CO2 plasma gasification of bakelite-based electrical switch waste feedstock

Abstract

Poor degradability of e-waste causes severe soil and water contamination. In recent times, plasma gasification has been an attractive way of solid waste management towards energy recovery considering the environmental benefits. To reduce the short end-of-life electrical products and net CO2 emissions, the low-grade feed of electrical switch waste (ESW) comprising of bakelite (BAK) is chosen for generating clean syngas through the plasma method using CO2. The influence of the feed rate of solid waste, feed CO2 gas and plasma torch power on the product yield and syngas composition is evaluated. Energy and exergy (2-E) analyses are performed to assess the feasibility of the process. The experiment results indicate a maximum syngas yield of ∼85% at the highest torch power of 1.6 kW, with high concentrations of H2 (24.36 vol%) and CO (43.61 vol%). At low torch power of 0.5 kW, the residual solid yield reaches 24.58%. Considering all the cases, syngas with a medium calorific value of up to 10.20 MJ/m3 is attained. For the optimum feed rate of 40 g/10 min, CO2 flow rate of 0.6 lpm and plasma power of 0.75 kW, the process achieved the highest cold gas and exergy efficiency of 42.33% and 35.99%, respectively. The obtained oil (viscosity = 6.43 cP, density = 0.975 g/ml, pH = 8.01 and LHV = 31.47 MJ/kg) is suitable for applications in combustion, transportation and chemical production after quality upgradation. The solid residue (volatile matter = 11 wt%, fixed carbon = 65.67 wt%, ash = 23.33 wt% and LHV = 15.51 MJ/kg) obtained containing Ba (70.42 wt%), Zn (3.87 wt%), Ti (3.25 wt%), etc. in the ash, can be used for making corrosion coating agents, alloys and paints after recovery. The oil analysis showed the formation of NH3 during the reaction at a high torch power of 1.6 kW. Lastly, the reaction mechanism of plasma gasification for the conversion of ESW into syngas is proposed.