Waste gas cleaning process

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. 

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. 

Chevalier, J., Rousseaux, P., Benoit, V, and Benadda, B., Environmental assessment of flue gas cleaning processes of municipal solid waste incinerators by means of the life cycle assessment approach, Chem. Eng. Sci, 58, 10 (May) 2053-2064, 2003. 

Rensfelt, Erik, and Ekstroem, Clas. Fuel gas from municipal waste in an integrated circulating fluid-bed gasification/gas-cleaning process, Energy Biomass Wastes, No. 12, pp. 891-906 (1989). 

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)... 

Rensfelt E. Ekstrom C. (1989) Fuel Gas from Municipal Waste in an Integrated Circulating Fluidized bed/Gas Cleaning Processes. Energy Biomass Wastes, 12, 811-906. 

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. 

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

LCA have been successfully utilised in the field of plastics waste management, for example, to assess differences in environmental performance between different waste incineration strategies [24] or related activities such as the flue gas cleaning process of plastic waste incinerators [25], to compare the environmental performance of different scenarios for the management of mixed plastics waste as well as that of specific plastic waste fractions [25-32]. 

The latest installations incorporate a waste heat boiler in the off-gas cleaning system to recover sensible heat from the rotary kiln off-gas. There is sufficient sensible heat in the off-gas from the SL/RN process to generate 500 to 700 kWh/t of DRJ, depending on the type of reductant used. 

With these waste-minimization techniques, methanol synthesis is relatively clean, and poses no unique environmental hazards. The need for environmental controls is more closely associated with the synthesis gas generation process. 

Human activities harmfully influence the environment and nature in many ways. The production of undesirable wastewater, waste gas, and liquid plus solid residues seems to be inevitable during chemical processes. The public is more sensitive to pollution of the aquatic environment and the depletion of clean water resources, because they have an immediate impact on daily routine and recreational activities. However, air pollution has an adverse impact on our health in the short and long term, and the problems of the greenhouse effect and the destruction of stratospheric ozone could extinguish life from the face of the Earth. These problems are enhanced by overpopulation and urbanization. Today, urban areas can be seen as monsters that consume large amounts of energy, matter, and freshwater and release all kinds of waste into the environment. 

In this new process the H2S/SO2 reaction is carried out in liquid sulfur at pressures in excess of five atmospheres. Typical Claus catalysts are still employed but temperatures are lower (below the dewpoint of sulfur) and thus the redox reaction occurs in the liquid sulfur phase at the surface of the catalyst. Vapor losses due to sulfur mist entrainment are reduced and interstage condensers in the tradition Claus train are not required thus avoiding wasteful heat transfer problems. The authors claim that overall sulfur recoveries in excess of 99% are possible without the use of tail gas clean up units. 

Adsorptive Processes. The use of activated carbon, sprayed into a dry/semi dry scrubbing unit along with lime or less frequently packed in an adsorption unit positioned after the particulate removal device and prior to the stack, has become a standard component in gas cleaning trains as a means of PCDD/F control on all sizes of plant fed with MSW or clinical waste. Other adsorptive media such as zeolites are also being tested. The inclusion of an adsorptive device in combustion systems fired with wood and agricultural wastes is not normally contemplated, and as noted above, an interesting issue to be resolved is whether different waste types generate flyash of different activities relative to PCDD/F formation. 

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