HIGH PERFORMANCE FILTERS

Description

A high performance filter is used to separate particulates larger than 2-500 µm from relatively clean liquid streams, typically water for process, cooling systems or for drinking.

In a fibrous depth filter, particulates are captured in a filter medium which comprises a pack of nylon or other synthetic fibres that are twisted and compressed to form a tight matrix. When the solids loading exerts a critical back pressure the filter is backwashed with water to remove the trapped particles. Backwashing is enhanced by a wringing action of the fibre element. The backwashing cycle times are very low, being only 3-5 minutes, and less washwater is used than with comparable filter types.

In another type, a stainless steel spiral coil is engineered to have precise filtration gaps as small as 12 µm when coiled tightly. At a set backpressure the tension on the filter is released. Backwashing takes only 3-5 seconds and can be controlled manually, by a PLC or by a timer. Several filters can operate in rotation to maintain a steady output.

High performance filters can be arranged in parallel to deal with larger throughputs. Alternatively, they can be used to continuously clean a side stream of a closed system.

Application

High performance filters are used as a pretreatment for deionising equipment, for desalination by reverse osmosis, and for ultrapure water production. They are used to filter potable water, process waters and cooling tower water. High performance filters can remove Legionella from cooling tower water systems, and turbidity and metal precipitates from effluents. Fibre depth filters can remove Cryptosporidium oocysts from water supplies.

High performance filters can be used to treat still or flowing waters and some types can be used to provide emergency drinking water from such sources when combined with chlorination.

Sizing

Single high performance filters can treat 250-1200 m3/day and remove 98 % of particles down to 2 µm. Higher throughputs can be obtained using banks of filters in parallel.

The treatment of a typical flow of about 100 m3/hour by a fibre filter would require a feed pump of about 10 kW, an air compressor of about 8 kW, a control panel of about 500 W, and a refrigerant air drier of about 200 W. The average power requirement would be about 8 kW.