EfW DEVELOPMENT GUIDANCE - Wrap

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WRAP – EfW DEVELOPMENT GUIDANCE – September 2012 3.3 Gasification Figure 3 – Gasification plant flow diagram (Otto Simon Ltd) Gasification is considered a commercial technology in the coal and chemicals industry and a variety of gasification designs are available such as up draft, down draft, entrained flow and fluidised bed reactors. Gasification is another thermal process during which a controlled amount of oxygen, air or steam is passed through the waste preventing full combustion. The process occurs at high temperatures, normally above 750 °C, producing syngas (‘synthetic gas’, which typically contains Carbon Monoxide, Hydrogen and Methane) and a solid residue or char. The syngas can be burnt to produce steam or converted via a prime mover such as a gas engine or turbine which can be used to produce electricity and heat. Gasification is considered as an advanced thermal treatment technology, and although not yet commercially proven in the UK using MSW, there are wood biomass gasification plants being established across the UK. The advantages of gasification plants are that they can be modular and the operating parameters can be varied to match the variety of feedstock composition. Feasibility and Good Practice Funding Planning Environmental permitting regulations Feedstock Outputs Financial Incentives Waste Incineration Directive Glossary Home Guide page 14
WRAP – EfW DEVELOPMENT GUIDANCE – September 2012 3.4 Pyrolysis Figure 4 – Pyrolysis plant flow diagram (Otto Simon Ltd) Historically the pyrolysis process has been used in the chemical industry to produce charcoal and coke from wood. During pyrolysis no oxygen is used; the waste undergoes thermal degradation at temperatures between 300 °C to 850 °C. The process typically produces a hydrogen rich syngas (which typically contains Carbon Monoxide, Hydrogen and Methane), a liquid oil and a solid char. The relative proportions of these products can be altered by the speed of the process and the temperatures at which the reactor runs. The syngas can be burnt to produce steam or converted via gas engines to produce electricity and heat or condensed to produce more oils. Pyrolysis is not yet developed at a commercial scale within the UK, although developmental projects are up and running and reference plants have been built within the EU to recover organic wastes. 3.5 Plasma gasification Plasma gasification techniques use an electric current, an inert carrying gas and powerful electrodes to create plasma - an ionised gas (not dissimilar to lightning). In plasma gasification, fuel or waste is fed to a reactor vessel where it comes into contact with electrically generated plasma and is heated to temperatures of up to 6,000ºC. Organic molecules are converted into a syngas that can be used to generate electricity and liquid fuels, while most metals melt or are vaporised and other inorganic solids are converted into a glass-like substance that can be marketed to the construction industry as an aggregate replacement. Feasibility and Good Practice Funding Planning Environmental permitting regulations Feedstock Outputs Financial Incentives Waste Incineration Directive Glossary Home Guide page 15
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