Peristaltic Pumping At Buxton

Watson-Marlow Bredel peristaltic pumps keep BLI cement plant in production round the clock

When Tarmac-owned Buxton Lime Industries (BLI) officially opened their new £110 million cement plant in Buxton in November 2004, annual cement manufacturing capacity was more than doubled to around 800,000 tonnes of packed and bulk Portland cement and masonry cement.

The original plant was built in 1966 and, after more than 30 years operation, was replaced with a new plant utilizing the best-available technology for cement production. The utilization of the waste clay washings from the stone processing plant was a critical part of the cement plant design.

Whereas the old plant used a conventional thickener to increase the solids content of the clay washings from around 5% w/w to 40% w/w, the new plant design replaced this system with two 15m diameter Eimco deep-cone paste thickeners (DCTs). Special design features of the Eimco DCTs mean that they are able to thicken the clay washings from around 5% w/w to 60% w/w.

At these high solids concentrations, the thickener underflow has special rheological properties which must be taken into consideration when designing the pumping system.

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

Unlike alternative technologies, peristaltic pumps can readily handle viscous, lumpy, or abrasive fluids, or those containing solids or particulates, with only the flexible hose coming into contact with the process fluid.

Further benefits of peristaltic pumps include their self-priming capabilities and their ability to be cleaned by back-flushing. Peristaltic pumps also offer a high level of repeatability and can be incorporated within a control system for metering or dosing applications.

A total of four Watson-Marlow Bredel SPX100 Duplex peristaltic pumps were installed in the new Buxton plant, with each of the two Eimco DCT units being served by a pair of pumps in a configuration designed to allow discharge from each thickener and simultaneous transfer between the DCT units if necessary, thereby guaranteeing plant availability in the event of a pipe blockage or pump failure.

Each compact pump unit has an electric motor driving twin pump heads that share common suction and discharge manifolds featuring 6in and 4in ANSI flanges respectively. All four pumps are connected to a common discharge manifold. Under normal operation, the pumps deliver underflow from the thickener at a rate of 27 tonnes/h, with the double duplex pumps giving a smooth, pulsation-free flow.

According to BLI, the ability to pump high solids concentration paste from the Eimco DCT units to the cement plant has resulted in significant benefits for the cement-making process. For example, the higher solids concentration has improved the thermal efficiency of the cement-making process by 40% and helped to reduce particulate emissions by 70%, sulphur dioxide by 60% and nitrogen oxides by 9%.

Nev Mosley, operations manager at the plant, commented: ‘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 24h a day.’

He added: ‘When the plant first commenced production, the innovative design meant that a certain amount of fine-tuning was necessary to optimize the process. The Watson-Marlow engineers were extremely helpful and very responsive when we approached them with a query. Their experience and expertise allowed them to make recommendations that we were able to implement successfully.’

For further information about the SPX100 Duplex peristaltic pumps, contact Watson-Marlow Bredel on tel: (01326) 370370; fax: (01326) 376009; email: [email protected]; or visit: www.watson-marlow.co.uk