Cooling water Backwashing

Typically, for cooling water makeup, the filtration rates are 4 to 6 gpm/sq ft of media surface area, with backwash rates of 10 to 12 gpm/sq ft for a period of 5 to 8 minutes. When the filter is used for removing suspended solids from recirculating cooling water, the filtration rate may be as high as 10 to 15 gpm/sq ft and the backwash rate 15 to 20 gpm/sq ft. 

Flow measurements showed flow rates lower than expected and backwashing was observed. The backwash contained brownish siliceous matter and other solid impurities. All three heat exchangers had silt and dirt deposits and partially plugged tubes. The tube ends were corroded and thinned down. Perforation of the tubes originated from inside (cooling water side). Pitting shows it to be underdeposit corrosion. 

Another method to reduce silting is to periodically inject air into the cooling water. Air injection must normally be more frequent to achieve the same results as with backwashing. This method is also more expensive and adds to the venting problem. It has the advantage, however, that no process upsets occur as experienced occasionally when backwashing. Air injection, to be effective, must be performed on a routine schedule. A timing mechanism may be used to inject air for short time Intervals over a period of several days. 

Strainers are provided at the SSWS pump discharges. The strainers are of the automatic backwash type and are designed to retain particles consistent with the fouling design limits of the component cooling water heat exchangers (see CESSAR-DC, Section 9.2.1.2.1.5). 

Fig. 1 schematically shows a cooling water circuit with preparation of the make-up water. Instead of the settling basin a gravel filter with backwash system may be used. A large basin or pond with spray equipment may be substituted for the relatively expensive cooling tower. 

Ammonium Nitrate Plants - In ammonium nitrate plants, wet scrubbers can be considered for prill towers and the granulation plant. Particulate emissions of 0.5 kg/t of product for the prill tower and 0.25 kg/t of product for granulation should be the target. Similar loads for ammonia are appropriate. Other effluents that originate in a nitrogenous fertilizer complex include boiler blowdown, water treatment plant backwash, and cooling tower blowdown from the ammonia and nitric acid plants. 

Methoxy-cis-19-norpregna-l,3,5(10),17(20)-tetraene A solution of 31 g (109 mmolesi of estrone methyl ether in 600 ml of benzene is added rapidly to a solution of 469 mmoles of ethylidenetriphenylphosphorane in 1.2 liters of DMSO. After heating under nitrogen at 60° overnight, the reaction is cooled, poured into ice water, and extracted with three portions of hexane, backwashed with three portions of water and the hexane removed. The crude product, dissolved in petroleum ether (bp, 30-60°), is filtered through 225 g of alumina (activity I). The residue from the eluate consists of 95 % cis- and 5 % tran5-isomers, as determined by vpc analysis. After recrystallization from ether-methanol, 26.3 g (82%) of cw-isomer is obtained mp 76.5-77.5° [a]o 60°. 

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