Novel filter coils solve plant filtration problem

Dean Palmer reports on a novel filter coil that has enabled production at a UK paper mill to return to normal, removing the threat of unplanned stoppages due to poor quality water

A patented filter coil has helped a UK paper mill solve its water filtration problems, allowing the plant to return to normal production, without unplanned stoppages due to poor quality of water.

Cross Manufacturing, based in Bath, supplied an automatic backwashing filter to the Georgia Pacific paper mill in Yorkshire because the mill was experiencing problems when the make up of the inlet water was altered to meet improved environmental standards.

The mill, which manufactures disposable paper products from recycled raw materials, demands a water supply of up to 11,000 litres per minute for production machinery that normally runs 24 hours a day, seven days a week.

Kevin Goss, papermaking projects engineer at the paper mill, commented: "To reduce overall water consumption, we added recycled water from our effluent treatment plant to our main raw water inlet source, in line with upgraded environmental guidelines.

"As a result, a certain amount of debris from our production and effluent treatment processes was re-introduced and began to overload the inlet filter fitted at that time. This precipitated excessive mechanical backwashing, which at times was still unable to prevent the filter from blocking completely," he explained.

Goss added that on such occasions the company had to bypass the inlet filter, which caused unfiltered water to reach production machinery. This, he said, led to problems such as blocked spray bar nozzles and filtration equipment in these areas of the plant, resulting in lost production while the plant was shut down for cleaning.

Goss contacted specialist filtration company John Morfield, who recommended replacing the existing filter with a Cross System 2000 filter.

System 2000 is a modular design, custom built to economically meet the exact operating criteria of each application. The requisite number of filter pods - each containing seven patented 'zero gravity' stainless steel filter coils - are fitted on manifolds to meet the maximum operating flow and pressure. Each filter pod is backwashed individually under PLC sequential control, so forward flow through the filter is never interrupted and there is no need to oversize or to provide dual redundancy.

The zero gravity filter coils are designed to open fully along their entire length to achieve completely effective backwashing using only a minimum amount of reversed water flow. The design therefore eliminates any need for scrapers or other inefficient mechanical backwashing devices.

Raised ridges on the filter coils define the absolute filter rating, which is selectable in a range of sizes from 12 to 400 microns. A turbo flow path in each filter pod keeps as much debris as possible away from the surface of the coils, further minimising backwashing frequency.

The Cross System 2000 installation at Georgia Pacific comprises eight filter pods, containing coils rated at 75 microns. The filter, which was installed by a local specialist pipework company and commissioned by Cross Manufacturing, is fully automatic with backwashing triggered by a preset pressure drop differential across the coils. Goss confirmed that the Cross filter has completely cured the problems that he had previously experienced, enabling production to return to normal and removing the threat of unplanned stoppages resulting from poor water quality.

Tom Shelley

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