Effect of feed flow rate variations on the distillation column
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May I ask everyone, what effects will sudden increases or decreases in the feed flow rate, or temperatures exceeding normal levels, have on the tower respectively? If the flow rate increases by 30% suddenly, will the kettle liquid and distillate also increase by 30%? In particular, what impact will these changes have on the variation in the top pressure? When these situations occur, how should the gas flow rate that needs to be discharged by the safety valve at the top of the tower be calculated? Thank you all!
Chemical engineering principles cover a lot on distillation calculations; by applying the basic formulas, one can obtain the answer.
As the feed increases, the pressure in the tower changes, and so does the vaporization rate; at this point, changes in the reflux within the tower result in components at the top and bottom of the tower being different from those before. Following this logic, the outlet flow at the top of the tower and the outlet flow at the bottom of the tower will not increase in proportion. The explanation is a bit insufficient; it’s better to consult the principles of chemical engineering, or even separation engineering.
Personally, I think what should be considered first is not the changes within the tower, but rather how changes in the feed affect the quality of the products at the top and bottom of the tower. After all, quality is the foundation of a company’s survival. Is the person asking this question conducting research and experiments on distillation towers? . . . :o
Actually, I am designing a pressure relief valve for the tower top, and I want to understand how changes in external conditions affect heat levels, which in turn influences the increase in pressure at the tower top, so that I can calculate the gas flow rate that needs to be discharged by the pressure relief valve. I don’t know how to use Pro II to simulate such situations, so when conducting theoretical analyses, I feel overwhelmed by the large number of variables; I hope someone with more experience can offer some guidance.
This is an operational issue related to distillation towers, and it cannot be handled by simply using the design calculations from chemical engineering textbooks. The distillate and the residue in the reactor certainly will not increase in proportion. At least it won’t reach that state any time soon. At this point, there is a process of adjustment: since the feed is in liquid form, it increases the liquid load in the stripping section, so it is necessary to increase the heating capacity at the bottom of the tower. After the vapor rises, increase the condensation volume at the top of the tower. At the same time, adjust the bottom discharge volume and reflux volume. I hope the 30% change mentioned by the original poster can also be adjusted back.
It is necessary to check the control circuit on site. If the temperatures of the reboiler bottom and the top sensitive plate remain constant, the reboiler heat load and the top reflux flow will increase by 30% in proportion.
As the feed flow rate increases, both the gas and liquid loads inside the tower increase. At the top and bottom of the tower, the distillates change; at such times it is necessary to check the pressure and temperature inside the tower. With cold feed and constant pressure, the gasification rate decreases; as a result, the concentration at the top of the tower drops, while the concentration at the bottom of the tower increases.
I think that as the feed rate increases, the pressure at the top of the tower should decrease; the separation efficiency of the products will decline, and the quality of the products obtained at the top of the tower will worsen. I’m not sure if this is correct