474 CEMENTS, LIMES, AND PLASTERS. 



her is recharged and the flues to the central stack and from the chamber 

 behind it are opened, thus making the newly filled chamber the end 

 term of the series. 



FIG. 110. Plan of Hoffmann kiln. 



As noted, the slurry charged into a Hoffmann kiln is necessarily in 

 the form of bricks. The expense of partly drying the slurry and mold- 

 ing it into bricks must, therefore, be charged against the kiln. Taken 

 as a whole the system is low in fuel consumption, but high in labor 

 cost, especially since skilled labor is required for all the operations. 

 Usually one chamber is loaded and one drawn each day. The out- 

 put per kiln per day will, therefore, depend on the size of the chambers. 



4. Continuous Shaft Kilns. 



Dietzsch kiln. In 1884 the Dietzsch kiln was first used in cement- 

 manufacture, and its advantages soon became known. It has been 

 in use at several American plants, and in the matter of fuel consumption 

 is, perhaps, the best type of kiln that can be employed. 



Dietzsch kilns are built in pairs, back to back, as shown in Fig. 111. 

 They are 60 to 75 feet h'gh, and consist of a cooling chamber at the 

 base D, a fire-chamber or "creuset" C, and a preheating chamber A. 

 It will be seen that these three parts of the kiln are not all in one ver- 

 tical alignment, but that the axis of the preheating chamber, though 

 parallel to the axis of the main kiln, is off to one side some distance, 

 so that the two portions of the structure communicate by a horizontal 

 passage B. 



Aalborg or Schofer kiln. The Aalborg kiln, soon introduced in 

 European cement practice after the success of the Dietzsch kiln had 

 proven the possibility of economical continuous kilns, has been used 

 at several American plants in a more or less modified form. The kiln 

 is shown in section in Fig. 112. It will be seen that it is essentially the 

 same as the Dietzsch, except that the preheating chamber, the burning 

 space, and the cooling chamber are all in the same vertical line. This 

 change, slight in appearance, economizes considerably in labor, for the 

 charge descends of itself, without the rehandling necessary in the Dietzsch 

 kiln. The mix is introduced through the charging opening A, while 

 the coal is charged through the shutes (shown in the figure about an 

 inch below A}. 



