COST OF POWER I33 



possess practical fuel value. The heating power of fuels con- 

 taining carbon and hydrogen is approximately expressed by the 

 formula: 



h= 145 (C+4-28H)' 



A manufacturer purchasing a quantity of fuel will do well 

 in having a sample thereof subjected to chemical analysis, and 

 the heat value is thus readily determined. Take as an illustra- 

 tion the analysis of Hocking Valley Coal, Table III, and the 

 heat value is as follows: 

 ' h = 14s (67 + 4.28 X 4.8) = 12,694 B. T. U. per pound. 



Heat Reqtiired for Producing Steam. — Water at 212° F. 

 takes up 966 B. T. U. when converted into steam of the same 

 temperature. Therefore if one pound of coal produces 12,694 

 heat units then a pound of such coal will produce 12,694/966 or 

 13.14 pounds of steam of 212° F. from water of the same tem- 

 perature. The amount of heat thus required to produce a 

 pound of steam is known as the latent heat of vaporization. 



In practice more heat is required for producing a pound of 

 steam, as the water that is converted into steam is usually at 

 a temperature much below 212° F. Possibly 60° F. will come 

 nearer to the temperature of the boiler feed water as used in 

 most creameries. Furthermore the steam in the boiler is heated 

 to a temperature exceeding that of 212° F. Consider that a 

 creamery is using boiler feed water at 60° F. and carrying a 

 steam-gauge pressure of 80 pounds, it will then require 1,153 heat 

 units for each pound of steam produced, or one pound of the 



above-mentioned coal will produce — ^— ^ or 1 1 pounds steam. 



1.153 

 Losses of Heat When Producing Steam. — If there were no 

 losses to consider it would be comparatively easy to determine 

 the amount of fuel of a known composition required for produc- 

 ing a definite amount of steam. It will be impossible even for 

 the most careful engineer to reach the theoretical efficiency. It 

 should be possible, however, for many engineers to materially 



' Siebel's Compend. o£ Mechanical Refrigeration and Engineering, igii, p. 96. 



