Environmental Protection Technology Series
NOX 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
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RESEARCH REPORTING SERIES
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TECHNOLOGY series. This series describes research performed to develop and
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work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
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does not signify that the contents necessarily reflect the
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EPA-600/2-76-013b
NOx ABATEMENT
FOR STATIONARY SOURCES
IN JAPAN
by
Jumpei Ando and Heiichiro Tohata
Chuo University
Kasuga, Bunkyo-ku, Tokyo
and
Gerald A. Isaacs
PEDCo-Environmental Specialists, Inc.
Suite 13, Atkinson Square
Cincinnati, Ohio 45246
Contract No. 68-02-1321, Task 6
ROAP No. 21ACX-130
Program Element No. 1AB014
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
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PREFACE
In 1973 the Japanese government set an ambient standard
for nitrogen oxides (NO ) that is more stringent than that
A.
in any other country of the world: 0.02 ppm daily average.
Regulations pertaining to NO emissions in motor vehicle
J\.
exhausts are in preparation. Emission standards for waste
gases from stationary sources are to be attained by mid-1975
by means of combustion control and removal of NO from tail
J\.
gases of nitric acid plants. Thus, with promulgation of the
ambient standard and of regulations to limit emissions from
both mobile and stationary sources, the responsible author-
ities are taking firm steps toward NO abatement. A serious
•?C
problem, however, is that the ambient standard is still far
out of reach in Japan, where energy consumption per unit
area of level land is 8 times that in the United States and
may be the highest in the world.
Because most people believe that attaining the ambient
standard will require removal of NO from flue gases (deni-
X
trification), many organizations have started to develop NO
y±
removal processes. Regulative action by local governments,
which tend to impose even more stringent regulations than
does the central government, is forcing industries to install
flue gas denitrification facilities. As these facilities
are operated, however, we find that denitrification appar-
ently is more difficult than desulfurization, for which
technologies are well-developed in Japan. In addition to
the technical difficulties of denitrification, there is some
111
-------
doubt as to whether the stringent ambient standard is
really necessary for protecting human health. Despite these
concerns, several commercial plants for flue gas denitri-
fication have started operation and many others are under
construction.
This report summarizes briefly the regulations for NO
is.
abatement in Japan, describes techniques for abatement by
means of combustion control, and analyzes in detail the
current technologies of denitrification by wet and dry
processes.
The information reflects technology and economics
current in January 1975.
IV
-------
CONVERSION FACTORS AND ABBREVIATIONS
CONVERSION FACTORS
The metric system is used in this report. Some of the
factors for conversion between the metric and American
systems are shown below:
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
1 kcal (kilocalorie) = 3.97 Btu
The capacity of NO removal systems is expressed in
x 3 3
normal cubic meters per hour (Nm /hr). One Nm /hr = 0.59
standard cubic foot per minute. For monetary conversion,
the exchange rate of 1 dollar = 300 yen is used.
ABBREVIATIONS
SCR Selective catalytic reduction
MW Megawatt
kW Kilowatt
SV Space velocity
v
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TABLE OF CONTENTS
Page
PREFACE iii
LIST OF FIGURES ix
LIST OF TABLES xii
1. STATUS OF NO ABATEMENT IN JAPAN 1-1
X
Regulations 1-1
2. COMBUSTION CONTROL 2-1
Background 2-1
Nippon Furnace Low-NO Burners 2-2
J\.
TRW Type Burner 2-2
SRG Type Burner 2-8
Daido Steel Low-NO Burner 2-8
X
MHI Slit Burner 2-12
IHI Divided-Flame Burner 2-14
Research on Fuel NO 2-14
Ji
3. NO REMOVAL BY WET PROCESSES 3-1
J\.
General Description 3-1
Sumitomo-Fuji Kasui Process 3-8
Tokyo Electric - Mitsubishi H. I. Process 3-11
Chiyoda Thoroughbred 102 Process 3-14
Nissan Permanganate Process 3-17
VI1
-------
TABLE OF CONTENTS (Continued).
Page
Tests by CRIEP on Sodium Sulfite Scrubbing 3-20
MON Alkali Permanganate Process 3-26
Kureha Reduction Process 3-27
Kawasaki Magnesium Process 3-29
Chisso Ammonia Scrubbing Process 3-31
Ube Alkali Scrubbing Process 3-34
Kobe Steel Process 3-34
4. DRY PROCESSES FOR DENITRIFICATION 4-1
General Description 4-1
Sumitomo Reduction Processes 4-7
Hitachi Shipbuilding SCR Process 4-22
Kurabo SCR Process 4-24
Tests on SCR Catalysts by CRIEP 4-27
Tokyo Electric - Mitsubishi H. I. 4-30
SCR Process
SCR Tests at Chubu Electric Power 4-32
Other Catalytic Reduction Processes 4-33
Ebara-Jaeri Electron Beam Process 4-34
Other Dry Processes 4-36
REFERENCES
vnx
-------
LIST OF FIGURES
Figure Page
2-1 Status of Combustion Control at 2-3
114 Plants
2-2 NFK-TRW Burner 2-6
2-3 Effect of NFK-TRW Burner 2-7
2-4 Principle of SRG Burner 2-9
2-5 Effect of SRG Burner 2-9
2-6 Daido Steel Low-NO Burners 2-11
J\.
2-7 Effect of RO Type Burner 2-11
2-8 Model of MHI Low-NO Burner 2-13
2C
2-9 Effect of MHI Low-NO Burner 2-13
JC
2-10 NOX Reduction by IHI Burner and 2-15
Other Means
2-11 Results at Test Furnace 2-17
2-12 Results at Test Furnace 2-17
2-13 Results at 125-MW Power Plant 2-17
2-14 Results at 125-MW Power Plant 2-17
2-15 Comparison of Conversion Ratio 2-18
at Power Plant and Test Furnace
2-16 Flame Temperature and Conversion 2-18
Ratio
3-1 Capital Cost for Ozone Plant 3-4
3-2 Relative Absorption Rate in 3-6
Various Systems
IX
-------
LIST OF FIGURES (Continued).
Figure Page
3-3 Flowsheet of Sumitomo - Fuji Kasui 3-9
Process
3-4 Flowsheet of Tokyo Electric - 3-12
Mitsubishi H. I. Process
3-5 Flowsheet of Chiyoda Thoroughbred 3-15
102 Process
3-6 Relation Between Oxidation Ratio 3-16
and Removal of S09 and NO
& J\.
3-7 Flowsheet of Nissan Permanganate 3-19
Process
3-8 Simplified Flowsheet of MON Process 3-21
3-9 Apparatus for Test 3-22
3-10 Effect of Na-SO., Concentration 3-25
3-11 Effect of O2 Concentration 3-25
3-12 Flowsheet of Kureha Process 3-28
3-13 Flowsheet of Kawasaki Magnesium 3-30
Process
3-14 Simplified Flowsheet of Chisso 3-32
Process
3-15 Flowsheet of Ube Process 3-35
3-16 NO0/NO Ratio and NO Removal 3-36
£* • X
4-1 Equilibrium Constants of Reactions 4-3
4-2 NO Removal Plant 4-9
A
4-3 Flowsheet of Denitrification Process 4-10
4-4 Flowsheet for Dirty Gas Treatment 4-10
4-5 Effect of NHo/NOx Mole Ratio on NO 4-11
Removal and Ammonia Emission
-------
LIST OF FIGURES (Continued).
Figure Page
4-6 Effect of Ammonia Decomposition 4-13
Composition
4-7 Effect of S03 on Catalyst Activity 4-14
4-8 Formation Temperature of NH.HSO. 4-15
4-9 Operation Data of HNM Plant 4-17
4-10 Result of Life Test 4-18
4-11 Simplified Flowsheet of Non-selec- 4-21
tive Catalytic Reduction Process
4-12 Flowsheet of Hitachi Shipbuilding 4-23
Process
4-13 Flowsheet of Kurabo SCR Process 4-26
4-14 Tests on Carriers 4-29
4-15 Tests on Catalysts 4-29
4-16 Flowsheet of Pilot Plant 4-31
4-17 Apparatus for Tests 4-35
4-18 Results with Different Intensities 4-37
XI
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LIST OF TABLES
Table Page
1-1 NO Emission Standards 1-3
x
2-1 Nitrogen Content of Fuels 2-1
2-2 Characteristics of Combustion 2-4
Modification Methods
3-1 Major Plants for NO Removal from 3-2
Flue Gas by Wet Process
3-2 Effect of Additives on NO Removal 3-23
X
4-1 Major Plants for Denitrification by 4-5
Selective Catalytic Reduction
4-2 Composition and Property of Carriers 4-28
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1. STATUS OF NO ABATEMENT IN JAPAN
A.
REGULATIONS
Ambient Air Quality Standard
An ambient standard for NO2, based on a recommendation
by the Special Committee of the Central Council on Environ-
mental Pollution Control, was set forth by the Cabinet and
announced by the Environment Agency in May 1973. The stan-
dard requires that ambient concentrations of NO, be kept
3 ^
below 0.02 ppm (about 0.04 g/Nm ) in a daily average of
hourly values; conformance with this standard is to be
attained within 5 years in most districts and within 8 years
in heavily polluted cities such as Tokyo and Osaka.
Compared with the national ambient standard in the
United States Standard (0.05 ppm yearly average, which is
close to 0.1 ppm daily average) and also with the German
standard, which approximates that in the United States, the
Japanese standard is very stringent. N0» concentrations in
large cities such as Tokyo and Osaka normally range from
0.03 to 0.04 ppm. In January 1975 the Environment Agency
reported that in only 3 cities among 147 was the NO- level
as low as 0.02 ppm or lower.
A motive for the stringent regulation was the frequent
occurrence of photochemical smog in Tokyo in 1972 (described
in a 1973 report). The smog, however, may not be similar
to that in California, which occurs at much higher NO
J\.
concentrations. Moreover, fewer warnings for photochemical
smog were issued last year than in 1972 in spite of a slight
increase in NO- concentrations. For these reasons it may be
1-1
-------
desirable to reevaluate the ambient standard on the basis of
additional scientific data, including medical data. Relax-
ing the standard, however, would probably be difficult in
Japan, where the people are deeply concerned with environ-
mental pollution.
Emission Standards
In August 1973 emission standards for NO were promul-
1^
gated for large stationary sources, classified as shown in
Table 1-1. These standards take into account the status of
abatement technology and are similar to those in the United
States. The emission standards may well be achieved in
1975.
The problem is, however, that several local governments
limit emissions of NO from new plants to very low levels.
,A
These limitations impose severe constraints upon construc-
tion of new NO - emitting facilities, such as electric power
3 x
plants.
Total Quantity Control
A supplement to the Air Pollution Control Law was
published in June 1974, as a "total quantity control law,"
designed to attaint the ambient standards by control of
pollutants from fuel burning, i.e. SO , NO , and particu-
X X
lates. This law is summarized as follows:
1) The Environment Agency designates the pollutants
and areas to which this law is applied. These are
called "designated pollutants," and "designated
areas."
2) The governers of local governments must determine
the necessary reduction of the designated pollu-
tants to achieve ambient standards in the desig-
nated areas.
1-2
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Table 1-1. NO EMISSION STANDARDS (August 1973)
X
I
CO
Boiler
Gas fuel
Solid fuel
Low grade coal
Liquid fuel
Crude tar
Metal heating furnace
Oil heating furnace
Nitric acid plant
NOX, ppm
New
150
480
180
200
170
200
Existing
170
600
750
250
280
220
210
200
Applicable
capacity,
NmVhr
40,000 for
new plants,
100,000 for
existing ones
10,000 for
new plants,
40,000 for
existing ones
All
Time limit
2 years for
existing
plants
3 years
°2
in gas, %
5
6
4
11
6
—
-------
In September 1974 the agency designated 11 areas,
including Tokyo and Osaka; it will add another 11 in the
near future. S02 was selected as the first designated
pollutant, for which the new ambient standard (0.04 ppm
daily average, published in 1973) must be attained by the
end of 1977. NO and particulates are to be designated
j\,
soon. Under the control law it is not possible in a de-
signated area to build a new plant without shutting down old
ones or vastly reducing pollutant emissions from both old
and new plants.
The required reduction of S02 emissions may be attained
by using expensive low-sulfur fuels or by applying flue gas
desulfurization, a technology that is well-developed in
Japan. Reduction of NO emissions is much more difficult.
j£
Nevertheless, several local governments such as Tokyo,
Osaka, Chiba, and Mie are preparing their own NO regula-
X.
tions for total quantity control, which could be even more
stringent than the national regulations. The authors
believe that the national ambient standard for NO should be
Jt
reevaluated before these local NO control regulations are
X
established.
NO Control for Motor Vehicle Exhausts
Jt ~ ~' L " ------ - - —
Control of NO emissions in motor vehicle exhausts to
j£
a level of 0.25 g/km or 0.40 g/mile was originally scheduled
for 1976. After several meetings in late 1974, however, the
Special Committee of the Central Council on Environmental
Pollution Control concluded that scheduled enforcement of
the maximum permissible limit should be postponed 2 years
owing to the technical difficulty involved, and that the
temporary limits should be 0.85 g/km for large cars (weigh-
ing over 1000 kg) and 0.6 g/km for small cars. Very recently
the Director-General of the Environment Agency recommended
1-4
-------
to the Minister of Transportation that the temporary limit
be set at 1.2 g/km, a value obtained by adding 40 percent to
the 0.85 g/km standard to account for fluctuations in engine
quality- The 1.2 gram limit is the same as that now prac-
ticed in California.
Some automobile manufacturers, such as Honda, Matsuda,
and Mitsubishi, have developed engines that yield low NO
.X.
emissions; however, two major manufacturers, Toyota and
Nissan, claim that it is technically impossible to supply by
1976 new engines with NO emissions under 0.9 g/km without a
j\.
substantial increase in fuel consumption.
Overview of NO Abatement Technology
""'''--"'•"• X - - - - - - mr_T
Technologies under development in Japan for control of
NO are similar to those being developed in the United
.X
States: combustion control, use of low-NO burners, two-
JC
stage combustion, off-stoichiometric combustion, and flue
gas recirculation. These and other NO control techniques
X
are under consideration and active development by many
groups including boiler manufacturers, electric power
companies, national research institutes, and universities.
Because the emission standards for stationary sources
must be attained by the summer of 1975, the control methods
are being applied to the larger-capacity plants. In addi-
tion, heavy oil, containing 0.1 to 0.4 percent nitrogen,
which has been the major fuel in Japan, has been replaced by
low-nitrogen oil or gas in many plants.
The Environment Agency estimates that even when 60
percent of the NO is reduced by control of combustion and a
Ji
change of fuel, about 20 percent of the total flue gas
should be treated to remove 90 percent of the NO by 1978,
A
and 30 percent should be treated by 1981 in order to attain
the ambient standard. The central and local governments are
1-5
-------
trying to promote the development of NO removal technology
J\.
by providing research funds and extending low-interest loans
for constructing NO removal plants. Further, the Japan
X
Iron and Steel Federation has established a $10 million fund
to promote basic and applied research on countermeasures for
NO control.
.X
Among various processes for flue gas denitrification,
dry catalytic reduction of NO by ammonia is typically used
Ji
in the presence of negligible amounts of SO and particu-
Jt
lates. The reduction process, however, can be used to treat
dirty flue gas containing SO and particulates, but not
A.
without additional difficulty. Wet processes using scrub-
bers have also been developed. The wet processes, however,
may be more difficult than catalytic reduction limestone or
lime, the cheapest absorbents useful for removal of S0_, is
not used for removal of NO , which is less reactive than SO0.
X £,
Moreover most of the wet processes entail treatment of
wastewater containing nitrates or nitrites. Some of them,
however, offer the advantage of simultaneous removal of SO
J\.
and NO .
J\.
Technologies for abatement of NO from stationary
sources are described in detail in the following sections.
1-6
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2. COMBUSTION CONTROL
BACKGROUND
Fuel in Japan
Heavy oil, residue of atmospheric distillation of crude
oil, has been the major fuel in Japan. In 1973 consumption
of heavy oil was about 140 million tons, while combustion of
coal as fuel was about 25 million tons. By comparison use
of domestic natural gas and imported LNG is still insignifi-
cant, although use of the latter is fast increasing.
The nitrogen contents of heavy oil, coal, and kerosene
are shown in Table 2-1. As is well-known, normally about 30
percent of the nitrogen is converted into NO on combustion
X
and is emitted together with thermal NO formed by the
X
reaction of nitrogen in air with oxygen. The major fuels
used until recently were grades B and C heavy oils, rela-
tively rich in nitrogen. Use of grade A oil, kerosene, and
natural gas has increased since the NO emission standards
xC
were set forth, although those low-nitrogen fuels are
expensive.
Table 2-1. NITROGEN CONTENT OF FUELS
Fuel
Heavy oil grade A
grades B, C
Coal
Kerosene
Nitrogen
content, %
0.005 - 0.08
0.08 - 0.35
0.5 - 2.5
less than 0.005
2-1
-------
Combustion Modification
Figure 2-1 shows results of an opinion survey concern-
ing combustion modification methods; the survey covered
about 100 plants, involving mainly industrial boilers and
some utility boilers and furnaces. Next to the change of
fuels, use of low-NO burners is the preferred control
H
method. Staged combustion and flue gas recirculation have
been adopted widely for utility boilers but not much for
industrial boilers because of the high investment costs.
Characteristics of the combustion .modification methods
are summarized in Table 2-2. Although these methods are the
most useful and practical for NO abatement, they have some
JC
disadvantages: they decrease heat efficiency, require large
installations, and increase emissions of other pollutants.
Their efficiency for NO abatement is naturally limited by
ji
the necessity of minimizing these problems.
NIPPON FURNACE LOW-NO BURNERS
X
Background
The developer is Nippon Furnace Kogyo Kaisha Ltd., one
of Japan's largest burner and furnace makers. Nippon Fur-
nace, has developed two types of low-NO burners: one is
J^.
the TRW type suitable for boilers, which has been commer-
cialized under a technical license agreement with Civiltech
Corp. (U.S.) in a joint venture with TRW, Inc.; the other is
a self recirculating gasification (SRG) burner, an original
product suitable for heating furnaces.
TRW TYPE BURNER
Description
This burner is designed to attain good mixing of air
and fuel, with rapid combustion. As shown in Figure 2-2,
2-2
-------
oo
t/1
LU
o
o
ac
a.
1/1
UJ
a.
o
it
CHANGE OF FUEL
LOW-NO¥ BURNER
rt
STAGE COMBUSTION
FLUE GAS
RECIRCULATION
WATER INJECTION
CHANGE OF
AIR RATIO
REDUCTION OF
THERMAL LOAD
REDUCTION OF
AIR PREHEATING
10
NUMBERS OF ANSWERS
2
IN USE UNDER CONSIDERATION TO BE USED
Figure 2-1. Status of combustion control at 114 plants,
(Results of opinion survey)
2-3
-------
Table 2-2. CHARACTERISTICS OF COMBUSTION MODIFICATION METHODS
Change of air ratio
Thermal load reduction
Less air preheating
Low-NO
A.
burner
Good mixing
Divided flame
Self- recirculation
k Stage burning
Stage combustion
Off-stoichiometric combustion
Flue-gas recirculation
Water (steam) injection
Change of fuel
Combustion chamber design
Thermal NOX
A B C D
© © © A
© © O ^
© O 0
o © ©
© @ ©
o © o ©
© ©
© ©
© ©
© O ©
© o o
© © © a
© o ©
Fuel NO
E F G H
O O ©
A ^ ©
©
O
o
0 0
0 0
O 0 A
0 O 0
A
o
o © ^
A
Problems
I J K L
A. X
o o o
X X
©
X
X
x x
X 0
©
Thermal NO
A: Temperature drop B: Decrease of 02 in burning zone
C: Decrease of retention time in high temperature zone
© Closely related O Related
D: Degree of decrease
© Large O Small A Varies with installations O Not clear
Fuel NO
E: Decrease of N in fuel F: Decrease of 02 in initial combustion zone
O Effective A Varies with installations
X Has adverse effect
G: Degree of decrease
© Large O Small A Varies with installations
* NO increase is possible
H: Ease of application
© Easily applied also to existing plants
O Needs some modification of installations
A Requires much modification
Problems to be considered
I: Decrease in heat efficiency
K: Need for large installation
J: Decrease in power generation
L: Increase in other pollutants
(dust, CO, hydrocarbons, etc.)
X Closely related A Related
O Varies with installations © Possibly improved
2-4
-------
the basic design is a single control element configuration,
whereby air is injected in a continuous cylindrical stream,
which mixes with the jets of fuel injected radially outward
through a large number of shaped ports. The air and fuel
are then further mixed by means of a deflector, which
serves both to complete the mixing process and as a flame
holder.
The intermixing of fuel and air produces a radial
conical flame pattern that is quite thin. Keeping the flame
front thin and flat, provides a maximum radiation surface
and allows rapid dissipation of heat from the flame. The
shape of the flame front ensures an extremely short nitrogen-
oxygen reaction time. Recirculation also reduces combustion
temperature. The effect of the burner is shown in Figure
2-3.
State of Development
TRW has supplied burners for oil with capacities rang-
ing from 4,560,000 to 24,100,000 kcal/hr: 11 units in Japan
and a few in the United States. A duel type for oil and gas
was commercialized in early 1975.
Advantages
The burner reduces not only NO but also soot emissions.
JC
It requires neither redesign of the boiler nor reduction of
load on the boiler combustion chamber. Less steam is
consumed, for fuel atomization.
Disadvantages
The device is applicable only to boilers. Pressure
drop at burner throat is high.
2-5
-------
\\\\\\\\ \\A\\\\\\A\\\\\\\\\\\\
FURNACE WALL
DIANT RADIATION
CYLINDRICAL AIR SHEET
FUEL
Y////////////////.
RECIRCULATION ZONE
RECIRCULATION ^ ZONE
Figure 2-2. NFK-TRW burner.
2-6
-------
200
o
o
UJ
O
UJ
a:
ce.
o
100
_L
I
20
EXCESSIVE AIR,
40
30
20
o
UJ
Figure 2-3. Effect of NFK-TRW burner.
(Heavy oil, N = 0.3%, 310 liter/hr)
2-7
-------
SRG TYPE BURNER
Description
Configuration of the SRG burner is shown in Figure 2-4.
Without requiring special power, the burner recircu-
lates air and part of the combustion products into the
burner tile by the jet energy of fuel and atomizing steam.
Because it accomplishes gasification burning of fuel, this
burner is called the self recirculating gasification (SRG)
burner. The angle of the atomizing nozzle is from 30 to 45
degrees. The effect of the burner is shown in Figure 2-5.
State of Development
Over 1000 natural-draft units have been sold in Japan.
Ten recently developed forced-draft units have also been
supplied.
Advantages
This burner is applicable to many types of industrial
furnaces in oil refining, petrochemical, iron and steel,
cement, and other industries. A wide turndown ratio under
stable flame conditions is attained. Oil, gas, and oil-gas
combination burners are available.
Disadvantages
The flame is shaped like a candle flame, and this shape
cannot be altered.
DAIDO STEEL LOW-NO BURNER
X
Background
The developer is Daido Steel Co., a steel producer with
a machinery division manufacturing burners and furnaces.
Daido has developed a self-recirculation burner under a
technical license agreement with Caloric Gesellschaft fur
Apparate Bau (West Germany).
2-8
-------
-GASIFICATION GAS*
1 CO, H2 RICH ;>
I'1 \ I I1'/
•\\\"^
GASIFICATION REACTION
C + 0— C0
CmMn + mH0^
/RE-COMBUSTION GAS«
--- '
COMBUSTION PRODUCTS
I V / C02-H20-N2
y °2' OTHERS
f//x\ Y^^;mf&$'KXl
FUE
CmHn
SECONDARY AIR
(02-N2)
Figure 2-4. Principle of SRG burner.
"350
NOX vs AIR RATIO, SRG BURNER
AND TANDEM BURNER
§ o i.o 1.1 1.2 1.3 1.4 1.5
AIR RATIO, X
N(L REDUCTION RATE, SRG vs TANDEM
1.1 1.2 1.3 1.4
AIR RATIO, X
Figure 2-5. Effect of SRG burner.
2-9
-------
Description
As shown in Figure 2-6, (A and B), injection of air
through a narrow space between the ring nozzle and combus-
tion chamber causes a pressure difference between them.
Thus a part of the combustion gas recirculates to the fuel
chamber to reduce the combustion temperature.
View (A) shows the original design of Caloric Gesel-
Ischaft. Because the high-temperature flue gas with rela-
tively few particulates jets from the combustion chamber,
where the combustion is completed, this type of burner is
suitable for heat treatment or drying. View (B) is the
modified type developed by Daido Steel. Because the flame
front is longer, heat dissipation from the flame is more
rapid than in the original design and this type of burner is
thus more efficient in NO reduction. Effects of the
X
burners are shown in Figure 2-7. Part of the fuel injected
into the fuel chamber by oil pressure, steam, or air reacts
with the recirculating hot gas to form intermediates such as
aldehydes and alkyl radicals, which are rapidly oxidized by
air from the ring nozzle.
Several units have been used for heating furnaces in
the nonferrous metal refining industry. This type of
burner can also be used for submerged combustion. Design
and tests of units of various sizes from 10 to 5 x 10
kcal/hr have been completed. A field test of the applica-
tion to a heating furnace for the iron and steel industry is
being planned.
Price and Operation Cost
Examples of price (December 1974) are as follows:
1 million kcal/hr $4,500
4 million kcal/hr $13,000
Operating costs are slightly higher than for ordinary
2-10
-------
(A) R TYPE
AIR
(B) RO TYPE
Figure 2-6. Daido Steel low-NO burners.
X
150
100
E.
Q.
50
ROTARY OIL BURNER
(OIL-PRESSURE ATOMIZING)
o
OIL-PRESSURE
ATOMIZING
AA*
STEAM
ATOMIZING
RO TYPE
BURNER
%.9 1.0 1.1 1.2 1.3
AIR RATIO
o . HEAVY OIL (GRADE A, 103-113 SL/br
a * KEROSENE (100 Jl/hr)
Figure 2-7. Effect of RO type burner.
2-11
-------
burners, because higher pressure is needed to recirculate
the combustion air.
Advantages
This burner is effective for NO reduction; formation
X
of carbon monoxide and particulates is very slight.
Disadvantages
Large-size units of over 5 million kcal/hr are diffi-
cult to construct. Residual oil cannot be used.
MHI SLIT BURNER
Background
The developer is Mitsubishi Heavy Industries Co. (MHI).
MHI is the largest heavy manufacturer in Japan, turning out
a wide variety of products including ships and boilers. MHI
recently developed a low-NO burner that is a kind of off-
ji
stoichiometric combustion gas burner.
Description
The basic structure of the burner is shown in Figure
2-8. Premixed fuel gas and air are fed to the combustion
chamber in three layers. In the middle layer the gas is
enriched, i.e. fuel with an off-stoichiometric quantity of
air; in the outer two layers fuel is diluted with excess
air. The overall air ratio is nearly 1, SQ that combustion
takes place at a very low oxygen concentration. Moreover,
this special type of atomizer is designed to produce a thin
film flame to enlarge the flame surface and thus reduce NO
it
emission through flame cooling and a self-recirculation
effect.
Test furnaces, with heat generating rates of 4 x 10
and 2.8 x 10 kcal/hr were operated with propane and methane
as fuels to study the effects of the burner. Some of the
results are shown in Figure 2-9. Application to liquid
2-12
-------
AIR RICH MIX
MIXER
-
4—
^
: _, C*
I
v
FUEL RICH MIX
Figure 2-8. Model of MHI low-NO burner,
200
evj
o
IT)
O
o:
8
100
80
60
50
40
30
20
10
\ \
FUEL: PROPANE
0 10 20 30
FLUE GAS RECIRCULATION RATIO, %
& CONVENTIONAL BURNER, 2 t/hr
o MHI LOW-NOX BURNER, 2 t/hr
a MHI LOW-NO¥ BURNER, 8 t/hr
A
Figure 2-9. Effect of MHI low-NO burner.
2-13
-------
fuels is being tested.
Advantages
NO emissions from gas fuels can be substantially
reduced when flue gas is also recirculated. Fuel NO may
A
also be decreased by off-stoichiometric combustion.
Disadvantages
The MHI burner is applicable only to limited types of
industrial furnaces.
IHI DIVIDED-FLAME BURNER
Description
The developer is Ishikawajima-Harima Heavy Industries
Ltd. (IHI), one of Japan's leading heavy manufacturers
working also on boiler construction. IHI has improved its
divided-flame burners, described in an earlier report, and
4
has developed several new ones. Burners developed for
power up to 600 MW gave satisfactory results in field tests.
This type of burner might be the cheapest means of reducing
NO emissions from existing boilers, because it requires
j*L
simply replacing the burner tip. The reduction, however,
does not exceed 40 percent for existing boilers although it
could reach 50 percent for new ones. Figure 2-10 illus-
trates the results of NO reduction for 16 commercial
2t
boilers with capacities larger than 200 t/hr. NO reduction
X
by this burner decreases with the increase of effects of
other control methods such as flue gas recirculation and
staged combustion.
RESEARCH ON FUEL NO 12
X
Background
Central Research Institute of Electric Power Industry
(CRIEP) has made extensive tests on combustion modification.
2-14
-------
Q
LU
O
O
A
>- Q£
CO LU
O =>
i— i OQ
I—
(_> LU
S5
LU —I
o: u_
OTHER MEANS
NONE
FLUE GAS RECIRCULATION (A)
STAGE COMBUSTION (B)
WATER INJECTION (C) (A) + (C)
(A) + (B)
ATOMIZING
PRESSURE STEAM
20 40 60
REDUCTION BY OTHER MEANS,
80
Figure 2-10. N0x reduction by IHI burner and other means
2-15
-------
Some of the results of tests on fuel NO are discussed
X
below.
Experimental Furnace
Fuel flow rate: 50 liters/hr
Burner: pressure-atomizing type (steam or air)
Heat generating rate: 2.48 x 10 kcal/m hr
Maximum air preheat temperature: 350°C
Maximum fuel preheat temperature: 150°C
Experimental Results
Figure 2-11 shows the correlation between NO concen-
JC
tration (corrected to 4% 02) and the amount of bound nitro-
gen in fuel oil. Various amounts of quinoline were added to
grade C heavy oil (N = 0.2%) to vary the nitrogen content in
the fuel. NO concentration increased linearly with N
X
content. Figure 2-12 shows that conversion of the bound
nitrogen to NO was strongly dependent on O9 concentration
H £.
and was independent of the amount of N in the fuel. Figures
2-13 and 2-14 show similar results of field tests carried
out at a 125-MW power plant. As shown in Figure 2-15 there
were some differences of conversion ratio in tests of the
different-sized units.
Figure 2-16 shows the flame-temperature dependence of
the conversion ratio.
2-16
-------
1000
800
600
400
200
o 0 = 3%
a 02 = 0.5%
? 00 = 0.25%
"0 0.4
o
i—i
i-
C£
z
o
t—I
oo
O
O
1.2 1.6
50
40
30
20
10
N IN FUEL, %
02 IN GAS
Figure 2-11. Results at
test furnace.
Figure 2-12. Results at
test furnace.
400
300
,* 200
100
POWER
PLANT (A)
D 02=4%
0.1 0.2 0.3 0.4
N IN FUEL, %
Figure 2-13. Results at
125-MW power plant.
50
40
30
co
cc.
20
o
10
POWER
PLANT (A)
2 3 4
02 IN GAS, %
Figure 2-14. Results at
125-MW power plant.
2-17
-------
40
30
o
I
o
I—I
oc
O
o
20
TO-/
02 IN GAS, %
Figure 2-15. Comparison of conversion ratio
at power plant and test furnace.
100
70
~ 50
2 30
OL
UJ
>
O
O
20
10
N
I
I
-4
4.8 5.2 5.6 6.0x10
RECIPROCAL OF FLAME TEMPERATURE, 1/°K
• Test furnace, pressure atomizing
A Test furnace, supersonic wave burner
o Power plant (A), 125 MW
Figure 2-16. Flame temperature and conversion ratio.
2-18
-------
3. NO REMOVAL BY WET PROCESSES
GENERAL DESCRIPTION
Major Wet Processes and Plants for NO Removal
In Japan, sodium scrubbing has been used to remove NO
from NO -rich gases produced in relatively small amounts at
metal-dissolving plants, nitric acid plants, etc. The by-
product solution containing sodium nitrate and nitrite is
purged after dilution except in nitric acid plants, which
recover them for limited use. In treating large amounts of
flue gas, neither purging nor recovery is acceptable. In
recent years, many wet processes for NO removal have been
X
developed with the aim of eliminating troublesome by-prod-
ucts or removing NO and SO simultaneously. Major pro-
cesses and plants are listed in Table 3-1.
Most of the NO in flue gas is present in the form of
NO, which is inactive and not easily absorbed by liquors.
NO is usually oxidized into NO- or N205/ which are much more
easily absorbed. For the oxidation, ozone is used in the
Chiyoda and Tokyo Electric-Mitsubishi H.I. processes; chlor-
ine dioxide, CIO-, in the Sumitomo-Fuji Kasui process;
sodium or potassium permanganate in the Nissan and MON
processes; and calcium hypochlorite, Ca(OCl)2, in the Kobe
Steel process. In the Ube and Kawasaki processes, NO- is
added to the gas to maintain the NO2/NO mole ratio at 1 to
promote the absorption.
In the processes being developed by the Central Re-
search Laboratory of Electric Power Industry (CRIEP),
3-1
-------
Table 3-1. MAJOR PLANTS FOR NO REMOVAL FROM FLUE GAS BY WET PROCESS
Process developer
Sumitomo Metal
Fuji Kasui
Sumitomo Metal
Fuji Kasui
Sumitomo Metal
Fuji Kasui
Chiyoda
Tokyo Electric
Mitsubishi H.I.
Tokyo Electric
Mitsubishi H.I.
Mitsubishi Metal
MKK, Nihon Chem.
Fed. of Electric
Power Ind .
Kureha Chemical
Fed. of Electric
Power Ind.
Kawasaki H.I.
Kobe Steel
Chisso Corp.
Type of process
Redox
Redox
Redox
Redox
Oxidation
absorption
Oxidation
absorption
Absorption
oxidation
Reduction
Magnesium
scrubbing
Redox
Reduction
Plant owner
Sumitomo Metal
Toshin Steel
Toshin Steel
Chiyoda
Tokyo Electric
Tokyo Electric
Mitsubishi
Metal
Kureha Chem.
EPDC
Kobe Steel
Chisso Pet.
Chem.
Plant site
Amagasaki
Fuji
Osaka
Kawasaki
Minami-
Yokohama
Minami-
Yokohama
Omiya
Nishiki
Takehara
Kakogawa
Goi
Capacity,
Nm3/hr
62,000
•
100,000
39,000
1,000
2,000
100,000
4,000
5,000
5,000
1,000
300
Source of 'gas
Boiler3
Furnace^
Boiler3
Boiler3
Boiler
Boilerb
Boiler3
Boiler3
Boiler0
Furnace6
Boiler3
Completion
December 73
December 74
December 74
1973
December 73
October 74
December 74
April 75
December 75
December 73
1974
By-product
NaN03, NaCl
N32S04
NaNOs, NaCl
N32S04
NaN03, NaCl
N32S04
Gypsum
Ca(N03)2
HN03
HN03
KN03
Na2S04
N2
Gypsum
Ca(N03)2
Gypsum
N2
(NH4)2S04
to
Oil-fired boiler.
Gas-fired boiler.
Coal-fired boiler.
Metal heating furnace
Iron ore sintering furnace.
-------
Kureha, and Chisso, NO is absorbed without oxidation under
the presence of a catalyst.
Various kinds of by-products are produced: nitric acid
by the Tokyo Electric-Mitsubishi H.I. process, potassium
nitrate by the MON process, ammonium sulfate by the Chisso
process, and calcium nitrate by the Kawasaki process. CRIEP
and Kureha intend to reduce NO into N_. In the Sumitomo-
Fuji Kasui and Chiyoda processes, a portion of NO is con-
X
verted into N2 and the rest into nitrate.
NO Oxidizing Agents
Oxidation of NO in the gas phase by ozone or chlorine
dioxide occurs much more rapidly than oxidation in the
liquid phase by permanganates or hypochlorites; although
permanganates and hypochlorites are strong oxidizing agents,
absorption of NO in the liquid phase is slow.
Ozone produced from air by an electrically driven ozone
generator is capable of oxidizing NO not only to NO? but
also to N2O5, which readily reacts with water or alkaline
solutions to form nitric acid or nitrates. Ozone, however,
is fairly expensive.
Converting the NO in flue gas from a 35-MW oil-fired
boiler into NO2 requires 400 to 600 kg/hr of ozone, assuming
that the gas contains 200 to 300 ppm NO. Figure 3-1 shows a
rough estimation of the capital costs for ozone generation.
Power consumption by an ozone generator is assumed to be
approximately 32 kWh per kilogram of ozone; the cost of
ozone calculated from the capital and power consumption is
roughly 1.3 to $1.5 per kilogram or 2.7 to $3.0 per cubic
meter; these values indicate that ozone costs 500 to $900
per hour for the 35-MW plant or 7 to $12 per kiloliter of
oil. Because of the high cost of ozone, therefore, NO
concentration in flue gas should be kept low by combustion
3-3
-------
50 TOO 200
OZONE GENERATION CAPACITY, kg/hr
Figure 3-1. Capital cost for ozone plant.5
3-4
-------
control to reduce ozone consumption.
Chlorine dioxide is also an effective oxidizing agent
but it adds a chloride to the by-product and complicates the
treatment.
Reaction of NO with Liquids
*" X. ' — -ii -' ••• »
When NO and N02 are present at high equal concentra-
tions, a substantial amount of N^O., is formed, which is
readily absorbed by an alkaline solution to form a nitrate.
NO + N0 = N0 (1)
2NaOH + N203 = 2NaN02 + H20 (2)
When NO concentration is low, as in ordinary flue gas,
1\.
N~O_, does not form in significant amounts even when the
NO/NO,, mole ratio is 1 and the absorption rate is low.
The reaction rate of NO2 with NaOH or water is much
lower than that of S0? with NaOH, as shown in Figure 3-2.
NO~ reacts fairly rapidly with sodium and ammonium sulfites.
The reaction of N02 with sulfites forms nitrites, N2 ,
and a small amount of N20. Although the reaction mechanisms
are not clear, the main reactions may be described simply as
follows:
3S03~~ + 2N02 + H20 = 2N02~~ + 2HS03~ + SO4~~ (3)
4SO3 + 2NO2 = 4S04 + N2 (4)
Reaction (4) is predominant when a large excess of
sulfite ion is present. Because alkali scrubbing of flue
gas containing S02 produces the sulfite ion, these reactions
are useful in the simultaneous removal of SO~ and NO .
2 x
NO hardly reacts even with sulfite solutions. Use of a
catalyst, however, can promote the reaction. CRIEP and
Kureha use a catalyst to absorb NO and to convert it into
N~ . Chisso uses a different kind of catalyst to reduce most
of the NO into NH .
3-5
-------
I 1.0
io.8
y 0.6
0.4
0.3
0.2
N02-H20 N02-NaOH
_L
I
I
0 0.5 1 24
GAS VELOCITY, m/sec
Figure 3-2. Relative absorption rate in
various systems (NO 200-1,000 ppm) .
3-6
-------
Concentrated sulfuric acid can absorb NO and N02, but
the reaction is not useful in flue gas treatment because of
the low reaction rate and the presence of much moisture in
flue gas.
Advantages and Disadvantages of Wet Processes
The advantages of the wet process over the dry process
(catalytic reduction) are as follows:
(1) Simultaneous removal of SO9 and NO is possible.
£* X
(2) Heating the gas to a high temperature (such as to 350
to 400°C in selective catalytic reduction) is not
necessary.
(3) The process is not disturbed seriously by dust as ,in
catalytic reduction.
(4) Although a wet process may be expensive, it may by-
produce a fertilizer such as potassium nitrate or
ammonium sulfate, whereas in selective catalytic
reduction a large amount of ammonia is converted into
N2.
Wet processes have the following disadvantages :
(1) Most processes use an expensive oxidizing agent.
(2) NO^ reacts much more rapidly than NO but still much
more slowly than S02. A large absorber is required.
(3) Concentration of the absorbing liquor, normally dilute,
uses much energy to recover useful by-products.
(4) Demand for the by-products is limited.
(5) Liquors containing nitrate or nitrite should not be
purged. Removing these compounds from wastewater is
difficult.
Generally, although wet processes are advantageous for
removal of SO-, they may be more troublesome than dry
processes for removal of NO .
X
3-7
-------
SUMITOMO-FUJI KASUI PROCESS (MORETANA PROCESS)
Background
The process developers are Sumitomo Metal Industries
Ltd. and Fuji Kasui Kogyo K. K. Sumitomo Metal is a large
steel producer, and Fuji Kasui is an engineering firm
concerned primarily with wastewater treatment. They have
jointly developed a process for simultaneous removal of SO
and NO . A semicommercial plant with a capacity of treating
X 3
62,000 Nm /hr of flue gas from an oil-fired boiler was
completed in 1973 at the Amagasaki Works, Sumitomo Metal.
Two commercial plants of relatively small size went into
operation recently (Table 3-1).
Process Description
A flowsheet of the process is shown in Figure 3-3.
Flue gas is first cooled to 55 to 65°C in a cooler by a
water spray- An oxidizing agent, gaseous chlorine dioxide,
C102, is added to the gas just before the scrubber; it
oxidizes NO into NO- within 0.5 second. The gas is then
introduced into a "Moretana scrubber" with four stages of
perforated plates, which provide excellent gas-liquid mass
transfer. In reaction of the gas with a sodium hydroxide-
sulfite solution, more than 98 percent of the SO- is ab-
sorbed to produce sodium sulfite, which reduces NO- into N-.
The main reactions involved are as follows:
2NO(g) + Cl02(g) + ^0 = N02 (g) + HCl(g) + HN03 (g)
HCl(g) + NaOH(aq) = NaCl(aq) + H20
HN03(g) + NaOH(aq) = NaNO3(aq) + H20
S02(g) + 2NaOH(aq) = Na2SO3(aq) + H20
2N02(g) + 4Na2S03(aq) = N2 + 4Na2S04(aq)
The use of stoichiometric amounts of C102 eliminates
about 90 percent of the NO in the gas. About half of the
X
3-8
-------
OXIDIZING
AGENT
1: BOILER 2: COOLER
3: SCRUBBER 4: MIST ELIMINATOR
5: AFTER BURNER 6: STACK
Figure 3-3. Flowsheet of Sumitomo -
Fuji Kasui process.
3-9
-------
removed NO is converted into N., and the rest into sodium
J\. £•
nitrate. A large excess of Na_SO-, is required for the
formation of N? . The CIO™ is produced by reacting NaClO_
with concentrated S02 and H2SO,.
2NaHS04
2NaCl03 + SO™ + H2SO4 = C102 + 2NaHSO4
When the flue gas contains 260 ppm NO , mainly in the
a
form of NO, 1500 ppm SO2 in flue gas derived from 3 percent
sulfur oil is not sufficient for the reactions and a small
amount of make-up NaSO-, is needed. The lower the concen-
tration of S02 in the flue gas, the larger the required
amount of make-up NaSO_.
The by-product of the scrubbing, a solution containing
NaCl, Na_SO , and NaN03 , is purged after dilution. Studies
are being directed toward recovering NaCl from the solution
and producing NaC10_ or at recovering Na2S04 and producing
NaOH and H_SO. by electrolysis.
3
Tests on ammonia scrubbing at a 25,000 Nm /hr pilot
plant are planned with a view to by-producing gypsum and
ammonia compounds for use in fertilizers.
Evaluation
Capital cost is in the range of 60 to $90 per kilo-
watt. Operating cost including depreciation (7 years) is
estimated roughly at $30 per kiloliter of oil or 7 mills per
kWh without wastewater treatment.
The scrubbing process is simple and the removal ratio
is high for both SO and NO . A major drawback of the
X X.
process is the by-production of liquor containing NaCl,
Na2S04, and NaN03 , which is difficult to treat. Use of
ozone in place of C102 is considered. When ozone is used,
the by-product liquor contains no NaCl but is still not easy
3-10
-------
to treat. Moreover, ozone is costlier than CIO . Applica-
tion of the process on a large scale may not be feasible
unless the liquor can be adequately treated.
Ammonia scrubbing may be a good way to eliminate
production of the troublesome sodium salts and to recover
useful by-products. The process may create a plume, however.
Moreover, the by-product, a mixture of ammonium nitrate,
chloride, and sulfate, is very hygroscopic and may not be
suited for use in solid fertilizer.
TOKYO ELECTRIC - MITSUBISHI H.I. PROCESS
Background
The process developers are Tokyo Electric Power Co. and
Mitsubishi Heavy Industries. Tokyo Electric Power, one of
Japan's nine major power companies, and Mitsubishi Heavy
Industries, one of the largest ship and machine producers in
Japan, jointly introduced a nitric acid by-producing process
from U.S.S.R. and constructed at the Minamiyokohama power
station of Tokyo Electric Power a pilot plant with a capa-
city of treating 2000 Nm /hr of flue gas from a natural-gas-
fired boiler. The plant was operated from December 1973 to
September 1974. A larger pilot plant (100,000 Nm3/hr) went
into operation in December 1974 at the same power station.
Process Description
A flowsheet of the smaller test unit is shown in Figure
3-4. The flue gas from the boiler is cooled, injected with
ozone, and introduced into an oxidizing tower, where NO is
.X
oxidized to N205- The gas is then treated with water in an
absorber to produce nitric acid of 8 to 10 percent concen-
tration, which is concentrated to 60 percent for industrial
use.
3-11
-------
U)
I
COOLER
GAS1
T
OZONE GENERATOR
r
SEA WATER
[CONDENSER
0
xioizir
TOWER
K
JG
^ 1
>
X
1
— »
i MIST
ELIM-
INATOR
w
Q
LIQUOR TANK
ABSORBER
.CLEANED _GAS___^
OZONE REMOVAL
TANK
TANK
Figure 3-4. Flowsheet of Tokyo Electric - Mitsubishi H. I. process.
-------
NO
N-Oc + H_O = 2HNO-.
^ j ^ j
As an alternative, the gas discharged from the oxi-
dizing tower is indirectly cooled by sea water, where mois-
ture in the gas condenses and reacts with N^O- to produce
dilute nitric acid of about 1 percent concentration. The
dilute acid may be decomposed into N- and H~0 by biological
treatment.
The effluent gas from the absorber or the condenser
contains a small amount of ozone. This effluent is treated
in an ozone removal tower with a reducing agent such as
sodium or calcium sulfite.
0, + Na2S03 = Na2SO. + 02
0., + CaSO3 + 2H20 = CaSO4'2H20 + O2
Performance
The smaller test unit was operated for about 9 months.
The gas contained 90 to 220 ppm NO , 8.5 percent C00, 16.8
5C ^
percent H20, and 2.6 percent 02 .
The NO removal ratio was kept over 90 percent by
X
control of oxidation temperature, 0.,/NO ratio, and oxida-
•j X
tion time. Ozone was almost entirely removed by the ozone
removal tower. The recovered nitric acid concentrated to 60
percent was pure enough to meet the relevant Japanese
Industrial Standard. In some tests, NO was oxidized into
NO.., with ozone (no oxidizing tower was needed in this case)
and treated with a sodium sulfite solution. More than 90
percent of the N02 was removed through the following reac-
tion:
2N00 + 3Na,SO, + H-O = 2NaNO0 + 2NaHSO, + Na^SO,
2. £ 5 £ 2. J24
3-13
-------
Process flow at the larger pilot plant (100,000 Nm /hr)
is similar to that shown in Figure 3-4. The plant has used
calcium sulfite for ozone removal and to by-produce gypsum.
No operation data have been disclosed.
Evaluation
The process is simple and suitable for treatment of
"clean gas" without SO_. High NO removal is achieved
^ A.
without production of waste liquor. On the other hand, the
use of ozone and the concentration of nitric acid are
costly. Moreover, the demand for nitric acid is limited.
The process might be more expensive than a selective cat-
alytic reduction process.
CHIYODA THOROUGHBRED 102 PROCESS5
Background
The process developer is Chiyoda Chemical Engineering
and Construction Co. Chiyoda has developed an SO? removal
process called Thoroughbred 101 and has constructed many
commercial plants. The process designated 102 entails a
simple addition of an ozone injection step to the 101
process for simultaneous removal of NO and S00. A pilot
3 x
plant (1000 Nm /hr flue gas from an oil-fired boiler) has
been in operation.
Process Description
A flowsheet of the process is shown in Figure 3-5.
Flue gas is cooled in a cooler to 50 to 60°C, injected with
ozone and air to oxidize NO into NO-, and then introduced
into a packed tower scrubber and treated with dilute sulfur-
ic acid containing a ferric iron catalyst. More than 60
percent of the NO and 90 percent of the SO9 are removed
X £.
(Figure 3-6). A portion of the removed NO forms nitric
J\.
acid and the rest forms N~ and N_0, both of which are harm-
3-14
-------
ABSORPTION-OXIDATION STAGE
GYPSUM PRODUCTION STAGE
GJ
I
M
cn
REHEATER
CLEAN GAS
CENTRIFUGE
PURGE STREAM
PRESCRUBBER ABSORBER OXIDIZER H2$04 RECEIVER MOTHER LIQUOR TANK
Figure 3-5. Flowsheet of Chiyoda Thoroughbred 102 process.
-------
100
o
oo
80
60
40
20
1.0
NO.
INLET GAS
N0¥ 600 ppm
/\
S02 1,500 ppm
TEMPERATURE 55°C
ABSORBER COLUMN
60 mm DIA. x
1000 mm HIGH
I
1.5
x VALUE IN NO.
2.0
Figure 3-6. Relation between oxidation ratio
and removal of SO- and NO .
Ci J\.
3-16
-------
less gases. The liquor discharged from the scrubber is
oxidized by air bubbles to convert SO, into SO. "" and
Fe into Fe . Most of the liquor is returned to the
scrubber; a portion is reacted with powdered limestone to
precipitate gypsum. The gypsum slurry is centrifuged. A
portion of the mother liquor is purged to prevent the
accumulation of nitric acid and impurities derived from flue
gas and limestone.
Evaluation
The process is simple and plant operation easy. The
NO removal ratio is not very high but is acceptable. The
J^
major drawback of the process is that wastewater containing
calcium nitrate is purged. For application on a large
scale, wastewater treatment for denitrif ication will be
needed but may not be easy. Another disadvantage is that
the process uses ozone, which is expensive. NO concentra-
Jt
tion of the flue gas should be kept low by combustion con-
trol in order to reduce ozone consumption.
NISSAN PERMANGANATE PROCESS7
Background
The process developer, Nissan Engineering, Ltd. , is a
subsidiary of Nissan Chemical Industries. Nissan has
developed an NO removal process using a potassium or sodium
2^
permanganate solution and has constructed four small commer-
cial units to treat waste gases from plants using nitric
acid, as shown below.
Capacity, Nm /hr
2000
100
1800
1500
Completion
October 1972
August 1973
August 1973
March 1975
3-17
-------
Process Description
A flowsheet of the process is shown in Figure 3-7.
Waste gas rich in NO is first washed with an alkali solu-
2i
tion to decrease the concentration to 200 to 500 ppm. (This
treatment is not needed when NO concentration in the gas is
j£
less than 500 ppm) . The gas is then treated with an alka-
line solution containing a permanganate to reduce NO to
J\.
below 50 ppm. The following reactions occur when potassium
compounds are used:
Reactions in alkaline solution:
NO + KMn04 + 2KOH =
3NO + KMn04 + 2KOH =
= KMnO. +
£ t. i 4 /
Main reaction in neutral solution:
NO + KMn04 = MnO2 + KNO- . .;,
The resulting Mn02 is separated and reacted with KOH to
produce K2MnO4 by the following reaction:
Mn02 + 2KOH + 1/2 O2 = K2Mn04 + H20
K-MnO, is subjected to electrolytic oxidation to regenerate
KMn04. About 0.6 to 1.0 kWh/gram mole K2Mn04 is required
for the electrolysis.
K2MnO4 + H2O = KMn04 + KOH + 1/2 H2
KNO- obtained by the reaction in an alkaline solution
is treated with sulfuric acid to release concentrated NO,
which may be returned to a nitric acid plant. KNO- obtained
by using a neutral solution can be treated by electrolysis
in a special cell to produce fairly pure HNO, (25-30% in
concentration) and a mixture of KOH and KNO-.
KN03 + H20 = KOH + HNO_
The power requirement is 0.5 to 0.7 kWh/gram mole KNO,.
3-18
-------
CLEANED GAS
WASTE
GAS
x,
f \
cf*m IDD co
SLRUDDhR
-f
£.
K9MnU. Uk
^ <- 1 REGENERATION
^ KMnO, + KOH KtbtntK/xiiun
i
i . I
N Mn02 KOH
J
^
^ IA1NN ^ rlLlhK ^ uwrv
HNUo
ELECTROLYSIS
Figure 3-7- Flowsheet of Nissan permanganate process
(NE-D process),
3-19
-------
KMnO. + NO = KN03 + Mn02
KNn04 + 2KOH +
2KMnO/l + 4KOH
4 Z Z 4 ^ <£
Manganese dioxide is converted to alkali permanganate
or manganate by a conventional process. The alkali nitrate
(and sulfate) solution obtained is concentrated to produce a
solid product, which can be used for fertilizer and other
purposes. A simplified flowsheet is shown in Figure 3-8.
Evaluation
An advantage of the process is by-production of potas-
sium nitrate, which is useful as fertilizer. The process
must be costly, however, because it consumes potassium
hydroxide and requires regeneration of potassium permangan-
ate .
TESTS BY CRIEP ON SODIUM SULFITE SCRUBBING8
Background
CRIEP (The Central Research Institute for Electric
Power Industry), which is financed by the nine major power
companies of Japan, has performed extensive fundamental
research in NO abatement including work on combustion
control and wet and dry processes for NO removal from flue
X
gas. CRIEP did laboratory work on NO absorption by a sodium
sulfite solution containing a ferrous compound and performed
tests with a small packed tower. CRIEP recently started to
cooperate with Kureha Chemical in further development of the
process.
Description of the Tests
Figure 3-9 shows the apparatus used in the laboratory
tests. The adsorption column is 36 mm in diameter and 150
mm high. One liter of sodium sulfite solution (10%) was
placed in the column to a depth of 100 mm. Nitrogen gas
3-20
-------
PURIFIED GAS
U)
I
to
WASTE GAS
I
WET-SYSTEM
ABSORPTION
FILTER
ALKALI
MANGANESE DIOXIDE
CONCENTRATION
CRYSTALLIZATION
REGENERATION
MOTHER LIQUOR
ALKALI NITRATE
(ALKALI SULFATE)
Figure 3-8. Simplified flowsheet of MON process,
-------
(2)
m u2 so2 o2 co2
T
D
O
o
0
o
O
•N
T
H
(3)
1
T
»°x
(4)
so2
(5)
GAS PREPARATION
ABSORPTION
ANALYSIS
(1) GAS HEATER (2) ABSORPTION COLUMN
(3) TRAP (4),(5) ANALYZER
(6) HOT WATER (7) POROUS PLATE
Figure 3-9. Apparatus for test (CRIEP).
3-22
-------
containing 265 ppm NO was bubbled from the bottom of the
column at a rate of 1.5 liters per minute into the solution
kept at 50°C. Various additives were tested to promote the
absorption. Ferrous sulfate and oxalate promoted the NO
absorption remarkably, as shown in Table 3-2.
Table 3-2. EFFECT OF ADDITIVES ON NO REMOVAL
Form of additive
None
Fe(S04)2
CuCl
Ni~ ( SO , ) „
2 43
CrCl3
CoCl3
FeC2°4
Cu(CH3COO)2
SnC204
Concentration
of additive, %
None
0.3
1
1
1
1
1
0.1
0.1
NO removal
ratio, %
15
95
52
5
18
20
98
34
19
pH of
liquor
9.8
6.6
7.9
8.3
7.5
5.2
7.8
7.3
9.1
Ferrous hydroxide precipitates when the solution is
neutral or alkaline. Addition of a small amount of ethylene
diamine tetraacetic acid (EDTA) prevented the precipitation
and further promoted the absorption. Figure 3-10 shows the
relationship of NO removal ratio to the concentration of
sodium sulfite solution containing a ferrous sulfate or
ferrous chelate (EDTA) compound. The NO removal ratio
reached more than 90 percent when the concentration of the
sulfite was more than 5 percent with the ferrous sulfate and
more than 0.4 percent with the ferrous chelate compound.
High oxygen concentration in the gas considerably decreased
the removal efficiency with the ferrous or ferric sulfate
but only slightly with the ferrous or ferric chelate com-
3-23
-------
pound (Figure 3-11).
Further tests were carried out with a small tower 200
mm in diameter and 2 m in packing height packed with Teller-
ette. A gas containing 365 ppm NO, 930 ppm SO2, and 3
percent 0~ was introduced from the bottom at a rate of 80
3
Nm /hr, while an absorbing liquor (10% sodium sulfite
solution containing 0.02 mole/liter ferrous chelate compound
at pH 6) was fed at a rate of 1800 liters/hr. The NO
removal ratio was 43 percent, an indication that about a 10-
m packing height was required for 90 percent removal. The
SO,, removal ratio was 98 percent. Tests are in progress to
study the form of NO in the liquor and determine a way to
reduce the absorbed NO into N~.
Evaluation
NO is not easily absorbed in many kinds of liquors and
is usually oxidized into NO- prior to scrubbing. In a
sodium sulfite solution containing a ferrous compound, NO is
absorbed fairly well. Although the absorption occurs slowly
and requires a high tower, elimination of the oxidation step
and expensive oxidizing agent is a considerable advantage of
the process. It is desirable to develop a good way to
convert the absorbed NO into a harmless or useful by-product.
Ferrous sulfate is not expensive but is affected by
oxygen in flue gas. The ferrous chelate compound is not
affected but is expensive and should not be lost during the
treatments. Flue gas normally contains a small amount of
chlorine, which tends to accumulate in the absorbing liquor
and is usually purged with wastewater. The purge of water
should be minimized or eliminated because it would cause the
loss of the chelate compound.
3-24
-------
a FERROUS SULFATE
•(EDTA-2Na)-
FERROUS CHELATE
0.1 0.2
10
ADDITIVE 0.01 mole/£ GAS 1.5 £/min PLATE
ABSORBING LIQUOR 1.0 £ NO 275 ppm
ABSORBING LIQUOR 50°C
Figure 3-10. Effect of Na2SO, concentration.
30
20
10
0
- Na2S03-NaHS03 10%
- OTHER CONDITIONS ARE SAME
AS IN FIGURE 3-10
i i i
12345678
02 IN GAS, %
CHELATE
10
Figure 3-11. Effect of 0- concentration.
3-25
-------
Evaluation
The process may be suited for treating relatively small
amounts of gas. Potassium hydroxide is costly, and the
demand for potassium nitrate is limited. Therefore, the
electrolysis of potassium nitrate to produce nitric acid and
potassium hydroxide may be needed for treating large amounts
of gas. The process, however, might be more costly than the
acid, because the Nissan process involves two electrolysis
decomposition. For flue gas containing S0~, a desulfuriza-
tion step should be applied first to reduce the consumption
of potassium hydroxide and permanganate.
MON ALKALI PERMANGANATE PROCESS
Background
The process developers are Mitsubishi Metal Co.,
Mitsubishi Chemical Machinery Mfg. (MKK), and Nippon Chemical
Industrial Co. Under the leadership of Professor T. Okabe,
Tohoku University, these three companies have jointly
developed the process. A pilot plant (300 Nm /hr flue gas
from an oil-fired boiler) started operation in November 1972
removing both NO and SO9. A large pilot plant (4000 Nm3/hr)
J\: £*
went into operation in December 1974 at the Omiya Research
Station, Mitsubishi Metal, in which flue gas is first washed
with a sodium hydroxide solution to remove SO- and is then
subjected to NO removal.
J\,
Process Description
NO (and also SO9) in waste gas are absorbed in an
X ^
alkaline solution containing alkali permanganate or mangan-
ate—for example, a KOH solution containing KNnO.. The NO
4 x
(and S0~) are absorbed and oxidized to form alkali nitrate
and sulfate while permanganate or manganate is reduced to
precipitate manganese dioxide, which is then filtered off.
3-26
-------
KUREHA REDUCTION PROCESS
Background
The process developer is Kureha Chemical Industry Co.
Kureha, a middle-size chemical company, has developed many
new processes that have been used commercially, including
those for oil gasification and wet desulfurization. Kureha
has tested NO removal by a sodium sulfite solution contain-
H
ing a catalyst and acetic acid, which promote the reaction
remarkably. A pilot plant with a capacity of treating 5000
Nm /hr of flue gas from an oil-fired boiler is under con-
struction at the Nishiki Works of Kureha. The pilot test is
assisted by the Federation of Electric Power Industry. The
Central Research Institute for Electric Power Industry
(CRIEP) recently started to cooperate with Kureha for
fundamental research of the process.
Process Description
A schematic flowsheet of the process and major chemical
reactions are shown in Figure 3-12. Flue gas containing SO-
and NO is first introduced into a desulfurization unit (1)
X.
where SO- is absorbed by a sodium acetate solution to
produce sodium sulfite and acetic acid. The treated gas is
sent to an auxiliary NO removal unit (2) (some NO0 is added
X ^
to the gas and treated with a limestone slurry to remove NO-
and equal amounts of NO). Calcium nitrite is by-produced.
The remaining NO is then absorbed at a main NO removal unit
X
(3) by a mixed solution of sodium sulfite and sulfate con-
taining acetic acid and a catalyst. A compound NH(S07Na)_
is formed by the absorption. The solution containing the
compound and sodium sulfate is treated in a unit (5) with
calcium acetate, to precipitate gypsum. The calcium acetate
is obtained in a deacetation unit (4) by reaction of acetic
acid and limestone. The liquor from the gypsum filter
3-27
-------
CO
I
CX3
CLEANED GAS
(1) 2CH3COONa +
(2) CaC03 + NO
(3) Na2S03 + S02 + NO
(4) 2CH3COOH + CaC03—
2CH3COOH
CaC03
CaC03
Na2S03
CH,COOH
•J
DEACETATION (4)
NOX REMOVAL
(MAIN )(3)
NOX REMOVAL
(AUXILIARY) (2)
(i)
DESULFURIZATION
(CH3COO)2Ca 1
Na2S04 NH(S03Na)2 ^pi
* FORM
CH.COON, 1
Jo I
Ca(N02)2
CATALYST
CaCO, ,
1 S
NH(SO,Na)7
UM •" (6) (7)
JION "
Na,SO. +
GYPSUM
1
GYPSUM _ ^vin.TTm, GYPSUM^
"* REGENERATION " »«»«„.»,•
1
Na2S04 + CATALYST
AIR
GAS
(5) Na2S04 + (CH3COO)2Ca
(6) NH(S03Na)2 •«•
(7) 2NH4S04S03Na •
2CH3COONa
NaHS0
Figure 3-12. Flowsheet of Kureha process.
-------
containing NH(S03Na)- is sent to a unit (6) in which the
compound is hydralized to form NH2SO.,Na, which is then
reacted with calcium nitrite to release nitrogen gas and to
by-produce gypsum and sodium sulfate (reactions 6 and 7).
Gypsum is separated, and the liquor containing sodium sulfate
and catalyst is sent through a catalyst regeneration unit to
the main NO removal unit.
X
Evaluation
The process has the advantage of removing both SO- and
NO while by-producing harmless nitrogen and useful gypsum.
The process, however, is very complex and the plant seems
costly and not easy to operate. Operational data of pilot
plant are needed for further evaluation.
KAWASAKI MAGNESIUM PROCESS
Background
The process developer is Kawasaki Heavy Industries, one
of the largest machine and plant manufacturers. They have
developed SO- removal processes using both sodium scrubbing
and magnesium scrubbing. Kawasaki also has tested a process
for simultaneous removal of SO- and NO by magnesium scrub-
bing and is constructing a pilot plant with a capacity of
treating 5000 Nm /hr of flue gas from a coal-fired boiler at
the Taenake Power Station, Electric Power Development Co.
The pilot plant is scheduled to go into operation in July
1975 under sponsorship of the Federation of Electric Power
Industry.
Process Description
A flowsheet of the process is shown in Figure 3-13. The
gas containing about 1000 ppm SO2 and 400 ppm NO is mixed
with NO- gas to adjust the NO2/NO ratio to 1 and is treated
with a magnesium hydroxide slurry to form magnesium sulfite
3-29
-------
CO
CO
o
FLUE GAS
(S02, NOX)
NO,
ABSORBER
H2S04 , '
LL
"NO
^g (NO.)
L J
M9SOJ
Ca(N03)2
GYPSUM
Figure 3-13. Flowsheet of Kawasaki magnesium process.
-------
and nitrite. The nitrite is separated and decomposed by
adding sulfuric acid to produce NO, which is oxidized to NO 2
and returned to the absorber. Magnesium sulfite is oxidized
into sulfate and reacted with calcium nitrate to precipitate
gypsum, which is returned to the absorber. The calcium
nitrate liquor formed by the reaction is partly returned to
the system for the reaction with magnesium sulfate and
partly obtained as a by-product.
Advantages
The process removes both SO9 and NO while by-producing
^ X
salable gypsum and calcium nitrate, which may be used for
fertilizer.
Disadvantages
The process is complex, and the plant may be costly.
It may not be easy to attain high NO removal efficiency.
,A
The use of calcium nitrate is limited.
CHISSO AMMONIA SCRUBBING PROCESS
Background
The process developer is Chisso Corporation, a fertili-
zer producer that recently expanded to the petrochemical
business. Chisso has developed a process for simultaneous
removal of SO~ and NO from flue gas by ammonia scrubbing
£* J\.
using a catalyst to by-produce ammonium sulfate. A pilot
plant (300 Nm /hr of flue gas from an oil-fired boiler) has
been operated.
Process Description
A schematic flowsheet of the process is shown in Figure
3-14. Flue gas containing S09 and NO is absorbed with an
£* X.
ammoniacal solution containing a soluble catalyst to reduce
the absorbed NO into NH_ by ammonium sulfite and bisulfite,
H J
which are formed from SO2 and ammonia. Most of the catalyst
3-31
-------
I
to
CLEANED J5AS^
i
I
NH-
ABSORBER
CATALYST
SE
PARATION
THERMAL
TREATMENT
EVAPORATION
CENTRIFUGE
Figure 3-14. Simplified flowsheet of Chisso Process.
-------
is separated from the product solution containing ammonium
sulfate and sulfite and intermediate compounds. The solu-
tion is oxidized by air and then heated to convert the
intermediate compounds into ammonium sulfate. The product
solution is concentrated in an evaporator to crystallize
ammonium sulfate, which is separated by a centrifuge. The
mother liquor, which contains a small amount of the catalyst,
is returned to the scrubber. The overall reaction may be
expressed simply as follows:
2ND + 5S0 +
For recovery of 80 percent of 200 ppm NO , the flue gas
X
should have more than 1200 ppm S0~.
Performance and Problems
The pilot plant has been operated for about a year.
Reaction of NO with the sulfite liquor is slow. The
x ^
removal ratios range from 60 to 80 percent. Use of a dilute
liquor is favorable for the absorption but necessitates much
evaporation for ammonium sulfate recovery. Therefore, NO
J\:
removal of about 70 percent using a moderate concentration
may be suitable. A portion of the catalyst is decomposed by
the treatments. The catalyst is not affected by nickel and
vanadium derived from flue gas. Chisso estimates the cost
for simultaneous removal of SO9 and NO to be about 30
& f±
percent more than the cost of SO- removal only.
Evaluation
The process has an advantage over other NO removal
A
processes in that it gives a useful by-product from recover-
ed S09 and NO . A disadvantage may be the difficulty in
£• A.
attaining a high NO removal ratio. Another difficulty is
jC
the possibility of plume formation, which is common to
ammonia scrubbing processes. For further evaluation,
operating data from a larger plant are required.
3-33
-------
UBE ALKALI SCRUBBING PROCESS
Background
The process developer is Ube Industries Ltd. Ube, a
large chemical company has operated a pilot plant for sodium
scrubbing of tail gas from a nitric acid plant using a
special type of scrubber. Commercial use of the process is
under consideration.
Process Description
A flowsheet is shown in Figure 3-15. To attain an
N02/N0 mole ratio of about 1, the Ube process adds to the
nitric acid plant tail gas, which contains 1000 to 3000 ppm
NO and has a low ratio, a small portion of the process gas,
a
which is rich in N0~. The mixed gas is treated with an NaOH
solution (about 3%) in a three- (or four-) stage tower with
a liquid depth of about 500 mm at each stage. The relation-
ship between the N09/N0 mole ratio of the gas and NO
^ X
concentration in the scrubber outlet gas is shown in Figure
3-16. Sodium nitrite and nitrate are recovered as by-
products.
KOBE STEEL PROCESS
Kobe Steel Ltd. developed an SO2 removal process using
a calcium chloride solution. Kobe has measured NO removal
x 3
for a pilot plant with a capacity of treating 1000 Nm /hr of
flue gas from an oil-fired boiler or an iron ore sintering
plant. NO is absorbed by a calcium chloride solution
JC
containing Ca(OCl)2 as an oxidizing and neutralizing agent.
By the reaction calcium nitrate is formed and chlorine is
evolved, which is caught in a separate absorber by a calcium
sulfite slurry to produce a calcium chloride solution and
gypsum. It is said that a high N0x removal ratio is at-
tained. Corrosion may be a problem, however. Also, means
3-34
-------
must be found for treating the by-products, calcium nitrate
and chloride.
CLEANED GAS
PROCESS
(N02 RICH)
TAIL GAS.
(NOV 1,000-3,000 ppm)
A
X
SCRUBBER
SPECIAL
DISPERSION
ELEMENTS
NaOH
AQ. SOLUTION
BLOWER
PUMP
NaN02
NaNO,
NaOH
AQ. SOLUTION
Figure 3-15. Flowsheet of Ube process.
3-35
-------
1,500
I 1,000
500
I
a PACKED TOWER
. BUBBLING TOWER
INLET GAS 300 1/hr
1.0
N02/N0 MOLE RATIO (INLET)
1.5
Figure 3-16. NO-/NO ratio and NO removal.
£* X
3-36
-------
4. DRY PROCESSES FOR DENITRIFICATION
GENERAL DESCRIPTION
Classification of Dry Processes
Dry processes for denitrification that have been
developed in Japan may be classified as follows:
1. Catalytic reduction (selective, nonselective)
2. Catalytic decomposition
3. Electron beam radiation
4. Absorption (by molecular sieve, gelatinous
silica, calcium silicate, etc.)
Among these, selective catalytic reduction has been
used most widely. Electron beam radiation has been tested
in a pilot plant. Small-scale tests of the dry absorption
process have been made, but essentially no data are avail-
able.
Principle of Catalytic Reduction of NO
1 •"" — - -" .-_--_ r.J Jv
For treatment of tail gas at nitric acid plants,
catalytic reduction of NO by H2, CO, CH., etc., has been
done for several years. As the catalyst, platinum carried
on alumina is used because of its superior reactivity; more
than 90 percent of the NO , which normally ranges in concen-
Ji
tration from 500 to 3000 ppm in the tail gas, is reduced to
N2 at 500 to 800°C at a space velocity (SV) of over 30,000.
For flue gas treatment, selective catalytic reduction by NH..
is preferred because concentration of 0- is much higher than
that of NO and reducing gases such as H~, CO, CH. are
X ^ 4r
consumed mainly by O9. Ammonia reacts not only with NO but
*• x
also with 02, as shown by the following reactions:
4-1
-------
+ 6NO = 5N2 + 6H2O (1)
+ 302 = 2N2 + 6H20 (2)
4NH3 + 502 = 4NO + 6H2
-------
1,000
500
to
o
o
CO
100
50
10,
JOO 1,
'0 200 400 600 80D 1,000
TEMPERATURE, °C
Figure 4-1. Equilibrium constants of reactions,
4-3
-------
Pilot and Commercial Plants with Selective Catalytic
Reduction (SCR) Processes
Many Japanese companies have developed their own
catalysts and tested them in pilot plants. Commercial
developers and pilot plants are shown in Table 4-1. Sumi-
tomo Chemical, the most advanced in this field, has com-
pleted five commercial plants for processing of clean gas
and is constructing two for dirty gas. Hitachi Shipbuilding
is constructing two commercial plants for treatment of dirty
gas; in this treatment, wet-process desulfurization will
precede the denitrification.
Advantages and Disadvantages of the SCR Process
The SCR process has the following advantages:
1. Compared with nonselective catalytic reduction,
SCR consumes much less reducing gas.
2. Compared with wet processes for NOX removal, the
SCR process is simple and requires less plant
space. Moreover, SCR gives no troublesome by-
products and necessitates no reheating of gas.
For removal of NO from clean flue gas, SCR may be the best
ji
of all denitrification processes so far developed. it has
the following disadvantages, however, particularly in
treatment of dirty gas.
1. Base-metal catalysts are not as reactive as
noble-metal catalysts; SV's of 4,000 to 7,000 are
normally used, as compared with a range of 50,000
to 150,000 with noble-metal catalysts. A large
amount of catalyst and a large reactor are re-
quired.
2. Catalysts are affected by dust and most are poi-
soned by 803 and SC>2. Because the catalysts are
made up of heavy metals, disposal of spent cata-
lysts may pose some problem.
4-4
-------
Table 4-1. MAJOR PLANTS FOR DENITRIFICATION BY SELECTIVE CATALYTIC REDUCTION
Process
developer
Plant owner
Plant site
Capacity
(Nm3/hr)
Source of gas
Completion
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Sumitomo Chemical
Hitachi Shipbuilding
Hitachi Shipbuilding
Hitachi Shipbuilding
Tokyo Electric-
Mitsubishi H.I.
Kurabo
Kurabo
Kansai Electric-
Hitachi Ltd.
Sumitomo Chiba
Chem.
Higashi Ninon
Methanol
Nihon Ammonia
Sumitomo Chem.
Sumitomo Chem.
Sumitomo Chem.
Sumitomo Chem.
Sumitomo Chem.
Kansai Oil
Idemitsu Kosan
Shindaikyowa Pet,
Chem.
Tokyo Electric
Kurabo
Kurabo
Kansai Electric
Sodegaura
Sodegaura
Sodegaura
Anegasaki
Anegasaki
Niihama
Sodegaura
Sodegaura
Sakai
Chiba
Yokkaichi
Minamiyokohama
Hirakata
Hirakata
Sakaiminato
30,000
200,000£
250,000*
100,000^
200,000^
200,000*
250,000
300,000
5,000
350,000
440,000
10,000*
5,000
30,000
4,000
Oil-fired boiler
Heating furnace
Heating furnace
Gas-fired boiler
Gas-fired boiler
Heating furnace
Oil-fired boiler
Oil-fired boiler
Oil-fired boiler
CO-fired boiler
Oil-fired boiler
Gas-fired boiler
Oil-fired boiler
Oil-fired boiler
Oil-fired boiler
July 1973
May 1974
Mar
Feb
Feb
Mar
May
May
Nov
Nov
Nov
1975
1975
1975
1975
1976
1976
, 1973
. 1975
, 1975
Jan. 1974
Nov. 1973
Aug. 1975
Jan. 1975
-------
Table 4-1 (continued). MAJOR PLANTS FOR DENITRIFICATION BY SELECTIVE CATALYTIC REDUCTION
Process
developer
Chubu-IHI-Mitsui Toatsu
Chubu-MKK
Mitsubishi H.I.
Kobe Steel
Plant owner
Chubu Electric
Chubu Electric
Mitsubishi H.I.
Kobe Steel
Plant site
Shinnagoya
Yokkaichi
Hiroshima
Kakogawa
Capacity
(NMVhr)
8,000
100
4,000
600
Source of gas
Oil-fired boilers
Oil-fired boilers
Oil-fired boilers
Sintering plant
Completion
Oct. 1974
Oct. 1974
Dec. 1974
May 1974
Clean gas; those without superscript are for treatment of dirty gas.
-------
For treatment of dirty gas, wet-process desul-
furization may be carried out first to remove most
of the dust, SO3, and SC>2 . In this case, the gas
temperature drops to 50 to 60°C and must then be
heated 350 to 400°C. A large heat exchanger and a
considerable amount of fuel are needed. Mists
from the scrubber may cause corrosion of the heat
exchanger and contamination of the catalyst.
4. An NH-j/NOx mole ratio of 1.0 to 1.5 is normally
used, although the theoretical ratio is about
0.67. Although a portion of the excess ammonia
decomposes in the reactor, a considerable amount
of it would remain in the treated gas and may
cause problems. For example, ammonia may combine
with SO^, which is present in a small amount even
after the wet scrubbing, to form ammonium bisul-
fate. Tendency of the bisulfate to condense in a
heat exchanger causes corrosion and decreases heat
transmission.
5. A simple calculation indicates that treating half
of the gas from stationary sources in Japan would
require 600,000 tons of ammonia yearly, which is
equivalent to two-thirds of the total nitrogen
fertilizer consumption in Japan. Because it is
estimated that the world's supply of nitrogen
fertilizer will run short for at least several
years, such a large amount of ammonia should be
used for fertilizer.
SUMITOMO REDUCTION PROCESSES
Selective Catalytic Reduction
Sumitomo Chemical Industries Ltd., has conducted
screening tests since 1971 with more than 1,000 catalysts
with base-metal oxides carried on alumina for selective
reduction of NO by ammonia. The tests have been both with
JC
dirty gas, containing SO and dust, and clean gas essenti-
.X
ally free from those contaminants. A plant with a capacity
to treat 30,000 Nm /hr of flue gas from an oil-fired boiler
has been operated since July 1973. A commercial plant with
a capacity of treating 200,000 Nm /hr of flue gas (clean gas
4-7
-------
from LPG burning) from a reformer at the Sodegaura plant,
Higashi Nihon Methanol Co. (HNM), went into operation in May
1974 (Figure 4-2). This may be the first commercial plant
for flue gas denitrification in the world. Recently, opera-
tion of four more commercial plants for treatment of clean
gas and construction of two commercial plants for treatment
of dirty gas were started (Table 4-1).
Process Description
A flow sheet of the HNM plant is shown in Figure 4-3.
Flue gas (clean gas) containing about 200 ppm NO (mainly
X.
NO) at 300 to 350°C is injected with ammonia at a NH,/NO
•J A.
mole ratio of 1 and introduced into a reactor containing a
base-metal catalyst. About 90 percent of the NO is reduced
to N2 by reaction with ammonia. The treated gas passes
through a fan and heat exchanger to a stack.
6NO + 4NH3 = 5N2 + 6H20
6N02 + 8NH- = 7N2 + 12H20
A schematic flow sheet of a plant for treatment of
dirty gas is shown in Figure 4-4. The gas from an oil-fired
boiler passes through an air heater, electrostatic precipi-
tator, heat exchanger, and fan to a gas heater, where the
temperature is adjusted to about 350°C. Ammonia is then
added. The mixed gas is introduced into a reactor contain-
ing a SO -resistant catalyst and then passes through a heat
X
exchanger and to a stack.
Status of Technology
Sumitomo has performed extensive basic studies with
pilot plants. Figure 4-5 shows the relationship of NH7/NO
mole ratio to denitrification efficiency and ammonia content
of the treated gas when a catalyst C-l was used for clean
gas at 300°C and 350°C with a space velocity (SV) of 7000.
4-8
-------
Figure 4-2. NO removal plant (HNM)
4-9
-------
1: REACTOR 2: BY-PASS 3: REFORMER
4: HEAT EXCHANGER 5,6,7 FAN
Figure 4-3. Flowsheet of denitrification process,
(HNM, clean gas)
HEAT
EXCHANGER
RfiTI FD
DUlLuK
E.P.
i
FAN HEATER
o
£=L
14
t
i
1
fr
REACTO
^
TO STACK
FUEL NH,
Figure 4-4. Flowsheet for dirty gas treatment.
4-10
-------
-------
When the mole ratio was larger than 1, the efficiency
exceeded 90 percent at 350°C and 85 percent at 300°C but the
treated gas contained a considerable amount of ammonia. The
ammonia concentration in the gas was higher at 300°C than at
350°C.
Figure 4-6 shows the effect of using catalyst A for the
decomposition of excessive ammonia together with catalyst
C-l. The ammonia concentration in the treated gas was kept
below 5 ppm even at the mole ratio 1.5 by the effect of the
catalyst A, while the denitrification efficiency stayed the
same or slightly increased.
Sumitomo has also developed catalysts resistant to SO .
Figure 4-7 shows the denitrification efficiencies of cata-
lysts D and C-l before and after being exposed to SO-,-
containing gas. Catalyst D was not affected appreciably by
SO.,, while C-l was seriously affected.
Other tests with catalyst D showed that the denitrifi-
cation efficiency was slightly higher with a gas containing
600 ppm NO than with a gas containing 100 ppm NO . Oxygen
X X
content of the gas above 1 percent showed no effect on
efficiency, which was a little lower with a gas containing
no oxygen. Water vapor showed no appreciable effect,
although there was a slight tendency toward lower efficiency
at high concentrations of water vapor.
Tests were also made on the formation of ammonium
bisulfate deposits in the heat exchanger. The relationship
of formation temperature to SO,, and NH, concentrations is
shown in Figure 4-8. Deposits may be prevented by keeping
the temperature higher or concentrations lower than the
values indicated in the figure.
4-12
-------
. 60-
* 40-
NH.JNOV MOLE RATIO
o /\
Figure 4-6. Effect of ammonia decomposition composition (A).
4-13
-------
100
80
. 60
40
20
SV = 7000
NH3/NO = 1
hr
-1
I
I
250 300 350
REACTION TEMPERATURE, °C
400
Figure 4-7. Effect of SO., on catalyst activity,
4-14
-------
1000
S03, ppm
1000
Figure 4-8. Formation temperature of NH4HSO4
(NH-, + S03 + H20 J NH4HS04)
Gas Gas Gas Liquid
4-15
-------
Performance of the Plants
The HNM plant was operated for 5 months continuously
without trouble after its start-up in May 1974. Operation
of the methanol plant and of the denitrification plant was
then discontinued for a few months because of over-produc-
tion of methanol but was resumed in February 1975. The flue
gas, derived from the burning of LPG and an off-gas, nor-
mally contains about 200 ppm NO and 7 percent 09. More
ji £
than 90 percent of the NO is removed at a temperature of
300°C, an NH-./NO mole ratio of 1, and an SV of 5000 to
j X
7000. The activity of the catalyst has shown essentially no
change since start-up. Some of the operation data, shown in
Figure 4-9, agree well with those of the basic tests, indi-
cating that the problems involving scale-up were solved by
adequate engineering. The denitrification efficiency was
kept above 90 percent even when the gas volume fluctuated
and reached 250,000 Nm /hr. Concentration of ammonia in the
treated gas was kept below 1 ppm by the use of the decom-
position catalyst.
The pilot plant for treatment of the oil-fired (dirty)
flue gas has been operated for over 4000 hours with no
serious problem. The gas normally contains 200 ppm NO
5C
(mainly NO) 730 ppm SO2, 30 to 40 ppm SO3, 5 percent O2 to
10 percent H«0, 12.4 percent CO*, and 72.6 percent N?.
Dust content is kept at 10 to 15 ppm by an electrostatic
precipitator. More than 85 percent of the NO has been
H
removed at temperatures of 330 to 350°C, an NH^/NO mole
•J .X
ratio of 1 to 1.5, and an SV of 4000 to 6000. Result of a
catalyst life test is shown in Figure 4-10. Dust concentra-
tions will be kept below 10 ppm in commercial plants now
under construction for dirty gas treatment.
4-16
-------
100
UJ
oc
0.7
079 1.0 1.1
NH3/NOX MOLE RATIO
1.2
100
(B)
-e—
90
80
•NH3/NO=1.2
ONH3/NO=1.0
250
300
REACTION TEMPERATURE, °C
350
400
NH7/NOV MOLE RATIO
*3 X
Figure 4-9. Operation data of HNM plant.
4-17
-------
on
o
100
90
x 80
70
I
1,000 2,000
ON-STREAM TIME, hr
3,000
Figure 4-10. Result of life test (catalyst D, dirty gas)
(NH,/NC>
J
= 1.0 - 1.8, SV = 4,000, 330°C) .
4-18
-------
Economics
Estimates of the plant cost and denitrification cost
(including depreciation for 7 years) are as follows:
Time of estimation Spring 1973
Plant HNM
Capacity, 1000 Nm /hr 200
Plant cost, $1000 830
Denitrification cost, 40
C/1000 Nm3
Plant cost, $/kW 12.6
Denitrification cost, 1.2
(mil/kWh)
The HNM plant requires about 30 kg/hr of ammonia and
about 800 kW power for a blower to compensate for the
pressure drop of the gas through the reactor.
The plant of Nihon Ammonia (250,000 Nm3/hr, clean gas)
cost $2 million ($25/kW). The present cost for a new plant
may be about $35/kW for clean gas. The cost may be more
than $80/kW for treatment of dirty gas, including a highly
efficient electrostatic precipitator but excluding a desul-
furization unit.
Evaluation
The process is simple and plant operation is smooth.
Resistivity of the catalyst to SO and very low emissions of
J\,
NH3 are other advantages. The process may be one of the
best now available for flue gas denitrification. On the
other hand, the plant cost and cost for denitrification of
dirty gas are quite high, although they may not be higher
than costs of other processes. Operation of the commercial
plants for dirty gas treatment will provide a basis for
further evaluation.
4-19
-------
Nonselective Catalytic Reduction
Sumitomo developed a process to treat tail gas from a
nitric acid plant containing 500 to 2000 ppm NO with 2 to
ji
3 percent 0«. The NO is reduced to N9 by reaction with
£ 1\. £*
hydrocarbons such as methane in the presence of a platinum
catalyst carried on alumina.
4NO + CH4 = C02 + 2H20 + 2N2
A commercial plant with a capacity of treating 22,500 Nm /hr
of tail gas was completed in August 1968. Another plant
(60,000 Nm /hr) went into operation in November 1972.
Process Description
A flowsheet of the process is shown in Figure 4-11.
The tail gas containing 500 to 1000 ppm NO with 2.2 to 2.4
A
percent 09 is heated to 430°C, mixed with methane (at 1.2
stoichiometry) , and introduced into a reactor with a commer-
2
cial honey comb- type platinum catalyst at 6.5 kg/cm pressure.
More than 90 percent of the NO is reduced to N_ at SV
J\. £
50,000 to 120,000. A considerable portion of the methane is
burned by 09 in the gas, and the temperature reaches 730°C.
^
The gas leaving the reactor at 730°C and containing 50 to 70
ppm NO passes through a waste-heat boiler and expander,
X
where heat and energy are recovered, and then goes to a
stack.
Economics
In 1968 the plant cost for 22,500 Nm /hr tail gas
treatment was $150,000. The denitrif ication cost, including
depreciation, was 20C/1000 Nm .
Evaluation
This process is suitable for gases containing 300 to
5000 ppm NO with less than 3 percent 09 and no SO or dust
x ^ x '
and also for plants that can utilize the recovered energy
4-20
-------
WASTE
GAS ^
HEATER
i
FUE
REACTOR
L
WASTE HEAT
BOILER
EXPANDER
I
to
Figure 4-11. Simplified flowsheet of non-selective
catalytic reduction process.
-------
and heat. Too much 0 in the gas would raise the reaction
temperature exceedingly and could harm the catalyst. The
platinum catalyst is effective but is poisoned by S0x> A
small amount of methane is discharged with the treated gas.
HITACHI SHIPBUILDING SCR PROCESS
Background
The process developer is Hitachi Shipbuilding and
Engineering Co. Hitachi developed a base-metal catalyst for
reduction of NO with ammonia and operated a pilot plant
3
with a capacity of treating 5000 Nm /hr of flue gas from an
oil-fired boiler from November 1972 to May 1974. Hitachi
operates another pilot plant with a capacity of treating
2000 Nm /hr of flue gas from burning of LNG. Life tests of
the catalysts have been carried out since June 1974 in a
small test unit with oil-fired flue gas. Tests will be made
with waste gas from an iron-ore sintering plant, a coke
oven, a cement kiln, and similar operations.
Hitachi Shipbuilding is now constructing two commercial
units. One is for Idemitsu Kosan (Chiba plant, 350,000
Nm /hr of refinery flue gas containing some S02). The other
is for Shindaikyowa Petrochemical Co. (Yokkaichi plant,
440,000 Nm /hr of flue gas from an oil-fired industrial
boiler). Both are to be completed by fall 1975.
Process Description
Flue gas is heated to 300 to 350°C by a heat exchanger
and then to 400 to 450°C by a heater (Figure 4-12). Ammonia
is injected, (NH../NO mole ratio of about 1) , and the gas is
•J J%.
then introduced into a reactor containing a base-metal
catalyst. About 90 percent of the NO is reduced to N
x 2"
The gas discharged from the reactor passes through the heat
exchanger and then goes to a stack.
4-22
-------
STACK
I
tv>
CO
BOILER
DUST
COLLECTOR
150°C
50°C
150°C
HEAT EXCHANGER
330°C
HEATER
430°C
DESULFUR-
IZER
430°C
NH-
REACTOR
Figure 4-12. Flowsheet of Hitachi Shipbuilding process
(An example of dirty gas treatment).
-------
At the Yokkaichi plant, Shindaikyowa Petrochemical Co.,
the flue gas from an oil-fired boiler containing a consider-
able amount of S02 will be first treated by the Wellman-Lord
process for removal of SO and dust. This plant would be
.X
the first commercial plant in the world for denitrification
of dirty flue gas in combination with desulfurization. At
the Chiba plant, Idemitsu Kosan, the flue gas from a refinery
containing some SO2 and dust will be introduced into the
reactor without desulfurization.
Economics
The investment cost for a 100-MW unit is estimated to
be $6 million, which is about equal to a desulfurization
unit with an equal capacity operating by the wet process.
The requirement of the treatment of 300,000 Nm /hr of flue
gas, assuming 90 percent removal of 200 ppm NO , is esti-
JC
mated to be as follows:
Electric power 1850 kW
Fuel 10.6 million kcal/hr
Ammonia 36.5 kg/hr
Cooling water 30 t/hr (can be recycled)
Evaluation
The catalyst is resistant to SO-. The process also has
the advantages and disadvantages common to selective cata-
lytic reduction processes as described earlier. Further
evaluation will follow operation of the two commercial
plants.
KURABO SCR PROCESS
Background
The process developer is Kurabo Industries. Kurabo,
originally a textile company, recently went into the pollu-
4-24
-------
tion control business and has constructed about one hundred
relatively small commercial plants for removal of SO^ by
sodium scrubbing. Kurabo has also developed an SCR process
for removal of NO and operated a pilot plant with a capa-
o
city of treating 5000 Nm /hr of flue gas from an oil-fired
boiler. A plant (30,000 Nm /hr of flue gas from an oil-
fired boiler) will be completed by November 1975.
Process Description
Flue gas containing dust and SO is mixed with ammonia
X.
at an NH /NO mole ratio of 1.2 and introduced at 420°C into
»j X
a reactor, which has a moving bed of a catalyst made of
copper and alumina, for example. More than 90 percent of
the NO is converted into N9 . The catalyst, contaminated by
A. ^
the dust and SO , is sent to a regeneration step. After
JC
dust re~noval treatment, the catalyst is electrically heated
to remove sulfur and carbon and to recover its activity.
The regenerated catalyst is returned to the reactor. The
gas discharged from the calciner is added to the outlet gas
from the reactor and sent to a desulfurization unit. The
process flow is shown in Figure 4-13.
Performance
Tests on the pilot plant with flue gas containing about
pm
results :
300 ppm NO and 500 to 2000 ppm S09 gave the following
5C ^
NO removal More than 90%
x
Dust removal More than 80%
Operation temperature 420°C
Space velocity 7000
Pressure drop in the 100 mm H_0
reactor
The time for one cycle of the catalyst including regenera-
tion was 100 to 200 hours.
4-25
-------
AIR
PREHEATER
TO DESUL-
FURIZER
AIR
AMMONIA
GENERATOR
KNORCA DENTIRIFICATION UNIT
Figure 4-13. Flowsheet of Kurabo SCR process.
4-26
-------
Evaluation
In this process, flue gas is subjected first to denitri-
fication and then to desulfurization; in most other SCR
processes the gas is first subjected to wet-process desul-
furization and then to denitrification, which requires much
energy for reheating. Thus, energy saving is an advantage
of the process.
On the negative side, the electrical heating would add
considerably to the cost and might cause some degradation of
the catalyst. For the desulfurization, ammonia scrubbing
such as developed by Kurabo may be suitable, but use of
other processes may present some problem because of the
presence of ammonia in the gas discharged from the NO
J\.
removal step. Operation of the semicommercial plant will
yield data for further evaluation.
TESTS ON SCR CATALYSTS BY CRIEP10
The Central Research Institute of Electric Power
Industry (CRIEP) tested the reactivity of catalysts in a
laboratory. Both commercial and synthetic catalysts (6
milliliters in a fixed bed) were tested at 100 to 500°C with
60 normal liters per hour of gas (SV 10,000) containing 220
to 260 ppm NO, 300 to 350 ppm NH3, 3 to 4 percent 02, and
1100 ppm S02. Some of the results with commercial catalysts
with an alumina carrier (G-41, V-0701, and G-51) and syn-
thetic catalysts with a granular reactive alumina carrier (2
to 4 mm, calcined at 550°C) are shown in Figure 4-14. The
results show that copper and chromium catalysts give high
reactivity at 300 to 350°C even in the presence of SO-.
Figure 4-15 shows results of tests with copper cata-
lysts on different carriers as specified in Table 4-2. The
best results were obtained with bauxite (from Australia),
4-27
-------
Table 4-2. COMPOSITION AND PROPERTY OF CARRIERS
Carrier
Active alumina
Bauxite
Kanuma earth
Active silica
earth
Composition of raw material, %
A1203
82.2
58.0
35.6
12.5
Si02
10.1
3.8
48.2
76.1
Fe2°3
1.7
7.3
2.6
1.5
CaO
3.3
-
-
0.4
Ti02
-
2.3
-
-
Loss on
ignition, %
2.7
28.5
13.5
8.0
Specific
surface area
of calcined
carrier, m^/g
367
210
227
272
I
to
00
-------
100
80
60
40-
<
20
B200300
_L
O BAUXITE, SHAPED
A BAUXITE, CRUSHED
D ACTIVE ALUMINA
A ACTIVE SILICA
EARTH, SHAPED
_ KANUMA EARTH,
* SHAPED
400 500
TEMPERATURE, °C
Figure 4-14. Tests on carriers (5% Cu)
lOOi
80
60h
UJ
ce.
x 40
20
°0 TOO 200 300 400
O 5%Cu, 3%Cr
& 5%Fe
D 6-41(7.5%Cr)
^7 5%Ni
C V-0701(5.6%V)
A 6-51(6.7%Mo,2.6%Co)
)0
TEMPERATURE, °C
Figure 4-15. Tests of catalysts (alumina carrier)
4-29
-------
which had been ground, shaped into cylinders (2.6 mm in
diameter and height), and calcined at 550°C for 3 hours.
The active alumina was not as good as the shaped bauxite.
Since the characteristics of alumina vary widely with
impurities and methods of preparation, it is likely that the
alumina carrier will be much improved.
TOKYO ELECTRIC - MITSUBISHI H.I. SCR PROCESS
Process developers are Tokyo Electric Power Co. and
Mitsubishi Heavy Industries. These companies have jointly
operated a pilot plant with a capacity of treating 10,000
Nm /hr of flue gas from a natural-gas-fired boiler at the
Minamiyokohama Station, Tokyo Electric. A process flowsheet
is shown in Figure 4-16. Flue gas from an economizer is
injected with ammonia, mixed in a mixer, and led to a reactor
with a base-metal catalyst. Flue gas temperature fluctuates
between 270 and 350°C as the boiler load varies between 25
and 100 percent. Efforts have been concentrated on develop-
ment of a catalyst effective in the above temperature range.
The flue gas contains 90 to 100 ppm NO (mainly NO),
X.
8.5 percent CO-, 16.8 percent H2O, and 2.6 percent 0-. A
catalyst has been developed with which more than 80 percent
of the NO is removed at an NH /NO mole ratio of 1 and a
X j X
space velocity of 10,000. Ammonia concentration in the
outlet gas is 10 to 20 ppm. Continuous use of the catalyst
for 3000 hours did not reduce the activity appreciably. No
increase in pressure drop in the reactor was observed.
Tests on a new catalyst have been carried out since November
1974 for further improvement.
The process has the advantages and disadvantages common
to SCR processes. Further reduction of ammonia in the
outlet gas is desired.
4-30
-------
ECONOMIZER
BOILER
I
U)
Figure 4-16. Flowsheet of pilot plant.
(Tokyo Electric - MHI SCR process)
-------
SCR TESTS AT CHUBU ELECTRIC POWER
Chubu Electric Power, one of the nine major power
companies, has conducted tests on two types of SCR processes.
Chubu-IHI-Mitsui Process
Chubu Electric has tested an SCR process jointly with
Ishikawajima Harima Heavy Industries (IHI), one of the
largest producers of boilers and machines; Mitsui Toatsu
Chemical, the largest fertilizer producer; and Mitisui and
Co., one of the two largest trading companies. A pilot
plant with a capacity of treating 8000 Nm /hr of flue gas
from a boiler burning low-sulfur oil or naphtha has been
operated at the Shinnagoya Station, Chubu Electric, since
October 1974. Flue gas is taken after either the economizer
or the electrostatic precipitator to study the effect of
dust. A simple dust eliminator is installed for the gas
from the economizer. A nearly continuous operation for 2
months resulted in more than 90 percent NO removal without
X
an increase in pressure drop in the reactor caused by the
dust. The catalyst is resistant to S02. Most of the ammonia
is decomposed in the reactor. The budget for the pilot test
is $1.4 million, including the costs for the plant, labor,
and everything needed for the test.
Chubu-MKK process
Chubu has tested another SCR process jointly with
Mitsubishi Chemical Machinery (MKK) in search of a new
catalyst that promotes the reaction of NO and ammonia at a
J\.
low temperature (200 to 250°C). A small pilot plant with a
capacity of treating 300 Nm /hr from an oil-fired boiler has
been operated at the Yokkaichi Station, Chubu Electric,
since September 1974. The budget is $100,000 excluding
labor costs. Flue gas from an electrostatic precipitator is
used for the test. The primary objective is to reduce the
4-32
-------
energy requirement for reheating the gas after wet-process
desulfurization. MKK recently started to use a catalyst
made of iron oxide, which is said to be resistant to SO2 and
works fairly well at the low temperature.
OTHER CATALYTIC REDUCTION PROCESSES
Kansai Electric Power
Kansai Electric Power Co., one of the nine major power
companies, has conducted tests on SCR jointly with Hitachi
Ltd., one of the biggest machine producers. A pilot plant
with a capacity of treating 4000 Nm3/hr of flue gas from an
oil-fired boiler (economizer outlet) has been operated since
January 1974 at the Sakaiminato Station, Kansai Electric.
Either crude or low-sulfur oil is burned in the boiler. The
first test was carried out for 4200 hours between January
and August 1974, removing more than 80 percent of the NO .
X
At the beginning of the test, dust in the gas caused some
problems that were gradually solved. After November 1974
the plant was partly modified, and the second test was
started. No details have been disclosed. The process seems
to have the advantages and disadvantages common to SCR
processes.
Mitsubishi Heavy Industries
Since December 1974 MHI has operated a pilot plant with
a capacity of treating 4000 Nm /hr of flue gas from an oil-
fired boiler by SCR in conjunction with a wet desulfuriza-
tion process. No data have been disclosed.
Osaka Oxygen Industries
Osaka Oxygen Industries (12-4, 2-chome, Utajima,
Nishiyodogawa-ku, Osaka) constructed four commercial plants,
each with a capacity of decolorizing 100,000 Nm /hr of flue
gas from a natural-gas-fired power generation engine by
4-33
-------
nonselective catalytic reduction using a noble-metal cata-
lyst developed by Engelhard, U.S.A. The flue gas contains
about 10 percent 09 and 500 to 600 ppm NO , including a
^ 5C
considerable amount of NO2. The noble-metal catalyst is
more active than a base-metal catalyst but is poisoned by
so2.
EBARA-JAERI ELECTRON BEAM PROCESS12
Background
The process developers are Ebara Manufacturing Co. and
Japan Atomic Energy Research Institute (JAERI). Ebara is a
large producer of water-treatment facilities that recently
went into the air pollution control business. Ebara, jointly
with JAERI, a government organization, has developed a
process for simultaneous removal of SO- and NO by electron
beam radiation. Following bench-scale tests, Ebara has
operated a pilot plant with a capacity of treating 1000
Nm /hr of flue gas from an oil-fired boiler. A larger pilot
plant with a capacity of treating 3000 Nm /hr of waste gas
from an iron-ore sintering plant is scheduled to be con-
structed in 1976 at Yahata Works, Nippon Steel Corp.
Process Description
A flow sheet of a bench-scale test unit is shown in
Figure 4-17. The reactor, 750 by 50 by 500 mm, is made of
stainless steel. An electron beam accelerator (Cockcroft-
Walton type) made by Hitachi, Ltd., was used. Flue gas
produced by burning oil and containing 600 to 900 ppm SO.,
and 80 ppm NO passed through an electrostatic precipitator
Jt
and into the reactor where it was exposed to the electron
beam. Electron bombardment produces sulfuric acid mist and
a powdery product and caught by another electrostatic preci-
pitator.
4-34
-------
1: FUEL OIL 2: BURNER 3: ELECTRON BEAM ACCELERATOR
4: REACTOR 5: DUST COLLECTOR 6: ANALYZER (S02, NOX)
Figure 4-17. Apparatus for tests.
4-35
-------
Figure 4-18 shows the results of the tests at 110°C.
About 90 percent of the NO was removed by an electron beam
X
of about 0.8 Mrad (radiation for 2 seconds of the beam with
an intensity of 4.31 x 10 rad/sec), while about 80 percent
of S02 was removed at 4 Mrad (radiation of the beam for 10
seconds). Radiation at lower temperature increased the
removal efficiency slightly. The form of the product
compound is not known.
The larger pilot plant (3000 Nm /hr) will cost more
than $1 million, including equipment for various tests and
measurements. Power consumption for the electron beam
accelerator is estimated at 1 MW for 100,000 Nm /hr of flue
gas (about 32 MW equivalent). It may be possible to make an
electron beam accelerator as large as 1 MW. Consequently,
treatment of 1,000,000 Nm /hr of flue gas from a 320-MW
boiler will require 10 accelerators.
Evaluation
The main advantage of the process is the simultaneous
removal of NO and S09 by consuming electric power only.
a £•
The power consumption is not very high compared with that of
other processes, which also require ammonia, lime, etc. The
investment cost, however, seems fairly high, since the
process requires accelerators and a highly efficient electro-
static precipitator. The by-product must be treated in a
large-scale operation.
OTHER DRY PROCESSES
Sumitomo Shipbuilding Activiated-Carbon Process
Sumitomo Shipbuilding and Machinery Co., Ltd. developed
an SO2 removal process with activated carbon and constructed
a prototype plant with a capacity of treating 175,000 Nm^/hr
of flue gas from an oil-fired boiler. Sumitomo has tested
4-36
-------
100
0123
TOTAL BEAM, Mrad
'4.31x105 rad/sec • 4.31x105 rad/sec
a8.61x105 rad/sec O 1.46x105 rad/sec
Figure 4-18. Results with different intensities,
4-37
-------
NO removal with activated carbon using ammonia. No data
X
have been disclosed.
Shell Cupric Oxide Process
Japan Shell Technology Co. constructed a desulfurization
unit with a capacity of treating 120,000 Nm /hr of flue gas
from an oil-fired boiler using the Shell cupric oxide process
at the Yokkaichi Refinery, Showa Yokkaichi Sekiyu. Japan
Shell has tested NO removal by injecting ammonia into a
X
reactor containing cupric oxide. It is said that a high NO
H
removal ratio can be attained because the copper oxide acts
as a catalyst for the reaction of NO and ammonia. No data
Ji
have been disclosed.
4-38
-------
REFERENCES
Descriptions in this report are based primarily on the
authors' visits to the denitrification plants, their discus-
sions with the users and developers of each process, and
data made available by them. In addition, the following
publications were used as references:
1. J. Ando and H. Tohata, NOX Abatement Technology in
Japan, EOA-R2-73-284 (June 1973) (in English).
2. K. Nagata, NOX Abatement by Combustion Technology Heat
Management and Pollution Control, Vol. 26, No. 3, page
10 (1974).
3. Y. Takahashi, MHI Low-N0x Burner, ibid, page 37.
4. S. Tsuji, IHI Low-N0x Burner, ibid, page 21.
5. H. Idemura, Simultaneous SC>2 and NOX Removal Process
for Flue Gas, Chemical Economy and Engineering Review,
Vol. 6, No. 8, 27 (1974) (in English).
6. M. Atsukawa, NOX Abatement Technology, page 116,
Kagakukogyosha (1973).
7. H. Kawasaki, N. Nakatani and T. Ishii, NOX Removal by
NE Process, J. Japan Petroleum Institute, 17,505 (1974).
8. M. Koizumi, T. Tanaka, and Y. Ishihara, Wet Process for
Nitrogen Oxide Removal from Flue Gas, Report of Central
Research Institute of Electric Power Industry, No.
74021 and 74031 (1974).
9. H. Oka, E. Ichiki and T. Shiraishi, Process removes NOX
efficiently, Hydrocarbon Processing 113, (Oct. 1974)
(in English).
-------
REFERENCES (continued).
10. H. Fukuzawa and Y. Ishihara, Catalytic Reduction of
Nitrogen Oxides by Ammonia (Part 1), Report of Central
Research Institute of Electric Power Industry, No.
74022 (1974).
11. K. Hoshizawa et al., Effect of Nitrogen in Fuel on NOX
Formation, ibid., No. 72095 (1973).
12. W. Kawakami and K. Kawamura, Treatment of Oil-fired
Flue Gas by Electron Beam, Denkikyokai Zasshi, 29 (Dec.
1973).
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO. 2
EPA-600/2-76-013b
4. TITLE AND SUBTITLE
NOX Abatement for Stationary Sources in Japan
7.AUTHOR(S)Jumpei Ando an(j Heiichiro Tohata (Chuo
University, Tokyo, Japan) and Gerald A. Isaacs
PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo-Environmental Specialists, Inc.
Suite 13, Atkinson Square
Cincinnati, Ohio 45246
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
January 1976
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1AB014; 21ACX-130
11. CONTRACT/GRANT NO.
68-02-1321, Task 6
13. TYPE OF REPORT AND PERIOD COVERED
Subtask Final: 7/74-3/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT The repOrt summarizes regulations for NOx abatement in Japan, describes
techniques for abatement by means of combustion control, and analyzes in detail
current wet and dry processes for denitrification of flue gases. The major fuel in
Japan is heavy residual oil. Lesser amounts of coal are used. Natural gas usage
is insignificant. Six different low-NOx oil burner designs are discussed. Eleven
major NOx scrubber plants have been completed or are nearing completion. Descri-
ptions of the major NOx removal processes are included. The chemistry of NOx
liquid reactions is discussed as it applies to the various scrubber processes: advan-
tages and disadvantages of the processes are listed. Ongoing research and develop-
ment projects in Japan are also discussed.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Air Pollution Oil Burners
Nitrogen Oxides
Combustion Control
Flue Gases
Fossil Fuels
Scrubbers
12. DISTRIBUTION STATEMENT
Unlimited
b. IDENTIFIERS/OPEN ENDEDTERMS
Air Pollution Control
Stationary Sources
Japan
Denitrification
19 SECURITY CLASS (fhixKiportj
Unclassified
20. SECURITY CLASS (This page/
Unclassified
c. COSATI Field/Group
13B 13A
07B
2 IB
2 ID
07A
21. NO. OF PAGES
116
22. PRICE
EPA Form 2220-1 (9-73)
4-41
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Book
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