Biomass - Using Anaerobic Digestion

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Biomass Technologies

A wide range of technologies have been developed to utilise the biomass resource. These vary from direct combustion in burner systems, to the production of more advanced biofuels, such as pyrolysis, through a variety of processing techniques.

Direct Combustion

Combustion systems for burning biomass vary from small stoves to multi-megawatt combined heat and power (CHP) systems. Combustion is best suited to biofuels with low moisture content, as it uses a portion of the energy to evaporate the water. The technology is usually limited to providing heating but it can also be used for electricity generation.

picture: boiler works

Biomass Boiler

Fermentation

This process can be used on certain sugar producing energy crops to produce ethanol, a simple alcohol. It uses a simple and well established method; yeast is added to the biomass and the mixture is then allowed to ferment under specific conditions. The resulting brew is then distilled to produce 'bio-ethanol'. This can be used on itís own in specialised combustion engines or it can be mixed with petrol to produce 'gasohol'.

picture: boiler

Fermentation System

Pyrolysis

Pyrolysis is the basic thermo-chemical process for converting solid biomass to a more useful liquid fuel, commonly called a bio-oil. This bio-oil can be used in existing oil-fired burners (with very little adjustment) to generate heat & electricity.

picture: boiler

The process involves heating solid biomass to a temperature of around 800oC, in the absence of oxygen. This forces the volatile substances out of the biomass, leaving a small quantity of solid biomass (char). The volatiles are then collected in liquid form as the bio-oil. This process produces a better quality of fuel as the oil can be transported easily and cheaply, and the solid char has a higher energy quality than the original fuel. It is also smokeless, which means it is suitable for home use.

Gasification

Gasification involves subjecting solid biomass to hot steam and air to produce a gaseous biofuel. This gas (also called synthesis gas) can be burned for heating, electricity production, or may be further converted to act as a substitute for almost any fossil fuel.

picture:gas flame

The advantage of this process is that the synthesis gas is a better fuel than the original solid biomass, and can be stored & transported more easily.