Selective catalytic reduction design

Improvements in engine and turbine design, along with the use of auxiliary equipment such as catalytic converters, selective catalytic reduction (SCR) units and the use of steam and water injection into turbines, combine to reduce overall emission levels. 

Postcombustion processes are designed to capture NO, after it has been produced. In a selective catalytic reduction (SCR) system, ammonia is mixed with flue gas in the presence of a catalyst to transform the NO, into molecular nitrogen and water. In a selective noncatalytic reduction (SNCR) system, a reducing agent, such as ammonia or urea, is injected into the furnace above the combustion zone where it reacts with the NO, to form nitrogen gas and water vapor. Existing postcombustion processes are costly and each has drawbacks. SCR relies on expensive catalysts and experiences problems with ammonia adsorption on the fly ash. SNCR systems have not been proven for boilers larger than 300 MW. 

Selective catalytic reduction (SCR) and selective noncatalytic reduction processes (SNCR) are widely employed in large industrial and utility boiler plants, as well as in municipal waste incineration plants and other combustion processes. They are used to complement mechanical improvements (such as low NOx burners and furnace design modifications) as an aid to reducing the emission levels of NOx, S02, and other noxious gases into the atmosphere. 

A mathematical model for the design of extruded honeycomb reactor for selective catalytic reduction of NOx... 

Example 25.5 A gas turbine exhaust is currently operating with a flowrate of 41.6 kg s-1 and a temperature of 180°C after a heat recovery steam generator. The exhaust contains 200 ppmv NOx to be reduced to 60 rng rn 3 (expressed as N02) at 0°C and 1 atm. The NOx is to be treated in the exhaust using low temperature selective catalytic reduction. Ammonia slippage must be restricted to be less than 10 mgm 3, but a design basis of 5 mg-rn 3 will be taken. Aqueous ammonia is to be used at a cost of 300 -1 1 (dry NH3 basis). Estimate the cost of ammonia if the plant operates... 

The actual issues of EuroV standards aim at optimizing engine s design to decrease the engine-out N(), emissions in order to avoid the need for expensive after-treatments in the exhaust line. Only some heavily loaded applications would need such NOx after-treatment. Today, two major technological ways of NOx treatment are identified the NOxTrap and the selective catalytic reduction with ammonia (SCR-NH3). 

Selected ion monitoring mode, mass spectrometer, 6 431 Selection, in chemical product design, 5 759, 772-776 Selective carburizing, 76 205 Selective catalytic reduction (SCR), 77 719-720, 79 626 See also Nonselective catalytic reduction SCR entries... 

Question 5 ("Is combustion with air the only chemistry intended at your facility ") can be answered YES in this case, assuming the "facility" being addressed is limited to the incinerator system. Due to the great number of combustion systems in operation, many other resources are available for ensuring safe design and operation of the combustion part of the incinerator facility. However, it should be noted that many combustors now have effluent treatment systems, such as selective catalytic reduction (SCR) systems, that involve intentional chemistry beyond the combustion reaction. 

A great effort is underway to develop reliable aftertreatment systems for lowering NOx emissions from diesel and LB engines. A variety of approaches have been proposed for NOx aftertreatment of advanced vehicles including lean NOx catalysts (LNC), NOx storage and reduction (NSR) catalysts, selective catalytic reduction with urea (urea-SCR), and plasma-assisted catalysis (PAC). Lean NOx catalysts are mainly designed to reduce NOx with unburned hydrocarbons already included in the exhaust stream in the presence of O2 but result in... 

M A Buzanowski and R T Yang, Simple design of monolith reactor for selective catalytic reduction of NO for power plant emission control, Ind Eng Chem. Res 29 2074 (1990). 

The 0 rigin o f t he c atalytic a ctivity i n t he v arious r eactions c atalyzed b y F e-zeolites h as been intensively debated over the last decade. In spite of the considerable efforts to characterize these materials, available data are not yet sufficient to conclude exclusively on the structure of the active iron. Binuclear iron species in FeZSM-5 have been designated as the active site in various reactions, including direct N2O decomposition, selective oxidation of benzene to phenol with N2O, and selective catalytic reduction (SCR) of NO c with hydrocarbons. However, in the last reaction, small oligonuclear species of composition Fc404 and isolated iron ions have also been proposed as active sites. ... 

In earlier work, Thomas and coworkers (1-3) found that NOx in a simulated NWP offgas (containing 2% CO, 3% CO2, 14% O2, 20% H2O and the remainder of N2) could be removed from levels of 10,000 - 30,000 ppm to 300-1,000 ppm by selective catalytic reduction with ammonia over a commercial H-mordenite catalyst (Norton NC-300) at 300-500 C. Based on these results and pilot plant tests, a conceptual process for NOx and CO removal has been designed by Westinghouse Idaho Nuclear Company, Inc. (WINCO). This process consists of three fixed bed... 

Santos A, Bahamonde A, Schmid M, Avila P, Garcia-Ochoa F. Mass transfer influences on the design of selective catalytic reduction (SCR) monolithic reactors. Chemical Engineering and Processing Process Intensification 1998 37 117-124. 

The combustion of natural gas with air is accompanied by formation of nitrogen oxides. This becomes significant above 1400-1500 C, which is easily surpassed in normal diffusion flames. The problem is solved by use of low NOx burners and further reduction can be obtained by cleaning the flue gas using selective catalytic reduction (SCR) with ammonia [510]. Low NOx burners have longer flames in order to limit the maximiun temperatures, but this has a significant impact on the heat flux and temperature profiles in the reformer, since it tends to make the flux profiles wider. The burner type must be taken into consideration in the design. 

Ren L, Zhu L, Yang C et al (2011) Designed copper-amine complex as an efficient template for one-pot synthesis of Cu-SSZ-13 zeolite with excellent activity for selective catalytic reduction of NOx by NH3. Chemical Communications 47 9789-9791... 

Hsieh M-F, Wang J (2011) Design and experimental validation of an extended Kalman filter-based NO,t concentration estimator in selective catalytic reduction system applications. Control Engineering Practice, 19(4) 346-353. 

Hsieh M-F, Wang J (2009) Nonlinear observer designs for Diesel engine selective catalytic reduction (SCR) ammonia coverage ratio estimation. Proceedings of the 48th IEEE Conference on Decision and Control, 6596-6601. 

Cho, S. M. and Dubow, S. Z., 1992, Design of a Selective Catalytic Reduction System for NOx Abatement in a Coal-Fired Cogeneration Plant, Proceedings of the American Power Conference, Chicago, IL, April 13-15, pp. 717-722. 

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