Patent Publication Number: US-7223080-B2

Title: Double-acting, high pressure cryogenic pump

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to high pressure cryogenic pumps and more particularly relates to a double-acting, reciprocating piston, high pressure (about 2,000 psi and greater) cryogenic fluid pump that provides venting of blow-by vapors between two sets of high pressure seals on a double-acting piston. 
   2. Background Information 
   The generation and accumulation of fluid vapors from blow-by leakage in high pressure cryogenic pumps is a significant problem unless the vapors are collected and condensed in cold low pressure liquid. This invention is directed to a method and apparatus for collecting, mixing, and condensing blow-by leakage vapors with cold suction liquid. 
   One type of double-acting, reciprocating, piston cryogenic fluid pumps is disclosed and described in U.S. Pat. No. 5,411,374 of A. Gram issued May 2, 1995. This patent describes a double-acting, reciprocating piston, cryogenic fluid pump mechanically coupled to a double-acting hydraulic piston motor. The double-acting, reciprocating piston, cryogenic fluid pump shown in the figures and described in the text does not contain any reference to a dual set of piston seals nor does it describe a venting provision relative to the seals. Another U.S. Pat. No. 3,456,595 of C. F. Gottzmann issued Jul. 22, 1969 discloses a double-acting, reciprocating, piston pump for low pressure pumping and metering cryogenic fluids.  FIG. 2  of this patent shows a double-action pumping cylinder having venting ports  28  in the working chamber. The venting system disclosed and described herein is to vent-off vapors formed during the suction stroke. The problem of venting “blow-by vapors” is not present in a low pressure pump. Another U.S. Pat. No. 3,181,473 of Duron, the inventor of the invention disclosed herein, issued May 4, 1965 and incorporated herein by reference describes improvements to a single-acting, reciprocating piston, high pressure, cryogenic fluid pump. A design feature disclosed and described in this patent traps and returns blow-by vapors to a cryogenic storage tank. 
   None of these patents teach or suggest an effective method for venting of blow-by vapors in double-acting pump. It would therefore be advantageous if a method could be conceived to handle this particular problem. 
   It is therefore one object of the invention to provide a sealing system as well as a venting system for a double-acting, high pressure reciprocating piston pump for pumping cryogenic fluids. 
   Another object of the present invention is to disclose a double-acting, high pressure reciprocating piston pump for cryogenic fluids that has a significantly reduced peak torque when compared with conventional single-acting pump of similar capacity and pressure rise. 
   Yet another object of the present invention is to provide a double-acting reciprocating piston pump that has smoother suction and discharge flows and less heat leak into the cryogenic fluid when compared with single-acting, reciprocating piston pump of similar capacity and pressure rise. 
   Still another object of the present invention is to disclose a double-acting, reciprocating piston, cryogenic fluid pump having a significantly improved suction performance due to the smoother inlet suction flow and less heat leak into the cryogenic fluid when compared with a single-acting, reciprocating piston pump of similar capacity and pressure rise. 
   Yet another object of the present invention is to disclose a multi-cylinder, double-acting, reciprocating piston, cryogenic fluid pump with improved venting of blow-by vapors. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The invention disclosed and described herein relates to the sealing system and accompanying blow-by venting system for double-acting, reciprocating piston, high pressure, cryogenic fluid pumps. Experience with single-acting reciprocating, high pressure, cryogenic fluid pumps has demonstrated a need to vent and recover blow-by vapors. Double-acting, high pressure, reciprocating piston cryogenic fluid pumps need a system for venting and recovering blow-by vapors also. 
   The double-acting reciprocating piston pump of the present invention disclosed herein has a unique combination equivalent to two in-line single-acting piston pumps each with a separate set of high pressure seals and a common venting system. 
   In one embodiment of the invention, the double-acting pump has a piston with two piston heads and two sets of seals on either side of a venting system. A venting passageway between the two sets of seals vents blow-by through a passageway that exits through the top of the piston rod or shaft. Thus as the piston reciprocates blow-by vapors are vented through the passageways in the piston head out through the central passageway in the piston shaft back to the source. 
   In a second embodiment of the invention, a pair of piston heads are formed on a piston shaft having spaced apart separate seals. The diameter of the piston shaft between the two piston heads is such that a manifold or passageway is formed for venting blow-by vapors. The blow-by vapors exit through passageways on either side of the pump cylinder housing. As the piston reciprocates, blow-by vapors are vented out through the passageways in the pump housing back to the source. 
   A double-acting, reciprocating piston, high pressure, cryogenic fluid pump has significant inherent advantages over conventional single-acting, reciprocating piston, high pressure, cryogenic fluid pumps. These advantages stem from the fact that each stroke of the double-acting piston is a pumping stroke. Thus there are two output strokes per turn of the crankshaft. Whereas a conventional, single-acting, single cylinder, cryogenic fluid pump has only a single output stroke per turn of its crankshaft. The suction inflow and discharge outflow of double-acting pumps are therefore nearly continuous. The suction inflow and discharge outflow for the single-acting pump are intermittent flows each requiring about one-half a turn of its crankshaft. 
   Also a double-acting pump having the same capacity as a single-acting pump is significantly smaller in physical size. This feature is very important for cryogenic fluid pumps because less liquid and less cool down time are required for system cool down, i.e., preparation for system startup. The nearly continuous flows to and from the double-acting pump allows a reduction in diameter of the suction and discharge piping. This factor may reduce heat leak into the cryogenic liquid. The smoother and reduced maximum rate of inflow to the double-acting pump reduces suction pipe fluid pressure drop due to decreased acceleration of the cryogenic fluid. Hence, decreased net positive suction pressure required for pump operation. The improved suction performance can eliminate the requirement for a boost pump and associated piping. 
   The peak torque required for double-acting pump operation is also about one-half that of a comparable output single-acting pump. Thus, the selection of the size of the drive motor and motor starting gear is correspondingly reduced. It should be noted that the inertia torque in high pressure pumping units is very small compared with the torque required for pumping. 
   Another advantage is that increased capacity can be obtained by using multi-cylinder, double-acting, reciprocating piston, cryogenic fluid pumps. By this it is meant that multiple, double-acting, reciprocating piston, cryogenic fluid pumps can be operated in parallel to increase capacity. 
   Summarizing, a double-acting, reciprocating piston, cryogenic fluid pump is essentially two, single-acting pumps cleverly packaged into a single cylinder machine. Although the following detailed description may contain many specifics, these should not be construed as limiting the scope of the invention but merely providing illustrations of the presently preferred embodiments of the invention. 
   The above and other objects, advantages, and novel features of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a double-acting, high pressure, cryogenic pump according to the invention. 
       FIG. 2  is a sectional view of an alternate embodiment of a double-acting, high pressure, cryogenic pump according to the invention. 
       FIG. 3  is a diagram in schematic form of multiple cylinder, double-acting, high pressure, cryogenic pumps mechanically coupled to a common driver. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   There are two embodiments of the double-acting, high pressure, cryogenic pump disclosed. In one embodiment, blow-by is vented through the piston rod while in the second embodiment, blow-by is vented through the pump cylinder housing. 
   Referring to  FIG. 1 , a cross sectional view of a double-acting, high pressure, cryogenic pump cold end  100  is illustrated. Double-acting piston  110  reciprocates in cylinder  112 . The drive system or mechanism that causes piston  110  to reciprocate (not shown) is connected to piston rod  114  as is well known in the art. This mechanism normally consist of a crankshaft, a connecting rod, and a crosshead with pin. Double-acting piston  110  is shown at about mid-stroke and moving toward the left as indicated by arrow  115  at the end of piston rod  114 . 
   Double-acting, high pressure, cryogenic pump  100  has a left side pump chamber  124  and a right side pump chamber  126 . Left side pump chamber  124  as illustrated is at discharge pressure and cryogenic fluid is being discharged via open discharge valve  120 . Pump fluid discharges from cold end  100  via discharge port  138 . At this time, right side pump chamber  126  is increasing in volume. Fluid is flowing into chamber  126  by suction via open suction valve  118 . Suction fluid is supplied from a storage tank (not shown) through suction pipe  136 . 
   A unique feature of the invention is double-acting piston  110  includes a pair of seals  128  adjacent left pump chamber  124  and  130  adjacent right pump chamber  126  on spaced apart piston heads  111  and  113 . Blow-by fluid that leaks past either of seals  128  and  130  flows axially and circumferentially along cylinder  112  through passageways  133  and  132  axially out of port  140  at the end of piston rod  114 . Thus, blow-by vapors and fluids exiting from port  140  mix and condense in source liquid inside insulated enclosure  134 . 
   The operation of the double-acting, high pressure, cryogenic pump  100  of  FIG. 1  is similar to the operation of conventional single-acting, high pressure, cryogenic pumps that are in successful application worldwide. One such single-acting, high pressure pump is disclosed and described in U.S. Pat. No. 3,181,473 issued May 4, 1965 to the same inventor as the invention herein and is incorporated by reference. The major difference is that double-acting piston  110  is split into a pair of piston heads  111  and  113  and has two sets of high pressure seals  128  and  130  and a blow-by venting system comprised of an axial passageway  132  and a second passageway  133  perpendicular to the axis of piston rod  114  communicating with the cylinder between seals  128  and  130  venting blow-by vapors and fluids through port  140 . Thus blow-by vapors and fluids exiting port  140  are recovered and mix and condense with the flow of suction fluid inside insulating enclosure  134  hence the condensed blow-by vapors cannot interfere with the normal operation of high pressure cryogenic pump. 
   An optional second embodiment of the double-acting, high pressure cryogenic pump is illustrated in  FIG. 2 . In this embodiment, double-acting, high pressure, cryogenic pump cold end  200  illustrated in cross section has a double-acting piston rod  214  having a double-acting piston  210  that reciprocates in cylinder  212 . As before, the mechanism, that causes piston  210  to reciprocate (not shown), is connected to piston rod  214 . The mechanism for reciprocating piston rod  214  consists of a crankshaft, a connecting rod, and a cross head with a pin well known in the art. As illustrated in  FIG. 2 , double-acting piston is comprised of a pair of separated piston heads  211  and  213  forming an annulus or passageway  232  between the piston heads that are approximately equal to the length of the stroke of piston rod  214 . 
   Double-acting piston  210  as illustrated in  FIG. 2  is at the right or upward end of its stroke and moving toward the left as indicated by arrow  215 . As illustrated, left side pump chamber  224  is at discharge pressure and cryogenic fluid is discharging via open discharge valve  220 . Pump fluid discharges from cryogenic pump cold end  200  via discharge port  238 . At this time, right side pump chamber  226  is increasing in volume. Cryogenic fluid is flowing into chamber  226  by suction via open suction valve  218 . Fluid is supplied by suction from the storage tank (not shown) through suction pipe  236 . As described previously, double-acting piston  210  has split piston heads  211  and  213  and two sets of seals,  228  at the left end and  230  at the right end each shown with three seals. Piston head  211  is annular and piston head  213  is butt ended. 
   A venting system for venting cryogenic fluid or vapors that creep or leak past seals  228  and  230  in piston heads  211  and  213  communicates with manifold or passageway  232  around piston rod  214 . Blow-by fluid and vapor that leaks past seals  228  and  230  flows into manifold  232  around piston rod  214  and is vented through passageways  240  and  241  on opposite sides of cylinder housing  212 . These exiting blow-by vapors and fluids mix and condense in suction source liquid inside insulated housing  234 . 
   The operation of the double-acting, high pressure, cryogenic fluid pump  200  of  FIG. 2  is similar to the operation of conventional single-acting, high pressure, cryogenic fluid pumps that are in operation world wide. The major difference is that double-acting piston  210  has two conventional sets of piston heads and conventional sets of high pressure cryogenic fluid seals,  228  and  230  (shown as three seals per set) forming an annulus or manifold  232  to vent blow-by fluids out through either or both passageways  240  and  241  in cylinder housing  212 . A pair of passageways  240  and  241  are shown however a single passageway would be sufficient. Blow-by vapors exit through passageways  240  and  241  and cannot interfere with the normal operation of high pressure, cryogenic fluid, piston seals  228  and  230 . 
   An application of the embodiments of either  FIG. 1  and  FIG. 2  is illustrated in the diagram in semi-schematic form of  FIG. 3 . In  FIG. 3 , an in-line, two cylinder, double-acting, reciprocating piston, cryogenic fluid pump  300  is comprised of a pair of cold ends  334  of multi-cylinder machine  300  that is like either of those illustrated in  FIG. 1  or  FIG. 2 . The respective double-acting piston  114  ( FIG. 1 ) or  214  ( FIG. 2 ) of each cold end  334  is mechanically coupled to a driver  350 . Power is input to drivers  350  via drive shaft  360 . Preferably the phase relationship of drivers  350  is about 90° for a two cylinder unit and about 120° for a three cylinder machine. Suction fluid is provided through inlets  336  and high pressure fluid exits through discharge ports  338 . 
   This invention is not to be limited by the embodiment shown in the drawings and described in the description which is given by way of example and not of limitation, but only in accordance with the scope of the appended claims.