Plasma gasification of agro-residues for syngas production: process optimization and system performance

Abstract

Syngas is one of the carbon-neutral biofuels derived from biomass through gasification that can replace fossil fuel usage. Plasma gasification performs better than conventional gasification in terms of syngas yield, quality, and the efficient cracking of heavy tar compounds. In this study, the performance evaluation of a direct current plasma torch-based gasifier (28 kW·h capacity) was tested using steam as a gasifying agent. The agro residues, viz., sunflower stalk, cashew nutshell, date palm husk, wheat straw, and tamarind pod, were chosen as feedstocks for plasma gasification. The temperature and flame length were selected as dependent variables to determine the gasification reaction, as temperature governs reaction kinetics and flame length indicates plasma heat distribution. The optimized plasma gasification conditions had three steam input ports in the plasma torch with 350 A and 20 V power inputs at a steam pressure of 150 kPa. Results revealed that the plasma gasifier showed higher efficiency (38.67%) with good syngas composition (%, volume fraction), averaging 22.27% carbon monoxide, 7.30% hydrogen, and 0.83% methane. The average specific syngas yield and higher heating value of the tested feedstock were 3.89±0.48 m³/kg and 3.95±0.30 MJ/m³, respectively. The plasma energy ratio of feedstock, energy closure, exergy efficiency, hot gas efficiency, and cold gas efficiency for the plasma gasifier correspond to average values for the tested agro residues and were found to be 0.10±0.01, 92.32%±4.71%, 29.68%±2.35%, 12.17%±0.75%, and 84.39%±5.57%, respectively. Syngas from agro residues through plasma gasification can be used to generate energy in prime movers such as internal combustion gas engines or gas turbines, owing to its favorable composition and heating value.

Graphical Abstract