Patent Grant
8616861
This disclosure relates generally to pneumatic or hydraulic systems that produce mechanical energy, or work. In particular, the disclosure relates to a pneumatic, or hydraulic, system with a regulator formed by a motor that enables pressure reduction of a fluid and produces mechanical energy that may be used to drive a compressor, or pump.
Many conventional pneumatic systems include a motor to which compressed air is delivered. In turn, the motor produces mechanical energy, or work, that may be used, for example, to power a hand-held tool. To control the pressure of compressed air delivered to the motor, the pneumatic system may also include a regulator positioned upstream of the motor. Compressed air is delivered through the regulator, causing a reduction in the pressure of the compressed air such that the pressure of compressed air delivered to the motor is at a desired level.
Wprod,20={dot over (m)}*(h3−h2) (1)
where h2 is the enthalpy of compressed air entering motor 20; h3 is the enthalpy of compressed air exiting motor 20; and {dot over (m)} is the flow rate of compressed air through system 10. In pneumatic system 10 illustrated by
Work Wprod, 20 produced by motor 20 is then used to actuate device 30. As previously mentioned, device 30 may be a hand-held tool powered by motor 20. Alternatively, device 30 may be an object that is lifted or moved, such as a hydraulic cylinder in a blowout preventer. Moreover, device 30 may be a generator. In short, device 30 may be any apparatus that is actuated by mechanical energy.
As compressed air flows through pneumatic system 10 and work Wprod, 20 is produced by motor 20, energy is removed from the compressed air as it passes through regulator 25 to enable pressure reduction of the compressed air. Because the energy removed is not utilized, it may be considered wasted. The amount of energy wasted Wwasted may be calculated using an Exergy Rate Balance Equation, which under the assumed conditions, simplifies to:
Wwasted={dot over (m)}*(h2−h1) (2)
Depending on the design configuration of regulator 25, the energy wasted Wwasted as the compressed air passes through regulator 25 maybe significant, and particularly so when compared to the amount of work produced Wprod, 20 by motor 20.
For exemplary purposes, the following conditions are assumed: the pressure P1 and temperature T1 of compressed air delivered from source 15 to regulator 25 are 20 MPa and 300° K, respectively; the compressed air flowrate {dot over (m)} through system 10 is 1 kg/second; a pressure reduction of 19 MPa occurs through regulator 25; and compressed air exits motor 20 with a pressure P3 of 0.2 MPa. Based on these conditions, the state of compressed air entering regulator 25 may be fully defined: pressure P1=20 MPa (given), temperature T1=300° K (given), enthalpy h1=267.80 kJ/kg, and entropy s1=5.25 kJ/kg. Next, the state of compressed air exiting regulator 25 and entering motor 20 may be fully defined. Given an assumed 19 MPa pressure reduction through regulator 25 and isentropic flow through regulator 25, the properties of compressed air exiting regulator 25 and entering motor 20 are: P2=P1−19 MPa, or 1 MPa, entropy s2=s1=5.25 kJ/kg, enthalpy h2=110.20 kJ/kg, and temperature T2=123.75° K. Lastly, the state of compressed air exiting motor 20 may be defined. Based on the assumed pressure P3=0.2 MPa at the exit of motor 20 and isentropic flow through motor 20, the properties of compressed air exiting motor 20 are: pressure P3=0.2 MPa (given), entropy s3=s2=5.25 kJ/kg, enthalpy h3=69.32 kJ/kg, and temperature T3=87.75° K.
Having fully defined the state of compressed air entering regulator 25, exiting regulator 25 (also entering motor 20), and exiting motor 20, the work produced Wprod, 20 by motor 20 is estimated to be 55 hp using equation (1). Also, the work wasted Wwasted as compressed air passes through regulator 25 is estimated to be 211 hp using equation (2). As demonstrated, a significant amount of energy is wasted during pressure reduction of the compressed air as it passes through regulator 25.
Accordingly, apparatus or systems that enable use of the energy removed from the compressed air during pressure reduction are desirable.
A system including a super efficient regulator is disclosed. In some embodiments, the super efficient regulator includes a motor driven by a first fluid, the first fluid decreasing in pressure and the motor producing mechanical energy as the first fluid passes through the motor, and a device powered by the mechanical energy produced by the motor, the device increasing a pressure of a second fluid. The first fluid exhausted by the motor and the second fluid exhausted the device have substantially equal pressures.
A system for producing mechanical energy. In some embodiments, the system includes a first source providing a first fluid, a fluid pressurization device, a second source supplying a second fluid, a first motor, and a second motor. The fluid pressurization device draws in the first fluid from the first source and increases the pressure of the first fluid. The first motor is driven by the second fluid, the second fluid decreasing in pressure and the first motor powering the fluid pressurization device as the second fluid passes through the first motor. The second motor receives a mixture of the first fluid from the first motor and the second fluid from the fluid pressurization device, whereby the second motor produces the mechanical energy.
Some methods for producing mechanical energy include conveying a first fluid through a first motor, powering a fluid pressurization device by the first motor as the first fluid passes through the first motor, increasing the pressure of a second fluid passing through the fluid pressurization device, and supplying at least one of the first fluid from the first motor and the second fluid from the fluid pressurization device to a second motor, whereby the second motor produces the mechanical energy.
Thus, embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with conventional pneumatic or hydraulic systems having a regulator, or similar pressure reduction device. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiment, and by referring to the accompanying drawings.
For a detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings in which:
The following description is directed to exemplary embodiments of a pneumatic or hydraulic system with an efficient or super efficient regulator. The embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and that the discussion is meant only to be exemplary of the described embodiments, and not intended to suggest that the scope of the disclosure, including the claims, is limited to those embodiments.
Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. Moreover, the drawing figures are not necessarily to scale. Certain features and components described herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness.
In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and connections.
Referring now to
In contrast to pneumatic system 10, pneumatic system 100 further includes a motor 110 in place of regulator 25. Thus, compressed air from source 15 passes through motor 110, rather than regulator 25, to motor 20. Like regulator 25, motor 110 enables a pressure reduction of the compressed air flowing therethrough. In this way, motor 110 may be considered a regulator. However, unlike regulator 25, motor 110 enables the production of mechanical energy, or work, that may be used in some manner. As such, motor 110 is considered an efficient regulator.
The amount of work produced by motor 110, Wprod, 110, may be calculated using the First Law of Thermodynamics, which under the assumed conditions, simplifies to:
Wprod,110={dot over (m)}*(h4−h1) (3)
where h1 is the enthalpy of compressed air entering motor 110; h4 is the enthalpy of compressed air exiting motor 110; and {dot over (m)} is the flow rate of compressed air through pneumatic system 100. In pneumatic system 100 illustrated by
Assuming motor 110 is configured to produce the same pressure reduction in compressed air passing through it as regulator 25 and isentropic flow through motor 110, the properties of compressed air entering motor 20 from motor 110 are the same as those of compressed air entering motor 20 from regulator 25 (i.e., P2=P4, T2=T4, h2=h4, and s2=s4). The work produced by motor 110, Wprod, 110, is then estimated to be 211 hp, assuming the same flow rate in through pneumatic system 100 as that through pneumatic system 10. Hence, replacement of regulator 25 with motor 110 enables the production of 211 hp of useful work. This is beyond that produced by motor 20, which was previously estimated to be 55 hp.
Flow through pneumatic system 100 is assumed to be isentropic. Further gains in the production of useful work may be realized under isothermal, rather than isentropic, flow conditions through motor 110.
The amount of work produced by motor 210, Wprod, 210, may be calculated using the First Law of Thermodynamics, which under the assumed conditions, simplifies to:
Wprod,210={dot over (m)}*(h5−h1) (4)
where h1 is the enthalpy of compressed air provided by source 15 to motor 110; h5 is the enthalpy of compressed air exhausted by motor 210; and {dot over (m)} is the flow rate of compressed air through pneumatic system 200. In pneumatic system 200 illustrated by
Assuming motor 210 is configured to produce the same pressure reduction in compressed air passing through it as regulator 25 and isothermal flow through motor 210, the properties of compressed air entering motor 20 from motor 210 are: P5=P1−19 MPa=1 MPa, T5=T1=300° K (given), h5=298.30 kJ/kg, and s5=6.20 kJ/kg. The work produced by motor 210, Wprod, 210, is then estimated to be 345 hp, assuming the same flow rate {dot over (m)} through pneumatic system 200 as that through pneumatic system 100. Hence, replacement of isentropic motor 110 with isothermal motor 210 enables an increase of 133 hp in useful work beyond that produced by isentropic motor 110, as well as an increase of 345 hp in useful work beyond that produced by regulator 25, which is none.
The amount of work produced by motor 20, Wprod, 20, may be calculated using the First Law of Thermodynamics, which under the assumed conditions, simplifies to:
Wprod,20={dot over (m)}*(h6−h5) (5)
where h6 is the enthalpy of compressed air exiting motor 20. Assuming isentropic flow through motor 20 and that motor 20 is configured to exhaust compressed air at a pressure of 0.2 MPa, the properties of compressed air exiting motor 20 are: s6=s5=6.20 kJ/kg, P6=0.2 MPa (given), h6=188.82 kJ/kg, and T6=188.82° K. The work produced by motor 20, Wprod, 20, is then estimated to be 148 hp, an increase of 93 hp beyond that produced by motor 20 when driven by compressed air from isentropic motor 110 or regulator 25. In other words, replacement of isentropic motor 110 or regulator 25 with isothermal motor 210 enables the work produced by motor 20 to nearly triple.
Work produced by motors 20, 210 is dependent upon the flow rate of compressed air supplied to each. Increasing the flow rate also increases the work produced by these devices. Thus, increasing the flow rate {dot over (m)} through system 200 will enable an increase in the production of useful work from motor 20. In some circumstances, such an increase in the flow rate {dot over (m)} may not be possible, or may be undesirable, such as when source 15 contains a limited supply of compressed air. In such circumstances, the flow rate of compressed air to motor 20 may be increased by utilizing the work produced by motor 210 to add compressed air to pneumatic system 200.
The amount of work produced Wprod, 210 by motor 210 was previously determined to be 345 hp. This work is used to power compressor 305. Compressor 305, in turn, draws in ambient air and compresses that air. Once compressed, the air exhausted by compressor 305 is mixed with compressed air provided by source 15 at a location 320 downstream of motor 210 and compressor 305. The mixture of compressed air from motor 210 and compressor 305 flows through motor 20, enabling motor 20 to produce work Wprod,20. Due to the increased flow rate through motor 20 resulting from the addition of compressed air by compressor 305, the work produced by motor 20 is increased relative to that produced by motor 20 in the absence of compressor 305. The increase in work produced by motor 20 is dependent upon the flow rate of compressed air through motor 20, which, in turn, is dependent upon the flow rate of compressed air exhausted by compressor 305. Thus, in order to determine the work produced by motor 20, the flow rate of compressed air exhausted from compressor 305 must first be determined.
Assuming isentropic flow through compressor 305, the flow rate of air {dot over (m)}c compressed by compressor 305 may be calculated using the First Law of Thermodynamics, which under the assumed conditions, simplifies to:
{dot over (m)}c=Wprod,210/(h7−ha) (6)
where ha is the enthalpy of air entering compressor 305 and h7 is the enthalpy of compressed air exiting compressor 305; and {dot over (m)}c is the flow rate of compressed air exiting compressor 305. In pneumatic system 300 illustrated by
To determine the flow rate of air {dot over (m)}c compressed by compressor 305, the properties of compressed air entering and exiting compressor 305 must first be defined. Assuming the pressure and temperature of ambient air entering compressor 305 are Pa=0.1 MPa and Ta=300K, respectively, the enthalpy of the ambient air ha is 300.30 kJ/kg, and the entropy of the ambient air sa is 6.87 kJ/kg. Assuming isentropic flow through compressor 305 and that the pressure of compressed air exhausted by compressor 305 is substantially equal to that of compressed air exhausted by motor 210, the properties of compressed air exiting compressor 305 are: P7=P5=1 MPa, s7=sa, T7=574.35K, and h7=580.50 kJ/kg. Substituting the enthalpy of air ha entering compressor 305 and the enthalpy h7 of air exiting compressor 305 into equation (6) above, the flow rate {dot over (m)}c of compressed air exiting compressor 305 is determined to be 0.92 kg/second.
Next, the amount of work produced by motor 20, Wprod, 20, may be calculated using the First Law of Thermodynamics, which under the assumed conditions, simplifies to:
Wprod,20=({dot over (m)}+{dot over (m)}c)*(h9−h8) (7)
where h8 is the enthalpy of compressed air entering motor 20 and h9 is the enthalpy of compressed air exiting motor 20. Due to the addition of compressed air to pneumatic system 300 by compressor 305, the flow rate through motor 20 is increased and equals the sum of the flow rate {dot over (m)} of compressed air supplied by source 15 and the flow rate {dot over (m)}c of compressed air exhausted by compressor 305, not simply the former as in the case of pneumatic systems 100, 200.
In order to estimate the work Wprod, 20 produced by motor 20, the state of compressed air both entering and exiting motor 20 must be defined. The compressed air entering motor 20 is a mixture of compressed air exhausted by motor 210 and compressor 305. Assuming mixing chamber conditions apply, meaning negligible heat transfer, work, and changes in potential energy, and kinetic energy, the enthalpy h8 of compressed air entering motor 20 may be calculated:
h8=({dot over (m)}c*h7+{dot over (m)}*h5)/({dot over (m)}c+{dot over (m)}) (8)
Under the defined conditions, the enthalpy h8 of compressed air entering motor 20 is 433.28 kJ/kg. Having determined the enthalpy h8 of compressed air entering motor 20 and knowing the pressure P8 compressed air entering motor 20, which is equal to the pressure of compressed air exhausted by motor 210 and compressor 305, the remaining properties of compressed air entering motor 20 may be determined: pressure P8=P5=P7, entropy s8=6.58 kJ/kg, and temperature T8=432.15° K.
Next, assuming isentropic flow through motor 20 and that motor 20 is configured to exhaust compressed air at a pressure of 0.2 MPa, the properties of compressed air exhausted by motor 20 are: entropy s9=s8, pressure P9=0.2 MPa (given), temperature T9=273.12K, and enthalpy h9=273.00 kJ/kg. Substituting the enthalpies h9 and h8 and the flow rates {dot over (m)}c and {dot over (m)} into equation (7) above, the work Wprod, 20 produced by motor 20 is determined to be 412 hp, approximately 7.5 times the amount of work produced by motor 20 when driven by compressed air from isentropic motor 110 or regulator 25 in the absence compressor 305 and approximately triple the amount of work produced by motor 20 when driven by compressed air from isothermal motor 110 in the absence compressor 305.
In some applications, it is desirable to maintain the work produced by motor 20 Wprod, 20 at a substantially constant level due to constraints imposed by device 30. For example, it may desirable to provide mechanical energy to device 30 at a substantially constant rate of 55 hp. As demonstrated above, pneumatic system 100 is configured to provide 55 hp of mechanical energy to device 30 when compressed air is provided from source 15 to motor 110 at a flow rate of 1 kg/second. Assuming the same flow rate of compressed air from source 15 to motor 110, pneumatic system 200 is configured to provide 148 hp of mechanical energy to device 30. Similarly, assuming the same flow rate of compressed air from source 15 to motor 210, pneumatic system 300 is configured to provide 412 hp of mechanical energy to device 30. Because significantly less mechanical energy is desired for device 30, the flow rate of compressed air supplied by source 15 to motor 110 of pneumatic system 100 and to motor 210 of pneumatic system 200 may be reduced to a level that enables motor 20 to produce only 55 hp. This enables less compressed air to be consumed from source 15. In applications where source 15 contains only a limited supply of compressed air, such as a portable tank having a finite storage volume, utilizing compressed air from source 15 at a lower rate enables device 30 to be powered for longer periods of time before source 15 is depleted. This is particularly desirable in applications where refill or replacement of source 15 is difficult or inconvenient, for instance in subsea applications.
As described, motor 210 enables pressure reduction of compressed air supplied by source 15 and produces useful work that drives compressor 305. Compressor 305, in turn, increases the flow rate of compressed air to motor 20 without increasing the flow rate of compressed air from source 15, and enables a reduction in the consumption rate of compressed air from source 15. For these reasons, the combination of motor 210 and compressor 305 is considered a super efficient regulator.
In some embodiments of the pneumatic system, wherein source 15 provides only a limited supply of compressed air, the pneumatic system may further include valves that enable continued operation of motor 210 when source 15 is depleted.
During operation of pneumatic system 400, valve 500 is in its first position, and compressed air is delivered from source 15 through motor 210 to motor 20, as previously described in connection with pneumatic system 300. Also, valve 505 is in its first position, and ambient air is drawn into compressor 305, compressed, and exhausted to motor 20. When source 15 is depleted such that the pressure of compressed air supplied to motor 210 is lower than necessary to drive motor 210, valves 500, 505 are actuated from their first positions to their second positions. The pressure differential between source 15 and the surrounding atmosphere 315 drives motor 210. In turn, motor 210 drives compressor 305, which draws in air from source 15, compresses it, and discharges the compressed air to motor 20. Thus, valves 500, 505 enable continued operation of pneumatic system 400 when source 15 is depleted below levels needed to drive motor 210.
In the above-described embodiments, the working fluid is air. However, in other embodiments of pneumatic systems 100, 200, 300, 400, the working fluid may be another type of gas, such as but not limited to nitrogen. Furthermore, pneumatic systems 100, 200, 300 may be modified to use a liquid, such as but not limited to hydraulic oil or hydraulic water, as the working fluid. In such cases, compressor 305 would necessarily be replaced with a hydraulic pump. Because compressor 305 and the hydraulic pump increase the pressure of fluid received by each, these devices may also be referred to as fluid pressurization devices.
While various embodiments have been showed and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings herein. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the apparatus disclosed herein are possible and within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.
This application claims benefit of U.S. provisional application Ser. No. 61/235,005 filed Aug. 19, 2009, and entitled “Super Efficient Regulator,” which is hereby incorporated herein by reference in its entirety for all purposes.
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