Screened Laterals Keep Ion-Exchange Beds in Place

Hitachi Electronic Devices (Greenville, SC) uses ultapure, deionized water for treating process water in the manufacture of television tubes. Any form of ion or mineral contamination degrades the tube's coatings, which has a negative effect on picture quality.

To treat process water, Hitachi employs a system of mixed-resin ion-exchange beds. In a continuous cycle, one of the two primary beds is always in operation while the other is being regenerated or on standby. Two polishing beds treat the water further, bringing resistivity to >17 mega-Ohms.

In the beginning, all was well. But after a few years of operation, plant managers were distressed to observe that costly resin was literally washing down the drain during regeneration. The system, as designed, had slotted laterals made of PVC plastic. During service, they flexed and eventually broke, altering their slot sizes and causing excessive media loss.

A permanent fix was suggested by the engineering staff of LEEM Filtration Products (Ramsey, NJ). The plastic laterals were replaced with LEEM's pipe-based Wedge Flow laterals. To form the laterals, the inner piping and the Wedge Flow screening were fabricated from corrosion-resistant Hastelloy alloy. The screening, made from wire with a triangular cross section helically wound over a series of longitudinal rods and welded at every intersection, is in turn welded over the outside of the pipe.

LEEM's pipe-based Wedge Flow Laterals

The benefits of the pipe-based Wedge Flow design include structural strength, uniform slot size that facilitates flow while restraining resin movement, corrosion resistance and ease of cleaning by backwash.

Size and design of the laterals are determined by the system size and flow characteristics. In the case of Hitachi, whose beds are designed for a flowrate of 350 gpm, the LEEM laterals range from 18 to 30 in. long, with pipe sizes of 1.25 to 1.5 in. dia.

For more information: LEEM Filtration Products, Inc., 25 Arrow Rd., Ramsey, NJ 07466. Telephone: 201-236-4833. Fax: 201-236-2004.