Distribution Characterizations Of Phase Holdups In Gas-Liquid-(Solid) Bubble Column Using Electrical Resistance Tomography

Bubble columns and air-lift loop reactors are widely used as gas-liquid (solid) reactors in many applications due to their simple construction, no mechanical transmission components, operation stability, low operating cost, high energy efficiency and good mass and heat transfer rates, such as hydrogenation, desulfurization, Fischer-Tropsch synthesis, fermentations, bio-reactions, coal liquefaction and waste water and gas treatment etc.. Developing qualities as well as quantitative understanding of the axial and radial holdup distribution in bubble columns, we can provide guidance in optimizing the existing reactors or developing and designing a novel reactor with high performance,which is very important to the more and more intense energy and environmental problems.The bubble behaviors and gas-liquid flow characteristics were measured using Electrical Resistance Tomography (ERT) in a transparent perspex acrylic bubble column with 2.5 m high and an inner diameter of 0.16m. The effect of superficial gas velocity, liquid conductivity value, liquid surface tension and viscosity on gas holdup, the axial and radial distribution characteristics of gas holdups were investigated in gas-liquid bubble column. Gas holdup was calculated by Maxwell equation based on liquid conductivity and mixture conductivity, and the liquid conductivity and mixture conductivity could affect the results by ERT. The gas holdup decreased with the increase of surface tension and increased with the viscosity. According to the average cross-sectional distribution of gas holdup, the radial gas holdup profiles were steeper at the central region of the reactor with an increase of gas velocity, namely the higher gas holdups at the centre and lower at the wall of the reactor. Meanwhile the operating conditions and physical properties would not affect the gas holdup profiles. From the three-dimensional image of the ERT time series, the gas mainly concentrated in the central at small superficial gas velocity, and with the superficial gas velocity increasing, the scope of gas distribution gradually widen. Furthermore the bubbles rised spiral in the reactor, and the greater the gas velocity was, the more clearly the tendency of upward was.Based on combined Electrical Resistance Tomography with the traditional differential pressure method, the influence of solid density, solid particle size, solid-phase addition on gas holdup were studied in gas-liquid-solid three phase air-lift loop reactor with 3.1 m high and an inner diameter of 0.09m. The relationship betweenε_s and gas velocity were discussed both in the riser and downer of the reactor. The results showed that, the loading amount of particle had little affect on gas holdup with polyurethane as the solid phase; the loading capacity and particle size had greater affect on gas holdup with glass beads as solid phase.The agreement between results obtained by ERT and differential pressure method was generally very good. The feasibility of combined techniques with ERT and differential pressure method to measure the phase holdups for three-phase was demonstrated.