Mantis proves its the right machine for energy crops
Mantis proves its the right machine for energy crops
By Jeremy Hunt
ITS certainly not cheap at around £180,000 but a new willow coppice harvester looks set to have a big impact on the UKs expanding acreage of energy crops.
A self-propelled demonstration model of the Mantis willow harvester, developed jointly by Biomass Energy and the Danish-owned Nordic Biomass, has been put through its paces in Cumbria to extol the advantages of "whole stem" harvesting using a machine mounted on rubber-crawler tracks.
There are also plans for the production of trailed and single row versions.
Damian Culshaw, the Edinburgh-based Biomass Energys development manager, says most other willow harvesters had been designed in Denmark where frozen ground at harvesting was very different to the wet and muddy conditions prevailing in the UK.
"This is a very exciting development for the UK energy crop market where harvesting conditions are usually a major problem," he says.
"One of the big difficulties we have here is harvesting in winter when ground conditions are extremely wet and are aggravated by the many trips needed from the field to haul chipped wood to the store.
"Not only has the Mantis been designed on crawler tracks to cause minimum rutting damage in-between the rows of willows but harvesting the crop as whole stems also has big advantages."
Conventional harvesting techniques chop the stems as they are cut requiring them to be moved from the field immediately in the form of wood chips.
The Mantis harvester does not chop the stems into chips so the cut willow rods do not need to be removed from the field. Instead, they can be stored "on site" cheaply and allowed to dry out with no significant degradation and when ground conditions are more favourable they can removed for storage or sale.
Hauling chopped biomass from fields in the winter months unnecessarily prolongs the harvesting operation, explains Mr Culshaw.
"Our approach avoids the need to use tractors and trailers on harvesting days and removes the risk of excessive mud being deposited on roads in wet conditions. This is fast becoming unacceptable to the public and is highly dangerous."
The 140hp Mantis self-propelled harvester operates as a twin-row machine and employs twin-circular saws at its business end. Output is said to be 1ha/hour (2.5 acres/hour).
In operation twin conveyors first sandwich the stems together before they meet the saw blades. Cut stems are then moved up a conveyor which transfers them from a vertical to a horizontal position and lays them on the carrier at the rear of the harvester.
Saw blades can be adjusted to cope with the different row widths encountered in UK grown crops. The use of rubber-crawler tracks – as well as providing a low ground pressure – are said to cause minimum disturbance to the roots of the willow stools during harvesting.
Carrier-bed capacity of the prototype machine demonstrated in Cumbria was 4t but this will be increased in future production machines – possibly up to 15 tonnes, says the manufacturer. For unloading, the stems are conveyed sideways off the carrier bed to produce a neat stack.
After harvesting the willow stems can be air-dried during storage and will reduce from 57% moisture at harvesting to 30% moisture by the end of the summer storage period. Yields range from 9-15 tonnes of dry weight willow/ha.
"Allowing the stems to dry avoids the need to transport unnecessary volumes of water contained in the fresh cut willows," adds Mr Culshaw.
Biomass Energys managing director John Seed says a plant with an annual capacity to handle 150,000 tonnes of energy crops would be operational in Cumbria within the next two years. Crop establishment is costing growers around £1100/ha; yield is approximately 10 tonnes of dry matter/ha and current returns are £30-£34/tonne.
"The expansion of the energy crop industry will be an evolution and not a revolution which is why its vital that UK growers have the right machines to do the job," he says.
"The next stage in the project is to develop specialist equipment to load and transport fuel to power stations as cheaply as possible during the spring and summer months." *