A Novel Ultrasonic Dynamic Drainage Tester, 2011 PaperCon Conference

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The Dynamic Drainage Jar (DDJ) is commonly used to assess furnish drainage. However, contrary to the drainage process in a commercial paper machine, drainage in a DDJ normally occurs without turbulence because any impeller mixing increases filtration resistance enormously. A novel Ultrasonic Dynamic Drainage Jar (UDDJ) has been developed to simulate the dynamic drainage conditions found in the forming section of a paper machine. In the UDDJ, ultrasound is directly imparted to the Jar, causing it to oscillate and produce turbulence near the screen. The apparatus is able to simultaneously measure drainage, retention, and web porosity. The influence of ultrasound on fines retention and drainage behaviour of a newsprint furnish were investigated at various impeller mixing speeds in the absence and presence of a cationic retention aid. The results indicated that the ultrasonic forces applied in UDDJ were able to prevent blocking of the filtration screen, to deflocculate the pulp, and to create and enlarge dewatering channels in the forming web. As a result, the ultrasound accelerated pulp drainage, reduced fines retention and produced a more porous web. In this manner, UDDJ resembles the drainage elements of a paper machine, although no low frequency pressure pulses were generated. The UDDJ could be a very useful laboratory tool to determine the drainage performance of furnishes and chemical additives under dynamic conditions.