Principles of naval engineering - Historic Naval Ships Association

Chapter 18. -DISTILLING PLANTScondensed in the condensing section and is dischargedto the test tanks as distillate.The first- effect distillate which was used inthe second- effect tubes to boil and vaporize thefeed in the second- effect shell is dischargedthrough the second- effect tube nest drain regulatorand is led to the distilling condenser byway of a flash chamber. The flash chamber is essentiallya receptacle within which the vapor, liberatedwhen the second- effect drains are reducedto a pressure and temperature corresponding tothe distilling condenser vacuum, is separatedfrom the condensate and directed to the distillingthecondenser. As may be seen in figure 18-6,flash chamber is located just outside of the second-effect shell.The distilling condenser circulating waterpump takes suction from the sea and dischargesthe sea water through the shell of the distillatecooler (which is external to the unit) and thenthrough the tubes of the distilling condenser.Some of the cooling water is then dischargedoverboard; but a portion (which is now calledevaporator feed) goes through the feed heatingsection of the distilling condenser, through theair ejector condenser, and through thefirst- effect vapor feed heater before it is dischargedto the first- effect shell. These paths ofthe distilling condenser circulating water and theevaporator feed may be traced in figure 18-5.As previously described, some of the seawater feed in the first- effect shell is boiled andvaporized by the supply steam. The remainingportion becomes more dense and has a highersalinity than the original sea water feed; thisdenser, saltier water is called brine to distinguishit from sea water. After a certain amountof sea water feed has been vaporized in the firsteffectshell, the remaining brine is led to thesecond- effect shell through a pipe that has a manuallycontrolled feed regulating valve installedin it. When the feed regulating valve is open, thehigher pressure in the first- effect shell causesthe brine to flow from the first- effect shell to thesecond- effect shell. After the brine has been usedas feed to generate vapor in the second- effectshell, the remaining brine is discharged overboardby the brine overboard discharge pump.FIRST-EFFECTSEPARATORSECOND-EFFECTSEPARATORDISTILLINGCONDENSERVAPOR FEEDHEATERAIR BAFFLESECOND-EFFECTTUBESFIRST-EFFECTTUBESFLASHCHAMBERBRINE PUMPSUCTIONFIRST-EFFECTDRAIN REGULATORDIVISION PLATESECOND-EFFECTDRAIN REGULATORFigure18-6.— Cutaway view of Soloshell double-effect distilling plant.45947.117