Study On Ultra-low Concentration Coal Bed Methane Combustion In A Fluidized Bed With Cu/γ-Al₂O₃as Catalytic Particles

Ultra-low concentration coal bed methane widely exists in coal mine methane;generally speaking, the concentration of methane does not exceed2%. Because of lowcalorific value, it is very difficult to be utilized. Development and utilization of coal iswidely in China, coal bed methane resources are very rich. Most of ultra-lowconcentration coal bed methane is untreated, discharged to the atmosphere directly,resulting in waste of energy resources, aggravating the atmospheric greenhouse effect.Studies how to utilize ultra-low concentration coal bed methane in a reasonable wayhave far-reaching significance for saving resources and protecting the environment.Fluidized bed combustion technology has the advantage of good fuel flexibility, lowemission combustion pollutants and high combustion efficiency; it is suitable for thelow calorific value gas combustion. At present, most of research on ultra-lowconcentration coal bed methane catalytic combustion use noble metal catalyst, however,combustion in fluidized bed using transition metal catalysts research reports rarely. Theusing cost of precious metal catalyst is high, and the quality has suffered serious lossdue to wear and tear in fluidized bed, it is unsuitable for industrial scale use. Therefore,study on transition metal catalyst in fluidized bed catalytic combustion of ultra-lowconcentration coal bed methane has important industrial practical value and academicsignificance.Based on this situation, with10wt.%Cu/γ-Al₂O₃were employed as catalystparticles, ultra-low concentration coal bed methane which the methane concentrationlower than2%combustion in a fluidized bed was studied experimentally andtheoretically. Gas-solid two phase flow in a fluidized bed and its influence to ultra-lowconcentration coal bed methane catalytic combustion characteristic were studied, theexperiment assessed the catalyst effect, thermal stability and mechanical properties ofCu/γ-Al₂O₃particles. The operation conditions on the influence of methane conversionwere studied, analyzed the catalytic combustion dynamic characteristics. According tothe experiment data, quoted precious metal catalysts experiment data, contrast thecombustion characteristic and dynamic parameters between Cu/γ-Al₂O₃particles andprecious metal catalysts.The results show that gas-solid two phase flow has a great influence on catalyticcombustion, increased fluidized velocity, methane conversion decreases and combustion reaction moves towards bed top. The continuous experiment showed thatthe catalyst particles have good thermal and mechanical stability. Raised bedtemperature and reduced the inlet methane concentration, the methane conversionincreases, combustion reaction moves towards bed bottom. In the experiment ofdynamic characteristics, the results show that when bed temperature below480℃,intrinsic kinetics control the reaction. When the bed temperature is over480℃, thecatalytic reaction of ultra-low concentration coal bed methane is influenced by diffusionaction. By the comparison of Cu/γ-Al₂O₃and precious metal catalysts, it is found thatwhen bed temperature exceeds600℃, Cu-based catalysts show good catalytic activity.From view of energy economy, the costs of Cu-based catalysts have obvious advantages.Because of having good catalytic effect, good thermal stability, and high mechanicalstrength, Cu-based catalysts were suitable for the catalytic combustion of low calorificvalue fuel gas in a fluidized bed.This study enriches the achievements of fuel gas used in fluidized bed; promotein-depth study of the catalytic combustion of low calorific value gas in a fluidized bed,results can provide experimental and theoretical basis for low calorific value gas in afluidized bed.