A rotating air distributor for rotary reactors such as rotary kilns for the gasification of biomass and other carbonaceous materials for efficient mixing and maximum conversion of solid biomass and other carbonaceous materials into synthesis fuel gas is disclosed. The invention includes a gas distribution port comprises of one main supply from which several discharge nozzles emerge at different angles and at different locations along the length of the reactor to provide distribution of gas throughout the intended length of the reactor. The discharge of gas from the gas distribution port is adjusted by the variable position of a plug inside the port that can be adjusted during the operation of the kiln to achieve optimum gas-solid interaction along the length of the reactor. The rotating action of the gas distribution port also facilitates and eases the passage of reacted biomass solid and other carbonaceous material residue through the reactor.