THE COST OF PASTEURIZING MILK AND CREAM. 9 



however, is practically doubled when steam is taken direct from the 

 boiler for pasteurizing instead of utilizing the exhaust steam. The 

 steam pressure is reduced from boiler pressure to about 3 pounds by 

 some form of reducing valve, consequently there is approximately as 

 much heat in the exhaust steam from the engine, or steam-driven 

 auxiliaries, as there is in steam taken from the boiler. The amount 

 of fuel mentioned above is for pasteurizing, and is not to be confused 

 with the total amount used in firing the boilers. In other words, 

 it is the fuel required to evaporate in the boiler a certain amount 

 of water which is used for the purpose of pasteurizing the cream. 

 With this arrangement the pasteurizing was done with heat that 

 would otherwise have been wasted, and furthermore it took a load of 

 67.1 horsepower off the boiler plant. 1 



TESTS NOS. 2, 3, AND 4. 



Tests Nos. 2 and 3 were also made with exhaust steam, but the 

 arrangements were different from the foregoing, as the exhaust 

 from the engines was piped directly into the heater. The only 

 load on the engines at the time was the pasteurizers and the centrif- 

 ugal cream separators, which amounted to very little. The exhaust 

 steam available, however, was sufficient to operate the pasteurizers 

 up to their full capacity. 



Referring to the summary of the tests in Table 2 it will be noted 

 that the fifth item, "Heat in steam required to drive pasteurizing 

 equipment," is blank except for test No. 4. The reason for this 

 is that the engine or steam-driven auxiliaries from which exhaust 

 steam was used for pasteurizing are considered in the light of pressure- 

 reducing valves, the mechanical power being, so to speak, a by- 

 product. That is to say, there is a loss of heat in steam due to drop in 

 pressure, and while the wire drawing of the steam through the valve 

 will superheat the steam to a certain extent, the loss may be con- 

 sidered the same for the purpose of this paper, regardless of whether 

 this drop is caused by passing through a pressure-reducing valve or 

 through a steam engine. In test No. 4 the steam used for pasteuriz- 

 ing was reduced in pressure by a valve, consequently the energy 

 represented by the difference in pressure and temperature of the 

 steam before and after passing through the reducing valve is a 

 clear loss. In neither case, however, was the heat lost due to drop 

 in pressure of the steam available for heating the cream. The 

 380,800 B. t. u. in column 4 represents the heat in the steam at 

 boiler pressure which was used in the engine for driving the pasteur- 

 izer, separator, shafting, etc., required in the process of pasteurizing, 

 and as the exhaust from the engine was allowed to go to waste it is 



!The use of exhaust steam for other purposes in milk plants is treated in Bureau of Animal Industry 

 Circular 209. 



