Column AP Control Via Heat to Reboiler

Before looking at the overall control scheme, let us discuss what is meant by the column impedance. 

Signal flow diagram for column pressure control via manipulation of condenser cooling water 

Relationship Between Boilup and Column Pressure Drop 

So far we have assumed that there is negligible lag in vapor flow between adjacent trays. This means that we treat the acoustic impedance Z oi between the bottom and top trays as a pure resistance approximately equal to 

If the individual RC sections are equivalent, or nearly so, then the impedance looking up from the reboiler is approximately  

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