More Details on the Plasma Gasification Process

The main aspect of gasification, whether it is plasma-arc plasma gasification or “traditional” gasification is to raise carbon–rich materials or waste to a high temperature in an oxygen–deficient reactor, where the materials break down thermochemically versus combustion.

This process is more efficient than incineration, has a significantly lower environmental footprint, while the syngas can be transformed into a number of end products (liquid fuels, power, chemicals, etc.).

The feedstocks for traditional gasification processes range from coal, the organic components of municipal waste and biomass while the range is even greater for plasma-arc plasma gasification processes, which can handle just about any waste stream with the exception of radioactive materials.

Due to the fact that gasification occurs pre-combustion (assuming the syngas would be burned to generate electricity), it supports easier carbon capture than incineration where the chemistry can be more complex.

Plasma-arc plasma gasification is just one type of gasification. Other common forms include (1) updraft, (2) downdraft, (3) fixed bed and (4) fluidized bed. The first two are quick similar with exception of the gas flow.

plasma-arc plasma gasification is just one type of gasification. Other common forms include (1) updraft, (2) downdraft, (3) fixed bed and (4) fluidized bed. The first two are quick similar with exception of the gas flow. This entry looks to discuss in slightly more in depth the differences between these types.

In the updraft (sometimes referred to as “counter current”), air/oxidant is injected from the bottom and the material enters at the top. Following gravity, the material is dried then reduced to char (pyrolyis) and finally any ungasified solid remnant is burned. This type has a high energy efficiency because of the heat exchange between the rising gas and descending material. The main issue is the high concentration of oils and/or tars in the syngas, which must be cleaned prior to any utilization, which can decrease the overall efficiency. Updraft gasifier usage is generally focused to direct heating applications as little to no gas cleaning is necessary. plasma-arc plasma gasification process is configured similarly in that the feedstock material is fed from the top, however it also has similarities to a fluidized bed (see below) in that the vitrified material in  plasma-arc plasma gasification is maintained in a somewhat molten form.

In a downdraft gasifier (or co current), the gas is drawn out from below through a combustion zone. The material and oxidant flow in the same direction. Compared to the updraft configuration, the gas tends to be cleaner with fewer tars – the reason being in a downdraft configuration the tars (product from any pyrolysis phase) have to pass through a higher-temperature oxidization zone. The key I in a downdraft design is temperature maintenance and if the feedstocks vary in composition and moisture content, this can be difficult to achieve. The gas must rapidly cooled prior to be used.

Finally, a fluidized bed, which is more common in large plants, has a hot bed of sand located at the bottom of the gasifier. Gas clean-up is key as many times tar and ash can be found in the syngas. Waste is typically shredded or pulverized prior to being fed from the top.

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