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22 MARINE REVIEW. [May 2, FORM OF DOUBLE-TUBE BOILER. A NEW TYPE OF STEAM GENERATOR INTENDED FOR MERCANTILE MARINE SERVICE IS DESCRIBED AT THE RECENT MEETING OF THE INSTITUTION OF NAVAL ARCHITECTS IN LONDON. By Mr. John Irving, member of the Institution.* Within recent years many papers dealing with water tube boilers have been read before this institution, but I now propose to describe the construction and performance of a boiler differing very much from any hitherto brought under its notice, so far as I am aware. About six years ago Mr. K. D. Noble and myself began to study the water tube boiler very closely, with a view of trying whether we could not design a boiler suitable for the mercantile marine; a boiler that would combine the ad- vantages to be gained from a use of higher pressures than are possible Fig.1 DOUBLE TUBE BOILER EXPERIMENTAL FURNACE, 9 3 6 [ins.12 oO OTH PAI NATTA NNN TER BS .WA WATER STEAM LEAD OR WOODITE AND LEAD RING. LOWER ENO in a cylindrical boiler, and the economy of space in the ship, with sim- plicity of construction, and an accessibility of parts that would recom- mend it to more general adaptation than the forms of water tube boilers then in use. At the outset we determined to avoid all steel castings, bent tubes complicated fastenings, or difficult flangings. When the idea of having the tubes double with a thin annular body of water between them, heated on both sides, first suggested itself to us, we at once saw the importance of determining the question of the possibility of Overheating the outer tubes. For this purpose a small furnace was built, in which we set two tubes, 4 in. diameter outside and 3-16 in. thick, having a 3-in, tube passing through the center of each, leaving an annular space of 5-16 in. The arrangement of the whole apparatus is shown in figure 1. Having made arrangements for feeding and firing the apparatus, we deliberately set to work to burn the outer tube if possible. With a strong coke fire, and a blast taken from the works' plate furnace blower equal to between 11 in and 12 in. of water, we found the circulation rapid and complete, and *Paper read at the last annual meeting of th Architects in London. & e Institution of Naval while the heat of the furnace was so sreat as to melt the fire bricks of which it was composed, the outer tube showed no sign of overheating. TABLE 1.--FORCED DRAFT TRIALS OF DOUBLE-TUBE BOILER CONDUCTED DURING SUMMER OF 1897. July 16. August 3. Date of thigh wes ae July 7. July 13. Condition of boiler? .;. 2%. <ci.%. Not lagged Lagging on steam drum only Water evaporated per hour, lbs. 5540 3890 5837 6880 Temperature of feed water, deg. 59 62 60 65 Mean steam pressure above at- mosphere; lbs. so... 160 200 200 200 Coals Sed. eo ine aes Scotch Scotch Welsh and Welsh Scotch Coal burned per hour, lIbs...... 896 619 625 746 Water evaporated per pound of Coal, Actial' 2) acn hGce Mae ees 6.18 6.28 9.34 9.22 Water evaporated per pound of coal, from and at 212%.25 4. 7.48 1:6 11,33 Tt Coal burned per sq. ft. of grate per boar, lbs. se 71.75 47.5 48 51% Air pressure from fan, in inches of 'water... .0i. 2602... 215: 12 2.0 2.1 Smokebox temperature, deg.... 600 540 650 About 650 Graterateaicsd thi oes. wae 13 13 13 13 Total heating surface, sq. ft.... 820 820 820 820 Ratio of heating surface to grate area, 63 sq. ft. Spiral retarders were placed in all the inner tubes during these trials. TABLE 2,--COMPARISON OF DOUBLE TUBE WITH CYLINDRICAL AND OTHER BOILERS, ALL ARRANGED AS FOR THE SAME POWER IN THE SAME STEAMER. : : Cylindri- Double lL abcock & Type of Boiler. cal. Tube. Wilcox. Belleville. Number of boilers......... 2 6 6 10 Height or diameter........ 14-ft.6 in: As ft. Aine 13 tt.0 in 13:ft,.0 in: WAGES oe eee er, coe Sas 8 tt. 3 in. 13 ft. 0'in 8 ft. 6 in. WON E Dera Soke he bea 20 tt. -8 in; I ft: 6 in, 12 it. 0 in & ft. 0 in; Heating surface .....:..... 9,183 sq. ft. 12,060 sq. ft. 12,840 sq. ft. 13,380 sq. ft. Fireerate: area: occ s. 3. 300 sq. ft. 234 sq. ft. 286 sq. ft. 479 sq. ft. Working pressure ......... 160 sq. ft. 250 sq. ft. 250 sq. ft. 300 sq. ft. Mength Of bars). occ. o s 6 ft. 6 ft. Ae 6 ft. 3 in. Boiler room area at floor..1,065 sq. ft. 1,008 sq. ft. 1,035 sq. ft. 1,334 sq. ft. Boiler room area at main : : GOO a Be ag 384 sq. ft. 276 sq. ft. 332 sq. ft. 468 sq. ft. Heating surface per sq. ft. of boiler room area...... S154-8q. ft; dS sqe tt. 12.4 sq. ft: 10 sq. ft. Total weight--boilers, up- take, and funnel......... 174 tons 156 tons 130 tons 186 tons Total weight--water ...... 84 tons 12 tors 17 tons 14.5 tons Total of boilers and water 258 tons 168 tons 147 tons 200.5 tons AP Pressure c.. aac oes Lin, 1 in. 1% in. Nil, Some time after this, when a new boiler was required for Messrs. William Denny & Bros.' joiner shop engine, electric lighting and other purposes, it was agreed to give our boiler a trial. We at once set to work and designed the boiler shown in fig. 2. As this boiler was always regarded as an experimental one, its details were in some parts more elaborate and capable of variation than would be the case in one con- structed on purely commercial lines. The outer tubes are 4 in. outside diameter and % in. thick. They are swelled at one end and screwed into both inner tube plates, and secured with jam nuts exactly like the ordi- nary stay tubes in a cylindrical boiler. The inner tubes are 234 in. out- side diameter, and pass through stuffing boxes in both outer tube plates. There are no inner tubes in the lowest row. The annular water space is 3% in. wide. The front water box is directly connected to the steam drum at its upper end. The lower end of this drum is formed into a box from which the down-comer tubes are led into the mud drum. This boiler being the first of its kind, it was thought advisable to provide a mud drum at the lowest part of the circtlation, and so arranged that all the water would pass through it. The total area through the down-comer tubes was made specially large in order that circulation throughout the entire boiler should be as free as possible, and that, for experimental purposes, this area could be varied. The small Galloway tube connecting the top of the lower water box with the steam drum is for permitting the escape into the drum of any steam which might form in the top of lower water box. All the flanging and riveting is quite within the daily ex- perience of boiler makers. The water boxes are stayed across with or- dinary screwed fire box stays, and with the exception of the stuffing boxes for the inner tubes, which were an engineer's job, the entire con- struction was carried out by the foreman boiler maker with his ordinary shop hands. Pressure of other work delayed the completion of the boiler for some time, but it was finally finished and passed the hydraulic test of 400 Ibs. in 'March, 1897. It was then decided that before being placed in position the boiler should be subjected to a series of the most exacting trials we could devise and carry out. For this purpose it was placed on the edge of the River Leven, removed as far as possible from all buildings. Tanks for measur- ing the feed water were connected to the feed pump, an excessively large fan was connected to the furnace, and we carried out the trials, the results of which will be found in table 1. The boiler was under steam for the greater part of each of the days noted as well as on many other days, when steam was got up for the purpose of making special observations. The feed water generally in use was the town's gravitation supply, but special trials were made, feeding with the river water, to see if any deposit was left in the annular tube space. No grit, sand or rust has ever been found there; the little we did discover was found mostly in the bottom of the lower water box and in the mud drum. The circulation in the tubes seems to be too rapid and complete for the deposit of any impurity. On one occasion we had ocular demonstration of the thoroughness of the circulation by getting up steam with the manhole door removed from the back end of the steam drum. As soon as the water began to get warm it could be seen flowing in a full and constant stream from the upper to the lower end of the drum. The boiler standing quite in the open air and only partially lagged, was very far from being in the most favorable working condition. Much better results would have been achieved had it been placed in a closed stoke hold, or formed one of a number of boilers arranged in battery. The results shown on the table speak for themselves and at present need not be further alluded to. Although provision was made for the difference of expansion between the outer and inner tubes, we have never been able to detect any. The fact that the hotter tube of the two is somewhat shorter than the other leads us to think that the difference is fairly compensated for in this way. The stuffing boxes form a convenient arrangement for withdrawing