Patent Application
20150139842
The present invention relates to an architecture for progressive cavity-type volumetric pumps allowing a significant increase in pump reliability and performance.
The progressive cavity pump—also referred to hereinafter by the abbreviation PCP—was invented by Rene Moineau in 1930 and current industrial PCPs correspond to the basic principles.
To describe the architecture of the PCP according to the invention, we begin by showing the operation of the conventional PCP while emphasizing the processes that affect the reliability and performance of this pump.
We then present the PCP according to the invention, as well as its operation and its ability to improve reliability and performance.
The architecture of the conventional PCP includes a metal helical rotor inside a helical stator that is elastic (of elastomer) or rigid (metal, of composite materials).
As can be seen in
In this sense, the PCP is a positive displacement pump capable of transporting various products: more or less viscous liquids, multiphase mixtures (liquid, gas, solid particles).
The stator 3, of elastomer, has radial thickness H1 in its concave portions and radial thickness H2 in its convex portions. For example, the stator 3 having an outer diameter of 7 cm has thicknesses of 2.5 for H1 and 1.5 for H2.
To ensure that the PCP 1 compresses the fluids (liquids and gases) with a virtually fluidtight seal between the cavities 4, the rotor 2 with its helical rotation exerts a compressive force on the elastomer of the stator 3. Given the risk of damage to the stator 3, the reliability of PCPs is a major issue in the industrial application of these pumps.
For example, the oil industry uses PCPs in deep wells to pump mixtures of oil, water, and gas, that are carrying solid particles. In the pumping conditions downhole, the elastomer of the stator 3, subjected to complex thermal, chemical, and mechanical processes (dynamic forces and pressure), expands and thus increases the forces exerted by the rotor 2 on the stator 3.
The service life of conventional PCPs is therefore considerably reduced.
Using the diagrams in
The operation of the conventional PCP 1 includes close contact, by the interference fit between the rotor 2 and the elastomeric stator 3, which ensures two combined functions:
Thus, to minimize leakage between the cavities 4, the rotor 2 exerts compressive force P1 on the stator 3, which deforms by a height h1, generally called the interference, along an interference length L1. In the case mentioned above, this length L1 is about 4 cm.
As a result, the interference h1 between the rotor 2 and the stator 3 provides virtually fluidtight cavities 4, thus limiting leakage.
At the same time, the helical motion of the rotor 2 generates a shear force Q1 on the stator 3. The greater the interference h1, the greater the compressive forces P1 and shear forces Q1, and the greater the risk of damage to the stator 3.
In practice, an initial interference h1 between the rotor 2 and the stator 3 is adopted; this is the result of a compromise between acceptable stresses and a relative fluidtightness to limit leaks. For example, for the abovementioned stator 3 having an outside diameter of 7 cm, an initial interference h1 of 0.5 mm is adopted.
However, in the downhole conditions of an oil well, the stator 3 undergoes changes leading to an increase in the thicknesses H1 and H2 of the stator 3 and in the interference h1 between the rotor 2 and the stator 3.
Several phenomena can lead to the increase in the thicknesses H1 and H2 of the stator 3 and in the interference h1.
Under these conditions, the interference h1 is the determining factor in the balance between fluidtightness and the contact forces between the rotor 2 and stator 3.
Analysis of the impact of the interference h1 on the compressive P1 and shear Q1 forces shows the risk of damage to the stator 3.
For this, we adopt the following notation:
In general, the functions f(V) are used to indicate the influence of the rotational speed V of the rotor 2 on the compressive P1 and shear Q1 forces, and on the interference h1 between the rotor 2 and stator 3.
The analytical formulation thus demonstrates the correlation between the interference h1 and the compressive P1 and shear Q1 forces; to facilitate interpretation, the other parameters are grouped together.
As can be seen in
The viscoelastic model (Bowden) yields expressions (1, 2), linking the compressive force P1 and interference h1:
P1=C1.f1(V).h13/2.E.R1/2 (1)
h1=C2.f2(V).(P1/E)2/3.R−1/3 (2)
Linear approximation (elastic model, Boussinesq) facilitates the interpretation (expressions 3, 4):
P1=C3.f3(V).h1.R.E (3)
h1=C4.f4(V).P1/(R.E) (4)
These relations (1,2,3,4) show that the compressive forces P1 are significant when the interference h1 is large. In addition, these forces are concentrated within a volume in the immediate vicinity of the contact surface S1 (
Therefore, the swelling of the stator 3 increases interference h1 and leads to significant compressive forces P1 concentrated at the contact surfaces S1. These contact surfaces S1, shown in
Relations (3,4) describe the elastic compression (Boussinesq) of the stator 3 as a result of compressive forces P1. If we denote the stiffness of the elastomeric stator as Ks, we find that the behavior of the stator 3 is equivalent to the response of an elastic spring at constant rotor speed V:
P1=Ks.h1h1=P1/Ks Ks=C3.E.R (5)
The helical motion of the rotor 2 generates a shear force Q1 which also depends on the interference h1 (
Q1=C5.f5(V).h1(1−h1/H1).E.R (6)
The shear forces Q1 exerted on the stator 3 are a function of the interference h1, Q1=F(h1); the greater the interference h1, the greater the risk of damaging the stator. However, as previously mentioned, conventional PCPs 1 must have an initial interference h1 of around 0.5 mm to ensure fluidtight cavities 4. Given the production conditions in oil wells (thermodynamic-chemical-dynamic), the stator undergoes an increase in thicknesses H1 and H2 of about 5 to 10%, and, depending on the properties of the elastomer, the interference increases by about 1 mm which means that it is multiplied by 2. Under these conditions, the compressive P1 and shear Q1 forces are also multiplied by 2. As for the dynamic forces exerted by the helical rotation of the rotor 2 on the stator 3, these depend on the rotational speed V of the pump; in order to produce (flows and pressures) under cost-effective conditions, PCPs rotate at the speed of 200-500 rpm. Given the pumping conditions in the well, the service life of an elastomeric stator 3 is significantly reduced; experience shows that the average is one year, but damaged stators have been observed after 1-3 months of operation.
The vibrations of the rotor 2 depend on the natural frequency of the rotor 2 and on the rotational speed of the pump and can be very significant, especially in the resonance between the rotor 2 and the rotational speed (frequency). The amplitude of the vibrations of the rotor 2, perpendicular to the axis X-X, creates increased interference h1, and therefore the compressive P1 and shear Q1 forces exerted on the stator 3 are also increased.
Thus, the operation of conventional PCPs 1 focuses the forces at the contact between the rotor 2 and stator 3, and often leads to degradation of the stator 3. In practice, the oil company must remove the damaged pump from the well and replace it; this is a long process, during which the well is no longer in production and therefore there is a significant economic impact.
The more recent PCP 24 which includes a rigid helical stator (metal, composite materials) is shown in longitudinal section in
In practice, the stator 25 made of a rigid material (metal, composite materials) is mounted inside the casing 19; then, the helical rotor 7 is inserted inside the rigid stator 25, with some clearance 26. The architecture of this PCP is similar to that of a conventional PCP: the difference lies in the fact that there is clearance 26 between the rotor 7 and the rigid stator 25.
This PCP 24 is used in particular for pumping viscous liquids (heavy oils); the rotor 7 carries the viscous liquid and a liquid film is formed in the clearance 26 between the rotor 7 and the rigid stator 25. Depending on the manufacturing method, this clearance is less than 1 mm
As a result, with no contact between the rotor 7 and the stator 25, the PCP 24 pumps the viscous liquids (heavy oils).
Given the existence of this clearance 26, the rotation of the helical rotor 7 at speeds of 200-500 rpm generates vibrations (resonance, unstable vibrations) and shocks between the rotor 7 and the stator 25.
For example, if the natural frequencies of the rotor 7 and/or the rigid stator 25 are of the same order of magnitude as that of the rotational speed (speed of 200-500 revolutions per minute), the forces due to vibrations and shocks are multiplied by 6-8; the rotor 7 and the stator 25 cannot resist these forces for very long.
The dynamic response of the PCP 24 with rigid stator 25 can damage the rotor 7 and/or stator 25. In these circumstances, the oil company must replace the pump, which is a major operation with significant economic impact.
The object of the present invention is to provide a more reliable PCP having a longer service life, in order to reduce production costs. To this end, the present invention aims to provide a new architecture for progressive cavity pumps (PCP) which significantly increases pump reliability and performance.
For these purposes, the invention proposes a progressive cavity pump comprising:
characterized in that said helical stator further comprises at least one compensator arranged within said casing, between the casing and said helical cylinder; said helical cylinder and said compensator being adapted to deform in a direction perpendicular to said longitudinal axis.
Thus, said compensators have open or closed deformable profiles for which the shape, dimensions, and materials used provide the necessary elasticity to compensate for deformations of said helical stator.
In some embodiments which are in no way limitative:
Ko≦( 1/9).M.W2
where:
The invention also relates to the application of a pump as mentioned above for pumping fluids, said fluids being liquids, viscous liquids, or gases, and for pumping multiphase mixtures of liquids and gases with solid particles.
The invention will be better understood by reading the following description, given purely by way of example and without limitation, with reference to the drawings in which:
The PCP pump 6 according to a first embodiment of the invention, illustrated in
The casing 19 is provided with an inlet opening 14 at one of its ends and with an outlet opening 15 at its opposite end.
The helical rotor 7 is adapted to rotate inside the helical stator 8 at a predetermined speed hereinafter called the rotational speed, in order to move a fluid from the inlet opening 14 towards the outlet opening 15.
The helical stator 8 comprises a thin elastic layer 9, generally of elastomer, a helical cylinder 10 having a central axis Y-Y coinciding with the longitudinal axis X-X of the casing 19, and compensators 11 able to deform in order to compensate for variations in the radial dimensions of the helical cylinder 10.
The helical cylinder 10 is generally made of metal or composite materials. It is suitable for transmitting to the compensators 11 the forces exerted by the rotor 7 on the elastic layer 9.
The helical cylinder 10 has a face 17 facing the casing 19, hereinafter referred to as the outer face 17, and a face 16 facing the rotor 7, hereinafter referred to as the inner face 16.
The helical cylinder 10 successively shrinks and grows in diameter along its length, forming on the outer face 17 and inner face 16 of the helical cylinder 10 a succession of concave portions 12 alternating with convex portions 13.
The elastic layer 9 has a constant thickness of between 0.5 and 2 centimeters, and preferably between 0.5 cm and 1.5 cm.
The elastic layer 9 is attached to the inner face 16 of the helical cylinder 10. The attachment may be achieved by adhesion, gluing, or by a hot working method and/or by mechanical attachment devices.
The compensators 11 are elastic and have deformable profiles. The compensators 11 are adapted to deform in a direction perpendicular to said longitudinal axis (X-X), on the one hand to compensate for expansion of the elastic layer 9 and on the other hand to reduce vibrations exerted by the helical rotor 7 on the elastic layer 9, when the helical rotor 7 rotates within the helical stator 8.
When the compensators 11 compensate for expansion of the elastic layer 9, the dimensions of the compensators 11 decrease in a direction perpendicular to said longitudinal axis (X-X) to compensate for the expansion of the elastic layer 9, the helical cylinder 10, and the helical rotor 7 during the entire period during which the pump is subjected to thermal, chemical, and pressure conditions causing this expansion.
When the compensators 11 are reducing the vibrations exerted by the helical rotor 7 on the elastic layer 9, the dimensions of the compensators 11 will successively shrink and expand in a direction perpendicular to said longitudinal axis (X-X) at a frequency equal to the frequency of rotation of the helical rotor 7, to compensate for the vibrations of the rotor 7.
According to the first embodiment of the invention, the compensators 11 are elastic and have closed profiles. For example, the compensators 11 are in the shape of an aluminum shell filled with air.
Alternatively, the compensators 11 consist of an aluminum shell containing rubber.
According to another embodiment, the compensators 11 are shells made of composite materials.
The compensators 11 are arranged within the casing 19 between the helical cylinder 10 and the casing 19. In particular, according to the first embodiment of the invention illustrated in
Advantageously, ring-shaped compensators 18 surrounding the helical cylinder 10 are also attached between each end of the helical cylinder 10 and each end of the casing 19.
The compensators 11,18 are attached to the casing 19 and to the helical cylinder 10, for example by fasteners or by welding.
The dimensions, shape, geometry, and thickness of the compensators 11 and the component materials of the compensators 11 are selected so as to:
For example, a compensator 11 having a cross-section that is elliptical in shape, with axes of 1.2 cm and 4 cm, made of an aluminum plate 2 mm thick, ensures a 70% reduction of the forces exerted by the rotor 7 on the elastic layer 9. Such a compensator 11 having an elliptical cross-section can be used in a casing 19 having an inner diameter measuring 7 cm (mentioned above).
In this casing 19, the thickness of the elastomeric elastic layer 9 can for example measure 1.5 cm and the helical cylinder 10 can be made of a metal plate having a thickness of about 2 mm
Therefore, the compensators 11 arranged in accordance with the invention give the pump the ability to deal with the thermodynamic-chemical-dynamic conditions of pump operation, thus improving the reliability and performance of the PCP 6.
To evaluate the efficiency of the compensators 11, the PCP 6 of the invention shown in
As can be seen in
This process thus results in the significant compressive P1 and shear Q1 forces exerted on the contact surface S1 between the helical rotor 2 and the helical stator 3. This leads to the risk of damage to the elastomeric helical stator 3.
As can be seen in
This helical cylinder 10 transmits the forces exerted on the elastic layer 9 to the compensators 11. The compensators 11 are able to compensate for the deformation of the elastic layer 9 and thereby reduce the interference h3 and the compressive P2 and shear Q2 forces. The compensators 11 transmit the forces to the casing 19.
At the same time, the compensators 11 help to reduce the dynamic forces generated by vibrations of the rotor 7 on the elastic layer 9. The vibrational properties of the compensators 11 depend on their shape, their dimensions, and the materials used. By choosing a specific form or using a certain material for the compensators 11, the natural frequencies of the rotor 7-helical stator 8 assembly are controlled, avoiding the resonance and instability of the dynamic response. Under these conditions, the compensators 11 reduce the vibrational components of the compressive P2 and shear Q2 forces.
Thus, the compensators 11 are capable of decoupling the natural frequencies of the helical rotor 7 and helical stator 8 assembly from the frequency of rotation of the helical rotor 7.
For example, it is common to observe in an oil field that the rotor 2 of the conventional PCP 1 has instabilities when rotating at 300 rpm. To avoid the degradation of the conventional PCP 1 caused by these instabilities, the oil company must reduce the rotational speed of the rotor 2 to 150 rpm, which decreases production.
With compensators 11, the PCP 6 stabilizes the vibratory response of the rotor 7 which bolsters its production capacity to 300 rpm, thus satisfying economical production conditions.
It follows that the operation of the PCP according to the invention reduces the compressive P2 and shear Q2 forces, thereby improving the reliability of the PCP 6.
As can be seen in
After the pump is placed in service, the thermal-chemical-dynamic process causes swelling of the elastic layer 9, where the thickness becomes H′3>H3, resulting in increased interference h′3>h3.
As can be seen in
As a result, the compensators 11 are sized to compensate for the swelling of the elastic layer 9 and to reduce the forces acting on the elastic layer 9. Their dimensions are chosen so as to maintain the initial interference, meaning h′3≈h3. When this interference h′3 is kept substantially constant, the contact forces of the helical rotor 7-elastic layer 9 assembly are maintained at the required level.
To achieve this, we must characterize the elasticity of the assembly of elastic layer 9-helical cylinder 10-compensators 11.
The formula (5) for the response of the elastomeric stator leads to the equivalent stiffness Ks (
h3=P2/Ks Ks=C3.E.R (7)
h′3=P′2/Ks
The deformation Xo of the compensator 11 due to the effect of the compressive force P2 reveals the stiffness of the structure Ko:
P2=Ko.Xo Ko=C7.Eo.I/r3 (8)
where Eo and I are the elastic modulus and the moment of inertia of the compensator 11, and r is the characteristic radius of the compensator 11. For example, in the case of the compensator 11 that is elliptical in shape, the characteristic radius r is the mean of the radii of the ellipse.
As mentioned, after the pump is placed in service (
h′3=h3+Δh (9)
The compensators 11 of the invention are preferably chosen such that the swelling of the elastic layer 9 is compensated for by the compression ΔXo of each compensator 11:
P′2=Ko.(Xo+ΔXo) (10)
which means that Δh is minimal if h′3≈h3:
and thus the initial interference h3 is kept substantially unchanged despite the swelling of the elastic layer 9.
The compensators 11 compensate for deformations of the elastic layer 9, and the forces exerted on the elastomer of the elastic layer 9 remain at the initial level.
Also, controlling the stiffness Ko of the compensators 11 facilitates controlling the dynamic response (particularly the natural frequencies), and thus prevents resonance with the vibrations of the rotor 7.
To this end, the compensators 11 according to the invention have a stiffness coefficient Ko which satisfies the following relation:
Ko≦( 1/9).M.W2 (12)
where:
At the same time, the choice of stiffness Ko of the compensators 11 provides control of the compressive and shear forces and of the vibrations.
Given the thermodynamic-chemical-dynamic conditions (vibrations), optimization of the compensators 11 keeps the forces exerted by the helical rotor 7 on the elastic layer 9 within the required reliability limits.
As mentioned, the conventional PCP 1 with elastomeric stator 3 focuses two functions on the contact surface S1 between the rotor 2 and stator 3: the relative fluidtightness and the high contact forces (compressive P1 and shear Q1 forces).
The PCP 6 according to the invention dissociates these two functions:
The operation of the PCP 6 according to the invention results in reduced forces exerted on the elastic layer 9 and improves pump reliability.
Elements that are identical or similar to the first embodiment of the invention (
According to this alternative embodiment, the compensators 21 have elastic open profiles (of metal or composite material), each placed between a concave portion 12 of the helical cylinder 10 and the casing 19.
The open compensators 21 are able to compensate for deformations of the elastic layer 9 and to transmit forces to the casing 19.
For example, for the PCP having a 7 cm outside diameter, the compensators 21 are aluminum and shaped like an inverted U that is 1.2 cm in height and 3 cm in width, with a thickness of about 2 mm
For example, said compensators 21 are shaped like a hollow pin having a tip and a broad base; said tip being arranged against said helical cylinder 10; said broad base being fixed against the inner face of said casing 19.
A PCP 22 according to the third embodiment of the invention is illustrated in
Elements that are identical or similar to the first embodiment of the invention (
In particular, this PCP 22 comprises a helical rotor 7 rotating within the helical stator 8, the elements of which are:
The compensators 23 are able to compensate for deformations of the elastic layer 9 and to transmit forces to the casing 19. For example, for a PCP 22 having an outer diameter of 7 cm, the compensators 23 are aluminum and have flat elliptical profiles, with axes of 1 cm and 2 cm and a thickness of about 1-2 mm
The PCP 27 according to the fourth embodiment of the invention is illustrated in
Elements that are identical or similar to the first embodiment of the invention (
According to this embodiment, the helical stator 28 comprises a rigid helical cylinder 29 and compensators 11 placed between the rigid helical cylinder 29 and the casing 19. In particular, the helical cylinder 29 is not covered with an elastic layer as it is in other embodiments of the invention.
The helical cylinder 29 is made of a metal or a composite material.
Advantageously, the compensators 11 provide the elasticity needed for the dynamic contact between the helical rotor 7 and helical stator 28.
Sizing the compensators 11 according to the above relation (12) leads to a stiffness Ko able to adapt the dynamic properties (particularly the natural frequencies) of the helical system 7-helical stator 28 in order to avoid shocks, resonance, and dynamic instability.
For the PCP 24 with rigid stator 25 known in the prior art and illustrated in
The arrangement of the compensators 11 in the helical stator 28 of the PCP 27 illustrated in
The compensators 11 provide the necessary elasticity for the dynamic contact (vibrations) between the helical rotor 7 and the helical stator 28, and transmit the forces to the casing 19.
For example, for the PCP 27 having a diameter of 7 cm, the compensators 11 are aluminum and have elliptical profiles with diameters of 1.5 cm and 5, with a thickness of around 2 mm
According to the embodiments illustrated in
According to a variant of the invention (not shown), the helical stator 8 has a single compensator that is helical in shape and is arranged about said helical cylinder 10.
Alternatively, the compensators consist of springs or accordion pleats.
In conclusion, we find that the conventional PCP 1 (with elastomeric stator) combines two functions at the contact between rotor and stator:
Thus, as has been explained, the thermodynamic-chemical-dynamic process causes an increase in volume of the stator, which results in excessive forces that can damage the stator.
Statistics show that the service life for these pumps in oil wells is about a year, but damaged stators have been observed after 1-3 months of operation.
The present invention proposes an architecture for a pump comprising a helical stator, which separates these two functions:
The invention allows reducing the dynamic forces (vibrations, shocks) exerted by the rotor on the elastic layer (elastomer) or on the rigid helical cylinder (metal, composite materials).
Thus, the PCP of the invention comprises compensators capable of decoupling the vibrations from the rotor and the elastic (elastomeric) or rigid (metal, composite materials) elements of the stator, to improve dynamic reliability and performance of PCPs.
The conventional PCP 1. A conventional PCP is being used in oil well production; considering the pumping conditions in the well, the initial rotor—stator interference h1=0.5 mm.
Changes in operating conditions leads to increased interference; currently a swelling of the stator of 5% of its thickness is observed, and there is increased interference h1=1 mm.
Accordingly, the new interference and the forces exerted on the elastic stator are twice as large. Given the behavior of the stator, whose elastomer is subject to cyclic stresses (S-N curve), the service life of the stator is divided by two.
With the PCP 6 of the invention, during well production the compensators compensate for swelling of the stator and the initial interference h1=0 5 mm is maintained with no significant change; the forces remain within acceptable limits.
Thus, the PCP 6 comprising a helical stator according to the invention has a service life of twice that of the conventional PCP 1; this is a significant technical and economic advantage.
To reduce the effect of longitudinal vibrations, this patent provides a “shock absorber” system (Energieabsorber 10, FIG. 1 of the patent).
Similar to a fluid bearing, the “shock absorber” dissipates the energy of longitudinal vibrations through a hydraulic maze. Indeed, the viscous friction of the flow of liquid within the hydraulic maze dampens the longitudinal vibrations by dissipating energy; is an absorber that dissipates energy by hydraulic friction (FIGS. 3,4,5 of the patent).
The chemical composition of the drilling mud does not produce swelling of the stator elastomer. Therefore, the swelling problem for the stator of PCPs used for pumping oil does not arise in the case of the downhole motor.
Also, the liquid of the shock absorber (hydraulic maze) is incompressible; this device can not compensate for transverse swelling of the elastic stator or for transverse vibrations.
The PCP that is the object of the invention comprises compensators (
Thus, we find that the operating conditions of the downhole motor have nothing in common with the pumping of oil.
The compensators are elastic elements made of metal or composite materials, deforming to compensate for variations in the volume of the stator (swelling of the elastic layer) and for transverse vibrations of the rotor.
They therefore have nothing of the hydraulic maze (hydraulic shock absorber) whose role is to dissipate the energy of longitudinal vibrations from drilling into the rock.
The architecture and operation of the PCP comprising a helical stator with compensators are very different from the downhole motor comprising a hydraulic shock absorber system as proposed by that patent.
As mentioned above, when pumping in an oil well, the thermodynamic-chemical-dynamic effect causes deformation of the stator elastomer (swelling). Oil drilling is quite different; the liquid of the drill motor consists of pressurized drilling mud injected from the surface.
The operating conditions of pumping in an oil well are very different from those when drilling.
The patent describes a stator comprising two elastomer layers. Under these conditions, the thermodynamic-chemical-dynamic effect of pumping oil generates differential distortions of the elastomeric stator.
The risk of the rotor causing damage to the two-layered elastomeric stator remains.
Therefore, the use of the two-layered elastomeric stator when pumping oil results in reduced reliability and service life.
The architecture and operation of the PCP comprising a helical stator with compensators are very different from the drill motor comprising a stator with two elastomer layers proposed by that patent.
When the frequency of vibration W3 of the helical rotor 7 and helical stator 8 assembly is equal to the frequency of rotation W of the helical rotor 7, the helical stator 8 and helical rotor 7 assembly vibrate in resonance. This leads to rapid deterioration of the pump.
The graph in
Thus, to have the helical stator 8 no longer vibrating in resonance with the rotation of the helical rotor 7, it is desirable that the ratio between the frequency of rotation W of the helical rotor 7 and the frequency of vibration W3 of the helical rotor 7 and helical stator 8 assembly be greater than 3.
Moreover, it is known that the stiffness Ko of a compensator is equal to the sum M of the total mass of the helical rotor 7 and helical stator 8 assembly, multiplied by the square of the frequency of vibration W3 of the helical rotor 7 and helical stator 8 assembly.
Ko=M.W
3
2 (15)
By combining relations (14) and (15), we obtain the following relation:
Ko≦( 1/9).M.W2 (12)
where:
Thus, the choice of stiffness Ko of the compensators 11 allows decoupling the natural frequencies of the helical rotor 7 and helical stator 8 assembly from the frequency of rotation of the helical rotor 7.
The helical cylinder 10 is rigid in all the embodiments described.
Advantageously, it is possible to arrange compensators all along the pump according to a distribution determined based on the deformation of the helical rotor 7 along the pump (natural vibration modes).
Said deformable compensators are elastic structures made of metal or composite materials, whose mechanical properties (elasticity, hysteresis) and high resistance to cyclic fatigue stresses (Wohler curve) ensure good pump reliability.
The distribution of said deformable compensators along the pump can be: continuous or discontinuous, uniform or non-uniform, of constant or variable density, of constant or variable stiffness. Indeed, during vibrations, the helical rotor-helical stator assembly is deformed all along the pump; for example, the deflection is greater at the ends. To compensate for deformations of the ends, the distribution of the compensators is adjusted, for example with a greater density near the ends of the pump.
Under these conditions, the movement of the helical rotor-helical stator assembly is as one unit, thereby eliminating the risk of shocks, phase differences, and instabilities between the helical rotor and the helical stator.
As a result, it is sufficient to design the stiffness Ko of the compensators 11 so as to significantly reduce vibrations of the PCP pump (
The deformable compensators 11 perform several functions:
As shown in
Indeed, with the stiffness Ko, the compensators 11 provide a strong reduction in vibrational forces on the rotor-stator assembly and significantly improve pump reliability.
The materials of the compensators are metal (steel, aluminum) and composite materials. The compensators are elastic structures that deform to compensate for movements (vibration) of the rotor-stator assembly. The mechanical properties of the required materials are: elasticity (linear and hysteresis) and the ability to withstand a large number of cyclic fatigue stresses (Wohler curve).
Metal materials (steel, aluminum) have these properties. In composite materials, there is a wide variety of high-strength structures with good behavior when subjected to cyclic stresses (Wohler curve).
| Number | Date | Country | Kind |
|---|---|---|---|
| 12/01519 | May 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2013/051189 | 5/28/2013 | WO | 00 |
