Patent Application
20180040226
The present disclosure relates generally to limiting cavitation in a pumping system, and relates more particularly to limiting cavitation by varying pumping speed or inlet pressure based on an indirect determination of a liquid pressure within the pump.
Pumps are used in all manner of commercial, industrial, and household applications, from small pumping mechanisms in household appliances up to large scale industrial and resource extraction systems, for example. While there are nearly as many different types of pump designs as there are pump applications, two common pump types are reciprocating pumps and rotary pumps. In a rotary pump, an impeller is commonly provided to suck liquid into the pump housing and discharge it at a pump outlet for whatever the end use might be. Reciprocating pumps generally include one or more plungers that travel in a linear manner, alternating between an intake stroke and a pumping stroke. Other known pumps include diaphragm pumps, rotary vane pumps, and still others.
In many applications, pumps operate to transfer a liquid without concern for varying a pressure of the liquid, with the primary purpose being simply to move the liquid from one place to another. In certain other applications it can be desirable to use a pump to increase the pressure of a liquid. Pumps used in hydraulic systems for working equipment or industrial systems, pressure washers, and hydraulic fracturing pumps to name a few examples generally increase the pressure of the working liquid at least several times, and potentially many times, over the pressure at which the liquid is supplied. Such pumps commonly operate under relatively harsh conditions, often reciprocating at high speeds and subjecting internal components to fairly extreme pressures.
In some instances, including some of the more heavy duty applications, the well-known phenomenon of cavitation can occur within the pump. In cavitation a transient bubble of vapor forms in the liquid and then collapses, producing a shockwave of sorts. While the results of cavitation in the nature of erosion, pitting, cracking or other damage to pump components are readily recognized, the physics behind cavitation and the circumstances that can lead to cavitation have long defied attempts at a deeper understanding. Complicating prior attempts at analysis is the diversity of pump designs and even variations in pump and working fluid behavior across the various different types of fluids that can be used. Commonly-owned U.S. Pat. No. 7,797,142 to Salomon et al. is directed to simulating cavitation damage, and proposes a computer-implemented method that simulates a potential for cavitation damage, and displays a histogram in which locations of vapor implosion pressure events can be visually distinguished on a surface of a modeled component.
In one aspect, a method of operating a pumping system includes moving a pumping element in a pump to transition a liquid between a pump inlet and a pump outlet in the pump, and receiving inlet pressure data indicative of an inlet pressure of a liquid at the pump inlet, and pumping speed data indicative of a pumping speed of the pump. The method further includes 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. The method still further includes varying at least one of the pumping speed or the inlet pressure, responsive to the determined value.
In another aspect, a method of setting up a pumping system for service includes 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. The method further includes 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. The method further includes generating a cavitation threshold model that is based on a subset of the plurality of 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.
In still another aspect, a pumping system includes a pump having 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. The pumping system further includes a control system coupled with the pump and having 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 is 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 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 includes 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 operate alert device responsive to the determined value.
Referring to
The pumping system 10 further includes a control system 50 having an electronic control unit (“ECU”) 52 that is structured to monitor and control various of the operating aspects of the pumping system 10. The electronic control unit or ECU 52 may be in communication with the transmission 18 so as to shift gears either autonomously or at the command of an operator. The ECU 52 may also be in communication with a throttle 17 of the engine 16 for analogous purposes of varying engine speed. The control system 50 may further include a sensor 54 such as a pressure sensor coupled with the pump 20, for example coupled to the manifold 38, and structured to monitor a parameter indicative of an inlet pressure at or close to the pump inlet 46. The control system 50 may also include a sensor 56 such as a speed sensor structured to monitor a parameter indicative of a speed of rotation of a crankshaft 40, for example, so as to produce pumping speed data indicative of a pumping speed of the pump 20. The pressure sensor 54 likewise produces inlet pressure data indicative of a pressure of the liquid at or close to the pump inlet 46. The description herein of the inlet pressure data and pumping speed data should not be taken to mean that the data is necessarily a direct representation or indication of the parameter of interest, but could be data that is indicative indirectly of a state of the parameter of interest. All that is contemplated is that the ECU 52 can receive data from the sensor 54 and data from the sensor 56 and determine or estimate or infer a pumping speed or an inlet pressure as the case may be.
The control system 50 also includes an operator interface 58 having pumping speed controls 60 and inlet pressure controls 62. In a practical implementation, during a hydraulic fracturing operation, or another operation where the pumping system 10 is being used, an operator can monitor the status of factors such as inlet pressure and pumping speed, and based upon alerts or other information provided by way of the operator interface 58 can adjust inlet pressure or pumping speed to various ends. As will be further apparent from the following description, an operator or the control system 50 itself, whether onboard the pumping system 10 or located elsewhere, can advantageously control either or both of inlet pressure and pumping speed to enable the pumping system 10 to operate relatively close to a cavitation threshold with reduced risk of any significant cavitation occurring. Thus, an operator may have a better understanding of how to operate a pumping system to increase productivity while reducing the chances of cavitation. Analogously, a pumping system control system as contemplated herein can be structured for increased productivity.
Referring also now to
Referring now to
To this end, it has been discovered that bore pressure in a pump can be related to pumping speed and inlet pressure according to the following Equation 1:
P
bore
=P
in
−[G]−[X]v
7/4
plunger
−[Y]a
plunger
−[Z]v
2
plunger
where:
The frictional loss term can be understood to be based upon viscosity of the liquid being pumped, and also upon a flow distance from the pump inlet to the bore whose pressure is sought to be determined. Accordingly, a relatively longer flow distance for a given liquid could be associated with a relatively greater value of the frictional loss term, and a shorter flow distance could be associated with a lesser value of the frictional loss term. The diameter of the inlet passage defining the flow length could also affect the magnitude of the frictional loss term, due to variation in pipe friction with variation in the diameter.
The inertial loss term can be understood to be based upon a density of the liquid being pumped, as well as a length of the path to the bore from the pump inlet, and also on the basis of the diameter of the inlet pipe. The structural loss term [Z]v2plunger may include a valve loss term that is based upon the opening size of the pump inlet, as determined by the geometry and position of an inlet valve. In the case of the inlet valve 68 in the pump 20, an opening position of the valve can affect the available flow area for liquid entering the bore 44, which available flow area will be less than an available flow area of the inlet passage.
The loss terms in the above Equation 1 will each include a numerical coefficient as noted, and in the above-illustrated case numerical coefficients G, X, Y and Z. The values of the numerical coefficients can be theoretical or empirically determined for a particular pump which is sought to be operated or evaluated or set up for service according to the present disclosure. Information as to the density and viscosity of a liquid of interest can also be empirically determined; or determined by consultation of outside references. It will therefore be appreciated that values of the numerical coefficients can vary depending upon the particular pump and the particular liquid of interest, however, the above Equation 1 is contemplated to be applicable across a range of pump types, including reciprocating pumps as well as rotary pumps, and a range of working liquid types as well. The understanding set forth herein as to the relationships among inlet pressure, pumping speed, and bore pressure can be exploited in operating a pump and pumping system according to the present disclosure and setting up the same for service. In particular, readily measured parameters including pumping speed and inlet pressure can be used to predict a bore pressure or a pressure value indicative of the bore pressure. The determined value may be a numeric value, for example, that indicates bore pressure in pounds per square inch (PSI), although the present disclosure is not thereby limited. The bore pressure, or potentially pressure in another bore within a pump, can be compared to a vapor pressure of the liquid being pumped, or to another value having a known relationship with the vapor pressure, to determine or predict when cavitation is expected. This enables a pump to be operated at a relatively higher pumping speed or a relatively higher inlet pressure, or both, with reduced risk of cavitation, and with reduced need for a safety buffer from the cavitation threshold.
Embodiments are contemplated wherein a computer such as the ECU 52 calculates a bore pressure based upon pumping speed and inlet pressure, however, in a practical implementation the above Equation 1 and associated principles can be used in populating a map for use in controlling or monitoring the operation of a pump. In the case of the pumping system 10, an operator can control pumping speed and potentially inlet pressure of the pump 20, and monitor operation of the pump 20 on the operator interface 58. The operator can use the pumping speed controls 60 and/or the inlet pressure controls 62 to adjust operation of the pump 20 as desired to optimize operation while avoiding risk of cavitation. Varying pumping speed could include shifting gears or changing engine speed. Varying inlet pressure could include adjusting mixer 28 to vary its outlet pressure. When a risk of cavitation is detected, or potentially actual cavitation is detected, the ECU 52 may output an activation signal to the alert device 64 to produce an operator-perceptible alert such as illumination of a light, sounding of an alarm, et cetera. The operator could also be provided with various indications that the pump 20 is operating according to safe conditions where cavitation is not expected, and a green light could be turned off, for instance, when what is considered a safe pumping speed and/or a safe inlet pressure is exceeded. As further described herein, bore pressure values calculated according to the principles set forth herein can be used to generate a cavitation threshold model that defines an operating curve for the pump 20 that can be used either by visual reference by an operator or by the ECU 52. These principles will be further illustrated by way of the description of the following example embodiments.
Referring to the drawings generally, but in particular now to
The process depicted in the flowchart 200 can be understood as monitoring of cavitation risk during increasing the pumping speed of the pump 20. By looping through the process of the flowchart 200 continuously or periodically pumping speed can be brought up to or close to a maximum allowable pumping speed, at which point the alert device 64 can be activated. There are a variety of other ways that pumping speed control could occur according to the present disclosure, as well as a variety of ways that inlet pressure control could take place either in parallel with or instead of varying pumping speed. It is nevertheless assumed that in many instances, an operator or the ECU 52 will seek to operate the pump 20 at as high a pumping speed as possible without risking or unduly risking cavitation. Rather than increasing the pumping speed at the block 240, a control process according to the present disclosure could seek to operate the pump 20 at a setpoint, and thus pumping speed could be either increased or decreased. In the case of a hydraulic fracturing application, the operator or the ECU 52 might control pump operation in the manner described for a relatively short time period, on the order of only a few minutes, to complete the hydraulic fracturing event, and then pump 20 appropriately operated to discontinue pumping liquid at all.
As indicated above, it is contemplated that the principles and discoveries set forth in the present disclosure can be applied to setting up a pumping system such as the pumping system 10 for operation. Referring to
From the block 310, the process may advance to block 320 to map 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 46 and a plurality of pumping speed values indicative of a pumping speed of the pump 20. The mapping of the plurality of bore pressure values could include addressing the stored values in a map or lookup table having a first coordinate that includes inlet pressure or the inlet pressure values, a second coordinate that includes pumping speed or the pumping speed values, and a third coordinate that includes the bore pressure or bore pressure values. The mapping depicted at the block 320 may be such that the bore pressure according to the map varies in a manner that is dependent upon both the inlet pressure and the pumping speed, and the varying will typically be non-linear.
From the block 320, the process may advance to block 330 to generate a cavitation threshold model that includes or is otherwise based upon a subset (less than all) of the plurality of bore pressure values populating the data structure, and defines an operating curve for the pump. The model could include for example all the bore pressure values in the map that are associated with likely or possible cavitation or only those values that represent a cavitation threshold not to be crossed. Rather than relying upon pure theoretical calculations to determine what combinations of pumping speed and inlet pressure establish the safe operating zone for the pump 20, values predicted according to the above Equation 1 and also simulation or other modeling can be used to arrive at the subject model and pump operating curve. Accordingly, while the mapping of the plurality of bore pressure values to the inlet pressure values and the pumping speed values may occur according to the above Equation 1, in setting up the pump 20 and the pumping system 10 for service some adjustments can be made based upon simulations or other data sources. Such adjustments could additionally or alternatively be qualitative, and based upon input from a technician.
To this end, referring now also to
Referring also to
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features, and advantages will be apparent upon an examination of the attached drawings and appended claims.
