Cracking unit fractionation reflux

The distillation column of the cracking unit has a high heat load; in order to remove the excess heat from within the column and maintain thermal balance there, cold reflux and circulating reflux are generally employed. Cold reflux generally refers to the subcooled liquid reflux used at the tower top. The so-called recirculation refers to the process of drawing out a portion of the liquid phase from a certain tray in the tower, cooling it through heat exchange, and then reintroducing it into the tower at a position above the trays from which the crude oil is extracted. This is because if top cooling reflux is used entirely, on the one hand the amount of cooling reflux will necessarily be large, and there will also be a severe imbalance in the gas phase load throughout the tower, resulting in an increased tower diameter. On the other hand, due to the low temperature at the top of the tower, it is difficult to make full use of most of this heat from the low-temperature reflux; it can only be cooled with air or cooling water, resulting in severe waste of heat. The amount of heat removed by the circulating return is determined on the premise that it does not affect the separation requirements of the product. Therefore, some current hydrocracking units have the following types of reflux streams, among which the last 4 are cyclic reflux streams: (1) tower top reflux, (2) mid-stage hot reflux, (3) mid-stage cold reflux, (4) mid-stage vapor-phase reflux, (5) mid-stage minimum reflux

Thank you. Then, if the gas-phase load on the distillation column is too high, how should the distillation reflux be adjusted? Is it decreasing? Under normal operating conditions, will increasing the reflux rate increase or decrease the pressure at the top of the tower?

Increasing the reflux rate reduces the top temperature, decreases the vapor load at the tower top, and lowers the pressure at the tower top