Analyzing Biogas Purification Using Low-Temperature Distillation For CO2 Capture: Exergetic And Economic Evaluation

As the world moves towards significant contributions to alternative energy sources, biogas and biomethane will play a significant role in the future. The biogas upgrading process to produce higher-purity biomethane while producing carbon dioxide as a by-product will find several applications. A low-temperature double-distillation method was developed and analyzed. Three biogas feed systems are discussed with typical biogas methane concentrations of 50%-mol, 60%-mol, and 75%-mol. The nitrogen refrigeration cycle provides the purification process at low temperatures. The design, simulation, sensitivity analysis were conducted using Aspen Plus software; energetic, exergetic, and economic analyses were performed accordingly, as well as improvement options suggested. The three systems with 1000 kmol/hr feed were designed to achieve 98.5%-mol methane purity while producing a higher-purity carbon dioxide stream. The simulations were conducted up to the level of a carbon dioxide-frozen-free environment. With methane content increasing from 50%-mol to 75%-mol in the biogas feed, the following can be achieved: reduction in the total power consumption from 22.97 MW to 20.77 MW and the specific energy consumption from 10.3 MJ/kgCH4 to 6.21 MJ/kgCH4; an increase in overall exergetic efficiency by 3%-point, and reduction in the total revenue requirements for the overall system (i.e., investment, operation and maintenance expenses, and fuel costs) from 259.68 million USD to 239.13 million USD.