Marine boiler

“ No braces or stays employed in the construction of marine boilers shall be allowed a greater strain than six thousand pounds per square inch of section, and no screw stay bolt shall be allowed to be used in the construction of marine boilers in which salt water is used to generate steam, unless said stay bolt is protected by a socket. But such screw stay bolts, without sockets, may be used in staying the fire boxes and furnaces of such boiler, and not elsewhere, when fresh water is used for generating steam in said boiler. Water used from a surface condenser shall be deemed fresh water. ”

“ We enter the stokehold through air-locks, closing one door before we can open the other, and find ourselves among sweating, grimy men, stripped to [Pg 274] the waist. As though life itself depended upon it they shovel coal into the rapacious maws of furnaces glowing with a dazzling glare under the “forced-draught” sent down into the hold by the fans whirling overhead. The ignited furnace gases on their way to the outer air surrender a portion of their heat to the water from which they are separated by a skin of steel. Two kinds of marine boiler are used—the fire-tube and the water-tube. ”

“ A.--Yes, in marine boilers this is a constant source of danger, which is only to be met by attention on the part of the engineer. If the water in the boiler be suffered to become too salt, an incrustation of salt will take place on the furnaces, which may cause them to become red hot, and they may then be collapsed even by their own weight aided by a moderate pressure of steam. ”

“ The fittings to a marine boiler are—funnel and air casings, up-takes and air casings, smoke boxes and doors, fire doors, bars, bridges, and bearers, main steam stop valve, donkey valve, safety valves and drain pipes, main and donkey feed check valves, blow-off and scum cocks, water gauge glasses on front and back of boiler, test water cock for trying density of water, steam cock for whistle, and another for winches on deck. ”

“ The marine boiler of to-day is in all its main features the same as it was ten years ago. The single-ended boiler, made with two, three, and sometimes four furnaces, is the simplest form, and for all powers under 500 indicated horse power is the most generally adopted. The double-ended form is largely used. It has been found more economically efficient than the single-ended form, by as much as ten per cent, in the writer's own experience. ”

“ In 1840 the average pressure used in marine boilers was only 7 or 8 lbs. to the square inch, the steam being made with the two-flue pattern of boiler, sea water being used for feed; as the steam pressure increased as now to 150 to 200 lbs. to the square inch, greater and greater difficulty was experienced from salt incrustation—in many cases the tubes did not last long and frequently gave much trouble, until the introduction of the surface condenser, which supplied fresh water to the boilers. ”

“ But in modern boiler shops little hand work is ever done; instead, plates 4 ft., 6 ft., or 8 ft. in diameter, and fire-box plates for locomotive boilers, have their entire flanges bent at a single squeeze between massive dies in a hydraulic press. In the case of the ends of marine boilers which are too large for such treatment, a special form of press bends the edges over in successive heats. The flanges of Adamson seams are rolled over in a special machine. A length of flue is rotated on a table, while the flange is turned over within a minute between revolving rollers. ”

“ Circulation in the outer sets of tubes is arranged for by outer circulating pipes of large diameter connecting the steam- and water-chambers. For the middle water-chamber several nearly vertical down-comers are provided in the centre of the boiler. Boilers of this type are extensively used in the British and German navies.
Material of Boilers.—In ordinary land boilers and in marine boilers of all types the plates and stays are almost invariably made of mild steel. For the shell plates and for long stays, a quality having a tensile strength ranging from 28 to 32 tons per sq. ”

“ It is evident that it must be a matter of considerable importance to reduce the space occupied by the machinery on board a vessel to the least possible dimensions. The marine boilers, therefore, are constructed so as to yield the necessary quantity of steam with the smallest practical dimensions. With this view a much more extensive surface in proportion to the size of the boiler is exposed to the action of the fire. ”

“ The Scotch Marine type of boiler used on steam ships, has slightly more grate area and slightly less heating surface than the locomotive type of boiler, because the rate of combustion is lower. Stationary water-tube boilers may have 2 to 3 times as much grate area and heating surface per 150horse-power as is found in locomotive boilers. If a poor type of fuel is to be used the area of the grate should be increased about inversely as the heat content of the fuel. ”

“ If the impurity is chemically suspended in the water, some one of the many substances which form the refuse from various manufactures, and which may contain suitable ingredients, should be used to counteract the effect of the impurity. Common soda will answer the purpose perhaps better than anything else. It must not be forgotten however that the blow-off apparatus must afterwards be used more frequently, to rid the boiler of the foreign matter, or the mischief will be increased. In marine boilers, constant attention is necessary to get rid of the saline deposit ”

“ No further great improvement in the boiler has taken place. The water-tube boiler is still in an experimental stage, and attention is now being directed to oil fuel, which will reduce the engine-room staff, ensure greater cleanliness and quicker despatch.
The result of these improvements in marine engines and boilers has been to reduce the consumption of coal from 4 lbs. per indicated horse-power to 1.4 lbs., which cannot be considered otherwise than a great achievement. ”

“ As there have come into use marine boilers made of steel and capable of standing a very high pressure, the low-pressure boilers of former days have become useless. With the advent of triple expansion cylinders, twin screws, and better and larger hulls, ships of the old type lost their value ”

“ These last in stationary boilers usually consist of valves kept in their seats against the steam-pressure in the boiler by levers carrying weights, but in marine and locomotive boilers the valves are kept closed by means of steel springs. One at least of the safety-valves is fitted with easing gear by which it can be lifted at any time for blowing off the steam. Blow-out cocks are fitted for emptying the boiler.
Openings must always be made in boilers for access for cleaning and examination. When these are large enough to allow a man to enter the boiler they are termed man-holes. ”

“ Nevertheless, marine boilers seldom last more than for 5 or 6 years, whereas land boilers made of the same quality of iron often last 18 or 20 years, and it does not appear probable that land boilers would last a very much shorter time if salt water were used in them. ”

“ Now since land boilers will consume 15 pounds, and marine boilers 10 pounds, per hour per horse-power, it follows that the spaces between the grate-bars, and the extent of grate surface, must be sufficient to allow 3000 cubic feet of air per hour in land boilers, and 2000 cubic feet in marine boilers, to pass through them for each horse-power, or, what is the same, for each foot of water converted into steam per hour. ”

“ The heads of two of the boilers are to be seen on the left of the view. They are called the starboard and larboard boilers—those words meaning right and left. That is, the one on the right to a person standing before them in the engine room, and facing them, is the starboard, and the other the larboard boiler. It is the larboard boiler which is nearest the spectator in the engraving.
The boilers, the heads of which only are seen in the engraving, are enormous in magnitude and capacity, extending as they do far forward into the hold of the ship. ”

“ The boilers are upright cylinders, about 5 feet in diameter and 16 feet high, with semi-spherical ends, provided inside with straight perforated diaphragms, between which the chips from one cord of wood are confined. A solution of caustic soda, at 12° B., is introduced with the chips, and fires are started in a furnace underneath. At other works the boilers are heated by steam circulating through a jacket which covers the bottom and sides of the boiler. ”

“ As the fuel supply of a vessel cannot easily be replenished on the high seas, economy in coal consumption is very desirable.
If you put a cold spoon into a boiling saucepan ebullition is checked at once, though only for a moment, while the spoon takes in the temperature of the water. Similarly, if cold water be fed into a boiler the steam pressure at once falls. Therefore the hotter the feed water is the better.
The feed heater is the reverse of the condenser. In the latter, cold water is used to cool hot steam; in the former, hot steam to heat cold water. There are many patterns of heaters. ”

“ Water is so weighty that a ship cannot carry more than a very limited quantity, and that for the immediate needs of her passengers. The boilers, in spite of their condensers, waste a good deal of steam at safety valves through leaking joints and packings, and in other ways. This loss must be made good, for, as already remarked, salt water spells the speedy ruin of any boiler it enters.
The distiller in its simplest form combines a boiler for changing water into vapour, with a condenser for reconverting it to liquid. ”

“ Smudges of dirt are not uncommon on a man’s face and hands, perhaps, but the begrimed Vulcans of the coal-burning ships have no counterpart on the oil burners, and the coal dust and the dingy stokehold is a far cry.
The Majestic’s boilers do not depend upon natural draft, but a set of four powerful fans draws the warm air from the turbine rooms through two great air shafts about seven feet in diameter and forces it under pressure beneath the boilers. These great air shafts total 1,000 feet in length, and a part of the air they supply is led to each boiler. ”

“ In steam-ships, where salt water is used for generating the steam, the incrustation on the sides of the boilers becomes a serious annoyance. It obstructs the communication of heat from the furnace to the water, and the metal is thus liable to become red-hot. Numerous plans have been adopted for the purpose of preventing the accumulation of salt on the sides of the boiler, the most common of which is to allow the water, when saturated with saline matter, to escape, and then to fill the boiler afresh. ”

“ Empty space is left in the tank above the fat and water at the outset sufficient to allow boiling, which space of course would be filled with steam and air. Heat is communicated to the mixture by introducing steam from the large iron boiler into the copper tank, creating a temperature causing a pressure of one hundred and fifty pounds to the square inch. ”

“ A pipe C is used for heating the liquor by means of waste steam at the commencement of the operation. The grass is fed into the boiler at the opening D. At E E are gauges for showing the height of the liquor in the boiler, F F F are pipes for the supply of steam, strong ley, and water, and the door G is for the discharge of the boiled grass. Each boiler is capable of holding 3 tons of esparto, and the boiling is completed in about two and a half hours, at [46] a pressure of from 35 to 40 lbs. per square inch. It is said that the boiler effects a saving both in time and the amount of soda used. ”

“ Express boiler is a term applied to rapid steaming small-tube boilers, capable of large power on small weight and using heavy forced draught. This type is rather less economical and is chiefly used for very fast vessels such as torpedo boats. ”

“ The quality sought in boiler construction is that the heating surface should be very large in proportion to the quantity of water to be heated. Special coal, anthracite or Welsh, is used in the navy on account of its great heating power and freedom from smoke; experiments have also been made with crude petroleum, or liquid fuel, which can be more quickly put on board than coal, requires the services of fewer stokers, and may be stored in odd corners unavailable as coal bunkers. ”

“ It should also be remembered that a certain amount of water is always formed by condensation in all boilers in which live steam is used. On the other hand, if too little water be added, the rags are liable to become “burned” and the fibre therefore weakened. During the operation the boiler should be made to revolve slowly, in order to produce thorough circulation of the liquor.
The boiling being completed, the pressure is allowed to fall, either by cooling or by blowing off from a cock usually provided for that purpose, and the liquor allowed to collect at the bottom of the boiler. ”

“ When steam is being raised, the super heater is flooded with water, which is drained out through a blow-off pipe before communication is opened with the steam-pipe. In large boilers of this type, two steam-chests are placed side by side connected together by two cross steam pipes and by the mud drum. Each, however, has its own separate feed supply. The largest boiler made has two steam chests 41/2 ft. diameter by 251/2 ft. long a grate surface of 85 sq. ft., and a total heating surface of 6182 sq. ”

“ A hard scale is equivalent to thickening the plate; and although this is sufficiently mischievous, the injury to the plates is much more rapid when a thicker but spongy deposit entirely prevents contact of the water and impedes the transmission of the heat. An attempt to illustrate this is given in Fig. 58, which is an enlarged view of a portion of such a boiler as is shown in Fig. 37. Pg 87 The money spent in boiler compositions would be better applied in securing a supply of proper water, or in filtering and purifying the water before it enters the boiler. ”