CHAPTER XXXV. 

 REQUISITES AND TREATMENT OF KILN FUELS. 



THE usual fuel in rotary-kiln practice is pulverized bituminous coal. 

 Oil, natural gas, and producer gas are, however, used at several plants, 

 while charcoal has recently been suggested for use in a projected 

 Arizona mill. These fuels will be discussed in the order named. 



Coal. 



Character of kiln coals. In order to be suitable for use in rotary 

 kilns the coal must be of the bituminous type, and preferably a gas- 

 coal. Coals high in fixed carbon and low in volatile matter, while giving 

 high temperatures, will not burn properly when pulverized and blown 

 into the kiln, for they are slow to ignite. The anthracite and semi- 

 bituminous coals are, therefore, ruled out, though they can be used 

 in small quantities mixed with gas-coal, if the mixture be pulverized 

 fine enough. 



For economic reasons the kiln coal should run as low in ash as pos- 

 sible. The ash not only lowers the heating value of the coal, but it 

 interferes with the composition of the mix, for much of it is always 

 taken up by the cement during burning. The presence of sulphur, in 

 amounts of over 1^ per cent, is also technologically a defect, and if the 

 sulphur averages over 2 per cent it is advisable to look up a better coal. 



As shown by the analyses below, the better coals actually used 

 range in composition about as follows: 



Volatile matter 30%-40% 



Fixed carbon 50%-60% 



Sulphur 0%- 1|% 



Ash 5%- 8% 



Analyses of kiln coals. The following table (194) of analyses of 

 kiln coals is fairly representative of the various types of coal actually 



in use in rotary-kiln plants. 



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