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<br />to <br />~ <br />"-1f <br />N <br />Q <br />C1 <br /> <br />phates and ammonia in the circulating water supports biological activity and <br />requires higher and/or more frequent chlorine dosages. Non-oxidizing bloc Ides <br />are available, but their cost usually limits application to smaller cooling <br />systems and on a periodic basis only In large systems. <br /> <br />.. <br /> <br />AI I of the process options are assumed to Include the appropriate chemical <br />treatment which Is compatible with the particular process option and system <br />materials and also be cost effective. The Lower Virgin River Unit and the <br />secondary sewage effluent both have common and unique chemical treatment <br />requirements. The costs for these chemical treatments are assumed to be <br />similar. <br /> <br />WATER TREATMENT OPERATING GUIDELINES AND DESIGN CRITERIA <br /> <br />The fol lowing Is a summary of the cooling tower operating guidelines and water <br />treatment design criteria used In this study for the development of water <br />treatment process configurations. These guidelines and design crIteria are <br />based on established electric utility opratlng experiences, EPRI's Design and <br />Operating Guidelines for Cooling Tower Systems and conservative engineering <br />practices. <br /> <br />.:., <br /> <br />Coo I I ng Tower Operat i ng Gu I de lines <br /> <br />This study considered both established and state-of-the-art cooling tower <br />operating guidelines. The guidelines are presented In Table 4.1. <br /> <br />!.- <br /> <br />TABLE 4-1 <br /> <br />COOLING TOWER OPERATING GUIDELINES <br /> <br />Parameter <br /> <br />OPERATI NG LIMIT <br /> <br />pH <br />Bicarbonate (mg/I as Ion) <br />Calcium (mg/I as Ion) <br />Silica (mg/I as Si02) <br />Magnesium Silicate (mg/I of Mg <br />as CaC03 times mg/I Silica) <br />Suspended Sol Ids (mg/I) <br />Total Dissolved Sol Ids (mg/I) <br />Phosphate, P04 (mg/I) <br /> <br />7.8 to 8.4 <br />80 to 150 <br />600 <br />150 <br />150,000 <br /> <br />150 <br />60,000 <br />5 <br /> <br />The guidelines reference those parameters that are necessary to control scal- <br />Ing and plugging In the circulating water system. The state-of-the-art cal- <br />cium and magnesium sllcate limits used In the study are based on extended <br />operating experience at Navajo, San Juan, Hunter and other western power <br />plants using the newer polyacrylate scale Inhibitors In their circulating <br />water systems. The state-of-the-art phosphate limit Is based on 30 plant- <br />years of operating history at a Texas station operating on a secondary ef- <br />fluent water source. Again, the use of scale Inhibitors has allowed this sta- <br />tion to extend their operating phosphate limit to 10 mg/I on low hardness <br />waters. <br /> <br />4-8 <br />