A method for admixing vapor and liquid flowing concurrently in a catalytic reactor between an upper catalyst bed and a lower catalyst bed thereof, the method comprising the steps of: providing a swirl box (40, 59, 82) comprising of a top wall (31, 51, 71), a side wall (14, 33, 53, 73) and a bottom wall (32, 52, 72) with an outlet opening (37, 57, 79); and providing one or more passageways for conducting the concurrent flow of said vapor and liquid in said reactor from the space above said swirl box (40, 59, 82) and into said swirl box (40, 59, 82); and providing one or more tangential inlet orifices (36, 56, 78) located in said passageways for said vapor and liquid to enter into said swirl box (40, 59, 82); and passing said vapor and liquid from the space above said swirl box (40, 59, 82) through said one or more tangential inlet orifice(s) (36, 56, 78) and into said swirl box (40, 59, 82) at said side wall (14, 33, 53, 73) and in a direction close to the flow direction of the swirling fluids inside the swirl box (40, 59, 82) adjacent the tangential inlet orifice(s) (36, 56, 78); where the angle between the flow velocity vector in said tangential inlet orifice(s) (36, 56, 78) and the flow direction of the swirling fluids inside the swirl box (40, 59, 82) adjacent the tangential inlet orifice(s) (36, 56, 78) is defined as α and where α<25°, and where the distance from the center of said tangential inlet orifice(s) (36, 56, 78) to the center of said outlet opening (37, 57, 79) is larger than two times the distance from the center of said outlet opening (37, 57, 79) to the rim of said outlet opening (37, 57, 79), and where said tangential inlet orifice(s) (36, 56, 78) has such a flow-through area relative to the flow rate of said vapor that the superficial vapor flow velocity in the tangential inlet orifice(s) (36, 56, 78) exceeds V v Dispersed as defined in equation (a) V v Dispersed = 1.08 m s × ρ L ρ v where: V v Dispersed is the superficial vapor flow velocity resulting in dispersed flow, and ρ L is the actual liquid density in kg/m 3, and ρ v is the actual vapor density in kg/m 3 during at least one operational phase of said reactor, for dispersion of the liquid into the vapor and/or the vapor into the liquid and for introducing a swirling flow inside said swirl box (40, 59, 82), and allowing said vapor and liquid to rotate around said outlet opening (37, 57, 79) for obtaining said admixing; and passing said vapor and liquid from said swirl box (40, 59, 82) through said outlet opening (37, 57, 79) to the space below said swirl box (40, 59, 82). providing a swirl box (40, 59, 82) comprising of a top wall (31, 51, 71), a side wall (14, 33, 53, 73) and a bottom wall (32, 52, 72) with an outlet opening (37, 57, 79); and providing one or more passageways for conducting the concurrent flow of said vapor and liquid in said reactor from the space above said swirl box (40, 59, 82) and into said swirl box (40, 59, 82); and providing one or more tangential inlet orifices (36, 56, 78) located in said passageways for said vapor and liquid to enter into said swirl box (40, 59, 82); and passing said vapor and liquid from the space above said swirl box (40, 59, 82) through said one or more tangential inlet orifice(s) (36, 56, 78) and into said swirl box (40, 59, 82) at said side wall (14, 33, 53, 73) and in a direction close to the flow direction of the swirling fluids inside the swirl box (40, 59, 82) adjacent the tangential inlet orifice(s) (36, 56, 78); where the angle between the flow velocity vector in said tangential inlet orifice(s) (36, 56, 78) and the flow direction of the swirling fluids inside the swirl box (40, 59, 82) adjacent the tangential inlet orifice(s) (36, 56, 78) is defined as α and where α<25°, and where the distance from the center of said tangential inlet orifice(s) (36, 56, 78) to the center of said outlet opening (37, 57, 79) is larger than two times the distance from the center of said outlet opening (37, 57, 79) to the rim of said outlet opening (37, 57, 79), and where said tangential inlet orifice(s) (36, 56, 78) has such a flow-through area relative to the flow rate of said vapor that the superficial vapor flow velocity in the tangential inlet orifice(s) (36, 56, 78) exceeds V v Dispersed as defined in equation (a) V v Dispersed = 1.08 m s × ρ L ρ v where: V v Dispersed is the superficial vapor flow velocity resulting in dispersed flow, and ρ L is the actual liquid density in kg/m 3, and ρ v is the actual vapor density in kg/m 3 during at least one operational phase of said reactor, for dispersion of the liquid into the vapor and/or the vapor into the liquid and for introducing a swirling flow inside said swirl box (40, 59, 82), and allowing said vapor and liquid to rotate around said outlet opening (37, 57, 79) for obtaining said admixing; and passing said vapor and liquid from said swirl box (40, 59, 82) through said outlet opening (37, 57, 79) to the space below said swirl box (40, 59, 82).