Developing and Using Modeling to Understand and Improve Industrial Oxygen Delignification Processes, TAPPICon25

In the present study oxygen delignification is modelled to evaluate industrial delignification processes. The model development is mainly based on the usage of two new measurements: gas bubble size measured in the feed of the reactor, and oxygen concentration measured in the residual gas after the reactor. The bubble size provides information on the oxygen mass transfer from the gas phase to the pulp suspension, and hence the concentration of dissolved oxygen in proportion to the saturation concentration in the reactor can be determined. The oxygen concentration in the residual gas gives information about how much oxygen is consumed and the partial pressure allows calculation of the dissolved oxygen concentration at the exit of the reactor.

This paper presents information obtained from studies made in seven industrial oxygen delignification processes, three softwood and four hardwood mills. These studies provided information about different parameters needed to model the processes. The most important are the speed of the delignification reaction, the consumption of oxygen and the saturation level of dissolved oxygen in the reactor, which is mainly determined by the oxygen bubble size.

In the long fiber processes, the oxygen reactors were practically saturated with oxygen, and in the short fiber processes, they were mainly not saturated. Modeling was then used to predict the way in which different changes would affect the delignification rate, and these changes were also tested in the mill trials. It was shown that the charge of oxygen can be optimized and delignification improved by decreasing oxygen bubble size. The modeling approach is still under development but has already been shown to be a very efficient tool to study and improve industrial oxygen delignification processes.

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