What a whopper! To feed anaerobic digester

Two of the largest hoppers ever built by Tong Peal are now being assembled into a Lincolnshire anaerobic digester, one of the first exemplar projects supported by the Environmental Transformation Fund.

The project is taking shape at Staples Vegetables plant at Wrangle, near Boston, where vegetables out-of-specification at the packhouse or bypassed in the field will be used to generate electricity for supply to the site and surplus for the grid.

The digester will need a constant flow of vegetables and also maize to maintain 24-hour a day operation and Tong Peal were tasked with designing and manufacturing suitable intake hoppers.

The hoppers had to be twice the size of any wed made before to store enough material for 24 hours working, says Charles Tong, managing director of Tong Peal.

Whats more, they also need to withstand the potentially corrosive nature of the material. We looked at technology used to handle other organic material including a muck spreader to come up with the final design.

To handle the daily load the two 130 cubic metre capacity hoppers had to be massive 19 metres long, four metres wide and four metres high. The hoppers were fitted with twin scrapers not hauled by rubber belts as with conventional intake hoppers but by chains resembling those used on a ships anchor.

The vegetables or maize are then picked up by spinning blades in a teaser assembly to provide a steady flow into the dosing modules where the diet is mixed with water before going into the digesters.

Tong Peal have been supplying us with machinery for our vegetable processing operation for many years, says Vernon Read, marketing director of Staples Vegetables. They have a reputation for reliability and where possible we prefer to support a local manufacturer.

The galvanised steel hoppers, made in modular form and each weighing 35 tonnes, are now being installed at the digester which is expected to begin operating in October and be running at some 50 per cent capacity by the end of the year.

Heat generated by the digestion will be used to chill packhouse areas through heat absorption coolers, reducing energy usage considerably, with excess heat warming the offices and staff buildings.

• The Environmental Transformation Fund is part of the Government response to the Stern Review on climate change.