Abstract: Method and arrangement for treatment of a gas-flow in connection with a NOx reducing catalyst (18) that include guiding the gas-flow through an exhaust gas treatment unit (18) having several ducts (21) with exchange of heat between the ducts (21). The ducts (21) are connected to an inlet and an outlet, respectively, at the exhaust gas treatment unit (18) so that the gas-flow occurs during exchange of heat between incoming and outgoing flows. Reduction of NOx compounds in the gas-flow is accomplished by means of the NOx reducing catalyst (18). An adaptation of the temperature of the exhaust gas treatment unit (18) is affected to the prevailing operating condition of the NOx reducing catalyst (18). The method and apparatus enable provision of the required exhaust gas temperature for NOx reduction, while also accommodating the temperature limitations imposed by sulphur absorption and regeneration subsystems.