Reactor for processing biomass, comprising a reactor enclosure having an input for receiving biomass and an output for outputting processed biomass; a transport unit for transporting biomass (1a; 1b) in the reactor enclosure from the input to the output; a first reactor section; a second reactor section positioned downstream from the first reactor section; a third reactor section positioned downstream from the second reactor section; the first reactor section comprising first gas injectors which are positioned below the transport unit and which are arranged to output a first gas through the biomass (1a; 1b) on the transport unit during operation, and first oxidant injectors which are positioned above the transport unit and which are arranged to provide first heat sources directing radiation heat energy to the biomass (1a; 1b) during operation; the second reactor section comprising second gas injectors which are positioned below the transport unit and arranged to output a second gas through the biomass (1a; 1b) on the transport unit during operation, and second oxidant injectors which are positioned above the transport unit and which are arranged to provide second heat sources directing radiation heat energy to the biomass (1a; 1b) during operation; the third reactor section comprising third gas injectors which are positioned below the transport unit and arranged to output a third gas through the biomass (1a; 1b) on the transport unit during operation; wherein the first, second and third gas injectors (11, 13, 15) are further arranged to output a first, second, and third gas, respectively, each having a low oxygen content, and the first and second oxidant injectors (12, 14) are arranged to output an oxidizing gas only, further comprising a control unit connected to the first, second and third gas injectors (11, 13, 15) and the first and second oxidant injectors (12, 14), wherein the control unit is arranged to control the amount and composition of gas mixture supplied by each of the first, second and third gas injectors (11, 13, 15) and the first and second oxidant injectors (12, 14). a reactor enclosure having an input for receiving biomass and an output for outputting processed biomass; a transport unit for transporting biomass (1a; 1b) in the reactor enclosure from the input to the output; a first reactor section; a second reactor section positioned downstream from the first reactor section; a third reactor section positioned downstream from the second reactor section; the first reactor section comprising first gas injectors which are positioned below the transport unit and which are arranged to output a first gas through the biomass (1a; 1b) on the transport unit during operation, and first oxidant injectors which are positioned above the transport unit and which are arranged to provide first heat sources directing radiation heat energy to the biomass (1a; 1b) during operation; the second reactor section comprising second gas injectors which are positioned below the transport unit and arranged to output a second gas through the biomass (1a; 1b) on the transport unit during operation, and second oxidant injectors which are positioned above the transport unit and which are arranged to provide second heat sources directing radiation heat energy to the biomass (1a; 1b) during operation; the third reactor section comprising third gas injectors which are positioned below the transport unit and arranged to output a third gas through the biomass (1a; 1b) on the transport unit during operation; wherein the first, second and third gas injectors (11, 13, 15) are further arranged to output a first, second, and third gas, respectively, each having a low oxygen content, and the first and second oxidant injectors (12, 14) are arranged to output an oxidizing gas only, further comprising a control unit connected to the first, second and third gas injectors (11, 13, 15) and the first and second oxidant injectors (12, 14), wherein the control unit is arranged to control the amount and composition of gas mixture supplied by each of the first, second and third gas injectors (11, 13, 15) and the first and second oxidant injectors (12, 14).