CAVITATION LIMITING STRATEGIES FOR PUMPING SYSTEM

• US 20180040226A1
• Filed: 08/05/2016
• Published: 02/08/2018
• Est. Priority Date: 08/05/2016
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Zhang, Yanchai, Dong, Zhaoxu, Hu, Xuefei
• Granted Patent: US 10,134,257 B2
• Time in Patent Office: Days
• CPC Class Codes: E21B 43/267 reinforcing fractures by propping
• CPC Class Codes: F04B 11/0041 by piston speed control F04B11/0058 takes precedence
• CPC Class Codes: F04B 17/05 driven by internal-combustion engines
• CPC Class Codes: F04B 2205/02 Pressure in the inlet chamber
• CPC Class Codes: F04B 2205/03 Pressure in the compression chamber
• CPC Class Codes: F04B 49/065 and making use of computers
• CPC Class Codes: F04B 49/103 Responsive to speed
• CPC Class Codes: F04B 51/00 Testing machines, pumps, or pumping installations
• CPC Class Codes: F04B 53/14 Pistons, piston-rods or piston-rod connections
• CPC Class Codes: F04B 53/16 Casings; Cylinders; Cylinder liners or heads; Fluid connections
• CPC Class Codes: F04B 53/22 Arrangements for enabling ready assembly or disassembly
• CPC Class Codes: G08B 21/182 Level alarms, e.g. alarms responsive to variables exceeding a threshold

Abstract

Operating a pumping system includes moving a pumping element to transition liquid through the pump, and determining a value based at least in part upon inlet pressure and pumping speed that is indicative of a pressure of the liquid within a bore susceptible to cavitation. Pumping speed and/or inlet pressure can be varied responsive to the determined value to limit cavitation.

Claims

1. A method of operating a pumping system comprising:

moving a pumping element in a pump to transition a liquid between a pump inlet and a pump outlet in the pump;

receiving inlet pressure data indicative of an inlet pressure of the liquid at the pump inlet, and pumping speed data indicative of a pumping speed of the pump;

determining a pressure value based at least in part on the inlet pressure data and the pumping speed data that is indicative of a pressure of the liquid within a bore in the pump susceptible to cavitation of the liquid; and

varying at least one of the pumping speed or the inlet pressure, responsive to the determined value.

2. The method of claim 1 wherein the pumping system includes a hydraulic fracturing rig having a mixer, and further comprising feeding a mixture containing the liquid and a proppant from the mixer to the pump.

3. The method of claim 2 wherein the varying of the at least one of the pumping speed or the inlet pressure includes varying the inlet pressure by way of varying an outlet pressure of the mixer.

4. The method of claim 1 further comprising outputting an activation signal to an operator alert device where the determined pressure value is indicative of expected cavitation of the liquid.

5. The method of claim 1 further comprising comparing the determined pressure value with a stored value that is based on a vapor pressure of the liquid.

6. The method of claim 5 wherein the stored value includes one of a plurality of stored values defining an operating curve for the pump.

7. The method of claim 1 wherein the receiving of inlet pressure data indicative of an inlet pressure of the liquid further includes receiving data from a pressure sensor exposed to the inlet pressure of the liquid, and wherein the pump includes a reciprocating pump having a rotatable crankshaft and the receiving of pumping speed data indicative of a pumping speed includes receiving data from a second sensor structured to monitor a parameter indicative of rotational speed of the rotatable crankshaft.

8. The method of claim 7 wherein the determining of the pressure value indicative of a pressure of the liquid within the bore includes determining a pressure value that is reduced relative to the inlet pressure according to the equation:

P_bore=P_in−

[G]−

[X]v^7/4_plunger−

[Y]a_plunger−

[Z]v²_plunger

where;

P_bore=pressure in the bore;

P_in=inlet pressure;

v=plunger velocity;

a=plunger acceleration; and

G, X, Y, Z are numeric coefficients dependent upon at least one of a density of the liquid, a viscosity of the liquid, or a structural attribute of the pump.

9. The method of claim 7 wherein the determining of a pressure value that is indicative of a pressure of the liquid in the bore includes determining a plunger bore pressure value indicative of a pressure of the liquid within a plunger bore in the pump.

10. The method of claim 9 wherein the determining of a pressure value further includes reading the plunger bore pressure value from a map having an inlet pressure coordinate and a pumping speed coordinate.

11. A method of setting up a pumping system for service comprising:

populating a data structure with a plurality of bore pressure values indicative of a pressure of a liquid in a bore within a pump of the pumping system positioned fluidly between a pump inlet and a pump outlet;

mapping the plurality of bore pressure values in the data structure to a plurality of inlet pressure values indicative of a pressure of the liquid at the pump inlet and a plurality of pumping speed values indicative of a pumping speed of the pump, such that bore pressure varies in a manner that is dependent upon both inlet pressure and pumping speed; and

generating a cavitation threshold model that is based on a subset of the plurality of the bore pressure values and a vapor pressure of the liquid;

the cavitation threshold model defines an operating curve for the pump, such that upon operating the pump according to the operating curve cavitation of the liquid within the bore is limited.

12. The method of claim 11 wherein the mapping of the plurality of bore pressure values in the data structure further includes mapping the plurality of bore pressure values such that bore pressure is reduced from inlet pressure according to a plurality of loss terms.

13. The method of claim 12 wherein the plurality of loss terms includes a frictional loss term, an inertial loss term, and a plurality of structural loss terms.

14. The method of claim 13 wherein the plurality of structural loss terms includes a gravitational loss term and a valve opening loss term.

15. The method of claim 13 wherein the mapping of the plurality of bore pressure values in the data structure further includes mapping the plurality of bore pressure values such that bore pressure is reduced from inlet pressure according to a plurality of numerical coefficients associated with the plurality of loss terms.

16. The method of claim 14 wherein the mapping of the plurality of bore pressure values further includes mapping the plurality of bore pressure values according to the equation:

P_bore=P_in−

[G]−

[X]v^7/4_plunger−

[Y]a_plunger−

[Z]v²_plunger

where;

P_bore=pressure in the bore;

P_in=inlet pressure;

v=plunger velocity;

a=plunger acceleration; and

G, X, Y, Z are numeric coefficients dependent upon at least one of a density of the liquid, a viscosity of the liquid, or a structural attribute of the pump.

17. The method of claim 12 wherein the generation of the model further includes selecting the subset of the plurality of bore pressure values according to a simulated bore pressure cavitation threshold.

18. A pumping system comprising:

a pump including a pumping element movable within a bore in a pump housing to transition a liquid between a pump inlet and a pump outlet in the pump housing;

a control system coupled with the pump and including a first monitoring mechanism structured to monitor a first parameter indicative of an inlet pressure at the pump inlet, a second monitoring mechanism structured to monitor a second parameter indicative of a pumping speed of the pump, and an electronic control unit;

the electronic control unit being coupled with each of the first monitoring mechanism and the second monitoring mechanism and structured to determine a pressure value indicative of a pressure of the liquid within the bore in the pump housing based at least in part on the inlet pressure and the pumping speed indicated by the first monitoring mechanism and the second monitoring mechanism, respectively;

the control system further including a cavitation alert device structured to produce an operator-perceptible alert indicative of expected cavitation of the liquid within the bore, and the electronic control unit being coupled with the operator alert device and structured to activate the operator alert device responsive to the determined value.

19. The pumping system of claim 18 wherein the pumping system is part of a hydraulic fracturing rig including a power supply structured to power the pump, and a mixer structured to feed the liquid to the pump.

20. The pumping system of claim 18 wherein the electronic control unit is further structured to determine the pressure value indicative of the pressure of the liquid within the bore based on values of the first parameter and the second parameter that satisfy the equation:

P_bore=P_in−

[G]−

[X]v^7/4_plunger−

[Y]a_plunger−

[Z]v²_plunger

where;

P_bore=pressure in the bore;

P_in=inlet pressure;

v=plunger velocity;

a=plunger acceleration; and

G, X, Y, Z are numeric coefficients dependent upon at least one of a density of the liquid, a viscosity of the liquid, or a structural attribute of the pump.