No one has done any research on ethylene distillation towers!

Ethylene and ethane distillation separation is a very mature industrial application technology, and each olefin plant has equipment. In terms of the number of plates, the ethylene distillation tower is usually the second largest tower after the propylene distillation tower. As far as its design is concerned, the physical properties of ethylene and ethane are relatively ideal and can be simulated by ordinary process simulation software. As far as its operation is concerned, because this tower is the most important product tower in the olefin plant, the operation control is very strict. The purity of the ethylene product at the top of the tower is usually analyzed online. The ethylene concentration in the tower bottom is also strictly controlled because it is related to the ethylene yield index of the entire plant. I don’t know what LZ wants to discuss?

I mainly do research on ethylene distillation simulation. The current mature simulation software (such as Honeywell's UNISIM) is based on the equilibrium stage. The equilibrium stage has many shortcomings, the most fatal of which is the "equilibrium assumption". In order to weaken this shortcoming, the concept of "plate efficiency" is introduced, but this assumption is reasonable only in the case of steady-state operation. In non-steady-state situations (half of them are non-steady-state in real life) this assumption becomes unreasonable! In order to avoid the unreasonableness of "plate efficiency", Taylor et al. proposed a non-equilibrium stage model for simulating the multi-component separation process. This model canceled the assumption of equilibrium stage and retained the assumption of full mixing stage. They proposed to use double-film theory to describe the mass transfer process between the vapor and liquid phases in the bubbling liquid on the tray, calculate the diffusion rate of each component in the vapor film and liquid film respectively, and use the mass transfer equation to calculate the composition of the vapor phase leaving the liquid phase, thereby improving the calculation accuracy of the vapor phase concentration. There is an important link in the non-equilibrium model: Mass transfer flux calculation. Currently, Zhejiang University and Tsinghua University have several doctoral theses on this subject, but I think they are not good enough! So I want to discuss it with experts!

What specific question does the author want to ask? I would rather know about the research on the intermediate reboiler of the ethylene distillation tower.

I want to ask: Mass transfer flux calculation In the simulation calculation of the ethylene distillation column, the intermediate reboiler is regarded as the equilibrium stage.

The equilibrium stage assumption for ethylene distillation is very mature, because this system is mainly for the separation of ethylene and ethane, and its physical properties are relatively ideal. Its plate efficiency has many practical operating experience parameters that can be obtained by inverse calculation more accurately. Therefore, the ethylene distillation towers of million-ton ethylene plants are currently simulated using the equilibrium stage assumption, and the design is very reliable. To adopt the total mixing hypothesis and use double-membrane control theory to simulate this mass transfer equilibrium process, I am afraid that there is still a lot of basic data and some mechanisms of double-membrane mass transfer of this system under high pressure that need to be studied. It may make some sense from the perspective of theoretical research, but it is completely unnecessary from the perspective of engineering design. It must be mentioned that some systems are indeed not suitable for using the equilibrium stage assumption, such as the alkali washing tower in the same separation process. For decades, there have been problems with the design of this tower using the equilibrium stage assumption, because the mass transfer, reaction, heat transfer and other processes of this tower are carried out at the same time, and the kinetics of various processes in different concentration ranges are very different. Therefore, it is difficult to accurately simulate using the equilibrium stage assumption. For a long time, the design of this tower has been compensated by engineering margins. Using other methods to solve this problem requires a lot of testing and related investment. Fortunately, last year during the communication with ASPEN, I learned that they have included the non-equilibrium stage hypothetical simulation of the alkali scrubber tower as a focus of their work in the past two years. They comprehensively consider the reaction, mass transfer and heat transfer, obtain a large amount of basic data through experiments, and clarify the control mechanism and correlation coefficient of the liquid film or gas film in this system, completely changing the simulation method of the alkali scrubber. I believe this problem can be solved in the near future.

The ethylene distillation column and the methanol distillation column are basically three-column distillation. It’s just that the number of theoretical plates and the actual number of plates should be somewhat different. Because the boiling points of the two are different. For professional design consultation, go to the Second Chemical Design Institute, they are professional!

I have completed the steady-state simulation of distillation using gPROMS, but now I cannot solve the problem of variable correlation when doing dynamic simulation! There are no experts in Haichuan who have used gPROMS to solve differential equations, or experts who have performed dynamic calculations. Could you please give me some pointers on the simplification of differential equations during dynamic simulations?

Hello, I have recently been using gPROMS to simulate a distillation tower, but the modeling problem of the distillation tower has not been solved. Can you send me a gPJ file of the simulation of the distillation tower you made? I'll refer to it for reference, haha, thank you very much.

Send your program over and I'll take a look. What went wrong?