A RAPID, SAFE, AND ECONOMICAL STEAM-GENERATOR.
It is an instructive study when we look back on the struggles of a great truth in reaching the light, to mark its tortuous and uneven path. When, however, the sight of the truth does flash upon the mind, we are startled at its nearness. The richest loads of ore crop out to the surface ; so that had we known of their existence, we had only to reach out our hand to gather up the riches. Such appears to be the case in reference to the process for generating steam. Ever since Watt made his "hay- stack" and "waggon-headed" boilers,—now obsolete,—engineers have been continually devising new methods of constructing boilers so as to generate steam more quickly, and at the same time to economize the fuel. The most improved Cornish single-flue boiler, which has accom-
plished so much, and all the intermediate boilers, down to the latest and best,—the multitubular boiler of the locomotive,—arc all alike de- fective, not only in their generating power, but in their liability to burst. Too much of their space is occupied by the water, without a corresponding extent of heating surface. In the locomotive boiler this evil is partially obviated by means of longitudinal tubes, which present a larger heating surface to the fire, and hence con- stitute a better generator of steam ; but the boiler is nevertheless equally liable to accident. Again, the safety valves of boilers in present use bear no proportion in area to the generating surface. It often happens that a boiler having 200 square feet of heating or generating surface, will have a safety-valve of only 10 or 12 square inches in area—a fruitful cause of accidents ; boilers often exploding whilst the safety-valve is blowing off! Boiler-plates, too, depend for their quality and strength mainly on a certain point in the original treatment of the metal composing them—on the capability of the puddler to keep the molten iron well agitated in the furnace. The mode employed in riveting boiler-plates together,—though the best hitherto devised,—is confessedly bad, from the fact that as the red hot rivet is hammered until it is cold, the iron becomes crystallized and weak, so that frequently the heads drop off. Mr. Fairbairn says that boilers are 50 per cent weaker in the riveted scam, than they are in the body of the plate, or than they would be if welded.
Steam boilers are not inaptly termed magazines of death. We our- selves once looked in the fireplace of a large boiler, and saw the red hot plates yawning—a moment more and fifty unfortunate men would have been hurled into eternity ; though in that instance the danger was averted by our warning. Other and serious objections are raised against the present construction of boilers. One is the immense quantity of fuel they require to keep up the steam, particularly in marine engines, where room and tonnage are objects of consideration. The large steamers on ocean voyages have as yet scarcely falsified the prophecy of Dr. Lardner, that steam navigation would not pay. Again, it has been found that the heat radiated from the large boilers of steam-ships in tropical climates is almost unbearable. Even on land, where space is less an object, how many are there who do not use steam apparatus, though they would gladly adopt it if the boiler could be dispensed with. Yet few attempts to dispense with the boiler have been made before Mr. Scott's successful effort.
Few are ignorant of the heating qualities of a worm in the fire. In most of the large houses the water for baths is heated by this process. No longer ago than August the 27th, we described in these pages Hay- den's "Patent Boiler" as being heated by a worm, by which means some forty gallons of water could be boiled in fifteen minutes.
Bearing in mind the fact of the greater heating surface of a pipe, and particularly of a worm, in comparison with the volume of water it con- tained, Mr. Scott cast about him for a solution to the question of how this worm could be made to supersede the boiler ? He looked into the face of Nature and saw the process of evaporation going on there. He saw how quickly the dew-drops are evaporated by the morning sun, or a mist dispelled by the action of the solar fire ; and noted that by the eva- porating effect of a drying atmosphere, how soon moisture is turned to drought. He watched the effects of the hot wind of the desert, and found that it parched, evaporated, dried up all moisture from everything con- taining it. He also saw that the denser the fluid, the longer it takes to evaporate. He saw and translated these phenomena of Nature, and per- ceived that to copy them was to adapt and appropriate the power and art of Nature herself. Mr. Scott at once understood that these natural laws of evaporation could be applied to the generation of a motive power, and that if it were properly applied, fuel might be saved, space economized, and explosions rendered next to impossible.
Mr. Scott's steam generator consists of lap-welded wrought-iron tubes, one-fourth of an inch thick, formed into a coil or helix—in general form like a sugar-loaf. The generator may consist of any number of coiled tubes one within the other, so as to occupy the whole space in the fur- nace. The plan increases the generating surface without increasing the space occupied by the machine, and at the same time it forms a generator of vast power. By using one coil the generating surface may be de- creased. Tubes of any diameter capable of being bent may be used ; for the coil possesses great strength iu the combination of its circular :Mr- faces ; and being spiral it is free to expand and contract within itself. As the generator has no joints or couplings, the tube being of one con- tinuous length, even to the extent of 200 feet, no leakage can take place. These coils will bear a pressure of 500 pounds to the square inch, with perfect safety. The safety-valve is of the same diameter as the tube or boiler, and does not present the disproportion to which we have alluded in other boilers.
In order to show more clearly the nature of the new generator, we will describe the size of one for a twelve-horse power engine, now in operation at the works of Mr. Finney, the engineer, of King Street, Poplar. A furnace is constructed of wrought-iron plates, about '2 t 6 inches to 3 feet in height and 4 feet in diameter ; partially into this furnace is put the base part of the coil or coils. The height of the coil is about 4 feet, and at the base it is a little smaller than the iron base or furnace ; on the top of the coil is fixed an iron tube about 3 feet 6 inches in height, and 14 inches in diameter. This small boiler is for the purpose of regulating the steam before it passes into the piston ; it is, like the tubes, made of welded iron, and is capable of standing a pressure of 500 pounds to the square inch. Surrounding the whole of this is a brick chimney, so that when you arc looking at the apparatus, sur- rounded as it is with brickwork, the appearance is that of a mere chim- ney to a boiler, whereas in this instance the whole is visible. An ordi- nary boiler for an engine of twelve-horse power would be 12 feet or more long, and from 4 to 5 feet in diameter. The space saved in the new construction is obvious, and its peculiar value for marine purposes is equally self-evident. The mode by which the steam is generated is this. 'Water is mixed with atmospheric air in the proportion of about 30 of air to one of water. The water is first heated to about 200 degrees by the exhaust steam from the engine or other means ; and the air is heated in tubes up to 400 or 500 degrees. Both air and water are then forced by their respective pumps through finely perforated discs of wire gauze ; they thus become intimately commingled, and they enter the coil in the form of mist or vapour—thus carrying out the operation of Nature. The coil has been previously heated, by means of the furnace, to a temperature varying from 800 to 1000 degrees Fahrenheit ; and thus steam is immediately formed of great elastic force.
Nor is this all : as the steam passes through each convolution of the coil, it becomes superheated, passing into the reservoir on the top before mentioned, which is also heated. If too much air is in the tubes, a little water can be admitted, which will prevent any injurious effect, such as the cutting of the valves, &c. These coils may be constructed so as to be inverted, or to be used in a horizontal manner; and in every instance room and fuel will be saved, and accidents prevented.
An engine moved by this means is worked at the rate of one shilling to three by the old method. Messrs. Finney informed us that the firm have sent one generator to Paris, another to Vienna, and they were then constructing one for Germany, besides several for home con- sumption.
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