Thursday 17 June 2010

Filter water flow control

High performance valve prevents filter media losses, reducing maintenance

Emerson Process Management’s high performance 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 (GB). The resulting elimination of filter media losses and subsequent downtime has enabled E.ON to reduce costs and improve availability as it provides steam for two local soda-ash plants.

The E.ON CHP facility is one of the largest of its type in Britain, generating 130MW of electricity for local residents and 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, cooled and pre-treated to remove any algae or silt, 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 £3,500 a year. The downtime for this maintenance also affected the plant’s ability to meet its steam requirements.

E.ON installed an eight-inch Fisher Control-Disk rotary valve to replace the original butterfly valve. The new valve has dramatically 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 due to water filter problems.

The improved performance reflects the Fisher Control-Disk valve's unique disk profile and true equal-percentage characteristics that enable it to adapt to changing process conditions and to provide control over a wide range. The valve provides between 15% and 70% travel without compromising capacity. This performance represents a significant improvement compared to standard butterfly valve designs that offer 25% to 50% of travel.

Neil Price, Improvement and Performance Coordinator, E.ON, said, “The Fisher Control-Disk valve not only controls the backwash flow rate more accurately, but also it delivers, when 100% open, a flow rate adequate to meet the water plant demands, without restrictions. Its performance and reliability led to savings of £3,500 a year and enabled us to improve our customer service.”

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