الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Biogas – a renewable energy source encompassing primarily CO2/CH4 mixture – can fuel vehicles if it is properly purified. Recently, cryogenic biogas purification (CO2 Liquefaction) witnesses a significant progress as a promising upgrading technique; however, the obstacle hinders its implementation is CO2 freeze-out causing crucial issues such as blockage pipes. Therefore, in this work, novel approach for improving the cryogenic separation of CO2/CH4 mixture is drawn. A new system is developed using one distillation column to mitigate CO2 freeze-out. The proposed process is simulated in ASPEN HYSYS and validated against experimental data, showing well agreement. Additionally, to reveal its efficacy, different configurations are modeled, starting from simple system, passing by a system with two columns, to the suggested one. The operating conditions – distillation pressure and temperature, number of trays, reflux ratio, feed tray location, and inlet composition – are optimized towards minimizing energy demand and diminishing frosting danger. With avoiding frosting presence, the suggested process can boost CH4 purity from 60% up to 97.2% (mol), matching natural gas standards, which has not been reached before in any previous studies using only one column, suitable for commercial uses. Also, a valuable by-product of high-purity liquid CO2 (above 99%) can be generated rather than being emitted into air. Furthermore, a new configuration is introduced to generate Liquefied biomethane (LBM) with very low CO2 concentration (<50 ppm). Compared to former cryogenic systems, the present process achieves not only the highest CH4 purity (97.2%) – even higher than when utilizing two columns – but also the least energy penalty (0.236 kWh/Nm3raw_biogas). Another comparison held against conventional approaches (e.g. water, amine and organic physical scrubbing, pressure swing adsorption and membranes) the proposed process stands among the highest in CH4 and CO2 purities generated, witnesses the lowest in methane loss, is among the least in energy consumption, and shows high competitiveness in investment cost. With these findings, cryogenic platforms can be applicable/promising purification approach.