The Irish Farmers Journal recently visited a farm in Co Louth that is in the business of producing dried willow chippings for use in woodchip biomass boilers.

Currently, the farm is supplying approximately 5t per week of these chippings to a district heating system company for use in 60 houses. This contract is set to increase to 100 houses in the coming months.

Excess chippings are sold for fire log production and used for the farmer’s own biomass boiler.

The construction of the shed and installation of drying equipment was undertaken by Barcrete Ltd concrete contactors last year, with the first load of willow arriving at the end of November.

Pictures 1 and 2

The shed is broken up into four compartments, two of which have underfloor drying systems, while the two on the outside are solely for storage of dried willow.

In picture 2, we see one of the storage compartments. All four are of equal measure at nearly 10 metres wide and 36 metres long.

The centre of the shed at its highest point reaches 13.75 metres (45ft).

Pictures 3 and 4

It costs approximately €1,500/acre to plant the willow trees, but the Department has a grant system in place which covers 50% of the cost. On this farm, the trees are harvested after three years at an average height of 25ft and a girth of over 1in. This yields in the region of 30t/acre of wet material (10t/acre/year).

Picture 5

The whole system is powered by diesel, but over the next month it is being transferred to electricity.

In this picture, we see the two 20KW axial fans with silencers, which drive the air down the central chamber and under the wood chipping piles at either side. These are similar to the fans used in jumbo jets and without the silencers would be heard up to five miles away.

The drying of willow chippings requires the use of an axial fan due to the need for high-volume low pressure, whereas with drying grain, the opposite is required. This is mainly due to the difference in bulk density.

Picture 6

Here we see the middle chamber of the shed, which lies 1ft lower than the ground level, with the two fans at the back. The lowered ground level allows for the numerous channels seen to let air flow under the willow chippings piled at either side. Each side can be closed off independently if only one of the compartments needs drying.

Picture 7

When the air is blown into the channels from the middle chamber, the pressure blows air up from the floors of the two drying houses through the specialised grates pictured. These channels have been installed every one metre and run across the entire width of the drying compartments.

The drying of 600t of wet wood takes two months on average if drying during the summer months, while this increases to three over the winter months.

The humidity in the air outside has a big bearing on the drying time.

To allow for chippings on the top of the pile to dry, it needs to be turned by a loader once every two to four weeks, again depending on the time of year.

Moisture levels of the willow chippings are reduced from 60% to 20% over this period. The willow weight nearly halves once dry and this procedure works out costing about €15/t.

While this farmer plants a large amount of willow himself, he also purchases another 80 acres at €20/t wet.

The cost of harvesting and transport is also extra on top of this, accounting for a further €20/t.

Including drying costs of €15/t and the fact that it takes nearly 2t of wet willow to achieve 1t of dried willow, the overall cost of production comes in at €110/t dried.

At the moment, the farmer is selling to a district heating company, where 1t of dried willow chippings is making €150.

Costs

A large portion of the costs for this project was accounted for by the steel grates in the drying compartments, which accounted for nearly €40,000. They had to be imported due to the fact that no manufacturer supplied them in Ireland at the time. The two fans and control unit of the system added a further €20,000 to this cost. The overall cost of the project was €500,000. This was part-funded by the LEADER programme, which granted 40% to the total.