ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Power consumption and gas–liquid dispersion in turbulently agitated vessels with vertical dual-array tubular coil baffles

Xun Wan, Yasuyuki Takahata, and Koji Takahashi

^aDepartment of Biochemical Engineering, Yamagata University, 4-3-16 Jyonan, Yonezawa-shi, Yamagata 992-8510, Japan

E-mail: koji@yz.yamagata-u.ac.jp

Abstract: In this work vertical dual-array tubular coil baffles arranged in groups of four, six or eight were investigated and the results compared with those from four planar baffles. The baffle coefficients for a single phase, along with the power consumption and gas hold-up in the gas–liquid phase of a system with the various baffle configurations for single and triple Rushton turbines are presented. Measurements were carried out using a dish-bottom vessel with an inner diameter of 0.29 m. Two ambient-temperature media were used as the liquid phase, namely, tap water and a 0.5 M Na₂SO₄ aqueous solution, representing coalescent and non-coalescent liquids, respectively. The results of the single-phase experiment revealed the coil baffles to have lower power numbers; when the baffle coefficient is ≥ 0.12, the mixing efficiency is the same as that for four planar baffles. The power consumption experiment using the gas–liquid phase showed that installing coil baffles prevented a large power draw in all types of media. In addition, the power draw characteristics are affected by the media. It was found that, because of the low K_B number, flooding occurred more readily with coil baffles than with planar baffles. Gas–liquid dispersion experiments in an air–water system indicated that, at a low gas flow-rate, the gas hold-up values of the coil baffles were almost 60 % higher than those of the conventional four baffles. However, this phenomenon was not observed in the Na₂SO₄ aqueous solution because of the existence of dead zones in viscous liquids. Finally, all the data from the power consumption and gas hold-up experiments on the gas–liquid phase were correlated.

Keywords: tubular coil baffles – Rushton turbine – power consumption – gas hold-up

Full paper is available at www.springerlink.com.

DOI: 10.1515/chempap-2015-0221

Chemical Papers 70 (4) 445–453 (2016)