MITSUBISHI HEAVY INDUSTRIES, LTD.
http://www.mhi.co.jp/indexe.html
DRY SELECTIVE CATALYTIC NOx REMOVAL SYSTEM
Mitsubishi Heavy Industries, Ltd. (MHI) began developing SCR in 1971, and the first
commercial application of SCR was made to LNG fired unit in 1978. MHI put forward our
development work from clean flue gas to dirty flue gas. Today, many SCR systems have been
supplied for coal, gas and oil fired flue gases.
1. Principle and Features
In the dry selective catalytic NOx removal system (SCR system), NOx in flue gas is
decomposed to N2 and H2O as shown below by injecting NH3 into the flue gas.
Principle of Denitrification Process
Features of this process are as follows :
(1) This system is of simple construction and its operation is easy.
(2) This system involves no moving part and its reliability is high.
(3) As NOx is decomposed into harmless N2 and H2O, by-product treatment is unnecessary.
2. Features of MHI's Catalyst
(1) High NOx removal efficiency
(2) Thermal stability
(3) No emission of secondary pollutants
(4) High resistance to SOx and dust
(5) High resistance to erosion
(6) Safe treatment of spent catalyst
* SCR supplied flue gas source
(1) Boiler
(2) Gas Turbine
(3)Diesel Engine
(4)Incinerator
(5) Chemical Furnace
* Supply record and start of the first commercial operation (Utility boiler only)
Sakai Chemical Industry Co., Ltd.
http://www.sakai-chem.co.jp/englishtop.htm
De-NOx catalyst
Introduction
Among various methods of NOx removal, the selective catalytic reduction of NO by NH3
over a titania based catalyst has been quite popular, because the titania based catalyst has a
high activity and high durability.
Sakai Chemical Ind.Co., Ltd. has greatly contributed to the development of this technology
through manufacturing the catalyst. The outline of this catalyst will be described us below.
SCR-Reduction
The main ingredient of nitrogen oxides in the exhaust gases from fuel fired boilers is nitric
oxide. In the existence of oxygen, nitric oxide reacts with ammonia according to the reaction
as follow.
NO + NH3 + (1/4)O2 = N2 + (3/2)H2O
Requirements for commercialized De-NOx catalysts
The quality of the De-NOx catalysts has been improved by the cooperation of catalyst makers
with plant makers. A present commercialized De-NOx catalyst is required to have the
following characteristics.
(1) stability
A. Thermal resistance
up to 500 deg. C for five year when used to conventional boilers
B. Resistance to poisoning
- acid sites
alkaline ,metal ions and alkaline earth metal ions
- oxidative active sites
SOx and arsenic oxide
C. Anti-abrasion
- worn by a hard dust
- anti-abrasion strength inversely proportional to catalytic activity
(2) High activity in a wide temperature range
250 deg.C - 350 deg.C
350 deg.C - 400 deg.C
gas fired boiler
oil and coal fired boiler
(3) Low conversion of SO2 to SO3
ammonium bisulphate and ammonium sulfate cause catalytic deactivation by pore plugging
and corrosion of downstream equipment.
(4) Low pressure loss in a catalyst layer and no dust deposition on the catalyst layer
To satisfy the requirements for commercialized catalysts, we developed honeycomb shaped
catalysts which had many halls to the gases flow containing V2O5. and / or WO3 supported on
a titania.
1) LS : Low Sulfur
2) MS: Middle Sulfur
3) HS : High Sulfur
KAWASAKI SELECTIVE CATALYTIC NOx REMOVAL
SYSTEM (S.C.R.) http://www.khi.co.jp/index_e.html
1. OUTLINE OF SCR SYSTEM
* SCR SYSTEM
The flue gas NOx removal process developed by Kawasaki is a selective catalytic NOx
reduction system (S.C.R. System), in which NOx in the flue gas is decomposed to N2 and
H2O by NH3, while flue gas passing through the catalyst layer as shown below.
Typical Configuration of SCR System
2. FEATURES OF SCR CATALYST
* FEATURES OF CATALYST
Grid honeycomb catalyst is available with suited content and geometry for versatile
application.
-
High NOx removal efficiency
High Dioxins removal efficiency
Thermal stability
No emission of secondary pollutants
High resistance to SOx and contaminant
High resistance to erosion
Proven long life
Safe treatment of spent catalyst
* BI-MODAL PORE SIZE DISTRIBUTION
- Combination of Macro and Micro Pore
- Macro Pore provides Quick Diffusion of Reactant (NOx, NH3) into Deep
Inside of
Catalyst. As well as, Micro Pore provide Large Surface Area including
Active
Point.
- Resulting High Activity and /or Low SO2 to SO3 Conversion
3. TREATMENT CAPACITY
a)
b)
c)
d)
Gas
Gas
NOx
NOx
Flow
:
10, 000 Nm3/h - 3, 000, 000 Nm3/h or over
Temperature
:
200 deg.C - 450 deg.C
Concentration at SCR Inlet
:
several ppm - 10000 ppm
Removal Efficiency
:
up to 95% on application
4. APPLICATION FILED
The NOx removal system was put into practical use in the boiler flue gas application at first,
and has come to be used for new various fields by adding the improved technique. The
following diagrams show an example of system flow of various application.
5. SCR EXPERIENCE
It is fifteen years and more since the 1st NOx removal system using SCR has been supplied
by KAWASAKI. The number of orders received during the period over 60 including the
licensees (JOY TECHNOLOGY, U.S.A., BABCOCK ANLARGEN, GERMANY, FISIA
SPA., ITALY).
IHI DRY SELECTIVE CATALYTIC NOx REMOVAL SYSTEM
Ishikawajima-Harima Heavy Industries Co., Ltd.
http://www.ihi.co.jp/index-e.html
Ishikawajima-harima Heavy Industries Co., Ltd. (lHI) began developing the selective catalytic
reduction (SCR) system in the early 1970's and first applied to utility boilers which emit a
large amount of flue gas in 1978.
Since then, IHI has delivered several tens of SCR systems for utility boilers, industrial boilers,
diesel engines and gas turbines as a high-performance, high reliability NOx removal system,
thus contributing to the protection of the global environment against acid rain and the like.
1. Principle
The principle of NOx removal by SCR system is the extremely simple process of adding
ammonia to flue gas which pass through catalyst layers, by which NOx is decomposed into
harmless nitrogen (N2) and steam (H2O).
2. Flow Sheet
The following flow sheet is a typical case of application of the SCR system.
Basic Flow Sheet for Boiler Flue Gas NOx Removal Plant
3. Features
1) Easy to operate; No specialized knowledge required for operation
2) Compact design; Low installation cost
3) Perfect matching with flue gas source
4) Catalyst and reactor both selectable to best suit the flue gas characteristics
5) Stable supply ensured of catalysts
6) No risk of secondary pollution
4. Performance
IHI-SCR system can be designed under the following conditions.
1) Processing gas capacity: 10,000 ~ 3,000,000 m3N/h
2) DeNOx efficiency: 30 ~ 95%
3) Gas temperature : 200 ~ 600 deg.C
5. Actual production
IHI-SCR systems have been supplied for the following applications in Japan.
Utility boilers: 34 systems
Industrial boilers: 8 systems
Gas turbines: 26 systems
Diesel engine: l system
Others: 5 systems
Total: 74 systems
IHl's SCR system technologies have already been introduced to the following companies in
three countries.
1) Foster Wheeler Energy Corporation (USA)
2) L.&C. Steinmuller GmbH (Germany)
3) Ercole Marelli Impianti Technologici S.p.A. (Italy)
More than 60 SCR systems for boilers, for gas turbine combined cycles, and for other flue gas
emission sources have been delivered by these licensees.
6. Examples
Chubu Electric Power Co.Hekinan P/S
700MW Coal-fired No.3 Boiler
Capacity: 2,153,000 m3N/h
DeNOx efficiency: 80%
Tokyo Electric Power Co.Yokohama P/S
350MW X 4 No.7 Combined Cycle Plant
IHI NOx Removal Plant DeNOx efficiency: 60%
Capacity: 1,870,000 m3N/h
DeNOx efficiency: 90%
Machida city clean Center Municipal Waste Incinerator
Capacity: 65,700 m3N/h
NOx REMOVAL SYSTEM BY SCR PROCESS
HITACHI ZOSEN CORPORATION
http://www.hitachizosen.co.jp/english/index-e.html
Nitrogen Oxides (NOx) is well known as one of the air pollutants. Therefore, NOx removal
technology has been getting more and more important to help preserve our environment all
over the world. Selective Catalytic Reduction (SCR) technique is the most famous NOx
reduction process. Ammonia (NH3) is injected into flue gas stream. In the presence of
catalyst. NOx contained in the flue gas reacts selectivity with NH3 and is converted into
nitrogen (N2) and water (H2O). Main reaction is expressed as follows.
4NO + 4NH3 + O2 ->4N2 + 6H2O
[Application of SCR Process]
SCR Process
Catalyst
[Features]
SCR process for NOx removal in flue gas has the following features.
:
:
:
:
:
:
:
Simple process
Low running cost
Easy operation
No secondary environmental pollution
High reliability
High NOx removal efficiency
Small pressure drop
[Capability of Flue Gas Treatment]
SCR Process is applicable from small NOx removal systems for heating furnaces to large
NOx removal systems for utility power plants. The followings indicate the smallest and the
largest SCR systems in our commercial experiences.
Smallest
Largest
:
:
Flue Gas Volume to be treated
5,000 m3N/h (0 deg.C, 1atm)
1.250,000 m3N/h (0 deg.C, 1atm)
[Application Field]
SCR process has been applied to a wide range field of stationary emission sources for NOx
reduction in flue gas. The followings show the example of our commercial applications.
:
:
:
:
:
Gas and Oil Fired Boilers
Gas and Oil Fired Turbines
Diesel Engines
City refuse Incinerators
Beaters, Furnaces and Reformers
[Example of Commercial Application]
SELECTIVE CATALYTIC REDUCTION SYSTEM OF
NITROGEN OXIDES
TAKUMA CO., LTD.
http://www.takuma.co.jp/index.html
This system reduces nitrogen oxides to nitrogen gas in the catalyst tower by mixing ammonia
with the exhaust gas at a temperature as low as 200 deg.C.
The catalyst tower is typically installed after the dust collector.
The reaction between nitrogen oxides and ammonia is expressed by the following formulae:
2NO + 2NH3 + (1/2) O2 -> 2N2 + 3H2O
NO + NO2 + 2NH3 -> 2N2 + 3H2O
[System outline]
Dilute ammonia is mixed with air prior to injection into the exhaust gas.
Ammonia can be supplied in an aqueous state or by liquefied ammonia cylinders or a
liquefied ammonia reservoir. The flowchart of the system is shown below using the liquefied
ammonia cylinders as an example, see Fig.1.
Fig.1 Catalytic nitrogen oxides reduction system with liquefied ammonia cylinders
[Characteristics]
The treatment allows for removing 50 to 95% of nitrogen oxides. Ammonia is required almost
in the same number of moles as the nitrogen oxides to be removed. A honeycomb type
catalyst (150mm square cell X approx. 1000mm) is used.
[Capacity]
This system has no limit on the treated gas volume.
[Sphere of application]
This system can be applied to any furnace exhaust gas, for example, one of Municipal Solid
Waste (MSW) incineration.
[Actual results]
Takuma has installed two catalytic nitrogen oxides reduction systems in MSW incineration
furnaces in Japan. A further two MSW incineration plants with the catalytic nitrogen oxides
reduction system are under construction.
Urea Reduction De-NOx System (U-CLEAR)
NIPPON SHOKUBAI CO., LTD.
http://www.shokubai.co.jp/english/e_index.htm
Co-generation become recognized a promising system supported by the Government's energy
policy as the global environmental preservation. To propagate co-generation, safe and simple
De-NOx system is required. 'Liquid ammonia or a queous ammonia have been used as a
selective NOx reducing agent, however Ammonia has been hard to apply to the co-generation
systems because ammonia is poisonous and difficult to handle. Therefore, a De-NOx process
using aqueous urea has been eagerly required and developed as safe and easy-to-handle
reducing agent.
Tokyo Gas Co., Ltd. and Nippon Shokubai Co., Ltd have jointly engaged in the development
of 'Urea Reduction De-NOx System' using aqueous urea as a reducing agent and established
Uclear system.
Principle
1. Features
1) Easy to handle
2) No malodor problem.
3) No requirement for secondary treatment
(waste water treatment)
4) Inexpensive reducing agent cost compared to aqueous ammonia.
5) Approx, same installation cost as that of the conventional system.
6) Compact plot plan.
2. System Flow
NONCATALYTIC REDUCTION SYSTEM OF NITROGEN
OXIDE
TAKUMA CO., LTD.
http://www.takuma.co.jp/index.html
By spraying aqueous ammonia or urea solution into the furnace, nitrogen oxide is reduced
into nitrogen gas Urea is usually used because it can be handled easily.
The reaction between nitrogen oxide and urea is expressed by the following formulae:
Overall reaction formulae:
2NO + (NH2)2CO + (1/2)O2- > 2N2 + 2H2O + CO2
Urea decomposition reaction in high temperature furnaces:
(NH2)2CO + H2O -> 2NH3 + CO2
Reaction of ammonia occurs after decomposition:
2NO + 2NH3 + (l/2)O2 -> 2N2 + 3H2O
[System outline]
Urea solution is injected together with compressed air or steam using dual fluid nozzles.
Fig.1 shows the flowchart of the noncatalytic nitrogen oxide reduction system.
Fig.1 Noncatalytic nitrogen oxide reduction system
[Characteristics]
The treatment allows for removing 30 to 70% of nitrogen oxide. The urea solution is injected
into an area of the furnace at approx. 800 deg.C. If the temperature is 1000 deg.C or more,
ammonia is decomposed with oxygen. The amount of urea solution injected should be
appropriately determined, keeping in mind that white smoke is generated if the ratio to the
equivalent is too large.
[Capacity]
This system has no limit on the treated gas volume.
[Sphere of application]
This system can be applied to any furnace exhaust gas, for example, one for Municipal Solid
Waste (MSW) incineration.
[Actual results]
Takuma has installed 11 noncatalytic nitrogen oxide reduction systems in MSW incineration
furnaces in Japan.