Numerical Modeling and Performance Evaluation of a New Biogas Purification System

In order to meet the challenges posed by dependence on fossil fuels, it is essential to develop an energy alternative based on renewable sources. Among alternative energy solutions, biogas occupies a prime position. However, before biogas can be used, it must be purified, which involves removing the carbon dioxide (CO<sub>2</sub>) and recovering the methane (CH<sub>4</sub>), thereby increasing the calorific value of the methane. The most innovative purification solution is cryogenics. Our aim in this work is to use cryogenics to purify biogas by liquefying the carbon dioxide it contains. To achieve this, we have designed and dimensioned the various components of a cryogenic purification unit for biogas production. Using the incremental method based on heat conservation equations, we simulated this purification process on the Aspen plus calculation code. Using the ADMI calculation code, we modeled the model equations to visualize the behavior of the various parameters to be controlled. The temperature, pressure and mass flow profiles affecting the desublimation of carbon dioxide were obtained. Furthermore, the sizing results show that a 450 W compressor and a condenser with a capacity of 2.5 kg are required. The temperature and pressure of the biomethane and carbon dioxide at the condenser outlet are -130°C and 15 bars. Simulations show curves for variations in temperature, pressure, rate of bio-methane recovery and carbon dioxide evacuation. They show that it is possible to produce biomethane with a purity of 96%, with a very negligible amount of carbon dioxide and a high lower calorific value (LCV) than raw biogas (9.83 kWh/m<sup>3</sup> higher than 6 kWh/m<sup>3</sup>), a significant value in energy terms, showing that this biomethane could be used for a variety of purposes.