Impregnation vessel with convergence side relief and method for heat injection at convergence

An impregnation vessel comprising:

• a vessel container including an upper inlet to receive cellulosic material;
• a lower discharge port to discharge the cellulosic material from a discharge section of the vessel container;
• a one-dimensional convergence section internal to the vessel through which passes a flow of the cellulosic material in the vessel;
• a cavity between an internal wall of the vessel and the convergence section, wherein the cavity has a lower opening to the cellulosic material in the vessel and an upper section shielded from the flow of cellulosic material in the vessel, and
• an input port in the vessel and opening to the cavity, wherein the input port is connectable to a source of hot liquid to be added to the cellulosic material in the vessel and the hot liquid is added to the cavity at a temperature above an average temperature of the cellulosic material in the vessel.

A method for heating cellulosic material in an impregnation vessel having an internal convergence, the method comprising:

• introducing cellulosic material to an upper inlet port in the impregnation vessel;
• adding a heated liquid to the vessel and forming a liquid level in a upper section of the vessel;
• heating the cellulosic material with the heated liquid as the cellulosic material flows downward through the vessel;
• detecting the flow of the cellulosic material below the liquid level and in the vessel through the internal convergence;
• introducing a hot liquid to a cavity in the vessel and behind the convergence, wherein the hot liquid is introduced to the cavity at a temperature above a temperature of the heated liquid;
• adding the hot liquid from the cavity to the flow of cellulosic material downstream of the internal convergence;
• heating the flow of cellulosic material downstream of the internal convergence with the hot liquid, and
• discharging the cellulosic material from a discharge port in a lower section of the vessel below the cavity and internal convergence.