Handle with care

By their very nature bulk solids are not that easy to move around. Some are easier than others, of course, and can flow - either unaided or in pneumatic systems - as easy as any liquid. But the design of handling equipment generally calls for specialist knowledge.

In large single product plants, that knowledge can come together in bespoke handling systems designed and built by a specialist contractor. Typical of such systems is the final product storage system at Hydro Polymers' PVC plant at Newton Aycliffe, Co Durham. York-based Portasilo Bulk Handling Systems acted as main contractor of the whole of this installation, including two 250tonne, 7m diameter by 22m tall aluminium silos, and all ancillary buildings and platforms. This project followed an earlier contract for two 4m diameter silos.

Such projects are very much at the 'bulk' end of the processing spectrum. But large, single product plants are increasingly been overtaken by the multi-product, multi-functional process plants that are common in the food, fine chemicals and pharmaceuticals sectors. Designing solids handling and storage facilities for such plants, with their rapidly changing inventories, again calls for the specialists.

Take for an example, the animal nutrition and health products manufacturer Nutec. One of the contracts handled by the company at its Staffordshire plant involves the measured blending of an additive to raw material, followed by final packaging and despatch. The raw material had been supplied in 20kg bags, but a radical rethink of the handling process was called for when the supply was switched to 1tonne FIBCs (flexible intermediate bulk containers). Based on earlier experience, Nutec turned to Flexicon (Europe) to design and supply a new handling system to replace the previous manual bag emptying.

The FIBCs are now positioned by fork-lift truck on to a frame above a receiving hopper. But unlike the traditional method of feeding the bag spout through an iris valve, the bulk bag/hopper interface is a manual Spout-Lock clamp ring above a pneumatically-activated Tele-Tube telescoping tube. Together, these devices enable operators to make a quick, dust-tight connection between the bag and hopper, and to automatically elongate the bag as it empties to promote flow.

Flexicon's Spout-Lock clamp and Tele-Tube telescoping tube can also be used on-line with pneumatic conveyor systems, again eliminating dust during untying, discharge, collapse and retying of bags. For applications requiring the retying of partially empty bulk bags, the company offers a Power-Cincher pneumatically actuated flow control valve.

According to another specialist handling company, Spiroflow, the need to untie bag spouts can be eliminated using its new bulk bag unloading station. This incorporates cone valve technology, which has long been the preferred means of discharging dry products from rigid bins. Using rigid bins, as opposed to flexible bags, however, can involve higher costs in cleaning and revalidating the empty containers. Spiroflow says it can now provide users in the pharmaceutical, food and chemical industries with a cost-effective handling solution by combining the cone valve with the cost benefits of bulk bags.

Convenient though they are in many applications, one drawback of bulk bags crops up when they have been emptied. They are not known as 'big bags' for nothing after all, and folding them up is not easy. But FIBC specialist Flomat Bagfilla International has come to the rescue with its patented BagFolder machine. The company says operators no longer have to wrestle with unwieldy discharged FIBCs and, more importantly, an integral extraction connection ensures the bags can be folded safely without discharging dust to the atmosphere.

By definition, FIBCs provide an intermediate stage in the solids handling process, but many processes require continuous conveying of materials from one process step to another, or to and from bulk storage facilities. Here again, specialist advice is needed. Spiroflow's Pro Screw flexible screw conveyor, for example, has been developed to ease the handling and increase the throughput of problematic products that may be cohesive and/or difficult to move.

The Pro Screw features a new bevelled screw design that increases interaction with cohesive products such as titanium dioxide, iron oxide and pigments to encourage their forward movement.

Although not quite as difficult to convey, distributing granulated sugar around its Bury St Edmunds plant prompted British Sugar to again call in another specialist. In this case, Geo Robson (Conveyors) of Sheffield was awarded a £750,000 contract to screen and deliver product for bulk out-loading and bagging, and for recirculating it back into the factory.

In the screening area, the process route has been simplified by taking out a number of elevators and extending an enclosed Robson Cleanflo belt conveyor that brings sugar from the scalping screen. The Cleanflo delivers product into a modified screw conveyor with three outlets, an arrangement that allows the repositioned vibratory screens to be fed in any combination.

Magnetic separators and metal detectors have been installed at all critical points in the system. When a detector is activated, a slug of sugar is run out into a 1 tonne bag for inspection - again highlighting the complementary, and specialist, nature of bulk solids handling equipment.