STATE GEOLOGIST. 307 
heaters, the extra cost for power would offset the gain. The case is 
different where coal is higher. 
In most cement plants now the main question seems to be how to 
cool the clinker in the quickest manner without reference to saving the 
heat, and hence coolers are installed without any attempt to economy. 
Some of these coolers: are merely iron towers with baffle plates, 
others are high iron cylinders which are kept filled with clinker which 
is discharged by gravity at the bottom, but 1n some cases the hot air is 
drawn out on top by the blowers, thus preheating part of the air. In most 
cases the clinker is simply heaped up in a large shed or in the open air 
in great piles from which the cool clinker is wheeled to conveyors taking 
it to the grinding machines. 
There are several systems of regenerating clinker coolers, viz.: 
I. Revolving cylinders. 
2 Vietticale cylinders: 
3. Grate coolers. 
Revolving Cylinders. —1. The first are cylinders arranged just 
beneath the rotary kiln, catching the clinker as it comes from the kiln, 
the connection between the kiln and cooler being made as air tight as 
possible. ‘The air passes over the discharged clinker into the rotary kiln, 
being thus preheated. In this case it is advisable to inject the 
Coal with) air under vas) high  asspressure aS possible; so that ‘as 
much as possible of the secondary preheated air be used. The 
inclination of the cooler may be the same as that of the kiln and it is, 
so to speak, a piece of the kiln broken off and lowered. Or the cooler 
“doubles up” beneath the rotary kiln, in which case its inclination is 
reversed, as in the apparatus patented by Navarro in 1891 (see figure 54). 
One cooling cylinder may serve for two kilns. In operation this is the 
simplest and most easily operated cooler, but its heating efficiency is not 
very great. This can be increased, however, by putting in stirring 
devices, especially by projecting steps along the sides of the cylinder. 
Vertical Cylinders——2. Of the vertical clinker cooler we have as 
probably the best example, the Wentz cooler (see figure 55), in which 
air is blown through a vertical pipe perforated at intervals, from which the 
air is distributed through masses of clinker which gradually moves down- 
ward between alternately cup and bell-like iron baffle plates. The heated 
air is collected in a circular space surrounding the cylinder and is then 
drawn into the kiln. For successful operation the apparatus requires a 
higher air pressure than is usually carried by the blowers. One cooler 
can take care of at least two kilns. 
Cooling Grates.—3. The grate cooler consists essentially of a cast iron 
grate or steps surrounded by a shell and a device for jarring the recep- 
