Sulfur Oxides Control Technology
In Japan
Interagency Task Force Report
June 30, 1978
Prepared For:
Honorable Henry M. Jackson, Chairman
immittee on Energy and Natural Resources
-------
SULFUR OXIDES CONTROL TECHNOLOGY
IN JAPAN
by
M.A. Maxwell
Chief, Emissions/Effluent Technology Branch
Industrial Environmental Research Laboratory
Environmental Protection Agency
Research Triangle Park, North Carolina
H.W. Elder
Manager, Emission Control Development Projects
Division of Chemical Development
Tennessee Valley Authority
Muscle Shoals, Alabama
T.M. Morasky
Manager, SO Subprogram
Air Quality Group
Electric Power Research Institute
Palo Alto, California
Interagency Task Force Report
June 30, 1978
Prepared For:
Honorable Henry M. Jackson, Chairman
Senate Committee on Energy and Natural Resources
-------
CONTENTS
Page
Figures iv
Tables v
Introduction 1
Energy Usage/Supply Trends 6
Regulation of SO. Emission in Japan 8
Overall Status of FGD in Japan 12
Status of FGD in the Japanese Utility Industry 16
Summary of Findings 20
References 25
Appendix (Individual Meeting Reports)
EPDC Isogo Station 26
EPDC Takasago Station 35
EPDC Takehara Station 45
Mitsui Aluminum Omuta Plant 54
EPDC Home Office 67
in
-------
Number
FIGURES
Page
1 Trend in Ambient SO- Concentration in
Japan, 1965-1975 9
2 FGD Growth Rate in Japan, 1970-1977 13
3 EPDC Isogo Plant - Chemico-IHI Process
Diagram 31
4 Isogo Station General Layout 32
5 Isogo Plant FGD System (Photograph) 33
6 Takasago Plant FGD System (Photograph) 39
7 EPDC Takasago Plant - Mitsui-Chemico
Process Flow Diagram 41
8 Takehara Plant FGD System (Photograph) 51
9 EPDC Takehara Plant - Babcock-Hitachi
Process Diagram 52
10 Mitsui Aluminum Plant FGD System
(Photograph) 60
11 Mitsui Aluminum Plant - Mitsui-Chemico
Process Diagram - Unit No. 1 61
12 Mitsui Aluminum - Mitsui-Chemico Process
Diagram - Unit No. 2 62
IV
-------
TABLES
Number Page
1 Plants Visited in Japan 4
2 Organizations Contacted in Japan 5
3 Energy Supply in Japan 7
4 Numbers and Capacities (100 Nm /hr) of FGD
Plants by Major Constructors 15
5 Capacities of Steam Power Plants and FGD
Systems in Japan 17
6 FGD Systems Applied to Power Plants
in Japan 18-19
7 Wastewater Purge from Lime/Limestone Systems 22
8 FGD System Specifications - Isogo Plant 34
9 EPDC Takasago Station - Power Plant/FGD
System Design and Performance Data 40
10 Operating History of No. 1 Unit, Takasago Plant 42-43
11 Operating History of No. 2 Unit, Takasago Plant 44
12 EPDC Takahara Station - Power Plant/FGD System
Design and Performance Data 53
13 Mitsui Aluminum Company - Power Plant/FGD System
Design and Performance Data 63
14 Mitsui - Chemico SO,, Removal Process - Materials
of. Construction 64
15 Mitsui - Chemico S0_ Removal System - Typical
Chemical Analysis of Reagents/Products 65
16 Mitsui - Chemico SO,., Removal System - Investment
and Operating/Maintenance Costs 66
-------
SULFUR OXIDES CONTROL TECHNOLOGY IN JAPAN
Introduction
At the request of the Honorable Henry M. Jackson, Chairman, Senate
Committee on Energy and Natural Resources, the Environmental Protection Agency
organized an interagency task force to evaluate the current status in Japan of
technologies for control of sulfur oxides. Specifically, the task force set
out to study the application of flue gas desulfurization (FGD) or "scrubber"
technology to coal and oil-fired utility and industrial power generating
facilities in Japan. The ultimate goals of the task force were three-fold:
(1) To evaluate the recent advances in Japanese scrubber technology
(2) To determine the basic circumstances surrounding the extremely
successful Japanese scrubber experiences to date
(3) To ascertain to what extent these experiences could be applied to
U.S. coal fired power generating facilities
The task force included the following individuals:
H. William Elder
Manager, Emission Control Development Projects
Division of Chemical Development
Tennessee Valley Authority
Muscle Shoals, Alabama
Michael A. Maxwell (Chairman)
Chief, Emissions/Effluent Technology Branch
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
-------
Thomas M. Morasky
Manager,. SO Subprogram
X
Air Quality Group
Electric Power Research Institute
Palo Alto, California
Representatives of Senator Jackson's staff and the Department of Energy
were also invited but were unable to participate due to prior commitments.
Dr. Jumpei Ando, a professor at Chuo University in Tokyo served as consul-
tant, interpreter .and guide during the visits. His knowledge of the subject
area and facility with both languages were invaluable in promoting effective
dialogue.
During the period January 30 - February 10, 1978, the task force visited
a number of organizations in Japan which are directly involved in some facet
of sulfur oxides control. The trip included visits to eleven scrubber plant
sites as well as discussions with most of the major scrubber system suppliers,
the Japan Environmental Agency, the Electric Power Development Corporation
(EPDC), the Ministry of International Trade and Industry (MITI), and the Aichi
Prefecture Environmental Research Center. Lists of plants and organizations
visited are given in Tables 1 and 2.
The EPDC and Mitsui Aluminum plants were selected for study because of
their similarity to U.S. utility scrubber applications (e.g., coal fired,
limestone scrubbing, U.S. developed scrubber, etc.). The Wellman-MKK process
at Nishinagoya and the Chemico-Mitsui process at Chiba were considered of
importance because these processes employing U.S. technology have been applied
at U.S. utility sites (e.g., Northern Indiana Public Service, Boston Edison
and Potomac Electric Power). Interest in the MHI process applications at
Owase and Shimonoseki resulted from the fact that MHI has provided about half
of the lime/limestone scrubbing systems currently in operation in Japan.
Finally, the Dowa and Kawasaki double alkali process applications were in-
cluded because these technologies involve promising 2nd generation alterna-
tives to lime/limestone scrubbing.
-------
A detailed report covering each of the plants and organizations visited is
being prepared for publication at a later date. In the interest of providing
timely information on the most significant findings, however, this report
primarily addresses application of FGD systems to coal-fired boilers in Japan.
The report also provides an overview of the Japanese energy picture, the
sulfur oxide regulatory framework, the general status of FGD in both the
industrial and utility sectors, and concludes with a summary of findings.
Details of the individual site visits to the coal fired plants are included as
an appendix. The report draws not only upon the prior knowledge of the task
force members and the observations noted during their stay in Japan but also
from several literature sources cited as references.
-------
Table 1. PLANTS VISITED IN JAPAN
Plant
Owner
EPDC
EPDC
EPDC
Mitsui Aluminum
Mitsui Aluminum
Idemitsu Kosan
Chuba Electric
Chuba Electric
Chugoku Electric
Naikai
Dowa Mining
Plant
Site
Takehara
Takasago
Isoga
Omuta
Omuta
Chiba
Nishinagoya
Owase
Shimonoseki
Tamano
Okayama
Plant
Type
C, U
c,
c,
c,
c,
0,
0,
0,
0,
0,
A
U
U
I
I
I
U
U
U
I
FGD
Process
Babcock-Hitachi
Chemico-Mitsui
Chemico-IHI
Mitsui-Chemico
Chemico-Mitsui
Chemico-Mitsui
Wellman-MKK
MHI
MHI
Dowa
Dowa
Capacity
(MW)
250
250
(2 units)
265
175
156
160
220
375
(2 units)
400
30 (eq)
50 (eq)
Absorbent
CaCO
CaC03
CaCO
CaCO
Carbide lime
MgO
Na SO
Ca(OH)2
CaCO
Al2(S04)3-CaC03
A12(SO.) -CaCO
By-Product
Gypsum
Gypsum
Gypsum
Gypsum
Sludge
Sulfur
H2S04
Gypsum
Gypsum
Gypsum
Gypsum
Year
Operational
1977
1975/76
1976
1975
1972
1975
1973
1976
1977
1976
1974
Japan Exlan
Saidalj i
0, I
Kawasaki
(2 units)
80
MgO-CaC03
Gypsum
1976
C = coal, 0 = oil, U = utility boiler, I = Industrial boiler, A - H SO, plant
-------
Table 2. ORGANIZATIONS CONTACTED IN JAPAN
Organization
Aichi Environmental Research Center
Chemico
Chiyoda Chemical Engineering & Construction Co.
Chubu Electric Co.
Chugoku Electric
Dowa Mining Co.
Electric Power Development Co. (EPDC)
Gadelius Co.
Idemitsu Kosan Co.
Japan Environmental Agency
Japan Exlan Co.
Kawasaki Heavy Industries (KHI)
Kureha Chemical Co.
Ministry of International Trade & Industry (MITI)
Mitsubishi Heavy Industries (MHI)
Mitsubishi Kakoki (MKK)
Mitsui Aluminum Co.
Mitsui Miiki Co.
Discussion Sites
Nagoya
Omuta
Tokyo
Nagoya, Owasa
Shimonoseki
Tokyo, Okayama
Tokyo, Isogo, Takehara,
Takasago
Okayama
Chiba
Tokyo
Saidaij i
Tokyo, Saidaiji
Tokyo
Tokyo
Tokyo, Hiroshima,
Owasa, Shimonoseki
Nagoya
Omuta
Omuta, Chiba
-------
Energy Supply/Usage Trends
Energy usage in Japan has increased rapidly during recent years and has
been heavily dependent upon imported oil. The oil crisis of late 1973 and the
serious inflation resulting therefrom have significantly affected Japan's
energy and environmental policies. As shown in the scenario in Table 3,
efforts are underway to shift the energy strategy away from imported oil which
now constitutes more than 70 percent of Japan's total energy supply. In 1975
Q
Japan imported nearly 3.0 x 10 kiloliters of crude oil containing almost
3.0 x 10 tons of sulfur. Since 90 percent of the sulfur in the crude "top-
ping" process remains with the residual oil fraction, more than 40 hydrodesul-
furization plants have been built since 1968 capable of treating around 30 per-
cent of the sulfur rich residual oil. Combustion of the remaining untreated
residual oil comprises about 75 percent of the total SO emissions in Japan.
X
About one fourth of the residual oil is burned in utility boilers with the
remainder spread among other industries.
Although Japan in the early 1960's mined over 50 million tons of domestic
coal yearly, coal production gradually dropped to around 20 million tons/year
as oil imports increased. Coal production is increasing, however, as a
result of recent central government policy aimed at strengthening the coal
mining industry and reducing dependence on oil imports. Use of domestic coal
in the utility industry has been promoted by the Ministry of International
Trade and Industry (MITI) through its "Sunshine" project and implemented by
the Electric Power Development Corporation (EPDC), a government/industry
funded corporation founded in 1952 to mitigate the serious power shortage in
the post-war period of economic reconstruction. EPDC has constructed and is
operating a number of coal-fired power plants equipped with FGD systems, each
of which was visited by the task force. Even though Japan imports over
60 million tons of coal annually, all has thus far been used for coke pro-
duction for the steel industry. Importing of coal for fuel has recently begun
and is expected to increase as more coal-fired power plants are built.
Imports of LNG as an ultra clean fuel are also increasing and will likely find
greater application in the more heavily industrialized and polluted areas.
-------
The "Sunshine" project was begun in 1974 in an attempt to assure a long
term stable supply of clean energy for the future by promoting research and
development work on new energy technologies. Energy technologies under develop-
ment include solar, geothermal, coal liquefaction/gasification and hydrogen.
Table 3. ENERGY SUPPLY IN JAPAN
1975
1985
1990
Hydro power (10 kW)
Conventional
Pumped storage
Geothermal (106 kW)
Domestic oil, gas
(106 kl)
Domestic coal
(106 t)
Atomic energy
(106 kW)
LNG (106 t)
Imported coal (10 t)
for steel industry
for fuel
New energy (10 kl)
Imported oil (10 kl)
Total
kl equivalent)
Amount
24.9
17.8
7.1
0.05
3.5
18.6
6.62
5.06
62.3
61.8
0.5
0.0
286.0
(%)
(5.8)
(0.0)
(0.9)
(3.3)
(1.7)
(1.8)
(13.1)
(0.0)
(73.4)
Amount
41.0
22.5
18.5
1.0
11.0
20.0
33.0
30.0
102.0
86.0
16.0
2.3
432.0
(%)
(3.9)
(0.3)
(1.7)
(2.1)
(7.4)
(6.4)
(12.4)
(0.4)
(65.5)
Amount
51.0
26.5
24.5
3.0
14.0
20.0
60.0
44.0
144.0
104.0
40.0
13.0
452.0
(%)
(3.9)
(0.7)
(1.7)
(1.8)
(11.2)
(7.7)
(14.1)
(1.6)
(57.1)
390.0 (100.0)
660.0 (100.0) 792.0 (100.0)
-------
Regulation of SO,., Emissions in Japan
During the post-war recovery period, sulfur oxide emissions in Japan
increased rapidly due largely to a sharp upswing in the combustion of sulfur
containing fossil fuels which accompanied the rapid economic growth. As can
be seen in Figure 1, however, since 1967 there has been a steady abatement of
this problem reflecting the effects of environmental laws and standards, the
use of low sulfur oil imports, the hydrodesulfurization of residual oil and
the widespread application of FGD systems. Between 1970 and 1975, the volume
of sulfur oxide emissions was reduced by 50 percent despite a 120 percent
increase in energy consumption during that period as the regulation of SO
emissions became much more restrictive. The ambient SO standard was tightened
from 0.05 ppm (yearly average) to 0.04 ppm (daily average) in May 1973 with a
target date of achievement by May 1978. Under this standard, the hourly
average should not exceed 0.1 ppm. The standard is much more stringent than
those in effect in the U.S. and West Germany.
The S0x emission standard enforced by the central government is carried
out under a program known as the "K-value system". Under this system, a
specific allowable quality of S0x emissions for each emitting source within a
given geographical area is calculated by the following equation:
Q = K x 10~3 He2
where Q = allowable S02 emissions in Nm3/hr
He = effective stack height in meters (actual stack height
plus plume ascent distance)
K = constant specified for each of 17 geographical regions
(different for new and existing sources)
-------
0.06
1965 1966 1967 1968
1969 1970 1971
YEAR
1972 1973 1974 1975
Figure 1. Trend in ambient SO2 concentration in Japan, 1965-1975.
-------
The level set for the K-value depends upon the air quality within the
region and on the number of emission sources. The most heavily industrialized
regions have the smallest K-value. The K-values have been revised downward
almost yearly since 1974 in an effort to further reduce emissions and thus
attain the May 1978 target date for achieving the ambient standard.
This "K-value" emission standard, however, has proven unsatisfactory in
keeping the ambient SO concentrations below 0.04 ppm in the large cities and
X
heavily industrialized areas. Therefore, in late 1974 the central government
promulgated a new regulation implemented by the prefectures restricting the
total mass of SO emissions from .each of the eleven most polluted regions.
X
Thirteen additional regions have since been added with the total area covered
now accounting for 34 percent of the sulfur oxides emission sources in Japan.
This new regulation has been largely instrumental in the recently reported
attainment of the ambient standard in 98 percent of the regions. Plants
smaller than 0.4 MWe equivalent are required to use low sulfur oil. Larger
plants have specific allowable emission rates established by the prefectural
governor which can be met by using ultra low sulfur oil or higher sulfur oil
in combination with FGD. New plants in the most restrictive regions, for
example, are required to use fuel/scrubber combinations equivalent to less
than 0.079 percent sulfur oil. These plants have generally elected to use
naphtha, kerosene, or gas.
For regions where total mass regulations have not been applied, SO
X
emissions are controlled by the K-value system. However, most larger plants
(particularly new ones) in these regions are controlled by industry agreements
with prefectural or city authorities. These controls are usually much more
stringent than those'required by the central government. For example, many
power plants in remote areas are required to use oil with sulfur contents less
than 0.3 percent or apply FGD to attain the equivalent sulfur reduction.
10
-------
One of the motivating factors behind the progress in SO abatement has
X
been the "Pollution-Related Health Damage Compensation Law" which has been in
effect since 1974. This law designates certain regions as polluted areas.
Inhabitants of these regions who are diagnosed by doctors as having pollution
related illnesses such as chronic bronchitis are designated as pollution-
3
related patients. Plants emitting more than 5-, 000 Nm /hr of flue gas are
assessed a tax based upon the total amount of S0~ emitted, even though the
emission regulations are being met. These tax proceeds are used to provide
medical care for these pollution-related patients. This tax rate in the more
heavily polluted areas has increased by a factor of 10 since 1975. Consequently,
a number of companies presently meeting the regulations are now considering
installing FGD plants because the resulting decrease in the tax may well
compensate for the FGD costs under certain conditions.
11
-------
Overall Status of FGD in Japan
Application of FGD systems in Japan has shown remarkably rapid progress
since 1972 as shown in Figure 2. This growth rate can be largely attributed
to several factors; (1) the elimination of the previous sizable cost differ-
ential between high sulfur fuels controlled by FGD and low-sulfur fuels and
(2) the increasing confidence in the reliability of FGD system operation.
However, this growth rate has begun to decline due to the following reasons:
(1) Ambient S0? concentrations in large cities and industrial districts
have been reduced to the range 0.02-0.03 ppm, almost achieving the
ambient standard of 0.016 ppm.
(2) The recent downturn in the Japanese economy has inhibited industry in
building new plants. The majority of the FGD systems were built
between 1970 and 1975 when the Japanese economy was growing rapidly.
(3) Saturation of the FGD by-product market and a decrease in the price
differential between high sulfur and low sulfur oil have resulted in
more extensive use of low sulfur fuels since Japan has little area
available for discarding of waste products.
Of lesser importance is the fact that the stringent NO emission standards
x
have resulted in a number of processes for simultaneous removal of NO and SO
xx
being developed. Rather than installing separate systems for NO and SO
X X
control, much of the industry is waiting for this new technology to be fully
demonstrated.
Nevertheless, the present government policy of increased use of coal (much
of it imported) for power production will necessitate the use of additional FGD
systems in the future. Three new coal fired utility units totaling 1175 MW
which will employ limestone-gypsum processes are presently under construction
and are scheduled for start-up in 1979/1980.
12
-------
1200
1970 1971 1972 1973 1974
YEAR
1975
1976 1977
APPROXIMATE
Figure 2. FGD growth rate in Japan, 1970 through 1977.
-------
Over 500 major FGD plants having a combined capacity of about (90,000,000
Nm /hr about (31,000 MWe equivalent) were operational in Japan at the beginning
of 1978. Table 4 summarizes these systems by constructor, process type and
capacity. Approximately half of the total capacity represents utility boiler
application (primarily oil fired) while the remainder includes industrial
boilers, sintering plants, smelters, sulfuric acid plants, etc.
Around 50 percent of the plant capacity use the lime/limestone process
producing usable gypsum; 16 percent use the indirect lime/limestone process
(double alkali type); 13 percent use regenerable processes to by-produce sul-
furic acid, elemental sulfur, and ammonium sulfate; and 24 percent use sodium
scrubbing to by-produce sodium sulfite or sulfate. The average plant size was
3 3
427,000 Nm /hr for the lime/limestone systems, 291,000 Nm /hr for indirect
3
lime/limestone systems, 378,000 Nm /hr for the regenerable processes and
3
59,600 Nm /hr for the sodium scrubbing plants. Around 80 percent of the
sodium scrubbing units by-produce sodium sulfite for use in paper mills while
the rest oxidize the sulfite to sulfate for either use in the glass industry
or disposal as wastewater.
In addition to the 392 sodium scrubbing units shown in Table 4, there are
around 500 small commercial sodium scrubbing systems having an average capacity
of 20,000 Nm3/hr.
14
-------
Table 4. NUMBERS AND CAPACITIES (1,000 Nra /hr) of FGD PLANTS BY MAJOR CONSTRUCTORS
Lime/Limestone
Plant Constructor
Mitsubishi Heavy Industries
(MHI)
Ishikawajima H. I. (IHI)
Hitachi, Ltd.
Mitsubishi Kakoki (MKK)
Kawasaki Heavy Industries
Tsukishima Kikai (TSK)
Chiyoda Chemical Engineering
& Construction
Oji Koei
Fuj i Kasui Engineering
Kurabo Engineering
Mitsui Miike-Chemico
Ebara Manufacturing
Nippon Kokan (NKK)
Kureha Chemical
Showa Denko
Gadlius
Sumitomo (SCEC)-Wellman
Mitsui Metal Engineering
Kobe Steel
Japan Gasoline
Dowa Engineering
Niigata Iron Works
Mitsui Shipbuilding
Sumitomo Heavy Industries
Total
33
17
13
2
4
1
7
4
3
4
5
1
94
(2)
Gypsum
(18,270)
(4,445)
(6,940)
(256)
(756)
(3,954)
(2,744)
(245)
(1,006)
(1,125)
(330)
(40,171)
Indirect
Lime/Limestone
Gypsum
6 (5,450)
4 (398)
14 (4,459)
5 (413)
11 (1,914)
1 (150)
5 (453)
1 (185)
47 (13,422)
Regenerable/Once through
/
0
2
13
1
1
1
2
6
2
1
1
30
SO S
(590)
(6,478)
(88)
(18)
(500)
(1,990)
(1,288)
(130)
(125)
(150)
(11,357)
Na2S°3
3
79
15
41
7
40
57
6
106
10
6
8
5
8
1
392
(292)
(4,351)
(603)
(913)
(256)
(4,042)
(4,280)
(270)
(3,751)
(1,167)
(62)
(1,431)
(1,372)
(1,291)
(160)
(24,241)
36
96
30
56
17
46
14
57
13
112
5
21
12
8
5
8
6
6
5
2
5
1
1
1
563
Total
(18,562!
(8,7961
(8,133!
(7,6431
(6,380]
(4,528)
(4,459)
(4,280)
(4,224)
(4,182)
(3,244)
(3,081)
(2,447)
(1,431)
(1,372)
(1,291)
(1,288)
(1,136)
(1,125)
(455)
(500)
(185)
(160)
(150)
(89,138)
Process type
(2)
Byproduct
-------
Status of FGD in the Japanese Utility Industry
As shown in Table 5, nine major private utility companies have produced
about 70 percent of the total steam electric power generated in Japan largely
using imported oil. The Electric Power Development Co. (EPDC) has been the
primary consumer of domestic coal for power production. However, coal fired
utility capacity presently accounts for less than 3 percent of the steam electric
power produced. The total capacity of the utility steam electric generating
industry (including those plants under construction) is 87,475 MW. This repre-
sents about 75 percent of the total utility power generated in Japan, with
hydro and nuclear comprising the remaining 20 percent and 5 percent, respectively.
The present FGD utility capacity in service in Japan stand at 10,076 MW
with another 3750 MW under construction or planned. This represents around 16
percent of the utility industry steam generating capacity. Comparable figures
for the U.S. utility situation show 11,508 MW of FGD capacity in operation with
an additional 44,171MW under construction or planned. This corresponds to
around 22 percent of the total U.S. coal fired power generating capacity.
Among the major power companies, Tokyo, Electric, Kansai Electric, and
Chubu Electric supply power to the largest cities and industrial complexes in
Japan. As may be seen from Table 5, these companies have elected to use low
sulfur fuels such as naphtha and LNG in heavily polluted sections of their
service areas due to their apparent concern that SC> emission standards may be
further tightened beyond the point easily achievable by FGD. Recent regulations
restricting total SCL mass emissions require large power plants in designated
regions to maintain stack SCL outlet concentrations below 50 ppm, thus necessi-
tating the use of low-sulfur fuel for reheat. More stringent standards may
reduce the use of FGD as an effective control strategy. Conversely, Hokuriku
Electric and Chugoku Electric have power plants more remotely located from the
large cities and hence have a larger percentage of their capacity using FGD
systems.
Table 6 shows a complete listing of FGD systems installed at power plants
in Japan.
16
-------
Table 5. CAPACITIES OF STEAM POWER PLANTS AND FGD SYSTEMS IN JAPAN
Power generation (MW)
Power Company
Hokkaido
Tohoku
Tokyo
Chubu
Hokuriku
Kansai
Chugoku
Shikoku
Kyushu
EPDC
Nilgata
Showa
Toyama
Mizushima
Sumitomo
Sakata
Fukui
Others
TOTAL
Existing
1,270
3,925
19,167
9,933
1,412
10,672
3,777
2,687
4,500
1,430
350
550
750
462
368
0
0
5,512
66,775
Under
Construction
1,225
1,200
4,400
3,800
1,000
1,200
1,800
450
2,700
1,000
350
0
0
0
250
700
250
375
20,700
Total (A)
2,495
5,125
23,567
13,733
2,412
11,872
5,777
3,137
1,376
2,430
700
550
750
462
618
700
250
5,887
87,475
FGD (MW)
Existing
0
550
283
970
600
930
1,350
900
1.376
1,280
175
400
250
156
156
700
0
0
Under
Construction
525
320
0
0
500
0
700
0
250
1000
175
0
0
0
0
0
250
0
Total (B)
525
900
0
970
1,100
930
2,050
900
1,626
2,280
350
400
250
156
156
700
250
0
B/A
(%)
21.0
17.6
1.2
7.1
45.6
7.8
36.8
12.5
22.6
93.8
50.0
72.7
33.3
33.8
25.2
100.0
100.0
0.0
10,076
3,750
13,826
15.8
-------
Table 6. FGD SYSTEMS APPLIED TO POWER PLANTS IN JAPAN
00
Power company
Tohoku
Tokyo
it
Chubu
ii
Hokuriku
Kansai
Chugoku
Hokkaido
Power station
Shinsendai
Hachinohe
Niigata
Niigata H.
Akita
Kashima
Yokosuka
Nishinagoya
Owase
n
Toyama
Fukui
Nanao
Sakai
Amagasaki
Osaka
M
Kainan
Mizushima
Tamashima
Shimonoseki
Higashitomakomai
Boiler
No.
2
4
4
1
3
3
1
1
1
2
1
1
1
8
2
1
3
2
4
4
2
3
2
2
1
1
MW
600
250
250
600
350
600
265
220
375
375
500
350
500
250
156
156
156
156
156
600
156
500
350
400
175*
500
FGD
MW
150
125
125
150
350
150
133
220
375
375
250
350
500
63
35
121
156
156
156
156
150
100
500
350
400
175
250
Process developer
Kureha-Kawasaki
Mitsubishi H.I.
Wellman-MKK
Mitsubishi H.I.
Kur eha-Kawa s aki
Hitachi -Tokyo
Mitsubishi H.I.
Wellman-MKK
Mitsubishi H.I.
n
Chiyoda
n
Not decided
Sumitomo H.I.
Mitsubishi H.I.
"
n
Babcock-Hitachi
n
n
Mitsubishi H.I.
Babcock-Hitachi
n
it
Mitsubishi H.I.
n
Not decided
Absorbent, precipitant
Na^SO , CaCO,.
CaO
Na SO
CaCO
Na2S03, CaCO^
Carbon,
CaC03
Na SO
CaO
n
, CaC03
Carbon
CaO
CaCO
n J
CaO
CaCO,
By-product
Gypsum
11
H SO.
Gypsum
n
n
n
H SO.
Gypsum
11
n
n
M
H SO.
Gypsum
n
n
n
"
11
n
M
II
II
II
II
II
Year of
completion
1974
1974
1976
1976
1977
1972
1974
1973
1976
1976
1974
1975
1978
1972
1973
1975
1976
1975
1975
1976
1974
1974
1975
1976
1976
1979
1981
*Coal fired boilers. Others are for oil fired boilers.
-------
Table 6. FGD SYSTEMS APPLIED TO POWER PLANTS IN JAPAN (Continued)
Power company
Shikoku
ii
Kyushu
n
EPDC
Niigata
Showa
ii
Toyama
Mizushima
Sumitomo
Sakata
ii
Fukui
Power station
Anna
Sakaide
Karita
Karatsu
n
Ainoura
n
Buzen
n
Takasago
ii
Isogo
Takehara
Matsushima
n
Niigata
Ichihara
ii
Toyama
Mizushima
Niihama
Sakata
n
Fukui
Boiler
No.
3
3
2
2
3
1
2
1
2
1
2
1
1
1
2
1
1
5
1
5
3
1
2
1
MW
450
450
375
375
500
375
500
500
500
250*
250*
265*
250*
500*
500*
350
150
250
250
156
156
350
350
250
FGD
MW
450
450
188
188
250
250
250
250
250
250
250
265
250
500
500
175
150
250
250
156
156
350
350
250
Process developer
Kureha-Kawasaki
n
Mitsubishi H.I.
ii
n
n
n
Kureha-Kawasaki
M
Mitsui-Chemico
n
Chemico-IHI
Babcock-Hitachi
Not decided
n
MHI
Showa Denio
Babcock-Hitachi
Chiyoda
Mitsubishi H.I.
IHI
Mitsubishi H.I.
n
Not decided
Absorbent, precipitant By-product
Na SO,,, CaCO.,
z d -J
Gypsum
n
CaO
CaCO
3,,
Na2SO.,, CaC03
CaCO,,
Na SO , CaCO
CaCO.,J
H SOT, CaCO
CaO J
CaCO
Year of
completion
1975
1975
1974
1976
1976
1976
1976
1977
1978
1975
1976
1976
1977
1980
1980
1975
1973
1976
1975
1975
1975
1976
1977
1977
*Coal~fired boilers. Others are for oil-fired boilers.
-------
Summary of Findings
Both the United States and Japan have emerged as world leaders in
developing and applying FGD technology. Application of FGD systems in Japan
has generally preceded that in the U.S., however, because of the serious air
pollution problems of the 1960's which resulted from the concentrated industry
density and its proximity to population centers. Over 500 major FGD plants
having a combined equivalent capacity of 27,500 MWe are presently in operation
in Japan. Around half of this total represents utility boiler applications
(predominantly oil fired), 98 percent of which produce usable gypsum from
lime/limestone or double alkali FGD processes. Comparable figures for U.S.
coal-fired utility applications show 11,508 MW of FGD capacity in service, of
which 94 percent are lime/limestone processes producing a discardable sludge.
Seven of the plants visited used lime/limestone scrubbing systems which
produced marketable gypsum for use in the wallboard and portland cement indus-
tries. The remaining four plants employ double alkali, Wellman-Lord and
magnesia scrubbing techniques which produce marketable gypsum, sulfuric acid
and elemental sulfur, respectively.
FGD technology is working well in Japan on both utility and industrial
applications. Each of the eleven scrubber installations visited was designed
for and routinely attained SO- removal efficiencies in excess of 90 percent
(93 percent average) while achieving operabilities exceeding 96 percent (98 per-
cent average). The performance of the coal fired units was not appreciably
different from that of their oil fired or industrial counterparts with respect
to S02 removal efficiency and scrubber system reliability. This outstanding
performance is typical of that generally reported for other FGD systems.
The successful operation of lime/limestone scrubbers in Japan had been
partially attributed earlier as a result of generally open loop operation
created by purging large quantities of process liquids. The extent of liquid
20
-------
blowdown, however, is variable; water removed from a Japanese lime/limestone
scrubber system via the gypsum produced and liquid purged is often quite
similar in quantity to that removed in a typical closed loop U.S. scrubber
system employing ponding. In order to define the Japanese FGD systems on a
basis comparable to those in the U.S., it is necessary to relate the quantity
of gypsum produced by an FGD system to the amount of process liquids purged,
thus establishing an effective pond disposal solids concentration. The ultimate
settled solids concentration in a closed loop disposal pond serving a closed
loop lime/limestone scrubbing system in the U.S. is generally in the 50 percent
range. Table 7 lists all data presently available relative to liquid purge
rates of lime/limestone FGD systems applied to Japanese utility boilers. It
thus appears that many Japanese plants operate with much tighter liquid loops
than some in the U.S. while others operate in a much more open loop fashion.
It is significant that the effective pond solids concentration for the plants
listed ranges from 29-77 percent with a midpoint of 53 percent. The data show
that two of the three coal fired FGD plants are, thus, relatively tight in
their water balance and could be considered closed loop if operated as a pond
disposal system in the U.S. However, the coal fired unit with the lowest S0_
inlet concentration is operated with a high blowdown rate, perhaps to insure
the high performance needed at this plant.
A number of differences became apparent during the course of comparing the
Japanese scrubber situation with that in the U.S.
The Japanese suppliers and users of FGD systems recognize and accept the
fact that scrubbers basically involve chemical processes requiring carefully
controlled operation by personnel specifically trained for this purpose. Many
utilities including EPDC contract with subsidiary companies to supply scrubber
system operating and sometimes maintenance services. These specially trained
personnel are not rotated into the power plant for other duties as is generally
the case with U.S. utilities.
21
-------
Table 7. WASTEWATER PURGE FROM LIME/LIMESTONE SYSTEMS
Effective
Process
Lime
Mitsubishi (MHI)
Mitsubishi (MHI)
Mitsubishi (MHI)
Limestone
Babcock-Hitachi
Babcock-Hitachi
Babcock-Hitachi
IHI-Chemico
Mitsubishi (MHI)
Mitsui-Chemico
User
Chubu Elec.
Kansai Elec.
Kyushu Elec.
Chugoku Elec,
Chugoku Elec.
EPDC
EPDC
Chugoku Elec.
EPDC
Plant Site
Owase
Kainan
Karita
Mizushitna
Tamashima
Takehara
Isogo
Shimonoseki
Takasago
MW
750
150
188
105
500
250*
525*
400
500*
Inlet
so2,
1,600
270
600
400
1,480
1,700
400
1,800
1,700
Waste
Water,
t/hr (A)
6
1.5
3.7
1.5
4
12
20
3
15
Gypsum,
t/hr
Solid Moisture
(B) (C)
30
0.9
2.2
0.9
19.0
11.2
9.0
16.2
17.4
3.0
0.1
0.2
0.1
1.9
1.1
1.6
1.8
1.8
wo. i_ c: J-
Ratio
(A+C)
(A+B+C)
0.23
0.64
0.64
0.64
0.24
0.54
0.71
0.23
0.49
i. I/LIU.
Solids
Concentration,
%
77
36
36
36
76
46
29
77
51
*Coal fired boilers
-------
The design of scrubber systems in Japan appears to have generally been
approached with a more conservative philosophy than that in the U.S. Speci-
fications provided by the user utility to the scrubber system supplier do not
appear to be more detailed than those supplied in the U.S. However, the user
expects and, in fact, demands that the scrubber system supplied perform with a
reliability compatible with that of the power generating plant. For example,
EPDC requires the scrubber system supplier to correct at his expense any
process/equipment problems that occur within a year after acceptance of the
system. This philosophy has generally resulted in scrubber systems which are
initially more expensive than their U.S. counterparts but which also have
required less subsequent modifications and maintenance as a result of fewer
operating problems. The fact that one supplier (MHI) has provided about half
of the lime/limestone scrubbing systems in Japan has undoubtedly enhanced the
reliability obtained.
The range of sulfur content of the coal burned in Japanese utility and
industrial boilers is significantly but not drastically lower than that used
in U.S. power generating systems. This sulfur content ranges from 0.7 percent
at EPDC's Isogo plant to 2.4 percent at Mitsui Aluminum's Omuta Plant with the
EPDC Takehara and Takasago plants each averaging around 2.0 percent. Because
of the high ash content and intermediate heating values of the Japanese coals,
the S09 concentration in the flue gas produced is equivalent to that produced
from U.S. coals of somewhat higher sulfur content. For example, the 2.4 per-
cent sulfur coal used in the Omuta plant results in an inlet SO- concentration
approximately equivalent to a 3.0 percent sulfur Midwest or Eastern coal.
Japanese FGD systems have been generally employed with flue gases having
SO inlets of 400-2300 ppm. It is significant that this range of inlet
sulfur values covers many of the scrubber systems presently applied to U.S.
coal fired utility boilers. However, there is no experience in Japan with the
higher sulfur coals currently used in conjunction with many U.S. utility FGD
systems. These higher S0? content flue gases are generally more inherently
difficult to scrub due to mass transfer limitations.
23
-------
Japan employs a stringent continuous monitoring and enforcement program
to insure that utility and industrial sources are in continuous compliance
with environmental regulations. Each prefectural government operates an
environmental research center (subsidized by the central government), most of
which are directly linked via telemetry systems to automatic monitoring sta-
tions located at major emission sources and key ambient sites. The existence
of these monitoring systems likely has been instrumental in assuring that
emission sources remain in constant compliance since violations would result
in fines and/or forced shutdown of the source.
In some areas where the ambient concentration of sulfur oxides is con-
sidered to be sufficient to cause health problems, an SO emission tax has
X
been levied. This tax system has been in effect since 1974 and applies to
plants emitting more than 5000 Nm /hr of flue gas. For example, plants in the
industrialized Chiba area are presently taxed at the rate of 345 yen/Nm of
3
SO emitted. For a typical 150 MW plant in this area emitting 100 Nm /hr SO
x „ x
after 95 percent SO control, the daily tax would exceed 828,000 yen (^$4200
equivalent). A number of companies are presently considering installing FGD
systems even though they are meeting the SO regulations using low sulfur fuel
X
since the resulting reduction in tax obligation may more than offset the cost
of FGD. These tax proceeds have been used for the medical care of patients
diagnosed as having pollution related illnesses such as chronic bronchitis.
The last difference can best be expressed as the sincere cooperative
spirit which appears to exist among Japanese industry (both users and sup-
pliers) and the regulatory agencies. The major emphasis on installing pollu-
tion control equipment occurred during a period of strong economic growth when
capital expenditures were easily absorbed. The central government has assisted
industry in many instances in constructing pollution control facilities by
providing low interest loans and allowing 7 year depreciation of the facilities.
The need for environmental controls for sulfur oxides was at the crisis level
in the late 1960's when Japan's scrubber installation program began to accelerate.
The national goal of a cleaner environment has been accepted by the utility
industry which has made a sincere effort to buy the best scrubbers available
and to operate them in the manner for which they were designed. Intangible
factors such as the Japanese culture/work ethic and the complex government/industry
interrelationship are also of importance but perhaps, the most difficult to
define.
24
-------
References
1. Elder, H.W. et al, Sulfur Oxide Control Technology - Visits in
Japan - August 1972 - Interagency Report, October 30, 1972.
2. Ando, J., Recent Developments in Desulfurization of Fuel Oil
and Waste Gas in Japan - 1973, EPA-R2-73-229, May 1973.
3. Hollinden, G.A. and Princiotta, F.T., Sulfur Oxides Control
Technology - Visits in Japan - March 1974, Interagency Report,
October 15, 1974.
4. Ando, J. and Isaacs, G.A.., S0? Abatement for Stationary Sources
in Japan, EPA-600/2-76-031a, January 1976.
5. Kawanishi, S., Environmental Laws and Regulations in Japan, Japan
Environmental Agency Report, February 1976.
6. Ando, J. and Laseke, B.A. , SO,, Abatement for Stationary Sources
^
in Japan, EPA-600/7-77-103a, September 1977.
7. Kagawa, T., Quality of_ the Environment in Japan-1977, Japan
Environmental Agency Report, November 1977.
8. Ando, J. "Status of SO and NO Removal Systems in Japan," in
X X
Proceedings: Symposium on Flue Gas Desulfurization - Hollywood,
Florida, November 1977 (Volume 1) EPA-600/7-78-058a, March 1978.
9. Ando, J. et al, SO^ Abatement for Stationary Sources in Japan -
March 1978, draft report to be published, prepared under EPA
Contract 68-02-2161.
10. Laseke, B.A., EPA Utility FGD Survey: December 1977 - January
1978, EPA-600/7-78-051a, March 1978.
25
-------
Electric Power Development Company
Ishikawaj ima-Harima Heavy Industries Company - Chemico Process
Meeting on January 31, 1978 at 1:00 p.m. at EPDC's Isogo Station.
Attendees
EPDC: Yasuyuki Nakabayashi, Senior Power Engineer
Toshig Hayase, Deputy General Manager, Thermal Power Department
Atsusi Murata, Assistant Power Station Superintendent
Study Team: Jumpei Ando, M. A. Maxwell, T. M. Morasky, H. W. Elder
Background and Summary
The Isogo power station of EPDC is located in Yokohama, a heavily indus-
trialized area near Tokyo. The environmental standards for the area are the
most stringent in the country and S09 emission from the plant is limited to
3
48 Nm /day—equivalent to 60 ppm. Tokyo Electric burns LNG in a neighboring
plant in order to meet the strict requirements so use of coal at the Isogo
plant presents a real challenge. The plant consists of two 265 MW units built
in the late 1960's. FGD units supplied by IHI-Chemico were added in 1976.
The boilers normally burn coal but can also fire low-sulfur oil. A 50-50
mixture of coal and oil is used occasionally depending on fuel availability
and cost. The coal is delivered by 5000-ton ships (300 vessels per year) from
Hokiado and Kyushu; also about 50,000 tons per year of imported coal is used.
The coal averages 6200 kcal/kgm and contains 16 percent ash. The maximum
sulfur content is 0.6 percent and it normally ranges from 0.3 to 0.5 percent.
The FGD system also is needed for particulate control. The plant is equipped
o
with electrostatic precipitators that reduce the ash loading to 0.6 gm/Nm and
26
-------
3
further reduction to 0.05 g/Nm is accomplished in the two-stage venturi
scrubber. The boilers operate at about 75 percent load factor with reduction
to 50 percent load during the night. The FGD system has effectively met the
emission requirements and reliability has been near 100 percent after the
startup period.
Process Description
The FGD system is similar to the Chemico design for U.S. installations
except that limestone is the absorbent. A flowsheet for the process is shown
in Figure 3. Two equipment trains each treat 900,000 Nm /hr. The system is a
retrofit installation and previously existing ID fans supply gas to new booster
fans to accommodate the FGD system pressure drop of 820 mm H~0. The gas is
cooled and cleaned in two-stage, fixed-throat venturi absorbers; the L/G in
both stages is about 70 gal/1000 ft . The pH in the first stage is 5.4 and
about 70 percent of the SO^ removal takes place in this stage. The pH in the
second stage is controlled at about 7. Overall stoichiometry is about 1.05.
The limestone is purchased in pulverized form (100 percent minus 325) and
slurried with fresh water to 15 percent solids. Limestone slurry is fed to
the second-stage absorber and the effluent is pumped to the first stage for
maximum utilization of the limestone. The recirculated slurry contains about
7 percent solids; dilution results from use of fresh water for mist eliminator
wash. A bleed stream from the first stage absorber is treated in a forced
oxidation system to produce gypsum. Facilities for sulfuric acid addition to
adjust pH are provided but they have not been needed. Gypsum is dewatered in
thickeners and centrifuges and except for a blowdown stream the clarified
liquor is returned to the absorber system. The blowdown is needed primarily
to control chloride concentration below 5000 ppm and the liquor is discharged
through a waste water treatment facility where the suspended solids, BOD, COD,
and pH are controlled. Dissolved solids are not regulated.
27
-------
The scrubber exhaust gas passes through a chevron-type mist eliminator
and is reheated to 120°C by direct combustion of low-sulfur oil; reheat adds
about 10 ppm S0? to the stack gas.
System Design and Performance
The FGD system components are described in Table 8. The area available
for the retrofit installation was small and the system was a tight fit. The
general arrangement is shown in Figure 4 and a photograph is shown in Figure 5.
The cylindrical ve'nturi absorbers are of the Chemico type with pie-shaped
chevron mist eliminator elements located in the horizontal position around the
circumference of the vessel at the scrubber outlet. The superficial velocity
below the fixed throat venturi section is about 10 ft/sec. The bottom of the
absorber vessel serves as the recirculation tank; spare recirculation pumps
are installed. The liquor rate is fixed so that during gas flow turndown the
L/G exceeds the design rate of 70 gal/1000 ft . The mist eliminator for each
unit is washed intermittently with fresh water at a rate of 21 tons/hr. The
scrubber is constructed from mild steel and is flake lined (applied with
brush). Piping is rubber lined. Pumps have stainless steel housings
and silicon carbide impellers.
A total of nine centrifuges are installed for dewatering gypsum; at full
load one is a spare for maintenance. Initially, flow distribution to the
centrifuges was by orifice plates. Because of erosion problems, they have
been replaced with control valves. The FGD systems have operated with a
reliability of near 100 percent since startup in 1976. No. 2 boiler was shut
down in March 1977 for its annual scheduled maintenance. No scaling was noted
in the absorbers. However, some slight erosion on the recycle pumps was
noted. No. 1 unit was inspected in May 1977. No major maintenance on the
absorber was required as a result of this inspection. However, the impeller
had to be repaired (hard facing applied) and a number of small valves were
replaced because of erosion. This appears to be expected by the plant per-
sonnel and these valves will be replaced routinely. The limestone slurry feed
valves are particularly subject to high erosion rates.
28
-------
Of the three scrubbing systems operating on coal-fired boilers of EPDC
the Isogo units operate with the most open loop concerning water balance.
This may account in part for the high reliability of these scrubbers. About
10 ton/hr/unit is blown down to maintain chloride to less than 5000 ppm in the
scrubbing liquor; this amount is equivalent to discharge of the product gypsum
as a 29 percent slurry. The high water usage results in part from use of
fresh water to make limestone slurry. Whenever recycle supernate from the
process is used to make fresh slurry, removal efficiencies drop and limestone
utilization rates decrease (probably the result of "blinding"). Plant personnel
feel that perhaps the fly ash solubles affect system chemistry in some unknown
manner.
The gypsum produced is low grade because of the high ash content (about
16 percent), and the relatively high moisture (15 percent). However, it is
suitable for use in cement and is sold for the cost of delivery.
Three operators per shift are required to operate both FGD trains. In
addition, two additional people are used on the day shift to perform routine
maintenance and chemical analyses. Also, one operator per day is used to
handle the gypsum intermittently and to handle limestone deliveries. The men
operating the scrubbers are assigned full time and are not rotated into the
power plant. This assures that the unit is operated as a chemical plant and
also helps account for the high reliability.
Analysis of Significance
The Isogo experience is particularly significant to the U.S. situation
for several reasons. The system design is quite similar to that provided by a
domestic vendor; the power plant is fired with coal; the process uses limestone,
and the regulations that must be met are severe. The high removal efficiency
(93 percent average) with limestone in venturi scrubbers is impressive and the
reliability approaching 100 percent is outstanding. Several factors appear
29
-------
to be important to the successful operation. Probably most important is the
low inlet S09 concentration. The 0.3-0.5 percent S coal allows use of limestone
in a venturi system where either a more reactive absorbent (lime) or an absorber
with more liquid holdup would be required with high-sulfur coal. Also, the
extremely high L/G for a low S09 concentration decreases the need for dissolu-
tion of CaCO_ in the absorber and reduces the "make per pass." The latter, in
combination with the high removal efficiency and the low stoichiometry undoubt-
edly reduces the scaling potential prevalent with limestone scrubbing and high
sulfur coal. The extremely fine particle size of the calcium carbonate also
is helpful.
The relatively high use of fresh water is added insurance against high
sulfate supersaturation levels and provides for good irrigation of mist elimina-
tor surfaces. It also results in a high blowdown rate that requires extensive
waste water treatment. It is significant that there is no regulation control-
ling dissolved solids content of effluents discharged to the sea. This is
understandable where the receiving body of water is already saline, but the
practicft may not be prudent for fresh water streams such as the water courses
adjacent to most U.S. power plants.
Use of "specialty" personnel for operation of the FGD system is particu-
larly instructive. It is likely that a cadre of trained personnel whose
primary responsibility is operation of a process-oriented system contributes
in a major way to a successful program. The fact that the system design
overwhelms the small amount of SO- that it sees certainly makes their job
easier.
30
-------
Figure 3.
EPDCISOGO PLANT
CHEMICO-IHI PROCESS DIAGRAM
MIXING CHAMBER
AFTER V_y BURNING
FURNACE
FROM BOILER IDF
1ST STAGE
ABSORBER
2ND STAGE RECIRCULATION
I 1 ABSORBER PUMP
RECIRCULATION
PUMP
CaS03SLURRY
SLURRY TANK
2ND STAGE
ABSORBER
CONC.
H2S04
TANK
OXIDATION
TOWER
OXIDATION
TOWER SUPPLY
PUMP
WASTE WATER
TREATING
EQUIPMENT
—H2S04
K OXIDATION TOWER
^- SUPPLY TANK
GYPSUM
STORAGE
FILTRATE FILTRATE
TANK PUMP
-------
OJ
iOO **0 *60 440 420 400 S«Q
H__I__I-!_I_J
1NL£T
Figure 4. Isogo Station Geneiral Layout
-------
Figure 5.
Isogo Plant FGD System
33
-------
Table 8. FGD SYSTEM SPECIFICATIONS
Plant Specifications
Boiler
Type
Evaporation rate
Flue gas volume
Fuel
Flue gas temperature
Draft control
Manufacturer
FW single drum radiation reheat,
natural circulation and indoor
840 tons/hr each
879,100 Nm3/hr (MCR) each
Coal
143°C (AH outlet)
Balanced draft
Ishikawajima-Harima Heavy Industries,
Company, Ltd.
Flue gas desulfurization system
Type
Gas volume
Efficiency of 803 removal
Efficiency of dust removal
Coal compositions
Absorbent
Byproduct
Gas reheating system
Area of installation
Manufacturer
IHI-Chemlco type, limestone liquid
scrubbing-gypsum recovery
900,000 Nm3/hr (MCR); 450,000 Nm3/hr
(night hours) each
90%
96.7%
Inherent water 4.2%
Ash content 16.0%
Calorific value 6,200 kcal/kg
Sulfur content 0.2-0.6%
Limestone 50 tons/day each (approx.)
Gypsum 120 tons/day each (approx.)
After-burning
8,000 m2 (total/approx.)
Ishikawajima-Harima Heavy Industries
Company, Ltd.
Main Equipment
Absorbent supply process
Limestone silo
Makeup pump
Absorption process
1st stage absorber
2nd stage absorber
Boost up fan
Gas volume
Draft
Motor power
Circulation pump
Gypsum production process
Oxidation tower feed tank
Oxidation tower
Oxidation blower
Air volume
Draft
Motor power
Thickener
Dehydrator
Solid content
Gas reheater
After-burning furnace
1,000 tons (common use for No. 1 boiler
and No. 2)
3 sets
1 stage venturi scrubber 1 set
1 stage venturi scrubber 1 set
Dual suction turbo-fan direct coupled to
motor shaft
13,400 m3/min each
820 mmAq
2,400 kw x 2 sets/unit
210 kw x 5/unit 195 kw x 5/unit
Vertical cylindrical type made of carbon
steel - 1 set
Vertical cylindrical type made of carbon
steel 2 sets/unit
Roots - blower
50 Nm3/min each
20,000 mmAq
200 kw x 3 sets/2 units
Sedimentation and concentration type -
1 set
Screw decanter type
1.05 tons/hr x 4 sets/unit
Horizontal cylindrical type
2,600 kg/hr - 1 set
34
-------
Electric Power Development Company
Mitsui-Chemico Limestone-Gypsum Process
Meeting on February 6, 1978 at 1:00 p.m. at EPDC's Takasago Station.
Attendees
EPDC: Mutsuaki Nakamura, General Manager, Takasago Power Station
N. Arai, Chief Engineer, Takasago Power Station
Study Team: Jumpei Ando, M. A. Maxwell, T. M. Morasky
Background and Summary
The Takasago Power Station of EPDC is located near Himeji on the Seto
Inland Sea and consists of two 250 MW coal fired units employing the Mitsui-
Chemico limestone-gypsum process. Unit No. 1 began commercial operation in
July 1968 and Unit No. 2 in January 1969. The FGD system for Unit No. 1
became operational in February 1975 followed by the Unit No. 2 system in March
1976. Both FGD systems are nearly identical in design to the Unit No. 2
system at Mitsui Aluminum's Omuta Plant. The units burn a blend of domestic
coals averaging 2.0 percent in sulfur content. The load profile of both units
varies from 250 MW during peak daytime hours to 125 MW at night. Flue gas
3 3
volume to each scrubber ranges from 840,000 Nm /hr to 500,000 Nm /hr, depending
upon generating load. A photograph of the FGD system is shown in Figure 6.
3
SO emissions from the station were previously restricted to 400 Nm /hr by
x
agreement with the local governments. However, under the more stringent total
mass emission regulations effective April 1, 1978, the allowable emissions have
3
been reduced to 243 Nm /hr (136 ppm) at full load.
35
-------
The FGD systems were designed for and have consistently achieved average
SO removal efficiencies exceeding 93 percent while maintaining an operability
of 99 percent. In addition, the scrubbers were designed to maintain particu-
3 3
late outlet concentrations below 0.05 g/Nm with inlets from the ESP of 0.1 g/Nm .
Key power plant/pollution control design and performance specifications are
given in Table 9.
Process Description
A flow sheet of the process is shown in Figure 7.
Flue gas from the boiler is split into three streams and sent to the
first stage scrubber (75 percent), pH control tower (20 percent) and oxidation
tower. The flue gas exiting these vessels is then merged, passes through the
second stage scrubber and is reheated directly (using 0.3 percent sulfur oil)
to 85°C'prior to passing into the stack. The process is characterized by the
pH control tower and oxidation reactor which utilize SO,., from the flue gas to
lower the slurry pH to 5.8, thus increasing alkali utilization without using
sulfuric acid. However, the system was originally designed for acid addition
to the pH control tower.
The system does not employ a precooler .although Mr. Aral (who previously
worked at the Isogo plant) felt that including a quench section would have
smoothed the operation.
Preground limestone (90 percent minus 325 mesh) is purchased, prepared
on-site as a 15 percent slurry using centrate and thickener supernate and fed
to the second stage scrubber at a stoichiometry of 1.0-1.05 that of the inlet
SO^. Process control is accomplished by measurement of flue gas volume and
SO- concentration which automatically determines slurry make-up volume required.
Fine tuning of the make-up feed rate is maintained by pH control in the second
stage scrubber, which is operated at pH 6.2 and L/G of 6.5 1/Nm3. Recycle
slurry from the second stage is fed to the first stage scrubber which operates
at pH 6.0 and L/G of 6.5 1/Nm . The recycle slurry is maintained at 5-6 percent
solids. An unspecified catalyst was originally added to the second stage
36
-------
scrubber reportedly to improve SCL removal efficiency, increase the oxidation
rate, and obtain a higher quality gypsum required for wallboard. However, the
catalyst is no longer used. The gypsum slurry from the oxidizer is pumped to
a thickener, concentrated to a 20 percent slurry and dewatered by centrifuge,
producing gypsum containing approximated 10 percent moisture.
Thickener overflow and the centrate are returned to the process for
limestone slurry make-up absorber liquid level adjustments and mist eliminator
washing. This supernate is also blown down (5 tons/hr for Unit No. 1, 10 tons/hr
for Unit No. 2) to maintain chloride concentration below 8000 ppm.
Four pass chevron type mist eliminators are provided for the second stage
scrubber which is sequentially washed with process liquor and fresh water.
Operating History
A detailed month by month operating history of the boilers/FGD systems is
shown in Tables 10 and 11. Scrubber system reliability has averaged 98 percent
since startup. As can be seen, the primary problem with Unit No. 1 involved
scaling of mist eliminators which were washed with process liquor. This mist
eliminator was replaced after about one year of operation and as a result
operability has increased. The Unit No. 2 mist eliminator is now washed
sequentially with fresh water and process liquor and has thus essentially
eliminated the scaling problem.
Plant personnel indicated that very few erosion problems have been encoun-
tered with the system. The limestone slurry feed control valve is not rubber
lined but fabricated of a .tantalum/niobium alloy which resists erosion. Other
materials of construction are comparable to those used in Mitsui Aluminum's
Unit No. 2 FGD system at Omuta.
The present procedure is to operate the affected boiler at half load if
the FGD system is shut down for corrective maintenance, provided that the FGD
37
-------
system on the other unit is in operation. The emission regulations have been
met in this fashion except on two occasions (September 1975 and February 1976)
when the Unit No. 1 boiler was required to shut down for about 30 hours.
Because of the stringent standards in effect after April 1978, however, future
load reductions will not be possible and instead, the boiler will be required
to shut down as a general practice until the scrubber problems are corrected.
The FGD system was originally designed for sulfuric acid addition for pH
conditioning and a "catalyst" to encourage limestone utilization and gypsum
oxidation. Presently neither acid-nor catalyst is required in the system to
obtain high limestone utilizations (gypsum contains only 4 percent calcium
carbonate) or increase oxidation efficiency (gypsum product contains zero
calcium sulfite).
The FGD systems are operated by a subsidiary company of EPDC. Three
men/shift are required to operate both scrubber systems with three men on the
day shift for maintenance (power plant personnel). Two additional men assigned
to the day shift for waste water treatment and ash handling work part-time on
the limestone receiving and gypsum handling/storage.
The capital investment for both FGD systems (total) was reported as
9.2 billion yen. Annualized operating costs for both units (including fixed
charges and reheat) are 8.01 yen/kwhr of which 1.15 yen/kwhr are attributable
to the FGD systems.
Analysis of Significance
The long term reliable performance of this plant is of significance to the
U.S. utility situation since the design parameters are similar in several
respects to those of many U.S. power plants employing FGD systems. Areas of
commonality include (1) the use of coal as fuel in a moderately large sized
boiler (250 MW) and (2) the use of a limestone scrubbing system based on U.S.
developed scrubber technology.
In addition, the other factors cited for the Takehara plant are applicable
here as well.
38
-------
Figure 6.
Takasago Plant FGD System
39
-------
Table 9
EPDC Takasago Station
Mitsui-Chemico SO., Removal System
Power Plant/FGD System Design and Performance Data
Boiler
Power generation capacity (MW)
Coal
Heat value (kcal/kg)
Sulfur content (%)
Load variation (%)
Unit No. 1
250
6000 (est.)
2.0
100-50
Unit No. 2
250
6000 (est.)
2.0
100-50
S00 Control System
2.
3
Flue gas rate (Nm /hr)
Inlet SO (dry ppm)
Inlet particulate (g/Nm )
Inlet gas temperature (°C)
Scrubber type
Scrubber capacity (Nm )
Absorbent
Outlet particulate (g/Nm )
Outlet SOX at stack (dry ppm)
Average SO- removal efficiency
Liquid purge rate (tons/hr)
Utility consumption
Electric power (kw)
Water (tons/hr)
Limestone/lime (tons/day)
Gypsum production (tons/day)
Availability (%)
799,000
1500-1700
0.1
150
2-stage venturi
842,000
limestone
>0.05
>100
93
5
6500
52
125
230
98.9
799,000
1500-1700
0.1
150
2-stage venturi
842,000
limestone
>0.05
>100
93
10
6500
52
125
230
98.7
40
-------
Figure 7.
EPDC TAKASAGO PLANT
MITSUI - CHEMICO LIMESTONE - GYPSUM PROCESS
FLOW DIAGRAM
CENTRIFUGE ABSORBENT
i FEEDTANK
BOOSTER FAN
1 f
irv
— r-~
« — OAIR
PH CONTROLLER
<-»
O
1
OXIDI2ER
-
AIR OVE
he
GYPSUM
STORAGE
I-®-
OVER FLOW TANK MOTHER LIQUOR
T A ni \j I WASTE
TANK i—ITREATMENT) ^
I WASTI
I ITREATM
AIN i
ABSORBENT
? t SILO(CaC03l
WEIGH
FEEDER
DRAIN
ABSORBENT
MAKE UP TANK
INERTS
-------
Table 10. OPERATING HISTORY OF THE NO. 1 UNIT, TAKASAGO PLANT
Month
1975
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
.p, Oct.
10 Nov.
Dec.
1976
Jan.
Feb.
Mar.
Apr.
May
June
July
Total
(A)
672
744
720
744
720
744
744
720
744
720
744
744
672
744
720
744
720
744
Hours
Boiler
Operation
(B)
616
360
318
717
720
743
744
690
744
720
715
744
664
687
219
744
720
744
FGD
Stop
(c) (&)
19
0
0
0
15
15
15
30
36
11
29
0
32
0
0
0
0
0
Boiler
Avail-
ability
(%)(*»)
99.9
100
95.9
100
100
96.1
100
95.4
92.3
30.0
100
100
100
FGD
Opera-
bilit
(%)
91.7
48.4
44.1
96.4
100
97.0
100
100
100
97.9
98.0
98.0
95.7
95.2
98.4
100
100
95.3
100
100
100
100
100
Remarks
Piping flange leak
Annual shutdown of
boiler
Mist eliminator
scaling
Mist eliminator
scaling
Mist eliminator
scaling
Mist eliminator
scaling
Fan vibration
Mist eliminator
scaling
Mist eliminator
scaling
(a) Due to troubles of FGD unit
(b) B/A (%)
(c) (A-O/A (%)
-------
Table 10. OPERATING HISTORY OF THE NO. 1 UNIT, TAKASAGO PLANT (Continued)
Month
1976
Aug.
Sept.
Oct.
Nov.
Dec.
1977
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
1978
Total
(A)
744
720
744
720
744
744
672
744
720
744
720
744
744
720
744
720
744
Hours
Boiler
Operation
(B)
744
720
744
720
744
744
672
0
513
744
720
717
744
720
744
720
744
FGD
Stop
0
0
62
5
8
5
0
0
0
10
0
0
0
0
43
0
0
Boiler
Avail-
ability
100
100
100
100
100
100
100
0
71.3
100
100
96.2
100
100
100
100
100
FGD
Opera-
bility
100
100
91.7
99.3
98.9
99.7
100
100
98.2
100
100
100
100
94.3
100
100
Jan.
744
744
0
100
100
Remarks
Cleaning of 1st stage
scrubber
Repair of duct
Repair of spray pipe
Cleaning of 1st stage
scrubber
Annual maintenance of
boiler
Fan vibration
Cleaning of 1st stage
scrubber
Cleaning of scrubbers
and reactors
Cleaning of 1st
reactor
(a) Due to troubles of FGD unit
(b) B/A (%)
(c) (A-O/A (%)
-------
Table 11. OPERATING HISTORY OF THE NO. 2 UNIT, TAKASAGO PLANT
Hours
Month
1976
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
1977
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
1978
Jan.
Total
(A)
744
720
744
740
744
744
720
744
720
744
744
672
744
720
744
720
744
744
720
744
720
744
744
Boiler
Operation
(B)
744
720
216
632
744
744
720
744
720
744
744
672
744
720
384
24
744
744
720
744
720
744
744
FGD
Stop
(C) (a)
0
0
0
0
0
0
0
43
0
5
0
79
10
0
0
0
0
0
0
0
78
0
0
Boiler
Avail-
ability
FGD
Opera-
bilit
Remarks
100
100
29
88
100
100
100
100
100
100
100
100
100
100
51.6
32.9
100
100
100
100
100
100
100
100
100
100
100
100
100
100
94.2
100
99.3
100
88.3
98.7
100
100
100
100
100
100
100
89.1
100
100
Annual maintenance
of boiler
Duct cleaning
Repair of gypsum
conveyor
Cleaning of pH
controller
Cleaning of duct
and pH controller
Cleaning of pH
controller and
reactor
(a) Due to troubles of FGD unit
(b) B/A (%)
(c) (A-O/A (%)
-------
Electric Power Development Company
Babcock - Hitachi Limestone-Gypsum Process
Meeting on February 7, 1978 at 1:00 p.m. at EPDC's Takehara Station.
Attendees
EPDC: Mr. N. Ichihara, Manager, Takehara Station
Mr. K. Oe, Vice Manager, Takehara Station
Mr. Fujiyama, Chief, Maintenance, Takehara Station
Study Team: Jumpei Ando, H. W. Elder, M. A. Maxwell, T. M. Morasky
Background and Summary
The Takehara Power Station of EPDC is located near Mihara on the Seto
Inland Sea and consists of two units. Unit No. 1 has a capacity of 250 MW
with an annual load factor of 75 percent and is fired by domestic Kyushu coals
blended on-site to achieve a 2.0 percent sulfur fuel with a 6000 K cal/kg >
heating value. Unit No. 1 was constructed in 1967 and was subsequently retro-
fitted with a Babcock-Hitachi limestone gypsum system which began commercial
operation in February 1977. Unit No. 2 is an oil-fired unit constructed in
1974 having a 350 MW capacity. Unit No. 2 burns 1.0 percent sulfur oil and
has no FGD system at present although this option is being considered in
conjunction with a new 700 MW coal fired unit scheduled for commercial operation
in 1982. This new unit will use imported coal (either Australia or China).
The decision as to whether FGD or low S coal will be used will be made by the
end of 1978 and will determine whether FGD will be needed on Unit No. 2. Key
power plant/pollution control system design and performance specifications are
given in Table 12. A photograph of the plant is shown in Figure 8.
45
-------
Since the plant is located in an area having no large cities, the environ-
mental regulations are relatively mild. SO emissions are restricted by the
3 X
Central Government to 468 and 503 Nm /hr for Units No. 1 and 2, equivalent to
600 and 620 ppm respectively at full load. However, by virtue of an agreement
with the city and prefec
3
to 195 Nm /hr (240 ppm) .
with the city and prefectural governments, Unit No. 1 SO emissions are limited
X
The Unit No. 1 FGD system has achieved an operability in excess of 97 per-
cent reflecting only three forced scrubber outages since start-up. The system
was designed for and has consistently achieved an average S0« removal efficiency
exceeding 93 percent.
Process Description
The process flow sheet for Unit No. 1 is shown in Figure 9. Flue gas
enters the scrubber from the induced draft fans that draw the gas from 98%
3
efficient electrostatic precipitators . The gas contains approximately 200 mg/Nm
3
of particulate matter and 1,730 Nm /hr of sulfur dioxide. The scrubber system
consists of two identical scrubbing trains and is designed to scrub about
800,000 Nm /hr. Flue gas upon entering the scrubbing system is split equally,
each portion entering a prescrubber venturi section where the gas is quenched.
The precooled flue gas then proceeds to a second stage scrubber containing
perforated plates for good gas-liquid contact. Gas flow through each scrubber
train is controlled by separate fans. Prior to exiting the second stage the
flue gas passes through a horizontal mist eliminator (vertical gas flow)
consisting of finned tube bundles. The cleaned gas is then reheated to
120° C using direct oil fired reheaters prior to exiting through a 200 meter
stack. Total pressure drop across the scrubber system is reported to be
650 mm H_0 (230 mm H20 in the prescrubber and 385 mm H^O in the scrubber) .
Fresh water is used to sequentially wash the mist eliminator. A complete wash
cycle is about 2 hours and requires about 5-10 ton/fresh water for each train.
46
-------
The scrubbing system uses a limestone slurry of 10% solids. The L/G ratio
in the second stage is about 7 liters/Nm . The slurry from the second stage
recycle tank is bled to the first stage prescrubber. The slurry in this tank
is recycled at an L/G of about 2 Iiters/Nm3. Slurry from this prescrubber
recycle tank is continuously bled to a pH adjustment tank where sulfuric acid is
added to lower the pH prior to the slurry being pumped to an oxidation tower.
After passing through the oxidation tower the slurry is then bled to a thickener
where initial solids separation occur and supernatant liquid is returned to
both recycle tanks for solids control. The underflow is then pumped to centrifuges
where final dewatering of the gypsum is accomplished by batch operation. The
byproduct gypsum contains about 10 percent moisture and is sold for use in the
cement and wallboard industries. Supernatant liquid from the centrifuges is
pumped to the limestone preparation tank to slurry the limestone. This super-
natant liquid contains substantial gypsum particles that act as seed crystals
which help in controlling scale and size/type of gypsum crystals ultimately
produced. In the second stage recycle tank slurry pH is controlled at 6.0 and
in the prescrubber recycle tank pH is maintained at 5.0.
Process control is accomplished by measurement of flue gas volume and S0~
concentration which automatically determines volume of make-up slurry required.
Liquor flow rate is kept constant during gas turndown.
Energy requirements for the FGD system (excluding reheat) were reported as
3.1 percent of unit power generating capacity.
Plant operators routinely blend coal to maintain inlet flue gas having
sulfur dioxide concentrations between 1550 and 1650 ppm. The plant has strict
specifications for the pulverized limestone delivered dry to the plant site.
Quality control of this limestone assures 95% through a 325 mesh, a minimum of
55.4 percent CaO and impurities limited to 1.14 percent. Supernatant liquid is
continuously blown down at a rate of 10-15 ton/hr to maintain a chloride level
of 3500 ppm in the slurry.
47
-------
Operating History
Since start-up in February 1977, the scrubber system has shown a very
high degree of reliability (98.6 percent), operating 5,396 hours until the
boiler was shut down for its annual maintenance outage on September 30.
During this period, the scrubber operation was halted three times while the
boiler was operated at half load using a mixture of coal and low sulfur oil in
order to meet the emission standards. On two of these occasions, one scrubber
train was shut down for 70 hours to clean plugged pump strainers servicing the
absorber slurry circulation tank. On the other occasion, both scrubber trains
were shut down to remove scale from the reheater ductwork.
The strainer plugging problem was solved by moving the strainers outside
the absorber for easy accessibility. The overall operability of the FGD
systems during this period was 97.4 percent for two-scrubber train operation
and 98.6 percent during one-scrubber train operation. Since this annual
maintenance outage, no problems have occurred that have required a scrubber
system outage.
The plant has experienced very few erosion/corrosion problems, likely due
to the type of materials in use throughout the scrubber system. All tanks and
piping are rubberlined, the absorber and ducts are all flake lined, the venture's
are constructed of acid resistant castable, the hot gas mixing chamber is
built of castable refractory and the pumps (casing and impellers) and slurry
control valves are made of a "special kind of stainless steel." The only
point in the system that the plant personnel predict a problem with erosion is
in the oxidizer feed line. However, they feel this can be routinely maintained
by replacement whenever the unit is down for its annual maintenance.
The system makes use of a gate type damper manually inserted and bolted
shut to isolate one train from the other in the event .of maintenance requirements.
Fresh water is used to wash the mist eliminators in the scrubber system. This
was recommended to them "by experience." It is believed that they went to
fresh water wash after the scaling experience in the mist eliminator.
48
-------
The plant uses a subsidiary company to operate the scrubber systems as in
the other EPDC plants. Two men/shift are required for scrubber operations
plus one part-time person from the fly ash system to handle limestone deliveries
and gypsum storage/loading. Three men are used during the day shift for
scrubber system maintenance. Plant management indicated that they would like
to reduce the maintenance staff to two persons but union problems presently
present this. Plant operators are not rotated into the power plant for other
duties.
The capital investment for the FGD unit (including the gypsum storage
house) was reported as 7.2 billion yen. Unit No. 1 annualized operating and
maintenance costs (including fixed charges and reheat) are 8.82 yen/kwhr of
which 1.73 yen/kwhr was FGD system related. By comparison, the annualized
operating costs for Unit No. 2 which burns a medium sulfur oil are 7.92 yen/kwhr.
Analysis of Significance
The Takehara FGD system had been in operation about 1 year at the time of
the visit and although the operating time may be insufficient to assess long-
term maintenance requirements, the performance has been outstanding. Both SO,,
removal efficiency and reliability have been excellent. This experience is
relevant to the U.S. situation because the system employs design features
similar to those offered by a U.S. supplier of limestone scrubbing systems.
The water balance is relatively tight, comparable to closed-loop sulfite
sludge pond systems in the United States, and the coal sulfur content is
within the range encountered in many U.S. installations. In one U.S. system
similar to the Takehara design operational problems with high-sulfur coal
diminished when the utility switched to a lower sulfur coal.
An important process difference compared to U.S. experience is use of
forced oxidation to produce gypsum. Recirculation of gypsum seed crystals
undoubtedly reduces scaling potential in the absorber. Other factors that
likely contribute to successful operation include the following:
49
-------
1. The plant is conservatively designed.
2. Inlet S0? concentration is reasonably stable as a result of coal
blending.
3. Limestone is purchased as a high-quality, finely ground absorbent.
4. Qualified personnel are permanently assigned to operate and maintain
the FGD system.
50
-------
Figure 8.
Takehara Plant FGD System
51
-------
EPOC TAKEHARA PLANT
BABCOCK HITACHI PROCESS DIAGRAM
— -t> STACK
FLUE GAS t- -
PRESCHUBBEH
No. 2 SCRUBBER
M04TANK (iH ADJUSTER
RAW WATER
GYPSUM
WASTE WATER
TREATMENT
Figure 9.
-------
Table 12
EPDC Takehara Station
Babcock-Hitachi SO., Removal System
Power Plant/FGD System Design and Performance Data
Boiler
Power generation capacity (MW) 250
Electrostatic precipitator efficiency (%) 98
Coal
Heat value (kcal/kg) 6000
Sulfur content (%) 2.0
Ash content (%) 23
Load variation (%) 100-40
Annual load factor (%) 75
SO Control System
z • ••
Flue gas rate (Nm3/hr) 809,000
Inlet SO (dry ppm) 1500-1700
x.
3
Inlet particulate (g/Nm ) 0.36
Inlet gas temperature (°C) 140
Prescrubber type venturi
Scrubber type _ perforated plate
Scrubber capacity (Nm ) 852,000
Absorbent 3 limestone
Outlet particulate (g/Nm ) >0.03
Outlet SO at stack (dry ppm) >100
Average S§2 removal efficiency (%) 93
Liquid purge rate (tons/hr) 10-15
Utility consumption
Electric power (kw) 7800
Water (tons/hr) 56
Limestone/lime (tons/day) 130
Gypsum production (tons/day) 225
Availability (%) 97
53
-------
Mitsui Aluminum Company, Ltd.
Mitsui-Chemico Lime/Limestone Processes
Meeting on February 9, 1978 at 9:00 a.m. at Miiki Power Plant, Omuta.
Attendees
Mitsui Aluminum Co.: Nagayasu Inagawa, Director, Miiki Plant
Akio Nagayoshima, Deputy General Manager,
Miiki Power Plant
Koshi Okamoto, Chief, Environmental Section
Mitsui Miiki Machinery Co.: Eiki Kojima, Process Engineer
Chemico Engineering Co.: Masao Kodama, Manager, Engineering Section
Study Team: M. A. Maxwell, T. M. Morasky
Background and Summary
The Miiki Power Plant in Omuta was built in the early 1970's by the
Mitsui Aluminum Company in order to provide a stable supply of electricity
required for the aluminum smelter simultaneously constructed. The plant was
designed to use locally mined Miiki coal (2.4 percent sulfur) for power pro-
duction and is the largest privately owned power station in Japan. Unit No. 1
(156 MW) began commercial operation in May 1971 and was later equipped (April
1972) with a Mitsui-Chemico lime scrubbing system using carbide sludge waste
from a nearby chemical plant in Denkikagaku. Unit No. 2 (175 MW) commenced
commercial operation in July 1975 employing a Mitsui-Chemico limestone process
which by-produces gypsum sold for use in the wallboard and portland cement
industries. The power plant is linked to the Kyushu Electric Company power
system to whom it occasionally sells surplus power. A photograph of the FGD
system is shown in Figure 10.
54
-------
Both units have achieved essentially 100 percent operability since start-
up except for one 10 day outage of the Unit No. 2 scrubber for modifications
to correct a mist eliminator carryover problem. Both units were designed for
and have consistently achieved S00 removal efficiencies in excess of 90 percent.
Key power plant/pollution control system design and performance specifications
are shown in Table 13.
Process Description
Unit No. 1
The process flow sheet for Unit No. 1 is shown in Figure 11. The system
consists of two scrubber trains, each capable of handling 75 percent of total
flue gas capacity (512,000 Nm /hr). Of additional interest is the 25 MW slip
stream prototype subsequently added to study the limestone/gypsum process
prior to application to Unit No. 2. Although this prototype is no longer in
operation, it reportedly could be restarted to provide 100 percent flue gas
treatment in conjunction with one train should the second train require shut-
down. Thus far this has not been necessary.
Flue gas passes through a two stage venturi scrubber (450 mm HO AP)
where S0? and residual particulate are removed. The cleaned flue gas is
reheated to 85°C prior to discharging through a 130 meter stack.
The system uses a mixture of wet (50-60 percent moisture) and dry (47 per-
cent moisture) carbide lime which is adjusted to a final slurry concentration
of 15 percent. Make-up slurry feed rate is manually controlled by recycle
slurry pH which is maintained at 8 (as opposed to 6.8 design). Recycle slurry
is normally maintained at around 5-6 percent suspended solids by weight.
Liquid/gas ratio for each stage is around 40 gal/1000 ACFM. Delay tank resi-
dence times for the first and second stages were reported as 20 minutes and
4 minutes respectively. A bleed stream from the first stage delay tank is
transported to a settling pond where the supernatant liquid is returned to the
55
-------
process for carbide lime make-up, absorber liquid level adjustments, and mist
eliminator washing. Four stage chevron type mist eliminators are provided for
both first and second stages and are intermittently washed with fresh water and
recirculated pond liquor. Gas velocity through the mist eliminator is around
2.7 meter/sec.
Unit No. 2
The process flow sheet for Unit No. 2 is shown in Figure 12.
Flue gas from the boiler is split into three streams and sent to the first
stage scrubber (75 percent), pH adjustment tower (20 percent), and oxidation
tower (5 percent). The three streams are then recombined, pass through the
second stage scrubber and are reheated to 85°C prior to passing into a 180 meter
stack.
Preground limestone (98 percent purity, 325 mesh) is purchased, prepared
onsite as a 15 percent slurry using thickener overflow, and fed to the second
stage scrubber at a stoichiometry of 1.0-1.05 times that of the inlet S0~.
Process control is accomplished by measurement of flue gas volume and SO-
concentration which automatically determines volume of make-up slurry required.
The second stage scrubber is operated at pH 6.0-6.3 and liquid/gas ratio
of 40 gal/1000 ACFM. Recycle slurry from the second stage is fed to the first
stage scrubber which operates at pH 5.6-5.9 and liquid/gas ratio of 40 gal/
1000 ACFM. Delay tank resistance time for first and second stage was reported
as 7 minutes each.
The pH of the bleed slurry from first stage scrubber is adjusted to 5.4-
5.8 in the pH "controller" as SO is absorbed. This technique replaces the
H^SO, addition required in other processes to solubilize calcium sulfite prior
to oxidation. The slurry is then pumped to a conventional oxidizer for con-
version to gypsum.
56
-------
A small amount of catalyst is added to the second stage scrubber re-
portedly to improve the S02 removal efficiency, increase the oxidation rate
and obtain a higher quality gypsum crystal required for wallboard. Mitsui
claims that at low pH in the oxidizer the catalyst promotes oxidation while
inhibiting oxidation at the higher pH values in the second stage scrubber.
The gypsum slurry from the oxidizer is pumped to a thickener, concen-
trated to a 20 percent slurry and dewatered by centrifuge producing gypsum
containing 5-8 percent moisture.
The thickener overflow and centrate are returned to the process for
limestone slurry make-up, absorber liquid level adjustments and mist eliminator
washing. Recycle of gypsum seed crystals from thickener into the absorber
reportedly aids in controlling size and type of gypsum crystals ultimately
produced.
Mist eliminator design and washing techniques are the same as for Unit
No. 1.
Operating History
Both FGD systems have operated quite well while achieving essentially
100 percent operability. The only FGD system forced outage occurred on Unit
No. 2 for 10 days during November 1975 when modifications were made to correct
a mist eliminator carryover problem. Otherwise, both systems have been in
continuous operation except during the annual power plant maintenance outages.
Both units were designed for and have consistently achieved SO,, removal
efficiencies exceeding 90 percent. Current local emission regulations require
that the outlet S0? concentration at the stack (after reheating) not exceed
230 ppm. Therefore, the units are operated to maintain a stack outlet SO-
concentration less than 200 ppm. There have reportedly been no violations of
this regulation during the operating life of the plant.
57
-------
Other than the early mist eliminator problem, few operational diffi-
culties have apparently been encountered. Some erosion of rubberlined butter-
fly control valves in Unit No. 2 was noted. Consequently, diaphragm valves
are considered preferable. Materials of construction of the FGD system com-
ponents are shown in Table 14.
Compared to the EPDC Takesago and Takehara plants, Unit No. 2 operates
with a more open water loop (27 percent solids effective pond concentration)
having a 20 ton/hr liquor purge rate to control chloride content at 1000 ppm.
The Miiki coal used is blended at the mine and has an average heating
value of ^6400 kcal/kg. The resulting blend is then mixed at the power plant
with around 30% low grade "slime" coal (coke fines) having an average heating
value of 4000 kcal/kg. This final mixture has an average heating value of
5800 kcal/kg and an average sulfur content of 2.4 percent.
Table 15 shows a typical chemical analysis of the process reagents/pro-
ducts.
Originally, 8 persons/shift were assigned to operate both scrubber systems
(including limestone receiving, gypsum production and gypsum shipping). Six
persons/shift now handle these functions but will reportedly decrease to
4 persons/shift this fall. In addition, 2 persons are assigned to maintenance
on the day shift. Operators spend about 1 year assigned to the FGD units
prior to being rotated into power plant functions.
The investment and annualized costs reported for the FGD systems are
shown in Table 16. Investment figures for Units No. 1 and 2 represent 1972
and 1974 costs, respectively, except for the prototype plant which represents
1974 costs. Annual costs are for the April 1976 - March 1977 period and were
reported to comprise 18 percent of the total cost of producing power.
58
-------
Analysis of Significance
The Mitsui-Chemico limestone/gypsum process appears to possess important
advantages relative to more conventional limestone scrubbing processes pro-
ducing a throwaway sludge requiring ponding or fixation. The high S09 removal
and limestone utilization efficiencies obtained using a two stage venturi
absorber are quite attractive for U.S. applications. However, the capital
costs for the process will likely be somewhat higher than for conventional
limestone systems due to the "pH controller" and complex oxidizer. This
facility is considered particularly relevant to many U.S. coal fired applica-
tions of limestone systems where 2300 ppm S09 inlet concentrations are
encountered.
59
-------
Figure 10.
Mitsui Aluminum Plant FGD System
60
-------
MITSUI ALUMINUM COMPANY
MITSUI - CHEMICO PROCESS DIAGRAM
UNIT NO. 1
THROW AWAY PROCESS
ABSORENTSILO
(CARBIDE SLUDGE)
ABSORBENT
MAKE UP TANK
PROTOTYPE GYPSUM PROCESS
ABSORBENT
MAKE UP TANK
Figure 11.
-------
MITSUI ALUMINUM COMPANY
MITSUI - CHEMICO LIMESTONE - GYPSUM PROCESS
FLOW DIAGRAM
UNIT NO. 2
ABSORBENT
SILO (CaCO3)
CENTRIFUGE ABSORBENT
i FEEDTANK
I
OVER FLOW TANK MOTHER LIQUOR
TANK
ABSORBENT
MAKE UP TANK
INERTS
Figure 12.
-------
Table 13
Mitsui Aluminum Company
Mitsui-Chemico S0? Removal System
Power Plant/FGD System Design and Performance Data
Unit No. 1 Unit No. 2
Boiler
Steam generation capacity (tons/hr) < 490 550
Power generation capacity (MW) 156 175
Electrostatic precipitator efficiency (%) 98.6 98.6
Coal
Heat value (kcal/kg) 5500-5800 5500-5800
Sulfur content (%) 2.4 2.4
Load variation (%) 100-50 100-50
(usually 100) (usually 100)
S0? Control System
Flue gas rate (Nm3/hr 512,000 552,000
Inlet S0x (dry ppm) 3 2100-2300 1900-2100
Inlet particulate (g/Nm ) 0.6 0.6
Inlet gas temperature (°C) 136 138
Scrubber type ., 2-stage venturi 2-stage venturi
Scrubber capacity (Nm ) 385,000 x 2 552,000 x 1
Absorbent o carbide lime limestone
Outlet particulate (g/Nm ) >0.06 >0.06
Outlet SO at stack (dry ppm) >200 >200
Average S§2 removal efficiency (%) 90+ 90+
Liquid purge rate (tons/hr) 90 20
Utility consumption
Electric power (kw) 3650 4240
Water (tons/hr) 36.5
Bunker C oil (kl/day) 15 18
Limestone/lime (tons/day) 110 110
Catalyst (kg/hr) 20
Gypsum production (tons/day) 180
Availability (%) 100 99
(100 since 11/75)
63
-------
Table 14
Mitsui Aluminum Company
Mitsui-Chemico SO,., Removal System
Materials of Construction
Absorber
Piping
Pumps
Valves
Ductwork -
Thickener -
Oxidizer
Carbon steel lined with FRP
Rubber lined (butyl)
Rubber lined casing, cast steel impeller
Ball valves (316 L stainless, Unit No. 2)
(304 L stainless, Unit No. 1)
Butterfly and diaphragm control valves - rubber lined
Flake lined in low temp., saturated gas area
carbon steel in high temp, area
Rubber lined
Flake lined
controller - Flake lined
Spray
Nozzles
Stack
Centrifuge
Dampers
Mist
Eliminator
Open pipe 304 stainless (Unit No. 1)
Open pipe 316 L stainless (Unit No. 2)
Phenolic resin lined
Stainless steel basket
Single Louver (high temp, area - carbon steel)
(low temp, area - flake lined)
4 pass polypropylene chevron
64
-------
Table 15
Mitsui Aluminum Company
Mitsui-Chemico SO,., Removal Processes
Typical Chemical Analysis of Reagents/Products
Fraction (% weight)
CaC03
CaO
Ca(OH)2
CaS03'l/2 H20
MgO
s.o2
F2°3
Na20
HC1 insoluble
Ignition Loss
Carbide Lime Waste Sludge
0.24
91.40
3.85
0.48
1.43
0.48
0.71
1.73
5.10
68.91
18.51
5.35
0.50
1.69
Limestone
55.3
9.3
0.3
0.2
0.3
43.0
Gypsum
0.13
94.82
0.15
0.076
2.34
65
-------
Table 16
Mitsui Aluminum Company
Mitsui-Chemico S0? Removal System
Investment and Operating/Maintenance Costs
Investment (Yen)
Annual (Yen/kwhr)
Utilities
Op erat ions/Maint enance
Fixed Charges
Total
Unit No. 1
1.1 x 109
0.7 x 109
25 MW prototype
0.443
0.113
0.283
0.839
Unit No. 2
4.0 x 10'
0.515
0.111
0.780
1.406
66
-------
Electric Power Development Company
Tokyo Offices
Meeting on January 31, 1978 at 10:00 a.m. at EPDC's Headquarters.
Attendees
EPDC: Mr. Yasuyoke Nakabayashi, Senior Power Engineer Chief Manager
Mr. Toshio Harpase, Deputy General Manager, Thermal Power Department
Study Team: Jumpei Ando, M. A. Maxwell, T. M. Morasky. H. W. Elder
Background
The Electric Power Development Company, Limited (EPDC) is a government
financed corporation founded in 1952 in order to mitigate the serious power
shortage in the post-war period of economic reconstruction. The principal
purposes of EPDC are to undertake the development of large scale or difficult
power development schemes or multiple purpose projects incorporating integrated
national land development plans. The company has total power development
schemes valued at some 800 billion Yen, the major part of which were financed
by the government. Since its establishment EPDC has completed 7000 MW of
generating capacity at 50 sites which are located throughout the country.
These include coal fired power plants constructed in accordance with the
national energy policy of de-emphasizing the nation's dependence on foreign
oil. The EPDC contributes much toward stabilizing the supply of electricity by
the wholesale of energy produced at the nationwide plants to private electric
utility companies serving their respective territories and by the effective
operation of its plants and the interchange of power between regions.
67
-------
Highlights of Meeting
The Electric Power Development Company as a matter of national policy has
constructed a number of coal-fired power plants. Five coal fired units are
owned and operated by EPDC at Isogo (2), Takehara (1) and Takasago (2). The
total megawatt capacity of these units is 1280 MW. All of these units are
equipped with limestone scrubbers producing a saleable gypsum product. Because
of these scrubbers the EPDC has obtained large in-house expertise on limestone
FGD. During our discussions with EPDC personnel an attempt was made to deter-
mine how this expertise has affected the company's philosophy on the design and
operation of limestone scrubbing systems. It became apparent through our
discussions that when ordering a scrubbing system from a supplier very general
specifications, based on performance and fuel fired are given. They do not
specify any scrubber availability figure. EPDC, however, expects the supplier
to provide a scrubbing system that will have an availability that matches the
availability of the boiler and turbine. EPDC requires a supplier of a scrubber
system to correct and solve any problems in equipment and/or process that may
occur within a year after acceptance of equipment. EPDC personnel feel that
flue gas velocity in a scrubbing system is a major design variable that is most
responsible for reliable scrubber operation. Velocities should be kept at a
minimum value to protect reheater sections by minimizing mist carryover from
the scrubber vessels. It is EPDC's philosophy to provide system redundancy for
pumps only. They usually specify one extra pump for every four. They also
feel that to have a good operating scrubber requires a good operating precipita-
tor to minimize erosion problems. During the meeting EPDC personnel stated
that scrubbing coal containing 0.7 percent sulfur or less offers no scaling
problems which they feel are partial function of process type. However, when
scrubbing coal greater than 0.7 percent sulfur some degree of scaling may be
"inevitable," but controllable to the extent that scrubber outages would not
be required between annual boiler maintenance shutdowns. For the two new coal
fired units planned for start-up in January 1981, EPDC anticipates firing a
1.2 percent sulfur coal blend. They are planning not to exceed 1.3 percent
sulfur in these new units.
68
-------
As a national policy EPDC must use coal for future power plants. If they
use a domestic coal, the government pays all depreciation costs of the scrubber
(seven year depreciation) and a scrubber maintenance cost for seven years
calculated at three percent of the initial capital investment. Since EPDC is
planning on a foreign coal supply in their two planned units they will not
qualify for the subsidy.
It was estimated that thirteen percent of the total capital investment of
a power plant is for FGD. A typical 500 MW unit costs approximately 150,000-
180,000 Yen/kw. An FGD system constructed on a 500 MW unit would cost approxi-
mately 20,000 Yen/kw. Scrubber operating costs were estimated by EPDC to be
about 1.2 Yen/kwh while total costs of producing electric power, including FGD
run about 10.0 Yen/kwhr.
Overview of Coal Fired Scrubbers at EPDC
All three utility sites of EPDC using scrubbers for sulfur dioxide control
on coal-fired boilers were visited. It was felt that these could best reflect
the status of the technology and the information obtained would more realistically
respond to the needs of the utility industry in the United States. As a result
of these plant visits a number of observations were noted that might contribute
to the high S09 removal efficiencies and reliabilities of these scrubbing
systems.
Both Japanese suppliers and users of FGD systems consider a scrubber to be
a chemical process. Operation of scrubbers requires constant control by personnel
trained to operate a chemical process. The raw materials flowing into these
chemical processes are controlled carefully to minimize upsets to the chemistry
and to operate them as close as possible to design, conditions. To maintain a
relatively constant SO inlet, the utility owner of an operating scrubber blends
his coal prior to firing. In addition all scrubbers operating on coal-fired
units had electrostatic precipitators operating ahead of them to minimize the
dust loading into the scrubbers. The precipitator performance is not allowed
to degrade even though the scrubbers could act as "polishers" for particulate
removal. They believe that allowing excessive amounts of fly ash into the
69
-------
scrubbing system will result in increased solubilities of unknown compounds
that may affect the chemistry of scrubbing as well as increase the erosive
characteristics of the slurry to a greater extent than what was designed for in
the scrubber. In addition, users of limestone scrubbers in EPDC buy dry pul-
verized limestone with strict specifications on size (over 90 percent through
325 mesh) and chemical composition (less than 1 percent of inerts and less than
1 percent magnesium compounds). This allows for a constant and reliable reagent
feed into the scrubbing process.
EPDC hires specially trained personnel to operate their scrubbers and do
not rotate them into the power plant for boiler operation. In fact, they
contract a subsidiary company for the personnel required to operate the scrubbers
at Isogo, Takasago and Takehara. It appears each plant has its own separate
contract with the subsidiary company since at some plants the contract included
scrubber maintenance as well as its operation and at others it included only
the operation.
Proper control of scrubbers in the EPDC system dictates that the chloride
concentrations in the scrubbing slurries are not allowed to increase to levels
considered potentially harmful either to the materials of construction, the
process chemistry and/or the gypsum product. This proper chloride level is
maintained by purging water from the process and therefore opening the water
loop somewhat resulting in not only low chloride concentrations but may also
contribute to subsaturation of calcium sulfate, thus minimizing scaling potential.
This factor can be considered one of the most helpful in operating their scrubbers
in a reliable manner.
All the scrubbers operating on these coal-fired units purge a certain
volume of water. Usually these purges are treated and must meet standards for
pH, BOD and COD as well as suspended solids; however, no limit has been placed
on dissolved solids for these blowdown effluents.
70
-------
In the United States, it had generally been felt by many that most Japanese
scrubber systems operated open loop. However, in comparing the blowdown figures
with the solids generated it appears that some plants operate with much tighter
water loops than some in the United States and others operate much more open
loop. For example, the ultimate settled solids in a limestone scrubbing
system in the United States employing ponding is about 50 percent with no
blowdown. To define the coal-fired Japanese systems so that they can be com-
pared on a equal basis to those in the United States it is necessary to relate
the reaction products (gypsum) produced in the scrubber to the purge water
blown down to calculate an effective pond disposal concentration. These theore-
tical calculations indicate the effective pond disposal solids concentrations
for the Japanese scrubbers on the EPDC coal fired units visited to be:
Isogo - approximately 29 percent solids
Takasago - approximately 51 percent solids
Takehara - approximately 46 percent solids
These results show that the Takasago and Takehara systems are relatively tight
in their water balance and could be considered closed loop if operated as a
pond disposal system in the United States. However, the Isogo scrubbers appear
to be somewhat comparable to some systems operating in the United States employ-
ing blowdown.
The EPDC scrubbers operating on coal-fired boilers are treating flue gas
streams that are generally more dilute with respect to SO,., concentrations than
are currently being treated by many U.S. utility scrubbing systems. Japanese
FGD systems have been employed typically to treat flue gases having an S02
inlet concentration range of 400-2300 ppm. These are significantly lower than
the 1600-4000 ppm inlet SO concentration requiring scrubbing by many U.S.
utility installations in the Midwest and East which present inherently more
difficult set of operating conditions.
71
-------
It is also significant to note that because of the somewhat lower heating
value of the Japanese coals they must be fired at a higher burn rate to gener-
ate the same amount of power as the typical U.S. utility burning Midwest or
Eastern coal. Such low grade coals produce a larger volume of flue gas and
greater S0? emissions per unit of generated power. On a megawatt basis, there-
fore, the EPDC scrubber system (as well as power plant) equipment capacity is
greater and capital and operating costs are higher than for the typical U.S.
utility burning higher heating value coal of a comparable sulfur content.
In conclusion, Japanese scrubbers as typified by the EPDC coal fired
installations do work efficiently and reliably. The reasons for this success
are numerous and varied, ranging from the dedication of the Japanese sup-
pliers/users to the generally less severe scrubbing conditions existing at
Japanese installations. However, it appears that the major reason for this
success is the utility user's willingness and ability to spend the necessary
money to buy the best scrubbing systems available for use at a specific site
and to operate them in the manner for which they were designed.
72
------- |