A catalyst tube for regenerative catalytic conversion of process gas in an industrial furnace comprising - a catalyst tube inlet for process gas to enter the catalyst tube and a catalyst tube outlet for process gas to exit the catalyst tube, which inlet and outlet are located at opposite ends of the catalyst tube; - an outer reactor tube ; - an inner tube that extends coaxially inside the outer reactor tube ; - a boundary located between the inner wall of the outer reactor tube and the outer wall of the inner tube ; - a first annular channel for catalytically converting process gas, which channel is defined by the inner wall of the outer reactor tube and the outer wall of the boundary , which channel is loaded with catalyst material; - a second annular channel for process gas to flow countercurrently or co-currently to the process gas flowing through the first annular channel, which second annular channel is defined by the inner wall of the boundary and the outer wall of the inner tube ; - an inlet barrier at the inlet end of the catalyst tube for preventing process gas to exit the outer reactor tube from the second annular channel and inner tube at the inlet end of the catalyst tube; - an outlet barrier at the outlet end of the catalyst tube for preventing process gas to exit the outer reactor tube from the first annular channel and from one of the second annular channel and the inner tube , while allowing process gas to exit the outer reactor tube from the other of the second annular channel and the inner tube ; wherein the inner tube, first annular channel and second annular channel each have an opening at the inlet side of the catalyst tube and an opening at the outlet side of the catalyst tube, wherein the catalyst tube inlet is fluidly connected with the opening of the first annular channel at the inlet end of the catalyst tube; the opening of the first annular channel at the outlet end of the catalyst tube is fluidly connected with either the opening of the second annular channel at the outlet end of the catalyst tube or the opening of the inner tube at the outlet end of the catalyst tube; the opening of the second annular channel at the inlet end of the catalyst tube is fluidly connected with the opening of the inner tube at the inlet end of the catalyst tube; and either the opening of the inner tube at the outlet end of the catalyst tube or the opening of the second annular channel at the outlet end of the catalyst tube is fluidly connected with the catalyst tube outlet. - a catalyst tube inlet for process gas to enter the catalyst tube and a catalyst tube outlet for process gas to exit the catalyst tube, which inlet and outlet are located at opposite ends of the catalyst tube; - an outer reactor tube ; - an inner tube that extends coaxially inside the outer reactor tube ; - a boundary located between the inner wall of the outer reactor tube and the outer wall of the inner tube ; - a first annular channel for catalytically converting process gas, which channel is defined by the inner wall of the outer reactor tube and the outer wall of the boundary , which channel is loaded with catalyst material; - a second annular channel for process gas to flow countercurrently or co-currently to the process gas flowing through the first annular channel, which second annular channel is defined by the inner wall of the boundary and the outer wall of the inner tube ; - an inlet barrier at the inlet end of the catalyst tube for preventing process gas to exit the outer reactor tube from the second annular channel and inner tube at the inlet end of the catalyst tube; - an outlet barrier at the outlet end of the catalyst tube for preventing process gas to exit the outer reactor tube from the first annular channel and from one of the second annular channel and the inner tube , while allowing process gas to exit the outer reactor tube from the other of the second annular channel and the inner tube ; <EOS>