A method for recovering heat from a flue gas from an engine, the method comprising: - supplying flue gas from the engine to a flue gas chamber of a heat exchanger, and supplying coolant liquid to a vaporization chamber of said heat exchanger, wherein said coolant liquid vaporizes in the vaporization chamber to give vapour, - using the vapour to drive an expansion device, thereby recovering said heat as mechanical work or electrical energy, preferably using a generator, and - condensing the vapour in a condenser downstream of said expansion device to give condensate, pressurizing the condensate in a pump to give pressurized condensate, and supplying the pressurized condensate to the vaporization chamber as said coolant liquid, wherein in said vaporization chamber said coolant liquid flows in contact with a heat exchanging wall in heat exchanging contact with flue gas in said flue gas chamber thereby causing vaporization of said coolant liquid, characterised in that said vaporization chamber comprises a plurality of flow-modifying structures that are arranged in series in the direction of the flow of coolant liquid and that are each configured for modifying the flow of the coolant liquid and the vapour in said vaporization chamber, wherein each of said flow-modifying structures (9a, 9b, 9c) comprises: - a first part wherein a channel for coolant is divided in two channels (18b, 18c) for coolant, - and a second part, arranged downstream of the first part, wherein at least two channels (18b, 18c) for coolant are combined into a single channel for coolant. - supplying flue gas from the engine to a flue gas chamber of a heat exchanger, and supplying coolant liquid to a vaporization chamber of said heat exchanger, wherein said coolant liquid vaporizes in the vaporization chamber to give vapour, - using the vapour to drive an expansion device, thereby recovering said heat as mechanical work or electrical energy, preferably using a generator, and - condensing the vapour in a condenser downstream of said expansion device to give condensate, pressurizing the condensate in a pump to give pressurized condensate, and supplying the pressurized condensate to the vaporization chamber as said coolant liquid, wherein in said vaporization chamber said coolant liquid flows in contact with a heat exchanging wall in heat exchanging contact with flue gas in said flue gas chamber thereby causing vaporization of said coolant liquid, characterised in that said vaporization chamber comprises a plurality of flow-modifying structures that are arranged in series in the direction of the flow of coolant liquid and that are each configured for modifying the flow of the coolant liquid and the vapour in said vaporization chamber, wherein each of said flow-modifying structures (9a, 9b, 9c) comprises: - a first part wherein a channel for coolant is divided in two channels (18b, 18c) for coolant, - and a second part, arranged downstream of the first part, wherein at least two channels (18b, 18c) for coolant are combined into a single channel for coolant. - a first part wherein a channel for coolant is divided in two channels (18b, 18c) for coolant, - and a second part, arranged downstream of the first part, wherein at least two channels (18b, 18c) for coolant are combined into a single channel for coolant.