EPA-450/3-74-014
January 1974
REPORT ON THE STATUS
OF LIME/LIMESTONE
WET SCRUBBING SYSTEMS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-4 50/3-74-014
REPORT ON THE STATUS
OF LIME/LIMESTONE
WET SCRUBBING SYSTEMS
by
Radian Corporation
8500 Shoal Creek Boulevard
P.O. Box 9948
Austin, Texas 78766
Contract Number 68-02-0046
EPA Project Officer: Robert T . Walsh
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, N. C. 27711
January 1974
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This report is issued by the Environmental Protection Agency to report technical
data of interest to a limited number of readers. Copies are available free of charge
to Federal employees, current contractors and grantees, and nonprofit organizations
as supplies permit - from the Air Pollution Technical Information Center, Environ-
mental Protection Agency, Research Triangle Park, North Carolina 27711, or from
the National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22151.
This report was furnished to the Environmental Protection Agency by
the Radian Corporation, Austin, Texas, in fulfillment of Contract No. 68-02-0046.
The contents of this report are reproduced herein as received from the Radian
Corporation. The opinions, findings, and conclusions expressed are those of
the author and not necessarily those of the Environmental Protection Agency.
Mention of company or product names is not to be considered as an endorsement
by the Environmental Protection Agency.
Publication No. EPA-450/3-74-014
11
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TABLE OF CONTENTS
1.0 SUMMARY 1
2.0 HISTORY OF COMMERCIALIZATION 3
2.1 Introduction 3
2.2 Initiation of Modern Development 4
2.3 General Description of Current Lime
and Limestone Wet Scrubbing Processes . . 6
2.3.1 Principles of Operation 7
2.3.2 Similarities Between the Process
Types 7
2.3.3 General Advantages and Disad-
vantages of Process Types 9
3.0 STATUS OF DEVELOPMENT IN LIME/LIMESTONE WET
SCRUBBING 11
3.1 Tabular Listing and Discussion of
Current and Planned Commercial-Size
Installations of Lime/Limestone Wet
Scrubbing Processes 11
3.2 Detailed Operating History of Selected
Major Installations 13
3.2.1 English Work 13
3.2.2 Union Electric 14
3.2.3 Kansas Power and Light 16
3.2.4 Commonwealth Edison 18
3.2.5 Mitsui Aluminum Company 19
3.2.6 Louisville Gas and Electric. ... 20
4.0 DISCUSSION OF THE SPECIFIC PROCESS PROBLEMS
AND SOLUTIONS 21
4.1 Scrubber and Pipe Plugging 22
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TABLE OF CONTENTS (Cont.)
Page
4.2 Chemical Scaling 24
4.3 Corrosion and Erosion 27
4.4 Demister/Reheater Operating Problems. ... 29
4.5 Solids Disposal 33
5.0 COMMERCIAL OPERATING CONDITIONS OFFERED BY
SUPPLIERS OF LIME/LIMESTONE WET SCRUBBING
SYSTEMS 34
BIBLIOGRAPHY
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1.0 SUMMARY
Six years of development work by government and
industry have resulted in lime/limestone scrubbing systems
which control fly ash and sulfur oxide emissions from electric
power generating stations. The systems represent new technology
which is currently being reduced to sound engineering practice.
When new technology is scaled up in first generation plants,
difficult operating problems are nearly always encountered,
a normal trend in chemical process development. As a result
of such first generation operating problems, the reliability
of lime/limestone scrubbing systems has been the subject of
much concern. Most agree that reliability has not been
demonstrated with finality.
A major field development program is now underway
on a national scale. Equipment vendors and utilities are
working in parallel with government agencies to increase the
reliability of commercially available equipment. Numerous
prototype and full scale installations are scheduled to be
on line by 1975. These plants may have operating problems,
and they will be more costly than those installed after the
process design has become more sophisticated. But the
experience gained from these systems will provide significant
advances in the achievement of widespread commercial acceptance.
This paper addresses the problems of poor reliability
which have caused some to be reluctant to accept what is now
commercially available. The following discussion shows in
detail how poor reliability has been the result of applications
engineering problems with specific hardware components and design
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parameters. The problems and their causes are clearly
identified and solutions which have been proposed and
implemented are described in detail and documented. Solutions
to some problems have been adequate and others are marginally
acceptable. One way of describing the problems is to divide
them in two categories, one category of problems resulting from
chemical causes and another category due to mechanical causes.
The problems of chemical origin are now better understood.
Methods of design and operation which prevent recurrence of
these problems have been devised and in some instances
demonstrated. The remaining mechanical problems are similar
to those which have already been solved in other applications.
It is suggested that since many of the causes of
poor reliability have been identified and since solutions have
been proposed and some have been demonstrated, there is reason
to be optimistic about acceptance and wide application of
lime/limestone wet scrubbing in the near future. At present
there are two systems (Mitsui and Paddy's Run) operating
successfully with only minor problems. It is not to be
expected that new installations will be trouble free. However,
it is reasonable to expect that with operating experience and
problem solving in present field installations along with the
application of techniques which have been applied in other
industries, lime/limestone wet scrubbing processes can be
operated with reliability.
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2.0 HISTORY OF COMMERCIALIZATION
2.1 Introduction
Some 40 years ago, workers in England initiated efforts
to control S03 emissions from fossil-fueled combustion sources
using a once-through water scrubber and a lime/-limestone process
installed on commercial-size boilers. The London Power Company
did pilot plant work at their Battersea and Bankside units
which led to full-scale gas-washing plants. The Howden-ICI
process was used commercially at the Tir-John and Fulham power
stations located in Swansea and London, respectively. Operation
there was done on a closed loop basis. These processes proved
successful in removing SOB and dust from stack gas and
demonstrated process feasibility using primitive equipment.
Process limitations such as highly acidic effluent, corrosion,
erosion, plugging, and "drooping plume" became evident (SL-030)
so that another result of this pioneering work was to define
further development needs. Scrubbing systems at the Battersea
and Bankside Plants, now associated with the Central Electricity
Generating Board, are currently in operation.
Modern development began in the United States in 1967
with work sponsored both by government and industry. After
six years, there are approximately twelve developers who have
either operated or are planning to operate in the near future
full scale installations of the lime/limestone wet scrubbing
process. (Full scale in this case is arbitrarily defined
as a unit with generating capacity of 100 MW or more.) A survey
of the seven suppliers who already have full scale experience
shows that most guarantee SOS removal in the 85 to 9070 range
(RA-074). There is virtually no restriction on sulfur content
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of the fuel, whether coal or oil, and module designs as large
as 150 MW, for units up to 800 MW, are offered.
It is expected that operating experience gathered by
these and other suppliers at existing or planned installations
will go a long way toward resolving the few operating problems
which still characterize lime/limestone wet scrubbing systems.
While work remains to be done involving optimization of the
•
processing steps, demonstrated reliability and commercial
acceptance are anticipated in the near future.
The purpose of this paper is to identify significant
steps in the development of lime/limestone wet scrubbing
processes, to indicate how past projects have contributed to
progress through identification of operating problems, and
finally to define current capabilities in designing efficient
and reliable systems. The discussion which follows includes
a chronological description of modern development (Section 2.2),
a description of the commercial process which resulted, (Section
2.3), a survey of current installations which indicates the
scope of on-going development work (Section 3.1), detailed
operating histories of six selected major installations
(Section 3.2) and a detailed discussion of specific operating
problems, their causes, and their solutions (Section 4.0). The
paper is concluded with a summary of process design and operating
conditions currently offered by vendors on a commercial basis.
2.2 Initiation of Modern Development
Six or seven years ago none of the processes available
for S0a control were considered capable of coping with the
emissions from modern, high capacity power plants (HA-145). The
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Division of Air Pollution of the U. S. Public Health Service
(now part of the Environmental Protection Agency) therefore
initiated a research and development program in this country
to develop a technically and economically feasible method of
curtailing sulfur oxide emissions. The early government program
was intended to be stimulatory and was not directed solely toward
limestone processes (nor is it now). Studies of the technical
and economic feasibility of a wide range of potential SO,
control processes were initiated. It was anticipated that lime-
stone based processes would have considerable potential, and
work was originally limited to dry processes to avoid
duplication of industrial effort. Government support later
expanded to include wet scrubbing processes and the Tennessee
Valley Authority conducted support work under an interagency
agreement investigating both wet and dry processes. Small
scale studies using a 3,400 m3/hr (2,000 ACFM) system at their
Colbert Steam Plant in Muscle Shoals, Alabama, gave 80 to 90%
S03 removal using a stoichiometric addition of 1.5 and a 10%
slurry of pulverized limestone (TE-012). Data generated there
formed the basis for TVA's present process concept. This
developmental work is being continued at TVA's Shawnee station
(30 MW), and results are being used in the design of the Widow's
Creek (550 MW) installations.
Most of the early industrial work was performed with
the limestone injection wet scrubbing process, notably by
Combustion Engineering (C.E). Brief initial pilot scale testing
at Detroit Edison showed the process to be successful in
removing S03 from flue gas. These results prompted C.E. to
install full scale units at Union Electric Company and Kansas
Power and Light Company. The Union Electric Meramec No. 2
unit was started up in late 1968 and experienced operating
problems including boiler pluggage, scaling, and low SOP
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removal efficiency. Numerous modifications failed to alleviate
the most serious problems, and the unit was abandoned in 1972
after nearly four years of intermittent operations.
C.E.'s limestone injection systems on units number
4 and later number 5 at Kansas Power and Light's Lawrence Energy
Center also served to identify numerous mechanical and operating
problems. Substantial equipment modifications have been
implemented in response to many of the major problems. Modified
methods of scrubber operation have been identified and a
schedule of frequent inspection and maintenance has been imple-
mented. With these practices the scrubbing system has been
available for operation when it is required during coal burning
operations at the Lawrence Center (SU-023).
C.E.'s entrance into the market sparked interest
among other parties in lime/limestone wet scrubbing. By the
early 1970's commercial systems were being offered by eight
additional vendors and efforts were underway to further
develop the technology. Notable examples are B&Ws Commonwealth
Edison - Will County installation and Chemico's wet scrubbing
system at Mitsui Aluminum Company. Some of the operating
problems have been investigated and resolved at the pilot level.
Process variations evolved and solutions to problems were
incorporated into full scale designs. Combustion Engineering,
after completing pilot plant work at their Kreisinger Development
Laboratory in Windsor, Connecticut, has successfully installed
a carbide sludge wet scrubbing system at Louisville Gas and
Electric's Paddy's Run Station. As a result of these efforts,
advances in scrubbing technology have been so rapid that most
experts in the field today agree that lime and limestone wet
scrubbing systems will be commercially accepted. Basic process
components for systems currently being offered commercially
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are described in the next section. The process description
is presented as a basis for understanding the discussions which
follow.
2.3 General Description of Current Lime and Limestone
Wet Scrubbing Processes
In order to fully understand operating problems
and solutions, the basic principles of the lime and limestone
wet scrubbing processes must be studied. This discussion
presents the principles of operation of each process, similar-
ities between the two scrubbing schemes, and general advantages
and disadvantages of each process.
2.3.1 Principles of Operation
The process flow arrangement for lime and limestone
wet scrubbing is presented in Figure 2-1. Flue gas from
the boiler enters a scrubber where it is contacted with an
alkaline slurry (either lime or limestone). The SOS in the
flue gas reacts with the dissolved lime or limestone to form
calcium sulfite and calcium sulfate. The clean gas leaving
the scrubber is passed through a demister and reheated before
discharge to the atmosphere.
The slurry leaving the scrubber is sent to a hold
tank where CaS03-%HsO and CaS04-2H80 crystals are precipitated.
Most of this slurry is recycled to the scrubber. A side
stream of high percent solids from the hold tank is passed
through a solid/liquid separator where the CaS04-2H20 and
CaS03-%H20, fly ash and undissolved limestone are removed
and disposed of. The liquid from the separator is recycled
to the scrubber after make-up water and fresh lime or limestone
have been added.
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Limestone
(Boiler Injec-
tion)
Boiler
00
I
Flue Gas
Clean
Gas
,1
Scrub-
ber
\t_v_v.v_
Hold
Tank
Lime/Limes tone
(Tail End Addition)
/ v.
Spray
Tank
Solid/Liquid
Separator
Solids to
Disposal
FIGURE 2-1 - GENERAL FLOW SCHEME FOR WET LIMESTONE/LIME PROCESSES
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The limestone injection processes originally offered
by Combustion Engineering involved direct addition of limestone
into the boiler followed by wet scrubbing of the flue gas. The
process currently marketed by the majority of vendors, lime/
limestone tail end addition, involves addition of lime or
limestone to the scrubber in the form of a slurry.
2.3.2 Similarities Between the Process Types
The lime and limestone scrubbing processes are
basically very similar. The process chemistry is almost
identical in both scrubbing schemes and both use essentially
the same four basic pieces of equipment. One exception is
the addition of a calciner to convert limestone to lime in the
lime scrubbing process. Also, the same operational problems
have been dealt with in both processes. These include plugging,
scaling, demisting, and solids disposal.
2.3.3 General Advantages and Disadvantages of Process Types
There are several advantages and disadvantages for
both the lime and limestone wet scrubbing processes. First,
lime is generally more reactive than limestone for SOB absorption.
This means th.it a given amount of SOS can be absorbed with a
smaller amount of lime than with limestone.
Second, lime's lower molecular weight (44% less than
limestone) helps reduce transportation costs. Costs for trans-
porting raw materials such as lime and limestone are based on the
tonnage shipped. Since the molecular weight of lime is less
than that of limestone, a smaller tonnage of lime will be required,
thus reducing the shipping costs.
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Still another advantage of the lime scrubbing system
is that less solids disposal is required. Due to the higher
reactivity of lime, less remains unreacted. Thus, there are
an estimated 16?0 less solids to be disposed of with the lime
system than with the limestone system. For an ash free process,
solids disposal requirements are estimated to be up to 30% less.
In some lime scrubbing systems a calciner is used
to convert limestone to lime. An additional advantage of the
limestone system is that this extra processing step is not
required.
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3.0 STATUS OF DEVELOPMENT IN LIME/LIMESTONE WET SCRUBBING
This section is designed to introduce the reader to
operating problems and solutions which have been experienced
by developers at major installations of the wet lime/limestone
scrubbing processes. The discussion will illustrate the scope
of ongoing development work. All current and planned commercial-
size installations of lime/limestone wet scrubbing processes
are listed in this section with discussions concerning develop-
mental highlights. Also presented are synopses of the operating
history of selected major installations including a discussion
of factors which influence performance and reliability.
3.1 Tabular Listing and Discussion of Current and
Planned Commercial-Size Installations of Lime/
Limestone Wet Scrubbing Processes
For the purposes of this report, commercial-size
installations are defined to be those with a flue gas rate
equivalent to that from a boiler with a generating capacity of
100 MW or larger. A comprehensive listing of such installations
is presented in Table 3-1.
Twelve of the systems listed in Table 3-1 will be in
operation by early 1974, the time frame for meeting EPA primary
new source standards.
Two installations of particular developmental interest
are the vertical and horizontal scrubbing systems to be installed
at SCE's Mohave Generating Station. These systems will be the
first to treat flue gas from boilers firing low-sulfur Western
coal. Scheduled start-up dates for these installations are late
1973 and mid-1974. Developments at these sites will help to
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1^
1
Utility Company
Kansas Power & Light
Kansas Power & Light
Conmonwea 1 t h Edison
Kansas City Power & Light
Kansas City Power & Light
Arizona Public Service
Louisville Gas & Electric
Duquesne Light
Kansas City Power & Light
Detroit Edison
Southern California
Kdison
Southern California
Edison
Ohio Edison
TVA
Northern Indiana Public
Service
Montana Power Company
Northern States Power
(Minnesota)
Southern California Edison
Salt River Project/Southern
California Edison
Public Service of Indiana
Columbus & Southern
Arizona Public Service
Arizona Public Service
Arizona Public Service
OPERATING AND PLANNED COMMERCIAL-SIZE LIME/LIMESTONE WET SCRUBBING INSTALLATIONS IN THE UNITED STATES
Developer
Combustion Engineering
Combustion Engineering
Babcock & Wilcox
Combustion Engineering
Combustion Engineering
Research-Co ttrel 1
Combustion Engineering
Chemico
Babcock & Wilcox
Peabody Engineering
SCE/S teams-Roger
Procon/UOP/Bechtel
Chemico
TVA
Not Selected
Combustion Equipment
Associates
Combustion Engineering
Not Selected
Not selected
Combustion Engineering
Not Selected
Not Selected
Not Selected
Not Selected
Status
(Start-Up Date)
Operating
(Late 1968)
Operating
(Late 1971)
Operating
(Early 1972)
Operating
(Late 1972)
Operating
(Late 1972)
Under Construc-
tion (Late 1973)
Operating
(April 1973)
Under Construction
(Nov. 1973)
Operating
(Mid 1973)
Under Construc-
tion (Late 1973)
Under Construc-
tion (Late 1973)
Under Construc-
tion (Early 1974)
Under Construc-
tion (Early 1975)
Under Construc-
tion (Mid 1975)
Planning Stage
(Mid 1975)
Under Construc-
tion (May 1975)
Under Construc-
tion (May 1976)
Planning Stage
(Late 1976)
Construction Nov. 1974
(March 1976)
Planning Stage (1976)
Planning Stagp
(1976)
Construction Late 1975
(October 1976)
Construction Mid 1976
(March 1977)
Construction Sept. 1975
(April 1977)
Type and Size New or
of Test Unit Retrofit
Coal-Fired, R
125 MW
Coal-Fired, N
430 MW
Coal-Fired, R
156 MW
Coal-Fired, R
100 MW
Coal-Fired, R
100 MW
Coal-Fired, R
115 MW
Coal-Fired R
70 MW
Coal-Fired, R
100 MW
Coal-Fired, N
820 MW
Coal-Fired R
180 MW
Coal- Fired, R
160 MW
Coal-Fired, R
160 MW
Coal-Fired, N
1650 MW- total
Coal-Fired, R
550 MW
Coal-Fired, N
500- MW
Coal-Fired, N
720 MW
Coal-Fired, N
1360 MW- total
Coal-Fired, R
1500 MW- total
Coal-Fired;. N
2250 MW-total
Coal-Fired, "
650 MW
Coal-Fired N
750 MW
Coal-Fired R
350 MW-total
Coal-Fired R
229 MW
Coal-Fired R
1600 MW-total
Fuel Type
3.5% S Coal
3.5% S Coal
3.5% S Coal
3.5% S Coal
3. SI S Coal
0.4- IX S Coal
3.0% S Coal
2.3* S Coal
5.07. S Coal
2.5-4.5% S Coal
0.5-0.8% S Coal
0.5-0.8% S Coal
4.3% S Coal
3.7% S Coal
3.07. S Coal
0.8% S Coal
0.8% S Coal
0.5-0.8% S Coal
0.5-0.8% S Coal
1.5% S Coal
0.75% S Coal
0.75% S Coal
0.757. S Coal
Absorbent
CiO
CaO
CaCOj
CaO
CaCOs
CaCO,
C8(OH)t
CaO
CaCO,
CaCO.
CaO
CaCO,
CaO
CaCO,
Not Selected
CaO/Fly Ash
CaCOs
CaO/CaCO,
Not Selected
CaCO,
CaO
Not Selected
Not Selected
Not Selected
Station/Location
Lawrence No. 4
Lawrence No. 5
Will County No. 1
Hawthorne No. 3
Hawthorne No. 4
CholU
Paddy's Run No. 6
Phillips
LaCygne
St. Clair No. 6
Mohave (Horizontal)
Mohave (Vertical)
Mansfield (2 units)
Widow's Creek No. 8
Kanakee No. 14
Colstrip No. 1
and t
Ana &
Sherburn County No.
and No. 2
Mohave (Horiz/Vert)
Navajo No. 1.. Z,
A-nA 1
ana j
Gibson
Conesville No. S
&nd 6
Four Corners
No. 1 and 2
Four Corners No. 3
Four Corners No. 4
and 5
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assess the technical and economic feasibility of flue gas
desulfurization processes in conjunction with burning of low
sulfur coal.
The last twelve installations listed in Table 3-1 are
scheduled to start up after mid-1974. Operating experiences
gained in the previous plants will be of value in selecting
appropriate operating conditions for future installations. The
hardware for plants based on today's technology may well have
problems that will have to be solved in the field. The effort
required to overcome these difficulties will be lessened because
of the knowledge now being accumulated.
3.2 Detailed Operating History of Selected Major
Installations
Several of the installations in Table 3-1 have
already provided valuable operating experience with the
lime/limestone wet scrubbing processes. A number of the
operating problems to be discussed in detail in Section 4.0
can be put into proper historical perspective by surveying
the operating histories of selected major installations.
Discussion below begins with operating experience at the
early English installations and proceeds to the latest
experience in the U. S. and Japan.
3.2.1 English Work
The London Power Company did pilot plant work in the
early 1930"s that led to full scale gas-washing plants at the
Battersea and Bankside power stations in London. Alkaline
water equivalent to 200 ppm of NaOH from the Thames River was
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used for scrubbing the gas on a once- through basis. At the top
of the final scrubbing unit, the gases were contacted with a sus-
pension of finely ground chalk (CaC03). During part of the
program lime was added for pH control but addition of lime to the
river water was said to cause scaling. The system removed about
9070 of the flue gas S03 but acidic effluent from the two stations
lowered the pH of the Thames to an undesirable level (TE-001) .
The once- through system also had the drawbacks of requiring
a large amount of water (effluent was mixed 15 to 20 times
its volume with condenser cooling water) and of cooling the
gas to an unduly low temperature (KE-024) . Units at both
stations are presently operating successfully. Maintenance is
performed during scheduled semiannual shutdowns, and unscheduled
-ms are rare (DE-091) .
The Howden-ICI tail-end wet scrubbing process was also
being developed in England about this time. The process was
used commercially at the Tir John and Fulham power stations
located in Swansea and London, respectively. In these plants,
lime, carbide lime, and finely ground chalk were tested. About
987o SOP and dust removal was achieved with stoichiometric
addition of lime or 30% excess chalk. Scaling was controlled by
circulating a high solids content slurry (up to 20 weight percent) ,
holding the slurry in a delay tank for a period to allow dissipa-
tion of super saturation, and use of "nonscaling" grid tower
packing (suspended wooden plates) . Serious corrosion and erosion
problems were encountered in unlined mild steel pumps and
washer tanks. Rubber linings were difficult to maintain at
pipe bends and axial flow pumps (TE-001) .
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3.2.2 Union Electric
After initial testing of the limestone injection plus
wet scrubbing process in 1966-67, Combustion Engineering
installed a full scale unit at Union Electric Company (Meramec
No. 2). The system was first operated in September 1968 and
immediately experienced problems with boiler and gas scrubbing
operations.
Injection of limestone into the Meramec No. 2 furnace
resulted in pluggage of reheaters and severe deposition of
lime reaction products in the convection pass of the furnace.
Soot blowers were installed to improve the cleanliness of the
reheaters. Attempts to remove deposits in the tubular air
heater with blowers and washing proved unsuccessful. High
pressure jet cleaning of the heat transfer surfaces was required
in the fall of 1970 and again in 1971 after only 18 days of
operation. Boiler operation problems at Meramec No. 2 were due
in part to boiler design itself. Narrow spacing of heat transfer
surfaces and a tubular air heater in the convection section
tended to promote plugging by lime reaction products.
Operating problems with the scrubbing system included
solids deposition at scrubber inlet and damper, severe scale
formation in marble beds, and low S03 removal efficiency. Modi-
fied configuration of the scrubber inlet duct together with the
installation of soot blowers successfully reduced solids deposi-
tion at the scrubber inlet and damper. Modifications to reduce
scaling included installation of a reaction tank and a surge
tank to provide holdup time for crystallization of calcium
sulfite and sulfate and to provide better lime utilization.
These modifications were unsuccessful in eliminating scale
formation in the marble bed and drains.
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The Meramec No. 2 system accumulated only 183 days of
operation between September, 1968, and June, 1971 (MC-081).
After four years of intermittent testing due to scrubber and
boiler plugging problems, the mutual decision was reached by
Union Electric and Combustion Engineering in 1972 to abandon
the unit.
3.2.3 Kansas Power and Light
Initial installation at Kansas Power and Light Co.'s
Unit No. 4 occurred in November of 1968. Immediately after
start-up problems were encountered with duct vibration, plugging
of marble bed and spray nozzles, and formation of ash cement at
the scrubber inlet. Other operational problems experienced
during the early stages of operation included corrosion, demister
and reheater pluggage, and mechanical failure of pumps. To
correct these problems, modifications were made which included
sand blasting and glass epoxy lining of scrubber internals,
installation of ladder vane distribution baffles and soot
blowers, and redesigning the recycle system to accept dilution
water from the pond. The system operated in this mode with
fair success through the winter of 1970-71 and into the spring
of 1971.
In the fall of 1971, the 430 MW No. 5 unit went on line,
sharing the solids disposal pond with the No. 4 unit. With the
additional flow of slurries supersaturated with respect to
CaS03 '%H30 and CaS04 '2HgO to the disposal pond, the recycle
scrubber spray water early in 1972 became supersaturated with
respect to calcium sulfate. The supersaturated spray water
caused severe scaling in the scrubber train. Efforts to
alleviate this problem took the form of the following measures :
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(1) increased L/G ratio to the range of 2.7 to
3.4 liters/cubic meter (20 to 25 gal/1000 ACF),
(2) increased solids content of recycle slurry,
(3) enlarged marble bed and demister areas to
lower the gas velocity,
(4) installed two additional scrubbers at
Unit No. 5,
(5) increased liquid flow to Unit No. 4.
After these modifications, tests were conducted for two weeks
in October, 1972. On the basis of results gathered during
this period, KP&L management expects to obtain 75% S0§ and 99+%
particulate removal during long-term continuous operation (SU-U23)
These changes have allowed Kansas Power and Light to
operate without building scale deposits In the scrubbing system.
Unfortunately, they have also caused other problems to worsen.
With the high solids content in the slurry, they are now
experiencing appreciably greater erosion of pumps and pipes.
Kansas Power and Light engineers believe this is caused largely
by fly ash in the recirculated slurry (there is no electrostatic
precipitator in the system). In addition to erosion problems,
the modifications have resulted in a greater tendency for solids
to build up on demister surfaces. Mud-like material is washed
off every other night during nightly load lessening. Also
problems with unequal gas distribution in modules have been
experienced with Unit No. 5. The latter boiler is normally
derated about 25% when burning coal. This is partially due
to scrubber related problems and partially due to increased
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slagging in the boiler. Despite these difficulties, the scrub-
bing systems on both Units No. 4 and No. 5 have been operable
whenever coal is burned in the boilers.
3.2.4 Commonwealth Edison
The most recent full scale work to be done on the
limestone tail-end addition process has been conducted at the
Babcock and Wilcox installation on Will County No. 1 (Common-
wealth Edison Company). Numerous problems have been encountered
since start-up in February, 1972: (1) serious carryover deposits
in the demister, (2) plugging of slurry lines, (3) wearing and plug-
ging of spray nozzles, and (4) significant scale deposits (GI-017).
Demister pluggage appears controllable using automatic washing
with make-up water via bottom sprays and other modifications.
Plastic absorber slurry nozzles were replaced with stainless
steel nozzles. Piping in the mill building was modified to
prevent plugging. System reliability due to mechanical problems,
economic disposal of sludge and scaling remain as major operating
problems.
Two additional problems have been encountered recently
at Will County No. 1 -- serious corrosion in reheaters and sul-
fite blinding of limestone. Stress corrosion has been a problem
with the stainless steel reheaters located downstream from the
absorbers. Attempts to alleviate this problem by replacing the
stainless steel with corten steel have been unsuccessful due to
attack of the corten steel by acid mist (GI-030).
Four instances of sulfite blinding have occurred since
start-up of the unit; three since spring 1973. The phenomenon
occurs in supersaturated solution and involves the rapid crystal-
lization of calcium sulfite onto undissolved limestone particles
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in the slurry. With limestone "blinded" by the sulfite crystals,
dissolution of limestone cannot take place to provide the
necessary alkalinity for S08 absorption. As a result, SO-,
absorption and the pH of the liquor drop sharply. Although
specific preventative measures have not been taken at Will
County (GI-030), it is reported that sulfite blinding is no
longer a problem.
3.2.5 Mitsui Aluminum Company
Two dual-stage venturi scrubbing systems have been
retrofitted to the 156 MW power plant of the Mitsui Aluminum
Company in Japan. This system his demonstrated continuous,
closed-loop operation since start-up in March 1972. The system
is designed for total liquor recycle, and it has operated in a
closed loop mode except for occasional periods of heavy rain
during typhoon season when flooding and overflow of the
disposal pond occurs.
The operational problems that have been reported at
Mitsui have been minor ones. These have included piling up of
particles in slurry tanks, erosion, damage to rubber pipe lining,
and thin scale deposits. Problems involving piling up of carbon
particles and erosion have been reduced by installing cyclone
separators to remove carbon particles and foreign matter
resulting from dry carbide sludge. Damage to rubber pipe lining
was eliminated by substituting an orifice for a butterfly valve.
Minor modification of mist eliminator sprays, proper pH control,
and strategic utilization of fresh make-up water have served to
eliminate scaling problems (SA-099). The scrubber has exhibited
reliable performance and the system is guaranteed for installa-
tion in the United States by Chemico.
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Although translation of Chemico's success in Japan
to application in the United States may not be direct, there
are some common features for the Mitsui plant and boilers
which are typical for the U.S. They are: retrofit of existing
coal-fired boiler, moderately efficient electrostatic precipi-
tators, installation on moderately large size boiler, production
of a throwaway product and availability of lime. Two similar
units using lime on coal boilers are being constructed in the
U.S. for Duquesne Light Company's Phillips Station and Ohio
Edison's Bruce Mansfield Station.
3.2.6 Louisville Gas^ and Electric
Successful application of a Carbide Sludge (Ca(OH8))
scrubbing system has been achieved in this country by Combustion
Engineering at Louisville Gas and Electric Company's Paddy's
Run Station. No scaling or plugging problems have been
encountered in over 3000 hours of closed-loop operation since
April 1973 (VA-068). The scrubbers have been available more
than 957o of the time that the boiler has been available.
Wash sludge is thickened, filtered, and disposed of as unfixed
landfill. The system removes 85 to 95% of the S02 in the flue
gas from a 70 MW boiler fired with 3.5 to 4.0 percent coal
(VA-068).
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4.0
DISCUSSION OF THE SPECIFIC PROCESS PROBLEMS AND
SOLUTIONS
Operating problems discussed in the previous
sections are in some cases peculiar to a specific design,
vendor or installation. More often, however, they are a
consequence of the basic process and mechanical design defi-
ciencies common to all early versions of lime/limestone
scrubbing processes. Because of this, significant progress
has been made as more full scale experience has been logged.
The rate of the improvement in process design and system
reliability is accelerating with each new unit that is brought
on line.
In this section specific operating problems are
analyzed. The following points are of interest.
• What is the history of the problem; where did
it first develop?
• Does the problem have a mechanical or chemical
origin?
• What steps have been taken to solve the problem
in various pilot and full scale installations;
have proposed and attempted solutions been appro-
priate with respect to the origin of the problem?
. Are there pilot or full scale installations that
have successfully overcome any of these specific
design deficiencies? If not, when might such
success be anticipated?
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This approach to assessing the development of lime/
limestone scrubbing technology eliminates much of the confusion
that can develop when comparing the success or failure of dif-
ferent vendors' processes under different operating conditions.
Specific problems encountered at both early and more
recent lime/limestone scrubbing installations are discussed
below. The information presented here is intended to accurately
demonstrate significant progress or lack of progress in each
area.
4.1 Scrubber and Pipe Plugging
The term plugging is used to describe mechanical
depositions of solid material on equipment surfaces. It is
distinguished from scaling which is caused by chemical reac-
tion on metal surfaces. Scaling is discussed in Section 4.2.
Plugging was experienced in the earliest full scale
operations and to a lesser extent in recent installations.
Combustion Engineering encountered massive buildup of lime
and fly ash materials at the inlet of their marble bed scrubbers
during operation at both Union Electric and Kansas Power and
Light (SU-023). These deposits were sufficient to require unit
shutdown on a day-to-day basis.
Scrubber inlet plugging is due to mechanical design
problems. Contact between hot, dry lime and fly ash solids and
partially wet scrubber inlet surface has been found to be
undesirable. In the injection plus scrubbing process installed
in the Meramec and Lawrence Stations, this contact cannot be
avoided. Installation of high pressure blowers to scour the
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scrubber proved to be a successful solution to inlet plugging.
The equipment used for this cleaning service is the same as
that used for maintaining clean surfaces in coal-fired boilers.
Scrubber inlet surfaces are accessible for in service
cleaning. Process piping and scrubber spray nozzles can be
cleaned in most cases only by shutting the system down. Combus-
tion Engineering also experienced pipe and nozzle plugging at
their Kansas Power and Light Lawrence No. 4 Unit. Large pieces
of solid material were found lodged in the spray nozzles. This
material was identified as scale that had broken off from other
equipment surfaces. Screens were installed on the slurry pump
inlets to prevent large pieces of solids from entering the nozzle.
In general, plugging problems in the slurry handling
system have been avoided by proper equipment design. Plugging
problems in the scrubber area have led many of the newer vendors
to use scrubber types with less complicated internals. Of the
vendors and developers now involved with lime/limestone scrubbing
systems most use relatively simple open contacting devices. These
include a two-stage venturi (Chemico), a single venturi followed
by an open spray tower or grid tower (Babcock & Wilcox, Research-
Cottrell, Combustion Equipment Associates, Tennessee Valley
Authority), and an open spray tower alone (Southern California
Edison, Joy Manufacturing Company, Peabody Engineering, Ontario
Hydro). These scrubbers are expected to provide reliable service
in slurry scrubbing applications. With the exception of mist
eliminator problems which are discussed separately, plugging is no
longer considered a serious obstacle to process reliability.
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To avoid plugging of process piping, slurry velocities
must be sufficient to keep solids from settling out. Decelera-
tion and stagnation may occur at bends in piping and areas of
roughness in the pipe. For these reasons, pipe bends should
be made with large radii of curvature, valves other than gate
valves should be avoided, smooth piping should be used, obstacles
in the flow path (uneven pipe joints, unnecessary valves, probes)
should be eliminated, and abrupt contractions or expansions in
piping diameter should be avoided (BE-145).
4.2 Chemical Scaling
Scaling is caused by chemical deposition of calcium
sulfite and sulfate solids on equipment surfaces. While the
effect of scaling on equipment operation is the same as that
of plugging, the causes and remedies of scaling are completely
different.
When sulfur oxide is removed from the flue gas in the
scrubber it enters the liquid portion of the circulating slurry.
In order to dispose of the SOS, however, it must be precipitated
as insoluble calcium salts. The scaling phenomena are closely
related to this precipitation step. A certain amount of time
must be allowed for this step to be completed. This is usually
termed delay time and is provided for in the scrubbing process
by allowing the slurry to pass through a large stirred tank
before being recirculated to the scrubber. If the slurry
entering the scrubber has not been allowed to precipitate
calcium salts, a portion of the SOP picked up during the
previous pass to the scrubber and the newly absorbed SOS will
tend to scale on the scrubber walls. In some cases scale deposits
can force unit shutdown after a period of only one or two days.
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More development and design effort has been spent on
scale prevention than perhaps any other aspect of process reli-
ability. Combustion Engineering encountered plugging and scaling
throughout the first two years of operating at Lawrence No. 4
(SU-023). The earliest approach to scale prevention was a series
of mechanical design changes. Materials used for some components
of the scrubber were changed to prevent scale from adhering to
their surfaces. The bottoms of the scrubbers at Lawrence No. 4
were covered with two inches of gunite and scrubber interiors
were sand blasted and epoxy lined. Other mechanical type changes
included modification of the recycle system ana installation of
soot blowers (SU-023). This experience showed, however, that
scaling was primarily a chemical problem. Neither special
materials nor periodic in-service washing was a successful
solution.
During and following the Combustion Engineering
experience at KP&L, vendors , including C.E., began to take a more
fundamental approach to scale prevention. The rate at which
the sulfite/sulfate solids precipitated in the system was known
to increase with the amount of circulating solids. Combustion
Engineering thus increased their designed solids concentration
from less than 2 to 8 weight percent. More recently most vendors
are designing high solids content systems. Design concentrations
up to 15% have been reported (RA-074).
Along with increased solids content, C.E. has
significantly increased the delay times for the spent slurry
after it exits the scrubber. Tank sizes have been increased
such that 15 minutes delay time is provided compared to five
minutes in the original KP&L design.
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Another significant design change intended to alleviate
scaling problems is the change in the so-called "liquid-to-gas
ratio" or L/G. This again resulted from basic consideration
of process chemistry. The potential for scale to form in the
scrubber is roughly proportional to the amount of SOS that is
absorbed by the slurry. If a large amount is absorbed by only
a small amount of slurry (i.e., L/G is low) then the capacity of
the liquid to hold the sulfur compounds is exceeded and the
excess forms an adherent scale on the surfaces of the scrubber.
When the liquid-to-gas ratio is increased, more liquid is
available to absorb a given amount of S02. The danger of
exceeding the scaling point is greatly lessened. Most vendors
now design their systems with L/G's far in excess of earlier
experiences. C.E. has increased their own design from 1.4
liters of slurry per cubic meter of flue gas (10 gal/1000 ft5)
to 3.4-4 liters of slurry per cubic meter of flue gas (25-30 gal/
1000 ft"'). Liquid-to-gas ratios now range as high as 13.5 liters/
cubic meter (100 gallons/1000 ft3) in some designs. While the
operating costs for these high liquid rates are not negligible,
increasing emphasis is being placed on system reliability.
These three key design changes for scale prevention —
high solids concentration, long delay times, and high L/G — have
been responsible for demonstrated success at new lime/limestone
scrubbing installations. The Chemico unit at Mitsui Aluminum
Company in Japan has a solids content of 3-5 weight percent and
an L/G of 5.1 to 7.9 liters per cubic meter (46-59 gal/1000 ft3)
(AN-056). This unit has operated without scaling for more than a
year (SU-031). The Paddy's Run Station at Louisville Gas and
Electric is reported to have operated without scaling since April
1973 (VA-068). In summary, these results demonstrate that it is
possible to design and operate new installations so that scaling
does not occur.
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4.3 Corrosion and Erosion
Surfaces in the wet scrubbing system that come in
contact with wet SO,, gas or acid scrubber liquor should be
constructed of acid-resistant materials to minimize corrosion.
Surfaces that come in contact with slurry solids should be
constructed of abrasion-resistant materials to minimize erosion
(RA-074). Materials selection for the limestone scrubbing
systems has played an important pirt in system reliability.
Early designs were based on sketchy information regarding the
physical and chemical properties of circulating slurries. As
a result, serious difficulties were encountered during long
term full scale operation.
Material used in the original Combustion Engineering
installation at KP&L's Lawrence No. 4 was principally unlined
carbon steel. The scrubber shell suffered severe corrosion in
the first year of operation before it was lined with glass flake
epoxy. Other materials of this type being offered are the
Ceilcote 100 and 200 series and Carboglass 1601 (RA-074).
Materials now being used for scrubber shells and internals
are usually stainless steel or lined carbon steels. Stainless
steel 316L was being used for reheater requirements at Commonwealth
Edison's Will County No. 1 Unit but suffered from stress corrosion
(GI-030). This has been shown to be a problem in areas where
chloride is present (RA-074). Stainless steel at Will County
No. 1 was replaced with corten steel which suffered acid corrosion
from mist eliminator carryover (GI-030). This problem can be
eliminated with the correct choice of materials.
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Experience with equipment erosion in lime/limestone
scrubbing systems is less well defined. One of the disadvantages
of using high solids concentration to avoid scaling is the
abrasive effect of the solids on spray nozzles, pumps, and piping.
Original spray nozzles at KP&L were made of plastic and erroded
badly. Spray nozzles are now made of either rubber lined carbon
steel or stainless steel.
Soft rubber or neoprene lined carbon steel can be
effective for pump and piping material under abrasive conditions
and temperature up to 175°F (RA-074). Rubber lined pumps have
been used with fair success at a number of major installations
(Will County, Mitsui, Paddy's Run, Shawnee). The most vulnerable
pump parts are the impeller blades where a pinhole in the rubber
lining can result in severe attack of the carbon steel underneath.
Larger diameter pipes can be lined with rubber or neoprene. At
both Mitsui Aluminum Co., and TVA's Shawnee Station, piping
above 5 to 6.35 centimeters I.D. (2-2.5 inches) is carbon steel
with internal neoprene lining (EL-030). Slurry piping smaller
than 5 to 6.35 centimeter diameter (2-2.5 inches) is of stainless
steel.
A less significant example of erosion in lime/limestone
wet scrubbing installations occurs in marble beds and TCA scrubbers
Combustion Engineering noted weight loss of marbles in their
scrubbers at both Union Electric and Kansas Power and Light
(SU-023). At the TVA pilot plant installation at the Colbert
Station, the polypropylene and polyethylene spheres in the TCA
scrubber averaged 16% weight loss after 500 hours operation with
5% or 15% solids (SC-124). Some spheres lost mechanical strength,
resulting in wall collapse. The glass marbles in the marble bed
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scrubber at the TVA-EPA installation at Shawnee have also shown
significant weight losses (EL-030).
4. 4 Demister/Reheater Operating Problems
Three of the previously mentioned design and operating
problems - plugging, scaling, and corrosion - have often occurred
in connection with demister and reheater equipment. Since this
experience is common to many of the full scale installations,
it is treated separately in this section.
As described in Section 3, the demisters/reheaters
are situated within the flue gas ductwork following the scrubber.
The demister simply functions as a mechanical barrier to fine
droplets of slurry which are carried out of the scrubber with
the cleaned flue gas. Demister operating problems are a conse-
quence of this basic dilemma. Efficient removal of entrained
mist requires close spacing between the demister elements placed
in the flue gas duct. This, however, makes the equipment subject
to plugging and very difficult to wash.
Demister plugging and/or scaling has been encountered
in many of the full scale scrubbing installations described in
Section 4. Several design modifications have been used in work-
ing towards eliminating this problem. Combustion Engineering,
for example, recognized that reduced gas velocity would aid in
demister maintenance by lowering the amount of slurry carryover
from the scrubber. Since the original start-up attempt at KP&L
Lawrence No. 5, they have added extra scrubber modules so that
the gas velocity through the system is reduced (SU-023).
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Increased distance between the scrubber bed and demister is
also desirable. This would be a difficult modification for
an existing scrubbing system and has not been practiced at KP&L.
Some more recent designs such as TVA's Widow's Creek
unit include demister elements in a horizontal section of duct
following a vertical rise and 90 degree bend after the scrubber
bed (MC-068). This arrangement is expected to have two major
advantages over previous designs. First, the demister is
physically remote from the scrubber bed. Dust, sludge or
droplets of slurry will have less chance of contacting the
demister. Secondly, in this situation, wash water used to
clean the demister blades can be more effectively drained from
the area.
One vendor, Joy Manufacturing Company, offers a
system using a wet electrostatic precipitator following the
scrubber. This equipment requires washing as do mechanical
demisters but does not depend on close spacing or tortuous paths
to separate the mist from the gas. Instead, the mist is removed
by electrical charge as in the conventional electrostatic precipi-
tator for dust control.
Mist eliminator plugging problems can probably be
eliminated by more conservative design in general. A combina-
tion of lower gas velocity and more space between the scrubber
and demister is probably most important to successful operation.
Improved wash systems should also contribute to improved system
reliability. Babcock and Wilcox experienced demister plugging
problems at Commonwealth Edison's Will County Unit (GI-017).
Along with other demister modifications, the washer nozzles were
relocated below the demister baffles in order to facilitate more
efficient washing. This appears to have controlled the demister
pluggage problem (SU-031).
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As described in Section 3 the flue gas reheater
follows the demister in the scrubber exit duct work. The
reheater designs proposed by developers and vendors have included
four options:
a. heat transfer using a single exchanger with
a once-through heat source,
b. heat transfer using a double exchanger and
recirculating heat transfer medium (this option
takes heat from the scrubber inlet gas and
transfers it to the exit gas),
c. direct fired reheat using clean fuel such as
distillate oil or natural gas, and
d. partial by-pass of hot flue gas around the
scrubber.
e. reheat by direct addition of externally heated air.
Options a and b require heat exchange equipment in the duct
work itself. This is most commonly a series of metal pipes
with a hot fluid flowing through them. Option c does not
require pipes in the duct work, but requires substantial quantities
of expensive clean fuel such as distillate oil or natural gas.
Option d can be used only where high SOS removal is not required.
Option e does not involve equipment surfaces which can be fouled,
does not offer a significant pressure drop and allows utilization
of waste heat. It has the disadvantage of the added expense of
an extra fan and oversized duct work and stack.
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In the cases where heat exchangers are placed in
the duct, any material passing through the demister may plug
or scale the reheater surfaces. This problem is compounded by
evaporation of mist containing high concentrations of dissolved
salts as well as suspended solids. Heat exchangers are subject
to the same difficulty as eliminators, since closed spacing of
tubes is necessary for efficient operation. This makes plugging
more difficult to avoid and complicates removal of deposits.
Early installations by Combustion Engineering at
Kansas Power and Light used a water heat exchanger placed in
the duct above the demister. Plugging, scaling, and corrosion
were all experienced. These' problems were reduced, however,
by redesigning the demister and installing soot blowers to keep
the reheaters clean (SU-023).
A bare tube steam heat exchanger with soot blowers
was used by Babcock and Wilcox at Commonwealth Edison's Will
County Unit No. 1. Some problems were encountered with vibra-
tion of the reheater tubes at higher gas flow rates (GI-017).
Baffles were installed successfully to reduce noise and vibration
of the reheater tubes.
Combustion of oil in direct fired burners has been
used by TVA at their Shawnee Station for reheat. Poor combus-
tion has resulted in unburned oil and soot deposits which ignited
on two occasions (EL-030). Installation of mechanical atomizing
nozzles and stainless steel sleeves has corrected the combustion
problem and made the reheat system operable, but oil flow is
restricted to a narrow range. Use of steam heat exchange is
planned for TVA's commercial size installation at Widow's Creek.
The main disadvantages of options a and b are higher
gas side pressure drop, greater investment, and possible fouling
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of heat transfer surfaces. Unlike options c and d, however,
they can interfere with boiler operation and thereby threaten
system reliability.
In summary, reheat is a design problem that will be
unique to each installation.
4 .5 Solids Disposal
Disposal of solid wastes generated by lime/limestone
wet scrubbing processes is currently receiving increased
attention as other problems more critical to reliability are
solved. In general, there are about 5 pounds of waste sludge
(dry basis, ash free) generated for every pound of sulfur in
burned coal. Likewise, there are about 3 pounds of fly ash
generated per pound of sulfur in coal. Thus the total throwaway
(sludge plus ash) requirement for scrubbing systems is about
2% to 3 times the normal coal ash disposal rate (JO-083).
Sludge can be handled and disposed of without
undue environmental effects using sound engineering practices.
A number of methods are being used or investigated for use
with limestone scrubbing plants now on-stream. Disposal cost
will be an important operating expense.
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5.0 COMMERCIAL OPERATING CONDITIONS OFFERED BY SUPPLIERS
OF LIME/LIMESTONE WET SCRUBBING SYSTEMS
As mentioned earlier, there are currently twelve
vendors offering lime/limestone wet scrubbing systems for
commercial application. Seven of the twelve already have full
scale experience. These suppliers have been surveyed to assess
the range of operating conditions being offered with their
systems. The results of this survey as presented by Raben
(RA-074) can be summarized as follows:
Contacting devices for S0a absorption include
Venturis, marble beds, quencher plus tray
absorber spray columns, TCA, and inspirating
scrubbers.
Lime and limestone are the most common alkali
materials but carbide sludge (impure slaked lime)
has also been used successfully at two installations
Liquid-to-gas ratios range from 3.3 to 10.7
liters/cubic meters (25-80 gallons/1000 ft3).
Lowest L/G's are used for marble beds. Highest
L/G's are common in spray columns. Venturi
scrubbers generally use mid-range values. In
general, L/G ratios are higher for limestone
systems than they are for lime systems.
Most systems can be designed for boilers firing
0.5 to 4.0% sulfur fuel. The one exception to
this are systems supplied by Research-Cottrell
which are presently offered only for low sulfur
coal burning applications.
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Limestone stoichiometries vary between 1.1
and 1.5. Lime stoichiometries are slightly
lower - between 0.8 and 1.3.
The amount of solids circulating in slurry
ranges from 5 to 15 weight percent with an
average solids content near 10 weight percent.
Hold tank residence times range from a low
of 3 minutes to a high of 15 minutes.
Module designs as large as 150 MW each for up to
800 MW are provided by U. S. suppliers. With regard to
construction lead times, from 24 to 36 months should be
allowed between requests for bids and start-up of the system
(RA-074, SU-031).
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BIBLIOGRAPHY
AN-056 Ando, Jumpei, Recent Developments in Desulfurization
_of Fuel Oil and Waste Gas .in Japan - 1973. EPA-
R2-73-229, Cincinnati, Ohio, Processes Research,
Inc., 1973.
BE-145 Berkowitz, Joan B., Evaluation of Problems Related
to Scaling in Limestone Wet Scrubbing, EPA-R2-73-
214, Final Report, Cambridge, Mass., Arthur D.
Little, Inc., 1973.
DE-091 Dennett, M., Station Superintendent, Bankside
Power Station, Central Electricity Generating
Board, Letter of 21 May 1973 to John 0. Copeland,
U. S. EPA, Office of Air and Water Programs.
EL-030 Elder, H. W., et al., "Operability and Reliability of
the EPA Lime/Limestone Scrubbing Test Facility",
Presented at the Flue Gas Desulfurization Sym-
posium, New Orleans, Louisiana, 14-17 May 1973.
GI-017 Gifford, D. C., "Will County Unit Limestone Wet
Scrubber", Presented at the 2nd International
Lime/Limestone Wet Scrubbing Symposium, New
Orleans, Nov. 8-12, 1971.
GI-030 Gifford, D. C., Private Communication, 27 August 1973.
HA-145 Harrington, R. E., "Current Status of Sulfur Dixoide
Control Technology", Int. _J. Sulfur Chem. Pt. B>
2(1), 57ff (1972).
-36-
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JO-083 Jones, Julian W. and Richard D. Stern, "Waste Products
from Throwaway Flue Gas Cleaning Processes —
Ecologically Sound Treatment and Disposal",
Presented at the Flue Gas Desulfurization
Symposium, New Orleans, Louisiana, 14-17
May 1973.
KE-024 Kenneway, T., "The Fulham-Simon-Carves Process for
the Recovery of Sulphur from Flue Gases",
J. Air Poll. Control Assoc. 1(4), 266-74 (1957).
MC-068 McKinney, B. G., A. F. Little, and J. A. Hudson, The
Widows Creek Limestone Scrubbing Facility. Pt.
1. Full Scale Facility", Presented at the Flue
Gas Desulfurization Symposium, New Orleans,
Louisiana, 14-17 May 1973.
MC-081 McLaughlin, J. F., Jr., "Sulfur Dioxide Scrubber
Service Record. Union Electric Co. — Meramec
Unit 2", Presented at the 2nd International Lime/
Limestone Wet Scrubbing Symposium, New Orleans,
Louisiana, November 1971.
RA-074 Raberi, I. A., "Status of Technology of Commercially
Offered Lime and Limestone Flue Gas Desulfuriza-
tion Systems", Presented at the Flue Gas Desulfuriza-
tion Symposium, New Orleans, Louisiana, 14-17
May 1973.
SA-099 Sakanishi, Jun and R. H. Ouiq, "One Years Performance
and Operability of the Chemico/Mitsui Carbide
Sludge (Lime) Additive S02 Scrubbing System",
Presented at the Flue Gas Desulfurization Symposium,
New Orleans, Louisiana, 14-17 May 1973.
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SC-124 Schultz, Jim, TVA, Private Communication, August 1973
SL-030 Slack, A. V., "Removing S02 from Stack Gases", Env.
Sci. Tech. 2(2), HO (1973).
SU-023 Sulfur in Utility Fuels: The Growing Dilemma, Pro-
ceedings, Technical Conference, Chicago, Oct.
25-26, 1972, New York, McGraw-Hill, 1972.
SU-031 Sulfur Oxide Control Technology Assessment Panel
(SOCTAP), Final Report on Projected Utilization
of Stack Gas Cleaning Systems by Steam-Electric
Plants, April 1973.
TE-001 Tennessee Valley Authority, Sulfur Oxide Removal from
Power Plant Stack Gas: Conceptual Design and
Cost Study, Use of Limestone in Wet Scrubbing
Process, Prepared for NAPCA by TVA under Con-
tract No. TV-29233A, Knoxville, Tenn., 1969.
TE-012 Tennessee Valley Authority, "Removal of Sulfur Oxides
from Waste Gases: Limestone Slurry Scrubbing:
Effect of Liquor: Gas Ratio and Temperature of
Inlet Gas", November 1970, pp. 19-31.
VA-068 Van Ness, R. P., Manager, Environmental Affairs,
Louisville Gas and Electric, Private Communica-
tion, 13 August 1973.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-74-014
2.
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
Report on the Status of Lime/Limestone Wet
Scrubbing Systems
5. REPORT DATE
30 January 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
NA
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
8500 Shoal Creek Boulevard
P. 0. Box 9948
Austin, Texas 78766
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
No. 68-02-0046
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina
13. TYPE OF REPORT AND PERIOD COVERED
27711
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The report presents results of a study of the status of lime and limestone
wet scrubbing systems for the removal of sulfur dioxide from flue gases of fossil
fuel-fired steam generators. The history of the systems, dating back 40 years,
is reviewed. A general description of current lime and limestone wet scrubbing
processes is given with a discussion of the similarities, advantages, and dis-
advantages of each process. Operating histories of several recent systems are
presented noting the successes and problems of each unit. Solutions to problems
of scrubber and pipe plugging, chemical scaling, corrosion and erosion, and
demister and reheater operating problems are discussed.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution
Chemical Reaction
Desulfurization
Design
Sulfur Dioxide
Limestone
Coal
Sulfur
Calcium Oxides
Combustion Products
Flue Gases
Air Pollution Control
Electric Power Plants
Boilers
13B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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EPA Form 2220-1 (9-73) (Reverse)
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