Advanced waste-to-energy solution comes to Australia

A new waste energy technology - high temperature thermal plasma - is being introduced to Australia by Zenergy Australia, in partnership with US-based Plasma Waste Recycling.

Based in Huntsville, Alabama, Plasma Waste Recycling (PWR) has developed proprietary technology that solves the problems related to disposal of municipal solid waste while generating renewable electricity. Formed in 2006, PWR comprises a team of science and engineering experts in the global plasma gasification industry.

In addition to municipal solid waste, PWR has experience in other commercially viable applications of plasma processes, including hazardous waste, medical waste, construction and demolition waste, pulp and paper mill waste, tyres, ore processing, spent catalyst recovery, fly ash vitrification, aluminium dross recycling and advanced ceramics manufacturing.

Municipal solid waste (MSW), everyday household garbage, consists of items such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances, paint, and batteries. Although great strides are being made to reduce the amount of waste being produced, there is still an immense amount of garbage being sent to landfills. Even incineration facilities, that inefficiently burn waste to generate energy, produce an ash by-product that must be sent to landfill. PWR offers an environmentally sound and technologically advanced waste-to-energy solution for the disposal of MSW that can make landfills a thing of the past.

The PWR process uses high-temperature thermal plasma to convert MSW to syngas, molten metal and vitreous slag. Because the process involves extremely high temperatures in a sealed vessel under negative pressure, the process is non-combustive and there is no ash residue. Air emissions are lower than the combustion of natural gas, and are easily within US EPA standards. The syngas is used to generate clean, renewable electricity which is sold to the power grid. The molten metal is cast as scrap steel and the slag is cast as building material aggregate or spun into mineral wool. All by-products are sold to generate additional revenue.

MSW is moved directly from the tipping floor pit into a hopper which gravity feeds PWR’s proprietary feeder. The reaction is controlled by the feed rate of the MSW into the reactor. The reaction is continuously monitored by sensing the temperature and composition of the syngas exiting the reactor, and the level of molten metal and slag in the reactor.

The reactor itself is a refractory-lined steel vessel. The plasma creates the extremely high temperature that converts the organic molecules of the entering MSW by dissociation into syngas, composed mainly of carbon monoxide (CO) and hydrogen (H₂) through endothermic reactions. The reactor interior is under negative pressure, which prevents hot gases from escaping to the atmosphere. Since the atmosphere in the reactor is reducing, metals in their metallic state are tapped into ingots as in a foundry. The slag is tapped separately.

The hot syngas exits the reactor and passes through a heat recovery boiler to lower its temperature, producing steam for use in generating electricity. The gas is kept at a sufficient temperature to prevent the formation of dioxins or furans. From there it passes through a scrubbing process. The syngas may then be used to generate electricity in a gas turbine combined cycle, a boiler and steam turbine, or a reciprocating engine. The renewable green electricity is sold to the grid and powers the entire plasma gasification plant.

PWR's plasma gasification technology can also be applied to convert any carbon-containing feedstock into clean energy and valuable by-products. These include biomass, biosolids, coal, tar sands, hazardous wastes and petroleum refining by-products.

Compiled by Glenn Johnson, Editor