United States
Environmental Protection
Agency
Air and Energy
Engineering Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-90/020 Jan. 1991
EPA Project Summary
LIMB Process Development
Studies
J. P. Gooch, G. H. Merchant, Jr., M. G. Faulkner,
E. B. Dismukes, and R. S. Dahlin
The report gives results of a 4-year
investigation of various aspects of
EPA's Limestone Injection Multistage
Burner (LIMB) technology. The investi-
gation, closely related to the demon-
stration planned and then undertaken
at Ohio Edison's Edgewater power plant,
concerned avoiding electrostatic pra-
cipitator (ESP) performance degrada-
tion, enhancing SO2 removal, and man-
aging wastes.
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 prefect that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering Infor-
mation at back).
Introduction
The technology known as LIMB (Lime-
stone Injection Multistage Burners) has
been under development by EPA for sev-
eral years as a means of retrofitting older
utility boilers to obtain lower emissions of
acidic gases that are precursors of acid
rain. There is concern with both nitrogen
oxides (NOX) and sulfur dioxide (SO2).
Multiple-stage burners offer a method for
towering NOX emissions; and limestone in-
jection in the boiler provides a means for
decreasing SO2 emissions.
Limestone is one of the calcium-based
sorbents that may be injected into a boiler
at high temperatures, above 1205°C, to
achieve partial removal of SO2. Hydrated
lime or CA(OH)2, another suitable sorbent,
is receiving most of the attention in current
developmental work. For example, hydrated
lime was the sorbent of choice in EPA's
recent demonstration of LIMB technology
at Ohio Edison's Edgewater power plant at
Lorain, OH. In that demonstration the in-
jection of hydrated lime in the boiler was
coupled with downstream humid'rfication
and cooling of the gas stream, which served
two purposes: 1) improving the collection
efficiency of suspended particulate matter
in the ESP, and 2) enhancing the removal
of SO2 by the sorbent. In that demonstra-
tion, furthermore, the supplemental injec-
tion of a hydrous calcium silicate down-
stream from the humidifier—a sorbent-in-
jection process known as the advanced
silicate (ADVACATE) process—was
evaluated briefly as a measure for further
enhancing the removal of SO2.
Scope of This Investigation
This research was a combination of
basic and applied studies in support of the
Edgewater demonstration. Studies in both
areas were concerned with three primary
aspects of LIMB process development: 1)
avoiding a degradation in the collection
efficiency of suspended matter in an ESP,
2) achieving a satisfactory degree of SO2
removal, and 3) finding satisfactory meth-
ods of disposing of LIMB wastes. The pro-
gram was organized under four tasks:
1. Studies of electrostatic precipitation.
These studies included a) experi-
mental work with a small ESP at-
tached to Southern Research's pilot-
scale combustor, b) tests of the full-
scale ESP operating at the Edgewater
demonstration site, and c) theoretical
work to revise an existing math-
ematical model of ESP.
2. Studies of flue gas humidification for
enhanced SO2 removal. This task in-
cluded experimental work both in the
laboratory and in the pilot-scale com-
bustor. It also included theoretical
work to develop a model of spray
humidification.
3. Analysis of LIMB waste management
options. This task consisted of labo-
ratory measurement of properties of
LIMB waste collected at the
Edgewater demonstration site.
4. Evaluation of the-ADVACATE pro-
cess for SO2 removal at low tem-
perature. This task was performed at
the Edgewater demonstration site
with a pilot-scale facility provided by
EPA.
Printed on Recycled Paper
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Conclusions
Studies of ESP. The use of the LIMB
process without humidificatipn causes an
unacceptable deterioration in the perfor-
mance of an ESP. At the Edgewater dem-
onstration, the deterioration was substan-
tial, even though the ESP is a large mod-
ern unit. At many other power plants where
the LIMB process may be adopted, the
ESPs are undersized and will be even
more adversely affected.
The use of spray humidification at
Edgewater, however, successfully over-
came the first adverse impact of LIMB. A
very limited degree of humidificatipn and
cooling allowed clear-stack conditions to
be regained. The extent of humidification
and cooling that is needed to achieve very
successful ESP operation, is^much Jess
than had been predicted from earlier labo-
ratory work, largely because of the unreli-
able estimation of the effects of added
water vapor and reduced temperature on
the electrical resistivity of the suspended
partbulate matter.
The use of water vapor for conditioning
LIMB ash seems less likely than SO3l an
alternative conditioning agent, to cause
difficulties In electrode rapping to clean
ESP collecting electrodes.
A revision of the previously developed
ESP model should improve the ability of
the model to predict ESP performance un-
der some of the limitations imposed by
LIMB, such as high mass loadings and low
current densities. Thus far, however, the
success of the model in these applications
has not been adequately tested. A simpli-
fied data entry routine will eliminate one of
the major sources of error in the use of the
model.
Studies of enhanced SO2 capture by flue
gas humidification. The principal conclu-
sions from the investigation in this area
are:
• Insofar as enhancement of SO2 cap-
ture at the Edgewater demonstration
of LIMB is concerned, humidification
^ bya watejvspjay wasjequired.
~"«~ ^Charge-augmented sorBenthumidifi-
cation (CASH)—entailing the charg-
ing of sorbent particles and water
droplets negatively and positively,
respectively—appears unlikely to
enhance sorbent reaction with SO2
under post-furnace conditions.
• So-called deliquescent additives that
are known to enhance SO2 capture by
Ca(OH)2 under low-temperature con-
ditions clearly must operate to some
extent by mechanisms other than
deliquescence per se.
The mathematical model gives an
improved appreciation of factors that
are critical to SO2 capture by Ca(OH)2
when the sorbent particles are sub-
ject to wetting. The model gives an
improved rational basis for upgrad-
ing the performance of duct pro-
cesses for SO2 removal.
Analysis of waste management options.
The properties of LIMB waste from
Edgewater are similar to those of simu-
lated LIMB waste from a pilot-scale com-
bustor. The data appear to confirm the
acceptability of disposal in a landfill. The
main concern is the need for treatment of
high alkalinity.
_Jnyestigatipn of the ADVACATE pro-
cess. TheA"D?A"CATE^rocess offers thlT
potential for greatly enhancing the removal
of SO2 that is accomplished with LIMB.,It
does so, however, with a substantially in-
creased concentration of entrained solids.
The ADVACATE process affords no mea-
surable removal of NOX. At the same time,
however, it causes no problem from a
change in the electrical resistivity of the
entrained solids.
J.P. Gooch, G.H. Marchant, Jr., M.G. Faulkner, E.B. Dismukes, and R.S. Dahlin are with Southern Research Institute, Birming-
ham, AL 35255-5305.
Louts H. Hovte is the EPA Project Officer (see below).
The complete report, entitled "LIMB Process Development Studies," (Order No. PB91-127688/AS; Cost: $17.00, subject to
change) wilt 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
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S7-90/020
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