Experimental study on the particle flow patterns in a cyclone dipleg with a trickle valve

An experimental apparatus including a dipleg and a trickle valve was established to simulate the operation of a suspended dipleg-trickle valve system of cyclone used in fluid catalytic cracking(FCC)unit.The flow regimes in the dipleg and the discharge modes in the trickle valve were studied by combining the observation of experimental phenomena with the analysis of transient pressure fluctuation.The results show that the flow regimes in the dipleg have two types-the dilute–dense phase coexisting falling flow and the dilute falling flow.Correspondingly,the trickle valve also has two discharge modes-the intermittent periodic dumping discharge and the continuous trickling discharge.The power spectrum density of pressure fluctuation displays that the gas–solids flow in the dipleg-trickle valve system is characterized by a low-frequency pulsation.The coherence coefficient explains the origin and propagation of pressure fluctuation in the system.Eventually,a map describing the flow regimes and discharge modes related to the operation parameters was proposed,which can provide a helpful guidance for the operation of cyclone dipleg-trickle valve system in FCC unit.

Experimental analysis of pressure characteristics of catalyst powder flowing down a cyclone dipleg

An experiment was carried out for investigating pressure behavior of catalyst powders, with a Sauter mean diameter of 63.6 μm, flowing downward in a cyclone dipleg with 150 mm inner diameter and 9000 mm high. Time mean pressure and time series of pressure fluctua- tions were measured at different axial positions in the dipleg with particle mass fluxes ranging from 50.0 to 385.0 kg m-2s t. The experimental results showed that the time mean pressure in the dipleg increased progres- sively from the top section to the bottom section. The experimental phenomena displayed that the fluidization patterns in the dipleg can be divided into two types on the whole, namely the dilute-dense coexisting falling flow and the dense conveying flow along the dipleg. In the dilute- dense coexisting falling flow, the dilute phase region was composed of a length of swirling flow below the inlet of dipleg and a dilute falling flow above the dense bed level. With increasing particle mass flux, the dilute-dense coex- isting falling flow was gradually transformed to be the dense conveying flow, and the exit pressure of the dipleg increased considerably. The pressure fluctuations were closely related to the flnidization patterns inside the dipleg. In the dilute-dense coexisting falling flow, the pressure fluctuations in the dilute flow region originated from par- ticle clusters, propagating downward as a pressure wave; however, the pressure fluctuations in the dense flow region originated from rising gas bubbles, propagating upward. When the dense conveying flow was formed in the dipleg,the pressure fluctuations originated mainly from instability of the feed and the compressed gas, propagating down- ward. The standard deviation of the pressure fluctuations indicated that the intensity of pressure fluctuations first increased and then decreased with increasing particle flux.