Experimental study and numerical simulation on a multi-stage counter-current continuous fluidized bed reactor for activating iron-based Fischer-Tropsch synthesis catalyst

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Rapid and robust activation of iron-based catalysts is critical for industrial Fischer-Tropsch synthesis. This work introduces a multi-stage, counter-current continuous fluidized-bed system that enables uninterrupted catalyst activation, addressing key limitations of conventional batch fluidized beds. Compared with previous studies that mainly addressed batch activation or conventional fluidized-bed activation, the novelty of this work lies in the combined cold-flow, CFD, and hot-flow validation of a multi-stage counter-current continuous fluidized-bed reactor for iron-based catalyst activation. Cold-flow tracer-based RTD experiments were conducted in a transparent acrylic reactor, and hot-flow activation tests were performed in a stainless-steel reactor under syngas at 265 °C and 0.2 MPa. Cold-flow experiments show that the inter-stage overflow design ensures unidirectional particle transfer, markedly suppresses back-mixing, and improves plug-flow behavior. The dimensionless variance of the residence time distribution decreases from 1.0 to 0.475, while the fitted tanks-in-series number increases from 1.0 to 2.34. CFD simulations accurately reproduce the observed hydrodynamics and extend the analysis to operating limits, predicting an upper gas-velocity threshold of 0.29 m/s under cold-flow conditions. Hot-flow simulations based on the validated model identify a slightly lower limit of 0.27 m/s, which provides practical guidance for reactor design and scale-up. Hot-flow experiments confirm stable fluidization at 265 °C and 0.2 MPa with continuous catalyst feeding and withdrawal. The catalysts activated in the multi-stage continuous system exhibit CO conversions of 51 to 53% and CH 4 selectivities of approximately 1% in a stirred-tank evaluation reactor, achieving performance comparable to that obtained with our batch fluidized bed activation method.