Abstract:
A high pressure slurry plunger pump is described which provides a clean fluid buffer around the suction and discharge valves of the pump and in some cases in the vicinity of the plunger seal mechanism in order to displace erosive slurry material and thus extend the life of the pump and improve pump efficiency.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to the general field of slurry pumps, and more particularly to slurry pumps having improved designs to address problems common in slurry pumps. 
       BACKGROUND 
       [0002]    The petroleum, chemical, and cement industries, among others, often require the transport of slurries (solid rich liquids) as part of their process handling. Particularly when these slurry pump systems must operate at higher pressures a number of design and maintenance issues arise. Some example pumps that can handle slurries are—piston (e.g., triplex), plunger, centrifugal, diaphragm, displacement pot and progressing cavity (eg. Moyno®) types. They are driven by hydraulic (pressure) and mechanical (mostly with a power transmission rod connected to a crankshaft) means. Any of these means can be powered by a number of prime mover types (electric motor, gasoline engine, natural gas engine, etc . . . ). Only the plunger and piston positive displacement pumps and the batch displacement pot types can handle the higher-pressure needs of industry. 
         [0003]    The problem in pumping slurries is that slurries are very erosive of the pump internal parts, especially on valves, seats, plunger, cylinders, pump heads and wherever the slurry flow direction changes and/or the slurry velocity is high, e.g. when in turbulence. The high velocities and rapid flow direction changes in a centrifugal pump, plus their inherent inefficiencies, makes centrifugal type pumps not the first choice for such high-pressure slurry applications. Progressing cavity type pumps can handle the solids content but cannot easily achieve the higher pressures desired due to the elastomer materials in the stator or pump. 
         [0004]    The DIAjet, a batch displacement pot type by BHR, is currently available for high pressure slurry pumping. It utilizes pressurized clean fluid with a separate pump (of any type, triplex is most common) that is then pumped into a pressure pot that contains a pre-mixed batch of slurry which is then displaced and discharged from the pot. Production or continuous slurry pumping is difficult with this batch type system, since several pots are needed and they have to be alternately restocked with slurry and resealed for use. 
         [0005]    But problems exist in pumping slurries with a positive displacement plunger or piston pump. In addition to the high velocity erosive nature of slurries, especially when flow direction changes, valving is also a problem. As a valve (inlet or discharge of type ball, flute, flapper, or other) closes, the area remaining for flow decreases and the slurry velocity increases (if rate stays the same) which increases the erosive ability of the slurry. Also a hardened steel valve closing onto a hardened steel seat with solids in between makes sealing difficult and results in damaged parts and/or lower efficiencies. The interfering solid particles can be crushed, if they are not too hard, still causing damage to valves and seats. At higher pressures and harder solid particles such interference becomes very damaging. Ceramic valves in these conditions could shatter quickly. Also, rapid velocity or flow pattern changes, as through valves seats, increases the rapid erosion wear of internal pump parts. 
         [0006]    Another problem in all slurry pumps is when fluid motion stops and the solids fall out of the carrier fluid. Cleaning out such solids out of the pump is a problem and requires considerable work. If the solid particles would settle and congregate near the fluid end, it would allow easier cleanout of the pump and resumption of pumping. 
         [0007]    A number of investigators have tried to address the problems of abrasive materials plugging or eroding cylinders, plungers, pistons and seals. Examples of this can be found in U.S. Pat. No. 3,104,619 to Swarthout, U.S. Pat. No. 4,023,469 to Miller, U.S. Pat. No. 4,157,057 to Bailey, U.S. Pat. Nos. 4,691,620, 4,598,630, and 4,476,771 to Kao. These investigators have developed a number of variations of flushing methods for rings and seals to keep them as free as possible of abrasive materials for longer effective operating lives. 
         [0008]    U.S. Pat. No. 7,118,349 (Oglesby), issued to the inventor of this application, addressed the issues that are especially pertinent to a piston pump and defined a pump assembly and a method for maintaining clean fluids in the vicinity of suction and discharge valves of piston pumps. 
         [0009]    As mentioned in a previous paragraph a plunger type of pump can also handle the higher-pressure needs of industry. A plunger type of pump can also face the problems described above related to the highly erosive nature of slurries. In a plunger pump, a volume of fluid in the cylinder is displaced by the plunger movement into the cylinder that pressurizes and expels the fluid out the discharge valve. The plunger is stroked axially through the cylinder to provide fluid inlet (as the plunger is withdrawn) and exit (as the plunger is re inserted). Unlike the piston pump, the plunger does not contact the cylinder wall at any time. A non-moving seal mechanism is connected to the cylinder at the base of the plunger and contains pressure and fluids by rings, rubber elements, ceramic elements and other packing materials. The plunger is driven by any number of means- crankshaft, power rod, cam and those are powered, in turn, by any number of prime movers. The cylinder can be made of any number of metals to contain the pressure and fluids. The plunger can be any number of metals or ceramics. The head and valves can be made of any number of metals and ceramics. 
         [0010]    There is a need then for significant improvements in the methods and apparatus for plunger type pumps used in slurry service, particularly in addressing the problems of abrasive materials and how to keep the abrasive materials away from the seal mechanism, cylinder, plungers, suction and discharge valves of the slurry plunger pump for improved operation and longer operating life. 
       SUMMARY 
       [0011]    The needs discussed above are addressed by the instant invention. 
         [0012]    One aspect of the instant invention is a slurry pump assembly including at least: an inlet chamber connected to a slurry supply, the slurry comprised of a solid material and a slurry carrier fluid; a suction valve, downstream of the inlet chamber, for admitting fluids and solid materials into a cylinder; a plunger in the cylinder for providing fluid movement and pressure; a means for driving the plunger through a suction and discharge stroke cycle; a seal mechanism attached to the cylinder, contacting the plunger; a discharge valve connected to the cylinder for discharging pressurized materials from the cylinder; and a clean fluid valve, connected to a clean fluid supply, configured to supply clean fluid into the immediate vicinity of the suction valve and the discharge valve. 
         [0013]    Another aspect of the invention is a slurry pump assembly including at least: an inlet chamber connected to a slurry supply, the slurry comprised of a solid material and a slurry carrier fluid; a suction valve, downstream of the inlet chamber, for admitting fluids and solid materials into a cylinder; a plunger in the cylinder for providing fluid movement and pressure; a means for driving the plunger through a suction and discharge stroke cycle; a seal mechanism attached to the cylinder, contacting the plunger; a discharge valve connected to the cylinder for discharging pressurized materials from the cylinder; and a clean fluid valve connected to a clean fluid supply configured to provide clean fluid into the cylinder at or near the seal mechanism. 
         [0014]    Another aspect of the instant invention is a method to displace slurry material and place clean fluid across the suction and discharge valves, plunger, cylinder and seal mechanism during the stroke cycles of a slurry plunger pump assembly including at least the steps of: injecting a specific volume of a clean fluid into the immediate vicinity of the suction and discharge valves during any portion of a suction stroke cycle; and flowing a slurry consisting of a solid material and a slurry carrier fluid through the suction valve and into the cylinder during any portion of the suction stroke cycle. 
         [0015]    Another aspect of the instant invention is a method to displace slurry material and place clean fluid across the suction and discharge valves, plunger, cylinder and seal mechanism during the stroke cycles of a slurry plunger pump assembly including at least the steps of: injecting a specific volume of a clean fluid into the immediate vicinity of the seal mechanism during any portion of a suction stroke cycle; and flowing a slurry consisting of a solid material and a slurry carrier fluid through the suction valve and into the cylinder during any portion of the suction stroke cycle. 
         [0016]    To insure that a clear and complete explanation is given to enable a person of ordinary skill in the art to practice the invention, specific examples will be given involving applying the invention to a specific configuration of a high pressure slurry pump. It should be understood though that the inventive concept could apply to various modifications of such high pressure slurry pump systems and the specific examples are not intended to limit the inventive concept to the example application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic of a configuration of the high-pressure slurry pump at an early suction stroke stage. 
           [0018]      FIG. 2  is a further schematic of a configuration of the high-pressure slurry pump near the middle of the suction stroke. 
           [0019]      FIG. 3  is a further schematic of a configuration of the high-pressure slurry pump near the end of the suction stroke. 
           [0020]      FIG. 4  is an alternate configuration of the high pressure slurry pump at an early suction stroke stage. 
           [0021]      FIG. 5  is depiction of an internal helical pattern of the cylinder and plunger. 
           [0022]      FIG. 6  is a longitudinal depiction of an internal helical pattern of the cylinder 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  is a schematic of a configuration of a high-pressure slurry pump of the plunger type, shown generally as the numeral  10 . Slurry material  16  is composed of a solid material and a slurry carrier fluid. The slurry carrier fluid could include a water-based fluid, an oil based fluid, a liquefied gas at pumping conditions, a solvent, an acid, or a base. Other chemicals may be added to viscosify or form a gel to help carry the solids or for corrosion inhibition or friction reduction or a chemical reaction (eg. a two component epoxy). A source of slurry material  16  to be pressurized and pumped is in communication with pump or slurry head  12  through valve  20 . Valve  20  can be a number of types of valves. A preferred type is a spring activated flapper type valve although other valves can be useful. The pump slurry head, shown generally as the numeral  12 , incorporates an inlet chamber  24 , a suction valve  28 , a discharge valve  32 , and a clean fluid valve  40 , which controls the flow of a supply of clean fluid  36  through an entry point  44 . The clean fluid is provided at a higher pressure than that of the slurry material  16  during the suction stroke. Clean fluid valve  40  might be an automated control valve responsive to signals from certain sensors, or could be, for example, a check valve in combination with a choke or pipe restriction to regulate overall flow rate into the system during the suction stroke. Inlet chamber  24  may be an actual chamber although all that is required is a small region immediately ahead of suction valve  28 , where either slurry material and/or clean fluid are introduced. Clean fluid entry point  44  can be in a variety of locations near to it&#39;s shown position but is generally in the immediate vicinity of the fluid end of the slurry pump that includes inlet chamber  24  and the suction  28  and discharge  32  valves. As used in this application the pump head  12  end of the pump that includes the suction  28  and discharge  32  valves is referred to as the fluid end. 
         [0024]    Connected at pump head  12  is an elongated cylinder  14  providing a path for a driving plunger  48 , which moves in a reciprocating fashion to provide the pressurizing and pumping action of the slurry material. 
         [0025]    Plunger  48  can be driven by an external power rod, as shown by rod  52 , or by crankshafts, cams, or other plungers or pistons. As used in this application this end of the pump is referred to as the power end. Any type of prime mover can ultimately provide the driving force to reciprocate the plunger. Any of these can be considered as a means for reciprocating said plunger  48  through a suction and discharge stroke cycle. A seal mechanism  68  is provided between plunger  48  and cylinder  14  at the base of plunger  48  to contain the pressure and fluids. It is connected to cylinder  14 , but contacts plunger  48  during its axial movement. It can have metal or ceramic sweeps or seal rings, and other contact packing for sealing with cylinder  14  and moveable plunger  48 . 
         [0026]    Pump action utilizing the clean flush of the instant invention is shown sequentially in  FIGS. 1 ,  2 , and  3  and described as follows: A specific volume (ranging from zero to full capacity of the pump) of clean fluid is injected, via clean fluid valve  40  and channels  44  into the vicinity of suction valve  28  at any part of the suction stroke. Clean fluid valve  40  might be an automated control valve responsive to signals from certain sensors, or could be, for example, a check valve in combination with a choke or pipe restriction to regulate overall flow rate into the system during the suction stroke.  FIG. 1  exhibits the beginning of the suction stroke as the plunger  48  withdraws from cylinder  14 , fluids are drawn into the cylinder  14 . When clean fluid  36  is injected into inlet chamber  24 , spring activated flapper valve  20  closes. This allows clean fluid to be placed at the suction valve  28  when it opens. As the suction stroke cycle continues, a set volume (from zero to full pump capacity) of clean fluid injection continues and is placed in the cylinder at the plunger&#39;s ‘slurry side’ face  56  to provide a buffer of clean fluid to keep it clear of solids on the return stroke that would impede the plunger&#39;s  48  movement or damage the plunger  48 , cylinder  14  or seal mechanism  68 . Clean fluid injection stops at a set plunger position or clean fluid volume. Optionally, as seen in these figures there can also be a flushing of slurry materials from the seal mechanism  68  area via clean fluid valve  66  and check valve  65  and these can be used simultaneously with the flushing on the fluid end of the pump from clean fluid valve  40 . Clean fluid valve  66  might be an automated control valve responsive to signals from certain sensors, or could be, for example, a check valve in combination with a choke or pipe restriction to regulate overall flow rate into the system during the suction stroke. 
         [0027]    As another embodiment during the suction stroke, clean fluid valve  66  opens to allow clean fluid to flow through an optional high pressure check valve  65  and into cylinder  14  at or near the seal mechanism  68 . This provides a clean fluid buffer to the seal mechanism  68 , plunger  48  and cylinder  14  from slurry solids. Again clean fluid valve  66  might be an automated control valve responsive to signals from certain sensors, or could be, for example, a check valve in combination with a choke or pipe restriction to regulate overall flow rate into the system during the suction stroke. 
         [0028]    As the suction stroke cycle continues, slurry now enters inlet chamber  24 , through open slurry valve  20 , through suction valve  28  and into cylinder  14 .  FIG. 2  shows a later part of the suction stroke cycle where slurry material from  16  is now flowing through open spring activated flapper slurry valve  20 , through suction valve  28  and into cylinder  14 . The initial volume of clean fluid is shown still protecting the front face  56  of plunger  48 , cylinder  14  and seal mechanism  68  and clean fluid valve  66  is still open at this time. 
         [0029]      FIG. 3  illustrates the final part of the suction stroke where clean fluid valve  40  again opens and flapper slurry valve  20  closes, allowing clean fluid to displace slurry material through suction valve  28 , clearing that valve and the pump head end  12  of slurry materials. This clean fluid allows suction valve  28  to close on clean fluid and it allows for the discharge valve  32  to open surrounded by clean fluid in the pump or slurry head  12 . The location in the vicinity of suction valve  28  now also contains clean fluids to reside around the suction valve  28  while it is closed. 
         [0030]    As the discharge cycle (not shown) begins, suction valve  28  closes due to pressure and plunger  48  advances into the cylinder  14  which discharges the final stage volume of pressurized clean fluid, followed by all of the slurry and finally the initial clean fluid flush volumes through discharge valve  32 . At the end of the discharge cycle, the clean fluid injected initially via valves  40  and  66  still buffers the plunger face  56 , plunger  48 , cylinder  14  and seal mechanism  68  and surrounds the discharge valve  32  during its closing action with sufficient clean fluid into the discharge line. 
         [0031]    An alternative embodiment of using the clean fluid injection technique is shown in  FIG. 4 . In this embodiment clean fluid is provided from line  71  through clean fluid valve  70  and check valve  69  to also inject some clean fluid at any portion of the suction stroke to provide clean fluids traveling through suction valve  28  and discharge valve  32  during the maximum flow periods seen in crankshaft powered pumps. As mentioned earlier, the clean fluid entry point can be in a variety of locations near to it&#39;s shown position but is generally in the immediate vicinity of the fluid end of the slurry pump that includes the suction  28  and discharge  32  valves. This embodiment can allow clean fluid flushing at the beginning and end of the suction stroke as well. 
         [0032]    In any flushing action and period, the volumes used can be from zero to full pump capacity. Flush timing and rate can be controlled to provide a steady slurry density output or maximize slurry output and density or to flush the pump for shut-down. 
         [0033]    An embodiment showing the use of automated control valves accompanied by sensors is shown in  FIGS. 1 ,  2 ,  3 ,and  4 , where the entry of clean fluid to displace the slurry mixture is controlled by valves  40 ,  66 , and/or  70 . These clean fluid automated control valves  40 ,  66 , and/or  70  operate based on plunger position in cylinder  14  which can be detected by any number of methods. In one embodiment of determining plunger position, sensors  64  monitor the position of plunger  48  in cylinder  14  by a transmitter  60  in plunger  48 . With valve  40  in  FIG. 1  open, the clean fluid flows through channel  44 , into inlet chamber  24  ahead of suction valve  28  and then into cylinder  14  at specified points in the stroke cycle. Valves  28  &amp;  32  are typically flute, ball or flapper types, but can be of any type. Control valve  66  opens in response to sensors  64  and flows clean fluids through high pressure check valve  65  into cylinder  14  at or near the seal mechanism  68 . 
         [0034]    The control, timing (on/off) and injected volume (length of time on), of this clean fluid injection/replacement is by one or more transmitters  60  on the plunger  48  and sensors  64  on the cylinder  14 . In the shown position sensing method, a transmitter  60 , such as a magnetic or radioactive source, is mounted in/on the plunger  48  (or crankshaft or power rod) and sensors  64  to identify and react to the plunger&#39;s  48  positions are mounted/installed on the outer wall of the cylinder  14 . These sensors/instruments  64 , which could be any number of types such  3 s magnetic, mass, radioactive, or density sensors, then signal the clean fluid valves to open and/or close. As an alternative the sensors  64  may be optical sensors that may or may not require transmitters  60 . 
         [0035]    An alternate embodiment (not shown) to control clean fluid entry is for position sensors/instruments installed on a connecting rod or on the crankshaft or cam, if these exist on a given model that relates plunger  48  position within the cylinder  14 . As an additional embodiment of the controlled addition of clean fluid, control valves  40 ,  66  and/or  70  could be controlled by sensing the crankshaft&#39;s position described above but as mechanical rotary valves operating directly off the crankshaft to deliver prescribed amounts of clean fluid during the stroke cycles. 
         [0036]    Slurry valve  20 , upstream of inlet chamber  24  is optional and only helps separate slurry from the clean fluid buffer, prevent dilution of the slurry circulation system and prevents buildup of settled slurry solids onto suction valve  28 . 
         [0037]    As an alternate embodiment, shown in  FIG. 4 , clean fluid valve  70  could inject clean fluids directly into pump head  12 , downstream of the suction valve  28 , or cylinder  14 . This would provide a buffering clean fluid into the immediate vicinity of both the suction valve  28  and the discharge valve  32  and seal mechanism  68  but would require utilizing a high-pressure check valve if the clean fluid valve is not rated for the operating pressure. 
         [0038]    In  FIG. 1  the internal surface of cylinder  14  is shown as smooth. In  FIG. 5 , to aid in keeping the slurry mixed during the stroke cycle, an optional internal surface of the cylinder  14  is shown in cross section that has a helical (single, double or other patterns) spiral path. For this option, a plunger  48  with an outer surface and a seal mechanism  68  with an inner pattern that both match the cylinder  14  pattern is required for maximum displacement efficiency. However, it is not required that plunger  48  pattern matches cylinder  14  as long as clearance is maintained. Plunger  48  with a matching spiral pattern must now rotate in cylinder  14  as it strokes. 
         [0039]      FIG. 6  is a longitudinal view, shown generally by the numeral  200 , of the embodiment of  FIG. 5 . The cylinder  14  in this view shows an internal surface with a helical spiral path  50 . Plunger  48  has an outer surface that matches the cylinder pattern. The resulting rotation of plunger  48  helps keep the slurry mixed during the stroke cycle, especially if paddles (not shown) are attached to plunger&#39;s slurry face  56 . 
         [0040]    Since some overlap of the protective nature of each proposed flushing step occurs, the clean fluid volumes in each step can range from zero to the full rate capabilities of the pump. Judicious allocation of clean fluids in the various steps can allow for steady slurry density expelled from the pump or maximizing slurry output regardless of density or flushing the pump in preparation for shut-down. 
         [0041]    The clean fluids can be any water (salt, fresh, brine), oil (mineral, diesel, hydrocarbon or other), liquefied gas, acid, base, solvent, or epoxy that is compatible with the carrier fluid. A viscous clean fluid stream that possesses a viscosity greater than the viscosity of the slurry carrier fluid would make the overall flushing performance more efficient by better clearing, protecting and suspending of solids out of the way of the valves  28  and  32 , seal mechanism  68  and plunger  48  and cylinder  14 . Less clean fluid volume is needed of a viscous clean fluid than a thinner clean fluid resulting in more slurry pumped and less wear of pump components. 
         [0042]    Pumping carrier fluids can be water (fresh, salt, brine, or only water base) or oils (mineral, diesel, hydrocarbons), a liquefied gas at pumping conditions, a solvent, an acid, or a base and with various chemicals added for viscosifiers, gelling agents, corrosion inhibitors, friction reducers, chemical catalysts or epoxies. 
         [0043]    By maintaining the pump assembly&#39;s pressure above certain critical pressures a number of useful gases can be maintained in their liquid fluid state and used as the slurry carrier fluid or the clean liquid. Examples of such desired phase changing fluids are carbon dioxide, halogenoalkanes (including chloroalkanes, fluoroalkanes, chloromethane, chlorofluoroalkanes, bromofluoroalkanes, hydrochloroflurocarbons), oxygen, nitrogen, chlorine, fluorine, noble gases (including helium, neon, argon), hydrocarbons (including methane and propane), ammonia, sulfur dioxide or other similar phase behaving gases/fluids. In many cases compatible gelling agents or viscosifiers would be required to suspend the slurry solids. 
         [0044]    As an example, one desirable example could be the use of carbon dioxide —CO 2 — as the carrier or clean fluid if the full pump assembly system is held above the critical pressure of CO 2 . The downstream system pressure must be pre-charged/pressurized to and maintained above the critical pressure before switching to the liquid CO 2 , or it will flash to gas in the pump, which is undesirable due to gas lock and solids settling in the pump. Pre-charging the pump and exit line to above the critical pressure entails pumping a non-volatile fluid ahead of the CO 2  until the pressure is acceptable or the use of a backpressure valve positioned downstream of the pump&#39;s discharge valve. Use of liquid CO 2  for the slurry carrier fluid and/or the clean flush/buffer fluid would allow for a completely dry and non-combustible abrasive jetting system. Use of other flush fluids, such as water or alcohols and similar products, is also possible with CO 2 . 
         [0045]    Another aspect of the instant invention that can be used for both piston and plunger pumps is the positioning of the cylinder so that the fluid slurry (suction and discharge) end is below the power end of the cylinder at an angle greater than the ‘angle of repose’ of the slurry&#39;s solid particles that would form if flow stopped. The ‘angle of repose’ of solid granular particles is an engineering term that is related to the solid particle&#39;s shape, density, surface area, and coefficient of friction and is that maximum angle that will form by the settling of the solid particles. This angle is normally between 30 to 50 degrees off horizontal. By pre-positioning the slurry pump cylinder to some angle greater than 30 degrees off horizontal, with the fluid end lower than the power end, most solid particles that settle will move toward the fluid end in the event of an emergency shutdown, allowing for easier cleaning and operation restarting. 
         [0046]    Multiple pumps in coordination (electronic, mechanical or connecting rod) are required for continuous slurry pumping, to provide a more uniform slurry density, and/or to increase the overall pumping rate over a given design. Although not shown, two or more slurry pumps of the design of the instant invention can be connected with a common means to drive both plungers to allow continuous, non-interrupted slurry pumping. An example of such combination would be triplex (3 pump assemblies) pumps utilizing a common crankshaft and prime mover. 
         [0047]    In addition to the embodiments of this invention illustrated in the accompanying drawings and described above, it will be evident to those skilled in the art that changes and modifications may be made therein without departing from the essence of this invention. All such modifications or variations are believed to be within the sphere and scope of the invention as defined by the claims appended hereto.