Special Issue Article
An energy-saving pumping system with novel springs energy storage devices: Design, modeling, and experiment
Advances in Mechanical Engineering 2017, Vol. 9(1) 1–11 Ó The Author(s) 2017 DOI: 10.1177/1687814016687450 journals.sagepub.com/home/ade
Hong jun Meng1, Long Quan1, Zhanlin Wang2, Cheng wen Wang1 and Yuan Lan1
Abstract For the traditional reciprocating pumping unit, it generally starts at the bottom dead point with full load and is accelerated when starting and decelerated when stopping, which not only requires great energy from the motor but also impact on the output torque of motor. In order to tackle the above problems, we propose an energy-saving smooth reversing pumping system, which could store the energy in deceleration by making use of springs, and the stored energy could be reused in acceleration after reversion. This novel system targets to make the motor starting with light load, which could reduce the fluctuation in motor torque, decrease the starting time. In this article, a dynamic model and an efficiency model are established to compute the polished rod load dynamometer card and efficiency of the pumping unit. It is shown that the installed springs could help to reduce the impact on the system when reversing, and significantly decrease the energy consumption. In addition, we set up the real pumping system with load test system to verify the effectiveness of the model establishment. Through the experiment, the proposed pumping system could save energy up to 9.204% as compared to the traditional reciprocating pumping system. Keywords Pumping system, mechanical modeling, high efficiency, energy saving, design
Date received: 5 June 2016; accepted: 9 December 2016 Academic Editor: Ramoshweu Lebelo
Introduction With the development of oilfield exploitation, artificial lifting methods by mechanical equipment are becoming increasingly prevalent.1 In oilfield production, mechanical lifting equipment is one of the major energyconsuming equipment. The 85% of lifting system used in the oilfield production is rod pumping system, which is composed of pumping unit, pumping rod, and motor.2 In the mid-1920s, Lufkin, a company from the United States, produced the first beam pumping unit in the world. Since then, among the rod pumping system, beam pumping system is widely used traditional pumping equipment. In the system, an AC asynchronous motor is connected to four-bar mechanism and
pumping rod through reducer, which could drive the pump under well to do vertical reciprocate motion in order to lift the downhole oil to ground. The beam pumping system has lots of advantages such as simple structure, high reliability, easy maintenance, etc. 1
Key Laboratory of Ministry of Education in Advance Transducers and Intelligent Control System, School of Mechanical Engineering, Taiyuan University of Technology, Taiyuan, China 2 School of Automation Science and Electrical Engineering, Beijing University of Aeronautics and Astronautics, Beijing, China Corresponding author: Hong jun Meng, Key Laboratory of Ministry of Education in Advance Transducers and Intelligent Control System, School of Mechanical Engineering, Taiyuan University of Technology, Taiyuan 030024, China. Email:
[email protected]
Creative Commons CC-BY: This article is distributed under the terms of the Creative Commons Attribution 3.0 License (http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/ open-access-at-sage).
2 However, the system owns some drawbacks like low efficiency (around 15%–20%) and high energy consumption.3,4 Additionally, the load exerted to beam pumping unit is periodical alternating load, in which there are big difference between maximum velocity and minimum velocity. Generally, the pumping unit starts from the bottom dead center that requires large moment of inertia. And in the normal working condition, the torque is usually small. However, because we have to choose motor according to the maximum torque required by the system, the output power of selected motor is only one-third of the rated power, which affects the factor of the motor. Furthermore, the load of the pumping system is not equal between up stroke and down stroke. Although the counterbalance could help to improve the imbalance condition, the result is not satisfactory. In practice, in most of the time on down stroke, the pumping unit is driven by the load that makes the motor in state of generator, which severely reduces the system efficiency.5 To solve the above problems, various pumping systems are introduced by researchers, including back-crank pumping system, suspension biased beam pumping system, beltdriven pumping system, down eccentric barbell pumping system, twin-horse head pumping system, etc.6 Those systems could only make an improvement in raising system efficiency, but they are not able to solve the above-mentioned problems. In 1990, lively, a company from the United States invented non-beam pumping system and obtained the patent with the title ‘‘Long stroke well pumping unit with carriage.’’7 In 2008, linear motor pumping system is developed by Y Gu et al.8 and Li et al.,9 and so on, which is also a non-beam pumping system. Various non-beam pumping systems have solved the problems because they do not rely on using increased stroke structure, and four-bar linkage structure for reversing.10 However, there is impact on the output torque of the motor in non-beam pumping system in period of start and stop, which would affect the reliability, system lifespan, and the energy consumption. Therefore, how to further improve the reliability and lifespan of non-beam pumping system is the essential portion of research in this article. Motivation of these, in this article, we will explore the modeling and experiment on energy-saving long stroke energy storage smooth reversing pumping system. This article is organized as follows. In section ‘‘System setup and schematic design,’’ we provide the system setup and schematic design of the pumping system. In section ‘‘ Modeling of the motor output force,’’ we give an output force model of motor within the system. The polished rod load analysis and efficiency analysis of pumping unit are presented in sections ‘‘The polished rod load analysis of pumping unit’’ and ‘‘Efficiency analysis,’’ respectively. Furthermore,
Advances in Mechanical Engineering simulation and experimental results are stated in sections ‘‘Simulation results’’ and ‘‘experimental results,’’ respectively. Finally, we conclude our results in section ‘‘conclusion.’’
System setup and schematic design For the traditional reciprocating pumping unit, the impact on the output torque of the motor when starting or stopping the unit would increase the energy consumption of the system. To tackle this problem, we offer one solution to achieve rational utilization of energy. The dynamic energy when the pumping unit in the reversing motion could be stored in another mechanical system. And then the energy stored could be reused to accelerate the motor in the pumping system. The proposed solution is presented in detail as follows.
Energy storage system using springs The schematic diagram of the pumping system is presented in Figure 1. The spring sets (2, 8) are installed in the upper and lower portion of the pumping system frame (3). And the AC frequency conversion motor and reducer (7) are installed on the bottom of pumping unit. On the top and bottom of the pumping system frame, there are sprockets and chain (9). One portion of the chain is fixed with the counterbalance (5). When the sprockets are powered with motor through the reducer, the counterbalance will be moved by the chain. In addition, the pumping rod is connected to counterbalance through belt (4) that is wrapped around the friction gear (1) at the other end. Therefore, when the counterbalance is moving up or down, the pumping rod will move up or down accordingly. Furthermore, the reversing, acceleration, deceleration, and uniform linear motion of the pumping unit are controlled by the electronic control cabinet (6). When the pumping unit is on the up stroke, the counterbalance is moving downward. The counterbalance then is in contact with the bottom spring set, and continuously moving downward to squeeze the bottom spring set until moving to the bottom dead center. Hence, the elastic potential energy is stored in the squeezed bottom spring set. Then, the motor will rotate in reverse direction, and the pumping unit is on the down stroke, which makes the counterbalance move upward. Obviously, the squeezed bottom spring set will help to accelerate the counterbalance movement until they are disengaged. The counterbalance is in uniform linear motion until in contact with the top spring set. The top spring set would be squeezed by the counterbalance until the top dead center. At this time, the elastic potential energy is stored in the squeezed top spring
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A B ĉ
Ċ
ċ Č
č
Ď
Figure 2. Velocity curve (A: velocity curve of the traditional reciprocating pumping unit and B: velocity curve of the energy stored reciprocating pumping unit).
Figure 1. Schematic diagram of the pumping system. 1: Friction gear; 2: top spring set; 3: pumping system frame; 4: belt; 5: counterbalance; 6: electronic control cabinet; 7: AC frequency conversion motor and reducer; 8: bottom spring set; 9: link chain.
set. Then, the motor would rotate in reverse direction, and the pumping unit is on the up stroke, which makes the counterbalance move downward. Similarly, the squeezed top spring set will help to accelerate the counterbalance movement until they are disengaged. The counterbalance is in uniform linear motion until in contact with the bottom spring set. The pumping unit will repeat the movement described above continuously.
Velocity curve of the pumping unit The velocity curve of the traditional linear reciprocating pumping unit is trapezoidal, which is clearly seen in Figure 2. From Figure 3, the acceleration of the traditional pumping unit in the period of start and stop is a constant and the value is a, one can get to zero when the traditional pumping unit is in uniform linear motion. Therefore, there are moments that the value of the acceleration of the traditional pumping unit changes from a to 0 or from 0 to a. The abrupt change in the acceleration could reduce the lifetime of the pumping unit. In the proposed solution, two spring sets are installed in the pumping system, which changes the velocity curve of the pumping system to be sinusoidal as shown in Figure 2. The resultant acceleration curve is presented in Figure 3. Obviously in Figure 3 curve B, there is no abrupt change in the acceleration, which could reduce the impact on the pumping unit and increase its lifetime.
Figure 3. Acceleration curve (A: acceleration curve of the traditional reciprocating pumping unit and B: acceleration curve of the energy stored pumping unit).
Modeling of the motor output force In this section, we only consider some moving components in the pumping system, such as top big friction gears, belt wrapped on the gear, end point of the belt at right-hand side that used to connect with the pumping rod, counterbalance, and top spring set and bottom spring set, which coincides with Figure 1. On up stroke, load on the right-hand side is pumping rod load and load from oil liquid column. While on down stroke, load on the right-hand side is only the pumping rod load (in this case, the load from the oil liquid column is zero). We present the mechanical model of counterbalance and spring sets in Figure 4. According to the velocity curve in Figure 2, calculate the output force of motor and the mechanical behavior of the spring sets in six stages (I, II, III, IV, V, and VI).
Up stroke stage (stage I) Force on the counterbalance can be shown as follows mP g + Fs1 + Fj F1 = mP a1
ð1Þ
Among these parameters mp is the mass of the counterbalance, g is the gravitational acceleration, n denotes stages of the pumping unit (n = 1, 2, . , 6), Fj is the
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Advances in Mechanical Engineering Sn is the displacement of the counterbalance (n = 1, 2, . , 6). When v1 = A1 v1 sin v1 t, v1 is sinusoidal. And we know that the curve of the spring motion is sinusoidal as well. Therefore, we aim to make the reversal motion of the pumping unit be sinusoidal motion. From Figure 2, we can obtain S1 = A1 A1 cos v1 t, and
Figure 4. Mechanical model of counterbalance and spring sets.
output force of the reducer, F1 is the force on the counterbalance in vertical upward direction, Fsn is the force on the counterbalance from spring sets (n = 1, 2, . , 6), and an is the acceleration of the proposed pumping system (n = 1,2, . , 6). Here, the force on the pumping rod and column of oil liquid is expressed as follows F2 f2 (m1 + m2 )g = (m1 + m2 )a1
ð2Þ
where m1 is the mass of the pumping rod, m2 is the mass of oil liquid column, F2 measures the force on the pumping rod and the liquid load in vertical upward direction, and f2 is the frictional force between the pumping rod and liquid. If F1 = F2 , Fd = Fj + J (a1 =r) + f1 , we have Fd = (m1 + m2 )g mP g + f1 + f2 J a1 Fs1 + m1 + m2 + mP + r
ð3Þ
where Fd is the output force of motor, r is the radius of the reducer output shaft, J is the total moment of inertial of the system, and f1 is the frictional force between motor and reducer. If Fs1 = (m1 + m2 + mP + (J =r))a1 , the output force of motor can be described as follows Fd = (m1 + m2 mP )g + f1 + f2
ð4Þ
1 a1 = k1 (A1 S1 ) m1 + m2 + mP + J r
ð6Þ ð7Þ
ð8Þ
ð9Þ
Here, vn is the angular velocity of the pumping system (n = 1, 2, . , 6), vn is the velocity of the pumping system (n = 1, 2, . , 6), and tn is the time for reversing (n = 1, 3, 4, 6).
Up stroke stage (stage II) Force on the counterbalance is defined by F1 = mP g + Fj
ð10Þ
Force on the pumping rod and oil liquid column is as follows F2 = (m1 + m2 )g + f2
ð11Þ
If F1 = F2 , Fd = Fj + f1 , we have Fd = (m1 + m2 )g mP g + f1 + f2
ð12Þ
V2 = V1 max
ð13Þ
Up stroke stage (stage III) From above equations, we have given out the force on the counterbalance of our system as mP g + Fj Fs2 F1 = mP a3
ð14Þ
Force on the pumping rod and oil liquid column is as follows F2 f2 (m1 + m2 )g = (m1 + m2 )a3
Motivated by these, we have
a1 = A1 v21 cos v1 t sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi k1 g v1 = m1 + m2 + mP + Jr sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 p m1 + m2 + mP + Jr t1 = = k1 4f 2 sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi k1 g V1 max = A1 m1 + m2 + mP + Jr
ð15Þ
When F1 = F2 , Fd = Fj + J (a3 =r) + f1 , we can get ð5Þ
where k1 is the stiffness of the top spring, An is the total squeezed quantity of the spring set (n = 1, 2, . , 6), and
Fd = (m1 + m2 )g mP g + f1 + f2 1 a3 + Fs2 + m1 + m2 + mP + J r
ð16Þ
Meng et al.
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ð26Þ
ð17Þ
Pgx = m1 an
ð27Þ
ð18Þ
where Pgs and Pgx are the inertial load of up stroke and down stroke, respectively; the elongation of pumping rod is denoted by l1 , then we have
If Fs2 = (m1 + m2 + mP + (J =r))a3 , we have
Fd = (m1 + m2 mP )g + f1 + f2 J a1 = k2 (A3 S3 ) m1 + m2 + mP + r
where k2 is the stiffness of the bottom spring set. When v3 = A3 v3 cos v3 t, we have S3 = A3 sin v3 t A3 v23
cos v3 t a3 = sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi k2 g v3 = m1 + m2 + mP + Jr sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 p m1 + m2 + mP + Jr t3 = = k2 4f 2 sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi k2 g V3 max = A3 m1 + m2 + mP + Jr
l1 = ð19Þ ð20Þ
ð21Þ
m2 gL EN1
ð28Þ
where the parameter E is the elastic modulus of steel, E = 2.1 3 105 MPa, and N1 is the cross-sectional area of the pumping rod. The amount of shortening of oil liquid column is denoted by l2 , and we have l2 =
ð22Þ
m2 gL EN2
ð29Þ
where N2 is the cross-sectional area of the pipe wall
The modeling for stages in down stroke is similar to the modeling for stages in up stroke as presented above. The total distance of the pumping unit in both up stroke and down stroke is computed as follows. Upstroke : Ss = A1 + A3 + V1 max t2 ; Down stroke : Sx = A4 + A6 + V4 max t5 ;
lg =
Pgs L Pgx L L + = (Pgs + Pgx ) 2EN1 2EN1 2EN1
ð30Þ
Here, lg is the amount of sucker rod shortening Sx = S l + lg = S l1 l2 + lg
ð31Þ
where A1 = A6 , A3 = A4 .
where Sx is the effective length of the pump, and S is the distance from the top dead point to the bottom dead point.
The polished rod load analysis of pumping unit
Vibration load
The polished rod load is one of the important parameters to describe the capability of the pumping unit, and it is also crucial in designing and selecting suitable pumping system for real applications.
Static polished rod load Pjs = (m1 + m2 )g
ð23Þ
Pjx = m1 g
ð24Þ
where Pjs is the static polished rod load of up stroke, and Pjx is the static polished rod load of down stroke.
Dynamic polished rod load e=
Nz N1 Ng N1
ð25Þ
Here, Nz is the cross-sectional area of piston, and Ng is the area of the pipe flow section
As we know, the pumping rod is elastomer that can be modeled by a lone spring. Assume that the suspension point is the origin of coordinates. The vibration of the pumping rod can be simplified into the longitudinal vibration of a slender rod with one end fixed and other ends free.9 The longitudinal vibration of the pumping rod can be described using wave equations as follows 2 ∂2 u 2∂ u = C ∂2 t ∂2 x
ð32Þ
Initial conditions: ujt = 0 = 0, (∂u=∂t)jt = 0 = V (x=L) Boundary conditions: ujx = 0 = 0, (∂u=∂x)jx = L = 0 The vibration load on suspension point created by the longitudinal vibration of the slender rod can be computed as follows FV =
‘ 8EN1 V X ( 1)n sin (2n + 1)v0 t p2 C n = 0 (2n + 1)2
ð33Þ
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where V = (l1 + l2 lg =0:5S)vn max , tmax = (p=2v0 ) = (L=C), u is the elastic displacement of rod at any cross section, C measures the elastic longitudinal wave propagation velocity in rod, and v0 is the circular frequency of free vibration. Hence, the vibration load is the periodic function of v0 t, and the period is 2p. The maximum vibration load happens when v0 t = 0:5p, 2:5p, . . . . However, due to the resistance in the oil well, the amplitude of vibration in the stroke is gradually reduced. Therefore, the maximum vibration load happens when v0 t = 0:5p.
Efficiency analysis The work done by the energy storage reciprocating pumping unit The work done on up stroke is as follows ðt3 Ys =
ðt3 Fd dt =
0
½(m1 + m2 mP )g + f1 + f2 vn dt
0
ð36Þ
= ½(m1 + m2 mP )g + f1 + f2 (A1 + v1 max t2 + A2 )
The work done on down stroke is as follows
Frictional load 1. Friction force between pumping rod and liquid column. The friction between pumping rod and liquid column happens on down stroke, which resists the pumping rod moving downward especially when the liquid is thick. The maximum frictional force can be calculated using approximate formula as follows11 f2 = fs = 2pm1 L
m2 1 vmax (m2 + 1) ln m (m2 1)
ð34Þ
ðt6 Yx =
ðt6 Fd vdt =
t3
(mP g m1 g + f1 + f2 )vn dt
t3
= (mP g m1 g + f1 + f2 )(A2 + v4 max t5 + A1 ) The work done on entire stroke is as follows Y = Ys + Yx
ð37Þ
where Ys is the work done by motor on up stroke, Yx is the work done by motor on down stroke, and Y is the work done by motor on entire stroke.
where m is the ratio between inner diameter of pipe and pumping rod diameter.
The work done by the traditional reciprocating pumping unit
2. Friction force between liquid and oil pipe. The friction force between liquid and oil pipe does not directly affect the movement of pumping rod. Nevertheless, it may increase the pressure when the piston moving upwards. Additionally, on account of the liquid flow in the pipe is small on down stroke, the friction between the liquid and oil pipe can be neglected on down stroke.12 The friction between liquid and oil pipe on up stroke can be computed as follows
Consider the output force of motor on down stroke. In the period of t1 , we have Fd = (m1 + m2 mP )g + f1 + f2 J 0 a + m1 + m2 + mP + r In the period of t2 , we have Fd = (m1 + m2 mP )g + f1 + f2
fs f2 = fx = 1:3
ð35Þ
where m1 is the oil viscosity, f1 = c1 Fd , and c1 is the friction coefficient of pumping unit.
Ys0
In the period of t3 , we can get Fd = (m1 + m2 mP )g + f1 + f2 + ðm1 + m2 + mP + Jr Þa03 The work done by traditional pumping unit on up stroke can be computed as follows13
J 0 a1 = (m1 + m2 mP )g + f1 + f2 + m1 + m2 + mP + r 1 a01 t12 + ½(m1 + m2 mP )g + f1 + f2 v1 t2 2 J 0 1 0 2 a 3 v1 t3 + a 2 t3 + (m1 + m2 mP )g + f1 + f2 + m1 + m2 + mP + r 2
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where a0n denotes the acceleration of the traditional pumping system (n = 1, 2, . , 6). Consider the output force of motor on down stroke. In the period of t4 , we have Fd = (mP m1 )g + f1 + f2 +
J m1 mP a04 r
In the period of t5 , we have Fd = (mP m1 )g + f1 + f2 In the period of t6 , we have Fd = (mP m1 )g + f1 + f2 + Jr mP m1 a06 The work done by traditional pumping unit on down stroke can be computed as follows J mP m1 a0 4 Yx0 = (mP m1 )g + f1 + f2 + r 1 0 2 a4 t4 + ½(mP m1 )g + f1 + f2 v4 t5 2 J mP m1 a0 6 + (mP m1 )g + f1 + f2 + r 1 v4 t6 + a06 t62 2 The work done in the entire stroke is as follows Y = Ys0 + Yx0
ð38Þ
The simulation model of system efficiency is as follows14 h=
Pe PM
ð39Þ
where h is the efficiency of the pumping system, Pe is the effective power of the system, and PM is the average input power of the system, or the average input power of the motor.
Q = 1440 3 PM =
p 2 D Sx na 4
1 Y hd T
Simulation results Assume that L = 1000 m, p0 = 0:2 MPa, pc = 0:22 MPa, diameter of pumping rod, dr = 22 mm , D = 56 mm, outer diameter of the pipe, dt = 77 mm, the thickness of pipe wall, dc = 3:96 mm, rm = 956kg=m3 , S = 6 m, mp =m1 +(1=2)m2 , m1 =50MPas, c1 = 0:018, J =2:543kg=m2 , r =0:24m, A1 =A2 = 0:4 m, v1max = v4max =0:63m=s,t1 =t3 =t4 =t6 =1 s, if Lc =300m, the submergence a = 70%,16 the rated power of the motor is 30 kW, and the efficiency of the motor is 90%. Based on the data in the assumptions above, the dynamometer card of polished rod load of our proposed pumping unit is presented in Figure 5. The dynamic polished rod load of out proposed unit is almost equal to the static load, which means the system is very stable. As mentioned earlier, the output torque of motor in the traditional pumping unit has abrupt change when start and stop the unit, whereas the proposed pumping unit could avoid the unexpected change on output torque of motor. From Figure 6, we can clearly see that the output torque of motor in the proposed pumping unit is very stable with time. In the proposed strategy, the energy storage system with spring set could not only assist the motor in reversing motion of pumping unit, but also store the extra
The formula to calculate the effective power recommended by oil industry standard is shown as follows15 QHrm g 86, 400
ð40Þ
where rm is the density of oil water mixture, Q is the actual oil production of the oil well, and H is the effective lifting height that can be calculated by H = Hd +
(p0 pc ) 3 103 rm g
ð41Þ
where Hd is the dynamic oil level, p0 is the pressure on the well head, and pc is the casing pressure of the well head
ð43Þ
where D is the diameter of the piston in the pump, n is the number of strokes, and a is the efficiency of the pump.
The effective power of the system
Ne =
ð42Þ
Figure 5. The dynamometer card of polished rod load of energy storage reciprocating pumping unit.
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Advances in Mechanical Engineering
Figure 8. Flow chart of the loading system.
Figure 6. The comparison on motor torque of traditional reciprocating pumping unit and proposed pumping unit.
Figure 7. The comparison on system efficiency of traditional reciprocating pumping unit and proposed pumping unit.
energy and reuse it. Therefore, it could reduce the energy consumption as compared to the traditional pumping unit. The energy consumption could be reduced by 10.46% with the proposed energy storage pumping unit shown in Figure 7.
researchers have been proposed in several literatures, such as hanging a weight on the polished rod, loading weight on a slope, electric damp loading, etc. However, those methods have some defects such as cannot consider all the components of the polished rod load of the pumping system, weak real time performance, and low accuracy. In our experiment, in order to avoid the defects mentioned above, we make use of actual measured polished rod load dynamometer card to generate the control signal on computer and input it to the control system. Then, the control system will pass the command to the servo valve to control the hydraulic cylinder, which could simulate the actual loading conditions of the pumping system. We aim to utilize the designed loading system in evaluating the static and dynamic performance of our proposed pumping system. The designed loading system of the pumping unit is actually a servo valve controlled hydraulic system. The loading system is composed of computer control system, servo valve, hydraulic cylinder, force transducer, and signal conditioning circuit, as presented in Figure 8. The computer control system outputs command the servo valve. Then, the hydraulic cylinder does work to the pumping unit controlled by the servo valve. The force exerted on the pumping system is then collected by the force transducer. This signal collected is sent back to the computer control system through signal conditioning circuit. In all, there is a closed-loop control in designed loading system.
The design of test system Experimental results Design of the load simulation system Load simulation system is a device in the laboratory to simulate the force on suspension center of the pumping unit. It can be used to evaluate the performance of pumping system in practice. Nevertheless, in practice, the value and direction of the velocity and acceleration of the belt are changing with time, which makes it hard to reproduce the loading conditions in the laboratory. Therefore, in order to solve this problem and provide solutions, various
The test system is composed of pumping unit and loading system, as presented in Figure 9. The pumping unit is connected to the hydraulic loading system through belt and connection mechanism. The experiment is conducted in our laboratory. To prevent the counterbalance from swinging, a rail and wheels are added to the pumping unit that ensures the counterbalance moving only in vertical direction. The location arrangement of rail, spring sets, and sensors are shown in Figure 10. The whole pumping system is shown in Figure 11. Additionally, the experiment parameters are presented in Table 1.
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Table 1. Experimental parameters. Parameter
Value
Unit
S1 k1 P mr + mo mp S
80 9.375 3 104 2.2 300 600 850
mm N/m kW kg kg mm
Figure 11. Whole proposed pumping system.
Figure 9. The structure diagram of loading system.
Figure 12. The motor start command signal.
0.1 0.08
The sinusoidal wave, shown in Figure 12, is used to control the speed of motor from starting. The actual speed of motor collected by sensor is shown in Figure 13, which has some fluctuations. We have compared the current collected from motor in the case of pumping system with and without spring sets. From Figure 14, the time used from starting the motor to smooth operation is 1 s. It is obvious that the current of motor is much smaller in the first second from starting
Speed (m/s)
Figure 10. Location arrangement of spring sets and sensors. 0.06 0.04 0.02 0
0
0.2
0.4 0.6 Time (s)
Figure 13. The speed of motor from starting.
0.8
1
10
Advances in Mechanical Engineering compared to the traditional reciprocating pumping system. The development research, including design, modeling, and experiment was done. The conclusions are as follows: 1.
2. Figure 14. The current from starting the motor in the case of pumping system with and without spring sets.
3.
4.
Figure 15. The current of motor when the motor is decelerating.
when there are spring sets installed in the pumping system. In addition, we have conducted experiment to record the current of motor when the pumping system is nearly reaching the end of up stroke, as shown in Figure 15. From Figure 15, the current of motor is slightly increased when the counterbalance is just contacting with spring set. Then, there is abrupt change in the current until a value maintained by 0.3 s, and finally, the current reduces to zero. We have computed the value of energy saving in whole stroke and the ratio of energy saving is 9.204%, which matches the result with the one obtained in mathematical simulation model.
Conclusion A pumping system, with novel springs energy storage devices, has a significant energy-saving effect as
Theoretical estimation and experimental measurement of the ratio of energy saving were carried out. Good matching was observed, and hence the parameters used for the theoretical estimation of the new energy-saving pumping system were validated. Based on characteristic analysis of new energy-saving pumping system, the ratio of energy saving was estimated as 9.204%. After the pumping system reaching the bottom dead center, it requires a big start torque for the motor to reverse the counterbalance in the traditional pumping system, whereas our proposed pumping system could reduce the start torque of motor, which could increase the lifespan of the motor. From the experiment, the dynamic polished rod load dynamometer card of proposed pumping system is presented in Figure 5. The dynamic polished rod load matches the static polished rod load in the whole stroke, which reduces the ratio of vibration and inertial energy. The velocity curve of the motor in proposed pumping system is sinusoidal, which makes the start and stop of the system smoother. Therefore, the proposed strategy could prolong the lifespan of the pumping system.
Declaration of conflicting interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (Grant No. 51605321, No. 51405327) and the Natural Science Foundation for Young Scientists of Shanxi Province, China (Grant No. 2014021024-1).
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