Fluidized bed hydrodynamic modeling of CO2 in syngas: Distorted RTD curves due to adsorption on FCC

Abstract

AbstractBubbles rising through fluidized beds at velocities several times superficial velocities contribute to solids backmixing. In micro‐fluidized beds, the walls constrain bubble sizes and velocities. To evaluate gas‐phase hydrodynamics and identify diffusional contributions to longitudinal dispersion, we injected a mixture of H2, CH4, CO, and CO2 (syngas) as a bolus into a fluidized bed of porous fluid catalytic cracking catalyst while a mass‐spectrometer monitored the effluent gas concentrations at 2 Hz. The CH4, CO, and CO2 trailing RTD traces were elongated versus H2 demonstrating a chromatographic effect. An axial dispersion model accounted for 92% of the variance but including diffusional resistance between the bulk gas and catalyst pores and adsorption explained 98.6% of the variability. At 300°C, the CO2 tailing disappeared consistent with expectations in chromatography (no adsorption). H2 and He are poor gas‐phase tracers at ambient temperature. We recommend measuring RTD at operating conditions.