Revisiting Problem 5.4, suppose the flow was controlled using a plug-disk globe valve and the initial design in the example assumed that the valve is fully open. What range of flow rates can be achieved if the valve can be throttled down to quarter open? When the valve is quarter open, what fraction of the pump work is lost across the valve?

Data From Problem 5.4

A process fluid is pumped from the bottom of one distillation column to another, using a  centrifugal pump. The line is standard commercial steel pipe 75 mm internal diameter.  From the column to the pump inlet the line is 25 m long and contains six standard elbows  and a fully open gate valve. From the pump outlet to the second column the line is 250 m  long and contains ten standard elbows, four gate valves (operated fully open) and a flowcontrol valve. The fluid level in the first column is 4 m above the pump inlet. The feed  point of the second column is 6 m above the pump inlet. The operating pressure in the first  column is 1.05 bara and that of the second column 0.3 barg.
Determine the operating point on the pump characteristic curve when the flow is such that  the pressure drop across the control valve is 35 kN/m².

The physical properties of the fluid are: density 875 kg/m³, viscosity 1.46 mN m^–2s. Also, determine the NPSH, at this flow-rate, if the vapour pressure of the fluid at the pump  suction is 25 kN/m² .

 

Transcribed Image Text:

Pump characteristic Flow-rate, m³/h Head, m of liquid 0.0 32.0 18.2 31.4 27.3 30.8 36.3 29.0 45.4 26.5 54.5 23.2 63.6 18.3