what is plasma?

Plasma cloud from the Tycho supernova.
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First discovered in 1879 by Sir William Crookes when he was conducting experiments with his Crooks tube to discover what was then called 'cathode rays' (electrons). The actual name for plasma however didn't come about till 1928 when Irving Langmuir compared the ionized gas to blood plasma.

Plasma is an ionized gas, which is a gas where electrons are flowing freely and giving positive or negative charges to atoms, making it a highly efficient conductor of electricity, generator of heat, and possess the ability to break down molecules into component atoms it can also produce an magnetic field. Plasma is extremely common in the universe some of the many examples of plasma include plasma televisions, neon lights to lighting strikes, St Elmo's fire, nebula and finally the internal furnaces of the Sun.

how it works

A plasma convertor is designed around five key stages; feed, convert, filter, polish, extraction.

First off the waste is delivered into the feed system, unlike some other Energy from Waste technologies, the system can handle any combination of solid, liquid and gaseous type wastes. The waste can then be placed through a pre-treatment process where it can be crushed into smaller pieces to expose more material to the plasma torch.

Diagram of a typical Plasma Convertor.
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The waste is passed through an airlock which prevents gases from escaping into the atmosphere. The insulated air-tight container will fire a plasma torch this generates a super-heated electrical field within the chamber, heating the waste to over 13,000°C. Any carbon based, or organic molecules become volatilized, that is turned into a synthetic gas (syngas). Inorganic compounds will become vitrified, or melted down and converted into an obsidian like substance and finally metals will melt down into a form of slag. An overflow mechanism is used to control the amount of slag available in the chamber at all times, ensuring that enough is left to maintain these high temperatures.

Utilising this process a plasma convertor can deal with almost all kinds of waste, including hazardous wastes such as toxic, chemical and medical.

StarTech plasma convertor. Click to enlarge.

After it has left the chamber the syngas is pumped into a series of filtration systems where it is cooled by using water injection and is filtered of all particulate matter (which can be fed back into the plasma convertor). This cooling process helps stop dioxins and furans as they require specific temperatures to form. The gas will then be reheated to create a series of catalytic reductions to reduce the amount of NOx and convert it into atmospheric nitrogen and water. A series of scrubbers will then remove any acids, chlorides, fluorides, sulphates, phosphates, sodium and calcium.

A turbine can be connected to the process to generate electricity, which can be used to not only power the plant, but provide an alternate clean source of renewable power to the community.

recoverable commodities

Outside the electricity generated by a plasma convertor, there are three main commodities that can be recovered, the individual amounts of which depends on the type of waste being feed into the convertor.

PCG Syngas.
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Synthetic gas (syngas) is the main output of the plasma convertor, made up mostly of hydrogen it can be used as a fuel source in power plants, in the creation of fuel cells for use in hydrogen powered vehicles. It can produce drinking water, heat and cool buildings and can be used in the rural and industrial sector in the production of a wide range of polymers, chemicals, fertilizers, pressure agents and more.

Slag is the only solid based product produced from a plasma convertor, depending upon how it is cooled the slag can create several types of commodities. These include an obsidian-like silicate material which can be used in concrete or asphalt, even shaped into bricks or pavement stones for use in the construction industry or even be used in the abrasives industry. Metals can also be extracted and on sold to various industries.

Metals, Slag and Obsidian-like materials.
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Rock wool can also be produced from the slag; this commodity is a highly efficient insulator with higher energy efficiencies then fibre glass, it's highly absorbent and lighter than water, with many potential methods of use in both the industrial and environmental segments.

Heat is also used and produced by a plasma convertor, excess heat is normally used to generate steam and thus electricity however the heat can also be funneled out to provide cleaner heating solutions to the community.