Although logs can be stored and transported conveniently when stacked, and the ease of air passage through a log pile allows good drying, they may not always be the most convenient form for automated handling and feeding. Also, the relatively small surface area to volume ratio is not ideal for efficient combustion or gasification.
Wood chips can form a much more uniform fuel that can flow and can be fed to a boiler to produce combustion, gasifier or other conversion system as a steady flow using an auger feed or a conveyor. :
Combustion is the by which flammable materials are allowed to burn in a boiler in the presence of air or oxygen with the release of heat.
What is combustion?
The basic process is oxidation. Combustion is the simplest method by which biomass wood chips can be used for energy, and has been used for millennia to provide heat. This heat can itself be used in a number of ways:
- Space heating
- Water (or other fluid) heating for central or district heating or process heat
- Steam raising for electricity generation or motive force
Biomass wood chips is the most common source of fuel which in effect “disintegrates” at temperatures of up to 900 degrees and the bi product is a high value bio-char which is approximately 2% of the volume of input materials. In order to increase efficiencies, the moisture content of biomass is required to be below 10%. On average a gasification power plant is 30% more efficient than combustion steam power plants and does not require a supply of water in order to generate electricity.
What is gasification?
Gasification is a partial oxidation process whereby a carbon source, is broken down into carbon monoxide (CO) and hydrogen (H2), plus carbon dioxide (CO2) and possibly hydrocarbon molecules such as methane (CH4)
This mix of gases is known as Synthetic or “syn gas”’ and the precise characteristics of the gas will depend on the gasification parameters, such as temperature, and also the oxidiser used. The oxidiser may be air, in which case the producer gas will also contain nitrogen (N2), or steam or oxygen.