A gasification reactor comprises a pressure shell; a reaction zone partly bounded by a tubular membrane wall enclosed by the pressure shell; at least one burner having a burner head, said burner head protruding the membrane wall; at least one cooling device arranged in the membrane wall and enclosing the burner head of at least one burner, the at least one cooling device comprising several concentric rings of increasing diameter, forming a truncated cone shape having a largest diameter opening facing the reaction zone and a smallest diameter opening facing the burner head, each ring being a conduit having an inlet and an outlet for a cooling medium, the smallest diameter opening for the burner head being located between the pressure shell and the membrane wall; the cooling device comprising at least one part-circular outer ring having an interruption.