Claims
- 1. A method for controlling a pumping system comprising a plurality of variable-performance centrifugal or axial pumps, each having a Minimum Continuous Stable Flow control limit, pertinent instrumentation, and a control system, the method comprising manipulating a performance of the pumps, such that all pumps arrive at their respective Minimum Continuous Stable Flow control limits substantially simultaneously as a process flow rate is reduced.
- 2. The method of claim 1, wherein signals from the pertinent instrumentation are used to scale a pump map for each pump, calculating a pump control variable, S, such that each pump's Minimum Continuous Stable Flow control limit has a value equal to the Minimum Continuous Stable Flow control limits of all other pumps.
- 3. The method of claim 1, wherein the pertinent instrumentation comprises instrumentation for measuring a value related to a volumetric flow rate.
- 4. The method of claim 1, wherein pump performance is changed by varying a pump's rotational speed.
- 5. The method of claim 1, wherein pump performance is changed by varying a throttling valve's opening.
- 6. The method of claim 1, wherein upon reaching a preset value of a pump control variable, S, a recycle valve is opened a predetermined amount as quickly as possible.
- 7. The method of claim 6, wherein the predetermined amount of valve opening is variable during operation.
- 8. The method of claim 7, wherein the predetermined amount of valve opening is based on the speed at which a pump's operating point is moving in the direction of zero flow.
- 9. The method of claim 8, wherein the predetermined amount of valve opening is repeated at intervals until the pump returns to a safe operating region.
- 10. The method of claim 1, wherein the plurality of pumps is controlled to achieve a desired balance when pumps are operating far from their Minimum Continuous Stable Flow control limits.
- 11. The method of claim 10, wherein the desired balance results in a minimum total power.
- 12. The method of claim 1, wherein the pump control variable, S, is calculated as:
- 13. The method of claim 1, wherein the pump control variable, S, is calculated as:
- 14. The method of claim 1, wherein the pump control variable, S, is calculated as:
- 15. The method of claim 1, wherein the control system comprises a master controller maintaining a main control-variable at its set point; and for each pump, at least one load-sharing controller maintaining a balance between all pumps sharing a pump load; each load-sharing controller being configured to equalize a distance from its pump's operating point to the Minimum Continuous Stable Flow control limit.
- 16. The method of claim 1, wherein the Minimum Continuous Stable Flow control limit is a function of the pump's operating conditions.
- 17. The method of claim 16, wherein the operating conditions, of which the Minimum Continuous Stable Flow control limit is a function, comprise a pump rotational speed.
- 18. An apparatus for controlling a pumping system comprising a plurality of variable-performance centrifugal or axial pumps, each having a Minimum Continuous Stable Flow control limit, pertinent instrumentation, means for manipulating each pump's performance, and a control system, the apparatus comprising means for maintaining substantially equal distances between all pumps' operating points and their respective Minimum Continuous Stable Flow control limits.
- 19. The apparatus of claim 18 including means for calculating a pump control variable, S, based on signals from the pertinent instrumentation, such that each pump's Minimum Continuous Stable Flow control limit has a value equal to the Minimum Continuous Stable Flow control limits of all other pumps.
- 20. The apparatus of claim 18, wherein the pertinent instrumentation comprises instrumentation for measuring a value related to a volumetric flow rate.
- 21. The apparatus of claim 18, wherein means for manipulating each pump's performance comprises means for varying a pump's rotational speed.
- 22. The apparatus of claim 18, wherein means for manipulating each pump's performance comprises means for varying a throttling valve's opening.
- 23. The apparatus of claim 18 including a control system for opening a recycle valve a predetermined amount as quickly as possible when a pump operating point reaches a preset value of a pump control variable, S.
- 24. The apparatus of claim 23 including a calculation unit for calculating a varying value for the predetermined amount of valve opening during operation.
- 25. The apparatus of claim 24 including means for basing the predetermined amount of valve opening on the speed at which a pump's operating point is moving toward zero flow.
- 26. The apparatus of claim 23 including means for repeating the predetermined amount of valve opening at intervals until the pump returns to a safe operating region.
- 27. The apparatus of claim 18 including a control system for controlling the plurality of pumps to achieve a desired balance when pumps are operating far from their Minimum Continuous Stable Flow control limits.
- 28. The apparatus of claim 27 including means to balance the pumps for minimum total power.
- 29. The apparatus of claim 18 including a calculation unit for calculating a pump control variable, S, as:
- 30. The apparatus of claim 18 including a calculation unit for calculating a pump control variable, S, as:
- 31. The apparatus of claim 18 including a calculation unit for calculating a pump control variable, S, as:
- 32. The apparatus of claim 18, wherein the control system comprises a master controller maintaining a main control-variable at its set point; and for each pump, at least one load-sharing controller maintaining a balance between all pumps sharing a pump load; the load-sharing controllers are configured to equalize a distance to the Minimum Continuous Stable Flow control limit.
- 33. The apparatus of claim 18 including means to calculate the Minimum Continuous Stable Flow control limit as a function of the pump's operating conditions.
- 34. The apparatus of claim 33, wherein the operating conditions, of which the Minimum Continuous Stable Flow control limit is a function, comprise a pump rotational speed.
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application contains disclosure from and claims the benefit under Title 35, United States Code, §119(e) of the following U.S. Provisional Application: U.S. Provisional Application Ser. No. 60/390,072 filed Jun. 20, 2002, entitled METHOD AND APPARATUS FOR CONTROLLING MINIMUM CONTINUOUS STABLE FLOW OF A PUMP STATION WITH MULTIPLE DYNAMIC PUMPS.
Provisional Applications (1)
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Number |
Date |
Country |
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60390072 |
Jun 2002 |
US |