Flow regimes and gas holdup in paper pulp–water–gas three-phase slurry flow

Abstract Hydrodynamic flow characteristics of solid–liquid–gas slurry made by intimately mixing fibrous paper pulp with water and air were investigated in a short, vertical circular column. The pulp consistency (weight fraction of pulp in the pulp–water mixture) was varied in the low consistency range of 0.0–1.5%. The test section was 1.8 m long, with 5.08 cm inner diameter. Mixing of the slurry prior to entering the test section was done using a patented mixer with controlled cavitation that generated finely dispersed micro-bubbles. Flow structures, gas holdup, and the geometric and population characteristics of gas bubbles in the gas–pulp–liquid three-phase flow were experimentally investigated, using visual observation, Gamma-ray densitometry, and flash X-ray photography. Superficial velocities of the gas and liquid/pulp mixture covered the ranges 0– 26 cm / s and 21– 51 cm / s , respectively. Five distinct flow regimes could be visually identified. These included dispersed bubbly, characterized by isolated micro-bubbles entrapped in fiber networks; layered bubbly, characterized by bubbles rising in a low consistency annular zone near the channel wall; plug; churn-turbulent; and slug. The dispersed and layered bubbly regimes could be maintained only at very low gas superficial velocities or gas holdups. Flow regime maps were constructed using phasic superficial velocities as coordinates, and the regime transition lines were found to be sensitive to consistency. The cross section-average gas holdup data showed that both the dispersed and the layered bubbly regimes could best be represented by the homogeneous mixture model. The drift flux model could best be applied to the reminder of the data when the plug and churn-turbulent flow regimes were treated together, and the slug flow was treated separately. The drift flux parameters depended on the pulp consistency.

[1]  J. S. Archer,et al.  Neural network based objective flow regime identification in air-water two phase flow , 1994 .

[2]  A. K. Biń,et al.  Hydrodynamics and ozone mass transfer in a tall bubble column , 2001 .

[3]  A. E. Dukler,et al.  Modelling flow pattern transitions for steady upward gas‐liquid flow in vertical tubes , 1980 .

[4]  J. Thibault,et al.  Chemical enhancement in the determination of KLa by the sulfite oxidation method , 1990 .

[5]  M. A. Valle,et al.  Momentum Transfer in Two-Phase Flow of Gas Pseudoplastic Liquid Mixtures , 1972 .

[6]  Douglas W. Reeve,et al.  Pulp bleaching : principles and practice , 1996 .

[7]  A. A. Bishop,et al.  NON-NEWTONIAN LIQUID-AIR STRATIFIED FLOW THROUGH HORIZONTAL TUBES--II , 1986 .

[8]  M. N. Biswas,et al.  Friction factor for gas-non-newtonian liquid flow in horizontal bends , 1991 .

[9]  Geoffrey F. Hewitt,et al.  Measurement of two phase flow parameters , 1978 .

[10]  Goichi Matsui,et al.  Automatic identification of flow regimes in vertical two-phase flow using differential pressure fluctuations , 1986 .

[11]  Geoffrey G. Duffy,et al.  Relationships between velocity profiles and drag reduction in turbulent fiber suspension flow , 1976 .

[12]  A. A. Bishop,et al.  Interfacial level gradient effects in horizontal newtonian liquid-gas stratified flow—i , 1986 .

[13]  W. J. Beek,et al.  The oxidation of aqueous sodium sulphite solutions , 1973 .

[14]  D. White,et al.  Experimental determination of gas migration velocities with non-Newtonian fluids , 1993 .

[15]  N. Zuber,et al.  Average volumetric concentration in two-phase flow systems , 1965 .

[16]  Said I. Abdel-Khalik,et al.  Macroscopic flow structures in a bubbling paper pulp-water slurry , 1995 .

[17]  C. P. J. Bennington,et al.  The yield stress of medium- and high-consistency mechanical pulp fibre suspensions at high gas contents , 1995 .

[18]  C. Bennington,et al.  Gas‐liquid mass transfer in low‐ and medium‐consistency pulp suspensions , 2000 .

[19]  G. Wallis.  One Dimensional Two-Phase Flow , 1969 .

[20]  Liang-Shih Fan,et al.  Flow structure in a three‐dimensional bubble column and three‐phase fluidized bed , 1994 .

[21]  R. Chhabra,et al.  Isothermal two-phase flow of air and aqueous polymer solutions in a smooth horizontal pipe , 1984 .

[22]  J. Grace,et al.  Mixing in pulp bleaching , 1989 .

[23]  Theodore J. Heindel,et al.  The effect of fiber consistency on bubble size , 1999 .

[24]  Hydrodynamics of Dispersed Liquid Droplets in Agitated Synthetic Fibrous Slurries , 1997 .

[26]  Richard T. Lahey,et al.  The measurement of phase separation in wyes and tees , 1981 .

[27]  Goichi Matsui,et al.  Identification of flow regimes in vertical gas-liquid two-phase flow using differential pressure fluctuations , 1984 .

[28]  Liang-Shih Fan,et al.  Bubble characteristics in three-phase systems used for pulp and paper processing , 1996 .

[29]  C. Bennington,et al.  Gas—liquid mass transfer in pulp suspension mixing operations , 1997 .

[30]  Lefteri H. Tsoukalas,et al.  Vertical two-phase flow identification using advanced instrumentation and neural networks , 1998 .

[31]  A. Johnson,et al.  A PHYSICALLY BASED CORRELATION FOR THE EFFECTS OF POWER LAW RHEOLOGY AND INCLINATION ON SLUG BUBBLE RISE VELOCITY , 1995 .

[32]  J. A. Jendrzejczyk,et al.  Application of chaos theory in identification of two-phase flow patterns and transitions in a small, horizontal, rectangular channel , 1996 .

[33]  Robert W. Field,et al.  Bubble Column Reactors , 1991 .

[34]  S. M. Ghiaasiaan,et al.  Liquid-side interphase mass transfer in cocurrent vertical two-phase channel flows , 1997 .