Waste gas cleaning

Particle size distribution relating to gas cleaning is well understood in the industry. This section deals with general rules of thumb. Certain important issues not included in this section are flue gas desulfurization, flue gas denitrification, hazardous waste gas cleaning, waste incineration gas cleaning, and removal of CO2 from flue gas. All these topics have special requirements, which must be considered separately in the design process. 

Related systems It should be noted that specific properties for applications could be enhanced by using solid solutions, doped materials, and composites, instead of pure ceria. For example, ceria-zirconia solid solution is a well known ceria based material for enhanced OSC and high ionic conductivity for solid state fuel cell components. It is also used in the three way catalysts for automobile waste gas cleaning, because of the improved thermal stability, surface area, and reducibility. The synthesis, structure, and properties of ceria-zirconia have been actively studied for a long time. Di Monte and Kaspar et al. presented feature articles on the nanostructured ceria—zirconia-mixed oxides. The studies on phase, structures, as well as the microstructures are discussed and reviewed (Di Monte et al., 2004). 

Fig. 2.3 Flow diagram ofTi02 production by the k) Evaporator I) TiCU superheater m) O2 su-chloride process, a) Mill b) Silo c) Fluidized- perheater n) Burner o) Cooling coil p) Filter bed reactor d) Cooling tower e) Separation of q) Ti02 purification r) Silo s) Gas purification metal chlorides f) TiCU condensation g) Tank t) Waste-gas cleaning u) CI2 liquefaction, h) Cooler i) Vanadium reduction j) Distillation ...

VDI Guidelines, Waste gas cleaning by adsorption - process and waste gas cleaning", VDI 3674, May (1998)... 

In summary, the biocatalytic process reduces raw material costs by a factor of four and the percentage of process costs for environmental protection (incineration, waste water treatment and waste gas cleaning) is cut down considerably from 21% to 1%. Compared with the chemical process the environmental protection costs were reduced by about 90% per ton of 7-ACA. 

Waste gases do not only contain solid or liquid particles as pollutants. They also contain gaseous and vapor contaminants. These pollutants are also dangerous to the environment. These pollutants cannot be separated from the waste gas by any of the methods described before. The methods for waste gas cleaning from gaseous and vapor pollutants can be classified into three major classes ... 

Catalytic methods of gas cleaning are used very often in modern industry as a result of the possibility of very deep cleaning of the waste gas. Up to 99.9% of pollutant can be separated from the waste gas by this method. However, the disadvantage of this method is the formation of new compounds, which must be use-able. In the example shown of waste gas cleaning from the H2S, the formed byproduct can be used in the chemical industry. However, the amount of sulfur formed in crude oil refineries is often so high that it cannot be moved completely to the chemical industry. It then becomes important to find new ways of using sulfur. 

Using only one of the described methods in the refinery for waste gas cleaning is impossible. Modern refineries have different schemes in their technological structure for gas cleaning, each consisting of many methods. It is only the use of many methods in combination that will allow us to achieve the needed cleanliness of the gas with optimum use of energy and chemical recourses of the refinery. 

Depending on the sulfur content in the crude oil, both types of crude oil refineries can have the plants for catalytic waste gas cleaning with the production of sulfur in their technological structure. If more sulfur is produced than the refinery can sell to the chemical industry, it is often reasonable to install plants for sulfuric acid production inside the refinery. 

VDI3674, Waste gas cleaning by adsorption. Process and waste gas cleaning, Beuth Verlag GmbH, 10772 Berlin, 1998. 

A variety of waste gas cleaning processes " are commercially available. They are used to remove organic vapors (solvents) from air emissions from various industries and product lines. The main applications of solvents in various industries are given in Table 22.1.1. 

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