Completed Research
Modeling, Scaleup and Optimization of Slurry Bubble Column Reactors for Fischer-Tropsch Synthesis
Laurent Sehabiague, PhD, 2012
(Thesis: University of Pittsburgh ETD)
The hydrodynamic and mass transfer parameters of gaseous mixtures of N2 and He, used as surrogate components for CO and H2 respectively, were measured in three Fischer-Tropsch (F-T) liquids in the presence and absence of solid particles (Al2O3, FeOx). The data were obtained in a pilot-scale (0.29 m ID and 3 m high) slurry bubble column reactor (SBCR) within wide ranges of operating conditions covering those of F-T synthesis. The manometric method, the Transient Physical Gas Absorption technique and the Dynamic Gas Disengagement technique were employed to obtain the gas holdup, the volumetric liquid-side mass transfer coefficient and the gas bubbles Sauter mean diameter, respectively. Statistical experimental design was used to investigate the effect of these operating conditions on those parameters. The gas-liquid interfacial area appeared to control the mass transfer behavior of the SBCR operating in the churn-turbulent flow regime.
A user-friendly simulator based on a comprehensive computer model for F-T SBCRs, taking into account the hydrodynamics, kinetics, heat transfer, and mass transfer was developed. Novel hydrodynamic and mass transfer correlations, covering wide ranges of reactor geometry, gas distributor types, and operating conditions were established using our experimental data and those available in the literature; and a new relationship between the axial dispersion of large gas bubbles and their average diameter were developed and included in the reactor model. All reactor partial differential equations, equation parameters along with the pertinent boundary conditions were simultaneously solved numerically using the finite elements method. Different kinetic rate expressions available in the literature for iron and cobalt-based catalysts were included in the simulator which was used to predict the effects of the operating conditions, such as catalyst concentration, pressure, temperature, H2/CO ratio, and superficial gas velocity on the performance of an F-T SBCR. The predictions showed that the performance of the reactor was strongly dependent on the catalyst type and the kinetic rate expression used. The simulator was also used to optimize the reactor geometry and operating conditions in order to produce 10,000 barrels per day of synthetic hydrocarbons.