United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA-600/S7-83-028 Sept. 1983
Project Summary
S02 Abatement for Coal-Fired
Boilers in Japan
Jumpei Ando
Strict ambient air quality standards
for sulfur dioxide (862) and nitrogen
oxides (NOX) in Japan mandate the use
of various air pollution control tech-
nologies. This report is a compilation
of information on the current status of
SO2 abatement technologies for coal-
fired boilers in Japan. It focuses on flue
gas desulfurization (FGD) and is based
on information gathered from utility
company representatives and FGD pro-
cess developers as well as the author's
research in the field. Various tech-
nologies including wet lime/limestone
and indirect lime/limestone FGD pro-
cesses and combined FGD/Selective
Catalytic Reduction (SCR) systems are
described in terms of process descrip-
tions, development and/or commercial
application status, and economics. De-
tailed operation data are given for many
of the processes.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Strict ambient air quality standards for
sulfur dioxide (SO2) and nitrogen oxides
(NOX) in Japan mandate the use of various
air pollution control technologies. This
report is a compilation of information re-
garding the current status of S02 abate-
ment technologies for coal-fired boilers in
that country. Many of the technologies
either have been or can be applied in the
U.S.
The total capacity of coal-fired utility
boilers in Japan is now4,300 MW(3.7%
of total utility power) and is expected to
reach 10,000 MW (5.6%) in 1985 and
22,000 MW( 10%) in 1990. Several coal-
fired industrial boilers also may be con-
structed in the future All of these boilers
will apply some type of flue gas desulfuriza-
tion (FGD) to reduce SO2 emissions.
Overviews
In sequence, the following paragraphs:
(1) give an overview of FGD use for all
types of boilers in Japan; (2) focus on the
wet lime/limestone process, the most
common FGD process applied to coal-
fired boilers; (3) describe other FGD pro-
cesses for coal-fired boilers, including
several modified wet lime/limestone pro-
cesses and a number of dry processes; (4)
discuss simultaneous removal of both SOX
and NOX as yet another approach to SOX
abatement presently used in Japan; and
(5) describes other coal utilization tech-
nologies (ag., gasification, liquefaction,
and fluidized-bed combustion) which have
been tested as methods of reducing SO2.
Flue Gas Desulfurization
FGD has been widely used for SO2
abatement in Japan and is considered to
be an accomplished technology. Over
1,200 commercial FGD units for various
gas (40,000 MW equivalent) of flue gas to
remove 85-95% of SO2. The principal
byproducts of FGD are gypsum, sodium
sulfite, and sulfuric acid. Table 1 sum-
marizes the approximate number and ca-
pacities of FGD units now in use in Japan.
Sodium scrubbing, producing sodium
sulfite or sulfate byproducts, is the simplest
FGD system. The sulfite can be sold to
paper mills, and the sulfate can be used for
glass production. Over 700 sodium scrub-
bing units with capacities of 3,000 -
300,000 NmVhrO-lOO MW equivalent)
were constructed in Japan between 1968
and 1974.
-------
Table 1. Approximate Number and Capacity of Japanese FGD Units Presently in Operation
Process
Sodium
Wet lime/limestone
Indirect lime/limestone
HSSO+ S, (NH4J2SO4 byproduct
Number
1,000
110
50
30
Capacity
(1.000 NrrP/hr)
50,000
55,000
15,000
12,000
Most Japanese utility boilers utilize wet
lime/limestone FGD scrubbing which pro-
duces salable gypsum. This type of FGD is
relatively inexpensive and produces gypsum
which can be used for cement setting
retarder and wallboard.
About 50 indirect lime/limestone FGD
process units are in use in Japan. The
indirect process is used mainly for medi-
um-sized gas sources with capacities of
50,000 - 500,000 NmVhr since scaling
problems for units of this size can be
prevented easily. However, it is more ex-
pensive than the lime/limestone process.
Another 20 FGD units are presently pro-
ducing a sulfuric acid byproduct Most of
these units use the Wellman-Lord process
to recover concentrated S02 for use in acid
production.
Two large Japanese ammonia scrubbing
units use ammonia in coke oven gas to
recover SO2 from boilers for ammonium
sulfate production. These recovery proc-
esses are not used extensively at power
plants because sulfuric acid or sulfur pro-
duction processes are more costly than
limestone-gypsum processes, and am-
monium sulfate is currently in oversupply.
Almost all Japanese FGD units use wet
processes. Dry processes were studied in
the early stages of FGD development, but
most of them have not been used because
these early investigations showed them to
have low S02 removal efficiencies and
high cost Only four dry process units are
in operation in Japan: three use carbon
adsorption, and one uses copper oxide
absorption. A few units use a semi-dry
process in which an alkaline slurry is
sprayed and a powdery sodium sulfite is
recovered. A semi-dry process being de-
veloped in the U.S. involves spraying lime
slurry to obtain a powdery calcium sulfite.
This method probably will not be used in
Japan because of difficulties with by-
product disposal and with attaining a high
S02 removal efficiency.
FGD processes available in Japan for
use with coal-fired units are listed in Table
2. Most of them are wet processes which
use lime or limestone reagents; one proc-
ess uses red mud. In addition, three dry
processes use activated carbon or electron
beams and have been tested for coal-fired
applications. The wet lime/limestone proc-
ess is described below; the other wet and
dry FGD processes are discussed later.
Wet Lime/Limestone FGD
Processes for Coal-fired Plants
Almost all Japanese coal-fired boilers
with capacities greater than 250 MW use
the wet limestone FGD process to remove
90-95% of S02. The outlet S02 con-
centration for these systems is typically
20-150 ppm.
Table 3 lists all commercial FGD units in
use or planned for coal-fired boilers in
Japan. All units utilize wet lime/limestone
scrubbing and, except for Mitsui Aluminum's
two units for industrial boilers, all are
applied to utility boilers. Figure 1 illustrates
the four types of lime/limestone processes
used in the FGD units.
Type I is the throwaway sludge system
commonly found in the U.S. Only one
Japanese unit is of this type. Type II
processes lower the pH to about 5 by
using three scrubbers and a catalytic ma-
terial for oxidation. The Type II system is
used in three units. Type III systems have
two-stage scrubbers and lower the pH of
the slurry from about 5 to about 4 by
adding a small amount of sulfuric acid.
This type requires a lower investment cost
than does a Type II process, and may be
preferable where sulfuric acid is available
for a reasonable cost. The Electric Power
Development Corporation (EPDC) has four
System III units.
The Type IV FGD process has a pre-
scrubber and uses sulfuric acid for pH
control. The Type IV process was de-
veloped and has been used by Mitsubishi
Heavy Industries (MHI) since the 1960s.
Nearly all of the limestone scrubbing units
Table 2. FGD Processes for Coal-Fired Units
FGD Process Developer
Mitsui Miike Machinery Co. (MMMCf
Ishikawajima-Harima Heavy Industries (IHI)"
Babcock Hitachi K K (BHKJ*
Mitsubishi Heavy Industries (MHIf
Chiyoda Chemical Engineering and
Construction fChiyodaJb
Kawasaki Heavy Industries (KHI)8
Dowa Mining (Dowa)b
Kobe Steef>
Kureha Chemical Industries (Kureha)b
Sumitomo Aluminum1'
Federation of Electric Power Co.c
Electric Power Development Co. (EPDC)
and Sumitomo Heavy Industries (SHIf
Mitsui Mining11
Ebara Corp.d
Reagent
CaO/CaCO3
CaCO3
CaCO3
CaCO3
CaC03
MgO and CaO
Aluminum sulfate
and CaCO3
CaC/2 and CaO
CH3COONa and CaO
Red Mud
Activated Carbon
Activated Carbon,
NH3
Activated Carbon,
NH3
NH3
(Electron Beam)
Byproduct
Sludge/gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Sludge
Sulfur
Sulfur
Sulfuric Acid
Ammonium Nitrate
sulfate
aCommericaL
^Tested with coal. Commercial operation with other gases.
'Tested for coal.
dTested with coal for simultaneous SO. and NOY removal.
-------
Table 3. Commercial FGD Units for Coal-Fired Boilers in Japan
Owner
Mitsui Aluminum
Mitsui Aluminum
EPOC
EPOC
EPDC
EPOC
EPDC
EPDC
EPDC
EPDC
Chugoku Electric
Chugoku Electric
Chugoku Electric
Chugoku Electric
Chugoku Electric
Chugoku Electric
Hokkaido Electric
Hokkaido Electric
Kyushu Electric
Kyushu Electric
Joban Joint
Joban Joint
Tohoku Electric
Tohoku Electric
Tokyo Electric
Tokyo Electric
Shikoku Electric
Shikoku Electric
Plant
Site
Omuta
Omuta
Takasago
Takasago
Isogo
Isogo
Takehara
Takehara
Matsushima
Matsushima
Shimonoseki
Shin-Ube
Shin-Ube
Shin-Ube
Mizushima
Mizushima
Tomato-Atsuma
Tomato-Atsuma
Omura
Minato
Nakoso
Nakoso
Sendai
Sendai
Yokosuka
Yokosuka
Saijo
Saijo
Boiler
No.
1
2
1
2
1
2
1
3
1
2
1
1
2
3
1
2
1
2
2
1
8
9
2
3
1
2
1
2
MW
156
175
250
250
265
265
250
700
500x3/4
500x3/4
175
75
75
156
125
156
350x1/2
600
156
156
600
600
175
175
265
265
175
250
N/R*
R
N
R
R
R
R
R
N
N
N
R
R
R
R
R
R
N
N
R
R
N
N
R
R
R
R
R
R
FGD
Constructor
MMMC"
MMMC
MMMC
MMMC
IHIC
IHI
BHKd
IHI
IHI
BHK
MHIe
MHI
MHI
MHI
BHK
BHK
BHK
MHI
MHI
MMMC
MHI
MHI
BHK
BHK
MHI
MHI
KHI'
KHI
Year of
Completion
1972
1975
1975
1976
1976
1976
1977
1982
1981
1981
1979
1982
1982
1982
1983
1983
1980
1984
1982
1983
1983
1983
1983
1983
1984
1984
1983
1984
Type
See Figure 1
1
II
II
II
III
III
///»
Ilia
IV
IV
lye
iyg
/v»
/V»
IV9
IV9
MB
IV
IV
III
W9
/V»
IV
IV
/V«
n/a
IV
IV
aNew or retrofit.
bMitsui Miike Machinery Co.
Ctshikawajima-Harima Heavy Industries.
dBabcock Hitachi K. K.
e Mitsubishi Heavy Industries.
'Kawasaki Heavy Industries.
9Selective catalytic reduction of NOX is also applied.
constructed since 1979 use the Type IV
process.
Table 4 shows the capacities, types of
scrubbers, and operational parameters of
the wet lime/limestone FGD units for coal-
fired utility boilers in use in Japan.
Most of the new FGD units for coal-fired
boilers either built since 1 978 or under
construction have a prescrubber with a
separate liquor loop to remove impurities
in flue gas such as fly ash, chloride, and
fluoride. They also employ low pressure
drop scrubbers and a rotating gas-gas
heater (heat exchanger) for gas reheating
and for water conservation.
All FGD units in Table 3 use limestone
ground so that over 95% passes through
325 mesh at a stoichiometry of 1.00-1.05
to remove 94-97% of inlet S02. Gas
reheating adds a small additional amount
of S02 so that the overall S02 removal
efficiencies are 90 - 95%. The dust removal
efficiencies of the units are 70-90%.
The most significant operational problem
associated with the lime/limestone FGD
process has been the formation of gypsum
scale in the scrubber and mist eliminator
systems. In Japan these scaling problems
have largely been solved, resulting in a
reliability rate of more than 99% for lime/
limestone FGD units.
Next to scaling, corrosion is the most
serious problem associated with FGD sys-
tems. This problem has been solved by
using suitable materials and good lining
fabrications. With these measures FGD
operations have become so reliable that
not a single FGD unit in Japan has a stand-
by scrubber, although most units have
stand-by pumps and centrifuges.
A limestone FGD unit for a 500 MW
coal-fired boiler requires 40-60 1/hr of
water. Water is fed into the Type II and III
process (Figure 1) scrubbers and into both
the prescrubber and scrubber of Type IV.
To prevent the accumulation of impurities
such as chloride and fluoride derived from
coal, 5-30 1/hr of wastewater must be
purged. In atypical FGD wastewater treat-
ment system, the wastewater from the
prescrubber and scrubber is treated with
lime to precipitate heavy metals and fluoride
prior to filtration. The filtrate is treated to
remove dithionate S20e= which can
cause a chemical oxygen demand (COD).
Treated FGD wastewater typically has a
pH of 6.5-8.5 and contains less than 10-
15 mg/l each of suspended solids and
COD, less than 15 ppm fluoride, and less
than 1 ppm oily material.
The estimated FGD cost for a 500 MW
coal-fired boiler with a limestone-gypsum
process unit and a gas-gas heater is shown
in Table 5. The annualized FGD cost in
1981 was about 1.9 ¥/kWhr.* About
70% of the cost consists of the fixed cost
with a 7 year depreciation schedule. When
the annualized cost is based on a 15 to 20
year depreciation schedule, as is commonly
done in the U.S., the annualized cost is
considerably lower.
Table 6 shows a rough estimated cost
for power generation at a 1000 MW plant
with FGD, Selective Catalytic Reduction
(SCR), and an electrostatic precipitator
(ESP) for flue gas treatment The estimated
annualized cost of power generation for
(') $1 =¥250.
-------
FG
m
ff
s
r
i
i
"^
ft
5
Pond
V////////////////A
CaC03
(ID
(HI)
(IV)
ws
WS
CH T
X/r 1 I ^>
Gypsum
FG: Flue Gas CG: Cleaned Gas S: Scrubber PS: Prescrubber
Ox: Oxidizer C: Centrifuge WS: Wastewater
Figure 1. Types of commercial wet lime/limestone processes for coal.
this coal-fired power station is 18 ¥/kWhr,
of which nearly 3 ¥/kWhr is for flue gas
treatment
Other FGD Processes for Coal
Although most FGD units for coal-fired
boilers use a standard limestone-gypsum
process, several modified lime/limestone
processes have also been developed Many
of these processes (Table 7) offer advan-
tages over the standard limestone-gypsum
process. Kawasaki Heavy Industries'(KHI)
magnesium-gypsum process, Dowa's alu-
minum sulfate-limestone process, Kureha
Chemical Industries' sodium acetate-lime-
gypsum process, and Kobe Steel's calcium
chloride lime-gypsum process all reduce
the possibility of scaling by using additives;
Chiyoda's jet bubbling process lowers the
pH to reduce scaling. Many of these proc-
esses are also characterized by low power
consumption, low investment costs, and
small amounts of wastewater. The red
mud process is a low cost process, but is
probably limited in its potential use.
Several dry FGD processes which use
activated carbon have been tested on coal
flue gas in an attempt to produce a sulfur
byproduct No information is available on
these processes.
Simultaneous SOX and NOX
Removal
The combination of selective catalytic
reduction (SCR) of NOX with wet process
FGD has been used commercially for several
coal-fired boilers in Japan since 1980. In a
combined system, the SCR reactor is located
between the boiler and the air preheater
and operates at 350-400°C. The flue gas
leaving the SCR reactor contains 1 -5 ppm
NHs, which is removed by the wet FGD
system. The ammonia causes no adverse
effects on lime/limestone FGD processes,
except that the wastewater from the FGD
system contains a small amount of NH3.
At some of the plants, NH3 in wastewater
is removed by conventional activated sludge
or ammonia stripping processes. Where
SCR is applied upstream, the concentration
of nitrate in wastewater derived from IMOX
in flue gas may be reduced.
Two SCR systems are available for flue
gas treatment from coal-fired boilers. One,
the "high-dust" system, treats flue gas
with full dust loads; the other, the "low-
dust" system, has a hot-side ESP up-
stream of the SCR reactor to remove fly
ash. The hot-side ESP is expensive but is
suitable for low-sulfur coals for which
cold-side ESP is not highly efficient
Tests on dry simultaneous removal of
SOX and NOX also have been conducted.
The electron beam process for simultane-
ous removal has been tested by the Ebara
Manufacturing Co. mainly for flue gases
from oil-fired boilers and iron-ore sintering
machines. In the U.S., AVCO, the licensee
of the Ebara process, has tested the
effects of coal fly ash on the electron beam
process.
The activated carbon process for the
simultaneous removal of SOX and NOxwas
tested by EPDC jointly with Sumitomo
Heavy Industries. A demonstration plant
will be completed by 1984. Activated
carbon processes also have been tested by
Mitsui Mining Co.
Wet simultaneous SO,/NOX removal
processes have been tested and applied to
several small commercial units. The wet
processes, however, may not be suitable
for large scale applications, particularly
coal-fired boilers. Large scale systems
need wastewater treatment to remove a
considerable amount of impurities including
nitrate and nitrite.
Other Coal-Utilization
Technologies
Other coal-utilization technologies such
as gasification, liquefaction, and fluidized-
bed combustion (FBC), have been tested
but may not be practical in Japan for
4
-------
Table 4. Operation Parameters of FGD Units
EPOC
Station Isogo
Boiler No.
Capacity (MW)
Gas treated f 1,000 Nm3 /hr)
FGD constructor
FGD start-up year
Inlet SO2 (ppm)
Inlet dust (mg/Nm3)
1st scrubber fprescrubberj
UG ( liter/ Nm3)
2nd Scrubber (scrubber)
L/C I 'liter/ 'Nm3)
Outlet SO2 (ppm)
Outlet dust (mg/Nm3)
SO2 removal efficiency (%)
Dust removal efficiency (%)
Pressure drop (mmH20)
Wastewater (t/hr)
Power requirement (%) k
Gas reheating facility
1
256
821
IHIa
May '76
450
1,500
Venturi
7
Venturi
7
20
50
95.5'
96.6 f
360 h
10
2.2
OF1
for Coal-Fired Utility Boilers (Limestone-Gypsum Process)
EPOC EPOC EPDC
Takasago Takehara Matsushima
1
250
792
MMb
Feb. 75
1,500
100
Venturi
6
Venturi
6
100
30
93.3 '
70.0
325h
7.5
2.6
OF'
1
250
793
BHKC
Feb. 77
1,730
100
Venturi
2.5
PPe
7
100
50
94.2'
87.5
615h
12
2.6
OF1
1
500x3/4
1,300
IHI
Jan. '81
1,000
300
Spray
3
Spray
15
60
30
94.0 a
90.0
145'
15
2.2
GGHm
2
500x3/4
1,300
BHK
July '81
1,000
300
Spray
3
Spray
15
60
30
94.03
90.0
133'
GGHm
Chugoku
Shimonoseki
1
175
610
MHId
July '79
770
1000
Spray
3
Packed
14
30
25
96.19
97.5
240 h
9
2.2
GGHm
Hokkaido
Tomato-Atsuma
1
350x1/2
610
BHK
Oct. '80
230
25
Venturi
2.2
PPe
5
10
5
95,7°
80.0
450'
2.2
1.7
GGHm
alshikawajima-Harima Heavy Industries.
bMitsui Miike Machinery Co.
°Babcock- Hitachi K. K
dMitsubishi Heavy Industries.
ePerforated plate.
'1-3% lower after reheating by oil-firing.
92-3% lower after gas reheating by gas-gas heater.
hBy two scrubbers and mist eliminators.
'By two scrubbers.
'Two scrubbers, mist eliminator, and gas-gas heater.
k Percent of power generated.
'Oil firing.
"'Gas-gas heater.
TableS. Estimated FGD Cost in 1981 (Assuming a new 500 MW coal-fired boiler, limestone-
gypsum process. 70% boiler utilization, 3,066,000 MWhr/year, inlet S02 1,000 ppm,
90% SO2 removal, 7 years depreciation, 10% interest.)
Investment Cost
(including gas-gas heater)
Annual Cost (millions of ¥)
Fixed Cost (25% of investment)
Power (2.1 % of power generated, 17 WkWhr)
Labor (13 persons)
Limestone (43,000 t) and chemicals
Others (maintenance, etc.)
Total
Gypsum (84,000 t, ¥2500Vt)
Total
Annual/zed Cost
16 billion *>
(32,000 WkW)
4,000
1,100
100
250
500
5,950
-210
5,740
1,87 WkWh
3$1 = ¥250.
several reasons. Liquefaction and gasifica-
tion are energy consuming and therefore
too costly because Japan has to import
coal. FBC processes with limestone to
remove S02 create ash disposal problems.
Moreover, SC>2 and NOX reduction by FBC
may not be sufficient to meet the stringent
Japanese regulations.
-------
Table 6. Estimated Power Generation Cost for a New 1000 MW Coal-Fired Boiler (1981)
Coal-fired Boiler
Investment cost ( ¥/kW)a
Power station excluding pollution control facilities 210,000
Flue gas desulfurization (90% efficiency) 30,000
Selective catalytic reduction (80% efficiency) 7,000
Electrostatic precipitator (99.5% efficiency) 4,000
Other pollution control facilities including ash disposal 17,000
Total 268,000
Annualized cost ( WkWhr)
Flue gas desulfurization 1.7
Selective catalytic reduction 0.7
Electrostatic precipitator 0.2
Other pollution control including ash disposal 1.7
Fuel (Coal at 15,000 ¥/ton) 6.4
Others 7.3
Total 18.0
Oil-fired Boiler
Annualized power cost with low-sulfur oil at 64,000 ¥/kl with electrostatic 21.0
precipitator ( WkWhr)b
a$1 =¥250.
b Including 7 years depreciation for pollution control facilities and 15 years depreciation for
power generation facilities.
Table 7. Other FGD Processes for Coal
Absorbent
By-Product
Process
Developer
Commercial
Application
Status of
Application for Coat
CaO, MgO
CaCO3
3, CaCO3
CaO, CH3COONa
CaO, CaC/2
Red Mud
Gypsum
Gypsum
Gypsum
Gypsum
Gypsum
Sludge
KHI
Oil-fired boiler
Chiyoda Oil-fired boiler
Dowa Various sources
Kureha Oil-fired boiler
Kobe Steel Sintering machine
Sumitomo Oil-fired boiler
Aluminum
Commercial in 1981
in West Germany,
in 1983 in Japan
23 MW test in U.S.
10 MW test in U.S.
1.5 MW test in Japan
1.5 MWtestin Germany
Possible commercial
Jumpei Ando is on the Faculty of Science and Engineering, Chuo University,
Tokyo. Japan.
J. David Mobley is the EPA Project Officer (see below).
The complete report, entitled "SOz Abatement for Coal-Fired Boilers in Japan,"
(Order No. PB 83-225 938; Cost: $20.50, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V'A 221'61
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
PS 0000329
------- |