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Biomass is a source of renewable energy that seems to be the most suitable replacement of diminishing fossil fuels today. The consequence of this diminishing is a rising price of fossil fuels, what means higher costs for the customer. There is also a difference in terms of environment when we compare biomass with other fuels. It is nearly CO2 neutral, what is its great advantage when we speak about environment pollution and greenhouse effect. Burning of biomass produces only that amount of CO2, which photo-synthetised within the plant body during its lifetime. On the other hand, we also need to consider sources used for biomass production, transport, etc. Biomass is in fact encapsulated solar energy transformed into organic matter by plants themselves.

Biomass can be organised by the amount of water present within the material into following groups:
  • DRY BIOMASS - It is mainly wood and wood waste, but also straw and other organic waste that can be burnt directly, or after a modest drying process
  • WET BIOMASS - Mainly liquid organic waste. This material can't be burnt directly; it is being used mainly in biogas processing technology
  • SPECIAL BIOMASS - Oily, amyloid and sugary crops/plants. Various special technologies are utilised to gain energy or fuels out of these sources. The fuels are for instance biodiesel, alcohol, etc.
By the state of the matter, the biomass can be organised as follows:
  • SOLID BIOMASS - Wood (pieces, pellets, briquets, chips, sawdust), agricultural products (straw, hays, high-speed growing energy products)
  • LIQUID BIOMASS - Biodiesel (produced mainly out of Swedish turnip), ethanol (produced mainly out of sugar cane, corn, potatoes, animal excrements)
  • GASEOUS BIOMASS - Wood gas (gasification of wooden or agricultural waste), biogas
The most spreaded type of biomass is wood in various forms (pieces, chips, pellets, sawdust...). The heat value of wood and another plant fuels varies not only by the kind of the wood or plant, but also very significantly by the moisture of a material. Optimal moisture to burn woodchips is at the level from 30 to 35%. However, optimal moisture to burn wood pieces is at the level of 20%. Too low moisture causes the burn process to have an explosive character, what means that a lot of energy goes away with combustion gases. Too high moisture causes that a lot of energy during the burn process is wasted to dry the material, so the combustion is incomplete. The amount of energy in 1kg of wood having 0% of water is approximately 5 kWh, however, relative moisture of extracted wood is at approximate level of 60%. This moisture drops down to 50% shortly after extraction. After this level, the natural drying process is significantly longer. There is no way of drying the wood completely in the real world. Residual water amount will always be at least at the level of 20% of dry wood's weight. Heat values of wood mass as well as alternative fuels are listed within following table. 

Additional information about energy using of wooden chips you can find here.
Attached file uses Slovak language.

Units of wood volume and their conversion: