
tentative plans for metal recovery from the residue. The planned metal
recovery has not been implemented to date.
Uppsala
Figure R-27 shows ash being discharged from the furnace and onto
the vibrating conveyor. Note the glowing steel because quenching is not
performed.
Figure R-28 shows the discharge end of the vibrating conveyor.
Detachable residue containers on rollers are used to collect residue for
later trucking to Hovgarden. The ash conveyor is at ground level. A shallow
elevator pit operating from ground level to one position below lowers and
raises the container for filling and removal. (See Figure R-29).
The quenched residue is hauled 4.4 km (7 mi) to the Hovgarden
landfill.
Horsens
The quenched residue is hauled to the adjacent landfill in a
dammed area of the fjord.
A sample of the burned residue is analyzed daily by the city
laboratory for combustible content by heating the dried residue in air to
600 C (1,112 F) for a long enough time to oxidize the combustible matter.
The following are some typical values of combustible content of the dry
solids in percent:
Day Week of Analysis (1977)
Sampled July 5 Aug. 10 Sept. 15
Monday
Tuesday
Wednesday
Thursday
Friday
3.1
0.8
1.6
2.0
3.2
3.8
2.4
3.0
5.6
2.9
4.0
1.8
2.4
3.5
2.0
-------
R-39
FIGURE R-27.
ASH BEING DISCHARED FROM FURNACE ONTO VIBRATING
STEEL CONVEYOR AT UPPSALA
-------
R-40
FIGURE R-28.
VIBRATING STEEL CONVEYOR DUMPING BOTTOM AND FLY ASH
INTO CONTAINER AT UPPSALA (Battelle Photograph)
-------
R-41
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R-42
These results indicate consistently good burnout. The plant
specification called for a value of 5 percent combustible. A daily check on
the trend of this number is a useful clue to the general performance of the
furnace. As in all analyses of heterogeneous materials, the size of sample
and mode of sample can be critical in producing useful numbers. An
occasional duplicate sample for the same day would be helpful in assessing
the data variability.
Copenhagen; Amager
Unfortunately, the ash handling system at Amager caused
considerable problems. Based on Amager's experiences, West was redesigned
and operates much better. Basically, Amager uses conveyors while West uses
a skip hoist.
Originally the Amager rubber ash conveyors let too much water and
fine ash into the tank bottom. The material would settle, buildup, and then
interfere with the conveying. There was excessive wear on rollers and nylon
bearings. Downtime for repair and fines removal was excessive.
To partially solve the problem, apron conveyors were replaced by
vibrating conveyors. They have also installed air pipes in the bottom of
the fines tank to keep the siftings in solution so they can be removed.
Another major difference is that Amager uses about 3 tonnes of
water per tonne of ash while West uses only 1 tonne of water per tonne of
ash. Boiler blowdown water is used.
Ash disposal at Amager is entirely different from the treatment at
West. The Amager ash is dropped into a hopper which feeds a conveyor as
seen in Figure R-30a. Ferrous material is extracted just before loading the
ash into the truck. The ash is then trucked (Figure R-30b) to reclaim
further portions of Amager Island. It is very profitable in that 1 m2 (1
yd2) of land reclaimed from the sea is worth 200 to 300 Dkr ($35-52). About
3 m3 (4 yd3) volume of ash is used to reclaim a 1 m2 ( 1 yd2) area. This
converts to a land value of $188,000 to $280,000 per acre.
Copenhagen; West
The subject of "ash" at West is discussed in two major parts. This
part on ash handling and processing discusses matters at the West plant
itself. The later part on ash recovery discusses physical and chemical
properties of processed ash as a usable gravel material. This following
part also discusses the encouraging environmental story of ash percolate
(leachate).
Ash Handling. The authors wish to thank Mssrs. Balstrup and
Pedersen for material included. West's experiences have been much better
than those of Amager. In contrast to Amager's rubber belt conveyors, West
uses a skip hoist as shown in the dump position in Figure R-3L
Also to be noted are the two flapper doors (swivel gates) that control
in-plant ash atmospheres to minimize dust and noise. When the hoist is
traveling or dumping, the bottom door is closed while the top door is open.
Ash thus accumulates in the ash chute. When the hoist returns and the chute
has filled, the top door is closed and the bottom door is opened to allow
the ash to fall into the hoist.
-------
R-43
^ I;
FIGURE R-30a. RUBBER ASH CONVEYOR AT
COPENHAGEN: AMAGER
FIGURE R-30b. FERROUS SEPARATION FROM ASH AT
COPENHAGEN: AMAGER
-------
R-44
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R-45
Figure R-32 is a diagram of the ash recovery plant. The ash leaves
the building and goes through a series of vibrators, sieves, magnets and
conveyors as shown in Figures R-33 through R-36. The processed ash less
than 45 mm is stored on the ash mountain.
Ash recovery. Ash recovery at Copenhagen: West is very advanced.
It was the subject of a 42 page report (English version available)
co-authored by the Danish Geotechnical Institute (DGI) and the Water
Quality Institute (WQI) entitled, "Cinders and Reuse". Sections of the
report were written by Mr. T. Balstrup (DGI) and by Mr. Sven Dige Pedersen
(WQI). The report is divided into two sections. The Geotechnical Qualities
of Cinders and Environmental Aspects Surrounding Combustion Cinders. Key
paragraphs have been repeated where it would benefit this report.
Back in the early 1970's, when Copenhagen: West was conceived, the
only clear alternative was to place cinders in a landfill with plastic
liners and a leachate collection system. Even by 1972 useable research
results were not available. Both WQI and DGI performed their work between
1972 and 1975. While research was being conducted, the plant continued to
place unprocessed ash in the Vestskoven landfill.
The research provided the following applications:
Application 1,
Application 2.
Application 3.
Base and foundation for small and
lightly traveled local roads
Bicycle paths
Parking lots
Application 4. Below floor building construction
Application 5. Foundations carrying light loads
The following numbers reflect the normal annual operation:
Quantities
Waste burned
Raw ash or crude cinders
Usable gravel cinders
Reusable billets
Ferrous metals
Caps and capsuls
Indentifiable tin cans
Metal strips, spoons, and scissors
Nail and screws
Scrap metal - big pieces
Scrap metal - small pieces
Tonnes
240,000 to 300,000
50,000 to 75,000
40,000 to 600,000
4,000 to 6,000
* na na
*Ferrous Distribution
20.8 percent
10.9 percent
10.4 percent
11.5 percent
17.7 percent
28.7 percent
Fly ash is not physically combined with bottom ash and was
excluded from the research because supposedly its cement-like properties
would interfere with the gravel-like applications. Fly ash at
Copenhagen:West is separately collected and separately disposed.
-------
R-46
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R-47
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R-48
FIGURE R-34. VIBRATING MACHINERY FOR ASH PROCESSING AT COPENHAGEN: WEST
-------
R-49
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FIGURE R-35. FERROUS MAGNETIC BELT FOR ASH RECOVERY PROCESSING AT COPENHAGEN: WEST
-------
R-50
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R-51
Road Test Procedures
" In order to establish a basis for initial evaluation and future
control, it was decided by DGI to employ the same test procedures for the
evaluation of sand and gravel materials. This was done with the full
knowledge that they were dealing with a product of another grain structure,
and without systematical experiences from full-scale plants."
" Laboratory tests included determination of grain density,
ignition loss, grain distribution analyses (Figure R-37), density
determinations by dry embedment and by Proctor tests, CBR test,
permeability and capillary tests, and finally determination of strength and
deformation characteristics by triaxial compression- and consolidation
tests. Technical results are presented in the report. Furthermore,
examinations have been made of crushing of grains of the cinders material
by means of poundng processes, and the deformation of the built-in cinders
due to repeated loads."
"At the conclusion of the combustion process the cinders are
cooled down by watering. They subsequently have a moisture content near 20
percent which corresponds to the maximum quantity for building. Tests were
carried out in a very rainy and cold period which did not change the
moisture content of the cinders, as a satisfactory drainage through the
cinders to the surrounding area took place."
"After sorting over a U5 mm screen which mainly retains tins and
large pieces of iron, the cinders appear as a homogenous material. It is so
esthetic that it does not resemble a waste product, and it can be used in
populated areas without problems. The sorted out large material comprises
only about 5 percent of the total cinders. In 1977, the process had matured
so that now 20 percent of the total cinders is removed for ferrous
recycling, reburning or direct landfilling. The cinders do not cause any
special dust- or smell nuisances."
"The main results from the field test show that for the graded
cinders a homogenous compacting is obtained which improves gradually with
the number of roller passages. On account of the good stregth quality of
the cinders, the compacting depth is limited. However, there is improvement
when vibration equipment is used. By compacting to optimum density, a
crushing of the grains of the cinders occurs. The drained layer of cinders
will retain its optimum moisture content even during periods with plentiful
precipitation."
"Laboratory tests furthermore demonstrate that a cemetation
occurs, which in the course of three to four weeks will increase the
strength and deformation qualities of the cinders by primary loads by 50 to
100 percent."
Parking Lot and Road Test Results
"A 15,000 m2 (161,400 ft2) parking lot was covered with 60 x 60 x
8 cm (12 x 24 x 3 inches) graded cinders with a 5 cm (2 inches) screen of
gravel ahve been used. The cinders were laid out loosely in up to 40 cm (16
inches) thickness and compacted. After almost one year's use, only
significant settlings ( 1 cm) have been registered."
"For a temporary road approach system with relatively heavy
traffic in Herlev municipality, the graded cinders have partly been used as
-------
R-52
100 /e Weight percent
Grain sizj d (mm)
0.06
Fine
Medium
Coarse
Sand-fraction
Fine
Coarse
Gravel-fraction
FIGURE R-37. The variation interval for the 16 mm fraction of graded
cinders before (solid line) and after (dotted line)
compacting by field tests-
-------
R-53
foundation and base. The construction work shows that the compacted cinders
without asphalt surface could carry the traffic without appreciable
problems during the work period, even during a spell with plentiful
precipitation, and that the compacted cinders by the successive replacement
of the moist site deposits could stand with an almost vertical slope two to
three meters tall. Settling and tracking tendencies will be followed for
the finished construction."
"This road section of approximately 120 m (39 feet) is made from 7
cm (3 inches) gravel asphalt concrete, 13 cm (5 inches) stable gravel and
28 to 38 cm (11 to 15 inches) graded cinders. After completion of the road
construction height surveys at 16 points of the road surface have been
carried out in the period January 1976 to February 1977. The measurements
indicate settlings of 0 - 5 mm. While the main part of the points with 28
to 38 mm indicate 5 - 10 mm frost heave in the period February - March
1976, the point which had been replaced with approximately 2 meters cinders
had frost heave of 5 mm. The original soil base consists of medium solid
marine clay."
"Finally, cinders have been used for foundations and base of local
roads and parking lots for a school in Ballerup. The foundation and base of
cinders was directly used as workroad during a period with precipitation
and changing thaw and frost. Apart from local softening of the uppermost
centimeter of cinders, no significant impediments for the work traffic were
registered. The moisture content of the cinders under the softened zone
correspond to the optimum level. Observations from these construction jobs
so far seem to validate the use of cinders for road construction purposes."
Environmental Tests. Since the autumn of 1971, the Water Quality
Institute (WQI) have carried out a series of tests for Copenhagen: West of
the environmental apsects by depositing and use of combustion cinders. The
following tests have been made:
- Accelerated washing out test on laboratory scale.
- Test of the washing out process form a non-covered cinders
depot.
- Tests for characterization of graded cinders.
- Tests of the washing out process from a parking lot, where
graded cinders are used as foundation material.
A most interesting and positive test result is caused by the pH of
the cinders being around pH 9-11. The strong alkalinity in ash is due to
the high concentration of carbonate. In this pH range, most of the heavy
metals are insoluble. Thus leaching of the heavy metals into ground water
is retarded. The next several paragraphs by Mr. Pedersen explain the
environmental chemistry in greater detail.
Liquid Percolate (leachate), Fresh Water, Sea Water
and Drinking Water Test and Results:
Unprocessed Cinders at Special Sanitary Landfill
"The depositing of cinders was done in "depots", shaped like big
hollows with the under-side two to three meters below ground. The dug out
earth is put up like a circular wall, so that the hollows are four to five
meters deep. On the inside the hollows are lined with a heavy, coherent
plastic diaphragm in order to prevent penetration of the percolate to the
-------
R-54
groundwater. The percolate runs to a centrally located pump well, from
which it can be picked up and analyzed."
"The object was to shed a light on the washing out process from
an uncovered cinders depot, and to establish if there are traces of
percolate in groundwater borings around the depositing site. Tests of
secondary groundwater and percolate of cinders from the locality in
Vestskoven where the cinders are deposited, were taken in the period from
June 1973 to October 1975."
"No measurings or analyses of groundwater samples have evidenced
any adverse influence from the percolate of cinders in this period."
"The concentration of macro ions (e.g. calcium, sodium, sulphate
and chloride) in the percolate is of the same size as the concentrations in
sea water."
"Among the examined trace elements, hereunder also heavy metals,
only the concentrations of arsenic are bigger than the concentration in the
groundwater samples in the test period from June 1973 to March 1974.
However, it is substantially smaller than the drinking water criterion for
arsenic."
"The concentration level for trace elements has not changed
essentially in the period 1974/75. In Table R-4 analytical values of trace
elements in the percolateare compared with the values for river water, sea
water, as well as various drinking criterions."
"The main cause of the low concentrations of trace elements in
the percolate is the high pH value (c.a.10) of the cinders which gives the
percolate a pH value of approximately 9. At this pH level all examined
trace elements are thermo-dynamically stable in a solid form. The trace
elements are either immune (non-corrosive) or passive (coated with a dense
skin of the corrosive product which prevents further corrosion) to attacks
of water. The redox (reduction-oxidation) conditions in the depot (greatly
reducing with hydrogen sulphide development) increases this tendency
further, as possible dissolved trace elements from the topside of the depot
will be tied up as very sparingly soluble sulphide deeper down in th depot.
The presence of complexing ions (NHij + , C1 , HCO^) will only to a lesser
extent be able to increase the solubility."
"No higher solubility of trace elements than the one observed up
till now can be expected, as long as the present pH- and redox conditions
are maintained in the cinders. A noticeable change will first occur if the
pH value of the cinders falls to pH 7 or lower. Such a change can only be
caused by a neutralization of the alkaline parts of the cinders with acidic
precipitation. The following calulation shows the length of time such a
neutralization will require:"
Alkalinity of cinders: 0.975 equiv./kg
Acidity of rain water: 10~4 equiv./l (pH4)
Quantity of cinders in depot 1: 15,600 tons
Quantity of percolate per year: 452 m3
"Neutralization time": 15.600 x 0.975 years = 336,500 years
452 x 10-14
"By the washing out from the depot some of the alkaline parts of
the cinders are removed. This means that a neutralization of depot 1 would
last less than the period indicated, but still a very long time (thousands
-------
R-55
TABLE R-4. ANALYTICAL VAULES OF TRACE ELEMENTS IN THE PERCOLATE
Analysis Fresh-
Variable Percolate water
1973-74 1974-75 Medium
Al
As
Pb
Cd
Cr(tot)
Fe
Cu
Hg
Mn
Zn
B
min. max. min. max.
<1 1080 2.5 108
4.5 16.5 10.6 20.5
2 <10 2 12
<0.1 <20 <1 <10
10 <50 <5 80
7 370 <100 300
<1 80 <1 24
<0.05 0.29<0.05 0.25
29 300 30 50
10 150 25 60
<250 560
240
0.4
5
<80
0.2
670
10
0.08
12
10
13
Sea Drinking Water Criterions
Water
WHO Sweden USA USA
10
3 50
0.03 100
0. 1 10
0.05
10 300
3 1000
0.03
3 100
10 5000
4600
150
200 50 100
100 50 50
50 10 10
50
200 300 300
50 1000 1000
2
50 50
1000 5000 5000
(1000)
Se
Ni
Co
Ag
2
<50
<50
40
<20
10
0.9
0.1
0.09 10
5
0.3
0.3
50 10
_
_
50
Measured minimum and maximum concentrations of trace elements in
percolate in the period June 1973 to March 1974, as well as March
1974 to October 1975, compared with the values for fresh water,
sea water, as well as different drinking water criterions. All
values are shown in ug/1.
-------
R-56
last less than the period indicated, but still a very long time (thousands
of years)."
Solid Processed Cinder and Soil Comparative Tests. By comparison
with soil analyses, it can be seen (Table R-5) that the following elements
in the cinders are present in a concentration which is greater than the
upper limit of the range of distribution for concentrations in cultivated
soil:
Cadmium
Chloride
Copper
Sodium
Lead
Sulphur (sulphate)
Zinc
Sodium and chloride mainly originated from wood and kitchen refuse (food
scraps). A small part of the chloride may have been produced by the
combustion of PVC which is present in the refuse in minute quantities.
Sulphate is presumed to originate mainly from cardboard and paper waste.
Zinc and cadmium are present in the ratio 460:1 which means that the main
part of cadmium in the cinders has its origin as metal residues (pollution)
in the zinc (normal ratio 100:1). The zinc is added from a great number of
sources. Copper presumbaly comes mainly from electrical wire, and to a
certain extent from copper-plated metal objects. Lead is presumed mainly to
originate from food tins, paint, and painted articles which are dyed with
lead pigment, as well as lead batteries.
The high pH value of the cinders, pH = 10.1, fixes the trace
elements so that no significant quantities will be washed away from the
cinders materials. In slightly acid surroundings, which may be found if
cinders are spread and plowed down, the quantity of elements accessible for
assimilation in plants will increase as the pH is lowered.
Test on Parking Lot in Ballerup. In the autumn of 1974, I/S
Vestforbranding received permission to layout a 40 cm (16 inches) deep
cinders as foundation of the parking area near Ballerup's town hall.
The Danish Environmental Protection Agency and Copenhagen's water
supply plant wanted tests to be made of the drainage from the area. When
the parking lot was built, a diaphragm was put under part of the cinders
foundation, so that there was direct drainage from the lower side of the
cinders material to a collection well. Furthermore, the whole area is
drained, so that it is possible to collect drain water which has passed
through the layer of gravel under the cinders.
Table R-6 shows the results of tests of percolate, drain water,
and water running off the surface of the parking area. The percolate from
the cinders layer (sorted cinders) has the character of diluted percolate
from the depot in Vestskoven, as it has been diluted four to eight times.
The concentration of the trace elements lead, cadium, copper, and zinc is
of the same magnitude as in the percolate from the Vestskoven depot, while
the concentration of chromium is smaller.
During the passage through approximately 1 m (1 yd) concrete,
gravel and the drain pipes, the percolate is oxidized, the ion strength is
reduced,and the main part of the nitrogen is absorbed by the gravel.
-------
TABLE R-5.
R-57
ELEMENT COMPOSITION OF SOIL AND CINDERS (ALL ANALYSES
MADE ON DRY MATERIAL)
Analyis Unit
Variable
Nitrogen g/kg
Phosphorus g/kg
Carbon g/kg
Chloride g/kg
Sulphate g/kg
Calcium g/kg
Sodium g/kg
Magnesium g/kg
Potassium g/kg
Aluminum g/kg
Arsenic rag/kg
Lead g/kg
Boron mg/kg
Cadmium rag/kg
Chromium mg/kg
Iron g/kg
Copper g/kg
Cobalt mg/kg
Mercury mg/kg
Maganese g/kg
Nickel mg/kg
Silver mg/kg
Zinc g/kg
+) : Converted
-H-) : Converted
Soil Variation
Width 1121
0.2 - 2.5
0.09 -2.7+)
7 - 500
0.75 -7.5
0.6 - 6
0.4 - 30
10 - 400
0.1 - 40
0.002 - 0.2
2 - 100
0.01 - 0.7
5 - 3000
7 - 550
0.002 - 0.1
1 - 40
0.01 - 0.3
0.1 - 4
10 - 1000
(0.01 - 5)
0.01 - 0.3
from sulphur .
from carbonate.
Soil Average
/12/
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13.7
6.3
5
14
71
6
0.01
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0.06
100
38
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8
0.03
0.85
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0.05
Cinders Average
0.66
2.71
124+)
81.5
10
32.2
7.6
2.6
3.2
21
8.8
1.56
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5.0
45
28
2.8
8.7
0.13
0.88
73
4.6
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R-59
The concentration in the drain water of the trace elements lead,
cadmium, chromium, and copper is less than or equal to that in the
percolate before passage through the gravel layer, while the concentration
of zinc is somewhat greater.
Water running off the surface had a lower chloride content than
the drain water. The concentrations of trace elements in water running off
the surface is bigger for lead (8 to 16 times), copper (1.5 to 3 times),
and zinc (2 to 6 times), while it is of the same low size for cadmium and
chromium.
During a situation in September 1975 with 21 mm (8.3 inches) of
precipitation, the quantity of precipitation was removed from the area in
the following way:
Evaporation: Ml percent
Surface run-off: 36 percent
Drainage: 23 percent
It has been calculated that with the use of a drain water
quantity of 23 percent per year per m^, a quantity of chloride is washed
away from the cinders which corresponds to the quantiy of chloride which is
added per m^ roadway/parking lot when there are five to nine applications
of road salt during the winter season. The washed out quantity of chloride
per year will decrease gradually as the present chloride in the cinders is
washed away. During the winter in 1973/74 there were 35 applications in
Copenhagen, and on some of these occasions, salt was distributed twice,
corrseponding to about 50 applications.
Furthermore, similar calculations show that the yearly washed out
quantities of the trace elements lead, cadmium, chromium, copper, and zinc
with the drain water from the area is smaller than the quantities which are
added to the area yearly through precipitation from the atmosphere.
The calculations show that a very long period of time will elapse
(thousands of years) before the alkaline parts of the cinders have been
neutralized by acid precipitation.
The washed out quantities of substance with the drain water from
the newly built parking lot will expectedly decline gradually as the area
is consolidated and the joints between the flagstones become compact. So
that the part of the precipitation which runs off the surface will
constitute an increasing share,while the part of the precipitation which is
removed from the area through drainage will constitute a decreasing share.
By using a dense surface dressing, such as asphalt and concrete,
the washed out quantities of substance from the cinders, other things being
equal, will be quite insignificant, as the quantity of drain water which is
a presupposition for a wash-out of the cinders will be extremely modest.
Cinders as Excellent Landfill Cover Material. An alternative
possible application for the cinders is the concentrated use of them to
cover dumping grounds. Here the alkaline percolate from the cinders will
help to reduce acid conditions in part of the dumping ground, so that the
total washing out of trace elements from the dumping ground is reduced.
However, the washing out of trace elements from the cinders themselves will
increase as the pH is reduced.
-------
S-l
Furnace Wall
General Comments
Most of the plants that were visited utilized water-tube cooling
of the furnace wall. This type of wall has been translated from
coal-burning to refuse-burning practice over the period since about I960.
In some cases the furnace is only partially water-cooled with the rest of
the wall formed of conventional refractory. In all cases where wall tubes
are used these tubes are a part of the boiler flow system. They are
pressurized to boiler pressure and they supply a mixture of heated water
and saturated steam to the boiler steam drum. Thus from a flow standpoint
they are considered an integral part of the boiler system.
However, from the standpoint of combustion, the wall tubes are an
essential part of the heat recovery from the flame that helps to cool the
gases to a temperature level that is safe for them to pass on the
super-heater and boiler convection banks. Thus the water-tube walls of the
overall boiler system are treated here as a separate component of the
combustion system while recognizing that they also constitute an important
element of the overall boiler.
Furnace Requirements
The complex variety of furnaces now in use has evolved because of
the interaction of several different requirements:
• Temperature: High pressure for steam power generation versus
low-pressure steam or hot water for heating only.
Low-pressure boilers are much cheaper to build, operate, and
maintain.
• Size: Small furnaces need not be water-cooled if waste
burning rates are moderate because the high
surface-to-volume ratio of the small chamber facilitates
cooling. Large furnaces are more likely to need water
cooling because the wall surface is relatively small in
proportion to the volume; hence, normal heat loss through
refractory walls becomes insufficient to keep the refractory
cool enough to survive.
• Refuse Heating Valve: The remarkable increase in heat value
of European municipal refuse since World War II, which has
markedly changed furnace wall design requirements.
• Fly Ash: The highly variable but active chemical nature of
the fine ash produced, which can foul and corrode water-tube
walls and boiler surfaces.
The heat value of waste underwent a steady rise as shown in Figure
S-1 because:
• Residential heating was converted from coal to oil which
produced no ash residue.
• Paper and plastic packaging of consumer products became
widespread.
Thus, in 1965, Tanner* stated:
"For, as the calorific value rises, the uncooled combustion
chamber leads to chamber temperatures that can no longer be
* Tanner, Richard, "The Development of the Von Roll Refuse Incineration
System", Sanderdruck aus Schweizerischen Bauzeitung, 83 Jahrgang, Heft
16. (1965)
-------
S-2
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S-3
controlled by air injection and fume feedback (flue-gas
recirculation) alone. Thus, the adoption of radiation
heating surfaces is becoming essential for refuse firing
systems as it has long been usual in firing systems involving
higher grade fuels."
In this latter phrase, Tanner was referring to the fact that coal- and
oil-fired furnaces, once refractory walled, had by the late 1940's, been
largely changed to water-tube wall construction.
A significant goal of heat recovery in these waste-to-energy plants
is to cool the exhaust gases to a temperature level of (177 to 260 C) 350 to
500 F where reasonably sized, high efficiency electrostatic precipitators
will be practical. However, up until the early 1960's, there was
considerable reluctance to involve the waste heat boiler surfaces too
closely with the furnace. In 1969, Hotti and Tanner* stated that a common
earlier attitude was: "The combustion chamber must not be cooled. Designers
thought that cooling would not permit reaching an adequately high combustion
temperature". However, as the heat value rose, for example, in Berne, the
average heat content rose from 1,160 Kcal/Kg (1,090 Btu/lb) in 1955 to 1,950
Kcal/Kg (3,510 Btu/lb) in 1964, rising furnace temperatures probably caused
increasing troubles with refractory maintenance. Accordingly, Hotti and
Tanner observed in 1969: "The trend of boiler development steered mainly
toward adjustable radiation heating surfaces in the combustion chamber..."
These same authors, Hotti and Tanner, then pointed out that at their next
plant at Ludwigshafen in 1967, "...the radiation surfaces surrounding the
combustion chamber can be studded and covered with rammed material or,
alternatively, stripped bare, as required". An earlier plant at Helsinki in
1961 had also used water-tube-walls. Thus, with this company, the transfer
of water-tube-wall technology from well-developed coal-burning practices to
waste-to-energy plants occurred in the mid-1960's.
Meanwhile, the first large water-tube-wall boiler, 264 tons/day,
had been installed at Essen-Karnap in 1960 as part of an existing coal-fired
power plant described by Moegling*. Pulverized coal was fired above the
refuse fuel bed.
During the same period, the Martin grate, originally applied to the
burning of brown coal, was adapted at Munich to water-tube-walled furnaces
for the large-scale burning of municipal refuse for power generation. Bachl
and Mykranz described the first Munich unit in an extensive article
published in Energie, in August, 1965. Pulverized coal was fired in a
separate furnace. In a second unit, the coal was fired directly above the
refuse.
Another system was developed by the municipal utility at
Duesseldorf during 1961-1965.
Air-Cooled Furnace Wall at Werdenberg
Figure S-2 shows a cross section of the single boiler in the small
Werdenberg-Leichtenstein plant at Buchs, Switzerland. Although this is a
very small boiler (12 tonne/hr (26,460 Ib/hr) rated steam capacity with a
peak capacity of 16 tonne/hr (35,275 Ib/hr)), in many ways, it embodies the
current culmination of evolution of the vertical pass, water-tube wall type
of boiler discussed earlier. Boiler pressure is 40 atm (590 psia) (4,052
kPa). It began operation in April, 1974. Undoubtedly, a significant factor
* Hotti, G. and Tanner, R., "How European Engineers Design
Incinerators", American City, June, 1969.
* Moegling, E., "Praxis der Zentralen Mullverbrennung am Biespiel
Essenkarnap", Brennst. - Warme - Kraft, V7, August 1965, 383-391.
* Bachl, H., and Mykranz, F., "Experiences With Refuse - Firing In A
High - Pressure Steam Power Plant", Energie, 17 P. 317-26, August 1965.
-------
S-4
1 Delivery Area
2 Bunker Door
3 Refuse Bunker
A Crane Pulpit
5 Crane
6 Refuse Grab Bucket
7 Charging Hopper
8 Incinerator Furnace
9 Step Grate
10 Ash Hopper
11 Residue Chute
12 Residue Basin
13 Residue Conveyor Belt
14 Steam Boiler
15 Air Cooled Condenser
16 Electrostatic Precipitator
17 Exhaust Gas Fan
18 Steel Chimney
19 Hot Water Heater
20 Feed Water Tank
21 Turbogenerator
22 Collected Flyash Conveyor
23 Feedwater and Heating Water
Pumps
24 Oil-Fired Stand-by Boiler
FIGURE S-2. PARTIALLY WATER-COOLED AND AIR-COOLED FURNACE AT WERDENBERG-
LIECHTENSTEIN (Courtesy of Widmer & Ernest)
-------
S-5
in its design is the presence on the vendor's engineering staff of a number
of experienced designers who had experience over the years working at Von
Roll with the same Dr. Tanner referred to in the earlier paragraphs on
boiler furnace evolution.
The sides of the furnace are composed of two different surfaces.
Near to the grate and for about 1.5 m (4 ft) above, the grate wall is
formed with about 85 air-cooled Kunstler (Zurich) cast iron blocks on each
side which allows a small amount of cooling air to enter the furnace
through narrow air gaps between adjacent blocks. The blocks are about 250
mm (10 in) tall and 20 mm (8.5 in) wide. Above the cast iron blocks, the
furnace wall is formed by Plibrico Super AB plastic refractory 150 mm (6
in) thick backed up by 250 mm (10 in) high-temperature calcium silicate
insulation. Figure S-2a is a diagram of the action of the Kunstler wall
blocks.
Thus, the lower quarter of the main furnace sidewalls are cooled
only by forced air flowing behind and through the wall blocks, but the
front and rear wall of that chamber are cooled by water-wall tubes similar
to the arrangement in the large, vertical open pass above the furnace. In
the "rear wall", which actually is a rear "arch" which slopes a little more
steeply than the sloping grate, there are 40 tubes closely spaced over the
width of the furnace. The Widmer & Ernst engineer stated that the
temperature in the furnace is 950 C (1,742 F).
This sloping rear roof is studded with 8 mm (0.3 in) diameter
studs, 22 mm (0.9 in) long. There are about 1,000 studs per square meter.
These tubes and studs are then coated with a 25 mm (1 in) thick coating of
Plibrico Super AB plastic refractory. In the newer plants, 40 mm thick
Plibrico coating is used. This thick coating reduces the heat absorption by
the covered tubes but serves as a protection against corrosion. It has been
very successful here and elsewhere. Apparently the decision to increase the
refractory coating thickness from 25 mm (1 in) as used here up to 40 mm
(1.6 in) in newer plants was made in order to increase the life of the
coating, as this coating is subject to deterioration' from cracking as it
heats and cools. In addition, the coating is mechanically eroded and
spalled by the action of heavy deposits of fused ash which adhere to the
coating then break off or are broken off during periodic cleaning. As
portions of the coating are broken away, patching is required to maintain
protection of the tubes. Apparently a thicker coating reduces the frequency
of patching required.
Welded studs and refractory coating are also utilized over the
entire lower half of the vertical, water-tube walled boiler pass
immediately above the furnace. This very common design of coating was
applied after corrosion was experienced in 1970 in a similar furnace at
Baden-Brugg, Switzerland, which required protection after only 2,000 to
3,000 hours of operation.
In the first pass, the water tubes are nearly tangent. The tubes
are carbon steel, 76.1 mm (3.0 in) in diameter, 4 mm (0.16 in) thick,
spaced on 78 mm (3.1 in) centers. Although the tubes are nearly touching,
they are not connected by welded fins to form a membrane wall. Apparently,
European boiler designers have been reluctant to use the welded fin,
membrane wall type of construction because of differential expansion
problems that might cause fatigue cracks to form. However, it is now
beginning to appear in some designs. In addition to providing the advantage
-------
S-6
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S-7
of air-tight wall construction, the welding of the tubes to form a
"membrane" wall helps to keep all of the tubes in line and straight rather
than allowing some tubes to bow inward or outward.
Second Boiler Pass. When the upward-flowing gases reach the top of
the first pass, they then are turned horizontally into the entrance of a
second water-tube walled vertical pass in which the gases are further
cooled as they flow downward. These water tubes have no studs nor coating
as, by this time, the gases are cooled so that corrosion and erosion are no
threat to water tubes. This second pass for gas cooling is similar to the
older and very successful Unit No. 3 at Zurich-Hagenholz described later.
Partially Water-Cooled Furnace at
Baden-Brugg, Switzerland
Figure S-3 is a cross section of a portion of the 2-unit,
two-boiler Baden-Brugg (1970) 200-tonne per day plant which is of interest
because it preceded the one-boiler Werdenberg (1974) plant by 4 years and
was designed by the same experienced designers.
A major difference from the later Werdenberg design is that, in
this older design at Baden-Brugg, there is no open second pass to cool the
gases before they reach the superheater.
The main furnace is largely refractory walled. Only the sloping
rear wall of the furnace is water-cooled. As the combustion gases rise out
of the partially cooled refractory walled furnace, they are accelerated
into the first or radiation pass, a tall open, vertical, water-tube walled
pass. The entering velocity to the pass is estimated to be about 5 m/sec
(16.4 ft/sec). This is a relatively high velocity and, because of the
eddies formed when the gases accelerate into this pass, this rather high
velocity may have been partly responsible for early failure of nine wall
tubes in the lower part of this first pass.
As a result of those failures, a 25 mm (1 in) silicon carbide
covering was added over the lower 5 m (16 ft) of these walls. However,
this increased the superheater outlet temperature 20 C (36 F). Hence, in
1974, in Boiler No. 1, the height of this covering was reduced to only 1 m
(3.28 ft). The silicon carbide covering is not held in place by welded
studs but by 20 mm diameter steel coils (see Figure S-4) which are anchored
to the tubes before being buried by the plastic refractory covering. Since
this coil-supported covering was applied, there have been no further
failures of wall tubes. The wall covering now needs minor patching every
year. Although this steel coil support for the refractory covering has
apparently served well in this installation, the manufacturer has since
used the more conventional welded steel studs at other plants to support
the refractory covering on the sloping rear wall of the main furnace.
The manufacturer believes that the failure of nine wall tubes was
caused primarily by reducing gases flowing against those tubes. The tube
material is C14UN15462-64, a typical carbon steel. They are 57 mm (2.24
in) in diameter with a 2.9 mm (0.11 in) wall thickness, and are spaced 59
mm on centers.
-------
S-8
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S-9
FIGURE S-4. HR. B. LOCHLIGER, ASSISTANT PLANT MANAGER, HOLDING STEEL
REINFORCING COIL FOR TUBE-COVERING MOLDED REFRACTORY
(Battelle Photo)
-------
S-10
1965 and 1972 Designs of Furnace
Wall in Duesseldorf
The five furnaces at Duesseldorf comprise an interesting example
of the evolution of water-tube wall furnaces for mass burning over the past
12 years. When the first pilot grate was built at this plant in 1961, the
use of water-tube walled furnaces for refuse was still in its infancy
because the heat value of European refuse was very low. From 1961 to 1975
at the Duesseldorf plant, the average lower heat value of refuse increased
70 percent, 4,292 J/kg to 7,314 J/kg (1,025 kcal/kg to 1,747 kcal/kg (1,845
Btu/lb to 3,145 Btu/lb)) (see Figure S-5).
Thus, so long as wet, high-ash refuse made combustion difficult,
designers were understandably reluctant to depart from the use of hot
refractory-walled furnaces. However, as the heat value of refuse increased,
furnace refractories were damaged by excessive furnace temperatures and the
merits of water cooling the furnace and thus of adding it to the heat
recovery loop became more and more attractive. However, the pilot plant at
Duesseldorf, burning 8 tonnes per hour, utilized an old refractory-walled
furnace, which had originally burned coal on a traveling grate at the
Flingern Power Plant. This pilot unit, using the first roller grate, was
operated intermittently for a total of 22,000 hours from 1961 to 1965 and
provided the design basis for a small plant at Rosenheim, and for the first
four full size units at Duesseldorf—the first of which was started in
November, 1965.
For the reasons cited earlier, when the design transition was made
in 1964-1965 from the old refractory-walled pilot furnace to the new,
full-scale units, No. 1 through 4, there was an understandable reluctance
to use a fully water-tube walled furnace. Although the lower heat value at
Duesseldorf refuse had risen to 1,220 kcal/kg (5,108 KJ/kg) (2,196 Btu/lb)
by 1963, that was still a relatively low level; hence, the need for some
refractory in the main* furnace to reflect heat to the raw refuse so as to
facilitate rapid ignition and burning.
Accordingly, the water-tube walls of the furnace itself in Units
No. 1 through 4, shown in Figure S-5, were protected by a 50 percent
aluminum oxide refractory curtain 250 mm (10 in) thick and spaced by a dead
air space 50 mm (2 in) wide in front of the vertical wall tubes. The tubes
are 70 mm (2.75 in) in diameter with 5 mm (0.2 in) wall thickness. The
distance between tubes is about 70 mm.
This type of unique sidewall construction was not used in Furnace
No. 5, built in 1972, which will be described later.
The sloping roofs of the furnaces are also cooled by tubes covered
by refractory.
First Open Boiler Pass, Units No. 1 Through 4. Burning is usually
not complete as the gases flow upward out of the main furnace. This means
that the ash particles carried in the burning gases are usually hot enough,
over 982 C (1800 F), to be sticky. Accordingly, enough volume must be
provided and that volume must be cooled for two reasons:
• Allow time for combustion to be completed, about 50 to 200
milliseconds
• Cool the gases so that deposits of ash particles will be dry
and will be below the corrosive range.
-------
FIGURE S-5. CROSS SECTION OF ONE OF BOILERS NO. 1-4 (COURTESY OF
STADTREINUNGS UND FUHRAMT DUESSELDORF)
1. Refuse hopper
2. Refuse feeder and roller
grate "system Duesseldorf"
3. Ignition burner
4. Heavy oil burner (both sides)
5. Economizer
6. Steam drum
7. Radiant water-tube-wall boiler
8. Boiler convection section
9. First and second stage super-
heater
10. High-temperature superheater
11. Steam discharge
12. Exhaust gas duct to electro-
static precipitator
13. Ash siftings removal
14. Wet residue conveyor
15. Residue removal to processing
plant
-------
S-12
Mr. K. H. Thoemen, Plant Manager, has described (1972) the design
of the first four boilers as follows*:
"For different reasons, among others' economy, the
construction and operation of large incinerator plants in Germany
has been put into the hands of municipal power plants or similar
institutions. This had the result that in the design of the
incinerator plants, the same design elements have been used as in
the design of coal-fired power plant steam boilers.
In 1967, after tube failures had been reported at other
incinerator plants, in Duesseldorf, the tubes just above the
furnace were inspected and at the lower area of the side walls,
the first indications of corrosion were found (Figure S-5).
As a means of protection, additional secondary air nozzles
were installed to build up a curtain of excess air in front of the
tubes. Furthermore, the endangered area was studded and covered
with a 1/2-inch layer of silicon carbide refractory. In other
plants, this method of protection already has been applied, with
similar good results.
In 1968, a tube rupture occurred in one of our boilers. The
cause was investigated and found to be corrosion by the flue gas.
Subsequent extensive inspections of the boilers demonstrated that
corrosion observed the year before had continued and reached the
tube surface above the protected area. Not only the side walls
but now the front wall was affected. Ultrasonic measurements
showed that it was necessary to renew about 30 to UO tubes in each
boiler for a length of about 7 feet. A considerable number of the
remaining tubes had to be reinforced by welding. Moreover, an
extended area of tube surface was studded and concealed."
In a further endeavor to stop wall tube wastage in the lower part
of the first boiler pass, more secondary air was added in the furnace roof
and a refractory arch or "guiding wall" was evolved at the top of the
furnace outlet (see Figure S-6). Thoemen explains this evolution as follows:
"To guarantee a better burnout and mixture of the flue gases
in the existing units, the following changes were accomplished.
The over fire secondary air was increased to about 25 to 30 percent
of the total air. But the experience is, that with the overfire
air by itself, a complete mixture of the gases cannot be obtained.
The relatively cold air does not blend with the gas but pushes it
aside.
The first step to change the configuration of the furnace was
done by the construction of a fire guiding wall. This is an
arch-like wall of firebrick, built in at the end of the furnace
front-roof. This guiding-wall hinders the direct flow of the
gases along the roof into the first flue. Furthermore, it is a
contraction of the profile of the furnace throat by which part of
the gas with high excess air from the end of the gases is forced
into the front part of the furnace. Because the secondary air
nozzles are located directly in front of the wall, a better
vortical intermixture of air and gas is achieved. The arch-like
configuration of the wall contracts the gas flow in the center of
the first flue which results in a more uniform directed gas stream.
* Thoemen, K. H., "Contribution to the Control of Corrosion Problems
on Incinerators with Water-Wall Steam Generators", Proc. ASME 1972
National Incinerator Conf., New York, 310-318.
-------
S-13
tleasur/ng
Pleasuring
tieasur/nq
{.ere/2
Secondary
+f * % *^/ / U ^1 f W
\\ a/r noztles
Measuring
Ley el *+
nrasuring.
ieye/3
FIGURE S-6. DIAGRAM OF LOCATION OF GUIDING WALL
AT TOP OF FURNACE OUTLET SHOWING
EFFECT ON OXYGEN DISTRIBUTION IN
GASES
-------
S-14
The experience with this guiding-wall is very good. Since
its erection in the years 1968 and 1969, tube corrosion in the
first pass has not continued or spread out. Stream tests with a
water-tank model and extensive gas analyses have proved the
efficiency for the uniformity and burnout of the gases."
This guiding wall in Furnaces No. 1 and 2 was formed of high
alumina content refractory and was not air cooled. In Furnaces No. 3 and
4, it was made of silicon carbide. Because of the high temperature to
which these refractories are subjected, they are now being converted to
air-cooled designs. Uncooled, their life was about 23,000 hours. The air
cooling arrangement is discussed later under "Secondary Air". Furnace No.
4 was converted in early 1976, Furnace No. 3 in early 1977, and Furnaces
No. 1 and 2 were to be converted to air cooling later.
Furnace Wall in Unit No. 5. The furnace for Unit No. 5, built in
1972, was altered in accordance with the experience gained in about 6 years
of operation of Units 1 through U. Also, the flow pattern in No. 5 was
radically altered because of the rising heat value of Duesseldorf refuse.
Instead of having the burning gases flow upward at an angle toward the
furnace outlet as in Units 1 through 4, a sloping, steam-generating,
water-cooled baffle was built in No. 5 above the fuel bed as shown (Point
"A") in Figure S-7, in such a way that the gases first flow nearly parallel
to the fuel bed; then at the end of the baffle, they turn and flow upward
toward the furnace outlet. This provides a longer flame path and residence
time for the hot gases resulting from the higher heat value of refuse.
One desirable achievement of this new design is that by the time
the gases reach the top of the furnace and pass into the first pass, they
are well mixed and cool enough to reduce corrosion. In late 1976, at the
Engineering Foundation Conference at Hueston Woods, Ohio, Thoemen* stated
regarding this new furnace in Boiler No. 5:
"Although the tubes of the first pass have not at all been
protected by ceramic lining, after more than 1 year of operation,
not any corrosion attack of the former kind was detected... The
construction forms a true combustion chamber in the front part of
the furnace. It is evident that in this combustion chamber, higher
temperatures are generated than in the elder units; hence, the
danger of slagging in the furnace had to be taken into
account...so that the furnace roof and the later fire-guiding wall
were designed as steam generating water-walls, to carry off
certain amounts of heat from the furnace."
However, because of slagging of the uncooled furnace
sidewalls, "...after 6,000 operating hours, the SiC lining of the
front part of the furnace was totally damaged. The furnace had to
be reconstructed with plastic refractory on an A^Og base. Now the
slagging problem appeared again, and during the following
operation period, several times heavy slag formation occurred at
the side walls, which made it necessary to shut the boiler down
and remove the slag. In order to achieve a further undisturbed
operation, the combustion was shifted to the end of the grate.
Instead of air, recycled flue gas was injected under the first
roll of the grate. Due to the oxygen reduction in the forward
combustion chamber, the main combustion zone moved one roll
Thoemen, K.H., "Contribution to the Control of Corrosion Problems on Incine-
rators with Water-Wall Steam Generators", Proc. ASME 1972 National Incinerator
Conf., New York, 310-318.
-------
S-15
Boiler Cociponents
1. Welded Fin Water Tube Walls
2. Superheater
3. Steam Drum
4. Boiler Convection Section
5. Economizer
FIGURE S-7. CROSS SECTION OF BOILER NO. 5 WITH ROLLER GRATE "SYSTEM
DUESSELDORF" (Courtesy Stadtwerke Duesseldorf Kraftwerke)
-------
S-16
downward along the grate. Consequently, the burnout time for the
flue gas was shortened, and after an operation time of about 1
year, the first corrosion on the tube surfaces of the front wall
of the first pass occurred.
Because of the unsolved problems with the furnace, the
endangered area, about 2 m (6.5 ft) in height, was studded and
lined with plastic refractory. Later, no further corrosion was
found in this zone."
Wall Construction in Unit No. 5. While the walls in Units 1
through M were either refractory or spaced water tubes backed by
high-temperature insulation, the nonrefractory water-tube walls in Unit No.
5 are "membrane walls"; that is, each tube has two welded fins, 10 to 12 mm
(0.4 to 0.5 in) facing the adjacent tubes. The joint between the fins is
also welded forming a solid, water-cooled membrane wall.
Wall Protection. When the first plastic-refractory coating was
applied to water-tube walls at Duesseldorf, the 10 mm (O.H in) diameter
studs were welded to the wall tubes at a density of 2,800 per m2 (260 per
ft2). Later this density was reduced to 2,200 per m2 (20H per ft2).
To cover the studs, a moldable form of silicon carbide is
preferred if an accumulation of slag is expected because SiC tends to repel
the adherence of sticky slag. Where slag is little problem, a plastic
refractory, such as Plibrico, 75 mm (2.9 in) thick is used.
Water-Cooled Furnaces at
Wuppertal and Krefeld
The six units at the relatively new plants of Wuppertal (1976) and
Krefeld (1976), Germany, both near Duesseldorf, are very similar and show
the influence of the experience gained by VKW at Duesseldorf. They are not
primarily power generating units; hence, steam temperature is moderate:
Wuppertal (350 C, 662 F), Krefeld (376 C, 709 F), in contrast to
Duesseldorf (500 C, 932 F).
Their furnaces are thoroughly water cooled in accordance with
the design and operating experience accumulated by VKW and its customers at
the Duesseldorf plant and various other plants. The 57 mm (2.3 in) wall
tubes are made of ST 35.81 steel, U mm (0.157 in) thick; and by means of
welded fins, they form a continuous membrane wall.
At the lower part of the combustion chamber, adjacent to the
roller grate, precast carbofrax blocks are used.
To protect the wall tubes of the combustion chamber from attack by
high-temperature flame impingement, they are studded and then covered with
silicon carbide. At Wuppertal, initially, part of the coating is 50
percent SiC and another part uses 80 percent SiC. For purposes of
observation, the amount and type of each coating varies in each furnace.
They consider this an experiment to observe which meets their conditions
best. Later they will settle on the type and arrangement which performs
best for future use when any replacements are needed.
At Krefeld, to protect the wall tubes of the furnace from
high-temperature flame impingement, they are studded and then covered with
90 percent silicon carbide. The welded steel studs are 10 mm (O.U in) in
-------
S-17
diameter and 20 mm (0.8 in) long. The silicon carbide coating is
approximately 50 mm (2 in) thick. The studs are applied at the rate of
2,100 per vf- (195 per ft^). The studs and coating are continued upward into
the radiation chamber for a distance of about 3 m (10 ft) above the refuse
feed opening.
At Wuppertal, as an extension of the protection afforded by the
SiC, the same coating is carried upward along the walls of the radiation
chamber for 2 or 3 m (6.5 to 9.8 ft).
During initial operation, water-washing of the boiler heating
surfaces was used periodically for cleaning. However, this probably posed
some threat through soaking of the refractory coating in the lower part of
the radiation chamber and combustion chamber. Water-washing is no longer
used. Instead, every 3,000 to 4,000 hours the surfaces are brushed clean
manually. So far, there has been no slag buildup anywhere in the system;
hence, only fine ash deposits need to be brushed off. This is unusual,
since many other waste-burning furnaces require periodic cleaning of heavy
deposits of fused ash and slag that adheres strongly to the sidewalls of
the combustion chamber. We can only conclude that these relatively new
furnaces are not being fired as intensely as are many others.
Because of the fact that the flue-gas scrubbing system is not yet
operational at Wuppertal, only two of the four furnaces are operated at a
time so as to limit the discharge of acid gases to the atmosphere. As has
been observed at several of the 30 visited plant, waste generation rates
leveled off in the mid 1960's and many plants were left with excess
capacity. Thus, since the beginning of plant operation in January, 1976,
and up to the time of our visit, May 20 and 26, 1977, or during an elapsed
time of about 11,000 hours, each of the four boilers had operated only
about 4,000 to 5,000 hours. While the intermittency of operation would not
preclude excessively intense operation of each boiler during brief periods,
the practical matter is that alternate means had obviously, already
previously been employed for disposal of the 525,600 tonne/year, which is
the theoretical full-time capacity of all four units potentially now
available. Thus, there may as yet be no great need nor perhaps much
pressure from any quarter to opereate the MVA units more intensively.
(Actually, as designed, this plant was intended to operate only three
boilers at a time, leaving the fourth unit for maintenance and standby).
From previous experience in the boiler industry, Mr. Temelli,
Assistant Plant Manager, indicated that he is fully aware of the multiple
problems of corrosion, erosion, and frequent maintenance requirements of
combustion and thermal equipment when it is severely overloaded. He
explained that because of the variable nature of refuse, if the nominal
load per furnace is 15 tonnes per hour (16.5 tons/hour), peaks will be
encountered of 18-19 tonnes per hour. To avoid the added maintenance
resulting from such peaks, these units are now operated at an average rate
of 13 tonnes per hour (14.3 tons/hour) or about 13 percent under rating.
Since there is no immediate need to more fully load these units, they will
probably continue to be operated conservatively.
So far, there has been no wall- or boilertube corrosion observed
after nearly 6,000 hours of operation of each unit. They are designed to
deliver steam at the rate of 46,000 kg/hr (101,200 Ib/hr) (50.6 tons/hr) at
a temperature of 350 C (662 F) and 27 bar (378 psia) (26.65 atm) or 2604
kPa.
-------
S-18
An unusual feature of the Krefeld furnaces is that dried sewage
sludge is fired in suspension in hot flue gases at a point near the lower
end of the radiation chamber and within the section that is coated with
silicon carbide. A substantial amount, 2.7 to 3.9 Nm^/sec (5,715 to 8,356
scfm), of hot flue gases are extracted from the first pass and is sent to
the sewage sludge hammermill. Because the sludge particles still carry
moisture (10 percent) and because the moisture having been vaporized out of
the sludge is still in the hammermill exit gas, when both the particles and
the vapor enter the hot radiation chamber,they will absorb considerable
heat before the particles become heated to their ignition temperature. For
these reasons, there is not as much energy available for steam generation
as in straight refuse burning and the radiation chamber is relatively small.
Change from Refractory to Water-tube Wall
at Paris-Issy
Figure S-8 shows one of the four boilers at Issy (1965) which
incorporated the results of much Parisian and other experience in high
temperature steam from waste fuel. The large, open first and second passes
seem to be designed to avoid high temperature corrosion problems; yet wall
and superheater corrosion have occurred because:
1. These boilers are overloaded by as much as one third.
2. The two open passes are large in volume and in width
which may provide less rapid convection heat transfer.
In 1975 the average input rate per operating furnace was 19.1
tonnes/hr (21.0 tons/hr) and in 1976 this rose to 19.9 (21.9). The
original design rate was 15 (16.5) which later was increased to 17 (18.7).
In 1975 and 1976 the four units operated 86.4 percent and 84.8 percent of
the total elapsed'time. This high intensity of operation is needed, but it
contributes to increased maintenance requirements, particularly because of
inevitably higher peak burning rates than the average. •
Issy is an excellent example of the historical development of the
Martin furnace. A previous section mentioned that Martin was selected in
part because both Martin and TIRU would use the Issy plant for
development. The following descriptions of stages document some of the
results from this cooperative developmental spirit.
Stage 1. Refractory Brick Walls. While the upper first pass
through the economizer section (built by CNIM) was water tubed, the
furnace or combustion chamber was originally lined with refractory brick.
Presumably the lack of combustion chamber gas cooling caused the first
pass side wall tubes to fail in 1966 after 5,000 to 6,000 hours. Probably
lag was also adhering to the refractory wall. For whatever reasons, the
owners decided to change the furnace wall.
Stage 2. Alumina Blocks Surrounding Wall Tubes. As a corrective
measure, the boiler tubes were extended down into the furnace combustion
chamber parallel to the grate. There are 3 such sloping tubes on each
side. They were 70 mm (2.7 in) in diameter, the tube wall thickness was 4
mm (0.2 in) and the spacing was 160 to 180 mm (6.4 to 7.2 in). A
specifically shaped silicon carbide block was designed to fit these tubes
and used as shown in Figure S-9. These were installed from the ash
-------
S-19
SI
w
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H X
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CO M
W J
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-------
S-20
discharger area up into the first pass above the secondary air jets.
Cement was used to bond the blocks together. While the ash would
not easily stick to the special blocks, it did stick to the cement mortar.
Eventually in operation or in cleaning, the slag (fused with the cement)
would come off—pulling with it the cement mortar. Combustion gases could
then penetrate to the tubes. Eventually some blocks began to crack and
fall. This system thus had to be replaced.
Stage 3. Plastic Silicon Carbide Surrounding Wall Tubes. The
third effort upon removal of the blocks in 1966 was to apply ten (10) tons
of plastic silicon carbide to each furnace. A basically dry cement mixture
of SiC and 8 percent 1^0 was packed and rammed around the tubes as shown
in Figure S-10. The material used was Carbofrax SiC798B. Two man-weeks
were required to install this plastic material. It should have lasted 5
years. The ash and slag stuck to the walls and would fall when the walls
were cleaned. The plastic had little firm anchorage.
Stage 4. Studded Wall Tubes Covered with Alumina. The fourth and
current stage uses welded studs covered with 42 percent A120 5 plastic
refractory. The alumina is cheaper than the silicon carbide and bonds
better at lower temperatures. The more expensive SiC has better wear once
a proper bond is made. However, sometimes it is difficult to heat it for a
long time at high enough temperature for a complete bond. Wall life has
been much better with the Stage 4 approach. During scheduled downtime,
more refractory is added around the studs in loosened, cracked, or fallen
areas.
Walls of First and Second Passes
These two empty radiation passes have volume of 290 m3 (10,234
ft3). The walls of these passes have suffered from tube wastage in
limited areas as follows:
Stage 1. Original Bare Water Tube Walls. Originally the wall
tubes were bare. The diameter was 70 mm (2.8 in) with a 4 mm (0.15 in)
wall thickness. After 15,000 hours, many of the tubes had severe metal
wastage or burst. Thin or burst areas are shown in Figure S-11.
Hypothetical reasons for metal wastage vary from (1) flame
impingement, (2) overheating of ash deposits, (3) alternating
reducing-oxidizing atmospheres to, (4) abrasive particles in gases.
Stage 2. Protective Shields Around Water Wall Tubes. Steel
shields were then applied to these sensitive areas.
Stage 3. Metal Deflector Baffles in Second Pass. Because the
superheater in the third pass was suffering erosive metal wastage, a metal
deflector baffle was installed near the turning point at the bottom of the
second pass. (See Figure S-12)
Stage 4. Plastic Silicon Carbide Surrounding Water Tubes in Wall.
To further reduce metal wastage, Carborundum's Carbofrax 798B was applied
to these areas in 1977.
-------
S-21
FIGURE S-9. ISSY ALUMINA BLOCKS SURROUNDING BOILER TUBES
Plywood e*»
Sel
FIGURE S-10. PLASTIC SILICON CARBIDE SURROUNDING BOILER TUBES
-------
S-22
Pass
FIGURE S-ll.
ISSY METAL WASTEAGE ZONES AND' AREAS OF
CORRECTIVE SHIELDING
-------
S-24
New Deflector
Baffle
Former Erosion
Point
FIGURE S-12.
ISSY NEW SECOND PASS DEFLECTOR BAFFLE TO
PROTECT THIRD PASS SUPERHEATER
-------
S-25
To sum up the Issy experience, wall tube corrosion in the open
first and second passes is being satisfactorily controlled by the use of,
shields, and plastic refractory alloy shields.
Wall Tubes at Hamburg-Stellinger Moor Plant
The furnace wall "story" at Stellinger-Moor (S-M) is the most
comprehensive and complex of all the plants visited. The plant manager,
Karl Heinz Arndt and the control engineering staff is experimentally
oriented, open minded and capable of making successful design changes.
Stage 1 (Original Construction). The furnace combustion chamber
is fully of water tube wall construction. Depending on wall location,
various protective refractories have since been added. The refractory
coating of the lower combustion chamber extends upward into the radiation
first pass to a level two meters above the front nose. The vertical water
tube walls in this combustion chamber are tangent tube construction. The
tube outside diameter is 7 cm (2.75 inches) with a 3.2 mm (0.125 inches)
wall thickness. The front and rear sloping walls are of welded fin tubes,
57 mm (2.25 in) diameter.
Three water headers slope downward, parallel and near the grate
as is shown in Figure S-13.These water header collectors are only near the
hotter part of the grate, i.e. after drying and before burnout. Wall
thickness tests were made on the west wall on April 22, 1977 after 27,000
hours of operation. The metal wastage pattern is clear. Maximum metal
wastage occurred 500 mm (19 in) from the measuring base line at the
hottest sidewall portion on the grate. At the worst point, the thickness
was still 2/3 of the measuring base line point.
Installing these three tubes on each wall appears to be an
excellent method of lowering the localized and very high gas temperatures.
These 18+ mm (0.719 inch) thick tubes will be easier to replace if
necessary than the higher-up and harder-to-reach 3.2 mm (0.125 inch)
boiler tubes.
Stage 2 (Simple Addition of Refractory). As time progressed and
tubes began to fail up in the boiler, plant officials began to experiment
with other measures to directly protect combustion chamber tubes and to
indirectly lower gas temperatures entering the downstream boiler passes.
Plant staff supplied a not-to-scale diagram dated October 29,
1976, that shows what had just been done to the combustion chamber. Four
refractory materials were used at locations shown in Figure S-14.
Plibrico supplied Plicast 14 (P14) (88-90 percent SIC) to be used
above the combustion chamber front roof where the raw refuse enters and
down along the sides of the grate where the ash abrades the wall. First, 6
mm (1/4 inch) studs were welded to the tubes at a density of 467 studs per
square meter. Then, Plistix 14, a 90 percent Silicon Carbide material, was
mixed with water and sprayed on the studded water tube walls.
Also Plibrico Plicast 40 (P40) was used on the hot portions of the
studded side water tube walls at a location above the sloping water headers.
The third material is Brohtal (B) which is 95 percent alumina
castable—a preformed brick. An experimental section was installed very
near the furnace entrance on only one side to counter the excessive
-------
S-26
Measuring Baseline
1. Lateral Wall Collector
2. Upper Grate Cooler Beam - Collector
3. Lower Grate Cooler Beam - Collector
Distance (mm)
Wall Thickness (mm)
0
18
100
16
200
14.7
300
13.5
400
12.4
500
11.8
600
.12.1
700
14.3
800
16.7
FIGURE S-13. METAL WASTAGE OF WATER HEADERS ABOVE
THE HOT SECTION OF THE GRATE AT HAMBURG:
STELLINGER-MOOR
-------
S-27
Roof Renewed With PI4
P40
Anchor
Anchor
Ash Discharge
PI4 Plistix 14
P40 Plicast 40
B Brohtal Special High Alumina
Castable
FIGURE S-14.,
OCTOBER 1976 ADDITIONS OF REFRACTORY TO HAMBURG STELLINGER-
MOOR FURNACE #1
-------
S-28
abrasion by refuse on the lower side walls. The steel studs themselves were
not only bare after 1/2 year but were also eroded away.
Brohtal is also used extensively at the second step at several
places. T bricks are placed in the sidewall above and at the lower end of
the sloping water headers. Note that anchors (and not studs) are used to
keep the bricks secure. A small amount of the Brohtal is used on the side
wall just after the fall from the second step and at the top of the third
step. Finally Brohtal is used just under the second grate and across the
furnace.
Stage 3 (Addition of Caps onto the Studs and More Refractory). In
May 1977, when Unit 1 was down for annual overhaul, several important
changes to the wall were made. The primary motivation was unhappiness with
the Plistix 14 (88-90 percent SiC). The material did not always stick to
the studs and 50 percent of the SiC surface area had to be repaired every
4000 hours. Apparently this very excellent and expensive material does not
fully bond to the studs unless the temperature can be raised to a very high
level 1200 C (2192 F), for a sufficient time.
The Hamburg officials knew of work at Oberhausen, W. Germany RFSG
where, the studs were covered with a cap as shown here:
These SiC caps were purchased from Didier Refractory Company of Weisbaden,
W. Germany. The lower grade (1/3 the cost) SiC 50 from Didier or a high
alumina refractory can be applied over the caps.
Figure S-15 shows where this cap and cement were experimentally
applied 5m? (54.9 ft2) on the side walls. The SiC is 40 mm (1.57 inches)
thick. At the time of Battelle's inspection visit in June, 1977, not enough
time had passed to determine results. Plant staff are expecting that should
results be satisfactory, S-M will probably replace more SiC 90 directly on
studs.
Another test is being run comparing the Brohtal high alumina
refractory with the Plibrico Erocist and also can be seen in Figure S-15.
Finally, Fleischmann's Fixoplanit 138 covering has been applied at
the second step and under the grate.
Furnace Wall (Radiation First Pass). Vertically rising above the
combustion chamber is the open radiation first pass. Unlike the fin tube
walls of the lower combustion chamber, these water tube walls are not
welded tangentially and have 5 mm (0.2 inches) spacing between 70 mm (2.75
in) tubes.
These unwelded tubes are free to bulge either out or into the
radiation chamber depending on the type and intensity of compressive
stresses. An apparently improperly positioned and operating rotating wall
sootblower, after 6200 hours of operation, eroded a hole in one of these
-------
Special High Alumina
Brohtal
Plibrico Erocist
Reiscnmann
Fixoplanit 138
FIGURE S-15. MAY 1977 ADDITIONS OF CAPS ONTO STUDS AND REFRACTORY TO
HAMBURG: STELLINGER-MOOR
-------
S-30
tubes bulging out into the furnace midway up the first pass. It is felt
that, if the lower fin tubes of the combustion chamber were extended
further up into the first pass, then the wall could have withstood further
abuse from the sootblower before failure. When the one tube failed, another
40 or 50 wall tube sections of thinning thickness were also replaced. There
has been metal wastage at other points and once per year, the thinning
tubes are routinely replaced.
Stellinger-Moor is one of the last units to have non-welded water
tube walls.
First Pass Roof. Some tube wastage has occurred at the top of the
first pass where sloping tubes form a suspended roof which continues over
the superheater and boiler convection section. These tubes carry saturated
steam from the front water tube walls of the first pass directly to the top
of the boiler drum.
Fortunately, the management has had the foresight to make a
detailed record of all measurements and everything done to the furnaces. A
September 21, 1976 entry to the maintenance record reports on the roof tube
problems. The original diameter of the tubes was 20 mm (2.75 inches) and
the original wall thickness was 3.6 mm (.14 inches). The measurements taken
were only on tubes that had shown signs of metal wastage, i.e. tubes
numbered 16 through 41.
As can be seen in Table S-1 the thickness had been reduced from
the original 3.6 mm (.14 inches) down to between 1.6 and 2.3 mm (0.06 and
0.09 inches). Of the twenty tubes measured, all but two, Number 18 and 39,
at 2.3 mm (0.09 inches) were replaced. Number 41 had previously been
replaced. When the renovated system was pressure tested, Number 37 failed
and had to again be replaced.
The corrosion of these roof tubes was related to incomplete
bonding of the SiC 90 that had been sprayed over metal studs on these large
tubes. Because the tubes carry saturated steam at 253 C (488 F) and not the
hotter superheated steam, the SiC refractory coating never got hot enough
for proper bonding, i.e. 1200 C (2192 F).
The plant staff have decided to change from the SiC 90 in favor of
a high-alumina plastic refractory. In other words, the superior heat
transfer characteristics of a properly bonded SiC 90 will be given up in
favor of the cheaper and more reliable high-alumina refractory.
First Pass Outlet
(Overflow Tubes at
Rear of Radiation First Pass)
The overflow tubes depicted below which carry the steam upward
from the wall to the steam drum have experienced erosion by the combustion
gases.
Furnace roof
o
-------
S-31
TABLE S-l. WALL-TUBE THICKNESS MEASUREMENTS OF SCREEN TUBES
AT THE REAR OF THE RADIATION FIRST PASS AT HAMBURG:
STELLINGER-MOOR
Tube (Number)
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37*
38
39
40
41
(Boiler Number 1)
Metal Thickness (mm)
1.8
1.9
2.3
2.2
2.0
2.0
0.0
2.0
2.0
1.9
1.7
2.0
1.8
1.9
2.1
1.9
1.8
2.3
1.6
Action
Tube replaced
Tube replaced
Tube not replaced
Measurement not taken
Measurement not taken
Tube replaced
Tube replaced
Tube replaced
Ruptured and replaced
Tube replaced
Tube replaced
Measurement not taken
Measurement not taken
Measurement not taken
Measurement not taken
Tube replaced
Tube replaced
Tube replaced
Tube replaced
Tube replaced
Tube replaced
Tube replaced
Tube replaced
Tube not replaced
Tube replaced
Was previously changed
* Tube 37 was replaced. It failed under the hydrostatic test apparently due
to faulty welding. It was replaced again.
-------
S-32
The eighteen (18) tubes are 70 mm (2.76 inches) in outside
diameter and 3.2 mm (0.126 inches) in thickness. The maintenance record
book of September 8, 1976 shows that tube number 10 failed and caused unit
stoppage. Table S-2 shows the results of measurements that showed an
uneven pattern of greater metal wastage in the center tubes. As a result
the other thin tubes numbered 5,6,9,12, and 13 were also replaced.
In application of the ultrasonic measuring technique, it is
recognized that the readings could be in error plus or minus 20 percent.
Accordingly if minimum acceptable thickness was, for example, 2.0 mm,
anything below 2.5 mm measurement should be replaced. The formula is:
X = 2.0 m = 2.0 = 2.5 mm
1.0 - .2 0.8
Fully Water-Cooled Furnace at Zurich-Hagenholz
Figure S-16 is a cross section of Unit Number 3 at the Hagenholz
plant which was installed in 1973.
The wall tubes are 57 mm (2.2 in) in diameter and are U mm (0.16
in) thick. The center-to-center spacing is 75 mm (3 in). In the first
pass, the maximum flue gas velocity is 4.38 m (1M.3 ft)/second. Following
in the second pass, the maximum flue gas velocity increases due to its
smaller cross-sectional area, to 6.66 m (22 ft)/second.
The wall construction is termed "welded fin". The fins connecting
the tubes are extruded with the tube. The procedure was developed by EVT
of Stuttgart. At the factory steel studs are welded to the furnace side of
the tubes to a density of 2000 studs/m2 (186 studs/ft2). The stud
orientation is radially out from the tube center. Therefore, with respect
to the relatively flat wall, the stud angles are different and result in a
better anchoring matrix as shown below:
Note: All dimensions
in millimeters
57dia
8dia
After the studded tubes had been installed at Hagenhholz, plastic
silicon carbide (SiC) was placed over the studs to a thickness of 12-15 mm
(0.5 to 0.6 in). The use of studs covered with SiC is only in the
-------
S-33
TABLE S-2. WALL TUBE THICKNESS MEASUREMENTS OF SCREEN TUBES
AT THE REAR OF THE RADIATION FIRST PASS AT HAMBURG:
STELLINGER-MOOR
Tube (Number)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
(Boiler Number 1)
Metal Thickness (mm)
3.3
3.3
3.3
2.8
2.4
1.8
2.5
2.9
1.8
0.0
2.7
2.2
2.3
2.8
2.7
2.8
2.9
2.9
Action
Thin and replaced
Thin and replaced
Thin and replaced
Thin and replaced
Ruptured and replaced
Thin and replaced
Thin and replaced
-------
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il : !»
SKSfflH!
OinMtaN^SS^fiM^i
11 »
S I i
;:A«ftjjJi!iR»,
!lJili,!l
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FIGURE S-16. FURNACE/BOILER CROSS-SECTIONAL VIEW OF
THE ZURICH: HAGENHOLZ UNIT //3
-------
S-35
combustion chamber and the lower 2/3 of the first pass as depicted in
Figure S-16. Mr. Baltensperger commented that the SiC should extend one or
two meters beyond where flames might be expected.
Figure S-17 is a picture taken of the studded SiC-covered walls
taken from across the active combustion chamber in Unit #3. As can be
seen, slag very seldom adheres to the SiC. Small amounts of slag will
accumulate but will fall off.
Sootblowers are not used in the first and second passes so that
any chance of a sootblower malfunction causing a tube rupture is eliminated.
After 30,000 hours, the combustion chamber wall tubes have
experienced only 0.1-0.2 mm (0.004 to 0.008 in) metal wastage. This is one
of the best wastage experiences in the world.
Two-thirds up the first pass (where the SiC stops), the flue gas
temperature falls to about 800 C (1472 F). Because of the relatively high
thermal conductivity of the SiC coating, absorption from a heat release
rate of 120,000 Kcal/m2-h (19,000 Btu/ft2-h) is feasible based on a heat
input rate of 48.3 Goal/hour (191.2 M Btu/h).
The SiC surface is rarely repaired on the 1000 hour inspections
but is occasionally repaired on the 4000 hour planned inspections. Studs
and SiC are repaired once per year during major overhaul.
Plant staff observed that to reduce wall tube corrosion the
vertical man-hole doors should be flush with the inside surface of the
furnace wall. Eliminating the recessed cavity will reduce gas impingement
and erosion by flyash as shown.
Refractory Furnace Wall at the Hague
In terms of predominant current practice for large furnaces, The
Hague plant built in 1968, is noteworthy in that the furnace sidewalls are
not water-cooled. What water-tube walled surface is used begins above the
furnace and extends from there upward to the top of the radiation chamber
(first boiler pass). The sloping rear roof of the furnace is water-cooled
but the tubes are completely covered by formed refractory block supported
between the tubes. Thus, there is very little cooling of the predominantly
refractory furnace. The furnace sidewall construction consists of one layer
of high-alumina firebrick plus insulation and a steel casing. The full wall
thickness is about 50 cm (20 in). This wall is modified alongside the
drying and main grate where the alumina brick is replaced by silicon
carbide brick to resist abrasion by moving refuse. This refractory wall has
needed little maintenance in nearly ten years' operation. The refractory
stops at about the level of the top of the feed opening. A horizontal
header for the higher wall tubes is located at that level and the wall
tubes extend upward from that level.
At first, in Units 1-3, the wall tubes in the radiation pass were
bare. The tubes in Units 1-3 are 63.5 mm (2.5 in) in diameter, 4 mm (0.160
in) thick, on 85 mm (3.4 in) centers and joined by a welded fin. However,
within the first year (1969), significant wastage of the wall tubes was
observed as well as in the radiant superheater suspended through the top of
the radiation pass. Accordingly, that superheater was shortened by 70 cm
(2.3 ft) and the wall tubes were studded with 10 mm (0.4 in) long studs and
then coated with 12 mm thick (0.5 in) silicon carbide. This coating was
carried up to just above the bottom of the shortened superheater.
-------
S-36
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-------
S-37
Another unique feature of The Hague plant is that it began
operation without any overfire air jets. Because of the early corrosion
problems referred to earlier, sidewall jets were added.
At first there was little slag accumulation on the refractory
sidewalls. However, in 1971 and 1972, after about three or four years'
operation, thick acumulation of slag developed on the sidewalls, especially
where the burning was intensified when the burning refuse dropped from the
drying grate onto the burning grate. Attempts were made to remove this slag
mass by means of water lances but this was deleterious to the refractory
wall. The thermal shock to the hot refractory wall caused it to tilt
inward. Then, continuous air injection was tried along the wall but the
build-up of slag continued. It is believed that this growing problem of
slag build-up was caused by a substantial rise in the heat value of Dutch
community refuse in that period. Relatively high grate burning intensities
were probably contributory to the problem.
The solution to the problem of sidewall slag accumulation at that
time was to reduce the load on each furnace. Instead of carrying the
average daily plant load of about 700 to 750 tonnes per day in two units,
each nominally rated at 360 tonnes/day (MOO tons/day); the third or spare
unit was brought into regular operation so that each unit had to handle
only about 230 to 250 tonnes per day (260 to 275 tons/day). However, it is
well established that, in this technology, normal wear and tear usually
requires a plant to have one spare unit so that each unit in turn can
benefit from a planned regular preventive maintenance program. It appears
that such considerations led, in 1971, to the order for Unit 4 which began
operation early in 1971*. The wisdom of this expansion is attested by the
fact, mentioned earlier, that the refractory furnace walls of Units 1-3
have required essentially no maintenance except slag removal in nearly ten
years' use. Operation of Units 1-3 at reduced rate has eliminated the slag
accumulations.
The annual waste input to the plant reached a peak of 229,000
tonnes in 1976. If Unit 4 had not been available that year, Units 1-3 would
have been overloaded which certainly would have caused much difficulty in
added maintenance costs and reduced availability. Assuming 5-1/2 days per
week operation, the 229,000 tonnes burned in 1976 in 52 weeks in three
units, (one spare), nominally rated at 360 tonnes/day each results in an
estimated operating rate of 800 tonnes/day or 111 percent of rated
capacity. Although no mention was made by plant staff of any recent return
of problems from sidewall slag build-up, its imminence may have encouraged
a decision to plan to install air-cooled Kunstler wall blocks in Unit 2 in
1978.
It is notable that the SiC covering on the studded wall tubes
requires little maintenance. During each year approximately four square
meters of coating is replaced in each boiler.
Figure S-2a shown earlier, shows, schematically, the arrangement
of the air flow through the patented, cast steel, Kunstler blocks which
will soon (in 1978) be added on Unit 2. Kunstler of Zurich has added this
modified air-cooled wall construction to over a dozen European plants since
1972. It is also not being incorporated into some new plants as original
construction. The system does appear to provide relatively cool sidewalls
so that sticky slag particles that may touch it are chilled and solidified
before they have time to fuse to the wall. The installation in Unit 2 at
-------
S-38
The Hague will provide an interesting test of block durability in a large,
heavily-loaded furnace.
Figure S-18 and S-19 show a similar wall cooling system using
perforated refractory blocks by Didi-er-Werke AG, Grunstadt, Germany were
jointly tested by Von Roll and which Von Roll is now applying at other
plants. The installation shown in these figures is at Solingen, West
Germany. Less air is required for cooling because the blocks are
refractory. Also in case of failure of the cooling air supply the
refractory can with stand some overheating.
Refractory Furnace Wall at Dieppe and Deauville
There are two major reasons why the relatively new Dieppe (1971) and
Deauville (1976) furnaces are not water-tube walled:
(1) The burning of only partially dried sewage sludge has a cooling
effect in the furnace; hence, extensive wall cooling is not
needed.
(2) The steam generated for heating the thin-film sludge dryers needs
to be only moderate pressure; hence, a much simpler refractory
wall furnace and cheaper firetube waste heat boiler can be used.
Accordingly, the only furnace cooling at Dieppe is a diagonal
furnace baffle. This baffle is formed of spaced, sloping tubes about 120 mm
(U.7 in) apart, which supports bricks shaped to fit the tubes. An estimated
100-150 C (180-270 F) gas temperature drop occurs as the gases flow upward
along the underside of the sloping baffle then pass through the spaced
tubes above the baffle and turn toward the vertical firetube boiler inlet.
It is estimated that about one sixth of the total heat is absorbed by the
baffle.
As the gases turn downward around the top of the baffle, they
decelerate causing the larger flyash particles to fall out and deposit on
the sloping baffle. The buildup of such deposits causes the top-side
cooling surface to become ineffective. Also, removal of the accumulated
deposit has been difficult. The top and bottom headers for the tubes in the
furnace baffle are studded with 40 mm (1.5 in) studs and covered with 80 mm
(3.1 in) of Plibrico castable refractory.
At Deauville, designed about 5 years later, there is no
water-cooled baffle. The furnace volume 80 us? (2823 ft^)is also much less
than at Dieppe. The furnace gases at Deauville pass directly to the
vertical firetube boiler.
The main furnace wall at both plants is 500 mm (1.6 ft) thick and
is enclosed in a 3 mm thick outer steel casing to minimize infiltration of
air. The fireside portion of the wall is built of 65 percent alumina brick.
No bricks have had to be replaced except one row of brick in the nose of
the front arch after 5 year's operation. Occasionally, broken bricks are
patched with Plibrico plastic refractory rammed into place. Explosions of
some types of refuse cause some refractory damage and push water out of the
clinker quench channel under the furnace. Occasionally, some of the formed
bricks in the water-cooled sloping baffle need to be replaced.
The use of refractory instead of water-tube walls entails some
loss of thermal efficiency but this loss is not important at either plant
so long as there is ample steam generated to dry the sludge.
-------
S-39
FIGURE S-18. PERFORATED AIR-COOLED REFRACTORY WALL BLOCKS
BY DIDIER AS INSTALLED BY VON ROLL AT THE
SOLINGEN PLANT, WEST GERMANY (COURTESY
VON ROLL)
FIGURE S-19. CONSTRUCTION PHOTOGRAPH
SHOWING AIR SUPPLY CHAMBERS
FOR THE REFRACTORY WALL
BLOCKS SHOWN IN FIGURE
S-18.
-------
S-40
Each furnace has a 6 million calorie/hr oil burner, but they are
never used.
Partially Cooled Refractory Wall at Gothenburg
Most of the main furnace at the Gothenburg plant (1970) is not
water-tube walled but is refractory, 0.58 m (1.9 ft) thick. The water tubes
of the first pass begins near the top of the furnace at about the level of
the top of the refuse feed entrance. The carbon steel tubes are tangent
welded, 76 mm (3 in) in diameter and U mm (0.16 in) thick.
The front and rear walls at the furnace are formed of spaced
water tubes covered with refractory. This minimal cooling of the furnace
coupled with a period of unusually high heat value of the refuse could have
combined to aggravate slagging and overheating problems that have occurred.
Although these boilers generate saturated steam at only 22 bar
(1M9 psia) (1,017 k Pa) and 217 C (123 F), which is well below the usual
tube-corrosion threshold, the lower one third of the water-tube walled
first pass was equipped with welded studs holding in place a 50 mm (2 in)
thick layer of high alumina plastic refractory. This was a successful
effort to protect those tubes from chloride attack. However, in July, 1975,
immediately above that coating, a tube began to leak in Boiler 2 after
20,830 hours of operation. Three weeks later, a similar leak appeared in
Boiler 1. Up to that time, no routine checks had been made of tube
thickness. After that experience, checks have been made twice a year at
specific locations throughout the boiler. The wastage rates in the first
and second passes now range between 0.1 and 0.2 mm per year (0.004 to 0.008
in).
In retrospect, it now appears that the tube wastage was caused by
the following:
• High refuse input rates
• High heat value of refuse
• Uneven distribution of air and combustion
• Excessive soot blowing.
Originally, each boiler was equipped with 21 soot blowers. There
were two sets in the first pass. Although the plant is for district heating
only (hence, does not need high-temperature steam), a small superheater was
placed in the third pass to generate superheated steam up to 300 C (572 F)
for soot blowing only. When the soot blowers were not in use, the
superheated steam was condensed in a heat exchanger in the boiler drum. The
soot blowers thus were assured of dry steam so as to avoid any erosive
impact on the boiler tubes by water droplets. However, they probably
cleaned the tubes too well and too often with the result that the bare
tubes were exposed to corrosion and probably erosion. In 1971*, it had been
first noted that the first pass blowers were cleaning exceptionally well.
This increased the possibility for corrosion. Accordingly, 11 of the 21
blowers have now been removed and the 10 remaining are used less frequently.
Another change was to add more refractory coating above that
originally installed in the first pass. That was done in three successive
steps until the coating extended upward to cover the lower two thirds of
the first pass water-tube wall.
Figure S-20 shows another change made to reduce wall tube wastage
Eighteen sidewall air jets on each side just below the wall tube header
-------
S-41
O
CM
I
C/3
O
-------
S-42
were blocked and replaced by downward angled jets in front and back. Also,
a rear nose formed of refractory-covered tubes was added to direct the
flame flow away from the rear wall. The slope of those tubes was later
modified to discourage buildup of loose ash deposits. Also, later the
location of the rear wall jets was moved farther forward toward the top of
the nose. The first rear wall nose was installed in Boiler 2 in December,
1975. The second was in Boiler 1 in March, 1976. The third was in November,
1976.
These measures plus the apparent reduction in refuse heat value
have reduced the tube corrosion rate to a point where plant staff estimates
that 30,000 hours of operation can be expected before some tube
replacements may be needed.
The cost of the boiler-furnace repairs and modifications in 1975
was about 5 million S.Kr. ($1,140,000). Ordinarily the staff expects
overall repairs to cost 10 skr/tonne ($2.07/ton).
Some wastage has occurred in the roof tubes of both the first and
second pass. This is being countered by a sprayed-on coating of silicon
carbide about 8 mm (0.031 in) thick. The same coating has been sprayed
opposite the soot blowers in the second pass. The durability of this
coating appears good after 1 year but has not yet been fully determined.
Ten sections of alloy-clad steel tubes are being tried in the
upper middle position of the wall of the second pass. These "sandwich"
tubes, made by Sandviken, have a wall thickness of 7.1 mm (0.28 in) coated
with an extruded stainless steel layer (0.063 in) thick. Although these
tubes cost 10 times as much as carbon steel tubes, experience with an
entire pass formed of these tubes at the Hogdalen plant built by Vereinigte
Kesselwerke (VKW) south of Stockholm indicates that for conditions at that
plant they are worth it in minimizing tube wastage.
Refractory Furnace at Uppsala
As with many small refuse-fired furnaces, the four furnaces at
Uppsala are not water cooled. Their completely refractory construction has
been satisfactory except for a major error in installation (1961) of
too-widely spaced support anchors in Furnace No. 4. This caused much
breakage and some occasional collapse of firebrick but has now been
corrected.
Only Furnace No. 4 in this plant was studied as it is the newest
one (1970). The width of the furnace is 2 m (6.5 ft) and the grate length
is 8.1 m (16.6 ft). At the far end of the furnace is an offset opening
where the hot gases leave the furnace at about 1,000 C (1,832 F) and make a
tangential entry beyond into the cyclonic, refractory aftercombustion
chamber.
Immediately above the grate, on both sides of the furnace are
cast iron plates cooled only by radiation and convection to the
surroundings. These plates are used to resist erosion caused by the motion
of the burning refuse against the wall. The cast iron surface extends
upward about 500 mm (20 in) above the grate. For community refuse, it has
been Brunn and Sorensen's experience that air cooling or water cooling of
these plates are unnecessary. For furnaces burning highly combustible
industrial refuse, water cooling of the plates is used.
-------
S-43
Immediately above the cast iron wear plates is a narrow band of
silicon carbide brick. These also resist erosion, will stand much higher
temperature than cast iron, and have the desirable characteristic of
resisting the adherence of molten slag.
The remainder of the furnace wall is built of Hoganas firebrick,
tradenamed "Krona", which is rated to withstand 1,600 C (2,912 F).
Originally, the first three furnaces were lined with "Chamotte" brick which
is naturally occurring clay which becomes a high-grade refractory when
fired. However, it is expensive: 14 S.Kr./brick ($2.80 § 5 Skr/$). All four
furnaces are now built of Krona, which costs about 4 Skr/brick ($0.80). The
wall thickness for Furnaces 1 through 3 is 1-1/2 brick. Furnace No. 4 is
only one brick thick. This causes a higher rate of heat loss which helps
prolong the life of the refractory. Some slag adheres to the wall but does
not accumulate to great thickness and is considered a protection for the
refractory.
At some points, the slag deposit appeared to have been hot enough
to flow down the wall but no erosion nor massive slag buildup was evident.
There is no slag accumulation in the aftercombustion chamber
following Furnace No. 4.
Refractory Furnace at Horsens
The original plant at Horsens was designed as a hot flue-gas
generator for sewage sludge drying in a rotary kiln; hence, the furnace
wall is refractory without any heat recovery at the walls. The first meter
(3.28 ft) of wall above the grate is formed of korund (45 percent silicon
carbide) brick to discourage slag adhesion. Above that, the wall was
originally firebrick but now castable or rammed refractory is used.
Originally, the furnace roof was a brick arch resting on steel
supports, but because of overheating of the steel, it has been replaced by
a poured flat roof of castable refractory supported externally. The new
roof was designed by Hoganas using Hoganas "ES" (extra strength)
refractory. It is stated to withstand 1,300 C (2,372 F). Its composition is
Si02—36 percent; A^O^—42 percent; and Fe203—6.1 percent.
Because the actual refuse fired has a heat value considerably
above the design value of 2,000 Kcal/kg, the furnace temperature in early
operation reached 1,400 C (2,552 F) instead of the design value of 950 C
(1,742 F). Large amounts of plastics were observed being mechanically cut
over the pit before placed into the feed chute. This overheated and warped
the fire brick furnace wall which has now been replaced by castable
refractory. In addition, furnace operation is now slowed to avoid
overheating when much "hot" industrial waste must be burned.
Secondary air can be injected through ports in the roof, but
these jets are seldom used except just enough to keep the air piping cool.
The refractory after-combustion chamber is 4.25 m (13-9 ft)
inside diameter, 3 m (9.8 ft) high on top of a 2 m (6.6 ft) conical
refractory hopper. Its intent is to provide gas mixing and burning time and
to remove coarse fly ash from the hot gas stream. The C02 content of the
gases leaving the chamber is in the range of 9 percent.
Originally the furnace exhaust wass cooled by a water spray. An
early problem with that arrangement was that some water dripped into the
ash hopper causing the ash to harden and stall the discharge screw.
-------
S-44
In 1977 the spray cooling tower was replaced by a hot water
boiler. Replacement of the spray chamber by the boiler eliminated this
problem.
Refractory Furnace for Hot Water Boilers
at Copenhagen West and at Amager
Volund furnace walls are refractory lined (and not lined with
water tube walls) inside a steel framework.
The six furnaces for both Amager and West (three each) were
designed and built at about the same time (1970) to supply hot water
boilers.
Volund originally chose Hoganas, a high-quality and expensive
refractory, for its furnace wall lining. The bricks themselves were not a
problem. The difficulty, however, was that there were not enough anchors
between the iron structural framework and the bricks. In addition, the few
original anchors were not properly welded and broke during thermal
expansion. Also, ash was accumulating or "slagging" on the walls.
As a result of the several problems, the furnace walls were
rebuilt. Fortunately the warranty period was still in effect. More anchors
were added. The anchor welding technique was changed.
To cure the ash slagging problem, silicon carbide was added to
the walls above the grate 0.5 to 0.7 m (1.5 to 2 feet). However, where the
flame is hottest and the 02 levels the greatest, the SiC is avoided as it
may oxidize. Hence, the lowest wall areas and some of the middle side wall
retain the Hoganas chamotte bricks.
Volund officials believe that, with proper anchoring, a
refractory wall furnace is less expensive and more reliable than a water
tube wall furnace. Having learned from the Amager experience, they now
specify a wall shown below:
Plastic Silicon Carbide,
beginning .5 to .7m
above grate
Flame
Thick Chamotte Bricks
Porous Chamotte Bricks
•Moler Blocks
Steel Plate
Furnace Room
225 60 150 mm
-------
S-45
The Moler blocks near the outside wall are unique to Denmark. The
clay is literally quarried or carved out off the deposit in the final
shape. (There is no normal mixing and blending of clays.) The blocks are
simply fired. The brick dimensions of 23.4 x 11.3 x 6.2 cm (9.2 x 4.5 x 2.5
inches) weigh 1.2 kg (2.6 pounds). This is slightly heavier than many
insulating fire bricks but much stronger.
The furnace roof is always arched if the span is less than 3 m
(10 feet). However, for wider roof sections, a steel structure is built
with many hangers. Specially shaped chamotte bricks are then suspended from
the anchors. Then granulated Moler particles are spread on top of the steel
and bricks. Finally, rock wool is added as the final insulation.
Rotary Kiln. Most Volund plants provide for only partial burning
in the furnace. Mr. E. Blach, formerly Chief Engineer of Volund, described
the system as follows:
"Pre-drying, ignition, and the first part of the combustion takes
place on the grate system ... but then the refuse slides into the
rotary kiln, where the final combustion and burning out takes place.
While in operation the rotary kiln turns slowly and thus creates
a perfect overturning of the burning refuse. The movement makes the
refuse travel a very long way and thereby stay for a long time in the
kiln. The system operates with the so-called divided flue
gas/combustion air circulation, e.g. the primary combustion air is
divided into two after having passed through the layer of refuse on the
grates, one part passing through the rotary kiln and one part passing
over the layer of refuse on the grates up to the top of the furnace,
from where it is brought back to the after burning chamber through the
previously mentioned connecting flue gas passage coming from the rotary
kiln.
Besides primary air, secondary air is added over the grate
sections as well as the rotary kiln in order to ensure for certain that
the flue gases are fully burned. By adding a surplus of primary and/or
secondary air a cooling of the combustion can be achieved, but this
cooling function can be achieved better and more effectively by using a
flue gas recirculation system, e.g., cooled flue gas is brought back to
the combustion zone, over the grates, and at the rotary kiln. While in
operation, this cooling function is done automatically so that the
temperature is kept at 900° - 1,000° C.
The rotary kiln is built up of an outer heavy steel plate, which
is lined with wear resistant fire-proof bricks on the inside. There is
an insulating layer between the bricks and the steel plate. The ends of
the kiln are furnished with special sliding seals and transition
sections. The whole construction rests on two sets of running and
guiding wheels. These wheels act as friction pinions, activated by
hydraulic motors.
The refractory bricks are anchored onto the steel shell. Moler
refractory was originally specified to be placed next to the steel shell.
Then next to the Moler refractory, Chamotte bricks of varying alumina and
silica content are used to line the inside of the kiln. The brick
composition is 85 percent silicon carbide at the inlet.
-------
S-46
To some extent, because of very high temperatures, the kiln is
self-cleaning. Slag does not normally accumulate on refractory walls.
However, at some other Volund plants slag "rings" occasionally form within
the kiln. Interestingly, this slag ring can gradually move down the length
of the kiln. It eventually disappears.
The grate/rotary kiln design is used for capacities from 5 t/h to
about 20 t/h, but can be built also in larger plants.
The carbon steel shell has an inside diameter of M m (13.1 feet).
Each kiln is 8 m (26 feet) long.
The kiln is sloped downward at a 3 degree angle and revolves
upwards of 12 revolutions per hour (rph). Normally it revolves at 6 to 8
rph. If the furnace operator is told by the crane operator that the refuse
is wet or if he sees a disturbance in the kiln, he can reduce the kiln
speed.
The original configuration had two support rings, two support
rollers, one thrust roller, and two drive support rollers all made from
high tensile-strength steel castings.
Later, Volund decided that the large spacing between rollers
caused excessive compressive forces and alternatively tensile forces to
open spaces in the lining depending on where the brick section was on its
rotation.
Everytime the furnace is stopped and cooled enough, the kiln is
inspected. Occasionally several rings of brick are replaced. Finally in
1977, after 7 year's (U2,000 hours) operation, the kiln was completely
rebuilt at a cost of 150,000 DKr.
During this major change, the brick used was respecified. Instead
of the very porous Moler brick, which was crushed under compressive
pressures once per revolution, a harder inner brick was used. Some
insulation quality was sacrificed but the temperature just outside the kiln
rose only 2 C (3.6 F) from before.
Heat Release Rates
Table S-3 compares the boiler-furnace dimensions and heat-release
rates for the 16 plants visited. There are many factors in the individual
plant designs which make them exceptional in some way and, therefore, not
strictly comparable. However, broadly, the range of volume heat release
rates implied in the original designs as shown in this table is instructive.
The highest rates attained were at the Hamburg:Stellinger-Moor,
plant which has had to resort to use of water sprays to temper very
combustible industrial refuse and also to water sprays in the hot gases to
protect the precipitators. This experience does not dictate that lower heat
release should be used but it does indicate that ample gas cooling should
be provided, not only in the furnace but in subsequent boiler passes.
Nearly as high release rates are reached at Wuppertal and
Zurich-Hagenholz and both incorporate considerable water-tube wall cooling
surface following the furnace.
All of these plants that have attempted to operate with flame
extending to regions of bare wall tubes have, sooner or later, had to stud
the tubes annd coat them with plastic refractory. This is distinctly
different from coal-burning practice where it is customary to operate with
bare tubes throughout the furnace. The important difference is that the
-------
S-47
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S-48
chlorides from refuse burning will attack even relatively cool water tubes
if the ash deposit or the tubes is heated by flame impingement. The
mechanism involved in this attack is discussed under corrosion. Silicon
carbide or alumina coating on studded wall tubes is demonstrating reliable
protection from such attack with little maintenance required. The coating
does impair heat transfer but additional surface can compensate for that
loss.
Many of the smaller plants are demonstrating reliable, low-maintenance
operation of completely refractory-walled furnaces. Especially where only
low-pressure steam or hot water is all that is needed, the complication of
high-pressure, water-tube boiler furnaces are unnecessary. Inherently these
plants will tend to recover energy less efficiently than a completely
water-cooled boiler furnace connected to a high-pressure steam-driven
turbo-generator, but with their simplicity goes also lower first and
operating cost. Neverless, in the long run, it appears that rising energy
costs will favor the more efficient, more costly techniques.
The successful utilization of very high heat release rates is
intimately related to the effective use of secondary air jets to assure
rapid combustion within the furnace. This is discussed in a later section.
-------
S-49
REFERENCES FOR
DATA IN FIGURE S-1
Andritsky, M., "Mullkraft werk Muenchen", Brennstoff-Warme-Kraft, May 19&2,
213-237.
Dirks, E., "Ten Years Incineration Plant Frankfurt", Proceedings,
Conversion of Refuse to Energy (CRE) Montreaux, Switzerland, Nov. 1975,
580-588.
Feindler, Klaus S., "Refuse Power Plant Technology - State of the Art
Review", Unpublished paper presented to the Energy Bureau, Inc., New
York, Dec. 16, 1976.
Tanner, Richard, "The Development of the Von Roll Refuse Incineration
System", Sanderdruck aus Schweizerischen Bauzeitung, 83 Jahrgang, Heft
16. (1965)
Since this report was drafted the following 2 additional papers have
been published which add specific information expecially pertinent to this
chapter on Furnace Wall:
Nowak, Franz, "Corrosion on Refuse Incineration Boilers, Preventive
Measures", Ash Deposits and Corrosion Due to Impurities in Combustion
Gases, R. W. Bryers, Editor, Hemisphere Publishing Co., Washington,
427-^36. (Proceedings International Conference on Ash Deposits and
Corrosion from Impurities in Combustion Gases, New England College,
Henniker, N.H., June 1977.
Feindler, Klaus S., and Thoemen, K.H., "308 Billion Ton-Hours of Refuse
Power Experience", Energy Conservation Through Waste Utilization,
Proceedings 1978 National Waste Processing Conference, Chicago, May 1978,
117-156, published by ASME, New York, 1978.
-------
T-l
SECONDARY (OVERFIRE) AIR
General Comments
All grate-burning of fossil fuels requires overfire air jets above
the fuel bed for smokeless, complete combustion.
Mass burning of refuse has very similar requirements. In addition,
at very high refuse burning rates in large furnaces, the turbulent mixing
provided by jets is of critical importance in assuring complete combustion
of the furnace gases before they reach the superheater. If this combustion
is not completed well ahead of the superheater, the ash deposits on the
tubes car. become overheated by the hot, burning gases and tube corrosion
can occur as discussed under Corrosion.
As with fossil-fuel practice the application of overfire air jets
for mass burning of refuse is still an art and from plant to plant the
details of application vary considerably. Some vendors are much more
committed to the application of highly intense overfire turbulence than are
others.
Principles of Overfire Jets
To abate smoke formation the unburned volatile gases rising from
the fuel bed must be mixed rapidly with ample oxygen. If this mixing does
not occur promptly the rich gases are very likely to decompose thermally
because of the high temperature, thereby releasing fine carbon particles
that form smoke and soot.
Because of the principle of prompt and early mixing just described
the jets should be relatively near to the fuel bed. But because of the
construction of some furnaces this is very difficult to arrange from either
the front or rear walls. Accordingly some furnaces are equipped vrith
sidewalls jets so that the jets can be located low in the furnace on a line
parallel to the sloping fuel bed. If such sidewall jets are suitably spaced
and staggered so that the opposing jets intermingles, mixing can be very
effective. However, if the jets are directly opposite each other and a^e
too closely spaced, they have a tendency to drive the flame toward the
center of the furnace where oxygen may be deficient. Such an arrangement,
then, can cause a longer flame to rise out .of the furnace center. A few
plants then use tertiary jets located higher up in the furnace wall to make
sure t^at rising tongues of flaming unburned gases are quickly mixed with
ample oxygen.
Because of the inherent limitations of sidewall jets just
described, many designers prefer front-wall and rear-wall or similarly
situated jets, because the main gas flow can often be mixed by such jets
without displacing the flame toward the center of the furnace.
In all cases, whether sidewall, front-wall or rear-wall care must
be taken to avoid too intense burning in the immediate area around the jet
opening. As the jet of air emerges into the chamber at high velocity, 50 to
100 m/s (15^ to 328 f/s), it induces rapid inward flow of furnace gas^s
along the wall toward the jet. If this rapid influx occurs in a region of
active burning the turbulent flow induced by the jet can cause intense
local burning and very high temperatures that can deteriorate either
refractory or water-tube walls and can aggravate slagging. If this
-------
T-2
phenomenon is observed, the solution is to reduce the secondary air jet
pressure on the few jets involved to a level where the induction effect is
minimal.
If such reduced jet velocity then impairs the desired mixing
effect in the main part of the furnace, tertiary jets should be considered.
Usually the quantity of overfire air supplied ranges from 10 to 25
percent of the total combustion air, primary plus secondary. Since most
furnaces already have ample excess air, the main objective of overfire air
jets is to provide good mixing not to add air. Thus additional air is
usually less important thai turbulence for intense mixing. Thus small jets
introducing very high velocity air are usually preferable because this
minimizes the amount of air added.
Table T-l shows the range of jet conditions employed in the plants
visited. The following discussion points out the features of each
installation and the drastic changes that have been made at a few plants to
improve jet performance. The art is still evolving.
Werdenberg-Leichtenstein
Figure T-l shows diagramatically that at Werdenberg, there are two
sets of overfire jets in each sidewall. The upper row of six jets on each
side consists of 60 mm (2.36 in) diameter jets in a horizontal row about 5
n (16.4 ft) above the grate to provide air and turbulent mixing where the
burning gases pass upward from the top of the furnace combustion chamber to
the first open boiler pass. The lower row of 12 jets on each sidewall are
1.8 m (5.9 ft) above the grate and along the inclined line parallel to the
grate. The air flow to the jets is modulated automatically according to
furnace outlet temperature by a motor operated valve. A high temperature
call? for more air to dilute and thus cool the gases.
The overfi**e air supply is taken from the bunker area. Blower
capacity is 30,500 m^/hr (17,934 cfra) at 20 C (68 F), at a static pressure
of 350 mm (13.8 in), total pressure of 385 mm (15 in).
The overfire air supply is taken from the bunker area, Blower
capacity is 30,500 m'/hr (17,934 cfm) at 20 C (68 F), at a static pressure
of 3r>0 mn (13-8 in), total pressure of 385 mm (15 in).
The manufacturer states that they prefer front and top (or rear)
wall jets over this sidewall jet arrangement and their future designs will
not use sidewall jets. The advantages seen from frontwall jets are:
• Better mixing
• Better air distribution in the furnace
t Shorter flame length
• Less carbon monoxide.
Tertiary (Sidewall Cooling) Air Supply
In addition to the overfire air, tertiary air is supplied near the
grate through Kunstler cast iron blocks in both sidewalls as shown
schematically in Figure T-2in the section on Furnace Wall. This air serves
both to cool the cast iron blocks and to provide upward flowing layer of
combustion air along the sidewalls for any rich gases that may be burning
there. It does not provide turbulent mixing. The air comes not fron the
bunker but from the furnace room. The forced air is supplied to the back or
-------
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"outside" of the blocks and flows in a generally downward direction behind
3 steel baffle and then upward until it finds its way into the furnace
through the gaps around the periphery of each block. A constant flow of
tertiary air is supplied to the blocks by a separately unmodulated blower
rated at 12,900 mVhr (7600 cfm) at 20 C at a static pressure of 180 mm
(7.1 in), total pressure of 190 mm (7.5 in). The 85 cast iron wall blocks
on each sidewall are made of. 27-30 percent chromium, 0.53 percent nickel,
with small amounts of titanium and molybdenum. Figure T-3 illustrates the
blocks being installed.
An alarm is sounded in the control room if the temperature of a
thermocouple on one of the blocks exceeds a set value. This temperature and
that of the steel structure nearby to the plate are both recorded in the
control room. At this small plant, no wall blocks have been replaced during
the 3 years of operation. Some abrasion of the blocks has been noted where
the burning refuse slides along the blocks. So far, the eroded area appears-
to have lost 1 to 3 nun of iron.
It can be seen that, the total capacity of secondary plus tertiary
air is ^3,400 m^/hr, substantially more than the 32,000 m^/hr available as
estimated to regulate the overfire air supply to maintain a furnace exit
CO? of about 9 or 10 percent. This is in the range of 120 percent excess
air. From a heat recovery standpoint, it would be desirable to have lower
excess air, but this manufacturer's experience apparently is that the
higher temperatures associated with lower excess air cause metal wastage
problems.
3eden-3rugg
At Baden-Brugg the secondary air is taken from the pit area.
Originally the air jets were in both sidewalls, 3 horizontal groups of 6
jets each located approximately one meter (3.28 ft) above the sloping
grate. However, as discussed earlier in the section on Furnace Wall, the
manufacturer concluded that a principal cause of early failure of 9 tubes
in the first open boiler pass was the corrosive action of very hot reducing
gases adjacent to those tubes. Also, the sidewall jets appeared to
encourage accumulation of slag on the walls. In an effort to achieve better
mixing of air and gases the secondary air system was converted in 197^ to
front-wall and rear-wall jets, all 64 mm (2.5 in) dia jets. There are 15
jets in the front refractory arch which enter the furnace at an angle of
about ^5 degrees directly above the first grate section. Fi gure T- H shows
the 15 jets on the back wall. The blower supplying these rear jets has a
capacity of 9000 Nim3/h (5292 cfm) at a pressure of JJOO mm (15.7 in) water.
The jets in the front of the furnace are supplied by a blower having a
capacity of 5000 :,'m3/h (3528 cfm) at 500 mm (19.7 in) water. The flow rate
to each set of jets can be modulated from the control room by means of
butterfly valves. The revised jet arrangement has been so satisfactory that
the manufacturer expects to utilize or.ly front and rear wall secondary air
jets in futurp designs.
Tertiary Air
Both furnaces are in process of being modified to 'incorporate
side-wall air cooling in the lower portion of the furnace similar to that
-------
T-7
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T-9
just described at Werdenberg. Figure T-5shows the planned arrangement of
8.5 m2 (91 ft2) of air-cooled cast iron blocks to be installed on both
sidewalls above the grate. The total air supplied to the blocks will be
6500 Nm^/h (3822 cfm) at a pressure of 190 mm (7.5 in) water.
Duesseldorf
This plant provides an interesting view of the evolution in the
application of overfire air to maintain complete combustion. Apparently the
experience with the first small pilot furnace from 1961 to 1965 led the
designers of Boilers No. 1-4 to specify only a nominal -secondary air flow
per boiler of 1,000 Nm3/hr (2,354 scfm) at a moderate pressure of 280 ram
(11 in) water. This air was supplied to a total of 44 nozzles in each
boiler distributed as follows:
• 18 pointing nearly downward in the water-cooled front roof
• 20 pointing at an angle down and forward in the water-cooled
rear roof
• Six in each refractory sidewall.
As discussed under Furnace Wall, in 196? an inspection of the
water-tube walls in the first open boiler pass immediately above the
furnace revealed tube wastage in the front wall which appeared to be caused
by the flow against these tubes of high-temperature flame having low oxygen
content. To obtain a higher oxygen content at that point, the number of
secondary air nozzles was increased. Also, the secondary air pressure was
increased from 280 nm (11 in) water to 500 mm (2?.6 in) water and the
available air volume was increased from 4,000 Ita^/hr (2,354 scfm) to 10,172
Nm3/hr (5,988 scfm).
In addition, in 1976, more secondary air was introduced in Boilers
No. 1-4 through the air cooled refractory arch or guiding wall which has
been described earlier. The air cooling system for this silicon carbide
arch has now been evolved to contain 62 air holes in two rows of 31 each.
Sixteen of the holes are 30 mm (1.2 in) diameter and 46 of them are 60 mm
(2.4 in) diameter. The secondary air flowing into the furnace through this
arch cooling system becomes heated to about 200 C (392 F).
Boiler No. 5 has a larger secondary air supply: 15,000 Nm^/hr
(8,828 cfm); and a considerably higher air pressure: 800 mm (31.5 ir.)
water. In addition to nozzles in the front and rear roof similar to Boilers
No. 1-4, there are three rows of six sidewall nozzles each, the lowest row
about 1.5 m (4.9 ft) above the parallel to the sloping grate line.
These overfire air systems have operated satisfactorily except
that at first there was insufficient air supply. In the air piping systems,
the individual nozzles have been connected to the air manifolds by flexible
steel hoses. Because of overheating some of these connections, they are
being converted to stainless steel hoses.
To control furnace temperature at the front where combustion is
most intense, some of the secondary air jets were converted to inject
>ecirculated flue gas in Boiler No. 5. However, that causes ash deposits in
the piping and requires additional maintenance; hence, will not be repeated
in Unit No. 6 which has been designed but not yet built.
-------
T-10
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Wuppertal
For the secondary air jets in the 4 furnaces at Wuppertal, one
radial blower for each furnace takes air from near the top of the boiler
room at a rate of 5.5 m^/sec (20,000 Nm3/hr) (11,650 scfm). The available
air pressure is 800 mm water static (31 in). This air is supplied to a
total of 60 overfire air jets which are 50 mm in diameter (2 in). There are
two rows of jets close together in the front wall," and two more rows in the
forward portion of the slanting rear wall. All of these jets are directed
downward at an angle. The front wall jets are just below the nose of the
front wall similar to ones in Figure S-5 under Furnace Wall so that their
downward direction provides somewhat opposed mixing to the burning gases
rising upward out of the furnace. The rear wall jets are just below the
nose of the rear wall and are directed slightly downward into the initial
burning zone of the furnace.
Actual air flow ranges from 12,000 to 14,000 Nmm3/hr (7000 to 8200
scfm). Normally the dampers controlling secondary air are not changed. The
plant manager explained that certain other plants also had tertiary air
jets positioned half way up in the radiation chamber to try to combat tube
corrosion near the top of that chamber but that at this plant, because of
the relatively modest steam temperature, 278 C saturated (442 F) at 27 bar
(392 psia) and 350 C (662 F) superheated, tertiary air was not believed to
be necessary.
Krefeld
The jet arrangement at the smaller Krefeld plant is almost
identical to that at Wuppertal. One Buttner-Schilde-Haas radial blower for
each furnace supplies air at a rate of 3.8 m3/sec (13,700 Nm3/hr) (7,980
scfm). The available air pressure is 970 mm water static (38 in). This air
is supplied to a total of 40 overfire air jets which are 70 mm (2.75 in)
diameter in the front wall and 50 mm in diameter (2 in) in the upper rear
wall. All of the jets are directed at an angle. The front wall jets are in
the nose of the front wall so that their downward direction provides
somewhat opposed mixing to the burning gases rising upward out of the
furnace. The rear wall jets are just below the nose of the rear wall and
are directed slightly downward into the initial burning zone of the furnace.
Paris: Issy le Moulineaux
At Issy, the secondary air is supplied by 2 fans, one, having an
output of 28,000 Nm3/hr (16,500 ft 3/min), delivers air to two rows of rear
wall jets. Each row has 16 nozzles. Another fan delivers up to 1)4,000
Nm3/hr (26,000 ft 3/min) to a single row of four (4) nozzles located 1 to 2
m (3 to 6 feet) above the front wall nose. These 2 secondary air systems
together provide 20 to 25 percent of the total air consumed.
The available jet air pressures for the front and rear wall jets
are different. The front wall pressure varies from an estimated 200 to 300
mm (8 to 12 in). However, the rear wall pressure varies from an estimated
300 to 400 nm (12 to 16 in).
-------
T-12
In the past, there has been some wastage of the nozzles. To
minimize such wastage air is flowing through the nozzles at all times. But
even with the wastage it has never been necessary to replace any nozzles.
Hamburg: Stellinger-Koor
An unusual feature of the secondary air system at Stellinger-Koor
is that secondary air is taken from the primary air system. Most future
designs will specify separate systems for primary and secondary air. The
secondary air blower capacity is 17,500 Nm^/hour (10,290 scfm) at 640 mm Ws
(25.2 in water) at 30 C (86 F).
There are 16 nozzles in one row above the front wall arch and
another 16 nozzles in the rear wall. A damper is used to control the air
volune. In Martin's designs in Japan, there are often three rows for
secondary air or a completely different tertiary air system due to the high
refuse moisture content. Occasionally some of the nozzles need repair due
to high temperature scaling of the alloy steel.
One principle in Martin's design to control corrosion is to
complete combustion by means of very high secondary air turbulence. In many
other plants combustion is more languid. Figure T-7is a photograph of an
anonymous furnace that illustrates the rather calm combustion environment
observed in so many European and American incinerators.
The shape of the flickering flame and details in the opposite wall
are apparert. Such conditions may, at times of high burning rate cause
delayed combustion, long flames and resulting boiler tube corrosion.
Figure T-8, taken, at Stel 1 inger-Moor however, is entirely
different. The three Martin plants visited (Parisrlssy, Hamburg;
Stellinr;er-Moor and Zurich: Hagenholz) all had furnaces of glowing red
particles bouncing through the gases and an atmosphere where it was
difficult to see the opposite wall.
The available air volumes and pressures at Stellinger-Moor are:
Static Quoted Actual Actual
Maximum Air Volume Pressure Pressure Apr 2, 1977 Nov 4, 1976
(Mm3/Hour Scfm (mm.WS) in.WS (mm.WS) in.WS (mrn.WS) la.WS (rnm.WS) In.WS
Primary Air 87,000 51,160 530 21 - - - - -
Secondary Air, Front 8,750 5,145 640 25 550 22 400 16 400 16
Secondary, Rear 8,750 5,145 640 25 200 8 520 21 500 20
Usually the pressure at Stellinger-Moor is higher in the front
wall nozzles if the heating value is high. The higher jet momentum helps to
push the intense flame further down along the grate to spread out the
burning over a greater area.
In further designs for Germany and Japan that are concerned with
:JOX, Martin expects it will have to increase the primary air and lower the
secondary air volume.
-------
T-13
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T-15
Zurich; Hagenholz
This plant is unusual in that odorus ventilation air from the
adjacent rendering plant is the exclusive source of secondary air.
Of the total combustion air, roughly 80 percent is primary air and
24) percent is secondary air. There are a total of UH air jets equally
divided between front and rear walls.
There is no secondary air preheating and the rendering air
temperatures average around 20 C (68 F). The maximum air volume is 15,000
Nm^/hour (9^00 scfm). At 730 mm Ws (12 in) while the back wall air pressure
is 5*10 mm Ws (21 in). These relatively high secondary air pressures create
high turbulence within the furnace.
Previously Figure T-7showed an anonymous furnace where secondary
air pressure is very low.
Figure T-9 however, shows a highly turbulent condition with no
discernable flame shape. This turbulence prevents delayed combustion which
according to various corrosion theories, is a possible cause of boiler tube
corrosion in RFSG.
The unusual fact is that Zurich: Hagenholz, Martin No. 3,
superheaters have experienced only 0.3 mm (0..012 in) metal wastage in
30,000 operating hours. This amazing lack of corrosion exists despite the
732 C (1350 F) flue gas temperature entering the superheater and the 1*27 C
(800 F) steam temperature leaving the superheater. The water tube walls
have a most acceptable 0.1 mm (0.00*1 in) metal wastage for the same time
period. This high turbulence along with many other factors share the credit
for very low corrosion rate.
Martin and Hagenholz personnel emphasized their rejection of
sidewall secondary air jets. Any sidewall jets, they claim, would cause CO
formation ind long flames to develop in the middle of the furnace. On June
8-10, 1977, the continuous C02 records varied between 8.2 percent and 11
percent.
Reliability of the secondary air system has been excellent. The
V-belts have not even been replaced after 30,000 hours. The nozzle jets
have remained open and clear despite slag buildup on the rear wall.
The Hague
Furnaces 1-3 at the Hague were originally installed in 1968
without secondary air jets. This was consistent with the original design
concept for this plant which was expected to be faced with the problems of
burning high-moisture, low-calorific-value waste. Thus, the potential
cooling effect of secondary air jets was probably deemed of greater
disadvantage than any gain that would accrue from the nixing action of air
jets.
However, as pointed out in the discussion of wall-tube and
.superheater corrosion, within the first year of operation, wastage of both
areas was observed and it w?s concluded that the temperatures in the
radiation pass (first pass) were, at times, excessive. Accordingly, after
one year's operation, nine secondary air jets were added on'each side of
each of Furnaces 1-3. They are about 50 mm (2 in) diameter and are located
in one horizontal row in the refractory sidewall just below the beginning
of the water-tube wall of the radiation pass. The jets are supplied with a
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T-16
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T-17
maximum of 21,000 Nmg/h (12,3*18 scfm) boiler room air by a radial blower
producing a maximum static pressure of 390 mm Ws (383^ Pa) 15.1 in water.
When Unit 1 was built, it was supplied with a similar horizontal
row of nine jets on each side close to the main burning grate. Figure
shows the secondary air manifold on the side of Furnace M. In addition to
the ten jets in the horizontal row there are two additional jet tubes
visible on a sloping line at the left. These are directly above the step in
the grates between the feed grate and the main burning grate with the slope
of line of jets conforming approximately to the slope of the angle of
repose of the refuse as it flows into the furnace. A useful detail of the
jet tubes shown in Figure T-lOis that each tube is lightly capped by.a
spring-loaded cover which can be easily lifted aside for inspection of the
jet and, if the jet entry into the furnace is observed to be clogged by ash
or slag, the buildup car be readily poked into the furnace by means of a
rod inserted through the tube.
It is not clear whether the addition of these secondary air jets
was beneficial. The plant staff appeared to prefer future application of
front-wall and ^ear-wall jets in view of the predominant experience
elsewhere that such jets appear to provide better mixing.
The walls of Unit 2 were soon to be modified to incorporate
Kurstler air-cooled wall blocks. Presumably, this method of introducing
lov-velooity sroondary air will replace the present wall jets. That furnace
pi ay then once more be operating without the mixing action of
moderate-velocity air jets. Whether this lack will affect furnace
performance remains to be seen.
Dieppe and Deauvillp
Initially, the refractory furnaces at Dieppe were operated without
overfire air but later front-wall jets were added, supplied by a blower
wit! Tiaxjrcun capacity of 5,000 Nra^/hr (29^0 scfra) at 150 mm water (1,170
Pa) (6 in). At Deauville secondary air is injected through six jets in each
sidewall.
Gothenberg"
At the Gothenberg plant the secondary air blowers can deliver to
each furnace 23,000 NmVhr (19,120 scfr.) at 250 to 280 mrc water (2.51 kPa
to 2.7^ kPa) (10.2 to 11.0 in). The estimated velocity in the air nozzles
is 2> ^./sec (115 fps).
Figure T-12shows changes that were made in 1975-76 to reduce tube
u,->st?-te. The 18 sidewall air jets on each side just below the wall tube
header ve^c blocked and replaced by 7 downward angled jets in front and 9
in the back. Fifteen of these jets are 80 mm (3 in) dia. but 3 of the front
orses are 150 mm (6 in) dia. Also, -a rear nose formed of refractory-covered
tubes was ^dded to direct the flame flow away from the rear wall. A slopin£
dotted line above that rear nose shows hov; the slope of the tube was later
modified to discourage buildup of loose ash deposits. Also, later the
location of the rearwall jets was moved farther forward toward the top of
the r.cse. The first rear wall nose was installed in Boiler 2 in December,
1975 (Week No. 18). The second was in Boiler 1 in March, 19TC (Week No.
10). Th3 third was in November, 1976 (Week No. 16).
-------
T-18
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T-20
These measures plus the apparent reduction in refuse heat value
have reduced the tube corrosion rate to a point where plant staff estimates
that 30,000 hours of operation can be expected before some tube
replacements may be needed.
The secondary air blowers take moist air from above the residue
quench channel to which, in winter, warm air is supplied from the top of
the furnace room.
Uppsala
For all 4 furnaces at Uppsala the secondary air is supplied by the
primary air blower. In Furnaces No. 1 through 3, there is only one sidewall
jet needed and not for turbulence. In Furnace No. 4, the secondary air is
automatically regulated by a smoke density meter.
Horsens
At Horsens, Denmark about 10 percent of the primary air volume is
available as secondary air at a pressure of 200 to 250 mm water (7.9 to 9.8
in). This air can be injected through ports in the furnace roof. However,
this air is seldom found necessary as sufficient burning time and gas
mixing are usually provided by the cyclonic after-combustion chamber which
is characteristic of Bruun and Sorensen plants. Hence, usually only enough
secondary air flows to cool the roof-ports and connected piping.
Copenhagen;Amager and West
Secondary (Overfire) Air - Boiler Room Cool Air. Both modern
plants at Copenhagen: Amager and VJest, are equipped with a secondary fan
which pulls cool air from the refuse bunker and supplies it to the furnace
as overfire air. Both also have hot flue gas recirculation fans.
The Nordisk Ventilator forced-draft 150 Hp belt-driven fan,
running at 1,670 rpm, car, pull 35,000 Nm^/hour (20,580 scfn). The
temperature is assumed to be 30 C (80 F) and the static pressure is 460 mm
water (18 in water).
The air is sent to two manifolds or. each side of the furnace and
above Grate III. Figure T-13shows secondary air nozzles.
Secondary (Overfire) Air - Flue Gas Recirculation Hot Air. During
only the first year of operation Amager used recirculated hot electrostatic
precipitator.
A 150 Hp motor drove the belt-driven fan at 1,460 rpm. The fan is
ratec! at 45,000 Nm^/hour (26,500 scfm) and delivered the 300 to 350 C (572
to 662 F) hot flue gas at 220 mm water (8.7 in water).
The use of ambient boiler room air at 30 C (86 F) or recirculated
flue gas air, 138 to 177 C (280 to 350 F), is determined by basic furnace
design and the refuse lower heating value (LHV). Assume that the furnaces
were nominally designed for refuse with a LHV of 2,000 kcal/kg (8373 kJ/kg)
(3GOO Btu/lb). If the LHV being burned is well over this design, value, then
cool ambient air, rich in C>2, might shock the refractory and cause the
Carborundum bricks to spall. Therefore, if the refuse is ""hot", then
-------
T-21
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T-22
recirculated flue gas air, poorer in 02, should be used. In contrast, if
the refuse is "cool" or.wet, then ambient boiler room, rich in 0%, should
be used. Of the European vendors visited, Volund is the only manufacturer
which arranges extensively to use recirculated flue gas.
The recirculation flue gas fan has a damper that is automatically
controlled. It sends a larger or smaller quantity of the flue gas back to
the furnace depending on the furnace combustion temperature. The dampers
are adjusted so that the furance temperature is always 900 to 1 ,<000 C (1652
to 1832 F).
At Amager, where the refuse is cooler than at West at 1,800
kcal/kg (7536 kJ/kg) (32^0 Btu/pound), they now use only ambient boiler
room air. Refractory life has improved. The air is not put through the back
wall where the flue gas recirculation air had been previously inserted.
West Units No. 1-3, unlike Unit No. H, use hot flue gas as
secondary air. The air is drawn from the flue gas leaving the hot
electrostatic precipitator.
Table T-2presents key design parameters for the four fans: (1)
F.D. primary air, (2) F.D. secondary air, (3) I.D. flue gas recirculation,
and (1)) F.D. flue gas recirculation.
The Plant staff report that the four fans for each furnace have
experienced only minor maintenance.
-------
T-23
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U-l
BOILERS
The term "boiler" has varying meanings as described below. As a
result this chapter has a unique organization with key headings as follows:
What is a Boiler
Summary of Boiler-Furnaces
General Boiler Designs
Comments about Specific Boilers
Superheater Sections of Boilers, General Comments
Comments about Specific Superheaters
Steam-to-Refuse Ratio
Boiler Cleaning
Metal Wastage (Corrosion and Erosion) of Boiler Tubes
References about Boilers
What is a Boiler?
In this research on refuse-fired steam-and hot water-generators
the most important single component of the plant and often the most costly,
is the boiler. However, as pointed out in 1966 by Fryling in "Combustion
Engineering,..." the word "boiler" may not convey the same meaning to all
engineers. The primary function of a boiler is to generate steam, and this
naturally suggests the use of the terms "steam generator" and "steam
generating unit" as equivalent to boiler. There have been some attempts to
restrict the meaning of the word "boiler" to that portion of a steam
generator in which water is transformed to the vapor phase, but these have
only led to confusion without gaining widespread acceptance. In a similar
sense, many have advocated the phrase "steam generator" or "steam
generating unit" as a more universal designation than boiler, but usage of
the latter persists in both lay and engineering circles. In fact, there is
much evidence to support the view that the word "boiler" is gaining
ascendancy. In simplest terms a boiler is a mechanical device to convert
water to steam."
However, some of the plants visited produce hot-water for district
heating systems. These are also said to use "boilers", although no actual
boiling of water occurs in those pressure vessels.
Figure U-1 shows a typical plant, the one at Baden-Brugg,
Switzerland. The figure shows an outer envelope designated "Refuse-fired
Steam Generator" which encompasses the entire operating system from the
refuse pit to the chimney. Inside that plant a smaller envelope encompasses
the boiler. This smaller area is a complex system of components which
varies considerably from plant to plant but which has one essential
characteristic: all of the components are interconnected as a fluid system
containing water or steam or a mixture of the two at essentially a constant
pressure throughout.
There is yet a third envelope loosely called the "boiler". More
properly, it would be called the "boiler convection section". It is the set
of tube bundles that actually transforms the preheated water (from the wall
tubes and the economizer) into steam. Usually the steam leaving the "boiler
convection section" will enter the superheater.
The predominant boiler type in the most advanced European
waste-to-energy systems is the water-tube-walled primary furnace plus a
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U-3
similar tube-walled radiant pass followed by various arrangements of
convection-tube sections. There are many variations of this arrangement
plus a few significant plants which still depend upon refractory-walled
primary furnaces, and a few small ones make very effective use of the
ancient firetube boiler principle.
Because of the many variations among even the newest plants, it is
evident that the evolution of waste-to-energy boiler-furnaces, which began
to use the water-tube wall concept in the 1960's, is still in progress.
This section of our report describes the background and current status of
that evolution.
Definition of Boiler Terms
Before discussing details of the various boiler systems the
following definitions are provided to assist the reader in understanding
the terms used. These definitions have been taken from the book "Combustion
Engineering" edited by Fryling.
Air Heater or Air Preheater - Heat transfer apparatus through
which air is passed and heated by a medium of higher
temperature, such as the products of combustion or steam.
Attemperator (Authors' definition) - A desuperheating device
to inject very pure water into the steam between superheater
bundles in order to control final superheated steam
temperature.
Boiler - A closed pressure vessel in which a liquid, usually
water, is vaporized by the application of heat.
Boiler (Authors' definition) - A closed pressure vessel, a
set of interconnected tubes and drums acting as a fluid
system containing water or steam or a mixture of the two at
essentially a constant pressure throughout that has a
function of producing superheated water, steam, or heated
steam.
Water Tube - A boiler in which the tubes contain water and
steam, the heat being applied to the outside surface. Also,
see Steam Generating Unit.
Bent Tube - A water tube boiler consisting of two or more
drums connected by tubes, practically all of which are bent
near the ends to permit attachment to the drum shell on
radial lines.
Fire Tube - A boiler with straight tubes, which are
surrounded by water and steam and through which the products
of combustion pass.
-------
U-4
Boiler Convection Bank - A group of two or more rows of tubes
forming part of a water tube boiler circulatory system and to
which heat is transmitted mainly by convection from the
products of combustion.
Boiler Slag Screen - A screen formed by one or more rows of
widely spaced tubes constituting part of, or positioned in
front of, a water tube boiler convection bank, and
functioning to lower the temperature of the products of
combustion and to serve as an ash cooling zone.
Desuperheater - Apparatus for reducing and controlling the
temperature of a superheated vapor. (Also called an
Attemperator).
Economizer - A heat recovery device designed to transfer heat
from the products of combustion to a fluid, usually feedwater.
Furnace Slag Screen - A screen formed by one or more rows of
tubes arranged across a furnace gas outlet, serving to create
an ash cooling zone for the particles suspended in the
products of combustion leaving the furnace.
Pendant Tube Superheater - An arrangement of heat absorbing
elements which are substantially vertical and suspended from
above.
Platen - A plane surface receiving heat from both sides and
constructed with a width of one tube and a depth of two or
more tub'es, bare or with extended surfaces.
Screen Tubes - A group of large diameter water tubes usually
located immediately before the superheater tubes to reduce
flue gas temperature and hence superheater tube corrosion.
Steam Generating Unit - A unit to which water, fuel, and air
are supplied and in which steam is generated. It consists of
a boiler furnace, and fuel burning equipment, and may include
as a component parts water walls, superheater, reheater,
economizer, air heater, or any combination thereof. Also, see
boiler.
Steaming Economizer - An economizer so designed that some of
the fluid passing through it is evaporated.
Stud Tube Wall - A wall containing water tubes covered with
refractory which is held in place by stud anchors attached to
the tubes.
Superheater - A group of tubes which absorb heat from the
products of combustion to raise the temperature of the vapor
-------
U-5
passing through the tubes above the temperature
corresponding to its pressure.
(a) Convection superheater - A superheater so arranged and
located to absorb heat from the products of combustion
mainly by convection.
(b) Radiant superheater - A superheater so arranged and located
to absorb heat mainly by radiation.
Summary of Boiler-Furnaces
European refuse has now reached high enough levels of heat value
that in large power-generating units consuming 300 tons/day and up, the
furnace is best cooled by water tubes. However, because of the corrosive
action of chloride deposits on these tubes, they must be covered by plastic
silicon carbide or alumina refractory held in place by welded studs. This
refractory coating must extend upward to protect the lower third or half of
the first or radiation pass.
Most superheaters suspended at the top of the first pass are
subject to rapid chloride corrosion because of overheating of the chlorides
in the ash deposits, especially when long flames reach up to them during
unavoidable "excursions" characteristic of mass burning. A long
water-cooled first pass, followed by a similar long open second pass,
appear to be very important in keeping the ash deposits on the superheaters
cool enough that chloride attack is minimized.
Ample secondary air up to 25 percent of the total combustion air,
delivered at high velocities from multiple small jets, is essential to
completing cpmbustion in the furnace and avoiding long flames which may
cause corrosion.
Excessive use of high-pressure steam-driven soot blowers is a
common source of tube erosion-corrosion. Use of a horizontal-flow type
superheater and boiler sections directly following the first or radiation
pass enables less drastic cleaning by gentle rapping of the vertically hung
tubes. But this is no insurance against chloride corrosion if the furnace
gases have insufficient flow path and time to cool before they strike the
superheater.
Costs for tube-corrosion-caused maintenance are unclear. They were
almost zero at Zurich and minimal at Werdenberg, Wuppertal, Krefeld,
Uppsala, Horsens, Copenhagen, and Dieppe-Deauville. They were highest at
Duesseldorf, Issy, The Hague, and Gothenburg. Through changes in operation
tube materials and shielding these plants have reduced the effects of
corrosion. None has abandoned the mass-burning approach and plans for
expansion or building additional plants continue at some locations.
Overall Boiler Design
It has taken a long time for some waste-to-energy plant designers
to become fully aware that refuse is not coal. Refuse is
• More variable
• Less dense, but subject to extreme variation in density,
especially if very wet
• High in chlorine
-------
U-6
• Always changing
• Usually has much higher alkali content in the ash
• Feeds poorly
• Can lose ignition if wet or can almost explode with threating
intensity.
Boilers and stokers, following well established design, have not
always been designed to cope with these properties. Accordingly,
refractories, tube walls, and superheaters have suffered.
Some designers still do not seem to be aware of these effects.
On the other hand, in about 1965 or 1967, someone in Martin and
Von Roll evidently began to perceive that the superheater must not be
located where, even momentarily, its ash deposits could become overheated.
Thus, the Paris (Issy) (1965) and Ludwigshafen (1967) designs had the
superheater after a second, open radiant, water-tube pass.
But Martin didn't use this again until 1971 at Kezo-Hinwil and
1972 at Hagenholz. And VKW even hung the superheater in the first pass as
recently as 1972 in Unit 5 at Duesseldorf. Then in 1976 at Krefeld and
Wuppertal, VKW placed the superheater beyond the first pass. Now in 1976,
Widmer & Ernst at Werdenberg has included the open second pass ahead of the
superheater.
Oddly, when Von Roll built Saugus near Boston in 1975, they
included no open second pass; but at Stapelfeld, to be completed in 1980,
Widmer & Ernst will. So the choice between the lower cost, close-coupled
boiler-superheater arrangement, and the more costly double-open pass is
still not clear among the various designers.
General Boiler Designs
The following sections summarize the significant details of the
various boiler configurations investigated. As has already been discussed
in earlier sections there are good reasons for the differences in plant
design that were encountered and there is much evidence of a continuing
process of evolution. At this time, 1977-78, it appears that the current
"best" boiler-furnace design in use for large, high-pressure units is the
completely water-tube-walled furnace and radiant section, studded and
coated with thin refractory in the intense burning zone, followed by one or
more long, open, vertical radiation passes preceding a convection-type
superheater and boiler-convection passes and an economizer.
However, an emerging newer philosophy is to follow the tall
water-tube-walled chambers by a long horizontal superheater and convection
section. This is called the "dacha" boiler because of its extended
horizontal configuration. Figure U-2 shows such a design for the proposed
Staplefeld plant at Hamburg. The purpose of this design is primarily to
enable all of the boiler convection tubes and, in many cases, the
superheater tubes as well, to be suspended vertically in the horizontal gas
passage. This arrangement makes it relatively easy to remove and replace
failed tubes from the top. It also facilitates the removal of ash deposits
from those vertical tubes by means of mechanical rapping. Thus, the common
threat of the erosive action of steam-jet soot blowers is eliminated. It is
too early to tell how effective this cleaning method will be in the long
run.
-------
U-7
FIGURE U-2. DACHA TYPE SUPERHEATER AND BOILER
CONVECTION ARRANGEMENT FOR PROPOSED
STAPELFELD PLANT AT HAMBURG (COURTESY
WIDMER & ERNST). S - Superheater
B - Boiler Convection Section
-------
U-8
It is notable that in Figure U-2 of the proposed Stapelfeld plant
(to begin operation about 1979) the platen-type superheater is preceded by
an open, water-tube-walled second pass to assure that the superheater is
not touched by excessively hot flame or furnace gases. Furthermore, it is
in a location such that it is completely shielded from furnace radiation. A
similar design philosophy is apparent at the Werdenberg and Zurich plants
to- be discussed later under superheaters. Both of these factors will
combine to keep the ash deposits on the superheater from becoming heated to
the point that chlorine may attack the metal. This is discussed at length
under "Metal Wastage".
Comments About Specific Boilers
Werdenberg Boiler
Figure U-3 shows a cross section of the single boiler in the small
Werdenberg-Leichtenstein plant started up in April, 1974 at Buchs,
Switzerland. Although this is a very small boiler: 12 tonne/hr (26,460
Ib/hr) rated steaming capacity with a peak capacity of 16 tonne/hr (35,275
Ib/hr), in many ways it embodies the current culmination of evolution of
the vertical-pass, water-tube wall type of boiler discussed earlier. Boiler
pressure is 39 bar (3930 KPa) 570 psia. Superheat temperature is 395 C (740
F).
The first pass above the furnace, the radiant pass, is water-tube
walled. The wall tubes are nearly tangent to each other. The tubes are
carbon steel, 76.1 mm (3.0 in) dia., 4 mm (0.16 in) thick, spaced on 78 mm
(3.1 in) centers. Although the tubes are nearly touching they are not
connected by welded fins to form a membrane wall. Apparently European
boiler designers have been reluctant to use the welded fin, membrane wall
type of construction because of differential expansion problems that might
cause fatigue cracks to form. However, it is now beginning to appear in
most new designs.
Second Boiler Pass. When the upward-flowing gases reach the top of
the first pass, they then are turned horizontally into the entrance of a
second water-tube walled vertical pass in which the gases are further
cooled as they flow downward. These water tubes have no studs nor coating
as by this time the gases are cooled so that corrosion and erosion are no
longer a threat to water tubes.
Boiler Operation. Reliability of this relatively new plant (1974)
was stated to be 100 percent except for scheduled shutdowns. Few repairs
have yet been required (1977) and at least a 20-year life is expected. An
amortization period of 20 years is common in Switzerland.
In 1975, the new plant was operated at an excessive rate for only
3 or 4 days per week. The remainder of the time, steam was supplied by the
oil-fired standby boiler. Design heat input is 14 x 106 kcal/hr (55 x 106
Btu/hr) (58.5 x 10^ kJ/hr). However, the actual input ranged up to 17-18 x
106 kcal/hr (71.4 x 10° Btu/hr) (75.3 x 106 kJ/hr) amounting to a 20 to 29
percent overload. Formal warning to the owner by the manufacturer of the
possiible deleterious consequences of such overloading led to subsequent
operation at more nearly normal loading. At the time of our visit, May 2-4,
-------
U-9
1 Delivery Area
2 Bunker Door
3 Refuse Bunker
A Crane Pulpit
5 Crane
6 Refuse Grab Bucket
7 Charging Hopper
8 Incinerator Furnace
9 Step Grate
10 Ash Hopper
11 Residue Chute
12 Residue Basin
13 Residue Conveyor Belt
14 Steam Boiler
15 Air Cooled Condenser
16 Electrostatic Precipitator
17 Exhaust Gas Fan
18 Steel Chimney
19 Hot Water Heater
20 Feed Water Tank
21 Turbogenerator
22 Collected Flyash Conveyor
23 Feedwater and Heating Wati
Pumps
24 Oil-Fired Stand-by Boiler
FIGURE U-3. SECTION THROUGH WERDENBERG-LIECHTENSTEIN WASTE-TO-ENERGY
PLANT, COURTESY WIDMER + ERNST (ALBERTI-FONSAR)
-------
U-10
1977, there appeared to have been no permanent damage resulting from the
period of overloading.
On April 1, 1977', the Swiss organization of Pressure Vessel
Inspectors issued a report on the inspection of this boiler. They reported
the boiler in good condition with some dirty surfaces but no unusual tube
wastage. Some steel supports in the superheater section showed some
corrosion.
In summing up the experience at this small, new plant, it appears
that conservative, multipass boiler design and relatively low firing rates
have nearly eliminated tube corrosion as a significant problem.
Baden-Brugg
Figure U-4 is a cross section of the two-boiler Baden-Brugg
200-tonne-per-day plant that started up in 1970. It is of interest because
it preceded the one-boiler Werdenberg (1974) plant by 4 years and was
designed by the same experienced designers. Steam pressure is 40 bar (4000
kPa) (590 psia), superheater temperature is 400 C (752 F).
A major difference from the later Werdenberg design is that in
this older design at Baden-Brugg, there is no open second pass to cool the
gases before they reach the superheater.
The main furnace is largely refractory walled. Only the sloping
rear wall of the furnace is water-cooled. As the combustion gases rise out
of the partially cooled refractory walled furnace, they are accelerated
into the first or radiation pass, a tall open, vertical, water-tube walled
pass. From this pass they enter the superheater consisting of vertical
sinuous tubes.
To summarize the Baden-Brugg plant experience, some wall tubes
have failed. This corrosion failure was stopped by applying wall refractory
coating. There has been superheater corrosion which is now under control as
discussed under superheaters.
Duesseldorf
Figure U-5 shows one of the four large boilers first started up at
Duesseldorf in November, 1965. Their design was based primarily on 4 years
(1961-1965) of developmental work using a new roller-type grate for refuse
applied to an old coal-fired refractory furnace in the municipal power
plant there. Referring back to Figure S-l showing the trend of heating
values of European refuse, it can be understood that in that early period
(1961-1965) the furnaces and boilers were designed for very low heat value
in the refuse. Accordingly, in these first four boilers there is little
water cooling of the furnace and no open second pass. As will be discussed
under "Superheaters", the suspended platen-type superheaters are located in
a potentially "hot" position at the top of the first, radiant pass. The
rather startling rise in heat value of Duesseldorf refuse, 70 percent
increase from 1961 to 1975, has caused corrosion problems for this very
"compact" boiler design.
The pilot unit burning 200 tonnes per day, was operated
intermittently for a total of 22,000 hours from 1961 to 1965 and provided
the design basis for a small plant (110 tonnes per day) at Rosenheim
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FIGURE U-5. CROSS SECTION OF ONE OF BOILERS NO. 1-4 (COURTESY OF
STADTREINUNGS UNO FUHRAMT DUESSELDORF)
1. Refuse hopper
2. Refuse feeder and roller
grate "system Duesseldorf"
3. Ignition burner
4. Heavy oil burner (both sides)
5. Economizer
6. Steam drum
7. Radiant water-tube-wall boiler
8. Boiler convection section
9. First and second stage super-
heater
10. High-temperature superheater
11. Steam discharge
12. Exhaust gas duct to electro-
static precipitator
13. Ash siftings removal
14. Wet residue conveyor
15. Residue removal to processing
plant
-------
U-13
(1964), and for the first four full size units at Duesseldorf—the first of
which was started in November, 1965.
For the reasons cited earlier, when the design transition was made
in 1964-1965 from the old refractory-walled pilot furnace to the new,
full-scale units, No. 1 through 4, there was an understandable reluctance
to use a fully water-tube walled furnace. Although the lower heating value
of" Duesseldorf refuse shown in Figure S-1 had risen to 1,220 kcal/kg (5,108
kJ/kg (2,196 Btu/lb) by 1963, that was still a relatively low level. Hence,
the need for some refractory in the main furnace to reflect heat to the raw
refuse so as to facilitate rapid ignition and burning. Final steam
temperature is 500 C (932 F).
The sloping roof of Furnaces No. 1 through 4 is in two parts as
seen in Figure U-5. The front roof is cooled by water tubes, as well as the
longer rear roof.
First Open Boiler Pass, Units No. 1-4. Burning is usually not
complete as the gases flow upward out of the main furnace. This means that
the ash particles carried in the burning gases are usually hot enough, over
982 C (1800 F), to be sticky. Accordingly, enough volume must be provided
to allow time and radiation to the gases so that deposits of ash particles
will be dry and will be below the corrosive range. The problems with
wall-tubes in these first four furnaces have been described under "Furnace
Wall".
Furnace in Unit No. 5. The furnace for Unit No. 5, built in 1972,
was altered in accordance with the experience gained in about 6 years'
operation of Units 1-4. Also, the gas flow pattern in No. 5 was radically
altered because of the rising heat value of Duesseldorf refuse. Instead of
having the burning gases flow upward at an angle toward the furnace outlet
as in Units 1-4, a sloping steam-generating water-cooled baffle was built
in No. 5 above the fuel bed as shown in Figure U-6 in such a way that the
gases first flow nearly parallel to the fuel bed. At the end of the baffle,
they turn and flow upward toward the furnace outlet. This provides a longer
flame path and residence time for the hot gases resulting from the higher
heat value of refuse.
One desirable achievement of this new design is that by the time
the gases reach the top of the furnace and enter into the first pass, they
are well mixed and cool enough to reduce corrosion.
However, because of slagging of the uncooled furnace sidewalls,
after 6,000 operating hours, the SiC lining of the front part of the
furnace needed replacement. This problem has been disucssed under "Furnace
Wall".
While the walls in Units 1-4 were either refractory or spaced
water tubes shielded by high-temperature insulation, the nonrefractory
water-tube walls in Unit No. 5 are "membrane walls"; that is, each tube has
two welded fins, 10 to 12 mm (0.4 to 0.5 in) facing the adjacent tubes. The
joint between the fins is also welded forming a solid, water-cooled
membrane wall.
Boiler (Convection Section). The convection section of the boiler
is located in the lower portion of the second pass as seen in Figure U-6.
Some erosion by fly ash has been experienced in this area. In Boilers NO.
-------
U-14
Boiler Components
1. Welded Fin Water Tube Walls
2. Superheater
3. Steam Drum
4. Boiler Convection Section
5. Economizer
FIGURE U-6. CROSS SECTION OF BOILER NO. 5 WITH ROLLER GRATE "SYSTEM DUESSELDORF"
(COURTESY STADTWERKE DUESSELDORF KRAFTWERKE)
-------
U-15
1-4, this occurred only at the outside of the first row of tubes where the
gas flow pattern caused a concentrated stream of fly ash to impinge against
the metal. In Boiler No. 5, after 28,000 hours, steel cladding was added to
shield these tubes against erosion.
The Duesseldorf plant has controlled wall tube corrosion by means
of rammed refactory coating on studded tubes. Because of the exposed
position of the superheater in the first pass, corrosion is still a problem
and tube shields, alloys, and coatings are still being tried.
Wuppertal and Krefeld
The six boilers at the relatively new plants of Wuppertal (1976)
and Krefeld (1976), Germany, both near Duesseldorf, are very similar and
show the influence of the experience gained by VKW at Duesseldorf. They are
not primarily power generating units; hence, steam temperature is
moderate—Wuppertal 350 C (662 F). Furthermore, neither of these newer
plants has a platen-type superheater suspended from the top of the first
pass. The boilers have membrane walls.
Figure U-7 shows the Wuppertal plant in which the 4 boilers each
consists of a completely open water-tube walled first pass followed by
second and third convection-type passes. The two Krefeld boilers are very
similar except that mill-dried sewage sludge is fired into the first pass
and most of the energy released in the plant by the burning of refuse is
used in drying this sludge.
As at Duesseldorf, the 57 mm (2.3 in.) water-tubes forming the
walls of the first radiataion pass are studded and coated to a height of
about 2 to 3 meters (6.5 to 9.8 ft) at Wuppertal and about 3 meters (9.8
ft) at Krefeld. The welded studs are 10 mm in diameter (O.H in), 20 mm (0.8
in) long, and are applied to the welded membrane walls at the rate of about
2,100/m2 (195/ft2). At Krefeld, the studs are covered with a 50 mm (2 in)
thick layer of 90 percent silicon carbide. At Wuppertal, part of the
coating is 50 percent SiC and another part 80 percent SiC as a comparative
trial to ascertain which works best under the conditions at the plant.
Both the Wuppertal and Krefeld plants are too new (1976) to
provide information on boiler reliability. Also at Wuppertal, only two
boilers are operated at a time while the flue gas scrubbers for acid gas
removal are being tessted. The Krefeld plant is also at part" load and has
not yet been finally tested. Hence, considerable time must elapse before a
sufficient operational period has been accumulated to enable evaluation of
these boiler designs.
Paris-Issy
Figure U-8 shows one of the four boilers at Issy (1965) which
incorporated the results of much Parisian and other experience with boilers
for waste fuel. The large, open first and second passes seem to represent
the latest design to avoid high temperature corrosion problems; yet wall
and superheater corrosion have occurred. This probably results from two
factors:
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U-17
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FIGURE U-8. ISSY-LES-MOULINEAUX INCINERATOR PLANT NEAR
PARIS, FRANCE.
-------
U-18
(1) These boilers are overloaded by as much as one third above
the initial design rate.
(2) The two open passes are large in volume and in width and
short which apparently provides less time for gas cooling.
The superheater is in the third pass.
In 1975, the average input rate per operating furnace was 19.1
tonnes/hr (21.0 tons/hr) and in 1976 this rose to 19.9 tonnes/hr (21.9
tons/hr). The original design rate was 15 tonnes/hr (16.5 tons/hr) which
later was increased to 17 tonnes/hr (18.7 tons/hr). In 1975 and 1976, the
four boilers operated 86.4 percent and 84.8 percent of the total elapsed
time. This high intensity of operation is needed but it contributes to
increased maintenance requirements, particularly because of inevitably
higher peak burning rates than the average.
Comparison of Ivry and Issy. Of special interest regarding the
evolution of waste-to-energy systems is the newer Paris-Ivry (June, 1969)
plant (Figure U-9), also run by TIRU-EDF and built by Martin about 4 years
later than Issy (started up in February, 1965). It has two much larger
Martin units, each rated at 40 tonnes/hr (44 tons/hr) for 2,500 kcal/kg
refuse (4,500 Btu/lb) (10,467 kJ/kg) or 50 tonnes/hr (55 tons/hr) for 2,000
kcal/kg refuse (3,600 Btu/lb) (8,374 kJ/kg). The grate area of each unit is
128 m* (1,377 ft2) and each grate is 12.8 m (42 ft) wide. The design is
almost identical to the Martin plant started at Hamburg in 1972 and
described in later sections.
Thus, at the lower heat value, the rated grate burning rate is
390.6 kg/m2/hr (79.9 Ib/ft2/hr). The corresponding heat release rate is
781,509 kcal/m2/hr (287,582 Btu/ft2/hr) (3,371 mJ/m2/hr).
These rates are high but not much higher than the actual rates in
1976 at Issy when each unit averaged 19.9 tonnes/hr. Again, it is
characteristic of mass burning units using refuse as fuel that there will
be repeated excursions to much higher rates. It is very likely during these
short periods that the chloride-containing deposits on the water-tube walls
and superheaters can become overheated. If they do, the evidence is strong
that chloride corrosion will occur. Thus, it is not surprising that during
a brief visit to Ivry in 1975, before this project began, it was learned
that the ninth different superheater cladding was then being tried in an
eventually successful effort to achieve more than a 1-year life for the
most exposed superheater tubes.
The superheater at Ivry differs from that at Issy in that the
platens are all pendant in the "dacha" style. Gas flow is horizontal. There
is no second radiant pass ahead of the superheater.
Steam temperature at Irvy is 470 C (878 F) while at Issy it is 410
C (770 F). At Irvy, steam pressure is 75 bars (1,088 psia) (7,501 kPa) and
at Issy, 50 bars (725 psia) (5,001 kPa). Although the closer coupling of
superheater-to-furnace at Irvy and its higher steam temperature would both
indicate a higher corrosion potential than at Issy, the corrosion
experience at both plants appears to be of about the same magnitude.
Hamburg-Stellinger-Moor
Figure U-10 shows one of the two Martin furnaces started up at
Stellinger-Moor in 1970. The City of Hamburg had already had long
-------
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U-21
experience with refuse as fuel beginning in 1896 with 12 batch-fired units
at Rohrstrasse equipped with waste-heat boilers. Accordingly, the two
boiler-furnaces burning about 50 tonne/hr total at Stellinger-Moor
incorporates the culmination of much valuable experience. However, the
unexpected rise in heat value of the refuse at Hamburg, since the
Stellinger-Moor plant was designed, has caused much difficulty with these
two boilers. Hamburg plants have long had problems with low-heat value
refuse. In fact, as described earlier, at the old Borsigstrasse plant,
there was a time in 1960 when the heat value dipped so low that the fire
went out.
Accordingly, the two present boilers were designed in 1968-1969
for a heat value of 1,500 kcal/kg (2,700 Btu/lb) (6,280 kJ/kg); but in 1974
to 1976, it was estimated to average 1,800 kcal/kg. Today, it is thought to
average 2,500 kcal/kg. Industrial waste frequently pushes the value much
higher with consequent overheating of the furnaces, superheaters, and
precipitators. Thus, two methods of water injection have been used to
alleviate this overheating:
(1) The refuse in the pit is sprayed with water when it is seen
to be very dry, such as from masses of tobacco cuttings and
bulk photographic film.
(2) Water is sprayed for cooling the gases ahead of the
precipitator when the gas temperature approaches 350 C (662
F).
Water-Tube Walls. As described under "Furnace Wall", the sidewalls
of the furnace are cooled by three large sloping headers on each sidewall.
Then a welded membrane wall extends upward into the first pass.
Rising vertically above the combustion chamber is the open
radiation-type first pass. Unlike the fin-tube membrane walls of the
combustion chamber, these water-tube walls are not welded and have 20 mm
(0.79 in) spacing between 70 mm (2.75 in) tubes.
As has been seen elsewhere, such unwelded tubes are free to bulge
either out or into the radiation chamber depending on the type and
intensity of thermal stresses.
An apparently improperly positioned and operating rotating wall
soot blower blew a hole in a wall tube bulging out into the furnace midway
up the first pass. It is believed that if the lower fin tubes of the
combustion chamber were extended further up into the first pass, then the
wall could have withstood further abuse from the soot blower before
bursting. When the one tube burst, sections of 40 or 50 other wall tubes
were replaced because of thinning due to corrosion. There has been metal
wastage at other points and once per year, the thinning tubes are routinely
replaced.
Stellinger-Moor is one of the last units to be built without
welded membrane tube walls.
First Pass Roof Tubes. Sloping tubes form a roof at the top of the
first pass which continues over the superheater section. These tubes carry
saturated steam from the front water tube walls of the first pass directly
to the boiler drum.
Fortunately, the management has had the foresight to make a
detailed record of all measurements and everything done to the furnaces. A
-------
U-22
September 21, 1976, entry to the maintenance record reports on the roof
tube problems.
The diameter of each tube is 25 mm (1 in) and the original wall
thickness was 3.6 mm (.11 in). The measurements taken were only on tubes
that had shown signs of metal wastage, i.e., tubes numbered 16 through 11.
The wall thickness had been reduced from the original 3.6 mm (.14 in) down
to between 1.6 and 2.3 mm (0.06 and 0.09 in). Of the 20 tubes measured, all
but two tubes were replaced.
The corrosion of these sloping roof tubes was related to the high
burning rates and to incomplete bonding of the SiC 90 that had been sprayed
over metal studs on these large tubes. Because the tubes carry saturated
steam at 290 C (483 F) and not the hotter superheated steam, the SiC
refractory coating never was heated enough for proper bonding, i.e., 1,200
C (2,190 F).
The plant staff have decided to replace the SiC 90 by a high
alumina plastic refractory. The superior heat transfer characteristics of
a properly bonded SiC 90 will be sacrificed in favor of the cheaper and
more reliable high alumina refractory.
Screen Tubes at Outlet of Radiation First Pass. All of the gases
leaving the first pass go between the screen of tubes which carry the steam
from the rear wall tubes over to the steam drum. These tubes depicted below
have experienced erosion by the combustion gases.
Furnace roof
O
The 18 tubes are 70 mm (2.76 in) in outside diameter and 3.2 mm
(0.126 in) in thickness and widely spaced. The maintenance record book of
September 8, 1976, shows that tube No. 10 in Boiler No. 1 burst and caused
unit stoppage. Measurements were taken that showed an uneven pattern of
greater metal wastage of the center tubes. As a result, five other thin
tubes were also replaced. Early in 1977, all 18 tubes were removed and
replaced with pipes having bolted shields.
As in other plants, this one has had good success in bolting
Sicromal 10 shields usually 6 mm (0.15 in) thick to vulnerable tubes. The
shields must usually be replaced every few months or years but this can
often be done at regular down periods. Table U-1 shows the composition and
characteristics of three Sicromal alloys.
Boiler Convection Section. The flue gases leave the superheater
and continue flowing horizontally as they enter the boilers' convection
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U-24
section. In this section, boiler-tube corrosion near the fixed position
soot blowers had been a serious problem. As in many other plants, reducing
the soot blower activity can provide increased tube life with no increase
in costs. The only penalty is a modest decrease in thermal efficiency.
Decreasing soot blower activity is recommended especially during seasons of
"excess" steam production. Methods exist for reducing activity, frequency,
and pressure for soot blowing.
First, as at Stellinger-Moor, many plants reduced the sootblowing
frequency. In this case, many blowers that had been blowing once per shift
are now schedueled to blow 1 to 3 times per week.
Secondly, the pressure has been reduced from 18 bars (1800 kPa)
(261 psia) to 14 to 16 bars (1400 to 1600 kPa) (202 to 232 psia).
The plant staff pointed out that the actual setting of blowing
frequency is a function of where the boiler is in its 4,000 hour cycle
between major overhauls. In the first 1,000 hours, they blow only one third
as often as before. If, however, they were in the last 1,000 hours, they
blow half as much.
In the last 2 years that the changes have been made, they have
experienced only five convection section tube failures per boiler, 10 in
all. Four of the five tube failures were repaired in April, 1977. Detailed
records are shown in the plant report to record maintenance activity. For
each major section of the plant, a master sheet is prepared having a
relevant standard sketch. These records for the April, 1977, repairs show
the 20 tubes that were replaced because they were thin and shows the four
tubes that burst.
Thus, the overall experience at Stellinger-Moor is that: (1)
unprotected water-tube wall tubes require partial replacement about once
per year due to corrosion, (2) High alumina refractory coating or welded
studs will protect tubes (3) the rapid increase of heat value of Hamburg
refuse has intensified many problems arising from overheating of the boiler
system, and (4) excessive use of steam-driven soot blowers causes corrosion
by repeatedly exposing fresh metal surface to new corrosive deposits. This
has been a common experience at many plants.
Zurich-Hagenholz
The unique features of the Hagenholz Boiler No. 3, by Martin,
featuring two long, open water-cooled passes ahead of the superheater have
already been mentioned. Figure U-11 shows another unique feature of this
boiler in that the refractory covering on the studded wall tubes extends
from the furnace up to above half the total height of the first pass. Thus,
despite the fact that this boiler furnace is fired at an extremely high
rate, the wall tubes have been protected from corrosive attack. The design
philosophy expressed by the plant manager was that the refractory coating
should extend 1 to 2 m (3.28 to 6.5 ft) above the level to which the
furnace flames might be expected to reach.
Officials have been most pleased with results. After 30,000
hours, the exposed first pass wall tubes have experienced only 0.1 to 0.2
mm (0.004 to 0.008 in) metal wastage.
The temperature at the top of the furnace level with the front
nose is 1,000 C (1832 F). Two-thirds up the first pass (where the SiC
stops), the flue gas temperature falls to 800 C (1,472 F). Using the
-------
0 Screen tubes at 3rd pass entrance
1 Coated water tube wall of combustion chamber
2 Coated water tube wall of ftrst pass
3 Water tube wall of second pass
4,5,6,7,& 8 Economizer bundles
9,10,11,& 12 Superheater bundles
FIGURE U-ll FURNACE/BOILER CROSS SECTION OF UNIT NO. 3 AT
ZURICH.-HAGENHOLZ (Courtesy Josef Martin Gmbh.).
-------
U-26
highly-thermally efficient SiC, a heat release rate of 94,000 Kcal/m3-hr
(10,530 Btu/ft3-hr) is possible based on a heat input rate of 33 Gcal/hr.
The SiC surface is rarely repaired on the 1,000 hour inspections.
SiC might be repaired on the 4,000 hour pldnned inspections. Studs and SiC
might be repaired once per year during major overhaul.
Screen Tubes. A minor function of screen tubes is to better hold
the furnace walls in alignment. A better flow of water is also a result.
Also, at many plants screen tubes have a third function. At Hagenholz, to
further reduce corrosion, flue gases pass between large, gently sloping
screen tubes at the base of the third pass. Flue gas temperatures are
reduced slightly to the benefit of superheater life. To some extent, these
relatively easy-to-replace screen tubes are sometimes considered "sacrifice
screen tubes". At the entrance to the third pass, the tubes have a diameter
of 70 mm (2.8 in) and a wall thickness of 4.5 mm (0.18 in). They are spaced
300 mm (12 in) apart.
Figure U-11a shows the details of the various tube arrangements
used at Hagenholz. Table U-1a shows typical gas temperature patterns.
The Hague
Three boilers installed in 1967-1968 by Von Roll at The Hague and a
later one in 1972 depict a part of the evolution of waste-to-energy boiler
design under (1) the impact of the rising heat value of refuse, and (2) the
need to reduce resulting boiler and superheater corrosion.
Figure U-12 shows the two boiler designs used at The Hague, the
superheaters are not fully shown in these cross-sections but will be shown
later. A more detailed figure of Boilers No. 1-2 is shown in Figure U-13.
The furnace in Units 1-3 were designed in 1966 for a maximum lower
heat value of 1,066 kcal/kg (3,270 Btu/lb) (8,653 kJ/kg). However, some dry,
bulky waste such as wooden crates and cardboard boxes can have a much larger
heat value, up to 4,000 kcal/kg (7,200 Btu/lb) (16,750 kJ/kg), and wetting of
such refuse to protect the furnaces and boilers has been necessary. Unit No. 4
was designed in 1970 for a lower heat value of 2,500 kcal/kg (4,500 Btu/lb)
(10,467 kJ/kg).
Boiler (Units 1-3). The overall boiler system was built in Holland
under a license for the Eckrohr design by Dr. Verkauf of Berlin. The first
three boilers are designed for a steam flow range of 18.8 to 37 tonnes/hr
(41,360 to 81,400 Ib/hr) at 40 bar (580 psia) and 425 C (797 F). The top of
the steam drum is 20.9 m (68.4 ft) above the ground.
Boiler (Unit 4). This boiler is slightly larger and much taller than
the first three, having a steam range of 18.8 to 40 tonnes/hr (41,360 to 88,000
Ib/hr). However, the maximum firing rate, 15 tonnes/hr, is the same as Units
1-3. The higher rating comes from an expected higher heat value in the refuse.
The top of the steam drum is 24.3 m (79.7 ft) above the ground floor.
In terms of predominant current practice for large furnaces, the
Hague plant is noteworthy in that the furnace sidewalls are not water-cooled.
The water-tube walled surface begins above the furnace and extends from there
upward to the tope of the radiation chamber (first boiler pass). The sloping
rear roof of the furnace is water-cooled but the tubes are completely covered
-------
U-27
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U-29
THE HAGUE UNITS 1, 2, 3
LONGITUDINAL SECTION
1 Refuse pit
2 Vibrating hopper
3 Feed chute
4 Feed grate
5 Main grate
6 Burnout grate
7 Clinker channel
THE HAGUE UNIT A
1 Refuse pit
2 Vibrating hopper
3 Feed chute
4 Feed grate
5 Main grate
8 Clinker pit
9 Settling tank
10 Combustion chamber
11 Boiler
12 Electrostatic precipitator
13 Stack
14 Feed water tank
15 Additional water tank
16 Condensate tank
17 Forced draft fan
18 Induced draft fan
19 Flue gas recycling
fan
6 Burnout grate
7 Clinker pit
8 Settling tank
9 Clinker channel
10 Boiler
11 Electrostatic precipitator
12 Induced draft fan
13 Stack
14 Forced draft fan
15 Overfire air fan
FIGURE U-12.
COMPARATIVE CROSS-SECTIONS OF THE TWO BOILER-FURNACE
SYSTEMS AT THE HAGUE PLANT. UNITS 1-3 WERE DESIGNED
IN 1965. UNIT 4 WAS DESIGNED IN 1971. (Courtesy of
Gemeentelijk Energlebedrijf Vuilverbranding)[Waste-
burning Energy Utility]
-------
U-30
by formed refractory block supported between the tubes. Thus, there is very
little cooling of the predominantly refractory furnace.
Boiler Convection Section. As can be observed in Figures U-12 and
U-13, the arrangement of the boiler convection tube bundles is unique in that
the gas, as it flows upward out of the first inclined tube bundle at an
estimated 600 C (1,112 F), is divided into two streams as it continues upward
in the third pass. Part of the gas flows into the second convection bundle,
also inclined, and then into the economizer. The remainder flows upward
through two passes of a tubular air heater. The amount of gas that flows along
each path can be controlled by two sets of multiple vane dampers, one located
at the outlet of the economizer and the other after the air heater. The design
estimate was that the gas leaving the economizer would be about 315 C (600 F)
and leaving the air heater it would be at 220 C (J»28 F). Actually these
temperatures will vary depending on the damper settings.
The convection section for Unit M is quite different from Units No.
1-3 as can be seen by comparing them in Figure U-12. The second pass is a
completely open water-tube-walled down-pass with the superheater banks
horizontal across the bottom of the third pass and thus far removed from the
furnace. The air heater was eliminated in Unit No. M and the third pass
contains not only the superheaters but also the two evaporator bundles and two
tubular economizers.
It appears that the slagging and corrosion problems that have occured
at The Hague have been caused primarily by the rapid increase in heating value
of the local refuse. The addition of overfire air jets plus wall-tube studding
and coating and reducing the firing rate somewhat appear to have largely
eliminated slagging and corrosion.
Dieppe (Deauvill-e)
Figure U-14 shows the plants at Dieppe and Deauville, France, which
need only relatively small fire tube boilers because most of the heat generated
is absorbed in drying and igniting the dewatered sewage sludge.
The only cooling of the furnace at Dieppe is the diagonal furnace
baffle shown in Figure U-lM. This baffle is formed of spaced, sloping tubes
about 120 mm (4.7 in) apart, which supports bricks shaped to fit the tubes. An
estimated 100-150 C (180-270 F) gas temperature drop occurs as the gases flow
upward along the underside of the sloping baffle than pass through the spaced
tubes above the baffle and turn toward the vertical firetube boiler inlet. It
is estimated that about one sixth of the total heat is absorbed by the baffle.
At Deauville, designed about 5 years later, there is no water-cooled
baffle. The furance volume is also much less than at Dieppe, which is about 80
m3 (2,823 ft3), and the furnace gases at Deauville pass directly to the
vertical firetube boiler.
The use of refractory instead of water-tube walls entails some loss
of thermal efficiency but this loss is not important at either plant so long as
there is ample steam generated to dry the sludge.
Each furnace has a 6-million calorie/hr oil burner, but they are
never used.
-------
U-31
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U-32
Outdoor tipping ari>a
Refuse pit
Crane and bucket
Feed hopper
Sludge Htoraec tank
Sludge pumps
Sludge dr>crj
Dried sJudge conveyor
Incineration grates
10. Furnace
11. Oil burner
12. Slower for dryer vapors
13. Primary «lr Mower
14. Residue quench ch.innel
15. Residue cart
It. Boiler
17. tbter-cooled condenser
18. Stean drum
19. Dust collector
20. Induced draft (an
21. Chimney
22. Cooling Baffle
Dieppe, Started Operation in 1971
Deauville, Started Operation in 1976
10.
11.
12.
1).
14.
IS.
16.
17.
18.
Crane
Refuse bunker
Feed hopper
Water storage
Sludge dryer
Dryer exhai.st blower
Secondary air blower
Furnace
Residue quench channel
Stein druv
toller
Shot cleaning feeder
Cr.lnney
Electrostatic precipicator
Air-cooled condenser
Induced draft fan
Transformer voon
Sludge storage
FIGURE U-14.
COMPARATIVE CROSS SECTIONS OF DIEPPE AND DEAUVILLE REFUSE-
BURNING PLANTS (COURTESY OF CITIES OF DIEPPE, DEAUVILLE,
AND VON ROLL, LTD. AND INOR S.A.)
-------
U-33
The vertical boilers at Dieppe were built by Sacoma with a heating
surface of 240 m2 (2,582 ft2). They are 6 m (19.7 ft) tall and 1.8 m (5.9 ft)
outside diameter. The 38? tubes are 52 mm (2 in) inside. The boilers were
designed to produce 7.5 tonne/hr (15,510 Ib/hr) of steam at 16 bar (1,600 kPa)
(232 psia). The saturated steam temperature is 180 C (356 F). Actually the
boilers operate at a pressure of about 10 bar (1,000 kPa) (145 psia) and an
output of 6.5 tonnes/hr (14,000 Ib/hr). Feedwater temperature is 140 C (284 F).
Design gas flow rate was 22,000 Nm3/hr (12,947 scfm). The flue gas
temperature leaving the boiler was about 350 C (662 F) when the plant started
up. However, it was found necessary to inject 5,000 m3/hr (2,943 cfm) of
secondary air by means of six nozzels located in the front wall. This air
diluted the flue gas and caused the boiler exit gas temperature to drop to
about 280 C (536 F). Such a high exhaust temperature represents a substantial
thermal loss but since there is ample heat for drying the sludge and, at
present, no other use for the heat, the loss is not serious for this particular
plant.
Every 3 months, each biler is drained and comnpletely cleaned
internally and externally by the plant staff using brushes and other small
tools.
Gothenburg-Savenas
Figure U-15 shows one of the three boilers built at Gothenburg by Von
Roll in 1971.
The three boilers are of the Eckrohr type built by Generator AB of
Gothenburg under license from Dr. Verkauf of Berlin. Rated steam capacity is
52.5 tonnes/hr (115,500 Ib/hr) of saturated steam at 22 bar (313 psia) (2,157
kPa). Overall height is 13 m (42 ft), width is 4.5 m (14.8 ft), and depth is
15.5 m (51 ft). There is no economizer. Steam temperature is 217 C (423 F).
This is another example of fairly large furnaces which are not
water-tube walled. The water-tube wall is seen to begin near the top of the
furnace at about the level of the top of the refuse feed entrance. The carbon
steel tubes are tangent welded, 76 mm (3 in) in diameter, and 4 mm (0.16 in)
thick.
The front and rear furnace walls are spaced water tubes covered with
refractory. This minimal cooling of the furnace coupled with a period of
unusually high heat value of the refuse may have combined to aggravate slagging
and roof tube problems. Above the nose of the front wall can be seen a
separate water-tube-walled combustion chamber for burning oil. Half of the
rated heat output of each boiler can be generated using low-sulfur, No. 5 fuel
oil.
Originally, each boiler was equipped with 21 soot blowers. There
were two sets in the first pass. Although the plant is for district heating
only (hence, does not need high-temperature steam), a small superheater was
placed in the third pass to generate superheated steam up to 300 C (572 F) for
soot blowing only. When the soot blowers were not in use, the superheated steam
is condensed in a heat exchanger in the boiler drum. The soot blowers thus were
assured of dry steam so as to avoid any erosive impact on the boiler tubes by
water droplets. However, they probably cleaned the tubes too well and too often
with the result that the bare tubes were exposed to corrosion and probably
erosion. In 1974, it had been first noted that the first pass blowers were
-------
U-34
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U-35
cleaning exceptionally well. Accordingly, 11 of the 21 blowers have now been
removed and the 10 remaining are used less frequently.
Some wastage has occured in the roof tubes of both the first and
second pass. This is being countered" by a sprayed-on coating of silicon carbide
about 8 mm (0.31 in) thick. The same coating has been sprayed opposite the soot
blowers in the second pass. The durability of this coating appears good after 1
year but has not yet been fully determined.
Ten sections of alloy-clad steel tubes are being tried in the upper
middle position of the wall of the second pass. These "sandwich" tubes, made
by Sandviken, have a wall thickness of 7.1 mm (0.28 in) and are coated with an
extruded stainless steel layer which is 1.6 mm (0.063 in) thick. Although these
tubes cost 10 times as much as carbon steel tubes, experience with an entire
pass formed of these tubes at the Hogdalen plant, built by Vereinigte
Kesselwerke of Duesseldorf south of Stockholm, indicates that for conditions at
that plant they are worth the cost in minimizing tube wastage.
To monitor first pass gas temperature, thermocouples have been
placed about 7 m (23 ft) above the grate.
In the third pass, which contains the boiler convection sections
and superheater, some tube erosion by soot blowers has occurred. This was
first countered by means of alloy half-round shields 1 mm (0.40 in) thick
made of Swedish steel designated 23-43. The shields were tack welded to the
tubes directly opposite the soot blowers. For simplicity, these were later
replaced by alloy angle irons strapped to the tubes. The angles are made of
20 percent chromium and 10 percent nickel steel. This material costs 40
skr/kg ($3.60/lb). They are fully successful in protecting the tubes from
soot-blower action and appear to survive about 6 months before requiring
replacement.
There is some evidence of slag accumulation on the refractory
walls. As changes were made in wall-tube coatings and secondary air
direction, this slag appeared to accumulate higher up on the walls. Some
thought is being given to the possible use of air-cooled wall blocks low in
the furnace to help alleviate this problem.
Second Pass. All of the wall coatings, roof coatings, and
convection-bank shielding have impaired somewhat the total boiler heat
absorption. To counter this loss, it is planned shortly to install in the
second pass three vertically suspended plattens of water tubes to increase
heat absorption in that pass.
Uppsala
The Uppsala waste-to-energy plant is a part of a much larger
environmental improvement and energy conservation program that was started
by the City Council in 1960.
The first delivery of heat was in August, 1961, from a portable
oil-fired boiler, and the first permanent oil-fired hot water generator at
the Kvarngarde Plant began operating in September, 1962. Since then,
expansion has materialized into a larger oil-fired hot water station in the
Bolanderna Plant and in the waste incineration plant, which began operating
at Bolanderna in 1961 where the steam produced is used to heat water for
district heating. The initial installation of two furnaces rated at 3
tonnes/hr and supplying hot gas to two waste heat boilers was built in 1960
-------
U-36
by Kochum-Landsverk and began operation in 1961. A third similar but larger
(3.5 tonne/hr) was added in 1965. A fourth furnace system, burning 5
tonnes/hr and feeding a third boiler, began operation in 1970. This newer
installation, built by Bruun and Sorensen, the principal subject for the
report on this plant, is shown in Figure U-16.
As with many small refuse-fired furnaces, these four furnaces are
not water cooled. Their completely refractory construction has been
satisfactory except for a major error in installation of too-widely spaced
support anchors in Furnace No. 4. This has caused much breakage and some
occasional collapse of firebrick. This has now been corrected.
All three boilers serving the four refractory furnaces are
water-tube boilers producing saturated steam at 15 bar (217.6 psia) (1,500
kPa). Saturation temperature is 138 C (389 F). The first two boilers use
forced circulation. Boiler No. 3, built by Maskinverken, Kallhall, Sweden,
under a license from Combustion Engineering Co. of Windsor, Connecticut,
U.S.A., uses natural circulation. The boiler steam capacities are:
No. 1
No. 2
No. 3
TOTAL
tonne/hr
10
15
J5
40
Ib/hr
22,000
33,000
33.000
88,000
The three boilers and four furnaces are cross manifolded so that
various combinations can be operated. However, all three boilers and all
four furnaces are rarely operated all at the same time.
Boiler No. 3» the newest boiler, is formed of an outer enclosure
of wall tubes plus banks of horizontal convection tubes. It receives hot
gases from a cyclonic after-combustion chamber.
The maximum gas temperature entering the boiler is about 700 C
(1,292 F). Incidentally, with 1,000 C leaving the furnace and 700 C
entering the boiler, this 300 C cooling represents a substantial energy
loss in passing through the after combustion chamber but, at the same time,
that cooling undoubtedly contributes to the slag-free, trouble-free
operation of that chamber as a gas mixing, burning, and dust removal
device. The nominal capacities of the components are as follows:
Furnace No. 1
Furnace No. 2
Furnace No. 3
Furnace No. 4
TOTAL REFUSE CAPACITY
Boiler No. 1
Boiler No. 2
Boiler No. 3
TOTAL STEAM CAPACITY
tonnes/hr
3.0
3.0
3.5
5.0
tons/hr
3.3
3.3
3.9
tons/day
72
84
84
108
10.0
15.0
15.0
11.0
16.5
16.5
88,000 Ib/hr
However, these total capacities are only ratings as the plant was
not intended to and never operates all components at full capacity. Usually
some components are down for service. The actual average plant burning rate
-------
VO
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-------
U-38
for 1976, 51,000 t/d was the equivalent of an average rate of about 200
tons/day based on a 5-day week. This is about 52 percent of rated capacity.
Figure U-17 shows a partial elevation of the new portion of the
plant added in 1971.
The relatively low steam temperature, 198 C (389 F), and the
customary firing at less than rating assures that boiler corrosion is
avoided at Uppsala.
Firetube Boilers
In three of the plants visited, most of the thermal energy
released is utilized to dry sewage sludge from the adjacent wastewater
treatment plants. The partially dewatered sludge is then burned with the
refuse. Thus, there is no need for high-pressure, high-temperature steam
and no need for high-pressure water-tube boilers. Hence, the much less
costly firetube boilers are used. The plants are small so 'that
water-cooling of the refractory furnaces is not required. Accordingly, the
hot gases pass from the refractory-walled combustion system into a simple,
vertical firetube boiler.
Horsens
Originally the plant at Horsens, Denmark had no boiler (see Figure
U-18). Instead the hot, partly cleaned gases leave the combustion chamber
at two points. From the top, they could flow vertically upward into a
water-sprayed cooling chamber and, hence, to the electrostatic
precipitator; or they could leave from the bottom hopper or horizontally
through a refractory-lined duct to enter the rotary sludge dryer. However,
the growing urgency throughout Denmark to conserve all available energy led
in 1977 to replacement of the spray cooler by a waste heat boiler to supply
hot water, not steam, for the existing district heating system. This is a
sitfple vertical firetube boiler built by the Danish Stoker and Heating
Company. It contains 540 tubes, 57 mm in diameter (2.25 in) and 4.5 m (14.8
ft) long. Its capacity is 7 Gcal/hr (27,776 M Btu/hr) 29.308 GJ/hr. Heated
water leaves the boiler at 110 C (230 F) and returns from the system at 80
to 90 C (176 to 184 F).
The top (exhaust) end of the boiler is accessible so that once
every 2 weeks all of the 540 tubes can be cleaned of soft ash deposits by
means of a powered rotating wire brush. This takes 6 to 7 hours every
Monday morning.
Hot Water Boilers
Two very large plants built by Volund in Copenhagen were visited.
They generate only hot water for district heating. Each plant,
Copenhagen-Vest and Amager, has a capacity of 864 tonnes/day (950 tons/day).
The corporate position of Volund is to avoid building very high
temperature steam systems, i.e., above 450 C (842 F). They will not sell
anything that would likely have corrosive failures within a year or two.
Volund has only two steam plants, both in Japan. They produce steam up to
the 350 C (662 F) level required.
-------
U-39
1. Crane and Bucket
2. Refuse Bunker
3. Crane Operator's Station
4. Furnace
5. Afterburner Chamber
6. Steam Boiler
7. Electrostatic Precipitator
8. Induced Draft Fan
9. Primary Air Zones
10. Residue Conveyor
11. Waste Oil Tank
FIGURE U-17. ARRANGEMENT OF UPPSALA PLANT
(COURTESY BRUUN AND SORENSEN)
-------
U-40
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U-41
The West and Amager plants, both built in 19.69 have Eckrohr
vertical water-tube wall boilers completely separate from and following the
combustion furnace. Figure U-19 shows these plants. The furnaces are
refractory followed by water-walled boilers, i.e., Volund units are not
"water-tube wall incinerators". The Eckrohr boilers were built under a
license from Professor Dr. Vorkauf of Berlin, W. Germany.
Figure U-20 is included to better show the water tube boiler
although it depicts the Moscow plant built in 1975-1976. The boiler
consists of four vertical water-tube walled passes which are completely
separate from the combustion chamber and rotary kiln.
When asked why the Eckrohr boiler was used instead of the
routinely specified Volund boiler, the reply evoked the Eckrohr features—
features that seemed popular in several other places in Europe:
• The four corner tubes are used not only to carry down- stream
water but also provide the structural support for the whole
boiler, thus reducing construction costs.
• The heat transmission is excellent.
• The circulation pattern is good.
• It has high efficiency.
• It is a natural circulation boiler.
The market for energy demands slightly higher temperatures at West
than at Amager as follows:
Energy Form
Water temperature leaving
plant
Water temperature returning
to plant
Heat output
Pressure (working)
West
"superheated" water
160 - 170 C
140 C (284 F)
21.5 Goal/hour
16 kg/cm2 (225 psi)
Amager
hot water
115 - 120 C
70 C (158 F)
20 Goal/hour
6 kg/cm2 (85 psi)
The key reason for higher temperatures at West is that an early
customer was the Copenhagen County Hospital that needed hotter water for
steriliztion and air conditioning.
The combustion gas inlet temperature to the boiler is around 800 C
(1472 F). The outlet combustion gas temperature range from 280 to 350 C
(536 to 662 F).
The boiler of Unit No. 4 at the West plant has 54 percent more
heating surface area than each of the Units No. 1-3: 1,713 m2 (18,432 ft2)
compared to 1,115 m2 (12,000 ft2).
A "Scott Wall", not found in many boilers, is a wall of tubes in
the middle of a pass. Its purpose is to absorb more heat, to help reduce
gas temperature, to increase residence time, and to redirect flue gases to
the hoppers so that more fly ash is dropped out.
Plant staff have been happier with Volund's Unit No. 4. It can
process 14 tonnes (15 tons) of refuse per hour. The dust accumulation on
-------
U-42
FIGURE U-19. ENGINEERING DRAWING OF COPENHAGEN: AMAGER (Courtesy
Of Volund)
-------
U-43
] -. 4,. - +
FIGURE U-20. MOSCOW PLANT SHOWING FOUR-PASS WATER WALL WASTE HEAT BOILER
SEPARATE FROM THE FURNACE (Courtesy of Volund)
-------
U-44
the tubes is lower and the boiler is easier to clean. The operational
availability is better and there have been longer run times.
The Volund organization is proud of the lack of corrosion in any
of the four furnaces over the 7-year period.
Units No. 1-3 Unit No. 4
Hours per year performance 6,500 6,500
Years of operation xj_ x2
= 45,500 13,000
Number of furnaces x3_ x1
Hours without corrosion 136,500 13,000
Superheater Sections of Boilers, General Comments
The following additional discussion is required because many of
the superheater sections have suffered metal wastage. Nine of the fifteen
plants visited employ superheaters to heat saturated steam from the boiler
to temperature levels that enable relatively efficient steam turbine
operation. Six of the plants do not generate power and therefore
superheated steam is unnecessary.
The degree of superheat employed is a matter of judgement: the
higher the steam temperature the more efficient the plant can be, but the
more likely it is to suffer superheater tube corrosion. The design steam
temperatures of the 9 plants using superheat are as follows:
Date of
First Steam Temperature
Operation £ F
Werdenberg-Liechtenstein 1974 395 743
Baden-Brugg 1970 400 752
Duesseldorf 1965,1972 500 932
Wuppertal 1976 350 662
Krefeld 1976 376 710
Paris - Issy 1965 410 770
Hamburg-Stellinger Moor 1972 410 770
Zurich-Hagenholz 1973 420 788
The Hague 1968,1974 425 797
There is a surprising spread in temperatures here indicating a
broad difference in philosophy toward the desired efficiency of energy
recovery, although most of the plants are seen to operate within the
relatively narrow range: (371 to 427 C) 700 to 800 F. Achieving reliable
operation at this level when burning potentially corrosive municipal
refuse, calls for great care in design and operation because of the
possibily chemically active nature of the flyash which inevitably coats the
superheater tubes. To cope with this threat there are many different
configurations of superheaters in use and a "best" design cannot yet be
chosen. The development process is still under way. Nevertheless, certain
preferable features of successful superheaters are emerging.
-------
U-45
Protective Deposits
Of major importance is to design the superheater and to operate in
such a way that a hard deposit of flyash always coats the tubes, because
such a deposit helps to protect the tube metal from corrosive attack. The
reality of this protective effect has become apparent to almost every plant
op-erator who has sought to operate a clean boiler through over zealous use
of soot blowers. On the other hand, to maintain good heat transfer the ash
deposit must not be permitted to become too thick.
A protective ash coating ranging between a minimum of about 3 mm
(0.120 in) and a maximum of 15 mm (0.6 in) appears to be in the desirable
range. Safe methods for controlling the thickness of this ash deposit will
be discussed later.
Deposit Temperature
The whole boiler and stoker design and operation are crucial in
arranging to keep the protective ash deposit on the superheater tubes from
becoming too hot. At some temperature, not well defined, that protective
deposit can reach a level where it is no longer protective, but becomes
chemically active. The mechanism by which the ash constituents will attack
the tube metal is not clear, but the various theories on tube corrosion
will be discussed later under corrosion. It appears that if the ash deposit
never exceeds a temperature of about 1300 F (7M C) the deposit is benign
and serves as a protection. In controlling the superheater tube to a safe
temperature level, plant operation is extremely important because
"excursions" in combustion rate can overheat an otherwise "safe" design. On
the other hand, some superheaters appear much more vulnerable to the
effects of temperature overruns than others, and thus some will tolerate
some gas temperature fluctuations without overheating the protective ash
deposits.
Example of Third Pass Superheater Location (Werdenberg - Liechtenstein)
At this stage of superheater development it appears that the most
successful design places the superheater as far away as possible from the
flame-filled furnace. Earlier Figure U-3 showed the boiler-furnace
superheater arrangement at the Werdenberg-Liechtenstein plant. After the
hot gases rise vertically out of the furnace they are required to flow
through 2 vertical water-tube-walled passes before they enter the 2 banks
of superheater tubes in the third pass. These banks are horizontal and
located at the entrance to the bottom of the pass. As in most plants,
superheat control is achieved by attemperator which injects treated
feedwater into the steam as it moves from the first bank of superheater
tubes to the second bank.
The gas flow pattern is straight upward through the banks as the
tubes are in line and not staggered. They are spaced 100 mm (4 in) on
centers in both directions. In future designs the manufacturer favors more
gas space between the superheater tubes. The design temperature for the gas
entering the first superheater section is 650 C. (1203 F).
A single cascade of falling steel shot for one period of 4 minutes
in each hour cleans the economizer and superheater. The top row of
-------
U-46
superheater tubes is protected by steel shields from the impact of falling
shot. Every 5,000 hours the economizer and superheater are washed by a
German company that specializes in boiler cleaning.
The plant began operation in April 1974. In 1974-1975, the new
plant was operated at an excessive rate amounting to a 20 to 29 percent
overload. Formal warning to the owner by the manufacturer of the possible
deleterious consequences of such overloading led to subsequent operation at
more nearly normal loading.
At the time of our visit, May 2-4, 1977, there appeared to have
been no permanent damage resulting from the period of overloading. However,
at the end of the first 11,000 hours of operation in 1976 the first row
(bottom) of horizontal superheater tubes had to be replaced because of
erosion. This could very well have been a direct result of overfiring the
system. The manufacturer expects that the first (bottom.) row of superheater
tubes may need replacement every 10,000 to 11,000 hours owing to erosion or
corrosion or a combination of both. Operations at this plant has not
continued long enough to reveal whether this actually is required. The fact
that only the first row of tubes was affected suggests that possibly the
protective deposit was mechanically eroded away by high-velocity flyash
particles during the period of overloading that occurred in 1974-75.
Example of First Pass Superheater Location (Duesseldorf)
In contrast to the conservative third pass design at Werdenberg,
which was made in about 1971 in preparation for construction in 1972 to
1971*, a much more compact arrangement was used at the much larger
Duesseldorf plant which started up in 1965 and was shown in earlier Figure
U-5.
In this plant the superheater is located immediately above the
furnace at the top-of the first or radiation pass. Hindsight now makes
clear that this superheater is more vulnerable to corrosion than the newer
Werdenberg design. Another major factor encouraging-more superheater
corrosion at Duesseldorf is that the steam temperature is nearly 111 C (200
F) higher than at Werdenberg 500 C (932 F) versus 395 C (?43 F). This high
temperature is required because the steam is supplied to the adjacent
Flingern municipal power plant.
The relatively close proximity of the superheater to the furnace
flame in the Duesseldorf plant was a natural choice based on fossil-fuel
practice. At the time these boilers were designed, 1963-64, although tube
corrosion had already appeared in other waste-burning plants, the causes of
that corrosion were unclear, and there was much inconclusive debate over
many different theories of corrosion that had been advanced. Even today
(1978) there remains considerable disagreement as to the principal causes
as discussed later under corrosion. However, the relatively mild
superheater corrosion at the small Werdenberg plant just described, and the
so-far negligible corrosion at the larger but similar Hagenholz plant at
Zurich, indicate that the remote positioning of the superheater away from
the furnace flame is an essential factor in avoidance of corrosion.
-------
U-47
Dacha Configuration
A more recent design of superheater being tried is to have the
vertically suspended platens located as shown earlier in Figure W-21 in a
horizontal second pass which follows the radiation pass. It is called the
Dacha boiler because of its long, strung-out shape (named after the female
dachshund). This superheater arrangement enables tube cleaning by means of
periodic mechanical rapping instead of by the more forceful conventional
steam-driven soot blowers. This again is a clear recognition of the
protective value of the ash deposits on the tubes. Experience indicates
that periodic rapping removes enough of the deposit to maintain acceptable
heat transfer while allowing enough of the deposit to stay on the tubes so
that they are protected against chloride attack. It is too early to tell
whether this is effective in reducing superheater corrosion but the
proponents of this design have been encouraged by trouble-free performance
so far.
Superheater Protection
Although some of the concepts presented in the following quotation
from Stabenow are slightly at variance with the interpretations just given
regarding superheater design, in the main they constitute sound advice on
the design, care and operation of superheaters.
"Many superheater problems do not arise during normal operation
but are easily caused during start-up periods. The following operational
guidelines should be considered to minimize start-up corrosion problems:-
Startup Situation That Leads to Unfortunate Consequences
"1. Superheater is dry until boiler water reaches 212°F.
a) Superheater tubes will reach gas
temperature during this period which may
cause tube deformation.
b) Overheated tube surfaces will burn-off
deposits and protective coatings.
c) During initial start-up, unitl full
furnace temperature is attained unburned
volatiles containing CO, 1^0, HCL, SOg and
other corrosive components will attack hot
superheater metal surfaces.
d) Uncooled superheater tubes are especially
vulnerable to stratified gas streams
during start-up period.
e) Boiler waterwall tubes containing hot
circulating boiler water are not subject
to such corrosive attacks. ( 500 F)
f) As soon as boiling takes place in the
steam drum, sudden shock-like cooling of
the superheater tubes takes place and
causes severe stresses in tube support
attachments.
g) Even when using alloy steels for the
superheater tubes, the problem is not
-------
U-48
solved but the tube life is only extended
for a longer period between replacements,
if the following precautions are not
followed.
Solution to the Startup Problem
"2. Recommendations for protection of superheater tubes during
start-up period.
"Superheater tubes in incinerator boilers may be
considered more vulnerable to corrosion than any other
boiler section, especially if they are subject to
frequent start-ups. The use of non-drainable
superheaters should be avoided since venting during
the warm-up period may cause difficulties due to
entrapped water in some tube loops. In contrast a
horizontal superheater is easily drained and vented
and steam can be bled-off as soon as the boiler water
reaches the boiling point.
"Due to the much slower heating-up of refuse fired
boilers the superheater tubes are subjected to a much
longer exposure to the rising furnace gas temperatures
which represents a critical period for possible
corrosive attack.
"In plants, where multiple incinerators are installed,
saturated steam may be drawn from an operating boiler
to keep the superheater tubes cool and free from
stresses during the start-up period. Once the boiler
under start-up has begun to generate its own steam,
the superheater section should be vented continuously
until the boiler is put into service.
"It is also important to keep a close watch on the
stack temperature as gas temperatures below the
dewpoint 177 C (350 F) may cause corrosion.
Utilization of the start-up or auxiliary burners will
assist in heating up the boiler much more rapidly thus
reducing the period of exposure of possible
superheater tube corrosion and consequently prolonging
their life expectancy.
Recommendations for Normal Operation
"3. Effects of combustion in the furnace on superheater tubes
during normal operation.
a) The life of the superheater tubes is
endangered not only during the start-up
period until full steam flow through the
tubes has been established, but the damage
can also occur during continuous operation
resulting from poor combustion conditions,
excessively deep refuse beds, lack of
proper undergrate air distribution and
insufficient overfire air penetration
through the burning zones.
-------
U-49
b) The furnace gas temperature must be
reduced by radiant absorption in the
primary and secondary furnaces to a point
below 1400 F, before entering the
superheater to prevent heavy fly-ash slag
deposits which can be removed only by
means of pow.er tools during semi-annual
shut-down periods. A multipass boiler
design has proven to alleviate this
problem to a minimum.
c) Assure uniform refuse feed rate and
distribution to stoker to obtain a thin
fuel bed that will ignite and burn rapidly
and continuously under controlled furnace
temperature conditions. Pile up of solid
waste displaces the fire and causes
distillation of volatiles which, if not
quickly ignited, will cause severe
corrosion. CO formation is the best
indicator of incomplete combustion. Where
CO can be measured, corrosion is apt to
occur. To overcome incomplete combustion
three preventive design steps must be
taken:
aa) All smoldering gases from the nearly
completed combustion in the area at
the rear end of the stoker must be
reheated and ignited in the high
temperature combustion zone for
final burn-out to reduce to a
minimum the occurence of traces of
non-aqueous condensibles.
bb) The violently burning solid waste
mass at the front end of the stoker
must receive intensive and highly
penetrating, turbulent, and overfire
air jet streams, preheated for rapid
completion of combustion, thus
eliminating the presence of any CO
or other harmful corrosive
constituents in the main gas stream.
cc) As the furnace is operated under a
slight negative pressure
infiltration of air other than that
supplied by the forced draft fan,
must be eliminated. Air leakage at
the feed chute section can cause
heavy slag formation, while false
air entry at the point of residue
discharge can cause wide
fluctuations in the stack gas
composition and its C02 content thus
-------
U-50
resulting in combustion instability
and reduced overall efficiency.
"The intensity and distribution of the overfire air as
previously described will greatly reduce the harmful
constituents in the gas stream, reduce the fly-ash
carry-over and greatly prolong the life of the
superheater and boiler tubes assuring long "on-stream"
availability of the steam generating incinerator
during the full annual season.
"Sootblowers can also be a source of trouble both in
the superheater and boiler sections. Excessive
sootblowing has a sandblasting effect on directly
exposed tubes and may penetrate through the protective
oxide coating on the tubes thus imperiling the bare
metal by corrosive attack and severe pitting. For this
reason alloy shields or welded studs covered with
silicon carbide should be applied to the tubes at
points in close proximity to the sootblower blast.
"Uneven distribution caused by low gas velocities over
the tube sections will result in unbalanced heating of
the tubes and may cause stress corrosion primarily at
tube bends".
Superheater Tube Materials
Many superheaters are made of carbon steel. However, the tube
corrosion experience in most units has encouraged a trend toward low-alloy
and, in some cases, high alloy steels. Table U-2 shows the superheater tube
materials used in most of the plants visited.
Tube Shields
Many different forms of metal tube shields have been tried,
sometimes on water-tube walls but usually on superheaters. The predominant
form is a half round shape made of alloy tubing with steel clamping straps
attached as shown in Figure U-21. The most common material used is Sicromal
as defined in earlier Table U-1.
The shield is clamped or tack-welded to the tube. Inevitably there
is a thin air space between shield and tube which can become filled with
fine ash so that heat transfer is impaired. Thus the shield metal
temperature is inevitably higher than the tube metal and it, thus, is
subject to more rapid corrosion. However, replacement of corroded shields
is much simpler than replacing tubes and can be scheduled during routine
maintenance periods. At Duesseldorf the shields are replaced every 3
months. At Baden-Brugg they are replaced every 6000 hours. Others last much
longer. It depends on the severity of exposure.
Sprayed silicon carbide coatings have been tried without long term
satisfaction. Coatings of alloy applied by welding are being tried at
Duesseldorf (See Figure U-22).
A few superheaters have been partially protected by rammed silicon
carbide held in place by welded studs. This method has not been as
successful as it has been in protecting wall tubes. It is much more
-------
U-51
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-------
U-52
FIGURE U-21. HALF SHIELDS FOR CLAMPING ON SUPERHEATER LEADING FACE AT
BADEN BRUGG (Battelle Photograph)
-------
U-53
FIGURE U-22.
HARD COATING ON BENDS OF SUPERHEATER TUBES TO BE INSTALLED
IN THE SECOND PASS OF BOILER NO. 5 (Photograph May 17, 1977)
-------
U-54
difficult or impossible to apply in many superheaters and, if used
extensively, would greatly reduce heat transfer.
Comments About Specific Superheaters
Braden-Brugg Superheater
An effective compromise between the vulnerable position of the
superheater at Duesseldorf and the remote location in the Werdenberg boiler
is the Baden-Brugg plant shown earlier in Figure U-21*. This plant was first
operated in November 1970.
In this arrangement, as the gases reach the top of the first
boiler pass they are turned 180 degrees and then pass downward through the
second water-tube walled pass which contains the superheater. Final steam
temperature is 400 C (752 F). The superheater tubes are vertical and .are
suspended from the top. They are 4 m (13 ft) long, 33.7 mm (1.32 in) dia.
and are spaced on 120 mm (4.7 in) centers. The superheater steel is 14
percent chromium, 3 percent molybdenum. At first they were 2.9 mm (0.11 in)
thick. Later the thickness was increased to 3.2 mm. Now they are 4 mm (0.15
in) thick. The final thick walled tubes were installed in Boiler No. 1 in
1972 and in Boiler No. 2 in 1974.
Although the gas flow through the superheater is mainly parallel
flow, the horizontal entry of the gases into the superheater from the first
pass is actually cross flow. Thus the hot gas, at a temperature of 700 C
(1292 F), carrying potentially erosive and corrosive flyash, impinges
against the 23 vertical superheater tubes in the first row. Initially this
caused some tube wastage and the first row of tubes was replaced in 1972
after barely a year's operation. Figure U-23 shows the longitudinal failure
of a Baden-Brugg first row superheater tube. Accordingly, in October 1973,
after 11,290 hours of operation in Boiler No. 1, half shields made of
Sicnomal 10 steel tubing (see Figure U-21) were clamped over the leading
face of the first row only. This is an 18 percent chromium alloy. Thicker
walled super-heater tubes have also been installed and an additional 17,810
hours had been achieved at the time of our visit on May 9, 1977. The
shields must be replaced about every 6000 hours. The plant management
estimates that the present superheaters will last 60,000 hrs. Again, the
fact that only the first row of superheater tubes has so far been affected
indicates that erosion of the protective ash coating may be exposing the
tubes to corrosion.
Although steam-actuated soot blowers are available for cleaning
ash deposits from the superheater tubes they are not used because of the
wide-spread experience that soot blowers often accelerate tube wastage by
removing the protective ash deposit. These superheaters are cleaned
manually every 6 weeks, on weekends, by means of compressed air nozzles
which can be inserted through the access doors in the wall of the
superheater passage.
Duesseldorf
While the vulnerable position of the Duesseldorf superheaters has
already been described in this section, it is instructive to follow the
experience with corrosion there and the steps taken to combat it. The
-------
U-55
FIGURE U-23.
BADEN-BRUGG RUPTURED FIRST ROW SUPERHEATER TUBE
(Battelle Photograph)
-------
U-56
following covers the superheaters for Units 1-4 built in 1964 and the later
Unit 5 built in 1971.
In all boilers at this plant, the high-temperature section of
superheater is a suspended platen type located at the top of the first open
boiler pass as shown earlier in Figure U-6. Experience at many plants has
indicated that it would be desirable to position the superheater at a
greater distance from the main furnace. For one thing, the gas cooling rate
is relatively slow as it rises in the first open pass toward the
superheater. Thus, if there are frequent burs'ts of high temperature gas
leaving the furnace because of the inhomogeneity of the refuse causing
erratic burning, there are then likely to be moments of excessive gas
temperature striking the exposed bends of the suspended platens. Also, in
the case of Units No. 1-4, shown earlier in Figure U-5, there is direct
radiation from the furnace to the platens which may contribute to
overheating any ash deposits on the platens.
The rest of the superheater sections in this plant are horizontal
type at the top of the second pass. Thus, the flow of steam through the
superheater sections is counter flow, with the steam first meeting
partially cooled gases as they pass through the horizontal sections in the
second pass. Then the partially superheated steam flows to the suspended
platen section in the first pass where it meets hotter gas in a range of
700-800 C (1292-1472 F).
The superheater for Units No. 1-4 is made up of three sections.
The superheater for No. 5 built in 1971 is in two sections. Material in
these five units and dimensions are as follows:
Units 1-4 Unit 5
First Section Second Section
Carbon: 0.12 - 0.20 0.1 - 0.18 0.15
Silicon: 0.15 - 0.35 0.15 - 0.35 0.15 - 0.5
Manganese: 0.5 - 0.7 0.4 - 0.7 0.4 - 0.6
Phosphorus: 0.04 0.04 -0.04
Molybdenum: 0.25 - 0.35 0.4 - 0.5 0.9 - 1.1
Chromium: None 0.7 - 1.0 2.0 - 2.5
Tube Diameter: 33.7 mm (1.33 in) 38 mm (1.5 in)
38 mm (1.5 in) 38 mm (1.5 in)
31.8 mm (1.25 in) 44.5 mm (1.75 in)
Tube Spacing: 150 mm (5.9 in) 150 mm (5.9 in)
150 mm (5.9 in) 150 mm (5.9 in)
600 mm (23.6 in) 600 mm (23.6 in)
Experiences with Superheater Corrosion. Thoemen, plant manager,
has recently (1976) published a review of corrosion: "In the time from
1970 to 1972, fireside corrosions of a considerable rate appeared on the
final stage platen superheaters on Boilers No. 1-4, which are installed at
the upper end of the first flue. The tube side, being directed against the
gas flow, showed a rapid material wastage at a rate up to 4,5 x 10""" m/h
(0.00018 in/hr). At first, this corrosion was interpreted as chlorine
corrosion under lack of oxygen. Gas analyses, however, showed, that in
these parts of the boiler, sufficient oxygen is present at any time. Only
extensive analyses of t'he deposits of the tubes have shown a
*Thoemen, K.H., "Review of Fours Years of Operation with an Incinerator
Boiler of the Second Generation", Proceedings ASME Conference on
Present Status and Research 'Needs in Energy Recovery from Wastes",
p 171-181 Hueston Woods, Ohio, Sept. 1976, ASME, New York, NY 10017.
-------
U-57
chlorine-corrosion released by transformation of alkalichlorides into
sulphates within the deposits. As a partial remedy, the endangered tube
parts were provided with protective shields in form of flat steel. This
proved to be sufficient, but as these steel bars are cooled insufficiently,
an inspection and eventually a partial renewal has to be made at every
shut-down of the boiler, approximately every 3 months. To cut down the
maintenance costs, another tube material was sought for better resistance
against this corrosion. This is an austenitic steel which has the German
standard sppecification: xSCrNi Nb 1613.
Its composition is:
C = (equal or less than ) 0.08 percent
Si = 0.25 - 0.55 percent
Mn = 1.10 - 1.4 percent
Cr = 15 - 17 percent
Ni = 12 - 14 percent
Nb = (more than) 10 times C.
"In 1972, platens of this material were installed. On occasion of a boiler
inspection, after 16,000 hr, no substantial material wastage could be
found. But lately (1976\ the first failure of these platen tubes happened.
The loss of material is strictly limited to the outside surface of 90° bend
of the U-shaped tube. The horizontal and vertical parts of the tubes are
completely unharmed. By the appearance of this damage, it can perhaps be
concluded that by bending the tubes not only a reduction of the thickness
of the outer wall occurs, but a structural change of the material occurs
too, which makes it sensitive to corrosion. Tests about this matter are
running, but not yet concluded, so that final statements cannot be made. In
relation to the corrosion rate of 1970, these tubes have been a significant
improvement, although no protective shields have been used on these tubes.
"Returning to the boiler which is in service since 1972, No. 5, it must be
said, that similar good experience with this unit has not been achieved.
Contary to the anticipated effect of a reduced susceptibility for
corrosion, considerable difficulty arose with this new unit too. There
occurred corrosion phenomena of kinds not known before.
"Although the corrosions of the wall tubes of the first boiler pass in No.
5 are under control, a totally different picture is presented in the
superheater area. Both the final stage superheater and the convection
superheater were affected by numerous attacks and damages since startup.
The tube failures of the superheaters have been as follows:
• 22 failures of convection superheater tubes (See No. 4
of Figure U-6
• 13 failures of final superheater tubes (See No. 2 of
Figure U-6).
"An accumulation of that kind of tube failures caused by corrosions has not
been observed in former years. The final (suspended platen) superheater
which is of nearly the same design and arrangement as in Boilers No. 1-4,
had to be renewed in two steps in the years 1973 and 1974. The cause of
this failure was a fault in the design. The 14 tube? of each platen
superheater had been welded together instead of being clamped. Hereby the
tubes were hindered in their expansion so that after a short operation
-------
U-58
period, they were completely twisted and no longer hung vertical at the
leading edge of the tubes, not only the outward tubes were endangered, but
the superheater platens presented larger surfaces to the corrosion attack.
With the renewal of the first half of this superheater, the first four
outer tubes of each platen were made of the same austenitic steel mentioned
earlier. But after about 6,000 hours of operation, one of these tubes
failed and the others showed considerable attack too. Investigations were
made in order to trace the cause of this short tube life, compared to that
of the same tubes in the other boilers. A new phenomenon was found not
known up to that date. On the presuperheater too, being located at the
upper end of the second gas pass as a convection tube bundle, corrosion
occurred to an extent not known from other boilers. Not only the tube bends
were affected, but at the middle section of the tube bends, the material
was carried away at the top side, the material loss at the middle sections
occurred at both sides of the tubes at an angle of about 30° to the
vertical axis as a longfaced erosion. In addition, not only the first or
second row of the tubes is affected, but the damages continued throughout
the whole upper tube bundle."
Causes of the Corrosion. "By search for the possible reasons of
this intensified corrosion, it was found that in 1973 about 1 year after he
start of operation of Boiler No. 5 a new situation had come up in the
method of operation. In May, 1973, a shredder-installation for bulky refuse
(wood of any kind, furniture, boxes, crates, etc.) was started. Due to
space arrangements between the shredder the boiler, most of the shredded
material is fed into this unit."
Thoemen's explanation of how this caused a concentration of
potassium chloride in the tube deposits is given in full in his
paper.
Thoemen's conclusions regarding corrosion protection for
superheaters is:
• Good mixing of refuse to avoid concentration of corrosive
salts in one boiler
• Clamp protective metallic shields on tubes at vulnerable
locations. He finds that a convenient alloy for this purpose
because it can be formed and welded is:
- Carbon: 0.1 percent
- Silicon: 1.0 percent
- Aluminum: 0.8 percent
- Manganese: 1.0 percent
- Chromium: 6.5 percent
The shield lasts 3 to 12 months.
• Use alloy steels in tubes
• Plasma-gun coating by metallic or ceramic materials. This
will be tried at Duesseldorf.
The earlier Figure U-22 shows a hard coating applied to the bends
of superheater tubes to be installed in 1977 in the second pass of Boiler
No. 5 to determine its usefulness in reducing tube wastage.
Soon after Boilers No. 1-4 began operation in 1965, a limited
amount of corrosion appeared in the top tube row of the horizontal
superheater sections in the-second pass. However, as soon as a protective
-------
U-59
deposit developed there, corrosion almost ceased. Thoemen described this
situation in 1972*:
"For the first time after about 1,000 hours of operation time, we
experienced comparatively severe corrosion on the tubes of the first stage
superheater at the side of the direction of gas flow. The uppermost rows of
tubes of the superheater carried, under a relatively small scale of
deposits, a heavy layer corrosion products. By thickness of this layer, it
had to be concluded that rapid wastage of these tubes could be expected.
However, as operations continued, the corrosion rate declined and has
reached a level which causes a barely measurable waste of material. The
tubes now are covered with a hard layer of deposits."
The importance of a protective deposit is thus emphasized. Also
the deleterious effect of any action, such as excessive soot blowing, is
emphasized. However, at this plant, excessive tube wastage because of soot
blowing has not occurred. Mr. Thoemen emphasized the importance of the
following in safe soot blowing:
• Steam lines must be well drained to avoid blasting slugs
of water against the tubes. Tubes are blown once per shift.
• Protective shields are very successfully used to guard
against soot blower erosion.
• Steam jet pressure must not be too high.
• A thermocouple in the steam line can be used as an operating
guide. The temperature should be well above saturation
temperature to avoid blowing slugs of water when the soot
blower is turned on.
Wuppertal
The 4-boiler plant built by VKW at Wuppertal in 1971-75 benefitted
from the experience nearby at Dusseldorf, also built by VKW. Figure U-24
showed earlier that the superheater is not a suspended platen hanging
directly above the furnace, as at Duesseldorf, but consists of horizontal
tubes in the second pass. When the furnace gases reach the top of the first
pass they turn through 180° at moderate velocity and flow downward through
the superheater sections which consist of two banks in series of horizontal
tubes installed in a sinuous manner. The nine rows of tubes in the first
section are formed of carbon steel designated ST. 35.8 II. The last two
rows in the second section are formed of alloy steel designated 15 mo 31.
This is the point of maximum steam temperature estimated at 420 C (788 F).
The design final steam temperature is 350 C (662 F). The tubes are not
staggered in the gas flow but are in-line with the center lines of the rows
225 mm (8.8 in) apart. The superheater is cleaned by steam blowers which
initially operated at 15 bar (1500 Kpa) 218 psig . However, because of
well-known experiences elsewhere with the high velocity of steam blowers
having a cutting or erosive action on adjacent tubes, these blowers are now
operated at a reduced pressure of 10 bar (1000 Kpa) 145 psia . Also, the
tubes likely to be eroded by the steam are covered on the exposed side by
6-mm thick (0.24 in) half-round steel shields made of Sicromal. So far the
shields tried of Sicromal 8 and 9 did not last long. Sicromal 10 seems to
be better. The composition and properties of Sicromal were given earlier in
Table U-1.
•Thoemen, K.H., "Contribution to the Control of Corrosion Problems on
Incinerators with Water-Wall Steam Generators", Proceedings 1972
National Incinerator Conference, New York, N.Y. P 310-318, ASME,
New York, N.Y. 10017.
-------
U-60
l&f&sttwy^^i^if; ''M<*$£
;•*•?
-------
U-61
The estimated gas temperature leaving the furnace radiation
section is 830 C (1526 F). As the gas enters the superheater it has cooled
to about 720 C (1328 F).
Superheat temperature control is provided by a spray-type
attemperator between the two sections. Attemperators are spray chambers
that inject demineralized water into the steam flow so that steam
temperature can be controlled to plus and minus 5° C. Maximum steam
temperature ahead of the attemperator is estimated to be 420 C (788 F).
Only 2 of the 4 Wuppertal units were being operated at a time in
1977 and it is too early to know whether the second-pass location of the
superheater was beneficial in elimination of corrosion.
The plant operator is experienced and well aware of the importance
of moderate, controlled burning in avoiding maintenance problems. Hence
this plant premises to develop a record of minimal tube corrosion.
Krefeld
The new plant built by VKW at Krefeld, also near Duesseldorf, is
very similar to the Wuppertal plant just described except that sewage
sludge is dried and burned in suspension above the refuse. The energy taken
up in drying is not available for much steam generation and for
superheating. Hence the superheater is smaller. Superheat temperature is
376 C (710 F). The superheater location in the second pass is the same as
at Wuppertal.
The superheater consists of 50 tubes, 51 mm (2.0 in) diameter with
a wall thickness of 3.6 mm (0.14 in) and formed of 35.8 I steel. The
composition of 35.8 I steel is as follows:
C 0.17 percent P 0.050
Si 0.35 S 0.050 ,
Mn 0.40 Cr 0.030
In West Germany this steel is identified under Standard No. 1.0305.
The gas temperature entering the superheater is estimated to be
700 to 750 C (1292 to 1382 F). There is one steam soot blower.
Not enough operation has yet occurred at Krefeld to enable
assessment of reliability of the superheater design. However its
performance should be similar to the nearly identical Wuppertal
superheaters. The possible exception would be a beneficial effect at
Krefeld of the sulfur from the sewage sludge helping to prevent chloride
attack.
Paris-Issy
Considering that this plant began operation in February 1965 when
superheater corrosion was poorly understood, the remote location of the
vertically suspended tubes in the third boiler pass indicates remarkably
astute design. Figure U-8 shows a cross section of one of the 4 Issy steam
generators. There are 2 large water-tube-walled boiler passes ahead of the
superheater. Apparently the main body of the superheaters has escaped
corrosion. But high velocity erosion of the lower tip of the platens which
-------
U-62
face the gas flow has occurred until the tubes were rearranged to allow
lower velocities.
The superheater tubes are suspended vertically in the third pass.
The original superheater tubes were 38 mm (1.5 in) in diameter. The
original design had 56 rows of tubes.
Operation of the units at 17 to 20 tonnes (19 to 22 tons) per hour
instead of the rated 15 tonnes (16.5 tons) per hour overloaded the
superheater tubes with deposits. With less cross-sectional area for gas
travel, the gas velocity was three times faster than design.
The ash buildup on the superheater tubes forced much gas to the
outside along the wall. Naturally the Iwoer corner of the far superheater
suffered from the very high velocity and high particulate loading. Baffles,
to better distribute the gas flow, were one of several solutions
implemented after flow model studies were completed.
Shields for Bottoms of Superheater Tubes. A new tube shield
designed was tried from 1967 to 1971. The two portions of Figure U-25
depict the shield arrangement.
Liquid Phase
Cement
4mm Thick Cast
Iron Shield
Dew Point Corrosion
FIGURE U-25. ISSY SHIELDS FOR BOTTOMS OF SUPERHEATER TUBES
The shields, made of cast iron, cover vertically the lower one and
one-half tubes as shown. The cast iron shields were ^ mm (0.16 in) thick.
The void was packed with a Narcoset (North American Refractories) liquid
phase filler cement.
This new shielding was supposed to protect the superheater tubes
for H to 5 years. However, superheater tubes began failing after 2 years or
11,000 hours. In an unusual manner the failure was attributed to the steam
soot blowers—not from erosion or regular corrosion but from condensation.
The steam would condense and absorb into the Narcoset packing. Thus at
times the wet packing would corrode the metal tube. When the above effect
was analyzed, the shields were discontinued. But metal wastage by erosion
continued.
Stage 3* (New Superheater with Wide Passes). The basic overloading
apparently could not be relieved. Finally in 1973, a new superheater was
installed which has given better service. Normal slag deposits were later
removed. The 56 rows of superheater tubes were replaced by 31 rows. The
tube diameter was increased from 38 mm (1.5 in) to *W.5 mm (1.77 in). The
-------
U-63
old tubes were spaced as shown in Figure U-26, as compared with the new
spacing.
Old
oooooo
oooooo
oooooo
New
FIGURE U-26. ISSY OLD AND NEW SUPERHEATER SPACING
Stage M. Manual Cleaning of Superheaters. With the wider spacing
between tubes, Issy has adopted manual cleaning of superheater tubes with
scrapers. So as to avoid erosion of the surface deposit and of the tubes by
soot blowers.
All of these measures have been helpful and although tube wastage
continues this new superheater had run 23,000 hours at the time of our
visit.
It is of particular interest that the water-filled screen tubes at
the entrance to the bottom of the third pass have not suffered extensive
corrosion while nearby the bends on the bottom of the vertically suspended
superheaters have required shielding to reduce corrosion.
Zurich-Hagenholz
Earlier Figure U-11 showed the superheater located in the Third
Pass of Unit No. 3 at Zurich-Hagenholz. Four horizontal tube bundles are
connected as shown on the following, Figure U-27.
There is a significant difference in tube configuration between
Martin's earlier Paris: Issy plant (1965) and their newer Zurich: Hagenholz
Unit No. 3 (1973). In Paris, the platens of superheater tubes were hung as
shown below, vertically in a "harp" design. (Also see earlier Figure U-8).
u
Paris: Issy
FIGURE U-27.
o °
o o
_- O t C. t O
Zurich: Hagenholz
SUPERHEATER TUBE ARRANGEMENTS AT ISSY AND HAGENHOLZ
-------
U-64
The Paris design, (designed in 1961) was later thought to develop droplets.
This would cause alternate rapid heating and cooling of the tube metal.
Proper heat transfer could not take place and metal temperatures would
reach the high-temperature corrosion range.
At Zurich: Hagenholz, however, (designed in 1971) the steam flow
is always downward such that nothing can become trapped. Heat transfer is
thus thought to be uniform and corrosion should be reduced.
The lower and hotter bundles are made from 15 Mo 3 low alloy steel
while the upper and cooler bundles are made from 35.8 II carbon steel. The
tube diameter is 31.8 mm (1.25 in) while the thickness is 4 mm (0.158 in).
The horizontal centerline spacing is 150 mm (6 in) and the vertical spacing
within a bundle is 50 and 100 mm (2 and 4 in).
The lower hottest first bundle has a maximum flue gas velocity of
6.65 m/sec (21.8 feet/sec) and average velocity slightly less at 6.45 m/sec
(21.2 feet/sec). The top three bundles, however, have a slower velocity at
a maximum of 6.25 m/sec (20.5 feet/sec) and an average velocity slightly
less at 5.75 m/sec (18.9 ft/sec).
To better control boiler exit steam temperatue (plus and minus 5°
C), an attemperator injects varying amounts of deionized, deaerated, and
demineralized water. The injected water is very pure to avoid scale
build-up inside the superheater tubes. The point of injecting is shown in
Figure U-28 as being between the lowest and the next bundle.
About 38,200 kg/hr (84,000 pounds/hour) of steam at 38 bar (551
psi) (3800 kPa) are produced. Note that the steam enters the superheater at
260 C (500 F) and then exits with a temperature of 420-42? C (788 to 800 F)
at the very bottom of the third pass. In a later design for Yokohama,
Japan, Martin tried a slightly different configuration as shown in Figure
U-29. In this design, the hottest tubes are the upper row of tubes in the
first bundle. The Yokohama design was probably motivated by the excessively
high percentage of total plastics, being 10 to 15 percent of the refuse
input.
The advantage of the Yokohama design is that a slightly cooler
temperature flue gas hits the hottest steam tube. Thus, the metal and tube
deposit temperature is less and there will be less corrosion. Zurich,
Yokohama, and Martin officials apparently believe that a slight reduction
in exit steam temperature is more than compensated by a reduction in
superheater metal wastage. Hence, the new Josefstrasse plant under
construction in Zurich will use the Yokohama design.
-------
U-65
Flue Gas Exit Temperature
500 C (932 F)
t
Steam Entrance Temperature
260 C (500 F)
3y.8 M Pl/ain/larb/n S/eel
5.8/11 Plaii/CarBon /tee
15/Mo / Low Alloy /tee
302 C
(575 F)Steam
643 C (1190 F)
732 C (1350 F)
Flue Gas Entrance Temperature
343 C
{650 F)Steam
Location of soot-
blower when its
nozzle failed
after 8,000 hours
- 385 C
(725 F)Steam
T
bj^J
(
./
O
O
O
Attemperator
Pure Water
420 - 427 C
(788 - 800 F)
Steam Exit Temperature
FIGURE U-28. SUPERHEATER FLUE GAS AND STEAM TEMPERATURE AND
FLOW PATTERNS AT ZURICH: HAGENHOLZ
* The last and lowest loop of the 3rd bundle and the entire 4th
bundle are made with 15 Mo 3 low alloy steel.
-------
U-66
Flue Gas Exit Temperature
500 C (932 F)
t
Steam Entrance Temperature
( 260 C (500 F)
302 C (575 F)
343 C (650 F)
V
380 C (715 F)
•O
highest temperature steam
Attemperator
Pure Water
•e-
^.427 C (800 F)
Steam Exit Temperature
385 C (725 F)
732 C (1350 F) Flue Gas Entrance Temperature
t
FIGURE U-29.
SUPERHEATER FLUE GAS AND STEAM TEMPERATURE
AND FLOW PATTERNS AT THE NEW ZURICH:
JOSEFSTRASSE PLANT
-------
U-67
Air Soot Blowers. As mentioned previously, there has (with one
sootblower incident exception) been virtually no corrosion of superheater
tubes in 30,000 hours. At 30,000 hours, metal wastage was determined to be
only 0.3 mm (0.012 in) at many points around the tubes. In part this
results from the use of air in the soot blowers.
The one exception ocurred after only 8,000 hours. A nozzle on a
fixed position, rotary sootblower fell off. As a result, high pressure
compressed air blew directly onto the tube sides. The nozzle failure was
detected and the tubes were inspected. None of the superheater tubes failed
but they had sufficient metal wastage to motivate replacement. Thus, after
8,000 hours, twenty (20) tube sections, averaging 5 m (16.U feet) per tube
each, were replaced. There have been no sootblower problems since.
The compressed air sootblowers are used daily. The two air
compressors supply a 1500 m3 (52,900 ft^) air tank with air at a 30 bar
(3000 kPa) U50 psig . The air released at the sootblower nozzle is at 15
bar (1550 Kpa) 225 psig . Officials expressed their preference for
superheater sootblowing with compressed air over steam even though the air
compressor costs about SF 250,000. As an official stated, "We use air for
sootblowing. If we used 10 tonnes steam per hour for sootblowing, we
wouldn't be able to sell it." Evidently selling the electricity required
for driving the air compressors is considered less important at this plant
than selling steam for district heating.
Once or twice per year, each Hagenholz boiler is manually cleaned
by the Hutte Company of Recklinghausen, West Germany (near Essen). Four or
5 men spend 7 or 8 days cleaning one boiler. An alkali chemical is used.
Sandblasting may be used for selected, hard to dissolve, deposits. The
procedure is basically as follows for most deposit areas:
1. Spray alkali (soak, low pressure spray)
2. Rinse with water
3. Spray alkali (second soak)
4. Rinse with water
5. Scrub with brushes and other tools
6. Sandblast difficult deposits
Cleaning all the tubes (walls and bundles) in all four passes normally
costs about 25,000 SF ($10,000). The dirty water coming out at the boiler
bottom has a pH of about 2 so lime must be added.
Plant staff have been experimenting with an "unbalanced compressed
air vibrator" for cleaning the superheater. Every two minutes, the upper
three bundles are vibrated. Every second or third months, they perform a
variation and interrupt the procedure for a half day.
At the older Borsigstrasse plant at Hamburg, the bundle wall
anchors are hit with a sledge hammer once per week.
Convection Section. Because of extensive use of water-tube walls
in all 3 boiler passes, Hagenholz Unit No. 3 does not have a regular boiler
convection section. From the superheater, the gases pass to the five-bank
economizer.
-------
U-68
Hamburg-Stellinger Moor
The Stellinger-Moor plant started up in 1972 utilizes vertically
suspended superheater platens in the second pass as shown in Figure U-10.
Thus the flame is usually completed before the gases reach to the top of
the first pass and turn to enter the superheater horizontally. If the plant
did not have to burn so much higher heat value refuse than what it was
designed for, or if the firing rate could be moderated, this relatively
exposed position of superheater might not be subject to unusual corrosion.
However, the boiler manufacturer, Walther and Company, probably anticipated
some corrosion because the superheaters were installed originally with
angle iron shields protecting the front row of tubes.
Figure U-30 shows the detailed arrangement of the 3 superheater
bundles.
Stage 1 (Original Construction). The plain carbon steel (ST 35.8)
tube used in the superheaters is 33.7 mm (1.33 inches) in diameter and 4 mm
(0.16 inches) thick. The design provides a heating surface area of 470 m2
(5057 ft2). Retractable sootblowers are used for cleaning deposits off the
tubes. Sootblowing has caused a fair amount of corrosion damage and has
motivated the following stages of improvement. Corrosion problems have
developed despite the Walther Company's originally shielded superheater
tubes.
Stage 2 (Adding Angle Iron). When the leading superheater row
began failing, despite the Walther shields, angle iron was welded to the
first row of tubes. This had the intended effect of protecting the first
row of tubes. However, the angle iron had the very damaging effect of
concentrating the flue gas as it was directed to the sides of second and
third row tubes as shown in Figure U-31.
Becaus-e of the Bernoulli effect, some gases were redirected away
from going straight down the open channel and instead have nonsymetrically
hit the front and one side of the tubes in the second and third rows. The
angle iron had a directing or aiming effect. Accordingly, this form of
shielding has been discontinued.
Stage 3 (Switch to Pressure Bent Pipes). Originally the pipes were
simply "stretch" bent. Unfortunately this form of bending gathers the
material on the inside curve, while thinning it out on the outside curve.
Thus, the front of the bottom loops, with less original thickness, would
wear out first.
Now, pressure bent pipes are installed as replacements. The
Walther Company can provide greater detail.
Stage 4 (Welded Curved Shields). Two factors continued to cause
corrosion. First, the retractable sootblower would remove deposits very
efficiently and thus enhance the rate of exposed metal wastage. The other
factor was continued erosion by the flyash in the flue gases.
To combat these problems, in April 1977, a series of 50 mm (2
inch) curved shields were welded next to each other along the front surface
of the first row of superheater tubes as seen in the several portions of
Figure U-32. Note the 135° angle. Sicromal 10 is the high temperature alloy
-------
U-69
West
East
South
1
2
3 '
Bundle 1
Tubes 1-6
/
, •
.1 —
_*
Bundle 2
Tubes 1-14
Bund
Tubes
1
— — -
le 3
j 1-12
North
FIGURE U-30.
THREE SUPERHEATER BUNDLES AT
HAMBURG: STELLINGER-MOOR
-------
U-70
CVJ
in
CVJ
10
-------
U-71
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-------
U-72
material used for these curved plates. This steel contains silicon,
chromium, and aluminum (See earlier Table U-1).
Perhaps 1 or 2 mm separate each shield. Note that the last shield
at the bottom of the superheater tube is extended further straight down and
thus away from the tube. This 'provides some protection of the very bottom
of the tube. At the tube's upper section, the same material is not welded
but formed in a U shape and bolted from the back side.
Experience has shown that when a weld fails and the tube bursts,
it is more economical to replace the entire tube than to repair the damaged
area.
Stage 5 (Superheater Repair Observation). While Battelle
researchers were visiting the plant on June 13, 1977, a superheater tube in
Boiler 2 failed and was losing 5 tons of steam per hour.
Repairmen removed about 1 m (3 feet) of four other tubes in order
to get to and replace the failed tube.
After performing hydrostatic tests, the boiler was put in service,
having been out of service almost two days.
The Hague
The Hague plant started in 1968, is another example of the
influence of fossil fuel design habits; one vertical superheater platen was
supended at the top of the first pass, very similar to the design of the
Duesseldorf plant.
Figure U-13 showed earlier the original superheater and boiler
arrangement for Units 1-3, as designed in 1965. The superheater was in two
sections The first section was a platen-type radiant superheater which was
inserted about 3.6 m (11.8 ft) downward from the water-cooled roof into the
radiation chamber (first pass). As subsequent experience has shown at other
plants, this was a particularly vulnerable location for a superheater. The
designer estimated that the flue gas temperature, as it rose in the
radiation chamber toward the superheater, would be about 955 C (1751 F).
With a steam temperature leaving the superheater of M25 C (797 F) the
temperature of potentially corrosive chloride salts on the superheater
surface could thus rise well over 500 C (932 F) both from contact by surges
of high temperature flame and from intense radiation from the incandescent
gases in the furnace below. Thus, in hindsight, it not surprising that the
pendant superheaters in Units 1-3 showed tube wastage within the first year
of operation. The solution to this attack was to shorten the platen by
about 70 cm (2.3 ft) and to increase the tube thickness from 2.9 to 5 mm
(0.12 to 0.2 in). After about five years and about 25,000 to 30,000 hours
operation, the pendant superheater was replaced at a cost of 60,000 Gl.
($24,600).
-------
U-73
The second superheater section, a sinuous convection type, is
shown in detail in Figure U-33 at the top of the second pass. A spray-type
desuperheater (attemperator) is located between the sections. The designer
estimated that the gases entering the second superheater section would be
about 900 C (1652 F) and leaving it would be 807 C (1U85 F). In this
section, corrosion was observed two or three years after startup. However,
the steam temperature there is lower and the corrosion rate is apparently
not rapid. This superheater section will also soon be replaced after about
10 years service.
*
Superheater (Unit 4). During the three years between 1968, when
Units 1-3 started up, and 1971, when Unit U was ordered, much had been
learned both at this plant and elsewhere about some of the causes of
superheater corrosion. One emerging lesson was that the superheater should
be as far removed as possible from the furnace flames. In this way any
potentially corrosive chloride depoosits on the tubes would not be
overheated by sudden surges of flames extending far above the furnace.
Also, the deposits would not be heated by intense radiation from the
furnace.
Accordingly, as seen in Figure U-34, the horizontal superheater
sections in Unit 4 are far removed from the furnace. Also, the entirely
open second pass, completely water-tube walled, provides cooling of the
gases before they reach the first superheater section at the bottom,
beginning, of the third pass. Thus, instead of an estimated gas temperature
of 955 C (1751 F) approaching the pendant superheater in Units 1-3, in Unit
4 the partially cooled gas entering the horizontal superheater bundle is
estimated to range from 530 to 630 C (986 F to 1166 F).
Another improvement helping to alleviate corrosive conditions was
to add secondary air jets in the sidewalls in Units 1-3 and to include them
in the initial design for Unit 4. These jets are located high in the
refractory sidewalls of the furnace, just below the coated water-tube wall
of the first (radiant) pass. They help to complete the burning quickly and
allow somewhat more time for the gas to cool as it moves through the passes.
The steam flow through the first (bottom) superheater section is
counter flow so that the hottest steam (U25 C) 797 F "meets" the hottest
gas. In the second superheater section of Unit 4 the steam and gas flows
are cocurrent.
The boiler redesign and air jets are just described have
eliminated superheater corrosion in Unit U except for some wastage in the
vicinity of the soot blowers. This is being satisfactorily controlled by
means of carbon steel shields covering the affected tubes. It is estimated
that the shields will need replacement every four years.
In Unit 4 the superheater tubes are made of 15 Mo 3 low alloy
steel, 38 mm (1.5 in) diameter and 3.6 mm (0.14 in) thick. The spacing
between the inline rows is 150 mm (5.9 in). In Units 1-3 this spacing was
only 80 mm (3.1 in). With this wider spacing, it is estimated that the unit
could run 8000 hours (nearly two years) before chemical cleaning of the
tube deposits would be necessary. However, tube thickness is checked once
per year, hence cleaning is needed each year before the thickness
measurements are made.
At first in Unit 4 the soot blowers were operated once per shift.
This caused tube erosion; hence the 20 bar (290 psia) blowers are no longer
-------
FIGURE U-33. WATER-TUBE WALL PORTION OF BOILERS IN UNITS 1-3, THE HAGUE, SHOWING
SUSPENDED PLATTEN-TYPE SUPERHEATER AT TOP OF RADIATION PASS, SCREEN
TUBES AT OUTLET FROM RADIATION PASS, SINUOUS TUBE CONVECTION-TYPE
SUPERHEATER AT TOP OF SECOND WATER-TUBE WALLED PASS, BOILER CON-
VECTION SECTIONS, ECONOMIZER, AND TUBULAR AIR HEATERS.
(Courtesy of Von Roll)
-------
U-75
THE HAGUE UNIT 4
1 Refuse pit
2 Vibrating hopper
3 Feed chute
4 Feed grate
5 Main grate
6 Burnout grate
7 Clinker pit
8 Settling tank
9 Clinker channel
10 Boiler
11 Electrostatic precipitator
12 Induced draft fan
13 Stack
14 Forced draft fan
15 Overfire air fan
FIGURE U-34.
CROSS-SECTION OF THE NO. 4 BOILER-FURNACE SYSTEM AT THE
HAGUE PLANT. UNIT 4 WAS DESIGNED IN 1971. (Courtesy of
Gemeentelijk Energiebedrijk Vuilverbrainding) [Wastenburn-
ing Energy Utility]
-------
U-76
used. Instead, the entire boiler system is cleaned aobut every three months
by a Dutch contractor: FA Conservator of Rotterdam. They use high pressure
jets of a solution of sodium carbonate to clean the ash deposits from the
tubes.
Plants Without Superheaters
As described earlier in this section, six of the visited plants
have no superheaters. High temperature steam for electrical production on
industrial processes is not needed from these plants. Instead hot water or
low temperature steam is used for district heating for sludge drying.
Tube and Wall-Cleaning Methods
In conventional boiler practice, the accepted method for removing
ash and carbon deposits periodically from the heating surfaces is by means
of steam-driven jets or "soot-blowers." However in refuse-burning practice
most plant operators have quickly learned that the high-velocity jets of
water slugs and steam from steam soot blowers can accelerate corrosion by
removing too much of the ash deposit. As discussed under metal wastage, the
ash deposit serves as a protective layer and corrosion inhibitor. When the
bare tube metal is exposed once or twice a day by excessive soot blowing,
high temperature chloride corrosion can be very rapid.
Accordingly some plants have abandoned soot-blowing completely.
Many have learned to use the soot blowers sparingly and then only in those
locations where occasional surface cleaning is particularly important to
satisfactory operation. Some have turned to compressed air blowers to avoid
any possibility of having slugs of steam-condensate being blasted against
the tubes during soot blowing. Others have arranged the convection surfaces
so that they can. be shot-cleaned by a periodic or continuous cascade of
steel or aluminum falling shot. Others use mechanical rapping of vertically
suspended tube banks.
Tables U-3 and U-iJ list the various furnace-boiler cleaning
techniques employed at the plants visited.
Werdenberg-Leichtenstein
The economizer and superheater at Werdenberg are shot cleaned.
Cleaning is achieved by the gravity fall of a shower of steel shot about 3
mm (0.120 in) dia which intermittently is delivered to a distributor at the
top of the economizer from which it falls by gravity through the gas
passages in the economizer and in the superheater. The falling steel shot
cleans deposited ash from the tubes and carries it down to an ash
separation system where it is removed from the shot and is transported to
be mixed in with the grate residue. The cleaned shot is then conveyed
pneumatically to the top of the economizer to repeat the cycle. The shot
cleaning process operates about 4 minutes every hour. Some systems use
aluminum shot.
The manufacturer feels that the trend will be toward vertical
configuration in superheater and convection section with periodic rapping
of the tubes to remove ash deposits. To minimize danger of tube metal
atigue from repeated flexing the amplitude of rapping should be manual 0.5
-------
U-77
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-------
U-78
TABLE U-4. METHODS USED TO CLEAN TUBES AND
WALLS OF EUROPEAN REFUSE-FIRED
ENERGY PLANTS.
A. Automatic Remote Controlled Soot Blowing
1. Fixed Position - rotary motion
2. Retractable Positions - spiraling motion
3. Steam
4. Compressed air
B. Mechanical Rapping
1. Automatic continuously operating hammers
2. Sledge hammering of boiler tube bundles by operator
3. Unbalanced compressed air vibrator
C. Automatic Shot Cleaning
1. Falling aluminum shot
?. Falling steel shot
D. Chemical Additive
1. Blowing inorganic "Gamlenite 8" dust to soften deposits
E. Non-Chemical and Manual Cleaning of Cooled Furnace
.*•
1. Compressed air manually operated nozzles
2. Small miscellaneous brushes
3. Manual scraping
4. Pneumatic hammering
5. Powered rotating wire brush for fire-tube boiler
F. Chemical and Manual Cleaning of Cooled Furnace
1. Soak with alkali, sodium carbonate or other chemicals
2. Rinse with high pressure water jets
3. Soak again
4. Rinse again
5. Scrub with brushes, pneumatic hammers and other tools
6. Sand blast difficult deposits.
-------
U-79
mm (0.02 in). Emphasis should be on rapid acceleration of the tube rather
than on greater amplitude to dislodge the deposits.
Baden-Brugg, Switzerland
At Baden-Brugg steam-actuated soot blowers are available but are
not used because of the widespread experience that steam soot blowers
accelerate tube wastage. The vertically hung superheaters are cleaned
manually on weekends every 6 weeks by means of compressed air nozzles
inserted through the access doors.
Duesseldorf
At Duesseldorf, excessive tube wastage because of soot blowing has
occurred only in the economizer. The plant manager emphasized the
importance of following in safe soot blowing:
• Steam lines must be well drained to avoid blasting slugs of
water against the tubes. Tubes are blown once per shift.
• Protective shields are very successfully used to guard against
soot blower erosion.
• Steam jet pressure must not be too high.
• A thermocouple in the steam line can be used as an operating
guide. The temperature should be well above saturation
temperature to avoid blowing slugs of water when the soot
blower is turned on.
The entire boiler is water cleaned in Units No. 1-4 every 2,000
hours. No. 5 is similarly cleaned every 5,000 hours. At first, the tubes
are sprayed for 10-12 hours at the rate of 10 m3/hr (44.0 gpm) to soak the
deposits. Then the weakened deposits are removed the next morning by means
of a high pressure water jet.
Wuppertal
During initial operation, water-washing of the boiler heating
surfaces at Wuppertal was used periodically for cleaning. However, this
posed some threat through soaking of the refractory coating in the lower
part of the radiation chamber and combustion chamber. Water-washing is no
longer used. Instead, every 3000 to 4000 hours the surfaces are brushed
clean manually. So far there has been no slag buildup anywhere in the
system, hence, only fine deposits need to be brushed off. This is unusual,
since many other waste-burning furnaces require periodic cleaning of heavy
deposits of fused ash and slag that adheres strongly to the sidewalls of
the combustion chamber. We can only conclude that these four relatively new
furnaces are not being fired as intensely as are many others, hence the
deposits of ash are soft and not fused.
The superheater is cleaned by steam blowers which initially
operated at 15 bar (1500 kPa) (218 psig). However, because of well-known
experiences elsewhere with the high velocity of steam blowers having a
cutting or erosive action or adjacent tubes, these blowers are now operated
at a reduced pressure.of 10 bar (10,000 kPa) (145 psia). Also, the tubes
likely to be eroded by the steam are covered on the exposed side by 6-mm
thick (0.24 in) half-round steel shields made of Sicromal. So far the
-------
U-80
shields tried of Sicromal 8 to 9 did not last long. Sicromal 10 seems to be
better. Table U-2 shows the composition and properties of Sicromal.
Krefeld
Because most of the energy from the burning refuse at Krefeld goes
to drying sludge the horizontal superheater is small. It has only one soot
blower. At the time of the interview, Spring 1977, there had not been
enough time to accumulate experience.
Paris; Issy
Corrosion difficulties from soot blower operation at Issy have
caused them to turn to periodic manual scraping of the superheaters.
Falling steel shot are used to clean the 4 banks of economizer
tubes.
Zurich-Hagenholz
The Hagenholz plant users compressed air soot blowers at 15 bar
(1655 kPa) (240 psi). An isolated case of superheater tube erosion or
corrosion occurred when a nozzle on a fixed position rotary soot blower
manufactured by Forest and Bergaman of Bristol, Belgium, fell off. As a
result, compressed air blew directly onto the tube sides. The nozzle
failure was detected after about 8000 hrs operation and the tubes were
inspected. None of the superheater tubes was burst but they had sufficient
metal wastage to motivate replacement, so, 20 tube sections, averaging 5 m
(16 feet) per tube in length were replaced. There have been no sootblower
problems since.
The compressed air sootblowers are used daily. The two air
compressors supply a 1500 m3 (52,940 ft3) air tank with air at a 30 bar
(450 psig). The air released at the sootblower nozzle is at 15 bar (225
psig). Officials expressed their preference for superheater soot-blowing
with compressed air over steam even though the air compressor costs about
SF 250,000 ($124,378).
Every 4,000 hrs, each Hagenholz boiler is manually cleaned by the
Hutte Company of Recklinghausen, West Germany (near Essen). Four or 5 men
spend 7 or 8 days cleaning one boiler. An alkali solution is used.
Sandblasting may be used for selected, hard-to-dissolve deposits. The
procedure is basically as follows for most deposit areas:
1. Spray alkali (soak, no pressure)
2. Rinse with water
3. Spray alkali (second soak)
4. Rinse with water
5. Scrub with brushes and other tools
6. Sandblast difficult deposits
Cleaning all the tubes (walls and bundles) in all four passes normally
costs about 25,000 SF ($10,000). The dirty water coming out at the boiler
bottom has a pH of about 2 so chalk must be added.
Plant staff have been experimenting with an "unbalanced compressed
air vibrator" for cleaning the superheater. Every two minutes, the upper
-------
U-81
three bundles are vibrated. Every second or third months, the procedure is
interrupted for a half day.
At the old Hamburg: Borsigstrasse plant, the bundle wall anchors
are hit with a sledge hammer once per week.
The compressed air sootblowers are fixed-rotary (and not
retractable). Hence, the nozzles are always oriented properly and not
directed against the steam tubes. The sootblower jets are fixed just
underneath the tube bundle.
The economizer is cleaned with falling steel shot (and not by
soot-blowers) thus avoiding potential problems.
A recent check in April, 1977, after 30,000 hrs operation, showed
that the original upperheater tubes had metal wastage of only 0.3 mm. The
water tube walls of the second pass had only 0.1 to 0.2 mm metal wastage on
the original tubes.
Hamburg-Stellinger-Moor
The retractable sootblower at Hamburg removed tube deposits too
efficiently and thus increased the rate of exposed metal wastage. Also
there was erosive abrasion by the ash in the high velocity flue gases. To
combat these problems, in April 1977, a series of 50 mm (2 inch) curved
shields were welded next to each other along the front surface of the first
row of superheater tubes as seen in the several portions of the previous
Sicromal 10, a high temperature alloy material was used for these curved
plates. About 1 or 2 mm separate each shield. The last shield at the bottom
of the superheater tube is extended further straight down and thus away
from the tube. This provides some protection of the very bottom of the
tube. At the tube's upper section, the same material is not welded but
formed in a U shape and bolted from the back side.
Because the economizer tubes would change position due to thermal
stresses, the wall-attached sootblower would then send high pressure steam
directly onto the tubes. These moving economizer tubes have been the cause
f four or five tube failures per year. To alleviate this problem, S-M has
decided to mount the sootblowers on the economizer bundles themselves.
Convection section near the fixed position sootblowers had been a
serious problem. As has been mentioned by several different plant managers,
reducing the sootblower activity can provide increased tube life with no
increase in costs. The only penalty is a modest decrease in thermal
efficiency. Decreasing sootblower activity is recommended especially during
seasons of "excess" steam production. Methods exist for reducing activity,
frequency, and pressure.
First, as at S-M, many plants reduce the soot-blowing frequency.
In this case, many blowers that had been blowing once per shift are now
scheduled to blow 1 to 3 times per week.
Secondly, at Hamburg, the pressure has been reduced from 18 bars
(1800 kPa) 260 psi to 1H to 16 bars (200 to 230 psi).
The actual determinataion of blowing frequency is a function of
where the boiler is in its 4,000 hour cycle between major overhauls. If
operation is in the first 1000 hours after maintenance, they blow only one
third as often as before. If, however, they were in the last 1000 hours,
they blow half as much.
-------
U-82
The Hague
In the newest unit, No. U, at The Hague, a widely spaced
superheater tube-bank has been installed. With this wider spacing it is
estimated that the unit could operate about 8000 hrs before chemical
cleaning of the tube deposits would be necessary. However, tube thickness
is checked once per year, hence cleaning by washing is done once a year to
enable the tube-wall thickness check to be made.
At first the soot blowers, operating at 20 bar (2000 kPa) 290 psi,
were used once per shift, but this caused tube wastage. Instead the entire
boiler system is now cleaned about every 3 months by a contractor: FA
Conservator of Rotterdam. They use high pressure jets of sodium carborate
solution to remove the tube deposits.
Dieppe and Deauville
The low-pressure, sludge drying and co-disposal plants at Dieppe
and Deauville use vertical firetube boilers which are normally cleaned
manually. At Dieppe the cleaning cycle is every 3 months. Each boiler is
drained and completely cleaned internally and externally by the plant staff
using brushes and other small tools.
The Deauville firetube boilers are of the same design,
manufacture, and capacity as at Dieppe, but the flyash deposits are cleaned
from the Deauville boiler tubes by falling steel shot pelllets, which are
fed periodically into the top of the boiler. After the shot falls through
the tubes, they then fall along with the dislodged ash into a conical
hopper situated directly beneath the boiler. The shot are then separated by
gravity from the lighter flyash and the shot are recirculated in a high
velocity air stream to the top of the boiler for another cleaninng cycle.
In addition to this cleaning process, the experience had been that
every 10 weeks it was necessary to hand clean persistent ash deposits from
the tube surfaces. However, in April, 1977, the staff began regularly to
blow into the furnace a fine inorganic dust known as Gamlenite 8 in order
to soften the ash deposits in the tubes so that the shot would remove them
and hand cleaning would not be necessary, About 2 to 3 kg (4.5 to 6.5 lb)
is blown in with air every 2 or 3 hours. According to the staff, this
additive has so far been entirely successful in making the tube deposits so
soft that they are readily removed by the shot, thus eliminating the need
for hand cleaning.
Gothenberg
The water-tube boilers at Gothenberg produce saturated steam
except for a small superheater to supply steam up to 3000 (572 F) for
soot-blowing only. Originally each boiler was equipped with 21 blowers.
These probably cleaned the tubes too well and some tube corrosion occurred.
Accordingly 11 of the 21 blowers were removed and the remaining 10 are now
used less frequently. Also on the tubes directly opposite the blowers
half-round alloy steel shields 1 mm (0.040 in) thick were tack welded to
the tubes. Later these were replaced by alloy angle irons strapped to the
tubes. The alloy is 20 percent Co, 10 percent Ni. The shields have been
-------
U-83
successful in protecting .the nearby tubes from soot-blower action but need
to be placed about every 6 months.
Uppsala
All three water-tube boilers are cleaned at Uppsala by falling
aluminum pellets. Figure U-35 shows a part of the pellet recirculation
system. The pellet storage bin holds 30 kg (66 lb) of pellets. Owing to
attrition, about 15 kg (33 lb) of pellets must be added per month. The
melting point of the pellets is about 750 C (1,382 F). The maximum gas
temperature entering the boiler is about 700 C (1,292 F).
About every 3 weeks, it is necessary to clean dust accumulations
up to 50 mm (2 in) thick at the entrance from the afterburner chamber of
Boiler No. 3. The deposit is easily brushed away. Steam jets will be tried
to replace brushing. No other boiler cleaning is required.
Horsens
The Horsens plant uses a simple vertical firetube boiler which
contains 540 tubes, 57 mm in diameter (2.25 in) and 4.5 m (11.8 ft) long.
The top of the boiler is accessible so that once every 2 weeks all of the
540 tubes can be cleaned of soft ash deposits by means of a powered
rotating wire brush. This takes 6 to 7 hours every Monday morning at the
same time that the air openings in the grates are being cleaned and the
siftings are being removed from beneath the grate.
Copenhagen;Amager and West
The large, hot-water, water tube boilers at the 2 similar
Copenhagen plants are cleaned by a variety of methods. At Amager, tube
cleaning has been an experimental matter. Sonic vibrating, mechanical
rapping and soot blowing have been tried. Now falling steel shot is used
routinely, On shutdown the 3 open passes are brushed manually.
The steel shot cleaning system was supplied by Eckstrom of
Stockholm, Sweden. As at Amager, the West economizers are fin-tubed with
small spaces. The spaces and corners became so clogged with flyash and
steel shot, that they will have to be replaced. Because of the clogging,
the economizers at both Amager and West have set the overhaul schedule for
the whole plant. Until the economizers are replaced, the unit will continue
to shutdown every 1,500 to 2,200 hours. The manufacturer's original
recommendation of cleaning every 3,000 hours would have been mainly to
restore efficiency. The economizer is cleaned manually with brushes.
Unfortunately, shot cleaning was not in the original design.
Therefore, on retrofit, the falling shot was down—concurrent to the flue
gas. In future economizer designs, both the gas flow and the steel shot
flow will be downward.
-------
U-84
FIGURE U-35.
SHOT PELLET CLEANING FEED SYSTEM AT
UPPSALA (Battelle Photograph)
-------
U-85
Metal Wastage (Corrosion and Erosion) of Boiler Tubes
Experience with Fossil Fuels
In fossil-fuel fired plants most boiler and superheater tubes
undergo such slow corrosion that tube wastage is virtually not a problem.
Usually the metal oxide layer on the fireside protects the tube from rapid
corrosion. However, in the 1
-------
U-86
Effect of Soot Blowing
Most plant operators have learned that cleaning off the ash
deposit and the underlying oxide scale too well and too often greatly
increases tube wastage. This experience demonstrates the importance of
building up a protective deposit on the tube metal surface and retaining it
there. Corrosion rates of superheaters where soot blowing is too frequent
will equal the high short-term rates experienced on new, clean surfaces.
This corrosion is the result of both oxidation and chloridation of the
metal surface.
A Proposed Corrosion Mechanism
The research on corrosion since 1969 for EPA by Miller, Vaughan,
Krause and Boyd* has shown that the important factor is: what goes on
inside the layer of ash adhering to the metal tubes.
Dale Vaughan, recently retired as one of the leaders of that
research at Battelle-Columbus, has summarized the work in an internal memo
as follows:
"The boiler tubes are exposed to the normal combustion gases
C02, CO, HC1, small amounts of sulfur oxides and organics,
excess air, plus vapors and solids of inorganic compounds. The
initial reaction is undoubtedly the formation of a thin oxide
layer on the boiler tube which is quickly coated with a deposit
containing large amounts of chlorine identified as a mixture of
potassium and sodium chloride with smaller amounts of heavy
metals. Hence, the tube metal is no longer exposed to the
gaseous combustion products but instead is exposed to the
deposit and/or the products of its reaction with the
gases.Studies of deposits after long exposure to incinerator
combustion products have shown that the chlorides are converted
to sulfates and that the chlorine content is thus reduced
significantly except at the metal surface where FeCl2 has
formed. The iron oxide layer is no longer in contact with the
metal surface, but instead chlorine is now the corrosive
species."
"Our corrosion data show that wastage of carbon steel increases
rapidly at about 100 F and again at 800 F. The first increase is
attributed to chloridation and the second to sulfidization. The
first increase coincides with the rapid attack of iron by
elemental Cl2 as shown by Brown, DeLong and Auld. ( )
Furthermore, their studies show that rapid attack of iron by HC1
does not occur until a temperature of about 900 F. Therefore, it
is doubtful that the HC1 content of the combustion products is a
significant contributor to metal wastage in the temperature
range where chlorine is the corrosive species. However, as
expected, Clj has not been detected in combustion gases but this
does not eliminate its existence as a product in the conversion
of metal chloride to metal sulfate. This occurs mainly in
*Krause, H.H., Vaughan, D.A., Miller, P.D., "Corrosion and Deposits
from Combustion of Solid Waste, Part II, Chloride Effects on Boiler
Tube and Scrubber Metals,* ASME Paper 73-WA-CD4, November, 1973.
•Vaughan, D.A., Krause, H.H., and Boyd, W.K., "Corrosion Mechanisms
in Municipal Incinerators Versus Refuse Composition", Proceedings
ASME Conference on Present Status and Research Needs in Energy
Recovery from Wastes, Hueston Woods, Ohio, Sept. 1976.
-------
U-87
deposits which are retained on boiler tubes and exposed for
sufficient time to the hot gases containing low concentrations
of sulfur oxides. When the Cl2 is released from the metal
chloride deposits at the tube surface the attack is very rapid.
However, our studies have shown that with a sufficient increase
in sulfur in the fuel, metal sulfates form rather than metal
chlorides in the fuel bed and combustion chamber, little or no
chlorine is found in the deposit, and the metal wastage is
markedly decreased even though the HC1 in the combustion gases
is increased some, 862 emission may increase depending on the
fuel mixture involved."
Thus, the major corrosive factor in refuse-fired boilers is
chloride attack. This goes on whether the furnace conditions are oxidizing
or reducing. That is, even when the furnace atmosphere is on the oxidizing
side, conditions within the mineral deposit at the tube surface may be
oxygen-free. Where chlorine, HC1, or sulfur are formed right next to the
tube metal, attack on the metal can occur, and Fecl2 or FeS will be the
corrosion products.
For example, electron probe and X-ray diffraction analysis of the
layers on corroded tubes shows that compounds exist there which could only
persist under reducing conditions, but at the same time, furnace gas
analysis in the vicinity usually shows oxidizing conditions.
In general, the European practice has been to "solve" the wall
tube corrosion-erosion problem by covering the tubes with silicon carbide.
Hence, the remaining corrosion problem is primarily on the superheaters.
Although there may be momentary excursions into reducing conditions in
spots around superheaters, it seems to be unlikely that many superheaters
are subjected to severe and massive flows of reducing gases. Yet the
superheater corrosion is common. And so are chlorides common in refuse—
the 0.5 percent in the bulk refuse quickly accumulated to become several
percent of the tube deposits, hence, their corrosive action at high
temperatures.
To summarize this subject: even in the very common condition with
refuse burning where oxidizing furnace gases are typical, the action of
chlorine and HC1 released in the zone next to the tube metal will be very
corrosive. One potential means for protecting the tubes has been found. By
study of steel probes inserted into incinerator gases, Vaughan and
co-workers have discovered that if the sulfur content of the refuse is
increased to two percent, the chlorine from the burning waste does not
appear in the ash deposits on the tubes, hence, the chlorine is not there
to corrode.
Another approach to reducing superheater corrosion has been to
place the superheater as far away as possible from the furnace flame, thus
giving the gases time enough to complete combustion and to cool to a safe
temperature level. However, at gas temperatures above 1000 F (538 C) this
protection is thought to be less effective than adding sulfur.
The authors recognize that some of the foregoing discussion of
corrosion is not fully consistent withh the views of many respected
authorities who are experienced in this field. Not all of the corrosion
mechanisms have been fully postulated and proven in acutal practice.
Accordingly there is room for well-informed opinion involving potential
disagreement on the causes and abatement of tube wastage. However, despite
-------
U-88
the existence of vexing discrepancies in viewpoint we are much impressed
that the operators at the 15 plants visited have achieved practical control
of tube wastage to quite acceptable levels. There is room for improvement
but the current level of control indicates that good progress has been made
toward practical control of the problem.
Reasons for Minimal Tube Corrosion
The most corrosion-free plant visited on this project was
ZurichrHagenholz. Although the superheated steam is produced at (420 C) 788
F, wall and superheater tube corrosion has been minimal compared to other
plants operating at such high temperatures. There appear to be many reasons
for this good experience. Most of those reasons were elicited as follows
from discussions with the plant designer, operator and builder. Other
plants provided additional points which are included in the following:
Management
1. In the original plant design corrosion is reduced if there is no set
cost limit, hence the best (efficient and reliable) boiler that
money could buy is selected.
2. Overdesign reduces the chance for overheating. A widespread
viewpoint: "You ought to build the best plant possible and the run it
at 80 percent of capacity".
3. Excellent management ensures that the properly designed plant is
observed, monitored, and controlled to run as it was intended.
JJ. Rotating job positions for each man enhances his understanding of the
complex plant and his spirit to run it properly.
Automatic Control
5. Well-placed and sensitive controls send instantaneous furnace roof
temperature readings to the feeder and grate controls. As a result,
flue gas, metal surface, and steam temperatures are kept within
limits and high temperature corrosion is avoided.
Start-up Procedures
6. The use of a standby boiler (Number 2 oil or waste oil) to be started
before the refuse is fired can be used to heat the primary underfire
air in a steam air preheater to 150 C--above the dew point
temperature.
7. The standby boiler can also supply steam to the refuse boiler to
preheat the tubes above the dew point tempereature to avoid wet
corrosion of the boiler, electrostatic precipitator, or the stack.
Refuse Handling
8. The crane operators take care to mix refuse in the pit so that a more
uniform fuel is available that will not cause wide swings in flue gas
temperatures.
-------
U-89
9. Positive refuse feeders introduce controlled amounts of refuse into
the furnace and minimize uncontrolled cascading that would cause poor
burning and formation of potentially harmful CO.
10. Various grate actions gently turn and distribute the refuse for
exposure to the flame combustion air.
Secondary Air
11. Preferably front and rear-wall overfire-air jets should be aimed to
develop a turbulent pattern low in the furnace. Flame lengths are
kept short and do not rise far into the first pass.
12. Side wall air jets are less effective in providing full furnace
mixing. (However, this is not meant to criticize Kunstler or Didier
air-wall blocks).
13. Secondary air up to 500 to 600 mmWs (20 to 24 in) causes intense
turbulence so that virtually all CO is eliminated before the flue
gases leave the combustion chamber. Alternating reducing - oxidizing
atmospheres are eliminated.
14. At Zurich the secondary (overfire air) from the neighboring rendering
plant "may" contain reduced sulfurs, etc., that may reduce corrosion
by forming sulfate deposits. However, the concentration of sulfur is
believed to be low and more investigation is needed to confirm any
hypothesis. The Ammonia concentration is often high and its effect,
if any, on corrosion is not known.
Furance Walls
15. The only successful protection for the walls of the combustion
chamber and the lower portion of the walls in the first pass is to
coat them with Silicon Carbide that was properly supported by studs.
16. A large, open, water-tube-walled second pass helps to protect a
superheater from being overheated.
17. The flue gases flowing in a large second pass flow at reduced
velocity which reduces the erosive effect of the particulates in the
gas as it enters the first row of superheater tubes.
Superheater
18. A superheater located in the third pass (and not the first or second
pases) faces cooler flue gases, with little or no CO.
19. If the superheater tubes are sinuous and horizontal, with downward
flow, stagnant steam pockets are less likely to occur to interrupt
heat transfer.
20. The use of in-line superheater tubes (and not staggered) allows flue
gases to pass more easily.
21. Low alloy and high alloy steels at the most exposed locations help to
minimize superheater corrosion.
22. Close control of the attemperator (desuperheater) between the
superheater bundles helps by keeping steam temperature nearly
constant.
-------
U-90
23. Simple alloy steel shields clamped to the most exposed tubes are
easily replaced during routine maintenance and are in widespread use
for minimizing tube wastage.
Economizer
2H. Economizers may also be equipped with a shield on the tubes that are
most exposed.
25. The use of a large economizer is helpful to recover energy and to
reduce flue gas temperatures entering the electrostatic precipitator.
Boiler Cleaning
26. Many plants use vibrators or hammers to shake deposits from
superheater bundles.
27. One plant uses compressed air (and not steam) sootblowers in the
superheater section. Thus, injurious slugs of water lying in inactive
sootblowers cannot harm the tubes upon startup.
28. If the sootblowers in the superheater section are fixed-rotary (and
not retractable), the nozzles are always oriented properly and not
directed right against the steam tubes. Also the sootblower jets can
be positioned just underneath the tube bundle.
29. A common practice is to manually clean the boiler fireside surfaces
with an alkali every 4,000 hours.
30. Sandblasting during cleaning should be limited to removing only
difficult tube deposits.
31. In some cases with lower flue gas temperatures in the first 1000
hours after cleaning, if much sulfur is present a ferrous sulfate
FeSOjj might form on the tubes instead of the more harmful FeCL2»
32. Many economizers and some boiler passes are cleaned with falling
steel shot (and not by sootblowers) thus avoiding potential erosion
and bare-tube corrosion problems.
Steam Condensers
Large quantities of steam are discharged in either water-cooled or
air-cooled condensers at 6 out of 15 plants as listed below:
Plant Mode of Cooling Steam
Werdenberg Air
Baden - Brugg Water
Wuppertal Air
Hamburg: Stellinger-Moor Air
Zurich: Hagenholz Air
Gothenburg: Savenas Air
Werdenberg - Liechtenstein
Figures U-36 presents two views of the small roof top air cooled
steam condenser at Werdenberg. Due to the complex energy scheme, most steam
produced is effectively used: little needs to be condensed.
-------
U-91
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FIGURE U-36. Two views of Air-cooled Condenser at Werdenburg.
(Courtesy of Widmer and Ernst)
-------
U-92
Baden - Brugg
The steam is condensed with heat transfer to water drawn from the
adjoining Limmat River. The condenser is cleaned once every 3 months.
Wuppertal
The largest set of air-cooled steam condensers seen on the tour
was at Wuppertal. Figure U-37 shows the condenser's underside where the
large fan blades are located. The overhead plant insert shows the condenser
(labeled 10) in relation to the entire plant.
The new Federal regulation on noise near an industrial facility
limits it to 35 dba. With two units out of four operating, this plant is
close to that limit. Accordingly, it is expected that sound absorbent
louvers will need to be installed beneath the condenser if a third furnace
is to be used. This was purposely built in the elevated position shown to
allow space for installation of sound absorbent surfaces.
Hamburg; Stellinger - Moor
The chronological story on the Stellinger - Moor condenser is
important to systems that might be built in the colder North American
climates.
Stage 1 (Original Construction). In contrast to Martin's Chicago,
Illinois and Harrisburg, Pennsylvania systems in America with horizontal
tubes, a common European practice is to have air cooled condensing tubes in
sloping roofs.
Originally the plastic fan blades were reset twice per year. In
the winter when not as much cooling was needed, they were set with very
little pitch. In the summer, the pitch was increased. Unfortunately, the
high summer pitch would cause the plastic fan blades to deform, slip,
break, or fall out.
In the event that both turbines are down, the condensers can
condense a limited 45 tonnes (49.5 tons) steam per hour. Thus, if a single
88 tonne/hour capacity turbine normally running at 60 tonne/hour capacity
suddenly fails, the 45 tonne/hour condenser will be 15 tonne/hour short in
capacity. This remaining 15 tonnes/hour will pass through the throttling
valve at a very high noise level.
Stage 2 (Changing Fan Speed Instead of Pitch). The problem was
resolved by setting the pitch low for winter needs and then not changing
the pitch throughout the year. In the summer, the motor speed is nowraised.
Maintenance on the fan has now been greatly reduced. They now overhaul and
balance the fans every two years. They clean the system every early summer
with high pressure water.
Stage 3 (Freezing Tubes Requiring More Thermocouples).The sloping
roof at Stellinger-Moor experienced freezing in six of its condenser fin
tubes once when it was - 20"C (-6° F). The single thermocouple was located
on one of the four headers and was on the protected leeward side of the
condenser. As a result, the reading was always above the danger level.
-------
U-93
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U-94
Unfortunately, the chill factor (temperature and wind velocity)
was much worse on the windward side and freezing occurred unnoticed. The
first sign of a problem was when the electrical turbine tripped out. They
now have four thermocouples, one for each header and these have readings on
both sides of the condenser.
Zurich; Hagenholz
Figure U-38 shows the roof-top condenser at Hagenholz. Large
vertical louvers, made by GEA of Bochum, West Germany, are installed on the
roof wall around the air-cooled steam condenser fan bottoms to abate noise.
Separately, the V-belt drive on the Condenser fans started
squealing at low speeds. They now have two-speed motors.
The condensing capacity is 75 tonnes (82.5 tons) per hour. At
present they condense about 40 tonnes (44 tons) per hour from the
extraction condensing turbines.
Previously, Hagenholz had freezing problems in the Winter. They
now feed steam first to what would otherwise be the coldest part of the
condenser.
Gothenburg; Savenas
Savenas was designed with utmost concern for architecturaal
features, aesthetics and concern for the environment. One of the key
concerns was noise.
To suppress the noise of the large fans which supply air to the
air-cooled condensers, they are enclosed in perforated louvered walls. This
has reduced the noise level 100 m (328 ft) from the plant from 58 to 50 dB.
Noise regulations now for new plants require 45 dB(A) in the day and 35 at
night. See vertical louvers in Figure U-39.
Steam-to-Refuse Ratio
A useful number in judging overall plant performance is the
evaporation ratio: weight of steam produced divided by refuse fired. This
ratio is particularly useful as an evaluation of a plant if it is calculated on
an annual basis. However, it is subject to many day-to-day variations and can
be particularly misleading when comparing plants. The most difficult variable
to measure, or even to estimate, is heat vlaue of the refuse. In many
communities, LHV (or HHV) is nearly constant, on others it is not, particularly
where industrial refuse is a major and highly variable component.
Another variable among plants is the temperature (and pressure) of the
steam produced. Although this can be precisely defined in each case, the heat
content (enthalpy) of steam can vary more than 25 percent from a low-pressure
plant for district heating to a high-pressure plant generating superheated
steam for power. Thus, in comparing evaporation ratios, the steam conditions
should always be considered, and we should try to evaluate the heat value of
the refuse.
Table U-5 illustrates the variations that can occur. The data for the
plant at Harrisburg, Pennsylvania are introduced for comparison because
extensive data were available for that plant which is a Martin system, similar
to many European plants;*
•"Performance of Steam Generating Incinerator", Battelle Report to
Harrisburg Incinerator Authority, 1974.
-------
U-95
FIGURE U-38. SLOPING AIR-COOLED STEAM CONDENSER TUBES AT ZURICH: HAGENHOL7
(Battelle Photol
-------
U-96
FIGURE U-39. LOUVERS BELOW INVERTED V-SHAPED AIR-COOLED STEAM CONDENSERS
AT GOTHENBURG: SAVENAS (Battelle Photograph)
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U-98
The Harrisburg results are from short-term tests and the efficiencies
shown are less consistent than for the other plants which are annual averages.
In such short-term tests, errors in sampling and analysis of refuse produce
inconsistencies. A particularly glaring example of the difficulty in reliable
sampling of refuse is the erroneous efficiency of 103 percent for the "average"
test at Harrisburg. The measured efficiencies in the last column were obtained
by reference only to the boiler losses measured when burning oil only at
Harrisburg and assumed to be the same for refuse.
The Gothenburg and Hagenholz plants are most nearly comparable.
Although their evaporation rates are quite different (3.1 versus 2.5), their
energy production rates (3,500 versus 3,^00 Btu) produced per pound of refuse
fired (8,141 versus 7,908 kJ/kg) are very similar. This close agreement while
the evaporation rates are quite different is a clear demonstration of the
unfairness that can result when comparing evaporation rates alone.
-------
V-l
SUPPLEMENTARY FIRING OF FUEL OIL. WASTE OIL AND SOLVENTS
Oil and Waste Oil Co-Firing - General Comments
Number 2 Fuel Oil can be fired at five of the surveyed plants. Waste
oil and/or solvents are fired at three plants. The oil firing capability is
summarized in Table V-l.
The reasons for supplmentary firing are:
• Emergency backup
• Routine firing when refuse burning ceases on weekends
• Preheat the RFSG upon startup
• Keep boiler and electrostatic precipitator "hot" to prevent dew
point corrosion when unit is down
• Supplmental fuel oil keeps furnace temperature at legal limit for
destruction of pathogens, etc.
• Additional energy for routine uses.
In designing a total system, it is important to also consider the
various reasons for not spending funds to install such supplemental firing
features. Often, if the refuse to energy plant does not have continuous
responsibility (as in the interruptible situation), the oil-fired backup will
not be installed and the revenue per 1,000 pounds of steam is much less. Such
situations include:
• Hot water to a district heating system where the system has other
oil fired district heating stations.
• Industrial process steam to a user that maintains his own older
conventional boiler ready for start up should there be
aninterruption in the supply of refuse derived steam.
• Electricity to an eletric network where the loss of refuse
derived electricity would have little effect on total network
operations.
• Drying and burning of sewage that can be postponed several hours
or days if the sludge storage tanks are large enough
• Energy to a physically adjacent conventionally fired energy plant
where the total standby responsibility rests with the neighboring
plant.
• A regional plan that mandates waste oil treatment and burning at
a distant facility.
Only 5 of the 16 plants described were designed with key functions
being served by fuel oil, waste oil or solvents.
-------
V-2
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-------
V-3
Oil and Waste Oil Co-Firing - Specific Comments
Werdenberg-Liechtenstein
Number 2 Fuel Oil. The energy demand is 7 days per week and the
steam is produced from burning refuse only 5-1/2 days per week. Therefore, an
oil-fired boiler was installed. This boiler is operated unmanned over the
weekends.
Baden-Brugg
Waste Oil. Figure V-l shows one of the two Elco air-atomizing oil
burners which are mounted at the side of each furnace toward the rear. (Figure
V-2 shows a similar sidewall burner at a hospital waste incinerator in Cologne,
West Germany.) These burners are for the purpose of firing waste oil when
available. About 50 percent of the waste oil comes for automoti ve serviice
stations and 50 percn)et from industry. This includes some oil emulsions.
The waste oil is first received into a large heated concrete settling
tank where it is heated by a heating coil to 50 C (122 F) and held for 3 days
to allow solids to settle. From this tank it passes through a fine mesh filter
to a day tank from which it is fired at varying rates up to a maximum of 800
kg/hr (1,761 Ib/hr) per boiler. The filter must be cleaned every 2 or 3
months. Figure V-3 is a schematic of the process located parallel to the
refuse pit.
Plant practice is to reserve the waste oil for firing when the refuse
is wet or to dispose of the oil when all oil-storage space is filled. Also, at
mid-day when the highest revenue can be realized from the sale of electricity,
the waste oil may be used. When firing oil, both burners on opposite sides of
each furnace are used. The burners require little maintenannce but are
inspected and cleaned every 2 months. They employ light oil for a pilot flame.
Some difficulty has been encountered with floatable substances that accumulate
at the top of the waste oil settling tank.
Duesseldorf
Number 2 Fuel Oil. The only auxiliary fuel used at this plant is No.
2 fuel oil which is used only for start-up or in an emergency. In Germany,
there is a legal requirement on incinerators that the combustion gases must
attain a level of 800 C (1,472 F). If there is very wet refuse or some other
cause for the furnace temperature to-fall below that limit, the oil burners can
be used to raise the temperature. Originally, Boilers No. 1-4 had three oil
burners at the top-front-center of the furnace between the feed chute and the
arch. Now there is only one burner per unit. The burner for No. 5 is on one
side. Maximum oil capacity per burner is 0.4 tons/hr (130 gal/hr).
-------
V-4
FIGURE V-l. OIL BURNER ON SIDE OF AND TOWARD REAR OF FURNACE FOR
FIRING OF WASTE OIL AT BADEN-BRUGG (Courtesy of Widmer
+ Ernst)
-------
V-5
-------
V-6
• - - .1 '•' /?-, -.- .' v 5 i' i ..•
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n dtesan B«haltem
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n in tfwi 0«l»n
vvrbrannt wvrden
nn.
FIGURE V-3. SCHEMATIC OF THE PROCESS OF WASTE OIL
FIRING
-------
V-7
Krefeld
Waste Oil. Krefeld was originally constructed with a waste oil
facility but has hardly ever been used. Figure V-M shows its location in a
separate one story building to the left of the tipping pits.
The process begins with filters that remove metal turnings, debris
and other coarse material. Sedimentation tanks then acts to remove free water.
Finally the improved oil passes through filters before entering the storage
tanks.
The cleaned oil was to have been burned by mist injection into the
furnace above the sewage sludge injection nozzles in the furnace first pass
about the grate.
The burners were designed to gorabust 1.2 tonnes (1.3 tons) per refuse
incinerator. With two lines, the combustion capacity was 58 tonnes (62 tons)
per day of reprocessed waste oil at Krefeld.
The original intent was fivefold as listed below:
• Remove waste oil from the environment
• Provide energy enrichment needed to support normal sludge
destruction in periods of heavy rainfall when the refuse
calorific content falls (but this has not been a problem)
• Provide energy enrichment needed to destroy sludge if the
dewatering system were to malfunction, i.e. if the sludge
entering the furnace was 23 percent H2o instead of the intended
10 percent H2^ (this also has not been a problem)
• Provide more energy in general
• Support national goals of energy conservation.
But as alluded to in the first paragrph, the facility is not used.
Several years ago, the Federal and reginal governments initiated a policy of
regionalizing industtrial waste treatment activities. A master plan was
developed. Included was a provision that all waste oils collected in the
Krefeld area would go to another facility.
Another factor was the alleged spirit of local waste oil generators
and collectors, who apparently had more economical alternatives. For these two
reasons the dormant plant may eventually be dismantled. In summary, Krefeld,
in relation to the industrial waste-plant, has suffered by th other plant's
"capacity creation by regulation".
Hamburg;Stellinger-Hoor
Methane Gas From the Sewage Treatment Plant. Formerly, methane gas
from the sewage treatment plant within the same sanitary park was fed into the
furnace. The practice has been discontinued. Today the gas is flared at the
sewage treatment plant.
-------
10
3.1
3.2
4.1
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•9
FIGUREV-4 . KREFELD WASTE-TO-ENERGY FACILITY: PLAN VIEW
(2)
2.1 Tipping area
2.2 Bulky refuse shear
2.3 Auxiliary tipping lane
3.1 Refuse bunker
3.2 Ash bunker
3.3 Ash loading area
4.1 Boiler house
4.2 Boiler pumps
4.3 Residue quencher
4.4 Primary air fan
4.5 Sludge-drying fan
4.6 Firing aisle
5.1 Washroom
5.2 Switch room
6.1 Turbine floor
6.2 Turbogenerator
6.3 Heat exchangers
6.4 Feedwater tank
7.1 Water treatment
7.2 Stairwell
8.0 Social room
9 Chimney
10 Waste oil facility
11 Cold water basin
13 Flue gas scrubbers
-------
V-9
Number 2 Fuel Oil. The Number 2 oil fired burner port is 6 meters
(20 feet) above the grate. The burner can be swung into the furnacce opening
when needed.
Usually, the oil burner is used 5 to 6 hours for start up. Operators
open a bypass and the ESP temperature is raised to 1800C. A cold ESP will not
work well.
An unusual use is if the feed chute becomes stuck, the oil burner can
be turned on to help keep the system stabilized.
Zurich;Hagenholz
Number 2 Fuel Oil, Waste Oil and Solvents. Hagenholz is equipped
with two Sulzer (of Zurich) fossil fuel boilers; one for Number 2 fuel oil and
another boiler for both waste oil and waste solvents. Some operating figures
are shown below:
Annual Totals
1974 1976
Number 2 fuel oil fired boiler #1 (operating
hours) 201 182
Waste oil and solvent fired boiler #2 (operating
hours) 1.486 2,099
Total (boiler - operating hours) 1,687 2,281
Number 2 fuel oil fired boiler #1 (tons of
steam) 1,413
Waste oil and solvent fired boiler #2 (tons of
steam) 11.244
Total (tonnes of steam produced) 12,657 14,536
Number 2 fuel oil burned (tons) 109 1C8
Waste oil burned (tons) 794 1,102
Waste solvents burned (tons) 71 113
Total (tonnes of material burned) 974 1,323
Waste oil collected (tonnes) 1,654 1,801
It would be incorrect to label these activities as co-firing. The
refuse burning areas are not connected at all to the oil burning areas. Max
Baltensperger feels very strongly that no other fuel should be fired in the
same cmbustion chamber as refuse because of inevitable problems of ash deposits
on boiler tubes.
-------
V-10
The Number 2 fuel oil boiler is only used to preheat the boiler and
the air preheater for the benefit of the electrostatic precipitator. The waste
oil burner boiler, however, is a completely separate system devoted to waste
oil destruction and energy recovery.
Reading of C02 and opacity (Ringleman scale) are used to control
these oil burning systems. There have been corrosion problems in the steel
stack of these waste oil boilers.
Figure V-5 shows the general layout of the solvent and waste oil
preparation area. The waste oil is heated and decanted. The oil, water, and
sludge are pulled off separately. The sludge at the bottom of the decanting
tank is mixed with the municipal solid waste in the pit. The oil overflow goes
to the boiler.
Copenhagen: Amager
Cofiring is not practiced at Amager. However, and for the record,
Volund did cofire with refuse and coal in a 3-1/2 tonne/day Gentofte in 1931.
The 40 year old units serving Copenhagen at Gentofte and at Fredericksburg were
replaced with the units at Amager and West.
Amager does not need standby capability because its baseload steam is
sent to the adjoining large electrical power and district heating plants.
Copenhagen: West
The refuse-fired hot water plant has no standby equipment and does
not fire waste oil. However, here is a conventional fuel oil district heating
plant adjacent. The base-load refuse-derived steam is fed into the peaking
oil-fired plant prior to entering the district heating network.
-------
V-ll
Item
Number
12.
13.
Activity
Waste Oil Processing and Solvent Mixing
Waste Solvent Receiving Station
(Diagram shows the first two Von Roll units but not the third Unit
from Martin.)
FIGURE V-5. WASTE OIL AND SOLVENT RECEIVING, PROCESSING AND MIXING
LAYOUT AT ZURICH:HAGENHOLZ
-------
W-l
CO-DISPOSAL OF SEWAGE SLUDGE AND REFUSE
Co-Disposal, General Comments
In 1977, the Europeans were well advanced over North Americans in the
combined destruction of refuse and sewage sludge within ther same system.
Sev-en (7) such plants were visited in Europe. (See Table W-l.) Several other
plants are listed as well. Of note is that each of the six major European
manufacturers have a co-disposal system in operation.
Most processes involve several stages of drying as listed in Table
W-2. Typically, an initial unit will convert incoming raw sewage sludge at
9^-96 percent moisture to 70-80 percent moisture. At this moisture level, the
sludge has a thick consistency that can lead to dramatic further moisture
reductions down to 5-20 percent. The third stage of several processes is to
burn the dried sludge.
From a reliability standpoint, each of the described processes does
work a respectable part of the time. Unfortunately, economic data was not
available for enough systems to perform any kind of economic analysis.
Co-Disposal, Comments About Specific Systems
Krefeld
VKW's third generation co-disposal technology has been constructed at
Krefeld, West Germany, several miles west of Duesseldorf. The primary waste
water treatment plant, see Figure W-l, is on the same property as is the refuse
treatment plant. At the time of the visit in 1977, only primary undigested
sludge was being piped underground to the co-disposal plant.
Figure W-2 is a schematic showing the overhead arrangements at
Krefeld.
A major portion of the energy released in the two Krefeld boilers is
utilized in the drying of sewage sludge from the adjacent waste water treatment
plant. As indicated in the dotted area in Figure W-2 innediately east of the
present settling tanks, an activated sludge treatment addition is being built.
This should be on line by 1980. This may have a significant effect on the
anount of energy required for sludge drying.
Figure W-3 shows the sludge handling system. The settled sludge is
now pumped without further treatment to flocculating tanks where a chemical
conditioner is added. Then, with a water content of about 91* percent, it is
pumped to one of four centrifuses which reduce the water content to about 74
percent. The removed wster is returned to the wastewater treatment plant.
The partially devatered sludge then flows to a surge tank and thence
to the larpe Bebccck mills, one per boiler, where it is mechanically
disintegrated by the high speed paddles in an atmosphere of air mixed with hot
flue gas which is taken from near the top of the boiler radiation pass as shown
in Figure W-M (Item 13). The hot flue gs's thus enters the mixing chamber
-------
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-------
W-4
Co-Disposal Plan
Scale House
Administration Building
Sewage Sludge Pipeline X*
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Ki
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Secondary Waste Water Treatment Plant
Primary Waste Wa
FIGURE W-l. KREFELD WASTE PROCESSING FACILITY;
WASTEWATER TREATMENT PLANT ON LEFT,
REFUSE-AND SEWAGE-SLUDGE-BURNING
PLANT ON RIGHT.
-------
W-5
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FIGURE W-3. KREFELD SLUDGE-PROCESSING AND BURNING
SYSTEMS (COURTESY VEREINIGTE
KESSELWERKE).
1. Thickener
2. Sludge Tank
3. Sludge pump
4. Flocculating tanks
5. Metering pumps
6. Centrifuges
7. Surge tank
8. Heated hammer mill
9. Boiler
-------
fa
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-------
W-8
conveyed in an atmosphere of vapor and partially cooling flue gas. Experience
has shown that if this saturated conveying stream is allowed to cool too much,
some of the vapor will be recondensed on the very large surface available on
the fine, sludge particles. Long experience with mill drying of brown coal has
indicated that the moisture content should not be allowed to become too low, as
this greatly increases fire and explosion hazard within the mill system.
It is estimated that the moisture content of the particles leaving
the mixl and entering the furnace is about five to ten percent. The lower
heating value is about ^30 KCAL/kg (1800 KJ/kg) (77^0 Etu/pound).
An unusual feature of this furnace is that the dried sev;age sludge is
fired in suspension in hot flue gases at a point (labeled #14 in Figure W-iJ)
near the lower enc ofthe radiation chamber and within the section that is
coated with silicon carbide. Because the sludge particles still carry moisture
(10 percent) and because the moisture having been vaporized 'out of the sludge
is still in the hammermill exit gas, when both the particles and the vapor
enter the hot radiation chamber they will absorb considerable heat before the
paricles become heated to their ignition temperature. At point #13 in Figure
VM, a substantial amount, 2.7 to 3.9 Nm3/sec (5715 to 8256 scfm), of hot flue
gases are extracted from the furnace and sent to the sewage sludge hammermill.
For these reasons, there is not as much energy available for steam generation
as in straight refuse burning, and the radiation chamber is relatively snail.
Figure W-5 shows the estimated conditions entering and leaving the
drying mill as a function of drying rate. At full design rate,the furnace
burns 12 tonnes/hr (13.2 tons/hr) of refuse plus 6.^3 tonnes/hr (7.1 tons/hr)
of dewatered sludge. If, because of a reduced heat value in the refuse or
because of an extra moisture load in the sludge, the first pass outlet
temperature fells below the legal limit of 800 C (1^72 F), supplemental oil is
fired automatically to maintain that temperature. No. 6 oil has been used for
this purpose, but it is used so infrequently that it is difficult to keep the
hot oil system in reliable condition. Accordingly, No. 2 distillate will be
used in the future. As discussed in the fuel oil and waste oil section, waste
oil can no longer be used.
Table W-3 shows the drying system design conditions as affecting the
estimated dust loading of the gases entering the electrostatic precipitator.
Three different levels of refuse heat are considered. Mote that the
"effective" grate area shown is H8.16 m? (518 ft2) as contrasted with the
estimated 35.7 (38? ftp) used in the section on heat release where only the
equivalent flat surface is considered.
Figure W-5 shows the calculated dust load of the flue gases for
various "flow rates" of ash across the grate. The three calculation points on
the curve correspond to the conditions in Columns marked 1, 2, and 3 in Table
W-3.
The approximate composition of the sludge corning to the centrifuges
at Krefeld is:
Dry solids 6.5 to 7.0 percent
Ash 2.8 to 3.2 percent
Ash/solids HO.O to 45 percent
If the sludge is held too long in the thickener, digestion causes a loss of
volatiles which affects its burning charateristics. Mr. Koerbel, the plant
-------
W-9
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W-12
manager, emphasized that a key element in successful processing is to keep it
moving.
At present, the quantity of sludge available is greater in relation
to the refuse quantity than would normally be encountered. It is estimated
that the sludge to the Krefeld plant comes from an area serving a population of
about 600,000 while the 1JOO tons of refuse per day is from a populatin of about
300,000. Some local plants such as Bayer process their own wastewater. When
the Krefeld wastewater plant is modified for secondary treatment, existing
regulations covering pre-treatment of industrial wastes will be enforced.
The sludge drying system was not operating during either day of our
visit, May 20, 23, 1977, and data could not be released on the drying system
performance because accceptance tests had not yet been run on the plant.
However, a published design heat balance is available from an article in VG3
Kraftswerkstechnic. A subsequent call to Grumman Ecosystems, the American
licensee for VKW, revealed that the sludge system are working very well. There
had been a modification after the Battelle visit to improve the sludge handling
from the hopper (under the centrifuge) to the mixing chamber. The sludge which
had been agglomerating along the way, now passes evenly and enters the mixing
chamber much more evenly.
Dieppp (and Deauville)
This confiring system patented world-wide by Von Roll for
steam-drying and cofiring sewage sludge with refuse was guaranteed at Dieppe to
handle 75 percent refuse and 25 percent dried sludge (by weight). At Dieppe,
there are two vertical LUWA dryers about 0.6 m (1.9 ft) inside diameter having
a nominal drying capacity of 900 liters/hr (238 gal/hr) of digested sludge
having a water content of 92 percent. At Deauville (50 miles away), there is
only one larger LUWA dryer having a nominal capacity of 1,100 liters/hr (271
gal/hr). Normally it operates at 900 liters/hr, 2J)-hours/day in the summer and
^ to 6 hours/day in the winter. Evidently, for the new Deauville plant, the
reliability of the LUWA dryer was deemed such that redundancy was unnecessary.
Dieppe was the first to use the LUWA dryer for sewage slud&e.
Figure V—l shows the two LUWA dryers. The inside of the dryer i s: a
smooth stainless steel cylinder having a surface of 5.3 ^2 (57 ft2) heated to
about 130 C (256 F) by saturated steam. See Figure W-8. The sludge is
delivered to the dryers by a dosing pump which sprays it agair.st the hot
surface which is rapidly scraped clean by vertical rotating blades attached to
a central shaft rotating at 250 rpm. Centrifugal force keeps the boiling
sludge against the hot steel surface as the blades force it to rotate. Gravity
causes the drying sludge particles to drift downward along the steel heating
surface. The product falling from the bottom of the dryer onto a belt conveyor
is partially dried sludge agglomerations having 40 to 45 percent moisture. A
television camera sighted on the conveyor enables the control room, operator to
monitor the sludge blow.
The conveyor delivers the clumps (seldom over 2") to a chute leading
to the refuse hopper. To eliminate dryer exhaust odor, the wet vapor from the
dryers is fed to the upper part of the furnaces. At the Deauville plant, tc
avoid having droplets returned to the furnace with the vapors, a steam-heated
-------
W-13
FIGURE W-7.
TOP OF TWO LUWA SLUDGE DRYERS AT
DIEPPE (COURTESY OF VON ROLL, LTD.)
-------
W-14
FIGURE W-8. CUTAWAY DRAWINGS SHOWING PRINCIPLE OF LUWA
DRYER (COURTESY OF VON ROLL, LTD.)
-------
W-15
vapor reheater is used to dry the vapor before it is injected into the furnace.
At Dieppe, a radioactive sludge feed indicator was installed but it is no
longer used.
An unkown amount of exccess steam is sent to a river water-cooled
condenser, the condensate from which is returned to the boiler.
Krings has prepared Table W-1 in which he estimated the amount of
excess heat generated by the Dieppe plant under three different rates of
operation. In that calculation, no explicit allowance was made for the heat
value of the partially dried sludge. That is a realistic policy for sludge
having a moisture content of MO percent or more. For although the partially
dried sludge does release some heat when burned, the amount released from the
sludge is not a large proportion of the total liberated in the furnaces.
Table W-5, from Eberhardt, shows the heat value of various raw
sludges. Figure W-9 from Eberhardt shows the relation of heat value to ash and
combustible content. From this, it is evident that although the combustible
portion of dry sludge may have a lower heat value of up to 10,000 Btu/lb (5,555
Kcal/kg), it is usually so diluted by ash and water that the net heat value is
low.
In 1973, test were run at Dieppe, one result of which was Figure W-10
by Krings showing the efficiency of the LUWA dryers. Three of the lowest
points .near the center of the figure show the results from fresh, undigested
sludge. This indicates that this digested sludge was more readily dried than
the raw sludge.
Some difficulty is experienced at both plants when fibrous materials
clog the dryer feeding system.
The operating group, Thermical-IIJOR, is required by its cor.tract with
the city of Dieppe to gather and submit performance data for the refuse and
wastewater plants. Tables W-6 and V.'-7 show the refuse plant results for the
year 1976. The total two-furnace operating time of 6,228 hours is 35 percent
based on p. total of two time is M5 percent. As indicated early in this report,
the Dieppe plant v:as sized in anticipation of considerable growth in load.
Tatle W-8 summarizes the refuse plant operation over the 5 years,
1972-1976. Load and performance have been quite steady over the period.
Korsens
The Horsens wastewater treatment plant serving a population of 33,000
was built adjnoent to the refuse burning.plant so that the difficult problen of
sewage sludge disposal could be assisted by partial drying of the sludge.
Figure W-ll is a schematic view of the plant in which the rotary kiln
type of dryer is emphasized.
Typical analyses by the city laboratory of sludge pumped to the dryer
are as follows:
pH
Dry Solids, percent
Combustible, percent of DS
May 2*4. 197*4
5.52
13.3
66.7
Sept. 5. 1977
7.2
6.5
H6.7
The sludge is coagulated at the wastewater plant by means of a
polyelectrolite and is then centrifuged before being pumped to the,dryer.
-------
W-16
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FIGURE W-9.
PLOT BY EBERHARDT OF RELATION OF
COMBUSTIBLE AND ASH CONTENT OF DRY
SEWAGE SLUDGE TO ITS LOWER HEAT VALUE
Source: Eberhardt, H., European Practice in
Refuse and Sewage Sludge Disposal
by Incineration, Proceedings,
1966 National Incinerator Conference,
ASME, New York, May, 1966, pp 124-143.
-------
W-19
f ~*i f ;""'f:":Trri"t~rr: r*"T"j-:::rrTT;~ :?
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ffidiencyj.oi; the dryer L^JiLJIJk:;
FIGURE W-10.
KRINGS RESULTS OF TESTS IN 1973
AT DIEPPE ON THE EFFECT OF TYPE OF
SLUDGE AND SLUDGE FEED RATE ON THE
EFFICIENCY OF THE LUWA THIN-FILM
DRYER
Source: .Krings, J., French Experience with Facilities
for Combined Processing of Municipal Refuse
and Sludge, Proceedings, CRE-Conference on
Conversion of Refuse to Energy, Montreaux
Switzerland, November 3-5, 1975.
y Water
0 Fresh Sludge - 97 Percent Water
© Digested Sludge - 98 Percent Water
A Digested Sludge - 95 Percent Water
(3 Digested Sludge - 92 Percent Water
-------
W-20
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W-24
The rotary kiln receives digested sludge from the sewage plant and
reduces it from it nominal 5 percent dry solids content to approximately 70
percent dry solids. Hot flue gases and sludge are fed into the rotary kiln at
the same end. The rotating part is carried on two rollers for axial control.
A special scoop system ensures effective contact between flue gases and sludge.
The rotary kiln is insulated with rockwool, covered with steel plate. The
inlet end is lined with refractory brick.
The incoming sludge is fed by a monopump and the dried sludge is
emptied by means of a spiral conveyor which leads the dried sludge to the
clinker transport system, directly out of the building to a storage area.
There are then four possibilities for displsal of the dried sludge:
(1) Deposit with the clinker
(2) Burn in the furnace
(3) Utilize as fertilizer
(4) At present, it is deposited in the landfill.
The kiln has the following specifications:
Rotary dryer diameter: 2.5 n (8.2 ft)
Length of dryer drum: 16 m (52.5 ft)
Incominc sludge: Approx. 5 percent dry solids
Outgoing matter: Approx. 70 percent dry solids
Capacity: 5 rr.3/hr (22 gpm) of wet sewage sludge
Inlet flue gas temperature: Approx. 900 C (1,652 F)
Outlet flue gas temperature: Approx. 225 C (427 F).
The sludge is reduced from approximately 5,000 kg/hr (11,000 Ib/hr) to
approximately 360 kg/hr (792 Ib/hr) by going through the drying process. This
represents an evaporation heat rate of about 2.70 Gcal/hr (10.2 M Btu/hr).
Some difficulty was encountered with odor from the kiln until high
enough operating temperatures were assured on startup and shutdown.
The recent retrofit of the furnace with a boiler (described in the
toiler chapter) to produce district heating hot water will change some of the
above numbers.
Copenhagen: West
While touring either the Copenhagen: West facility or the Hague plant,
these researchers observed a sewage sludge tanker truck disgourging material
into the pit over .the refuse. The crane operator would then distribute the wet
refuse over the other material.
Because the furnace/boiler was drawing its combustion air from the
refuse pit, odor would not escape from the building. However when one stands
above the pit near the hoppers and near the primary air intake vent, the odors
are most pronounced.
Harris'ourg, Pennsylvania, U.S.A.
Battelle, under contract withh the U.S. EPA has been testing the
hypothesis that the sulfur inherent in sewage sludge will (when mixed with
chloride containing Defuse in the pit) inhibit formation of corrosive chloride
deposits on boiler tubes. Initial results are positive and promising.
-------
• W-25
Ingolstadt
Of the 30 plants visited in Europe by Battelle staff, 15 were viewed
during two-hour walk-through tours. Ingolstadt, Vest Germany was viewed while
75 percent constructed. Figure W-12 shows a schematic of the plant. Because
of the small print, the verbal description appearing at the bottom is repeated
below:
Activity One: Pretreated (filter-press, vacuum or centrifugally
dried) sludge with a moisture content of 75-80 percent 1^0 is charged
into a hopper and transported by a chain conveyor to the storage tank
(sludge silo) that is equipped with a mixing device. Controllable
screw-conveyors extract the sludge from the stora'ge tank and transport
it to the twin mixing worm.
Activity Two: This twinmixing worm is also fed with already dry
sludge that is mixed with the wet sludge to a mixture of sludge with a
mositure content of 35-^0 percent 1^0. After this mixing the sludge
in trickling form is inserted into the flue gas down duct. The flue
gases are extracted from the refuse incineration combustion chamber
with an approximate temperature of 850 degree C (1600 degree F) and
fall downwards together with the sludge to a hammermill. Before the
hot gases and the sludge reach the hammermill, the heat exchanger and
evaporation and drying process starts. In the mill the sludge is
disintegrated in very small particles (dust) and dried under the
influence of heat.
Activity Three: The gas-sludge mixture is transported through a
vertical upv:ards duct (suspension dryer), where final drying takes
place. In a cyclone the sludge is separated from the flue gases and
falls via a rotary vlave and a duct into the dry sludge storage tank
(intermediate bunker). The moist flue gases are further cleaned in a
multicyclone ane reintroduced into the combustion chamber by aid of an
exhaust vapor fan. The flue gas sstream is controlled by dampers and
can be bypassed into the extracted flue gas stream to maintain a set
tenpe^ature. The separated, dry sludge with a moisture content 5-15
percent 1^0 in the intermediate storage tank can be extracted via
rotary valves ard be used as follows:
to be mixed with the wet sludge
- to be introduced and burned in the combustion chamber
in suspension above the grates
to be filled into bags for use as fertillizer, depending
or contamination, especially heavy metals.
A certain amount of dried sludge has to be stored in the intermediate
tank for the purpose of mixing to the wet sludge at start-ups.
Whenever necessary the installation is insulated against heat losses.
An'automatically operated measurement and control system allows
supervision and control of the installation from the main control room.
Activity Four: Sludge incineration. A fan generates-the necessary
air for pneumatic transprot of the dry sludge tg the refuse
incineration combustion chamber. The sludge burners are developed to
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-------
W-27
burn dried sludge and ensure a fast and total thermal reduction of the
sludge in suspension above the gates. There is one burner installed
on each side of the combustion chamber.
Biel
The Mura, Binne environmental part at Biel, Switzerland was another
plant briefly visited. Figures W-13 and W-1H present the overhead plan and
actual view of this wastewater treatment plant, the co-treatment plant and the
compost area. These researchers made no attempt to collect design or operating
data.
Aerobic Composting Danoklin Plus Bridge. Refuse.is received .and
either goes to a Bema shredder or a Buhler hammermill. Some of the
sized-reduced material along with sewage sludge is injected into a Dano rotary
kiln. (See Figure W-15) where the residence time is 2 to 3 days. At the drum
exit, the material is screened. Particles under 25 mm (1 inch) are transported
to the outside composting area shown in Figure W-16. The rotating bridge turns
the material over two times per week so that aerobic decomposition can
continue. This continues for H to 6 month prior to sale to vineyards. Some of
the material is further sieved and sold as pig feed. (See Figure W-17).
Anaerobic Composting (Bricolari Press). The other size-reduced refuse
and sev;age goes through (1) a tromirel (60 mm mush size), (2) a high speed rotor
to separate glass, (3) a second screening to collect particles under 6 mm (.25
inch), (Jl) a buffer storage. Sewage sludge is then dried slightly from 95
percent tc 80 percent v:ater in a centrifuge. Next, the refuse (less than 5 mm
jn si?e) is mixed with the sewage sludge (80 percent water) in a double screw
mixer.
The Bricolari compactor press then produces the 500 x 200 x 200 mm (2^
x 8 x 8 inch) bricks at a combine^ moisture content of 50 to 55 percent water.
The bricks are stacked as shown in Figure W-16 for ^ to 5 weeks. The apparent
advantage to the Bricolari process over the Dano/kiln/bridge aerating system in
several fold. The Bricolari process, being aerobic requires less time thus
permitting higher turnover and less land use. Once the Bricolari brick is
formed and slacked, there ir. no activity uutil shipment. To repeat this
compares with the aerobic turning of material by the crane 2 to 3 timer per
week fc~ ^ to 6 months.
-------
W-28
FIGURE W-13. OVERHEAD PLAN FOR THE ENVIRONMENTAL PARK
AT BIEL, SWITZERLAND
A Administration
B Workshops
C Cloakroom, Showers,
Restrooms, Cafeteria
1 Balance Bridge (30 t)
2 3 Refuse Silos
3 Composting Control Room
4 Biological Stabilizer Halls
5 Sifting Room
6 Compost Unloading Bridge
7 Layers Location
8 Qualitv Composting Hall
9 Silo for Sifting Residues
and for Industrial Wastes
Furnace
Smoke Stack
Slags Location
10
11
12
13
Used Oils Settling
Is Room for Compressors, heating
equipment and emergency generator
15 Screw Pump Station
16 Control Rootn
17 Mechanical Grate
18 Oil-Sand Separator
19 Flow Channels
20 Primary Settling Basin
21 Rainwater Discharge
22 Aeration Tank
23 Secondarx Settling Basis
24 Mud Recirculating Screw Pumps
25 Discharge intn the Nidau-Buren Canel
26 Primarx
DiKesti^n Tank
27 Secondarv
28 Thickeness
29 Scairwav, Methane Gas Desulfurat ion
30 Gasmeter
FIGURE W-14. AERIAL PHOTO OF ENVIRONMENTAL PARK
AT BIEL, SWITZERLAND
-------
W-29
This Dano Kiln
has been r
and replace
by a
Bricolari
Press
FIGURE W-15. ORIGINAL DANO KILNS FOR COMPOST INITIATION
AT BIEL, SWITZERLAND (RETENTION TIME 2-3 DAYS)
FIGURE W-16. AERATION TURNING BY PIVOT BRIDGE
FINAL COMPOSTER AT BIEL, SWITZERLAND
(RETENTION TIME 4-6 MONTHS).
(Notice residential neighborhood
in background).
-------
W-30
FIGURE W-17. PIG FEED MADE FROM DIGESTED
SEWAGE SLUDGE AND REFUSE
-------
W-31
-------
X-l
AIR POLLUTION CONTROL
Development of Emission Controls
Particulates
The emergence of the refuse-fired steam generator in Europe in
the 1960's was a direct result of the growing desire for pollution
control-particularly control of flyash that made nuisances of many old
incinerators. That is, the very dusty, hot gases from the incineration
process had to be cooled before practical high efficiency flyash control
could be applied; and the most logical means for cooling that gas is by
means of a boiler to produce useful hot water or steam. In some cases,
usually small plants, where energy recovery was not attractive, the gas
cooling has been achieved not through heat recovery but by means of water
sprays or air-cooled heat exchangers. However this energy wasteful practice
has not become widespread.
Regardless of the method used for cooling of the dusty flue gas,
the almost universal method for particulate removal from the partly cooled
gases has been electrostatic precipitation, (ESP). Here again the
considerable experience already developed in coal-burning practice was
available to guide the application of ESP's to RFSG. One attempt was made
to apply cloth filtration (baghouse) at Neuchatel but, although the system
is still in operation, the results obtained were not outstanding.
Table X-1 shows the characteristics of the ESP's at the plants
visited.
Precipitator Maintenance
Reliability of ESP's has been excellent except where the inlet
gases have been too hot: above about 260 C (500 F). This has caused very
rapid corrosion and deterioration of the precipitator. In most cases this
overheating has been caused by an unanticipated increase in the heat value
of the municipal refuse or wearing of the grate systems. Then if the boiler
heating surfaces were not amply designed to cope with the resulting
excessive heat release in the boiler-furnace, the gases pass on to the
precipitator at high enough temperature to cause serious corrosion. In some
cases this overheating may not occur until toward the end of a long period
of operation when the heating surfaces are heavily coated by ash. Many
plants then shut down for thorough boiler cleaning, usually after 3000 to
UOOO hours.
Gases
Some attention is now being given to controlling gaseous
emissions - HC1, HF and S02- However these gases are not emitted in high
concentrations, and their ambient levels in the vicinity of even the
largest plants is probably so low that no attempts have been made to
measure nor to estimate them continuously in the surrounding air. Instead
their control is considered just because they are perceived to be bad. At
-------
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X-3
present only in VJest Germany are new or modified plants now required to
control gaseous emissions. The emission permitted levels (at OC, 32 F,
corrected to 7 percent CC^) are:
HC1: 100 mg/Nm3 (62 ppm) 0.083 lb/1000 Ib gas
HF: 5 mg/Nm3 (11 ppm) 0.008 lb/1000 Ib gas
S02 500 mg/Nm3 (175 ppm) 0.^6 lb/1000 Ib gas .
(only in areas with high ambient SOX levels)
Accordingly only in Germany are scrubbers being tried. None was
working satisfactorily at the new plants visited which had just installed
new scrubbers. However, except for the very major maintenance problem
always caused by the corrosiveness of acidic scrubber water, HC1 should not
be difficult to cortrol because it is highly soluble in water. HF should
also be absorbed in a scrubber but the scant data available on HF emissions
indicates that the German limit of 11 ppm at 7 percent CC>2 is readily met
without scrubbers. Similarly, the sulfur content of refuse is so low that
the probable capture of 25 to 59 percent of the sulfur by the alkalis in
the ash means that SC>2 control will often be unnecessary to meet the 175
ppm emission limit in Germany.
One vexing aspect of scrubbers is that the saturated gas leaving
the scrubber often creates a highly visible white steam plume. It may
actually be a very clean plume but its appearance calls attention to
possible emissions. Also if conditions are such as to produce large water
droplets in the plume the resulting "rain" will be acidic because no
scrubber removes 100 percent of the acid gas. The solution to a white plume
and its acid rain is to reheat the plume to about 80 C (176 F) by means of
steam-heated heat exchangers. However, reheaters consume energy and are
subject to plugging and corrosion. One practical solution to this problem
will be used at Wuppertal. The plan is to scrub a major part but not all of
the gar, to a level surpassing the allowable limit, meanwhile by passing the
unoleaned portion of the hot gas to a mixing and reheat section. The
resulting reheated mixture can then be discharged without visible plume or
acid rain while still being within the allowable emission limit.
Measured Gaseous Emissions
Table X-2 shows the results of emissions measurements at selected
plants. The very large differences in HC1 emissions among the plants is
expalinable only by the great diversity of materials in MSW. Probably
variations in the amount of polyvinyl chloride burned is the major cause of
the large differences.
Gaseous Emission Limits
Table X-3 shows the emission limits applicable to refuse burning
in the countries visited.
So far only in Germany and Sweden is there any limit on gaseous
emission?, and even in Sweden the value of 40 mg/Nm3 (approx. 20 ppm) of
total acid gases is not a limit but a signal: if a plant exceeds that
emission level it must undertake a study of feasible means to control
emission. Presumably then actual control requirements will depend on the
-------
X-4
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-------
X-5
TABLE X-3. EMISSION LIMITS, mg/Nm
(Parentheses indicate C0~ level to
which the concentration is adjusted)
COUNTRY
W. Germany
Switzerland
France
PARTICULATES HC1
mg/Nm mg/Nm
1 tonne/hr
1-4 tonne/hr
4-7 tonne/hr
7- (15) tonne/hr
100(7) 100(7)
100(7) 500(7)
1,000(7)
600
250
150
HF S02
3 3
mg/Nm mg/Nm
5(7) 500(7)
300(7)
_ _
(1)
over(15)tonne/hr 80
Holland
100(7)
Sweden
180(10)
40(10)
(2) (2)
(2)
Denmark
USA
small plants
large plants
180(10)
150 (11)
1,500
1,500
(3)
(1)
(2)
(3)
Estimated from incomplete data.
Total acid equivalent - Exceeding this total, 40 mg/Nm3 for all acid gases,
feasible control system.
S02 plus S03>
The conversions to volume units are:
HC1
HF
multiply mg/Nm3 by Q.62 to get ppm
;; ;; 1.12 to get PPm
0.35 to get ppm
To convert particulates: mg/Nm3 to grains/scf, multiply by 43 x 10~5
-------
X-6
cost of feasible control and whether the need for improvement in local
atmospheric quality levels warrant that expenditure.
Trends in Emissions Control
As can be seen from Table X-3 and the prior discussion,
particulate control in these plants is excellent and high standards are
regularly achieved. There is no strong trend in Europe to further control
particles nor to control gaseous emissions. Many agencies appear to be
awaiting the demonstrated effectiveness and reliability of the acid gas
scrubbers now going through normal problems of startup in Germany at
Wuppertal, Krefield and Kiel which latter plant was visited briefly. If
these eventually prove out to be as effective, maintainable and relatively
as economical as ESP's there will probably be a trend to apply them more
widely, especially in densely populated areas where ambient pollution
levels are high. On the other hand, there are no data available to
demonstrate the specific needs for elimination of HC1 and HF from the
ambient air. Hence, if their removal turns out to be as formidable a task
as SOp control has been for coal-fired plants, the control of HC1 and HF
emission may become limited to those situations where a specific measurable
need can be shown.
Specific Comments about Air Pollution Control at Plants Visited
Werdenberg-Liechtenstein
During our 3-day visit to this plant, there was no visible plume
most of the time and even when visible, it was only barely so againt a very
clean sky. Pollution control at this small plant is by a single-field
electrostatic precipitator by Elex. Without the hopper it is 9.3 m high,
5.7 m wide, and 5.9 m deep. It has a flow rate of 83,000 m^/hr at (^8,800
cfm) at 274 C (525 F). Average velocity is 0.67 m/sec (2.2 ft/sec). The gas
composition and deupoint at the precipitator during the compliance test was:
• C02 - 5.4 percent
• HpO - 30.5 percent
• Dewpoin't - 51 C (12*4 F).
Particulates are now limited to 100 mg/Nm^ (0.0438 grains/ft^) corrected to
7 percent C02- When tested, it achieved 88 mg/Nm3 (0.038 grains/ft^).
Bypassing of precipitators has not been permitted since 1972.
The precipitator and its duct configuration were tested
beforehand by Elex in a small water model to assure a uniform flow pattern.
To distribute the gas flow ahead of the charging section, there are
perforated plates in series containing 5 cm holes. The spacing of the
collector plates is about 300 mm (11.8 in) providing 17 parallel flow
passages. Residence time is 5.9 sec. Total plate area is 1,142 m2 (12,288
ft2) with a projected area of 952 m2 (10,2*13 ft3). The plates are cleaned
imtermittently by a bottom rapper. The charging electrodes are cleaned by a
rapper at the top.
Power consumption is 29 5
-------
X-7
The fly ash hoppers are approximately 50 degree inverted pyramids
electrically heated and covered with 10 cm (U in) of insulation. The
collected ash is removed continuously by screw conveyors with discharge
into the main residue quench tank.
The precipitator was guaranteed to achieve 97.5 percent
efficiency and to emit no more than 100 mg/Nm^, wet, at 7 percent C02.
So far, the precipitator has needed no repairs. It is cleaned
once per year when the boiler is cleaned. For personnel protection, the
access doors cannot be opened before an 8-multiple key sequence is
processed.
To achieve even lower particulate emissions from future plants,
the manufacturer is considering the use of two-field precipitators.
Baden-Brugg
There was no visible plume at any time during our 3-day visit to
the Baden-Brugg plant. Pollution control is by 2 single-field Elex
electrostatic precipitators followed by 2-stage multicyclones. Without the
hopper the precipitators are 7 m high, ^.45 m wide, and 7 m deep. They have
a flow rate of 6^,000 Nm^/hr. (37,65*1 scfm). Average velocity is 0.7 m/sec
(2.3 ft/sec). The gas at the precipitator contains 6-7 percent carbon
dioxide. Particulates are now limited to 100 mg/Nm3. When this plant was
designed, the allowable limit was 150 mg/NnP. When tested by the
manufacturer, it achieved 110 mg/Nm-. With the multi-cyclone alone the
emission was MOO mg/NnH.
The precipitators and their duct configuration were tested
beforehand by Elex in a small water model to assure a uniform flow pattern.
Residence time is 5.9 sec. Total plate area is 612 m^ (5587 ft') with a
projected area of 952 m2(iO,2U7 ft3). The plates are cleaned intermittently
by a bottom rnpper. The charging electrodes are cleaned by a rapper at the
top. Output capacity is 55 KVA at 55,000 volts and 506 ma.
The fly ash hoppers are approximately 50 degree inverted pyramids
electrically heated and covered with 10 cm (*J in) of insulation. The
collected ash is removed continuously by star feeders with discharge
directly downward into the main residue quench tank.
The precipitator was guaranteed to achieve 97 percent efficiency.
Assuming an inlet loading of 5 grams/Nm3 the measured efficiency was 97.8
percent.
So far, the precipitator has needed no repairs. It is cleaned
once per year when the boiler is cleaned. For personnel protection, the
access doors cannot be opened before an 8-multiple key sequence is
processed.
To achieve even lower particulate emissions from future plants,
the manufacturer is considering the use of two-field precipitators.
The precipitators have suffered no serious corrosion during the
normal weekend shutdowns. Initially cracks in the porcelain insulators
caused arcinc but this was cleared up by replacing them with other ceramic
insulators. In 29,000 hours of operation over 7 years there have been no
electrodes not plates replaced.
-------
X-8
Duesseldorf
The four original boilers at Duesseldorf which started in 1965
were equipped with two Lurgi Electrostatic Precipitators having a design
efficiency of 99 + percent. In each precipitator, the gas flow is divided
into 28 passages, each 0.225 m (8.5 in) wide. The height of the passage is
6.27 m (20.6 ft) and its flow length is 5.75 m (18.9 ft). Total projected
collection area in each precipitator is 2020 m2 (20,800 ft2). The inlet
flow area is 37.5 m2 (406 ft2) and the design velocity is 1.1 m/s (3.7
ft/s). Design flow rate was 39,000 Nm3/hr (22,952 scfra).
Table X-4 by Konopka* gives the results of two precipitator tests
at this plant in 1967 by the government testing organization, Technische
Ubervachungs Verein Rheinland, e.v. (TUV). The report indicated that in one
test, the combustible content of the collected dust was 6.6 percent and its
resistivity at 220 C (^32 F) was 6 x 10? ohm-cm. Similar values were
recorded by TUV at Munich and Stuttgart.
Boilers No. 3 and 4 are served by an identical precipitator to
that serving Nos. 1 and 2. Boiler No. 5 is served by a third precipitator.
All three precipitators arc connected by a manifold to a single chimney. By
means of mulit-vane butterfly dampers, the flow from any two boilers can be
fed to either three precipitators. The damper blades are 57^ mm (22 in)
wide and are shaped to present a "knife edge" to upstream and downstream
flow when open. This shape helps to minimize deposition of ash on the
blades. The upstream edge of each blade is made of manganese steel. To
further discourage deposition and erosion, each blade is shielded upstream
by a manganese steel I-bar positioned 20 mm (0.79 in) upstream. The damper
assembly was made by Uarmekraft-Gesellschaft-Stober Morlock of
Recklinghausen, Germany.
The installation of precipitator No. 3 for Boiler No. 5 by
Rothemulle in 1972 was preceded by a flow model study although the
approaching flor pattern produced by the flue gas manifold was not modeled.
It has two fields and 30 rows of collector plates spaced 300 mm (11.8 in)
apart. The plates are 10 m (32.8 ft) high and each field is 3 m (9.8 ft)
long. Effective projected collector surface is 3,600 m2 (38,730 ft2).
Perforated distributor plates produced an excellent velocity flow
distribution entering the first field at an average velocity of 0.83*1 m/s
(2.7^ f/s). Residence time is 7.2 seconds.
A power supply of 95.5 KVA is available to each field at 55 KV.
No-flow vol'tage is 78 KV. Normal current is 600 ma, maximum 900 ma. Power
consurption per field is 33 Kw.
Rapping is by means of gravity hammers operated automatically in
a prescribed sequence. Unlike many outdoor precipitators, these hoppers are
not heated. They ,are covered with 100 mm (3.9 in) of insulation. There is
no problem of condensation causing sticking of the ash in the hoppers
because there is no storage of fly ash there.
Originally, the ash removal system was pneumatic but this was
abandoned after 2 years and was replaced by screws. Some modification of
the fitting of the screws to the hoppers was needed to facilitate ash
removal.
One 2^-hour test by TUV showed the particulate emission rate to
range from 30 to 100 mg/Nm3 corrected to 11 percent C02 (0.0352 to 0
grains/ft-).
•Konopka, A.P., "Systems Evaluation of Refuse as a Low Sulfur Fuel,
Part 3 - Air Pollution Aspects", ASME Preprint 71-WA/Inc-1, 1971, ASME,
New York, NY, 10017.
-------
X-9
TABLE X-4. RESULTS OF TWO PERFORMANCE TESTS BY TUV ON A PRECIP-
ITATOR AT THE DUESSELDORF REFUSE PLANT
ft3/S
3
Actual Gas Volume m /S
ft3/S
Test Number
Firing Mode
o
Rated Gas Volumes m /S °C
°F (V Design)
°C (Measured at ESP
°F (V Actual)
1,000 ACFM °F
Percent of Rating (Percent)
Actual (Test) ESP Inlet Dust Cone. (g/Nm )
(gr/SCF)
Actual (Test) ESP Outlet Dust Cone. (g/Nm )
(gr/SCF)
Guaranteed Collection Efficiency (Corrected for Actual
Test Conditions per Manufacturer's Corrosion
Factors (Percent)
Actual (Test Collection Efficiency) (Percent)
ESP Design Gas Velocity at Rated Volume (m/sec)
(ft/sec)
ESP Actual (Test) Gas Velocity (v) (m/sec)
(ft/sec)
Design Migration Velocity (ft/sec)
Actual Migration Velocity (ft/sec)
ESP Electrical Energization Data
Secondary Kilovolts Inlet (KV) (Inlet/Outlet)
Secondary Mill-amps (MA) (Inlet/Outlet)
Input Power (Kilowatts) (Inlet/Outlet-)
Power Density-Watts per 1,000 ACFM (Inlet/Outlet)
2
Power Density-Watts per ft (Inlet/Outlet)
Field Strength-Kilovolts per Inch (Inlet/Outlet)
1
Refuse
44.00260 C
1,550.0@500 F
Outlet) 43.0@235 C
1,520.0@455 F
91.00455 F
97.7
11.0
4.31
0.036
0.0158
98.35
99.67
1.16
3.82
1.14
3.74
0.408
0.399
31.5/29
265/267
8.3/7.7
91.7/85
0.401/0.372
0.74/0.68
2
Refuse
44.0@260 C
1,550.0@500 F
43.5@242 C
1,535.0@460 F
92.0@405 F
98.9
13.1
5.69
0.042
0.0184
98.95
99.68
1.16
3.82
1.15
3.77
0.319
0.406
31/29
313/310
9.7/9.0
105/97.7
0.466/0.432
0.73/0.68
NOTE: N = corrected to 0°C and 760 mm Hg; 0.0736 mm Hg. water vapor pressure.
-------
X-10
The applied voltage on the precipitators must be continuously
recorded as required by the county licensing board. The record must be
stored fa1" 5 years.
The availability f-or service of the individual precipitators is
shown by the record for a 2-year period:
Availability, Percent
1975 1976
Precipitator No. 1 99.3 99.2
Precipitator No. 2 99.6 100.0
Precipitator No. 3 100.0 92.7
Figure X-1 is an example of two of the operation and maintenance
computer cards which are used at the plant to maintain systematic records
on the precipitators and other components.
Wuppertal
Scrubber. The pollution control equipment at Wuppertal is unique
in that the four conventional electrostatic precipitators are followed by
two scrubber? to remove most of the HC1 and HF emitted. At the time of the
plart visit, May 1977, the scrubber system was still under construction,
hence, no data are available on scrubber performance. The performance
criteria is that emission of HC1 shall not exceed 100 mg/Nm^ corrected to 7
percent CO?" ?he ducting is arranged so that when, as normal, three units
are burning, the gases from only two will pass through the scrubbers. The
unscrubbfd hot gases will then be mixed with the cool, scrubbed gases,
about 60 C (1'iO F), for purposes of reheat to about 200 C (390 F) to
sugirert exhaust plume buoyancy and invisibility.
Precjpitator. The four electrostatic precipitators vere
manufactured by Buttner-Schilde-Haas under license from Svenska
Flaktfstriken. They are 7.95 m high, 7.15 m wide, and 10.2 m deep (26 x 23
x 33 ft). Table X-5 shows the precipitator design characteristics.
struction was not preceded by a flow model investigation. No performance
date, were available at the time of the visit, Hay 1977.
At first there was some problem with ash buildup in the fly ash
hoppers but an increased slope of the hopper sides eliminated that problem.
Initially, there was some problem from vibration of the induced
ri^aft f^ns caused by dust deposits on the blades. Improved control of
burning appears to have eliminated that problem.
At the tine of the visit the scrubbers were not yet completed and
the precipitators had not been tested. The appearance of the stack plume
and plant was extremely clean and attractive.
A striking and very unique indication of the need to keep this
plant clean is that a public swimming pool is within clear sight of the
plant in the narrow valley below. Figure X-2 showing the pool, was
photographed from the plant conference room window. The distance from the
plant property to the pool is about 120 m (UOO ft).
-------
X-ll
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-------
X-12
TABLE X-5. PRECIPITATOR DESIGN CHARACTERISTICS
AT WUPPERTAL
Gas flow rate
Maximum gas temperature
Clean gas conditions
(at 220 [428 F] and 8% C02)
Number of fields
Projected collecting surface
Residence time
Particle drift velocity
Free gas flow area
Gas flow velocity
Number of power packs
Input power
Operating voltage
Power
Current
Power consumption
Hopper heaters (2)
SI Units
100,000 Nm3/h
290 C
100 mg/Nm3
2
2,810 m2
7.0 sec
8. 24 cm/s
48.8 m2
1.03 m/s
2
380 V/50 hz
45 KV
46 KVA
600 mA
27.6 kw
220 V/8 kw
ENG. Units
58,860 scfm
554 F
0.044 gr/scf
2
30,230 ft2
7.0 sec
0.23 f/s
525 ft2
3.4 f/s
2
380 V/50 hz
45 KV
46 KVA
600 mA
27.6 kw
220 V/8 kw
Source: Courtesy of Vereinigte Kesselwerke.
-------
X-13
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-------
X-14
Krefeld Co-disposal Plant
At the refuse-sludge co-disposal plant at Krefeld, the exhaust
gases are cleaned by two electrostatic precipitators and by two scrubbers.
Table X-6 gives the design characteristics of the precipitators. No test
data are yet available on precipitator performance. The precipitator was
built by Buttner-Schilde-Haas of Krefeld, a member of the Babcock group,
under license from Svenska Flaktfabriken. While visiting this plant, May 20
and 23, 1977, the stack plume from single boiler operation was usually
invisible. At one period, during startup with the heavy oil burner, some
smoke was observed, apparently because the system was cold and the outer
portions of the oil flame were quenched before combustion was complete.
Scrubbers at Krefeld. In accordance with the new Federal
Regulation of 197*1, referred to earlier as T. A. Luft, a scrubber system
has been added to the Krefeld plant following the precipitator and also
following the induced draft fan. The scrubbers installed by Lugar are
designed to achieve the following emissions:
HC1: 100 mg/Nm3
S02: 100 mg/Nm3
HF : 5 mg/Nm3
NOX: 265 mg/Nm3 (Not subject to regulation)
All corrected to 7 percent C02.
Figure X-3 shows the water systems for the entire plant including
the scrubber. The sketch of the scrubbers implies that the scrubbers are
simple vertical spray-type units with some provision for demisting. A
separate fan and steam-heated air heater is used for mixing hot air with
the cool, saturated gases leaving each scrubber.
No test data are yet available on the flue gas cleaning system.
Assuming that the scrubber system can be brought to a high level of
reliable operation, this plant will then become one of the most advanced
waste-to-energy plants in the world .
Paris; Issy
The Issy-les-Moulineaux plant in Paris is relatively old (1965)
but has excellent emission control. The four furnaces, each with a Lurgi
electrostatic precipitator (ESP) feed into two chimneys.
Furnace Exit Conditions. Each boiler supplies 130,000-150,000
Nm3/hr of 300 C (572 F) temperature combustion gases to the precipitators.
A typical boiler exit gas composition adjusted to 7 percent C02
is as follows:
Particulates 2000 to 5000 mg/Nm3
C02 7 percent
02 11 percent
N2 69 percent
H20 13 percent
S02 100 to MOO mg/Nm3(35 to 140 ppm)
NO* 100 to 200 mg/Nm3 (49 to 98 ppm)
-------
X-15
TABLE X-6. CHARACTERISTICS OF THE TWO
KREFELD PRECIPITATORS
3
Gas quantity 86,000 Nm /h
Gas temperature 300° C
o
Raw gas dust load at 10% CO, 4.5 g/Nm
^ 3
Cleaned gas dust load at 7% C02 100 mg/Nm
Number of electrical fields 2
Number of rapped fields 2
Active length 7.2 m
Active width 6.5 m
Active height 7.5 m
Gas passages 26
3
Active volume 351 m
2
Collector plate projected area 2,810 m
2
Collector plate effective area 3,800 m
Gas velocity 1.025 m/s
2
Cross sectional area 48.75 m
Residence time 7.02 s
Drift velocity 3.29 m/s
Number of power supplies 2
Electrical characteristics 45 kV eff.
Sparking voltage 64 kV
S
Secondary current 600 mA
m
Sparking current 1,020 mA eff.
Power input per field 46 kVa
Power consumption 27.6 kW
Power to rappers 4 x 0.055 kW
Insulation heaters 8 x 2.0 kW
2
Current density 0.426 mA/m
3
Sparking current density 3.42 mA/m
Source: Courtesy Vereinigte Kesselwerke.
-------
X-16
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FIGURE X-3. SUPPLY AND WASTEWATER SYSTEMS
AT KREFELD.
Clear water from wastewater treatment plant
1.
2. City water
3. Well water
4. Percolation well
5. Wastewater canal
6. Well water reservoir
7. Cold water discharge
8. Flocculating tank
9. Sludge centrifuge
10. Quench tank
11. Ash bunker
12. Settling tank
13. Boiler feedwater treatment
14. Neutralizing tank
15. Washroom
16. Sanitary wastes
17. Exterior hydrants
18. Tipping floor hydrants
19. Fire control cannon-bunker
20. Oil tank
21. Flue gas scrubber
22. Neutralization tank
23. Lime mixing tank
-------
X-17
• HC1 1100 to 1600 mg/Nm3 (685 to 1000 ppm)
• HP traces
The particle size distribution less than 10 uM is 7.5 percent to 10.0
percent.
Precipitator Characteristics. Disregarding the hopper, each
precipitator is 15.5 m (51 feet) high 9.2 m (30 feet) wide and 10.2 m (33
feet) deep. A dividin guillotine damper wall is located inside each
precipitator. This permits half a precipitator to operate if the other half
is under repair. The design was not preceeded by a flow-model study.
The average flow velocity in the ESP is 0.925 m (3 feet) per
second. Two perforated plates at the ESP entrance uniformly distribute the
gas flow. The units have two (2) fields in series. Each unit has 4,320
collection plates that are approximately 40 cm (15.7 in.) wide and curved
at each edge. These collector plates are spaced 20 cm (7.9 in.) from the
wires. The impact of falling hammers cleans the plates.
The output voltage is 76,000 volts and the output current is 0.42
amperes. The capacity is 30 Kva.
The pyramidal fly ash hoppers have no method for heating. Flyash
is removed pneumatically. Ivry also has pneumatic removal but later Martin
installations have used screws to remove flyash. Efficiency was guaranteed
at 98 percent.
A notable philosophy of TIRU management is that full air
pollution stack tests are conducted once per month. This is discussed later
under stack sampling methods. Table X-7 shows the results of 4 tests in
February 1977. The particulate emissions are well within the allowable 80
mg/Nm3 corrected to 7 percent CC-2 which is the limit for this large
refuse-burning plant.
Hamburg: Stellinger-Moor
Because of high-firing rates and high heat values the gas
temperature entering the 2 precipitators at the Stellinger-Moor plant have
suffered.
Stage 1. (Original Construction). The two-field ESP manufactured
by Rothemuhle was designed to process 90,560 Nm3/hr (53,250 scfm) when the
furnace is operated at 130 percent of nominal capacity.
The flue gas entering temperature had been around 350 C (662 F).
This is well above recommended temperature levels and has been the source
of high temperature corrosion and mediocre performance of the ESP. The exit
temperatures ranged from 250 to 300 C (482 to 572 F).
The maximum flow velocity is 1.16 m/sec (3.8 feet/sec). The
insulation is 8 cm (3.1 in) thick.
Mechanical rappers remove the flyash which falls into the
pyramidal hoppers. In wintertime, the hoppers are heated electrically.
Flyash is removed by a service conveyor leading to the residue conveyor.
The guaranteed particulate efficiency was 98.9 percent. The
original construction had a single duct leading from the bottom of the
economizer section to the electrostatic precipitator (ESP) on the building
roof. With all new equipment and with much supervision, the plant had
-------
X-18
TABLE X-7. PARIS-ISSY AIR POLLUTION TEST RESULTS
Furnace
UNITS No. 1 No. 2 No. 3
Date (1977) 2/28 2/25 2/23
Rate of Incineration (refuse tonnes/ 20.11 19.16 15.73
No. 4
2/22
18.43
hour)
Rate of Steam (Steam tonnes/ 30.82 32.46 28.97 31.11
Production hour)
Temperature at Furnace (° C) 880 928 956 896
Roof
Temperature at Boiler (° C) 334 308 388 283
Exit
Volume leaving ESP (Nm3/hour) 100,190 95,250 97,910 108,910
Humidity leaving ESP (%) 12.2 13.1 16.8 11.9
Emission Leaving ESP
co2
°2
Particulates (@7% C02)
S02 and SO (@7% C02)
NO and N02 (@7% C02)'
HC1 (@7% C02)
3
(mg/Nm )
(mg/Nm )
3
(mg/Nm )
(mg/Nm )
6.1
11.0
42
126
97
1,335
6.5
10.8
36
130
141
1,509
7.1
9.4
59
132
138
1,744
6.2
11.1
47
139
163
1,074
Source: TIRU Division Controle Technique
Section Laboratoire et Essais
-------
X-19
passed the air pollution compliance test with readings between 112 and 145
mg/Nm3 which were below the legal limit of 150 mg/Nm3 (9.065 gr/scf)
adjusted to 7 percent CC^.
As the years have passed, with the equipment becoming older and
somewhat corroded, plant operations may be more casual and on some
occassions the refuse feeding may be jerky. For whatever combinatin of
reasons, the later air pollution tests showed a 200 mg/Nm3 (0.08? gr/scf)
result. This was unacceptable and something had to be done.
Stage 2. (Flue Gas Water Spray Cooler). In 1975, a flue gas water
spray cooler was added and began spraying 1100 liters per hour (4.8
gal/min) or 1.1 tonne/hour (1.2 ton/hour) of water. The ensuing tests
showed that particulate emissions had decreased to 50 to 80 mg/NnH (0.022
to 0.035 gr/ft3), well within the German limit of 100 mg/Nm3.
The testing was done by Dr. Reimer of "P. Goepfert and H. Reimer"
in Hamburg and Professor Zinn of the University of Hamburg. It is assumed
that the test method used followed the TUV procedure which is the standard
in Germany.
Zurich; Hagenholz
The Martin boiler-furnace unit at Hagenholz, Unit No. 3, is
equipped with an Elex precipitator having a maximum gas flow rate of 95,580
Nm3 (56,200 scfm) assuming that the refuse lower heating value is 2800
kcal/kg (5040 Btu/pound) and that 11,800 kg per hour (13 tons per hour) are
burned. The mean velocity is 0.814 m/sec. (2.67 f/s) The furnace/boiler
emits flue gas with 2500 mg/Nm3 (1.09 gr/scf) of particulate.
The Elex ESP has a cross-sectional area of 74.1 m2 (797 ft2). The
effective surface collection area is 3560 m2 (38,306 ft2).
Elex felt that it has enough experience and a flow-model study
was not performed. Mr. Erick Moser, the technical assistant lamented that,
"There is never enough information on (inlet) gas and dust composition."
Flue gases must pass through a perforated plate and a series of
baffles before entering the electric field. The output voltage is 78 kv
with an effective output curent of 2,430 ma.
The unit is cleaned by mechanical rapping with a hammer. Flyash
falls through pyramidal hoppers and is removed by a feedscrew.
The insulation is 80 mm (3.1 in) thick. In the winter, the hopper
is electrically heated.
The flue gas temperature entering the ESP is usually 280 C (536
F). If it rises to above 300 C (572 F), there is serious danger of high
temperature corrosion from chloride attack. The chloride attacks the steel
until it becomes spongy and short circuits become common.
Plant staff cautioned against closing the plant on weekends. They
have observed other plants that develop dew point corrosion at the 150 C
(302 F) flue gas temperature level. When this boiler-furnace is shut down
eight (8) hours for the 1000 hour planned inspection, the ESP is kept warm
by the 150 C (302 F) steam from the oil-fired stand-by boiler. The ESP is
thus cooled only twice per year - during the 4000 hour planned inspections.
Whenever the input voltage falls below 78 kv and cannot maintain
a 65 kv charge across the fields, then operators know that excessive short
-------
X-20
circuiting is occuring and that inspection and maintenance should soon
follow.
When Units No. 1 and 2 were built at Hagenholz in 1969, the Swiss
air pollution law limited emissions to 150 mg/Nm^ corrected to 7 percent
C02 but the Zurich request for proposals specified a 100 mg/Nrn^ limit
(0.0135 gr/scf). The two-field Elex ESP followed by the Rothemuehle
multi-cyclone more than met the requirements and average 70-90 mg/Nm3
during compliance tests. The original compliance test for one of the first
units produced the following:
Units No. 1 and 2
Particulates - total 72 mg/Nm3 0.03 gr/scf
Particulates - over 30 urn 15 mg/Nm3 0.006 gr/scf
C02 7.7 percent
02 ' 9.2 percent
H20 15.7 percent
S02 219 mg/Nm3 76 ppm
HC1 531 mg/Nm3 331 ppm
Later, after the units had been operating over the critical 300 C
(572 F) limit, corrosion began and later readings changed to 120 mg/Nm
(0.052 gr/scf). As a result Units 1 and 2 were derated to lower firing
rates. When Unit No. 3 was built in 1973, the regulation had been tightened
to 100 mg/Nm3 for particulates. The RFP thus specified 75 mg/Nm3. During
the compliance test, conducted by EMPA, an excellent reading of 42 mg/Nm'
(0.018 gr/scf) was recorded. Assuming an inlet loading of 2500 mg/Nm3 and
an output reading of 42 mg/Nm3 means that the unit operates at an
efficiency of 98.3 percent.
Unit No. 3
Particulates - total
C02
H20
S02
HC1
HF
ZnO
Pb
SI Units
42 mg/Nm3
8.4 percent
12.0 percent
220 mg/Nm3
840 mg/Nm3
11 mg/Nm3
4.7 mg/Nm3
0.37 mg/Nm3
Eng. Units
0.018 gr/scf
—
—
82 ppm
560 ppm
13 ppm
0.002 gr/scf
0.0002 gr/scf
Now that the third generation Josefstrasse is being built (Martin
is the designer), the RFP specification has been tightened further to 50
mg/Nm3 (0.022 gr/scf). As of this writing, the plant is under construction
and thus no compliance test has been made. Officials have been so pleased
with the Elex precipitator at Hagenholz (marketed by American Air Filter in
the U.S.), that it was easily chosen for the next plant at Vosefstrasse.
The Federal Switzerland Government had a financial incentive
program several years ago that motivated construction of many refuse fired
steam generators. A condition for the Federal money was that the plant pass
-------
X-21
its compliance test. Prior to passing the test, vendors would have to wait
for their money or the city would have to obtain a short term bank loan.
This policy has done much to ensure plants with well controlled emissions.
The program still exists on paper, but funds have not been nearly as
plentiful as in years before. In many Swiss regions there has been
overbuilding of these plants and several persons have mentioned that
Switzerland is "saturated" with RFSG's.
The Hague
Each of the 4 units at the Hague is equipped with an
electrostatic precipitator. Those for Units 1-3 were made by a Swedish
company. No. 4 was built by Rothemuhle of West Germany. Gas flow rate is
90,000 Nm3/h (52,965 scfto).
There are two electrical fields per precipitator. Preliminary
model flow tests were made for the Unit 4 precipitator only. Average
velocity is 2 m/sec (6.5 fps). Entering flow is distributed across the
passage by a perforated plate. There are 204 plates per field, each 7 m by
0.3 m (23 ft by 1 ft). Plate spacing is 0.3 m (1 ft). Cleaning of the
plates is by mechanical rapping. Rectifier output is 40,000 volts with 15
cm (6 in) of insulation but are unheated. The hopper for Unit 4 is heated
electrically. The collected ash is sluiced to a flyash setting tank.
The precipitators for Units 1-3 were guaranteed to achieve an
emission level of 100 mg/Nm3 (0.0437 gr/scf) corrected to 7 percent C02«
They have been tested twice in ten years. The last showed an emission of
only 55 mg/Nm3 (0.024 gr/scf). Unit 4 was guaranteed for 80 mg/Nm3 and in
September 1974, when tested emitted only 19 mg/Nm3 (0.008 gr/scf). Its
efficiency was stated to be 99.6 percent with two fields and 85 percent
with one field.
The refuse burned in Units 1-3 had a much higher heat value than
expected, with the result that there were times when the gases leaving the
economizers were as high as 330-350 C (626-662 F), far above the safe
operating temperature for the precipitators. As a result, the plates
rapidly corroded and had to be replaced. Because of that experience the
temperature entering the precipitators is now held below 270-280 C (518-536
F). When the economizer exit temperature begins to exceed about 225 C (437
F) plans are made to clean the boiler heating surfaces. These practices
have almost eliminated plate corrosion.
Some corrosion has been found near the top of the last field
caused by excessive temperatures. Attempts are made to hold it to 250 C
(482 F), but at times it reaches 300 C (572 F). Hopefully the planned
installation of additional heat absorbing surface in the second pass of the
boilers will help to reduce the precipitator temperature.
-------
X-22
Dieppe-Deauville
Flue Gas dust is removed from Dieppe gases by a vane-type 56-tube,
multiple cyclone separator following each boiler built by Louis Prat of Paris.
The design flow rate is 22,000 Nm3 hr (12,940 scfm). Initial gas temperature
was 350 C (662 F) but after secondary air jets were added in the front wall, it
dropped to 280 C (536 F). Pressure drop at 350 C (662 F) is 62 mm water (2.4
in) 608 Pa. Figure X-4 shows a 155 mm diameter cast alloy vane for imparting
spin to the gases entering each of 56 collector tubes in the dust collector.
It is warranted to collect 92 percent of the dust, giving an emissin of 400
mg/m3 (0.17 gr/scf at 450 C) (842 F). The initial measured emission was 320
mg/Nm3 (0.27 lb/1,000 Ib gas) (0.14 gr/scf). This emissin rate would not
comply with many current emission limits for particulates.
The collected dust falls continuously through a lock chamber
controlled by two cam-operated cast iron flap valves into a screw which
discharges it to the grate residue quench channel. The staff are well aware
that failure to keep this lock chamber gas-tight will allow reentrainment of
the collected ash with consequent vane and collector tube erosion. The flap
valves are serviced every 6 months to assure their tightness.
The newer plant at Deauville does not have a multicyclone but uses
instead an electrostatic precipitator which has an inherently higher collection
efficiency. It was designed for an emission rate of 150 mg/Nm3 (0.06 gr/scf).
When handling a volume of 20,000 Nm3 hr (11,760 scfm). The Dieppe and
Deauville plants meet the French emission limits for particulates which are on
a sliding scale as shown earlier in Table X-2. After neighbors complained
about noise from the plant, a noise silencer was placed on top of the stack as
shown in Figure X-5.
Gothenburg
The 3 units at Gothenburg, each rated at 12.5 tonnes/hr (13.8 ton/hr)
are served by three electrostatic precipitators built by Svenska Flaktfabriken,
each has a design flow rate of 100,000 Nm3/hr (58,850 scfm). Flow model test
were not used in the design. Average velocity was 1.15 m/sec (3.8 fps).
Particle residence time was 4.8 sec. There are two fields.
When the precipitators were tested in 1973, the guaranteed emission
limit of 150 mg/Nm3 (0.06 gr/scf) corrected to 10 percent C0£ was exceeded.
Accordingly, the manufacturer provided an additional smaller precipitator along
side the three others to which a portion of the gas is bypassed. The result is
lower velocity, longer residence time, and the combination now meets the 150
mg/Nm3 design limit. Regulations require that the precipitators be tested
twice per year.
Some corrosion has been found near the top of the last field caused
by excessive temperatures. Attempts are made to hold it to 250 C (482 F), but
at times it reaches 300 C (572 F). Hopefully the planned installation of
additional heat absorbing surface in the second pass of the boilers will help
to reduce the precipitator temperature.
-------
X-23
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X-24
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Uppsala X-25
Originally in 1962, the Uppsala plant had only mechanical dust
collectors for air pollution control. Then at the time the fourth furnace
was installed in 1970, two electrostatic precipitators were installed
serving all furnaces, as shown in Figure X-5. An unusual feature of
Precipitator No. 1, serving Furnaces No. 1 through 3, is that it is
followed by a multiple cyclone dust collector due to concern that large
flakes of charred paper would escape the precipltator. There are 200
cyclones, each 200 mm (7.9 in) in diameter. However, similar cyclones were
not included in Precipitator No. 2 because centrifugal action of the Bruun
and Sorensen after-combustion chamber which follows No. 4 furnace usually
breaks and burns any such large flakes before they reach the precipitator.
Table X-8 shows the results of performance tests on No. 2
precipitator servind Furnace No. 4 in 1972. The resulting particle emission
rate of 15 to 38 mg/Nm3 (0.0066 to 0.017 grains/scf) is well within the
Swedish (Statens Naturvardsverk) standard of 85 mg/Nm3. Table X-8 shows
later measurements of gaseous emissions from the original three furnaces.
The second precipitator has required almost no maintenance. Only
one electrode has needed replacement in 5 years. There is some wet
corrosion of the steel expansion joints in the long duct leading outdoors
from the precipitators to the chimney. These joints have, therefore, been
replaced by heavy-coated nylon fabric. However, in the precipitator serving
the first three boilers, 100 electrodes have been replaced since 1971 due
to corrosion.
The dust hoppers are heated and when the system is not operating,
a fan circulates air in the hoppers to prevent moisture buildup.
Figure X-7 shows the exterior of Precipitator No. 1. Figure X-8
shows the ducts leading the exhaust gases to the ten-flue chimney.
Horsens
At Horsens some flyash is removed mechanicaly in the cyclonic
after-combustion chamber. The partially cleaned gases are then cooled in
the boiler and pass to an electrostatic precipitator built by Svenska
Flaktfabriken according to the general specifications as follows:
Flow rate: 36,000 Nm3/hr (21,186 scfm)
Entering temperature:
With spray cooler 300 C (572 F) (Prior to 1977)
With boiler 220 C (428 F) (After 1977)
Dust load (at 10 percent (X^):
Entering 5 g/Nm3 (2.194 gr/scf)
Leaving (max) 180 mg/Nm3 (0.078 gr/scf)
Rectifier 50 kv. 800 ma
Precipitator volume 134.4 m3 (4,730.9 ft3)
Average flow area 21 m2 (226 ft*)
Velocity at stp 0.48 m/sec (1.6 fps)
The precipitator design was preceded by a flow model study which
was deemed essential because of the complicated flow patterns produced by
the combined flow of gas partially from the spray cooler and partially from
the sludge dryer. In March, 1977, it was tested twice by the Horsens
Levendsmiddellaboratorium (Environmental Laboratory, formerly the
Veterinarian and Food Lab). The emission results were 165 and 178 mg/Nm3
corrected to 10 percent C02-
The outdoor precipitator is insulated with 100 mm (4 in) of
rockwool encased in aluminum. Mechanical rapping is provided for both
-------
X-26
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-------
X-27
TABLE X-8. PERFORMANCE TEST DATA ON PRECIPITATOR
NO. 2 SERVING FURNACE NO. 4 (COURTESY
OF UPPSALA KRAFTWARME, AB)
Date (1972)
Time of Day
Waste Burning Rate, kg/h
Steaming Rate, kg/h
o
Gas Flow Rate, Nm /sec
3
Gas Flow Rate, Nm /hr
Gas Flow Velocity, m/sec
Gas Temperature in Precip., C
Gas Temperature before Precip., C
Moisture, Volume Percent
Humidity, Percent
Dew Point, C
CO- Leaving Boiler, Percent-
CO- Entering Precipitator, Percent
Draft After Boiler, mm Water
Damper Position, Percent
Precipitator Voltage, kv
2
Plate Current, mA/m
Primary Current, A
Dust Loading
Wet Gas, Entering, g/Nm
Wet Gas, Leaving, g/Nm
0
Dry Gas, Entering, g/Nm
0
Dry Gas, Leaving, g/Nm
Collection Efficiency, Percent
Dust Collection Rate, kg/h
Test 1
8:08 a.m.-
9:41 a.m.
4,560
11,500
8.13
29,300
0.71
205
210
—
—
—
7.5
8.0
58
35
31.7
0.33
55.7
0.694
0.013
0.789
0.015
98.13
22.9
Test 2
11:00 a.m.-
1:46 p.m.
4,560
15,100
8.13
29,300
0.71
208
216
13
0.7
51
9.9-10.1
9.7
70
36
33.5
0.33
55.7
0.815
0.017
0.937
0.020
97.91
22.9
Test 3
2:51 p.m.-
4:30 p.m.
4,560
14,900
8.13
29,300
0.71
208
218
11
0.6
48
9.3-9.4
8.0
69
34
32.5
0.33
55.8
0.687
0.034
0.772
0.038
95.06
22.9
-------
X-28
TABLE X-9. RESULTS OF GASEOUS EMISSION MEASUREMENTS FROM
ORIGINAL THREE FURNACES AT UPPSALA (APRIL 23,
1974) (COURTESY UPPSALA KRAFTVARME AB)
Test Number
Time, a.m. , p.m.
Steam Production Rate,
tonnes/hr
3
Gas Volume Sampled, Nm
CO-, Percent Dry Gas
00, Percent Dry Gas
3
S02, mg/Nm , Dry Gas
S0_, mg/Nm ,corr. to 10
Percent C07
3 ^
HC1, mg/Nm , Dry Gas
HC1, mg/Nm , corr. to 10
Percent C00
1
9:00-9:45
22.4
0.106
110
170
73
114
2
9:57-10:47
22.4
0.111
110
170
79
124
3
11:00-11:48
22.4
0.078
6.4
10.4
210
330
34
53
4
12: 12:45
23.9
0.103
60
90
14
22
-------
X-29
FIGURE X-7. ELECTROSTATIC PRECIPITATORS RETROFITTED FOR UNITS
#1 AND #2 OUTSIDE AT UPPSALA (Battelle Photograph)
-------
X-30
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-------
X-31
charging electrodes and collector plates. The collection hoppers are
electrically heated to prevent condensation.
The flyash is removed from the hoppers by a Redler conveyor. At
first, the dry flyash was added to the wet grate residue but that produced
intolerable dust. Then the flyash was mixed with the sludge leaving the
drying kiln but a chemical reaction occurred. Now they are attempting to
form clinker with the sludge in the kiln. If the metal content is not high,
it might have some value as- soil nutrient. Tests by the environmental
laboratory have established that the flyash is not harmful if ingested by
animals.
The plant staff are well pleased with the precipitator
performance as it has required minimal maintenance, although they observe
that some degradation of collection efficiency has occurred in M years of
operation.
Copenhagen; Amager and West
Both at Amager and West, Rothemuhle two field electrostatic
precipitators (ESP) are the sole means of air pollution control now in
effect. Plant officials were hesitant about this and had thought of the
need to add a mechanical cyclone collector after the ESP. They wanted to
make sure that the larger paper particles would for certain be captured.
Therefore, they mandated that room should be available for adding the
cyclones later if necessary. The space is outlined with dash lines in the
previous Figure X-10. As discussed later, there has been no need to add any
cyclones.
The ESP inlet gas flow is 107,000 Nm3/hour (62,916 scfm). The
temperature is designed to be around 300 C (572 F) with a 350 C (662 F)
maximum. Because of the clogging economizer section of the boiler, there
have been many excursions well above 350 C (662 F). As a result, there has
been some corrosion at the top and front end of the ESP. Volund estimates
the inlet loading to be 7.5 g/NnP.
Flow-model studies were not conducted before installation. The
average flow velocity is 0.86 m/sec (2.8 ft/sec). The maximum is 1 m/sec (3
ft/sec). Each ESP field has two rectifiers. Volund would permit a one-field
ESP only on a small system where the regulations are not as stringent. A
Volund brochure describes their system as follows:
"In the electrostatic filter the speed of the smoke (gas) is
reduced to approximately 1 m/s, after which the smoke passes
between vertically suspended, electrically earth connected
profiled steel sheets. The mutual distance between the sheets is
about 25 cm. Tightly stretched between the sheets are a great
number of steel wires, equipped with spikes. The steel wires are
insulated when hung and are connected with an 80,000 volt direct
current generator. When the smoke slowly passes this system of
negatively charged steel wires, the dust particles carried along
will be electrically charged and will therefore be pulled over
onto the earth-connected (grounded) sheets. Thus, a continuous
layer of dust will gradually be formed on the sheets and can be
shaken off by hard blows on the sheets. This causes the lumps of
-------
X-32
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X-33
dust to drop into accumulation funnels from which the dust is
removed by means of an automatic transport system, is moistened,
and sent to the slag pit.
"The total efficiency of the electrostatic filter is more
than 98 percent. During 1972, approximately 5,000 tons of flyash
was separated through Amagerforbraending's filters."
Even though the ESP is housed inside the normally warm
furnace/boiler room, the ESP hoppers are equipped with electric heaters.
When the room temperature falls to 10 C (50F), the heaters are turned on to
prevent possible dew-point corrosion in the ESP.
Flyash is removed from the bottom of the ESP hoppers
pneumatically. The pneumatic tube dumps onto a conveyor belt for transport
to the ash bunker.
Upon startup, the unit exceeded the 150 mg/Nm3 limit for
particulates. The primary reason was that a standard ESP (without special
entrance vanes) was used to clean a very highly loaded flue gas. The Amager
estimate of 7.5 g/Nm^ compares with more typical inlet loadings of around 5
g/Nm3. The action of the rotary kiln generates higher dust loadings.
Because of noncompliance, Rothemuhle responded to its guarantee.
They then did conduct flow model tests. Turning and guide vanes were added.
The tests proved so successful that they again concluded that cyclones
would not have to be added.
The new Danish air pollution regulations specify limits for
particulates, HC1, and S02 (corrected to 11 percent 02 and 7 percent C02).
Amager tests show that the unit is now well within the limits.
Design of Actual
Danish Law Amager Plant
Particulates (mg/Nm3) 150 60 - 90
HC1 (mg/Nm3) 1,500 700 - 900
S02 and S03 (mg/Nm3) 1,500 200 - 300
Because of the HC1 and S02 gases are in compliance, no scrubber
has been needed. A new feature of the law is that particulate tests are to
be made every month. The sampling point is 50 m up the 150 m chimney. The
respected Danish Boiler Testing Company is employed to perform the tests.
One emissions analysis reported is as follows:
Nitrogen (N2) 66.40 percent
Oxygen (02) 12.40 percent
Carbon Dioxide (C02) 12.40 percent
Water (H20) 8.64 percent
Hydrogen Chloride (HC1) 0.06 percent
Sulfur Dioxide (S02) 0.01 percent
Unidentified and Measuring Errors 0.09 percent
TOTAL 100.00 percent
Volund officials repeated a 'statement heard elsewhere in Europe
and America that, "for each 1 percent above 96 percent efficiency, the ESP
urchase price doubles". This, is only a crude approximation. However, it
makes the clear point that going from clean air emissions to very clean air
emissions is very expensive.
-------
X-34
Volund is also considering a modest sized spray chamber before
the ESP. The added moisture should improve the particle's action when on
the electrodes by reducing particle resistivity.
As the result of a study, flyash is not mixed with botton ash so
that the bottom ash can be recovered and used as "non-cementing" gravel.
The Danish regulation for particulates is 150 mg/Nm^ corrected to
11 percent C-2 and 7 percent CC^. At West the so corrected reading was well
within limits at 90 mg/Nm^. The Danish Boiler Testing Company made the
measurements. It was such an expected low actual reading that caused
Rothemuehle not to put in the cyclone collector. However, if the reading
were higher, Rothemuehle (at its expense) would have had to install the
cyclone.
Stack Sampling Methods
Because the measured performance of pollution control equipment
is so crucially dependent upon the measurement methods used an effort was
made to learn the details of the measurement procedures used. In many cases
the plant staff were unfamiliar with the exact methods used because the
tests are usually conducted by an outside agency which specialized in
emission measurements. A notable exception was at the Issy-le-Moulineaux
plant at Paris which is operated by the Service du Traitment Industrial des
Residus Urbans (TRIU). TRIU is a profit oriented division of the
state-owned electric utility Electricite de France. TRIU has a trained
three-person sampling team which tests each precipitator about once per
month. Figure X-10 shows the sampling system used. The flue gas is sampled
for 10 minutes at each point up to about 48 points, depending in the size
of duct and local circumstances. Not only does this team sample TRIU plants
but they are available and do some contract sampling for other facilities.
Four obvious advantages of having such a regularly working team for
emissions measurements are:
1. The team is kept active and skilled for this difficult and
demanding task which is often neglected if carried on as an
infrequent, part-time activity.
2. The plant operator has frequent data showing where the plant
stands regarding compliance with applicable limits.
3. If equipment deterioration occurs the management is alerted
for corrective action before the condition reaches a crisis
stage precipitating possible complaints from neighbors.
U. The regular updating of plant emission records is useful in
informing environmental control groups on the long term and
short term performance of the pollution control equipment.
Earlier in this section on Control Equipment, Table X-7 showed
the results of gaseous and particulate emission tests using this method at
Issy on four different days in February 1977. All of these tests showed
particulates to range from 36 to 59 mg/Nm^ well within the required 80
mg/Nm3 at 7 percent C02 (the equivalent of 137 mg/Nm3 at 12 percent C02,
0.06 gr/scf), although the boiler load and exit temperature varied widely,
indicating considerable variation in fuel-bed burning conditions.
In West Germany a similar particulate sampling system is used as
shown in Figure X-11. This is prescribed in considerable detail in
-------
X-35
Heated Chamber
Pump
Gas Meter
Cooling Bath With Two Immerse^
Flasks For Condensate
^y^l~
Gas
Water
FIGURE X-10. DIAGRAM OF EQUIPMENT FOR MEASUREMENT OF DUST LOADING AND
MOISTURE CONTENT OF A GAS. (Courtesy of TIRU)
-------
X-36
1. Sampling nozzle
2. Suction probe (heated)
3. Filter (heated)
A. Pressure gage
5. Orifice and differential pressure gage
6. Suction pump
7. Velocity probe and gage
8. Thermocouple and potentiometer
9. Gas analyzer
10. Barometer
11. Ambient thermometer
12. Clock
FIGURE X-ll.
APPARATUS FOR ISOKINETIC DETERMINATION OF THE DUST CONTENT
OF FLOWING GASES (VDI KONMISSION REINHALTUNG DER LUFT)
REFERENCE: Verein Deutsche Ingenieure - Richtlinen, Messen Von Partikeln,
Staub Messungen In Strotnenden Gases, Gravimetrische Bestim-
mung der Staubbeladung (VDI-Guidline, Measurement of Particles,
Dust Measurement In Flowing Gases, Weight Determination Of
Dust Loading VDI 2066, October 1975).
-------
X-37
Guideline Number 2066 (VDI 2066) of the German Society of Engineers (VDI),
October 1975 edition.
The sampling methods used in other countries were not learned
although it appears that the VDI Guideline is used as a guide in
Switzerland and other countries.
In Denmark the sampling is often done under contract by a team
from a Danish Technical Group.
-------
Y-l
START-UP AND SHUT-DOWN PROCEDURES
General Comments
Detailed comments about such procedures were sought at four
facilities. Starting up a unit can take anywhere from 2 to 24 hours depending
on how much the furnace had cooled from the last firing.
Often a light oil burner is used to preheat the boiler and
electrostatic precitptator. A slight variation is that the oil burner is
almost always kept on during shut-down to prevent dew point corrosion of the
boiler and electrostatic precicitator.
-------
Y-2
SPECIFIC SYSTEM COMMENTS
Duesseldorf
Start-Up. The following start-up procedure was described by the plant
manager, Mr. Thoemen:
• Check all access ports, assure that all workers are outside, that
internet equipment appears in order. -This check takes 1 hour.
• Preheat the boiler with steam from the intermediate pressure line.
This takes 4 to 8 hours.
• Fill the boiler with feedwater and build the pressure to 20 atm
(275 psig).
• Adjust the steam flow to blow out any condensate from super-heater
and set valve about 40 percent open.
• Start primary air fan at minimum flow, start grate rollers and
start hot condensate flow through air prehheater.
• Over the next 45 minutes, complete the following:
- Fill refuse feedchute
- Start refuse feeder
- Cover first two rollers with refuse
- Light oil burner
- Increase feed gradually at rate governed by rate
of rise of superheat temperature
- Start flow of steam to Flingern Power Plant.
The total elapsed time for this start-up procedure is usually 8 to 10
hours.
Normal Shut Down.
Crane stops filling chute.
Increase furnace draft to maximum.
Reduce primary air.
Empty chute onto grate over a period of 2 'to 3 hours.
Complete burnout of refuse on bed over a period of 1 to
1-1/2 hours.
Stop steam flow to main line.
Vent steam to intermediate line.
Continue primary air fan for 4 to 6 hours.
Turn off fans to allow final cooling by natural draft.
After 24 hours, begin repair work on unit.
Emergency Shut Down.
If a tube fails, shut off steam flow to main line.
Shut off primary and secondary air.
Extinguish fire with fire hoses.
- Complete extinguishment takes 5 to 6 hours.
Turn grate off.
Stop feedwater pumps.
Empty grate.
Shared Services. Typically when there is starting or shutdown of any
key component at Duesseldorf, the operator fills out any one of several
specialized computer cards (See Figure Y-1). These are used in a computer
-------
Y-3
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FIGURE Y-l . SAMPLE DATA CARDS USED IN PLANT DATA
SYSTEM AT DUESSELDORF
-------
Y-4
program to keep track of operating hours, downtime, etc. Klaus Feindler,
technical director of VKW's American licensee, Grumman Ecosystems, points out
an advantage of having the refuse system as part of a larger energy system.
This computer program was really developed for use at the neighboring Flingern
Power Plant. Similarly emergency shutdowns and annual major overhauls can be
handled in part by trained power plant technicians. This permits lower staff
levels for normal operation at the refuse fired steam generating plant.
Zurich
The Number 2 fuel oil is put into a separate boiler package which
produces 150 C (302 F) steam. This helps to eliminate dew point corrosion.
Steam from this oil boiler is also used to heat tubes in the air preheater,
also to 150 C (302 F). The electrostatic precipitator is turned on after about
1/2-hour. After about 1-1/2 hours, fairly dry ann hiogh calorific value waste
is fed into the furnace and the charge is lit.
When the unit is stopped for its 1,000 hour inspection, the ESP is
kept hot to prevent dew point corrosion.
The Hague
The Von Roll organization provides each plant with a detailed
operating guide including specific procedures for startup to avoid over-heating
and damage to the system. At this plant tghe operator is also required to
follow established curves showing the rate of rise of furnace temperature,
economizer outlet temperature, and steam flow rate. Through-out the period of
startup of a unit which normally will take 18-24 hours the operator plots the
critical parameters on a startup chart so that the active curve for each
parameter is plotted alongside the prescribed startup curve which has been
established from experience. Thus, the startup chart serves as a guide to the
operator and, when completed, provides a record of any excursions that may have
occurred during the process. This is one more indication of Mr. Postma's
careful management at this plant that is reflected in relatively low
maintenance and operating costs.
Horsens
The plant is down Saturday and Sunday for repairs. The other 5 days
of operation is not at a steady pace but is on a varied schedule as follows:
Monday
Monday
Tuesday
Wednesday
Thursday
Friday
Friday
6:00 a.m.
2:00 p.m.
10:00 p.m.
6:00 a.m.
10:00 p.m.
Startup everey other Monday
On alternate Monday mornings the
boiler and grate are cleaned which
delays plant startup until 2:00 p.m.
Operation is then continuous.
Operation around the clock.
Operation around the clock.
Shut down
Start up
Shut down
-------
Y-5
Thus, of the total of 120 hours in a 5-day week, the plant operates
hours one week and 96 hours on the alterante weeks. After Christmas and
Easter, the load is such that 7-day, around the clock operation is required.
On weekend shutdowns, the induced draft fan is kept operating at a low
rate to keep the system ventilated and dry. The refractory setting remains
warm so that at the time of startup Monday morning thhe air flow entering the
boiler is still about 400 C (752 F).
-------
APPENDIX
-------
REFERENCES
FOR
SPEC REPTS 1 & 2
(These references are also listed
at the point of use in the
individual chapters.
They are assembled again
here for easy access.)
-------
Andritsky, M., "Mullkraft werk Muenchen", Erer.nstoff-Uarme-Kraft, May 1962,
213-237.
Balstrup, T., and Pedersen, S.D., "Cinders and Reuse" Danish Geotechnical
Institute and Water Quality Institute, Copenhagen 1975.
Brown, K.H., Belong, W.B., and Auld, J.R., "Corrosion by Chlorine and by
Hydrogen Chloride at High Temperatures," J. Ind. Eng. CHem., V01. 39, 19^7,
p. 839-811.
Brunner, D.R., Keller, D.J., "Sanitary Landfill Design and Operation", U.S.
EPA, 1972.
Christensen, A., "Furnace with Grate for Combustion of Refuse of and Kind",
U.S. Pat. 2,015,8142, October 1, 1935.
Dirks, E., "Ten Years Incineration Plant Frankfurt", Proceedings,
Conversion of Refuse to Energy (CRE) Montreaux, Switzerland, November 1975,
580-588.
Eberhardt, H. , European Practice in Refuse and Sewage Sludge Disposal by
Incineration, Proceedings, 1965 National Incinerator Conference, ASME, New
York, May, 1965, pp. 12^-1^3.
Engdahl, R.B., "Identification of Technical and Operating Problems of
Nashville Thermal Transfer Corporation Waste-to-Energy Plant, Report No.
BMI-19^7 to U.S. Energy and Development Administration, February 25, 1976.
FeJndler, K.S., "Refuse Power Plant Technology - State of the Art Review",
Unpublished paper presented to the Energy Bureau, Inc., New York, December
16, 1976.
Feindler, K.S., and Thoemen, K.H., "308 Bullion Ton-Hours of Refuse Power
Experience", Energy Conservation Through Waste Utilization, Proceedings
1978 National Waste Processing Conference, Chicago, May 1978, 117-156,
published by ASME, New York, 1978.
Fryling, G., "Combustion Engineering", Combustion Publishing Co., New York,
1966.
Hirt, R., "Die Verwendung von Kehrichtschlake als Baustoff fur den Strassen
ban" (Use of Processed Incinerator Ash for Read Building) Report to City of
Zurich, Switzerland from Technical University cf Zurich, October 1975.
-------
Hotti, G., and Tanner, R.t "How Europena Engineers Design Incinerators",
American City, June 1969.
Kaiser, E.R., "Refuse Composition and Fuel-Gas Analyses from Municipal
Incinerators", National Incinerator Conference, ASME, New York, 1961, p.35-51.
Krause, H.H., Vaughan, D.A., Killer, P.D., "Corrosion and Deposits from
Combustion of Solid Waste, Part II, Chloride Effects on Boiler Tube and
Scrubber Metals", ASME Paper 73-KA-CD1, November, 1973.
Krings, J., French Experience With Facilities for Combined Processing of
Municipal Refuse and Sludge, Proceedings, CRE-Conference on Conversion of
Refuse to Energy, Montreaux, Switzerland, November 3-5, 1975.
Lindberg, L., "Survey of Existing District Heating Systems", Nuclear
Technology, Vol. 38.
Lowry, H.H., "Chemistry of Coal Utilization", First Edition, Vol. 1, p. 1311,
Table 1.
Nowak, F., "Corrosion of Refuse Incineration Boilers, Preventive Measures", Ash
Deposits and Corrosion Due to Inpurties in Combustion Gases, R.W. Byers,
Editor, Hemisphere Publishing Co., Washington, 127-1I36. (Proceedings
International Conference on Ash Deposits and Corrosion from Impurties in
Con-.bustion Gases, New England College, Hennikcr, N.H., June 1977.
Perry, Chemical Engineers Handbook, Fifth Edition, p. 91^, McGraw-Hill, New
York, 1973.
Tanner, R., "The Development of the Von Roll Refuse Incineration System"
Sanderriruck aus SchweizerJschen Bauzeitur.g, 83 Jahrqanq, Heft 15, 1905.
(Origin German, later translated to French, English and Italian).
Theomen, K.H., "Contribution to the Control of Corrosion Problems on
Incinerators. Kith Water-Wall Steam Generators", Proceedings 1972 National
Incinerator Conference, New York, N.Y., p. 310-318, ASME, New York, N.Y., 10017.
Thoemen, K.H., "Review of Four Years of Operation with an Incinerator Boiler of
the Second Generation", Proceedings ASME Conference on Present Status and
Research Needs in Energy Recovery from Wastes", p. 171-181 Hueston Woods, Ohio,
September 1976, ASKE, New York, N.Y. 10017.
-------
Vaughan, D.A., Krause, H.H., and Body, W.K., "Corrosion Mechanisms in Municipal
Incinerators Versus Refuse Composition", Proceedings ASME Conference on Present
Status and Research Needs in Energy Recovery from Wastes, Hueston Woods, Ohio,
September 1976.
Wahlman, E., "Conversion of Heating systems in U.S. Buildings, Proc. Swedish
District Heating Workshops, Swedish Trade Cormission, 333 N. Michigan Avenue,
Chicago, 60601, 1978.
Wahlman, E., "Energy Conservation Through District Heating and A Step by Step
Approach", Proc. Swedish District Heating Workshops, Swedish Trade Commission,
333 N. Michigan Avenue, Chicago, 60601, 1978.
EPA: "Solid Waste Management Guidelines", 1976.
*Hainburg, City of, "Workers' Payment Plan for Household Wastes, Street
Cleaning and Truck Parking", prepared by Kair.burger Studt Reinigung (Hainburg
Sanitation Office).
Verein Deutsche Ingenieure - Richtlinen, Messsn Von Partikeln, Staub Messeungen
in Stromenden Gases, Gravimetrishche Bestir.mung der Saubbe-ladung (VDI -
Guideline, Measurement of Particles, Dust Measurement in Flowing Gases, Weight
Determination of Dust Loading VDI 2056, Octccer 1975).
Amager-forbraending Interessentskab (Amager-refuse incinerator for the public
welfare). A colorful public relations description of the plant from all
aspects.
I/S Anager-forbraending. The 1975-1976 Ar.nual Report of plant financial
results.
"Affaldsbehandling (Refuse Treatment-Volume Reduction by Different Treatment
Methods"), A Volund publication.
3alch, E., "Plants for Incineration of Refuse" published by A/S Volund. An
excellent 25-page technical paper telling hcv Volund and its competitors build
refractory, water-tube wall, and rot.ary kiln furnances for refuse distruction
and energy production.
-------
LIST OF PERSONS CONTACTED
Persons and Titles
The Battelle investigators are please to acknowledge the very
competent, energetic and generous assistance which we received from the
following.
Werder.berg - Liechtenstein
Robert Giger, Plant Manager
Hansruedi Steiner, Widtner 4 Ernst
Peter Nold, Widmer 4 Ernst
Theodor Ernst, Widtner 4 Ernst
Robert Hardy, U.S. Representative, Widmer 4 Ernst
Baden-Brugg
Herr E. Leundi, Assistant Plant Manager
Herr Zumbuhl, President, Zweckverbancf Kericht-Verwertung Region
Braden-Brugg
Peter Nold, Engineer, Widmer + Err.st
Theodor Ernst, President, Widmer + Ernst
Robert Hardy, U.S. Representative, Widmer + Ernst
Duesseldorf
Stadtwerke Duesseldoft
- Karl-Heinz Thoenen, Works Xanarer
- Uwe Anderson, Assistant Works Manager
Vereinigte Vesselwerke
- Dr. Werner Schlottman
Grumisan Ecosystems, Inc.
- Klaus Feindler
Stadtreining v. Fuhrarat
- Dr. Helmut Orth
-------
Wuppertal
Werner Schlottman, Vereinigte Kesselwerke
Hans Norbisrath, Project -Engineer, Vereinigte Kesselwerke
Sedat Temelli, Assistant Plant Manager and Chief Engineer
Klaus Feindler, Grumman Ecosystems, Inc.
Peter Ahrens, Plant Financial Manager
Edgar Buchholz, Plant Technical Manager*
Volksv.'irt Horst Masanek, Plant Comercial Manager*
Krefeld
Werner Schlottman
Hans Norbisrath
Klaus Feindler
Jurgen Boehme
Wilhelm Korbel
Heinz Stogmuller
Paris: Issy
M. Defeche
M. Jullier.
M. Rameaur
K. Cherdo
Walter J. Martin
Sid Malik
George Stabenow
M.J. Collardeau
M. Finet
M. Monterat
Vereinigte Kesselwerke, (VKW), Dusseldorf
Vereinigte Kesselwerke, (VKW)', Dusseldorf
Grumman Ecosystems, Inc., Bethpage, L.I., NY
Vereinigte Kellelwerke, (VKW), Dusseldorf
Krefeld Plant Manager
Vereinigte Kesselwerke, (VKW), Dusseldorf
T.I.R.U. Offices, General Manager
T.I.P..U. Offices, Manager of Technical Services
T.I.R.U. Plant, Plant Manager
T.I.R.U. Plant, Assistant to the Plant Manager
J. Martin Gnbtt, Munich, W.G.
Universal Oil Products, Chicago USA
Consultant to UOP, E. Stroudsburg PA. USA
Head of the Division "Residus Urbains" (Urban
Waste) French Ministere de la Culture et de
1'Environment
T.I.R.U. Head of the Division of Pollution
Control
City of Paris, Assistant to the Chief of the
Cleaning Service
* Mr. Buchholz was interviewed on a previous October, 1976 trip.
** Mr. Masanek was not interviewed but should be mentioned because of
his responsibilities.
-------
Hamburg; Stellinger-Moor
Karl Heinz Arndt
Igor Schmidt
Hans Rudolf Timm
Klaus Von Borck
Weiner Gossteuck
George Stabenow
Heinz Weiand
Zurich: Hagenholz
Max Ealtensperger
Erich Moser
R. Hirt
Herr Lackmann
Herr Uidmer
Heinz Kauffmann
George Stabenow
Wettman
Herr Puli
The Hague
Johan G. Postrca
John I'.. Kehoe, Jr.
Beat C. Ochse
Richard Scherrer
Stellinger Moor, Plant Manager
Stellinger Moor, Operations Manager
Stellinger Moor, Maintenance Supervisor
City of Hamburg, Landfill Engineer
City of Hamburg, Chief Construction Engineer
Consultant tc UOP, E. Stroudsburg, Pa., USA
Projects Manager, Martin, Munich, W. Germany
Chief of Waste Disposal and Cleaning
(Abfuhrwesen) for City of Zurich
Technical Assistant Chief
Professor at Zurich Technical Institute
(Conducted study of ash disposal)
Hagenholz Operations Manager
Hagenholz Engineering Manager or Administration
Manager
Projects Manager, Martin, Munich, W. Germany
Consultant tc UOP, East Stroudsburg,
Pennsylvania USA
9
Hagenholz Assistant Operations Manager
The Hague, Plant Manager, Gemeentelijk
EnergiebecJrijf Vuilverbranding, The
Hague, Netherlands
Wheelabrator-Frye, Inc., Energy Systems
Division, Vice President and General
Manager, Hsnpton, NH, USA
Von Roll, Ltd., Environmental Eng.,
Zurich, Switzerland Div., Poject Engineer
Von Roll, Ltd., Environmental Eng.,
Zurich, Switzerland Div., Project Engineer
(now of VJidmer & Ernst)
-------
Dieppe (and Deauville)
K. Jean Fossey
M. Bernard Montdesert
M. Aime Marchand
M. Hervee
Beat C. Ochse
John M. Kehoe, Jr.
David B. Sussman
Gothenburg; Savenas
Bengt Rundqwist
Gian Rudlinger
Beat C. Ochse
Kurt Spillrcan
Uppsala
Niels T. Hoist
Dieppe Plant Manager
Dieppe Plant Chief Engineer
Director, General des Services
techniques, Dieppe
Asst. Manager, Deauville Plant
Project Engineer, Von Roll, Ltd.,
Environ. Eng. Div., Zurich
Vice President and General
Manager, Wheelabrator-Frye
Inc., Energy Systems Div.,
Hampton, N.H.
Project Monitor, U.S. EPA,
Resource Recovery Div.,
Washington, D.C.
Director, Gothenburg (Savenas)
Plant
Chief Operating Engineer,
Gothenburg (Savenas) Plant
Project Engineer, Vol Roll, Ltd.,
Zurich
Project Engineer, Vor. Roll, Ltd.,
Zurich
Brunn ar.d Sorensen A/S
The Waste Treatmment Department
Aaboulevarden 22
8000
Aarhus C, Denmark
Telephone: (06) 12 ^2 33
Telex: 6-^45 92
-------
Horsens
Bengt Hogberg
S. A. Alexandersson
Hans Nordstrom
Hans Nyman
Karl-ErickBerg
Hans Momann
Hans Sabel
Erling Petersen
Flinn Larsen
Harry Arnun
Holger Sorensen
Nels Jurgen Herler
Niels T. Hoist
Paul Sondergaard-
Christensen
Allan Sorensen
Brunn and Sorensen A/S
Stockholn Representative
Brunn and Sorensen A/S
Manager, Waste Treatment Dept.
Uppsala Plant Engineer
Uppsala Kraftvarme AB
Sopforbraenningsanlaggningen
Bolandsuerket
Bolandsgatan
Box 125
S-75104
Uppsala, Sweden
Telephone: (018) 15 22 20
Uppsala Chief Engineer
Uppsala Works Engineer
Uppsala Managing Director
Uppsala Works Director
City Director of Solid and Water
Waste Management
Horsens Plant Manager
City Engineer, Horsens
Burgomeister, City of Horsens
Engineer, Horsens Plant
Vice President, Bruun and
Sorensen, Aarhus
Engineer, Eruun and Sorensen,
Aarhus
Engineer, Bruun and Sorensen
Aarhus
-------
Copenhagen; Amager
Gabriel Silva Pinto
II. Rasmussen
Evald Blach
Jorgen Hildebrandt
Per Nilsson
Thomas Rosenberg
Architect
Consulting Building
Engineers
Consulting Mechanical
Copenhagen; West
Mr. G. Baltsen
Gabriel S. Pinto
K. Rasmussen
K. Jensleu
e. Blach
Project Manager, Main Plant
Layout, Volund
Chief Engineer, Sales Activities
Volund
Former Chief Engineer, Volund
Plant Manager-, Amager Plant
Chief of Development Department
Civil Engineer of the
Renholdnings Selskabet
Sales Manager, International
Incinerators, Inc., Atlanta,
Georgia, Builder of Volund-
type systems in North America
J. Maglebye Architectural Office
Rambcll & Hannemann
Copenhagen Gas and Electricity
Services
Director of Copenhagen: West
Project Manager, Main Plant Layout,
Volund
Chief Engineer, Sales Activities,
Volund
Civil Engineer, I/S Vestforbraending,
Ejbyracsevej 219, 2600 Glostrup,
Denmark
Former Chief Engineer, Ex-Volund
-------
Addresses and Phcr.e Numbers
Refuse Fired Hot Water Generation Plant
Amager Forbraending
Kraftvaerksuej
2300 Kobenhauns
Denmark
Tele: Su 351
Vendor Headquarter
Volund
11 Abildager
Glostrup 2600
Denmark
Tele: 02-U52200
Telex: 33150
Collection Organization
Renholdnings Selskabet
Since 1898
Forlandet, 2300 Kbh. S
Amager Island
Copenhagen
Denmark
Danish Boiler Manufacturer's Association
WEKA-VERLAG Gmbh
8901 Kissinng
Augsburgerstrasse 5
Hillerup
Denmark
Tele: 08233-5171
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waste Management, inc.
900 Jorie Boulevard • Oak Brook, Illinois 60521 -312/654-8300
July 30, 1979
U.S. Environmental Protection Agency
Resource Recovery Division A-W 462
Washington, D.C. 20460
Attention: David B. Sussman
Re: Contract No. 68-01-4376
Dear Mr. Sussman:
We at Waste Management, Inc. appreciate being given the opportunity to
review the draft of the extensive report prepared by Philip Beltz and his
staff at Battelle.
Prior to offering our comments, two statements must be made and accepted.
Firstly, that Waste Management, Inc., through its license agreement with
Volund, is committed to the concept of mass-burning of municipal refuse using
refractory-walled furnaces, and is thus necessarily biased in its judgement,
and secondly that the Battelle staff, while having spent a considerable
period gleaning information from the constructors and operators of energy
conversion plants, have nevertheless colored the content of the report to
reflect their own conclusions and opinions. No one can inspect so many
operations without developing a preference for a certain system and cer-
tainly the editorialising and definitive statements within the report
reflect this.
Insofar as the folks at Battelle have been contracted to do just this,
it would be inappropriate to argue with their preference, except where state-
ments made in the text are either incorrect or need considerable qualification.
This is where we have tried to be of assistance in rendering this report to
be the valuable, accurate reference book that it should be.
Specifically, our comments are these:
Ref. p. A.I. par. 3 and 5. "The early units were refractory-walled and
thus the steam quality (temperature and pressure) was limited." and "the
water-tube wall furnace/boiler" has the refuse combustion section surrounded
by vertical or sloping steel tubes in parallel generate a major fraction
of the steam produced. This increases efficiency and allows a much higher
quality steam to be produced.
Steam is generated by the transfer of heat from flue gas (the product
of the refuse combustion) to water, via the netal walls of boiler tubes.
The efficiency of the boiler is a function of the gas flow pattern and the
tube metal surface area. The quality of steam produced is determined by
the feed-water pressure, tube wall thickness and location and size of the
superheater.
Whether a furnace utilizes a refractory-walled or water-walled combus-
tion chamber is of absolutely no consequence in the final quality (temperature
and pressure) of the steam.
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Page 2
Most European incinerators incorporate Eckrohr boilers and it is these
devices alone which determine the steam quality, not the combustion system.
The question of whether or not there nay be advantages from an efficiency
point of view between the two systems is discussed in the attached paper writ-
ten by Gunnar Kjaer of Volund U.S.A.
Ref. p.A.27. The refractory wall furnaces are generally less expensive
and would have technical difficulties raising jsteam temperatures to much above
260C (500F).
Until the nineteen-fifties, refractory-wall furnaces were the major sys-
tem utilized throughout the world for raising steam, using all fuels from
refuse to coal and oil. Steam temperatures and pressures were determined by
the design of the boiler alone and are not in any way affected by the nature
of the combustion zone construction.
Steam temperatures in excess of 1000 F are commonplace in boilers with
refractory walled furnaces.
The major consideration in refuse-fired furnaces is the quality of the
flue gas (which is the same regardless of whether refractory or water wall
furnace is employed.) When tube-metal tenperatures exceed 700 F, extensive
chloride corrosion occurs so that a selection must be made between high steam
temperatures (and the attendant high turbine efficiencies) or low maintenance
costs associated with low-temperature operations.
There is no technical difficulty whatsoever in generating high temperature
steam with a refractory-wall furnace. It is simply poor practice, as the re-
peated failures in operating water-wall units has demonstrated.
Ref. p.A-53. Pit Doors
It is our opinion that this section should also address the common Euro-
pean practice of piling the refuse above the level of the closed doors in order
to further utilize the available hopper capacity.
Ref. p.A-58. Kockum-Landsverk was a Swedish company (formerly a licensee
of Volund) and is no longer in the incineration business.
Volund is represented in the United States solely by Volund U.S.A. (VUSA),
with whom Waste Management, Inc. has a marketing agreement.
Ref. p.A-103 par. 5 and 6 infer a clear division between the capabilities
of refractory-wall and water-wall furnace systems.
In fact, some waterwall manufacturers have chosen to offer units generat-
ing high-pressure steam, while some refractory wall manufacturers have preferred
to offer only low temperature systems. The decision, as discussed in earlier
pages, is based soley on economic implications - higher temperature steam
means higher tube failure rate and thus higher operating costs regardless of
which system is used.
Within Secion B, Gunnar Kjaer of Volund U.S.A. has identified a number of
specific errors in the inventory tabulation which are listed below:
The following comments serve to correct some of the inaccuracies in the
list of Refuse-Fired Energy Systems. The corrections apply primarily to
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Page 3
Denmark and Sweden, in which countries I have intimate knowledge of the refuse-
incineration market. However, it may be assumed that other geographical areas
of the world also need further scrutiny before the lists and the book are suf-
ficiently correct to justify publication.
The comments relate to the plants as numbered on the attached copy of
the list.
DENMARK
Plant No. 1, 2 and 3 (Aalborg); This is one plant with two lines, in-
stalled in the buildings of a former compost producing plant. Line No. 1 was
designed and installed by E. Rasmussen in 1968 using a Flynn & Emrich grate
design. The technical data given under plant No. 1 are correct. E. Rasmussen
incinerator division was acquired by Bruun & Sorensen in 1970. Since 1973,
line No. 1 has been on stand-by only. Line No. 2 was designed and installed
by V«5lund in 1972 and the technical data given tinder plant No. 2 in the list
are correct. Plant No. 3, Aalborg, does not exist, but is a (partly erroneous)
duplication of the information under (1).
A completely new plant, Aalborg II, is presently being installed and will
be operating in 1980. It is designed, manufactured and constructed by Vj6lund
and will have 2 lines, each 8 M.T./hr. and will produce high pressure hot
water for district heating. The building, now near its completion, will have
room for a total of 4 lines, each with 10 M.T./hr. capacity.
Plant No. 5 and Plant No. 39 are the sane plant. Correct "date begin
operation" is 1969. Location: City of Aarhus in an area within the city known
as Tilst.
Plant No. 7; Correct name of location: Br^ndby. Second line of same
capacity begins operation in 1979.
TPlant No. 12, Frederiksberg; Heat medium - steam for district heating
(each boiler 7.5 t/hr., 12 bar, 190 C, 17000 lbs./hr., 178 psi, 375°F).
Plant No. 14, Gentofte; Heat medium - steam for electricity generation
(each boiler 7.5 t/hr., 14 bar, 350°C, 17000 lbs/hr., 210 psi, 660°F).
Plant No. 17, Herning; The first 3 t/hr. line was installed in an exist-
ing gas work building and began operation in 1964. It was closed down and
demolished in 1971 following the start of operation of the first line of a
completely new plant in a different location, Herning II. This new plant
had one line, capacity 3 t/hr., to be followed in 1973 by a second line, cap-
acity 4 t/hr.
Plant No. 19 is the same as plant No. 38. Location: Taastrup. Technical
data given under No. 19 are correct.
Plant No. 21, Horsens; Capacity 5 t/hr., 120 M.tpd.
Plant No. 26, Nyborg (Kommunekemi); No electricity production, but use of
steam for internal use with balance being sold to the hot water district heating
scheme via a heat exchanger.
Plant No. 28, Odense-Dalum: Closed down in 1972.
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Page 4
Plant No. 33 and 34 are two lines in the same plant. Technical data are
correct. However, the first line, 3t/hr., was installed by B & S in 1970 and
the second line, 4 t/hr., was installed by V^lund in 1973.
Plant No. 36 and 37 are two lines in the same bulling.
Plant No. 40, Weston; Energy - high pressure hot water for industrial use.
It should finally be mentioned that Danish environmental standards dis-
tinguish between plants with refuse handling capacities over and under 5 metric
t/hr. For plants handling more than 5 M. t/hr., particulate emission is limited
to 0.065 grains/dscf at 7% CO-. This standard can not be met by the mechanical
type filter (multicyclones, etc.) installed in many smaller plants built before
the present guide lines were introduced in 1974.
Therefore, many of the smaller plants are restricted, even where duplicate
lines have been installed, to operate one line only, at any given time in order
to keep hourly throughput below the 5 M.t/hr. limit. This applies to plants
No.'s 1, 11, 13, 15, 16, 17, 18, 20, 23, 25, 27, 30, 31, 33-34 and 36-37.
On this basis, daily rated capacity per system for these plants perhaps
should be that of one unit.
SWEDEN
Plant No. 1, Boras: Heat medium - steain, 10.3 + 10.3 + 16.5 M.t/hr., 10
bar, 2850C (22700 + 22700 + 36500 lbs./hr., 150 psi, 545°F). Cogeneration of
electricity and H.P.H.W. district heating.
Plant No. 8 and 9, Linkoping, are three lines in the same plant.
Plant No. 10, Stockholm-Lovsta: Built by V^lund-Landsverk in 1938. Re-
fractory wall furnace, refuse-fired hot air generator. Plant burns H, C, LI.
Capacity: 4 lines each 7.5 M.t/hr. Originally electricity generation. Line
No. 5, 12.5 M.t/hr. installed in 1965 by V{$lund-Landsverk. In 1968 two lines
were fitted with rotary type dryers for thermal drying of non-dewatered, digested
sludge. Designer/Manufacturer: AB Torkapparater, Stockholm.
Plant No. 11, Lulea: Duplicate information. For correct information, see
plant No. 12.
Plant No. 12, Lulea; Is correct with the following additions: In addition
to the production of hot water for district heating this plant uses the combus-
tion gases to dry undewatered sludge in rotary type dryers supplied by AB Tork-
apparater, Stockholm.
Plant No. 14, Sodra Sotenas; Location in the Gothenburg Archipelago. To
the best of my knowledge, there is no energy utlization.
Plant No. 21 and 22, Stockholm-Solna are the same plant: Two lines have
been refurbished by B & S as mentioned under Plant No. 22. Total capacity,
3x4 Mt/hr.
Plant No. 25, Sundsvall; Steam is used for electricity production and
industrial process steam.
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Page 5
UNITED KINGDOM;
Coventry! Unless recent modifications have taken place, no electricty is
generated, but steam is used for internal use, driving fans, hydraulic pumps,
etc. via individual direct drive steam turbines. In addition, energy is sold
for indutrial space heating for the nearby Chrysler car factory.
FRANCE:
Paris-Ivry; The furnace capacity of this plant has been downrated from
2 x 50 M.t/hr to 2 x 40 M.t/hr. following nodifications of the water wall fur-
naces.
Finally, please note that Table A-25 incorrectly informs that Copenhagen
Amager and Copenhagen West produce steam.
The succesive sections relate to actual information received from local
contacts during the survey, and are beyond our perview to comment.
We would caution, however, that such comments as appear on page X-16;
The appearance of the stack plume was extremely clean and attractive and the
stack plume was usually invisible, are necessarily subjective and while we do
not question the interpretation (on a two day visit with periodic observation)
we cannot help believing that these statements color and prejudge actual long-
term performance of the systems.
We hope that our comments together with those of our Danish collegues
(being sent direct) are helpful to you in finalizing the report.
Regards,
Gunnar Kjaer
President, Volund U.S.A.
Peter J. Ware
Director of Enginering
Waste Management, Inc.
cc: Philip R. Beltz
Battelle Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Please note also the attached comments, Ref. page A-103, paragraph 7,
-------
June 28, 1979
Waterwall Furnaces vs. Refractory Lined Furnaces
The advantages and disadvantages of water-wall cooled incinerators
compared with refractory lined incinerators has been debated in
Europe for nearly two decades. Prior to the late 50's refuse
incineration furnaces were, as a matter of course, built with
refractory lined walls. It was widely accepted that the primary
purpose of the refuse incinerator was to dispose of refuse. That
refuse incineration is best accomplished in a refractory lined
furnace has never been disputed. This is because the high heat
capacity of the refractory lining keeps the combustion process
going, even when charges of low heat value refuse (due to high
moisture or high ash content) are fed into the furnace.
The radiation heat from the furnace walls enable the incinerator
to handle portions of refuse which are not, in themselves, auto-
combustible. The result is the maximization of volume reduction
and a residue with a minimum content cf putrescible matter and
unburned carbon.
The refractory lined furnace was to seme extent, perhaps, more
necessary in the 40's and 50's than today because of the lower heat
value of the refuse at that time and zhe different composition.
Refuse in the Western industrialized world has changed considerably
since the 40's and 50's, in quantity as well as in composition.
The ash and putrescible content has been reduced. The considerable
increase in refuse quantities that has taken place is, generally,
in the form of highly volatile material, i.e. paper and plastic.
The result is a much higher overall heat release from.each.ton of
refuse. However, with so much of the heat value tied up with the
high volatile matter, the stabilizing effect produced by refractory
brickwork in the furnace is desireable in order to burn the less
combustible portion.
Another result of the increasing refuse quantities in the late
50's and 60's has been a demand for larger units. In Europe energy
utilization from the refuse has been a matter of course ever since
the V01und company built the world's first continuously operating
incinerator in Denmark in 1930. This unit produced electricity from
the refuse. V01und and most of its licensees as well as newcomers
-------
- 2 -
to the European incineration field have generally subscribed to the
idea of heat utilization from the refuse. However, Vtflund was for
a long time the only company with in-house expertise and experience
in both boiler design and manufacture as well as in incinerator
design and manufacture.
As a result, most other incineration plant designs have been based
on experience gained from boilers for conventional solid fuels and
not on experience with solid waste. Thus, we find that these systems
tend to reflect primarily traditional boiler design requirements
such as:
— High efficiency
— High pressure stability, i.e. the ability to withstand
the required static pressure on the water/steam side
with minimum use of material in boiler tube walls.
— Good steam quality without water droplets.
Only rarely, however, has adequate consideration been given to the
special thermal conditions applicable to the incineration of domestic
refuse^ This became even more evident as larger incinerator units
were required which began to approach the size of small power station
boilers.
This has resulted in essentially conventional power plant boilers
been constructed with an incineration grate included. Serious
corrosion problems have plagued many of these systems along with
problems resulting from slagging and sintering of ash and clinker
on the boiler surface after only a few years of operation.
Dew point corrosion, in plants with heat utilization is rare in
boilers or in auxiliary equipment, i.e. gas ducts, electrostatic
precipitators or I.D. fans. The exhaust gas temperature can easily
be maintained well above the dew point temperature for the acids
and the flue gases.
High temperature corrosion, on the other hand, presents a serious
threat to the availability and also to the operational efficiency
of the plant.
The reasons for high temperature corrosion are, today, well under-
stood, and it is generally agreed that the following conditions
should be avoided:
— The presence of local streaks of incompletely burnt
gases in 'the gas passages of the boiler.
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- 3 -
— Boiler wall temperatures (metal temperatures) exceeding
350-400° C. (650-750° F.)
— The presence of a layer of flyash or clinker in a melting
phase on the boiler surface.
Recent investigation indicate that the most dangerous conditions are
caused when incompletely burned-out gases come in contact with the
boiler walls thereby causing fluctuation between oxidizing and reducing
atmospheres in the presence of high temperatures and.corrosive gases.
If these streaks of reducing atmosphere can be avoided then the
metal temperature in itself seems less important.
The occurence of melting temperatures in the flyash and clinker
layer, too, is often caused by this local combustion of unburned
gases raising the temperature locally above the melting point.
It is, therefore, very important to avoid the streaks of reducing
atmosphere in the boiler. This problem must be solved before the
gas reaches the boiler rather than in the boiler itself.
Despite all efforts to mix the waste properly before it is fired
into the furnace, waste remains a very heterogeneous fuel which
burns with varying velocities and oxygen requirements. Therefore,
local streaks of unburned gases with high carbon monoxide content
as well as temperature fluctuations will occur immediately above
the grate, despite the presence of excess air. These conditions
are further promoted by the very wide grate areas necessary in high
capacity incinerators.
Gases only mix effectively when they are of the same temperature.
Therefore, the combustion gases must be retained in the combustion
zone long enough to ensure that the gases are completely burned out
and properly mixed so that a homogeneous oxidizing atmosphere is
created prior to entering the boiler,
Vtflund's two-way gas system and the special after-burning chamber
allows the time, temperature and turbulence necessary for complete
combustion of the gases before they enter the boiler.
The flyash particles consist mainly of easily meltable clinker.
which remain "soft" down to a temperature of approximately 600 C.
(1100 F.). Even after the surface of the flyash particles is
cooled below that temperature, the center remains soft for some time,
increasing the risk of the particles sticking to the boiler surface
when they flatten on impact.
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- 4 -
The degree of clinker slagging anc sintering is often the decisive
factor in determining when an incinerator must be taken out of
operation for maintenance. Therefore, it is important that flyash
particles are burned out completely and are effectively cooled down
before entering the convection part of the boiler, where the boiler
tubes are positioned.
The first objective is achieved in the after-burning chamber. The
second is met by designing the gas passages to allow sufficient
time in the radiation zone of the boiler.
These objectives, we believe, are oest achieved through a design
incorporating a separate furnace and boiler. Compared with the
integrated boiler design (water-wall furnace) the separate furnace
and boiler design generally requires a marginally higher investment
and, in addition, the heat recovery is, in theory, of marginally
lower efficiency.
However, when operating costs are considered, the economics change
dramatically. The ultimate decision is between marginal theoretical
efficiency ~ and reliability and availability.
Today, few, if any European inciners-or designer/manufacturers still
offer a pure water-wall furnace for "incineration of urban refuse.
Furthermore, specification for maximum steam outlet temperatures
from incinerators are frequently being downgraded to 650-750 F ~
following the many incidents of serious superheater corrosion
experienced over the last 10 years or so.
Existing water-wall furnaces in operation in Europe have experienced
severe erosion and corrosion problems in the water-wall sections.
This has largely been a result of the previously mentioned fluctuation
between oxidizing and reducing gas atmospheres in the furnace.
Theoretically, the water-wall incinerator furnace can be operated
with less excess air than the refractory wall incinerator because
no air cooling is required for the furnace walls. It is this
theoretical reduction in excess air that has produced the marginally
higher fuel-to-energy efficiency.
However, the problem of corrosion of the water-walls has caused the
plant operators and designers to increase substantially the amount
of excess air, resulting in the elimination of this marginal boiler
efficiency. Unfortunately, in most cases, increasing the excess
air has not been sufficient to solve the corrosion problem.
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- 5 -
Water-wall manufacturers, therefore, have now begun to install
refractory linings inside the water walls in the furnaces. The
immediate effect has been a reduction in furnace throughput
capacity. For instance, the very large water-wall furnaces at the
Ivry Incineration Plant in Paris have"had their capacity ratings
reduced from 50 to 40 metric tons per hour (1320 to 1C56 short tons
per day per unit) as a result of the relining required to deal with
corrosion problems. In addition, fuel to energy efficiency has,
of course, been reduced as well.
New so-called water-wall furnaces are, today, as a matter of course
being designed with a refractory lining up to the end of the com-
bustion zone. However, in a recent paper presented a- the meeting
of the Corner Tube Boiler Manufacturers' Association, a representative
of one of the leading manufacturers of water-wall furnaces pointed
to the still existing risk of corrosion in water-wall furnaces as a
result of cracks in the refractory lining. It was pointed out that
this corrosion would occur mainly in the areas where the refractory
supports are welded to the water wall.
The same manufacturer according to a study completed for the U.S.
Energy Research and Development Administration, (now 3ept. of Energy)
acknowledges the advantage of the refractory furnaces with respect
to reliability. A previous incineration plant with refractory lined
furnaces built by this company in Lausanne, Switzerland is now
nearly 20 years old and is still available nearly 90 per cent of
the time. The best that the same company has ever achieved with
their early water-wall furnace designs has been about 75 per cent
availability, and even today with their modernized water-wall
designs the company will not guarantee more than 80 per cent
availability.
Today, even where water-wall furnaces are installed in Europe most
are refractory lined in the combustion zone. While the theoretically
higher efficiency has been diminished by the design changes required
by the problems discussed above, modified water-wall furnaces are
still being specified by some consultants. It is understandable,
given the time delay between European and American experience in
incineration technology, that it will still be sometime before the
North American market focuses on the greater reliability and actual
fuel-to-energy efficiency of the refractory lined incinerator furnace.
Gunnar Kjaer
-------
Environmental Systems Group
40 UOP Plaza-Algonquin & Mt. Prospect Roads
Des Plames, Illinois 60016
Telephone 312-391-2341
August 30, 1979
Mr. David-B. Sussman
Resource Recovery Division (AW-462)
U.S. Environmental Protection Agency
Washington, D.C. 20460
SUBJECT: Evaluation of European Refuse-Fired
Energy Systems Design Practices.
Review of Draft Report Volumes I tc IV
Dear Mr. Sussman:
In accordance with your request, both UOP Inc. Solid Waste Systems and our
technical collaborators, Josef Martin Company of Munich, West Germany, have
reviewed the subject report prepared by Battelle Columbus Laboratories.
Josef Martin Company's review and comments were airmailed to you directly
from Germany on August 22, 1979, with a copy to us. We have reviewed these
comments and fully concur with Martin. In addition, we have also noted a
few typographic errors, which we are sure will be corrected in editing. We
have also observed that some tables have lost legibility in size reduction
and printing, particularly Table A-15 on page A-40 and Table A-17 on.page
A-47.
On page A-54, paragraph two, the sentence after, "since all of " is not
clear. The statement appears to imply 'bne of the units at most plants is
down at all times." We suggest this sentence should be re-written to read,
"For the purposes of scheduled maintenance, when one of the units is shut-
down and remaining unit(s) cannot process all the refuse delivered at the
plant, a pit capacity of 5-6 days storage is normally provided."
On page A-55, the first paragraph, second sentence states, "The most used
shear is manufactured by Von Roll." This statement appears questionable.
We assume the authors mean that all of the Von Roll plants visited had shears
manufactured by Von Roll.
On Table A-21, page A-58, "Universal Oil Products" should read "UOP Inc."
On page A-59, second paragraph, "range in rates" should read "ratio of rates."
-------
Mr. David B. Sussman,
U.S. EPA
August 30, 1979
Page Two
Page A-64, Table A-23, first line "room" should read "Ram."
Page A-71, Table A-24 - Overfire air per tonne for,Paris Issy plant appears to
be too high. Appears total combustion air (4235 M ) is shown as overfire.
Only 20-25% of combustion air is used as overfire.
We appreciate the opportunity of being allowed to review the subject draft re-
port and hope you will find our comments useful.
We commend you and the authors of this most comprehensive report on European
technology.
Very truly yours,
R. W. Seelinger
Engineering Manager
Solid Waste Systems
Pt
c: Josef Martin Co.
uop
-------
JOSEFMARTIN FEUERUNGSBAU GMBH
MOLLVERBRENNUNGSAN LAG EN -ROCKSCHUBROSTE-ENTSCH LACKER
Josef Mortln Feuerunjjsbou GmbH, Postf. 4O 12 28, 8 Munchen 4O
Mit Luftpost - By airmail
Mr. David B. Sussman
Resource Recovery Division
(AW 462)
U.S. Environmental Protection Agency
Washington, D.C. 20460
U.S.A.
1925
\2<
1075
IhrZelohen
Ihre Nnchrlcht vom
Unser Zelchen
Wd/AH
MCinohen
Leopoldetr. 248
22 August, 1979
SUBJECT: Battelle Laboratories
Report: Evaluation of European Refuse-Fired
Energy Systems Design Practices
Dear Mr. Sussman:
We refer to your recent agreement with Mr. Phil Beltz of
Battelle covering possible corrections of the above-men-
tioned report. This report reached us only on }1 July 1979
so that the short period (deadline: 31 August 1979) indi-
cated by you for submission of suggested corrections, al-
lowed only a perusal for basic errors and misunderstand-
ings and no thorough discussion.
We would praise the Battelle authors for their thorough
and detailed summary and discussion of all technical in-
formation gathered on the occasion of their visits to the
various European refuse incineration plants with generation
of energy. It is understandable that in view of the great
number of data confusions or mistakes crept into now and then,
especially since there was the problem of the different lan-
guages, too.
-------
JOSEF MARTIN FEUERUNGSBAu GMBH Mr. David Sussmanvv|Tv>/ - 2 -
Battelle Report
Wd/AH
22 August, 1979
Our perusal of the 4 volumes has mainly been concentrated
on the passages referring to plants of the 'Martin system.
Sometimes, we have also commented on general theories and
philosophies of Battelle, however, would clearly state that
we do not always share the authors1 opinions.
We were somewhat disappointed at the fact to find again a
great part of the errors and mistakes already contained in
the preceding trip reports of Hamburg-Stellinger Moor,
Paris-Issy-les-Moulineaux and Zurich-Hagenholz and mean-
while corrected with our letters dated 22, 23 and 26 Fe-
bruary 1979.
Also the corrections submitted by TIRU in their letter to
Battelle dt. 23 February 1979 have not been considered.
Due to the short period allowed to us we have no possibi-
lity of discussing this report with the plant managers of
the 3 Martin plants mentioned. Therefore, we are not in a
position to judge whether our clients agree to publications
of data covering, for example, capital and operating costs
or of way of financing. We hope that Battelle has obtained
our clients1 permission.
Furthermore, we have not corrected any misprints nor trans-
lation errors.
We are enclosing photostats of the pages where we have made
corrections (marked in pink).
We kindly ask you or Battelle to modify the corresponding
pages of the draft report to the effect of real information.
-------
JOSEF MARTIN FEUERUNGSBAU GMBH Mr. David Sussman \k***^ - 3 -
Battelle Report
Wd/AH
22 August, 1979
We would still briefly comment on a few pages, as follows:
Pages A-l, A-66, A-6?, A-103, 1-2, S-4, U-8
A great misunderstanding seems to have crept into here in
so far as Mr. Tanner is called the originator of the modern-
day water-tube wall refuse incinerator/boiler. Mr. Tanner
may be called the originator of the waste heat boiler for
refuse incineration plants, however, never the originator
of the modern-day water-tube wall refuse incinerator/boiler.
You may look: this up in the two publications mentioned by
Battelle on page A-67. Many years before Von Roll, Martin
have equipped the furnace walls with boiled Bfibes and this
was severely criticized by Von Roll in competitions.
Page A-4
The quantity burned by the Hamburg-Stellinger Moor plant in
1976 was 200,556 mt refuse. The quantity of 420,680 mt in-
dicated by Battelle refers to both Hamburg refuse incinera-
tion plants (Stellinger Moor and Borsigstrasse).
Pages A-61 and Q-8
1. On Hamburg-Stellinger Moor
Battelle has obviously misinterpreted an information ob-
tained from Hamburg-Stellinger Moor. From the beginning
of commissioning up to the year 1976, always individual
grate bars only had been replaced, if required, during
the annual maintenance periods of the stoker firing equip-
ment in Hamburg-Stellinger Moor. Prom the year 1976 on-
wards, however, this maintenance schedule has been changed,
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JOSEF MARTIN FEUERUNGSBAU GMBH Mr.. David Sussman ^JTtJ - 4 -
Battelle Report
Wd/AH
22 August, 1979
Since 1976, during the annual shut-downs for maintenance,
it is no longer usual to replace individual grate bars,
but to replace complete grate bar steps. Each step con-
sists of 25 grate bars. The removed grate steps are re-
furnished in the plant's own workshop, individual grate
bars are replaced, if required, and then the refurnished
steps are held ready for the next maintenance shut-down.
In the first year (1976) this procedure was applied, a
great many bars, viz 24 % mentioned by Battelle, were re-
placed. In the second year, only 15 /»* in the third year
1978 only 10.5 % were replaced, and it is expected that
the replacement rate will go down to a figure from 5 to
10 % in the course of further operating years.
The above information was confirmed to us by the Hamburg-
Stellinger Moor plant management on '22 August 1979 over
the phone.
You will certainly agree with us that we demand that the
figure of 24 % indicated by Battelle in the report, is
changed to "less than 10 %", as it is completely wrong
and may even do harm to our reputation, as compared to
our competitors.
2. Zurich-Hagenholz
Also the figure of 7 % mentioned here is wrong. Upon in-
quiry, the plant management confirmed us on 22 August 1979
over the phone that within 40,000 operating hours only
32 grate bars were replaced, thus only approx. 0.8 $/year.
The figure of 7 % indicated by Battelle is a composite
value of all spare grate bars of the two older Von Roll
units No. 1 and No. 2 and of the Martin unit No. 3. Here,
too, we demand correction.
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JOSEF MARTIN FEUERUNGSBAU GMBH Mr. David Sussman \^ \$ - 5 -
Battelle Report
Wd/AH
22 August, 1979
Page G-3
Contrary to Kaiser and Perry we have found out that in case
of municipal refuse the difference between higher heating
value HHV and lower heating value LHV is approx. 10 to 15 $:
For example:
for refuse at about HHV = 5000 Btu/lb the difference is
approx. 11 %
for refuse at about HHV = 4000 Btu/lb the difference is
approx. 15 %
Therefore, the formulas indicated by Battelle are very doubt-
ful.
Pages R-10 and R-13
The photo R-7 shows a Martin ash discharger of the Bazen-
heid/Switzerland refuse incineration plant.
Here, too, we demand correction.
Page S-58
We think it necessary to clarify the term "Combustion Volume",
otherwise the volume heat release ratesmentioned in table S-3
are not comparable.
Page U-27
The furnace roof tubes are part of the first, stage super-
heater, are thus flown through by saturated steam or some-
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JOSEF MARTIN FEUERUNQSBAU GMBH Mr. David Sussman \^*\$ - 6 -
Battelle Report
Wd/AH
22 August, 1979
what superheated steam. During start-up or shut-down of
the boiler, radiation and too low a steam flow may cause
local overheating of the tube wall, resulting in wall
thickness reduction in the course of time. These tubes
were never covered with SiC material.
Pages U-81 and U-83
The Yokohama-Totsuka plant has a completely different
superheater design and should not be mentioned in this
connection.
Page X-3
The regulation "TA-Luft" refers the indicated emissions to
11 % 02, and not to 7 % CO^.
We hope that you or Battelle will still make the corrections
mentioned above and indicated on the enclosed photostats, if
not, the value of the otherwise quite good Battelle report
would be reduced considerably.
Very truly yours,
JOSEP MARTIN
Peuerungsbau G.m.b.H.
ppa.:
ENCLOSURES
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/: . ___ \\tieelabTator-Trye Inc.
ENERGY SYSTEMS DIVISION
JOSEPH FERRANTE. JR. u
Hamplon, New Hampshire 03S42
Reg.onal Vice President Tel. 1603' 926-5911
September 12, 1979
Mr. Philip R. Beltz
Projects Manager
Energy and Environmental
Systems Assessment Section
Battelle Columbus Laboratories
505 King Avenue
Columbus. Ohio 43201
Dear Phil:
You are in receipt of Von Roll's August 20th comments
to your draft report, entitled "European Refuse-Fired Energy
Systems - An Evaluation of Design Practices". The purpose
of this letter is to relate some of our reactions to Volume I
of this four-volume effort. I have also attached a copy of
Von Roll's remarks which we received. I believe they are
similar, if not identical, to the ones you already have.
In general, the report is excellent and makes a substan-
tial contribution to the literature dealing with the subject.
The following are some points to clarify to avoid misleading
the uninformed reader.
• The inference is made that the approach to be used
in Harrisburg is new. In reality, the use of steam
to buildings' adsorption chillers is not new and has
been widely practiced in major cities in the U.S.
including New York and Boston. The second paragraph
is therefore misleading. (Page A-33).
• Although "spending money for features to reduce
corrosion and erosion generally increases invest-
ment" is true, it is a worthwhile investment to do
so. The impact of the additional investment is
minimal in comparison with the costs to maintain
and replace boiler tubes without corrosion reduction
features. (Page A-45, First Paragraph).
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Mr. Philip R. Beltz
Page Two
September 12, 1979
• It is not only the tax free bonding which favors
private ownership in America; rather investment
tax credits and accelerated depreciation are very
important in making the private ownership decision.
(Page A-46, Paragraph 2).
• It should be noted that in a third Munich unit,
refuse is fired separately with coal. Munich has
since concluded that coal and municipal solid waste
should not be co-fired. (Page A-68).
• The second to the last paragraph should read "when
Wheelabrator-Frye Inc. built the Boston North Shore
plant in Saugus, Massachusetts, using the 'Von Roll
design..." (Page A-72).
e The expression, "American thrust towards co-firing"
is an overstatement. This should read, "... some
of the American experimental efforts towards co-
firing..." The inference that there is an American
thurst in moving towards co-firing is not wholly
justifiable. (Page A-92, Fourth Bullet).
• The dump fee costs indicated are misleading in that
they suggest that they are real costs. In actuality,
the disposal costs are much higher. (Page A-99,
Second Bullet).
• It is misleading to suggest that the tipping floor
method is an "American" system when in reality, the
pit and crane method is more prevalent. The tipping
floor method should not be given the characterization
"American." (Page A-99, Next to Last Paragraph).
• The listing of U.S. installations is very misleading
in that it includes:
Proposed projects which may never be built.
Projects which have been abandoned.
Non-municipal waste projects.
- Non-energy recovery projects.
Experiments.
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Mr. Philip R. Beltz
Page Three
September 12, 1979
To include as comprehensive a list is not justi-
fiable in a report on refuse-fired energy systems,
since it leaves the impression that the U.S. has
89 implemented systems, when in reality there are
less than 20 bona-fide refuse-to-energy projects
in the U.S. Furthermore, the U.S. listing is not
compatible with listings of other nations since it
includes proposed projects, non-energy recovery
projects, etc.
To leave the listing of U.S. systems in its present
form would be a detriment to the report. (Pages
B-57 - B-67).
• Why are Martin plants referenced as such in the
report, while other manufacturers' plants are only
referred to by the city in which they are located?
The editors should be consistent. (Page 1-29).
We trust that these comments can somehow be incorporated
in your final report to EPA and appreciate the opportunity to
have been involved in this project.
O
// Joseph Ferrante, Jr.
t/
/pel
cc: David Sussman
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VON ROLL COMMENTS ON THE BATTELLE REPORT ON
EUROPEAN REFUSE-FIRED ENERGY SYSTEMS
(Transcribed from Telex received 08/21/79)
As your just finished and very detailed report is mainly
a tool for decision making for now and for the future, we think
it is very essential, that as far as Von Roll's grate design
is concerned, the report should concentrate on the design Von
Roll is now applying and should report on the design given up
by Von Roll in 1978 and inspected in the four rather old plants,
only as far as it is necessary for a better understanding of
our design applied now. We have discussed this problem with
you and you have promised to consider a rewriting of the pages
Q-9 to Q-14 due to the very short time, Von Roll had available
for reviewing the entire report we are concentrating on the
key items of our design, the grates and boiler. We ask you to
use the following text for replacing the existing version in
your report:
Von Roll Gra-e
1. FJ gures: Please change figures as follows:
Figure Q-2: Two steps of Von Roll Grate using
reciprocating forward-feed design.
(Courtesy of Von Roll Ltd.)
(Picture as shown in draft under
Figure Q-3.)
Figure Q-3: Improved Von Roll reciprocating step
grate in refractory walled furnace.
(Courtesy of Von Roll Ltd.)
(Picture as shown in draft under
Figure Q-2.)
2. Text for Pages Q-9 to Q-14:
Figure Q-2 shows in more detail the old standard Von Roll
sloping reciprocating grate as it is used in most of Von Roll
plants built before 1978. This original Von Roll grate, which
is still in use in many of the larger Von Roll plants involves
the alternating forward motion of adjacent grate "plates".
For smaller furnaces (that is 5 tons per hour or less) and
particularly also for high calorific value trade waste Von Roll
began 15 years ago install an improved grate composed of alter-
nate fixed and moving rows in which each entire moving row of
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- 2 -
grate plates moves forward and backward together, thus elimin-
ating the relative motion and grinding action between adjacent
grate blocks. Von Roll is now applying this design to all new
furnaces regardless of size. For existing plants, a grate
system was developed by Von Roll, which can be mounted on top
of the existing grate understructure and several plants have
been modified in the meanwhile. Figure Q-3 shows a section
of the modified grate at the Von Roll Gothenburg plant.
For new plants Von Roll developed the R-grate. A proto-
type of this grate is in operation since 1976 at the Von Roll
Fribourg plant in Switzerland. The new system consists of a
hydraulically driven feeding ram for volumetric charging and
of a grate 6 to 12 meters long, 1.8 to 10.5 meters wide and
with a declination of 18 degrees. The grate is built-up by
3 to 24 identical grate units linked together. For average
and high heating values no grate steps are provided anymore,
as this was done by Von Roll in its older design (see figure
Q-2). For low heating values, however, grate drops still are
provided also at the new R-grate to rearrange the heavy fuel
bed as it tumbles down from an upper to a lower grate. Because
of the "opening up" of unburned combustible surfaces as this
tumbling action occurs, this point is in the furnace, one of
the intense burning. To provide enough air at this point, in
some plants, air is being admitted through the wall of the step
to" assure amply oxygen supply for the increased combustion rate.
The grate unit is the basic unit of the new R-grate system.
Each unit consists of support structure, lateral sealing elements,
four fixed transversal grate support, hoppers, zone separation
walls and hydraulic drive units. The so-called drive carriage
with the four mobile transversal grate support beams connected
to the hydraulic drive is mounted on the support structure. The
grate blocks are mounted on the fixed as well as on the mobile
transversal grate support beams.
The drive carriage moving the four mobile rows of blocks.
is equipped with rollers running on inclined guiding tracks and
supported by the two parallel longitudinal frame elements of
the carriage. The guiding tracks are mounted on the longitu-
dinal supports of the support frame.
The hollow grate block is equipped with cooling fins,
enables forced cooling resulting in reduced wear and increased
life span. The blowing of primary air through rectangular
openings cast into the grate blocks results in high pressure
loss enabling uniform distribution of the combustion air
throughout the fuel bed independent from its thickness or
distribution on the grate surface. Even substantial varia-
tions of the fuel bed do not change the uniformity of air
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- 3 -
distribution apart from negligible deviations. The chrome
steel cast grate blocks are laterally machined. Each row
of blocks is individually clamped together. Approx. 1,5 0/0
of the total grate surface of one section consists of air
outlets.
The clamping device of the mobile block rows consists
of two identical clamping brackets holding the clamping pins
and the tie rods. The locking brackets are inserted in the
first and last block of each row and frictionally connected
by the tie rods located underneath the grate blocks. The
fixed rows of grate blocks are locked in a similar way. This
locking system reduces on one hand grate riddlings to a mini-
mum, on the other the blocks remain firmly pressed together
even in operating condition, preventing undesirable escape
of air between them and securing continuous forced cooling.
The grate drive is hydraulic. Each grate unit is driven
by two parallel cylinders mounted on the two lateral longi-
tudinal supports of the support construction. The cylinder
rods are connected to the drive carriage by shackle joints
and move it for and back on the inclined guiding tracks. The
grate blocks supported by the transversal beams move in the
same rythm. The angular grate block form and the rapid stroke
movement result in an excellent shifting and stoking effect.
The fire spread evenly across the entire width of the grate
at minimum dust development.
This grate drive system enables utilization of small and
lightweight drive cylinders (approx. 16 kg/cylinder) for easy
and quick exchange. Mounting or removal of a cylinder can be
effected during operation owing to the newly developed drive
and control system enabling control of each single drive unit
separately. Therefore grates consisting of several grate
units may operate at reduced load even during exchange of a
cylinder.
The drive of the individual grate unit is not continuous
as usual for today's systems but by electronic impulse control.
Each grate sections is assigned the most suitable number of
strokes depending on average waste heating value and progress
of combustion. This number of impulses determines the respec-
tive waste travelling speed in the range of the respective
grate unit. Based on combustion progress the optimum number
of impulses is determined and adjusted for each grate section.
By this system the impulse number (number of strokes) of
the whole grate can be uniformly increased or reduced for re-
spective throughput alterations. The relation of the operating
speed of the individual grate units, however, remains unchanged.
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- 4 -
Owing to the application of electronic components it is possible
at any time during operation to change the respective number of
impulses of individual grate sections. Grates in boilers for
heat recovery may for instance be controlled relative to the
steam production by controlling the intervals between strokes.
Automatic firing control facilitates operation considerably
since the operating staff has to control manually only in the
case of a change of throughput.
Feeding Ram
Most important prerequisite of any automatic operation is
uniform feeding. Von Roll applies a hydraulically driven feeding
ram. It can be best compared with a drawer turned upside down.
This drawer moves on a horizontal surface. The stroke speed
is continuously variable by a remote oil flow control. The
back stroke is effected at constant speed. Similar to the grate
the ram is controlled with respect to steam production. Con-
trary to the grate, however, the stoke speed is continuously
adjusted without any significant alteration of the waste quantity
per stroke.
General Boiler Design
(Page U-8 to U-10)
Von Roll would like to comment, that the so-called tail-end
boiler, consisting of a vertical waterwall combustion room and
a horizontal convection section with hanging vertical tube bundles
is a Von Roll development, applied first in the Lnadshut and in
the Fuerth plant in Germany in 1971. A special feature of this
boiler type is its inexpensive mechanical boiler cleaning by
rapping of the bundles. This design is a very successful im-
provement towards high boiler availability. Since Landshut, Von
Roll provided this boiler type for the plants in Mulhouse, France
(1972), Quebec, Canada (1974), Angers, France (1974), Dijon,
France (1974), Nyborg, Denmark (1975), Bezons, France (1975),
Kempton, Germany (1975), Saugus, USA (1975), Emmenspitz,
Switzerland (1976), Moncada, Spain (1975).
The only plant with some reservations about the quality
of this boiler design is Saugus whereas the boiler unit number 1
at Landshut in the meanwhile is in operation fro approx. 51'000
hrs. without the need of a mechanical cleaning. We would like
to draw your attention to that subject on a paper given at the
CRE Conference in Montreux in 1975.
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- 5 -
The adaption of this boiler type by WE for Hamburg-
Stapelfeld can simply be considered as a copy done by former
Von Roll employees.
Finally, we would like to mention, that in the list of
worldwide inventory of waste-to-energy systems we are missing
some Von Roll plants. We are airmailing you today one newest
reference list. Please note also, that the Volund Company did
not participate at the delivery of the Nyborg Plant in Denmark.
ya 18285
SW-176C.2
•U.S. Gi VLE.-MLKT PMVTINC G! I'ICK : 197') 0-311-132/145
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