Heat exchanger

A heat exchanger of a thermosyphon heat pipe configuration for transferring heat between a first process stream and a second process stream through a heat transfer fluid medium, said heat exchanger comprising:

• a closed shell comprising a wall, an upper portion, a lower portion, and a horizontal diameter, the closed shell enclosing a volume fully filled with a vapour phase and a liquid phase of said heat transfer fluid medium, said heat transfer fluid medium being confined within said volume, the horizontal diameter being a longest chord of a circular region of the closed shell and being parallel to a liquid surface of the liquid phase, the closed shell further comprising:
• a condenser comprising a plurality of first process stream passages in the form of straight tubes;
• and
• a reboiler comprising a plurality of second process stream passages in the form of straight tubes, said condenser being arranged above said reboiler, wherein
• a disengagement zone has height and horizontal cross-sectional area sufficient to enable separation of said vapour phase and said liquid phase of said heat transfer fluid medium by gravity, said disengagement zone spaces a first bundle of said plurality of first process stream passages of said condenser from a second bundle of said plurality of second process stream passages of said reboiler by a first gap that has a height greater than a tube pitch of the second process stream passages such that said first bundle is discrete and separate from said second bundle, said first bundle is located at the upper portion of the closed shell such that a distance from the first bundle to the horizontal diameter is greater than a distance from the first bundle to the wall of the closed shell at the upper portion, said second bundle is located at the lower portion of the closed shell such that a distance from the second bundle to the horizontal diameter is greater than a distance from the second bundle to the wall of the closed shell at the lower portion, and said first bundle is at a greater distance from said separation of said vapour phase and said liquid phase than said second bundle;
• each of said plurality of first process stream passages is surrounded by said vapour phase and each of said plurality of second process stream passages is immersed in said liquid phase;
• and
• said heat transfer fluid medium and heat exchanger horizontal cross-sectional area are selected so that heat transfer fluid medium vapour velocity is sufficient to avoid flooding of the heat exchanger.