Saturated steam is depressurized and then used in a heat exchanger – is the area of the heat exchanger sufficient?
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Everyone, I have a question: The original factory designed 6 barg of saturated steam for heating hot water, raising the temperature of the water from 25°C to 50°C; the condensate from the heat exchanger is discharged through a drain valve； It has been suggested that 6 barg of saturated steam be directly depressurized to 4 barg first, and then sent to the heat exchanger, with the excess steam being discharged through a drain valve. Is this approach feasible? In my opinion, reducing the saturated steam pressure from 6 barg to 4 barg turns it into superheated steam; theoretically, this could result in insufficient heat exchange area in the heat exchanger, thereby affecting the efficiency of heat exchange ； However, some argue that the superheated steam from 4barg will eventually turn into condensate, which is then discharged through the steam trap; moreover, the temperature of this condensate is lower, which helps to save energy. How can this be explained? Thank you all
It’s just thermal energy conversion – why is there an additional step of pressure reduction?
Thank you for your reply. When the area of the heat exchanger is sufficient, it does help to reduce steam consumption to some extent, but the impact is not significant
How can it turn into superheated steam after pressure is reduced? It should still be saturated steam, right?
Direct pressure reduction is achieved through saturated steam; since different pressures correspond to different saturation temperatures, there will be a certain degree of superheat while the enthalpy remains unchanged. However, the main change is in volume, which requires recalculation of parameters such as the diameter of the tubes on the steam side of the heat exchanger, the flow capacity inside the heat exchanger, and the heat exchange area. Yet if the heat exchanger does not have a subcooling section, the energy-saving effect of this approach is not significant. It is recommended that such a steam-water heat exchanger should have a certain subcooling section, allowing for counterflow heat exchange between the supply water and the condensate water in order to achieve energy savings. It is also possible to add an additional water-water heat exchanger before the steam-water heat exchanger, connecting the condensate water to this water-water heat exchanger; this will yield even better energy-saving results. Plate heat exchangers can be used, as they require less space.
Thank you for the reply; the heat from the condensate is also not wasted
Do not use it at reduced pressure, as there will be energy loss; it is still recommended to use liquid-liquid heat exchange for the condensate, so as to recover the heat from the condensate
By reducing the pressure from 6 bar to 4 bar, the temperature difference for heat transfer decreases; therefore, the heat exchange area should need to be increased