The issue with the reboiler pressure.
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This post was last edited by konglongmaomi on 2018-8-1 09:33. The reboiler at the bottom of the tower is heated by steam; a temperature control valve is installed on the steam inlet line to receive temperature signals from the bottom of the tower. The steam supply pressure is 4 barg, and a trap is installed at the reboiler outlet. The official pressure for condensate water is 1.5 barg. I came up with the idea that a trap is not a component used for throttling and pressure reduction; since it operates continuously in an open state to drain water, the pressure before the trap remains around 1.5 barg, although it might be slightly higher. So the condensate in the reboiler should be around 1.5 barg, at the saturation temperature corresponding to 1.5 barg pressure. The process package design manufacturer believes that the temperature control valve does not cause significant pressure reduction; therefore, the pressure of the steam condensate should be 4 barg, with the temperature of the condensate corresponding to the saturated temperature. So, the steam trap functions as a throttling element. . . This issue actually mainly affects the calculation of the reboiler size; I would appreciate some guidance from those with more experience~~~ Thank you!
A hydrophobic valve (water removal device) serves only the function of draining water; it opens when there is water present and closes when there is no water – it is a mechanical component that operates in this manner. It is normal for the “flow rate” control valve for steam feed to respond to changes in the temperature at the bottom of the tower. As for the pressure of the condensate, it is generally set to be the same as the pressure upstream; for example, if it is 4 BARG in your case, then the condensate pressure should also be set at 4 BARG, with the only difference being the phase change. Finally, the size of the reboiler depends on the heat source required, the steam supply, as well as the efficiency and area of the heat exchange surface. These are the insights I’d like to share
If you want higher efficiency, then add a vacuum device
If you want higher efficiency, then add a vacuum device
My practical experience: When the reboiler has a sufficiently large area, the temperature of the finally saturated condensate is approximately 20°C higher than the temperature of the medium being heated by the reboiler, even in cases where the reboiler has a large enough area and the lower part of the reboiler is submerged by condensate.
This post was last edited by ylb913 on 2018-8-12 at 15:42. Recently, I discussed the issue of recovering steam from condensate with an expert from a design firm. The expert’s estimate for the temperature of the condensate at the outlet of the reboiler was the same as what I had mentioned earlier, namely 20°C above the temperature at the bottom of the tower. In fact, the expert didn’t put it that way directly; instead, he said that when the temperature at the bottom of the tower is 120°C, the condensate temperature is 140°C, and when it is 130°C, the condensate temperature is 150°C. Of course, a sufficient heat exchange area for the reboiler is a prerequisite. Take a stripping tower with a bottom temperature of 132°C, heated by steam at 0.8 MPa, as an example: at the beginning of operation after maintenance, the lowest pressure in the condensate tank at the reboiler’s outlet was 0.38 MPa (with a gauge pressure of 0.4 MPa; the temperature of saturated steam at this pressure is 151°C). However, generally, the pressure in the condensate tank starts to rise after three months of operation, and it reaches nearly 0.8 MPa after six months, making it impossible for steam to enter the system. As a result, steam must be supplied directly at the bottom of the tower (for this reason, valves were installed at the inlet and outlet of the reboiler, allowing them to be isolated for cleaning; in such cases, steam is supplied directly at the tower bottom instead of using the reboiler). The reason for this is that the medium being reboiled contains coke particles, and as these particles accumulate continuously inside the reboiler’s shell side, the heat exchange efficiency declines over time. ——This is to state that “the heat exchange area of the reboiler is large enough” is a prerequisite.