Studies On The Internals Of Bubble Column Reactor

Terephthalic acid is the most important feed stock in the field of polyester, which is usually produced via oxidation of p-xylene in acetic acid. The reactors in both mid-temperature and high-temperature technology are bubble column reactors. Bubble column reactor has its own strong points such as simple structure, low construction and operating cost, good heat transfer property. But the factors that high superficial gas velocity, large diameter and intense turbulent in the PX oxidation reactor may lead to high gas hold-up in the core area, low near the wall;and large bubble diameter in the core area, small near the wall. At the same time, liquid move upward in the core area, downward near the wall. As a result liquid circle in the whole column is formed. When the column diameter increases, this flow status gets worse. Ultimately the overhigh liquid velocity may lead to a gas short circuit in the core area. The non-uniformity of liquid velocity profile along the radial may be the main difficulty in scale up of the bubble column reactor. To suppress the upward high velocity in the core of the column, the resistance internals with lateral fins on a vertical bar were installed on the center line of a bubble column. Experiments were carried out to investigate the effects of the internal number, size and shape on gas-liquid velocity profiles along the radial. The measured velocity profiles show that existence of the internals can remarkably reduce the velocity in the core area, leading to a relatively uniform distribution. The resistance density function was introduced to characterize the effect of the internals, and a simplified quasi-homogeneous fluid model was adopted to simulate the liquid velocity profile in the bubble column with internals. The calculating results approximately agree with the experiments. Also, the existence of internals increases the mass transfer coefficient. Especially under high superficial gas velocity, the enhancement on k_La is remarkable. Thereafter, analyses on hydrodynamic for the dehydration column of mid-temperature technology reactor are carried out, and the poor tray efficiency is attributed to insufficient foam height above the tray. Reduction of the open area is suggested as an effective way to increase the foam height as well as the tray efficiency. The results show that when the open area decreased from 22.7% to 17.1%, Murphree efficiency increases from 23% to 36%.