Foaming is likely to occur in a distillation column after changes in its operation
Thread Content
Our facility is equipped with a wastewater stripping tower, which is designed to separate light-phase components such as methanol from the wastewater. Normally, the bottom of the tower contains 98% water along with some heavier organic compounds, while the top of the tower contains 50% water along with light-phase components such as methanol. Recently, due to process requirements, we want more water at the top of the tower; we aim for a water content there of around 70% to 80%, roughly speaking – it’s not a very high requirement. During the process of changing the operation, it was found that the tower was difficult to operate and the pressure difference across the tower tended to increase; my preliminary analysis is that flooding had occurred. My question is, if the operation of the distillation tower is changed and we consider extreme scenarios, what if the feed to this tower becomes single-component water, with a stable reflux rate and top product removal established. Won’t the gas-liquid load capacity of that tower decrease? In other words, I need to use less steam and generate less reflux in my current operations in order to ensure the proper functioning of the tower without experiencing liquid flooding. The above are my guesses; I hope those who are experts in design can help analyze them
The main purpose is to remove methanol from the wastewater, right? Just reduce the reflux temperature; we don’t need reflux at all, and there’s no problem with that
This is similar to the operation of a methanol stripping tower for catalytic MTBE; it is essential to maintain a low tower pressure. For detailed procedures, the original poster can look up information related to MTBE – it might be helpful!
{:3_60:} Isn’t it just equivalent to increasing the content of the heavy components at the top of the tower? By moving the feed inlet upward and the extraction outlet downward, the amount of reflux is reduced, and thus the amount of steam used is also decreased. If you have a large amount of material stored in your tower, and there is significant gasification at the bottom, the pressure difference will definitely be high. In such cases, it’s necessary to increase the rate of extraction and reduce the thermal and material loads. After trying it a few times, you’ll get used to it; no amount of explanation is as good as trying it yourself
"What is the purpose of increasing the water content to 70% to 80%? Is it to recover more water, or is it because the required methanol concentration has been reduced, allowing for less steam to be used? Reducing backflow and lowering the liquid inflow amount can prevent liquid overflow
That’s more or less what it means. My question is that after making the changes to the operation, the composition at the top of the tower has become heavier, and the entire tower has deviated from its original design. Under such circumstances, from a design perspective, is it necessary to reduce backflow and steam in order to ensure the normal operation of the tower? If it is necessary to deviate from the original design parameters, how exactly should the adjustments be made, and why?
A low tower pressure is indeed needed; I can understand that. Because the components at the top of the tower have become heavier, the tower pressure cannot increase as much as it would like to. Practical experience shows that the tower pressure is much lower than the designed value. So I’m a bit worried about determining the appropriate low pressure level; are there any other parameters that can be used as a reference to avoid other problems arising from operating at low tower pressures?
Thank you for your advice; I know that by trying a few more times, I can figure out the balance point. But the device is operating normally; my shift is short, so it’s not possible to conduct extensive tests. So I want to find someone who understands design to determine a direction, and then make adjustments little by little
Yes, that’s exactly our goal. I did reduce the steam and reflux, which caused the water content at the top of the tower to reach 95%, but even with a significant reduction in pressure difference, it remains high. There is also the concern that the tower might leak. So now the reflux has been increased again; by accumulating the light components, the pressure difference returned to normal. I think it’s probably because the reduction last time was too large. So I’m looking for someone who understands design to ask: how can one determine the right level of parameter adjustment, and what indicators can be used as a reference?
Isn’t the purpose of your separation to remove methanol and water vapor from the bottom of the tower? So what if the pressure difference is high, or what if there’s leakage? This isn’t a distillation tower; the separation requirements apply only inside the distillation vessel, so there’s no need to adjust things according to the principles of a distillation tower