Demineralized-water preheater

The invention belongs to the technical field of heat exchangers used in synthesis ammonia production, and particularly relates to a demineralized-water preheater which comprises a lift tube box, a left tube plate, a pull rod, a shell pass shell assembly, heat exchange tubes, a baffle plate, a right tube plate and a right tube box. Tube plates and the heat exchange tubes are connected by adopting strength welding and strength expanding; in each tube plate strength expanding part, two ring grooves with the width being 3mm and the depth being 0.5mm are formed at a 6mm distance; the heat exchangetube wall thickness is expanded into the tube plate ring grooves by using a hydraulic tube expander, and the outer walls of the heat exchange tubes on the rest parts tightly fit to the inner walls oftube plate holes, so that gaps between the tube plates and the heat exchange tube are eliminated; the tube plates select 16Mn (carbon steel) forge pieces as materials, S32168 materials with the thickness being 6mm are surfacin