Thermodynamic And Experimental Study Of Direct Methane Production From Coal

Methane production from coal has great significance for the clean conversion and utilization of coal and the optimization of terminal energy structure. This dissertation focused on the reaction system of coal, steam, and CO2sorbent, and the method of direct methane production from coal was realized by integrating reaction and separation, endothermic and exothermic processes all in one reactor. Thermodynamic analyses, constant-volume reaction experiments, fix-bed reaction experiments, and fluidized-bed experiments were conducted. The main contents are shown as below:1. Thermodynamic Equilibrium Analysis of Direct Methane Production from CoalThe effects of temperature, pressure, Ca/C ratio, and H2O/C ratio on direct methane prodcution were studied by thermodynamic equilibrium analysis, and the proper reaction conditions for direct methane production from coal were determined. Considering the self heat balance of direct methane reactor and CaO regeneration reactor, the highest carbon conversion rate of gasification was obtained.2. Study of Direct Methane Production from Coal by Constant-Volume ExperimentsThe effects of residence time, temperature, pressure, Ca/C mole ratio and H2O/C mole ratio were investigated by constant-volume experiments. The experimental results were consistent with results of thermodynamic equilibrium analysis. For the typical reaction condition, the methane content could exceed62%, while the CO and CO2contents were as low as0.1%in the product gas. The extended reaction time could improve the methane yields greatly. The increasing pressure and decreasing temperature will improve the methane production by changing the equilibrium condition of methanation. Due to the CO2absorption effect of CaO, the methane concentration in production gas for direct methane production from coal was44%higher than that of hydrogasification.3. Study of Direct Methane Production from Coal by Fix-bed ExperimentsThe comprehensive effects of CaO and steam will significantly affect the methane production. The pyrolysis, steam gasification, and pyrolysis with CaO, could only take up a very small part of methane production, while the stratification of CaO and coal will cause a significant decrease in methane production. The peak methane production rate appeared at temperature of550℃-600℃, and a sufficient promoting effect of methane production was found by the increase of pressure, while the effect of increasing temperature for the methane production was not so obvious as for hydrogen production. Steam injection at lower temperature had a higher methane and hydrogen production, while C2and C3hydrocarbons were decreased rapidly due to the steam reforming reaction.4. Study of Direct Methane Production from Coal by Fluidized-bed ExperimentsThe effects of steam pressure and Ca/C were investigated by continuous fluidized-bed experiments. An excessive amount of steam would improve the hydrogen production while inhibit methane production by promoting methane steam reforming reaction. The methane and hydrogen yields were both reached its peak rate at steam pressure of3.3MPa. The researches of different Ca/C conditions showed that the average methane production would reach its peak at Ca/C=0.5. And the further incease of CaO would not have positive effect for methane production. The carbon conversion in fluidized-bed experiment was close to the simulation that considering the CaO regeneration, and the methane and hydrogen yields were very close to the simulation results.