Particulate control catalysts

Ness S.R., Dunham G.E., Weber G.F. and Ludlow D.K., SCR catalyst-coated fabric filters for simultaneous NO and high-temperature particulate control, Environmental Progress 14 69 (1995). 

Doyle J.B., Prish E.A. and Downs W. (Babcock and Wilcox Co.), Integrated injection and bag filter house system for SOx-NOx-particulate control with reagent/catalyst regeneration, U.S. Patent 4,793,981 (1988). 

Catalytic technologies are usually employed to deal with pollutants emitted by the exhaust systems of motor vehicles and which are subject to regulation (nitrogen oxides, hydrocarbons, CO and particulates). Specific catalysts have been developed in each case as a function of the regulatory requirements and particular characteristics of the emission. Thus, three-way catalysts are highly efficient at controlling emissions produced by engines... 

The Clean Air Act Amendments of 1970, which followed the original Clean Air Act of 1967, set national air quality standards for six criteria air pollutants NOx, SOx, ozone, carbon monoxide (CO), particulates and lead. The result was the removal of lead from gasoline and the installation of emission control technologies, including baghouse filters for particulate control, wet and dry scrubbers for SOx control and automobile exhaust catalysts for controlling hydrocarbons (HC), CO and NOx. As a consequence, lead emissions have been dramatically reduced, SOx emissions are being controlled, and automobile CO, HC and NOx emissions have decreased by nearly a factor of 10 (over uncontrolled emissions). In spite of these dramatic improvements, in 1989 approximately 130 million people in the U.S. lived in 96 areas which did not meet air quality standards either in ozone, in carbon monoxide, or in both [2]. 

The technology of growing carbon nanotubes from the vapor phase dates back to 1991 when they were first found [11] in arc discharge experiments. Nanotubes can be obtained by chemical vapor deposition, laser evaporation, arc discharge, and carbon ion bombardment [62], Addition of particulate metal catalysts creates a more controlled growth habitat and helps growth of whiskers with greatly enhanced dimensional uniformity. 

NH3-SCR unit into these locations in existing plants is costly and faces space limitations. Therefore, new low-temperature SCR catalysts working at around 150-200 °C can be located downstream of the solid-particulate control device, near the stack. 

In magnesium casting, sulfur dioxide is employed as an inert blanketing gas. Another foundry application is as a rapid curing catalyst for fiirfuryl resins in cores. Surprisingly, in view of the many efforts to remove sulfur dioxide from flue gases, there are situations where sulfur dioxide is deliberately introduced. In power plants burning low sulfur coal and where particulate stack emissions are a problem, a controlled amount of sulfur dioxide injection improves particulate removal. 

Diesel engines, which are used in the larger vehicles, are important sources of particles and NOx, but emit relatively low amounts of CO and HCs. Diesel particulate emissions can, over time, be controlled. The control of NOx is problematic, and an appropriate technology is not available. Lean NOx catalysts are being pursued but conversion efficiencies remain low. 

The fluidised bed is only one of the many reactors employed in industry for gas-solid reactions, as reported by Kunii and Levenspiel.25 Whenever a chemical reaction employing a particulate solid as a reactant or as a catalyst requires reliable temperature control, a fluidised bed reactor is often the choice for ensuring nearly isothermal conditions by a suitable selection of the operating conditions. The use of gas-solid fluidised beds... 

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