Flow distribution arrangement for a steam generator

Claim 1

A vapor generator in which heat is transferred from a primary to a secondary fluid to vaporize the latter, said vapor generator comprising: a vertically oriented shell, a plurality of U-shaped tubes disposed in said shell so as to form a tube bundle having an open lane adjacent the tubes having the shortest radius bends, a head portion having a tubesheet with holes for receiving said tubes and a dividing plate which cooperates to form headers for each end of the U-shaped tubes, a primary fluid inlet nozzle in fluid communication with one header, a primary fluid outlet nozzle in fluid communication with the other header, whereby the primary fluid flows through the tubes forming a hotleg and a coldleg portion of the tube bundle, a wrapper disposed between the tube bundle and the shell to form an annular chamber adjacent the shell, a secondary fluid inlet ring disposed to introduce influent secondary fluid to the upper portion of the annular chamber, said secondary fluid inlet ring having ports so disposed therein that the majority of the secondary fluid is introduced into that portion of the annular chamber adjacent the hotleg portion of the tube bundle, said secondary fluid ring having said ports so disposed that no secondary fluid is introduced to that portion of the annular chamber adjacent the said open lanes, said annular chamber being generally free from obstructions, whereby the flow distribution of secondary fluid across the tubesheet is improved.