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A variety of waste products can be used as fuel in the Stein Pyrolysis Unit Process including crops, tyres, wood-chips, sewage sludge, bio-fuels, industrial waste and municipal solid waste (MSW).
The feedstock is shredded to a size of about 15mm so that rapid heating of the fuel core can be achieved. Air and oxygen are removed prior to the material being fed at a constant rate into the Pyrolysis Unit retort where the conversion process takes place.
The thermal treatment of the feedstock takes place in three distinct stages:
Stage 1, the incoming fuel is pyrolysed at high temperature in the almost total absence of oxygen. This separates the gas and oils in the fuel from the solids, and leaves a carbonaceous char.
The gas is of good quality and is not contaminated by the products of combustion, as combustion cannot take place without oxygen. As there is no air, the gas is not diluted by nitrogen, which helps to maximise its calorific value. Some oil and tar carryover is inevitable, but these are recovered and fed back into the retort.
The char left over from the process is a clean fuel (charcoal) that is used in the second stage.
Acid components, sulphur, chlorine and heavy metals are removed from the fuel with the gas and so the char does not contain any impurities/pollutants, acids, noxious gases or precursor chemicals such as sulphur and chlorine.
The gas produced is scrubbed of particulate matter, acid gases and any condensable organic compounds by a combination of cyclone separation followed by a venturi quench scrubbing stage, which is a packed bed scrubbing stage.
Stage 2, rather than being sent to landfill, the carbonaceous char produced by the pyrolysis stage is combusted at high temperature to generate hot flue gases that are used to heat the outside of the pyrolysis retort and drive the reactions taking place within it (as described in Stage 1).
This combustion stage is fully compliant with the waste incineration directive WID and includes 2 seconds gas residence time at over 850°C, with HEPA ceramic filtration for fine dust particulates. Any resulting ash is melted within the combustion chamber and is extracted to form a vitrified slag that can be used as a construction material.
Stage 3, the cleaned syngas is combusted in either a reciprocating engine, gas turbine or boiler to produce heat and power.
The heat produced in the process can be used to provide heating and hot water to surrounding properties and/or it may be used in the fuel drying process.
Overall the process offers an efficient and flexible energy generation system.
