United States
                     Environmental Protection
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                     Research and Development
EPA/600/S7-87/021  Feb. 1988
&ERA          Project Summary
                     Wall-Fired  Boiler Design Criteria
                     for  Dry Sorbent  S02  Control with
                     Low-NCX Burners
                     R. K. Mongeon
                       Recently, attention has focused on
                     dry sorbent SO2 control technology
                     which, in  conjunction with low-NOx
                     burners, can reduce two main acid rain
                     precursors, SO2 and NOX. This report
                     assesses the impact of Limestone In-
                     jection Multistage Burner (LIMB) tech-
                     nology on  wall-fired utility boilers for
                     both new and retrofit designs.
                       Past and ongoing development work
                     is  reviewed to form  a basis for the
                     remaining evaluations.
                       Historical and projected design trends
                     are examined for unit sizes, heat release
                     rates,  fuel properties, and air pollution
                     control systems. Riley Stoker wall-fired
                     boilers are used for  the  survey and
                     compared  with the entire wall-fired,
                     coal-fired utility boiler population.
                      The  influence of dry sorbents and
                     staged combustion burners on boiler
                     design is reviewed and potential problem
                     areas are noted. The review covers the
                     sorbent (including storage and handling),
                     the boiler and its appurtenances, and
                     related flue gas cleanup and handling
                     systems. In addition, a selection ratio-
                     nale is developed for selecting a poten-
                     tial host site for demonstrating the LIMB
                      A generic process design is developed
                     for LIMB systems for both new units
                     and as retrofits to existing units. Three
                     unit sizes are considered — 200, 400,
                     and 600 MWe. Capital and annualized
                     cost estimates are prepared.
                      This Protect 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 docu-
                     mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
  Renewed interest is being expressed in
Limestone  Injection Multistage Burner
(LIMB) technology as a low cost SO2 and
NOX control approach for coalfired boilers.
During the 1960s  and 1970s the tech-
nology was investigated with little suc-
cess. Recent activity has  focused on
gaining a better understanding of the
process fundamentals. This activity has
demonstrated that LIMB can be a simple,
cost effective control strategy to reduce
emissions from  coal-fired power plants
and utility boilers.
  Simultaneous NOX/S02 control systems
are applicable to both new and retrofit
units. LIMB technology involves the use
of low-NOx  distributed-mixing burners
with injection  into the furnace of an
alkali-based solid sorbent for S02 removal.
The  U.S.  Environmental  Protection
Agency (EPA) is taking a  leading role in
funding the development of such emission
control techniques.
  One of the major objectives of the
EPA's LIMB program is  to  assess the
impact of LIMB technology on utility boiler
design. This project develops boiler design
criteria for application of dry sorbent S02
control technology with Iow-N0x burners.
It consists of four major tasks:
  • A review of the dry sorbent injection
    technology data base.
  • Historical  and  projected design
    trends and the  implication of im-
    plementing the LIMB process.
  • Development of a selection rationale
    for candidate host sites.

in the 150-300 MW size range located I
within the 31-state region east  of  or
bordering the Mississippi River. Regula-
tory, technical, and economic issues have
been considered in developing the list.
  A generic process design is developed
for low NOX/SO2 control systems  using
dry sorbent injection for SO2 control on
wall-fired coal-fired steam generating
units. Second generation low-NOx  burn-
ers are utilized for NOX reductions. Two
major categories are considered:  those
for new unit designs, and those for retrofit
of existing  units. Additionally, both low
and high sulfur coals are utilized for the
new unit designs. In each of the  three
broad categories of units, three sizes are
considered, 200,400, and 600 MWe.
  The generic process designs  consider
various components and  systems from
sorbent delivery to  stack discharge and
ash/sorbent  collection  and  disposal.
Equipment specifications were developed
and, for  retrofit units,  necessary design
changes were incorporated into individual
  The report develops  capital cost esti-
mates for new 200, 400, and 600 MW
units burning  high  sulfur coal  and also
low sulfur coal. In  addition, retrofit re-
quirements are costed out for existing
units burning  high sulfur coal. Capital  '
cost estimates are also prepared for the
new,  high sulfur coal plants  with two
different SO2 control systems: one set of
plants had LIMB in combination with a
supplemental dry scrubber, and the other
had a wet limestone scrubber.
  Total plant costs  and differential cost
estimates are developed for the various
scenarios. Letters of inquiry were sent to
various vendors to secure budget esti-
mates for major balance of plant equip-
ment associated with  LIMB technology.
Boiler costs were supplied by Riley Stoker.
   The EPRI Economic Premises  dated
December 15,1982 are used for preparing
the costs reported  herein. The supple-
ment used for retrofit  of existing plants
was issued May 1, 1983. All estimates
were prepared to EPRI Class II tolerances,
representing a significant improvement
in the quality of the  figures over that
originally asked for  in the study.
   The high sulfur fuel used was Illinois
No. 6 coal. The low sulfur fuel was Gillette
Powder  River Basin coal. Limestone was
selected for the various analyses per-
formed.  Note  that,  since this study was
initiated,  the  focus  on  sorbents  has
shifted, and calcium hydroxide is currently
being favored. However, since this study
was  quite far  along, the  analyses were
  • Generation of a  generic  process
    design for both new and retrofit units,
    including capital and annualized cost
  The work was performed by Riley Stoker
Corporation  and  its  subcontractors.
Energy and  Environmental  Research
Corporation and Stone and Webster
Engineering Corporation.

  The  first portion  of  this project is a
review of the dry sorbent data base. It is
intended to provide background informa-
tion on dry sorbent SO2 control tech-
nology. It includes a review of past and
ongoing investigations from fundamental
SO2/CaO  reaction kinetics to full-scale
boiler demonstrations. The data are used
later in the project to  evaluate the im-
plications of LIMB technology on boiler
design, cost, effectiveness, and operability.
  Five areas are covered in the report:
  • A description of the LIMB process.
  • A review of parametric  studies of
    sorbent injection.
  • A review of past and planned boiler
  • A summary of known and expected
    impacts of LIMB on boiler operation,
    availability, and downstream equip-
    ment (e.g., electrostatic precipitator)
  • A review of possible combinations
    of LIMB with post-treatment systems.
  To aid in evaluating the design changes
or features necessary to  incorporate  dry
sorbent SO2  control  on  Riley Stoker
pulverized-coal-fired boilers, a  survey was
conducted, going  back  to  1957. This
survey is directed at wall-fired (single or
opposed) units but also included the Riley
Stoker  Turbo  Furnace pulverized-coal-
fired boiler population for informational
purposes. The  survey  focuses on  units
with capacities greater than 100 MW.
General design and operational param-
eters are compiled and curves plotted for
ease  in projecting design trends.  For
example,  furnace  geometry and heat
releases are shown with respect to time
period. By comparing to the entire wall-
fired  coal-fired boiler  population,  Riley
Stoker units are shown to be representa-
tive of the overall group of steam gen-
erating units.
  The use of dry sorbents to capture SO2
and its influence  on  power  plant per-
formance is contained  in the project
report.  Field trials,  pilot scale  results,
laboratory  tests,  engineering analyses,
and fundamental process information  are
used  to assess the potential problems
which might be caused by the use of dry
sorbents in power plants. Each component
of the  steam generator,  its auxiliaries,
and associated equipment is evaluated,
and  potential  problems  are  assessed.
Most often, use of dry sorbent injection
will not cause  any problems in power
plant operation; sometimes, minor prob-
lems are expected. Three potential prob-
lem areas have been identified:
  • The uncertainty of the influence of
    dry sorbent injection on slagging in
    the radiant furnace and fouling on
    the  convective  heat  recovery
  • Increased  problems  in  collecting
    flyash due to higher resistivities and
    increased dust loadings.
  • Disposal of flyash and dry sorbent
    wastes because  of  larger  (double)
    amounts of material and the lack of
    experience in handling waste which
    may undergo an exothermic reaction
    during water sluicing.
  The report, utilizing information devel-
oped earlier in the project, identifies  a
selection rationale which can be used in
determining an optimum host site. This
rationale is used to select potential host
sites for retrofit of LIMB technology in
order to provide  capital  and operating
costs in another area of the project. The
methodology selected can 'oe  used to
select an individual unit or a complete
utility power station. The report covers
three broad areas:
   • Description of the selection rationale
   • Retrofit application criteria.
   • Identification of candidate  units for
     application of LIMB technology.
   The methodology chosen is a decision
analysis type. Not all wall-fired coal-fired
units or stations are candidates for con-
version. Each should be evaluated on its
own merits and the potential risks con-
sidered before any decisions are made to
move ahead. In the selection  rationale
process, macro and micro views are con-
sidered. Objectives are listed and classi-
fied as essential or desirable and are not
necessarily limited to technical consider-
ations. Economics, space availability, and
sorbent type are equally strong factors.
Three  important  areas of  concern are:
operational features, retrofit  require-
ments, and being representative of cur-
rent design practice.
   The report identifies 42 units suitable
for further consideration for retrofit  of
LIMB S02/NOX control technology. The
units were selected from the population
of wall-fired pulverized coal utility boilers

 lone for  limestone. Major conclusions    Table 1.    Cost Comparisons
 are unchanged.
  In all of the case studies, the LIMB-
 only alternative  is  the  least  expensive
 regardless of size. LIMB-only is acceptable
 as an S02 control technology for retrofit
 applications.  New  units  require the
 combination of LIMB and a dry scrubber
 or the use of a wet scrubber to meet
 NSPS  requirements of 70-90%  SO2
Capital Costs

Level/zed Busbar Costs
Cost Per Ton of SO2
  Removed ($/ton)




Results and Discussion
  Two of the major precursors of acid
rain are NOX and S02. A major source of
these precursors is the combustion  of
coal, much of which takes place in utility
boilers for the generation  of electricity.
The incentives for developing new, simple,
cost effective control strategies to reduce
emissions are increasing  rapidly.  One
technology— limestone injection in con-
junction with multistage (Iow-N0x) burn-
ers — appears to be viable for both retrofit
and new unit designs.
  Combined with dry scrubber technology
in the back end, LIMB can meet or exceed
New  Source  Performance  Standards
(NSPS) criteria. In addition, LIMB-only or
LIMB in conjunction with back-end clean-
»up  is consistently under the cost of wet
flue gas desulfurization (FGD) systems as
noted in this report.  Cost comparisons
are made on the basis of capital invest-
ments (dollars per kilowatt based on a
January 1986 start-up), levelized busbar
power costs in mills  per kilowatt hour,
and the cost per ton  of S02 removed.
Three plant sizes are used in the com-
parison studies, 200,400, and 600 MWe.
Additionally,  LIMB-only,  LIMB  with a
supplemental dry scrubber,  and  a wet
scrubber system are compared on each
  Costs are  obtained  for the various
technologies from vendor quotations, and
estimates  are generated  based on an
EPRI Class II design  and cost estimate
classification. This puts the project con-
tingencies in the  15-30% range. The
vendor quotations are supplemented with
recent design studies and purchase costs
adjusted to the current cost index. Labor
is computed  based on labor/material
ratios for similar work and adjusted for
site conditions and expected average labor
  Table 1 represents the cost comparisons
arrived at in  the report. Only the 400
MWe plant size is used here for the sake
of brevity. Low sulfur coal is used for
LIMB-only with 70% SO2 removal, while
high sulfur coal with 90% S02 removal is
used for LIMB with a dry scrubber and
the wet FGD system.
  The  comparison shows LIMB-only to
be the  least costly alternative, although it
would  not meet present NSPS demands.
LIMB with a supplemental dry scrubber
can  meet the criteria in a cost effective

  Based  on the  work accomplished  in
this  project, LIMB with a supplemental
dry scrubber is cost effective and viable
(able to meet NSPS requirements) for the
reduction of the major acid rain precur-
sors, NOX and S02. On a dollars per ton of
S02  removed basis, LIMB with a supple-
mental dry scrubber is approximately 80%
the cost of a wet FGD system regardless
of whether the plant size is 200, 400, or
600 MW. The cost per ton of SO2 removed
is made up of fixed operating costs, capital
costs, variable operating costs, and con-
sumables cost.
  The report shows that, on the basis of
the extensive studies  performed,  LIMB
should  be a major consideration  for
utilities when reductions in NOX and/or
S02  are  necessary. Demonstrations, in-
cluding  and  in  addition to  the EPA
sponsored project at Ohio Edison's Edge-
water  plant,  would not  only  provide
proof-of-concept, but confirm capital and
operating cost levels for the technology.
  ft. K. Mongeon is with Riley Stoker Corporation, Worcester, MA 01610.
  David G. Lachapelle is the EPA Project Officer (see below).
  The complete report, entitled "Wall-Fired Boiler Design Criteria for Dry Sorbent
    SO2 Control with Low-NO* Burners."  (Order No. PB 88-113 485/AS; Cost:
    $38.95, 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

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