Effect of regenerated standpipe flow pattern on catalyst transport in fluid catalytic cracking unit

Standpipe is a pipeline that constitutes one of the components in the downstream portion of the catalyst circulation loop in a fluid catalytic cracking (FCC) unit, facilitates catalyst transportation between reactor and regenerator. This study measured pressures of the regenerated standpipe on a 1.0 Mt/a FCC unit to elucidate the underlying cause of the observed catalyst transportation. The results indicated that multiple flow patterns coexist within the standpipe, rather than a single dense-phase flow. The characteristic parameters of the static and dynamic pressure were intimately connected to the aforementioned flow patterns. The dynamic pressure data indicated that pressure dominant frequency and amplitude could employed in the identification of flow patterns. The packed bed flow had a pressure frequency ranging from 0 to 3.3 Hz, and a dominant frequency amplitude of 0.8, 1.8 and 2.2 Hz, allowed diagnosis of poor catalyst transport. The study demonstrated that the standpipe structure and catalyst mass flow rate were the key factors affecting gas-solid flow degassing by allowing for multiple flow patterns in the standpipe. The influence of aeration on the flow patterns was also discussed here, with an improper aeration rate resulting in reaction temperature fluctuations ranging from 0.5 to 23 °C.