By analyzing solid holdup signals in the jet influence zone of risers,the characteristics of clusters were studied.The solid holdups inside clusters and their distribution ranges were calculated under the cases of both upward and downward feed jets.Moreover,the effects of the jet velocity on the cluster character-istics were analyzed.The solid holdups inside clusters have higher values and wider distribution ranges in the upward feed injection zone than in the downward zone,implying that the number of individual particles in a cluster is unstable under the influence of upward jets.For the case of downward jets,cluster formations in the jet influence zone of risers can more easily maintain stability,offering a better mix-ing environment for jets and particles.As the jet velocity increases,the solid holdups inside clusters in the riser wall of the upward injection zone increase accordingly,while the distributions of solid holdups inside clusters have no significant changes if the feed jets are downward.This phenomenon confirms that improved operational flexibility can be obtained if downward jets are mixed with the prelift gas-solid flow in risers;