United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-065 July 1984
Project Summary
Results of the First 2 Years of
Commercial Operation of an
Organic-Acid-Enhanced FGD
System
R. L Glover, G. E. Brown, J. C. Dickerman, and O. W. Hargrove
The U.S. EPA has sponsored research
to develop organic-acid-enhanced flue
gas desulfurization (FGD) technology
for existing and new coal burning facil-
ities. A 1981 EPA-sponsored demon-
stration program at Springfield City
Utilities' Southwest Power Plant
(SWPP), near Springfield, MO, showed
that adipic acid and dibasic acid (DBA)
greatly enhanced FGD performance.
SWPP has continued to use DBA to
comply with the 1971 SO2 emissions
standard under which they are regulat-
ed. Thus. SWPP became the first
commercial-scale system to use an
organic additive to enhance SO2 remov-
al.
This report documents the first 2
years (1982 and 1983) of commercial
operation of the DBA system at SWPP.
During 1982 and 1983, SWPP aver-
aged an SO2 emission rate of less than
1.0 Ib SO2/106 Btu. Conversely, in
1980 (prior to DBA addition), SWPP
averaged about 5 Ib SO2/106 Btu. FGD
system reliability was also greatly im-
proved, averaging 97.9 percent in 1982
and 98.7 percent in 1983, compared to
45 percent in 1980. The SO2/O2 con-
tinuous emissions monitoring system
also exhibited excellent reliability, ex-
ceeding 97 percent. Overall, DBA has
increased the flexibility of the SWPP
system and, most importantly, allowed
SWPP to operate in compliance.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search 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 infor-
mation at back).
Introduction
EPA's Industrial Environmental Re-
search Laboratory at Research Triangle
Park (IERL-RTP) has an ongoing research
and development program to improve the
performance of lime/limestone flue gas
desulfurization (FGD) systems. One of the
most promising aspects of that effort has
been the use of organic acids as buffering
agents to increase soluble alkalinity in
limestone FGD systems. Adipic acid was
identified as a suitable additive because
of physical properties, availability, and
cost. After extensive laboratory-, pilot-,
and prototype-scale studies on adipic-
acid-enhanced limestone systems, EPA,
in 1981, sponsored a full-scale demon-
stration at SWPP.
Nine months of testing was conducted
at SWPP. Four months were spent at the
beginning of the program investigating
adipic acid addition in a forced oxidation
system. Better than 90 percent SO2
removal was achieved in a 49-day run,
the longest continuous operating period
at SWPP at that time. Next, adipic acid
addition achieved 85 - 95 percent SO2
removal in a natural oxidation system
over a period of 3-1/2 months.
Finally, a mixture of organic dibasic
acids (DBA) was tested over a 6-week
period following the adipic acid testing.
DBA, a by-product of adipic acid manu-
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vx
facturing, contains adipic, glutaric, and
succinic acids, and is less expensive than
adipic acid. Testi ng at SWPP showed DBA
to be very effective in enhancing FGD
system performance, resulting in a signif-
icant decrease in SO2 emissions.
An analysis was then performed to
determine the most cost-effective option
which would enable SWPP to comply
with the 1971 SO2 emissions standard.
Options considered included increasing
the slurry rate to the scrubbers, convert-
ing the scrubbers to spray towers, adipic
acid enhancement, and DBA addition.
Lower costs associated with the DBA
option, as well as its demonstrated effec-
tiveness, led SWPP to select DBA for
long-term use. In doing so, SWPP became
the first commercial-scale facility to utilize
DBA in an FGD system application. This
report documents commercial operation
of SWPP's DBA system, between January
1982 and December 1983.
Program Objectives
Since operation at SWPP represents
the first commercial scale use of an
organic acid-enhanced FGD system, IERL-
RTP personnel decided it would be useful
to the industry to document system
performance following the demonstration
program. Consequently, in May 1982,
Radian Corporation was contracted to
monitor S02 emissions and the overall
process conditions at SWPP. The primary
objectives of this program were to evalu-
ate the performance of the DBA-enhanced
system and to note any long-term effects
on the process. A secondary objective
was to document the performance of the
continuous emissions monitoring equip-
ment in 1982 to determine the ability of
that equipment to collect data as required
in the 1979 revisions to the utility NSPS.
A brief description of the SWPP system
and a summary of the monitoring pro-
gram results are presented here.
FGD System Description
The SWPP FGD system consists of two
parallel tray tower modules, each sized to
handle 60 percent of the design flow. The
coal typically contains 3.5 - 4.0 percent
sulfur, corresponding to inlet flue gas
concentrations of 2000 - 2600 ppm SOz.
Limestone preparation, sludge dewater-
ing, and sludge disposal systems are
common to the two modules.
Figure 1 shows the overall flow scheme
for the FGD system. The flue gas enters
the presaturator, where it is cooled by
clarified liquor (supernatant) from the
thickener. The gas then passes through
three levels of gas/liquid contact trays,
the mist eliminator, and out of the stack.
No flue gas reheat is used.
Slurry is circulated from the reaction
tank below the scrubber through spray
nozzles above the top level of trays.
Makeup limestone is added from the
limestone storage tank to the reaction
Thickener
Overflow
Limestone
Supernatant
(Thickener Overflow)
Return to Process
Vacuum
Filter
Sludge to
Landfill
Figure 1. SWPP FGD flow scheme.
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tank to maintain the pH set point. Solids
are first settled in the thickener, and the
thickener underflow slurry is dewatered
on a vacuum filter belt. The resulting
sludge is mixed with fly ash in the pug mill
and trucked to an on-site landfill. Super-
natant (thickener overflow) from the
dewatering operation is returned to the
FGD modules as presaturator and mist
eliminator wash water. Additional super-
natant water is utilized in the limestone
preparation area.
A temporary DBA feed system was
installed to add DBA solution on a con-
tinuous basis. DBA is delivered on site in
6000 gal. (22,710 liter) tank trucks. Hot
water (~140°F, 60°C) was circulated
through a steam jacket surrounding the
tank to inhibit DBA crystallization.
Initially, DBA was pumped from the
tank truck to the ball mill sump. The feed
rate was set manually. After the DBA was
mixed with the freshly ground limestone
slurry from the ball mills, the mixture was
pumped to the limestone storage tank.
Since the limestone handling equipment
was common to both scrubber modules,
both scrubbers operated at essentially
the same DBA concentration. Later (in
September 1982), the DBA feed system
was modified to allow DBA to be fed
separately into the reaction tank of either
scrubber.
In May 1983, SWPP began operating
with a permanent DBA feed system,
including an 18,000 gal. (68,000 liter)
stainless steel storage tank, an immersion
heater, two 30-gpm(114liters/min)DBA
circulation pumps, feed lines to the
individual modules, and a source of
heated flush water. SWPP estimates the
cost of the permanent system at approxi-
mately $300,000. To date, SWPP has
reported no problems with the permanent
feed system.
Program Results
Analysis of the SWPP FGD system
operation in 1982 and 1983 shows that
the DBA-enhanced system is continuing
to perform well. SO2 emissions averaged
less than 1.0 Ib SO2/106 Btu (430 ng/J)
in 1982 and 1983, compared to about 5 Ib
SO2/106 Btu (2170 ng/J) in 1980 (before
DBA use). FGD system reliability averaged
nearly 98 percent in 1982 and almost 99
percent in 1983, compared to 45 percent
in 1980, before the adipic acid demon-
stration program.
The flexibility of the DBA-enhanced
system was well demonstrated in 1982
as SWPP personnel adjusted conditions
to minimize scaling in the mist eliminators
before installing limestone classifiers.
The pH set point was reduced, from the
5.4 used during the DBA demonstration,
to 5.0. The reduced pH resulted in in-
creased limestone utilization which
helped maintain mist eliminator reliabil-
ity. Higher DBA concentrations were
required with the lower pH setting, which
resulted in a higher DBA consumption
rate; i.e., 30 Ib DBA/ton S02 (15 g/kg
S02) removed compared to 15 Ib/ton (25
g/kg) in the demonstration program. How-
ever, system reliability was maintained at
a very high level in spite of a poor
limestone grind. The installation of lime-
stone classifiers in late 1982 permits
operation at higher pH with good lime-
stone utilization. 1983 results reported by
SWPP show that DBA consumption was
reduced to about 25 Ib per ton S0z(5 g/kg
S02) using the new classifier system.
Further reduction in DBA consumption
may be possible.
Finally, the continuous emissions mon-
itoring (CEM) system performed very
well. Although called upon to operate
nearly all of 1982 (except for boiler
outages in April and December), average
system reliability was 97 percent. Only
minor problems were experienced, most
of which involved power interruptions to
the DART® microprocessor. During 1983,
very few problems were noted with the
CEM system.
Conclusions
SWPP's FGD system continues to per-
form very well with respect to both
reliability and S02 reductions. DBA has
increased the versatility of the FGD
system as shown by the successful
operation at pH 5.0. SO2 emissions were
well within the 1.2 Ib S02/106 Btu (520
ng/J) limit, and the reliability of both the
FGD system and the CEM system through-
out 1982 and 1983 were excellent. The
following conclusions can be drawn from
this program:
• Use of DBA allows SWPP to remain in
compliance with the S02 regulation.
An average S02 emission of less than
1.0 Ib SO2/106 Btu (430 ng/J) was
measured in 1982 and 1983 with DBA
addition compared to 5 Ib SO2/106 Btu
(2170 ng/J) in 1980, before the adipic
acid demonstration program.
• DBA greatly increases the flexibility of
the FGD system, allowing successful
operation over a wide pH range. Opera-
tion at a reduced pH, in conjunction
with better utilization of fresh water to
the FGD system, allowed SWPP to
achieve an overall reliability of 97.9
percent in 1982, and 98.7 percent in
1983.
• Limestone classification and grinding
circuit performance is important to
overall system performance. In 1982,
DBA consumption at SWPP was about
30 Ib/ton S02 (15 g/kg SO?), due
primarily to operating at a lower pH
and a decrease in recycle pump per-
formance. A limestone classification
system was installed in late 1982,
enabling the system to operate at a pH
of 5.6-5.8 with good limestone utiliza-
tion. Higher pH operation reduced the
DBA consumption rate to about 25
Ib/ton S02 (5 g/kg S02) in 1983.
Further reductions in DBA consump-
tion may be possible.
• Finally, CEM systems can be reliable in
commercial operation. The CEM sys-
tem at SWPP was 97 percent reliable
during 1982. The relative accuracy
remained well within tolerance limits
set by EPA. Based on these results, the
CEM system can reliably and accurate-
ly supply the data necessary to com-
pute 30-day rolling average emission
rates over a long period.
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R. Glover, G. Brown, J. Dickerman, and 0. Hargrove are with Radian Corp., A ustin,
TX 78759.
J. David Mobley is the EPA Project Officer (see below).
The complete report, entitled "Results of the First 2 Years of Commercial
Operation of an Organic-Acid-Enhanced FGD System," {Order No. PB 84-207
679; Cost: $10.00, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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