STEAM BOILERS 151 



6 ft. or less in width; two such burners may be used in furnaces 

 from 6 to 14 ft. wide; and for furnaces over 14 ft. in width 

 three burners should be installed. If narrow-flame burners 

 are used, their number will have to be greater. 



Location of Burners. The burners may be installed in the 

 centers of the fire-doors, if desired, and this practice is fre- 

 quently followed. In case only one burner is employed, it 

 may be placed in a suitable opening in the boiler front, between 

 the fire-doors. Another method that has been used is to insert 

 the burners below the fire-doors. So far as combustion is 

 concerned, the location of the burner is of little importance, 

 provided there is a sufficient air supply admitted under proper 

 conditions; but the heat developed may be utilized to better 

 advantage by exercising care in placing the burners. The 

 flames should not be directed against the side walls, but should 

 be approximately parallel thereto, with the tip of the burner 

 about 6 or 8 in. above the brick covering of the grate. It is 

 the usual practice to direct the flame from the front to the 

 back of the furnace; but in some installations of water-tube 

 boilers of the Stirling and Babcock & Wilcox types, the burners 

 have been placed at the rear of the furnace, so as to direct the 

 flames toward the front. This was found to be advantageous, 

 as the combustion was completed in the portion of the furnace 

 having the greatest cross -section, where the rapid expansion 

 of the gases due to the heat generated could be accommodated 

 most readily. 



Necessity for Straining of Oil Fuel. The crude oils used for 

 fuel come from wells drilled in the earth, and as a result they 

 contain varying proportions of sand and dirt. The denser 

 and more viscous the oil, the greater is the tendency for it to 

 retain impurities in suspension. If the oil is stored for some 

 time in tanks, and is left undisturbed, some of the heavier 

 dirt will settle to the bottom and thus be separated from the 

 oil; but if the oil is taken direct from the wells to market, 

 little or none of the dirt will be removed. Even fuel oil, 

 which undergoes a preliminary heat treatment to separate 

 the more volatile hydrocarbons from it, may not be free from 

 foreign matter. It may be assumed, therefore, that all oil 

 fuel contains dirt and sand, and as a consequence there arises 



