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.