Undergraduate course design: countercurrent two-effect simulation
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Hello, teachers on the forum. I have an ASPEN simulation file for a process design; I spent a long time trying to get it to work, thinking it would succeed, but it failed at the final stage. The design requirements are as follows: two-effect operation in series, with high pressure in the first effect and atmospheric pressure in the second effect. The quality fraction at the top of the tower is required to be 0.93, while it should be 0.0001 at the bottom of the tower. In a simple series of two towers, the heat loads at the top and bottom of the towers are equal. When these values are applied to a two-effect system, it turns out that the heat load obtained after passing through the heat exchangers is much lower than what’s needed. But logically, this shouldn’t happen; even if there are some heat losses, the difference shouldn’t be so large. I hope the teachers can give me some guidance. The file contains some data from my simulations of a simple two-tower system, and the image shows the flow diagram of the two-effect system I designed. I really appreciate it if everyone could offer me some suggestions. Thank you very much.
Is the ratio between the B15 and B16 dividers set according to the reflux ratio?
Actually, there seems to be a problem with this design. It would be more reasonable for the fluid to pass through a gas-liquid separator after coming out of the reboiler in the second tower (with parameters set at 0 load and 0 pressure), rather than being discharged directly, unless it’s a thermosiphonic reboiler that is being used. I haven’t seen your source files, but this requires first simulating the two towers separately, then extracting the data. After that, the condenser of the first tower and the reboiler of the second tower need to be separated, before finally combining the condenser with the reboiler. It’s important to note whether a kettle-type reboiler or another type is selected when simulating the towers separately; the default choice is usually a kettle-type reboiler