A cyclone separator provided with an inlet for receiving gas and solid particles, + a gas outlet at its upper end and a lower tubular part, wherein the lower tubular part is provided with a closed lower end, through which closed lower end a substantially vertical particle withdrawal conduit extends from a position below the closed lower end to a position in the tubular part and below the inlet for receiving gas and solid particles, said conduit being provided with openings to withdraw solid particles from the cyclone separator and wherein said conduit has a smaller cross-sectional area than the lower tubular part, thereby defining a space between conduit and inner wall of the lower tubular part, wherein in the lower part of said space main means to add a primaxy fluidizing medium are present.