Part of the Acorn Archive
Hearts of Oak
Distillation of Seawater, on Ship
DISTILLATION OF WATER FROM THE SEA.
"In Dr. Normandy's apparatus the combustion of one pound of coal yields from 14 to 20 pounds of potable water. The apparatus is extensively adopted in the British Navy, the Cunard Line, and many other important emigrant and merchantile lines"
A pennyworth of coal (4 lbs) should yield between 7 and 10 gallons of drinkable water.
From The Scientific American June 6th 1885
THE DISTILLATION OF SEA WATER.
In a general sense, fresh water is obtained from sea water by simply generating steam from the sea water, passing the said steam through a surface condenser, and filtering the resulting water. The obtaining of fresh water in this way has been in practice on board sea-going ships for many years.
It is supposed by some authorities on this subject that the first time fresh water was thus obtained at sea was by an old captain of a brig which ran short of water, and he cut up some pewter dishes into strips, which he bent and soldered into a pipe. He, with the carpenter's aid, fitted a wooden lid in one of the cooking boilers, and fixed one end of his pipe in it. He next sawed a water cask in half, bored a hole in the bottom of one half, and took his pipe through it, filling the space round the pipe with sea water. Thus he extemporized a worm and still or condenser. The distilled water, however, was scarcely drinkable. Not to be beaten, however, the captain got some pieces of charred wood which he put in the water, which so far improved it as to render it at all events fit to sustain life, and our skipper brought his brig and her crew safely to port. What suggested the use of charcoal to his mind history does not tell.
For many years past, scarce any sea-going vessel leaves port that is not fitted with a properly constructed distiller; and one conspicuous advantage attending this practice is that each ship thus fitted to the satisfaction of the Board of Trade inspector is allowed to sail with only half the quantity of fresh water on board which she should have if not provided with a distiller.
The distiller and filter occupy very much less space than that which would be occupied by the casks or tanks of water otherwise required to be carried.
Sea water distillers are usually fitted in connection with the winch and its boiler, which latter supplies the steam both for distillation and to drive the engine working its circulating pump. Smaller distillers are worked without a pump, the cooling water merely passing through by gravitation. These smaller affairs again are of two kinds, the one being mounted at one end of the cooking hearth, a two oven hearth with distiller at one end, a supply pipe to admit air to aerate the water; a cock where fresh water is drawn off; a pipe conveying cooling water to the condenser, placed on three little feet on top of the boiler, whose steam rises up a central pipe to the dome top, where it expands out and returns downward through a number of tubes about 1 inch diameter, in which it is condensed, collected in a bottom chamber, and drawn off through the cock. A distiller of this size would make about thirty gallons of fresh water per day. Very frequently a distiller is mounted separately, and placed near the winch or donkey boiler, which supplies it with steam, the lower part being then used as a filter. The diameter is from 15 inches to 18 inches the outer casing being either iron or copper.
Another form of distiller is one like the above, but larger, and having a small donkey engine and circulating pump attached thereto. As a rule these distillers are vertical, but larger apparatus are arranged horizontally.
To give ourreaders some general idea of size, weight, and produce of water, we may say that a plain cylindrical distiller, mounted on a square filter case,measuring 3ft 9ins high, weighing 4½ cwt, will distill twelve gallons per hour. A larger size, measuring 6ft 2ins high, and weighing about 23 cwt, will give 85 gallons; while a still larger one, measuring 7 ft.high and weighing 32 cwt., yields 150 gallons. These have no pumps. When an engine and pump are fitted, the weight is increased from about 80% in the smaller to 50% in the larger sizes.
An immense advantage attends the use of those distillers that are combined with a winch boiler. Of course, the chief use of the winch is while in dock;some use is made of it at sea to do heavy pulling and hauling, to wash decks, and in case of emergency the circulating pump is used as a fire engine. Were it not, however, for the distiller, the winch boiler would simply be idle lumber at sea. The distiller, however, finds useful employment for it, and has also this excellent effect, that as steam is pretty constantly kept up for the distiller, in the evil event of a fire the boiler is ready to work at once. In horizontal types of distiller an engine and pump are mounted on a cast iron casing as a bed, and in this casing is placed a number of tubes through which the steam passes to be condensed, the whole being simply a surface condenser with engine and pump above.
Another type is that of a small single-flued horizontal boiler with combustion chamber and twenty or thirty return tubes, in fact, the present high-pressure marine boiler on a small scale. A boilerof this sort, measuring 4ft to 5ft long, 3ft 9ins to 4ft 6ins diameter, would have a horizontal donkey engine on a bed at its side, and at the end of the engine a vertical cylindrical condenser.
Few have done more, perhaps none so much, as Dr. Normandy to make seawater distillation not only a success as a source of water supply, but also to supply it at a minimum cost for fuel. He by a peculiar arrangement of pipes embodied something of the regenerative system in his apparatus, using the heat taken from one lot of steam to generate more, and again the heat from this he used over again. The defect of his older arrangements was undue complexity and consequent trouble to keep inorder.
One of these full-powered steamers will indicate, say, 5,000 horse-power, and assuming her engines to use 25lb of steam per indicated horse-power, or 2¼ gallons, she could distill some 12,000 gallons of water per hour. As no appreciable pressure of steam need be maintained, the boilers would suffer little from deposit, especially if regularly blown out. Hard firing need not be resorted to; indeed, it would be injudicious, as, of course, priming must be carefully guarded against.
Of course, the saltwater distilled will affect the working, not exactly of the distillers, but of the boilers. If the water in the harbor, as is not improbable, is muddy, some method of filtering it before pumping it into the boilers ought, if at all practicable, to be resorted to, for the twofold reason of preserving the boiler plates from muddy deposit, and also to prevent priming, which would certainly ensue from the use of muddy water.
No doubt the medical staff take care that the distilled water is alike thoroughly aerated and efficiently filtered. The most successful method of aerating is, we believe, to cause the current of steam as it enters the condenser to suck in air by induced current along with it. The filtering ought not to present any difficulty, as at all events sand enough can be had. Charcoal, however, is another affair, and all distilled water ought to be brought into contact with this substance.