| dc.description.abstract | Part Ⅰ:
The average composition of biogas is 60-70% methane (CH4), 30-40% carbon dioxide (CO2), 0-4000 ppm hydrogen sulfide (H2S), and other trace gases. Both CH4 and CO2 emission are the causes of global warming. Furthermore, CH4 is estimated to have a global warming potential (GWP) of 28-36 over 100 years. Its influence on the greenhouse effect cannot be underestimated.
In the first part of study, PSA simulation program was applied to separate biogas. The adsorbent was chosen based on adsorption data from literature, Afterwards, we chose three commercial adsorbents to compare their performance, including activated carbon, zeolite 5A and zeolite 13X, and the sorbent parameters were calculated from experimental data of the adsorption equilibrium curve. We used 13X zeolite produced by COSMO as adsorbent due to its high CO2/CH4 selectivity. In the second part of study, a 2-bed 8-step PSA process is utilized to separate biogas (36% CO2, 64% CH4 and 100 ppm H2S) after desulphurization and water removal from the Institute of Nuclear Energy Research. After the basic-case simulation, the top product CH4 purity was 95.8 % with 90.9% recovery and the estimated mechanical energy consumption was 0.68 GJ/tonne-CH4. To find the optimal operating conditions, this study combined the simulation of 2-bed 8-step PSA process with design of experiments (DOE) method. After simulation analysis, the study showed a top product CH4 purity of 99.5% with 91.3% recovery, and 0.015 ppm H2S purity, which is suitable to be injected into the natural gas grid (>95% CH4), satisfying the standard of natural gas pipeline and can be used as fuel. The mechanical energy consumption was estimated to be 0.86 GJ/tonne-CH4.
Part Ⅱ:
In view of serious global warming problem and the massive energy waste in renewable energy, power-to-gas (P2G) is currently an energy storage technology actively promoted by the European Union. This technology includes water electrolysis and methanation reaction, and the latter often reacts with excess carbon dioxide. After the reaction, the gas composition is CO2, CH4, C2H6 and a small amount of H2. In this research, we will develop a CO2 purification technology from the outlet gas of methanation by simulation of pressure swing adsorption (PSA) process. First, we will find at least two commercial adsorbents from literature data and the data of adsorption isotherm by experiments. Then, we will establish a simulation program of dual-bed eight-step PSA to develop a CO2 PSA purification process with CO2 product purity above 70%.
In the first part of study, we found suitable commercial adsorbents based on literature data and experimental measurement of equilibrium adsorption. After calculating the selectivity of CO2/CH4 and CO2/C2H6, we chose the zeolite 13X produced by COSMO as the adsorbent in this study. In the second stage, we conducted the PSA simulation program CO2 purification with a dual-bed eight-step process. This research used 67.9% methane, 30% carbon dioxide and 2.1% ethane as the feed, and after the simulation, the study showed a top product CH4 purity of 84.66% with 95.53% recovery, a bottom product CO2 purity of 84.03% and waste CO2 purity of 91.30%, both reaching the target of 70% CO2 purity. Therefore, the process can recycle this product to the reaction of methanation, in order to reduce CO2 emissions and improve the efficiency of carbon cycle. | en_US |