COST OF POWER I35 



pounds of steam per horse-power hour. It is to be assumed that 



the average creamery engine will be operated at a greater loss of 



steam and it may be fair to estimate that it will require 40 



pounds of steam per horse-power hour. The heat required to 



produce that amount of steam at 80 pounds gauge pressure 



from water of 60° F. is equal to 1,153 X 40 = 46,120 B. T. U. 



The per cent of the heat converted into mechanical work is 



equal to 



2,154=; X 100 



-^ = 5-5 per cent. 



46,120 



Methods by Which Heat Losses Are Reduced. — The ex- 

 haust steam from the engine contains much heat. By saving at 

 least a part thereof, it will result in a reduction of amount of 

 fuel required. The exhaust steam may be used for heating the 

 boiler feed water and wash water, for pasteurization, for heating 

 the building, etc. The losses are furthermore reduced by proper 

 firing, by keeping the boiler clean, and by keeping boiler and 

 steam pipes properly insulated. 



I. Value of Exhaust Steam for Heating the Feed Water. — It 

 has been stated that it requires 1,153 B. T. U. of heat for pro- 

 ducing a pound of steam, 80 pounds of gauge pressure, from 

 water at 60° F. It should be possible to heat the water by 

 exhaust steam to 200° F. before the water enters the boiler. 

 Water of 200° F. when converted into steam of 80 pounds 

 pressure will require only 1,153 — 140 = 1.013 B. T. U. The 

 saving of heat in this instance is 



140 X 100 



= 12.14 per cent. 



I-IS3 

 Table IV ' gives the percentage of saving in fuel by pre- 

 heating the boiler feed water from various initial temperatures 

 to different final temperatures. 



Table V • gives the annual cash saving of fuel on a 40 

 horse-power boiler by heating the feed water from various 

 initial temperatures to a final temperature of 200° F. 



' Circular 209, B. A. I., 1913. 



