Experimental study on catalytic conversion and flow characteristics of ortho-para hydrogen in tubular packed-bed converters at liquid nitrogen temperature

Ortho-para hydrogen conversion is a critical process in hydrogen liquefaction. However, comprehensive data and correlations on the ortho-para hydrogen conversion and pressure drop within catalyst packed beds across the typical range of Reynolds numbers encountered in converters/heat exchangers are still lacking. This study established an experimental setup to measure the catalytic conversion of ortho-para hydrogen and the associated pressure drop in tubular packed-bed converters in the liquid nitrogen temperature range. The effects of the particle size of iron oxide catalysts (20–80 mesh), space velocity (1.5–22 kg/(m³·s)), and packed-bed porosity (0.27–0.46) on the catalytic conversion of ortho-para hydrogen, along with the pressure drop characteristics, were examined at around 77 K and 2 MPa. A correlation was further developed for estimating the outlet concentration of para hydrogen with given space velocity, which would be useful for determining the catalyst dosage based on the targeted conversation rate in the product. Furthermore, by modifying the coefficients for viscous and inertial resistance on the basis of the Ergun equation, pressure drop correlations for packed-bed catalytic converters with different particle sizes were proposed, with remarkably improved predictive accuracy. This work offers critical prediction correlations for the design of ortho-para hydrogen catalytic converters/heat exchangers.