![]() ![]() There are quite a few reasons why superheated steam is not as suitable for process heating as saturated steam: Greater amounts of superheat are more difficult, and often uneconomic to deal with and (for heating purposes) are best avoided. This small degree of superheat is removed readily in the first part of the heating surface. HPIs often desuperheat steam to within about ten degrees of superheat. To be clear on this point, in most cases, saturated steam should be used for heat transfer processes, even if it means desuperheating the steam to do so. This is more likely to be because superheated steam is already available on site for power generation, being the preferred energy source for turbines, rather than because it has any advantage over saturated steam for heating purposes. (Note: The values used for the temperature and energy content in the following examples are from steam tables)Ĭan superheated steam be used in process heat exchangers and other heating processes?Īlthough not the ideal medium for transferring heat, superheated steam is sometimes used for process heating in many steam plants around the world, especially in the HPIs (Hydrocarbon Processing Industries) which produce oils and petrochemicals. ![]() The thermodynamic efficiency of a heat engine such as a turbine, may be determined using one of two theories: The solution is to supply the turbine with superheated steam at the inlet, and use the energy in the superheated portion to drive the rotor until the temperature/pressure conditions are close to saturation and then exhaust the steam.Īnother very important reason for using superheated steam in turbines is to improve thermal efficiency. Not only would this promote waterhammer, but the water particles would cause severe erosion within the turbine. This means that saturated steam would get wetter and wetter as it went through the successive stages. Turbines have a number of stages the exhaust steam from the first rotor will be directed to a second rotor on the same shaft. If the steam was at saturation temperature, this loss of energy would cause some of the steam to condense. ![]() The energy to make this happen can only have come from the steam, so logically the steam has less energy after it has gone through the turbine rotor. Superheated steam has its applications in, for example, turbines where the steam is directed by nozzles onto a rotor. ![]()
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