Powders delivered with minimal air

Tom Shelley reports on a more efficient way of transferring powders using pneumatic conveying systems

A hopper that changes its shape as solids are emptied from it could make the process of powder handling far more efficient. The idea helps powder conveying systems – especially those based on pneumatics – to discharge or meter powder so that it does not get stuck in the hopper. Not does it end up with too much air content, which wastes space in the receiving vessel. A sensing feedback system influences the bulk flow properties of the material, so that it flows into the receiving vessel in an optimum way. Varying the shape of the throat in real time prevents blockages. The end result is that equipment used for handling and storing bulk powders will be more efficient. There is a reduction in spillages and dust generation and. Filling efficiency is improved by around 5% and there is less risk of blockages. Hopper systems can also be made more lightly and cheaply – since they will no longer have to survive blows from a 15-pound “Birmingham Screwdriver” to eliminate clogs. Richard Farnish, a consultant with the Wolfson Centre for Bulk Solids Handling Technology at the University of Greenwich in Chatham, had been studying the loading of coal. He realised there were circumstances under which more material flowed out of a hopper when the aperture was smaller. “We found a more efficient way of passing powders through a hopper into a receiving vessel without completely fluidising them – a true ‘Eureka’ moment,” he says. “Our development enables higher discharge rates with reduced dust emissions and reduced space requirements in receiving containers.” The system requires a controller – either PC or PLC – that can run different programs according to materials, a sensor and some electrics. To protect the intellectual property, three new patents have been taken out. Receiving containers range from road and rail tankers, down to 25kg bags. Road tanker drivers often drive around after a first filling, in order to settle the load so that more can then be put in. Otherwise, a nominal 30 tonne tanker will only be able to transport 25 tonnes of load. Bags normally have to be made with a certain amount of porosity so they can de-aerate. Until this happens, a pile of inflated bags on a pallet can be very unstable. The development applies to powders that have been transported pneumatically and also to those that have become aerated by other types of conveyor. The same methods are applied to the hopper through which it passes: instrumentation is used to establish the state of the material, and modifications are then made to the material itself and, if necessary, to the geometry of the throat in real time. “The technique modifies the properties of the bulk material, so that it has just the right amount of air to ensure discharge without fluidising it or generating unnecessary dust,” says Farnish. “Several major companies have already expressed an interest. The real market is those companies that deal with products that are traditionally difficult to handle.” The Wolfson Centre for Bulk Solids Handling Technology Pointers * A new design of hopper throat, which can adjust its geometry in real time, improves the handling of bulk powders * It reduces the air content in the powder being delivered to the receiving vessel * The technique also controls the nature of the material flowing out of the hopper in real time Sand lifted into train boxes with no effort A railway worker has invented and patented a method of using pneumatics to elevate sand from a drum and use it to fill sand boxes on trains Trickles of sand have been run onto the tracks in front of train wheels to improve adhesion since the early days of railways. Until now, this has always involved a person lifting a container with a spout and using it to fill the boxes manually. Keiron Schwarz, who works at a railway depot in Chester, says: “I came up with the idea when the problem of lifting sand dispensers was raised as an ongoing problem at a health and safety meeting.” The machine uses a compressed air-driven venturi pump in the base of the drum to draw in sand and entrain it in an air stream. Pressure of 100psi lifts 4kg per minute. The whole unit sits on a porter’s type two wheeled trolley and includes an infrared sensing system to turn the motor off when the sandbox is full and inhibit use if the box is full already. Blue and orange beacons signal when in use. Tests started in November 2005 and six machines have been made and are in use. Mr Schwarz is in now in negotiations with a view to putting it into commercial production. Inventorlink Products