AEA Technology is close to commercial applications of plasma technology to combat toxic gaseous pollutants such as hydrocarbons and dioxins.
Applications are expected in the semiconductor, pharmaceutical and chemical industries and as an end of pipe treatment for incinerator gases. AEA Technology has demonstrations under way in four industries, says Norman Jorgensen, its environmental systems product manager.
Several different systems of creating a plasma at ambient temperatures are used. The microwave method is at the most advanced stage of development. This essentially uses microwave oven technology to strike a plasma between two electrodes in the pipe carrying the gases. It introduces energetic electrons into the gas stream, one of the effects of which is to break down pollutants. The key is to optimise the design of the electrodes to get the maximum energy into the gas stream and maximise destruction of the pollutants at the highest possible electrical efficiency.
Jorgensen says a 150mm microwave unit could cope with a flow of hundreds of litres/minute. Typical applications would be exhaust gases in a municipal waste incinerator, or upstream of pumps in semiconductor plants to destroy chlorine and fluorine compounds which reduce pump life.
The basic technology is well-known, rugged, cheap and high power, and has been shown to give very high destruction efficiencies in a test using HCFC refrigerants, which are difficult to break down.
In the pulsed corona system a plasma is struck between a spiral electrode running along the pipe with a straight electrode at the centre. This is a lower power technology than the microwave method but is more suited to high gas flows, because it causes less obstruction, and where particles are present in the flow.
It has been demonstrated on an incinerator exhaust with a flow of 1000m3/hour and will destroy hydrocarbons, dioxins, and furans, as well as oxidising oxides of nitrogen and sulphur to higher oxides which can be more easily dealt with by wet scrubbing.
Jorgensen says further development is needed to increase electrical efficiency, but it appears this increases with scale.
He believes plasma techniques will prove effective for intermediate concentrations and hard to destroy pollutants.
By David Fowler