xvEPA
nited States
nvironmental Protection
Agency
Office of Water
& Waste Management
Washington, DC 20460
SW 175C.2
June 1979
Solid Waste
A Technical and
Economic Evaluation
Of the Project
In Baltimore, Maryland
Volume II
-------
Prepublication issue for EPA libraries
and State Solid Waste Management Agencies
A TECHNICAL AND ECONOMIC EVALUATION OF THE
PROJECT IN BALTIMORE, MARYLAND
Volume II
This report (SW175c) describes work performed
for the Office of Solid Waste under contract no. 68-01-4359
and is reproduced in four volumes as received from the contractor.
The findings should be attributed to the contractor
and not to the Office of Solid Waste.
Volume I of this report is the executive summary
and is available from the Office of Solid Waste (order no. 719).
Volumes II, III, and IV will be available from the
National Technical Information Service
U.S. Department of Commerce
Springfield, VA 22161
U.S. ENVIRONMENTAL PROTECTION AGENCY
1979
-------
This report was prepared by Systems Technology Corporation, Xenia, Ohio,
under Contract No. 68-01-4359.
Publication does not signify that the contents necessarily reflect the views
and policies of the U.S. Environmental Protection Agency, nor does mention
of commercial products constitute endorsement by the U.S. Government.
An environmental protection publication (SW175c) in the solid waste
management series.
-------
PREFACE
This report is a complete technical, economic, and environmental evalua-
tion of the Landgard® Demonstration Plant at Baltimore, Maryland. Because of
its bulk and to serve a twofold purpose, the report is presented in four
volumes: an executive summary, the report proper, an analysis of the problems,
and the appendices. Intended particularly for resource recovery planners and
administrators, the executive summary briefly and succinctly describes the
Landgard® concept and Baltimore application for the state-of-the-art advance-
ment in the processing of municipal mixed solid waste. In addition, it
presents an introductory problem analysis of most of the major innovations
that proved ineffective, caused serious shutdowns, and required redesign or
abandonment. As the second, third, and fouth volumesxare detailed in-depth
accounts of the evaluation, they were prepared primarily for the designer.
Of the four volumes, only the executive summary has been prepared for wide
distribution in a paper copy format. The second, third, and fouth volumes
are reproduced on microfiche, which is readily available throughNJJTIS.
-------
ABSTRACT
One of the first efforts in this country to demonstrate solid waste
resource recovery technology was the Baltimore Landgard® project which was
a joint venture between the City of Baltimore, the U.S. Environmental
Protection Agency (EPA), the Maryland Environmental Service, and Monsanto
EnviroChem. The Baltimore plant was designed and built by Monsanto
EnviroChem to thermally process (pyrolyze) 907 Mg (1000 tons) per day of
mixed municipal solid waste, convert it to energy (in the form of steam),
and recover magnetic metals and glassy aggregate. Although the plant has
never been fully operational in its original design configuration, con-
siderable knowledge has been gained from it concerning resource recovery
from municipal solid waste. The numerous equipment breakdowns and the
inability of the plant to comply with air pollution standards accounted for
the major difficulties encountered during the project. Major equipment
problems were encountered with the storage and recovery unit, the refrac-
tory in the thermal processing vessels, the main induced-draft fan, the
residue discharge drag conveyor, and the slag discharge screw conveyor.
Despite the fact that the designer recommended converting the plant to a
conventional incinerator, plant performance has been sufficiently encour-
aging to warrant continued investment and operation by the City of Baltimore.
One of the primary reasons for this attitude by the City is that the rotary
processing kiln has been demonstrated to be an excellent primary reaction
vessel. Although the present plant is not environmentally acceptable
because of high particulate emissions, this problem will be resolved by the
installation of two electrostatic precipitators.
The thermal efficiency of the plant was determined to be approximately
56 percent for an average feed rate of 454 kg per minute (30 tph). The plant
has a capital cost of approximately $22 million, an annual operating and
maintenance cost of $3 million, and an annual steam revenue of $1 million.
The net operating cost, based on historical operating data, is $64.10 per Mg
($58.20 per ton) of refuse processed. However, if the annual throughput of
67,000 Mg (74,000 tons) could be substantially increased to 270,000 Mg
(300,000 tons), operating cost could be reduced to $7.80 per Mg ($7.10 per
ton) of refuse processed.
This report is submitted in fulfillment of Contract No. 68-01-4359 by
Systems Technology Corporation (SYSTECH) under the sponsorship of the
U.S. Environmental Protection Agency. This report covers a period from
October 1, 1975 to April 30, 1978.
ii
-------
CONTENTS
Preface i
Abstract ii
Figures v
Tables x
List of Unit Conversions xvi
Acknowledgment xvii
1. Background 1
2. Plant Description and Analytical Operation Review 6
Receiving module 7
Size reduction module 19
Storage and recovery module 49
Thermal processing module 81
Energy recovery module 172
Residue separation module 206
General plant 227
3. Mass and Energy Balance 239
Waste preparation subsystem 240
Thermal processing subsystem 245
4. Environmental Assessment 264
Stack emissions 264
Solid residues 267
iii
-------
CONTENTS (continued)
Plant process waters 275
Fugitive emissions 277
Noise 279
5. Economic Evaluation 288
Background and purpose 288
Operating and maintenance costs 292
Capital costs 295
Revenues 305
Net operating costs 306
6. Administrative Assessment 307
Parties involved 307
Organization of groups involved 308
Overall effects of organization 313
Conclusions 313
7. Future plant 315
Ongoing and proposed modifications 315
Second generation facility 320
iv
-------
FIGURES
Number Page
1 Process flow diagram of the Baltimore Landgard
facility 8
2 The receiving module 9
3 An example of the weight tickets used at the
pyrolysis plant 11
4 Refuse truck routing plan 13
5 Schematic of the receiving building 15
6 Refuse truck discharging to the direct dump chute 16
7 Empty storage pit 17
8 Full storage pit 18
9 Size reduction module 20
10 Storage pit bulldozers 21
11 An exploded view of the apron conveyor 23
12 A typical section through a storage pit conveyor 24
13 A typical section through a shredder feed conveyor 26
14 Control panel in main control room 27
15 Link failure on shredder feed conveyor 28
16 Schematic of a hammermill shredder '.33
17 Rebuilt shredder hammers 34
18 Worn shredder hammers 34
19 Fenwa*ll sensor and extinguisher 38
-------
FIGURES (continued)
20 A recording ammeter graph of shredder current 41
21 Probability plot of shredder current 42
22 Shredder discharge conveyor 47
23 Storage and recovery module 50
24 Transfer tower 52
25 Refuse jam at the elevating conveyor discharge 54
26 Magnetic drum separator system and bypass chutes 57
27 Stored.material spreader 62
28 Schematic of the storage and recovery unit 65
29 Buckets used in the storage and recovery unit 66
30 Bridging of refuse against silo walls 69
31 Loosening of the waste in the storage and
recovery unit 70
32 Buckets undercutting the refuse pile in the
silo 70
33 Ten bucket chains contacting the refuse pile in
the silo 72
34 Twenty bucket chains contacting the refuse pile in
the storage and recovery unit 72
35 Uniform width bucket wear show (type B) 73
36 Differential width bucket wear shoe (type C) 74
37 Elongated bucket wear shoe (type D) 75
38 Regular bucket wear shoe (type E) 76
39 Floor wear measurement points 78
40 Thermal processing module 83
41 Schematic of the ram feeders 87
vi
-------
FIGURES (continued)
42 Deformed ram snouts 90
43 Schematic of the kiln 93
44 The kiln 94
45 Kiln discharge during standby operation 94
46 Kiln Flights 95
47 Kiln auxiliary equipment 97
48 Kiln Tunnions 98
49 Kiln processing zones 100
50 Kiln residue slag balls 102
51 Vortex gas flow in the kiln 104
52 Conical expansion of kiln ends and
corrective slots 106
53 Gas purifier 112
54 Schematic of the gas purifier 113
55 Fallen orifice baffle wall in the gas
purifier 116
56 Deteriorated refractory and etched mortar
in the gas purifier 117
57 Fallen orifice baffle wall in the gas purifier 118
58 Slag taphole dam with V-notch weirs 119
59 Plugged slag taphole . 120
60 Propane burners in the slag taphole 129
61 Original residue quench tank and conveyor 134
62 Modified residue quench tank and conveyor 137
*
63 Schematic of the seal tank 140
64 Butterfly valve quench air damper 145
vii
-------
FIGURES (continued)
65 Gas scrubber 147
66 Process flow diagram of the gas scrubber 149
67 Induced-draft fam rotor 165
68 Induced-draft fan rotor vane 165
69 Dehumidifier 166
70 Dehumidifier inlet vestibule 169
71 Dehumidifier outlet vestibule 169
72 Area fumigation by exhaust gases 171
73 Dehumidifier condensate pipe corrosion 171
74 Energy recovery module 173
75 Schematic of the waste heat boilers 188
76 Fly ash accumulating on the first row of
boiler tubes 190
77 Schematic of the jug valve 196
78 Jug valve 197
79 Fly ash build-up in the boiler inlet duct 199
•
80 Slowdown surge tank and separator 202
81 Residue separation module 207
82 Magnetic metal separation conveyor •. 224
83 Waste preparation subsystem sampling points 241
84 Waste preparation subsystem mass and energy
balance 246
85 Thermal processing subsystem sampling points 247
86 Kiln mass and energy balance 254
87 Gas purifier mass and energy balance 257
viii
-------
FIGURES (continued)
88 Boiler mass and energy balance 261
89 Thermal processing subsystem mass and
energy balance 262
90 Total plant mass and energy balance 263
91 Noise survey 281
92 Noise survey 282
93 Noise survey 283
94 Noise survey 284
95 Noise survey 285
96 Noise survey 286
97 City administration structure pertaining
to pyrolysis plant 310
98 Original procurement procedure for the
City of Baltimore 312
99 Proposed future plant look 316
ix
-------
TABLES
Number Page
1 Chronology of Landgard Development
2 Design variations in St. Louis Landgard
prototype and full-scale Baltimore facility 2
3 Chronology of Landgard Demonstration at
Baltimore 3
4 Receiving area time study 12
I
5 Apron conveyor preventive maintenance schedule 31
6 Shredder hammer wear 36
7 Shredder power consumption 37
8 Shredding rate 40
9 Shredder preventive maintenance schedule 44
10 Vibrating pan conveyor preventive maintenance
schedule 49
11 Shredded refuse conveyor preventive
maintenance schedule 56
12 Magnetic drum separator preventive maintenance
schedule 60
13 Stored material spreader preventive
maintenance schedule 63
14 Life of bucket wear shoes 77
15 Floor wear data 79
16 Storage and recovery unit preventive
maintenance schedule 82
17 Ram feeder preventive maintenance schedule 91
-------
TABLES (continued)
Number Page.
18 Kiln refractory 95
19 Kiln preventive maintenance schedule 110
20 Kiln feed hood preventive maintenance
schedule Ill
21 Gas purifier preventive maintenance
schedule 121
22 Preventive maintenance schedule 126
23 Preventive maintenance schedule 127
24 Fuel oil burner system preventive maintenance
schedule 132
25 *'uel oil pumps preventive maintenance
schedule 133
26 Quench tank preventive maintenance schedule 138
27 Quench tank conveyor preventive maintenance
schedule 138
28 Seal tank preventive maintenance schedule 144
29 Screw conveyor preventive maintenance
schedule 144
30 Gas scrubber preventive maintenance schedule ........ 150
31 Scrubber water pump preventive maintenance
schedule 153
32 Caustic unloading pump preventive maintenance
schedule 155
33 Sludge pump preventive maintenance schedule 158
34 Clarifier preventive maintenance schedule 160
35 Floe feed system preventive maintenance
schedule 161
36 Sump pump preventive maintenance schedule 162
XI
-------
TABLES (continued)
Number Page
37 Induced draft fan preventive maintenance
schedule 167
38 Dehumidifier fan preventive maintenance
schedule 172
39 Brine pump preventive maintenance schedule 176
40 Degasifier pump preventive maintenance
schedule 180
41 Deaerating heater preventive maintenance
schedule . . 182
42 Agitator preventive maintenance schedule 184
43 Feedwater pump preventive maintenance
schedule 186
44 Micrometer measurements of boiler tubes 191
45 Boiler tube corrosion 191
46 Boiler preventive maintenance schedule 194
47 Jug valve preventive maintenance schedule 200
48 Fly ash transfer system preventive maintenance
schedule 205
49 Vibrating screen conveyors 208
50 Residue flotation unit 211
51 Separation air compressor 212
52 Roto screen preventive maintenance schedule 213
53 Thickener preventive maintenance schedule 216
54 Pressure pump preventive maintenance
schedule 217
55 Underflow pump preventive maintenance
schedule 218
xii
-------
TABLES. (continued)
Number Page
56 Vacuum belt filter preventive maintenance
schedule 220
57 Vacuum pump preventive maintenance schedule 221
58 Filtrate pump preventive maintenance
schedule 222
59 Rubber belt residue conveyor preventive
maintenance schedule 223
60 Magnetic metal separator preventive
maintenance schedule 226
61 Atomizing steam boiler preventive
maintenance schedule 229
62 Instrument air compressor preventive
maintenance schedule 233
63 Instrument air drier preventive maintenance
schedule 234
64 Dust collector preventive maintenance
schedule 236
65 Wastewater lift station pump preventive
maintenance schedule 238
66 A comparison of refuse composition 243
67 Refuse composition 244
68 Residue composition 251
69 Kiln off-gas composition . 252
70 Average ash chemistry of gas purifier slag 255
71 Composition of gas purifier exit gases 256
72 Dry electrostatic precipitator test of
boiler exit gases 265
73 Boiler and scrubber outlet gases 266
xiii
-------
TABLES (continued)
Number Page
74 Hydrocarbon analysis of boiler and scrubber
outlet gases 266
75 Emission spectrographic scan of slag 269
76 Slag leachate analysis 270
77 A comparison of kiln and incinerator residues . 271
78 Residue putrescible content 271
79 Microbial analysis of residue 272
80 Residue leachate analysis 273
81 Boiler fly ash chemistry 274
82 Boiler fly ash analysis of aqua regina
solubles 275
83 Average analysis of various process waters 276
84 Dust levels 278
85 Microbial levels in refuse dust 278
86 Analysis of receiving building air 280
87 Noise levels during soot blowing 287
88 Scenario operating parameters . . 290
89 Operating and maintenance unit cost data 293
90 Projected annual operating and maintenance
costs 295
91 Operating and maintenance cost per cost
center 296
92 A summary of EPA capital cost classifications 298
93 Capital costs (exclusions/additions) 300
xiv
-------
TABLES (continued)
Number Page
94 Equipment costs and useful life reported
by selected vendors 301
95 Projected scenario capital cost summary 302
96 Summary cost center distributions 303
97 Capital costs per EPA cost center including
adjustments 304
98 Subsystem capital costs 305
99 Project cost summary 306
xv
-------
LIST OF UNIT CONVERSIONS
Description
Length
Area
Volume
Mass
Pressure
Temperature
Energy
Density
Energy /Mass
Mass Loading
Concentration
Power
SI
Unit
meter
centimeter
millimeter
micrometer
square meter
cubic meter
liter
kilogram
megagrams
kilopascal
celsius
joule
kilowatt
Symbol
(m)
(cm)
(mm)
(mm)
(m2)
(m3)
(1)
(kg)
(Mg)
(kPa)
CC)
(J)
(kg/m3)
(MJ/kg)
(g/DSCM) -
(yi/D
(kw)
English Equivalents
Unit
3.28 feet
0.394 inches
39.37 mils
1.0 micron
10.76 square feet
35.31 cubic feet
0.264 gallons
2.20 pounds
1.10 tons
0.145
5 fahrenheit/9-17.8
9.48 x 10~4
.0624
431
0.437
1.0
0.06
Symbol
(ft)
(in.)
(ft2)
(ft3)
(gal)
(Ibs)
(t)
(lbs/in.2)
(F)
(Btu)
(lbs/ft3)
(Btu/lb)
(gr/DSCF)
(ppm)
(MJ/min)
-------
ACKNOWLEDGMENT
This evaluation program was performed under EPA Contract No. 68-01-4359,
"Technical and Economic Evaluation of the EPA Demonstration Resource Recovery
Project in Baltimore, Maryland."
The EPA Project Officer was Mr. David B. Sussman of the Office of Solid
Waste, Washington, D.C.
Testing was carried out at the demonstration facility in Baltimore,
Maryland with the cooperation of the City plant staff and the Monsanto
on-site engineering staff. The contribution of both of these groups has
been greatly appreciated. The contribution of Dr. H. G. Rigo and
Richard.Eckels, along with other staff members, is also acknowledged.
Systems Technology Corporation would like to express its gratitude to
the above named individuals and all others associated with this evaluation.
xvii
-------
•
H
•
BALTIMORE LANDGARD® FACILITY
-------
SECTION 1
BACKGROUND
Monsanto became involved in solid waste processing in 1967 when they
commissioned an internal study to determine the best methods of solid waste
disposal. By August 1968 they had determined that direct pyrolysis was an
attractive method of solid waste disposal warranting further investigation.
Monsanto's Landgard® process was subsequently developed, and an evaluation
was begun. Early in 1969 a benchscale unit was designed and operated in
Dayton, Ohio, for concept confirmation. The results were sufficiently en-
couraging that by June 1969 a 32-MgPD (35-TPD) prototype kiln was operating
in St. Louis, Missouri. Another 32-MgPD (35-TPD) unit was placed in operation
in Kobe City, Japan, by Kawasaki Industries, a licensee of the Landgard®
process. The Baltimore project wos begun in late 1972 and officially
initiated in January 1973. Table 1 is a review of the developmental period
of the Landgard® technology.
TABLE 1. CHRONOLOGY OF LANDGARD® DEVELOPMENT
Date Stage Of Development
Fall 1968 Bench-scale prototype, Dayton, Ohio;
0.27 to 0.54 MgPD capacity, 0.3- x 1.5-m kiln
Spring 1969 Small-scale prototype, St. Louis, Missouri;
32 MgPD, 1.2- x 6.1-m kiln
Spring 1974 Small-scale prototype, Kobe City, Japan;
32 MgPD, 1.2- x 6.1-m kiln
Nov. 1974 Full-scale prototype, Baltimore, Maryland;
907 MgPD, 6.1- x 30.5-m kiln
Most of the design data for the Baltimore facility were projected from
the experience gained at the prototype unit located in St. Louis, Missouri.
This unit was operated from fall 1969 until late 1971 but was never contin-
uously operated for more than 1 week.
A number of differences existed between equipment items and operational
procedures at the St. Louis prototype and the Baltimore facility (Table 2).
These variations limited the applicability of the St. Louis experience and
became even'more critical when the scale-up factor of 32 was considered.
-------
TABLE 2. DESIGN VARIATIONS IN ST. LOUIS LANDGARD® PROTOTYPE
AND FULL-SCALE BALTIMORE FACILITY
Prototype facility (32 MgPD)
Full-scale facility (907 MgPD)
Concrete slab receiving area
(tipping floor)
Use of rubber belt conveyors
in receiving area
Use of vertical shaft shredders
for size reduction
Non-slagging gas purifier
No heat recovery system
Stack
Secrew-type residue discharge
conveyor
Materials separation in
residue quench tank
No slag/spillback removal
system
No magnetic separation before
pyrolysis
Thickener for char dewatering
Two propane burners in kiln,
no burners in gas purifier
Entrance of shredded refuse
into storage and recovery
unit before entrance into
kiln
Dozer pit
Use of steel apron conveyors in
receiving area
Use of horizontal shaft hammer-
mills for size reduction
Slagging gas purifier
Two waste heat boilers and
economizers
Dehumid if ier
Drag-type residue discharge
conveyor
Separate materials separation
equipment components
Secrew conveyor slag/spillback
removal system
Magnetic drum separator before
pyrolysis
Thickener and vacuum belt filter
for char dewatering
Two main burners and four safety
burners in kiln, three burners
in gas purifier (all using #2
fuel oil), plus two propane
burners in gas purifier
Ability to direct shredded refuse
to storage and recovery unit
or directly to kiln
-------
In 1972 the City of Baltimore and Monsanto EnviroChem entered into an
agreement to design and construct a 907-MgPD (1,000-TPD) resource recovery
facility to be installed in the City of Baltimore, where it would be owned
and operated by the municipal government. In conjunction with this agreement,
a grant from the U.S. Environmental Protection Agency (EPA) and a grant/loan
from Maryland Environmental Services were obtained for supplemental funding
of the Baltimore facility in the amount of $10 million. Table 3 outlines the
major events that occurred in conjunction with the demonstration.
TABLE 3. CHRONOLOGY OF LANDGARD® DEMONSTRATION AT BALTIMORE
DATE STAGE OF DEVELOPMENT
July 14, 1972 Monsanto proposal submitted
Sept. 8, 1972 Monsanto proposal grant awarded
Oct. 11, 1972 Original contract submitted
Jan. 10, 1973 Amended contract approved
Construction design begun
Nov. 4, 1974 Plant debugging begun
Jan. 31, 1975 Construction completed, plant commissioned
Nov. 1, 1975 Supplemental agreement made for Phase I and
II modification projects
Jan. 1, 1976 Phase I modification work begun
April 23, 1976 Phase I modifications completed
May 6, 1976 Phase I operations begun
Aug. 9, 1976 Phase II modifications begun
Nov. 5, 1976 Phase II modifications completed
Nov. 6", 1976 Phase II operations begun
Jan. 31, 1977 Project termination recommended by Monsanto
Feb. 18, 1977 Monsanto personnel leave site; decision
made by City to continue testing
Under the agreement, the City of Baltimore was responsible for obtaining
an acceptable site, bearing site preparation costs, and supplying the oper-
ating and maintenance personnel and budget for the plant at the outset of the
demonstration. Agreements were made for the sale of the recovered byproducts:
steam, glassy aggregate, and magnetic metal. The duration of these agreements
was for the period of the demonstration (1 year).
Under the terms of the agreement, Monsanto EnviroChem was responsible
for providing manpower during the grant demonstration on a contracted level
of 70 man-days per month. The responsibility of this staff was to train and
supervise the City's operating and maintenance personnel before and during
the demonstration period.
-------
The design, procurement, and construction effort was contracted to be
completed within 18 months of contract award. Although the general process
design was already complete at the time of contract award, the specific
design details of the Baltimore facility were not. As a result, the 18-month
schedule was exceptionally short for the total effort required.
Construction of the facility was supervised by Leonard Construction, a
wholly-owned subsidiary of Monsanto EnviroChem. Leonard Construction had
historically been responsible for the construction of sulfuric acid plants
designed by Monsanto EnviroChem. Members of the construction group remained
on site to supervise the implementation of equipment modifications made
during the start-up phase of the project. As shown in Table 3, construction
required 24 months to be completed, rather than the 18 specified in the
contract. However, portions of the facility were released in a staged fashion
starting in late October 1974. A phased start-up effort was thus allowed,
beginning with the receiving area and continuing through the process line as
each process area was released by construction. The presence of construction
personnel in -the area of operating equipment created some minor operational
problems.
From January 21 through November 1, 1975, the facility operated for
short periods, but no sustained operation was achieved. During this period,
extensive operational testing was performed to determine the optimum operating
characteristics of the facility. Numerous mechanical and operational problems
were encountered, and modifications were made on the equipment items in an
attempt to alleviate some of these problems. Major problems encountered at
this stage of the demonstration were: (1) difficulty with storage and
recovery unit material retrieval, (2) kiln refractory failure, (3) excessively
high kiln temperatures and an unstable kiln process, (4) residue drag conveyor
failure, (5) ram feeder jamming, (6) gas purifier slag tap-hole plugging,
(7) high induced draft fan vibration, and (8) high stack gas particulate
emission levels. Variations in the mode of operation were executed in an
effort to alleviate these problems, but only minor success was achieved.
By late 1975, Monsanto EnviroChem acknowledged the failure of the plant
to meet the emissions and reliability guarantees. At that time, Monsanto
agreed to forfeit their $4 million liability to the City of Baltimore and
renegotiated a new contract with the City. (The second contract is referred
to as the Supplemental Agreement.) At this time, EPA supplied an additional
$1 million to provide the total requirement of $5 million that Monsanto
believed would bring the plant to an acceptable level of operation. The
plant was inoperative from late 1975 to May 1976 to allow modifications hoped
to improve the mechanical reliability of plant equipment.
Subsequent to this first phase of modification, the plant operated at a
higher percentage of on-stream time than at earlier stages of the demonstra-
tion, but satisfactory levels had not yet been reached. Operational testing
was continued through the period to further define the modifications required
to improve plant reliability. As a result of the longer periods of continuous
operation accompanying the improvements, three weeks versus one week, a new
group of problems became apparent—erosion of the refractory in the gas
-------
purifier, wear in the storage and recovery unit, corrosion/erosion of the
induced draft fan impeller and scrubber auxiliaries, and inability to operate
the materials recovery area on a continuous basis. Although the problems
experienced earlier in the demonstration occurred less frequently during this
period, none of them were completely resolved.
The facility was shut down again for 3 months late in 1976 to complete a
second phase of modifications. During this period, major changes were made
in the process equipment in a continuing effort to increase reliability. The
results of these modifications were significant, and a definite increase in
on-stream time occurred. The replacement of the kiln refractory, utilizing a
rotary pour technique and stainless steel fiber reinforced coarse refractory,
has solved the failure problem of the kiln refractory. No major failures
have occurred in this area since the replacement was made. The addition of a
circumferential air inlet duct at the residue discharge end of the kiln
helped to reduce the refractory problem and improve process control stability.
Oil- and propane-fired burners placed in the slag taphole in the gas purifier
to minimize plugging had a positive effect, but the problem still recurred
after the modification. Attempts to prevent refractory failure in the gas
purifier failed, as did those aimed at reducing corrosion in the scrubber
system. The decision was made during this period to abandon attempts at
operating the residue separation area, pending acceptable functioning of the
thermal processing area. It was also decided that a dry electrostatic pre-
cipitator would be required to reduce plant stack emissions to an acceptable
level.
Despite the fact that the plant operated at the highest level of through-
put experienced during the demonstration (64,760 MgPY or 71,400 TPY), Monsanto
EnviroChem recommended that the project be terminated and left the facility
in February 1977.
The City of Baltimore has continued to modify the plant without the
assistance of Monsanto EnviroChem and intends to change the basic design to
achieve higher plant reliability. The City no longer operates the storage
and recovery unit or the wet gas scrubber; rather, both units are simply by-
passed because they are unable to perform adequately. Despite the efforts
made to date, the process still does not operate on a continuous basis. The
major remaining problems are the refractory failure in the gas purifier, slag
taphole plugging, slag removal screw conveyor jamming, and failure of the
plant to meet emissions standards. The design phases have been completed,
and construction has been initiated on modifications to change the gas
purifier from a slagging to a nonslagging operation. An electrostatic pre-
cipitator is being installed to replace the wet gas scrubber and to control
the level of particulate emissions, and a stack is being erected in place of
a ground-level dehumidifier unit.
The City of Baltimore has received additional Federal funding through
the Economic Development Administration that will be used to implement the
modifications outlined above. The City intends to continue to utilize the
process (for their solid waste) as part of their overall waste disposal
plan.
-------
SECTION 2
PLANT DESCRIPTION AND ANALYTICAL OPERATION REVIEW
The Landgard® Demonstration Plant at Baltimore, Maryland, was designed
to handle mixed municipal solid waste with the two-fold objective of reducing
the mass and volume of the waste to a minimal residue for the most economical
landfill disposal and of recovering the energy and reusable materials in the
waste.
This section describes the plant subsystems and components, their opera-
tional interrelationships and performance, and their required maintenance and
modifications. In addition, this section details and analyzes the subsystem/
component functioning, compares the subsystem/component design and actual
performance, and offers suggestions or recommendations for plant equipment
and operational procedure modification.
To simplify the comprehensive analysis and description of the Landgard
process implementation at the Baltimore facility, the plant has been divided
into seven subsystems or modules. In this report, the term "module" denotes
the functionally integrated plant components which make up a subsystem that
performs, in general, a specific primary operation or serves a supporting
role in the performance of one or more operations in the overall plant process.
Accordingly, the nomenclature for each module was selected to represent
the primary operation of the functionally integrated components constituting
the given module as designed. The seven modules, therefore, are (1) Re-
ceiving, (2) Size reduction, (3) Storage and recovery, (4) Thermal processing,
(5) Energy recovery, (6) Residue separation, and (7) General plant.
Since some of the plant subsystems and components were discontinued at
different stages of the demonstration period and for various reasons, the
following summary of the modules describes their status during the initial
plant operation.
The receiving module weighs the refuse in the city packer trucks and
then stores the dumped waste until it can be fed to the size reduction module.
In the second module, the refuse is shredded and discharged to the storage
and recovery module which discharges the refuse at a controlled rate to the
thermal processing module or to chutes which bypass the storage and recovery
unit for direct discharge to the thermal processing module. In this fourth
module, most of the shredded refuse is gasified and combusted; then the
gaseous products are discharged to the energy recovery module, the fifth
module, and the solid residue is transported to the residue separation module,
-------
the sixth module. While the energy in the gaseous products is recovered in
the energy recovery module by producing steam from the sensible heat, the
solid residue is separated in the residue separation module into streams of
various types of reusable materials and waste. Finally, the seventh and last
module, the general plant module, provides processes and systems that are
common to two or more of the other modules.
Figure 1 presents a simplified flow diagram of the Baltimore Landgard
plant. In the following sections detailing each of the seven modules, the
given module is indicated by the shaded areas in the adaptation of this
figure.
Most of the plant unreliability, that is, occasions when the entire
plant had to be shut down, were due to operational or equipment failures in
the storage and recovery and the thermal processing modules, as discussed
later. After a short operational period, the residue separation module was
discontinued because of marginal economics and the extensive manpower re-
quirements.
RECEIVING MODULE
As represented by the shaded areas in Figure 2, the receiving module was
designed to accept the mixed municipal solid waste delivered by city packer
trucks as they entered the plant with minimal waiting time. The shaded areas
in this figure indicate the principal section of this module, namely, the
weighing scale, the tipping floor, and the storage pit.
To provide for a continuous stream of trucks, ten truck dumping bays are
available on the tipping floor and the storage pit has ample capacity for the
surge waste deposits. The waste accumulation is normally sufficiently deep
to permit preparing a constant-volume flow of refuse onto conveyors for
transfer to the size reduction module.
The receiving module has had few operational problems because of the
simplicity of the equipment and procedure.
Refuse Truck Weighing System
The refuse in each truck entering the Baltimore pyrolysis plant is
measured by simply subtracting the tare weight from the load weight registered
in the plant's weighing system.
The truck weighing system consists of a Toledo Model 820-8130 load cell
type, 45-Mg (50-ton) motor truck scale with a 3.0-m (10-ft) by 15.2 m
(50-ft) platform and a steel-framed structure with glass on all four sides
which houses an operator's scale-control panel. The scale is equipped with a
digital indicator, card reader, math module, and source record punch. The
arrangement with the large-scale platform rather than that for measuring the
axle weight of vehicles was selected because of its operational speed and
simplicity. To ensure that no truck weight would exceed the scale limit, the
45-Mg (50-tort) capacity was chosen since this weight is greater than the
legal load for Maryland trucks.
-------
MAGNETICS
00
TIPPING
FLOOR
STOR-
AGE
PIT
SHREDDER
SHREDDER
VACUUM BELT
.FLOATATION
4
UCHAR
MAGNET
GLASS
GASES SOLIDS
— KILN -
JJ BURNERS
COMBUSTION AIR
• QUENCH AIR
GAS
EDWATER
i
!$
i
ECONO-
MIZER
1 1
1 1
MI7FR
(y
BOILER
FLY ASH
-
IW
^S
FLY ASH
BOILER
-*•-
f
. ,_
V
J
1
X
r*~~
N
1
~j'
1
1
I
s
1
"1
1
1
1
STEAM
1
i
i
s
l J
i
i
t
..
/
r\_
\— JUG VAL
i
1
i
i
INDUCED
DRAFT
FAN
BOILER FEEDWATER
DEHUMIDIFIER
\
EXHAUST TO
ATMOSHPERE
Figure 1. Process flow diagram of the Baltimore Landgard® facility.
-------
MAGNETICS
VACUUM BELT
FLOATATION
4
GASES SOLIDS
I—- KILN *•
CHAR
MAGNET
GLASS
BURNERS
COMBUSTION AIR
QUENCH AIR
EDWATER
t
I
cf*r\Mr\.
tX»UNU
MI7FR
1
1
ppriMru
1 1* L. fc
Jcf | \_x " Dl IDICICD
,ly rUnlrltn
BOILER
^ rLY Aol I
. M» Fl Y A^SH
BOILER
I
—
X
y
—
— -
^
._/-_
v
j
^~-
^
i
-
^ >
STEAM
1
I
i
I
\l J
--)] '
Ai
N— jyQ v
i
i
INDUCED
DRAFT
FAN
i- MIZER
i
. j
BOILER FEEDWATER
DEHUMIDIFIER
I
EXHAUST TO
ATMOSHPERE
Figure 2. The receiving module (shaded area).
-------
In a modification to the original receiving schedule of 6 days per week
(Monday through Saturday), 7 a.m. to 4 p.m., the Saturday operation was
reduced to 5 hours, 7 a.m. to 12 p.m., so that only one scale clerk working
with limited overtime would be required thereby conforming to the hiring
constraints imposed during the plant start-up period.
The weighing system was designed to accommodate three types of vehicles:
(1) packer trucks which would normally collect and dump the city's curbside
refuse on regular schedules and which would have known tare weights,
(2) transfer trailers which would be handled in a similar manner as the
packer trucks, and (3) privately owned and operated trucks which would not be
scheduled and which would require tare weighing. However, because of limita-
tions during the plant start-up and initial operation, only the city packer
trucks have thus far been allowed to enter the plant. When plant operations
approach the design capacity, transfer trailers will likely be used to reduce
hauling costs.
To eliminate operator error in recording the load weight of each truck,
the weighing system design included the following: First, a plastic card
with the truck number and tare weight was prepared for each city packer
truck. Then, as a truck enters the plant, the scale operator would insert
the truck's card in the control panel. Next, as the gross weight of the
truck was measured on the scale, the net weight would be automatically
calculated and printed along with all the pertinent information on the punch
card weight ticket for subsequent processing by the City computers (see
Figure 3). However, because of the excessive delays in the computer process-
ing, the cards have not been used as intended, and the operator has been
recording the information manually.
In addition to the punch cards currently not being used as intended,
their retrieval as trucks enter the plant frequently causes truck backups
because of the excessive time that the scale clerk needs in trying to find
the appropriate cards. A tentative remedy to this situation could be painting
the tare weight on the side of each truck and having the scale clerk manually
enter both the truck number and the tare weight into the scale system. The
results of a receiving area time study are shown in Table 4.
As shown in Figure 4, the truck-routing plan through the plant requires
that trucks pass through the processing area before being weighed to prevent
truck back up from interferring with traffic on the public thoroughfare.
This routing not only disrupts the normal flow of people and service vehicles
in the processing area but also poses a safety hazard to personnel and
equipment.
The scale operator communicates with the truck drivers through an
intercom system and gives them their weigh-in tickets through an air-lock
Deibolt drawer installed in the scale house to maintain a comfortable temper-
ature for the operator. However, the indirect voice transmission coupled
with the drawer operation has further delayed the operator-driver transaction
and contributes to the truck back ups. In view of this delay and the scale
house temperature control difficulty discussed in the next paragraph, a
sliding window or a door on the scale side of the house would provide a
10
-------
1 |0q76l02 OOOC
•o. IDAVITR.
DATE TIME TRUCK
NO.
OOOC
ACCT.
NO.
0000(
TARE
WEIGHT
I385703657C 080K 1 (•(
1 M E
DOLLAR) ICTS £ 5
*~ u a <
GROSS NET COST J S » 1 "
WEIGHT WEIGHT (CHARGE) 5 2 £ 5 jj
1 7 II 1 ) 1 1 1 1
,rH(#V!Rr CITY OF BALT|MORE
VyP^Ry VaHIr SQUD WASTE PROGRAM
PAYMENT
TYPE SOURCE
REFUSE TYPE VEHICLE TYPE
1. CITY 1. HOUSEHOLD
2. CASH («OVT. COLL.)
8, CREL.T 2. HOUSEHOLD
(PRIV. COLL.)
«. INDUSTRIAL
4. COMMERCIAL
1. MIXED
1. COMPACTOR
2. GARBAGE (FRONT LOADER)
8. RUBBISH 2. COMPACTOR
4. BULKY OBJECT* (REAR LOADER)
6. ASHES
8. COMPACTOR
8. OTHER (SIDE LOAOIR)
B. COVERNMENT
(MUNICIPAL)
8. OTHER
4. ROLL-OFF DUMP
(CONTAINER)
! TRANSFER TRAILER
D. DUMP
7. STAKF BODY
B. PANEL
B. STATION WAGON
0. PRIVATE
Ct 5IOZOI \
s s \
. 5 g » WEIGHT TICKET \
H S = 1 1 i ROUTE NO. n i o Q r o ]
-ii t g 5 NUMBER U 1 £ C)DO
« 60 52 64 ROUTE NO.
CAPACITY WEATHER TEMPERATURE WIND
(CUBIC YARDS) 1. CLEAR 0. BELOW O 1. CALM
1. 1-2 2. SHOWERS 1. 0-20 2. BREEZY
2. 3-5 8. RAIN 2. 21-30 8. STRONG
3. 8-10 4. SNOW 3. 3 1-40
4.118 / 4. 4 1-50
B. 20-23 1 « „— ^ / B. 61-80
0.24.28 1 \ ' jf * • 81-70
7. 80-38 »\ |J/ »y gdls" ^- '1-80
B. 40-48 \] / (^^1 r Bl'90
8. 60-88 • l\ / H f' ABOVE *°
°' 88t ' /Oudr* /
1 ^^ / i
V >^
^ CREDIT CUSTOMER'S SISNATURB I
Figure 3. An example of the weight tickets used at the pyrolysis plant.
-------
TABLE 4. RECEIVING AREA TIME STUDY*
Test No.
3
8 9 Average
Time (Seconds)
Travel, enter plant
to scale
Weighing
Travel, scale
to dump
Dumping
Travel, tipping floor
to plant exit
Total time in plant
50 45
25 35
15 -
105 -
45 -
240 -
48
32
26
384
40
530
49
40
19
212
37
357
53 51
42 22
12 24
163 256
33
- 386
67
28
23
219
28
365
61
47
17
227
48
400
61
24
23
250
35
393
54
33
20
227
38
381
* No traffic delays during tests, trucks travelling unobstructed through
plant.
12
-------
DRAINAGE CHANNEL
Figure 4. Refuse truck routing plan.
-------
better means for the operator-driver transactions. In addition, the communica-
tion between the scale and tipping floor operators could be improved con-
siderbly by relocating the scale house closer to the tipping floor or by
interconnecting the two sites with telephones or radios.
The temperature in the scale house is difficult to control because of
the poor insulation of the four glass walls. Rather than increasing the
capacity of the heating and cooling system within the house as was done, it
would be better to enclose the walls, except the area for the proposed
sliding window or door, with adequate insulating materials since the operator
has no need for extended visibility. Moreover, the operator's equipment
should be positioned close to the proposed window or door since the operator
wastes much time and motion with the existing arrangement.
The Toledo Scale Company provides maintenance service for the scale
system under a contract with the City. Thus far, the scale has performed
satisfactorily and required only minor maintenance and calibration.
Tipping Floor
After being weighed, the loaded trucks drive to the receiving building
and enter the tipping floor area to discharge their load into a storage pit.
Description
The tipping floor (Figure 5) is a 51 m (168 ft) by 24 m (80 ft) concrete
slab which is elevated 4.4 m (14.5 ft) above the bottom of the storage pit.
On the tipping floor beside the storage pit are the truck bays which are
aligned and equally separated except for the one at each end. Each of the
two end bays, which extend further toward the storage pit center, is equipped
with a chute for direct dumping onto an apron conveyor. The two conveyors,
one at each end, are recessed in the storage pit floor and extend across the
width of the pit. At the other eight bays, the trucks simply dump their
loads on the storage pit floor.
The tipping floor was designed to handle up to 50 trucks per hour. Even
if the two end truck bays remain inoperative, as discussed below, the
experience to date indicates that the tipping floor will be able to handle
the peak loads if the plant were to operate at design capacity. The tipping
floor has one operator whose responsibilities are (1) to direct each truck
to a particular bay so that an orderly traffic flow is maintained and the
refuse is evenly distributed in the storage pit, and (2) to move truck
spillage and other debris from the floor into the storage pit.
Operating Experience
Originally, each bay had steel-pipe stops to prevent the trucks from
backing into the storage pit. However, because their clearance was designed
for an empty truck, they were consequently severely damaged and were replaced
with concrete stops about 30 cm (12 in.) high.
14
-------
TIPPING FLOOR
DIRECT DUMPING CHUTE
APPROACH RAMP
STORAGE PIT CONVEYOR
RECEIVING BUILDING
STORAGE PIT
SHREDDER FEED CONVEYOR
Figure 5. Schematic of the receiving building.
-------
The two end bays, those that are each equipped with a chute for direct
waste dumping (Figures 5 and 6) onto the apron conveyor, are no longer used
because of frequent waste jamming at the bottom of the chute. The jamming
was due to the chute design, that is, the convergent sides of the chute
produced too small a cross-sectional area for the waste to pass. The decision
to not use these bays was further motivated because the direct dumping allowed
certain loads containing large concentration of low density materials (paper
or hay) to enter the shredder directly (not mixed) and subsequently plug the
shredder, material-handling equipment, or both.
Figure 6. Refuse truck discharging to the direct dump chute.
The tipping floor in the area of the direct dump bays had settled,
likely because the fill had not been compacted enough before the floor itself
was poured. However, after the floor was restored, there has been no further
settling.
Because of its insufficient clearance, a hanging fire wall installed
between the tipping floor area and the adjacent area above the storage pit
has been damaged by the opened rear doors of the trucks. To prevent such
damage would require increasing the clearance from 5 m (16 ft) to 6 m
(20 ft) or removing the wall.
In the plant design, the tipping floor and storage pit areas were
enclosed to protect people and equipment from inclement weather and to pre-
vent wind from scattering refuse. Exhaust vents in the roof coupled with the
large open doorways for the trucks were to suffice for the exiting of dust
16
-------
and exhaust fumes. However, as discussed in the environmental section of the
report, there has been a excessive build up of dust and fumes in the tipping
floor area which could be sufficiently reduced by installing exhaust fans in
the existing vents.
The truckers' use of the portable toilets on the tipping floor has
frequently disrupted and delayed the flow of traffic. Consequently, a comfort
station should be made available in an area where the parked trucks would not
interfere with the traffic flow.
Storage Pit
The storage pit provides the means for receiving and temporarily storing
the refuse.
Description
The reinforced concrete storage pit, shown in Figures 7 and 8 is a
34 m (112 ft) by 24 m (80 ft) wide floor with 4.4 m (14.5 ft) high walls.
The pit volume therefore is 3590 m (126,000 ft.3). On the basis of loose
refuse with a 160-kg/m3 (10-lbs/ft3) bulk density, the pit has a design
capacity of 590 Mg (650 tons) of waste. As mentioned above, an apron con-
veyor at each end of the pit is recessed in the pit floor and extends across
the width of the pit. Since these conveyors are considered part of the size
reduction system, they are detailed later.
Figure 7. Empty storage pit.
i 1
-------
Figure 8. Full storage pit.
A fire prevention system for the pit consists of a fire cannon at each
end of the tipping floor and an overhead dry pipe sprinkler system. If a
fire occurs, the system automatically activates and stops the pit conveyor to
prevent the spread of fire. The fire cannons are also used to clean loose
debris from the tipping floor and residual waste from the emptied pit floor.
Any water entering the pit is removed by two sump pumps installed beneath
each pit conveyor. In addition, a ground-level opening provides access for
the pit operations, maintenance, and cleaning, and an air-conditioned en-
closure adjacent to the pit serves as an observation booth for visitors.
During the development of the material-handling equipment system to be
used in the storage pit, the costs and operational capabilities of overhead
cranes, such as those used in incinerator receiving pits, were evaluated
against those of bulldozers. Since two cranes would be required to keep each
of the conveyors loaded whereas one bulldozer would suffice to load both, and
since the costs for the cranes would be 5 to 10 times more than those for the
bulldozers, the bulldozers were selected as the preferred type of material-
handling equipment. Nevertheless, crane mounts were installed to permit, if
later desired, retrofitting the building with cranes.
Operating Experience
As stated above, the storage pit has a design capacity of 590 Mg
(650 tons) of refuse based upon its 3590-m3 (126,000-ft3) volume and a bulk
L8
-------
density of 160 kg/m3 (10 lbs/ft3) for loose refuse. Operational data for
such refuse have verified this design capacity. However, operational data
for the refuse compacted by the bulldozers have indicated a pit capacity of
1100 Mg (1200 tons) for packed refuse. Since test data for well-compacted
refuse show bulk densities up to 480 kg/m3 (30 lbs/ft3), the average of
320 kg/m3 (20 lbs/ft3) for the bulk densities of the loose and the well-
compacted refuse would yield a pit capacity of 1200 mg (1300 tons). These
computations, therefore, substantiate a pit capacity of 1100 Mg (1200 tons)
for packed refuse.
Thus far the pit operation has been capable of attaining the designed
refuse reception rate of 180 Mg per hour (200 tph) and the pit has required
no maintenance other than cleaning.
SIZE REDUCTION MODULE
The size reduction module has the primary function of shredding the
heterogenous solid waste stream into pieces of relatively uniform size to
facilitate the material handling and thermal processing of the waste.
Although not indicated in Figure 9, whose shaded areas represent the
size reduction module, the first components to contribute to the size re-
duction function are two bulldozers assigned to the storage pit. Operating
one at a time and working from the top of the pile to compact the refuse as
well as to protect the pit floor, the bulldozers push the refuse toward and
onto two conveyors, one at each end of the pit. The storage pit conveyors
discharge their waste load onto shredder feed conveyors which in turn dis-
charge the waste into parallel shredders. Finally, the shredded refuse
discharged from each shredder falls onto an inclined vibrating pan, called
the shredder discharge conveyor, to complete the module components.
The shredders have not been able to attain their design capacity because
of the frequent stopping of the feed conveyors. These stops were due to the
uneven waste loading which overloaded the shredder which, in turn, shut down
the feed conveyors. Initially, shredder explosions caused a few shutdowns
until the shredder venting was modified and a Fenwall explosion suppression
system was installed.
Storage Pit Bulldozers
The bulldozer functions are to distribute the accumulating piles of
refuse below the truck bays within the storage pit for maximum temporary
storage and, concurrently, to ultimately move the refuse onto the two storage
pit conveyors. In turn, these conveyors transport the refuse to shredder
feed conveyors, as discussed below. The normal operational procedure calls
for one bulldozer operating at a time in the storage pit. To both protect
the concrete floor of the pit and perform initial refuse compacting, the
bulldozer works from the top of the pile to spread successively accumulating
layers as the bulldozer pushes the refuse toward the two pit conveyors.
19
-------
MAGNETICS
S3
o
VACUUM BELT
FLOATATION
4
-J.J.-
BURNERS
COMBUSTION AIR
GASES
—- KILN
BURNERS
BOILER FEEDWATER
i
DEHUMIDIFIER
\
EXHAUST TO
ATMOSHPERE
Figure 9. Size reduction module (shaded area).
-------
Description
The bulldozers are Allis-Chalmers Model HD11D track-type vehicles equipped
with 8.4 m3 (300 ft3) landfill blades for a design pushing capacity of
160 Mg (175 tons) of solid waste per hour. The bulldozer blades and tracks
are covered with rubber guards to reduce wear and damage on the pit floor.
Operating Experience
The original schedule for bulldozer operation called for a 16-hour day
during a 6-day week. This schedule was based on the shredder design capacity
of 45 Mg (50 tons) of refuse per hour and a post shredder storage capacity of
1815 Mg (2000 tons). Since the past shredder storage is not presently in use,
the daily operation was increased to 24 hours.
The rubber guards covering the blades and tracks have required frequent
repair and replacement because of their heavy wear. To prevent overheating
and to reduce internal wear, the bulldozers must be cleaned of dust and
debris, as shown in Figure 10, after each 8-hour operation. In addition
(because of dust accumulating between the radiator and its splash guard),
excessive overheating of the bulldozers has required removing the splash,
blade, and heat guards from the bulldozers. Although the bulldozer mainte-
nance performed by the City Center Garage is generally adequate with apparently
reasonable costs, much operational time is lost because of transporting them
to and from the garage and the difficulties in coordinating maintenance
schedules with the garage personnel. The time lost in cleaning and main-
taining the bulldozers is particularly critical when the bulldozers must be
operated continuously to maintain the required feed flow on the pit conveyors.
Figure 10. Storage pit bulldozers.
-------
The efficiency of the storage pit operations depends on the bulldozer
operator's competence, his ability to see the waste levels on the pit con-
veyors, and his communication with the chief plant operator in the control
room who starts and stops the conveyors. Since there is no direct means of
communication between the control room and the bulldozer, a control room
messenger must walk over to the bulldozer operator to inform him of the chief
plant operator's plans and directions.
Initially, the bulldozer operator frequently overloaded the conveyors
because the accumulating refuse layers rose to heights which obscured his
vision. To correct this condition, flashing lights were installed in the pit
to indicate when the conveyors were operating and a leveling bar was installed
over each conveyor to prevent the waste level from exceeding the maximum
height for normal operation. However, since some conveyor jamming and fail-
ures due to overloading have continued, a mirror or television system might
be installed to further guide the bulldozer operator.
Storage Pit and Shredder Feed Conveyors
As mentioned above, the wastes loaded onto the storage pit conveyors are
transferred directly onto the shredder feed conveyors. The latter conveyors
in turn discharge the waste into two shredders contained in the adjacent
shredder buildings. The pit and feed conveyors are interlocked so that the
pit conveyor cannot run unless the feed conveyor is operating. Figure 5
shows a side view of the pit and feed conveyor alignment.
Description
Both the storage pit and the shredder feed conveyors, shown in Figure 5,
are Rexnord piano-hinged 1.8-m (6-ft) wide apron conveyors. They are con-
structed of carbon steel with apron pan cleats every third flight, a con-
tinuous bottom pan, overlapping side wings, side chains, bushed steel rollers,
a frame, roller chain tracks, and guides (Figure 11).
Designed to run at a fixed speed of 1.5 meters per minute (5 fpm) , the .
storage pit conveyor at each end of the pit is 15.5 m (50 ft) long and is
installed in a hopper recessed 1.2 m (4 ft) below the pit floor to facilitate
the conveyor loading from the floor. The hopper is formed by a steel wall
from the conveyor to the pit floor level on one side and a steel wall from
the conveyor to the tipping floor level on the other side (see Figure 12).
As previously discussed, the direct dump chutes at the tail end of each pit
conveyor are not being used because of the chute jamming and the passage of
some low density and unshreddable materials which damaged or plugged the
shredder and the material handling equipment. Therefore, only bulldozers are
currently loading these conveyors.
Designed to run at a fixed speed of 4.6 m per minute (15 fpm), the
shredder feed conveyors are each 24 m (80 ft) long, have a 30° elevation
angle, and are so aligned with the storage pit conveyors that the pit con-
veyor discharge falls vertically onto the tail end of the feed conveyors.
22
-------
APRON CONVEYOR
ROLLER
CONVEYOR CHAIN
Figure 11. An exploded view of the apron conveyor.
23
-------
HOPPER LOADING
"ft
o o
777
REX OUTBOARD
ROLLER SUPPORTED
APRON CONVEYOR
O o
p
O 6
Figure 12. A typical section through a storage pit conveyor.
24
-------
Each feed conveyor is enclosed in a sheet metal gallery which connects the
receiving and shredder buildings. The feed conveyors have continuous
1.1-m (3.5-ft) high-skirts on both sides and pans with vertical pusher
plates as shown in Figure 13.
Operating Experience
To enable the chief operator in the main control room (Figure 14) to
operate the pit conveyors with greater flexibility, and especially to main-
tain a constant load on the conveyors (as measured by the shredder current)
as the bulk density of the refuse varies, the designed fixed speed of
1.5 m per minute (5 fpm) was changed to a variable speed from 0 to 3 m per
minute (0 to 10 fpm). Since the storage and recovery unit is currently being
bypassed, the feed rate of refuse to the thermal processing area can be
regulated by varying the speed rate of the pit conveyors.
The following provisions were instituted to improve the bulldozer
operator's efficiency in loading the pit conveyors to the proper level:
(1) flashing lights were installed to inform the operator when the conveyors
are running; (2) lines were painted on the hopper walls to indicate the
maximum refuse levels on the conveyors; and (3) a fixed bar was installed
above each of the storage pit conveyors to reduce the peaks of trash on the
conveyors. After several geometric configurations were tested, a bar with a
rounded bottom edge facing the oncoming refuse flow was selected. However,
when the waste level rises on a bar so that the jamming back pressure over-
loads the conveyor, the shear pin connecting the motor and drive sprockets
breaks to protect the conveyor from damage. Such shear pin failures
frequently require completely removing the bar to clear the jam. In addition
to the bulldozer operator not allowing the waste to exceed the desired level,
such jammings could be minimized by replacing the fixed bar with a tensioned
one which would move away as-the back pressure approaches an overloaded
condition.
One of the pit conveyors sustained major damage when a solid steel
object jamming in a pinch point caused the overstress and failure of a con-
veyor link. Since the shear pin was improperly installed in the drive
socket, the motor continued to drive the conveyor while other links as well
as pans were damaged.
Waste accumulating in the return run of the shredder feed conveyors had
frequently compacted and jammed the conveyor with the subsequent breakage of
the shear pin and extensive downtime. To minimize such failures, a drop-out
chute was installed on the return pan so that the refuse retained on the
return run would fall onto the shredder discharge conveyor.
Another frequent cause of extensive feed conveyor downtime was due to
the failure of the chain links on the side of the pans. These links connect
the pans on the conveyor and engage with the drive sprocket to move the
conveyor. As waste wedged between the links and the drive sprocket, it
caused the links to cantilever (Figure 15) and, consequently, to be over-
stressed to failure. The failures of the link caused a successive
25
-------
42" SKIRT BOARD
(V*" PLATE)
RETURN TRACK
12 GA. DRIBBLE-
PAN
PAN REINFORCING CHANNEL
CONVEYOR SUPPORT BEAMS
GALLERY
REX OUTBOARD
ROLLER SUPPORTED
APRON CONVEYOR
ASCE 40# RAIL
1
Figure 13. A typical section through a shredder feed conveyor.
-------
Figure 14. Control panel in main control room.
27
-------
STRESS CONCENTRATION ON CHAIN LINK
CHAIN LINK
DRIVE GEAR
NORMAL LINK SUPPORT
PLANE OF CONCENTRATED STRESS
CRUSHED CAN WEDGE
UNDER CHAIN LINK
OBJECT WEDGED BENEATH LINK
Figure 15. Link failure on shredder feed conveyor.
28
-------
overstressing and failure of other links. After the head sprocket and chain
were enclosed within a steel guard to prevent waste from accumulating within
them, the chain links remained intact.
Because of waste jamming at the point where the pit conveyor transfers
the refuse to the feed conveyor, the original 122-cm (48-in.) long pusher
plates, which had been installed on the feed conveyor to keep waste from
sliding down its 30° incline, were replaced by 45-cm (18-in.) long staggered.
plates to minimize the jamming. In addition, pusher plates were installed on
the pit conveyor to prevent waste from bridging in the hopper.
To prevent the spillage and wear due to waste moving behind the sidewall
plates of the conveyors, rubber skirts were bolted to both sideboards of the
four conveyors and installed at each of the head and tail pulleys. While the
skirts have effectively restricted the spillage, they sustain severe wear and
damage.
Spillage at the gap between the two conveyors was especially severe
since the pit conveyor, particularly its pusher bars, pushed the waste in
such a way that it tended to fall into the recessed pit below the conveyors.
To prevent this spillback, the tail ends of the two feed conveyors were
retrofitted with steel plate gates, which pivot on their horizontal axes, and
with gate stops, so that the gates swing only in the travel direction, to
prevent waste from falling backwards. Although the gates were initially only
marginally effective, design improvements have made them satisfactory.
Since the continuous bottom pan of the pit conveyor carries any carryover
waste down the return run, the tail end of the conveyor was enclosed so that
the waste would pass around the tail pulley and then be forced up the con-
veyor by the pusher plates. This modification prevents refuse accumulation
at the tail end.
The fire protection system so interlocks the pit and feed conveyors that
whenever it detects burning waste in one conveyor, it automatically stops
both conveyors to prevent the fire from spreading to the other conveyors.
All material-handling conveyors in the other sections of the plant are
similarly interlocked. The pit conveyor also interlocks with the feed con-
veyor so that a a stoppage of the latter automatically stops the former.
However, if the shear pin in the drive sprocket of the feed conveyor fails,
the interlock is defeated and the motor continues running. This design de-
ficiency could be remedied by installing a zero speed sensor on the tail
pulley of the feed conveyor whose signal would feed to the interlock control.
The feed conveyor also interlocks with the shredder so that two condi-
tions must be satisfied for the feed conveyor to continue running: (1) the
shredder must be operating to prevent its being plugged, and (2) the shredder
amperage must be below the maximum set by the chief operator in the control
room to prevent shredder overloading. Although the setting is generally at
110 amps, it can be varied from 0 to 140 amps.
29
-------
Television cameras were installed with a direct view of the feed con-
veyor and an view of the pit conveyor so that the monitor in the control room
could detect unshreddable objects in the feed stream, conveyor overloading,
and shear pin failure.
Maintenance
/
Because of the damage caused by grit and large metal pieces in municipal
refuse, the operational disruptions due to waste spillage and jamming and
the continued severe service with its extreme wear, the pit and feed conveyor
requires extensive cleaning and maintenance. In summary, the rubber sidewall
skirts must be serviced frequently; shear pins, rollers, axles, and bushings
must be replaced periodically; and chain tensions and alignments must be
adjusted routinely. Table 5 lists the preventive maintenance schedule for
the pit and feed conveyors.
Shredders
Installed in parallel buildings, the two shredders receive refuse from
shredder feed conveyors (discussed in the last section), reduce most of it to
particles smaller than 15 cm, and discharge all the waste to an inclined
vibrating pan (shredder discharge)- conveyor directly under each shredder.
As detailed later, the shredder operation consists basically of a
horizontal rotor swinging 28 freely pivoting hammers toward the downward flow
of refuse which falls on one side of the rotor. The combined hammer torque
and centrifugal forces pulverize brittle materials such as glass; compact
ductile materials such as steel cans; and tear shearable materials^ such as
paper, wood, and textiles. Particles smaller than 15 cm pass through
15-cm-square opening in a semicylindrical grate which is concentric with the
lower half of the hammer rotation. Particles passing through the grate fall
directly onto the vibrating pan. Particles larger than 15 cm are forced
upward and around the swinging rotor for repeated hammering until they either
pass through the grate openings, are ultimately thrown into an oversized
chute, or are separately removed from the shredder. This chute is built into
an access door on the side opposite the refuse downfall. The chute entrance,
which is 30 cm wide (originally 60 cm), entends along the rotor length at a
constant height above the sweep of the hammer rotation. The chute exit is
also above the vibrating pan.
The reduction in the refuse particle size with the consequent increase
in waste surface area accelerates the subsequent thermal processing; produces
a more homogeneous refuse for easier waste handling, storage, and recovery;
and enhances vector (insect and rodent) control by distributing the smaller
food waste particles throughout the refuse. However, some of the dis-
advantages of shredding are some pulverized glass enters the kiln-off gas as
particulate and some causes severe wear of the motor bearings, the conveyor
idlers, floor, bucket chains, and drag conveyor equipment in the storage and
recovery unit.
30
-------
TABLE 5. APRON CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Daily
Inspect gearmotor unit for oil leaks or unusual sounds.
Weekly
Adjust the chain tension while the chain is in motion to allow a
slight sag in the chain under the headshaft sprockets.
Check the flights for loose bolts and material buildup; repair or
replace all damaged flights.
Replace any damaged chain at once; never use new chain with old
sprockets or new sprockets with old chain.
Inspect pans; check apron and pan bead opening for proper spacing
or distortion.
Check housekeeping, buildup causes excess wear.
Inspect the centers around the chain, load carrying, and tension
members of the apron conveyor unit:
Check sidebar inner faces for wear caused by misalignment.
Check for missing cotter pins.
Look for frozen rollers.
Inspect around pots of chain for wear.
Inspect sprockets for alignment and check excessive tooth wear.
Lubrication:
''' Chain reducer
(Winter - Paradene 430)
(Summer - Paradene 1000)
Drive chain (Paradene 430).
Flat chain (Paradene 430).
Monthly
Grease all bearings and outboard rollers (LiEP2).
Oil the flap gates on the conveyors (Paradene 430).
Bi-monthly
Check oil and grease for contamination.
Semiannually
Change oil in gear reducer and examine backstop for worn or damaged
springs on shredder feed conveyors.
Change grease at pillow block bearings with plugs out and conveyors
running.
CONTINUED
31
-------
TABLE 5. (Continued)
Change drive chain oil (Paradene 430).
Grease motor (LiEP2).
Check motor, alarm, and interlock circuit, operation of gear change
system push buttons and drive motor.
Lubricate and inspect pull cord switch.
Check operation of speed indicator pulser and meter.
Annually
Grease vari-drivers (LiEP2).
Megger motors.
Description
As shown in Figure 16, each shredder is a Jeffery Model 990 horizontal
shaft rotary hammennill which is powered by a Louis Allis 800-hp motor with
a V-belt drive train. The hammermill is enclosed on all four sides by rein-
forced steel plates on the outside and identical, but removable, wear plates
on the inside with an access door on the side opposite the refuse inlet. The
area for the refuse downfall extends, as an explosion vent, without any hori-
zontal obstruction from the hammermill through the roof of the shredder
building. The semicylindrical grate with 15-cm (6-in.) square openings, as
mentioned above, consists of hardened steel sections and forms the bottom of
the shredder.
The rotor is made of steel, measures approximately 1.8 m in diameter,
2.3 m in length, and has a drive system consisting of 16 rubber V-belts. A
shaft extending between each of the four paired rotor arms supports seven
hammers. Each hammer is a rectangularly shaped, hardened-steel block with
two symmetrical holes in the sides. The hammer weighs 82 kg (180 Ibs.) and
measures approximately 42 cm (17 in.) long, 25 cm (10 in.) high, and 15 cm
(6 in.) wide. Since each hammer can be installed with one hole and then the
other and turned 180° while using each hole, it has four impact faces.
Figures 17 and 18 show used and rebuilt hammers.
The major auxiliary equipment for each shredder consists of a hydraulic
system, a pumped oil lubricating system, a dust collection system, and an
explosion suppression system.
The hydraulic system supplies pressure to operate the access door for
cleaning and maintenance and the pin puller (the mechanism to extract and
insert the mounting pins for the hammers). The major system components
32
-------
VERTICAL FEED CHUTE AND
EXPLOSION RELIEF DUCT
FENWALL
EXPLOSION
SUPPRESSION
BOTTLE
FENWALL
EXPLOSION
SENSOR
ROTOR SIDE PLATE
REMOVABLE ACCESS DOOR
CUTAWAY OF DISCHARGE GRATE
SHREDDER DISCHARGE CONVEYOR
Figure 16. Schematic of a hammermill shredder.
33
-------
Figure 17. Rebuilt shredder hammers.
Figure 18. Worn shredder hammers.
-------
include: (1) a 15-hp pump which has the twofold function of opening and
closing the access door and of manipulating the mounting pins for hammer
changes, (2) a 2-hp pump to hold the access door closed during shredder
operation, and (3) an oil heater and heat exchanger to keep the fluid
viscosity constant as the ambient temperature varies.
As detailed later, the shredders are interlocked with the shredder
motor, the hydraulic system, the lubricating system, the access door, the
rotor-vibration monitor, and an explosion suppression system.
The pumped oil lubricating system supplies lubricating oil to the two
main shredder bearings at each end of the rotor. These bearing must be well
lubricated because of their critical function anJ need to sustain extreme
loads. The major system components include a bearing oil pump and an oil
heater and heat exchanger to maintain a constant oil viscosity as the ambient
temperature varies.
Each shredder has dust pick-up points which connect to the plant dust
collection system. The plant dust collection system and the explosion
suppression system are both detailed later.
Operating Experience
The removable wear plates on the inside of the reinforced steel sides
that enclose the shredder are still the original units. Although they
evidence minor wear, these plates, as intended, have provided a sacrificial
wear surface and ensured the structural integrity of the shredder. In ad-
dition, the refuse downfall opening extending to the roof for the venting of
explosion pressures has remained free of horizontal obstructions as shredder
modifications were installed.
The 15-cm (6-in.) square openings in the grate were intended to pass
particles with a nominal 7.5-cm (3-in.) size. Although the stream character-
ization dat.a, detailed later, shows that the nominal shredded refuse size is
less than 2.5 cm (1 in.), some pliable materials, such as plastics and
textiles, larger than 15 cm (6 in.) have been sufficiently deformed to pass
through the openings, and other large materials have entered the downstream
conveyors from the oversize chute in the shredder. Such large materials,
particularly textiles, have impeded the subsequent waste handling and process-
ing operations.
The original hammers were intended to be rebuilt after shredding about
1815 Mg (2000 tons) of waste with each of the four faces. The restoration
consisted of two phases: the first to reshape the hammer to its original
configuration by using a standard weld material, and the second to apply two
coatings of a hard facing material. Because of the excessive wear rates of
the hard facing material, an abrasive-resistant material was applied as a
third coating. Although the third coating increased the hammer life, it did
not prove cost effective.
35
-------
As a result of the foregoing experience, the restorable hammers were
replaced with -disposable ones made of special alloys which impart a hardness
throughout the hammer rather than primarily on the surface. A comparison of
the restorable and disposable hammer wear rates shown in Table 6, reveals
that the disposable hammers have a much longer life. Because of .excessive
wear during the periods shown in Table 6, the useful life of the restorable
and disposable hammers is 1815 Mg (2000 tons) and 3450 Mg (3800 tons) per
face respectively.
TABLE 6. SHREDDER HAMMER WEAR*
Period
Hours per face
Mg per face
Restorable Jeffrey Hammers
11/29/76
12/16/76
01/09/77
01/25/77
03/01/77
12/12/76
01/09/77
01/22/77
02/23/77
03/11/77
04/25/77
04/04/77
05/10/77
Average
12/18/76
12/23/76
01/24/77
02/27/77
03/12/77
12/23/76
01/21/77
02/07/77
03/10/77
03/19/77
05/03/77
05/09/77
05/15/77
104.
89.
103.
141.
130.0
119.0
97.
96.
141.0
109.0
59.0
54.0
58.5
100.2
.5
,0
,5
,5
,5
.5
3099
1929
2788
3243
2910
2939
2520
1650
3159
2991
1905
1715
1860
2516
04/25/77 - 05/08/77
Disposable ESCO Hammers
140.0 4354
* City Daily Operation Reports and Maintenance Log.
In addition to increased hammer life, the disposable hammer appears to
require less power to shred a given mass of refuse, as shown in Table 7-
The cost comparison of the restorable and the disposable hammers depends
on the number of times that the former can be rebuilt. Because of decreasing
structural strength, the manufacturer recommends that the maximum number of
hammer restorations be limited to two. A cost comparison of the two types of
hammers revealed that the new hammers have proved to be more economical.
36
-------
TABLE 7. SHREDDER POWER CONSUMPTION
Date
3/20/77
3/17/77
4/27/77
5/07/77
5/09/77
Hammers
Worn Jeffrey
Rebuilt Jeffrey
New ESCO
Worn ESCO
New ESCO
Average
Amperes
67.55
70.97
62.48
52.4
67.57
Mg/hr.
28.1
32.4
35.4
27.2
38.1
kwh/Mg
9.8
9.1
7.4
8.0
7.4
$/Mg*
0.32
0.30
0.24
0.26
0.24
* $0.033 per kw-hr.
As intended, the rotor belt drive system has protected the rotor by
slipping or breaking when unshreddable materials have jammed the rotor.
Although the rotor has operated at high wear rates and has occasionally
stopped abruptly, it has never locked nor had a major operational deficiency.
The original 60 cm (2 ft) width of the oversize chute was reduced to
30 cm (1 ft) so that the larger materials would be further shredded before
being thrown into the chute. However, since textiles and paper can now more
readily plug the smaller chute, unshreddable materials frequently accumulate
within the shredder.
Although the dust collector system has been augmented by installing
gaskets and skirts at all shredder openings, excessive dust and waste part-
icles continue to fill the shredder building and threaten the operation of
the shredder motors. Dust accumulating on the ventilation screens and heat
transfer fins impair the fin effectiveness causing the motors to overheat.
Moreover, the dust itself has a serious fire and explosion potential.
Explosion Suppression System
Two types of explosions occur in shredders. One type, which accounts
for most of the explosions, is due to the deflagration of combustibles such
as dust and fumes, accumulating in the shredder ductwork. The other type is
caused by the detonation of such individual objects as gas cylinders and
dynamite.
After an explosion had severely damaged one of the shredders, the
venting system was modified and a Fenwall explosion suppression system was
installed in each shredder. Besides a structural reinforcement, the shredder
vent was redesigned to change the original converging sidewalls to diverging
sidewalls for a greater venting capacity. In addition, a cage with a roof
was installed above the vent outlet on the roof of the shredder building.
The cage was intended to prevent metals from projecting through the vent and
rain from entering the vent.
37
-------
Designed to suppress only explosions caused by deflagrations, the
Fenwall system consists primarily of paired pressure sensors and extinguisher
bottles attached to the exterior surface with ports into the interior
(Figures 16 and 19). To ensure optimum protection, these pairs were in-
stalled at strategic locations throughout the shredder body, the outlet duct,
the dust collection unit, and the shredder discharge duct. Each extinguisher
bottle, a spherical metal vessel, contains nitrogen gas as the dispersing
medium, which is under a pressure of 2070 kPa (300 psig), and hydrochloro-
bromide liquid, the principal suppressent agent. When the pressure wave
preceeding the main shock wave of a deflagration strikes the sensor, the
sensor activates the extinguisher bottles. Then the nitrogen gas, which
discharges at a high rate, projects and scatters the hydrochlorobromide
throughout the shredder. While the nitrogen depletes the oxygen to reduce
the combustion, the hydrochlorobromide reacts with the radicals in the flame
zone to suppress the deflagration before it generates the explosive force of
its main shock wave.
Figure 19. Fenwall sensor1 and extinguisher.2
18
-------
After each of several sensor activations, with rarely any evidence of
explosive effects, a Fenwall representative called to the site has investi-
gated and reported the cause of the sensor activation and restored the system
for continued service. The Fenwall Company guarantees that the total system
downtime after each activation will be less than 36 hours. One activation
was due to refuse plugging and compressing air in the detector tube, and two
others, which occurred without the discharge of the extinguisher bottles,
were due to either a system malfunction or a maintenance deficiency.
Since the modification of the shredder vents and the installation of the
Fenwall systems, the shredders have not been damaged by explosions. However,
tests have shown excessive dust accumulation in the pipes connecting the
Fenwall system to the shredder after about 250 Mg (275 tons) of waste has
been processed through the shredder. Such dust accumulations impede the
functioning of the sensors and the discharge of the extinguisher bottles.
While some pipes have been protected with dust covers, others that cannot be
so protected (because of their location) must be manually cleaned after each
shift. In order to eliminate this problem, a design has been submitted for
an automatic air purge system to prevent excessive dust accumulations anywhere
in the Fenwall system.
Shredder Capacity
Although each shredder was designed to handle 45 Mg (50 tons) of wastes
per hour with an instantaneous maximum rate of 68 Mg (75 tons) per hour, the
maximum and average rates observed during the current study were 41 and 27 Mg
(45 and 30 tons) per hour, respectively (Table 8). The lower rates were due
to plant personnel running the shredders far below capacity because of the
frequent shredder overloads which stopped the feed conveyors. A plot of the
shredder motor current in Figure 20 indicates the motor tendency to become
overloaded as indicated by the transient current peaks. When the feed con-
veyor overloads the shredder, an interlock stops the conveyor until an auto-
matic restart with a 2-minute delay reactivates the conveyor. By reducing
the delay time to 10 seconds, the shredder processing rate can be raised to
between 36 and 41 Mg (40 to 45 tph) per hour. The shredder capacity has also
increased when refuse retained in the storage pit has been so compacted and
sheared by the bulldozer operation that it enters the shredder with a smaller
particle size and greater bulk density. Like the feed conveyors, the
shredders have been handling wastes whose bulk densities are less than
those designed for.
The probability plot of the shredder current in Figure 21 indicates that
the shredder operation is generally in an unloaded condition that should per-
mit increasing the shredder feed rates. However, because of the motor tending
to become overloaded with transient waste peaks, a higher feed rate would
require increasing the horsepower of the drive unit or distributing the waste
more evenly over the feed conveyors.
Shredder Interlocks
Each shredder is equipped with the following interlocks to ensure its
safe and efficient operation. Three separate interlocks protect the motor as
39
-------
TABLE 8. SHREDDING RATE*
DATE
7/23/76
7/24/76
7/25/76
7/27/76
7/28/76
7/29/76
8/ 5/76
8/ 6/76
8/ 7/76
8/ 8/76
ll/ 7/76
ll/ 8/76
11/12/76
11/16/76
11/17/76
11/18/76
11/27/76
11/28/76
11/29/76
11/30/76
12/ 8/76
12/10/76
12/11/76
12/12/76
12/14/76
12/15/76
12/16/76
12/17/76
12/18/76
12/19/76
12/20/76
12/21/76
12/22/76
12/23/76
I/ 9/77
1/10/77
1/11/77
1/12/77
Mean
Standard Deviation
Mg/hr
24.2
28.9
25.1
24.5
23.0
24.2
25.9
26.5
36.3
35.2
31.1
31.3
25.8
28.2
23.6
32.8
27.5
23.8
27.2
21.5
21.0
34.0
31.6
28.4
28.2
15.0
31.0
31.2
19.6
18.2
32.1
27.3
17.6
19.1
29.6
22.4
31.7
22.5
26.98
5.24
DATE
1/13/77
1/14/77
1/15/77
1/16/77
1/18/77
1/19/77
1/20/77
1/21/77
1/23/77
1/24/77
2/ 1/77
21 2/77
21 4/77
21 6/77
21 6/77
21 7/77
2/23/77
2/24/77
2/25/77
2/26/77
2/27/77
3/ 1/77
3/ 2/77
3/ 3/77
3/ 4/77
3/ 5/77
3/ 6/77
3/ 8/77
3/ 9/77
3/10/77
3/11/77
3/12/77
3/13/77
3/14/77
3/15/77
3/16/77
3/17/77
3/18/77
3/19/77
Mg/hr
17.7
26.0
26.5
11.0
28.5
32.0
26.6
20.2
28.7
15.5
21.2
30.8
35.3
20.7
24.7
31.8
22.3
26.5
25.0
23.4
26.0
26.7
26.6
28.8
29.5
31.3
35.9
29.6
30.1
32.1
27.9
32.8
30.0
33.4
28.3
33.3
32.0
28.3
33.1
*Source: City Daily Operation Summary
40
-------
V _.X y -V _; \ _ \
\ \ \ \rt « V V
Figure 20. A recording ammeter graph of shredder current.
-------
160.0
146.0
130.0
99.99
99.9 99.8
99 98 95 90 80 70 60 SO 40 30 20
10
2 1 0.5 0.2 0.1 0.05 0.01
116.0
CO
3
W
W
g
1
CO
100.0
86.0
70.0
66.0
40.0
26.0
0.01 O.OS 0.1 0.2 0.5 1 2
20 30 40 50 60 70 80 90 95 98 99
99.8 99.9
99.99
Figure 21. Probability plot of shredder current.
-------
follows: One interlock stops the feed conveyor when the motor current is
above 110 amps for more than 6 seconds, and the second and third interlocks
shut off the motor when the current is above 130 amps for more than 12 seconds
and above 200 amps for more than 2 seconds, respectively.
In order to ensure proper lubrication of the shredder bearings, there
are two interlocks: one shuts down the shredder when the lubricating system
is not functioning and the other does the same when the oil temperature
exceeds 81°C (175°F). In order to ensure that the access door is securely
closed for shredder operation, there are two interlocks: one to make certain
that the hydraulic system is applying the required pressure on the door and
the other to ensure that a door locking pin is in position. Still another
interlock ties in with the rotor vibration monitor so that the shredder
operation is stopped whenever the vibration becomes excessive.
When the Fenwall system was installed, an interlock was added to allow
shredder operation only when the system is armed. To prevent jamming the
shredder and transporting burning refuse from one conveyor to another, the
feed and discharge conveyors are so interlocked that the shutdown of the
latter stops the former.
Maintenance
Because of the abrasives, particularly broken glass and sheared metal,
and their high velocities in the shredder, the hammer, grate, rotor, and
sidewall plate surfaces obviously sustain severe wear.
Since the hammers have the highest wear rates, they require the most
maintenance. During the current study, turning or rotating the hammers
required 4 hours with three men, replacing them required 8 hours and three
men, and the restoration of a restorable hammer required 6 hours. The
replacement of one set of grates after 63,500 Mg (70,000 tons) of waste had
been processed required 8 hours with three men. Although the rotors and
sidewall plates have not yet been replaced, it is estimated that their effec-
tive lives will handle 100,000 and 200,000 Mg (110,000 and 220,000 tons) of
refuse, respectively The rotor replacement will require about 16 hours with
three men.
The belts, which require routine adjustment to maintain the proper
tension, must be replaced periodically. Operating time has been lost because
of drive deficiencies due to inadequate maintenance that allowed belts to
slip and become damaged and because of the eccentric loading on the motor-
mounting platform that shifted the drive assembly out of alignment.
Except for the sensor ports which the plant personnel rod out after each
shift, the explosive suppression system is maintained by the Fenwall Company.
Before the initial start-up, the rotor bearings had to be replaced
because of their having been idle for several months. One of the drive
shafts on the shredder motor required remachining and another had to be
replaced when a misalignment caused its bending.
The shredder preventive maintenance schedule is shown in Table 9.
43
-------
TABLE 9. SHREDDER PREVENTIVE MAINTENANCE SCHEDULE
Open main motor safety switch.
Clean with a fire hose:
Replace hammers cracked at the eye.
Replace all broken pins.
Cracks in grate bars and spiders should be noted in log. A large
crack should be repaired immediately.
Check wear on side liners.
Replace broken bolts, all bolts should be tight.
Check for lube and hydraulic leaks.
Clean around the bearing housing.
Check V-belts for tension + wear (1" deflection with 50 Ibs. pull)
Check bearing -lube oil level. (Paradene X1000)
Weekly (40-50 hours)
Clean all welds.
Check for wear on spider ends, hammers, liners, etc.
Check frame welds.
Change filters after first 40-50 hours.
Check hydraulic level. (Paradene 430)
Check all drive components for damage or excess wear.
Clean dirt and dust off drive motor, lubrication, and hydraulic systems.
Investigate anything abnormal.
Check vibration.
Check coupling alignment.
Balance flow indicator.
Monthly
Check motor idle current.
Check RTD for temp, and temp, spread.
Check vibration.
Grease motor bearings. (LiEP2)
Quarterly
Clean and flush circulating oil lubrication system and refill with clean
oil and change filters. (Paradene X1000) (Purolator #6666063,25
micron filter element).
Grease coupling and jacks lift bearings. (LiEP2)
Rebuild and hardface spider ends, hammers, and liners, where required.
Check coupling alignment.
~~~~CONTINUED
44
-------
TABLE 9. (Continued)
Semiannually
Clean and flush all bearing housing and change filter element.
(Paradene X1000) (Purolator #6666063).
Remove all hammers and pins. Check rotor for balance. Check rotor
shaft for runout using a dial indicator.
Clean and flush hydraulic system. Refill with new oil. (Paradene 430)
(#5610 Char Lyn filter).
Replace all side liners and discharge chute liners that are extremely
worn.
Grease motors. (LiEP2)
Check and megger motor.
Check heaters.
Check RDT monitor, clean when necessary.
Check bearing condition.
Check vibration switches.
Check close mechanical interlock for quadrant.
Check quadrant hold and pin puller motors.
Check quadrant hold switch interlock.
Check lubricating oil pressure switch, bearing temperature thermisters,
temperature monitor and shutdown.
Check motor starter cabinet - clean if necessary.
Check control panel conveyor shutdown.
Check C05 relay, GFR and cabinet heater.
Check cooling water control switch.
Check all alarms.
Check motor control circuits and contactors for cleanliness.
Annually
High pot motors.
Check calibration of C05 and 80 relays.
Check operation of watt loss relay.
45
-------
Shredder Discharge Conveyors
The refuse discharged from each shredder falls vertically into an
inclined vibrating pan (called the shredder discharge conveyor) which in turn
transfers the waste to a rubber belt conveyor (called the shredder refuse
collection conveyor, which is discussed later).
Description
Each of the two discharge conveyors is a Stevens-Adamson, power-
imbalanced, vibrating (Vibra Coil) pan assembly approximately 2 m (6 ft) wide,
4.5 m (15 ft) long, and 0.3 m (1 ft) deep. The pan portion of the conveyor
is made of abrasion-resistant steel with extra heavy steel-plate pan con-
struction. The pan is mounted on the structural steel supports of a heavy
structural steel base for standard rigid floor mounting. Centered directly
below the shredder refuse outlet, the steel base was initially bolted to the
concrete floor. The pan is installed at a 5° decline. A positive mechanical
eccentric drive vibrates heavy-duty, low-stress, power-regenerating steel
coil springs and, in turn, the pan. Heavy-duty stabilizer bars mounted in
rubber bushings guide the pan through its linear oscillation.
To relieve any explosion pressure within the shredder, the pan is
equipped with a horizontal duct that vents to atmosphere. A screen and a
deflector plate in the duct prevent the discharge of any high velocity
projectiles which could cause personal injury.
Operating Experience
When initially anchored directly to the concrete floor, the pan assembly
transmitted such extreme vibration to the floor and then through the entire
shredder building that some of the sensitive instruments in the control room
about 12 m (40 ft) from the shredder building malfunctioned. To effectively
reduce this vibration transmission required installing isolation springs
between the floor and the structural steel support. Consequently, concrete
inertia blocks were installed on the base of the pan for the resistance
needed to vibrate the pan with the eccentric drive operation (Figure 22).
To prevent cutting or tearing the rubber belt conveyor as the refuse
fell from the pan conveyor, the discharge chute of the conveyor was originally
equipped with deflection plates installed 61 cm (2 ft) apart and at an
approximate 60° slope. After the plates had frequently plugged the chute
with consequent waste backup on the pan and into the shredder, they were
removed. The plates proved to be unnecessary since the belts have remained
intact after the plate removal.
During extremely cold weather, waste not cleaned off the pan conveyor
before the end of a shredder shift caused severe jamming during the next
shift. When the shredder was restarted with the retained waste frozen to the
pan conveyor, new waste could not pass down the conveyor and accumulated back
up into the shredder where the hammers compacted and forced it through the
grate causing severe jamming.
46
-------
SHREDDER
OSCILLATING SPRINGS
PINNED RETAINING
ARMS
SHREDDED
REFUSE
COLLECTING
CONVEYOR
BYPASS CHUTE
CONVEYOR PAN
BELT DRIVEN
ECCENTRIC SHAFT
ELECTRIC
MOTOR
EXTEND
FRAME
UNDER
MOTOR
CONCRETE
INERTION BLOCKS
ISOLATION
SPRINGS
Figure 22. Shredder discharge conveyor.
-------
The pan conveyor was designed to transfer from the shredder to the
rubber belt conveyor 283 cu. m (16,000 ft3) per hour of refuse shredded to a
bulk density of 240 kg/m3 (15 lb/ft3) for an equivalent mass flow of
68,000 kg per hour (150,000 Ib/hr). However, since the design bulk density
is much greater than the measured bulk density of 50 kg/m3 (3 lb/ft3), the
actual pan conveyor capacity is far below its design capacity. Although the
pan conveyor has jammed when the bulk densities are extremely low, 20 kg/m3
(1.3 lb/ft3), it has performed satisfactorily when the bulk densities are
about 50 kg/m3 (3 lb/ft3). Because of the reduced capacity of the entire
shredder system, the limiting effect of the pan conveyor on the overall plant
operation cannot be determined.
Jamming caused by variations in the waste density are especially critical
below the shredder discharge because of the small 46 cm (18 in.) clearance
between the vibrating pan and the shredder outlet. Since the shredder support
frame is directly above the pan, such jamming could be minimized by either
lowering the pan for more clearance or increasing its incline for better
flow. A preliminary study, however, indicated that the improved refuse flow
would not justify these costly modifications.
When waste jams below the shredder discharge, its removal requires from
8 to 24 hours because of the difficulty in gaining access to the constricted
area and the further compacting of the refuse by the shredder. To minimize
these jams, the plant personnel continue the pan conveyor vibration several.
minutes after each shredder shutdown and, as discussed above, no longer use
the truck bays which dump directly onto the storage pit conveyors. Conse-
quently, the bulldozers scatter and compact all refuse, particularly concen-
trations of such low-density material as paper and hay, so that the refuse
ultimately fed to the shredders is more homogeneous and has a greater average
density.
Rubber skirts installed at the base of the shredder have minimized, but
not completely eliminated, escaping dust and particles which scatter through-
out the shredder building.
Maintenance
The pan conveyors have required the normal amount of maintenance expected
with such vibrating equipment. However, the isolation springs and their
retaining bolts have broken frequently; heavier duty springs or an alternative
spring material could be substituted to minimize these failures.
Because of the severe service, overloading, and jamming, several links
on one of the pan conveyors have failed. In addition, one of the eccentric
drive shafts for the pan conveyor had bent excessively. Although the drive
shaft is one of the most carefully engineered components, this particular
shaft probably failed because of jamming where the waste compacted against
the shredder support beams so restricted the conveyor motion that the shafts
and links push against an unyielding mass.
The preventive maintenance schedule for these units is detailed in
Table 10.
48
-------
TABLE 10. VIBRATING PAN CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check for abnormal noise or vibration.
Make visual inspection for loose or missing bolts, linkages, or broken
spring units.
Lubricate pillow block bearings, connecting rods, and drive shaft
bearings. (LiEP2)
Quarterly
Check belts for tension and wear.
Semiannually
Grease motor bearings. (LiEP2)
Check motor, alarms, and interlocks.
Annually
Megger motor.
STORAGE AND RECOVERY MODULE
As represented by the shaded areas in Figure 23, the storage and re-
covery module was designed for a storage capacity of 1800 Mg (2000 tons) of
shredded refuse which would normally suffice for the continuous recovery of
shredded refuse at a controlled rate so that the thermal processing module
could continue operating during the night, weekends, and holidays when the
receiving and size reduction modules are not operating. The module was also
designed to remove large pieces of magnetic metal from the shredded refuse
stream.
The first of the functionally integrated components in this module are
two shredded refuse conveyors aligned in series: a horizontal conveyor which
collects the refuse from the shredder discharge conveyor and then an inclined
conveyor which, upon receiving the shredded refuse from the collection con-
veyor, elevates the waste to a transfer tower. Within the tower, the shredded
refuse is discharged near a magnetic drum separator.
49
-------
MAGNETICS
TIPPING
FLOOR
t
REFUSE
STOR-
AGE
PIT
SHREDDER
I
VACUUM BELT
FLOATATION
-J.J-
I I
CHAR
• MAGNET
GLASS
BURNERS
COMBUSTION AIR
GASES SOLIDS
-* KILN
SPILLAGE
&SLAG
BURNERS
QUENCH AIR
BOILER FEEDWATER
j
INDUCED
DRAFT
FAN
SHREDDER
BOILER
r- IVIU.L.I i _— ^_—
\
L •> FLY A^SH
rpnwo «^
i
i
1
l
i
i
i
\i J
__y_
)r
<\
N — JUG V
/
t
AL
MIZER
BOILER
DEHUMIDIRER
BOILER FEEDWATER
EXHAUST TO
ATMOSHPERE
Figure 23. Storage and recovery module (shaded area).
-------
While it was operative, the magnetic drum separator removed from the
refuse stream most of the magnetic metals and deposited them on a vibrating
screen conveyor which discharged metal pieces over 15 cm (6 in.) for truck or
hopper removal and returned the rest to the shredded refuse stream.
In the ductwork below the magnetic metal separating system are two flop
gates which operate in synchrony to direct the shredded refuse flow onto the
shredded refuse transfer conveyor for refuse transport to the storage and
recovery unit or to a bypass chute for direct refuse delivery to the kiln
feed conveyor in the thermal processing module. As discussed below, the
storage and recovery unit has been discontinued and only the bypass chute is
used.
When the silo storage and recovery unit was operating, the shredded
refuse transfer conveyor transferred the waste to a spreader at the top of
the silo for the even distribution of the dumped refuse on the silo floor.
Then, as detailed in the following subsections, the stored refuse was re-
covered for its discharge at a controlled rate onto the kiln feed conveyor.
The magnetic drum separator was discontinued for the threefold reason
that the magnetic accumulations in the drum impeded the drum effectiveness,
the vibrating screen conveyor plugged excessively, and, as discussed in the
section for the thermal processing module, the retention of the larger metal
pieces with their high densities facilitated the sinking and removal of the
kiln residue in the residue quench tank.
The normal usage of the storage and recovery unit terminated when the
wearout of the silo concrete floor precluded using most of the refuse recovery
(retrieval) equipment. Then after a short period of limited usage, various
operational difficulties prompted the discontinuance of the unit entirely.
Therefore, the module is currently used only to transport the shredded refuse
to the thermal processing module.
Shredded Refuse Conveyors
Except for their function, length, and powering, the three shredder
refuse conveyors—collection, elevation, and transfer—are basically the
same. The refuse discharged from the shredder falls vertically onto the
collection conveyor which in turn discharges the shredded refuse to also fall
vertically onto the elevating conveyor. The latter conveyor then transports
the waste up to the top of the transfer tower, shown in Figure 24. There, as
designed, the waste would pass near the magnetic drum separator for iron
removal and then the remaining refuse would be conveyed either to the storage
and recovery unit by the transfer conveyor or directly to the kiln feed
conveyor through a bypass chute.
Description
Manufactured by the Bulk Systems Division of the Jervis B. Webb Co.,
each of the shredded refuse conveyors is a rubber belt conveyor 1.9 m (6 ft)
wide with equal-leng'th, steel-roll, troughing idlers set at 35°. The
51
-------
Figure 24. Transfer tower.
troughing idlers are on 1.2 m (4 ft) centers except in the loading area where
they are on 0.6 m (2 ft) centers. The trough transition idlers at each end
of the conveyors consist of 20° idler rollers, and the return idlers are a
self-cleaning disk type. The head pulley on each conveyor is a crown-faced,
welded-steel, conveyor pulley with 1-cm (0.5-in.) thick, herring bone groved,
rubber lagging, and the take-up tail pulley is a bare-crown-faced steel
pulley. Two knife-edge, rubber counter-weighed belt wipers are installed in
series with the head pulley of each conveyor.
At each load transition point, the conveyors are enclosed by a hood
which is attached to a dust collection system and which was originally fitted
with rubber skirts. Further, each conveyor is enclosed entirely by a weather-
proofed gallery. In addition to weather protection, the gallery was designed
to contain waste spillage.
The collection conveyor is a 50-m (165-ft) long horizontal belt driven
at 88 m (290 ft) minute by a 7.5-hp electric motor. This conveyor runs
beneath the shredder discharge conveyors and perpendicular to its flow.
The elevation conveyor is a 50-m (165-ft) long, 20° inclined rubber belt
driven at 91 m (300 ft) per minute by a 20-hp electric motor.
The transfer conveyor is 37.4-m (123-ft) long, 20° inclined rubber belt
driven at 94 m (310 ft) per minute by a 7.5-hp electric motor.
52
-------
The progressively higher conveyor speeds, 88 m (290 ft), 91 m (300 ft),
and 94 m (310 ft) per minute, were intended to ensure that the waste dumped
at the transfer points would be carried away without any retained on a con-
veyor return run.
Operating Experience
The three shredded refuse conveyors were designed to operate 16 hours
per day, 6 days per week. However, because of the suspension of the storage
and recovery unit, only the collection and elevating conveyors are being run.
Further, because of the continuous operation of the size reduction module,
the latter two conveyors are being operated 24 hours per day, 6 days per week.
On the basis of bulk densities between 160 and 400 kg/m3 (10-25 lb/ft3)
the conveyors were originally for a capacity of 182 Mg (200 tons) per hour
that would handle the refuse of three shredders. However, since the measured
bulk densities have ranged from 18 to 80 kg/m3 (1-5 lb/ft3) these conveyors
would likely limit the waste flow if the existing two shredders were operated
at their design capacity. Moreover, if the third shredders were installed,
the entire shredded refuse conveyor system would have to be redesigned.
However, in view of the low shredder capacity, the conveyors thus far have
generally not had excessive lateral overflows due to volume overloading.
Consequently, whereas the conveyor system was overdesigned, it should be
capable of conducting the currently normal waste flow because of the reduced
shredder operation.
The three shredder refuse conveyors are so interlocked that the shutdown
of one stops the preceding conveyors to prevent waste from piling up.
Similarly, the elevating conveyor was interlocked with the magnetic drum
separator, and the transfer conveyor was interlocked with both a high-level
alarm and the discharge conveyor in the storage and recovery unit. When the
elevating conveyor was interlocked with the transfer conveyor, it could
continue running, regardless of the transfer conveyor operation, whenever the
waste bypass gate was open.
The refuse on the 20° incline of the elevating and transfer conveyors
have tended to slip on the smooth-faced belts or remain stationary with the
belt movement whenever the gravitational force exceeds the adhesion force.
Except for solid waste with an unfrozen moisture content between 10 and
40 percent, the refuse generally has insufficient adhesive force when it is
dry, frozen, or light with bulk densities such as those for paper and similar
materials. The resultant waste slippage has contributed to the jamming,
plugging, and overloading of the conveyor belts and transfer duct work.
Since the too-steep 20° incline cannot be reduced, the slippage could be
controlled only by roughing the belts or installing belt cleats. However,
such modifications have not been implemented because they would hamper the
effectiveness of the belt wipers and intensify the cleaning maintenance.
Most of the operational problems with the shredded refuse conveyors have
dealt with the control of waste spillage and dust, particularly at the
transfer points (Figure 25). These problems have been aggrevated by the need
53
-------
"7*
Figure 25. Refuse jam at the elevating conveyor discharge.
to remove the rubber skirts from the transfer hoods, as discussed below, and
the current ineffectiveness of the belt wipers on each conveyor. These
wipers have so worn that they no longer clean the belts and allow waste to
spill on the return runs of the conveyor belts.
The rubber skirts attached to the conveyor hoods at the transfer points
were designed to complement the dust collection system in containing the
large amount of dust lofted from the vertically falling waste. However,
these skirts had to be removed because their excessive drag on top of the
belt waste restricted the belt movement and caused the backup of light-
density materials.
To partially solve the waste spillage and dust problem, the pile height
on the conveyors was reduced by increasing the belt speed. This required
installing larger motors (5 hp vs. 2 hp) on the conveyor. However, because
of the increased oil viscosity in the gears, these motors are difficult to
start in cold weather. In addition, the increased motor torque requirements
at start-up, because of the faster belt velocity, have frequently caused
motor overloading and shutdown.
Since the shredded refuse conveyors form a single-line link with no
redundancy, any conveyor failure will shut down the waste preparation and
consequently the entire plant processing.
v.
-------
Maintenance
Except for the waste spillage and dust control, the shredded refuse con-
veyors have generally required only routine maintenance to keep the conveyors
lubricated and aligned. Jammings at the transfer points, particularly those
due to waste slippage on the inclined conveyors, have required 8 to 16 hours
to clean. Also, several lubricating fittings installed on the conveyor
rollers have had to be replaced because of their breaking off. In addition,
a set of pillow block bearings and a tail pulley have also had to be replaced
because of .failures likely due to highly abrasive glassy grit. The preventive
maintenance schedule for these conveyors is shown in Table 11.
Magnetic Drum Separator System
The magnetic drum separator was designed to extract magnetic materials,
particularly those which entered the refuse stream through the shredder over-
sized chute, from the discharge of the shredded refuse elevating conveyor and
then deposit the extracted materials onto the vibrating screen conveyor.
The vibrating screen conveyor was designed to divide the metallic mat-
erials deposited by the magnetic drum separator into two sizes: (1) materials
larger than 15 cm to be discharged into a truck or hopper for metal recycling
or disposal, and (2) materials smaller than 15 cm to be returned to the
shredded refuse stream for conveyance to either the storage and recovery unit
or to the bypass chutes.
Description
The magnetic drum separator consists of a 1.8-m (6-ft) diameter hollow
drum rotating counterclockwise at approximately 60 rpm with a stationary
magnet inside. The separator is suspended 0.5 to 0.6 m (20 to 24 in.) above
the head pulley of the shredded refuse elevating conveyor. As the waste is
discharged from the elevating conveyor to fall freely, the magnetic metals
are drawn and adhere to the drum at the 7 o'clock position while the remain-
ing refuse falls to the bypass chute flop gate below. As the drum rotates,
magnetic materials adhere to the drum in the magnetic field area and then
fall off onto the vibrating screen conveyor at the 4 o'clock position where
the magnetic field is no longer effective (Figure 26). Steel-plate vanes
0.6 m (2 ft) wide and 10 cm (4 in.) high along the drum circumference prevent
slipping materials from remaining in the magnetic field.
The separator is interlocked with the vibrating screen conveyor and the
sprinkler system so that it cannot operate unless the conveyor is running to
prevent depositing material on the inoperative conveyor, and the sprinkler
system is turned on to prevent the transfer of burning material.
Manufactured by Linkbelt-FMC, the vibrating screen conveyor is a floor-
mounted, single-decked, vibrating scalper screen with a 1.2-m (4-ft) by
2.4-m (8-ft) feed plate and a 1.2-m (4-ft) by 1.8-m (6-ft) screen area
yielding a total area of 1.2 m (4 ft) by 4.2 m (14 ft). The frame is a steel
construction, and the feed box has an abrasion-resistant renewable liner.
The screen openings were originally 15 cm (6 in.) square.
55
-------
TABLE 11. SHREDDED REFUSE CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check idlers, belt alignment, and neatness at tail pulley.
Check oil level in reducers. (Paradene 475)
Monthly
Check take ups for worn parts; idlers and cables to counterweight;
safety cables and cable switch boxes, connections, and especially
belt wipers.
Operate inspection gates.
Remove and clean breather cap on gear reducer.
Lubrication:
Head and tail pulleys, idlers and pillow blocks, and sprockets,
(LiEP2)
Take up cable pulleys. (Paradene 475)
Quarterly
Check V-belts.
Change gear reducer oil. (Paradene 475)
Semiannually
Grease motors. (LiEP2)
Check motor, alarms, and interlocks.
Inspect and lubricate pull cord switch.
Annually
Megger motor.
56
-------
NONMAGNETIC
REFUSE CHUTE
SHREDDED REFUSE
TRANSFER CONVEYOR
MAGNETIC DRUM SEPARATOR
VIBRATING
SCREEN
CONVEYOR
UNDERSIZE
MAGNETIC
METAL CHUTE
FLOP GATES
(IN BYPASS
POSITION)
BY-PASS CHUTES TO
KILN FEED CONVEYOR
Figure 26. Magnetic drum separator system and bypass chutes.
57
-------
Operating Experience
The separator was designed to be operated whenever the shredders were
running, that is, 16 hours per day, 6 days per week. However, because of the
operational problems, discussed below, and the poor quality of the recovered
metals, the separator operation was suspended.
With a burden feed depth of 0.4 m (16 in.), the separator was designed
to extract up to 12.7 Mg per hour (14 tph) of metals from a waste stream of
159 Mg per hour (175 tph). However, with these design requirements, waste on
top of magnetic materials was also drawn to the drum surface and carried over
into the recovered metal stream. This burden depth resulted in a 68 percent
recovery rate and the waste carryover decreased the metal purity to approxi-
mately 88 percent. Such impurity requires that the metal stream be. further
refined before the recovered metal can become commercially acceptable. While
the magnetic drum separator was operational, the conveyor, as designed, was
capable of matching the separator capacity of 12.7 Mg per hour (14 tph)
during the scheduled 16 hours per day, 6 days per week.
At the drum rotational speed of about 60 rpm, tin cans and other small
ferrous materials generally flew off the drum rather than falling off the
drum and onto the vibrating screen conveyor. To minimize this condition and
the resultant cleanup requirement, the drum was enclosed with a screen.
Consequently, after a steady-state condition developed within the enclosure,
all such materials fell onto the conveyor.
— In addition, because of the magnetic strength required for operation
with a 0.4-m (16-in.) burden depth, numerous metals drawn to the drum surface
became so magnetized that they stayed fast to the drum in such accumulations
that they retarded the effectiveness of the magnetic field and intensified
the cleaning maintenance. Moreover, steel components in the separator
structure became similarly magnetized to attract and retain excessive amounts
of metallic materials.
To prevent materials discharged by the magnetic drum separator from
accumulating on the sharp edge of the screen formed by its side board required
removing this board and any protrusions into the discharge path. In addition,
because of the insufficient clearance between the screen and "the discharge
duct work when the conveyor vibrated, several inches of plate had to be
removed from the ducts. The plate removal in turn required a rubber flap
installation to minimize leakage.
When rags, wire, and chain had continually plugged the screen openings,
the 15-cm (6-in.) squares were replaced with 15-cm (6-in.) wide slots extend-
ing the entire screen length. While the slots were intended to allow the
materials to slide through the inclined screen as the conveyor vibrated, the
materials continued to plug because of their draping over the screen-length
bars.
58
-------
For a short period of time, a steel plate was placed over the screen
openings on the vibrating conveyor to direct all of the recovered magnetic
metal stream to a truck through the oversize chute. This was attempted
because ferrous materials with alloy coatings, such as tin cans, have a
higher market value when recovered before thermal processing (which vaporizes
the alloys). The low purity of the recovered metal, discussed previously,
and the consequent problem of floating residue in the residue quench tank,
discussed later, have resulted in the suspension of the magnetic drum sepa-
rator system operation.
Future designs of magnetic drum separators should consider (1) reducing
the burden depth at the separator inlet so that with a smaller-strength
magnet (a) refuse would not be carried along with metallic materials to
pollute the metal stream and (b) materials would not be so magnetized that
they would adhere permanently to the drum surface, (2) establishing an
optimum drum rotational speed such that metal temporarily attaching to the
drum surface would fall off onto the vibrating screen conveyor rather than
fly away from the drum, and (3) constructing the drum of nonmagnetic
materials.
Since elongated materials such as wires and textiles are apt to bridge
and plug a screen, vibrating screen conveyors of the type described above
should be applied only when the appropriate material size is carefully
controlled. The basic parameters of such conveyors should be further re-
searched before applying existing designs or developing new ones.
Maintenance
Except for cleaning, the separator required minor preventive maintenance
(Table 12) during its limited operation. However, before the separator could
become operative during its initial start-up, a factory representative had to
'adjust the separator mechanism.
«
The vibrating screen conveyor had required continual checking and much
maintenance because of excessive drive belt wear and the difficulty in
keeping the belts on the sheaves. Since the drive motor is stationary while
the driven unit is on the vibrating pan, the varying drive belt tension
causes the belts to jump off the sheaves and, of course, sustain severe wear.
The preventive maintenance schedule for the vibrating screen conveyor includes
(1) semi-annual check of the motor bearings, alarm, and interlock and lubri-
cation of the bearings (LiEP2), and (2) annually megger the motor.
Storage and Recovery Bypass Chutes
The unit bypass chutes make up one of the two routes for the continuance
of the refuse and undersize magnetic metal streams after being discharged
from the shredded refuse and the vibrating screen conveyors, respectively.
The other route is to the storage and recovery unit. The following descrip-
tion covers the means of directing the refuse flow to one route or the other
as well as the bypass chutes themselves.
59
-------
TABLE 12. MAGNETIC DRUM SEPARATOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check reducer and chain.
Check oil level in gearmotor. (EPS)
Check bearing and chain lubrication. (Paradene 430)
Quarterly
Change gearmotor oil. (EPS)
S emiannually
Change bearing and chain oil. (Paradene 430)
Grease motor. (LiEP2)
Check output voltage and amperage to magnet for all three phases,
Lubricate off/on switch for magnet.
Check drum motor, alarm, and interlock.
Annually
Megger motor.
Description
As designed, the refuse discharged from the shredded refuse elevating
conveyor and the undersize magnetic metals discharged from the vibrating
screen conveyor were to be conducted to either of two routes by operating two
pneumatically controlled steel flop gates. The two flop gates are installed
at the junctions of the two sets of inverted Y-shaped duct work below the
elevating conveyor and the vibrating screen. One branch of the Y in both
sets of duct work discharges onto the shredded refuse transfer conveyor that
feeds to the storage and recovery unit while the other branch becomes the
storage and recovery bypass chutes which feed to the kiln feed conveyor
(Figure 26).
Again, as designed, the refuse was to be directed to the silo system
bypass chutes only when the silo system was inoperative or filled as deter-
mined by the chief operator in the control room. One switch controls both
gates so that all refuse flows to the same point. The bypass chutes are
30-inch-square, steel-plated ducts designed to handle refuse of average
density.
60
-------
Operating Experience
Refuse has frequently jammed in the ductwork because of (1) refuse with
low density, wires, or textiles, (2) the tendency for the gate to not shut
completely when the grate is being closed with refuse passing through the
ductwork, and (3) refuse slippage on the kiln feed conveyor. Consequently,
accesses with sliding doors were installed to facilitate the jam removals.
Moreover, although the gates were trimmed for adequate clearance (since they
were originally too large to allow for free movement), dust and grit entering
the pneumatic system near the gates have caused the gates to jam or shift
when in the bypass position. Such gate malfunctions have contributed further
to the refuse jamming in the ductwork. As previously suggested, a light
indicating the gate position should be installed to inform the chief operator
in the control room of the gate status.
The refuse fed directly to the thermal processing module through the
bypass chutes cannot be weighed since the routing of the chutes is beyond the
belt scale on this conveyor and the scale, according to its manufacturers,
should not be moved nearer to the conveyor discharge end. In addition,
bypassing the scale decreases the efficiency of the automatic process control
in the thermal processing system because the control in linking directly to
the belt scale depends on its weight measurement. These deficiencies could
be remedied by installing a second belt scale on the shredded refuse elevating
conveyor.
A baffle and rubber skirt were added to the bypass chute discharge above
the kiln feed conveyor to control the falling refuse. While this installation
minimized the waste spillage, it had a negligible- effect in containing the
dust.
Although the pybass chute duct work is generally satisfactory, future
designs should include the following to minimize jamming and the consequent
cleaning maintenance: larger ducts, smoother duct contours, and relief areas
in the ducts opposite the flop gates to prevent waste from accumulating
between the gate edge and the duct work wall when the gates are opened with
waste flowing in the duct work.
Maintenance
The bypass duct work and gates have required little maintenance other
than routine cleaning of the solenoid valves to operate the flop gates. The
operation of the solenoid valves, the air supply pressure, and the condition
of the pneumatic cylinders should be checked annually as a preventive main-
tenance measure.
Stored Material Spreader
As discussed in the next section, the operation of the storage and
recovery unit has been suspended indefinitely. While the system was opera-
tional the shredded refuse conveyor would discharge the waste at the top and
center of the silo shell. Then the refuse would fall onto a floor-centered
cone whose slope would cause the waste to slide toward the silo periphery.
61
-------
The stored material spreader, installed directly below the discharge area and
on the silo vertical centerline, was designed to further distribute the waste
to facilitate both the storage and the subsequent recovery of the refuse.
Description
The spreader was designed to distribute up to 136 Mg per hour (150 tph)
of refuse with a bulk density between 160 and 400 kg m3 (10 to 25 Ib/ft3) .
In its original configuration, the spreader was a two-arm rotary plow
which made one rotation a minute. As the waste pile rose to above three-
fourths of "the silo height, the rotary plow would force the uppermost waste
layers further toward the silo periphery. However, as explained below, the
spreader was modified to incorporate a rotary distribution chute. With the
two-arm plow left intact but not used and the spreader assembly still geared
to make one revolution a minute on the silo vertical centerline, the chute
was intended to make the waste distribution over the floor more uniform.
The chute assembly rotates on wheels with a discharge chute projecting
oblique (Figure 27).
Figure 27. Stored material spreader.
62
-------
Operating Experience
Throughout the spreader operation with both the two-arm rotary plow and
the rotary distribution chute, the lower-than-designed bulk density of the
waste distribution from the shredders had no appreciable effect on the
spreader performance.
While the two-arm rotary plow was effective in sweeping away the upper
layers of the refuse piles, it could not distribute the waste with the
desired uniformity. Consequently, rather than allowing the refuse to freely
fall and pile up, the rotary distribution chute was introduced to ensure a
uniform distribution.
During the initial rotary chute operation, the chute rotation was
hampered because the load concentration at the chute discharge imbalanced the
weight distribution on the wheels. Therefore, a three-point-support truck
wheel system was installed to ensure an even load on all wheels. In addition,
sealed bearings were installed in the chute assembly to minimize wear due to
pulverized glass. After these modifications, the rotary chute had no down-
time and required only the preventive maintenance detailed in Table 13.
TABLE 13. STORED MATERIAL SPREADER PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check condition of drive wheel, drive chain, gear reducer, and
carrying rollers.
Check oil level in gear reducer. (EPS)
Lubricate drive chain. (Paradene 430)
Semiannually
Change, reduce oil. (EPS)
Oil chain. (Paradene 430)
Grease cam followers and motor. (LiEP2)
Storage and Recovery Unit
The storage and recovery unit was designed to provide a 2-day refuse
supply that would permit the thermal processing system to continue operation
over the weekend when refuse was not delivered to the plant. However, when
the wear-out of the silo floor precluded normal waste recovery operations,
the silo was used only for emergencies such as when the bypass chutes jammed.
Then after a short period of such usage, the entire silo system operation was
indefinitely suspended.
63
-------
As discussed in the previous section for the stored material spreader,
the refuse initially dumped into the silo would fall about the floor-centered
cone and the successive dumpings would progressively more toward the silo
periphery. Therefore, the last deposits with their greater circumferential
distributions and floor area extent would be the first subject to the floor
removal operations. Consequently, the waste would generally be removed in
the reverse order of dumping or in a first-in last-out sequence.
Description
On the basis of a bulk density of 400 kg per cu m (25 Ib/ft3), the
storage and recovery unit was designed for a waste input of 181 Mg per hour
(200 tph), a storage capacity of 1815 Mg (2000 tons), and a waste output of
38 Mg per hour (42 tph).
Manufactured by Atlas, the silo is a steel-plated conical shell 18 m
(60 ft) high, with a 24 m (80 ft) diameter (which protects the refuse from
wind and precipitation) mounted above a concrete floor. As shown in the
cutaway view in Figure 28, the major silo components are (1) a floor-centered
hollow cone, (2) three sweep bucket chains, (3) a bucket chain-drive system
(pullering), and (4) a discharge drag, chain conveyor which extends in a
trough across the silo diameter and beneath the cone.
The floor-centered cone was designed to distribute the falling refuse
over the floor area and to serve as a pivot for the trailing end of the
bucket chain sweeps. Constructed of 0.6-cm (0.25-in.) steel plate and
anchored to the floor, the original cone has a 2.4-m (8-ft) base diameter and
a 3.6-m (12-ft) height. \
The sweep bucket chains were designed to pull the floor-level^refuse
from the pile and then push it and successively falling layers of refuse to
the discharge conveyor. Each chain consists of a series of rectangularly
shaped buckets each connected to its adjacent buckets by solid steel pins.
'iy
As discussed below, the original four chains with 10 buckets each were
replaced by three chains with 20 buckets each. With the front side and
bottom open, each bucket is fabricated of 1-cm (.375-in.) thick steel plates
which are mounted on 2.5-cm (1-in.) thick wear shoes. Each bucket (Figure 29)
is 46 cm (18 in.) wide, 81 cm (32 in.) long, and 40 cm (16 in.) high for a
volume of 0.15 m3 (5 ft3). The loading end of each chain was attached to the
chain-drive system which pulled the chains in a rotary sweep around the floor
while the trailing free-moving end tended to pivot about the floor centered
cone.
The chain-drive system consists of a motor-driven, wheel-mounted ring.
The ring ran between guide rails along the floor periphery and was driven by
two variable-speed D.C., motors, a 70 hp lead motor and a 30 hp support
motor.
Extending across the silo diameter and beneath the floor-centered cone,
the discharge drag chain conveyor runs in a trough constructed of abrasion-
resistant steel below the floor level. A tunnel beneath the trough provides
64
-------
STORED MATERIAL SPREADER
SWEEP PULL RING -
Ul
DRAG BUCKET CHAIN
CENTER CONE
DISCHARGE CONVEYOR TROUGH
SHREDDED
REFUSE
TRANSFER
CONVEYOR
GALLERY
KILN FEED CONVEYOR GALLERY
Figure 28. Schematic of the storage and recovery unit.
-------
FRONT VIEW
SIDE VIEW
BOTTOM VIEW
BUCKET TOOTH
BUCKET TOOTH
CONNECTING EAR
WEAR SHOES
Figure 29. Buckets used in the storage and recovery unit.
66
-------
for both the conveyor return run and personnel access. Steel bars were
spaced at intervals across the top of the trough to reduce the waste load
bearing on the conveyor. The conveyor consists of two runs of welded-steel,
box-type drag chains. In addition, the trough was equipped as follows with a
waste-level sensor installed near the drag conveyor discharge. A weighted
bar was pinned to the center of a freely turning rod which lies across the
trough. One end of the bar rests on the conveyor. When the cross rod pivots
with the rise or fall of the waste level, its rotation provided the means for
measuring the height of the waste level.
To supply the thermal processing system with refuse at the desired rate,
the discharge conveyor was regulated as follows by the control room operator.
First, the mass per unit time of the refuse carried on the kiln feed conveyor,
as indicated by the signal transmitted from the weight scale on this conveyor,
was compared with the corresponding mass per unit time established for the
thermal processing system. To match the respective mass rates, the speed of
the discharge conveyor was varied. Since the effectiveness of the conveyor
operation depended on maintaining the conveyor waste level at 90 percent of
capacity, the speed of the motor-driven ring pulling the bucket chains was
also varied according to the signal transmitted by the waste-level sensor.
The discharge conveyor and ring speeds could be regulated in an auto-
matic, a semiautomatic, or a manual mode. In the automatic mode, the ring
speed was automatically controlled to maintain the conveyor waste level at
90 percent of capacity. The operator established the mass per unit time for
the thermal processing system and the conveyor speed was automatically
adjusted for a waste discharge at a corresponding mass per unit time. In the
semi-automatic mode, the operator established the volume per unit time of the
waste to be discharged by the conveyor and the speeds of both the conveyor
and the ring were automatically controlled to maintain the set volume rate.
In the manual mode, the operator regulated the speeds of both the conveyor
and the ring to obtain a desired mass or volume rate. The control circuit
protected the conveyor from jamming in the automatic and semi automatic
modes, but not in the manual mode.
The discharge conveyor was interlocked with both the kiln feed conveyor
and the ring-drive system. The first interlock stopped the discharge conveyor
when the kiln feed conveyor was shut down and the second interlock stopped
the bucket chain sweeping when the discharge conveyor was not running.
However, the ring-drive system could operate in a timer mode which overrode
these interlocks so that the bucket chains could be pulled for 30 seconds
every 5 minutes to prevent their becoming fixed in the piling waste. The
ring-drive system was also interlocked with the shredded refuse transfer
conveyor so that this conveyor stopped when the drive system was not pulling
the bucket chains. Still another interlock was provided through a high-level
sensor in the floor storage area so that the transfer conveyor would stop
when the silo storage capacity was reached.
Operating Experience
After-the silo structure was erected, it had to be reinforced since it
was not designed to support the additional weight of the stored material
67
-------
spreader and the shredded refuse transfer conveyor at the top of the silo
cone.
Although the silo system had never been loaded to capacity, the measured
bulk densities indicate that it could have handled the design capacity.
While the shredder limitations precluded reaching the design input rate, the
system attained the design output rate under optimal conditions.
As stated above, the silo storage and recovery system was intended to
supply the thermal processing system with refuse over the weekend when no
refuse was being delivered to the plant. However, the refuse stored on
Monday in an empty silo would remain at the bottom of the pile until the
weekend when the silo was emptied. If the silo was not completely emptied
over the weekend, the refuse at the bottom of the pile would not be removed
for at least another week. In actual operation the silo was rarely emptied
and the refuse at the bottom of the pile remained in storage for several
months. The extended storage resulted in an extremely dense mass of refuse
that had to be removed manually.
In addition to the refuse compacting at the floor level because of
extended storage and the bucket action, the bucket function of loosening and
carrying the waste was further impeded because of the shredder failure to
perform to design specifications. Waste pieces larger than 15 cm (6 in.),
such as textile strands and wires, so intermingled with each other and other
refuse that they both made the bucket digging difficult and caused bridging,
especially along the silo walls, that prevented the waste above from falling
(see Figure 30). Moreover, as the pile diameters decreased, the refuse was
still more difficult to remove because of the fewer number of buckets con-
tacting the refuse in the bucket chain sweep. In the early silo operation,
the last 100 tons of waste had to be loosened with pitchforks before the
buckets could remove the waste (Figure 31).
On one occasion when shredded waste that had been stored in the silo for
several months caught fire and was thoroughly wetted by the fire department,
it became the equivalent of paper mache. The mass was so dense that several
hundred sticks of dynamite had to be exploded in the debris before it was
loose enough for manual removal.
The measured bulk densities of the refuse in the bucket chains were
about half the design densities. Moreover, the bucket breakup of the waste
compacted on the floor further decreased the bulk density of the waste re-
moved by the buckets. Consequently, to supply the discharge conveyor with
refuse at the design mass rates and to provide the additional bucket force to
break up the compacted refuse, the motor-driven ring for the bucket chain
sweeps had to be operated at speeds up to 4 times the design speed.
To limit the increase in the speed of the bucket chain sweeps, the
buckets, the bucket chains, and the bucket chain sweep area were all modified
to make the refuse removal more effective. To this end, teeth were installed
at the face of each bucket (Figure 32). Fabricated from 1-inch-square bar
stock, the teeth lengths ranged from 6 to 12 inches according to the chain
68
-------
OUTER SHELL
INNER SHELL
BUCKET CHAINS
Figure 30. Bridging of refuse against silo walls,
69
-------
Figure 31. Loosening of the waste in the storage and recovery unit.
Figure 32. Buckets undercutting the refuse pile in the silo.
-------
location of the buckets in which they were installed. However, the teeth
lost their effectiveness as they became bent. To improve the bucket per-
formance and wear, the manufacturer recommended using buckets twice as large
as the existing ones.
The bucket chain and the bucket chain sweep area modifications were
intended to increase the refuse removal capability by increasing the bucket
contact with the refuse pile. Accordingly, the original floor-centered cone
was replaced by a larger one with a 7-m (23-ft) base diameter and a 9-m
(30-ft) height to both reduce the sweep area and to cause a better waste
distribution for a proportionately greater bucket chain contact with the
refuse pile. Providing further increase in the chain-refuse contact was the
replacement of the original four chains with 10 buckets each by three chains
with 20 buckets each. The three chains rather than four were used in the
later configuration to prevent chain interference and jamming because of the
greater number of buckets in each of the three chains (Figures 33 and 34) .
The lack of sufficient operational time precluded determining the relative
wear of the three and four bucket chains.
Other changes to improve the waste removal operation included improving
the waste storage conditions so that the waste compacting could be minimized.
To this end, the silo was emptied periodically with intervals less than a
month, and the maximum amount of waste stored in the silo was limited to
450 Mg (500 tons).
The high speeds of the bucket chain sweeps greatly increased the wear
ratio of the bucket shoes and the silo floor. After tests indicated that the
shoe wear rates were such that the shoes would have an effective life of only
2 months, the geometries and materials for an alternative shoe were investi-
gated (Figures 35 to 38). As shown in Table 14, Astrolloy proved to be the
most desirable material. However, since this material would extend the
effective shoe life to only 5 months, it was unsatisfactory.
The floor wear was particularly important because of the high cost to
repair or replace the floor. Monsanto determined the floor wear rate by
measuring the elevation of the silo floor at various locations before and
after a certain period of operation (Figure 39). As shown in Table 15, test
results projected that the floor would wear out (floor level reduced by
100 mm (4 in.), after 80 operational days. This projection compared well
with the actual figure when the floor wear-out was evidenced by the exposure
reinforcing steel in the floor concrete. By this time, 67,000 Mg
(74,000 tons) of refuse had been processed for an equivalent of 80 operational
days with a refuse throughput of 907 Mg (1000 ton) per day. Much of the
high rate of floor wear was due to construction materials not being of the
high-grade, wear-resistant types recommended by the manufacturer. Although a
floor resurfacing with flint aggregate and epoxy binder would have extended
the floor surface life, it would still have worn out too soon if the high
speeds of the bucket chain sweeps had been continued.
71
-------
10 BUCKET CHAIN
REFUSE PILE
Figure 33. Ten bucket chains contacting the refuse pile in the silo.
Figure 34. Twenty bucket chains contacting the refuse pile in the silo,
72
-------
1
T
r—10"
8
Figure 35. Uniform width bucket wear show (type B).
73
-------
Va" R
»
T'
i'-io"
~7
B7A
Figure 36. Differential width bucket wear shoe (type C).
74
-------
CM
-55/8
Figure 37- Elongated bucket wear shoe (type D)
75
-------
2'-0"
CO
T
s
5%
Figure 38. Regular bucket wear shoe (type E).
76
-------
TABLE 14. LIFE OF BUCKET WEAR SHOES*
String Bucket
# #
1 1
2
3
4
5
6
7
8
9
10
2 1
2
3
4
5
6
7
8
9
10
3 1
2
3
4
5
6
7
8
9
10
4 1
2
3
4
5
6
7
8
9
10
U
Shoe
Type
C
C
C
C
C
C
C
C
C
C
B
B
B
B
B
B
B
B
B
B
D
D
D
D
D
D
D
D
D
D
E
E
E
E
E
E
E
E
E
E
Material
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
ASTRALLOY
ASTRALLOY
Tl-Steel
Tl-Steel
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
ASTRALLOY
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Tl-Steel
Life
(Hours)
6181
2809
1478
7083
8395
2481
2809
3222
3222
2229
1976
2481
1976
2229
1976
2073
2881
3076
1842
1552
3695
3076
4223
2437
2437
1475
1209
1225
1060
1129
3076
2054
4223
1965
2566
2172
1739
2352
1642
1603
*Monsanto Modification Evaluation^ A09-211, 10/4/76, Unpublished data.
77
-------
CONE
00
vw vjy v_y v^ v^
OUTFEED CONVEYOR
(18) (19)
SOUTHEAST
DOOR
Figure 39. Floor wear measurement points.
-------
TABLE 15. FLOOR WEAR DATA*
4/30/76 - 9/30/76
680 Hours of Operation
Point
2
3
4
5
7
8
9
10
11
12
13
14
15
16
17
18
19
21
23
Elevation
Difference
nun
4.57
7.32
8.39
14.94
36.27
36.27
4.27
5.79
5.79
5.79
5.79
4.27
6.71
6.71
11.28
14.94
19.51
1.22
19.51
Wear Rate
mm/ day
0.16
0.26
0.31
0.52
1.26
1.26
0.15
0.21
0.21
0.21
0.21
0.15
0.24
0.24
0.40
0.52
0.69
0.04
0.69
*Monsanto Modification Evaluation, A09-210, 10/4/76, Unpublished data.
79
-------
While the silo floor was still usable for bucket chain operation, floor
surfacing worn away from the top edge of the trough had exposed the trough
side plates to bucket snagging. Consequently, a sacrificial wear plate was
installed at the trough edge to protect the plates.
Occasionally when the discharge conveyor was not running, waste accumu-
lating above the trough had locked the conveyor in place. Since the piled
refuse precluded working from above, the conveyor had to be released by
jogging the drive motor at the motor site or by working in the access tunnel
to remove refuse through trough openings that were cut into the side of the
trough for such unjammings. The jamming was aggrevated when the bars across
the trough had to be removed because of oversize particles, such as textile
strands and wires, bridging over the trough and preventing refuse from
falling onto the conveyor. In addition, the high discharge conveyor speeds
required to meet the design refuse discharge ratio caused excessive wear on
the drag chains.
Refuse frequently jammed 'at the area where the discharge conveyor dumped
refuse into the hopper supplying the kiln feed conveyor. In this area, the
discharge conveyor passed under the silo shell and the discharge conveyor
drive motor. As the conveyor emerged from the silo where the piled waste had
compacted the refuse on the conveyor, the exiting refuse would expand and
contact the silo wall and drive motor above. The clearance was inadequate
because it was based on the design bulk densities which, as mentioned above,
were much more than those measured. In addition to a suggestion to increase
the clearance, the manufacturer had recommended using multiple discharge
conveyors to improve performance as well as to minimize jamming. Initially,
the hopper convergence made the jammings more severe. However, the hopper
was later modified to eliminate the convergence. Jammings at this area were
also caused by frozen or low^-density refuse slipping on the kiln feed con-
veyor. These jammings were prevented by coating the conveyor belt with belt
dressing (adhesives) and stationing a man at the site for refuse clearing as
jams started.
After the silo floor had worn out, the silo system was operated during
emergency situations only with a front-end loader used to push the refuse
onto the discharge conveyor. To permit the loader access and operation, a
door was installed in the silo wall and the bucket chains and floor-centered
cone were removed. While the discharge conveyor could be loaded properly,
the manual operation precluded using the waste discharge rate controls, and
the loader could not be operated when waste was dumped into the silo because
of the excessive dust. Ultimately, as mentioned above, the operation of the
entire silo system was suspended indefinitely.
Maintenance
The storage and recovery unit required extensive routine and emergency
maintenance. Much of the plant downtime during the early demonstration
period was due to failure in this system. The following paragraphs summarize
some of the more significant maintenance experiences.
80
-------
The bucket chains had to be frequently repaired or replaced because of
damage sustained when they were buried under the waste piles. The replace-
ment of the bucket wear shoes every 2 months requires about 100 man-hours.
One of the drive motors for the ring pulling the bucket chains had to be
rebuilt twice because of water damage when water backed up into the motor pit
when the wastewater lift station failed. To reduce the drive ring vibration,
the original drive sprockets for the ring were replaced with machine-cut
sprockets. The oil misters on these sprockets required routine repair and
dust and debris cleaning. The drive ring broke twice and had to be welded
each time. Although the wheels carrying the drive ring were routinely lubri-
cated and cleaned of debris, their bearings occasionally failed because of
glass grit. The guide rails for the drive ring had to be straightened
frequently.
Both the motor and the head pulley of the discharge conveyor had to be
replaced because of damage sustained when they were overloaded during con-
veyor jams. After the head pulley bearings and bearing grease seals failed
because of glass grit and had to be replaced, a shield was installed to
protect the bearings.
Table 16 summarizes the routine silo system maintenance recommended by
Atlas and Monsanto.
THERMAL PROCESSING MODULE
As indicated by the shaded areas in Figure 40, the thermal processing
module begins with the shredded refuse being conveyed to ram feeders for the
subsequent gasification and combustion of the refuse to yield gaseous products
for the production of steam in the energy recovery module and ends with the
boiler flue gases being cleaned of acid and particulate before their discharge
through a dehumidifier to the atmosphere.
In this module, much of the processing and equipment, particularly the
kiln, is unique to the Landgard process. The shredded refuse is thermally
processed to produce combustion gases with sensible heat and relatively inert
residue, that is, some uncombusted char along with ash and other inert solids.
Most, but not enough, of the acid and particulate in the boiler flue gas were
removed by the original wet gas scrubber. Of various modifications and
innovations to increase the particulate removal, only a surfactant addition
was able to reduce the particulate level of the gas to comply with Federal
standards but not enough to meet the State of Maryland requirements. Con-
sequently, it was decided to replace the scrubber with an electrostatic
precipitator.
As discussed in the preceding section, the shredded refuse was designed
to be fed from the transfer tower to either the storage and recovery unit
before its discharge onto the kiln feed conveyor" or the bypass chute for its
direct discharge onto the kiln feed conveyor. While the storage and recovery
unit was operative, a belt scale on the kiln feed conveyor measured the mass
rate of the refuse and thereby provided the means for controlling the amount
81
-------
TABLE 16. STORAGE AND RECOVERY UNIT PREVENTIVE MAINTENANCE SCHEDULE
Watch pull ring one complete revolution.
Inspect wheels for normal operation.
Listen for abnormal sounds.
Inspect sweep drive assembly, chain over sprockets, sprockets, keys
bearings, outfeed chain, outfeed drive and chain tension.
Check oil level in mist resevoir.
Weekly
Check discharge conveyor gear reducer and gear reducers in storage
section.
(Winter - Paradene 475)
(Summer - Paradene X1000)
Monthly
Check oil mist lubricator for proper function, (be sure it is misting)
the pressure should be 40 psi on top gauge.
Check Falk speed reducers for abnormal heat, noise, or leakage.
Check random pins on buckets for wear.
Lubricate drag and drive chain (Paradene 430).
Grease verticle wheel supports, thrust wheel axles, pillow block bearings,
and reducers (LiEP2).
Quarterly
Change oil in discharge conveyor gear reducer.
(Winter - Paradene 475)
(Summer - Paradene X1000)
Lubricate level paddle on discharge conveyor (LiEP2).
Semiannually
Check drive couplings, bucket wear plates, buckets for wear, grizzley
plates for wear and damage, pins on buckets, and replace as required.
Change oil in sweep speed reducer, and discharge conveyor.
(Winter - Paradene 475)
(Summer - Paradene X1000)
Check drive coupling lubrication (LiEP2).
Lubricate polyspeed motor on sweeps (LiEP2).
Check for contaminates.
•
Annually
Change drive couplings, lubrication (LiEP2).
82
-------
MAGNETICS
00
VACUUM BELT
FLOATATION
_-J.J.__
M_ _
- -J-T\^ •"- MAGNET
GLASS
BURNERS
COMBUSTION AIR
SPILLAGE ^. ,
&SLAG f»11" J
BURNERS [£
BOILER FEEDWATER
DEHUMIDIFIER
EXHAUST TO
ATMOSHPERE
Figure 40. Thermal processing module (shaded area).
-------
of refuse delivered to the ram feeders. However, with the discontinuance of
the storage and recovery unit, the mass rate of the shredded refuse stream to
the ram feeders can no longer be measured since the discharge of the silo
bypass chute is upstream of the belt scale design position.
The ram feeders were designed to convey the shredded refuse to the kiln
by extruding it through confining tubes in order to maintain an air seal
since the kiln operates under a negative pressure. Within the kiln, which is
declined and continuously rotating, the refuse tumbles forward while under-
going thermal reactions to first gasify most of the waste and then combust
enough of the gas and carbon char to sustain the thermal processes. As the
residue falls at the lower end into a water seal and quench tank with a drag
conveyor for the residue removal, the combustion gases exit at the upper end
to flow to the gas purifier. Fans supply the combustion air needed for the
kiln, gas purifier, and various burners which provide supplemental heat and
serve as ignition sources.
In the gas purifier, the combustion of the kiln off gases is normally
completed as molten slag in the gas stream is thrown to the vessel walls to
slide down to and out of a slag taphole. A two-fold screw conveyor in the
water seal tank of both the slag taphole and the feed hood at the upper and
refuse feed end of the kiln discharges the slag and other material into
trucks for landfill disposal.
Two quench air dampers were retrofitted in the exit duct of the gas
purifier to cool the gases sufficiently so that the initial slagging of the
boiler tubes with molten slag would be eliminated. The additional air also
completed the burning of any uncombusted gaseous products, As mentioned
above, the wet gas scrubber, designed to reduce the particulate concentration
in the boiler flue gases to prescribed levels, is being replaced by an
electrostatic precipitator. Just before the dehumidifier, which completes the
module, is the induced draft fan that pulls the combustion gases through the
entire module.
Much of the thermal processing module is unique and developmental, and
there is no redundancy in the module. Consequently, equipment and operational
malfunctions have been numerous, and their occurrences have been critical
since they have usually caused shutdowns of the entire plant. Among the
major or critical components causing plant shutdowns are the refractory in
the kiln and gas purifier, the ram feeders, the residue drag conveyor, the
two-fold screw conveyor, and the induced draft fan. Among the operational
problems have been the plugging of the slag taphole, which has caused plant
shutdowns, the poor control and instability of the kiln thermal processing,
and the excessive particulate level of the flue gases exiting the wet gas
scrubber.
Kiln Feed Conveyor
Designed to receive shredded refuse from either the discharge conveyor
in the storage and recovery unit or the by-pass chute, the kiln feed conveyor
transfers the refuse into the dual ram feed hoppers where the refuse is
forced into the kiln.
84
-------
Description
Except for its 1.2-m (4-ft) width, the kiln feed conveyor is the same
type of trough belt conveyor as the three shredded refuse conveyors discussed
previously. The kiln feed conveyor rises on a 22° incline for the first 32 m
(100 ft) and then smoothly levels to become horizontal. Its design average
and surge capacities are 39 and 57 Mg (43 and 63 tons) of refuse per hour.
In addition to emergency shutdown cords along each side, the kiln feed con-
veyor is interlocked with the ram feeder hydraulic pumps so that it stops
when the pumps shut down.
Operating Experience
Designed to operate continuously with the kiln, that is, 24 hours per
day, 7 days per week, the conveyor has generally operated according to this
schedule except for a seventh day each week reserved for maintenance during
the demonstration period.
The feed conveyor has had excessive spillage and slippage. Since the
bulk density of the refuse averaged 90 kg/m3 (5.6 lb/ft3) as compared to the
design bulk density of 208 kg/m3 (13 lb/ft3), the volumetric flow rate has
been inadequate when the conveyor operates at design mass flow rates causing
spillage. Spillage has been severe especially at the discharge of the by-
pass chute where the feed conveyor has insufficient clearance for low-density
refuse and at the feed conveyor discharge above the ram feed hoppers. To
reduce the spillage, the conveyor belt speed was increased to 60 mpm
(200 fpm).
As discussed above for the other inclined conveyor, slippage was due to
dry, low-density, and frozen refuse. To reduce the slippage, the rubber dust
curtains at the refuse transfer points along the feed conveyor were removed,
and the feed conveyor was sprayed with belt dressing (adhesive coatings) to
temporarily hold the refuse. However, the curtain removal allowed excessive
dust, particularly from the vertically falling discharge of the by-pass
chute, to disperse throughout the feed conveyor area.
Maintenance
Except for the following emergency situations, the kiln feed conveyor
has generally required only routine preventive maintenance (Table 11). On
three occasions, the conveyor was severly damaged by fire because of failure
of the induced draft fan or refuse combustion in the ram feed hoppers.
Possible means of preventing such damage would be using a pan conveyor in
conjunction with the feed conveyor or installing a gate to shield the con-
veyor belt.
Belt Scale
When the kiln feed conveyor carried refuse from the storage and recovery
unit, the belt scale on the conveyor sensed the mass per unit time and trans-
mitted a signal to the control room where the measured mass per unit time was
85
-------
compared with the corresponding mass per unit time established for the refuse
flow in the thermal processing system. If the two rates did not agree, the
speeds of the bucket chain sweep and the discharge conveyor in the storage
and recovery unit were changed accordingly.
Description
The belt scale is a Merrick Type L440E Weightometer incorporating a belt
speed sensor, a weight signal transducer, and a totalizer. The scale is
installed on an idler at an inclined part of the kiln feed conveyor.
Operating Experience
The belt scale had the same operational schedule as the kiln feed
conveyor. Except for the failure of one circuit board and a totalizer
measurement error of about 2 Mg (2 tons) per hour, the scale had no opera-
tional malfunctions or deficiencies. The totalizer measurement error was due
to the mechanic'al splicer on the conveyor which could be corrected by re-
placing the existing splices with vulcanized one.
However, the function of the scale had been limited to the refuse dumped
by the storage and recovery unit discharge conveyor. The scale placement is
below the discharge point of the by-pass chute, and the scale cannot be moved
above this point to weigh the refuse from the by-pass chutes because of the
scale operational requirement that the conveyor run be continuously straight
before as well as after the scale position. • Since the silo system operation
has been indefinitely suspended, the shredded refuse could now only be
measured by installing a belt scale on the shredded refuse elevating conveyor.
Maintenance
The belt scale has required only periodic cleaning and calibration,
monthly lubrication of the scale bearings, and semiannual lubrication of
the speed sensor.
Dual Ram Feeders
As the kiln feed conveyor discharges the shredded refuse into dual ram
feed hoppers, the ram feeder system serves the two-fold purpose of extruding
the refuse into the kiln and of so compacting the refuse during the extrusion
that the densified waste maintains an air seal for the kiln.
The kiln feed conveyor may also discharge the refuse onto a by-pass
chute which slides in and out of the feed shroud above the hoppers. The by-
pass chute was intended as a means of transfering refuse onto trucks for
landfill disposal when the storage and recovery unit was being emptied.
Description
With reference to the cutaway view in Figure 41, refuse dumped into the
feed shroud falls into two parallel, semicylindrical hoppers which are separ-
ated by a waste stream splitter. The ram feeder for each hopper is a
86
-------
FEED CHUTE
00
SIGHT PORT
HYDRAULICAU-Y
OPERATED
DIVERTER 1
QATE
FLOW SPLITTER
RAM CHUTES
(EXTENDING
INTO KILN)
ORIGINAL SHAPE
Figure 41. Schematic of the ram feeders.
-------
two-piece telescopic cylinder. The outer cylinder, 1.2 m (4 ft) in diameter
and 2.0 m (6 ft) in length, has side bars that move on nylon tracks along
slots in the hopper walls; and the inner cylinder, 0.6 m (2 ft) in diameter
and 0.8 m (2.5 ft) in length, also has side bars that similarly move on nylon
tracks along slots in the inner circumferential area of the outer cylinder.
When both cylinders are fully retracted, their front faces align with the
rear wall. As the two cylinders advance as a unit, they serve as a single
ram to push the refuse toward the outlet tube called a ram tube or snout.
Then when the outer cylinder stops at the limit of its travel, the inner
cylinder telescopes to act as a smaller-diameter ram.
Each ram feeder is activated under electrical control by a hydraulic
system which is powered by a 100-hp motor. With a capacity for 170 liters
(45 gallons) of hydraulic fluid per minute, each hydraulic system has a
pressure override that increases the normal pressure of 10,345 kPa (1500 psig)
to a maximum pressure of 20,685 kPa (3000 psig). The pressure override was
intended to clear refuse jamming in the ram tubes.
Each ram feeder operates independently of the other and has a variable
speed ranging from 30 seconds to 5 minutes per cycle. The independent opera-
tion and the variable speed were introduced both to adapt to a varying dis-
charge load into the two hoppers and to supply the kiln with a fairly steady
refuse flow. The ram feeders are interlocked to the kiln feed conveyor so
that a complete feeder shutdown automatically stops the conveyor. The
hoppers are also equipped with water sprays which can be manually activated
in the case of a fire in the ram snouts or hoppers.
As the kiln feed conveyor continuously dumps refuse into the feed shroud,
the waste falls directly into the hoppers or onto the cycling rams. When the
outer cylinder of each ram feeder reaches the limit of its stroke, the inner
cylinder telescopes under the continued hydraulic pressure to ram the refuse
toward and into the ram tube until it strikes a mechanical switch at its full
extension. Then the flow of hydraulic fluids reverses to retract the two
cylinders. When both cylinders are completely retracted to complete the
cycle, the start switch is activated to repeat the cycling.
The ram tubes extend from inside the ram feeder housing, through a feed
hood, and then into the kiln. The feed hood is aligned with and contiguous
to both the ram feeder housing and the kiln. Fabricated of 316 stainless
steel to withstand the kiln temperatures, the tubes are approximately 1.2 m
(4 ft) in diameter and 4 m (12 ft) in length, the tubes originally had
internal baffles to restrict and further compact the refuse for the kiln air
sealing.
Operating Experience
The ram feeders were designed for the same operational schedule as the
thermal processing; that is, 24 hours per day, 7 days per week. However,
because of the current plant operating and maintenance schedules, the ram
feeders run only 6 days a week but still 24 hours a day.
88
-------
Originally, the ram feeders were operated by a single set of controls in
the control room. To provide the control room operator with visual imagery
of the ram feeder performance, a closed-circuit television was installed with
the camera positioned at the feeder sight port. However, after the camera
was damaged several times by heat from fire that backed up from the kiln
during induced draft fan failures, the camera was removed. While it was
operative, the television monitoring did not provide an adequate view for
proper control. Consequently, because of the criticalness of the ram feeder
operation, a man was stationed at the sight port to inform the control room
operator of the continuous feeder performance, and manual pressure override
controls were installed near the feeders for local supportive control.
Among the operational problems has been the impossibility of conducting
preventive maintenance in the ram feeder housing while the feeders are
operating. In addition, when the feeders are jammed by waste that cannot be
cleared with the high-pressure override, the entire plant must be shut down
to allow manual removal of the waste jam. Also the reciprocating action of
the ram feeders has caused excessive wear on the electrical connections to
the mechanical sequencing switches mounted on the ram feeders.
Waste spillage behind and below the ram feeders poses a fire hazard.
Dust and glassy grit accumulate in the hydraulic pumps and cause severe wear
of all moving parts. The rotary equipment, therefore, should be placed in a
sealed enclosure or moved far enough from the waste stream. In addition, the
glassy grit severely abrades the nylon tracks that guide the motion of the
ram cylinders.
Because of faulty design or fabrications, the original ram tubes or
snouts, failed during the first heat-up when cooling water in the tubes
boiled and burst the tubes. Unknown to the operating crew, the escaping
water flowed into the kiln where it wetted the refractory lining as well as
the refuse and impeded the kiln processing. Consequently, the ram snouts
were replaced with newly designed ones made of 316 stainless steel. The new
snouts, however, became badly deformed from intense heat in the feed hood and
in the snouts themselves. Such heat (greater than 1000°C, 1800°F) was due to
kiln process upsets and refuse fires within the snouts during ram jammings.
As a result of the snout deformation, the refuse flow in the snouts be-
came so restrictive that numerous jams occurred within the snouts. To
allievate the constriction, the baffles inside the tubes were removed and the
snout ends were cut at a 45° angle (Figure 42). But then the waste compact-
ness and in turn the air sealing were so reduced that the air leakage into
the kiln increased the kiln processing temperature. To minimize the snout
deformation, Monsanto recommended that snouts be constructed of 330 stainless
steel and equipped with heat shields and ring stiffeners.
The hydraulic unit cooling system was originally a once-through water
system using City water. Because of the low pressures of the plant water
supply, the original system was changed to a dual system by adding a water
recycling system which will be discussed later.
89
-------
Figure 42. Deformed ram snouts.
To prevent refuse from falling onto a jammed feeder, a diverter gate
was installed on the outside wall of each hopper and at a level just below
the sight port (Figure 41). Each gate is a hinged flat plate which swings
to the waste stream splitter when actuated by a 25-cm, pneumatic-powered
cylinder controlled by a solenoid valve.
The hydraulic system seals have been damaged because of the corrosive-
ness of the Pydraul used as the working fluid in the hydraulic system. In
addition, glassy grit and dust have impeded the operation of the system
sequencing valve.
When only one ram feeder was operational from March 10 through
March 18, 1977, it had an average output of only 25.3 Mg per hour (27.9 tph)
whereas the design capacity for each feeder is 27 Mg per hour (30 tph).
The output capability depends on the moisture content and the bulk density
of the incoming refuse. At one point in time, water was added to the low
bulk density refuse to improve the performance of the ram feeders. During
the March operation, the moisture content was low compared with that in the
summer, and the measured bulk densities, as discussed above, were generally
much lower than the design bulk densities.
The hydraulic pipes originally installed on the ram feeders were
replaced with hoses to better absorb the hydraulic shock. These hoses,
however, frequently sustained leaks and breaks.
90
-------
Maintenance
The hydraulic system has required considerable maintenance. For example,
hoses have to be frequently repaired because of leaks or breaks sustained
from high fluid pressure and pressure shock pulses, and 0-rings have required
routine replacement. The preventive maintenance schedule for the dual ram
feeders is shown in Table 17-
TABLE 17. RAM FEED PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check cylinders and hoses for leaks or noise.
Check for smooth operation, visible wear, and neatness.
Check hydraulic package for pressure, leakage, noise, vibration, and
shock.
Check hydraulic oil level (Pydraul 50-E).
Monthly
Check pressure setting on hydraulic valves and notify instrument
technician to adjust as required to prevent system shock.
Check nylon shoes for wear - replace if necessary.
Check filters on the inlet and outlet of the pump (elements #361992 and
#923070); clean or replace as required.
Lubricate large guides (Pyroplex EP2).
Lubricate small guides (Molycote).
Semiannually
Test for wear and proper operation.
Change filter elements (#361992 and #923070).
Lubricate motors (LiEP2).
Check motor, alarms, interlocks, oil heaters, limit switch cables, low
hydraulic pressure.
Check and lubricate speed changer and indicator system.
Inspect all solenoid valves.
Clean and lubricate local control cabinets.
Annually
Megger Motor.
Grease motor bearings (LiEP2).
Calibrate ram feeder pressure gauges.
Change hydraulic reservoir fluid (Pydraul 50-E).
Review preventive maintenance schedule.
91
-------
Kiln
The shredded refuse extruded into the kiln by the ram feeders is dried,
pyrolyzed, and then combusted in a high-temperature, substoichiometric
atmosphere. After this processing, the ash, other inert solids, and some
uncombusted carbon char are discharged into a water quench for cooling before
their removal by a drag conveyor.
In the Landgard process, the primary release of thermal energy takes
place in the kiln during the endothermic pyrolysis reaction. In the kiln,
the refuse is exposed to high temperatures in an oxygen deficient atmosphere
and subsequently is chemically decomposed (pyrolyzed) into combustible,
pyrolytic gases, such as CH*,, H2, and other hydrocarbons. The heat to
pyrolyze the refuse is supplied by combusting the carbon char, remaining
after the pyrolysis reaction has been completed, and some of the pyrolytic
gases.
Air and fuel oil to burn the char and provide auxiliary heat are in-
jected at the discharge end of the kiln. The hot gas flow is counter to that
of the refuse, and upon exiting the kiln in the area above the refuse
entrance, the hot gases mix with air for combustion in the gas purifier
(afterburner) which produces a hot gas stream for energy recovery.
Description
As shown in the cutaway views of Figure 43, the kiln is a refractory-
lined, cylindrical, rotating, inclined vessel 6 m (20 ft) in diameter and
30.5 m (100 ft) in length. The kiln, along with the drive system and support
trunnions, was manufactured by Kennedy Van Saun. The kiln processing is
monitored by an optical pyrometer, thermocouples at each end of the kiln, and
an 02/C02 gas analyzer in the kiln feed hood. Burners at the discharge hood
supply heat for system heat-up and initial combustion. Variable-volume fans
inject combustion air into the kiln through inlets in the end of the discharge
hood and through an air bustle (Figure 44) around the seal at the discharge
end of the kiln.
The kiln shell is fabricated from 22 mm (0.875 m) thick mild steel with
the exception of the first 46 cm (18 in.) of the feed end which is fabricated
from 316 stainless steel. The ends of the kiln have stainless steel angles
mounted on the steel shell to help hold the refractory (Figure 45). Axial
slots 6 mm wide and 60 mm long in each end of the kiln on a 25-cm center
allow for thermal expansion of the kiln shell, particularly at these points.
The kiln is lined with a 23-cm (9-in.) layer of Kaiser stainless steel
fiber-reinforced, high-strength castable refractory. Variations in process
temperatures along the kiln length have required different refractory mater-
ials in each of the processing zones (Table 18).
The internal surface of the kiln has two types of projections, called
lifters, which move and disperse the trash in the vessel: plates or "flights"
at the feed end of the kiln and pipes, or "spikes", further down the kiln in
the processsing zone (Figure 46).
92
-------
.-
KILN FLIGHTS
RAM SNOUTS
EMERGENCY STACK
CROSSOVER DUCT
FEED HOOD
KILN SPIKES
9" CASTABLE
REFRACTORY
COMBUSTION AIR
BUSTLE
KILN LEAD BURNER AND COMBUSTION FAN INLET
/
REFUSE COMBUSTION AIR
FAN INLET
FIRE HOOD
KILN HEAT-UP BURNER AND
COMBUSTION FAN INLET
SIGHT PORT
OPTICAL PYROMETER
ACCESS DOOR
Figure 43. Schematic of the kiln.
-------
Fi8ure 45. Kiln discharp,
^^ durin§ "andby operation,
94
-------
TABLE 18. KILN REFRACTORY
Distance from
feed end (m)
0 -
0.7 -
6.2 -
9.8 -
17.1 -
29.7 -
0.7
6.2
9.8
17.1
29.7
30.5
Refractory type
type
Coarse
Coarse
Coarse
Coarse
Coarse
Coarse
26
26
26
30
30
30
Weight %
fiber
3
2
0
0
2
3
Type of
fiber
304
304
330
330
*
*
*
,'r
* Stainless steel
Figure 46. Kiln Flights.
95
-------
As waste is extruded into the kiln, the flights are designed to move the
refuse away from the feed area in order to minimize spillback into the seal
tank below the feed hood. The flights are arranged in a helical pattern of
six rows, each with twelve flights, spaced 1.3 m (51 in.) apart, the rows
form a 60° angle with the longitudinal axis of the kiln. The rows begin
0.5 m (1.5 ft) from the feed end and extend 5.6 m (18.4 ft) down the kiln.
Fabricated from 6-mm (0.25-in.) thick 330 stainless steel, each flight is
welded to a 76-mm (3-in.) schedule 80 pipe. The pipe is welded to a pipe
sleeve which in turn is welded to the kiln shell. While all plates are 76-cm
(30-in.) long, those near the feed end are 40-cm (16-in.) high in order to
pass under the ram snouts, and the rest are 60-cm (24-in.) high.
The spikes are designed to disperse the refuse so that more particles
are exposed to the hot gases for the greater efficiency and higher rate of
the processing reactions. The spikes are arranged in six longitudinal rows
which are evenly spaced around the kiln circumference. Starting 6.3 m
(21 ft) from the feed end and extending an additional 14.4 m (47 ft) down
the kiln, each row has eight spikes with 1.8 m (6 ft) between the successive
spikes. Fabricated from 330 stainless steel, each spike is 90-cm (36-in.)
high. Like the flights, each spike is a 76-mm (3-in.) schedule 80 pipe
welded to a pipe sleeve which in turn is welded to the kiln shell.
As shown in Figure 47; the rotary kiln is gear-driven by a 150-hp
electric motor beneath the kiln midpoint. A water-cooled eddy current coup-
ling (clutch) connects the drive motor to a variable-speed Falk gear reducer
which in turn drives a pinion gear. The coupling is protected by a pressure
switch that shuts down the drive system whenever the water pressure drops
below a preset level. At the midpoint of the kiln bottom, the pinion gear
meshes with a ring gear mounted around the kiln circumference. Enclosed in a
sealed shroud to prevent rain from entering the gears, both gears are
lubricated by a splash lubrication system.
The start-up sequence for the drive unit requires that the electric
drive motor be up to operating speed before the clutch is engaged. Therefore,
the kiln is equipped with a motor start/stop button, a speed control dial, a
start/stop button for the eddy current clutch, and a jog run selector switch
for the eddy current clutch. To start the kiln, the selector switch should
be in the jog position. After the motor is started, the clutch is engaged by
depressing the clutch start button. The speed control dial is then increased
from 0 to the desired operating speed. When the kiln is up to speed, the
selector switch is placed in the run position to complete the start-up
sequence.
As a back-up power supply in the event of motor failure, the kiln has an
air-cooled, 4-cylinder gasoline engine. This emergency drive system has a
clutch power takeoff, a positive drive coupling, and an electric start.
The kiln is supported by two pairs of trunnions that maintain the kiln
in position while allowing it to rotate. Each pair is approximately
7.6 m (25 ft) from the respective kiln ends with one trunnion in each pair
being 30° to one side of the longitudinal line along the kiln bottom and the
other trunnion being 30° to the other side (Figure 48). These trunnions
96
-------
PINION GEAR
EMERGENCY DRIVE
\
EDDY CURRENT GEAR REDUCER
THRUST ROLLERS
V
VO
FEED HOOD
RIDING RINGS
FIRE HOOD
*
TRUNNION
CARRYING
ROLLERS
Figure 47. Kiln auxiliary equipment.
-------
RIDING RING
vo
00
TRUNNION CARRYING
ROLLERS
Figure 48. Kiln Trunnions.
-------
contact two bearing rings which extend around the circumference of the kiln.
The rings slide around the kiln until the kiln shell expands at operating
temperature to form a "shrink" fit. Each set of trunnion bearings has an oil
bath lubricating system with cooling water tubes to maintain a constant
temperature.
A Leeds & Northrup optical pyrometer monitors the temperature of the
kiln refractory at the discharge end of the kiln. With a temperature range
from 590° to 1260°C (1100° to 2300°F), the pyrometer is water-cooled to
prevent heat damage from the high process temperature.
The negative pressure produced by the induced draft fan for the kiln
process is maintained by the air-sealed hoods at each end, that is, the
inlet or feed hood at one end and the discharge or fire hood at the other
end. The air sealing for each hood consists of a water seal at the bottom
and a triple-ply sheeting wrapped around the kiln at its junction with the
hood. The sheeting is formed so that it presses against the kiln circumfer-
ence when bolted to the hood. The three plies are two sheets of asbestos
cloth with a rubber-coated woven brass fabric between them.
Fabricated from reinforced carbon steel and lined with 23-cm (9-in.)
thick castable refractory, the feed hood is 2.7 m (9 ft) wide, 7.3 m (24 ft)
long, and 8.6m (28 ft) high. Its bottom water seal provides the means for
discharging spillback and dust from the kiln onto a screw conveyor (which
will be discussed later). On top of the hood is an emergency stack 2.4 m
(8 ft) in diameter and 3.4 m (11 ft) in height. A counterbalanced lid on the
stack is closed during normal operation and opened automatically when the
power fails or the main induced draft fan stops to allow the escape of
combustible gases. Operated by a pneumatic-powered cylinder under solenoid
valve control, the lid is air-sealed by a water trough into which the lid
fits.
Fabricated of the same materials as the feed hood, the fire hood has a
rounded top and is 8.4 m (28 ft) long and 7.8 m (26 ft) high; its width
increases uniformly from 1.2 m (4 ft) at the bottom to 1.4 m (5 ft) at the
top. The hood is submerged 5 cm (2 in.) in the bottom water seal which pro-
vides the means for discharging the kiln processing residue ash, other inert
solids, and some uncombusted char. In addition to an air inlet bustle, a
sight port, and the optical pyrometer, the hood contains kiln combustion
burners and air fans which will be discussed later.
As the shredded refuse tumbles down the kiln incline, it undergoes
thermal processing in three zoned, but somewhat overlapping, stages where the
temperatures progressively increase (Figure 49). The three stages are drying,
pyrolysis, and combustion. In the drying process, an endothermic reaction,
the heat is supplied by hot gases formed in the combustion stage. In the
pyrolysis process, also an endothermic reaction with the heat similarly
supplied by the hot gases from the combustion stage but at a higher tempera-
ture, the refuse is decomposed into combustible gases such as C02, CO, H2,
CH<,, and other hydrocarbons. In the combustion process, an exothermic
reaction, carbon char and some pyrolytic gases are combusted to provide the
99
-------
COMBUSTIBLE GAS
o
o
SOLID WASTE
HOT GASES
HEAT
H20
DRYING ZONE
HEAT
/ r
COMBUSTIBLE GAS
PYROLYSIS ZONE
AIR
RESIDUE
COMBUSTION ZONE
Figure 49. Kiln processing zones.
-------
heat for the endothermic drying and pyrolysis reactions and thus make the
entire processing sequence self-sustaining. The three thermal processes
are controlled by limiting the combustion air (supplied by the fans in the
kiln feed hood) to a fraction of the stoichiometric requirement.
The main method of heat transfer in the kiln is radiation, but some
convective heat transfer occurs between the refuse, the gases, and the
refractory within the kiln. The description of the thermal processes
occurring within the kiln are detailed in the kiln model (Appendix A) .
Operating Experience
As verified by the low carbon monoxide and detectable oxygen levels in
the kiln-off gas, the kiln functions more like a controlled air incinerator
than as a pure pyrolytic reactor. However, the kiln operation as a substoi-
chiometric pyrolysis reactor has two advantages over the typical incinerator
operation. First, since the amount of air flowing through the kiln is
limited with a consequent lesser turbulence and velocity of the gases,
fewer solids are entrained in the kiln-off gas. Second, since the combustion
air flows above rather than through the refuse bed, only small amounts of
particulate are lofted into the kiln-off gas stream. While a low-energy
scrubber could theoretically remove the particulate to comply with emission
standards, some metals in the refuse are reduced and vaporized in the kiln
because of the reducing conditions. This metal vapor is later oxidized in
the gas purifier which produces a condensation aerosol (similar to those
formed in incinerators) that is difficult to remove from the discharge
gases.
To complete the waste burnout while preventin-g the formation of slag
clinkers requires continuous regulation of the process control parameters
because of the variation in refuse mass rate, moisture content, and composi-
tion. The three basic process control parameters are the combustion air
supply rate, the kiln rotational speed, and the supplementary fuel rate.
The regulation of the combustion air supply controls the amount of
pyrolysis gas and carbon char combusted and in turn the amount of heat re-
leased and supplied to the drying and pyrolysis reactions. The air supply
regulation, therefore, is the primary means of controlling the reaction
rates of the three thermal processes.
As the kiln speed is increased or decreased, the retention time and
agitation of the refuse are proportionately more or less and, consequently,
the temperature and processing rate of the refuse are changed accordingly.
The kiln speed is varied primarily to provide fast response conditions
for the alleviation of crisis situations such as when large slag balls are
being formed luring process upsets (Figure 50).
101
-------
Figure 50. Kiln residue slag balls.
The processing heat can also be controlled by regulating the rate of
the supplemental fuel oil injected into the kiln. Such control, however,
is used only when other controls are not successful. Usually, supplemental
fuel is used during the kiln heat up before normal thermal processing of
refuse and during normal thermal processing to fire only the main kiln
burner and the safety burners. The safety burners were installed to prevent
explosive gas accumulations.
To ensure the proper and thorough thermal processing requires monitoring
the process performance indicators and accordingly adjusting the process
control parameters. A major indicator of proper process control is the
degree of residue burnout (residue quality). This is particularly important
since it affects the operation of the residue separation module. The
operation of this module, however, has been suspended indefinitely. When
the refuse is properly processed, there is a maximum heat release for
thermal recovery, a minimum putrescible content for landfill disposal, and
a minimum accumulation of unburned waste floating on the surface of the
residue quench tank. When the refuse is overly processed, the refuse tends
to fuse into large slag balls. Since these balls (sometimes larger than
1m, 3 ft) will not pass through the residue bypass and may damage the
residue tank conveyor, they must be removed from the conveyor by a mobile
crane. Currently, the residue quality is monitored visually by a man
stationed in the residue discharge area.
102
-------
The optical pyrometer was intended to sense the ash temperature so
that a low temperature would indicate a refuse underprocessing and a
high temperature would indicate a refuse overprocessing and conditions
for likely slag ball formation. However, when the pyrometer was originally
placed in the fire hood opposite the point where ash discharges from the
kiln and focused on the ash, it could not give valid measurements because
of particles lofted into the gas stream and slag accumulating on the
lens. After the pyrometer was moved to the opposite side of the hood
and focused on the kiln refractory lining, it operated satisfactorily.
The pyrometer was replaced once because of heat damage sustained when
the cooling water to the pyrometer stopped flowing.
As another important indicator for regulating the process control
parameters, the 02-C02 analyzers were intended to monitor the composition
of the kiln off-gas thereby indicating the amount of excess air in the
kiln. The analyzer has a water-cooled probe which is inserted into the
hot gas duct and an aspirator for extracting the gas sample. While the
analyzer has a much faster response to process changes than the temperature
indicators, it has never functioned properly because of the continuous
failure of its water-cooled probe.
Early in the demonstration, considerable kiln operational difficulties
occurred. While the kiln was designed for plug flow (Figure 49), a
vortex gas flow (Figure 51 developed in the pyrolysis and combustion zones.
This vortex allowed pyrolytic gases to flow to the combustion zone where
they were mixed with air and combusted resulting in extremely high tempera-
tures and, subsequently, slagging of the residue. It is also possible that
a pyrolytic gas and air mixture developed within this vortex and exploded
causing the large pressure pulses observed early in the demonstration.
To rectify this situation, an air distribution bustle was installed
around the circumference of the kiln at the discharge end. Combustion air
which originally entered the kiln as a concentrated steam is now distributed
around the circumference of the kiln. This modification has improved the
kiln operation considerably and also has a beneficial cooling effect on the
shell and refractory at the discharge end of the kiln.
During the plant shakedown, the kiln had numerous operational defi-
ciencies related to the integrity of the kiln refractory, the strength of
the flights and spikes, and the effects of high temperature on the kiln
shell. To whatever extent, faulty installation, improper material specifi-
cation, and process instabilities all contributed to the kiln failure to
perform as designed.
Supplied by General Refractory, the original kiln refractory was a
low-temperature type for the first 23 m (75 ft) beginning at the feed end
and a high-temperature type for the last 8 m (25 ft) extending to the fire
end. Before any waste was fired some refractory spalled off and after only
a bald spot developed. Since the spalling was due to improper installation,
the contractors agreed to a financial settlement. After refuse was fired,
103
-------
o
-p-
COMBUSTIBLE
_ GAS
SOLID WASTE
i
1
HOT GAS
/ \
/ \
| AIR/FUEL MIXTURE i
I /
\ /
\ /
^ COMBUSTIBLE f
i GAS '
AIR
^_
RESIDUE
Figure 51. Vortex gas flow in the kiln.
-------
other refractory disintegrations were due to ram -snout failures that allowed
cooling water to thermally shock and shatter the hot refractory. Consequently,
the first 8 m (25 ft) of the refractory from the feed end was replaced with
an A. P. Green coarse aggregate refractory. As detailed later, the last
meter (3 ft) of refractory at the fire end fell out because of the kiln shell
expansion at the high process temperatures. Although unsuccessful, segmented
castably refractory with floating anchors was tested in several configurations
to repair this fallout
Holes in the refractory for the flights and spikes provided breaks in
the refractory structure which widened whenever a flight or spike was
removed. Since the patches to fill these holes as well as those to repair
other areas continually fell out, the entire kiln lining was replaced with
the presently installed monolithic layer of refractory.
After 6 months of operation and many temperature cycles, the new
refractory was in good condition. Although there were minor cracks, no
large pieces of refractory had fallen out.
Most of the current refractory loss is due to spalling, particularly
during the heat-up arid cool-down cycle when the different coefficients of
expansion and contraction for the slag and refractory have the greatest
effect. When the slag and refractory cool off and the slag adheres firmly
to the refractory, the slag with its greater contraction cracks. Then, when
the kiln is rotated during the next heat up, the brittle slag breaks off
with a portion of the attached refractory.
The original kiln shell was fabricated of mild steel with 46 cm (18 in.)
on each end of the kiln made of 310 stainless steel. Since stainless steel
has a larger coefficient of expansion than mild steel, the kiln ends expanded
into a conical shape (Figure 52) when the kiln was hot. During one run, the
shell so expanded away from the refractory that about a meter of refractory
at the fire end fell out. This refractory was not replaced on the assumption
that the slag buildup would provide sufficient protection for the shell.
However, the kiln was so badly damaged during this run that the first 5 m
(16 ft) of the shell had to be replaced. To provide for the shell expansion,
the replacement was made of mild steel and the ends of the kiln shell were
slotted (Figure 52).
When the kiln was relined, the original 310 stainless steel spikes were
replaced with 330 stainless steel pipes. After 6 months of operation, the
spike deterioration was negligible except for some spikes that were bent by
a large slag ball rolling down the kiln.
Originally, the flights were constructed of 310 stainless steel and
each consisted of a plate welded to two posts. Also the original flight
arrangement was four rows of flights on the quarter points with the rows
extending axially from the feed end to 2 m (6 ft) beyond the ram snouts, or
4.5 m (15 ft) down the kiln. Although this configuration allowed considerable
amounts of refuse spillback, the spillback increased to an unacceptable
level when the flights were temporarily removed. Consequently, two alternate
flight designs were tested—one being a sliding plate supported by two posts
105
-------
o
o\
EXPANDED END
(WHEN HOT,
BEFORE SLOT)
REGULAR SHAPE
Figure 52.. Conical expansion of kiln ends and corrective slots.
-------
and the second, which was selected, being a plate welded to a single post.
In addition, the 4-row configuration was changed to the present 6-row
helical pattern. Moreover, the construction material for the flights was
changed from 310 stainless steel to 316 stainless steel and finally to
330 stainless steel. After six months of operation, the current flights
showed negligible deterioration.
During the shakedown, a new motor had to be installed in the electric
drive system. The dynamic coupling in the system has frequently overheated
when unusually low ambient temperatures have frozen the cooling water lines
to the coupling. Since the coupling overheating also interferes with the
feedback signal from the kiln drive, the speed controller does not sense any
kiln rotation, resulting in the controller excessively increasing rotational
speeds of the kiln.
The start-up of the kiln rotation has been difficult when slag buildup
has inbalanced the shell. It has also been aggravated when the start-up
procedures, such as jogging the drive and bringing the motor up to speed,
are not performed in the proper sequence described previously.
Continuously leaking of lubricating oil from the kiln ring gear required
three separate gear modifications, including replacement of the rain shield
over the drive gear, before the leak was finally stopped.
To ensure the capability of starting the kiln emergency drive, the
drive was originally equipped with a hand crank starter. However, this
manual starter was replaced with an electric one after many personal
injuries had been sustained during the cranking.
The kiln trunnions must be kept in nearly perfect alignment to prevent
excessive wear or overheating. Metal flaking off the trunnions and the ring
supports is a potential cause of equipment malfunctions. Graphite flakes
have proved to be more effective than powder in lubricating the ring supports.
During extremely cold weather, particularly when the system is cool and
water has not been drained from the system piping, the freezing of the
cooling coils for the trunnion lubrication bath has caused valves, couplings,
and pipes to break. To ensure effective operation when the system is hot,
the lubrication system for each trunnion is shielded from the heat radiated
from the processing kiln and gas purifier.
The kiln stack lid was originally lined with castable refractory. How-
ever, after the refractory deterioration had caused a lid imbalance which in
turn impeded the automatic system capability of opening the lid as required,
the refractory was successfully replaced with a blanket insulation held by
wire mesh. As a result of the exposure of the stack lid to severe heat and
flame when it is opened, the lid has become warped and the insulation lining
has fallen out twice. To maintain a seal with the warped lid, the level of
water in the seal trough at the top of the stack had to be raised. When
the lid opens, the escaping hot gases burn and damage nearby wires and other
equipment because of the low profile of the stack above the feed hood.
107
-------
For various reasons, the emergency stack lid has failed to open or has
been difficult to open. When the induced-draft fan has an emergency shutdown
and the stack lid fails to open, combustion gases accumulating in the kiln
produce a positive pressure. This positive pressure forces hot gases into
the ram tubes where the refuse ignites and the fire spreads to the ram feed
hoppers where it subsequently damages the rubber belt and the head pulley of
the kiln feed conveyor. In one instance, when a power surge overloaded the
equipment protection circuits, all the system equipment was shut off.
Although the induced draft was off, which requires that the emergency system
be activated, the air compressor which supplies the pneumatic force for the
lid opening was also off. Consequently, the kiln feed conveyor was so badly
damaged that refuse could not be processed for two days. This system would
work much better if the stack lid was designed to open by gravity when the
pressure was relieved from the cylinder.
The feed hood has had very few operational deficiencies. Although
large slag deposits accumulate in the hood, they have not adversely affected
the refuse processing or the integrity of the refractory lining. However,
when refuse is.being processed, the hood view ports serve little value since
the flames within the hood completely obscure the vision of the hood interior.
During the early stages of the demonstration period, pressure pulses
within the kiln caused the fire hood to vibrate so severely that it had to
be structurally reinforced. In addition, since the refractory brick in the
fire hood is not water resistant, all bricks wetted by the residue quench
water have deteriorated.
Originally, the circumferential shell-hood junction at each end of the
kiln was enclosed by a steel labyrinth seal. However, because of the insuf-
ficient clearance to allow for the thermal expansion while not restricting
the kiln rotation, the original seals were replaced with the triple-ply
sheeting of rubber coated woven brass fabric within two sheets of asbestos
cloth. The present seals, however, must be replaced six times a year because
of the damage sustained by the blowback of process gases, excessive heat,
and wear. Moreover, the replacement is excessively time-consuming and can
be made only when the system is cool. To minimize such damage and the
resultant downtime, a properly designed steel labyrinth could serve as a
protective base for the triple-ply seal.
The kiln has generally proven satisfactory for refuse handling and
thermal processing. While the refractory deficiencies have apparently been
remedied, desirable improvements would include better process control for
greater system stability, more effective gas temperature measurement and gas
composition analysis techniques and instruments, more extensive use of
automatic system controls, and closer operator monitoring of the entire
processing. Many of the kiln operational deficiencies will be discussed
later in the problem analysis volume of this report.
108
-------
Maintenance
After the modifications prompted by the demonstration experience, most
of the emergency maintenance in the kiln has been limited to trunnion mal-
functions because of freezing in the water-cooling coils. Except for the
replacement of the shell-hood junction seals, the other routine maintenance
requirements, namely those for repairing the kiln lining, aligning the kiln,
lubricating the moving components, and checking the electrical system, have
required normal time and effort. The preventive maintenance schedules for
the kiln and the kiln feed hood are shown in Tables 19 and 20 respectively.
The kiln fire hood preventive maintenance consists of zeroing, calibrating,
and checking the operation of the pressure indicator annually.
Gas Purifier
The kiln-off gases collecting in the feed hood are discharged through
the crossover duct into the gas purifier (see Figures 53 and 54). With
provisions for gas mixing and retention, the gas purifier, functioning
basically as an afterburner for the kiln-off gases, serves the two-fold
purpose of combusting all inflammable gases and of removing particulate from
the gas stream by a cyclonic action. The combusted gases are air-quenched
before being discharged to the boilers for energy recovery. The particulate
flows as liquid slag into a taphole where it falls into a water quench
within a seal tank below the gas purifier where it is removed by a screw
conveyor.
Description
The gas purifier is a horizontal, cylindrical, carbon-steel shell
sloped 4 percent toward the inlet end where the slag taphole is located
directly beneath the inlet port (Figure 54). Lined with a ring of high-
temperature, 23-cm (9-in.) thick alumina brick refractory, the shell is 16 m
(0.625 in.) thick, 5.5 m (18 ft) in diameter, and 15 m (50 ft) long, and has
a tangential inlet and an axial outlet. The gas purifier originally had two
semicircular baffle walls installed perpendicular to the longitudinal axis
of the vessel, one at the top of the vessel and the other at the bottom of
the vessel. The upper and lower walls were 5 and 7 m (16 and 23 ft)
respectively, downstream from the inlet, and the lower wall had a hole in
its base to allow slag to flow under it. The slag taphole was originally
1.4 m (4.5 ft) wide and 2 m (6 ft) long. Directly beneath the slag taphole
is the slag quench which, as part of the seal tank, will be discussed later.
The tangential inlet is formed by the crossover duct which connects the
kiln feed hood to the gas purifier. The duct, 2.1 m (7 ft) in diameter, is
lined with castable refractory 115 mm (4.5 in.) thick. Both the kiln off-
gas combustion fan and the dust collection fan discharge into the crossover
duct.
109
-------
TABLE 19. KILN PREVENTIVE MAINTENANCE SCHEDULE
Check all moving parts for lubrication.
Check water flow to trunnion bearings and couplings.
Lubricate the kiln helical girth gear and pinion through the inspection
door of the gear guard (Gulf EP115).
Be sure the supply of graphite slabs is ample to lubricate the tire for
one day.
Check and adjust if necessary the distance "x" on each carrying roller
assembly.
Observe the position of the trust tire with respect to the two thrust
rollers and adjust the carrying bearing slightly to "FLOAT" the kiln.
Check lubrication:
Carry roller bearings (EPS).
Gasoline engine (Super HDX20).
Weekly
Check emergency kiln drive:
Easily started.
Antifreeze during freezing weather.
Check the lubrication of helical ring gear and position (Gulf EP115).
Grease emergency drive shaft bearings (LiEP2).
Check drive reducer oil level.
(Winter - Paradene X1000)
(Summer - Paradene X1500)
Monthly
Grease thrust roller bearings (LiEP2).
Check emergency drive speed reducer oil levels.
(Winter - Paradene X1000)
(Summer - Paradene X1500)
Lubricate jaw coupling with open gear (800).
Quarterly
Grease drive shaft couplings and outboard bearings pinion shaft (LiEP2)
Apply molycote to tires.
~~CONTINUED
110
-------
TABLE 19. (Continued)
Semiannually
Complete inspection.
Check reducers.
Check oil in emergency drive engine (Super HDX20).
Change oil in auxiliary drive Falk speed reducer.
(Winter - Paradene X1000)
(Summer - Paradene X1500)
Change carry roller bearing roller lube (EPS).
Change oil in helical ring and pinion gear (Gulf EP115).
Lubricate output shaft spider under coupling guard at dynamatic and at
electric motor (LiEP2).
Check motor, alarm, interlock, speed tachometer, and speed indicator
alignment.
Alignment
Megger motor.
TABLE 20. KILN FEED HOOD PREVENTIVE MAINTENANCE SCHEDULE
Annually
Check operation of solenoid valve.
Check air supply pressure.
Check condition of pneumatic cylinder.
Check operation of electrical system.
Zero and calibrate feed hood off gas temperature indicator controller.
Zero and calibrate millivolt to current converter.
Check condition of thermocouple.
Zero, calibrate, and check operation of pressure indicator.
Ill
-------
Figure 53. Gas Purifier.
112
-------
GAS/PURIFIER PILOT BURNER
GAS PURIFIER START-UP BURNER
AND FAN INLET
9" BRICK
REFACTORY
THERMOWELL
SLAG HOLE
BAFFLE WALL
SLOTTED QUENCH
AIR DAMPER
DUST
COLLECTION
FAN INLET
CROSSOVER DUCT
CROSSOVER
COMBUSTION
AIR FAN INLET
BUTTERFLY VALVE
QUENCH AIR DAMPER
Figure 54. Schematic of the gas purifier,
113
-------
The axial outlet for the gas purifier has an inside diameter of
3 m (10 ft) and is sloped toward the inlet end to allow molten slag to flow
toward the slag hole. The outlet is refractory-lined with high-temperature
alumina brick 23 cm (9 in.) thick. A sample port for the C02 analyzer is in
the top of the outlet duct. The outlet duct makes a 90° horizontal turn 3 m
(10 ft) downstream of the gas purifier and connects to the refractory-lined
horizontal duct work to the boiler inlets. Two quench air dampers on the
90° elbow will be detailed later.
Two thermocouples project from the vessel side into the gas stream, one
midway and the other three-fourths of the way down the vessel length. These
thermocouples are enclosed in ceramic thermowells to protect them from the
high temperature and the corrosiveness of the process gas.
There are two sight ports for observing the slag hole, one directly
above the hole and the other in the vessel disc at the inlet end.
Operating Experience
Air from the dust collection and kiln off-gas combustion fans is mixed
with kiln off-gases in the crossover duct. As the mixture enters the gas
purifier, it is ignited by a pilot burner in the gas purifier. With the
entrained particulate maintained in a fluid state by temperatures of about
1300,C (2350,F), the combined tangential and gravitational forces throw the
fluid particulate to the walls. Then as molten slag, the removed particulate
flows down the sloped floor to the slag taphole and falls into the water
quench where it becomes frit.
When the flow rate and composition of the kiln-off gas vary, the combus-
tion air input must be delicately controlled to maintain the process tempera-
tures. The amount of excess air supplied for the combustion reaction can be
automatically or manually controlled to produce temperatures high enough for
the particulate maintenance in the fluid state, the most important condition
in the gas purifier operation. However, to produce such temperatures re-
quires operating near the peak of the stoichiometric curve with little or no
excess air because of the low heating value of the kiln-off gas. Such
operation is somewhat unstable since a low temperature could indicate either
too much excess air or insufficient combustion air for heat release. Conse-
quently, it is difficult to control the temperature automatically. Moreover,
since the air combustion is usually not completed because of the limited
excess air, some carbon monoxide and hydrocarbons escape in the exit gas.
Fuel oil is added to maintain the process temperature only when little or no
waste is being fed to the kiln and, consequently, less kiln-off gas is being
produced.
The amount of excess air in the gas purifier cannot be determined
reliably since the C02 analyzer, similar to the unit for the kiln, has
functioned sporadically. Consequently, other indicators of the gas purifier
performance have become more important in the monitoring needed to adequately
control the processing in the gas purifier.
114
-------
Since the kiln-off gas supplied to the gas purifier collects in the
kiln feed hood, the operational characteristics of the gas purifier can be
anticipated by monitoring the kiln. If the kiln is underprocessing the
refuse, the heating value of the kiln-off gas entering the gas purifier will
be very low. If the temperature is high, air has probably leaked through
the air seal at the ram feeders and combusted much of the pyrolytic gas in
the feed hood; therefore, the amount of combustible gas normally flowing to
the gas purifier will be severely depleted. In any event, the temperature
measured by the two thermocouples in the gas purifier is the primary indicator
of the gas purifier operation. Another important indicator is the condition
of the molten slag flow down the vessel walls and into the slag taphole as
observed through the view ports in the gas purifier.
The gas purifier was designed for a maximum temperature of 1540°C
(2800°F) and an average temperature of 1100°C (2000°F). However, to maintain
a fluid slag, the average operating temperature was increased to 1370°C
(2500°F) with some temperatures exceeding 1650°C (3000°F), the maximum temp-
erature of the thermocouple recorders. Consequently, the thermocouples
failed, and the high temperatures were the primary cause of failure of the
refractory in the gas purifier.
The design gas residence time in the gas purifier was 1.25 seconds, but
because of the higher temperature and mass flow rates, the actual operating
residence was reduced to 0.85 second. Although the reduced time limited the
degree of vessel combustion, it increased the amount of particulate removed
because of the greater intensity of the cyclonic flow.
During the demonstration period, the slag taphole frequently became
clogged with solidified slag that had chilled because of temperature fluctu-
ations during irratic operations. When operating, the vessel is filled with
flames that obscure vision of the hole. The feeding of refuse to the kiln
had to be interrupted daily for 15 minutes to determine the hole status.
However, since this procedure increases the temperature fluctuations and
therefore the conditions for slag chilling and clogging, an alternative
method should be developed for the hole monitoring.
The baffle walls were designed to make the temperature profile in the
gas purifier more uniform by forcing the stream of particulate-laden gas to
change directions. As described above, the original system had two semi-
circular walls separated by 2 m (6 ft) with one wall at the top and the
other at the bottom of the vessel surface to force the gas stream down and
then up. After the original walls were damaged, they were replaced by a
single donut-shaped 50-cm (20-in.) thick wall with a 3 m-(lO-ft) diameter
orifice in the wall center (Figure 55). Built with Charles Taylor Tamul
refractory brick, the new wall had an operational life of about 50 days.
Although most of the bricks had separated and fallen because of the slag
chemical effects which had deteriorated the bricks and etched out the mortar
between them (Figure 56), the bottom section of the wall remained intact
until the gas purifier was relined (Figure 57).
115
-------
Figure 55. Orifice baffle wall in the gas purifier.
116
-------
Figure 56. Deteriorated refractory and etched mortar in the gas purifier.
117
-------
Figure 57. Fallen orifice baffle wall in the gas purifier.
The operational life of the thermocouples inserted into the gas purifier
was only 7 to 10 days because of the high temperatures and the chemical
effects of the gas and slag. Many thermowell shields tested to protect the
thermocouples failed in a short time.
Initially, the slag flowed slowly in a thin film over the edge of the
slag taphole exposing a large surface area of the slag for possible heat
loss. While the solidification of the slag in the slag taphole could have
numerous causes, two possible causes were low slag hole temperatures due to
radiant heat loss to the quench water or the cooling effect of the relatively
cool steam evaporated from the quench water in the seal tank. To prevent
the solidifying, an oil burner was installed in the hole to elevate the
temperature. However, the long, narrow burner flame impinging on the hole
wall damaged the refractory and burner combustion air entering the hole
cooled and solidified the slag when the burner was not firing. Consequently,
the burner was removed.
After the failure of the burner to minimize the slag solidifying the
next efforts were intended to reduce the heat loss from the hole area and to
modify the conditions leading to slag solidfying. To this end, the size of
the slag hole was reduced and a cantilevered edge was built around the hole
so that the slag would fall more sharply into the hole. Also insulation and
a smooth lip made of A. P. Green 88P refractory were installed in the hole,
and a dam with a V-notch weir on two sides constructed of A. P. Green 90P
118
-------
refractory was installed around the hole (Figure 58). The dam and weirs
were designed to so converge the slag flow so that a smaller slag area would
be in contact with the cooling surfaces. Since the slag continued solidifying
over the hole, the dam height on the sides of the kiln crossover duct was
doubled to form a gas flow screen that would minimize particulate impingement
on the opposite side of the hole. The operational life of the dam is limited
to about 80 days because of erosion and the slag and gas chemical effects.
Figure 58. Slag taphole dam with V-notch weirs.
After the foregoing modifications also failed to prevent the slag hole
plugging (Figure 59), two propane burners were installed on the slag hole
sidewall, 90° to the right of the original burner position, and the original
oil burner was reinstalled. Although expensive, the propane burners have
good flame patterns for the hole application. After sustaining damage from
the high radiant heat in the gas purifier, these burners were shielded by
corrugated sheet metal. Before the oil burner was reinstalled, its air and
fuel pressures were modified to produce a bushy flame pattern. While the
oil burner was much more effective then before, the propane burners were
still needed intermittently to prevent the slag from plugging the hole.
With the mortar deteriorating more rapidly than the brick, the vessel
refractory lining thickness decreased about 1 mm (0.04 in.) each operational
day. Consequently, the refractory in the gas purifier has a very short
life. Moreover, the rising skin temperatures of the vessel as the refrac-
tory thickness decreases threaten the structural integrity of the vessel.
When skin temperatures as high as 370°C (700°F) were measured, the entire
vessel was water-cooled to protect it from thermal damage.
119
-------
Figure 59. Plugged slag taphole.
The saddle supports for the vessel could not maintain the proper align-
ment for the gas purifier because of the extreme vessel expansion and con-
traction. These thermal changes also caused a foundation pillar to crack.
Originally, the dust collection fan discharged into the crossover com-
bustion air fan which in turn discharged into the crossover duct. Since the
flow and pressure characteristics of the crossover combustion air fan were
such that excessive pressure pulses were produced in the kiln, the fan con-
figuration was modified so that the dust collection fan discharged directly
into the crossover duct, and, as recommended by Monsanto, the duct for the
crossover combustion air fan was reduced to one-third of its original size.
In addition to improving the gas mixing, these modifications helped to
equalize the temperatures in the gas purifier. To further reduce the pres-
sure pulses, a lattice wall was installed in the crossover duct. However,
when this wall proved to be of little value and became filled with slag,
and it was subsequently removed.
Many refractory failures occurred in the area where the crossover duct
enters the gas purifier because of the intense erosion due to the direc-
tional change of the gas stream.in this area and the high temperature due to
this area being immediately downstream of the combustion air inlets.
120
-------
Before the gas purifier performance can be considered satisfactory, the
slag hole plugging must be further reduced and the refractory lining must be
redesigned to minimize its current excessive deterioration.
Maintenance
Although the gas purifier required little routine maintenance (Table 21)
since it has no moving parts, the thermocouples and thermowells must be
replaced frequently, and the slag hole plugging must be checked and cleared
continually. The refractory repair and replacement continue to be the major
maintenance requirement.
TABLE 21. GAS PURIFIER PREVENTIVE MAINTENANCE SCHEDULE
Annually
Zero and calibrate:
Temperature indicating controller.
Millivolt current convector.
Off gas combustion air flow indicator and transmitter.
Check condition of thermocouple.
Zero, calibrate, and check operation:
Gas purifier pressure indicator.
Gas purifier discharge pressure indicator.
Combustion Air Fans
Six fans, three for the kiln and three for the gas purifier, supply air
for combustion of the shredded refuse in the kiln, the kiln-off gas in the
gas purifier, and the supplemental fuel oil in both the kiln and the gas
purifier. To permit the control of the combustion and thermal reactions, the
fans are each equipped with inlet dampers and/or manual slide gates whose
settings establish the volumetric rate of air intake and the distribution of
the discharged air, respectively.
Description
Each of the six fans is a centrifugal type manufactured by Chicago
Blower. The three fans for the kiln are a refuse combustion air fan, a
turbine-driven kiln combustion air fan, and a motor-driven kiln combustion
air fan. The three fans for the gas purifier are a gas purifier combustion
air fan, a crossover combustion air fan, and a dust collection fan. Except
121
-------
for the dust collection fan, the air flow rate of each fan is regulated by an
inlet damper. Fitted to each damper is an automatic Bailey pneumatic con-
troller whose damper adjustments are governed by the operator in the main
control room.
Located on the ground beside the kiln fire hood and driven by a 125-hp
motor, the refuse combustion air fan projects the air into a discharge duct
equipped with a manual slide gate. When the gate is open, the air flows in a
concentrated stream directly into the fire hood; when it is closed, the air
flows to an air bustle which directs the air around the circumference of the
fire hood for its uniform distribution within the kiln vessel.
To provide air for burning the supplemental fuel oil in the kiln heatup
and standby burner, the turbine-driven kiln combustion fan is installed
directly below this burner and discharges all air into its windbox. The fan
is driven by a Cappus Model RL steam turbine which is powered by steam from
either the atomizing steam boiler or the main waste heat boilers discussed
later.
To supply air for burning the supplemental fuel oil in the main kiln
on-stream burner and some additional combustion air for burning refuse in the
kiln, the motor-driven kiln combustion fan is installed directly below this
burner. Driven by a 40-hp motor, this fan projects the air into a discharge
duct equipped with a manual slide gate. When the gate is open, the air flows
to the burner windbox; when it is closed, the air flows to the air bustle in
the kiln fire hood.
To provide air for burning the supplemental fuel oil in the start-up
burner at the inlet end of the gas purifier, the gas purifier combustion air
fan is installed directly below this burner. Driven by a 100-hp motor, this
fan discharges all air into the burner windbox.
Designed to provide the gas purifier with the air for burning the kiln-
off gas, the crossover combustion air fan is located beneath the crossover
duct between the kiln feed hood and the gas purifier. Driven by a 125-hp
motor, this fan projects all air into the crossover duct which discharges
into the gas purifier.
Intended to provide additional air for burning the kiln-off gas in the
gas purifier, the dust collection fan is located below the ram feeder housing
behind the kiln feed hood. Driven by a 75-hp motor, this fan projects the
air into two discharge ducts each equipped with a manual slide gate. One of
these ducts terminates at an atmospheric vent near the fan, and the other
branches into two ducts both connecting to the crossover duct.
The five motor-driven fans are interlocked with the induced-draft fan so
that they will stop whenever the induced-draft fan has an emergency shutdown.
The turbine-driven fan has an overspeed safety device which stops the fan
whenever its speed exceeds a preset limit.
122
-------
Operating Experience
As described above, the air intake and distribution of the fans is
regulated by inlet dampers and/or manual slide gates in the discharge ducts.
The damper for the refuse combustion air fan is operated in either the
manual or the automatic mode. In the manual mode, the operator in the main
control room sets the control dial for the damper positioning at a desired
percentage of the air flow capacity. In the automatic mode, the damper
setting is automatically determined by the product of the mass rate of
refuse into the kiln as measured by the belt scale and a variable air-to-
refuse ratio set by the operator. Usually operated with a damper setting of
less than 50 percent, the fan has an operational range of 90 to 530 m3
(3,180 to 18,700 ft3) per minute. The manual slide gate in the discharge
duct is usually completely closed so that virtually all the air flows to the
air bustle for its uniform distribution within the kiln.
The damper setting for the turbine-driven kiln combustion fan, which
supplies air for the kiln heatup and standby burner, is automatically deter-
mined by the product of the rate of fuel oil into the burner and a variable
air-to-fuel ratio set by the operator. Usually operated with a damper
setting of less than 25 percent, the fan has an operational range of 120 to
370 m3 (4,240 to 13,070 ft3) per minute.
The damper for the motor-driven kiln combustion fan, which supplies
combustion air for both the kiln on-stream burner and the refuse burning, is
automatically set similarly as the damper for the turbine-driven kiln
combustion fan. This fan has an operational range of 160 to 680 m3 (5,650
to 24,010 ft3) per minute. The manual slide gate in the discharge duct is
generally nearly closed so that most of the air flows to the air bustle.
The damper for the gas purifier combustion air fan, which supplies air
to the start-up burner in the gas purifier, is automatically set in a manner
similar to the dampers for the two kiln burner combustion fans. While the
maximum capacity of this fan has not been measured, its minimum capacity is
335 m3 (11,830 ft3) per minute.
The motor for the crossover combustion air fan, which supplies air for
burning the kiln-off gas in the gas purifier, is usually off during operation.
When operated in the manual mode, the operator in the main control room sets
the control dial for the damper positioning at a desired percentage of the
air flow capacity. When operated in the automatic mode, the dampers were
automatically modulated to maintain a predetermined gas purifier temperature.
The fan has an operational range of 225 to 670 m3 (7950 to 23,660 ft3) per
minute.
As mentioned above, the dust collection fan is not equipped with an
inlet damper. The manual slide gate in the duct to the atmospheric vent is
rarely opened, and the similar gate in the discharge duct which branches
into two ducts connecting to the crossover duct is always opened. This gate
is usually at a fixed position since adjustments have a negligible effect on
the airflowI
123
-------
Since the fan selection was based on the required maximum capacity plus
a large safety factor rather than on the operational range, the minimum
capacities of the fans have exceeded the normally required operating flow.
The capacities of the crossover combustion air fan and the gas purifier
combustion air fan were especially high since the kiln-off gases required
less air than estimated for total combustion. The high capacity of the
former fan produced a back pressure in the crossover duct which in turn
produced such a positive pressure in the kiln feed hood that pyrolytic gases
were forced through the kiln air seal. Also, the high capacity of the
latter fan so projected the flame front into the gas purifier that the
temperature at the inlet was lower than those downstream. Consequently, the
motor for the crossover combustion air fan is usually off, and the motor for
the gas purifier combustion air fan is now used only during heatup and
standby operation.
Designed primarily to induce the air flow through the cyclone dust
collectors in the size reduction and the storage and recovery modules, the
dust collection fan originally discharged into the inlet of the crossover
combustion air fan located beneath the crossover duct between the kiln feed
hood and the gas purifier. However, when the operation of the crossover
combustion air fan was discontinued, two discharge ducts connected directly
to the crossover duct replaced the one to the inlet of the crossover com-
bustion air fan. The new ducting had the two-fold purpose of providing two
balanced-in jets whose direct discharge into the duct would improve the
mixing of the kiln-off gas and the combustion air and of eliminating dust
accumulation in the crossover combustion air fan.
In addition, to prevent pressure pulses within the kiln vessel from
flowing back through the fans, orifice baffles were installed in the two
kiln burner windboxes, and a diverter baffle was installed in the discharge
duct of the refuse combustion air fan. However, these baffles caused higher
discharge velocities and backpressures on the fan side of the baffles.
As mentioned previously in the section on the kiln, the air bustle was
retrofitted in the kiln fire hood to improve the stability of the combustion
and thermal reactions within the the kiln. Since the air bustle with its
more uniform distribution of the air flow improved the efficiency of the
combustion air usage as well as the stability of the combustion processes,
it reduced the amount of combustion air needed. In addition, the improved
airflow has minimized residue slagging at lower feed rates.
Although the wire mesh filter screen on the end of the atmospheric vent
for the dust collection fan clogs rapidly, it is very inefficient since most
of the particulate is fine dust. Consequently, a more effective type of
filter system is needed.
Pieces of rag and dust accumulating on the dust collection fan rotor
caused blower imbalance and frequent cleaning. After glass grit falling
from the ram feeder housing had abraded the fan bearings, a protective roof
was installed over the entire dust collection fan assembly.
124
-------
Maintenance
While the dust collection fan must be cleaned regularly to prevent
severe vibration, shaft misalignment, and bearing damage, the other fans have
required only scheduled preventive maintenance (Tables 22 and 23). The
Bailey pneumatic controllers have occasionally required corrective maintenance
to remedy malfunctions due to their operation in a dirty environment. How-
ever, routine prevention maintenance has generally sufficed for their proper
functioning.
Burners and Supplemental Fuel Systems
The burners in the kiln and gas purifier were intended primarily for the
two-fold purpose of providing the heat to initiate the thermal processes
and then, after the thermal reactions become self-sustaining, of serving as
ignition sources. The reactions are self-sustaining when the gasification
is sufficient to drive the endothermic processes in the kiln and to maintain
the process temperature in the gas purifier (afterburner). This condition
usually takes effect about 45 minutes after the ram feeders have started
extruding the shredded waste into the kiln.
Description
Except for two propane burners, the 11 kiln and gas purifier burners
are part of the No. 2 fuel oil burner system. This system includes a storage
tank, two parallel fuel oil pumps, a receiver (accumulator) tank, two kiln
main burners, four kiln safety pilot burners, a gas purifier main burner, a
gas purifier pilot burner, and a slag taphole burner. In addition to the
two propane burners which are also used for the slag taphole, the propane
burner system consists of three propane storage tanks and a vaporizer unit.
The fuel oil storage tank, which also supplies the fuel to the steam-
atomizing boiler, is above ground at the rear of the plant about 300 m
(1000 ft) from all processing vessels. The tank has a working capacity of
453,600 liters (1200,000 gallons) and a total volume of 502,740 liters
(132,825 gallons). The tank, constructed of 5-mm (0.25-in.) carbon steel,
is equipped with a digital readout level indicator.
Supplying all fuel oil burners, the two fuel oil pumps are Worthington
centrifugal units. Installed on a slab near the storage tank, the pumps
have parallel piping to permit the operation of one pump while the other
serves as a spare. However, the pumps can be operated simultaneously for
maximum oil flow. Each pump is powered by a 20-hp motor and has a capacity
of 1,890 liters (500 gallons) per minute at a pressure of 1,035 kPa (150 psig)
and a fuel oil density of 875 kg m3 (54.7 lb/ft3).
Installed in the kiln fire hood, the two kiln main burners are steam-
atomized 95,000 MJ/hr (90 M Btu/hr) John Zink units: one is the heatup and
standby burner usually set at 69,000 MJ (65 M Btu) per hour and the other is
the on-stream lead burner usually set at 13,000 MJ (12.5 M Btu) per hour.
Each burner 'is equipped with a flame scanner, FIA Safety controls, and a
125
-------
TABLE 22. PREVENTIVE MAINTENANCE SCHEDULE
Kiln Combustion Air Fan, and Turbine
Check oil level in turbine and governor.
Monthly
Check bearing and turbine for vibration or excessive heat, and reducer
oil level.
Lubricate fan bearings and coupling (LiEP2).
Change the oil in both reservoirs on the turbine and check for any
moisture (Paradene 430).
Semiannually
Change reducer oil (EPS).
Grease motor (LiEP2).
Annually
Zero, calibrate, and check operation:
Fan discharge pressure indicator.
Steam to kiln combustion air fan turbine pressure indicator.
Clean, lubricate, and calibrate:
Air supply pressure to inlet vane drive.
Kiln combustion air fan low discharge pressure alarm.
Kiln combustion air fan low discharge pressure switch.
126
-------
TABLE 23. PREVENTIVE MAINTENANCE SCHEDULE
Refuse, Kiln, Crossover, Gas Purifier Combustion Air and Dust Collection Fans
Monthly
Visually check V-belts for tension and wear.
Check bearings and motors for vibration or excessive heat.
Lightly grease refuse air fan bearings (LiEP2).
Quarterly
Grease wheel shaft in kiln, gas purifier, crossover combustion
air, and dust collecting fans.
S emiannually
Check motor, bearing condition, alarms, and interlocks.
Annually
Check V-belts for tension and wear.
Check bearings and motor for vibration.
Clean balance rotor if necessary.
Megger and lubricate motor (LiEP2).
Zero and calibrate:
Temperature ratio station.
Current to pneumatic convector.
Clean, lubricate, and check air supply pressure to inlet valve drive
unit.
Zero, calibrate, and check operation of pressure indicator.
127
-------
high-energy ignitor. The ignition of each burner is controlled locally by a
free-standing.control panel and remotely by the control room.
Located in the kiln feed hood, the four kiln safety pilot burners are
steam-atomized Peabody units each incorporating a combustion air fan and
having a fixed firing rate of 74 MJ (70,000 Btu) per hr. While the ignition
of each burner is controlled remotely by the control room, the combustion air
for each is regulated by a control on the burner assembly.
The main, or start-up burner for the gas purifier is a steam-atomized
John Zink unit with a capacity of 169,000 MJ (160 M Btu) per hr. The start-up
burner is in the center of the inlet of the gas purifier. Immediately above
the start-up burner is the pilot burner for the gas purifier. Also a steam-
atomized John Zink burner, the pilot burner has a fixed firing rate of
1,055 MJ (1 M Btu) per hr and an induced draft since, unlike the start-up
burner, it does not have a fan source supplying combustion air. Like the two
kiln main burners, the two gas purifier burners are each equipped with a
flame scanner, FIA safety controls, and a high-energy ignitor. Also the
ignition of each of the two gas purifier burners is controlled locally by a
free-standing control panel and remotely by the control room.
The fuel oil burner installed in the slag taphole is a Peabody RIO
steam-atomized unit with a fixed firing rate of 3,200 MJ (3 M Btu) per hr.
Equipped as the two kiln main burners, this burner also has a horn to sound a
flame failure and a built-in combustion air fan with local start/stop con-
trol. The ignition is controlled locally by a free-standing control panel.
Located about 50 m (165 ft) from all processing vessels, the three
propane storage tanks each have a capacity for 1,890 liters (500 gallons).
Operated nearby and in conjunction with the slag taphole fuel oil burner, the
two propane burners (Figure 60) are John Zink units. Equipped with a flame
scanner and a solenoid-operated shutoff valve, each of the propane burners
has a capacity of 3,165 MJ (36 M Btu) per hr.
Operating Experience
Except for the fuel oil storage tank overflowing through the fill line
and an incident when vandals closed the manual valves in the fuel oil pump
lines while the pumps were operating, there were no disruptions in the tank
and pump operations. The tank overflowing was remedied by installing a check
valve in the fill line.
The firing rate of the kiln heatup and standby burner is manually set at
a desired percentage of its capacity. Since this burner has the primary
purpose of maintaining the kiln temperature when refuse is not being pro-
cessed it is usually turned off when the kiln reactions become self-sustaining.
The burner nozzle was modified several times before the current tip was
installed to produce a long 12-m (40 ft) cylindrical flame pattern.
128
-------
Figure 60. Propane burners in the slag taphole.
Like the kiln heatup burner, the firing rate of the kiln on-stream lead
burner is manually set at a desired percentage of its capacity. While this
burner was intended to ignite any .combustible gases accumulating in the kiln
fire hood and to provide supplemental heat for sustaining the thermal pro-
cessing in the kiln vessel, its need is questionable since the kiln thermal
reactions have been self-sustaining and the combustible gas accumulations are
unlikely because of the high temperature and turbulence in the fire hood.
Moreover, the kiln has operated satisfactorily without the firing of either
of the two main burners. The nozzle for this burner was also modified
several times before the current tip was installed to produce a short
spherical flame pattern.
The four kiln safety pilot burners were intended to ignite any com-
bustible gas/air mixtures that might develop in the kiln feed hood because of
air leaking through the ram feeder and hood seals. However, like the kiln
on-stream lead burner in its function as an ignition source, the need for the
safety burners is also questionable since the development of the explosive
gas pockets is unlikely with the prevailing high temperature and turbulence
in the feed hood.
129
-------
Nevertheless, the additional safety factor that these burners provide
may outweigh their cost. The original induced-draft, John Zink safety
burners were replaced with the current Peabody burners, each incorporating a
combustion air fan. The original John Zinc burners relied on induced-draft
openings for combustion air. However, when positive pressure pulses occurred
within the kiln, the hot pyrolytic kiln gas blew back through the burners
extinguishing the flames and thermally damaging the burners. These burners
were replaced with the Peabody safety burners described earlier because the
combustion air fan incorporated into each burner prevented any blowback
through the burners during positive pressure pulses within the kiln.
As designed, the gas purifier start-up burner has provided the heat to
establish and maintain the process temperature of the gas purifier exit gases
whenever there is an interruption of the refuse processing within the kiln.
As the thermocouple at the rear of the gas purifier senses the process
temperature and transmits a corresponding signal to the control room, the
control system automatically adjusts the burner firing rate whenever the
process temperature varies from the temperature set by the operator.
The need for the gas purifier pilot burner, whose prime purpose is to
serve as an ignition source, is questionable since the process temperature
established by the gas purifier start-up burner, 1300°C (2350°F), is suffi-
cient to ignite the kiln-off gas. In fact, the gas purifier has frequently
processed the kiln-off gas satisfactorily without the firing of this burner.
Moreover, any of the three burners in the slag taphole could serve as the
ignition source.
Intended to minimize the solidifying of the molten slag in the slag tap-
hole, the Peabody fuel oil burner installed in the hole is operated contin-
uously during standby and deslagging periods as well as during the kiln-off
gas processing.
Operated intermittently whenever solidified slag begins to accumulate,
the two propane burners in the slag taphole have a fixed firing rate. The
air inlet to each burner is regulated so that the minimum amount of air may
enter the hole and cool the slag whenever the burner is off.
The burner ignition system has proved extremely unreliable because of
the apparent underdesign of the ignition transformer, the exposure of
circuits and contacts to weather, the deterioration of the ignition wire
insulation, and the operational complexity of the ignition cycle.
Since many fuel oil burner malfunctions have been due to the steam
fouling of the burner filters and strainers, several operators have stated
that air atomizing would be preferable to the current steam atomizing. In
further support of this contention, no additional equipment would be needed
since an air compressor is available, the steam-atomizing boiler had had
numerous malfunctions, and the pneumatic lines would be much easier to
maintain. In addition, the high radiant heat environment of the burners has
caused many burner malfunctions and electrical wiring failures. After a
burner failure, the purge of the burner system delays the restart of the
130
-------
burners and, consequently, allows the processing temperature to drop. The
lack of automatic temperature controls in all burners also increases the
burner operational requirements.
Originally, the two kiln main burners and the gas purifier start-up
burner were each interlocked with their respective combustion air fans as
follows: If the discharge pressure switch in the burner windbox failed to
detect the pressure due to the fan airflow, the burner would be shut off.
However, when the baffles were installed in the two kiln main burners, as
discussed above the airflow was so changed that the pressure sensor could
no longer properly detect its presence. Consequently, all burner inter-
locks were disconnected.
Maintenance
The fuel oil burners sustained many steam and oil leaks which required
extensive corrective maintenance. Of the four kiln safety pilot burners
in the feed hood, the one in the emergency stack of the hood has required
frequent "repair because its wire insulation was usually melted or burned
when the stack lid opened. The preventive maintenance schedules for the
fuel oil burner system and the fuel oil pump are shown in Tables 24 and 25,
respectively.
Residue Quency Tank and Conveyor
After the shredded refuse has been processed in the kiln, the residue
(ash, othaji;inert solids, and some uncombusted carbon char) tumbles into the
kiln fire hood where it falls vertically into a water bath contained by the
residue quench tank. As the residue settles to the bottom of the tank, a
drag chain conveyor transports it along the tank bottom and then up a
continuous incline which serves first as the forward end of the tank and then
as a dewatering deck. As the residue ascends the dewatering deck, it
either continues to the top of the incline where it is discharged onto the
vibrating residue screen conveyor in the residue separation building or
falls en route through a flop gate whenever the gate is opened into a truck.
Since the residue quench tank completely encloses the bottom of the
fire hood while still allowing the residue discharge, it serves as an air
seal to maintain a negative pressure within kiln fire hood and vessel as
well as a means for cooling the hot residue and then removing it.
Description
As shown in Figure 61, the residue quench tank is a carbon steel con-
struction with a rectangular base, vertical side walls, and outwardly
oblique end walls. Sloping at a 25° angle from the horizontal, the forward
end wall is part of a continuous, constant-width incline which serves as a
dewatering deck above the water level. The upper surface of the tank bottom
131
-------
TABLE 24. FUEL OIL BURNER SYSTEM PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Inspect all safety burners, tips, and fire-eye for cleanliness.
Check fire-eye and pilot ignition for cleanliness.
Check operation of oil pump, pump motor, and oil pressure controller.
Check operation of alarm contactors, boiler feedwater level switch,
level and shutdown alarms.
Check condition of programming controller.
Check for proper voltage on secondary ignition transformer.
Check general condition of pressure impulse line.
Check proper operation of pressure controllers (on/off and hi/low fire)
Grease motor bearings (LiEP2).
Quarterly'
Replace filter in kiln safety burner and slag hole Peabody burner.
Semiannually
Pull burner tips on kiln heatup and standby burner, kiln on-stream
burner, gas purifier heatup and standby burner and inspect for
erosion or damage.
Inspect all filters and change if necessary.
Clean strainers in kiln heatup and standby burner, kiln on-stream
burner, gas purifier heatup and standby burner.
Check all burner blower motors.
Check alarm.
Check operation and cleanliness of kiln heatup and standby burner,
kiln on-stream burner, gas purifier heatup and standby burner and
burner blower pressure switches.
Check ignition conditions of kiln heatup and standby burner, kiln
on-stream burner, gas purifier on-stream burner, gas purifier heatup
and standby burner.
Check condition of all burner pressure gauges and solenoid valves.
Annually
Check all burner electrical controls, timers, and relays.
Megger motors.
132
-------
TABLE 25. FUEL OIL PUMPS PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check bearings, oil level, seals.
Monthly
Tighten nuts—teflon sticks on three valves at pumps and two at oil tank.
Quarterly
Lubricate bearings with pyroplex (EP2).
Grease valves at pump and tank (LiEPZ).
Semiannually
Grease motor (LiEP2).
Annually
Zero, calibrate, and check operation:
Fuel oil pump discharge pressure indicators.
Fuel oil system pressure indicator.
Clean and lubricate:
Fuel oil totalizing indicator.
V8 fuel oil storage tank level indicator.
133
-------
Figure 61. Original residue quench tank and conveyor.
and the entire incline is lined with abrasion-resistant steel plate. The
tank is 2.3 m (7.5 ft) high and was designed to contain 42 m3 (1500 ft3) of
water with a 30-cm (12-in.) freeboard. The makeup water filling the tank
consists mostly of clarifier underflow, discussed later, and some city
water.
As mentioned above, a flop gate in the bottom of the dewatering deck
allows the residue to fall into trucks for landfill disposal before it
reaches the top of the incline for discharge onto the vibrating residue
screen conveyor in the residue separation building. Pneumatically operated,
the gate is as wide as the deck and 60 cm (24 in.) long.
On the residue discharge run, the drag chain conveyor extends along 11 m
(36 ft) of the horizontal part of the tank and then along the 21 m (69 ft)
of the entire 25° incline. The conveyor consists of two parallel chains of
welded steel links connected at 60-cm (2-ft) intervals by vertically posi-
tioned drag flights constructed of 6-mm (0.25-in.) thick abrasion-resistant
steel channel. Driven by a 40-hp motor, the conveyor runs at 9 m (30 ft)
per minute. The drag chain conveyor was designed to transport 45 m3
(1600 ft3) of residue per hour.
The drag chain conveyor is interlocked to the vibrating screen conveyor
so that it cannot run unless the screen conveyor is operating.
134
-------
Operating Experience
While the conveyor width extends close to the original tank side walls,
residue falling between the walls and the conveyor required installing
artificial walls which slope downward from the original walls to extend just
above and inside the conveyor. In addition, a catwalk and better lighting
were installed around the tank for safer and more efficient working
conditions.
Originally the only provision for draining the tnak was a small 76-mm
(3-in.) I.D. pipe which rapidly plugged with solids during the initial
operation. Consequently, a door was installed on the side of the tank to
gain access to the tank area for cleaning as well as to drain the tank.
However, this removal of the water with its considerable waste content
contaminates the environment, as discussed later in the environmental
assessment of the plant, because the water flows directly into a nearby
drainage channel without any treatment.
During the plant shakedown, grizzly bars were placed across the top of
the tartk to prevent large slag balls from jamming the conveyor. However,
when the residue accumulating over the bars became so excessive that the
entire plant processing had to be shut down to remove the debris, the bars
were removed.
When the tank water level was increased to provide a better air seal,
the freeboard was so reduced that the tank has been constantly overflowing.
This condition has been aggravated by the water level controllers, called
bubblers, frequently malfunctioning because of their rapidly becoming plugged
with floating solids.
Whenever there are sufficient accumulations of the carbon char part of
the residue floating on the water, the char continues to burn until it fuses
into slag and sinks. This burning and slagging, however, is less severe
than it was when magnetic materials were removed from the shredded refuse
stream. The greater density of these materials accelerated the sinking
process.
To rapidly vent the kiln vessel whenever there is an emergency shutdown
of the induced-draft fan, interlocks open both the lid of the emergency
stack in the kiln feed hood and an emergency drain in the residue quench
tank. Then as the water drains to break the air seal in the fire hood, a
draft is established for airflow into the fire hood and out of the feed
hood. Controlled by a pneumatically operated valve, the emergency drain has
never functioned properly because of its tendency to jam and valve and
because of valve malfunctions. Nevertheless, the kiln vessel has always
been satisfactorily vented in the emergency situation since the turbine-
driven combustion air fan has provided a sufficient air flow through the
vessel and out of the feed hood.
135
-------
While the drag chain conveyor has a design capacity of 45 m3 (1600 ft3)
of residue per hour, the actual volumetric flow rate varies considerably
with the residue quality. When the quality is poor with large quantities of
unprocessed refuse, the drag flights are usually completely full. When the
quality is good, the drag flights are only about one-third full. When the
residue quality is poor and slag balls are formed from overprocessed refuse,
the slag balls occur approximately every third flight. Despite the.marked
differences between the design residue bulk density of 800 kg per m3
(50 lb/ft3) with a moisture content of 50 percent and the average measured
bulk density of about 1600 kg per m3 (100 lb/ft3) with a moisture content of
31 percent, the major deficiency in the conveyor design was due to the
underestimation of the maximum particle size. Whereas the design maximum
was 10 cm (4 in.) with an occasional 60-cm (24-in.) long pipe, slag balls
have been as large as 2 m (6 ft) in diameter.
In the original conveyor configuration when the return run was within
the residue quench tank (Figure 61), the slag balls caused two types of
conveyor failure. In one type, because of their excessive loading, the slag
balls would break the shear pin and damage the drag flights. In the other
type, slag balls falling on the conveyor return run would either pass
partially through the return run to become wedged between the drag flights
of the return and discharge runs or be carried over to the rear of the tank
to become wedged between the conveyor and the section of the tank end wall
near the tail sprocket. On one occasion, the entire tail sprocket was
pulled out due to slag ball jamming. Therefore, the conveyor was completely
redesigned to provide greater structural strength and motor power, and the
return run was changed to travel over the kiln fire hood and then down to
the tail sprocket (see Figure 62) After these modifications, the flights
have withstood the loads better with considerably less damage and the shear
pin rarely breaks.
After the return run was placed over the fire hood, excessive residue
accumulated on the return deck since residue retained on the drag flights' as
the flights started the return run would dry and flake off, especially when
agitated by the wind or the conveyor vibration. Therefore, to minimize the
residue retention as well as the wedging of cans between the chain and the
head sprocket, relief notches were cut into the drag flights.
As the links in the conveyor chain stretch, and the chain consequently
becomes loose, the conveyor has an oscillating motion during the return run.
The motion consists of jerky starts and stops with the conveyor vibrating
between the conveyor idlers. To overcome the chain looseness, the diameter
of the idlers was increased, and the chain has teen tensioned" by removing a
link or adjusting the return guide rail.
To provide a detector of slag balls forming in the kiln and ascending
on the drag conveyor, a horizontal shaft with vertical bars welded to it was
installed across the sides of the dewatering deck. With the rods extending
to the upper extremity of the drag flights, the shaft rotated a constant
angular sweep when only a flight contacted the rods. Since a switch contact
was activated with each such rotation, the shaft assembly also served as a
136
-------
Figure 62. Modified residue quench tank and conveyor.
zero speed sensor, that is, as a means of monitoring the conveyor running.
When a slag ball extending above the flights contacted the rods, the shaft
rotated further than the normal sweep and accordingly tripped a switch which
activated an alarm. However, after large slag balls had severely damaged
this slag detector because of the limited clearance between the horizontal
shaft and the drag conveyor, the shaft assembly was replaced with a photo-
electric detector. The latter detector has functioned adequately except for
instances when steam from the residue blocks the light path. While this
light path interference prompted consideration of a sonic detector, such a
detector has not as yet been purchased.
To prevent slag balls from interfering with the head sprocket drive
system, the sides of the dewatering deck above the residue flop gate bypass
were removed to allow slag balls to fall off the deck before reaching the
head sprocket. However, slag balls larger than 1 m (3 ft) in diameter must
be removed by a small mobile crane.
Maintenance
Table 26 is the preventive maintenance schedule for the residue quench
tank.
The drag conveyor has required considerable emergency maintenance in
addition to the normal routine maintenance (Table 27). Before the conveyor
was redesigned, there were frequent pin shearings, flight damages, chain
link breaks, and chain jumps off the lead sprocket. In addition, the motor
137
-------
TABLE 26. QUENCH TANK PREVENTIVE MAINTENANCE SCHEDULE
Semiannually
Check operation of solenoid valve.
Check air supply pressure.
Check condition of pneumatic cylinder.
Zero and calibrate current pneumatic converter.
Annually
Check operation of solenoid valve, air supply pressure, operation of
pneumatic cylinder, and electrical system.
Check operation of level switches, low level alarm, and pressure switches,
TABLE 27. QUENCH TANK CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check drag for loose bolts, damaged flights or support brackets, unusual
wear, and unusual noise.
Check tension on drag chain, adjust as required.
Check reducer for abnormal heat, noise, and oil level (Paradene 475).
Check alignment of head shaft.
Top up lubricant in drive chain (Paradene 430).
Grease headshaft and idler shaft bearings (LiEP2).
Shutdown
Drain and clean tanks.
Inspect tanks and wear plates for wear or damage.
Check drag guides for damage.
Check tailshaft bearings and sprocket.
Semiannually
Change reducer oil (Paradene 475).
Lubricate coupling and motor (LiEP2).
Check motor, alarm and interlocks, zero speed switch and bearings.
Lubricate bearings (20 W motor oil).
Annually
Megger motor.
138
-------
had to be realigned and its drive and coupling repaired, and the guide rails
had to straightened. After the conveyor modifications, however, very few
pins have sheared and the chain links have remained intact although the
flights are still damaged and the chain continued to jump the head sprocket
but much less frequently than before the modification.
After the above mentioned provisions and procedures were introduced to
minimize the chain loosening, the adjustments to maintain the required chain
tension have been minor, and a straightening of the chain guide is not likely
to be needed again.
Seal Tank and Screw Conveyors
The air seal for both the kiln feed hood and the gas purifier is main-
tained by a single water quench tank into which the bottom of the feed hood
is submerged at one end and the bottom of the slag taphole of the gas
purifier is submerged at the other end. In the tank below each of the two
submerged bottoms is a screw conveyor, one for the spillback and dust dis-
charged from the feed hood and the other for the molten slag discharge
from the slag taphole. As the respective discharges fall into the water to
be cooled and shattered into frit while settling, the conveyors transport the
frit toward the middle of the tank where a third screw conveyor, called the
frit transfer conveyor, elevates and dewaters the frit before discharging it
into a dump truck for landfill disposal.
Description
The water-filled seal tank common to the kiln feed hood and the gas
purifier is a horizontal carbon steel construction in an inverted triangle
configuration with a rounded bottom to accommodate the spillback and slag
conveyors. With a design freeboard of 15 cm (6 in.), the tank is 16 m
(52 ft) long and 1.1 m (3.5 ft) deep. Figure 63 shows the bottoms of the
kiln feed hood and the slag tap hole of the gas purifier submerged in the
seal tank. The tank is equipped with a water recirculating system which
includes a surge tank, a level controller, a recirculation pump, and two
nozzles that protrude through the slag hole periphery and below the water
level in the slag discharge area.
Extending from outside the tank at the kiln end to the transfer conveyor,
the water-submerged, 10-m (33-ft) long spillback conveyor runs along the tank
bottom and is supported at its inlet end by a pillow block bearing and at
its discharge end by a hanger bearing. The water seal at the junction of the
conveyor shaft and tank end is maintained by a teflon-coated, fiber-packed
gland. The conveyor is powered by a 7.5-hp motor which is installed at the
exterior end of the conveyor shaft.
Like the spillback conveyor, the slag conveyor extends from outside the
tank at the gas purifier end to the transfer conveyor. With the same type of
placement, bearings, and water seal as the spillback conveyor, the slag con-
veyor is 5.8 m (19 ft) long and is driven by a 10-hp motor also installed at
the exterior'end of the conveyor shaft.
139
-------
BOTTOM OF KILN
FEED HOOD
MOTOR
MOTOR
BOTTOM OF
SLAG TAP HOLE
SPILLBACK
SCREW CONVEYOR
SLAG SCREW
CONVEYOR
SEAL TANK
Figure 63. Schematic of the seal tank.
-------
From the discharge area of the spillback and slag conveyors, the
7.8-m (25.5-ft) long transfer conveyor is inclined at a 30° angle to rise
out of the water for frit dewatering before discharging the frit into a
truck. The transfer conveyor is powered by a 7.5-hp motor installed at its
discharge end and is supported at its inlet end by a thrust bearing and at
its discharge end by a pillow block bearing. The spiral flights above the
water line are notched to accelerate the frit dewatering.
The slag and spillback conveyors are interlocked with the transfer
conveyor so that they will shut down if the transfer conveyor stops to pre-
vent the buildup of frit at the inlet end of the transfer conveyor.
Operating Experience
As with the residue quench tank in the kiln fire hood, the seal tank,
common to the kiln feed hood and gas purifier, has been constantly overflowing
after the water level was raised to provide a better air seal. In addition,
the very small tank drain, 76 mm (0.3 in.), the only opening in the original
tank, rapidly plugged with solids. The water level controller malfunctions
caused low water level whenever its bubbler was plugged with solids. When
the bubbler was so clogged, the pressure in the controller air line remained
high irrespective of the water level which in turn caused the inlet water
valves to remain closed. Since the tank had to be cleaned as well as drained
when the tank drain was plugged, a door was installed in the tank for this
two-fold requirement. However, the door is difficult to open without getting
wet, and the water with its environmentally objectionable content is dis-
charged directly onto the ground without any treatment.
During the shakedown period, the tank rotated slightly whenever a screw
conveyor torqued because of slag balls jamming between the conveyor and a
tank side. Consequently, the tank was sufficiently reinforced with structural
steel to resist the torquing.
The abrasiveness of the frit coupled with the screw conveyor forcing the
grit along the tank surface has caused such severe wear that leaks have
developed in the tank bottom.
Since the tank water within the submerged part of the slag taphole
becomes stagnant and is much hotter than the rest of the tank water, a water
recirculating system was installed. As intended, the cooler water in the
slag taphole would have two desirable effects: First, since a lesser amount
of the relatively cool steam would rise into the gas purifier, not as much of
the molten slag would solidify, and consequently the plugging of the slag
tap-hole would be reduced. Second, the molten slag falling into the cooler
water would be shattered more thoroughly into frit or formed into smaller
balls since large masses of molten slag cannot be cooled fast enough for
complete fritting. As a minimum benefit, the limiting of the slag ball size
would be very desirable since the large slag balls have been the most damaging
factor in the conveyor operation.
141
-------
When the water recirculating system was installed, process water would
overflow a weir in the seal tank and flow by gravity in a trough to the surge
tank where -the recirculating pump would force the water through the two
nozzles in the slag taphole periphery and into the water within the submerged
part of the hole. Since the surge tank was not equipped with sludge removal
equipment, it had to be cleaned frequently because of excessive accumulations
of solids settling within the tank. Consequently, the inlet pipe for the
recirculating pump was moved to the seal tank itself and a screen was placed
before the pump inlet to prevent solids from damaging the pump and plugging
the nozzles. However, after the pump was damaged by grit that flowed through
the screen and the nozzles continued to plug, the operation of the water
recirculating system was suspended. Stopping of the recirculating system did
not seem to increase the plugging of the slag taphole or decrease the frit-
ting of the molten slag.
Originally, there was only one bottom conveyor which extended along the
entire length of the seal tank and was driven by a single motor installed on
the conveyor shaft outside the tank at the kiln end. When the conveyor began
to flex excessively, it was converted into two separate bottom conveyors by
cutting it at the inlet end of the transfer conveyor and then installing a
hanger bearing on each side of the cut and a second motor and drive system on
the conveyor shaft outside the tank at the slag taphole end. Since the
hanger bearings were initially close to the conveyor feed stream, they blocked
the flow of large slag balls and, therefore, were moved to the conveyor ends.
As the hanger bearings are submerged and water-lubricated, they sustain
abrasion from the grit in the seal tank water.
After the original single bottom conveyor was separated into the spill-
back and slag conveyors and the flights were installed in the kiln vessel to
move the shredded refuse more effectively down the kiln (as discussed above),
the spillback into the kiln feed hood was so reduced that the spillback
conveyor has had a minimum loading except for the occasional falling of kiln
refractory or wire mesh from the kiln emergency stack lid into the tank.
In contrast to the spillback conveyor, the slag conveyor has had
excessive loads that have frequently broken its shear pin. While the strength
of the shear pin has been progressively increased to keep the conveyor opera-
tional, the greater capacity to handle the excessive loads has caused the
conveyor spiral flights to bend. When the conveyor continued to be over-
loaded, the drive mechanism was upgraded and the original 5-hp motor was
replaced with the current 7.5-hp motor. Then while fewer pins were sheared,
both the slag conveyor and the transfer conveyor screws became so badly
damaged that they were replaced with new screws that have a stronger shaft
and spiral edges double the thickness of the original ones. In addition, the
pitch was decreased from 45° to about 10°.
To monitor the turning of the slag conveyor screw, a zero speed switch
was installed on the drive shaft of that conveyor. However, if the pin
linking the drive shaft and the screw fails, the switch will erroneously
continue to indicate that the screw is still turning.
142
-------
The design capacity of the slag and transfer conveyors was based upon a
frit bulk density of 800 kg per cu m (50 lb/ft3) while the average measured
bulk density has been 1600 kg per cu m (100 lb/ft3). The conveyor performance
has been adversely affected more, however, by the discrepancies between the
maximum design particle size of 8 cm (3 in.) and the actual particle sizes.
Slag balls as large as 30 cm (12 in.) have fallen into the seal tank and onto
the slag conveyor. Most of the conveyor failures have been due to slag balls
wedging between the conveyor flights and the tank sides.
The numerous screw conveyor failures have caused the shutdown of the
entire plant to prevent slag frit accumulations in the seal tank that would
eventually plug the slag tap hole.
Originally, the trough for the transfer conveyor was misaligned so that
the continuous rubbing of the conveyor against the trough damaged the con-
veyor hanger bearing and abraded holes into the trough until the trough was
aligned and structurally reinforced. In addition, the original hanger bear-
ing at the bottom of the conveyor was replaced by a thrust bearing with a
water flush. Notches were cut into the conveyor spiral flights above the
water line to facilitate the frit dewatering.
Since the transfer conveyor has to carry frit with bulk densities about
twice the design bulk density up its 30° incline, it has occasionally evi-
denced overloading that may require a larger motor.
The access to all three conveyors and the seal tank is difficult because
of their elevations and the lack of platforms. Although the drive system at
the discharge end of the transfer conveyor is on a platform, the platform is
isolated and 6 m (20 ft) above the ground level.
The electric switch boxes for each of three screw conveyors are in the
residue separation building. Since this location is too remote for ready
access, the boxes should be transferred to the motor control center adjacent
to the control room.
Maintenance
All three screw conveyors have required frequent tightening replacement
of the packing. After the various modifications to the conveyors because of
the many shear pin failures and replacements during the shakedown period, the
pins still require replacement but much less frequently. Since its instal-
lation on the slag conveyor, the zero speed switch has required considerable
repair and was replaced once. Both the pillow block and the hanger bearing
for the slag conveyor have required replacement. On one occasion when the
water flush was turned off, the thrust bearing for the transfer conveyor
had to be replaced. On another occasion, the drive system for the slag
conveyor required the repair of the drive sprocket safety lever and the
installation of a new hub and bushings on the drive sprockets. The pre-
ventive maintenance schedules for the seal tank and the screw conveyors are
shown in Tables 28 and 29.
143
-------
TABLE 28. SEAL TANK PREVENTIVE MAINTENANCE SCHEDULE
Annually
Check operation of level valve.
Check operation of solenoid valve.
Check operation of low level alarm.
Check operation of level switches.
TABLE 29. SCREW CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check oil level in all three gear boxes.
(Winter - Paradene 475)
(Summer - Paradene X 1000)
Check oil level in chain guards.
Grease thrust bearing on the frit transfer conveyor (LiEP2).
Quarterly
Lubricate couplings and pillow block bearing (LiEP2).
Check packing on spillback and slag conveyors, repack if necessary.
S emiannually
Check moving parts for wear.
Check flight thickness at outside edge, and for bent flights.
Check discharge spouts for excessive wear.
Change oil in the reducer.
(Winter - Paradent 475)
(Summer - Paradene X 1000)
Change drive chain oil (Paradene 430).
Grease motors (LiEP2).
Check motor, flexible cord, and zero speed station for proper operation.
Lubricate local start/stop/job stations.
Annually
Megger motor.
Grease motor bearings (LiEP2).
Waterproof (WD-40 or CR226).
144
-------
Quench Air Dampers
As the combusted kiln-off gases pass through the horizontal elbow of the
gas purifier exit duct to be directed to the waste heat boilers, they are
cooled by dilution with ambient air which enters the duct through two openings
on opposite sides of the elbow. Since the exit gases contain entrained
molten slag, the cooling was designed to quench and solidify the slag before
the gases reach the boilers. The air is drawn through the openings because
of the negative pressure established within the duct by the induced-draft
fan. Each quench air opening is equipped with a manually operated damper to
control the air flow.
Description
Each of the two quench air openings is approximately 75 cm (30 in.) in
diameter and is lined with castable refractory. One opening is on the inside
of the elbow and above the horizontal axis of the gas purifier exit duct, and
the other opening is on the outside of the elbow and below the horizontal
axis. The upper opening is equipped with a John Zink MA30 slotted stator and
air register (Figure 53), and the lower opening is fitted with a butterfly
valve damper (Figure 64).
Figure 64. Butterfly valve quench air damper,
145
-------
Constructed of carbon steel plate, the stator of the slotted air damper
is a cylinder open on one end and closed on the other. With the closed end
extending vertically outward, the open end is welded to the duct surface
around the opening. Evenly spaced around the stator circumference are eight
large slots 20 by 36 cm (8 by 14 in.) and one small slot 6 by 36 cm (2.5 by
14 in.). Since the total stator slot area (0.60 m2, 6.5 ft2) is larger than
the opening area (0.46 m2, 5 ft2), the slotted air damper ceases to control
the air flow when the exposure of its slots approaches the maximum extent.
Like the stator, the air register is a carbon steel cylinder with slots
matching those in the stator. The air register is equipped with a manual
rigid handle to vary the stator slot openings and, accordingly, the air flow.
Constructed of 315 stainless steel, the butterfly valve damper has a
70 cm (28 in.) diameter. When the damper is completely opened and closed,
the inlet air area is 0.46 and 0.06 m2 (5 and 0.6 ft2) respectively. The
damper setting is positioned by a manual chain pulley which extends to the
ground. To provide access into the gas purifier exit duct and for damper
maintenance, this damper is hinged.
Operating Experience
Early in the demonstration, the gas purifier exit gases had temperatures
of about 1100°C (2000°F) upon entering the inlet to the waste heat boilers.
Since this temperature would maintain the gas-entrained slag in the fluid
state, molten slag impinged, solidified, and accumulated on the boiler tubes.
Consequently, the exit duct of the gas purifier was retrofitted with the
quench air openings and dampers that reduced the inlet temperatures to about
870°C (1600°F). As a result, the gases were cooled sufficiently to solidify
the slag before the gases entered the waste heat boiler area. Moreover, the
air entering the openings is usually sufficient to complete the combustion of
the gases exiting the gas purifier with an excess air level of approximately
67 percent.
Although the register for the slotted air damper had jammed in the open
position because of heat expansion, this jamming has not posed an operational
problen. As subsequently learned, the slotted air damper must remain com-
pletely open while the setting of the butterfly valve damper is varied to
produce the optimum quench air flow. The rate of the quench air flow is
detailed later in the mass and energy balance section.
Maintenance
The only maintenance required of the opening and dampers has been the
routine lubrication of the dampers.
Gas Scrubber
A gas scrubber was chosen as the system to treat the flue gases for air
pollution control because it could remove acid as well as particulate at a
lower capital, operation, and maintenance cost than any other type of treat-
ment system. The scrubber treats the hot' flue gases which either have passed
146
-------
through the waste heat boilers and economizers or have bypassed these units
by flowing through a jug valve after leaving the gas purifier.
Description
The gas scrubber is a reinforced concrete, vertical, 10-m (33-ft)
diameter, cylindrical spray tower 21 m (69 ft) high (Figure 65). The bottom
2 m (6 ft) of the scrubber is filled with water to provide a working water
volume of 132,000 liters (35,000 gallons). The gas inlet, which is a 2.4 m
(8 ft) wide and 4.8 m (16 ft) high rectangular duct, enters the scrubber
tangent to the vertical with the lower extremity of the duct 3 m (10 ft) above
the bottom of the scrubber. The gas exit duct, which is centered in the top
of the scrubber, is 2.4 m (8 ft) in diameter.
Figure 65. Gas scrubber.
To protect the steel ductwork from thermal damage, the horizontal section
of the inlet duct is lined with 23-cm (9-in.) anchored brick, and the sloping
transition duct is lined on the floor with 23-cm (9-in.) brick and on the
roof and sides with 11-cm (4-in.) of gunite.
As the flue gases to be treated pass through the inlet duct, they are
quenched by the water spray within the duct. Upon entering the scrubber near
the bottom, the gases flow cyclonically upward to the gas exit duct at the
top of the scrubber. Immediately after the inert to the exit duct, the
ductwork turn 180° to extend vertically downward to the induced draft fan
which draws the gases through the entire thermal processing and energy re-
covery areas.
147
-------
As the gases rise to the exit duct, they are cooled and scrubbed of
their entrained particulate and vapors by falling fine water droplets which
are sprayed by the water recirculating system at the top of the scrubber.
The water collecting at the bottom of the scrubber serves as a wet well for
the water recirculating system.
To prevent corrosion within the recirculating system, a pH control
system maintains a neutral pH in the recirculation water by adding a caustic
material to the water. In addition, a solids separation system removed the
suspended solids from the recirculation water. The water recirculating, pH
control, and solid separation systems will be detailed later. Figure 66 is
a schematic of the entire gas scrubber system.
Operating Experience
Since the scrubber had not removed enough particulate to comply with the
Federal and State of Maryland particulate emission standards, the following
innovations were tested to increase the particulate removal: the constant
use of the inlet-duct quench sprays, both a low and a high recirculating
flow, a low recirculating water pH, and the addition of a surfactant to the
recirculating water. Except for the surfactant addition, the innovations had
a negligible effect on increasing the particulate removal. While the
surfactant addition increased the particulate removal sufficiently to meet
the Federal standards, the increased removal was still not enough to comply
with the Maryland standards. Consequently, an electrostatic precipitator is
being installed to replace the scrubber.
Besides the scrubber inability to remove the particulate sufficiently,
its primary function, the scrubber operation allowed excessive amounts of
solids to settle on the scrubber bottom because of the 10-minute retention
time along with the low flow velocities of the particulate-laden water within
the scrubber bottom. The solids accumulated rapidly until reaching the depth
of the scrubber pump suction pipe when a steady-state condition developed
with a solids depth of 1 m (3 ft). Since the scrubber has no sludge removal
equipment, the sludge had to be removed manually with a vacuum truck during a
plant shutdown.
Because of the solid accumulations, the scrubber drain, which is only
75 mm (3 in.) in diameter, clogged rapidly. Then the access manhole had to
be opened to clear as well as to drain the scrubber. However, since the
particulate-laden water has been discharged directly to the ground surface,
this practice is environmentally unacceptable.
The epoxy coating to seal the scrubber water basin deteriorated rapidly
and flaked off. As discussed later, the epoxy flakes interfered with the
recirculating water system. Although small leaks developed in the foundation,
they were quickly repaired. A spider baffle directly below the gas exit
corroded and fell out. This baffle, a horizontal disc with vertical radial
plates on top to function as flow straighteners, was designed to remove water
droplets and to prevent the short-circuiting of gases through the scrubber.
Some of the malfunctions of the induced draft fan may have been due to water
droplets within the scrubber exit gases.
148
-------
COMBUSTION
GASES
COMBUSTION
GASES
I
GAS
SCRUBBER
18%
CAUSTIC
CYCLONE
SEPARATOR
1
STRAINER
PROCESS
WATER
uJ
SCRUBBER PUMP
PH
[MONITOR
OVERFLOW
SUMP
PUMP
OVERFLOW
SUMP
OVERFLOW
INDUCED
DRAFT FAN
BEARING
COOLING WATER
DEHUMIDIFIER
UNDERFLOW
(SLUDGE)
CONDENSATE TO RESIDUE! QUENCH TANK
Figure 66. Process flow diagram of the gas scrubber system.
-------
The scrubber inlet wall and ceiling refractory was replaced and the new
refractory was coated with a water sealer to prevent damage from the inlet
water spray. However, after the new refractory had soon deteriorated, it was
repaired and then replaced with A. P. Green Steelcom castable refractory and
the brick sides were sandblasted and coated with a different water sealer.
Maintenance
While the inlet refractory and outlet baffle required repair and replace-
ment, the gas scrubber itself has required only the preventive maintenance
detailed in Table 30.
TABLE 30. GAS SCRUBBER PREVENTIVE MAINTENANCE SCHEDULE
Annually
Zero and calibrate:
Scrubber water return flow transmitter.
Scrubber water return flow indicating controller.
Low water flow alarm.
Scrubber water to clarifier flow indicating controller.
Flow transmitter.
Current to pneumatic converter.
Scrubber water to clarifier flow valve.
Zero, calibrate, and check operation:
Scrubber Water pumps discharge pressure indicator.
Scrubber Water pumps discharge temperature indicator.
Scrubber gas intake pressure indicator.
Water to gas scrubber pressure indicator.
Check operation of scrubber pump ammeters.
Check condition of solenoid valve.
Zero and calibrate:
Level indicating controller.
High and low level alarms.
Level switch (differential pressure).
Check condition of purgemeter/flow controller.
Zero, calibrate, and check condition:
Level control valve.
Gas scrubber emergency spray control valve.
Scrubber Water Recirculating System
The scrubber water recirculating system continually pumps water from the
bottom of the scrubber to ,the top of the scrubber where a water distribution
150
-------
system sprays fine water droplets to remove the particulate and vapors from
the flue gases flowing from near the bottom of the scrubber to the exit duct
at the top of the scrubber.
Description
The scrubber water recirculating system consists basically of two
centrifugal pumps mounted on a concrete foundation adjacent to the scrubber
and the following water distribution system mounted at the top of the
scrubber: four horizontal circumferential tier headers with each header
connecting to 12 lances and with each lance containing eight or nine nozzles.
The two centrifugal pumps are Goulds Pump Inc., Model No. 3415 hori-
zontal units with a split casing. Driven by a 400-hp motor, each pump has a
rated capacity of 13,000 liters per minute (3,500 gpm) at a total dynamic
head of 107 m (350 ft) and 1,780 rpm. A three-position switch permits
operating either or both of the pumps.
The pumps are connected by a 30-cm (2-ft) diameter schedule 80 steel
pipe to the four tier headers which are made of 15-cm (6-in.) diameter
schedule •SO steel pipe. Constructed of 4-cm (1.5-in.) diameter schedule 40
steel pipe, each of the 12 lances is approximately 2 m (7 ft) long. Each
lance has eight whirljet No. 3/8-BX5525 nozzles made of hardened 440 stain-
less steel with an orifice diameter of 7.1 mm (0.28 in.). Each of these
nozzles has a rated flow of 30 liters per minute (8 gpm) at a pressure of
690 kPa (100 psig). In addition, 8 of the 12 lances has a Fueljet No. 1-H557
nozzle at the end. Also made of hardened 440 stainless steel, this nozzle
has an orifice diameter of 9.3 mm (0.33 in.) and a rated capacity of 92 liters
per minute (24 gpm) at a pressure of 690 kPa (100 psig).
A water level controller with a bubble-type sensor and a pneumatic valve
regulates the flow of city water into the scrubber basin to maintain to
ifcaintain a constant 2-m (6-ft) water level in the bottom of the scrubber. An
overflow drain in the side of the scrubber ensures that the water does not
exceed the 2 m (6 ft) level.
The sprays in the tangential inlet duct for the flue gases are normally
supplied with some of the pumped water but with city water when the pumps
fail.
Operating Experience
The operating total dynamic head (discharge pressure) for the pumps was
lower than the design head. With a given discharge pressure, a pump operates
at a corresponding volumetric flow rate; but as the discharge pressure
decreases, the flow rate increases and the efficiency decreases. Consequent-
ly, since the operating pressure was lower than the design pressure, the
pumps operated at extremely high volumetric rates and therefore overloaded
the motor. To minimize the motor overloading, the pump discharge valves were
partially closed to limit the flow and to increase the discharge pressure.
151
-------
The abrasiveness, high solids content, and pH variability of the recircu-
lated water cause severe wear and numerous malfunctions of the pumps and the
water distribution system. After both pumps had severely corroded, the
original bronze fitted shafts were replaced with ones made of 316 stainless
steel. In addition, city water was used to cool the pump packing glands. To
reduce the pump wear attributed to the pump drawing down the water surface in
a cone of depression that allowed cavitation air to enter the pump, a steel
plate was installed above the pump suction pipe. Nevertheless, the pumps
continued to wear excessively because of the water corrosiveness. Various
pump packings, such as teflon and blue afrian asbestoes graphite, were tested,
but with little success, to reduce the constant pump leaking.
The lances and nozzles have plugged rapidly, especially those at the end
of the tiers where the water distribution terminates since the tiers are not
continuous. Since the installed lances and nozzles are difficult to clean,
they have to be removed and sent to the maintenance shop for their blowout
with compressed air. As corrosion and erosion wore out the lances and
nozzles, the nozzles would ultimately slip out of alignment and therefore
require tightening because of the criticalness of the spray pattern; some
nozzles were so worn that they fell off the lances. Nozzles made of various
types of materials were tested, but none proved to be sufficiently corrosion
resistant.
Maintenance
Frequent maintenance requirements have included lance and nozzle clean-
ing and repair, nozzle tightening and replacement, and tightening of the pump
packing. A few leaks in the lance flanges required minor repairs.
Among the one-time requirements were the repair of a pump housing, the
remachining of a pump rotor, the installation of a new 0-ring, and a bearing
change. In addition, one of the pump motors had to be repaired because of
broken fan blades and a worn shaft. After the fuses had blown when a pump
motor shorted to the ground, the high voltage wiring on the motors was
replaced.
Table 31 details the scrubber water pump preventive maintenance schedule.
Scrubber Water pH Control System
As the gas scrubber removes particulate and vapors from the flue gases
passing through the scrubber, the particulate and water-soluble condensed
vapors collect in the scrubber basin water which is continuously recirculated.
Since the vapors contain acids, mainly HCL and some H2SO<,, the scrubber water
pH control system adds caustic to the scrubber water to maintain a neutral or
slightly basic pH.
Description
The scrubber water pH control system consists of the following: (1) a
caustic unloading pump to discharge the caustic from the delivery truck,
152
-------
TABLE 31. SCRUBBER WATER PUMP PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check stuffing box, bearings, temperature, and oil level (Paradene 430)
Check pump to motor alignment.
Check pump oil level.
Monthly
Check motor idle, current, and vibration.
Quarterly
Lubricate coupling (LiEP2).
Semiannually
Change bearing oil (Paradene 430).
Pull pump housing and inspect and check clearances if necessary.
Change motor oil (Paradene 415).
Check motor heaters, motor control circuits, and contactors.
Check and megger motors.
Check alarms and interlocks.
Annually
Check calibration of all C05 and 86 relays and operation of watt loss
relay.
Lubricate motor bearings (Paradene 415).
(2) a caustic feed tank to receive, store, and supply the caustics as needed,
(3) a caustic feed tank agitator to keep the caustics in the feed tank well
mixed and in suspension, (4) a caustic feed pump to pump the caustic from the
feed tank to the scrubber, (5) a monitor to sense the pH of the water dis-
charged from the scrubber water recirculating pump, and (6) a controller to
regulate the caustic pumped from the feed tank to the scrubber.
Installed in the water treatment building, the caustic unloading pump is
a Laborus Pump Co. horizontal centrifugal pump with auxiliary prime. Driven
by a 7.5-hp motor, the pump has an open impeller and a casing, both made of
cast iron, and a satellite-shaft-trench, grease-lubricated packing gland for
abrasion protection. The pump has a design capacity of 550 liters per minute
(145 gpm) at a total dynamic head of 12 m (40 ft) of water, a liquid density
of 1,280 kg per m3 (180 lb/ft3), and a viscosity of 3.0 centipoise.
Adjacent to the water treatment building, the caustic feed tank supplied
by the Willard G. Sherman Co. is an enclosed 3.6-m (12-ft) diameter carbon
steel cylinder.4.5-m (15-ft) high for a total volume of 47,300 liters
153
-------
(12,500 gallons). With 61 cm (24 in.) of freeboard, the tank has a working
volume of 40,900 liters CIO,800 gallons). Four 30 cm (2 ft) wide baffles
extending along the inside length of the tank were designed to facilitate the
caustic mixing within the tank.
Mounted on top of the caustic feed tank is a propeller-type carbon steel
agitator supplied by the Cleveland Mixer Corporation. The caustic feed tank
agitator is driven by a 7.5-hp motor.
Also installed in the water treatment building, the original caustic
feed pump was a Wilder air-operated, diaphragm slurry pump. This pump has a
design capacity of 11.4 liters (3 gallons) per minute at a total organic head
of 12 m (40 ft) of water. A recycle line in the pump configuration permits
continuous pump operation while the pump intermittently feeds caustic to the
scrubber through a pneumatically operated valve in the pump side stream
discharge.
The pH monitor, a Unilock electronic sensor, is mounted in a sample line
in which scrubber water runs continuously from the discharge piping of the
scrubber water recirculating pump to the clarifier overflow sump (described
below). As the monitor senses the pH of the scrubber water recirculated to
the water distribution system at the top of the scrubber, it transmits a
corresponding signal to the pH feed controller.
As activated by the monitor-transcribed signals, the pH feed controller,
a Fischer-Porter unit, regulates the setting of the pneumatically operated
valve in the discharge side stream of the caustic feed pump which flows to
the scrubber.
Operating Experience
After the initial runs with lime as the design caustic material, an
inspection of the scrubber revealed that the scrubber water basin had large
deposits of sludge and that the nozzles had plugged. Since the sludge
accumulations and nozzle plugging was attributed to the lime, an 18 percent
sodium hydroxide solution was introduced as the caustic material.
However, since the original Wilden pump was designed for pumping a lime
slurry, a pump with a larger capacity was required to handle the sodium
hydroxide solution. Consequently, the operation of the Wilden pump was
discontinued and a gravity flow line that discharged to the clarifier over-
flow sump was used until another pump could be procured. Also, the caustic
feed tank agitator was not needed since it was intended for the lime that
was in a slurry, whereas the sodium hydroxide was in solution. Although much
more expensive than the lime, the sodium hydroxide was not successful in
eliminating excessive solid accumulations at the bottom of the scrubber.
The newly ordered pump is a Goulds Pump Inc. centrifugal unit driven by
a 3 hp motor. The design capacity of this pump is 76 liters per minute
(20 gpm) at a total dynamic head of 16.8 m (55 ft) of water. The new pump,
however, has not been used since it arrived after the scrubber operation was
suspended.
154
-------
The pH monitor and controller both frequently malfunctioned. Conse-
quently, most of the pH measurements and the corresponding caustic feed
adjustments were made manually.
Originally, the sample point for pH monitor was installed in the bed of
solids at the bottom of the scrubber. Since the pH content there varied
negligibly in comparison to the recirculating water, the monitor was placed
in the sample line from the discharge piping of the scrubber water recircu-
lating pump to the clarifier overflow sump. Because of the low velocity flow
in the sample line, the water frequently froze during cold weather. In
addition, the pH measurements as displayed in the control room readout com-
pared to the manual measurements evidenced the frequent need for calibration
adjustments in the monitoring system.
Maintenance
The caustic unloading pump required only minor cleaning and repair. In
addition to cleaning, the original caustic feed pump required motor re-
alignment and the installation of new packing. The seam of the caustic feed
tank had to be rewelded to stop a leak. The pH monitor required continual
maintenance and was removed for cleaning during each scrubber shutdown.
The caustic storage tank preventive maintenance includes annual zeroing,
calibration, and operational check of the tank level pressure gauge, the
purgemeter flow controller, and the tank temperature indicator.
The caustic unloading pump preventive maintenance schedule is shown in
Table 32.
TABLE 32. CAUSTIC UNLOADING PUMP PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check for leaks, and check grease in oil cup.
Check bearings, and lubrication in the bearing housing.
Monthly
Fill packing grease cup (LiEP2).
Semiannually
Change oil (Paradene 415).
Grease motor (LiEP2).
Scrubber Water Solids Separation System
The scrubber water solids separation system removes suspended solids
from the scrubber water to reduce wear in the recirculating system and to
prevent the plugging of the water distribution nozzles.
155
-------
Description
The scrubber water solids separation system consists of the following:
(1) a strainer in the direct recirculating water line to remove large
particles, (2) a cyclone spearator next in the direct recirculating water
line to remove particles ranging from 70 to 100 microns, (3) a clarifier in
a bleed-off stream from the direct recirculating water line to remove smaller
particles, (4) a clarifier overflow sump, (5) a sump pump to pump the water
collected from four sources to the bottom of the scrubber, (6) a clarifier
underflow sludge pump to pump the sludge to the residue quench tank and (7) a
flocculant feeding system to promote particle coalescing and settling in the
clarifier.
The strainer is a basket-type, removable screen that is installed in the
direct recirculating water line shortly after the discharge of the recir-
culating pumps. Also in the direct recirculating water line and after the
strainer is the cyclone separator contained in a carbon steel vessel with an
approximate 200-liter (53-gallon) volume. The cyclone separator is a Krebes
desander with a capacity ranging from 4,500 to 13,250 liters per minute
(1,200 to 3,500 gpm).
The bleed-off stream feeding to the clarifier starts at a point in the
direct recirculating water line just beyond the cyclone. The clarifier is a
12 m (40 ft) in diameter carbon steel tank with a concrete bottom sloped 1:12
toward the center of the tank. The tank has. a 3.4-m (11-ft) depth, 36 cm
(14 in.) of freeboard, and an overflow weir on its periphery. The bleed-off
stream inlet and the sludge outlet are in the center of the tank. On each
side of a supporting and rotating tank-centered pier is a double rake assembly.
The upper rake at the water level collects scum, and the lower rake aligned
with the sloped bottom pushes and slides the sludge toward the sludge outlet.
The clarifier overflow passes to the sump which also collects condensate
from the dehumidifier and the bearing cooling water from the induced-draft
fan, both to be discussed later, and the water in the sample line to the pH
monitor discussed above. The sump has a 2,500 liter (3,300 gallons) capacity.
The sump pump, which pumps the water in the sump to the bottom of the
scrubber, is a Swaby Model 6H-4 vertical unit. The pump impeller and shaft
are of iron construction, and the pump bearings are made of lignum vital.
Driven by a 20-hp motor, the pump has a rated capacity of 3,700 1pm (975 gpm).
An on/off float switch permits intermittent pump operation. If the pump
fails, the sump overflow passes to the sewer.
The clarifier underflow sludge pump, which pumps the sludge to the
residue quench tank in the kiln fire hood, is a Goulds centrifugal water-
sealed unit. Driven by a 3-hp motor, the pump has a design capacity of
380 1pm (100 gpm) at a total dynamic head of 15 m (50 ft) of water. The pump
casting and impeller are made of cast iron, and the pump shaft and liners are
made of steel. The pump also has a water-flush seal.
156
-------
Contained within the water treatment building, the flocculant feed
system consists of a storage tank, two feed tanks, aspirator feed system to
supply dry flocculant to the water line connecting to both feed tanks, and a
pump to pump the flocculent from the feed tanks to the clarifier. Each feed
tank is a cylindrical vessel with a total volume of 2,100 liters (555 gallons)
and a working volume of 1,900 liters (500 gallons). Center-mounted at the
top of each feed tank is an agitator supplied by the Clevelend Mixer Corpora-
tion. Powered by 1-hp motor, the agitator shafts and their blade propellers
are made of stainless steel. Each of the feed tank outlets is valved to the
pump to permit pumping the flocculant from either tank. Driven by a 0.5-hp
motor, the pump is a Milton Roy positive displacement unit with a design
capacity of 5 1pm (1.3 gpm).
Operating Experience
As previously mentioned, a large amount of solids settle within the
scrubber. This is the only solids removal before the scrubber water reaches
the scrubber water recirculating pumps. When the solids fill the scrubber
bottom to the level of the pump suction pipe, a steady state condition occurs
and then there is no solids removal before the scrubber water recirculating
pumps. This may have caused some of the severe wear the pumps experienced.
Since the strainer is an integral part of the pump discharge line which
has no bypass, it can only be cleaned when the pump is turned off during a
plant shutdown. During two periods, one when the epoxy coating on the bottom
part of the scrubber sloughed off and the other when plastic in the scrubber
inlet gas was removed by in the scrubber during cold testing of the kiln, the
strainer clogged and subsequently ruptured.
The cyclone separator has removed only 9 kg (20 Ibs.) of solids per day
with sizes greater than 37 microns. Whenever the separator was shut down
without first blowing down the solid accumulations in it, it plugged. More-
over1, the blowdown has had to be done manually since the automatic blowdown
has never worked well.
Since the bleed-off stream to the clarifier is only about 1,500 1pm
(400 gpm), a small fraction of the pump rated capacity of 13,000 1pm
(3,500 gpm), the suspended solids concentration in the scrubber basin and
consequently in the recirculating water eventually reaches a steady-state
condition. The level of solids concentration during this condition is con-
siderably higher than that designed for because of the large amount of
particulate in the scrubber inlet gas. Consequently, the nozzle in the water
distribution system have been plugging continually. An attempt was made to
increase the water flow to the clarifier for greater solids removal, but the
small pipes in the clarifier system could not handle the higher flows. When
the plant is shutdown, water "freezing in the clarifier impedes the clarifier
start-up. Also whenever the sludge pipe clogged, the pipe had to be cleared
since the clarifier has no drain and there is no other way to drain and clean
the clarifier. However, the clarifier has functioned as intended since the
suspended solids content in the clarifier overflow has usually been at the
design level.
157
-------
The sump pump has had to be replaced several times because of severe
bearing wear. Also the pump has sustained severe corrosion because of the
acidic dehumidifier condensate flowing into the sump and the caustic added
directly to the sump.
Originally the sludge pump operated intermittently as it was turned on
and off by the level controller in the residue quench tank within the kiln
fire hood. The off operation allowed the suction line to plug with solids
and to freeze during cold weather. Moreover, the line was very difficult to
clear because of the inaccessability of the underflow sludge piping. Conse-
quently, a recycle line was installed to permit continuous pipe operation.
The flocculant feed system was used only a short time because it soon
became apparent that the suspended solids in the clarifier inlet water would
settle rapidly without any flocculant (polyelectrolyte).
Maintenance
The strainer required frequent cleaning, but it could only be cleaned
during downtimes because of the lack of a bypass in the pump discharge line.
Leaking valves in the cyclone separator had to be repaired frequently. While
the clarifier required maintenance only once when a sludge removal rake was
sheared, the sump pump has required considerable maintenance: The pump was
rebuilt several times; the pump shaft was replaced once and refurbished once;
the bearings were replaced twice; and two automatic grease feeders were
installed to ensure adequate bearing lubrication. In addition, the pump seal
housing was dismantled once for lubrication.
Except for the clearing of the section line, the sludge pump has required
only preventive maintenance (Table 33). Since the flocculant feed system
operated for the short while, no maintenance information was acquired.
TABLE 33. SLUDGE PUMP PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check bearing oil level (Paradene 430).
Monthly
Check bearing and seals.
S emiannually
Change bearing oil (Paradene 430).
Grease motor (LiEP2).
Check pumps and alarm.
Annually
Megger Motor.
Zero, calibrate, and check operation of pressure indicator,
158
-------
The preventive maintenance schedules for the clarifier, flow feed system,
and the sump pump are shown in Tables 34 through 36.
Induced-Draft Fan
The induced-draft fan is downstream from the scrubber and adjacent to
the scrubber base (Figure 65). The fan produces a draft which draws the kiln
combustion products through the kiln, the gas purifier, the waste heat
boilers, and the scrubber to the fan itself. Then the fan blows the exhaust
gases with sufficient pressure to discharge them through the dehumidifier to
the atmosphere.
Description
Driven by a 2,000-hp motor, the fan is a horizontal centrifugal unit
with a double inlet. A damper in each inlet box is pneumatically positioned
by a Bailey proportioning controller. The fan rotor and casing are con-
structed of Corten® steel, and the inlet is made of 316 stainless steel. At
the suction inlet, the fan has a design flow rate of 7,800 m3 per minute
(275,500 CFM) at 82°C (180°F) and a negative pressure of 75 cm (30 in.) of
water.
Sensors on the fan monitor, the bearing oil temperature, and transmit a
corresponding signal for the temperature readout in the control room. The
fan bearing lubrication oil is water-cooled with city water.
Constructed of Corten steel without a refractory lining, the suction
inlet duct is 2.4 m (8 ft) in diameter and extends from the top of the
scrubberr to the fan housing. Just above the duct inlet at the top of the
scrubber, the duct makes a 180° vertical bend to extend vertically toward the
ground. Just after the 180° turn, a long steel plate spans the duct interior
to straighten the gas flow to the fan housing. As the duct approaches the
fan housing, it separates into two ducts, one for each of the two separated
sides of the fan housing. The two cones for the duct discharge are installed
just above the rotor and the two sides of the fan housing.
Also made of Corten steel, the fan exit duct is 2.4 m (8 ft) in diameter.
After extending horizontally from the bottom of the fan housing, the exit
duct makes an upward 90° turn. The outside of the duct bend has horizontal
slots in a step configuration to allow the removal of water droplets. The
area behind the slots in enclosed with Corten steel to contain the air.
After the slots, the duct makes another 90° bend to return to the horizontal.
Then the duct extends approximately 28 m (92 ft) for its discharge into the
dehumidifier.
Operating Experience
The frequent need to rebalance the induced-draft fan because of its
excessive vibration had caused numerous shutdowns of the entire processing
system. While the various consultants hired by Monsanto and the City could
not agree*on the factor or combinations of factors causing the excessive
vibration, the factors considered as having the highest potential were as
159
-------
TABLE 34. CLARIFIER PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check power drive chains for unusual noise or vibration.
Check reducers for noise or leaks.
Check agitator for broken paddles.
Check lubrication:
Agitator reducer.
(Winter - Paradene 430)
(Summer - Paradene 475)
Agitator reducer coupling (LiEP2).
Winsmith (GMCTDW).
(Winter - EPS)
(Summer - EPS)
Thrust shaft bearing (LiEP2).
Worm shaft bearing (LiEP2).
Gear boxes.
(Winter - EP5)
(Summer - EPS)
Semiannually
Drain tank.
Check the tank, hose down walls and floor.
Check tightness of all bolts.
Check truss arms and note whether they are sweeping in the samen plane.
Adjust tie angles or adjustable back to each truss arm for most effec-
tive and equalized cleaning.
Replace any broken or badly bent squeegees.
Refill tank and resume normal operation.
Change oil in agitator reducer.
(Winter - Paradene 430)
(Summer - Paradene 475)
Change oil in Windsmith (GMCTDW).
Change oil in gearboxes.
(Winter - EP5)
(Summer - EPS)
Change oil in drive chain (Paradene 430).
Grease coupling and drive shaft bearings (LiEP2).
Grease motors (LiEP2).
Check motors and alarms.
Annually
Check and dismantle roller chain coupling.
Megger motor.
160
-------
TABLE 35. FLOG FEED SYSTEM PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check packing, motor, and housing.
Check lubrication in two reservoirs:
Diaphram plunger (Paradene 415)
Gear housing (EPS).
Quarterly
Change oil in both reservoirs:
Diaphram plunger (Paradene 415)
Gear housing (EPS).
S emiannually
Grease motors.
Zero, calibrate, and check operation of:
Pressure indicator.
Level pressure gauge.
Check condition of purge meter flow controller.
161
-------
TABLE 36. SUMP PUMP PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check oil level in oil cup on cooling water sump pump.
Monthly
Check all motors.
Check for unusual bearing noise and lubricate if necessary.
Check condition and operation of float switches and lubricate
(WD-40 and CR226).
Quarterly
Check sump basin sediment level.
Change oil in lubricator on .cooling water sump pump.
Change grease in pumps (LiEP2).
Semiannually
Grease motors (LiEP2).
Check motor, condition of float switches, and lubricate (WD-40 and
CR226).
Annually
Megger Motor.
162
-------
follows: (1) buildup of solids on the rotor, (2) erosion of the rotor due to
water droplet and/or particulate inpactions, (3) corrosion of the rotor from
acidic condensate, (4) unstable fan foundation, (5) resonance of the system's
critical and rotational speed, and (6) movement of the rotor on the shaft.
To monitor the vibrations, the fan was instrumented with a sensor to
detect the horizontal displacement of the inboard and outboard fan bearings
and to transmit a corresponding signal to a readout behind the instrument
panel in the control room. The readout assembly activated an alarm if the
displacement on either bearing was greater than 0.25 mm (10 mils) and shut
down the fan if either displacement was greater than 0.38 mm (15 mils).
After the original rotor wore out, it was replaced with the spare rotor,
and XAR-15 stainless steel wear plates were installed on the impinger (con-
cave) side of the vanes to retard corrosion and erosion of the rotor. The
wear plates, however, wore out within 2 months, which was shorter than the
period for the original blades. In any event, the wear plates were removed
to eliminate their possible contribution to the fan imbalance. The corrosion
and erosion continued until the fan operating conditions changed from those
with a wet gas, as designed, to those with a dry gas, as discussed later.
The potential of the solids buildup on the rotor for being a prime cause
of the excessive fan vibration increased greatly after the observation that
rotor sandblasting before rebalancing increased the time between the required
balances. Consequently, to minimize solids buildup and corrosion, a low
pressure (138 kPa, 20 psig), low flow (200 1pm, 52 gpm) water spray system
was installed. As pumped from the clarifier, the water sprayed on the rotor
contained Calgon CL-69, a corrosion inhibitor. The spray had a negligible
affect in preventing the excessive vibration and may have increased it.
Later, a test with a high volume, low pressure water spray also produced
negligible results. Therefore, either the sprays did not reduce the solids
buildup or the solids buildup did not cause the excessive vibration.
Many tests were conducted to analyze the resonance frequency of the fan
rotor, fan housing, fan foundation, and other fan components. Most of the
consultants concluded from the test results that resonance was not causing
the excessive fan vibration.
To isolate the fan from the inlet duct to the fan, an expansion joint
was installed in that duct. In addition, the fan bearing oil was changed
from the winter to the summer grade since the oil temperature was always
above the maximum specified for winter grade oil, and the bearings were
rebabitted from the circular configuration to an eleptical one. These
modifications, however, had no apparent affect in preventing the excessive
vibration.
Then to prevent rotor movement on the shaft, the rotor was welded to the
shaft. Since the welding did not prevent the excessive vibration, the rotor
movement was eliminated as the sole vibration factor.
163
-------
After Monsanto's departure, the City made the following modifications
and changes which eliminated the excessive vibration: (1) the mass of the
fan foundation was increased by connecting the fan foundation to the scrubber
foundation, (2) the wet gas scrubber operation was discontinued; consequently,
with the fan handling dry rather than wet gas, the gases did not contain the
water droplets, but they did have a higher inlet temperature and contains
more particulate and acidic vapors and some water, and (3) the original
rotor, which had been refurbished, was reinstalled because of the long lead
time to procure a new one after the spare rotor had worn out. Figure 67
is a picture of the worn out spare rotor and Figure 68 is a close-up picture
showing holes worn through the rotor vane. Since these modifications and
changes altered the previous operating conditions, some of the prime potential
factors causing the excessive fan vibration could not be isolated and
identified.
However, some of the potential excessive fan vibration factors were
eliminated in the following course of events. During the Spring of 1977 when
the Baltimore Gas.and Electric Company did not accept all of the plant's
steam production, as usual at this time of the year, the City dumped the
unused steam into the scrubber. Then to maintain the scrubber exit gas
temperature below 200°C (400°F), the City reactivated the scrubber. But then
the fan vibration, which had remained below 0.025 mm (1 mil) for a 6-week
operational period, increased within a day to 0.25 mm (10 mils) necessitating
the shutdown of the system. Therefore, the stability of the fan foundation,
the temperature of the fan inlet gas, and the intrinsic rotor conditions were
not the sole causes of the excessive fan vibration since these conditions
remained the same when the excessive vibration recurred.
In view of the above, the water droplets and solids buildup would be the
principal candidates for determining the cause of the excessive vibration.
The actual cause, however, may have been resolved when the fan rotor was
cleaned without rebalancing after the previous shutdown since the subsequent
fan vibration in the dry gas mode was less than 0.025 mm (1 mil). The solids
buildup on the rotor, therefore, may have been the prime cause of the exces-
sive vibration.
After the foregoing system shutdown following the unused steam dumping
into the scrubber, the City installed a steam muffler to handle the steam so
that the fan could continue to operate in the dry gas mode. Since the muffler
installation, there has not been any excessive fan vibration or significant
corrosion or erosion.
During normal operation, the fan has operated as designed with suffi-
cient capacity. On one occasion, however, the fan discharge pressure in-
creased substantially with the consequent corresponding reduction of the fan
volumetric capacity when the dehumidifier had plugged with solids after the
scrubber was turned off. With the scrubber inoperative, the particulate flow
to the dehumidifier was higher and there was no condensate flow to keep the
dehumidifier clean. After the dehumidifier was cleaned, the discharge
pressure was reduced to normal and the fan consequently had sufficient
capacity.
164
-------
Figure 67. Induced-draft fan rotor.
Figure 68. Induced-draft fan rotor vane,
165
-------
Two conditions had prevented proper damper movement. One condition
developed when the damper bushings corroded and locked. To remedy this
condition, brass bushings were installed and lubricated well. The second
condition developed when the set screws coupling the bushing and the damper
shaft had slipped. This slippage asynchronized the dampers and consequently
imbalanced the loads on each side of the fan. This condition was remedied by
inserting a connecting pin through the damper shaft to the bushing.
Maintenance
The major maintenance item for the fan was the rotor rebalancing which
was required every 2 weeks before the scrubber operation was discontinued.
A consultant usually did the rebalancing. When the fan was vibrating exces-
sively, the bearings had to be replaced or rebabitted often. Several times
the fan had to be cleaned and sandblasted.
The fan housing occasionally required welding to repair holes caused by
severe corrosion and erosion. After the drain for the fan housing had fre-
quently plugged, a new drain was installed. In addition, the motor was
returned to the factory for tests and repairs to verify that the magnetic
center was properly located. The induced-draft fan preventive maintenance
schedule is shown in Table 37.
Dehumidifier
The flue gases exiting the induced-draft fan are passed through the
dehumidifier (Figure 69) to reduce their moisture content before their
discharge to the atmosphere. Consequently, the gas plume is variably reduced
depending on the ambient air conditions.
Figure 69. Dehumidifier.
166
-------
TABLE 37. INDUCED DRAFT FAN PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check vibration of fan and motor bearings.
Check inlet damper for smooth, balanced operation.
Check lubrication needs.
Check cooling water flow to bearings (15 1pm).
Check motor oil level.
(Winter - Paradene 415)
(Summer - Paradene 430)
Monthly
Check damper linkage, and bearing lubrication.
(Winter - Paradene 415)
(Summer - Paradene 430)
Check motor idle current.
Check RTD's for temperature and temperature spread.
Quarterly
Grease coupling (LiEP2).
S emiannually
Open all access doors.
Inspect impeller and damper for cleaning and reconditioning requirements,
Clean or balance rotor as required to prevent failure.
Disassemble and inspect coupling.
Check bearings.
Pull damper bushings and install grease fittings.
Change shaft bearing oil.
(Winter - Paradene 415)
(Summer - Paradene 430)
Molycote damper bushings.
Change motor oil.
(Winter - Paradene 415)
(Summer - Paradene 430)
Check motor heaters.
Check alarms and interlocks.
Check motor control circuits and contactors.
Check and megger motor.
Check calibration of all C05 and 86 relays, GFR, differential current
trip and operation of watt loss relay.
CONTINUED
167
-------
TABLE 37. CONTINUED
Annually
High pot motor.
Check bearing high temperature trip and lower position start switch.
Zero and calibrate:
Pressure transmitter.
Current to pneumatic convector.
Pressure indicating convector.
Check condition of purgemeter/flow controller.
Clean, lubricate, calibrate, and check air supply pressure to inlet
drive unit.
Zero, calibrate, and check operation:
Fan discharge pressure indicator.
Fan intake pressure indicator.
Check operation of ammeter.
Description
The dehumidifier is a 14 m (45 ft) by 18 m (60 ft) carbon steel vessel
elevated about 2 m (7 ft) above the ground to allow the vertical flow of
ambient air through the vessel. The discharge duct from the induced-draft
fan connects with the dehumidifier inlet vestibule which extends the entire
length of the dehumidifier and divides the vessel into two equal sides.
On each side of the central inlet vestibule (Figure 70) are three bays
connected to an outlet vestibule (Figure 71) which completes the side of the
vessel. In each bay, the lower part contains an array of 208 outward cross-
flow heat exchanger tubes, and the upper part contains an array of light
inward cross-flow distribution pipes. As the gases flow horizontally through
the heat exchanger tubes in each bay, the vertical flow of ambient air around
the tubes cools the gas and condenses most of the moisture in the gas. Then
the gases exiting those tubes rise through a mist collector in the outlet
vestible to enter the distribution pipes. As the gases resume flowing
horizontally but in the opposite direction, the vertical flow of ambient air
around the pipes continues the gas cooling and moisture condensation.
Finally, the gases escape through holes in the distribution pipes to blend
with the rising air and emerge into the atmosphere. The elevation of the
air-gas mixture discharge to the atmosphere is about 9 m (30 ft) above the
ground level.
Baffles in the inlet vestibule are designed to equalize the gas flow
into each bay. The 208 heat exchanger tubes in each bay are arrayed on
equilateral triangle centers of 106 mm (4.2 in.). Constructed of carbon
168
-------
Figure 70. Dehumidifier inlet vestibule.
Figure 71. Dehumidifier outlet vestibule.
169
-------
steel the tubes each have a 60 mm (2.4 in.) inner diameter and a 3.9 mm
(0,15 in.) wall thickness. Encircling each tube are 0.5 cm (0.2 in.) spaced
carbon steel fins each with a 98 mm (3.8 in.) diameter and a 1.3 mm (0.05 in.)
thickness.
The mist eliminator in each outlet vestibule is a 15 cm (6 in.) thick
1.2 m (4 ft) by 5.6 m (18 ft) mesh constructed of stainless steel. The eight
distribution pipes for each bay are 41 cm (16 in.) diameter schedule 10
rubber-coated pipes each having nine 114 mm (4.5 in.) diameter holes along
the top of the pipe. Both the heat exchanger tubes and the distribution
pipes are sloped for the condensate flow to the outlet vestibule. The con-
densate collecting in the outlet vestibules flows by gravity through a common
100 mm (4 in.) diameter pipe to the clarifier overflow sump.
Below each bay is a 3.7 m (12 ft) diameter, variable blade pitch,
fiberglass propeller fan to produce the vertical flow of ambient air around
the heat exchanger tubes and the distribution pipes. Each fan is driven by a
30-hp motor and equipped with a high-vibration cut-out switch to prevent the
fan being damaged by excessive vibration.
Operating Experience
While the dehumidifier was designed to minimize, not eliminate, the
plume it has not been effective when ambient temperatures are below 0°C
(32°F), especially when ice forms on the fans. As the ice accumulates, the
fans become imbalanced and vibrate above the vibration level of the pro-
tective cut-out switch. With the fans off, the density and size of the plume
increases markedly. However, the icing could be prevented if the fans were
moved to the top of the bays since the exiting gas-air blend would keep the
fan temperature above the icing condition.
Originally, the gas distribution to the bays was very poor since most of
the flow went to the last bay on each side. Although baffles were installed
for better gas distribution, some of the bays are still overloaded and others
underloaded. Consequently, the dehumidifier has never attained its design
efficiency.
Scaling in the heat exchanger tubes has substantially reduced the heat
transfer efficiency. During one period when the scrubber was shut down, the
heat exchanger tubes, the outlet vestibules, and the mist eliminators had
become plugged with solids. As discussed above, this condition caused a
substantial increase in the discharge pressure and corresponding decrease in
the volumetric flow of the induced-draft fan.
The low-level dehumidifier discharge (about 9 m, 30 ft above the ground
level) is environmentally unacceptable. If the scrubber is operative, the
resultant large and dense plume can cause serious fogging and icing conditions
on the new interstate highway adjacent to the plant. If the scrubber is
inoperative, the resultant high acid concentration in the vapor can be
injurious to people and equipment (Figure 72).
170
-------
The acidic content of the flue gases has severely corroded such dehumid-
ifier components as the vessel shell and the heat exchanger tubes. In
particular, the condensate drain lines have corroded through because of the
low pH of the condensate (Figure 73").
Figure 72. Area fumigation by exhaust gases.
»^
yx&
JT.'4<«
Figure 73. Dehumidifier condensate pipe corrosion.
171
-------
Maintenance
Except for preventive maintenance (Table 38), the dehumidifier fans have
required only new cam roller bearings. After a short operational period, the
blade pitch of one of the fans had to be reset. The condensate drain lines
were replaced after they had corroded through.
TABLE 38. DEHUMIDIFIER FAN PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check reducer oil for sludge or condensation.
Check oil level in reducers, and check reducers for oil leaks.
Grease fan bearings (LiEP2).
S emiannually
Change reducer oil.
(Winter - Paradene 430)
(Summer - Paradene 475)
Grease propellor hubs (Molycote EP2).
Grease motors (LiEP2).
Check motors.
Check alarm and vibration switches.
Annually
Megger motors.
Check operation of fan ammeters.
Zero and calibrate:
Remote manual blade pitch control station.
Current to pneumatic converter.
Fan blade positioners.
Check bearing condition of fan blade conditioners.
Check air lines and air supply pressure to fan blade positioners.
ENERGY RECOVERY MODULE
The energy recovery module, as represented by the shaded areas in
Figure 74, recovers the sensible heat in the combustion gases discharged from
the gas purifier in the thermal processing module by producing steam to be
sold to the local utility company.
172
-------
MAGNETICS
VACUUM BELT
FLOATATION
4
I
TIPPING
FLOOR
r
REFUSE
STOR-
AGE
PIT
BURNERS [jr^
BOILER FEEDWATER
GASES SOLIDS
h— KILN •"
UCHAR
MAGNET
^
GLASS
I BURNERS
^) COMBUSTION AIR
INDUCED
DRAFT
FAN
SHREDDER
SHREDDER
BOILER FEEDWATER
DEHUMIDIFIER
\
EXHAUST TO
ATMOSHPERE
Figure 74. Energy recovery module (shaded area).
-------
Until refractory failures and gas leakage prompted its sealing, a jug
valve in the' gas purifier and boiler outlet ductwork controlled the gas flow
to two parallel waste heat boilers by diverting surplus gas directly to the
gas scrubber in the thermal processing model. Initial slagging of the heat
exchanger tubes in each boiler and its attached economizer was eliminated by
installing quench air dampers in the exit duct of the gas purifier. The
boiler-economizer assemblies are equipped with soot blowers to periodically
remove ash accumulations on the tube banks and a fly ash collection system
which had to be modified because of continued ash plugging throughout the
system. Some of the steam produced has had to be wasted by passing it
initially through the gas scrubber and then later through a steam muffler,
especially during the spring and fall when the steam demand is low.
Although not indicated in Figure 74, the following subsystems for the
boiler feedwater treatment are integral components in the energy recovery
module: (1) a water softening system to remove from the city water the
calcium, iron, magnesium, and other ions that could cause scaling in the
boilers; (2) a degasifier system to remove carbon dioxide from the feedwater;
(3) a deaerating heater for preheating the feedwater and removing oxygen from
it; (4) a chemical system to complete the oxygen removal and prevent the
precipitation of the scale—inducing and sludge—forming metallic ions;
and (5) two feedwater pumps, a motor-driven pump for boiler startup operation,
and a turbine-driven pump for continuous operation after the start-up. Of
the feedwater treatment systems, only the degasifier has not operated properly;
however, its need has been only marginal because of the low concentration of
bicarbonates in the city water.
Water Softening System
In the process of preparing city water as feedwater for the waste heat
boilers, the water softening system removes from the water the divalent
metallic cations, such as calcium, iron, and magnesium, that would cause
scaling the the boilers. The removal consists of exchanging monovalent
metallic sodium cations in a synthetic ion exchange resin with the divalent
metallic cations as city water flows through a softener tank. When the
divalent metallic cation have saturated the resin, they are exchanged with
sodium cations when a brine solution is pumped through the tank in the phase
of the system cycling to regenerate the resin with the sodium cations.
Upon leaving the softener tank, the feedwater flows to the degasifier
for further treatment.
Description
The water softening system consists of (1) three parallel water softener
tanks to perform the divalent metallic and sodium cation exchanges, (2) a
brine tank into which salt is pumped from a delivery truck and then a properly
proportional quantity of water is poured into the tank to prepare the brine
solution, and (3) a pump to supply the softener tanks with the brine. The
three softener tanks and the brine pump are installed in the water treatment
building, while the brine tank is outside of and adjacent to that building.
174
-------
Supplied by the L. A. Water Treatment Division, each of the three water
softener tanks is a Model 206CP3T vertically arranged cylindrical pressure
tank. Constructed of welded steel with a baked plastic lining 0.10 to
0.18 mm (4 to 7 mils) thick, each tanks is 1.5 m (5 ft) in diameter and 1.5 m
(5 ft) in height with a working volume of 2650 liters (700 gallons), a
freeboard volume of 190 liters (50 gallons) and therefore a total volume of
2840 liters (750 gallons). Each tank contains 2265 liters (600 gallons) of
synthetic ion exchange resin (LA101) which allows a flow-through capacity of
1700 liters per minute (450 gpm) of water and a feedwater capacity of
1,135,500 liters (300,000 gallons) between the resin regenerations. In
addition, each tank is equipped with a low-pressure switch which activates an
alarm in the control room when the water pressure drops below a preset
pressure, and a water flow integrator which activates an alarm in the control
room when a preset volume of feedwater has flowed through the tank.
The operation of the three softener tanks was designed so that two tanks
could handle the required feedwater flow while the third was available for
the resin regeneration.
The brine tank, which was supplied by the Morton Salt Company, is a
Model FG1015 vertically arranged cylindrical tank completely enclosed except
for a gooseneck vent at the top. Constructed of fiberglass-reinforced plastic,
the tank is 3 m (10 ft) in diameter and 4.5 m (15 ft) in height with a
working volume of 31,775 liters (8,400 gallons), a freeboard volume of
2,265 liters (600 gallons) and therefore a total volume of 34,040 liters
(9,000 gallons). The tank is equipped with a Morton Model AH water-level
indicator.
Also supplied by the L. A. Water Treatment Division, the brine pump is a
horizontal centrifugal PVC (polyvinyl chloride) pump. The pump has a rated
capacity of ISO liters per minute (40 gpm) at a total dynamic head of 45 m
(150 ft) of water. It is operated only when the resin in a softener tank is
being regenerated.
Operating Experience
During normal operation when the water flow integrator would sound the
alarm indicating that the preset volume of feedwater had passed through a
softener tank, the prescribed procedure called for the operators manually
initiating the regeneration process which would then proceed automatically.
However, whereas the operators were required to check the water hardness once
during a shift, they would check the water hardness before each manual
initiation of the regeneration.
While the water-level indicator in the brine tank was installed to
signal the need for reordering salt, the operators ascertained the need by
checking the specific gravity of the brine solution as well as considering
the water level because of the unreliability of the indicator functioning and
the constant proper proportioning of the water and salt content in the brine
tank.
175
-------
High humidity and condensate in the water treatment building have
damaged the electric controls of the water softening system.
The automatic valves in the brine feedlines to the softener tanks have
occasionally remained shut because of salt accumulations. Therefore, there
have been instances when the softener tanks have resumed the feedwater flow
without having their resin regenerated. When there are such salt accumu-
lations and there is need to clear the lines or to clean or repair the pump,
the pressurized brine sprays violently at any opening. A pressure relief
valve installed in the discharge line of the brine pump would eliminate this
condition.
Maintenance
The brine piping has required occasional repairs. The check valve on
the brine tank and the brine pump were each replaced once.
The preventive maintenance schedule for the water softeners consist of
quarterly checks on the operation of all electrical controls and readout
units, all valves, the galloned out alarm, and lubrication of the timer
motors.
The brine tank preventive maintenance schedule includes annual checking
and cleaning of the flow indicator, solenoid valve, and solenoid valve timer
which must also be lubricated.
The brine pump preventive maintenance schedule is shown in Table 39.
TABLE 39. BRINE PUMP PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check bearing temperature (maximum 107°C).
Check pump, stuffing box, and check for leaks.
Quarterly
Grease pump (Pyoplex EP2),
S emiannually
Grease motor (LiEP2).
176
-------
Degasifier System
After its discharge from the water softening system, the feedwater for
the waste heat boilers flows to a degasifier system. In the given order the
following processes take place in the degasifier system to remove carbon
dioxide from the feedwater: (1) the pH reduction to 5.5 by a sulfuric acid
system to reduce the solubility of carbon dioxide before the feedwater enters
a degasifier tank, (2) the carbon dioxide removed from the water in the
degasifier tank where the feedwater distributes at the top of the tank falls
through a lattice-like column (packing) to provide the maximum area for water
surface exposure and where atmospheric air vertically blown by a fan through
the column serves as a stripping agent to remove the carbon dioxide, and
(3) the neutralization of the feedwater by a caustic system which increases
the pH to 7.2 as the feedwater is discharged from the degasifier tank.
With the mixture of carbon dioxide and air discharged to the atmosphere,
the degasified and neutralized feedwater proceeds to the deaerating heater
for oxygen removal before being pumped to the waste heat boilers.
Description
Supplied by the L. A. Water Treatment Division and installed in the
water treatment building, the degasifier system comprises three subsystems
each with several components: (1) a sulfuric acid system, (2) the degasifier
equipment system, and (3) the caustic system.
As mentioned above, the sulfuric acid system decreases the pH of the
feedwater to 5.5 in order to reduce the solubility of the carbon dioxide
before the feedwater enters the degasifier tank. This system consists of
(1) a sulfuric acid storage tank, (2) a sulfuric acid pump, and (3) a de-
gasifier ac-'.d controller. The storage tank is a 208 liter (55 gallon)
carboy which contains 93 percent sulfuric acid. The sulfuric acid pump, a
Milton-Ray Model R-12A simplex positive displacement diaphragm unit, pumps
the sulfuric acid from the carboy to the PVC pipe between the water softeners
and the degasifier tank. Direct-driven by a 1/4-hp motor, the pump has a
cast iron liquid end with special stainless steel trim for acid service. The
pump inlet piping is stainless steel and the outlet piping is PVC. The
degasifier acid controller pneumatically regulates the flow rate of the
sulfuric acid pump according to two signals transmitted to it: a pH signal
from a glass pH electrode in a continuous sample line flowing from the de-
gasifier tank to a drain and a flow rate signal from an orifice flowmeter in
the degasifier pump discharge line. The degasifier tank, where the carbon
dioxide is removed from the feedwater, is a vertically arranged cylindrical
tank installed in a pit about 2 m (7 ft) below floor level. Constructed of
carbon steel and lined with 5-mm (0.2-in.) thick rubber, the tank is 1.7 m
(5.6 ft) in diameter and 4-m (13-ft) high to provide a total volume of
8,700 liters (2,300 gallons). At the top of the tank is a spray header which
evenly distributes the incoming feedwater over the entire circular area. The
bottom 2.3 m (7.5 ft) of the tank serves as a water surge tank, or wet well,
with a 5,100 liter (1,350 gallons) volume to collect and store the degasified
feedwater until it is pumped by either of the degasifier pumps. An overflow
177
-------
pipe is 2.7 m (9 ft) above the,bottom of the tank, of 0.4 m (1.3 ft) above
the normal maximum water level. Between the overflow pipe and the top of the
tank is a diameter-wide stripping column. This column provides the maximum
area for water surface exposure to the vertically blown atmospheric air which
serves as the stripping agent for the carbon dioxide removal from the feed-
water. The column is a lattice-like structure of Maspak packing.
Installed on the outside of the degasifier tank and just above the level
of the tank overflow pipe, the degasifier fan is a horizontal centrifugal
blower manufactured by New York Blower. The fan is direct-driven by a 2-hp
motor and has a capacity of 28 m3 per minute (1,000 CFM) at a pressure of
10 cm (4 in.) of water. In the same pit as the degasifier tank are two
degasifier pumps arranged in parallel so that one pump may be operative while
the other serves as a spare. Each pump is an Allis-Chalmers Model 4311
horizontal centrifugal pump with a closed impeller. Direct-driven at
1,760 rpm by a 20-hp motor, the pump has a capacity of 1,900 1pm (500 gpm) at
a total head of 27 m (90 ft) of water.
As discussed above, the caustic system neutralizes the feedwater by
increasing the pH to 7.2 as the feedwater is discharged from the degasifier
tank. This system consists of (1) a caustic storage tank, (2) a caustic
transfer pump, (3) a caustic mixing tank, (4) a caustic mixing tank agitator,
(5) a caustic feed pump, and (6) a degasifier caustic controller. The caustic
storage tank is a vertically arranged cylindrical tank supplied by the
Willard L. Sherman Company. Constructed of carbon steel, the tank is 1.5 m
(5 ft) in diameter and 2.7 m (9 ft) high. With 44 cm (18 in.) of freeboard,
the tank has a working volume of 4,160 liters (1,100 gallons) to store 18 or
50 percent caustic, whichever is available on the local market. The tank is
equipped with a bubble-type level indicator and thermostatically controlled
electric heaters to prevent the caustic solution from freezing. As the means
for transferring the caustic solution from the caustic storage tank to the
caustic mixing tank, the caustic transfer pump is a Goulds Model 3199 hori-
zontal centrifugal pump. The pump casing, nozzles, and impeller are made of
cast iron; the pump shaft and shaft sleeve are constructed of 316 stainless
steel; and the mechanical seal is made of BP 171. Direct-driven at 3,500 rpm
by a 1.5-hp motor, the pump has a capacity of 110 Iph (30 gph) at a total
head of 12 m (40 ft) of water.
The caustic mixing tank, supplied by the Willard L. Sherman Co., Inc.,
was designed to prepare a dilute (18 percent) sodium hydroxide solution from
a 50 percent sodium hydroxide solution. Constructed of carbon steel, the
tank is 1.2 m (4 ft) in diameter and 2 m (7 ft) high. The tank has a flat
bottom and top with a hole in the top to accommodate the agitator. With
40 cm (16 in.) of freeboard, the tank has a working volume of 1,800 liters
(475 gallons). The tank is equipped with a bubble-type level gauge. Supplied
by the Clevelend Mixer Corporation, the caustic mixing tank agitator is a
Model FGB-1/3 vertical propeller agitator. At the top and bottom of the
1.5-m (5 ft) shaft are dual 49 cm (19 in.) diameter propellers each having
three steep-pitch marine blades. Constructed of carbon steel, the shaft and
impellers are driven at 420 rpm by an electric motor.
178
-------
The caustic feed pump transfers the sodium hydroxide solution from the
caustic mixing tank to the suction line of the degasifier pump for the feed-
water neutralization. This pump is a Milton-Ray Model R-100A simplex,
positive displacement, diaphragm pump. The pump has a cast iron liquid end
with special steel trim for caustic service. Direct-driven at 1,750 rpm by
a 3-hp motor, the pump has the capacity for a discharge varying from 0 to
20 Iph (0 to 5.3 gph) at a total head of 30 m (100 ft) of water. The de-
gasifier caustic controller regulates the caustic feed pump flow to maintain
a 7.2 pH as governed by a pH signal transmitted from a glass pH electrode in
a continuous sample line flowing from the degasifier pump discharge to the
degasifier tank.
Operating Experience
Although the degasifier system is a type commonly used and an off-the-
shelf item, the acid and caustic systems have never operated properly and
therefore have been used rarely. However, since the city water has a low
concentration of bicarbonates, the need for these systems has generally been
marginal at most.
When the acid and caustic systems have been operative, the pH decreases
and increases have been excessive because both the caustic and the sulfuric
acid feed pumps have too large a capacity, and both the caustic and the
sulfuric acid concentrations in the respective solutions have also been too
high.
The PVC piping for the acid system developed frequent leaks during the
limited system usage.
The check valve on the discharge line of the acid pump was relocated
after it allowed water to enter the acid pipe, for the water reaction with
the acid caused the pipe overheating which in turn produced a leak. After
the check valve was replaced to prevent this condition, the large PVC pipe
between the water softeners and the degasifier system developed a leak,
unrelated to the check valve replacement, which had to be repaired.
On one occasion when the pit for the degasifier tank and pumps had
filled with water and there is no sump pump to discharge such water, the
degasifier pump motors sustained water damage and had to be replaced.
In summary, the entire degasifier system has not operated long enough to
permit a comprehensive assessment of its operation and maintenance.
Maintenance
The degasifier stripping column and fan have required only preventive
maintenance. Annually the degasifier level valve, level controller, high-
and low-level alarms and switches, and caustic and degasifier pumps discharge
pressure indicators must be zeroed, cleaned, and calibrated. The degasifier
fan requires semiannual lubrication (L1EP2).
179
-------
The maintenance requirements for the sulfuric acid pump have included
frequent cleaning and rebuilding, priming of the suction pipe, adjustment of
the bypass, relocation of the check valve, and replacement of a length of
pipe to eliminate leaks.
The caustic feed pump was repiped twice, and the pump diaphragm was
replaced once. The sulfuric acid and caustic feed pumps require weekly
checking of the oil level in the air bleed filter reservoirs, and the pump's
liquid, and for leaks. Semiannually the oil in the reservoir must be changed
(EPS).
The degasifier pumps were realigned after a new coupling was installed,
and as mentioned above, the degasifier pump motors were replaced after
sustaining water damage. In addition, the bearing and mechanical seal for
one of the degasifier pumps was replaced. The preventive maintenance
schedule for these pumps are shown in Table 40.
TABLE 40. .DEGASIFIER PUMPS PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check bearing temperature (maximum = 82°C):
If hot, change lubricant.
If remains hot, then check bearings.
Quarterly
Check grease lubrication for saponification.
Check stuffing box.
Check mechanical seals for leakage.
Lubricate (LiEP2).
S emiannually
Check alignment of pump to motor.
Inspect all piping supports.
Grease motor (LiEP2).
Annually
Remove the rotating element. Inspect for wear and wearing clearances
and order replacement parts if necessary.
Remove any deposit or scaling and clean stuffing box.
Measure total dynamic suction and discharge head as a test of pipe
connection and compare with past test.
Inspect check valves, especially the one which safeguards against
water hammer when the pump stops.
180
-------
Deaerating Heater
As pumped from the degasifier tank, the softened and degasified feedwater
for the waste heat boilers flow to the deaerating heater for oxygen removal.
In the deaerating heater, the feedwater is preheated and deaerated by either
the steam exhaust from the boiler feedwater pump turbine, high-pressure steam
from the boilers, or both. During the deaerating heater processing, the
steam condenses to become part of the feedwater, the released oxygen escapes
through a vent in the heater, and the preheated and deaerated feedwater flows
to either the turbine-driven or the electric-driven boiler feedwater pump to
be pumped to the waste heat boilers.
Description
Supplied by the L. A. Water Treatment Division, the deaerating heater is
a Model L-N-8.5-260 horizontally arranged cylindrical, spray-type feedwater
tank. Constructed of carbon steel, the tank is 2.6 m (8.5 ft) in diameter
and 7 m (23 ft) long. The tank has a working volume of 20,400 liters
(5,400 gallons) and a total volume of 31,800 liters (8,400 gallons). The
valves and inlet section are made of 304 stainless steel.
The tank has three sight glasses to observe the full range of the water
level. The operating tank level is set at 28 cm (11 in.) above the center-
line. If the level exceeds 38 cm (15 in.) above the centerline, an alarm is
activated in the control room. If the level falls below the minimum for the
boiler feedwater pumps, a low-level switch shuts off the pumps. The high-
pressure steam entering the tank is regulated by a steam control valve whose
positioning is a function of the tank pressure.. Also the feedwater entering
the tank is regulated by a Fischer-Governor Co. No 657-Ed pneumatically
operated water-level control valve to maintain the water level at a 28 cm
(11 in.) above the centerline.
To protect the boilers, an emergency waterline with a manual valve
directly connects the city water supply to the deaerating heater if the feed-
water piping or equipment fails.
Operating Experience
Since the deaerating heater is standard equipment typical of that used
in most boiler facilities, most of the malfunctions have been due to piping
leaks, especially those induced by freezing conditions. Consequently, the
tank placement in a protected environment should be considered.
Although the tank was designed for an outlet temperature of 121°C
(250°F) and an internal pressure of 64 kPa (10 psig), the operating temper-
atures and pressures have generally been about 105°C (220°F) and 35 kPa
(5 psig).
To prevent water hammering when the high-pressure steam control valve
was opened causing the entering steam to rapidly evaporate the condensed
steam in the line, a 2.5-cm (1-in.) bypass steam line was installed around
that valve.
181
-------
Maintenance
The water-level control valve for the feedwater flow into the tank and
the actuator in the modulating high-pressure steam valve were replaced.
Sight glasses, valves, and pipes broken by freezing were also replaced.
Table 41 presents the preventive maintenance schedule for the deaerating
heater.
TABLE 41. DEAERATING HEATER PREVENTIVE MAINTENANCE SCHEDULE
Annually
Zero and calibrate level valve, intake from degasifier.
Check operation.of solenoid.
Clean and calibrate:
Magnetic alarm switch.
Level controller.
Steam pressure valve from boilers.
Pressure indicating controller.
Zero, calibrate, and check operation:
Temperature indicator gauge.
Feedwater pressure indicator.
High water level switch.
Low water level switch.
High and low water level alarms.
Boiler Feedwater Chemical System
The boiler feedwater chemical system supplies two chemical solutions to
the feedwater: in the deaerating heater a sodium sulfite solution to ensure
complete oxygen removal from the feedwater and thereby to prevent boiler
corrosion, and in the boilers a chelate solution prepared with ethylenediamine-
tetraacetic acid (EDTA) to prevent the precipitation of any divalent metallic
cations thereby minimizing scaling and sludge formation.
Description
Supplied by the Milton-Ray Co. and installed in the water treatment
building, the boiler feedwater chemical system comprises two subsystems:
one for the sodium sulfite solution and the other for the chelate solution.
Each subsystem consists of a tank, an agitator, and a pump.
The sodium sulfite tank is a vertically arranged cylindrical tank with a
flat bottom and a flat hinged top. Constructed of carbon steel and mounted
on legs, the tank has a 76-cm (30-in.) diameter and a 46-cm (18-in.) height
182
-------
for a total volume of 190 liters (50 gallons) with 14 cm (5 in.) of free-
board. Mounted to the tank by a portable clamp, the sulfite solution agitator
consists of a vertical 316 stainless steel shaft and propeller driven by a
1/4-hp motor. The pump to transfer the sulfite solution from the tank to the
deaerating heater is a Model R-120A simplex, positive displacement, propor-
tioning diaphragm pump with an adjustable discharge and a cast iron liquid
end. Driven at 1,760 rpm by a 1/4-hp motor, the pump has a rated capacity of
23 Iph (6 gph).
The chelate tank is a vertically arranged, cylindrical, polyethylene
tank with an open top and a flat bottom. Mounted on legs in a metal frame,
the tank has a 69-cm (27-in.) diameter and a 107-cm (42-in.) height for a
total volume of 400 liters (105 gallons) with 5 cm (2 in.) of freeboard. All
piping, valves, and strainers are PVC. Also mounted to the tank by a portable
clamp the chelate solution agitator is a Model 102-0115-116 agitator. Its
shaft and impeller are made of 316 stainless steel and are driven at 1,760 rpm
by a 1/4-hp motor. The pump to transfer the chelate solution from the tank
to the deaerating heater is a Model FR 231-A-78 duplex, positive displacement
pump with an independent adjustable flow and a 316 stainless steel liquid
end. The pump is driven at 1,140 rpm by a 1/2 hp motor, and the flow capacity
of each Jiead is 60 Iph (16 gph) at a pressure of 2,275 kPa (330 psig).
Operating Experience
The solutions for each tank are prepared daily by manually feeding the
dry chemicals and water into the respective tank and then mixing the solutions
with the agitators. The solutions are pumped continuously throughout the
rest of the day. Since the system components are standard units typical of
those used in most boiler facilities, their performance is generally the same
as the conventional norm. Except for occasional freezing or plugging of the
chelate lines, -the boiler feedwater chemical system has operated well.
Maintenance
After a short operational period, the motor for the sulfite tank agitator
had to be replaced. The piping for both pumps had to be frequently repaired
because of numerous leaks. The chelate pump fractured a pressure plate which
had to be replaced; the pump itself had to be repaired after it jammed; and
the pump strainer was replaced.
As preventive'maintenance, the sulfite and chelate pumps required weekly
checking of the liquid ends for leaks, and the lubrication and oil level in
the reducer. Semiannually the oil in the reducer required replacement
(EPS).
The preventive maintenance schedule for all the agitators including the
sulfite and chelate agitators is shown in Table 42.
183
-------
Boiler Feedwater Pumps
The boiler feedwater pumps pump the pretreated and preheated feedwater
from the deaerating heater and through the economizers to the waste heat
boilers.
TABLE 42. AGITATOR PREVENTIVE MAINTENANCE SCHEDULE
Quarterly
Check reducer for vibration, leaks, or noise.
Check motor for vibration or heat.
Check reducer gear box lubrication on both floe feed tank agitator
and caustic tank agitator (LiEP2).
Check reducer gear boxes on chemical feed tank agitator.
(Winter - EPS)
(Summer - EPS)
Semiannually
Check reducer for vibration, noise, leaks.
Check motor for vibration or heat.
Change oil in chemical feed tank agitator reducer gear box.
(Winter - EPS)
(Summer - EPS)
Lubricate shaft bearing on chemical feed tank agitator (LiEP2).
Grease all motors (LiEP2).
Description
There are two boiler feedwater pumps: a startup pump also functioning
as a spare which is driven by a 200-hp motor, and a post-startup continuously
running pump which is driven by a steam turbine. Each pump is a Peerless
Model TUT-9 7.5 cm (3 in.), four-staged, horizontally split case, centrifugal
pump with mechanical seals, water-cooled stuffing box, and a bearing housing
directly coupled to the drive source. Also each pump has a design capacity
of 2,120 1pm (560 gpm) at 3,500 rpm and a total head of 320 m (1,050 ft) of
water.
The steam turbine is a Cuppus Model TP22L horizontal unit equipped with
an automatic, differential pressure, steam-feed governor set to maintain the
feedwater discharge pressure at 587 kPa (85 psig) above the steam pressure.
A horizontal separator installed in the steam inlet line to the turbine
removes all solid and liquid impurities. The separator shell is constructed
of carbon steel, and the separator element is made of 304 L stainless steel.
184
-------
The following built-in provisions maintain the feedwater flow to the
boilers and protect the pumps. The two pumps are interlocked so that the
discharge pressure of the turbine-driven pump falls below 2,650 kPa
(385 psig), the electric-driven pump is automatically started. If the
turbine speed exceeds the rated speed by 20 percent, safety trip mechanism
stops the steam flow to the turbine. In addition, a relief valve prevents
excessive back pressure in the turbine case.
Operating Experience
As designed, the electric-driven pump was to operate at start-up and
until the steam main would be hot and up to pressure. Then the turbine-
driven pump could be started and the electric-driven pump turned off. How-
ever, the electric-driven pump has been operated much more than originally
planned because of the following: First, since the plant operation was very
irregular during the demonstration period, the steam main was often not up to
temperature and pressure long enough to permit starting the turbine-driven
pump. And second, the turbine-driven pump was shut down for repairs much of
the time because of the diaphragm failures which occurred when the electric
pump was started and the pressure at the discharge of the turbine-driven pump
was so reduced that the diaphragm could not withstand the excessive differ-
ential pressure across it.
Both pumps have vibrated excessively and sustained minor leaks at the
seals. The feedwater valves have had to be throttled back because of valve
erosion due to low-flow conditions. Consequently, to reduce the erosion, the
valves were coated with stellite, a hard, wear-resistant, and corrosion-
resistant alloy.
Maintenance
Shortly after the initial start-up, the electric-driven pump was returned
to the factory for major repairs when an inspection of the pump revealed that
the impeller had broken into several pieces. After the repair, the pump has
required only minor maintenance such as alignment, repair of a leak in the
bearing cooling water lines, and replacement of set screws in the seal ring
with stainless steel set screws after the original set screws had eroded.
Although the diaphragm in the governor of the turbine was replaced
several times, as mentioned above, most of the maintenance on that pump
involved its piping. In addition, the turbine-driven pump had to be cleaned
once.
The preventive maintenance schedule for these pumps is shown in
Table 43.
Waste Heat Boilers and Economizers
During normal operation, the gas purifier discharge gases are cooled
with ambient air entering the duct through quench air dampers and then enter
the two parallel waste heat boilers, where their sensible heat is recovered
185
-------
TABLE 43. FEEDWATER PUMP PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check mechanical seal, bearings, turbine condition, and turbine oil
level (Paradene 430).
Monthly
Change oil in turbine.
Turn turbine lube screw on packing one half turn.
Quarterly
Grease bearings (LiEP2).
Lubricate coupling on turbine.
Semiannually
Grease motor (LiEP2).
Check motor alarm and interlocks.
Check automatic start switch.
Annually
Megger motor.
Zero, calibrate, and check operation of feedwater pump discharge pres-
sure indicator.
in the form of steam. Upon exiting the boilers, the gases flow through the
economizers Cone attached to each boiler without intermediary ductwork) to
preheat the boiler feedwater and then combine to proceed to the gas scrubber.
Fly ash depositing on the boiler and economizer heat exchanger tubes as
the gases pass through are removed by the steam jetted from built-in soot
blowers. At the bottom of the boilers and economizers, below the tube banks,
are hoppers into which the ash falls for its discharge into the fly ash
collection system. Counter to the gas flow, the feedwater passes through the
economizers to the boilers.
The boiler-produced steam has been sold to the Baltimore Gas and Electric
Company, used within the plant, and vented to the gas scrubber. The steam
delivered to the Baltimore Gas and Electric Company flows through a steam
186
-------
main to the Ledenhal Station which is about a mile away from the Landgard
plant. At this station, the delivered steam passes through a steam entrain-
ment separator to remove water, scale, and other nongaseous impurities
before it enters the distribution line for the steam routing to various
remote sites.
Description
The two parallel waste heat boilers and economizers, manufactured by
Erie City, are installed beside the gas purifier. The schematic drawing in
Figure 75 shows the boiler and economizer configuration. Each of the boilers
is designed to produce 56.7 Mg per hr (125,000 Ib. per hr) of saturated steam
at a pressure of 2,277 kPa (330 psig).
In the conventional arrangement, the boiler consists of a steam drum at
the top and center of the boiler shell and two mud drums at the bottom and
respective sides of the boiler shell. With the three drums aligned along the
entire length of the boiler, a bank of heat exchanger tubes in a partial
oblique but generally vertical pattern connects the steam drum with the two
mud drums. Both the drums and the tubes are constructed of carbon steel.
The steam drum has a 121 cm (48 in.) inner diameter and a total volume
of 13,200 liters (3,500 gallons). With a normal operating water volume of
7,750 liters (2,000 gallons), the steam drum has the optimum surface area for
water evaporation into steam and an ample water depth to ensure the continuous
water supply to fill the tubes and the mud drums. Each mud drum has an
86-cm (34-in.) inner diameter and a total volume of 6,600 liters
(1,950 gallons). Suspended solids accumulating in the mud drums are
periodically removed by discharging part of the mud drum water to the blow-
down system. Consisting of tubes each with a 51-mm (2-in.) outerdiameter,
the bank of heat exchanger tubes has a total water volume of 12,400 liters
(3,250 gallons) and provides 940 m2 (10,000 ft2) of heat exchange surface
area between the boiler water and the gas purifier exit gases. The gases
make a single pass through the tube tank.
For the single gas pass through the boiler tubes, the tube bank is en-
closed at the top and on the sides by a duct with an airtight refractory
lining (shell). Below the bank of boiler tubes are refractory-lined hoppers
to collect and discharge the fly ash removed from the tubes.
Each boiler is equipped with such accessories as safeties, vents, and
blowdown valves; pressure and water gauges; an internal steam purifier; a
feedwater distribution pipe; automatic soot blowers; and an electric system
to remotely read the boiler drum water level.
The boiler shell is insulated with fiberglass to prevent heat loss, and
the insulation is covered with painted steel sheet metal to protect it from
the weather.
Upon exiting the boiler, the gases make a double pass through the
economizer. The economizer is a bank of heat exchanger tubes, each with a
51-mm (2-in.) outer diameter. Each economizer has a total water volume of
187
-------
ECONOMIZER
BOILER
DISCHARGE DUCT
oo
ROTARY SOOT BLOWERS
BOILER MUD DRUMS
RETRACTABLE SOOT BLOWERS
STEAM DISCHARGE
DUST HOPPERS
STEAM DRUM
BOILER TUBE BANKS
INLET DUCT SWING GATE
BOILER INLET DUCT
ROTARY VALVE
Figure 75. Schematic of waste heat boilers.
-------
7,560 liters (2,000 gallons) and provides 710 m2 (7,650 ft2) of heat exchange
surface area between the feedwater and the gases. Fly ash hoppers, similar
to those in the boiler, lie below the tube bank. In addition, the ductwork
for the gas flow through the economizer and the insulation for the economizer
shell are similar to those for the boiler. The gases exiting the two
economizers combine and then flow through ductwork to the gas scrubber.
The steam produced in each boiler combine to be; delivered to the
Ledenhal Station of the Baltimore Gas and Electric Company, used within the
Landgard plant, or vented to the gas scrubber, as mentioned above. When the
steam is not used, it is directed to the gas scrubber through a vent con-
sisting of an insulated steel pipe with a manual valve. When the steam is
sold to the Baltimore Gas and Electric Company, it is delivered through a
steam main to the Ledenhal Station, which is about a mile away from the
Landgard plant. Designed for a steam flow of 91 Mg per hr (200,000 Ib.
per hr), the steam main is an insulated steel pipe with a 30-cm (12-in.)
diameter. Lying mostly underground, the steam main from the Landgard plant
to the Ledenhal Station has ball-type expantion joints and seven fairly
evenly separated condensate traps, each with a manhole access. At the
Ledenhal Station, the steam passes through a steam entrainment separator to
remove water, scale, and other nongaseous impurities before the steam enters
the distribution line for the steam routing to various remote sites. The
steam entrainment separator is a Wright-Austin Type 31LS horizontal, line-
type separator with a carbon steel shell and a 304 stainless steel separator.
The line size for the separator is 40-cm (16-in.) schedule 40.
The steam-jetting soot blowers to remove the fly ash accumulating on
the heat exchanger tubes in the boilers and economizers are of three types—
all manufactured by Copes-Vulcan. Of the five evenly spaced soot blowers
along the side cf each boiler, the first three from the gas inlet end are
Model T20E retractable units. When operated, this model ejects steam to
dislodge the soot while both traversing and rotating into and out of the
boiler tube bank. The transverse and rotational speeds are both 1 mpm
(3.3 fpm). The last two soot blowers on the side of each boiler are each
automatic rotary-type units. Since these two soot blowers are stationary and
remain in a fixed position within the tube bank, they rotate only while
ejecting steam. The four soot blowers evenly spaced along the side of each
economizer are all of the same type, namely, Model D-5 manual, rotary-type
unit. Since this unit is also stationary, it similarly rotates only while
ejecting steam. While the automatic rotary-type model is driven by a motor,
the manual rotary-type model is operated by pulling a chain.
Operating Experience
As previously discussed, the slagging of the boiler tubes had been
eliminated by installing the quench air dampers in the exit duct of the gas
purifier. The ambient air entering the ducts has cooled the gas entering the
boiler inlet ducts from 1100°C (2000°F) to 900°C (1600°F) which is well below
the ash fusing temperature of 1150°C (2100°F). In addition, the previous
slagging had also plugged the fly ash hoppers and jammed the rotary valves in
the bottom.of these hoppers.
189
-------
Research conducted by Vaugh, Krause, Miller, and others of Battelle
Laboratory prompted the concern that fly ash accumulating on the first few
rows of the boiler tubes (Figure 76) could cause tube corrosion, especially
since the intensity of the corrosion is a function of higher temperature.
However, measurements of these tubes showed no significant decrease in their
outer diameters (Table 44) or the tube wall thickness (Table 45). Moreover
the fly ash buildup on these tubes would not appreciably decrease the heat
transfer since the tube area involved is only a small fraction of the total
heat transfer area. In any event, the fly ash buildup on these tubes could
be minimized by installing a soot blower closer to the boiler gas inlet.
Insofar as the investigation or treatment of the interior tubes is concerned,
there is no access way or method to inspect or manually clean their fire
sides.
Figure 76. Fly ash accumulating on the first row of boiler tubes.
190
-------
TABLE 44. MICROMETER MEASUREMENTS OF BOILER TUBES*
Outside diameter
perpendicular to flow
(mm)
Outside diameter
parallel to flow
(mm)
Outside diameter
original
(mm)
Boiler No. 1
Boiler No. 2
50.52
50.67
50.54
50.58
50.52
50.33
50.62
50.45
50.64
50.49
50.43
50.52
50.8
50.8
50.8
50.8
50.8
50.8
* June 8, 1977
TABLE 45. BOILER TUBE CORROSION*
Inlets
Economizers
Thickness Thickness
Boiler No. 1 Boiler No. 2
(mm) (mm)
3.56 3.30
3.43
3.68
3.43
3.94
4.32 - 4.45
4.06
Thickness
original
(mm)
3.43
3.43
3.43
3.43
3.43
3.81
3.81
* Unpublished Monsanto Date, October 22, 1976.
191
-------
Because of the varying mass rate of the shredded refuse fed to the
thermal processing module, it was difficult to produce steam with a constant
rate and pressure. Even when the thermal processing module operated at the
maximum capacity of 38 Mg per hour (42 tph), the boilers did not reach the
design steam rate of 91 Mg per hour (200,000 Ib. per hour). This inability
can be attributed to the ambient air entering the quench air dampers the high
heat losses through the gas purifier wall, the gases bypassing the boilers
through the jug valve, and the reduction of the fuel oil burned in the kiln.
In addition to the steam-producing deficiencies within the Landgard
plant, a substantial amount of the steam discharged into the main to the
Ledenhal Station has been lost en route because of the high ground water
level which results in much of the steam main and the condensate trap man-
holes being under water. In addition, some steam has leaked through the main
expansion joints. Moreover, although the amount of steam produced is much
less than that designed, the Baltimore Gas and Electric Company has had
insufficient need in the spring and fall to purchase all the steam produced.
Even during periods of high steam demand, the operators at the Ledenhal
Station have generally been unwilling to adjust their steam production so
that all steam produced at the Landgard plant could be passed through the
steam main to the station.
When the steam was directed to the Ledenhal Station, it had to be
throttled considerably since the pressure in the Ledenhal steam main is only
1,035 kPa (150 psig) while the design pressure of the steam generated at the
Landgard plant is 2,277 kPa (330 psig). When the automatic valve to throttle
the steam flow occasionally malfunctioned, a safety valve opened to relieve
the explosive steam pressure. Moreover, some of the safety valves were
installed facing down. Obviously, steam emitted from such valves oduld have
seriously injured personnel in the vicinity. i
When the steam could not be delivered to the steam main or used within
the Landgard plant, it had to be vented to the gas scrubber. But as
discussed previously, the vented steam caused the resumption of the excessive
vibration of the induced-draft fan. Consequently, the steam muffler was
installed to permit wasting the steam without passing it through the gas
scrubber.
:J.
Initially, when there were no boiler pressure readouts in the control
room, the operators had to read a boiler-mounted dial gauge to check the
pressure in each boiler. While remote pressure gauges were later installed
in the control room, the operators questioned their accuracy.
During the winter, the small water lines frequently froze, especially
the sampling line. In addition, the blowdown lines of the mud drums froze
occasionally, particularly during the periods between blowdowns when there
was no flow in the lines.
Since the main steam valves have been difficult to open, an equalizing
line should be installed around such valves to permit easier opening. In
addition, many of the small isolation valves have a maximum pressure rating
below the design boiler pressure.
192
-------
When the soot blowers are operating, steam condensing within the blowers
cause water hammering, which could be eliminated by installing drain lines in
the blowers.
Frequently, during standby operation and when the shredded refuse flow
to the thermal processing module has been erratic, there has not been enough
steam pressure for the soot blowers in their once-per-shift operation. An
access platform was installed on the side of each economizer to permit easier
manipulation of the chains rotating the soot blowers.
The fly ash hoppers in the boilers and economizers have frequently
plugged because of the large amount of ash removed from the heat exchanger
tubes during each soot blowing and the bridging of agglomerated fly ash lumps
across the hopper walls. To facilitate clearing away the ash accumulations
in the economizer hoppers, pipes were installed in the sides of the hoppers
to permit horizontal rodding. However, the inadequacy of this method proved
that the ash could be effectively cleared only by removing the rotary star
valve assembly and rodding the hoppers vertically. The hopper plugging could
possibly be eliminated by making the hopper outlets larger and/or by operating
the soot blowers more often.
Maintenance
Most of the boiler and economizer maintenance requirements were for
single or occasional malfunctions. A few times, the blowdown and steam
regulator valves became locked in position and had to be freed and the
tsight glass on a water level gauge had to be replaced. The soot blower
fuses werewreplaced frequently. One of the economizers required a new main
valve. Aftoer the feedwater modulator valves were severely worn due to the
high velocitils vaused by their throttling, each valve was repaired by
replacing the piston and rebuilding the seat.
Table 46 details the boiler preventive maintenance schedule.
'_•»
Boiler Ducts and Jug Valve
t
The jug valve was designed to control the gas flow from the gas purifier
to the boilers, economizers, and gas scrubber by diverting the unneeded por-
tion of gas directly to the gas scrubber.
Description
Figure 74 shows the relative positions of the gas purifier exit duct,
the jug valve, the boiler inlet and outlet ducts, and the gas scrubber inlet
duct—all briefly described as follows: Midway between the two boiler inlet
ducts, which connect to the gas purifier exit duct, is the jug valve which is
a movable circular disk within a vertical cylinder. The vertical cylinder
with its bottom open to the top of the gas purifier exit duct connects the
horizontally aligned boiler outlet and scrubber inlet ducts which are elevated
above the gas purifier exit and the boiler inlet ducts (Figure 77).
193
-------
TABLE 46. BOILER PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check gear box oil level on retractable soot blowers.
Monthly
Check all rotary gates for noisy operation.
Lubricate "PN" rotary gates:
Grease bearings (LiEP2).
Check oil level in reducer.
(Winter - EPS)
(Summer - EPS)
Lubricate "G" rotary gates:
Grease sleeve bearings (LiEP2).
Check oil level in reducer (EPS).
Rotary and retractable soot blowers:
Check operation cycle.
Check for steam leaks. Correct immediately.
Check valves. Tightly seated.
Check packing glands for proper tightness.
Clean off dirt and rust.
Check that mounting is secure.
Check cams and moving parts for lubrication.
Rotary valves lubrication:
Oil drive gears and all other moving parts (Paradene 430).
Retractable soot blowers:
Check chain for proper lubrication. Should rust form use special
aerosol penetrating oil (CV1#39837, 139036).
Check gear box oil level (Super V10W-30).
Quarterly
Grease shaft bearings (both sides), worm gear, and all other moving
parts on butterfly valves.
Check for smooth operation, especially sprocket of worm.
Check operation and clean inking system of flow recorder, pressure
recorder.
Semiannually
Change gear motor oil on rotary gates "PN".
(Winter - EPS)
(Summer - EPS)
CONTINUED
194
-------
TABLE 46. CONTINUED
Change gear motor oil on rotary gates "6" (EPS).
Change gearbox oil on retractable soot blowers (Super V10W-30).
Rotary soot blowers, check power pack gearbox oil (Super V10W-30)
Check rotary valve, blower and compressor motors.
Check bearing condition.
Check compressor pressure switch and low pressure alarms.
Check dust collecting sequencing system.
Check operation of soot blower control system.
Check condition of limit switches and lubricate.
Lubricate soot blower control relays (WD-40 or CR226).
Lubricate motor bearings (L1EP2).
Annually
Change oil in rotary soot blower power pack gear box.
Zero and calibrate:
Export steam pressure indicating controller.
Export steam pressure recorder.
Export steam transmitter.
Export steam back pressure indicating controller.
Pressure valve.
Zero, calibrate, and check operation:
Level transmitter.
Level indicating controller.
Boiler Ireedwater flow transmitter.
Square root converters.
Flow indicating controller.
Computing relay.
Flow transmitter.
Boiler high level alarm.
Boiler low level alarm.
Level indicators.
Pressure indicator.
Economizer temperature indicators.
Flow recorder.
Boiler feedwater valve.
Gas inlet pressure gauge.
Gas exit pressure gauge.
Clean level electrode chamber.
195
-------
SCRUBBER INLET DUCT
GAS PURIFIER
EXIT DUCT
10
JUG VALVE
(ENERGY RECOVERY POSITION)
BOILER
INLET
DUCTS
Figure 77. Schematic of the jug valve,
-------
Within the vertical cylinder is a valve shaft with a disk (Figure 78)
that is moved up or down to control the gas flow as follows: When the disk
is lowered below the area connecting the boiler outlet duct to the scrubber
inlet duct, all the gas passes into the boiler inlet ducts; when the disk is
raised above this area, all the gas flows into the scrubber inlet duct
because of the greater negative pressure there; and when the disk is posi-
tioned within the area connecting the boiler outlet duct to the scrubber
inlet duct, the gas flows to both the boiler inlet ducts and the scrubber
inlet duct. The relative amounts of gas to the boilers and the scrubber
depends on the disk positioning in this area.
Figure 78. Jug valve.
197
-------
Extending axially from the gas purifier, the gas purifier outlet is a
circular duct with a 3.5-m (11-ft 6-in.) diameter. The duct is made of steel
and lined with high temperature alumina brick which is 23-cm (9-in.) thick.
Each of the boiler gas inlets is a rectangular duct, 2.8-m (9-ft 5-in.)
wide by 1.2-m C2-ft 10-in.) high, constructed of carbon steel and lined with
castable refractory. To isolate a boiler for auxiliary repairs or emergency
shutdown, each inlet duct has a swing gate which is a winch-operated block
valve. The valved part of the gate with the winch above it forms a section
of the inlet roof.
Each of the economizer exhaust gas outlets is also a rectangular duct.
With inside dimensions of 1.3 m (4 ft 6 in.) high by 5.5 m (17 ft 6 in.)
wide, the duct is made of steel with a gunnite refractory which is 1-cm
(1/2-in.) thick. The two outlet ducts connect to a common horizontal header
running perpendicular to the ducts. The header is a circular steel duct with
no refractory lining and has a 2.4-m (8-ft) diameter. In the middle of the
header is the exhaust gas outlet duct. Within the header and between the
header outlet and each of the economizer outlet ducts is a butterfly valve.
Adjusted by manually operated chains, the two butterfly valves provide the
means for controlling the gas flow through the parallel boiler-economizer
assemblies thereby maintaining equal steam pressures in the two boilers.
The header outlet duct, also referred to as the boiler outlet duct as
mentioned above, extends horizontally to flow through the vertical cylinder
portion of the jug valve into the gas scrubber inlet duct. The last 4 m
(12 ft) of the boiler outlet duct up to the jug valve is lined with gunnite
refractory which is 10 cm (4 in.) thick.
The jug valve (Figure 78) is a globe valve with a sectioned refractory
disk which moves up and down the cylindrical shaft of the valve. With a
2.4-m (8-ft) diameter and a 2.7-m (9-ft) stroke, the disk is raised and
lowered by a variable-speed, DC drive at speeds between 0.5 and 16.8 mpm.
While the speed can only be adjusted in the field, the valve may be operated
either at the field control station or from the control room. The shaft and
top of the valve are cooled by airflow induced through two inlet slots in the
shaft.
Operating Experience
After the original castable refractory in the gas purifier outlet duct
had failed, it was replaced with the alumina brick refractory mentioned
above. Then after brick on the top edge of the boiler inlet ducts continued
to fall out, the top edge of the inlet was changed from its rectangular shape
to an arch which eliminated the brick fallout.
Since the gases flowing through the gas purifier outlet duct and the
boiler inlet ducts contain large amounts of fly ash, and since the ducts are
horizontal, considerable amounts of ash accumulate on the duct floors and
must be manually removed periodically (Figure 79. After a 3-month operation,
198
-------
Figure 79. Fly ash build-up in the boiler inlet duct.
the ash accumulates to depths up to 30 cm (1 ft). Because of the limited
access and the confined working area, the ash removal may require three men
for 2 days.
The boiler inlet ducts originally had refractory-lined steel guillotine-
type gates. After the heat had badly deformed these gates and slag and fly
ash had accumulated in the slots to make the gate operation difficult and
inefficient, the original gates were replaced with the current swing gates.
However, the new gates occasionally jammed, and slag and fly ash accumulations
on the gates so prevented their proper sealing that air would leak into the
boilers. Moreover, while a closed swing gate would stop the gas flow suf-
ficiently to prevent steam production in a boiler, the heat within the boiler
shell would still be prohibitive for performing repairs in the boiler area.
After the quench air dampers were retrofitted in the gas purifier exit
duct to cool the boiler inlet gases below the ash fluid temperature and
thereby prevent the boiler tube slagging, thermocouples were installed in the
boiler inlet ducts, and temperature readouts for them were added to the
monitoring instruments in the control room. Consequently, the control room
operators could then efficiently adjust the dampers to keep the boiler inlet
temperatures below the ash fluid temperature.
A door was cut into the economizer outlet header duct to gain access to
the butterfly valves. Whenever the valves jammed, they had to be cleared
since there is no other means for adjusting the gas flow distribution such
that the boilers would have equal pressure.
199
-------
After the gas purifier gases flowing directly to the gas scrubber inlet
duct had excessively heated the boiler outlet duct near the jug valve, the
last 4 m (12 ft) of the duct up to the valve was lined with the gunnite
refractory as mentioned above.
After the original jug valve refractory, a single piece of refractory,
continued to fall out in pieces and had to be patched, it was replaced with
castable segmented refractory to make repairs faster. In addition, gas
leaked through the valve when its disk was lowered below the area for the
scrubber inlet duct because slag and fly ash buildup on the valve and its
seat prevented the complete valve closure.
Because of the continuing refractory failure in the jug valve, and
particularly because of the gas leakage through the valve with its disk in
the lowered position, the disk was sealed. Consequently, all the gas purifier
exit gas flows only to the boiler inlet ducts.
Maintenance
Except for the system modifications and the emergency maintenance
discussed above, the boiler inlet ducts and the jug valve have required only
the preventive maintenance listed in Table 47.
TABLE 47. JUG VALVE PREVENTIVE MAINTENANCE
Monthly
Check for smooth operation, unusual noises, and heat in the reducer.
Check gear motor reducer oil level (EPS).
Semiannually
Change reducer oil (EPS).
Grease motor (LiEP2).
Check motor.
Check control circuit and position of indicator system.
Check operation of load cell shutdown system.
Check motor voltage control system.
Check position of all limit switches.
Annually
Megger motor.
200
-------
Slowdown System
Located between the water treatment building and the boiler-economizer
assembly near the economizer end, the boiler blowdown system consists basic-
ally of a separator and a surge tank. After the blowdown water enters the
separator, the steam is vented to the atmosphere and the water flows to the
surge tank for its discharge to the sewer.
Description
The blowdown for each boiler consists of two separate water removals:
one for the steam drum where some of the water is constantly removed for the
twofold purpose of keeping the dissolved solids concentration at a level
between 1,400 and 1,800 mg per liter and of removing any floating scum; and
the second from each of the two mud drums where water is removed once per
shift, every 8 hours, to maintain a low-level concentration of suspended
solids in the mud drums.
In each boiler, there is a blowdown line at each end of each of the two
mud drums and one blowdown line for the steam drum. About 10 percent of the
water entering the steam drum is constantly removed by skimming water from
the water surface in this drum. As stated above, some of the water in each
of the mud drums is blown down in each shift.
The water in each blowdown line flows under boiler pressure through
insulated pipes to the common separator which is mounted above the surge tank
(Figure 80). Upon entering the separator, the blowdown water is flash-cooled
from 2,280 kPa (330 psig) to atmospheric pressure. The steam produced in the
separator is vented to the atmosphere through a steam muffler mounted above
the separator an' the remaining water flows to the surge tank. Supplied by
Wilson Engineering Corporation, the blowdown separator is a Model 24-V3FX
centrifugal separator and its steam muffler is a Model 20-FM-10 unit.
While the surge tank continuously discharges water to the sewer, the
water entering the tank has a short detention time. The surge tank is a
vertically arranged cylindrical steel tank with a total volume of
26,500 liters (7,000 gallons), a retained water volume of 4,400 liters
(1,150 gallons) before water overflows to the sewer, and a working water
volume of 21,000 liters (5,550 gallons) before the water overflows to the
ground. City water can be fed into the sewer discharge line to cool the
blowdown water sufficiently to prevent thermal shock to the sewer tile.
For each boiler, a water-cooled sample line is installed on the steam
drum blowdown line to collect samples for boiler water analysis. The sample
line is enclosed in a heat exchanger shell with city water as the cooling
fluid flowing through the shell.
Operating Experience
Water hammer occurs when the mud drums are blown. During the winter,
the steam spraying from the separator has often condensed into water droplets
201
-------
STEAM
SLOWDOWN'
FRENCH DRAIN
EXHAUST MUFFLER
SLOWDOWN
SEPARATOR
Tl
OVERFLOW TO
GROUND
SLOWDOWN
SURGE TANK
OVERFLOW
TO SEWER
COOLING
WATER SUPPLY
X
-w-
SEWER
Figure 80. Slowdown surge tank and separator.
202
-------
which have frozen on the ground to make nearby walkways and steps hazardous;
also some valves have frozen.
Platforms had to be added beside the boiler shells to permit ready
access to the blowdown valves. Although these valves are at the base of the
boiler shells, they are still 2 to 3m (7 to 10 ft) above the ground level.
Fly Ash Collection System
As previously discussed, the fly ash accumulating on the banks of the
heat exchanger tubes in the boilers and economizers is periodically removed
by the soot blowers to fall into the fly ash hoppers below the tube banks.
The function of the fly ash collection system is to gather the fly ash
emitted from the hoppers and to discharge the cumulative ash into slag trucks
for landfill disposal.
Description
In each of the two boiler-economizer assemblies, there are six fly ash
hoppers-—four in the boiler shell and two in the economizer shell. All six
are aligned along the assembly centerline. During the initial operation, a
continuous fly ash collection pipe formed a horseshoe pattern to connect in
series the outlets of the six hoppers of one boiler-economizer assembly and
then the outlets of the six hoppers of the other assembly. At one end of the
horseshoe line, a blower was installed to pneumatically force through the
line the ash from all 12 fly ash hoppers; and at the other end, a dust
collector subsystem was installed to gather and discharge the cumulative ash
for landfill disposal.
On the bottt/ui of each of the 12 fly ash hoppers is a rotary valve which
maintains an air seal while allowing the discharge of the fly ash. Each of
these valves is a 20-cm (8-in.) diameter Ducon star valve which has a cast
iron rotor and housing. Driven by a 3/4-hp rotor, the valve has a capacity
of 225 liters per hour (8 ft 3/hr.) The ash collection is accomplished via a
pneumatic pipe which begins at the blower and ends at the dust collector
subsystem.
The fly ash blower is a Chicago Model 21-15-20 centrifugal turbo-pressure
blower with an inlet filter and an outlet control damper. Direct-driven at
3,500 rpm by a 20-hp motor, the blower has a capacity of 34 m3 per minute
(1,200 cfm) at a discharge pressure of 71 cm (28 in.) of water.
Upon receiving the cumulative fly ash, the dust collector separates the
fly ash from the air stream for the air venting to atmosphere and the ash
discharge into slag trucks for landfill disposal. The dust collector has a
design air flow rate of 34 m3 per minute (1,200 cfm) and a design solids flow
rate of 363 kg per hour (800 Ib per hour).
The dust collector subsystem consists of a container to receive the
cumulative ash, tubular bags to filter the air into the atmosphere, a hopper
to receive the falling ash, a vibrator attached to the hopper to accelerate
the ash discharge, a rotary valve on the bottom of the hopper to function as
203
-------
the fly ash hoppers in the boilers and economizers, and an air compressor to
generate pulsed air for the tubular bag blowback. The total filter area of
the tubular bags is 23 m3 (250 ft2). Equipped with an automatic start-up
control, the air compressor is a single-stage, single-acting unit with a
V-belt drive. The air compressor has a capacity of 0.2 m3 per minute (7 cfm)
and is set to maintain the air receiver at a pressure of 587 to 621 kPa
(85 to 90 psig). The entire dust collector subsystem was supplied by Flex
Kleen.
Operating Experience
During the early operation of the Landgard plant, the fly ash collection
system operated sporadically because of ash plugging throughout the system.
Some of the plugging was due to the jamming of the rotary valves. These
jammings were successfully eliminated by trimming the valves.
Some potential causes of the plugging were moisture and large pieces of
fused ash particles entering the collection pipe. Moisture was considered as
a potential plugging factor because of the condensation on the economizer
tubes during start-up and other low-flow conditions. Such condensed moisture
falling into the collection pipe is especially critical since the first and
last of the series-connected hoppers are under the economizers. Therefore,
when water forms on the economizer tubes and falls into the hoppers, the ash
initially entering the collection pipe and the dust collector are moistened.
The moistened fly ash forms large lumps or a slurry that cannot be moved
pneumat ically.
As the fly ash builds up on the heat exchanger tubes, the small ash
particles coalesce into large masses which slough off in pieces as large as
8 cm (3 in.). Such pieces are too large to be moved by the pneumatic system
and therefore remain stationary in the collection pipe to block the following
ash. Large ash masses forming in the dust collector have bridged and plugged
the dust collector hopper. The vibrator attached to this hopper has had
little effect in dislodging such ash accumulations.
In any event, the major plugging factor has been the large mass of fly
ash removed from the tube banks during the soot blowing periods. When the
soot blowers are operating, each of the 12 fly ash hoppers had discharged up
to 7 kg per minute (15 Ib per minute) of ash. This ash flow rate is 10 times
greater than the design ash flow rate.
To increase the pneumatic force, the original blower motor was replaced
with a larger unit, the 20-hp motor mentioned above. However, the plugging
throughout the fly ash collection system continued. Therefore, to prevent
the buildup of fly ash in the boilers and economizers, the pneumatic
collection pipe was removed and a 208-liter (55-gallon) drum was placed under
each of the 12 fly ash hoppers as a temporary expedient. Although not as yet
implemented, some other means of removing the ash should be developed since
the drums can only be removed by manually manipulating them with a hand
truck, a very laborious effort.
204
-------
Maintenance
The rotary valves must be periodically lubricated with grease, although
fly ash intermingling with the grease causes considerable wear. In addition,
the rotary valve on the dust collector hopper has required minor repair.
Some of the rotary valves were repaired or replaced because of damage sus-
tained by construction materials, such as welding rods, that had been left in
the boiler and economizer shells. The preventive maintenance schedule for
the fly ash dust collector is shown in Table 48.
TABLE 48. FLY ASH TRANSFER SYSTEM PREVENTIVE MAINTENANCE SCHEDULE
Check compression oil level.
(Winter - Super HDX 20)
(Summer - HDX 30)
Drain air receiver, drop legs, etc.
Check for unusual noise, failure to compress, overheating, vibration,
slippage, and check the belts.
Adjust pressure difference between 1-10 cm water gauge.
Monthly
Check rotary valve, motor, reducer, and chain.
Check and tighten all bolts on the air compressor, check all air con-
nections, joints, and lines for leaks.
Check V-belt for misalignment and tightness (1 cm play midway between
pulleys).
Check and tfgnten clamps on dust collector filter bags.
Check inlet air filter, check safety for sticking, and check belt
tension.
Lubrication:
Check oil in rotary valve gear motor
(Winter - EP5)
(Summer - EP8)
Quarterly
Check compressor valves.
Grease rotary valve bearings (EP2).
Oil chain (Paradene 430)
Semiannually
Check condition of bags.
Change compressor oil.
(Winter - Super HDX 20)
(Summer - HDX 30)
Grease motor (LiEP2)
205
-------
RESIDUE SEPARATION MODULE
The residue separation module (Figure 81) was designed to separate the
residue produced in the thermal processing module into three materials—
magnetic metal, which was to be sold to a scrap dealer; glassy aggregate,
which was to be used as an asphalt aggregate; and carbon char, which was to
be landfilled unless a use for it could be proven.
The residue drag conveyor discharges the residue to the residue separ-
ation screen, and the portion of the residue passing through the screen falls
into the residue separation unit. Then the char portion of the residue is
separated by flotation. The char slurry is screened and dewatered by a roto
screen, a thickener, and a vacuum belt filter. The char from the vacuum belt
filter is conveyed and stacked on the ground by two char conveyors operating
in series. Magnetic metals are then separated and discharged into trucks.
The remaining glassy aggregate is conveyed and stacked on the ground by the
glassy aggregate conveyors.
Evaluation of this module is difficult since it had a very short oper-
ating period. Performance of the module is very dependent on the quality of
residue from the thermal processing area.
Residue Separation Screen
When the residue separation module is operated, kiln residue is dis-
charged from the residue drag conveyor to the residue separation screen
within the residue separation building. The screen allows residue particles
smaller than 20 cm (8 in.) to pass through the screen falling into the
residue separation tank. Residue particles greater than 20 cm (8 in.), such
as slag, slide down the screen and are discharged into a truck or hopper
outside the building for disposal.
If the residue separation module is bypassed and the residue is dis-
charged from the residue drag conveyor through the bypass gate into trucks,
cover plates are installed over the separation screen to restrict the residue
from entering the residue separation tank. This procedure allows the unit to
operate as a vibrating pan conveyor so that carryover residue is discharged
to the residue truck (located under the bypass gate) for subsequent disposal.
Description
The residue separation screen is a vibrating screen conveyor supplied by
the Materials Handling Division of the FMC Corporation. The conveyor is
constructed of carbon steel 1.3 cm (0.5 in.) thick with abrasion-resistant,
replaceable steel liner plates 1 cm (3/8 in.) thick. The conveyor is belt
driven by a 3 hp motor and has a design capacity of 2,500 kg/hr (5,500 Ib/hr)
at a density of 800 kg/m3 (50 lb/ft3). The conveyor, sloped at an angle of
17°, is 2.7-m (9-ft) long and 0.9-m (3-ft) wide.
206
-------
MAGNETICS
GASES SOLIDS
— KILN
TIPPING
FLOOR
STOR-
AGE
PIT
SHREDDER
BURNERS
COMBUSTION AIR
SHREDDER
QUENCH AIR
EEDWATER
1
_ MI7FR
1
1
1
^ MIZFR
'iSJ^*" PURIFIER
BOILER
"*• FLY ASH
fc. pi Y A*?H
BOILER
-
1
— — —
H^
Xh
—\
1
-1
^
V
• -
N
-
s
' J
STEAM
1
"t
1
I
|
\l J
A
\— JUG \i
I
1
r
..
,'
AL
INDUCED
DRAFT
FAN
BOILER FEEDWATER
DEHUMIDIFIER
\
EXHAUST TO
ATMOSHPERE
REFUSE | SCALE |
Figure 81. Residue separation module (shaded area).
-------
Operating Experience
The residue separation screen experienced many problems similar to the
vibrating screen conveyor discussed earlier. Drive belts wore out quickly
because the screen vibrated while the motor was stationary. The screen also
jammed quickly with wire. In addition, accessibility was poor, making
cleaning and maintenance difficult.
As mentioned earlier, the I-beam, on which the bypass gate pneumatic
cylinders are mounted, blocks the large slag balls, causing a jam on the
conveyor. Underprocessed residue, which has a high moisture content, does
not move down the incline very well. A portion of the discharge chute from
the residue conveyor to the residue separation screen was removed to allow a
greater clearance for slag balls to slide down the conveyor.
The cover plate, which is installed over the screen when the residue
separation module is not in use, allowed residue to leak through and cause
problems with the residue flotation unit.
Maintenance
Maintenance has required placing the pulleys back on the sheaves,
replacing the pulleys, and aligning the sheaves. Some bolts that have
vibrated loose or sheared were replaced. The preventive maintenance schedule
for this unit is shown in Table 49.
TABLE 49. VIBRATING SCREEN CONVEYORS
Weekly
Lubricate bearings lightly (LiEP2).
Quarterly
Check V-belts for:
Tension.
Broken bolts; replace if necessary.
Rubber mounts location and wear; replace if damaged.
Semiannually
Grease motors (LiEP2).
Check motors, alarms, and interlocks.
Grease motor bearings (LiEP2).
Annually
Megger motor.
208
-------
Residue Flotation Unit
Residue that has passed through the residue separation screen falls into
the water-filled tank of the residue flotation unit which is inside the
residue separation building. The residue is then mixed with the water and
agitated by air from an air compressor. This process causes the lower density,
carbon-rich char to float and flow over a weir through an open flume to the
roto screen. A washed, heavy fraction containing metals and glass sinks and
is removed from the unit by a drag conveyor that transfers this material to
the sinks discharge conveyor.
Description
Supplied by the Jeffrey Manufacturing Co., the residue flotation unit
includes a separation tank, an air compressor, and a drag conveyor. The
separation tank is 1.6 m (5 ft 3 in.) high, 1.2 m (4 ft) wide, and 6.7 m
(22 ft) long. Water depth in the tank is maintained at 1.5 m (4 ft 10 in.)
for a water volume of 12,000 liters (3,200 gallons) and 12.7 cm (5 in.) of
freeboard. Water (5,675 1pm or 1,500 gpm) and air (125 kg/hr or 276 Ib/hr)
at a combined pressure of approximately 165 kPa (24 psig) enter the tank
through nine 3-cm (1 3/16-in.) nozzles on the side of the tank near the
bottom.
The overflow weirs are located at the top of the tank on the sides. The
air compressor is an air-cooled, reciprocating, belt-driven model mounted on
an air receiver. The compressor has a capacity of 1.7 m3/min (60 ft3/min)
and is equipped with a water-cooled moisture separator and automatic drain.
The drag conveyor consists of two single strands of Rex "H" mill chain
with a drag flight- that are 0.9 m (36 in.) long, 21.6 cm (8.5 in.) high, and
spaced 30 cm (12 in.) apart throughout the chain. The conveyor travels at a
speed of 7.8 m/min (25.5 ft/min) and is powered by a 2-hp motor. The drag
conveyor will not operate unless the sinks discharge conveyor is operating;
and if the drag conveyor does not operate, the residue bypass gate will open.
Operating Experience
Because of the limited operation of the residue separation module,
little operating experience has been obtained for this unit. As mentioned
earlier, a floater problem already exists in the residue quench tank. Since
the floaters must be removed in any event, all the char should be removed
from that tank with flotation equipment and overflow weirs, as with the
prototype. Installation of such equipment in the residue quench tank would
entirely eliminate the need for a residue flotation unit.
The overflow weirs and the flume to the thickener were enlarged to allow
a greater char slurry flow, and doors were cut in the tank to permit easier
access for cleaning.
One unusual aspect of the drag conveyor is that it pushes instead of
pulls. A problem is caused by the drag line which is made of chain that
works better in tension than in compression. Monsanto recalculated the drag
209
-------
conveyor loads and determined that the motor was undersized and that the
conveyor was not strong enough. The unit was never modified, however,
because the residue separation module had a low repair priority.
When the residue separation module is not operated, some residue falls
through the gaps in the residue separation screen cover plates into the
residue flotation unit. This buildup continued until it was too high to be
removed by the drag conveyor. To keep the conveyor clear, the unit was
cleaned and run for a short period each shift. This procedure worked until
the water in the tank froze. After it was cleaned out again, the water level
was dropped and the conveyor was run continuously.
The residue flotation unit did not separate very well. The flow to the
thickener often included glass, aluminum, underprocessed paper, and rags.
The flow to the sinks discharge conveyor often contained large amounts of
char. Since the water and air entered the tank through a common nozzle,
plugging of these nozzles became a problem.
Maintenance
Because the conveyor is underdesigned, the most common maintenance
procedure for this unit has been to replace sheared pins. Other maintenance
resulting from underdesign of the conveyor includes replacing flights,
cleaning the tank, returning the chain to the sprocket, and tightening the
chain.
The nozzles were cleaned twice and reconditioned once. A leak that
required welding developed in the open flume, and the drag conveyor zero
speed switch was rewired. The preventive maintenance schedules for the unit
and the separation air compressor are shown in Tables 50 and 51 respectively.
Roto Screen System
The roto screen system is installed inside the residue separation
building and consists of a roto screen and an oversized floats conveyor.
The roto screen: (1) removes residue particles larger than 0.6 cm (0.25 in.)
from the carbon-char-rich overflow slurry flowing to the thickener, and
(2) discharges them on the oversize floats conveyor that carries these
particles to a bin outside the building. The char slurry that passes through
the screen goes to the thickener adjacent to the residue separation building.
Removal of these larger particles minimizes pluggage of the thickener pipes
and pumps.
Description
The roto screen is a variable speed, horizontal drum filter constructed
of stainless steel. The screen has a field control station and a high-
liquid-level alarm. Also the screen is interlocked so that it will not
operate if the oversize floats conveyor is not running; and if the screen is
not running, the residue bypass gate will open. The oversize floats conveyor
210
-------
TABLE 50. RESIDUE FLOTATION UNIT
Monthly
Check for loose bolts, damaged flights or brackets, unusual wear
and noise.
Check tension on drag chain.
Check reducer for unusual noise or heat, and check oil level
(Paradene 475).
Check heat shaft alignment.
Top up lubricant in drive chain (Paradene 430).
Grease valve stems, pillow block bearings, and head shaft bearings
(LiEP2).
Shutdown
Drain and clean tanks.
Inspect tanks and wear plates for wear or damage.
Check drag guides for damage.
Check nozzle0 for pluggage, damage, and erosion.
S emiannually
Change reducer oil (Paradene 475).
Check motor, alarms, and interlocks.
Check operation of zero speed switch and lubricate (20 W motor oil)
Grease motor bearings (L1EP2).
Annually
Megger motor.
211
-------
TABLE 51. SEPARATION AIR COMPRESSOR
Drain any condensate from receiver and traps.
Check for any unusual noise or vibration.
Check oil level in compressor.
(Winter - Super HD X 20)
(Summer - Super HD X 30)
Weekly
Clean air filter in solvent and dry it.
Clean all external parts of compressor and driver.
Manually test safety valve for sticking.
Monthly
Inspect entire air system for leaks.
Inspect oil for contamination and change if necessary.
Check bolt tension and wear.
Quarterly
Inspect valve assemblies.
Check oil in compressor.
(Winter - Super HD X 20)
(Summer - Super HD X 30)
S emiannually
Grease motor (LiEP2).
Check motor and alarm.
212
-------
is a flat, sliding rubber belt conveyor 30 cm (12 in.) wide and 7.6 m
(25 ft) long. A 3/4-hp motor drives the conveyor, which is equipped with a
field control station only.
Operating Experience
The roto screen was added as a modification and has worked well in
solving many of the thickener's problems.
The motor for the oversize conveyor burned out because it was located
outside the residue separation building and was not weatherproof. The
conveyor ends very close to the building, making it difficult to place a bin
under the discharge. Since the belt is the sliding bed type, material builds
up on its underside, causing poor tracking and an overload condition.
Maintenance
No maintenance information is available for the roto screen. The
oversize conveyor has required installation of a new motor repair to the
bearings, and lacing of the belt. The preventive maintenance schedule for
the roto screen is shown in Table 52.
TABLE 52. ROTO SCREEN PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check screen, wiper, side plates, etc. for damage.
Grease bearings and vari-speed (LiEP2).
Check oil in vari-speed reducer.
Semiannually
Change oil in vari-speed reducer (EPS).
Check motor.
Annually
Megger motor.
213
-------
Thickener
The carbon-char-rich overflow slurry from the residue separation unit
passes through the roto screen and flows to the thickener in an open flume.
The slurry solids settle within the thickener, are collected at the bottom,
and are pumped as a thickened slurry to the vacuum belt filter by the
thickener underflow pump. The clarified water flows over the wier in the
thickener to the thickener overflow sump and is recycled to the residue
separation unit by the thickener pressure pump.
Description
The thickener is a 12.2-m (40-ft) diameter, carbon steel, open-top tank
with a concrete bottom. The tank is adjacent to the residue separation
building above the ground and has a peripheral water depth of 3.4 m (11 ft).
The bottom is sloped toward the center 12.5 percent to allow a center water
depth of 4.1 m (13.5 ft). The thickener is equipped with center-pier-
supported, center-driven mechanisms for scum collecting and sludge raking.
The unit was designed to receive 6,200 1pm (1,640 gpm) of water containing
0.9 percent solids (carbon, glass, ash, and nonferrous metals). The design
overflow was to have a solids concentration of 100 mg/1 and a flow of
5,750 1pm (1,520 gpm). The design underflow from the thickener was to have
a solids concentration of 10 percent and a flow of 450 1pm (120 gpm). A
flocculant concentration of 2.0 mg/1 was to be maintained in the thickener by
the addition from the flocculant system (described in the section on the
scrubber solids separation system). If the rake mechanism halts, both a
local horn alarm and a remote alarm in the control room will sound.
The underflow pump is a horizontal, centrifugal solids pump with a rated
capacity of 750 1pm (200 gpm) at a total dynamic heat of 12.8 m (42 ft).
The pump has an open vane impeller and is belt-driven by a 5-hp motor.
The thickener pressure pump is a Worthington Model 8-LR-13-B, horizontal,
centrifugal, split-case pump. Driven by a 50-hp electric motor, the pump has
a capacity of 6,960 1pm (1,840 gpm) at a total dynamic heat of 15.2 m (50 ft).
Operating Experience
Although little operating experience has been obtained for the thickener,
many problems have been observed. The tank was not equipped with a drain so
when the underflow pump suction pipe clogged there was no easy way to drain
the tank. Neither was there an easy access to clear the clogged pipe until
numerous cleanouts were installed. The underflow pump suction pipe has
clogged more than once during the short operating period, possibly because of
the glass in the char, or a pipe too small to handle the flow. The pipe was
clogged with cans before installation of the roto screen and the screen on
the end of the plume. Installation of a flush line to blow back this line
could possibly help clear the pipe. To help prevent plugging, a diaphragm
valve was installed on the underflow pump discharge, and a recycling line was
installed from the discharge to the inlet plume to keep the underflow moving
in the pipes. The motor for the underflow pump was elevated above the sump
after the latter filled and the motor burned out.
214
-------
When the underflow pipe clogs, other problems occur. If the thickened
slurry is not removed, it continues to thicken until it cannot be pumped. At
this point, it also gets too thick for the rake mechanism to move, causing
damage to it.
The rake mechanism was also modified to allow maximum inlet flume
clearance by removing projections. The scum collector plate was also raised
to allow the whole length of the plate to break the water surface. Freezing
occurs in the winter when the thickener is not in use. During these periods,
the system should be drained.
Maintenance
During the limited operating period of the residue separation module,
the thickener and the pressure pump have only required the preventive
maintenance detailed in Tables 53 and 54. The thickener underflow pump has
required replacement of gaskets and bearings, tightening of flanges, rewiring
of the motor because it rotated in the wrong direction, and installation of a
cleanout line. A new submersible pump was installed to replace the old pump.
The preventive maintenance schedule for the underflow pump is shown in Table
55.
Vacuum Belt Filter System
The thickened carbon-char-rich slurry is pumped to the vacuum belt
filter by the thickener underflow pump. The thickened slurry is then de-
watered to form a cake, which is discharged to the char transfer conveyor.
The vacuum air and filtrate water flow to the vacuum receiver, where the
water and air separate. The water falls to the bottom of the receiver and is
pumped by the filtrate pump to the wash sump pump, which in turn pumps the
filtrate to the open flume that flows to the thickener. The air in the
vacuum receiver is pumped by a vacuum pump through a snubber to decrease the
noise level and further separate the liquid/air mixture before discharging to
the atmosphere. City water is used to continuously clean the return run of
the belt. This wastewater flows to the separation sump pump, which pumps it
to the open flume to the thickener.
Description
The vacuum belt filter is a top-loading, horizontal unit with 7.7 m2
(83 ft2) of effective surface area. The one-piece molded belt is under
continuous vacuum. The unit is equipped with an open-top, overflow-type
feedbox with adjustable V-notch weirs to distribute the thickened slurry
uniformly across the full width of the belt. The unit is equipped with
vacuum manifold assemblies connected by flexible connectors to vacuum pans.
Also included is a continuous wash system with wash headers on the return
run, spray nozzles, and a waste collection drip pan extending the full length
of the belt filter cloth to collect the belt wash and possible spills. The
head pulley is driven by a variable speed, 5-hp motor with chain and sprocket
drive to deliver a belt speed of 1.5 to 6.0 mpm (5 to 20 fpm). The unit is
215
-------
TABLE 53. THICKENER PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check power chain drive for unusual noise, vibration, or heat.
Check reducers.
Check lubrication:
Winsmith.
(Winter - EPS)
(Summer - EPS)
(LiEP2)
Worm shaft and shaft bearings (LiEP2).
Worm, gear, and ring drive reservoirs.
(Winter - EPS)
(Summer - EPS)
S emiannually
Drain tank, clean and hose down wall and floor.
Check and tighten all-bolts.
Check truss arms and note whether they are sweeping in the same plane.
Adjust tie angles or adjustable brace to each truss aim for most
effective cleaning.
Replace any broken or badly bent squeegees.
Lubricate the chain drive (Paradene 430).
Change oil in Winsmith.
(Winter - EPS)
(Summer - EPS)
(8MCTW)
Change oil in worm, gear, and ring drive reservoirs.
(Winter - EPS)
(Summer - EPS)
Lubricate motor (LiEP2).
Check motors and alarms.
Annually
Check and dismantle roller chain coupling.
Megger motor.
216
-------
TABLE 54. PRESSURE PUMP PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check bearings, couplings, and packing.
Lubricate all valves (LiEP2) and take-up of teflon stick.
Quarterly
Lubricate pump bearings (polyplex EP2).
Semiannually
Grease motor (LiEP2).
Check motor and alarm.
Annually
Megger motor.
Zero, calibrate, and check operation of discharge pressure indicator.
217
-------
TABLE 55. UNDERFLOW PUMP PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check bearings, belts, packing, and motor bearings.
Lubricate all valves (LiEP2) and take-up on teflon stick.
Quarterly
Lubricate bearings (LiEP2).
Semiannually
Grease motor (LiEP2).
Check motor and alarm.
Annually
Megger motor.
Zero, calibrate, and check operation of discharge pressure indicator.
designed to (1) dewater 38,800 kg/hr (85,500 Ib/hr) of a 10 percent solids
slurry, and (2) to produce 16,200 kg/hr (35,600 Ib/hr) of 24 percent solids
cake, 375 1pm (100 gpm) of filtrate, and 75 1pm (20 gpm) of belt wash water.
The vacuum receiver is a cylindrical, dished-head, vertical tank 0.9 m
(3 ft) in diameter and 1.8 m (6 ft) high. The tank is equipped with a
vacuum gauge and a high-level probe.
The filtrate pump, mounted on the vacuum receiver, is a horizontal,
centrifugal pump rated at 100 gpm at a total dynamic heat of 20.7 m (68 ft)
of water.
The wash sump pump is a vertical, centrifugal pump with a capacity of
950 1pm (350 gpm) at a total dynamic heat of 13.7 m (45 ft) of water. The
pump is equipped with a vertical float switch and cover. In case of pump
failure, the sump is equipped with an overflow line to the separation pump.
The vacuum pump is a horizontal, positive displacement, rotary lobe,
water-sealed vacuum pump with a rated capacity of 56.6 CMM (2,000 CFM) at a
negative gauge pressure of 51 cm (20 in.) .-of mercury. The pump is equipped
with a vacuum relief valve in the inlet piping.
The snubber is a vertical, cylindrical steel tank 56 cm (22 in.) in
diameter and 138 cm (72 in.) high. The water removed by the snubber is
discharged to the separation sump.
218
-------
The separation sump pump, supplied by Standard Power, is a vertical,
centrifugal pump with a capacity of 190 1pm (50 gpm) at a total dynamic head
of 9 m (30 ft) of water. The pump is equipped with a float switch control
and a cover.
Operating Experience
Operating experience obtained during the short operating period has
revealed that the vacuum belt filter operates acceptably after some minor
debugging, but that the unit requires substantial operating manpower. Some
of the debugging modifications included replacement of a straight discharge
from a pipe onto the filter with the distributing feedbox. Another modifi-
cation was the change from thickener overflow water to city water for use in
filter washing after the spray nozzles continually plugged.
A grit-settling box was installed to allow the glassy grit washed from
the filter to settle out before entering the separation sump and possibly
damaging the pump. However, no equipment exists for removing the glassy grit
from the settling box. The amount of glassy grit in the char is much greater
than anticipated and could increase the wear of the system significantly.
Maintenance
Before the glassy grit settling box was installed, the grit damaged the
separation sump pump to the extent that the seals and impeller were replaced.
The filter cloth for the vacuum belt filter was replaced after it was damaged
during the construction period, and it was mended a few times during the
brief operating period. The other pieces of equipment required only pre-
ventive maintenance. The preventive maintenance schedules for the vacuum
belt filter, the vacuum pump, and the filtrate pump are shown in Tables 56,
57, and 58.
Char Conveyors
Carbon char discharged from the vacuum belt filter falls onto the char
transfer conveyor, which carries the char to the char stacker conveyor. The
char stacker conveyor takes the char to a storage pile or directly into
trucks for landfill disposal.
Description
Both of these conveyors are Barber-Green, rubber belt, trough conveyors.
They are 61 cm (24 in.) wide, with rubber belt wipers at the head pulley and
are driven by 3-hp electric motors. The two conveyors are interlocked so
that the transfer conveyor will not operate unless the stacker conveyor is
operating. Both units are equipped with local controls and remote controls
in the control room.
The transfer conveyor is horizontal and operates at a speed of 30 mpm
(110 fpm). The stacker conveyor is inclined at an angle of 18°, is 24 m
219
-------
TABLE 56. VACUUM BELT FILTER PREVENTIVE MAINTENANCE SCHEDULE
Each shift
Lubricate cloth roll bearings and aligning roller heads (Pyroplex EP2)
Check filter cloth for biasing and wrinkling.
Align rollers.
Check for side leaks and adjust rubber side seals if necessary.
Check take up pulley springs by measuring lengths of spring guide
showing in spring enclosure: 1 cm - not operating,
flush - operating.
Grease cloth roll bearings and aligning roller heads (Pyroplex EP2)
Weekly
Inspect flexible connections for leaks and alignment.
Check belt alignment.
Lubrication:
Drive chain (brush on EPS).
Pulley bearings (EP2).
Cloth take-up mechanism (EP2).
Aligning tension rod assembly (EP2).
Drainage belt alignment mechanism bearings (EP2).
Drainage belt roll bearings (Pyroplex EP2).
Monthly
Examine the belt for wear or damage and for trapped abrasive material
between it and the pulley or vacuum pan.
Check the cloth rolls for solids build up and free turning on bearings,
Check loose assemblies, connections, bolts, and piping.
Inspect the wash pipe for direction and pattern of spray.
Clean all nozzles.
Clean line strainers.
Check zerk fitting on top of reducer (EP2).
Check cyclodrive, vari-drive, and reducer oil level.
(Winter - Paradene 430)
(Summer - Paradene X1000)
Grease vari-drive reducer (LiEP2).
CONTINUED
220
-------
TABLE 56. CONTINUED
Semiannually
Clean and inspect the extractor for general condition during shutdown.
Wash out the wash troughs or drip pan feed box. Release tension on
cloth and inspect. Change cyclodrive and vari-drive reducer oil.
(Winter - Paradene 430)
(Summer - Paradene X1000)
Check motor, bearings, and alarm.
Annually
Megger motor.
TABLE 57. VACUUM PUMP PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check pumps for hot spots and vibration.
Check V-belts for tension and wear.
Check inlet and discharge pressure, and temperature performance standards.
Check oil level (Paradene X1000).
Quarterly -
Grease motor (LiEPZ).
Semiannually
Check alarm and interlock.
Check high temperature cut-off switch.
Check high liquid level shutdown switch.
Annually
Megger motor.
Zero, calibrate, clean, and check operation of water flow indicator
rotometer.
221
-------
TABLE 58. FILTRATE PUMP PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check pump, belts, drive, and packing.
Fill oil reservoir to center of sight glass (Paradene 430)
Semiannually
Grease motor (LiEP2).
Check motor, alarm, and interlock.
Annually
Megger motor.
(80 ft.) long, and operates at a speed of 46 mpm (150 fpm). The discharge
end of the stacker conveyor can be rotated in a small arc by manually pushing
it on a track.
Operating Experience
Except for the belt wipers, the char conveyors have worked Well. The
belt wipers do not clean the belt adequately, and they wear out rapidly,
allowing a constant buildup to develop beneath the conveyors. A chute to
guide the char from the stacker conveyor to the truck would be heipful in
preventing material spills and blowing char. A divertable chute would be
helpful in preventing spills when channging trucks.
Maintenance
The char conveyors have required only the preventive maintenance detailed
in Table 59 during their short operating period.
Magnetic Metal Separation System
The portion of the residue that sinks in the residue separation tank is
removed by the drag conveyor in that unit and is discharged onto the sinks
discharge conveyor. A magnetic metal separation conveyor suspended above the
sinks discharge conveyor removes all magnetic metal and deposits it on the
iron transfer conveyor. The iron transfer conveyor discharges the magnetic
metals and discharges them into a truck for sale to a scrap metal dealer.
The portion of the residue remaining after magnetic separation (glass, ash,
char, and nonmagnetic metals) is discharged by the sinks discharge conveyor
onto the aggregate screen.
222
-------
TABLE 59. RUBBER BELT RESIDUE CONVEYOR PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check alignment and tension of belts, belt lacing, belt wear or damage,
and belt wipers for wear and proper action against belt.
Check idlers for lubrication, wear, and buildup.
Check motor reducer, belts, and guards.
Check general buildup.
Note any vibration or noise.
Check gear reducer oil level (EPS).
Clean sight glasses where necessary.
Monthly
Lubricate gear reducer, shaft bearings, and belt wiper assembly (LiEP2),
Quarterly
Grease idler bearings, exterior bearings (LiEP2).
Change reducer oil (EPS).
Oil stocker drive chain.
(Winter - Paradene 430)
(Summer - Paradene 475)
Semiannually
Grease motors (LiEP2).
Check motors, alarms, and interlocks.
Inspect and lubricate pull cord switch.
Annually
Megger motors.
223
-------
Description
The magnetic metal separation system is located within the residue
separation building. The sinks discharge conveyor is a 106 cm (42 in.) wide,
flat rubber-belt conveyor with 15 cm (6 in.) skirt boards. The conveyor,
supplied by Barber-Green, operates at a speed of 15 mpm (50 fpm) and is
driven by a 1-hp motor. The conveyor is equipped with field controls and
remote controls within the control room. This conveyor is interlocked with
the aggregate screen and will not operate unless the screen is operating.
The magnetic metal separation conveyor is a suspended rubber belt
conveyor with an electromagnet in the head pulley. The conveyor is aligned
perpendicular (Figure 82) to the sinks discharged conveyor and has a design
capacity of 9 Mg/hr (10 tph). The conveyor, supplied by the Eriez Magnetics
Co., is driven by a 5-hp motor and has an 8-kw electromagnet. The unit is
equipped with field controls and a remote start/stop switch in the control
room. The belt is 61 cm (24 in.) wide and is designed to operate with a 5 cm
(2 in.) of burden.
Figure 82. Magnetic metal separation conveyor.
224
-------
The magnetic metal transfer conveyor is a 61-cm (24-in.) wide, troughed
rubber belt conveyor. Supplied by Barber-Green, this conveyor is driven by a
3-hp motor and operates at 30 mpm (100 f pm). Also included with the unit are
a field control station and a remote start/stop switch in the control room,
two discharge chutes, and a local chain-operated flop gate to control the
discharge flow to either chute.
Operating Experience
The sinks discharge conveyor has had a problem with spillage but has
otherwise operated satisfactorily.
The magnetic metal separator produced a fairly clean product but had
serious equipment problems. The original belt on the magnetic metal separator
was plastic, and it was damaged by dry rot and cracking. The belt was
replaced with a belt made of stainless-steel-reinforced rubber. Because of
the pushers on the belt, belt wipers could not be installed. This situation
allowed material to build up on the belt and cause a spillage problem.
Originally, the belt moved very quickly throwing the metal. Belt speed of
the magnetic metal spearator was reduced, and a plate was installed at the
discharge to reduce the velocity of the separated magnetic metal.
As with the char conveyors, belt wipers were a problem with the magnetic
metal transfer conveyor. An extra chute was added so that either of two
trucks could be filled. This procedure reduced the total truck driver time
and also prevented the spills that occurred during the truck change with one
chute. The discharge chute clogged several times. The clogging was due
wither to magnetic metal buildup within the chute when the trucks were not
moved soon enough or to wire or spring wedging in the converging part of the
chute.
Maintenance
In addition to the required preventive maintenance for the sink discharge
and magnetic metal transfer conveyors shown in Table 59, the sinks discharge
conveyor required frequent alignment.
The belt for the magnetic metal separator was replaced three times and
spliced once. The shaft bearing for this conveyor was also replaced once.
The preventive maintenance schedule for this conveyor is shown in Table 60.
Glassy Aggregate Conveyors
The portion of the residue remaining on the sinks discharge conveyor
after the magnetic metals are removed is discharged onto the aggregate
screen conveyor. The aggregate screen conveyor removes all residue particles
larger than 1.2 cm (0.5 in.) and discharges them to a dump box outside the
residue recovery building. The residue particles smaller than 1.2 cm (0.5 in.)
pass through the screen onto the aggregate transfer conveyor. The aggregate
transfer conveyor carries the glassy aggregate to the aggregate stacker
conveyor, which discharges it to the glassy aggregate storage pile.
225
-------
TABLE 60. MAGNETIC METAL SEPARATOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check oil level with magnet cold.
Check expansion tank pressure relief valve for freeness.
Check temperature (normal operating temperature is 60°C - 80°C above
ambient); check further if not hot.
Check for proper belt tracking and adjust if necessary.
Check for leakage of oil.
Check motor and reducer for noise, vibration, or excessive heat.
Check V-belts for tension and wear.
Lubricate bearings (LiEP2).
Check reducer oil level (Paradene 475).
Semiannually
Check transformer oil in electromagnet; when cold.
Change reducer oil (Paradene 475).
Grease motor (LiEP2).
Check output voltage and amperage to magnet for all three phases.
Lubricate off/on switch for magnet.
Check motor and alarm.
Annually
Megger motor.
Description
The aggregate screen conveyor, supplied by the FMC Corporation, is a
vibrating pan conveyor 2.6-m (8 ft 6 in.) long and 0.9-m (3 ft) wide at an
angle of 17.5°. Originally, the conveyor had long rectangular openings
1.2-cm (0.5-in.) wide. The conveyor is belt driven by a 3-hp motor and has a
field-mounted control station and a remote start/stop switch in the control
room.
The aggregate transfer and stacker conveyors are both 60-cm (24-in.)
wide, rubber belt, troughed conveyors supplied by Barber-Green. Both con-
veyors are equipped with a field-mounted control station and a remote start/
stop switch in the control room.
The aggregate transfer conveyor is 54 m (177 ft) long and operates at a
speed of 30 mpm (100 fpm). The conveyor is driven by a 3-hp motor and is
interlocked to prevent operation unless the stacker conveyor is operating.
226
-------
The aggregate stacker conveyor is 31 m (102 ft) long and is inclined at
an angle of 17°. The conveyor is driven by a 3-hp motor and operates at a
speed of 46 mpm (150 f pm). Another 3-hp motor is used to move the discharge
end along an arc to make a larger storage pile.
Operating Experience
During the brief period that these conveyors were operated, very few
operational or equipment problems developed. The rubber belt conveyors had
the same problems as the other rubber belt conveyors, such as spillage and
poor belt wiper performance and wear.
Because of the great reductions in cross section, the chute to the
aggregate screen jammed on a few occasions. The screen had the same problem
as the other vibrating pan conveyors in that the motor was on a stationary
mount and the conveyor vibrated, damaging or throwing the belts.
Most of the nonmagnetic metals (especially brass and copper) are dis-
charged as oversize particles from the aggregate screen conveyor.
Since the screen is too close to the ground to install a larger box, the
screen openings were increased after large amounts of material were separated
by the screen causing the frequent changing of the drop box. The aggregate
screen conveyor, as with the other vibrating screens, was blinded by wire and
required frequent cleaning.
Because the brakes for the stacker conveyor work only while the unit is
on, the unit must be kept on to prevent it from being blown around by the
wind. The stacker conveyor thus used power even when not in use.
Maintenance
As with the other vibrating conveyors, the belts for the aggregate
screen conveyor were placed back on the sheaves after falling off. The
preventive maintenance schedule for the vibrating conveyor was shown in
Table 49.
The two rubber belt conveyors were each adjusted twice so they would
track properly. The preventive maintenance schedules for these conveyors are
shown in Table 59.
GENERAL PLANT MODULE
Certain pieces of equipment cannot be considered a portion of a one
module, but rather a portion of the general plant. Such equipment usually
performs a utility function.
227
-------
The major pieces of equipment for the general plant module are as
follows:
1. Atomizing steam boiler
2. Plant water system
3. Instrument air system
4. Dust collection system
5. Sump pumps
6. Wastewater lift station
Though most of this equipment caused some problems, the atomizing steam
boiler and the dust collection system never performed adequately.
Atomizing Steam Boiler
The atomizing steam boiler is located outdoors, adjacent to the kiln
fire hood. According to original design, the boiler was required to provide
atomizing steam for the fuel oil burner system and steam to drive the turbine-
driven., kiln-combustion air fan.
Description
The atomizing steam boiler is a small fire-tube boiler with a design
steam capacity of 1,570 kg/hr (3,450 Ib/hr) at a pressure of 1,380 kPa
(200 psig). The boiler is fired using No. 2 fuel oil, and it is provided
with its own feedwater system in the water treatment building.
Operating Experience
Immediately after the initial start-up, the frequent failures of the
atomizing steam boiler caused serious problems. Because this unit supplied
the atomization steam to the burners, the failure of the boiler "caused all
the burners to go out, shutting down the entire process. Many of the
problems were electrical and weather-related because this unit is typically
used indoors.
To improve boiler reliability, a standby or auxiliary feedwater pump was
installed, and the drive for the integral combustion air fan was changed from
a 5-hp turbine to a 7.5-hp electric motor. A low steam pressure alarm was
also added to indicate when the boiler was malfunctioning.
When these modifications failed to increase the reliability of the unit,
an auxiliary steam line was installed from the header of the waste heat
boilers. This change was accomplished so that the atomizing steam boiler was
required during heat up.
Several other problems were encountered in addition to boiler re-
liability. Most of the valves are above the boiler and out of reach; so, the
operators used a portable ladder until a permanent ladder was installed.
The blowdown line originally discharged above the ground in mid air. Because
228
-------
this situation could result in serious injury to plant personnel, the blow-
down line was extended below ground in a French drain.
When the boiler continued to be a problem, the decision was made to use
steam from the Baltimore Gas and Electric Co. for start-up, thus eliminating
the need for the boiler. As mentioned in the burner section, the need for
this boiler could be eliminated by using air-atomized burners.
Maintenance
In addition to the preventive maintenance shown in Table 61, the boiler
required emergency maintenance frequently. Valves often had to be repaired
or replaced. To repair leaks, gaskets were replaced, bolts were tightened,
piping was replaced, and the packing at joints was tightened and replaced.
The feedwater pump was rebuilt, and the motor coupling for the auxiliary pump
was aligned. The fan motor bearings required replacement, and numerous
gauges and sight glasses were installed.
TABLE 61. ATOMIZING STEAM BOILER PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check feedwater pump packing.
Grease feedwater pump bearings (LiEP2).
Quarterly
Check feedwater pump packing.
Grease feedwater pump bearings, blow down valve, air blower bearings
on boiiar (LiEP2).
Check coupling.
Semiannually
Grease motors (LiEP2).
Check feedwater pump and blower motors.
Check bearing condition and lubricate if necessary.
Check boiler feedwater reservoir level controller and feedwater valve.
Annually
Megger motors.
229
-------
Plant Water System
The plant water system consisted of a potable city water supply and a
recycled cooling water system. The city water is used for sanitary purposes,
cooling water, make-up water, boiler feedwater, and fire prevention. A
looped main line allows plant operation without interruption while major
portions of the in-plant water lines are being repaired. The recycled cooling
water system supplies cooling water to the kiln trunnions, kiln drive clutch,
stack lid seal, gas analyzers, and ram coolers.
Description
Most of the city water supply piping is underground. From the water
main underneath the street in front of the plant, a 20-cm (8-in.) pipe is
used to convey the water into the plant. The flow of water into the plant is
measured by a meter located just inside the plant fence. Beyond the meter,
the piping branches into two distinct 20-cm (8-in.) pipes that connect again
at the rear of the plant to form a loop. A block valve is located at the
beginning of each line and at the junction of the two lines at the rear of
the plant. A low pressure alarm is mounted on the 15-cm (6-in.) line to the
water softeners. Backflow preventers are installed in the water supply lines
to the process equipment.
The recycled cooling water system consists of a receiving basin kiln
that receives heated cooling water from the users. A 5 hp Gould pump is used
to pump this water to a Marley (75 ton) cooling tower. The cooled water is
then pumped back to the users by a 10-hp Gould pump. All motors have local
start/stop stations only. The portion of the system used to cool the gas
analyzer probes is equipped with Worthington 1.5 1 and 1 hp cooling water
booster pumps. A dual city-water backup system is provided for the equipment
cooled by recycled water. The recycled cooling water line to the eddy
current coupling of the kiln drive is equipped with a switch that will
activate an alarm in the control room and stop the kiln drive motor in the
event of low water pressure.
Operating Experience
The major problem with the city water supply has been one of reliability.
The loss of city water or low water pressure has caused a few emergency
shutdowns plus various other problems. Loss of city water has resulted from
broken water mains outside the plant, repair to water mains outside the
plant, and the repair of a fire hydrant pipe within the plant. The water
supply system was connected to the smaller of the two water mains in the
street in front of the plant instead of the larger, as originally designed.
Based on a computer simulation by Monsanto, the smaller main could not supply
the water demand of 7,570 1pm (2,000 gpm) while maintaining a pressure of
345 kPa (50 psig). Because of the insufficient water supply and pressure for
a kiln, rams, stack lid, and gas analyzer probes, a water recycling system
was added as a modification.
230
-------
To prevent the loss of operating time when city water is lost, an
elevated storage tower should be installed. Such a tower should also solve
the problem of low water pressure.
More block valves are required within the water supply loop so that
small areas can be repaired without disruption to more than half of the water
system.
One of the major problems with the recycled cooling water system has
been freezing. Freezing rarely occurs if the plant is operating, but it can
be a significant problem if the plant is down during below freezing con-
ditions. Since some lines, such as kiln trunnion coils, cannot be insulated
and heat traced, the entire system should be drained during downtime.
Maintenance
The city water supply system required no maintenance except for the
repair of a frozen fire hydrant that ruptured. The water recycling system on
the other hand has required considerable repiping to repair freeze damage.
Instrument Air System
The instrument air system is used to provide dry, oil-free, compressed
air to pneumatic controls and cylinders throughout the plant.
Description
The instrument air system consists of a Worthington 625-rpm, single-
stage compressor capable of delivering 2.75 m3min (97.3 ft^/min) of com-
pressed, oil-free air at a maximum pressure of 786 kPa (125 psig). A Kellogg-
American, single-stage, single-acting compressor is installed as a spare
capable of delivering 2.04 m3/min (72 ft3/min) of compressed, oil-free air
at a pressure of 690 kPa (100 psig). The units share two common receivers—
one in the water treatment building, and one by the rams. The receivers are
cylindrical, vertical, steel pressure tanks.
The air-drying steam is composed of a primary unit consisting of a
Deltech heatless dual chamber air dryer with prefilter and a spare unit
installed in parallel, a Pall Trinity heat-reactivated, dual-chamber air
drier.
Operating Experience
The present spare unit was originally installed as the primary unit with
no spare. The compressor had insufficient capacity and was unreliable, so
the present larger primary unit was installed.
The system has operated well except that the spare unit has failed to
start when the pressure dropped below the set point on a few occasions. To
avoid condensation in the standby compressor, a cooling water condensation
trap was installed.
231
-------
Also the purge valve for the regeneration of the air drier jammed
frequently.
The receiver by the ram was not originally installed but was added as a
modification when it was realized that the pneumatic lines to the stack lid
had insufficient surge capacity.
Maintenance
In addition to preventive maintenance (Tables 62 and 63), the major
maintenance requirement was to repair cooling water lines. Compressor rings
were required, and the low pressure switch was replaced. To stop an oil
leak, the inspection plate was tightened, and the compressor valves froze
once.
Dust Collection System
*
The system collects dust-ladden air from the shredders, the storage and
recovery unit, the transfer tower junction points, the ram feed hopper, and
the shredded refuse conveyor transfer points. The large dust particles are
removed by cyclonic action in the dust collectors and are discharged through
the bottom to the shredded refuse stream. The air and the smaller dust
particles are pneumatically conveyed through a length of steel duct to the
dust collection fan, which creates the suction draft that induces the air
flow throughout the system. The duct collection fan discharges the air and
fine dust into the kiln crossover duct. The dust is then combusted in the
gas purifier to eliminate dust and odors.
Description
All of the dust collectors were supplied by the Ducon Co. and are
equipped with neoprene-stripped, cast iron, non-spark rotary valves.
The dust collection fan is discussed in detail in the combustion air fan
section.
One dust collector is located inside each shredder building, with
collection points at the shredder feed conveyor discharge and the transfer
point from the shredder discharge conveyor to the shredded refuse collection
conveyor. The collector in one shredder building also collects at the
transfer point from the shredder refuse collection conveyor to the shredded
refuse elevating conveyor. Both dust collectors are designed for an air
flow rate of 142 m3/min (95,000 ft3/min) at an inlet suction pressure of 10
cm (4 in.) of water. Both collectors discharge the large dust particles to
the shredded refuse collection conveyor.
The dust collector located in the enclosed top of the storage and
recovery unit has only one collection point. This point is where the shredder
refuse transfer conveyor discharges to the stored material spreader. The
collector is designed for an air flow of 28 m3/min (1,000 ft3/min) and an
inlet suction pressure of 5 cm (2 in.) of water. The collector discharges
the large dust particles to the storage and recovery unit.
232
-------
TABLE 62. INSTRUMENT AIR COMPRESSOR PREVENTIVE MAINTENANCE SCHEDULE
Check oil pressure.
Drain condensate from receiver and traps.
Check for any unusual noise or vibration.
Check oil level.
(Winter - Super HD X 20)
(Summer - Super HD X 30)
Weekly
Clean air filter with solvent and dry it.
Clean all external parts of compressor and driver.
Manually test safety valve for sticking.
Monthly
Inspect entire air system for leaks.
Inspect oil for contamination and change if necessary.
(Winter - Super HD X 20)
(Summer - Super HD X 30)
Check belt tension and wear.
Check oil filter screen.
Quarterly •
Change oil.
(Winter - Super HD X 20)
(Summer - Super HD X 30)
Inspect valve, assemblies, rings, and clearances.
Clean oil filter screen.
Disassemble; inspect and clean oil pressure relief valve.
Semiannually
Grease motor (LiEP2).
Annually
Clean and calibrate instrument air pressure alarm and switch.
Zero, calibrate, and check operation of discharge pressure indicator.
233
-------
TABLE 63. INSTRUMENT AIR DRYER PREVENTIVE MAINTENANCE SCHEDULE
Weekly
Check operating condition:
Line pressure.
Line temperature.
Inlet flow.
Inspect Aquadex Moisture Indicator (make sure bleed is open).
Check pressure difference across prefilter and afterfilter.
Greater than 69 kPa (10 psig).
Check purge indicator for air flow.
Quarterly
Check outlet dew point (should be - 40°F).
Check prefilters, replace as required.
Check blowdown relief valves and the condition of the element.
S emiannually
Inspect and replace prefilters and afterfilter cartridges as required.
Change Alumina afterfilters.
Annually
Inspect desicant and replace if necessary.
Inspect and clean or replace seats on check valve.
Inspect and clean solenoid valves.
Change prefilters if not done during Quarterly or Semiannually inspection.
234
-------
The transfer tower dust collector has collection points at (a) the
discharge of the shredded refuse elevating conveyor, (b) the transfer point
from the storage and recovery outfeed conveyor to the kiln feed conveyor,
(c) the transfer point where the bypass chute deposits on the kiln feed
conveyor, and (d) the tail end of the shredded refuse transfer conveyor below
the discharge from the shredded refuse elevating conveyor. The collector is
designed for an air flow of 56 m3/min (2,000 ft3/min) and a suction inlet
pressure of 5 cm (2 in.) of water. The collector discharges the large dust
particles to the kiln feed conveyor.
The kiln feed dust collector, located in the ram enclosure, has one
collection point from the ram feed hoppers. The collector is designed for
an air flow of 14 to 42 m3/min (500 to 1,500 ft3/min) at an inlet suction
pressure of 25 cm (10 in.) of water. The large dust particles are discharged
to the ground.
Operating Experience
The dust collecting system has performed poorly. A dust buildup of
2.5 cm (1 in.) per week is not uncommon in the areas serviced by the dust
collection system. High velocities occur at the collection points causing
entrainment of large particles, plugging of the rotary valves on the
collectors, and deposits on the dust-collection fan, as discussed earlier.
When plugging occurred, there was no access to the system to alleviate this
problem, so access doors were installed in the dust collector, and quick-
disconnect couplings were installed to allow dissembly of the duct for
cleanout.
The double-acting flop gates on the collectors were changed to star
rotary valves, and the angle of the discharge ducts from the dust collectors
was increased to prevent plugging.
Originally, little could be done to control the flows from each
collection point. This problem was solved by adding slide gates in the
ducts.
The shredder inlet collection points were modified twice to prevent the
pickup of large pieces of refuse. First screens were tried, but they plugged
rapidly. Finally the inlet was changed to allow for rapid expansion of the
flow area. The subsequent reduction in velocity then caused large refuse
particles to settle out of the dust air stream.
The collection point at the discharge of the storage and recovery
outfeed conveyor was disconnected because numerous jams occurred there and
the collection hood limited access for clearing the jams.
Many of the dust collection ducts became plugged between the collection
point and the dust separator because of the long ducts. The dust skirts at
the conveyor transfer points were removed because they restricted the flow of
refuse on the conveyor.
235
-------
Maintenance
The preventive maintenance schedule for the dust collectors is shown in
Table 64. Other maintenance for the dust collectors has mainly been to
repair the drive for the rotary valves, sprockets, cams, and chains. The
gear for one of the motors wore out and was replaced, and a bent driven shaft
on one of the valves was straightened.
TABLE 64. DUST COLLECTOR PREVENTIVE MAINTENANCE SCHEDULE
Monthly
Check all rotary gates.
Check gearmotor oil.
(Winter - EPS)
(Summer - EPS)
Lubricate chain and linkages (Paradene 430).
Lubricate cams and followers (LiEP2).
Semiannually
Change gearmotor oil.
Check motor and alarm.
Check bearing condition and replace if necessary.
Annually
Megger motor.
Sump Pumps
The two storage pit sump pumps, located below each storage pit conveyor,
pump the wash water from the receiving area to the sanitary sewer. The
storage and recovery unit sump pump pumps wash and drain water from the
outfeed conveyor tunnel to the sanitary sewer. The quench pit sump pump,
located next to the residue quench tank, pumps process water from the quench
pit area to the sanitary sewer.
Description
The sump pumps for the storage pit and for the storage and recovery unit
are vertical with a design capacity of 378 1pm (100 gpm) at a total dynamic
head of 12 m (40 ft) of water. These units are supplied by Swaby (Model 3B-3)
and are designed to pump wastewater containing solids up to 2.5 cm (1 in.) in
236
-------
diameter. The pumps have local controls only and are provided with an on/off
float control. The pumps are protected from solids plugging by a screen
around the sumps that must be manually cleaned and by a purge stream of water
from the discharge line to agitate settled solids.
The quench pit sump pump is vertical with a design capacity of 190 1pm
(50 gpm) at a total dynamic head of 9 m (30 ft) of water. The pump is supplied
by Swaby (Model BUL 4200) and is designed to pump wastewater containing
solids. The pump has local controls only and is provided with an on/off
float control.
Operating Experience
Originally, no screens existed around the sump pumps for the storage pit
and the storage and recovery unit. But spillback from the storage pit con-
veyors plugged the pumps, causing overheating and failure. Installation of
the screens helped, but they also plugged resulting in water accumulation.
Another problem with the pumps was that their discharge was lower than
the sewage lift station, and the pumps had no check valves. When the lift
station went out of service, the water backed up into the sumps. To solve
this problem, the pump discharges were changed to be higher than the lift
station.
The quench pit sump pump has continually failed as a result of the large
solids concentration in the water. The quench pit sump has been cleaned and
backflushed several times because of the solids accumulation within the sump.
Maintenance
Sump pump maintenance has mostly consisted of electrical repairs to the
motors. Both of the storage pit sump pumps, which were grounded out after
being submerged, were dried and reinsulated. The float switches also re-
quired repair or replacement. One of the storage pit sump pumps required new
bearings, shaft, and bushings.
The preventive maintenance schedule for these pumps was shown in Table 36.
Wastewater Lift Station
The wastewater lift station receives the plant wastewater from the plant
sewer system and pumps it to the city sewer system.
Description
The wastewater lift station is an Ecodyne package system consisting of
a wet well, two sewage pumps, and a local control system. The local control
system is made up of a hand/off/automatic switch for each pump, four level
switches, and a base pump alternator. The four level switches include a low-
level switch that shuts off all pumps, a middle switch that starts the base
pump, a high-level switch that starts the high-level pump, and a high
237
-------
high-level switch that sounds a local siren. Each of pump is designed for
946 1pm (250 gpm) at a total dynamic head of 11.4 m (38 ft).
Operating Experience
Even though the wastewater lift station is a standard package system, it
was originally unreliable. After the pump gaskets and check valves were
replaced and vacuum breaks were installed, the system was very reliable.
Maintenance
Since the above modifications were made, the unit has required only the
preventive maintenance shown in Table 65.
TABLE 65. WASTEWATER LIFT STATION PUMPS PREVENTIVE MAINTENANCE SCHEDULE
Daily
Observe and check:
Float switch, sewage pump, and vacuum priming operation.
Mechanical seals.
Water trap bottles.
Cleanliness.
Monthly
Remove the electrode and clean any coatings and any deposits or scale
from the electrode housing.
Replace electrode if more than half consumed.
Remove water trap bottles and clean out any water deposits in the jars,
Lift the float mechanism to ensure that it is operating freely.
Check pumps and motors for vibration and abnormal heat.
Check seals for leaks.
Test check valves for proper seat.
Check floats and float switches.
Check starts, sequence timer, relays, etc.
Inspect and clean prime electrodes.
Check vacuum pump, ensure no vacuum leaks.
Se^ annually
Lubricate blower bearing (Paradene 415).
Grease motors (LiEP2).
Check motor.
238
-------
SECTION 3
MASS AND ENERGY BALANCE
INTRODUCTION
This section evaluates the operational efficiency of the Baltimore
Landgard Plant in terms of mass and energy balances as derived from the
characterizations (compositions and flow rates) of the plant's process
streams. The balance data also serves as a means for performing an economic
evaluation of the Baltimore plant and for guiding the design of future plants.
The information for preparing the mass and energy of balances was
extracted from data gathered by Monsanto, the City of Baltimore, and SYSTECH.
While TRW and the Environmental Elements Corporation also collected data,
their data are not relevant to the mass and energy balances since they pertain
to the particulate emissions at the gas purifier, boiler, and scrubber outlets.
This information, however, is discussed in Section 4, Environmental Assessment,
and is detailed in Appendix B.
The City of Baltimore has been continually recording operational data
from the plant start-up to the present. Also from the plant start-up but
only to February 1977, Monsanto conducted extensive sampling*. SYSTECH1 s data
sampling extended from November 1976 through June 1977 when an on-site team
also monitored the entire plant operation. In addition, SYSTECH performed
two one-week sampling batteries with a four-man team during June and August
of 1977 to make its data bank more comprehensive.
To facilitate the preparation and presentation of the mass and energy
balances, five of the plant's seven modules (see Section 2) were grouped in
two operational categories: (1) waste preparation consisting of the re-
ceiving, the size reduction, and the storage and recovery modules and
(2) thermal processing consisting of the thermal processing and the energy
recovery modules. The sixth module in the Section 2 presentation, namely the
Residue Separation module, is not included in this section since it was
rarely used and its operation has been discontinued. The seventh module,
namely the General Plant, is included in the discussion of the entire plant.
Also to simplify the data evaluation, the sample data was normalized to an
average refuse feed rate of 31.75 Mg/hr (35 tph).
For convenience, the modules in the respective operational categories
are hereafter collectively referred to as subsystems, that is, the waste
preparation subsystem comprising the receiving, the size reduction, and the
storage and recovery modules, and the thermal processing subsystem comprising
the thermal processing and the energy recovery modules.
239
-------
This section briefly summarizes the sampling techniques and the process
stream characterizations for each of the two subsystems and presents the mass
and energy balances for the following: (1) the waste preparation subsystem;
(2) the kiln, gas purifier, and waste heat boiler-economizer assembly within
the thermal processing subsystem and the thermal processing subsystem itself;
and (3) the entire plant. In addition, Appendix B presents the complete data
sets, the detailed sampling and data reduction techniques, and other balances.
WASTE PREPARATION SUBSYSTEM
The incoming process streams (inputs) in this subsystem are refuse,
diesel fuel, water, and electricity. While the refuse leaving the subsystem
remains the same in quantity and composition as the refuse entering it, the
mass and energy of the other process streams exit the subsystem as follows:
The diesel fuel is used up by the storage pit bulldozers; the water supplied
to cool the shredder bearings is discharged to the sewer; and the energy in
the electricity used is dissipated to the ambient air.
As indicated by the encircled callout numbers in Figure 83, the refuse
stream has been characterized at the following sampling points in the waste
preparation subsystem: the truck scale, the storage pit, the storage pit
conveyors, the shredded refuse conveyors, the storage and recovery unit, and
the kiln feed conveyor. The sampling points and reference numbers in the
following discussions correlate with the callout numbers in Figure 83.
The mass rates of the incoming and outgoing refuse are based on the
weights read at the truck scale and the measurements taken by the belt scale
on the kiln feed conveyor, respectively (see Figure 83, 1 and 2). While the
rates may differ because of the varying refuse storage, the total mass of the
incoming refuse eventually equals the total mass of the outgoing refuse.
The bulk density of the refuse at the various sample points was measured
by weighting a known volume of refuse. Accordingly, the bulk* densities were
as follows for sample points 3, 4, 6, 8, and 10. In the storage pit (3), the
bulk density of the refuse ranged from 144 kg/m3 (9 lb/ft3) for loose refuse
to 498 kg/m3 (31 lb/ft3) for compact refuse. On the storage pit conveyor
(4) before the refuse shredding, the average bulk density was 122 kg/m3
(7.6 lb/ft3); while on the shredded refuse elevating conveyor (6) after the
refuse shredding the average bulk density was 50 kg/m3 (3 lb/ft3). Then in
the storage and recovery unit (8), the bulk densities ranged from 200 kg/m3
(12 lb/ft3) for the waste normally transferred to the discharge conveyor to
400 kg/m3 (25 lb/ft3) for the refuse at the bottom of the piled waste.
Finally, the bulk densities of the refuse leaving the silo on the kiln feed
conveyor (10), varied as follows with the quantity of the refuse stored in
the storage and recovery unit:
Storage (Mg) Bulk Density (kg/m3)
450 to 720 148
80 to 450 118
0 91
240
-------
REFUSE
TRUCK
SCALE
ro
*>
t-1
DIESEL ~UEL
STORAGE
PIT
CITY WATER
MAGNETIC
METAL
i
SHREDDERS
MAGNETIC
SEPARATOR
WATER TO SEWER
STORAGE AND I
RECOVERY
UNIT
9
^—•<
BYPASSS
• BELT
SCALE
REFUSE
Figure 83. Waste preparation subsystem sampling points.
-------
The refuse particle sizes before and after the shredding process was
determined by taking samples from the storage pit conveyor (4) and the shredded
refuse elevating conveyor•(6), respectively, and then measuring the sizes by
sieve analysis. Both refuse streams had a wide range in size distribution.
The nominal particle size (50 percent by weight finer) before shredding was
86 mm (3.5 in.), which is slightly larger than the nominal specification of
76 mm (3 in.) for the shredder discharge, and the nominal particle size after
shredding was 13 mm (0.5 in.).
The composition of the unshredded refuse was determined by analyzing
manual and photographic sorts of samples from the storage pit (3). Except
for a higher concentration of glass, the composition of the Baltimore refuse
compared closely with the average composition of the refuse in other cities,
as indicated in Table 66. The composition of the shredded refuse was
determined by performing proximate, ultimate, ash, and optical emission
spectographic analyses of samples from the kiln feed conveyor (10). Table 67
summarizes the proximate, ultimate, and ash analyses detailed in Appendix B,
which also includes the optical emission spectrographic data.
Since the magnetic metal separator has been discontinued, it is not
included in the mass and energy balance. However, while it was operative,
the metal recovered in the magnetic metal separator (7) was found to be
5.4 percent of the mass of the shredded refuse stream. A manual sort of one
grab sample of the recovered metal revealed a metal purity of 88 percent with
a recovery percentage of 68 percent.
The flow rate of the water to cool the shredder bearings was measured by
clocking the time to fill a container of known volume with the water discharge
to the sewer (5). The measured rate for each of the two shredders was
25.5 liters (6.7 gallons) per minute, or a total of 51 liters (13.4. gallons)
per minute. The slight increase in the heat content (energy) of the cooling
water through the shredders is assumed to be supplied by a portibn of the
electricity used by the shredder motor and is assumed to be lost to the
surroundings.
As measured by a split core ammeter, the electric power consumed in the
waste preparation subsystem averaged 476 kw, which equals an energy consumption
rate of 28.6 MJ/min (0.027 M Btu/min).
The diesel fuel used by the storage pit bulldozers (3) was measured by
daily reading the totalizer on the plant's diesel fuel pump. When refuse was
being processed, the diesel fuel consumption averaged 208 liters (55 gallons)
per day and 0.55 liter per Mg (0.13 gallon per ton) of refuse was processed
over a range of refuse feed rates. When refuse was not being processed as
during standby and downtime periods, the diesel fuel consumption averaged
64 liters (17 gallons) per day. Assuming a density of 0.87 kg/1 (7.2 lb/
gallon) and heat content of 45.2 MJ/kg (0.019 M Btu/lb), the diesel fuel mass
and energy rates are 0.125 kg/min (0.275 M Btu/lb) and 5.7 MJ/min
(0.005 M Btu/min), respectively.
242
-------
TABLE 66. A COMPARISON OF REFUSE COMPOSITION
NJ
LO
CATEGORY
•
Paper %
Inert %
Glass %
Metals %
Organics %
Miscellaneous %
Moisture (Wt %)
Bulk Density
, (kg/m3)
Heating Value
(MJ/kg)
BALTIMORE,
MARYLAND*
43
1
15
9
32
19
122
9.3
ST. LOUIS,
MISSOURIt
54
4
7
14
21
24
122
10.7
FRANKLIN,
OHIO*
40
3
9
11
37
HEMSTEAD,
NEW YORK§
43
10
9
39
NCRR1T
43
5
10
9
33
ERIE COUNTY,
NEW YORK **
46
3
6
7
37
25
163
10.8
*Values measured by Systech.
tValues from "St. Louis Demonstration Final Report: Refuse Processing Plant Equipment, Facilities, ,
and Environmental Evaluations," by D.E. Fiscus, et. al., Midwest Research Institute, Kansas City,
Mo., 19 March, 1976.
iValues from Municipal Refuse Disposal, Public Administration Service 1970, Interstate Printers
and Publishers, Inc., Danville, Illinois.
^Composition and Physical Characteristics," by Dah-Nien Fan, 1974 Summer Fellow, National Center
for Resource Recovery, Inc., Washington, D.C.
**Values averaged form "Torrax- A Slagging Pyrolysis System For Converting Solid Waste To Fuel Gas,"
by John Z. Stoia, Operations Manager, Carborundum Environmental Systems, Inc., no date, covers
period 1969-1973.
-------
TABLE 67. REFUSE COMPOSITION
Analysis
Proximate (%)
Moisture
Volatile Matter
Fixed Carbon
Ash
Sulfur
Heat Content (MJ/kg)
Ultimate (%)
Carbon
Hydrogen
Nitrogen
Oxygen
Ash (%)
Aluminia
Chromic Oxide
Cupric Oxide
Ferric Oxide
Lead Oxide
Lime
Manganese Dioxide
Magnesia
Nickel Oxide
Phosphorous Pentoxide
Potassium Oxide
Silica
Sodium Oxide
Sulfur Trioxide
Titania
Zinc Oxide
Minimum
As Rec'd Dry
8.50
20.46 25.49
1.13 1.28
8.27 10.31
0.05 0.07
6.02 6.80
20.31
0.46
0.19
5.80
1.11
0.04
0.11
1.73
0.11
2.51
0.11
0.29
0.01
0.35
0.22
26.12
2.05
0.29
0.40
2.02
Average
As Rec'd Dry
19.47
37.54 46.80
6.69 8.36
36.29 44.80
0.13 0.16
9.31 11.61
31.07
1.95
2.32
19.76
11.52
0.04
0.11
14.77
0.11
5.75
0.11
0.79
0.01
0.55
0.58
55.21
5.60
0.51
0.52
2.02
Maximum
As Rec'd Dry
39.70
57.51 75.18
21.55 26.85
54.73 63.35
0.18 0.23
13.06 14.49
40.67
5.58
6.65
42.09
44.85
0.04
0.11
64.78
0.11
11.51
0.11
1.60
0.01
0.66
1.05
74.80
9.00
0.63
0.75
2.02
244
-------
Noise levels within the plant were measured by a hand-held noise meter.
Dust levels in the receiving building, shredder buildings, and storage and
recovery unit were measured with a low-volume personnel sampler. In addition,
a grab sample of dust from one shredder building was analyzed for bacteria
concentrations. Gas concentrations in the receiving building air were measured
by Monsanto with gas tech tubes and by SYSTECH with an automatic carbon
monoxide detector. The resultant environmental data are presented and dis-
cussed in Section 4, Environmental Assessment.
Figure 84 presents the mass and energy balance for the waste processing
subsystem. This figure assumes the following: (1) all the refuse changed
negligibily in mass and heat content while passing through the subsystem;
(2) the mass and energy of the diesel fuel was lost, as work and heat, to the
surroundings; and (3) the heat generated by the electric power was dissipated
to the surroundings. The energy efficiency of the subsystem (the quotient of
the output energy in the refuse, divided by the input energy in the refuse,
diesel fuel, and electricity) was 99.2 percent.
THERMAL PROCESSING SUBSYSTEM
The incoming process streams (inputs) to this subsystem include refuse,
fuel oil, propane, air, water, boiler feedwater chemicals, and electricity.
The outgoing process streams (outputs) from this subsystem include kiln
residue, gas purifier slag, boiler fly ash, stack gases with entrained
particulate, wastewater, steam, and low-grade heat lost to the atmosphere.
The encircled callout numbers in Figure 85 indicate the sampling points
for the process streams in the thermal processing subsystem. As for the
waste preparation subsystem, the sample points and reference numbers in the
following discussions correlate with the callout numbers in this figure.
At the outset of SYSTECH1s characterizing the Baltimore plant process,
the intent was to take a sufficient number of measurements to verify Monsanto fs
process balances, However, it soon became apparent that SYSTECH would have
to acquire independent data because of the process and equipment changes made
after the Monsanto data were collected. Moreover, the Monsanto data did not
approximate the simultaneous measurements required for a process balance.
Since the variation of the refuse composition and feed rate and of the
process operation made it difficult to calculate an adequate mass and energy
balance for the thermal processing subsystem, a balance was developed for a
standby condition with no refuse flow to provide controlled data points. The
controlled data points were sought in order to acquire data for points that
are very difficult to measure, such as the quench air flow and the gas purifier
heat transfer.
Of all the SYSTECH tests, only one was conducted while the refuse
stream flowed to the storage and recovery unit. Nevertheless, the refuse
feed rate was therefore known while approximately steady-state conditions
prevailed. Consequently, a balance for this test was developed by working
from the boiler discharge (20) backwards through the thermal processing
245
-------
REFUSE
454
4,224
kg/min
MJ/min
DIESEL FUEL
0.1 kg/min
6 MJ/min
WATER
51 kg/min
ELECTRICITY
29 MJ/min
WASTE
PREPARATION
SUBSYSTEM
REFUSE
—'• ^-
454 kg/min
4,224 MJ/min
COMBUSTED DIESEL FUEL
0.1 kg/min
6 MJ/min
WASTEWATER
51 kg/min
OTHER HEAT LOST
29 MJ/min
Figure 84. Waste preparation subsystem mass and energy balance.
246
-------
AIR
PROPANE.
SPILLBACK AND SLAG M10 ]
REFUSE
GAS PURIFIER
11
AIR
_Y_L
EXIT GASES
GHf
FUEL OIL
DEAERATING
HEATER
STEAM TO
ATMOSPHERE
STEAM
SALT
CITY WATER
STEAM TO BG&E
ECONOMIZER
LOSSES
BOILER
FLY ASH
FLY ASH SLOWDOWN
Figure 85. Thermal processing subsystem sampling points.
247
-------
subsystem. The boiler discharge was selected as the starting point since its
measurement is considered the most accurate and reliable of all the gas flow
measurements. Then all inputs to the subsystem were summed with leakage air
calculated by forcing the balance. Only a small error was introduced by so
forcing the balance since the leakage was less then 3 percent of the total
subsystem input.
Then the data for the other SYSTECH tests were analyzed and evaluated
according to the estimated refuse feed rates and the average values for the
proximate and ultimate refuse analyses. The estimated feed rates were based
on the average shredder discharge of 31.75 Mg/hr (35 tph) and the refuse
levels observed on the shredded refuse conveyors. Next, from the data
measured and derived, both a mass and an energy balance for the thermal
processing subsystem were prepared from the data for each test. In the
resultant mass balances, the mass outputs deviated from the mass inputs by
3.65 percent on the average. Most of the mass output deviations were within
3 percent of the mass inputs. In the resultant energy balances, the deviations
of the energy outputs from the energy inputs ranged from 1.4 to 19 percent,
with most of the energy output deviations being within 10 percent of the
energy inputs. Finally, to prepare the mass and energy balances for the
kiln, gas purifier, boilers, and total plant, the seven SYSTECH tests that had
estimated refuse feed rates of 530 kg/min (35 tph) were selected and their
data were averaged.
Appendix B presents the Monsanto data along with the resultant mass and
energy balances. In the development of these balances, the mass balances
were first prepared by selecting tests with the most complete data and then
adjusting reasonable estimates for the unmeasured flow rates according to the
known data for a perfect balance of the mass inputs and mass outputs. Then
from the perfect mass balances, the energy balances were calculated. In the
resultant energy balances, the deviations of the energy outputs from the
energy inputs ranged from Q.I to 7.1 percent, and the standard deviation was
2.3 percent which reflects good agreement for field measurements.
In the following paragraphs, the process stream characterizations, that
is, compositions and flow rates, are generally ordered according to their
interrelationships as well as their relevance to the sequence of the mass and
energy balance presentations. Therefore, preparatory to the presentation of
the mass and energy balance for the kiln, the next paragraphs deal with the
composition and flow rates of the process streams pertinent to the kiln
except for the incoming refuse which was detailed in the preceding section
for the waste preparation subsystem.
While the fuel oil composition was determined by two ultimate analyses
which are detailed in Appendix B, the fuel oil flow rates were computed from
hourly and daily readings of the totalizer (9) which measured the fuel oil
flow to the fuel oil pumps. During normal operation, the process burners are
usually set at a fixed firing rate. Consequently, their fuel oil consumption
is independent of the amount of refuse processed. However, because of the
248
-------
different burner tips and minimum firing rates during the successive evaluation
periods, the fuel oil consumption varied as summarized below:
Period Consumption (1/hr)
11/01/76 to 12/21/76 738
01/18/77 to 03/11/77 265
03/05/77 to present 600
The flow rate of the fuel oil to the two main kiln burners (3) was
registered by a flow indicator on the main control panel. The fuel oil flows
to the kiln safety burners, the slag hole fuel oil burner, and the gas
purifier pilot burner were known since these burners have fixed firing rates.
While the gas purifier heatup burner is generally used only during standby
and heatup operations and the fuel oil flow to it is varied, its flow rate
was computed by subtracting the sum of the other burner flow rates from the
total fuel oil consumption rate. During standby operation, the fuel oil
consumption averaged 3,000 1/hr (800 gal/hr). The firing rates for the
various burners were discussed in the previous section. For the balance,
the density and heat content of the fuel oil were assumed to be 0.892 kg/1
and 45.5 MJ/kg.
The flow rate of the propane used by the two slag tap hole burners (21)
was determined by monitoring the propane deliveries to the plant and then
dividing the total quantity of propane received by the number of hours between
deliveries. The average propane consumption rate was 155 1/hr. For the
balance, the density and heat content of the propane was assumed to be 2 g/1
and 50.2 MJ/kg, respectively.
Except for the airflow rates through the dust collection fan and the
quench air dampers, the flow rates of the combustion air were measured by a
hand-held anemometer at the fan inlet cowls (2, 7, and 8). The flow rate for
the air flow through the dust collection fan was measured by a pitot tube
inserted into the fan discharge duct, and the flow rate of the airflow through
the quench air dampers is discussed later. Although the airflow rates through
the process fans, except the dust collection fan, were varied considerably,
the following approximate rates were typical when refuse was being processed:
•
Fan Flow (CMM)
Refuse combustion air fan 350
Turbine-driven kiln combustion fan 200
Motor-driven kiln combustion fan 500
Gas purifier combustion air fan 200
Crossover dust combustion air fan 450
Dust collection fan 365
The leakage air, calculated as previously discussed, was included in
each of the'balances.
249
-------
Most of the water input to the thermal processing subsystem is consumed
as boiler feedwater. Varying directly with the steam production rate, the
flow rate of the boiler feedwater was monitored by observing the flow indi-
cators in the control room or the totalizer on the water softeners (11). The
flow rate of the cooling water to the induced-draft fan bearing was measured
by clocking the time to fill a container of known volume with the water
discharged from the fan bearing to the sewer. Design data were used to
estimate the flow rate of makeup water fed to the recycled cooling water
system. The flow rates of the water for the gas scrubber operation and for
the gas purifier cooling are not included since the gas scrubber is being
replaced by an electrostatic precipitator and the gas purifier cooling is not
representative of normal operation. Monsanto determined the flow rates of
the makeup water for the residue quench tank and the seal tank by noting the
changes in the water levels of the tanks while the makeup water to the tanks
was turned off for a specific time period. The calculation of the boiler
chemical consumption was based on the design concentration and the boiler
feedwater flow rates.
The electrical power consumption of the subsystem was computed by
measuring the power consumed by the individual pieces of equipment with a
split core ammeter and then summing the measurements. Then considering that
the gas scrubber would be replaced by the electrostatic precipitator with an
assumed power consumption of 500 kw, the total electric power consumption was
estimated to be 1,500 kw while refuse was being processed, which equals an
energy consumption rate of 84 MJ/min.
The skin temperatures of the various vessels and ducts were measured by
a portable surface contact pyrometer and a portable optical pyrometer. This
could not be done for the gas purifier since it was cooled by random water
streams. The skin heat loss for the gas purifier was calculated using the
"standby" balance as discussed above.
The flow rate of the kiln residue was computed as a fraction of the flow
rate of the shredded refuse by dividing the net weight of the residue as
measured on the residue trucks during a given period by the net weight of the
shredded refuse as measured by the belt scale on the kiln feed conveyor
during the same period. Although the residue flow rate varied considerably,
it was 44 percent of the refuse flow rate on the average.
•
The kiln residue samples for the composition analysis were collected in
a bucket as the residue fell through the bypass opening in the residue
conveyor. As routinely determined, the moisture content and bulk density of
the residue were on the average 31 percent and 1,600 kg/m3 (100 lb/ft3)
respectively. Table 68 summarizes the proximate, ultimate, and ash analyses
for the residue. Sieve analysis of the residue revealed that on the average
only 3 percent of the residue by weight had .a particles size larger than
102 mm (4 in.) and 62 percent had a particle size smaller than 5 mm (0.2 in.).
Most of the larger particles were metals such as cans and scrap pieces. The
fluid ash fusion temperature of the residue was about 1100°C (2000°F).
250
-------
TABLE 68. RESIDUE COMPOSITION
Proximate (%)
Moisture
Volatile Matter
Fixed Carbon
Ash
Sulfur
Heat Content (MJ/kg)
Ultimate (%)
Carbon
Hydrogen
Nitrogen
Oxygen
Ash (%)
Aluminia
Ferric Oxide
Lime
Magnesia
Phosphorous Pent oxide
Potassium Oxide
Silica
Sodium Oxide
Sulfur Trioxide
Titania
Minimum
As Rec'd Dry
0.10
0.00 0.00
0.09 0.10
15.08 28.98
0.01 0.01
0.59 0.73
3.00
0.08
0.07
<0.09
2.58
1.61
2.89
0.46
0.30
0.29
38.76
3.82
0.51
0.18
Average
As Rec'd Dry
27.34
3.88 5.74
4.20 6.75
64.65 87.52
0.11 0.16
2.43 3.90
6.82
0.23
0.37
1.01
3.80
13.74
4.97
0.69
0.63
0.52
62.67
6.73
0.55
0.75
Maximum
As Rec'd Dry
51.66
8.33 12.20
28.62 55.01
94.74 98.53
0.26 0.27
4.07 7.03
15.48
0.35
1.23
2.08
4.91
43.58
6.15
0.85
0.89
0.74
75.40
12.12
0.58
2.03
251
-------
During mid 1975, Monsanto extensively sampled the kiln-off gas at the
feed hood (2). The gases were characterized by orsat readings and several
methods to define the particulate loadings, size distribution, and composition.
However, since the data were acquired under conditions different from the
present conditions because of the subsequent operational changes in the kiln,
the data is presented only in Appendix B.
Four methods were used to analyze the composition of the kiln-off gas in
the crossover duct (5). While Monsanto conducted a mass spectrographic
analysis, SYSTECH used orsat measurements and gas chromatography (flame
ionization detection and thermal conductivity) for the composition analyses.
Table 69 summarizes the average values obtained by each of the four methods.
The values for the mass spectrographic analysis differ from those for the
orsat measurements and the thermal conductivity analysis primarily because of
the changes in the kiln operation. The low values for the flame ionization
detection analysis were probably due to a leak in the sampling line.
TABLE 69. KILN-OFF GAS COMPOSITION (VOLUME %)
ANALYSIS
Gas
Mass
Spectographic
Orsat
Flame
Ionization
Detection
Thermal
Conductivity
Nitrogen
Carbon Dioxide
Hydrogen
Carbon Monoxide
Oxygen
Methane
Argon
Ethylene
Acetylene
Ethane
Benzene
Propane
iso-Butane
n-Butane
61.99
13.57
9.16
10.03
2.21
1.46
0.67
0.32
0.10
0.09
0.04
•••M •••__
14.42
_ ._
5.62
0.90
0.20
0.06
0.01
0.01
0.00
0.01
60.4
12.1
*
7.3
1.2
0.97
*Interference
252
-------
The long-chain hydrocarbon oil and grease concentrations in the kiln-off
gas were measured by first passing a known volume of the gas through a series
of impingers containing xylene. Then after the oil and grease concentration
in an aliquot was determined by gas chromatography, the total oil and grease
collected was calculated by multiplying the concentration by the total
volume of the xylene impinger solution. Finally, the total oil and grease
was divided by the toal volume of an air sample measured by a dry gas meter.
The oil and grease concentrations in the kiln-off gas averaged 5 mg/m3
(215 mg/ft3). The heating value of the kiln-off gas (5) in the crossover
duct was 3.4 MJ/m3 (92 Btu/ft3) on the average. The calculations were based
on the more complete mass spectrographic analysis and the foregoing oil and
grease data with the assumption that the oil and grease had a heating value
of 39.5 MJ/kg (17,000 Btu/lb).
The temperaute of the kiln-off gas (5) in the crossover duct was
measured by a portable SYSTECH thermocouple and checked with a city thermo-
couple permanently installed inside the fire hood. The temperatures generally
ranged from 650°C (1200°F) to 1100°C (2000°F) and averaged about 815°C
(1500°F).
The velocity of the kiln-off gas (5) in the crossover duct was measured
by a 1.5 m (5 ft) s-type pitot tube and a horizontal oil-filled manometer.
The flow rates of the kiln-off gas averaged 1,615 kg/mm (3,553 Ib/min) during
seven SYSTECH tests when the refuse feed rate was approximately 31.75 MG/hr
(35 tph).
The flow rate of the atomizing steam used by the kiln burners was
assumed to be 18 kg/min (40 Ib/min) on the basis of design data. While the
kiln temperature of the kiln shell varied considerably, they averaged about
175°C (350°F). The flow rate of the water evaporating from the residue
quench tank and the seal tank was estimated as 5 kg/min (11 Ib/min), and the
flow rate of the spillback into the seal tank as only about 0.5 kg/min
(1 1-b/min).
Figure 86 presents a typical kiln mass and energy balance. This balance
is based on the seven SYSTECH tests when the refuse feed rate was estimated
to be 530 kg/min (35 tph) . The reference point for the energy calculations
was 0°C (32°F). On the basis of this balance, the kiln energy efficiency
(the quotient of the energy in the kiln-off gas divided by the total input
energy) was 72 percent.
Before the gas purifier vessel was rebricked and randomly water-cooled,
the average skin temperatures increased from 200°C (400°F,) to 350°C (650°F)
as the refractory thickness decreased.
As continually measured by weighing each truck load of slag (16), the
flow ratio of the slag emitted from the gas purifier averaged 1.77 percent of
the refuse input rate on a wet-to-wet basis and 1.93 percent on a dry basis.
To collect samples for the slag composition analysis, a bucket was
placed in ,the slag trucks at a position directly under the discharge of the
253
-------
REFUSE
530 kg/min
4930 MJ/min
FUEL OIL
5 kg/min
246 MJ/min
AIR
1218 kg/min
36 MJ/min
STEAM
18 kg/min
50 MJ/min
WATER
5 kg/min
1 MJ/min
ELECTRICITY
7 MJ/min
KILN
KILN OFF GAS
1615 kg/min
3784 MJ/min
RESIDUE
161 kg/min
810 MJ/min
HEAT LOST TO
SURROUNDINGS
651 MJ/min
SPILLBACK
0.5 kg/min
5 MJ/min
Figure 86'.. Kiln mass and energy balance.
254
-------
slag conveyor. The moisture content and the bulk density of the slag were on
the average 14 percent and 1690 kg/m3 (106 lb/ft3), respectively. As measured
by sieve analysis, more than 80 percent of the slag particles were smaller
than 5 mm (0.2 in.) which indicates that the slag generally fritted into fine
particles.
The average ash chemistry of slag is shown in Table 70, while the ash
chemistries and spectrographic analyses of various slag samples are detailed
in Appendix B and Section 4, Environmental Assessment, respectively. The
fluid ash fusion temperature of the slag was about 1350°C (2460°F) for samples
taken by Monsanto and 1100°C (2000°F) for samples taken by SYSTECH. While
Section 4 presents the results of a slag leachate test, Appendix B discusses
the test procedure.
TABLE 70. AVERAGE ASH CHEMISTRY OF GAS PURIFIER SLAG
Constituent Percent by weight
Alumina 15.13
Carbon 0.10
Chromic oxide 0.05
Ferric oxide 3.57
Lime 9.22
Magnesia 1.83
Nickel oxide 0.06
Phosphorous Pentoxide 2.27
Potassium oxide 1.56
Silica 55.98
Sodium oxide 4.50
Stannic oxi-a 0.23
Sulfur trioxide 0.16
Titania 2.38
Zinc oxide 0.34
To determine the composition of the gas purifier exit gas (11), SYSTECH
utilized orsat measurements, and Monsanto performed spectrographic and total
hydrocarbon analyses. Table 71 presents the average gas composition. The
SYSTECH data indicates that the gas purifier operation was near the stoichio-
metric level. The higher oxygen levels in the Monsanto data were probably
due to the data being collected during standby conditions.
As measured by a permanently installed thermocouple in the gas purifier,
the temperature of the gases exiting the gas purifier was generally about
1300°C (2350°F).
255
-------
TABLE 71. COMPOSITION OF GAS PURIFIER EXIT GASES
Total
Orsat Mass Hydrocarbons
(Vol %) Spectographic
Nitrogen - 78.5
Carbon dioxide 12.6 5.0
Oxygen 0.3 14.7
Carbon monoxide 1.8 1.7 -
Hydrogen - 1.0
Methane - Trace 1.0
Total hydrocarbon as (CH*) - - 38.0
Argon - 0.8
As for the kiln-off gas, a 1.5-m (5-ft) S-type pitot tube and a horizontal
oil-filled manometer were used to measure the flow rate of the gas purifier
exit gas (11). On the average, the flow rate was 2670 kg/min (5874 Ib/min)
during the seven SYSTECH tests when the average refuse feed rate was 530 kg/min.
(35 tph).
On the basis of the design data, the flow rate of the atomizing steam
used by the gas purifier burners was estimated to be 7 kg/min (15 iS/min),
and the flow rate of the water evaporating from the seal tank at the slag tap
hole was estimated to be 8 kg/min (18 Ib/min). The characterization, of the
propane stream is not presented in this section since the propane stream
effects on the mass and energy balances would be negligible.
Figure 87 presents a typical gas purifier mass and energy balance which
is also based on the seven SYSTECH tests. On the basis of this balance, the
gas purifier energy efficiency (the quotient of the energy in the gas purifier
exit gas divided by the total input energy) was 84 percent.
The flow rate of the air entering the gas purifier outlet through the
slotted and the butterfly quench air dampers in the gas purifier exit duct
was calculated on the basis of the duct opening and the pressure differential.
While the slotted damper was always completely open and the air flow through
it therefore varied with differential pressure only, the butterfly damper
opening was regulated and the air flow through it varied with both the damper
setting and the differential pressure. Accordingly, a set of flow rate
curves was prepared for both dampers. The curves are presented in Appendix B.
From these curves, the flow rate of the air through the dampers was estimated
to be 1055 kg/min (2322 Ib/min) when the average refuse feed rate was
530 kg/min (1166 Ib/hr, or 35 tph). The mixture of the gas purifier exit gas
and the air entering the gas purifier outlet through the quench air dampers
became the boiler inlet gas discussed in the next paragraph.
256
-------
KILN OFF GAS
1615 kg/min
3784 MJ/min
FUEL OIL
12 kg/min
532 MJ/min
AIR
1044 kg/min
31 MJ/min
WATER
2 kg/min
1 MJ/min
STEAM
7 kg/min
19 MJ/min
ELECTRICITY
2 MJ/min
GAS
PURIFIER
GAS PURIFIER EXIT GAS
2674 kg/min
3665 MJ/min
SLAG
8 kg/min
17 MJ/min
HEAT LOST TO
SURROUNDINGS
686 MJ/min
Figure 87. Gas purifier mass and energy balance.
257
-------
The analysis of orsat measurements revealed that the boiler inlet gas
(13) had the following approximate composition:
Volume (%)
Carbon dioxide 8.5
Oxygen 8.7
Carbon monoxide 0.0
These volume percentages indicate that the quench air provided sufficient
excess air (67 percent) to complete the gas combustion. A permanently in-
stalled thermocouple provided measurements of the boiler inlet gas (13)
temperature.
Like the procedure for the kiln residue characterization, the flow rate of
the boiler (18) and economizer (16) fly ash was computed as a fraction of the
flow rate of the shredded refuse by dividing the net weight of the fly ash
collected in the drums under the fly ash hoppers during a given period by the
net weight of the shredded refuse transported on the filn feed conveyor during
the corresonding period. The average flow rate of the fly ash was 0.09 percent
of the refuse flow rate on a wet basis and 0.011 percent on a dry basis.
To collect fly ash for the composition analysis, a sample was taken from
each drum in proportion to the amount of fly ash in the drum and then the
samples were composited. The bulk density of the fly ash was 880 kg/m3
(55 lb/ft3). Since much of the fly ash had agglomerated, the individual
particle sizes could not be determined. However, the agglomerated pieces had
the following size distribution: 76 percent were-smaller than 5;mm,
20 percent were between 5 and 25 mm, and 4 percent .were between 25 and 50 mm.
;li
The fluid ash fusion temperature of the boiler fly ash was 1190°C
(2175°C). Section 4, Environmental Assessment, discusses the ash chemistry
and the analysis of the aqua regina solubles for the boiler fly ash.
The analysis of orsat measurements revealed that the boiler exit gas
(20) had the following approximate composition:
Volume (%)
Carbon dioxide 8.1
Oxygen 9.5
Carbon monoxide 0.6
While data gathered by the Environmental Elements Corporation indicate
that the moisture content of the gas at the boiler discharge (21) was about
20 percent, measurements taken by SYSTECH show that it was about 12 percent.
Again with a 1.5-m (5-ft) S-type pitot tube and a horizontal oil-filled
monometer to measure velocity, the flow rate of the gas in the boiler dis-
charge (21) duct was on the average 3730 kg/min (8205 Ib/min) during the
seven SYSTECH tests when the average refuse rate was 530 kg/min (35 tph).
258
-------
As measured by a portable thermocouple with a dial gauge, the temperature of
the boiler discharge gas was 190°C (375°F) on the average. Appendix B pre-
sents the ash chemistries of the particulate in the boiler exit gas.
The city water (12) was sampled twice to verify that the water is low
in total solids (138 mg per liter) and in hardness (77 mg per liter) as
determined in analyses by the Purification Section, Water Division, Bureau of
Operations, Department of Public Works, City of Baltimore. The boiler feed-
water (13), the boiler water (20), and the constant blowdown from the boiler
steam drums were also sampled. While the total solids concentration in the
boiler feedwater was approximately the same as that in the city water, the
hardness of the boiler feedwater was virtually zero. Since the boiler water
and the constant blowdown each had a total solids concentration of about
1130 mg, the blowdown rate was about 10 percent of the feedwater rate, which
is the Monsanto design value. The boiler water and constant blowdown has a
pH of 10.5 and an alkalinity concentration of 400 per liter. The iron
concentration in the constant blowdown was much higher than that which could
be accounted for by the iron concentration in the boiler feedwater.
As derived from readings of both flow meters in the control room and
totalizing flow meters on the water softeners, the flow rate of the boiler
feedwater was approximately 1226 kg/min (2698 Ib/min) during the seven
SYSTECH tests.
On the basis of readings of the dials mounted on the deaerating tank,
the temperature and pressure of the feedwater in the deaerating heater (14)
were generally 106°C (222°F) and 34.5 kPA (5 psig), respectively. From
calculations based on the cross-sectional area of the heater vent opening
and the pressure differential between the vessel and the atmosphere, the
steam loss through the vent was 5 kg/min (11 Ib/min) . The skin temperature
of the deaerating heater was 93°C (200°F) on the average according to the
measurements of a surface contact pyrometer. The feedwater temperature at
the economizer outlet (17). as read from permanently installed dial thermo-
couples, was generally 208°C (407°F). On the basis of this temperature, the
economizers accounted for about 20 percent of the waste heat recovered by the
boiler-economizer assemblies.
While the flow rate of the steam from each boiler (19) was read from the
meters in the control room, the flow rate of the steam from both boilers as
delivered to the local utility company was read hourly on the company's
totalizing meter and transmitted to the Landgard plant. The steam delivered
to the utility company was 1028 kg/min (136,000 Ib/hr) on the average.
Calculated as a function of the boiler operating pressure, the line losses in
the steam main from the plant to the company averaged 32 kg/min (70.4 Ib/min).
The atomizing steam used in the mass and energy balance is the sum of the
atomizing steam used by the kiln and. gas purifier burners. Since the motor-
driven feedwater pump was on line during most of the test evaluation periods,
this pump is represented in the balance calculations rather than the turbine-
driven feedwater pump.
259
-------
Figure 88 presents a typical boiler mass and energy balance. Like the
previous balances, this balance is based on the seven SYSTECH tests. On the
basis of this balance, the boiler energy efficiency (the quotient of the
energy in the generated steam divided by the energy in the boiler inlet gas
and feedwater) was 77 percent.
Figure 89 presents a typical mass and energy balance for the entire
thermal processing subsystem. According to this balance, also based on the
SYSTECH data, the energy efficiency of the subsystem was 49 percent.
For the following discussion preparatory to the presentation of the
typical total plant mass and energy balance, the plant inputs are refuse,
air, water, fuel oil, gasoline, diesel fuel, propane, electricity, and
boiler chemicals. Also, the plant outputs are stack gas, kiln residue, gas
purifier slag, fly ash, wastewater, steam, and lost heat. Although the plant
balance excludes the residue separation module and the gas scrubber for the
reasons cited above, Appendix B presents the process stream characterizations
for these two units. Also as stated above, the balance calculations include
the 300 kw assumed for the electrostatic precipitator which is replacing the
gas scrubber.
As computed from daily readings of the main water meters on the plant
boundary, the average flow rate of the city water used by the entire plant
was 1448 1pm (383 gpm) . The flow rate of the wastewater discharged frdm the
plant was 242 1pm (63 gpm) on the average. This flow rate was computed by
clocking the time to fill the wet well of the wastewater lift station while
the lift pump was turned off. The averages of measured temperatures and
pH's of the wastewater were 40°C (104°F) and 10.5, respectively.
Appendix B and Section 4, Environmental Assessment, present and discuss
respectively, the results of the analyses of grab samples of the wastewater
and various other process water streams.
The data to compute the total plant electrical power consumption con-
sisted of the measurements of the individual units taken with the split core
ammeter and the 15-minute computer printouts generated and provided by the
Baltimore Gas and Electric Company. The average electrical power consumption
was 142 kw during downtime, 1109 kw during standby operation, and 1800 kw
during normal plant operation. The projected total plant power demand when
the electrostatic precipitator has replaced the gas scrubber is 2200 kw.
The flow rate of the plant gasoline, used mainly by the residue trucks,
was computed from daily readings of the totalizer on the gasoline pump. The
average gasoline consumption was 620 Ipd (164 gpd) during normal plant
operation and 93 Ipd (25 gpd) during downtime.
Figure 90 presents a typical total plant mass and energy balance, which
is also based on the seven SYSTECH tests. Based on this balance, the total
plant energy efficiency (the quotient of the output energy in the delivered
steam divided by the total input energy) was approximately 46 percent.
260
-------
BOILER INLET GAS
3730 kg/min
3696 MJ/min
BOILER FEEDWATER
1226 kg/min
108 MJ/min
ELECTRICITY
9 MJ/min
HEAT
RECOVERY
MODULE
HEAT LOSS
63 MJ/min
BOILER EXIT GASES
3730 kg/min
1016 MJ/min
STEAM TO UTILITY
1028 kg/min
2847 MJ/min
STEAM LINE LOSS
32 kg/min
90 MJ/min
DEAERATOR VENT
5 kg/min
12 MJ/min
SLOWDOWN
136 kg/min
125 MJ/min
ATOMIZING STEAM
25kg/min
69 MJ/min
Figure 88. Boiler mass and energy balance.
261
-------
REFUSE
530 kg/min
4930 MJ/min
AIR
3317 kg/min
99 MJ/min
FUEL OIL
17 kg/min
778 MJ/min
WATER
1233 kg/min
110 MJ/min
ELECTRICITY
70 MJ/min
THERMAL
PROCESSING
SUBSYSTEM
RESIDUE
161 kg/min
810MJ/min
SPILLBACK AND SLAG
9kg/min
22 MJ/min
FLY ASH
0.4 kg/min
DEAERATOR VENT STEAM
5kg/min
12 MJ/min
SLOWDOWN
136 kg/min
125 MJ/min
OTHER WATER TO SEWER
80 kg/min
STEAM
1060 kg/min
2937 MJ/min
Figure 89. Thermal processing subsystem mass and energy balance.
262
-------
REFUSE
530 kg/min
4930 MJ/min
AIR
3317 kg/min
99 MJ/min
FUEL OIL
17 kg/min
778 MJ/min
GASOLINE
0.4 kg/min
24 MJ/min
DIESEL FUEL
0.1 kg/min
6 MJ/min
PROPANE & BOILER
CHEMICALS
NEGLIGIBLE
WATER
1638 kg/min
166 MJ/min
ELECTRICITY
126 MJ/min
BALTIMORE
PYROLYSIS
PLANT
RESIDUE
161 kg/min
810 MJ/min
SLAG
8 kg/min
17 MJ/min
FLY ASH
0.4 kg/min
STACK GAS
3730 kg/min
1016 MJ/min
STEAM
1028 kg/min
2847 MJ/min
WASTEWATER
534 kg/min
91 MJ/min
SURFACE HEAT LOSS
1415 MJ/min
OTHER HEAT LOSSES
168 MJ/min
Figure 90. Total plant mass and energy balance
263
-------
SECTION 4
ENVIRONMENTAL ASSESSMENT
The environmental assessment determines both positive and negative
impacts of the facility on the environment. Since the Landgard concept was
evolved to solve environmental problems associated with solid waste, the
Baltimore plant would be expected to have a positive net environmental
impact. Degradation of land and groundwater is reduced by thermally
processing solid waste before landfilling. With proper plant design, this
positive land impact should not be offset by air or water assaults. As
presently configured, however, the Baltimore plant does not live up to these
high expectations. The discharge of large amounts of particulate with the
combustion products, and the surface discharge of various process wastewaters
have a substantial negative impact on air and surface water quality. But
fortunately, the completion of certain modifications to the Baltimore plant
will enable it to be an environmentally good neighbor and comply with
pollution control regulations.
The Landgard concept involves gasification of solid waste with integrated
combustion and recovery of the energy potential of the gaseous products to
generate steam. The emissions from this plant consist of steam, combustion
products with entrained particulate, solid residues, and liquid wastes.
Emissions from the Landgard plant can be considered either from the
viewpoint of the pollution receiver (air, water, and land impacts) or the
pollution producer (the plant). Because of the complexity of sorting out the
air, water, and land impacts, this report will examine the five major types
of pollutants produced within the plant—stack emissions, solid residues,
plant process waters, fugitive emissions, and noise contamination.
STACK EMISSIONS
The stack at the Baltimore plant is used to direct the discharge of the
products of combustion from the process. As a result, the emissions of
interest are particulates and gas.
Particulate Emissions
The original design concept presumed that the gas flow through the
primary reaction chamber (kiln) was (1) over the solids bed and (2) of low
velocity, so that the carryover of particulate would be minimized, much as it
is in a starved-air incinerator. After discovering high particulate loadings,
the designer theorized the formation mechanism to be as follows: When the
264
-------
atmosphere in the primary chamber (kiln) was maintained at substoichiometric
levels, several of the oxidized metals found as coatings on solid waste were
reduced to their elemental forms and vaporized. Salts were similarly
volatilized. These vapors were then reoxidized and eventually formed a
condensation aerosol. As a result of this phenomenon and the carryover of
fines from the kiln, the kiln-off-gas particulate loadings were higher than
expected.
Though the scrubber performed admirably and in fact exceeded its design
specifications for percent particulate removal, the plant could not meet the
State of Maryland particulate emission standards of 0.069 g/DSCM
(0.03 gr/DSCF).
Monsanto and the City of Baltimore thus tested a portable, single-cell
electrostatic precipitator to determine if it could enable the plant to meet
the particulate emission requirements of the State. The pilot precipitator
was tested on a side stream of the boiler exit gases that had an average
inlet particulate loading of 0.6 g/DSCM (0.26 gr/DSCF). This single-cell
unit resulted in exit loadings of less than 0.069 g/DSCM (0.03 gr/DSCF).
The plant is presently being upgraded to replace the wet scrubber with
electrostatic precipitators to control the particulate emissions. As a
result, much of the historical data concerning particulate emissions from the
plant are no longer applicable.
To anticipate future emissions compliance before the electrostatic
precipitators are actually installed, the combustion products will be examined
before they reach the scrubber at the boiler discharge, and the previously
conducted portable electrostatic precipitator tests will be used to generate
data. The test results shown in Table 72 indicate that the electrostatic
precipitators will allow the Baltimore plant to comply with particulate
emission standards.
TABLE 72. DRY ELECTROSTATIC PRECIPITATOR TEST OF BOILER EXIT GASES*
Rapping
Pressure
(kPa)
83
110
83
110
69
—
Velocity
(m/s)
0.67
0.67
0.91
0.91
1.22
Voltage
(kv)
44
49
47
48
50
47
Current
(ya/m2)
462
344
355
312
312
355
Inlet
Loading
(g/DSCM)
0.595
0.538
0.592
0.698
0.549
3. 810t
Outlet
Loading
(g/DSCM)
0.030
0.047
0.065
0.049
0.091
0.079
Efficiency
(%)
94.8
91.1
89.2
92.1
83.0
97.7
* White, S. J., Jr., Environmental Elements Corporation.
Application Survey City of Baltimore Pyrolysis Plant.
Maryland, 1976. p. VI.
t Blowing soot.
Precipitator
No. 7364. Baltimore,
265
-------
Gaseous Emissions
The scrubber was designed to remove gaseous contaminants as well as
particulates. Tables 73 and 74 relate both boiler and scrubber exit gaseous
emissions rates and reveal that the scrubber removes approximately 80 percent
of the halogens, sulfur dioxide, and short-chain hydrocarbons. Little sulfur
trioxide or nitrous oxide, and very few long-chain hydrocarbons are removed
by the scrubber.
TABLE 73. BOILER AND SCRUBBER OUTLET GASES
Boiler Outlet
(mg/SCM)
Scrubber Outlet
(mg/SCM)
Gas
Sulfur dioxide (S02)
Nitrogen oxides (NOx)
Sulfur trioxide (S03)
Chlorides (C1-)
Fluorides (F-)
Mean
390.3
10.6
36.1
713.5
7.7
Standard
Deviation
89.2
12.7
10.1
605.4
3.2
Mean
74.8
9.0
24.7
74.2
1.3
Standard
Deviation
104.1
7.0
10.7
80.3
0.5
Removal
(%)
81
15
32
90
83
TABLE 74. HYDROCARBON ANALYSIS OF BOILER AND SCRUBBER OUTLET GASES*
Length Of
Hydrocarbon
Chain
Concentration of n-alkanes
Boiler outlet
(mg/SCM)
Scrubber outlet
(mg/SCM)
Removal
Cl
C2
C3
C4
C5
C6
C7
C8
C9-C12
85
<0.6
833
1,634
<0.6
682
1.2
1.0
t
13
<0.6
234
564
<0.6
584
t
t
t
85
—
72
65
—
14
—
—
~—
* TRW Environmental Engineering Division. Source Emissions Tests for
Industrial Research Labs. EPA 68-01-2988, U.S. Environmental Protection
Agency, Cincinnati, Ohio 1977. p.24.
t Not detectable.
266
-------
The replacement of the scrubber with electrostatic precipitators will
solve the particulate emission problem but will increase the gaseous emissions
from the boiler because electrostatic precipitators have no effect on gaseous
emissions. However, installation of a tall stack will have a beneficial
effect. The neutral to negative bouyancy of the combustion products cooled
in the dehumidifier often fumigate the immediate downwind area with noxious
gases. The stack will disperse these gases so that their concentrations will
be lower when they reach ground level.
Gaseous emissions are highly variable. Product gas compositions vary
not only with plant load and excess air levels in the primary chamber, but
also with the composition of the solid waste feed stream. As a result, it is
impossible to determine the exact concentrations of gases emitted from the
plant.
As far as criteria pollutants are concerned, no limits presently exist
on incinerator emissions of sulfur dioxide or oxides of nitrogen. Sulfur
dioxide in the stack gas averages 390 mg/SCM, with a relative standard
deviation of 0.25. Nitrogen oxides in the stack gas average 11 mg/SCM, with
a relative standard deviation greater than 1. Because of the high variability,
it is impossible to say what the absolute emissions are, but the sulfur
dioxide and nitrogen oxide emissions are within the legal limits for boilers
fired with solid fossil fuels.
The sulfur trioxide (S03) emissions from the plant are on the order of
35 mg/SCM, or approximately 10 percent of the sulfur dioxide level. The
total hydrocarbons leaving the plant are on the order of 3,240 mg/SCM; they
are predominantly C<, hydrocarbons. The presence of this amount of a large
hydrocarbon implies that the gases in the gas purifier are not being properly
combusted because of improper mixing and low excess air.
Halogens are also emitted from the plant. Emission rates of 714 mg/SCM
for hydrogen chloride and 7 mg/SCM for hydrogen fluoride have been observed.
The significance of these emissions cannot yet be assessed, because too few
toxicological and epidemiological data exist to determine whether or not
these stack concentrations translate to ground level concentrations of concern.
Nevertheless, gaseous emissions from this plant are within or below the
range from a solid-fossil-fuel-fired boiler plant, and as a result, they
should have no more adverse environmental impact than a coal plant of similar
size.
SOLID RESIDUES
In addition to entrained gases and particulates resulting from the
gasification of solid waste, other solids are directly emitted from the
plant. These are discharged in the form of slag from the gas purifier,
primary residue from the kiln discharge, and fly ash from airborn material
de-entrained in the waste heat boilers and economizers.
267
-------
Gas Purifier Slag
Approximately 2 percent of the refuse fed to the Baltimore process
reports as slag. This slag comes from solids entrained in the gaseous
combustion products from the primary chamber (kiln). The solids are collected
as they melt and de-entrain on the walls of the gas purifier. This material
is maintained in a molten stage by a constant heat transfer from the radiant
fireball in the gas purifier. The slag flows by gravity down the walls of
the purifier and through a slag taphole in the bottom. As the slag drips
through the taphole, it falls into a water bath, where it is quenched. Rapid
chilling of the slag causes the material to fracture and form a relatively
fine frit.
The frit has a bulk density of 1700 kg/m3 and contains 14 percent
surface water. The slag is approximately 50 to 60 percent silica, with
aluminum the next most significant element (Table /O).
While there .are significant quanitites of other metals in the slag, most
are in the form of relatively insoluble metal oxides. The most significant
heavy metals in the slag are Barium, Lead, Tin, and Zinc (Table 75).
In a leaching test of the slag in water (Table 76), the supernatant was
found to have neutral pH, low BOD and COD, total solids of 440 mg/1, and
metal levels of 0.5 mg/1 or below (except for iron, which had a level of
approximately 10 mg/1). As a result, slag can be viewed as inert and should
have no adverse impact on the land with proper disposal in a sanitary landfill.
Initial tests of the structural characteristics of the slag indicate
that it can be used as a fill or building material. Once a reliable slag
source has been created, further work should be done to verify that this
material can indeed be used instead of simply occupying space in an approved
sanitary landfill.
Kiln Residue
Kiln residue results from the gasification of solid waste in the rotary
kiln. While progressing through the kiln, the waste is heated to dry and
devolatilize it. A portion of the carbon contained in the remaining solids
is then combusted to provide heat for the previous endothermic gasification
reactions, and a portion of the fixed carbon char remains. As a result, when
the plant is operating properly approximately 44 percent of the refuse fed to
the kiln is discharged. If the waste is burned to completion so that no
char is present, approximately 33 percent of the refuse is discharged as
residue.
The failure to operate the residue separation module has a negative
environmental impact. The magnetic metals and glassy aggregate portions of
the residue were to be recycled, thus, considerably reducing the amount to be
landfilled. The recycling of magnetic metals would also reduce the amount of
iron that could be leached from the residue.
268
-------
TABLE 75. EMISSION SPECTROGRAPHIC SCAN OF SLAG*
Constituent
Date and Time
6/20/75
0800
6/21/75
1500
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Germanium
Iron
Lead
Magnesium
Manganese
Molybdenum
Nickel
Phosphorous
Potassium
Silicon
Silver
Sodium
Strontium
Thallium
Tin
Titanium
Vanadium
Zinc
1-10
>0.005
>0.005
0.100-1.000
>0.001
>0.001
0.010-0.100
>0.001
3-30
0.010-0.100
0.001-0.010
0.010-0.100
>0.001
1-10
0.100-1.000
0.500-5.000
0.010-0.100
0.001-0.010
0.001-0.010
0.010-0.100
0.200-2.000
3-30
0.001-0.010
2-20
0.010-0.100
>0.001
0.100-1.000
0.500-5.000
0.001-0.010
0.100-1.000
1-10
>0.005
>0.005
0.100-1.000
>0.001
>0.001
0.010-0.100
>0.001
3-30
0.010-0.100
0.001-0.010
0.010-0.100
>0.001
1-10
0.100-1.000
0.500-5.000
0.010-0.100
0.001-0.010
0.001-0.010
0.010-0.100
0.200-2.000
3-30
0.001-0.010
2-20
0.010-0.100
>0.001
0.100-1.000
0.500-5.000
0.001-0.010
0.100-1.000
* Herrington, R. C., D. E. Honaker, and B. G. Ward. Baltimore Landgard®
Process Characterization. Monsanto Enviro-Chem Systems, Inc. No. 7240,
St. Louis, Missouri, 1976. Table 40.
269
-------
TABLE 76. SLAG LEACHATE ANALYSIS (April 27, 1977)
Item Amount
pH (mg/<£.)
BOD (mg/£)
COD (mg/£)
TS (mg/£)
VS (mg/£)
Cl~ GngAQ
Total coliforms (MPN/100 mO
Cr (Total mg/£)
Pb Gng/£)
Ni Ong/-^)
Cu (mg/£.)
Zn ' Gag/^)
Fe Cmg/-e)
Hg (jig/£)
7.3
19.0
31,0
440.0
200.0
49.0
<3,0
<0.05
<0.5
<0.2
<0.05
<0.01
10.5
<0.01
The kiln residue has a bulk density of approximately 1600 kg/m3
(100 lb/ft3). Even though the mass reduction is only 56 percent, the volume
reduction of the refuse is 96 percent because of the tenfold difference
between the bulk density of the refuse and the residue. Volume reduction is
important since it affects landfill life.
The moisture content of the kiln residue, which is approximately
30 percent, is higher than that of the slag because of the porous structure
of the char. Such a structure greatly increases the effective surface area
and traps water. This excess water greatly increases the weight of the
residue requiring disposal and becomes a nuisance when it drains out of the
truck and onto the road during transportation to the landfill.
Table 77 shows that the proximate and ultimate analyses of residue from
the kiln are very similar to those of the residue from an incinerator re-
ceiving similar refuse.
The average ash analysis of the kiln residue (Table 68) reveals that
silica and iron are the major components .of the ash. Though the iron could
be leached from a landfill, both of these materials are relatively inert.
The putrescible content of the residue (Table 78) is based on the use
of a BOD test. The results reveal that the residue is not totally oxidized
and also quantify the portion of the residue that would decompose as a result
of biological activity.
270
-------
TABLE 77. A COMPARISON OF KILN AND INCINERATOR RESIDUES
Incinerator*
Constituent
Moisture (%)
Ash (%)
Volatile matter (%)
Fixed carbon (%)
Sulfur (%)
Heating value (MJ/kg)
Carbon (%)
Oxygen (%)
Hydrogen (%)
Nitrogen (%)
Chlorine (%)
As
Received
37.01
57.36
3.94
1.69
—
—
—
—
—
—
—
Dry
__
91.04
6.26
2.70
.22
2.4
7.17
2.08
.77
.25
.17
Kilnt
As
Received
27.34
64.65
3.88
4.20
.11
2.4
—
—
—
—
—
Dry
—
87.52
5.74
6.75
.16
3.9
6.82
1.01
.23
.37
—
* City of Baltimore Incinerator #4.
tt Average values.
TABLE 78. RESIDUE PUTRESCIBLE CONTENT
Date
Time
Source
Putrescibles* (%)
COD (%)
9/11/75
9/11/75
9/12/75
9/13/75
9/14/75
1/31/77
3/1/77
4/28/77
4/28/77
0600
1600
1600
1600
1600
1500
—
—
1630
Kilnt
Kilnt
Kilnt
Kilnt
Kilnt
Kiln
Kiln
Kiln
Incinerator §
0.0113
0.0130
0.0129
0.0115
0.0098
0.04
0.1710
0.11
0.24
—
—
—
—
7.39
18.2
12.6
4.6
* Based on BOD5.
t Herrington, R. C., D. E. Honaker, and B. G. Ward. Baltimore Landgard®
Process Characterization. Monsanto Enviro-Chem Systems, Inc. No. 7240.
St. Louis, Missouri, 1976. Table 38.
§ City of Baltimore Incinerator #4.
271
-------
Though the composition of the residue varies considerably with different
degrees of burnout, the microbial concentration is affected to an even greater
degree. If the residue is processed properly, it is effectively sterile as a
result of the high temperatures within the kiln, as shown by the first two
dates in Table 79. If the kiln residue is underprocessed, the microbial
levels are orders of magnitude higher, as shown by the third date in Table 79.
The table also reveals that the microbial level in incinerator residue is
within the range of microbial levels for similarly processed kiln residue.
TABLE 79. MICROBIAL ANALYSIS OF RESIDUE
Date
2/1/77
3/1/77
4/29/77
4/29/77
Residue
source
Kiln
Kiln
Kiln
Incinerator*
Standard
plate count
(organisms/g)
6,400
8
7,65 x 107
3,200
1'otal coliform
(MPN/g)
^^^
0
0.2
0
Fecal
streptococci
(MPN/g)
,
0
0.9
0
* City of Baltimore Incinerator #4.
Leaching tests of kiln and incinerator residue (Table 80) reveal that
the supernatant had a neutral pH, low BOD and COD, total solids of approxi-
mately 300 mg/1, and metal levels of 0.5 mg/1 or below, except for nickel and
iron, which had concentrations of less than 3 mg/1. Both of these residues
could therefore be viewed as similar and relatively inert. They should have
no adverse impact on the land with proper disposal in a sanitary landfill.
Fly Ash
During the recovery of heat from the combustion products leaving the gas
purifier, much of the entrained material solidified by the quench air is de-
entrained as it passes through the tube banks of the boilers and economizers.
Approximately 0.09 percent of the refuse fed to the process reports as ash
from the bottom of the boilers through a combination of settling in the
relatively low-velocity waste heat recovery boiler and impaction onto the
boiler tubes. This ash is 30 percent silica and, surprisingly, 15 percent
sulfur trioxide (Table 81).
The fly ash tends to contain large quantities of metals (Table 82), a
characteristic typical of fly ash from coal-fired boilers. The only heavy
metals found in significant amounts in the fly ash, however, are lead and
zinc. Since the metals are in the form of relatively insoluble metal oxides,
leaching should not be a problem.
272
-------
TABLE 80. RESIDUE LEACHATE. ANALYSIS
Incinerator*
Constituent Kiln 4/29/77
BOD (mg/1)
COD (mg/1)
Total solids (mg/1)
Volatile solids (mg/1)
Chlorides (mg/1)
Total coliform/100 ml
Cr (mg/1)
Pb (mg/1)
Ni (mg/1)
Cu (mg/1)
Zn (mg/1)
Fe (mg/1)
Hg (yg/1)
pH
28
28.9
290
170
94
<3
<.05
<.5
.5
<.05
.05
2.9
<.01
7.3
23
21.4
310
120
70
<3
<.05
<.5
1.2
<.05
.18
1.2
<.01
7.3
* City of Baltimore Incinerator #4.
273
-------
TABLE 81. BOILER FLY ASH CHEMISTRY
Composition (%)
Constituent 6/25/76* 7/20/77
Alumina
Chromic oxide
Ferric oxide
Lime
Manganese dioxide
Magnesia
Nickel oxide
Phosphorus pentoxide
Potassium oxide
Silica
Sodium oxide
Stannic oxide
Sulfur trioxide
Titania
Zinc oxide
Undetermined
13.40
0.10
7.20
12.10
0.13
2.20
<0.01
4.40
34.20
7.80
0.20
2.40
3.20
12.67
17.61
3.67
11.18
3.99
2.07
4.08
28.42
9.60
14.89
2.51
1.98
Harrington, R. C., D. E. Honaker, and B. 6. Ward. Baltimore Landgard®
Process Characterization. Monsanto Enviro-Chem Systems, Inc. No. 7250.
St. Louis, Missouri, 1976. Table 6.
274
-------
TABLE 82. BOILER FLY ASH ANALYSIS OF AQUA REGIA SOLUBLES*
Element Percent by Weight
Ag
Al
B
Ba
Ca
Cd
Co
Cr
Cu
Fe
Mg
Mn
Mo
Ni
Pb
Sb
Si
Sn
Ti
V
Zn
0.039
4.45
0.020
0.026
4.46
0.034
0.0046
0.028
0.13
3.12
0.84
0.12
0.014
0.019
1.64
0.045
0.61
0.15
0.92
0.043
' 1.89
* Unpublished Monsanto Data.
The environmental impact of land disposal of Landgard fly ash is not
expected to be significantly worse than that of similar materials from coal-
fired boilers.
The fly ash is free of large amounts of carbon and has a size distribu-
tion and appearance similar to coal-fired power plant fly ash. This fly ash
can possibly be used, therefore, as a construction material in lightweight
aggregate building blocks, lightweight concrete, and soil stabilization.
This supposition must be verified in the future, however.
PLANT PROCESS WATER
Normally, the only discharge to the sewer consists of sanitary waste-
water, boiler blowdown, and feedwater treatment system discharge. All process
water in the plant is closed loop and discharges to the sewer only upon
emergency draining of the various tanks. The average wastewater flow to the
sewer from the Landgard plant is approximately 242 1pm (64 gpm) , and ranges
from 110 to 1970 1pm (29 to 520 gpm). Of this flow, 28 1pm (7 gpm) is clean
275
-------
water being used for cooling various bearings on fans and other equipment
throughout the plant. This water could be reused as makeup water for the
various tanks, or it could be added to the recirculating cooling water system.
An analysis of wastewater effluent to the sewer is shown in Table 83, which
shows that this wastewater has low concentrations of most constituents
except dissolved solids.
TABLE 83. AVERAGE ANALYSIS OF VARIOUS PROCESS WATERS
Effluent Slag Residue Residue truck
Constituent to sewer quench quench drainage
pH (mg/-O
Alkalinity (mg/£)
Acidity (mg/£)
BOD5 (mg/£)
COD (mg/£)
Chlorides (mg/£)
Suspended solids (mg/£)
Total solids (mg/£)
Volatile solids (mg/£)
Volatile suspended
solids (mg/£)
Hardness (mg/£)
Sulfide (mg/£)
Sulfite (mg/£)
Sulfate (mg/£)
Iron (mg/£)
TKN (mg/£)
Total phosphorous (mg/£)
Standard plate count (Organism/ml)
Total coliform (MPN/ml)
Fecal streptococci (MPN/ml)
Lead (mg/£)
Mercury (mg/£)
___
81
24
81
247
110
1,094
368
36
227
0.0
0.4
127
3.4
2.6
0.4
69,000
155
184
0.1
.002
9.7
94
16
260
272
782
386
92
7.0
1.5
1.11
6
0
1
0.35
0.001
10.3
313
626
1,583
3,207
495
8,890
4,528
273
401
5.3
0.47
37,000
0
11
.75
.004
9.7
670
535
6,320
7,765
11,900
4,560
1,653
82
0.9
15.7
41
0
105
70
.019
Wastewater is discharged to other than the sanitary sewer only when the
kiln seal tank, the residue quench tank, or the scrubber is emptied. The
original design called for the discharge from these components to the sewer,
but the 7.5-cm (3-in.) drain pipes for these tanks proved to be too small and
plugged. To drain the tanks, it was necessary to install gasketed doors that
could be opened to allow the process water to flow onto the ground. The
emptying of these tanks is practiced infrequently. To remedy this situation,
the tanks could ba equipped with larger discharge pipes, a back flushing
276
-------
system, or dikes for subsequent collection and disposal to the sanitary
sewer. Such alternatives would prevent this wastewater from infiltrating the
groundwater beneath the processing area or from flowing to a body of surface
water.
As shown in Table 83 the slag quench tank process water has COD and
solids concentrations similar to municipal sewage. The low BOD5 and micro-
organism levels of the slag quench indicate that this wastewater cannot be
treated biologically. This process water has a high pH and heavy metal
(iron and lead) concentration than municipal sewage. The pH is not a problem
because of the low alkalinity, and the heavy metals are not a problem because
this water is discharged to a large sewage system where its small volume per-
mits dilution to safe levels.
The residue quench tank process water has much higher pollutant con-
centration as compared to the slag quench process water, but it is much more
amenable to biological treatment (Table 83). Again, this wastewater can be
safely discharged to a sanitary sewer, since this procedure is resorted to
only during emergencies and the sewage system is large.
Approximately one-twentieth of the volume of the kiln residue is dis-
charged from the rear tailgate of the dump truck as drainage water. Based on
analysis of this discharge (Table 83), this wastewater should not be
discharged to the surface but should be collected and sewered, since it does
not meet water quality standards. The forthcoming modification of the residue
separation building will remedy this situation.
Because of the refuse, residue, slag, and fly ash that cover the ground
in the processing area, surface runoff could also cause deterioration of
local surface water quality. Though it may not be required by law, sewering
the storm runoff from the process area may be advisable.
Except for storm runoff from the nonprocessing areas, all water dis-
charged from the plant should be disposed of in the sanitary sewer. Most of
the wastewater will be only slightly purified by biological treatment at a
municipal sewage treatment plant. The high concentrations of heavy metals in
some of the process waters could have a bactericidal effect at the sewage
treatment plant if the wastewater is not sufficiently diluted. But since the
stronger process waters are discharged very infrequently and the volume is
small, the effect on the final effluent from the sewage treatment plant
should be minimal.
FUGITIVE EMISSIONS
Fugitive emissions in the work place include dust, microorganisms, and
gases that might have adverse health effects.
Dust loadings in the Baltimore plant range from 0.009 to 0.025 g/m3
(Table 84). They are highest in the receiving area, where the waste is being
discharged from packer trucks. This dust is biologically active, with the
standard plate counts in the range of 111,000 counts/g (Table 85)—comparable
277
-------
TABLE 84. DUST LEVELS
Date Location Loading (g/m3)
51 3/77 Receiving building 0.025
51 3/77 Rams 0.0092
51 4/77 Transfer tower 0.0198
5/5/77 A3 -Shredder 0.0146
5/ 5/77 Transfer tower 0.0167
51 9/77 Z9-Z10 Transfer 0.0094
5/11/77 Atlas 0.0104
TABLE 85. MICROBIAL LEVELS IN REFUSE DUST
Organism Concentration
Standard plate count (counts/g) 111,000
Bacteria* (counts/g) 27,000 - 730,000,000
Salmonella* Present
Fecal coliform* (MPN/g) 1,400 - 512,000
Fecal coliform* (MPN/g) 2,400
Fecal streptococci (MPN/g) 2,400
Staphylococcus aureus (MPN/g) 460
Enterovirus (PFU/g)* 735 - 171,232
Bacteriophage (PFU/g)* 27,000 - 900,000
St. Louis Demonstration Final Report: Refuse Processing Plant Equipment,
Facilities, and Environmental Evaluation, 1976. D. E. Fiscus, ed. Midwest
Research Institute, Kansas City, Missouri. Tables 26 and 27, pp. 113-114.
278
-------
to the levels found at the Union Electric resource recovery facility in St.
Louis. The dust levels throughout the Baltimore plant are sufficient to
produce a 2.5 cm (1 in.) dust layer over most of the operating equipment
within a week. This nuisance can be improved upon by proper air handling and
dust collecting equipment.
The significance of biological activity in samples of work-place dust
collected in Baltimore is totally unknown and beyond the scope of this report.
Significant epidemiological work must therefore be performed to determine
whether or not the handling of solid waste poses an environmental hazard for
the worker. Some of the plant personnel have developed skin irritations that
they associate with the plant dust.
Carbon monoxide is a workplace hazard because it causes insidious toxicity
and possible death. The threshold limit value (TLV) for carbon monoxide is
50 yl/1. Throughout the monitoring of the Baltimore plant, peak carbon
monoxide levels of 100 to 190 yl/1 were observed at the edge of the tipping
floor when more than two trucks were present (Table 86). In the refuse pit,
levels of 35 yl/1 were observed, whereas levels on the tipping floor ranged
from 34 to 70 yl/1. These carbon monoxide levels could probably be sub-
stantially improved by installing fans in the roof ventilators of the re-
ceiving building.
At present, only the laborer who directs the refuse trucks to the
various tipping bays is exposed to carbon monoxide in the tipping floor area
8 hr/day. Though the peak limits greatly exceed the TLV, this worker is
usually away from the trucks and in an area where the levels are much lower.
The periodic nature of the truck dumping also limits his exposure.
The dozer operator is exposed to carbon monoxide in the storage pit air
for 8 hour per day, but the level there is less than the TLV.
Refuse truck drivers and laborers are exposed to the highest levels of
carbon monoxide, but only for short periods of time. No significant con-
centrations of carbon monoxide were found elsewhere in the plant. It can,
therefore, be concluded that carbon monoxide poses no work hazard in this
facility.
NOISE
For an 8-hour exposure, noise levels must be kept below 90 dBA to
comply with OSHA regulations. The noise level throughout the majority of
the Baltimore plant was less than 90 dBA (Figures 91 through 96). The general
plant area was usually in the range of 80 to 90 dBA. Noise levels ranged
upward of 120 dBA in the vicinity of the retractable soot blowers, and they
registered about 90 dBA near the rotary soot blowers (Table 87). The high
noise from the soot blowers is of an intermittent nature, and workers in the
immediate environment use ear plugs or headsets while operating this
equipment.
279
-------
TABLE 86. ANALYSIS OF RECEIVING BUILDING AIR
Date
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
6/25/76t
4/27/77t
4/27/77
4/27/77
ft/27/77
4/27/77
4/27/77
4/27/77
4/27/77
4/27/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
4/28/77
5/03/77
5/03/77
5/03/77
5/03/77
5/03/77
5/03/77
5/03/77
5/03/77
5/03/77
Time
0955
0958
1003
1006
1008
1015
1015
0945
0950
1020
1022
1030
1040
1045
1050
1300
1300
1300
1300
1300
1300
1300
1300
1300
1015
1015
1015
1015
1015
1015
1015
1015
1020
1025
0930
0930
0930
0930
0930
0930
0930
0930
0930
Test
H2S
C2H3CL
SO 2
NH3
C12
NO
N02
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
Concentration
Location (yl/£)
North side
North side
North side
North side
North side
North side
North side
Northeast corner
Northeast corner
Southeast corner
Southeast corner
Dozer cab
Dozer cab
Dozer cab
Dozer cab
Northwest corner
West central side
Southwest corner
Northeast corner
East central side
Southeast corner
North storage pit
South storage pit
Central storage pit
Northwest corner
West central side
Southwest corner
Northeast corner
East central side
Southeast side
North storage pit
South storage pit
East central side
East central side
Northwest corner
West central corner
Southwest corner
Northeast corner
East central corner
Southeast corner
North storage pit
South storage pit
Central storage pit
<1.0
1.0
*
*
< .5
2.0
<1.0
50
50
50
>50
>25
40
40
40
23
4
5
22
15
20
16
16
3
41
38
50
10
56
68
31
58
98
130
70
36
34
150
190
170
160
160
35
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
1
2
2
2
2
5
5
4
4
3
1
Comments
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Truck
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Trucks
Truck
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
&
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
1
1
1
2
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozer
Dozers
Dozers
Dozers
Dozers
Dozers
Dozer
Dozer
Dozer
Dozer
Dozer
Dozers
* None detected.
t Herrington, R. C., D. E. Honaker, and B. 6. Ward. Baltimore Landgard®
Process Characterization. Monsanto Enviro-Chem Systems, Inc. No. 7250
St. Louis, Missouri, 1976. Table 10.
280
-------
ALL SYSTEMS RUNNING
00
DRAINAGE CHANNEL
GLASSY AGGREGATE
STORAGE
Figure 91. Noise survey (dBA are circled). Date and time: 2/25/77, 0900.
-------
00
NO
Z14 - ONE RAM WORKING
A3 — ONE SHREDDER RUNNING
DRAINAGE CHANNEL
SHREDDER A2
BLDG.
PARKING / BUILDING BY
LOT / OTHERS
GLASSY AGGREGATE
STORAGE
Figure 92. Noise survey (dBA are circled). Date and time:3/10/77, 0830.
-------
NJ
00
u>
NO TRUCK TRAFFIC
Z-14 IS ONLY RAM WORKING
A3 SHREDDER IS ONLY ONE
WORKING
Z-3&Z-5 NOT RUNNING
DRAINAGE CHANNEL
SWITCHGEA
BUILCHNQ BY /U O 1(11
OTHERS TO
GLASSY AGGREGATE
STORAGE
Figure 93. Noise survey (dBA are circled). Date and time: 3/17/77, 1600.
-------
to
00
DRAINAGE CHANNEL
SHREDDERS RUNNING — 1
RAMS RUNNING — 2
TRUCKS IN RECEIVING
A. 2 TRUCKS — 1 DOZER
B. 1 TRUCK - 1 DOZER
C. 1 DOZER
GLASSY AGGREGATE
STORAGE
Figure 94. Noise survey (dBA are circled). Date and time: 4/28/77, 1000.
-------
to
00
Ui
Z4 Z6 RUNNING
A3 SHREDDER — RUNNING
BOTH RAMS — RUNNING
1 DOZER IN IDLE
DRAINAGE CHANNEL
SWITCHGEAR i-.
BUILDING BY /U O
OTHERS /O
Figure 95. Noise survey (dBA are circled). Dace and time: 5/5/77, 1700.
-------
to
oo
1 SHREDDER OPERATING
2 RAMS OPERATING
A. 2 TRUCKS 1 DOZER IN IDLE
B. 1 TRUCK 1 DOZER
C. 1 DOZER
DRAINAGE CHANNEL
GLASSY AGGREGATE
STORAGE
Figure 96. Noise survey (dBA are circled). Date and time: 5/13/77, 0930.
-------
TABLE 87. NOISE LEVELS DURING SOOT BLOWING
Soot blower Soot blower Noise level
No. type (dBA)
1
2
3
4
5
6
7
8
9
10
11
12
Retractable
Retractable
Retractable
Retractable
Rotary
Rotary
Rotary
Rotary
Retractable
Retractable
Retractable
Retractable
110
117
114
120*
90
94
94
90
120
110
105
105
* Pulses up to 130.
A noise level above 90 dBA also exists near the induced-draft fan.
In this area, noise is reflected from the fan as well as from the various
tanks within the immediate vicinity, and the cumulative impact exceeds 90 dBA.
The one point of high noise level near the C8 fan is a low-access area
in which workers need not work for 8 hours. Any employees stationed there
for a repair task while the process is on line are equipped with ear plugs
and protected from the potential hazard. Consequently, noise is not con-
sidered to be a major problem at the Baltimore Landgard facility.
287
-------
SECTION 5
ECONOMIC EVALUATION*
BACKGROUND AND PURPOSE
This section presents the costs associated with construction and
operation of the Baltimore Landgard system as well as cost projections on
various plant operating and system characteristics. This analysis is in
accord with the EPA's Accounting Format,t but it does not necessarily conform
to Generally Accepted Accounting Principles (GAAP). A discussion of how the
Accounting Format deviates from GAAP is presented in Appendix C.
The EPA Accounting Format was developed to facilitate economic com-
parisons of resource recovery systems. It consists of two formats that are
designed to reflect actual and normalized resource recovery system costs and
revenues. The actual accounting format is designed to reflect costs and
revenues of a recovery system incorporating site-specific parameters. The
normalized accounting format removes the site-specific aspects of parameters
affecting plant costs (cost of land and labor rates for example) and other-
wise compensates for varying local conditions. The normalized format thus
permits comparisons with other systems.
Each of the two formats contains three components—capital costs,
operating and maintenance costs, and revenues. Capital costs are categorized
as those for land, site preparation, design, construction, real equipment,
other equipment, contingencies, start-up and working capital, and finance and
legal services. Operating and maintenance costs are broken down into ex-
penditures for salaries, employee benefits, fuel, electricity, water and
sewer, maintenance, replacement equipment, residue removal, other overhead,
taxes and licenses, insurance, management fees, and professional services.
Revenues are categorized by recovered materials sold. Definitions of the
above categories may be found in EPA's Accounting Format.
* The economic analysis presented in the section was prepared and documented
by Arthur Young & Company.
t U.S. Environmental Protection Agency. Accounting Format. SW-157.6, 1976.
288
-------
When costs and revenues are calculated according to the above formats,
the following items can be determined:
o Average annual capital costs
o Capital cost per throughput ton
o Total annual operating and maintenance costs
o Operating and maintenance costs per ton
o Total revenues per throughput ton
o Net operating cost/profit
In addition, capital and operating and maintenance costs are allocated
to seven cost centers to facilitate translation of the Baltimore experience
to other plant designs. The cost centers correspond to the major subsystems
within the plant: Receiving, size reduction, storage and recovery, thermal
processing, energy recovery, residue separation, and general plant.
Because of the erratic operating status of the plant, the continuing
equipment modifications, and the methods by which the City of Baltimore
records Landgard operating costs, the economic evaluation was somewhat
modified. Three operating scenarios were derived by SYSTECH and utilized by
Arthur Young & Company to support the cost calculations and presentation
(Table 88). These scenarios were developed to account for the inoperation of
various subsystems (i.e., the residue separation and gas scrubber system) and
for proposed plant improvements (i.e., the electrostatic precipitator). In
addition, the scenarios compensate for the limited and erratic operating
status of the plant by providing projected costs and revenues based on varying
degrees of plant availability. Thus the costs accumulated under the account-
ing formats depict projected as opposed to actual costs and revenues.
The method by which the City of Baltimore records Landgard operating
costs is inadequate for evaluation purposes because it employs a modified
accrual- basis of accounting. Under this method, revenues are not recorded
when earned, but rather as received; expenses on the other hand, tend to be
recorded when incurred, regardless of when they are paid. This recording
method does not provide for the proper matching of revenues and expenses.
For example, this system does not require accounting for inventories such as
fuel oil. Purchases of fuel oil thus charged to expense as purchases and do
not really reflect fuel consumption costs for a given period. To achieve a
proper matching of revenue and expense, fuel purchases would have to be
established in an inventory and charged to expense when actually used.
The three scenarios are primarily distinguished by their varied operating
statuses. The first scenario's operating status corresponds to the plant's
performance from November 1976 to July 1977, and is characterized by frequent
plant shutdowns. The second scenario's operating status is based on an
expanded operating staff and more efficient administrative procedures. These
changes in plant operation are estimated to increase the average continuous
plant operating period more than twofold. The third scenario's operating
status is based on the most optimistic operating conditions possible and on
equipment improvements that are presently being initiated. As a result, this
289
-------
TABLE 88. SCENARIO OPERATING PARAMETERS*
Scenario 1:
Scenario 2:
Scenario 3
Operating schedule:
Operating status (days):
Normal processing, t
Standby, §
Heating and cooling, IT
Downtime, **
Refuse feed rate:
Mg/hr
Mg/yr
Steam production (kg/hr):
Normal processing
Standby
Staffing:
Plant manager
Plant supervisor
Clerk typist
Chief operators
Field operators
Ram operators
Equipment operators
Laborers
Scalemen
Engineers
Laborers/chauffeurs
Maintenance supervisor
Electricians
Mechanics
Welders
Oilers
Instrument technicians
Total staffing
Fuel consumption (£/hr):
No. 2 fuel:
Normal processing
Standby
Heating and cooling
Downtime
24 hr/day, 24 hr/day, 24 hr/day,
6 days/week, 7 days/week, 7 days/week,
24 shutdowns/yr 8 shutdowns/yr 4 shutdowns/yr
104
56
48
157
27
67,000
50,000 (2/3)
35,000 (1/3)
35,000
1
1
1
5
5
3
3
5
1
7
1
2
3
2
40
660
3,260
1,960
0_
264
21
16
64
32
203,000
59,000 (2/3)
35,000 (1/3)
35,000
1
1
1
4
12
4
7
1
1
5
1
2
6
1
1
1
49
660
3,260
1,960
0_
312
18
8
27
36
270,000
66,000
35,000
1
1
1
4
8
4
5
1
1
4
1
1
4
1
1
1
39
660
3,260
1,960
0-
CONTINUED
290
-------
TABLE 88. CONTINUED
Gasoline :
Normal processing
Standby
Heating and cooling
Downtime
Diesel fuel:
Normal processing
Standby
Heating and cooling
Downtime
Electricity consumption (kw) :
Normal processing
Standby
Heating and cooling
Downtime
Water consumption (£/day) :
Normal processing
Standby, ft
. . Heating and cooling
Downtime
Sewer flow (£/day) :
Normal processing
Standby
Heating and cooling
Downtime
Scenario 1:
620
620
• 93
93
208
208
64
64
2,100
1,109
1,109
142
1,595,380
1,195,780
187,780
187,780
395,380
355,780
187,780
187,780
Scenario 2:
620
620
93
93
208
208
64
64
2, 1QQ
1,109
1,109
142
1,835,140
1,195,780
187,780
187,780
419,140
355,780
187,780
187,780
Scenario 3:
620
620
93
93
208
208
64
64
2,100
1,109
1,109
142
2,021,620
1,195,780
187,780
187,780
437,620
355,780
187,780
187,780
* Provided by SYSTECH.
t Constitutes processing of waste.
§ Constitutes onstream with no processing of waste,
1f Involves startup and cool-down of kiln.
** No activity, plant shut down.
ft 35 Mg/hr of steara.
291
-------
scenario represents the longest continuous plant operating period. The
manner in which scenario operating parameters were derived is further
explained in the discussion of operating and maintenance costs.
Operating status is not the only major difference in scenario parameters.
Others include variation in refuse feed rate, steam production, and staffing.
Refuse feed rate estimates were based on City and SYSTECH data, and they
range from the average (Scenario 1) to the maximum (Scenario 3) recorded
refuse shredding rate-, Steam production estimates were also based on City
and SYSTECH data, but for Scenario 3, it was also assumed that the market
could absorb all steam produced from the Landgard system throughout the year.
Staffing estimates for Scenarios 2 and 3 were based on engineering judgments,
whereas actual plant staffing is used for Scenario 1.
OPERATING AND MAINTENANCE COSTS
Because of t.he discontinuous plant operations and the lack of compati-
bility between City accounting records and EPA guidelines, the initial step
of auditing and gathering historical operating and maintenance cost infor-
mation was not possible. As an alternative, operating and maintenance costs
were projected utilizing engineering and operating judgment provided by
SYSTECH.
Parameters and data were provided for three separate sets of operating
conditions. All costs that are ultimately reflected in the EPA classification
categories are based on the scenario parameters (Tables 88 and 89). For each
scenario, all subsystems are considered operable except for the storage and
recovery unit and the residue separation module. Also, the electrostatic
precipitator is considered to be installed and operational as a replacement
to the gas scrubber system. A discussion of how these parameters were
developed follows.
As illustrated in Table 88, the operating status of the plant has been
broken into four categories: downtime, heating and cooling of the process
area, standby, and normal processing. Each scenario reflects a different
level of plant operation.
Scenario 1 is based on actual plant operating history during the 9-month
period from November 1976 to July 1977. During this period, the plant
operated an average of less than 2 weeks continuously, and it was shut down
approximately 6 days between runs. This average cycle continued throughout
the period monitored. Thus, during the course of a year, the plant would be
shut down 24 times for a period of 6.5 days per shutdown. Furthermore, each
time the plant was shut down, there would be an accompanying 1-day period for
cooling the system before the downtime, and a 1-day period for heating the
system in preparation for operation. The 24 shutdowns therefore lead to an
additional 48 days of plant unavailability. During operation it was decided
to halt the processing of waste on Sundays to allow the staff to perform
necessary maintenance functions. Process temperatures were maintained by
firing fuel oil. In addition to the 33 days of nonscheduled standby, this
scheduled standby time would account for yet another 23 days per year of
plant unavailability. Emergency maintenance or process deviations (upsets)
292
-------
TABLE 89. OPERATING AND MAINTENANCE UNIT COST DATA*
Item
Amount
Salary rates (annual, FY 77-78)
Plant manager
Plant supervisor
Clerk typist
Chief operators
Field operators
Ram operators
Equipment operators
Laborers
Scalemen
Engineers
Laborers/chauffeurs
Maintenance supervisor
Electricians
Mechanics
Welders
Oilers
Instrument technicians
Employee benefits rate
(% of salary costs):
Fuel rates:
No. 2 fuel oil
Gasoline
Diesel fuel
Electricity rate
Water and sewer rates
(quarterly basis):
First 141,500 t consumed
Next 1,275,000 t consumed
Any additional water consumed
Chemical costs:
Sulfite
Chelate
$24,250
20,061
7,572
16,277
14,765
14,765
9,518
8,570
7,313
17,326
8,216
17,327
10,360
12,728
10,742
8,216
17,450
16.74
$0.083/£
0.095/£
0.092/£
$0.03/kwh
$0.127/1,000 liters
0.079/1,000 liters
0.053/1,000 liters
$0.616/kg
1.210/kg
All cost information obtained between 5/77 and 7/77.
293
-------
would account for an additional day and a half of standby. Thus on a yearly
basis, the plant would be available for a total of 104 days of onstream time
(365 days minus 157 days of downtime, 48 days of heating and cooling, and
56 days of standby).
The operating status changes in scenario 2 were based on an extension of
the existing plant operation with an expanded operating staff and more
efficient administrative procedures. It appears likely that changes in plant
operation can increase the average continuous plant operating period to
slightly over a month. If this is assumed, the number of maintenance down-
times would be approximately eight per year. If the number of downtimes are
reduced, the duration of each will increase. Therefore, it is assumed that
each duration will average eight days, yielding a total downtime of 64 days.
Heating and cooling periods remain at 2 days per downtime, yielding a total
of 16 days for heating and cooling. Standby time on Sunday could be elimi-
nated by expanding the staff to the proper size. The final assumption made
for this scenario is that standby time for maintenance and operational
emergencies can be reduced by 21 days. As a result, the total available
operating time is 264 days (365 days less 64 days downtime, 16 days heating
and cooling, and 21 days standby).
The assumptions made for scenario 3 are based on the most optimistic
operating conditions likely to occur, given the projected equipment improve-
ments presently being initiated. This scenario assumes an increase in labor
productivity and a market for all of the steam produced. The operating
status of scenario 3 provides for quarterly, 1-week maintenance shutdowns,
accounting for 27 days of downtime. The heating and cooling periods are,
again, 2 days each, accounting for an additional" 8 days of downtime. It is
assumed that annual emergency standby time can be reduced to 18 days under
optimal conditions. These assumptions provide for a total available operating
time of 312 days (365 days less 27 days of downtime, 8 days of heating and
cooling time, and 18 days of emergency standby). This estimate closely
corresponds with Monsanto's original projections for the plant's level of
operation, but was determined on an independent basis.
Table 90 illustrates the projected operating and maintenance costs in
accordance with EPA's Accounting Format. Each scenario shows wide variations
in cost per Mg throughput, which are primarily attributed to the differences
in the operating reliability of the plant. Projected annual operating and
maintenance costs do not differ greatly for any of the scenarios, but the
projected number of Mg processed under each scenario depends on the number of
scenario operating days and has a major effect on cost per Mg.
Another major influence is that all material-related costs except fuel
(i.e., chemicals, water and sewer, and electricity) increase in proportion
to the number of tons processed. Fuel costs for Scenario 2 and 3 are less
than Scenario 1 because of the decline in the number of days of standby, and
heating and cooling. Although scenario 1 has fewer operating days, the
increased fuel consumption during standby, and heating and cooling operations
results in higher fuel costs.
294
-------
TABLE 90. PROJECTED ANNUAL OPERATING AND MAINTENANCE COSTS*
Item
Scenario 1
Scenario 2
Scenario 3
Salariest
Employee benef itst
Fuel§
Electricity
Water and sewer
Maintenance
Chemicals
Residue removal
Other overhead
Total annual operation
and maintenance costs
Operating and maintenance
costs/Mg
$428,000
72,000
700,000
293,000
20,000
1,024,000
3,000
77,000
196,000
$2,813,000
$42.00
$569,000
95,000
558,000
463,000
35,000
972,000
8,000
77,000
196,000
$2,973,000
$14.60
$457,000
77,000
570,000
523,000
43,000
1,025,000
11,000
77,000
196,000
$2,979,000
$11.00
* 1977 dollars.
t Excludes those salary and benefit costs applicable to residue removal.
§ Excludes input fuel costs applicable to residue removal.
Operating and maintenance costs were then normalized in accordance with
EPA's Accounting Format guidelines. The normalized costs roughly coincide
with the projected scenario costs and are presented in Appendix C.
Finally, projected Scenario 1 operation and maintenance costs were
allocated to the seven EPA established cost centers as defined in the Request
for Proposal (RFP) (Table 91). Costs were initially allocated to all cost
centers except the residue separation module. General plant costs were then
allocated to the remaining cost centers on a proportional basis determined by
each cost center's existing dollar amount.
After costs were allocated to the five cost centers, it was then possible
to determine separately the annual operating cost of waste and preparation
and energy recovery. The annual operating cost of waste preparation is
estimated at $641,000, and that of energy recovery is estimated at
$2.2 million.
CAPITAL COSTS
Capital costs billed for the pyrolysis plant were identified through
examination of the City of Baltimore's accounting records. The capital
expenditures related to the pyrolysis plant are charged to Capital Projects
295
-------
TABLE 91. OPERATING AND MAINTENANCE COSTS PER COST CENTER (SCENARIO 1)
S3
VO
Cost classification:
Salaries
Employee benefits
Fuel
Electricity
Water and sewer
Maintenance
Chemicals
Residue removal
Other overhead
Total
General plant allocations:
Salaries*
Remaining costst
Total
Grand total
Total cost
$ 428,000
72,000
700,000
293,000
20,000
1,024,000
3,000
77,000
196,000
2,813,000
2,813,000
Receiving
$ 22,000
4,000
—
5,000
—
102,000
—
—
—
133,000
69,600
* 17,800
87,400
220,000
Size
reduction
$ 14,000
2,000
—
34,000
4,000
105,000
—
—
—
159,000
69,600
21,200
90,800
250,000
Storage and
recovery
..
—
—
$ 5,000
—
85,000
—
—
—
90,000
69,600
11,900
81,500
171,000
Thermal
processing
$ 44,000
7,000
688,000
215,000
6,000
479,000
—
77,000
—
1,516,000
69,600
203,100
272,700
1,789,000
Energy
recovery
„
—
—
$ 10,000
10,000
253,000
3,000
—
—
276,000
69,600
37,000
106,600
383,000
General
plant
$348,000
59,000
12,000
24,000
—
—
—
—
196,000
639,000
—
—
--
—
* Salaries were distributed equally to all cost centers.
t The remaining general plant costs were allocated on a. pro rata basis.
-------
Fund accounts. All of Monsanto's Original Contract expenditures and most,
but not all, of the Supplemental Agreement expenditures are contained in
these accounts.*
Once expenditures relating to the capital costs were ascertained, a
research and review of the Capital Extract listing was undertaken. Through
an examination of selected source documents relating to the voucher/check
numbers, approximately 98 percent of the Extract costs were researched.
Expenditures were investigated and scrutinized to determine whether they were
a. Properly chargeable to the project;
b. Properly classified as capital expenditures as opposed to
operating expenses; and
c. Materially accurate for reclassification per EPA Accounting
Format and cost centers.
During the detailed review, adjustments to the reported amounts were
necessary because certain operating and maintenance costs were charged as
capital expenditures, and vice versa.
Because of insufficient data, many expenditures cannot be separated as
to their construction versus real equipment components. To segregate costs
by construction and real equipment, it is necessary to have access to
engineering estimates that include the labor input factor per equipment item.
These data were not available, however, this situation was particularly acute
for expenditures related to the Supplemental Agreement. For the most part,
the Supplemental Agreement invoices exhibited integrated cost items en-
compassing both construction and real equipment. As a result, certain
integrated costs are put under one cost classification.
Results of the capital cost analysis in accordance with EPA's Accounting
Format are illustrated in Table 92. The net capital costs total
$20.5 million. This figure results from adding the unbilled costs incurred
by Monsanto to the costs recorded in the Capital Expenditures Extract.
Another interesting point is that construction and real equipment costs
account for 85 percent of the total costs.
Capital Cost Adjustments
To facilitate economic comparisons with other resource recovery systems,
the capital costs were adjusted according to the Accounting Format to reflect
more accurately the costs that would be incurred if the plant were duplicated
elsewhere. Thus as part of the financial review of the capital costs in-
curred by the pyrolysis plant, an investigation of certain cost exclusions
and additions to the project was performed. These additional adjustments
include the following:
As of March 3, 1977, costs of $404,593, which were incurred by Monsanto for
the construction of the plant, were not recorded in the Capital Expenditure
Extract.
297
-------
TABLE 92. A SUMMARY OF EPA CAPITAL COST CLASSIFICATIONS '
CO
Title description
12 Extra work
03 Design studies
*4 Site
flS Inspection
id Structures and
improvements:
original contract
supplemental agreement
other costs
#7 Utilities
#8 Furniture and equipment
#9 General
Additional equipment
Total
Land
«••
—
$486,411
—
46,208
—
45,870
—
—
—
—
578,489
Site preparation
$121,343
—
27,540
—
400,991
—
—
—
—
—
—
549,874
Design
$11,500
18,165
—
—
1,144,040
—
—
—
—
—
—
1,173,705
Construction
$194,243
__
—
—
6,708,838
3,804,385
—
27,898
—
—
—
10,735,364*
Real
equipment
$380,854
__
—
—
5,741,248
—
—
—
—
—
10,758
6,132,860t
Other Financing
equipment and legal
$95,499 —
__ —
—
—
599,765 $64,000
—
147
—
—
—
250,763
946,027 64,147
Cost not
researched
$41,497
63,081
5,345
36,910
—
55,064
21,611
3,199
48,461
76,782
351,9505
Total
$803,439
59,662
577,032
5,345
]4, 742, 000
3,804,385
101,081
49,509
3,199
48,461
338,303
20,532,41611
* $4,108,039 of these costs include both real equipment and construction costs that cannot be separated.
t $371,587 of these costs Include both real equipment and construction costs that cannot be separated.
§ The $351,950 represents costs not researched through examination of vouchers and is only 1.7% of the total costs.
V This sum includes $404,593 of unbilled supplemental agreement costs.
-------
— Exclusion of unique and nonrecurring cost;
— Restatement of contributed or nominal cost items;
— Exclusion of costs attributed to the residue separation and gas
scrubber systems;
— Inclusion of costs attributed to the construction of an electrostatic
precipitator;
— Inclusion of costs attributed to residue disposal;
— Inclusion of indirect costs; and
— Restatement of costs in 1977 dollars.
These adjustments account for the plant's experimental status, the
inoperative and replaced plant subsystems, and the inclusion of specified EPA
cost elements not included in the Capital Expenditure Extract. The cost
exclusions/additions relating to replaced and inoperative subsystems are
consistent with the scenarios developed for the projection of operating and
maintenance costs. The net impact of these adjustments in the capital cost
classifications are illustrated in Table 93.
Capital costs incurred and subsequently adjusted were then classified
according to EPA guidelines set forth in the Accounting Format. The estimated
useful life of the facility and the total interest to be paid had to be
determined to complete EPA's capital cost format.
Estimated Useful Life of the Facility
The useful life of the facility was determined through reference to
Internal Revenue Service (IRS) guidelines for depreciable assets. The IRS
depreciation regulations, as set out in Revised Procedures 72-10, state that
the useful life for solid waste disposal plants has a lower limit of
14.5 years. With due consideration of the experimental nature of the
pyrolysis plant, utilization of the lower limit seems appropriate.
As a means of tesing the validity of the 14.5 years useful life, in-
quiries were made of select vendors (Table 94).
Based on the cost of equipment items in Table 94, the estimated useful
life of the facility is 17 to 18 years. This does not greatly differ from
the IRS lower limit.
Interest to be Paid
The Baltimore landgard project was primarily financed through: (1) pro-
ceeds from the sale of city-owned real estate that was designated specifically
for capital and economic development (approximately $6 million), (^) grants
obtained from the State of Maryland ($4 million), and (3) the Federal
Government ($7 million).
Since the interest expense associated with the construction of the plant
was minimal, a cost was inputted that would represent total debt financing
charges. The latest issuance of debt in the City of Baltimore was in
April 1977. The effective yield on the bond was 5.3 percent. If this most
299
-------
TABLE 93. CAPITAL COSTS (EXCLUSIONS/ADDITIONS)
CO
O
o
Calibration
Costs before
exclusions/
additions
Original
contract cost
items restated
Supplemental
agreement
cost items
restated
Exclusion of
material
recovery
system costs
Exclusion of
gas scrubber
system costs
Inclusion of
ESP costs
Inclusion
of inputted
landfill
costs:
Scenario 1
Scenario 2
Scenario 3
Inclusion
of inputted
finance
charge :
Scenario 1
Scenario 2
Scenario 3
Costs
restated
in 1977 $:
Scenario 1
Scenario 2
Scenario 3
Land
$578,489
573,321
573,321
573,321
573,321
573,321
693,557
935,056
1,054,264
693,557
935,056
1,054,264
849,304
1,117,368
1,249,689
Site
preparation
$549,874
505,030
505,030
505,030
505,030
505,030
505,030
505,030
505,030
505,030
505,030
505,030
668,975
668,975
668,975
Design
$1,173,705
1,045,764
1,045,764
1,045,764
1,045,764
1,045,764
1,072,817
1,127,154
1,153,976
1,072,817
1,127,154
1,153,976
1,448,709
1,509,023
1,538,795
Construction
$10,735,364
9,985,088
6,900,571
6,361,182
5,969,647
7,409,687'
7,511,887
7,717,161
7,818,488
7,511,887
7,717,161
7,818,488
9,454,472
9,682,326
9,794,799
Real '
equipment
$6,132,860
5,490,799
5,490,799
4,998,970
4,694,199
5,825,659
5,843,694
5,879,919
5,897,800
5,843,694
5,879,919
5,897,800
7,497,866
7,538,076
7,557,924
Other
equipment
$946,027
878,953
878,953
878,953
878,953
878,953
878,953
878,953
878,953
878,953
878,953
878,953
1,153,825
1,153,825
1,153,825
Finance
and legal
$64,147
56,990
56,990
56,990
56,990
56,990
56,990
56,990
56,990
395,866
407,941
413,902
416,364
428,439
434,400
Other
costs
$351,950
347,822
347,822
347,882
347,822
347,822
380,887
447,299
480,081
380,887
447,299
480,081
471,935
545,652.
582,040
Total
capital cost
$20,532,416
18,883,767
15,799,250
14,768,032
14,071,726
16,643,226
16,943,815
17,547,562
17,845,582
17,282,691
17,898,513
18,202,494
21,961,451
22,643,684
22,980,447
-------
TABLE 94. EQUIPMENT COSTS AND USEFUL LIFE REPORTED BY SELECT VENDORS
Useful life
Description Cost (years)
Storage & recovery unit $367,300 20
Waste heat boilers 829,821 20
Kiln 1,336,209 10
Waste Collector conveyor 305,674 20
Waste gas fan 149,618 20
Electrostatic precipitator 2,571,500 20
recent interest rate is used and a 20-year maturity on the bonds is assumed,
the inputted finance costs for the project are derived for each of the
scenario costs according to EPA guidelines.
The summary capital costs according to EPA's Accounting Format are
presented in Table 95. Again, wide variations occur in costs per Mg, pri-
marily because of projected differences in the operating reliability of the
plant.
All All capital costs identified throughout the Capital Expenditures
Extract, as well as additional equipment expenditures, were separately
researched for reclassification by cost center.
Summary cost center distributions are presented in Tables 96 and 97.
Table 96 illustrates cost center distribution before the cost exclusions and
additions. Table 97 presents the final capital cost allocation for each of
the three scenarios with the inclusion of the adjustments. The conversion of
these cost center summaries into subsystem costs in accordance with EPA's RPF
is shown in Table 98.
Nearly 75 percent of the costs pertain to the construction of the energy
recovery subsystem. The thermal processing module separately accounts for
approximately 50 percent of the total plant capital costs, whereas the energy
recovery module accounts for 25 percent of total plant capital costs.
The Accounting Format provides guidelines and instructions for converting
costs to a normalized basis. The results of this normalization for the
pyrolysis plant are presented in Appendix C.
Because detailed cost information is unavailable, only 10 percent of
the total capital costs could be normalized. Cost components that could be
normalized include construction, real equipment, and other equipment. The
construction cost could not be adjusted because of a lack of information
concerning man-hours and overall labor input. Equipment costs could not be
adjusted because of lack of information for segregating freight costs.
301
-------
TABLE 95. PROJECTED SCENARIO CAPITAL COST SUMMARY
Item
Scenario 1
Scenario 2
Scenario 3
Capital cost ($):
Land
Site preparation
Design
Construction
Real equipment,
including replacements
Other equipment,
including replacements
Contingencies
Startup and working
capital
Financing and legal
Other costs
Total initial capital
investment ($)
Estimated useful life
of facility (years)
Total interest to be
paid ($)
Total capital cost ($)
Annual capital cost (.$)
Annual throughput (Mg)
Capital cost per Mg ($)
$ 849,000
669,000
1,449,000
9,454,000
7,498,000
1,154,000
416,000
472,000
21,961,000
14.5
13,684,000
35,645,000
2,458,000
67,000
36.70
$ 1,117,000
669,000
1,509,000
9,682,000
7,538,000
1,154,000
428,000
546,000
22,643,000
14.5
14,109,000
36,752,000
2,535,000
203,000
12.50
$ 1,250.QOO
669,000
1,539,000
9,795,000
7,558,000
1,154,000
434,000
582,000
22,981,000
14.5
14,319,000
37,300,000
2,572,000
270,000
9.50
302
-------
TABLE 96. SUMMARY COST CENTER DISTRIBUTIONS
U)
u>
Title
descriptions
#2 Extra work
#3 Design and
studies
#4 S^te
#5 Inspection
#6 Structures and
improvements :
original contract
supplemental agreement
other costs
07 Utilities
#8 Furniture and
equipment
#9 General
Additional equipment
Total
Size Storage and
Receiving reduction recovery
•~
—
—
$1,339,006 $1,230,067 $1,122,649
13,756 296,431 92,614
—
—
—
—
2,605 5,547
1,355,367 1,532,045 1,215,263
Thermal
processing
—
—
—
$4,400,025
2,628,861
—
—
—
—
2,606
7,031,492
Energy
recovery
$ 127,645
—
2,840
—
3,083,785
330,542
—
—
—
—
— -
3,544,812
Residue
separation
—
—
—
$857,626
24,400
—
—
—
—
17,941
899,967
General
plant
$ 675,794
18,165
511,111
—
2,708,842
417,781
46,017
27,898
--
—
232,822
4,638,430
Other
costs*
$ 41,497
63,081
5,345
—
—
55,064
21,611
3,199
48,461
76,782
315,040
Total
$ 803,439
59,662
577,032
5,345
14,742,000
3,804,385t
101,081
49,509
3,199
48,461
338,303
20,532,416
* Not researched or identified.
t This sum includes $404,593 of unbilled supplemental agreement costs.
-------
TABLE 97. CAPITAL COSTS PER EPA COST CENTER INCLUDING ADJUSTMENTS*
Cost center
Scenario 1
Scenario 2
Scenario 3
U)
o
Receiving
Size reduction
Storage and recovery
Thermal processing
Energy recovery
Total
$ 2,197,000
2,236,000
1,827,000
10,284,000
5,417,000
21,961,000
$ 2,198,000
2,237,000
1,828,000
11,075,000
5,305,000
22,643,000
$ 2,141,000
2,238,000
1,829,000
11,466,000
5,307,000
22,981,000
Dollar amounts for receiving and energy recovery decrease because of the method of allocation.
The indirect costs (general plant) are allocated based on each remaining cost center's relative
percentage of direct costs. As thermal processing direct costs increase, their subsequent
share of the interest costs increases, resulting in decreased costs for receiving and energy
recovery.
-------
TABLE 98. SUBSYSTEM CAPITAL COSTS
Scenario Waste preparation Energy recovery
1 $6,260,000 $15,701,000
2 6,263,000 16,380,000
3 6,208,000 16,773,000
REVENUES
The City of Baltimore maintains separate accounts for recording revenue
from sales of ferrous metals, non-ferrous metals, and steam produced by the
pyrolysis plant. But because steam is the only product being sold, a complete
economic analysis of revenues could not be performed. Accordingly, the
scenario approach has been followed for projected steam revenues only.
The City of Baltimore entered into a contract with the Baltimore
Gas & Electric Company for the sale of steam generated by the plant. The
contract provided the City with a market for most of the steam produced,
thereby limiting supply and demand problems. The contract provided for a
variable price for the steam based on the fluctuating price of No. 6 crude
oil. With the contract formula, the latest available price for steam
approximates $6.88/1000 kg ($3.13/1000 Ibs) of steam. When this figure is
applied to the individual scenarios, the following annual revenues are
derived:
Scenario: Steam revenue
1 $ 978,432
2 2,176,612
3 3,435,494
The differences in steam revenues are primarily attributed to the
greater number of operating days in scenarios 2 and 3, which cause greater
steam production. The steam revenue from Scenario 3 is much greater than
that of Scenario 2 because Scenario 3 assumes that market demand is strong
throughout the year and that all steam produced can be received by the market.
Steam revenues were then normalized per EPA guidelines. The guidelines
call for using a price of $3.31/1000 kg ($1.50/1000 Ibs) of steam. This
figure results in the following annual revenues for each scenario:
Scenario; Steam revenue
1 $ 470,000
2 1,046,448
3 1,651,680
305
-------
NET OPERATING COSTS
The net operating costs for each scenario were computed by deriving
total costs and revenues. The scenarios' projected and normalized costs were
transferred from the pertinent exhibits yielding total costs. Revenues per
Mg were derived by dividing the revenues under each scenario by annual
throughputs. The net operating costs are presented in Table 99.
In evaluating the net operating cost per Mg, certain factors should be
considered. First, the figures are not indicative of the cost per Mg in-
curred by the City of Baltimore. The City's costs are much less because of
Federal and State project funding. Second, the manner in which costs are
treated does not totally conform with GAAP.
If costs were presented in accordance with GAAP, the cost on a per-Mg
basis would be less because only depreciable assets would be included in the
accumulation of .net operating costs. Land and site preparation costs would
not be recognized as contributing to the net operating cost. Although other
Accounting Format variations from GAAP occur, they do not significantly
affect the net operating cost.
TABLE 9-9. PROJECTED COST SUMMARY*
Cost
category
Capital costs
Interest
Operating and
maintenance costs
Total costs
Revenues
Net cost
Scenario It
($/Mg)
$22.60
14.10
42.00
78.70
14.60
64.10
($/ton)
$20.50
12.80
38.10
71.40
13.20
58.20
Scenario 2§
($/Mg)
$ 7.70
4.80
14.60
27.10
10.70
16.40
($/ton)
$ 7.00
4.30
13.30
24.60
9.70
14.90
Scenario 31F
($/Mg)
$ 5.90
3.60
11.00
20.50
12.70
7.80
($/ton)
$ 5.30
3.30
10.00
18.60
11.50
7.10
* In 1977 dollars.
t Annual throughput is 67,000 Mg/year (74,000 tons/year).
§ Annual throughput is 203,000 Mg/year (223,000 tons/year).
1F Annual throughput is 207,000 Mg/year (300,000 tons/year).
306
-------
SECTION 6
ADMINISTRATIVE ASSESSMENT
INTRODUCTION
Nontechnical problems were encountered in the Baltimore Landgard®
demonstration as a result of the project's overall administrative structure.
This structure involved several diverse groups: (1) the Federal government,
(2) the State government, (3) the City of Baltimore municipal government, and
(4) the industrial designer of the facility, Monsanto EnviroChem. The
complications originated from the number of groups involved, their diverse
internal organizations, and their mode of interaction.
This situation resulted in a highly complex overall organization that
caused time-consuming and confusing decisions. The operating staff was at
times confused about who had authority over the operation and who was
directing their efforts. The confusing and laborious decision making process
had a negative impact on the effectiveness of the operating staff, who needed
to take decisive action in emergency situations that arose during the demon-
stration. The turnover rate in personnel created a lack of continuity and
resulted in redundant actions that increased confusion and delayed the
demonstration.
All parties involved in the project were attempting to achieve their own
goals, which were sometimes at odds.
PARTIES INVOLVED
The four parties involved in the Baltimore Landgard® demonstration
facility were:
1. The Federal government, who provided $6 million in funding for the
demonstration through EPA;
2. The State government, which provided a grant/loan of $4 million to
the City of Baltimore for construction of the facility to be repaid
from revenues derived from selling recovered resources at the
facility;
307
-------
3. The City of Baltimore, who owned and operated the facility; and
4. Monsanto EnviroChem, the system designer who was responsible for the
design, construction, and startup of the facility and who guaranteed
its performance.
The City, Monsanto, and EPA all had an interest in having the facility
in operation as early as possible. The City required a plant that could
reliably process municipal solid waste to replace their Reedberg incinerator
and landfill, which was to be closed in 1974. Monsanto wanted a marketing
tool to establish their credibility in the field of resource recovery from
solid waste. And EPA wanted an operating facility to prove that resource
recovery was a viable alternative to landfill disposal of solid waste. The
wide publicity that the project received further increased the pressure on
everyone to expedite the startup. This need precluded the testing and
experimentation necessary to refine the process equipment and the process
operation to the level required for optimum system operation. The demon-
stration thus failed to show the potential reliability of the Landgard®
pyrolysis process. Rather, it showed the level of operation for the original
design configuration of the process, independent of refinements that should
have been made as experience was gained.
ORGANIZATION OF THE GROUPS INVOLVED
EPA Organization
The Federal involvement in the project was the result of funding made
available to the City of Baltimore from the EPA grant. Five percent of the
Federal grant money was withheld from the project to guarantee compliance of
the City and Monsanto EnviroChem with the terms of the grant.
Monsanto Organization
The Monsanto organizational structure was established to supply technical
and administrative support during the startup of the demonstration facility
and to supervise plant operation through the demonstration period. This
group was supported by technical and administrative groups at the main
offices of Monsanto EnviroChem at their process group center in Chicago,
Illinois. At the beginning of the demonstration, the onsite team consisted
of the project manager, a process control engineer, a design engineer, and
two inexperienced engineers who were also new employees. The instrument/
electrical capability was supplied by a contract instrument technician whose
primary assignment was to perform the initial checkout of the plant instru-
mentation as construction was completed. In addition to supervising the
operation during the startup and demonstration periods, the Monsanto staff
also had the responsibility for training the plant operating staff before
startup. The Monsanto staff was likewise to supply the shift engineering
capability during plant startup.
Because of the degree and number of problems encountered during the
startup period, an expansion of the staff supplied by Monsanto was required.
308
-------
The first addition consisted of an experienced Monsanto plant maintenance and
operating person, and an experienced Monsanto instrument man. As the demon-
stration progressed, it was realized that complete design and construction
capability would be required onsite for the necessary modifications. To
achieve this end, the administration of the project was delegated to a higher
level of management in Monsanto, and an onsite assignment of the supervisor
of project management was made by Monsanto. In addition, the entire process
engineering group located in St. Louis was brought onsite, thus adding three
more process engineers to the field team. Design capability was provided by
assigning the original project engineer, two design engineers, a contract
designer, and the supervisor of the electrical engineering group to the field
site. An office manager and assistant construction superintendent were also
added to the field team. These personnel were added to the field team over a
period of 6 to 12 months after project initiation. Although this increased
staff did much to salvage the project, it would have been advisable to supply
them at an earlier stage of the project.
The relocation of company personnel to a temporary job site remote from
the home offices had a negative effect on the performance of the employees
assigned to the site. This factor is typical of all startup situations and
should be taken into account during the planning stages of the work. The
condition was aggravated during the Baltimore demonstration because of the
indeterminate duration of the assignments. Those employees who were assigned
temporarily to the project created a problem of discontinuity. Because tasks
were not necessarily completed by the person who initiated it, the efficiency
with which assignments were carried out was affected negatively.
City Organization
As shown in Figure 97, the administration of the Baltimore Landgard®
pyrolysis plant falls under the Department of Public Works of the City of
Baltimore. Specific responsibility for the plant is assigned to the
Sanitation Division through the plant manager, who is assigned onsite.
During the demonstration period, however, the Sanitation Division staff
operated in conjunction with an onsite project engineer who reported directly
to the head of the Department of Public Works. This administrative structure
was in effect during the construction and startup phase of the demonstration
facility. The main task of the project engineer was to represent the City in
all decisions made by Monsanto EnviroChem and EPA concerning plant operation.
This project engineer was assigned onsite, and in practice, he superseded the
plant manager in the operational responsibility for the facility.
As further detailed in Figure 97, the plant superintendent reports to
the plant manager and is responsible for the process.operation of the plant.
He is reported to by the chief operators and the labor foreman. The main-
tenance supervisor also reports to the plant manager. The plant mechanics
and instrument/electrician report to him, although they follow the shifts
with the chief and field operators. The major problem encountered- with this
type of organization is that the maintenance and operation functions are
never formally coordinated until the top level of plant management is reached.
309
-------
r
Head of the Dept.
of Public Works
Project
Engineer
I
Sanitation Dept.
Division Head
Incinerator Chief
Plant Manager
Maintenance
Supervisor
Office
Staff
Plant
Superintendent
Instrument/
Electrician
Mechanics
Labor
Foreman
Chief
Operator
Laborers
Equipment
Operators
Field
Operator
Figure 97. City administration structure pertaining to
pyrolysis plant.
310
-------
Such a setup interferes with expedient decision making in that it precludes
certain actions during the shifts because no individual present is responsible
for coordinating maintenance and operation. Delays in decision making and
frustration in plant operators result from this lack of authority.
Another difficulty encountered in the City's organizational structure as
the temporary project engineer who effectively ran the project by bypassing
the normal chain of command. The results were confusion among the City
personnel and lack of committment and involvement on the parts of the plant
manager and the head of the Sanitation Division. These passed-over executives
were in charge of executing the methods of operation, but they had no part in
establishing them. Thus, the plant manager tended to modify methods in-
stituted by the project engineer as soon as the latter was replaced. When
the plant manager and the head of Sanitation were later required to make
decisions, their lack of involvement and experience made it necessary for
them to begin the learning process at an inappropriate stage of plant
operation.
MonsantoTs supply of all engineering support during startup effectively
bypassed another required City function — that of engineering support to
the operating staff. Again, the result was lack of committment and a need
for City engineers to learn lessons that were mastered by Monsanto engineers
earlier in the project. As a result of this structure, the City assigned no
full-time engineer to the plant and developed no laboratory or quality control
capability. This situation continued after the Monsanto personnel had
departed from the job site, leaving the City with minimal experienced en-
gineering^ capability with respect to the operation of the pyrolysis plant. A
consultant hired by the City provided the project's only continuity in
engineering.
Changes in the City staff during the course of the demonstration program
created a lack of continuity in the decision making process. The impact of
this situation was compounded by the existence of a City hiring freeze on all
public works personnel. The project engineer and project manager were thus
not replaced; instead, the plant superintendent was promoted to plant manager,
and one of the chief operators became plant superintendent. Effective
administration of the pyrolysis plant was thus severely hampered by the
inability^ to hire employees with the requisite professional backgrounds. The
hiring freeze also severely limited the maintenance and operating departments
as the normal turnover of employees occurred. Operating and maintenance
personnel who resigned or were transferred were not replaced, thus placing a
greater burden on the already overworked plant staff. This situation can be
directly related to subsequent downtime because of the need to schedule
routine maintenance on Sundays. Because of the reduced personnel, operators
and maintenance staff were required to work overtime to properly staff the
plant.
City procurement and accounting procedures also created impediments to
the project. The Baltimore procurement procedure (Figure 98) was a typical
municipal design for coping with routine, fixed-budget projects; it did not
employ the emergency procedures required in process plants. The Baltimore
Landgard® facility is a moderately complex industrial process, and downtime
311
-------
INFORMAL BID fc2,000-$5,000
SEN 1 hVhHY 2 WEEKS "*
TO VENDORS
1 t BID 1
2 OR MORE VENDORS
SUBMIT BIDS
PYROLYSIS PLANT
SUBMITS
REQUISITION
i
BUYER REVIEWS
AND CATAGORIZES
< $2,000
PURCHASE ORDER
WRITTEN AND
MAILED
t*
^
POSTED AND
ADVERTISED
BUYER PREPARES
BID PACKAGE
It t
PURCHASE ORDER
WRITTEN AND MAILED
TO LOWEST BIDDER
VENDOR REQUESTS
BID PACKAGE
BOARD QUESTIONS
BUYER
(1 WEEK DELAY)
jf REJECTION
BID PACKAGE IS
SENT TO VENDORS
*
VENDORS
SUBMIT BID
t
BUYER REVIEWS
AND MAKES FORMAL
RECOMMENDATION
*
BOARD OF ESTIMATES
CONSIDERS BID
BID OK
FORMAL LETTER OF
ACCEPTANCE IS SENT
TO PUSCHASING
1
PURCHASE ORDER IS
WRITTEN TO
ACCEPTABLE VENDOR
Figure 98. Original Procurement Procedure for the City of Baltimore
312
-------
is indeed costly. But the Baltimore procurement procedures took an average
of 4 weeks for requests over $2000. In an emergency, the most expedient
procurement required at least 2 weeks to execute. The problem was aggravated
by the fact that most purchases exceed $2000 for this size industrial facility.
Because of the unworkable nature of this procedure, the City modified it
after the demonstration period.
The accounting control techniques used by Baltimore and many other
cities are also not conducive to the most efficient operation of solid waste
resource recovery facilities. Since municipal operating departments seldom
involve revenues, the budgetary systems do not directly account for any
system operating income. System operations efficiency is thus difficult to
measure, as is the relative attractiveness of alternate methods of disposal.
Among the economic penalties resulting from downtime at the Baltimore plant
were lost revenues of approximately $12,000 per day. But because there was
no method in the City accounting system to relate this cost directly to plant
operation, the City administration was unaware of the magnitude of this
penalty.
The lesson to be learned is that planners and engineers must be aware
of administrative requirements for the operation of resource recovery
facilities. This knowledge must then be used to determine the feasibility of
municipal operation and the need to modify the existing administrative
systems.
OVERALL EFFECTS OF ORGANIZATION
While aff agencies involved, worked toward the successful performance
of the denpmstation, their particular interests, responsibilities, and
orientat-iQH differed widely. Any decision-making had to be approved in a
varying;$hain relationship by the City of Baltimore, Monsanto, and EPA.
Consequently, their varying interests and perspectives caused delays,
especially in the plant shutdown periods, and hampered plant operation and
administrative functions.
The need for Monsanto to maintain technical credibility with both the
City and &PA potentially interfered with effective decision making because of
Monsanto*1Tnecessarily defensive posture regarding plant designs. In addition,
the city*scneed for a reliable facility minimized the fact that the Landgard®
facility was a demonstration project, and a prototype that required extensive
testing and refinement. The City's position in all decisions was aimed at
making the process operational in the near-term. Thus, it was unlikely that
the process ever operated anywhere near optimum levels of performance during
the demonstration.
CONCLUSIONS
In future implementations of resource recovery facilities, all parties
involved should clearly delineate their goals and needs relating to the
project. These goals must be compatible with those of the others involved in
the endeavor. The nature of the project and the mode of execution must be
313
-------
carefully reviewed and planned so that the needs of all parties are adequately
met. The structual organization of each entity involved must also be examined
with a view to their functions in the project.
The arrangement whereby the City of Baltimore provided an operating
staff to aid Monsanto in the checkout and startup of the facility proved to
be overly complicated. Many of the difficulties encountered could have been
avoided had the system designer carried the project through the acceptance
testing stage without the active involvement of the client (the City of
Baltimore). If the project agreement had been made incorporating this strategy
at the beginning of the project, a more efficient execution could have been
achieved. A conscious attempt to minimize the number of groups involved in
the decision making process and to place the responsibility and authority for
acceptable performance on one entity would have improved the probability of
success.
A city that considers owning and operating a resource recovery facility
should review its applicable administrative structures to determine their
compatibility with the efficient operation of such a facility. Adequate
contingencies should be allowed for extensive changes in manpower and oper-
ating budgets for first-of-a-kind units put in service. For the Baltimore
facility, three to four times the originally estimated number of startup
personnel were required, and the period needed for the demonstration was
twice as long as originally estimated. The extensive modifications that were
necessary nearly doubled the originally estimated cost of the facility.
314
-------
SECTION 7
FUTURE PLANT
The demonstration facility at Baltimore has been evolving during the
entire evaluation period, and the City of Baltimore is continuing this process
to improve plant performance. As system reliability is improved, the concept
is anticipated to become economically attractive. A likely configuration of
a second generation process based on the experience gained at the Baltimore
installation will be discussed in this section to show the level of com-
plexity and investment required for a facility patterned after the Baltimore
concept.
ONGOING AND PROPOSED MODIFICATIONS
The City of Baltimore is continuing to modify the pyrolysis facility to
increase process reliability and to simplify operation and maintenance.
Design and construction efforts involved in these modifications are being
accomplished through joint funding from the City of Baltimore and the Federal
government through monies made available by an Economic Development Admini-
stration Public Works Grant. The goals of these modifications are threefold:
(1) to bring the stack emissions into compliance with State regulations,
(2) to resolve those problems that have caused extensive plant downtime
during the demonstration period, and (3) to simplify the overall process and
thus reduce the potential for additional operational difficulties. Four
major areas are being modified to accomplish these goals. First is the
replacement of the entire gas scrubbing system with electrostatic precipi-
tators. Second, the gas purifier is being redesigned from a slagging to a
nonslagging operation. Finally, the storage and recovery unit and the residue
separation module (which have not been operated by the City during the final
stages of the demonstration) will be eliminated from the process (Figure 99).
The ensuing discussions will consider the motivation for the present
modifications, a plant description of the work being performed, the advantages
and disadvantages associated with each specific modification, and a hypo-
thetical future-plant design.
Replace Gas Scrubbing System With Electrostatic Precipitators
The inability of the existing wet scrubber to control particulate
emissions has required the replacement of the unit with electrostatic pre-
cipitators. A portable electrostatic precipitator has been tested on a
portion of the boiler discharge gas stream at the plant and was found to
perform acceptably.
315
-------
o\
Tfl^^w^Tr
RESIDUE
TIPPING
FLOOR
STOR-
AGE
PIT
^3o
RAMj«i1
GASES • SOLIDS
— KILN ••
BURNERS
COMBUSTION AIR
INDUCED DRAFT
FANS
AIR
I I BURNER
ELECTROSTATIC
PRECIPITATORS
REFUSE
Figure 99. Proposed future plant look.
-------
Electrostatic precipitators have been applied extensively for the
control of emissions from incinerators, and they are well proven in this
application. The basic modification will involve removal of the wet gas
scrubber and replacement with two parallel electrostatic precipitators.
Because of corrosive components in the stack gas, it will be necessary to
maintain a higher inlet temperature to the electrostatic precipitators than
was the case with the wet scrubber, which neutralized any condensed acids.
This higher temperature will be accomplished by removing the existing
economizers. The present wet-gas induced draft fan will be replaced by two
dry fans installed in parallel to provide redundancy. The dehumidifier
system will be replaced by a tall stack to provide elevated discharge of the
process gases. All of the auxiliaries associated with the scrubber; pumps,
clarifier, etc. will also be removed.
To minimize the maintenance and operating requirement placed on the
City's staff by installation of the electrostatic precipitator, the City has
contracted with the equipment vendor for maintenance. This step should
further improve the reliability of this section of the plant.
The primary advantage associated with the electrostatic precipitators is
compliance with emissions regulations. The modification will eliminate the
vapor plume accompanying the stack emission and the need for liquid and
sludge handling equipment in the air pollution control area. A major cost
saving will be realized through the elimination of the large caustic con-
sumption associated with wet scrubber operation (the single largest operating
expense associated with the plant). The dry system will eliminate the
extensive downtime experienced because of problems with the wet-gas fan, and
the corrosion and freezing problems in the wet-gas handling system.
The disadvantages associated with this modification include reduced
boiler efficiency and increased power consumption because of the large
electrical demand of the electrostatic precipitator. Both of these factors
will have a deleterious effect on overall plant efficiency. Elimination of
the wet scrubber system will also result in increased level of acid vapors
and low chain hydrocarbons in the stack gas. The benefits of having a con-
tracted maintenance agreement may be offset by the City's dependency on an
external source for their maintenance requirements. Downtime could increase
if the vendor does not respond promptly.
Gas Purifier Modification
The extensive downtime experienced as a result of slag tap-hole plugging
during the demonstration has resulted in a new design for the gas purifier to
transform it from a slagging to a nonslagging configuration. The existing
operation of the vessel involves excessively high operating temperatures to
maintain the slag material in a molten state so that it can flow to the slag
tap-hole to be removed. These high operating temperatures have contributed
to major refractory problems in the lining of the vessel.
The gas purifier modifications are designed to keep process temperatures
in the vessel below the slag fusion temperature, thereby permitting operating
of the vessel in the nonslagging mode. To accomplish this objective, the gas
317
-------
purifier will be relocated farther from the kiln to allow dissipation of
sensible heat in the kiln off-gas. Heat dissipation will be accomplished
through the increased heat transfer surface area of the ductwork between
the kiln and the gas purifier. This reduction in the sensible heat of the
off-gas will in turn contribute to a reduction in the process temperature in
the gas purifier. An increase in the volume of the gas purifier and in the
amount of excess combustion air supplied to the gas purifier will further
reduce the reaction temperature in the vessel. This change is a direct
extension of existing incinerator knowledge.
Equipment changes necessitated by the change from a slagging to a
nonslagging operation will involve (1) replacement of the existing slag tap-
hole and slag handling system with ash hoppers in the bottom of the reactor
vessel, and (2) installation of a drag conveyor fly ash handling system.
These changes should eliminate the need for the quench air inlets at the
discharge of the gas purifier, since the temperature of the gases at this
point will be compatible with the process temperature requirement at the
boiler inlet.
The claimed advantage of this modification will be the elimination of '
refractory and thermocouple failures in the gas purifier resulting from the
high operating temperatures and slag attack. This modification should greatly
reduce downtime associated with gas purifier operation and accompanying
maintenance costs. Downtime related to slag tap-hole plugging and slag
handling equipment failures should also be eliminated with this modification.
Furthermore, operation of the gas purifier at high excess air levels should
simplify the control characteristics of the vessel. This modification will
provide a safer work environment because of the lower design skin temperature.
The major disadvantage of this modification will be the decrease of
thermal efficiency as a result of the increased heat losses designed into the
equipment. Downtime may occur as the result of process upsets that cause
elevated temperatures and subsequent formation of molten slag. When cooled,
the slag will jam the fly ash handling equipment. The probability for such
an eventuality is minor, but it should be considered in the design and
operation of this equipment.
Elimination of the Storage and Recovery Unit
Because the storage and recovery unit failed to operate satisfactorily,
the City has decided to eliminate it from the process stream. The primary
problem in the unit has been the inability of the system to retrieve the
material from the storage vessel at low storage volumes. To counter this
difficulty and provide the required feed rate to the thermal processing area,
the system must be operated at high speeds, a situation that results in
drastically accelerated wear of the equipment. The floor of the storage silo
is presently worn out after 6 months of operating time. The vendor has
suggested several designs to remedy the problem at costs ranging from
$250,000 to $700,000. The hesitancy of the vendor to guarantee the modifi-
cations has made the City decide that the risk is too great to justify the
investment.
318
-------
The equipment changes required to implement this modification involve
utilization of the existing bypass system installed in the transfer tower. A
belt scale had to be installed on the elevating conveyor before the bypass
chute to measure the flow of waste to the thermal processing area. While the
system is being operated in this mode, it will be necessary to operate only
one shredder at a time to avoid overloading the kiln feed system. In this
mode, the only control that the operators have over the feed rate to the
thermal processing area is through the variable-speed conveyors that feed
each shredder.
The advantages in replacing the storage and recovery unit are that a
high-maintenance piece of equipment is eliminated, system energy consumption
is reduced, and that operation of several pieces of equipment is eliminated
thereby simplifying the overall process operation.
The disadvantages involved in implementing this modification are a
reduced ability to control the input rate to the thermal processing area,
limited throughput rate of 27 Mg per hour (30 tons per hour) vs. design of
38 Mg per hour (42 tons per hours), and the elimination of surge capacity
after the shredders. In the event that the shredders or one of the transfer
conveyors downstream of the shredders fails, the entire process must be shut
down, since no storage capacity exists after the shredders. By locating the
entire storage capacity of the plant in the receiving building, the storage
capability is reduced, and 24-hour operation of the size-reduction module
becomes necessary. Experience has shown a tendency for shredded waste to jam
in the bypass ductwork, and some downtime is anticipated as a result of this
condition during future operation of the system in the bypass mode. Modifi-
cations to the bypass ductwork would reduce the problem, but the City has no
intention of making them at this time. Another negative aspect of eliminating
the storage and recovery unit is that the automatic process control system is
bypassed because the main sensing device in the control loop is installed as
part of the storage and recovery system. There are no present plans for the
City to replace or relocate this equipment.
Elimination of the Residue Separation Module
Elimination of the residue separation module involves replacement of
all separation equipment in the existing area with a simple transfer station
that will direct the flow of pyrolysis residue to dump trucks for subsequent
landfill disposal. The primary reason for eliminating this processing area
is the inability of the installed equipment to perform satisfactorily in the
existing configuration.
This modification would involve installation of a dump chute and hopper,
removal of building panels, and a change in the structural steel in the
building. The area would need to be paved to allow trucks access to the
dumping area. A relocation of the motor controls presently installed in the
materials recovery building will be required, but most of these controls are
involved in the residue separation equipment presently installed, and thus
would be eliminated.
319
-------
Advantages of eliminating the materials recovery process are reductions
in labor, materials, and power necessary for plant operation. This modifi-
cation also alleviates the need for further investment in modifications to
the area. The existing method of loading residue trucks will be improved
with the process occurring in an enclosed, paved area. This mode of operation
will also allow for a wider variation in residue product quality than possible
when the residue is separated, since separation equipment requires strict
quality control of the product material to accomplish efficient separation.
Finally, a major improvement achieved by eliminating the residue separation
module is a simplification of the process.
The disadvantage of eliminating the materials recovery area is the loss
of a revenue source that has growth potential as market conditions change in
the future. This modification also increases the quantity of material to be
disposed of, thereby increasing the disposal cost of this residue. The
operating cost for this area will not be significantly reduced because of the
necessity for operating 24-hour transportation of the residue to the ultimate
disposal site. The increased, moisture content of the transported material
has resulted in spillage along public roadways between the plant and the
disposal facility. This problem has already been the source of some com-
plaints by residents along that route.
SECOND GENERATION FACILITY
The next generation resource recovery facility based on the rotary kiln
concept will have a substantially different configuration than the Baltimore
plant. This section considers possible configurations that the system might
assume, based on the present state-of-the-art. An infinite number of
alternate schemes could be suggested based on recent experience in the field
of resource recovery from solid waste. The suggestions here, however, are
primarily the result of specific experience gained in Baltimore.
Areas that performed acceptably and that are economically competitive
with functionally similar processes are as follows:
1. Receiving area
2. Size reduction
3. Primary thermal processing area (rotary kiln)
4. Heat recovery area
Areas that failed to perform effectively in the existing configuration
on either an economic or technical basis are:
1. Storage and recovery unit
2. Secondary thermal processing area (gas purifier)
3. Emissions control system
4. Residue separation module '
For purposes of this discussion, it will be assumed that those areas
operating acceptably will be retained in the second generation plant design.
But, there are potential improvements that can be made to increase the
operating efficiency of these units. Assuming that storage after the shredder
320
-------
is not necessary, the shredders should be resized to match the capacity of
the thermal processing area to maximize waste throughput. This assumption is
reasonable in view of operating experience that has shown the kiln feeders
to provide sufficient surge capacity to accomodate variations in material
feed rate from the shredders. The existing configuration limits thermal
processing area throughput because of shredding rate limitations. In
addition, parallel transfer conveyors from each shredder to the thermal
processing area should be installed. This provides the redundancy required
to insure maximum equipment availability.
An alternate size reduction system based on lower-cost equipment such as
flail mill may prove attractive. Without the storage and recovery system in
the process line, refuse particule size control becomes less critical, and
other candidates for this function become attractive.
Another possibility is the installation of a primary trommel ahead of
the size reduction units. The large-diameter trommel used at Recovery I in
New Orleans has been demonstrated to increase the efficiency of shredder
operation and appears to be particularly attractive as a possible addition to
the Landgard® process. This unit removes a large percentage of the glass
present in the waste stream before shredding. The effect of this configur-
ation has been to increase material throughput and reduce wear on the shredder
units. An accompanying benefit is the reduction in the ash and glass con-
tained in the fuel product. This reduction would lessen the tendency for
slag formation in the thermal processing area and reduce the quantity of ash
and residue to be handled in the process equipment. Problems have been
encountered, however, in removing floating ash from the residue quench tank
when magnetics were removed ahead of thermal processing (see kiln experience).
If a trommel were employed, a mechanism would need to be developed to assist
in removing the floating ash from the residue quench tank. The nominal cost
and substantial benefits that could be realized with this piece of equipment
make it an attractive component for use in the Landgard® process. This
approach would allow material separation before thermal processing and would
minimize the number of times material has to be handled during processing.
Alternatively, a trommel could be used in place of the shredders to
remove the cans and glass from the process stream and thereby achieve the
benefits noted above. Observations of the size characteristics of the
Baltimore waste indicate that the larger particles are in the burnable
category and could be fed directly to the process kiln.
Although the kiln has been made to operate acceptably, there are several
improvements that should enhance process control of this vessel. These
changes would involved locating process monitoring and control equipment at
the midpoint of the kiln. By installing air inlets at various points along
the kiln (by mounting fans on the kiln shell) the reaction occurring in the
kiln can be more precisely controlled than is the case when attempting to
accomplish this entirely from the discharge end of the vessel. Gas compo-
sition and temperature monitoring probes would also need to be mounted along
the kiln to utilize effectively the improved control equipment. This equip-
ment is all state-of-the-art in industries using process kilns, and it should
prove reliable when adapted to this application.
321
-------
Preliminary studies performed with the kiln model developed by Systech
indicate that the geometry of the processing kiln in Baltimore is not the
optimum for effective processing. Further theoretical work is required to
refine the optimal kiln proportions for processing municipal solid waste at
specific feed rates.
An alternative to the proposed modification of the gas purifier would be
to employ a waterwall concept to cool the gas stream rather than to discharge
the heat into the atmosphere. A waterwall-type vessel contains water tubes
either on or embedded in the internal surface of the vessel walls. Water
flows through these tubes and is warmed by the heat evolved from the process.
The configuration of this type of vessel is similar to that of a boiler. The
heat transferred in this system would be used to preheat the boiler feedwater
and would thereby be recovered. The waterwall tubes would be covered with a
layer of refractory to protect them from heat damage or slag attack on the
inner surface of the vessel. By operating the gas purifier at a high excess
air level and by using a waterwall vessel, the process could be operated in a
nonslagging mode without the substantial loss of efficiency that would occur
in the proposed modifications.
Because the Landgard® system has been determined to be a technically
feasible system for the disposal of municipal solid waste, further investi-
gations of this system are warranted. The low reliability of the existing
system precludes its economic viability and must be overcome before further
system development. The configuration existing .at the Baltimore facility is
not believed to be optimal, and the development of new process components are
recommended. Although the modifications being executed by the City of
Baltimore are having a negative effect on process efficiency, the aim of
simplifying the process is the key to commercial development. Any further
development of the system should be in the direction of simplification and
reduction of capital and operating costs. As new components are demonstrated
in the application of resource recovery from municipal solid waste, they
should be considered in conjunction with the Baltimore processing concept.
ya 1712b
SW-175C.2
-* U.S. GOVERNMENT PRINTING OFFICE: 1979-281 147:80
322
------- |