Processing vessel

A processing vessel comprising:

• a vessel body having an inner wall and a discharge orifice at its lower end;
• a temperature control element disposed inside said vessel body comprising at least one flow passage through which a temperature control medium, for at least one of heating or cooling, is caused to flow, wherein said temperature control element defines an inner barrel in which a processing material is accommodated in heat exchange relation with said temperature control element;
• means for spatially fixing said temperature control element in said vessel body proximate to and spaced from said inner wall thereby defining an unfilled chamber between the temperature control element and the inner wall of said vessel body;
• closure means for enclosing said chamber between said vessel body and said temperature control element thereby creating a closed chamber;
• means for substantially preventing said processing material from entering said closed chamber:
• and
• means for openly communicating the interior of said inner barrel with said closed chamber, without communication with space exterior to said vessel, whereby the pressure in said inner barrel is substantially the same as the pressure in said closed chamber.