Part 40 (1/2)

The aenerated is determined from the steam consumption of the prime movers It has already been indicated that such consumption can vary over wide limits with the size and type of the apparatus used, but fortunately all types have been so tested that manufacturers are enabled to state within very close liiven set of conditions It is obvious that conditions of operation will have a bearing on the steam consumption that is as important as the type and size of the apparatus itself This being the case, any tabular inforiven on such steam consumption, unless it be extended to an impracticable size, is only of use for the ures on this consumption should in all cases be obtained from the manufacturer of the apparatus to be used for the conditions under which it will operate

To the steam consumption of the main priain it is impossible to make a definite state wholly upon the type and the number of such auxiliaries For approximate work, it is perhaps best to allow 15 or 20 per cent of the steaines, for that of auxiliaries Whatever figure is used should be taken high enough to be on the conservative side

When any such figures are based on the actual weight of steaives the actual evaporation for various pressures and te to one boiler horse power (345 pounds of water per hour frorees), may be of service

With the steam requirements known, the next step is the determination of the number and size of boiler units to be installed This is directly affected by the capacity at which a consideration of the econo conditions which will exist The other factors entering into such determination are the size of the plant and the character of the feed water

The size of the plant has its bearing on the question froeneral obtained froe units, that labor cost decreases with the nue than for seneral decrease in the coeneral the cost per horse power of any design of boiler decreases with the size of units To illustrate this, it is only necessary to consider a plant of, say, 10,000 boiler horse power, consisting of 40-250 horse-power units or 17-600 horse-power units

The feed water available has its bearing on the subject froe units are not advisable where the feed water is not of the best

The character of an installment is also a factor Where, say, 1000 horse power is installed in a plant where it is knohat the ultimate capacity is to be, the size of units should be selected with the idea of this ultimate capacity in mind rather than the amount of the first installation

Boiler service, from its nature, is severe All boilers have to be cleaned fros, etc, are a necessity Thisthe number of boilers to be installed, to allow a certain nuular boilers must be taken off the line

With the steam requirements determined for a plant of hly advisable to install at least two spare boilers where a continuity of service is essential This per or repairs and still allows a spare boiler in the event of so out of a tube or the like Invest more nor less than insurance on the necessary continuity of service In small plants of, say, 500 or 600 horse power, two spares are not usually warranted in view of the cost of such insurance A large plant is ordinarily laid out in a number of sections or panels and each section should have its spare boiler or boilers even though the sections are cross connected In central station work, where the peaks are carried on the boilers brought up from the bank, such spares are, of course, in addition to these banked boilers Fro boilers alone, the number of spare boilers is determined by the nature of any scale that may be formed If scale is forh for good operating results, by cleaning in rotation, one at a ti will naturally increase

In view of the above, it is evident that only a suggestion can be made as to the number and size of units, as no recoeneral, it will be found best to install units of the largest possible size co conditions, with the total power requireive proper flexibility of load, with such additional units for spares as conditions of cleaning and insurance against interruption of service warrant

In closing the subject of the selection of boilers, it may not be out of place to refer to the effect of the builder's guarantee upon the detern to be used Here in one of its most important aspects appears the responsibility of the manufacturer Emphasis has been laid on the difference between test results and those secured in ordinary operating practice That such a difference exists is well known and it is now pretty generally realized that it is the responsible uarantees are necessary, subures which may readily be exceeded under test conditions and which may be closely approached under the ordinary plant conditions that will be met in daily operation

OPERATION AND CARE OF BOILERS

The general subject of boiler room practice may be considered from two aspects The first is that of the broad plant econoestion as to thethe best economical results with the apparatus at hand and procurable The second deals rather with specific recommendations which should be followed in plant practice, reco not only to economy but also to safety and continuity of service Such reco of the nature of stea apparatus and its operation, as covered previously in this book

It has already been pointed out that the attention given in recent years to stea practice has co between the results being obtained in every-day operation and those theoretically possible The aenerating end of a power plant, however, is coiven to the balance of the plant, but it reatest assurance of a return for the attention given

In the endeavor to increase boiler room efficiency, it is of the ute results are to be judged With the theoretical efficiency obtainable varying so widely, this standard cannot be placed at the highest efficiency that has been obtained regardless of operating conditions It is better set at the best obtainable results for each individual plant under its conditions of installation and daily operation

With an individual standard so set, present practice can only be improved by a systeree hich operating results will approximate such a standard will be found to be directly proportional to the aiven the operation For such supervision to be given, it is necessary to have not only a full realization of what the plant can do under the best operating conditions but also a full and co under all of the different conditions thatshould be ed that the results may be directly compared for any period or set of conditions, and where such results vary from the standard set, steps s Such a record is an important check in the losses in the plant

As the size of the plant and the fuel consu of results beco of but a fraction of one per cent in the fuel bill represents an a into thousands of dollars annually, while the expense of the proper supervision to secure such saving is se plants are necessarily elaborate and complete In the smaller plants the same methodssaving in fuel and an inappreciable increase in either plant organization or expense

There has been within the last few years a great increase in the practicability and reliability of the various types of apparatus by which the records of plant operation enious and, considering the work to be done, is remarkably accurate From the delicate nature of some of the apparatus, the liability to error necessitates frequent calibration but even where the accuracy is known to be only within limits of, say, 5 per cent either way, the records obtained are of the greatest service in considering relative results So theiven below

[Illustration: 2400 Horse-power Installation of Cross Drum Babcock & Wilcox Boilers and Superheaters at the Westinghouse Electric and Manufacturing Co, East Pittsburgh, Pa]

Inasmuch as the ultimate measure of the efficiency of the boiler plant is the cost of steaenerated and fuel consumed Records of temperature, analyses, draft and the like, serve as a check on this consu the distribution of the losses and affording aconditions where improvement is possible

Coal Records--There arethe coal used These are ordinarily accurate within close limits, and where the size or nature of the plant warrants the investment in such a device, its use is to be recommended The coal consumption should be recorded by sohts of coal purchased The total weight gives no way of dividing the consumption into periods and it will unquestionably be found to be profitable to put into operation sohed as it is used In this way, the coal consu any specific period of the plant's operation, can be readily seen The simplest of such hing on scales of the fuel as it is brought into the fire roohts