The present invention is related to a circulating fluidized bed gasification or combustion system (1) using coal or biomass as raw material and comprising a combustion/gasification reactor (2); a cyclone (3) which is in connection with the reactor (2) so as to seperate solid particles from gas flow; a downcomer (4) which is in connection with the reactor (2) and the cyclone (3), extends along the reactor (2), and enables solid particles captured by the cyclone (3) to be sent to the combustion/gasification reactor (2) again; a distributing plate (5) which is in connection with the reactor (2) and provides primary gas supply to the system (1) homogeneously; at least one conduit which is positioned parallel to the downcomer (4); an ejector (7) which is positioned on the downcomer (4) vertically, comprises at least one nozzle (6) spraying pressurized gas towards the reactor (2).