Equilibrium modeling of thermal plasma assisted co-valorization of difficult waste streams for syngas production

The rising quantities of difficult waste streams are a global concern. Prudent utilization of difficult wastes such as sewage sludge (SS) or refuse derived fuel (RDF) can be a small but crucial step to answer the challenges of waste management coupled with the fulfillment of global energy requirements. Lately, thermal plasma is employed globally to process difficult waste streams because of its several inherent advantages including the potential to produce H₂-rich syngas. In this investigation, an equilibrium model was developed with the H₂O-Ar stabilized DC arc plasma employing RDF and SS with an objective to assess the optimal process parameters, gas yield, distribution of syngas components and reactor efficiency. The influence of reactor temperature (800 to 1600 °C at SS 30 wt%) and sludge content (0 to 100 wt% at 1200 °C) on syngas constituents, gas yield, LHV, residual carbon and ash was evaluated. The maximum gas yield was noticed as 0.83 kg gas per kg fuel at 1200, 1400 and 1600 °C with a LHV of 11 MJ N⁻¹m⁻³. Maximum H₂and CO volume fractions of 62 and 34 respectively were also observed at 1200, 1400 and 1600 °C. The maximum H₂was obtained as 67 vol% at 0 wt% SS whereas the minimum (43 vol%) was achieved at 100 wt% SS. Highest amounts of residual carbon (0.20 kg kg⁻¹fuel and 0.35 kg kg⁻¹fuel) were observed at 800 °C and 0 wt% SS, respectively. The highest reactor efficiency of 53% was realized at 100 wt% RDF (the comparison was performed at 1200 °C). The results of the investigation are encouraging to employ thermal plasma as potentially sustainable and environmentally friendly technology to co-valorize difficult waste streams.