Oxygen Delignification Model Using the Ji, Vanska, and van Heiningen Equation

Abstract
By: Tom Mullen, Process Engineering LLC
An updated oxygen delignification model was developed based on the Ji, Vanska and van
Heiningen equation and the mass transfer equation where the value of Kl in the parameter Kla
was estimated. The process parameters, [OH‐] (concentration), PO2, and temperature in the rate
equation were varied to evaluate their relative impact on delignification rate. A 4°C (from 90 to
94°C) temperature increase raised the delignification rate by approximately 20%. A 10%
increase in NaOH concentration (e.g., from 3 to 3.3 g/l) raises the delignification rate by
approximately 6%. A .1Mpa pressure increase (e.g., 1‐1.1) increased the delignification rate by
2%. The model base case was established at:
Kappa: 30
NaOH concentration [NaOH]: 3.0g/l
Temperature: 90°C
Pressure: 1.0 Mpa
Consistency: 12%
Residence time (ex. O2): 60 minutes
The model calculated a base case outlet Kappa of 18.1 (39.6% delignification). Data from
Reference 2 was used to estimate the value of Kl assuming an initial bubble diameter of
0.01cm, a phase ratio of 140 cm3/lt (Xg) and a Kla of 0.004 (1/sec). The base case parameters
were varied to determine their net impact on delignification. Consistency had the greatest
effect. Oxygen bubble size had a substantial impact on the oxygen partial pressure at the fiber
surface. 

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