Shell-and-tube apparatus for heat recovery from a hot process stream

A shell-and-tube apparatus comprising a vessel with an exchanging section and a separating section within said vessel,

• wherein said exchanging section contains a bundle of U-tubes having respective tube inlet ends and tube outlet ends, and a chamber around said tubes, said chamber being in communication with an input for a process stream, said separating section comprises a collection chamber in communication with said outlet ends of the tubes;
• wherein said apparatus has an input for an evaporable liquid medium and a chamber within said vessel for receiving said evaporable liquid medium through said input, which is in communication with said tube inlet ends;
• wherein said evaporable liquid medium has a temperature, which is lower than the temperature of said process stream so that, during operation, said tubes are exposed to said process stream while the process stream traverses said chamber around said tubes, and the evaporable medium is heated and at least partially evaporated by flowing inside said tubes, and the at least partially evaporated medium is admitted to said collection chamber after leaving said tubes;
• wherein in said separating section, vapour fraction and liquid fraction separate from said at least partially evaporated medium;
• wherein said chamber for receiving said evaporable liquid medium is not part of said separating section;
• wherein no separation of vapour takes place in said chamber for receiving said evaporable liquid medium;
• wherein each tube has a first straight portion starting from the inlet end, where the evaporable medium flows downward, a second straight portion where said medium flows upwards until it reaches the outlet end of the tube, and a U-shaped portion that connects said straight portions;
• wherein the vessel comprises an outlet for non-evaporated liquid medium;
• and
• wherein the apparatus is configured to mix, externally to the vessel, a portion of non-evaporated liquid medium extracted from the outlet for non-evaporated liquid medium with the evaporable liquid medium fed to said input for evaporable liquid medium.