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.