A Feasibility Study of Power Generation Using Biogas from Cellulosic Materials

Abstract

Biomass is an important renewable energy resource in Thailand, but some lignocellulosic agricultural residues are still not utilized. Thus, this research aimed to evaluate the feasibility of electricity generation using biogas produced from lignocellulosic agricultural residues. The study firstly identified high potential lignocellulosic resources, and then searched for high-efficiency pretreatment methods, hydrolysis processes and biogas reactors. Six different sizes of biogas engines, ranging from 200 to about 2,000 kW were used in this feasibility study. Levelized unit costs of electricity generation were evaluated both n the cases of pretreated and non-pretreated lignocellulosic feedstocks. The results showed that rice straw and sugarcane tops and leaves have high potential as lignocellulosic feedstocks for biogas production. In this study, steam explosion and enzymatic hydrolysis processes were selected for converting the feedstocks to sugar. Upflow anaerobic sludge-fixed film (UASFF) reactor was selected for feedstock pretreatment. Levelized unit costs from the calculation for the cases of 187 kW to 1,966 kW biogas engines were 9.29 Baht/kWh to 4.77 Baht/kWh for rice straw and 11.29 Baht/kWh to 6.21 Baht/kWh for sugarcane top and leaves, respectively. Due to the relatively high cost of the pretreatment process, the calculated electricity unit costs were higher than the electricity buyback rate (including the adder rate). In the case of non-pretreated feedstocks, the continuous stirred-tank reactor (CSTR) was selected for biogas production. When using non-pretreated rice straw and sugarcane top and leaves as feedstocks, the calculated levelized unit costs of 187 kW to 1,966 kW biogas engines were 8.17 Baht/kWh to 4.55 Baht/kWh for rice straw and 9.37 Baht/kWh to 5.39 Baht/kWh for sugarcane top and leaves, respectively, which were also higher than the electricity buyback rate. To promote the power generation from biogas produced from lignocellulosic biomass, the buyback rate should cover the levelized unit cost. Thus, the adder rate for biogas produced from lignocellulosic biomass should be higher than the current one.