Some companies focus on processing municipal solid waste (MSW) via plasma-arc plasma gasification. In this application, MSW is generally shredded, then fed into the plasma-arc plasma gasification reactor with very limited and calculated volumes of oxygen or air. The syngas produced is cleaned and then used to make electricity.  The vitrified product is still produced by the plasma-arc plasma gasification process. As mentioned previously, this is a glass-like byproduct, known as vitrified slag, does not leach out. This material has more uses than ash from conventional gasification, including as insulation material, flooring tiles and garden blocks. A recent article cited that plasma-arc plasma gasification technology can generate 816 kWh per ton of MSW.

Dioxins are an issue often cited in the marketing literature of many plasma gasification waste-to-energy technology suppliers as an area where plasma gasification may be superior to other thermal waste processing options. Studies have shown the majority of dioxins are formed within the cooler regions of processes via flyash catalyzed processes, involving chlorine and organic compounds (usually called products of incomplete combustion) in so called de-novo synthesis reactions.

It has been demonstrated (see below table) that the higher temperatures from PEAT’s plasma gasification waste-to-energy process provides for substantial conversion of the organic constituents of the waste and therefore significantly reduces the likelihood of downstream dioxin formation. (There is some credence in the claims that the reducing conditions present inplasma gasification processescould minimize dioxins as the precursor formation reactions usually require excess oxygen).

Dioxins form when all of the following constituents present: carbon, hydrogen, chlorine, and oxygen in appropriate quantities. Once all these elements are present in sufficient quantities, the temperature must also be high enough to promote the formation of such a complex compound, and not so high that the molecules formed become unstable. This temperature zone has been widely estimated to be between 200°C and 450°C. However temperature is not the only mitigating factor as there could be dioxin precursors in the off-sygas/pre-cleaned syngas leaving the plasma gasification reactor thus PEAT’s plasma gasification waste-to-energy systems provide for rapid quenching of the gas (i.e Venturi quench). This is to avoid the de-novo synthesis temperature window.

Plasma pyrolysis and plasma-arc plasma gasification, like incineration, are options for recovering value from waste by thermal treatment. Both pyrolysis and plasma-arc plasma gasification convert feedstocks/wastes into energy by heating the waste under controlled conditions. Whereas incineration converts the input waste into a combusted flue-gas that can then be used to recover thermal energy (usually in the form of steam) and ash, pyrolysis and plasma-arc plasma gasification deliberately limits the conversion so that combustion does not take place directly. Instead, they convert the waste into potentially valuable intermediates that can be further processed for materials recycling or energy recovery. Pyrolysis and plasma-arc plasma gasification offer more scope for recovering products from waste than incineration.

One of the benefits associated with plasma-arc plasma gasification is that plasma-arc plasma gasification reactors do not require moving grates and the smaller volume of gases generated means that the plasma-arc plasma gasification reactors can accommodate the required minimum residence times in a smaller volume. Further, the smaller gas production and reducing environment within plasma-arc plasma gasification reactors does facilitate smaller sized air pollution control systems.

Daniel Ripes talks about plasma gasification on the David Pakman show

Plasma pyrolysis and plasma gasification, like incineration, are options for recovering value from waste by thermal treatment. Both pyrolysis and plasma gasification convert feedstocks/wastes into energy by heating the waste under controlled conditions. Whereas incineration converts the input waste into a combusted flue-gas that can then be used to recover thermal energy (usually in the form of steam) and ash, pyrolysis and plasma gasification deliberately limit the conversion so that combustion does not take place directly. Instead, they convert the waste into potentially valuable intermediates that can be further processed for materials recycling or energy recovery. Pyrolysis and plasma gasification offer more scope for recovering products from waste than incineration.

The last blog discussed plasma gasification, however more information on plasma pyrolysis is warranted.

Plasma pyrolysis takes place in reactors where oxygen is either absent or only present in very low concentrations. Pure pyrolysis is rarely used by itself, but followed by a downstream combustion or plasma gasification stage that converts pyrolysis tars into end-products that are more re-usable, such as the synthetic gas or “syngas.”

Plasma pyrolysis and plasma gasification are often used interchangeable because both produce an energy-rich product gas, however they are somewhat different. Some plasma companies convert the tars to carbon monoxide and hydrogen in a secondary cracking reactor (main reason for this two stage is tighter control over the syngas/flue gas production), while in other configurations, the plasma gasification (or partial combustion for some) reactions take place in the very same reactor, thus further blurring the boundaries between the two reactions. PEAT’s Plasma Thermal Destruction and Recovery systems are designed whereabouts plasma pyrolysis and plasma gasification occur in the very same reactor.