Economic assessment of biogas-to-electricity generation system with H 2S removal by activated carbon in small pig farm

Abstract

This study was conducted to assess the economic feasibility of electricity generation from biogas in small pig farms with and without the H 2S removal prior to biogas utilisation. The 2% potassium iodide (KI) impregnated activated carbon selected as H 2S adsorbent was introduced to a biogas-to-electricity generation system in a small pig farm in Thailand as a case study. With the average inlet H 2S concentration of about 2400 ppm to the adsorption unit, the H 2S removal efficiency could reach 100% with the adsorption capacity of 0.062 kg of H 2S/kg of adsorbent. Under the reference scenario (i.e., 45% subsidy on digester installation and fixed electricity price at 0.06 Euro/kWh) and based on an assumption that the biogas was fully utilised for electricity generation in the system, the payback period for the system without H 2S removal was about 4 years. With H 2S removal, the payback period was within the economic life of digester but almost twice that of the case without H 2S removal. The impact of electricity price could be clearly seen for the case of treated biogas. At the electricity price fixed at 0.07 Euro/kWh, the payback period for the case of treated biogas was reduced to about 5.5 years, with a trend to decrease at higher electricity prices. For both treated and untreated biogas, the governmental subsidy was the important factor determining the economics of the biogas-to-electricity systems. Without subsidy, the payback period increased to almost 7 years and about 11 years for the case of untreated and treated biogas, respectively, at the reference electricity price. Although the H 2S removal added high operation cost to the system, it is still highly recommended not only for preventing engine corrosion but also for the environment benefit in which air pollution by H 2S/SO 2 emission and impact on human health could be potentially reduced.