The influence of pressure on the liquid hold-up in a cocurrent gas-liquid trickle-bed reactor operating at low gas velocities

The influence of reactor pressure up to 6.0 MPa on the dynamic liquid hold-up in the trickle-flow regime with superficial gas velocities up to 5.2 cm/s has been investigated for water, ethanol and aqueous 40% ethyleneglycol, with nitrogen as the gas phase. Without gas flow, i.e. single-liquid trickle-flow operation, the reactor pressure has no influence on the dynamic liquid hold-up, which can be well correlated by means of the Reynolds and Galileo numbers. For Rel < 11 the hold-up proportional to Re0.36l and for Rel >> 15 to Re0.55l. This is probably due to a transition between laminar and turbulent film flow. According to the literature the dynamic liquid hold-up is not affected by low gas velocities under atmospheric conditions. The experiments show that in the case of two-phase flow operation at elevated pressures the hold-up decreases at relatively low gas velocities and even more so at higher pressures. This effect has been explained quantitatively by means of the ratio between the pressure gradient and the gravitational force. In addition, the change in the dependence of βdyn on Rel has not been observed anymore: at low Reynolds numbers the hold-up is already proportional to Re0.55l.