SCR Technologies

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

Hyeon Kim, M. and Nam, l.-S. (2004) New opportunity for HC-SCR technology to control NO emission from advanced internal combustion engines, in Catalysis, 18, (ed. J.J. Spivey), Royal Society of Chemistry, pp. 116-185. 

Is SCR technology suitable for application in mobile sources of NOx such as trucks and ships ... 

Wet air pollution control (WAPC) devices are used to treat exhaust gases from stainless steel pickling operations, thereby generating wastewater, which are treated using the selective catalytic reduction (SCR) technology in which anhydrous ammonia is injected into the gas stream prior to a catalyst to reduce NO, to nitrogen and water. The most common types of catalysts are a metal oxide, a noble metal, or zeolite. 

The previous section has evidenced that NH3-SCR technology has been used successfully for more than two decades, to reduce NOx emissions from power stations fired by coal, oil and gas, from marine vessels and stationary diesel engines. NH3-SCR technology for high-duty diesel (HDD) vehicles has also been developed to the commercialization stage and is already available as an option in the series production of several European truck-manufacturing companies starting from 2001. For mobile source applications, the preferred reductant source is aqueous urea, which rapidly hydrolyses to produce ammonia in the exhaust stream. 

SCR for heavy-duty vehicles reduces NOx emissions by 80%, HC emissions by 90% and PM emissions by 40% in the EU test cycles, using current diesel fuel (<350 ppm sulphur) [27], Fleet tests with SCR technology show excellent NOx reduction performance for more than 500000 km of truck operation. This experience is based on over 6 000 000 km of accumulated commercial fleet operation [82], The combination of SCR with a pre-oxidation catalyst, a hydrolysis catalyst and an oxidation catalyst enables higher NOx reduction under low-load and low-temperature conditions [83],... 

The SCR technology fits at the best the off-cycle risk in EuroVI context, because this technology does not release CH4 and its continuous operation makes the treatment... 

The SCR technology is also considered for the control of NO emission in diesel vehicles. Here the SCR catalyst is typically placed after the diesel oxidation catalyst (DOC), which is used to oxidize CO and UHCs and to convert part of the NO to NO2. In this way, the SCR catalysts can take advantage of the fast SCR reaction to enhance significantly the de-NO efficiency at low temperature (Figure 13.4). The fast SCR reaction is based on the following stoichiometry ... 

Although the standard urea-ammonia SCR technology is nowadays well established and used world-wide for the control of NO, from stationary sources, additional applications are predicted in large gas turbines, incinerators, stationary diesel engines and the cement and glass industries in view of the enforcement of stricter emission limits and of the high cost of alternative very efficient primary methods. 

Concerning the application of the urea SCR technology to the abatement of NO emissions from vehicles, although the first commercialization for heavy-duty diesel... 

Finally, the advances in the identification of the pathway of the reduction of stored NO, where ammonia is suggested as the intermediate product in the formation of nitrogen, may favor the improvement of the combined NSR + SCR technology that has been proposed by several car manufacturers to make NO removal by NSR more effective and at the same time to limit the ammonia slip. 

The SCR technology can be used in any nitric acid plant. The costs per tonne of CO2 equivalents removed range from 1.3 to 3.0 EUR. The reductant (natural gas or LPG) is the largest cost item in these processes and makes up 20% to 60% of the total costs221. 

New Opportunity for HC-SCR Technology to Control NOx Emission from Advanced Internal Combustion Engines... 

A few classicaV studies on the reactivity of HCs to reduce NOx with catalysts indicated that the use of such reductants for controlling mobile NOx emissions was quite attractive to the automotive industry, thereby the advent of a new type of HC-SCR technology in the mid-1980s. An example may be the treatment process of the tail gas from nitric acid production plant via ammonia oxida-tion. The process includes the usual injection of excessive amounts of HCs over supported noble metals such as Pt, Pd and Rh to eliminate the yellowish stack plume due to 0.1 - 0.5% NOx, mainly NO2, from the nitric acid plant. 

Challenges in HC-SCR Technology up to Early 1980s. - In this period, an attempt to use HCs as a possible reductant for the removal of NOx in exhaust streams from stationary and mobile sources was established mainly with supported and unsupported metal oxides, in addition to supported noble metals. Several catalysts could promote this type of NOx reduction under appropriate conditions, among them being those consisting of these metal constituents. 

Because of such strong demand for advanced HC-SCR technology applicable to automobile NO emission controls, Volkswagen AG and Bayer AG in Germany examined a variety of zeolitic catalysts on which NO from ICEs reacts... 

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