Chapter 7—AUXILIARY MACHINERYdistiller condenser vacuum. The vacuum isdependent upon the temperature and quantity ofthe circulating water, and the proper operationof the air ejectors. Too low an overboarddischarge temperature of the distiller condensercirculating water is accompanied by efficiencylosses in the distilling plant. The overboarddischarge temperature should be kept as high aspossible, without exceeding the desired 20°Ftemperature rise through the distiller condenser.In addition, limiting the quantity of circulatingwater tends to prolong the service life of the tubesand tube sheets. When troubles occur which arenot caused by improper operating procedures, aninspection should be made of the condenser cir-culating water system to determine the cause offaulty operation.Preventive maintenance procedures should becarried out to ensure that the circulating waterpump is maintained in good material condition.The maintenance and repair procedures for thispump are similar to those for the other pumpsof the plant.Routine procedures should be carried out toensure the proper setting and maintenance of theback-pressure regulating valve. If this valve is notfunctioning properly,the valve should bedisassembled, the valve parts replaced, and thenecessary repairs to the valve made, before itsfaulty operation interferes with the operation ofthe distilling plant.To ensure that the condenser circulating watersystem is clean and free from scale and foreignmatter, the piping should be inspected at regularintervals. The operators of the distilling plantshould inspect and clean the strainers, in accord-ance with the PMS, to prevent accumulations offoreign matter from interfering with theproper operation of the plant.Improper DrainageFailure of the distilling plant to producedesigned output when the pressure above theorifice is 5 psig and the first-effect tube nestvacuum is several inches of mercury alwaysindicates improper drainage of the distiller con-denser or of one of the evaporator tube nestssubsequent to the first effect. Complete floodingof the flash chamber gage glass is also a positiveindication of improper draining of the condenser,but the fact that the level appears to be in the gageglass or below is not necessarily an indication ofimproper drainage because air leaks at the gageglass fittings may indicate a false liquid level.A temperature difference of more than 5 °Fto 10°F between the last-effect shell temperatureand the temperature of the distillate at thedistillate cooler inlet is another indication ofimproper drainage; however, the fact that thetemperature difference is within the proper rangedoes not necessarily indicate proper drainage.Scale deposits are unlikely to form in thedistilling condenser tubes if the plant is properlyoperated and a full flow of circulating water ismaintained. However, if scale deposits do occur,the tubes must be cleaned.Venting of the vapor side of the distiller con-denser is continuously accomplished by the airejector. Venting of the saltwater side of this andother units of the distilling plant need not be con-tinuous. While starting the plant, and once everywatch thereafter, the vents on all saltwater headsshould be opened until all air is expelled and asolid stream of water appears, then the ventsshould be closed.Constant Brine DensityThe concentration of brine in the evaporators,to a certain extent, has a direct bearing on thequality of the distillate, and since varying quan-tities of brine discharged overboard may affectthe operating conditions, the quantity of brinedischarged and the brine density must be kept asconstant as possible.If the brine concentration is too low, there willbe a loss in capacity and economy. If the brineconcentration is too high, there will be an increasein the rate of scaling of the evaporator heatingsurfaces, and the quality of the distillate will beimpaired.The brine density, which should never exceed1.5/32, is dependent mainly on the quantity ofbrine pumped overboard and the amount offreshwater being produced. The density must bechecked frequently during each watch andadjusted to the required density. On older distill-ing plants, the brine density is adjusted by meansof a hand-controlled valve located in the discharge7-27
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