Low temperature and elevated pressure steam gasification of Illinois coal.

摘要

Coal is an important source of energy, but the stricter environmental regulations have made coal combustion difficult. Thus, there is a need to investigate new processes that would utilize this precious energy source. In this research steam gasification of an Illinois coal for methane production (IBC 101) was investigated at low temperature and high pressure in both catalytic and noncatalytic processes. Catalyst tested in this research were salts of potassium, sodium, iron, nickel and molybdenum. Experiments were performed on both raw and demineralized coal samples at 500-700{dollar}spcirc{dollar}C and 500-1000 psig. Coal can be steam gasified in presence of catalyst(s) at lower temperature (500{dollar}spcirc{dollar}C) and elevated pressure (500 psig) to produce substantial quantities of methane. Under these conditions almost 60% of coal was gasified in 30 minutes with a binary catalyst system. No carbon conversion was attained in noncatalytic process, under these conditions. The lower temperatures prevent coal from charring as quickly and thus a significantly higher rate of gasification is observed (rapid rate gasification). The gas analyses of the experiments revealed that no methane was produced in absence of catalyst and at lower temperatures and elevated pressures the reaction of methane formation was the primary reaction (almost at 90-95% of the equilibrium). At lower pressure reaction of syn gas formation is minimized. Contrary to previous reported information, sodium has been shown to be an extremely effective catalyst in this process. This is due to low temperature operations which prevent the catalyst volatilization and thus the catalyst remains on the substrate surface. Substantial synergistic effects were observed with the binary catalyst systems of alkali and transition metals in raw coal steam gasification. These effects were more pronounced for the potassium/iron system. These effects observed with the binary system indicate the possibility of a trinary system (mineral in coal as the third catalytic species). The low temperature operations will reduce the energy cost of gasification process. This is the main cost that makes these processes uneconomical. At low temperatures catalyst loss due to volatilization and tie-up with mineral is minimized and thus catalyst recovery should be easier.