New transition in the three-phase moving
bed
Trickle-to-pulse transition under effects of particle
moving
The solid state is a vital difference between the novel three-phase
moving bed and the conventional trickle bed. Therefore, the solid flow
rate was set to several values to investigate the effects of particle
moving on the flow regime transition. Due to the following two aspects,
this work only focuses on the transition between the trickle flow and
the pulse flow. Firstly, as stated in the introduction, the industrial
reactors are often operated close to the flow transition boundary
between trickle flow and pulse flow to realize better mass transfer
rates and catalyst utilization. Secondly, there is no efficient method
to identify the bubble flow in the trickle bed reactors except the
visualization
method.
However, when particles start to move, the bubbles could not be observed
clearly from the sidewall in a cylindered three-phase moving bed, thus
it is hard to identify the transition from pulse flow to bubble flow.
Therefore, the experimental studies in this work are restricted to
trickle and pulse flow regimes.
In the cocurrent downflow
three-phase moving bed, it was observed the presence of trickle flow and
pulse flow which almost had the same characteristics as those presented
in the typical trickle bed. The transition from the trickle flow to the
pulse flow in the three-phase moving bed was mainly determined by the
standard deviation of pressure drop and
visual
observation. The typical images and videos used to identify the flow
regime transition are given in supporting information. The variations of
pressure drop and the standard deviation of pressure drop with the
liquid mass flow rate at a given gas mass flow rate are shown in Figure
3, which also shows a comparison with the observed flow regime
transition. It can be seen from Figure 3 that the standard deviation of
pressure drop increases suddenly at a certain liquid mass flow rate
under all solid flow rates, and the corresponding increasing points vary
with the solid flow rate. In addition, the increasing points of standard
deviation are close to the observed transition points between trickle
flow and pulse flow. This can be explained by the fact that under these
conditions, the gas-liquid interaction increases suddenly due to the
appearance of pulses, indicating the flow regime transforms from trickle
flow to the pulse flow.