SLURRY PRESSURIZATION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application is a non-provisional application of provisional application 62/457,447, filed February 10, 2017, the disclosure of which is incorporated by reference herein. This application also claims priority to US Application 15/888, 133 filed February 5, 2018, US Application 15/888, 140 filed February 5, 2018 and US Application 15/888, 154 filed February 5, 2018.

TECHNICAL FIELD

[0002] The present disclosure relates generally to a slurry injection system, and, more specifically, to a method and system for using at least a pair of tanks to enable a continuous injection process. BACKGROUND

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Pumping of process fluids are used in many industries Process fluids may be pumped with various types of pumps such as centrifugal, positive displacement or use of a pressurized drive fluid acting upon the process fluid. A slurry is one type of process fluid used in a process. Slurries are typically abrasive in nature. Slurry pumps are used in many industries to provide the slurry into the process. Sand injection for hydraulic fracturing (fracking), high pressure coal slurry pipelines, mining, mineral processing, aggregate processing, and power generation all use slurry pumps. All of these industries are extremely cost competitive. A slurry pump must be reliable and durable to reduce the amount of down time for the various processes.

[0005] Hydraulic fracturing of gas and oil bearing formations requires high pressures typically up to 15,000 psi (103421 kPa) with flow rates up to 500 gallons per minute (1892 liters per minute). The total flow rate using multiple pumps may exceed 5,000 gallons per minute (18927 liters per minute).

[0006] Slurry pumps are subject to severe wear because of the abrasive nature of the slurry. Typically, slurry pumps display poor reliability, and therefore must be repaired or replaced often. This increases the overall process costs. It is desirable to reduce the overall process costs and increase the reliability of a slurry pump.

[0007] Other components of the slurry injection system also have weaknesses due to the abrasive slurries travelling therethrough. Check valves, rapid changes in pressure, erosion or "wire drawing" caused by high velocity fluid and pipe joints themselves all are subject to failure. Further, pressure vessels are used and if a large number of penetrations in the tanks are used, those places are also subject to cracking failure.

SUMMARY

[0008] The present disclosure is directed to a method and system that allows abrasive slurries to be injected into a very high-pressure process stream with minimal wear on the system components. The system provides high reliability due to the reduced amount of wear.

[0009] In one aspect of the disclosure, a slurry injection system comprises a low pressure clear fluid manifold, a high pressure clear fluid manifold and a plurality of clear fluid pumps receiving clear fluid from the low pressure manifold. The plurality of clear fluid pumps pressurize the clear fluid into high pressure clear fluid and communicates the high pressure clear fluid into the high pressure clear fluid manifold. The system further includes a blender unit having low pressure slurry therein and a mixer in fluid communication with the high pressure clear fluid manifold through a first valve. A slurry pressurizer is in fluid communication with the high pressure clear fluid manifold through a second valve, the mixer, the blender unit and the low pressure clear fluid manifold. The slurry pressurizer forms high pressure slurry by pressurizing the low pressure slurry from the blender unit using high pressure clear fluid from the high pressure clear fluid manifold. The slurry pressurizer communicates high pressure slurry to the mixer and communicating low pressure fluid to the low pressure clear fluid manifold. The mixer mixes the high pressure slurry and clear fluid from the first valve to form a mixture that is communicated to an injection site.

[0010] In another aspect of the disclosure, a method of operating a slurry injection system comprising a low pressure clear fluid manifold, a high pressure clear fluid manifold, a plurality of clear fluid pumps, a blender unit, a mixer, and a slurry pressurizer comprises receiving clear fluid from the low pressure clear fluid manifold at the plurality of clear fluid pumps, pressurizing the clear fluid into high pressure clear fluid at the plurality of clear fluid pumps, communicating the high pressure clear fluid into the high pressure clear fluid manifold from the plurality of clear fluid pumps, communicating high pressure clear fluid from the high pressure clear fluid manifold to the mixer through a first valve, communicating the high pressure clear fluid from the high pressure clear fluid manifold to the slurry pressurizer through a second valve, pressurizing, by the slurry pressurizer, low pressure slurry from the blender unit using high pressure clear fluid from the high pressure clear fluid manifold to form high pressure slurry, communicating low pressure fluid from the slurry pressurizer to the low pressure clear fluid manifold, blending, at a mixer, the high pressure slurry with high pressure clear fluid from the second valve to form a slurry mixture, and communicating the mixture to an injection site.

[001 1 ] In another aspect of the disclosure, a system for injecting slurry from a slurry source into a slurry injection site comprises a first elongated tank comprising a first end having a first volume and a second end having a second volume, said first volume separated from the second volume, a first pipe having a first end external to the first elongated tank receiving clear fluid and a second end coupled to the first volume and a plurality of slurry valves fluidically coupled to the first elongated tank. The plurality of slurry valves have a first state communicating high pressure slurry from the second volume to the slurry injection site and a second state communicating low pressure slurry into the second volume. A plurality of clear fluid valves are fluidically coupled to the first elongated tank and communicate high pressure clear fluid to the first volume in the first state and communicate low pressure clear fluid from the first volume in the second state.

[0012] In yet another aspect of the disclosure, a method of injecting slurry at a slurry injection site using a slurry injection system having a first elongated tank having a first volume and a second volume comprises using a plurality of slurry valves fluidically coupled to the first elongated tank. The method further comprises in a first state, communicating high pressure slurry from the second volume to the slurry injection site and in a second state, communicating low pressure slurry to the second volume. The method further comprises using a plurality of clear fluid valves fluidically coupled to the first elongated tank, in a first state, communicating high pressure clear fluid to the first volume, and, in a second state, communicating low pressure clear fluid from the first volume.

[0013] In yet another aspect of the disclosure, a system for injecting slurry from a slurry source into a slurry injection site includes a first elongated tank comprising a first end having a first volume and a second end having a second volume, said first volume separated from the second volume. The system further includes a first pipe having a first end external to the first elongated tank receiving clear fluid and a second end coupled to the first volume. The system further includes a second elongated tank comprising a first end having a third volume and a second end having a fourth volume, said third volume separated from the fourth volume. The second elongated tank has a second pipe having a first end external to the second elongated tank that receives clear fluid and a second end within the third volume. A plurality of slurry valves fluidically are coupled the first elongated tank and the second elongated tank. The plurality of slurry valves have a first state communicating high pressure slurry from the second volume to the slurry injection site and communicating low pressure slurry to the fourth volume and a second state communicating low pressure slurry to the second volume and high pressure slurry from the fourth volume to the slurry injection site. A plurality of clear fluid valves are fluidically coupled to the first elongated tank and the second elongated tank and communicate high pressure clear fluid to the first volume and communicate low pressure clear fluid from the third volume in a first state and communicating low pressure clear fluid to the first volume and high pressure clear fluid to the third volume in a second state.

[0014] In a further aspect of the disclosure, a method of injecting slurry at a slurry injection site using a slurry injection system having a first elongated tank having a first volume and a second volume and a second elongated tank having a third volume and a fourth volume comprising using a plurality of slurry valves fluidically coupled to the first elongated tank and the second elongated tank, in a first state, communicating high pressure slurry from the second volume to the slurry injection site, and communicating low pressure slurry to the fourth volume. In a second state, communicating low pressure slurry to the second volume, and communicating high pressure slurry from the fourth volume to the slurry injection site. Using a plurality of clear fluid valves fluidically coupled to the first elongated tank and the second elongated tank, in a first state, communicating high pressure clear fluid to the first volume, and communicating low pressure clear fluid from the third volume in a first state and, in a second state, communicating low pressure clear fluid to the first volume, and communicating high pressure clear fluid to the third volume.

[0015] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0017] Figure 1 A is a schematic view of a slurry injection system according to a first example of the present disclosure.

[0018] Figure 1 B is a schematic view of a slurry injection system according to a second example of the present disclosure.

[0019] Figure 1 C is a side view of a horizontally disposed tank for use in the slurry injection system.

[0020] Figure 1 D is a side view of an alternative configuration of a tank disposed horizontally.

[0021 ] Figure 1 E is a cross-sectional view of the tank of Figure 1 D.

[0022] Figure 1 F is an alternative cross-sectional view of the tank of

Figure 1 D.

[0023] Figure 1 G is a schematic view of a slurry injection system according to a third example of the present disclosure.

[0024] Figure 1 H is a cross-sectional view of a piston formed according to the example of Figure 1 G.

[0025] Figure 1 1 is a schematic of a first example of a one tank system with high pressure clear fluid depressurization.

[0026] Figure 1 J is a schematic of a second example of a one tank system without high pressure clear fluid depressurization.

[0027] Figure 2A is a cross-section of an exemplary three-way valve in a first position.

[0028] Figure 2B is a cross-section of the exemplary three-way valve in a second position.

[0029] Figure 3A is a second example of an exemplary three-way valve in a first position.

[0030] Figure 3B is a second example of the exemplary three-way valve in a second position.

[0031 ] Figure 3C is a cross-section of a first example of a two-way switch.

[0032] Figure 3D is a cross-section of a second example of two two-way switches having two housings and a common actuator in a first position.

[0033] Figure 3E is a cross-section of the second example of the two two- way switches of FIG 3D in a second position. [0034] Figure 3F is a cross-section of a third example of a two-way switch.

[0035] Figure 3G is a cross-section of a fourth example of two two-way switches having two housings with a common actuator in a first position.

[0036] Figure 3H is a cross-section of a fifth example of the two-way switches of FIG 3G in a second position.

[0037] Figure 4A is a first example of a table for the various valve settings used during operation of the example of Figure 1 A.

[0038] Figure 4B is a second example of a table for the various valve settings used during the operation of the example illustrated in Figure 1 B.

[0039] Figure 4C is a third example of a table for the various valve settings corresponding to FIG 1 E.

[0040] Figure 5 is a flowchart for a first example of a method for operating the system.

[0041 ] Figure 6 is a flowchart of a method for switching states between a first tank and a second tank injection slurry.

[0042] Figure 7A is a timing chart of an injection system for a multiple unit slurry injection system with a dwell time.

[0043] Figure 7B is a timing chart of the injection system for a multiple unit slurry injection system with no dwell time.

[0044] Figure 8A is a schematic of a slurry injection system disposed on trailers.

[0045] Figure 8B is an enlarged cross-sectional view of the static mixer of

FIG. 8A.

[0046] Figure 9 is a flowchart of a method for operating the system of Figure 8.

DETAILED DESCRIPTION

[0047] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. The use of the words "low" and "high" are used relative to the pressures suitable for use in fracking. "Low" pressure is suitable for movement of fluids into or out of pipes. "High" pressure is on the order suitable for fracking which is typically thousands of pounds per square inch.

[0048] A slurry injection system 10 is illustrated for injecting slurry into a high pressure injection site 12. The injection system 10 may be used alone or in a multi- unit injection system such as the injection system unit 10A illustrated in fluid communication with the injection site 12. The injection systems 10, 10A may be operated using a common controller 20 such as a programmable logic controller (PLC). The controller 20 may be used to control the plurality of valves within the injection system 10 and the injection system 10A based on feedback from sensors such as flow rate sensors 22, 24. The flow rate sensors 22, 24 generate a first flow rate signal and a second flow rate signal.

[0049] The injection system 10 is used for injecting slurry from a slurry source such as a slurry tank 30 using a slurry circulation pump 32. The slurry, under low pressure from the circulation pump 32, is communicated to a first tank 40A and a second tank 40B through a low pressure slurry inlet pipe 34. As set forth below, the low pressure slurry is communicated to one tank at a time.

[0050] The first tank 40A and the second tank 40B may be cylindrical or elongated in shape and disposed in a vertical or any angle above horizontal manner as is illustrated. As will also be described below, it may be possible that the tanks may be positioned in a horizontal position. The tanks 40A, 40B have respective vertical longitudinal axes 42A, 42B, respectively. The tanks 40A, 40B each have a respective end cap 44A, 44B. The tanks 40A, 40B have respective first ends 46A, 46B and second ends 48A, 48B. The first end 46A of the first tank 40A has a first volume 50 of clear fluid and the second end 48A of the first tank 40A has a second volume 52 of slurry. The second tank 40B has a third volume 54 of clear fluid at the second end 46B and a fourth volume 56 of slurry at the second end 48B. The volumes 50, 52, 54 and 56 vary during the process.

[0051 ] The tanks 40A, 40B each include a longitudinally extending pipe 60A, 60B. The pipes 60A, 60B may be coaxial with the longitudinal axes at 42A, 42B. Each pipe 60A, 60B may extend from outside of the respective end caps 44A, 44B through an opening 62A, 62B. The pipes 60A, 60B extend to the first ends 46A, 46B through the second ends 48A, 46B of the tanks 40A, 40B.

[0052] A flow distribution plate 64A, 64B may be disposed at the ends of the pipes 60A, 60B toward the first ends 46A, 46B of the tanks 40A, 40B. The flow distribution plates 64A, 64B distribute incoming clear fluid across the diameter of the tanks to minimize the mixing of clear fluid with the slurry.

[0053] Each tank 40A, 40B is separated by a separation region 68A, 68B. While the region may be a defined area, in a hydraulic fracturing configuration, clear fluid may be separated from slurry naturally due to the less dense nature of the clear fluid. Should some mixing occur, the concentration of the slurry may be compensated for this. In this example, the clear fluid is disposed at the first ends 46A, 46B of the tanks 40A, 40B. The slurry is disposed at the second ends 48A, 48B. The clear fluid may be water, water mixed with chemicals or slurry additives such as ethylene glycol or other types of hydraulic fluid. "Clear", in this manner, refers to fluid that does not contain the particles of the slurry.

[0054] The slurry may contain various types or sizes of sand particles such as small quartz particles. The slurry may also include other types of chemicals to improve the lubrication and movement of the hydraulic fracturing particles therein.

[0055] The end caps 44A, 44B are affixed to the tanks 40A, 40B and may include conical portions 70A, 70B, respectively. The conical portions 70A, 70B may have a larger diameter toward the second volumes 42, 56 and taper to a smaller diameter at the bottom or outer end of the end caps 44A, 44B (longitudinally away from the second volumes 42, 56). The end caps 44A, 44B may also include cylindrical portions 72A, 72B that are coupled to a plurality of slurry valves. The plurality of slurry valves may include outlet valves 80A, 80B and inlet valves 82A, 82B. Valves 80A, 80B are used for communicating slurry under high pressure from the tanks 40A, 40B, respectively. In operation, the valves 80A, 80B may alternately communicate slurry from the second ends 48A, 48B of the respective tanks 40A, 40B.

[0056] Inlet valves 82A, 82B communicate fluid from the slurry inlet pipe

34 into the respective tanks 40A, 40B. The inlet valves 82A, 82B may operate alternately so that each of the valves 82A, 82B does not operate at the same time.

[0057] The valves 80A through 82B may be check valves that operate in the manner described below. That is, in general, one tank is receiving high pressure clear fluid to force high pressure slurry from the tank while the other tank is receiving low pressure slurry and removing low pressure clear fluid therefrom.

[0058] The injection site 12 has an injection manifold 94 that is in communication with a pipe 96 that extends from the check valve 80A and a pipe 98 that extends from the check valve 80B. [0059] A plurality of clear fluid valves are used for communicating clear fluid to and from each of the tanks 40A, 40B and are in fluid communication with a high- pressure clear fluid pump 90 and a clear fluid tank 92.

[0060] The clear fluid tank 92 supplies clear fluid to the high-pressure pump 90 through pipe 100 and the flow rate sensor 24. A pipe 102 supplies pressurized clear fluid to a three-way valve 1 10. The three-way valve 1 10 has an inlet port 1 10A, a first outlet port 1 10B and an outlet port 1 10C. A pipe 1 12 fluidically communicates fluid from the outlet port 1 10C to the injection manifold 94 (or pipe 96 which leads to the injection manifold 94). A pipe 1 14 communicates high pressure clear fluid from the outlet port 1 10B to a second three-way valve 120. The valves 1 10 and 120 may be referred to as high pressure valves. A bypass valve 124 may also communicate fluid from the high pressure pump 90 to the pipe 1 14 through pipe 126. The valve 124 may be a two-way valve used to controllably pressurize port 1 10B and pipe 1 14 during changing states. The operation of valve 124 will be described in further detail below. The three-way valve 1 10 communicates fluid from the inlet port 1 10A to either the outlet port 1 10B or the outlet port 1 10C under control of the controller 20.

[0061 ] The three-way valve 120 selectively communicates high pressure clear fluid from the inlet port 120A to either the first outlet port 120B or the second outlet port 120C. Outlet port 120B is in fluid communication with the pipe 60A through pipe 128. Outlet port 120C is in fluid communication with the pipe 60B through pipe 130. Valve 120 is under control of the controller 20.

[0062] A three-way valve 140 is used for selectively communicating low pressure clear fluid from the tanks 40A and 40B under control of the controller 20. In particular, valve 140 has an inlet port 140A in fluid communication with pipe 60A through pipe 142. The valve 140 also has an inlet port 140B in fluid communication with pipe 60B through pipe 144. An outlet port 140C of valve 140 is in fluid communication with the clear fluid tank 92. The fluid from the outlet port 140C is in fluid communication with the flow rate sensor 22 and a two-way flow control valve 146. Both the valves 140 and 146 are controlled by the controller 20. The amount of fluid communicated to the tank 92 may be controlled by selectively controlling the amount of fluid flowing through the valve 146. The fluid communicated through the valves 140 and 146 is under low pressure as will be described in further detail below. The closed inlet port 140A or 140B of valve 140 is under high pressure due to the high pressure slurry operation. A pipe 148 communicates fluid from the valve 146 to the tank 92. [0063] A three-way valve 150 is also in communication with the tanks 40A and 40B. In particular, the valve 150 includes an inlet port 150A in fluid communication with the pipe 60A through pipe 152. Inlet port 150B is in fluid communication with the pipe 60B through pipe 154. Outlet port 150C of valve 150 is in fluid communication with the pipe 148 through pipe 156. The valve 150, as will be described in more detail below, is used for equalization or reduction of the pressure within the tanks 40A, 40B. The valve 150 is used for communicating clear fluid from the first volume 50 and the third volume 54. The valve 150 selectively communicates high pressure clear fluid from either the inlet port 150A or port 150B to the outlet port 150C which ultimately communicates clear fluid through the pipe 156 to the tank 92. The pipe 156 may be directly input into the tank 92 or fluidically coupled to pipe 14B. The valve 150 is used to lower the pressure within the highly pressurized tanks prior to when the state of the valves 1 10, 120 is changed. Ultimately, the use of the valve 150 helps reduce the overall pressure and thus the effort to switch valves 1 10 and 120 is lower and potential for valve wear and erosion is reduced.

[0064] Pipes 60A and 60B may also be in fluid communication with a respective valve 160A, 160B. The valves 160A and 160B are at the lowest point of the respective pipes 60A, 60B and are used to purge air from the volume within the respective 40A, 40B.

[0065] A check valve 170 may also be in communication between the injection manifold 94 and the pump 90. In the illustration, check valve 170 is fluidly coupled between the pipe 102 and the injection manifold 94. The check valve 170 is used for directing the flow from the high pressure pump 90 to the injection manifold during upset conditions such as when the fluid paths, the high pressure valves or pipes associated therewith become blocked or equipment, such as the valves, fail. The check valve 170 may also include a spring 172. The spring 172 keeps check valve 170 closed until the upstream pressure (at the pipe 102) exceeds the downstream pressure (in the pipe 96) by a certain amount.

[0066] The valves 1 10 and 120 may be referred to as high pressure clear fluid valves. Valve 124 may also be included as a high pressure clear fluid valve. Valves 140 and 146 may be referred to as low pressure clear fluid valves. The valve 150 sees a combination of high pressure at the inlet ports 150A, 150B and low pressure at the outlet port 150C. The valve 124 is used for pressurizing the pipe 1 14 at a certain rate with high pressure clear fluid as will be described in more detail below. Collectively, the valves 1 10, 120, 124, 140 and 146 may be referred to as clear fluid valves. The plurality of clear fluid valves communicates both high pressure and low pressure fluid to and from the tanks 40A and 40B.

[0067] The valves 1 10, 120 and 140 are capable of handling extreme high pressures such as 15,000 psi (103421 kPa) at flow rates at hundreds of gallons per minute to provide such sealing force over 50,000 pounds (344737 kPa) may be provided against the valve seat. An extremely high differential is present. However, the valve 150 may be used to lower the overall pressure during switching. The purpose of valve 1 10 is to isolate the system by diverting the high-pressure clear fluid flow to the slurry line 96 through pipe 1 12. After system isolation, valve 150 can bleed of residual high pressure thereby placing components of the system at relatively low pressure. The operation of the valves will be described in more detail below. Although the valves are described as "three-way valves" and "two-way valves" and "check valves", other types of valves may be substituted therein. The three-way valves may be implemented in a plurality of two-way valves. Of course, other types of valves may be substituted from the valves. Check valves may, for example, be two-way valves controlled by the controller 20.

[0068] The valves 1 10, 120, 124, 140, 146 and 150 may be controlled by the controller 20 through the use of electrical signals therefrom. Other valves such as 160A and 160B, although not illustrated in communication with the controller 20, may also be electrically controlled thereby. In addition to electrically, valves 1 10, 120, 124, 140, 146, 150, 160A and 160B may also operate hydraulically or pneumatically

[0069] Referring now to Figure 1 B, an injection system 10' is illustrated and labeled identically to that of Figure 1 A. The system 10' illustrated in Figure 1 B operates identically to that set forth in Figure 1 A and may also be part of a multi-unit system. The difference between the systems 10 and 10' is the three-way valve 150 has been replaced by a pair of two-way valves 21 OA and 210B for pressure reduction. The two-way valves 21 OA, 210B are used for communicating high pressure clear fluid to the clear fluid tank 92. The pipe 152 receives clear fluid from the pipe 60A which in turn is communicated through pipe 156 to the clear fluid tank 92. The valve 210B receives clear fluid from the pipe 60B through pipe 154. The valve 210B communicates clear fluid through the pipe 156 to the clear tank. For simplicity in overall maintenance and the like, the two-way valves 21 OA and 210 B may be identical to that of valve 124. That way, maintenance is made easier due to the commonality of parts. The valves 21 OA and 210B all operate at a high differential and thus may need to be serviced more than the other valves in the system which operate with low pressure differentials between the inputs and the outputs.

[0070] The valves 21 OA and 21 OB are in electrical communication with the controller 20. That is, the controller 20 may control the opening and closing of the valves 21 OA, 210B. As will be described in more detail below, the valves may be operated so that either 21 OA or 210B are open but not both.

[0071 ] Referring now to Figure 1 C, the tank 40A is disposed vertically. The same reference numerals set forth in Figures 1 A and 1 B are used in Figure 1 C. Because of the higher density of slurry within the tank 40A, the denser slurry will settle toward the bottom of the tank 40A. This results in the clear fluid therein pushing a greater amount of fluid near the top relative to the bottom of the tank in the horizontal direction. As is illustrated, the interface 68A' is generally at an angle where the top portion is closer to the endcap 44A.

[0072] Referring now to Figure 1 D, an alternative embodiment of the horizontal tank 40A is set forth. In this example, a plurality of partitions 180 are used to define a plurality of horizontal channels 182. The partitions 180 help reduce the amount of departure of the interface 68A" from vertical. In this example, the partitions 180 are formed with a plurality of types that extend in the longitudinal direction. The pipes in this example are cylindrical in shape and have gaps 184 therebetween. The gaps 184 also define horizontal channels within the tank 40A.

[0073] In Figure 1 D, the endcap 44A' is modified to have an enlarged conical portion 70A'. The conical portion 70A' extends in a vertical direction so as to be in fluid communication with the horizontal channels 182. That is, the diameter of the conical portion 70A' adjacent to the channels 182 has been increased. Thus, the conical portion 70A' redirects slurry both to and from the check valves 82A and 82B.

[0074] Referring now to Figure 1 E, a cross-sectional view of one example of the tank 40A is set forth. As can be seen, gaps 184 are disposed between the partitions 180 so that horizontal channels 182 are formed. The partitions are cylindrical in shape and may be formed by pipes. The pipe 60A provides clear fluid to the distributor plate 64A and distributes the clear fluid through the channels 182 and gaps 184 formed by the partitions 180.

[0075] Referring now to Figure 1 F, a plurality of partitions are illustrated having radially extending walls 190 that extend from the pipe 60A to the inner wall of the tank 40A. The walls 190 divide the tank into pie-shaped sectors 192. The pie- shaped sectors 192 may be further divided by a concentric wall 194. The concentric wall 194 shares a center point with the tank 40A and the pipe 60A. The walls 190, 194 act as a partition to reduce the amount of displacement of the slurry in an angular manner as illustrated in Figure 1 D.

[0076] Referring now to Figures 1 G and 1 H, a slurry injection system 10" has each of the tanks 40A and 40B with a physical divider between the clear fluid between the first volume 50 and the second volume 52 and between the third volume 54 and the fourth volume 56 rather than the regions 68A, 68B described above. The tank 40A may be disposed horizontally (Figs 1 A and B), vertically (Figs 1 C-F) or at angles therebetween. The physical divider may be a piston 220A that has a first opening 222 for receiving the pipe 60A. A piston 220B configured in the same manner may be used in tank 40B around pipe 60B. The piston 220A is loosely fit around the pipe so that the piston 220A can freely travel along the pipe 60A as the pressure of the clear fluid changes. By providing the piston 220A, a more complete separation of the clear fluid and the slurry is provided with less chance of mixing with the slurry. With very high fill and discharge rates, some turbulence may occur and the slurry may mix with the fluid in the configuration of Figs. 1 A and 1 B. Further, the tanks 40A, 40B may be oriented in a horizontal position. Providing pistons 220A, 220B also enables the use of the tanks in a horizontal to prevent the mixing of the different fluids within the tank. In tank 40A, the piston 220A is shown in a first position and dotted in a second position. Thus, the piston 220A may move in a longitudinal direction parallel to the longitudinal axis of the tank.

[0077] When the piston 220A reaches the end cap 44A, a flap 230 disposed within an opening 232 may open by rotating at the hinge 234. The flap 230 may be a spring-loaded flap and when a sufficient amount of pressure differential is formed between the two sides of the piston 220A, the flap 230 may provide some clear fluid through the opening 232. The hinge 234 may instead be spring-loaded to provide a resistance from the flap 230 opening until the piston 220 reaches the end cap 44A of the tank 40A. The dotted flap illustrates the open position of the flap 230. It may be desirable to allow a small amount of clear fluid from volume 50 to travel through the conical portion 70A into the cylindrical portion 72A and into opening 62A of the end cap 44A so that the clear fluid flows just past check valve 80A and into the pipe 96. The conical shape minimizes flow turbulence of the slurry out of the tanks 40A, 40B. This allows the check valve 80A to close within clear fluid and thus in a cleaner environment. Tank 40B may also be operated in a similar manner in that the clear fluid may transmit through the piston 220B so that the check valve 80B closes in a cleaner environment. The force needed to open the flap 230 by overcoming the spring force may be relatively small. That is, only a few pounds per square inch may be sufficient to open the flap to allow the fluid to flush the check valves 80A or 80B.

[0078] Referring now to Figure 1 E, the same reference numerals are used to indicate the same components as Figures 1 A-1 D. In this example, only a single tank 40A is provided with the attached components in the slurry injection 10"'. In this example, the tank 40A may be configured in the same manner as set forth in Figures 1 A or 1 G in that the separation region 68A or the piston 220A (of FIG 1 G and 1 H) may be set forth between the first volume 50 and the second volume 52.

[0079] One difference between Figures 1 A-1 H and Figure 1 1 is the lack of a slurry tank 30 and pump 32. In this example, the check valve 82A is in fluid communication with a low pressure slurry manifold 240. The low pressure slurry manifold 240 may be a common source shared between multiple tanks in a multiple tank type system. Of course, a slurry tank 30 and pump 32 may be in communication with the low pressure slurry manifold 240. Another difference between Figure 1 E and Figures 1 A-1 H is the lack of a high pressure pump 90 and a low pressure fluid tank 92. A low pressure clear fluid manifold 242 is used to receive the low pressure fluid from the port 140A'. A high pressure clear fluid manifold 244 is in communication with the valve 1 10. Although the pump 90 is not illustrated in this example, a high pressure clear fluid pump may be used somewhere in the system for generating the high pressure within the high pressure clear fluid manifold 244.

[0080] In this example, the flow rate sensor 24' has been modified to be positioned downstream of the valve 1 10 rather than between the clear fluid tank and the pump as illustrated above. The flow rate sensor has been labeled 24' to indicate its change of position. However, the flow rate sensor 24' generates a flow signal corresponding to the amount of flow into the pipe 60A and thus into the tank 40A.

[0081 ] The valves 120 and 140 illustrated above have been changed from three-way valves to two-way valves and are indicated as valve 120' and 140'. Port 120B' is in fluid communication with the pipe 60A. Likewise, port 140B' is also in fluid communication with the pipe 60A. Port 120A' is in fluid communication with the flow rate sensor 24', pipe 1 14 and valve 124 and port 1 10B of valve 1 10.

[0082] The slurry injection system ^lv may be referred to as an asynchronous system. In the previous figures, the fill rate of given tank is no faster than the discharge rate of the second tank. However, by increasing the fill rate of the slurry, the slurry fill duration can be substantially reduced and the higher capacity high pressure slurry for each tank is increased.

[0083] In operation, the three-way valve 1 10 communicated fluid from port 1 1 OA through 1 1 OB. The high pressure fluid enters pipe 1 14 and flow rate sensor 24'. The valve 120' communicates fluid from port 120A' to 120B' and into the pipe 60A. It is presumed that the tank 40A was previously filled with low pressure slurry. The high pressure clear fluid forces high pressure slurry through check valve 80A and to the injection site 12 through the injection manifold 94. As in a similar manner to that set forth above, when the flow rate sensor 24' indicates the volume of clear fluid has flushed the slurry from the tank 40A and, if desired, passed check valve 80A, the three- way valve 1 10 is commanded to divert fluid from port 1 1 OA to outlet port 1 10C. Valve 21 OA is open which depressurizes the pipe 60A and the tank 40A by communicating fluid to the low pressure clear fluid manifold 242. Valve 120' is closed and valve 140' is open under low pressure. Thereafter the valve 210 is closed. Low pressure slurry from the low pressure slurry manifold 240 opens the check valve 82A to allow low pressure slurry to enter the tank 40A and expel clear fluid through the pipe 60A. The clear fluid leaves the tank 40A and pipe 60A through the open valve 140'. The opening and closing of the valves is under the control of the controller 20. The flow rate sensor 22 is used to indirectly determine the amount of slurry that has entered the tank 40A. When the amount of slurry as determined by monitoring the flow of clear fluid out of the tank, valve 140' is closed and valve 120' is open. The valve 124 is open which directs high pressure clear fluid from the high pressure clear fluid manifold 244 to be communicated to the pipe 1 14 through the pipe 126. After some pressure is built up in pipe 1 14, valve 1 10 communicates high pressure clear fluid from port 1 10A to port 1 10B and valve 124 is closed. High pressure clear fluid then enters the pipe 60A through valve 120' and check valve 82A is closed and check valve 80A is open.

[0084] The valve 170 is configured in a similar manner to that described above relative to the spring 172. That is, the valve 170 may also include a spring 172 in a similar manner to that set forth above. Valve 170 opens when a sufficient force is between the high pressure clear fluid manifold 244 and the pipe 96 or the injection site 12. Again, the valve 1 70 is open when damage to the valve or other components of the system is present or flow conditions have been upset. The valve 170 should be open when the upstream pressure is about 100 pounds per square inch higher than the downstream pressure. This ensures that the valve will not open during normal operation. [0085] Referring now to Figure 1 F, the same components set forth in Figure 1 E are labeled in the same manner. In this example, the slurry injection system 10 ^IV has valves 120' and 140' that are presumed to be robust enough to be switched under high pressure. Thus, there is no pressure relief using valves 1 10 and 124 as in the previous examples. In this example, the flow rate sensor 24' measures the amount of high pressure clear fluid that is communicated to the pipe 60A through the valve 120'. Valve 140' is closed. Clear fluid displaces slurry through the check valve 80A. When the amount of slurry through the check valve 80A has reached clear fluid as determined by the flow rate sensor 24' and thus the volume of fluid, the valve operation is reversed in that valve 120 is closed while valve 140 is open. This allows the tank 40A to be depressurized and low pressure slurry is then communicated to the tank to restart the process. When the amount of clear fluid that leaves the tank corresponds to a desired amount of slurry being input to check valve 80A, the valves 120' and 140' are reversed in operation.

[0086] Referring now to Figures 2A and 2B, a valve 250 suitable for use as valve 1 10 or 120 in Figures 1 A-1 C is set forth. The valve 250 has a housing 252 which may be cylindrical in shape. The housing 252 includes an inlet or central port 254, a first outlet port 256 and a second outlet port 258. A pair of valve seats 260, 262 extends from the interior cavity 264 of the housing 252. The valve seat 260 is disposed between the inlet port 254 and the outlet port 258. The valve seat 262 is disposed between the inlet port 254 and the outlet port 256.

[0087] An actuator 270 has a spindle 272 which has a first valve disk 274 and a second valve disk 276 fixable coupled thereto. The valve disk 274 is disposed between the inlet port 254 and the valve seat 262. The valve disk 276 is disposed between the inlet port 254 and the valve seat 260. Packing 280 may be disposed between the spindle 272 and the housing 252 to facilitate longitudinal movement of the spindle 272 and the valve disks 274 and 276 as in the direction illustrated by the arrows 282 and to prevent leakage of fluid from cavity 264. In Figure 2A, the valve disks 274, 276 and spindle 272 are moved in a longitudinally outward direction away from the actuator 270 so that the fluid flows between the inlet port 254 and the outlet port 258 as illustrated by the path 284. In Figure 2B, the spindle is moved in the rightmost position toward the actuator 270 so that fluid travels from the inlet port 254 to the outlet port 256.

[0088] The actuator 270 may be various types of actuators such as an electrical actuator or a hydraulic actuator. In this example, an electric actuator has been used. The actuator 270 is sized to move the disks 274, 276 so that high pressure flow between the inlet port and one of the outlet ports is provided (once resumed during the state switching process). Further, the path corresponding to Figure 1 A is a high pressure clear fluid path of clear fluid. The other port which is closed is at a low pressure. The low pressure port corresponds to tank 40A or 40B depending on the state of operation. The high pressure input to the housing "pushes" the closed valve disk against the corresponding valve seat to ensure a very high closing force to prevent leakage. Because the high pressures are relieved during the switching process, the actuator is sized to overcome very little force (a little more than the packing places on the spindle 272).

[0089] Referring now to Figures 3A and 3B, a valve 250' is illustrated having the same reference numerals as Figure 2A and 2B except for the changed components. The valve 250' illustrated in Figure 3A and 3B is suitable for use as valve 140 illustrated in Figures 1 A-1 C. In this example, the valve seats 260 and 262 have been changed to valve seats 260' and 262'. In this example, the valve seats 260', 262' are moved closer to the central port 290, which is an outlet port. The valve disks 274 and 276 are moved outboard of the valve seats 260' and 262'. In this example, the valve 250' has one outlet port 290 and two inlet ports 292, 294. One of the inlet ports is at low pressure and one is at high pressure during operation. The open port is at low pressure. The high pressure on the valve disk at high pressure forces it in communication with the associated valve seat. For example, in Fig. 3A, valve disk 274 is forced against valve seat 262'. In Figure 3B, valve disk 276 is forced against valve seat 260'. In Figure 3A, fluid path 296 communicates fluid from the second tank 40B to the outlet port 290 through fluid path 296. In Figure 3B, fluid is communicated from tank 40A to outlet port 290 through fluid path 298. In each of the cases of Figures 2A-3B, a gap between the valve disks and the valve seats allows fluid to pass therethrough.

[0090] Referring now to Figure 3C, a two-way valve 310 may be used to replace the three-way valves illustrated in Figures 1 A-1 F. That is, more than one two- way valve may be used to replace the three-way valves illustrated in the example set forth above. For a two-tank operation, two two-way valves may be used to replace a three-way valve. The valve 310 may also be used in a one tank solution as valves 120' or 140'. The valve 310 includes a housing 312 that has an inlet port 314 and an outlet port 316. The housing 312 includes packing 320 through which an actuator rod 322 extends therethrough. The actuator rod 322 includes a valve disk 324 which is moved by an actuator 326 coupled to the rod 322. The valve disk 324 may be displaced against the valve seats 326. When the valve disk 324 contacts the valve seat 326, the valve 310 is sealed and thus no flow from the inlet port 314 to the outlet port 316 takes place. In this example, when each of the three-way valves are replaced with two-way valves, each valve may have an independent actuator 326 to allow independent control. Thus, each two-way valve may have greater freedom in valve timing.

[0091 ] Referring now to Figures 3D and 3E, a pair of two-way valves 310 are illustrated coupled to a common actuator 326. The common components of each valve are primed. In Figure 3D, the right valve 310' is open while the left valve 310 is closed. In Figure 3E, the left valve 310 is open and the right valve 310' is closed. By providing the exact same functionality as a three-way valve, the examples illustrated in Figures 3D and 3E may have some manufacturing advantages in resisting very high pressure operations due to the small size of each valve component.

[0092] Referring now to Figure 3F, a two-way valve 330 suitable for draining low pressure fluid from a tank is set forth. In this example, a port 332 is an inlet port within the housing 334. The inlet port 332 communicates fluid to a drain port 336. The housing 334 has packing 340 that receives the actuator rod 342 coupled to the actuator 344. The rod 342 moves the valve disk 350 toward or away from the valve seat 352. In Figure 3F, the valve seat 352 is spaced apart from the valve disk 350 and thus fluid flows between the inlet port 332 and the outlet port 336. As mentioned above relative to Figure 3C, the actuator 344 may be provided for each valve so that when two two-way valves replace a three-way valve, independent timing and control may be performed by the actuators for each valve.

[0093] Referring now to Figures 3G and 3H, two valves 330, 330' may be in communication with a common actuator 344. In Figure 3G, the left valve 330 is closed and the right valve 330' is open. The common components of valve 330 are primed in valve 330'. In Figure 3H, the left valve is open and the right valve is closed. It should be noted that the valve disk 350 is located between the valve port 332 and the valve seat 352. When closed, the high pressure forces the valve disk 350 against the valve seat 352.

[0094] Referring now to Figure 4A, a state table illustrating a transition of the valves from a first state to a second state is set forth. The first state "A" corresponds to the tank 40A injecting high pressure slurry into the injection site 12 while high pressure clear fluid is an input to the first tank 40A. At the same time, tank 40B is receiving low pressure slurry from the slurry tank 30 and expelling clear fluid to the fluid tank 92. During the first state illustrated as "A" in Figure 4A, valve 80A is open, valve 82A is closed, valve 82B is open and valve 80B is closed. Three-way valve 140 is communicating fluid from port 140B to port 140C to the clear fluid tank 92. Valve 120 is communicating clear fluid from port 120A to 120B. Valve 1 10 is communicating clear fluid from port 1 1 OA to port 1 1 OB which ultimately communicates fluid through valve 120 and into tank 40A. Valve 124 is closed and valve 146 is partially open.

[0095] In the table set forth in Figure 4A (and 4B), the bolded cells indicate a change in the valve state. Thus, only the bolded cells will be described in the various states A1 -A5. To begin the transition to state A', multiple valve states are changed in sequence. State A1 is achieved by changing the state of the three-way valve 1 10 to communicate fluid from inlet port 1 1 OA to outlet port 1 10C. The high pressure clear fluid from the pump 90 is diverted to the injection manifold 94. The high pressure clear fluid is no longer directed through the valve 120.

[0096] In state A2, the valve 150 is switched from communicating clear fluid from between port 150B and port 150C to communicating clear fluid from between port 150A and port 150C. The switching pressure differential of the valve 150 is reduced since the high pressure fluid is no longer being communicated to tank 40A through valve 120 due to the relief of high pressure clear fluid flowing to the injection manifold 94 through valve 1 10.

[0097] In state A3, the depressurization of the tank 40A results in the check valves 80A, 82A and 82B switching states. That is, valve 80A is closed, valve 82A is open, and valve 82B is closed. Check valve 80B remains closed for this portion of the state change. The three-way valves 140 and 120 are also changed in state. That is, valve 140 switches to communicate clear fluid from port 140A to port 140C. Three- way valve 120 communicates fluid from port 120A to port 120C. Notice, the switching of valves 120 and 140 are performed when low pressures are at all the ports.

[0098] In state A4, valve 124 is open which results in the check valve 80B being open. By opening the valve 124, pipe 1 14 and thus the flow through valve 120 is increased. Port 1 10B also sees an increased pressure.

[0099] In state A5, valve 124 is closed and valve 1 10 is switched in state to terminate the diversion of high pressure clear fluid from the pump 90 to the injection manifold 94. That is, valve 1 10 switches states so that clear fluid is communicated between inlet port 1 1 OA and outlet port 1 10B. The switching is performed while both ports 1 1 OA and 1 10B are under a high pressure due to the diversion of high pressure clear fluid through valve 124. [0100] In this example, states A1 -A5 are switched 0.20, 0.3, 0.2, 0.25 and 0.20 seconds respectively for a total switching state time of 1 .15 seconds. Of course, the timing may be adjusted based on various conditions.

[0101 ] In state A', a steady state of operation is achieved with check valve 80A closed, check valve 82A open, check valve 82B closed, check valve 80B open, and three-way valve 140 communicating low pressure fluid to the tank40A. Valve 120 is communicating high pressure clear fluid to the tank 40B which results in high pressure slurry being injected into the injection site 12 through the injection manifold 94. The valve 150 is communicating fluid from tank 40A while valve 124 is closed. Valve 146 is partially open. As will be described in more detail below, the switching of the valves takes place based upon comparison from the signals from the flow rate sensors 22 and 24. A comparison of the flow signals from flow rate sensors 22 and 24 are compared. The flow rate sensor signals correspond to the volume of clear fluid entering one tank and leaving the other tank.

[0102] Referring now to Figure 4B, operation of the injection system 10' is illustrated. All of the states are the same except for the valve 150 has been replaced by the valves 21 OA and 210B. In steady state A, valve 21 OA is closed and valve 210B is open while the remaining valves are the same as in Figure 4A. In state A1 , valves 21 OA and 210B remain closed and open, respectively. In step A2, valve 21 OA is open while valve 201 B is closed. This allows the pressure in the first tank 40A to be depressurized or relieved of pressure. In the remaining states A3-A5, valve 21 OA remains open while valve 210B is closed. Likewise, in steady state A', valves 21 OA and 210B are open and closed, respectively.

[0103] Referring now to Figure 4C, a state diagram illustrating the operation or position of the valves of Figure 1 E is set forth. In the slurry discharge state, valve 80A is open, valve 82A is closed, valve 120' is open, valve 140' is closed, valve 1 10 is open, valve 124 is closed and valve 21 OA is closed. Valve 146 is partially closed so that the flow to the low pressure clear fluid source is regulated. The state A illustrated a slurry discharge state in steady state operation. To transition through the process after slurry has been fully discharged as indicated by the output of the flow rate sensors, state A1 operates in the same manner except for valve 1 10 has diverted flow to the manifold 94. The remaining states are the same. In state A2, valve 80A is closed and valve 21 OA is open. This allows the tank 40A to be depressurized.

[0104] In state A3, valves 82A, 120' and 140' are switched states so that valve 82A is open, valve 120' is closed and valve 140' is open. In state A', slurry begins to fill the tank. Slurry fills the tank until a predetermined amount of clear fluid is discharged as determined by the flow rate sensor 22. In state A'-1 , the slurry discharge cycle is started by changing the states of valves 120' to open and 140' to closed. This stops the slurry fill. In state A' -2, the valve 1 10 is open. The system then continues in this state which corresponds to state A where slurry is discharged. The process then starts over again.

[0105] Referring now to Figure 5, a method of operating the system set forth in Figures 1 A-1 H is set forth. In step 510, the second volume 52 is filled with slurry in tank 40A and a first volume 50 is filled with clear fluid. In step 512, a third volume 54 of the second tank is filled with clear fluid which is reduced by filling the fourth volume 56 with slurry from the low pressure slurry tank 30.

[0106] In step 514, the plurality of high pressure valves 1 10 and 120, in particular, communicate high pressure clear fluid from the pump 90 and into the pipe 60A. In response to communicating the high pressure clear fluid, step 516 moves the region 68A toward the end cap (downward in Fig. 1 A) and high pressure slurry is communicated through the check valve 80A into the injection manifold 94 and injection.

[0107] In step 518, a fourth volume 56 is fluidically coupled to allow the slurry from the slurry pump 32 and slurry tank 30 to increase the fourth volume. In response to increasing the fourth volume, clear fluid is reduced within the third volume which is displaced through the pipe 60B and is fluidically communicated through the valves 140 and 146 into the clear fluid tank 92. In step 522, the fluid flow rate of fluid from the tank 92 is measured by flow rate sensor 24. In step 524, a second fluid flow rate is determined from fluid flowing from the third volume 54 into the tank 92. That is, the amount of clear fluid from the tank 40B communicated to the clear fluid tank 92 is measured. In step 526, the controller 20 compares the first fluid flow rate and the second fluid flow rate. The flow rates correspond to the volumes entering and leaving tank 92. In step 528, the drain valve 146 is controlled in response to comparing so that the flow through the valve 146 is increased or decreased based upon the comparison. Ultimately, the amount of fluid flowing from the second tank may be controlled so that the amount of slurry ready to be injected from the second tank 40B is available when the tank 40A is depleted of slurry. Preferably, while draining the tank 40A of slurry, the amount of clear fluid may extend through the end cap and just past the check valve 80A so that the check valve 80A closes in a clean fluid environment rather than in a slurry environment in step 530. It is desirable to have the tank 40B and thus volume 56 at a process maximum before states A1 -A5 of Figures 4A and 4B are performed. [0108] In step 532, the plurality of clear fluid valves are controlled to cause tank 40A to depressurize. This takes place in states A1 and A2 of Figures 4A and 4B.

[0109] In step 534, the valves are changed in state in steps A3-A5 so that the second tank 40B is pressurized while tank 40A is depressurized and fills with slurry. The switching process is described below.

[01 10] Referring now to Figure 6, the switching of the valves in the states between state A and state A' is illustrated in flowchart form. In step 610, if the desired amount of clear fluid being removed from the second tank 40B has been reached, the switching process begins. As mentioned above, this corresponds to the flow rate or volume determined by the flow rate. Step 610 uses the comparison of step 526 to make this determination. In step 612, the process of switching from state A to A' of Figures 4A and 4B is set forth. In step 614, high pressure clear fluid is redirected to the injection manifold through the three-way valve 1 10. In step 616, the first tank 40A is coupled to the clear fluid tank through valve 150. Check valve 80A closes in step 618 when the pressure in the tank 40A is reduced. The pressure reduction may be to or nearing to ambient pressure. In step 620, the state of the three-way valves 150 and 120 are also changed as the valves are changed toward state A'.

[01 1 1 ] In step 622, the pipe to the three-way valve 120 is pressurized by opening the valve 124. In step 624, and in response to the bypass valve 124 being closed, valve 82B is closed and check valve 80B is open. Thereafter, in step 626 the state of the three-way valve 1 10 is changed to communicate high pressure clear fluid to tank 40B through the three-way valve 120. In step 628, high pressure slurry is discharged from tank 40B. In step 630, the check valve 82A is open to force clear fluid from the tank by displacing the clear fluid with low pressure slurry from the tank 15 and the slurry circulation pump 32. In step 632, clear fluid is communicated to the tank 92 through the valve 140 and valve 146.

[01 12] Referring now to Figure 7A, a timing diagram for a multiple unit system is set forth. Each unit referred to in Figure 7A comprises a pair of tanks. In Figure 1 , only two units are illustrated. However, as mentioned above, a plurality of units are set forth. In this example, five units, unit 1 -unit 5, are controlled having staggered starts of two seconds. That is, unit 1 starts at time 0 while unit 2 starts at 2 seconds, unit 3 at 4 seconds, unit 4 at 6 seconds, and unit 5 at 8 seconds. A small dwell time such as one-half second may be used in between each cycle for each unit to accommodate slightly slower cycle rates or other variations. That is, the nominal cycle illustrated in Figure 7A is 9.5 seconds with a one-half second dwell time therebetween. Unit 1 restarts after the dwell time at 10 seconds, unit 2 at 12 seconds, unit 3 at 14 seconds, unit 4 at 16 seconds and unit 5 at 18 seconds.

[01 13] By staggering the start times, the amount of slurry injected during the process may be maintained and gradually increased and decreased compared to a condition when the units would be in sync in terms of start times. Synchronized units may cause stress in the piping, valves and other components. The number of units may equal the cycle time divided by the switching time plus the dwell time which is multiplied by an integer. In this case, the cycle time is 10 seconds divided by the 2 second. The results are 5 units to obtain minimal flow variation. However integer multiples 10, 15 or 20 units (or more) may also be used to minimize flow variation.

[01 14] Referring now to Figure 7B, a timing chart of a system is set forth using single tank control such as the single tank of Figures 1 E and 1 F above. Single tank control with rapid slurry charging is set forth in Figure 7B. In this example, each unit has a nominal five-second cycle time with four-second slurry discharge and a one- second slurry fill. In this example, no dwell time is assumed. However, a dwell time may be used in operation. The ratio of the slurry fill time to the slurry discharge time is 1 :5. That is, the discharging of slurry takes place 80% of the time and slurry filling takes place 20% of the time. This is increased over the embodiments including two tanks in which half the time the tank is charging while the other half of the time the tank is discharging.

[01 15] Referring now to Figure 8A, a slurry concentrate pressurizer configuration 810 is illustrated. In this example, clear fluid is provided from a clear fluid source such as a reservoir 812 or tank. The reservoir 812 is in fluid communication with a low pressure pump 814. Clear fluid from the reservoir 812 enters a low pressure clear fluid manifold 816. The low pressure clear fluid manifold 816 is in communication with a trailer 818. Because the systems are moved from wellsite to wellsite, mounting the system components to a trailer is suitable. The trailer 818 may also be referred to as a "missile." The trailer 818 has a portion of the low pressure clear fluid manifold 820 and a portion of a high pressure clear fluid manifold 822 coupled thereto. The low pressure manifold 820 is in fluid communication with a plurality of high pressure clear fluid pumps 830. The pumps 830 may be referred to as fracking pumps. The plurality of pumps 830 may all be disposed on trailers 832 that may be hooked to a semi for easy transport from fracking site to fracking site. One or more pumps 830 may be disposed on each trailer 832. Each of the pumps 830 draws low pressure fluid from the low pressure manifold 820 through an inlet pipe 840 and discharges high pressure clear fluid through an outlet pipe 842. Only one each of pipes 840 and 842 are labeled. The high pressure manifold 822 is in fluid communication with a static mixer 852 though a two-way valve 850. The static mixer 852 is in communication with a well head 854. The high pressure clear fluid manifold 822 is in fluid communication with a slurry pressurizer 860 through a valve 862. A controller 864 is used to control the valves 850, 862 so that a portion of the high pressure clear fluid transmits through the valve 850 and a portion of the high pressure clear fluid is communicated to the slurry pressurizer 860. The controller 864 may be a programmable logic controller (PLC) that acts in response to one of more flow rate sensors 866A, 866B or 866C. Of course, flow rate sensors 866A, 866B, 866C may be disposed at various locations throughout the system 810 and generate flow signals that the controller 864 uses to control the system.

[01 16] The slurry pressurizer 860 receives high pressure clear fluid and generates high pressure slurry through an output pipe 870 which is in fluid communication with the mixer 852. That is, the pipe 870 is in fluid communication with a point between the valve 850 and the mixer 852. The mixer 852 forms a mixture of concentrated high pressure slurry from slurry pressurizer 860 and water from the valve 850.

[01 17] The slurry pressurizer 860 also receives low pressure slurry from a blender unit 872 through a pipe 874. The blender unit 872 may also receive additive from an additive tank 876 which is in fluid communication with a dosing pump 878. The dosing pump 878 communicates the fluid from the additive tank 876 into the blender unit 872. The additive within the additive tank 876 may comprise a gel or other types of additive using in the fracking process. The slurry unit 872 may blend slurry, fluid and additives to form the low pressure slurry.

[01 18] A centrifugal separator 880 receives low pressure fluid from the slurry pressurizer 860. The centrifugal separator 880 may separate any residual slurry from within the low pressure discharge and communicate the slurry matter to the blender unit 872 through the pipe 882 for re-use. The separator 880 may also communicate clear fluid to the low pressure manifold through pipe 884.

[01 19] The blender unit 872 may also receive low pressure clear fluid from the low pressure manifold 816 through a pipe 886. The low pressure clear fluid may be used to form the slurry.

[0120] In operation, the slurry pressurizer 860 may be disposed on a trailer 890. The slurry pressurizer unit 860 may be one or more of the examples set forth in Figure 1 A-1 F. Both single or double tank slurry injection units may be used for the slurry pressurizer 860. In operation, the controller 864 controls the valve 850. The valve 850 may be used to create a differential pressure between a pipe 892 and pipe 870. The differential pressure may be 75 psi or less. The valve 862 may be precisely controlled so that the pressure thereacross is between 1 and 20 psi. Valve 850 may be designed to not fully close. That is, a predetermined amount of flow through the valve 850 so that a predetermined amount of pressure differential is present across the valve 850. For example, a 100 psi pressure differential may be used. The valve cannot fully close preventing accidental overpressurizing of the pumps and the piping. A suitable valve may be a leaky butterfly valve or a ball valve that is not allowed to physically close due to the geometry therein.

[0121 ] Referring now to Figure 8B, the static mixer 852 is illustrated in further detail. The static mixer 852 has mixing elements 910 set forth therein for mixing the slurry and clear fluid communicated through the valve 850. The mixer 852 blends the clear fluid and the concentrated slurry from the slurry pressurizer 860 that is received through the pipe 870.

[0122] In the example set forth in Figures 8A and 8B, the fracking pumps are supplied by a single low pressure clear fluid line. The slurry pressurizer 860 draws low pressure clear fluid and returns low pressure clear fluid back to the clear fluid manifold 816. These connections minimize the amount of piping in a system. The centrifugal separator 880 separates the slurry particulates from the low pressure clear fluid to negligible amounts so that a minimum amount of particulates are in the clear fluid when entering the high pressure pumps. If various ones of the pumps 830 fail, the system can continue to pressurize slurry with minimal effect on the operation. The trailers 832 containing the pumps 830 may easily be maneuvered to allow additional or replacement pumps to be quickly connected to the trailer 818.

[0123] Because of the configuration, all the high pressure slurry mass is provided by the trailer containing the slurry pressurizer 860. The slurry pressurizer 860 may use vertical cylinders which keep the slurry in drive fluid from excessive mixing. As mentioned above, pistons may also be used within the various tanks to prevent mixing of the fluids therein, particularly if the tanks are disposed at another angle other than vertical. The valves within the slurry pressurizer have a generally low cycle rate of once every five to ten seconds versus six times per second in a typical fracking pump. Valves designed for low velocities and materials that minimize erosion from concentrated slurry may be used. [0124] Some slurry processes use 0.5 pounds of sand per gallon of high pressure clear fluid or about 0.75% concentration by weight. Highly dense slurry may contain five pounds of sand per gallon. Based on the ratio, the slurry pressurizer 860 may only need to handle a flow of approximately 10% of the total high pressure clear fluid flow to achieve a desired slurry concentration downstream of the mixer 852. The additive tank 876 may pass the additives through the slurry pressurizer 860 and the capacity of the slurry pressurizer may be reduced. Because the slurry pressurizer 860 may provide a highly concentrated slurry due to the later mixing within the mixer 852, the system may be referred to as a slurry concentrate pressurizer.

[0125] Referring now to Figure 9, a method for operating the system of

Figures 8A and 8B is set forth. In step 930, clear fluid is received from a tank or reservoir at a low pressure pump. In step 932, the low pressure clear fluid is communicated to a low pressure manifold. The low pressure is not high enough to operate the slurry pressurizer illustrated in Figure 8. In step 934, a plurality of clear fluid pumps that are coupled to both a high pressure clear fluid manifold and a low pressure clear fluid manifold increase the pressure of the low pressure clear fluid. In step 936, the high pressure clear fluid generated at the plurality of clear fluid pumps is communicated to a high pressure clear fluid manifold.

[0126] In step 938, a portion of the high pressure clear fluid is communicated from the high pressure clear fluid manifold through a mixer through a first valve. In step 940, a portion of the high pressure clear fluid from the high pressure clear fluid manifold is communicated to a slurry pressurizer through a second valve. In step 942, the flow through the first valve and second valve is adjusted based on a flow rate or a pressure monitored within the system.

[0127] In step 944, additives may be added to the low pressure slurry. For example, the additives may be a gel or other types of additives suitable for improving the slurry fracking process. Step 944 is an optional step. Additives may be communicated to a slurry unit from a tank and a dosing pump.

[0128] In step 946, low pressure slurry is communicated to the slurry pressurizer. In step 948, high pressure slurry is communicated to the mixer from the slurry pressurizer. In step 950, the low pressure clear fluid from the slurry pressurizer is communicated to a separator. The low pressure clear fluid is the result of the pressure transfer at the slurry pressurizer of high pressure from the high pressure clear fluid to the increase in pressure of the low pressure slurry to high pressure slurry. In step 952, the slurry residue may be extracted at a separator. The clear fluid may have a small amount of slurry therein. In step 954, the separated slurry at the extractor is communicated to the slurry unit and is later used for reinjecting to the slurry pressurizer. In step 956, low pressure clear fluid is communicated to the low pressure clear fluid manifold from the separator. Should the clear fluid have an acceptably low amount of slurry particles therein, the separator may be eliminated from the system.

[0129] Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.