Gas evolution and syngas heating value from advanced thermal treatment of waste using microwave-induced plasma

It is a well-understood phenomenon that the use of diminishing fossil fuels is causing disturbances in atmospheric dynamics. This coupled with global population growth has resulted in increased energy demands, and increased waste loads. In order to tackle both important issues, energy-from-waste (EfW) technologies have been of great interest to the industry sector. Moreover, recently implemented fiscal incentives have significantly reduced investor risk, and incentivised deployment. A novel EfW technology known as ‘plasma-arc’ can be considered as one of the most effective methods for the thermal treatment of waste. However, due to the exceptionally high operating and maintenance costs, it is being discredited by some for its commercial viability. Microwave-induced plasma, a novel method of producing high temperature plasma, is thought to be much more energy efficient and so has the potential to be a commercially viable treatment route for residual wastes. This study investigates the evolution, and heating value, of syngas derived from microwave-induced plasma pyrolysis of waste. Three triplicate commercial and industrial waste samples were treated under pyrolysis conditions for 25–30 min. Analysed gasses included CO, CO2, H2O, CH4, C2H2 and many other hydrocarbons. CO, CO2, and H2O accounted for >90% of the detected gas mass, with only small amounts of hydrocarbons. Most gas species exhibited a similar evolutionary signature: rapid increase to production peak at approximately 200 s, followed by a steady decline until the sample had been depleted. Preliminary gasification trials showed a large increase in gas mass with the addition of oxygen, and a change in the gas evolution signature. Syngas heating value was determined to range from 11.39 MJ/Nm3 to 17.44 MJ/Nm3, consistent with other pyrolysis studies.