Gasification environmental considerations

The water/carbon slurry formed in the quench vessel is separated from the gas stream. This slurry flows to the carbon recovery system. Removal of the carbon from the slurry water is usually necessary for environmental considerations. Furthermore, for improved thermal efficiency, the recovered carbon can be recycled to the gasification reactor by dispersing it in the feedstock. If the fresh feed does not have too high an ash content, 100% of the carbon formed can often be recycled to extinction. 

Thermochemical conversion processes have met resistance from the environmental community and the public. An essential difference between direct combustion, pyrolysis, and gasification is that the latter two are intermediate processes for producing gaseous, liquid, and solid products that can be used in a wide variety of applications. Pyrolysis processes can be optimized for the production of biocrade oils. In the case of chemical and fuel production, the emissions from a direct process effluent can be avoided, although consideration must be given to emissions from the ultimate use of these products as they are used or combusted downstream. 

Although resource recovery and recycling are receiving considerable attention today, most solid waste is still disposed of in a sanitary landfill. Even though it is widely recognized that placing solid wastes in a landfill is a misuse of potentially valuable resources, this practice will continue until economic and environmentally acceptable alternatives are found. One such alternative, the gasification of the paper fraction of solid waste is considered in this report. 

The catalyst is not sensitive to sulfur or other oxo poisons, which is another environmental advantage. Together with the simple but effective decantation, which allows the withdrawal of organic and other byproducts at the very moment of separation, accumulation of activity-decreasing poisons in the catalyst solution is prevented. Therefore no special treatment or purification step is necessary. This reduces the environmental burden still further. For a considerable time the oxo units at Ruhrchemie s plant site were even supplied with syngas derived from coal produced by the TCGP (Ruhrchemie/Ruhrkohle s version of the Texaco coal gasification process). In various cases this can be an important factor as far as local resoruces are concerned. 

Fluidized beds have been studied during the last 35 years with an effort that is almost unique for a single type of process operation. Many thousands of articles, patents, several textbooks (i- ) and many review articles on special subjects appeared, while a considerable number of symposia have been devoted to this subject. This reflects also a wide spread use of fluid beds in physical operations and as a chemical reactor in chemical, petroleum, environmental, metallurgical and energy industries. Old applications like gasification of coal (Winkler generator, 1926) and combustion of coal are reviving. 

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