Sunday, March 31, 2013

Coppice and biomass boiler

Firstly a Big Thank You must go to David at Kingston Maurward College (KMC) for making our visit a very informative and interesting one and of course thanks to those that made it out for the visit too!

The afternoon began with a walk to the field containing the coppice, made up of 10 varieties of Willow, and a detailed Q&A about its running with questions being answered by David. He went on to advise the crop was planted in April 08, and has since grown to heights between 6 and 12ft, so not a bad start considering the summer weather!


The willow arrives in Rods, sourced from Lincolnshire, these were planted using a hand operated machine which cuts a length of willow rod and subsequently plants it.

A total of 7000 rods were planted, with the recognised average being 10,000 per hectare. David advised that the planted willow has a potential 25 year lifespan. Any early cuttings can also be used to plug gaps in the initial planting.

Surprisingly, David advised during the preliminary stages of planning KMC were required to complete an Environmental Impact Assessment (EIA) in order to get permission to plant, this being due to the potential changes in local habitat and the possibility of the willow trees being unsightly to those living along the A35xnot something one would expect when wanting to plant lots trees!

Harvest usually takes place after 2-3yrs, though David implied there have been thoughts of an initial harvest in spring 09 which helps increase the amount of re-growth for the next harvest. In a full harvest yields can be around 10t per hectare.

At present harvesting would most likely be done using a fingerbar mower, though in later years this may not be possible due to the size of trunk on the willow. Any early cuttings can also be used to plug gaps in the initial planting.

This has also thrown up an issue for KMC in that most large scale coppicing takes place in the North/North East and this means most of the machinery required for cutting/processing the coppice may need to be transported to Dorset, the implication of this being a greater carbon footprint than desired. Such machinery can harvest and process the willow all in one reducing the need for multiple handling/processing and can therefore potentially improve/reduce carbon inputs.

This has spurred David and his colleagues to consider the future of coppice in Dorset and the South West and the potential of KMC to become a base for the harvesting/processing equipment making it easier for other farms in Dorset to source the required equipment needed without increasing their carbon inputs.

The need to balance carbon inputs is of course very important as any imbalance of such as from transportation (whether it be transporting harvesting equipment or transporting the final cut product) then takes the coppice from being carbon neutral to carbon negative which then negates the whole ethos behind the idea of coppicing!

Ok, so on to the Biomass Boiler, a Kalorina 2206 made by Tatano. This model has a min output of 53kW and a max of 70kW and is currently providing heat to three homes on campus.

Below: the boiler can be seen in action as the auger feeds in more wood pellets. Behind David is the 1.5t hopper, this is filled with a 1t bag of pellets dropped in from above using a telescopic forklift. Luckily the roof on the hut opens up for this!

The boiler is capable of burning several types of fuel, from cereals like wheat and barley (the husk and not the straw) to logs and wood chip. However the start up has to be done using the current chosen fuel, wood pellets. These pellets are of low moisture content (5-10%) and are a by-product of the timber industry so are a great form of reuse from a waste stream. The pellets are fed to the boiler from a 1.5t hopper via a pair of augers.

David advised the main issues regarding the boilers use is the timing of the augers in relation to the demand of heat required with a secondary issue of too much being fed into the boiler resulting in too much smoke and subsequent complaints from locals.

Though it worth pointing out this has been resolved and it has been burning cleanly and efficiently since. One issue regarding different fuel types apart from having to start up on wood pellets are the residues, as cereals are found to have higher tar content and can tar up the boiler meaning higher maintenance implications.

To close the visit off we had a brief discussion regarding energy and I was keen to point out some facts relating to energy production in the UK, mainly bad ones, but also some encouraging points too!

All in all a great informative afternoon was had by all who came and should anyone have any question regarding energy, whether it be relating to reducing the amount needed in the home to producing your own renewable energy then email us and I’ll endeavour to help!

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