Sealing device for a vessel suitable to contain fluids under pressure and/or granular material in movement, to achieve a fluid-tight seal in an aperture made in the lateral wall of said vessel, into which aperture a shaft is inserted in a through manner and with play, said sealing device comprising: - first sealing means configured to be disposed in contact with said shaft in the zone of said aperture and configured to follow possible axial and flexional movements of said shaft, while still allowing a possible rotation of said shaft with respect to them and to said lateral wall, - second sealing means, comprising at least a containing body and a flexible connection element and configured to be disposed in said aperture with a first part configured to be fixed to said lateral wall and a second part connected in sealed manner with said first sealing means to allow reciprocal movements of said first sealing means and said lateral wall, wherein said first sealing means comprise a plurality of sealing rings, disposed coaxial to said shaft and in contact with the latter, and a containing tube to contain said sealing rings and to constrain said sealing rings in a determinate axial position with respect to said shaft, and wherein said lateral wall of said vessel comprises an interface flange, characterized in that a closing flange is configured to be connected to said interface flange and is connected to a flanged end of said containing body by means of attachment means (47, 48) and is positioned in contact with said containing tube and with said flexible connection element to keep said first sealing means in a determinate axial position with respect to said shaft and in that the sealing device comprises a frame, positioned outside and coaxially to said flanged end of said containing body, constraint elements (53, 54) being associated to said frame and to said flanged end to allow the movement of said closing flange with respect to said vessel only along a first transverse axis, orthogonal to the longitudinal axis of said shaft. - first sealing means configured to be disposed in contact with said shaft in the zone of said aperture and configured to follow possible axial and flexional movements of said shaft, while still allowing a possible rotation of said shaft with respect to them and to said lateral wall, - second sealing means, comprising at least a containing body and a flexible connection element and configured to be disposed in said aperture with a first part configured to be fixed to said lateral wall and a second part connected in sealed manner with said first sealing means to allow reciprocal movements of said first sealing means and said lateral wall, wherein said first sealing means comprise a plurality of sealing rings, disposed coaxial to said shaft and in contact with the latter, and a containing tube to contain said sealing rings and to constrain said sealing rings in a determinate axial position with respect to said shaft, and wherein said lateral wall of said vessel comprises an interface flange, characterized in that a closing flange is configured to be connected to said interface flange and is connected to a flanged end of said containing body by means of attachment means (47, 48) and is positioned in contact with said containing tube and with said flexible connection element to keep said first sealing means in a determinate axial position with respect to said shaft and in that the sealing device comprises a frame, positioned outside and coaxially to said flanged end of said containing body, constraint elements (53, 54) being associated to said frame and to said flanged end to allow the movement of said closing flange with respect to said vessel only along a first transverse axis, orthogonal to the longitudinal axis of said shaft.