Double plate flow distributor

A vapor generator comprising a vertically extending cylindrical shell section;

• a tubesheet rigidly secured to said shell section adjacent the lower end thereof, a bundle of U-shaped tubes disposed within said shell section, said tubes including respective upflow and downflow legs connected to said tubesheet, said upflow legs being spaced apart from said downflow legs so as to define a diametral tube-free zone therebetween, means for introducing a first heat exchange fluid into said shell, means for removing said first heat exchange fluid from said shell, means for introducing a second heat exchange fluid into said upflow legs, means for removing said second heat exchange fluid from said downflow legs, a cylindrical shroud disposed coaxially within said shell section surrounding said tube bundle said shroud together with said shell section defining an annular space therebetween, means for passing said first heat exchange fluid into said tube-free zone, said means for passing including a first plate extending through said zone and rigidly connected to said shroud along its side edges, said first plate being adjacent said downflow legs of said U-shaped tubes, a second plate extending through said zone and spaced away from said first plate, said second plate being adjacent said upflow legs of said U-shaped tubes and rigidly connected to said shroud, said second plate contacting the inner wall of said shell section at opposite ends thereof, and a plurality of ribs connected between said plates, said shroud being formed with openings therethrough to permit passage of said first fluid from said annular space into said tube-free zone between said plates, said openings extending above and below at least one of said ribs to permit passage of said first heat exchange fluid into said tube-free zone above and below said one rib, said ribs including vertically extending sections connected to sloped sections sloping in a direction extending upwardly from the center of said vapor generator toward said shell section, said vertical sections being spaced apart from one another to allow for distribution of said first fluid along the length of said tube-free zone and across said tubesheet therebelow, and means for directing said first heat exchange fluid from said tube-free zone toward said upflow legs of said U-shaped tubes, said means for directing including an opening formed in said second plate and extending substantially across the lateral expanse of said second plate.