A treatment vessel for treating lignocellulosic material comprises a main section having a first end and a second end, and an outlet section that is conical or frustoconical and tapers from a first end joined to the second end of the main section towards a second end having an outlet opening. A conical body is arranged within the treatment vessel, the vertex of the conical body pointing away from the main section. The conical body is positioned such that the base thereof is positioned within a perpendicular distance (d) from a transition plane (T) defined by the junction between the first end of the outlet section and the second end of the main section, wherein the perpendicular distance (d) is or less of the diameter (D) of the main section. A half angle () of the conical body is 0.5-20 less, preferably 5-15 less, such as 10 less, than a half angle () of the outlet section.

A treatment vessel for treating lignocellulosic material comprises a main section having a first end and a second end, and an outlet section that is conical or frustoconical and tapers from a first end joined to the second end of the main section towards a second end having an outlet opening. A conical body is arranged within the treatment vessel, the vertex of the conical body pointing away from the main section. The conical body is positioned such that the base thereof is positioned within a perpendicular distance (d) from a transition plane (T) defined by the junction between the first end of the outlet section and the second end of the main section, wherein the perpendicular distance (d) is or less of the diameter (D) of the main section. A half angle () of the conical body is 0.5-20 less, preferably 5-15 less, such as 10 less, than a half angle () of the outlet section.