The Use of Ley Crops (Silage) as a Feedstock for Anaerobic Digestion Plants
 With the increasing interest in AD from both farming and waste management interests we thought that we would write a short note on the use of crops as a fuel which will be a primary feedstock (probably with other crop feedstocks) for Biofuel AD Plants, and may also be valuable to act as a fuel reserve as a strategy to ensure adequate feedstock availability for plant operation during seasonal feedstock scarcity.
Cultivation, harvesting and treatment of ley crops is certainly a strategy adopted in certain Scandinavian countries which use biofuels, and at least one MSW plant in these nations also uses silage in this way.
 Storage
Silage is readily stored, and if there is adequate land available on-site storage can be held, making it an available feedstock during bad weather conditions and in northern climates, even during periods when highways become impassable.
Silage is provided under contract by partner farms, are also contracted for the cultivation of ley crops to be used for biogas production.
The leys are allowed to lie for two or three years and a high percentage of clover (in the region of 25% of the seed) is included in the mixture. This provides nitrogen fixing for to the intended improvement of the soil structure and the gives the farmer the additional (or primary) value of ley as a preceding crop within the rotation.
As such, the leys are a part of the normal crop rotation of the farms.
According to the present rules for EU-subsides the ley may be cultivated on land that is set aside. (Please check this as this may change with time.)
The ley is also undersown, either in a cereal crop, or in spring oil-plants.
Undersowing, fertilising and management shall are carried out on the farm in accordance with the requirements given by the Anaerobic Digestion Plant operator, who will seek to maximise calorific value in the feedstock etc, to suit the AD process in the plant.
Harvesting is done at the same time of the year as for "normal", large-scale silage-making of ley crop for cattle.
At harvest, the crop is wilted and finely chopped with a precision chopper.
In order to achieve high efficiency, minimise costs and to obtain a substrate that has the intended properties for digestion, the harvesting is also often organised by the Anaerobic digestion plant operator, using specialist agricultural contractors.
The crop is preserved in the normal way as silage in plastic bags.
The silage is taken out from the bags by a wheel loader and is transported to the biogas plant as required, and for some biogas /biofuel plants this may be done continuously throughout the year.
One such example is the Svensk Vaxtkraft, Anaerobic Digestion Plant where the Contractor is Ros Roca International www.rosroca.de ,
HAASE also supply a system for Silage Digestion. The images show the HAASE silage digester located near Neumünster in Germany.
If you have comments to add to this article we would be very pleased to receive them and, if appropriate, add them to this page. (October 2007: Thanks HAASE for the images!)
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