Numerical exploration of the flow regime transition of a novel catalytic cracking reactor and operation mode analysis

The maximizing isoparaffins (MIP) reactor has multiple reaction zones by expanding the diameter of the middle section of the conventional equal-diameter FCC riser to produce high-quality gasoline. This study aimed to probe the flow regime transition and corresponding regulation of such diameter-transformed reactors using multiscale CFD simulations with twelve-lump kinetics. It was found that a choking plateau that appears in a low-velocity, equal-diameter riser was captured at a much higher solid concentration in the new reactor when considering reactions, while the plateau disappears and becomes a slowly ascending slope under cold-model conditions. Using the particle circulating mode instead of the fixed mode gives rise to large fluctuations in solids flow and reaction rate in the first zone, but the formation of fast fluidization in the expanded second zone can help stabilize the flow behaviors and product yield. This finding sheds light on the design and operation of diameter-transformed fluidized beds. [Display omitted] •An industrial MIP riser is simulated under cold-model and reactive conditions.•The smooth flow regime transition is captured by cold-model simulation.•The flow regime transition with abrupt choking is captured by reactive simulation.•The particle conveying mode affects flow regime transition in different manners.