United States
Environmental Protection
Agency
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
process.
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).
Introduction
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.
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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
components.
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
estimates.
The work was performed by Riley Stoker
Corporation and its subcontractors.
Energy and Environmental Research
Corporation and Stone and Webster
Engineering Corporation.
Procedure
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
demonstrations.
A summary of known and expected
impacts of LIMB on boiler operation,
availability, and downstream equip-
ment (e.g., electrostatic precipitator)
performance.
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
surfaces.
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
method.
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
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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
removal.
LIMB-
Only
LIMB
W/DS
WET
FGD
Capital Costs
($/kW)
Level/zed Busbar Costs
(mills/kW-hr)
Cost Per Ton of SO2
Removed ($/ton)
49
20
860
178
27
910
274
33
1110
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
analysis.
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
rates.
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
manner.
Conclusions
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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