Green circular economy of co-gasification with municipal solid waste and wood waste in a novel downdraft gasifier with rotating grate

Abstract

Municipal solid waste has become an issue to be addressed with the rapidly growing human population. With implementation of circular economy strategy, this waste can be recovered as an energy resource, assuring a sustainable growth with minimal wasting. However, huge diversity in municipal solid waste often led to complication of processing. Thus, this study proposed a modified downdraft gasifier designed specifically for such heterogeneous feedstock, which includes municipal solid waste and wood waste. The dimensions of the tamarind wood were measured to be 10 cm in length and 6 cm in diameter. The moisture content of the wood was found to be 5.3 %. In this modified downdraft gasifier, the air for the gasification process is fed downward into a rotary grate with an internal air distribution system that is mounted at the reactor's bottom. Separate hot zones were developed as homogeneous and heterogeneous oxidation occurred progressively in the modified gasifier. The suggested gasifier operated at a capacity of 100 kg/h, with air supplied at 150 kg/h and equivalence ratio of 0.3–0.5. Producer gas with the highest calorific value (1250 kcal/Nm3) was produced at the mixed ratio of 50:50 (by mass), with a rate of 250 m3/h. The minor energy and mass imbalance of 1.7 % and 0.2 %, respectively between input and output can be accounted for by environmental heat loss, moisture content and unburned carbon in the ash. The gasifier maintained a consistent syngas flow rate and achieved a cold gas efficiency of 85.6 %. Based on the obtained result, municipal solid waste was successfully transformed into producer gas, with mass and energy balance been adequately maintained.