Head Calculation

[Falcon03]

Our strategy is to minimize feed inventory, one example we are currently running with three FCC charge pumps in order to maintain the required feed throughput into the unit. The current Tank level is 9.8 meter and we would like to reduce the TK level to 6.7 meter, my question is what will be the effect of reducing the TK level from 9.8 M to 6.7 M in order to maintain low inventory ON THE THREE PUMPS OPERATIONS.

Is it true that the lower the suction head the higher the discharge flow will be which will impact on the pump Amps. In other word that to be able to run with three pumps at min TK level we have to watch pumps amps?

What will be the calculation procedure?

Thanks in advance for your help,

 

[TD2K]

I'm not sure what you are asking. Your FCC charge pumps would be on some type of flow control and I'm assuming your flow control valve isn't wide open.

As you lower the suction tank level, the pumps' suction pressure and therefore the discharge pressure drops on a 1:1 basis (remember: the pumps' produce a constant head for a fixed flow). To maintain the same flow with the reduced discharge pressure from the pump, the control valve must open to compensate for the reduced discharge pressure from the pumps .

But, since flow and therefore head for the pumps are fixed, the Hp requirement is the same.

Bottom line, you just are wasting a bit less energy in the form of dP over your control valve. Plus, the reduced tank level will reduce your NPSHA.