United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-85/031 May 1985
Project Summary
'/ I '
Co-Firing of Solid Wastes and
Coal at Ames: Pulverized Coal
A. W. Joensen, J. L. Hall, J. C. Even, D. Van Meter,
P. Gheresus, G. Severns, S. K. Adams, and R. W. White
The objectives of this research were
to conduct an in-depth evaluation of
the environmental, economic, and
technical aspects of the resource and
energy recovery system in Ames,
Iowa. The system includes recovery of
ferrous metals, preparation, storage,
and cofiring of the refuse-derived fuel
(RDF) with coal in the power plant
owned by the City of Ames to pro-
duce electric power.
The evaluation period was three
years, and this report covers the third
year of research. It includes evalua-
tions of the refuse processing plant
operation, economics of the total
system and individual subsystems,
flow stream characterization, and per-
formance and environmental emis-
sions of the suspension-fired steam
generator. Data acquired during the
first year's evaluation were previously
reported in "Evaluation of the Ames
Solid Waste Recovery System. Part I-
Summary of Environmental Emissions:
Equipment, Facilities, and Economic
Evaluations" (EPA-600/2-77-205).
This Project Summary was devel-
oped by EPA's Hazardous Waste
Engineering Research Laboratory, Cin-
cinnati, OH, to announce key findings
of the research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
The Ames solid waste recovery system
is a continuously operating system that
processes municipal solid waste (MSW)
to produce a shredded RDF that is burned
with Iowa-Western coal mixtures in the
tangentially fired steam generator in the
Ames municipal power plant. This system
consists of a nominal 136-Mg/day
(150-ton/day) process plant, a 454-Mg
(500 ton) Atlas storage bin, pneumatic
transport systems, and the power plant
boiler. The process plant incorporates two
stages of shredding, ferrous metal recov-
ery, and an air classification (density)
separator.
The full report presents results and con-
clusions of the third-year effort of an
evaluation of the Ames solid waste recov-
ery system, including the process plant
studies and boiler environmental and ther-
mal performance characterizations. The
detailed study objectives are listed in the
following section.
This evaluation is a major research pro-
gram funded by the Environmental Pro-
tection Agency (EPA) and the Department
of Energy (DOE). Project tasks are being
performed jointly by the City of Ames,
Iowa, the Engineering Research Institute
(ERI) of Iowa State University, the Ames
Laboratory/DOE, and MRI. The EPA
funding was used to provide for all man-
power, major field equipment purchases,
power plant and process plant modifica-
tions, laboratory analyses of process plant
stream characterization, and other sup-
plies used in the evaluation of both the
power plant and process plant. The DOE
funding was used to provide laboratory
analysis of all field samples procured from
the power plant testing. Additional finan-
cial support was provided by ERI, the City
of Ames, and the American Public Power
Association.
System Description
The Ames solid waste recovery system
consists of three major subsystems: the
process plant, the Atlas storage bin, and
the existing steam generators of the mu-
nicipal power plant which were modified
-------
to burn RDF. A general flow diagram is
shown in Figure 1. The MSW enters the
45.4 Mg/h process line where primary
shredding, ferrous removal, and second
stage shredding occurs. The RDF pro-
duced from the air density separator
(ADS) is transported 152.4 m to the
454-Mg Atlas storage bin through a 36 cm
diameter pneumatic transport line. Rejects
are subjected to further ferrous removal
and are then trucked to the municipal
landfill.
The RDF is reclaimed from the storage
bin by four bucket sweeps which drop the
material into two infeed conveyors for the
pneumatic transport 61 m to the power
plant through two, 20 cm diameter pipes.
The RDF is injected into the two opposite
corner burners of the 35-MW tangentially
fired steam generator. The RDF is burned
as a supplemental fuel along with the
Iowa-Western coal mixture in suspension,
and RDF dropout material is burned on a
bottom hopper dump grate installed in
1978.
The tangentially fired boiler (No. 7) is a
Combustion Engineering Company, Type
VU-40S steam generator using balanced
draft operation with a Ljungstrom regen-
erative air heater and an ESP but no
economizer. The two-drum unit operates
at 5,860.8 kPa and 485°C steam quality
and 163,296 kg/h of steam flow.
Combustion air is drawn from the upper
part of the building, passed through the
forced draft fan through the air heater,
and enters the furnace through the corner
burner assemblies via two main wind-
boxes. Flue gases produced by the fuel
combustion in the furnace pass over the
primary and secondary superheater tube
banks through the convection bank, the
air heater, and then through the
American-Standard ESP and the induced
draft fan (both located outside the
building). The flue gases are discharged
out the 61-m chimney or stack. Boiler
pump discharge feed water is used for
superheated steam temperature control,
and this spray water is injected between
the primary and secondary superheater
sections.
Process Plant Paniculate
Emissions and Dust Evaluation
Particulate emissions from the roof ven-
tilators of the refuse plant were evaluated
by EPA Method 5 particulate sampling
techniques. Extensions were added to
each of the roof ventilators on the refuse
plant to facilitate the samplng. Twenty-
four sampling locations on each of two
perpendicular traverses across the
diameter of the roof ventilator ducts were
used, for a total of 48 sample points. At
each sample point, the sampling train was
operated for 3 min, meaning that a total
sample was collected over 144 min of
operation. The amount of particulate col-
lected was then determined on both a
volume and a time basis. The results are
reported later in this summary under
Power Plant Emission Characterization.
In addition to sampling emissions from
the roof ventilators, high volume ambient
air samplers were placed in the plant to
determine the dust concentration at
specific locations.
The ambient air in the refuse processing
plant was sampled at three general eleva-
tions in the plant by means of high vol-
ume samplers modified to contain 10 cm
(4 in.) diameter quartz fiber filters on
which the particulate matter collected as
the sample train operated. Each sample
train was operated for 15 min. The weight
of sample was then determined for the
time span of the test and recorded for
each location in the plant.
The three levels sampled in the plant in-
cluded the floor level in the general vicini-
ty of the first and second stage shredders
Municipal
Solid Waste
Shredder
Ferrous -*-
Non-Ferrous Separation
Rejects <-
Non-Ferrous -<-
Aluminum -^
Heavy Rejects
Air Density Separation
(Air Classification)
Air
Combustible
Refuse Derived Fuel
Ames Municipal Power Plant
Stoker Fired Boiler - 7.5 MW
Stoker Fired Boiler - 12.5MW
Pulverized Coal Fired Boiler - 35 MW
RDF
Iowa and Colorado Coal
Figure 1. Flow diagram of the Ames solid waste recovery system.
2
-------
and below the air density separator
(ADS). The mid-level location sampling
was adjacent to the ADS and underneath
the bucket elevator in the processing
plant. Upper level samples were taken at
a walkway in the plant and at the top of
the bucket elevator.
Following the weighing of the samples,
several representative filters were analyzed
to ascertain the typical elements present
in the dust and the amounts. The amount
of dust in the ambient air of the process-
ing plant and the results of the trace ele-
ment analysis are also presented under
Power Plant Emission Characterization.
Power Plant
In this study, it was determined that
two major factors could be controlled at
various levels. These factors were the
steam generator load, based either on
steam flow generated or megawatts of
power generated, and the amount of
RDF, based on heat energy input to the
boiler. The levels chosen were 60, 80, or
100% nominal steam generator load, and
0, 10, or 20% RDF. To obtain sufficient
data for statistical analysis, a factorial ex-
perimental design with three replications
was devised for the steam generators, as
summarized in Table 1. The statistical
design was a 3 by 3 (three loads, three
values of EOF, and three replications) full
factorial experiment with 27 runs. To as-
certain compliance with Iowa's Envi-
ronmental Quality rules, additional mis-
cellaneous testing was done. During these
tests, the location of the RDF injection
point was changed.
To satisfy the objectives of the en-
vironmental emission study, all ap-
propriate input and output streams
associated with the operation of the
steam generator unit were sampled. A
block diagram showing the sample loca-
tions of entering and leaving streams is in-
cluded as Figure 2. The tests on unit No.
7 are summarized in Table 1. All inputs to
and outputs from the steam generator
were evaluated, including fuel, combus-
tion air, bottom ash, steam, fly ash, and
stack gas. All the sampling was con-
ducted on a regular basis except the
organic species, which were sampled on
intermittent days as manpower, instru-
mentation, and equipment would allow.
Economic Evaluation
For 1976, 1977, and 1978, total annual
expenses remained relatively constant in
that the decreasing principal and interest
were approximately balanced by the in-
Table 1. Test Matrix for Unit No. 7 Experimental Runs
Percent """»» nur
Load
60%
80%
100%
80%
(Wyoming coal)
100%
(Wyoming coal)
100%
(Wyoming coal)
0%
3 runs
(1976)
3 runs
(1976)
3 runs
(1976)
3 runs
(1978)
3 runs
(1978)
10%
2 test runs
(1977)
-
3 runs
(1978)
3 runs
(1978)
20%
-
-
3 runs
(1978)
3 runs
(1978)
Compliance resfs8
4 runs
(1978)
"RDF injection nozzles relocated to below the coal injection nozzle.
creasing operating and maintenance
costs.
Table 2 shows the relative percentages
of operating and maintenance costs al-
located to salaries, contractual expense,
commodities, and principal and interest.
Contractual expenses were higher than
salaries during all three years. Principal
and interest accounted for nearly half of
the operating and maintenance costs.
Total operating cost per megagram aver-
aged $27.82 in 1976 and $23.87 in 1977.
Net cost per megagram averaged $12.47
in 1978, compared with $15.73 in 1976
and $12.61 in 1977. These data are sum-
marized in Table 3.
Process Plant Emission
Characterization
The paniculate effluent from the ven-
tilator ducts on the refuse plant and the
particulate in the ambient air of the pro-
cess plant were sampled by appropriate
methods.
Table 4 summarizes the particulate
emissions from the three roof ventilators
in operation during this study. Over the
144-min sampling period, the sampling
train filters collected particulate effluent in
the amounts shown. It should be noted
that the emission levels were very low
and, in fact, were virtually invisible to
observers.
Power Plant Emission
Characterization
The average of heating values, ultimate
analysis, and trace elements analysis for
both coal and RDF used during the tests
on unit No. 7 are as follows: The ash con-
tent of the RDF was higher than that of
the coal used during 1978, and both the
heating values and the amount of sulfur in
the RDF were lower than that of the coal
for the comparison runs made during this
study. The significance of these observa-
tions is that as the amount of refuse used
in the boiler unit is increased an increased
amount of ash will be generated due to
the use of refuse. The additional amount
of ash was expected to show up partially
as fly ash and partially as bottom ash.
Consequently, as the RDF increased, the
amount of particulate emissions was ex-
pected to increase. This was also in
agreement with the previous data ob-
tained on traveling grate stoker unit Nos.
5 and 6 during 1976 and 1977 studies on
the traveling grate units.
Because the sulfur content in the RDF
was lower than that in the coal, it was
also expected that the oxides and sulfur
emitted from the smokestack would de-
crease significantly with increases in RDF.
Based on the tabulation of trace ele-
ments from the fuel samples, the RDF
contained significantly more copper, lead,
titanium, and zinc than coal used as a
fuel. As a consequence, the emissions of
these four elements were expected to in-
crease significantly. The most important
of the three elements would be the lead
because of its toxicity. Therefore, some
additional ambient air sampling was per-
formed on a random basis during the 1978
experiments. Germanium, iron, and sulfur ,
were found in smaller concentrations in
the RDF than in the coal, but there did
-------
Flow Rate
Ultimate Analysis
Heating Value
Chemical A nalysis
& Trace Elements
Ash Softening Temperature
Filter Particulate
Trace Elements
Impinger Water Trace
Elements
Emission Rates of
Particulate
Particulate Trace
Elements
Impinger Water Trace
Elements
Emission Rates of Particulate
and Gaseous Species
Particulate Sizing
Humidity
Barometer
Intake
Temperature
Volume Flow
Density
Ultimate Analysis
Heating Value
Chemical A nalysis
& Trace Elements
Ash Softening
Temperature
Flow Rate
Chemical Analysis &
Trace Elements
Softening Temperature
Flow Rate
Chemical Analysis &
Trace Elements
Softening Temperature
Figure 2. Sampling locations.
Table 2. Solid Waste Plant Operating Expense Distribution, 1976-1978
Operating and maintenance Principal and
Labor Contractual Commodities interest
Year
Total
1976
1977
1978*
Average
13.91
18.91
16.73
29.16
24.40
29.25
53.52
6.50
9.21
9.98
50.43
47.48
44.04
46.48
100
100
100
100
"January to September data only.
Tabl«3. Total Operating Expenses and Revenues for the Ames Solid Waste Recovery
Processing Plant, 1976-1978
Year
1976
1977
1978"
Total
operating
expense
($)
1,033, 186
1,047,734
784,740
Total
revenue
1$)
448,721
494,309
411,190
Total
net
cost
1$)
584,465
553,425
373,550
Refuse
processed
IMg)
37, 137
43.890
29.958
Total
cost/Mg
t$/Mg)
27.82
23.87
26.19
Net
cost/Mg
l$/Mgl
15.73
12.61
12.77
'January through September only.
not appear to be a significant difference
between RDF and coal in the relative
amounts of the other elements.
The uncontrolled emissons generally in-
crease with RDF except for the 100%
load data using coal only. Otherwise all
the runs show significant increases in par-
ticulate emissions as the amount of RDF
increases. It is also apparent from this
plot that the initial data obtained using
coal only on this boiler in 1976 and 1977
indicate a reverse trend in terms of par-
ticulate emissions. The expected par-
ticulate would be higher at 100% load
than at 60% load as was the case for the
1978 data. This reversed trend in the 1976
data is believed to be related to difficulties
in operation of the paniculate collector on
unit No. 7 during 1976 and 1977. How-
ever, it should be emphasized that the
scale for the emissions is significantly ex-
panded and that all the emissions with
100% coal as the only fuel are within 2.8
to 3.9 g/MJ of heat energy input.
-------
Table 4. Ames Refuse Processing Plant Paniculate Emissions
Roof ventilator
Roof ventilator
EPA
Run No.
350
351
352
353
32.16
29.77
37.19
23.26
mg/std m3
18.94
36.14
53.80
31.35
20.85
25.27
31.14
9.798
Average standard deviation
Total
71.95
91.18
122.13
64.41
87.42
±25.74
0.516
0.422
0.518
0.343
g/s
0.209
0.453
0.629
0.368
0.449
0.538
0.632
0.201
Total
1.174
1.413
1.779
0.912
1.320
±0.368
The controlled emissions generally in-
creased with increases in RDF. This result
was expected, since the amount of ash in
the RDF was proportionally larger than
that in the coal. For the 100% coal runs
(0% RDF), the decrease in the emissions
at 80 and 100% load for the 1978 data
was a result of the repair of the ESP late
in 1977. Difficulty was experienced with
the ESP during 1976 and 1977. Some of
the plate retainers in the ESP had failed,
which rendered them ineffective during
the test runs in 1976 and 1977. This is one
reason why the emissions for the 60, 80,
and 100% loads in 1976 and 1977 appear
to be significantly higher than the emis-
sions for the corresponding loads in 1978.
Thus, the data obtained in 1978 are much
more representative of the usual perform-
ance of unit No. 7. Furthermore, the data
of 1978 show very consistent trends in the
direction anticipated based on the fuel in-
put analysis.
The effect of RDF on ESP collector effi-
ciency drops consistently with increases in
RDF. These trends were very consistent
for the data obtained in 1978 and showed
the ESP efficiency to be higher at 80%
load than at 100% load. The effect of the
repair between 1977 and 1978 data is also
apparent in this figure. For example, for
the coal-only runs, the collector efficiency
increased from 93.4 to 94.4% at 100%
load and from 94.9 to 96.8% at 80% load,
thus demonstrating the effect the repair
of the ESP had on its performance.
The oxides of sulfur (SOX) emitted from
the boiler decreased significantly with in-
creases in RDF. This decrease amounted
to about 50% for 80 and 100% boiler
loads in going from 0 to 20% RDF. Thus,
an advantage of using RDF with coal is
that relatively high-sulfur coal can be used
and EPA standards can still be met.
The oxides of nitrogen (NOX) generally
decreased with increases in RDF at all
boiler loads. The decrease was in the
range of 10 to 20% and was somewhat
dependent on boiler load as the RDF was
increased up to 20%. The NOX emissions
generally decreased less for the 1978 data
than for the 1976-1977 data. This might
represent better operation of the boilers
and better control of the combustion zone
temperatures for the experimental runs of
1978.
Except for the 100% load, 20% RDF
data point, the chloride emissions for the
suspension-fired boiler increased linearly
and significantly with increases in RDF.
The boiler experienced as much as a ten-
fold increase in chloride emissions as the
RDF increased from 0 to 20% for all boiler
loads in 1978. The chlorides in the stack
emissions are believed to have come from
the chlorinated hydrocarbons in the RDF.
The chlorides dropped in the 1976-1977
data because of the dropout of RDF into
the bottom hopper; the bottom grates
had not yet been installed.
A series of 19 trace elements were
sampled from all input and output streams
associated with the operation of steam
generator unit No. 7. Table 5 lists the
trace elements detected in the input fuels
of coal and RDF used during the test. The
elements selected for analysis are listed by
rank order, and the ranking was deter-
mined by the concentration given in parts
per million (ppm). The standard deviations
are also listed. Another column shows the
amount of the trace element listed on the
basis of mass per unit of energy input to
the boiler. The values listed in Table 5 are
overall averages for both coal and RDF.
The trace elements with higher propor-
tions of concentration in coal than in RDF
are identified in this table as strontium,
beryllium, nickel, and germanium. The
elements that were not detected based on
the detection limit of the analytical in-
strumentation are also indicated. Elements
relatively high in concentration in the RDF
were zinc, lead, copper, manganese,and
vanadium.
Conclusions
The major result of this project is that
RDF can be burned successfully when
combined with coal in both stoker-fired
and suspension-fired boilers to produce
electric power. The net cost per mega-
gram to produce this RDF fuel was $15.73
in 1976, $12.61 in 1977, and $12.47 in
1978. The yearly reduction in these net
costs was due to plant improvements and
increased value of the energy contained in
RDF.
Major improvements which were made
in the Ames solid waste recovery system
Table 5.
Trace Element Content of Coal and RDF Used as Fuel in Boiler Unit No. 7
Coal
RDF
Lever*
Levef
Element
Strontium1'
Vanadium
Manganese
Zinc
Berylliumf
Lead
Tin
Chromium
Nicker*
Copper
Germanium1'
Gallium
Antimony
Selenium
Thallium
Mercury
Arsenic
Cadmium
Cobalt
ppm
86±28
83±16
76±23
66±41
37± 12
36±13
20±5
19±7
18±5
15±3
5.3 ±0.9
2.5±0,5
BDL
BDL
BDL
BDL
BDL
BDL
BDL
ng/J
2.92 ±1.15
2.92± 1. 15
2.92±0.52
2.39± 1.46
1.55±0.49
1.26±0.48
0.71 ±0.17
0.74±0.35
0.63±0.17
0.52±0.08
0.19±0.04
0.09±0.02
BDL
BDL
BDL
BDL
BDL
BDL
BDL
Element
Zinc
Lead
Copper
Manganese
Vanadium
Strontium
Chromium
Tin
Antimony
Gallium
Nickel
Selenium
Cadmium
Germanium
Thallium
Mercury
Arsenic
Beryllium
Cobalt
ppm
763±345
613±289
572±854
194 ±47
154 ±32
46±11
34±8
27 ±8
25±17
16±3
14±4
8±1
6.4±8.1
1.7±0.3
BDL
BDL
BDL
BDL
BDL
ng/J
4.65±2.13
3.89 ±2.27
3.5815.74
1.18±0.33
0.94±0.19
0.28±0.04
0.28±0.04
0.17±0.06
0.15±0.11
0.10 ±0.02
0.09±0.03
0.05±0.01
0.04±0.05
0.01 ±0.00
BDL
BDL
BDL
BDL
BDL
Note: BDL signifies the element is below the analytical instrumentation detection limit.
"Values listed are overall averages for the coal and RDF used during 1978 tests.
''Trace elements with higher proportions in coal than in RDF.
-------
during the three-year comprehensive
study are as follows:
Addition of dump grates to the
35-MW suspension-fired steam gen-
erator
Relocation of RDF fuel input nozzles
on the 35-MW suspension-fired
steam generator to feed RDF below
instead of above the coal nozzles
Addition of a grit removal system at
the processing plant to improve the
quality of the RDF
Addition of a dust control system at
the processing plant to decrease the
occurrence of failure of electric
motors and mechanical equipment,
as well as to improve the worker en-
vironment
Addition of two crew conveyors at
the Atlas storage bin to allow two
pneumatic transport lines to pick up
RDF from all four drag conveyors and
thus reduce the speed of the pull-ring
buckets and the wear on the storage
bin floor
Replacement in 1979 of mechanical
collectors with new ones for emis-
sions control of the two stoker-fired
steam generators to meet environ-
mental regulations and permit cofiring
of RDF and coal in the stoker boilers
The study of boiler performance
showed the necessity to improve the
quality of RDF in order to reduce slagging
and increase boiler performance. A grit
removal system was added in the process-
ing plant which achieved a 24.5% in-
crease in heating value of the RDF, from
11,408.7 to 14,209.1 kJ/kg, and a 54.5%
decrease in ash, from 20.99 to 9.55%.
Additionally, the boiler fouling impact of
RDF was reduced.
The addition of the dump grate was the
most significant change. This facilitated
the successful cofiring of RDF with coal
in the suspension-fired steam generator.
The relocation of the RDF injection nozzle
to a point below the coal injection was
found to be important in its effect on
lowering emissions.
Suspension-fired boiler efficiency
decreased 3.3 percentage points when
operating at 80% steam load with 20%
heat input from RDF and decreased 1.33
percentage points at 100% steam load
with 20% heat input from RDF. This
decrease was attributed to an increase in
moisture loss when RDF is fired. Some
furnace slagging was encountered during
the period prior to installation of the grit
removal system but was reduced after the
quality of the RDF was improved by the
addition of the grit removal system.
Stack paniculate emissions increased
slightly with corresponding increases in
RDF as a fraction of the fuel input and
was due to the presence of lighter RDF
particles and increased mass flow. Stack
particulate emissions decreased after the
RDF injection nozzle was relocated below
the coal burners.
Oxides of nitrogen (NOX) and oxides of
sulfur (SOX) both decreased while
chlorides increased with an increase in
RDF burning. No discernible trends within
the data scatter were noted concerning
formaldehyde or hydrocarbon emissons.
Increased emissions of the trace elements
zinc, copper, lead, and gallium cor-
responded to increases in RDF.
The two stoker-fired boiler units, used
as backup to burn RDF, were modified
with new mechanical collectors in 1979.
These units previously had difficulty
meeting particulate emission standards
while only firing coal. Subsequent tests
conducted on these units by the City of
Ames indicated that coal plus RDF can be
successfully burned and meet particulate
emission standards as a result of this
modification along with the grit removal
system at the process plant.
A. W. Joensen, J. L Hall, J. C. Even, D. Van Meter. S. K. Adams, P. Gheresus, G.
Severns, andR. W. White are with Iowa State University, Ames, IA 50011.
Michael Black is the EPA Project Officer (see below).
The complete report, entitled"Co-Firing of Solid Wastes andCoal at Ames: Pulverized,"
fOrder No. PB 85-183 044/AS; Cost $28.00. subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
&U. S. GOVERNMENT PRINTING OFFICE:1985/559 111/10848
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
OCQC329 PS
U S ENVIR PROTECTION JGENCY
REGION 5 LIBRARY
230 S DEARSCRN STREET
CUCAGO IL £0604
------- |