Catalytic Gasification Process

The process is based on the concept that alkali metal salts (such as potassium carbonate, sodium carbonate, potassium sulfide, sodium sulfide, and the like) will catalyze the steam gasification of coal. In addition, tests with potassium carbonate showed that this material also acts as a catalyst for 

The bed is fluidized by a mixture of steam and recycled carbon monoxide-hydrogen. Unreacted steam is condensed and the acid gases (CO2, H2S) are removed by conventional acid gas treatment. The product (methane) is separated from the carbon monoxide and hydrogen by a cryogenic process. The solid product (which is actually a mixture of char, coal minerals, and the catalyst) is removed on a continuous basis the majority of the catalyst is recovered and recycled. 

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Figure 2.8. Schematic diagram of catalytic gasification process (SNG synthetic natural gas). From Hirsch et al. (1982). Science 215, 121-127, reprinted with permission. Copyright 1982 American Association for the Advancement of Science.

Whilst the basic process for generation and conversion of syngas is well established, production from biomass poses several challenges. These centre on the co-production of tars and hydrocarbons during the biomass gasification process, which is typically carried out at 800 °C. Recent advances in the production of more robust catalysts and catalytic membrane reactors should overcome many of these challenges. 

Figure 17.6 illustrates a gasification process integrated with the calcium looping process. Once the water gas mixture is formed at the exit of the gasifier, calcium oxide fines are injected into the fuel gas stream. As the fuel gas flows past the WGS catalyst, the WGS reaction takes place and forms additional C02. The injected CaO sorbent particles react with C02 and H2S in the gas stream, thereby allowing further catalytic WGS reaction to occur. The reactions involved in the calcium looping scheme are... 

H-Coal A coal gasification process. Crushed coal is mixed with process-derived oil and catalytically hydrogenated in an ebullated bed under pressure at 455°C. The catalyst is a mixture of cobalt and molybdenum oxides on alumina. Developed by Hydrocarbon Research from the 1960s and piloted in Catlettsburg, KY, from 1980 to 1982. See also CSF, H-Oil, CSF, Synthoil. 

An indirect hydrogenation process that is still under development is catalytic gasification. In this process, a catalyst accelerates the gasification reactions, resulting in the formation of hydrogen and CO, at relatively low temperatures. This process also promotes catalytic formation of methane at the same low temperature within the same reactor. Catalyst deactivation and costs have been a major impediment to the commercialization of this process. 

After World War II, direct liquefaction of coal became uneconomical as the use of lower-cost petroleum products became more widespread. However, the German process of indirect coal liquefaction, the Fischer-Tropsch process, continued to hold some interest. The Fischer-Tropsch process first involved production of a carbon monoxide and hydrogen-rich synthesis gas by the controlled gasification of coal followed by a catalytic reaction process to yield a valuable mixture of hydrocarbon products. Simplified Fischer-Tropsch reactions are shown by the following equations ... 

Elliott, D., Neuenschwander, G., Phels, M., Hart, T., and Zacher, A., Chemical processing in high-pressure aqueous environments. 6. Demonstration of catalytic gasification for chemical manufacturing wastewater cleanup in industrial plans, Indust. Eng. Chem. Res., 879-883, 1999. 

Furlong, L. E. and Nahas, N. C., "Catalytic Coal Gasification Process Research and Development", 10th Synthetic Pipeline Gas Symposium, Oct., 1978. 

For catalytic gasification, we believe that the potential for cost reduction is greater. For example, for the SNG process that we are now developing with DOE for bituminous coal, and for a pioneer plant, we estimate a potential reduction in gas cost over existing technology of about two times our estimated reduction for the thermal processes. In this regard, we have not had the opportunity to evaluate other newer processes that involve... 

The first case covers for example flue-gas treatment, which requires the filtration of fly-ash and the reduction of NOx, or gasification processes, where particulates and high-boiling tars have to be removed. An example of the second case is that of combustion processes, where incomplete combustion leads to the emission of carbonaceous particulates. The most relevant topic in this category is the reduction of diesel particulate emissions ( diesel soot ) by catalytic filtration. A more exotic example is the reaction cyclone for the thermal conversion of biomass, which also combines chemical reactions and separation in one apparatus, though its separation mechanism is not filtration. 

Calcined dolomites are the most widely used nonmetallic catalysts for tar conversion in biomass gasification processes.626-631 They are relatively inexpensive and are considered disposable. However, they are not very robust and quickly undergo attrition in fluidized-bed reactors. Consequently, dolomites find most use in fixed-bed catalytic reactors. Tar conversion efficiency is high when calcined dolomites are operated at high temperatures (900°C) with steam. Olivine, another naturally occurring mineral, has also demonstrated tar conversion activity similar to that of calcined dolomite. Olivine is a much more... 

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