Abstract:
Methods and apparatus for controlling the flow through a compressor with a valve assembly comprising a rotating body having an outer surface. The rotating body is disposed within a valve cavity in the compressor. A non-contacting seal operates to limit the flow of fluid between the outer surface of the rotating body and the valve cavity. An aperture is disposed through the rotating body. A drive assembly rotates the rotating body such that the aperture intermittently allows fluid to bypass the non-contacting seal as the rotating body is rotated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   BACKGROUND 
   The present invention relates generally to methods and apparatus for controlling the flow of gases through compression equipment. More particularly, the present invention relates to methods and apparatus for check valves for compression equipment. Still more particularly, the present invention relates to check valves with rotating closure members. 
   Reciprocating compressors employ a cyclic process for compressing fluids that involves the suction of low pressure fluid into the compressor, compressing that fluid, and allowing the discharge of pressurized fluid from the compressor. Valves, generally known as check valves, are used to control the suction and discharge of fluids into and out of the compressor. 
   Many existing suction and discharge valves for the positive displacement compression equipment consist of plates, springs and seats. The operation of this valve is such that the valve plate lifts up from the seat by the gas forces and the spring forces the valve plate to reseat itself. This action causes the valve parts to flex in a fatiguing manner each time the piston cycles. This fatiguing action limits the life of the valve components to a short duration, typically less than a year. As a result, the suction and discharge valves require frequent maintenance, which amounts to very high cost due to product loss and component replacement cost. 
   In order to extend the useful life of conventional check valves, designers often seek to minimize the flexing of the component parts. In order to minimize the flexing, the valve lifting height is limited, which also limits the area available for the flow of fluids. Because the area available for flow is a limiting factor in the capacity of the pump, reducing this area often leads to designs utilizing multiple valves. Multiple valves not only increase the initial capital cost of the equipment but also increase the cost of maintenance. 
   The variables used to design conventional valves are numerous and designers historically rely heavily on empirical and experimental data in determining lifting height and opening pressures. Once a conventional check valve system is designed and built, the operation of those valves is limited to the operating parameters originally selected. Therefore, any change the fluid physical properties, thermodynamic properties and operational procedures may negatively affect the performance of the compression equipment and lead to even shorter life for the check valves. 
   Thus, there remains a need to develop methods and apparatus for controlling flow through compression equipment that overcome some of the foregoing difficulties while providing more advantageous overall results. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   The embodiments of the present invention are directed toward methods and apparatus for controlling the flow through a compressor with a valve assembly comprising a rotating body having an outer surface. The rotating body is disposed within a valve cavity in the compressor. A non-contacting seal operates to limit the flow of fluid between the outer surface of the rotating body and the valve cavity. An aperture is disposed through the rotating body. A drive assembly rotates the rotating body such that the aperture intermittently allows fluid to bypass the non-contacting seal as the rotating body is rotated. 
   In certain embodiments a compressor assembly comprises a compressor chamber in fluid communication with a valve cavity, which is in fluid communication with a fluid conduit. A valve body is disposed within said valve cavity. A non-contacting seal limits the flow of fluid between said valve cavity and said valve body. An aperture is disposed through said valve body. A drive assembly rotates said valve body such that said aperture is intermittently in fluid communication with said compressor chamber and said valve cavity. 
   In some embodiments, the valve body comprises a cylindrical shell having a closed end and an open end in fluid communication with said compressor chamber. The aperture penetrates the cylindrical shell of said valve body. In certain embodiments, the drive assembly comprises a magnet mounted to the closed end of the cylindrical shell and a motor coil affixed to the compressor. A power supply is electrically connected to said motor coil such that an electrical current applied to the motor coil cause the magnet to rotate. The non-contacting seal is disposed axially adjacent to either side of said aperture and comprises a labyrinth sealing surface on the outside surface of said rotating body and a babbitted surface disposed on the valve cavity. 
   In certain embodiments, the valve body comprises a disk with a shaft extending from an axial face of said disk. An aperture penetrates axially through said disk. The drive assembly comprises a magnet mounted to the shaft and a motor coil affixed to the compressor. The non-contacting seal comprises a labyrinth sealing surface on an outer cylindrical surface of the disk and a babbitted surface disposed on the valve cavity. 
   In selected embodiments, a method for operating a valve controlling fluid flow through a compressor comprises disposing a valve body within a valve cavity, wherein the valve body comprises one or more apertures therethrough. The flow of fluid between the valve body and the valve cavity is limited by a non-contacting seal. The valve body is rotated so as to intermittently allow fluid to bypass the non-contacting seal through the one or more apertures. The valve body may be rotated by applying an electrical current to a motor coil affixed to the compressor, wherein a magnet affixed to the valve body rotates in response to the electrical current applied to the motor coil. 
   Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. 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 embodiments of the invention, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
       FIG. 1  is a cross-sectional view of a reciprocating, positive displacement compressor utilizing prior art check valves; 
       FIG. 2  is a cross-sectional elevation view of a check valve assembly constructed in accordance with embodiments of the invention; 
       FIG. 3  is a cross-sectional plan view of the check valve assembly of  FIG. 2 ; 
       FIG. 4  is a cross-sectional elevation view of a check valve assembly constructed in accordance with embodiments of the invention; 
       FIGS. 5A and 5B  are views the rotating body of the check valve assembly of  FIG. 4 ; 
       FIGS. 6A and 6B  are views of the stationary body of the check valve assembly of  FIG. 4 ; 
       FIG. 7  is a cross-sectional elevation view of a check valve assembly constructed in accordance with embodiments of the invention; and 
       FIG. 8  is a cross-sectional plan view of the check valve assembly of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , a reciprocating compressor assembly  10  includes a compression chamber  12  having suction inlet  16  and discharge outlet  14 . Piston  18  moves into and out of compression chamber  12  Suction valve  22  is disposed within inlet  16  and controls the flow from fluid supply  28  into compression chamber  12 . Discharge valve  20  is disposed within outlet  14  and controls the flow from compression chamber  12  into fluid outlet  30 . As piston  18  moves out of compression chamber  12 , the pressure within the chamber decreases and suction valve  22  is opened allowing flow  24  to enter the chamber As piston  18  moves back into compression chamber  12 , the pressure within the chamber increases and discharge valve  20  is opened allowing pressurized flow to be expelled from the chamber. 
   Referring now to  FIGS. 2 and 3  a rotating valve assembly  200  is shown. Valve assembly  200  is installed within compressor  201  and comprises rotating body  202  and drive system  220 . Rotating body  202  is a cylindrical body forming flow chamber  204 . Windows  208  provide flow paths for gases to move between flow chamber  204  and compressor gas passages  206 . Non-contacting seals  210 , comprising labyrinth sealing surface  212  and babbitted surface  214 , on either side of windows  208  restrict the flow of gases between rotating body  202  and compressor  201 . Low contact force seal  216  also provides a circumferential seal between rotating body  202  and compressor  201  between seals  210  and windows  208 . Thus, rotating body  202  is sealed on all sides to ensure that the gas can only flow through windows  208 . 
   Rotating body  202  is rotatably connected to compressor  201  via shaft  218 . Rotation is enabled by drive assembly  220  including bearing  222 , motor coil  224 , magnet  226 , and electrical leads  228 . Rotating body  202  is supported by bearing  222 . Motor coil  224  is fixed to compressor  201  and remains stationary. Magnet  226  is fixed to rotating body  202  and causes the body to rotate in response to a current applied to coil  22  through leads  228 . This current can be adjusted to vary the speed of rotating body  202 , which is monitored by probe  230  (keyphaser). Plate  232  supports rotating body  202  and drive assembly  220  and is connected to compressor  201  via bolts  234 . Valve cap  236  covers plate  232  and provides a passageway for electric leads  228  and probe  230 . 
   Bearing  222  may be a journal thrust bearing or, in certain embodiments could be an antifriction roller type bearing, a single or double antifriction back-to-back ball bearing, or a hydrodynamic bearing, and/or a combination of the above bearings. In alternate embodiments, drive assembly  220  may comprise an induction motor or a DC motor as an alternative to the high speed motor with permanent magnet as shown. 
   As rotating body  202  rotates, windows  208  are intermittently in fluid communication with gas passages  206 . When window  208  is lined up with gas passage  206 , gas can pass through window  208  either into or out of flow chamber  204 . If being used as a suction valve, gas passes from gas passages  206  into flow chamber  204  as body  202  rotates. If being used as a discharge valve, gas passes from flow chamber  204  into gas passages  206  as body  202  rotates. When windows  208  are not in fluid communication with gas passages  206 , compressor  201  is either in the compression cycle or intake position. The speed of rotation of the rotating body  202  can be synchronized to the piston stroke such that windows  208  are in fluid communication with gas passages  206  as the compression cycle needs to discharge or pull in gas. 
   The compressor control system, or plant main control system, known as DCS, can be utilized to synchronize the alignment of the stationary window with the opening of the rotating body. Synchronization can be achieved by monitoring the piston stroke, which is directly and physically connected to the compressor main driver. As the piston reaches near its top dead center, the stationary and rotating widows will also align themselves. To positively verify this alignment, pressure sensor  239  can be located in the cylinder side of the valve chamber. When the pressure inside the chamber reaches the pressure limit set for the valve chamber, the controller may speed up or slow down the rotating valve body  202  via driver assembly  220  so that the windows line up. 
   The size of windows  208  and the rotating speed of body  202 , including any timing delays, can be selected based on the piston stroke and/or other compression cycles. Rotating body  202  may have one or more windows to allow the gas flow. The size and the shape of windows  208  may be selected based on the quantity, speed and thermodynamic properties of the gas (pressure, temperature, molecular weight, velocity etc). For example, window  208  could be a circular hole of any diameter or could also be a rectangular or any polygonal shape. The material of construction of the valve body could be any type of metal or composite materials which are suitable for the process gas usage. 
   The compressed gas flow through windows  208  is ensured by the arrangement of seals  210 ,  216  located between rotating body  202  and compressor  201 . Seals  210  are non-contacting seals where a close relationship is maintained between two surfaces but the surfaces do not actually contact. Seals  216  may be low-contact force seals where there is contact between the two surfaces but the contact force is very low. The use of non-contact and low contact force seals provide a system that provides very long seal life and very little friction-created drag on rotating body  202 . 
   One type of seal that may be used is a combination of conventional type labyrinth seals  210  with brush type seals  216 . Labyrinth seals  210  comprise a stationary, smooth soft surface (babbitted design)  214  and labyrinth teeth  212  integral with the rotating body  202 . This arrangement can also be reversed such that the stationary part would consist of the labyrinth teeth design and the rotating part being the soft and smooth babbitted surface. Brush type seal  216  may be used to ensure gas flows only through the windows  208 . 
   Additionally, other types of seals such as mechanical seals, dry gas seal, oil seal, brush seal, simple bushing seal, honey comb seal and other type of seals are also possible seals that could be utilized to seal and ensure that the gas flows through windows  208 . Also the size, quantity of gas flow and configuration of the seal will be selected based on the thermodynamic and velocity of the gas going through the valve body as in conventional seal selection and design criteria. In certain applications, the seals may be located on the inside of rotating body  202  and seal against a cylinder disposed inside the body. 
   Referring now to  FIGS. 4–6B  a rotating valve assembly  400  is shown. Valve assembly  400  is installed within compressor  401  and comprises valve assembly  402  and drive system  420 . Valve assembly  402  comprises stationary body  409  and rotating body  402 , which comprises shaft  403  and ported body  404 . Rotating ports  408  and stationary ports  411 , when aligned, provide a flow path for gases to move between chamber  413  and gas passages  406 . Non-contacting seals  410 , comprising labyrinth sealing surface  412  and babbitted surface  414 , on the circumference of ported body  404  restricts the flow of gases between rotating body  402  and compressor  401 . Low contact force seal  416  provides a seal between rotating body  402  and stationary body  409 . Thus, rotating body  402  is sealed on all sides to ensure that the gas can only flow through ports  408 ,  411 . 
   Rotating body  402  is rotatably connected to compressor  401  via shaft  418 . Rotation is enabled by drive assembly  420  including bearing  422 , motor coil  424 , magnet  426 , and electrical leads  428 . Rotating body  402  is supported by bearing  422 . Motor coil  424  is fixed to compressor  401  and remains stationary. Magnet  426  is fixed to rotating body  402  and causes the body to rotate in response to a current applied to coil  422  through leads  428 . This current can be adjusted to vary the speed of rotating body  402 , which is monitored by probe  430 . Plate  432  supports rotating body  402  and drive assembly  420  and is connected to compressor  401  via bolts  434 . Valve cap  436  covers plate  432  and provides a passageway for electric leads  428  and probe  430 . 
   Bearing  422  may be a journal thrust bearing or, in certain embodiments could be an antifriction roller type bearing, a single or double antifriction back-to-back ball bearing, or a hydrodynamic bearing, and/or a combination of the above bearings. In alternate embodiments, drive assembly  420  may comprise an induction motor or a DC motor as an alternative to the high speed motor with permanent magnet as shown. 
   As rotating body  402  rotates, ports  408  and  411  are intermittently aligned to provide fluid communication between chamber  413  and gas passages  406 . If being used as a suction valve, gas passes from gas passages  406  into chamber  413  and if being used as a discharge valve, gas passes from chamber  413  into gas passages  406 . When ports  408  and  411  are not aligned, compressor  401  is either in the compression cycle or intake cycle. The piston stroke is determined from the crank angle. The speed of rotation of the rotating body  402  can be synchronized to the piston stroke such that ports  408  and  411  are aligned as the compression cycle needs to discharge or pull in gas. 
   The size and arrangement of ports  408  and  411  and the rotating speed of body  402 , including any timing delays, can be selected based on the piston stroke and/or other compression cycles. The size and the shape of ports  408 ,  411  may be selected based on the quantity, speed and thermodynamic properties of the gas (pressure, temperature, molecular weight, velocity etc). For example, port  408  could be a circular hole of any diameter or could also be a rectangular or any polygonal shape. The material of construction of the valve body could be any type of metal or composite materials which are suitable for the process gas usage. 
   Referring now to  FIGS. 7 and 8 , another rotating valve assembly  700  is shown. Valve assembly  700  is installed within compressor  701  and comprises rotating valve body  702 . Rotating body  702  includes flow port  708  and shaft  718 . Flow port  708  provides a flow path for gases to move between chamber  704  and gas passage  706 . Non-contacting seals  710 , comprising labyrinth sealing surface  712  and babbitted surface  714 , on the circumference of body  702  restrict the flow of gases between rotating body  702  and compressor  701 . Low contact force seal  716  provides a seal between rotating body  702  and compressor  701 . Thus, rotating body  702  is sealed on all sides to ensure that the gas can only flow through port  708 . 
   Rotating body  702  is rotatably connected to compressor  701  via shaft  718 . Rotation is enabled by the same type of drive assembly which is shown in  FIG. 3  as drive assembly  220  and /or in  FIG. 4  which is shown as drive assembly  420 . As rotating body  702  rotates, port  708  is intermittently aligned with gas passage  706  and chamber  704  in order to provide fluid communication between chamber  704  and gas passage  706 . If being used as a suction valve, gas passes from gas passage  706  into chamber  704 , while if being used as a discharge valve, gas passes from chamber  704  into gas passage  706 . When port  708  is not aligned, compressor  701  is either in the compression cycle or in static position. The speed of rotation of the rotating body  702  can be synchronized to the piston stroke such that port  708  is aligned as the compression cycle needs to discharge or pull in gas. 
   The size and arrangement of port  708  and the rotating speed of body  702 , including any timing delays, can be selected based on the piston stroke and/or other compression cycles. The size and the shape of port  708  may be selected based on the gas flow quantity, speed and thermodynamic properties of the gas (pressure, temperature, molecular weight, velocity etc). For example, port  708  could be a circular passage of any diameter or could also be a rectangular or any polygonal shape. 
   The material of construction of the valve body could be any type of metal or composite materials which are suitable for the process gas usage. This example of the embodiment most generally will be utilized when the compression gas stream, such as H 2 S or others, is very corrosive and ordinarily very difficult and expensive to be handled by conventional valves. This configuration allows the corrosive gas stream to be channeled through the valve body without being in contact with any valve components other than the seals which can be protected by clean and non-corrosive buffer gas. 
   As described in the above embodiments, the rotating components require no physical contact with the stationary components, including the seal assemblies. Therefore, the wear and tear as experienced by other methodologies including existing conventional system have been eliminated. The rotating valve can also be arranged in any orientation and the sealing surface does not have to be perpendicular to the axis of rotation. Because of the flexibility in arrangement of components and orientation of the axis of rotation, many other configurations of the rotating valve are possible. For example, the axis of rotation may be disposed at any desired angle relative to the sealing surface. 
   All of the valve components, including the drive system, can be fully contained within the confinement of the valve pocket. Because no rotating components project outside of the valve pocket, no dynamic seals are required and the compression gas is fully contained within the pocket, protecting the environment from any contamination whatsoever. This isolation may also allow a clean buffer gas, compatible with process gas, to be used for the protection of the drive assembly to ensure long life for all the system components. 
   While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting by size, shape and/or directionality of the rotating body against the stationary body. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.