EPA-600/2-76-013a
January 1976
Environmental Protection Technology Series
S02 ABATEMENT FOR
STATIONARY SOURCES IN JAPAN
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
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recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service. Springfield. Virginia 22161.
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EPA-600/2-76-013a
SO2 ABATEMENT
FOR STATIONARY SOURCES
IN JAPAN
by
Jumpei Ando
Chuo University
Kasuga, Bunkyo-ku, Tokyo
and
G.A. Isaacs
PEDCo-Environmental Specialists, Lie.
Suite 13, Atkinson Square
Cincinnati, Ohio 45246
Contract No. 68-02-1321, Task 6
ROAPNo. 21ACX-130
Program Element No. 1AB013
EPA Task Officer: Norman Kaplan
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
January 1976
-------
FOREWORD
This report describes recent developments in desulfuri-
zation technology in Japan up to January 1975, with emphasis
on recovery of SO- in lime/limestone-based processes.
Section 1 provides background information on energy usage in
Japan; currently available fuel resources, including imports;
regulations limiting ambient concentrations and emissions of
SO2; and projected requirements for abatement measures to
meet the regulations.
Section 2 reviews briefly the current status of desul-
furization technologies, including hydrodesulfurization of
oil, decomposition of residual oil, gasification of oil and
coal, and flue gas desulfurization (FGD).
The next three sections examine in detail the major FGD
processes operating in Japan, in the categories of wet
lime/limestone processes (Section 3), indirect lime/lime-
stone processes (Section 4), and other processes for SO-
recovery (Section 5).
Section 6 describes the major by-products of the var-
ious processes, and Section 7 summarizes some of the tech-
nical and economic aspects of the FGD systems, with evalu-
ation of their potential for application in the United
States.
111
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CONVERSION FACTORS AND ABBREVIATIONS
CONVERSION FACTORS
The metric system is used in this report. Following
are some factors for conversion between metric and English
systems:
1 m (meter) = 3.3 feet
1 m (cubic meter) = 35.3 cubic feet
1 t (metric ton) = 1.1 short tons
1 kg (kilogram) = 2.2 pounds
1 liter =0.26 gallon
1 kl (kiloliter) =6.29 barrels
The capacity of flue gas desulfurization plants is expressed
in Nm /hr (normal cubic meters per hour)
1 Nm /hr = 0.59 standard cubic foot per minute
L/G ratio (liquid/gas ratio) is expressed in liters/Nm .
1 liter/Nm = 7.4 gallons/thousand standard cubic
feet
For monetary conversions, the exchange rate of 1 dollar =
300 yen is used.
ABBREVIATIONS
FGD Flue gas desulfurization
HDS Hydrodesulfurization
BPSD Barrels per stream day
MW Megawatts
L/G Liquid/gas ratio (see above)
Nm /hr Normal cubic meters per hour
-------
TABLE OF CONTENTS
Page
FOREWORD
CONVERSION FACTORS AND ABBREVIATIONS V
LIST OF FIGURES xi
LIST OF TABLES xv
1. ENERGY USAGE, FUEL RESOURCES, AND ENVIRONMENTAL 1-1
STANDARDS
Energy Usage 1-1
Oil Supplies and Sulfur Content 1-2
Ambient and Emission Standards for SO2 1-4
Requirements for S02 Abatement 1-6
2. STATUS OF DESULFURI ZATION TECHNOLOGIES 2-1
Introduction 2-1
Status of Hydrodesulfurization (HDS) of Heavy 2-2
Oils
Decomposition of Residual Oil and Gasification 2-5
Desulfurization
Status of Flue Gas Desulfurization 2-11
3. WET LIME-LIMESTONE PROCESSES FOR S02 RECOVERY 3-1
Introduction 3-1
Mitsubishi-JECCO Lime-Limestone Process 3-8
Chemico-Mitsui and Mitsui Miike Lime -Lime stone 3-22
Processes
VI1
-------
TABLE OF CONTENTS (continued)
Page
Babcock-Hitachi Process 3-30
Chuba-MKK Process 3-35
Kobe Steel Calcium Chloride Process 3-37
Sumitomo-Fuji Kasui Process 3-42
Other Wet Lime/Limestone Processes 3-45
4. INDIRECT LIME-LIMESTONE PROCESS 4-1
Introduction 4-1
Showa Denko Sodium-Limestone Process 4-4
Kureha-Kawasaki Sodium-Limestone Process 4-9
Nippon Kokan Ammonia Scrubbing Process 4-14
Chiyoda Dilute Sulfuric Acid Process 4-25
Dowa Aluminum Sulfate Process 4-34
Kurabo Ammonium Sulfate Lime Process 4-42
Other Indirect Lime/Limestone Processes 4-48
5. OTHER PROCESSES FOR S02 RECOVERY 5-1
Introduction 5-1
Wellman-MKK Sodium Process 5-3
Onahama-Tsukishima Magnesium Process 5-11
Other Wet Processes 5-14
Shell Copper Oxide Process 5-19
Other Dry Processes 5-25
6. BY-PRODUCTS 6-1
Introduction 6-1
Sulfuric Acid 6-3
viii
-------
TABLE OF CONTENTS (continued)
Page
Elemental Sulfur 6-5
Ammonium Sulfate 6-6
Calcium Sulfite 6-7
Gypsum 6-8
7. COMPARATIVE EVALUATION 7-1
Wastewater 7-1
Economics 7-4
Technical Evaluation 7-6
Potential for Application in the U.S.A. 7-10
REFERENCES
IX
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LIST OF FIGURES
Figure Page
2-1 Material Balance for Residual Oil Decomposi- 2-7
tion by the Flexicoking Process
2-2 Material Banance of the Kureha Process 2-7
2-3 Flowsheet of Kureha Process 2-9
3-1 Schematic Flowsheet of Wet Lime/Limestone 3-3
Process
3-2 Flowsheet of Mitsubishi-JECCO Lime/Limestone 3-12
Process.
3-3 Single-Tower System 3-14
3-4 Onahama Plant, Onahama Smelting 3-16
3-5 Kainan Plant, Kansai Electric 3-16
3-6 Yokosuke Plant, Tokyo Electric 3-17
3-7 Tower Mill at Yokosuka Plant 3-17
3-8 By-Product Gypsum at Kainan Plant, Kansai 3-21
Electric
3-9 Influence of Slurry pH on Oxidation Rate and 3-21
HSO7 Concentration
3-10 Omuta Plant, Mitsui Aluminum 3-23
3-11 Sludge Pond at Omuta Plant, Mitsui 3-23
3-12 Flowsheet of Chemico-Mitsui Lime Process 3-26
3-13 X-Ray Diffraction Pattern of Sludge from 3-27
Scrubber
3-14 Flowsheet of Mitsui Miike Limestone-Gypsum 3-28
Process
XI
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LIST OF FIGURES (continued)
Page
3-15 Effect of Catalyst on S02 Removal Efficiency 3-28
3-16 Flowsheet of Babcock-Hitachi Limestone-Gypsum 3-32
Process
3-17 Mizushima Plant, Chugoku Electric 3-24
3-18 Flowsheet of CM Process 3-36
3-19 Flowsheet of Kobe Steel Process 3-39
3-20 Solubility of Lime in Calcium Chloride Solu-;' 3-40
tion
3-21 Vapor Pressure of SO2 3-40
3-22 L/G and SO2 Removal Efficiency 3-40
3-23 Vapor Pressure of H2O 3-40
3-24 Simplified Flowsheet of Moretana Process 3-44
3-25 Flowsheet of Chemico-IHI Process 3-47
4-1 Flowsheet of Showa Denko Process 4-5
4-2 Scrubbers 4-6
4-3 By-Product Gypsum 4-6
4-4 Availability of Chiba Plant Since 1973 4-7
4-5 Flowsheet of Kureha-Kawasaki Process 4-10
4-6 Shinsendai Plant, Tohoku Electric 4-11
4-7 Schematic Flowsheet - Nippon Kokan Ammonia 4-15
Scrubbing Process
4-8 Jinkoshi Scrubber 4-17
4-9 Ammonia-Lime Process 4-17
4-10 Nippon Kokan Ammonia-Lime Process 4-18
4-11 Jinkoshi-NKK Type Scrubber 4-20
4-12 Flowsheet of Chiyoda Process 4-27
xii
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LIST OF FIGURES (continued)
Figure Page
4-13 Temperature and Oxidation Ratio with 4-29
Catalysts
4-14 Catalyst Consumption 4-29
4-15 Liquid/Gas Ratio and S02 Removal 4-30
4-16 Double-Cylinder Type Reactor 4-30
4-17 Toyama Plant, Hokuriku Electric 4-32
4-18 Toyama Plant, Hokuriku Electric 4-32
4-19 Abosi Plant, Daicel Co. 4-33
4-20 S02 Absorbing Capacity of the Liquors 4-36
4-21 Boiling Point of the Liquor Containing S02 4-36
4-22 S02 Absorbing Capacity of Dilute Liquors 4-36
4-23 Flowsheet of Dowa Aluminum Sulfate - Limestone 4-38
Process
4-24 Okayama Plant, Dowa Mining Absorbers, 4-40
Oxidizers
4-25 Okayama Plant, Dowa Mining 4-40
4-26 Relationship of SO2 + HSO3 Concentration to 4-43
Partial Pressure of S02
4-27 S02 Removal Efficiency at the Test Unit 4-43
4-28 Flowsheet of Kurabo Ammonium Sulfate Gypsum 4-45
Process
4-29 Oxidation Rate of Sulfite Ion 4-45
4-30 Tamashima Plant, Jurarey 4-47
4-31 Flowsheet of Tsukishima Double-Alkali Process 4-50
5-1 Flowsheet of the Wellman-MKK Process 5-4
5-2 Layout of the FGD Plant at Nishinagoya Station 5-5
5-3 Nishinagoya Plant, Chuba Electric 5-9
Xlll
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LIST OF FIGURES (continued)
Figure Page
5.4 Simplified Flowsheet of Onahama-Tsukishima 5-12
Process
5-5 Flowsheet of IFP Process Offered by Toyo 5-17
Engineering
5-6 Flowsheet of TSK Sulfix Process 5-18
5-7 Yokkaichi Plant, SYS 5-20
5-8 Flowsheet of Shell Process 5-21
5-9 Reactor 5-22
6-2 Price of By-Products 6-2
6-3 Demand for and Supply of Gypsum in Japan 6-9
6-4 Photomicrograms of By-Product Gypsum 6-10
6-5 Strength of Various Types of Gypsum and 6-15
Concrete
6-6 Process for GPC Production 6-15
6-7 Scanning-Type Electron Photomicrograms of 6-16
Broken Surface
xiv
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LIST OF TABLES
Table Page
1-1 Possible Supplies of Primary Energies 1-2
1-2 Imports of Crude Oil by Sources 1-3
1-3 Imported Crude Oil and Average Sulfur Contents 1-3
1-4 Heavy Oil Shipments and Average Sulfur Con- 1-4
tents
1-5 Values of k 1-5
1-6 Capacity of Power Generation in Japan 1-6
1-7 Use of Fuels by Nine Major Power Companies 1-7
1-8 FGD of Fuel Oil Required to Attain 0.04 ppm 1-8
SO2 in Environment
2-1 Hydrodesulfurization Plants Built by 1971 2-3
2-2 Hydrodesulfurization Plants Completed Between 2-4
1972 and 1974
2-3 Prices of Heavy Oils 2-5
2-4 Hydrodesulfurization Plants to be Completed 2-6
After 1974
2-5 SO2 Recovery Processes and Plant Capacities 2-12
3-1 Major Sulfur Dioxide Scrubbing Installations 3-2
in Japan
3-2 Example of Operation Parameters of FGD Plants 3-4
By-Producing Gypsum and Calcium Sulfite
3-3 Amounts of Wastewater and Gypsum 3-9
3-4 Wet Lime-Limestone Process Plants Using the 3-11
Mitsubishi-JECCO Process
xv
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LIST OF TABLES (continued)
Table Page
3-5 Operation Data: Kansai and Tokyo Plants 3-18
3-6 Plants Using the Mitsui Miike Limestone 3-25
3-7 Example of the Composition of By-Product 3-29
3-8 Plants Using the Babcock-Hitachi Process 3-31
3-9 Plants Using the Moretana Process 3-42
4-1 Indirect Lime-Limestone Process 4-2
4-2 Plants Using the Kureha-Kawasaki Process 4-9
4-3 Annual Requirements for Operation of the 4-22
Nippon Kokan Processes
4-4 Estimated Cost of NKK Type Ammonium Sulfate 4-23
System
4-5 Estimated Cost of NKK Type Ammonia-Lime 4-24
System
4-6 Commercial Plants Using the Chiyoda Process 4-26
4-7 Size of Towers Required for the Chiyoda 4-28
Process
4-8 Composition of Solutions in Figures 4.20 and 4-35
4.21
4-9 Plants Using the Kurabo Ammonium Sulfate Lime 4-42
Process
4-10 Minimum L/G Ratio Required for 95 Percent SO, 4-44
Removal
4-11 Design Base of S02 Absorber 4-44
4-12 Estimated Costs of Kurabo Process 4-29
5-1 Sulfur Dioxide Scrubbing Installations in 5-2
Japan that By-Produce Sulfuric Acid and
Sulfur
5-2 Specifications for Main Equipment
xvi
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LIST OF TABLES (continued)
Table Page
6-1 Sources and Uses of Sulfuric Acid in Japan 6-4
6-2 Supply of and Demand for Sulfur 6-5
6-3 Blending of Materials 6-17
6-4 Properties of Gypsum and GPC 6-17
7-1 Wastewater from FGD Plants 7-2
xvn
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1. ENERGY USAGE, FUEL RESOURCES, AND ENVIRONMENTAL STANDARDS
ENERGY USAGE
Energy usage in Japan has increased rapidly over recent
years and has been heavily dependent on imported oil. The
oil crisis of late 1973 and the serious inflation resulting
from it have strongly affected Japan's energy and environmen-
tal policies. Strenuous efforts are now being applied to
development of atomic energy and to the import of LNG and
coal. Use of imported crude oil, which has constituted more
than 70 percent of the total energy usage in Japan and has
been the major source of S02 emissions, is expected to
continue increasing at an annual rate of 6 to 7 percent, as
against increases of 20 to 30 percent in the past. Although
technologies for desulfurization of heavy oil have progressed
steadily, construction of many plants planned for gasifica-
tion of oil has been postponed or abandoned, mainly because
of inflation; in recent months the already high investment
cost for such plants has more than doubled.
Annual increases in energy consumption in Japan aver-
aged 11 percent during the past several years and are ex-
pected to continue at about 6 percent for a few years to
come. An energy supply plan has been proposed recently by
the Energy Research Committee of the Ministry of Internation-
al Trade and Industry (MITI) (Table 1-1). During the period
from 1972 to 1985, the amount of imported oil will double,
but its proportion in total energy usage will decrease from
75 to 61 percent. Over the same period the sum of domestic
energies and atomic power will increase in the range of 14 to
20 percent.
1-1
-------
Table 1-1. POSSIBLE SUPPLIES OF PRIMARY ENERGIES
Hydroelectric power, lO^ MW
3
Geothermal energy, 10 MW
1972
20
0.03
Domestic oil and gas, 10 kl 3.7
Domestic coal, 10 t
Atomic power, 10 MW
Imported LNG, 106 t
Imported coal, 10 t
Imported oil, 10 kl
28
1.8
1
50
270
1980
min.
27
0.4
5.5
20
22
24
94
400
max.
29
1
11
20
25
29
104
450
1985
min.
29
1
13
20
50
36
111
500
max.
33
6
30
20
70
62
121
600
Per-capita energy consumption in Japan was one-fifth
that in the United States in 1965 and one-third in 1972.
Consumption per acre of level land is now about 8 times that
in the U.S. and may be the highest in the world; this high
level of energy consumption presents increasingly serious
problems of energy supply and environmental protection.
OIL SUPPLIES AND SULFUR CONTENT
Most of the oil imported to Japan is in the form of
crude oil (Table 1-2). About 80 percent of the crude oil
comes from the Middle East and is rich in sulfur. In addi-
tion, some heavy fuel oil is being imported. Even though
the average sulfur content of imported crude oil decreased
from 1.82 percent in 1968 to 1.50 percent in 1972, the total
amount of sulfur in imported oil reached nearly 4 million
tons in 1972 (Table 1-3).
In Japan, most of the crude oil is treated by topping
(atmospheric distillation). The residual oil from topping,
known as "heavy oil", is used for fuel. From 100 parts
crude, 55 parts heavy oil is obtained on the average.
Approximately 90 percent of the sulfur in crude remains in
the heavy oil. The sulfur content of heavy oil from Khafji
1-2
-------
Table 1-2. IMPORTS OF CRUDE OIL BY SOURCES'
(in 106 kiloliters; 1 kl = 6.29 bbl)
Source
Middle East total
Saudi Arabia
Kuwait
Neutral Zone
Iran
Others
Southeast Asia
U.S.S.R.
Others
Total
1969
150.4
29.0
14.3
18.4
75.2
13.6
16.7
0.6
0.9
168.6
1970
169.2
28.6
18.2
18.8
84.8
18.8
23.5
0.6
2.1
195.3
1971
182.2
30.0
19.7
18.8
91.8
22.1
25.1
0.5
3.6
211.4
1972
190.4
40.8
21.7
19.3
87.5
21.0
31.0
0.4
5.5
227.3
Table 1-3. IMPORTED CRUDE OIL AND AVERAGE SULFUR CONTENTS
Low sulfur
Medium sulfur
High sulfur
Total
Average
sulfur, %
1968
Amount ,
106kl
16.0
73.3
52.6
141.9
Ratio,
%
11.2
51.5
37.3
100.0
1.82
1970
Amount ,
106kl
36.6
117-7
41.0
195.3
Ratio,
%
18.7
60.3
21.0
100.0
1.58
1972
Amount,
106kl
48.8
135.3
44.0
228.1
Ratio,
%
21.4
59.3
19.3
100.0
1.50
1-3
-------
crude can be as high as 4 percent. Hydrodesulfurization of
heavy oil has been carried out since 1968. The average
sulfur contents and the amounts of heavy oil shipped by
refineries are shown in Table 1-4.
Table 1-4. HEAVY OIL SHIPMENTS AND AVERAGE SULFUR CONTENTS
Amount, 10 kl
Sulfur, %
1967
70.0
2.50
1969
82.6
2.06
1971
109.3
1.74
1973
134.6
AMBIENT AND EMISSION STANDARDS FOR SO2
Regulations of SO_ emissions have become more stringent
with time. The ambient standard for SO- concentration was
changed from 0.05 ppm (yearly average) to 0.04 ppm (daily
average) in May 1973. By the new standard, the hourly
average should not exceed 0.1 ppm and the daily average
should not exceed 0.04 ppm.
The emission standard is given by the following equa-
tion:
Q = k x 10~3 He2
Q: Amount of sulfur oxides, Nm /hr (1 Nm /hr = 0.59 scfm)
k: The value shown in Table 1-5.
He: Effective height of stack, meters (1 meter =3.3 ft)
In an effort to reduce total SO- emissions by 11 per-
cent from the previous year, the k values, which determine
permissible emissions, were also changed, as shown in Table
1-5.
1-4
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Table 1-5. VALUES OF k
Tokyo, Osaka, etc.
Chiba, Fuji, etc.
Omuta , Ube , etc .
Kyoto, Toyama, etc.
For existing plants
1972
6.42
7.59
9.34
1974
3.50
4.67
6.42
8.76
For new plants
1972
2.92
3.50
5.26
5.26
1974
1.17
1.75
2.34
2.34
For a new 500 MW plant, to meet the standards in the Tokyo
and Osaka areas, the sulfur content of oil must be below 0.3
percent, even with a 200-meter stack. The new emission
standard, however, has proved unsatisfactory in keeping the
ambient concentrations below 0.04 ppm in large cities and
heavily industrialized areas. To attain the environmental
standard by March 1978, the central government issued a new
regulation in November 1974 to restrict the total amount ot
S02 emissions in the following eleven polluted areas: (1)
Tokyo (2) Chiba (3) Yokohama, Kawasaki (4) Fuji (5) Nagoya
(6) Handa (7) Yokkaichi (8) Osaka, Saki (9) Kobe, Amagasaki
(10) Kurashiki, Mizushima (11) Kitakyushu. The new regu-
lation applies to plants using more than 0.1 to 1.0 kilo-
liter of oil per hour (0.4 to 4.0 MW equivalent). A certain
number between 0.1 and 1.0 is to be assigned to each pre-
fecture by the Governor, and the amount of allowable SO- is
calculated by one of the following formulas, to be selected
by each prefecture.
Q = a x W (1)
Q: Amount of allowable SO2
a: A constant to ensure S02 abatement
W: Amount of fuel used by each plant
b: A constant between 1.00 and 0.80 to be selected
by the prefectural governor
1-5
-------
x Cm/Cm0
(2)
C : Maximum ground-level concentration to ensure
SO abatement
C : Maximum ground-level concentration due to each
m0
plant
Q0: Amount of SO- being emitted.
The amount of S0_ allowed for each plant is being
calculated by each prefecture and will be determined by the
middle of 1975. The new regulation requires substantial
reduction of SO2 emission. For areas to which the new
regulation does not apply, SO2 emission limits will be
specified by the k value, which will become lower year by
year.
REQUIREMENTS FOR S02 ABATEMENT
The capacity of electric power generation in Japan is
shown in Table 1-6. The total capacity has increased re-
markably, approaching 100,000 MW in 1973. The use of coal
decreased during the last 5 years, while oil consumption
more than doubled. Now nearly 70 percent of Japan's total
electric power is generated by oil-firing.
Table 1-6. CAPACITY OF POWER GENERATION IN JAPAN
(Thousands of megawatts)
Hydroelectric
Thermal (oil)a
Thermal (coal)
Atomic
1967
17.1
18.7
13.4
0.2
1969
19.3
25.2
14.4
0.5
1971
20.2
41.5
13.6
1.3
1973
22.6
64.2
6.3
2.2
Includes a minor amount of gas-firing.
1-6
-------
The fuels used in 1972 and 1973 by the nine major power
companies, which account for more than 70 percent of Japan's
total power generation, are listed in Table 1-7. The power
companies have been recently planning to use large amounts
of low-sulfur fuels such as crude oil, naphtha, and LNG to
replace heavy oil. Oil companies, which oppose the plan of
the power companies because it would require drastic changes
in oil refining, have been trying to reduce the sulfur
content of heavy oil by hydrodesulfurization and also to
develop gasification processes.
Flue gas desulfurization has so far been used mainly by
industries other than power companies, because the industries
have had difficulty in obtaining low-sulfur fuels. The use
of flue gas desulfurization by the power companies repre-
sented only about 400 MW in 1973 but will probably increase
to 10,000 MW in 1977.
Table 1-7. USE OF FUELS BY NINE MAJOR POWER COMPANIESa
Coal, 106 t
Heavy oil, 106 kl
Crude oil, 106 kl
Naphtha, 106 kl
LNG, 106 kl
LGL, 106 kl
Natural gas, 108 Nm3
8 3
Coke oven gas, 10 Nm >
1972
Amount
6.4
30.4
17.8
0.2
0.7
0.0
1.8
2.6
S, %
0.55
1.01
0.89
0.12
0.00
0.00
0.80
1973
Amount
4.2
31.6
23.0
2.4
1.3
0.7
2.3
4.1
S, %
0.52
0.82
0.59
0.09
0.00
0.04
0.00
0.65
These companies produce 71 percent of Japan's total electric
power.
1-7
-------
Table 1-8 shows an estimation by MITI of the amount of
fuel oil that must be subjected to flue gas desulfurization
to attain the ambient standard of 0.04 ppm SO2, assuming
that the oil contains 2 percent sulfur on the average and 90
percent of the SO2 in the flue gas is removed. In 1975,
1976, and 1977, the oil so treated will amount to 1637,
4
2362, and 2720 x 10 kl, respectively; these values are
equivalent to power capacities of 9000, 13,000 and 15,000
MW. In addition, other waste gases, such as those from
sulfuric acid plants, Claus furnaces, sintering plants, and
smelters will be treated by desulfurization.
Table 1-8. FGD OF FUEL OIL REQUIRED TO ATTAIN
0.04 ppm SO2 IN ENVIRONMENT
(104 kl oil)
Power
Chemical industry
Paper industry
Petroleum industry
Metal industry
Textile industry
Ceramic industry
Total
1973
141
89
143
43
30
11
20
477
1974
450
184
239
43
36
17
57
1026
1975
625
349
371
133
46
46
67
1637
1976
1027
490
413
207
51
92
81
2361
1977
1166
568
433
237
53
174
90
2721
1-8
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2. STATUS OF DESULFURIZATION TECHNOLOGIES
INTRODUCTION
Among various ways of desulfurization, hydrodesulfuri-
zation (HDS) of heavy oil has been adopted widely since
1968. In 1973 about 30 percent of all heavy oil underwent
HDS, by-producing about 700,000 tons of elemental sulfur.
The desulfurized oil and the imported low-sulfur oils have
been used mainly by power companies for utility boilers.
Other industries have had difficulty in obtaining low-sulfur
fuel and have been practicing flue gas desulfurization
(FGD).
The easiest method of FGD, sodium scrubbing to by-
produce sodium sulfite salable to paper mills, was first to
become popular. FGD processes that by-produce gypsum and
sulfuric acid became popular after 1972 as the supply of
sodium sulfite filled the demand.
Generally speaking, FGD costs less than does HDS, which
requires large amounts of catalyst and hydrogen. For users
of fuel, it is easier to burn desulfurized oil than to
operate FGD plants. If oversupply of desulfurization by-
products were to occur, elemental sulfur from HDS offers
advantages over other by-products. For these reasons, use
of both HDS and FGD will continue to grow.
In 1972 and 1973, desulfurization of heavy oil by
gasification was considered promising because sulfur in oil
may be reduced to below 0.2 percent equivalent, a reduction
that may be needed in future but seems difficult to attain
by HDS. Many companies, mostly oil companies, planned to
construct commercial gasification plants. Most of the
plans, however, have been given up or postponed recently,
2-1
-------
for several reasons: (1) the high investment costs, which
have been further raised by inflation; (2) the poor ability
of the gasifiers to follow changes in operating loads of
utility boilers; and (3) the recent development of HDS
technology, which has made it possible to reduce sulfur
content to 0.3 percent or even lower. It seems more rational
to decompose residual oil from vacuum distillation of heavy
oil that cannot be treated by HDS than to gasify heavy oil.
At present two commercial plants are under construction to
decompose residual oil to gas oil, gas, and coke or pitch.
Although gasification of coal was performed many years
ago, development of this process was abandoned as oil became
much cheaper than coal. With the present drastic increase
in oil prices, tests of coal gasification have been resumed.
STATUS OF HYDRODESULFURIZATION (HDS) OF HEAVY OIL
Most Japanese oil refiners have installed HDS plants
since 1968 (Tables 2-1 and 2-2). There are two methods of
HDS: (1) Vacuum gas-oil HDS, in which the vacuum gas-oil
obtained by the vacuum distillation of heavy oil is desul-
furized to about 0.2 percent sulfur. This treatment is
fairly easy but the residual oil from the distillation
contains approximately 40 percent of the heavy oil which is
rich in sulfur and metallic impurities that cannot be desul-
furized. (2) Topped-crude HDS, in which heavy oil is direct-
ly treated. It is difficult to reduce sulfur content below 1
percent by this process; however, since 1 percent sulfur oil
has become unsatisfactory for use in many places, several
oil companies, including Idemitsu Kosan and Mitsubishi Oil,
have started to build new plants to reduce sulfur to 0.3
percent or less by using new catalysts and two reactors in
series. Hydrogen consumption required to decrease sulfur
from 1.0 to 0.3 percent is nearly twice that required to
reduce it from 1.7 to 1.0 percent.
2-2
-------
Table 2-1. HYDRODESULFURIZATION PLANTS BUILT BY 1971
Refiner
Idemitsu
Kosan
Fuji Oil
Ota Nenryo
Daikyo Oil
Nippon Oil
Showa Oil
Kyushu Oil
Mitsubishi Oil
Maruzen Oil
Seibu Oil
Nippon Mining
Koa Oil
General Oil
Kashima Oil
Daikyo Oil
Kansai Oil
Koa Oil
Toa Nenryo
Total
Plant site
Chiba
Sodegaura
Wakayama
Umaokoshi
Negishi
Kawasaki
Oita
Mizushima
Chiba
Yamaguchi
Mizushima
Mar if u
Sakai
Kashima
Umaokoshi
Sakai
Osaka
Kawasaki
Process
UOPa
CRC
ER & E
Gulf
CRC
Shell
Shell
UOP
Union
Shell
Bulfa
CRC
ER & E
UOPa
Gulf
ER & E
CRC
ER & E
Completed
1967
1968
1968
1969
1969
1969
1969
1969
1969
1969
1970
1970
1970
1970
1970
1971
1971
1971
Capacity per day
Oil, BPSD
40,000
23,000
25,000
17,500
40,000
16,000
14,000
30,000
35,000
4,000
27.760
8,000
31,000
45,000
17,500
20,000
12,000
51,000
456,760
Sulfur, tons
265
100
180
110
190
66
55
100
165
28
165
39
73
265
77
88
55
220
2,241
Topped-crude HDS processes; other processes are vacuum gas-oil
HDS.
2-3
-------
Table 2-2. HYDRODESULFURIZATION PLANTS COMPLETED BETWEEN 1972 AND 1974
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 Oil
Kansai Oil
Showa Yokkaichi Oil
Mitsubishi Oil
Total
Plant site
Negishi
Himeji
Chiba
Kawasaki
Sakaide
Oita
Yokkaichi
Yamaguchi
Muroran
Nagoya
Mizushima
Nagoya
Sakai
Yokkaichi
Mizushima
Process
CRC
Gulfa
UOP
ER & E
CRC
UOP
Shell
Shell
CRC
CRC
Gulfa
ER & E
Shell
UOPa
Year of
completion
1972
1972
1972
1972
1972
1972
1972
1972
1973
1973
1974
1974
1974
1974
1974
Capacity
oil, BPSD
28,000
40,000
60,000
9,000
15,000
25,000
35,000
1,000
40,000
30,000
3,240
37,000
2,000
5,000
45,000
375,240
Topped-crude HDS; other processes are vacuum gas-oil HDS.
2-4
-------
Cost of desulfurization, including both fixed and
running costs to reduce sulfur in heavy oil from 4 to 1
percent, was about $7 (¥2100)/kl in 1972 and has nearly
tripled for plants to be constructed. Considerable addi-
tional cost will be required to reduce sulfur to 0.3 percent
or below. The prices of heavy oils of various sulfur con-
tents are shown in Table 2-3.
Table 2-3. PRICES OF HEAVY OILS
(Dollars per kiloliter)
Grade
High sulfur
Medium sulfur
Low sulfur
(S
(S
(S
= 2.5%)
= 1.0%)
= 0.3%)
1972
17-19
22-24
Late 1974
55-60
75-85
85-95
Because of the large difference between the prices of
high- and low-sulfur oils and because of the new severe
regulations on S0? emission, many HDS plants are under
construction or being designed (Table 2-4). If it is as-
sumed that vacuum gas-oil HDS plants operate 7000 to 7500
hours a year and topped-crude HDS plants operate 6000 to
6500 hours, nearly 70 percent of the total heavy oil will be
treated in 1978.
DECOMPOSITION OF RESIDUAL OIL AND GASIFICATION DESULFURIZATION
Flexicoking
A commercial plant with a capacity of treating 50,000
bbl/day of heavy oil by vacuum distillation and 21,000
bbl/day of residual oil from the distillator (asphalt) by
Flexicoking is under construction and scheduled to be com-
pleted by the end of 1975 at Kawasaki refinery, Toa Oil. A
rough material balance is shown in Figure 2-1. Vacuum gas
oil from the distillator and gas oil from the Flexicoker
will be treated by HDS (Gofiner). High-calorie gas will be
2-5
-------
Table 2-4. HYDRODESULFURIZATION PLANTS TO BE COMPLETED AFTER 1974
Refiner
Nippon Mining
Asia Oil
Asia Oil
Toa Oil
Fuji Oil
Maruzen Oil
Idemitsu Kosan
Idemitsu Kosan
Idemitsu Kosan
Seibu Oil
Nippon Oil
Nippon Oil
Toa Nenryo
General Oil
Kashima Oil
Kashima Oil
Daikyo Oil
Nippon Oil
Koa Oil
Toa Nenryo
Toa Nenryo
Toa Nenryo
Mitsubishi Oil
Nansei Oil
Nippon Mining
Kyushu Oil
Fuji Kosan
Fuji Kosan
Nipponkai Oil
Hiuga Nenryo
Nippon Oil
Total
Plant site
Mizushima
Yokohama
Sakaide
Kawasaki
Sodegaura
Chiba
Chiba
Tokuyama
Aichi
Yamaguchi
Shimomatsu
Shimomatsu
Wakayama
Kawasaki
Kashima
Kashima
Yokkaichi
Yokohama
Marifu
Shimizu
Shimizu
Kawasaki
Mizushima
Nishihara
Funakawa
Oita
Onahama
Onahama
Toyama
Hosojima
Muroran
Capacity
oil, BPSD
60,000
30,000a
28,000a
46,000
35,000
60,000a
34,000
45,000
50,000a
45,000a
61,000
25,000a
65,000a
40,000a
40,000
25,000a
15,000
33,000a
30,000a
30,000
58,000a
54,000a
35,000
55,000a
30,000
70,000
12,000
18,000a
50,000a
50,000a
22,000a
1,251,000
rear of
completion
1975
1975
1975
1975
1975
1975
1975
1975
1975
1975
1976
1976
1976
1976
1977
1977
1977
1977
1977
1977
1977
1977
1977
1977
1978
1978
1978
1978
1978
1978
1978
Topped-crude HDS; other values are for vacuum gas-oil HDS.
2-6
-------
VACUUM
DISTILLATION
HYDRODESULFURIZATION
HEAVY OIL
TOO
58
GOFINER
FLEXICOKER
1
COKE 1
->• LOW-SULFUR OIL
-*• SULFUR
22
HIGH-CALORIE GAS 5
LOW-CALORIE GAS 6
NAPHTHA 8
Figure 2-1. Material balance for residual oil decomposition
by the Flexicoking process.
KHAFJI
RESIDUAL OIL
18,300 BPSD
H2S 10.5 ton/day
LOW-SULFUR FUEL GAS
126 kl (oil equivalent)/day
CRACKED OIL 14,300 BPSD
PITCH 885 ton/day
Figure 2-2. Material balance of the Kureha process
2-7
-------
sold to an adjacent steel producer, low-calorie gas will be
consumed by Toa Oil, and the coke will be sold. The in-
vestment cost was estimated initially to be about $140
million (¥40 billion); negotiations are now underway for
reestimation because of inflation.
Kureha Process (Eureka Process)
Kureha Chemical Industry, which has established a
process of crude oil gasification to produce olefins, has
recently developed a new process to decompose the residue
from vacuum distillation of heavy oil (asphalt) using steam
to produce a cracked oil (60-70%), gas (about 5 wt %), and
pitch (25-30%)(Figure 2-2). A commercial plant owned by
Eureka Industry Co. (established jointly by Kureha Chemical,
Fuji Oil, Arabia Oil, and Sumitomo Metal) with a capacity of
treating about a million tons of residual oil yearly is
under construction at Sodegaura, Chiba prefecture, and will
be completed by summer 1975.
A flowsheet of the process is shown in Figure 2-3. The
residual oil containing 4 to 5 percent sulfur is maintained
at 500°C for several hours in reactors. The steam serves as
a heat carrier and distillation promoter. The investment
cost of the commercial plant is estimated to be about $20
million (¥6 billion) within battery limits. Process require-
ments are as follows:
Power 3200 kW
Steam 30 t/hr
Fuel oil 10 kl/hr
Cooling water 1000 kl/hr
Pure water 44 kl/hr
Chemicals $500 (¥150,000)/day
Operators 4 persons per shift
The residual oil will be supplied by Fuji Oil. The
cracked oil will be sent to Fuji Oil for hydrodesulfuriza-
2-8
-------
FRACTIONATOR
K)
I
>-FUEL GAS
^CRACKED OIL
TO WASTEWATER
*" TREATMENT
^CRACKED OIL
L.P. STEAM
j PITCH >
CHTH
Figure 2-3. Flowsheet of Kureha process.
-------
tion. The gas from the reactor contains about 10 percent
H^S, which will be removed by a conventional process using
^ 3
an amine. The purified gas (about 16,000 kcal/m ) will be
used for fuel. The pitch, which contains 4 to 7 percent
sulfur, will be used by Sumitomo Metal as a binder of coal
for coke production. The strength of the coke is increased
by the pitch.
Ube Process
Ube Industries has been operating a prototype gasifica-
tion plant with a capacity of treating 200 t/day of heavy
oil. Heavy oil is gasified with oxygen and steam at 850°C
under atmospheric pressure to produce high-calorie gas.
Efforts have been concentrated on attaining long-term stable
operation. The longest continuous operation period attained
so far is nearly one month. Low-sulfur heavy oil has been
used because desulfurization facilities have not been in-
stalled yet. An IFF reactor will be installed for the
desulfurization after more stable operation is reached.
Coal Gasification
The Coal Research Center has recently resumed tests on
coal gasification. Pilot plants with capacities of treating
5 tons and 40 tons will be completed by January 1975 and by
the end of 1976, respectively, in Yubari, Hokkaido. Coal
will be gasified in a fluidized bed under 10 atmospheres
pressure at 800 to 900°C with air and steam to produce a
low-calorie gas (1200 to 1500 cal/m ). A wet process will
be used for desulfurization of the gas. The Coal Research
Center has developed a fluidized drying process for coals
which has been used commercially.
Electric Power Development Co., which has used coal for
utility boilers, is considering introducing coal gasifica-
tion technology from abroad. Because the Lurgi process
seems unsuitable to Japanese coal, which has a slagging
tendency, processes being developed in the United States are
under consideration.
2-10
-------
STATUS OF FLUE GAS DESULFURIZATION
Table 2-5 shows major S0» removal processes, numbers of
plants, and the total capacities (amounts of gas treated).
The Table includes plants in operation and under construc-
tion and those ordered before October 1974. Most of the
plants ordered will be completed by the end of 1976. The
sum of the capacities is 60 million Nm /hr- which is equiv-
alent to 20,000 MW. About half of the gas is from utility
boilers; the rest is from industrial boilers and other
sources, such as sulfuric acid and iron ore sintering plants.
The wet lime-limestone Mitsubishi-JECCO process is most
widely used, treating more than one-fourth of the total gas
in Japan.
A salient feature of the desulfurization efforts in
Japan is that they are oriented toward processes that yield
salable by-products. 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. About 65 percent of the S0_ recovered at the
plants listed in Table 2-5 is converted into salable gypsum,
15 percent into sodium sulfite, 15 percent into sulfuric
acid, and the rest into waste calcium sulfite and sodium and
ammonium sulfates. Because use of desulfurization is in-
creasing rapidly, the supply of by-products may soon exceed
the demand.
Two processes for removal of H_S from coke-oven gas and
other gases have been recently developed and are widely used
in Japan. One is the Takahax process developed by Kinon
Chemicals, which uses an alkaline solution containing a
catalyst (1, 4-naphthoquinone-2-sulfonic acid) as the
absorbent. The other is the Fumaks process developed by
Osaka Gas Co. jointly with Sumitomo Chemical Engineering Co.
using an alkaline solution containing 0.1 percent catalyst
(picric acid) as the absorbent. The total capacity has
exceeded 2 million Nm /hr. Both processes by-produce
elemental sulfur.
2-11
-------
Table 2-5.
SO2 RECOVERY PROCESSES AND PLANT CAPACITIES
Process
Mitsubishi- JECCO
Kureha-Kawasaki
Wellman-MKK
Chiyoda
Oji
Babcock-Hitachi
IHI-TCA
Mitsui Miike
Tsukishima-Bahco
Kurabo
Showa Denko-Ebara
Chemico-IHI
Kureha
Wellman-SCEC
Nippon Kokan
Tsukishima
MKK
Fuji Kasui
Chemico-Mitsui
Hitachi-Tokyo E.P-
Chemico-Mitsui
Showa Denko
Chubu-MKK
Kurabo
Dowa
Nippon Kokan
Nippon Kokan
Absorbent
CaO, CaCO3
Na2SO3-CaC03
Na2S03
H2S04-CaC02
NaOH
CaC03
NaOH
CaCO3
NaOH
NaOH
Na2SO3-CaC03
CaCO3
NaOH
Na2S03
NH3
Na2SO3-CaO
NaOH
CaO, CaCO3
MgO
C-CaCO3
Ca(OH)2
NaOH
CaC03
(NH4)2S04-CaO
By-product
Gypsum
Gypsum
H2S04
Gypsum
Na2S03
Gypsum
Na2SO3
Gypsum
Na2S03
Na2S03
Gypsum
Gypsum
Na2SO3
H2S04
(NH4)2S04
Gypsum
Na2S04
Gypsum
SO2 S
Gypsum
CaS03
Na2SO3
Gypsum
Gypsum
A12 (SO4) 3~CaCO3 Gypsum
CaO
(NH4)2S03-CaO
Gypsum
Gypsum
Number
of plants
31
6
11
13
49
5
26
5
20
70
16
2
8
6
1
4
17
7
1
1
1
2
2
4
2
2
1
Total
capacity,
10 3 Nm3/hr
17,908
5,925
5,320
4,341
3,839
3,191
2,787
2,739
2,655
2,580
2,458
1,800
1,431
1,298
760
714
693
682
500
420
385
370
311
303
280
227
150
2-12
-------
3. WET LIME-LIMESTONE PROCESSES FOR S02 RECOVERY
INTRODUCTION
S0_ removal plants using wet lime-limestone processes
with capacities larger than 20 MW equivalent are listed in
Table 3-1. The Mitsubishi-JECCO process has been used most
widely for oil-fired boilers, iron-ore sintering plants,
etc., whereas the Chemico-Mitsui and Mitsui Miike processes
have been applied to coal-fired boilers. Five other pro-
cesses have also been used, mainly for flue gas from oil-
fired boilers. Many of the plants use lime to obtain a high
SO,, removal efficiency—more than 90 percent—which is
required in many districts in Japan. Limestone scrubbing
removes 85 to 90 percent of the S0_ at 0.9 to 1.2 stoichi-
ometry with a scrubber nearly twice as tall as that used
with lime.
A schematic flowsheet is shown in Figure 3-1; this flow
is common to most processes except the Chemico-Mitsui and
Mitsui Miike processes, which do not use coolers (prescrub-
bers). The flue gas is passed from an electrostatic precipi-
tator through a cooler, scrubber, mist eliminator, and
reheater and led into a stack. Types of scrubbers and
examples of operation parameters are listed in Table 3-2.
Calcium sulfite formed by the reaction of SO- with lime or
limestone slurry is oxidized by air bubbling into gypsum,
which is then centrifuged. Major components and character-
istics of the process are described in the following para-
graphs .
3-1
-------
Table 3-1.
u>
to
MAJOR SULFUR DIOXIDE SCRUBBING INSTALLATIONS IN JAPAN
(LIME-LIMESTONE SCRUBBING)
Process developer
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Chemico-Mitsui
Mitsui Miike
Mitsui Miike
Mitsui Miike
Bahco-Tsukishima
Babcock-Hitachi
Babcock-Hitachi
Ishikawa j ima-TCA
Sumitoma-Fuji Kasui
Chubu-MKK
Chubu-MKK
User
Kansai Electric
Ohaharaa Smelter
Kawasaki Steel
Kansai Electric
Tohoku Electric
Tokyo Electric
Kyushu Electric
Kawasaki Steel
Kawasaki Steel
Kawasaki Steel
Kansai Electric
Teijin
Mizushima Power
Niigata Power
Kyushu Electric
Kyushu Electric
Kyushu Electric
Kyushu Electric
Chugoku Electric
Chugoku Electric
Mitsui Aluminum
Mitsui Aluminum
Mitsui Aluminum
Elec. Pow. Dev.
Yahagi Iron
Chugoku Electric
Chugoku Electric
Chichibu Cement
Sumitomo Metal
Ishihara Sangyo
Mitsubishi Gas
Plant site
Amagasaki
Onahama
Chiba
Kainan
Hachinoe
Yokosuka
Karita
Mizushima
Mizushima
Chiba
Amagasaki
Ehime
Mizushima
Niigata
Katsura
Katsura
Ainoura
Ainoura
Owase
Owase
Omuta
Omuta
Omuta
Takasago
Nagoya
Mizushima
Tamashima
Kumagaya
Kokura
Yokkaichi
Yokkaichi
Absorbent
Ca(OH)2
Ca (OH) ,
Ca(OH>2
Ca(OH)2
Ca(OH),
CaCO,
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
CaCO 3
CaCO 3
CaCO 3
CaCO 3
CaCO3
Ca(OH),
Ca(OH)2
Ca(OH)2
CaCO 3
CaC03
CaCOs
Ca(OH)2
CaC03
CaCO 3
Ca(OH)2
Ca(OH)2
CaC03
Ca(OH)2
MWa
30
29
37
150
125
130
175
232
279
130
125
83
192
117
250
175
250
250
375
375
119°
25C
175C
250°
26
104
500
62
32
77
22
Type of plant
Utility boiler
Copper smelter
Sintering plant
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Sintering plant
Sintering plant
Sintering plant
Sintering plant
Industrial boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Industril boiler
Industrial boiler
Industrial boiler
Utility boiler
Sintering plant
Utility boiler
Utility boiler
Diesel engine
Heating furnace
Industrial boiler
Industrial boiler
Year of
comple-
tion
1972
1972
1973
1974
1974
1974
1974
1974
1975
1975
1975
1975
1975
1975
1975
1976
1976
1976
1976
1976
1972
1974
1975
1974
1971
1974
1975
1972
1974
1974
1974
Gypsum,
tons/
day
20
400
15
20
50
20
70
120
90
27
40
85
95
43
70
45
95
95
330
330
d
20
200
200
25
25
350
22
25
50
12
Actual for boilers and equivalent gas flow for others (at 3,100 Nnr/hr per MW).
Boilers are oil-fired unless otherwise noted.
Coal-fired.
Waste sludge of calcium sulfite.
-------
WATER
FLUE GAS
COOLER
130°C
AFTERBURNER
i 12Q1C_
OXIDIZER
tSCRUBBER PH CONTROLLER
CENTRIFUGE
.WATER
!AIR
WASTEWATER
! | f
NEUTRALIZER Ca(OH)2, CaC03
n
GYPSUM
Figure 3-1. Schematic flowsheet of wet lime/limestone process.
-------
Table 3-2.
CO
EXAMPLE OF OPERATION PARAMETERS OF FGD PLANTS BY-PRODUCING
GYPSUM AND CALCIUM SULFITE
Process developer
Hot lime-limestone ;
Mitaubishi-JECCO
Mitsubishi-JECCO
Cheraico-Mitsui
Mitsui Miike
Babcock-Hitachi
Chubu-MKK
Ishikawajima
Sumitomo-Fuji Kasui
Absorbent,
precipitant
(stoichiometry)
process
Ca(OH)2 0.9-1
CaCC3 0.9-1
Ca(OH)2 1-1.05
CaC03 0.9-1
CaC03 1-1.2
CaCO3
Ca (OH) 2
Ca(OH)2 1-1.2
Indirect lime- limestone process
Kureha-Kawasaki
Showa Denko
Nippon Kokan
Chiyoda
Kurabo
Oowa
Hitachi-Tokyo Elec .
Na2S03, CaC03
Na2S03, CaC03
(NH4)2S03, Ca(OH)
dil.H2S04, CaC03
(NH4)2S04> Ca(OH)
A12(S04)3/ CaC03
Carbon, CaC03
Capacity,
103 Nm3/hr
.550
400
385
70
320
250
100
60
400
500
150
750
! 5
140
420 .
Type of
absorber
GPb
GP
Venturi
Venturi
ppC
Screen
TCA
ppC
GPb
Coned
Screen
Tellerette
Tellerette
Tellerette
Packed®
Slurry or
solution
pH cone . , %
6-7 15
5-6 12
7 3-5
6 5
6.2 7-B
6 10
2
6 10
7 20
6.8 25
6 30
1 2-4
3-4 10
3-4 10
L/G,
liters/
Mm3
6-7
7-8
10-15
10-15
7
10
7
10
1-2
1-2
2
30-45
6-10
3-9
Gas
velocity,
m/sec
3
3
4
4
3
4
3
1
2
1.5
0.5
Pressure
dropa
mm H2<3
150
120
400
500
80
450
200
250
50
100
480
802 802
in, out,
PPU ppu
800
250
2,000
2,000
400
1,500
700
1,000
800
1,400
700
600
1,500
600
500
75
30
200
200
40
200
50
50
20
40
30
50
80
20
80
Moisture
in
gypsum, %
8-10
7-8
CaSO3
10-15
7-8
10-12
10-15
10-12
6-7
8-10
8-10
7-9
8-10
10-12
9-11
Pressure drop includes that of absorber and mist eliminator.
Grid packed.
Perforated plate.
Four scrubbers.
Six towers.
-------
Cooler
Flue gas first enters the cooler (prescrubber), where
the gas is sprayed with water. The cooler, which is not
commonly used in the United States, has three functions:
(1) cooling and humidifying the gas to aid in prevention of
scaling in the scrubber; (2) protecting coatings and pack-
ings made of plastic; (3) removing dust and other impurities
in the gas that were not caught by the electrostatic precipi-
tator. This is useful in obtaining high purity by-products
with good commercial value. Because impurities in the gas,
such as dust and chloride, accumulate in the liquor, a
portion of the liquor is sent to the water treatment system,
neutralized to precipitate heavy metals, filtered, and then
usually purged.
Scrubber
Scrubber design varies among the processes. The scrub-
ber is a plastic grid packed tower for Mitsubishi-JECCO, a
venturi for Chemico-Mitsui and Mitsui Miike, a TCA with
polyethylene balls for Ishikawajima, a Bahco type for
Tsukishima, a stainless steel screen type for Chubu-Mitsu-
bishi Chubu-MKK (CM), and perforated plates for Babcock-
Hitachi and Sumitomo-Fuji Kasui processes. The reliability
of the Mitsubishi-JECCO and Chemico scrubbers has been well
demonstrated in Japan. The former has less pressure drop.
The TCA scrubber has a high SO2 removal efficiency but
presents the problem of wearing of balls. The Bahco and
screen type scrubbers might be more susceptible to scaling.
The perforated plate scrubber for the Sumitomo-Fuji Kasui
process (Moretana type) is designed to give extreme turbu-
lence producing foam layers 15 to 20 inches thick; a high
SO_ removal efficiency is attained while heavy mist is
formed.
For the Chemico-Mitsui and Mitsui Miike processes,
which use no cooler, the scrubber is operated with a dilute
3-5
-------
slurry at a high L/G ratio to prevent scaling. The by-
product contains a considerable amount of impurities, as
described in Section 6.
Oxidation
The rotary atomizer invented by JECCO has been used for
the Mitsubishi-JECCO, Babcock-Hitachi, and Chubu-MKK pro-
cesses because of its high efficiency and reliability.
Different types of oxidizers have been developed for other
processes. A low pH (3.5 to 4.0) is desirable for oxidation
of calcium sulfite slurry. This is attained with a pH
controller by adding a small amount of sulfuric acid, as is
being done at many plants, or by using flue gas and a cata-
lyst, as in the Mitsui Miike process. The facilities to
produce gypsum, pH controller, oxidizer and centrifuge
account for about 30 percent of the total investment cost.
Nevertheless, production of gypsum has been growing in
Japan. Mitsui Aluminum Co. which has been producing waste
calcium sulfite sludge will change the process to by-produce
gypsum, as described later. By-production of calcium
sulfite sludge and its stabilization, as it is being done in
the United States, might be of much interest in the future
in Japan when there is an oversupply of gypsum.
Saturated- or Unsaturated-Mode Operation
Scaling has been the largest problem for the wet lime-
limestone process. It is known that the formation of gypsum
crystals tends to cause the scaling. A theory of unsatur-
ated-mode operation (operation without the presence of
2
gypsum) has been developed recently in the United States
and applied successfully to the operation of Paddy's Run
Station, Louisville Gas and Electric Company. The theory is
based on the fact that when the degree of oxidation of
calcium sulfite is below 20 percent, sulfate ions could be
contained in calcium sulfite crystals replacing sulfite ions
and thus preventing the formation of gypsum crystals. The
3-6
-------
author's X-ray diffraction study of sludge obtained from
Omuta plant, Mitsui Aluminum Co., supports the theory, as
discussed later.
In most plants in Japan, the 02/SO2 ratio of flue gas
is high and oxidation in the scrubber exceeds 20 percent,
resulting in the formation of gypsum crystals. In order to
ensure scaling-free operation in such a saturated mode,
improvements have been made in the design, fabrication, and
operation of the plants. Use of good quality seed of gypsum
crystals is an important key to the prevention of scaling.
Scaling tends to occur most readily on mist eliminators. In
many plants, mist eliminators are washed with fresh water to
prevent scaling, but this procedure increases the amount of
wastewater. In some plants - for example, Kainan plant of
Kansai Electric operating by the Mitsubishi-JECCO process -
the mist eliminator is washed with a supernatant of calcium
sulfite-gypsum slurry in some improved way without any scale
formation.
Water Balance
Fresh water, about 1 ton per 10 MW, is fed into the
cooler to lower the flue gas temperature from a range of 130
to 140°C to a range of 55 to 60°C. Most of the water is
volatilized or recycled and a portion is usually purged
after being treated. In most plants, the mist eliminator
and by-product gypsum are washed with fresh water. The
amount of the input water usually exceeds the output, i.e.
water is taken into gypsum as water of crystallization and
moisture. (Moisture content of gypsum after being centri-
fuged is normally about 10 percent.) Therefore, a portion
of the liquor discharged from the gypsum centrifuge is also
sent to the wastewater treatment system and then purged. In
Japan it is allowable to purge water after treating it to
meet the regulations on pH, heavy metals, COD, etc.
3-7
-------
To minimize the use of fresh water and the emission'of
wastewater, some plants feed the water discharged from the
cooler into the scrubbing system, wash the mist eliminator
with a supernatant of the calcium sulfite-gypsum slurry, and
omit the water wash of the product gypsum. Still some water
is purged from the system to prevent the accumulation of
chloride and other impurities, because chloride promotes
corrosion and also impairs the quality of gypsum for use in
wallboard.
The amounts of wastewater and of by-product gypsum at
five plants are shown in Table 3-3. For the three plants
using the Mitsubishi-JECCO process, the water ratio (A+C)/
(A+B+C) ranges from 0.37 to 0.64 and is lower with the
higher concentration of S02 in flue gas. In plants using
other processes, the ratios are higher.
In the United States, calcium sulfite sludge containing
about 50 percent moisture is discarded while the supernatant
and filtrate are recycled without releasing any water. This
system is called "closed loop" operation, although the water
ratio is about 0.5. Compared with the closed loop, the
actual amount of water removed is about equal for the Karita
plant and less for the Owase plant using the Mitsubishi-
JECCO process.
MITSUBISHI-JECCO LIME-LIMESTONE PROCESS
State of Development
Mitsubishi Heavy Industries (MHI) constructed the first
wet-lime process plant in 1964, licensed by Japan Engineering
Consulting Co. (JECCO). The plant is located at Koyasu
Fertilizer Works, Nippon Kokan, and treats a tail gas from a
sulfuric acid plant emitted at a rate of 62,500 Nm /hr and
containing 2200 ppm S00. Although several problems, including
£f
scaling and corrosion, were encountered at the beginning of
the operation, these have been solved by the cooperation of
MHI and Nippon Kokan. Recently MHI constructed several
3-8
-------
Table 3-3. AMOUNTS OF WASTEWATER AND GYPSUM
Process
Mitsubishi- JECCO
Mitsubishi- JECCO
Mitsubishi- JECCO
Babcock-Hitachi
Chubu-MKK
User
Kansai Electric
Kyushu Electric
Chubu Electric
Chugoku Electric
Ishihara Chem.
Plant site
Kainan
Karita
Owasea
Mizushima
Yokkaichi
MW
150
175
750
105
85
SO2'
ppm
270
800
1,480
400
1,300
Waste-
water,
t/hr
(A)
1.5
2.9
14.0
4.0
4.0
Gypsum,
t/hr
Solid
(B)
0.9
2.9
29.0
0.9
2.2
Water
(C)
0.1
0.3
2.9
0.1
0.2
Water
ratio
(A+C)/
(A+B+C
0.64
0.52
0.37
0.82
0.67
u>
Designed value; the plant is under construction.
-------
plants, which are operating satisfactorily. Many new plants
are under construction, as shown in Table 3-4.
Process Description
Figure 3-2 shows a flowsheet of a lime-process plant at
Amagasaki Station, Kansai Electric, with a capacity of
treating 100,000 Nm /hr of flue gas from oil-fired boilers.
Waste gas is first washed with water to remove dust and to
cool the gas to about 60°C. 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 with the dust. The filtrate is used for slak-
ing of lime. The cooled gas is then sent to an absorbing
step. Two plastic-grid packed absorbers in series are
housed in one tower. 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, and a portion of the sul-
fite is converted to bisulfite. The pH of the slurry dis-
charged from the No. 1 absorber is 4 to 4.5. The concentra-
tion of the slurries in the absorbers is about 15 percent.
A relatively high liquid/gas ratio (6 to 7 liters/Nm ) is
used to prevent scaling.
The pH of the slurry is then adjusted to 3.5 to 4 to
promote oxidation in the following step. If required, a
small amount of sulfuric acid, normally less than 1 ton per
100 tons of inlet S0_, 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 JECCO) at
a pressure of 4 to 5 atmospheres (44 to 58 psig) and a
temperature of 60 to 80°C. The atomizer is effective in
producing fine bubbles and is free from scaling, erosion,
and corrosion. The gas leaving the oxidizer contains some
3-10
-------
Table 3-4. WET LIME-LIMESTONE PROCESS PLANTS USING THE MITSUBISHI-JECCO PROCESS
oo
I
No.
1
2
3
4
5
6
7
8
9
10
LI
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
User
Nippon Kokan
Kansai Electric
Onahama Refining
Kawasaki Steel
Yoshino Gypsum
Kansai Electric
Tokyo Electric
Tohoku Electric
Kyushu Electric
Kawasaki Steel
Kansai Electric
Niigata Power
Kawasaki Steel
Kawasaki Steel
Teijin
Mizushima Power
Tohoku Electric
Chubu Electric
Chubu Electric
Kawasaki Steel
Toyobo
Kashima Power
Kyushu Electric
Kyushu Electric
Kyushu Electric
Kyushu Electric
Confidential
Confidential
Confidential
Confidential
Confidential
Plant
site
Koyasu
Amagasaki
Onahama
Chiba
Tokyo
Kainan
Yokosuka
Hachinohe
Karita
Mizushima
Amagasaki
Niigata
Mizushima
Chiba
Ehime
Mizushima
Niigata
Owase
Owase
Mizushima
Iwakuni
Kashima
Karatsu
Karatsu
Ainoura
Ainoura
Capacity,
Nm3/hra
62,500
100,000
92,000
120,000
12,000
400,000
400,000
380,000
550,000
750,000
375,000
530,000
900,000
320,000
270,000
611,600
420,000
1,200,000
1,200,000
750,000
200,000
431,000
730,000
570,000
730,000
730,000
1,100,000
1,100,000
1,200,000
475,000
1,200,000
Source of gas
H2SO4 plant
Utility boiler
Copper smelter
Sintering plant
Industrial boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Sintering plant
Utility boiler
Utility boiler
Sintering plant
Sintering plant
Industrial boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Sintering plant
Industrial boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
Utility boiler
SO2, ppm
inlet
2,200
700
20,000
600
1,400
550
250
850
800
830
500
700
500
800
1,700
1,050
550
1,500
1,500
550
1,400
1,000
550
550
880
880
950
950
1,600
500
550
outlet
200
70
100
60
130
60
40
85
75
40
50
70
40
64
60
40
55
35
35
40
50
100
70
70
110
110
50
50
50
65
65
Absorbent
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
CaC03
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
CaCOa
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
CaC03
Ca(OH)2
Ca(OH)2
Ca(OH)2
Ca(OH)2
CaCO3
CaC03
CaC03
CaCO3
CaC03
CaCO,
CaCO3
CaC03
Ca(OH)2
Ca(OH)2
Year of
completion
1964
1972
1972
1973
1973
1974
. 1974
1974
1974
1974
1975
1975
1975
1975
1975
1975
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
1976
a 1000 Nm3/hr = 590 scfm - 320 kW.
-------
.EXHAyST_GAS FROM_BOILER
SCROBBE1T
i r
[NG'.TQI
Ca(OH)2 •(• S02-^CaS03
Ca(OH)2 + C02-».CaC03
COOLING!TOMER
CaC03 + S02-*"CaS03 + C02
CaSO- + 02—>CaSO.
AFTERBURNER
MIST CATCHER
AIR
LOW SULFUR
FUEL OIL
QUICK LIME
(CaO) SILO
pH ADJUSTING
(SULFURIC ACID)
OXIDIZING TOWER
THICKENER
STOCK SOLUTIO
TANK
CENTRIFUGAL
SEPARATOR
SLAKED LIME Ca(OH)^
SLAKER
SEPARATED Q.
SOLUTION TANK
Figure 3-2. Flowsheet of Mitsubishi-JECCO lime/limestone process
(Amagasaki plant, Kansai Electric)(Two-tower system).
-------
SO_, and is returned to the absorber. The gypsum is centri-
fuged. All of the liquor is returned to the system. The
gypsum grows into large crystals; moisture content after
centrifugation is only 8 to 10 percent. The gypsum thus
obtained is of high purity and good quality, 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. More than 90 percent of the S0_ is recovered.
For most of the later plants, a single-absorber system,
as shown in Figure 3-3, is used to reduce the plant cost.
Plant No. 29 (in Table 3-4) will use a double-absorber
system to remove 97 percent of the SO^ (1600 ppm) with
limestone. For the single-absorber system, a cooling tower
and an absorbing tower are put together. Flue gas goes up
the cooler and down the absorber. In this system, the pH of
the outlet slurry discharged from the absorber tends to be
higher than that in the double-absorber system. Consequent-
ly, a considerable amount of sulfuric acid, 5 to 10 tons per
100 tons of inlet S0_, is normally required for pH adjusting
prior to the oxidation step.
Status of Technology
By means of extensive studies with a pilot plant,
Mitsubishi has determined that scaling can be prevented by
shape and arrangement of the grid in the absorber; by adjust-
ment of the slurry concentration, pH, and liquid/gas ratio;
and by addition of gypsum crystal seed and by thorough
mixing of the lime in the circulating slurry.
The Amagasaki plant has been in continuous operation
for most of the time since operation began in April 1972,
except for the period of shutdown of the power plant. The
desulfurization plant treats a flue gas containing about 700
ppm SO- to recover about 90 percent of the S02- This plant
was operated with a closed loop, emitting no water at all,
for 3 months after start-up. But, as chloride and other
3-13
-------
COOLER ABSORBER
WATER
GAS
CaO
(CaC03)
MIST AFTER
ELIMINATOR BURNER
CENTRIFUGE
pH CONTROLLER OXIDIZER
GYPSUM
Figure 3-3. Single-tower system (Mitsubishi-JECCO process)
3-14
-------
impurities derived from fuel, lime, and water accumulated in
the circulating liquor, symptoms of corrosion of the struc-
tural material appeared and quality of the by-product
gypsum decreased. Since then a small amount of water has
been removed from the system to maintain the impurities
under a certain level. The Onahama plant (No. 3 in Table
3-4; Figure 3-4), which treats a waste gas from a copper
smelter (92,000 Nm /hr, S02~20,000 ppm), had some scaling
problem at the beginning. Because a large amount of lime
slurry was fed from the top of the second scrubber to absorb
more than 99 percent of the SO- of very high concentration,
the pH of the slurry at the upper part of the scrubber was
too high and the slurry absorbed CO- to form CaCO^, which
caused the scaling. Some modification was made to charge
the lime slurry into several places and thus the problem was
solved. High-pressure washing for about 3 hours once every
month or so is adequate, since the deposits tend to be soft.
The plant has been producing 400 tons of gypsum per day, all
of which has been used for wallboard by Onahama-Yoshino Co.,
a company established for wallboard production using the
by-product. Operation of other plants (Nos. 4 - 10 in
Table 3-4) has been good since start-up, except for the
Hachinohe plant, Tohoku Electric, which experienced mechanical
troubles, due partly to misoperation, that required more
than 2 months to resolve. Yoshino Gypsum has been producing
calcium sulfite (without oxidizer) and has been using the
sulfite for a special purpose. Operational data for the
Hainan plant, Kansai Electric (Figure 3-5), and Yokosuka
plant, Tokyo Electric (Figure 3-6), are listed in Table 3-5.
Both use the single-absorber system.
At the Yokosuka plant, Tokyo Electric, limestone is
ground in a vertical wet mill (Figure 3-7) to a particle
size averaging 25y. About 90 percent of the limestone
charged to the scrubber is reacted with SO- to recover about
84 percent of the S02. Sea water is used for gas cooling,
3-15
-------
r
Figure 3-4. Onahama plant, Onahama Smelting,
Figure 3-5. Kainan plant, Kansai Electric,
3-16
-------
•
r
Figure 3-6. Yokosuka plant,
Tokyo Electric.
Figure 3-7. Tower mill at
Yokosuka plant.
-------
Table 3-5. OPERATION DATA: KANSAI AND TOKYO PLANTS
Gas treated, Nm /hr
Type of boiler
Load factor ,- %
Sulfur in fuel oil, %
S02 in flue gas, ppm
©2 in flue gas, %
Absorbent
Stoichiometry
SO2 recovery, %
pH of scrubber liquor
L/G, liter s/Nm3
Turndown ratio
Pressure drop, Cooler
v™ H2° Absorber
Demister
Power requirement, kW
Start-up date
Availability since
start-up, %
Moisture in gypsum, %
Use of gypsum
Kansai Electric,
Hainan
400,000
Hitachi (600 MW)
100 - 80
0.5 - 1
250 - 550
2.4
Ca (OH) 2
0.9 - 1
85 - 95
6-7
7
1/4
50
30
20
1,650
December 1973
Over 95
8-10
Cement , board
Tokyo Electric,
Yokosuka
400,000
CE (265 MW)
100 - 30
0.5
250
4.7
CaCO3
0.9 - 1
80 - 90
5-6
7
1/4
50
30
25
2,000
February 1974
Over 95
8-10
Board
3-18
-------
and some mist from the cooler goes into the absorber. To
prevent the accumulation of chloride, a considerable amount
of wastewater is emitted after being treated.
At the Kainan plant, Kansai Electric, industrial water
is fed into the cooler. The mist eliminator is washed with
a supernatant of the calcium sulfite-gypsum slurry- Tech-
nology has been developed for scale-free washing with the
saturated solution. Water washing of by-product gypsum
(Figure 3-8) is omitted. About 1.5 tons/hr of wastewater are
emitted to prevent the accumulation of chloride derived from
fuel. The amount of wastewater will be less than that of
the by-product gypsum for the new plants that treat flue gas
containing more than 1000 ppm SO . Considerable oxidation
£m
of calcium sulfite occurs in the scrubbers of both the
Yokosuka and Kainan plants because 02/S02 ratios are high.
The slurry discharged from the scrubber of the Tokyo plant,
Yoshino Gypsum Co., which treats relatively concentrated SO2
(1400 ppm), also contains a considerable amount of gypsum
because the gas contains much oxygen. Little oxidation
occurs in the absorber of the Onahama plant because of the
very high SO9 concentration.
4
Basic Chemistry and Technology
The reasons for use of a plastic-grid packed tower as
the absorber are the large mass transfer coefficient for SO-
absorption, low pressure drop, simple structure, and stabil-
ity of performance for load variation. MHI has developed
formulas for calculation of scrubber size, based on a re-
action model in which the dissolution of lime is the rate-
determining step:
log Yin = Ka C0P0(1 - n) |'
Yout
" T
yn — * f • f—\
i\a — A . C „ (TT)
3-19
-------
where
Y ., Y. : S0~ concentration at the outlet and inlet,
ppm
P0: Gas pressure in scrubber, atm
C0: Effective Ca concentration in slurry,
kg-mole/m3
n: Ca reactivity
Z: Effective height of scrubber, m
2
G1: Superficial gas velocity, kg-mole/m -h
L/G: Liquid-gas ratio, liter/Nm
Ka: Mass transfer coefficient based on the rate
of Ca dissolution, 1/hr atm
In the packed tower, coarse grids are used so as to
prevent mesh choking by the slurry. On the basis of the S02
absorption reaction mechanism mentioned above, grids with
large spacing are sufficient from the standpoint of SO-
removal efficiency.
MHI has also studied the oxidation reaction of calcium
sulfite. The reaction of equation (1) below is considered
to advance through a medium of bisulfite as shown in equations
(2) and (3); the reaction mechanism has been proved by
correlations among mass transfer coefficient of the oxidizing
tower, pH value, and bisulfite ion concentration, as shown
in Figure 3-9.
CaS03=l/2 H2O + 1/2 O2 + Aq = CaSO4«2H2O + Aq (1)
HS03~ + 1/2 O2 (in solution) = SO42~ + H+ (2)
CaSO3- 1/2 H2O + H+ = Ca2+ + HSO3~ + 1/2 H2O (3)
Ca2"1" + S042~ + 2H20 = CaS04-2H2O (4)
3-20
-------
Figure 3-8.
By-product gypsum at Kainan plant,
Kansai Electric.
-M
(O
o o
O E
ID
~
<^> a
CO i— <
3 concentration.
3-21
-------
Evaluation
Stable operation of the Mitsubishi-JECCO process has
been well demonstrated. High S02 recovery and good quality
of salable gypsum are other advantages. The capital and
operating costs are estimated to be lower than those of the
double-alkali and Wellman-Lord processes. Because of these
features, MHI is the leading constructor of desulfurization
plants in Japan. The plant cost, however, has now reached
$60/kW. Further simplifications, such as reduction of the
size of the cooler, may be desirable.
MHI has recently started tests with flue gas from a
coal-fired boiler. The results should indicate the applicability
of the process in the U.S.
Although the total amount of water leaving the system
as moisture in gypsum and wastewater is about equal to that
being discarded in the U.S in sludge that contains about 50
percent water, the volume of wastewater should be further
reduced or eliminated for application in the U.S. Use of
sulfuric acid should be also eliminated; this may be achieved
by use of the two-tower system.
CHEMICO-MITSUI AND MITSUI MIIKE LIME-LIMESTONE PROCESSES
State of Development
Mitsui Miike Machinery Co. has constructed a desulfurization
unit using Chemico scrubbers at the Omuta plant, Mitsui
Aluminum Co. (Figure 3-10). This plant has operated smoothly
since its start-up in April 1972 treating a flue gas from a
156-MW coal-fired boiler to by-produce a calcium sulfite
sludge (Figure 3-11). Because of the limited landspace
available for discarding the sludge, Mitsui Miike has re-
cently developed a process to produce gypsum by using lime-
stone as the absorbent along with a catalyst to promote the
reaction. The reason for the use of limestone is the low
cost and the shortage of carbide sludge at the Omuta plant.
A prototype plant (25 MW equivalent) started operation in
3-22
-------
Figure 3-10. Omuta plant, Mitsui Aluminum.
:/ 5"-^"
i"1- *.
Figure 3-11. Sludge pond at Omuta plant, Mitsui
3-23
-------
October 1974 at the Omuta facility. Four commercial plants
are under construction (Table 3-6). All use Chemico scrubbers
to treat flue gas from coal-fired boilers.
Description
A flowsheet of the first operation of the Chemico-
Mitsui process generating calcium sulfite sludge is shown in
Figure 3-12. Some of the operation parameters are shown in
Table 3-2. Because this plant is familiar in the United
States, having been described by many people, ' further
description is not needed here except for noting of a recent
finding by the author. X-Ray and microscopic tests of the
calcium sulfite sludge discharged from the scrubber indi-
cated the absence of gypsum, although chemical analysis of
the solids shows that 5 to 10 percent oxidation occurred.
This finding indicates the possibility that some of the
SO ~ ions in calcium sulfite are replaced by SO ~ ions and
supports the theory of "unsaturated mode operation" proposed
2
by Borgwardt. Although the solution may be saturated with
the solids formed by the replacement, it is not saturated
with gypsum and thus the possibility of scaling is minimized.
The X-ray diffraction pattern is shown in Figure 3-13 in
comparison with that of a solid containing some gypsum.
A flowsheet of the Mitsui Miike limestone-gypsum process
is shown in Figure 3-14. Flue gas is treated in two venturi
scrubbers in series with a countercurrent flow of limestone
slurry containing a metallic catalyst. The resulting cal-
cium sulfite slurry is then fed into a pH controller, where
the slurry contacts a portion of flue gas (5 to 10 percent
of the total) to lower the pH and to complete the reaction
of limestone with S0_. The slurry is then pumped into an
oxidizing tower, into which air is blown from the bottom to
convert the sulfite into gypsum. The gypsum slurry is
centrifuged. Most of the liquor from the centrifuge is used
to prepare a limestone slurry. A small portion of the
liquor is sent to a wastewater treatment system to prevent
the accumulation of impurities.
3-24
-------
Table 3-6. PLANTS USING THE MITSUI MIIKE LIMESTONE PROCESS
User
Mitsui Aluminum
EPDCa
EPDC
Mitsui Aluminum
Mitsui Aluminum
Plant
site
Omuta
Takasago
Takasago
Omuta
Omuta
Capacity,
MW
25
250
250
175
156
S02, ppm
In
2,350
1,500
1,500
1,930
2,000
Out
200
100
100
190
200
Dust, g/Nm
In
0.6
0.1
0.1
0.6
0.6
Out
0.06
0.05
0.05
0.06
0.06
Year of
completion
Nov. 1974
Jan. 1975
Oct. 1975
April 1975
Sept. 1975
Electric Power Development Co.
3-25
-------
I.D. FAN
BOILER
FLUE GAS
u>
to
A SCRUBBER
B SCRUBBER
1st STAGE
^J/ENTURI
REHEAT
FURNACE
DEMISTERS
2nd STAGE
VENTURI
RECYCLE PUMP,
1st STAGE
RECYCLE PUMP
+ -J
WET CARBIDE PIT
MAKE-UP SLURRY
FEED PUMP
MAKE-U
SLURRY TANK
S777
DRY CARBIDE PIT
RECYCLE SLURRY
MAKE-UP SLURRY
BLEED SLURRY
RETURN LIQUOR
ASH POND LIQUOR
RETURN PUMP,
WASTE DISPOSAL POND
NOTE: ONLY ONE SCRUBBER SYSTEM PRESENTLY IN OPERATION.
• INDICATES A CLOSED VALVE
f« INDICATES A CLOSED DAMPER
Figure 3-12. Flowsheet of Chemico-Mitsui lime process (Omuta).
-------
60
50
40
30
20
10
OMUTA PLANT, MITSUI ALIMINUM CO.
O CaS03 ' 1/2 H20
• UNKNOWN, POSSIBLY
CaS03 • 1/2 H20
• CaS03 ' 2H20
50-
40
30
20
10
TOKYO PLANT, YOSHINO GYPSUM CO.
20
25
30
35
40
Figure 3-13. X-Ray diffraction pattern of sludge from scrubber.
3-27
-------
STACK
FLUE 1ST 2ND AFTER BURNER
GAS SCRUBBER SCRUBBER
T
MILL
I—>>
TANK
ICO,
THICKENER
PH
CONTROLLER
,->| I i FILTER
H\** NLU I RA- 1
-J I 1 1 LIZER ciimrc
»——J rcMTDTCiirc oLUUht
'AIR
LIZER
GYPSUM
Figure 3-14. Flowsheet of Mitsui Miike limestone-gypsum process
95
90
LU
o:
o
CO
85
0.9 1.0 1.1 1.2
STOICHIOMETRY (FOR INLET S02)
Figure 3-15. Effect of catalyst on S02 removal efficiency.
3-28
-------
The catalyst prevents the formation of a calcium sul-
fate coating on calcium sulfite and carbonate and thus
promotes both the reaction of the carbonate with S02 and
the oxidation of the sulfite into sulfate, as shown in
Figure 3-15 and Table 3-7, which are based on pilot tests.
There is virtually no loss of catalyst into gypsum because
gypsum can be washed well. In the wastewater treatment, the
catalyst can be precipitated in the form of hydroxide by
raising the pH. The catalyst thus can be returned to the
absorbing system.
Table 3-7. EXAMPLE OF THE COMPOSITION OF BY-PRODUCT
(stoichiometry 0.95; values in percent)
Absorbent
CaCO3 + Catalyst
CaC03 only
CaSO4«2H20
98.2
71.0
CaS03
0.7
15.3
CaC03
trace
12.3
Since its start-up, the prototype plant at Omuta has
been operated smoothly. Tests of the by-product gypsum for
wallboard production have shown that although the gypsum is
pure enough and useful, further improvement of the crystal
shape is desirable for higher strength. The by-product from
the Takasago plant, Electric Power Development Company
(EPDC) will be used for cement.
Evaluation of the Process
The Chemico-Mitsui lime-calcium sulfite process at the
Omuta plant has proved to be highly reliable because of the
unsaturated-mode operation. Sludge disposal, however, is a
big problem in Japan. The Mitsui Miike process has an
advantage of producing usable gypsum requiring no sulfuric
acid and might suit U.S. application. But the capital
required is about 50 percent higher for the lime-calcium
sulfite process. Where cheap sulfuric acid is available, a
3-29
-------
simpler oxidizing system using a small amount of sulfuric
acid could be more economical. If about 80 percent oxida-
tion is sufficient to improve the properties of the sludge,
the oxidizing system may be much simplified. The sludge
pond should be sealed to prevent leakage of water containing
the catalyst.
BABCOCK-HITACHI PROCESS
State of Development
Hitachi Ltd. has constructed a desulfurization unit at
Mizushima Station, Chugoku Electric, using the Babcock and
Wilcox process. The unit has a capacity of treating 320,000
Nm /hr of flue gas from an oil-fired boiler. The process
by-produces salable gypsum. The unit was put in operation
in November 1973. Hitachi is now constructing four plants,
as shown in Table 3-8. A scrubber unit is used for each
plant except the Tamashima plant, Chugoku Electric, which
will install four units, three for normal use and one for
backup.
Process Description
The scrubber is of the standard B and W type, a venturi
followed by a perforated plate absorber (Figure 3-16). The
venturi serves as a cooler and humidifier rather than a dust
removal unit. A limestone slurry, 105 to 110 percent of
stoichiometric amount, is used. The pH of the circulating
slurry in the absorber is 6.2, the L/G ratio 7 liters/Nm
(50 gal./lOOO scf), the gas velocity 2 m/sec, and the solids
concentration 7 to 8 percent. The treated gas is passed
through a mist eliminator (one-pass, four-section chevron
with a trap-out tray below it). Total pressure drop is 750
mm H-O. The wash liquor from the eliminator is circulated
from the tray to the thickener and back to the mist elimin-
ator again. A portion of the calcium sulfite slurry from
the circulation tank is sent continuously to a reactor to
convert the remaining calcium carbonate into gypsum by
3-30
-------
Table 3-8. PLANTS USING THE BABCOCK-HITACHI PROCESS
User
Chugoku Electric
Asahi Chemical
Kansai Electric
Chugoku Electric
Kansai Electric
Plant
site
Mizushima
Mizushima
Osaka
Tamashima
Osaka
Capacity,
MW IOC
105
150
160
500
160
)0 Nm /hr
320
481
500
1480°
500
S02/ ppm
Inlet
400
1480
550
1500
550
Outlet
40
50
50
50
50
Year of
completion
Nov. 1973
Mar. 1975
Apr. 1975
June 1975
Jan. 1976
All from oil-fired boilers.
Four scrubbers.
3-31
-------
TO STACK
GAS TO ABSORBER
U)
I
U)
to
H2S04
OXIDIZER
Figure 3-16. Flowsheet of Babcock-Hitachi limestone-gypsum process.
-------
adding sulfuric acid and then is fed into an oxidizer, which
uses a JECCO rotary atomizer. The gypsum is centrifuged,
and the product gypsum, containing 7 to 8 percent moisture,
is sold.
Performance
The Mizushima plant (Figure 3-17) underwent test opera-
tion for 5 months following its start-up in November 1973.
There was some trouble with solids deposition in the sump
below the venturi and the absorber. This problem has been
eliminated by modifying the structure. In addition, a
deposit of fine-grained scale (0.2 mm) formed on the ID fan
and caused a vibration. The fan is now being washed. For
the new plants to be built, a booster fan will be used in
place of the ID fan.
Commercial operation started in April 1973, and plant
availability since that time has reached 96 percent. Inlet
SO2 concentrations range from 300 to 500 ppm and outlet
concentrations from 20 to 50 ppm. Oxidation of sulfite in
the scrubber reaches 90 percent because of the low S02
concentration and high 0- concentration (5%) . Energy
consumption is about 2.3 percent for the scrubber system and
2.5 percent for reheat. The make-up water (19 t/hr) is added
to the clarifier overflow tank. Of the 19 tons, 4 tons is
bled from the system to prevent accumulation of impurities
such as chloride and magnesium.
Evaluation
Operation of the Mizushima plant, Chugoku Electric,
seems to be fairly good, but the SO2 concentration is low
and the amount of wastewater is relatively large. Oppor-
tunities for further evaluation will be afforded by opera-
tion of the plants of Asahi Chemical (Mizushima plant) and
Chugoku Electric (Tamashima plant), which will start during
1975 to treat flue gas containing about 1500 ppm S02.
3-33
-------
Figure 3-17. Mizushima plant, Chugoku Electric,
3-34
-------
CHUBU-MKK PROCESS (CM PROCESS)
State of Development
Mitsubishi Chemical Machinery (MKK) jointly with Chubu
Electric Power, has developed a wet-lime/limestone process
using a screen type scrubber. The first commercial plant
using a limestone slurry was built at Yokkaichi plant,
Ishihara Industries, and went into operation in March 1974.
The unit has a capacity of treating 250,000 Nm /hr of flue
gas from oil-fired boilers. The second plant using a lime
slurry is near completion at the Yokkaichi plant, Mitsubishi
Gas, with a capacity of treating 70,000 Nm /hr of flue gas
from an oil-fired boiler.
Process Description
A flowsheet of the unit for Ishihara Industries is
shown in Figure 3-18. Flue gas is first cooled with a water
spray and then introduced into an absorber, which has a
spray in the lower part and several screens set at an angle
in the upper part. A limestone slurry (3 to 10 percent
solids) flows on the screens forming liquid films, which
absorb SO2. Gas velocity in the scrubber (4 by 4.8 by 16.8
m, stainless steel) is about 4 m/sec and the pressure drop
is 200 mm H~0. The pH of the slurry into the absorber is
6.2 to 6.3 and that of the effluent nearly 6. A stoichi-
ometric amount of limestone (minus 325 mesh) is used to
remove about 90 percent of the SO- (1300 ppm). The L/G
3
ratio in the scrubber is about 10 liters/Nm . As the flue
gas contains about 5 percent oxygen, about 40 percent of the
calcium sulfite is oxidized in the absorber into gypsum. A
portion of the slurry from the absorber is sent to an oxi-
dizer after pH adjustment with sulfuric acid and oxidized
into gypsum with air by use of a JECCO rotary atomizer.
The gas leaving the absorber is passed through a mist
eliminator and heated by an afterburner to 120°C. The oil
consumption is about 5 percent of the oil for boilers. The
mist eliminator (chevron type) is washed with fresh water.
3-35
-------
U)
I
U)
CTt
AFTER BURNER
P
--l--{
CaC03
(CaoT
0
OXIDIZER
I SCRUBBER
=><
WATER
FLUE
GAS
COOLER
r*
*__
DUST
H,SOL
0
WATER
\
GYPSUM
Figure 3-18. Flowsheet of CM process (Ishihara Chemical).
-------
About 20 t/hr water is fed into the cooler, in which 16
t/hr is volatilized. The difference, about 4 t/hr, is
discharged from the system after being treated. The mist
eliminator is washed intermittently with fresh water.
Considerable portions of the mother liquor of gypsum slurry
and wash water of gypsum are also discarded. The by-product
gypsum, about 50 t/day, is sold for wallboard production.
Evaluation
The process is simple and can attain 90 percent removal
of SO2 using limestone. Some scaling problems occurred,
mainly on the wall of the scrubber, in the early operation
period. To prevent the scaling Ishihara seems to use much
fresh water, which results in the emission of much waste-
water. Further improvement would be required to reduce the
amount of wastewater.
The plant cost 810 million yen ($2.7 million, as of
1973) . The Wellman-MKK process plant at Chubu Electric
Power (620,000 Nm /hr) cost 2000 million yen at an even
earlier period. MKK estimates that the Wellman-MKK process
would cost about one-third more than the limestone scrubbing
process.
KOBE STEEL CALCIUM CHLORIDE PROCESS (CAL PROCESS)
State of Development
Kobe Steel Ltd. has developed a process which uses a 30
percent calcium chloride solution dissolving lime as an
absorbing liquor. A pilot plant with a capacity of treating
50,000 Nm /hr of waste gas from an iron ore sintering plant
was operated from June to December 1974. Two commercial
plants, each with a capacity of treating 375,000 Nm /hr of
waste gas from iron ore sintering, are to be completed
soon—one at Amagasaki Works, Kobe Steel, in November 1975,
and the other at Nadahama Works, Kobe Steel, in January
1976.
3-37
-------
Process Description
A flowsheet of the process is shown in Figure 3-19.
Waste gas is first cooled in a cooler to which calcium
chloride solution (about 5 percent, from a gypsum centri-
fuge) is fed to cool the gas to about 70°C and to remove
most of the dust. The solution is concentrated to about 30
percent and is sent to a scrubber system after dust removal
by filtration. The gas is then led into an absorber in
which a calcium chloride solution (about 30 percent, at pH 7
dissolving lime) is sprayed to remove more than 90 percent
of the SO~. The gas is then passed through a mist elimina-
tor and sent to a stack. The liquor discharged from the
absorber at pH 5.5, containing calcium sulfite, is sent to a
centrifuge to separate most of the solution, which is sent
to a tank where calcium hydroxide is dissolved to raise the
pH to 7. The calcium sulfite sludge from the centrifuge is
repulped with water and some sulfuric acid to produce a
slurry at pH 4. The slurry is oxidized by air bubbles into
gypsum, which is then centrifuged. The liquor from the
centrifuge, containing about 5 percent calcium chloride, is
returned to the cooler.
Theory
Calcium chloride solution can dissolve 6 to 7 times as
much lime as does water (Figure 3-20). The solution con-
taining lime absorbs SC>2 more rapidly but CO- and O- more
slowly than does milk of lime. High SO- removal can be
attained using a relatively low L/G ratio (Figures 3-21 and
3-22). The vapor pressure of the solution is low (Figure
3-23); less water is evaporated in the cooler and absorber
and thus the temperature of the liquor in the absorber
reaches 70°C, as compared with 55 to 60°C in usual wet
processes. The temperature of the treated gas is higher,
resulting in a smaller energy requirement for reheating.
Calcium chloride reduces the oxidation of calcium sulfite.
3-38
-------
COOLER
ABSORBER
MIST ELIMINATOR
GAS
TANK
T
DUST
TANK
CENTRIFUGE
Ca(OH)
IATER
OXIDIZER CENTRIFUGE
AIR
TANK
SLURRY WASHING
TANK
t
GYPSUM
Figure 3-19. Flowsheet of Kobe Steel process (Cal process).
-------
o
o
to
o
0.8
0.6
0.4
S 0.2
10 20 30 40 50 60
CaCl2 g/lOOg Sol.
Figure 3-20. Solubility of
lime in calcium chloride
solution.
o.
Q-
O
oo
3000
2000-
1000-
0 1
Figure 3-21. Vapor pressure
of SOo-
100-
90-
80
~ 70
LU
60-
Inlet S02 1500 ppm
1
10
L/G, 1/m3
Figure 3-22. L/G and SO2 re-
moval efficiency.
150
to
o:
o
o
CM
50
30 40 50 60 70
LIQ. TEMP, °C
Figure 3-23. Vapor pressure
of H20.
3-40
-------
Operation
The pilot plant was operated nearly continuously from
June 1974 to the end of the year, treating mainly waste gas
from an iron ore sintering plant containing 200 to 400 ppm
S02 and 15 to 16 percent 02. About 90 percent of the SO- is
removed at an L/G ratio of 2. At a ratio of 1, scaling
occurred on the wall of the absorber, but operation at L/G 2
or higher could prevent it. Oxidation of calcium sulfite in
the absorber is rather low (about 30 percent) for the high
oxygen and low S02 concentrations because of the effect of
the chloride. The reason for use of the calcium sulfite
centrifuge is to reduce the calcium chloride concentration
in the oxidizer; the oxidation occurs fairly rapidly at the
5 percent concentration. The centrifuged gypsum is not
washed with water and contains about 10 percent liquor
(about 0.5 percent calcium chloride) but is useful as re-
tarder of cement setting.
Corrosion has been the main problem. Stainless steel,
plastic, and rubber linings are used for the material.
Because the lower part of the cooler where the hot gas is
introduced was corroded severely, the part was replaced by
titanium, which is durable.
The mist eliminator is washed intermittently with the
calcium chloride solution. Because calcium chloride is
hygroscopic, the eliminator always keeps wet; although some
solid matter is deposited on the eliminator, it does not
form hard scale and can be washed away. No wastewater was
purged during the 6 months' operation, although some liquor
was lost when the rubber lining of pumps was repaired.
Concentrations of magnesium and other impurities increased
in the liquor but caused no problem.
Evaluation
The process has the following advantages and disadvan-
tages as compared with other wet-lime processes. Advan-
tages: (1) high SO2 removal efficiency, (2) relatively high
3-41
-------
outlet gas temperature, (3) no need for sulfuric acid
addition for pH control prior to the oxidation, and (4) use
of low L/G ratio and less water. Disadvantages: (1) need
of a thickener and two centrifuges, and (2) greater corrosion
problem.
Although the pilot plant was operated without scaling
and wastewater problems, further evaluation must await
operation of a larger plant with a higher concentration of
SO- over a longer period.
SUMITOMO-FUJI KASUI PROCESS (MORETANA PROCESS)
State of Development
Sumitomo Metal Industries Ltd. has developed a lime/-
limestone process jointly with Fuji Kasui Kogyo K. K. using
the Moretana scrubber, which is a sort of perforated plate
scrubber. A test plant with a capacity of treating 62,000
Nm /hr of flue gas from an oil-fired boiler has been operated
at the Amagasaki plant, Sumitomo Metal, since May 1973.
Several commercial plants have recently been completed or
are now under construction, as shown in Table 3-9.
Table 3-9. PLANTS USING THE MORETANA PROCESS
User
Sumitomo Metal
Sumitomo Metal
Ide Paper
Yokohama Rubber
Sumitomo Metal
Sumitomo Metal
Sanyo Kokusaku Pulp
Meiji Seika
Plant site
Amagasaki
Wakayama
Fuji
Onomichi
Wakayama
Kokura
Kozu
Ashigara
Gas treated,
Nm3/hr
62,000
25,000
60,000
29,000
370,000
92,000
140,000
30,000
Source
of gas
Boiler
S.P.a
Boiler
Boiler
S.P.a
H.F.b
Boiler
Boiler
Completion
May 1973
June 1974
Dec. 1974
Dec. 1974
Jan. 1975
Apr. 1975
Apr. 1975
Apr. 1975
Iron ore sintering plant.
Heating furnace.
3-42
-------
Process Description
A flowsheet of the process is shown in Figure 3-24.
Flue gas passing through an electrostatic precipitator is
cooled in a prequench scrubber and then introduced into a
main scrubber (Moretana scrubber). The treated gas is
passed through a mist eliminator and an oil-fired reheater.
Lime or limestone slurry is fed to the main scrubber. The
bleed stream of the reacted slurry is treated with sulfuric
acid to reduce pH and sent to an oxidizer designed by Fuji
Kasui. Calcium sulfite is oxidized by air or oxygen into
gypsum, which is centrifuged.
Status of Technology
The Moretana scrubber is fitted with four perforated
plates made of stainless steel. The holes range from 6 to
12 mm in diameter and the plates are 6 to 20 mm thick. Both
dimensions are varied depending on the specific scrubbing
situation. The free space in the cross section ranges from
25 to 50 percent. The bottom tray serves mainly as a gas
distributor and the upper three serve as absorbers. The gas
and liquid flows are so adjusted as to maintain a liquor
head of 10 to 15 mm on each plate. The gas velocity is
higher than in usual scrubbers. The design gives extreme
turbulence, producing a foam layer 400 to 500 mm thick. The
mist eliminator is a set of vertical chevron sections mounted
in a horizontal duct after the scrubber. Design data for
the Amagasaki plant, Sumitomo Metal, are as follows:
L/G ratio
Gas velocity in scrubber
Solids content of slurry
pH
Stoichiometry
Fresh water make-up
5.4 liters/Mm
(about 40 gal./lOOO scf)
4 to 5 m/sec
3 to 8 percent
inlet: 8.5-8.8
outlet: 6.5 - 6.7
1.05 - 1.2
15 t/hr
3-43
-------
FLUE GAS
U)
I
4*
*»
NEUTRALIZATION
TANK
ICENJRIFUGE
GYPSUM
GYPSUM
Figure 3-24. Simplified flowsheet of Moretana process.
-------
Evaporation 6 t/hr
Purge stream 9 t/hr
Mist eliminator wash 1.2 t/hr
The Amagasaki plant has been operated well, reducing
S02 emissions from 800 to below 10 ppm. It has been found
that keeping the oxidation in the scrubber below 20 percent
helps prevent scaling.
Evaluation
The process is similar to the Babcock-Hitachi and
Mitsubishi-JECCO processes except for the use of the More-
tana scrubber. The scrubber is highly effective for SO?
removal but causes much mist and a large pressure drop. The
Amagasaki plant has been used also for tests of simultaneous
removal of S02 and N02 by sodium scrubbing, and therefore
has not been operated continuously for a long period with
lime scrubbing. Operation of commercial plants, which
started recently, should allow further evaluation.
OTHER WET LIME/LIMESTONE PROCESSES
IHI-TCA Process
Ishikawajima-Harima Heavy Industires Ltd. (IHI) has
constructed two units at the Kumagaya plant, Chichibu Cement
Co., each with a capacity of treating 104,000 Nm /hr of flue
gas from diesel engines. Flue gas is first cooled to below
80°C by a cooler, introduced into two TCA absorbers in
series, and reacted with milk of lime. The product calcium
sulfite is oxidized by air into gypsum after pH adjustment.
A low slurry concentration (2 percent) is used to reduce
erosion of the plastic balls.
IHI has started construction of another unit for
Shikoku-Sumitomo Joint Thermal Power with a capacity of
treating 450,000 Nm /hr of flue gas from an oil-fired boiler
containing 1300 ppm SO2 and 0.1 g/Nm dust. The unit will
be completed by January 1976. About 90 percent of the S02
3-45
-------
and 50 percent of the dust will be removed by a limestone
slurry. Tests on balls of different materials are under
way.
Chemico-IHI Process
IHI has started building two units, each with a capacity
of treating 900,000 Nm /hr of flue gas from a coal-fired
utility boiler (265 MW), at Isogo Station, Electric Power
Development Co., using Chemico scrubbers (Figure 3-25). The
flue gas passing through an electrostatic precipitator will
be introduced into two Chemico venturi scrubbers in series.
A limestone slurry will be fed to the second scrubber and
then countercurrently to the first scrubber. The calcium
sulfite sludge from the first scrubber will be oxidized by
air after pH adjustment with sulfuric acid. The first unit
is to be completed by early 1976 and the second in late
1976.
Isogo Station is now burning a low-sulfur coal (0.3
percent S) and will burn a coal with 0.6 percent sulfur
after completion of the desulfurization units. Limestone
will be ground to pass 325 mesh 95 percent. About 80 per-
cent of the SO- will be removed. The method of gypsum
disposal has not been decided. Although the flue gas will
be first passed through an electrostatic precipitator, the
scrubber inlet gas will contain a considerable amount of fly
ash with relatively low concentrations of S02; the product
gypsum will contain much fly ash and may not be suitable for
cement or wallboard manufacture.
Kawasaki Lime-Magnesium Process
Kawasaki Heavy Industries originally constructed a wet-
lime process plant for Jujo Paper Co. (Akita plant, 84,000
Nm /hr) in 1973 using a multi-venturi type of low-pressure-
drop scrubber, which suffered from scaling. Kawasaki later
found that addition of magnesium helped prevent scaling and
went on to develop a lime-magnesium process. Flue gas is
3-46
-------
BOILER
E.P.
-•©--r
I.D. FAN
AFTERBURNER
GYPSUM
WASTEWATER
TREATMENT
RETURN LIQUOR
TANK
Figure 3-25. Flowsheet of Chemico-IHI process (Isogo plant, EPDC).
-------
first cooled and then treated with a mixed slurry of calcium
and magnesium hydroxides and gypsum. The reaction product—
calcium and magnesium sulfites and gypsum—is oxidized by
air after pH adjustment with sulfuric acid. The oxidation
forms magnesium sulfate solution and gypsum, which are
separated by means of a thickener and a centrifuge. The
magnesium sulfate solution (about 5 percent) is sent to a
reactor in which lime is added with make-up magnesium hy-
droxide to precipitate magnesium hydroxide and gypsum, which
are sent to the absorber.
Two commercial plants are under construction—one for
the Saidaiji plant, Nippon Exlan, and the other for the
Okazaki plant, Unitika. Both will have a capacity of treat-
ing about 250,000 Nm /hr of flue gas from an industrial
boiler and will be completed by the end of 1975. Limestone
will be used in place of lime in one of the plants. More
than 90 percent of the SO- will be removed by using a stoich-
iometric amount of lime or 1.1 to 1.2 stoichiometric lime-
stone. The gypsum does not grow very well and contains
about 0.5 percent magnesium sulfate but is useful as re-
tarder of cement setting.
Tsukishima Process (TSK Process)
Tsukishima Kikai Co. (TSK) constructed a wet-lime
process plant (20 MW equivalent) using Bahco scrubbers at
Nagoya plant, Yahagi Iron Co., in 1972. The process is
similar to other Japanese processes. There is no plan to
build other plants.
Nippon Kokan Process
Nippon Kokan has operated since 1964 a wet-lime process
plant (at Koyasu), treating tail gas from a sulfuric acid
plant. The system was constructed by Mitsubishi Heavy
Industries using the Mitsubishi-JECCO process. Based on the
experience, Nippon Kokan developed its own wet-lime process,
which is similar to the Mitsubishi-JECCO process except for
3-48
-------
the use of a spray tower type absorber. A commercial plant
for Nippon Sheet Glass
is under construction.
for Nippon Sheet Glass Co. (Yokkaichi plant, 120,000 Nm /hr)
3-49
-------
4. INDIRECT LIME-LIMESTONE PROCESS (DOUBLE-ALKALI TYPE)
INTRODUCTION
Many double-alkali-type processes that use lime or
limestone as a precipitant have been developed in Japan,
including those that use an acidic solution or acid as the
absorbent. The Hitachi-Tokyo Electric process uses activ-
ated carbon as the absorbent and limestone as the precipi-
tant. All of those processes are classified in the category
of "indirect lime-limestone process". Installations with
capacities greater than 20 MW equivalent are listed in Table
4-1. The operation parameters are shown in Table 3-2.
Wet Process
The various processes use different absorbents; a
sodium sulfite solution is used for the Showa Denko, Kureha-
Kawasaki, and Tsukishima processes; an ammonium sulfite
solution for the NKK process; an acidic ammonium sulfate
solution for the Kurabo process; an aluminum sulfate solu-
tion for the Kowa process; and a dilute sulfuric acid with
iron sulfate for the Chiyoda process. The pH values of the
solutions are maintained at 6 to 7 for ammonium and sodium
sulfites, 3 to 4 for ammonium and aluminum sulfates, and 1
for sulfuric acid. The L/G ratios are 1 to 2 (7 to 14
gal./lOOO scf) for the solutions 6f pH 6 to 7, 3 to 10 for
solutions of pH 3 to 4, and 30 to 50 for the acid at pH 1.
The more acidic the solution, the lower the SO2 absorption
capacity, the lesser the problem of scaling, and the easier
the reaction with limestone. Limestone can be reacted with
a sodium bisulfite solution, as in the Showa Denko and
Kureha-Kawasaki processes, but the reaction occurs slowly
4-1
-------
M
Table 4-1. INDIRECT LIME-LIMESTONE PROCESSES
(double alkali)
Process developer
Nippon Kokan
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Chiyoda
Kureha-Kawasaki
Kureha-Kawasaki
Kureha-Kawasaki
Showa Denko
Showa Denko
Showa Denko
Showa Denko-Ebara
Showa Denko-Ebara
Showa Denko-Ebara
Showa Denko-Ebara
Showa Denko-Ebara
Showa Denko-Ebara
Showa Denko-Ebara
Tsukishima
Tsukishima
Kurabo Engineering
Kurabo Engineering
Dowa Mining
Hitachi-Tokyo
Absorbent
precipitant
(NH4)2S03, Ca(OH)2
dil.H2S04> CaCO}
dil.H-SO,, CaCO,
dil.H2S04, CaC03
dil.H2S04, CaCOj
dil.H2S04, CaC03
dil.H2S04, CaCOj
dil.H2S04, CaC03
dil.H2S04, CaC03
Na-SO,, CaCO,
ft J J
NajSO^, CaCO 3
NaoSO_ i CaCO.
* j j
NajSO,, CaCOj
Na2SO,, CaCOj
Na.SO,, CaCOj
Na2S03, CaC03
Na-,30-, CaCO.*
€, J J
Na2SO,, CaCOj
Na2S03, CaC03
Na2S03, CaC03
Na.SO., CaCO.
23 3
Na2SO3, CaCO3
Na-SO,, Ca(OH)2
Na-SO,, Ca(OH),
& J fc
(NH)2S04, Ca(OH)2
(NH4)2S04, Ca(OH)
A12(S04)3, CaCOj
Carbon, CaCO3
User
Nippon Kokan
Fuji Kosan
Mitsubishi Rayon
Daicel
Mitsubishi Chem.
Plant site
Keihin
Kainan
Otake
Aboshi
Yokkaichi
Mitsubishi Pet. Chem. Yokkaichi
Hokuriku Electric
Hokuriku Electric
Denii Kagaku
Tohoku Electric
Shikoku Electric
Shikoku Electric
Showa Denko
Showa Pet. Chem.
Kanegafuchi Chem.
Nippon Mining
Yokohama Rubber
Nisshin Oil
Poly Plastic
Kyowa Pet. Chem.
Toho Zinc
A j inomoto
Kinuura Utility
Daishuwa Paper
Kurarey
Daicel
Dowa Mining
Tokyo Electric
Toyama
Fukui
Chiba
Shinsendai
Shintokushima
Sakaide
Chiba
Kawasaki
Takasago
Saganoseki
Hiratsuka
Isogo
Fuji
Yokkaichi
Annaka
Yokkaichi
Nagoya
Fuji
Tamashima
Aboshi
Okayama
Kashima
MWa
46
50
27
31
130
230
250
350
37
150
450
450
150
62
93
37
27
27
65
46
43
25
63
85
31
53
82
150
Type of plant
Sintering plant
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Utility boiler
Utility boiler
Industrial boiler
Utility boiler
Utility boiler
Utility boiler
Industrial boiler
Industrial boiler
Industrial boiler
H2SO4 plant
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
HjS04 plant
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
H2SO4 plant
Utility boiler
Year of
completion
1972
1972
1973
1973
1974
1974
1974
1975
1975
1974
1975
1975
1973
1974
1974
1973
1974
1974
1974
1974
1974
1974
1974
1975
1974
1975
1974
1972
Gypsum,
tons/day
15
21
21
23
60
35
180
290
35
40
300
300
110
70
80
CaSO3
20
30
70
35
70
25
40
45
30
40
24
50
* Actual for boilers and equivalent gas flow for other plant*. Boilers are oil-fired.
-------
and requires large reaction vessels. Lime is used for the
Tsukishima, NKK, and Kurabo processes.
For the Chiyoda, Dowa, and Kurabo processes, the S02
absorbents are contacted with air to oxidixe sulfite to
sulfate. Limestone or lime is then added to precipitate
gypsum. For other processes, limestone or lime is added
first to precipitate calcium sulfite, which is then oxidized
into gypsum. Gypsum crystals produced in the double alkali
type process, are usually larger than those produced in the
wet lime-limestone process. Moisture content of the by-
product gypsum after centrifugation ranges from 6 to 12
percent as compared with 8 to 15 percent for the wet lime-
limestone process.
The liquor from the gypsum centrifuge is returned
mainly to the scrubber system. Softening of the liquor,
which is usally needed to prevent scaling, is not necessary
when an acidic solution at a pH below 4 is used.
At most plants, a small portion of the liquor is purged
to maintain concentrations of chloride, magnesium, and other
impurities under a certain level. Calcium sulfite obtained
by the slow reaction of limestone and sodium bisulfite grows
into fairly large crystals, which are not difficult to
handle. On the other hand, lime reacts rapidly with a
sodium bisulfite solution to give very fine crystals of
calcium sulfite like those produced by the wet lime-lime-
stone process.
Carbon Absorption
Another type of indirect lime-limestone process is dry
activated carbon absorption, which is used in the Hitachi-
Tokyo Electric process. The carbon that has absorbed SC^ is
washed with water to give a dilute sulfuric acid of 15 to 20
percent concentration. The acid is treated with powdered
limestone to produce gypsum, which is centrifuged to 10 to
12 percent moisture. The process requires large absorption
4-3
-------
towers because gas velocity is kept low (0.5 m/sec) to
obtain 80 to 90 percent removal of the SO,. Hitachi has
3
recently operated a 3000 Nm /hr pilot plant in which SO- is
absorbed with a carbon slurry. The resulting sulfuric acid
is treated with limestone to obtain gypsum.
SHOWA DENKO SODIUM-LIMESTONE PROCESS
State of Development
Showa Denko K. K., one of the largest chemical companies
in Japan, has developed a sodium-limestone process. About
10 commercial plants have been constructed by Showa Denko
and Ebara Manufacturing Co. a licensee of the process (Table
4-1).
Process Description
Figure 4-1 shows a flowsheet of the Chiba plant, Showa
Denko, with a capacity of treating 500,000 Nm /hr of flue
gas from oil-fired boilers (two 75-MW boilers) containing
1200 to 1500 ppm S02 and 4 to 5 percent 02. The flue gas at
160°C is introduced into four vertical-cone type scrubbers
arranged in parallel, washed with a sodium sulfite-bisulfite
solution at a pH of about 7, passed through a mist elimina-
tor, reheated by afterburning, and led to a stack. The
absorbent liquid is charged from the bottom of the scrubbers,
blown up by the gas, and flows back to the liquor inlet by
gravity (Figure 4-2). Very good contact between gas and
liquid particles ensures about 95 percent removal of SO2 and
80 percent removal of dust at L/G 1.1 (about 8 gallons/1000
scf). The liquor discharged from the scrubber has an
Na-SO-j/NaHSOo mole ratio of about 1.4. Most of the liquor
^ -3
-------
SCRUBBER
MIST
ELIMINATOR
- <
FLUE Q&S»| * '
FLUE
OXIDIZER
H20
Figure 4-1. Flowsheet of Showa Denko process (Chiba plant, 500,000 Nm3/hr).
-------
Figure 4-2. Scrubbers (Chiba plant)
Figure 4-3,
By-product gypsum (Chiba plant)
4-6
-------
The calcium sulfite is separated from the sodium sul-
fate solution by filtration; the solution is returned to the
scrubber. Calcium sulfite is reslurried and 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 (Figure 4-3).
2CaS0
= 2 (CaS0
2NaHSO
The bisulfite solution is led to the reactor.
Status of Technology and Plant Operation
Since start-up of the Chiba plant in January 1973, no
problems have occurred with the scrubbing system but occa-
sional problems have occurred with the limestone reaction
system. Whenever trouble occurs, fuel is changed to a low-
sulfur oil containing about 1 percent sulfur, the flue gas
is kept treated by the scrubbers, and some of the sodium
sulfite solution is stored in a tank until the trouble is
over and the whole system resumes operation. The avail-
ability of the whole system from July 1973 to October 1974
is shown in Figure 4-4.
100
£ 50
CO
<:
Jul.
Sep.
Nov .
Jan.
Mar.
May
Jul . Sep
1973
1974
Figure 4-4. Availability of Chiba plant since 1973.
4-7
-------
The reaction of limestone and sodium bisulfite is
carried out at 90°C for 2 hours. This reaction is delayed
by the presence of much magnesium ion in the liquor. There-
fore, a portion of the liquor is purged from the system to
prevent the accumulation of magnesium ion derived from
limestone. The amount of wastewater is about one-half that of
gypsum, which reaches about 130 t/day. The gypsum, con-
taining about 9 percent water and less than 300 ppm Na, has
been sold for wallboard. The sodium sulfate is decomposed
at 60°C at 90 minutes retention time. Some of the operation
paramters are as follows:
Percent oxidation in the system
Pressure drop in scrubber
Power requirement
Capital cost (late 1973)
Desulfurization cost since
start-up
7-8.5 of absorbed S02
250 mm H20
110 kwh/kl oil or 2.2 per-
cent of generated power
$43 (¥13,000)/kW
4 mills/kWh
Evaluation
The scrubber is very effective for the removal of both
SO, and dust. High S09 removal efficiency is attained, by-
£ &
producing gypsum using limestone. The scrubber operation
can be continued even when other process equipment is
undergoing repairs. Consumption of sodium hydroxide is low.
Among its disadvantages, the process is more complex
than the wet lime-limestone process. The capacity of a
scrubber is limited. Use of sulfuric acid is undesirable
for plants whose by-product calcium sulfite or gypsum must
be discarded.
4-8
-------
KUREHA-KAWASAKI SODIUM-LIMESTONE PROCESS
State of Development
Kureha Chemical Industry Co. jointly with Kawasaki
Heavy Industries has developed a sodium-limestone double-
alkali process. The first commercial plant was constructed
by Kawasaki at Shinsendai Station, Tohoku Electric Power.
Four plants are under construction or being designed (Table
4-2).
Table 4-2.
PLANTS USING THE KUREHA-KAWASAKI PROCESS
(All for oil-fired boilers)
User
Tohoku Electric
Shikoku Electric
Shikoku Electric
Confidential
Kyushu Electric
Plant site
Shinsendai
Shintokushima
Sakaide
Buzen
Capacity,
MW
150
450
450
350
250x2
Inlet
S02 ' PPm
600-800
1,000
1,000
1,000-1,300
(1,000-1,300)
Date of
completion
Jan. 1974
Sept. 1975
Oct. 1975
Aug. 1976
Dec. 1976
Process Description
A flowsheet of the Shinsendai plant is shown in Figure
4-5, and plant facilities in Figure 4-6. About one-fourth
of the flue gas from a 600-MW oil-fired boiler, passed
through an electrostatic precipitator by a forced-draft fan,
is fed into a venturi-type precooler and then into a packed-
grid-type scrubber, where the gas is washed with a sodium
sulfite solution (about 20 percent) at pH 7.0 and a L/G
ratio of nearly 2 liters/Nm3 (about 12 gal./lOOO scf). The
gas is then passed through a mist eliminator, reheated by an
afterburner, and led into a stack.
The liquor discharged from the scrubber at pH 6.5 is
first filtered to remove carbon dust and then passed through
a series of five reactors, where powdered limestone, ground
in a vertical tower mill to pass 325 mesh, is reacted to
precipitate calcium sulfite and regenerate sodium sulfite.
4-9
-------
AFTERBURNER
RECYCLE LIQUOR-*-
I
H
O
FLUE GAS
CaS042H20
CENTRIFU6E
Figure 4-5. Flowsheet of Kureha-Kawasaki process.
-------
Absorber
Reactors and
oxidizer
Figure 4-6.
Shinsendai plant, Tohoku Electric
(Kureha-Kawasaki process).
4-11
-------
2NaHSO- + CaCO- = Na0SO^ + C0« + H00
3 3 23 22
A stoichiometric amount of limestone is used and more
than 90 percent is reacted in the reactors heated with
steam. The pH of the slurry at the outlet is 7.3. The
calcium sulfite (50 percent slurry) is separated on a vacuum
filter and washed to remove sodium sulfite. The filter cake
(about 60 percent water) is repulped to 10 percent slurry,
treated with sulfuric acid to reduce the pH, and oxidized by
air bubbles in an oxidizer (at 2 atmospheric pressure)
developed by Kureha and Kawasaki. The gypsum slurry is
centrifuged to less than 8 percent moisture; the separated
liquid is recycled to repulp the calcium sulfite.
A portion of the sodium sulfite is oxidized into sul-
fate in the scrubber by oxygen in the flue gas. A side
stream of liquor from the scrubber is treated to decompose
the sulfate by reaction with sulfuric acid and calcium
sulfite.
Na2S04 + 2CaS03 + H2S°4 + 4H2° = 2(CaSO4"2H20) + 2NaHS03
The slurry from the desulfation unit is filtered, and
the gypsum is sent to the oxidizer for use as a seed to op-
timize crystal growth; the separated sodium bisulfite solu-
tion is heated and stripped to generate SO2. The solution
is recycled to the desulfation unit to reduce sulfuric acid
consumption.
Performance
The Shinsendai plant has been operated smoothly since
its start-up in January 1974. Inlet S02 concentrations
range from 600 to 800 ppm and outlet concentrations are
lower than 10 ppm. The pressure drop in the scrubber and
mist eliminator is 200 mm H2O. There have been no scaling
or plugging problems. Even if scale forms, it will not
accumulate to an appreciable thickness for several years
4-12
-------
because the concentration of calcium ion in the circulating
liquor is less than 10 ppm.
About 20 tons/hr of water are charged to the system and
the same amount is removed by volatilization, as water of
crystallization, and as moisture of gypsum. No wastewater
has been emitted so far. Because magnesium derived from
limestone accumulates in the liquor and interferes with the
reaction of limestone and sodium bisulfite, a water treat-
ment unit to remove magnesium has been installed.
The plant can be operated by two persons per shift.
Evaluation
The SOp removal efficiency is very high (over 97 per-
cent) . Gypsum grows into large crystals and can be centri-
fuged to a very low moisture content (5 to 6 percent) and
thus the loss of sodium is low. Other advantages include
the use of limestone and smooth operation. The process,
however, is complicated and requires many pieces of equip-
ment. The capital cost was $50/kW in 1973 and may be double
that amount in 1974. Moreover, a considerable amount of
sulfuric acid is required. Therefore, the process may not
be suitable for the U.S., where such high SO« removal effi-
ciency and good quality of gypsum are not required.
Kawasaki has been testing the electrolysis of sodium
sulfate to produce sodium hydroxide and sulfuric acid. If
this can be done successfully the desulfurization process
step will be eliminated; the side stream from the scrubber
will be cooled to crystallize sodium sulfate, which will be
separated and subjected to the electrolysis. The by-product
sodium hydroxide will be used for make-up and the sulfuric
acid for decomposition of the unreacted limestone. Although
this process seems sound theoretically, operation of the
whole system may be complex.
Although emission of no wastewater is another advantage
of the process, some means to remove chloride in the liquor
will be required after a long run.
4-13
-------
NIPPON KOKAN AMMONIA SCRUBBING PROCESS
State of Development
Nippon Kokan, one of the largest steel producers in
Japan, has developed an ammonia scrubbing process to combine
ammonia in coke-oven gas with SO- in a waste gas from an
iron-ore sintering plant. A prototype plant with a capacity
of 150,000 Nm /hr of waste gas has been operating at Keihin
Works in the following two ways: 1) ammonium sulfite formed
by the reaction is oxidized to produce ammonium sulfate; 2)
ammonium sulfite is treated with lime to precipitate calcium
sulfite, which is oxidized by air into gypsum, and to re-
cover ammonia, which is returned to the absorbing system.
Because of the recent world shortage of nitrogen fer-
tilizer, Nippon Kokan has decided to install two large
desulfurization units that by-produce ammonium sulfate. One
of them, with a capacity of treating 760,000 Nm /hr of waste
gas, will be completed at Fukuyama Works, Nippon Kokan, by
the end of 1976; the other, with a capacity of 1,130,000
Nm /hr, will be completed at Ogishima Works by late 1977.
In both plants SO- in waste gas from iron-ore sintering
plants will be combined with ammonia in coke-oven gas.
For the sintering, at present, 95 parts of low-sulfur
powdery iron ore (S = 0.03 percent) and 5 parts of coke (S =
0.55 percent) are used, and the waste gas contains about 250
ppm SO-. After the full-scale desulfurization units are
installed, cheaper high-sulfur iron ore will be used to give
about 400 ppm SO- in waste gas. The SO- will be reduced to
30 ppm by scrubbing.
Process Description
A detailed flowsheet of the prototype plant for the
ammonium sulfate process is shown in Figure 4-7. Waste gas
issuing from the sintering plant at a rate of 150,000 Nm /hr
at 110 to 130°C contains 250 to 500 ppm SO-, 10 to 12 per-
3
cent O2, 40 to 60 ppm chloride, and 0.05 g/Nm dust. After
being passed through an electrostatic precipitator the gas
is introduced into a cooler (spray tower) to remove most of
4-14
-------
KMMIM J»UATt WDO
IIQUO*
tn
ZJ SOLUTIO^ TMXSFE* PUW
(ioo • /hr •«»
ABSOUING SOLUTION PUKP ,
FOR COOLING TOWR (100 •3/lvr HI)
AISOMIN6 SOLUTION PUMPS
FOR ABSOAIIN6 TOHER
(ISO «3/»r M» I 3)
SOLUTION TRANSFER PUMP
(100 m'/to H>)
MtOKIUH SULFATE
CIRCULATING PIMP
(ISO m>tttr HI)
ANNON1UM JULFITE AISORIIW SOLUTION
AWONIIM IISUIFITE ABSORB INC SOLUTION
AMHONIUI SM.MTE WIH£» LIQUOR
Ol!AIU[«: |,NM I I4.SOOH
NMWIA AliOMINE TOWtl I.SMM I IS.SOOH
AMKMIIM SAFATC SAIVMTOl! I.ISM I 1S.JOON
• OIIOATIOK TAWtt
EVAPORATOIt
MO* i I.OOOM
1MM I I.OOOM
Figure 4-7. Schematic flowsheet - Nippon Kokan ammonia scrubbing process.
-------
the chloride and dust and then into a Jinkoshi type scrubber
(Figure 4-8), in which five stages of screens are placed
with some inclination. An ammoniacal solution of about 30
percent concentration flows on the lower three stages form-
ing a liquid film, which absorbs SO,,. Water flows on the
upper two stages and reduces the plume, which is formed by
the ammonia scrubbing of S02. About 95 percent of the S02
is removed when the pH of the solution is about 6. Very
little ammonia is lost when the pH 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 re-
turned to the scrubber to absorb S02. The rest of the
solution is sent to an oxidizer, where the sulfite is oxi-
dized into sulfate by air bubbles produced by rotary atom-
izers. The ammonium sulfate solution is evaporated to
produce crystal ammonium sulfate.
For the ammonia-lime process (Figures 4-9 and 4-10),
the SO- absorbing part is the same as in the ammonium sul-
fate process except that no coke-oven gas is used. A por-
tion of the liquor from the scrubber is sent to a reactor
and is reacted with milk of lime (10 percent concentration)
under normal pressure at 100°C. The ammonia released here
is sent to the ammonia absorber to be absorbed by the liquor
from the scrubber. Calcium sulfate and sulfite are precipi-
tated in the reactor. The slurry from the reactor is acidi-
fied with sulfuric 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 of good quality
is obtained. The gas from the oxidizer contains S02 and is
sent to the scrubber.
4-16
-------
Figure 4-8. Jinkoshi scrubber (Nippon Kokan)
Figure 4-9. Ammonia-lime process (Nippon Kokan)
4-17
-------
I
M
00
GAS TO^ STACK
i
SCRUBBER'--,
Ca(OH),
GAS TO PRESCRUBBER
MAKE-UP
(NH4)2S04
RECOVERED WATER
[JJ CENTRIFUGE
X
f~~*!
WASTE GASA
pH OXIDIZER NEUTRALIZE
PRESCRUBBER
SO, RECOVERY
' SECTION
SLUDGE
I
NH, RECOVERY
J SECTION
I I
REGENERATION ,'GYPSUM PRODUCTION i WATER RECOVERY
SECTION SECTION SECTION
Figure 4-10. Nippon Kokan ammonia-lime process,
-------
Status of Technology
The Jinkoshi type scrubber at the Keihin Works is 19
meters high with a cross section of 4.7 by 7.7 meters. It
uses an L/G ratio of about 2 liters/m ; gas velocity is 3 to 4
meters/sec. The pressure drop in the scrubber is about 300
mm H_0.
A model of the scrubber to be used at the Fukuyama
Works (760,000 Nm /hr) is shown in Figure 4-11. In order to
maintain a uniform gas flow, fine mesh screens will be
placed in parallel to the five-stage screens and about 2
inches above them. The pressure drop in the scrubber will
be 350 mm H~O. During a recent operation of the Keihin
£f
plant by the ammonia-lime process, the concentration of SO-
was low (about 250 ppm) and that of oxygen high (12 percent).
Consequently, extensive oxidation occurred in the scrubber,
yielding liquor of the following composition:
(NH4)2S04 2.0 moles/liter
(NHJ-SO. 0.4 mole/liter
NH4HS03 0.6 mole/liter
(NH4)2S203 0.03 mole/liter
These composition data show that the oxidation ratio
was 70 percent. Tests with a gas containing 700 ppm SO-
showed that the ratio was 50 percent and that SO- concen-
tration in the scrubber outlet gas was 50 ppm.
When coke-oven gas is used as the source of ammonia, a
larger amount of ammonium thiosulfate, (NH4)2S_03, is
formed. As the thiosulfate is hardly oxidized in the oxi-
dizer, it is decomposed by addition of sulfuric acid to the
liquor discharged from the oxidizer.
4-19
-------
TREATED
GAS EXIT
REFINING
SECTION
SCREEN
ABSORBING
SECTION
SCREEN
COOLING AND WASHING
SECTION
INLET TO FLUE GAS
TO BE TREATED
-Kr-t-^-Kr-t-
-LT
I*
FEEDING DILUTED
AQUEOUS SOLUTION
RETURNING DILUTED
AQUEOUS SOLUTION
FEEDING
ABSORBING
SOLUTION
FEEDING COOLING AND
WASHING LIQUID
ABSORB ING-^^
SOLUTION
Figure 4-11. Jinkoshi-NKK type scrubber,
4-20
-------
Plume formation has been a problem because the treated
gas has been emitted without reheating. In tests at the
Keihin Works with a portion of the gas (3100 Nm /hr), the
plume almost disappeared when the gas was heated to 130°C
with an afterburner. An afterburner will be installed at
the Fukuyama plant and a wet electrostatic precipitator at
the Ogishima plant to allow comparison of the effectiveness
of these devices in reducing plume emissions.
Economics
Table 4-3 lists the annual requirements for operation
of plants of different capacities by the ammonium sulfate
process using coke-oven gas and by the ammonia-lime process.
Estimated costs for both processes are listed in Tables 4-4
and 4-5.
4-21
-------
Table 4-3. ANNUAL REQUIREMENTS FOR OPERATION OF THE
NIPPON KORAN PROCESSES
1
Ammonia, t
Water, 1000 t
Steam, t
Power, MW-hr
H2S04, t
NaOH, t
CaO, t
Oil, kl
By-product, t
Ammonium sulfate process
300,000
Nm3/hr
332
332
14,110
11,122
1,577
8,300
6,640
500,000
Nm3/hr
498
498
20,750
17,928
1,826
13,280
9,960
800,000
Nm3/hr
830
830
34,860
28,137
3,362
20,750
16,600
Ammonia-lime process
300,000
Nm3/hr
191
166
27,400
12,100
482
69
2,610
8,300
6,930
500,000
Nm3/hr
315
282
47,300
20,200
796
114
4,520
13,280
11,500
800,000
Nm3/hr
498
448
71,500
32,300
1,270
181
7,190
20,750
18,500
The following conditions are assumed: inlet S02 concentration is 400
ppm, outlet 40 ppm, and the gas is reheated to I30°C.
4-22
-------
Table 4-4. ESTIMATED COST OF NKK TYPE AMMONIUM SULFATE SYSTEM (EARLY 1973)
o
Amount of treated gas, Nm /hr
Construction cost [A] (¥ 1000)
Fixed charges [B] {¥ 1000)
Interest, depreciation [B,]
Repair [B-]
Insurance [83]
Administration [64]
Variable expenses C (¥ 1000)
Labor [C.J
Secondary materials [C2]
By-product [D] (¥ 1000)
Desulfurization [E] (¥ 1000)
Unit desulfurization (¥/kl)
1
300,000
810,000
192,774
146,529
24,300
972
20,973
184,458
12,000
172,458
33,200
344,032
1,650
2
500,000
1,100,000
264,704
198,990
33,000
1,320
31,484
280,521
12,000
268,521
49,800
495,515
1,420
3
800,000
1,400,000
345,258
253,260
42,000
1,680
48,318
439,496
12,000
427,496
83,000
701,754
1,250
Remarks
B =
Br
ID —
D M".
B4=
C =
¥ 2
E =
B1 + B2 + B3 + B4
0.1809 x A
0.03 x A
0.0012 x A
0.1 x B2 + B3 + C
C + C
ul L2
,000,000 x 6 men/year
B + C - D
-------
Table 4-5. ESTIMATED COST OF NKK TYPE AMMONIA-LIME SYSTEM (EARLY 1973)
Amount of treated gas, Nm /hr
Construction cost [A] (¥ 1000)
Fixed charges [B] (¥ 1000)
Interest, depreciation [B.,]
Repair [B-]
Insurance [B_]
Administration [B.]
Variable expenses [C] (¥ 1000)
Labor [C.J
Secondary materials [C~]
By-product [D] (¥1000)
Desulfurization [E] (¥ 1000)
Unit desulfurization (¥/kl)
1
400,000
850,000
210,370
153,765
25,500
1,020
30,085
274,334
14,000
260,334
69,720
414,984
1,488
2
800,000
1,200,000
311,909
217,080
36,000
1,440
57,389
536,453
14,000
522,453
139,440
708,922
1,271
3
1,500,000
1,900,000
513,916
343,710
57,000
2,280
110,926
1,049,978
14,000
1,035,978
277,200
1,286,694
1,230
Remarks
B = BI + B2 J
B., = 0.1809 x
B2 = 0.03 x A
B3 = 0.0012 x
B4 = 0.1 x B2
c = cx + c2
¥ 2,000,000 x
E = B + C - D
h B3 + B4
A
A
+ B3 + C
7 men/year
-------
Evaluation
The scrubber is effective and capable of treating a
large amount of gas, up to 1,500,000 Nm /hr with one scrubber.
In the ammonium sulfate process, both SO,, in waste gas and
ammonia in coke-oven gas are utilized. In the ammonia-lime
process, salable gypsum of good quality is obtained with no
scaling problem.
Negatively, the formation of thiosulfate necessitates
additional facilities and the plume problem might not be
entirely solved.
CHIYODA DILUTE SULFURIC ACID PROCESS7
Outline of the Process
Chiyoda Chemical Engineering and Construction Co. has
developed a unique process for SO,, recovery. The flue gas
is washed with dilute sulfuric acid, which contains an iron
catalyst and is saturated with oxygen. SO- is absorbed and
oxidized 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. Commercial
plants using the Chiyoda process are listed in Table 4-6.
Description
A flow sheet is shown in Figure 4-12. Flue gas is
first treated by a prescrubber to eliminate dust and to cool
the gas to 55°C. The cooled gas is led into a packed tower
absorber containing 2-inch Tellerette. Dilute sulfuric acid
(2 to 5 percent H2SO4), which contains ferric ion as a cata-
lyst and is saturated with oxygen, and fed to the packed
tower. About 90 percent of the 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 oxi-
dation. Most of the acid is returned to the absorber at 50
to 60°C, saturated with oxygen. Part of the acid is treated
with powdered limestone (74 percent under 200 mesh) to
4-25
-------
Table 4-6. COMMERCIAL PLANTS USING THE CHIYODA PROCESS
Owner of plant
Nippon Mining Co.
Fuji Kosan Co.
Mitsubishi Rayon Co.
Tohoku Oil Co.
Daicel Co.
Amagasaki Co.
Hokuriku Elect. Co.
Mitsubishi Chem. Co.
Mitsubishi Pet. Chem. Co.
Mitsubishi Pet. Chem. Co.
Gulf Power Co.
Denki Kagaku Co.
Hokuriku Elect. Co.
Toyama Kyodo Elect. Co.
Hokuriku Elect. Co.
Location
Mizushima
Hainan
Otake
Sendai
Aboshi
Kakogawa
Toyama
Yokkaichi
Yokkaichi
Yokkaichi
Florida, U.S.A.
Chiba
Fukui
Kusajima
Toyama
Capacity, Nm /hr
33,500
157,200
90,000
14,070
100,000
36,200
750,000
400,000
150,000
700,000
85,000
120,000
1,050,000
750,000
750,000
Gas source
Glaus plant
Boiler & Glaus
Boiler
Glaus plant
Boiler
Waste gas from
waste liquid
treatment
Power boiler
Boiler
Boiler
Boiler
Power boiler
Boiler
Power boiler
Power boiler
Power boiler
Completion
Nov. 1972
Nov. 1972
Jan. 1973
Feb. 1973
Nov. 1973
Feb. 1974
May 1974
May 1974
Sept. 1974
Sept. 1974
Nov. 1974
Feb. 1975
May 1975
Sept. 1975
April 1976
-------
*»
-J
"^/FLUrGTS**
FILTER| f—» WASTEWATER
Figure 4-12. Flowsheet of Chiyoda process (Toyama plant, Hokuriku Electric)
-------
produce gypsum. A special type of crystallizer has been
developed to obtain good crystalline gypsum 100 to 500
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.
A small amount of wastewater is discharged to prevent the
accumulation of chloride in the circulating liquor because
it promotes corrosion.
Status of Technology
The iron catalyst is less reactive at low temperatures
but is as reactive as manganese catalyst at operating tem-
peratures above 50°C (Figure 4-13). 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 4-14).
The towers of commercial plants are provided with rubber or
FRP linings. Stainless steel is also usable; ferric cata-
lyst works also as a corrosion inhibitor.
A high L/G ratio is required to attain high SO- recovery,
as shown in Figure 4-15; large pumps and a fairly large
absorber and oxidizer are required, as shown in Table 4-7.
Table 4-7.
SIZE OF TOWERS REQUIRED FOR THE CHIYODA PROCESS
(meters)
Capacity, Nm /hr
200,000
400,000
Absorber
Diameter
9.9
16.5
Height
16.5
16.5
Oxidizer
Diameter
4.5
7.0
Height
20.9
20.9
A double-cylinder type reactor (Figure 4-16) including
an oxidizing section in the center and a scrubbing section
in the outer part has been developed recently. The absor-
bing liquor goes down the scrubbing section, then goes up in
the oxidizing section and overflows to the scrubbing section.
The reactor allows some savings in floor space and investment
cost.
4-28
-------
<*>
»•.
O
2
O
H
I
H
X
O
100
80
60
40
20 h
0
tfmmmmmm •••••
..
Mn
I
0
Figure 4-13
20 40
TEMPERATURE, °C
60
Temperature and oxidation
ratio with catalysts.
>1
•O
u
o
o
a
u
1 .4
1.0
0.6
0.2
I
1,000 2,000
S02 CONTENT, ppm
0.3
0.2
0.1
3,000
Figure 4-14. Catalyst consumption.
4-29
(0
•d
I
C71C
EH
W
>H
-------
01
O
in
100
80
60
40
20
LIQUID/GAS RATIO, liter/Mm3
50 100
—O—PHYSICAL-CHEMICAL ABSORPTION
(CHIYODA)
—A—PHYSICAL ABSORPTION
FLUE GAS CONTAINING 1,300 ppm S02
I I I I I I I I I I I
200 400 600 800
LIQUID/GAS RATIO, gal./I,000 SCF
1,000
Figure 4-15. Liquid/gas ratio and
SO2 removal.
GAS OUTLET
LIQUOR
DISTRI-
BUTOR
GAS
INLET
LIQUOR
OUTLET
]DDDDQ[
VX V/ V/ NX
LIQUOR. OUTLET
AIR
INLET
LIQUOR
INLET
Figure 4-16. Double-cylinder type reactor.
4-30
-------
Performance
Except for minor early troubles, the Toyama plant,
Hoduriku Electric, (750,000 Nm /hr) has been in smooth con-
tinuous operation since its start-up in May 1974 (Figures
4-17 and 4-18). SO2 concentrations are about 600 ppm in the
inlet gas, 40 ppm in the scrubber outlet, and 60 ppm after
reheating to 145°C. The particulate contents are 20 to 30,
5 to 10, and 20 to 30 mg/Nm , respectively. An L/G ratio of
30 liters/Nm (about 210 gal./lOOO scf) is used. The power
requirement is 4500 to 5000 kW at full-load operation treat-
ing 500 to 600 ppm SO-. Wastewater (10 to 20 t/hr) is
emitted to maintain the chloride concentration of the liquor
under a certain level. Gypsum grows into large crystals
(Figure 6-7, M); moisture content is 6 to 8 percent after
the gypsum is centrifuged.
Other plants using the Chiyoda process have also oper-
ated well. For example, Aboshi plant, Daicel Co., has been
in smooth operation since its start-up in November 1973.
The plant uses the two-tower system (Figure 4.19) and treats
flue gas from an oil-fired boiler at a rate of 100,000
Nm /hr. S02 is reduced from 1500 ppm to 80 to 100 ppm at an
L/G ratio of about 40 (about 300 gal./lOOO scf) and the gas
velocity in the absorber is 0.6 m/sec. The air requirement
for oxidation has been about 5 times stoichiometric; the air
flow is about 2000 m /hr. Gypsum crystals are smaller than
those by-produced at the Toyama plant (Figure 6-7, N) and
the gypsum contains about 10 percent moisture after being
centrifuged. The product is gray, containing a small amount
of carbon dust. Still it is sold for wallboard production.
It was intended to purge wastewater at a rate of 0.5 t/hr to
keep the magnesium concentration under control. However,
since the oil contains 30 to 40 ppm chloride and the make-up
water contains 20 to 30 ppm, such a purge would allow the
chlorine concentration in the circulation liquor to go as
high as 1000 ppm, which is considered too high from the
4-31
-------
Figure 4-17. Toyama plant, Hokuriku Electric
(Reactor and prescrubber).
Limestone
tank
Crystallizer
'.uLfuric acid
tank
Figure 4-18. Toyama plant, Hokuriku Electric.
4-32
-------
fJH^a $
Mriwiuzsr. . *v?~5.-JS
Prescrubber
^
Absorber
Oxidizer
Figure 4-19. Abosi plant, Daicel Co.
4-33
-------
standpoint of stress corrosion. The current purge is 2 t/hr
of liquor at pH 6 to 8. Total water make-up is 20 t/hr.
Economics
The capital cost was about $30/kW at the time of
construction between December 1971 and April 1973. With
recent sharp inflation, the cost would be $65 to 70 at
present. The Hokuriku plant is operated by two operators
per shift. The requirements at 95 percent load operation
are process water 64 t/hr, fuel for reheating 3 t/hr, steam
1.5 t/hr, and limestone 1.5 t/hr. The amount of by-product
gypsum is 2.7 t/hr at full load. The desulfurization cost
including depreciation (15 percent yearly) is $13/kl oil for
the Toyama plant and $20/kl for the new plants to be constructed.
Evaluation
The process is simple and the plant is easy to operate.
Even in the event that the gypsum-producing system must 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 percent in this case, but SO2
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.
Disadvantages are that large pumps and a fairly large
scrubber and oxidizer are required. Operation of the new
plant of Gulf Power Co. in Florida will allow evaluation of
applicability of this process to coal-fired boilers.
DOWA ALUMINUM SULFATE PROCESS
Outline of the Process
This aluminum sulfate process has been developed by
Dowa Mining Co. Dowa is one of the largest manufacturer of
nonferrous metals in Japan, owning many smelters and sulfuric
acid plants. The aluminum sulfate process has been developed
to desulfurize waste gas from smelters, roasters, and sulfuric
acid plants. The principle of the process is as follows:
4-34
-------
SO- is absorbed in a solution of basic aluminum sul-
fate, A12(S04)3-A1203, of pH 3 to 4 to form A12(S04)3«A12(S03)
The liquor is oxidized by air into A12(SO.)3/ which is then
treated with powdered limestone to precipitate gypsum and to
regenerate the basic aluminum sulfate solution.
Absorption:
Oxidation:
Neutralization:
3S02 =
A12(S04)3-A12(S04)3
3/2 02
+ 3CaC0
3(CaS04.2H20)
State of Development
After tests with a pilot plant with a capacity of 300
•5 3
Nm /hr, a small commercial plant (3300 Nm /hr) was constructed
at the Mobara Works of Taenaka Mining and started operation
in October 1972 to treat waste gas from a molybdenum sulfide
roaster containing 7500 ppm SO, at 100°C. Two commercial
3
units, each with a capacity of treating 150,000 Nm /hr of
tail gas from a sulfuric acid plant, have been built at
Okayama Works of Dowa. One started operation in June and
the other in September 1974. A pilot plant with a capacity
of treating 3000 Nm /hr of flue gas from an oil-fired boiler
has also been in operation. Mitsui Shipbuilding Co. recently
joined Dowa for further development of the process.
Absorbing Liquor
The relations between the composition of basic aluminum
sulfate liquor (Table 4-8) and SO2 absorbing capacity and
the boiling point of the liquor after the SO2 absorption are
shown in Figures 4.20 and 4.21.
Table 4-8. COMPOSITION OF SOLUTIONS IN FIGURES 4.20 AND 4.21
No.
I
II
III
A12O_ in solution g/1
Free
34.4
40.0
45.5
Combined
66.1
58.2
53.2
Total
100.5
98.2
98.7
Basicity, %
34.2
40.8
46.1
4-35
-------
120
25°C IIA
25°C IIB
120
o
co
80
- 40
I I
III
II
0 2 4 6 8 10
SO2, % IN WASTE GAS
Figure 4-20. S0_ absorbing capacity
of the liquors.
0 20 40 60 80 100
SO2 CONTENT IN 1 LITER
OF LIQUOR (gram)
Figure 4-21. Boiling point of
the liquor contain-
ing SO-.
20 r
i.
OJ
IB
i-
0>
LU
to
O.
o
15
10
o
1—4
5
O
O
O
CO
Al 0.7 MOLE/LITER
BASICITY 19.3%, 23°C
Al 0.21 MOLE/LITER
BASICITY 14.9%,
23°C
Al 0.105 MOLE/LITER
BASICITY 14.9%, 20°C
WATER 20°C
0 2,000 4,000 6,000
S02 CONCENTRATION IN GAS PHASE (ppm)
Figure 4-22. SO_ absorbing capacity of dilute liquors.
4-36
-------
Optimum concentration as well as basicity of the ab-
sorbing liquor are selected according to the S02 concentra-
tion of the gas and the removal efficiency required. Nor-
mally liquors at pH 3 to 4, which are more dilute than those
shown in Table 4-8 are used. The relations between the
composition and SO2 absorbing capacity of the dilute liquors
are shown in Figure 4-22.
Figures 4-20 and 4-22 show the S0? absorbing capacity
of liquors at 20 to 30°C for the treatment of tail gas from
a sulfuric acid plant. For treatment of flue gas the liquid
temperature normally reaches 55 to 60°C and thus the S02
absorbing capacity is considerably lowered.
Process Description
A flowsheet of the process is shown in Figure 4-23.
The waste gas is led into an absorber—a TCA scrubber at the
Taenaka plant and a packed tower at the Okayama plant. Each
has a spray for cooling in the lower part. The liquor from
the absorber is led into a tank to which make-up aluminum
sulfate is added. The liquor from the tank is sent to an
oxidizer, where aluminum sulfite is oxidized into sulfate by
small bubbles of air. The oxidizer, which has no moving
parts, has been developed by Dowa. Twice the stoichiometric
amount of air is used (in design). Most of the oxidized
solution is returned to the absorber; a portion is sent to
a neutralizer and treated with powdered limestone (mostly
under 200 mesh) under conditions suitable for the crystal
growth of gypsum.
The slurry from the neutralizer passes through the
thickener and is then centrifuged. All of the liquor from
the thickener and the centrifuge as well as the wash water
of the gypsum are returned to the absorber.
For treatment of flue gas, a cooler is installed to
cool the gas temperature to 80°C using a portion of the
scrubber liquor. A packed tower is used for the scrubbing.
4-37
-------
CLEANED GAS
* * -
1
|_ * CaCO,
WASTE 1
GAS
*
i r
MAKE-UP __J— *— 1
AT /cn \ 1 *? 1- - - fc
,_L
3 4
, A
I
1
1
n T n
H
5
1
p—
R
L_
Al2w"*»J3 i c. r *• Mir\
1 ABSORBER 4 REACTOR
2 TANK 5 THICKENER
3 OXIDIZER 6 TANK
\
••*
J— 1
i
^
_J
~1
1 7\
\ '
GYPSUM
7 CENTRIFUGE
8 TANK
Figure 4-23.
Flowsheet of Dowa aluminum sulfate
limestone process.
4-38
-------
Performance
The Taenaka plant has been in operation since October
1972 recovering more than 95 percent of the SO2 (7500 ppm)
at an L/G ratio of 5 liters/Nm3 (35 gal./lOOO scf). There
is no appreciable problem of scaling. The pipings required
cleaning once every several months during the early operation
to remove soft deposits, but no cleaning has been needed
since 1974.
The units at Okayama (Figures 4-24 and 4-25) have been
in smooth continuous operation since their start-up in June
and September 1974, except for a scheduled stop of the first
unit for one day in October for inspection, in which no
problem was observed. SO? concentration at the inlet has
ranged from 400 to 700 ppm and at the outlet from 2 to 29
ppm at an L/G ratio of 2.5 liters/Nm and liquor temperature of
25°C. The gas velocity in the tower is 1.3 m/sec. A plastic-
packed mist eliminator is placed at the top of the absorber.
No reheating of the gas is required because the temperature
is close to the outside temperature and no plume is formed.
The 02 concentration of the inlet gas is about 5 percent.
About two-thirds of the absorbed SO- is oxidized in the
absorber; the remarkable oxidation is caused by catalytic
action of a small amount of ferric ion. Thus the amount of
air to the oxidizer has been substantially reduced from the
design value, which was twice that of the S0« absorbed. The
concentration of magnesium in the liquor has also increased
slightly during the operation but no wastewater has yet been
purged.
Tests with a flue gas from the burning of heavy oil,
the gas containing 1500 to 1700 ppm SO2/ have indicated that
an L/G ratio of about 8 is required to recover 95 percent
SO2. Addition of a small amount of a soluble metallic
catalyst has lowered the L/G ratio to 5 for 95 percent
recovery. The catalyst promotes not only S02 absorption but
also oxidation. Tests with a flue gas containing 7 to 8
4-39
-------
Figure 4-24. Okayama plant, Dowa Mining
Absorbers (both sides), ox-
idizers (middle).
Figure 4-25.
Okayama plant, Dowa Mining
(Reactors and thickeners).
4-40
-------
percent oxygen using the catalyst have indicated that oxi-
dation occurred completely in the absorber and thus the
oxidizing tower may not be needed.
If some wastewater must be purged to reduce impurities
such as chloride and magnesium, a portion of the liquor will
be neutralized with lime to precipitate hydroxides of alum-
inum and the metallic catalyst, which will be returned to
the system.
A small amount of aluminum is contained in the gypsum
but does not affect the quality of wallboard and cement
produced from the gypsum. The aluminum concentration is
about 0.5 kg per ton of gypsum.
Economics
Investment cost (in late 1974) is about $18/Nm /hr or
$55/kW. Following are operating requirements for the plant,
which treats 300,000 Nm /hr of tail gas containing 650 ppm
CaC03 0.714 t/hr $15/t
A12(S04)3 solution 15 kg/hr 4C/kg
S02:
03 8%)
Water 7.1 t/hr 3.3C/t
Electricity, about 1000 kW
(may be reduced to 600 kW) 3.7<=/kw
Operator 1 per shift
These values indicate that both the investment and the
operating costs are fairly low.
Evaluation
The process is simple and the plant is easy to operate.
Limestone is used, and more than 95 percent of the S02 is
removed at a relatively low L/G ratio. Essentially no
scaling occurs and no wastewater is generated. Investment
and running costs are low. These features indicate that
this process is promising also for flue gas treatment.
4-41
-------
KURABO AMMONIUM SULFATE LIME PROCESS
In this process developed by Kurabo Industries, Ltd.
SO- is absorbed by a slightly acidic ammonium sulfate solution
at pH 3 to 4. The solution is then oxidized by air to give
an acidic ammonium sulfate solution, which is then treated
with lime to precipitate gypsum and to allow recovery of
aqua ammonia, which is returned to the absorbing system.
Ammonium sulfate can be produced, if desired.
State of Development
Kurabo has built several small ammonia scrubbing plants
in addition to many sodium scrubbing plants. Plume forma-
tion, the greatest problem with ammonia process, has been
fairly well solved by the use of a cold, dilute solution;
this method may not be suitable for larger plants, however.
Kurabo has recently developed a method to use an acidic
ammonium sulfate solution as the absorbent to eliminate the
plume and has successfully operated a 2-MW equivalent test
unit. Four commercial plants are presently under construc-
tion (Table 4-9).
Table 4-9. PLANTS USING THE KURABO AMMONIUM SULFATE LIME PROCESS
User
Kurarey
Daicel
Bridge stone
Bridgestone
Plant site
Tamashima
Aboshi
Tosu
Tochigi
Capacity, Nm /hr
100,000
163,000
60,000
80,000
Date of completion
Jan. 1975
Mar. 1975
Aug. 1975
Oct. 1975
Theory of Absorption with Ammonium Sulfate Solution
Plume can be eliminated by use of an acidic absorbing
liquor because the vapor pressure of NH, is less than 1 ppm
with a solution at a pH lower than 4 (Figure 4-26). The
acidic ammonium sulfate solution has a greater capacity for
SO2 absorption than plain water or a saturated calcium
4-42
-------
to
o
I/O
10
-2
10
-3
10
NH^MOLEJLITER) '-
io~3 io-2
S02 + HS03 , MOLE/LITER
Figure 4-26.
Relationship of SO- +
HSO- concentration to
partial pressure of SO2
(60°C).
100
o
CM
O
00
80
:nlet S02
550 ppm
D 800 ppm
ol ,000 ppm
pH 3.7,60°C
j i
8
L/G, LITER/Nm
10
Figure 4-27.
SO2 removal efficiency at the
test unit (5000 Nm3/hr)
Tower diameter, 1 m
Packing height, 2 m
Packing Netring HA-18
•Gas velocity 1.3-1.7 m/sec
4-43
-------
sulfate solution, as shown in Figure 4-27. because of the
smaller pH drop due to the following equilibrium in the
ammonium sulfate solution:
H+ + SO,
HSO,
The minimum L/G ratio (liters/Nm ) required to remove
95 percent of the S02 is shown in Table 4-10. Basic data
for the design of S02 absorbers obtained through the pilot
tests are shown in Table 4-11.
Table 4-10. MINIMUM L/G RATIO REQUIRED FOR 95 PERCENT S02 REMOVAL*
(liter/Nm3)
Absorbing liquor
Composition
CaS04-2H20 - H2O
0.25 mole/1 (NH4)2S04
0.5 mole/1 (NH4)2S04
1.0 mole/1 (NH4)2SO4
Initial pH
7.0
3.5
3.5
3.5
Inlet S02 concentration, ppm
1000
14.0
6.2
5.1
4.2
2000
21.2
7.3
5.8
5.4
3000
27.2
9.4
7.2
6.3
At 60°C.
Table 4-11.
DESIGN BASE OF SO2 ABSORBER
Packing
Tellerette L type
Netring HA- 18
L/G ratio,
liter/Nm3
8
8
Pressure
drop,
mm H20
100
100
Space
velocity,
m/sec
2
1.5
Height of
packing,
m
4
3
Process Description
The flowsheet of the process is shown in Figure 4-28.
Flue gas is first led into a KBCA scrubber and then into a
packed tower absorber. The main function of the KBCA scrubber
is to cool the gas to 60°C and to concentrate the absorbing
4-44
-------
I
4^
U1
CLEANED GAS
FLUE GAS
WATER
AIR
Ca(OH)2
WATER
tl
>
1
« —
rt
2
r
-fc-
^
1
k
fc. . —
i
r
1
1
2
3
KBCA SCRUBBER
OXIDIZER
ABSORBER
4 SLAKING TANK
5 REACTOR
6 LIQUID CYCLONE
7 CENTRIFUGE
8 THICKENER
9 AQUA AMMONIA TANK
Figure 4-28. Flowsheet of Kurabo ammonium
sulfate gypsum process.
70~3
H , MOLE/LITER
Figure 4-29. Oxidation rate of
sulfite ion (40°C)
(HS03+)<10-2 mole/liter
( M++) 2x10-4 mole/liter
-------
liquor (ammonium sulfate solution). More than 90 percent of
the SO2 is removed. The gas is then reheated by the after-
burning of oil. The liquor from the packed tower absorber
is sent to the KBCA unit, concentrated, and then led into an
oxidizer. The pH of the liquor in the oxidizer is adjusted
to from 3 to 4 by adding dilute aqua ammonia and the sulfite
in the liquor is oxidized into sulfate by small bubbles of
air formed by introducing a jet stream of circulating liquor
accompanying air into a pool of the liquor. About 5 times
the stoichiometric amount of air is used. Tests have shown
that Fe catalyst gives an optimum oxidation rate at pH 4
and Mn at pH 3 (Figure 4-29). Actually no catalyst is
added for oxidation because it occurs fairly rapidly at a
3
rate of 0.8 to 1.0 kg mole/m /hr; presumably small amounts
of vanadium and iron derived from the fuel help the oxida-
tion.
Arrangement of the Tamashima plant is shown in Figure
4-30. Most of the liquor from the oxidizer is returned to
the absorber, and a portion is sent to a set of three reac-
tors, where the liquor is treated with milk of lime to
precipitate gypsum. In order to raise the concentration of
the slurry and to increase the retention time of gypsum for
better crystal growth, a portion of the slurry is sent to a
liquid cyclone. The gypsum is returned to the reactor and
the liquor, which contains some gypsum, is sent to a thick-
ener. The overflow from the thickener is returned to the
reactor- and the other portion of the slurry is sent to a
centrifuge. The liquor from the centrifuge and wash water
are sent to an aqua ammonia tank, and the aqua ammonia is
sent to the oxidizer.
The concentration of the absorbing liquor is normally
about 0.5 mole of ammonium sulfate per liter at an L/G ratio
of 8 liter/Nm3. It can be raised to 2.5 moles at the same L/G
ratio without an appreciable decrease of S02 removal effi-
4-46
-------
Figure 4-30. Tamashima plant, Kurarey (Kurabo process)
-------
ciency. The amount of water added to the system, to dis-
solve lime and to wash gypsum, is usually less than that
volatilized in the cooler. Therefore, some water is intro-
duced into the cooler to maintain the water balance. Occa-
sional purging may be required to prevent buildup of chlor-
ide. The by-product gypsum contains about 9 percent moisture
with a bulk density of about 1.06 and pH 8. The average
crystal size is 40 to 60 microns. The gypsum can be used as
an additive for both wallboard and cement.
Ammonium sulfate can be obtained easily by concen-
trating the solution from the oxidizer. In this case, a
nearly saturated solution (2.5 to 3 moles/liter) is used as
the absorbent.
Cost Estimation
A cost estimation is shown in Table 4-12.
Evaluation
No plume is emitted, and no scaling occurs. Both
oxidation and crystallization of gypsum are accomplished at
50 to 60°C without external heating. The pH of the liquor
is kept over 3 to prevent corrosion. All steps are carried
out at atmospheric pressure. A closed system can be a-
chieved. Ammonium sulfate can be produced easily, if de-
sired. The softening step of the circulating liquor is not
needed.
Disadvantages are that the process is not simple,
limestone cannot be used, and the L/G ratio is higher than
for conventional ammonia scrubbing.
OTHER INDIRECT LIME/LIMESTONE PROCESSES
Tsukishima Sodium-lime Process
Tsukishima Kikai Co. (TSK) has constructed a plant
using a sodium-lime double-alkali process (Figure 4-31) for
Kinuura Utilities. The Nagoya plant (60 MW) started opera-
tion in June 1974 (Table 4-1). Sodium bisulfite formed by
4-48
-------
Table 4-12. ESTIMATED COSTS OF KURABO PROCESS'
(1 dollar = 300 yen)
Investment cost, $ thousands
Fixed cost, $ thous./yr
Depreciation
Interest
Total
Running cost, $ thous./yr
Ammonia, $230/t
Lime, $30/t
Oil for reheating, $100/kl
Industrial water, 3
-------
U1
o
Na2C03 MAKE-UP
TANK CaS03 FILTER
GYPSUM FILTER
Ca(OH);
LINE TANK
H2S04 OR S02
REACTOR GYPSl
DESULFATINS SECTION
Figure 4-31. Flowsheet of Tsukishima double-alkali process.
-------
reaction of sodium sulfite and S02 is reacted with lime in
three reactors in series to precipitate calcium sulfite and
to regenerate sodium sulfite. Calcium sulfite is filtered,
repulped, and oxidized by air into gypsum. Sodium sulfate
formed by oxidation of the sodium sulfite is decomposed by
reaction with the calcium sulfite and sulfuric acid, as in
the Showa Denko process. S0_ concentrations range from 750
to 1300 ppm at the inlet and from 90 to 120 ppm at the
outlet.
A plant for Daishowa Paper Manufacturing Co. (Fuji
plant, 85 MW) will be completed in June 1975. S0~ concen-
trations will be 1300 ppm at the inlet and 60 ppm at the
outlet. Sodium sulfate will be separated from the liquor by
cooling and crystallization. About 0.5 t/hr of the sulfate
will be obtained as a by-product.
Hitachi-Tokyo Electric Carbon-Limestone Process
Hitachi Ltd. with Tokyo Electric Power has developed a
dry carbon process. A flue-gas desulfurization plant (150
MW) at the Kashima Station, Tokyo Electric Power, has been
in operation using the process since 1972. Dilute sulfuric
acid (17 percent) is obtained by washing the carbon which
has absorbed SO_ with weak sulfuric acid and water and is
^
treated with limestone to precipitate gypsum of good quality-
The centrifuged supernatant liquor contains fine particles
of gypsum, so fine that recycling for carbon washing would
plug the carbon. Therefore, the liquor is sent to a waste-
water treatment system and then purged.
As an alternative, the station has operated a 15-MW
test unit in which the acid is concentrated to 50 to 70
percent by contact with the hot gases between the electro-
static precipitator and absorbers, and then reacted with
powdered limestone. By the heat of reaction most of the
water is eliminated to produce nearly dry gypsum, which is
pelletized by extrusion to form cylindrical pellets about 20
4-51
-------
mm in diameter and 50 mm long. The pellets are suitable for
charging into a cement mill and also may be suitable for
landfill or throwaway material.
A 3000 Nm /hr pilot plant using a carbon slurry as the
absorbent has been operated successfully at Hitachi's main
laboratory. The resulting H-SO. is neutralized with lime-
stone to give gypsum.
Nippon Steel Chemical Sodium-Lime Process
Nippon Steel Chemical Co. constructed a sodium-lime
double-alkali process plant with a capacity of treating
20,000 Nm /hr of flue gas from an oil-fired furnace in
1972. The plant has been in operation by-producing a
sludge consisting mainly of calcium sulfite, which is used
for landfilling with other materials. There is no plan to
build other plants.
4-52
-------
5. OTHER PROCESSES FOR SO2 RECOVERY
INTRODUCTION
About one hundred relatively small sodium scrubbing
plants are operating in Japan by-producing mainly sodium
sulfite and some sodium sulfate. Those processes were
reviewed in the 1973 technology status report , and not much
progress has occurred since then. Major plants using other
processes are listed in Table 5-1.
Wellman-Lord Process
Many plants using the Wellman-Lord process have been
constructed by Mitsubishi Chemical Machinery Co. (MKK) and
also by Sumitomo Chemical Engineering Co. (SCEC). The
reliability of the process has been well demonstrated. A
main problem in the process is the oxidation of sodium
sulfite into sulfate, which does not absorb S02. The sulfate
must be removed from the system, resulting in the loss of
sodium and the need for wastewater treatment.
Magnesia Scrubbing
Three plants are operated, with different magnesium
scrubbing processes, by Mitsui Mining, Onahama-Tsukishima,
and Chemico-Mitsui. A common feature of these processes is
the production of large MgSO.,-6H2O crystals (200 microns or
so), which are much easier to filter and dry than are the
small MgS03=3H20 crystals. Neither the Mitsui Mining nor
Onahama plant has encountered any problem in the filtration
and drying steps, which were troublesome at Boston Edison
Co. The Idemitsu Kosan plant, which recently started oper-
ation of a process based on the Chemico-Mitsui process,
returns the recovered SO2 to a Claus furnace for sulfur
production; the other plants by-produce sulfuric acid.
5-1
-------
(Jl
I
to
Table 5-1. SULFUR DIOXIDE SCRUBBING INSTALLATIONS IN JAPAN THAT
BY-PRODUCE SULFURIC ACID AND SULFUR
Process developer
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-MKK
Hellman-SCEC
Hellman-SCEC
Hellman-SCEC
Hellman-SCEC
Hellman-SCEC
Ohahama-Tsukishima
Mitsui Mining
Chemico-Mitsui
Sumitomo Shipbuilding
Shell
Mitsubishi-IFP
TEC-IFP
Absorbent
Na2S03
Na2S03
Na2S03
Na2S03
Na2S03
Na2SO3
Na2SO3
Na2S03
Na2S03
Na2S03
Na2S03
Na2s°3
NBjSO,
MgO
MgO
MgO
Carbon
CuO
(NH4)2S03
(NH4)2S03
User
Japan Synth. Rubber
Chubu Electric
Japan Synth. Rubber
Toyo Rayon
Mitsubishi Chem.
National Railways
Kurashiki Rayon
Company SKD
Toa Nenryo
Sumitomo Chiba Chem.
Fuji film
Sumitomo Chiba Chem.
Sumitomo Chem.
Onahama Smelter
Mitsui Mining
Idemitsu Kosan
Kansai Electric
Showa Yokkaichi
Maruzen Oil
Fuji oil
Plant site
Chiba
Nishinagoya
Yokkaichi
Nagoya
Mizushima
Kawasaki
Okayama
Yokkaichi
Kawasaki
Chiba
Fuji
Chiba
Niihama
Onahama
Hibi
Chiba
Sakai
Yokkaichi
Shimozu
Chiba
MW*
70
220
150
103
186
217
127
124
23
120
50
180
50
28
25
162
53
45
14
3
Type of plant
Industrial boiler
Utility boiler
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Claus furnace
Industrial boiler
Industrial boiler
Industrial boiler
Industrial boiler
Copper smelter
H2SO. plant
Claus and boiler
Utility boiler
Industrial boiler
Claus furnace
Claua furnace
Year of
completion
1971
1973
1974
1975
1975
1975
1975
1977
1971
1973
1974
1975
1975
1972
1971
1974
1971
1974
1974
1974
By-product,
tons/day
H2S04 40
H2S04 80
H2SO4 40
H2S04 45
H2S04 80
H2S04 100
H2S04 60
H2S04 55
S
H2S04 50
Liquid S02 12
H-SO. 80
H2S04 23
H,S04 220
H2S04 16
S
H2S04 15
S
S
S
* Actual for boilers and equivalent gas flow for others. Boilers are oil-fired.
-------
Ammonia Scrubbing-IFF Processes
Two relatively small plants, each with an ammonia
scrubber and IFF reactor to by-produce elemental sulfur,
were constructed by Mitsubishi Heavy Industries and Toyo
Engineering. Both have encountered problems and are now
being improved.
Dry Processes
Three dry processes are being applied to prototype
plants: two activated-carbon processes by Hitachi-Tokyo
Electric and by Sumitomo Shipbuilding, and the Shell copper
oxide process. In addition, pilot plants using the dry
sodium absorption process followed by the decomposition of
the resulting sodium sulfate have been operated by Tsukish-
ima Kikai Co. and by the National Research Institute of
Pollution and Resources. Mitsubishi Heavy Industries and
Chubu Electric Power have recently given up the activated-
manganese process because of the difficulty in achieving 90
percent recovery and the economical disadvantage.
WELLMAN-MKK SODIUM PROCESS
State of Development
Mitsubishi Chemical Machinery Co. (MKK) has constructed
several desulfurization plants using the Wellman-Lord process
(Table 5-1).
g
Process Description
A flowsheet and layout of the plant at Nishinagoya
Station, Chubu Electric Power, are shown in Figures 5-1 and
5-2. The plant has a capacity of treating 620,000 Nm /hr of
flue gas from a 220-MW boiler which burns 3 percent sulfur
oil. Specifications for the main equipment are shown in
Table 5-2. The flue gas passing through an electrostatic
precipitator is water-washed and cooled to 58°C in a pre-
cooling section in the lower part of a scrubber and then
passed through an absorbing section (three stages of sieve
trays) to wash with a sodium sulfite solution
Na2S03 + SO2 + H2O = 2NaHS03.
5-3
-------
AHkCK
Ui
so, PKcaa. cowveerre
OZOUE
OJOOftTlOU
Figure 5-1. Flowsheet of the Wellman-MKK process (Nishinagoya Station,
Chubu Electric Power).
-------
en
I
ui
«. -, ft MTKMSD
*•".. \ 0»«,M«
•••-..;>•, DDDDDDOO
N-W ^-r ****
WHOM '*-«. ••«..••..
Irteo ^jw *«.. •••
Figure 5-2. Layout of the FGD plant at Nishinagoya Station.
-------
Table 5-2. SPECIFICATIONS FOR MAIN EQUIPMENT
(NISHINAGOYA PLANT, CHUBU ELECTRIC)
Name of
equipment
Item
Specification
Absorber
Fan and duct
Evaporator
Evaporator-heater
Evaporator-
circulation pump
Absorption liquid
supply tank
Regenerative
liquid tank
Converter
Sulfuric acid
tank
Type
Capacity
Size
Type
Capacity
Wind press
Type
Capacity
Main size
Type
Main size
Type
Capacity
Total head
Type
Capacity
Main size
Type
Capacity
Main size
Type
Press. Temp
Main size
Type
Capacity
Main size
Rectangle, sieve-tray system
620,000 Nm3/hr x 1 unit
9m x 14m x 25.7m (height)
Centrifugal blade-type fan
660,000 Nm3/hr x 1 unit
650 mm H20
Vertical cylinder type
18.3 t/hr x 1 16.4 t/hr x 1
4.4 m0 x 917m (height)
Vertical, single current type
by placed
1.7m0 x 10m (height) x 2 units
Axial-flow pump
9700 m3/hr
2.5m
Vertically-placed cylindrical
type
412 m3 x 1 unit
8.5m0 x 9.7 m (height)
Cone-roof
487 m3 x 1 unit
9.3m0 x 8.2m (height)
Vertically-placed cylindrical
type
0.2 kg/cm2 435 - 632°C
2.6m0 x 8.9m (height)
Cone-roof
925 m3 x 2 units
9.7 m0 x 10.7m (height)
5-6
-------
The pH and composition of absorbing liquor are as
follows:
Inlet
Outlet
pH
7.3 - 7.5
5.5
Na2S03, %
20
7
NaHS03, %
2
22
Na2S04, %
5
5
The gas is then passed through two mist eliminator
units. The first a chevron above the sieve trays and the
second a packed vessel (Tellerette packing) in the duct
after the scrubber. The gas is reheated by an afterburner
to 140°C in winter and 110°C in summer.
The scrubber effluent, rich in sodium bisulfite, is
heated in a double-effect evaporator by steam to crystallize
sodium sulfite and to regenerate S02.
Sodium sulfite is separated by centrifuge, dissolved in
water, and returned to the absorber. SO2 gas containing
steam is cooled in a condenser to separate water and sent to
a sulfuric acid plant. The tail gas from the acid plant is
treated by a small auxiliary scrubber for SO2 removal.
The Chubu unit is built almost entirely of stainless
steel.
Water Treatment System
Many pieces of equipment are required for the water
treatment. A portion of the sodium sulfite is oxidized in
the scrubber by oxygen in the flue gas to form sodium sul-
fate. A small amount of sodium thiosulfate forms in the
evaporator. Neither the sulfate or the thiosulfate can
absorb S02 and must be removed from the liquor. To remove
the sulfate, a portion of the liquor from the evaporator
feed tank is sent to a crystallizer, and cooled to 0°C to
crystallize the sulfate, which is separated from the liquor
by a centrifuge. The liquor from the centrifuge is returned
to the feed tank. As the sulfate crystals contain a small
amount of sodium sulfite and bisulfite, they are dissolved
5-7
-------
in a purge stream from the liquor from the precooling section
of the scrubber and further treated along with a small
amount of purge stream from the liquor from the sodium
sulfite centrifuge containing the thiosulfate. The mixed
liquor is treated with sulfuric acid to decompose the sul-
fite, bisulfite, and thiosulfate; it is then aerated (the
SO- released is sent to the auxiliary scrubber), oxidized
with ozone for further decomposition of the thiosulfate,
settled to precipitate solids, neutralized with sodium
hydroxide, and then discharged into the sea along with other
wastewater from power plants. The chemical oxygen demand
(COD) is thus kept below 10 ppm, as required by regulations.
The amount of wastewater from the desulfurization plant
is 70 t/day, of which 40 t/day is derived from the purge
stream from the precooling section.
MKK does not use an oxidation inhibitor, as does Sum-
itomo Chemical Engineering Co., to reduce the formation of
sodium sulfate, because any oxidation inhibitor would in-
terrupt the abatement of COD in wastewater.
9
Performance
The plant was started up in May 1973 (Figure 5-3). At
the beginning of the operation a few problems were encoun-
tered, such as vibration of the sieve assembly, difficulty
in controlling the draft at the ID fan at low load, and high
turbidity of the by-product acid. Those problems were
solved in a few months, and the plant has been in smooth
operation since then. Typical operation data are shown
below:
Inlet S02 1800 ppm
Outlet SO- 140 ppm (scrubber outlet)
^ 3
L/G ratio 0.7 liter/Nm (about 5 gal./
1000 scf)
Pressure drop 500 mm H»O (scrubber and mist
. eliminator)
Make-up sodium hydroxide 7 t/day
5-8
-------
U1
I
10
Absorber
Evaporator
Figure 5-3. Nishinagoya plant, Chubu Electric,
-------
By-product sulfuric acid 80 t/day
Steam Total 24 t/hr (19 t/hr for
evaporation)
Oil for reheating (0.5 percent S)
2.5 kl/hr for reheating to 140°C
1.5 kl/hr for reheating to 110°C
Oil for boiler (3 percent S) 50 kl/hr
Of the make-up sodium hydroxide (7 t/hr), about half is
used to compensate for the loss by sodium sulfate formation
and the rest for other losses.
A major feature of the Nishinagoya plant is the expen-
sive and highly automated control system. The main control
is for the amount of liquor fed to the scrubber, which is
varied to keep a uniform SO2 concentration in the scrubber
exit gas; the boiler load is used as an advance signal for
changes. Only two operators are required.
The high degree of automation is required because of
the widely fluctuating load; the capacity factor is 42
percent and the boiler is shut down every week end. This
wide variation makes necessary other control measures in
addition to automation. The surge volume after the scrubber
was designed to be large enough to allow the evaporator and
acid plant to continue operating at minimum load during
shutdown of the boiler and main scrubber. The acid plant
is difficult to restart if it is shut down. The small aux-
iliary scrubber has been installed to scrub the acid plant
tail gas during such periods.
The liquor is distributed over the sieve trays by a
spray system in order to provide good gas-liquid contact
even at low gas flow. As the liquor readily flows down the
tray when the load falls below 110 MW, the L/G ratio is
increased and the liquor feed rate is kept at a minimum of
18 m /hr to maintain high desulfurization efficiency.
5-10
-------
Evaluation
The Nishinagoya plant is reliable and easy to control.
The plant cost, however, is high - about $6 million in 1972-
73, including $1 million for the control system. The cost
is about 30 percent higher than cost of the wet lime/lime-
stone system. The consumption of sodium hydroxide and steam
and the volume of wastewater are also fairly high. If
wastewater containing sodium sulfate is not purged, some
means will be needed to decompose the sodium sulfate to
recover sodium hydroxide.
ONAHAMA-TSUKISHIMA MAGNESIUM PROCESS3'8
State of Development
Onahama Smelting and Refining Co. jointly with Tsukishima
Kikai Co. (TSK) developed a magnesium scrubbing process and
constructed a plant at the Onahama Works, Onahama Smelting
and Refining Co., with a capacity of treating 90,000 Nm /hr
of waste gas from a reverberatory furnace; the gas contains
15,000 to 25,000 ppm S02- The plant has been operated since
January 1973, by-producing concentrated SO2 gas (10 to 13
percent), which is used for sulfuric acid production.
Process Description
A simplified flowsheet of the process is shown in
Figure 5-4. The waste gas passing through an electrostatic
precipitator and cooler is treated in one of two TCA scrub-
bers, each 4.5 m in diameter and 27 m high, with a magnesium
hydroxide slurry. Well-grown crystals of MgSO_«6H.O are
formed by the reaction with SO2 and are easily centrifuged.
The sulfite is dried in a special dryer with indirect heat-
ing (3 m in diameter, 25 m long) and then calcined in an
oil-fired rotary kiln (3.4 m in diameter, 52 m long). Coke
is added to reduce magnesium sulfate formed in the scrubber
and dryer. The regenerated MgO is slaked and recycled. The
kiln off-gas is washed and fed to the acid plant.
5-11
-------
Ol
I
M
to
J5AS_ ^
ESP
COOLE
Mg(OH)2
SLURRY
¥ / 1
-»i
1
1
1
•->
A
BSO
i
• w _ __ _J I
H2SO
REHEATER I I
MgS03 ' 6H20 CARBON
CENTRIFUGE
KBtK
„
WATER
r
5LAKER
MgO
3 ROTARY KILN H£j
EL
^
Figure 5-4. Simplified flowsheet of Onahama-Tnukishima process.
-------
Performance
SO- in the waste gas is reduced from 15,000 to 25,000
ppm to less than 100 ppm; the removal efficiency is better
than 99.5 percent. The main problem with the process has
been scaling on the scrubber walls due to the crystalliza-
tion of magnesium sulfite. The current practice is to use
two scrubbers alternately every two weeks or so and remove
the scale by washing with sulfuric acid. Since installation
of the extra scrubber, overall system availability has been
good. Ball wear has also been a problem, necessitating
replacement every few months. The balls are made of poly-
ethylene.
Centrifuge and dryer operation has been trouble-free.
Oxidation in the system is about 10 percent. The coke gives
adequate reduction; the concentration of MgSO« in MgO from
the kiln is less than 1 percent. Some larger agglomerates
of MgO, formed during the calcination, are ground for slaking.
Steam consumption is not more than 0.13 t/t SO-, and MgO
make-up is less than 0.08 t/t S02. The loss of MgO is
caused mainly by MgO dust in the kiln gas, which is washed
before passing to the sulfuric acid plant. Consideration is
being given to recovery of the MgO.
Evaluation
The whole system is working well except for the scaling
in the scrubber. The scaling may be caused by the very high
SO- concentration and may not be a problem for usual flue
gas treatment. For treating such concentrated gas, the TCA
scrubber may not be the best choice. With some improvement,
the process may be very useful, particularly for plants that
need sulfuric acid.
5-13
-------
OTHER WET PROCESSES
Sodium Scrubbing Processes By-Producing Sodium Sulfite or
Sulfate
More than 100 sodium scrubbing units in Japan yield
sodium sulfite or sulfate as by-products. Most have capacities
of 10,000 to 150,000 Nm3/hr (the largest one is 300,000
Nm /hr) and treat gases from oil-fired and Kraft recovery
boilers, sulfuric acid plants, glass smelting furnaces, and
similar operations. Various types of scrubbers are used to
recover 90 percent or more of the S02. Major constructors
are Oji and Kurabo (Table 2-5).
In most plants, S02 is absorbed with a sodium sulfite
solution to give a sodium bisulfite solution, which is then
neutralized with sodium hydroxide to produce the sulfite. A
portion of the sulfite solution is returned to the scrubber
and the rest is sold to paper mills in the form of solution
or crystal. Usually sodium hydroxide solution is not used
directly for flue gas treatment because it also absorbs CO2.
Hitachi Ltd. has developed a semi-wet process that uses
sodium hydroxide solution directly for flue gas treatment.
The solution is sprayed from the top of a tower to which a
flue gas is introduced at about 170°C . A powdery product
containing sodium sulfite (about 60 percent), sulfate, and
carbonate (about 20 percent each) is formed and is caught by
dust collectors. The product can be used for Kraft pulp
production. A few commercial units based on this process
have been constructed.
In about 20 units the sodium sulfite is oxidized into
sulfate by bubbling air into the solution. The sulfate is
either purged or recovered as crystal to be used in glass
manufacture and other industries.
Wellman-SCEC Process
Sumitomo Chemical Engineering Co. (SCEC) has constructed
several plants using the Wellman-Lord process, as shown in
Table 5-1. The SCEC process is similar to the Wellman-MKK
process except that SCEC uses a sodium sulfite centrifuge
5-14
-------
and an oxidation inhibitor. The inhibitor depresses the
oxidation of the sulfite into sulfate to less than half but
also affects the oxidation of reducing compounds in waste-
water. Still, the COD of wastewater can be reduced to below
20 ppm, as required by local regulations.
The recovered S02 is used in various ways: it is
returned to a Glaus furnace at the Kawasaki plant, Toa
Nenryo; used for sulfuric acid production at the Chiba
plant, Sumitomo Chiba Chemical; and used as liquid SC>2 at
the Fuji plant, Fuji Film Co., which went into operation a
few months ago. In addition to the plants listed in Table
5-1, a unit is under construction at Wakayama Refinery, Toa
Nenryo, to treat 20,000 Nm /hr of tail gas from a Glaus
furnace to recover S0«, which will be returned to the Claus
furnace.
Magnesium Scrubbing Processes
In addition to the Onahama-Tsukishima process, two
other magnesium scrubbing processes are being used commercially.
Mitsui Mining and Smelting Co. in 1971 constructed at Hibi
)
3
Works a unit treating tail gas (80,000 Nm /hr; 1500 to 2000
ppm S02) from a sulfuric acid plant using its own process,
A cross-flow-type absorber is used, and MgSO_-6H20 is formed.
The sulfite crystal is separated by a centrifuge from the
solution, which contains some magnesium sulfate formed by
oxidation. The sulfite is dried in a rotary dryer and then
calcined in an indirect calciner at 750°C. The regenerated
SO- is returned to the acid plant. The magnesium sulfate
solution is concentrated to produce MgSO4*7H_0, which is
sold for fertilizer and other uses.
Mitsui Miike Machinery Co. recently constructed for
Idemitsu Kosan (Chiba refinery) a Chemico-process plant with
a capacity of treating 500,000 Nm /hr of tail gas from a
Claus furnace. The plant went into operation in November
1974. No details of operation have yet been disclosed.
5-15
-------
Mitsui Shipbuilding Co. constructed a pilot plant using
the Grillo process (magnesium manganese scrubbing) as pre-
viously reported. There has been no notable development
since.
Ammonia Scrubbing - IFF Process
Mitsubishi Heavy Industries has constructed a plant
with a capacity of treating 27,000 Nm /hr of tail gas from a
Claus furnace for Maruzen Oil Co. at Shimozu refinery. The
system incorporates ammonia scrubbing and thermal decompo-
sition with the IFF process to produce elemental sulfur.
The plant went into operation early in 1974 but has had many
problems. Several modifications have been made for improve-
ment.
Toyo Engineering constructed a similar plant (6000
Nm /hr, for Fuji Oil Co. at Chiba refinery), which went into
operation in June 1974 (Figure 5-5). This plant also has
encountered many problems and is now under modification.
The ammonia scrubbing - IFF process is not simple and
plant operation apparently is not easy. Capacity may be
limited because of the limited size of the submerged com-
bustion unit.
Tsukishima Sulfix Process
Tsukishima Kikai Co. (TSK) has been licensed by SCA of
Sweden for the Billerud process, designed to reduce sodium
sulfite in waste liquors by injecting the liquor into an oil
burner operating under partial oxidation conditions. TSK
has recently performed pilot plant work on adapting the
Billerud process to reduction of sodium sulfite obtained
from sodium scrubbing of waste gas (Figure 5-6). Sodium
sulfite solution from the scrubber is reduced in the reactor
and the resulting sodium carbonate is collected in an elec-
trostatic precipitator. The reactor effluent gas containing
4 to 7 percent H~S is sent to a Claus furnace or treated by
^ 3
the Takahax process to convert H2S into sulfur. There is
no plan yet to build a commercial plant.
5-16
-------
I
H
•sj
SECONDARY^
EVAPORATOR\
STACI
SULFUR
RESERVOIR
SULFUR
Figure 5-5. Flowsheet of IFF process offered by Toyo Engineering.
-------
ui
H
00
STACK GAS
ABSORBER
SULFUR RECOVERY
SYSTEM
STEAM
PRECIPITATOR
REACTOR HEAT
RECOVERY
BOILER
•
.••%•
COOLER
BOILER
NaHS
ALKALI SOLUTIO
STORAGE
FILTER
OXIDIZER DISSOLVER
C
SULFUR
SULFUR STORAGE
Figure 5-6. Flowsheet of TSK Sulfix process.
-------
SHELL COPPER OXIDE PROCESS
State of Development
This process has been developed by the Shell group,
Netherlands. Shell built a pilot plant at Pernis (1000
Nm /hr) in 1967 and has operated it for over 20,000 hours.
Japan Shell Technology Co. (2-5, 3-chome, Kasumigaseki,
Chiyoda-ku, Tokyo) has been the licensor of the process in
the Far East. The first commercial plant, with a capacity
of treating 125,000 Nm /hr of flue gas from an oil-fired
boiler, was constructed at Yokkaichi refinery, Showa Yok-
kaichi Sekiyu (SYS) (Figure 5-7). The plant went into
operation in August 1973 by-producing concentrated SO- gas,
which is sent to a Glaus furnace for elemental sulfur pro-
duction.
11 12
Process Description '
The flowsheet of the process at SYS is shown in Figure
5-8. Flue gas at 400°C containing 1300 ppm S02 flows into
one of two parallel reactors (Figure 5-9), where about 90
percent of the S0_ is absorbed by CuO (impregnated into
alumina granules) to form CuSO.. After about 90 minutes
"acceptance flow," the gas is shifted to the other reactor.
Steam is introduced into the first reactor for a short time
to purge the flue gas, and then a reducing gas (hydrogen at
SYS) is passed through the reactor, producing a regeneration
off-gas that contains S0_, steam, some hydrogen and inert
matter. The CuSO is reduced to copper metal in this re-
generation step. After the regeneration is over, steam is
introduced again to purge hydrogen prior to the introduction
of flue gas. The total time of the hydrogen and steam
injections is equal to that of the flue gas injection and
thus the two reactors serve as "acceptor" and "regenerator"
alternately. One cycle takes about 3 hours. The metallic
copper formed in the regeneration step is immediately oxi-
dized in an early stage of acceptance by oxygen in the flue
gas. Therefore, the actual accepting material is CuO.
5-19
-------
Figure 5-7. Yokkaichi plant, SYS
(Shell process).
5-20
-------
en
I
REGENERATION GAS
EXCESS SO, TO
ABSORBER STRIPPED 2
OFF-GAS WATER CLAUS UNIT
TREATED
FLUE GAS
OPEN
BYPASS
FLUE GAS
TO REACTOR
JBLOWER
REGENERATION
OFF-GAS
400°C
BOILER
FEED WATER
ABSORBER! *
"-S"
STRIPPER
g-* STEAM
ACCEPTANCE TIME:120 m1n.
Figure 5-8. Flowsheet of Shell process (Yokkaichi plant, SYS).
-------
TREATED FLUE GAS
PURGE OFF-GAS
PURGE
REGENERATION
GAS
VALVE
t
REGENERATION
OFF-GAS
FLUE GAS
Figure 5-9. Reactor
(Shell process).
5-22
-------
Because the SO- flow rate from the regenerator varies
from nil to maximum every 90 minutes, a wet-type absorber-
stripper system is installed to produce a uniform flow to
the Claus furnace. The regenerator off-gas is passed through
a waste-heat boiler and a quench column and then introduced
into the absorber. In the absorber, SO- is absorbed in
water under some pressure. More than 99.5 percent of the
S02 is recovered. The absorber off-gas containing hydrogen,
hydrocarbons, and a little SO2 is sent to the boiler for
burning and S02 recovery. The liquor discharged from the
absorber is sent to the stripper to release SO2, which is
sent to the Claus furnace.
Performance
The SYS unit encountered a few problems after its
start-up in August 1973. The problems included corrosion of
the quench column and sticking of PRC valve on a hydrogen
by-pass line; both have been solved. Another problem has
been plugging of the waste-heat boiler tubes due to the
deposit of ferrous sulfate formed by corrosion of carbon
steel by regenerated SO-. The plugging may be eliminated by
the use of stainless steel.
The unit underwent the thousandth cycle in January
1975, an indication that net operation reached 3000 hours.
The copper acceptor has shown a slight decrease in activity,
but since the SO- recovery is still satisfactory - nearly 90
percent - the acceptor can be used for many more cycles.
Precautions have been taken to eliminate any danger
that could occur from the use of hydrogen. For example, the
hydrogen is diluted so that the gas has no explosive poten-
tial even when mixed with some flue gas. The vessels are
designed to resist a considerable pressure, which might be
produced in case hydrogen is burned. Neither explosion nor
burning has been experienced.
Steam is injected to the stripper, from which a consid-
erable amount of wastewater containing 20 to 40 ppm (weight)
5-23
-------
sulfur compounds is discharged. Hydrogen consumption runs
to 0.19 to 0.20 kg/kg S recovered.
Evaluation
The reactors are smaller than those of dry carbon
absorption processes with an equal capacity, indicating the
high reactivity of the copper acceptor. The wet absorber-
stripper may be a drawback for other installations, however,
since the stripper requires a considerable amount of steam
and produces wastewater. The water must be treated before
being used for some purpose, for example, as a boiler feed.
There may be other ways to work up the SO- regenerated. In
a larger plant with several reactors, it may be possible to
eliminate the absorber-stripper system.
The Shell process may not be suitable for existing
boilers with normal flue gas temperatures of 120 to 150°C,
because the gas must be heated to 400°C. For a new power
plant, the unit may be installed between the boiler and the
air preheater to reduce the required temperature adjustment.
A high-efficiency hot electrostatic precipitator, which may
be fairly expensive, will be required in this case. On the
other hand, the treated flue gas may be cooled in an air
preheater to as low as 100°C because the flue gas is free
from SO^, and thus a considerable energy saving, about 1.5
percent of the fuel input to the boiler, will be achieved.
Another point to be considered in applying the process
to utility boilers is the fluctuation of the operating load.
Although a hydrogen production plant may be able to change
the operating load, it may be difficult for the plant to
follow the variation of the boiler load.
Two years ago the capital cost of the SYS plant was ¥
1.0 billion ($3.3 million), excluding the hydrogen plant and
Glaus furnace, which are part of other refinery facilities.
The process is more expensive than the wet-lime process but
has the advantages of requiring no reheating and of pro-
ducing sulfur. Moreover, the Shell process may have a
5-24
-------
capability for simultaneous removal of NO and SO by
H •"•
ammonia injection into the acceptor, because copper oxide
can act as a catalyst for the reaction of NO and ammonia to
J\:
form nitrogen.
OTHER DRY PROCESSES
Carbon Processes
Sumitomo Shipbuilding and Machinery Co. constructed a
carbon absorption plant with a capacity of treating 175,000
Nm /hr of flue gas from an oil-fired boiler for Kansai
Electric at its Sakai Station. S0~ is absorbed by moving
beds of activated carbon. After the S02 absorption, the
carbon is heated again in moving beds by an inert gas to
release SO-, which is used for sulfuric acid production.
The plant has been operated smoothly since 1972.
Hitachi Ltd. constructed a carbon process plant for
Tokyo Electric Power. This plant also has been operated
well. But there is no plan to build a new plant with either
the Hitachi or the Sumitomo process, possibly because of the
high investment cost and the difficulty of attaining SO2
recovery of more than 90 percent. Hitachi Shipbuilding has
given up the development of a carbon process using heated
steam for regeneration.
Mitsubishi Manganese Process
Mitsubishi Heavy Industries constructed a dry manganese
process plant for Chubu Electric Power at its Yokkaichi
Station. The plant has a capacity of treating 400,000
Nm /hr of flue gas from an oil-fired boiler and came on-
stream in 1972. Operation and further development of the
process were given up recently, possibly because of the
economic disadvantages and the difficulty of attaining more
than 90 percent S02 recovery.
5-25
-------
Hitachi Shipbuilding Reduction Process
National Research Institute of Pollution and Resources
is working on a process for SO_ absorption with powdered
sodium carbonate followed by decomposition of the product
sodium sulfate by a reducing gas to produce H2S. There has
been no recent progress.
5-26
-------
6. BY-PRODUCTS
INTRODUCTION
Recently in Japan about 6 million tons yearly of SO-
have been emitted, mainly by the burning of heavy fuel oil.
Desulfurization efforts have been made in earnest since
1966. Among various desulfurization processes, those which
first became popular were hydrodesulfurization of heavy oil,
by-producing elemental sulfur, and sodium scrubbing of waste
gases, by-producing sodium sulfite (Figure 6-1). A wet lime
process plant that by-produces salable gypsum has been in
operation since 1964 but not until 1972 was construction
started on many plants by-producing gypsum. Processes that
give by-product sulfuric acid, elemental sulfur, and calcium
sulfite have been developed since 1971. The discarding of
calcium sulfite sludge is not as widespread in Japan as it
is in the United States because of limitations on land
available for disposal. '
Since many desulfurization plants are to be built, it
is likely that in the future the supply of by-products will
far exceed the demand and that a substantial portion of them
will have to be discarded. Gypsum is generally considered
the most reasonable by-product because the demand for it is
increasing and because it can be discarded easily. The
various by-products from waste gas desulfurization processes
are discussed in the remainder of this section.
Sodium Sulfite
The author has reported earlier on the sodium scrubbing
processes by-producing sodium salts. The reasons for the
rapid development of the processes are their simplicity and
6-1
-------
10,000
to
•o
c
o
>- O)
o o
CL
-------
the usefulness of the by-product sodium sulfite for paper
mills. More than 100 plants have been installed, mainly to
treat effluents from relatively small gas sources, industrial
boilers, and chemical plants. Yearly production of sodium
sulfite has reached 320,000 tons and has already filled the
demand and caused a decrease in the selling price (Figure
6-2). Nevertheless, the SO- recovered as sulfite is only 4
percent of the total emission. Asahi Glass Co. recovers SO2
from a glass furnace to produce sodium sulfite, which is
oxidized into sulfate and returned to the furnace. There is
not much demand for sodium sulfate, either. Several smaller
plants produce waste sodium sulfite or sulfate solution.
Not many additional sodium scrubbing plants are expected to
be built in the future.
SULFURIC ACID
The sources and uses of sulfuric acid in Japan are
listed in Table 6-1. Pyrite, which was the major source of
the acid, has been gradually replaced by smelter gas and
sulfur. Production of the acid by flue gas desulfurization
was begun in 1971. The production capacity is expected to
reach 900 tons/day in 1975. But continuing rapid development
cannot be expected because the increase in the demand is
only 200,000 to 300,000 tons yearly.
The Wellman-Lord process has been the major process for
production of sulfuric acid. At present, five plants are in
operation that use the process and seven are under construc-
tion. The sulfuric acid production capacity of those plants
will reach 760 tons/day by the end of 1975.
An SO- recovery plant using the Sumitomo activated-
carbon process has been in operation at the Sakai Power
Station of Kansai Electric, treating 150,000 Nm3/hr of flue
gas from an oil-fired utility boiler. One advantage in
producing sulfuric acid from the recovered SO- by the Well-
man-Lord and Sumitomo processes is that the vessels used for
6-3
-------
Table 6-1.
SOURCES AND USES OF SULFURIC ACID IN JAPAN
(thousands of tons)
Source
Smelter gas
Pyrite
Sulfur
Others
Total
Use
Fertilizer
Others
Total
1971
3,120
3,260
130
65
6,575
2,176
4,429
6,605
1972
3,783
2,340
398
126
6,647
2,321
4,486
6,807
1973
4,310
1,692
855
148
7,005
2,304
4,736
7,040
6-4
-------
producing the acid are small because of the high S02 con-
centration of the gas to be fed into the acid plant—nearly
100 percent for Wellman and 10 to 20 percent for Sumitomo,
as compared with 6 to 10 percent for the gas produced by
pyrite or sulfur burning. There is no plan, however, to
install a larger carbon process plant.
Two magnesium scrubbing plants are in operation using
the Mitsui Mining process and the Onahama-Tsukishima process.
Both are installed in copper smelters with sulfuric acid
plants. The former treats 75,000 Nm /hr of tail gas from a
sulfuric acid plant and the latter 84,000 Nm /hr of conver-
ter gas containing 2 percent S0_. The recovered SO,, is
sent to sulfuric acid plants.
ELEMENTAL SULFUR
Recently in Japan the supply of elemental sulfur has
been provided mainly as the by-product from hydrodesulfuri-
zation of heavy oil (Table 6-2).
Table 6-2.
SUPPLY OF AND DEMAND FOR SULFUR
(thousands of tons)
Supply
Demand
Mined
Recovered
Imported
Total
Domestic
Export
1972
11
560
12
583
545
48
1973
0
685
59
744
678
56
1974 (estimate)
0
792
59
851
752
57
Four processes are currently producing sulfur as a by-
product of waste gas desulfurization: (1) the Wellman-Lord
process with a Glaus furnace; (2) the Shell process with a
Glaus furnace; (3) ammonia scrubbing with an IFF reactor,
6-5
-------
and (4) magnesia scrubbing with a Glaus furnace. A plant
with process (1) has been in operation since 1971 at the
Kawasaki plant of Toa Nenryo, treating tail gas (66,000
Nm /hr) from a Glaus furnace; the gas contains 6000 ppm SO2.
Two plants using processes (2) and (3) have started operation
recently; the Shell process is used at the Yokkaichi plant
of Showa Yokkaichi Oil, treating flue gas (110,000 Nm3/hr)
from an oil-fired industrial boiler, and ammonia scrubbing
is used at the Shimozu plant of Maruzen Oil, treating tail
gas (41,000 Nm /hr) from a Glaus furnace. A plant with
process (4) started operation recently at the Chiba plant of
Idemitsu Kosan, to treat 468,000 Nm /hr tail gas from a Glaus
furnace and an industrial boiler. The recovery of SO2 from
tail gas of the Glaus furnace to return to the furnace may
be achieved fairly economically, but the by-production of
sulfur at power plants would be costly. The sulfur by-
producing processes will be further developed when the
oversupply of other by-products becomes obvious.
Elemental sulfur has also been recoverd by hydrogen
sulfide recovery processes. The Takahax process yields a
fine powder of sulfur, intended for use in agricultural
chemicals. Not many new uses for sulfur have been studied
in Japan, as they have been in the U.S.A.
AMMONIUM SULFATE
Ammonium sulfate was produced until recently at the
Yokkaichi Plant of Chubu Electric using the Mitsubishi
manganese process. The plant discontinued operation re-
cently because of the difficulty of removing more than 90
percent of the SO2 in the flue gas and the economical
disadvantage.
Until a few years ago there were several ammonia scrub-
bing plants treating tail gas from sulfuric acid plants to
by-produce ammonium sulfate. All of the plants were shut
down because of the oversupply of ammonium sulfate. Now
6-6
-------
there are a few small ammonia scrubbing plants treating flue
gas to produce a dilute ammonium sulfate solution to be
discarded. The discarding of ammonium sulfate solution is
to be restricted because it can cause a eutrophication
problem. Because of the present shortage of nitrogen fer-
tilizers in developing countries, a few companies are now
considering building ammonium scrubbing plants to by-produce
ammonium sulfate for export. Nippon Kokan has developed a
process by which SO- in waste gas and ammonia in coke-oven
gas are both recovered to produce ammonium sulfate and has
started construction of two large units. There is some
doubt, however, as to whether a market for ammonium sulfate
can be secured until several years from now.
CALCIUM SULFITE
Not much calcium sulfite has been produced in Japan
because of limitations on its use and on landspace for
discarding it. Mitsui Aluminum Co., which has produced
calcium sulfite sludge since 1972, is going to use the
gypsum production process for new installations because of
the poor properties of the sludge. There is no focus on
sludge stabilization, as there is in the U.S.A.
The calcium sulfite obtained by the wet-lime processes
usually consists of very small crystals about 0.1 micron
thick and about 1 micron long; the material is not easy to
filter. Calcium sulfite from the sodium-limestone processes
of Showa Denko and Kureha-Kawasaki grows into much larger
crystals about 1 micron thick and 10 to 30 microns long. At
the Saganoseki Smelter of Nippon Mining Co., the sulfite
obtained by the Showa Denko process is filtered by a vacuum
filter, mixed with copper ore, and fed into a smelter for
recovery of SO-. For discarding, the sulfite produced by
the sodium-limestone process might be better than that from
the wet-lime process.
6-7
-------
Lion Fat and: Oil Co. , jointly with Idemitsu Kosan, has
recently produced a synthetic paper from fairly pure calcium
sulfite and polyethylene, at a weight ratio of about 70:30.
This new product has some defects and is now undergoing
improvement.
GYPSUM
Marketing of Gypsum
Most of the big S02 recovery plants now under construc-
tion or being planned are oriented toward the by-production
of gypsum for the following reasons: (1) Japan has plenty of
limestone. (2) The value of other by-products, such as
sodium salts, sulfuric acid, and ammonium sulfate, will not
increase much since they are already in oversupply. (3)
Production of elemental sulfur from SO2 in waste gases is
not easy. (4) Japan has little available land on which to
dump calcium sulfite sludge. (5) Demand for gypsum has been
increasing considerably. (6) Gypsum is suitable for dis-
carding in case of oversupply.
The demand for and supply of gypsum in Japan is illus-
trated in Figure 6-3. All of the by-product gypsum has been
used so far for wallboard production and as a retarder for
cement setting because there has been a slight shortage of
gypsum in Japan since 1971. But since so many desulfuriza-
tion plants by-producing gypsum are to be installed, over-
supply of gypsum is considered likely to occur in the future.
Even at present there is a tendency toward oversupply be-
cause of a sharp decrease in wallboard production caused by
a current slump in housing construction.
Use of Gypsum for Wallboard and Cement
For wallboard production, gypsum of an appropriate
crystal size (longer than about 30 microns, thicker than
about 10 microns) and purity are favored. Gypsum obtained
from oil-fired flue gas and from most other gases usually
meets these requirements (Figure 6-4).
6-8
-------
8
c
o
c
o
4~
—
o >-
Z —1
S Q-
UJ ^3
O CO
Oil
B
C
OS
R
P
DEMAND
OU
B
C
>-
_i
0.
o.
oo
OS
R
P
OU
B
C
OS
R
P
—
1970 1973 1976
YEAR
2 ~
DEMAND C:CEMENT B:BOARD OU:OTHER USES
SUPPLY P:PHOSPHOGYPSUM R:RECOVERED OS:OTHER SOURCES
Figure 6-3. Demand for and supply of gypsum in Japan.
6-9
-------
;2WC'.
(M) HzSCU-CaCO, process(Chiyoda,
Hokuriku Electric, Toyama)
(N) HaSCU-CaCO, process
(Chiyoda,Daleel,Aboshi)
(0) Al?(30V)5-CaCO, process
(Dowa, Okayama)
(P) "-ar buii-ii j J J^-Ca'JO , process
(Hitachi - T o ky o Fi 1 ec tric)
(Kashima)
Figure 6-4. Photomicrograms of by-product gypsum (xlOO)
6-10
-------
(E) Ca(OH)2 scrubbing
(Mitsubishi-JP'.CCO ,0naharaa)
(F) CaCO, scrubbing(Mitsubishi-
JECCO, Tokyo K1ectrie,Yokosuka)
f£& 'S^jt^bS'jyi '../tf%
, :£& £V2V *? ^3^ 7/"
X: ^ ^W^ /^ •
-------
(I) Na2SOj-CaCOj process
(Showa Denko, Chiba)
->••**-$}
(J) NaaSOi-CaCOi process
(Kureha-Kawasnki, Tohoku
Electric, Shinsendai)
(K) (N!U )230,-Ca(OH)2 process
(Nippon Kokan, Keihin)
(N:U)2:;,^.-Ca(OH)2 process
( Kur-jbo, Hirakata)
Figure 6-4 (continued).Photomicrogram of by-product gypsum (xlOO)
6-12
-------
The by-products are nearly white or light brown. Most
of the wet process plants in Japan incorporate a cooler or a
prescrubber, where the gas is sprayed with water for cooling
as well as for humidifying and removing most of the dust
that has not been caught by an electrostatic precipitator.
There is a recent trend toward simplifying the process by
reducing the size of the cooler and discharging the dust-
containing liquor from the cooler to the scrubber without
filtration. The dust goes into gypsum, which is then fairly
colored. Users of gypsum for cement and wallboard have
gradually become accustomed to the colored product because
the small amount of dust derived from the oil-fired flue gas
passed through an electrostatic precipitator has no adverse
effect. The gypsum obtained at the new plant of Mitsui
Aluminum Co. from a coal-fired flue gas by the Mitsui-Miike
process contains about 5 percent fly ash, which is acceptable.
The gypsum to be obtained at Isogo plant, EPDC, by treating
a flue gas from low-sulfur coal will contain much more fly
ash and may be useless not only for board but also for
cement.
The thickness of gypsum crystals is generally an im-
portant factor in the strength of wallboard. Crystals
obtained from the wet-limestone processes (Figure 6-4, F and
H) are not very long but have considerable thickness and are
ideal for use in wallboard.
For use as a retarder in cement setting, gypsum should
contain less than about 10 percent moisture because wet
gypsum tends to form a "bridge" in the hopper and cannot be
charged smoothly to the cement mill. Normally the by-
product gypsum contains less than about 10 percent moisture
after being centrifuged. Well-grown gypsum crystals produced
by some of the indirect limestone processes (100 to 500 microns;
Figure 6-4, I and M) contains only 5 to 7 percent moisture
after being centrifuged. The presence of sodium in gypsum
can adversely affect the property of cement but the amount
6-13
-------
of sodium in gypsum produced by the sodium-limestone process
is negligible because of the simplicity of washing due to
the large crystal size. Fly ash, about 10 percent in gypsum,
has no ill effects. Calcium sulfite can be used also for a
retarder in cement setting, replacing a portion of the
gypsum. Magnesium sulfate and calcium chloride in amounts
less than 0.5 percent may have no ill effects on board and
cement production.
Gypsum for Building Material
Because a considerable oversupply of gypsum may occur
in the future, many groups are investigating new uses of
gypsum. The most promising new use is as a building mater-
ial. The usual type of calcium sulfate hemihydrate (3 type)
has lower strength than concrete (Figure 6-5). The hemi-
hydrate of a type has a much larger crystal size and higher
strength than 3 type but is fairly expensive. The form II
anhydrite, which is obtained by heating gypsum at 950 to
1000°C, hydrates fairly rapidly and increases in strength
when a small amount (1 to 2 percent) of potassium sulfate is
added. Recent tests by Onoda Cement Co. have shown that an
anhydrite of good quality can be obtained with by-product
gypsum from S02 recovery if the fly ash content is less than
about 5 percent. A larger amount of fly ash tends to de-
crease the strength.
Technology for reinforcement of gypsum with glass fiber
ha's been developed recently in England. The reinforced
gypsum from a type hemihydrate has compression, bending, and
tensile strengths equal to and an impact strength higher
than asbestos-reinforced concrete.
Gypsum Plastic Composite
An important defect in gypsum as a building material is
its lack of resistance to water. To eliminate this weak-
ness, a gypsum plastic composite (GPC) has been recently
developed in Japan through the cooperation of Mitsui Toatsu
Chemical and Taisei Construction Co. (Figure 6-6). Usually
6-14
-------
in
a.
CO
co
CO
Ixl
OL
Q_
6,000
II-ANHYDRIDE W/G=0.35
4,000 -
2,000
a-HEMIHYDRATE W/G=0.36
3 -HEMIHYDRATE W/G=0.6
ft -HEMIHYDRATE W/G=0.7
AGING, week
400
300 ~,
- 200
- TOO
C3
LU
oc
co
co
co
o
o
Figure 6-5.
Strength of various types of gypsum and
concrete (W/G and W/C mean weight ratio
of water against gypsum and cement, re-
spectively) .
GYPSUM
ADDITIVE
WATER
MIXING
MOLDING
DRYING
EVACUATION
RESIN MONOMER
CATALYST
IMPREGNATION
POLYMERIZATION
FINISHING
t
PRODUCT
Figure 6-6. Process for GPC production.
6-15
-------
a resin monomer such as methyl methacrylate (MMA) or styrene
is used for impregnation. The monomer is polymerized by a
thermal catalytic means. Some results of tests with MMA are
shown in Tables 6-3 and 6-4. GPC has superior strength,
resistance to water, acid and base, and also good workabil-
ity and semi-incombustible property. It may, therefore, be
used as a high-grade building material.
Observations of the broken surface of pieces of ordin-
ary gypsum and GPC by a scanning-type electron microscope
have shown that for gypsum, crystals were not broken but
came apart from each other by stress (Figure 6-7), whereas
for GPC, each crystal was broken, requiring a great stress.
This explains the high strength of GPC.
(M) Gypsum
(N) GPC
Figure 6-7. Scanning-type electron photomicrograms
of broken surface (x 1500).
6-16
-------
Table 6-3,
BLENDING OF MATERIALS
No.
A
A1
B
B1
3-hemihydrate
100
100
100
100
Glass
fiber
0
0
3
3
Water
57
57
63
63
MMA
0
35.5
0
38.1
Table 6-4. PROPERTIES OF GYPSUM AND GPC
NO.
A
A1
B
B1
Specific
gravity,
G/ml
1.274
1.699
1.214
1.663
Compress ive
strength,
kg/cm2
132
720
99
790
Bending
strength,
kg/cm^
52
196
68
274
Wearing,
nun/1000
revolutions
8.0
0.8
20.0
1.0
6-17
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7. COMPARATIVE EVALUATION
In this section the various FGD processes are consid-
ered with specific reference to (1) their output and treat-
ment of wastewater and (2) their capital and operating
costs. A technical evaluation of the major process cate-
gories follows, with discussion of their potential for
application in the United States.
WASTEWATER
As shown in Table 7-1, most Japanese FGD plants purge
wastewater, mainly to prevent the accumulation of impurities
in the circulating liquor. One of the impurities is chlorine,
which is derived from fuel and process water. The accumu-
lation of chlorine causes corrosion. Magnesium is derived
from lime or limestone and interferes with the reaction of
sodium sulfite and limestone.
In the Wellman-Lord process., sodium sulfate and thiosul-
fate accumulate and disturb S02 absorption. The amount of
wastewater from the Nishinagoya plant using the Wellman-MKK
process is relatively small but the water requires extensive
treatment because it contains reducing compounds. Waste-
water from processes by-producing gypsum contains essentially
no reducing compounds because the processes include an
oxidation step; the wastewater can be treated by simple
neutralization and filtration.
The Mitsubishi-JECCO process gives less wastewater than
do others; the water ratio ranges from 0.37 to 0.64 (Table
7-1). The Chiyoda process gives more wastewater because it
uses an acid as the absorbent, which makes it necessary to
7-1
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Table 7-1. WASTEWATER FROM FGD PLANTS (OIL-FIRED BOILERS)
-j
to
Process
Mitsubishi-JECCO
Mitsubishi-JECCO
Mitsubishi-JECCO
Babcock-Hitachi
Chubu-MKK
Showa Denko
Chiyoda
Chiyoda
Hellman-HKK
User
Kanaai Electric
Kyushu Electric
Chubu Electric
Chugoku Electric
Ishihara Chemical
Showa Denko
Daicel Co.
Hokuriku Electric
Chubu Electric
Plant
site
Kainan
Karita
Owasea
Mizushima
Vokkaichi
Chiba
Aboshi
Toyaraa
Nishinagoya
Capacity,
MH*
150
175
750
105
85
150
31
250
220
Inlet
S02
ppra
270
800
1,480
400
1,300
1,400
1,400
610
1,800
Waste-
water
t/hr(A)
1.5
2.9
14.0
4.0
4.4
3.5
2.0
15.0
3.0
Gypsum, 5/hr
Solid (B)
0.9
2.9
29.0
0.9
2.2
5.2
1.0
7.5
Moisture (C)
0.1
0.3
2.9
0.1
0.2
0.5
0.1
0.7
Hater
ratio
A+C
(A+B+C)
0.64
0.52
0.37
0.82
0.67
0.45
0.68
0.73
Haste-
water,
kg/MW-hr
10
17
19
34
47
23
64
60
14
Designed valuei the plant ia under construction.-
-------
keep the chlorine content lower for prevention of corrosion.
Wastewater can be reduced by using a material with greater
corrosion resistance, but this would increase the capital
cost.
Many states in the U.S.A. prohibit the discharge of
wastewater but allow the discarding of calcium sulfite
sludge, which normally contains about 50 percent water. The
water ratio is about 0.5 in this case, about the same as in
the Mitsubishi-JECCO and Showa Denko processes.
It has been argued that the purge of wastewater in
Japan may be one of the important factors contributing to
scale-free operation, because the degree of saturation of
the scrubber liquor might be lowered by adding much fresh
water. A calculation based on operational data, however,
shows that the ratio of the flow rate of purge stream and
scrubber liquor is only about 1 to 1500 for the Mitsubishi-
JECCO process, an indication that the small amount of purge
water may not be significant for the degree of saturation.
Two commercial plants using the wet process have not
purged any wastewater yet. One of them, which went into
operation in January 1974, is the Shinsendai plant, Tohoku
Electric, using the Kureha-Kawasaki sodium-limestone process.
The plant is equipped with a facility for removing magnesium
from the circulating liquor. The chloride content has
gradually increased and has reached 7000 ppm in the liquor;
some tendency for corrosion has been manifest. Chloride
is leaving the system with gypsum which has 6 to 7 percent
moisture. It seems that the chloride input and output have
been almost equalized at the 7000 ppm concentration.
Another plant that has not purged wastewater is the
Okayama plant, Dowa Mining, which went into operation in
September 1974 using the Dowa aluminum sulfate-limestone
process. Magnesium in the liquor has increased, but chlor-
ide has not increased appreciably. The plant treats tail
gas from a sulfuric acid plant, which may contain less
7-3
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chloride than does flue gas. Moreover, the gas temperature
is lower and less input water is needed. In the long run,
removal of magnesium and chloride may be required, particu-
larly for the treatment of flue gas.
The Amagasaki plant Kansai Electric Power, which is
based on the Mitsubishi-JECCO lime process, operated for the
first three months without any wastewater. As chloride
content of the liquor increased substantially, plant oper-
ators started to purge some water (after being treated) to
lower the chloride concentration. It may be more practical
to purge some water after treating it than to install addi-
tional facilities for magnesium removal and to use expensive
corrosion-resistant materials.
Many of the plants with dry absorption processes have
wet systems after the absorption and are not free from
wastewater. Both the Kashima plant, Tokyo Electric, using
the Hitachi carbon process, and the Yokkaichi plant, Showa
Yokkaichi Sekiyu (SYS), using the Shell process, have purged
more wastewater than do some of the plants listed in Table
7-1.
ECONOMICS
The investment cost for an FGD plant is lowest with a
simple sodium scrubbing process that by-produces sodium
sulfite. The demand for the sulfite, however, is limited,
and further notable development of the process cannot be
expected. Among other FGD processes, the wet-lime/limestone
process requires the least investment cost. The cost for a
unit with a capacity of 450,000 to 750,000 Nm /hr (150 to
250 MW) was $25 to 30/kW in early 1973 and is $60 to 65/kW
at present. The cost for indirect lime/limestone processes
is estimated to be 5 to 30 percent higher. The Dowa process
may entail the least capital investment among the indirect
processes because of its simplicity and the requirement for
relatively small vessels. The Kureha-Kawasaki sodium-lime-
stone process seems most costly because it requires many
7-4
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vessels, including one for removal of magnesium from the
circulating liquor; the process is advantageous however, in
that no wastewater is purged. The Wellman-Lord process
seems to be as costly as the Kureha-Kawasaki process because
it requires many units of equipment for wastewater treat-
ment. The investment cost for the dry processes could be
even more than for the Kureha-Kawasaki and Wellman-Lord
processes because dry processes require large absorbers and
relatively complicated systems for treatment of the absorbed
so2.
The operating costs are also the lowest for the wet-
lime/limestone process and may be the highest with some of
the dry processes that consume a reducing gas such as hy-
drogen.
For a new FGD unit with a capacity of 450,000 to 750,000
Nm /hr, the desulfurization cost including the running and
fixed costs (depreciation for 7 years) would be $17 to 20/kl
oil (about 4.5 mil/kWhr) for wet-lime/limestone process and
about 30 percent more for expensive processes. Two years
ago, the cost was $5 to 7/kl oil, while the price difference
between low- and high-sulfur oils was also $5 to 7/kl. At
present, the price of low-sulfur oil is $25 to 30 more per
kiloliter than that of high-sulfur oil (Table 2-3), and the
big difference is encouraging the construction of many FGD
and HDS (hydrodesulfurization) plants.
Thermal electric power generation costs about 2 cents/
kWhr at present and FGD adds 20 to 30 percent to the power
cost. This high energy cost has started to affect the
Japanese economy. Oversupply of FGD by-products - sodium
sulfite, sulfuric acid, and gypsum - is inevitable and will
cause additional difficulty (Figures 6-1 and 6-2). By-
production of elemental sulfur from FGD will become more
important in Japan as in the U.S.A. However, the sulfur-by-
producing FGD processes are very costly except for oil
refineries already equipped with Claus furnaces. The HDS of
7-5
-------
oil might be a better way for sulfur by-production.
Generally speaking, the manufacturers and users of FGD
plants in Japan tend to prefer excessively elaborate systems
and to install deluxe plants in order to ensure smooth
automatic operation under variable conditions and to obtain
very high S02 recovery and clean by-products. This tendency
may have been induced by the fact that the authorities allow
the FGD cost to be added to the cost of the product - power
cost for power companies, for example - while in many states
in the U.S.A. this is not allowed. The process developers
and plant constructors should make further efforts to sim-
plify the processes and to reduce construction costs.
TECHNICAL EVALUATION
Dry Processes
Until several years ago the dry processes were con-
siderably more promising than the wet processes because no
reheating of the gas is required and also because of pos-
sible elimination of wastewater. In practice, however, most
dry processes include a wet process for treatment of the
recovered S02 and thus are not free from wastewater. The
advantage that no reheating is required cannot compensate
for the disadvantages - the need for a large absorber and
regeneration facility and the use of an expensive absorbent
or reducing agent.
Chubu Electric Power abandoned its prototype plant (130
MW) based on the activated manganese process after operating
it for about 2 years.
Although other plants based on the dry process are
being operated and a few other processes are being tested,
there are no plans to build more plants with the dry process.
Very recently another advantage of the dry process has
been recognized in connection with flue gas denitrification,
for which a selective catalytic reduction at 300 to 350°C
appears promising. As the catalyst for the reduction tends
7-6
-------
to be contaminated by SO3/ S02, and dust in flue gas, those
should be minimized prior to the reduction. The wet process
is not favorable because much reheating of the gas is needed.
To reduce the temperature adjustment, it may be preferable
to treat the hot gas at about 350°C from the boiler with a
high-efficiency hot electrostatic precipitator, a dry-
process desulfurizer, and a denitrification unit, and then
send the gas into an air preheater. The high-efficiency hot
electrostatic precipitator is expensive, but such a system
may be used if regulations requiring flue gas denitrifica-
tion are enforced.
Wet Lime/Limestone Process
Wet lime/limestone processes are most promising in
Japan, as in the United States. The main difference is that
in Japan virtually all of the by-product is oxidized into
gypsum, except at the Omuta plant, Mitsui Aluminum Co.
The Mitsubishi-JECCO process has been most widely used
because of its reliability and low energy consumption.
"Saturated operation" without scaling problems has been
achieved in contrast to the "unsaturated operation" at the
Paddy's Run station of Louisville Gas and Electric and at
the Omuta plant. Most plants based on the Mitsubishi-JECCO
process have so far treated gases with low SO- concentration
(300 to 800 ppm) except for a plant of Onahama Smelter,
which treats gas containing 15,000 to 25,000 ppm SO-.
Operation of many larger plants now under construction to
treat flue gas with higher SO- concentration will allow
further evaluation.
The Chemico-Mitsui process also gained much fame from
successful operation of the Omuta plant treating coal-fired
flue gas. There has been much argument concerning the
reason for the scale-free operation. In addition to the
"unsaturated operation," careful control seems to be the key
to success. For example, the pH of the slurry is being
measured manually because an automatic pH meter might not be
quite as reliable. The Mitsui-Miike process has an advantage
7-7
-------
in that it achieves high SO- removal with limestone and
effects pH control without sulfuric acid, similarly to the
two-tower system of the Mitsubishi-JECCO process. Those
processes would be useful also in the U.S.A. provided that
the by-product gypsum can be utilized.
Operation of the Mizushima plant, Chugoku Electric
Power, using the Babcock-Hitachi process has been carried
out smoothly for several months. Further evaluation of the
process and of other wet lime/limestone processes will
require longer operation of larger plants.
Indirect Lime/Limestone Process
Among the double-alkali-type processes, the Chiyoda
process and the sodium-limestone processes of Showa Denko
and Kureha-Kawasaki have been widely employed, presumably
because of their good performance and use of limestone. The
Chiyoda process is simple and plant operation is most easy,
although it requires a big absorber and a high L/G ratio.
Operation of a pilot plant of Gulf Power Co. in Florida,
which will commence shortly using the Chiyoda process, will
allow evaluation of the applicability to flue gas from coal-
fired boilers.
The sodium-limestone processes are rather complicated
because they include a sodium sulfate decomposition step.
The processes require large land space and relatively high
investment cost. On the other hand, sodium consumption is
low - about one-fifth that required for a Wellman^Lord
process plant of equal capacity that does not use an oxygen
inhibitor.
The Dowa aluminum sulfate process seems promising
because of its simplicity of operation at a relatively low
L/G ratio, and use of limestone. The process may be useful
not only for tail gas but also for flue gas. Both the NKK
and Kurabo processes use ammonia scrubbing and can produce
either gypsum or ammonium sulfate. NKK uses an ammonium
sulfite solution at pH 6 with an L/G ratio of 2. Plume
7-8
-------
formation is the main problem for this type of ammonia
scrubbing. Recently a technique for plume prevention has
been developed by Catalytic Co., U.S.A., jointly with TVA
using a precise adjustment of the composition of liquors in
three or four stages in the scrubber. Such fine control may
not be carried out easily for the treatment of waste gas
from a sintering plant, whose flow rates and SO- concentrations
fluctuate very frequently.
The Kurabo process uses an ammonium sulfate solution of
pH 3.5 to 4.0 and is essentially free from plume problems
although a high L/G ratio (about 8) is required. This
process might be advantageous in districts where plume
emissions are severely restricted. On the other hand, the
NKK process may be advantageous for ammonium sulfate pro-
duction because the concentration of the absorbing liquor is
higher, and less energy is needed for crystallization.
Generally, the indirect processes are 5 to 30 percent
more expensive than the wet lime/limestone processes but are
safer with respect to scaling problems. Double-alkali
processes using sodium scrubbing are costly because they
require a desulfation step. As investigators continue to
improve the technology for wet lime/limestone processes,
expensive indirect processes may not be used widely unless
regulations are tightened to require more than 97 percent
S02 removal, for which the sodium processes are advantageous.
Indirect processes that use acid or acidic solutions may be
useful for plants where precise control of the operation is
difficult.
Other Wet Processes
Among other processes, the Wellman-Lord (W-L) process
has been used widely in Japan because of its smooth opera-
tion and of the short supply of sulfuric acid caused by the
shutdown of several old acid plants that used pyrite as raw
material. The major problem for the process is the waste-
water, containing sodium sulfate, sulfite, and a small
7-9
-------
amount of thiosulfate. With the increasing severity of
wastewater regulations, the difficulty of wastewater treat-
ment for the W-L process is becoming apparent. The use of
an oxidation inhibitor by SCEC to reduce the formation of
sulfate and the amount of wastewater increases the diffi-
culty of removing the COD (chemical oxygen demand) in the
water.
The magnesium scrubbing process, which also produces
sulfuric acid, needs fuel for calcination whereas the W-L
process requires steam. For the magnesium process, waste-
water is no problem, but plant operation may not be as
satisfactory as with the W-L process. With further improve-
ment, the magnesium process could be advantageous for sul-
furic acid production; the W-L process may be more suitable
for by-production of elemental sulfur because of the high
concentration and purity of the regenerated SO_.
In Japan, gypsum, sulfuric acid, sodium sulfite, etc.
have been considered more valuable by-products than sulfur.
Thus, Japanese industry has shown little or no interest in
sulfur-producing FGD processes. However, as the supply of
these former products begins to exceed the demand, more
effort will likely be concentrated on the development of
sulfur-generating FGD processes.
POTENTIAL FOR APPLICATION IN THE U.S.A.
Differences Affecting Process Application
Several considerable differences in circumstances in
the U.S.A. and Japan affect the feasibility of applying the
Japanese processes.
(1) In the U.S.A., gypsum and sulfur from natural sources
are plentiful and cheap, whereas these materials are
scarce in Japan. By-products from desulfurization can
be sold for a good price in Japan, a fact conducive to
the development of recovery processes.
7-10
-------
(2) In the U.S.A., most plants have enough space to abandon
waste products, whereas in Japan the space limitations
necessitate maximum utilization of by-products.
(3) In the U.S.A., about 60 percent of the electric power
is generated by burning coal, which gives much fly ash.
In Japan most power plants burn oil, which gives little
fly ash or dust. This is an advantage for recovery of
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 for
chemical plants to utilize desulfurization by-products
and for power plants to use chemicals.
(5) In Japan many plants are close to cities. More than 90
percent removal of SO2 or less than 100 ppm SO2 in
emitted gas is usually required. In the U.S.A. about
80 percent desulfurization or 300 ppm S02 in the gas is
usually acceptable.
(6) Regulations of the purge of wastewater in many states
in the U.S.A. are more stringent than in Japan.
These differences strongly affect the types of processes
to be used and design of the plants. Any Japanese process
to be applied in the U.S.A. should be modified to suit local
conditions. For example, wastewater should be minimized or
eliminated, while prescrubbers and scrubbers can be smaller.
Possibility of Gypsum Production in U.S.A.
FGD processes producing gypsum are highly advanced and
widely used in Japan, while in the U.S.A. throwaway calcium
sulfite processes are common. The author envisions a pos-
sibility for the U.S.A. to generate a considerable amount of
by-product gypsum in the future. At present the U.S.A.
imports about 6 million tons of gypsum yearly.
It is natural that U.S. producers of cement and wall-
board should be reluctant to use the by-product because they
have no experience with it and are concerned about possible
7-11
-------
difficulties. The situation was the same in Japan about 10
years ago: the cement and wallboard producers started to
use phosphogypsum - the by-product of phosphric acid pro-
duction from phosphate ore as shown in Figure 6-4 B and C -
only after they were forced to do so by a shortage of nat-
ural gypsum. They have gradually realized that by-product
gypsum is useful and reliable. FGD gypsum is better than
phosphogypsum because it contains no harmful impurities such
as phosphoric acid and fluorine, which can affect the qual-
ity of cement and wallboard. Japanese producers no longer
hesitate to use FGD gypsum.
Many Japanese FGD plants use sulfuric acid to lower the
pH of calcium sulfite slurry so as to promote the oxidation
into gypsum, but this may not be convenient in most plants
in the U.S.A.
Sulfuric acid may be unneeded with a two-absorber
system, in which the pH of the discharged slurry can be
lowered to a suitable level for the oxidation. Installation
of the additional absorber, oxidizer, and centrifuge re-
quired for gypsum production would add 40 to 50 percent to
the investment cost of the plants with conventional throwa-
way sludge process. Yet the advantage to be gained might
offset the additional expenses in some districts in the
U.S.A., where imported gypsum is used for cement or wallboard
production or where no land is available for sludge disposal.
Gypsum also offers an advantage as a throwaway mater-
ial. Gypsum may be piled up to 100 feet high, as is done at
phosphoric acid plants in Florida, and thus allows great
saving of land space as compared with the use of calcium
sulfate sludge ponds.
Wastewater
In many states in the U.S.A. wastewater discharge is
prohibited, whereas in Japan most FGD plants purge some
water after treating it. When no water at all is discharged
from the system, impurities derived from fuel and process
7-12
-------
water will accumulate in the circulating liquor and cause
trouble. Discarding of sludge, which usually contains about
50 percent water, also disposes of considerable amounts of
the impurities and may prevent their accumulation in signifi-
cant amounts. When gypsum that contains less than 10 per-
cent moisture is discharged without any wastewater, the
chloride concentration in the liquor would normally reach
5000 to 30,000 ppm, depending on the chlorine content of
fuel and process water. Although the high concentrations of
chlorine may not increase scaling in "saturated operation"
as it may in "unsaturated operation," they will promote
corrosion and necessitate the use of corrosion-resistant
materials. It might be feasible for U.S. plants to purge a
small amount of water after giving proper treatment, in-
cluding the removal of heavy metals and other undesirable
components.
7-13
-------
REFERENCES
The process descriptions in this report are based
primarily on the author's visits to the desulfurization
plants, his discussions with the users and developers of
each process, and data made available by them. In addition,
the following publications were used and are cited as
references.
1. The Petroleum Industry in Japan 1973, The Japanese
National Committee of the World Petroleum Congress
(Mar. 1974)
2. Borgwardt, R.H. EPA/RTP Pilot Studies Related to Un-
saturated Operation of Lime and Limestone Scrubbers,
EPA FGD symposium (Nov. 1974 in Atlanta)
3. Ando, J. Recent Developments in Desulfurization of Oil
and Waste Gas in Japan (1973) EPA-R2-73-229, Office of
Research and Monitoring, U.S. EPA, Washington, D.C.
(May 1973)
4. Atsukawa, M., K. Matsumoto, et. al., Removal of S02
from Flue Gas by Wet Process, Mitsubishi Heavy In-
dustries Report (Mar. 1974)
5. Elder, H. W., F. T. Princiotta, G. A. Hollinden and S.
J. Gage, Sulfur Oxide Control Technology, Visits in
Japan—August 1972, U.S. Government Interagency Report,
Muscle Shoals, Alabama (Oct. 30).
6. Yoshida, S., Chemical Economy and Engineering Review,
Vol. 6, No. 3, pp 37-42 (Mar. 1974)
7. Noguchi, M., Status of the Chiyoda Thoroughbred 101
Process, EPA FGD symposium (Nov. 1974)
8. Hollinden, G. A. and F. T. Princiotta, Sulfur Oxide
Control Technology, Visits in Japan—March 1974, U.S.
Government Interagency Report (Oct. 1974)
9. Kawaguchi, K., The Largest Stack Gas Desulfurization
Plant, 220 MW Full Scale at Chubu Power (JAPAN) Nishi-
Nagoya Plant by Wellman-Lord Process, Thermal and
Nuclear Power Vol. 25 No. 208 (1973)
-------
10. All, M. A. J., Material Science, 4(5), p. 398 (1969)
11. Ploeg, J. E. G., E. Akagi, and K. Kishi, "Shell's Flue
Gas Desulfurization Unit at Showa Yokkaichi Sekiyu K.
K. "Petroleum International, Vol. 14, No. 4 (July 1974)
12. Pohlenz, J. B., "The Shell Flue Gas Desulfurization
Process" EPA FGD Symposium (Nov. 1974, in Atlanta)
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPAr600/2-76-013a
ZZI
4. TITLE AND SUBTITLE
SC>2 Abatement for Stationary Sources in Japan
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHoms)jumpei An(Jo (chuo University, Tokyo, Japan)
and Gerald A. Isaacs
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORSANIZATION NAME AND ADDRESS
PEDCo-Environmental Specialists, Inc.
Suite 13, Atkinson Square
Cincinnati, Ohio 45246
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21ACX-130
11. CONTRACT/GRANT NO.
68-02-1321, Task 6
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Subtask Final: 7/74-3/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
report describes the status of desulfurization technology in Japan up to
January 1975, with emphasis on the recovery of SO2 in lime/limestone based proc-
esses. It discusses the current status of desulfurization technologies, including
hydrodesulfurization of oil, decomposition of residual oil, gasification of coal and oil
and flue gas desulfurization (FGD). Major Japanese FGD processes are examined in
detail. Technical and economic aspects of the systems are discussed, and the proc-
esses are evaluated for potential U. S. application. Principal by-products of the
various systems are discussed. The report also contains background information
on energy usage, fuel resources, and projected pollutant abatement requirements in
Japan.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Air Pollution
Sulfur Dioxide
Calcium Oxides
Limestone
Fossil Fuels
Oils
Sp.rtihhers
Residual Oils
Decomposition
Coal
Gasification
Flue Gases
Desulfurization
Energy
b.lDENTIFIERS/OPEN ENDED TERMS
Air Pollution Control
Stationary Sources
Japan
Hydrodesulfurization
Fuel Resources
c. COSATI Field/Group
13B
07B
08G
21D
11H
13H,07A
21B
07D
15. DISTRIBUTION STATEMENT
^nlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
202
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA For.-n 2220-1 (9-73)
7-17
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