A compact, economic scrubber to improve farm biogas upgrading systems

International audienceThis paper presents a new biogas upgrading technology with its theoretical and experimental study and an application at farm scale. This process is designed for flows of raw biogas up to 50 Nm3/h (55% CH4 and 45% CO2). The upgrading system includes a physical absorption of CO2 at 7-10 bars in water and desorption at atmospheric pressure. First, the authors improved the traditional bottom column design to avoid usual formation of biogas bubble and leaks. As a second technological breakthrough, process water was successfully recycled using a static mixer to enhance CO2 desorption from the water. Finally, the scrubbing system is entirely characterized; carbon dioxide absorption into the column is modeled thanks to the transfer unit height (HTUOG) and the number of gas transfer units (NTUOG); desorption step of CO2 is performed into the static mixer at atmospheric pressure and modeled. Experiments with this new scrubber were conducted in farm with raw biogas; inlet flow rates ranged between 15.6 and 42 Nm3/h. Upgraded biogas up to 77% (QG=40.7 Nm3/h and QL=8.243m3/h and P=7.924 bar and T=285K) is possible with good absorption efficiency (57.5%) and high methane recovery ratio (94%) and low power consumption (0.26 kWh/Nm3).Through the comparative analysis of the experimental results with the modelling proposed, authors are providing good references to evaluate this simple and cheap compact technology on a real farm biogas plant and its potential for fuel combustion engines