Hydrodynamics Behavior of a Gas-Solid System in an Industrial Scale CATOFIN® Dehydrogenation Reactor

Industrial iso-butane dehydrogenation reactors are among the largest chemical reactors that are currently being used in the petrochemical industry. In the CATOFIN^® dehydrogenation technology from 3 to 11 parallel reactors are operated in a batch wise mode, making the dehydrogenation process continuous. Moreover, these reactors are being operated horizontally with respect to the feed inlet with a typically reactor volume of 400 - 700 m³. Due to these dimensions and the feed throughput (up to 200 tons/h hydrocarbons and 800 tons/h air) the internal reactor hydrodynamics, including heat, mass and momentum balances, are highly complex and involve multiple chemical engineering principles. Hydrocarbon feed rate, air feed rate, operational cycle, inlet temperatures, operational pressures, amount of catalyst, and reaction performance are the main parameters that determine the fluid behavior affecting hydrocarbon conversion and selectivity. This work reports the results achieved with the implementation of an unique experimental and mathematical method that highlights insights occurring in the hydrodynamics of a CATOFIN^® reactor during operations. In particular, computational fluid dynamics (CFD) simulations were developed and validated with operational data obtained from two CATOFIN^® plants in the Kingdom of Saudi Arabia. Furthermore, experimental efforts have confirmed the “down-scalability” of simulation model and has confirmed the hydrodynamics behavior as predicted by the model and experienced in the plant.

This abstract summarizes intensive experimental and modelling efforts in the kinetics and hydrodynamics of a gas-solid iso-butane dehydrogenation reaction (towards iso-butylene) using an industrial Chromia-based catalyst. In the experimental part of this work, the kinetics and mass-transfer have been addressed using a lab- and pilot-scale reactor setup, which provided the relevant data to determine intrinsic and partly extrinsic kinetics of the Chromia-based iso-butane dehydrogenation reaction. Heat supply, catalyst-bed configuration, catalyst-pellet size and residence time have been varied as major parameters to the dehydrogenation kinetics. Furthermore, the hydrodynamics were majorly affected by the catalyst-pellet configuration and temperature gradient over the radius and axes of the vertical reactor.

Computational fluid dynamics simulations have been applied to address the effect of the industrial catalyst-bed configuration where the temperature and pressure profiles over the fixed-bed were simulated under the obtained kinetic regime as provided in the experimental work. Furthermore, computational fluid dynamics could provide a correlation between axial and radial temperature profiles and observed chemical conversion of iso-butane. Additionally, the pressure drop profiles were correlated to the observed residence time, which subsequently determines the chemical conversion of iso-butane to iso-butylene. The use of computational fluid dynamics, in combination with lab-scale experimental kinetic data, has provided a great contribution to the understanding of the hydrodynamics at an industrial scale iso-butane dehydrogenation reactor.

Finally, the obtained computational fluid dynamics simulation results were correlated to the real plant data by comparing the obtained chemical yield of iso-butylene (downstream to the reactor section), temperature and pressure profiles.

In conclusion, this abstract shows the strength of combining computational fluid dynamics and experimental validation resulting in semi-empirical recommendations and improvements for real plant operations in the dehydrogenation of iso-butane to iso-butylene.