Peristaltic pumps give smooth flow and long-term reliability

Buxton Lime Industries (BLI), a Tarmac company, officially opened its new cement plant in Buxton, UK, in November 2004. At a cost of 110million this was a substantial investment but the state-of-the-art facility more than doubled BLI's cement manufacturing capacity and presented opportunities for the company to enter new markets. Annual output is in the region of 800,000 tonnes of packed and bulk Portland cement and masonry cement.

The cement plant at BLI converts the waste clay washings from the stone processing plant into cement. The original plant was built in 1966 and, after more than thirty years' operation, was replaced with a new plant utilising the best available technology for cement production. The utilisation of the waste clay washings in the new cement plant was a critical part of the plant design.

Originally the plant used a conventional thickener to increase the solids content of the clay washings from around 5 to 40 per cent w/w. The thickened slurry was then fed to the old cement plant. The new plant design replaced the conventional thickener with two 15m diameter Eimco Deep Cone Paste thickeners (DCTs). The special design features of the new Eimco DCTs means that they were able to thicken the clay washings from around 5 to 60 per cent w/w. At these high solids concentrations, the thickener underflow has special rheological properties that must be taken into consideration when designing the pumping system.

Peristaltic pumps were selected to transfer the paste underflow from the DCTs to the cement plant because the wide range of flows required, combined with the accurate control that could be achieved with variable-speed peristaltic pumps.

Advantages of peristaltic pumping

Unlike alternative technologies, peristaltic pumping can readily handle viscous, lumpy, or abrasive fluids, or those containing solids or particulates. In addition, highly aggressive or corrosive fluids can be pumped - with only the flexible hose coming into contact with the process fluid. Further benefits of peristaltic pumps include the ability to self-prime and the way in which they can be cleaned by back-flushing. Peristaltic pumps can easily be incorporated within a control system for metering or dosing applications, with excellent repeatability achievable.

A total of four Watson-Marlow Bredel SPX100 Duplex peristaltic pumps are installed in the Buxton plant, with each of the two Eimco DCTs is served by a pair of pumps in a configuration designed to allow discharge from each thickener and simultaneous transfer between DCTs if necessary, guaranteeing plant availability in the event of a pipe blockage or pump failure. Each compact pump unit has an electric motor driving twin pumpheads that share common suction and discharge manifolds having 6in and 4in ANSI flanges respectively. In the Buxton plant, all four pumps are connected to a common discharge manifold. Under normal operation, the pumps deliver from the thickener at a rate of 27 tonnes per hour, and the double duplex pumps give a smooth, pulsation-free flow.

The ability to pump high solids concentration paste from the Eimco DCTs to the cement plant has had significant benefits to the cement making process at BLI. The higher solids concentration has improved the thermal efficiency of the cement making process by 40 per cent.

Exceptional reliability

Nev Mosley, the Operation Manager at the plant, comments: "The thickener underflow is not the easiest fluid to handle, but peristaltic pumping is the best technology without a doubt. Watson-Marlow's pumps have proved to be extremely reliable and the pumps are operating around the clock as a vital element of the production process. We have not needed to change the flexible hoses in the pumps since September 2005, despite the pumps running continuously 24 hours per day."

When the plant first commenced production, the innovative design meant that a certain amount of fine-tuning was necessary in order to optimise the process. Nev Mosley states: "The Watson-Marlow engineers were extremely helpful when we approached them with a query. They were very responsive and their experience and expertise enabled them to make recommendations that we were able to implement successfully."

For more information about the SPX100 Duplex peristaltic pumps, please contact Watson-Marlow Bredel or visit the website at www.watson-marlow.co.uk.