The invention relates to a circulating fluidized bed apparatus, comprising a combustion chamber (CC) with at least one outlet port (OP) at its upper end (UE) to transfer a mixture of gas and solids from said combustion chamber (CC) into at least one subsequent separator (SP) and from there at least partially back into the combustor chamber, wherein the combustion chamber (CC) is ring-shaped, comprising an inner wall (IW) and an outer wall (OW), arranged at a distance to each other in a radial direction of the combustion chamber (CC), and at least two intermediate walls (SW), which extend between the inner wall (IW) and the outer wall (OW) and in spaced relationship in a circumferential direction of the combustion chamber (CC), thereby subdividing the combustion chamber (CC) into a corresponding number of sections (CO), arranged adjacent to each other in the circumferential direction of the combustion chamber (CC).