CHAPTER 18 



DISTILLING PLANTS 



Naval ships must be self-sustaining as far 

 as the production of fresh water is concerned. 

 The large quantities of fresh water required 

 aboard ship for boiler feed, drinking, cooking, 

 bathing, and washing make it impracticable to 

 provide storage tanks large enough for more than 

 a few days' supply. Therefore, all naval ships 

 depend upon distilling plants to meet the require- 

 ments for large quantities of fresh water of ex- 

 tremely high chemical and biological purity. 



PRINCIPLES OF DISTILLATION 



All shipboard distilling plants not only per- 

 form the same basic function but also perform 

 this function in much the same way. The distil- 

 lation process consists of heating sea water to 

 the boiling point and condensing the vapor 

 to obtain fresh water (distillate). The distilla- 

 tion process for a shipboard plant is illustrated 

 very simply in figure 18-1. 



At a given pressure, the rate at which sea 

 water is evaporated in a distilling plant is 



VAPOR 



SEA WATER 



BRINE 



DISTILLATE 



HEAT SOURCE 



75.284 

 Figure 18-1.— Simplified diagram of shipboard 

 distillation process. 



dependent upon the rate at which heat is trans- 

 mitted to the water. The rate of heat transfer to 

 the water is dependent upon a number of factors; 

 of major importance are the temperature differ- 

 ence between the substance giving up heat and the 

 substance receiving heat, the available surface 

 area through which heat may flow, and the coef- 

 ficient of heat transfer of the substances and ma- 

 terials involved in the various heat exchangers 

 that constitute the distilling plant. Additional 

 factors such as the velocity of flow of the fluids 

 and the cleanliness of the heat transfer surfaces 

 also have a marked effect upon heat transfer in 

 a distilling plant. 



Since a shipboard distilling plant consists of 

 a number of heat exchangers, each serving one 

 or more specified purposes, the plant as a whole 

 provides an excellent illustration of many 

 thermodynamic processes and concepts. Prac- 

 tical manifestations of heat transfer— including 

 heating, cooling, and change of phase— abound in 

 the distilling plant, and the significance of the 

 pressure-temperature relationships of liquids 

 and their vapors is clearly evident. ^ 



The sea water which is the raw material of 

 the distilling plant is a water solution of various 

 minerals and salts. In addition to the dissolved 

 material, sea water also contains suspended 

 matter such as vegetable and animal growths and 

 bacteria and other micro-organisms. Under 

 proper operating conditions, naval distilling 

 plants are capable of producing fresh water which 

 contains only minute traces of the chemical and 



Much of the information given in chapter 8 of this 

 text has direct and immediate apphcation to the study 

 of distilling plants. Applicable portions of chapter 8 

 should be reviewed, if necessary, as a basis for the 

 study of distilling plants. 



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