(88d) Innovative Design for Improved Contact of Hydrocarbon Feedstock with Catalyst in a Downer Reactor

Down flow reactor (downer) in a circulating fluidized bed configuration such as Fluid Catalytic Cracking (FCC) unit is achieving importance in the industry due to its inherent capability of reducing the back mixing of catalyst with reacting hydrocarbon stream. The flow of gas and solids in a downer reactor approaches to ideal plug flow against the flow in conventional upflow in a circulating fluidized bed (riser) with significant back mixing. This makes the residence time distribution in a downer reactor narrower compared with a riser and hence, higher selectivity towards olefinic products and lower yield of undesired products.

However, the downer reactor lacks in the configuration for better contact of hydrocarbon stream and catalyst resulting in lower conversion of feedtstock. An innovative design has been developed to improve the initial contact of hydrocarbon and catalyst in a downer reactor. In this design, the reactor is the annular section of two concentric pipes and the catalyst allowed to fall freely into the annular downer reactor as annular curtains. A cold flow pilot plant has been installed based on in-house design for generating the hydrodynamic data. The current paper describes about the distribution of catalyst in the annular downer reactor confirming its superiority in contacting the hydrocarbon stream with catalyst.