A heat exchanger vessel (1) comprises a tubular outer shell (2) in which a bundle of substantially parallel heat exchanging tubes (7) is arranged between a pair of perforated disk-shaped partitioning walls (5, 6), an inlet (9) and outlet (10) for a first fluid, and at least one inlet (13, 14) and at least one outlet (16) for a second fluid, wherein at least one inlet (14) for the second fluid is provided with particle injection means for injecting cleaning particles into the space between the outer surfaces of the heat exchanger tubes (7) and the inner surface of the tubular shell (2) of the heat exchanger vessel (1) and at least one outlet (16) for the second fluid is connected to means for removing particles from the second fluid and for recirculating particles to at least one inlet (14) of the second fluid.