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Wood chips biofuels: moisture, price and energy

Wood chips biofuels: moisture, price and energy
The energy efficiency of biomass depends on its moisture content, so measuring it allows optimum energy efficiency.

Moisture measurement, shared references

How optimising the energy efficiency of wood chips biofuels? One key aspect: moisture content measurement. Classification and specifications are detailed in the EN 14961-4 norm “Solid biofuels –Fuel specifications and classes– Part 4: Wood chips for non industrial use”. These are function of:
- their origin and source (wood chips from logs, barks, trimmings, short rotation coppice, wood residues, fibres and wood constituents from wood processing, used wood –as long as they do not contain heavy metals or halogenated organic compounds as a result of treatment-…),
- their particle size,
- their moisture content (w-%) according to the EN 14774-1 and 14774-2 “Solid biofuels – Determination of moisture content– Oven dry method”,
- their calorific value (Q - MJ/kg) or their bulk density (KWh/loose m3) as received.

Optimum energy efficiency

Biofuels supply contracts rely on these criterions to determine the reliability of the energy supplied to boiler rooms and to optimise boilers efficiency. Thus, the megawatt hour (MWh) supplied is guaranteed and energy efficiency of wood chips biofuels improved. On the basis of a survey conducted with manufacturers of boilers, biofuels suppliers as well as heating operators, the EN 14961 norm has been the subject of a simplified classification* for wood chips biofuels. So the client has an operational tool with simple criterions –moisture content and particle size especially- to draw up specifications and favor competition between producers.
At the end, that’s the boiler that allows the optimal energy efficiency depending on biofuels wood chips as well as the acceptable range of moisture content and particle size. The control of the boiler is function of variations of the moisture content and the particle size of the incoming biomass.

On-site moisture meters
Although the recognized reference method for moisture content measurement is the oven dry method, there are on site portable moisture meters that facilitate the implementation of contracts. Of course, the measurement precision depends on the representativeness of samples and the carefulness with which measuring is carried out.
Among these moisture meters, some have been specifically designed for different biomasses, such as wood chips, sawdust, wood shavings or miscanthus, and meet specifications of the EN 14961 norm. They allow measuring wood chips of P16 or P45 sizes up to 60%. First the biomass to be measured is weighted to identify the right calibration curve; then the correct calibration being selected, moisture content is displayed on the moisture meter.
These instruments are used by several organizations that promote biomass in Europe (Austria Germany and Italy) and by many players of the biomass business (heating operators, biomass producers and clients).

* see “Classification professionnelle des combustibles bois déchiquetés” March 2011 -CIBE

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