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The Plasma Gasification Process

In plasma gasification, fuel or waste is fed to a reactor vessel where an electrically generated plasma at a temperature of 20,000 C° is present. When the fuel or waste is exposed to the plasma it is heated to a very high temperature (>2,000C°), which causes the organic compounds in the fuel or waste to dissociate into very simple molecules such as hydrogen, carbon monoxide, carbon dioxide, water vapour and methane. These simple molecules, that are all gases, are allowed to continuously flow from the reactor to gas cooling and cleaning equipment. Ash and other inorganic material present in the fuel or waste is melted down to a complex liquid silicate that flows to the bottom of the reaction vessel.

Simple schematic of a plasma gasifier
Simple schematic of a plasma gasifier

Metals that are present also melt and flow to the bottom of the reactor vessel, where they can either mix with the silicate, or if present in a large enough quantity, float on the bottom of it as a separate layer. The liquid melt is allowed to flow continuously from the vessel to a water quench where the liquid silicate melt is cooled to a non leachable, non toxic, obsidian like solid silicate. Some metals are not melted. Instead, they vapourise and pass out of the reactor vessel with the gases formed by the organic material. When they enter the cooling equipment for the gases, they condense to fine metal particulates. Halogen and sulphur compounds present in the fuel are converted to hydrogen halides and hydrogen sulphide, and pass out of the reactor with the other gases.

Carbon rods used for plasma gasification
Carbon rods used for plasma gasification

The gas from the reactor has a low to medium calorific value, and is therefore suitable as the fuel for a gas fired power generation unit. However, after leaving the reactor, the gas is still contaminated with a number of undesirable compounds, such as hydrogen chloride and metal particulates, that can cause damage to machinery and the environment. The gas is therefore cleaned in various process equipment. The cleaned gas, similar in quality to natural gas, is then fed to a compressor and storage facility ready for use. The most typical use of the gas is as fuel for power generation, although it can also be used as a feedstock for chemical processes. For example, the production of methanol. When used as a fuel for power generation, more power is usually produced than is consumed by the gasifier. Therefore, electrical power can be exported for sale, or used for onsite purposes. For high calorific value wastes and fuels the power exported can be four times that consumed by the gasifier.


 
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