Renewables for biomass
Other sources for renewable biomass that can be used for production of bioenergy can be derived from amongst others palm kernel shells, press cake (the remains of vegetable oil production), coffee shells, sunflower husks, wood chips and wood pellets, cashew shells, molasses etc.
Wood pellets are made from compacted sawdust and waste wood from the wood industry or produced from wood that derives from specially cultivated timber plantations for energy such as Eucalyptus forests. The pellets are extremely dense and can be produced with a low humidity content (below 10%) that allows them to be burned with a very high combustion efficiency.
Their high density also permits compact storage and rational transport over long distance. The industrial size pellets can be conveniently blown from a tanker to a storage bunker or silo. Current techniques prevent longer storage of conventionally produced wood pellets though wood pellets produced using torrefraction can be stored for longer periods.
Without proper standards wood pellets are commonly traded using DIN or Ö-Norm standards. Specifications generally are as follows: less than 10% moisture, pellets are uniform in density, have good structural strength and low dust and ash content. Because the wood fibres are broken down by the production process, there is virtually no difference in the finished wood pellets between different wood types. Pellets can be made from nearly any wood variety, provided the pellet press is equipped with good instrumentation, the differences in feed material can be compensated for in the press regulation.
The energy content of wood pellets is approximately 4.8 MWh/ton (or about 17 million BTU/ton). Every 2.2 mtons of wood pellets used prevents 1,000 litres of mineral oil being burnt, saving approximately 2 tonnes of CO2. Therefore wood pellets are considered to be a clean and CO2-neutral bioenergy source.
