Regarding vapor-liquid separation
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Dear seniors, I’ve run into a problem recently. The situation is as follows: there is a vertical shell-and-tube heat exchanger, in which saturated water vapor flows from top to bottom in the shell side, at a temperature of around 130°C (corresponding pressure). This vapor is used to heat the cold water on the tube side. Under the current operating conditions, the vapor does not condense completely; there is still a considerable amount of vapor remaining, meaning that the outlet of the shell side consists of a mixture of vapor and liquid. Now, in order to obtain the heat absorbed by the heat exchange tubes, it is necessary to calculate how much steam has turned into condensed water (ignoring heat loss to the surrounding environment of the jacket). For various reasons, the shell side operates in an open-loop manner with no recirculation. It is now necessary to determine the amount of condensate at the shell side outlet, but it seems that there is no good way to separate the two at present. If it’s at atmospheric pressure, it’s easy to handle, but since there is a certain pressure at the outlet, allowing direct connection to the atmosphere will inevitably lead to flashing, preventing the recovery of condensed water. Therefore, a transition device is necessary to achieve vapor-liquid separation under a specific gauge pressure. I would appreciate some guidance from those with experience in this area. . . . . . (I’m not very good at learning*; I posted without following the rules. If there are any issues with that, please let me know.) )
Under the operating conditions specified on the first floor, it should be impossible to recover steam through expansion; therefore, it is recommended to install a drain valve to reduce the steam flow and increase the subcooling of the condensate, thereby achieving the purpose of recovering the condensate.
A water ring vacuum pump equipped with a buffer tank can be used to achieve gas-liquid separation. ! ~
The steam flow can be reduced or a cyclone demister can be installed
Reduce the steam flow rate without compromising the heat exchange efficiency.
As long as the temperature of the condensate is above 100 degrees, flash vapor will inevitably be generated at normal pressure! In other words, if you don’t want flash vapor to form, you must cool the condensate below 100 degrees. This depends on whether your heat exchanger can be designed in such a way as to achieve this degree of subcooling; if not, flash vapor is inevitable. However, the presence of flash vapor doesn’t mean that it’s impossible to recover the condensate, as only a small portion of it turns into flash vapor – the majority remains as condensate. A drain valve can be installed at the outlet of the heat exchanger, connected to a flash tank. But personally, I think a flash tank isn’t really necessary!
Agree with the suggestion from Floor 5: reduce the steam flow rate without compromising the heat exchange efficiency! :handshake
Thank you all for your suggestions; I think I now have new ideas. . .
In fact, the amount of flashing can be calculated based on the pressures before and after. Specific heat and latent heat of vaporization are both easy to find, right? It’s sufficient to know either the temperature or pressure before flashing.
You can design your own gas-liquid separator; it’s very simple
The pressure at the outlet of your heat exchanger is caused by the pressure of the entrained steam. To effectively separate steam from condensate, it is accurate to say that steam should not escape from the steam outlet of the heat exchanger – which is equivalent to steam leakage. A suitable steam trap should be installed at the steam outlet of the heat exchanger. This ensures that your heat exchanger can make full use of the thermal energy of the steam, as well as the thermal energy of some of the condensed water. And no steam will leak either. Your problem is then solved. Whether to add a steam flash tank depends on the amount of condensate you have. If it is relatively large and the secondary flash vapor can be utilized in later stages, an additional flash tank can also be added. Otherwise, you can simply send the condensate coming out of the steam trap directly to the storage tank. Last edited by Lao Dao on 2009-3-16 14:14]
It is recommended to install a steam trap or a flash tank equipped with a glass tube. A steam trap can effectively separate vapor from liquid, and a flash tank with a glass tube can also achieve effective vapor-liquid separation; it is slightly larger in size. The level of condensate can be observed through the glass tube, and by recording the increase in condensate volume over a period of time while the outlet valve of the flash tank is closed, it is possible to understand the heat transfer performance of the heat exchange equipment.
What the original poster is mainly trying to do is to calculate the amount of heat absorbed by the heat exchange tubes; in fact, there is no need to calculate the amount of condensate produced – it is sufficient to determine how much heat is absorbed by the medium being heated. This can be calculated using the specific heat capacity of the medium, the temperature difference between the inlet and outlet, and the flow rate of the medium. This is just my humble opinion, for reference only
Steam control valve assemblies are installed at the inlet to regulate the steam flow, while drain valve assemblies are installed at the outlet to remove condensate, thereby improving heat exchange efficiency