Has anyone worked on a forced-circulation reboiler? Could you give some advice?
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The medium is saline, requiring the use of a forced-circulation reboiler. During the process, I wasn’t very clear on some fundamental principles, which led to many issues in the simulation. So I would like to ask for advice. It would be best to have seniors who can provide the design process parameters (reactor bottom temperature, inlet and outlet temperatures of the cold stream in the reboiler, vaporization rate, flow rates, pump diameter, and outlet pressure) as a reference, which can also help identify the source of the problem. 1. Is the outlet pressure of the reboiler fixed at the same level as the pressure at the bottom of the tower? 2. I set the vaporization rate at the bottom of the tower to 0.03; should this value be reduced further? Consider that the circulation is driven by a pump. 3. With a vaporization rate of 0.03, the circulation rate is approximately 100,000 kg/hr. For a circulation rate of 0.01 at 250,000 kg/hr, are there any requirements regarding pumps for a forced-circulation reboiler? 4. The flow rate is very high, but under conditions that satisfy the heat exchange requirements, the flow velocity in the tube side is very low (less than 1 m/s), which is puzzling, unless the tube length is increased. On the other hand, forced-circulation reboilers require a higher flow rate. 5. Is the forced-circulation reboiler a theoretical stage or? Is there any reference, such as the one-pass design of a thermal siphon reboiler? My understanding is that the temperature at the reboiler outlet is higher than that at the bottom of the tower, and the rising vapor phase mainly results from the heating and vaporization of the liquid at the tower bottom by the cold stream from the reboiler. Is that correct? Thank you first!
The one-pass vaporization rate of a thermosyphon reboiler is not just 3%–5%; forced circulation should at least enable a vaporization rate of 15%–20%.
1. The outlet of the reboiler is the bottom of the tower; the pressures are almost the same. 2. A vaporization rate of 0.03 is sufficient. 3. The pump should be able to meet the requirements regarding circulation pressure and flow rate. 4. If the flow velocity in the tube side seems too low, use a longer and thinner tube. 5. The vapor phase is mainly generated by heating in the reboiler; the vapor you mentioned can be ignored
Thank you for your answer. 1. The outlet pressure of the reboiler tubes is still different from that of the tower bottom, right? The outlet pressure at the inlet to the tower bottom is the same. 3. The pump seems quite large; can a double-pass reboiler be chosen? I’m afraid there might be a traffic jam at the turn. Are there any previous cases that can be used as a reference? Thank you
1. What I mean is that they are almost identical. 3. The pump is large, and the vaporization rate you use is also relatively conservative; it’s a double-pass system: L, with the gas-liquid mixture flowing through the tube pass
The layer owner is right. Let’s discuss this further: the driving force behind thermal siphon effect is the concentration difference. Since some of the material vaporizes under heat exchange conditions, the density inside the heat exchange tubes decreases. As a result, the density of the material at the bottom of the tower is relatively high, which drives the material to circulate inside the heat exchange tubes； Another vaporization issue is that once the material is pushed back due to the density difference, it ends up at a height higher than the bottom of the tower. The pressure here is certainly lower than that at the bottom of the tower, while the pressure in the heat exchange tubes remains constant. As a result, the pressure of the material exiting the heat exchange tubes is also slightly higher than that at the outlet. This causes the material to flash as soon as it exits, and the vaporization that occurs during this flashing process accounts for a significant proportion! The above are my personal opinions!