Analysis of Liquid Hydrogen Production from Methane and Landfill Gas

摘要

Several process flowsheets were conceived and analyzed, using Aspen Technology'sHYSYS?chemical process simulator for the production of liquid hydrogen from methaneand landfill gas. Hydrogen (H2) was produced by the autothermal pyrolysis of methane(CH4). The energy required for CH4 pyrolysis was derived from its partial combustion.The outlet stream of the autothermal reactor is a gaseous mixture containing CH4, H2, carbonmonoxide (CO), carbon dioxide (CO2) and water. This stream was separated into itscomponents by cryogenic distillation. The portion containing CH4 and CO passed through ahigh temperature gas conditioning reactor (HTGCR) or a low temperature gas conditioningreactor (LTGCR). The recycled stream was then mixed with the main stream from theautothermal methane pyrolysis reactor and redirected to the separation process. Fiveflowsheet scenarios were conceived and analyzed.The extent of H2 recovery from these processes were as high as 99.99% with hydrogen purityat 99.9999% level. The feedstock methane and landfill gases were utilized at 99.99% level.These processes generate high-purity carbon dioxide in liquid form that can be collected andsold or easily sequestered. The total process efficiencies calculated exceeded 81% and 79%for methane and landfill gas, respectively. The highest exergy efficiency was about 57%(for methane) and 51% (for landfill gas); assuming 10% heat loss from the process and 30%cryogenic refrigeration process efficiency. The ratio of CO2 to H2 produced in these processesvaried in the range of 3.027 to 4.219 (g/g).