This invention relates to steam generators for nuclear power plants and more particularly to such steam generators which utilize recirculated liquid to preheat incoming liquid.
In a steam generator utilizing a first heated fluid to convert a second fluid to steam, the pressure of the steam is a function of the logarithmic means temperature difference (LMTD) between the two fluids. Thus, by increasing the LMTD, the pressure of the steam can be increased.
An obvious way to increase the LMTD is to raise the temperature of the primary fluid. However, in nuclear steam generating systems, the temperature of the primary fluid is a limiting factor in the design of the system and is normally set at a maximum allowable safe value.
Increasing the LMTD may also be accomplished within the steam generator by providing a preheater chamber in which feedwater is heated to a temperature lower than the boiling point. Examples of steam generators which include preheaters can be found in U.S. Pat. Nos. 3,804,069; 3,896,770 and 3,916,843. The increased complexity of a steam generator resulting from the addition of a preheater section increases the probability of excessive corrosion, increased sludge collection, and water hammer problems. The present invention combines the simplicity of a recirculating steam generator with the performance advantages of a preheat unit.