A novel unit operation to remove hydrophobic contaminants

Abstract

For mills making paper with recovered fiber, removal of hydrophobic contaminants is essential for trouble-free operation of paper machines. Significant cost savings on paper machine operation can be achieved by reducing deposits, which results in better quality, reduced downtime, increased fiber yield, and reduced energy consumption.Bubble nucleation separation (BNS) is a relatively new process for removing hydrophobic particles. When vacu-um is applied to a slurry, dissolved gas bubbles nucleate on hydrophobic particles and drag them to the surface for easy removal. We constructed a 16-L batch unit to evaluate the effect of operating parameters on removal of hydro-phobic particles, using statistical design of experiments. These results were used to guide our design of a 16-L con-tinuous unit. We tested this unit on laboratory and mill samples. The removal of 60%–80% of hydrophobic particles was achieved with a low reject rate of < 2%.Following on this success, we built a 200-L pilot unit and tested it in our pilot plant. With promising results there, we installed the pilot unit at a commercial paper recycling mill. Over the course of several mill trials, we showed that it was possible to remove a considerable amount of suspended solids from paper machine white water with less than 2% rejects. Unfortunately, due to the unit only treating 50 L/min and the mill flow being 12000 L/min, we were not able treat a sufficient portion of the white water to know whether a large-scale implementation of BNS would improve paper machine runnability.

Citation

Houtman, Carl; Aziz, Salman; De Jong, Robert; Doshi, Mahendra. 2020. A novel unit operation to remove hydrophobic contaminants. TAPPI Journal. 19(4): 207-217.