Fluidyne Gasification Archive

Coppice Willow in Northern Ireland



Having been involved with research into the gasification of coppicing willow since 1983 in England, and later in 2000 in Northern Ireland, I had a rare opportunity in late May 2011, to visit one of these activities, on the farm of Tom and Mary Hegan near Dungannon, County Tyrone, N.Ireland. As dairy farmers, they had like many other farmers, found that poor economic returns, just forced them out of the business. Having been encouraged to plant coppice willow as a fuel crop, after a very slow start, the economic returns, are gradually swinging out of the red to justify all the hard work, as it should, for those who choose to set foundations in place for renewable energy supplies.
 
Much of the information on coppice fuel wood as a crop, originated in Scandinavian countries, along with the original planting and harvesting machines, but adapting these practices for use in the smaller, muddy hill farms of N.Ireland has proven quite a challenge. Having grown the crop, the tribulations of harvesting method, chipping directly off the field, then drying with forced warm air, or cutting complete stems, and atmospherically drying in stacks, has required considerable time for these growers to put appropriate methods in place.
 
On Tom and Mary's farm, they chose to cut complete stems and dry atmospherically, then chip the bundles in a modified chipper, which unfortunately was not on site to see during my visit. My previous experience, only allowed us work with willow chipped directly off the field, so I was very impressed to see the quality of the chip, chipped after the stems had been first dried in stacked bundles. In this case, the fuel was for a boiler combustion application, so specifically, I was looking for clean cut chip without stringy ends, and free from decomposition caused by storing wet. The quality control of the harvesting cycle begins with the cutting of the stem, requiring the twin saws to be sharpened professionally every few hours This is to prevent any high speed vibrations developing after a quick sharpen in the field, and maintain the ability for faster machine travel down the rows.
 
Drying the bundles in stacked rows by trial and error, has eventually over nearly 10 years, shown how to best lay the stacks to suit this farms location, and let nature help out with the drying cycle. The learning continues each season, and I was impressed with the huge effort going into improving every facet of this activity, just to maintain the quality of the fuel chip delivered to their clients. In particular, was a final sieving to drop out any stringy ended chip that might clog the clients auger fuel feeders.
 
Supply of the final fuel chip, is done in association with other growers, and supplied by their group marketing arm called "Northern Bio Energy". Clearly, as the quality and reliability of supply is established, more end users will be encouraged to switch over to biomass for their energy applications.
 
Although I do not normally report on the issues of growing mono tree fuel wood plantations, I did see the effects of how the Blue Willow Beetle (Phratora vulgatissima) can stunt the growth rate of coppicing willows. This was only affecting about three of the outer boundary rows, but the height of these stems were shorter, and there was more fine tip wood at a cost to reducing stem diameters. Spraying will control these insect populations, and of course trim the finely balanced economics of growing these fuels, but thanks to the determination of farmers like Tom and Mary Hegan, another increment of infrastructure is being added to the reliability of renewable energy implementation.
 
Doug Williams.
August 2011
 
 

This batch of willow was older than normal when cut, having a butt diameter of 3" due to the grower not having a market for his fuel wood a year or so earlier. Cutting age of coppice willow, is generally every two years, but location and growing conditions can affect this dramatically.

Stored for drying in rods before chipping on a high point of the farm, it has been found that rates of drying can vary considerably depending on which way the stacks are formed.

Another view of the previous stack, shows the high proportion of thin tip wood that is less than useful in fuel destined for combustion applications. Containing potassium and sodium, tip wood fines can cause clinkering and ash related problems.

Trials to establish the value of covered drying of coppice willow rods, showed that depending on the orientation of the stacks, outside drying could be faster.

In an attempt to refine the handling and storage of drying rods, these stackable cages were tested then discarded as a practical solution, and not cost effective.

Only just set up on a long trailer to move the stacks of cut and dried rods, this hydraulic grab has made a significant improvement to handling this difficult crop. There were many examples of experimental equipment of ingenious design around the farm, and a tribute to this farmers raw courage to change from dairying to growing biomass as a fuel crop.

This coppice willow stem cutter was designed for Scandinavian conditions. Towed at a row off-set to the tractor, the upper horizontal conveyers draw the rods to the centre, where the twin saws cut off the stems. The upper conveyer chains which are at right angles to the front chains, pull the stems backwards, and lay the horizontally on the trailer deck. These are then pushed off side ways in heaps for collection. There had to be many very expensive modifications made to this machine to accommodate the hilly conditions of many growing areas in N.Ireland, and the smaller odd shaped fields.

This is the chipped dry fuel ready for delivery to a boiler installation, and I was surprised at the quality of the chip which did not show any rot or decomposition. Coppice willow chipped straight off the fields, must be dried quickly, or it begins to decompose within hours of chipping.

This large screen is used to separate out mainly the stringy lengths that drag through the chipper blade without cutting, thus avoiding problems at the delivery end of the fuel to the boiler.  Quality control of the chip has for this group of suppliers, provides an excellent example of hard work paying off, as the economics of growing biomass fuel is now swinging in favour of the growers.

The down side of mono culture for any crop, is the risk of infestations that see rapid build up of pest populations. These eaten leaves are from the boundary rows around the side boundaries of the willow plantations. Caused by the Blue Willow Beetle (Phratora vulgatissima), these rows were obviously less vigorous in growth compared to the inner rows.

Here is the culprit, the Blue Willow Beetle, that in N.Ireland can be found normally infesting Dock weeds.

One beetle can rapidly breed large colonies with egg numbers like these. At cost to the grower, spraying is the only answer at this point in time.