Heat exchanger for cooling process gases which are under high pressure and temperature

DETAILED DESCRIPTION What I claim is: 1.
A heat exchanger for cooling process gases which are under high pressure and high temperature, with withdrawn heat being used for high pressure steam generation in accordance with natural circulation principles to influence cooling medium flow, said heat exchanger comprising in combination: a housing having at least one process gas inlet and at least one process gas outlet; a tube sheet extending across the inside of said housing separating the housing into a process gas plenum and a coolant gas plenum above the process gas plenum; the coolant plenum being divided into two chambers by said tube sheet, said chambers being separated from one another to provide a first chamber for inlet coolant-steam and a second chamber below the first chamber for outlet coolant-steam in order to provide coolant-steam circulation; and a U-tube bundle suspended on said tube sheet in said housing and extending into the process gas plenum from the coolant plenum, each U-tube of said U-tube bundle having the upper portion of a first leg of the "U" at least some of said tubes being in the form of a double tube having an inner tube surrounded by an annular conduit, the inner tube being in open communication with the first chamber and the annular conduit being an open communication with the second chamber, the remaining portion of said first leg continuing as a single tube through the bight of said U-tube and into a second leg thereof which second leg opens into the second chamber, whereby said inner tube has the function of a gravity tube for delivering coolant steam into the U-tube whereby said annular conduit and said single tube have the function of risers constructively arranged to maintain U-tube guidance of cooling medium flow so that by application of natural circulation principles cooling- medium-circulation instabilities are avoided during starting phases and during pressure fluctuations.
2.
A heat exchanger in combination according to claim 1, in which said annular conduit of said double tube has a larger diameter than does said single tube, the U tube ends being arranged quadratically in said tube sheet in such a way that a smaller diameter single tube is arranged between every two larger diameter double tubes