Question

Birch wood is pulped at the conditions described above using a cookign schedule listed in the table below, which shows that it takes 1.5 hours to heat up the entire wood liquor mixture to 160 degrees celsius. One can notice that the mixture is heated up at a constant rate of 1 degree celsius/minute from 80 degrees celisius to 140 degrees celsius, and then at a rate of 2/3 degrees celsius/minute from 140 degrees celsius to 160 degrees celsius. Then the temperature remains at 160 degrees celsius for another 1.5 hours. What is the H-factor when the cook is terminated at the final time of three hours?

Table 1
Digester heating	TEMPERATURE
Sequence TIME	(C)
(Hours)
0	80
0.5	110
0.75	125
1	140
1.25	150
1.5	160
1.5-3.0	160

Answer 1

H-factor is a kinetic model for the rate of delignification in kraft pulping. It is a single variable model combining temperature (T) and time (t) and assuming that the deligification is one single reaction.

H-factor depends on both time and temperature with the temperature dependence being strong.

Since the heating time in this case is 90 min and the system is at 160 oC for 90 min the H - factor in heat-up process can be calculated to be 82.

The H - factor in cooking is calculated to be 595

So the combined Total H - factor will be 677