United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-86/036 Feb. 1987
&EPA Project Summary
EPA LIMB Development and
Demonstration Program
Status Report (April 1985)
G. Blair Martin
This report summarizes the technical
status of the Limestone Injection Multi-
stage Burner (LIMB) program and dis-
cusses the planned program leading to
commercialization by 1990. It provides
a background on the emissions of SO2
and NOX from coal-fired utility boilers
and a discussion of critical aspects of
the LIMB process. It also provides an
overview of the LIMB process and the
program approach, followed by a de-
tailed discussion of results and plans
for each major technical area of the pro-
gram.
The goal of the LIMB program is to
provide a low cost technology for con-
trol of SO2 and NOX for coal-fired boil-
ers. In the U.S. the dominant source of
SO2 is existing coal-fired utility boilers,
which also contribute about 20 percent
of the total NOX emissions. Although
there are existing technologies for con-
trol of SO2, there are advantages to
emerging technologies which can be
retrofitted at a reasonable cost and
achieve at least 50 percent control of
both SO2 and NOX. LIMB is one emerg-
ing technology which has the potential
to accomplish this goal in a more cost
effective manner than currently com-
mercial technologies.
The LIMB program, which grew out
of EPA's work on low-NOx burner de-
velopment, was initiated in 1981. EPA
has provided substantial funding for
the basic technology development and
scaleup. In addition, as the technology
was developed, resources were made
available to accelerate the availability
of LIMB for widespread private sector
commercialization.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle 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 or-
dering information at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) is developing Limestone
Injection Multistage Burners (LIMB) as a
potentially low cost control technology
for sulfur dioxide (S02) and nitrogen
oxides (NOX). The LIMB program is
structured to provide an understanding
of the controlling factors in the process
and to establish a basis for private sec-
tor commercialization. The program has
received funding since 1981. Congress
increased FY 84 and FY 85 funding by $5
million and $6.5 million, respectively.
S02 and NOX are two major pollutants
resulting from the combustion of fossil
fuels. Coal-fired utility boilers account
for about 75 percent of the S02 and 20
percent of the NOX emissions in the
United States. For the 180,000 MW of
coal-fired boiler capacity east of the
Mississippi River, this amounts to ap-
proximately 16.5 million tons* of SO2
and 4 million tons of NOX emitted per
year. Only about 10 percent of these
boilers are subject to New Source Per-
formance Standards (NSPS) controls
for S02 and NOX. The other 90 percent
of these existing boilers have a remain-
ing useful life of up to 30 years. The vast
majority of these are wall-fired and tan-
gentially fired boilers.
*For those more familiar with metric units, see con-
versions at the end of Project Summary.
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The seriousness of the acid rain prob-
lem and the importance of various acid
precursor sources are still being de-
bated; however, control of S02 from
utility boilers is a major element in all
proposed strategies. In addition NOX
has been associated with forest damage
mechanisms. Proposed reductions of
SO; range from 5 to 12 million tons per
year, and the issue of an NOX offset is
being debated.
Control Technology Options
The choice of S02 and/or NOX control
strategies will have a significant effect
not only on the ability to achieve any
mandated reduction but also on its cost
to the nation. The final decision on the
technology mix will be based on the
availability, specific performance, cost,
and overall economic impact on the na-
tion, including socioeconomic factors
such as displacement in the work force.
The control technology options com-
mercially available are coal switching,
coal cleaning, and various types of flue
gas desulfurization (FGD) systems. In
addition, some early analyses have indi-
cated that a low capital cost technology
would be attractive even at moderate
S02 removal (e.g., 50 percent control).
Although several approaches are being
developed, none of the potential low
cost alternatives have been demon-
strated. One such rapidly emerging
technology, based on injection of sor-
bents (i.e., limestone and other alkaline
solids) into the boiler for direct capture
of S02 from the combustion gases, is
LIMB.
LIMB Program Structure
There is a considerable body of back-
ground information on sulfur capture
by injection of sorbents into a conven-
tional boiler. The information includes
the experience in the U.S. with sorbent
injection through a number of boilers in
the late 1960's and early 1970's, some
current experience in Germany on both
brown coal boilers and other small-
scale experimental facilities, and EPA
testing using the distributed mixing
Iow-N0x burner with sorbent injection
in a pilot-scale facility.
This background information was
used in structuring the LIMB program
which was initiated by the EPA in 1981.
LIMB combines sorbent injection for
S02 control with Iow-N0x burners for
NOX control. Low-NOx burners of vari-
ous designs have been developed by
both EPA and private industry and are
suitable for retrofit applications. S02
control by sorbent injection is an
emerging technology which has been
developed by the EPA. The reaction of
S02 with sorbents (i.e., limestone and
other alkaline solids) is well known
under proper conditions (e.g., wet FGD).
LIMB is based on injection of a sorbent
directly into the furnace and its subse-
quent reaction with gas-phase S02 to
form a dry calcium sulfate. The amount
of S02 that can be captured is depend-
ent on the type and amount of sorbent,
sorbent injection method and its mixing
with combustion gases and fly ash in
the furnace, and the time/temperature
profile in the boiler. The relative simplic-
ity of the technology lends itself to a
relatively low cost retrofit on a wide va-
riety of systems. The program has been
structured to give the best probability of
achieving the stated goals of moderate
(50-60 percent) S02 and NOX control at
low cost, with applicability to the major
portion of the existing boiler popula-
tion. A secondary objective is to im-
prove the SO2 removal efficiency to 70-
90 percent for new sources. To achieve
this, work has concentrated in four
major areas:
Generic R&D
The program is centered around
generic R&D to provide a complete un-
derstanding of the important factors in
sulfur capture by sorbents. This work is
performed in experimental systems
which simulate conditions in a boiler
without being subject to hardware con-
straints.
Wall-Fired Boiler Technology
The wall-fired boiler, one of the two
major types of boilers, has been the
subject of initial LIMB development be-
cause both the R&D background and
large-scale experimental facilities were
available. This area includes prototype
burner testing for process scaleup and a
full scale demonstration.
Tangentially Fired Boiler
Technology
Tangentially fired boilers are the
other major boiler type. Due to firing
system differences the gas flow and
thermal conditions are different than
wall-fired boilers. Work is concentrated
in prototype system testing for applica-
tion of generic R&D results.
Technology Generalization
To be widely accepted, a well defined
set of criteria for application of LIMB to
a wide range of boiler designs, coals,
and sorbents is necessary. A limite
number of demonstrations alone ma.
not be sufficient for widespread privat.
sector commercialization. A key ele-
ment of the overall program is to pro-
duce the required confidence in the in-
formation and methodologies for
applying LIMB R&D to site-specific
design decisions for any given boiler.
This will be accomplished by a combi-
nation of models of critical elements of
the process and supporting measure-
ments on operating boilers to verify
those models. The generalization effort
will also evaluate the operational im-
pacts of LIMB and provide information
to assess its role in overall national acid
precursor control strategies.
Technical Status
This section provides a brief sum-
mary of the overall technical status for
each of the four major program areas
discussed above. Technical details and
plans for each area are presented in a
later section.
Generic R&D
The LIMB program has been based on
the premise that a complete under-
standing of the process is necessary to
give the maximum probability of suc-
cessful commercialization by the pri-
vate sector. Generic R&D is relatively in-
dependent of the hardware-specific
constraints of practical boilers and pro-
vides information essential for applica-
tion of LIMB to all boiler designs.
The R&D has provided an excellent
insight on the effects of critical process
parameters on SO2 capture. It has
shown how these parameters affect sor-
bent activation and subsequent sulfur
capture as a function of combustion
system conditions. It has also provided
an understanding of fly ash/sorbent
mixture characteristics as related to
slagging, fouling, and particulate cap-
ture. As a result of these findings, it has
been concluded that limestone alone
will not achieve the LIMB sulfur capture
goals for many units in the U.S. boiler
population. To address the problem we
are developing at least two alternate
sorbent approaches that appear capa
ble of meeting or substantially exceed
ing the goal of 50-60 percent capture
however, before these sorbents can b<
used, a more complete characterizatior
of this activity (as a function of type am
preparation) is necessary. The researcl
is performed in a coordinated effort in
volving both in-house and extramura
investigators.
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In-house research has identified the
jse of high surface area sorbents as a
key factor in obtaining high sulfur cap-
ture. ("High surface area" as used in
this context refers not only to the exter-
nal surface of the particles but also to
the internal surfaces which occur in the
form of porosity.) It has been shown
that high surface area can be generated
external to the combustion process and/
or in-situ. These materials, which are
processed limestone (e.g., hydrates),
have shown the potential for sulfur cap-
ture in excess of 70 percent. The
planned extramural R&D addresses
methods for obtaining highly reactive
sorbents, for optimizing reaction condi-
tions to achieve maximum capture, and
for minimizing sorbent costs.
Another key factor is the interaction of.
sorbents with mineral matter which can
either enhance or degrade the sorbent
reactivity. The most promising results
indicate that it may be possible to add
small amounts of relatively inexpen-
sive, innocuous promoters (mineral
compounds) which will enhance sor-
bent activity. Sulfur captures approach-
ing those of high surface area sorbents
have been achieved with promoted
limestone in limited bench scale experi-
ments. It also appears that promoters
can significantly improve the perform-
ance of high surface area sorbents (e.g.,
hydrates). A significant portion of the
research effort is devoted to develop an
understanding of the enhancement
mechanisms and to provide the basis
for use in practical systems. Note that a
similar understanding is necessary for
other sorbent/mineral matter interac-
tions which can inhibit sulfur capture
and which affect slagging, fouling, and
collection characteristics of the particu-
late,,... n., ,., ...
Wall-Fired Boiler Technology
Extensive prototype testing of wall-
fired boiler low-NOx burners has been
conducted to evaluate sulfur capture
potential with injection of conventional
sorbents. A substantial data base exists
for both NOX and S02 control potential
of a number of experimental and com-
mercial burners. Additional work will
support site-specific decisions for the
wall-fired demonstration and to evalu-
ate improved sorbent performance.
The demonstration of LIMB was ini-
tiated in 1984, and funding was com-
pleted in FY 85. The contract for the
wall-fired demonstration, which is co-
funded by the State of Ohio and by Bab-
cock & Wilcox (B&W), was awarded in
September 1984 to B&W. LIMB will be
installed on a 105 MW single-wall-fired
unit at the Edgewater station of Ohio
Edison Company. The final site-specific
design for the installation was com-
pleted in February 1986. Long-term test-
ing over a 1-year period will begin in
July 1987, and a report documenting
the design approach and performance
evaluation is scheduled for completion
in early 1989.
Tangentially Fired Boiler
Technology
Small pilot-scale R&D has been con-
ducted for tangentially fired systems
with sorbent injection. Since technol-
ogy must be scaled up to provide guid-
ance for commercialization, prototype
work will be initiated in a large-scale ex-
perimental facility with a firing system
producing a vortex flow field typical of
that boiler class. In addition, an EPA/in-
dustry cooperative testing R&D pro-
gram will be conducted on a small
boiler (20-40 MW) to evaluate sulfur
capture potential, operability, and reli-
ability over short periods, with the abil-
ity to evaluate different fuels and sor-
bents. The prototype work will
concentrate on evaluation of optimum
sorbents and injection methods to max-
imize S02 capture.
Technology Generalization
For widespread use of the LIMB tech-
nology, the R&D results must be inte-
grated with the full-scale boiler demon-
stration results to provide guidance for
commercialization by the private sector.
The program includes: 1) process anal-
ysis to evaluate applicability and eco-
nomics for specific systems; and
2). process modeling to provide a
methodology useful for site-specific de-
signs. The process analysis emphasizes
LIMB system options for application to
different boiler classes in the population
and for minimizing the cost per unit S02
removal. The process modeling will
provide component models for thermal
history, sorbent activation and reaction,
injection, and mixing. The models will
be validated against measurements
taken on actual boilers, both with and
without sorbent injection.
The role of LIMB in any national acid
precursor strategy will be dependent on
S02/NOX control performance and cost
as compared to other technologies. The
process models will be used to evaluate
the applicability of LIMB based on fac-
tors such as: boiler design and size, re-
maining useful life, load factor, coal sul-
fur, and site-specific considerations.
Since acceptance by the utility indus-
try is necessary to achieve widespread
private sector commercialization of
LIMB, the EPA and the Electric Power
Research Institute (EPRI) have instituted
periodic technical information ex-
changes on R&D projects. In addition,
two EPA/EPRI co-sponsored sympo-
siums have been held where LIMB re-
lated R&D papers have been presented.
Conclusion
The LIMB R&D program has provided
a detailed understanding of the key
processes governing sulfur capture
with sorbents. While it appears that
limestone alone will not achieve pro-
gram goals, several other promising
sorbents have been identified. Based on
the R&D results and cost estimates of
the use of these sorbents, LIMB shows
substantial promise as a S02 and NOX
control technology for retrofit applica-
tions, as compared to the capital and
cost per ton of SOa removed for conven-
tional flue gas desulfurization. The on-
going R&D program should resolve the
remaining technical questions and pro-
vide a basis for widespread private sec-
tor commercialization. The demonstra-
tion at Edgewater will be a major factor
in accelerated commercialization of
LIMB and acceptance by the industry for
wall-fired boilers.
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The EPA author G. B. Martin is with the Air and Energy Engineering Research
Laboratory, Research Triangle Park, NC 27711.
P. Jeff Chappel is the EPA Project Officer (see below).
The complete report, entitled "EPA LIMB Development and Demonstration
Program Status Report (April 1985)," (Order No. PB 87-119 343/AS; Cost:
$11.95, 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
Official-Business
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