Novel dense skin hollow fiber membrane contactor based process for CO2 removal from raw biogas using water as absorbent

摘要

CO2 removal from raw biogas is required in order to meet standards for the gas grid or as a vehicle fuel. Among biogas upgrading available techniques, pressurized water absorption using packed column (PWA) is one of the most well-established technique. In this work, a novel absorption/desorption loop using dense based hollow fiber membrane contactor (HFMC) process and water as absorbent is proposed and investigated by simulation. Thanks to the ability of dense membranes to withstand a high transmembrane pressure, neither water depressurization before the desorber nor water recompression before the absorber is needed. 1D modeling based on a resistances in series approach is used for the modeling of both absorption and desorption units. HFMC process performances are compared to state of the art packed column (PWA) process reported in literature. Using commercially available dense based HFMC, the process is able to recover 96.6% of CO2 and reach biomethane purity of 98%. The corresponding energy requirement is of 0.17 kWh/Nm(3) of raw biogas, which is 20 to 35% lower than that reported for packed column based process, under comparable gas inlet conditions and product specifications. HFMC process offers absorption intensification factor of about 1.68, corresponding to a volumetric reduction of about 68% of the absorption unit. Under the investigated operating conditions and due of the preponderant liquid side mass transfer resistance, process selectivity is mainly controlled by the absorbent selectivity. Without flash recovery, CH4 loss is of about 8%. No significant methane loss reduction is obtained from increasing membrane selectivity from 17 to 60 with membrane mass transfer coefficient of 5.10(-4) and 5.10(-5) m/s respectively. Perspectives for further process optimization are exposed.