Plasma arc waste disposal

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Plasma arc waste disposal is a method of waste management that uses high electrical energy/high temperature created by an electrical arc to break down human waste primarily into elemental gas and solid waste (slag). The process has been intended to be a net generator of electricity (depending upon input wastes) and to reduce the requirements for redirecting waste to landfill sites. This technology is used primarily to process small scale industrial waste, military, and medical/biological wastes because the high electricity consumption required to achieve the high temperatures necessary for decomposition make it uneconomic for processing municipal wastes

Principle of Operation Relatively high voltage, high amperage electricity is passed between two electrodes, spaced apart, creating an electrical arc. Inert gas (Air or inert gases under pressure) is passed through the arc into a sealed containment containing waste material, temperatures as high as 13,000°C (25,000°F) are reached in the arc. The temperature one meter from the arc can reach temperatures as high as ~4000°C (~8,000°F). At these high temperatures most types of waste are broken into basic elemental components in a gaseous form, and complex molecules are atomized (separated into individual atoms).

The reactor operates at a slightly negative pressure, meaning that the feed system is complemented by a gaseous removal system, and later a solid removal system. Depending on the input waste (plastics tend to be high in hydrogen and carbon), gas from the plasma containment can be removed as Syngas, and may be refined into various fuels at a later stage.

The first plasma based waste disposal system in the USA is scheduled to come into operation in St. Lucie County, Florida. The county states that they hope to not only avoid further landfill, but completely empty their existing landfill—4.3 million tons (3.9 million metric tons) of waste collected since 1978—within 18 years.[1] The plant is scheduled to come into operation in 2009, and to produce 600 tons (550,000 kg) of solid rubble from around 3000 tons (2.7 million kg) of waste per day at around 5500°C.

Two similar but smaller plants are in operation in the world, both located in Japan. Two similar facilities run by different companies in Australia and Germany closed after failing to meet emissions standards.

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[edit] Concerns

Dioxin emissions are possible from plasma arcs when chlorine is present. Process gas cleanup is necessary when gasifying waste streams such as municipal waste streams known to contain heavy metals, chlorine/fluorine, sulfur, etc.

In 2004, the city of Honolulu considered a plasma arc/torch proposal for processing municipal solid waste. The city's Department of Environmental Services evaluated the plasma process and found that using plasma arc/torch technology would significantly boost waste disposal costs (High Electricity inputs) without accurately considering environmental advantages.[2] City of Honolulu press release, March 30, 2004: City to Brief Council on Plasma Arc Recommendations for Landfill. It is important to note, that at this stage, no municipal-waste disposal sized plasma arc facilities have as yet been constructed, and therefore pose a considerable technological and budgetary challenge to even the largest municipalities. While some believe Federal funding is required to make better progress on this e means of waste disposal, (which is scientifically not the same principle as waste Incineration, others note that basic thermodynamics show electric costs to be unavoidably high when processing wet wastes such as municipal wastes.

The technology, of using plasma arc to treat waste has not changed significantly in principle from initial concept inception, other than the practicality (limited use of land space for land-fills), and technological (large scale use of technology versus small scale i.e. plasma arc is currently favoured as a means to destroy medical, and hazardous waste to date), logistical (transportation infrastructure requirements), and budgetary challenges are also present. Plasco Energy Group Inc. is nearing completion in approx. March 2007 of a plasma-arc waste demonstration plant in Ottawa, Canada at the Trail Road Landfill, for the specified use of 100 metric tonnes per day volume of waste.

The stability, and quality of the syngas has been questioned, regarding impurities, and requirements for future refinement.

One other issue regarding plasma systems is in the life of their liners. The liner is an important aspect of separating the high interior temperatures of the plasma system from the [metal] shell of the plasma container. Liners are highly susceptible to both chlorine attack and to local variabilities in [high] temperatures - both of which would be found with typical municipal waste systems, and are not likely to last more than a year in service.

[edit] References

  1. ^ [1] USATODAY.com

[edit] See also

[edit] External links

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