The key elements in the supply chain are chipping, transport, storage and quality control. For specific advice please contact your local woodfuel officer or the woodfuel research centre.
Chipping
Turning woody material into logs or chips is a straightforward operation. Making sure that the logs or chips meet the needs of energy markets is more complex. Supply chains must be robust and reliable, quality control is essential to make sure the product is consistent and meets customers specifications, and cost and pricing must be clearly understood.
Chipping equipment
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Chippers vary in size from the small hand-fed chipper for dealing with arboricultural waste to machines which can chip large diameter roundwood with outputs of over 100 tonnes an hour. Buying a chipper is a considerable investment and the characteristics, outputs and costs need to be considered before purchase. Chipping can be carried out at any stage from terrain-chipping at stump to a centralised chipping facility at a fixed location, so it will be important to consider what type of machine will suit your supply chain.
Type of chipper: the three main types of chipper are disc, drum and screw. They are categorised by the device used to produce the chips:
Disc - Rotating knives sometimes with backing plate for support.
Drum - Knives mounted around drum
Screw - A spinning conical screw with sharpened outer edges.
Anyone using a wood chipper is required to undergo appropriate training. Free leaflets on using chippers and on training and certification are published by the Agricultural and Forestry Advisory Group and are available from the Health & Safety Executive.
Drying and storage
Quality control in the wood chip supply chain must ensure that wood chips are able to consistently meet the specified moisture content for the market you are supplying. Woodchips, when produced from freshly felled trees can be up to 70% moisture. Larger boilers over 400kW output may be able to burn wet woodchips, smaller boilers need dry chips of a moisture content of 30% or less.
Drying the chips increases their calorific value and also reduces their bulk density which can in turn reduces transport costs. Stems and logging residue can be left in the forest for a year or 18 months to dry before chipping, or else the freshly harvested products can be chipped and dried later. The latter option has health hazards associated with fungal growth and requires a drying shed, but chipping drier material is harder on the machinery. If left in a wet pile, woodchips can begin to degrade through the composting actions of micro organisms. Some kind of forced drying facility is needed to produce the highest grade of woodchips. Woodchip driers can be designed using similar principles to a grain-drying floor or mobile woodchip-drying trailers can be used. More information can be found in Information Note ODW 18.06, which is available from Forest Research.
Quality control
Standards have been developed for solid fuels including wood chips (CEN 355). The main criteria are:
- raw material
- size of chip
- moisture content
In the detailed standard other criteria such as sulphur, nitrogen and chlorine content are also specified.
Useful articles
FR Info Note 9-98 Chipping
Chip 'n' Shred Forest Machine Journal 5/05