[Technical Exchange Post] [Daily Question] Principles of Chemical Engineering 129: Saturated Steam and Superheated Steam (August 2)
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(Original background: This issue was encountered during the process design; some engineers believed that the steam would be superheated, while others thought it would remain saturated steam.) Steam in chemical plants is the most commonly used heating source. Saturation steam is usually chosen for heating, as it has a high heat transfer coefficient ； The heat transfer coefficient of superheated steam is much lower than that of saturated steam (by an order of magnitude). Please discuss the following: is the steam in a saturated state or a superheated state? The utility system supplies saturated steam at 0.8 MPa, which is then reduced to 0.6 MPa for use in heating the reboiler; there is no water makeup system in between. Under these conditions, is 0.6 MPa steam in a saturated state or a superheated state? If you have encountered similar situations in production equipment, it means the factory is actually even better.
I’m facing this problem right now. Should heat transfer oil or steam be used? Whether to use saturated steam or superheated steam, the medium needs to be heated to 240 degrees.
The steam after pressure reduction should also not be superheated steam
Choosing a heating medium to heat to 240°C is a problem. The saturated vapor pressure is relatively high.
Based on what you’ve described, reducing pressure without reducing temperature – we have also used that approach.
Yes, this relates to the issue of equipment manufacturing; therefore, it is still recommended that owners use heat transfer oil.
Under these conditions, 0.6 MPa steam is in a saturated state
It is in a superheated state; the temperature of the 0.6 superheated steam is around 180°C.
Personally, I understand this to be superheated steam, as only the pressure is reduced while the temperature remains unchanged. The steam pressure after passing through the control valve is 0.6 MPa, and the temperature corresponds to the saturation temperature at 0.8 MPa. However, in actual use, heat is dissipated through the pipes and valves, and the steam may contain superheated water; as a result, this degree of superheating is quickly reduced, and the steam again becomes saturated steam in practical applications.
Theoretically, pressure is reduced without a decrease in temperature； In actual production, it might be saturated steam (since there is condensate in the pipes during steam transmission); those with production experience can share what really happens, hehe