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Harvest Wood Fuels - Full Article - SEWN Aug 2010

Harvesting Locally?

When it launched it’s newly built factory near Farnham, Surrey in September 2008 Harvest Wood Fuels was the only commercial wood pellet manufacturer in the South East of England. It is still one of only two or three pellet manufacturers in the region.

From the beginning harvest have aimed to source their raw material as locally as possible but, being based in the most wooded borough (Waverley) of the most wooded county in the country, this hasn’t been as straightforward as it may seem. While the pellet market has grown rapidly and Harvest have benefited from this, most of the company’s sales have been from pellets bought in from other UK suppliers.

The problem lies in the logistics and cost of collection and harvesting wood, in a county where the forestry industry infrastructure is almost non existent.

Wood pellets are made either from sawdust, wood chip or shredded waste wood and the moisture level of the raw material needs to be 15% or lower to make a good pellet. To maximise sustainability pellets should be made from waste material or from wood which has no other useful purpose; each part of the tree should generate as much added value as possible.

The company currently sources dry sawdust from sawmills in the South East, but outside of the immediate locality, due to a shortage of appropriate material. However sawdust, lightweight and bulky, is costly to transport, and quality is difficult to control; making good pellets requires a consistent raw material but sawmills often use wood of mixed species, both soft and hard woods and of varying moisture levels.

While dryer would enable Harvest to take in 'green' sawdust from local sawmills, there is not enough material generated from the small local sawmills to enable their pellet press (a new one is being installed this summer) to operate at the full capacity of 2,500 tonnes per annum. The company has therefore been looking at other options.

Most of Surrey's woodlands are not managed and there is a huge under-utilised wood resource in the county. Much of it is classified as ‘low grade’ woodland, currently with few markets in the timber trade. The trees are typically of a small diameter and, in the absence of other markets, are well suited as a raw material for making wood pellets; however Harvest have been discovering the difficulties in making this source of raw material cost effective.
Firstly to harvest the whole tree is more costly than chipping the whole tree into a trailer and then moving it from site. This is because the tree is felled (either by chainsaw or harvester) and then needs to be de-limbed and the trunk or stem wood cut to length, loaded onto a forwarder and then onto a lorry trailer for transporting by road to its destination. For Harvest as there is so much woodland coming into management in the immediate vicinity, it should be possible to forward the wood directly from the woodland to the pellet plant, eliminating the need and cost of a haulier. Secondly the 'brash' is then either chipped or baled for transportation off site - most locations are not allowed to burn the brash on site and it therefore needs to be disposed of. These are all additional costs over whole tree chipping.
Pellets sold into the domestic pellet market need to conform to a strict specification as outlined in the new EN Plus standards, awaiting publication at the time of writing; these standards propose maximum or minimum limits for various parameters such as ash content, moisture level, pellet durability, calorific value and so on. The standards are designed to ensure the trouble free running of boilers.
This means that round wood used as a raw material for pellets needs to be de-barked, to reduce ash levels, another process which pushes up the cost per tonne of the raw material. (Although there is a beneficial side effect of de-barking in that it reduces the amount of time the wood takes to air dry.) When air dried the de-barked logs can be chipped, which exposes new surfaces to the air which in turn further dries the wood, (it doesn't work chipping first as newly cut wood is too wet and composts). A drying floor may or may not also be used to store the wood chip and dry it further.

Initial trials by Harvest Wood Fuels show that the chip will typically have a moisture content of 18%. This will need to be hammer milled into smaller wood fibres which are then fed into an air dryer, (Harvest plan to use wood pellets as a heat source), and dried down to the required 12-15% moisture level for pellet production.

The whole process is onerous and expensive but if efficiency savings can be made, through for instance, reduced transport costs, it should be possible to make work in practice, bringing both a secure supply of raw material to Harvest and a return to the woodland owner. Another alternative for Harvest is the use of ‘clean’ waste wood, usually shredded pallets, which is both affordable and of a low moisture level; but there are issues with quality and the material needs to be carefully screened to prevent contamination with coloured/ treated pallets and metal. In practice the solution for Harvest is likely to be a combination of all three raw material sources.


Notes to editor:

Wood pellets are used cost between 3.5p – 4.5p per kWh; this compares favorably with oil and LPG. Mains gas prices are similar/ slightly below wood pellets but will rise in the near future.

A domestic wood pellet boiler costs between £7,500-20,000 to install with a likely generous heat incentive payment (the Renewable Heat Incentive) from next April.

With a bulk pellet storage hopper the boiler is as automated as a gas or oil fired boiler, with bulk deliveries of pellets by blower lorry in the same manner as LPG or oil is delivered.