United States
                    Environmental Protection
                    Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park.NC 27711
                    Research and Development
EPA/600/S8-89/059 May 1990
v>EPA         Project Summary
                    Municipal Waste Combustion
                    Assessment:  Fossil  Fuel
                    Co-Firing
                   V.J. Land rum and R.G. Barton
                     Fossil fuel co-firing, defined as the
                   combustion  of refuse derived fuel
                   (RDF) with another fuel (usually coal)
                   in a device designed primarily  to
                   burn the  other  fuel,  is  generally
                   confined  to  commercial  and utility
                   boilers.  This report identifies  RDF
                   processing operations and various
                   RDF types; describes such fossil fuel
                   co-firing technologies as  coal fired
                   spreader stockers,pulverized coal
                   tangentially fired boilers, and cyclone
                   fired boilers;  and  describes the
                   population of coal fired boilers that
                   currently co-fire RDF, have previously
                   co-fired RDF but  have ceased to do
                   so,  and have been used  in RDF  co-
                   firing demonstration  projects. Model
                   plants  are  developed  and good
                   combustion  practices are recom-
                   mended.
                     This  Project Summary  was
                   developed by EPA's  Air and Energy
                   Engineering Research Laboratory,
                   Research Triangle Park,  NC,   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
                     Fossil   co-firing is defined as  the
                   combustion of RDF with another fuel
                   (usually coal) in  a device  designed
                   primarily   to  burn the other fuel.This
                   report provides an overview of fossil fuel
                   co-firing technology and identifies  the
                   extent to which  fossil  fuel  co-firing is
                   practiced.

                   Currently Co-Firing
                     Four facilities currently co-fire  RDF.
                   The  Madison  Gas  and Electric's Blount
Street Power Plant includes two 50 MWe
front wall fired pulverized coal boilers
modified to co-fire RDF by installing RDF
injectors between the bottom two  burner
levels. A drop grate was added  to the
boilers to ensure complete burnout of the
ash generated by the RDF. RDF supplied
about  15% by weight of the fuel used by
the boilers (12% of  total heat input). No
major problems  have  been reported.
Minor problems occurred with the
formation of clinkers on  the  grate.
Despite the lack of  firing problems, the
additional operating costs associated with
co-firing RDF make it uneconomical
without special price concessions and
subsidies from the City.
   The Ames, Iowa, City Power Plant
includes  a 35 MWe tangentially fired
pulverized coal boiler  modified to burn
RDF and a  65 MWe  front wall fired
pulverized coal unit originally  designed to
burn RDF Air transport RDF  injectors on
both units are located  just  above  the
primary combustion zone. In  addition,
both units are equipped with drop grates.
The 35 MWe unit fires 18% by  weight
RDF (12% of total  heat input). The 65
MWe unit fires 20% by weight RDF (10%
of total heat input). Problems reported are
related to handling the RDF feed and the
resulting ash. The variable nature of RDF
makes it difficult to  maintain continuous
feed with a  relatively constant heat
content. Wires and  non-ferrous metals
create significant ash handling problems.
The RDF feeding system frequently jams,
damaging the machinery. Originally, tube
wastage was observed around  the drop
grate due to  the reducing atmosphere
produced by ash burning on the grate.
This problem was remedied by installing
refractory around  the grate.  The plant
operators report that RDF co-firing  m

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their boilers is not financially advanta-
geous  because of high  maintenance
costs.
   Baltimore Gas and Electric Company
operates -two  200  MWe cyclone  fired
boilers  modified  to co-fire  RDF by
installation of RDF injection equipment in
the  cyclone.   Initially,  erosion  was
observed on the cyclone  wall opposite
the RDF injection port. The installation of
a deflection plate eliminated the problem.
The RDF is an average  of 5 to  10% by
weight  (3 to 5% total heat  input) of the
total fuel fed  to the  boiler.  No major
problems have been reported operating
with RDF.  The  utility  has  not  yet
identified the  impact of firing RDF on
operating  and maintenance  costs;
however,  it reports that,  from a fuel cost
standpoint,  RDF co-firing  is  financially
attractive. The  RDF  purchase contract
requires the utility to pay only 80% of the
price they would pay for  an  equivalent
amount of coal  (on a heating value basis),
resulting in a fuel cost savings of 20%.
   The City  of  Lakeland,  Florida's
Mclntosh  Power Plant includes  a 364
MWe opposed burner, pulverized  coal
fired boiler  designed  to co-fire RDF and
coal. The coal burners are located at four
elevations on  the front  and rear walls.
Two air  transport RDF injectors  are
located on  each side wall at the same
elevation  as  the upper coal burners. The
boiler is also equipped with drop grates.
Only 1% of the mass fired in the boiler is
made up of RDF.  Lakeland reports no
operating problems,  no excess  tube
wastage,  slagging or fouling. They report
that firing RDF appears to be financially
viable when operating costs  alone are
considered.  However,  when  debt
retirement on the processing plant is also
considered, the unit does not quite break
even.

Dicontinued Co-Firing
   Six facilities have previously co-fired
RDF but  have  discontinued this practice.
The Oscar  Mayer Steam Generating
Plant in Madison, Wisconsin, consists of
a spreader  stoker traveling grate system
modified  to burn RDF. The facility had  a
capacity  to burn  up to  60 tons  (54
tonnes) of  RDF per  day.  Oscar Mayer
reports that there  was  little  economic
incentive  to continue co-firing RDF.  They
found overhead and  maintenance costs
to be prohibitive. In addition, the quality
of  the  RDF  varied  excessively for
convenient use. However, the facility still
has the capacity to  co-fire RDF if the
economic situation changes.
   The Union Electric, St. Louis Meramec
Plant has two 125 MWe tangentially fired
pulverized coal boilers modified to co-fire
RDF.  There are four vertically  arranged,
tilting  coal  burners in each corner. RDF
injectors were  installed,  one in each
corner between the second and third coal
burners. Dump  grates were not  added.
The RDF supplied an average of  10% of
the   total  heat   input.  Problems
experienced included  plugging  and
jamming of the  RDF feed system and
excessive  abrasion  from  the RDF feed
particles due to the high glass and grit
content of  the  RDF. The excessive
abrasion caused frequent leaks  in  the
feed  lines  which had to be continually
repaired resulting  in extremely  high
maintenance costs. Boiler efficiency was
decreased  due  to  the higher  moisture
and ash content of RDF compared to coal
and increased unburned  combustibles in
the bottom ash.
   The  Wisconsin  Electric's Oak  Creek
Station  has two 310  MWe  tangentially
fired pulverized coal boilers modified to
co-fire RDF.  There are  five tilting coal
burners in each  corner.  Four  RDF
injectors were  installed,  one in each
corner,  above the top coal burners. No
dump grates  were  added. The  RDF
supplied an average of 15% of the total
heat  input. The  facility  experienced
excessive abrasion  of the RDF feed lines
because of the glass and grit in the RDF
as well  as  increased slagging.  Solidified
slag  collected  at  the bottom  of  the
furnace  and choked off bottom ash flow.
Deslagging involved the use of shotguns
and dynamite to blast loose slag deposits
and required 4-5 hours.  Deslagging was
required 12-15  times  per  month during
co-firing as  opposed to  7-10 times per
month during operation with coal alone.
   Four  Rochester,  New York,  Gas and
Electric units  are tangentially  fired,
pulverized coal  boilers with capacities of
42, 62, 62,  and 75 MWe. Two  RDF
injectors were installed in  each  unit in
opposite corners above the coal burners.
Two units received dump grates and two
did not.  The RDF supplied an average of
15%  of the total heat input.  Problems
experienced included pluggage of RDF
feed lines  and large clinker formation on
dump grates. Boiler efficiency decreased
because of the  higher moisture and ash
content of RDF  compared  to coal,
increased  excess air  levels,  and
increased  amounts  of  unburned
combustibles in bottom ash.
   The  Commonwealth Edison, Chicago
Crawford Station includes one 200 MWe
and one 325 MWe tangentially fired,
pulverized coal boilers modified to co-fire
RDF.  The  modifications included installa-
tion of two  RDF injectors in two opposite
corners of each furnace  (four  per unit).
Dump  grates  were  not  installed.  The]
average heat input provided by the RDF
was  10%. Problems included  plugging
and excessive  abrasion of the  RDF feed
lines, increased volume and particle  size
of bottom  ash,  and  increased  slag
accumulation.
   The United Illuminating Harbor Station
in Bridgeport,  Connecticut,  includes an
80 MWe cyclone  boiler previously used
to co-fire RDF. The RDF  was  a  dry
powder with  a heat content of 7800 Btu/lb
(1.81 x 107  J/kg). The RDF provided ar
average heat input  of  30%.  No  majoi
problems were  associated with co-firing
RDF.   The  facility  ceased  co-firing
because  the  RDF  processing  plan"
closed.

Co-Firing  Demonstrations
   Two facilities were involved in RDF co
firing demonstration  projects.  The  B.L
England Station includes  one  129 MW<
cyclone fired unit which was  used to co
fire RDF  as  part of an 18 day  feasibility
demonstration  study. The RDF  wa:
injected through the secondary air duct
in the cyclone.  The facility  was able ti
burn 2550 tons  (2313  tonnes) of RDI
during  the 18-day test. Stable  operatioi
was maintained only when RDF was  les
than 15% of the total heat  input  to th
boiler.  Severe  fouling  and  slaggin
problems were  experienced  and the a
heater  plugged  rapidly,  forcing
shutdown of  the unit. In addition, a har
tenacious ash that could only be remove
with jackhammers fouled the reheat«
surfaces. Unit efficiency was  significant!
affected  by RDF co-firing.  The  un
gradually derated from 129 to 100 MWi
Emissions increased significantly whe
co-firing RDF.  Particulate emissions ar
precipitator power levels  increased by
factor of  3.  Because of these  problem
Atlantic Electric concluded that RDF c<
firing was unacceptable.
   The Milwaukee  County   Institution
Power Plant  includes one  spreader stok
boiler  rated at  110,000 Ib/hr (49,8J
kg/hr) of  steam that was  used  to  co-fi
RDF during  a 9 day test  with  3 days
performance testing. The  RDF  consist!
of about 21% by weight of the coal/RC
mixture and  about 11 % by heating vali
No significant feeding problems  we
encountered.  The coal/RDF mixtu
clinkered  more frequently than cc
alone. Also,  some RDF fell  into the a
pit unburned. The boiler  was  unable
achieve steam generation rates that h
been  easily attained when firing  c<
alone,  reportedly  due to the volumel
limitations  of the  spreader  feed

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equipment  when firing the less dense
  Dal/RDF mixture.  Erratic steam rates
jere also experienced, reportedly due to
non-uniform mixing of  the coal and RDF.
Particulate  carryover  did  not  increase
significantly,  reportedly  due to using
densified RDF rather than fluff RDF.

Conclusions
   RDF co-firing affects many aspects of
boiler operation  and  performance,
including boiler efficiency, flue gas flow
rates,  stack emissions,  bottom  ash
production,  slagging and fouling. Boiler
efficiency decreases with  RDF  co-firing
because of  increased flue gas production,
increased   unburned  carbon, and  fuel
moisture losses.  Flue gas  flow rates
increase as the amount of RDF co-fired
increases primarily  due   to  the
requirement for increased  excess air to
account for variability  in  RDF feeding.
Compared to coal, RDF typically has low
sulfur  concentrations,  high chlorine
concentrations, and  a  high ash  content.
Thus, co-firing RDF typically increases
HCI  emissions  and  decreases  SOX
emissions. In  general, particulate
emissions  increase  with  RDF co-firing.
CO emissions from RDF  co-firing  with
coal  are not significantly changed  from
coal-fired  boiler  CO  levels.  NOX
 missions from RDF co-fired systems are
.*ot expected to be significantly  different
than  those  from coal-fired  systems. The
only  dioxin data available on  co-fired
units were from  a study  co-firing about
20% RDF by weight. No dioxins or furans
were  detected in  the emissions.  In,
addition, emissions  tests have been*
performed at seven coal fired boilers. No
CDD or CDF emissions  were  detected
from any of these facilities. The available
emissions  data  from  boilers  burning
100% RDF indicate that  highly  variable
CDD/CDF  emissions may occur under
normal operating  conditions.  However,
the conditions under  which  substantial
CDD/CDF  emissions  occur  are  not
expected   to be  encountered  under
normal  operation in  an  RDF  co-fired
system.
   Bottom ash production increases  by  af
factor of 2 or 3 when 10-20% RDF is co-'
fired  on a heat input basis because  RDF
has a higher specific ash content (Ib/Btu)
than coal. RDF co-firing may increase the
potential for slagging  and fouling  and
result in increased  maintenance costs,
and  decreased boiler efficiency  and
availability.

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  V. Landrum and R. Barton are with Energy and Environmental Research Corp.,
     Durham NC 27707.
  James D. Kllgroe is the EPA Project Officer (see below).
  The complete report, entitled "Municipal Waste Combustion Assessment: Fossil
     Fuel Co-Firing," (Order  No.  PB90  159 831/AS Cost: $17.00 (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:
            Air and Energy Engineering Research Laboratory
           U.S. Environmental Protection Agency
           Research Triangle Park. NC 27711
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EPA/600/S8-89/059

                   MOTCTIO.  IOEIICI
     CHICAGO

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