Conclusion

A novel reactor configuration with cocurrent downflow of gas, liquid, and solid phases, named as the three-phase moving bed, is proposed for slow three-phase reactions with a large catalyst loading and a rapid deactivation rate of catalyst. A cold-flow experimental apparatus of three-phase moving bed is established to study the transition between the trickle flow regime and the pulse flow regime by the standard deviation of pressure drop and visual observations.
The flow regime map describing the transition between the trickle flow and the pulse flow in the three-phase moving bed is constructed. It is found that the flow regime boundary from the trickle flow to the pulse flow shifts towards higher liquid mass flow rate as the solid flow rate increases. Based on visual observations, pressure drop and dynamic liquid holdup analyses, a conclusion can be drawn that the particle movement affects the formation of local liquid blockages. This effect is explained as follows: (1) an increase in the solid flow rate results in a higher bed porosity and larger interstices between the particles, (2) the dynamic liquid holdup and the mean liquid film thickness decrease with the solid flow rate, (3) the movement of particles will destroy the liquid pockets or plugs between particles. As a result, the liquid films can not collapse in the interstices between the particles to form liquid blockages and initiate the pulses. Therefore, a higher liquid mass flow rate is necessary for the formation of the pulse with the increasing solid flow rate. An empirical correlation is derived from the experimental data for the prediction of the transition between the trickle flow and the pulse flow. The average absolute relative error of this correlation is 1.67%.
The effects of the particle moving on the radial liquid distribution are investigated with a liquid collector placed at the outlet of the bed. The results show that at a given gas and liquid mass flow rates, the movement of the particles will promote the radial diffusion of the liquid and improve the liquid distribution when the solid flow rate is less than a critical value. But further increasing the solid flow rate, the liquid distribution will become worse than that in the trickle bed. The critical solid flow rate increases with the increasing liquid mass flow rate. In total, compared to the trickle bed, the movement of the particles can increase the freedom of manipulating the performance of the reactor.