United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-88/013 Nov. 1988
 Project  Summary

 Development  of  Sorbent
 Injection  Criteria  for  Sulfur
 Oxides Control from  Tangentially
 Fired  Coal  Boilers

 R. W. Koucky, J. L. Marion, and D. K. Anderson
  The report describes a program to
develop design criteria for injection
of dry sorbents into tangentially fired
furnaces for the  control of sulfur
oxides (SOX) emissions. The program
included  aerodynamic cold-flow
testing and  mathematical modeling
of sorbent injection, demonstration
testing of SOX emissions control in a
14.7 MW thermal  tangentially fired
Boiler Simulation Facility (BSF), and
development of recommendations for
sorbent injection  in a  tangentially
fired boiler demonstration of the
process.  The Isothermal  flow
modeling led to  development  of
sorbent  injection systems for
tangentially fired  furnaces which
provide  high  levels of sorbent
dispersion.  A sorbent dispersion
mathematical  modeling technique
was  developed to support flow
modeling  in identifying  and
optimizing  sorbent   injection
locations and methods.  Sorbent
injection  tests  in  the  BSF
investigated the following variables:
sorbent  type,  injection location,
injector tilt,  injection velocity,
number of injectors, and carrier air
flow rate.  Sulfur capture efficiency
up to  50% was achieved at a Ca/S
molar ratio  of 2:1 with  calcium
hydroxide  sorbent treated with
calcium lignosulfonate. A procedure
was developed for specifying sorbent
injection locations  and methods for a
full-scale  demonstration  of the
sorbent  injection process  in  a
tangentially fired utility boiler.
   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 trie same title (see
Project Report ordering information at
back).
 Introduction
   Furnace sorbent  injection is being
 developed  as an approach for sulfur
 dioxide (SOg) control for coal-burning
 utility  boilers. The process is attractive
 for retrofit of existing boilers since the
 capital equipment requirements are less
 than for other options such as  flue gas
 desulfurization, and the estimated overall
 sulfur  reduction cost  per ton of sulfur
 removed from flue gas  is less than for
 these  options. In the furnace sorbent
 injection  process,  sorbent,  usually
 calcium  hydroxide [Ca(OH)2]  or
 limestone (CaCOa), is injected above the
 flame  zone  and mixes  with flue  gas
 containing  SC>2  The  SC>2 reacts
 chemically with lime (CaO), formed from
 the sorbent, to make solid calcium sulfate
 (CaS04). The CaS04 is removed with fly
 ash in  paniculate collection equipment.
   A significant fraction  of the existing
 boilers in  the  U.S. that  would  be
 candidates  for  retrofit  with  sorbent
 injection technology are tangentially fired

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utility boilers. Tangential firing introduces
special considerations for the design of
sorbent  injection systems due to the
unique aerodynamics in the  sorbent
mixing  region  of tangentially  fired
furnaces.  Therefore, a  program was
established to address the criteria for the
location and method of sorbent injection
in tangentially fired  coal-burning
furnaces  in order to  provide the  most
effective removal of sulfur oxides,
   The program included four tasks:
   Task A - Cold  flow  modeling  of
           sorbent injection systems.
   Task B - Mathematical modeling  of
           sorbent injection  systems,
           SOa capture performance,
           and  furnace  thermal
           performance.
   Task C - Combustion testing  of
           sorbent       injection
           location/injector  design
           combinations in a pilot scale
           Boiler  Simulation  Facility
           (BSF).
   Task D - Sorbent  injection  system
           design  recommendations
           for  a full-scale  tangentially
           fired boiler demonstration.

Cold Flow Modeling
   The cold flow modeling consisted of
three screening  levels designed to lead
to the selection of injector design/location
combinations  for combustion testing. In
the first screening level, flow visualization
tests of 16 injector configurations were
conducted.  Each  configuration was
evaluated at up to  three  injector carrier
air velocities and three injector nozzle tilt
positions.  The   11   best  injector
configurations from the  first screening
level were   evaluated  in the  second
screening level,  which  consisted  of
three-dimensional  velocity  profile
measurements and mixing studies using
a  methane tracer gas  measured  by a
laser  absorption spectrophotometer. In
the third screening  level,  the five
configurations which  demonstrated the
best performance in  the second level
testing  were tested  over a  range  of
simulated furnace operating  conditions
using the same techniques  utilized
during the first two screening levels.
   The isothermal  flow modeling was
performed in the Large  Scale  Furnace
Aerodynamics Test Facility  (LSFATF).
The facility was a  0.46-scale simulation
of the BSF used in Task C. The  inflow
modeling   tests,   supported  by
mathematical  modeling,  developed
several sorbent  injection systems  which
provide high levels of sorbent dispersion
for a wide  range of  sulfation tem-
perature  windows and  corresponding
sorbent injection locations.

Mathematical Modeling
   The mathematical modeling effort was
divided into three subtasks.  One  was
thermal modeling to provide furnace gas
temperature  predictions.  Thermal
modeling was  conducted to  design the
BSF, to select  candidate sorbent injector
locations  for both the  isothermal  flow
studies and the combustion testing at the
BSF, and to interpret BSF test results  in
order  to  optimize  SC>2  capture
performance at the BSF.  The  second
modeling subtask was sorbent dispersion
modeling which was conducted  using a
computational fluid  dynamics (CFD)
code.  It was shown  that  CFD  can
effectively simulate sorbent mixing in the
upper part of a tangentially fired furnace
and can be an effective design  tool for
selecting  and optimizing sorbent injector
locations and  methods.  In  the  third
mathematical  modeling subtask, a  SOa
capture  performance  model   was
developed by application of a proprietary
computer code. The model predicts SC>2
capture  as  a  function  of  furnace
geometry, furnace temperature profile
and  operating   conditions,  sorbent
injection  parameters, and  the inherent
    capture performance of the sorbent.
Combustion Testing
   Combustion testing was performed in
a large  pilot-scale tangentially fired test
furnace  to evaluate and optimize sorbent
injection  concepts  developed  from
isothermal and mathematical  modeling
studies.  Objectives  of  the  combustion
testing were to:
  1. Evaluate  SOa  capture performance
    for  various  injection  locations,
    designs, and operating conditions.
  2. Evaluate three  hydrated  lime
    sorbents, including a hydrated lime
    treated with calcium lignosulfonate.
  3. Optimize SOa capture performance.
  4. Refine the  sorbent  injector design
    guidelines developed in the cold flow
    and mathematical modeling tasks.
  5. Create a data base for sorbent
    injection  system design guidelines
    for tangentially fired boilers.
  Combustion testing was performed in
C-E's new 14.7 MW thermal (50x106
Btu/hr) BSF.  This  facility was  designed
and built by  C-E specifically to support
the sorbent  injection  design  criteria
program.  The  BSF  represents a
significant contribution toward EPA's goal
of commercializing in-furnace  sorbent
injection technology for SOa control. Th
facility  accurately  models   th
time/temperature history, volumetric heal
release  rate,  heat  absorption,   and
aerodynamic  characteristics  of  a large
utility boiler.  Both  the lower and  upper
furnaces  are modeled so that the region
of the boiler where  SOa capture reactions
take place is properly represented.
  Tests were performed using an eastern
bituminous  coal containing 2.7 to 3.2%
sulfur.  More  than  160 tests  were
performed,  including baseline tests
upper furnace  temperature  char-
acterization  tests,  and  NOX  mea-
surements as well  as sorbent injectior
tests over a range of Ca/S molar ratios
sorbent  types,  injector tilts, sorben
carrier  air  velocities,  and  injectoi
locations. The BSF  was  found to  b«
representative of a large utility boiler ir
terms of operation, heat  release,  ga;
time/temperature profile, carbon burnout
and  NOX/SO2  emissions. With hydratec
lime  sorbent  treated with  calciun
lignosulfonate, SC>2 capture efficiency o
up to 50% was obtained at a Ca/S mola
ratio of 2:1 for selected test conditions.


Design Recommendations
   In program  Task D, a sorbent injecto
design procedure  for tangentially  fire<
furnaces  was developed. This procedun
applies the  design guidelines, experi
mental  methods,  and computationa
methods developed  in the first threi
tasks of  the  program. By this step-by
step procedure, injector design  feature:
are optimized including injector elevation
peripheral location,  size and  shape, am
operating conditions. This procedure wi
be  applied  in selecting  the sorben
injector designs for the tangentially firei
furnace  sorbent injection demonstratio
program.


Conclusions
   This  program  led to the following
major conclusions:

  1. Isothermal  flow modeling  provide
    sorbent  injector  designs  fo
    tangentially fired furnaces with  hig
    levels of  sorbent  dispersion for
    wide range of sulfation temperatur
    windows and corresponding sorbet
    injection  locations. Specific design
    were selected  and tested in the 14.
    MW thermal BSF.

  2. For furnaces in which the beginnin
    of the sulfation temperature windo
    is at or  near the arch elevatioi
    injection  from  a position  low  in ft

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front wall provides effective  sorbent
dispersion.
For furnaces in which the beginning
of the sulfation temperature  window
is below the arch, tangential injection
from the corners of the unit provides
very effective  sorbent penetration
and  dispersion across the furnace
plan area.
Thermal modeling using  proprietary
C-E  design  codes  provided
significant support to the program for
the design of the BSF, selection of
injector locations  for  both  the
isothermal  flow  studies  and BSF
combustion  testing,  and  in
interpretation of BSF test results.
Computational fluid dynamic (CFD)
modeling  provides  an  effective
simulation  of the flow patterns  and
mixing in  the  upper part  of
tangentially fired  furnaces.  CFD
simulation  in combination with cold
flow modeling  can  be  used  to
identify and optimize sorbent injector
locations and operating  conditions
for dry sorbent injection systems for
SC>2 control  in  tangentially fired
furnaces.
6.
7.
A model was developed to predict
SOa capture as a function of furnace
geometry,  furnace  temperature
profile, operating conditions, sorbent
injection  parameters,  and  the
inherent SO2 capture performance of
the sorbent by  application  of a
proprietary C-E computer code.
The model will be applied in scaling
up  results  of  this program for a
demonstration  of dry  sorbent
injection technology in a tangentially
fired utility boiler.
The  BSF  was   found   to   be
representative of a large utility boiler
in  terms of operation,  volumetric
heat release,  gas  time/temperature
history, carbon  burnout,   and
        emissions.
8. Three  sorbents were  tested at the
  BSF  firing  an  eastern  U.S.
  bituminous  coal containing on
  average 3%  sulfur. Sorbent A was
  untreated Black River hydrated  lime,
  Sorbent  B  was   untreated
  Marblehead  hydrated  lime,  and
  Sorbent C was Marblehead hydrated
  lime  treated  with   calcium
    lignosulfonate. SO2  capture  varied
    with  sorbent type.  Typical SO2
    capture  performance  results at a
    calcium/sulfur  molar  ratio of  2:1
    were:  Sorbent A,  25-30%; Sorbent
    B,  30-40%;  and  Sorbent  C,  35-
    50%.
 9. Although most sorbent injection tests
    were run for a  constant 20-minute
    interval,  longer  tests  showed  that
    S02 capture  could be  increased by
    10  or  20% (or 4  to 10 percentage
    points)  by  extending   sorbent
    injection  to 1 hour. This was  due to
    deposition of reactive  sorbent  on
    heat transfer surfaces.
10.  Optimum S02 capture was obtained
    by  injection into  the region  where
    furnace gas temperatures range from
    1230 to 1290°C.
11.  Injector tilt was demonstrated to be
    an  effective approach  for  injecting
    sorbent into the optimum location.

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  R. W. Koucky, J. L.  Marion, and D.  K. Anderson  are  with Combustion
       Engineering, Inc.. Windsor, CT 06095.
  Samuel L Rakes is the EPA Project Officer (see below).
  The complete report,  entitled  "Development of Sorbent Injection Criteria for
       Sulfur Oxides Control from Tangentially Fired Coal Boilers," (Order No.
       PB 88-238 357/AS; Cost: $32.95, 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:
          Air and Energy Engineering Research Laboratory
          U.S. Environmental Protection Agency
          Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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