Gasification with pure oxygen or hydrogen
Gasification with pure oxygen or pure hydrogen (or hydrogasification) may provide better alternatives to the air blown or indirectly heated gasification systems. This depends greatly on reducing the costs associated with oxygen and hydrogen production and improvements in refractory linings in order to handle higher temperatures. Pure oxygen could be used to generate higher temperatures, and thus promote thermal catalytic destruction of organics within the fuel gas. Hydrogasification is an attractive proposition because it effectively cracks tars within the primary gasifying vessel. It also promotes the formation of a methane rich gas that can be piped to utilities without any modifications to existing pipelines or gas turbines, and can be reformed into hydrogen or methanol for use with fuel cells.
Plasma gasification or plasma discharge uses extremely high temperatures in an oxygen-starved environment to completely decompose input waste material into very simple molecules in a process similar to pyrolysis. The heat source is a plasma discharge torch, a device that produces a very high temperature plasma gas. Plasma gasification has two variants, depending on whether the plasma torch is within the main waste conversion reactor or external to it. It is carried out under oxygen-starved conditions and the main products are vitrified slag, syngas and molten metal. Vitrified slag may be used as an aggregate in construction; the syngas may be used in energy recovery systems or as a chemical feedstock; and the molten metal may have a commercial value depending on quality and market availability.
Such processes use high-energy microwaves in a nitrogen atmosphere to decompose waste material. The waste absorbs microwave energy increasing the internal energy of the organic material to a level where chemical decomposition occurs on a molecular level. The nitrogen blanket forms an inert, oxygen free environment to prevent combustion. Temperatures in the chamber range from 150 to 3500C. At these temperatures, metal, ceramics and glass are not chemically affected.