Distillation column operation
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This post was last edited by TDI5 on 2011-3-5 00:45. Our facility has a packed tower that operates under negative pressure, with bottom heating achieved through thermal siphon self-circulation. The diameter of the bottom circulation pipeline is 200. Additionally, there is a forced circulation pump at the bottom of the tower, with a pipe diameter of 40. Under normal conditions, the tower is heated through thermosiphonic self-circulation; the opening of the forced circulation pump at the bottom of the tower for returning fluid back into the tower is very small. The main function of this pump is to facilitate the removal of material from the bottom of the tower. During one drive, the valve of the heat siphon circulation pipeline at the bottom of the tower was not opened, leaving the bottom of the tower in a forced circulation mode. As the temperature at the bottom of the tower increased, and due to the low temperature in the tank, the valve on the circulation pump’s return line to the tower was slightly opened; in other words, the forced circulation rate was increased slightly. As a result, the temperature of the first layer of packing at the bottom of the tower, as well as the temperatures of the layers above it, rose sharply. The pressure at the bottom of the tower increased, the pressure difference across the tower increased, the pressure at the top of the tower rose, the liquid level in the reflux tank increased, and the amount of reflux flow increased. However, the temperature at the bottom of the tower is lower than the temperature of the first packing layer at the bottom of the tower. At that time, it was thought that there was some flooding, so the amount of heating steam was reduced; as a result, the bottom pressure of the tower, the top pressure of the tower, the pressure difference across the tower, and the liquid level in the reflux tank all decreased. However, the temperature at the bottom of the tower remains lower (or equal to) the temperature of the first layer of packing adjacent to it, and the temperature at the top of the tower fails to drop. What is the reason for this? Why doesn’t the temperature at the bottom of the tower rise, while the temperatures at points above it do? The temperature of the kettle is also lower than that of the adjacent upper packing. Thank you
In similar situations, the cause was not found.
Reply to 2# chryy: What exactly is the situation you guys are facing?
Reply to 1# TDI5: I hope to get explanations from everyone. Thank you
Cause analysis: 1. The composition of the material while driving is different from that during normal production; there is too much light component and too little or no heavy component. The rapid temperature increase can prevent the formation of thermal siphonage within the reboiler, resulting in a large temperature difference between the inlet and outlet of the reboiler. 2. It is recommended to turn on forced circulation during the next start-up; if the flow rate of the forced circulation pump permits, open the circulation manual valve fully and supply steam gradually, paying attention to the temperature difference between the inlet and outlet of the reboiler. 3. During startup, pay attention to the feed flow rate of the distillation tower; it is advisable for this rate to be above 60% of the capacity to facilitate operation.