Method for determining pump flow without the use of traditional sensors

Abstract

A technique for determining pump flow without using traditional sensors features steps and modules for creating a calibrated power curve at closed valve conditions at several speeds; calculating coefficients from a normalized power curve based on a pump's power ratio; and solving a polynomial power equation for flow at the current operating point. The calibrated power curve may be created by increasing the speed of the pump from a minimum speed to a maximum speed and operating the pump with a closed discharge valve. This data is used to correct published performance for shutoff power and best efficiency point power at rated speed in order to determine the pump's power ratio. It is also used to accurately determine closed valve power at the current operating speed. The pump's power ratio is determined by the equation: Pratio=Pshutoff @100%/PBEP—corr. The polynomial power equation may, for example, include a 3rd order polynomial equation developed using coefficients from the normalized power versus flow curve, and corrections may be made for speed, hydraulic efficiency and specific gravity in the polynomial power equation. Complex roots may be determined to solve the 3rd order polynomial equation using either Muller's method or some other suitable method, and the calculated actual flow may be determined for a specific operating point.

Description

BRIEF DESCRIPTION OF THE DRAWING

The drawing includes the following Figures:

FIG. 1 is a block diagram of a basic pump system according to the present invention.

FIG. 2 is a flowchart of basic steps performed according to the present invention by the controller shown in FIG. 1.

FIG. 3 is a block diagram of a controller shown in FIG. 1 for performing the basic steps shown in FIG. 2.

FIG. 4 is a graph of curves of % error (HP) versus speed (RPM) using various methods such as cubic interpolation, method X and affinity laws.

FIG. 5 is a graph of curves for power (HP) versus speed (RPM) @ closed valve condition for actual drive power, tuned power, and affinity methods.

FIG. 6 is a graph of curves for power (BHP) versus flow (GPM) for actual drive power, pricebook (w/seal) published data and tuned power corrected data with polynomial curve fits also shown for each data set.

FIG. 7 is a graph of normalized curves for % power (HP) versus % flow (RPM) at 1700, 2200, 2800, 3570 RPMs actual and as calculated.

FIG. 8 is a graph of curves for tuned power (BHP) versus flow (GPM) for actual flow and calculated flow.

Claims

1. A method for determining pump flow in a centrifugal pump, centrifugal mixer, centrifugal blower or centrifugal compressor comprising: creating a calibrated power curve at closed valve conditions at several speeds;calculating coefficients from a power vs flow curve based on a pump's power ratio; andsolving a power equation for flow at the current operating point.

2. A method according to claim 1, wherein the calibrated power curve is created by increasing the speed of the pump from a minimum speed to a maximum speed while operating the pump against a closed discharge valve and collecting speed and power data at several speeds.

3. A method according to claim 2, wherein the closed valve power data is corrected to a specific gravity equal to 1.

4. A method according to claim 2, wherein for small hp pumps applied on liquids with specific gravity other than 1.0, mechanical losses (such as seals and bearings) can be compensated for in the measured closed valve power readings as follows: PSO—N=[(PMeas—N %−(Mech Loss×NAct/NRated))/SG]+(Mech Loss×NAct/NRated),

5. A method according to claim 2, wherein for sealless pumps eddy current loss estimations must be removed from the actual closed valve power readings.

6. A method according to claim 2, wherein for higher power pumps, to minimize heating of the pumped liquid the shutoff power at 100% speed can be calculated from the equation: PSO—100%=(N100%/N60%)KSO×PSO—60%,where KSO is a shutoff exponent with a typical value of 3.0.

7. A method according to claim 2, wherein the closed valve power at any speed can be accurately determined by the following cubic interpolation method: A=(PSO—30%)/(N30%),B=(PSO—60%−PSO—30%)/(N60%−N30%),C=(B−A)/(N60%−N30%),D=(PSO—100%−PSO—60%)/(N100%−N60%),E=(D−B)/((N100%−N30%), andF=(E−C)/(N100%); andwherein the shutoff power at any speed is calculated as follows: PSO—N %=A(NACT)+C(NACT)(NACT−N30%)+F(NACT)(NACT−N30%)(NACT−N60%),

8. A method according to claim 2, wherein the published power at the best efficiency point at rated speed is corrected based on actual closed valve power data.

9. A method according to claim 8, wherein the published power at best efficiency point is corrected according to the equation: PBEP corr=(PSO100%−PSO)+PBEP,

10. A method according to claim 1, wherein the pump's power ratio is determined by the equation: Pratio=Pshutoff @100%/PBEP—corr.

11. A method according to claim 1, wherein the power equation is a polynomial equation developed using coefficients from the power versus flow curve.

12. A method according to claim 11, wherein the polynomial power equation is: 0=[(PBEP CORR(a))/((QBEP)3(ηHBEP—CORR))](QAct)3+[((NAct)(PBEPCORR)(b))/((NRated) (QBEP)2(ηHBEP—CORR))](QAct)2+[((NAct)2(PBEP CORR)(c))/((NRated)2(QBEP)(ηHBEP—CORR))](QAct)+(PSON %−(PACT/S.G.)),

13. A method according to claim 12, wherein accuracy for small hp pumps applied on liquids with specific gravity other than 1.0, can be compensated for mechanical losses (such as seals and bearings) in the polynomial power equation by adjusting PACT as follows: PACT CORR=[((PACT−(Mech Loss×NAct/NRated))/S.G.)+(Mech Loss×NAct/NRated)].

14. A method according to claim 12, wherein for sealless pumps eddy current loss estimations are removed from the actual power reading in the polynomial power equation.

15. A method according to claim 11, wherein corrections are made for speed, hydraulic efficiency and specific gravity in the polynomial power equation.

16. A method according to claim 15, wherein complex roots are determined to solve the polynomial equation using either Muller's method or some other suitable method.

17. A method according to claim 16, wherein the calculated actual flow is determined for a specific operating point.

18. A method according to claim 1, wherein the steps of the method are performed on a variable frequency drive (VFD) or a programmable logic controller (PLC).

19. A method according to claim 1, wherein the determined flow value may be used as input to a PID controller to control flow without the need for a flowmeter or other external instrumentation.

20. A controller for determining pump flow in a centrifugal pump, centrifugal mixer, centrifugal blower or centrifugal compressor comprising: a module configured for creating a calibrated power curve at closed valve conditions at several speeds;a module configured for calculating coefficients from a power vs flow curve based on a pump's power ratio; anda module configured for solving a power equation for flow at the current operating point.

21. A controller according to claim 20, wherein the calibrated power curve is created by increasing the speed of the pump from a minimum speed to a maximum speed while operating the pump against a closed discharge valve and collecting speed and power data at several speeds.

22. A controller according to claim 21, wherein the closed valve power data is corrected to a specific gravity equal to 1.

23. A controller according to claim 21, wherein for small hp pumps applied on liquids with specific gravity other than 1.0, mechanical losses (such as seals and bearings) can be compensated for in the measured closed valve power readings as follows: PSO—N=[(PMeas—N %−(Mech Loss×NAct/NRated))/SG]+(Mech Loss×NAct/NRated),

24. A controller according to claim 21, wherein for sealless pumps eddy current loss estimations are removed from the actual closed valve power readings.

25. A controller according to claim 21, wherein for higher power pumps, to minimize heating of the pumped liquid the shutoff power at 100% speed can be calculated from the equation: PSO—100%=(N100%/N60%)KSO×PSO—60%,where KSO is a shutoff exponent with a typical value of 3.0.

26. A controller according to claim 21, wherein the closed valve power at any speed can be accurately determined by the following cubic interpolation method: A=(P SO—30%)/(N30%),B=(PSO—60%−PSO—30%)/(N60%−N30%),C=(B−A)/(N60%−N30%),D=(PSO—100%−PSO—60%)/(N100%−N60%),E=(D−B)/((N100%−N30%), andF=(E−C)/(N100%); andwherein the shutoff power at any speed is calculated as follows: PSO—N %=A(NACT)+C(NACT)+C(NACT−N30%)+F(NACT)(NACT−N30%)(NACT−N60%),

27. A controller according to claim 21, wherein the published power at the best efficiency point at rated speed is corrected based on actual closed valve power data.

28. A controller according to claim 27, wherein the published power at best efficiency point is corrected according to the equation: PBEP corr=(PSO100%−PSO)+PBEP,

29. A controller according to claim 20, wherein the pump's power ratio is determined by the equation: Pratio=Pshutoff @100%/PBEP—corr.

30. A controller according to claim 20, wherein the power equation is a polynomial equation developed using coefficients from the power versus flow curve.

31. A controller according to claim 30, wherein the polynomial power equation is: 0=[(PBEP CORR(a))/((QBEP)3(ηHBEP—CORR))](QAct)3+[((NAct)(PBEPCORR) (b))/((NRated) (QBEP)2(ηHBEP—CORR))](QAct)2+[((NAct)2(PBEP CORR)(c))/((NRated)2(QBEP)(ηHBEP—CORR))](QAct)+(PSO—N %−(PACT/S.G.)),

32. A controller according to claim 30, wherein accuracy for small hp pumps applied on liquids with specific gravity other than 1.0, can be compensated for mechanical losses (such as seals and bearings) in the polynomial power equation by adjusting PACT as follows: PACT CORR=[((PACT−(Mech Loss×NAct/NRated))/S.G.)+(Mech Loss×NAct/NRated)].

33. A controller according to claim 30, wherein for sealless pumps eddy current loss estimations are removed from the actual power reading in the polynomial power equation.

34. A controller according to claim 30, wherein corrections are made for speed, hydraulic efficiency and specific gravity in the polynomial power equation.

35. A controller according to claim 34, wherein complex roots are determined to solve the polynomial equation using either Muller's method or some other suitable method.

36. A controller according to claim 35, wherein the calculated actual flow is determined for a specific operating point.

37. A controller according to claim 20, wherein the controller includes, or forms part of, a variable frequency drive (VFD) or a programmable logic controller (PLC).

38. A controller according to claim 20, wherein the determined flow value may be used as input to a PID controller to control flow without the need for a flowmeter or other external instrumentation.

39. A system having a controller for determining pump flow in a centrifugal pump, centrifugal mixer, centrifugal blower or centrifugal compressor, the controller comprising: a module configured for creating a calibrated power curve at closed valve conditions at several speeds;a module configured for calculating coefficients from a power vs flow curve based on a pump's power ratio; anda module configured for solving a power equation for flow at the current operating point.

40. A pump system according to claim 39, wherein the calibrated power curve is created by increasing the speed of the pump from a minimum speed to a maximum speed while operating the pump against a closed discharge valve and collecting speed and power data at several speeds.

41. A pump system according to claim 40, wherein the closed valve power data is corrected to a specific gravity equal to 1.

42. A pump system according to claim 40, wherein for small hp pumps applied on liquids with specific gravity other than 1.0, mechanical losses (such as seals and bearings) can be compensated for in the measured closed valve power readings as follows: PSO—N=[(PMeas—N %−(Mech Loss×NAct/NRated))/SG]+(Mech Loss×NAct/NRated),

43. A pump system according to claim 40, wherein for sealless pumps eddy current loss estimations are removed from the actual closed valve power readings.

44. A pump system according to claim 40, wherein for higher power pumps, to minimize heating of the pumped liquid the shutoff power at 100% speed can be calculated from the equation: PSO—100%=(N100%/N60%)KSO×PSO—60%,where KSO is a shutoff exponent with a typical value of 3.0.

45. A pump system according to claim 40, wherein the closed valve power at any speed can be accurately determined by the following cubic interpolation method: A=(PSO—30%)/(N30%),B=(PSO—60%−PSO—30%)/(N60%−N30%),C=(B−A)/(N60%−N30%),D=(PSO—100%−PSO—60%)/(N100%−N60%),E=(D−B)/((N100%−N30%), andF=(E−C)/(N100%); andwherein the shutoff power at any speed is calculated as follows: PSO—N %=A(NACT)+C(NACT)(NACT−N30%)+F(NACT)(NACT−N30%)(NACT−N60%),

46. A pump system according to claim 40, wherein the published power at the best efficiency point at rated speed is corrected based on actual closed valve power data.

47. A pump system according to claim 46, wherein the published power at best efficiency point is corrected according to the equation: PBEP corr=(PSO100%−PSO)+PBEP,

48. A pump system according to claim 39, wherein the pump's power ratio is determined by the equation: Pratio=Pshutoff @ 100%/PBEP—corr.

49. A pump system according to claim 39, wherein the power equation is a polynomial equation developed using coefficients from the power versus flow curve.

50. A pump system according to claim 49, wherein the polynomial power equation is: 0=[(PBEP CORR(a))/((QBEP)3(ηHBEP—CORR))](QAct)3+[((NAct)(PBEPCORR) (b))/((NRated) (QBEP)2(ηHBEP—CORR))](QAct)2+[((NAct)2(PBEP CORR)(c))/((NRated)2(QBEP)(ηHBEP—CORR))](QAct)+(PSO—N %−(PACT/S.G.)),

51. A pump system according to claim 49, wherein accuracy for small hp pumps applied on liquids with specific gravity other than 1.0, can be compensated for mechanical losses (such as seals and bearings) in the polynomial power equation by adjusting PACT as follows: PACT CORR=[((PACT−(Mech Loss×NAct/NRated))/S.G.)+(Mech Loss×NAct/NRated)].

52. A pump system according to claim 49, wherein for sealless pumps eddy current loss estimations are removed from the actual power reading in the polynomial power equation.

53. A pump system according to claim 49, wherein corrections are made for speed, hydraulic efficiency and specific gravity in the polynomial power equation.

54. A pump system according to claim 53, wherein complex roots are determined to solve the polynomial equation using either Muller's method or some other suitable method.

55. A pump system according to claim 54, wherein the calculated actual flow is determined for a specific operating point.

56. A pump system according to claim 39, wherein the controller includes, or forms part of, a variable frequency drive (VFD) or a programmable logic controller (PLC).

57. A pump system according to claim 39, wherein the determined flow value may be used as input to a PID controller to control flow without the need for a flowmeter or other external instrumentation.