A large-scale coking reactor including a housing provided with a chamber and with outer and inner chamber frames, a displaceable outer door elastically compressed against the outer frame and formed with a respective elastic peripheral seal compressible against the frame and with an outer high temperature membrane interposed between the door and the seal and elastically pressed thereagainst to seal the door opening, a displaceable inner door spaced from the outer door and formed with an inner high temperature membrane interposed between the inner door and the inner frame to fit elastically the inner frame, the inner and outer doors being releasably interconnected upon displacing the outer door, so that the doors are mounted in the housing to be operatable either selectively or in combination with one another.