Distillation column, forced circulation reboiler issues
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In a distillation tower, due to the relatively high boiling points of the components, forced circulation is used at the bottom of the tower to feed the material into the reboiler; that is, the material from the bottom of the tower goes into a circulation pump, from there to the reboiler, and then back into the tower. A flow control orifice plate is installed on the return port of the reboiler to prevent too much material from vaporizing inside it, while a small flow rate is extracted from the pump outlet. Question: What consequences can occur if the flow rate and head of a circulation pump are insufficient? ?
The insufficient flow rate and head of the circulation pump directly affect the amount of material that enters the reboiler. A decrease in this amount of material affects the material in the upward airflow, thereby reducing the workload of the tower. If the amount of material in the upward airflow falls below the minimum required level, the tower cannot function properly
Intuitive parameter changes: 1 Rising liquid level in the tower reactor. 2 The temperature of the tower kettle drops. 3 The liquid level in the reflux tank drops. 4 The reboiler is prone to scaling.
This reduces the discharge volume from the top of the distillation column and increases the liquid level in the bottom of the column. If this condition persists for an extended period, the material in the bottom of the column will deteriorate or even coker under prolonged heating, leading to blockages in the bottom of the column and the reboiler
Firstly, the amount of steam consumed will decrease, the temperature at the bottom of the tower will drop, the liquid level at that location will rise, while the liquid level in the reflux tank will fall. It is common to increase the opening degree of the valve controlling the heating steam supplied to the reboiler, but the amount of steam itself does not increase. It is recommended to use one circulation pump in operation and another as a backup, and to regularly switch and clean the inlet filters. Additionally, it is advisable to install an additional pump for extracting liquid from the bottom of the tower; using the same pump for both extraction and circulation can lead to issues when the extraction volume is high, as this may affect the circulation volume and cause operational fluctuations.
Ultimately, this prevents the material from being extracted, reduces the liquid level in the tower bottom, and even poses a risk of a dry tower
I would like to add that if the pump pressure is too low, the pressure inside the reboiler will also decrease. Even with a flow control orifice at the outlet, the gas phase volume will increase accordingly. Two-phase flow can cause increased vibrations in the reboiler, affecting its service life.