The Technology

The Gasplasma® process is based on three well-proven commercial technologies:

• fluidised bed gasification, which produces syngas contaminated with tarry particulates and solid chars - developed by a world leading manufacturer which has over 90 reference plants

• plasma arc treatment, which converts chars and tars into clean syngas, destroys dioxins and immobilises heavy metals - based on Tetronics' proven plasma process

• a power island, which consists of well-proven gas engine technology and a conventional heat recovery system for highly efficient power generation

How the technology works

The Gasplasma® process comprises a conventional fluid bed gasification plant to convert organic waste material into a very clean, hydrogen rich gas, known as a synthetic fuel gas.

The gasifier is a vertical refractory lined cylinder with a bed made up of sand that is fluidised by passing a mix of oxygen and steam through it, causing it to ‘boil'. The use of oxygen and steam allows the conditions within the gasifier to be carefully controlled, maintaining a starved air atmosphere. At the high temperatures of operation (around 900˚c), material fed into the gasifier thermally breaks down into a syngas which contains a considerable amount of energy potential.

In a straight gasification process, the syngas would then be oxidised (i.e. mixed with air) and combusted in an adjoining or nearby combustion chamber. The heat produced would be used to make steam that in turn would drive a steam turbine, generating power. However, small-scale steam cycle power plants are relatively inefficient in that they convert only around 20% of the energy in the feedstock into power.

The plasma arc treatment thermally ‘cracks' the dirty syngas (from the gasifier) breaking up its complex molecular structure and reforming it into a much simpler structure resulting in a clean hydrogen-rich fuel gas of consistent calorific value.

The syngas leaves the plasma converter at high temperature and requires cooling which is undertaken by conventional heat exchangers. It is then cleaned further to remove any last traces of acid gases such as sulphur and chlorine before being fed into gas engines. This achieves much higher electrical generating efficiencies of 35-40%, and exports substantially more than half the total electrical output.

Conventional combustion, gasification and pyrolysis processes produce significant quantities of one or more of bottom or grate ash, toxic fly ash, chars, tars and acetates which are hazardous and whose disposal and transport is increasingly expensive. The fluid bed gasifier incorporated into the Gasplasma® process also creates a significant amount of char and ash (the percentage depends on ash material within the feedstock - usually 10-15% from MSW).

The Gasplasma® process, however, will recover all of this material as a form of recycled aggregate called Plasmarok® and so provides a solution that results in a minimal amount of residues having to be sent to landfill.

The ash material from the gasifier is simultaneously melted and forms a molten slag in the plasma vessel which is continuously tapped off and, as it cools, it sets into a granite-like glassy slag material which is a dense, hard, environmentally stable recyclate capable of being re-used as building aggregate. It can also be granulated in water as it cools to produce, for instance, pipe bedding. PlasmarokTM is recognised by the UK Environment Agency as a recyclate.

The volume reduction is very substantial, with the volume of inert slag being around 200 times less than the volume of the original feedstock material.

The Gasplasma Process