“An increasing number of operators in the energy from waste (EFW) and recycling sectors are looking to materials handling solutions with lower capital expenditure, reduced running costs, improved operational reliability and environmental sensitivity. Operators are moving away from labour-intensive materials handling systems and leaning toward cost-effective automated options.”
These are the observations of Demag Cranes & Components sales director Paul Bartlett, who advocates an intermediate buffer store, fed by an automated overhead travelling crane and grabbing bucket. He believes that such a system offers a number of advantages over conventional bulk materials systems, such as walking floors, conveyors, bunkers, silos and hoppers.
“The fact that the buffer store is crane-fed also eliminates heavy investment in mechanical shovels and materials handling vehicles”
“Crane-fed, intermediate buffer store systems are proven technology in the mass burn incineration sector, but take-up in the EfW and general recycling industries has been relatively slow,” he says. “In terms of capital cost, intermediate buffer stores require far less civil works than bunkers and silos. The fact that the buffer store is crane-fed also eliminates heavy investment in mechanical shovels and materials handling vehicles, which would otherwise be required to feed the processing area.”
Bartlett also believes that the buffer store option offers considerable savings in operational costs: “A low-maintenance, fully automated crane system permits 24-hr unmanned and uninterrupted operation, ensuring that the buffer store is continuously stocked.” He also points out that there are positive health and safety implications because there is no need for operators to access the potentially hazardous materials handling area.
As an example of a successful crane-fed, intermediate buffer store application, Bartlett cites Rabbit Group subsidiary Enviropower’s EfW plant in Lancing, West Sussex. The facility processes biomass from the construction and demolition industries, diverting some 50,000 tonnes of material a year from landfill to power generation. Electricity generated at the plant is used to power all site operations, with surplus energy, representing some 85% of electricity generated by the facility, exported to the grid.
The materials handling system installed at the facility comprises a 10-tonne safe working load with a 13.25m span and a double girder grabbing crane, on which is mounted a wire rope hoist with a 10cu m bucket grab on a 12.4m hook path.
The crane system can perform 21 cycles/hour. Each cycle comprises lowering of the bucket on to 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. Finally, the bucket is hoisted to its top position, with simultaneous cross and long travel back to the original position.
The ‘intelligent’ system is programmed to lift biomass from the pile of material and deposit it into each of two input feeds, when sensors indicate that the combustors require replenishment.
For Bartlett, the Enviropower system shows a number of operational positives: “Automation of the crane system offers significant advantages in terms of efficiency, reliability and longevity, even in this arduous operating environment.
“The system operates within pre-set tolerances, extending the lifecycle of the equipment. Automatic operation also eliminates the possibility of impact damage to bucket grabs and the walls of the fuel store which may result from manual operation. Electricity can also be recovered from the crane system’s electrical motors during braking operations and fed back into the grid to further reduce operating costs.”