An Algorithm for predicting the Hydrodynamic and Mass Transfer Parameters in Slurry Bubble Column Reactors for Fischer-Tropsch Synthesis

摘要

A large number of experimental data points obtained in our laboratory as well as from the literature, covering wide ranges of reactor geometry (column diameter, gas distributor type/open area), physicochemical properties (liquid and gas densities and molecular weights, liquid viscosity and surface tension, gas diffusivity, solid particles size/density), and operating variables (superficial gas velocity, temperature and pressure, solid loading, impurities concentration, mixtures) were used to develop empirical as well as Back-Propagation Neural Network (BPNN) correlations in order to predict the hydrodynamic and mass transfer parameters in slurry bubble column reactors (SBCRs). The empirical and BPNN correlations developed were incorporated in an algorithm for predicting gas holdups (epsilon_G, epsilon_(G-Small), epsilon_(G-Large)); volumetric mass transfer coefficients (k_La, k_(La-Small), k_La_(-Large)); Sauter mean bubble diameters (d_S, d_(S-Small), d_(S-Large)); gas-liquid interfacial areas (a, a_(Small), a_(Large)); and liquid-side mass transfer coefficients (k_L, k_(L-Small), k_(L-Large)) for total, small and large gas bubbles in SBCRs. The developed algorithm was used to predict the effects of reactor diameter and solid (alumina) loading on the hydrodynamic and mass transfer parameters in the Fisher-Tropsch (F-T) synthesis for the hydrogenation of carbon monoxide in a SBCR. The predictions showed that increasing the reactor diameter from 0.1 to 7.0 m and/or increasing the alumina loading from 25 to 50 wt. percent significantly decreased epsilon_G, k_La_(H2) and k_La_(CO) and increased d_S. The decrease of the total gas holdup was found to be controlled by the holdup of small gas bubbles. The increase of the Sauter mean bubble diameter increased both k_(LH2) and k_(LCO), however, the decrease of the total gas holdup coupled with the increase of d_S resulted in a dramatic decrease of the gas-liquid area, a and subsequently kLaH2 and k_La_(CO). Thus, in the churn-turbulent flow regime, the hydrodynamic and mass transfer behaviors of the F-T SBCR were controlled by the holdup of small gas bubbles and the gas-liquid interfacial area, a.