32 
BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 
and, as has been shown, yields of pulp per unit of wood are also 
increased, and consequently more pulp is secured per cook. The 
greater plant capacity thus obtained would result in a proportionate 
decrease of operating costs per ton of pulp. 
Figure 16 shows the production of pulp per 24 hours continuous 
operation for each 100 pounds of wood capacity of digester as influ- 
enced by various durations of cooking. The curve was derived from 
the experimental data, assuming a one-hour period for blowing the 
digester after completing a cook and for charging the next cook, and 
a similar period for 
attaining maximum 
cooking pressure. 
Thus, for a three-hour 
period at maximum 
pressure, the total 
time between the 
charging of two con- 
secutive cooks is five 
hours. Computation 
shows that decreas- 
ing the duration at 
maximum pressure 
from eight to Hve 
hours increases the 
daily output 48 per 
cent, while a decrease 
from ten to three 
hours increases the 
output 156 per cent. If the time allowed for blowing and charging 
the digesters and for raising the digester pressure is decreased, the 
increase in the daily output will be even more pronounced as the 
duration of cooking is shortened. 
% 
n 
c t- 
1 \ 
i V 
« \ 
B- • \ T 
* V 
« V 
E S it 
j 150 ^ 
£ S^ 
& "V 
2 ^ 
B s < 
3 no ^ 
g WU *v 
a. - " •**"■«*. 
^ 
50 — 
234567 8 9 10 111213 
DURATION AT MAX. PRESSURE-HOURS 
Fig. 16.— Effect of duration of cooking on production in 24 hours. 
STEAM CONSUMPTION. 
While the consumption of steam varies with the duration of cook- 
ing, it is influenced also by the pressure maintained in the digester 
and more by the relative volumes of the liquor charge. Under the 
testing conditions employed, the volume of liquor varied both with the 
amount of caustic soda charged (the concentration being constant) 
and with the concentration (the amount of chemical being constant) . 
Since the heating was accomplished by steam blown directly into the 
digester, a measure of the amount of steam used is afforded by the 
increase in the volume of liquor during cooking. 1 The effects of the 
1 The steam used was not perfectly dry, containing a small amount of moisture or ''priming.' 5 How- 
ever, as the steam was of approximately the same moisture content for all tests, the "condensation" was 
proportional to the amount of steam used. 
