Off Nozzle Elevation

The value of H- is useful when elevation adjustments are made to vessel heights during plant layout or when the vessel can be located at a minimum elevation. The coefficient for P2 in the above equation is the elevation difference between the downcomer and rizer nozzle. If this is other than 3 feet, the correct dimension, in feet, should be inserted. 

The downcomer nozzle cannot be lower than Hx. Af replaces AP in the above equation and is the sum of the downcomer pipe, riser and exchanger friction losses  

Many towers have a bottom draw-off pump. NPSH requirements usually elevate the process 

For the minimum of downcomer length the return line nozzle elevation H ) must be known. Inserting H2 = Hi + H3 into the AP equation and solving for Hi  

Af is again the sum of the actual resistances of the reboiler plus the downcomer and riser pipe plus the inlet and outlet losses at the vessel and exchanger. 

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