Why has the steam flow rate in the reboiler increased?
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I have a question: The steam from the reboiler is used to heat and strip wastewater. Normally, the opening of the steam control valve is around 30%, and the amount of steam used is about 10 tons (at 1.0 MPA). After the steam exits the reboiler, the condensate goes into the condensate separation tank; steam at 0.4 MPA is produced at the top of this tank, while condensate comes out from the bottom. With all other conditions remaining unchanged, why does increasing the steam pressure at the top of the separation tank from 0.4 MPA to 0.7 MPA result in an increased steam flow rate? Even with the same opening of the control valve, the amount of steam used increases by 1–2 tons compared to before. I’m not sure what the principle behind this is Those who know it, please explain the reason. Thank you. Flowchart
When the steam pressure at the top of the separation tank is increased from 0.4 MPa to 0.7 MPa, the steam flow rate to the reboiler increases by 1–2 tons, primarily due to changes in the overall pressure and temperature of the steam system. First, increasing the pressure of the steam at the top will raise the pressure and temperature in the separation tank. Steam has higher thermal energy and temperature at high pressures, so the heat it transfers also increases. With the opening degree of the control valve remaining constant, as the heat load and temperature requirements inside the reboiler increase, more steam is needed to maintain the reboiler’s operational efficiency and temperature conditions; as a result, the steam consumption naturally increases. Secondly, an increase in pressure can also lead to changes in the steam density within the system, resulting in the same volume of steam containing more mass; in other words, the mass of steam flowing out at a given valve opening increases. In summary, as the steam pressure at the top of the separation tank increases, in order to meet the heating efficiency requirements of the reboiler as well as account for the density changes caused by pressure, the flow rate and amount of steam naturally increase. .
In simple terms, since the heat transfer amount remains unchanged, the efficiency of steam utilization is low, so more steam is naturally required
What was said upstairs is correct. Furthermore, regardless of whether the control valve is located upstream or downstream of the reboiler steam pipeline, if the flow rate increases, its opening degree will definitely increase, though by a small amount; thus the increase is not very noticeable.
Increasing the pressure in the flash tank means that the saturation temperature of the steam condensate rises, which results in a decrease in steam utilization efficiency and an increase in flow rate