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A decision making guide to the feasibility of small scale pellet production from timber and timber co-products
Wood pellets are a dense, convenient form of wood fuel that burn well in purpose built stoves and boilers. They are a common sustainable fuel in North America and many mainland European countries but are at an early stage of development in the UK. Most pellets are being made in large purpose built mills usually attached to sawmills. In the UK much of the sawmill bulk co-product that could be converted to pellets has an alternative market but there are a number of smaller businesses (sawmills, joinery workshops and furniture businesses) that produce waste material from a few tonnes per year to a few thousand tonnes per year.
Coed Cymru has worked with Farm Feed Systems and Dragon Machinery to develop a small scale pellet mill system that will process from 40kg/hour up to 250kg per hour. There has been considerable interest from individuals and small businesses in the potential to convert wood waste into pellets and so turn a liability into economically profitable product. However, because pellet making is not straight forward and because success will depend on a number of factors, we have compiled the following list to help determine the degree of difficulty. The list is not intended to provide a definitive yes or no, or to put you off, but to make you aware of the issues to be considered.
Raw Material
Softwoods and hardwoods can be pelletted. The throughput (kg/hour) will tend to be less with hardwood, possibly down to half, though this will depend on the die. Also, different softwoods have different pelleting characteristics.
It can be in the form of off-cuts and other solid timber residues as well as shavings, chip and sawdust. With the possible exception of sawdust, it should all be processed through a shredder and/or hammer mill.
However, the form of the material (coarse shreddings, fine sawdust etc) can affect the ability to produce a good pellet.
It should be from solid wood (as opposed to composites such as chipboard).
It should not have been subjected to treatments containing heavy metals or halogens. Generally, unpainted palletwood is probably fine but nails and chipboard corner blocks have to be removed.
The presence of bark will give a higher ash content (and may cause wear on the die). High ash content may not matter depending on which pellet standard is to be achieved and whether the combustion system can cope with it. Whole trees, prunings, slabwood short rotation coppice and non-wood farm residues or energy crops may need careful consideration.
Some exotic timber species such as iroko may have a high mineral content and so lead to higher ash levels.
The quantities should be sufficient to ensure optimal operation of the mill (ie hundreds of tonnes per annum at least, depending on the mill's throughput). At present there is no pellet mill that will only take a few bags a week from the dust extractor. It might be worth considering a small briquetter instead.
Before committing yourself, you should work with the pellet mill manufacturer to ensure that the mill will satisfactorily process your material.
Moisture Content of Raw Material
This is very important. The industry norm for pellets is said to be 15% by weight. We have used our mill on wood with a moisture content between 9 and 18% and add vegetable oil and/or water or steam if necessary to facilitate pelleting.
Drying material of high moisture content such as prunings, thinnings and whole trees (freshly felled spruce can be over 60% water) can be very expensive both in energy consumption and the capital cost of the equipment.
Consistency of Raw Material
Pellet manufacture will be easiest with a constant supply of highly consistent material (species, moisture, physical form).
The Farm Feed Systems mill that we have been working with is capable of pelletising a fair range of materials. However, the operating parameters need to be modified when handling different materials in order to ensure constant pellet quality. This could mean increased labour costs, which could be avoided by appropriate 'intelligent' automation of the equipment.
One solution would be to ensure some form of segregation of feedstock (pine one day, oak the next etc)
Market for Pellets
How and where the pellets are to be used or sold are probably the most important considerations for those wishing to manufacture pellets.
If you will use them yourself for heating then the economics can be calculated in terms of fuel saved and capital expenditure on new heaters/boilers.
Generally it is likely that you will be producing far more pellets than you can consume so will need to find a market to cover costs. The current (May 2006) oil equivalent price for pellets is £160 per tonne. Pellets in bags sold in smaller quantities could possibly attract twice this price.
With small scale pellet production particular care must be taken to ensure profitability. Having to pay for raw material may erode profits, so pelleting a waste material that is free or that would otherwise incur significant disposal costs (transport, landfill) becomes an attractive proposition.
There is a growing market for pellets, and arguably these would grow faster if there were more supply options. You should talk to suppliers of pellet stoves and boilers.
Pellet standards need to be considered. There are European standards that are being considered for adoption in the UK although they are not compulsory. The Renewable Energy Association, now merging with the British Pellet Club, and the National Energy Foundation can help. Poor quality pellets will damage your reputation (as well as boiler feed systems). Domestic pellet stoves and boilers can be very demanding on quality whereas some industrial boilers will be more forgiving.
For further information on small scale pelleting contact Andy Stewart at Coed Cymru 01686 650777 (andys@coedcymru.org.uk)
Coed Cymru, The Old Sawmill,
Tregynon, Newtown,
Powys SY16 3PL
Tel 01686 650 777
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