United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-83-027 July 1983
Project Summary
NOx Abatement for Stationary
Sources in Japan
Jumpei Ando
Strict ambient air quality standards
for SQ2 and NO,, in Japan mandate the
use of various air pollution technologies.
This report is a compilation of informa-
tion on the current status of NOX abate-
ment technologies for stationary sources
in Japan. The author obtained this
information from electric power com-
panies, various industries, and de-
velopers of numerous technology pro-
cesses as well as from his own original
research in the field. The report focuses
on the Combustion Modification (CM)
and Selective Catalytic Reduction (SCR)
NO, abatement technologies. Informa-
tion is provided on the development
status, pilot and demonstration plant
tests, technological problems, and
costs associated with the use of these
technologies in Japan. Detailed opera-
tion data are given to describe the
commercial operation of SCR plants.
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).
Standards and Ambient
Concentrations
Recent air pollution control efforts in
Japan have concentrated on NOX abate-
ment since ambient S02 concentrations
already have been drastically reduced in
response to stringent standards. In 1 978,
the ambient air quality standard for N02
was amended from 0.02 ppm to 0.04 -
0.06 ppm as a daily average. In regions
with N02 concentrations above 0.06 ppm,
the concentration will be reduced to 0.06
ppm by 1985. In regions with N02
concentrations of 0.04 - 0.06 ppm, efforts
will be made to keep the concentrations
from substantially exceeding the present
level In areas with concentrations below
0.04 ppm, efforts must be made to main-
tain those levels. The new NO2 standard is
relaxed compared with the previous stan-
dard, 0.02 ppm as a daily average, but is
still more stringent than the U.S. standard
of 0.05 ppm as a yearly average.
In regions with large cities (such as
Tokyo and Osaka), ambient N02 concen-
trations often exceed the standards, reach-
ing 0.07-0.08 ppm as daily averages. The
prefectoral governments of Chiba, Kanaga-
wa, and Mie have established even more
stringent regulations and plan to reduce
N02 concentrations to 0.04 ppm from the
current 0.05-0.06 ppm. Even in regions
with N02 concentrations below 0.04 ppm,
NOX reduction is often required by local
governments to prevent any further in-
crease.
Nearly 2 million tons/yr of NOX are
emitted in Japan, 60% from stationary
sources and the rest from mobile sources.
In large cities such as Tokyo and Osaka,
about 60% of the NOX is emitted from
mobile sources.
NOX emissions from gasoline-engine
passenger cars manufactured since 1978
have been controlled by stringent regula-
tions. The current limit is 0.25 g/km (8%
of the NOX emissions from cars in 1973).
NOX emissions from diesel-engine buses
and trucks have been reduced to about
50% of the 1974 level. For stationary
combustion sources, emission standards
based on advanced combustion modifica-
tion technology have been applied to re-
duce NOX by 30-70%.
With these efforts, ambient N02 con-
centrations are no longer increasing despite
a continuing increase in the number of
stationary and mobile sources. However,
it is difficult to lower current N02 con-
-------
centrations in large cities and industrial
regions without more effective emission
controls for diesel-engine cars and sta-
tionary sources.
NOX Reduction for Stationary
Sources
Nearly all NOX emissions are produced
by the combustion of fossil fuels. In
Japan, the major combustion fuel is heavy
oil. This residue of the atmospheric distil-
lation of crude oil has been used at the rate
of nearly 200 million kl (kiloliters)/yr. Coal
use decreased markedly between 1965
and 1 975 and currently accounts for only
3% of Japan's total energy supply. How-
ever, coal consumption is expected to
triple in the next 10 years. Imported LNG
also accounts for about 3% of the energy
currently used and is expected to nearly
triple in 10 years.
Large stationary sources such as utility
boilers have reduced NOX emissions 50-
7096 by applying combustion modifica-
tions (CM) including low excess air com-
bustion, staged combustion, flue gas re-
circulation, and Iow-N0x burners. As a
result the NOX concentration in flue gas
from utility boilers is minimal--150-300
ppm for coal, 80-120 ppm for oil, and 40-
60 ppm for gas firing. Smaller boilers and
furnaces have reduced NOX 30-50% by
using Iow-N0x burners or by switching
from heavy oil to kerosene.
For additional NOX abatement, several
flue gas treatment (FGT) processes have
been developed. Of all the processes,
selective catalytic reduction (SCR), which
uses ammonia and a catalyst at 300-
400°C to control NOX, is presently the
most advanced technology. Over 1 50
commercial SCR plants are in operation to
remove 80-9096 of the NOX emissions.
Selective noncatalytic reduction (SNR),
which uses ammonia at 800-1,000°C to
remove 30-5096 of IMOX emissions, has
been developed and applied to about 20
furnaces and industrial boilers. Wet and
dry simultaneous SOX and NOX removal
processes also have been developed but
have not been applied commercially except
for several small units.
SCR has been used most often for flue
gas treatment because of its simplicity
(which enables unattended operation),
relatively high NOX removal efficiency (80-
9096), and relatively low cost Most of the
new coal-fired utility boilers being planned
will have SCR units. SCR will also be
needed for some of the existing boilers
even in regions with NOX concentrations
below a 0.04 ppm daily average, due to
local policies which forbid any increase in
NOX levels. For example, when a new
boiler is installed at a power station, not
only the new boiler, but also some of the
existing boilers, will be required to have
SCR units so that total NOX emissions
from the station do not increase.
SCR is usually used with CM. For most
boilers and furnaces, CM is applied first
followed by SCR in order to meet the
stringent regulations. For over 90% NOX
reduction, the combination of CM (to re-
duce 35-50% of the NOX emissions) and
SCR (to remove 80-8596 of the remaining
NOX) is usually more economical than SCR
by itself.
Typical examples of uncontrolled and
controlled NOX concentrations in utility
boiler flue gas are shown in Table 1.
Examples of NOX regulations and emis-
sions from utility boilers are shown in
Table 2.
A new combustion process, in-furnace
NOX removal, has been developed to re-
move about 50% of NOX by injecting a
small portion of the fuel above the flame,
followed by air addition to ensure complete
combustion. Using this process, along
with CM for utility boilers, NOX may be
reduced to 100 ppm for coal, 50 ppm for
oil, and 20 ppm for gas.
Fluidized-bed combustion, gasification,
and liquefaction of coal all have been
tested in Japan, but these technologies
are not as advanced there as they are in the
U.S. This is because Japan must import
coal and because these technologies are
unable to meet the stringent Japanese
NOX emission regulations. Most of the
new coal-fired boilers in Japan will use
conventional pulverized coal combustion
with CM, SCR, and FGD.
SCR and SCR/FGD
Characteristics
SCR problems of the past have been
solved by recent improvements. The major
problems were: 1) poisoning of the catalyst
by SOX in the gas, 2) dust plugging of the
catalyst, and 3) deposition of ammonium
bisulfate in the air preheater downstream
of the SCR reactor. Catalyst poisoning has
been eliminated by using catalysts based
on Ti02 instead of AI203 or Fe203- The
use of parallel-flow honeycomb, tube, or
plate catalysts or a parallel passage reactor
eliminates dust plugging. Ammonium
deposits can be prevented by maintaining
the concentration of unreacted ammonia
in the reactor outlet gas below 5 ppm and
using a low-oxidation catalyst To do this,
0.82 -0.95 mole NH3 is usually used per
mole NOX to obtain 80-90% NOX removal
with less than 5 ppm unreacted NH3,
while S02 oxidation is kept below 1 %.
SCR and FGD system applications to
boilers and other gas sources are shown
schematically in Figure 1. SCR is easily
applied to boiler economizer outlet gas al
300-400°C as shown in the A portion of
the figure. For S0x-rich gases, FGD may
be applied downstream of SCR as shown
in B. At an early stage of development,
SCR was applied downstream of FGD
systems, as shown in C, to protect the
catalyst from SOX attack System C, how-
ever, is expensive; it requires large amounts
Table 1.
Examples of Controlled and Uncontrolled NOX Concentrations in Utility Boilei
Flue Gas
Outlet NOX Concentration, ppm
Percent Control
Fuel
Gas
Oil
Coal
Without
Control,
ppm
200
300
600
Controlled
by
CM
50
WO
250
Controlled
by CM
and SCR
10
20
50
by CM
70
67
58
by SCR
83
80
80
Total
%
Control
95
93
91
Table 2.
Fuel
Gas
Gas
Oil
Oil
Coal
Coal
Examples of NOX Regulations and Emissions from Utility Boilers, ppm
Boiler Central Government Local Agreement Actual Emission
Existing
New
Existing
New
Existing
New
100
60
150
130
400
400
60
10
100
25
159C
170
60°
8"
WO3
20*
1703
160"
"By combustion modification (CM).
bBy CM and selective catalytic reduction (SCR).
cDesired by local government.
dBy CM and partial SCR
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of energy for gas reheating. System B has
become popular as S0x-resistant catalysts
have been developed.
System D is often used for flue gas from
a low-sulfur coal. In this system, the boiler
economizer outlet gas is first treated by a
hot electrostatic precipitator (ESP) and
then by SCR and FGD. A cold ESP is not
highly efficient for flue gas from low-sulfur
coal. For high- and medium-sulfur coals,
system B is preferable. System B may also
be useful for low-sulfur coal if both the
cold ESP and the FGD unit are designed-
for sufficient dust removal.
Low-temperature catalysts have been
used for 200-250°C gases such as that
produced by coke ovens, as shown in
system E of Figure 1. Since ammonium
bisulfate deposits on the catalyst at these
low temperatures, the catalyst requires
occasional heating to 400°Cto remove the
bisulfate.
When wet FGD is applied downstream
of SCR or SNR, the ammonia present in
the reactor outlet is caught by the FGD
system and goes into the wastewater. In
some cases it may be necessary to use the
activated sludge process to remove am-
monia from the wastewater.
Cost of NOX Abatement for
Stationary Sources
The investment cost for a combustion
modification system is shown in Table 3.
Costs range from ¥400* to 8007 Mm3 of
flue gasor¥1,200-2,400/kW for 55-70%
reduction using a combined Iow-N0x
burner, staged combustion, and flue-gas
recirculation system.
SCR costs for new 700 MW gas-, oil-,
and coal-fired utility boilers are shown in
Table 4. For cost estimation purposes, it
was assumed that flue gases leaving the
boiler economizer at 330-400°C are treated
in two equal-size reactors in parallel and
that unreacted NH% is kept below 5 ppm.
The investment cost for 80% IMOX removal
is about ¥2,500/kW for gas, ¥4,100-
6,200/kW for oil and ¥6,700-8,400/kW
for coal. The cost differences are due to
the varying amounts of catalyst required.
For example, a small amount of a very
active catalyst is used for gas streams
while a larger amount of a less active
catalyst which is resistant to SOX and dust
erosion is used for dirty flue gas (oil or coal
streams). Compared with 80% removal,
90% removal costs 1 5% more for gas, 25-
30% more for oil, and 30% more for coal.
The investment cost of an SCR system for
an existing boiler is 10-50% more than for
a new boiler.
B
370
sc/?
370
AU
150
ESP
-LA
Stack
370
SCR
370
AH
150
100
370
370
AH
150
ESP
150
fc»
FGD
\
•
H
w
SCR
B
370
Hot
ESP
370
Heater
Electrostatic Precipitator
Figure 1. SCR and FGD system arrangements in use in Japan. (Numbers indicate gas
temperature in °CJ
Table 3. CM Investment Cost
Method NOX removal, % ¥/Nm3
¥/kW
$/kWa
Low-NOx Burner
Combined System1'
20-40
50-70
100-200
400-800
300-600
1200-2400
1.2-2.4
4.8-9.6
(*) $1 =¥250.
a$1 =¥250.
hLow-NOx burner, staged combustion, and flue gas recirculation.
The dirtier the gas, the shorter the life of moved is lower with NGyrich gas. The
the catalyst Therefore, the annualized cost per pound for 80% removal is 10-1 7
SCR cosi/kWhr is higher when SCR is percent lower than the cost for 90% re-
used with dirty gas. On the other hand, the moval. NOX removal of 90% with a low
annualized cost per pound of NOX re- level of unreacted NH3 (about 5 ppm) is
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Table 4. SCR Cost for 700 MW New Boiler (1981 Cost) (70% Boiler Utilization 4.292.000 MWhr/yr)
Fuel
Inlet NOX, ppm
Catalyst
Type
Cost lO6*/™3
Life, years
NOX Removal, percent
Investment Cost8,
1000 */kW
Annual/zed cost*,
¥/kWhr
Low-S High-S Low-S High-S High-S
Gas Oil Oil Coal Coal Coal
60 100 200 300 300 600
Pellet Honeycomb Honeycomb Honeycomb Honeycomb Honeycomb
3.0 3.3 3.3 3.5 3.5 3.5
43 3 2 2 2
80 90 80 90 80 90 80 90 80 90 80 90
2.47 2.80 4.13 5.11 6.23 7.93 6.69 8.51 7.26 9.10 8.44 10.7t
0.17 0.20 0.28 0.35 0.44 0.56 0.59 0.76 0.65 0.82 0.81 1.04
"Including initial charge of catalyst civil engineering, and test operation.
*Including 10% interest and 7 years depreciation.
not easy to obtain with a large amount of
gas from a utility boiler, because both gas
velocity and NOX concentrations vary a-
cross the duct at the reactor inlet
The investment and annualized SCR
costs for 80% S02 removal for coal-fired
boilers are about one-third of those for
90% S02 removal using the wet lime/
limestone FGD process. On the other
hand, SCR is more expensive than CM.
Although the investment cost of SCR for a
gas-fired boiler is similar to that of CM in
the combined system (Table 3), the annuah
ized cost of SCR may be considerably
higher than CM, which has low operating
costs. Therefore, for NOX abatement, CM
should be used first and SCR should be
used in combination with CM when CM
alone is not sufficient to meet control
regulations. One CM technique, flue gas
recirculation, is relatively expensive and is
not highly efficient for coal. For this
reason, flue gas recirculation may not be
useful when SCR is applied to coal-fired
boilers.
The costs of other FGT processes are
uncertain because they have not been
used widely in continuous commercial
operation. However, experience with
Thermal DeNOx, a type of SNR used with
an oil-fired utility boiler, indicates that its
cost is about half that of SCR although the
NOX removal efficiency is also half as
much (40% versus 80%).
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 "NO* Abatement for Stationary Sources in Japan,"
(Order No. PB 83-207 639; Cost: $37.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
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
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Penalty for Private Use $300
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