Vacuum distillation, the issue of heavy components
Thread Content
For vacuum distillation, where the product is obtained at the top of the tower and the product quality is frequently unsatisfactory due to excessive levels of heavy components, what should be done to increase the reflux ratio, reduce the amount of heavy components, and prevent flooding of the tower?
OP, is your vacuum level the same as the designed value, and is the corresponding top temperature the same? If there are no problems, could driving the temperature up too quickly be causing the heavier components to reach the top of the tower? Is there a problem with the liquid distributor at the top of the packed tower?
My opinion: 1. Has it been produced normally before? Is driving always like this? 2. Are the design conditions in line with actual operating conditions, and is the design reasonable? 3. Check the redistributor; in my experience, towers with a height of more than 200 mm require special attention to the design of the redistributor. 4. Also check the level of vacuum and the rate of temperature increase
Check if there are any issues with the vacuum. The heating rate is too fast, and the temperature control at the bottom of the tower is too high. Increase the reflux rate, reduce the amount taken from the top of the tower, and allow some product to be taken from the bottom of the tower; there may be problems with the material balance throughout the tower. Is the liquid level at the bottom of the tower within the normal range? Generally, it should be between 60-70%
Reducing pressure necessarily means reducing the steam flow rate to the reboiler! What are your tower design parameters like?
Reducing the feed rate or lowering the temperature at the bottom of the tower can also decrease the output from the top of the tower. Also, was the tower designed to be high enough during the design phase?
If it fails frequently, does it pass sometimes? Check whether the steam feed and pressure are fluctuating, whether the feed flow is highly variable, and whether the reflux flow is at a constant level. If the tower still doesn’t meet the standards after being built, there might be a problem with the design. Check the material-pressure curve to see if the vacuum level is appropriate. Several people upstairs mentioned the distributor; if there are issues with the selection of the distributor or its distance, it can lead to severe dead zones at the edges of the trays, affecting the separation efficiency!
Reply to 1# Wang Yilin: Try reducing the temperature at the bottom of the tower
Check if there are any issues with the vacuum. The heating rate is too fast, and the temperature control at the bottom of the tower is too high. Increase the reflux rate, reduce the amount taken from the top of the tower, and allow some product to be taken from the bottom of the tower; there may be problems with the material balance throughout the tower. Is the liquid level at the bottom of the tower within the normal range? Generally, it should be between 60-70%
The tower is not overloaded; the vacuum level is within the specified range. Adjust the temperature!
Reducing the heating amount and lowering the temperature at the bottom of the tower should increase the purity of the light components at the top of the tower