Pyrolysis

The thermal degradation of waste in the absence of air to produce gas (Syngas), liquid and solid char fractions. The Syngas is then generally burnt to raise steam and create electricity, but many plants are exploring the option of cleaning the Syngas for use in a gas engine or separating the gas into usable fractions such as hydrogen for use, as an example, of liquid fuels which in turn may be eligible under the RTFO. The solid residue (sometimes described as a char) is a combination of non-combustible materials and carbon.

The process generally requires an external heat source to maintain the temperature required and to avoid the introduction of air. There are a range of different types of approach, often aligned to the waste being processed, and include fixed bed reactors, batch or semi-batch reactors, rotary kilns, fluidized bed reactors, microwave assisted reactors and some innovative solutions like plasma or solar reactors .

Typically, lower temperatures of between 300C to 850C are used during Pyrolysis of materials such as MSW. Pyrolysis processes tend to prefer consistent feedstocks and there is a limited track record of commercial scale Pyrolysis plant accepting MSW but a better track record of, for example, Pyrolysis of Biomass .