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

[92 SEA WATER DISTILLATION. of vertical type can be used. Its economy is, however, considerably less than that of the Cornish type of boiler. The vertical boiler will consume about 20 to 25 per cent, more coal for an equal evaporative power. The Cornish or Lancashire type of boiler requires to be set in brick- work, the vertical does not. 44. Whatever type is used, it is well to avoid cross tubes, and, in fact, all internal work, as far as possible, that will get incrusted with scale. All interior appliances should be arranged so as to avoid difficulties in cleaning off the scale. The flue or flues of the boiler should not be fitted too close to the bottom, as the passage between the bottom of the shell and the tube is readily filled with deposit. 2. The Size of the Boiler. 45. The proper size of the boiler to suit multiple dis- tillation for a specified production and specified type of apparatus—i.e., whether single, double, treble, or quad- ruple distillation—is a matter to be looked at from different standpoints. Some makers advocate larger boilers than others do for the same work. To have the same size boiler for salt feed as for fresh feed would ob- viously be erroneous, because no allowance would be made for the extra feed required for a sea-water feed, nor for the gradual loss of power caused by the heating surfaces getting furred over. 46. In estimating the size and power of a boiler for a set of distilling apparatus, the quantity of primary water contributed, and the steam pressure needed, must first be determined, having regard to the succeeding pressures in the evaporators ; and due allowance must be made for the quantity and temperature of the boiler feed.