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Biomass on the move

Enviropower’s £12.5 million renewable energy facility processes biomass, typically timber and cardboard waste from the construction and demolition industries, for the generation of electricity. This biomass material is reclaimed from builders’ skips operated by Rabbit Skips, also part of the Group. As a result, some 50,000 tonnes of biomass per year, which would have been otherwise sent to landfill, is now used in the renewable energy process.

At the planning stage, Rabbit Group’s management team investigated several materials handling options, including walking floors, conveyor systems and silos/hoppers. These solutions were all deemed to have disadvantages in terms of capital cost and the efficient storage and movement of biomass material.

It was decided that an overhead travelling crane system, with a bucket grab, was the most efficient and cost effective solution. At this stage, the company entered into negotiations with equipment supplier Demag.

Enviropower plant manager Mick Adams says: “Our decision to work with Demag on this project was based on the company’s reputation for quality and reliability, as well as an industry recommendation, highlighting Demag’s proven expertise in the energy from waste industry.”

To meet the specific materials handling operations at Enviropower’s plant, Demag designed, manufactured and installed a 10t SWL, 13.25m span, double girder grabbing crane. Mounted on the crane is a wire rope hoist with a 10 cu m bucket grab on a 12.4m hook path.

The system has cross travel speeds of 3-30m/min, long travel speeds of 4-70m/min and hoisting speeds of 1-16m/min. The crane system is able to perform 21 cycles per hour. Each cycle comprises lowering of the bucket onto the material, grab closure, hoisting to the top position, simultaneous cross and long travel to output position, lowering the bucket and opening the grab to deposit material into the store, before finally hoisting the bucket to its top position, with simultaneous cross and long travel back to the original position.

The crane system is fully automated to permit 24 hour unmanned and uninterrupted operation, with radio remote control also available for manual operation. The “intelligent” system is programmed to lift biomass from the highest pile of material in the fuel store and deposit it into each of two input feeds, when sensors indicate that the combustors require replenishment.

Automation of the crane system offers significant advantages in terms of operational efficiency, reliability and longevity. All normal braking is electrically controlled, reducing wear and tear on brakes and gearboxes. In automatic mode, the system operates within pre-set tolerances, extending the life cycle of the equipment. Automatic operation also eliminates the possibility of impact damage to bucket grabs and the walls of the fuel store, causing system down time, which may result from manual operation.

A number of features were incorporated within the system design, to meet the extremely arduous operating environment. Motors are inverter driven for smooth control of movement and accurate positioning accuracy, reducing the amount of airborne dust in the workplace. The crane also has thermal protection in all motions, together with IP55 rated enclosures on all motors and panels. Safety features include overload protection, anti derailment and slack rope detection.

A closer look at Lancing

Enviropower’s Lancing facility processes up to 150 tonnes of biomass per day, with an output capacity of over 5MW. The electricity generated at the plant is used to power all operations at the site, while any surplus energy, which represents some 85% of electricity generated by the facility, is exported to the grid.

The plant incorporates a number of environmentally friendly initiatives, including high efficiency flue filters, which minimise air pollution from the combustion process.

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