Abstract: The present invention concerns a combustion reactor (300) for chemical looping combustion (CLC) configured to operate in a fluidised bed, comprising: a lower chamber (320) forming a first reaction zone for the combustion of a hydrocarbon feedstock in the presence of particles of an oxidation-reduction active mass, comprising a first side wall and being configured to include a dense fluidised bed; an elongate upper chamber (340) with smaller passage cross-section than that of the lower chamber, forming a second reaction zone for the combustion of gaseous effluents originating from the combustion in the lower portion, comprising a second side wall and being configured to include a dilute fluidised bed; an intermediate portion (330) connecting the two chambers, and including an inner wall forming a right angle with the side walls of the two chambers. The invention also relates to the facility and the CLC process incorporating such a reactor (300).