EPA/600/2-90/038
August 1990
FUEL-EFFICIENT SEWAGE SLUDGE INCINERATION
by
Michael J. Walsh, Albert B. Pincince, and Walter R. Niessen
Camp, Dresser & McKee Inc.
Boston, MA 02108
Contract No. 68-03-3346
Project Officer
Donald S. Brown
Water and Hazardous Waste Research Division
Risk Reduction Engineering Laboratory
Cincinnati, OH 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
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DISCLAIMER
The information in this document has been funded wholly or in part by
the United States Environmental Protection Agency under Contract
68-03-3346 to Camp Dresser & McKee Inc. It has been subject to the
Agency's peer and administrative review, and it has been approved for
publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased
generation of materials that, if improperly dealt with, can threaten
both public healtli and the environment. The U.S. Environmental
Protection Agency is charged by Congress with protecting the Nation's
land, air, and water resources. Under a mandate of national
environmental laws, the agency strives to formulate and implement
actions leading to a compatible balance between human activities and the
ability of natural systems to support and nurture life. These laws
direct the EPA to perform research to define our environmental problems,
measure the impacts, and search for solutions
The Risk Reduction Engineering Laboratory is responsible for planning,
implementing, and managing research, development, and demonstration
programs to provide an authorizitative, defensible engineering basis in
support of the policies, programs, and regulations of the EPA with
respect to drinking water, wastewater, pesticides, toxic substances,
solid and hazardous wastes, and Superfund-related activities. This
publication is one of the products of that research and provides a vital
communication link between the researcher and the user community.
This project was undertaken to document realistic cost and energy
requirements for a fuel-efficient sludge incineration facility and to
highlight operational, managerial, and design features that contribute
to the fuel-efficiency of the incineration process. The information
herein was based on plaint site visits, available literature, and design
and operation experience.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
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Abstract
The purpose of this report is to evaluate the status of incineration
with low fuel use as a sludge disposal technology. Four sludge
incineration facilities are evaluated with regards to energy
requirements, life-cycle costs, operation and maintenance requirements,
and process capabilities. The four facilities represent a range of
sludge thickening, conditioning, dewatering, and incineration
technologies.
This report provides the reader with a summary of realistic cost and
energy requirements for a well-operated, fuel-efficient sludge
incineration facility and highlights operational, managerial, and design
features that contribute to the fuel efficiency of the incineration
process. This information provides the reader with a basis to evaluate
both the applicability of incineration as a sludge processing
alternative for future facilities and the cost and energy efficiency of
existing incineration facilities. This information is useful to
regulatory personnel and design engineers who are evaluating sludge
disposal technologies for new or upgraded facilities and to operators of
existing facilities who are attempting to make their operation more cost
and energy effective. This project covers a period from July 1987 to
September 1989.
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CONTENTS
Page
List of Tables vi
List of Figures vii
1. INTRODUCTION
Report Objectives 1
Background 1
Project Methodology 4
2. CONCLUSIONS
Keys to Success 12
Economic Evaluation Summary 15
Energy Evaluation Summary 17
3. PLANT INFORMATION
Upper Blackstone WPCF 22
Metropolitan WPCF 28
Duffin Creek WPCF 35
Cranston WPCF 43
4. ECONOMIC COMPARISON OF FACILITIES
Basis of Analysis 50
Adjustments to Raw Cost Data 61
Plant Comparisons 67
5. ENERGY EVALUATION OF FACILITIES
General 81
Basis of Analysis 82
Facility Comparisons 85
REFERENCES 96
APPENDIX A Metropolitan WPCF Case Study Report 97
APPENDIX B Upper Blackstone WPCF Case Study Report 151
APPENDIX C Duffin Creek WPCF Case Study Report 190
APPENDIX D Cranston WPCF Case Study Report 239
APPENDIX E Summary of Operation and Maintenance 273
Costs at Current Loading Condition
APPENDIX F Summary of Operation and Maintenance 282
Costs at System Capactiy
APPENDIX G Capital Cost Summary Tables 291
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LIST OF TABLES
Table Title page
1 List of Possible Fuel-Efficient Incineration Facilities 7
2 Fuel-Efficient Incineration Facilities 9
3 Facility Unit Costs 63
4 Comparison of Annual Solids Handling Costs For Sludge
Thickening 68
5 Comparison of Annual Solids Handling Costs Sludge
For Digestion at Duffin Creek 69
6 Comparison of Annual Solids Handling Costs For
Conditioning and Dewatering 72
7 Comparison of Annual Solids Handling Costs For
Sludge Incineration 74
8 Comparison of Annual Solids Handling Costs
For Total Solids Train 78
9 Energy Inputs and Outputs for Levels Evaluated 87
10 Estimate of Energy Requirement for Level A 88
11 Estimate of Energy Requirement for Level B 90
12 Estimate of Energy Requirement for Level C 91
13 Estimate of Energy Requirement for Level D 92
14 Estimate of Energy Requirement for Level E 94
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LIST OF FIGURES
Figure Titie Page
1 Effect of Load on Unit Costs 18
2 Comparitive Energy Consumption 20
3 Upper Blackstone WPCF Solids Handling Schematic 23
4 Metro WPCF Solids Handling Schematic 31
5 Duffin Creek WPCF Solids Handling Schematic 37
6 Duffin Creek WPCF Incineration System Schematic 39
7 Cranston WPCF Solids Handling Schematic 45
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SECTION 1
INTRODUCTION
REPORT OBJECTIVES
The purpose of this report is to evaluate the status of incineration
with low fuel use as a sludge disposal technology. Four sludge
incineration facilities are evaluated with regards to energy
requirements, life-cycle costs, operation and maintenance requirements,
and process capabilities.
This report provides realistic cost and energy requirements for a
fuel-efficient sludge incineration facility and highlights operational,
managerial, and design features that contribute to the fuel efficiency
of the incineration process. This information provides a basis for
evaluating both the applicability of sludge incineration and the cost
and energy efficiency of existing incineration facilities. This
information is useful to regulatory personnel and design engineers who
are evaluating sludge disposal technologies for new or upgraded
facilities and to operators of existing facilities who are attempting to
make their operation more cost and energy efficient.
BACKGROUND
Sludge handling and disposal has become the major operational concern at
a great many wastewater treatment facilities for several reasons:
o Sludge production has increased as effluent standards have
become more stringent and treatment facilities have provided a
higher level of treatment.
o Public concern regarding odors, increased traffic, and
noticeable air emissions has increased.
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o Sludge disposal has become increasingly difficult because of
concerns about pathogens, toxic organics, and metals, and
because of increased difficulty is siting residual disposal
areas.
o Sludge disposal has become very costly. An evaluation of four
major secondary facilities in the greater Toronto area showed
that between 50 and 60 percent of each facility's total
operation and maintenance budget is dedicated to solids
handling and disposal (1).
For these reasons, developing improved means of sludge handling and
disposal has become a top priority within the wastewater industry. This
report will evaluate the status of one sludge disposal technology;
sludge incineration with low fuel use.
Because of its simplicity and relatively low cost, municipal sludge
incineration was a popular sludge processing alternative until the mid
1970s. Dramatic increases in the price of fossil fuel coupled with
increased sensitivity to air pollution problems from incinerator
emissions made sludge incineration less attractive. Also, secondary
wastewater treatment, which was implemented at many facilities, resulted
in more sludge, and sludge that was more difficult to dewater.
Incineration, therefore, became more costly to incinerate. Other
problems that hampered fuel-efficient incineration then, and still
continue to hamper fuel efficiency, include (2):
- Sludge cake not dry enough for autogenous combustion.
- Mechanical problems with equipment.
- Variations in quantity and quality of the sludge
resulting in system upsets.
- Problems handling slag, clinkers, screenings, grit, and scum.
- Difficulties operating incinerators that were oversized in
design.
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- Inability to monitor key process operational parameters.
- Operator training which is absent, incomplete, or not updated.
- Emission standards not being met.
- Odor problems and visible emissions.
- Corrosion and plugging problems associated with heat recovery
equipment.
- Lack of coordination in the design of the individual unit
processes in the solids train.
- Lack of coordination between dewatering operators and incinerator
operators.
- Difficulty in maintaining uniform operation conditions that
minimize pollutant formation and emissions.
Because of these factors, many incineration facilities were mothballed
in favor of more cost effective or less problematic sludge handling
alternatives.
Today, many factors are creating a renewed interest in sludge
incineration. Some of the advantages that are again making sludge
incineration attractive include:
Volume Reduction
In many areas, the scarcity of available land has made siting a
landfill large enough to provide for 20 years of sludge disposal
impossible. Incineration reduces the volume and weight of wet
sludge by over 95 percent (mass reduction on a dry weight basis
of 40 to 75 percent), thus reducing the amount of area required
for residual disposal to a minimum.
Energy Recovery
In recent years, many advances have been made in the ability to
recover heat from the incineration process and reuse the energy
throughout the plant. This has significantly increased the cost
effectiveness of the incineration process.
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Sludge Thickening/Dewatering
Recent improvements in sludge thickening and dewatering
technology have made it possible to obtain a relatively dry cake
from primary/waste activated sludge mixtures. This reduces the
auxiliary fuel requirements of the incineration process, making
incineration more cost effective.
Emission Control
Improvements in emission control technology have made it
possible to meet existing emission standards on a consistent
basis.
A 1988 EPA survey of publicly owned treatment works (POTWs) demonstrates
the importance of the incineration process in municipal sludge disposal.
Approximately 21 percent of the sludge produced at the 15,305 facilities
included in the survey was .Incinerated (3). In the future, some of the
facilities that now landfill or land apply their sludge will be forced
to seek alternative disposal methods because available undeveloped land
is scarce and more stringent land application regulations might be
implemented. Facilities that ocean dump sludge are currently being
forced to seek alternate disposal methods. Many of these facilities
will evaluate incineration as one of the solids handling alternatives.
This report and the appended case-study reports provide a basis for
evaluating the role of sludge incineration in meeting these future
needs.
PROJECT METHODOLOGY
The project was performed in three phases. Phase I and Phase II of the
project were completed in September 1988.
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Phase I - Identify and gather information on operating facilities
The purpose of Phase I was to identify 15 to 20 fuel-efficient
incineration facilities operating in North America. To identify these
facilities, several manufacturers, consultants, and EPA personnel
working in the field of sludge incineration were contacted. These
contacts yielded a list of 49 possible fuel-efficient incineration
facilities (see Table 1). To verify the information provided by these
contacts and have a basis for narrowing this list down to 15 to 20
facilities suitable for further study, these 49 facilities were
telephoned and asked to provide general information such as operational
status, fuel consumption, heat recovery capability, and willingness to
provide more detailed operations data. Out of the 49 facilities
contacted, we found 20 facilities that might be self-sustaining or fuel
efficient. These facilities were then arranged by furnace types and
sludge conditioning methods, as presented in Table 2.
Phase II - Select properly operated facilities for in-depth performance
evaluation
The purpose of Phase II was to select three or four facilities that
would be suitable for an in-depth performance evaluation to be completed
in Phase III. To be considered a good candidate for an in-depth
performance evaluation, the following characteristics were desirable:
- low auxiliary fuel consumption by the incineration system
a knowledgeable operations and maintenance staff
a facility on-line long enough to have optimized the
incineration process and developed a reasonable backlog of
operations and maintenance data
- no major design flaws
generally good operations record in areas other than auxiliary
fuel consumption (i.e. air emissions, sludge dewatering, odor
control, etc.)
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at least one facility should have received grant funding under
the EPA Innovative Alternative (I/A) Technology Grant Program
Based on these criteria, the list of 20 facilities developed in Phase I
was screened down to the following seven facilities:
1. Upper Blackstone WPCF, Worcester, MA
2. San Mateo WPCF, San Mateo, CA
3. Indianapolis WPCF, Indianapolis, IN
4. Metro WPCF, Minneapolis, MN
5. Duffin Creek WPCF, Toronto, Canada
6. Lakeview WPCF, Toronto, Canada
7. Cranston WPCF, Cranston, RI
Only one of these seven facilities, the Cranston WPCF, received grant
funding under the EPA Innovative Alternative (I/A) Technology Grant
Program.
Each of these seven facilities was visited to collect additional
information and to assess first-hand if the facility would be a good
candidate for further study..
Based on the criteria presented previously, four facilities were
selected for Phase III study. The name, location, and technology
utilized at each of these four facilities is listed below.
1. Upper Blackstone WPCF, Worcester, MA
Polymer chemical conditioning
Belt filter press dewatering
Multiple-hearth incineration.
2. Metro WPCF, Minneapolis, MN
Thermal sludge conditioning
Polymer chemical conditioning
Roll press dewatering
Multiple-hearth incineration
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TABLE 1
LIST OF POSSIBLE FUEL-EFFICIENT
INCINERATION FACILITIES
Location (by state)
Plant Name
Multiple Hearth Incinerators
Walnut Creek, CA
Central Contra Costa Sanitary District
San Mateo, CA
San Mateo STP
Hartford, CT
Hartford STP
Naugatuck, CT
Naugatuck Treatment Co.
Waterbury, CT
Waterbury STP
Indianapolis, IN
Indianapolis STP
Cedar Rapids, IA
Cedar Rapids STP
Worcester, MA
Upper Blackstone STP
Kalamazoo, MI
Kalamazoo STP
St. Paul, MN
Metropolitan STP
Kansas City, MO
Blue River STP
St. Louis, MO
Lemay Plant
Concord, NC
Rock River Regional WWTF
Greensboro, NC
N. Buffalo WWTF
Princeton, NJ
Stony Brook Regional WWTF
Wayne, NJ
Mt View STP
Rochester, NY
Frank E. Vein La re WPCF
Akron, OH
Akron WPCF
Warren, OH
Warren STP
Toronto, Ontario
Ashbridges Bay STP
Chester, PA
Delora-Chester WPCF
Colmar, PA
Hartfield Township STP
Cranston, RI
Cranston WPCF
Nashville, TN
Nashville Central WPCF
Arlington, VA
Arlington Central WPCF
Charlottesville, VA
Rivanna Water and Sewer Authority
Green Bay, WI
Green Bay STP
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TABLE 1
(continued)
LIST OF POSSIBLE FUEL-EFFICIENT
INCINERATION FACILITIES
Location (by state)
Plant Name
Fluidized Bed Incinerators
Redwood City, CA
S. Bayside WPCF
Lake Tahoe, CA
South Lake Tahoe STP
Kansas City, KS
Kaw Point Plant
Kansas City, KS
Kansas City Plant No. 20
Lynn, MA
Lynn Regional WPCF
Duluth, MN
Western Lake Superior Sewerage District
Lincoln Park, NJ
Two Bridges STP
North Bergen, NJ
North Bergen STP
Raritan, NJ
Somerset-Raritan WPCF
Union Beach, NJ
Bayshore Regional WPCF
Port Washington, NY
Port Washington STP
Mechanicville, NY
Saratoga County Sewerage District
Southampton, NY
Southampton STP
Utica, NY
Oneida County WPCF
Toronto, Ontario
Lakeview STP
Toronto, Ontario
Duffin Creek WPCF
King of of Prussia, PA
Matsunk STP (Trout Run)
North Charleston, SC
North Charleston STP
Electric Infrared Incinerators
Decatur, GA
Snapfinger Creek STP
Gainesville, GA
Flat Creek STP
Fayetteville, NC
Fayetteville STP
Piano, TX
Rowlett Creek STP
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TABLE 2
FUEL ErriCIKHT
CHCIHSRATTON FACILITIES
Sludge Conditioning/ Multiple Hearth Fluidized Bed Electric Infrared
Devatering Method Installations Installations Installations
Ziapro Thermal
Sludge Conditioning
Metropolitan STP, MN
Green Bay STP, WI
San Mateo STP, CA
Ashbridges Bay STP, Ontario
Lakeview STP, Ontario
Belt Filter Presi
Dewatering
Indianapolis STP, IN
Upper Blackstone STP, MA
Delot«-Chester WPCF, PA
Blue River STP, MO
S. Buffalo WWTF, NC
North Bergen STP, NJ
Saratoga County Sewerage District, NY
Oneida County WPCF, NY
Sonerset-Raritan WPCF, NJ
Bayshore Regional WPCF, NJ
F i 11« r Press
Dewate ring
Cranston WPCF, RI
Rock River Regional WWTF, NC
Duffin Creek WPCF, Ontario
south Bayside WPCF, CA
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3. Duffin Creek WPCF, Toronto, Canada
Polymer chemical conditioning
Filter press dewatering
Fluidized-bed incineration
4. Cranston WPCF, Cranston, RI
Lime and ferric chloride chemical conditioning
Filter press dewatering
Multiple-hearth incineration
Phase III - Complete in-depth performance evaluations at four fuel-
efficient facilities
Each of the four facilities selected for Phase III study was visited a
second time for a two-day to three-day period to obtain plant records
and detailed information regarding operation and maintenance costs and
requirements, capital costs, and energy requirements for the
incineration system. The incineration system was taken to be the entire
solids train, including sludge thickening, chemical conditioning or
thermal sludge conditioning and sidestream treatment, sludge dewatering,
sludge incineration, air emissions control equipment, energy recovery
equipment, and ash disposal. A detailed case-study report that
summarized and evaluated this information was prepared for each of the
four facilities. Each case-study report included:
- A summary of the net energy energy requirements of the
individual system components (sludge thickening, dewatering,
incineration, etc.) and of the system as a whole.
A summary of operation and maintenance costs (labor, energy,
consumables, materials) for each unit process and the system as
a whole.
A summary of capital costs for each unit process and the system
as a whole.
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A discussion of operational, managerial, and design features
that contribute to the facility's fuel efficiency.
The four case-study reports provide the data base for this report and
are included in the Appendix.
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SECTION 2
CONCLUSIONS
The results of this study are summarized in this section. Design and
operation and maintenance practices which contribute to the energy
efficiency of the incineration process are discussed, and estimates of
capital costs, operation and maintenance costs, and energy consumption
for a fuel-efficient sludge incineration system are presented. Each of
these subjects are discussed in detail in subsequent report sections.
It should be noted that the estimates of cost and energy consumption
that are presented in this study reflect plant operation under current
emission control regulations. Changes in these regulations could
significantly impact the cost and energy efficiency of the incineration
process. Exhaust gas temperatures for the three multiple-hearth
furnaces considered in this study range from 900°F (480°C) to 1100°F
(590°C). None of the three multiple-hearth systems employs afterburning
of the furnace exhaust gas stream, although two of these three
installations have an afterburner chamber incorporated into the
incineration system. Each of these facilities employees a venturi wet
scrubbing system. If new air emission regulations require operation of
an afterburner for all multiple-hearth systems, cost and energy
requirements for multiple-hearth incineration will increase
significantly. Requirements for more sophisticated emissions control
technologies will increase the capital, labor, and power costs for
sludge incineration. This potential for future increases in cost and
energy consumption should be considered when applying the figures
presented in this study.
• KEYS TO SUCCESS
Although each facility visited as part of this study had several unique
features which contributed to the success of the facility, there were
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some common operational and management features that operators at each
facility agreed were essential to a fuel-efficient sludge incineration
system. These features are discussed here.
Sludge Equalization
A uniform sludge flow to the incineration system is essential, both in
term of quantity and quality. Each time the quality or quantity of the
furnace feed changes, optimum burn conditions within the furnace change
and the operator must adjust the excess air level, rabble arm rotation
speed, auxiliary fuel use, or some other operational variable to
maintain complete combustion conditions. If the sludge feed is kept
uniform, the operator does not have to make major adjustments to the
furnace and can instead concentrate on fine tuning the incineration
system.
To create a uniform furnace feed, some sludge storage and mixing should
be provided within the solids train. The sludge mixing will create a
homogeneous sludge stream and avoid changes in sludge characteristics
such as solids and volatiles content. Sludge storage will provide some
buffer in the system to protect the furnace from day-to-day fluctuations
in sludge production and allow changes in the furnace feed rate to be
made gradually. Sludge storage also allows the incineration system to
be taken off-line for regular maintenance and equipment calibration.
Staff Motivation/Training
The real key to any successful sludge incineration facility is in the
plant operations and maintenance staff. An incineration system is a
relatively complex system to operate and maintain. The operations staff
must understand the effect that changes in excess air level, rabble arm
speed, and other operational variables have on the combustion process,
and the effect that the performance of the preceding solids handling
processes on the furnace's operation. The maintenance staff must have
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the manpower and skill to provide regular maintenance on a variety of
equipment. The development of a good operations and maintenance staff
starts with plant management. Management must create a positive working
environment that motivates the plant staff. Some of the key points to
developing such an environment are:
- Staff Communication
Communication between the operators of each solids handling process is
essential. Operators must understand how the performance of each unit
process directly effects the performance of subsequent unit processes
and recognize the importance of communicating information regarding
changing sludge conditions to other operators. Management can encourage
this by implementing programs such as a rotating employee program or by
forming problem solving committees comprising of engineers, operators
and maintenance personnel from throughout the solids handling facility.
- Staff Training
Management should encourage the plant staff to pursue advanced levels of
training through in-house programs, operator certification programs,
graduate level engineering programs, and activity in professional
organizations and societies. This has a very positive impact on the
attitude of the staff. It increases the staff's knowledge, encourages
the exchange of ideas with other people within the industry, and creates
a sense of staff pride regarding their facility. A knowledgeable plant
staff is better able to optimize the operation of the solids train and
identify new ways to improve the efficiency of the system through
process modifications.
Maintenance Program
A strong maintenance program is a key component of any successful sludge
incineration operation. A strong maintenance program increases the
cost-effectiveness and energy efficiency of the incineration process by:
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- Reducing auxiliary fuel use by minimizing unscheduled
maintenance shutdowns.
Minimizing costs for replacement materials by extending the
useful life of furnace components such as the refractory
brickwork and other ancillary equipment.
Providing the operators with the information necessary to
operate the incinerators fuel-efficiently by keeping the
instrumentation and monitoring equipment operable and
up-to-date in terms of current technology. This insures that
the operators receive the information required to operate the
furnace in an energy-efficient manner.
Management must provide the plant staff with an adequate budget to
operate and maintain the solids handling facility. If budget allowances
do not allow for regular equipment maintenance, equipment falls into a
state of disrepair and, eventually, will require major repair or
replacement. Over the life of a facility, it is more economical to pay
the annual cost of proper preventive maintenance than to reduce annual
maintenance costs to a minimum and pay for major repairs on a periodic
basis.
ECONOMIC EVALUATION SUMMARY
Based on the evaluation presented in Section 4, the following ranges
represent a reasonable estimate of capital and operation and maintenance
costs for a well-operated sludge incineration system operating at
capacity, including furnaces, heat recovery system, air pollution
control system, and ash disposal system.
Annual Operation &
Maintenance Costs $ 70 to $ 90/dry ton ($77 to $99/dry tonne)
Amortized System
Capital Costs $100 to $125/dry ton ($110 to $138/dry tonne)
Total Annual Costs $170 to $215/dry ton ($187 to $237/dry tonne)
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The following ranges represent a reasonable estimate of capital and
operation and maintenance? costs for a complete, well-operated incineration
solids train operating at capacity, including thickening and dewatering.
Annual Operation &
Maintenance Costs $180 to $200/dry ton ($198 to $200/dry tonne)
Amortized System
Capital Costs $200 to $230/ton ($220 to $253/dry tonne)
Total Annual Costs $380 to $430/dry ton ($418 to $473/dry tonne)
All costs are presented on the basis of dewatered sludge cake.
It is important to recognize the limits of these costs estimates.
Estimates of capital costs are presented on the basis of dollars per ton
of installed capacity, allowing for a reasonable amount of reserve
capacity. It must be recognized that capital costs can vary
significantly due to site-specific factors such as subsurface
conditions, local materials costs, size constraints, construction market
conditions, and the amount of redundancy built into the system. These
factors make it difficult to generalize about capital costs, therefore
the capital cost figures presented here should be applied carefully.
Estimates of operation and maintenance costs are based upon operation at
system capacity. System O&M costs can vary significantly over the life
of a facility. Many unit processes require essentially the same
operator attention, the same maintenance attention, and the same power
consumption whether the process is lightly loaded or loaded to capacity.
As a result, operation and maintenance of these unit processes is much
more cost effective on a dollar per ton basis when the system is
operating at design capacity.
The degree to which operation and maintenance costs for a particular
facility may vary over the life of the facility depends upon the
difference between initial and design year sludge quantities, the use of
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multiple units rather than one large unit in equipment selection, and
other design factors. A system that operates at a fairly constant
sludge feed throughout its design life will see little change in per ton
operation and maintenance costs. A system that is sized for a design
year loading that is substantially greater than initial loading
conditions will likely experience a significant change in per ton
operation and maintenance costs over the system's design life.
Figure 1 shows the relationship between the unit costs and the fraction
of capacity in use. The curves and points are plotted for operation and
maintenance only and for operation and maintenance plus amortized
capital costs, for incineration only and for the total system. Because
the Duffin Creek solids train was evaluated for two system capacities
(one for digestion and dewatering and one for incineration), total
system costs for Duffin Creek could not be included in this curve.
Actual per ton operation and maintenance costs for sludge incineration
at the four subject facilities ranged from 6 percent to 186 percent
greater than the per ton costs estimated for operation at capacity. The
fluctuation in per ton costs over the design life of an incineration
system should be considered when using the figures presented in this
study.
ENERGY EVALUATION SUMMARY
Energy efficiency can be examined on several levels:
o Level A - Compare the facilities on the basis of auxiliary fuel
consumed within the furnaces only.
o Level B - Same as Level A, except consider energy inputs to the
heat/auxiliary boiler equipment, the emission control
equipment, and the ash disposal system. Steam produced
and utilized outside of the incineration system is
considered an energy output.
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RATIO OF LOAD/ CAPACITY
Incineration Only O&M
Incineration Only Total Costs
Entire System O&M
Entire System Total Costs
Capital
FIGURE 1
EFFECT OF LOAD ON UNIT COSTS
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o Level C -
Same as Level B, except that electricity for equipment is
considered an energy input.
o Level D - Same as Level C, except include energy inputs to the
sludge conditioning/dewatering system.
o Level E - Same as Level D, except include energy to the entire
solids handling train. Auxiliary fuel, electricity for
equipment, and electricity for general building
requirements are considered energy inputs.
Figure 2 shows the results for the five levels of analysis.
The following generalizations cam be made regarding the energy
consumption of a well-operated sludge incineration facility:
- Annual auxiliary fuel consumption within the furnace itself
should be in the range of 7 to 9 gallons of fuel per dry ton
(29 to 38 liters/tonne) of sludge cake processed (Level A).
If a waste heat recovery system is included in the incineration
system, the incineration system can be a net energy producer if
only auxiliary fuel (no electricity) is considered an energy
input to the system (Level B).
- If both auxiliary fuel and electricity are considered energy
inputs to the incineration system, an incineration system with
a waste heat recovery system may still be a net energy producer
if operating at maximum efficiency (Level C). Under these
conditions, the Metro and Duffin facilities approach the goal
of being a net producer at their current loading rates. It is
possible that, if these facilities approach the goal of being a
net producer at their current loading rates. It is possible
that, if these facilities were operating at capacity, the
increase in energy efficiency that results from complete
equipment utilization may make the Duffin and Metro facilities
net energy producers under these conditions.
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100.8
20.3
¦rf"
w
v\-
9.3 9.0
LEGEND
k-$y = UPPER BLACKST0NF.
^ WPCF
MF.TRO WPCF
: DUFFIN CRHF.K WPCF
= CRANSTON WPCF
LEVEL A
-2.6
LEVELB
LEVELC
LEVEL D
LEVELE
Figure
2. Comparative
Consumption
-------
If the definition of the incineration system is expanded to
include the sludge conditioning/dewatering system, the goal of
net energy production by the incineration system does not
appear achievable (Level D).
Total energy consumption for a solids train utilizing sludge
incineration can vary widely depending on the thickening and
dewatering technologies utilized. Based on the results of this
evaluation, total energy consumption for a well-operated solids
train may range from 5 million to 9 million Btu per dry ton
(5.8 million to 10.4 million kj per dry tonne) of sludge cake
processed (Level E).
Overall, the evaluation demonstrates that a variety of
technologies can achieve energy-efficient sludge incineration.
The most complex systems (Duffin Creek and Metro) proved to be
very energy efficient under each set of conditions evaluated.
The simplest system (Upper Blackstone) also proved to be very
energy efficient, especially in terms of overall energy
consumption by the entire solids train (Level E).
-------
SECTION 3
PLANT INFORMATION
The following four facilities have been evaluated as part of this study:
1. Upper Blackstone WPCF, Worcester, MA
2. Metro WPCF, Minneapolis, MN
3. Duffin Creek WPCF, Toronto, Canada
4. Cranston WPCF, Cranston, RI
This section provides an overview of the technology used at the four
facilities and discusses the major technical and managerial aspects that
contribute to each facility's successful operation. A more-detailed
evaluation of the cost and energy requirements for each facility is
included in Section 4 and Section 5 of this report.
UPPER BLACKSTONE WPCF
Plant Overview
The Upper Blackstone WPCF is a secondary wastewater treatment facility
located in Millbury, MA. Treatment processes in the liquid train
include aerated grit removal, primary settling, aeration, final
settling, and chlorination prior to discharge to the Blackstone River.
The solids handling processes include flotation thickening of the waste
activated sludge, storage and mixing of the waste activated and primary
sludges, blending, belt filter press dewatering of the blended sludges,
sludge incineration, and ash disposal by landfilling. The facility went
into operation in 1976. The plant was designed to treat an average day
flow of 56 MGD (2,500 L/s). Currently, the facility treats sua average
flow of 36 MGD (1,600 L/s) and processes approximately 30 dry tons (27
dry tonnes) per day of dewatered sludge cake. A schematic of the solids
train is shown in Figure 3.
-------
WASTE
ACTIVATED
SLUDGE
POLYMER
ADDITION
PRIMARY
SLUDGE
SLUDGE
HOLDING
TANK
SLUDGE
HOLDING
TANK
BLEND
TANK
BELT FILTER
PRESS
DEWATERING
MULTIPLE
HEARTH
INCINERATION
DISSOLVED AIR
FLOTATION
THICKENING
-------
Solids Processing
The solids handling train includes two sludge holding tanks, one
dedicated to primary sludge and one dedicated to waste activated sludge.
The primary sludge holding tank acts as a gravity thickener. Typically,
sludge is pumped to the holding tank at 1 to 2 percent solids and leaves
the tank at about 5 to 7 percent solids. A gravity overflow line
returns a constant flow of supernatant to the primary settling tanks.
Waste activated sludge is constantly drawn from the final settling tanks
and pumped to four dissolved-air flotation (DAF) thickeners. The DAF
feed from the clarifiers is typically 0.7 to 0.8 percent solids. The
thickened waste activated sludge (1VJAS) is typically 4 to 5 percent
solids. No polymer is used before thickening, although the equipment to
do so exists. Thickened waste activated sludge is pumped to storage.
Sludge from the primary holding tank and the waste activated sludge
holding tank is fed to two sludge mixing tanks. Sludge is pumped to the
mixing tanks at a waste activated to primary sludge ratio of about 1.6 :
1 by volume. Scum and grease are mixed with the sludge at these blend
tanks. The sludge is mixed mechanically over a detention time of about
3 hours. The feed from the sludge mixing tanks to the belt filter press
(BFP) dewatering units is generally 5 to 6 percent solids.
The original plant design included four vacuum filters for sludge
dewatering. The plant staff has replaced two of the vacuum filters with
two belt filter press units. The two remaining vacuum filters are no
longer used. The sludge at Upper Blackstone dewaters exceptionally
well. A feed of 5 to 6 percent solids will generally thicken to 10 to
12 percent across the belt filter gravity zone and dewater to about 27
percent solids across the compression zone. The excellent
dewaterability of the sludge at Upper Blackstone may be partially
attributed to the industrial waste load in the influent stream.
-------
Incineration System
Upper Blackstone has three multiple-hearth furnaces. Each furnace has
10 hearths. None of the furnaces is equipped with heat recovery
systems. The incineration system is operated round the clock, seven
days per week. The incineration process is extremely fuel efficient.
The system frequently operates autogenously for extended periods of time
and annually consumes approximately seven gallons of fuel oil per ton
(29 L/tonne) of dry solids, including start-up and cool-down periods.
Operators are given a great deal of flexibility in how to control the
furnace, but are given the following common set of goals:
maintain a minimum combustion temperature of 1250°F (675°C) to
control air emissions.
do not allow the combustion temperature to exceed 1500°F
(815°C) to prevent clinker formation and avoid refractory
damage
burn as little auxiliary fuel as possible
maintain a minimum oxygen level of 8 percent (dry basis) to
insure complete combustion and avoid smoke in the stack exhaust
- maintain hearth no. 4 as the combustion hearth
The variables adjusted to achieve these goals are left to the operator's
discretion. The operator monitors the furnace by observing the stack
exhaust, opening doors on the furnace to observe the fire itself, and
observing the hearth temperature profile and oxygen level from the
control panel. It is important that the operator observe the fire
directly at times and not rely completely on temperature sensors because
localized hot or cool spots may result in misleading readings.
Operators generally control the furnace by adjusting the flow rate of
-------
combustion and cooling air. Top-hearth exhaust temperatures range from
800° F to 1000°F (426° C to 537°c). Particulates are removed by a venturi
wet scrubber and impingement tray scrubber arranged in series with a
pressure drop of 20 inches (51 cm) w.c. Ash is landfilled on-site.
Keys To Success
Operating experience at Upper Blackstone provides the following insights
into fuel-efficient incineration operation.
Storage and Mixing -
The use of storage and mixing tanks to maintain a consistent sludge
feed to the dewatering and incineration processes is essential to
avoid system upsets that would result in the use of auxiliary fuel.
A uniform sludge feed is required to maintain optimum feed
conditions.
Job Rotation Program -
The Upper Blackstone facility has installed a job-rotation program
in which operators are moved to a different area of the plant every
two weeks. The plant staff believes that the job-rotation program
has been a very effective management tool. It allows operators to
understand and appreciate how the efficiency of a process is
affected by the preceding unit and helps relieve the boredom and
complacency that can result from operating the same piece of
equipment each day. The job-rotation program encourages teamwork
and focuses the operator's attention on the overall goal of saving
fuel in the incineration system rather than on the operation of an
individual process.
Maintenance -
The implementation of a strong maintenance program is essential to
fuel-efficient operation. During the facility's early years of
operation, furnaces had to be removed from service frequently
-------
because of minor maintenance problems. During this period, the easy
to check, high-profile items were being addressed during maintenance
shutdowns, while less obvious, but equally important, maintenance
items were being overlooked. These frequent shutdowns were very
costly in terms of auxiliary fuel and labor.
To eliminate this, the plant staff instituted a regular
preventive-maintenance program. The program has two main features -
a regular rotation schedule and a detailed checklist. The rotation
schedule provides for rotation of the furnaces every six months
between operating, maintenance, and standby modes. The detailed
checklist consists of 210 items that must be addressed during a
furnace's maintenance shutdown period (see Appendix). Maintenance
personnel consider the development of this checklist as a turning
point in their operation. During each maintenance period, every
item on this checklist must be checked and signed off by a
maintenance worker and supervisor. This checklist system insures
that minor items that can be easily overlooked are addressed during
each maintenance shutdown period. Since the implementation of this
checklist procedure, the furnaces have regularly been able to stay
in service for the full six-month operating period, thus reducing
unscheduled shutdowns to a minimum and reducing auxiliary fuel use
for heat-up and cool-down periods.
Temperature Control -
Consistent temperature profile and maintaining controlled heat-up
and cool-down periods should be maintained. As a result of this
strategy, the 12 year old furnaces have never suffered any
significant refractory damage.
Preventive Maintenance -
Plant management believes that the plant's success is a tangible
result of their philosophy regarding operation and maintenance.
-------
Plant management is willing to pay the annual cost of properly
operating and maintaining the solids train in order to avoid
periodic large cost repair items. At Upper Blackstone, management
believes that the annual cost of proper system maintenance is a good
investment in reducing the incineration system's life-cycle cost.
The development of an excellent maintenance program has increased the
cost-effectiveness and fuel efficiency of the incineration process in
several ways:
1. Decreasing auxiliary fuel use by minimizing unscheduled maintenance
shutdowns. These shutdowns increase fuel use because of the fuel
needed for startup.
2. Decreasing costs for replacement materials by extending the useful
life of furnace components such as refractory brickwork and
ancillary equipment.
3. Providing the operators with the information necessary to operate
the incinerators fuel-efficiently by keeping the instrumentation and
monitoring equipment operable and up-to-date in terms of current
technology. This insures that the operators receive the information
required to operate the furnace in an energy-efficient,
environmentally sound manner.
METROPOLITAN WPCF
Plant Overview
The Metropolitan Waste Control Commission (MWCC) owns and operates 12
wastewater treatment facilities serving the Twin Cities (Minnesota)
Metropolitan Area, the largest plant of which is the Metropolitan
(Metro) Wastewater Treatment Facility. The Metro plant has undergone
-------
several upgrades since its original construction in 1938. From 1980 to
1983, the solids processing facilities underwent a major renovation
aimed at improving the fuel efficiency of the incineration process.
During that period, the incinerators were completely shutdown and the
sludge was land applied. Today, the upgraded facility is in full
operation and all sludge produced at the facility is incinerated.
The secondary wastewater treatment system has the capacity to treat an
average day flow of 250 mgd (11,000 L/S) and a peak flow of about 375
mgd (16,400 L/s). The primary treatment system is designed to treat up
to 655 mgd (28,700 L/s). The plant currently receives an average flow
of 220 mgd (9,600 L/s) and peak flows as high as 700 mgd (30,700 L/s).
Plant influent averages about 220 mg/L BOD and 200 to 250 mg/L TSS.
Approximately 180 dry tons (163 tonnes) of dewatered sludge cake are
processed at the plant daily.
Solids Processing
Sludge handling processes include thickening, sludge storage, heat
conditioning (Zimpro), decanting, dewatering, and incineration. A
schematic of the solids train is shown in Figure 4.
The facility contains 6 gravity thickeners and 12 dissolved air
flotation thickeners. Primary sludge is gravity thickened along with
the bottom sludge from the dissolved air flotation thickeners (DAF) and
the sidestream flow from the roll press dewatering system. Gravity
thickener influent is increased from about 0.5 percent solids to between
6 and 7 percent solids. Waste activated sludge is thickened by
dissolved air flotation. The waste-activated sludge is thickened from
about 0.75 to 1 percent solids to about 3 percent solids. Polymers are
not used.
Sludge storage is provided before thermal conditioning. Die storage
tanks receive all the thickened waste activated sludge and about 35
-------
percent of the thickened primary sludge. The stored sludge is mixed
with air. The remaining 65 percent of the primary sludge bypasses the
heat conditioning process.
The 8 Zimpro heat-conditioning units are operated at 380°F (193°C) and
325 psig (2.2 kPa). Each has a capacity of about 40 gpm (2.52 L/S).
About 4,200 lb/hour (1905 kg/hr) of steam are required for each unit.
This steam is provided by the waste heat recovery boilers. The Zimpro
heat exchangers are cleaned with nitric acid on a regular basis to avoid
scaling. Typically, four reactors are in operation and four are in
reserve.
The heat conditioned sludge is conveyed to decanting tanks. The
decanting process produces a sludge with 12 to 13 percent solids.
Overflow from the decant tanks is treated by a rotating biological
system (RBC units) before return to the primary clarifiers. Odorous
gases from the decant tanks are used as combustion air in the
multiple-hearth furnaces (MHF). Sludge produced by the RBC system is
returned to the DAF thickeners for treatment and disposal.
The heat conditioned sludge and the primary sludge that bypasses heat
conditioning are mixed in blend tanks before dewatering. The blended
sludge is dewatered on 4 Ingersoll-Rand Vari-Nip twin-roll presses.
About 18 pounds of cationic polymer is used per ton of dry solids (9
kg/tonne). Cake solids average 32 percent. A drier cake could be
produced by directing a larger percentage of the primary sludge to the
heat conditioning process. However, the staff has found that the
optimum cake solids for the MHF system is 31 to 34 percent solids. A
drier cake results in burning in the upper hearths of the MHF units and
makes the furnace difficult to control.
In addition to the roll presses, eight diaphragm filter presses and
eight vacuum filters are available for sludge dewatering. In the year
considered by this evaluation (1987), the roll presses were used
exclusively for sludge dewatering.
-------
WASTED
ACTIVATED
SLUDGE
i OVERFLOW
— TO KBC
UNITS
PRIMARY
SLUDGE
STORAGE
TANKS
DECANT
TANKS
BLEND
TANKS
THERMAL
CONDITIONING
HAULED
OFF-SITE
FILTER
PRESS
DEWATER1NG
INCINERARION
ROLL
PRESS
DEWATERING
GRAVITY
THICKENING
DISSOLVED AIR
FLOTATION
THICKENING
-------
Incineration System
The incineration system consists of 6 eight-hearth MHF units. Four of
these units are active and two are kept as reserve. Only the four
active units have heat recovery systems. Four retired furnaces are also
located within the facility.
Each active furnace is 22 feet (6.7 m) in diameter. The furnace
combustion hearths (hearth nos. 3 and 4) are designed with double the
normal hearth volume to insure complete combustion. Each furnace is
configured with a zero hearth afterburner, although no fuel is ever
added at this hearth. State air emission regulations require an exhaust
gas temperature of 1000°F (537°C).
The furnaces are generally operated at an excess air level of about 200
percent. Odorous off-gases from the sludge holding tanks, the thermal
conditioning decant tanks, and the dewatering area are fed to the
furnaces as combustion air. A maximum combustion hearth temperature of
1600°F (870°C) is maintained to avoid clinker formation and maintain the
required 1600°F (870°C) exhaust gas temperature. Because the system is
generally operating in the autogenous mode, the operators generally
control the system by adjusting the excess air as required. Furnaces
are generally loaded at about 75 percent of capacity to accommodate
short term fluctuations in sludge production and to allow for the
feeding of a drier sludge that would require more combustion/cooling air
at the same loading rate.
The incineration system is very fuel efficient and generally operates
autogenously. Fuel is required to take the furnaces out of service for
regularly scheduled maintenance. Overall, the system averages about
1100 cubic feet (31 cubic meters) of natural gas per dry ton of sludge,
which is equivalent to about 7.6 gallons of fuel oil per dry ton (32
L/tonne) of sludge.
-------
Scum is pumped from the primary tanks to three skimming tanks, where it
is separated from the transport water. The scum is decanted and heated
in a decant hopper. The decanted scum is macerated and fed to the
combustion hearth at a rate of 60 to 100 gallons (227 to 379 liters) per
hour. Scum entering the furnace must be carefully metered to prevent
sudden temperature fluctuations within the furnace. Operator
communication and tight control of the sludge feed and excess air supply
are necessary to maintain control as scum is pumped into the furnace.
The scum has a heating value of about 15,000 Btu per pound (33,1000
BtuAg) of liquid.
The Metro staff has implemented a very effective maintenance program
aimed at discovering and correcting minor equipment problems before the
problems become major problems. Each month, the entire dewatering and
incineration system is taken out of service for an intensive, 16-hour
maintenance overhaul. All equipment and instrumentation is reviewed
during these shutdowns. Once each year, the entire solids handling
train is taken out of service for a more detailed maintenance
inspection. This annual shutdown is scheduled for the summer months
when sludge production is low. These shutdowns are possible because the
solids train was designed with adequate sludge storage and excess
process capacity.
Heat is recovered from the furnace exhaust gas stream by a waste heat
boiler system. In addition to the typical waste heat boiler, the plant
staff has added an economizer section that increases the energy
efficiency of the heat recovery system. Steam is generated by the waste
heat boilers at 425 psig (2.9 kPa). The steam is used for the following
applications:
First Priority - Provide of required Zimpro steam
Second Priority - Drive steam turbines for furnace induced-draft (ID)
fans, water pumps, and auxiliary boilers. This
reduces steam pressure from 425 psig (2.9 kPa) to 125
psig (0.9 kPa).
-------
Third Priority - Satisfy plant heating requirements. Exhaust steam
from the ID fans is used a second time to provide
building heat. This second use reduces steam pressure
from 125 psig (0.9 kPa) to 15 psig (0.1 kPa).
The waste heat boilers always generate enough steam to meet the needs of
the thermal conditioning process. If additional steam is available, second
and third priority demands are also met. An auxiliary boiler system is
used to supplement the steam production by the waste heat boiler system for
second and third priority uses.
Air emissions control is achieved with a venturi wet scrubber with a 30
inch (76.2 cm) w.c. pressure drop and a packed tower with 2 to 3 inches (5
to 7.6 cm) w.c. pressure drop arranged in series. Flue gases pass
sequentially through the waste heat boiler and economizer, a pre-cooler, a
venturi scrubber, a sub-cooler, a mist eliminator, and the ID fan. Ash is
landfilled at an on-site ash pit.
Keys To Success
Operating experience at the Metro facility provides the following insights
into fuel-efficient incineration operation.
Storage -
Storage in the solids train is essential. Storage helps the
operator maintain a steady sludge feed to the incinerator in terms
of quality and quantity and it allows the staff to completely shut
down the incineration system for short periods of time on a regular
basis to perform maintenance tasks.
Communication -
Communication between operators of different processes, between the
operators and the maintenance crews, and between operators on
different shifts helps develop consistency in the system's operation
-------
and creates an atmosphere of cooperation among the entire staff.
The Metro staff forms committees comprising engineers, maintenance
personnel, and operators to address specific process problems.
These committees produce innovative solutions to difficult problems
and serve to encourage communication among the plant staff.
Motivation -
Management has created a very positive work environment at the Metro
plant. By encouraging employees to pursue technical advancement
through advanced education and professional organizations and by
providing the staff with a budget that allows for experimentation
and process improvements, management has developed a very motivated
staff that is always looking for new ways to improve the solids
handling processes.
DUFFIN CREEK WPCF
Plant Overview
The Ontario Ministry of the Environment owns and operates the Duffin
Creek Water Pollution Control Plant, a secondary wastewater treatment
plant serving greater Toronto. The facility began operation in 1980.
It currently has a treatment capacity of 48 million U.S. gallons per day
(2,100 L/s). Three future expansions are planned which will increase
the capacity to 192 mgd (8,400 L/s). The first of these plant
expansions is now under construction. Currently, Duffin creek treats an
average day flow of 47 mgd (2,100 L/s) and processes about 26.6 dry tons
(24.1 dry tonnes) per day of dewatered sludge cake. A schematic of the
solids processing train is shown in Figure 5.
Solids Processing
At the Duffin Creek facility, waste activated sludge is returned to the
primary clarifiers and co-settled with the primary sludge. Hie
-------
co-settled sludge is drawn off the clarifiers at 5 percent solids and
sent to a two stage anaerobic digestion system (four digesters total).
Retention time in the digesters is about 20 days. The digesters serve
to provide (1) sludge feed equalization to dewatering and sludge
disposal; (2) digester gas, which is used as a source of fuel for
preheating combustion air in the furnace hot-windbox and for the
auxiliary boiler system; and (3) an effective means of blending scum
into the sludge. In addition, the digested sludge is much less odorous
than raw sludge. This eliminates the need for odor control in the
dewatering and incineration areas. The digestion process reduces the
volatile content of the sludge from 60 percent to about 40 percent.
The digested sludge is stored and then fed to 4 diaphragm filter
presses. The filter presses replaced belt filter presses. The belt
filter press units produced a cake with 21 to 22 percent solids. This
was not dry enough to achieve autogenous combustion. To reduce fuel
use, the plant staff replaced the belt filter press units with the
filter presses.
The sludge feed to the diaphragm filter presses is conditioned with
polymer. The filter press cake averages about 32 percent solids. The
filtration/diaphragm squeeze time for each cycle is about 2 hours.
Total cycle time including preparation time and other downtime averages
about three hours. Each press cycle produces about one dry tonne (1.1
dry ton) of cake.
The cake must be conveyed from the dewatering building to the
incineration building. The original installation included a series of
horizontal and vertical screw conveyors, the longest of which was about
200 feet (61 meters). This system worked well with the belt filter
press cake (22 percent solids), but could not handle the filter press
cake (33 percent solids). The increase in cake dryness resulted in
frequent maintenance shutdowns from bearing failures. As a result, a
concrete-type slurry purrp was installed on a trial basis. The pump
-------
WASTE ACTIVATED
SLUDGES
POLYMER
HOLDING
TANKS
SLUDGE
DIGESTION
FILTER
PRESS
DEWATERJNG
FLUID IZED-BED
INCINERATION
(HOT WINDBOX)
DESIGN)
ADDITION
-------
conveys the sludge cake about 500 feet (150 meters) through a pipeline
from a storage hopper in the dewatering building to a storage hopper in
the incineration building. The cake is then screwed into the furnace
bed. After overcoming some initial start-up problems (pipe diameter too
small), the pump has performed very well.
The staff believes that there are both operational and maintenance
benefits to the pipeline system. The staff reports that the pipeline is
neater and less odorous than the screw conveyor, and that the cake burns
better when pumped directly into the bed. The staff now uses the slurry
pump on a full-time basis and has abandoned the screw conveyors. The
plant staff plans to install a second slurry pump to pump cake from the
storage hopper preceding the furnaces to the furnace bed.
Incineration System
The incineration system at Duffin Creek consists of two fluidized bed
furnaces (hot windbox design), a waste heat boiler system, a venturi
scrubber, and a tray scrubber (see Figure 6). Under normal operation,
digester gas is used to fuel the hot windbox (HWB), which preheats the
combustion (fluidizing) air. Flue gas from the furnace passes through
the heat exchanger, to transfer heat to the HWB air feed. The flue gas
then passes to a waste-heat boiler, which produces steam to be used for
building heat and to drive the combustion (fluidizing) air blowers. If
the HWB temperature is so high that preheating of the HWB air feed is
not necessary, the hot flue gases can bypass the heat exchanger and be
fed directly to the waste heat boiler, thereby increasing steam
production. The high furnace exhaust gas temperature (1560°F/850°C) and
lengthy freeboard retention time (greater them 5 seconds) insure
complete combustion and eliminate the need for an afterburner. To
supplement the waste-heat boilers, two auxiliary boilers are available
to (1) make up the difference between the plant's heating requirements
and the heat production of the waste heat boilers; and (2) provide steam
during start-up periods to drive the steam turbines that power the
combustion air blowers.
-------
550 °C
"1020 °F
DIGESTER
GAS
850 C
1560 °F
HEAT
X-CH ANGER
n
AMBIENT AIR
1650 F
HOT
900 °C
1 ,
WINDBOX
850 °C
1560 °F
FLUIDIZED
BED
FURNACE
800 °C
1470 °F
tr
FUEL
' OIL
T
1
1
_i
WASTE
HEAT
BOILER
SLUDGE
NATURAL GAS
LEGEND
GAS FLOW
-- FUELFEED
— STEAM FLOW
360 °F
180 °C
I
ATMOSPHERE
k
TRAY
STACK
VENTURI
270'
' 520'
C
F
-*¦ STEAM USES
— BUILDING HEAT
_ DRIVE STEAM TURBINES
~ FOR FLUIDIZING AIR BLOWERS
- HEAT FOR DIGESTION
-------
The incineration system now operates very fuel efficiently. Under
normal operation, the combustion process is almost always autogenous.
Some fuel is used to take the furnaces in and out of service. Overall,
about 9 gallons of fuel oil per dry ton (37.6 liters/tonne) of sludge is
burned in the reactor and hot windbox. Digester gas is burned in the
hot windbox and in the auxiliary boiler system. Natural gas is also
used as a fuel source for the auxiliary boiler system.
Currently, the digester gas pressure will only allow the staff to
operate one of the two auxiliary boilers at any given time. The staff
is working to increase the gas pressure in the system such that both
auxiliary boilers will be able to operate from the digester gas feed.
This will decrease natural gas consumption and increase utilization of
the system's "free" fuel source.
This fuel-efficient operation is the result of two modifications to the
original reactors. The furnaces were originally designed to process a
combination of wastewater sludge and paper waste. During construction,
it was decided that paper waste would not be added to the furnace. As a
result, the furnaces were oversized by a factor of 4. This resulted in
operation at very high excess air rates with very high fuel use. To
remedy this problem, a layer of refractory brick was added around the
inside of the furnace bed. This reduced the bed diameter by 36 inches
from 18 feet (5.5 meters) to 15 feet (4.6 meters). Also, several of the
tuyeres were plugged to reduce the air flow to the furnace. These
modifications served to downsize the furnaces so that they could be
operated fuel efficiently at current sludge production rates. When
additional capacity is required in the future, the refractory brick will
be removed and the tuyeres unplugged. This will restore the original
capacity of the furnaces.
Plant management believes that the proper operation of a fluidized-bed
system does not require an inordinate amount of staff training or an
exceptionally skilled plant staff. During normal operation, the
-------
operator will monitor the hot-windbox temperature, the bed temperature,
and the oxygen level in the flue gas to detect changes in the furnace's
operating condition. Furnace temperature and the flue-gas oxygen level
vary in response to changes in the percent solids or the percent
volatiles of the feed. The operator can react to these changes in
sludge quality by adjusting the air feed rate, adjusting the sludge feed
rate, or by modulating the auxiliary fuel rate to the reactor burners.
The plant staff reports that the feed to the furnace is kept fairly
constant in terms of sludge quality and quantity due to the sludge
storage and blending provided within the solids train. This makes the
furnace easier to operate; major adjustments in the control variables
are rarely required.
A reactor is generally operated as the lead furnace for one year and
then taken completely out of service for a two-month maintenance
overhaul. Once each week, the incineration system is taken out of
service for four hours for a maintenance check. All instrumentation and
equipment that is accessible is checked and calibrated. No fuel is
required to restart furnace operation, because the sand bed retains
heat.
Emissions control is achieved with a wet scrubber and cooling tower
arranged in series. No afterburner is required. Wet ash removed by the
scrubbing system is gravity thickened, dewatered to about 60 percent
solids using a vacuum filter, and landfilled.
Keys To Success
Operating experience at the Duffin Creek Water Pollution Control Plant
offers several insights into fuel efficient incineration.
Digestion -
Experience at Duffin Creek demonstrates that digestion can be part
of a successful incineration process. Tfie digesters serve several
-------
functions. They provide storage within the solids train, offer an
excellent means of incorporating scum into the sludge, produce a
sludge that can be dewatered without an odor problem, and produce an
end product (digester gas) that can be used as a fuel source in the
incineration system. These positives must be balanced against the
negative impact of the destruction of combustibles prior to
incineration.
Conveyance System -
Experience at Duffin Creek shows that the means of conveying the
sludge to the incinerator is a critical part of the solids train
that should not be overlooked in design. The conveyance system must
be dependable and have the capacity to meet the system's demands.
Breakdowns in the conveyance system result in furnace shutdowns
which require auxiliary fuel. Cement-type pumps are a viable option
to screw conveyors.
Heat Storage -
The heat storage in the fluidized bed reactor provides additional
protection against system upsets. This heat storage allows the
operators to shutdown the system for short periods of time without
auxiliary fuel use. This makes it easier to perform regular
maintenance on the furnace and allows the operators to run the
furnace at an optimum feed rate rather than try to lengthen the runs
with a light feed rate to avoid shutdowns.
Fluidized-Bed Technology -
The plant staff reports that a fluidized bed furnace is easy to
operate and control. There are few operation parameters to monitor
and the heat sink built into the furnace provides protection against
system upsets resulting from changing sludge quality. Proper
operation of the system does not require an inordinate amount of
staff training.
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CRANSTON CASE STUDY
Plant Overview
The Cranston Water Pollution Control Facility is a secondary wastewater
treatment facility designed to treat sanitary, industrial, and septage
wastes from the City of Cranston, Rhode Island. An upgrade of the
original primary treatment facilities was completed in 1981. Treatment
processes in the upgraded liquid train include screening, aerated grit
removal with detritors, grease flotation, primary settling, biological
secondary treatment utilizing the activated-sludge process, and
chlorination.
An upgrade of the sludge dewatering and thickening systems was completed
in 1985. An upgrade of the incineration system was completed in 1986.
The present solids handling processes consists of gravity and
dissolved-air flotation thickening, storage, mixing, chemical
conditioning with lime and ferric chloride, filter press dewatering, and
multiple-hearth incineration. Digesters from the original facility are
now used as sludge holding tanks. The incineration system is operated
intermittently, and these storage tanks are used to store thickened
sludge during periods when the dewatering/incineration system is
off-line. During periods when the incineration system is taken out of
service for an extended period of time, dewatered sludge cake is hauled
off-site for landfilling.
The upgraded facility is designed to handle an average day flow of 23
mgd (1,000 L/s). Currently, the facility treats an average flow of 10
mgd (400 L/S) and processes about 9 tons (8.2 tonnes) per day of
dewatered sludge cake. A plant schematic of the solids processing train
is shown in Figure 7.
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Plant operations at the Cranston Facility are currently in a state of
transition. Following the completion of the upgrade to the solids train
in 1986, the gravity and dissolved-air flotation thickeners were rarely
used, because of operation and maintenance problems. During this
period, secondary sludge was returned to the primary clarifiers and
co-settled with the primary sludge. The thickening units were by-passed
and sludge was sent directly to the sludge blend tank and the subsequent
filter press dewatering process.
In June of 1988, several process changes were implemented. The gravity
and dissolved air flotation thickeners were put back into service. The
primary and secondary sludges are now settled and thickened separately
and blended prior to dewatering, although equipment breakdowns have
forced the facility to operate in the co-settling mode at times. Plant
management reports that the facility has at times been understaffed.
Because of these process changes and staffing problems, the operation of
dewatering and incineration systems has not yet been optimized.
Solids Processing
The solids handling train begins with separate thickening of the primary
and waste activated sludges utilizing gravity thickeners and
dissolved-air flotation thickeners, respectively. The sludge feed to
the gravity thickeners averages between one and two percent suspended
solids and the sludge feed to the dissolved-air flotation thickeners
averages about .5 percent suspended solids. The concentration of the
individual thickened sludges is not measured.
Thickened sludge is fed either to a sludge storage tank or to a sludge
blend tank. Currently, the dewatering and incineration system is
operated on a five day per week schedule because of low sludge
production. Sludge produced and thickened over the weekend is stored in
two sludge storage tanks that were formerly used as digesters and fed to
the dewatering/incineration processes during the following week.
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WASTE
ACTIVATED
SLUDGE
CHEMICAL
ADDITION
PRIMARY
SLUDGE
BLEND
TANK
LANDFILL
BELT FILTER
PRESS
DEWATERING
INCINERATION
SLUDGE
STORAGE
(OLD DIGESTERS)
DISSOLVED AIR
FLOTATION
THICKENING
GRAVITY
THICKENING
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Generally, fresh sludge is processed on Monday and Tuesday and weekend
sludge is paced into the system at midweek. This mode of operation has
a negative impact on the dewatering/incineration system. When weekend
sludge is mixed into the dewatering feed, the quality of the sludge
changes significantly. This makes it difficult to optimize the chemical
conditioning requirements for the dewatering process; therefore the
effectiveness of the dewatering process decreases. Under these
conditions, the furnace is very difficult to control because the
concentration and volatile fraction of the sludge cake feed are
fluctuating.
The sludge feed to the blend tank averages about 3.5 percent solids, but
can range from 1.5 to 5 percent solids. Detention time in the blend
tanks averages about 16 hours. Blended sludge is fed first to chemical
conditioning tanks where ferric chloride is added and then to
flocculation tanks where lime is added. Typically, a ferric chloride
dosage of 6 to 7 percent and a lime dosage of 15 to 20 percent are used.
A polymer conditioning system is also available, but the lime and ferric
conditioning system is used exclusively. The staff hopes that future
improvements in polymer effectiveness will someday make polymer a viable
conditioning alternative for their system.
Sludge is dewatered in three fixed-volume filter presses, each with 104
plates (105 chambers), 1.5 meter by 2 meter. Plates are made of cast
iron. Volume of each chamber is 2.17 cubic feet (0.06 cubic meters) and
total press volume is 228 cubic feet (6.46 cubic meters). The filter
presses operate at a pressure of 90 psi (0.6 kPa). Press time varies
from 2.5 to 4 hours. The product cake averages 26 to 27 percent solids.
Each filter press discharges into a storage bunker. The purpose of
the bunkers is to provide the equalization storage necessary to
transform the batch output from the filter press dewatering process into
a continuous feed for the incineration system. Each bunker has a usable
capacity of 900 cubic feet (25 cubic meters), which equates to almost
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four filter press loads of 228 cubic feet (6.46 cubic meters) each. In
practice, the usable capacity of these bunkers has been severely limited
because of bridging problems. To avoid bridging, the operators store no
more than about half a pressload in any one bunker.
Under each bunker is a conveyor that transports the cake to a surge bin
which precedes each furnace. A weigh belt is installed to insure that a
consistent mass of cake is withdrawn from the surge bins and fed to the
furnaces. However, the weigh belt is only able to deliver a consistent
mass of cake if the density of cake remains consistent. Variations in
the quality of the sludge cake (septic sludge from storage tanks versus
fresh sludge) results in variations in the furnace feed rate. Also,
probes within the storage bins which are intended to control the
conveyor feed rate are not always operable. Problems with this
conveying system have at times shutdown the entire
dewatering/incineration system.
Incineration System
The incineration system consists of two six-hearth furnaces. One is a
Crouse unit that was installed as part of the plant upgrade and went
on-line in 1986. One is a Nichols furnace that is about 40 years old,
but was rarely used until the upgraded incineration facility went
on-line in 1986. The new Crouse furnace is the larger of the two
furnaces, with a diameter of 18.75 feet (5.7 meters). The smaller
Nichols furnace has a diameter of 14.25 feet (4.3 meters). Each furnace
has an external afterburner chamber and a separate scrubbing and heat
recovery system. The furnaces were designed for operation in the
pyrolysis (starved air) mode, but have only operated in this manner
during start-up.
The older (and smaller) Nichols furnace was operated full time from
start-up in spring of 1986 to the fall of 1987. At that time, several
problems forced the staff to take the Nichols furnace out of operation.
Among the problems were center shaft damage, refractory damage, and
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damage to rabble teeth on hearth No. 1 and No. 2. Since that time, the
Crouse furnace has been used exclusively.
The Crouse furnace is severely underloaded and therefore is difficult to
operate in a fuel-efficient manner. The furnace is operated on a 5 day
per week schedule at a loading rate of approximately 3200 wet pounds
(1450 kg) of dewatered cake per hour. The staff has found that the
optimum feed rate for the furnace is about 5,200 wet pounds (2360 kg) of
sludge cake per hour but, because of a lack of sludge, the furnace is
almost always operated at less than optimum feed rates.
Typical sludge cake requires auxiliary fuel for combustion of the
relatively low solids and volatiles content of the sludge feed.
Unscheduled system shutdowns due to equipment failures have also
hampered the fuel efficiency of the incineration operation. These
shutdowns, both scheduled and unscheduled, and the quality of the sludge
feed result in the equivalent of 76 gallons of fuel oil consumption per
dry ton (317 liters/dry tonne) of sludge cake.
Top-hearth gases pass through an external afterburner chamber, although
no auxiliary fuel is used. The staff reports that the combustion
temperature averages about 1300°F (704°C) and the top hearth temperature
averages 850°F to 900°F (454°C to 482°C). Gases then pass through a
waste heat exchanger (currently off-line), a variable-throat venturi
scrubber, and an inpingement tray scrubber/sub-cooler before discharge
to the atmosphere. The scrubbing system is designed for a pressure drop
of 25 inches (63.5 cm) W.C. The heat exchanger transfers heat at a hot
gas/heating oil interface and then at a heating oil/Vater interface.
The final product is hot water which can be used for space heating
throughout the plant. This system was put into operation in the Fall of
1987. The system worked successfully in the 1987/1988 heating season,
but in June 1988 had to be taken off-line due to a severe corrosion
problem. The system has not yet been put back into operation.
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Keys To Success
The design and operating experience at Cranston WPCF offers several
insights into fuel efficient sludge incineration.
Consistent Sludge Feed -
Operators at the Cranston facility emphasize the importance of
consistency in the operation of the incineration system. Any
changes to the system should be made gradually. A consistent sludge
feed is essential to fuel-efficient operation.
Operation Schedule -
Operation of a multiple-hearth furnace on a five day per week
schedule is very costly because of the fuel required to maintain
stand-by temperatures over the week-end. Unscheduled shutdowns due
to maintenance problems also significantly increases auxiliary fuel
use.
Storage Design -
Sludge hoppers should be designed to avoid bridging. A large
fraction of the sludge storage at Cranston is lost because bridging.
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SECTION 4
ECONOMIC COMPARISON OF FACILITIES
BASIS OF ANALYSIS
To develop a meaningful economic comparison between the four subject
facilities, the raw cost data included in the appended case-study
reports must be put into a format that allows an equal comparison
between facilities. To accomplish this, the effect of variations in
plant capacity, variations in each facility's current loading condition,
and variations in each facility's unit costs for labor and consumables
must be eliminated to the extent possible. Costs particular to a
specific facility such as the cost to treat an exceptionally strong
sidestream flow or the cost credit for heat recovered from the
incineration process must be accounted for in the analysis. This
section describes the methodology developed to account for these
factors and presents the findings.
Limits of The Solids Handling/Heat Recovery System
In general, the solids handling train considered extended from the
clarifiers through the incineration system. Specifically, this
evaluation considered all capital and operation and maintenance costs
relating to the following unit processes:
Upper Blackstone WPCF
Pumping of the primary and waste activated sludges from the
clarifiers through the solids train
Flotation thickening of the waste activated sludge
Storage and mixing of the waste activated and primary sludges
Polymer sludge conditioning
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Sludge dewatering utilizing belt filter press units
Sludge incineration utilizing multiple hearth incineration
- Air emission control
Ash disposal
Note that capital costs for the original sludge dewatering
system (vacuum filtration) are not included in this evaluation.
Metropolitan WPCF
Pumping of the primary and waste activated sludges from the
clarifiers through the solids train
Gravity thickening of the primary sludge
- Flotation thickening of the waste activated sludge
Storage and mixing of the waste activated and primary sludges
Thermal sludge conditioning of the blended primary and waste
activated sludges
Decanting of the thermally conditioned sludge
Treatment of the decant tank overflow using a rotating
biological system (RBC units)
- Polymer sludge conditioning
Sludge dewatering utilizing roll presses
Sludge incineration utilizing multiple hearth furnaces
Air emission control
Ash disposal
Heat recovery utilizing a waste heat boiler system
Operation of an auxiliary boiler system to supplement the waste
heat boiler system
Note that capital costs for equipment that was not in use
during the study period (stand-by and retired dewatering
technologies and retired incinerators) are not included in the
evaluation.
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Duffin Creek WPCF
Pumping of the primary and waste activated sludges from the
clarifiers through the solids train
Sludge digestion
- Polymer sludge conditioning
- Sludge dewatering utilizing diaphragm filter presses
- Sludge incineration utilizing fluidized bed furnaces
Air emissions control
- Ash disposal
- Heat recovery utilizing a waste heat boiler system
- Operation of an auxiliary boiler system to supplement the waste
heat boiler system
Note that capital costs for the original sludge dewatering
system (filter presses) are not included in this evaluation.
Cranston WPCF
Pumping of the primary and waste activated sludges from the
clarifiers through the solids train
- Gravity thickening of the primary sludge
Flotation thickening of the waste activated sludge
- Sludge storage and blending of thickened waste activated and
primary sludges
Chemical sludge conditioning utilizing lime and ferric chloride
- Sludge dewatering utilizing fixed-volume filter presses
- Sludge incineration utilizing multiple hearth furnaces
Air emissions control
Ash disposal
Note that costs relating to the heat recovery system are not
included in this evaluation. The heat recovery system was not
in operation during the study period.
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Hie solids handling processes at each of the four facilities produce a
filtrate stream that must be returned to the head of the plant for
treatment. This return load typically totals 5 to 10 percent of the
influent BOD and TSS loading. At the Upper Blackstone, Duffin Creek,
and Cranston facilities, the load from the sidestream flow falls into
this typical range. At the Metro facility, the sidestream flow is of
much higher strength due to the heat conditioning process and must be
treated to reduce its strength before it can be returned to the head of
the plant. The cost to treat the sidestream flow that is returned to
the head of the plant is considered to be equal at the four facilities,
and this cost is not considered in the evaluation. The higher level of
sidestream treatment required at the Metro facility represents an
additional cost to the solids handling system that must be accounted for
in the economic evaluation. For this reason, the capital and operation
and maintenance costs associated with the rotating biological treatment
(RBC) system used for sidestream treatment at the Metro facility are
included in the economic evaluation.
The incineration systems at both the Metro and Duffin Creek facilities
include waste heat recovery. This recovered heat is used to generate
steam, which is used in several applications throughout each facility.
Some of these applications are external to the incineration system (i.e.
provide building heat) and therefore represent an energy output from the
incineration system. This energy output should be accounted for as a
cost credit to the incineration system. Some of the steam is consumed
within the incineration system (i.e. to drive fluidizing air blowers or
induced-draft fans) and, therefore, its use does not constitute a cost
credit. The waste heat recovery systems at the Metro and Duffin
facilities were reviewed to determine which applications should qualify
as a cost credit to the incineration system.
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Plants with waste heat recovery systems must have an auxiliary boiler
system to supplement steam generation from the waste heat boilers during
periods of low sludge production or high steam demand. The auxiliary
boiler system is considered a part of the incineration/heat recovery
system; therefore fuel input to the auxiliary boilers and steam
generated by the auxiliary boilers is accounted for under the
incineration system. For the purposes of this evaluation, costs to
operate the waste heat and auxiliary boilers were included under costs
for the incineration system. The value of the recovered heat used in
other areas of the facility was credited to the incineration system.
At the Metro facility, steam generated by the waste heat recovery system
is used in the following applications:
1. To provide 100% of the steam required for the thermal
conditioning process.
2. To drive steam turbines for the furnace induced draft fans,
boiler feedwater pumps, auxiliary boilers, and some
miscellaneous turbines.
3. To provide building heat throughout the facility.
Some steam is used twice, once in a high-pressure application and a
second time in a low-pressure application. For example, steam may be
used first to drive the induced-draft fans, which reduces steam pressure
from 425 psi to 125 psi (2.9 kPa to 0.9 kPa) and then to provide
building heat, which reduces steam pressure from 125 psi to 15 psi
(0.9 kPa to 0.1 kPa).
Because the Metro thermal conditioning process is part of the
incineration system, the conditioning process is not "charged" for the
steam received from the furnace waste heat recovery system. Steam used
to drive turbines for the induced draft fans, boiler feedwater pumps,
and auxiliary boilers is also considered an internal system use;
therefore no cost or energy credit can be taken for these applications.
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Steam used to drive miscellaneous turbines outside of the incineration
system and steam used to feed the plant heating loop is considered to be
an energy output from the incineration system. A cost credit for this
energy is taken by the incineration system. The amount of this cost
credit is determined as follows:
- For steam used to drive miscellaneous turbines external to the
incineration system, the cost credit is based on the equivalent
electrical cost to drive these turbines.
For steam used to provide building heat, the cost credit is
based on the cost to generate an equivalent amount of steam
using auxiliary boilers.
At the Duffin Creek facility, steam generated by the waste heat recovery
system is used in the following applications:
1. To drive steam turbines that power the furnace fluidizing
(combustion) air blowers.
2. To provide heat for the digestion process.
3. To provide building heat throughout the facility.
Steam used to drive the fluidizing air blowers is an internal use;
therefore no credit is taken for this application. Heat provided to the
digestion process is also considered an internal system use, therefore
no credit is taken for this application. The digestion process provides
digester gas to the incineration system for use as a "free" fuel source
and the incineration process provides "free" heat to the digestion
process. The free use of digester gas as a fuel source compensates the
incineration system for the loss of volatiles within the digestion
process. Steam used to feed the plant heating loop is considered to be
an energy output from the incineration system; therefore a credit is
taken for this application. The cost credit is based on the cost to
generate an equivalent amount of steam using auxiliary boilers.
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Operation & Maintenance Costs
Operation and maintenance costs for each facility were obtained through
a review of plant records and discussions with each plant staff. For
the Duffin Creek, Metropolitan, and Upper Blackstone facilities, 12
months of complete pleint records spanning from 1987 to 1988 were
available. Because of the process and personnel changes at the Cranston
facility since mid 1988, only six months of usable plant records were
available.
Cost data were broken down into six categories; (1) labor; (2)
electricity; (3) fuel (either fuel oil or natural gas); (4) chemicals;
(5) materials and supplies; and (6) contracted services. Each category
is defined and discussed below.
Labor -
Labor costs at each facility were determined through an evaluation of
plant records and discussions with plant management. Plant records were
used to determine total labor costs for the entire solids train and
average labor rates (including benefits) for each plant staff. Plant
management at each facility estimated the typical allocation of labor
for each unit process.
Electricity -
Although the intent of this project was to present actual cost and
energy data based upon plant records, the lack of available data made
this task impossible at three of the four facilities evaluated. Only
the Metro facility hcis records of actual metered electrical consumption
broken down by unit processes, and even in this case there is no way to
segregate equipment consumption from general consumption for lights,
HVAC, and other building needs. The Cranston, Upper Blackstone, and
Duffin Creek facilities essentially have one electrical meter for the
entire facility with no means of breaking down the total consumption at
the facility into each unit processes.
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in each of the appended case-study reports, an equipment list including
connected horsepower and typical hours of operation for each piece of
equipment was developed. However, several factors make it difficult to
develop accurate estimates of electrical consumption based upon
connected horsepower. For instance, a filter press may operate 24 hours
per day, but the filter press feed puxnp and other ancillary equipment
only operate a small fraction of that time. Also, equipment such as an
induced-draft fan may in fact be operating 24 hours per day, but very
rarely operates at its maximum connected horsepower. As a result,
estimates of electrical consumption that are based upon connected
horsepower are generally inflated.
Because of the lack of plant data and the problems associated with
estimating electrical consumption based upon connected horsepower, the
following methodology regarding electrical consumption was adopted:
1. Records of actual metered electrical consumption were used for the
Metro facility. Note that these metered figures include both
equipment related electrical consumption and consumption for
building-related requirements such as lighting and HVAC.
2. Electrical consumption for the Cranston, Upper Blackstone, and
Duffin Creek facilities was estimated as follows:
The building area allocated for each unit process was
estimated.
Electrical requirements for building-related energy consumption
(heating, cooling, lighting, and ventilation) were estimated
based upon an annual requirement of 40 kwh/square foot/year
(430 kWh/square meter/Year). This number represents an average
consumption figure based upon data presented in the EPA
publication entitled Energy Conservation in Municipal
Wastewater Treatment (4).
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Electrical requirements for thickening and dewatering equipment
were estimated based upon the following typical values:
Dissolved Air Flotation (DAF)
Thickening
Gravity Thickening
Sludge Digestion
Belt Filter Press Dewatering
Filter Press Dewatering
60 kWh/ton (66 kWh/tonne)
0.25 kWh/ton
60 kWh/ton
15 kWh/ton
30 kWh/ton
(0.27 kWh/tonne)
(66 kWh/tonne)
(16.5 kWh/tonne)
(33 kWh/tonne)
All of these values are taken from the Water Pollution Control
Federation Manual of Practice No. FD-2 Energy Conservation in the
Design of Wastewater Treatment Facilities (5). Estimates of
electrical consumption for chemical conditioning are based upon
curves presented in this same reference.
Electrical consumption for sludge pumping was estimated based on
upon curves presented in the EPA publication entitled Energy
Conservation in Municipal Wastewater Treatment.
Electrical consumption for sludge storage was estimated based
upon curves presented in the EPA publication entitled Estimating
Sludge Management Costs (6).
Electrical requirements for the incineration systems at the
Cranston and Upper Blackstone facilities was based upon curves
presented in the EPA Process Design Manual Sludge Treatment and
Disposal (7). These curves cannot be used to estimate electrical
consumption at the Duffin facility because the major source of
electrical consumption in the Duffin incineration system, the
fluidized air fan, is steam driven. Therefore, electrical
consumption for the Duffin incineration system was based upon
connected horsepower, excluding the fluidized-air fan.
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This methodology was checked for reasonableness by applying the
procedure outlined above to the Metro facility and comparing estimated
electrical consumption figures to actual consumption figures. Using
this methodology, estimates of the Metro facility's electrical
consumption came within 3 percent of the actual consumption measured at
the facility.
Based on this test, the methodology applied to estimate electrical
consumption is thought to be reasonable.
Fuel -
This category includes fuel oil and natural gas consumed by the furnaces
and the auxiliary boiler system. All fuel consumption figures are
based upon plant records.
Chemicals -
At each facility, the major chemical consumption is for sludge
conditioning before dewatering. At the Duffin Creek and Metro
facilities, a small quantity of chemicals is also used within the
incineration system for boiler feedwater preparation. All consumption
figures are based upon plant records.
Materials & Supplies -
This category refers to miscellaneous materials and supplies purchased
by the plant staff for maintenance purposes. Included in this category
are costs incurred for retractory repair, replacement of rabble teeth,
repairs to heat exchangers, and other equipment overhaul costs.
Estimates of this cost item are based upon plant records and discussions
with the plant staff.
Contracted Services -
This category includes outside consultants or contractors used by the
plant staff to assist in operation and maintenance tasks. Costs in this
category can vary widely from plant to plant. The Metro and Upper
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Blackstone facilities rarely use outside contractors for O&M purposes.
The Cranston facility uses outside contractors extensively because of a
shortage of in-house staff. The Duffin facility uses outside
contractors to assist in general housekeeping and clean-up duties.
Estimates of this cost item are based upon plant records and discussions
with the plant staff.
Estimating Capital Costs
Capital cost data also present several problems. Accurate capital cost
information for any facility is very difficult to obtain and, even if
accurate data are obtained, it is very difficult to compare capital cost
data from different facilities. There are several problems inherent to
any evaluation of capital costs. Often, records regarding original
capital costs are incomplete or difficult to interpret. Some facilities
are bid as a large lump sum contract and capital costs for individual
unit processes are not available. Some facilities are constructed in
stages, making it difficult to accurately piece together information
from a series of contracts spanning several years. In some instances,
it is possible to get accurate original cost information, but the
facility is so old that it is questionable as to whether the costs can
be updated accurately using available cost indices.
The four facilities included in this study were selected, in part, in an
effort to minimize these potential problems. The four selected
facilities all had very complete records of original capital costs and
the management at each facility was very helpful in interpreting this
information. Still, it is inevitable that the problems outlined above
influenced this evaluation to some extent.
Assuming that accurate capital cost information could be obtained from
each facility, several additional problems make it difficult to make a
meaningful comparison of capital costs from different facilities. The
capital costs for two similar facilities can be very different depending
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on site-specific factors such as subsurface conditions, local materials
costs, site constraints, construction market conditions, and other
construction considerations. Hie amount of reserve capacity built into
a facility also significantly affects construction costs. The amount of
reserve capacity allowed for in the design phase can depend on factors
such as site-specific constraints, plans for future expansion, and the
design consultant's and owner's philosophy regarding system redundancy.
All these factors make it difficult to generalize about capital costs.
Original capital costs for each facility were updated to 1988 dollars
using the Engineering News Record (ENR) cost index. At three of the
four subject facilities, the original dewatering technology was
subsequently replaced by a new technology. In these cases, capital
costs for the replacement dewatering equipment were used so that
equipment costs for each unit process were not double counted. Updated
capital costs were amortized assuming a 40 year useful life for all
structures, a 20 year useful life for all equipment, and a discount rate
of 8 percent.
ADJUSTMENTS TO RAW COST DATA
Cost data from the four subject facilities cannot be used for comparison
purposes in its raw form, because of (1) local and regional variations
in unit costs for labor, electricity, fuel, and other consumables; and
(2) differences between plant capacities and current plant loads.
Accounting for Variations in O&M Unit Costs
Because of local and regional variations in unit costs, some cost data
from facilities located in different regions cannot be compared on an
equal basis. The variation in unit costs can make a facility's
operation and maintenance expenditures appear artificially high or low.
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To account for the variations, operation and maintenance costs for the
four facilities were converted to a common set of unit costs. This
eliminated inequities resulting from variations in unit costs at the
four facilities.
To select a reasonable set of standard unit costs for use in this
evaluation, the unit costs from each facility were reviewed. These
costs are presented in Table 3. Based on these data, the following set
of standard unit costs were selected for use in this evaluation:
A standard unit value was developed for steam produced by the waste heat
recovery systems at the Duffin Creek and Metro facilities. This value
was to be based on the cost to generate an equivalent amount of steam
using auxiliary boilers. Plant records at the Duffin facility are
arranged such that the cost to operate and maintain the boiler system is
included in the overall cost for the incineration system and cannot be
easily segregated. However, plant records at the Metro facility clearly
distinguish between operation and maintenance costs for the furnaces and
operation and maintenance costs for the boiler system. From these
records, it was determined that the overall cost for the Metro auxiliary
boiler system to generate steam was about $7.00 per 1000 lb. ($0.15Ag)
of steam, including fuel, labor, and materials and supplies. This
figure is based on the standard unit costs. The cost credit computed
for steam produced by the Duffin Creek and Metro incineration systems is
based on this unit cost of $7.00 per 1000 lb ($0.15/kg)»
Labor
Electricity
Fuel oil
Natural Gas
$15.00 /hour
$ 0.045/kw-hour
$ 0.75 /gal ($0.20/liter)
$ 4.00 /1000 cubic feet
($0.14/cubic meter)
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TABLE 3
FACILITY UNIT COSTS
Item Cranston Metro Upper Duffin Average
WPCF WPCF Blackstone Creek* Cost
Labor ($/hour)**
-Operations $14.00 $18.00 $12.50 $14.71 $14.80
-Maintenance $14.00 $22.00 $12.50 $14.71 $15.80
Electricity ($Aw-hour)
$0,060 $0,037 $0,047 $0,037 $0,045
Fuel Oil ($/gal)
Natural Gas ($/1000cf)
$0.90 $0.59 $0.74 $0.74
$6.30 $2.50 $3.56 $3.50 $3.97
* U.S. Dollars
** Includes benefits
1 gallon - 3.7854L
1 cubic foot - 0.028317 cubic meters
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Some operation arid maintenance costs, such as the cost for materials and
supplies and the cost for contracted services, cannot be standarized.
Chemical costs for sludge conditioning are also difficult to standarize
because of the many variables that influence conditioning costs. Each
facility has a different dewatering technology and therefore has
different chemical conditioning requirements. However, the adoption of
the standard unit costs outlined above does equalize the operation and
maintenance costs for the four facilities to the extent possible.
Accounting for Different Capacities and Loadings
The current loads to the four facilities range from 9 dry tpd (8.2 dry
tonnes per day) of dewatered cake to 177 dry tpd (161 dry tonnes per
day) of dewatered cake. This large range in loading conditions
introduces inequities resulting from economy of scale.
The load on a plant (versus design capacity) cam have a significant
impact on operation and maintenance costs. A system generally operates
most cost efficiently when operating at or near its design capacity.
For example, some processes require essentially the same operator
attention, the same maintenance, and the same power consumption whether
the process is lightly loaded or loaded to capacity. As a result, unit
costs are less when operating at design capacity. For this reason, it a
facility operating at design capacity should not be compared directly
with a facility that is in the early stages of its design life.
Because of the influence of the difference between load and capacity,
costs were evaluated for operation at current loads and for operation at
capacity. To estimate the costs at capacity, the capacity of each
solids handling system was estimated, and costs for operation at
capacity were developed.
The capacity of each solids train was taken to be the maximum amount of
sludge that the solids train could process while maintaining a
-------
reasonable amount of stand-by capacity. Applying a uniform definition
of "reasonable stand-by capacity" to the four facilities eliminates
inequities resulting from the variation in each facility's design
reserve capacity.
The determination of the capacity of each solids train was based on
engineering judgment. Each unit process in each solids train was
reviewed with regards to capacity and the limiting process in each train
was identified. It was assumed that a reasonable amount of stand-by
capacity must be retained within the system. In some cases, the
capacity of one unit process severely limited the capacity of the solids
train as a whole. In these instances, it was assumed that the capacity
of the limiting process would be expanded to match the capacity of the
rest of the solids train, in these cases, the capital cost of the
existing facility was added to the estimated capital for the additional
equipment.
The Duffin Creek facility presented a unique situation regarding system
capacity. As discussed in Section 3, capacity of the incineration
system installed at the Duffin Creek facility exceeds the current sludge
production. The furnaces were subsequently modified to operate
efficiently at a reduced loading. The capacity of the existing solids
train at the Duffin Creek facility is 30 dry tpd (27.2 dry tonnes per
day) of dewatered sludge cake. However, the capacity of the existing
furnaces could be expanded from 30 tpd (27.2 dry tonnes per day) per
unit to 60 tpd (54.4 dry tonnes per day) per unit by returning the
furnaces to their original installed capacity. No new construction or
equipment installation would be required. It would be very difficult to
accurately estimate the cost of the extensive construction that would be
required to upgrade the digestion and dewatering systems to match the
full capacity of the incineration system. Therefore, two capacity
figures are used for the Duffin Creek Facility. The capacity of the
Duffin Creek solids train is rated at 30 dry tpd (27.2 dry tonnes per
day) of dewatered sludge cake and the capacity of the Duffin Creek
incineration system is rated at 60 dry tpd (54.4 dry tonnes per day) of
dewatered sludge cake.
-------
The evaluation of each facility's system capacity is summarized as
follows:
Facility
Estimated Additional
Capacity Equipment Required
(dry tons of
dewatered sludge)
Upper Blackstone WPCF
Duffin Creek WPCF
- digestion/dewatering
- incineration
Metro WPCF
Cranston WPCF
60 dry tons/day additional belt filter press
30 dry tons/day
60 dry tons/day
240 dry tons/day
30 dry tons/day
none
none
additional gravity thickener
additional gravity thickener
dry tons/day = 0.907 dry tonnes/day
Capital costs for the Duffin Creek facility were further adjusted to
minimize the effect of excessive redundancy. The capacity of the
existing Duffin dewatering system is about 30 dry tons (27.2 dry tonnes)
per day, but the dewatering building was sized to accommodate a future
expansion of the dewatering system. If the dewatering building had been
sized to house only the existing dewatering equipment, the building size
could be cut almost in half. To account for this excess building space,
the structural cost for the Duffin dewatering system was adjusted to
reflect the cost of the actual required building volume. This is the
only instance in which building costs were adjusted to minimize the
effect of oversized structures.
Each facility's expenditures for labor, electricity, chemicals, and
other consumables were scaled up to reflect operation at capacity.
Projections of design year operation and maintenance expenditures are
-------
based upon the raw costs data presented in the appended case study
reports. Costs were scaled up based upon the percent increase in sludge
production, the increase in the number of units on-line under average
conditions, or some other appropriate parameter.
To project fuel consumption by the Metro and Duffin auxiliary boiler
systems when operating at capacity, it was assumed that the same total
amount of steam would be produced by the boiler systems, that the steam
produced by the waste-heat boilers would increase in proportion to the
projected increase in sludge production, and that steam production by
the auxiliary boiler systems would decrease accordingly.
PLANT COMPARISONS
In this section, cost information on the four treatment plants is
evaluated for the current operation (with the equipment not loaded to
capacity) and for operation at capacity. Costs for the individual
processes and for the total process train (from thickening through
combustion) are analyzed. Cost information is presented on the basis of
dry ton of dewatered sludge cake processed. Tables detailing capital
and operation and maintenance costs for each facility under both current
loading and capacity loading conditions are appended.
Sludge Thickening and Digestion
The Metro, Upper Blackstone, and Cranston facilities all employ gravity
thickening of the primary sludge and flotation thickening of the waste
activated sludges. The Duffin Creek facility utilizes sludge digestion.
Per ton costs for these unit processes are presented in Tables 4 and 5.
These observations can be made:
o Capital costs for the Cranston facility are on the high end of the
range because its gravity thickeners are housed. The Metro and
-------
cr>
CO
CAPITAL
LABOR
ELECTRICITY
FUEL
CHEMICALS
MATERIALS i SUPPLIES
CONTRACTED SERVICES
TOTAL OUl
TOTAL COST
TABLE 4
COMPARISON Or ANNUAL SOLIDS HAHDLIHG COSTS
FOR SLUDGE THICKENING ($/BRI TON)
METRO (1)
CAPACITY CURRENT
UPPER
BLACKSTONE (2)
$25.98
12.54
7.23
0.00
0.23
4.35
0.22
24.57
$50.55
$ 35.13
12.71
9.10
0.00
0.23
4.41
0.22
26.68
$61.81
CAPACITY
$13.10
4 .75
4.10
0 .00
0 .00
0.39
0.00
9.24
$22.34
1 dry ton = 0.9072 dry tonnes
The solids train capacity for each facility is estimated as follows:
Hetro 240 tpd of dewatered cake
Blackstone 60 tpd of dewatered cake
Cranston 30 tpd of dewatered cake
CURRENT
$26.10
5.48
1 .80
0.00
0.00
0.39
0.00
10.67
$36.77
CRANSTON (3)
CAPACITY
$50.28
25.41
3.87
0.00
3.61
3.65
0.24
36.79
$87.07
CURRENT
$165.77
27.79
10 .36
0.00
3.61
6.02
0.78
48.56
$214.33
Current average loading condition for each
facility is estimated as follows:
Metro 177.5 tpd of dewater cake
Blackstone 30.1 tpd of dewatered cake
Cranston 9.1 tpd of dewaterd cake
(1) Includes sludge pumping from the clarifiers, flotation thickening of Waste Activated Sludge, and gravity thickening of primary
sludge.
(2) Includes sludge pumping from the clarifiers, flotation thickening of waste Activated Sludge, and storage of thickened W.A.S.
and primary sludge. (Note that the primary sludge holding tank acts as a gravity thickener.)
-------
TABLE 5
COMPARISON OF ANNUAL SOLIDS HANDLING COSTS
FOR SLUDGE DIGESTION AT DUFFIN CREEK
($/dry ton)
DUFFIN CREEK (1)
AT CAPACITY
CURRENT
CAPITAL
$ 54.19
$ 60.43
LABOR
5.04
5.50
ELECTRICITY
6.14
6.66
FUELO
0.00
0.00
CHEMICALS
0.00
0.00
MATERIALS & SUPPLIES
0.75
0.75
CONTRACTED SERVICES
1.50
1.50
TOTAL O&M
13.42
14.42
TOTAL COST
$ 67.62
$ 74.85
1 dry ton = 0.9072 tonnes
(1) Includes sludge pumping from the clarifiers and sludge digestion.
-------
Blackstone facilities have uncovered gravity thickeners. Capital
costs for the Duffin Creek digestion system are greater than the
typical sludge thickening capital cost.
o Labor costs vary widely among the four facilities. Costs for the
Cranston facility are very high as a result of the many maintenance
problems experienced by the thickening equipment.
o Cost of chemicals for flotation thickeners is highly dependent upon
the characteristics of the waste activated sludge and can vary
widely from plant to plant. Chemical costs for the Cranston
facility are higher than the Metro facility. The Upper Blackstone
facility does not employ any chemical conditioning.
o Cranston's high costs for thickening are expected. The staff has
only operated the thickening equipment for a short period of time
and is still in the process of optimizing the operation. Also, the
thickening equipment has required a great deal of maintenance to be
restored to working order.
o O&M costs for digestion at Duffin Creek are lower than the average
cost for sludge thickening.
o Total costs for the Cranston facility are high for the reasons
outlined above. Total costs for sludge digestion are comparable to
the total costs for sludge thickening.
Sludge Conditioning And Pewatering
The Metro, Upper Blackstone, and Duffin Creek facilities all utilize
polymer sludge conditioning before dewatering. The Metro facility also
employs thermal sludge conditioning. Sludge dewatering at these three
facilities is accomplished utilizing roll presses (at Metro), belt
filter presses {at Upper Blackstone), and diaphragm filter presses (at
-------
Duffin Creek). The Cranston facility utilizes lime and ferric chloride
for sludge conditioning and fixed-volume filter presses for sludge
dewatering. See Table 6 for costs.
The observations can be made:
o Capital costs for the Upper Blackstone facility are very low. At
the Duffin Creek and Cranston facilities, most of the capital costs
are dedicated to the dewatering equipment (filter presses), whereas
at the Metro facility, most of the capital costs are dedicated to
the sludge conditioning equipment.
o Labor costs for the Metro facility are higher than the other three
facilities. The high labor cost at the Metro facility is
attributable to the complexity of the sludge conditioning system.
o Chemical requirements are considerably less for Upper Blackstone
than for Duffin Creek. Costs for lime and ferric sludge
conditioning are much higher than for polymer conditioning costs.
o The low electrical cost for the Upper Blackstone facility reflects
the low energy consumption of a belt filter press installation. The
higher electrical cost at the Metro facility reflects the additional
equipment and building space required for the thermal sludge
conditioning process.
o Costs for materials and supplies contracted services are low for all
four facilities.
o Labor and chemicals are the major cost items at each facility.
o Total conditioning/dewatering costs for the Upper Blackstone are
very low. Costs for the other three facilities fall in a fairly
narrow range, with amortized capital costs constituting about 40
percent of the total annual system cost.
-------
TABU 6
OOKPARISOM OF AIWUAL SOLIDS BANDLUIG COSTS
FOR SUJDGK OOtroiTIOWIHG/DEHATERING ($/DR3T TOR)
LABOR
ELECTRICITY
FUEL
CHEMICALS
METRO (1)
CAPACITY CURRENT
$ 65.26 $ 88.24
49.43 51.47
11.63 12.40
0.00 O.OO
13.19 13.90
UPPER
BLACKSTONE (2)
CAPACITY CURRENT
$ 18.47 $ 36.81
19.75 25.79
2.87 5.22
0.00 0.00
7.26 7.26
PUFFIN CREEK (3)
CAPACITY CURRENT
$ 47.95 $ 53.47
39.45 39.60
4.94 5.35
0.00
21.06
0.00
21.20
CRANSTON 14)
CAPACITY CURRENT
$62.64 $206.50
19.28 33.84
6.78 15.51
0.00 0.00
55.07 55.97
MATERIALS s. SUPPLIES
CONTRACTED SERVICES
TOTAL O&M
6.97 7.14 2.37
0.51 0.53 0.00
81.73 85.44 32.24
TOTAL COST $147.00 $173.68 $ 50.71
1 dry ton = 0.9072 dry tonnes
The solids train capacity for each facility is estimated as follows:
Metro
Blackstone
Duffin
Cranston
240 tpd of dewatered cake
60 tpd of dewatered cake
30 tpd of dewatered cake
30 tpd of dewatered cake
2.37
0.00
40.64
$ 77.45
10.77
3.32
79.54
$127.49
12.01
3.34
81.50
$134.97
Current average loading condition for each
facility is estimated as follows:
Metro 177.5 tpd of dewater cake
Blackstone 30.1 tpd of dewatered cake
Duffin 26.9 tpd of dewatered cake
Cranston 9.1 tpd of dewaterd cake
7.67
0.00
88.79
$151.43
16.26
0.00
121.57
$328.07
(1> Includes thermal sludge conditioning, roll press dewatering, and treatment of the thermal conditioning sidestream (RBC system)
(2) Includes polymer conditioning and belt filter press dewatering.
(3) Includes polyaer conditioning and dewatereing with diaphragm filter presses.
-------
Sludge Incineration
The Metro, Upper Blackstone, and Cranston facilities all have multiple
hearth furnaces. The Duffin Creek facility has a fluidized-bed system.
See Table 7 for costs.
These observations can be made:
o Capital costs for the Upper Blackstone facility are very low.
Capital costs for the Metro and Duffin Creek facilities include
waste heat and auxiliary boiler systems.
o The low labor cost at the Cranston facility is the result of a fewer
staff compared to desired operation practice.
o Electrical costs are heavily influenced by the amount of building
space allocated for the incineration system, because of electrical
consumption for building needs such as lighting and HVAC.
o Total fuel costs have been broken down into fuel consumed in the
furnace and fuel consumed in the auxiliary boiler system. Fuel
consumption within the furnace, including cool-down and heat-up
periods, is very low for the Metro, Blackstone, and Duffin Creek
facilities. The Duffin Creek cost includes furnace fuel oil
consumed both within the reactor and within the hot windbox. It does
not include any cost for digester gas burned within the hot windbox.
This is considered a free fuel source.
o Current furnace fuel consumption at the Cranston facility is very
high. This is a result of the 5 day per week operation schedule,
the frequent unscheduled maintenance shutdowns, the light furnace
loading during operating periods, and the low volatility and solids
concentration of the sludge cake. These shutdowns, both scheduled
(weekends) and unscheduled, consume a great deal of auxiliary fuel.
-------
TM1LE 7
—1
4=-
METRO (1>
COMPARISON OF AIWUAL SOLIDS HANDLING COSTS
FOR SLUDGE ISdNERKTIOW ($/ERX TOO)
UPPER
BLACKSTONE (2)
CAPITAL
LABOR
ELECTRICITY
CAPACITY
$124.58
59.40
12.94
CURRENT
$168.45
63.68
16.95
FUEL
- FURNACES
- AUX BOILERS
CHEMICALS
MATERIALS f. SUPPLIES
CONTRACTED SERVICES
COST CREDIT
TOTAL OfcM
TOTAL COST
4.22
14.56
0.86
10.95
1.76
23.62
89.17
$257.62
CAPACITY
$ 47.S6
29.45
10.57
4.65
4.16
7.19
0.86
10.66
1.81
17.62
79.40
$203.98
1 dry ton = 0.9072 dry tonnes
The solids train capacity for each facility is estimated as follows:
Metro 240 tpd of dewatered cake
Blackstone 60 tpd of dewatered cake
Duffin 60 tpd of dewatered cake
Cranston 30 tpd of dewatered cake
0.00
5.39
0.00
0.00
50.05
$ 97.61
CURRENT
$ 94.80
29.45
13.69
4.65
0.00
5.39
0.00
0.00
53.17
$147.97
DUFFIN CREEK
CAPACITY
$ 93.74
29.78
6.27
6.46
0.45
2.50
21.92
13.97
6.20
75.14
$168.88
CURRENT
$209.07
50.75
10.33
6.46
21.04
2.51
45.57
17.70
13.84
140.51
$349.58
Current average loading condition for each
facility is estimated as follows:
Metro
Blackstone
Duffin
Cranston
177.5 tpd of dewater cake
30.1 tpd of dewatered cake
26.9 tpd of dewatered cake
9.1 tpd of dewatord cake
<1) Includes incineration, heat recovery, ash disposal, and auxiliary boiler systems.
{2) IncludeB incineration and ash disposal systens.
(3) Includes incineration, heat recovery, ash disposal, and auxiliary boiler systems.
(4) Includes incineration, heat recovery, and ash disposal system.
CRAM5TON (3)
CAPACITY CURRENT
$118.02 $389.07
19.42 42.78
7.66 25.26
7.50
O.OO
4.02
17.69
0.00
56.28
$174.30
42.15
0.00
6.32
44.50
0.00
161.01
-------
The Blackstone facility uses no outside consultants for operation
and maintenance tasks. The Metro facility very rarely uses outside
consultants. The Duffin Creek facility utilizes outside contractors
for general housekeeping duties and for ash disposal (tipping fee).
The cost for contracted services is highest at the Cranston
facility, reflecting the many major repairs that have been required
at the facility and the current manpower shortage at the facility.
As described previously, a cost credit is taken for steam generated
by the waste heat/auxiliary boiler system that is used in an
application external to the incineration system. The credit for the
Metro facility is significantly higher than for the Duffin Creek
facility. This is a reflection of the steam utilization at each
facility. About 53 percent of the steam generated by the Metro
system is used in applications outside of the sludge processing
system, whereas only about 23 percent of the steam generated at the
Duffin Creek facility is used in applications outside of the sludge
processing system. At both facilities, steam used to drive
combustion air fans results in a cost credit in the form of reduced
electrical costs.
Cranston's current total operation and maintenance costs are high as
a result of excessive auxiliary fuel consumption and the frequent
need for outside consultants. Cranston's projected per ton
operation and maintenance costs for operation at system capacity are
about 35 percent less than the current operation and maintenance
costs. This wide range of costs is the result of the large
difference between the current and capacity loading conditions.
Fuel costs were adjusted to reflect future operation on a round the
clock, seven day per week schedule with a minimum of system
shutdowns.
Costs for the Blackstone facility are very low. No major repairs
have been required at the Blackstone facility; therefore costs for
materials and outside contractors are minimal. The facility
-------
frequently operates autogenously; therefore costs for auxiliary fuel
are very low. Costs for the Metro and Duffin Creek facilities fall
in the middle of the cost range. Based on this information, a
reasonable range of Q&M costs for a well-operated sludge
incineration facility is $70 to $90/dry ton ($77 to $99/dry tonne)
for plants operating at capacity.
o It is interesting to note the impact that fuel consumption can have
on total O&M costs. Many of the O&M costs for a facility are
somewhat fixed, but auxiliary fuel costs can be directly influenced
by operation practices. This is reflected in the O&M costs for
these four facilities. At the facilities that operate autogenously
much of the time, the cost of auxiliary fuel is a relatively minor
O&M cost (less than 5% of total O&M costs). At the Cranston
facility, auxiliary fuel costs are very significant, making up about
25% of the total O&M budget.
o Total system costs for the Upper Blackstone facility are
exceptionally low, even for a well-operated facility. The other
three facilities provide a more realistic range of costs for what
one would expect from a well-operated facility. Costs for the
Metro, Duffin, and Cranston facilities range from $169 to $204/dry
ton ($186 to $224/di:y tonne) at capacity. Based on this
information, a reasonable estimate of total (capital and O&M) costs
for incineration at a well-operated sludge incineration facility
operating at capacity is about $200/dry ton ($220/dry tonne) of
sludge cake processed.
Total Solids Handling Costs
Table 8 summarizes total capital and operation and maintenance costs for
the entire solids train.
t
-------
These observations can be made:
o Capital costs for the Upper Blackstone facility are exceptionally
low and cannot be considered typical. If the costs for Blackstone
facility are disregarded, the average capital cost for the remaining
three facilities (operating at capacity) is $214/dry ton ($236/dry
tonne) wit a fairly tight range of $196 to $231/dry ton ($216 to
$255/dry tonne). Based on this information, a reasonable estimate
of capital costs for a solids train incorporating sludge
incineration is $200 to $230/dry ton ($220 to $254/dry tonne) when
operating at capacity.
o Total operation and maintenance costs for Upper Blackstone are
exceptionally low and cannot be considered typical. Based on
information from the other three plants, a reasonable estimate of
total O&M costs for a well-operated incineration solids train is
$180 to $200/dry ton ($198 to $220/dry tonne) when operated at
capacity.
o Total costs (capital and O&M) for Upper Blackstone are exceptionally
low and cannot be considered typical. Based on information from the
other three plants, a reasonable estimate of total annual costs
(including capital) for a well-operated incineration solids train is
$380 to $430/dry ton ($418 to $473/dry tonne) when operating at
capacity.
A review of Table 8 shows consistently low costs for the upper
Blackstone facility. The exceptionally low operation and maintenance
costs for the Blackstone facility can only be explained as the product
of a small, highly skilled staff having fully optimized the operation of
each unit process within the solids train. At each of the facilities
evaluated, labor costs represent the largest single O&M item, especially
if one considers the contracted services item as an extension of the
staff labor cost. Upper Blackstone has been able to minimize labor
-------
TABLE 8
COMPARISON or AHNUAL SOLIDS HANDLING COSTS
FOR TOTAL SOLIDS TRAIN (5/DRI TOR)
METRO
CAPACITY
CURRENT
CRANSTON
CURRENT
DUFFIN CREEK
CAPACITY
UPPER
BLACKSTONE
CURRENT
THICKENING/DIGESTION
CAPITAL
OfcM
TOTAL
$ 25.98
24.57
50.55
$ 35.13
26.68
61.81
50.28
36.79
87.07
$165.77
48.56
214.33
$ 54.19
13.42
67.62
$ 60.43
14.42
74.85
S 13.10
9.24
22.34
$ 26.1
10.67
36.77
00
CONDITIONING/DEWATERING
- CAPITAL
- OlM
- TOTAL
INCINERATION
$ 65.26
81.73
147.00
$ 88.24
85.44
173.68
$ 62.64
88.79
151.43
$206.50
121.57
328.07
$ 47.95
79.54
127.49
$ 53.47
81.50
134.97
$ 18.47
32.24
50.71
$ 36.81
40.64
77.45
- CAPITAL
- OU4
- TOTAL
$124.58
79.40
$203.98
$168.45
89.17
$257.62
$118.02
56.28
$174.30
$389.07
161.01
$550.08
$ 93.74
75.14
$168.88
$209.07
140.51
$349.58
$ 47.56
50 .05
$ 97.61
$ 94.80
53.17
$1*57.97
TOTAL SOLIDS TRAIN
CAPITAL
OlM
TOTAL
$215.82
185.70
401.52
$291.82
201.29
493.11
$230.94
181.86
412.80
$761.34
331.14
1092.48
$195.88
168.10
363.98
$322.97
236.43
559.40
$ 79.13
91.53
170.66
$157.71
104.48
262.19
1 dry ton = 0.9072 dry tonnes
The solids train capacity for each facility is estimated as follows:
Metro
Blackstone
Duffin
Cranston
240 tpd of dewatered cake
60 tpd of dewatered cake
30 tpd of dewatered cake
30 tpd of dewatered cake
Current average loading condition for each
facility is estimated as follows:
Metro 177.5 tpd of dewatet cake
Blackstone 30.1 tpd of dewatered cake
Duff in 26.9 tpd of dewatered cake
-------
costs by developing a well-rounded staff that is able to effectively
operate and maintain the facility with an absolute minimum of people.
The staff's optimization of each unit process has minimized the
consumption of energy, chemicals, and other consumables.
Major factors contributing to the process efficiency at Upper Blackstone
are the design of the facility and the characteristics of the sludge
being processed at the facility. The design of the facility included
equalization storage and sludge blending, both of which serve to
minimize changes in the sludge quality and quantity. Also, the sludge
at Upper Blackstone thickens and dewaters exceptionally well (E.G. 5-6%
solids feed to dewatering and 27% solids cake product vs 23% solids cake
at typical BFP facility). These factors make it easier for the staff to
control and optimize each unit process in the solids train. This
combination of an excellent staff, a well-designed facility, and a
sludge with excellent dewatering properties has resulted in an extremely
cost effective sludge processing system.
Table 8 also demonstrates that per ton costs for a facility can vary
significantly depending on how the cost data are presented. The
variation in per ton capital costs is directly related to the percent
capacity currently utilized at each facility. For example, per ton
capital costs for the Duffin Creek incineration system are about halved
when projected to operation at capacity because the system is currently
operating at about one-half of its capacity. Differences in per ton
operation and maintenance costs are the results of the changes in
process efficiency that a system experiences during its design life.
Per ton operation and maintenance costs will always be least when the
system is operating at capacity because of the increased efficiency of
power, labor, materials, etc. that result from the complete equipment
utilization.
-------
This variation iri system costs over the life of a facility should be
considered when reviewing the tables presented in this study. During
the life of each of these facilities, per ton operation and maintenance
costs will vary significantly. This variation can be reduced through
the use of multiple units rather than single large units in equipment
selection, the accurate estimation of initial and design year sludge
quantities, and other design features. However, every facility will be
affected by this life-cycle cost variation to some extent.
-------
SECTION 5
ENERGY EVALUATION OF FACILITIES
GENERAL
Energy efficiency is one of the primary measures of the success of a
sludge incineration operation. Often, the terras "autogenous" or
"self-sustaining" are used to describe the incineration process.
Strictly speaking, these terras describe conditions in which no auxiliary
fuel is required to maintain the steady-state condition within the
furnace. The heat required to dry the incoming sludge, increase the
dried sludge temperature to ignition temperatures, maintain the burn
temperature, compensate for radiation losses within the furnace, and
allow for complete combustion of all solids and gases is provided by the
sludge itself.
For the purposes of determining eligibility for alternative technology
grant funding preference, the EPA construction grants program defines
self- sustaining incineration, differently, as follows:
"In order to be eligible for the alternative technology grant
funding preference, an incineration system must be a net energy
producer or 'self-sustaining' (including the energy used for
sludge dewatering, combustion and pollution control equipment).
To meet this requirement, extremely energy efficient equipment
and operating procedures (such as codisposal) have to be used
for collecting and recovering heat energy" (8).
Clearly, there are there are several ways to evaluate the energy
efficiency of an incineration system depending on how one defines the
system's energy input and output. The analysis presented here will
evaluate all energy inputs to and outputs from both the incineration
system alone and the solids train as a whole. The information will be
-------
presented so that readers may draw conclusions regarding the energy
efficiency of the incineration system, depending on how they choose to
define the system's energy inputs and outputs. The evaluation will als<
allow a comparison of various sludge thickening, conditioning, and
dewatering technologies and each solids handling system as a whole.
BASIS OF ANALYSIS
System inputs & Outputs
Energy inputs and outputs for each of the four facilities can be broken
down as follows:
Upper Blackstone
Energy Inputs - Electricity
Natural Gas
Fuel Oil
Energy Outputs
None
Metropolitan WPCF
Energy Inputs
Electricity
Natural Gas
Energy Outputs
Steam
Duffin Creek WPCF
Energy Inputs
Electricity
Fuel Oil
Natural Gas
Energy Outputs
Steam
Internal Transfer
Digester Gas
-------
Cranston WPCF
Energy Inputs - Electricity
- Natural Gas
Energy Outputs - None
Note: A heat exchanger was installed at the Cranston facility to
recover waste heat from the incineration system. However, the
heat exchanger has experienced severe corrosion problems and
therefore has not operated for a long enough period to evaluate
its potential for energy recovery.
Evaluation of Plant Data
The evaluation of energy requirements is based on raw plant data.
Energy consumption figures for each facility were determined as follows:
1. Electrical Consumption
See discussion in Section 4 regarding the methodology used to
estimate electrical consumption.
2. Consumption of Auxiliary Fuel
Total consumption of auxiliary fuel for each facility was obtained
directly from plant records. From the Metro plant records,
auxiliary fuel consumption within the furnaces could be
distinguished from fuel consumption within the auxiliary boiler
system. For the Duffin Creek facility, fuel consumption within the
incineration/auxiliary boiler system could not be broken down as
easily. Duffin Creek plant records include total consumption
figures for each form of auxiliary fuel, but do not distinguish
between fuel consumed within the hot windbox, the furnaces, and the
-------
auxiliary boiler system. Discussions with the plant staff indicate
that fuel oil is very rarely used other than in the furnace burners.
Therefore, it will be assumed in this evaluation that all fuel oil
consumed within the incineration system is consumed within the
furnace.
At each of these facilities, a significant amount of the auxiliary
fuel consumed in the furnaces is used during start-up, cool-down,
and hot stand-by periods. However, only the Metro facility records
fuel consumption during these periods.
Energy Comparisons
To allow different forms of energy consumption to be compared on an
equal basis, each form of energy must be converted to an equivalent
unit. Throughout this evaluation, energy consumption is presented both
in raw form (kwh of electricity; cubic feet of natucal gas; gallons of
fuel oil; pounds of steam) and on the basis of equivalent Btu value
(British Thermal Units). This allows an equal comparison of various
forms of energy consumption. Hie following conversion factors are used
(9):
Fuel Oil - 138,000 Btu/gallon (38,500 kJ/L)
Natural Gas - 1,000 Btu/cubic foot (37,300 kJ/cubic meter)
Digester Gas - 600 Btu/cubic foot (22,400 kJ/cubic meter)
Electricity - 10,000 Btu/kWh (accounts for inefficiency of
electrical generation process)
Steam - Metro: 1,481 Btu/pound (3265 BtuAg) based upon
plant records
Duff in Creek: 1,572 Btu/pound (3465 BtuAg) at 260
psi; and 520°F.
-------
FACILITY COMPARISONS
The preceding section shows that the results of an energy evaluation are
heavily influenced by how energy inputs and outputs for the incineration
system are defined. This section summarizes the results of the energy
evaluation and presents the results in a format that allows comparison
between the four facilities. The four facilities are compared on the
following levels:
Level A - Compare the facilities on the basis of auxiliary fuel
consumed within the furnaces only. For the purposes of this
evaluation, auxiliary fuel is expressed in terms of
equivalent gallons (liters) of fuel oil.
Level B - Same as Level A, except consider energy inputs to the waste
heat/auxiliary boiler equipment, the emission control
equipment, and the ash disposal system. Steam produced and
utilized outside of the incineration system is considered an
energy output from the Metro and Duffin facilities.
Digester gas will be considered a free fuel source and,
therefore, will not be considered an energy input to the
Duffin system.
Level C - Same as Level B, except that electricity for equipment is
considered an energy input.
Level D - Same as Level C, but consider energy inputs to the sludge
conditioning/dewatering system.
Level E - Same as Level D, but consider energy inputs to sludge
thickening or digestion. Auxiliary fuel, electricity for
equipment, and electricity for general building requirements
are considered energy inputs.
-------
In all cases, auxiliary fuel consumption refers to the consumption of
fuel oil and natural gas. Digester gas used by the Duffin Creek
incineration system is not considered an energy input in this
evaluation. The free use of digester gas as a fuel source compensates
the Duffin Creek incineration system for the loss of sludge volatiles
resulting from the digestion process. If digester gas were considered
an energy input, this would add about 38,000 million Btu to the total
Duffin Creek energy input for each case.
The energy inputs and outputs for each alternative are summarized on
Table 9.
Table 10 presents estimates of fuel use for the Level A analysis. Fuel
use for furnace startup and shutdown varied considerably, as follows:
The value for Upper Blackstone is estimated by the plant staff. Because
short-term shutdowns do not require auxiliary fuel in a fluidized bed
system, fuel use for start-up at Duffin Creek is assumed to be 0.
Although no data are available for Cranston, it is certain that most of
the total fuel consumption is due to the intermittent operation schedule
and frequent maintenance shutdowns.
For the Level A analysis (examining fuel use in the furnaces only), the
Upper Blackstone, Metro, and Duffin facilities all fall within the
fairly narrow range of fuel consumption of 7.4 to 8.6 gallons/dry ton
(28 to 36 liters/dry tonne) with the Metro facility having the lowest
fuel consumption under normal operating conditions. Note that each of
the four facilities must use some auxiliary fuel at times to maintain
steady-state burn conditions.
Upper Blackstone
Metro
Duffin Creek
Cranston
0
not available
3 percent
35 percent
-------
TABLE 9
ENERGY INPUTS AND OUTPUTS FOR LEVELS EVALUATED
LEVEL
ENERGY FORM A B C D E
INPUTS
AUXILIARY FEED IN
FURNACE XXX
ELECTRICITY TO FURNACE X
ELECTRICITY TO DEWATERING
ADD OTHER PROCESSES AND
BUILDING ELECTRICITY
OUTPUTS
STEAM X X X X
X
X
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TABLE 10
ESTIMATE OF ENERGY REQUIREMENT TOR LEVEL A
(MILLION Btu/YEAR)
UPPER
ENERGY FORM BLACKSTONE
Energy Input
Natural Gas 6,800
Fuel Oil 4,400
Total 11,200
Equivalent Gallons
of Fuel Oil/Dry Ton 7.4
DUFFIN
METRO CREEK CRANSTON
68,400 35,000
11,700
68,400 11,700 35,000
7.7 8.6 76.4
NOTE: Unless otherwise noted, all figures are based on 1987/1988 plant
records.
Gallons = 3.785 L
Ton - 0.9072 tonne
-------
Table 11 presents the estimated fuel use for the Level B analysis. In
Level B, fuel used in the furnace and the waste-heat/auxiliary boiler
equipment is considered an energy input, and steam and electricity
produced by incineration and used outside the incineration system, which
includes heat conditioning, are considered energy output.
This scenario shows that if only fuel oil and natural gas are considered
energy inputs to the incineration system (including auxiliary boiler
system) and credit is taken for steam production, the Metro incineration
system is a net energy producer and the Duffin Creek incineration system
comes very close to meeting this goal.
Table 12 presents the estimated fuel use for the Level C analysis. For
Level C, electricity is considered an energy input to the furnace and
the waste-heat/auxiliary boiler equiment, as well as fuel. Steam and
electricity produced by incineration and used outside the incineration
system, which system includes heat conditioning, are considered energy
output.
Under this scenario, none of the four facilities qualifies as a net
energy producer, although the Metro and Duffin Creek facilities approach
this goal.
Table 13 presents the estimated fuel use for the Level D analysis.
Level D considers energy inputs to sludge conditioning and dewatering,
incineration, and the waste-heat/auxiliary boiler equipment. Steam and
electricity produced by incineration and used outside the incineration
system are taken as energy output. This level is the same as the
definition used by the EPA construction grant program for
"self-sustaining" incineration.
Under this scenario, net energy consumption increases significantly for
each facility. None of the four facilities can be considered a net
energy producer.
-------
TABLE 11
ESTIMATE OF ENERGY REQUIREMENT FOR LEVEL B
(MILLION Btu/YEAR)
UPPER DUFFIN
ENERGY FORM BLACKSTONE METRO CREEK CRANSTON
Energy Input
Natural Gas 6,800 304,400 51,700 35,000
Fuel Oil 4,400 11,700
Total 11,200 304,400 63,400 35,000
Energy Output
Steam 305,500 61,000
Electricity 22,100
Total 0 327,600 61,000 0
Net Comparison 11,200 -23,200 2,400 35,000
Equivalent Gallons
of Fuel Oil/Dry Ton 7.4 -2.6 1.8 76.4
NOTE: All figures are based on 1987/1988 plant records.
Gallons = 3.785 L
Ton = 0.9072 tonne
-------
TABLE 12
ESTIMATE OF ENERGY REQUIREMENT FOR LEVEL C
(MILLION Btu/YEAR)
UPPER DUFFIN
ENERGY FORM BLACKSTONE METRO CREEK CRANSTON
Energy Input
Natural Gas 6,800 304,400 51,700 35,000
Fuel Oil 4,400 11,700
Electricity to Furnace 18,000 30,000 6,500 9,000
Total 29,200 334,400 69,900 44,000
Energy Output
Steam 305,500 61,000
Electricity 22,100
Total 0 327,600 61,000 0
Net Comparison 29,200 6,800 8,900 44,000
Equivalent Gallons
of Fuel Oil/Dry Ton 19.3 0.8 6.6 96.0
NOTE: All figures are based on 1987/1988 plant records.
Gallons = 3.785 L
Ton «s 0.9072 tonne
-------
TABLE 13
ESTIMATE OF ENERGY REQUIREMENT FOR LEVEL D
(MI LI. I ON Btu/YEAR)
UPP1SR DUFFIN
ENERGY FORM BLACKSTONE METRO CREEK CRANSTON
Energy Input
Natural Gas 6,800 304,400 51,700 35,000
Fuel Oil 4,400 11,700
Electricity for furnace .18,000 30,000 6,500 9,000
Electricity for
conditioning/
dewatering 1,600 76,000 3,300 2,200
TOTAL 30,800 410,400 73,200 46,200
Energy Output
Steam 305,500 61,000
Electricity 22,100
Total 0 327,600 61,000 0
Net Comparison 30,800 82,800 12,200 46,200
Equivalent Gallons
of Fuel Oil/Dry Ton 20.3 9.3 9.0 100.8
NOTE: All figures are based on 1987/1988 plant records.
Gallons « 3.785 L
Ton = 0.9072 tonne
-------
Table 14 shows the energy requirements for Level E. In this analysis,
the energy inputs include all fuel and electricity requirements from
sludge pumping through incineration, including waste-heat and auxiliary
boiler equipment and electricity for general building requirements.
Steam and electricity produced by incineration and used outside the
incineration system are taken as energy output.
This alternative shows a wide range of energy consumption figures for
each unit process, reflecting the variety of technologies employed by
the four facilities. The total energy conumption by the Upper
Blackstone, Metro, and Duffin Creek solids handling trains ranges from
5.3 to 8.2 million Btu per dry ton (5.8 to 9.0 million Btu per dry
tonne) of sludge cake processed.
Energy consumption at the Cranston facility is significantly higher,
primarily due to the auxiliary fuel consumption by the incineration
system.
Based on these figures, a reasonable estimate of total energy
consumption by an energy-efficient solids handling train employing
sludge incineration would be 5 to 9 million Btu per dry ton (5.8 to 10.4
million kJ per dry tonne) of sludge cake processed.
SUMMARY
Based upon this evaluation, the following generaliziations can be made
regarding the energy consumption of a well-operated sludge incineration
facility.
Annual auxiliary fuel consumption within the furnace (Level A)
should be in the range of 7 to 9 gallons of fuel per dry ton
(29 to 38 liters/tonne) of sludge cake processed.
-------
TABLE 14
ESTIMATE OF ENERGY REQUIREMENT FOR LEVEL E
(Btu/dry ton)
ENERGY FORM
UPPER
BLACKSTONE METRO
DUFFIN
CREEK CRANSTON
Energy Input
Natural Gas
Fuel Oil
Electricity for sludge pumping
Electricity for thickening
Electricity for blending & mixing
Electricity for digestion
Electricity for storage
Electricity for conditioning/
dewatering
Electricity for sidestream
treatment
Electricity for combustion
TOTAL
620,000 4,700,000 5,270,000 10,540,000
400,000
20,000
10,000
0
0
0
0
610,000
1,050,000 1,420,000
0
0
440,000
1,190,000
20,000
0
0
1,480,000
20,000
420,000
0
30,000
2,300,000
90,000
0
0
1,100,000 1,890,000 1,190,000 3,350,000
3,040,000 3,730,000 2,300,000 5,610,000
6,240,000 13,210,000 11,460,000 21,920,000
Energy Output
Steam
Electricity
TOTAL
0 4,720,000 6,210,000
0 340,000 0
0 5,060,000 6,210,000
0
0
Net Comparison
6,240,000 8,150,000 5,250,000 21,920,000
Equivalent Gallons of Fuel
Oil/Dry Ton
45
59
38
159
NOTE: All figures are based on 1987/1988 plant records.
Gallons « 3.785 L
Ton «* 0.9072 tonne
-------
If a waste heat recovery system is included in the incineration
system, the incineration system can be a net energy producer if
only auxiliary fuel (no electricity) is considered an energy
input to the system (Level B).
If both auxiliary fuel and electricity are considered energy
inputs to the incineration system, (Level C), an incineration
system with a waste heat recovery system may still be a net
energy producer if operating at maximum efficiency. Under
these conditions, the Metro and Duffin Creek facilities
approach the goal of being a net producer at their current
loading rates. It is possible that, if these facilities were
operating at capacity, the increase in energy efficiency that
results from complete equipment utilization may make the Duffin
Creek and Metro facilities net energy producers under these
conditions.
If the definition of the incineration system is expanded to
include the sludge conditioning/dewatering system (Level D),
the goal of net energy production by the incineration system
does not appear achievable.
Total energy consumption for a solids train utilizing sludge
incineration can vary widely depending on the thickening and
dewatering technologies utilized. Based on the results of this
evaluation, total energy consumption for an energy efficient
solids train may range from 5 million to 9 million Btu per dry
ton (5.8 million to 10.4 million kJ per dry tonne) of sludge
cake processed.
Overall, the evaluation demonstrates that a variety of
technologies can achieve energy-efficient sludge incineration.
Hie most complex systems (Metro and Duffin Creek) proved to be
very energy-efficient under each set of conditions evaluated.
The simplest system (Upper Blackstone) also proved to be very
energy efficient, especially in terms of overall energy
consumption by the entire solids train (Level E).
-------
REFERENCES
1. Proctor & Redfern Group, "Development of a Methodology To
investigate The Cost-Effectiveness of Various Sludge Management
Systems", prepared for the Department of Supply and Services Canada,
January 1988.
2. U.S. Environmental Protection Agency, "Improving Design and
Operation of Multiple-Hearth and Fluid Bed Sludge Incinerators",
July 1986.
3. Draft Regulatory Impact Analysis of the Proposed Regulation for
Sewage Sludge Use and Disposal, November 1988.
4. U.S. Environmental Protection Agency, "Energy Conservation in
Municipal Wastewater Treatment" EPA Contract No. 68-03-2186, Task 9,
March 1978.
5. Water Pollution Control Federation, "Energy Conservation in the
Design and Operation of Wastewater Treatment Facilities? Manual of
Practice FD-2", 1982.
6. Environmental Protection Agency, "Estimating Sludge Management
Costs", October 1985.
7. Environmental Protection Agency, "Sludge Treatment and Disposal",
September 1979.
8. U.S. Environmental Protection Agency office of Water Programs
Operations (WH-546), "Construction Grants 1985 (CG-85)", EPA Report
No. 430/9-84-004, July 1984.
9. William F. Owen, "Energy in Wastewater Treatment", Prentice-Hall,
Inc., New Jersey, 1982.
-------
I. GENERAL INFORMATION
Address:
Phone Number:
Contact:
Consultant:
Year Began Operation:
Design Average Flow:
APPENDIX A
METROPOLITAN WATER POLLUTION
CONTROL FACILITY
Metropolitan Wastewater Treatment Plant
2400 ChiIds Road
St. Paul, MN 55106
(612) 772-7222
Nadim Shamat
Process Engineer
Sludge Processing & Incineration
Toltz, King, Duvall, Anderson & Assoc., Inc.
St. Paul, MN
Walter Thorpe, Project Engineer
Original plant - 1938
Latest upgrade - 1978 to 1983
Primary System 250 mgd
Secondary System 250 mgd
Design Peak Flow (Max Day): Primary System 655 mgd
Secondary System 375 mgd
1987 Average Flow:
1987 Max Day Flow:
1987 Average Influent CBOD: 198 mg/1
1987 Average Influent TSS: 190 mg/1
1987 Average Effluent CBOD: 11 mg/1
1987 Average Effluent TSS: 12 mg/1
Permitted Effluent CBOD:
201 MGD
approximately 700 MGD
Permitted Effluent TSS:
Plant Overview:
October to May 24 mg/1
June to September 18 mg/1
30 mg/1
The liquid treatment train includes screening, aerated grit removal, primary
settling, biological secondary treatment, final settling, chlorination, and
dechlorination prior to discharge to the Mississippi River. Solids handling
processes include flotation thickening of waste activated sludge, gravity
-------
thickening of primary sludge, separate storage of thickened waste activated
sludge (TWAS) and thickened primary sludge, thermal conditioning of the
thickened sludge, sludge dewatering using roll presses, sludge incineration,
and ash disposal by landfilling. A small amount of sludge is hauled
off-site for disposal. Diaphragm filter presses and vacuum filters are also
available for sludge dewatering. At this time, the roll presses are the
primary dewatering equipment and the vacuum filters and filter presses serve
as backup units.
A schematic of the solids handling system is attached. Sludge quantities
presented in this schematic are based on 1987 plant operating data. These
quantities are taken directly from plant operating records. For some unit
processes, there is a minor discrepency between the total input quantities
and the total output quantities., These minor discrepencies are attributed
to sampling variations.
II. UNIT COSTS
ITEM
UNIT COST
Labor ($/hour) *
$18.00 (operations)
$22.00 (maintenance)
Polymer ($/#)
$.048/wet #
$.658/dry #
$.37/100 gal
$. 037Aw_hr
City Water ($/100 gal)
Electricity ($Aw-hr)
No. 2 Fuel Oil ($/gal)
Natural Gas ($/100 cf)
$.90/gal
$2.50/1000 cf
Chlorine ($/ton)
$177.63/ton
* Includes benefits
-------
Q 3.2* MOD
OVERFLOW
\D
<£>
TSS 239 mg/1
ROLLATCTO
GRAVITY
THICKENER
Q .439 MOD
TS 8.3 ipd
TS 4534 mg/1
167.6 DRY Ipd
518.3 WET tpd
32.3% IS
174.4 DRY ipd1
6.2% TS
FIjOAT SLUDGI-
Q .78 mgd
TS 83.6 tpd
TS 2.57%
TSS N/A
TSS N/A
182.1 ipd
SLUDGE
Q .145 MGD
TS 75.5 Ipd
TS 12.5%
TSS N/A
TSS N/A
Q ,
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III. SLUDGE TRANSFER PUMPING
Transfer Pump
No.
Units
HP
Hours/Day
Of Operation
KW-HR/
Day**
Annual
Cost
Waste Activated Sludge
to Thickening
10
2
total
operating*
75
24
2,685
$ 36,300
Primary Sludge Pumps
to Thickening
22
6
total
operating*
75
24
8,056
$108,800
Sludge Transfer Pumps
to Holding Tanks
20
8
total
operating*
75
24
10,742
$145,100
Sludge Transfer Pumps
to Thermal Conditioning
- to reactor
14
5.7
total
operating*
20
24
2,041
$ 27,600
- to decant tanks
12
3.8
total
operating*
60
24
4,082
$ 55,100
Sludge Transfer Pumps
to Dewatering
8
2.3
total
operating*
30
24
1,235
$ 16,700
TOTAL
28,840
$389,600
* Under average conditions
** Based on connected horsepower
IV. WASTE ACTIVATED SLUDGE THICKENING
1. GENERAL INFORMATION
Technology: Dissolved Air Flotation Thickeners (DAF)
Date Installed: 1979
Manufacturer: Eimco
No. of Units: 16
under average conditions, operate:
annual 9 units (1987 records)
summer 8 units
winter 16 units
-------
2. Design Information
Unit Diameter (feet): 55 feet
Sidewater Depth (feet): 10 feet
Unit Surface Area
(square feet): 2,250
Total Surface Area
(square feet): 36,000
Solids Loading Rate
(psf/day): 18 #/sf-day
Air:Solids Ratio: .02 - .04
Unit Capacity (dry tpd): 20
3. Operating Information (Based on 1987 records)
WAS to Thickening: 3.28 mgd
0.69% TSS
94.4 tpd TSS
0.78% Total Solids
107 tpd TS
Note that the DAF influent includes the waste sludge from the RBC
sidestream treatment system.
Average Loading Rate
(psf/day): 10.8 # TS/sf-day
9.3 # TSS/sf-day
Typical Sludge Volume
Index (SVI): 150
Average Pressurized
Effluent Recycle Flow: 15.6 mgd
Hydraulic Loading: W.A.S. Feed 243 gpnyAtfut (3.28 mgd total)
Recycled Effluent 1179 gpm/unit (15.62 mgd total)
Total 1422 gpm/unit (18.9 mgd total)
Average Hydraulic Loading
(sludge + recycle): 960 gal/sf-day
Air Pressure (psig): 74 psig
Air Flow (cfm): 20,000 cfnyunit
Air to Solids Ratio
(# air/# solids): average .044
-------
Typical depth of
Sludge Blanket:
30 inches
Chemical Addition
(type & amount):
Have ability to add polymer, but are currently
not adding any chemical.
Solids Capture:
93%
Process Output:
Overflow Stream
2.4 mgd
639 mg/1 TSS
6.4 tpd TSS
2039 mg/1 TS
20.4 tpd TS
Overflow stream can be used as dilution (cooling) water for the Zimpro
sidestream, returned to the gravity thickeners, or added to the
secondary influent stream.
Bottom sludge is pumped to the gravity thickeners.
4. COST INFORMATION
A. Capital
Facility Planning Estimate of Construction Cost: $13,277,000
This cost was taken from the Toltz, King, Duvall, Anderson, & Assoc.
Inc. study entitled Sludge Processing And Disposal At The Metropolitan
Wastewater Treatment Plant, Volume II, January 1974. This cost is
indexed at an ENR of 210(h If updated to September 1988 ENR of 4535,
the estimated construction cost would be $28,670,000.
Actual Capital Cost (bid + change orders):
Facilities were constructed from 1978 to 1982 at a cost of $14,079,900.
Costs updated to September 1988 ENR of 4535 are as follows:
equipment $ 4,150,500
structural $ 15,828,400
Total $ 19,978,900
Float Sludge
0.78 mgd
2.,6 % TS
83.6 tpd TS
Float sludge is pumped to the sludge storage or holding tanks.
Bottom Sludge
0.04 mgd
3.1 % TS
5.2 tpd TS
-------
These costs includes the installation of 16 DAF thickeners,
construction of thickener galleries and service areas, pipe tunnels,
and installation of appurtenances such as chemical, electrical, HVAC,
and odor control systems. For additional project description, see the
appended advertisement for bids for Project No. 400. (Note that Project
No. 400 includes construction of an RBC return liquor treatment
facility. This cost has been broken out and included in Section XIII
of this report.)
B. O&M (Based on 1987 operations & maintenance expense reports)
ITEM CONSUMPTION ANNUAL
LEVEL COST
Operations Labor 47.1 hr/day $ 309,300
Maintenance Labor 46.6 hr/day $ 373,800
Electricity 8,318,000 kw-hr/year $ 323,700
Chemicals None
Contracted Services (maintenance) $ 3,500
Materials & Supplies
- operations $ 100,700
- maintenance $ 139,700
Total $1,250,700
Note that the DAF thickener area and the RBC sidestream treatment
system share an odor control system. The O&M costs for this odor
control system are split between the DAF O&M costs presented above and
the RBC O&M costs presented in Section XIII of this report. For
further description of the odor control system, see Section XV of this
report.
Facilities Planning Estimate Of Annual O&M Costs: $422,000
Taken from previously referenced Toltz, King, Duvall Anderson & Assoc.
Inc. January 1974 study.
-------
5. ENERGY CONSUMPTION
Equipment
Float/Underflow
Sludge Collectors
16
13.5
total
operating
24
3
730
Float Sludge Draw Off Pump
8
operating
24
25
3,580
Underflow Sludge Draw Off Pump
16
13.5
total
operating
24
30
7,250
Overflow Return Pumps
3
1
total
operating
24
30
540
Polymer Feed Pumps
16
0
total
operating
—
—
—
Recycle Pumps
16
13.5
total
operating
24
100
24,170
Odor Control Equipment**
152
3,640
TOTAL
39,910
* Based on connected horsepower.
** For further information, see Section XV B of this report.
Electrical Requirements as Projected
in Facilities Planning (kw-hr/yr): Not available
Actual Annual Electrical
Requirements (kw-hr/day): 39,910 based on connected horsepower
22,790 based on metered values
Note: The metered electrical use includes pumping of the thickened waste
activated sludge to the sludge storage tanks.
V. GRAVITY THICKENING
1. GENERAL
Type of Sludge: Primary only
Thickener overflow is returned to the head of the plant or sent to the
sidestream treatment unit (See Section XIV). Thickener underflow is
pumped to the sludge holding or sludge storage tanks.
-------
2. DESIGN INFORMATION
No. Tanks: 6
Diameter (feet): 65
Depth (feet): 10
unit Surface Area (square feet):
Total Surface Area (square feet):
Solids Loading (psf/day):
3. OPERATING INFORMATION (Based on
Input Breakdown:
Primary Sludge
Rollate
Dilution water
DAF Underflow
Total
Percent Solids of Sludge Feed:
Average Loading Rate (#/sf/day):
Peak Loading Rate (#/sf/day):
Minimum Overflow Rate (gal/sf/day):
Average Overflow Rate (gal/sf/day):
Average Depth of Sludge Blanket:
Odor Control:
Output Breakdown (1987 records):
Underflow
3,300
20,000
20
1987 data)
6.15 mgd
148.6 tpd TS
0.44 mgd
8.2 tpd TS
1.85 mgd
5.2 tpd TS
0.04 mgd
5.2 tpd TS
8.5 mgd
167.2 tpd TS
0.47%
17 # TS/sf/day
26 # TS/sf/day
350 gal/sf/day
430 gal/sf/day
4.7 feet
Chlorine addition
(tanks are not covered)
0.462 mgd
6.67 % TS
128.5 tpd TS
-------
Overflow 8.0 mgd
395 mg/1 TSS
13.2 tpd TSS
1433 mg/1 TS
47.8 tpd TS
The values presented above are taken directly from the 1987 operation
summary sheets. The plant staff reports that these figures are not
accurate due to flow metering problems and difficulties obtaining a
representative sample for solids analysis. For this reason, the
figures presented above are not displayed in the solids handling
schematic shown on page 3 of this report. Instead, the output from the
gravity thickening process is calculated as follows (reference solids
handling schematic for clarification):
1. Gravity thickened sludge that by-passes the thermal conditioning
system.
Sludge feed to dewatering 182.1 tpd TS
Decant tank underflow 75.5 tpd TS
Gravity thickened sludge that by-
passes the thermal conditioning system 106.6 tpd TS
2. Gravity thickened sludge that is fed to the thermal conditioning
system.
Zimpro reactor feed 141.1 tpd TS
DAF thickener float sludge 83.6 tpd TS
Gravity thickened sludge fed to the
thermal conditioning system 57.5 tpd TS
Total gravity thickened sludge underflow.
Sludge that by-passes the thermal
conditioning system 106.6 tpd TS
Sludge feed to thermal
conditioning system 57.5 tpd TS
Total gravity thickener underflow 164.1 tpd TS
4. COST
A. Capital
Facility Planning Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders):
The gravity thickeners were not part of the recent plant modifications.
These units were part of the original treatment facility. Original
-------
capital costs for these older areas of the plant are not available. It
is estimated that the gravity thickening facilities would have a
construction cost of approximately $5,900,000 in 1988 dollars.
B. O&M (Based on 1987 operations and maintenance expense reports)
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
Maintenance Labor
Chemical Addition (chlorine)
Plant Water
Electricity
Contracted Services
757 hr/month
969 hr/month
88 tons/year
$ 163,500
$ 255,900
$ 15,000
0 gpd
857,600 kw-hr/year*
$ 36,700
- operations
- maintenance
Materials & Supplies
- operations
- maintenance
S 7,900
$ 3,100
$ 8,800
$ 36,500
Total
$527,400
* The 1987 Region II (see subsequent below) Electrical Usage Summary Sheet
showed a metered electrical usage of 643,200 kw-hr/year through October
1. This figure was projected for the entire 12 months to be 857,600
kw-hr/year (643,200/.75).
Note that for in-house organizational purposes, the Metro staff divides the
solids handling processes into two regions as follows:
Region I - Flotation and gravity thickening, sludge storage, thermal
conditioning, and sidestream treatment systems.
Region II - Dewatering, scum, and incineration systems.
5. ENERGY CONSUMPTION
Annual Electrical Requirements (kw-hr/yr): 857,600 kw-hr/year (metered)
Note: The metered electrical use includes pumping of the gravity thickened
sludge to the sludge storage tanks.
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VI. SLUDGE STORAGE TANKS
1. GENERAL INFORMATION
These tanks are designed such that thickened sludge from the DAF units and
the gravity thickeners can be input to the tanks and the tanks can
discharge to the dewatering process or to other sludge storage or holding
tanks. Under normal operation,, all the thickened waste activated sludge
and a portion of the thickened primary sludge is input to these tanks and
the tanks discharge to the thermal conditioning process (see process
schematic on page 3). The tanks are covered and are air mixed.
2. DESIGN INFORMATION
No. Tanks: 8
Length (feet): 135
Width (feet): 30
Depth (feet): 25
Unit Volume (million gal): 0.75 mg
Total Volume (million gal): 6.0 mg
3. OPERATING INFORMATION
TWAS/Primary Sludge Ratio: The storage tanks typically receive all the
TVJAS and a portion of the thickened primary
sludge. The 6 MGD capacity equals about 7
days of sludge storage.
4. COST INFORMATION
A. Capital
Facility Planning Estimate of Capital: $4,900,000
This cost was taken from the Toltz, King, Duvall, Anderson, & Assoc.
Inc. study entitled Sludge Processing And Disposal At The Metropolitan
Wastewater Treatment Volume II, January 1974. This cost is
indexed to an ENR of 2100. If updated to September 1988 ENR of 4535,
the estimated construction cost would be $10,582,000.
Actual Capital Cost (bid + change orders):
Included under Project No. 402. Reference Section VII of this report.
-------
B. O&M (Based on 1987 operations & maintenance expense records)
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
Maintenance Labor
Chemical Additions
(odor control)
Electricity
Contracted Services
(maintenance)
Materials & Supplies
- operations
- maintenance
50.9 hr/day
47.6 hr/day
2,864,000 kw-hr/year **
$ 334,300 *
$ 382,100 *
$ 28,500
$ 110,200
$ 700
$ 17,200
$ 32,300
Total
$ 905,300
* Note that the labor costs presented here are very high for a sludge
storage facility. It is likely that some of the labor costs charged to
the storage facility account should have actually been charged to other
solids handling processes.
** This metered value was obtained from the 1987 Region II Electrical Usage
Summary Sheet.
Facilities Planning Estimate Of Annual O&M Costs: $105,000
Taken from previously referenced Toltz, King, Duvall Anderson & Assoc.
Inc. January 1974 study.
5. ENERGY CONSUMPTION
Rated HP of Air Compressors: 150
No. of Compressors: 10
Typical Hours of Operation: 24 hour/day
Annual Electrical Requirements
(kW-hr/yr): 9,802,400 (calculated from connected load)
2,864,000 (metered)
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VII. THERMAL CONDITIONING SYSTEM
1. GENERAL
Thickened waste activated sludge and a portion of the thickened primary
sludge are thermally conditioned in a Zimpro system. Sludge flows through a
grinder, low pressure pump, and then a high pressure pump before entering
the heat exchanger and reactor portions of the thermal conditioning system.
High pressure steam and air are added to the sludge in the thermal reactor.
Conditioned sludge flows from the reactor into decant tanks, which act as
gravity thickeners to conentrate the sludge. Decant tank overflow is
treated at the RBC return liquor treatment system. The system's heat
exchangers and reactors are washed with a dilute nitric acid after about 300
hours of operation.
2. DESIGN INFORMATION
No. Reactors:
Unit Capacity (gpm sludge):
Unit Capacity (dry tpd @ 4%
Reactor Detention Time:
No. Decant Tanks:
Diameter (feet):
Sidewater Depth (feet):
Heat Exchanger Material
of Construction:
3. OPERATIONAL INFORMATION
Operating Temperature
and Pressure:
Operating Flow:
Reactor input:
8
175
TSS): 40
15 minutes
4
60
20
316 L Stainless Steel
(based on 1987 records)
375 F and 325 psi
average 3.8 units operating at
170 gpm sludge feed/unit
.928 mgd
33,685 mg/1 TSS
130.4 tpd TSS
3.65 % TS
141.1 tpd TS
74.4 % volatile solids
42,640 mg/1 COD
pH 6.2
-------
Reactor Output: 20,695 mg/1 TSS
80.1 tpd TSS
3.36 % TS
130.0 tpd TS
72.6 % volatile solids
41,720 mg/1 COD
pH 5.0
Note that reactor input solids (141.1 tpd TS) do not equal reactor
output solids (130.0 tpd TS). This minor discrepency (8.5%) is
attributed to sampling variations.
Steam input:
An average of 15,922 lb/hour of steam is fed to the thermal conditioning
system. This equates to an average steam input of 4190 #/hour/reactor,
or 8 gpny'reactor.
Solids Solubilized:
Decant Input:
Decant Output:
Underflow
50.3 tpd
0.928 mgd
20,695 mg/1 TSS
80.1 tpd TSS
3.36 % TS
130.0 tpd TS
72.6 % volatile solids
pH 5.0
0.145 mgd
12.5 % TS
75.5 tpd TS
64.8 % volatile solids
pH 5.4
Overflow 0.78 mgd
15,372 mg/1 TS
50 tpd TS
8,424 mg/1 BOD
27.4 tpd BOD
18,924 mg/1 COD
Note that the decant input solids (130.0 tpd TS) do not equal reactor
output solids (125.5 tpd TS). This minor discrepency (3.6%) is
attributed to sampling variations.
4. COSTS
A. Capital
Facility Planning Estimate of Capital: $17,861,000
This cost was taken from the Toltz, King, Duval1, Anderson, & Assoc.
Inc. study entitled Sludge Processing And Disposal At The Metropolitan
-------
Wastewater Treatment Plant, Volume II, January 1974. This cost is
indexed to an ENR of 2100. This cost estimate included the construction
of the thermal conditioning building, the decant tanks, and the heat
treatment equipment. If updated to September 1988 ENR of 4535, the
estimated construction cost would be $38,600,000.
Actual Capital Cost (bid + change orders):
The building to house the thermal conditioning system was constructed
from 1977 to 1982 at a cost of $16,397,900. This project (Project No.
402) included the construction of the thermal conditioning building
(approximately 275 ft * 103 feet; 3 story), four decant tanks, eight
sludge storage tanks, and a building to house appurtenances for the
sludge storage system (approximately 275 ft * 35 ft; 2 story). The
thermal conditioning system was installed from 1980 to 1983 at a cost of
$12,282,500 (Project No. 401).
Total project costs updated to September 1988 ENR of 4535 breakdown as
follows:
equipment $ 10,972,000
structural $ 26,400,000
Total $ 37,372,000
For additional project description, see appended advertisement for bids
for Project No. 401 and Project No. 402.
B. O&M (Based on 1987 operations & maintenance expense records)
ITEM CONSUMPTION ANNUAL
LEVEL COST
Operations Labor 178.4 hr/day $ 1,172,000
Maintenance Labor 47.1 hr/day $ 378,300
Chemicals (acid) $ 22,700
Electricity 7,645,000 kw-hr/year* $ 311,100
Contracted Services
(maintenance) $ 17,300
Materials & Supplies
- operations $ 34,600
- maintenance $ 204,700
Total $ 2,140,700
* This metered value was obtained from the 1987 Region II Electrical Usage
Summary Sheet.
Note: The electrical cost for the sludge transfer pumping from the storage
tanks to the thermal conditioning system is included in this table.
-------
For odor control purposes, odorous off-gases from the reactor area and the
decant tanks is used as combustion air in the MHF system. The electrical
cost to convey this odorous air stream to the incineration system is
included in the above table.
5. Energy
Equipment
HP
No.
Units
Hrs/Day
KW-HR/Day
Sludge Grinders
2
163 (total)
240
Low Pressure Pumps
20
14
(6 standby)
163 (total)
2,440
High Pressure Pumps
60
12
(4 standby)
82 (total)
3,670
Process Air Compressors
125
10
82 (total)
7,650
Underflow Sludge Pumps
25
8
15 (total)
280
Decant Overflow Pumps
20
4
30 (total)
450
Scum Pumps
10
4
24 (total)
180
Total
14,900
Annual Electrical Requirements (kw-hr/yr): 5,438,500 (calculated)
7,645,000 (metered)
Note that the metered electrical usage exceeds the calculated electrical
usage. This is because some sources of consumption such as the fans that
transfer odorous off gases to the MHF system and the building lighting are
not accounted for in the above table.
VIII. SLUDGE HOLDING TANKS
1. GENERAL INFORMATION
These tanks are designed to accept thickened sludge from the gravity
thickeners, flotation thickeners, sludge storage tanks, or decant tanks and
discharge sludge to the dewatering process or to sludge storage tanks.
Under normal operation, these tanks receive a mixture of thermally
conditioned sludge from the decant tanks and thickened primary sludge from
the gravity thickeners. Air mixing is provided.
2. DESIGN INFORMATION
No. Tanks: 2
Length: 64 feet
Width: 36 feet
Sidewater Depth: 15 feet
-------
Unit Volume: 0.26 mgd
Total Volume: 0.52 mgd
3. COST INFORMATION
A. capital
Facility Planning Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders):
These tanks are part of the original vacuum filter sludge dewatering
system. Original capital costs for these older areas of the plant are
not available. It is estimated that the construction cost for these
tanks would be approximately $100,000 in 1988 dollars.
B. O&M
Included in Section IX O&M costs.
4. ENERGY REQUIREMENTS
Equipment No. Units Hr/Day HP KHW/DAY
Air Compressors 4 24 30 2,148
* Included in the metered electrical usage for sludge dewatering.
IX. SLUDGE DEWATERING
Note: Three dewatering technologies; roll presses, filter presses, and
vacuum filters, are available at the Metro facility. In 1987, roll presses
were used as the primary dewatering device. The vacuum filters were not
operated for a significant period of time. The filter presses were
operated for significant periods of time in the months of February, March,
April, and May. Information and operating data for both the roll presses
and filter presses will be presented here.
A. Roll Press Dewatering
1. GENERAL INFORMATION
Technology: Roll Presses
Date Installed: 1982
Manufacturer: Ingersoli-Rand
-------
2. DESIGN INFORMATION
No. Presses: 4
Diameter (feet): 3
Length (feet): 10
Unit Capacity: 90 dry tpd
Feed Solids: 6%
Cake Solids: 35%
Solids Recovery: 95%
Polymer Dose: 5 to 10 lb/dry ton
3. OPERATING PARAMETERS (Based on 1987 operating data)
Sludge Feed:
In normal operation, a mixture of heat conditioned TOAS, heat
conditioned primary sludge, and primary sludge that did not receive
heat conditioning is fed to dewatering. At times, all of the sludge
by-passes the heat conditioning system and goes directly to dewatering.
Average feed to Dewatering:
174.4 dry tpd (calculated)
6.2 % TS
69.0 % volatiles
Gravity Thickened Sludge/ Decant Ratio:
- By volume 3.1/1
- By Mass 1.6/1
Heat Value of Cake: 10,500 Btu/# VSS
Average No. Units
In Service: 2.3
Polymer Type: Nalco 7287
Polymer Dosage: 1987 average 18.1 dry #/ton
As the percent of thermally conditioned sludge increases, the polymer
dosage increases.
Frequency of Testing to Optimize Polymer Dosage:
Operators adjust the polymer feed rate once per shift based on vat
pressure.
-------
Other Chemicals:
Capability to apply lime and ferric chloride exists, but is not
necessary.
Cake Product (1987 data):
518.3 wet tpd
167.6 dry tpd
32.3 % solids
70 % volatiles
Solids Capture: 95.3%
Roll Pressure: Ranges 100 - 2000 lbs/linear inch
Sidestream Strength: .439 mgd
(Rollate) 4,533 iug/1 TS
8.3 dry tpd
Odor Control:
Odorous gases from the dewatering area are conveyed to the incineration
area and used as combustion air.
Historical data provides the following summary of roll press
performance for various sludges.
Heat-Treated And
Primary Sludge Primary Sludge
% Solids of Feed 6.2% 5.7%
% Solids of Cake 31.9% 31.4%
Polymer Dosage 19.0 8.9
(dry #/dry ton solids)
4. COST INFORMATION
A. Capital
Facilities Planning Estimate of Capital: $4,993,000
This cost was taken from the Toltz, King, Duvall, Anderson, & Assoc.
Inc. study entitled Sludge Processing And Disposal At The Metropolitan
Wastewater Treatment Plant, Volume II, January 1974. The cost is
indexed to an ENR of 21007 At the time of this report, the recommended
plan was to expand and upgrade the existing vacuum filtration
dewatering system. This cost estimate included 8 new vacuum filters,
-------
construction of an expansion to the dewatering building, and necessary
electrical and mechanical work. If updated to September 1988 ENR of
4535, the estimated construction cost would be $10,780,000.
Actual Capital Cost:
The roll presses were installed in the original sludge dewatering
building. Four vacuum filters were removed and replaced with four roll
presses. Removal of the vacuum filters and preparation of the building
for the roll presses was completed under Project No. 405 at an
approximate cost of $172,000. Installation of the roll presses was
performed under Project No. 404 at a cost of $3,685,900.
Total project costs updated to a September 1988 ENR of 4535 breakdown
as follows:
equipment $3,994,900
structural $ 778,400
Total $4,773,300
For additional project description, reference appended advertisement
for bids for Project No. 404 and Project No. 405.
B. O&M (Based on 1987 operations and maintenance expense records)
ITEM CONSUMPTION ANNUAL
LEVEL COST
Operations Labor
Maintenance Labor
Polymer
Other Chemicals (Lime)
Electricity
Materials & Supplies
- operations
- maintenance
Contracted Services
- operations
- maintenance
175.7
75.2
18.2
hr/day
hr/day
#/dry ton
4,600,000 kw-hr/year*
$
$
$
$
$
$
$
$
$
1,153,600
603,700
767,700
12,900
169,200
11,000
74,500
0
4,800
Total
$ 2,797,400
* Based on projected values presented in the 1987 Region III Electrical
Usage Summary Sheets.
Facilities Planning Estimate Of Annual O&M Costs: $612,000
Taken from previously referenced Toltz, King, Duvall Anderson & Assoc. Inc.
January 1984 study.
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5. ENERGY CONSUMPTION
Equipment HP NO. UNITS* HRS/DAY KW-HR/DAY
Roll Presses
60
2.3
24
2470
Sludge Feed Pumps
30
2.3
24
1235
Filtrate Pumps
20
1.5
24
540
Polymer Feed Pumps
2
2.3
24
80
Total
4325
* Have 4 of each piece of equipment available. This column shows the
average number of units in operation in 1987.
Annual Electrical Requirements (kw-hr/year):
1,578,600 kw-hr/year (Based, on connected horsepower)
4,600,000 kw-hr/year (Based on projections by plant staff)
Note that the metered electrical usage includes electricity used to convey
the odorous gas stream to the incineration system for odor control
purposes, building lighting, and other miscellaneous sources of
consumption.
B. Filter Press Dewatering
1. GENERAL
The filter press units serve as a back-up technology to the roll presses.
In 1987, the filter presses were operated for significant periods of time
during the months of February, March, April, and May. All operating data
presented in this section will be based on this demonstration period.
During this period, the presses were used in conjunction with the roll
presses. The filter presses were used exclusively to dewater thermally
conditioned sludge rather than a thermally conditioned/gravity thickened
mixture.
2. DESIGN INFORMATION
Type of Press: Diaphragm type with a water-compressed
diaphragm (Lasta)
No. Presses: 8
Filter Service Area Per Unit: 1,666 square feet
Plate Size (approximate): 1,500 mm * 1500 mm
Discharge Volume Per Press: 39 cubic feet
-------
Cake Wet Density (approximate):
Cycle Time:
Unit Capacity (approximately):
No. Surge Bins:
Surge Bin Capacity:
70 pounds/cubic foot
24-30 minutes
30 dry tons per day
8
800 cf/unit
3. OPERATING PARAMETERS (Based on 1987 data)
Note: Because these units were only operated from February through May in
1987, "average" operating parameters will be presented in two ways: (1) an
annual (365) day average; and (2) a four month (February to May) average.
Sludge Feed:
Thermally conditioned sludge
Average No. Units in Operation:
Four month average
1.5
Annual average
0.5
Average No. Press Cycles Per Day:
Four month average
54
Annual average
18
Feed Sludge
Four Month
Annual
Average
Average
Flow
.047 mgd
.016 mgd
Total Solids
11.9 %
11.5 %
Total Solids
23.3 dry tpd
7.7 dry tpd
Sidestream (Pressate)
Four Month
Annual
Average
Average
Flow
.03 mgd
.011 mgd
TSS
2878 mg/1
2398 mg/1
TSS
.36 dry tpd
.11 dry tpd
Total Solids
47 %
48 %
Volatile Solids
67.1 %
66.6 %
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Sludge cake
Four Month
Average
Annual
Average
Wet Cake
65.98 tpd
21.8 tpd
Dry Cake
30.04 tpd
9.9 tpd
% Solids
45.5 %
45.5 %
Volatile Cake
20.55 tpd
6.8 tpd
% Volatiles
68.4 %
68.7 %
4. COST INFORMATION
A. Capital
Facilities Planning Estimate of Capital: See Section IX A.
Actual Construction Cost:
An addition to the existing dewatering building was constructed from
1977 to 1981 to house the filter press units (Project No. 406) at a
cost of $12,800,700. The filter press units (8 units) were installed
from 1980 to 1983 (Project No. 401) at an approximate cost of
$4,094,200. Total project costs updated to a September 1988 ENR of
4535 breakdown as follows:
equipment $ 2,882,700
structural $ 14,435,600
Total $ 17,318,300
For additional project description, reference the appended
advertisement for bids for Project No. 401 and Project No. 405.
B. O&M
The filter presses were operated for such a short period of time in
1987 that good O&M cost information could not be obtained. Cost
information obtained from this short testing period would not be
representative of a full year of operation.
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X. GRIT, SCREENINGS, AND SCUM DISPOSAL
GRIT DISPOSAL: Landfilled
SCREENINGS DISPOSAL: Landfilled
SCUM AND GREASE DISPOSAL:
Scum is pumped from the primary tanks to 3 skimming tanks where it is
separated from the transport water. Scum is decanted and heated in a
decant hopper. Decanted scum is pumped at 1500 gal/hour to preparatory
units where the incinerator feed pumps are located. The preparartory
system includes "Muffin Monster" maceration prior to incineration. Each
incinerator has 2 ports on the combustion hearth that can accept 60 to 100
gal/hour of scum. The scum temperature must be maintained at 180 F to 190
F as it passes through the transport system. Scum entering the furnace
must be metered carefully to prevent wild temperature fluctuations within
the furnace. Operator communication and tight control of the sludge feed
and excessive air supply are necessary to maintain control of the furnace
as sludge is pumped into the system. The decanted scum/grease heating
value is about 15,000 Btu/liquid f.
XI. INCINERATION
1. GENERAL INFORMATION
Technology:
Date Installed:
Multiple Hearth Incineration
2 units in 1982
1 unit in 1972
3 units in 1968
1 unit in 1952 (retired)
3 units in 1938 (retired)
Manufacturer:
No. of Units:
2 - 1982 units: BSP
3 - 1968 units: BSP (1 with heat recovery)
1 - 1972 unit : Nichols (with heat recovery)
6 (2 of which are in reserve capacity)
Note: As part of the 1983 plant upgrade, 2 new units equipped with heat
recovery were installed and 2 of the 4 existing units were refurbished and
equipped with heat recovery.
Diameter:
22 feet
2. DESIGN INFORMATION
No. of Hearths Per
Unit: 8+0 hearth afterburner
Note that no auxiliary fuel is generally used in the afterburner chamber.
The cake feed by-passes the zero hearth. A large drophole allows the
sludge to drop directly to HEARTH No. 1 Hearths No. 3 and 4 are double the
-------
normal hearth depth to insure complete combustion by providing additional
mixing of the volatiles and combustion air at combustion temperatures.
Hearth Area Per unit (excluding afterburner): 2,100 square feet
Wet Solids Loading:
- average 11 psf/hour
- maximum 15 psf/hour
Approximate Unit Capacity (30% to 45% cake solids):
- average 60 - 70 dry tpd
- maximum 80 - 90 dry tpd
Air Supply
- Combustion Air (max) '760 lb/min
- Cooling Air (max) 630 lb/tain
- Excess Air Ratio (min) 75 %
Afterburner Data:
- temperature 1200 - 1400 F
- residence time 1.4 seconds
3. OPERATING PARAMETERS
Operation Schedule:
24 hr/day
7 day/week
Cake Feed (based on 1987 data):
Total Cake Produced On-Site:
Plate & Frame Filter Press Cake
Roll Press Cake
Vacuum Filter
Total
Cake Hauled Off-Site
For Disposal *
Cake To Incineration
9.9 dry tpd
167.5 dry tpd
0.1 dry tpd
177.5 dry tpd
7.6 dry tpd
(23.1 wet tpd)
169.9 dry tpd
(517 wet tpd)
*In 1987, a small amount of cake was disposed of off-site to complete a
three year agreement signed in 1985. This cake is lime stabilized and
land applied at area farms. In 1985, there was still some question as
to the ability of the incineration system to dispose of all of the
Metro sludge 365 days per year. Therefore, the Metropolitan Sewer
Board entered into a three year agreement to land apply some sludge at
-------
area farms as a safety valve in case of an emergency shutdown of the
incineration system. During this three year period, the incineration
system has demonstrated that it can handle all sludge production
without requiring a reserve disposal option. As a result, the land
application contract was not renewed and all sludge production was
processed by the incineration system in 1988.
Average Loading Rate: 517 wet tpd total
2.53 dry ton/hour/unit
5060 dry #/hour/unit
The staff prefers to operate each furnace at about 75 percent capacity.
This allows some excess capacity to provide a buffer against fluctuations
in daily sludge production and to allow short term maintenance shutdowns.
Average Hours Of Operation: 66.9 hours/day
No. Units typically in Operation: 2.8 average
Speed of Rabble Arms: 50 rev per hour
Percent Excess Air: average 207% excess air
14% oxygen concentration in flue gas
Average Wet Solids Loading: 7.35 psf/hour
Average Volume of Shaft
Cooling Air Returned As Consumption Air: None
Total Air Feedrate: 22,000 to 23,000 cfnv^incinerator
Air from the dewatering area, the sludge holding tanks, and the Zimpro
decant tanks is used as combustion air in the furnaces. Typical air
volumes are as follows:
Sludge holding tanks 6,000 cfm
Zimpro decant tanks 3,000 to 4,000 cfm
Dewatering Area 40,000 to 50,000 cfm
The plant staff is currently installing hoods over the dewatering
equipment to capture the odorous gases emitted by the dewatering
process. This will isolate the odorous gas stream from the building
air supply, thereby significantly reducing the air volume which must be
treated for odor control. This will significantly reduce the 40,000 to
50,000 cfm of air flow from the dewatering area that is currently used
as combustion air in the incineration system. The reduction in air
flow from the dewatering area will free up son© air capacity in the
incineration system and allow the plant staff to utilize odorous gases
from other process areas (scum hoppers find holding tanks) as combustion
air.
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Temperature Profile of incinerator (degrees F):
* Hearth 0 1120
* Hearth 6 500
Hearth 1 1140
* Hearth 7 250
* Hearth 2 1450
Hearth 8 150
Hearth 3 1600
* Hearth 4 1030
Hearth 5 840
* These hearths have 2 burners/hearth.
All other hearths have no burners.
Ash Fusion Temperature: 1900 F
Operation Guidelines:
In a non-autogenous incineration system, the major operation control is
the input of auxiliary fuel to maintain combustion temperatures. In an
autogenous system such as the Metro system, the major operation control
is the input of combustion air to the furnace. The furnace temperature
profile is controlled by varying the combustion air supply. The air
supply can be targeted for any hearth or any combination of hearths.
Each furnace is loaded at about 75 percent capacity under average
conditions to accomodate short term fluctuations in sludge production
and to allow for the feeding of a drier sludge that would require more
combustion/cooling air at the same wet loading rate. Operators strive
to maintain a combustion hearth temperature of 1600 F to allow complete
combustion and avoid the formation of clinkers.
Maintenance Schedule:
The Metro staff has implemented a very effective maintenance program
aimed at discovering and correcting minor problems before they become
major problems. Each month, the entire dewatering and incineration
system is taken out of service for an intense 16 hour maintenance
overhaul. All equipment and instrumentation are reviewed during these
shutdowns. Once each year, the entire solids handling train is taken
out of service at once for a more detailed maintenance inspection.
This annual shutdown is scheduled for the summer months when sludge
production is low. These shutdowns are possible because the solids
handling system has been designed with a reasonable amount of sludge
storage and excess capacity.
-------
4. COST INFORMATION
A. Capital
Facilities Plan Estimate of Construction Cost: $6,444,000
This cost was taken from the Toltz, Duvall, Anderson, & Assoc. Inc.
study entitled Sludge Processing And Disposal At The Metropolitan
Wastewater Treatment Plant, Volume II, January 1974. this cost is
indexed to an ENR of 2100. At the time this report was written, the
recommended plan was to modify the existing furnaces by upgrading the
air pollution control system and installing a heat recovery system.
Installation of additional furnaces was not included in this cost
estimate. If updated to September 1988 ENR of 4535, the estimated
construction cost would be $13,920,000.
Actual Capital Cost (bid + change orders):
Additions and modifications to the incineration system were completed
from 1978 to 1983 under Project No. 407 and Project No. 408. Under
Project No. 408, an addition to the existing incineration building was
constructed to house two new furnaces and new air pollution control and
heat recovery systems. Modifications to the four existing furnaces was
also completed under this project. Under Project No. 407, two new
furnaces with air pollution control equipment and all necessary
appurtenances were installed in the new building addition. Costs for
these projects breakdown as follows:
PROJECT ORIGINAL CONSTRUCTION COST
CONSTRUCTION COST UPDATED TO ENR=4535
Project No. 408
- building addition
- furnace modifications
$ 88,755,300
$ 4,000,000
$ 92,759,900
$ 5,791,800
Project No. 407
- furnace installation
$ 10,313,400
$ 24,984,500
TOTAL
$ 103,068,700
$ 123,536,200
Total project costs breakdown as follows (ENR 4535)
equipment
structural
$ 30,776,300
$ 92,759,900
Total
$ 123,536,200
-------
For further project description, reference the appended advertisement
for bids for Project No. 407 and Project No. 408.
B. O&M (Based on 1987 operations and maintenance expense reports)
O&M costs for the incineration system and the boiler system (waste heat
recovery and auxiliary boilers) will be presented separately so that
fuel use by the furnaces and fuel use by the boilers can be
differentiated.
Furnace O&M Costs
ITEM
CONSUMPTION
ANNUAL
LEVEL
COST
Operations Labor
304
hr/day
$ 1,998,500
Maintenance Labor
286.5
hr/day
$ 2,300,800
Natural Gas
68,359,000
cf/year *
$
129,900
No. 2 Fuel Oil
None
Chemicals
None
Electricity
18,139,700
kw-hr/year**
$
679,300
Contracted Services
- operations
$
3,200
- maintenance
$
101,200
Materials & Supplies
- operations
$
46,500
- maintenance
$
511,500
TOTAL
$
5,770,900
* Taken from 1987 incineration process annual summary sheets
** 1987 Region III Electrical Summary Sheets show an electrical use of
13,604,250 kw-hr through October 1, 1987. This figure was projected
for 12 months to obtain an estimated annual use of 18,139,000
kw-hr/year (13,604,250 /.75).
-------
Boiler O&M Costs
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
Maintenance Labor
Natural Gas
No. 2 Fuel Oil
Water
Chemicals (boiler
feedwater)
Electricity
Contracted Services
- operations
- maintenance
Materials & Supplies
- operations
- maintenance
TOTAL
Steam "Sales" to Other
Plant Areas **
NET COST
163 hr/day
hr/day
236,064,500 cf/Vear
None
6,046,300 kw-hr/year*
$ 1,073,200
$ 0
$ 627,400
$ 14,900
$
$
$
$
$
$
55,500
223,700
800
8,800
71,600
64,700
$ 2,140,600
$ 696,300
$ 1,444,300
* 1987 Region III Electrical Summary Sheets show an electrical use of
4,534,750 through October 1, 1987. The figure was projected for 12
months to obtain an estimated annual use of 6,046,300 kw-hr/year
(4,534,750/.75).
** Heat is recovered from the incineration process utilizing a waste
heat boiler and an additional economizer section that increases the
energy recovery efficiency from 33.5% to about 40%. Most of the
recovered heat is utilized by the Zimpro thermal conditioning
process. Excess steam production is utilized to provide building
heat and drive steam turbines. This excess steam produced by the
incineration process should be considered an energy and cost credit.
See Section XI for a detailed breakdown of steam use.
-------
5. ENERGY CONSUMPTION
information requested here pertains to the four lead furnaces.
Equipment
No. Units Rated HP Hrs/day kw-hr/day
Operation *
Stack Jacket Ambient
Air Fans
Plant Water for Scrubber
Induced Draft Fan **
Slurry Pump
Ash Vacuum Pump
Shaft Cooling Air Fan
Primary Combustion Air Fan
Secondary Combustion Air Fan
Shaft Drive
Conveyors
Total
3
4
4
4
4
10
30
500
125
30
40
150
10
1
24
0
24
24
24
24
24
0
31,670
35,800
0
6,710
2,150
10,740
720
180
87,970
* Based on connected horsepower
** The induced draft fans are driven by a steam turbine when excess
steam is available. This partially offsets the electrical
consumption by this equipment.
Furnace Annual Electrical Requirements (kw-hr/year):
Based on connected horsepower: 22,476,300 for 2.8 units
Based on metered values: 18,139,000
-------
Annual Fuel Use:
No. 2 Fuel Oil
Natural Gas
Equivelent Fuel Oil *
gal/dry ton
cubic feet/dry ton
gal/dry ton
1984
0
654
4.7
1985
438
544
3.9
1986
9
655
4.7
1987
0
1102
7.6
* Total fuel consumption (fuel oil and natural gas) expressed as
gal/dry ton of No. 2 fuel oil.
The previous table reflects fuel consumption for the furnaces only.
This does not include consumption be the auxiliary boiler system. This
table does include fuel consumed during furnace start-up and cool-down
periods.
Note that fuel use increased significantly in FY 1987. This increase
is attributed to a requirement for a zero hearth temperature of 1000 F
that went into effect in 1986.
Annual Fuel Use For Start-up and Cool-Down Periods (cf/year):
Natural Gas 23,134,000 cf/year (373 cf/dry ton)
Fuel Oil 0 gal/year
Annual fuel Use For Auxiliary Boiler System:
Natural Gas Fuel Oil
(cf/year) (gal/year)
Auxiliary Boiler No. 1 100,387,900 0
Auxiliary Boiler No. 2 135,676,600 0
Total 236,064,500 0
6. ENERGY RECOVERY
Technology:
Waste heat boilers with economizer sections. These WHB units are tube
type exchangers with an upper and lower drum ("o" type boiler).
-------
Waste Heat Boilers:
No. Units
Normal Pressure Drop
Inlet Temperature
Outlet Temperature
Capacity
Economizer:
Normal Pressure Drop
Outlet Temperature
Capacity
Energy Recovery Efficiency:
1.5" w.c.
1000 - 1400 F
500 - 600 F
17,000 lb/hr
1.0" w.c.
400 - 500 F
17,000 lb/hr
without economizer section 33.5%
with economizer section 40%
Auxiliary Boilers:
No. Units
Capacity
Steam Production:
70,000 lb/hr
Annual Production
(#/Year)
Average Hourly
Production
(#/Year)
Auxiliary Boiler No. 1
78,449,600
8,955
Auxiliary Boiler No. 2
113,407,300
12,945
Subtotal
191,856,800
21,900
Waste Heat Boiler
245,639,900
28,040
Total Steam Production
437,496,800
49,940
Steam Pressure: 425 psi
-------
Steam Use:
Steam pressure is reduced to lower pressures prior to use in plant
processes or for plant heating. Steam use is prioritized as follows:
First Priority - Provide 100% of required Zimpro steam.
Second Priority - Drive steam turbines for ID fans, water pumps, and
auxiliary boilers. This reduces steam pressure from 425 psi to 125
psi.
Third Priority - Provide 100% of plant heating requirements. Steam
used to drive the ID fans is used a second time to provide building
heat. This reduces steam pressure from 125 psi to 15 psi.
Enough steam is always available to meet the needs of the Zimpro
process. If extra steam is available, second and third priority
demands are also met.
Steam Utilization:
Note that some steam is used twice, once to drive steam turbines and a
second time for building heat (HVAC). Both uses will be detailed in
these tables.
1. Steam Turbines (reduces steam pressure from 425 psi to 125 psi)
Steam Turbine
Operation
Hours
Electrical Cost
Savings
* Incinerator Turbines
(Induced Draft Fans)
Unit No. 7
Unit No. 8
Unit No. 9
Unit No. 10
1588
807
240
38
$190,500
$ 21,700
$ 2,900
$ 500
Subtotal
2673
$215,600
* Boiler Feedwater Turbines
Unit CP24
Unit CP25
Unit CP26
Unit CP27
Unit CP28
343
316
2218
4000
1853
$ 1,000
$ 1,000
$ 6,700
$ 12,000
$ 5,600
Subtotal
8730
$ 26,300
-------
* Auxiliary Boiler Turbines
Unit No. 1
594
$ 17,800
Unit No. 2
151
$ 9,500
Subtotal
745
$ 27,300
Misc. Turbines
16,165
$ 81 600
TOTAL
28,313
$350,600
* These processes are directly part of the incineration/steam
generation process and therefore are considered a system
operating cost. No cost credit to the incineration/heat
recovery system can be claimed for these uses.
** These steam uses are external to the incineration/steam
generation system,, therefore a cost credit can be taken for
these uses.
2. Process Use
Process Annual Steam Average Hourly Dollar Value
Use Steam Use Of Steam
(#/year) (#/hour) ***
** Chlorination System 319,420 36 $ 1,000
* Thermal Conditioning 139,476,100 15,922 $415,600
* Boiler Feedwater Prep. 42,336,000 4,833 $126,200
** HVAC (Building Heat) 205,952,700 23,510 $613,700
Total 388,084,200 44,301 $1,156,500
* These processes are directly part of the incineration/steam
generation process are therefore are considered a system
operating cost. No cost credit to the incineration/heat
recovery system can be claimed for these uses.
** These steam uses are external to the incineration/steam
generation system, therefore a cost credit can be taken for
these uses.
*** The dollar value of this steam is based on the cost to generate
steam using the auxiliary boilers. The auxiliary boilers
generate steam at a fuel cost of $2.98/1000 lb. steam.
-------
3. System Energy Credit
A. BTU Credit
Process
Annual Steam
Use
(lb/year)
Electrical
Savings*
(kw-hr/year)
Total
Energy Credit**
(BTU/year)
Chlorination System 319,420
HVAC System 205,952,700
Misc. Turbines —
Total
206,272,120
2,205,400
2,205,400
4.73 * 10~8
3.05 * 10*11
2.20 * 10*10
3.27 * 10*11
* Based on $.037/kw-hr
** Based on the following conversion factors
Steam 1481 Btu/#steam
Electricity 10,000 Btu/kw-hr
B. Cost Credit
Process Cost Credit
Chlorination System $ 1,000
HVAC System § 613,700
Misc. Turbines $ 81,600
Total Credit $ 696,300
XII. AIR EMISSIONS CONTROL
1. GENERAL INFORMATION
Technology:
Venturi wet scrubber (30 inches pressure drop) and packed tower (6 foot
deep; 2 to 3 inches pressure drop) arranged in series. Each furnace
has a top hearth (zero hearth) afterburner which is currently not used.
Flue gases sequentially pass through a waste heat boiler, an economizer
section, a precooler, a venturi scrubber, a subcooler, a mist
eliminator, and an I.D. fan.
-------
Precoolers:
Normal Pressure Drop
Outlet Temperature
Water Flow Rate
Venturi Scrubbers:
Operating Pressure
maximum
minimum
Water Flow Rate (maximum)
0.5" w.c.
180 F
250 gpm
33" w.c.
20" w.c.
venturi nozzle
venturi weir
Liquid To Gas Ratio
Gas Temperature s
Inlet
Outlet
Subcooler:
Pressure Drop
Inlet Temperature
Outlet Temperature
Water Flow Rate
(maximum)
Liquid To Gas Ratio
Diameter
Mist Eliminator
Emissions Standards:
opacity
particulates
odor
250 gpm
250 gpm
10 gal/1000 ACFM
180 F
130 to 150 F
2.0" w.c.
130 - 150 F
60 - 80 F
2000 gpm
33 gal/1000 ACFM
10 feet
polyprolyene mesh
packed tower - 3 trays
20 units for any 6 minute average
1.3 #/dry ton feed
150 odor units/#
-------
Results of Last Emissions Test:
Stack No. 8 Stack No. 10
Parameter June 7, 1988 * June 28, 1988 *
Copper
175
330
Nickle
31
27
Lead
325
551
Zinc
2484
4306
Cadium
469
611
Chromium
53
40
Arsenic
25
31
Selenium
15
24
Particle Mass
Emission (lbs/dry ton)
0.786
1.290
* All units are micrograms/ cubic meter unless otherwise noted.
Complete test results are appended to this report.
Opacity is monitored continuously and recorded on a strip chart.
Violations are noted automatically on the chart. During 1986, flue
gases were in compliance with opacity emissions standards 99.93% of the
time.
Stack height:
Original 80 foot
Have added silencers which have increased the stack height by 10 feet.
These silencers reduce noise emissions from the ID fans.
Building Height:
Stack Diameter:
Scrubber Water Treatment:
Scrubber Water
Characteristics:
about 65 feet
foot
Returned to primary treatment.
7,060 gpm (includes all coolers and scrubbers)
10 mg/1 TSS
10 mg/1 BOD
XIII. ASH DISPOSAL
1. GENERAL INFORMATION
Technology:
Ash has been disposed at on-site ash ponds since incineration began in
1938. Four ponds with a total volume of 250,000 cubic yards are
available on-site. Wet ash is stored in these ponds and the
supernatant from the ponds is pumped back to the aeration tanks.
-------
For a period of time, a contractor was removing ash from the pit and
transporting the ash by railroad to South Dakota to be processed for
the recovery of precious metals. This company removed about 2/3 of the
ash that had been accumulating in the pit since 1938. The removal of
this ash has created a great deal of on-site ash disposal capacity.
The contract for ash removal was canceled this year.
Location of Ash Landfill (on-site/off-site): On-site
Total Annual Volume of Ash Generated (cy/year): 42,600 cy/year
(33 #/cf and 52 tpd)
2. COST INFORMATION
A. Capital
Cost of Truck(s): $70,0000
Tipping Fee at Landfill (if commercially operated): N/A
B. O&M
O&M costs for the ash removal system are included in the incineration
O&M costs (Section XI).
XIV. BIOLOGICAL SIDESTREAM (RECYCLE) TREATMENT
1. GENERAL INFORMATION
Technology: Rotating Biological Contactors (RBC)
Date Installed: 1979-1980
Manufacturer: Autotrol
No. Units: 50
2. DESIGN INFORMATION
RBC Units
No. Units
Diameter
Length
Unit Surface Area
Total Surface Area
50
12. feet
23 feet
90,000 square feet
4,500,000 cubic feet]
-------
Final Settling Tanks
No. Units 2
Width 37 feet
Length 91 feet
Depth 12.5 feet
Overflow Rate 200 gpd/square foot
3. Operating Information
Source of Flow:
Overflow from thermal conditioning (Zimpro) decanting tanks. Overflow
from the DAF thickeners used to dilute the Zimpro stream.
Flow Treated (gpd): 1.38 mgd
INFLUENT EFFLUENT
Soluble BOD (mg/1): 2056 * 699
TSS (mg/1): 1135 792
* Note that influent BOD and TSS values are low because the influent
waste stream is diluted to reduce the water temperature from about
100 F to about 85 F. Decant overflow averages about 8,400 mg/1 BOD
and 18,900 mg/1 COD.
Sludge Disposal:
Waste sludge from the RBC system (about 9 tpd) is incorporated into the
DAF influent for treatment and disposal.
4. COST INFORMATION
A. Capital
Facilities Plan Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders):
Facilities were constructed from 1978 to 1982 at a cost of $14,079,900
(Project No. 400). Costs updated to a September 1988 ENR of 4535 are
as follows:
-------
equipment $ 4,150,500
structural $ 15,828,400
Total $ 19,978,900
These facilities include the rotating biological treatment system (50
RBC units), two settling tanks for the RBC system, and two
physical-chemical treatment systems (see Section XV).
These facilities were modified in 1983 - 1984 at a cost of $1,706,300
(Project No. 400A). These modifications included the acid proof lining
of concrete surfaces, installation of additioal piping and pumps, and
repairs to fiberglass dome covers. Project costs updated to a
September 1988 ENR of 4535 are as follows:
equipment $ 331,000
structural $ 1,551,700
Total $ 1,882,700
For additional project description, reference the appended
advertisement for bids for Project No. 400 and Project No. 400a.
O&M
ITEM
CONSUMPTION
ANNUAL
LEVEL
COST
Operations Labor
11
hr/day
$
73,900
Maintenance Labor
25
hr/day
$
200,750
Chemicals
$
69,000
Electricity
2,740,000
kw-hr/year *
$
80,900
Materials & Supplies
- operations
$
35,600
- maintenance
$
52,500
Contracted Services
(maintenance)
$
11,800
Total
$
524,450
* Based on 1987 Region 11 Utility Summary Sheets
ENERGY CONSUMPTION
Equipment HP NO. UNITS HRS/DAY KW-HR/DAY
RBC Shaft Drives 7.5 50 total 24 3810
28.4 operating on average
Annual Electrical Requirements (kw-hr/year): 2,740,000 (metered)
-------
XV. PHYSICAL-CHEMICAL SIDESTREAM (RECYCLE) TREATMENT
1. GENERAL INFORMATION
Technology: Flocculation/Sedimentation with Lime, Ferric, or Polymer
Date Installed: 1979 to 1980
Source of Flow: Overflow from gravity and DAF thickeners.
Sidestream from roll presses.
This system is no longer used, therefore no operating information, capital
or O&M costs will be presented.
XVI. ODOR CONTROL SYSTEMS
The following odor control systems are used to treat odorous off-gases from
solids handling processes:
Process Area Odor Control System
DAF Thickener Area 2 stage, packed bed chemical scrubber (4 units)*
Sludge Storage Tanks 2 stage, packed bed chemical scrubber (1 unit)
Sludge Processing Building Odorous gases to incineration (2 units)**
Decant Tanks Odorous gases to incineration
Sludge Holding Tanks Odorous gases to incineration
RBC Disk Area See DAF Thickener area *
RBC Settling Tanks 2 stage, packed bed chemical scrubber (1 unit)
* The DAF thickener area and the RBC disk area share this odor control
system, although the system is currently used primarily for the RBC
system.
** This includes odorous gases from the dewatering area.
Odor control for each process area will be detailed below. Although
odorous gases from many process areas are used as combustion air in the
incineration system, not all odorous gas streams can be treated in this
manner because of the limited air requirements of the incineration system.
Therefore, some wet scrubbing systems are necessary.
A. Sludge Storage Tanks
1. GENERAL INFORMATION
Technology: Two stage, packed bed, countercurrent flow, chemical scrubber
Date Installed: 1979
No. Systems: 2
-------
2. Operating Information
Source of Gas Flow: Sludge storage tanks
Average Gas Flow Treated (cfm): 22,000
Chemical Dosage:
Sodium Hydroxide/Potassium Hydroxide 50 gpd (50% solution)
Sodium Hypochlorite 50 gpd (15% solution)
3. COST INFORMATION
Capital and O&M costs for this system are included in the costs presented
in Section VI of this report (Sludge Storage Section).
4. ENERGY CONSUMPTION
Equipment
HP
No.
units
Operation
Hrs/Day
Kw-hr/Day
Chemical Feed Pumps
50
8 total
2 operating
24
1790
ID Fans
100
4 total
1 operating
24
1790
Other
2
2
20
60
Total
3640
Annual Electrical Requirements (kw-hr/year): 1,328,600 (based on connected
horsepower)
B. RBC Disk Area
1. GENERAL INFORMATION
Technology: Two stage, packed bed, countercurrent flow, chemical scrubber
Date Installed: 1978
No. Units: 4
2. Design Information
System Capacity: 3 units at 18,000 acfm
1 unit at 25,000 acfm
Static Pressure: 3 units at 14 inches w.c.
1 unit at 15 inches w.c.
-------
3. Operating Information
Source of Gas Flow: RBC disk area
Note that this system can also treat off-gases from
the DAF thickener building, although this
capability is currently not used.
Average Gas Flow Treated (cfm): 25,000 cfm
Chemical Dosage:
Sodium Hydroxide/Potassium Hydroxide - about 600 gpd (50% solution)
Sodium Hypochlorite - 600 gpd (15% solution)
4. COST INFORMATION
Capital costs for this system are included under Section IV (Project
No. 400). O&M costs are split between the DAF thickeners (Section IV)
and the RBC sidestream treatment system (Section XIV).
5. ENERGY CONSUMPTION
EQUIPMENT
HP
NO.
UNITS
HRS/DAY KW-HR/DAY
Chemical Feed Pumps
ID Fans
Other
Total
50
100
2
152
8 total
2 operating
4 total
1 operating
24
24
20
1790
1790
60
3640
Annual Electrical Requirements (kw-hr/year): 1,328,600 kw-hr/year
C. RBC Settling Tanks
1. GENERAL INFORMATION
Technology: Two stage, packed bed, countercurrent flow, chemical scrubber
Date Installed: 1978
No. Systems: 1
2. Operating Information
Source of Gas Flow: RBC Settling Tank
-------
Average Gas Flow Treated (cfm): 6000
Chemical Dosage:
Sodium Hydroxide/Potassium Hydroxide 100 gpd (50% solution)
Sodium Hypochlorite 100 gpd (15% solution)
3. COST INFORMATION
Capital and O&M costs for this system are included under Section XIV
(RBC treatment systems) of this report.
4. ENERGY CONSUMPTION
Equipment HP No. Operation
Units Hrs/Day Kw-hr/Day
Chemical Feed Pumps 20 4 total 24 700
2 operating
ID Fans 40 1 24 700
Other 5 1 20 75
Total 1475
Annual Electrical Requirements (kw-hr/year): 538,400 kw-hr/year
(Based on connected
horsepower)
XVII. COST SUMMARY TABLES
The following tables attempt to (1) estimate a reasonable construction cost
for the existing Metropolitan WPCF solids handling facilities in 1988
dollars; (2) convert the construction cost to an annual cost; and (3) ,
present a total annual cost (capital plus O&M) for each unit process.
Capital costs have been estimated by updating the original construction
costs to 1988 dollars using the Engineering News record (ENR) cost index.
Operation and maintenance costs have been summarized based on the tables
presented earlier in this report.
It should be emphasized that construction costs for such a facility are
very difficult to estimate and, even if estimated accurately, are very
difficult to use in comparison with other facilities. In reviewing these
costs, the reader should consider the following comments:
Building prices for two sirailiar facilities can be very different
depending on such site-specific factors such as depth of ledge, local
materials costs, site constraints, construction market conditions, or
other construction considerations.
-------
METRO VPCF
CONSTRUCTION COSTS
PROCESS
UPDATED
CONSTRUCTION
COST
(ENR = 4 535)
AMORTIZED
CAPITAL
COST
K.A.S. Thickening
-structures
-equipment
-total
Primarv Sludee Thickenine
-structure?
-equipment
-additional structure
-additional eauipment
- total
Thermal Conditioning
-structures
-eauipment
-total
Sludge Dewatering *
-structures
-equipment
-total
Sludge Incineration
-structures
-equipment
-total
RBC Sidestream Treatment
-structures
-equipment
-total
S15.828.400
S4,150,500
519,978.900
55.400,000
S500,000
S235,500
S21.800
S5,900,000
S26.400,000
310,972,000
S37,372,000
5778,400
$3,994,900
$4,773,300
$92,759,900
$30,776,300
$123,536,200
$17,380,100
$4,481,500
$21,861,600
capital costs.
Sl.7 50.000
S526 ,000
S3,331,000
$472,000
510,913.000
$1,914,000
* Based on roll press dewatering
-------
HETBO VPCF
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COST
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t TOTAL
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t/U
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COST
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10
IMS.100
0.42
...
t:
t.A.S. Tkicktaiai
tl.TS6.t00
1(11,100
nil.too
10
10
1240.400
13.(00
13,000,700
10
13,008,TOO
l.tt
120
in
in
Priaarj Sludge Ttictcniai
|52(,009
MIM0O
Hi,TOO
10
tis.ooo
MS,100
111,001'
(1,OS),400
10
11.0(1,400
3.0<
K
ii
in
Slid(e Stonfe luki
Id
ITU,400
1110,too
10
121,S00
1(1,SOI>
1TU0
im.ioo
10
190%.300
2.(1
...
IM
114
Tbertil Co«ditioaia|
11,111.000
ll.SS0.300
till.too
10
122.tOO
.235,300
f17,309
S5. ilndie prodictioa of HT.5 lt| ton ptr iij of demurtd cut.
Ill Tku lite ittt tsclidci piipiaf froi tkt priurr ill itcotdirt
dirifitri to the *l»d(t tbicktiiil procMi.
All (abtfqitit il«d|t pv>apia| ii iicladtd in tk» ipproprialr
»»it proctts lint jtea.
i(t lacladed ia tail process capital co*U
iSI IncWdtd ia Krfail condilioain( rapiLai cotU
1(1 Butt on roll prtii demtctiil cotli
|7) Included in the mciarratioa capital coila
Dole *11 c««<» art bated on I SIT coiiaiplioa rtconii.
-------
The amount of reserve capacity built into a facility can significantly
affect construction costs. The amount of reserve capacity allowed for
during design can depend on several factors such as site-specific
constraints, plans for future expansion or growth, and the design
consultant's philosophy concerning system redundancy.
In converting the estimated construction cost to an annual cost, it was
assumed that all structures would have a useful life of 40 years and all
equipment would have a useful life of 20 years. A discount rate of 8
percent was assumed to determine the capital recovery factor. Capital
costs for the dewatering system reflected the costs for the roll press
dewatering system only.
XVIII. SUMMARY OF ENERGY REQUIREMENTS
The following table summarizes energy consumption requirements for each
unit process. To allow a true comparison of energy efficiency with other
facilities, each form of energy consumption (electricity, fuel oil, natural
gas, steam) has been converted to a common unit (BUJs). The energy
consumption of each unit process has been determined based on tables
presented earlier in this report. Energy credits have been accounted for
where applicable. The net energy consumption for each unit process and for
the system as a whole has been determined and expressed on a per ton basis.
Factors used to convert each energy form to a BTU basis appear at the
bottom of the table. These factors reflect the BTUs of energy required to
produce a kw-hour of electricity and a pound of steam. These conversion
factors account for inefficiencies in the production of electricity and
steam.
XIX. LESSONS LEARNED
The operating experience at the Metro Facility provides some insights into
fuel efficient incinerator operation.
Storage in the sludge handling train is essential. Storage helps the
operator maintain a steady sludge feed to the incinerator in terms of
quality and quantity and it allows the operator to completely shut down the
system for short periods of time to perform regular maintenance tasks.
Communication between the operators of different processes, between the
operators and maintenance crews, and between operators on different shifts
developes consistency in the system's operation and creates an atmosphere
of cooperation amoung the entire staff. This works to improve the
consistency and the quality of the' sludge feed to the incinerator. A daily
newsletter is distributed to the staff to inform them of pertinent
information such as operational problems that transpired the previous day,
how these problems were resolved, and how these problems could be avoided
in the future. The staff also forms committees comprised of engineers,
operators, and maintenance personnel to discuss O&M problems. Each
commitee addresses a particular problem. Hie comraitee will evaluate a
problem, brainstorm for solutions, and recommend process improvements and
modifications to resolve the problem. The committee will then continue to
-------
HETIO KFCf
2NBEC7 BEQUIXEHEMTS t'Ot SOllliS
HANDLING PBOCESSES
PBOCESS
8LBCTRICIT1
IIV-Bl/mBI
hhct CONSUKPTIOH
HJ8L OIL HATWAL CAS
IGAL/TIAE) ICf/TEAEI
TOTAL 1TIU
COHiUHED
Signer rsgiiT
STEAM EUCTtimr
U/UAII {Iw-HE/YEAG)
TOTAl. RTll
I'REOIT
VET RTll
rOHSUKVTIOH
1 TOTAL
MT BTU
CONStHtPTIOH
BTUi f'HV TO«
I
Sludie hiotti
3,920.500
0
0
39.205.000.000
0
li
i>
39.205,0(0.000
T.421
(05.132
V.A.S. TJiclitMiiJ
J,318,<00
0
0
8), 184.000.000
11
0
i|
83.184,000,090
IS,751
1,233,951
Priiir; Slud
-------
monitor progress in resolving the problem and decide if further corrective
actions are necessary. Copies of some of the staff memorandums that have
been developed as a result these committee meetings are appended to this
report.
Management has created a very positive atmosphere to work in at the Metro
Facility. By encouraging employees to pursue technical advancement through
advanced education and professional organizations and by providing the
staff with a budget that allows for experimentation and process
improvements, management has developed a very motivated staff that is
always looking for new ways to improve the solids handling processes.
-------
Metropolitan
Waste Control
Commission Office Memorandum
DATE*
All Concerned 9-14-88
Dave Quast
Scum System Meeting, September 7, 1988
A Scum System meeting was held on Wednesday, September 7, 1988, from
1:15 P.M. to 2:15 P.M. in the Training Room. The following people
were present:
OPERATIONS: SHOP:
Beecher Vallencourt Sr. Jim Driver
Dan Nalezny Reed Santa
Gene Law Denis Gorecki
Dave Quast
Jack Klein
The following items were discussed:
1. SCUM DECANT ROOM EQUIPMENT
a. Regarding the suggestions made at the last meeting to prevent
running the Koyno pumps dry and wearing out stators
prematurely, it was decided that installing a recirculation
line around the pump is the best place to start. A descrip-
tion of a Pump Failure Detector was distributed to the main-
tenance personnel for review. This device (similar to a
pressure switch) may also be tried.
b. Lab results are expected this week from Twin Cities Testing
regarding viscosity data of heated scum for pump design data.
In-house lab results are also expected in the near future for
BTU, TVS and scum particle size information which nay illumi-
nate reasons for scum pipe plugging and grinder failure.
c. The final steps for the 200 gptn scum decant return pump are
taking place. It may be ready for trial this week.
d. The blue line Fisher back pressure controller was installed
this week. Now the pressure is controlled in both scum loops
without the need for adjustment. The 408 Scum System Data
Sheet will be slightly modified to record the actual back
pressure rather than the controller settings. Squeeze valves
were also replaced during the last week of August. These
will be inspected every 6 weeks.
-------
All Concerned
September 14, 1988
Page 2
«. The hot water system for flushing the loop lines and hosing
down the floor was checked thoroughly. The heater can only
keep the water heated to above 1S0*F if the flow is less than
60 gpm. To assure that flow doesn't exceed this, an orifice
flow controller will be installed in the effluent water line
going to the Pick Heater.
f. In an attempt to determine the cause of periodic surges of
problems with scum equipment and pipes, scum samples are
being analyzed. Four samples were submitted to the labora-
tory (an East and West Primary sample from two different
days) for Total Volatile Solids and BTU analysis. The lab is
devising a test for grit content and size in the scum. West
and East Primary scum is also being kept separated to try to
pinpoint problems.
2. SCUM PIPE
a. The loop line temperature and pressure monitoring on the com-
puter will continue to be used as a tool for determining
causes of plugged pipes and/or pump failure.
b. There may be a segment of scum pipe in the loop that has poor
contact with the heat tape. The 300 foot loop lines will be
inspected for any "dead spots".
c. Recent plugging at the prep units has not been related to any
foreign particles in the lines out of the ordinary. It may
be related to the hot air blow back. Air flow and
temperature meters will be installed on the purge lines. A
minor modification may be made if store air preheating is
necessary.
d. The work order for the trial modification on prep unit #7 (to
extend the 2" loop line and pump to the main floor closer to
the incinerator port) has been written. The pipe design is
being worked on.
3. SAFETY
a. Confined space training will take place at 2:00 P.M. on
Wednesday, September 14, 1988 for A and B shifts in the F«I
#2 Control Room. This training will briefly cover safety
aspects of skimming tank cleaning. Safety plans more general
confined space training by the end of the year for all
operators.
b. Scum air sample results will be released soon.
-------
All Concerned
September 14,. 1988
Page 3
3. SAFETY (Cont'd)
c. Some general nafety aspects related to the scum decant room
involving fire hazards and emergency procedures were brought
up. These will be discussed with Safety.
The next meeting will be during the week of September 19, 1988. The
time and place will be announced later.
DQsBJ
-------
APPENDIX B
UPPER BIACKSTONE
WATER POLLUTION CONTROL FACILITY
I. GENERAL INFORMATION
ADDRESS: UPPER BLACKSTONE WPCF
Route 20
Millbury, MA. 01527
Phone Number:
(508) 755-1286
Contact:
Arthur Levesque
Plant Manager
Year Began Operation:
1976
Design Engineer:
Fay, Spofford & Thomdike
George Reece
Design Average Flow:
56 MGD
Design Peak Flow:
Max Day 83 MGD
Max Hour 119 MGD
FY 1987
FY 1988
Average Flow:
36 MGD
33 MGD
Max Day Flow:
60 MGD
Average Influent BOD:
109 mg/1
121 mg/1
Average Influent TSS:
122 mg/1
151 mg/1
Average Effluent BOD:
7 mg/1
8 mg/1
Average Effluent TSS:
11 mg/1
11 mg/1
Influent loads have increased over the past
year due to an increase in sludge and septage
accepted from outside sources. Septage is fed
directly into the influent stream at the head
of the plant. Thickened sludge (> 4% solids)
accepted from outside sources is added to the
TV2AS storage tanks. About 40 truckloads of
septage and thickened sludge are now accepted
daily.
-------
Permitted Effluent CBOD: winter 30 mg/1
summer 10 mg/1
Permitted Effluent TSS: winter 30 mg/1
summer 15 mg/1
Other Effluent Requirements: Ammonia nitrogen requirements
and
2
mg/1
- monitor effluent ammonia nitrogen
concentration in May
- from June 1 to June 15, average weekly
ammonia concentration < 5 mg/1
- from June 15 to Oct. 31, average weekly
average monthly ammonia concentration <
mg/1 and daily peak concentration < 2.5
Plant Overview: The liquid treatment train includes aerated
grit removal, primary settling, activated
sludge treatment, and chlorination prior to
discharge to the Blackstone River.
Nitrification is practiced from late May until
October 31. Solids handling processes include
flotation thickening of waste activated
sludge, separate storage of thickened waste
activated sludge (TWAS) and unthickened
primary sludge, blending of the TWAS and
primary sludges, sludge dewatering using belt
filter presses, sludge incineration, and ash
disposal by landfilling on-site.
A schematic of the solids train showing FY
1988 average process loadings is attached.
II. UNIT COSTS
Unit costs are based on 1987-1,988 records.
ITEM UNIT COST
Labor ($/hour)
12.50
Polymer ($/liquid #)
0.0845
City Water ($/100 gal)
0.114
Electricity ($Aw-hr)
0.047
No. 2 Fuel Oil ($/gal)
0.59
Natural Gas (S/100 cf)
0.3564
Chlorine ($/ton)
450.00
-------
III. SLUDGE PUMPING
1. GENERAL
TRANSFER
PUMP
NO.
UNITS
UNIT
HP
UNIT
CAPACITY
Primary Sludge Pumps
Waste Activated Sludge
Pumps
Thickened Waste Activated
Sludge Pumps
6
3
4
7.5 HP
5 HP
5 HP
200 gpm
250 gpm
250 gpm
Note: 3 of the pumps are dedicated to the DAF top collectors. 1 pump is
dedicated to the DAF bottom sludge draw off. This pump is used
intermittently.
Transfer from holding
tanks (2) to blend tank
10 HP
230 gpm
Note: Usually, 2 of the 3 pumps are operated; 1 dedicated to primary sludge
and 1 dedicated to thickened waste activated sludge
Belt filter press
feed pumps
3
2
Plant water pumps
Note: Usually 2 of the 2700 gpm pumps are operated.
5 HP
150 HP
50 HP
115 gpm
2700 gpm
1000 gpm
2. MAINTENANCE NOTES
Primary sludge pumps:
Waste activated sf^udge pumps:
Transfer pumps from storage
tanks to blend tanks:
Require an average of 30 hours/\reek of
maintenance time.
Require an average of 4 hours/week of
maintenance time to keep sludge flow meters
calibrated.
These pumps tend to be a high maintenance
item*because of the gritty quality of the
sludge being pumped. About 16 hours/Week is
required for regular maintenance. Approxi-
mately $l,000/year is spent on supplies and
materials to maintain these pumps.
-------
T.W.A.S. FROM
OUTSIDE SOURCES
— 4.400#/d
WASTE
ACTIVATED
SLUDGE
60.200#/d
30.25 tpd
26.2%
— 0
NO CHEMICALS
TO HEAD ,,
OF PLANT iT
ASH TO
LAND FILL
25.800#/d
1.5%
POLYMER
ADDITION
- 80 WET lb
DRYTON
PRIMARY
8 PRY lb
DRYTON
SLUDGE
24.500#/d
' 5.5%
1 MGD
375 mg/1 TSS
3.130#/d
— 442#/d
TO HEAT
OF PLANT ^ |_
SLUDGE
HOLDING
TANK
SLUDGE
HOLDING
TANK
BELT FILTER
PRESS
DEWATERING
MULTIPLE
HEARTH
INCINERATION
DISSOLVED AIR
FLOTATION
THICKENING
-------
3. COSTS
ITEM
CONSUMPTION ANNUAL
LEVEL COST
Operations Labor
0 hr/day $0
Maintenance Labor
50 hr/week $32,500
Electricity
18,000 kWH/year $800
Chemicals
None
Materials & Supplies
$1,000
TOTAL
$34,300
Note: Records of actual metered electrical consumption are not available
Therefore, electrical consumption is estimated based upon curves
presented in the EPA publication entitled Energy Conseration in
Municipal Wastewater Treatment.
IV. WASTE ACTIVATED SLUDGE
THICKENING
1. GENERAL INFORMATION
Technology:
Dissolved Air Flotation Thickeners (DAF)
Date Installed:
1976
Manufacturer:
Envi rex
No. of Units:
4
Thickening Area (sf/unit):
1136
Sludge Volume Index (SVI):
60 to 200 depending on time of year.
2. OPERATING PARAMETERS
WAS to Thickening (#/day): range 18,000 to 36,000
FY 1988 average 34,600 f/day
Design Average Loading Rate (psf/day): 10 without polymer
Design Peak Loading Rate (psf/day): 36 with polymer
-------
Actual Average Loading Rate (psf/day):
Actual Peak Loading Rate (psf/day):
Air Pressure (psig):
Effluent Recycle Ratio (% of influent flow):
6 without polymer
8 without polymer
40
Hydraulic Loading:
W.A.S. Feed
Plant water
Air to Solids Ratio (# air/# solids):
Typical depth of Sludge Blanket:
Unthickened Percent Solids:
Thickened Percent Solids:
Chemical Addition (type & amount):
Solids Capture:
Sidestream Strength (Q, TSS & BOD):
300 gpm
110 gpm/unit
440 gpm total
Not Available
12 to 18 inches
typical .7% to .8%
typical 4% to 5%
Have ability to add polymer,
but are currently not adding
any chemical.
90+ %
1 MGD
375 mg/1 TSS
250 mg/1 BOD
3. COST INFORMATION
A. Capital
Facility Planning Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders): Cost indexed to October 1973
ENR = 1934
Structures
Equipment
$739,700
$290,000
Total $1,029,700
Includes costs for DAF thickeners, ancillary equipment, and building space.
Cost of Modifications/Expansions (year): None
-------
B. O&M
O&M costs are based on Fiscal Year 1988 consumption records.
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
Maintenance Labor
Electricity*
- Equipment
- Building
Chemicals
Replacement Materials
TOTAL
3 hr/day
10 hr/month
378,900 kWH/year
770,000 kWH/year
None
$13,700
$ 1,500
$17,800
$36,200
$ 3,300
$72,500
*Reference Section 4 for basis of electrical consumption estimates.
Maintenance Concerns:
4. ENERGY CONSUMPTION
In 8 years, have spent about $20,000 on new chains.
Every 5 years, about $4,000 is spent on a new gear
drive. Other maintenance supply costs have been
minor.
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of 60 KWH per dry ton (reference WPCF Manual of Practice No.
FD-2 Energy Conservation in the Design of Wastewater Treatment Facilities)
and a consumption of 40 KWH per square foot of building space for lighting,
HVAC, and other general building needs.
Typical Hours of Operation (hr/day): 4 units operating 24 hour/day
Electrical Requirements as Projected
in Facilities Planning (kw^-hr/yr): Not Available
-------
Estimated Annual Electrical Requirements (kw-hr/day):
Equipment
Building
TOTAL
V. SLUDGE STORAGE TANKS
378,900
770,000
1,148,900
Two storage tanks, one dedicated to primary sludge and one dedicated to
thickened waste activated sludge are used to equalize the flow prior to
dewatering.
The primary sludge storage tank acts as a gravity thickener. An overflow
line returns a cofiistant flow of supernatant to the primary settling tanks
by gravity.
The waste activated sludge tank accepts thickened sludge from outside
sources. These outside sources contributed about 2.2 tons per day of
T.W.A.S. in FY 87. No mixing is provided in the T.W.A.S. holding tank,
supernatant is withdrawn from this tank.
1. GENERAL
No. Tanks: 2
Tank Size:
Tank Diameter:
Tank Depth:
Aeration:
Mixing:
No
450,000 gallon
55 ft
26 ft SWD
None
In the primary sludge tank, some agitation is
provided by a shallow mechanical mixer, but
complete mixing is not achieved. The mixer is
primarily used to break up a scum layer that forms
on the top of the tank. No mixing is provided in
the waste activated sludge tank.
2. OPERATING INFORMATION
A. PRIMARY STORAGE TANK
Percent Solids of Sludge Feed:
Percent Solids of Product:
range 1% to 5%
average 1.5%
range 5% to 10%
average 5.5%
Chemical Addition:
None
-------
Average Loading Rate:
Hydraulic Sludge Feed:
Detention Time:
FY 1987
FY 1988
200,000 GPD
2.25 days (avg)
18,400 #/day
25,800 #/day
B. WASTE ACTIVATED STORAGE TANK
Percent Solids of Sludge Feed:
Percent Solids of Product:
Chemical Addition:
Average Loading Rate:
4% to 5%
4% to 5%
None
FY 1987: Estimated 38,100 #/day
(includes thickened sludge from outside
sources)
FY 1988: Estimated 35,900 #/day
(includes thickened sludge from outside
sources)
Detention Time: 4.7 days (avg)
3. COST
A. Capital
Facility Planning Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders): Costs indexed to October 1973
ENR = 1934
Structures
Equipment
Total
$291,000
$ 60,000
$351,000
Includes costs for holding tanks, building space, and sludge transfer
pumps.
Cost of Modifications: No major modifications have been made.
-------
B. O&M
ITEM CONSUMPTION ANNUAL
LEVEL COST
Maintenance Labor 200 hr/year $2,500
Chemical Addition None
Plant Water None
Electricity 1,200 kw-hr/year $ 100
Replacement Materials $ 0
TOTAL $2,600
Maintenance Concerns: Once each year, the primary sludge storage tank is
taken out of service for a period of 10 to 14 days
to be cleaned. During this period, 1 primary
clarifier is used as a sludge storage tank.
Cleaning labor totals about 200 manhours.
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of .25 KWH per dry ton (reference WPCF Manual of Practice No.
FD-2 Energy Conservation in the Design of Wastewater Treatment Facilities).
Rated HP of Mixer (primary sludge tank): 20 HP
Typical Hours of Operation: 3 hr/day (not used every day)
Estimated Electrical Requirements (kw-hr/yr): 1,200
VI. SLUDGE BLENDING TANKS
1. GENERAL INFORMATION
No. of Tanks: 2 (usually only 1 tank in use)
Tank Size: 20,000 gal/tank
Mixer Manufacturer: Philadelphia
-------
2. OPERATING INFORMATION
TWAS/Primary Sludge Ratio: typical 1.7 to 1.5 : 1 by volume
Average Detention Time: 3 hour
Percent Solids of
Blended Sludge: 5% to 6%
3. COST INFORMATION
A. Capital
Facility Planning Estimate of Capital: Not available
Actual Capital Cost (bid + change orders): Included in cost of sludge
processing complex.
B. O&M
ITEM CONSUMPTION ANNUAL
LEVEL COST
Operations Labor 1.5 hr/day $ 6,800
Maintenance Labor 4 hr/month $ 600
Chemical Additions None
Electricity 10,000 kw-hr/year $ 500
Replacement Materials $ 0
TOTAL $ 7,900
Maintenance Concerns: Once per shift, rags that accumulate at the bar rack
are raked. Once each month, the tank is taken out
of service for 1/2 day to clean rags from the
mixers.
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon curves presented
in the EPA publication entitled Estimating Sludge Management Costs.
Rated HP of Mixers: 20
No. of Mixers: 1/tank
-------
Typical Hours of
Operation:
Estimated Electrical
Requirements (kw-hr/yr):
VII. SLUDGE DEWATERING
24 hrs/day (1 tank)
10,000
The original plant design included 4 vacuum filters for sludge dewatering.
Two of the original four vacuum filters have been replaced by plant staff
with two belt filter press units. The two remaining vacuum filters are no
longer used.
1. GENERAL INFORMATION
Technology:
No. of Units:
Unit Size:
Date Installed:
Belt Filter Press
2
2 meter belts
1 in 1982
1 in 1985
Manufacturer:
2. OPERATING PARAMETERS
Average feed to Dewatering (#/hour):
Average Hydraulic Loading:
Komiine-Sanderson
2725
FY
1986
2485
2500
FY
1987
2690
2525
FY
1988
2465
FY 1983
FY 1984
FY 1985
sludge feed 100 gpm
polymer dosage 24 gpm
washwater 80 gpm
Parameter
FY 83 FY 84 FY 85 FY 86 FY 87 FY 88
Ton D.S. To BFP (tpd)
24.7
23.7
25.4
24.8
27.8
30.2
Avg % Volatiles
61.8
60.9
64.8
63.4
62.2
66.1
Avg Feed to Dewatering (#/hour)
2725
2500
2525
2485
2690
2465
Avg Loading Rates (#/ta-hr)
1360
1250
1275
1240
1350
1230
BFP Cake (tpd)
84
73
96
92
100
115
Percent Solids of Feed
6.0
5.4
5.3
5.3
5.6
5.2
Percent Solids of Cake
28.1
26.0
26.5
27.0
27.6
26.2
-------
Percent Solids of Cake:
Belt Material:
Polymer Type:
Polymer Dosage
(#/ton dry solids):
Frequency of Testing to
Optimize Polymer Dosage:
Other Chemicals:
Average 26% to 27%
Range 22% to 36%
Polypropylene
Liquid polymer Calgon WT2136
80 to 100 wet pounds/dry ton solids
No lab testing is performed. The operator adds
just enough polymer to prevent sludge from
squeezing out of the pressure zone of the BFP.
Polymer was formerly prepared in a batch feed
system. This resulted in significant waste.
If the dewatering operation shut down
unexpectedly during an operating period, the
unused portion of the polymer batch would go
bad during the down period and have to be
discarded. The batch system also tended to
produce an inconsistent polymer feed in terms
of quality due to uneven mixing and varying
polymer age. The batch system was replaced
with a "Polyblend" system which produces the
polymer mix on a continuous basis, thereby
eliminating polymer waste and providing a
consistent polymer blend. This system saved
15% in polymer costs in its first year of
operation.
Capability to apply lime and ferric chloride
exists, but is not utilized.
Solids Capture: 95+ %
Sidestream Strength
(Q, TSS & BOD): 1000 mg/1 BOD
600 mg/1 TSS
pH « 6
3. COST INFORMATION
A. Capital Costs
Facility Planning Estimate of Capital: Not available
Actual Capital Cost (bid + change orders):
The original bid cost for the dewatering area was for a vacuum
filtration operation. The dewatering area was subsequently modified to
accomodate belt filter press units. Original bid costs are indexed to
October 1973 costs (ENR « 1934)
-------
Structures $1,047,800
Equipment $ 700,000
Total $1,747,800
Cost of Modifications:
Two of the original vacuum filters have been removed and replaced with
two belt filter press units, one in 1982 and one in 1985.
1982 unit: This unit was installed by the plant staff. Total cost was
$105,000 for machine and rigger to install machine. This figure does
not include the cost for plant labor or for a polymer system. The
existing polymer system was modified for use with the BFP.
1985 unit: Was also installed by plant staff. Total cost was less
than the 1982 unit cost.
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor*
Maintenance Labor**
Polymer
Other Chemicals
Electricity***
- Equipment
- Building
Replacement Materials****
TOTAL
39 hr/day
78 hr/Week
86 #/dry ton
None
164,300 KWH/year
1,046,600 KWH/year
$177,900
$ 50,700
$ 79,800
$ 7,700
$ 48,100
$ 26,000
$390,200
* 1 operator 24 hour/day
1 senior operator 6 hour/day
1 swingman 9 hour/day
** The maintenance department considers the dewatering and incineration
building as one work area. No distinction is made between time spent
in the dewatering area and the incineration area. Two maintenance
-------
workers are assigned full-time to the dewatering/incineration area.
One electrician and one instrumentation technician spend about 20% of
their time in the dewatering/incineration area. For the purposes of
this evaluation, it is assumed that these workers split their time
50/50 on the incineration and dewatering unit processes. Labor for
general housekeeping duties and for oversight by the maintenance chief
is also included in the labor estimate. The estimated maintenance
hours breakdown as follows:
full-time technician
electrical technician
instrumentation technician
general housekeeping
maintenance chief
Total
40 hours/Veek
4 hours/Veek
4 hours/Week
20 hours/week
10 hours/week
78 hours/week
*** See Section 4 for the basis of the estimate of electrical consumption.
****Replacement Materials: The original belts used lasted only 1200 hours
per belt. These belts have been replaced with a seamless polypropylene
belt that has a life of 5000 to 8000 hours per belt. A set of new
belts costs about $6,000 and takes 3 men about 4 hours to install.
Belts are replaced when the edges fray. Belts removed from the BFP
units are re-used in other less wear applications. Other materials
costs associated with the BFP are as follows:
Rollers/Bearings $5,000/yr/BFP
Motors/Pumps $3,000/yr/BFP
Support Equipment
(Polymer feed, etc.) $5,000/yr
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of 15 KWH per dry ton and a consumption of 40 KWH per square
foot of building space for lighting, HVAC, and other general building needs
(reference WPCF Manual of Practice No. FD-2 Energy Conservation in the
Design of Wastewater Treatment Facilities).
Typical Hours of Operation
(no. units;hrs/day): 1 unit - 24 hr/day
Estimated Electrical Requirements (kw-hr/year):
Equipment 164,300
Building 1,046,600
TOTAL 1,210,900
-------
VIII. VACUUM FILTRATION DEWATERING
The following information regarding the former method of sludge dewatering,
vacuum filtration, is provided for comparison purposes.
1. GENERAL INFORMATION
Technology:
No. of Original Units:
No. of Existing Units:
Unit Size:
Date Installed:
Date Removed:
Manufacturer:
2. OPERATING PARAMETERS
Percent Solids of Feed:
Percent Solids of Cake:
Chemical Dosage:
Solids Capture:
3. ENERGY CONSUMPTION
Rated HP of Unit:
Typical Hours of Operation
(no. units;hrs/day):
Vacuum Filtration
2 (could not now be used because
discharge conveyor has been rerouted for
BFP)
12 foot diameter? 14 feet long;
528 SF effective area
1976
1 in 1982
1 in 1985
Envi rex
6% to 7%
28% to 29%
15 % Lime
4 % Ferric Chloride
Not as good as BFP units
90 HP/unit
2 units at 24 hrs/day
IX. GRIT, SCREENINGS, AND SCUM DISPOSAL
GRIT DISPOSAL: Landfilled
SCREENINGS DISPOSAL: Landfilled
SCUM AND GREASE DISPOSAL:
Mixed with sludge in sludge blending tanks, dewatered, and incinerated.
Typically, about 450 gpd of scum is processed. The plant staff has
-------
found that up to 1000 gpd of grease and scum can be processed without
interfering with the dewatering process. Feed rates greater than 1000
gpd can blind the BFP belt, reducing the percent solids of the product
cake.
X. INCINERATION
1. GENERAL INFORMATION
Technology:
Date Installed:
Manufacturer:
No. of Units:
No. of Hearths Per Unit:
Diameter:
2. OPERATING PARAMETERS
Multiple Hearth Incineration
1976
Envi rotech
3
10
22' - 3"
Cake Feed System:
A serpentix endless conveyor system that originally serviced the vacuum
filters has been shortened and rerouted to receive cake from the BFP
units. There is no cake storage between the BFP units and the MHF
units, so a steady feed to the dewatering process must be maintained to
create a uniform feed to the furnaces.
Design Peak Loading Rate:
18000 wet pounds per hour (4.6 wet pounds/sf hearth area) of dewatered
cake with 20% solids and 70% volatiles
Average Loading Rate:
2500 dry pounds per hour (2.5 wet pounds/sf hearth area) of dewatered
cake with 26% solids and 66% volatiles (FY 1988)
No. Units typically in Operation:
Rotational Speed of Rabble Arms:
Percent Oxygen in the Exhaust Gas:
1 unit in operation
1 unit in stand-by mode
1 unit in clean/maintenance mode
60 to 70 seconds per revolution
typically 10% to 11%
-------
Average volume of Shaft Cooling Air Returned As Combustion Air:
0 to 201 depending on the operator. Shaft air going up the stack
rather than being recycled tends to act as a plume suppresant,
especially in the winter.
Sludge Characteristics:
Last sludge analysis was performed in 1979 when lime and ferric were
still being used for chemical conditioning prior to dewatering with
vacuum filters. The results were as follows:
4380 Btu/# solids
10,000 Btu/# volatiles
41.7% volatiles
Temperature Profile of Incinerator (degrees F):
1979 1988
1979 1988
Hearth
1
760
900
Hearth 6
480
400
Hearth
2
1025
1110-1570
Hearth 7
290
300
Hearth
3
1160
1190-1570
Hearth 8
190
200
Hearth
4
1460
760-1410
Hearth 9
145
150
Hearth
5
1380
590-1210
Hearth 10
130
100
In 1979, scum was injected directly into the furnace on hearth no. 5. This
along with the changing characteristics of the sludge has altered the
typical temperature profile (in 1979 were using vacuum filters with lime
and ferric chloride sludge conditioning).
3. COST INFORMATION
A. Capital
Facilities Plan Estimate of Capital: Not available
Actual Capital Cost (bid + change orders):
Capital costs are indexed to October 1973 costs (ENR = 1934)
Structures
Equipment
Total
$1,543,000
$3,083,900
$4,626,900
-------
Costs include the three incinerators, air pollution control equipment,
ancilliary equipment, and structure.
Cost of Modifications: No major modifications have been performed.
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor*
Maintenance Labor**
Fuel use
- Natural Gas
- No. 2 Fuel Oil
Chemicals
Electricity***
Equipment
Building
Replacement Materials****
TOTAL
42 hr/day
84 hr/week
6,789,000 cf/year
31,848 gal/year
None
1,800,000 KWH/year
1,542,200 KWH/year
$ 191,700
$ 54,600
$ 24,200
$ 18,800
$ 82,800
$ 70,900
$ 53,300
$ 496,300
* 1 operator 24 hour/day
1 senior operator 6 hour/day
1 swingman 12 hour/day
** The maintenance department considers the dewatering and incineration
building as one work area. No distinction is made between time spent
in the dewatering area and the incineration area. Two maintenance
workers are assigned full-time to the dewatering/incineration area.
One electrician and one instrumentation technician spend about 20% of
their time in the dewatering/incineration area. For the purposes of
this evaluation, it is assumed that these workers split their time
50/50 on the incineration and dewatering unit processes. A third
maintenance technician is assigned to the incineration area when an
incinerator first comes off-line to begin the routine maintenance
program. Labor for general housekeeping and for oversight by the
-------
mairtoenamce chief has been included in the labor estimate,
breakdown! for maintenance labor is as follows:
The
full-time maintenance technician
electrical technician
instrumentation technician
general {housekeeping
maintenance chief
swinpani (2 months/year during
incin. rotation)
40 hours/week
4 hours/Veek
4 hours/week
20 hours/week
10 hours/Veek
6 hours/Veek
Total 84 hours/Veek
*** Reference Section 4 for the basis of the electrical consumption
estimates.
****lnstrumesitation equipment costs about $30,000/Vear. Of this $30,000,
about $2(0,000 is spent to buy new equipment to replace outdated
technology and about $10,000 is spent on spare parts to keep the
existing equipment operable. Installation of new, up-dated equipment
often results in significant O&M cost savings. For instance, a
recently installed oxygen analyzer has 1/2 the power draw of the former
unit and has reduced the potable water use in the plant by 1/2.
Every 6 months, an incinerator is taken off-line for routine
maintenance. This maintenance period begins by hiring an outside
consultant to inspect the furnace for refractory damage. Because of
the care shown by the operations staff in controlling temperature
fluctuations during regular operation and during heat-up and cool-down
periods, there has never been major refractory damage to any of the
three incinerators. The plant staff follows up this inspection with an
extensive maintenance program that is outlined in the following
section. Typical materials costs for this maintenance program are as
follows:
Refractory Inspection $250/inspection
$500/year
Rabble Tooth Replacement $6,600/year
Refractory Repair $3,800/year
Bearings $l,700/year
These major cost items represent about 80% of the total maintenamce
cost for materials and supplies.
Maintenance Concerns:
The desired maintenance schedule is to rotate the three furnaces every
6 months between the operating, maintenance, and stand-by modes. Over
the past few months, furnaces have been taken out of operation more
-------
frequently (every 2 to 3 months) due to the dropholes clogging more
frequently. A significant increase in fuel use generally is a good
indicator that some dropholes are clogged. The increase in drophole
clogging is attributed to the changing characteristics of the sludge
being processed (more thickened waste activated sludge and septage
being accepted from outside sources).
It takes about 1 week for a furnace to cool from operating temperature
to ambient temperature. It takes about 3 days and 1,000 gallons of
fuel to heat the furnace from ambient temperature to operating
temperature. In an emergency situation, a furnace could be taken out
of service, have minor repair work completed, and returned to operation
in a 2 week period.
During the 12 month shut-down period, the plant maintenance staff
completes a 210 point checklist of items that must be inspected before
the furnace is returned to duty. Each item is signed off both by the
technician performing the inspection and a maintenance supervisor that
reviews his work. Maintenance personnel consider the development of
this checklist as a turning point in their operation. Prior to having
the checklist, incinerators often had to be shutdown shortly after
going on-line due to minor maintenance problems. During this period,
the easy to check, high profile items were being addressed during the
maintenance down periods, while less obvious, but equally important,
maintenance items were being missed. These shut-downs were very costly
in terms of fuel use and labor. Since the development of the
checklist, incinerators have routinely completed the 6-month operation
period with no need for maintenance shut-downs. Some of the major
items that are checked are:
1. Clean all dropholes.
2. Clean any sludge build-up on the hearths.
3. Remove clinkers.
4. Remove build-up on burners.
5. Check cooling air fans, shaft air fans, and other equipment for
signs of wear.
6. Rotate rabble teeth from hot hearths (hearth nos. 1 to 5) to cool
hearths (hearths 6 to 10) to increase their useful life.
A complete copy of the checklist is appended to this report.
Operation Guidelines:
Operation of a MHF involves control of the following variables:
- rotational speed of the rabble arms
- excess air level
- auxiliary fuel use
- volume of shaft cooling air returned as combustion air
- volume of the sludge feed
-------
•>
There are no published rules that an operator must follow to insure
that the furnace will perform properly. Operation of a MHF involves
the manipulation of several variables which could be adjusted in
different ways to achieve the same result. No two operators control
the furnace in exactly the same way. However, operators at the Upper
Blackstone facility are encouraged to achieve the following common
goals:
- maintain a minimum combustion temperature of 1250 degrees F for air
emissions control
- do not allow the combustion temperature to exceed 1500 to avoid
clinkers
- burn as little auxiliary fuel as possible
- maintain a minimum excess oxygen level of 8 percent (dry basis) to
insure complete combustion and avoid smoke in the stack exhaust
- maintain hearth no. 4 as the combustion hearth
The variables adjusted to achieve these goals are left to the
operator's discretion, but minimization of fuel use is emphasized. The
operators monitor the furnace by observing the stack exhaust, opening
doors on the furnace to observe the fire itself, and observing the
hearth temperature profile and the percent excess oxygen in the exhaust
gas from the control panel. It is important that the operator directly
observe the fire and the stack exhaust and not rely completely on
temperature sensors because localized hot or cool spots may produce
misleading readings.
As a result of maintaining a consistent temperature profile and
maintaining controlled heat-up and cool-down periods, the 12 year old
furnaces have never suffered any significant refractory damage. The
operations staff has found that a 27% BFP cake (5.5% BFP feed) burns
autogenously and is easy to control. At times the percent solids of
the cake increases to 30-31%. At this percent solids, the incinerator
is difficult to control because the sludge burns on the upper hearths,
resulting in smoking problems.
Operator Training:
The Upper Blackstone facility has installed a job-rotation program in
which operators are moved to a different area of the plant every two
weeks. This job-rotation program has been a very effective management
tool. It allows operators to understand and appreciate how the
efficiency of a process is affected by the performace of the preceding
unit and helps relieve the boredom and complacency that can result from
operating the same piece of equipment each day. The job-rotation
program encourages teamwork and focuses the operator's attention on the
overall goal of saving fuel in the incineration system rather them on
the operation of an individual process.
New emplyees assigned to the incineration area are teamed with a senior
staff memeber who is very experienced in the operation of the
incineration system. The senior staff member will provide hands-on
-------
operating training for the new employee. Generally, it takes about two
months for a new operator to reach the point where he can monitor the
furnace without direct supervision. At all times, a senior operator
who is proficient in the operation of the furnace is on-duty within the
plant. If conditions in the furnace begin to change, the junior
operator can call on this senior operator for guidance. Although most
operators are able to learn the basics of furnace operation in two
months, there is no concrete schedule for operator training. Training
time for each new operator must be determined on a case-by-case basis.
Some operators become proficient in furnace operation very quickly
while others take longer than two months to feel comfortable with the
furnace.
Operation of an autogenous incineration facility requires
knowledgeable, attentive, cooperative operators throughout the solids
train. The implementation of the job-rotation program and the hands-on
approach of management has helped develope such a staff at Upper
Blackstone.
4. ENERGY CONSUMPTION
Equipment Hated HP
Plant Water for Scrubber
150
Induced Draft Fan
300
Slurry Pump
75
Ash Vacuum Pump
40
Shaft Cooling Air Fan
20
Combustion Air Fan
40
Shaft Drive
15
Conveyors
5
Total
536
(runs 120)
(runs 221)
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption for equipment is estimated based upon
Figure 3-113 of the EPA publication entitled Energy Consumption In
Municipal Wastewater Treatment and electrical consumption for general
building needs such as lighting and HVAC is estimated based upon a value of
40 KWH per square foot of building space.
Estimated Annual Electrical Requirements (kw-hr/year):
Equipment - 1,800,000
Building 1,542,000
TOTAL 3,342,200
-------
Annual Fuel Use:
Fiscal Year BTU/Dry Ton Gallons Fuel/Dry Ton
FY 83 556,500 4.0
FY 84 1,273,253 9.2
FY 85 577,265 4.2
FY 86 564,000 4.1
FY 87 977,416 7.1
FY 88 1,014,148 7.3
Includes start-up and cool-down fuel
Note: 1 therm natural gas = 100,000 Btu
1 gallon No.2 fuel oil = 138,000 Btu
Annual Fuel Use For Start-up and Cool-Down Periods (gal/year): about 2,000
XI. AIR EMISSIONS CONTROL
1. GENERAL INFORMATION
Technology:
Venturi wet scrubber and impingement tray scrubber arranged in series
with a pressure drop of 20 inches w.c. No afterburner.
Date of Last Emissions Test:
All 3 furnaces were tested during start-up. In 1984, 1 furnace was
tested. The results showed .69 i particulate per dry ton. No
emissions testing has been performed since 1984.
Stack height: 75 foot
Stack Diameter: 4 foot
Exhaust Gas Flow: Typically about 21,000 cfm
Exhaust Temperature: Typically 100 F to 120 F
Scrubber Water Treatment: Returned to primary clarifiers
Scrubber Water Characteristics (Q,TSS,BOD): 1328 gpm (includes all coolers
and scrubbers)
TSS 60 mg/1
-------
XII. ASH DISPOSAL
1. GENERAL INFORMATION
Technology:
Ash is removed from the lower hearth by a vacuum system and transferred
to a storage silo. Three times each week, the silo is emptied and the
ash is trucked to an on-site landfill.
Location of Landfill (on-site/off-site): on-site
Total Annual Volume of Ash Landfilled (cy/year): 4000 to 5000
2. COST INFORMATION
A. Capital
Cost of Truck(s): $43,000 (expected life 15 years)
Cost of Landfill (if owned by district): Not available
Tipping Fee at Landfill (if commercially operated): N/A
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
hr/day
$ 0
Landfill Maintenance*
36 hr/week
$ 23,400
Truck Mileage/Maintenance
$ 900
Materials/Supplies**
$ 5,000
TOTAL
$ 29,300
* 24 manhours/Veek for hauling
12 manhours/Veek for loading time at landfill
** Cover material is now applied at a 50/50 ash/cover ratio. Cover
material is now obtained on-site. If State requirements for cover
material change and cover material must be hauled to the landfill from
an off-site location, cover material costs could increase to about
$20,000/year.
-------
XII. OPERATIONS MANPOWER ALLOCATION
The operations unit works 3-8 hour shifts per day. Each shift consists
of 5 men allocated as follows:
1 senior plant operator
1 BFP operator
1 incinerator operator
1 operator dedicated to the liquid train
1 "inside man" who acts as a swing man for the solids handling
processes. His responsibilities include checking the sludge blanket
of the DAF units and adjusting the skimmer timer accordingly,
emptying ash and clinkers from the incineration area, and general
clean-up duties.
For the purposes of this evaluation, the hours for operators who split time
between several processes have been further broken down as follows:
senior plant operator
There are 20 people (4 crews) in the operations unit. Each day, 3 crews
are on duty and one crew is off duty. On each crew, the operators are
rotated every 2 weeks to a new position (BFP operator, incinerator
operator, etc.) in an effort to develop a well-rounded staff that is
knowledgeable of the entire system, rather than one unit process.
XIII. MAINTENANCE MANPOWER ALLOCATION
The maintenance unit works 1-8 hour shift, 5 days per week. The
maintenance department consists of 16 people. Some maintenance workers are
assigned full-time to a particular area of the plant while some workers
move from area to area, depending on where the greatest need is. When an
operations or maintenance staff member discover a maintenance problem, they
fill out a work order and submit it to the maintenance department. Each
morning, the maintenance chief reviews the work orders, consults with the
senior plant operator if necessary, and prioritizes the work orders
accordingly. An estimate was made of the breakdown of maintenance time
dedicated to each unit process. The results are as follows.
1 maintenance chief
2 workers assigned full-time to the dewatering/incineration area
3 workers assigned full-time to plant housekeeping
incineration
dewatering
liquid end
6 hours/day
6 hours/day
12 hours/day
"inside man"
incineration
dewatering
thickening
12 hours/day
9 hours/day
3 hours/day
-------
3 workers assigned full-time to groundkeeping duties
1 worker assigned full-time to the machine shop
1 full-time clerk
1 worker assigned full-time to lubricating equipment as required
1 electrician who spends about 20% of his time in the
dewatering/incineration area
1 instumentation technician who spends about 20% of his time in the
dewatering/incineration area
2 workers assigned on an as-need basis
For the purposes of this evaluation, maintenance hours for people who split
time between several processes were further broken down as follows:
maintenance chief
Swingman assigned to incineration for 2 months/year during the period when
incinerators are rotated.
housekeeping detail
XIV. COST SUMMARY TABLES
The following tables attempt to (1) estimate a reasonable construction cost
for the existing Upper Blackstone solids handling facilities in 1988
dollars; (2) convert the construction cost to an annual cost; and (3)
present a total annual cost (capital plus O&M) for each unit process.
Capital costs have been estimated by updating the original 1973
construction costs to 1988 dollars using the Engineering News Record (ENR)
cost index. Operation and maintenance costs have been summarized based on
the tables presented earlier in this report.
It should be emphasized that construction costs for such a facility are
very difficult to estimate and, even if estimated accurately, are very
difficult to use in comparison with other facilities. In reviewing these
costs, the reader should consider the following comments:
The original (1973) construction costs presented in this report are
based on the project's Certificate of Completion. Many of the costs
presented in this document are lump sura items that are included as a
general construction cost. It is difficult to assign these costs to a
particular unit process. We have, to the extent possible, attempted to
apportion these construction costs to each unit process based on
building areas, building volumes, or some other reasonable parameter.
Still, it is difficult to accurately disaggregate many of the lump sum
items into a cost for each unit process.
incineration
dewatering
10 hours/week
10 hours/Veek
incineration
dewatering
20 hours/week
20 hours/week
-------
UPPF.R BLACKSTONE WPC]¦
CONSTRUCTION COSTS
PROCESS
ORIGINAL
CONSTRUCTION
COST
(ENR = 19 3 4)
UPDATED
CONSTRUCTION
COST
(ENR = 4 5 4 2)
ANNUAL
CAPITAL
COST
Waste activated sludse
thickening
-structures
-equ ipmen t
-total
Siudse holding tanks
-structures
-equipmen t
-tota1
Sludse dewaterine
-structures
-equipment
-total
Sludge incineration
-structures
-equipment
-total
$7 39,700
S 2 9 0,000
S1,029,700
S291,000
S60 , 000
S 3 51 ,000
Si ,04 7 ,800
S7 00,000
SI,74 7,800
$ 1,543, 000
S3,083 , 900
S4,626,900
SI.737,200
S6R 1 , 100
32,418,300
S683 , 400
S 1 40,90 0
S824,300
S2 ,460 , 800
SI ,644 ,000
S 4,104,700
S3,023,700
$ 7,242,500
S10,866,300
S145.700
S6 9,4 00
S215. 100
Soi.300
S 1 4 , 4 0 0
S 71,700
S206 .400
Si67 . 4 00
S 3 7 3,800
S303 ,900
S7 3 7 , 600
Si,04 1 ,500
-------
'WER fcUrHSTOKE KPCf
ANNUAL COSTS FOB SOUQS
HANDLING P80C8SS83
(-S0CESS
CAPITAL
LaBOB
ELECTIICITT
FUEL
CHEMICALS
KAltBlALS
TOTAL
ANNUAL COST
V 1nUL CAHTAL MST
ANNUAL COST 1/DkMiWlll
OAK COST
1/0ST TO* (21
TOTAL COST
J/StI TOM
Sludie Puipinit
01
132,$00
1800
JO
10
ll.OUli
134,301'
1.2(1
to.1)0
13.11
$3.12
V.t.S. Tkickcnint
tm.ieo
115.200
154.000
JO
(0
I3.30D
mi.ttp
10.40V
13.82
18.61)
ll(.42
Koldinf/Blend Tanls
JTI.TOj
13.300
$600
10
10
10
192.20»
:.37H
13.27
10.St
11.23
SMie Devaterinf
HOI,(00
1218,600
155,800
10
123,860
nr. .oou
|73(,6Mj
M.Tn
118.47
135.52
153.33
Sludft Incineration
Sl.04l.S00
12(6,300
1153,100
10.000
to
153.300
11.531.8HC
Si.601
147.it
145.17
132.73
Ask Disposal
Ml'
<23.(00
to
1300
10
j5 .liu.i
113,300
1.06V
10.00
12.67
12.(7
TOTAL
tl .712.700
1555,300
1264.300
113,900
113.800
JHK6M
12.765,801'
lu&.oov
173.12
(34.03
1173.15
Kith Afterburner
1123.03
1208.15
ill based on sjstei desi{» capacity of (0 in tons per day.
121 Based on FT88 i»era
-------
Building prices for two similiar facilities can be very different
depending on such site-specific factors such as depth of ledge, local
materials costs, site constraints, construction market conditions, or
other construction considerations.
- The amount of reserve capacity built into a facility can significantly
affect construction costs. The amount of reserve capacity allowed for
during design can depend on several factors such as site-specific
constraints, plans for future expansion or growth, and the design
consultant's philosophy concerning system redundancy.
- The dewatering area at Upper Blackstone was originally designed for
vacuum filters rather than belt filter press units. If the facility
had originally been designed for belt filter press units, the
dewatering area could have been much smaller, thereby significantly
reducing construction costs.
- Based on recent manufacturer's quotes received for other projects, we
believe that incineration equipment costs have increased at a greater
rate than the ENR cost index. As a result, incineration equipment
costs presented in this table may be low.
In converting the estimated construction cost to an annual cost, it was
assumed that all structures would have a useful life of 40 years and all
equipment would have a useful life of 20 years. A discount rate of 8
percent was assumed to determine an appropriate capital recovery factor.
XV. SUMMARY OF ENERGY REQUIREMENTS
The following table summarizes energy consumption requirements for each
unit process. For the purposes of this table, the auxilliary fuel use for
sludge incineration has been expressed in terms of gallons of No. 2 fuel
oil, although in reality a combination of fuel oil and natural gas is used.
The plant staff prefers to use natural gas as the auxilliary fuel source
because it is more economical than fuel oil, but during winter months when
the demand for natural gas is high, the District is forced to switch to
fuel oil. Currently, the facility does not operate an afterburner as part
of its emissions control system. The existing operation has been able to
meet all current air emissions regulations without the use of an
afterburner (reference air emissions section). It is difficult to predict
future changes in air emissions standards and their subsequent affect on
existing operations. However, if more stringent air emissions regulations
are imposed in the future, the installation of an afterburner may be
required at all sludge incineration facilities to control the possible
products of incomplete combustion. Operation of an afterburner is very
costly in terms of auxiliary fuel use. The lack of data regarding the
composition of Upper Blacksone's sludge makes it difficult to project the
exact amount of fuel that would be consumed by an external afterburner.
However, based on experience at similiar facilities, it is estimated that
operation of an external afterburner would increase auxiliary fuel use at
the Upper Blackstone Facility from about 7 gallons of fuel per dry ton of
sludge to about 67 gallons of fuel per dry ton. This would increase
-------
incineration costs by about $35 per dry ton of dewatered cake if fuel oil
were used to fire the afterburner or about $29 per dry ton if natural gas
were used. This potential increase in auxiliary fuel use is reflected in
the attached table.
The Upper Blackstone incineration system does not utilize any heat recovery
equipment. An Energy Audit Report prepared by CDM in 1982 investigated the
cost effectiveness of installing a heat recovery system as a means of
energy conservation. The system considered consisted of a series of heat
exchangers which would recover heat from the flue gases to be used for
heating water. The system would generate hot water at 140 F to be used
mainly for heating the sludge management building and scum pipe cleaning.
The system would be shutdown during the summer months when building heat is
not required. It was determined that this system would result on
approximately $13,100 in annual savings at a capital cost of $68,000 (1982
dollars), resulting in a payback period of 5.1 years. Several other energy
conservation plans presented in the study had shorter payback periods. As
a result, this heat recovery plan was never implemented. Because there is
no obvious use for recovered heat at Upper Blackstone (such as year-round
building heat or a sludge drying system), the implementation of a
heat-recovery system has not been a priority item.
LESSONS LEARNED
Operating experience at the Upper Blackstone Facility provides some
insights into fuel-efficient incinerator operation.
The use of storage and mixing tanks to maintain a consistent sludge feed to
the dewatering and incineration processes is essential to avoid system
upsets that would require the use of auxiliary fuel. A constant sludge
feed is required to maintain optimum operating conditions.
The implementation of a job-rotation program has made the staff recognize
that the success of the incineration process is dependent upon the
performance of the preceeding solids handling processes.- Operation
throughout the solids train is focused on delivering a consistently dry
feed to the incinerator. Operators at each step in the solids handling
processes strive to remove as much water as possible from the sludge.
The development of an excellent maintenance program has increased the
cost-effectiveness and fuel efficiency of the incineration process in
several ways:
1. Reducing auxiliary fuel use by minimizing unscheduled maintenance
shutdowns.
2. Minimizing costs for replacement materials by extending the useful
life of furnace components such as the refractory brickwork and
other ancilliary equipment.
-------
UPPE1J OLACKSTONE Wl'CF
ENERGY KKOU 1KKMKNTS KOH SOI.IDS
HANDLING PROCESSES
PROCESS
KL.KCTU 1C1TY
IKW-HH/YR)
Bw iId i ntf Kqu ip
Total
fuel Oil.
(GAI./YEAK1
FUEL Oil.
IGAI./URY
TOTAL UTU
CONSUMPTION
UTU PER :
DRY TON !
;S1ulI«(! I'timpintf
--
18,000
18,000
0
0
0
0 '
JW.A.S. Thickening
770,000
37 B,900
1,14 8,900
0
0
1 1 .189,000.000
1 , 04 5,738
! Ito Id i ni!/B1 end Tanks
—
I 1.200
I 1 . 200
0
0
0
0
Sb'iudKc Dewtttcring
1.046,600
164,300
1.210,900
U
0
12, 109,00C,000
1 , 102, 17 1
.'Sludge Incineration
-without afterburner
1 ,800,000
1,542,200
3,342,200
80.200
7 . 3
11 ,4 89,600,000
4 ,049,479
! -with afterburner
1 .800,000
1.542,200
3,34 2 ,200
736 , 100
6 7
135,003,800,000
12,288,154
NOTK: Conversion factors used are as follows:
Electricity 10.000 BTU/KW-HR
Fuel Oil 138,000 BTU/«al
All figures ore bused on FY 1988 consumpt i on records ami
-------
3. Providing the operators the information necessary to operate the
incinerator fuel-efficiently by keeping the instrumentation and
monitoring equipment operable and up-to-date in terms current
technology. For example, a key control parameter for the operator
is the percent excess oxygen in the exhaust gas. However, an
exhaust gas oxygen analyzer is a difficult piece of equipment to
keep in operable condition because it is a fairly sensitive piece
of equipment that must operate in a dirty, thermally stressful
environment. At many facilities, the system's original oxygen
analyzer is no longer functioning, but the plant staff has not
bothered to replace the unit. As a result, the operators must, in
effect, run the furnace blindly. At Upper Blackstone, equipment
such as the exhaust gas oxygen analyzer is calibrated regularly and
replaced if breakdowns make the equipment inoperable or if new,
superior technology becomes available.
A major key to the success of this maintenance program has been the
development of a 210 point checklist of items which must be addressed
during a maintenance shutdown period. This insures that each incinerator
is thoroughly examined before being returned to service, which in turn
reduces repair costs and saves fuel by identifying minor problems before
they become major problems and minimizing unexpected shutdowns during
operation periods.
The sludge at Upper Blackstone dewaters exceptionally well. While this
success can be partially attributed to operator attention, it is possible
that an industrial influence in the influent wastewater stream has a
positive affect on the dewatering characteristics of the sludge. The
characteristics of each facility's sludge is influenced by the
characteristics of that facility's influent stream. Some facilities may be
fortunate enough to begin their solids handling process train with a sludge
that by its nature dewaters better than sludge from similiar facilities.
-------
. CFT UK£ U-J—
INCINERATOR HO. __
EXPECTED ON LINE
FIRE BOX
rabble down all sab
clean drop boles . ..
inspect refectory repair as necessary
check buraer.eonee- cJ**: Uj - rvt
, * ' <*V t*-Wil. - •
BABBLE 6T8TEH "
—. T--
(
inspect all teeth
swap upper teetb to lower hearth where possable
replace burned & bent teeth
inspect rabbis arm & root for cracks
check <11 lute caps.
CENTER SHAFT L DRIVE ' *
Drain k replace-oil in stsp bearing -
ci£8nc^e£^&B^et8Vo1 ^ pinion Koar for vear
regreass bevel t pinion gear
grease upper bearing
fill sand seals .
change oil in Falk reducer It drive.
check clutch for wear
check clutch springs for propor tension
beck coupling & motor bearings
check oil seals
check Reeves drive-belts-shoave fc beari'figs
cheek mounting bolts
clean & touch up paint
( PACE 1 OP 6 PAGES )
IPSP.
DATE 81 COMMENTS
* I
4
-------
( PAGE 2 OF 6 PAGES )
POOLING AIR SYSTEM
I
Check air intake raceway for water
Check belts .
lubricate motor, fc. Impeller hearings
Repack incinerator]shaft seal
Clean impeller.. .J ..... ..
Check mercury svitoh
Tighten hold.down, bolts. _
t
Clean 6 touch'up paint .'
SLURRY PUMP ;
Check belts
leek seal & bearings
Repack pump
lubricate fit operate mil valves
Check check valve for wear
Inspect hold down bolts
Clean & touch up paint
lubricate motor & bearings-Check coupling
ASH SYSTEM
Clean lateral.lint.
Clean hopper '
Check bindicator. probs _ • ' •
Clean fc lubricate, air. gate
Clean t lubricate hopper door track & cable
Tighten bolts
r ispect & lubricate vacuum breaker
Clean pit
DATE
INSP.
BY
COMMENTS
-------
( PAGE 5 OF 6 PAGES )
gCKUBBER SYSTEM „ ....
i
Inspect 4. clean impingement plates_
Clean plant, water, flow meter _. ,
Clean plant. water_strainer.
Check spray noztlas :J
Inspect venturi.fc.breaching for .brick damage ...
Operate venturi.fc. check hoot & pine!
lubricate piston.&.guides . v .
Clean water seals .. *
Check plenum gaskets & tighten .....
Lubricate & operate all valves
BURNER SYSTEMS
(
open burner fronts
Inspect burner cone -Wok -f>>- ftra,*\f*£/
Clean nowles fc fine 0' .... *r 0
Clean scanner & pilot ports . . ... .
Set ignition p.oints . *- .
Inspect combustion air'linage _
Clean oil strainer
Inspect & lubricate latch valve ...
Inspect sir, oil, sad gas piping for^leaks
Check all gauges
Operate l lubricate all valveii „.
Inspect.high ...voltage wire ( ignition ),'
Inspect burner control *ox . i
(
DATE
>jJ/
INSP.
BY
COMMENTS
-------
( PAGE 4 OP 6 PAGES )
.R SYSTEM
Blow out all air. lines
Cheek drying. system &. strainer.
Cheek regulators L^
Check. all air, gauges^ ^
Fill all air lute jars
Inspect piping .^orlletfts^
(
OIL fc OAS SYSTEM
Rebuild Vikifcg oil_puapa
Check all gauges
lubricate & operate..all valves,
"nepect all piping for leaks
vie«p filters
Operate Mepeon valve
Check oil tanks ftir water .
Inspect gas nanafold & solenoids
— IHSP.
DATE BY COMMENTS
I.P. PAW
fann* S///io.v* . .
Clean & balance Inpeller "
Inspect inlet & exhaust dashers
Inspect it lubricate linkage
Inspect air operators
Clean brushes fc coooutator ( motor )
Inspect & lubricate coupling & motor
lubricate or repack bearings
f ispect nount for cracks
Check bold down bolts
hv°°S
Clean is touch up paint t-vrf"T.
-------
( PAGE 5 OP 6 PAGES )
f ORCED DRAFT PAN .
Check coupling .
Operate & lubricate damper valvoa
Inspect air operator & speed control
Inspected & lubricate bearing
Tighten hold down bolts
Clean & touch up paint
COMBUSTION AIR FAS
Clean imnpellerfc screen •
Inspect tt lubricate coupling & bearings
Tighten bold down bolts
llean t touch up paint _____
CONVEYOR SYSTEM
Clean belt & rollers
• • . • -
Adjust belt for tracking
Clean & lubricate seals linkage
Clean & lubricate drop damper & chute
Change scraper blade & adjust '
Calibrate scale
Clean & touch up'paint
DATE
W-
COMMENTS
V
MISCELLANEOUS
?6nc,v& Aoc?s
"nspect & lubricate by pass damper
Bolw scub lines
Lift grates & clean incinerator top «
Touch up all paint
Tighten all hangers fc belts •
//JSp&Gr* GoKK*tlb*/
-------
V rMt, o ft t> rAii&b )
ELECTRICAL
(
Air & vacuum clean all panels ft. controls
Clean contacts on all starters & contactors
Replace all light bulbs as necessary .
Inspect burner boxes & scanners .
Test anunciator.system ... .
Operate all safety.cutouts•& interlocks
Bump all motors
Clean & touch up paint on panels
Axap^- reading on all motors '
- «,Cn-»cg . '
Clean brushes on I.D. fan motor.
IHSTKUHEKTATION
, *
^ in all meters fc recorders
Calibrate All meters fc recorders
Replace'all pads, Ink & charts
Inspect fc calibrate o2 analyzer
Replace damaged thermocouples .
Calibrate all thermocouples
Test safety limits fc trips
Run 30 ain. 6606 test on scale .......
Clean instrument air lines & filters.
Inspect terminal boards 6 strips.. ;
Soap test instrument, air lines ..
DATE
w
COMMENTS
C
-------
APPENDIX C
DUFFIN CREEK
WATER POLLUTION CONTROL FACILITY
I. GENERAL INFORMATION
Address:
Phone Number:
Contact:
Design Engineer:
Duffin Creek WPCF
901 McKay Road
Pickering, Ontario
Canada L1W3A3
(416) 686-2003 (main plant)
(416) 686-2007 (incin area)
R.J. (Bob) Barnaby
Supervisor of Dewatering and Incineration
Proctor & Redfern
Dave Filman
(416) 445-3600
The following Proctor & Redfern study was used as the primary reference for
all of the capital costs and many of the operation costs presented in this
case study report:
"Development Of A Methodology To Investigate The Cost-Effectiveness Of
Various Sludge Management Systems"; The Proctor & Redfern Group, January
1988.
Year Began Operation:
1980
Design Average Flow:
40
MIGD
(48
MGD)
Design Peak Flow:
100
MIGD
(120
MGD)
Current Average Flow:
42
MIGD
(50
MGD)
Current Peak Flow:
100+MIGD
Average influent BOD:
134
mg/1
Average influent TSS:
196
mg/1
Average Effluent BOD:
19
mg/1
Average Effluent TSS:
10
mg/1
Permitted Effluent BOD:
15
mg/1
Permitted Effluent TSS:
15
mg/1
Other Effluent Requirements:
Phosphorus
1
mg/1
-------
Plant Overview:
Treatment processes in the liquid train include screening, grit removal
with detritors, primary settling, phosphorus reduction with the
addition of ferrous sulfate,conventional activated sludge process,
secondary settling, and chlorination prior to discharge to Lake
Ontario. The solids handling train includes co-settling of the primary
and secondary sludges, anaerobic digestion, sludge storage, sludge
dewatering with membrane filter presses, and incineration with a fluid
bed reactor.
A plant expansion is currently in the design/bid phase. The expansion
will increase plant capacity to 80 migd (96 mgd). The new liquid
treatment facilities will mirror the existing facility. Improvements
to the solids train will be performed in two phases. Additional
digesters and membrane filter presses will be installed as part of the
first construction phase. A third fluid bed incinerator will not be
required until flows reach the 55 to 60 migd range (current flow is 42
migd), so installation of a third furnace will be delayed to the second
construction phase. Additional details of the plant expansion will be
provided in subsequent sections.
A schematic of the solids train showing 1987 average condition process
loadings is attached.
II. UNIT COSTS
Base unit costs on 1987 records.
ITEM
UNIT COSTS*
CANADIAN
U.S.
Labor ($/hour)**
$ 17.94
$
14.71
Polymer ($Ag,#)
$ 5.15/kg
$
1.92/#
Electricity ($/kw-hr)
$ 0.045
$
0.037
No. 2 Fuel Oil ($/liter,gal)
$ 0.237/1
$
0.74/gal
Natural Gas ($/cubic meter,
$ 0.15/m
$
0.35/100 cf
cubic foot)
Steam***
$ 51/1000kg
$
19/1000#
*Based on exchange rate of $1 Canadian ¦> $.82 U.S.
~~Includes employee benefits
***Unit price used in recording "sales" of energy from one unit process to
another unit process.
-------
59,300 kg/day
130.700 #/day
5.2% SOLIDS
60% VOLATILES
27,100 kg/day
59,700 #/day
4.6% SOLIDS
24,100 kg/day
53,200 #/day
32% SOLIDS
40% VOLATILES
HOLDING
TANKS
WASTE ACTIVATED
SLUDGES
SLUDGE
DIGESTION
FILTER
PRESS
DEWATERING
FLUIDIZED-BED
INCINERATION
(HOT WINDBOX)
DESIGN)
ADDITION
-------
III. SLUDGE TRANSFER PUMPING
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption will be based upon curves'presented in the
EPA publication entitled Energy Conservation in Municipal Wastewater
Treatment.
Transfer Pump
No.
Units
HP
Kw-hr/
year
Annual
Electrical Cost
Canadian U.S.
Raw Sludge Pumps
Digested Sludge Pumps
Filter Press Feed Pumps
Dewatered Cake Pumps*
TOTAL
4
1
4
1
15
15
30
75
8,500
6,800
1,500
1,000
$400
$300
$100
$100
$900
$300
$300
$100
$100
$800
*For further description of the incineration feed system, see Section IX.
IV. SLUDGE DIGESTION
1. GENERAL INFORMATION
Technology:
Date Installed:
No. of Units:
Tank Height:
Tank Diameter:
Tank Volume:
Type of Cover
(fixed or floating):
Anaerobic Sludge Digestion
Two-stage digestion system
1980
4 (2 primary digesters and 2 secondary
digesters)
9.1 meters (30 feet)
33.5 meters (110 feet)
8074 cubic meters/unit (285,000 cf/unit)
Floating
-------
External Heat Source (heat exchanger):
2 Leitch concentric tube heat exchangers per unit
2 Dorr-Oliver spiral heat exchangers per unit
The Leitch heat exchangers are the primary means of providing heat to
the digesters. They serve to transfer heat from the plant hot water
loop ( 75 C/167 F) to the primary digesters. The spiral heat
exchangers were added in an attempt to utilize available heat from the
flue gas scrubber water. The intent was to transfer heat from the
scrubber water (90 F) to the digester sludge feed. This system has
never operated for an extended period because of plugging problems on
the sludge side of the exchanger. The plant staff is considering two
solutions to this problem: (1) the installation of more narrow bar
racks at the influent channel to reduce the size of particles in the
sludge; and (2) using the spiral exchangers for heating plant water
rather than heating sludge.
Operating History:
The digesters were originally installed as an interim sludge
stabilization process. The liquid train of the original treatment
facility was completed about one year before the solids train was
scheduled for completion. Sludge was to be stabilized and landfilled
until the incineration system was ready for operation. Digestion was
to be used as the temporary stabilization process. When the
incineration system was complete, the digesters were raothballed and the
raw sludge was dewatered and incinerated. This operation resulted in a
major odor problem. The staff concluded that raw sludge could not be
processed without some odor control system for the dewatering and
incineration areas. It was decided that the cheapest, easiest way to
remedy the odor problem was to put the digesters back on-line.
Operation of the digesters solved the odor problem. The solids
handling processes are currently operating with virtually no noticeable
odor. The only odor control technology used in the solids train is a
chemical masking agent for the dewatering area. The use of digesters
in the solids train has eliminated what was a serious odor problem.
The destruction of volatiles in the digestion process would normally
make digestion incompatible with an incineration process. This is not
the case at Duffin Creek because the digester product gas is used to
fire the hot wind box of the furnace. The loss of volatiles resulting
from the digestion process is compensated for by the utilization of
digester gas as a fuel source.
Future Operation:
Four new digesters (2 primary and 2 secondary) will be installed as
part of the plant expansion.
-------
2. OPERATING PARAMETERS
Type of Sludge Feed:
Solids Feed (kg/day):
% Volatiles of Feed:
Digested Solids (kg/day):
% Volatiles of Digested
Solids:
Degree of Stabilization
(% reduction in volatile
solids):
Loading Rates:
% Solids Feed:
% Solids of Digested
Solids:
Continuous or
Intermittent Feed:
Design Mean Cell,
Residence Time:
Actual Mean Cell
Residence Time:
Operating Temperature:
Operating pH:
Method of Mixing in
Primary Tanks:
Supernatant Treatment
Co-settled primary and waste activated sludges
59,300 kg/day (130,700 #/day)
60%(volatiles are low because of addition of
ferrous sulfate for phosphorus removal)
27,100 kg/day (59,700 #/day)
40%
34%
2,4 kg volatile solids per cubic meter per day
of digester capacity (.15 # volatile
solids/cubic foot/day)
5.2%
4.6%
Intermittent
20 days
12.8 days
primary units 37 C
99 F
primary units 7.4 avg
Gas recirculation with 6 Aero Hydraulic units
per tank. The plant staff reported that
mixing with these units is very poor. As part
of the plant expansion, an external mixing
system will be included in the new digesters
and retrofitted in the existing digesters.
Returned to head of plant
-------
Supernatant
Characteristics: Avg Q = 1364 cubic meter/day
TS =2.3%
3. COST INFORMATION
A. Capital
Facilities Planning Estimate of Capital: Not Available
A facilities planning level report was prepared in the early 1970s, but
changes in the recommended plan that were made between the report and
design stages were so substantial that the costs presented in the
report would not be useful. The recommended plan presented in the
report included thermal conditioning and did not include digestion or
filter press dewatering. Also, the original plan was based on a 30
migd design flow rather than the final 40 migd design flow. For these
reasons, costs presented in the facilities planning level reports were
not considered relevent.
Actual Capital Cost (bid + change orders): See attached table.
Cost of Modifications/Expansions (year): None
B. O&M
ITEM
Operations Labor
Maintenance Labor
Electricity
Chemicals
Ma te r i als/Suppli es
Other Purchased Services
Total
CONSUMPTION
LEVEL
8 hr/day
1 hr/day + 2 months/yr
1,456,200 kw-hr/year
None
ANNUAL COST
CANADIAN U.S.
$
37,300
$
30,600
$
12,300
$
10,100
$
65,500
$
53,900
$
9,000
$
7,400
$
18,000
$
14,800
$142,100 $116,800
Note: The digestion and incineration processes are considered to be
connected processes; therefore the digestion process does not take a credit
for the digester gas used in the furnace hot wind box and the incineration
process does not take a credit for heat provided to the digester building.
-------
CAPITAL COSTS - SLUDGE DIGESTION
Construction/
Original
Updated
Updated
Contract
Major Cost
Purchase
Construction
Construction
Construction
Construction
No.
Item
Date
ENR
Cost
Cost *
Cobt *
(Canadian
{Canadian
( U.S.
$1,000)
$1,000)
$1,000)
7
Gen, Construction
June 1977
2541
$2,894
$5,165
$4,235
Purchased Equipment:
7
Primary Covers
Feb 1977
2505
$423
9766
$628
7
Mixing Mechanism
Nov 1976
2486
1138
$252
$206
7
Secondary Covers
April 1976
2327
$712
$1,388
$1,138
7
Heat Exchangers
March 1976
2317
$79
• 155
$127
7
Supernatant Selector
May 1976
2357
$54
$104
$85
7
Sludge Pumps
July 1976
2414
$36
$68
$55
19/20
Plant Changes
Sept 1982
3878
$56
$65
$54
19/20
Plant Changes
Nov 1982
3918
$49
$57
$47
Total
$4,441
$8,018
$6,575
* Updated to September 1988 ENR = 4535
Source: This table is based on information presented in the
Proctor &. Redfern study entitled:
Development Of A Methodology To Investigate The
Cost Effectiveness Of Various Sludge Management Systems
-------
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of 60 KWH per dry ton (reference WPCF Manual of Practice No.
FD-2 Energy Conservation in the Design of Wastewater Treatment Facilities)
and a consumption of 40 KWH per square foot of building space for lighting,
HVAC, and other general building needs.
Rated HP of Unit Mixers: 4 units at 15 HP/unit
Electrical Requirements as
Projected in Facilities
Planning (kw-hr/yr):
Estimated Annual Electrical
Requi rements (KWH/yr):
Not Available
Equipment 1,431,200
Building 25,000
Other Energy Consumptions:
Volume of Gas Produced:
Volume of Gas Used at Site:
Volume of Gas Flared:
Percent Methane in Product Gas:
Product Gas Uses:
TOTAL 1,456,200
None
11,700 cubic meters/day (413,200 cf/day)
8892 cubic meters/day (314,000 cf/day)
2808 cubic meters/day (99,200 cf/day)
Not Available
When the furnace is operating, digester gas is always provided to the
furnace hot wind box (HWB). If the fuel demand at the HWB exceeds the
digester gas supply, the difference is made up with natural gas. The
HWB temperature should not exceed 900 C (1650 F). If the available
supply of digester gas exceeds the amount required to maintain a 900 C
HWB temperature, the extra digester gas can be used to fuel an
auxiliary boiler if there is a need for additional steam.
Auxiliary boilers are required to start the incineration system because
the fluidizing air blowers are driven by steam turbines. The auxiliary
boilers are also used to make up the difference between the plant's
heating requirements and the heat production of the waste heat boilers.
Approximately 4900 cubic meters/day (173,500 cf/day) of digester gas is
utilized in the hot wind box of the FBF. Hie balance is consumed in
the auxiliary boilers. The plant staff is working to increase
utilization of the digester gas. In the past, only one of the two
auxiliary boilers could be operated using digester gas. The gas
pressure was too low to allow both auxiliary boilers to operate
-------
simultaneously using digester gas. Therefore, some natural gas always
had to be supplied to the auxiliary boilers. The staff is now in the
process of refurbishing the boiler system such that both auxiliary
boilers will be able to operate using digester gas alone with no
natural gas.
V. SLUDGE HOLDING TANKS
These tanks serve to provide equalization storage within the solids train
and blend the sludge from the 2 digestion systems into one homogenous
sludge.
1. GENERAL
No. Tanks: 4
Tank Size:
Aeration:
Mixing:
Mixer Manufacturer:
60,000 gallon
None
Mechanical
2 - Lightnin Mixers
2 - Flight Mixers
2. COST
Note - Plant staff report that mixing in these
tanks is inadequate.
A. Capital
Facility Planning
Estimate of Capital: Not Available
Actual Capital Cost
(bid + change orders): Included in the dewatering area capital costs.
Cost of Modifications: None
B. O&M
O&M costs associated with the sludge holding tanks are very minor. These
tanks are maintained by the dewatering staff; therefore the O&M costs for
the tanks are included in the dewatering budget.
3. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon curves presented
in the EPA publication entitled Estimating Sludge Management Costs.
-------
Rated HP of Mixer:
4 at 7.5 HP; 575 V? 8 amp
Typical Hours of
Operation:
24 hours/day
Estimated Electrical
Requi rements
(KWH/yr):
18,000
VI. SLUDGE DEWATERING
GENERAL INFORMATION
Technology
Membrane Filter Press (side bar design)
4
No. of Units
Unit Size
88 - 1200 mm * 1200 mm plates
Plate Material:
Rubber coated steel
Date Installed:
1985
Manufacturer
Edwards & Jones
Plate Arrangement:
The plates alternate between diaphragm plates and standard plates.
Operating History:
From 1980 to 1985, 6 belt filter press units were used for sludge
dewatering. The belt presses produced a cake with about 20% solids.
In 1985, the belt filter presses were replaced with filter presses in
an effort to produce a drier cake and reduce auxiliary fuel costs.
Future Operation:
Four additional membrane filter presses will be installed as part of
the plant expansion. The new presses will be installed in the existing
dewatering building. To make room for the new filter presses, the
mothballed belt filter presses were recently removed and sold. Because
this building was originally designed for belt filter presses, the
building layout is not optimum for filter presses. The four existing
filter presses have 88 - 1200 mm plates. Four additional presses of
this size would not fit in the existing building. The new filter
presses will have 60 - 1500 mm plates. These presses are shorter than
the existing presses, but provide a comparable plate area. The
installation of filter presses in a building designed for belt filter
presses also presented ci structural problem. The floor slab was not
structurally designed to support the weight of a filter press, so the
filter presses must be supported by columns which extend down to the
-------
building foundation. The new presses will be overhead bar design to
allow the operators easier access to the machine when scraping the
plates. Equipment manufacturers are currently bidding on this project.
Centripress technology was considered for this application, but
existing installations reported poor solids capture and heavy
sidestream flows. For this reason, the centripress was eliminated from
further consideration.
2. OPERATING PARAMETERS
Reference attached tables summarizing 1987 operating parameters for the
dewatering process.
Average Loading Rate (# cake/day):
The dewatering/incineration system was in operation 276 days in 1987.
Most of the 89 days of downtime was due to regular maintenance needs.
An unscheduled 3 week shutdown occurred in November when sand leaking
into the hot windbox made the system inoperable. During this period,
sludge was stored in a reserve secondary clarifier. When normal
operation resumed, the stored sludge was paced back into the system.
For this reason, two feed rates will be presented; one based on a 276
day/year operation and one based on a 365 day/year operation.
276 day:
365 day:
No. Units in Operation:
35.2 dry ton/day ( 31.9 dry tonnes/day)
26.7 dry ton/day ( 24.1 dry tonnes/day)
Average Loading Rate
{cf/cycle):
Average Loading Rate
(#/cycle):
Typical Cake Thickness:
Prima ry/WAS RATIO:
Percent Solids of Feed:
Percent Solids of Cake:
Polymer Type:
4 units operate 24 hours/day each day except:
(1)
(2)
15 hours downtime from Saturday night
until Sunday morning
4 hours of maintenance downtime every
Wednesday morning
3 cubic meter/cycle (106 cf/cycle)
3 wet tonnes (1 dry tonnes)/cycle
6600 wet # (2200 dry #)/cycle
37 mm
60/40
3% to 5%
Average 32% (range 28% to 36%)
Allied Chemical 757
-------
DUFFIN CREEK DEWATERING SUMMARY
(U.S. Units)
MONTH
INPUT
X SOLIDS
OUTPUT
X SOLIDS
CAKE X
VOLATILES
POLYMER
CONSUMED
(#/ton)
DRY TONS
PRODUCED
JAN
5.2
31.9
38.22
15.7
1006
FEB
4.2
29.4
40.99
17.1
705
MARCH
4.3
30.8
39.11
14.3
874
APRIL
3.6
32.4
39.8
26.8
800
MAY
4.6
34.3
45.67
12.5
671
JUNE
4.6
32.5
40.3
14.9
862
JULY
4.1
31.4
36.94
17.5
774
AUG
5.4
33.2
35. 11
15.9
702
SEPT
4.7
31.8
38.51
16.9
998
OCT
4.6
32.6
40.62
18.3
962
NOV
4.4
33.7
41.75
17.5
457
DEC
5.0
34.9
41.81
18.3
1026
TOTAL
9834
AVG
4.56
32. 41
39.90
17.11
Polymer cost is $1.94/#
-------
DUFFIN CREEK DEWATERING SUMMARY
(Metric Units)
MONTH
INPUT
X SOLIDS
OUTPUT
% SOLIDS
CAKE X
VOLATILES
POLYMER
CONSUMED
(kg/tonne)
DRY TONNES
PRODUCED
JAN
5.2
31.9
38.22
7.9
912.2
FEB
4.2
29.4
40.99
8.6
639.3
MARCH
4.3
30.8
39.11
7.2
792.7
APRIL
3.6
32.4
39.8
13.5
725.8
MAY
4.6
34.3
45.67
6.3
608.3
JUNE
4.6
32.5
40.3
7.5
781.8
JULY
4.1
31.4
36.94
8.8
702.1
AUG
5.4
33.2
35.11
8.0
637.0
SEPT
4.7
31.8
38.51
8.5
905.0
OCT
4.6
32.6
40.62
9.2
872.4
NOV
4.4
33.7
41.75
8.8
414.2
DEC
5.0
34.9
41.81
9.2
930.8
TOTAL
8921.6
AVG
4.56
32.41
39.90
8.6
Polymer cost is $5.15/kg
-------
Polymer Dosage
(#/ton dry solids): Based on 1987 data - Average: 5.4 kg/dry tonne
(10.8 #/dry ton)
Frequency of Testing to
Optimize Polymer Dosage: Every 12 ho rs
Location of Polymer Addition:
The polymer preparation system consists of dry storage, 2 polymer mix
tanks, and 2 polymer storage tanks (1500 gallons/each). Polymer is
taken from the storage tanks by one of 4 Moyno pumps and injected into
a pipe loop from which tine filter press feed pump can draw polymer.
The filter press feed pumps (6 total with 2 as stand-by units) are
positive displacement pumps manufactured by Thomas Willett & Co., Ltd.
A measured amount of polymer is injected into the Willett pump on the
suction stroke. Polymer that is not injected into the Willett pump
continues around the loop and is returned to the polymer storage tanks
(see attached figure). The polymer dosage injected by each pump stroke
can be varied by adjusting the Moyno pumps to increase the pressure in
the polymer feed loop. This "Polymeter System" is supplied by Allied
Colloids. This polymer system is able to adjust easily between periods
of heavy polymer vise and periods of no polymer use and is therefore
compatible with a filter press operation. The plant staff believes
that the polymer loses some of its effectiveness as it passes through
the Willett pump because of shearing. To correct this, the plant staff
plans to modify the feed system such that the polymer will be fed on
the discharge side of the Willett pump. It is believed that this may
save 20% to 25% in polymer costs.
Other Chemicals: None
Rate of Pressure Applied & Pacing of Flow to Filter Press:
Sludge/Polymer is pumped at 450 gpm for 70 minutes at a pressure of 120
to 150 psi. Diaphragm air pressure is applied for 40 minutes at 150
psi. Cake unloading takes about 20 minutes for a complete cycle time
of 2 hours and 10 minutes.
Cycle Time (Filtration/
Diaphragm Squeeze Time): 2 hours and 10 minutes
Loading Rate: 0.45 lb/sf-day
No. Cycles Per Day: Avg 30
Max 34
Note that 4 units operating 24 hours/day with a cycle time of 2 hour and 10
minute would have the potential to complete 44 cycles/day. With all 4
units operating round the clock,the maximum number of cycles per day at
Duffin Creek is 34. it would seem that even though the operation time for
each cycle is about 2 hours and 10 minutes, the actual total cycle time is
-------
about 3 hours when repair time, preparation time, and other downtime is
considered.
Type of Membrane
Cloth Used:
Cloth Washing Frequency:
Cloth Life:
Use of Precoat:
Solids Capture:
3. COST INFORMATION
A. Capital
Facilities Planning
Estimate of Capital:
Actual Capital Cost:
Cost of Modifications:
Monofilament Polypropylene
Once per month (takes about 6 hours)
Because lime is not used for conditioning,
acid wash is not required.
9 months
None
98+%
Not Available
See attached table.
See attached table.
The attached table shows the capital cost for the original chemical
conditioning and belt filter press installation and the capital cost
for the subsequent filter press installation. By updating all costs to
a current (September 1988) ENR cost index and substituting the filter
press equipment cost for the belt filter press equipment cost, one can
develop complete capital cost for each dewatering system. These
construction costs are summarized as follows:
System
Capital Cost*
ENR - 4535
Belt filter press dewatering/ $6,352,000
chemical conditioning
Filter press dewatering/ $7,889,000
chemical conditioning
*U.S. dollars
Note that the difference between capital costs for the two dewatering
systems is not as great as one would expect. The design engineer for
these projects informed us that procurement problems and last minute
changes in the design lead to significant cost increases in the belt
filter press installation.
-------
CAPITAL COSTS - SLUDGE CONDITIONING/DEWATERING
Conatruction/ Original Updated Updated
Purchase Conatruction Construction Construction ConBtruction
Date ENR Cont Coat * Coat «
(Canadian (Canadian ( U.S.
$1,000) $1,000) $1,000)
Contract
No.
Major Cost
Item
ro
o
CTl
CHEMICAL CONDITIONING
9 Gen. Construction Oct 1978
Purchased Equipment:
9 Polymer Equip Feb 1978
Total
BELT FILTER PRESS INSTALLATION
9 Gen. Construction Oct 1978
Purchased Equipment:
9 Belt Filter Presses Aug 1976
9 Screw Conveyers July 1978
Total
FILTER PRESS MODIFICATION
22 Gen. Construction June 1984
Purchased Equipment:
22 Filter Presses Nov 1983
22 Screw Conveyors March 1984
22 Conveyors Jan 1985
22 Conveyors Sept 1982
19/20 Plant Changes Nov 1982
Total
2851
2681
2851
2445
2821
4161
4133
4118
4172
3878
3918
$843
$137
$2,798
$930
$188
11 ,404
*1,315
$246
$36
$191
130
$1,280
$232
$1,512
$4,451
$1,725
$302
$6,478
SI ,530
$1,443
$271
$39
$223
$150
$3,657
$1,050
$190
$1 ,240
$3,650
$1,414
$248
$5,312
$1 ,255
$1,183
$222
$32
$183
$123
$2,999
* Updated to September 1988 ENR = 4535
Source: This table is based on information presented in the
Proctor. & Redfern Btudy entitiled:
Development Of A Methodology To Investigate The
CoBt Effectiveness Of Varioun Sludge Management Systems
-------
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL COST
CANADIAN U.S.
Operations Labor
Maintenance Labor
Polymer
Other Chemicals
(Odor Control)
Electricity
Materials/Supplies
Other Purchased Services
Total
57 hr/day
14 hr/day*
10.8 #/dry ton
1,166,900 kw-hr/year
$373,100
§ 91,400
§245,800
§ 8,000
$ 52,500
$143,800
$ 40,000
$954,600
$305,900
$ 74,900
$201,600
$ 6,600
$ 43,200
$117,900
$ 32,800
$782,900
*Averaged over a 7 day work week.
The maintenance staff actually works a 5 day work week, averaging 20
hours/day.
Maintenance Concerns:
The press cloth is washed down once per month. No acid wash is
required because lime is not used in the operation. The staff uses an
automatic washing machine which only needs to be positioned properly.
The membrane clothes were replaced for the first time after 10,880
operating hours. Cloth replacement requires 4 maintenance personnal
for about 16 hours (64 manhours total).
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of 30 KWH per dry ton (reference WPCF Manual of Practice No.
FD-2 Energy Conservation in the Design of Wastewater Treatment Facilities)
and a consumption of 40 KWH per square foot of building space for lighting,
HVAC, and other general building needs.
Estimated Electrical Requirements (kw-hr/year):
Equipment 326,900
Building 840,000
TOTAL 1,166,900
-------
Other Sources of
Energy Consumption: None
VII. CAKE STORAGE/EQUALIZATION
Each filter press discharges into a 3 cubic meter (106 cubic foot) live
bottom hopper. Each hopper holds about 1 filter press cycle of sludge.
Each furnace is preceeded by a 12 cubic meter (424 cubic foot) storage tank
to further equalize the cake feed to the furnaces.
VIII. GRIT, SCREENINGS, AND SCUM DISPOSAL
GRIT DISPOSAL: Landfilled
SCREENINGS DISPOSAL: Landfilled
SCUM AND GREASE DISPOSAL: Scum is added at the digesters and
subsequently dewatered and incinerated.
Approximately 10,000 gallons per week of scum
is processed.
IX. INCINERATION
1. GENERAL INFORMATION
Technology:
Start-Up Date:
Manufacturer:
No. of Units:
System Description:
Fluidized Bed Incineration w/ Hot Wind Box
1981
Reactor - Dorr Oliver
Heat Exchanger - Canadian Shack
Waste Heat Boiler - Foster Wheeler
Combustion Air Blower - Spencer 8 stage
centrifugal blower
2 (1 in operation at a time)
Each incineration system consists of a hot wind box (HWB) fluidized bed
furnace, a heat exchanger, a waste heat boiler, a venturi scrubber, and
tray sub-cooler (see figure on page 34). Under normal operation,
digester gas is used to fuel the hot windbox which preheats the
combustion (fluidizing) air. Flue off-gases from the furnace are
passed through a heat exchanger which transfers heat from the hot flue
gases to the HWB air feed. The flue gases then pass to a waste heat
boiler which produces steam to be used for building heat and to drive
the combustion (fluidizing) air blowers. Two auxiliary boilers are
available to (1) make up the difference between the plant's heating
requirements and the heat production of the waste heat boilers; and (2)
provide steam during start-up periods to drive the steam turbines that
power the combustion air blowers. If the HWB temperature is so high
-------
that preheating of the HWB air feed is not necessary, the hot flue
gases can bypass the heat exchanger and be fed directly to the waste
heat boiler, increasing steam production.
Reactor Diameter (bottoin/top):
Original Diameter: 5600 mm bed/ 6200 mm freeboard
(18.4 ft/ 20.3 ft)
The reactor bed diameter has since been reduced by 36 inches by adding
a layer of refractory brick around the inside of the furnace.
Future Operation:
It is estimated that one of the existing furnaces has the capacity to
handel the. sludge generated from a 55 to 60 migd flow (current plant
flow is 42 migd). Plans to expand plant capacity to 80 migd are
currently in the design phase. As part of the first construction
phase, the liquid train and the downstream solids handling processes
will be expanded. The installation of a third furnace will be delayed
to a second construction phase to be undertaken when plant flows
approach 55 migd. The installation of a third furnace will maintain
proper redundancy in the incineration system (2 furnaces operating; 1
furnace stand-by).
Sludge Feed System:
As part of the original design, dewatered cake was transferred from the
dewatering building to the incineration building by a series of
horizontal and vertical screw conveyors. The screw conveying system
would transport cake from the filter press discharge hoppers located in
the dewatering building to a pair of storage hoppers located in the
incineration building. The total conveyor length is about 500 feet.
Another screw conveyor would then transfer the cake from the storage
hoppers into the furnace. The screw conveying system operated
satisfactorily when 20% cake produced by belt filter presses was being
transferred to the incineration building. When the belt presses were
replaced with filter presses, the screw conveyors had problems
transporting the drier (33% solids) cake. Motor burnouts and bearing
failures became common. In 1966, the plant staff decided to install a
Schwing slurry pump on an experimental basis to evaluate its
effectiveness as an alternate cake transfer system.
A Schwing slurry pump capable of pumping slurries with a solids content
of up to 80% was installed in the dewatering building. The modified
conveying system consists of a screw conveyor that transfers cake from
the filter press discharge hoppers to a hopper in the dewatering
building which feeds the Schwing pump. The dewatered cake is then
pumped about 500 feet from the dewatering buiding to the incineration
building. In the original piping layout, the cake was piped directly
into the bed of the furnace, bypassing the cake storage tanks in the
incineration building. The pumping system experienced some problems
-------
during its first' year of operation due to high pressures and plugging
in the pipeline. The problem with high pressures was alleviated by
increasing the diameter of the sludge piping from 6 inch to 8 inch.
The plugging problems occurred where the pipeline entered the furnace.
Sludge at this point would dry out and clog the pipeline. To alleviate
this, the sludge pipeline was modified to discharge into the storage
hoppers preceding the furnaces. The existing screw feeder is used to
transfer the cake from the hopper to the furnace bed. This system has
been operating successfully since February of this year.
Overall, the plant staff has been very pleased with the performance of
the Schwing pump. The sludge pumping system is cleaner, less odorous,
and more reliable than the screw conveying system. The plant staff
plans to purchase two additional Schwing pumps. The two new Schwing
pumps will be used to transfer cake from the dewatering building to
storage hoppers in the incineration building. The existing Schwing
pump will be moved from the dewatering building to the incineration
building and used to pump cake from the storage hoppers into the
furnace bed. The staff believes that the plugging problems that have
occurred in the past will not be a concern with this alignment. The
pumping distance from the hopper to the furnace bed will be very short,
so the sludge velocity in the pipeline should remain high enough to
avoid sludge drying in the pipeline and plugging the pipe. The staff
believes that there are both operational and maintenance benefits to
pumping directly into the furnace bed. The pipeline is neater and less
odorous than the screw conveyor, and the staff believes that the cake
burns better when pumped directly to the furnace bed, although no
concrete reason for this could be determined.
The Ashbridges Bay WPCF in Toronto also has a Schwing pump that is
being used to directly feed dewatered cake to a multiple hearth
furnace. The pump has been in operation for about one month.
2. OPERATING PARAMETERS
Reference attached table which summarizes the 1987 operating data.
Operation Schedule:
% Solids of Cake Feed:
% Volatiles of Cake Feed:
Normally operate 24 hr/day each day except:
(1) 15 hours downtime from Saturday night
until Sunday morning
(2) 4 hours of maintenance downtime every
Wednesday morning
32%
40%
-------
Average Loading Rate:
The dewatering/incineration system was in operation 276 days in 1987.
Most of the 89 days of downtime was due to regular maintenance needs.
An unscheduled 3 week shutdown occurred in November when sand leaking
into the hot windbox made the system inoperable. During this period,
sludge was stored in a reserve secondary clarifier. When normal
operation resumed/ the stored sludge was paced back into the system.
For this reason, two feed rates will be presented; one based on a 276
day/year operation and one based on a 365 day/year operation.
276 day: 35.2 dry ton/day ( 31.9 dry tonnes/day)
365 day: 26.6 dry ton/day ( 24.1 dry tonnes/day)
Peak Loading Rate (dry #/day):
The furnaces were originally designed to burn a combination of
wastewater sludge and paper mulch. The furnace was sized accordingly
with a capacity of 9600 dry #/hour of 30% cake with 70% volatiles.
During plaint construction, it was decided that paper mulch would not be
burned in the furnaces. As a result, the furnaces were grossly
oversized for a sludge only operation, leading to excessive fuel use.
To decrease the capacity of the reactors, refractory brick has been
added to the bed walls to decrease the bed diameter by 36" and several
of the tuyeres have been plugged to reduce the air flow to the furnace.
The new capacity for each furnace is 40 dry tonnes per day (44 tpd).
When sludge production increases in the future, the capacity of the
furnace will be increased by removing the extra layer of refractory
brick and unplugging several of the tuyeres.
Type of Fuel:
1. Digester gas (22,400 kJ/cubic meter; 600 BTU/cf) for the hot
windbox. Digester gas cannot be fed to the furnace burners.
2. No. 2 oil (45325 J/g) for the reactor burners and, if necessary,
for the hot wind box. Fuel oil can also be burned in the
auxiliary boilers.
3. Natural gas cannot be burned in the reactor or the hot windbox
because a feed line was not provided. Natural gas is used as
primary fuel for the auxiliary boilers.
Note: 90 to 95 percent of the fuel consumption is in the hot
windbox or auxiliary boiler system. Very little fuel is consumed
in the reactor itself.
Freeboard Retention Time: Greater than 5 seconds
Air System: Push through system that maintains a 3 psi
pressure in reactor and hot wind box. No ID
fan.
-------
DUFFIN CREEK INCINERATION SUHXAS7
(U.S. Units)
HONTB
NO. DAYS BBACTOB
BBACTOB SUN BOUS3
OPBBATION
m OIL
TONS CONSUMED
PBOCBSSED(gallons)
OIL
COST
(»/«al>
NATU&AL
GAS
-------
DUPPIM CREEK INCINERATION SURKABT
(Retric Unitg)
HOKTH
NO. DATS SEACTOB DBT OIL
BBACTOR RUN HOURS TONNES CONSUMED
OPEBATION PBOCBSSED (liters)
OIL
COST
(1/1)
NATURAL
GAS
(cu/«)
GAS
C08T
(t/cui)
ASH
PRODUCED
(k|)
ASB
LANDFILL
($/k|)
DIGSSTBR
CAS
(eu/i)
;ak
28
419.3
912
4102
10.289
188770
$0,161
640301
$0,021
224571
FSB
14
329.(5
639
14994
$0,289
204384
$0,161
306600
$0,021
161748
HABCH
11
537. n
793
38420
$0,289
209925
$0,161
560430
$0,021
192360
APBIL
26
488.85
725
24996
$0,227
151159
$0,145
466020
$0,021
142724
MAT
20
319.55
608
15150
$0,227
50232
$0,145
288100
$0,021
117744
JUH8
25
494 .5
782
3636
$0,227
70855
$0,145
541758
$0,021
127394
JUL!
24
463
702
14382
$0,227
70957
$0,145
472540
$0,021
138700
AUG
15
348.7
$37
25152
$0,227
59814
$0,145
610550
$0,021
97367
SEPT
27
527 .2
905
50768
$0,227
76920
$0,145
527000
$0,021
193265
OCT
27
547
872
33710
$0,227
105982
$0,145
610900
$0,021
96540
NOV
10
271.25
414
18478
$0,197
98620
$0,145
234800
$0,021
158859
DEC
23
588.85
931
76206
$0,197
175025
$0,145
635120
$0,022
142030
TOTAL
276
5295.4
8920
319994
1462643
5894119
1793302
AVG
$0,237
$0,149
$0,021
-------
Depth of Sandbed:
Normal 3 ft
Fluidized 5 ft
No. Units typically in
Operation:
Percent Oxygen in Flue Gas:
Total Air Feedrate:
Temperature Profile of
Incinerator:
Auxiliary Fuel Consumption:
3. COST INFORMATION
A. Capital
Facilities Plan Estimate
of Capital:
Actual Capital Cost
(bid + change orders):
Cost of Modifications:
1 unit in operation
1 unit in cold stand-by mode
4% to 5%
Original 23,000 cubic meter/hr (actual)
13,540 cfm
Current 10,000 cubic meter/hr (actual)
5,885 cfm
See attached sketch.
C F
Preheated combustion air 550 1020
Hot Windbox Product Air 900 1650
Bed Temperature 800 1470
Freeboard Temperature 850 1560
Heat Exchanger Product 760 1400
Waste Heat Boiler Steam 270 520
Venturi Inlet Temperature 180 360
Tray Sub-Cooler Inlet 50 122
Stack Exhaust 20 70
Fuel Oil
Natural Gas
Digester Gas
9 gal/dry ton
5,333 cf/dry ton
6,539 cf/dry ton
Not Available
See attached tables
None
The cost of the heat recovery system including the waste heat boilers
is included in the incineration capital costs. The capital costs for
the auxiliary boiler system is included in the boiler facilities
capital costs.
-------
550 °C
1020 ° F
1650 °F
HOT
wo °C
1
WINDBOX
850 C
1560 °F
HEAT
X-CHANGER
L
ATMOSPHERE
AMBIENT AIR
850 °C
1560° F
FLUIDIZED
BED
FURNACE
800 °C
1470 °F
tr
DIGESTER
GAS
FUEL
" OIL
A
i
i
WASTE
HEAT
BOILER
SLUDGE
NATURAL GAS—-
LEGEND
GAS FLOW
FUELFEED
STEAM FLOW
360
180
I
>F
'C
TRAY
SUB-
STACK
VENTURI
270'
520'
STEAM USES
BUILDING HEAT
DRIVE STEAM TURBINES
FOR FLUIDIZING AIR BLOWERS
HEAT FOR DIGESTION
-------
B. O&M
ITEM CONSUMPTION ANNUAL COST
LEVEL CANADIAN U.S.
Operations Labor
68
hr/day
$
447,800
$
367,200
Maintenance Labor
20
hr/day*
$
132,400
$
108,600
Fuel Oil
9
gal/dry ton
S
75,800
$
62,200
Natural Gas
5,333
cf/dry ton
$
217,900
$
178,700
Chemicals**
$
30,000
$
24,600
Potable Water
S
110,000
$
90,200
Electricity
2,253,400
kw-hr/year
$
101,400
$
83,400
Mate ri als/Suppli es
§
403,200
$
330,600
Other Purchased Services
§
80,000
$
65,600
Total Cost
$1,598,100
$1,311,100
Operations Credit for
"Sale"
$
449,700
$
368,700
of Excess Steam
Net Cost
$1,
,148,400
$
942,400
Note that there is no charge for digester gas used to fire the hot wind box.
*Averaged over a 7 day week.
Hie maintenance staff actually works a 5 day week, averaging 28 hours/day.
**Chemical treatment for waste heat boiler feedwater.
Maintenance Concerns;
Reactors are typically operated for one year and then shut down for a 2
month maintenance overhaul. It takes about 2 weeks for the furnace to
cool to ambient temperatures to allow maintenance work to begin.
Manholes in the reactor allow for access. During operation periods, a
backlog of work orders detailing items that must be addressed during the
maintenance shutdown is kept on file.
Each Wednesday morning, the system is taken out of operation for four
hours. All instumentation and equipment that is accessible are checked
and calibrated.
-------
CAPITAL COSTS - INCINERATION/HEAT RECOVERY
Contract
No.
Major Cost
Item
Construction/
Purchase
Date
Original
Updated
Updated
Construction Construction Construction Construction
ENR
Cost
(Canadian
$1,000)
Cost *
(Canadian
91,000)
Cost *
( U.S.
$1,000)
INCINERATION
13 Building
15 Equip Foundation
18 Incin Stack
Purchased Equipment:
Incinerators
Screw Conveyors
19/20 Plant Changes
Total
BOILER FACILITIES
15 General Const
Purchased Equipment:
Steam Generators
Boiler Stack
To tal
Jan 1979
Aug 1978
March 1979
Aug 1977
July 1978
Sept 1982
Aug 1978
March 1978
March 1979
2,872
2,829
2,886
2,611
2,821
3,878
2,829
2,693
2,886
$6,326
$516
$881
$4,840
$771
$510
$2,939
$164
$434
$9,989
$827
$1,384
$8,407
$1 ,239
$596
$22,443
$4,070
$259
$682
$5,011
$8,191
$678
$1,135
$6,893
$1,016
$489
$18,403
$3,337
$213
$559
$4,109
* Updated to September 1988 ENH = 4535
Source: This table is based on information presented in the
Proctor & Redfern study entitled:
Development Of A Methodology To Investigate The
Cost Effectiveness Of Various Sludge Management Systems
-------
A dust problem when removing fly ash from the heat exchanger and boiler
was corrected by allowing the ash to accumulate until it reaches a
stabilized level.
There have been infrequent failures (one failure each system) of the
expansion joints in the heat exchanger.
There have been problems with sand leaking in the tuyeres and
accumulating in the HWB. This happened once in 1986 and once in 1987.
When this happens, the furnace must be taken off-line and allowed to
cool completely before work in the windbox can begin. It takes a
minimum of 3 weeks to cool the furnace, remove the sand from the
windbox, and put the furnace back into operation. During operation, the
amount of sand in the windbox can be monitored through a window in the
windbox.
The hot gas damper has been re-designed in each system. The original
damper seal was not tight, allowing fly ash to escape from the gas
system.
When a furnace is taken off-line, sand that has accumulated in the bed
has to be removed to maintain the normal operating sand level. The
decrease in air flow resulting from the plugging of several tuyeres has
resulted in a significant amount fly ash not being blown from the
furnace. An effort has been made recently to maintain air flow levels
that are high enough to remove all fly ash from the furnace. This will
keep the amount of sand in the furnace at a constant level.
The outer casing of the furnaces have not experienced any corrosion
problems. However, some corrosion has occurred on the outer shell of
the waste heat boiler. The shell was corroding from the inside out due
to cracks in the refractory brick, so some refractory repair was
required to curtail the corrosion.
The addition of ferrous sulfate for phosphorus removal has resulted in a
scaling problem in the venturi scrubber.
Operation Guidelines:
The operations staff seem very comfortable with fluidized bed
incineration system. The goal of the operation is to maintain a bed
temperature of about 800 C (1500 F) while using a minimum amount of
auxiliary fuel. This bed temperature will produce a flue gas
temperature of 800 C to 850 C (1500 to 1560 F), which is high enough to
insure complete combustion and eliminate the need for an afterburner.
During normal operation, the operator will monitor the hot windbox
temperature, the bed temperature, and the oxygen level in the flue gas
to detect changes in the furnace's operation condition. Changes in
furnace temperatures can be brought about by a change in the percent
solids or the percent volatiles of the sludge feed. The operator can
react to these changes in sludge quality by adjusting the air feedrate,
-------
adjusting the sludge feedrate, or using auxiliary fuel to fire the
reactor burners. For instance, if the sludge feed becomes wetter, the
operator can maintain a steady bed temperature by either turning on a
reactor burner or cutting back the sludge feed. By manipulating these
variables, the operator can control the furnace. Because of the storage
and blending areas provided within the solids train, the feed to the
furnace is kept fairly constant in terms of sludge quantity and quality.
This makes the furnace much easier to operate, as major adjustments in
the control variables are rarely required.
The original instrumentation system was designed to be fully automated,
but the weigh scale monitoring the feed to the furnace never operated
properly so the staff switched to manual control. The staff does plan
to upgrade the instrumentation system next year. The upgraded
instrumentation system will be automated, using a computer to control
the combustion system.
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available. Typical
electrical consumption figures or curves cannot be applied to the Duffin
system because the fluidizing air blowers are steam turbine driven.
Therefore, equipment electrical consumption will be based upon the connected
horsepower of equipment other than the fluidizing air blowers. Electrical
consumption for lighting, HVAC, and other general building needs will be
estimated based upon a unit consumption of 40 KWH per square foot.
Equipment Rated HP Hrs/day kw-hr/day
Operation
Fluidizing (Combustion)
Air Blower 600 24 *
Water Pumps for Freeboard Almost Never
Temperature Control
Purge Air Blower 100 24 1790
~There is no electrical cost for these blowers as they have steam turbine
drives.
Estimated Annual Electrical Requirements (KWH/year):
Equipment 653,400
Building 1,600,000
TOTAL 2,253,400
-------
Total Annual Fuel Use (gal/year):
Based on 1987 operating data:
Fuel Oil 319,994 L 84,544 gal
Natural Gas 1,462,643 in 51,652,799 cf
Digester Gas 1,793,302 m 63,329,922 cf**
**Balance of the digester gas that is utilized at the plant site (314,000
cf/day) is consumed in the auxiliary boilers.
Annual Fuel Use For Start-up and Cool-Down Periods (gal/year): Almost none.
Use of Excess steam Generated by WHB:
- building heat throughout the plant
- steam to drive the 485 kw steam turbines that power the fluidizing
(combustion) air blowers
- heat for digestion (for details of this system, refer to digestion
section)
- as sludge production increases and more waste steam is made
available, a generator will be installed to produce electricity for
plant use.
Steam Pressure/Temperature: 260 psi
520 F
Steam Production/Distribution: Reference the attached tables.
Steam production is split about 50/50 between the waste heat boilers and
the auxiliary boilers. About half of the steam produced is used to
drive the fluidizing (combustion) air blower and about half is used in
the plant heating loop. The heating loop provides building heat to the
following 5 areas of the plant:
Area 1 Digester building
Area 2 Administration building
Area 3 Incineration and dewatering buildings
Area 4 Detritor and raw water lift buildings and pump gallery
Area 5 Maintenance and chlorine buildings
A cost credit is taken by the incineration staff for building heat
provided to Area 2, Areei 4, and Area 5. For in-house bookkeeping
purposes, the incineration area pays to operate the waste heat and
auxiliary boilers and "sells" the heat product to other areas of the
plant. Each month, the cost to produce 1000 kg of steam is determined
and used as the unit coi>t for billing other areas of the plaint for steam
sales. Area 1 and Area 3 are not billed for heat as these areas are
considered part of the incineration system.
-------
The following table summarizes the 1987 steam distribution to the five
areas and the amount charged for this steam (see attached tables for
more detailed breakdown):
AREA % TOTAL STEAM COST COST
(CANADIAN $) (U.S. $)
1
38
341,738
280,225
2
10
89,929
73,740
3
12
107,917
88,490
4
22
197,848
162,235
5
18
161,875
132,740
TOTAL
100
899,300
737,430
The heat provided to Areas 2, 4, and 5 results in a cost credit to the
incineration system of $449,652 Canadian ($368,715 U.S.).
The O&M cost table presented on page 26 shows an annual energy cost
(fuel oil, natural gas, and electricity) of $395,100 Canadian ($324,300
U.S.) for the incineration system. The total value of the energy
produced by the incineration system is taken to be $899,300 by the
plant staff. Based on these in-house econcomics, it would appear that
the incineration system is a net energy producer with a net energy
value of $504,200 Canadian.
However, this evaluation can be misleading because the unit cost used
for steam sales is based on the cost to produce the steam and may not
reflect the true energy value of the steam. For this reason, the
incineration system was evaluated in terms of BTUs of energy input and
BTUs of energy output to determine the true net energy consumption- of
the system (Reference the attached schematic). The BTU conversion
factors used in this evaluation are as follows:
Fuel Oil 138,000 BTU/gal
Natural Gas 1,000 BTU/cubic foot
Digester Gas 600 BTU/cubic foot
Steam* 1,572 BTU/# steam
Electricity** 10,000 BTU/kw-hr
*The energy value of 260 psi steam at 520 F is 1273 BTU/cf. A typical
boiler is approximately 90% efficient in the combustion process and
approximately 90% efficient in converting this heat energy to steam,
resulting in an overall efficiency of 81%. Therefore, an energy value
of 1572 BTU/# steam (1273/.81) was used in this evaluation. This is
the amount of energy required to produce 260 psi, 520 F steam if an
auxiliary boiler is used.
**This figure accounts for inefficiency in the production of electricity.
It is assumed that electrical production is about 38% efficient.
-------
An incineration system's energy efficiency is generally measured by its
consumption of auxiliary fuel to sustain the combustion process. This is
difficult to measure at Duffin Creek because here the incineration system
is taken to be the furnace, the waste heat boilers, and the auxiliary
boilers. This system provides steam to drive turbines and to feed the
plant heating loop. It is impossible to break out the exact amount of fuel
consumed by the furnace itself. The system must be evaluated as a whole,
with the energy input to the system compared to the energy output.
The system was evaluated for 3 scenarios. The scenarios vary in terms of
how the energy input to the system is defined.
Scenario 1: Only fuel oil and natural gas are considered energy
inputs to the system. Digester gas is considered a
"free" source of energy from the solids train. The free
use of digester gas is the energy credit that balances
the loss of volatiles in the digesters. Electricity is
not considered.
Scenario 2: Fuel oil, natural gas, and electricity are considered
energy inputs to the system. Digester gas is again
considered a "free" source of energy.
Scenario 3: Fuel oil, natural gas, electricity, and digester gas are
all considered energy inputs to the system.
In all cases, the energy output from the system is taken to be the pounds
of steam provided to the plaint heating loop. Steam used to drive the steam
turbines for the fluidizing air blower is not considered an energy output,
as this energy is consumed within the incineration system. All consumption
values are based on 1987 data.
The results of the evaluation are as follows:
Scenario 1
Energy Input (1,000,000 BTU/Year)
Fuel Oil 11,700
Natural Gas 51,600
TOTAL 63,300
Energy Output (1,000,000 BTU/Year)
Steam to Heating Loop 61,000
Net Consumption
2,300 million BHI/year
equivalent to 1.7 gal/dry ton of sludge
-------
Scenario 2
Energy Input (1,000,000 BTP/Year)
Fuel Oil
Natural Gas
Electricity
11,700
51,600
22,500
TOTAL
85,800
Energy Output (1,000,000 BUJAear)
Steam to Heating Loop 61,000
Net Consumption
24,800 million BTU/year
equivalent to 18.3 gal/dry ton of sludge
Scenario 3
Energy Input (1,000,000 BTU/Year)
Fuel Oil 11,700
Natural Gas 51,600
Electricity 22,500
Digester Gas 38,000
TOTAL 123,800
Energy Output (1,000,000 BTU/Year)
Steam to Heating Loop 61,000
Net Consumption
62,800 million BTU/year
equivalent to 46.3 gal/dry ton of sludge
This evaluation shows that the energy efficiency of an incineration system
depends to a great extent on how one defines the energy input to the
system, if one considers auxiliary fuel use (fuel oil or natural gas) to
be the primary measure of the efficiency of an incineration process and one
considers digester gas as a "free" source of fuel provided by the solids
train, then the Duffin incineration system comes very close to being a
self-sustaining energy system (scenario 1). As the definition of energy
input is expanded, the net energy consumption increases accordingly
(scenarios 2 and 3).
It should be noted that the net energy consumption of the system is likely
to decline in the future as sludge production increases and utilization of
the digester gas improves. Increased sludge production will result in
-------
STEAM PRODUCTION/DISTRIBUTION
(METRIC UNITS)
STEAM
PRODUCTION (KG)
STEAM
DISTRIBUTION
MONTH
AUXILIARY
BOILBR
WASTE HEAT
BOILER
TOTAL
STEAM
FLUIDIZING
KG
AIR
TURBINE
$
HEATING
KG
LOOP i
$ :
JAN
1,886,770
1,959,290
3,845,060
1
,593,340
93,386
2,036, 150
119,339 !
FEB
2,217,670
1,247,840
3,465,510
1
,251,910
82,087
2,213,600
145,145 ;
MARCH
2,104,328
2,171,800
4,276,128
2
,043,450
149,803
2,232,678
163,675 !
APRIL
1,584,500
1,233,720
2 ; 81 8 , 3 2 0
1
, 781 ,630
82,712
1,036,690
48,128 I
MAY
1,327,850
947,500
2,275,350
1
,214,290
57,350
1,061,060
50,115 }
JUNE
• 778,150
1,647,700
2,425,850
1
,879,100
93,992
546,750
27,351 !
JULY
1,063,870
1,326,370
2,390,240
1
,759,400
82,498
630,840
29,581 !
AUG
893,070
1,364,830
2,257,900
1
,325,060
68,532
932,840
48,248 !
SEPT
1,174,110
2,307,400
3,481 ,510
2
,003,360
79,793
1,478,150
58,874 j
OCT
1,429,450
1,932,040
3,361,490
2
,078,600
87,259
1 ,282,890
53,862 !
NOV
.2,379,250
792,250
3,171,500
1
,030,750
34 ,416
2,140,750
71,474 !
DEC
2,649,900
It 624,090
4,173,990
2
, 161,630
89,707
2,012,360
83,518 ;
TOTAL
19,488,018
18,454,830
37,942,848
20
, 122,520
1,
001,535
17,604,758
899,310 *
-------
STEAM PRODUCTION/DISTRIBUTION
(U.S. UNITS)
STEAM
PRODUCTION (!)
STEAM
DISTRIBUTION
MONTH
AUXILIARY
BOILER
WASTB HEAT
BOILER
TOTAL
STEAM
FLUIDIZING AIR
t
TURBINE
%
HBATINQ
1
LOOP J
$ ;
JAN
4,157,369
4,319,451
8,476,819
3,512,677
76,577
4,488,896
97,858 i
FEB
4,889,075
2,750,988
7,640,063
2,759,961
67,311
4,880,103
119,019 !
MARCH
4,639,202
4,787,950
9,427,152
4,504,990
122,838
4,922,162
134,214 i
APRIL
3,493,409
2,719,859
6,213,268
3,927,781
67,824
2,285,487
39,465 j
MAY
2,927,378
2,088,859
5,016,237
2,677,024
47,027
2,339,213
41,094 !
JUNE
1,715,509
3,632,519
5,348,029
4,142,664
77,073
1,205,365
22,428 i
JULY
2,345,408
2,924,115
5,269,523
3,878,773
67,648
1,390,750
24,256 j
AUG
1,968,862
3,008,904
4,977,766
2,921,227
56,196
2,056,539
39,563 S
SEPT
2,588,443
5,086,894
7,675,337
4,416,607
65,430
3,258,729
48,277 i
OCT
3,151,365
4,259,375
7,410,741
4,582,482
71,552
2,828,259
44, 167
NOV
5,245,295
1 ,746,594
6,991,889
2,272,391
28,221
4 ,719,497
58,609 !
DEC
5,841,970
3., 360,009
9,201,978
4,765,529
73,560
4 ,436,449
68,485
TOTAL
42,963,284
40,685,518
83,648,803
44,362,108
821,259
38,811,449
737,434 i
* Not Available
>
3
-------
STUB HLOmiOH (IC STttKj
BaiMiti irei
ill
Ptb
Hirck
Ipril
lif
June
J»lr
Ul
Sepl
Ocl
Nov
Dec
Telil
1 Total
Difester Bui idiot
tu.ijt
Ml, 10
Ml,<11
1)1,)I2
403,20)
207, M
211,11)
lit,11)
5(1,(91
(81,(98
813,(85
111,01
U»),«58
0.11
idiiiiitrilioi BaiMiil
m.iis
£21,3*0
221,20
10),£61
10(,I0(
51,515
(1,011
33,114
117,915
121,28)
211,07$
101,111
1,1(0,(11
0.10
Ibciieritioi t Dmtctiif
luiUin|l
215,112
211,121
121,10)
121,121
15,510
15,101
III,Ml
111,111
151,917
251,8)0
2(1,411
2,112,511
0.12
Otlritor 1 tin lift tiildieii
4 Palp CilWrj
(11,IS)
iti.m
01,11)
221,on
21),ill
120,215
111,115
205,225
315,11)
282,2)(
119,)()
112,11)
3,173,547
0.22
Itioloiace I CMoriae
laildiila
lit,591
1U.44I
101,812
IK, (04
1)0,HI
58,(15
111,551
Id,>11
2((,0(7
230.KO
395,335
3(2,22S
3,l(l,IS(
O.lt
Tctll
2,931,ISO
2,213,(00
2,212,(T»
1,011,(10
1,0(1,0(0
SIS,150
(10,MO
932,140
1,lit,ISO
1,212,190
2,MO,ISO
2,D12,)(t
11,(04,lit
-------
STIAH COST ALLOCATION
(U.S. I)
Building Area
Jt6
Feb
March
April
Hay
June
Jul*
Aug
Sept
Oct
Nov
Dee
Total
Dicetter Buildim
137,186
145.227
151,001
914,997
115,616
18,522
19,218
115,034
118,345
11(,784
122,211
12M24
1280,225
1 Adaiaiatration Building
19,786
111.901
113,(21
13.941
14,109
12,2(3
12,126
13.956
14,821
14,417
15,8(1
18.849
171,742
laciaeratioa A Dt*»terin|
Boildiad
111,743
114,282
116,106
14,736
14,931
12.691
12,911
14,748
15,193
>5,300
>7,033
18,218
188,492
t Detritor I law Lift Buildiaf 111,529
A Puip Gallery
$25,184
129,527
18,682
19,041
14,934
15,331
18,104
110,621
19,717
112,894
115,067
11(2,235
I HiiitesiRce 1 Cklorise
Buildi b(*
111,(14
(21,423
124,158
17,101
17,397
14,037
14.357
17.122
18,(90
11,950
110,549
112,327
1132,738
Total Coat
(91,853 1119,011 $134,212
139,465
141,094
122,427
124,257
139,5(4
148,276
144,167
*158,(08
1(8,485
1731,432
Total Coat Credit
141,929
159,509
167,106
119,732
120.5(7
111.214
<12.129
119.783
(24,138
122,083
129,304
134,242
(368,115
l Steal provided to Ueie areai ii recorded n a
-------
STEAK COST ALLOCATIOM
ICaaadiaa t|
Buildiai irca
¥*Q
Feb
M • »aV
niiku
April
Ksj
Jul'
July
Auk
Sept
Oct
Not
Dec
Total
Difeiter Buildiac
145,349
(55,155
(62,196
(18,289
(19,044
(10,393
(11,241
(18,334
(22,312
(20,468
(27,160
831,1)7
041,138
1 Adtiaiitratios Buildiaf
111,934
(14,514
(16,361
(4,813
(5,011
(2,735
(2,958
(4,825
(5,881
(5,386
(7,141
(8,352
(81,911
InciaeratioD I Oewateri&g
Buiidinti
114,321
(17,417
(19,641
(5,775
(6,014
(3,282
13,550
(5,790
(7,065
(6,(63
(8,577
(10,022
(101,111
l Detritor 4 Raw Lift Buildial 126,255
1 Puip Cillirj
(31,932
(36,001
(10,588
(11,025
(6,01?
(6,508
(10,615
(12,952
(11,850
(15,724
(18,374
(191,141
i Naiatenaace I Chlorine
Buildup
121,481
(26,126
(29,461
(8,663
(9,021
(4,923
15,325
(8,685
(10,597
(9,695
(12,865
(15,033
(161,(15
Total Coit Hit.140 1 145, 1 (4 1 183,(73 ('48, 128 150, 1 15 12?,350 1:3,582 148, 249 (58,813 (53,862 J71.471 $83,518 »S39,JOT
Totil Coit Credit |59,S?0 172,512 181,836 124,064 125,05? 113,675 (14,791 (24,125 129.(36 (26,931 (35,736 141,759 (44),652
» Steai provided to Ueie area» it recorded at a
-------
greater steam production from the waste heat boiler. This will reduce
auxiliary boiler use and therefore reduce the consumption of natural gas
and fuel oil. Increased utilization of digester gas will also reduce the
amount of auxiliary fuel consumed in the auxiliary boilers. Although this
increase in steam production (energy output) will be balanced somewhat by
an increase in energy required to burn the additional sludge (energy
input), it is believed that the growth in energy output will exceed the
growth in energy input.
X. AIR EMISSIONS CONTROL
1. GENERAL INFORMATION
Applicable Air Emissions
Standards: Ontario Standards
Technology: Venturi wet scrubber and cooling tower
arranged in series with a pressure drop of 7
inches w.c. No afterburner.
Scrubber Manufacturer: Ducon-Mikropul Limited
Date of Last Emissions Test:
An extensive emissions test was performed about 2 years ago. Although
the Ministry of the Environment has not yet released an official report
summarizing the test results, the staff has been informed informally
that all emissions standards were met easily.
Stack height: 209 ft
Scrubber Water Treatment: Returned to head of plant
Scrubber Water
Characteristics
(Q,TSS,BOD): Not Measured
XI. ASH DISPOSAL
1. GENERAL INFORMATION
Technology:
The original dry ash handling system has been mothballed. As part of
the existing system, wet ash is thickened in a gravity thickener, the
thickened ash is dewatered to about*60% solids using a vacuum filter,
and the dewatered ash is landfilled. An outside contractor is
responsible for hauling and disposing of the thickened ash.
Location of Landfill: Off-site at a landfill in Pickering
-------
DUFFIN CREEK - REGULATION >04 ASSESSMENT (10)
Ctfrwt Ret, )OI
Rt|uUtcd
A«f. Cane. ¦ Emliakon CakM Cone @POt
Over * hr Rate Mai. Cone 1/2 t> A«|
HibwI (ut/ml) ((face) (u|/m)) (uj/rn))
SUM*
4
I.4JXI0"'
I.0IX10-*
)
AMm*
10,57%
J.I2XI0-J
l.tJXtO"'
.
Ananic
I
). 42X10"*
2.MXI0-*
7)
Baron
ft
2.71XIO-*
2.07X10-*
100
Barium
in
».iixio-*
~.79X10-*
-
BarylUtOTi
0
0.00
aoo
•
Catebss
ii,«y
s.?4xirl
~.miP-»
27
CmMuni
t>
4.70X10-'
».JOX10-*
J
Cafealt
>
7.JIXJ0-*
J.»XI0">
.
Ct»—>lMW>
!»
~,)JXIP-»
OJXIO-J
M
Ccpjtt
m
I.MX10-)
7.74X10"'
100
k«n
i.m
1.01X10*3
7.IJXI0-*
10
1,0)7
J.UX10-'
2.WX10-*
-
1,00*
7. MX 10-J
>.~1X10-2
100
Moumtii
n
2.71X10"*
2.07X10-)
100
i
J.42XIO-*
2.41X10-*
.
),W
1.29X10-J
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-------
Total Annual Volume
of Ash Landfilled:
About 6,000 tonnes
(6,600 tons) per
year
2. COST INFORMATION
A. Capital
Cost of Trucking:
$54/load Canadian
$44/load U.S.
1 load =10 tonnes
¦ 11 tons
Tipping Fee at Landfill:
$22/tonne Canadian
$16.4/ton U.S.
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
CANADIAN
COST
U.S.
Operations Labor
2 hr/day
$ 13,100
$ 10,700
Maintenance Labor
1 hr/day
$ 6,600
$ 5,400
Trucking
6,600 tons/Year
$ 32,400
$ 26,600
Tipping Fee
6,600 tons/year
$132,000
$108,200
Total
$184,100
$150,900
XII. ODOR CONTROL
For each solids handling process, provide the means of odor control used
and provide the appropriate capital and O&M information.
OPERATIONS & MAINTENANCE COSTS
CONTROL CAPITAL LABOR CHEMICAL ELECTRIC MATERIALS
PROCESS TECHNOLOGY COST COST COST COST COST
Sludge
Storage none
Dewatering aerosol spray $5,000 $4,000 $8,000 Nil $0
masking agent
Incineration
Building none
-------
XIII. MANPOWER ALLOCATION
The plant staff at Duffin Creek is divided into three distinct groups, each
with a division supervisor (see attached schematic):
1. A dewatering/incineration staff that is responsible for the operations
and maintenance of the dewatering and incineration systems. The sludge
holding tanks and the chemical conditioning system are considered part
of the dewatering system.,
2. A plant operations staff that is responsible for the operation of all
unit processes other than the dewatering and incineration processes
(liquid train and sludge digestion).
3. A plant maintenance staff that is responsible for the maintenance of
all unit processes other than the dewatering and incineration
processes.
The dewatering/incineration staff handles all maintenance for the
dewatering and incineration systems except for instrumentation and
electrical work. When electrical or instrumentation maintenance is
required in the dewatering or incineration areas, the dewatering/
incineration staff borrows an instrumentation technician or a electrician
from the plant operations staff. It is estimated by plant supervisors that
a electrician and an instrumentation technician from the plant maintenance
staff each spend about half their time (26 weeks/year) in the dewatering
and incineration areas. In addition, general plant housekeeping duties
(sweeping, general cleaning, etc.) are contracted out to an outside firm.
The dewatering/incineration staff consists of 27 operators and maintenance
personnel. Operations personnel are divided into four shifts working on a
rotation program of 12 hour shifts. Each operator averages a 40 hour work
week. Maintenance personnel work a conventional 5 day, 40 hour week. The
27 person staff :is divided up as follows:
1. Dewatering Staff
A. Operations
2 operators/shift * 4 shifts - 8 operators
on day shift only, have: 1 foreman
1 floater
Total 10 operators
B. Maintenance
1 shift/day with 2 maintenance personnel assigned to the dewatering
area
-------
2. Incineration Staff
A. Operations
2 operators/shift * 4 shifts = 8 operators
on day shift only/ have: 3 floaters
1 clerk
Total 12 operators
B. Maintenance
1 shift/day with 3 maintenance personnel assigned to the
incineration area
3. Total
A. Operations
total of 22 operators
B. Maintenance
total of 5 maintenance personnel
XIV. COST SUMMARY TABLES
The following tables attempt to (1) estimate a reasonable construction cost
for the existing Duffin Creek solids handling facilities in 1988 dollars?
(2) convert the construction cost to an annual cost; and (3) present a
total annual cost (capital plus O&M) for each unit process. Capital costs
have been estimated by updating the original construction costs to 1988
dollars using the Engineering News Record (ENR) cost index. Operation and
maintenance costs have been summarized based on the tables presented
earlier in this report.
It should be emphasized that construction costs for such a facility are
very difficult to estimate and, even if estimated accurately, are very
difficult to use in comparison with other facilities. In reviewing these
costs, the reader should consider the following comments:
- Building prices for two similiar facilities can be very, different
depending on such site-specific factors such as depth of ledge,
local materials costs, site constraints, construction market
conditions, or other construction considerations.
- The amount of reserve capacity built into a facility can
significantly affect construction costs. The amount of reserve
capacity allowed for during design can depend on several factors
such as site-specific constraints, plans for future expansion or
growth, and the design consultant's philosophy concerning system
redundancy.
-------
DUFF1N CREEK WPCF
CONSTRUCTION COSTS
(U.S. DOLLARS)
PROCESS
UPDATED
CONSTRUCTION
COST
(ENR = 4535)
AMORTIZED
CAPITAL
COST
Sludge Digestion
-structures
*4,235,000
$355,100
-equipment
$2,340,000
$238,300
-total
$6,57 5,000
5593,400
Sludge Conditioning/Dewatering
-structures
$5,883,000
$493,300
-equipment
$2,006,000
$204,300
-total
$7,889,000
$697,600
Sludge Incineration
-structures
$13,341,000
$1,118,800
-equipment
$9,170,000
$934,000
-total
$22,511,000
-------
cum < ciEti «icr
tWUtl COSTS FGt SUIOi
DAHDllHli fiOCliSIS
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-------
In converting the estimated construction cost to an annual cost, it was
assumed that all structures would have a useful life of 40 years and all
equipment would have a useful life of 20 year life. Capital costs for the
filter press dewatering system only were included in these tables.
XV. SUMMARY OF ENERGY REQUIREMENTS
The following table summarizes energy consumption requirements for each
unit process. To allow a true comparison of energy efficiency with other
facilities, each form of energy consumption (electricity, fuel oil, natural
gas, digester gas, steam) has been converted to a common unit (BTUs). The
energy consumption of each unit process has been determined based on tables
presented earlier in this report. Energy credits have been accounted for
where applicable. The net energy consumption consumption for each unit
process and for the system as a whole has been determined and expressed on
a per ton basis.
Note that the freeboard temperature in the fluidized bed furnace is over
1500 F. Many multiple-hearth incineration facilities (i.e. Upper
Blackstone WPCF) currently operate with a flue gas temperature of 800-1000
F. If more stringent air emissions regulations are imposed in the future,
the installation of an afterburner may be required at all multiple-hearth
facilities to control the possible products of incomplete combustion.
Operation of an afterburner is very costly in terms of auxiliary fuel use.
However, the fluidized bed furnace normally operates with a flue gas
temperature in excess of 1500 F, thereby insuring complete combustion and
eliminating the need for an afterburner. For this reason, when comparing
fluidized bed facilities vs multiple-hearth facilities in terms of economy
and energy consumption, the economic and energy impacts of an afterburner
for the muliple-hearth facility should be included in the comparison.
XVI. LESSONS LEARNED
Operating experience at the Duffin Creek Water Pollution Control Facility
offers several insights into fuel-efficient incinerator operation.
Experience at Duffin Creek demonstrates that digestion can be part of a
successful incineration process. The digesters serve several functions.
The digestion process provides sludge storage within the solids train,
offers an excellent means of incorporating scum into the sludge, produces a
sludge that can be dewatered without odor problems, and produces an end
product that can be used as a fuel source for the incinerator. These
factors offset the negative impacts of the digestion process, chiefly the
destruction of combustibles prior to the incineration process.
Experience at Duffin Creek shows that the means of conveying the sludge to
the incinerator is a critical part of the solids train that should not be
overlooked in design. The conveyance system must be dependable and have
the capacity to meet the system's demands. Breakdowns in the conveyance
system results in incinerator shut-down and start-up periods that require
-------
ivmn rmi ntf
MUCT ktnUiaKEOTS (Ok S0LI1-S
KUHISU HACKiM
HOCKS
IIICTRICITT
iiv-it/ruti
•«i Id in Iqait
Tetil
IHE1GT COKSDMPTIOM
FUEL OIL UTUIll CtS HblSTK CIS
icti/mti icF/ntii icmttu
stim mm
IIWUI
TOTAL ITQi
pusuim*
ineiot mm
OICfSTII CtS STFAK
icr/Yum umtii
TOUl BTl'
CtElilT
HT Bt»
COUbWTIOII
1 total
ITU
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8Tn/oai tou
i
Shift Fulfill
--
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> 0
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111.100,00
O.iOl
11.141
Sludft Diltilioi
IS.000
1.01,200
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I 0
0
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17.141.401.tit-
lSl.lll.POO
0
10.500.000,Ml
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11.000
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I
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4,112.111
14,514 SI,(S2,1)1
(i.ni.ttt
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110,141,(22,lit
ISI.IIMM
3t.lll.UJ
151.500,000,000
H.UM22.12
190.001
1,014,IT0
lOTt: Ilcclriciti 1».OBO ITU/kw-kt
Stru lilt ITU/I
di|tiltr Cti (00 ITV/cf
Fael Oil 111,000 ITU/|«I
*»Unl Gu 1100 OTU/cF
-------
auxiliary fuel use. Cement-type pumps are a viable option to belt and
screw conveyors.
Sludge storage and equalization throughout the solids train is essential to
fuel-efficient incineration. This storage buffers the furnace against
changes in sludge quantity and quality.
In addition to sludge storage, the heat storage in the fluidized bed
provides additional protection against system upsets. This heat storage
allows operators at Duffin Creek to burn 18 hours per day at an optimum
feed rate rather than 24 hours per day at a light feed rate. The heat
storage helps make the success of the incineration system less dependent on
the success of the preceding treatment processes.
A fluidized-bed furnace is easier to operate and control than a
multiple-hearth furnace. There are fewer operational parameters to monitor
and the heat sink built into the furnace makes it less susceptible to
upsets. Operators seem very comfortable with the system.
-------
APPENDIX D
CRANSTON
WATER POLLUTION CONTROL FACILITY
I. GENERAL INFORMATION
Address;
Phone Number:
Contact:
Design Engineer:
Year Began Operation:
Design Average Flow:
Design Peak Flow:
Current Average flow:
Current Peak Flow:
Average Influent BOD:
Average Influent TSS:
Average Effluent BOD:
Average Effluent TSS:
Permitted Limits:
BOD, monthly
TSS, monthly
Fecal Coliform, monthly
Ammonia
Plant Overview:
Cranston wpcf
140 Pettaconsett Avenue
Cranston, Rhode Island 02920
(401) 467-5511
(401) 461-1000
ext. 2190
Donald Benz
Administrative Engineer/Acting Superintendent
Universal Engineering
100 Boylston Street
Boston, MA
Project Engineer: Dave Press
Upgrade to the dewatering and thickening systems
complete in 1985. The upgraded incineration
system went on-line in 1986.
23 mgd
Max Hour
Max Day
44 mgd
36 mgd
10 mgd (includes 35,000 gpd of septage)
23 mgd
133 mg/1 (1987)
165 mg/1 (1987)
17 mg/1 (1987)
10 mg/1 (1987)
30 mg/1
30 mg/1
200/100 ml
Treatment processes in the liquid train include screening, grit removal with
detritors, primary settling, biological secondary treatment utilizing the
-------
activated sludge process, secondary settling, and chlorination. The solids
handling train consists of separate thickening of the primary and waste
activated sludges using gravity thickening (primary) and dissolved air
flotation (DAF) thickening (waste activated), sludge blending, dewatering with
fixed-volume filter presses, and multiple-hearth incineration. Three
digesters from the original treatment facility are now used as sludge holding
tanks. These tanks can be used to hold sludge during periods when the
dewatering/incineration system is off-line.
Operating History:
Plant operations at the Cranston Facility are currently in a state of
transition. At the time of our first visit in September 1987, the gravity
thickeners and the DAF thickeners were not on-line. Waste activated sludge
was returned from the secondary clarifiers to the primary clarifiers and
co-settled with the primary sludge. The thickening units were bypassed and
sludge was sent directly to the sludge blend tank and the subsequent filter
press dewatering process.
In June of 1988, a new administrative engineer took over the facility and
implemented several process changes. Under normal operating conditions, waste
activated sludge is no longer returned to the primary clarifiers to be
co-settled. The DAF and gravity thickeners were put back on-line so that the
primary and waste activated sludges could be settled and thickened separately.
Since July 1988, the facility has operated primarily in this separate
thickening mode, although equipment breakdowns have forced the staff to
operate in the co-settling mode at times. The new administrative engineer has
also implemented an aggressive maintenance program aimed at getting broken
equipment back into operable condition.
The plant is currently understaffed. The plant staff is budgeted for 6
maintenance personnel, 12 plant operators, 10 solids processing operators, and
4 senior operators. This staff is responsible for the operation and
maintenance of the wastewater treatment facility and all pump stations in the
collection system. Plant management recognizes that there is a staffing
problem and is currently exploring the possibility of going to a private
contract operations arrangement.
The solids handling facilities at Cranston are currently operating with a
significant amount of excess capacity. As a result, the incineration process
must operate on a five day cycle rather than a more fuel efficient seven day
operation. However, two developments are taking place that may significantly
increase the quantity of sludge to be processed in the near future. One
relates to the level of treatment provided at the Cranston facility. The 1985
plant upgrade was designed to provide tertiary level treatment. Due to a lack
of available grant funding, the tertiary treatment processes were not
constructed. However, the plant staff believes that the State regulatory
agancies will require that tertiary level treatment be implemented in the near
future. Tertiary treatment processes would produce a significant amount of
additional sludge.
-------
A second development relates to the State policies regarding sludge
landfilling. State regulatory agencies are in the process of imposing severe
restrictions on the quantities of sludge that may be landfilled in Rhode
Island. As a result, many communities that now landfill their sludge will be
searching for new disposal alternatives, one of which would be to transport
their sludge to Cranston to be incinerated. There is the possibility that the
Cranston WPCF could become a regional sludge processing facility.
Attached is a schematic of the solids handling train which presents sludge
quantities based on 1988 data. Note that the quantities presented here are
all 365 day averages. Because the dewatering and incineration processes
actually operate on a five day per week schedule, quantities presented in this
schematic could be multiplied by 7/5 to obtain true average day quantities for
these processes. Also, the schematic shows average day cake disposal split
beween two technologies; sludge incineration and landfilling. Again, these
are 365 day averages that do not reflect the true operating schedule. In
reality, all sludge cake is incinerated when the incineration system is
operational. When the incineration system is shutdown due to maintenance
problems or equipment failures, all sludge cake is landfilled until the
incineration system is back on-line.
II. UNIT COSTS
Unit costs are based on 1987-1988 records.
ITEM
UNIT COST
Labor ($/hour)
Lime ($/#)
Ferric Chloride ($/#)
Electricity ($/kw-hr)
Natural Gas ($/therm)
HCl
$ 14.00/hour *
$ 83.90/dry ton
$ ,1155/Vet lb.
(30% solution)
$ 0.06/kw-hr
$ 0.6256/100 cf
$ 0.95/ gal
* includes benefits
III SLUDGE PUMPING
Records of actual metered electrical consumption are not available.
Therefore, electrical consumptions will be based upon curves presented in the
EPA publication entitled Energy Conservation in Municipal Wastewater
Treatment. Based on this source, it is estimated that electrical consumption
for sludge pumping at the Cranston facility totals 9,400 kWh/year.
-------
.14 mgd
.5% TSS
5900*/day TSS
WASTE
ACTIVATED
SLUDGE
.05 mgd
3.5% TSS
14,700#/day
58% VOLATTLES
CHEMICAL
ADDITION
3700#/day
PRIMARY
SLUDGE
.077 mgd
1.6% TSS
10,200#/day TSS
INCINERATION
LANDFILL
BELT FILTER
PRESS
DEWATERING
GRAVITY
THICKENING
DISSOLVED AIR
FLOTATION
THICKENING
SLUDGE
STORAGE
/m rv rvi/~» r rrrn r \
l/iUco i i^j\o;
-------
IV. WASTE ACTIVATED SLUDGE THICKENING
1. GENERAL INFORMATION
Technology: Dissolved Air Flotation Thickeners (DAF)
Date installed: on-line April 1985
Manufacturer: Envirex
No. of Units: 2
2. DESIGN INFORMATION
Tank Dimensions: effective length 41.25 ft
effective width 14.75 ft
Sidewater Depth: 9 ft
Effective Surface Area: 600 sf/unit
1200 sf total
Solids Loading Rate: 2 lb/sf-hr
3. OPERATING INFORMATION
After plant start-up, the dissolved air flotation thickeners were not used
until August of 1988 because of electrical problems. All information
presented here will be based upon operating experience during the period
from early August 1988 to the end of December 1988.
Average Operating Flow:
FLCW DAF NO. 1 DAF NO. 2
Recycle Flow .37 mgd off-line
Sludge Flow .12 mgd
Total Flow .49 mgd
Operation Schedule: 365 days
Sludge Feed (#/day): 5900 #/day
% Solids of Sludge Feed: .5% TSS
% Solids of Thickened Sludge: Not Measured
Polymer Use: Not Measured
Odor Control: None
-------
4. COST INFORMATION
A. Capital
Facility Planning Estimate
of Capital: Not Available
Actual Capital Cost
(bid + change orders):
The entire upgrade of the solids handling train was completed under one
project (Contract No. 2A). This project was awarded in 1981 and completed in
1985. The Certificate of Payment for Contract 2a is appended to this report.
Although the entire upgrade was bid as a lump sum, the total cost has been
roughly broken down into process areas (thickening/ de- watering,
incineration) by identifying major equipment costs and proportioning building
costs based on the area occupied by each unit process. Costs for the
thickening process (both gravity and DAF thickening) beakdown as follows:
Original Updated (ENR-4540)
Construction Construction
Cost Cost
equipment $ 2,500,000 $ 3,100,000
structures $ 2,200,000 $ 2,700,000
Total $ 4,700,000 $ 5,800,000
This includes the cost for 1 gravity thickener, 1 DAF unit, electrical and
mechanical items, and a single level building (approximately 125 ft * 70 ft)
to house the thickening equipment.
B. O&M
Item
Level
Consumption Annual
Cost
Operations Labor
Maintenance Labor
Polymer
Electricity
Replacement Materials
Total
8 hr/day
4 hr/week
400,600
kwh/year
$ 40,800
$ 2,900
$ 12,000*
$ 24,000
$ 20,000**
$ 99,700
Spent $6,000 on polymer in the last 6
months of 1988.
** Spent $10,000 on replacement parts and
outside contractors during the last 6
months of 1988.
-------
5. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of 60 kwh per dry ton (reference WPCF Manual of Practice No. FD-2
Energy Conservation in the Design of Wastewater Treatment Facilities) and a
consumption of 40 kwh per square foot of building space for lighting, HVAC,
and other general building needs.
Equipment
No. Units
HP
Recycle Pumps
Air Blowers
DAF Thickeners
Polymer Metering Pumps
Thickened Sludge Pumps
2
2
2
2
2
30
5
4
1.5
7.5
Estimated Electrical Consumption (kWh/year):
Equipment
Building
TOTAL
64,600
336,000
400,600
V. GRAVITY THICKENING
Until August of 1988, the gravity thickeners were not used because of
plugging problems. All information presented here will be based upon
operating experience during the period from early August 1988 to the end
of December 1988.
1. GENERAL
No. Units:
Type of Sludge:
Primary only
2. DESIGN INFORMATION
Tank Diameter:
Tank Depth:
Unit Surface Area:
Solids Loading:
38 ft
11 ft
1134 sf
20 to 30 lb/sf-day (primary only)
6 to 10 lb/sf-day (primary + waste
activated)
-------
3. OPERATING INFORMATION
Percent Solids of Sludge Feed:
Percent Solids of Product:
Sludge Feed:
Average Loading Rate
(#/sf/day):
Average Overflow Rate
(gall/sf/day):
Maintenance Concerns:
about 1.6% TSS
not measured
.077 mgd
10,200 #/day
9
124
The discharge line plugs with rags
frequently.
-------
4. COST
A. Capital
Facility Planning Estimate
of Capital: Not Available
Actual Capital Cost
(bid + change orders):
The entire upgrade of the solids handling train was completed under one
project (Contract No. 2A). This project was awarded in 1981 and
completed in 1985. Although the entire upgrade was bid as a lump sum,
the total cost has been roughly broken down into process areas
(thickening, dewatering, incineration) by identifying major equipment
costs and proportioning building costs based on the area occupied by
each unit process. Costs for the thickening process (both gravity and
DAF thickening) breakdown as follows:
Original Updated
Construction (ENR=4540)
Cost Construction
Cost
equipment $ 2,500,000 $ 3,100,000
structures $ 2,200,000 $ 2,700,000
Total $ 4,700,000 $ 5,800,000
This includes the cost for 1 gravity thickener, 1 DAF unit, electrical
and mechanical items, and a single level building (approximately 125 ft
* 70 ft) to house the thickening equipment.
B. O&M
Item
Consumption
Annual
Level
Cost
Operations Labor
8 hr/day
$ 40,800
Maintenance Labor
2 hr/Veek
$ 1,500
Electricity
364,500 Kwh/year
$ 21,900
Service Contracts
**
$ 2,600
Total
$ 66,800
*Spent $1300 on service contracts in the last 6 months of 1988.
5. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an equipment
consumption of .25 kWh per dry ton (reference WPCF Manual of Practice
No. fd-2 Energy Conservation in the Design of Wastewater Treatment
-------
Facilities and a consumption of 40 kwh per square foot of building space
for lighting, HVAC, and other general building needs (note that the
gravity thickener is housed).
Equipment
No. Units Hr/Day* HP KWH/Day
Gravity Thickener
Thickened Sludge Pumps
Transfer To Chemical
1
2
24
24
2
5
40
180
Conditioning
3
24
20 1,080
Total
1,300
Estimated Annual Electrical Requirements (kWh/year):
Equipment
Building
TOTAL
500
364,000
364,500
VI. SLUDGE STORAGE TANKS
The original primary plant included three sludge digesters. These
digesters are now used as sludge storage tanks, in the current
operating mode, sludge is dewatered and incinerated on a 5 day per week
schedule. Sludge produced during the weekend is stored in the two
sludge storage tanks and fed to the dewatering/incineration processes
during the following week. Generally, fresh sludge is processes on
Monday and Tuesday and weekend sludge is paced into the system at
midweek. This mode of operation has a negative impact on the
dewatering/incineration system. Sludge drawn from the storage tank has
a much lower volatile content than the fresh sludge that is produced and
processed immediately. When weekend sludge from the storage tank is
mixed into the dewatering feed, the quality of the sludge changes
significantly. This makes it difficult to optimize the chemical
conditioning requirements for the dewatering process, therefore the
effectiveness of the dewatering operation decreases. Under these
conditions, the furnace is very difficult to control because the percent
solids and the percent volatiles of the sludge cake feed are
fluctuating. To control the furnace under these conditions, the
operator will often be forced to use auxiliary fuel to maintain
combustion temperatures.
VII. SLUDGE BLEND TANK
1. GENERAL
No. Tanks: 2
Tank Dimensions: 26 ft * 28.5 ft
-------
Tank Depth:
Mixing:
Mixer Manufacturer:
2. OPERATING INFORMATION
9 ft
Mixing provided by propeller mixers.
Diffused air is available for mixing,
but is not used because this system
encourages odor problems.
Chemineer
Percent Solids of Sludge Feed: Range 1.5% to 5% TSS
Average 3.5% TSS
58%
Same as feed
None
about 16 hours
Percent Volatiles of Feed:
Percent Solids of Product:
Chemical Addition:
Detention Time:
3. COST
A. Capital
Actual Capital Cost (bid + change orders): Included in dewatering costs
B. O&M
Item
Consumption
Annual
Level
Cost
Operations Labor
2 hr/day
$ 10,200
Maintenance Labor
4 hr/week
$ 3,000
Electricity
30,000 KWH/year
$ 1,800
Chemicals*
$ 4,300
Replacement Materials**
$ 24,000
Total
§ 43,300
* Potassium permanganate used for odor control. This passive
system forces off gases to pass through one of four 55 gallon
drums filled with potassium permanganate prior to discharge to
the atmosphere.
** Have spent $12,000 in the past six months on repairs to the
mechanical mixers. Typically, rags get caught in the
propellers, creating a torque load on the mixer shaft.
-------
4. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon curves
presented in the EPA publication entitled Estimating Sludge Management
Costs.
Rated HP of Mixers 2 § 20 HP Am it
Typical Hours of Operation: 24 hour/day
Annual Electrical Requirements
(kw-hr/year): 30,000
VIII. CHEMICAL CONDITIONING
1. GENERAL INFORMATION
Both a lime and ferric conditioning system and a polymer conditioning
system were provided. During design, it was recognized that lime and
ferric conditioning would be required in the early years of the plant
operation, but it was believed that future improvements in polymer
effectiveness may someday make polymer a viable conditioning
alternative. Currently, the lime and ferric conditioning system is used
exclusively. A general description of each system follows.
In the lime and ferric conditioning system, sludge is pumped to chemical
conditioning tanks where it is mechanically mixed with ferric chloride.
The sludge then flows by gravity to a flocculation tank where lime is
added and the sludge is gently stirred. Conditioned sludge is drawn
from the flocculation tank and fed to the filter press. The ferric
chloride storage and feed system consists of a ferric storage tank
(usable storage capacity of 17,860 gallons), two chemical metering
pumps, and a dilution and transport system. The lime storage and feed
system consists of a dry lime storage silo, a dry lime feeder, a lime
slaker, a lime slurry holding tank, and chemical metering pumps.
The polymer system consists of a concentrated liquid polymer storage
tank (usable storage volume 3380 gallons), a package polymer dilution
system consisting of a mixing tank and polymer and dilution water pumps,
a diluted polymer storage tank, and diluted polymer metering pumps.
Concentrated polymer is diluted to a 2 percent solution at the dilution
mix tank and is further diluted to a 1 percent solution before adding
the polymer to the sludge.
IX. SLUDGE DEWATERING
1. GENERAL INFORMATION
Technology; Fixed Volume Filter Press
Side Bar Type
No. of Units: 3
-------
Date installed: 1985
Manufacturer: Eimco
See attached figures showing general press component description and
filter press system process flow (taken from Universal Engineering
Operation and Maintenance Manual for City of Cranston Solids Handling
Facilities)-
2. DESIGN INFORMATION
Thickened Sludge Quantities (dry lb/day):
Design - 79,500 (design year 2000)
Average - 77,900 (design year 2000)
Mimimum - 58,200 (design year 1980)
Chemical Conditioners (dry lb/day):
Lime Design Average 15,900
Range 5,800 - 23,900
Ferric Design Average 4,000
Range 1,800 - 8,000
Design - 100,500 (design year 2000)
Average - 97,900 (design year 2000)
Total Conditioned Sludge (dry lb/day):
Design - 100,500
Average - 97,900
Minimum - 59,600 (design year 1980)
No. High Pressure
Piston Type Sludge
Feed Pumps: 6
% Cake Solids: Design - 35
Range - 25 to 40
Operating Cycles: 2.5 hour
Operating Pressure: 100 psi
Cake Volume (cf/day):
Design - 4,100
Average - 4,000
Minimum - 2,400
Unit Size: 104 plates (105 chambers)
1.5 m * 2.0 m plates
can be expanded to 115 chambers by adding 10
additional plates
-------
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WATER CONTROL FACILITY
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-------
Chamber Volume:
2.17 cubic feet
Cake thickness
1 inch
Total Press Volume: 228 cubic feet
can be expanded to 250 cubic feet
Plate Material:
Cast Iron
Clothe Cleaning Agent: Hydrochloric Acid
3. OPERATING INFORMATION
Operating Schedule: 24 hours/day
5 days/Week
Average Sludge Feed
to Dewatering (#/day):
The dewatering system feed averages about 14,700 #/day on a 365 day
average. In actual practice, the dewatering facility operates on a 5
day per week schedule at a loading rate of about 20,600 #/day.
Primary/WAS Ratio: about 1.6 : 1
Percent Solids of Feed: Range 1.5% to 5% TSS
Average 3.5% TSS
Ferric Chloride Dosage: 6% to 7%
Lime Dosage: 15% to 20%
Frequency of Testing to Optimize
Chemical Dosage: Daily
Cake Product (#/day):
The dewatering system produces approximately 18,200 #/day of cake on a
365 day average. In actual practice, the dewatering facility operates
on a 5 day per week schedule and produces about 25,500 #/day.
Percent Solids of Cake: Average 26.4 % (1988)
Rate of Pressure Applied & Pacing of Flow to Filter Press:
Can fill at 10,000 to 15,000 gpm at 80 psi (fast fill) or can fill at
5,000 to 10,000 gpm at 100 psi.
Average No. Filters In Use: 1.9 (1988)
-------
Cycle Time :
No. Cycles Per Day:
Type of Cloth Used:
Cloth Washing Frequency:
Use of Precoat:
Solids Capture:
Sidestream Strength:
Operation/Maintenance Problems:
The core blowers which clear liquid sludge from the center ports of the
plates do not operate.
The drip trays which collect the filtrate and washwater are badly
corroded. As a result, some of the filtrate and washwater leaks through
the drip tray and mixes in with the dewatered sludge cake.
4. COST INFORMATION
2.5 to 4 hours m press cavity (no
allowance for discharge time)
Avg 7
Max 10 (when operating with a backlog)
Polyester
As Needed (may range from a few days days
to three or four months)
None
Not Measured
Not Measured
A. Capital Facilities Plan Estimate of Capital: Not Available
Actual Capital Cost:
The entire upgrade of the solids handling train was completed under one
project (Contract No. 2A). This project was awarded in 1981 and
completed in 1985. The Certificate of Payment for Contract 2A is
appended to this report. Although the entire upgrade was bid as a lump
sum, the total cost has been roughly broken down into process areas
(thickening, dewatering, incineration) by identifying major equipment
costs and porportioning building costs based on the area occupied by
each unit process. Costs for the dewatering process beakdown as
follows:
Original Updated (ENR=4540)
Construction Cost Construction Cost
equipment $ 2,200,000 $ 2,700,000
structures $ 4,000,000 $ 4,900,000
Total $ 6,200,000 $ 7,600,000
This includes the cost for the chemical feed systems, the filter
press units, and the building space to accomodate these systems.
-------
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
102 hr/week
$
74,300
Maintenance Labor
24 hr/week
$
17,500
Line *
$
78,400
Ferric Chloride *
$
103,200
Electricity
1,113,600 kw-hr/year
$
66,800
Replacement Materials *
$
30,000
Total
$
370,200
* Projected annual costs based on the last 6 months of 1988
5. ENERGY CONSUMPTION
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon an eqipment
consumption of 30 kwh per dry ton (reference WPCF Manual of Practice No.
FD-2 Energy Conservation in the Design of Wastewater Treatment
Facilities) and a consumption of 40 kwh per suare foot of building space
for lighting, associated with the chemical feed system was made based
upon curves presented in the EPA publication Energy Conservation in
Municipal Wastewater Treatment.
Equipment No. Units HP
Chemical Mix Tank Mixer 1 2
Flocculation Tank Mixer 1 3
Air Compressor 1 30
Fast Fill Pumps 3 total 50
1.9 avg. operating
Consolidation Pumps 3 total 25
1.9 avg. operating
Lime Slakers 2 30
Lime Slurry Pumps 3 7.5
Lime Slurry Metering Pumps 2 7.5
Ferric Metering Pumps 2 1
Total 4955
* In operation 5 days/Veek
-------
Estimated Annual Electrical Requirements (kw-hr/year):
Equipment
Building
TOTAL
219,600
894,000
1,113,600
X. CAKE STORAGE/EQUALIZATION
Each filter press discharges into a sludge bunker. The purpose of these
bunkers is to provide the equalization storage necessary to transform
the batch output from the filter press dewatering process into a
continuous feed for the incineration system. Under each blinker is a
conveyor that transports cake from the three bunkers to a common
conveyor which transports the sludge to a sludge feed bin which preceeds
each furnace. Cake from this sludge feed bin is withdrawn at a
consistent rate to the furnace. This system was designed to be highly
automated. A weigh belt feeder was installed to control the output from
the sludge feed bin to the furnace. This was provided to insure that a
consistent mass of sludge is delivered to the furnaces.
Each sludge bunker was designed with a usable capacity of 900 cubic
feet, which equates to almost four filter press loads of 228 cubic feet
each. Bunker dimensions are 25.75 feet long by 11.4 feet high with a
tapered width of 5 feet at the bunker top and 4 feet at the bunker
bottom. Unfortunately, a bridging problem has severly limited the
usable capacity of these bunkers. To avoid bridging, the operators
store no more than about half a press load at a a time in a hopper.
Because one-half press load takes about 2.5 hours to burn and because
the cake hoppers are ineffective, the filter presses are used to provide
storage for equalization. However, loads from different filter presses
(stored in different hoppers) can be blended when fed to the
incinerators.
Each sludge feed bin has a usable capacity of 220 cubic feet. Output
from these bins was designed to be controlled by the subsequent weigh
belt feeder. Probes were installed within the bin to monitor the depth
of cake within the bin. These probes would automatically control the
speed of the cake conveyor which transfers cake from the sludge bunkers
to the feed bin. If the feed bin became too full, the probes would
automatically turndown the cake conveying system. There have been
problems with this automated feed system. The weigh belt system would
maintain a steady feed if the quality of the cake was consistent.
However, variations in the percent solids of the sludge cake and in the
quality of the cake (digested sludge versus raw sludge) have resulted in
variations in the furnace feedrate. Problems with the probes in the
feed bins have also limited the effectiveness of the automated conveyor
system. At other times, the probes do work properly, but the conveying
system has difficulty turning down enough to match the probe's signal.
Problems with the conveying system have at times resulted in the
shutdown of the entire dewatering/incineration system.
-------
In addition, the drip trays which separate the filter press discharge
area from the sludge storage bunker have experienced a severe corrosion
problem. As a result, filtrate and cloth washwater often leak through
the drip tray and mix with the bunker sludge, reducing the effectiveness
of the dewatering process.
XI. GRIT, SCREENINGS, AND SCUM DISPOSAL
GRIT DISPOSAL: Landfilled
SCREENINGS DISPOSAL: Landfilled
SCUM AND GREASE DISPOSAL:
A scum concentrator is used to concentrate and homogenize the grease and
scum. The unit is manufactured by the Walker Process Corporation and is
called a Grease Preparation System. The system is essentially a 2-stage
gravity separation device. This grease and scum mixture is then fed to
the incinerator at 1 gpm.
XII. INCINERATION
1. GENERAL INFORMATION
Technology: Multiple Hearth incineration
No. Units: 2
Manufacturer: 1 by Nichols
1 by Crouse
Date Installed:
One unit (Nichols) is about 40 years old, but was rarely used until
1986. The second unit (Crouse) was placedon-line in fall of 1986.
Operational Status:
When the upgraded incineration system went on-line in 1986, the Crouse
unit experienced several start-up problems that severly limited its
operation. The EPA limited operation of the Crouse unit to about 80% of
its full capacity because of emmissions problems during start-up. A
lack of sludge also made it difficult to operate the bigger Crouse
furnace efficiently. As a result, the Nichols furnace was operated full
time from start-up in spring of 1986 to the fall of 1987. At this time,
several problems forced tJie staff to take the Nichols furnace out of
operation. Among these were problems with the center shaft, refractory
damage, and damage to rabble teeth on hearth no. 1 and hearth no. 2.
Since this time, the Crouse furnace has been used exclusively. Each
furnace has a separate scrubbing and heat recovery system.
-------
No. of Hearths Per Unit: Crouse - 6 hearth
Nichols - 6 hearth
Each furnace also has an external afterburner chamber
Diameter: Crouse - 18 ft 9 in; hearth area 1657 sf
Nichols - 14 ft 3 in; hearth area 957 sf
2. OPERATING PARAMETERS
Operating Schedule: 5 days per week
24 hours/day
Design Peak Loading Rate:
The Nichols furnace has a rated capacity of 4,600 wet pounds per hour of
dewatered cake with 35% solids. The Crouse furnace has a rated capacity
of 8,890 wet pounds per hour of dewatered cake with 28% solids.
Average Loading Rate:
The sludge cake feed to the incineration system averages 14,200 #/day
for a 365 day average. However, the furnace normally operates on a 5
day per week schedule at a loading rate of approximately 19,900 #/day
(3200 wet #/hour). It has been found that the optimum feed rate for the
Crouse furnace is 5,200 wet pounds per hourbut, because of a lack of
sludge, the furnace is almost always operated at less than optimum feed
rates.
No. Units typically in Operation:
Average Hearth Loading Rate:
1 unit in operation unit in stand-by
mode
2 #/sf-hour (Crouse furnace)
Rotational Speed of Rabble Arms: minimum 1 rpm
Percent Excess Air:
Cannot be measured accurately because of air leaking into the top hearth
of the furnace.
Average Volume of Shaft Cooling Air Returned As Consumption Air: Varies
The furnaces were designed for operation in the pyrolysis (starved air)
mode, but have only operated in this manner during start-up. To operate
in the convential incineration mode, air must be introduced into the
furnace eithier by recycling the center shaft cooling air or by opening
access doors on the hearths. Typically, the access doors are kept
closed, therefore all combustion air must first pass through the center
shaft. Recycled center shaft cooling air can be delivered to any hearth
or combination of hearths. The operator must adjust the recycle rate of
the cooling air to match the excess air requirements within the furnace.
Because the flue gas oxygen analyzer does not produce usable data, the
operator must visually observe the stack emissions as a guide to the
current excess air requirements within the furnace.
-------
Typical Temperature Profile of Incineration System (degrees F):
Hearth Temperature
(degrees F)
Hearth 1
875
Hearth 2
1220
Hearth 3
1380
Hearth 4
1475
Hearth 5
890
Hearth 6
490
Cooling Shaft Air
140
Afterburner Chamber
730
Subcooler Temperature
60
Although auxiliary fuel is never used in the afterburner, the gas
temperature usually rises slightly as it passes through this chamber, as
the addition of air completes the combustion of remaining volatiles.
3. COST INFORMATION
A. Capital
Facilities Plan Estimate of Capital: Not Available
Actual Capital Cost (bid + change orders):
The entire upgrade of the solids handling train was completed under one
project (Contract No. 2A). This project was awarded in 1981 and
completed in 1985. The Certificate of Payment for Contract 2A is
appended to this report., Although the entire upgrade was bid as a lump
sum, the total cost has been roughly broken down into process areas
(thickening, dewatering, incineration) by identifying major equipment
costs and proportioning building costs based are occupied by each unit
process. The incineration costs breakdown as follows:
Original
Construction Cost
Updated (ENR=4542)
Construction Cost
equipment
structures
Total
$ 8,400,000
$ 2,400,000
$12,400,000
$ 10,300,000
$ 2,900,000
$ 13,200,000
-------
This includes the cost to install the new furnace, the cake conveying
system, and the air pollution control and heat recovery systems, the
cost to refurbish an existing furnace, and the cost for building space
apportioned to the incineration system.
B. O&M
ITEM
CONSUMPTION
LEVEL
ANNUAL
COST
Operations Labor
102
hr/Veek
$
74,300
Maintenance Labor
24
hr/Veek
$
17,500
Fuel Use *
35,000,000
CF/YEAR
$
219,500
Chemicals
None
Electricity
1,864,400
kw-hr/year
$
111,800
Equipment Service Contracts **
$
127,800
Replacement Materials
$
11,000
Totals
$
561,900
*The cost for natural gas is based on the period from July 1, 1987 to
July 1, 1988. Because of the metering system at the Cranston facility,
it is impossible to distinguish between gas consumed within the furnace
and gas used for building heat. However, during the 1987-1988 heating
season, the waste heat recovery system was in full operation and
provided essentially all of the required building heat. Therefore, all
natural gas consumed during this period was used in the furnaces,
**Major repair items that were contracted out in 1987 included:
- replace oxygen analyzer $12,500
- replace rabble arms $24,600
- repair transfer conveyor $38,200
- repair transfer conveyor $27,600
- instrumentation repair $24,900
Operation Guidelines:
The Crouse furnace is designed to be very automated. Under normal
operation, the distribution of combustion air to the hearths is set by
the position of the dampers and remains constant. If all
instrumentation equipment was fully operational, the combustion air
feedrate would be controlled automatically by the percent oxygen in the
exhaust gas. The burners would be controlled by temperature probes in
the incinerator. The automatic controls would maintain a constant
sludge feed rate by adjusting the conveyor speeds. The operator would
set the sludge feed rate and desired hearth temperatures and essentially
allow the furnace to operate itself.
-------
However, the plant staff has experienced several problems with this
automated control system. The flue gas oxygen analyzer does not produce
useful information. The gate controlling the drop chute at the top of
hearth no. 1 does not operate properly. The gate allows air to enter
the top hearth through the sludge feed opening. This additional air
introduced at the top hearth results in misleading readings by the
oxygen analyzer. The oxygen analyzer will record that there is plenty
of excess oxygen in the flue gas stream even when there is a shortage of
oxygen within the furnace. As a result, the operators must ignore the
oxygen analyzer data and adjust the excess air level based on visual
inspection. The operators observe the stack emissions regularly and if
the stack begins to smoke, the excess air level is increased. The
temperature probes within the furnace do operate properly and the
burners are generally controlled automatically by the probes, although
the operators do manually override this system at times.
The automated conveyor system does not deliver a consistent feed to the
furnace. This is due in part to problems with the probes used to
monitor cake levels within the sludge bunkers and feed bins and in part
due to the variability in the sludge cake. Even when working properly,
the weigh belt system can only deliver a consistent sludge feed to the
furnace if the sludge produced by the dewatering process is fairly
consistent. In the current five day per week operation mode, sludge
produced over the weekend is stored in sludge storage tanks (formerly
used as digesters). When the incineration system is started up on
Monday morning, fresh sludge is fed to the furnace to establish good
burn conditions. It is not until midweek that the staff begins to feed
sludge that has been stored since the weekend to the
dewatering/incineration system. Because of its age, this sludge has a
much lower volatile content and does not dewater as well as the fresh
sludge. This variability in the quality of the sludge feed makes it
impossible for the dewatering process and the subsequent conveying
system to deliver a consistent sludge feed to the furnace. As a result,
the furnace is very difficult to control.
Operations/Maintenance Concerns:
- Much of the incineration equipment is very inaccessible, making it
very difficult to perform regular maintenance or necessary repairs.
In some instances, equipment was squeezed into a location without
proper clearance, making it impossible to work on the equipment. In
other instances, equipment was installed at a high elevation without
ladders or catwalks to provide access.
- The plant staff has had a very difficult time getting useful
information from the instrumentation. Much of the instrumentation
equipment, such as the flue gas oxygen analyzer and the cake weigh
belts, does not provide accurate information because of other
failures within the incineration system. As a result, the operators
often must operate the furnace blindly. The only way for the
operator to gauge the effectiveness of the combustion process is to
observe the quality of the stack emissions. This is a very
ineffective way to operate the furnace, as the operator is not able
to identify changing conditions within the furnace until visible
stack emissions resulting from incomplete combustion develop.
-------
- A lack of process understanding among the operators has resulted in
several operations problems. The incineration process is a
relatively complex process. Several variables can be adjusted to
achieve a desired result. Operators need some experience with the
system to learn how the furnace will react under different
circumstances. This learning process has been hampered by the
problems with the system instrumentation and the manpower shortage at
the plant.
- The facility is understaffed, making it very difficult to implement a
preventive maintenance program.
- Typical sludge cake requies auxiliary fuel consumption because of the
relatively low solids and volatiles content of the sludge (26% solids
and 47% volatiles). This problem is made worse by the frequent
furnace shutdowns resulting from a lack of sludge and equipment
failures. The current level of sludge production only allows for a 5
day per week operation schedule and, even with this reduced schedule,
the furnaces must be operated well below their optimum feed rate.
Each Friday, the lead furnace is slowly brought down from combustion
temperature to a stand-by temperature of 900 F. On Monday morning,
the furnace is slowly returned to combustion temperature. In
addition to these scheduled shutdowns, frequent equipment failures
have resulted in several unscheduled shutdown periods. When there is
an equipment failure, the operators and maintenance staff usually
cannot be sure how long the furnace will be out of service. If it
appears that it will only be for a short period, the combustion
hearth temperature is maintained at 1200°F during the shutdown.
These shutdowns, both scheduled and unscheduled, result in a
tremendous amount of auxiliary fuel use.
4. ENERGY CONSUMPTION
Equipment
Rated HP
Center Shaft Drive
Center Shaft Cooling Air Fan
Clinker Grinder
Clinker Ash Screw
ID Fan
Ash Bucket Elevator
Ash Screw
Ash Conditioner Screw
Belt Conveyor
Weigh Belt Conveyor
Transfer Sludge Conveyor
Sludge Combustion Air Fan
Sludge Feed Bin Conveyor
Ash Rotary Air Lock
Ash Cooler
Burner Air Fan
Sludge Shredder
Instrument Air Compressor
Total
246.5
15
25
3
1.5
100
1.5
2
3
1.5
1
7.5
25
5
1
2
40
5
7.5
-------
Records of actual metered electrical consumption are not available.
Therefore, electrical consumption is estimated based upon Figure 3-113
of the EPA publication entitled Energy Conservation in Municiapl
Wastewater Treatment and electrical consumption for general building
needs such as lighting and HVAC is estimated based upon a value of 40
kwh per square foot of building space.
Estimated Total Annual Electrical Requirements (kw-hr/year):
Annual Auxiliary Fuel Use::
During the period from July 1, 1987 to July 1, 1988, 35,000,000 cubic
feet of natural gas were consumed at the Cranston facility. During this
heating season, the waste heat recovery system was operable and was able
to meet virtually all of the facility's building heat needs. Therefore,
all of the natural gas consumed during this period was utilized by the
furnaces. This natural gas consumption level equates to about 13,540
cubic feet per dry ton of sludge, or the equivelent of about 98 gallons
of fuel oil per dry ton. It is impossible to break this fuel use down
into fuel consumed during start-up and cool-down periods and fuel used
during steady state operation, but it is safe to conclude that this very
high fuel consumption is a direct result of the five day operation
schedule and the frequent unscheduled maintenance shutdowns.
5. ENERGY RECOVERY
The exhaust gases from the furnace pass through a waste heat exchanger.
The heat exchanger transfers heat at a hot gas/heating oil interface and
then at a heating oil/water interface. The final product is hot water
which can be used for space heating throughout the plant. The
temperature of the gas at the heat exchanger outlet is about 400 to 500
F. The waste heat recovery system was put into operation in the Fall of
1987. The system worked successfully in the 1987-1988 heating season,
but in June 1988 had to be taken off-line due to a severe corrosion
problem. The corrosion occurred on the gas stream side of the exchanger
and was so severe that all the heating oil leaked from the exchanger.
The incineration system is now operating without heat recovery.
VIII. AIR EMMISSIONS CONTROL
1. GENERAL INFORMATION
Technology:
Top hearth gases pass through an external combustion chamber where,
although no auxiliary fuel is used, the gas temperature rises slightly
as the addition of air completes the combustion of remaining volatiles.
Gases then pass through a waste heat exchanger, a water spray precooler,
a variable throat venturi scrubber, and an impingement tray
scrubber/subcooler prior to discharge to the atmosphere. Hie scrubber
system is designed for a pressure drop of 25 inches W.C.
Equipment
Building
TOTAL
900,000
964,000
1,864,000
-------
Scrubber Manufacturer: Caston
Date of Last Emmissions Test:
Stack height: 50 feet
Building Height: 35 feet
Scrubber Water Treatment: Passavant Lamellar System
Scrubber Water Characteristics (Q,TSS,BOD):
Lamellar Influent 115 mg/1
Lamellar Effluent 15 mg/1
Flow 225 to 300 gpm
XIV. ASH DISPOSAL
1. GENERAL INFORMATION
Technology:
Dry ash system consisting of a bucket elevator, a screw conveyor, and a
storage silo before discharge to a truck for hauling. Location of
Landfill (on-site/off-site): Johnston, RI Total Annual Volume of Ash
Landfilled (cy/year): 1550 cy/year (assumed .6 cy ash/dry ton of cake
incinerated).
2. COST INFORMATION
A. Capital
Cost of Truck(s): In 1981, purchased 2 trucks at $80,000/unit and
1 payloader at $80,000.
Cost of Landfill (if owned by district): N/A
Tipping Fee at Landfill (if commercially operated): $29/ton
B. O&M
ITEM CONSUMPTION ANNUAL
LEVEL COST
Operations Labor 8 hr/day $ 40,800
Maintenance Labor 0 hr/day $ 0
Tipping Fees $ 20,000
Replacement Materials $ 10,000
Total $ 70,800
-------
XV. MANPOWER ALLOCATION
The current operations and maintenance staff is budgeted for 10
operators dedicated to the solids train and 4 maintenance personnel for
the entire facility. The 10 operators each work a 40 hour week covering
the Monday thru Friday round-the-clock operation. The maintenance
personnel work a conventional 40 hour week of Monday thru Friday, 8
hours per day. The plant staff has had a problem filling some vacant
positions, so the staff is often operating with even less personnel than
is allowed for in the budget. When a complete staff is available,
available labor hours are typically split between unit processes as
follows:
The plant management realizes that the treatment facility is
understaffed and alternatives such as contract operations are being
explored to correct the situation. Outside contractors are used
extensively to assist the plant staff with mechanical, electrical, and
process control problems.
COST SUMMARY TABLES
The following tables attempt to (1) estimate a reasonable construction
cost for the existing Cranston WPCF solids handling facilities in 1988
dollars; (2) convert the construction cost to an annual amortized cost;
and (3) present a total annual cost (capital plus O&M) for each unit
process. Capital costs have been estimated by updating the original
construction costs to 1988 dollars using the Engineering News record
(ENR) cost index. Operation and maintenance costs have been summarized
based on the tables presented earlier in this report.
It should be emphasized that construction costs for such a facility are
very difficult to estimate and, even if estimated accurately, are very
difficult to use in comparison with other facilities. In reviewing
these costs, the reader should consider the following comments:
- Building prices for two similiar facilities can be very different
depending on such site-specific factors such as depth of ledge,
local materials costs, site constraints, construction market
conditions, or other construction considerations.
Operations Staff Maintenance Staff
(10 operators) (4 personnel)
DAF Thickening
Gravity Thickening
Sludge Blending
Sludge Dewatering
Incineration
Ash Disposal
Subtotal
Liquid Train
Total
56 hours/week
56 hours/week
28 hours/week
102 hours/week
102 hours/Veek
56 hours/week
400 hours/Veek
0 hours/week
400 hours/week
160 hours/week
102 hours/week
4 hours/week
2 hours/week
4 hours/week
24 hours/week
24 hours/week
0 hours/week
58 hours/week
-------
CRANSTON WPCF
CONSTRUCTION COSTS
PROCESS
UPDATED
CONSTRUCTION
COST
(ENR = 4540)
AMORTIZED
CAPITAL
COST
Slusge Thickening
-structures
$2,700,000
$226,400
-equipment
$3,100,000
$315,700
-total
$5,800,000
$542,100
Sludge Dewatering
-structures
$4,900,000
$410,900
-equipment
$2,700,000
$275,000
-total
$7,600,000
$685,900
Sludge Incineration
-structures
$2,900,000
$243,200
-equipment
$10,300,000
$1 ,049,100
-total
$13,200,000
-------
'HWm VKF
AHHIHI COSTS F01 SOU 1)5
HAHOtlHG fROCESih'
to
o
HtCCESS
CAPITAL
LA80S SLECTBICtTf
FUEL
CHEKICALS KiTKItlALS
t SULLIES
COkTSACTtO
SEtYI'.tS
TOTAL
COST
I K'TAL
AHHlla COST
capital cost ojb cost total cost
lim TO* I/01T TOM 1/08! TOM
Slud0
13.133.(0(1
loo.m
1230
13(5
1595
Dote: At) coiti ire kited on MSI conigiotioi records.
lit capital coeti bued on September Dili colt index.
Cipittl coitt bue btVn conterted to • 1/drj toe bull
bued on tie iritei cipicit; ot )0 dry tpd.
OAK colli Uve been converted to e 1/drj ton bitii
bttrd en 1338 slodite production of S.I dry tpd of demtered cjke.
I Included in priurj sludte Uickenint capital coiW
>> Included in tlulie dm»terint cipltil coiti
-------
- The amount of reserve capacity built into a facility can
significantly affect construction costs. The amount of reserve
capacity allowed for during design can depend on several factors
such as site-specific constraints, plans for future expansion or
growth, and the design consultant's philosophy concerning system
redundancy.
In converting the estimated construction cost to cin annual cost, it was
assumed that all structures would have a useful life of 40 years and all
equipment would have a useful life of 20 years. A discount rate of 8
percent was assumed to determine an appropriate capital recovery factor.
XVII. SUMMARY OF ENERGY REQUIREMENTS
The following table summarizes energy consumption requirements for each
unit process. To allow a true comparison of energy efficiency with
other facilities, each form of energy consumption (electricity, fuel
oil, natural gas, steam) has been converted to a common unit (BTUs).
The energy consumption of each unit process has been determined based on
tables presented earlier in this report. The net energy consumption for
each unit process and for the system as a whole has been determined and
expressed on a per ton basis. Factors used to convert each energy form
to a BTU basis appear at the bottom of the table. These factors reflect
the BTUs of energy required to produce a kw-hour of electricity and a
pound of steam. These conversion factors account for inefficiencies in
the production of electricity and steam.
XVIII. LESSONS LEARNED
The design and operating experience at Cranston WPCF offers several
insights into fuel-efficient sludge incineration.
Operators at the Cranston facility emphasize the importance of
consistency in the operation of the incinerator. Any changes to the
system should be made gradually. A consistent sludge feed is essential
to fuel-efficient operation.
Operation of a multiple hearth furnace on a five day per week schedule
is very costly because of the fuel required to maintain stand-by
temperatures over the week-end. Unscheduled shutdowns due to
maintenance problems also significantly increases auxiliary fuel use.
Sludge hoppers should be designed to avoid bridging. A tremendous
amount of sludge storage at Cranston is being lost because of bridging.
-------
CBAH3T0U IfPCP
EHRBGT BBQUIBBKBNT3 FOB SOLIDS
HANDLING PBOCBSSS3
BNEEG? CONSUMPTION
PS0CE3S
SLSCTBICIT7 «
IKK-HE/TBAR1
BuLldioc Equip
Total
FUEL OIL
tCALy TEAR)
NATURAL GAS
(CF/TBARI
TOTAL 9TU!
CONSUMED
I TOTAL STU
CONSUMPTION
BTU/DRT TON
t!
Sludje Puipiaf
-
9,<00
9,400
0
0
94,000.000
0.131
28.300
V.A.3. Tiiclreniaj
335,000
64,600
400,600
0
0
4,006,000.000
5.501
1,206.082
Priiarj Sludje Thickeninl
3S4.000
5G0
364.500
0
0
3,645,000.000
5.011
1,097,396
Sludge Blending
—
30.000
30.000
0
0
300,000,000
0.411
90.321
Sludfe Deuaterinf
854,000
219,800
1,113,500
0
0
11.136.000,000
15.291
3.352.702
Slud|e Incineration
96<.000
900,000
1,864,000
0
35.030,000
53.640.000.000
'3.6EX
16.149.330
TOTAL
2.553,000
1,224,100
3.782,100
0
35,000,000
12,521,000,000
iOO.COl
21,924,131
NOTE: ElectricitT 10,000 BTU/kv-br
Fuel Oil 138,000 8TU/«al
Natural Ga« 1000 8TU/cf
it Based on 1988 sludge production of 9.1 drj tpd of dewatered sludge cake,
t All elctrical consuiption values are based upoo
comcted horsepower. Actual letered values
are'not available.
-------
APPENDIX E
SUMMARY OF OPERATION AND MAINTENANCE
COSTS AT CURRENT
LOADING CONDITION
-------
Reproduced from iiPli
best available copy.
Out OUTS NA SOLIDS INCUl] MDCXSSSS
a* ciaotovr tnAomo (uumcn
cumucm
MATERIALS COtrmCTCD TOTAL
QfEXXCALS 4 SVfPLILS SCWlCtS OU1 COST
COST
atEorr
WtT
om cost
% total wcr
IttT COST S/T*Y TOW
to
-J
3llK%« ruapinq* $ ft
V.A.S. T¥iich«niA4| 513.000
Prlasry tlu^
fliickMin^ 310,708
SlttffO Storsq* Tsnks » 5)9,300
Th«nHl Conditioning 1.2)4.(00
Sludfo Oovstoiin?
Sludqs Zncinocstion'
ftoiloc Systo*
fCBC «y«tM
tcma.
1.173.700
1.2S1.000
112.400
197,100
5 176,560
374.300
II.too
121.900
344.000
207,000
126.300
272,100
121.300
271,400
944,300
0
$ 0 $ 0 $ 0 5 176,500 $ o $ 176,500 1.15%
0 HO,400 1,500 1,1)1,200 0 1,131,200 1.67%
15,000 45,300 11,000 420.600 0 420,600 3.21%
26,500 49,500 700 746,900 0 746.900 5.7)1
22.700 239,100 17.100 1,957.900 0 1,141,900 14.25%
760,600 15,500 4,*00 2,451,600 0 2,451,600 11.10%
0 551,000 104,400 4.995.100 0 4.995,100 11.21%
55.500 151,200 9,600 2,325.100 1,541,200 711.900 6.00%
69,000 11,100 11.600 419,300 0 419,300 3.75%
16,293,400 $2,461,00ft $1,217,700 $971,300 51,457,300 $163,100 514,564,200 51,543,200 513,041,000 100.00%
1 dvy too ¦ 0,9072 4cy
*1M» tin* !t«* includes puffin? tram tho pris*ry *n4 ••con4*ry clstiCUrs to th« sludqo lhi«k*ninq pr
-------
TABLE K—2
I7PPKH BLACKSTOBE WPCF
0(K COSTS rOR SOUDS RAHDLIHG PROCESSES
AT CURBEHT LOADIHG COWDTTIOH
($/TKAR)
PROCESS
LABOR
ELECTRICITY
TUEL
CHEMICALS MATERIALS
TOTAL
OIH COST
* TOTAL
O&M COST
OiM COST
$/DRY TOH'
Sludge Fuaping
W.A.S. Thickening
Holding Tanks
Blending/Dewataring
Sludge incineration
Ash Disposal
1
LP
TOTAL
$ 39,000
18,200
5,000
283,300
295,500
28,000
$667,000
$ 800
51,800
100
57,400
150,400
0
$260,500
$ 0
0
0
0
51,100
0
$51,100
0
0
79,800
0
0
$79,800
$ 1,000
3,300
0
26,000
53,500
5,900
$89,500
$ 40,800
73,300
3,100
446,400
550,300
33,900
$1,147,800
3.55%
6.39%
0.27%
38.89%
47.94%
2.95%
100.00%
$ 3.71
6.67
0.29
40.64
50.09
3 .08
$104.47
1 dry ton ¦ 0.9072 dry tonnes
ROTE: All costs adjusted based on the unit costs developed in Section 4.
-------
>
TABLE K-3
DUFTIH CREEK KPCF
om COSTS FOR S0UC6 BANDUNG PROCESSES
AT CURRQVT LQADI1IG CGKDITIGH
($/TTEAH)
PROCESS
LABOR
ELECTRICITY
FUEL
CHEMICALS MATERIALS
PURCHASED
SERVICES
TOTAL
OfcM COST
COST NET
CREDIT OfcM COST
* TOTAL NET
NET COST S/OBY TOW
to
^4
Sludge Fusing $ 0
Sludge Digestion 54,100
Sludge Devatering 388,BOO
Sludge Incineration 481,BOO
(ji Ash Disposal 16,500
TOTAL $941,200
$ 1,000 $ 0 $ 0
0 0
52,500 0 208,200
101,400 270,000 24,600
0 0 0
$219,300 $270,000 $232,800
$ 0 $ 0 $ 1,000 $ 0 $ 1,000 0.04% $ 0.09
7,400 14,800 140,700 0 140,700 $.06 14.33
117,900 32,800 800,200 0 800,200 34.47 B1.S0
420,800 65,600 1,364,200 135,900 1,228,300 52.91 125.12
26,600 108,200 151,300 0 151,300 6.52 15.39
$572,700 $221,400 $2,457,400 $135,900 $2,321,500 100.00% $236.43
1 dry ton » 0.0972 dry tonnes
NOTE: All costs based on 1987 consumption records and 19B7 sludge production <9832 tons/year of dewatered cake).
All costs presented in U.S. dollars and based on September 1988 cost index.
-------
TABUI E—4
CRABSTOH wcr
OkM COSTS ros SOLIDS HAHDU3IG PROCESSES
TOR CURRENT LQADHIS OOKDITICH
(S/YEAB)
PROCESS
LABOR
ELECTRICITY
MATERIALS CONTRACTED TOTAL
FUEL CHEMICALS It SUPPLIES SERVICES O&M COST
* TOTAL OlM COST
OtM COST ?/DRY TON
to
-1
Sludge Processing $ 0 $ 500 $0 $ 0 $0 $0 $ 500
W.A.S. Thickening 46,900 17,500 0 12.000 20,000 0 96,400
Primary Sludge Thickening 45,400 16,400 0 0 0 2,600 64,400
Sludge Blending Tanks 14,100 1,400 0 4,300 24,000 O 45,800
Sludge Dewatering 98,300 50,100 0 181,600 30,000 0 360,000
Sludge Incineration 142,100 83,900 140,000 0 21,000 147,800 534,800
TOTAL $346,800 $169,800 $140,000 $197,900 $95,000 $150,400 $1,099,900
1 dry ton » 9.9072 dry tonnes
'Include* ash disposal costs.
NOTE: All costs adjusted based on unit costs developed in Section 4.
All costs based on 1988 average dewatered sludge.cake production of 9.1 dry tpd.
0.05% $ Q.IS
8.76% 29.02
5.85%
3.98%
32.72%
48.62
19.39
13.19
108.38
161.01
-------
MU *-5
amuscM or mmal aduk iMW.nn com
rot sijjdck mcmrns
JOT CUWDfT IZM0ENO UIUITION
($/TWI
(I)
BtACKSTOWE C?j
ro
-4
CO
MWUfcL COST
$/OT
% total
$/Tff
LAW*
nxcmicrrr
rucL
OOMCMi
mrauALs i sufplxcs
CONTRACTU) SCKVYCtS
Terr XL out
TOST QkCfilt
$2,276,000 $15.13
•23.700 12,11
Jl».<00 9.10
v 0.W
0.2)
4.41
0.21
26.66
TOTAL COST
96.14%
20.
14.72%
o.oo%
0.27%
7.12%
0. 36%
43.16%
0 0.00 0.00%
$4,004,200 $61.11 100.00%
IS ,000
215,100
14,500
1,720,>00
AIWUAL COST
$/trr
% TOTAL
$/DT
$2S6,iOO
60,200
52,700
0
0
4,300
0
111,200
o
$404,000
$26.10 10.99%
5.41 14.90%
4.10 1J.04%
O.OO 0.00%
0.00 0.00%
0.39 1.06%
0.00 0 00%
10.67 29.01%
0.00 0.00%
$36.71 100.00%
awryrow 131
novum, cost i/trr
$550,600
92,200
34,400
0
12 ,000
20.000
2,600
161,300
0
$7U.B00
% TOTAL
$/CT
$165.71
27.79
10.36
0.00
0. 78
49.56
0.00
$214.33
1 dry too • 0.9012 dry t«iuvt*
All cotti b«o*d on »VfC*9« loading condition:
Nitrt 177.5 tpd of (hw>«rtd ilud^i cako
IlickitMa 20.1 Ipd of dovatorod iltK^r «l«
CiiMton 9.1 tpd of dowtarad aludga cako
Xl 1 cook* botod on unit cofto dawolo^od in section 4.
(1) Inclu4*i alodgo {Maplftq trow tbo clacifiors, flotation thickaninq of V.A.S., and qtaviky tfciclionin? of primary
12) Includai tlu4q« puapln^ (im tho cla«ifiora, flotation thicVminq *>t W.A.S., and of thickanad w.A.S. and priMry
cludqo. IHoto that tho pnaory ilud^o holding tank acta is a gravity thickonar. I
(3) (Kiu4*i ilvdfo ^liif (
-------
TABLE E~6
COMPARISON OF ANNUAL SOLIDS HANDLING COSTS
FOR SLUDGE DIGESTION
AT CURRENT LOADING CONDITION
<$/YEAR)
ANNUAL COST
DUFFIN (1)
$/DT
% TOTAL
$/DT
CAPITAL
$593,400
$60.44
80.73%
LABOR
54,100
5.50
7.35%
ELECTRICITY
65,400
6.66
8.90%
FUEL
0
0.00
0.00%
CHEMICALS
0
0.00
0.00%
MATERIALS & SUPPLIES
7,400
0.75
1.00%
CONTRACTED SERVICES
14,800
1.50
2.01%
TOTAL O&M
141,700
14.42
19.26%
TOTAL COST
$735,000
$74.85
100.00%
1 dry ton =» 0.9072 dry tonnes
All costs based on unit costs developed in Section 4.
All costs based on average sludge production of 26.9 tpd of dewatered
sludge cake.
(1) Includes sludge pumping from the clarifiers and sludge digestion.
-------
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-------
APPENDIX F
SUMMARY OF OPERATION AND
MAINTENANCE COSTS AT
-------
CUM COSTS PCM SOUtR HMIIJBD WDSSKS
AT STSTBW CAMCITT
PROCESS
IABQR
rLccnucrrr
MATERIALS
CHEKICALS t SV7PLIE5
CONTRACTED TOTAL
snnncts otM cost
COST
CMDIT
!«rr
0(J4 COST
* T7TAL ITT
WET COST S/TBV TOW
to
00
u>
Slu4?a
W.A.S. lhickaftlit?
Ftiaary Slud9«
ltiicktoinf
Sludft Sto(«9« Tanks
conditioning
Sludqa oavatariaq
Sludga incineration*
•oiUc Syata*
MC SyitM
TOTAL
$ 0 $ 174,500
614.009 405,200
414,100
626,200
1.669,400
1,837,700
4,310,700
892,400
197,100
51,500
171,100
462,200
261,600
961,300
272,100
123,300
$10,631.tOO $2,715,600
1 dry too • 9*9072 dry torm
0 $ 0
0 0
0 20.200
0 28,500
0 54,000
0 1,071,600
364,600
629,800
0
75,300
69,000
60,400
49,500
H9,000
114,000
797,100
136,300
88,100
$994,400 $1,250,600 $1,944,900
4,700
14.700
700
26,000
6,400
149,100
9,600
11,800
$ 176, M0
1,414,600
561,100 0
876.700 0
2, M0,600 0
3,243,300 0
6,482,800 0
2,015, W0 1.543,200
489,300 0
$ 176,500
1,414,600
561,100
876,700
2,SS0,600
J.243,*00
6,482,800
472.300
489,300
$223,000 $17,830,300 $1,543,290 $16,287,190
Shi* Hm it« lacludn puaplnq fro* tha prlaary and a aeon da ry elariflara to tha stadga thicKaninq procasa.
*Ineludaa aah dlapoaal coita.
All eoata adjuatad baaad on iyit«a capacity of 240 dry tpd of davatarad cik«.
All aubaaquant aludqa pu^inq it if>clud*d in tha appropriata unit procaas Una itas.
All eoata ratiact oparatlon at aatlaatod syntaa capacity of 240 dry tpd of davatarad caka.
3.45
5.39
15.69
H.94
39.85
2.90
3.01
100.00%
$ 2.01
16.15
6.41
10.01
29.12
17.02
74.00
5.40
5.59
-------
TABLE T-2
UPPER BLACKS TONE WPCF
OUt COSTS FOR SOLIDS HANDLING PROCESSES
AT SYSTEM CAPACITY
($/TKAR)
PROCESS
LABOR
ELECTRICITY
FUEL
CHEMICALS MATERIALS
TOTAL
O&M COST
% TOTAL
OtM COST
O&M COST
$/DRY TOW
Sludge Pumping
W.A.S. Thickening
Holding Tanks
Bliriding/Dewatering
K) Sludge Incineration
CO
ib-
Ash Disposal
TOTAL
$ 78,000
20,000
6,000
432,500
588,700
56,200
$1,181,400
$ 20,800
68,800
100
62,800
231,400
0
$383,900
102.100
$102,100
$ 0 $ 2,000
0 6,600
0 0
159,000 51,800
0 106,600
0 11,800
$159,000 $178,000
$ 100,800
95,400
6,100
706,100
1,028,800
68,000
$2,005,200
4.89%
4.63
0 .30
34 .25
49 .91
3.30
100.00%
$ 4.60
4.36
0.28
32.24
46.98
3.07
$91.53
1 dry ton = 0.9072 dry tonnes
All costs redect operation at estimated systen capacity o£ 60 dry tons per day of devatered cake.
-------
iMtc r-j
om oosts worn 90006 twn.nK noaessc
mt &ia'gw opacity
($/T*Al)
K)
00
tJI
wpcgss
Slutffl Minq
Slud}« Oiftftien
Sludqt DwatttiAf
IABQR
cLXCTHicmr
CHQIlCALS HATEH1ALS
PURCHASED
SERVICES
TOTAL
OU1 COST
COST
CREDIT
OU* COST
% TOTAL KTT
pgr cost %/tmt
$ 0 $ 1.700 $
55.200 €*.$00
432*000
$497,200
94.100
$121.)00
0 230.600
0 $230,600
8,200
117.900
$ 0
16.400
36.400
$126,100 $ *2,900
$ 1,700 $ 0 $ 1,700
10.300 0 145,300
871.000 0 971,000
$i,oie.ooo $ o $1,018,000
0.10% $ 0.16
7.99 13.27
47.31 79.54
55.30* $ 93
Sludgo Incineration
Ash Disposal
$614,900
16,900
$652,100
$137,300 $151,300 $ 54.700 $420,900
0 0 0 59.700
$65,600 $1,445,300 $135,800 $1,309,500 35.57 59.79
240.400 336.100 0 336,100 9.13 15.35
$137,300 $151,300 $54,700 $490,000 $306,000 $1,791,400 $135,900 $1,645,600
44.70*
$75
TOTAL 100% $169
1 dry ton • 0.9972 dry toims
KIR: Jdl costs prsssntod in U.S. dollars and bosod on StptHfetr 1999 cost indai.
All costs adjusted basod on tho unit costs dsv«lopod in Section 4.
* fcaflocts operation at asti«at*d digastioiv'dowatorinq syitn capacity of 30 dry tpd of dsv»t»ro<] cak«.
* ftalfocts oporstion at astiaat«d incinaration systosi capacity of 60 dry tpd of davatarad caha.
-------
TABLE F-4
CltAlfSTOlV MPCF
OU1 COSTS rOB SOLIDS BMDUHG PROCESSES
AT SYSTEM CAPACITY
($/YKAR)
PROCESS
LABOR
ELECTRICITY
FUEL
CHEMICALS
MATERIALS CONTRACTED TOTAL
t SUPPLIES SERVICES OHM COST
% TOTAL OtM COST
OfcM COST $/DRV TOM
Sludge Punping $ 0
W.A.S. Thickening 141,700
Prinary Sludge Thickening 136,500
Sludge Blending Tanks 42,300
Sludge Dewatering
t-o Sludge Incineration
01
cn
Ash Disposal
168,800
168,800
43,800
$701,900
$ 1,200
24,700
16,500
1,400
72,800
83,900
0
$200,500
$ 0
0
0
0
0
82,100
$ 0
39,600
0
4,300
598,700
82,100 $642,600
$ 0
40,000
0
24,000
60,000
11,000
33,000
$168,000
$ 0
0
2 ,600
0
0
127,800
65,900
$196,300
$ 1,200
246,000
155,600
72,000
900,300
473,600
142,700
$1,991,400
0.06% $ 0.11
12.35 22.47
7.81
3 .62
45.21
23 .78
7.17
100.00%
14 .21
6.55
82.22
43 .25
13.03
$182
1 dry ton » 0.9072 dry tonne
All costs adjusted based on the unit costs developed in Section 4.
All capital reflect operation at estimated system capacity of 30 dry tons per day of dewatered cake.
-------
to
00
-J
CKWAR130R CT JWOL 90UU SNVtlM GD9TS
m sumcs roamuw
AT &I&W1 OPACITY
(S/TVABI
HETHO (11
% TOTAL
cost t/w >/trr
UPPER
MACKSTOHE (?)
% TOTAL
AMWAL COST S/PT $/PT
$*.276,000 $25.99 551.40
1,099,300 12.54 24.SO
6)3.300 1.23 14.30
Q 0.00 0.00*
20,200 0.2) 0.46
381,000 4.35 ft.60
19.400 0.22 0.44
2.152.*00 24.57 49.60
(4.421.200 $50.55 100.001
1 dry ton • 0.901} dry tow*
Ml costs sro Ui«4 on oparation at oyston capacity.
All cost* adjusted baa ad on tha unit coats davalopad In section 4.
Itw solids train capacity for aach facility la astiaatad as follows:
tot to 240 tpd of davatarad caka
llaekitcM 60 tpd of
-------
TABLE F-6
COMPARISON OF ANNUAL SOLIDS HANDLING COSTS
FOR DUFFIN CHEEK SLUDGE DIGESTION
AT SYSTEM CAPACITY
($/YEAR)
DUFFIN (1)
ANNUAL COST
$/DT
% TOTAL
$/DT
CAPITAL*
$593,400
$54.19
80.15%
LABOR
55,200
5.04
7.45%
ELECTRICITY
67,200
6.14
9.08%
FUEL
0
0.00
0.00%
CHEMICALS
0
0.00
0.00%
MATERIALS & SUPPLIES
8,200
0.75
1.11%
CONTRACTED SERVICES
16,400
1.50
2.22%
TOTAL O&M**
147,000
13.42
19,85%
TOTAL COST
$740,400
$67.62
100.00%
1 dry ton = 0.9072 dry tonne
{1) Includes sludge pumping from the clarifiers and sludge digestion.
All costs are based on operation at the estimated system capacity of 30
dry tpd of dewatered cake.
$/dry ton = $1.10/dry tonne
-------
TMU r-7
CTWAJUOT or 90CJXS IMDLDIC COSTS
rca cavmanK md naovmtiv;
at 3tstoi otacttt
t$/T*A*>
ilL
fO
oo
vo
GATRAL
LfcSC*
CUCT1ZCTTT
run,
CXKCALS
KAXDtEALS
ft sumacs
COCmtACTCD
soRvrccs
total out
total cost
AWtPU. COW S/PT % TOTAL
$ >.71?,000 $ 65.26 44.40%
4,330,400 49.45 33.63%
11. <3
1.011,600
0
'1.011,100
7.m
0.00 0.00%
13.lt 0.17%
<10,600 <.97 4.74%
44.900
7,159,000
0.51
11.7)
0.35%
55.60
BtAC*3T0WC <21
AWUAL COST S/XTT % TOTAL
curriw O)
AHWUAL COST S/DT % TOTAL
OUtfSTaW Ml
AIWUAL COST S/VT % TOTAL
$12,076,100 $147.00 100.00%
$404,400
432,500
02,100
0
159,600
51,100
0
706,100
$1,110,500
$11.47
19.75
2.17
0.00
7.20
16.42%
16.95%
5.66%
0.00%
14.12%
2.37 4.66%
0.00
17.24
$50.71
0.00 %
63.56
too.00%
I dry ton • 0.9072 dcy tenn*
All costs adjusted bosad oo tha will coots davolopod In Soction 4.
Jdl mill irt boaod m oporatlon it oyotaa capacity.
$ 525.000 $47.95 37.41%
432,000 39.45 30.95%
54,100 4.94 3.16%
0 0.00 0.00%
230.600 21.06 16.52%
117,900 10.77 &.45%
36.400 3.32 2.61%
671,000 79.54 67.39
$1,396,000 $127.49 100.00%
$ 615.900 $ 62.64 41.36%
211.100 19.26 12.73%
* 74,200 6.71 4.47 %
0 0.00 0.00%
603,000 55.07 36.36%
•4,000
7.67 5.07 %
0 0.00 0.00 %
972,300 66.79 56.64%
$1,656,200 $151.43 100.00%
ifco solids train capacity (or aacti facility U astlsatod so foil***:
ftotr* 240 tpd Of davatarod cafco
llaekitoM 60 tpd of dawatorad eako
Puffin 30 tpd of dawotorad caka
Cranaton 30 tpd of dovatarad caka
(1) Includes thorool tlwtya conditioning, roll pcoos dowstarin?, and tTiitwnt of tho thermal conditioning iid«str«
-------
i£>
O
(1)
AIWUAL COST $/PT % TOTAL
tMU M
cckmjusc* or mkm. solids
stuoct ncmauiiii
<$/YW)
VPPCT
BLACKSTOWt 121
MtVUAL COST $/OT % TOTAL
$10,911,400 $124.44 <1.01%
).zoi,ioo 59.40 29.12%
sLscnacmr
met
- mm«c«i
- Aus »oilar«
aamcxu
KAftAlALS
ft suvrucs
oownuwrnro
SCXVJCE5
COST atEDZT
TOTAL OfcM*•
TOTAL COST
1,1)1,400
364,600
62*,190
75,300
12.94 4.14 %
4.16 2.04 %
1.19 J.52 %
0.84 0.42 %
' 1)5.400 10.66 5.22 %
151,700 1.11 0.69 %
|i.S4J.200| -11.62 -0.6)%
6,955,100 79.40 11.92
$17,661,(00 $201.91 100.00%
$1,041,500 $47.36 46.71%
644.900 29.45 )0.16%
2)1,400 10.51 10.61%
SO J,100 4.65 4.17 %
0 O.OO 0.00 %
116,400 5.19 5.5) %
0 0.00 0.00 %
0 0.00 0.00%
1,096,600 50.05 51.29
$2,1)1,100 $97.(1 100.00%
1 day t«A a 0.f072 dry t«m«
All costs adjuatod b«i«d on tho unit coatt davalopod in s«et(M 4.
All coat* aro baaod on it lyitM ctpacity.
Ttv« lneinoration iy«tM ciptcity for «tch facility is at follow:
«atro 240 tpd of
-------
APPENDIX 6
CAPITAL COST
SUMMARY TABLES
-------
TABLE G-l
METRO WPCF
CONSTRUCTION COSTS
PROCESS
UPDATED
CONSTRUCTION
COST
(ENR = 4535)
AMORTIZED
CAPITAL
COST*
W.A.S. Thickening
- structures
- equipment
- total
Primary Sludge Thickening
- structures
- equipment
- additional structure**
- additional equipment**
- total
Thermal Conditioning
- structures
- equipment
- total
Sludge Dewatering***
- structures
- equipment
- total
Sludge Incineration
- structures
- equipment
- total
RBC Sidestream Treatment
- structures
- equipment
- total
$ 15,828,400
$ 4,150,500
$ 19,978,900
$
$
$
$
$
5,400,000
500,000
235,500
21,800
5,900,000
$ 26,400,000
$ 10,972,000
$ 37,372,000
$ 778,400
$ 3,994,900
$ 4,773,300
$ 92,759,900
$ 30,776,300
§123,536,200
$17,380,100
$4,481,500
$21,861,600
$ 1,327,300
$ 422,700
$ 1,750,000
$
$
$
$
$
452,900
51,000
19,800
2,300
526,000
$ 2,213,700
$ 1,117,300
$ 3,331,000
$ 65,100
$ 406,900
$ 472,000
$ 7,778,800
$ 3,134,600
$10,913,400
$ 1,457,600
$ 456,400
$ 1,914,000
*Based upon a discount rate of 8%. Assumes all structures will have a
useful life of 40 years and all equipment will have a useful life of 20
years.
~~Additional gravity thickener.
***Based on roll press dewatering capital costs.
-------
TABLE G-2
UPPER BLACKSTONE WPCF
CONSTRUCTION COSTS
PROCESS
updated
CONSTRUCTION
COST
(ENR = 4535)
AMORTIZED
CAPITAL
COST*
Waste Activated Sludge
Thickening
- structures
- equipment
- total
Sludge Holding Tanks
- structures
- equipment
- total
Sludge Dewatering
- structures
- equipment
- additional equipment**
- total
Sludge Incineration
- structures
- equipment
- total
$1,737,200
$ 681,100
$2,418,300
$683,400
$140,900
$824,300
$2,460,800
$1,644,000
$ 300,000
$4,404,800
$ 3,623,700
$ 7,242,500
$10,866,200
$145,700
$ 69,400
$215,100
$57,300
$14,400
$71,700
$206,400
$167,400
$ 30,600
$404,400
$ 303,900
$ 737,600
$1,041,500
*Based upon a discount rate of 8%. Assumes all structures will have a
useful life of 40 years and all equipment will have a useful life of 20
years.
**Additional belt filter press.
-------
TABLE G-3
DUFFIN CREEK WPCF
CONSTRUCTION COSTS
(U.S. DOLLARS)
PROCESS
UPDATED
CONSTRUCTION
COST
(ENR = 4535)
AMORTIZED
CAPITAL
COST*
Sludge Digestion
- structures
- equipment
- total
Sludge Conditioning/Dewatering
- structures**
- equipment
- total
Sludge Incineration
- structures
- equipment
- total
$4,235,000
$2,340,000
$6,575,000
$3,824,000
$2,006,000
$5,830,000
$13,341,000
$ 9,170,000
$22,511,000
$355,100
$238,300
$593,400
$320,700
$204,300
$525,000
$1,118,800
$ 934,000
$2,052,800
~Based upon a discount rate of 8%. Assumes all structures will have a
useful life of 40 years and all equipment will have a useful life of 20
years.
**Adjusted to correct for excessive building volume.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before complet
-
1. REPORT NO. 2.
F.PA/ 600/2-90/03S
3.
4. TITLE AND SUBTITLE
Fuel-Efficient Sewage Sludge Incineration
5. REPORT DATE
August 1990
6. PERFORMING ORGANIZATION CODE
7. AOTHOR(S)
Michael J. Walsh, Albert B. Pincince,
and Walter R. Niessen
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND AOORESS
Camp, Dresser & McKee, Inc.
One Center Plaza
Boston, MA 02108
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Contract #68-03-3346
12. SPONSORING AGENCY NAME ANO ADDRESS
Risk Reduction Engineering Laboratory—Cincinnati, OH
Office of Research and Development
U.S. Environmental Protection Agency
/-vir AC*%ro
13. TYPE OF REPORT ANO PERIOD COVERED
Final — 5/87 to 9/89
14. SPONSORING AGENCY CODE
EPA/600/14
iVSuralaM-f noTk
Work Assignment Manager: Donald S. Brown, FTS 684-7630, (513) 569-7630
16. ABSTRACT
A study was performed to evaluate the status of incineration with low fuel use
as a sludge disposal technology. The energy requirements, life-cycle costs, operation
and maintenance requirements, and process capabilities of four sludge incineration
facilities were evaluated. These facilities used a range of sludge thickening,
conditioning, dewatering, and incineration technologies.
The results provided realistic cost and energy requirements for a fuel-efficient
sludge incineration facility and highlighted operational, managerial, and design
features that contributed to the fuel efficiency of the incineration process. This
information provides a basis for evaluating both the applicability of sludge incinera-
tion in future facilities and the cost and energy efficiency of- existing incineration
facilities.
,7. KEY WORDS AND OOCUMENT ANALYSIS
a. DESCRIPTORS
b. IOENTIFIE RS/OPEN ENOEO TERMS
c. COSATl Field,'Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (tins tieporti
UNCLASSIFIED
X 1 . 11 w. r r
304
20. SECURITY CLASS (This p
------- |