Heat and Mass Transfer Effect in Slurry Bed Fischer-Tropsch Reactors

摘要

One of the advantages claimed for slurry bed reactors is the ability to operate at lower hydrogen to carbon monoxide ratios than either the fixed bed or fluid bed. Reasons for this difference have not previously been fully established. The present investigation has concentrated on two factors which may contribute to the ability of the slurry reactor to tolerate lower hydrogen/CO ratios. These are: (1) greater isothermicity, and (2) mass transfer effects on the gas-liquid interface in the slurry reactor. Work with small diameter fixed bed reactors has shown that there is a critical temperature at which plugging of the reactors using an iron catalyst will occur. The exact temperature is a function of both the hydrogen/CO ratio and the space velocity. A difference of 10 to 15 exp 0 C separates operability from non-operability. It is therefore likely that in the critical temperature range around 300 exp 0 C hot spots on the catalysts may be the cause of plugging and deactivation at low hydrogen/CO ratios and that such hot spot development can be inhibited by operation in the liquid phase. The influence of mass transfer on the hydrogen/CO ratio in the liquid phase of a slurry reactor has been analyzed theoretically, again using an iron catalyst. It was determined that even under circumstances where the gas-liquid mass transfer resistance is a small fraction of the over-all resistance, differences in the solubilities and diffusivities of hydrogen and carbon monoxide can give rise to liquid phase hydrogen/CO ratios which differ substantially from that of the gas fed to the reactor. The direction and magnitude of the change in the liquid phase ratio is dependent on the consumption ratio of hydrogen respectively carbon monoxide, the interfacial area for mass transfer from the bubble face, the Damkohler number and the space velocity of the feed gas. (ERA citation 07:052553)