Hydrodynamic characteristics of cocurrent upflow and downflow of gas and liquid in a fixed bed reactor

The residence time distribution (RTD) of a bench-scale multiphase reactor has been investigated in the present study using air as a gaseous phase and water as a liquid phase. Two different sizes (1.1 and 0.3 mm) of silicon carbide were used as diluent for the catalyst bed. In the entire study, equal volumes of catalyst and diluent were used in the bed. The ranges of air and water velocities were kept at such levels as to simulate the liquid hourly space velocities and hydrogen/oil ratios of typical bench-scale hydroprocessing units. The experiments were conducted in both upflow and downflow modes of operation in the reactor. The two modes of operation showed wide differences in RTD when a larger size of diluent was used. However, the differences in RTD in both the modes of operation were eliminated by using a smaller size of diluent. The effect of gas and liquid velocities on different hydrodynamic parameters such as bed Peclet number of liquid, mean residence time of liquid and operating liquid holdup were also investigated for these two levels of diluent size.