United States
                     Environmental Protection
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
                     Research and Development
EPA/600/S2-85/114 Dec. 1985
&EHV          Project Summary
                    Co-Firing  of Solid Wastes and
                    Coal  at Ames:  Stoker  Boilers
                    J. L. Hall, A. W. Joensen, D. Van Meter, J. C. Even, W. L. Larsen, S. K. Adams,
                    P. Gheresus, G. Severns, and R. W. White
                      This research program's objectives
                     are to conduct an in-depth evaluation of
                     the environmental, economic, and tech-
                     nical aspects of the resource and energy
                     recovery system located in Ames, Iowa.
                     The  recovery system includes recovery
                     of ferrous and aluminum metals, prepa-
                     ration of the refuse-derived fuel (RDF),
                     storage for the RDF, and co-firing the
                     RDF with coal  in the City of Ames-
                     owned power plant to produce electric
                      The full report includes evaluations of
                     the refuse processing plant operation,
                     economics of the  total system  and
                     individual subsystems,  flow stream
                     characterization, performance of the
                     stoker-fired steam generators, and en-
                     vironmental emissions  of the stoker-
                     fired steam generators. Previous studies
                     at the Ames plant have been reported in
                     three U.S. Environmental Protection
                     Agency reports: EPA/600/2-77/205,
                     "Evaluation of the Ames Solid Waste
                     Recovery System, Part I—Summary of
                     Environmental Emissions: Equipment,
                     Facilities, and Economic Evaluations;"
                     EPA/600/7-79/229, "Evaluation of
                     the Ames Solid Waste Recovery Sys-
                     tem, Part II—Performance  of  the
                     Stoker-Fired Steam Generators;"  and
                     EPA/600/7-79/222, "Part III—Envi-
                     ronmental Emissions of the  Stoker-
                     Fired Steam Generators."
                      This Project Summary was developed
                     by EPA's Hazardous Waste Engineering
                     Research Laboratory, Cincinnati, 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
  The Ames Solid Waste Recovery Sys-
tem is a continuously operating system
that is processing municipal solid waste
(MSW) for use as a supplemental fuel in
the steam generators of the Ames M unic-
ipal  Power Plant.  The total system
consists of a nominal 136-Mg/day (150-
ton/day) processing plant, a 454-Mg
(500-ton) Atlas storage bin, pneumatic
transport systems,  and the existing
municipal power plant. The processing
plant incorporates two stages of shred-
ding, ferrous and nonferrous metal
recovery, and an air density separator.
The three steam generators consist  of
one pulverized coal tangentially fired unit
and two stoker-fired return traveling grate
spreader units.
  The full report is concerned with the
following objectives:
• Evaluation of the refuse processing
   plant performance
• Economic evaluation of the Ames
   Resource Recovery System
• Characterization of the material flow
   streams within the refuse processing
   plant and the refuse-derived fuel pro-
• Evaluation of the performance of the
   stoker-fired boilers
• Measurement of environmental emis-
   sions from the stoker-fired boilers
• Determination of boiler tube corrosion
   in the stoker-fired boilers.
  The full report on this project presents
the results and conclusions of the tests
performed through the second year  of
evaluations(1977), and contains separate

sections on each of the above six listed

Plant Description
  This section addresses the operating
experience of the general plant and the
following subsystems:

 • Tipping Floor
 • Shredder System
 • Air Density Separator System (ADS)
 • Rejects
 • Ferrous Metal Separation System
 • Aluminum Separation System
 • Pneumatic Conveying System (PSI)
 • Atlas Bin
  Figure 1 is a block flow diagram of the
processi ng plant. MSW is delivered to the
tipping floor which is 48 m by 32 m and
has two entrances and exits. One is for
commercial  trucks  and the  other  for
private automobiles and pickup  trucks.
The commercial trucks are weighed on a
truck scale, and the private vehicles are
simply counted.  A  front-end loader  is
used to push the MSW onto the infeed
conveyor C-1.
  Raw refuse first enters the plant pro-
cessing system via infeed conveyor C-1
into  the first stage shredder, then  via
conveyor C-3 through the second stage
shredder.  A  magnetic belt separator
removes ferrous metal from the material
flow stream between the first and second
stage shredder. Conveyor C-6 transports
the material from the  second stage
shredder into the air density separation
subsystem. Light material is transported
via a pneumatic conveying system to a
storage bin (Atlas bin) prior to transport to
the electric power generating plant. The
heavy material drops out of the ADS onto
conveying belts where it is transported to
a reject bin. Material in the reject bin is
periodically transported by truck to a land-
fill. Additional ferrous metal recovery is
achieved from the ADS heavy material by
a magnetic tail pulley and a magnetic
head pulley. This ferrous metal is added
to the ferrous metal  recovered  by  the
magnetic belt separator.
  An  aluminum  separation system
(Almag) composed of  a trommel  screen
and an electrical eddy current separator
          Air to Fan


— Rott
— Fligl

try Feeder
'Hating Conv.
tt Conv.




Tail Pulley
                                                          I Non-Comb. \
                                                          I Surge Bin  \~
                                                          I	I
                                                 C - Conveyors
                                                 E - Bucket Elevators
                                                 ADS - Air Density Separator
                                                 PSI - Pneumatic Conveying System
                                                 Atlas Bin - Storage Bin for RDF
                                     J Almag System\    I   Reject    \
                                     "J (Inoperative)  |    I   Hopper   I
                                      .	,	1    I	--J
                                            '                 .Landfill

                                      |  Aluminum  \
                                      |  Storage    \
Figure 1.   Flow diagram of Ames Solid Waste Processing Plant.


was originally installed at the plant, but
this system  is now inoperative.  It is
shown in dotted lines in Figure 1.
  Operation of the process plant during
1977 represented the second year of
operation. Processing occurred on a 5-
day/week basis.

Economic Evaluation
  This section  presents  an economic
evaluation of the Ames Solid Waste
Recovery System for 1977, its second full
calendar year of operation.  The experi-
ence gained in the first year of operation
(1976) resulted in a  reduction of overall
operating  expenses during 1977. While
some costs were obviously reduced (e.g.,
lower overall costs),  others actually in-
creased.  Those costs which increased
were electrical energy and replaced parts
primarily as a result of general economic
  Initial capital expenditures have been
estimated at $6.3 million, while initial
capital investment for the refuse process-
ing plant  alone has  been estimated at
$4.1 million, and the capital costs of the
storage bin  and  pneumatic transport
system are estimated at $1.3 million.
  The total plant expenses during 1977
were  $992,270. This amount includes
depreciation and interest on the capital
expenditures and  the refuse processing
operational  costs. Total  revenue was
$498,626 which was derived from the
sale of RDF, metals, wood chips, and
paper; fees charged  for commercial and
private haulers; and reimbursements and
  The  amount of refuse  processed in
1977 was 43,891  Mg (48,381 tons).
Based on  this amount, the net cost for
processing the refuse was  $13.90/Mg
($12.61 /ton). The average usage of elec-
trical  energy was 52 kWh/Mg of pro-
cessed refuse.

Flow Stream Characterization
  Initial flow stream sampling began July
5, 1977, and continued through July 13,
1978, in order to allow for characteriza-
tion on a monthly  and a seasonal basis.
Sampling was conducted at 12 locations.
Eleven locations were inside the process
plant and one on top (inlet) of the Atlas
storage bin.
  Samples were taken by using a  con-
tainer attached to the end of a rod and
passing it back and forth in a free-fall flow
stream until the container was  full.
Samples were taken at 1.5  hr intervals
beginning approximately  15 min after
process plant start-up. Weekly composite
samples for each location were gener-
ated, and from these, appropriate sub-
samples were prepared for the various

Performance of the Stoker-Fired
Steam Generators
  The  conceptual design of the  solid
waste recovery system specified burning
RDF in suspension in the pulverized coal-
fired unit 7 (33 MW) at a firing rate of 20%
(by heat input) or about 7.26 Mg/hr.
Initial operation in fall 1975 resulted in a
high dropout of unburned material into
the bottom ash hopper. The power plant
then began burning RDF  in the stoker-
fired boilers  until a  solution  could be
developed.  The final solution was the
installation of a dump grate at the furnace
bottom. It was concluded that a dump
grate configuration is also necessary in
small- to moderate-sized suspension-fired
steam generators.
  The major research emphasis was on
the thermal and environmental evaluation
of the stoker-fired units.
  Unit 5 is a Riley RP steam generator
with a Riley overthrow  spreader and
traveling grate. Unit 6 is a Union Iron
Works steam generator with a Hoffman
underthrow spreader and continuous
return traveling grate.
  The  RDF  is pneumatically conveyed
from the Atlas storage bin through two
31.5 cm transport lines and is blown into
the furnace approximately 3.4 m above
the grate. Two rows of nozzles in the rear
furnace wall and two rows of nozzles in
the front  wall supply overfire air for
turbulent mixing of the furnace gases.
  Both units have dry pneumatic vacuum
grate  ash hopper and mechanical col-
lector hopper ash removal systems.
  Initial program objectives were to test
boilers 5 and 6 at 60%, 80%, and 100% of
rated steam load and at RDF firing rates
(based on heat energy input) of 0%, 20%,
and 50%. Three tests were made at each
condition.  The experience gained from
firing  unit  5 at 100% load with RDF
demonstrated that this firing condition
was not practical. For unit 6, nine tests
were performed at 80% load. High panic-
ulate emissions occurred during tests at
80% of steam load, with varying RDF flow
rates. A block diagram showing all sample
locations and type of samples collected is
shown in Figure 2.

Environmental Emissions of the
Stoker-Fired Boilers
  The preceding section includes descrip-
tions of the  Ames  stoker-fired steam
generators used for the tests. Both units
have dry pneumatic vacuum bottom and
fly ash removal systems. Mechanical dust
collectors are installed on both units.
  For this study, the independently con-
trolled variables were load, based on
steam flow, and RDF quantity, based on
heat energy input to the boiler. Nominal
load levels selected were 60%, 80%, and
100% of rated capacity; RDF quantities
were 0%, 20%, and 50% of heat energy
  For each steam flow and each quantity
of RDF, three experimental runs were
accomplished. For  unit 5 the statistical
design was 3x3x3 full factorial experi-
ment with 27 runs needed to fill the data
matrix of the experiment. These experi-
mental runs were  accomplished during
1976. After observing the operation of
unit 5, a steam load of 80% was chosen as
typical of boiler demand. Also at 80% load
wall slagging was reduced, and excess air
supplied for the coal and RDF combustion
was optimum. Therefore, nine additional
tests selected at 80% load were accom-
plished on unit 6. Testing of two boilers of
similar type but different size allowed the
investigators  to observe whether boiler
size had any effect on emissions.
  Sampling of effluents was done accord-
ing to EPA-prescribed techniques. Stack
effluents, including particulate samples,
were obtained at numerous prescribed
points in the  stack  cross section. Three
sampling trains operated simultaneously.
An additional train was located before the
particulate collector. Input fuel and grate
ash were sampled at regular 1-hr inter-
vals throughout the test period and then
mixed to yield a composite sample. Hopper
(fly) ash was sampled at the completion of
each experimental run. Combustion airto
the boiler was monitored by wet and dry
bulb thermometry. Steam flow  rate,
temperature,  and  pressure were also
recorded at regular  intervals.
  The sampling was  conducted on a
regular basis except that of heavy organic
species, which were sampled intermit-
  The composite coal and RDF  samples
were analyzed in the Ames laboratory.
Ultimate  analyses  and heating values
were obtained by standard ASTM  meth-
ods. Trace elements were determined by
x-ray fluorescence (XRF).
  The size distribution of the particulates
after the dust collector was determined
by an Andersen cascade impactor. Par-
ticulate samples obtained with the EPA
Method 5 sampling train were analyzed
by SRF. The impinger solutions from the

     Flow Rate
     Ultimate Analysis
     Heating Value
     Chemical Analysis
       & Trace Elements
     Ash Softening Temperature
     Filter Paniculate
       Trace Elements
     Impinger Water Trace
     Emission Rates of
   Paniculate Trace
   Impinger Water Trace
   Emission Rates of Paniculate
     and Gaseous Species
   Paniculate Sizing
     Volume Flow
     Ultimate Analysis
     Heating Value
     Chemical Analysis &
      Trace Elements
     Ash Softening
                                                                                Flow Rate
                                                                                Chemical Analysis &
                                                                                  Trace Elements
                                                                                Softening Temperature
                                     Flow Rate
                                     Chemical Analysis &
                                       Trace Elements
                                     Softening Temperature
Figure 2.   Sample locations and items sampled.
Method 5 train were analyzed with an
inductively coupled plasma system.
  The gases COz, CO, Oz, and N2 in the
stack were determined by Orstat tech-
niques. EPA Method 7 was used for
evaluation of N0« levels,  and  the  EPA
Method 6 train was  used  for measure-
ment of SOX and chlorides. Grab samples
of stack gas were obtained for measure-
ment of Ci through C5 hydrocarbons by
gas chromatography.  Several modifica-
tions of the EPA Method  5 train were
used to collect samples for analysis of
aldehydes and ketones, chlorides, mer-
cury, and  other trace metallic elements.
All inputs to and outputs from each boiler
were evaluated including fuel,  combus-
tion air, bottom-ash,  steam, fly ash, and
stack gas.
  Polynuclear aromatic compounds were
sampled by drawing stack gas through a
column of macro-reticular resin and also
by extraction from particulates collected
in the stack. Gas chromatography and
mass spectroscopy were used for identi-
  The uncontrolled particulate emissions
from unit 5 have no discernible trend
within the data scatter for 1976. However,
the data taken  during 1977 indicate a
nearly linear increase in  emissions of
about 30% from 0% RDF to 50% RDF at a
boiler load of 80%. This trend is similar to
that indicated for unit 6, but the effect is
much less exaggerated in unit 5. At 100%
load, unit 5  was not stable in operation
when the amount of RDF was increased
to 50% which may account for consider-
able uncertainty in  the  data  at this
operating condition. The scatter in the
1976 data also reflects changes in uncon-
trolled factors  in the tests while the
operators were learning how to run the
boilers when burning RDF  with coal.
   Uncontrolled  particulate emissions
from unit 6 increase about 100% in a
nearly linear fashion from 0% RDF to 50%
at boiler loads of both 60% and 80%. The
trends for the data for 1976 are similar to
those of the data for 1977. However, at
80% load, the magnitude  of the  uncon-
trolled particulate emissions on unit 6
was about one-third higher during 1976
than during 1977. In large part, this may
reflect the learning  experience of  the
boiler operators in controlling the amount
of additional air routed to the boiler for
burning  the fuel. Increased  air flow
through the boiler appears to help carry
proportionately more fine  particulates
through the boiler passages to the partic-
ulate collectors.
  The increase in uncontrolled particu-
lates with increases in RDF is believed to
be due to the additional amount of air
routed into the stoker-fired  boilers in
order to  properly burn the RDF and to
maintain a proper firebed on the boiler
grates. The  air flow  through the boiler
appears  to carry additional particulate
matter (fly ash) through  the boiler pas-
sages in nearly direct proportion to the
amount of the increase in air with RDF.
The effect  on unit  6 is exaggerated
because of its physical size  in cross
sections is  about the  same as unit 5.
However, boiler 6 generates  12 MW,
while boiler 5 generates  7.5 MW. Thus,

the air flow through boiler 6 is significant-
ly larger than that through boiler 5.

  RDF in combination  with  coal  was
successfully fired in the stoker boilers
with no insurmountable problems. The
operation of the boiler improved in terms
of stability and consistency of  measured
variables from  1976 to 1977.  This is
believed to be a "learning effect" on the
part  of the boiler operators in properly
firing the RDF and coal mixtures.
  The combustible properties of the fly
ash and the bottom (grate) ash became
similar as the RDF approached 50%. The
ash softening point of the ash lowered
and  the fouling index became more
detrimental as the RDF was increased in
the fuel input.
  Uncontrolled  particulate emissions
tended to increase  with corresponding
increases in  the RDF  fraction  of  fuel
input. This appears to be a result of both
lighter particulates and increases in air
flow through the boiler when burning
RDF. Controlled emissions also appeared
to increase with increases of RDF on unit
6, but the trend was uncertain  on unit 5.
  Both the oxides of nitrogen  (NOX) and
oxides of sulfur (SOX) decreased while
chlorides increased significantly with
increases in RDF. No discernible trends
within the data  scatter were noted con-
cerning formaldehyde  or  hydrocarbon
emissions.  Increased emissions of  the
trace elements copper,  lead, and  zinc
correspond to increases  in RDF.  Further
studies of the trace  element  emissions
are being performed.
  Further studies are still in progress at
the Ames facility. Thus, more  specific
conclusions cannot be made at this time.
The final data from Ames, both economic
and technical, will provide valuable design
information for future plants and will aid
operators of  existing waste-to-energy
J. L Hall, A. W. Joensen. D. Van Meter, J. C. Even. W. L Larsen, S. K. Adams. P.
  Gheresus. and G. Sever ns are with Iowa State University, Ames, I A 50011; and
  R. W. White is with Midwest Research Institute, Kansas City, MO 64110.
Michael Black is the EPA Project Officer (see below).
The complete report, entitled "Co-Firing of Solid Wastes and Coal at A mes: Stoker
  Boilers,"(Order No. PB 86-115 151/AS; Cost: $22.95, 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
                                                                             . S. GOVERNMENT PRINTING OFFICE:1986/646-l 16/20735

United Slates
Environmental Protection
                     Center for Environmental Research
                     Cincinnati OH 45268
Official Business
Penalty for Private Use $300

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