De-NOx catalyst

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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.

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


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

- 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

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. 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 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


[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. 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. 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. 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.

Lingjuan Ma Lingjuan Ma