Abstract:
A reciprocating drive system that utilizes energy available from pressure changes in flowing fluid systems, said drive used for the injection of additives into pipelines. The reciprocating drive includes a hydraulic accumulator having a gas chamber connected to a gas pipeline to contain said gas, whereby variation in the elevated pressure of the pipeline is reflected in the pressure applied to an incompressible fluid in a hydraulic conduit. The drive is capable of recycling gas used to drive the system back into pipelines.

Description:
[0001]    This is a Continuation-in-part of U.S. patent application Ser. No. 10/326,406 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a reciprocating drive system.  
         FIELD OF THE INVENTION  
         [0003]    Reciprocating drive systems are often used to drive ancillary equipment, such as a pump that may be used for the injection of additives into pipelines.  
         DESCRIPTION OF THE PRIOR ART  
         [0004]    It is frequently necessary to inject an additive into a well or pipeline. These installations are often located in remote locations so the systems must be self-contained. Due to road conditions in some remote locations, chemicals which ate injected into pipelines cannot be transported to the site for months at a time, and standard sources of power to run the injection system may not exist. Examples of additives that might be injected into pipelines include; chemicals for the prevention of line freezing due to hydration, chemicals that disperse waxes or asphaltene, and chemicals that prevent corrosion of pipelines. Therefore, there is a need for pipeline injection systems that offer both dependable and accurate metering, as well as having the capability to operate without traditional sources of power.  
           [0005]    A number of different types of systems are available on the market for the injection of chemicals into remote pipelines or wellheads. Many of these systems utilize the natural gas carried by a pipeline as a prime mover. Use of natural gas for this purpose, however, is fraught with numerous problems.  
           [0006]    A first problem with this type of system is that the natural gas used to drive the system is exhausted into the atmosphere, as the majority of these systems are unable to recover the gas. Pipeline natural gas open contains high levels of hydrogen sulphide, which is toxic and harmful to the environment. As a result, a number of governmental regulations have recently been put in place to restrict the release of natural gas into the environment. Further, the loss of natural gas to the environment represents a substantial, cumulative economic loss to operators.  
           [0007]    An additional problem of using gas driven systems is a difficulty in controlling the mass of additive injected per unit of time. Gas driven systems suffer in performance due to the high compressibility of gas. Specifically, such systems are often typified by erratic piston motion, and as a result valve damage can also occur. Further, injection systems are required to operate efficiently at as low a pressure as possible so as not to restrict movement of gas within pipelines any more than necessary.  
           [0008]    An alternative form of injection uses air/oil hybrid systems, but these are also characterized by specific deficiencies. Such systems often experience a loss of oil caused by the reciprocating motion of a piston rod. As a result of the oil loss, gas can replace oil in the system. Mixing of gas and oil in this manner causes a frothing of the oil component of the system, which can lead to erratic and uncontrolled movement of the piston rod used to inject the additive.  
           [0009]    It is therefore an object of the present invention to obviate or mitigate the above disadvantages.  
         SUMMARY OF THE INVENTION  
         [0010]    A reciprocating drive for use with a gas pipe line carrying gas at an elevated pressure, said drive comprises a drive rod, a pair of fluid motors each having a reactive surface acting on the rod to move the rod in opposite directions upon application of fluid pressure thereto. A valve is connected between the pipeline and the motors and operable to direct gas from the pipeline to one or other of the motors. A reversing mechanism acts on the valve to change periodically the setting of the valve and reverse direction of movement of the rod. The speed control device controls the rate of movement of the drive rod. The speed control device comprises a body of incompressible fluid disposed in a pair of chambers interconnected by a hydraulic conduit. Each of the chambers includes a cylinder and a piston moveable within the cylinder upon movement of the rod to vary the volume of the chamber. The chambers are arranged relative to one another such that a decrease in the volume of one of the chambers causes a corresponding increase in the volume of the other of the chambers The speed control valve further comprises a flow control valve located in the conduit and a hydraulic accumulator connected to the conduit. The accumulator has a first chamber in communication with said conduit to contain the uncompressible fluid and a second chamber connected to said gas pipeline to contain the gas, whereby variations in the elevated pressure of said pipeline are reflected in the pressure applied to the incompressible fluid in the conduit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings wherein:  
         [0012]    [0012]FIG. 1 is a schematic representation of a pipeline additive installation.  
         [0013]    [0013]FIG. 2 is a schematic representation of the components used in the system of FIG. 1.  
         [0014]    [0014]FIG. 3 is a representation of an alternative embodiment of the components used in FIG. 2.  
         [0015]    [0015]FIG. 4 is a further embodiment of the component shown in FIG. 3.  
         [0016]    [0016]FIG. 5 is a representation of the alternative configuration of cylinders shown in FIG. 2.  
         [0017]    [0017]FIG. 6 is a sectional view of a further embodiment.  
         [0018]    [0018]FIG. 7 is a view similar to FIG. 6 of a yet further embodiment, and  
         [0019]    [0019]FIG. 8 is a view of a portion of FIG. 7 on an enlarged scale. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring therefore to FIG. 1, a pipeline additive system generally indicated  10  is connected to a pipeline  12  at a location where there is a pressure drop in the pipeline such as that provided by a restriction such as an elbow indicated at  14 . The elbow  14  provides a pair of spaced locations along the pipeline such that there is a small but discernible difference in pressure of gas in the line. The system  10  includes a reservoir  16  containing a supply of additives and connected to a pump  18  through a supply line  20 . A check valve  22  controls the direction of flow from the reservoir  16  to the pump  18 . The pump  18  discharges the additive through a supply line  24  and check valve  26  to the pipeline  12 . The pump  18  is driven by a drive assembly  28  that utilises the pressure of the gas or fluid in the pipeline  12  as its motive force. A supply line  30  is connected between the pipeline  12  and drive assembly  28  and an exhaust line  32  is similarly connected between the drive assembly and the pipeline  12 . The connection of the supply line  30  and exhaust line  32  is at respective ones of the spaced locations along the pipeline such that there is a discernible pressure difference between the two locations.  
         [0021]    Further details of the drive assembly and pump may be seen from FIG. 2. The pump  18  is a reciprocating pump having a cylinder  34  with an elongate internal chamber  36 . A piston rod  38  is slideable within the chamber  36  to induce fluid through the supply line  20  and expel it from the discharge line  24 , which are in communication with the chamber  36 .  
         [0022]    The piston rod  38  extends from the pump  18  through a pair of actuators  40 ,  42 . The actuator  40  has a cylinder  44  within which the rod  38  slides and a piston  46  secured to the rod  38 . The piston  46  divides the cylinder  44  into a pair of chambers  48 ,  50 . The actuator  42  similarly includes a piston  52  secured to the rod  38  and defining a pair of chambers  54 ,  56 .  
         [0023]    The piston rod  38  carries a pair of adjustable stops  58 ,  60  that co-operate with a toggle mechanism  62  to actuate a valve  64 . The valve  64  is a two position four way valve that controls the supply of gas from the inlet  30  to respective ones of the chambers  50 ,  54  and similarly connects the chambers  50 ,  54  to the exhaust line  32 .  
         [0024]    The chambers  48 ,  56  are connected to one another through branch conduits  66 ,  68  that are each connected to an accumulator  70 . Adjustable flow restrictors  72 ,  74  are included in the branch conduits  66 ,  68  respectively to control the flow of fluid between the chambers  48 ,  56  through the accumulator  70 . The accumulator  70  has a gas chamber  76  that is connected through a branch conduit  80  to the inlet  30  and a hydraulic chamber  78 . The pressure in the gas chamber  76  thus corresponds to the pressure supplied to the inlet of the valve  64 . The chambers  48 ,  46  and the hydraulic chamber  78  of the accumulator  70  are filled with an incompressible hydraulic fluid, typically an oil, so that movement of the rod  38  causes displacement of fluid between the chambers  48 ,  56  and  78 . A pair of check valves  85  are connected in parallel to the flow restrictors  72 ,  74  and allow flow from chamber  78  to respective ones of the chambers  48 ,  56 . A relief valve  88  is also provided in each of the lines  66 ,  68  to provide protection from over pressure of the system.  
         [0025]    The supply line  30  includes a filter  82  and pressure regulator  84  to control fluctuations in the pressure supplied to the valve  64 . A back pressure valve  86  is connected in the exhaust line  32  to inhibit reverse flow of gas through the valve assembly.  
         [0026]    In operation, with the components in the relative position shown in FIG. 2, the piston rod  38  is fully retracted from the chamber  36  which is filled with the additive drawn from the reservoir  16 . Pressure from the inlet  30  is supplied through the valve  64  to the chamber  54  and the chamber  50  is connected through the exhaust line  32  to the lower pressure zone of the pipeline. The pressure difference between the chamber  54  and chamber  50  induces movement of the piston rod  38  to expel fluid from the chamber  36 . The rate of movement of the rod  38  is controlled by the flow rate through the restrictor  72 ,  74  which is proportional to the pressure differential applied across the restrictors. Any variation in volume between the chambers  48  and  56  is accommodated by compression of the gas in the chamber  76 . As the piston rod moves to expel fluid from the chamber  36  through the discharge  24 , the abutment  58  contacts the toggle  62  and moves the valve  64  into its alternative position. In that position, the higher gas pressure is applied to the chamber  50  and the chamber  54  connected to the exhaust  32 . The direction of movement of the rod  38  is thus reversed causing the chamber  36  to again expand and draw additive into the chamber  36 . The rate of movement of the piston rod  38  again is controlled by the flow of fluid through the branch conduit  66 ,  68  to maintain the speed at the desired rate. The reciprocal motion will continue to dispense the additive from the chamber  36  at each reversal utilising the gas supplied in the pipeline in a closed system. The stroke length of the piston rod may be adjusted by positioning the abutments  58 ,  60  at different locations along the piston rod  38  between the two actuators  40 ,  42  to co-operate with the toggle  62  at different points during the stroke.  
         [0027]    Because the rate of movement of the rod is determined in part by the pressure difference across the restrictor  72 ,  74  it is necessary to prevent variation in the rate of movement due to fluctuations of the gas pressure within the line, which are in turn supplied to the chambers  50 ,  54 . Variations in the gas pressure are transmitted through the branch conduit  80  to the gas chamber  76  and thereby cause a corresponding increase in the pressure in the fluid chamber  78 . Thus, an increased pressure in the drive chambers  50 ,  54  due to an increase of pressure in the supply line  30  will cause a corresponding increase in the chamber  78  and maintain the pressure differential across the restrictor  72 ,  74  constant. The rate of movement of the piston rod  30  therefore remains constant and the volume of additive dispensed per unit of time can be maintained. The application of the gas pressure effectively pressure compensates the flow control valves provided by restrictors  72 ,  74  to maintain a substantially constant flow rate.  
         [0028]    The check valves  85  permits air that may be trapped in the chambers  48 ,  56  to be vented to the accumulator chamber  78 . The relief valves  88  are set above the typical system pressure, for example to 600 psi to permit relief of the system. This may occur for example, with an increase in ambient temperature when the system is shut off and could otherwise result in seal failure.  
         [0029]    In the above embodiment, each of the branch conduits contains a restrictor  72 ,  74 . However, as shown in FIG. 3 in which like components will be denoted with like reference numerals with a suffix “a” added for clarity, a single variable restrictor  74   a  is included in the branch conduit  68   a  The single restrictor  74   a  may be used to control the flow of fluid through the accumulator  70   a  and branch conduit  66   a . Again the pressure in the chamber  76   a  is adjusted with variations of the inlet  30  to maintain the pressure differential across the restrictor  74   a , substantially constant.  
         [0030]    A further embodiment is shown in FIG. 4 which permits control of the speed at different rates in opposite directions. In the embodiment of FIG. 4, the branch lines  66   b ,  68   b  are interconnected by a pair of cross flow lines  100 ,  102 . Each of the cross flow lines  100 ,  102  includes a check valve  104  and a variable flow restrictor  74   b . The check valves  104  are oppositely facing and that inhibits flow in opposite directions through each of the lines  100 ,  102 . The accumulator  70   b  is similarly protected by a pair of check valves  106 . In this embodiment the accumulator  70   b  acts as a pressurized reservoir. The accumulator  70   b  provides fluid to chambers  48   b  and  56   b  as these chambers lose fluid during operation. The accumulator  70   b  ensures that fluid that is lost during operation is replaced in order to ensure that gas and fluid are not mixed. The flow through each of the restrictors  74   b  may be adjusted independently and therefore the rate of movement of the piston rod  38  in each direction may be different.  
         [0031]    In the embodiments shown in FIGS. 2, 3 and  4  the actuators  40 ,  42  have been shown in spaced relationship with the toggle mechanism  62  located between. Other arrangements of the actuator may be utilised as shown in FIG. 5. In FIG. 5 a , the rod  38  extends through both sides of the actuator  42  to provide for double acting power transfer on both advance and retraction.  
         [0032]    In the arrangement shown in FIG. 5 b , the actuators  40 ,  42  abut each other on opposite sides of a partition  90  and the toggle mechanism  58 ,  60  may be moved externally of the actuators  40 ,  42 . The partition  90  separates the oil, chambers  48 ,  56  with the gas chambers  50 ,  54  outboard of the partition. The rod  38  may extend through the cylinder  42  similar to  5   a  as shown in ghosted outline. In a further arrangement shown in FIG. 5 c , a pair of actuators  40 ,  42  are supplemented by an additional actuator  110  to provide additional surface area to move the piston rod  38  in each direction, thereby providing more power (Force×Distance). The actuators  40 ,  42  are arranged as in FIG. 5 a  with oil chambers  48 ,  56  and gas chambers  68 ,  66  respectively. If preferred, the gas chambers may be incorporated in a single actuator with oppositely acting oil chambers paired on the other actuators.  
         [0033]    In a further embodiment shown in FIG. 6, the gas chambers  48 ,  54 ,  56  actuators  40 ,  42  are combined with a diaphragm device  200 . The device  200  has an external housing  201  and an internal diaphragm  203  to which the rod  38  is secured. The oil chambers  48 ,  56  are similarly combined in separate hydraulic dashpot  202 . The dashpot  202  includes a piston  204  sliding in a cylinder  206  and connected through ports  208  to the accumulator  210 . Pipeline pressure is applied to the accumulator through conduit  80   c . The restrictors  72 ,  74  are incorporated in valve block  212  located in the body of the accumulator  210 .  
         [0034]    Flow of gas to the opposite sides of the diaphragm  200  is controlled by a valve block operated through stops  58   c ,  60   c  to reverse the porting of the valve. The function of the device is similar to that described above, with the diaphragm  200  providing the reciprocal motive force and the pipeline pressure acting through the conduit  80   c  to maintain flow through the restrictors in valve block  212  at the required rate.  
         [0035]    In a further embodiment shown in ghosted outline in FIG. 6, additional diaphragm devices are attached to the drive system in order to provide a greater surface area. Addition of one or more diaphragms to the disclosed embodiment is preferred if: (1) a greater force is required to operate the drive, for example if a large volume chemical injector is driven or (2) if a lower supply differential exists that requires a greater surface area to obtain a desired force,  
         [0036]    In the above embodiments, the valve  64  is shown as two position four way valve operated through the toggle mechanism. The use of the toggle mechanism provides a progressive movement of the valve between its two possible positions and in certain circumstances it has been found that stalling of the drive may occur due to internal function and/or the reduction of the differential pressure available. Should the valve stall in an intermediate position, restarting of the drive as the differential pressure returns is difficult. In order to overcome these difficulties a valve actuating mechanism as shown in FIG. 7 has been utilised. Like reference numerals will be used to denote like components with a suffix d added for clarity.  
         [0037]    Referring therefore to FIG. 7, a drive assembly  28   d  is connected to a pump  18   d  through a shaft coupling  300 . The coupling  300  is formed at one end of the drive shaft  38   d  that extends through a dash pot assembly  202   d  to a diaphragm  203   d . The diaphragm  203   d  is located in a housing  201   d . A piston  204   d  is secured within a cylinder  206   d  located within the dash pot  202   d  with the chambers  48   d ,  56   d  defined on opposite sides of the piston  204   d . The chambers  48   d ,  56   d  are connected through internal passageways and valving to accumulator  210   d . The internal valving functions to provide the control described in FIG. 2 through  4  above and need not be described in further detail at this time,  
         [0038]    A bi-stable valve assembly  64   d  is mounted on the diaphragm device  200   d  on the opposite side to the dash pot  202   d . The valve assembly  64   d  includes a bistable valve actuator mechanism  302  and a valve assembly  304 . The valve actuator mechanism  302  is connected to an extension of the shaft  38   d  through a lost motion coupling  306 . The coupling  306  includes an axial slot  308  formed in the shaft  38   d  and receiving a pin  310 . The pin  310  is mounted to a cylindrical nose  312  of a carrier  314 . The shaft  38   d  is a sliding fit within the nose  312  and may slide relative to the carrier  314  within the limits of the slot  308 . The nose  312  has an end face  316  that faces an end wall  318  of an enclosure  320  within which the carrier  314  is located. The carrier  314  is formed as two housings  322 ,  324  separated on a common radial plane. The housing  322  has an end face  326  that is oppositely directed to the end face  316  of the nose  312 . The end face  326  faces an end wall  328  of the enclosure  320  so that the carrier  314  may move axially within the enclosure  320  between the limits imposed by the end walls  328 ,  318 .  
         [0039]    The carrier  314  supports a conical spring  330  whose periphery  332  is secured between the two housings  322 ,  324 . The conical spring has a radially inner aperture  334  that is secured to a valve actuator  336 . The conical spring is a bistable element formed from a planar annulus of spring steel that is pre-stressed to adopt a conical free body configuration. Such springs are available commercially under trade name “Clover Disk” and provide a pair of stable position, one on each side of a median plane.  
         [0040]    The valve actuator  336  extends to a valve housing  338  of the valve assembly  304  and carries a valve spool  340 . As can best be seen in FIG. 8, the spool  340  has a central land  342  with oppositely directed scaling faces  344 ,  346 . The land  342  is located in a central distribution chamber  348  to which the pressure port  30   d  is connected. The chamber  348  has a pair of radial walls  350  extending radially inwardly to overlap the sealing faces  344 ,  346  respectively. The spool  340  extends through a central aperture in the walls  350  to supply chambers  352  that communicate with respective supply ports  354 ,  355  respectively. The supply ports  354 ,  355  are connected to opposite sides of the diaphragm  203   b . Exhaust chambers  360 ,  361  are located on either side of the supply chambers  354 ,  355  and carry lip seals  362  that are selectively engageable with the spools  340 . The terminal, portions of the spool  340  have lands  364  that are engageable with the lip seals  362  when the spool is in one of its extreme positions. The exhaust chambers  360  are connected to the exhaust line  32   d  which is also connected to the gas side of accumulator  210   d  through port  80   d.    
         [0041]    In operation, the supply line  30   d  supplies high pressure gas to the central distribution chamber  348 . The sealing face  344  of land  342  is in sealing engagement with the radial wall  350  and so prevents flow from the high pressure port to the supply port  354  in that position, the land  364  is clear of the lip seal allowing the supply port  354  to communicate past the lip seal to the exhaust chamber  361  and exhaust line  32   d . The chamber  348  is in communication with the supply port  355  that therefore supplies pressure fluid to one side of the diaphragm  203   b . In this position, the lip seal  362  is scaled against the land  364  to isolate the exhaust port  360  from the supply port  355 . The pressure differential applied to the diaphragm  203   b  thus initiates movement of the shaft  38   d  toward the pump  18   d . The movement causes displacement of the piston  204   b  within the cylinder  206   d  and thereby transfers hydraulic fluid from one side of the piston to the other in a controlled manner.  
         [0042]    During the initial movement, the slot  308  slides past the pin  310  to leave the carrier  314  in the position shown in FIG. 7. The carrier  314  is held in that position by the action of the conical spring  330  which applies a force to the valve actuator  336  to hold the scaling face  344  against the face  350 . The bias of the spring  330  thus holds the face  350  of the carrier  314  against the end face  328  and maintains the carrier  314  in a stable position.  
         [0043]    As the shaft  38   d  continues its movement, the terminal portion of the slot  308  engages the pin  310  and initiates movement of the carrier  314  away from the wall  328 . As the valve actuator  336  cannot move axially with the carrier  314 , the spring  330  is moved over center causing the actuator  336  to slide axially and move the sealing face  346  into engagement with the radial face  350 . In that position, the actuator  336  cannot move any further and the bias within the spring  330  causes the carrier to move axially until the end face  316  engages the end wall  318 . The inherent bias in the spring  330  thus acts on the valve actuator  336  to maintain the land in sealing engagement. In that position, the supply port  354  is sealed from the exhaust port  32   d  by virtue of the lip seal  362  and is connected to the pressure port  30   d . Similarly, the supply port  355  is isolated from the pressure port but connected to the exhaust port  360  by disengagement of the lip seal  362  from the land  364 . The pressure differential across the diaphragm  203   b  is thus reversed causing a return movement of the shaft  38   d . The lost motion device  306  permits return motion until such time as the pin  310  is again engaged and the over center action of the spring  330  causes a reversal of the spool and carrier.  
         [0044]    It will be seen that the actuating mechanism  28   d  provides a bias of the valve into one of two positions with the reversal of direction being effected in an immediate manner. This ensures that the valve cannot occupy a position in which both sides of the diaphragm are connected to a common port and this ensures that the pressure differential available will be applied across the diaphragm to effect movement of the pump.