A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

2o8 SEA WATER DISTILLATION. 83. It will be observed that in this arrangement the exhaust steam from the pump is made to go into the boiler feed heater. This is done with a view to use the higher pressure and, consequently, hotter steam available foi feeding water into the boiler at the highest temperature possible. Steam from (2) being at a lower pressure, and consequently lower temperature, does well enough to heat the feed to the evaporators. The upper pipe (A) is best partitioned off, so that the pressure of the exhaust steam can be kept up, whilst it is inside the tubes of the first heater. When the two steams, (1) and (2), have imparted their latent heat, and are converted into water, then all the waters (or condensed steams) go into the bottom pipe (B), and run into the condenser tubes, together with any steam that lias not been condensed inside the heater tubes. 84. It will be seen that by utilising the exhaust steam from the pump, the heat of the steam used to drive the pump is to a great extent retrieved. The steam to the pump is high-pressure boiler steam—that is, the hottest steam of the whole apparatus—and to waste or misuse such heat would make, as before-mentioned, a very great difference in the economy of the working of the apparatus. 85. If the pump exhaust steam were led direct to the distiller tubes, some heat would be saved, but the saving would be less, as this mode of using the exhaust steam would, in fact, be single distillation only (with its lowest grade of economy), whereas by using the exhaust steam for heating the boiler feed, the heat of such steam is transferred to the boiler, and is thus indirectly given a multiple effect instead of only a single effect. 86. The pump exhaust may, however, be otherwise used to good purpose, thus (1) instead of this exhaust steam