Patent Description:
The present disclosure relates to a pressure exchanger, and more specifically, a pressure exchanger for hydraulic fracking that can reduce wear of an end cover and a rotor.

A pressure exchanger is a device that can exchange pressure energy between a high-pressure fluid stream and a low-pressure fluid stream. A common use for pressure exchangers is in Sea Water Reverse Osmosis (SWRO) desalination plants. The pressure exchanger can exchange pressure energy between a high pressure fluid stream and a low pressure fluid stream while separating the two fluid streams by a liquid barrier or interface formed in a rotor of the pressure exchanger. For instance, the liquid barrier or interface may be defined by a fluid volume remaining in the duct of the rotor (i.e., dead volume) of one or both of the streams. The pressure exchanger may use the remaining dead volume in the rotor as the separating interface or barrier to avoid excessive mixing of the two fluid streams in the rotor.

Hydraulic fracturing or fracking is a process to develop a well for gas or oil extraction by injecting fracking fluid including solid particles to bedrock. For example, a fracking process may involve injecting to rocks high pressure fluid (e.g., water) to form and increase fractures in the rocks and proppants such as sand or ceramic materials to prevent the collapse of fractures when pressure is removed. Generally, the fracking process may use positive displacement pumps having check valves to generate and supply the high pressure fracking fluid. However, the fracking particles included in the high pressure fluid may accelerate wear on the pumps and valves, and thus may increase cost for the fracking process and decrease the reduced life time of such components.

In some cases, a pressure exchanger may be used in a fracking process. For instance, the fracking process may include a pump that operates only on clean fluid without fracking particles and that provides the clean fluid to the pressure exchanger. The pressure exchanger may then transmit pressure energy of the clean fluid to fracking fluid including proppants, i.e., fracking particles. In some cases, the pressure exchanger may serve as a sacrificial item having far less cost than the pump. The pressure exchanger for the fracking process may be prone to the wear issues associated with an interference between the pressure exchanger and the proppants, which limits its operational cycle and commercial applicability.

In some cases, the pressure exchanger for a fracking operation may be made of a material having a high strength such as tungsten carbide. However, an end cover of the pressure exchanger may still interfere with the proppants in the fracking fluid. For example, the proppants may get crushed between a sealing area of the end cover and an edge of a rotor duct of the pressure exchanger. Therefore, the wear issues on the end cover and the rotor may still limit the commercial applicability of a pressure exchanger for fracking operations.

<CIT> describes a pressure exchange device that utilizes an integral high pressure boost pump that is in fluid communication with a pressure exchange unit. An optional low pressure boost pump unit may also be provided. The pressure exchange unit comprises a rotating rotor assembly inside a housing to transfer the pressure of a fluid from one high pressure fluid to another low pressure fluid.

<CIT> describes a system including a frac system with a hydraulic energy transfer system configured to exchange pressures between a first fluid and a second fluid, and a flush system configured remove particulate out of the hydraulic energy transfer system.

In the present specification the units PSI and GPM are used. <NUM> PSI= <NUM> kilopascal. <NUM> GPM = <NUM><NUM>/ min.

The present disclosure describes a pressure exchanger for hydraulic fracturing or fracking that can help to prevent premature wear of the pressure exchanger. For example, the present disclosure describes improved structures and flow management techniques to supply a flush volume of clean fluid to one side of the pressure exchanger with fracking fluid to separate the fracking fluid from an end cover and a rotor of the pressure exchanger.

In some examples, the pressure exchanger according to the present disclosure can help to prevent or reduce wear on the rotor and the "dirty" end cover that communicates the fracking fluid. For example, the end cover may include a flush port connected to a low pressure port to provide clean fluid (e.g., water) to thereby flush or displace fracking fluid in the rotor such that the fracking fluid can be moved away from a sealing area of the end cover. The flush port can have a clearance gap greater than a size of the proppant particles to avoid crushing of the fracking particles with a wall that defines the flush port or the rotor.

A pressure exchanger according to the present invention is set out in claim <NUM>. A system according to the present invention is set out in claim <NUM>. Further advantageous developments of the present invention are set out in the dependent claims.

One or more implementations of the present disclosure will be described below. These described implementations are only exemplary of the present disclosure. As discussed in detail below, the described implementations relate generally to hydraulic processing, and particularly to a fracking plant that uses a pressure exchanger to increase pressure of fracking fluid including solid particles. In some implementations, the pressure exchanger can be applicable to processes that transport slurry, ore, and corrosive or erosive fluids.

<FIG> is a circular cross-sectional view showing an example of a pressure exchanger used in a fracking operation in related art.

The pressure exchanger receives and discharges fracking fluid, which is depicted as black in <FIG>. The fracking fluid includes proppants particles, which are depicted as white dots in the fracking fluid. The pressure exchanger includes a rotor <NUM>, a first end cover <NUM> located at a first side (e.g., the left side in <FIG>) of the rotor <NUM>, and a second end cover <NUM> located at a second side (e.g., the right side in <FIG>) of the rotor <NUM>.

The rotor <NUM> can rotate about an axis <NUM> that extends through the rotor <NUM>. The end covers <NUM> and <NUM> may include central sealing areas <NUM> and <NUM> that are disposed at central areas of the end covers, respectively. In addition, outer portions of the end covers <NUM> and <NUM> may be referred to as outer sealing areas that face and contact sides of outer portions of the rotor <NUM>. For example, the outer portions are disposed radially outward relative to central areas of the end covers <NUM> and <NUM>. The rotor <NUM> may include multiple rotor ducts <NUM> that extend through an inside of the rotor <NUM> along the axis <NUM> extending through the sealing areas <NUM> and <NUM>. The rotor <NUM> may have a high-pressure side (e.g., lower side in <FIG>) and a low-pressure side (e.g., upper side in <FIG>) with respect to the axis <NUM> and configured to rotate about the axis <NUM>.

The first side of the rotor <NUM>, which faces the first end cover <NUM>, may receive and discharge the fracking fluid. The second side of the rotor <NUM>, which faces the second end cover <NUM>, may receive and discharge clean fluid (e.g., water) without the proppants. The rotor ducts <NUM> may define a dead volume <NUM> that acts as a separating barrier between the fracking fluid and the clean fluid. The dead volume <NUM> may move back and forth along the rotor ducts <NUM> for each revolution of the rotor <NUM>. The dead volume <NUM> or barrier may have a gradual concentration of the proppants. For instance, the dead volume <NUM> may define a concentration gradient between a first concentration at one side facing the first end cover <NUM> and a second concentration at the other side facing the second end cover <NUM>. The first concentration may be equal to a concentration of the fracking fluid, and the second concentration may be virtually zero as facing the clean water side.

The pressure exchanger may receive a low pressure fracking fluid stream <NUM> through a low pressure inlet port <NUM> that is connected to the first end cover <NUM> and configured to receive the fracking fluid. The pressure exchanger may discharge a high pressure fracking fluid stream <NUM> through a high pressure outlet port <NUM> that is connected to the first end cover <NUM>. The high pressure outlet port <NUM> may be configured to discharge the fracking fluid that has passed at least a portion of the rotor ducts <NUM>.

The pressure exchanger may also include a high pressure inlet port <NUM> connected to the second end cover <NUM> and configured to receive a high pressure clean water stream <NUM>, and a low pressure outlet port <NUM> connected to the second end cover <NUM> and configured to discharge a low pressure clean water stream <NUM>. The high pressure inlet port <NUM> and the high pressure outlet port <NUM> are disposed at the high-pressure side of the pressure exchanger with respect to the axis <NUM>, and the low pressure inlet port <NUM> and the low pressure outlet port <NUM> are disposed at the low-pressure side of the pressure exchanger with respect to the axis <NUM>.

On the high-pressure side of the pressure exchanger, the high pressure clean water stream <NUM> enters the high pressure inlet port <NUM> and pushes onto the dead volume <NUM> to thereby gradually displace the fracking fluid stream <NUM> through the high pressure outlet port <NUM>. The high pressure clean water stream <NUM> may move through some of the rotor ducts <NUM> from the end cover <NUM> to the outer sealing area of the end cover <NUM>, where the proppant particles in the fracking fluid or the dead volume <NUM> may be randomly crushed due to the extremely tight clearance between the end cover <NUM> and the rotor <NUM>. Thus, the end cover <NUM> and the rotor <NUM> at the high-pressure side may suffer from an accelerated cavitation damage or impact damage due to the crushing of the proppant particles.

On the low-pressure side of the pressure exchanger, the low pressure fracking fluid stream <NUM> enters the low pressure inlet port <NUM> and pushes onto the dead volume <NUM> to thereby gradually displace the low pressure clean water stream <NUM> through the low pressure outlet port <NUM>. The low pressure fracking fluid stream <NUM> may move through some of the rotor ducts <NUM> from the end cover <NUM> to the central sealing area <NUM> of the end cover <NUM>.

The low-pressure side of the pressure exchanger may also suffer from wear problems when the clean water and the dead volume <NUM> in the rotor ducts <NUM> are depressurized after passing the outer sealing area of the end cover <NUM>. For example, the low pressure fracking fluid stream <NUM> introduced through the low pressure inlet port <NUM> may pass the sealing area <NUM> based on rotation of the rotor <NUM>. In order to transfer the fracking fluid from the low-pressure side (e.g., low pressure fracking fluid stream <NUM>) to the high-pressure side (e.g., high pressure fracking fluid stream <NUM>), a portion of the rotor ducts <NUM> may cross the sealing area <NUM>. In this case, a portion of the proppant particles in the fracking fluid may be randomly crushed on edges of the sealing area <NUM> due to a narrow clearance or gap between the end cover <NUM> and ends of the rotor ducts <NUM> facing the sealing area <NUM>. On the other hand, the end cover <NUM> may not have similar wear problems because the dead volume <NUM> blocks the fracking particles from being transferred to the low pressure clean water stream <NUM>. That is, the clean water can pass both the central sealing area <NUM> and outer sealing area of the end cover <NUM> without any crushing damage due to the fracking particles.

<FIG> is a block diagram showing an example system for hydraulic fracking using a pressure exchanger in related art. A pressure exchanger <NUM> may have the same structure as the pressure exchanger described above with <FIG>. For example, the pressure exchanger <NUM> may receive a high pressure clean water stream <NUM> and a low pressure fracking fluid stream <NUM>, and discharge a low pressure clean water stream <NUM> and a high pressure fracking fluid stream <NUM>. In some case, in the example system shown in <FIG>, the pressure exchanger <NUM> may operate to output <NUM> gallon per minute ("gpm") of the high pressure fracking fluid stream <NUM>. The fracking fluid output from the pressure exchanger <NUM> may be guide by a pipe <NUM> and used to develop an oil or gas well. The output flow rates of the pressure exchanger <NUM> in <FIG>, e.g., <NUM> gpm and <NUM> gpm, are just examples for explanation of the system, and the output flow rates may vary in other examples.

The system may further include a water tank <NUM> configured to receive water, a feed pump <NUM> connected to the water tank <NUM>, a high-pressure pump <NUM> connected to the feed pump <NUM> and configured to supply the water to the pressure exchanger <NUM>, and a blender <NUM> configured to supply the fracking fluid stream <NUM> to the pressure exchanger <NUM>.

Referring to the example shown in <FIG>, the water tank <NUM> may receive (i) <NUM> gpm of water from an external water supply through a feed line <NUM> and (ii) <NUM> gpm of water from the pressure exchanger <NUM> through another feed line <NUM>. The water tank <NUM> may deliver an outflow of water with <NUM> gpm via the feed pump <NUM> to the high-pressure pump <NUM>. The high-pressure pump <NUM> may operate at a relatively high pressure, for example, <NUM>,<NUM> pound per square inch ("psi"), and discharge water with a less flow rate (e.g., <NUM> gpm) due to volumetric compression under the high pressure. The high-pressure pump <NUM> may supply the high pressure clean water stream <NUM> to the pressure exchanger <NUM>.

The blender <NUM> may receive some of the low pressure clean water stream <NUM> from the pressure exchanger <NUM> and proppant particles or fracking chemicals through a feed line <NUM> to generate the fracking fluid. For example, the blender <NUM> may receive <NUM> gpm of water and <NUM> gpm of proppants, and discharge about <NUM> gpm of the low pressure fracking fluid stream <NUM> to the pressure exchanger <NUM>. The flow rate <NUM> gpm of the proppants or fracking chemicals supplied into the blender <NUM> may be equal to the flow rate of water fed back to the water tank <NUM>.

In some cases, the input flow rate and the output flow rate of the pressure exchanger <NUM> may not exactly match each other due to compression of fluid or integral leakage of water in the pressure exchanger <NUM>. For example, the pressure exchanger <NUM> may need to receive more fracking fluid or water than a target output flow rate (e.g., <NUM> gpm) considering loss of water due to the internal leakage. In some cases, the leakage water may be discharged with the low pressure clean water stream <NUM>. For instance, <FIG> illustrates an increase of the output flow rate of the high pressure clean water stream <NUM> from the input flow rate <NUM> gpm to the output flow rate <NUM> gpm of the low pressure clean water stream <NUM>.

<FIG> is a circular cross-sectional view showing an example of a pressure exchanger for hydraulic fracking according to the present disclosure.

For example, a pressure exchanger <NUM> is configured to receive and discharge fracking fluid depicted as gray in <FIG>. The fracking fluid includes proppants particles depicted as black dots in the fracking fluid in <FIG>. The pressure exchanger <NUM> includes a rotor <NUM>, a first end cover <NUM> located at a first side (e.g., the left side in <FIG>) of the rotor <NUM>, and a second end cover <NUM> located at a second side (e.g., the right side in <FIG>) of the rotor <NUM>.

The rotor <NUM> can rotate about an axis <NUM> that extends through the rotor <NUM>. For example, the rotor <NUM> may mechanically rotate about a shaft that extends along the axis <NUM>. In some cases, the shaft may be rotated by a driving device such as a motor. In some implementations, the rotor <NUM> (or the shaft of the rotor <NUM>) can be configured to rotate by a flow entering to the rotor <NUM>. For instance, the pressure exchanger <NUM> can further include a ramp structure that includes an inclined surface with respect to the axis <NUM>. The inclined surface of the ramp structure can be configured to face and contact incoming flow streams (e.g., fluid stream <NUM> (e.g., high pressure clean water stream <NUM>) or fluid stream <NUM> (e.g., low pressure fracking fluid stream <NUM>)). Based on pressure of the incoming flow streams applied to the inclined surface of the ramp structure, the rotor <NUM> can rotate about the shaft relative to the end covers <NUM> and <NUM>.

In some implementations, a rotation speed of the rotor <NUM> can be determined based on the arrangement of the incline surface of the ramp structure. For example, the rotation speed of the rotor <NUM> may be determined based on increasing or decreasing an inclined angle of the incline surface with respect to the axis <NUM>. In some examples, the rotation speed of the rotor <NUM> may be determined based on increasing or decreasing an area or a number of the incline surfaces arranged in the ramp structure. In some examples, the rotation speed of the rotor <NUM> may vary based on a pattern of the inclined surface of the ramp structure.

Alternatively or in addition, the rotation speed of the rotor <NUM> can be controlled by adjusting a flow rate or pressure of the incoming streams. For example, the rotation speed of the rotor <NUM> can be increased based on an increase of the flow rate of the incoming fluid stream <NUM>. The rotation speed of the rotor <NUM> can be decreased based on a decrease of the flow rate of the incoming fluid stream <NUM>. In this example, the rotation speed of the rotor <NUM> may depend on the flow rate of the incoming fluid stream <NUM>.

In some implementations, the rotation speed of the rotor <NUM> can be controlled independent of the flow rate of the incoming fluid stream <NUM>. For example, the rotor <NUM> can be rotated by a separate driving device such as a motor. In another example, one or more components of the pressure exchanger <NUM> may be replaced to adjust the rotation speed of the rotor <NUM> while keeping the same flow rate of the incoming fluid stream <NUM>. In particular, the end cover <NUM>, the end cover <NUM>, rotor <NUM>, or the ramp structure of the rotor <NUM> having the inclined surface can be replaced to adjust the rotation speed of the rotor <NUM>. In some examples, the end cover <NUM> and the end cover <NUM> may include the ramp structure having the inclined surface.

The end covers <NUM> and <NUM> may include central sealing areas <NUM> and <NUM> that are disposed at central areas of the end covers, respectively. The central sealing area <NUM> may be spaced apart by a minimal clearance from a first side of the rotor <NUM> to provide tight sealing between the end cover <NUM> and central portions of rotor ducts <NUM> to block passage or leakage of the fracking fluid between the end cover <NUM> and the central portions of rotor ducts <NUM>. In some examples, the central sealing area <NUM> may be in contact with the first side of the rotor <NUM> to block the passage or leakage of the fracking fluid.

In addition, outer portions of the end covers <NUM> and <NUM> may be referred to as outer sealing areas that face side surfaces of outer portions of the rotor <NUM>. The outer sealing areas are disposed radially outside of the central areas of the end covers <NUM> and <NUM>. In some examples, the outer sealing area of the end cover <NUM> may be spaced apart by a minimal clearance from the first side of the rotor <NUM> to provide tight sealing between the end cover <NUM> and an outer portions of rotor ducts <NUM>. That is, in some cases, the outer sealing area of the end cover <NUM> may provide a tight sealing clearance between the end cover <NUM> and the outer portions of rotor ducts <NUM> to block passage or leakage of the fracking fluid between the end cover <NUM> and the outer portions of rotor ducts <NUM>. In some cases, the outer sealing areas of the end cover <NUM> may be in contact with the first side of the rotor <NUM> to block passage or leakage of the fracking fluid.

The rotor <NUM> may include multiple rotor ducts <NUM> that extend through an inside of the rotor <NUM> along the axis <NUM> extending through the sealing areas <NUM> and <NUM>. The rotor <NUM> may have a high-pressure side (e.g., the lower side in <FIG>) and a low-pressure side (e.g., the upper side in <FIG>) with respect to the axis <NUM>, and the rotor <NUM> is configured to rotate about the axis <NUM>.

The first side of the rotor <NUM> may face the first end cover <NUM> that includes a pair of apertures configured to communicate first fluid or fracking fluid including fracking particles. For instance, the first fluid may include proppants including solid particles such as sand, chemicals, etc., for a fracking operation. The second side of the rotor <NUM> may faces the second end cover <NUM> including a second pair of apertures that are configured to communicate second fluid or clean fluid (e.g., water) without proppants.

In some implementations, the first end cover <NUM> can further define a flush port (e.g., hole or aperture) that is configured to supply the second fluid into the first side of the rotor <NUM> in a state in which the first pair of apertures of the first end cover <NUM> communicate the first fluid with the first side of the rotor <NUM>. In some cases, the flush port may refer to a pipe <NUM>. In some cases, the flush port can be connected to a flush inlet duct or pipe <NUM> configured to supply a flush volume of clean water to the first side of the rotor <NUM> while the first pair of apertures of the first end cover <NUM> communicate the first fluid with the first side of the rotor <NUM>.

In some examples, the flush port or flush inlet duct <NUM> is spaced apart from the first side of the rotor <NUM> and defines a clearance gap <NUM> between a first end (e.g., a radially outer end) of the flush inlet duct <NUM> and the first side of the rotor <NUM>. For instance, the first end of the flush inlet duct <NUM> may be in communication with one of the first pair of apertures of the end cover <NUM> through the clearance gap <NUM>. In some cases, a size of the clearance gap <NUM> may be greater than a size of the fracking particles such that the fracking particles can pass the flush port without being crushed. For example, the size of the clearance gap <NUM> can be greater than a maximum size (i.e., the greatest size) of the fracking particles.

A second end (e.g., a radially inner end) of the flush port or flush inlet duct <NUM> may define a tight clearance <NUM> with the first side of the rotor <NUM>. For example, the tight clearance <NUM> may be narrower than the clearance gap <NUM>. In some examples, the second end the flush inlet duct <NUM> may be connected to and in contact with an outer side of the center sealing area <NUM>, and an inner side of the center sealing area <NUM> defines the tight clearance <NUM> with the first side of the rotor <NUM>. The flush inlet duct <NUM> can be configured to supply the second fluid into the first side of the rotor <NUM> to push the first fluid toward the second side of the rotor <NUM> such that the first fluid moves to be separated from the center sealing area <NUM>. As such, the flush volume supplied through the flush inlet duct <NUM> can reduce wear on the end cover <NUM> by eliminating or reducing occurrences of a contact between the fracking particle and the center sealing area <NUM>.

The rotor ducts <NUM> may define a dead volume <NUM> that acts as a separating barrier between the fracking fluid and the clean fluid. The dead volume <NUM> may move back and forth along the rotor ducts <NUM> for each revolution of the rotor <NUM>. The dead volume <NUM> or barrier may have a gradual concentration of the proppants. For instance, the dead volume <NUM> may define a concentration gradient between a first concentration at one side facing the first end cover <NUM> and a second concentration at the other side facing the second end cover <NUM>. The first concentration may be equal to a concentration of the fracking fluid, and the second concentration may be virtually zero as facing the clean water side.

In some implementations, where the flush inlet duct <NUM> is connected to one of the first pair of apertures of the end cover <NUM> to supply the flush volume, the rotor <NUM> may define the dead volume <NUM> having the concentration gradient that is asymmetric with respect to the axis <NUM>. For example, a first cross-section area of the dead volume <NUM>, which faces the incoming fracking fluid, may be greater than a second cross-section area of the dead volume <NUM>, which faces the outgoing fracking fluid. The asymmetry of the dead volume <NUM> may depend upon the flush volume.

The pressure exchanger <NUM> can include a low pressure inlet port or duct <NUM> connected to the first end cover <NUM> and configured to receive a fracking fluid stream <NUM>, and a high pressure outlet port or duct <NUM> connected to the first end cover <NUM> and configured to discharge a fracking fluid stream <NUM> that has passed at least a portion of the rotor ducts <NUM>. For instance, each of the low pressure inlet port <NUM> and the high pressure outlet port <NUM> may include a pipe, a tube, a connector, or the like. The low pressure inlet port <NUM> may be in communication with the flush port <NUM> through the clearance gap <NUM> as discussed above.

The pressure exchanger <NUM> can also include a high pressure inlet port or duct <NUM> connected to the second end cover <NUM> and configured to receive a high pressure clean water stream <NUM>, and a low pressure outlet port or duct <NUM> connected to the second end cover <NUM> and configured to discharge a clean water stream <NUM>. For instance, each of the high pressure inlet port <NUM> and the low pressure outlet port <NUM> may include a pipe, a tube, a connector, or the like. The pressure exchanger <NUM> may be configured to transmit pressure energy of the high pressure clean water stream <NUM> received through the high pressure inlet port <NUM> to the fracking fluid stream <NUM> received through the low pressure inlet port <NUM>. For instance, a pressure of the outgoing fracking fluid stream <NUM> may be greater than a pressure of the fracking fluid stream <NUM>, and a pressure of the outgoing clean water stream <NUM> may be less than a pressure of the high pressure clean water stream <NUM>.

The high pressure inlet port <NUM> and the high pressure outlet port <NUM> may be disposed at the high-pressure side of the pressure exchanger <NUM> with respect to the axis <NUM>, and the low pressure inlet port <NUM> and the low pressure outlet port <NUM> may be disposed at the low-pressure side of the pressure exchanger with respect to the axis <NUM>. The rotor <NUM> may rotate about the axis <NUM> in a direction from the high-pressure side to the low-pressure side as shown in the black downward arrow in <FIG>.

On the high-pressure side of the pressure exchanger <NUM>, the high pressure clean water stream <NUM> can be introduced through the high pressure inlet port <NUM> and push onto the dead volume <NUM> in the rotor ducts <NUM> to thereby gradually displace the fracking fluid stream <NUM> through the high pressure outlet port <NUM>. The rotor <NUM> can be configured to, based on rotation of the rotor <NUM>, move the high pressure clean water stream <NUM> through some of the rotor ducts <NUM> in a direction from the end cover <NUM> toward the outer sealing area of the end cover <NUM>.

In some implementations, the high pressure clean water stream <NUM> may include an additional flush volume <NUM> to prevent the proppant particles in the outgoing fracking fluid from being crushed between the end cover <NUM> and the rotor <NUM>. For example, the flush volume <NUM> may overlap with or cover an edge area of the outer sealing area of the end cover <NUM> to separate the fracking fluid from the edge area of the outer sealing area of the end cover <NUM>. Thus, the additional flush volume <NUM> may help to reduce wear on the end cover <NUM>. In some examples, the flush volume <NUM> may be less than a volume of the fracking water discharged through the high pressure outlet port <NUM>. For instance, the high pressure outlet port <NUM> can be configured to receive (i) a first volume of the fracking fluid from the low pressure inlet port <NUM> and (ii) a second volume (i.e., the flush volume <NUM>) of clean fluid from the high pressure inlet port <NUM>, where the second volume is less than the first volume.

The flush volume <NUM> may also attribute to the asymmetry of the dead volume <NUM> with respect to the axis <NUM>. For example, the dead volume <NUM> may reach an outermost rotor duct <NUM> at the low-pressure side facing the low pressure inlet port <NUM> and the first end cover <NUM> in a radial direction of the rotor <NUM>. On the other hand, the dead volume <NUM> may be spaced apart from an outermost rotor duct <NUM> at the high-pressure side facing the high pressure outlet port <NUM> and the first end cover <NUM> in the radial direction of the rotor <NUM>.

On the low-pressure side of the pressure exchanger <NUM>, the low pressure fracking fluid stream <NUM> can enter the rotor ducts <NUM> through the low pressure inlet port <NUM> and push onto the dead volume <NUM> to thereby gradually displace the clean water stream <NUM> through the low pressure outlet port <NUM>. The low pressure fracking fluid stream <NUM> may move through some of the rotor ducts <NUM> from the end cover <NUM> toward the central sealing area <NUM> of the end cover <NUM>.

In some examples, the pressure exchanger <NUM> may be configured to, based on rotation of the rotor <NUM> and the flow management techniques described above, control the low pressure fracking fluid stream <NUM> not to contact the central sealing area <NUM> of the end cover <NUM>. In addition, the end cover <NUM> may not suffer from wear problems because the dead volume <NUM> blocks the fracking particles from being transferred to the clean water stream <NUM>. That is, the clean water can pass both the central sealing area <NUM> and the outer sealing area of the end cover <NUM> without any crushing damage due to the fracking particles.

<FIG> is a cross-sectional view showing an example of an end cover including a flush port. The rotor <NUM> (see <FIG>) can rotate in the direction indicated with an arrow at the fracking fluid stream (i.e., low pressure port) <NUM> of the first end cover <NUM>. The dotted circle in <FIG> represents the cylindrical cross-section at <FIG>.

In some implementations, as shown in <FIG>, the first end cover <NUM> can have high pressure port <NUM>, low pressure port <NUM>, and flush port <NUM> that extend in a circumferential direction about a center of the first end cover <NUM> and that also extend in a radial direction with respect to the center of the end cover <NUM>. The low pressure port <NUM> can be spaced apart from the flush port <NUM> to thereby define the clearance gap <NUM>, while the flush port <NUM> is in contact with the sealing area <NUM> or defines the thigh clearance <NUM>. The high pressure port <NUM> can carry the additional flush volume <NUM>.

<FIG> illustrates a block diagram of an example system for hydraulic fracking using a pressure exchanger according to the present disclosure. For example, a system <NUM> includes the pressure exchanger <NUM> (see <FIG>) described above that includes the rotor <NUM>. The pressure exchanger <NUM> is configured to supply the high pressure clean water stream <NUM>, the low pressure fracking fluid stream <NUM>, and a flushing volume of clean water through the flush port <NUM>. In addition, the pressure exchanger <NUM> is configured to discharge the high pressure fracking fluid <NUM> and the low pressure clean water stream <NUM>.

Specifically, as described above with regard to <FIG>, the pressure exchanger <NUM> includes the first end cover <NUM> disposed at the first side of the rotor <NUM>, where the first end cover <NUM> defines a first pair of apertures configured to communicate the first fluid including the fracking particles, and the flush port <NUM> configured to receive the first portion of the second fluid in a state in which the first pair of apertures communicate the first fluid with the first side of the rotor <NUM>. The flush volume of the second fluid supplied through the flush port <NUM> can help to prevent premature wear issues on the end cover <NUM> by separating the fracking fluid from a sealing area of the end cover <NUM>.

The pressure exchanger <NUM> may further include the second end cover <NUM> disposed at the second side of the rotor <NUM>, where the second end cover <NUM> defines a second pair of apertures. The second pair of apertures of the second end cover <NUM> are connected to the high pressure inlet port <NUM> and the low pressure outlet port <NUM> and configured to communicate the second fluid (e.g., water). In some implementations, the pressure exchanger <NUM> can be configured to, in a state in which the flush port <NUM> supplies the second fluid into the first side of the rotor <NUM>, supply the additional flush volume <NUM> of the second fluid from the high pressure inlet port <NUM> to the high pressure outlet port <NUM> through an outer portion of the plurality of rotor ducts <NUM>. The additional flush volume <NUM> may be less than a volume of the first fluid discharged through the high pressure outlet port <NUM>.

The system <NUM> further includes a blender <NUM> configured to generate a first fluid (e.g., fracking fluid) including fracking particles and to supply the first fluid to the first side of the rotor <NUM>. The system <NUM> further includes a water tank <NUM> configured to receive the second fluid (e.g., water). The water tank <NUM> is configured to supply a first portion of the second fluid to the first side of the rotor <NUM> (e.g., the high pressure clean water stream <NUM>) and a second portion of the second fluid to the second side of the rotor <NUM> through the flush port <NUM>. A first flow rate of the first portion of the second fluid can be much greater than a second flow rate of the second portion of the second fluid. For example, the second flow rate (e.g., <NUM> gpm) can be <NUM> to <NUM>% of the first flow rate (e.g., <NUM> gpm).

The system <NUM> may further include a feed pump <NUM> connected to the water tank <NUM>, and a high-pressure pump <NUM> connected to the feed pump <NUM> and configured to supply water to the pressure exchanger <NUM>. The system <NUM> may further include a plurality of pipes that connect components of the system <NUM> and that are configured to carry water or fracking fluid. Accordingly, the reference numerals in <FIG> may refer to pipes and ports as well as the fluid carried by the pipes or ports.

In some implementations, as shown in the system <NUM>, the pressure exchanger <NUM> may operate to output <NUM> gpm of the high pressure fracking fluid stream <NUM>. The high pressure fracking fluid stream <NUM> may be guided through a discharge pipe <NUM> and provided to a fracking operation to develop an oil or gas well, or for some other operations such as slurry transportation. The output flow rates of the pressure exchanger <NUM> shown in <FIG>, e.g., <NUM> gpm of the fracking fluid and <NUM> gpm of water, are just examples for explanation of the system <NUM>, and the output flow rates may vary in other examples.

The water tank <NUM> may receive (i) <NUM> gpm of water from an external water supply through a feed line or pipe <NUM> and (ii) <NUM> gpm of water from the pressure exchanger <NUM> through another feed line or pipe <NUM>. The water tank <NUM> may output <NUM> gpm of water, and deliver an outflow of <NUM> gpm via the feed pump <NUM> to the high-pressure pump <NUM>. The high-pressure pump <NUM> may operate at a relatively high pressure, for example, <NUM>,<NUM> psi, and discharge water with a less flow rate (e.g., <NUM> gpm) due to volumetric compression under the high pressure. The high-pressure pump <NUM> may supply the high pressure clean water stream <NUM> to the pressure exchanger <NUM>. In some examples, each of the feed pump <NUM> and the high-pressure pump <NUM> may include a motor.

The blender or pump <NUM> may receive and mix some of the low pressure water stream <NUM> discharged from the pressure exchanger <NUM> and proppant particles or fracking chemicals through a feed line <NUM> to generate the fracking fluid. For example, the blender <NUM> may receive and mix (i) <NUM> gpm of water out of <NUM> gpm of the low pressure clean water stream <NUM> and (ii) <NUM> gpm of proppants. The blender <NUM> may discharge about <NUM> gpm of the low pressure fracking fluid stream <NUM> to the pressure exchanger <NUM>. The flow rate, <NUM> gpm, of the proppants or fracking chemicals into the blender <NUM> may be equal to the flow rate of water fed back from the low pressure clean water stream <NUM> to the water tank <NUM> through the pipe <NUM>.

In some implementations, the system <NUM> may further include a branch pipe <NUM> that is connected to the feed pump <NUM>, the high-pressure pump <NUM>, and the flush port <NUM> of the pressure exchanger <NUM>. For example, the branch pipe <NUM> may be configured to divide the second fluid (e.g., <NUM> gpm) received from the feed pump <NUM> into the first portion (e.g., <NUM> gpm) to be supplied to the high-pressure pump <NUM> and the second portion (e.g., <NUM> gpm) of the second fluid to be supplied to the flush port <NUM>.

In some implementations, the system <NUM> may further include a connector <NUM> that branches the low pressure clean water stream <NUM> to supply water to the water tank <NUM> and the blender <NUM>. For example, the connector <NUM> is configured to divide water (e.g., <NUM> gpm) from the low pressure clean water stream <NUM> into a third portion and a fourth portion of water and to supply the third and fourth portions of water to the water tank <NUM> and the blender <NUM>, respectively. In some examples, a third flow rate (e.g., <NUM> gpm) of the third portion of water may be fed back to the water tank <NUM> through the pipe <NUM>. In addition, a fourth flow rate (e.g., <NUM> gpm) of the fourth portion of water may be supplied to the blender <NUM> through a pipe <NUM>. That is, the flow rate of water supplied to the blender <NUM> may be much greater than the flow rate of water fed back to the water tank <NUM>. For example, the third flow rate may be about <NUM> to <NUM>% of the fourth flow rate.

In some examples, the input flow rate and the output flow rate of the pressure exchanger <NUM> may not exactly match each other due to compression of fluid or integral leakage of water in the pressure exchanger <NUM>. For example, the pressure exchanger <NUM> may receive more fracking fluid or water than a target output flow rate (e.g., <NUM> gpm) considering loss of water due to the internal leakage. In some cases, the leakage water may be discharged with the low pressure clean water stream <NUM>. For instance, <FIG> illustrates that <NUM> gpm of the output flow rate of the high pressure clean water stream <NUM> increases to <NUM> gpm of the low pressure clean water stream <NUM> due to the leakage inflow of water.

Claim 1:
A pressure exchanger (<NUM>) for hydraulic fracking, the pressure exchanger (<NUM>) comprising:
a rotor (<NUM>) configured to rotate about an axis (<NUM>), the rotor (<NUM>) defining a plurality of rotor ducts (<NUM>) extending parallel to the axis (<NUM>), each rotor duct (<NUM>) extending between a first side and a second side of the rotor (<NUM>) that are spaced apart from each other;
a first end cover (<NUM>) disposed at the first side of the rotor (<NUM>), the first end cover (<NUM>) defining a first pair of apertures configured to communicate a first fluid including fracking particles; and
a second end cover (<NUM>) disposed at the second side of the rotor (<NUM>), the second end cover (<NUM>) defining a second pair of apertures configured to communicate a second fluid,
characterised in that the first end cover (<NUM>) further defines a flush port configured to supply the second fluid into the first side of the rotor (<NUM>) in a state in which the first pair of apertures communicate the first fluid with the first side of the rotor (<NUM>).