C hapter 18. -DISTILLING PLANTS 



distilling condenser. A two- stage or three- stage 

 air ejector, a distillate cooler, and a feed water 

 heater are also provided. Feed water passes 

 through the tubes of the distillate cooler, the 

 stage distilling condenser, and the air ejector 

 condenser. In each of these heat exchangers the 

 feed picks up heat. The final heating is done by 

 low pressure steam admitted to the shell of the 

 feed water heater. From this heater the feed 

 water enters the first- stage feed box and comes 

 out through orifices into the flash chamber. As 

 the heated feed water enters the chamber, a por- 

 tion flashes or vaporizes because the pressure 

 in the chamber is lower than the saturation pres- 

 sure corresponding to the temperature of the hot 

 feed. The vapor condenses on the tubes of the 

 first- stage distilling condenser. The feed which 

 does not vaporize in the first chamber passes to 

 the second chamber. The process is repeated in 

 each stage and the brine remaining in the last 

 stage is removed by the brine overboard pump. 

 Vapor formed in each stage passes through a 

 vapor separator and into the stage distilling con- 

 denser, where it is condensed into distillate. The 

 distillate passes through a loop seal on its way 

 to the distilling condenser of the next stage. The 

 distillate pump removes the distillate from the 

 last stage and discharges it through the distillate 

 cooler and the solenoid- operated dump valve to 

 the ship's tanks. 



The general arrangement of a two- stage 

 flash- type unit is shown in figure 18-9; a five- 

 stage unit is shown in figure 18-10. The major 

 circuits are shown in each illustration. 



Vertical Basket Distilling Units 



Some recent ships are equipped with vertical 

 basket distillingunits. Aunitof thistypeis shown 

 in figure 18-11. The unit shown has two effects; 

 however, some units of this type have more than 

 two effects. 



The vertical basket unit consists of two or 

 more evaporators, a distiller condenser, vapor 

 feed heaters, a distillate cooler, and air ejectors. 

 The major difference between a vertical basket 

 unit and a submerged tube unit is in the design 

 of the evaporators. In the vertical basket unit, 

 each evaporator consists of a vertical shell in 

 which a deeply corrugated vertical basket is in- 

 stalled. Figure 18-12 shows a sectional view of 

 the evaporator and basket. 



Low pressure steam is admitted to the inside 

 of the first- effect basket. This steam boils the 



feed water in the space between the outside of 

 the basket and the shell of the evaporator. The 

 condensate resulting from the condensation of 

 steam drains downward and is returned to the 

 boiler feed system. The vapor generated from 

 the boiling sea water feed passes through the 

 cyclonic separator above the evaporation sec- 

 tion, where most of the entrained liquid particles 

 are removed from the vapor by centrifugal force. 

 The vapor continues on through the second vapor 

 separator (called the "snail"), where the re- 

 maining water droplets are separated from the 

 vapor. The liquid particles from both of these 

 separators drain downward and become part of 

 the brine drains. 



The vapor generated in the first- effect shell 

 passes from the steam dome of the first- effect 

 shell. It goes through the vapor feed water heater 

 and then enters the steam chest and evaporator 

 basket of the second- effect shell. The first- ef- 

 fect vapor boils the second- effect feed and thus 

 causes the generation of second- effect vapor. 

 The second- effect vapor goes through the cy- 

 clonic separator and the snail in the second- 

 effect shell. From the steam dome, this vapor 

 then goes to the distilling condenser, where the 

 vapor is condensed on the outside of the tubes. 

 The second- effect distillate drains down and col- 

 lects in the flash tank. 



As the first- effect vapor is being used to boil 

 the second- effect feed, some of the vapor con- 

 denses. This distillate drains downward into the 

 second- effect steam chest and is discharged to 

 the flash tank at the bottom of the distilling con- 

 denser, where it mixes with the distillate formed 

 from the second- effect vapor. The distillate is 

 removed from the flash tank by the distillate 

 pump and is discharged through the distillate 

 cooler and the solenoid-operated dump valve to 

 the ship's tanks. Should the salinity of the 

 distillate exceed 0.065 epm, the dump valve auto- 

 matically dumps the distillate to the bilges. 



Sea water flows through the tubes of the dis- 

 tillate cooler and the distilling condenser, creat- 

 ing a suction for the brine pump and maintaining 

 a back pressure for the feed system. About ?5 

 percent of the sea water passes through supple- 

 mentary heating sections in the distilling con- 

 denser to the air ejector condenser, and feeds 

 the evaporator shells in parallel. As the sea 

 water passes through the air ejector condenser, 

 it condenses the air ejector steam; the resulting 

 condensate drains to an atmospheric drain tank. 



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