alone, there is no additional fuel required to generate steam containing a definite 

 number of heat units whether such units be due to superheat or saturation. 

 That is, if 6 per cent more fuel is required to generate and superheat to 100 

 degrees a definite weight of steam, over what would be required to produce the 

 same weight of saturated steam, that steam, when superheated, will contain 6 

 per cent more heat units above the feed water temperature than if saturated. 



The statement that for an additional number of heat units generated in the 

 furnace of a boiler equipped with a superheater, there will be an equivalent 

 increase in the number of heat units appearing in the superheated steam over 

 saturated, is based, as indicated, upon an equal efficiency for the boiler and 

 superheater as for the boiler in which no superheater is installed. As a matter 

 of fact, the efficiency of a boiler and superheater, where the latter is properly 

 designed and located, will be slightly higher for the same set of furnace conditions 

 than would be the efficiency of a boiler in which no superheater were installed. 

 A superheater, properly placed within the boiler setting in such a way that the 

 products of combustion for generating saturated steam are utilized as well for 

 superheating that steam, will not in any way alter furnace conditions. With a 

 given set of such furnace conditions, for a given amount of coal burned, the fact 

 that additional surface, whether as boiler heating or superheating surface, is 

 placed in such a manner that the gases must sweep over it, will tend to lower 

 the temperature of the exit gases. It is such a lowering of exit gas temperature 

 that is the ultimate indication of added efficiency. Though the amount of this 

 added efficiency is difficult to determine by test, that there is an increase is 

 unquestionable. 



Where a properly designed superheater is installed in a boiler, the boiler 

 heating surface, in the generation of a definite number of heat units, is relieved 

 of a portion of the work which would be required were these heat units delivered 

 in saturated steam. This results either in a reduction in the capacity at which 

 it is necessary to operate the boiler itself, apart from the superheater, in the 

 developing of a definite number of boiler horse power, with a consequent saving 

 in the apparatus due to a decreased load, or it enables the same number of horse 

 power to be developed from a smaller number of boilers, with the boiler heating 

 surface doing the same amount of work as if no superheaters were installed. 

 Such a superheater needs practically no attention, is not subject to a large upkeep 

 cost or depreciation, and performs its function without in any way interfering 

 with the operation of the boiler. 



Following the course of the steam in the plant, the advantage of the use of 

 superheated steam is next seen in the general absence of water in the pipes. 

 While it is possible for a pipe through which superheated steam is flowing to also 

 carry water, there is usually an entire absence of such water in the piping 

 system, especially where the piping is well covered. The thermal conductivity of 

 superheated steam, that is, its power to receive from or to give out heat to surround- 

 ing bodies, is much lower than that of saturated steam and its heat, therefore, 



3* 



