Turbocompressor antisurge control by vibration monitoring

1. A method of antisurge control for a turbocompressor instrumented with at least one vibration sensor, an antisurge controller, and an antisurge valve, the method comprising:

(a) selecting a frequency band;

(b) operatively receiving into the antisurge controller a first set of vibration data from the at least one vibration sensor when the turbocompressor is not in surge;

(c) calculating, in the antisurge controller, a background vibration level based on the first set of vibration data in the frequency band;

(d) operatively receiving a second set of vibration data into the antisurge controller from the at least one vibration sensor whether the turbocompressor is in surge or not;

(e) calculating, in the antisurge controller, a current vibration level based on the second set of vibration data in the frequency band;

(f) calculating, in the antisurge controller, a process variable as a function of the background vibration level and the current vibration level;

(g) selecting a set point, R;

(h) comparing the process variable to the set point, R in the antisurge controller; and

(i) manipulating the antisurge valve based on a comparison of the process variable to the set point, R.

2. The method of claim 1 wherein manipulating the antisurge valve comprises opening the antisurge valve based on the comparison of the process variable to the set point, R.

3. The method of claim 1 wherein manipulating the antisurge valve based on the comparison of the process variable to the set point, R comprises:

(a) determining if the turbocompressor is in surge based on the comparison of the process variable to the set point;

(b) comparing a turbocompressor operating point to a surge control curve on a turbocompressor performance map; and

(c) if the turbocompressor is in surge, moving the turbocompressor surge control curve based on the comparison of the operating point to the surge control curve.

4. The method of claim 1 wherein the frequency band is selected based on tests run on the turbocompressor.

5. The method of claim 1 wherein a vibration data type comprises one of displacement, vibration, or acceleration.

6. The method of claim 1 wherein calculating a background vibration level comprises:

(a) repeatedly transforming the vibration data using a fast Fourier transform over a predetermined period of time;

(b) repeatedly calculating a vector norm for the vibration data within the frequency band over the predetermined period of time; and

(c) calculating an average vector norm based on the vector norm values calculated repeatedly over the predetermined period of time.

7. The method of claim 6 wherein the vector norm comprises a root mean square value.

8. The method of claim 1 wherein calculating a current vibration level comprises:

(a) transforming the vibration data using a fast Fourier transform; and

(b) calculating a vector norm for the vibration data within the frequency band.

9. The method of claim 8 wherein the vector norm comprises a root mean square value.

10. The method of claim 1 wherein the vibration data comprises displacement data, and wherein calculating a process variable comprises:

(a) calculating a difference, d, between the current vibration level and the background vibration level;

(b) calculating an absolute value of d; and

(c) calculating a ratio, r, of the absolute value of d and the background vibration level.

11. The method of claim 10 wherein comparing the process variable to the set point comprises:

(a) computing a difference, r−R, by subtracting the set point, R, from the ratio, r, of the absolute value of d and the background vibration level; and

(b) calculating a second process variable by subtracting an absolute value of the difference, r−R, from the value of the difference, r−R.

12. The method of claim 11 additionally comprising:

(a) passing the second process variable into a proportional, integral, differential (PID) loop as a PID loop process variable;

(b) calculating an antisurge valve set point within the PID loop; and

(c) manipulating a position of the antisurge valve based on the antisurge valve set point.

13. The method of claim 10 wherein comparing the process variable to the set point comprises determining if the process variable is greater than the set point.

14. The method of claim 1 wherein the vibration data type comprises one of velocity data or acceleration data, and wherein calculating a process variable comprises calculating a ratio, r, of the current vibration level to the background vibration level.

15. The method of claim 14 wherein comparing the process variable to the set point comprises:

(a) computing a difference, r−R, by subtracting the set point, R, from the ratio, r, of the current vibration level to the background vibration level; and

(b) calculating a second process variable by subtracting an absolute value of the difference, r−R, from the value of the difference, r−R.

16. The method of claim 15 additionally comprising:

(a) passing the second process variable into a PID loop as a process variable;

(b) calculating an antisurge valve set point within the PID loop; and

(c) manipulating a position of the antisurge valve based on the antisurge valve set point.

17. The method of claim 14 wherein comparing the process variable to the set point comprises determining if the process variable is greater than the set point.

18. The method of claim 1 wherein selecting a set point comprises selecting a set point as a function of the background vibration level.

19. The method of claim 18 wherein the function of the background vibration level comprises a linear function.

20. The method of claim 1 wherein operatively receiving vibration data from the at least one vibration sensor comprises acquiring data comprising one of radial shaft displacement, radial shaft velocity, radial shaft acceleration, axial shaft displacement, axial shaft velocity, or axial shaft acceleration.

21. The method of claim 1 wherein operatively receiving vibration data from the at least one vibration sensor comprises acquiring data from the at least one vibration sensor operatively affixed to an exterior of the turbocompressor.

22. The method of claim 1 wherein the selected frequency band is a function of a rotational speed of the turbocompressor.

23. An apparatus for providing turbocompressor antisurge control, the apparatus comprising:

a turbocompressor;

at least one vibration sensor comprising a proximity probe, a velocimeter or an accelerometer, said vibration sensor producing a signal related to a measured vibration level;

at least one of an antisurge controller or a vibration monitor comprising:

Fourier transform calculating software to calculate a Fourier transform to calculate a background vibration level when the turbocompressor is not in surge, and a current vibration level, both the background and the current vibration levels calculated within a predetermined frequency band and based on the measured vibration level acquired from the at least one vibration sensor;

process variable calculating software to calculate a process variable as a function of the background vibration level and the current vibration level;

comparative software to compare the process variable to a set point, R; and

output software that uses a result of a comparison of the process variable to the set point, R, to calculate an output, and manipulate an antisurge control valve based on the output.

24. The apparatus of claim 23 wherein the at least one vibration sensor is disposed to sense at least one of axial shaft vibration or radial shaft vibration.

25. The apparatus of claim 23 wherein at least one of the antisurge controller or the vibration monitor further comprise:

PID loop software to calculate an antisurge valve set point; and

a PID output operatively connected to the antisurge control valve by which the antisurge valve set point is transmitted to the antisurge control valve.

26. The apparatus of claim 23 wherein at least one of the antisurge controller or the vibration monitor further comprise:

an operating point calculating function software to calculate a turbocompressor operating point;

second comparative software to compare the turbocompressor operating point to a turbocompressor surge control curve; and

a turbocompressor surge control curve recalculation function software to move the turbocompressor surge control curve based on the comparison of the turbocompressor operating point to the turbocompressor surge control curve.

27. A method of antisurge control for a turbocompressor instrumented with at least one vibration sensor, and an antisurge valve, the method comprising:

(a) selecting a frequency band;

(b) acquiring a first set of vibration data from the at least one vibration sensor when the turbocompressor is not in surge;

(c) calculating a background vibration level based on the first set of vibration data in the frequency band;

(d) acquiring a second set of vibration data from the at least one vibration sensor whether the turbocompressor is in surge or not;

(e) calculating a current vibration level based on the second set of vibration data in the frequency band;

(f) calculating a process variable as a function of the background vibration level and the current vibration level;

(g) selecting a set point, R;

(h) comparing the process variable to the set point, R; and

(i) manipulating a position of the antisurge valve based on the comparison of the process variable to the set point.

28. The method of claim 27 wherein comparing the process variable to the set point, R, comprises:

(a) determining if the turbocompressor is in surge based on the comparison of the process variable to the set point;

(b) comparing a turbocompressor operating point to a surge control curve on a turbocompressor performance map; and

(c) if the turbocompressor is in surge, moving the turbocompressor surge control curve based on the comparison of the operating point to the surge control curve.

29. The method of claim 27 wherein the frequency band is selected based on tests run on the turbocompressor.

30. The method of claim 27 wherein a vibration data type comprises one of displacement, vibration or acceleration.

31. The method of claim 27 wherein calculating a background vibration level comprises:

(a) repeatedly transforming the acquired vibration data using a fast Fourier transform over a predetermined period of time;

(b) repeatedly calculating a vector norm for the acquired vibration data within the frequency band over the predetermined period of time; and

(c) calculating an average vector norm based on the vector norm values calculated repeatedly over the predetermined period of time.

32. The method of claim 31 wherein the vector norm comprises a root mean square value.

33. The method of claim 27 wherein calculating a current vibration level comprises:

(a) transforming the acquired vibration data using a fast Fourier transform; and

(b) calculating a vector norm for the acquired vibration data within the frequency band.

34. The method of claim 33 wherein the vector norm comprises a root mean square value.

35. The method of claim 27 wherein the vibration data comprises displacement data, and wherein calculating a process variable comprises:

(a) calculating a difference, d, between the current vibration level and the background vibration level;

(b) calculating an absolute value of d; and

(c) calculating a ratio, r, of the absolute value of d and the background vibration level.

36. The method of claim 35 wherein comparing the process variable to the set point, R, comprises:

(a) computing a difference, r−R, by subtracting the set point, R, from the ratio, r, of the absolute value of d and the background vibration level; and

(b) calculating a second process variable by subtracting an absolute value of the difference, r−R, from the value of the difference, r−R.

37. The method of claim 36 additionally comprising:

(a) passing the second process variable into a PID loop as a PID loop process variable;

(b) calculating an antisurge valve set point within the PID loop; and

(c) manipulating a position of the antisurge valve based on the antisurge valve set point.

38. The method of claim 35 wherein comparing the process variable to the set point comprises determining if the process variable is greater than the set point.

39. The method of claim 27 wherein the vibration data type comprises one of velocity data or acceleration data, and wherein calculating a process variable comprises calculating a ratio, r, of the current vibration level to the background vibration level.

40. The method of claim 39 wherein comparing the process variable to the set point comprises:

(a) computing a difference, r−R, by subtracting the set point, R, from the ratio, r, of the current vibration level to the background vibration level; and

(b) calculating a second process variable by subtracting an absolute value of the difference, r−R, from the value of the difference, r−R.

41. The method of claim 40 additionally comprising:

(a) passing the second process variable into a PID loop as a process variable;

(b) calculating an antisurge valve set point within the PID loop; and

(c) manipulating a position of the antisurge valve based on the antisurge valve set point.

42. The method of claim 39 wherein comparing the process variable to the set point comprises determining if the process variable is greater than the set point.

43. The method of claim 27 wherein selecting a set point comprises selecting a set point as a function of the background vibration level.

44. The method of claim 43 wherein the function of the background vibration level comprises a linear function.

45. The method of claim 27 wherein acquiring vibration data from the at least one vibration sensor comprises acquiring at least one of radial shaft displacement, radial shaft velocity, radial shaft acceleration, axial shaft displacement, axial shaft velocity, or axial shaft acceleration.

46. The method of claim 27 wherein acquiring vibration data from the at least one vibration sensor comprises acquiring data from the at least one vibration sensor operatively affixed to an exterior of the turbocompressor.

47. The method of claim 27 wherein the selected frequency band is a function of a rotational speed of the turbocompressor.