Plasma Arc Waste Disposal
Plasma arc gasification is a waste treatment technology that uses high electrical energy and high temperature created by an electrical arc gasifier. This arc breaks down waste primarily into elemental gas and solid waste (slag), in a device called a plasma converter. The process has been intended to be a net generator of electricity, depending upon the composition of input wastes, and to reduce the volumes of waste being sent to landfill sites. Principle of OperationRelatively high voltage, high current electricity is passed between two electrodes, spaced apart, creating an electrical arc. Inert gas under pressure is passed through the arc into a sealed container of waste material, reaching temperatures as high as 13,871°C (25,000°F)[1] in the arc column. The temperature one meter from the arc can reach ~4000°C (~7,200°F)[2]. At these 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. ConcernsIn 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 increase waste disposal costs without offering worthwhile environmental advantages.[6] City of Honolulu press release, March 30, 2004: City to Brief Council on Plasma Arc Recommendations for Landfill. While some believe Federal funding is required to make better progress on this means of waste disposal (which is not the same principle as waste incineration), others note that basic thermodynamics show electricity costs to be unavoidably high when processing wet wastes such as municipal wastes, using plasma power alone. The technology of using plasma arc to treat waste has not changed significantly in principle from initial concept inception. Practical (limited use of land space for land-fills), technological (large-scale use of technology versus small-scale, e.g. plasma arc is currently favoured as a means to destroy medical and hazardous waste), logistical (transportation infrastructure requirements) and budgetary considerations all affect the viability of individual projects. It is important to note, that at this stage, no municipal-waste disposal sized plasma arc facilities have as yet been constructed, and therefore they pose a considerable technological and budgetary challenge to even the largest municipalities. An issue regarding plasma systems that rely on high temperatures for processing 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. References
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