MANUFACTURE OF NATURAL CEMENTS. 



233 



All the kilns are 25 feet in height and have an output of 60 barrels 

 of cement each. The kilns are charged to the top with fuel and cement 

 rock, in the proportion of about 300 Ibs. of fuel to 2500 Ibs. of rock. 

 The fuel used is coal, the sizes being nut, pea, and slack in about equal 

 amounts. Seven or eight days are required, on the average, to "turn 

 a kiln", including charging, burning, and drawing. This corresponds 

 to a fuel consumption of about 18 per cent on the weight of cement 

 produced. In explanation of this high fuel account the reader is 



FIG. 43. Kilns and loading-tracks, Fort Scott, Kan. 



referred to the discussion on page 224, where it is shown that the amount 

 of fuel used necessarily increases with the percentage of lime and mag- 

 nesia. A high-limed cement and the Howard cement is exception- 

 ally high in lime therefore requires a very high fuel consumption. 



Fuel consumption. The fuel consumption in natural-cement plants 

 is extremely variable, as is shown by the results tabulated below. The 

 variation is caused in some parts by differences in kiln management 

 and character of fuel, but more largely to differences in the composi- 

 tion of the cement. The cements of lowest index demand calcination 

 at high temperatures, while those of high index may be burned at very 

 low temperature. 



