Biogas Upgrading by Physical Water Washing in a Micro-Pilot Absorption Column Conducted at Low Temperature and Pressure

The European Energy Policy has currently two main goals to reach: to minimize exposure to volatility of fossil fuel prices and to reduce of greenhouse gas (GHG) emissions. To reach these targets a practical way, among the others is represented by the biogas production by anaerobic digestion (Bonoli et al., 2014) (AD) and its upgrading to biomethane. In this work the absorption of CO2 is studied using a column working at atmospheric pressure and low temperature (5<20 °C) to investigate the feasibility of the process and analyze from an economical point of view the advantage of avoiding the use a pressurized system. A glass laboratory-pilot absorption column was used for gathering the experimental data. It is a column 1 meter high, thermostated using water and filled with 40 cm of structured packing (Sulzer CX), adapted to operate continuously. A synthetic biogas was prepared mixing a stream of CO2 (>99%) and a stream of methane (>99.9 %) in order to reproduce a typical raw biogas composition, i.e. molar fraction of methane of about 0.6. The internal temperature was monitored by a thermocouple and the inlet and outlet flow of biogas (G) was measured using a mass flowmeter while the water flow rate (L) was monitored using a magnetic induction flowmeter. The compositions were determined using a 3000A micro-Gas Chromatograph Agilent, previously calibrated. The temperature was varied between 6.5 and 20 °C and the water flow rate between about 0.5 and 5 L/h. The composition of the gas exiting the micro-pilot plant was monitored every 5 minutes until the stationary condition.