The present invention relates to a fluidized bed reactor system made up of at least two fluidized bed reactors, comprising at least one main reactor (1) in the form of a circulating fluidized bed and a secondary reactor (2) in the form of a circulating fluidized bed, and also a particle line comprising a particle separator for transporting fluidized bed particles from the main reactor into the secondary reactor, characterized in that, in the lower region of the respective reactor, a line (10) connects the secondary reactor (2) to the main reactor (1) for transporting fluidized bed particles.