SEPA
                                United States
                                Environmental Protection
                                Agency
                                Industrial Environmental Research
                                Laboratory
                                Research Triangle Park NC 27711
                                Research and Development
                                EPA-600/S7-82-059  Dec. 1982
Project  Summary
                                Application  of  LIMB to
                                Pulverized  Coal  Boilers
                                A Systems  Analysis
                                Limestone  Feed and
                                Boiler  Systems
                                C. W. Arnold and R. C. Burt
                                 The report gives results of a systems
                                analysis of the application of Lime-
                                stone Injection Multistaged  Burner
                                (LIMB) technology to pulverized coal
                                boilers. This study was conducted as
                                part of a larger U. S. EPA program to
                                develop the LIMB technology. The
                                report evaluates alternative limestone
                                handling,  preparation,  and injection
                                methods and  boiler system impacts
                                associated with LIMB applications.
                                Downstream  emission control sys-
                                tems are not addressed.
                                 LIMB simultaneously reduces sulfur
                                oxides (SOx) and nitrogen oxides (NOX)
                                emissions from pulverized coal boilers.
                                It is based on using low NO* combus-
                                tion techniques in combination with
                                dry limestone injection into the furnace
                                for simultaneous SOX control. Study
                                aims were to evaluate alternative
                                concepts for application of the tech-
                                nology, assess potential system prob-
                                lems related to its application, and
                                identify engineering solutions to those
                                problems. Further  goals were  to
                                identify information needs and recom-
                                mend studies to acquire this informa-
                                tion.
                                 Conceivably, all new boilers could
                                be designed to handle any foreseeable
                                impacts associated with LIMB; how-
                                ever, the  practicality of LIMB as a
                                retrofit technology depends on its
                                compatibility with existing boiler
                                systems. Sufficient information is not
                                yet available to accurately gauge its
                                applicability as a retrofit technology;
                                however, the study identified potential
                                system impacts, situations where the
                                impacts will likely be minimized, and
                                design or operating procedures for
                                dealing with them.
                                  This Project Summary  was devel-
                                oped by EPA 's Industrial Environ-
                                mental 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
                                  EPA's LIMB program  is  an effort to
                                develop an effective but  inexpensive
                                emission control technology for pul-
                                verized coal boilers that  will simul-
                                taneously  reduce sulfur oxides (SO,)
                                and  nitrogen oxides (NO,) emissions.
                                The technology is based on using low
                                NO*  combustion techniques  in com-
                                bination with  dry limestone injection
                                into the furnace for simultaneous SOX
                                control.
                                  The need for effective low-cost tech-
                                niques for control of  SO, and NOX

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emissions  has become  apparent in
recent years  because of increased
public awareness of the  problems
associated  with  acid  rain.  The long-
range transport and transformation of
SOx and NO, are believed to be major
factors contributing to acid rain forma-
tion. In addition, these pollutants also
degrade local air quality, present health
hazards, and  participate  in  photo-
chemical smog formation. To address
these problems, effective  low-cost
control techniques  are needed that are
applicable to  both  new  and existing
sources of these pollutants. The LIMB
program seeks to develop such a tech-
nique for pulverized coal boilers which
represent a  major  source of S0«  and
NOx emissions.
  The multiyear LIMB program, initi-
ated in fiscal year 1981, is based on the
results of earlier studies conducted on
low NOx combustion techniquesand dry
sorbent  injection. The  program is
planned to  result in a complete LIMB
technology  design  package.  To accom-
plish this  objective EPA  has initiated
research and  development  activities
including fundamental  studies and
bench- and pilot-scale experiments.
  Along with these research activities
EPA also initiated  a systems analysis
task that includes this report. A major
objective of the  analysis  task is to
evaluate  alternative concepts  for  ap-
plication of the technology to pulverized
coal boilers, to assess  potential system
problems related to its application,  and
to identify engineering  solutions to
those problems. This includes analyses
of alternative limestone preparation and
injection schemes,  boiler system  im-
pacts associated with LIMB,  and  im-
pacts on downstream  emission control
systems. (The current report does not in-
clude analyses of downstream control
systems.) Additional goals are to identify
 information gaps related to system im-
pacts and  to  recommend  studies or
experiments to acquire the  needed in-
formation.


Project Analyses
  The report gives detailed results of
several investigations/evaluations
carried out  as part  of the project.
  To form a basis  for  later technology
evaluations, investigations  were  first
made of the  physical and  chemical
properties of coals commonly burned
in U. S. boilers and of the types of lime-
stones potentially available for use with
LIMB. These properties are summarized
and discussed in the report for a range
of coal and limestone types.
  Investigations  were also  conducted
into the design and operation of various
types of raw material handling, prepara-
tion,  and  injection  equipment. The
report  describes how the  equipment
design and operation  are influenced by
such factors as raw material grindabil-
ity,  hardness, moisture content, and
desired ultimate particle size. Based on
this  information, evaluations were
made of several potential  limestone
preparation and injection schemes and
their  relative advantages and disad-
vantages  were compared.  The basic
schemes analyzed were:
  (1) Crushed limestone and raw coal
     mixed,  pulverized together, and
     injected through the burners.
  (2) Ground limestone and raw coal
     mixed,  passed  through the coal
     pulverizers together, and injected
     through the burners.
  (3) Ground limestone pneumatically
     mixed with pulverized coal and
     primary air and injected through
     the burners.
  (4) Separate furnace  injection of
     ground limestone through com-
     bustion air ports or other ports in
     the furnace walls.
Also, several variations of  these four
basic schemes were considered.
  Investigations  were also  conducted
into the design and operation of various
types of pulverized coal boilers in use
today. The influence of such factors as
design coal  type and boiler age  on
various design variables (e.g., furnace
size, convection  pass spacing, soot-
blower design, and ash removal system
design) is described in the report. Also
described are the likely influences of
LIMB on  boiler operation,  taking  into
account such factors as coal type and
boiler design. This includes evaluations
of the impacts of LIMB on the boiler ash
loading and ash removal system opera-
tion, slagging and fouling tendencies,
and  energy requirements.  Critical
information  needs  and  methods of
dealing with potential operating prob-
lems were also  identified.
  The  analyses described above led to
several major conclusions and recom-
mendations.

Conclusions
  Conceivably, all new boilers could be
designed  to  handle  any foreseeable
impacts associated  with  LIMB; how-
ever, the practicality of LIMB  as a retrofit
technology depends on its compatibility
with existing boiler systems.  To be
compatible,  technology application
should not require major boiler design
modifications or severe boiler operation
impairments. LIMB is still under develop-
ment so sufficient information is not yet
available to  accurately  gauge its ap-
plicability as a retrofit technology;
however, the study identified potential
system impacts associated with LIMB,
situations where these impacts will
likely be minimized, and design or oper-
ating  procedures  for   dealing  with
these  impacts.
  The major factors influencing the
compatibility of LIMB appear to  be the
coal properties and designs of the boiler
furnace,  convection section, and ash
removal systems. Depending on these
factors, potential problems arising from
LIMB  applications include  increased
furnace  slagging, plugging of tight
convection section passes, overloading
or plugging of ash removal systems, and
incomplete  coal combustion.  If not
severe,  these problems can be dealt
with  through  alterations  in  boiler
operating  procedures or minor system
design modifications.
  No major  system problems are ex-
pected with  application  of  limestone
handling, preparation,  and injection
equipment other than potential space
limitations at some existing facilities.
Limestone feed  systems will have to
handle limestone feed rates of about 10-
30% of the  coal feed  rate. Several
potential  limestone  preparation  and
injection schemes  are possible  which
would allow  injection through the
burners, secondary or tertiary air ports,
or other ports installed  in the furnace
walls  Any one of these schemes could
prove  best for a particular  application
depending on 562 control considera-
tions and the existing coal feed system
design. Not much data are available on
the dry  grinding  characteristics of
limestone, but measurements of lime-
stone  properties should ensure ade-
quate limestone feed system design.
  Applications where  LIMB appears
most  compatible with   existing boiler
systems are those which fire low rank
coals. In these  applications, the  coal
properties and designs of the furnace,
convection section, and ash removal
system all appear well suited for LIMB.
  However,  system  impacts will be
larger with  bituminous coal  units.
Bituminous coals generally have higher
sulfur levels than lower rank coals, and
hence require injection of larger quanti-

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ties of limestone. These larger injection
rates require  larger  limestone feed
system capacities, result in larger feed
system power  requirements, increase
boiler thermal losses, and increase ash
loadings handled by the boiler and ash
removal  systems.  Also, limestone
injection  in these units may increase
the tendencies for  furnace  slagging,
convection pass erosion, and plugging
of convection passes and ash removal
systems.
  The potentially most critical problems
of those  mentioned above concerning
the application of LIMB technology to
bituminous coal  units  result from
interactions between limestone and ash
particles. These interactions may result
in decreased ash fusion temperatures
which, together with the increased ash
loadings, may cause increased furnace
slagging  and plugging of tight convec-
tion passes. This  effect is not likely to
occur  with low rank coals due to
differences in  ash chemistry. Another
related problem  is that many older
bituminous coal  units remove econo-
mizer ash with wet sluicing systems.
With LIMB, this ash will contain large
quantities  of  calcium and  sulfates.
When exposed to water it will likely ex-
hibit cementitious properties causing
plugging  of sluicing systems. Wet sluic-
ing systems for economizer ash are not
typically  used on  units firing low rank
coals.
  Thus it appears that LIMB will be most
easily  retrofit on  units firing low rank
coals.  However, about 75% of the
existing  boiler population on  a total
capacity  basis were designed to fire
bituminous  coal.  Further, bituminous
coal units account for an even larger
percentage of  existing SOx emissions.
For these reasons,  LIMB  must  be
applied to bituminous coal units in order
to have a large impact on existing SOX
emissions. In this study, some potential
problems were identified concerning
the application of LIMB to bituminous
coal units.  Further  evaluations are
needed to define the magnitudes of
these problems and to engineer solu-
tions to them.

Recommendations
  Recommendations  from this study
include: (1) research and development
activities that might be undertaken to
better understand  and respond to
system impacts associated  with the
application of LIMB technology; and (2)
additional engineering analyses which
would  further define  system impacts
and problems, engineering solutions to
those problems,  and the compatibility
of LIMB with the existing boiler popula-
tion.

Research  and Development
Needs
  Several research needs related to the
limestone feed and boiler systems were
identified in this  study: measurements
of limestone  grinding characteristics
and of the  impacts  of LIMB on boiler
slagging and fouling tendencies,  ash
entrainment,  ash physical  properties,
and convection section erosion.
  The most critical research need is to
determine the effect of LIMB on slag-
ging and fouling,  especially in bitumi-
nous coal units. Limestone injection tests
in some bituminous coal units have
resulted in severe  deposit buildup
and plugging in the convection passes.
This buildup could result from a com-
bination of  increased  solids  flow,
reduced ash fusion temperatures,  and
tight tube spacmgs. Some reports from
these tests indicated that the deposits
were sticky at normal gas temperatures
but became friable when cooled, indi-
cating that  the ash  melting properties
were important.
  Correlations of  ash fusion tempera-
tures with composition  and various
slagging indices are available to predict
the effects of increased calcium content
on ash slagging tendencies. Also, direct
laboratory  measurements have been
made of the impacts  of increased levels
of limestone on thefusion temperatures
of ash/limestone mixtures.  However,
these types of tools  or tests presume
100% interaction between the ash  and
injected limestone particles.  None of
them model the dynamics of limestone/
ash interactions in the furnace. The true
extent of interaction  is unknown, but is
probably related to the conditions under
which the limestone  and ash particles
come into contact
  As a result, bench- or pilot-scale tests
should be considered in which lime-
stone particles  are injected into a
furnace operated  so that a variety of
peak flame temperatures and time/
temperature relationships occur. These
tests should include  injection through
the burners and through ports located at
other furnace temperature zones. Air
cooled probes can  be placed down-
stream  in  various temperature  zones
reflective  of  radiant and convection
sections in order  to  measure  ash
deposition  rates. Also,  various  ash
strength and friability  tests can  be
conducted on the deposited samples.
  Other  research  objectives  should
include measurements of the influence
of LIMB on total ash entrainment and
ash  physical properties since these
factors  can  influence  ash removal
system  design and  operation. Tests
should include collection of  ash sam-
ples from various points  in the furnace
and  convection section. The samples
should be analyzed for calcium content
and mixed with water to determine the
ash settling and cementitious properties,
both of which are especially important
in the operation of wet ash removal
systems (the degree of ash entrainment
determines the necessary ash removal
system design capacity). Entrainment
and  physical properties should be
measured as functions of both injected
limestone particle size and combustion
gas flow rate.
  Another useful test objective is to
determine the influence of LIMB on
erosion  in the convection  passes, but
this would require relatively  long term
testing.  Limestone injection will  sig-
nificantly increase the  total flue gas
solids loading. Also, limestone inerts
include  those compounds thought to
contribute most to erosion (SiOz and
FeaOa). Testing would involve measure-
ment of the change in weight of metal
probe samples in the convection section
of a pilot unit.
  Other research needs include studies
of limestone grinding characteristics.
As indicated in the report, simultaneous
grinding of coal and limestone may be a
desirable alternative  at  facilities with
excess pulverizer capacity.  However,
the effects of simultaneous grinding are
relatively unknown. Tests  might be
considered of simultaneous grinding for
ranges of coal and limestone types, inlet
limestone rock sizes, and pulverizer
designs. The test objective would be to
observe: the adequacy of mixing of coal
and limestone; the effects of limestone
addition  rate on pulverizer capacity,
power requirements, and reliability; and
the effects of simultaneous grinding on
resulting coal and limestone particle
size  distributions. A  related research
need (which may prove  valuable in
design of limestone feed systems) is to
develop  a  data base of Hardgrove
Grindability Index, hardness,  and parti-
cle specific gravity values for a range of
commercially available limestone types.

Engineering Analysis Needs
  Several areas have been identified in
which additional  engineering analyses

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    would  be useful. These include ad-
    ditional analyses of  the boiler system,
    analyses  of  downstream emission
    control systems,  and overview type
    analyses of the system as a whole.
      Important information  for assessing
    the  usefulness  of LIMB as a  retrofit
    technology includes  the design profile
    of the existing boiler population. Limited
    material on this subject is presented in
    the report; however,  more specific data
    are  available. Specifically, computer
    data bases containing  substantial
    information on utility boilers are availa-
    ble.  Conceivably, this information could
    be cross-referenced with  information
    from available FGD system data bases
    or survey reports to provide a fairly
    complete picture of  the existing boiler
    population and the nationwide potential
    for LIMB retrofit applications.
      An  additional  worthwhile effort
    would  be to research  the furnace
    dimensions, plan areas, or heat release
    rates of the existing boiler population.
    This information would provide insight
    about potential  unit  derating resulting
    from retrofit of LIMB technology. Such
    derating may  be brought about by the
    large flame volumes and/or  burner
    dimensions of  the  low NOX  burner
    techniques instrumental to the applica-
    tion of LIMB technology.
      For a complete systems  analysis,
    engineering evaluations are also needed
    of the impact of LIMB on downstream
    particulate  control systems. Flue gas
    solids loadings  are  greatly increased
    and the  particle  characteristics are
    altered by LIMB. Analyses should  be
    conducted to evaluate which particulate
    control systems are best suited for LIMB
    applications and to choose the best
    methods for upgrading existing  control

    if U S. GOVERNMENT PRINTING OFFICE.  1982	659-O17/O876
         systems in LIMB retrofit applications. A
         related need is to evaluate alternatives
         for recovering unused sorbent from the
         fly ash and recycling it to the boiler.
           Finally, overall system material and
         energy  balances and  cost  analyses
         should be conducted for a number  of
         cases involving different coal types,
         system sizes, limestone injection rates,
         injection system designs, and particu-
         late  control system designs. These
         analyses would  serve to summarize
         total system impacts resulting  from
         LIMB application and to highlight areas
         of technological and cost benefits
         associated with LIMB.
           C. W. Arnold and R. C. Burt are with Radian Corporation, Durham, NC 27705.
           James H. Abbott is the EPA Project Officer (see below).
           The complete report, entitled "Application of LIMB to Pulverized Coal Boilers—
             A Systems Analysis: Limestone Feed and Boiler Systems," (Order No. PB
             83-114 553; Cost: $ 17.50, 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:
                   Industrial Environmental 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
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use S300
             0000329

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