32 



BULLETIN 80, U. S. DEPARTMENT OP 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 five 

 hours increases the 

 daily output 48 per 

 cent, while a decrease 

 from ten to three 



Fig. 16. — Effect of duration of cooking on production in 24 hours. ., . . 



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. 



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 



i The steam used was not perfectly dry, containing a small amount of moisture or "priming." 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. 







































































































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