Plasma arc waste disposal

Plasma Converter redirects here. For references in popular culture, see Back to the Future.

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 composition input wastes, and to reduce the volumes of waste to being sent to landfill sites.

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Principle of Operation

Relatively high voltage, high current electricity is passed between two electrodes, spaced apart, creating an electrical arc. Inert gas or air under pressure is passed through the arc into a sealed container of waste material, temperatures as high as 13,871°C (25,000°F)[2] are reached in the arc column. The temperature one meter from the arc can reach ~4000°C (~7,200°F)[3]. 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.

Locations

Existing Facilities

Yoshii, Utashinai, and Mihama-Mikata, Japan (Hitachi Metals Ltd.)

Three similar but smaller plants are in operation in Japan -- a 166 ton/day "pilot" plant in Yoshii, co-developed by Hitachi Metals Ltd. and Westinghouse Plasma, which was certified after a demonstration period in 1999-2000; a 165 ton/day plant in Utashinai City, completed in 2002; and a 28 ton/day plant commissioned by the twin cities of Mihama and Mikata in 2002 [Williams, Jenkins & Nguyen (2003), " ", University of California Davis, Department of Biological and Agricultural Engineering, Special Report prepared for the California Integrated Waste Management Board pursuant to Interagency Agreement – IWM-C0172: 23, ]. An unknown source has stated that at least one of the plants in Japan has not managed to produce more energy than it consumes. Two similar facilities run by different companies in Australia and Germany closed after failing to meet emissions standards.^{[citation needed][1]}

Ottawa, Ontario, Canada (Plasco Energy Group Inc.)

A new and different type of plasma arc waste conversion that uses plasma to refine gases produced during waste conversion, rather than to destroy waste by brute force as do other plasma systems, has recently shown itself to be successful on a full commercial scale. Plasco Energy Group Inc. completed a plasma-arc waste demonstration plant in Ottawa, Canada at the Trail Road Landfill, to process 100 metric tonnes per day volume of municipal solid waste. Unlike other plasma waste processing facilities, Plasco Energy Group's process does not use plasma to destroy waste, but rather to refine gases produced during waste conversion, in order to allow them to be used to run an internal combustion gas engine and produce industry-leading low emissions. On October 24, 2007, the Plasco Trail Road facility began delivering power to the grid. The Plasco conversion system, which uses plasma to refine gases rather than expose them to extremely high temperatures, and whose liner is composed of refractory brick rather than metal, is not susceptible to premature attack of vessel liners. Its emissions are also much lower than any other thermal waste processing system, and by converting waste to CO2 and water, rather than to methane, the greenhouse gas emissions of the process are much less than competing technologies such as landfills.

Farringdon, Oxfordshire, England (Advanced Plasma Power)

Advanced Plasma Power ^[2] have built a plasma gasification modular test facility in Farringdon, Oxfordshire, England that uses Refuse Derived Fuel RDF feedstock to produce hydrogen, syngas, energy and vitrified gravel.

Planned Facilities

St. Lucie County, Florida (GeoPlasma)

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.^[3] 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.

Tallahassee, Florida (Green Power Systems)

The city of Tallahassee, Florida has signed the largest plasma arc waste to energy contract (35MW) to date with Green Power Systems to process 1,000 tons daily from the city and several surrounding counties. Completion of the project is scheduled for October 2010.

Hirwaun, South Wales (EnviroParks Limited)

EnviroParks Limited ^[4] plan (31/9/07) a consortium to build an Organic Park in Tower Colliery at Hirwaun, South Wales. This includes Plasco Energy Group Inc, plasma gasification plant with Northern Irish anaerobic digestion specialists B9 Organic Energy, US-owned agricultural waste specialists Agritec Systems Ltd and York-based oil processing specialists Ebortec Ltd, as well as Austrian firm Biodiesel Technologies GmbH. This could eliminate the need for future incinerators (EfW facilities) to divert Municipal Solid Waste from Landfill.

As much as £60 million is being put into the project by EnviroParks Ltd and its partners, to establish organic waste and mixed waste treatment facilities next to the Tower Colliery at Hirwaun. The Hirwaun site itself is large enough for the processing of over 250,000 tonnes of non-hazardous waste a year. Initially, though, an anaerobic digestion plant will be designed to handle 50,000 tonnes of organic wastes a year, with the potential for a 100% expansion.

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 without offering worthwhile environmental advantages.[4] 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 scientifically 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

See also

• Waste management
• Electric arc
• Plasma (physics)