PRODUCING SODA PULP FROM ASPEN. 



35 



CHEMICALS PER TON OF PULP. 



The chemicals directly employed in the manufacture of soda pulp 

 affect cost of production, in that the full amount of alkali charged to 

 the digester can not be recovered, while the bleaching powder after 

 being used is of no further value. The curves in figures 18 and 19, 

 expressing the effects of the 

 cooking conditions on the 

 amounts of chemicals em- 

 ployed per ton of air-dry, 

 bleached pulp, were derived 

 from the experimental data 

 as explained on page 48, ap- 

 pendix. The amounts shown 

 are less than those generally 

 employed in commercial prac- 

 tice, for several reasons: (1) 

 The yields of pulp are higher; 

 (2) the losses on bleaching 

 are less; (3) the amounts of 

 chemical charged per pound 

 of wood are less; and (4) the 

 amounts of bleach required 

 are less. Whether or not 

 pulp mills can duplicate or 

 approach these results, the 

 general trend of the curves 

 would not be affected. 



2200 



2000 



180Q 



1600 



1400 



1200 



1000 



800 



1800 



1600 



1400 



1200 



1000 













/ 

















/ 













s/s" 











































iJ 













9 



A 



>e 













.20 30 .40 



POUNDS NaOH PER POUND OF WOOD 



"\ 









,„ 



f ' 



• 





\ 

















\ 



Ns. 





13 





10 











14" 





-12* 









2 4 6 8 10 12 

 DURATION AT MAX. PRESSURE-HOURS 



SODA ASH. 



1400 



© 1200 



1000 









19 



<8 ( 



Ji 





"* 



22 



2lj 



20 













60 



70 80 90 100 110 120 

 MAX.PRE5SURE-PDS.PER SO.. IN. 



1300 



1100 



SO 60 70 80 90 .00 110 

 CONCENTRATION NaOH- CRAMS PER LITER 



The amounts of caustic 

 soda and sodium carbonate 

 charged to the digester in the 

 several groups of tests have 

 been calculated to show the 

 equivalent amounts of com- 

 mercial soda ash (58 per cent 

 Na 2 0) per ton of bleached 

 pulp produced. (Fig. 18.) 

 Increasing the amounts of 

 caustic soda charged per pound of wood obviously results in increas- 

 ing amounts of soda ash per ton of pulp, and the decreased yields 

 of pulp resulting from the more thorough cooking make the effect 

 more pronounced. A bend is found in the 'curve at the point of 

 maximum yield, since for amounts of caustic below this point the 

 yields decrease rapidly and their influence on the amount of soda 

 ash employed per ton of pulp becomes more apparent. 



Fig. 18. — Effects of cooking conditions on amount of 

 soda ash employed per ton of pulp. 



