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

Abstract

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 fluctuations were measured at different axial positions in the dipleg with particle mass fluxes ranging from 50.0 to 385.0 kg m−2 s−1. The experimental results showed that the time mean pressure in the dipleg increased progressively 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 coexisting 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 fluidization patterns inside the dipleg. In the dilute–dense coexisting falling flow, the pressure fluctuations in the dilute flow region originated from particle 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 downward. The standard deviation of the pressure fluctuations indicated that the intensity of pressure fluctuations first increased and then decreased with increasing particle flux.