A plate heat exchanger arrangement, which comprises at least - a first plate pack, and - a second plate pack, which first plate pack and second plate pack are formed by heat exchange plates having at least two openings and arranged on top of each other, and the heat exchange plates are attached to each other as plate pairs, the inner parts of which plate pairs are arranged in connection with each other via flow passages (2a, 2b, 3a, 3b) formed by the openings of the heat exchange plates, wherein primary circuit of the heat exchanger is formed between the openings in the heat exchange plates, - a common outer casing surrounding the first plate pack and the second plate pack, which outer casing comprises a longitudinal cylindrical shell and end plates (5a, 5b) arranged at both ends of the shell, - an inlet and outlet connections (6a, 6b) of the first plate pack, which are connected with the flow passages (2a, 2b) of the first plate pack, - an inlet and outlet connections (7a, 7b) of the second plate pack, which are connected with the flow passages (3a, 3b) of the second plate pack, - an inlet connection and an outlet connection (8b, 8c) for heat exchange medium flowing inside the shell, which connections are arranged through the outer casing, wherein a secondary circuit is formed between connections of the outer casing arranged in connection with the spaces between the plate pairs of the plate pack, characterized in that the first plate pack and the second plate pack are arranged adjacent to each other inside the common outer casing, and the first plate pack has a diameter, defined by the outer edges of the heat exchange plates, which is greater than a diameter of the second plate pack, and at least one partition plate is arranged between the first plate pack and the second plate pack, which partition plate has a size which corresponds at least the size of the plate pack having the greater diameter and the partition plate is further arranged to elongate from an outer surface of the plate pack to an inner surface of the shell at one side of the plate pack for forming multiple passes for heat exchange medium in the shell side of the heat exchanger, and wherein the first and the second plate pack has common shell side in the heat exchanger arrangement, wherein a single heat exchange medium is arranged to flow inside in the shell side of the plate heat exchanger arrangement. - a first plate pack, and - a second plate pack, which first plate pack and second plate pack are formed by heat exchange plates having at least two openings and arranged on top of each other, and the heat exchange plates are attached to each other as plate pairs, the inner parts of which plate pairs are arranged in connection with each other via flow passages (2a, 2b, 3a, 3b) formed by the openings of the heat exchange plates, wherein primary circuit of the heat exchanger is formed between the openings in the heat exchange plates, - a common outer casing surrounding the first plate pack and the second plate pack, which outer casing comprises a longitudinal cylindrical shell and end plates (5a, 5b) arranged at both ends of the shell, - an inlet and outlet connections (6a, 6b) of the first plate pack, which are connected with the flow passages (2a, 2b) of the first plate pack, - an inlet and outlet connections (7a, 7b) of the second plate pack, which are connected with the flow passages (3a, 3b) of the second plate pack, - an inlet connection and an outlet connection (8b, 8c) for heat exchange medium flowing inside the shell, which connections are arranged through the outer casing, wherein a secondary circuit is formed between connections of the outer casing arranged in connection with the spaces between the plate pairs of the plate pack, characterized in that the first plate pack and the second plate pack are arranged adjacent to each other inside the common outer casing, and the first plate pack has a diameter, defined by the outer edges of the heat exchange plates, which is greater than a diameter of the second plate pack, and at least one partition plate is arranged between the first plate pack and the second plate pack, which partition plate has a size which corresponds at least the size of the plate pack having the greater diameter and the partition plate is further arranged to elongate from an outer surface of the plate pack to an inner surface of the shell at one side of the plate pack for forming multiple passes for heat exchange medium in the shell side of the heat exchanger, and wherein the first and the second plate pack has common shell side in the heat exchanger arrangement, wherein a single heat exchange medium is arranged to flow inside in the shell side of the plate heat exchanger arrangement.