Designing of Small Scale Fixed Dome Biogas Digester for Paddy Straw

Abstract

With the advancement in biogas technology over the years, many biogas reactor designs have been developed so far as a result of alteration in biomass as feed-stocks. The current study is focused on one of the abundant agro-residue present in our country, paddy straw as waste; mostly burnt in the fields and cause air pollution, soil infertility and depletion of potential energy source. In this prospect, fixed dome digester was selected as base for designing and modification in a digester. The modified digester model was designed for thermophilic conditions (50-55^oC) to enhance the biogas yield, provide constant temperature, with a provision of agitation, recycling and insulation. Further the mathematical modeling of fixed dome digester with the capacity 1 to10 m³/day was performed by considering the gas production rate of 0.012 m³/day/kg of the biomass (size 1mm). The parameters like diameter, height, active slurry volume, gas storage volume, gas yield, pressure of gas, stress pattern of digester were calculated using the developed mathematical model by scaling- up a lab scale data. For a batch, assuming D:2H (D = dia; H = height), the feeding of biomass was calculated on wet basis for 1 m³ and 10 m³ digesters as 84kg and 834kg, respectively. A stirrer provided to digester to enhance the mass transfer, gas yield and prevent sludge and scale formation.