Issues encountered during the startup of the distillation tower
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When starting up the distillation tower to increase its throughput, we fed 40% of the required amount of material directly, and then raised the temperature of the reactor bottom. At first, both the temperature at the reactor bottom and at the top of the tower increased; however, when the temperature at the top reached 40 degrees, it stopped rising. We continued to increase the heat input, but with no effect. The pressure at the top of the tower was more than 10 KPa higher than normal, so we suspected the presence of other gases inside. Therefore, we vented gas from the top of the tower, and it took a little over an hour for the situation to improve significantly. Could any expert tell me why this is the case?
Before starting the machine, there is usually air inside the distillation tower. After the plant is shut down, it can be due to the prevention of negative pressure in the tower from damaging the equipment (in most cases, these are atmospheric pressure towers); or it can be the result of negative pressure developing in the tower (in most cases, these are pressurized towers), leading to gradual leakage; or it may occur during maintenance work. During operation, for a distillation tower that is isolated from the atmosphere, it is necessary to release this air.
It is caused by the presence of non-condensable gases at the top of the tower; this increases the tower pressure, preventing the light components of the material from reaching the top of the tower and thus hindering proper condensation.
After a short-term shutdown of a distillation tower, there is still a certain temperature present; as this temperature drops, the tower pressure also decreases, and it is possible for the pressure to fall below atmospheric level. Therefore, it is necessary to fill the tower with a protective gas (usually N2, an inert gas) to keep the pressure above atmospheric level, thereby preventing air from entering the tower and reacting with the materials inside. When the tower is to be restarted, this gas must be removed; otherwise, the temperature of the tower will not rise.