Quality of biomass fuels

Fuel quality is of vital importance and it must be considered both during planning of a system
and each time fuel is purchased.

Fuel type and specification

There are biomass systems designed to make use of a very wide range of biomass feedstock, however most systems are designed to operate efficiently using a particular fuel type and specification.  Smaller systems in particular, and especially domestic scale systems, will be designed and configured to use fuel within a relatively narrow band of specification.

Supply of fuel

When a biomass installation is being planned, the intended fuel supply must be planned at the same time with careful consideration of what is available locally (preferably within 20-30 miles) in sufficient quantities.  It may be appropriate to obtain higher density fuels, such as wood pellets, from further afield.

The local presence of trees, or even a tree surgeon with a chipper, does not necessarily mean that there will be a suitable fuel supply.  Many wood chip boilers, for instance, are designed to burn chips with a maximum moisture content of 35%, or even less.  While this can usually be achieved in Alberta by suitable air drying of small round wood (SRW), freshly cut ('green') wood and tree surgery wastes will be of much higher moisture content, typically 50-60%, and this will cause many such boilers to shut down.  Other systems, however, are designed to use this kind of fuel, though tend to be slightly larger and more expensive.

Moisture content of wood chips is not easily gauged without using a specialist moisture probe, or, more reliably, by weighing a sample before and after oven drying.  Well seasoned logs tend to show radial cracks, however the simplest method of ensuring a good quality, consistent supply is to find a reliable local supplier.

The size and shape of chips is also important.  Chippers designed for woodfuel use produce even chips of a well defined range of sizes; general purpose chippers can tend to produce long slivers that can cause blockages in fuel feed systems.

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