A PRECIPITATOR FOR SEA WATER.
It is quite possible to prepare sea water in such a way as to practically prevent any serious deposit forming from it.
The process employed is to add to the sea water a known quantity of precipitator powder consisting chiefly of soda ash, and having done this in a closed vessel, to heat the mixture by blowing into it waste steam, until a pressure of from 5lbs. to 10lbs. is created; under these circumstances practically all the magnesium and calcium salts separate from the water and are easily got rid of by filtering it under pressure into the hot-well.
A precipitator 6 ft. 4 in. high and 3 ft. in diameter, holds a ton of water, and the time taken, from the first running the sea water in, to its delivery into the hot-well, need not exceed 1 hour and 15 minutes, so that in practice, giving plenty of time between the makes, it would be perfectly easy to prepare 8 to 12 tons in the 24 hours with a small precipitator of the size named. The prepared water has a density of l⁄32nd, and may with safety be evaporated until its density is 5⁄32nds, the salts present not crystalizing out until a density of from 6⁄32nds to 7⁄32nds is reached.
In preparing sea water in the way proposed, every precaution must be taken to add slightly less of the precipitant than is necessary to entirely throw down the calcium and magnesium salts, as it is manifestly impossible in practice to guard against small quantities of sea water finding way into the boiler either from leaky condensers or else being fed in by the engineer during some emergency, and if under these conditions any excess of the precipitant were present in the boiler, a bulky precipitate would be thrown down and cause trouble, although it would not bind into a solid scale.
Briefly recapitulated the means which are best adapted for preventing the formation of the dangerous organic and oily deposits considered are:
I. Filtration of condensed water through a coke column.
II. Free use of the scum cocks.
III. The use of water of considerable density rather than of fresh water.
IV. The use of pure mineral oil lubricants in the smallest possible quantity.