Part 35 (2/2)

The lower limit of the stack temperature, as has been shown in the chapter on draft, is more or less fixed by the teood combustion With natural draft, this lower lirees

Capacity--Before the capacity of a boiler is considered, it is necessary to define the basis to which such a term may be referred Such a basis is the so-called boiler horse power

The unit of ineers is the ”horse pohich is equivalent to 33,000 foot pounds per minute

Stationary boilers are at the present ti

_Work_, as the terh space, while _power_ is the _rate_ of work or the amount done per unit of time As the operation of a boiler in service implies no motion, it can produce no power in the sense of the tereneration of steay of the fuel which is in the fory is converted into energy of ines developed the saht be designated as one having a definite horse power, dependent upon the aine horse power its stea of boilers, though it would still be inaccurate, if the terh custom, be interpreted to indicate that a boiler was of the exact capacity required to generate the steam necessary to develop a definite a, however, is obviously impossible when the fact is considered that the amount of steam necessary to produce the same power in prime movers of different types and sizes varies over very wide li fro of the tere of the boiler trials at the Centennial Exposition, 1876, at Philadelphia, ascertained that a good engine of the type prevailing at the time required approximately 30 pounds of steam per hour per horse power developed In order to establish a relation between the engine power and the size of a boiler required to develop that power, they recommended that an evaporation of 30 pounds of water frorees Fahrenheit to steae pressure be considered as _one boiler horse power_ This recoineers as a standard, and when the term boiler horse power is used in connection with stationary boilers[58] throughout this country,[59] without special definition, it is understood to have this

Inasrees Fahrenheit is the generally accepted basis of comparison[60], it is now customary to consider the standard boiler horse power as recommended by the Centennial Exposition Comrees This will be 30 pounds e pressure and 100 degrees feed temperature, or 11494 30 11494 = 34482, or approximately 345 pounds Hence, _one boiler horse power is equal to an evaporation of 345 pounds of water per hour frorees Fahrenheit_ The term boiler horse power, therefore, is clearly a measure of evaporation and not of power

Aof a boiler adopted by boilersurfaces Such a es in no way the definition of a boiler horse power just given It is simply a statement by theconditions or conditions which may be specified, will evaporate 345 pounds of water fro surface provided The a surface that has been considered by345 pounds froed froressed At the present ti surface is ordinarily considered the equivalent of one boiler horse power a manufacturers of stationary boilers In view of the arbitrary nature of such rating and of the widely varying rates of evaporation possible per square foot of heating surface with different boilers and different operating conditions, such a basis of rating has in reality no particular bearing on the question of horse power and should be considered merely as a convenience

The whole question of a unit of boiler capacity has been widely discussed with a view to the adoption of a standard to which there would appear to be a estions have been offered as to such a basis but up to the present time there has been none which has met with universal approval or which would appear likely to be generally adopted

With the iven above, that is, a measure of evaporation, it is evident that the capacity of a boiler is a measure of the power it can develop expressed in boiler horse power

Since it is necessary, as stated, for boiler manufacturers to adopt a standard for reasons of convenience in selling, the horse power for which a boiler is sold is known as its normal rated capacity

The efficiency of a boiler and the maximum capacity it will develop can be determined accurately only by a boiler test The standardpages, thesethe recommendations of the Power Test Coht out in 1913[61] Certain changes have been made to incorporate in the boiler code such portions of the ”Instructions Regarding Tests in General” as apply to boiler testing

Methods of calculation and such matter as are treated in other portions of the book have been omitted from the code as noted

[Illustration: Portion of 2600 Horse-power Installation of Babcock & Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the Peter Schoenhofen Brewing Co, Chicago, Ill]

1 OBJECT

Ascertain the specific object of the test, and keep this in view not only in the work of preparation, but also during the progress of the test, and do not let it be obscured by devoting too close attention to matters of minor importance Whatever the object of the test may be, accuracy and reliabilityto end

If questions of fulfillment of contract are involved, there should be a clear understanding between all the parties, preferably in writing, as to the operating conditions which should obtain during the trial, and as to theto be followed, unless these are already expressed in the contract itself

A may be noted:

Determination of capacity and efficiency, and how these couaranteed results

Comparison of different conditions or methods of operation

Determination of the cause of either inferior or superior results

Comparison of different kinds of fuel

Detern or proportion upon capacity or efficiency, etc

2 PREPARATIONS