Gas Dispersion in the Oxygen Delignification Process, 2018 PEERS

There has been little or no knowledge about the state of gas dispersion in the oxygen delignification process. This paper presents a new on-line method for measuring oxygen bubble size distribution in the process as well as results from the studies made in the softwood and hardwood line, for example:

• In softwood line the average volumetric bubble size was about 0.1 mm and in the hardwood line it was nearly ten times higher. In both lines there was considerable variation in the measured bubble size over the long term.
• In both lines an increase in the rotation speed of the mixer had a clear decreasing effect on the bubble size, and oxygen charge had a clear increasing effect on the bubble size.
• In the softwood line no coalescence of bubbles in the reactor was observed, but in the hardwood line some coalescence of larger bubbles occurred in the reactor.
• In the test conducted in the hardwood line, the usage of defoamer had a clear increasing effect on the oxygen bubble size.
• In the hardwood line, reactor pressure had a clear effect on the delignification rate, which indicates that decreasing the oxygen bubble size in this case should also have an increasing effect on the delignification. 

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