Plant for the chemical looping combustion of a solid hydrocarbon feedstock generating particles of unburnt residues and employing particles of an oxygen-carrying solid, said plant comprising: - a reduction reactor operating as fluidized bed in order to carry out the combustion of said solid hydrocarbon feedstock in contact with the particles of the oxygen-carrying solid , said reactor having a parallelepiped shape; - an oxidation reactor operating as fluidized bed in order to oxidize the reduced particles of the oxygen-carrying solid originating from the reduction reactor by bringing into contact with an oxidizing gas ; - a solid/solid separator surmounting said reduction reactor in order to separate the particles of the oxygen-carrying solid from the particles of unburnt residues contained in the gas/solid mixture resulting from said reduction reactor , said solid/solid separator comprising a chamber of parallelepipedal shape comprising: - a lower part operating as dense phase and an upper part operating as dilute phase; - at least one inlet of parallelepipedal shape for the gas/solid mixture originating from the reduction reactor , said inlet emerging in the upper part of the chamber and being equipped at its top with means for distribution of said gas/solid mixture in the chamber which extend over the entire length of said inlet; - at least one drain placed in the lower part of the chamber ; - at least one outlet located in the upper part of the chamber . - a reduction reactor operating as fluidized bed in order to carry out the combustion of said solid hydrocarbon feedstock in contact with the particles of the oxygen-carrying solid , said reactor having a parallelepiped shape; - an oxidation reactor operating as fluidized bed in order to oxidize the reduced particles of the oxygen-carrying solid originating from the reduction reactor by bringing into contact with an oxidizing gas ; - a solid/solid separator surmounting said reduction reactor in order to separate the particles of the oxygen-carrying solid from the particles of unburnt residues contained in the gas/solid mixture resulting from said reduction reactor , said solid/solid separator comprising a chamber of parallelepipedal shape comprising: - a lower part operating as dense phase and an upper part operating as dilute phase; - at least one inlet of parallelepipedal shape for the gas/solid mixture originating from the reduction reactor , said inlet emerging in the upper part of the chamber and being equipped at its top with means for distribution of said gas/solid mixture in the chamber which extend over the entire length of said inlet; - at least one drain placed in the lower part of the chamber ; - at least one outlet located in the upper part of the chamber . - a lower part operating as dense phase and an upper part operating as dilute phase; - at least one inlet of parallelepipedal shape for the gas/solid mixture originating from the reduction reactor , said inlet emerging in the upper part of the chamber and being equipped at its top with means for distribution of said gas/solid mixture in the chamber which extend over the entire length of said inlet; - at least one drain placed in the lower part of the chamber ; - at least one outlet located in the upper part of the chamber . <EOS>