EPA-R2-73-229
May 1973
Environmental Protection Technology Series
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EPA-R2-73-229
Recent Developments in Desulfurization
of Fuel Oil and Waste Gas
in Japan - 1973
by
Dr. Jumpei Ando
Processes Research, Inc.
2900 Vernon Place
Cincinnati, Ohio 45219
Contract No. 68-02-0242
Program Element No. 1A2013
EPA Task Officer: Frank T . Princiotta
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
May 1973
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This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
11
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Foreword
The sulfur abatement policy in Japan has undergone notable changes
during the past year. Restrictions on S0_ emissions have become so
rigid that heavy oil with 1$ sulfur produced by topped-crude hydrodesul-
furization—heretofore regarded as the most promising method—is proving
unsatisfactory for large power plants. Power companies now wish to
burn large amounts of crude oil, naphtha and ING in place of heavy oil
but it is not easy to do so because this requires drastic structural
changes in the oil industry. To reduce sulfur in heavy oil to less than
0.5$, much effort has been made recently to develop gasification
desulfurization.
Waste-gas desulfurization has continued to grow remarkably. At
present, about sixty commercial and prototype plants ranging in unit
capacity from 30,000 to 250,000scfm and many other smaller plants are
in operation. The reliability of waste-gas desulfurization, especially
that by the wet process, has been generally recognized, thus prompting
power companies to plan many larger commercial plants based on this
process.
The present paper describes the recent developments in desulfuri-
zation efforts in Japan up to March 197? with emphasis on waste-gas
desulfurization.
April 1973
Dr. Jumpei Ando, Professor
Faculty of Science and Engineering
Chuo University
Kasuga, Bunkyo-ku, Tokyo
iii
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Recent Developments In Desulfurization of Fuel Oil
and Waste gas in Japan (197?)
Contents
1 Fuel and regulation of SOp in Japan
1.1 Supply of energy
1.2 Oil and sulfur
l.J Ambient and emission standards for S02
1.4 Sulfur abatement policy of government
1.5 Trends of fuels and desulfurization
2 Hydrodesulfurization of heavy oil
3 Gasification desulfurization of heavy oil and residual oil
3.1 Outline
3.2 Production of fuel gas by gasification desulfurization
of heavy oil (Ube process)
3*3 Other processes for gasification of heavy oil
4 Outline of waste-gas desulfurization
5 Wet-alkali and double alkali processes
5.1 Kureha sodium-limestone process
5*2 Showa Denko sodium-limestone process
5>3 Hitachi sodium process and sodium-lime process
3*4 Nippon Steel Chemical sodium-lime process
5.5 NKK ammonia process and ammonia-lime process
5.6 Wellman-HKK sodium process
5.7 Wellman-SCEC sodium process
5.8 Oji sodium process
5»9 Tsukishima sodium process
iv
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5*10 HH-TCA sodium process
3.11 MKK sodium process (Evergreen process)
5.12 Kurabo sodium process and ammonia-lime process
5.13 Other sodium processes
6 Vet-lime (limestone) process
6.1 Miteubishi-JECCO lime(limestone)-gypsum process
6.2 Mitsui-Chemico lime process
6.3 Babcock-Hltachi limestone-gypsum process
6.4 HH-TCA lime gypsum process
6.5 Other wet-lime processes
7 Other vet processes
7.1 Chiyoda dilute sulfurlc acid process (Thoroughbred 101 process)
7.2 Mitsui Mining magnesium process (Hibi process)
7.3 Onahama magnesium- process
7.4 Kawasaki magnesium process
7.5 Mitsui-Grillo magnesium-manganese process
7*6 Chemico-Mitsui magnesium process
7.7 MHI-IFP ammonia process
7.8 Hitachi Shipbuilding sodium hypochlorite process
8 Dry processes
8.1 Hitachi activated carbon process
8.2 Sumitomo activated carbon process
8.3 Mitsubishi manganese process (DAP-Mn process)
8.4 Shell cupric oxide process
8.5 Other dry processes
9 New processes for H_S recovery
9.1 Takahax process
9*2 Fumaks and Rhodacs processes
9.3 IFP-MHI process
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10 Economic aspects
10.1 Absorbents and by-products of desulfurization
10.2 Cost comparison of dry and wet processes for waste-gas
desulfurization
10.3 Comparison of hydrodesulfurization, gasification
desulfurization and flue-gas desulfurization
11 Significance of application in U.S.A. of waste-gas
desulfurization processes developed in Japan
11.1 Difference in circumstances
11.2 Wet-lime (limestone) process
11.3 Double-alkali process
11.4 Other major processes with gypsum by-production
11.3 Processes to regenerate S02
11.6 Other processes
Remarks
The units of measurements and costs are expressed in the American way
using inches, feet, gallons, barrels, grains, pounds, tons (short tons),
cents, dollars, etc.
The exchange rate, $1 = ¥308, is used.
Abbreviations
BPSD: Barrels per stream day &!.: Gallon, gallons
BPCD: Barrels per calendar day in.: Inch, inches
MW: Megawatts Ib: Pound, pounds
soft Standard cubic feet bit Barrel
scfm: Standard cubic feet per minute bbl: Barrels
acfm: Actual cubic feet per minute t: Ton, tons
L/G: Liquid/gas ratio (gallons/1,OOOscfm)
vi
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1 Fuel and regulation of SO. in Japan
1.1 Supply of energy
Energy supply in Japan is characterized by its rapid increase and
heavy dependence on imported oil. The annual increases averaged
during the past several years (Table l.l). Per-capita energy consumption
in Japan was one-fifth that in the United States in 1965 and one-third
in 1971> Consumption per acre of level land is now about eight times
that in the U.S. and may be the highest in the world, resulting in
serious environmental problems.
T2
Table 1.1 Supply of primary energy (10 kcal)
Electric power
Hydraulic
Nuclear
Coal
Domestic
Imported
Oil
Domestic
Imported
Natural gas
Domestic
Imported (LNG)
Other energy sources
Total
1965
18?
0
316
136
7
959
1967
170
2
296
209
8
1,319
1969.
188
3
285
333
8
1,840
1971
213
20
203
357
8
2,349
20
0
i 29
1,656
22
0
29
2,055
26
2
22
2,707
27
13
16
3,206
1975
(estimate)
212
102
226
627
8
3,425
29
45
17
4,704
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Oil imports have increased at a rate of about 20$ yearly. In 1971»
73$ of Japan*s total energy supply depended upon imported oil. Coal
for fuel has been decreasing; imported coal which is on the increase
is used to produce coke for the steel industry. Even though supply
of nuclear energy and import of LNG (liquefied natural gas) are
increasing, the dependence on petroleum is likely to keep growing for
some time to come.
1.2 Oil and sulfur
Most of imported oil is in the form of crude oil. About 80$ of the
crude oil comes from the Middle East and is rich in sulfur. As oil
companies are seeking low-sulfur oil, the average sulfur content.in
imported oil decreased from 1.93$ in 1967 to 1.56$ in 1971. Still
the total amount of sulfur present in imported oil reached nearly 4
million tons in 1971.
Table 1.2.1 Crude oil imports and their sources
(in million of barrels) '
District 1967 1969 1971
Middle East 717-7 959-2 1,184.4
Par East 52.2 122.6 193.1
U.S.S.R. 10.7 3.8 J.I
Other districts 6.3 12.6 30.2
Total 786.9 1,098.2 1,410.8
In Japan, most of crude oil is treated by topping (atmospheric distillation).
The residual oil from topping is known as "heavy oil" and is used for fuel.
Prom 100 parts crude, 55 parts heavy oil is obtained on the average.
Approximately 90fo of the sulfur in crude remains in heavy oil. Heavy oil
from Khafji crude has a sulfur content as high as 4$.
Consumption of heavy oil amounted to 441 million barrels in 1967 and to
745 million barrels in 1971. In 1971» about one-fourth of the heavy oil
was subjected to hydrodesulfurization giving 287,000 tons of sulfur as
by-product. Still nearly 3 million tons of sulfur in heavy oil burned
produced nearly 6 million tons of SO-, constituting the chief source of
SO. emissions.
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About 30$ of heavy oil was burned in electric power stations and the
rest in other plants and buildings (Table 1.2.2). In 1970, about
24$ of the total SO. emission was derived from power stations, 19$
from the steel industry, 16$ from the ceramic industry, 15$ from the
chemical industry, and the rest from other sources.
Table 1.2.2 Consumption of heavy oil
(in millions of barrels) '
1967 1969 1971
Electric power 119.3 18?.5 222.9
Chemical industry 45.9 53.6 79.4
Steel industry 44.7 58.3 76.0
Ceramic industry 50•6 61.1 66.4
Other uses 180.1 250.3 299.8
Total 440.6 610.8 744.5
1.3 Ambient and emission standards for
The ambient standard for SO. has been set out as follows:
l) The hourly average SOp concentration should not exceed 0.2ppm in
not less than 99$ of the total number of hours in a given year.
2) The daily average SO- concentration should not exceed 0.05ppm in
not less than 70$ of the total number of days in a given year.
3) The hourly average SO- concentration should not exceed O.OJppm in
not less than 88$ of the total number of hours in a given year.
4) The yearly average of hourly concentrations should not exceed O.OJppm.
In many industrial districts and in some large cities, SO- concentration
exceeds the standard. The time limit to attain the standard was first
set for 1978 and this was recently moved up to 1975- Moreover, the
standard itself might be tightened in near future.
The emission standard is given by the following equation:
q = k x 10"5 He2
q: amount of sulfur oxides, NmVhr (iNm'/hr = 0.59scfm)
k: tho value shown in Table 1.3.1
He: effective height of stack, meters (l meter = 3.3ft)
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before 1971
11.7
12.8
14.0
17.5
after 1972 before 1971
6.42
7-59
7.59
9.34
5.26
5.26
5.26
after 1972
2.92
3.50
3.50
5.26
Table 1.3>1 The values of k
_ For existing plants For new plants
bj
Tokyo, Yokohama, etc.
Chiba, Ichihara, etc.
Kitakyushu, etc.
Omuta, etc.
As shown in Table I.J.I the k values were lowered in 1972 to meet the stringent
ambient standard. The smallest value 2.92 has been set for new plants in
such districts as Tokyo, Yokohama, etc. This means that a 1,OOOMW plant
in these districts with an effective stack height of 1,000 feet (actual
height about 400 feet) is required to use oil with less than 0.25$ sulfur.
The emission standard allows smaller consumers to use fuel with higher
sulfur contents. However, there are regulations on sulfur content of oil
enforced in specific areas in addition to the above national standards.
For example, an ordinance issued by the governer of Tokyo is shown in
Table 1.3-2.
Table 1.3.2 Ordinance on sulfur content of fuel oil (Tokyo)
Plants Buildings
Consumption of Maximum S Consumption of Maximum S
oil ($) oil (#)
(liters/day)* (liters/day)
City area 1,000 to 4,000 1.3(1.5)** 300 to 10,000 1.0(1.3)*
4,000 to 10,000 1.0(1.3) over 10,000 0.5(1.0)
over 10,000 0.5(1.3)
Other areas 1,000 to 10,000 1.3(1.7) 300 to 10,000 1.0(1.3)
over 10,000 1.0(1.3) over 10,000 " 0.5(1.0)
* 1,000 liters = 6.29 barrels 10,000^day is equivalent to 1.6MW.
** Parenthesized figures are for existing plants and buildings.
Other figures are for those to be newly built.
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1.4 Sulfur abatement policy of government^'
The targets for sulfur reduction have been established from the view-
point of achieving and maintaining the environmental quality standards
for sulfur oxides. Three types of areas requiring countermeasures have
been differentiated for the purpose of establishing the targets(Table 1.6).
Excessively populated areas are defined as having excessive population and
extremely polluted air due to the disorderly establishment of industries.
Polluted areas are not populated excessively but suffer from pollution'
which exceeds environmental quality standards. Threatened areas require
preventive measures due to the possibility of pollution exceeding
environmental quality standards if the sulfur content of fuels is not
reduced. The number of threatened areas is expected to increase in the
future.
Average sulfur content of all fuels for industry, general public
requirements and other sectors should be lowered from the 2.5$ of 1967
to 1.5^ in 1973 and 1.13f$ in 1978.
Table 1.4 Targets for sulfur reduction
_ 1967 __ 1973 __ 1978
Quantity Sulfur Quantity Sulfur Quantity Sulfur
(millions of ($J) (millions of (fa (millions
« _ • \ " * * _ _ « • ** » » .
bbl) bbl) of
Excessively
polluted areas 144.5 2-41 274-2 0.90 346.0 0.55
Polluted areas 82.2 2.51 178.0 1.30 289.3 0.80
Threatened areas - - 173.0 1.45 340.0 1.00
All sectors of
the economy 401.9 2.5 976.2 1.50 1,383.8 1.15
L Heavy oil, raw crude oil for combustion and liquefied natural gas
are included in fuels. Quantities are given in terms of heavy oil.
2 Sulfur contents have been adjusted after taking into consideration
the effects of flue-gas desulfurization, which is substantially equal
to the reduction of sulfur content in fuels by means of desulfurizing
of heavy oil.
More rapid sulfur abatement than is shown in Table 1.4 may be required
because of the situation of the ambient standard as was described in 1.3.
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In order to attain these goals, several methods have been employed
including the lowering of sulfur content of imported crude oil, import
of LNG, desulfurization of heavy oil and waste gas. The Agency of
Industrial Science and Technology, MITI, awarded contracts to several
groups for the development of processes for flue-gas desulfurization
(dry processes) and heavy-oil desulfurization (topped-crude hydrodesulfuri-
zation) expending 0.5 million dollars between 1966 and 1971. MITI has
recently set up a new program for the development of "closed systems."
Under this program financial aid has been awarded to Ube Industries for
the development of gasification desulfurization of heavy oil which will
be described in J.2.
MITI has been helping oil companies to promote hydrodesulfurization of
heavy oil by paying them $0.26/bl heavy oil subjected to the treatment.
MITI is advising industries to increase the capacity of hydrodesulfuri-
zation to a million BPSD and that of flue-gas desulfurization to 4*300MW
by 1975.
Trends in fuels and their desulfurization
Fuels consumed in power plants are shown in Table 1.5.1. The use of coal
has decreased. Although low-sulfur fuels—crude oil for direct combustion
and LNG and natural gas—have been used in increasing amounts, the use of
heavy oil has increased markedly.
2}
Table 1.5*1 Fuels consumed by power companies* '
1967 1969 1971
Heavy oil (millions of barrels) 119-3 187.5 222.9
Crude oil (millions of barrels) 13.8 24.8 69.2
Coal (millions of tons) 28.0 26.8 15.3
LNG (millionc of tons) 0 0.1 0.8
Natural gas (billions of ncf) 0.2 0.1 4.6
* These companies produce 07f$ of Japan's total electric power.
Until recently, topped-crude hydrodesulfurization of heavy oil by which
sulfur is reduced from 4 to 1% was considered to be the most promising
way of desulfurization. The present stringent regulation on S0_ emissions,
however, rendered oil with 1% sulfur unsatisfactory for new power plants.
Even for existing plants, restrictions on S0y emissions which are more
stringent than official regulations are compeled by inhabitants. Under
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such situationf major power companies plan to use large amounts of low-
sulfur fuels such as crude oil, naphtha and LNG replacing heavy oil
(Table 1.5.2).
2}
Table 1.5.2 Use of fuels by nine major power companies* '
Used Planned
1971 1972 1973 1974 1975 1976
Coal (millions of tons) 9.6 6.7 4-7 4-4 4.1 3.3
Heavy oil (millions of barrels) 183.7 187.3 146.6 134.3 114-4 H6.1
Crude oil (millions of barrels) 69.! 112.7 188.9 221.7 254-5 274.0
Naphtha (millions of barrels) 0 1.9 15-4 44-0 60.3 67-3
LHG (millions of tons) 0.8 0.8 1.4 2.5 3«9 4.8
Natural gas (billions of scf) 4.6 6.0 6.4 6.7 7.3 7.9
LGL (millions of barrels) 0 0 2.8 3.4 4-7 4-7
Total (millions of barrels in 284.9 323-9 367-5 416.9 454.1 483.7
terms of heavy oil)
Flue-gas desulfurization (Ml/) 110 357 2,700 3,700 4,800
* These companies produce 71$ of Japan's total electric power.
Oil companies oppose the plan of the power companies because drastic changes
in the oil refineries will be required to carry out the plan. The oil
companies are now much interested in gasification desulfurization of heavy
oil by which sulfur can be reduced to 0.2$ and are trying to build commercial
plants to supply the gas to power stations.
Vaste-gas desulfurization has developed remarkably, with more than sixty
commercial and prototype plants now in operation. Most of the plants built
so far are of relatively small capacity and designed to treat waste gas
from industrial boilers, chemical and smelting plants, etc. Major power
companies have recently decided to build larger plants. The total capacity
of the destilfurization plants of the major power companies will increase
from the 35fMW in 1972 to 2,700MW in 1974 and to 4,800Mtf in 1976 (Table 1.5-2).
Further increases in capacity will be needed because in 1976 it will still
be only 6"/j of the total power capacity G,000,OOOMW.
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2 Hydrodesulfurization of heavy oil
Many hydrodesulfurization plants have been built since 1967 by oil
companies in various districts of Japan (Tables 2.1 and 2.2). Four of
them use the topped-crude desulfurization process (or the atmospheric
residual desulfurization process which is often referred to as the
direct process) and others the vacuum gas-oil desulfurization process
(indirect process). By the direct process, sulfur in oil can be reduced
from 4$ to 1$ (Figure 2.1) but the life of catalyst is a problem.
Moreover, product oil containing 1$ sulfur will be unsatisfactory for
large power plants to be built. Although four other plants are under
construction at present (Table 2.2), it is unlikely that many plants will
be constructed in future. Among the four plants in operation, two use
the UOP process (Figures 2.3 and 2.4),tha other two use the Gulf process
(Figure 2.5), both of which are equipped with fixed-bed reactors. These
plants have been operated for about 60$ of the total hours in 1972 on
the average. Pilot plant tests have been carried out by the Government
Chemical Research Institute with a moving-bed reactor and by Nippon Oil
with suspended-bed reactors. All of these processes were described in detail
by the present author in his 1972 report.1) There has been no remarkable
development in these processes during the past year.
By the indirect process, heavy oil is first distilled under vacuum. The
distillate (vacuum gas oil) is desulfurized down to 0.2$ sulfur without
significant technical trouble (Figures 2.2 and 2.6). The desulfurized
oil is normally mixed with the residue of vacuum distillation which is
difficult to be desulfurized. The mixed oil contains 2.4$ sulfur when
heavy oil with 4-0/j sulfur is treated and is not satisfactory to meet the
requirements for S0_ control. Therefore, it is desirable to use the
desulfurized vacuum gas oil with 0.20$ sulfur for fuel and the residual
oil for other purposes. One of the promising ways of utilizing the residual
oil is thermal decomposition with the gasification desulfurization as will
be described in the following chapter.
The amounts of sulfur by-produced from hydrodesulfurization of heavy oil
annually from 1968 to 1975 are shown in Table 2.3« The amount of recovered
sulfur in 1972 was less than expected due to the fewer operation hours of
topped-crude desulfurization plants, resulting in a temporary shortage of
sulfur in Japan.
8
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Table 2.1 Hydrodesulfurization plants built by 1971
Refiner
Idemltsu
Kosan
Fuji Oil
Toa Nenryo
Daikyo Oil
Nippon Oil
Showa Oil
Kyushu
Oil
Mitsubishi
Oil
Maruzen
Oil
Seibu Oil
Nippon
Mining
Kba Oil
General
Oil
Kashima
Oil
Daikyo Oil
Eansai Oil
Kba Oil
Toa Nenryo
Total
Plant site
Chiba
Sodegaura
Wakayana
Umaokoshi
Negishi
Kawasaki
Oita
Mizushima
Chiba
Yamaguchi
Mizushima
Marifu
Sakai
Kashima
Umaokoshi
Sakai
Osaka
Kawasaki
Process
TOP*
CRC
ER&E
Gulf
CRC
Shell
Shell
HOP
Union
Shell
Gulf*
CRC
ER&3
UOP*
Gulf
E5&U
CRC
ER&E
Completed
1967
1968
1968
1969
1969
1969
1969
1969
1969
1969
1970
1970
1970
1970
1970
1971
1971
1971
Capacityfper day)
Oil BPSDl Sulfur tons'
40,000 265
25,000 100
25,000 180
17,500 110
40,000 190
16,000 66
14,000 55
30,000 100
35,000 165
4,000 28
27,760 165
8,000 39
31,000 73
45,000 265
17,500 77
20,000 88
12,000 55
51,000 220
456,260 2,241
* Topped-crude hydrodesulfurization processes; those without
asterisks are for vacuum gas-oil hydrodesulfurization.
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Table 2.2 Hydrodesulfurization plants built after 1971
Refiner
Nippon Oil
Idemitsu Kosan
Kyokuto Petroleum
Toa Nenryo
Asia Kyoseki
Kyushu Oil
Showa Yokkaichi Oil
Seibu Oil
Nippon Oil
Toa Oil
Nippon Mining
Toa Nenryo
Toa Oil
Kansai Oil
Showa Yokkaichi Oil
Mitsubishi Oil
Total
Plant site
Negishi
Himeji
Chiba
Kawasaki
Sakaide
Oita
Yokkaichi
Yamaguchi
Muroran
Nagoya
Mizushima
Wakayaoa
Nagoya
Sakai
Yokkaichi
Mizushima
Process
CRC
Gulf*
HOP
ER&E
CRC
HOP
Shell
Shell
CRC
CRC
Gulf*
ER&E*
ER&E*
Shell
TOP*
Year of
completion
1972
1972
1972
1972
1972
1972
1972
1972
1973
1973
1974
1974
1974
1974
1974
1975
Capacity
oil (EPSD)
28,000
40,000
60,000
9,000
15,000
25,000
35,000
1,000
40,000
30,000
3,240
45,000
37,000
40,000
5,000
45,000
469,240
* Topped-crude hydrodesulfurization; those without asterisks are
for vacuum gas-oil hydrodesulfurization
10
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Table 2.3 Amount of sulfur recovered by hydrodesulfurization
of heavy oil (tons) '
1969 1970 1971 1972 1975* 1974* 1975*
Topped-crude
desulfurization 259 376 502
Vacuum gas-oil
desulfurization 387 414 425
Total 74 171 287 511 646 790 927
* Estimated values assuming 6,600 hours' operation for topped-crude
desulfurisation plants and 7fOOO hours' operation for vacuum gas-oil
desulfurization plants in a year.
11
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o j)w /
^Gasoline.etc.80
Heavy oil 100
/o Ji t\af\
JSulfur, naphtha,
etc. 10
Desulfurized oil
90 (5 = 1.0<)
Figure 2.1 Rough material balance in topping and
topped-crude hydrodesulfurization (direct process)
IX)
De sulfur!zati on
Heavy oil
100(S-4.0$)
vacuum
gas oil
62(S-2 9SS)
Desulfurized oil 56(S-0.2^)
i
r
Don-t^iinl ^41 1Q f C — Z Qc/\ •Unn-.r.. «4
Vacuum
distillation
(5 = 2.
Figure 2.2 Rough material balance in vacuum gas-oil
hydrodesulfurization ( Indirect process)
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VjJ
A, A1 : Reactors B: Hot separator C: Hot flash drum
D: Cold flash drum E: Cold separator F: Compressor
Figure 2.3 Flow sheet of UOP (RCD) Isomax process
Desulfurized oil
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Figure 2.4
Topped-crude hydrodesulfurization plant
( Kashima Oil Co.)
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Hydrogen
plant
Heavy oil
I—V\M/v—'
Reactor
A
Heater
Reactor
B
Heater
Scrubber
Separator
A
Separator
B
Figure 2.5 Flow sheet of Gulf process
Gas
Naphtha
Recti-
fier
Furnace
oil
Desulfurized
oil
-------
Hydrogen
Vacuum gas oil
A: Reactor B: High pressure separator D: Low pressure separator
Figure 2.6 Vacuum gas-oil desulfurization process
Desulfu-
rlzed oil
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3 Gasification desulfurization of heavy oil and residual oil
3.1 Outline
Gasification desulfurization of heavy oil and residual oil from vacuum
distillation has been recently considered an important means of producing
low-sulfur fuel since the demand for fuels containing less than 1$
sulfur has increased sharply. Toa Oil Co. has decided to adopt the
Flexicoking process developed by ER&E, USA. A plant with a capacity
of treating 18,OOOBPSD of oil will be completed in Kawasaki by early 1975-
Other oil companies, Toa Nenryo, General Oil, Asia Oil, Idemitsu Kosan,
Nippon Oil, etc. are also interested in gasification desulfurization.
Two chemical companies, Ube Industries and Kureha Chemical Industries,
have developed their own process.
By the Ube process virtually all of the feed oil is converted to a fuel
gas with a very low sulfur content (0.02$). Much oxygen is required in
this case. On the other hand, by the Flexicoking process residual oil
from vacuum distillation of heavy oil is subjected to thermal decomposition
to obtain fuel oil with a relatively low sulfur content and the remaining
tar or coke which is rich in sulfur is gasified and desulfurized. This
process may be less expensive consuming as it does less oxygen, but overall
sulfur removal is not as high as by the Ube process. Both the cost and
the desulfurization ratio vary with the degree of gasification.
An erample of the process to reduce sulfur to 0.2$ is shown in Figure 3«1«1«
Heavy oil is first distilled under vacuum. Most of the residual oil is
heated to 5008C to be decomposed into gas, oil, tar, and a small amount
of coke. The oil from the decomposition step is subjected to hydrodesulfuri-
zation together with the distillate from the vacuum distillation. A small
portion of the residual oil from the distillation is subjected to partial
oxidation to produce hydrogen for the hydrodesulfurization. The tar from
the decomposition stop is reacted with oxygen to produce gas which is
subjected to desulfurization together with the gas from the decomposition
step.
From 86,200BPCD of heavy oil (31.5 million barrels per year) containing
4.1$ sulfur, 70,9103PCD of liquid fuel (4-024 million tons per year)
containing 0.23$ sulfur and 108 million scf per day of fuel gas (722,000
tons per year in terms of heavy oil) containing 0.02$ sulfur with a heat capa-
city 170 kilboalories per scf are obtained along with 530 tons per day
of elemental sulfur. The average sulfur content of the produced fuels
is 0.2$. The yield of the desulfurized fuel is 92.6$.
A cost estimation for the process is shown in Table 3>1* The cost is
$1.74 per barrel of product in terms of heavy oil assuming 6,130 hours'
17
-------
operation in a year. The cost is higher at fewer operation hours. The
process Includes the gasification of about 18$ of feed oil. The more
the gasification the lover the sulfur content of the product and the
higher the cost. The relationship of product sulfur content and cost is
shown in Figure 3*1*2. The cost increases markedly as the sulfur is
reduced to below 0.2$.
Table 3*1 Cost estimation for the production of low-sulfur
fuel by decomposition and gasification of heavy oil
as shown in Figure 3.1.1.
(Seawater for cooling 5.8 mil/t, industrial water 14*6 mil/t,
pure water 175 mil/ton, electric power 16.2 mil/kWh, fuel
25.9 mil/10,000 kcal, oxygen 0.37 mil/scf, hydrogen 0.50 mil/sof,
steam $2.05/t. 6,130 hours' operation in a year.)
Investment cost Processing cost
(aillions of dollars) (millions of dollars/year)
On site 89.3
Off site 35-7
Patent fee 4.8
Catalyst 1.05
Other 12.8
Total 143.65
Fixed cost
Depreciation
Maintenance
Labor
Management
Interest
Tax
Insurance
Subtotal
Variable cost
Total
13.25
3-75
1.36
3.86
8.52
1.27
0.21
32.22
18.36
50.58
Processing cost for one barrel (heavy oil conversion basis) equals $1.74/bl.
18
-------
Kuwai t
heavy
oil
86,200
BPCD
Vacuum distillate
51,700 BPCD S=3.0#
TNaphtha l,300BPCb"[
| ^^^^^^^^^^^^B^^H^^H^^^^^^^^^^^^M
Vacuum
distillatior
123,000
BPSD
Vacuum
residue
3^,500
BPCD
32,200BPCD
Hydrogen
2.300BPCD
-L-l
Desulfuri-
zation
9^,OOOBPSD
5=0.
Oil
(5=0.2%)
65.000BPCD
Light oil
14.200BPCD
Naphtha
U,6lOBPCD
Gas
{ Hydrogen
I
Thermal
decomposition
46,OOOBPSD
Coke
ash
35t/CD Tar
Gas
Gasificatiqn
18,OOOBPSD
Hydrogen
production
3.300BPSD
12.500BPCD
Gas
Sulfur
recovery
?60t/SD
Suli
'ur
530t/CD
Oxygen
6,
38.3xlO°SCF/D
Liquid fuel
70.910BPCD
Fuel gas
Gasification
ratio = I5.25g
Total fuel
in terms of
heavy oil
Yield 92.
Partial oxidation
Figure 3.1.1 Flow sheet of heavy oil decomposition
to produce fuel oil and gas (S=0.2#
-------
r\>
o
3 .
1 ••
CO
O
U
0
-H 1 1 1 1 I—
0.1 0.2 0.3 0.4 0.5 0.6
Sulfur
Figure 3.1.2 Processing cost of heavy oil to produce low-sulfur fuel
•5)
-------
3.2 Production of fuel gas by gasification desulfurization
of heavy oil (Ube process) '
Developer Ube Industries Ltd.
2-1, Nagatacho, Chiyoda-kuf Tokyo
Process description Heavy oil is charged into a reactor with oxygen and
steam and undergoes partial oxidation at 050°C under atmospheric
pressure (Figure 3.2.1). In the reactor, silica-alumina particles
including an additive are fluidized to promote the gasification of
heavy oil. The gas leaving the reactor is cooled to 450°C in a quencher
placed above the reactor by spraying residual oil from a distillator.
The silica-alumina particles are fluidized also in the quencher and are
gradually coated with carbon. The carbon-coated particles are sent to
a high-temperature reactor placed under the reactor. In the high-temperature
reactor, the particles are fluidized to remove the carbon by reactions with
oxygen and steam.' at 1,200°C. The cleaned silica-alumina particles go up to
the reactor.
The product gas contains hydrogen, hydrocarbons , carbon oxides, hydrogen sulfide,
and a small amount of sulfur dioxide (Table 3>2.l). The gas is cooled,
condensed and treated in a distillator. The residual oil from the
distillator is sent to the quencher and high-temperature reactor. The
distillate is cooled in a condenser to separate gas oil, which is then
returned to the reactor. The gas from the condenser is sent to a preabsorber,
where S0_ and a portion of H_S in the gas is absorbed by an ammonium sulfite
solution according to the following equation:
3(NH4)2S03 + S02 + 2H2S = 3(NH4)2S203 + 2H20
Ammonium thiosulfate thus formed is concentrated and decomposed in a
decomposer to release S0? and ammonia, which are pent to an IFF reactor.
The gas from the preabsorber is compressed and led into a H~S absorber,
where H_S is absorbed by a K.CO, solution.
KHCO, + KES
H-S is regenerated from the solution by heating and sent to the HT
reactor to react with S09 and to produce elemental sulfur.
2H2S + S0? = 3S + 2H20
As SOp from the decomposer is not sufficient to react with H2S, a portion
of the by-produced sulfur is burned by air to form GO- which is led into
the IFP reactor. Ammonia passes through the IPP reactor without reaction
and is returned to the preabsorber. The composition of the gases before
and after the desulfurization step is shown in Table 3-2.2.
21
-------
Table 3.2.1 Material balance before and after
the decomposition (by weight)
Input Output
Feed oil 1,000
Oxygen 552
Steam 560
Total 2,029
H2
CH.
C2H4
Other hydrocarbons
CO
co2
°2
N2
H2S
so2
Organic sulfur
Gas oil
Steam
Total
26
120
216
521
348
581
2
2
36
4.7
1-3
82.7
450
2,092
Table 3.2.2 Composition of the gases before and after
the desulfurization (volume $)
H2
Other hydrocarbons
CO
C02
02
N2
H2S
S02
Organic sulfur
Before desulfurization
21.8
12.5
12.9
7-5
20.7
22.0
0.1
0.6
1.8
0.1
0.03
After desulfurization
26.8
15-3
15.8
9.1
25-4
6.7
0.1
0.7
0.01
0
0.01
22
-------
State of development A pilot plant to treat 55 tons of heavy oil per
day has been operated since 1969. The construction of a prototype plant
to treat 275 tons of heavy oil per day (40MW equivalent) was started in
April 1972 with financial aid from MITI. The gasification unit of the
prototype plant has been completed and is now in operation. The
desulfurization unit will be completed in April 1973- A. commercial
plant to supply fuel gas to a 500MW plant would be equipped with six
gasification units each with a capacity of treating 550 tons of heavy oil
per day and a desulfurization unit.
Advantages High-sulfur heavy oil and residual oil can be utilized. More
than 99$ of sulfur is removed. Far smaller desulfurization facility than
in flue gas desulfurization because of the smaller amount of gas with higher
concentrations of sulfur compounds.
Disadvantages Much oxygen is required. Separation of H^S from the gas
containing olefines and carbon dioxide is not quite easy. The entire
gasification process is not suitable for fuel supply to power plants
that frequently undergo large changes of operation load because it is not
easy to change the load of the gasification plant and it requires large
tanks to store the gas.
Economics The prototype plant with a capacity to treat 275 tons of heavy
oil per day cost $5 million including the desulfurization unit.
Investment cost for a commercial plant with a capacity to treat 3,300 tons of
oil per day (500MIJ equivalent) is estimated at $20 million including
oxygen production and desulfurization units. The cost for a million
kilocalories of product gas is estimated at $3.1 when the plant operation
is carried out for 7f900 hours a year and about Sj.^for 6,100 hours. The
relationship of cost to plant size is shown in Figure 3*2.3* Figure 3*2.3
shows that the fuel gas produced by a 500MW equivalent plcjit is much cheaper than
LNG and can compete with naphtha in cost as well as in sulfur content.
23
-------
Oxygen
Steam
Heavy |
oil
Waste gas
8
Air
Fuel
gas _
13
12
I
•Sulfur
Light oil
1: Quencher 2: Reactor 3: High-temperature reactor 4: Cyclone
6: Condenser ?: Cooler 8: Preabsorber 9: Compressor 10: Condenser
11: Decomposer 12: Sulfur burner 13: IFF reactor 1^: Regenerator 15:
Figure 3.2.1 Flow sheet of Ube process
5: Distillator
absorber
-------
Figure 3.2.2 Prototype plant for gasification
desulfurization by Ube process
-------
ro
ON
-------
3.3 Other processes for gasification of heavy oil
3.3-1 Kureha process
Kureha Chemical Industries (1-8, Horidomecho, ITihonbashi, Chuo-ku, Tokyo)
has recently operated a pilot plant to decompose residual oil from vacuum
distillation 220 Ib/hr at 1,600-2,200°P "by means of high temperature gas
or steam. The reaction is carried out very rapidly in 1/1,000-1/100
second to produce olefinos (C^E. and C,Hg), fuel gas, and tar and pitch
with special qualities. There is no plan yet to build a larger plant
because good uses for the tar and pitch have not been found yet.
3«3>2 Japan Gasoline process
Japan Gasoline Co. (?-4t Otemachi, Chiyoda-ku, Tokyo) has been trying
to develop a process for power generation by gasification desulfurization
of heavy oil, as was described by the present author in his 1972 report.
The process features the ppjrtial oxidation of heavy oil with air under pressure
and also the use of gas and steam turbines for power generation. No notable
progress has been made during the past year or so.
3.3.3 TEC process
Tokyo Engineering Co. (TEC, 2-5» 3-chome, Kasumigaseki, Chiyoda-ku, Tokyo)
has developed a now catalytic process to gasify heavy hydrocarbons. With
the process, not only the distillates such as naphtha and gas oil, but
also all kinds of hydrocarbon oils including crude oil, atmospheric
residue and vacuum residue can be completely gasified by steam reforming •
reaction with almost no carbon deposit on the catalyst surface. The
product of this process is a mixture of hydrogen, methane, CO and C0?
which can be used as fuel gas. A joint development program has been
launched to exploit the potentials of this process by TEC and Tokyo Gas Co.
27
-------
4 Outline of waste-gas desulfurization
Major commercial and prototype plants in operation and under construction
for SO, removal and recovery are listed in Tables 4-1 to 4«4- The tables
show aoout 40 plants (70 units) in operation with a total capacity of
about 5,000,000 scfm and several plants under construction. Nearly a half
of the plants treat flue gas from oil-fired boilers and the rest waste gases
from pulp plants, sulfuric acid plants, smelteries, iron ore sintering
plants, Glaus furnaces, etc. The unit capacity of most of the desulfuri-
zation plants ranges from 20,000 to 250,000scfm. There are many other
smaller commerci?,! plants treating waste gas from various sources which
are not listed in the tables. The capacities of the desulfurization plants
in operation total 6,000,000scfm.
Major electric power companies were interested in dry processes but have
recently decided to build many large plants using wet processes as shown in
Table 4«5« The capacities of the desulfurization plants of the major power
companies will total 2,?OOMV in 1974, 3.700MW in 1975, and 4,800MW in 1976
(Table 1.6).
A salient feature of the desulfurization efforts in Japan is that they are
oriented toward processes that yield salable by-products. Of the plants
in operation about 60$, in terms of capacity, use sodium scrubbing to produce
sodium sulfite and sulfate for paper mills (Table 4«l), 27$ other recovery
processes to produce concentrated S0_, sulfuric acid and gypsum (Tables
4.2 and 4»3)» and only 13$ removal processes to produce waste by-products
such as solid calcium sulfite and solutions of ammonium sulfate and sodium
sulfite or sulfate (Table 4.4).
This is because Japan is subject to limitations in domestic supply of
sulfur and its compounds as well as in land space available for disposal
of useless by-products. The by-produced sodium sulfite, however, has
already filled the demand. Host of the plants now planned (Table 4*5) as
well as the pilot plants in operation (Table 4.6) aim at the production of
salable gypsum or sulfuric acid. As desulfurization is making rapid progress,
it will not be long before the supply of by-products runs ahead of demand.
28
-------
Table 4.1 Major S0? recovery plants by sodium scrubbing (charge: NaOH)
ro
vo
Process developer
Oji Paper
Oji Paper
Oji Paper
Oji-Jinkoshi
Kureha Chemical
Xureha Chemical
Kureha Chemical
Ehowa Denko
Showa Denko
Showa Denko
Shov.-a Denko
Tsukishima
Bahco-Tsuki shima
Bahco-Tsukishima
Gadelius
Cadelius
Hitachi Ltd.
Ishikawajiraa-TCA
Ishikawaj ima-TCA
Mitsubishi(MKK)
Mitsubishi(MKK)
Product.
User
Ka2SO
Oji Paper
Tokai Pulp
Daio Paper
Oji Paper
Kureha Chemical
Mitsui Toatsu
Konan Utility
Showa Eenko
Ajinomoto
Nippon Phosphoric
Asia Oil
Sumitomo Mining
Daishowa Paper
Daio Paper
Hokuetsu Paper
Plant site
Kasugai
Shimada
Mi shima
Tomalcomai
Nishiki
ITagoya
Konan
Kawasaki
Kawasaki
Sodegaura
Yokohama
Toyo, Besshi
Yoshinaga
lyomishima
Niigata
Sanyo Kokusaku Pulp Asahikawa
Jujo Paper Mivakojima
Tsurumi Soda Yokohama
Mitsuisenpoku Oil Sakai
Asahi Glass Amagasaki
Asahi Glass Tsurumi
Unit capacity(l.OOOscfm)
805(in 12 units)a'b
467(in 5 units)*
470(in 6 units)b
400(in 4 units)8"
176a, l?6a
112a
123a
80a
159a
47°
142a
82°, 88
129b, 65b, 26l
88^, 70a
100b, 100b
77b
57a
35a
C8a, 88a, BQS
416
130e
d
Date of completion
1966-1972
1970-1972
1972
1971-1972
1968
1971
1972
1970
1971
1971
1972
1970
1971
1972
1971
1972
1972
1971
1973
1972
1973
a: Oil-burning boiler
d: Smelting furnace
b: Kraft recovery boiler
e: Glass furnace
c:
plant
-------
Table 4.2 S0« recovery plants by wet process to produce gypsum
Process developer
Mitsubishi-JECCO
Kitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Bahco-Tsukishioa
Ishikawaj itia-TCA
Ishiliawejima-TCA
Ishikawaj ima-TCA
Kawasaki R.I.
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Flppon Kokan
Nippon Steel Chem.
Showa Denko
Absorbent
Ca(OH)2
Ca(OE)2
Ca(OH)2
Ca(OE)2
ca(on)2
Ca(OE)2
Ca(OH)2
Ca(OE)2
Ca(OE)?
Ca(OB)2
, CaCO-
t CaCO-
t CaCO,,
BH3, Ca(OH)2
NaOH, Ca(OE)
NaOH, CaCO,
User
Nippon Kokan
Kansai Electric
Onahama S. 5: R.
Tomakomai Chem.
Kawasaki Steel
Yahagi Iron
Mitsubishi Metal
Chichibu Cement
Chichibu Cement
Jujo Paper
ITippon Kining
Fuji Kosan
Mitsubishi Rayon
Tohoku Oil
Daicel Ltd.
Nippon Kokan
Nippon Steel Chem.
Showa Denko
Plant site
Koyasu
Amagasaki
Onahama
Tomakomai
Chiba
Nagoya
Onahacia
Kunagaya
ICumagaya
Akita
Mzushiioa
Hainan
Otake
Sendai
Aboshi
Keihin
Sakai
Chiba
Unit capacity
Cl.OOOscfm)
37°
59a
54d
71
70"
6lh
611
20
g
59e
02£
340s
Date of completion
1968
1972
1972
1972
1973
1971
1972
1972
1973
1973
1972
1972
1973
1973
1973
1972
1972
1973
a: Oil-burning boiler
d: Smelting furnace
h: Diesel generator
b: Kraft recovery boiler
f: Glaus furnace
c: Sulfuric acid plant
g: Sintering plant
-------
Table 4-3 Other major plants for SO- recovery
Process developer
Vet process
Vellman-Lord(MKX)
Wellman-Lord(MKK)
Wellman-Lord(MKK)
Vellman-Lord(SCEC)
Vellman-Lord(SCEC)
Mitsui Min. & Sm.
Cnahama-Tsuki shima
Mitsubishi-IIT
Dry process
Sumitomo S.M.
Mitsubishi H. I.
Hitachi Ltd.
Shell
Absorbent
NaOH
NaOH
NaOH
NaOH
NaOH
MgO
MgO
NH/H
Carbon
MnO , MH-
x 5
Carbon
CaCO,
CuO
Product
Cf\ TT Gf\
3 2' 24
Qf\ T? on
b°2f 24
S02, H2S04
so2, s
Cf\ TT Gf^
S02, H2S04
S02, H2SO
S02, H2S04
so2, s
S02, H2S04
(NH4)2S04
E2S04
Gypsum
so2> s
User
Japan Synth. Rubber
Chubu Electric
Ninon Synth. Hubber
Toa Nenryo
Sumitomo Chiba Chem.
Mitsui Min. & Sm.
Onahama Smelt.
Maruzen Oil
Kansai Electric
Chubu Electric
Tokyo Electric
Showa Y. S.
Plant site
Chiba
Nishinagoya
Yokkaichi
Kawasaki
Chiba
Hibi
Onahama
Vakayama
Sakai
Yokkaichi
Kashima,
Yokkaichi
Unit capacity
(l.OOOscfm)
118a
365 a
237a
35f
212a
47°
A
53
r
24
100a
193a
250a
71a
Date of
completion
1971
1973
1973
1971
1973
1971
1972
1974
1971
1972
1972
1973
a: Oil-burning boiler
d: Smelting furnace
c: Sulfuric acid plant
f: Claus furnace
-------
Table 4«4 Major plants for S0? removal (waste product)
ro
Process developer
Kurabo Ind.
Kurabo Ind.
Kurabo Ind.
Kurabo Ind.
Kurabo Ind.
Kurabo Ind.
Mitsubishi E.I.
Toyobo Co.
Toyobo Co.
Kawasaki H.I.
Bahco-Tsukishima
Ishikawaj ima-TCA
Ishikawa j ima-TCA
I shikawaj ima-TCA
Chemico Kitsui
Absorbent Product
Waste NaOH Na2S04
NH, (NH4)2S04
NH, (NH4)2S04
NaOH Ha2SO.
NaOH UajSO^,
NaOH Na?S04
NaOH Na0SO,
Waste NaOH Na_SO,
Waste NaOH Na^O,
NaOH Na2SO.
NaOH Na2SO_
NaOH Na-SO.
NaOH Na2S04
NaOH Na2S04
Ca(OH)2 CaSO,
User
Kurabo Ind.
Mitsubishi Elec. Co.
Ishigasome Sarashi
Bridgestone Tire
Itengo
Kanzaki Paper
Ilorinaga Milk
Toyobo Co.
Toyobo Co.
Sumitomo Rubber
City of Tokyo
Eokushin Goban
Eidai Sangyo
Nissan Ho tor
Mitsui Aluminum
Plant site
Hirakata
Aiaagasaki
Tokyo
Tokyo, Nasu
Ibaraki
Ainagasaki
Tama
rforiguchi
Shogawa
Kobe
Odai
Osaka
Osaka
Oppama
Omuta
Unit capacity
(l.OOOscfm)
32a
24a
14a
71a, 28a
30a
24a, 24a
31a
26a
24a
17a
no1
26a
24a
67a
226J
Year of
completion
1970
1971
1971
1972
1972
1972
1972
1970
1971
1972
1972
1971
1972
1972
1972
a: Oil-fired boiler
j: Coal-fired boiler
i: Burning of sludge from sewage treatment plants
-------
Table 4*5 Flue-gas desulfurization plants of major power
companies to be completed in 1973 and 1974 (Oil-fired boiler)
Power company
Tokyo Electric
Tohoku Electric
Tohoku Illcctric
Chubu Electric
Kansai Electric
Xansai Electric
Chugoku Electric
Shikoku Electric
Eokuriku Electric
Plant site
Yokosuka
Eachinoe
Shinsendai
Nishinagoya
Amagasaki
Kainan
Mizushima
Shintokushima
Shinminato
Capacityfrltf)
130
125
150
220
125
150
100
150
250
Process developer
Mitsubishi-JECCO
Mitsubishi-JECCO
Kureha- Kawasaki
Vellman-Lord(in^)
Mitsubishi-JECCO
Mitsubishi-JECCO
Babcock-Sitachi *
Kureha- Kawasaki
Chiyoda
Absorbent
CaCO,
Ca(OE)2
NaOH, CaCO,
NaOH
Ca(OE)2
Ca(OE)2
CaCO^
NaOE , CaCOj
E-SO., CaCO,
Product
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
-------
Table 4.6 Major pilot plants for S0« recovery
Process developer
Wet process
Grillo-Mitsui S. B.
Kawasaki H.I.
Hitsui II.B.-Chemico
Hitachi S.B.
Xureha-IIawasaki
Showa Denko
Babcock-aitachi
Kurashiki Boseki
Furukawa Ilining
Hitachi Ltd.
ITippon Kokan
Dry process
National R.I.P.R.
Sumitomo S.M.
Absorbent
Product
Plant site
Unit capacity(scfnp
MfeO, MhO
Ca(OH)?
CaC07
NaCIO, CaCO-
NaOH, CaCO,
ITaOH, CaCO,
CaCO,
Nil,, Ca(OH)2
HHj, Ca(OH)2
NaOH, Ca(OH)?
Ca(OH)2
^oo3
Carbon
SO H SO
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gj'psum
Gypsum
Gypsum
Gypsum
so2, s
H2S04
Chiba
ICakogava
Omuta
Maizuru
Nishiki
I'Zawasalci
I'ure
Eirakata
Osaka
r!byasu
Ka.wagu.chi
710
2,900
1,200
290
2,900
5,900
1,000
5,900
350
880
1,200
120
5,900
-------
5 Vet-alkali and double alkali processes
7 8}
5.1 Kureha sodium-limestone process ' '
Developer Kureha Chemical Industry Co.
1-8, Horidomecho, Nihonbashi, Chuo-ku, Tokyo
State of development Kureha first developed a sodium scrubbing process
to produce solid sodium sulfite to be sold to paper mills as was
described in the 1972 report of the present author. In addition to two
176,000scfm plants operated by Kureha since 19^9. two plants have been
licenced, one to Mitsui Toatsu Chemical (I12,000scfm) which began
operation in September 1971, and the other to Konan Utility (l23,000scfm)
which started operation in late 1972. Since the demand for sodium
sulfite is limited, Kureha has recently developed a sodium-calcium
double-alkali process. Tests with a small pilot plant led to the
construction of a larger pilot plant (3,000scfm) which has been in
operation since July 1972. The larger pilot plant program is a joint
effort with Kawasaki Heavy Industries. Two commercial plants will be
completed in 1974 to treat flue gas from oil-fired boilers at power
companies, one at Shinsendai station, Tohoku Electric Power (l50MW),and
the other at Shintokushima station, Shikoku Electric Power (150MW).
Process description A flow sheet of the sodium-calcium process is shown
in Figure 5>1* The scrubbing system consists of a venturi scrubber
where water is used to remove particulates and to cool the gas followed
by a rubber-lined, grid-packed scrubber where S0_ is absorbed in a sodium
sulfite solution. The water from the dust scruboer is discharged at
a pH of about 2.5. The pH of the liquor from the absorber is controlled
to 6.0-6.3> With an inlet concentration of l,500ppm S0?, 98$ removal is
achieved; the liquid gas ratio is 7gal/l,000ft* of gas. The feed to the
absorber contains 20-25$ sodium sulfite and has a pH of 7-8; the calcium
content was reported to be about 30ppm. The scrubber discharge contains
about 10$ sodium sulfite, 10$ sodium bisulfite, and 2-3$ sodium sulfate.
Limestone pulverized in a wet mill equipped with a cyclone classifier
is fed continuously along with scrubber liquor into an atmospheric
pressure vessel where sodium bisulfite reacts with limestone to form
calcium and sodium sulfites.
2NaHSO, + CaCO,—* CaSO,'1/2^0 + NBgSO, + 1/2H20 + COg
The reaction temperature is somewhat higher than the scrubber temperature
which is about 140°F; residence time for conversion is about 2 hours.
The slurry from the decomposer is passed through a centrifuge where the
calcium sulfite crystals are separated from sodium sulfite liquor, which
is then returned to the scrubber.
35
-------
The calcium aulfite is reacted with air at atmospheric pressure in an
oxidizer developed by Kureha. Gypsum is removed from the oxidizer
discharge stream by a centrifuge. The product is suitable for use in
wallboard and cement.
Oxidation of sulfite in the scrubbing and decomposition steps results
in the formation of sodium sulfate which cannot be regenerated by
reaction with limestone. In order to control the sulfate level, a
sidestream from the scrubber discharge is mixed with calcium sulfite
crystals and sulfuric acid is added. The net effect is to convert the
sodium sulfate to calcium sulfate and produce sodium bisulfite for recycle.
Gypsum is separated by a centrifuge and added to the oxidizer loop.
+ CaS03'l/2H20
CaS(yi/2H20 + Na2SO + 5/2H20- -»CaSCy2H20 + 2NaHSO,
Status of pilot plant operation The pilot plant (3,000scfm) has been
operated continuously since its completion in July 1972 except for the
scheduled shutdown for inspection in September and December. Almost
no scaling was observed. Operation of the centrifuges has given
effective separation of solid and liquid phases. Both calcium sulfite
and gypsum discharged from the centrifuge are dump solids which can be
transported by solid-handling equipment, if desired. The crystals of
gypsum grow to around 100 microns. The flue gas contains about 6$
oxygen. About 7$ of the recovered SO. is oxidized to form sodium
sulfate. The sulfuric acid requirement for the decomposition of the
sulfate is 125$ of the theoretical amount. Therefore, about 8.7$ of
the product gypsum is derived from sulfuric acid.
Economics For the production of a ton of gypsum, 1,200 Ib of limestone,
18 Ib of caustic soda (100$) for make-up, 100 Ib of sulfuric acid (98$),
340kWh of electric power, 1,460 Ib of steam, and 18 tons of water are
required. Investment cost is uncertain, but the investment requirement
would be split among the process steps as follows:
Absorption 30$, Decomposition 30$, Sulfate conversion 10$,
Oxidation
Advantages High recovery of SOp is achieved with limestone. No scaling.
Sodium suifate is decomposed to recover sodium bisulfite and gypsum.
Good quality of salable gypsum is obtained. Both gypsum and calcium
sulfite discharged from the centrifuge have less moisture and are easy
to handle.
Disadvantages The process is less simple than the lime-gypsum process.
The use of a considerable amount of sulfuric acid it disadvantageous
for plants where the product calcium sulfite or gypsum must be discarded.
36
-------
Fuel
Air
Limestone
Make-up
NaOH
Waste
£!LV
I
fi
NaHSOj
NaHSO-a (Na2SO/g.)
Air
i
Gypsum
(1) Reheater (2) Absorber (3) Mill and classifier
(4) Decomposition tank (5) Centrifuge (6) Sulfate conversion tank
(?) Air compressor (8) Oxidjzer (9) Centrifuge
Figure 5.1 Flow sheet of Kureha sodium-limestone process
-------
7 8}
5.2 Showa Denko sodium-limestone process '
Developer Showa Denko K.K.
341 Shiba Miyamotocho, Minato-ku, Tokyo
Ebara Manufacturing Co. Ltd.
11-1, Asahimachi, Haneda, Ota-ku, Tokyo
State of development Showa Denko, jointly with Ebara, recently constructed
commercial plants for S0_ recovery by sodium scrubbing to produce sodium
sulfite for paper mills. The plants include Kawasaki plant (88,000scfm)
of Showa Denko, Kawasaki plant (l59»000scfm) of Ajinomoto, and Yokohama
plant (I42,000scfm) of Asia Oil for flue gas from oil-fired boilers, and
Sodegaura plant (47»000scfm) of Nippon Phosphoric Acid to treat tail gas
from a sulfuric acid plant. As demand for sodium sulfite is limited,
Showa Denko and Ebara have started joint tests on sodium-calcium process
to by-produce salable gypsum. A pilot plant (5,900scfm) has been in
operation at Kawasaki plant of Showa Denko since 1971* A commercial
plant to treat 540,000scfm of flue gas is being constructed at Chiba plant,
Showa Denko, to start operation in June 1973*
Process description The Showa Denko-Ebara process features the use of
a vertical-cone type absorber as shown in Figures 3*2.1 and 5*2.4.
A liquid (sodium sulfite solution) is charged from the bottom, blown up
by the gas to absorb SCL, and flows back to the liquor inlet by gravity.
Very good contact between gas and liquid particles is attained ensuring
95-98$ desulfurization at a liquid/gas ratio of 7-14 gal./l,000scf
(Figure 5«2.2). Pressure drop ranges from 8 to 15 in.H_0. A flow sheet
of the sodium-calcium process is shown in Figure 5.2.3* Flue gas from
an oil-fired boiler containing l,500ppm S0_ and about 1 grain/cf dust is
led directly into the scrubber; 95$ of the S0? and about 60?& of the dust
is removed by a sodium sulfite solution. Most of the liquor discharged
from the scrubber is recycled to the scrubber. A portion of the liquor
is led to a reactor and treated with pulverized limestone.
2NaHSO, + CaCO, = Na^SO, + CaSO, + H-O + CO,
The calcium sulfite is separated from the sodium sulfate solution; the
solution is returned to the scrubber. Calcium sulfite is oxidized in
an oxidizer to form gypsum. As sodium sulfate gradually forms in the
solution and tends to accumulate, a portion of the liquor discharged
from the scrubber is sent to a sulfate conversion step to maintain the
sulfate concentration at a certain level. In the conversion step, the
sulfate is treated with calcium sulfite and sulfuric acid to produce
gypsum and sodium bisulfite.
Na2SO. + 2CaSO, + HgSO. + 2H20 = 2(CaSO.'2H20) + 2NaHSO,
The bisulfite solution is led to the reactor.
-------
Status of technology The pilot plant has been operated for nore than
one year without serious trouble. Both lime and limestone have been
used for comparison. Limestone reacts slowly with sodium bisulfite
requiring a few hours. By using lime the reaction proceeds rapidly.
However, limestone will be used in the commercial plant because it is
much cheaper than lime, and moreover, larger crystals of gypsum is
obtained with limestone. An oxidizer developed by Showa Denko and Ebara
will be used in the commercial plant. The oxidation proceeds a little
more slowly but the crystals of gypsum grow larger than with a rotary
atomizer developed by JECCO.
Advantages The scrubber is very effective for desulfurization.
recovery of SO. is achieved consuming limestone.
High
Disadvantages The process is less simple than the lime-gypsum process.
The use of a considerable amount of sulfuric acid is a demerit for
plants whose by-product gypsum or calcium sulfite must be discarded.
Economics The estimated desulfurization cost for a 120,000scfm plant
for 95?6 removal of SOU is shown below.
Plant cost $1.7 million
7,000 hours operation in a year
By-product gypsum 192,000 tons/year
Requirements (ib per bl oil)
NaOH
0.56
H2S04
5.0
Variable cost
Fixed cost
Desulfurization
CaO
55.8
cost
Water
560
$0
SO
SI
SO
• 33lAl
.687A1
.018/bl
•936A1
Steam
0.38
oil
oil
oil
oil
Electricity
10(kVh)
f without credit for gypsum)
(with credit for gypsum)
39
-------
Gas
Gas-liquid
separator
Absorbing
section
I
28 feet
I
I
I
I
Liquid
Figure 5.2.1 Vertical-cone type
absorber for 60,OCOacfm
150
faO
-P
0)
rH
-P
3
o
100 ..
50 ..
Csj
O
CC
L/G =
L/G =
) 1,000 2,000 3,000 4,000
SOp ppm of inlet gas
Figure 5.2.2 Relation between
liquid/gas ratio (gal./l,000scf)
and SO,, removal (pH 6.5)
-------
Sulfate treatment
Mist
eliminator
-O ! O
Recycle Reslurry
tank
tank
6--
Tank
Air
Figure 5»2.3 Showa Denko sodium-limestone process
-------
Figure 5.2.4- Kawasaki plant of Showa Denko
( sodium scrubbing, 88,000scfm )
-------
5.3 Hitachi sodium process and sodium-lime process '
Developer Hitachi Ltd.
2-8, Otemachi, Chiyoda-ku, Tokyo
5-3-1 Semi-wet sodium process
Process description Flue gas from oil-fired boiler at about 350°F after
passing through a dust eliminator is introduced into a reactor into
which sodium hydroxide solution is fed and mixed with the gas by a mixer
(Figure 5»3-1). By the heat of the gas, moisture is removed and a powdery
product consisting of sodium sulfite, sulfate and carbonate (for example
Na-SO, 60$, NagSO. 20#, and Na^CO. 20$) is formed which is caught by a
multiclone, electrostatic precipitator, or bag filter. The product is
usable for kraft pulp production. The temperature of the outlet gas from
the dust eliminators is kept above 210°F. The S0_ concentration of the
inlet gas is about l,300ppm and that of the outlet gas 100 to l^Oppm.
The dust content of the outlet gas to stack is 0.02-1 grain/scf and
is below the emission standard. The size of the reactors for different
amounts of gas is shown below:
Amount of gas (scf.ni) Size of reactor (feet)
Diameter Height
11,800 7.9 62.7
30,000 9.6 82.5
59,000 14.8 92.4
State of development Two commercial plants of Jujo Paper Co. are in
operation; one was completed at Jujo plant (l6,500scfm) in August 1971
and the other at Miyakojima plant (57,000scfm) in October 1972.
Advantages The process is very simple. Reheating of the gas is not
required when the temperature of the inlet gas is higher than 300°F.
Pressure drop is relatively small. No wastewater.
Disadvantage CO. in the gas is also absorbed consuming caustic soda.
Use of the product is limited.
-------
t
Flue gas
Reactor
Dust
collector
To stack
t
NaOH
1
'By-product
Figure 5-3.1 Hitachi semi-wet sodium process
-------
5*3.2. Sodium scrubbing (sodium sulfate production)
Process description Flue gas is first led into a cooler to which
a portion of an absorbing liquor is fed for cooling, partial
desulfurization, and dust removal (Figure 5.3*2). The gas is then
led into a dual-flow tray scrubber which has multistage horizontal
plates with many holes about a half inch in diameter. Absorbing
liquor (sodium sulfite solution) goes down from the top stage to
the bottom through the holes while the gas goes up from the bottom
through the holes forming numerous bubbles. The reacted liquor
containing sodium bisulfite is neutralized with sodium hydroxide to
regenerate the sulfite and is then returned to the scrubber. A
portion of the sodium sulfite solution is led into an oxidizer to
oxidize the sulfite into sulfate by introducing air bubbles. The
sulfate solution is filtered for dust removal and put into the
wastewater system. The size of the scrubber to reduce the SO-
content from 1,000 to lOOppm and dust from 20 to 2mg/scf is snown below.
Amount of gas (sefm) Size of scrubber (feet)
11,800
35,000
58,000
88,000
State of development Two commercial plants with capacities 14»000scfm
and 35fOOOscfm have been in operation since August 1972.
Advantages The dual-flow tray scrubber is effective for removal of
both SO. and dust. The process is simple and operation is easy.
Disadvantages Caustic soda is fairly expensive. Omission of a large
amount of sodium sulfate might constitute a limiting factor in future.
Diameter
7.2
12.9
16.5
19.8
Height
24.1
28.7
33.0
36.3
-------
NaOH
Boiler
&
Water
After-
burner
Air
Oxidizer
Waste
liquor
Fan
Scrubber
Dust
separator
Figure 5.3.2 Hitachi sodium sulfate process (waste product)
-------
5.3«3 Sodium-calcium process
Process description A flow sheet of the process is shown in Figure
5.3.3. The absorbing system is similar to that described in 5.3.2.
A portion of the circulating solution containing sodium sulfite with
some sulfate is reacted with milk of lime in a reactor to produce a slurry
consisting of sodium hydroxide solution and solid calcium sulfite with
some gypsum. The solids are separated from the solution by a thickener
and a centrifuge; the solution is returned to the absorbing step and the
solids are fed into an oxidizer where calcium sulfite is oxidized by
air bubbles to produce salable gypsum. Sulfuxic acid is used for pH
adjustment of the slurry in the oxidizer. Hitachi has found an optimum
condition for the conversion of sodium sulfate to gypsum.
State of development A pilot plant with a capacity of treating flue
gas (SSOscfm) from an oil-fired boiler has been in operation.
Economics The requirements and products for 90$ removal of SO- (l,500ppm)
of flue gas is as follows:
Amount of gas treated (scfnQ
11.800 29.400 58.800 88.200
Requirements
Ca(OH)2 (Ibs/hr) 1?6 429 858 1,28?
Water (tons/hr) 1.3 3-3 6.6 9.9
Electric power (kW) 120 250 460 660
Steam (ibs/hr) 154 418 836 1,254
Products
Gypsum (ibs/hr) 440 1,078 2,156 3,234
Some make-up canstic soda is also required. The desulfurization cost
including depreciation (7 years) and assuming 8,000 hours operation in
a year is estimated to be about $l,14/bl for 29,400scfm, $0.94/bl for
58,800scfm, and $0.?3A1 for 117t600scfm.
Advantages High recovery of S0_ is achieved and salable gypsum is by-
produced without scaling problems. Essentially no wastewater is emitted.
Disadvantages The process is less simple than the lime-gypsum process.
Sulfuric acid is required.
-------
00
Gas
After-burner
•>
•fl
Milk of lime
NaOH
Make-up
NaOH
/\
Thickener
Reactor
CaSC-3 slurry
Fan Scrubber
jNaOH
i
i
Air
Liquo
D-K]
Calcium sulfite
filter
Gypsum filter
—Q I
Tank Oxidizer
Tank
Gypsum
Figure 5*3*3 Flow sheet of Hitachi sodium-lime process
-------
5.4 Nippon Steel Chemical Sodium-lime process
Developer Nippon Steel Chemical Co. Ltd.
17-2, 6-chome, Glnza, Chuo-ku, Tokyo
Process description S02 in waste gas is absorbed by a sodium sulfite
solution in two two-stage venturi type scrubbers in series developed by
Hiura Kagaku Sochi Co.(Figure 5»4). The liquor discharged from the
scrubber normally contains about 10$ sodium sulfite and bisulfite and
about 5$ sodium sulfate. A large portion of the liquor is neutralized
with a sodium hydroxide solution and recycled to the scrubbers. The
rest of the liquor is reacted with milk of lime (5$ in excess) to
precipitate calcium sulfite with some sulfate and to form a sodium
hydroxide solution. The slurry is sent to a thickener. The concentrated
slurry from the bottom of the thickener is fed to a vacuum filter. The
filtered cake contains 50 to 60$ moisture. The filtrate and the overflow
from the thickener (sodium hydroxide solution) is used along with make-up
sodium hydroxide to neutralize the liquor discharged from the scrubber.
The desulfurization ratio reaches 96 to 98$. The sodium sulfate concent-
ration in the circulating liquor gradually increases until it reaches
about 10$ but it is likely that it does not exceed 10$. The filtered
cake consisting of 90$ calcium sulfite, 3$ gypsum and 3$ calcium hydroxide
is used for land-filling.
State of development A commercial plant to treat 12,000scfm gas from
an oil-fired furnace for rock wool production was completed in 1972 and
has been in operation since. S0? concentration in the gas is reduced
from 730 to 23ppm by the scrubbing.
Economics The plant cost $231,000. Estimated costs of larger plants
are listed below.
Capacity (scfm) 29,400 58,800 118,000
Investment cost ($)438,000 711,000 1,156,000
The operation cost assuming that the gas contains l,500ppm SO. and that
93$ of the SOp is removed is shown below.
Requirement Cost
per ton of oil Unit cost 8/ton of oil
Sodium hydroxide 15-4 Ib 0.032 S/lb 0.428
Milk of lime
(carbide sludge) 134 Ib 0.0043 S/lb 0.580
Water 0.6t 0.032/ton 0.019
Electric power 66kWh 0.097 SA^ 0.643
Total 1.67
-------
Advantages High SO,, removal. No wastewater. No scaling.
Disadvantage Accunrulation of sodium sulfate In the liquor necessitates
the circulation of the liquor In a large amount.
50
-------
Waste gas
i
. _J
*—
.Ca(OH)2
Make-up NaOFI
Scrull'H Scrubber
Absorption step
Regeneration step
Figure 5.^ Flow sheet of Nippon Steel Chemical sodium-lime process
-------
789)
5*5 NEE ammonia process and ammonia—lime process *
Developer Nippon Eokan Eabuahlkl Ealsha
1-1-3i Otemachi, Chiyodaku, Tokyo
Process description Waste gas at 250°F from an Iron ore sintering plant,
containing 400 to l,000ppm S02 is first led into an electrostatic
precipitator and then cooled to 140°P in a cooler with water spray
(Figure 5.5.1). The gas is then led into a screen type scrubber
(Jinkoshi type, Figure 5.5.2) for the absorption of SO. by a liquor
containing ammonium sulfite. In the scrubber 16 mesh screens of stainless
steel are placed with some inclination in five stages. On three of the
screens placed at the middle of the scrubber, the ammonium sulfite
solution flows slowly forming a liquor film which readily absorbs S0«.
On the other two screens placed at the upper part of the scrubber,
water flows slowly forming a water film to decrease plume formed by the
reaction of SO. and ammonia. About 95$ of SO- is removed when the pH
of the circulating liquor is about 6. Virtually no ammonia is lost when
the pH of the liquor is 6 or below.
The outlet liquor containing ammonium bisulfite is sent to an ammonia
absorber. Coke oven gas containing a small amount of ammonia is introduced
into the absorber. The liquor is sprayed to absorb ammonia and to form
an ammonium sulfite solution. A large portion of the solution is returned
to the scrubber to absorb S0_. The rest of the solution is sent to an
oxidizer where the sulfite is oxidized into sulfate by air bubbles
produced by rotary atomizers. The ammonium sulfate solution is evaporated
to produce crystal ammonium sulfate.
Nippon Ebkan has recently developed an ammonia-lime double alkali process
(Figure 5.5.3). The SO. absorbing part is the same as in the ammonia
process except that no coke oven gas is used. The liquor from the scrubber
contains about (NH.)2SO, 7«5$t NH.HSO- 7.5$ and (NHj-SO. 15$. A portion
is sinx to a reactor and Is reacted witfi milR of lime (1C
of the liquor
concentration) under normal pressure at 210°F. The ammonia released here
is sent to the ammonia absorber to be absorbed by the liquor from the
scrubber. Calcium sulfate and sulfite are precipitated in the reactor.
The slurry from the reactor is acidified with sulfurlc acid to adjust
the pH to 4 to promote oxidation. The slurry is then led into an oxidizer
equipped with rotary atomizers to convert calcium sulfite 'to gypsum,
which is then centrifuged. Salable gypsum with a good quality is obtained.
The gas from the oxidizer contains S02 and is sent to the scrubber.
State of development After tests with a pilot plant to treat 17,000scfm
of waste gas from the iron ore sintering plant, a prototype plant to treat
88,000scfm gas to produce ammonium sulfate by reaction with coke oven gas
was completed in early 1972 at the Keihin works of Nippon Ebkan.
52
-------
Additional units for the ammonia-lime double alkali process were
completed in November 1972. The construction and the operation of
the plants have been carried out as a research project by Japan Iron &
Steel Federation.
Statue of technology The Jinkoshi type scrubber capable of treating
88,000scfm gas is 56 feet high with a cross section of 14 feet x 23 feet.
The following conditions are used for SO- absorption:
L/G 12gal/l,000scf Gas velocity 7 to IJft/sec.
Pressure drop 10 to 12 inches HgO
Inlet SO. 400 to l,000ppm Outlet S02 15 to 50ppm
The outlet gas is at 140 °P and is not preheated; heavy plume is observed
from the stack. Tests have indicated that the plume becomes slight when
the gas is reheated to 180 'F and nearly invisible at 240 °F.
When coke oven gas is used as the source of ammonia, H^S in the gas is
absorbed to form thiosulfate.
2H2S + 2SO ~ + 2HSO " — > JSgO "" + JHgO
The thiosulfate is not oxidized into sulfate in the oxidlzer. It is
decomposed by addition of sulfuric acid to the liquor discharged from
the oxidlzer.
By the decomposition SO- is released which is sent to the scrubber.
Elemental sulfur formedT>y the reaction is removed by filtration.
In the ammonia-lime process, the oxidation of calcium sulfite into sulfate
is hindered under the presence of thiosulfate. Therefore, it is better
not to use coke oven gas in this case. To make up a small amount of ammonia
(about 5$) lost from the system, ammonium sulfate is added to the reactor
to react with lime and to generate ammonia. The pH in the reactor is
maintained at about 11 to ensure gypsum crystal growth in the reactor.
To promote the oxidation of calcium sulfite present in the slurry from
the reactor, the slurry is acidified to pH 4 ty addition of sulfuric acid
and then led into the oxidlzer. Gypsum grows into big crystals (100
to 300 microns) and can easily be centrifuged to a low moisture content
(about 10$). The liquor from the centrifuge which is acidic is neutralized,
clarified and returned to the system. No wastewater is emitted.
53
-------
Advantages The screen type scrubber is effective for SO. removal with
a relatively low pressure drop. A large amount of gas, up to about
300,000scfm can be treated in one scrubber. By the ammonia process,
both SO, in waste gas and ammonia in coke oven gas are utilized to
produce salable ammonium sulfate. By the ammonia-lime process, salable
gypsum of good quality is obtained with no scaling problem. No wastewater
is emitted.
Disadvantages When coke oven gas is used, hydrogen sulfide in the gas
necessitates additional facilities. The screen in the scrubber is
subject to corrosion under inadequate operating condition.
Cost estimation A cost estimation for the ammonia-lime process to treat
flue gas from an oil-fired boiler is shown in the following table in
comparison with that for the lime-gypsum process developed by Nippon
Kokan which is similar to the Mitsubishi-JECCO lime gypsum process (6.1).
Table 5.5 Cost estimation ($1 = ¥308)
(SO. in inlet gas l,400ppm, in outlet gas 70ppm)
Ammonia-lime process Lime-gypsum process
Amount of gas treated (scfm)
Investment cost (Si, 000)
Fixed cost ($l,000/year)
Depreciation
Labor (7 persons)
Repair
Insurance
Management
Variable cost ($l,000/year)
Electric power (^Ll mil/kWh)
Steam (@$1.5/ton)
Industrial water (^5 mil/ton)
Seawater($5 mil/ton)
Quick lime (@$ 13.1 /ton)
Slaked lime l@$15. I/ton)
Sulfuric acid(@S28.3/ton)
Ammonia (@$87.6/ton)
Fuel (@S35. I/ton)
Product ffVDSum (@$5.8./ton)
Desulfurization cost ($/bl)
With revenue from gypsum
Without revenue from gypsum
235.000
2,110
382
45
63
2
95
168
96
4
168
45
37
326
-226
0.69
0.82
882.000
4,545
822
45
136
5
353
634
383
14
688
180
148
1,295
-899
0.58
0.72
235.000
2,273
409
45
68
3
84
191
3
1
276
262
-220
0.
0.
882.000
5,844
1,055
45
175
7
295
822
11
2
951
1,006
-883
64 0.52
77 0.66
-------
Coke-oven gas
Gas to stack
{Scrubber
Ammonia absorber
Gas
Cooler
If
'ill.
L
w
<
.<
aterl i
I
Cooler '
=D •
ii
0
-
u
-
Ts
CX*-
Purified
coke-oven gas
T
I
"2 | 'J
1
Absor
ber
O-
Filter
Tank
Oxidizer
ira
Air Ammonia
Tank
Evaporator
Ammonium
sulfate
FiKure 5.5.1 Nippn Kokan ammonium sulfate process
-------
Figure 5.5.2 Keihin plant, Nippon Kokan
( Ammonia scrubbing, 88,000scfm )
56
-------
Recovered water
Gas to stack
VJl
NJ
gas
Prescrubber
Gas to prescrubber
scrubber Water absOrber
recovery
section
Thi ckener
Sludge
Reactor pH
adjusting..
tank
Neutra-
lizer
NH-j recovery J
section j
NHo regeneration
section I
Figure 5.5.3 Nippon Kokan ammonia-lime process
Gypsum , Water
production ; recovery
section « section
-------
7
5.6 Wellman-MKK sodium process '
Developer Vellman-Lord, U.S.A.
Mitsubishi Chemical Machinery (MKK)
6-2, 2-chome, Marunouchi, Chiyoda-ku, Tokyo
Process description Flue gas is first washed by a prescrubber installed
in the lower part of the sieve tray absorbtion tower (Figure 5»6.l).
The partially cleaned gas rises in the tower while contacting a
countercurrent flow of a concentrated sodium sulfite solution which
eliminates more than 90$ of the inlet SO. to form sodium bisulfite.
Mist droplets are removed by the eliminator and demister combination
in the upper part of the tower and the gas is discharged at about 265°F
after reheating in the oil-fired after-burner. A sodium bisulfite
solution is discharged from the absorption tower and is stored in a
surge tank before it is sumped to an evaporator. In the evaporator
the sodium sulfite solution is heated with steam and decomposed into
S02 gas and sodium sulfite.
Na2SO_ + S02 + HpO "—»2HaHSO,
The S0? concentration in the gas leaving the evaporator is 90$ after
the water vapor is condensed in a cooler. In this evaporator, sodium
sulfite is gradually concentrated and crystallized. The crystalline
sodium sulfite is centrifugally separated from the mother liquor,
dissolved in a condensate from the cooler, and the solution is recycled
to be used as absorbent. The recovered SO, is used for sulfuric acid
production. Tail gas from the acid plant Is led into the absorption tower.
Sodium sulfite is gradually oxidized into sulfate by the oxygen in the
flue gas. To keep Na.SO. concentration to a minimum and optimum figure,
a small portion of the mother liquor is purged; this purge liquor is
used for gas cleaning in the prescrubber. The bleed is taken off this
prescrubber circuit for the purpose of removing contaminants, which
otherwise would build up in the system. The major contaminants are
sodium sulfate and sodium polythionate. The purge stream is subjected
to wastewater treatment that involves the following: (l) addition of
H.SO. to convert NaSO* and NaHSO, to Na-SO.; S0_ evolved is sent to
the lulfuric acid plant; (2) alkali is addSd to form the hydroxide of
soluble metal ions (vanadium, nickel, iron); this precipitates them as
hydroxides; (3) removal of solids by filtering; (4) neutralization by
adding H2SO/. The final wastewater is a largely clear concentrated
solution of sodium sulfate. This effluent eventually is sent to the bay.
State of development A commercial plant designed to treat 118,000scfm
of flue gas from oil-fired boilers has been in operation since June
1971 at Chiba plant, Japan Synthetic Rubber Co. A larger plant with a
capacity of treating 365»000scfm of flue gas from oil-fired boilers is
under construction at Nishinagoya Station, Chubu Electric Power Co. to
58
-------
start operation in July 1973* It has been recently decided to build
a 237,000sofm plant (flue gas from oil-fired boiler) for Japan Synthetic
Rubber Co. at Yokkaichi.
Status of technology In Chiba plant, Japan Synthetic Rubber, flue gas
from two oil-fired boilers (130 tons/hr each) is treated by two 16-ft
square sieve tray absorption towers at a rate of 90,000scfm per absorber.
A photograph of the plant is shown in Figure 5*6.2. The plant came
on-stream in June 1971 and has been operated for more than 8,000 hours
in a year. Figure 5.6.3 shows operation performance of the unit from
start-up until March 1972. The SO- concentration in inlet gas normally
ranges from 1,000 to 2,000ppm and that in outlet gas from 100 to 200ppm.
The major problem associated with the process is the necessity to bleed
a waste stream from the absorber liquor circuit to avoid build-up of
contaminants, primarily sodium sulfate. The following tabulation
summarizes the present composition of absorber and waste streams:
Absorber feed Absorber out Wastewater to Vastewater after
treatment treatment
Na2S03
Na2S20_a
Na2S04
Suspended
solids
PH
COD
Flow rate
a
16-19$ by wt 2-4$
0 14-17$
5-7$ 5-7$
- -
-
-
-
,0e + H-0 — ^ 2NaHSO, .
! 5 z ' 5
0
4-6$
3-6$
1-2$
(I0,000-20,000ppm)
5-5-5
20,000ppm
-
0
0
7-16$
2-10ppm
7+0.1
200ppm
1-1.5 tons^ir
Clear sodium sulfate solution is emitted from Chiba plant. In new plants
to be built in future, the sodium sulfate solution will be evaporated to
produce solid sodium sulfate as a by-product or treated with lime to
precipitate gypsum and to recover a. sodium hydroxide solution, thus
eliminating the wastewater.
Economics The investment cost of the Chiba plant was $2,600,000 including
the cost for sulfuric acid plant. The plant consumes approximately
755»000bbl/year of fuel and produces 13,200 tons/year of sulfuric acid.
The requirements of the desulfurization plant are shown below.
Make-up caustic soda 3-4 Ib/bl oil for 86-93$ recovery of SOg
°
After-burner fuel 10.5 IbA1 oil *o heat to 266°F
Steam 175 lb/bl °H
Cooling water 6.5 tons/bl oil
59
-------
The investment cost for Nishinagoya plant, Chubu Electric (365,000scfm)
is $5,200,000 including the sulfuric acid plant with a capacity of 90
tons/day.
Advantages Stable reliable operation. High recovery of SO,. The
sulfuric-acid plant is much smaller than usual because the concentrated
SOp recovered is used.
Disadvantage The treatment of sodium sulfate formed by the oxidation is
not simple.
60
-------
-------
Figure 5.6.2 Chlba plant, Japan Synthetic Rubber
( Wellman-MKK process )
62
-------
2000
200
Note:
(A):Onlrifurr sUrl
(B):lst shut eln«rn for plait inspection
(C): Crntnfu_T bypass tost
(D):Mixf
-------
5.7 Wellman-SCEC sodium process
Developer Wellman-Lord, U.S.A.
Sumitomo Chemical Engineering Co. (SCEC)
33-5§ 3-chome, Kongo, Bunkyo-ku, Tokyo
Process description Tail gas from a Claus furnace, 38,800scfm at 930°F,
containing about 7,000ppm SO. is cooled to 660°F in a waste-heat boiler,
to 210°F in a cooling tower with water spray, and then to 160°F in a
heat exchanger. This cooling method was used because gas containing much
SO- at 210-660°F is quite corrosive. The cooled gas is introduced into
an absorber with a three-stage sieve tray to which a sodium sulfite
solution at pH 6.2 to 6.4 is charged. About 93$ of SO- is recovered in
the absorber.
Sodium bisulfite solution at pH 5.7 to 6.0 is discharged from the absorber,
led to an evaporating crystallizer, and heated to 210°F to separate a gas
(50$ SO- and 50$ water vapor) and crystalline sodium eulfite from the
solution. The gas is cooled in a condenser to remove water. The product
gas, which contains more than 99$ SO-, is sent to a Claus furnace. The
solid sodium sulfite is dissolved in water from the condenser and returned
to the abosrber. The remaining solution is recycled to the crystallizer.
A portion of the solution is taken out of the system to remove impurities
and the sodium sulfate formed by oxidation.
An oxidation inhibitor developed by Sumitomo Chemical Co. has been used
in the process. Without the inhibitor 3 to 5$ of total sodium compounds
in the plant is converted 'to sulfate in a day. By the use of the
inhibitor, oxidation is reduced to about 40$ resulting in a substantial
decrease in the consumption of sodium hydroxide. The use of the inhibitor
has been licensed by Sumitomo Chemical Co. to Wellman-Lord.recently.
State of development A commercial plant designed to treat 38,BOOscfm of
tail gas from a Claus furnace has been in operation since July 1971 at
Negishi Refinery, Toa Nenryo to return the recovered SO. to the Claus
furnace. Another plant with a capacity of treating 212,000scfm of flue
gas from an oil-fired boiler is under construction at Chiba plant,
Sumitomo Chiba Chemical; the recovered SO. will be used for sulfurlc
acid production.
Advantages Stable operation and high recovery of SO-. Formation of
sodium sulfate is substantially reduced by the use of the oxidation inhibitor.
Disadvantage Treatment of sodium sulfate is not simple even though the
amount of the sulfate is reduced by the use of the inhibitor. Cooling of
the high-temperature gas containing much S0? is not simple because of
its corrosiveness.
-------
Economies The total investment cost for the 38,800-scfm plant was
$1.94 million. In addition, $0.64 million was required for the cooling
system for the tail gas including a waste-heat toiler, cooling tower,
and heat exchanger.
It is estimated by Sumitomo Chemical Engineering that when this type of
desulfurization plant is used for a 250MW oil-fired power plant to treat
441,000scfm of flue gas, the cost to remove 90$ of S0« would
be'about $0.78/bl of oil. Reheating of the waste gas by an after-burner
would require $0.1 - 0.15 more.
65
-------
Absorbe:
Water
Waste
gas
CT\
NapSQ-* solution
Crystallizer
Conden
ser
\
\<
o-
entrifuge
.^£entri
-O O*-
NaHS03 so lilt ion
NaOH
Figure 5.7 Flow sheet of Wellman-SCEC process
-------
7}
5.8 Oji sodium process '
Developer Oji Paper Co*
4-7-5t Ginza, Chuo-ku, Tokyo
Process description OJi has constructed many sodium scrubbing plants
to produce sodium sulfite for paper mills by using OK scrubbers
developed by Oji and also Jinkoshi scrubbers developed by Kanagawa PIL.
The OK scrubber is of the spray type and has been used mainly for the
treatment of waste gas from kraft recovery boilers. Up to about
150,000scfm gas can be treated by the scrubber to remove 95$ SO- and 70
"to 90$ of dust from the recovery boiler gas with a pressure drop of
2 to 2.5 in. H20. The Jinkoshi scrubber is of the screen type and has
been used for flue gas from oil-fired boilers.
The OK scrubber was described in the 1972 report by the present author.
A flow sheet of a prototype plant (265,000scfm) with Jinkoshi scrubbers
is shown in Figure $.6. The gas is first treated by a prescrubber in
which screens (about 10 mesh, made of stainless steel SAS 33) are placed
nearly vertically. The screens are set in frames about 3*3 feet wide and
7 to 10 feet long. Water flows slowly on the screens forming films. Dust
is removed and the gas is moistened by the water films. The gas is then
led into a scrubber where screens are placed with inclination. The
scrubber is 12 feet wide, 14 feet deep and 36 feet high. A sodium sulfite
solution with some sodium hydroxide is fed onto the screen to form
films to absorb S02 giving a solution of sodium sulfite. Most of the
sulfite solution is recycled with addition of sodium hydroxide; a
portion of the sulfite solution is bypassed and obtained as a product
to be used for paper mills. S0~ removal was about 80$ with three stages
of screens and 95$ with nine stages when the gas velocity in the scrubber
was between 2 and 12 feet/sec; desulfurization was not appreciably affected
by the gas velocity within the above range. The pressure drop per stage
of screen was 0.5 in. H90 at a gas velocity of 3 feet/sec and 0.6 in. H90
at 12 feet/sec. * *
As the liquor in the prescrubber became acidic and corroded the screens,
the prescrubber was eliminated in commercial plants in which the gas is
cooled with water sprays and fed to a scrubber. A scrubber to treat
130,000scfm of flue gas is 23 feet wide, 17 feet deep and 36 feet high.
State of development The following plants have been in operation:
67
-------
Commercial plants by Oji process
Type °f
scrubber
OK
OK
OK
OK
OK
OK
OK
Jinkoshl
Jlnkoshl
User
Oji
Tokai
Oji
Chuetsu
Honshu
Oji
Oji
Oji
Oji
Plant Number of
site scrubbers
Kasugai
Kasugai
Sendai
Kushiro
Ebetsu
Mishima
Tomakomal
Tomakomai
8
3
1
1
2
1
6
2
2
Capacity Late of
(l.OOOscfm) completion
628 1966 to 1969
204
118*
68
153
108*
470
288*
306*
1970
1970
1971
1971
1971
1972
1971
1972
* For oil-burning boilers. Others are for Kraft recovery boilers*
Advantages The OK scrubber is simple and cheap. It features a small
pressure drop (1.5 to 2.5 in. H.o). The Jinkoshl scrubber is quite
effective for S02 recovery and oust removal with a small power consumption.
Disadvantages Demand for sodium sulfite is limited. The screens of the
Jinkoshi scrubber undergo corrosion when the scrubber is not operated
properly.
68
-------
,
Flue SSL
Fan
Water
NaOH
solution
Gas
cru
J
P
?«
,v\»
»\»i\
»iV
\l»«\«
bl
1
J
i
D6
r
r
x-
i
Gas
»
T
i
..r
"L
f
3-.^
^ ^ ^
«
^
^ ^
^ ^ ^
^ ^
*.^ *"*
^ ^ ^
Scrubber
solution
HO O-U
Figure 5.8 Flow sheet of prototype plant by Jinkoshi-OJi process
-------
5»9 Tsukishima sodium process
Developer Tsukishima Kikai Co.
17-15t 2-bhome, Tsukuda, Chuo-ku, Tokyo
Process description 80. in waste gas is absorbed by a sodium sulfite
solution to form sodium bisulfite. The bisulfite solution is neutralized
with sodium hydroxide to form the sulfite. A portion of the sulfite
solution is recycled to the absorption system; the rest if filtered to
remove dust and is obtained as by-product sodium sulfite (solution or
solid) to be used for paper mills. Otherwise, the sulfite solution
is oxidized with air by an oxidizer to produce sodium sulfate which is
either discarded in solution form or utilized as solid sodium sulfate.
More than 90$ of S0« is removed.
State of development More than 20 plants are in operation. Some of
the larger ones are shown in Table 5«9»
Advantages The process is simple and operation is easy. The Bahco
scrubber is effective not only for SO- removal but also for elimination
of dust.
Disadvantages Demand for sodium sulfite and sulfate is limited. Sodium
hydroxide is fairly expensive. Restrictions on sodium sulfate emission
might become stringent in future.
70
-------
Table 5«9 Desulfuxization plants by Tsukishima
User
Shimura Kako
Sumitomo Mining
Sumitomo Mining
Mitsui Senpoku Oil
Daishowa Paper
Hiroshima City
Osake City
Yahagi Iron
Daio Paper
Daio Paper
Tokyo Metropolis
Daishowa Paper
Plant site
Muroran
Toyo
Besshi
Sakai
Yoshinaga
Hiroshima
Osaka
Nagoya
lyomishima
lyomishima
Odai
Yoshinaga
Capacity
(l.OOOscfm)
11. 7a
82.3b
88. 2a
8.8°
3
129.4d
10. 5e
10. 5e
r
47. 01
70.6d
j
88. 2d
117.6s
j
97.1d
so2
(p-pm*
18,000
4,000
1,700
1,000
1,000
4,000
1,700
1,700
1,000
1,700
Type of absorber Product
Bubbling
TCA
Packed tower
Packed tower
Bahco
Banco
Bahco
Bahco
Bahco
Bahco
Spray tower
3ahco
Na2SO,( solid)
Na2SO,( solid)
Na2SO,( solid)
Na2S04( solid)
Na2SO,( solution)
Ha2SO.(waste)
Na2SO.(waste)
Gypsum
Na^SO, (solution)
Na2SO,( solution)
Na2SO. (waste)
Na2SO, (solution)
Year of
completion
1970
1970
1970
1971
1971
1971
1971
1971
1972
1972
1972
1972
a; Smelting plant
d: Oil-fired boiler
b: Sulfuric acid plant
e: City-mud burning
c: Claus furnace
f: Iron-ore palletizing plant
-------
After-burnei-
>• To stack
Filter
Waste
gas
>
p
A
1
1 0
1 ^
Neutralizer
\
Air
\ product/ product or waste
Figure 5.9 Simplified f]ow sheet of Tsukishima process
-------
5.10 IHI-TCA sodium process '
Developer IshikawaJlma-Harima Heavy Industries Ltd.
2-2-1, Otemachi, Chiyoda-ku, Tokyo
Process description Flue gas from a boiler is first cooled in a cooler
with water spray and then introduced into a turbulent contact absorber
(TCA scrubber, in two stages) with polypropylene balls to absorb SO-
with a sodium sulfite solution. More than 90$ of the SO- is removes.
The sodium bisulfite solution thus formed is then reactea with sodium
hydroxide to produce a sodium sulfite solution, a portion of which is
returned to the absorber and the rest is fed to an oxidizer after being
filtered to remove dust. The oxidizer is provided with an atomizer
invented by IHI and called "Smoke Atomizer." Compressed air at 5 to 6
atmospheric pressure is introduced into the atomizer to give many small
bubbles. Sodium sulfite is oxidized into sulfate which is either
abandoned with wastevater or recovered to produce salable sulfate. The
concentration of the sulfate solution from the oxidizer is about 15$
to give the waste product,and higher to give the salable product.
State of development A unit with a capacity of treating 35»000scfm flue
gas to recover sodium sulfate was built at Yokohama plant, Tsurumi Soda
Co. in 1971. Three units each with a capacity of treating 88,000scfm flue
gas to recover sodium sulfate are under construction at Sakai plant of
Mitsui Senpoku Oil Co. Several units have been built recently to produce
waste sodium sulfate solution, including one in Oppama plant, Nissan
Motor Co. with a capacity of treating 67,000scfm flue gas and smaller ones.
Advantages High recovery or removal of SO- is achieved. " Operation
as well as maintenance is easy.
Disadvantages Sodium hydroxide is expensive. Demand for sodium sulfate
is limited.
73
-------
Boiler
A
I
i
Flue gay
TCA scrubter
Gas to scrubber
Water
NaOH tank
n
Filter
! Oxldizer
Tank
Sludge i ir
Tank
Discharge
Air
Figure 5.10 Flow sheet of IHT-TCA sodium process ( wasse Na2SC>4)
-------
5.11 MKK sodium process (Evergreen process)
Developer Mitsubishi Chemical Machinery (MKK)
6-2, 2-chome, Marunouchi, Chiyoda-ku, Tokyo
Process description Waste gas from glass melting plant is treated in
an absorber with a sodium hydroxide solution (Figure 5-9). More than
97$ of SO2 is recovered to form sodium sulfite. Most of the dust in
the gas consisting mainly of very small particles of sodium sulfate
and also most of the SO, mist in the gas are recovered by the solution
and by a special mist eliminator placed at the upper part of the absorber.
The bisulfite solution is neutralized with sodium hydroxide to regenerate
the sodium sulfite solution which is partly returned to the absorber and
partly sent to an oxidizer after pH adjustment. In the oxidizer, the
sulfite solution is oxidized into sulfate by air. Heavy metals derived
from the dust and dissolved in the solution are precipitated by raising pH
with sodium hydroxide. The precipitate and the dust are then filtered off*
The filtrate is neutralized with sulfuric acid and evaporated. Anhydrous
sodium sulfate is crystallized from the solution, centrifuged, dried in
a flash dryer, and caught by a cyclone. The product sodium sulfate Is
of high purity and is used for glass production.
State of development A commercial plant with a capacity of treating 41,000scfm
gas from a glass melting furnace at Kansai Factory, Asahi Glass Co. has
been in continuous operation since its start in November 1972. Another
plant (I29,000scfm), under construction at Keihin Factory, Asahi Glass Co.,
is to come on-stream in June 1973•
Advantages High recovery of SO. and dust is attained. The process is
simple and operation is easy. No water is wasted.
Disadvantage Demand for sodium sulfate is limited.
-------
Reheater
NaOH
Cyclone
CTi
Air
1: Mist separator 2: Neutralization tank J: Heater
Figure 5.11 Flow sheet of Evergreen process ( Na2SO^ recovery)
-------
7}
5.12 Kurabo sodium process and ammonia-lime process'7
Developer Kurabo Industries
2-41» Kitakyutaromachi, Hlgashi-ku, Osaka
Process description SO. In waste gas Is absorbed by sodium sulfite or waste
alkaline solution in a special type of scrubber (KCBA scrubber) developed
by Kurabo. The reacted solution is neutralized by sodium hydroxide or
waste alkali and then oxidized at 50 to 60°C by introducing air under normal
pressure using a small amount of catalyst to convert sodium sulfite to sulfate.
The sulfate solution is abandoned with other wastewater.. Ammonia is also
used for SO^ removal, to produce waste ammonium sulfate solution.
The KCBA scrubber resembles a multijet . scrubber (Figure 5*12). The gas
to be treated is first mixed with the solution in a scrubber consisting
of a diffuser and header, and then led into a solution tank in fine bubbles.
The gas is then passed through a demister and reheated to 2JO°F by an
after-burner. For the oxidation, vessels similar to the KCBA scrubber are
used. Kurabo has recently been working on a double alkali process using
ammonia and lime. An ammonium sulfite solution (jfo concentration) is used
for the absorption. The ammonium bisulfite solution thus formed is neutralized
with ammonia to form ammonium sulfite, which is then oxidized into sulfate.
Slaked lime is added to the sulfate solution to precipitate gypsum and to
recover ammonia. Salable gypsum -of a good quality is obtained. Pressure
drop in the scrubber is between 2 and 4 inches H-O.
State of development More than 30 commercial plants using waste alkali
or sodium scrubbing and two commercial plants using ammonia scrubbing
are in operation to treat waste gas from chemical plants and small boilers.
Many others are under construction. The unit capacity ranges from 3tOOO
to 35fOOOscfm. S6me of the larger units are listed in Table 4*4* The
ammonia scrubbing unit at Amagasaki plant, Mitsubishi Electric Co.
features very light plume which is almost invisible. Low concentration
and low temperature (40°C) of the solution may help plume abatement. For
the ammonia-lime process a pilot plant with a capacity of 2,900scfm is
in operation but there is not yet a definite plan to build larger plants.
Size of the KCBA The sizes of KCBA scrubber tanks are shown in Table 5.12.1.
Table 5.12.1 Sizes of KCBA scrubber tanks
Size in feet
Width Length Height
Capacity(scfm)
3,000 4.7 12.8 8.6
12,000 8.4 12.8 8.6
35,000 22.8 13.8 8.6
77
-------
Economics A cost estimation is shown in Table 5.12.2.
Table 5*12.2 Cost estimation for Kurabo Processes
(Sulfur in heavy oil 2.5$; S02 removal 90$; Slaked lime 820/t;
By-produced gypsum $6/t)
Capacity (l.OOOscfm) 35 35 35 59
Absorbent NaOH NaOH NH, NH,
Ca(OH)2 Ca(OH)2
Product Waste Waste
NagSO, Na^SO. Gypsum Gypsum
Investment cost ($1,000) 130 195 390 550
Annual cost ($1,000)
Fixed cost 23 33 68 98
Running cost 140 182 146 218
By-product revenue 0 0 -26 -46
Total 163 215 188 2?0
Desulfurization cost
($/taWh) 1.38 1.95 1.58 1.38
($/bl) 0.88 1.25 1.00 0.88
Advantages The KCBA scrubbers are effective in removing S0« and also dust.
Less plume from ammonia process is another advantage.'
Disadvantage The scrubber requires a fairly large floor space and may not
suit very large plants.
-------
Gas
Gas
Water
Alkali
t
To oxldizer
1: Diffuser and header 2: Liquor tank
3: Demister b- After-burner
Figure 5.12 KCBA scrubber
79
-------
5.13 Other sodium processes
5*13*1 Toyobo process
Toyobo Engineering Co. (2-8, Hamadori, Lojima, Kita-ku, Osaka) has
developed a TVR scrubber, which is a combination of a spray tower
and a special absorber, and has built two commercial plants recently
to remove S0~ in flue gas:from industrial boilers (24,000 and 26,000scfm).
Waste alkaline solution is used as the absorbent; waste sodium sulfite
solution is produced (Table 4«4).
5.13>2 Kawasaki process
Kawasaki Heavy Industries (16-1, 2-chome. Nakamachidori, IKeda-ku, Kobe)
has recently built three sodium-scrubbing plants, each with a capacity
of treating 17,000-34,OOOscfm gas by Solivore scrubbers (see 7.4).
In one of the plants sodium sulfite is recovered; waste solutions of
sodium sulfite and sulfate are produced in the other two plants*
5.13.3 Gadelius process
Gadelius Co. Ltd. (4-5, Kbjimachi, Chiyoda-ku, Tokyo) has -recently built
several sodium-scrubbing plants using SF-venturi scrubbers (Table 4.1).
80
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6 Vet-lime (limestone) process
7 8)
6.1 Mitsubishi-JECCO lime (llmestone)-gypsum process ' '
Developer Mitsubishi Heavy Industries
5-1i 2-chome, Marunouchi, Chiyoda-ku, Tokyo
Japan Engineering Consulting Uo.
1-4, Ogawamachi, Kanda, Chiyoda-ku, Tokyo
Process description Waste gas is first washed with water for dust removal
and cooling to about 140°F. As the water becomes acidic and dissolves
metallic components of dust, it is neutralized with milk of lime to
precipitate metallic ions, which are filtered off together with the dust.
The filtrate is used for slaking of lime. The cooled gas is then sent to
an absorbing step. At three plants built recently two plastic-grid packed
absorbers in series, which are put together in one tower, are used as
shown in Figures 6.1.1 and 6.1.2. (For new plants which are being
designed a one-absorber system will be used.) Milk of lime is fed to the
No. 2 absorber. The gas is introduced into the No. 1 absorber and then into
the No. 2 absorber. The slurry discharged from the No. 2 absorber is
a mixture of calcium sulfite and unreacted lime with a small amount of
gypsum. The slurry is then led to the No. 1 absorber, where the remaining
lime is reacted to form calcium sulfite, a portion of the sulfite is
converted 'to bisulfite. The pH of the slurry discharged from the No. 1
absorber is 4-4*5. The concentration of the slurries in the absorbers
is about 15$. A relatively large liquid/gas ratio (20-50 gal/1,OOOscf)
is used to prevent scaling.
The pE of the slurry is then adjusted to about 4 to promote oxidation in
the following step. If required, a small amount of sulfuric acid,
normally less than one ton per 100 tons of inlet SOp, is added to the
slurry for the adjustment. The slurry is then sent to an oxidizing tower
where the sulfite and bisulfite are converted to gypsum by air oxidation
using rotary atomizers invented by Japan Engineering Consulting Co.(jECCO)
at a pressure of 50-57psig and a temperature of 120-180°F. The atomizer
is quite effective in producing fine bubbles and is free from scaling,
erosion and corrosion. The gas leaving the oxidizer contains some SO-,
and is returned to the absorber. The gypsum is centrlfuged. All of
the liquor and wash water are used for the gas washing and cooling step.
The gypsum grows into large crystals; its moisture content after centrifu-
gation is only 8-10$. The gypsum thus obtained is of high purity and good
quality, which make it suitable for use in cement and gypsum board. The
gas from the No. 2 absorber is passed through a demister, reheated, and
led to a stack. Wash water of the mist eliminator is also used in the
system. Normally no wastewater is emitted from the system. More than
of SO. is recoveredo
81
-------
State of development Pour plants are in operation and five others
are being constructed or designed as shown in the following table:
Capacity Number of Year of
User Plant site (acfm) Absorbent absorbers completion
Nippon Kbkan Koyasu 37,000 Ca(OH)2 2 1964
Kansai Electric Amagasaki 59,000 Ca(OH)2 2 1972
Onahama Smelting Onahama 54,000 Ca(OH)- 2 1972
Tomakomai Chemical Tomakomai 35,000 Ca(on)2 2 1972
Kawasaki Steel Chiba 71,000 Ca(OH)2 1 1973
Tokyo Electric Yokosuka 235,000 CaCO. 1 1974
Kansai Electric Kainan 235,000 Ca(OH)2 1 1974
Tohoku Electric Hachinoe 224,000 Ca(OH)2 1 1974
Kansai Electric Kainan 221,000 Ca(OH)2 1 1974
Status of technology Based on extensive studies with a pilot plant,
Mitsubishi lias succeeded in scale prevention. Scaling can be prevented
by the use of a suitable material, shape, and arrangement of the grid
in the absorber, by the adjustment of the slurry concentration and pH
as well as of the liquid/gas ratio, by the addition of gypsum crystal
seed and thorough mixing of lime and the circulating slurry.
The Amagasaki plant has been in continuous operation since its start in
April 1972 except for the period of shutdown of the power plant. The
desulfurization plant treats a fraction of flue gas 86,000scfm from a
156MW boiler containing about 700ppm S0? to recover about 90$ of the S0«.
The gas velocity in the absorber is about 11 feet/sec. The pressure
drop in the whole system including the cooler, absorbers and demister is
6 in.H-0. More than 95$ of calcium eulfite is oxidized into gypsum in
the absorbers due to the low S02 concentration; the oxidizing tower is
almost unnecessary. The amount of water added to the system is maintained
equal to that removed from the system by evaporation in the cooler, by
hydration of gypsum, etc. No water is wasted from the plant.
The Onahama plant treats 54,000scfm of gas from a copper smelter containing
20,000-25,OOOppm S02. More than 99.5$ of the S0p is recovered with a
stoichiometric amount of lime by feeding milk of lime mainly to the No. 2
and partly to the No. 1 absorber. The SO- content of the outlet gas is
less than 50ppm. The plant came on-stream at the end of October 1^72
and has been in continuous operation without trouble except for a period
of scheduled shutdown for inspection at the end of November. No scaling
was observed at the inspection. The gas supplied from the smelter is a
82
-------
wet gas at 155°F and results in less evaporation of water in the system.
Therefore, the amount of water fed to the desulfurization plant slightly
exceeds that by evaporation, hydration, etc. A small amount of water
is wasted after "being treated for pollution control. About 450 tons/day
gypsum is produced; three oxidizing towers are provided for the oxidation
of calcium sulfite into gypsum; little oxidation occurs in the absorbers
due to the high concentration of SOp.
A one-absorber system will be used for the new plants to save invest-
ment cost. To ensure high S0? recovery excessive amounts of the
absorbents,about 105$ of stoichiometric for lime and about 110$ for
limestone, will be used. For pH adjustment prior to oxidation, a
considerable amount of sulfuric acid will be required to convert the
excessive absorbent to gypsum. Other facilities and treatments are the
same as in the two-absorber system.
In the limestone scrubbing plant in Yokosuka, seawater will be used for
cooling flue gas from an oil-fired boiler. The seawater is gradually
concentrated in the gas-cooler and therefore should be wasted after
being duly treated. Salable gypsum of high purity and good quality will
be by-produced using limestone as absorbent*
Economics Investment cost for the Amagasaki plant (59,000scfm) was
$1.46 million including various equipment for automatic control and for
tests, while that for Tomakomai Chemical (31,000scfm) was $0.32 million.
The cost for larger plants (224,000-235,OOOscfm) is estimated to be
82.6-2.9 million in battery limits. The desulfurization cost for a
plant to treat 100,000-150,OOOscfm gas from an oil-fired boiler is
estimated at $0.67-0.88/bl of oil containing 2.5-3.0$ sulfur, including
depreciation and credit on gypsum at $6/t.
Advantages High recovery of S02 is attained and good-quality gypsum is
obtained using either lime or limestone without scaling problems. The
rotary atomizer is quite effective for oxidation, involving no operational
problem. No water is wasted when gas at temperatures above 250°F is
treated. Seawater can be used for cooling, although in this case the
used seawater should be discharged.
Disadvantage Lime is more expensive than limestone. Although limestone
is used for the absorbent, an appreciable amount of sulfuric acid is
required to produce gypsum of high purity and good quality. Oversupply
of gypsum might occur v/ithin several years if too many gypsum-producing
desulfurization plants are built.
83
-------
Washing i
and
cooling
Water
—»»-
Gas
Stack coolinT J
water i
i
^S
Demister Blower
rH r&Y
6^ o«-j L_-
Oo
Lime
Milk of 3ime
Cooling water
»•
Lime
Thlck-
!Alr,, ener
nl
Neutralizer
Thick-
ener
*O
bentri-
I fuge
Soot
Liquor tnak
Figure 6.1.1 Flow sheet of Mitsubishi-JECCO lime-gypsum process
Seed
crystal
tank
-------
Figure 6.1.2 Amagasaki plant, Kansai Electric
Power Co. ( Mitsubishi-JECCO process)
-------
7 8 10 }
6.2 Mitsui-Chemico lime process" ' '
Developer Chemlco, U.S.A.
Mitsui Aluminum Co. (Miike Power Station), Omuta
Constructor Mitsui Miike Machinery Co. Ltd.
1-1, 2-chome, Muromachi, Nihonbashi, Chuo-ku, Tokyo
Process description Chemico scrubbers (two-stage venturi, Figure 6.2.1)
are u?ed for S02 and dust removal from flue gas from coal-fired boiler
(156MW). Carbide sludge (primarily calcium hydroxide) is used as
absorber. Figure 6.2.2 presents a description of the total scrubber
system. A photograph of the installation is shown in Figure 6.2.3* The
flue gas (302,000scfm) after passing through an electrostatic precipitator
contains 0.3 grain/scf of dust and 1,800 to 2,200ppm of S02 at 300°F.
About 75$ of the gas is handled by the scrubber. Two scruBbers were
installed but one of them has been used with the other as a back-up. The
gas flows down through the first venturi section, up through the mist
eliminator section, then passes through the second venturi and mist eliminator
sections, is reheated and exhausted to a stack along with the unscrubbed
fraction of the gas. Milk of lime is mixed with the discharge from the
second venturi; the mixed slurry is partly recycled to the second venturi
and partly fed into a delay tank. The slurry in the delay tank is sent
to the first-stage venturi. The discharge from the first venturi,
consisting mainly of calcium sulfite with small amounts of calcium sulfate.
unreacted calcium hydroxide and. fly ash, is sent partly to a delay tank
and partly to a disposal pond about a mile from the plant. The decanting
or settling of the solids takes place there and the supernatant from the
pond is recycled to the scrubbing system to prepare milk of lime and also
to wash mist eliminators. The outlet gas from the scrubber contains
0,1 grain/scf of dust and 200 to JOOppra of S0«.
Status of technology The scrubber is 33 feet in diameter and 66 feet high,
is constructed of stainless steel, and is lined with glass flake reinforced
polyester material. The following operation conditions have been used:
L/G (venturi + spray) 1st stage, 46 to 59 gal/1,OOOscf
2nd stage, 42 to 55 gal/1,OOOscf
Stoichiometry 100 to 105$ as pure Ca(OH)?
Percentage solids in slurry 3-5$
Total pressure drop 16 in.E_0
Prior to the completion of the plant, extensive pilot plant tests were
carried out by Mitsui Aluminum Co. leading to the establishment of
operation know-how for scale prevention. Precise control of pH to a
certain narrow range is important for the scale prevention.
State of development Operation of the commercial plant started in March
1972. After 8 months of satisfactory continuous operation, the plant
was subjected to a scheduled shutdown for inspection, which revealed
essentially no scaling. Operation was resumed soon and has since been
86
-------
carried out smoothly. The waste disposal pond has a capacity for
holding solids discharged over a period of several years* However, to
eliminate any possible pollution with sulfite ion in wastewater which could
be emitted when the facilities are cleaned in a periodical shutdown of
the plant for inspection, some means of converting calcium sulfite to gypsum
will be adopted within 1973* Tests have shown that the gypsum can be used
for gypsum board and cement although it contains a small amount of fly
asn.
Economics The commercial plant cost $3.3 million including two scrubbers.
The desulfurization cost is a little less than 1 mil/kWh. About 70$ of
the desulfurization cost is accounted for by depreciation and interest.
Advantages Stable operation without scale formation is achieved, removing
both SOp and dust satisfactorily. Carbide sludge, a cheap source o'f lime,
is used. The Chemico scrubber is suited for treating a large amount of
gas.
Disadvantage Large amounts of slurry and water must be recycled because
of the use of high L/G and low slurry concentration in order to ensure
scale prevention.
8?
-------
Washing
liquor
Washing
liquor
Liquor
for spary
Cleaned
gas
Washing
liquor
Liquor
for
Mist
eliminator
Washing
liquor
Mist
--•• eliminator
_^. Washing
liquor
Washing liquor
Figure 6.2.1 Chemico two-stage venturi scrubber
88
-------
Boiler
flue gas
oo
.D. Fan
t
1
•*-
A
Reheat Demist*
furnace
r
I
Stack
Wet carbide pit
Makeup
Blurry
tank
j | >—^2nd stage
• recycle
^^"^^^ • "^^^"^ w ^B^^MJI •.
Makeup slurry
feed pump
Aah pond liquor
return pump
Dry carbide pit
_____ Recycle slurry
___ . ___ Makeup slurry
__.._ Bleed Blurry
___ Return liquor
Note: Only one scrubber system presently in operation'.
• indicates a closed valve during 2/72 to 9/72.
M indicates a closed damper during 2/72 to 9/72.
Waste disposal pond
Figure 6.2.2 Mitsul-Chemlco lime process
-------
Figure 6.2.3 Omuta plant, Mitsui Aluminum Co.
( Mitsui-Chemlco process )
90
-------
6.3 Babcock-Hltachi limestone-gypsum process
Developer Babcock-Hitachi Co. Ltd.
2-8, Otemachi, Chlyoda-ku, Tokyo
State of development The process is based on a wet-limestone process
developed by Babcock and Wilcox, U.S.A. Some modification of the process
has been made to produce gypsum with good quality which is salable in
Japan. A pilot plant (l,800scfm) has been in operation since late 1972
at the Kure plant of the company. Construction of a prototype plant
with a capacity of treating 170,000scfm 6f flue gas from an oil-fired
boiler (lOOMtf equivalent) has been recently started at Mizushima Station
of Chugoku Electric Power Co., with commissioning scheduled for late 1973*
Process description A scrubber developed by Babcock and Vilcox is used
(Figure 6.3). Tlue gas is cooled in a cooling section of the scrubber
and led into an absorbing section where SO, is reacted with a slurry
containing powdered limestone to form calcium sulfite. The desulfurized
gas is passed through a demister section, is reheated either by a heat
exchanger with steam or by an after-burner, and is emitted. The limestone
is finely pulverized by a wet mill, classified and led to a circulation
tank, and fed to the scrubber. About 110 to 115$ of stoichiometric
amount of limestone is used. The slurry reacted with S0« is also led
into the circulation tank. A portion of the slurry from the circulation
tank is continuously sent to a reactor to convert the remaining
limestone into gypsum by addition of sulfuric acid and then fed into an
oxidizer to convert calcium sulfite to gypsum with air bubbles. The
gypsum slurry is led to a thickener and then to centrifuges. Salable
gypsum of good quality is obtained. The water from the thickener and
centrifuges is returned mainly to the wet mill and partly to the demister
for washing. Essentially no wastewater is emitted.
Further modification of the process is planned to increase the desulfuri-
zation rate and to reduce the use of excessive limestone and also
sulfuric acid.
Advantages Limestone, the cheapest absorbent, is used. Salable gypsum
is obtained. Less possibility of scaling than by using lime as the
absorbent. Essentially no wastewater is emitted.
Disadvantages A considerable amount of sulfuric acid is required to
produce salable gypsum. Limestone should be very finely pulverized to
attain high recovery of S0_.
91
-------
NO
r\j
I To stack
i
Heat
exchanger
( or after-
burner)
Flue gas
Gas to absorber
j
Oxidizer
Thickener
Gypsum
Limestone
circulation
tank
Centrifuge
Figure 6.3 Flow sheet of Babcock-Hitachi limestone-gypsum process
-------
6.4 IHI-TCA lime gypsum process '
Developer Ishlkawajima-Harima Heavy Industries Ltd*
2-2-1, Otemachi, Chiyoda-ku, Tokyo
Process description Turbulent contact absorbers (TCA) with polyethylene
balls in three stages are used for the wet-lime process. Flue gas is
cooled to below 190°F by a cooler, introduced into one (No. l) TCA scrubber
with water for dust removal, and then into another (No. 2) TCA scrubber
with milk of lime for desulfurization. The milk of lime is converted
mostly to. calcium sulfite and partly 'to bisulfite removing 90 to
96$ of SO„ in the gas. The slurry from the No. 2 scrubber is put into
a recycle tank, mixed with lime, and returned to the No. 2 scrubber.
A portion of the circulating slurry is sent to a thickener. The top
liquor from the thickener is returned to the recycle tank; the concentrated
slurry from the thickener is led into as oxidizer after pH adjustment.
Gypsum formed by the oxidation of calcium sulfite is centrifuged. The
wash water discharged from the No. 1 TCA scrubber is filtered to remove
dust and is recycled. A portion of the filtered water is used for the
pH adjustment of the calcium sulfite slurry prior to the oxidation.
State of development A commercial unit with a capacity of treating
6l,000scfm of flue gas from a diesel engine generator was installed at
Kumagaya plant, Chichibu Cement Co. in 1972. Another unit of equal size
is under construction in the same plant. No.oxidizer is needed for
these plants because a high concentration of oxygen (11 to 12$) and a
low concentration of SO- (JOOppm) result in complete oxidation in the
TCA scrubber. Another TCA scrubber for the wet-lime process was installed
at Onahama plant, Mitsubishi Metal Co. in 1971 to treat 70,000scfm of
waste gas from a copper smelting plant.
Status of technology Low slurry concentration (2$) is used to reduce
the erosion of the plastic balls. High L/G ratio (more than 50 gal./l,000scf)
is used to prevent scaling. Scaling is apt to occur on the under surface
of the grid; therefore, the surface is washed with sprays of slurry from
underneath. The gypsum grows into large crystals; its moisture content
after centrifugation is 10-15^. The gypsum is used as a retarder of
cement setting. A mist eliminator is placed at the upper part of the
No. 2 scrubber. Since a high velocity of gas in the scrubber would blow
up some of the slurry to the eliminator and cause scaling, the velocity
is kept below 10 feet/sec.
Advantage High recovery of S0« is attained.
Disadvantages Low slurry concentration and high L/G ratio are required.
Use of powdered limestone as an absorbent is difficult because of the
wearing of the plastic balls.
93
-------
To TCA 1
Boiler
Blower
Lime
1"
_i_
TCA
i
V
*
c
n
>•
*
i
TCA
2
T,
^
i
>
C
CaSO^
*'
r
1
Yf
Thickener
<
>
I
I
—T
>•
A
^
Oxidl
*i
zer ''
Y Cent
'9
rifuge
-d
Tank
Gypsum
Liquor
tank
Figure 6.4- IHI-TCA lime-gypsum process
-------
6.5 Other wet-lime processes
6.5*1 Tsukishima-Bahco process
Tsuklshlma Klkal Co. (l7-15f 2-chome, Tsukuda, Chuo-kuf Tokyo)
a wet-lime process plant at Nagoya Factory, Yahagi Iron Co. The
plant is designed to treat 47,000scfm waste gas containing 2,000ppm S02
from a pelletizlng plant of pyrite cinder. A Banco scrubber and
carbide sludge (mainly calcium hydroxide) are used to absorb SO^.
Calcium sulfite thus formed is oxidized with air by an oxidizer
developed by Tsukishima. The plant went into operation in December
1971 and encountered some scaling problem, which has nearly been solved.
6.5-2 Mitsui gypsum process
Mitsui Miike Machinery Co. (2-1-1, Muromachi, Nihonbashi, Chuo-ku, Tokyo)
has operated a pilot plant with a capacity of treating l,180scfm of flue
gas from a coal-fired boiler with a slurry containing pulverized
limestone and a small amount of catalyst which promotes the reaction
between S0? and limestone and also the oxidation of calcium sulfite into
gypsum. Tne by-produced gypsum has a good quality and can be used for
a retarder of cement setting.
6.5.3 Nippon Kbkan lime-gypsum process
Nippon Kbkan (l-l-l, Marunouchi, Chiyoda-ku, Tokyo) has developed a
lime-gypsum process based on several years' experience operating a
lime-gypsum process plant at Kbyasu built by Mitsubishi Heavy Industries
using the Mitsubishi-JECCO process. The Nippon Kokan process resembles
the Mitsubishi-JECCO process.
6.5*4 Kawasaki lime process
Kawasaki Heavy Industries (16-1, 2-chome, Nakamachidori, Ikeda-ku, Kobe)
is constructing a wet-lime process plant designed to treat 52,900scfm
of waste gas from a kraft-recovery boiler at Akita Factory, Jujo Paper
Co. Solivore scrubbers (see 7*4) are used. The plant will be completed
by May 1973-
95
-------
7 Other vet processes
7*1 Chlyoda dilute sulfuric acid process
BIU.IIUM.C acia process 7 ft)
(Thoroughbred 101 process)'* '
Developer Chiyoda Chemical Engineering & Construction
1580 Tsurumi-cho, Tsuruml-ku, Yokohama
Outline of the process Flue gas is washed with dilute sulfuric acid
which contains an iron catalyst and is saturated with oxygen. SO.
is absorbed and converted to sulfuric acid. Part of the acid is
reacted with limestone to produce gypsum. The rest is diluted with
gypsum wash water and returned to the absorber.
Description A flow sheet is shown in Figure 7*1«1> Flue gas is first
treated by a prescrubber to eliminate dust and to cool the gas to
140°|f. The cooled gas is led into a packed tower absorber containing
1 inch Telleretts. Dilute sulfuric acid (2 to 5$ H-SO.) which contains
ferric ion as a catalyst and is nearly saturated with oxygen, is fed to
the packed tower. About 90$ of SO- is absorbed, and partly oxidized
into sulfuric acid.
The product acid is led to the oxidizing tower into which air is bubbled
from the bottom to complete the oxidation. Most of the acid at 120-150°F
nearly saturated with oxygen is returned to the absorber. Part of the
acid is treated with powdered limestone (minus 200 mesh) to produce
gypsum. A special type of crystallizer has been developed to obtain good
crystalline gypsum 100 to 300 microns in size. The gypsum is centrifuged
from the mother liquor and washed with water. The product gypsum is of
good quality and salable.
The mother liquor and wash water are sent to the scrubber. The amount
of input water—wash water and the water to the prescrubber—is kept equal
to the amount of water lost by evaporation in the scrubbers and by
hydration of gypsum. No wastewater is emitted.
State of development The operation of a pilot plant (6,000scfm) has led
to the construction of the following commercial plants:
Table 7.1.1 Commercial plants by Chiyoda process
t User Plant site Source of gas Size, scfm Completion
Nippon Mining Mizushima Glaus furnace 20,600 October 1972
Fuji Kosan Kainan Oil-fired boiler 94,100 October 1972
Mitsubishi Rayon Otake Oil-fired boiler 52,900 December 1975
Tohoku Oil Sendai Claus furnace 8,200 January 1973
Daicel Ltd. Aboshi Oil-fired boiler 59,000 October 1973
Hokuriku Electric Shinminato Oil-fired boiler 442,000 June 1974
Mitsubishi Yokkaichi Oil-fired boiler 413,000 December 1974
Petrochem.
96
-------
Status of technology The iron catalyst Is less reactive at low
temperature but is as reactive as manganese catalyst at operation
temperatures above 120°F (Figure 7.1.2). It is not poisoned by
impurities in the gas, even when flue gas from a coal-fired boiler
is used. Catalyst loss is very small (Figure 7«1«3)» The towers of
the commercial plants are provided with rubber or FBP linings.
Stainless steel is also usable; the ferric catalyst works also as a
corrosion inhibitor.
A large L/G ratio is required to attain high SO- recovery as shown in
Figure 7.1.4; large pumps and fairly large absorber and oxidizer are
required as shown in the following table.
Table 7.1.2 Size of towers (feet)
Absorber Oxidizer
Capacity (scfuQ Diameter Height Diameter Height
117,600 29.7 49-5 13.4 62.7
294,100 49.5 49.5 21.1 62.7
A double-cylinder type reactor (Figure 7-1-5) including an oxidizing
section in the center and a scrubbing section in the outer part has
been developed recently instead of using two towers. The absorbing
liquor goes down the scrubbing section, then goes up in the oxidizing
section and overflows to the scrubbing section. The reactor enables
some savings to be made in floor space and investment cost.
Advantages The process is simple and the plant is easy to operate.
Even in the event that the gypsum-producing system has to be stopped
for a day or two for repairs, the absorbing system can be operated
continuously. The concentration of sulfuric acid increases by 1 or
2?o in this case but S0« recovery is not decreased. Catalyst is cheap
and is not poisoned by impurities in the gas. Salable gypsum of good
quality is obtained from limestone without scaling problems.
Disadvantage Large pumps and a fairly large scrubber and oxidizer are
required. A large L/G is required when S0_ concentration of inlet gas
is high.
97
-------
Table ?.1.3 Cost estimation* ($1 = ¥308)
(Inlet gas S02 l,000ppm, dust 0.08 grain/scf)
(Outlet gas SO- lOOppm, dust 0.04 grain/scf)
Plant cost ($) (A)
Fixed cost (S/year) (B)
Direct cost ($/year)
Limestone (0.25tf/lb)
Electricity (Q.7$/kMh)
Water (8(2/1,000 gal.)
Fuel oil (S3. ISA1)
Steam (0.1?0/lb)
Catalyet (60/lb)
Labor (i!2,000/year/capita)
Maintenance
Subtotal (C)
Net running cost (B -»• C = D)
Overhead (s) (]# of C)
Running cost (D + 3)
Desulfurization cost (($/bl)
without by-product 1 ,*/*.,,._.
... 1 iJ/MWiu
credit V. v '
Capacity
00014W
(1.51 x 106scfin) (0.95
17.2 x 106
3.10 x 106
430,000
789,000
25,/!00
1,035,400 '
39,700
11,000
14/1,000
344,000
2,C1C,500 1,
5,918,500 4,
330,200
6,256,700 4,
0.645
r) 0.992
500MI/
x 10 scfm)
12.5 x 106
2.25 x 106
272,000
529,000
17,000
640,700
?5,100
8,000
96,000
250,000
3/15,000
095,800
221,500
317,300
0.712
1.095
250IW
(0.475 x 10 scfin)
7.0 x 106
1.26 x 106
135,600
308,000
8,400
325,600
12,600
4,000
96,000
140,000
1,030,200
2,290,200
123,600
2,413,300
0.797
1.225
* Estimation iiade by Chiyoda in February 1973
98
-------
i
I
Water
Prescrubber
Reheater
vO
Dust
eliminator
Waste gar
•i
i
Limestone Water
Q
Dilute
"I
*
Air
•O
Water
Absorber Oxidizer
Centrifuge
Water
J
Co oil
., "'t
c
"—O
Crystal11zer
Gypsum
Figure 7.1.1 Flow sheet of Chlyoda Thoroughbred 101 process
-------
•P
OS
O
•H
4->
«S
•a
100
80
60
20
0
60 80 100 120
Temperature (°F)
Figure 7.1.2 Temperature and oxidation ratio
with catalysts
OS
TJ
O
4-5
H
cd
4J
0)
o
1.0
0.6
0.3
1,000 2,000 3,000
S02 content (ppm)
Figure 7.1.3 Catalyst requirement
100
-------
5
rH
CO
0
B
0)
fc
CM
O
CG
inn
"
80 •
•
60 •
t
} f\
*KJ ,
1
20 ,
0
— y
^^~ys~
^St*^ ~A
*r £ — '
a^*
x-'
X
X x Physical-chemical absorption
(Chiyoda)
<\ A Physical absorption
Flue gas containing l,300ppm S02
1 1 1 1 1 1 1 I 1 1 I
0
20C ^00 600 800 1,000
Liquid/gas ratio ( gal./l,000scf)
Figure 7-1.^ Liquid/gas ratio and SOg removal
T Gas outlet
Liquor
distri-
buter
Liquor outlet
4 ».
Liquor
outlet
Liquor
inlet
Figure 7.1.5 Double-cylinder type reactor
101
-------
Figure 7.1.6 Mlzushlma plant, Nippon Mining
( Chlyoda process )
102
-------
7.2 Mitsui Mining magnesium process (Hibi process) '
Developer Mitsui Mining and Smelting Co. Ltd.
1-1, 2-chome, Ifuromachi, Nihonbashi, Chuo-ku, Tokyo
Process description The Hibi process features absorption of SOg by
magnesium hydroxide slurry in a special cross-flow type absorber
developed by Mitsui Mining and Smelting Co. Magnesium sulfite
formed by the reaction is calcined to regenerate S0« and MgO. The
recovered SO- is used for sulfuric acid production. A flow sheet
of the process is shown in Figure 1.2. The absorber consists of an
empty chamber with two rotating shafts with many spoons. Magnesium
sulfite slurry (concentration 10$, pH 7) is charged onto the rotating
spoons and sprinkled in small particles in the chamber. Two absorbers,
12 feet wide, 14 feet long and 16 feet high are used in series to
treat 53fOOOscfm of gas (47fOOOscfm tail gas of sulfuric acid plant
and 6,000scfm gas from a dryer). The SOj concentration of the inlet
gas ranges from 1,500 to 2,000ppm and tiiat of outlet gas from 100 to
200ppm. Pressure drop by the absorber is only 0.4 !»• H-0. L/C of
about 13 gal./l,000scf is used. Magnesium bisulfite is formed in the
slurry, which is then reacted with magnesium hydroxide to form magnesium
sulfite. A large portion of the slurry is recycled to the absorber. The
rest of the slurry is centrifuged to separate crystalline magnesium sulfite
MgSO,«6H_0 from a liquor containing magnesium sulfate formed by oxidation
of the sulfite; about 7 to 10$ of the sulfite is oxidized during the
absorption step.
The solid sulfite is then dried in a rotary dryer by hot gas to convert
MgSO,'6H,,0 into MgSO,'H-0. The gas from the dryer (6,000scfm) contains
some SOp "and is returned to the absorber. The dryer discharge is then
decomposed into TlgO, C0? and EJ3 by indirect heating to 1,300 to 1,380°F
in a kiln made of a special heat-resistant alloy. The gas from the kiln
contains 10 to 20$ 30- and is returned to the sulfuric acid plant. About
7 to 10$ of magnesium sulfite charged is oxidizod into sulfate during the
heating steps. The discharge from the kiln, consisting of MgO with a
small amount of I-5gSO., is returned to the absorption step. The magnesium
sulfate solution froii the centrifuge is concentrated in a vacuum crystallizcr
to obtain crystalline T1gSOA'7n,,0 which is contrifuged and used for fertilizer
and other uses. *
State of development A commercial plant with a capacity of treating
47fOOOscfm t?.il gas from a sulfuric acid plant has been on-stream since
October 1971.
Advantages The abnorber has little possibility of scaling because of
the simple structure. The operation is not hindered even when scaling
occurs. Indirect heating of the sulfite gives concentrated SO- gas
suitable for sulfuric acid production.
103
-------
Disadvantages The size of the absorber is limited because the rotating
shaft more than." 12 feet long would cause mechanical trouble during the
operation. It is not easy to treat more than 60,000scfm of gas in one
absorber with SO- recovery higher than 90$. Demand for magnesium sulfate
is limited. *
-------
Absorber
Absorber
Tail gas
ffl
Mist
separator
Fan
I
Tank
L
Make-up MR(OH)
Mg(OH)2
SC>2 to
H2SC-4
plant
11
MgSO-j.6H20 slurry
Tank
Fan
Mg(OH),
i Centrifuge
Hot gas 1f
r-T HJ
i i LH
tMgSO^ •
, 6H20
Dryer |I
KLln
D
solution
'1*
L-J.-J. A
Water
MgO
r~
Hydrator
Fuel
oil
Vacuum
crystalli
zer
-EZEH—i
Centri-
fuge
Figure 7. 2 Flow sheet of Mitsui Mining magnesium process
-------
7.3 Onahama magnesium process
Developer Onahama Smelting and Refining Co. Ltd.
5-2, 1-chome, Otemachi, Chiyoda-ku, Tokyo
Tsukishima Kikai Co.
17-15» 2-chome, Tsukuda, Chuo-ku, Tokyo
Process description Waste gas from a copper smelting plant (53»000scfm
containing 15,000-25,000'ppn S0«) after passing through an electrostatic
precipitator and a cooler is"treated by an absorber 13.2ft in diameter
and 89ft in height with a magnesium hydroxide slurry. Magnesium
sulfite is formed by absorbing more than 99-5$ of the S02, centrifuged,
dried in a dryer 10ft in diameter and 83ft in length, ana then decomposed
in a rotary kiln 11.2ft in diameter and 172ft in length using carbon and
fuel. The decomposition produces magnesium oxide and a gas containing
13-1 jfo SOy* The former is returned to the absorbing step after being
slaked; tne latter is used for production of concentrated sulfuric acid
at a rate of 6,600t/month. As the gas contains much S0~ and less oxygen,
the oxidation of magnesium sulfite into sulfate in the absorbing step is
virtually none.
State of development A commercial plant has been in operation since
December 1972.
Advantage High recovery of S0?.
Disadvantage When the process is applied for the treatment of flue gas,
some oxidation will occur in the absorbing step requiring the treatment
of the water-soluble magnesium sulfate.
106
-------
Absorber
Reheater
S02 for
E. P. Cooler
Gas
Mg(OH)2
slurry
1
1
T
1
HI H2t>U^ plJ
I J 1 £ H- *-
1 T I
MgSO-j'6H20 ar
Centrifuge Dryer Hotary kiln
r* — 1
FT fel
i^fater
Figure 7.3 Simplified f]ow sheet of Onahama magnesium process
-------
7)
7.4 Kawasaki magnesium process '
Developer Kawasaki Heavy Industries Ltd.
16-1, 2-chome, Nakamachidori , Ikeda-ku, Kobe
Process description The process features the use of magnesium hydroxide
obtained from seawater as an absorbent and two-stage absorbers to obtain
large filterable crystals of magnesium sulfite (Figure 7«4»l)» Flue gas
is first cooled in a scrubber and led into the first absorber and then the
second absorber. A magnesium hydroxide slurry (about 5$ solid) is fed
into the second absorber to form magnesium sulfite, which is then led
into the first absorber to form magnesium bisxilfite. The bisulfite is
reacted with magnesium hydroxide in a crystallizer to produce magnesium
sulfite MgSO-^IUO in large crystals with an average size of about JOO
microns. The sulfite is easily centrifuged; moisture content of the
centrifuge discharge is only about 7$- The sulfita can be calcined to
release S09 and to produce laagnesium oxide which is used for the
absorption of S00.
Solivore type scrubber and absorbers are used (pigures 7-4-2 and 7«4«?)«
In the scrubber, water is sprayed before and after a venturi. Adiabatic
expansion occurs as the gas passes through the venturi, resulting in a
lowering of temporature and condensing of moisture on the surface of
dust particles. The particles of (lust readily stick together to form
larger particles which are removed easily. In the absorbers the slurries
are sprayed through a special type of nozzles. About 90jS of dust and 95$£
of S0? are reuovcd. Pressure drop is low with the Salivore scrubber.
For example, the drop is 4-5 in.HpO with a Solivors scrubber as compared
with 28-3? in.H^O for usual venturi scrubbers.
State of development A pilot plant of the absorption step with a
capacity of treating 2, yftOscZm of flue gas from an oil-fired boiler has
been in operation. Bench-scale tests on the calcination step was also
made. There is no plan yet to construct a commercial plant including
the calcination step. But it is likely that Kawasaki will build a
commercial plant using the scrubbing step followed by the oxidation
step of magnesiua sulfite to produce a waste magnesium sulfate solution.
Using the Solivore scrubbers, Kawasaki has recently constructed three
commercial plants based on the sodium process and is constructing a
commercial plant: based on the lime process (see 5-1J.4 and 6.5.4).
Advantages The Solivore scrubber is highly effective for the removal
of both dust and SO, with a low pressure drop. Filterable magnesium
sulfite is obtained!
Disadvantages The structure of the Solivore scrubber is not simple;
the scrubber could be more expensive than usual venturi scrubbers and
might have some possibility of scaling when lime is used as the absorbent.
108
-------
To stack
Flue gas
Water
Mg(OE)2
Water
1
1
]
\
i
i
/
K
F
1
~n
y
i
\
;
i
>
-*
i
i
i
i
*
.
i
2
r
(..
—
*
t
m WW «^ •
h
t
1
1
t
3
^^r
1 '
i V
Mg(HS03
\
1
L
r
8 "*
i
>
>2
|
£
"
t
•f
i
1
1
I
1
V
1
J
-
>
• 6K20
lJ Prescrubber 2: No.l absorber
3: No.2 absorber ^: Crysuallizer
5: Separator 6: Centrifuge
?: Tank 8: Mother liquor tank
Figure 7.^.1 Kawasaki magnesium process
109
-------
H
o
Gas
Gas
/m /i\\
//\\
Liquor or
slurry
Liquor
or
slurry
Liquor or
slurry
Clean gas
Sludge
Figure 7.4.2 Sollvore scrubber
1st stage
venturi
2nd stage
venturi
Clean
gas
Figure 7.4.3 Two-stage
multi Solivore. scrubber
-------
7 8^
7.5 Mitsui-Grillo magnesium-manganese process * '
Developer Grillo Werke, Vest Germany
Mitsui Shipbuilding Co.
5-6-4, Tsukiji, Chuo-ku, Tokyo
Process description Flue gas is first cooled in a cooler with water
sprayo and then desulfurized in a spray tower with a slurry containing
magnesium and manganese oxides. Sulfites and sulfates of both magnesium
and manganese are formed which are then dried in a spray dryer at about
(560°F. The dried product is reacted in a fluidized bed roaster at
about 1,700°P with a reducing gas formed by combustion of oil to release
SO. and to regenerate magnesium and manganese oxides. The gas leaving
the roaster containing 7~9/$ S0? is passed through a cyclone, boiler,
heat exchanger, and an electrostatic preoipitator, and used for sulfuric
acid production. More than 90?S of S00 in the flun gas is recovered.
The presence of manganese promotes the desulfurization, oxidation of
magnesium sulfite into sulfate, and also the decomposition of magnesium
sulfate by the roe sting.
State of development llitsui was licensed by Grillo to use the absorption
step, developed the regeneration stop including the roaster, and built
a pilot plant. The capacity of the pilot plant is 700scfm for the absorp-
tion step and equivalent to 3»000scfm for the regeneration step;
operation of the roaster has been carried out intermittently.
Status of technology The operating conditions for the absorption step
is as follows: gas velocity in the absorber, 36ft/sec; L/G, 14 gal/1,OOOscf;
solids concentration, 30& pll of recirculating slurry, 6-7. The presence
of manganese eliminates the need for a reducing agent in the roasting
step as in the Chenico process.
Advantages High recovery of S0_ is attained with a relatively small
scrubber absorber. Manganese promotes the decomposition of the sulfates.
Disadvantages A large dryer is required. The 50? concentration of the gas
for sulfuric acid plant is not high.
Economics The estimated investment and desulfurization costs for
commercial plants with various capacities are listed below.
Capacity (l.OOOscfnQ
Investment cost
(millions of dollars)
Desulfurization cost*
U/bl oil)
118
3.08
1.01
m
7.46
0.70
589
11.36
0.73
1.177
20.77
0.65
* including depreciation (14.3/, a year) and credit for sulfuric
acid (;i4.6/t).
Ill
-------
Water
Cooler
Flue
gas
Demister
Furnace
Filter
Dust
Cyclone
E.P,
Fluidized-bed
roaster
Boiler
Air
I
I
i
S02
I
I
I
I »
Heat
exch-
anger
Regenerated magnesium-manganese oxides
Figure 7.5 Flow sheet of Mitsui-Grillo process
-------
7*6 . Chenico-Mitsui magnesium process
Developer Chenlco, U.S.A.
Constructor Mitsui 111 ike Machinery Co.
P-l-1, Muromachi, Hihoribashi, Chuo-ku, Tokyo
Process description SO- in waste gas is absorbed with magnesium
hydroxide slurry to form magnesium sulfite. The sulfite is filteredt
dried, and calcined to release S0_ and to form magnesium oxide. The
oxide is slaked with water to form magnesium hydroxide slurry which is
used for the absorption of SO-.
State of development Mitsui Mike Machinery Co. has operated a pilot
plant desienpd to treat l,500scfm flue gas. Recently it has been decided
to build a conmercicl plant with a capacity of treating 294fOOOscfra of
tail £p.s froia a Glaus furnace at Chiba refinery, Idemitsu Kosan. The
plant will cost aboxit $6.3 million and will be completed by February 1974-
113
-------
7}
7.7 MHI-IFP ammonia process"
Developer Mitsubishi Heavy Industries
5-1, 2-chome, Marunouchi, Chiyoda-ku, Toky6
Process description This process is a combination of ammonia scrubbing
with thermal decomposition and the IFF process to produce sulfur from
SO. and H.S (Figure 7>7)> A hot waste gas containing S0« is first
introduce! into a cooling section at a lower part of a reactor, where
the gas is contacted with an ammonium sulfite solution. The gas is
cooled and a portion of S0? is absorbed to form bisulfite while the
solution is concentrated. The gas is then led into an absorbing section,
where most of the S0« is absorbed by an ammonium sulfite solution. The
bisulfite solution is discharged from the absorbing section and neutralized
with ammonia coming from an ammonia recovery section and an IFF reactor
to form an ammonium sulfite solution. Host of the sulfite solution is
recycled to the absorbing section and a portion is sent to the cooling
section. The gas is then passed through an ammonia recovery section,
reheated and emitted.
The liquor discharged from the cooling section of the reactor contains
ammonium sulfite, bisulfite, sulfate (formed by oxidation of the sulfite),
and some thiosulfate (formed by a small amount of H.S in ammonia from
the IFP reactor). The liquor is led into a first-stage evaporator where
ammonium sulfite and bisulfite are decomposed to form ammonia, S02 and
water vapor. Ammonium sulfate and thiosulfate are decomposed in a
sulfate reduction reactor by the reaction with H?S on heating to form
aamonia, SO- and water vapor.
NH.HSO, = NIL + H20
,S0, = ZKE
. 2
= 4S0
,
The gases formed by the decomposition are sent to an IFF reactor along
with H?S to produce molten sulfur.
2H2S + S02 = 3S + 2H20
The gas leaving the I7P reactor contains ammonia, water vapor, and small
amounts of S0_ and H_S, and is led into the absorber along with the waste
gas containing SO,,.
11A
-------
State of development The ammonia scrubbing and the decomposition steps
have been developed by Mitsubishi Heavy Industries since 1962. The
IFF process has been developed by I.P.P., France. A commercial plant
with a capacity of treating l6,000scfm of tall gas from a Claus furnace
is under construction at Shiiaozu (Wakayama) plant, Maruzen Oil Co. to
start operation in 1974•
Advantages Elemental sulfur is obtained as a by-product. ITo wastewater.
S02 in waste gas and HpS in tail gas can be recovered simultaneously.
Disadvantages The process is not simple. Not easy to apply to plants
which have no IIS.
115
-------
Water
recoverj
tower
Absorber
Cooler
Waste
gas
X
X
A A A
Make-up
NH3
—Q
-C
NH3
Eva]
rato]
r
00-
*
T
>
X
t
. }
-&-
NH3
Dust
; i c
Reactor
f
I
I
I.F.P
reactor
-*
Fue
- — •
After-burner
Sulfur
Hydrogen sulfide
~T
I
Foul acid gas
Figure ?.? Flow sheet of M.H.I.- I.F.P. process
-------
7.8 Hitachi Shipbuilding sodium hypochlorite process
Developer Hitachi Shipbuilding & Engineering Co*
1-47t Edobori, Nishi-ku, Osaka
Process description Waste gas is treated by a scrubber with a pH
8.5-10 solution of NaCIO (about 2 Ib/galContaining some calcium hydroxide.
About 95$ of SO- is removed to precipitate gypsum which" is then filtered off.
NaCIO + H20 + S02 = H,,SO, + NaCl
H2S04 -i- Ca(OIl)2 =
The filtrate contains NaCl and small amounts of sulfuric acid and impurities.
Calcium hydroxide is added to the filtrate to precipitate the impurities
with some gypsum, which are then filtered off. The filtrate is subjected
to electrolysis to regenerate the absorbing solution which contains
NaCIO and Ca(OE),,.
State of development A pilot plant with a capacity of treating 300scfm
of flue gas has been in operation.
Advantage High recovery of S0_ is attained and gypsum is by-produced
without scaling problems.
Disadvantage The process includes electrolysis and might be fairly costly.
117
-------
OO
j To stack
A
-|
Hydrogen
NaCIO, Ca(OH)2
4
After-burner Centrifuge
•
NaCl, Gypaum
Fan Scrubber and
crystallizer
Pump
Electric
Centrifuge power
I
Lime i • '
Electro-
lysis
Gyps1 urn
Waste
gypsum
Pump
Figure 7.8 Flow sheet of Hitachi Shipbuilding sodium hypochlorite
process (HD process)
-------
8 Dry process
8.1 Hitachi activated carbon process ' '
Developer Hitachi Ltd.
2-8, Otemachi, Chiyoda-ku, Tokyo
Process description Flue gas from oil-fired boiler (247>000scfn) at
280°F after passing through an electrostatic precipitator is led into
adsorbers with fixed beds of activated carbon (particle size about 1/4 in.)
The adsorption system consists of two parallel trains of three towers
in series (Figure 8.1). Each tower has three fixed beds and operates at
a gas velocity of about 1.5 ft/sec. The vessels are of mild steel
coated with a phenolic resin. The operation of each tower is cyclic with
adsorption, washing, and drying occurring sequentially in each bed.
During the wash stage, gas flow is diverted by louvered dampers to
another bed. The total cycle time is 65 hours; 7 hours wash and the rest
for drying and ?.dsorption. The adsorbed SO., oxidizes in place to SO,
and is collected as ?0$ n«SO. by water washing. Removal efficiency of
SO- in the gas is above 30fa. The acid is reacted with pulverized
limestone to produce salable gypsum. Batch centrifuges are used to separate
the product. After the gypsum is removed, the liquor is discharged to
the wastewater treatment system. Soot in the liquor would plug the carbon
pores if the effluent were recycled for washing the beds.
State of development The 247»000scfm plant has been in operation at
Kashima station, Tokyo Electric Power since 1972.
Prior to the construction, a pilot plant (90,000scfm)
was operated at Goi station, Tokyo ISlectric Power. During the operation
of the pilot plant, tests were made to concentrate the weak acid to 65$
by submerged combustion. However, operating problems and economics
indicated that production of gypsum would be a better approach for the
larger plant at Kashima. At Kashima, attempts have been made to eliminate
the wastewater from the Gypsum production step. For example, the vreak
sulfuric acid is concentrated to 50 to 70/5 by contacting with flue gas
and then reacted with pulverized limestone. Excessive water is volatilized
by the heat of tLe reaction. Dry gypsum, suitable as a retarder of cement
setting, is obtained. A small pilot plant based on this process has been
in operation.
Economics The 247,000scfm plant cost £5.0 million including 550 tons of
activated carbon which costs $87/ton. About 20jJ of the carbon is
consumed in a year. The desulfurization cost including depreciation
(in 7 years) and revenue frou by-produced gypr.uni ($6/ton) is estimated
to be Sl.l/bl oil or 1.7 mil/kUh.
119
-------
Advantages The process is simple. Operation is safe and easy. The
gas temperature is maintained above 210°F so that no reheating is
required. Good quality gypsum is obtained.
Disadvantages Investment and demilitarization costs are higher than those
by vet processes. A considerable amount of wastewater is emitted although
it is neutral and does not contain much impurity. The new step for gypsum
production can eliminate wastewater but requires the concentration of
sulfuric acid.
120
-------
Wash water to
Mutrtllutioo Unk
Na-CB t«nk
LIquor
Gypsum for
dlseharga
L.JL_I
Flgirre 8.1.1 Hitachi activated carbon process
-------
Figure 8.1.2 Kashima plant, Tokyo Electric Power
( Hitachi activated carbon process )
122
-------
8.2 Sumitomo activated carbon process'' '
Developer Sumitomo Shipbuilding and Machinery Co. Ltd.
2-1, 2-chome, Otemachi, Chiyoda-ku, Tokyo
Process description Moving beds of activated carbon are used for S02
recovery A flow sheet is shown in Figure 6.2. Flue gas from an
oil-fired boiler at 205°F (lOO.OOOscfm) is first led into a mechanical
collector for dust removal, then cooled to 250°F by water spray. The
gas is split between two parallel vessels containing moving beds of
granular activated carbon. The system is designed to recover 80J» of the
S02 when oil containing 2^ sulfur is burned. The carbon is introduced
at the top of the adsorber and moved downward, "hile the gas flows
across the bed. The loaded carbon is transferred by an inclined conveyor
to the top of a single desorption tower where the moving bed is contacted
with hot inert gas at 600 to 700°F in a cross flow configuration to
release SO.. The inert gas is produced by controlled combustion of
butane, Tne SO, concentration in the desorber exhaust gas is controlled
to a range of 10 to 20$. A large portion of the gas is returned to the
desorber through a heat exchanger and the rest is sent to a sulfuric acid
plant of a conventional contact process. Tall gas from the sulfuric acid
plant is returned to the SOj absorption system. The carbon after the
desorption is cooled to 220*5" at the lower part of the desorber, screened
to remove fines, and returned to the absorber.
State of development A pilot plant treating 6,000scfm flue gas was put in
operation in1967- A prototype plant with a capacity of treating 100,000scfm
was completed by the end of 1971 at Sakai Plant, Kansai Electric Power and
put in operation in February 1972. The plant has been under nearly
continuous operation except for a few months' boiler outage.
Sumitomo has also developed a wet-desorption process in which the loaded car-
bon on a. horizontally moving bed is continuously washed with water to
produce dilute sulfuric acid of 10 to 20Jo concentration. A pilot plant
with a capacity of treating 6,000scfm has been in operation with this system.
Status of technology The carbon bed of the prototype plant moves very
slowly requiring two days for one cycle. Nearly lj£ of the carbon is
consumed in one cycle mainly by mechanical degradation forming powder and
psjtly by chemical reaction. Tests have been made to improve the quality
of the carbon and also to reuse the powdered carbon by granulation. The
ratio of the inert gas for the desorption to the flue gas is maintained
at 200.
Sconociics The prototype plant coct £2.8 million including the sulfuric
acid plant with a capacity of producing 20 tons of sulfuric acid (
concentration) por day. The carbon costs
123
-------
Advantages The gas temperature is reduced only slightly, so that no
reheating is required. The process is simple and operation is safe and
easy. The continuous cross flow of gas and carton ensures stable
adsorption and desorption. Very little wastewater is emitted. Concentrated
sulfuric acid is obtained by the dry desorption process.
Disadvantages Investment cost is relatively high. The desulfurization
cost seems to be relatively high as well unless cheaper activated carbon
is available. By the wet-adsorption process, the carbon consumption is
less but the product acid is weak.
12k
-------
Conveyor from desorter
Flue gas from
oil-fired boiler
exchanger /*\
1—cf
Conveyor to dcsorter
Water (res.)
pump treatment tank
n
Hot air furnace
Air fan Fan
i
Desorb. tower
Cooling .
installation
Heavy oil
Low press
steam
Liquid
butane
Dust
Seals
treatment tank
reservoir
Figure 8.2.1 Siomitomo activated carbon process
-------
Figure 8.2.2 Sakai plant, Kansai Electric Power
( Sumitomo activated carbon process )
126
-------
7)
8.3 Mitsubishi manganese process (DAP-Mh process)''
Developer Mitsubishi Heavy Industries
"" 5-1, 2-chome, Harunouchi, Chiyoda-kut Tokyo
Process description Activated manganese oxide MnO -nS-O in powder form
"(5 to 150 microns in size) is charged into an absorber, and is dispersed
and carried by flue gas. The powder is caught by a multiclone and electro-
static precipitator with an efficiency of 99.99$. About 90$ of S0« in
the gas is removed, forming magnesium sulfate. The powder caught Is
a mixture of the oxide and sulfate with some dust from the boiler. Most
of the powder is returned to the absorber. The rest is treated with
water to dissolve the sulfate; the unreacted oxide which is insoluble in
water is centrifuged and returned to the absorber; the dust is removed
during this step. The manganese sulfate solution is treated with ammonia
and air to precipitate activated manganese oxide. The mother liquor is
concentrated to obtain solid ammonium sulfate which has more than 99$ purity.
State of development A prototype plant to treat 150,OOONm /hr flue gas
Trom an oil-fired boiler was completed at Yokkaichi, Chubu Electric Power
in 1967 under contract with the Agency of. Industrial Science and Technology.
A semicommercial plant to treat 193,000scfm gas (110IIW equivalent)
has been in operation since February 1972 at Yoklcaichi.
Operation of semicommercial plant The plant deals with half of the flue
gas from a 22011W oil-fired boiler; the resb of the gas is emitted without
being desulfurized. Therefore, oil with a relatively low sulfur content
has been burned giving a flue-gas S0« concentration of about 900ppm. The
temperature of the inlet gas is 275°F and tliat of outlet gas 230°F. The
outlet gas contains JOppin S0_ (9($ recovery) and less than 0.005g'rain/scf dust,
The pressure drop by the absorber is only 0.4 in.II-O; that of the whole
system including the dust eliminators is 6 in.H-0. The operation has
been carried out satisfactorily except for an erosion problem of the
centrifuge for separating the unreacted manganese oxide. The power
station is shut dovn several times a month, and moreover, the operation
load varies frequpntly due to changes in power demand. The desulfurization
plant is well automated for ease of shutdown, restart, as well as for the
control of operation load. However, when the amount of inlet gas decreases
to below half of the normal volume, dispersion of the manganese oxide as
well as the dust removal efficiency of the multiclone become unsatisfactory.
Economics The investment cost for the semicommercial plant (llOMW) is
S4«5 million. The desulfurization cost would be a little more than $l/bl
oil.
Advantages The absorbent, which is highly reactive and in powder form,
enables S02 to be recovered at a high rate. Pressure drop through the
absorber is very low. Temperature drop in the gas is also small. The
gas temperature after dcsulfurization is kept at 230°F.
Disadvantages The desulfurization cost is relatively high. Demand for
ammonium sulfate is decreasing.
12?
-------
Flue
H
ro
oo
"I St
ir
lAbsor-- |
ber Multi- i Clean
1 ' ""lone1 gas
Ammonia •*
recovery
Water
, Ammonia
Seawater
T Evaporator
Steam
Ammonium
sulfate
Air
Figure 8.3.1 Flow sheet of Mitsubishi DAP-Mn process
-------
• -* jSUScSt HR
Figure 8.3.2 Yokkaichi plant, Chubu Electric
Power Go. ( 193,000scfm, Mitsubishi
manganese process )
129
-------
8.4 Shell cupric oxide process
Developer Shell Group, Netherland
Licensor in. the Far East Japan Shell Technology Co.
2-5, 3-chome, Kasumigasekl, Chiyoda-ku, Tokyo
Process description SOg in flue gas at 750°F is absorbed by a cupric
oxide catalyst held by an aluminum carrier. The cupric sulfate thus
formed is then reduced with a reducing gas rich in liydrogen to release
SO- and regenerate the cupric oxide.
Cu + 1/20, = CuO
CuO + S02 + 1/?02 = CuSO.
CuSO. + 2E- = Cu + S0« + 2H«0
4 r. 22
Txro towers packed with the cupric oxide absorbent are provided, the two
alternating between absorption and regeneration every hour. The life of
the absorbent is estimated to be about 8,000 cycles. The S02 gas recovered
will be led into a Glaus furnace to react with hydrogen sulfide gas to
produce elemental sulfur. In plants which have no source of hydrogen
sulfide, a portion of the S0~ gas is reduced to form hydrogen sulfide.
State of development A plant with a capacity to treat 70f600scfm flue gas
from an oil-fired boiler is under construction at Yokkaichi Refinery,
Showa Yokkaichi Sekiyu Co. to start operation in August 1973. This plant
will be the world's first commercial plant to use the Shell process;
Shell has made pilot plant tests in the Netherlands to treat 590scfm gas.
Advantages The temperature of the outlet gas is high, so that no reheating
is required. Elemental sulfur is obtained as a by-product.
Disadvantage Application is not easy for planbs which have neither
reducing gas nor hydrogen sulfide.
130
-------
Boiler
?50°F
Heat
recovery
Glaus
furnace
H20
. Sulfur
J
Reducing gas
Figure 8.4 Flow sheet of Shell cupric oxide process
-------
8.5 Other dry processes
8.5*1 Hitachi Shipbuilding reduction process
Hitachi Shipbuilding & Engineering Co. (1-47> Edobori, Nishi-ku, Osaka)
made bench scale tests of a reduction process originally developed by
Chevron Chemical, U.S.A. to reduce SO- and NO to sulfur and nitrogen
simultaneously by reacting with carbon monoxiae in the presence of a
catalyst. As the catalyst was readily damaged by oxygen and water vapor
present in small amounts in the gas, improvements have been made by
Hitachi on the process as well as on the catalyst. By the improved
process, vanadium and nickel in flue gas which are poisonous to the catalyst
are first removed, then most of SO. is absorbed by an iron-manganese oxide
forming sulfates. The gas is then reacted with carbon to form carbon monoxide.
The gas containing carbon monoxide is again reacted with the iron-manganese
oxide for further desulfurization and is finally subjected to NO removal
by reduction in the presence of a catalyst. The sulfates are decomposed
by heating to release SO. and to regenerate iron-magnesium oxide. A pilot
plant (5,900scfm) is under construction at Sakai refinery, Kansai Oil to
start operation in May 1973-
8.5>2 NHIPR active sodium carbonate process
National Research Institute of Pollution and Resources (188, Kotobukicho,
Kawaguchi-shi, Saitama Prefecture) has operated a pilot plant (lOOscfm)
to absorb S02 with sodium carbonate powder, as was described in the 1972
report. Sodium sulfate formed by the reaction is reduced by a reducing
gas (H- and CO) to produce H_S and to regenerate sodium carbonate.
There has not been much progress during the past year or so, except for
some improvement in the reduction process. The reduction process is not
simple and seems fairly costly.
132
-------
9 New processes for HpS recovery
9.1 Takahax process
Developer Klnon Chemicals
3-3t 1-chome, Ginza Nishl, Chuo-kuf Tokyo
Process description Hydrogen sulfide is recovered by an alkaline solution
at pE 8 to 8.5 containing a newly developed catalyst 1,4-naphthoquinone-
2-sulfonlc acid, which precipitates elemental sulfur rapidly. The
catalyst is readily regenerated by introducing air into the solution.
H2S
= NaHS + NaHCO-
SO-jNa
+ NaHS +
?H
S
+ 1/2 02
SO-jNa
More than 99.8$ of hydrogen sulfide in coke oven gas, petroleum gas,
etc. is recovered. 1,4-naphthoquinone is recovered easily from the
sludge by-produced when phthalic anhydride is produced from naphthalene.
It can also be directly synthesized at a high yield. It can be easily
converted to l,4-naphthoquinone-2-sulfonic acid, which is soluble in
water. Two towers—absorber and oxidizing tower—are used for the cleaning
of fuel gas, etc. (Figure 9-1, A). For the desulfurization of waste
gas, one tower is used into which both air and the gas containing
hydrogen sulfide are introduced (Figure 9.1, B). The recovery of hydrogen
sulfide is not hindered by the impurities in the gas such as hydrogen
cyanide and oil mist. If required, hydrogen cyanide can also be removed
in the form of a rhodanate.
135
-------
The following values have been adopted recently as operating conditions.
Alkali concentration
pH
Catalyst concentration
Make-up chemicals
Power requirement
About ttfo as Na.CO,
8 to 8.5
0.05 - 0.07 moles/gallon
Catalyst: 0.01 mole/lb of
recovered sulfur
Alkali: 0.15 Ib/lb of recovered
sulfur
1.4kWh/l,OOOscf gas
State of development The process has been adopted recently in about
100 plants in Japan. Some of the plants are shown below.
User
Plant Capacity
site (l.OOOscfm)
Sumitomo Metal
Kawasaki Steel
Yamato Boseki
Kuraray Co.
Futamura Chem.
Toyobo
Nippon Steel
Nippon Steel
Vakayama
Chiba
Yokkaichi
Yokkaichi
47
15
26
59
6
35
147
147
Source
of gas
Coke oven
Coke oven
Rayon plant
Rayon plant
Cellophane plant
Rayon plant
Coke oven
Coke oven
Year of
completion
1971
1971
1972
1972
1972
1973
1973
1974
The process has undergone improvement recently. The improved process
(New Takahax process)will be used for Nippon Steel's Yokkaichi plant,
where two units are being built to treat 147,000scfm of coke oven gas
each.
Possible application The Takahax process has so far been utilized
chiefly in the town gas industry and iron industry, especially for the
desulfurization of coke oven gas. Since the catalyst is highly stable
and active, the process is thought to be applicable to various gases
regardless of the concentration of hydrogen sulfide. for example for
the recovery of hydrogen sulfide from hydrodesulfurization of heavy oil
as well as the sulfide in the tail gas of a Claus furnace. Also in
treating waste fermentation gas, the process is utilized to give methane
gas which may be used as a heat source for boilers.
The new Takahax process may be helpful in removing heavy metals in
wastewater by using hydrogen sulfide which is quite effective in
precipitating heavy metals but has not been used for that purpose because
of the difficulty in treating the gas released to the air.
-------
Economics The Takahax process and the Thylox process are compared
below with regard to investment and operation costs. The investment
cost for treating 5,900scfm for 2.2 grains/scf ILS by the Takahax
process is as follows:
Remote-control system 8230,000
Field operation system $204*000
On the other hand, the Thylox process costs $306,000, or about 40$ more.
The cost per l.OOOscf of raw gas calculated from fixed and variable costs
is:
Takahax process about 2.10
Thylox process about 4*20
The Thylox process requires an additional expenditure of 2.00 or so for
arsenic removal.
Advantages Both investment and operation costs are low. Very high
recovery of H^S—more than 99.856—is attained. Operation is so easy
that unattended operation is possible. The catalyst is not poisonous,
so that the by-product sulfur is useful.
Disadvantage The filtered sulfur is powdery and contains some alkali;
washing is required for utilization.
135
-------
i Air
Clean gas A
i
Absor-
ber
Gas
( H2S )
1
•*
L-Q-1
F
bfl
*•
1
n
Oxidizer
[~|* — Catalyst
* K Alkali
--M^'-!- Air
i 1
^ i i
liter Waste liquor
TTTTT1 * treatment
1 III II *
1
Air
1
•
!
Filter
ri...
hQ^
i
Sulfur
n_
Catalyst
rail
Sulfur
Waste gas, air
(A) Two-tower system
(B) One-tov/er system
Figure 9.1.1 Flow sheet of Takahax process
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9.2 Fumaks and Rhodacs processes
Developer Osaka Gas Co. Ltd.
Sumitomo Chemical Engineering Co*
3-33, Hongo, Bunkyo-ku, Tokyo
Process description Gas containing EyS Is washed In a spray tower
with the Fumaks solution — an alkaline solution containing 0.1$
catalyst (picric acid) in 2-3$ aqueous solution of sodium carbonate
or in dilute aqueous ammonia (Fumaks process). More than 99$ of the
HgS is absorbed by the following reaction:
NH..OH -f H_S = NH.HS + EJO
4242
The liquid that has absorbed EJS is sent to a regeneration tower, where
the liquid is sprayed to contact air and to undergo the following
oxidation reaction:
picric acid
NH4HS + 1/202 -- » NH4OH + S
Sulfur is precipitated, then filtered off. The regenerated aqueous
ammonia containing picric acid is recycled to the absorption step.
The by-produced sulfur contains about 48$ water after the filtration.
More than 99$ sulfur Is contained on a dry basis. The sulfur can be
used for sulfuric acid production.
When the gas contains both H_S and ECN as in the case of coke oven gas,
those can be removed by the following reaction (Rhodacs process):
+ H2S + xS
(NH4)2Sx+1 + HCN
The sulfur required for the reaction can be produced by the Fumaks
process. Thus by the combination process of Fumaks and Rhodacs, H.S
and HCN in the gas can be removed simultaneously. The following
chemicals are consumed by the combination process:
Picric acid 30 Ib/ton HgS
Ammonia 0.3 Ib/ton H_S and 1.2 Ib/ton HCN
State of development Nineteen commercial plants using the Fumaks process
and two commercial plants using the combination process have been built
in various parts of Japan. Some of them are shown in the following table.
137
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Process
VmapVa
Fuaaks
Fumaka
Combination
Combination
User
Osaka Gas
Osaka Gas
Osaka Gas
Amagasakl Coke
Sumlkin Kako
Amount of gaa
Plant site treated (scfm)
Sakal 21,200
Nishljima
Kobe
Ohama
Kashlma
11,800
8,200*
34,700
47,000
Completed
1968
1970
1970
1972
1972
Oil gasi other figures are for coke oven gas.
Advantages The process is simple and operation is easy. High recovery
of H.S is attained by the Fumaks process using a cheap catalyst which
is not poisonous. HJ3, HCN and NH, in coke oven gas can be removed
simultaneously by the combination process.
Disadvantage The by-produced sulfur contains much moisture with some
alkali and needs to be washed for utilization.
138
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Gas
outlet
Gas in]e
inlet
Absorber
Cata
lyse
Filter
Sulfur
Regenerator
I I
Figure 9.2
Flow sheet of Fumaks (Rhodacs) process
159
-------
7)
9.3 IFP-MHI process '
Developer ITT, France
Mitsubishi Heavy Industries
5-1, 2-chome, Marunouchl, Chiyoda-ku, Tokyo
Process description Tail gas from Glaus furnace containing H^S and SOg
is treated by an IFF reactor to recover sulfur. The outlet gas from
the reactor which usually contains 1,000-1,500ppm SQ~ and H^S is led into
an incinerator to burn H.S to form SO,, and then passed through a
waste-heat boiler. Since further desulfurization is required today, the
gas is then subjected to sodium scrubbing to reduce the SOp content of
the outlet gas to below lOOppm. The sodium sulfite formed by the
scrubbing is oxidized with air into sodium sulfate; the sulfate solution
is discarded.
State of development The following plants have been built recently by
Mitsubishi:
User Plant site Capacity (ecfm) Completed
Nippon Oil Negishi 16,700 1971
Idemitsu Kosan Hyogo 15,700 1972
Showa Oil Kawasaki 3,300 1972
Kyokuto Oil Chita 10,900 1972
Advantages The IFP process is simple and operation is easy. Molten
sulfur of high purity is obtained.
Disadvantage The content of S0_ and H^S of the outlet gas from the IFF
reactor is fairly high so that additional sodium scrubbing is required in
many districts.
140
-------
I.P.P. reactor
/i\
Tail
gas
i >-To stack
Absorber 1
Incinerator
-•*
I.F.P. catalyst
Waste
heat
boiler
NaOHJ
I
Oxi-
dizer
Air
V
S
solution
Figure 9.3 Flow sheet of IFP-MHI process
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10 Economic aspects
10.1 Absorbents and by-products of desulfurization
The cost of absorbents for S0_ is compared in Table 10.1.1.
Table 10.1.1 Costs of absorbents14'
Requirement per ton of
Absorbent
Caustic soda
Ammonia
Magnesium oxide
Slaked lime
Limestone
Activated carbon
Cost (J/t). (A)
67
67
44
17.5
5.8
940
Amount (ton). (B)
1.25
0.53
0.63
1.16
1.56
Cost (8). CA
83.8
35-5
27.7
20.3
9.0
xB)
* Required to form sulfite or sulfate.
Limestone is the cheapest while activated carbon is most expensive.
Since limestone is much cheaper than lime or slaked lime, there is a
tendency to use pulverized limestone as in the processes of Mitsubishi-JECCO,
Babcock-Hitachi, Kureha-Kawasaki, and Showa Denko.
For the production of waste sulfate or sulfite solution, either caustic
soda, ammonia or magnesium oxide may be used. Although caustic soda is
most expensive it has been used in most of the plants which produce waste
products as shown in Table 4*4* This is because the scrubbing can be carried
out most easily with sodium hydroxide, while ammonia tends to give plume
problem and magnesium oxide is not as easy as sodium hydroxide solution
to handle because it is insoluble in water.
The supply of sulfur and its compounds related to desulfurization is
shown in Table 10.1.2. Their prices are shown in Table 10.1.3.
-------
Table 10.1.2
Sulfur
Mined
Recovered
Total
Sulfuric acid
from pyrite
from smelter gas
from sulfur
Total
Gypsum
Mined
Phospho-gypsun
Other
Total
Sodium sulfite
4)
Supply of sulfur and its compounds '
(1,000 tons of material)
1968 1969 1970 1971 1972
283
97
380
4,576
2,719
0
7,295
627
2,607
277
3,511
268
180
179
354
4,524
2,972
0
7,496
619
2,677
288
3,584
307
120
297
417
4,303
3,242
17
7,562
596
2,829
577
4,002
398
47
414
461
3.348
3,770
210
7,328
627
2,862
656
4,165
420
18
526
544
2,747
4,343
295
7,385
565
3,134
704
4,403
435
Table 10.1.3 Price of sulfur and its compounds (l/t)
1967 1968 1969 1970 1971
Sulfur 73
Sulfuric acid 26
By-produced gypsum 4*4
Sodium sulfite (anhydrous) 64
4)
25
4.7
62
54
26
4.4
61
68
27
6.1
58
50
23
6.7
60
The domestic supply of and demand for sulfur and its compounds have been
fairly well balanced so far; both their exports and imports have been
quite limited. Mined sulfur has been decreasing and recovered sulfur
increasing. Most of the recovered sulfur recently has been derived from
hydrodesulfurization of heavy oil (Table 2.3). The price of sulfur has
decreased with the increase in recovered sulfur.
The production of sulfuric acid from pyrite has been declining while that
from smelter gas has expanded. Since 1970, the use of sulfur for production
of the acid has been prohibited by the government and has been permitted
-------
only for one company. The acid by-produced from desulfurlzation of
waste gas is not much yet. The demand for the acid is expected to
increase by about 5$ yearly.
Most of the gypsum supply in Japan has been derived from the by-product
of vet-process phosphoric acid. About 60$ of total gypsum! has been
used for retarder of cement setting and about J0$ for plaster board.
There was some oversupply of gypsum before 1970 but a little supply
shortage has occurred after 1970 resulting in a price rise. Demand
for gypsum, is expected to continue to increase at a fairly high rate of
7-10$ yearly. Most of the desulfurization plants to be built aim at
the production of gypsum. Therefore, it is possible that a considerable
oversupply will occur in future necessitating abandonment of a substantial
amount of the by-produced gypsum or calcium sulfite unless some new uses
are developed.
The supply of sodium sulfite has increased remarkably since 1967* Most of
the increase is due to the by-product of waste-gas desulfurization. In
1970, about 50$ of the sulfite was derived from the by-product. A
considerable oversupply this year has caused price drops* Although the
demand (mainly from paper mills) will continue to increase, not so many
desulfurization plants to recover the sulfite will be built in future as
was in the past.
10.2 Cost comparison of dry and wet processes for waste-gas
desulfurization
The investment costs for major desulfurization plants are listed in
Table 10.2.
Table 10.2 Investment costs for major desulfurization plants '
Plant Capacity Cost
Process User site (l.OOOscfm) (millions of dollars)
Dry process
Hitachi Tokyo Electric Kashima 250 5.45
(carbon)
Mitsubishi Chubu Electric Yokkaichi 193 4.65
( manganese)
Sumitomo Kansai Electric Sakai 100 2.75
(carbon)
-------
Vet process
Mitsubishi-JECCO Kansai Electric Amagasaki 59 l>4o
Mltsubishi-JECCO Tomakomai Chem. Tomakomai 35 0.32
Wellman-Lord-MKK Japan Synth. Rub. Chiba 118 2.60
Showa Denko Shova Denko Kawasaki 88 0.81
Showa Denko Ajinomoto Kawasaki 159 1*79
Nippon Kbkan Nippon Kbkan Keihin 88 3*25
Mitsui-Chemico Mitsui Aluminum Omuta 226 3>25
The cost is generally cheaper for the wet process than for the dry process.
Since usually about 10$ of the desulfurization cost is accounted for by
fixed cost including depreciation and interest, the wet process with
reheating of gas is more economical than the dry process. The desulfurization
cost with the dry process ranges from $1 to $1.2 per barrel of heavy oil
or $1.6 to $1.9 per MWhr while the cost usually ranges from $0.8 to $1
per barrel of heavy oil or $1.2 to $1.6 per MWhr for the wet process.
One of the common disadvantages to the wet process was the necessity
of wastewater treatment. However, certain processes such as Mitsubishi-
JECCO and Chiyoda have succeeded in eliminating of wastewater by balancing
the water input for cooling, washing, etc. with the output by evaporation,
hydration of gypsum, etc. On the other hand, the dry process is not
always free from wastewater.
Thus the advantage of the wet process over the dry process has become clear.
Major power companies formerly interested in the dry process have recently
decided to build many desulfurization plants using the wet process
(Table 4. 5).
10.3 Comparison of hydrodesulfurization, gasification
desulfurization and flue-gas desulfurization
Figure 10.3 illustrates the relation between the desulfurization cost
and sulfur content of products of topped-crude hydrodesulfurization and
gasification desulfurization of heavy oil. The figure also illustrates
the relation for flue-gas desulfurization; the desulfurization ratio is
expressed in terms of the sulfur content of the oil for comparison.
By hydrodesulfurization it is not easy to reduce the sulfur in oil to
below 1?6. Although it may be possible to reduce it to 0.5#, the cost
would increase substantially. By gasification desulfurization, sulfur can
be reduced to below 0.1# but the cost is fairly high as was described in
3.1. Flue-gas desulfurization, especially that by the wet process, is
-------
advantageous in that it is available at low cost and for high removal of
SO.. One of the advantages to the desulfurizatlon processes for oil is
that elemental sulfur Is recovered. By some flue-gas desulfurlzation
processes such as the Vellman-Lord-Pover Gas process of the U.S.A. and
the MHI-DT process, S02 can be converted to elemental sulfur. Although
the desulfurlzation COST may be higher than with flue-gas desulfurization .
processes that by-produce gypsum, etc., It might be less than with gasification
desulfurization. Another advantage to oil desulfurization processes is
that the product oil or gas, with a low sulfur content, can be supplied
not only to power plants but also to miscellaneous small plants and
buildings where flue-gas desulfurization cannot be carried out economically.
It seems logical, therefore, that large consumers of fuel such as power plants
use flue-gas desulfurization and small consumers use low-sulfur fuel
produced by desulfurization of oil.
-------
3.0 T
2.5 ..
2.0 ..
1.5 ••
!0
o 1.0
0.5-
0
Hydro-
desulfurization
Flue-gas desulfurization
0.2 0.4 0.6 0.8
Sulfur (%)
1.0 1.2
Figure 10.3 Comparison of desulfurizaticn costs
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11 Significance of application in U.S.A. of waste-gas
desulfurization processes developed in Japan
11.1 Difference in circumstances
There are considerable differences in circumstances between the U.S.A.
and Japan which should be realized in evaluating the Japanese processes
for application in the U.S.A. The main differences are as follows:
(1) In the U.S.A., gypsum and sulfur from natural sources are plenty
and cheap while these are quite limited in Japan. By-products
from desulfurization can be sold for a good price in Japan, which
fact is conducive to the development of the recovery processes.
(2) In the U.S.A., most plants have enough space to abandon waste
products, while in Japan such space is quite limited necessitating
maximum utilization of by-products.
(3) In the U.S.A., about 60$ of electric power is generated by coal burning,
which gives much fly ash. In Japan most power plants burn oil which
gives little dust—an advantage in recovering by-products with high
purity.
(4) In the U.S.A., many power plants are located far from chemical
plants. In Japan power and chemical plants are usually close to each
other; hence it is easy to utilize desulfurization by-products in
chemical plants and also to use chemicals in power plants.
(5) In Japan many plants are close to cities. More than 90$ removal of
SO- or less than lOOppm SO, in emitted gas is usually required,
while in the U.S.A. about 80$ desulfurization or JOOppm SO- in the
gas is usually acceptable.
These differences considerably affect the type of processes and design
of the plants. For example, the sodium scrubbing process (to produce
sodium sulfite) which has been most popular in Japan so far would not have
as much chance for application in the U.S.A. Any Japanese process to be
applied in the U.S.A. could be modified to suit better the local conditions
in that country.
11.2 Wet-lime (limestone) process
Scaling problems As is well-known, scale formation has been the most
baffling problem for the wet-lime process. However, three wet-lime process
plants built in Japan recently have been free from scaling problems—they
are Amagasaki plant, Kansai Electric (Mitsubishi-JECCO process), Onahama
148
-------
plant, Onahnma Smelting (Mitsubishi-JECCO process), and Qmuta plant,
Mitsui Aluminum (Mitsui-Chemico process). The Amagasaki plant has
been in operation for a year and a half treating flue gas from an
oil-fired boiler containing 700-900ppm S02; the S02 concentration is
much lower than in flue gas from coal-fired boilers in the U.S.A.
The Onahama plant treats waste gas from a copper smelting furnace
containing 20,000ppm SO. and has been in operation for four months
since its start in late 1972. On the other hand, the Omuta plant treats
flue gas from a coal-fired boiler containing fly ash and 1,300-2,OOOppm
S0_, which is similar to U.S. flue gas. The power plant at Omuta,
however, supplies electric power to aluminum reduction furnaces and the
operation load does not change so much as with usual power stations.
Thus conditions of these desulfurization plants may not be exactly the
same as those typical in the U.S.A. However, the smooth operation of
these plants seems to have proved that scaling is not an inevitable
problem for the wet-lime process and can be prevented by proper plant
design and operation. Operation of the plants including those under
construction should be observed over longer periods to reach a final
conclusion as to scaling.
Calcium sulfite or gypsum In Japan today, all desulfurization plants which
use lime or limestone aim at the production of salable gypsum. Omuta plant
of Mitsui Aluminum Co. (Mitsui-Chemioo process) which has produced waste
calcium sulfite will also convert the sulfite to salable gypsum. However,
it is possible that in future a considerable amount of the by-product
would be abandoned in the form of gypsum or calcium sulfite. In the
U.S.A., conversely, all of the by-produced calcium sulfite is being
abandoned now but it is possible that some plants which have not enough
space for waste-ponds will produce either salable or throw-away gypsum.
By-produced gypsum from flue gas from coal-fired boilers can be used for
gypsum board and cement if the fly ash content is reasonably low, as has
been proved in the tests of Mitsui Miike Machinery with Mitsui Aluminum
Co. (6.2). Even throw-away process gypsum has the following advantages
over calcium sulfite: Gypsum does not increase the chemical oxygen demand
of ambient water. Gypsum grows into much larger crystals than does the
sulfite and precipitates easily into smaller volume thus reducing the
required waste-pond size. In case of truck transportation of the by-products,
gypsum can be handled much more easily because moisture content of the
centrifuge discharge can be reduced to as low as 10J6f while calcium
sulfite is not easily filtered and the filter cake normally contains 60$
of water. On the other hand, the disadvantage to the waste-gypsum process
is that an oxldlzer is required except in certain cases such as in Amagasaki
Plant of Kansai Electric (6.1) and Kumagays Plant of Chichibu Cement (6.4),
and also that gypsum is more soluble in water than calcium sulfite, although
the latter may not be important.
-------
Use of limestone and sulfuric acid Limestone scrubbing will be used
in Tokoeuka Plant, Tokyo Electric (Hitsubishi-JECCO process) and Mizuahioa
Plant, Chugoku Electric (Babcock-Hitachi process). In both plants limestone
In excess of stolchtometric will be vised to attain high SO. removal, and
thus some sulfuric acid will be required to convert the unreaoted limestone
to gypsum in order to obtain a. salable product. For many power plants in
the U.S.A., is may not be as convenient as in Japan to use sulfuric acid.
When lime is used for absorbent, it is not necessary to use the acid
because excessive lime is unneeded. In plants based on the Mitsubishi-JECCO
lime-gypsum process, sulfuric acid is used on some occasions to lower the
pH of calcium sulfite slurry in order to promote the oxidation into gypsum.
It is not difficult, however,to maintain the pH of the slurry discharged
from the absorber low enough for oxidation, particularly when the SO.
concentration in the flue gas is relatively high (over l,000ppm or so).
If it is required to lower the pH, the acidic liquor formed in the prescrubber
(or cooler with water sprays) can be used in place of sulfuric acid as has
been carried out in the IHI-TCA process (6.4)» although the by-product
gypsum will be contaminated with dust. Even with the limestone-gypsum
process it may be possible to eliminate the use of sulfuric acid, particularly
when the S02 concentration in the gas is fairly high and 80-85$ removal is
satisfactory as in many power plants in the U.S.A. For example, Mitsui
Miike Machinery Co., at the pilot plant operation as described in 6.3*2,
has used a catalyst which is said to promote not only the reaction between
SO- and limestone but also the oxidation of calcium sulfite obviating the
use of sulfuric acid to produce salable gypsum.
11.3 Double-alkali process
The following three types of double-alkali process have been developed in
Japan:
Sodium-lime Nippon Steel Chemical, Hitachi Ltd.
Sodium-limestone Kureha-Kawasaki, Showa Denko
Ammonia-lime Nippon Kbkan, Kurabo
The main problem with the sodium processes is the difficulty of conversion
of sodium sulfate (formed by oxidation of the sulfite) to gypsum. A
relatively weak solution has been used by Nippon Steel Chemical and also
by Hitachi to optimize the conversion, resulting in the circulation of
relatively large amounts of liquor. By the sodium-limestone processes of
Kureha-Kawasaki and Showa Denko, sulfuric acid is required for the conversion.
Where cheap sulfuric acid is available, the limestone process might be
more economical than the lime process because of the cheapness of limestone.
With the limestone process, crystals of calcium sulfite grow fairly well
so that the filter cake has less moisture and is easy to handle for trans-
portation. This may be an advantage when these processes are applied in
150
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the U.S.A. to produce throw-away calcium sulfite which has to be carried
by trucks because of a lack of space to build a waste-pond nearby.
With the ammonia process It is much easier to convert the sulfate
solution to gypsum. Moreover, ammonia is much cheaper than caustic soda.
A common disadvantage to the various ammonia proces8es(however( is the plume
problem.
Amagasaki Plant, Mitsubishi Electric Co. (Rurabo process) features very
light plume (3.12). Although the plant is relatively small and uses a
dilute liquor at low temperature, operation of the plant might indicate
that the plume problem may hot be unavoidable in ammonia scrubbing'. The
tests at Nippon Kbkan also indicated that the plume problem could be
solved (5.5). If so, the ammonia-lime process would be advantageous over
the sodium-lime process.
Although the double-alkali processes in general feature freedom from scaling,
it is less simple than the wet-lime or wet-limestone process. The
consumption of some alkali is another drawback. If plant based on the
wet-lime and wet-limestone processes could be operated without the scaling
problem, the double alkali process might lose its ralson d'etre. It will
take, however, some time to reach a conclusion about the significance of
the processes.
11.4 Other major processes with gypsum by-production
There are two other major processes which by-produce gypsum—the Hitachi
carbon process and the Chlyoda dilute sulfuric acid process. Although
the absorbents as well as the reactions are entirely different, they have
some common features in by-producing dilute sulfuric acid which is then
reacted with limestone, in the ease of scale-free plant operation, and in
the use of fairly large absorbers.
When flue gas from a coal-fired boiler is treated, the fly ash would pose
a problem in the carbon step, even though most of the ash could be
removed by a prescrubber. The Chlyoda process is said to work satisfactorily
in treating coal-fired gas. As dilute sulfuric acid has a small capacity
of SO2 absorption, the Chiyoda process may suit better the treatment of
gases with a relatively low S02 concentration, unlike the wet-lime or
limestone process by which a higher desulfurization ratio is reached more
easily with higher concentrations of SO.. The elimination of wastewater
is an advantage to the Chiyoda process, as well as of the Mitsubishi-JECCO
process.
11.5 Processes to regenerate S0_
There are many processes by which the absorbed S0_ is regenerated for
higher concentration by heating or by reduction. These processes are
classified in the following way based on the absorbents:
151
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Sodium scrubbing Wellman-MKK, Wellman-SCEC
Magnesium scrubbing Mitsui Mining, Onahama Smelting,
Chemico-Mitsui, Kawasaki, Mitsui-Grillo
Carbon absorption Sumitomo Shipbuilding
Cupric oxide Shell
Ammonia scrubbing MHI-IFP
Commercial plants constructed by MKK and SCEC in 1971 based on the
Wellman-Lord process have been in smooth operation, demonstrating the
reliability of the process. One problem with this process that calls for
solution Is the emission of wastewater containing sodium sulfate* The use
of an oxidation inhibitor by SCEC is useful in reducing the sulfate but
further Improvement is desired.
Magnesium scrubbing processes also involve the problem of oxidation of a
portion of magnesium sulfite into sulfate which is soluble in water and
is not as easy as the sulfite to be thermally decomposed. Where there
is some demand for magnesium sulfate, the Mitsui Mining process (7*2)
may be useful. The use of the sulfate, however, is very limited.
The Kawasaki process features the production of filterable magnesium
sulfite. The Mitsui-Grillo process is characterized by the use of
magnesium with a small amount of manganese which promotes the SO, recovery
and also thermal decomposition of magnesium sulfate. These two processes
have been tested in pilot plants; there is no definite plan yet to build
larger plants.
The Sumitomo carbon process is characterized by a smooth and safe operation
and also by the fact that it gives no wastewater. The decrease of carbon
consumption as well as the production of cheaper activated carbon is
desired for the improved economics of the process.
The commercial plant by the Onahama process (7*3) has been on-stream
since the end of 1972 but no detailed information has been released yet.
With the Shell and MHI-IFP processes middle size commercial plants are
under construction both of which will by-produce elemental sulfur by the
reaction of regenerated SO- with H.S. Operation data of these plants would
be useful in further evaluation of the processes.
11.6 Other processes
11.6.1 Sodium scrubbing
Sodium scrubbing with by-production of sodium sulfite has been the most
popular way of SO. recovery in Japan since sodium sulfite has been sold to
352
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paper producers for a reasonable price. Sodium scrubbing by-producing
waste solution of sodium sulfite or sulfate has recently been used in
many plants which emit smaller amounts of S02, because this is the
easiest way of S02 removal. Also in the U.S.A. there may be many
plants to which the sodium scrubbing processes may be conveniently
applied.
11.6.2 Processes with by-production of ammonium sulfate
Yokkaichi plant of Chubu Electric (DAP-Mn process) has solved some problems
encountered at the beginning and is now on-stream fairly well. Ammonium
eulfate by-produced in this process, however, may not be a good product
for most power stations in the U.S.A. Where the sulfate is useful, it
may be by-produced more economically with ammonia scrubbing of flue gas,
provided that the plume problem can be solved.
11.6.3 HS recovery processes
The Takahaz, Fumaks, and Fumaks-Bhodacs processes have been adopted
recently in many plants in Japan mainly for H-S removal from coke oven
gas because higher recovery is attained at lower cost than by conventional
processes. The Takahax process features a broad applicability; H-S in
various waste gases can also be removed efficiently. Powdered sulfur by-
produced in the Takahax and Fumaks processes, would be useful for
agricultural chemicals. The Fumaks-Rhodacs combination process features
the simultaneous recovery of HgS, HCN and NH, in the gas. These processes
may be useful also in the U.S.A.
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References
The descriptions In the present report are based primarily on the
author's visits to the desulfurlzation plants, discussions with the
users and developers of each process and also on data made available by them.
In addition, the following publications have been used as references:
1) J. Ando, Recent Developments in Desulfurization of Fuel Oil and Waste
Gas in Japan (1972), prepared for U.S. Environmental Protection Agency
under Contract No. CPA-70-1 (Task 16) through Processes Research, Inc.,
Jan. 1972 (in English)
2) Enerugi Tokei (Energy Statistics), Ministry of International Trade and
Industry (MITI) Japan, 1972
3) Air Pollution Control in Japan, Environment Agency, Japan, Hay 1972
(in English)
4) Sekiyu to Sekiyu Kagaku (Petroleum and Petrochemistry), Vol. 16,
No. 8, 1972
5) Jushitsuyu Bunkaigljutsu Chosahokokusho (Report on Heavy Oil Decomposition
Technology) MITI, March 1972
6) G. Navata, Kbgyo Gijutsu (Industrial Technology), Agency of Industrial
Science and Technology, MITI, Jan. 197?
7) Halendatsuryu no Subete (All About Waste-gas Desulfurization), Jukogyo
Shimbunsha, Nov. 1972
8) H. V. Elder, F. T. Princiotta, G. A. Hollinden, and S. J. Gage,
Sulfur Oxide Control Technology, Visits in Japan—August 1972, Interagency
Technical Comittee, U.S.A., Oct. 1972
9) M. Yokoi, Ryusan to Kbgyo (Sulfuric Acid and Industry), Vol. 26,
No. 1, 1973
10) J. Sakanishi, ibid.
11) F. Nishimi and Y. Ikeda, 24th Technical Meeting, the Sulfuric Acid
Association of Japan, Oct. 1972
12) K. Kiflhi and R. F. Bauman, Kogal Boshisangyo (Pollution Control Industry),
Dec. 1972
13) Process Handbook, Sekiyu Gakkai (Petroleum Society) 20 (1973)
14) J. Ando, PPM, Jan. 1973
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-R2-73-229
3. Recipient's Accession No.
4. Tide and Subtitle
Recent Developments in Desulfurization of Fuel Oil and
Waste Gas in Japan -- 1973
$• Report Date
May 1973
6.
7. Author(s)
Dr. Jumpei Ando
8- Performing Organization Re pi.
No.
9. Performing Organization Name and Address
Processes Research, Inc.
2900 Vernon Place
Cincinnati, Ohio 45219
10. Project/Task/Work Unit No.
Task 11
11. Contract/Grant No.
68-02-0242
12. Sponsoring Organization Name and Address
EPA, Office of Research and Monitoring
NERC/RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
13. Type of Report & Period
Covered
14.
15. Supplementary Notes
16. Abstracts The repor(. documents development, demonstration, and control activities
currently in progress in Japan on Japanese processes pertaining to SO2 recovery
from waste gases. It also discusses hydrodesulfurization of heavy oils and gasi-
fication desulfurization of heavy and residual oils in Japan. It presents process
description, state of development, advantages, disadvantages, economics, and
flow sheets for 28 processes (4 dry and 24 wet) for SO2 removal and recovery from
waste gases, with less detailed information on 9 other processes. The trend in
waste gas treatment is from dry to wet processes yielding salable byproducts. Most
plants built in Japan for the hydrodesulfurization of heavy oil utilize the indirect,
rather than the direct, process. Four processes are described for the gasification
desulfurization of heavy oil and residual oil: the Ube process is included in detail,
with lesser information on the other three processes.
17. Key Words and Document Analysis. 17o. Descriptors
Air pollution
Desulfurization
Fuel oil
Exhaust gases
Sulfur dioxide
Heavy oils
Gasification
Residual oils
Economic analysis
17b. Identifiers/Open-Ended Terms
Air pollution control
Stationary sources
Hydrodesulfurization
Gasification desulfurization
Ube process
17e. C.OSATI Field/Group
13B
18. Availability Statement
Unlimited
19. Security Class (This
Report)
UNCL/
-ASS1F1ED
Class (This
20. Security Class (This
Page
UNCLASSIFIED
21- No. of Pages
155
22. Price
FORM NTIS-33 IREV. 3-72)
155
USCOMM-OC MBS2-P72
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