Part 7 (1/2)
Further, the circulation results directly fron of the boiler and requires no assistance from ”retarders”, check valves and the like, within the boiler All such mechanical devices in the interior of a boiler serve only to con and should not be used
This positive and efficient circulation assures that all portions of the pressure parts of the Babcock & Wilcox boiler will be at approxi from unequal tehout the boiler is at the temperature of the steam contained, a condition to be secured only by proper circulation, danger fro is minimized, or at least limited only to effects of the water fed the boiler Where the water in any portion of the boiler is lower than the te to the pressure carried, whether the fact that such lower temperatures exist as a result of lack of circulation, or because of intentional design, internal pitting or corrosion will almost invariably result
Dr Thurston has already been quoted to the effect that the admitted safety of a water-tube boiler is the result of the division of its contents into s construction, while the danger froely lier, however, that such legs may explode due to the deterioration of their stays, and such an explosion ht be almost as disastrous as that of a shell boiler The headers in a Babcock & Wilcox boiler are practically free froer of explosion Were such an explosion to occur, it would still be localized to aboiler and the header construction thus aler from such a cause
Staybolts are admittedly an undesirable element of construction in any boiler They are wholly objectionable and the only reason for the presence of staybolts in a boiler is to enable a cheaper form of construction to be used than if they were elin flat-stayed surfaces, or staybolt construction under pressure, corrosion and wear and tear in service tends to weaken so an increased strain on other parts greatly in excess of that for which an allowance can be made by any reasonable factor of safety Where the construction is such that the weakening of a single part will produce a marked decrease in the safety and reliability of the whole, it follows of necessity, that there will be a corresponding decrease in the working pressure whichboilers, the use of such flat-stayed surfaces under pressure presents difficulties that are practically unsurmountable Such surfaces exposed to the heat of the fire are subject to unequal expansion, distortion, leakage and corrosion, or in general, to ainst the fire-tube boilers in the consideration of water-tube boilers as a class in comparison with fire-tube boilers
[Illustration: McAlpin Hotel, New York City, Operating 2360 Horse Power of Babcock & Wilcox Boilers]
Aside from the difficulties that may arise in actual service due to the failure of staybolts, or in general, due to the use of flat-stayed surfaces, constructional features are encountered in the actual manufacture of such boilers that make it difficult if not impossible to produce a first-classof such a boiler to so design and place the staybolts that all will be under equal strain Such unequal strains, resulting froreatly multiplied when such a boiler is placed in service Much of the riveting in boilers of this design must of necessity be hand work, which is never the equal ofconstruction ordinarily requires the flanging of large plates, which is difficult, and because of the nu of theof such plates
In vertical or se flat-stayed surfaces under pressure, these surfaces are ordinarily so located as to offer a convenient lodging place for flue dust, which fuses into a hard mass, is difficult of re on with no possibility of detection
Where stayed surfaces or water legs are features in the design of a water-tube boiler, the factor of safety of such parts must be most carefully considered In such parts too, is the determination of the factor most difficult, and because of the ”rule-of-thumb” determination frequently necessary, the factor of safety beconorance As opposed to such indeterminate factors of safety, in the Babcock & Wilcox boiler, when the factor of safety for the drum or drums has been determined, and such a factor may be determined accurately, the factors for all other portions of the pressure parts are greatly in excess of that of the drum All Babcock & Wilcox boilers are built with a factor of safety of at least five, and inasreatly in excess of this figure, it applies specifically to the druree of safety than a considerably higher factor applied to a boiler in which the shell or any riveted portion is acted upon directly by the fire, or the sa flat-stayed surface construction, where the accurate deter factor of safety is difficult, if not impossible
That the factor of safety of stayed surfaces is questionable may perhaps be best realized from a consideration of the severe requireulations of the Board of Supervising Inspectors, U S Government
In view of the above, the absence of any stayed surfaces in the Babcock & Wilcox boiler is obviously a distinguishi+ng advantage where safety is a factor It is of interest to note, in the article on the evolution of the Babcock & Wilcox boiler, that staybolt construction was used in several designs, found unsatisfactory and unsafe, and discarded
Another feature in the design of the Babcock & Wilcox boiler tending toward added safety is its manner of suspension This has been indicated in the previous chapter and is of such nature that all of the pressure parts are free to expand or contract under variations of te with any part of the boiler setting The sectional nature of the boiler allows a flexibility under varying tees that practically obviates internal strain
In boilers utilizing water-leg construction, on the other hand, the construction is rigid, giving rise to serious internal strains and the method of support ordinarily n is not only unerous, due to the fact that proper provision is not made for expansion and contraction under te construction are not ordinarily provided with mud drums This is a serious defect in that it allows impurities and sediment to collect in a portion of the boiler not easily inspected, and corrosion may result
Economy--That the water-tube boiler as a class lends itself more readily than does the fire-tube boiler to a variation in the relation of grate surface, heating surface and coain, the construction made possible by the use of headers in Babcock & Wilcox boilers appears as a distinct advantage
Because of this construction, there is a flexibility possible, in an unlihts and widths that will satisfactorily meet the special requirements of the fuel to be burned in individual cases
An extended experience in the design of furnaces best suited for a wide variety of fuels has made The Babcock & Wilcox Co leaders in the field of economy Furnaces have been built and are in successful operation for burning anthracite and bituas-house tar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blast furnace gas, by-product coke oven gas and for the utilization of waste heat froreat number of Babcock & Wilcox boilers now in satisfactory operation under such a wide range of fuel conditions constitutes an unimpeachable testimonial to the ability to meet all of the many conditions of service
The li econoreater draft area is possible in water-tube boilers does not of necessity indicate that proper advantage of this fact is taken in all boilers of the water-tube class In the Babcock & Wilcox boiler, the large draft area taken in connection with the effective baffling allows the gases to be brought into inti surfaces and renders such surfaces highly efficient
In certain designs of water-tube boilers the baffling is such as to render ineffective certain portions of the heating surface, due to the tendency of soot and dirt to collect on or behind baffles, in this way causing the interposition of a layer of non-conductingsurfaces
In Babcock & Wilcox boilers the standard baffle arrangement is such as to allow the installation of a superheater without in any way altering the path of the gases fron In certain water-tube boilers the baffle arrangement is such that if a superheater is to be installed a con is necessary Frequently to insure sufficiently hot gas striking the heating surfaces, a portion is by-passed directly fro over any of the boiler heating surfaces Any such arrangement will lead to a decrease in econo it should be avoided
Capacity--Babcock & Wilcox boilers are run successfully in every-day practice at higher ratings than any other boilers in practical service
The capacities thus obtainable are due directly to the efficient circulation already pointed out Inas headers has a direct bearing in producing such circulation, it is also connected with the high capacities obtainable with this apparatus
Where intelligently handled and kept properly cleaned, Babcock & Wilcox boilers are operated in many plants at from 200 to 225 per cent of their rated evaporative capacity and it is not unusual for the periods of peak load
Dry Steam--In the list of the requirements of the perfect steaenerated has been pointed out The Babcock & Wilcox boiler will deliver dry steaher capacities and poorer conditions of feed water than any other boiler now manufactured Certain boilers will, when operated at ordinary ratings, handle poor feed water and deliver steam in which the moisture content is not objectionable When these sah overloads, there will be a direct tendency to prie of h This tendency is the result of the lack of proper circulation and once e of the headers of the Babcock & Wilcox boiler, resulting as it does in the securing of a positive circulation
In the design of the Babcock & Wilcox boiler sufficient space is provided between the stea point to insure the stea or again picking up any particles of water in its passage even at high rates of evaporation Aiven for a co surface before the steam is carried from the boiler These two features, which are additional causes for the ability of the Babcock & Wilcox boiler to deliver dry stea of the steam and water space of the boiler From the history of the development of the boiler, it is evident that the cubical capacity per horse power of the steam and water space has been adopted after numerous experienerally understood function of such device has been pointed out As stated, the function of the ”dry pipe” in a Babcock & Wilcox boiler is si pipe and this stateardless of the rate of operation of the boiler