A gas mixing arrangement for mixing a process gas (MF) of a process plant, which arrangement comprises a gas duct (10a) for flow of said process gas, a mixing plate section (24) arranged in the gas duct (10a) and comprising at least one mixing plate (42, 44) arranged at an angle with respect to a main flow direction (C) of said process gas flowing through the gas duct (10a). The arrangement further comprises a guide vane section (22) arranged upstream of said mixing plate section (24) to cooperate therewith in mixing the process gas (MF) flowing through the gas duct (10a), the guide vane section (22) comprises a first group of guide vanes (26) arranged to direct a first gas flow portion (GP1) in a direction towards a first side wall (34) of the gas duct (10a), and a second group of guide vanes (28) arranged to direct a second gas flow portion (GP2) in a direction towards a second side wall (36) of the gas duct (10a), said second side wall (36) being opposite said first side wall (34).