A heat exchange system comprising: - a single apparatus having an area immersed in a fluid bath and a free space at the head in which a vapour phase is accumulated, - at least an inlet gate for one or more flows of cold material coming from an external cold source and at least an inlet gate for one or more flows of hot material coming from an external hot source, - one or more heat exchange surface(s) (6, 7, 8) which yield heat to the flows of cold material, - one or more heat exchange surface(s) (9, 10, 11) which absorb heat from the flows of hot material - at least an outlet gate for at least a flow of cooled material and at least an outlet gate for at least a flow of heated material by means of said heat exchange surfaces, - said system contains all the heat exchange surfaces (6, 7, 8, 9, 10, 11) in the single apparatus, - said heat exchange surfaces (6,7,8,9,10,11) are - completely immersed in the fluid bath and are fluidly connected to the hot and cold sources, external to said system, through the flows of material, said system characterized in that: it comprises at least one interspace open at both ends, situated inside said apparatus and completely immersed in the fluid bath, - the heat exchange surfaces (6, 7, 8) which yield heat to the flows of cold material are situated inside the interspace and the heat exchange surfaces (9, 10, 11) which absorb heat from the flows of hot material are situated in the space between said interspace and the walls of the apparatus. - a single apparatus having an area immersed in a fluid bath and a free space at the head in which a vapour phase is accumulated, - at least an inlet gate for one or more flows of cold material coming from an external cold source and at least an inlet gate for one or more flows of hot material coming from an external hot source, - one or more heat exchange surface(s) (6, 7, 8) which yield heat to the flows of cold material, - one or more heat exchange surface(s) (9, 10, 11) which absorb heat from the flows of hot material - at least an outlet gate for at least a flow of cooled material and at least an outlet gate for at least a flow of heated material by means of said heat exchange surfaces, - said system contains all the heat exchange surfaces (6, 7, 8, 9, 10, 11) in the single apparatus, - said heat exchange surfaces (6,7,8,9,10,11) are - completely immersed in the fluid bath and are fluidly connected to the hot and cold sources, external to said system, through the flows of material, it comprises at least one interspace open at both ends, situated inside said apparatus and completely immersed in the fluid bath, - the heat exchange surfaces (6, 7, 8) which yield heat to the flows of cold material are situated inside the interspace and the heat exchange surfaces (9, 10, 11) which absorb heat from the flows of hot material are situated in the space between said interspace and the walls of the apparatus. - the heat exchange surfaces (6, 7, 8) which yield heat to the flows of cold material are situated inside the interspace and the heat exchange surfaces (9, 10, 11) which absorb heat from the flows of hot material are situated in the space between said interspace and the walls of the apparatus.