Valve Improves Backwash Flow Control At CHP Plant

Emerson Process Management's Fisher Control-Disk valve has improved backwash flow control within the water treatment system at E.ON's combined heat and power (CHP) plant in Northwich, Cheshire. The resulting elimination of filter media losses and subsequent downtime has enabled the energy company to reduce costs and improve availability as it provides steam for two local soda-ash plants. The E.ON CHP facility generates 130MW of electricity for local residents and is capable of supplying approximately 500 tonnes of steam every hour for two nearby soda-ash (sodium carbonate) production plants in Winnington and Lostock.

Make-up boiler feed water is obtained from the River Dane; it is cooled and pre-treated to remove any algae or silt and is then passed through one of six filters before being sent to a holding tank. The filters are cleaned by air scouring and backwashing to remove any material blinding the filter. The facility has had problems controlling this backwash flow. The original butterfly valve used in this process could not provide a steady flow rate, causing media to be lost through the filters. As a result, the filter media had to be replaced or refilled at an average cost of GBP3,500 a year.

The downtime for this maintenance also affected the plant's ability to meet its steam requirements. E.ON installed an 8in (20cm) Fisher Control-Disk rotary valve to replace the original butterfly valve. According to Emerson, the new valve has improved backwash flow control without compromising capacity at peak demand. Since it was installed, the plant has not lost any filter media or experienced any downtime owing to water filter problems. The valve provides between 15 per cent and 70 per cent travel without compromising capacity. This performance represents an improvement compared with standard butterfly valve designs that offer 25 per cent to 50 per cent of travel.

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