Supply water temperature for catalytically deoxygenated water
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I would like to ask: in a catalytic reaction system, when the temperature in the middle section of the external heat exchanger is 500 degrees and the pressure of the medium-pressure steam is 3.5 MP, by how much does the temperature of the deoxygenated water entering the steam drum need to exceed a certain value before water starts to vaporize prematurely inside the heat exchange tubes, thereby affecting the efficiency of heat extraction? Thank you...
The temperature of saturated steam corresponding to 3.5 Mp is around 235°C; this depends on the flow conditions related to external heat extraction as well as the overall temperature distribution. It is difficult to determine an exact value for the temperature in the middle area where external heat extraction takes place, as it is 500°C there. Based on the information you provided and practical experience, it can be estimated that a drum temperature of ≤220°C should not affect the overall efficiency of external heat extraction. It’s not necessarily correct; it’s just for discussion.
Bro, no matter what the temperature of the feedwater is, as long as the pressure inside the steam drum is 3.5 Mpa, the water temperature inside the drum will be 235 degrees as mentioned above, and this won’t have much impact on heat extraction to the outside. If the temperature is too high, it is necessary to consider whether vaporization occurs inside the economizer, as this can affect its efficiency or lifespan.
I can’t agree with the view you mentioned. If water has a boiling point of 235 at a pressure of 3.5 MPa, and the temperature of the water inside the steam drum is also 235, then as soon as the water enters the heat transfer tubes, it will vaporize rapidly, thereby affecting the efficiency of heat transfer in those tubes... So I think the temperature should be lower than 235
Even though the boiling point of water at 3.5 MPa is 235 degrees, the transformation of water at 235 degrees into steam at 235 degrees represents a phase change. The latent heat of vaporization for water at 3.5 MPa is approximately 1752 KJ/kg. This is far too much compared to the heat required for a temperature increase! So as long as the liquid level in the drum is normal, the water will not vaporize quickly once it enters the heat exchange tubes, and this will not affect the heat exchange efficiency of the tubes!
Previously, although I was aware of the concept of latent heat of vaporization, I didn’t know the specific values, nor was I clear about the heat transfer rate of the heat exchange tubes in the external heat exchanger. I used to think that the fluidization effect in the external heat exchanger varied from case to case, which meant that the location where the water vaporized inside the heat exchange tubes should differ as well. Now it seems I was overthinking it; it’s likely that once the water enters the heat exchange tubes, its residence time there varies depending on the fluidization conditions caused by the external catalyst. It is only after the water vaporizes that the water vapor bubbles rise due to their lower density and enter the steam drum. Hmm... Thank you, Director Longfeng. Hehe...
The drum contains saturated water; the water that is heated from the outside is also saturated water. Inside the tube bundle, the saturated water turns into a mixture of saturated water and saturated vapor. During this process, the temperature remains constant, only the vaporization rate changes.
It should be noted, however, that if the circulation volume is insufficient or there is a deviation in the water flow to the tube bundles, it is possible for all of the vaporization tube bundles to overheat and burn out.
Got it. Thank you. I was wrong before. Um...
It depends on the overall fluidization condition of heat removal from the outside, as well as the overall temperature distribution.