Dear all, we have a over-design pump in the plant, so the minimum flow control valve (hand control valve) can not close fully even when the pump is operating over 100% load that results in high electric power consumption. Here is some data of this pump:
1. PFD process required:
Standard API 610 10th Edition
- Density at P.T kg/m3: min/norm/max = 950/920/900
-Viscosty at P.T cst: <3.33
- Vap. press at P.T. MPa(a): 1.73
******Operating condition:
- Suction temperature (deg.C) Min/Norm/Rated= 75/79/90
- Suction press. MPa(g) Min/Norm/Rated= - / - / 1.98
- Discharge press. MPa(g) Min/Norm/Rated= - / - / 15.4
- Diff.press MPa: Min/Norm/Rated= - / - / 13.42
- Head m: Min/Norm/Rated= - / - / 1487
- Capacity m3/h: Min/Norm/Rated= - / 89.3 / 103
- NPSH available m: 10 (when taking saturation of pumped solution into consideration)
- Max.Shut-off press MPa(g): 19
- FLow control: continous
- Flow control by: Range: 30-100%
- Seal type: Mech.
******CONSTRUCTIONS FEATURES
- Casing: Centerline
- Split: Radial
- Impeller: Close
2. Designed: Main pump with booster pump
a. Booster pump:
- Suction temperature (deg.C) Min/Norm/Rated= 75/79/90
- Suction press. MPa(g) Min/Norm/Rated= - / - / 1.98
- Discharge press. MPa(g) Min/Norm/Rated= - / - / 2.702
- Diff.press MPa: Min/Norm/Rated= - / - / 0.722
- Head m: Min/Norm/Rated= - / - / 80
- Capacity m3/h: Min/Norm/Rated= - / 89.3 / 103
- NPSH available m: 10 (when taking saturation of pumped solution into consideration)
- Max.Shut-off press MPa(g): 3.0
- FLow control: continous
- Flow control by: Range: 30-100%, minimum flow: 35 m3/h
- Impeller dia.
- Seal type: Mech.
b. Main pump:
- Suction temperature (deg.C) Min/Norm/Rated= 75/79/90
- Suction press. MPa(g) Min/Norm/Rated= - / - / 2.702
- Discharge press. MPa(g) Min/Norm/Rated= - / - / 15.4
- Diff.press MPa: Min/Norm/Rated= - / - / 12.698
- Head m: Min/Norm/Rated= - / - / 1407
- Capacity m3/h: Min/Norm/Rated= - / 89.3 / 103
- NPSH available m: >80
- Max.Shut-off press MPa(g): 20.8
- FLow control: continous
- Flow control by: Range: 30-100%, minimum flow: 35 m3/h
- Impeller dia.
- Seal type: Mech.
C. Motor Driver:
- 800 kW
-Speed 2978 rpm
-6600V/3Ph/50Hz
- Gear for main pump: Kw/ratio: 800/2.265
3. Current Status in operation:
- Flow rate: >90 m3/h
- Temperature at suction: 79 deg.C
- Suction pressure: 1.86 Mpa(g)
- Discharge pressure: 16.3 MPa(g)
- Discharge control valve: 71%
- Minimum control valve (circulation): 65%
- Amper: 77A, 6.6kV
- Consumed Power: 795 kWh per hour
4. Questionare:
Easy to see that the pump is overdesign (when we want to close minimum control valve, we must close more discharge control valve which cause discharge pressure increasing over acceptable value >170 barg), kindly please give me your recommendation for each following ideas:
- To use VSD/Inverter to reduce Motor speed, but this will change all performances of booster and main pump/System performance with a high CAPEX and maybe not effective when the booster pump power/head decreases and maybe can not protect the main pump avoid cavitation if any...
- To reduce impeller of the main pump:
- To reduce inpeller of the booster: the booster pump power/head decreases and maybe can not protect the main pump avoid cavitation if any...
....
How do you think about above solutions or any other ideas please,
Thank you,
Nguyen