United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 2771
Research and Development
EPA/600/S7-88/004 June 1988
&EPA. Project Summary
U.S./German LIMB Technology
Transfer
J.L. Reese, R. Payne, and Y. Chughtai
This report presents key findings
of a program in which the U.S. EPA
participated in a program sponsored
by the Umweltbundesamt (UBA), the
German equivalent of the EPA. The
UBA program included retrofitting the
700 MWe Weiher III utility boiler of
the Saarbergwerke AG with staged-
mixing burners for NOx control, and
sorbent injection for SOx control.
This program was considerably re-
duced in scope because of
restrictions placed upon the utility by
local environmental officials con-
cerning the classification of the fly
ash generated in the process. During
the limited testing period, S<>2
emissions were reduced 8 to 64%
depending on Ca/S molar ratio and
other operating conditions. The
program originally planned at Weiher
was ultimately conducted at the 48
MWe Tiefstack Unit 6 of Hamburgishe
Elektrizitats-Werke AG. Moderate
levels of SOa control were achieved
(22% with limestone, and 43% with
calcium hydroxide). An analysis of
the test results suggests that the use
of more reactive sorbents could
increase the SO2 removals to 30%
and 60% at a Ca/S ratio of 2, for
limestone and calcium hydroxide,
respectively.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to an-
nounce 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
Control of SOX emissions by dry
sorbent injection into boiler furnaces was
extensively explored in the U.S. during
the late 1960's and early 1970's with
limited success. Typically, SOX removal
efficiencies of 18 to 40% were achieved
for a variety of boilers over a wide range
of calcium-to-sulfur (Ca/S) molar
ratios. At economic Ca/S ratios of 1.3 to
2.0, sulfur capture was typically 20 to
33% respectively. These lower (than
expected) removals were attributed to:
deadburning of sorbent, and decom-
position of the resultant calcium-sulfur
complex at high temperatures, and;
inadequate mixing (contacting) of the
sorbent with the combustion gases
These results were not competitive with
the high (80 to 90%) SOX removal
efficiencies of wet scrubbers. Conse-
quently, further work with dry sorbents
was abandoned around 1973.
More recently, attention refocused on
dry sorbent SOX control, prompted by: (1)
a reexamination of reaction chemistry
that indicated differences from what was
previously accepted; (2) new combustion
conditions and mixing patterns that
appeared to favor sorbent injection in a
manner different than previously
employed; (3) a need for low-cost NOX
and SOX controls to support acid rain
control strategies, and; (4) pilot-scale
tests that showed improved SOX capture
with more reactive sorbents. The EPA
acronym for this low-NOx/SOx approach
is LIMB (Limestone Injection Multistage
Burner). EPA-sponsored development
programs were underway, and at the time
of this project, significant work was in
progress in the Federal Republic of
Germany.
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In this project, the U.S. EPA
participated in a program sponsored by
the Umweltbundesamt (UBA), the
German equivalent of the EPA. The
scope of the UBA program included
retrofitting the 700 MWe Weiher III utility
boiler of the Saarbergwerke AG with
staged-mixing burners for NOX control,
and sorbent injection for SOX control.
The retrofit was performed by L&C
Steinmuller GmbH, a major German
boiler manufacturer. The program was to
be the first full-scale evaluation of LIMB
technology and presented a unique
opportunity for EPA to participate in the
program at relatively modest cost. All
data developed in the program would be
shared between the Federal Republic of
Germany and the United States. EPA's
participation was essentially concerned
with emissions monitoring and charac-
terization of particulate, slagging and
fouling, and determination of gas and
particle temperatures which are critical
parameters to the successful application
of LIMB technology. Additionally, this
program would augment on-going
EPA-sponsored development programs
and design criteria studies, and provide
an essential link between EPA pilot-
and prototype-scale data and full-
scale data in the U.S.-sponsored LIMB
development effort. Testing at Weiher III
was limited to about 3 days of actual
testing, due primarily to severe restric-
tions by local (German) environmental
officials regarding disposition of the
modified fly ash, and the boiler owner's
concerns about deposits in the
electrostatic precipitator (ESP). As a
consequence, the planned measure-
ment program for EPA was later
performed at the Tiefstack Boiler 6 of
Hamburgishe Elektrizitats-Werke.
Summary of Sorbent Injection
Tests at Weiher III
Weiher III is a 700 MWe coal-fired
unit operated by the German utility
Hamburgishe Elektrizitats-Werke AG
(HEW). The furnace has two combustion
chambers and 24 staged-mixing
burners. Twelve burners each are
installed in the front and rear walls in
three elevations by four burners
horizontally. Groups of four burners are
each served by one mill, and are
supplied with sorbent through an
injection system. Sorbent is transported
by compressed air.
The results of tests with two burners
in 1982 were good enough to
recommend equipping all 24 burners of
the boiler with sorbent injection. These
tests were started after considerable
delay, due mainly to the classification of
the fly ash as "hazardous waste" by the
Landesamt fur Umweltschutz und Was-
serwirtschaft - LFU (Office for Envi-
ronmental Protection).
The baseline tests without sorbent
injection were performed in August 1984,
to collect data on naturally occurring
sulfur capture (due to alkaline material in
the coal ash), ash characteristics, and
process data for the boiler, air heater,
and ESP.
The originally planned program of
sorbent injection tests had to be
considerably reduced due to the
restrictions imposed relative to ash
disposal. Abbreviated tests were planned
with CaCC>3 and Ca(OH)2 at different
boiler loads, Ca/S molar ratios, and
injection planes. These tests were
scheduled to take 3 days for each
additive.
After receipt of official approval to
conduct the sorbent injection tests in
November 1984, the tests were
immediately started. The first sorbent
used was pulverized limestone. It was
observed during the course of these
tests that the 4:1 molar ratio required at
full boiler load could not be attained. The
problem appeared to be related to the
ejector design. A maximum flow
corresponding to a Ca/S of 2.5 was
achievable. However, when the six
injection lines were run in parallel for
continuous feed to all burners, the
maximum possible limestone flow was
found to be equivalent to a Ca/S molar
ratio of about only 1.4. Full load tests
with sorbent to all burners were
conducted at molar ratios between 0.5
and 1.4. Due to the reduced rate, there
was a wide variation in SOa capture
results. Those obtained indicated only a
general trend. Calcium utilization
decreased with increasing molar ratio
and was on the order of 10 to 20%.
Typical SC-2 captures at full load were in
the range of only 8 to 12%, at Ca/S ratios
of 0.7 and 1.4 respectively. Limited tests
were run at 60% load, and Ca/S ratios of
2.5 and 4.0 were achievable. An
improvement in both calcium utilization
and SO2 capture was observed. At Ca/S
of 2.5, the calcium utilization was 11%
with an S02 capture of about 28%. At
Ca/S of 4, the calcium utilization was
16%, with an SC>2 capture of 64%. No
effects attributable to variation on the
injection point (upper or lower burner
plane) on the calcium utilization could be
ascertained.
After completion of the 3-day tests
with limestone, the ESP was inspected.
Heavier than normal dust deposits were
found on the discharge electrodes an
plates in the middle and the final cleanin.
zones of the ESP. These deposits wel
sticky, and had a high fines content; i.e
66% of the material was smaller than 81
The material also had high sulfur conten
The deposits could not be remove
through normal blowing and rapping. Th
higher fouling tendency in the middle an
final ESP stages was attributed to th
higher fines content in these stage
resulting from sorbent injection. Thi
higher dust loading, and the increase i
fly ash resistivity, produced a higher loa
on the middle and final ESP stages.
The propagation of deposits on th
ESP surfaces, which could not b
removed by normal means, was a ke
factor in the boiler owner's decision I
discontinue further sorbent injectic
tests.
The Weiher III operating staff hav
meanwhile made several efforts to clee
the ESP By switching off paths in tr
preliminary and middle ESP stages, the
have reduced deposits in the final stac
areas. A recent inspection of the ES
surfaces has shown that there are r
deposits left.
The measurement program for EP
that was originally scheduled for tr
Weiher power station was later performe
at the HEW Tiefstack power static
during November and December 1985.
Summary of Sorbent Injection
Tests at Tiefstack
A temporary injection system w<
installed by HEW on Boiler 6 to evalua
the process. The application of sorbe
injection to Boiler 6 was evaluated by tl
Energy and Environmental Resean
Corporation (EER) as a subcontractor
L&C Steinmuller, GmbH, for the U.
EPA. The evaluation involved fie
measurements at Tiefstack durir
injection tests and the use of models
the sulfation process to aid in tl
interpretation of the test results. Tl
objectives of the program were to use tl
field test results to directly evaluate tl
effects of sorbent injection on S(
emissions and boiler performance,
evaluate the valididty of the proce
models, and to use the models to ident
optimum injection paramenters ai
estimated maximum SC>2 reductions.
The boiler evaluated in the progra
Tiefstack Unit 6, was constructed in 19
by Durr Werke AG. The boiler
tangentially fired with low-sulfur bil
minous coal. The steam flow co
figuration is once-through, with t
steam used for electrical generation a
district heating. The maximum rat
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flow is 160,000 kg/hr (352,000
r) at 783K (950 °F) and 14,000 kPa
psig).
The temporary sorbent injection
system was installed and operated by
the HEW utility. Sorbent was fed from
pneumatic trucks to a small feed hopper
inside the boiler house, and then fed into
a pneumatic transport line with a rotary
feeder and ejector. Air for transport and
injection was supplied by a rotary air
blower. Injection velocity was varied by
changing the transport air flow rate, or by
varying the nozzle diameter. Due to
limitations of the injection system design,
and the use of existing observation ports,
sorbent was injected through only one or
two nozzles using available ports on the
boiler. Injection parameters varied during
the test were: (1) number of nozzles (one
or two), (2) injection velocity, (3) boiler
load, and (4) sorbent type (limestone or
hydrated lime).
Reductions of SC>2 obtained during
the field test were somewhat lower than
anticipated, based on the low quench
rate of the boiler. Field measurements
confirmed that the injection temperature
was near optimum. Subsequent eval-
uations therefore focused on the
dispersion of the sorbent and sorbent
reactivity.
The results indicate SC>2 removal
rates of 22% and 43% at a Ca/S ratio of
2, with high calcium limestone and a
calcitic atmospheric hydrate, respec-
tively. In view of the apparently low
quench rate on this unit, these results
were considered to be somewhat
disappointing. However, evaluation of the
data suggests that the results are, in fact,
consistent with bench-scale data and
with current understanding of process
controlling parameters. Temperature
measurement on the boiler, supported by
heat transfer modeling, confirmed a
quench rate of approximately 140K/sec
(250°F/sec), and a temperature at the
sorbent injection elevation of 1520K
(2280°F), which is considered to be
close to optimum. Also, contrary to initial
expectations, sorbent/flue gas mixing
with one and two nozzles had little
impact on SC>2 removal rates. The boiler
data were found to be relatively
insensitive to variations in injection
parameters. Additionally, small-scale
isothermal model tests indicated
adequate sorbent dispersion for all
configurations studied. Bench-scale
sorbent testing under comparable
conditions of injection temperature and
quench rate yielded SOa capture data
close to those obtained on the boiler.
These data indicate also that the
reactivity of the test sorbents is low
compared to other similar commercially
available materials. The use of alternate
sorbents could be expected to increase
SC>2 removal at Tiefstack to approx-
imately 30% and 60% at a Ca/S ratio of
2, for limestone and calcitic atmospheric
hydrate, respectively
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J. Reese and R. Payne are with Energy and Environmental Research Corp.,
Irvine, CA 92718, and Y. Chughtai is with L & C Steinmuller GmbH,
Federal Republic of Germany.
David G. Lachapelle is the EPA Project Officer (see below).
The complete report, entitled "U.SJGerman LIMB Transfer Technology," (Order
No. PB 88-195 6801 AS; Cost: $12.95, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
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, NC27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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