Abstract: The invention concerns a heat exchanger (1, 40) comprising: a first container body (2, 50); a first tube bundle (3, 57) arranged inside the first container body (2, 50); two tube plates (4, 51; 5, 52) for supporting the first tube bundle (3, 57); an evaporation chamber (2a) defined between the first container body (2, 50), the first tube bundle (3, 57) and the tube plates (4, 51; 5, 52); an inlet head (8, 53) and an outlet head (9, 54) communicating with each other through the first tube bundle (3, 57); an inlet way (10) and an outlet way (11) for the passage of a first fluid through the heads (8, 53; 9, 54) and the first tube bundle (3, 57); an inlet mouth (12) through which a second fluid flows into the evaporation chamber (2a). A superheating unit (20, 44) of the second fluid, associated with the first container body (2, 50), is provided.