leaks, improper operation of air ejectors, insufficientflow of seawater, or ineffective use of heat transfersurface in the distilling condenser.Air LeaksMany distilling plant troubles are direct results ofair leaks. Air leaks in the shells of distilling plants causea loss of vacuum and capacity. You must take extremecare when making up joints, for they must be kept tight.Periodically test the joints under pressure for leaks.When the plant is in operation, use a candle flame to testall joints and parts under vacuum. When the plant issecured, you can use air pressure or soapsuds for testing.Air leakage may also be detected by hydrostaticallytesting the various parts of the plant. You should takethe necessary precautions not to exceed the maximumlimit of the test pressure specified by the manufacturer.Saltwater LeaksDefective tube(s) on the heat exchangers can belocated by means of an air or a hydrostatic test. Youshould follow the recommended procedure according tothe manufacturer’s instructions.Air EjectorThe steam pressure at the nozzle inlet of the airejector must not be less than that for which the ejectoris designed (stamped on the nameplate). Pressures at theair ejector nozzles may be 10 to 15 psig higher than theminimum specified by the manufacturer.The primary causes of air ejector problems are lowsteam pressure, wet steam, an obstructed nozzle, or aclogged steam strainer. Problems are usually indicatedby a failure to obtain or to maintain the required vacuum.If a problem is due to low steam pressure or wet steam,you should increase the steam pressure, install adrainage trap, or devise a manual solution. A cloggednozzle or strainer must be removed and cleaned. Youshould use special reamers to clean the air ejectornozzles. You should NEVER use a sharpedged tool toclean nozzles! Improper tools will damage the nozzlesurfaces and impair the efficiency of the air ejecter.Procedures for testing air ejectors can be found inthe manufacturer’s technical manual. In general, thesame maintenance procedures should be followed fordistilling plant air ejectors as for air ejectors for the maincondensers.You should inspect the air ejector strainer accordingto the PMS. Failure to keep the strainer clean will causea reduced or fluctuating vacuum. When a strainer or anozzle becomes damaged, you should replace it.Insufficient Circulating WaterAn insufficient flow of circulating water is indicatedwhen the temperature of the water rises more than 20°Fwhile passing through the condensing section of thedistiller condenser. The last-effect shell pressure isdirectly dependent upon the distiller condenser vacuum.The vacuum is dependent upon the temperature andquantity of the circulating water and the properoperation of the air ejectors. Too low an overboarddischarge temperature of the distiller condensercirculating water is accompanied by efficiency losses inthe distilling plant. The overboard dischargetemperature should be kept as high as possible, withoutexceeding the desired 20°F temperature rise through thedistiller condenser. In addition, limiting the quantity ofcirculating water tends to prolong the service life of thetubes and tube sheets. When troubles occur which arenot caused by improper operating procedures, youshould inspect the condenser circulating water systemto determine the true cause of the faulty operation.You must carry out preventive maintenanceprocedures to ensure that the circulating water pump ismaintained in good material condition. You should alsocarry out routine procedures to ensure the proper settingand maintenance of the back-pressure regulating valve.A regulating valve that is not working properly must bedisassembled and repaired before its faulty operationinterferes with the operation of the distilling plant.You should inspect the condenser circulating watersystem pipings at regular intervals for cleanliness aswell as for scale or foreign matter. The operators of thedistilling plant shouldaccording to the PMS.Improper Drainageinspect and clean the strainersIf the distilling plant fails to produce the designedoutput when the pressure above the orifice is 5 psig andthe first-effect tube nest is several inches of mercury,this is an indication of improper drainage of the distillercondenser or of one of the evaporator tube nestssubsequent to the first effect. Complete flooding of theflash chamber gauge glass is also a positive indicationof improper draining of the condenser. Because the levelappears to be in the gauge glass or below is notnecessarily an indication of improper drainage. Air leaks8-5
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