Using online bubble size and total dissolved solids measurements to investigate the performance of oxygen delignification, TAPPI JOURNAL June 2018

ABSTRACT: The main target of oxygen delignification is to continue delignification that started in cooking in a more selective manner than occurs in the digester (i.e., remove a substantial fraction of the residual lignin using oxy-gen and alkali at a moderate temperature). Delignification with oxygen is a gentler way of reducing the kappa num-ber than extended cooking. Lowering inlet kappa to bleaching also decreases bleaching chemicals consumption and, because of this, reduces organic wastewater load from bleaching. We studied the performance of oxygen delignification by installing bubble size imaging systems and refractome-ters, which measure dissolved dry solids in the oxygen stage feed. Based on these measurements, we gathered information about gas dispersion (bubble size distribution) and the behavior of dissolved matter in the hardwood mill’s oxygen delignification stage. Our goal was to investigate the effects of different variables on the oxygen stage’s gas dispersion, kappa reduction, yield, and pulp quality. Gas dispersion improved (i.e., average bubble size decreased) when the chemical mixer speed increased. Increasing the mixer speed and the amount of oxygen yielded higher kappa number reductions and increased the amount of dissolved organic matter.

Application: Methods described here could help mills adjust the oxygen charge and gas dispersion in delignification processes and allow for future monitoring and controlling of the oxygen process.

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