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<br />- <br />'. <br /> <br />'<':!' <br />"'.... <br />C'J Electrodialysis (ED or EDR) is applicable to raw water treatment, sldestream <br />~) treatment of the cooling tower circulating water and wastewater concentration. <br />~ For the reference raw water chemistry, ED Is a commercially proven process for <br />makeup water treatment. ED has been Installed at approximately five domestic <br />power plants for demlneral izer pretreatment, and at a larger number of foreign <br />plants for similar use. <br /> <br />To our knowledge, electrodialysis as a sidestream treatment process for power <br />plant cooling water systems has been studied, but not tested. The technically <br />vlabll ity for this appl ication would be similar to applying ED In a wastewater <br />concentration mode. <br /> <br />ED Is being appl led for wastewater concentration at the ESCOM power plant com- <br />plex In South Africa. In this application, ED Is used as a pre-concentrator <br />for a wastewater evaporator. No operating data has yet been generated from <br />this Installation. <br /> <br />,-;. <br /> <br />'," <br />~~: <br />/. <br /> <br />" <br /> <br />ED has not been applied domestically for power plant wastewater concentration. <br />Analogous domestic applications include the concentration of cooling tower <br />blowdown at an oil refinery, the concentration of saline water at the Bureau <br />of Reclamation La Verkln Springs Test Facll ity, and the concentration of RO <br />blowdown at the Los Banos test facility. These experiences have shown that ED <br />for wastewater concentration has technical and economic promise. However, the <br />wastewater quanitles resulting from the Lower Virgin River unit and secondary <br />sewage effluent made ED uneconomical for further consideration In the process <br />screening. <br /> <br />, <br />" <br /> <br />Vapor ComprA~~lon Evaporator~ <br /> <br />Vapor compression evaporation (VCE) applied to the concentration of power <br />plant wastewaters Is commercially proven technology. These units are long <br />tube, vertical, failing film, evaporators using a vapor compression cycle. <br />The wastewater Is fed to the evaporator, mixed with a concentrated slurry, and <br />continually recirculated to the top of the evaporator where It Is distributed <br />to the Inside wal I of each tube as a thin film. As the thin film falls down <br />the Inside of the tubes, water Is converted to steam. As this steam condenses <br />on the shel I side of the tubes, It gives up Its heat of condensation and Is <br />collected In the product tank. The release of the heat of condensation causes <br />more water to be evaporated from the brine Inside the tubes. The energy to <br />drive the system Is suppl led by the compressor drive which Is normally an <br />electric motor. <br /> <br />Over two dozen VCE units, ranging In feedwater capacities from 150 to 600 gal- <br />lons per minute, have been Instal led at power stations and have demonstrated <br />rei lable performance using a seeded slurry process for calcium sulfate scale <br />control. In addition to concentrating power plant wastewaters, the VCE sys- <br />tems have produced a high quality distil late suitable for condensate makeup <br />with minimal treatment. <br /> <br />VCE's were selected for the development of process options because of proven <br />performance and applicability. <br /> <br />4-6 <br /> <br />I <br />1 <br />