Study Of Reactive Sorption Enhanced Steam Reforming Of Biogas For Hydrogen Production

China has abundant biogas, which is a kind of renewable clean energy resource. Developing a new technology of producing hydrogen from biogas not only minimizes the pollution of direct emissions of biogas, but also increases the added value of biogas to produce hydrogen. The thesis for the first time proposed and studied the reactive sorption enhanced steam reforming of biogas (ReSER-Biogas) for hydrogen production. High-purity H2 at relative lower temperature could be obtained directly by ReSER process which has great significant for efficient hydrogen production from biogas.Firstly, a thermodynamic model of ReSER-Biogas reaction was established to simulate and calculate the methane conversion and hydrogen concentration of outlet gas under different operation conditions. The simulation results show that ReSER-Biogas can reduce reaction temperature, decrease CO2 and CO concentration of the product, and obtain high-purity H2 directly. To obtain the same concentration of hydrogen in the product, ReSER-Biogas can lower the reaction temperature by 150 ℃ compared to the process without sorption enhanced reforming. When reaction temperature is at 550℃ and CO2 removal ratio increases to 0.99, the theoretical calculation shows that methane conversion is 94%, and H2 concentration can reach 98% without CO and CO2 in the product gas. This demonstrates the feasibility of ReSER-Biogas for high-purity H2 production directly.Secondly, on the basis of thermodynamic simulation results, the ReSER-Biogas process was investigated over the mixture of Ni catalyst and CaO adsorbent in a fixed bed reactor, under the temperature of 540-600℃, CO2 volume content of 20-40% and steam to carbon mole ratio of 2-4. The experiment results show that:under the conditions of the calcium to carbon ratio is 1.31 and the range of temperature is 540-600 ℃, using nano-CaO based adsorbents, the CO2 removal rate of adsorption section reached to 0.99. The optimium reaction condition of ReSER-Biogas was reaction temperature of 580 ℃, steam to carbon mole ratio of 3 and CO2 to CH4 mole ratio of 0.43, H2 concentration of 91.8% with CO concentration of 0.35% and CH4 conversion of 76% were obtained. Compared to biogas steam reforming process, the H2 purity obtained by ReSER-Biogas process increased more than 20%, and CO concentration in the effluent decreased more than 10 times, with the methane conversion improved over 10% under the same condition. The experiment results demonstrated ReSER-Biogas can produce high-purity H2 directly with lower reaction temperature, less CO concentration in the product gas and higher methane conversion.Then, on the basis of thermodynamic calculations and experimental results, the ReSER-Biogas process for hydrogen production was established by using chemical simulation software of Aspen Plus, to determine the optimum operating parameters for ReSER-Biogas. The simulation results showed:the optimum operating parameters were reaction temperature of 580℃, steam to carbon mole ratio of 3, and calcium to carbon mole ratio of 2.75. Under the condition of optimum operating parameters, ReSER-Biogas process obtained high hydrogen production rate of 2.35 m3 H2/m3 Biogas, high energy conversion efficiency of 94.7%, and high hydrogen production on unit energy consumption of 0.00063 m3 H2/kJ. In comparision with conventional biogas steam reforming process which has the largest hydrogen production rate during current techniques of hydrogen production from biogas, the hydrogen production rate of ReSER-Biogas process increased by 42%, with energy conversion efficiency increasing by 24%. In addition, compared with reactive sorption enhanced reforming process of coke oven gas (ReSER-COG), the hydrogen production rate of ReSER-Biogas process increased by 30%, and energy conversion efficiency increased by 24%. The simulation and comparison results showed that ReSER-Biogas for hydrogen production has the strongest technical advantages.The researches of the ReSER-Biogas for hydrogen production in this thesis provide a theoretical basis for achieving the goal of energy-saving and efficient hydrogen production from biogas.