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A pneumatic control innovation for biomass transport

11 March 2011

The loading and discharge of dusty materials into and from railway wagons can be a hazardous process, especially if the materials are prone to ignition. In a recent project involving the transport of biomass to Drax Power Station, pneumatic actuators and pneumatic logic proved the safest approach to wagon door control

Currently producing 12% of the UK’s electricity needs Drax is the largest, most efficient coal-fired power station in the UK. On current forecasts, it will also become responsible for around 15% of the UK’s renewable electricity, with biomass featuring prominently. It is estimated that by implementing co-firing (coal and biomass), Drax’s CO2 output will be reduced annually by 2.5 million tons. However, the transportation of biomass material - typically made up of organic matter, such as crops grown specifically for energy generation, wood from forestry processing, and agricultural residues from processing or harvesting - does present its own issues.

In recent years GB Railfreight (GBRf) has been working on this problem and its most recent innovation is a newly modified biomass wagon, manufactured with the help of partners, Midland ACS, wagon owners VTG Rail UK, W H Davis, and Lloyds Register Rail.

GBRf took an existing HYA wagon and fitted it with roof doors to counteract the blow-off and rain spoilage normally associated with an open top wagon. Biomass that becomes moist can ignite randomly within the pile, posing a hazard. Another factor that needed to be considered was dust cloud hazard during loading and unloading. These safety issues called for a sophisticated system to control both the opening and closing of the wagon doors. Electrical devices were ruled out because of the ignition hazard, so in view of the safety requirements, pneumatics presented the best solution.

Drax project engineer, Andrew Brade said he knew what he wanted the control system to achieve, but confesses he didn’t know quite how to go about it – at which point, Midland-ACS stepped to the fore with a design proposal.

The first issue to be resolved by the Wolverhampton based pneumatics specialist was the need for two systems on each wagon –3.5bar to instigate the top door cycle and 5bar to instigate both top and bottom door cycles - but with only one pipe connecting them. A pneumatic pressure switch on each wagon controls the cylinders that open or close each door, depending on where in the cycle the wagon happens to be. The cylinders operating the top doors incorporate pilot valves that ensure the doors cannot open during transit and a scotch bolt locking system to provide additional security. The bottom doors are also mechanically latched to achieve the necessary safety requirements.

The loading and unloading sequence is initiated via a magnetic switch installed on each side for the top doors and three on each side that operate the bottom doors individually. The same switches also close the doors on completion of loading or discharge. Key valves are also incorporated into the wagon logic control system to provide selection between manual or automatic door operation. The complete system, including pneumatic actuation and pneumatic control logic, was designed in-house by Midland-ACS, taking into account all operational and safety requirements.

Although the original project was undertaken for biomass transportation, it is thought that these wagons and automated pneumatic controls might also be used for the transportation of other materials, including those that are not as dense, or susceptible to wind carriage and water damage – aggregates being a prime example.

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