296 ANNUAL REPORT 
The reasons for requirements one and two are, of course, obvious. 
In regard to the sulphur it must be said that it may give rise to con- 
siderable trouble if too great in amount. By keeping the fire reducing 
in character much of the sulphur may be carried off in the gases without 
absorption by the cement and in exceptionally bad cases a small amount 
of coal low in sulphur may be ground with the raw mixture. This, 
together with the reducing conditions and the high temperature, will 
keep out any dangerous amount of sulphur. Ovxidizing burning condi- 
tions, i. e., firing with excess of air, will invariably tend to retain a ereat 
deal of the sulphur of the coal in the cement. Searching investigations 
in regard to the absorption of sulphur by cement in the rotary kiln have 
not yet been carried out. 
There is no practical method for eliminating the sulphur from the 
coal. Even when coal is converted into gas fuel, which admits of a treat- 
ment with chemical reagents, through scrubbing apparatus, it cannot be 
wholly desulphurized at reasonable cost. 
Since in the white hot kiln, the fine particles of coal ash are 
fluxed or fused into the cement and become a part of it, it is evident 
that its importance depends on the composition as well as on the 
amount. A siliclous ash is bound to give rise to more serious dis- 
turbance than a basic ash. But we are able to eliminate the ash, if neces- 
sary, by gasification, a perfectly practical procedure. In this manner 
many coals otherwise unsuitable can be used successfully. This problem 
is sure to be’ met by some manufacturers and the use of very high- ash 
coals, obtained at a low cost, will thus become possible. 
Producer Gas.—It has been said that fuel gas has too low a calorific 
power for use in the rotary kiln, but this opinion is evidently wrong for 
fuel gas made under proper conditions. ‘The productron of generator 
gas is not a process as thoroughly understood by many who operate 
generators as would be desirable, and hence the results are often ex- 
tremely irrational. For firing a rotary kiln bituminous coal is best used 
in the generator. In brief, the latter consists of a circular shaft (see 
figure 52) provided with a flat grate and a coal charging device on top. 
After a fire has been built up, coal is charged till a heavy bed of ignited 
coal is formed with a comparatively cool zone on top. A certain amount of 
steam is blown in; the amount must be so regulated that not more than 
800 pounds of steam is brought in for each ton of carbon. Some gener- 
ators are provided with a revolving grate which ejects the ash and coal 
clinkers mechanically. The Taylor generator, which represents a good 
sample of a modern gas producer, is of this construction. The steam jet 
not only introduces steam, but also regulates the amount of air taken in- 
to the generator. We can distinguish three zones in the producer: 
A. The ash zone. 
B. The combustion zone. 
C. The distillation zone. 
