Abnormal operation of the distillation tower
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The polysilicon raw material purification tower was operating normally from the start of parameter tuning, but recently it was found that the tower pressure had dropped, with no pressure drop inside the tower (0.005 MPa). Of course, the liquid layer is very thin, and even when the valves are opened to their maximum, steam cannot be introduced. The heat exchange area has been calculated, and there is a large margin of capacity; the drain valve is working properly and shows no signs of blockage, and the steam inlet valves are also in good condition. Please help analyze the reason.
First, check whether the feed rate and return flow rate have decreased, and also verify if there are any issues with these two gauges. Next, examine the level of liquid in the distillation tank as well as the distillation volume to see if there are significant changes in the output compared to before. Analyze the type of tray, whether there is a corrosive medium present, whether there is a possibility that the opening rate of the trays has increased, and whether excessive gas flow at a certain stage could have caused the lower trays or the gas caps on those trays to fall off Lower pressure means lower load; therefore, the parameters related to the load should be eliminated one by one, starting from the simpler ones and moving on to the more complex ones, from those that occur easily to those that occur less frequently.
Also, check to make sure there are no issues with the liquid level gauge of the reboiler.
It is possible that an excessive amount of non-condensable gas has accumulated inside the tower, occupying the heat exchange surface and thereby reducing the effective heat exchange area. This issue can be addressed by increasing the pressure of the exhaust gases by fully opening them manually, thereby increasing the temperature of the hot oil and water in the reboiler
The feed and discharge volumes are normal; the backflow volume has decreased significantly. Since there is no pressure drop, the backflow volume naturally decreases. It is a conventional sieve plate tower, without liquid drop pipes or distillate trays.
Are the temperatures all normal? Please provide more details, OP. The absence of pressure drop indicates that the load on the tower is low.
Has the quality of the product from the top of the tower changed? If not, and your reflux volume has decreased while your feed rate remains unchanged, that means steam consumption has been reduced. Then why open the steam valve fully? Could it be that the temperatures at certain points in the tower have dropped? Consider the following points: 1. Has the composition of the material fed into the tower changed? This depends on whether there are any changes in the process used to produce the reaction mixture. 2. With the steam valve fully open, check whether the pressure on the steam side of the reboiler is much higher than before. 3. If this is the case, carefully verify whether the liquid level gauge in the tower is functioning properly; this symptom can also occur when the tower is empty. 4. After debugging, there will still be some changes until normal production is achieved; the process parameters should be adjusted based on whether the quality of the product from the distillation tower meets the required standards. I hope this helps you.
If the steam flow cannot be increased, is the temperature at the bottom of the tower higher than normal? Based on the phenomena you described, it can be preliminarily inferred that there is insufficient heat exchange within the reboiler, which results in less steam being generated and a lower pressure difference inside the tower ； At the same time, less steam is consumed, and the flow rate does not increase (the flow rate remains almost unchanged even when the valves are adjusted over a wide range)
There is no pressure drop inside the tower; the pressure at the bottom of the tower is low, so the temperature also drops, and the reflux flow rate is low. The product from the bottom of the tower is of good quality, while the product from the top is of poor quality
If the quality of the product from the top is poor, then you need to increase the reflux rate and reduce the amount of distillate output; or you can opt for full reflux until the product from the top meets the required standards before proceeding with extraction. It’s not possible for the product from the top to remain substandard even when full reflux is used, right?