Abstract:
A gas-liquid-solid three-phase ebullated-bed reactor with an inner diameter of 286 mm and a height of 7.2 m was used to conduct intermittent liquid phase and continuous gas phase operations. The three-phase system was composed of water, air and Al
2O
3 spherical particles. The macroscopic liquid circulation velocity was measured at a solid holdup of 12% ~ 30% with a superficial gas velocity of 0.086 ~ 0.216 m/s. In this study, the tracer method was used to determine the concentration curves of multiple tracers at the inlet and outlet of the reactor. The axial dispersion coefficient of the liquid phase was solved by MATLAB software. Substituting it into the definition of Einstein's diffusion coefficient produced the liquid circulation velocity. The experimental results show that at a certain solid holdup, as the superficial gas velocity increases, small bubbles gradually gather into large bubbles. The rising velocity of the bubbles continues to increase, and the liquid circulation velocity also increases accordingly. Increasing the superficial gas velocity significantly increases the liquid circulation velocity. At a constant superficial gas velocity, as the solid holdup increases, both the large bubble holdup and the bubble rise velocity increase. This subsequently causes the liquid circulation velocity to increase. However, because the increase of solid holdup hinders the circulation of liquid to a certain extent, as the solid holdup increases, the increase rate of the liquid circulation velocity continues to decline. It is suggested that an optimal value for the solid holdup exists.