Combined heat exchanging and fluid mixing apparatus comprising: - a first conduit (44,44') for guiding a cool fluid through the first conduit, the first conduit comprising a cool fluid inlet and a cool fluid outlet (48,48'); - a second conduit (55,55') for guiding a hot gas through the second conduit, the second conduit comprising a hot gas inlet and a hot gas outlet; - a heat conductive element (2,2') arranged between the first conduit (44,44') and the second conduit (55,55') for transferring heat from the hot gas to the cool fluid, the heat conductive element having a length defining a maximum longitudinal extension for a heat exchanging process in the apparatus, the apparatus further comprising - a third conduit (45,45') for guiding an exhaust fluid, the third conduit (45,45') comprising an exhaust fluid inlet arranged at one end of the third conduit (45,45') for introducing the exhaust fluid into the apparatus for mixing of the exhaust fluid with the hot gas and for a chemical reaction of the so formed exhaust fluid/hot gas mixture in the second conduit (55,55'), wherein the third conduit (45,45') is provided with more than one openings (21,21') for passing the exhaust fluid from the third conduit (45,45') into the second conduit (55,55'), wherein the more than one openings (21,21') for introducing the exhaust fluid into the second conduit are arranged within the maximum longitudinal extension for the heat exchanging process in the apparatus, wherein the more than one openings (21,21') are arranged at a same longitudinal position with respect to the second conduit (55,55'), and are arranged along a length of the third conduit (45,45'), wherein the more than one openings (21, 21') are arranged in the heat conductive element, characterized in that the third conduit is arranged on a same side of the heat conductive element (2,2') as the first conduit (44,44'). - a first conduit (44,44') for guiding a cool fluid through the first conduit, the first conduit comprising a cool fluid inlet and a cool fluid outlet (48,48'); - a second conduit (55,55') for guiding a hot gas through the second conduit, the second conduit comprising a hot gas inlet and a hot gas outlet; - a heat conductive element (2,2') arranged between the first conduit (44,44') and the second conduit (55,55') for transferring heat from the hot gas to the cool fluid, the heat conductive element having a length defining a maximum longitudinal extension for a heat exchanging process in the apparatus, the apparatus further comprising - a third conduit (45,45') for guiding an exhaust fluid, the third conduit (45,45') comprising an exhaust fluid inlet arranged at one end of the third conduit (45,45') for introducing the exhaust fluid into the apparatus for mixing of the exhaust fluid with the hot gas and for a chemical reaction of the so formed exhaust fluid/hot gas mixture in the second conduit (55,55'), wherein the third conduit (45,45') is provided with more than one openings (21,21') for passing the exhaust fluid from the third conduit (45,45') into the second conduit (55,55'), wherein the more than one openings (21,21') for introducing the exhaust fluid into the second conduit are arranged within the maximum longitudinal extension for the heat exchanging process in the apparatus, wherein the more than one openings (21,21') are arranged at a same longitudinal position with respect to the second conduit (55,55'), and are arranged along a length of the third conduit (45,45'), wherein the more than one openings (21, 21') are arranged in the heat conductive element, characterized in that the third conduit is arranged on a same side of the heat conductive element (2,2') as the first conduit (44,44').