CHAPTER XXXII. 

 CEMENT BURNING: FIXED KILNS 



THE preceding chapters have been devoted to a discussion of the 

 raw materials for Portland-cement manufacture, and to the processes 

 and methods of preparing a mixture of these materials for the kiln. In 

 the present and following chapters the next stage of the industry will 

 be taken up that of burning the raw mix into cement clinker. 



Fixed or Stationary Kilns. 



The earliest type of kiln used in Portland-cement manufacture was a 

 simple vertical bottle-shaped kiln closely similar to those used in the 

 burning of lime and natural cements. This was largely succeeded by 

 improved types of stationary kilns in Germany and France, while 

 in the United States the rotary kiln has become standard. Though 

 stationary kilns are now very rare in American practice they have some 

 undoubted advantages in localities where fuel is expensive and labor 

 is cheap. As American engineers may soon have to consider the pos- 

 sibility of manufacturing cement in Central and South America, where 

 these fuel and labor conditions are fulfilled, it has been considered 

 advisable to discuss the improved type of stationary kilns in some 

 detail. A list of references to the more important papers on the sub- 

 ject is also given at the end of the chapter. 



In order that the relationships of the various types of fixed or sta- 

 tionary kilns may be clearly understood, it will be well to group them 

 in classes according to the general principles on which their construc- 

 tion and operation are based. Four such groups can be formed: 



1. Dome or intermittent kilns. 



2. Dome kilns with drying accessories. 



3. Ring or Hoffmann kilns. 



4. Continuous shaft kilns. 



These classes will be described in the order named. 



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