Effect of Defoamer on the Gas Content and Performance of O2 washers – Mill Case Study, 19PEERS

In brownstock washers, the application of defoamer is required to improve mat drainage and to control foam to enable the washers to operate efficiently. Pulp air content is a very important factor that must be considered because increasing air content clearly decreases washer capacity. Air in the pulp retards its drainage. Free air which passes along with the fibers can create permanent foam that blocks channels, and when it breaks, it flocculates impurities, which are accumulated in the bubbles.

In this study, two different defoamers with various dosages and dosage points were tested in the oxygen stage of a hardwood line. In addition to the process, measurements and their changes were monitored using an on-line gas content measurement unit and on-line process refractometers (measuring total dissolved solid content, TDS). The bubble size of the O2 stage pre-washer’s feed pulp was measured using a bubble monitoring system (bms). The results showed that the defoamers and their point of dosage had a clear effect on the air content of the pulp suspension and thus on the operation of the washer both before and after the oxygen stage. Choosing suitable dosage points, defoamers and dosages can intensify the performance of the washers. This also has a great effect on the dewatering and thus the filtrate balances. 

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