Application of hot-wire anemometry for experimental investigation of flow distribution in micro-packed bed reactors for synthesis gas conversion

Abstract

The knowledge of the flow distribution inside microstructured reactors is valuable e.g. for improving the reactor design, developing flow distributors, and optimizing the catalyst loading method. The applicability of the hot-wire anemometry (HWA) technique for experimental determination of the flow distribution inside a multi-stack micro-packed bed reactor is demonstrated for the first time. The anemometry data is then evaluated in relation to the reactor performance for methanol synthesis under relevant industrial operating conditions. A 400 µm long hot-wire connected to a constant temperature anemometer was applied for scanning the flow out of a specially designed reactor model, clamped on a motorized table equipped with a precise positioning system. The anemometry measurements revealed a nonuniformity in the catalyst packing, partially resulting from the reactor design. The flow distribution is poorer for smaller particles and for wider particle size distributions, and worsens as the superficial flow velocity (and the pressure drop) decreases. The effects of the packing nonuniformity on the reactor performance appear minor under methanol synthesis conditions. They could, however, turn out significant upon pushing the overall conversion in the whole reactor towards equilibrium as the synthesis reaction is exothermic, and temperature increase does alleviate the problem. The reactor design should be modified instead.