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32 3 THE Marine REVIEW A NEW TYPE OF MARINE FIRE-TUBE BOILER. The Engineer of London has published the following article and drawings from Colonel G. Scialpi, of the Italian royal navy (naval architects' branch), at present stationed at Leg- horn: It is well known how the fire tube boiler, both in its Scotch and locomotive shape, fell out of favor when it proved un- suitable to the increased needs of modern warships. These needs required an increase in the power of machinery, and with this object forced draft was tried with disastrous results. -- The marine fire tube boiler has since its appearance | been characterized by a defective design and performance, which refer chiefly to the circulation, to the short run of gases, and, as to the Scotch type, to the size of furnace. Notwithstanding these defects, which are, however, very im- portant from a tactical or economical point of view, the fire tube boiler lasted for years, and the necessity of its substitution was only felt when it could no longer answer the new exigencies. The water tube boiler, which took the place of the fire tube boiler, on the other hand, was not new as to the principle of its construc- tion. Why, we might ask, was it not found natural to shorten the way to the introduction of the water tube boiler, so advantageous as it appeared for its lightness, compactness, and greater security, without awaiting the final failure of the tank boiler? The answer is not possible unless it be admitted that some features existed in the tank boiler not to be found in the new one, and which could not be given up without profound consideration. These features consist in the composition and the distribution of the heating surface, the weaker part of which--the tubes--is not exposed to causes of failure peculiar to the water tube boiler, and in which the repairing of a tube failure is easier, and does not necessarily entail throwing the boiler out of work. The boiler illustrated is intended to retain the advantages of the tank boiler without its disadvantages. The committee appointed by the admiralty in 1900 to con- sider certain questions respecting modern types of boiler for naval purposes formulated as follows* the three principal requirements of marine boiler from a tactical point of view.--(1) Rapidity of raising steam and of increasing the "number of boilers at work; (2) reduction to a minimum of danger to the ship from damage to boilers from shot or shell; (3) possibility of removing damaged boilers, and replacing them by new boilers in a very short time, and without opening up the decks or removing the fixtures of the hull. The first is very important, but it must not be estimated beyond its proper value, which should not be exaggerated, as M. Bertin says. The time required for starting the engines is shortened by the rapidity with which the boiler gets under steam, only because this rapidity admits of.anticipating the heating of the engines, which operation takes several hours, according to the size of the machinery. The technical con- dition necessary to satisfy this first item is the activity of the circulation of the water. As to the security requirement, it must be taken in a relative sense. "On land, and in the neighborhood--not immediate--of the boiler," as M. Bertin says, "the water tube boiler gives an incontestable and full security; the effect of an explosion does not extend very far. But on board ship one can no longer speak of security after the disaster of the Sarrazin and of the Jaureguiberry." A condition that must be satisfied for this requirement consists in reducing the quantity of water; but an exaggera- tion in the reduction of the water leads to' an extreme sensibility of the boiler to the variations in the running of the engines and in the managing of the fires. The third condi- tion imposes either the adoption of small sized boilers which | *The Engineer, March 15, 1901, page 275. condition agrees with the preceding one, or of a boiler which could be taken to pieces of a size that can pass through the hatchways. ee oe Ae If to these requirements, to which the ordinary tank boiler does not answer, be added the principal defects of the same boiler, especially of the Scotch type, namely: (4) Deficiently proportioned furnace room; (5) shortness of the run of the flame and the hot gases; (6) unfitness for forced draft; we have before us the essential conditions to be satisfied in a design of a maritime fire tube boiler more properly intended for warship purposes. The preceding considerations induced me to _ design and construct a type of fire tube boiler--illustrated by Figs. 1 and 2--which may be called a "marine boiler with tubular heaters." This boiler is composed of the fol- lowing principal parts:--(1) The furnace compartment, or lower vessel. The furnace is of a box shape without bottom, the sides are inclined to the vertical line, the crown is of cylindrical form, the height above the grate is liberally designed as to the length of the grate. To the back plate of the furnace a tubular ring is attached, which constitutes a lengthening of the direct heating surface, and concurs in giving a good development to the flames beyond the bridge before they reach the combustion chamber. A box, wholly similar to the furnace case, constitutes the shell of the furnace compartment. Between the furnace case and the shell there is contained a water space. (2) Several tubular heaters-- four according to the drawing--placed in two vertical rows above the furnace compartment, which are, like the latter, in- clined to a horizontal plane. These heaters are cylindrical vessels of steel plate full of water, between the ends of which fire tubes extend, fitted as in tank boilers. The external sur- face of the heaters and the interior of the fire tubes are lapped by the flue gases. (3) An upper vessel, or steam chamber, which contains water in its bottom and the lower part of which is, like the superior heaters, lapped by the hot gases. (4) Circulation tubes, which are nearly vertically situated at both ends of the upper vessel, and set up communication be- tween this vessel and the lower ones. There are two sets of these tubes, viz., the back and the front ones. The former act as return tubes, and extend from the bottom of the upper vessel to the bottoms of the other vessels. The latter start from the top of these lower vessels and carry into the super- ior vessel the mixture of steam and water. (5) The casing, which constitutes also the walls of the combustion chamber and of the smoke box, covered with either fire-bricks or non- conducting material, according to the temperature of the flue gases which come in contact with it. A diaphragm is placed in the casing between the lower and the upper heaters, which forces the gases to turn twice before they reach the base of the funnel. The boiler I have described is, I may say, an elementary one; but it is to be understood that beyond a certain grate area it is convenient that the boiler should be made up of two such elements having the water spaces and smoke boxes in common, as shown in Figs 3 and 4. The principal data of the first boiler are the following: PleAm piessite (fs ee 200 lb. Durect heating: suriace. 4.6 6 cei cic. uo Pe 74.0 sq. ft. Heating surface of the heaters and of the Upler vessel ce ee a 2646 * Voi Heatme suttace. 3 ee Aa85. rete ater fe ee ee 14.730 Water space oo oa ee ee: bes 60.3 cu. ft. Pieaml s09Ces 1 kee as 8° Weight of boiler, excluding uptakes and Dee i ee ee: 4.134 tons Weight of the fittings, brickwork, and grate Ware ey ee ne ree 2203" otal weight.of empty boiler... 2... 00... Gia07, Total weight of boiler with water at normal el ee 5.007 And the principal data of the second one are: Piro Presse <2). ee 200 lb. Piteet Weatmie suttaee... ok oe 172.5 sq. ft.