Patent Application
20180180042
The present disclosure relates generally to a pump and, more particularly, to a submergible cryogenic pump having a linear electromagnetic motor drive.
Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone or by a mixture of natural gas and diesel fuel. Stationary equipment may also use an engine powered by natural gas. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications, producing less greenhouse gas.
Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100° C. to −162° C. The liquefied natural gas is then drawn from the tank by gravity and/or by a boost pump, and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel may be gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with cryogenic pumps located external to the tank of liquid natural gas involves cooling the pump down before it can be started. To achieve this, external cryogenic pumps use expensive and complicated cool-down circuits and procedures. Additionally, leakage can cause problems for external pumps. External pumps require complicated and expensive seals and bearings to prevent or reduce leakage. External pumps additionally require expensive and complicated systems for the cold end of the pump handling the liquid fuel. For example, cold-end systems include ventilation, purging, and temperature monitoring.
To reduce cost and complexity, some cryogenic pumps are installed inside the tank and submerged in the liquid natural gas. Submerging an electric motor in high pressure liquid natural gas, however, creates other problems. For example, the pump and motor generate heat, boiling the immediately surrounding liquid natural gas. Additionally, the rotating components of electric motors and rotating pumps present additional problems. For example, rotating bearings are prone to wear, and because they are submerged in high pressure liquid at cryogenic temperatures, they are difficult to access for service or replacement. Rotating pumps also consume large amounts of energy and have complex and expensive components.
To address these issues, some pumping systems have used linear electromagnetic drives to reciprocate a piston partially disposed in liquid. An exemplary pump is disclosed in U.S. Pat. No. 6,506,030 which issued to Kottke on Jan. 14, 2003 (“the '030 patent”). The pump includes a piston assembly inside a cylinder. Bushings support the piston and a linear electromagnetic drive system forces the piston to reciprocate within the cylinder. At the cold end of the pump, the piston reciprocates in the dispensing chamber to pump liquid during the down stroke. At the warm end of the pump, the piston reciprocates in a reservoir chamber which stores energy during the upstroke to be used in the next down stroke. Sealing members fluidly separate the dispensing chamber from the reservoir chamber. Bushings support and guide the piston. Friction between the piston and each of the sealing members and bushings generate heat. To minimize undesirable heat transfer into the liquid fuel, an adaptive plate insulates the cold end of the pump submerged in the fluid from the warm end which is not submerged. Additionally, the cold end is insulated by a thermal jacket.
While the pump of the '030 patent may help address some of the difficulties associated with using a linear electromagnetic drive to reciprocate a pump piston in a high pressure cryogenic tank, it presents additional problems. For example, the bushings and sealing member add undesirable complexity and cost because they are prone to wear and require frequent and expensive maintenance. Additionally, they generate unwanted heat, making submerging the pump completely in the liquid undesirable for this design.
The disclosed pump is directed to overcoming one or more of the problems set forth above and/or elsewhere in the prior art.
In one aspect, the present disclosure is directed to a fully submergible dual-action cryogenic pump. The cryogenic pump includes a housing having an interior compartment, and the interior compartment has an inner peripheral surface, a first end, and a second end. The housing is configured to receive a liquid into the interior compartment when submerged in the liquid. A free piston is contained within the interior compartment of the housing, and the free piston includes an axis, a first end, a second end, and an outer peripheral surface. A first compression chamber is formed between the first end of the free piston and the first end of the interior compartment. A second compression chamber is formed between the second end of the free piston and the second end of the interior compartment. An electromagnetic drive is configured to reciprocate the free piston along the axis. A sealing area is formed by the outer peripheral surface of the free piston sealing with the inner peripheral surface of the interior compartment between the first compression chamber and the second compression chamber.
In another aspect, the present disclosure is directed to a fully submergible dual-action cryogenic pump system. The pump system includes a housing having an interior compartment. The interior compartment has an inner peripheral surface. The housing is configured to receive a liquid into the interior compartment when submerged in the liquid. A piston includes an outer peripheral surface, an axis, and a length along the axis. An electromagnetic drive is configured to reciprocate the piston when the piston is contained within the interior compartment. A sealing area is formed by the outer peripheral surface of the piston sealing with the inner peripheral surface of the interior compartment when the piston is contained within the interior compartment.
In another aspect, the present disclosure is directed to a method of pumping a cryogenic liquid using a pump submerged in the cryogenic liquid. The method includes electromagnetically reciprocating a free piston enclosed within a housing of the submerged pump along an axis of the free piston. The method also includes allowing the cryogenic liquid to alternately flow into a first compression chamber inside the housing and into a second compression chamber inside the housing. The method also includes alternating between discharging the cryogenic liquid from the first compression chamber and from the second compression chamber. The method also includes electromagnetically rotating the free piston about the axis of the free piston.
In one embodiment, illustrated in
An electromagnetic drive 40 is configured to reciprocate the free piston 26 along its axis 28 when the free piston 26 is contained inside the housing 16. The free piston 26 includes a magnetic portion 50 responsive to electromagnetic fields. The electromagnetic drive 40 includes a plurality of electric coils 42 encircling the axis 28 of the free piston 26. The electric coils 42 may be enclosed within a separate structure as shown in
In the embodiment illustrated in
In another embodiment, however, the over-stroke length 76 at the first end 22 of the interior compartment 18 may be different from a second over-stroke length (not shown) at the second end 24 of the interior compartment 18. And alternatively, in another embodiment, the ends 30, 32 of the free piston 26 may contact the ends 22, 24 of the interior compartment 18 at each end of the stroke of the free piston 26. That is, the over-stroke length 76 may effectively be zero.
Referring again to the embodiment illustrated in
The one-way valves 52, 56, 58, 60 may be any suitable type of one-way valve known in the art. Although the one-way valves 52, 56, 58, 60 are shown as separate valves disposed outside of the housing 16, alternatively, they may be integrally formed with the housing 16. And although the intake valves 52, 56 are illustrated near the ends 22, 24 of the interior compartment 18 of the housing 16, alternatively, the intake valves 52, 56 may be disposed at any suitable location. Instead of separately formed valves, alternatively, the intake valves 52, 56 may simply be formed as the intake fluid line 55 directly connected to the interior compartment 18 of the housing 16 at a location (not shown) that is intermittently sealed by the free piston 26 as the free piston 26 reciprocates.
A primer pump 54 fluidly connects the first and second compression chambers 36, 38 to the liquid 6 surrounding the housing 16. The primer pump 54 is fluidly connected with the first compression chamber 36 through the first one-way intake valve 52 and an intake line 55. Similarly, the primer pump 54 is fluidly connected with the second compression chamber 38 through the second one-way intake valve 56 and the intake line 55. Alternatively, in another embodiment, the one-way intake valves 52, 56 may be directly fluidly connected (not shown) to the liquid 6 surrounding the housing 16 without a primer pump 54 and/or the intake line 55.
In the embodiment illustrated in
The outer peripheral surface 34 of the free piston 26 is configured to seal with the inner peripheral surface 20 of the interior compartment 18 without a piston sealing ring. Other variations may include the use of sealing elements at other locations on the cryogenic pump 10.
To form the sealing area 62, the outer peripheral surface 34 of the free piston 26 and the inner peripheral surface 20 of the interior compartment 18 are formed to precise tolerances, and the surfaces 20, 34 have smooth finishes. Preferably, the peripheral surfaces 20, 34 are machined to have an average roughness measurement between 0.01 micrometers and 0.1 micrometers. In other embodiments, the average roughness measurement may be less than 0.01 micrometers. Preferably, the radius 66 of the outer peripheral surface 34 of the free piston 26 is between 0.01 micrometers and 2 micrometers less than the radius 67 of the inner peripheral surface 20 of the interior compartment 18.
The sealing area 62 may prevent leakage between the first compression chamber 36 and the second compression chamber 38 at a high pressure differential, for example up to around 500 psi or more. In theory, however, some trace amounts of leakage are possible. Because the free piston 26 is enclosed within the housing 16, any leakage from one compression chamber flows to the other compression chamber. For example, any leakage from the first compression chamber 36 flows to the second compression chamber 38. Thus, the cryogenic pump 10 may prevent external (to the housing 16) leakage.
In the embodiment illustrated in
In one embodiment, reciprocation of the free piston 26 within the interior compartment 18 of the housing 16 may cause a small and controlled amount of friction-generated heat along the sealing area 62. This heat vaporizes the immediately surrounding liquid 6, creating a gas layer between the outer peripheral surface 34 of the free piston 26 and the inner peripheral surface 20 of the interior compartment 18. The gas layer is disposed along the sealing area 62 and reduces friction thereby facilitating reciprocation of the free piston 26. In this way, the gas layer may act like a linear gas bearing along the sealing area 62.
Alternatively, in another embodiment, solid dry lubricants are used to reduce friction along the sealing area 62. This may reduce friction-generated heat and prevent the gas layer from forming such that the outer peripheral surface 34 of the free piston 26 directly contacts and slides along the inner peripheral surface 20 of the interior compartment 18. In this embodiment, one or more of the outer peripheral surface 34 of the free piston 26 and the inner peripheral surface 20 of the housing 16 may include solid dry lubricants. The solid dry lubricants may include, for example, molybdenum disulfide (MoS2), sintered silicon carbide (SiC), tungsten(IV) sulfide (WS2), graphite, or a combination thereof. The solid dry lubricants may be embedded, fused, or diffused into the free piston 26 and/or the interior compartment 18. For example, thin film of the solid dry lubricants may be formed on one or more of the peripheral surfaces 20, 34, using any suitable technique, for example, conventional sputtering deposition or ion beam assisted deposition. In this embodiment, the solid dry lubricants help facilitate low friction reciprocation of the free piston 26.
No bushings or separate support structure are necessary between the free piston 26 and the interior compartment 18 of the housing 16. Rather, the inner peripheral surface 20 of the interior compartment 18 supports and guides the free piston 26 along its axis 28 during reciprocation. As explained above, low friction between the peripheral surfaces 20, 34 generates minimal heat and reduces wear.
In one embodiment, the free piston 26 may be rotated to reduce wear along the sealing area 62. For example, the electromagnetic drive 40 may be configured to rotate the free piston 26 about its axis 28 to reduce wear on the free piston 26 and housing 16 potentially caused by small variations in shape or surface finish. In the embodiment illustrated in
Alternatively, the cryogenic pump 10 may use any suitable configuration to rotate the free piston 26 as known in the art to electromagnetically rotate a shaft. Although the second magnetic portion 68 is separate from the magnetic portion 50 in this embodiment, instead, in other embodiments, magnetic portion 50 and the second magnetic portion 68 may be formed together as one continuous magnetic portion. That is, the electromagnetic drive 40 may be configured to both reciprocate and rotate the free piston 26 by acting on the magnetic portion 50.
In the embodiment illustrated in
The cryogenic pump 10 may be manufactured using any suitable method. In some embodiments, the housing 16 is manufactured as two separate parts (not shown). The two parts (not shown) of the housing 16 are assembled with the free piston 26 disposed in the interior compartment 18 of the housing 16. The two parts of the housing 16 may be sealed together using any suitable method. For example, they may be sealed using fasteners, adhesives, welding, etc. Alternatively, the housing 16 may be manufactured as a tube (not shown) with separate end caps (not shown). Once the free piston 26 is placed within the interior compartment 18 of the housing 16, the end caps are attached to the tube to seal both ends of the tube. Any suitable method may be used to attach the end caps to the tube to enclose the free piston 26 within the housing 16. For example, the end caps may be sealed to the housing 16 using fasteners, adhesives, welding etc. Additionally, any other suitable manufacturing technique for producing a housing 16 with an internally contained free piston 26 may be used.
The cryogenic pump 10 may be installed inside a tank 8 of cryogenic fuel. Installing the cryogenic pump 10 within the tank 8 may include directly mounting the housing 16 to the inside of the tank 8 to secure it therein. Alternatively, a mounting bracket (not shown) may be mounted to the tank 8 and the housing 16 may be mounted to the mounting bracket. The mounting bracket may isolate vibrations generated from the movement of the locomotive 14 or other machinery, to reduce wear on the cryogenic pump 10. In some embodiments, the cryogenic pump 10 may be assembled during installation. For example, the steps described above for enclosing the free piston 26 inside the housing 16 may be performed during installation.
In the embodiment illustrated in
In the embodiment illustrated in
The magnetic portion 50 of the free piston 26 is disposed within the outer wall 70 of the free piston 26. Any suitable material responsive to magnetic fields may be used to form the magnetic portion 50. For example, the magnetic portion 50 may be a permanent magnet. The magnetic portion 50 may disposed generally in the middle of the free piston 26 along the axis 28. Each of the electromagnetic drive 40 and the magnetic portion 50 has a length measured along the axis 28. As shown in the embodiment illustrated in
The dimensions of the various parts of the cryogenic pump 10 are selected to optimize multiple design considerations. For example, the volumes of the compression chambers 36, 38 determine the volume output of the cryogenic pump 10 per reciprocation cycle. The volumes of the compression chambers 36, 38, in turn, are a product of the stroke length 74 and the cross sectional area (not shown) of the free piston 26 in a plane orthogonal to its axis 28. In one embodiment, the free piston 26 has a diameter between 15 mm and 25 mm, and the stroke length 74 of the free piston 26 is between 90 mm and 110 mm.
The disclosed cryogenic pump 10 finds potential application in any fluid system where high-pressurization of cryogenic fluids is required. For example, the disclosed cryogenic pump 10 may be used in mobile (e.g., locomotive) or stationary (e.g., power generation) applications having an internal combustion engine that consumes the fluid pressurized by the disclosed cryogenic pump 10. Operation of the cryogenic pump 10 will now be explained.
Detailed operation of the cryogenic pump 10 will now be explained. In one embodiment illustrated in
Alternatively, however, in another embodiment, liquid 6 surrounding the housing 16 may flow directly into the interior compartment 18 without a primer pump 54 (not shown). In this embodiment, the movement of the free piston 26 draws the liquid 6 directly into the compression chambers 36, 38. Specifically, as the free piston 26 translates to the left as illustrated in
Referring again to the embodiment illustrated in
Reciprocation of the free piston 26 will now be explained in more detail.
A system of valves 52, 56, 58, 60 facilitate the flow of liquid 6 into and out of the interior compartment 18. The intake valves 52, 56 allow the liquid 6 to alternately flow into the first compression chamber 36 and the second compression chamber 38 inside the housing 16. The cryogenic pump 10 alternates between discharging the liquid 6 from the first compression chamber 36 and from the second compression chamber 38 through the exhaust valves 58, 60.
The disclosed cryogenic pump 10 may provide a high-pressure supply of fuel in a simple, low maintenance, and submergible configuration. The cryogenic pump 10 creates a sealing area 62 between the outer peripheral surface 34 of the free piston 26 and the inner peripheral surface 20 of the interior compartment 18 of the housing 16. This may eliminate the need for piston sealing rings that are both prone to wear and generate undesirable heat from friction. Eliminating these sealing members may reduce maintenance costs, down time, and the amount of heat generated from friction. Thus, the cryogenic pump 10 may be completely submerged in a cryogenic fuel without introducing undesirably large amounts of heat to the liquid fuel. Completely submerging the cryogenic pump 10 may also eliminate costly and complicated systems associated with completely and partially external pumps.
It will be apparent to those skilled in the art that various modifications and variations can be made to the pump of the present disclosure. Other embodiments of the pump will be apparent to those skilled in the art from consideration of the specification and practice of the pump disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
