Biogas quality upgrading by carbon mineralization with calcium hydroxide solution in continuous bubble column reactor

Abstract

Biogas is produced when certain kinds of bacteria digest organic substances in an anaerobic environment. Typical raw biogas consists of about two thirds of methane (CH4) and one third of carbon dioxide (CO2). Even though raw biogas can be used directly to generate power, but the large volume of CO2 reduces the heating value of the gas, increasing compression and transportation costs and limiting economic feasibility. In this work, the raw biogas from small scale digester was upgraded by counter-current contacting it with a saturated Ca(OH)2 solution in a bubble column contactor to capture CO2. The bubble column comprises of a cylindrical column 7.3 cm in diameter and 100 cm high and is equipped with a perforated plate gas distributor. The CO2 content in upgraded biogas exit from top bubble column was sampled and measured using Gas Chromatography. The effect of ratio raw biogas to Ca(OH)2 solution flow rate with different liquid height and concentration of Ca(OH)2 solution on CO2 removal were investigated. The results showed that CO2 removal depends on the superficial velocity of the biogas, the flow rate of the Ca(OH)2 solution, the liquid height. The absorption of CO2 increases as the absorbent flow rate increases and decreases as the gas flow rate increases. The use of Ca(OH)2 above the solubility shown in the continuous process showed higher absorption of CO2. However, the increasing CO2 absorption is not significant with increasing Ca(OH)2 concentration. The highest absorption of CO2 obtained in the continuous process is 79.34 %.