Part 17 (1/2)
Such a gain is dependent upon the class of engine and the power plant equip a superheater installation, all of the factors entering into each individual case should be considered and balanced, with a view to deter in relation to cost, hly economical plants, where the water consuain will be less than would result from the use of superheated steaher It is i possible but, broadly, it rees of superheat in the large and econoines, in which there is a large ratio of expansion, to frorees of superheat for the less econoned superheater will tend to raise rather than to decrease the boiler efficiency, it does not follow that all superheaters are efficient, for if the gases in passing over the superheater do not follow the path they would ordinarily take in passing over the boiler heating surface, a loss ases are passed over the superheater and are allowed to pass over only a part or in so surface
With rees, where the piping is properly installed, there will be no greater operating difficulties than with saturated steauarantee satisfactory operation with superheated stearees, apparatus of a special nature must be used and it is questionable whether the additional care and liability to operating difficulties will offset any fuel saving acco difficulties, with the degrees of superheat to which this article is limited, have been entirely overcos with superheated steam has been widely discussed It is an undoubted fact that while in some instances superheated steas, in others cast-iron fittings have been used with 150 degrees of superheat without the least difficulty The quality of the cast iron used in such fittings has doubtless a large bearing on the life of such fittings for this service The difficulties that have been encountered are an increase in the size of the fittings and eventually a deterioration great enough to lead to serious breakage, the develophtly, the breaking of a flange fro The latter difficulty is undoubtedly due, in certain instances, to the for bolts tended to distort the metal
The Babcock & Wilcox Co have used steel castings in superheated stea period and experience has shown that this eneral tendency toward the use of steel fittings In European practice, until recently, cast iron was used with apparently satisfactory results The claiineers was to the effect that their cast iron was of better quality than that found in this country and thus explained the results secured Recently, however, certain difficulties have been encountered with such fittings and European engineers are leaning toward the use of steel for this work
The degree of superheat produced by a superheater placed within the boiler setting will vary according to the class of fuel used, the form of furnace, the condition of the fire and the rate at which the boiler is being operated This is necessarily true of any superheater swept by the main body of the products of combustion and is a fact that should be appreciated by the prospective user of superheated steaned superheater, however, such fluctuations would not be excessive, provided the boilers are properly operated As a ainst in the use of superheated steam is that a maximum should not be exceeded While, as stated, there may be a considerable fluctuation in the temperature of the steam as delivered from individual superheaters, where there are a number of boilers on a line the temperature of the combined flow of steam in thefro of various furnace conditions of one boiler by another
[Illustration: 8400 Horse-power Installation of Babcock & Wilcox Boilers and Superheaters at the Butler Street Plant of the Georgia Railway and Power Co, Atlanta, Ga This Company Operates a Total of 15,200 Horse Power of Babcock & Wilcox Boilers]
PROPERTIES OF AIR
Pure air is a en While different authorities give slightly varying values for the proportion of oxygen and nitrogen contained, the generally accepted values are:
By voluen 7909 per cent
By weight, oxygen 2315 per cent, nitrogen 7685 per cent
Air in nature always contains other constituents in varying amounts, such as dust, carbon dioxide, ozone and water vapor
Being perfectly elastic, the density or weight per unit of voluression with the altitude This fact has a direct bearing in the proportioning of furnaces, flues and stacks at high altitudes, as will be shown later in the discussion of these subjects The ativen in Table 12
The weight and volume of air depend upon the pressure and the temperature, as expressed by the formula:
Pv = 5333 T (9)
Where P = the absolute pressure in pounds per square foot, v = the volume in cubic feet of one pound of air, T = the absolute terees Fahrenheit, 5333 = a constant for air derived froas
The weight of one cubic foot of air will obviously be the reciprocal of its volume, that is, 1/v pounds
TABLE 27
VOLUME AND WEIGHT OF AIR AT ATMOSPHERIC PRESSURE AT VARIOUS TEMPERATURES _______________________________________ | | | | | | Volurees | in | Cubic Foot | | Fahrenheit | Cubic Feet | in Pounds | |_____________|____________|____________| | | | | | 32 | 12390 | 080710 | | 50 | 12843 | 077863 | | 55 | 12969 | 077107 | | 60 | 13095 | 076365 | | 65 | 13221 | 075637 | | 70 | 13347 | 074923 | | 75 | 13473 | 074223 | | 80 | 13599 | 073535 | | 85 | 13725 | 072860 | | 90 | 13851 | 072197 | | 95 | 13977 | 071546 | | 100 | 14103 | 070907 | | 110 | 14355 | 069662 | | 120 | 14607 | 068460 | | 130 | 14859 | 067299 | | 140 | 15111 | 066177 | | 150 | 15363 | 065092 | | 160 | 15615 | 064041 | | 170 | 15867 | 063024 | | 180 | 16119 | 062039 | | 190 | 16371 | 061084 | | 200 | 16623 | 060158 | | 210 | 16875 | 059259 | | 212 | 16925 | 059084 | | 220 | 17127 | 058388 | | 230 | 17379 | 057541 | | 240 | 17631 | 056718 | | 250 | 17883 | 055919 | | 260 | 18135 | 055142 | | 270 | 18387 | 054386 | | 280 | 18639 | 053651 | | 290 | 18891 | 052935 | | 300 | 19143 | 052238 | | 320 | 19647 | 050898 | | 340 | 20151 | 049625 | | 360 | 20655 | 048414 | | 380 | 21159 | 047261 | | 400 | 21663 | 046162 | | 425 | 22293 | 044857 | | 450 | 22923 | 043624 | | 475 | 23554 | 042456 | | 500 | 24184 | 041350 | | 525 | 24814 | 040300 | | 550 | 25444 | 039302 | | 575 | 26074 | 038352 | | 600 | 26704 | 037448 | |650 | 27964 | 035760 | | 700 | 29224 | 034219 | | 750 | 30484 | 032804 | | 800 | 31744 | 031502 | | 850 | 33004 | 030299 | |_____________|____________|____________|
Example: Required the volue pressure per square inch at 115 degrees Fahrenheit
P = 144 (147 + 603) = 10,800
T = 115 + 460 = 575 degrees
5333 575 Hence v = ----------- = 284 cubic feet, and 10,800