EP2971770A2

EP2971770A2 - Natural gas compressing and refueling system and method

Info

Publication number: EP2971770A2
Application number: EP14720835.9A
Authority: EP
Inventors: Andrew Nelson; Pedro Santos; Jeremy Pitts
Original assignee: OSCOMP SYSTEMS Inc
Current assignee: HICOR TECHNOLOGIES Inc
Priority date: 2013-03-14
Filing date: 2014-03-14
Publication date: 2016-01-20
Anticipated expiration: 2034-03-14
Also published as: EP2971770B1; WO2014153110A3; WO2014153110A2; US20140271257A1

Abstract

A refueling system for natural gas users (e.g., natural gas vehicles) includes a two- stage compression system that compresses low-pressure gas in a natural gas supply line to compressed natural gas (CNG) pressure for use by a user. A single motor drives both a first stage rotary compressor and a rotary hydraulic pump that powers a second-stage liquid piston compressor. The motor, first stage compressor, and pump may be co-axially aligned. Booster vessels store compressed gas to augment the system's compressed gas delivery flow rate when desired. The booster vessels may be recharged with compressed gas when the system is not delivering gas to a user. Hydraulic liquid may be pumped into and out of the booster vessels during booster vessel discharge and recharge, respectively, to maintain a desired pressure within the vessels.

Description

NATURAL GAS COMPRESSING AND REFUELING SYSTEM AND METHOD

CROSS REFERENCE

[0001] This application claims the benefit of priority from U.S. Provisional Application

No. 61/783,781, filed March 14, 2013, titled "Natural Gas Home Refueling System," the entire contents of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present disclosure relates to a home refueling gas compression system and method for use with natural gas vehicles (NGV).

2. Description of Related Art

[0003] Currently, NGV infrastructure is lacking due to the high capital costs associated with construction of public NGV filling stations. Typical gas compression systems are physically too large and/or expensive to operate in a normal home.

SUMMARY OF EMBODIMENTS OF THE INVENTION

[0004] One or more aspects of the present disclosure provides an economic home refueling system (HRS) that allows consumers to realize the economic and convenience benefits of NGV vehicles and at-home refueling. One or more aspects of the present disclosure provides a commercial refueling system.

[0005] One aspect of the present disclosure relates to a gas compression system configured to compress gas. In some embodiments, the gas is natural gas. The system comprises one or more each of a first stage compressor, a second stage compressor, a hydraulic pump, and/or other components. Each stage of compression may be accomplished through the use of compressors either in series or in parallel. Hydraulic pumps may also be used in series or parallel to achieve desired hydraulic flow rates. The first stage compressor(s) is configured to compress the gas to a first pressure level and provide the gas for the second stage compressor(s) at the first pressure level. The second stage compressor(s) is configured to compress the gas from the first pressure level to a second pressure level. The hydraulic pump(s) is configured to provide pressurized hydraulic fluid for the second stage compressor(s). During a suction cycle for the second stage compressor(s), one or more first valves control a flow of the gas from the first stage compressor(s) and one or more second valves control a flow of the hydraulic fluid from the hydraulic pump(s) such that the second stage compressor(s) fills with the gas from the first stage compressor(s) with little to no re-expansion of gas, to optimize efficiency. During a compression cycle for the second stage compressor(s), the one or more first valves control the flow of gas from the first stage compressor(s) and the gas in the second stage compressor(s), and the one or more second valves control the flow of hydraulic fluid from the hydraulic pump, such that the second stage compressor(s) fills with hydraulic fluid and compresses the gas in the second stage compressor(s). During a discharge cycle for the second stage compressor(s), the one or more first valves control the flow of gas from the first stage compressor(s) and the gas in the second stage compressor(s), and the one or more second valves control the flow of hydraulic fluid from the hydraulic pump(s) and the hydraulic fluid in the second stage compressor(s) such that the gas in the second stage compressor(s) is pushed by the hydraulic fluid out of the second stage compressor(s) at the second pressure level for dispensing via a dispensing port(s)

[0006] In some embodiments, a "cascade" fill system comprised of one or more storage pressure vessels with necessary valves and piping may be used. Pressure vessels may hold up to and including the maximum second pressure level of the system. In times of high demand, the compressed gas stored in the pressure vessels could be directed to the suction side of the liquid piston compressor to boost its compression cycle, reducing temperature rise during compression and increasing mass flow rate during times of peak demand. In some embodiments, the compressed gas stored in the pressure vessels, if at full discharge pressure, could be sent directly to the discharge side of the compression system. While stored compress gas is being discharged from the storage pressure vessels, the hydraulic pump may be used to back-fill the pressure vessels with hydraulic liquid to mitigate losses due to gas expansion in the pressure vessels, improving efficiency while ensuring that the majority of stored gas is utilized. During times of inactivity on the discharge side, the compression stages would be used to re-charge the storage pressure vessels. During the re-charge cycle, compressed gas would enter the storage vessels, forcing hydraulic liquid out. By keeping the storage vessels at pressure at all times, filled with either compressed gas of hydraulic liquid, expansion losses would be mitigated.

[0007] In some embodiments, the first pressure level is (a) at least 50, 100, 150, 200,

250, 300, 350, 400, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, and/or 2000 psig, (b) less than 2500, 2000, 1750, 1500, 1250, 1000, 750, 500, 400, 300, 200, and/or 100 psig, (c) between 50 and 2000 psig, and/or (d) between any ranges nested within such ranges.

[0008] In some embodiments, the second stage compressor is a liquid piston compressor and the first stage compressor is a rotary compressor. In some embodiments, the second pressure level is (a) at least 100, 200, 500, 1000, 2000, 2500, 3000, 3500, 4000, 4500, and/or 5000 psig, (b) less than 6000, 5500, 5000, and/or 4000 psig, (c) between 100 and 6000 psig, (d) between any two of the lower and upper values discussed herein, and/or (d) between any ranges nested within such ranges. In some embodiments, the first stage compressor is configured to receive the gas at a base pressure level from a natural gas line of a home via an inlet port of the system.

[0009] In some embodiments, the system comprises a motor configured to drive a first drive-shaft of the first stage compressor and a second drive-shaft of the hydraulic pump. The motor may be co-axially located with the first drive shaft and the second drive shaft, or may be configured in another arrangement. The first drive shaft and second drive shaft may be integrated into a single or multiple drive shafts with the motor.

[0010] In some embodiments, the gas compression system is a home refueling system configured for use with natural gas vehicles. The gas compression system may be configured to compress the gas responsive to the dispensing port being coupled with a natural gas vehicle. In some embodiments, the gas compression system is used for gas compression in commercial applications. In some embodiments, the gas compression system is used for gas compression in applications requiring as much as, for example, 25, 50, 75, 100, 125, 150, or 200 HP.

[0011] In some embodiments, the first stage compressor and the second stage compressor are configured such that the gas compression is near-isothermal. The first stage compressor and/or the second stage compressor may be configured such that gas temperature rise as a result of compression is mitigated with atomized liquid injection. Atomized liquid injection may also be used at any other point in the cycle to reduce gas temperature. Atomized liquid injection may be achieved through the use of a single or a multitude of injection valves, nozzles, or ports. Liquid injection geometry, pressure, reservoir size, and other parameters may be altered to optimize cooling effects. Indirect cooling methods, such as a liquid cooling jacket surrounding the liquid piston cylinder, may be used to extract heat of compression to achieve near-isothermal compression.

[0012] In some embodiments, the system may include a housing configured to contain the first stage compressor, the second stage compressor, the one or more first valves, the one or more second valves, a motor, the dispensing port, an inlet port, and or other components of the system. The housing may be configured to be mounted to a wall in a home. The inlet port may be configured to couple with a natural gas line of the home (e.g., a residential natural gas supply line). The housing may be hermetically-sealed. Hermetic sealing may be energized by pressurized hydraulic liquid used in the main compression circuit. [0013] In some embodiments, the system may include a parallel second stage compressor configured to compress the gas from the first pressure level to the second pressure level and provide the gas at the second pressure level for dispensing via the dispensing port. The first stage compressor may be configured to provide the gas for the parallel second stage compressor at the first pressure level. The hydraulic pump may be configured to provide the pressurized hydraulic fluid for the parallel second stage compressor. The one or more first valves and the one or more second valves may be configured such that the suction cycle in the second stage compressor corresponds to a compression cycle in the parallel second stage compressor, and the compression cycle in the second stage compressor corresponds to a suction cycle in the parallel second stage compressor.

[0014] Another aspect of the present disclosure relates to a method for compressing gas.

In some embodiments, the gas may be natural gas. The method comprises compressing the gas to a first pressure level and providing the gas for a second stage compressor at the first pressure level; providing pressurized hydraulic fluid for the second stage compressor, and compressing the gas from the first pressure level to a second pressure level with the second stage compressor. During a suction cycle, a flow of the gas and a flow of the hydraulic fluid are controlled such that the second stage compressor fills with the gas at the first pressure level. During a compression cycle, the flow of gas, the gas in the second stage compressor and the flow of hydraulic fluid are controlled such that the second stage compressor fills with hydraulic fluid and compresses the gas in the second stage compressor. During a discharge cycle the flow of gas, the gas in the second stage compressor, the flow of hydraulic fluid, and the hydraulic fluid in the second stage compressor are controlled such that the gas in the second stage compressor is pushed by the hydraulic fluid out of the second stage compressor at the second pressure level for dispensing via a dispensing port. In embodiments where two or more liquid pistons are used in parallel, the liquid pistons may be mechanically connected to increase efficiency. In

embodiments with multiple liquid pistons, a hydraulic switching block with 4 or more ports may be used to control the flow of compressed hydraulic liquid between liquid pistons.

[0015] In some embodiments, the second stage compressor is a liquid piston compressor and the second pressure level is up to about 3600 psig and/or any of the pressures and ranges discussed herein for the second pressure level. In some embodiments, the gas compression is for home refueling of natural gas vehicles. The compression of the gas may be responsive to coupling the dispensing port with a natural gas vehicle. In some embodiments, the gas compression is near-isothermal. Gas temperature rise as a result of compression may be mitigated with atomized liquid injection. In some embodiments, gas temperature may be reduced post-compression through the use of a cold-line cooler in which the compressed gas would flow with or against cooled hydraulic liquid to transfer heat out of the compressed gas into the hydraulic liquid. A single cooler may be used to remove heat from the hydraulic liquid and simplify system design.

[0016] In some embodiments, the method may include compressing the gas from the first pressure level to the second pressure level and providing the gas at the second pressure level for dispensing via the dispensing port with a parallel second stage compressor, providing the gas for the parallel second stage compressor at the first pressure level, and providing the pressurized hydraulic fluid for the parallel second stage compressor. The suction cycle in the second stage compressor may correspond to a compression cycle in the parallel second stage compressor. The compression cycle in the second stage compressor may correspond to a suction cycle in the parallel second stage compressor.

[0017] Another aspect of the present disclosure provides a two-stage gas compression system configured to compress gas. The system includes a rotary power source having an output shaft; a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft; a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and a positive-displacement second stage compressor. The second stage compressor has a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to a user. The second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump.

[0018] According to one or more embodiments, the pump comprises a rotary hydraulic pump driven by a pump drive shaft that is driven by the output shaft. According to one or more embodiments, the first stage rotary compressor comprises a compressor drive shaft that drives the compressor and is driven by the output shaft. According to one or more embodiments, the output shaft, pump drive shaft, and compressor drive shaft are co-axial with each other.

According to one or more embodiments, the first stage rotary compressor and hydraulic pump are commonly disposed within a sealed shell.

[0019] According to one or more embodiments, a shaft driven by the rotary power source extends between the first stage rotary compressor and pump; a seal is disposed between the first stage rotary compressor and pump, the seal surrounding the shaft that extends between the first stage rotary compressor and pump; and during operation, pressurized liquid in the pump aids the seal in discouraging gas in the first stage rotary compressor from leaking into the pump. According to one or more embodiments, the hydraulic pump is disposed above the first stage rotary compressor. According to one or more embodiments, the second stage compressor is disposed within the sealed shell.

[0020] According to one or more embodiments, the system is a home refueling system configured to compress natural gas from a residential natural gas supply and supply compressed natural gas to a compressed natural gas vehicle; the system comprises a dispensing port operatively connected to the second stage gas outlet, the dispensing port being configured to connect to the compressed natural gas vehicle to provide second stage compressed gas to the vehicle; and the first stage gas inlet is configured to receive gas at a base pressure level from a natural gas supply line of a residential natural gas supply.

[0021] According to one or more embodiments, the first stage compressor and the second stage compressor are configured such that the gas compression is near-isothermal.

[0022] According to one or more embodiments, the system includes at least one atomized liquid injector connected to at least one of the compressors and configured to provide atomized liquid into the at least one of the compressors to cool the gas being compressed in the at least one of the compressors. According to one or more embodiments, the at least one atomized liquid injector is operatively connected to the liquid outlet of the pump such that during operation, pressurized hydraulic liquid is provided by the pump to the atomized liquid injector and injected as an atomized liquid into the at least one of the compressors. According to one or more embodiments, the system includes: a hydraulic liquid passage loop leading from the hydraulic liquid outlet of the pump, through the at least one atomized liquid injector, into the at least one of the compressors, and back to the hydraulic liquid inlet of the pump; and a hydraulic liquid cooler disposed in the hydraulic liquid passage loop, the cooler being configured to cool hydraulic liquid in the loop and thereby remove heat that is transferred from gas to the liquid. According to one or more embodiments, the system does not include a separate gas cooler to cool the gas. According to one or more embodiments, the hydraulic liquid cooler is the only component of the system that is configured to actively remove heat from the system.

[0023] According to one or more embodiments, the at least one of the compressors comprises the first stage compressor and the second stage compressor. According to one or more embodiments, the at least one atomized liquid injector comprises: at least one first stage atomized liquid injector connected to the first stage compressor and configured to provide atomized liquid into the first stage compressor, and at least one second stage atomized liquid injector connected to the second stage compressor and configured to provide atomized liquid into the second stage compressor.

[0024] According to one or more embodiments, the hydraulic fluid is an ionic liquid.

[0025] According to one or more embodiments: the second stage compressor comprises a first hydraulic piston compressor; the system further comprises a second positive-displacement hydraulic piston compressor having a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to the user; the second hydraulic piston compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump; and the system further comprises a controller that is configured to operate the first hydraulic piston compressor out of phase from the second hydraulic piston compressor.

[0026] According to one or more embodiments, the system includes a booster vessel operatively connected to the pump and second stage compressor, the booster vessel having a discharge mode and a recharge mode. According to one or more embodiments, the discharge mode comprises a mode in which (a) compressed gas in the booster vessel is discharged to the user, and (b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel. According to one or more embodiments, the recharge mode comprises a mode in which (a) second stage compressed gas flows from the second stage compressor to the booster vessel to refill the booster vessel with compressed gas, and (b) hydraulic liquid drains out of the booster vessel.

[0027] According to one or more embodiments, the system includes a controller that is configured to control the flow of hydraulic liquid out of the booster vessel so as to control a pressure within the booster vessel during the recharge mode.

[0028] According to one or more embodiments, the discharge of compressed gas from the booster vessel during the discharge mode comprises direct discharge from the booster vessel to the user.

[0029] According to one or more embodiments, the discharge of compressed gas from the booster vessel during the discharge mode comprises discharge from the booster vessel through the compressor to the user.

[0030] According to one or more embodiments, the discharge mode comprises a boosted discharge mode in which: (a) compressed gas in the booster vessel is discharged to and combined with a flow of compressed gas provided by one of the compressors, and (b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel.

[0031] According to one or more embodiments, the system includes a controller that is configured to control the flow of hydraulic liquid into the booster vessel so as to control a pressure within the booster vessel during the discharge mode. According to one or more embodiments, the controller is configured to maintain a pressure within the booster vessel between lower and upper pressure thresholds during the discharge and recharge modes.

[0032] According to one or more embodiments: the booster vessel comprises a first booster vessel; the discharge mode comprises a first discharge mode; the recharge mode comprises a first recharge mode; the system further comprises a second booster vessel having a second discharge mode and a second recharge mode; the second discharge mode comprises a mode in which (a) compressed gas in the second booster vessel is discharged to the user, and (b) hydraulic liquid is pumped from the pump into the second booster vessel to take the place of compressed gas being discharged from the second booster vessel; and the second recharge mode comprises a mode in which (a) second stage compressed gas flows from the second stage compressor to the second booster vessel to refill the second booster vessel with compressed gas, and (b) hydraulic liquid drains out of the second booster vessel.

[0033] One or more aspects of the present disclosure provide a method of using a two- stage gas compression system to compress gas, the system comprising a rotary power source having an output shaft; a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft; a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and a positive-displacement second stage compressor having a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to a user, wherein the second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump. According to one or more aspects of the present disclosure, the method comprises receiving a gas at the first stage gas inlet; operating the rotary power source, which causes the output shaft to drive the first stage compressor, thereby compressing the gas in the first stage compressor into first stage compressed gas;

causing the first stage compressed gas to flow from the first stage gas outlet into the second stage compressor via the second stage gas inlet; operating the rotary power source, which causes the output shaft to drive the pump and pump hydraulic liquid into the second stage compressor, thereby compressing the first stage compressed gas disposed within the second stage compressor into second stage compressed gas; and discharging the second stage compressed gas from the second stage compressor to a user.

[0034] According to one or more embodiments, the gas comprises natural gas, methane, a different hydrocarbon gas, and/or mixtures of different hydrocarbon gases. According to alternative embodiments, the gas may comprise other types of gases (e.g., non-fuel gases, non- hydrocarbon gases, inert gases, etc.).

[0035] According to one or more embodiments, the method includes injecting atomized liquid into at least one of the compressors while the at least one of the compressors is compressing gas. According to one or more embodiments, the injecting comprises transferring pressurized hydraulic liquid from the liquid outlet of the pump to an atomized liquid injector, and atomizing the pressurized liquid to create the atomized liquid.

[0036] According to one or more embodiments: the system comprises a hydraulic liquid passage loop leading from the hydraulic liquid outlet of the pump, through the at least one atomized liquid injector, into the at least one of the compressors, and back to the hydraulic liquid inlet of the pump, and a hydraulic liquid cooler disposed in the hydraulic liquid passage loop; and the method further comprises using the cooler to cool hydraulic liquid in the loop.

[0037] According to one or more embodiments, the method further comprises alternately operating a booster vessel in a discharge mode and a recharge mode. According to one or more embodiments, operating the booster vessel in the discharge mode comprises simultaneously (a) discharging compressed gas from the booster vessel to the user during the discharging of the second stage compressed gas from the second stage compressor to the user, and (b) pumping hydraulic liquid from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel. According to one or more embodiments, operating the booster vessel in the recharge mode comprises simultaneously (a) transferring second stage gas from the second stage compressor to the booster vessel to refill the booster vessel with compressed gas, and (b) draining hydraulic liquid out of the booster vessel.

[0038] According to one or more embodiments, the pumping of hydraulic liquid from the pump into the booster vessel maintains a pressure within the booster vessel above a predetermined lower threshold. According to one or more embodiments, the draining of hydraulic liquid out of the booster vessel maintains the pressure within the booster vessel below a predetermined upper threshold.

[0039] One or more aspects of the present disclosure provide a compressed gas supply system comprising: a compressed gas supply line configured to supply compressed gas to a user; a hydraulic pump configured to provide pressurized hydraulic liquid; and a booster vessel having a discharge mode and a recharge mode. According to one or more embodiments, the discharge mode comprises a mode in which (a) compressed gas in the booster vessel is discharged to the user, and (b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel. According to one or more embodiments, the recharge mode comprises a mode in which (a) compressed gas flows from the compressed gas supply line to the booster vessel to refill the booster vessel with compressed gas, and (b) hydraulic liquid drains out of the booster vessel.

[0040] According to one or more embodiments, the compressed gas supply line is part of a compressor system comprising at least one compressor.

[0041] According to one or more embodiments, the discharge mode comprises a boosted discharge mode in which (a) compressed gas in the booster vessel is discharged to and combined with a flow of compressed gas flowing through compressed gas supply line to increase a compressed gas flow rate provided by the system to the user, and (b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel.

[0042] According to one or more embodiments, the system includes a controller that is configured to control the draining of hydraulic liquid out of the booster vessel so as to control a pressure within the booster vessel during the recharge mode.

[0043] According to one or more embodiments, the system includes a controller that is configured to control the pumping of hydraulic liquid into the booster vessel so as to control a pressure within the booster vessel during the discharge mode.

[0044] According to one or more embodiments, the system includes a controller that is configured to maintain a pressure within the booster vessel between lower and upper pressure thresholds.

[0045] One or more aspects of the present disclosure provide a method of providing compressed gas to a user, the method comprising alternately operating a booster vessel in a discharge mode and a recharge mode. According to one or more embodiments, operating the booster vessel in the discharge mode comprises (a) discharging compressed gas from the booster vessel to the user, and (b) pumping hydraulic liquid from a pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel. According to one or more embodiments, operating the booster vessel in the recharge mode comprises (a) transferring compressed gas from the compressed gas supply line into the booster vessel to refill the booster vessel with compressed gas, and (b) draining hydraulic liquid out of the booster vessel.

[0046] According to one or more embodiments, the pumping of hydraulic liquid from the pump into the booster vessel maintains a pressure within the booster vessel above a predetermined lower threshold. According to one or more embodiments, the draining of hydraulic liquid out of the booster vessel maintains the pressure within the booster vessel below a predetermined upper threshold.

[0047] According to one or more embodiments, operating the booster vessel in the discharge mode comprises: (a) discharging compressed gas from the booster vessel to the user while discharging compressed gas from a compressed gas supply line to the user to increase a compressed gas flow rate provided to the user, and (b) pumping hydraulic liquid from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel.

[0048] These and other aspects of various embodiments of the present invention, as well as the methods of operation and functions of the related elements of structure and the

combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. In one embodiment of the invention, the structural components illustrated herein are drawn to scale. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. In addition, it should be appreciated that structural features shown or described in any one embodiment herein can be used in other embodiments as well. As used in the specification and in the claims, the singular form of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

[0049] All closed-ended (e.g., between A and B) and open-ended (greater than C) ranges of values disclosed herein explicitly include all ranges that fall within or nest within such ranges. For example, a disclosed range of 1-10 is understood as also disclosing, among other ranged, 2- 10, 1-9, 3-9, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] For a better understanding of embodiments of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

[0051] FIG. 1 illustrates an overview of a home refueling system in accordance with various embodiments.

[0052] FIG. 2 illustrates a home refueling system process flow diagram in accordance with various embodiments.

[0053] FIG. 3 illustrates a home refueling system process flow diagram for a dual piston embodiment in accordance with various embodiments.

[0054] FIG. 4 is a rendering of a home refueling system in accordance with various embodiments.

[0055] FIG. 5 is a home refueling system bill of materials in accordance with various embodiments.

[0056] FIG. 6 provides top, front, side, and perspective illustrations of external surfaces of a housing of a home refueling system in accordance with various embodiments.

[0057] FIG. 7 provides top, front, side, and perspective illustrations of components housed by a housing of a home refueling system in accordance with various embodiments.

[0058] FIG. 8 illustrates a first stage gas compressor and a hydraulic pump in accordance with various embodiments.

[0059] FIG. 9 illustrates an electric motor driver for a co-axial gas compressor and hydraulic pump in accordance with various embodiments.

[0060] FIG. 10 illustrates a second stage liquid piston compressor in accordance with various embodiments.

[0061] FIG. 11 illustrates an integrated post-compression filter/dryer unit in accordance with various embodiments.

[0062] FIG. 12 illustrates a hermetically sealed mounting package in accordance with various embodiments.

[0063] FIG. 13 illustrates a method for compressing gas in accordance with various embodiments.

[0064] FIG. 14 illustrates a controller configured to control various components of the system. [0065] FIGS. 15 and 16 are side diagrammatic views of the motor, compressor, and pump of the system of FIG. 1.

[0066] FIGS. 17-21 are process flow diagrams for a refueling system in accordance with various embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

[0067] One or more embodiments of the present invention provide an affordable home- refueling system for use with natural gas vehicles (NGV). A two-stage compression system compresses low-pressure gas in home natural gas lines to compressed natural gas (CNG) pressure for NGV refueling. This hybrid system is comprised of two stages whose near- isothermal mechanisms allow for high efficiency operation and may eliminate gas coolers to reduce costs, both fiscally and spatially. The use of hydraulic liquid compression in natural gas allows for near-isothermal compression of residential natural gas from a range of residential line pressures, from about 0.05 psig to about 50 psig for example, up to pressures as high as standard CNG pressure, about 3600 psig for example. Home refueling systems may allow for greater market penetration of NGVs, which may shift demand in various countries (e.g., the U.S.) away from imported oil and toward domestic natural gas resources.

[0068] FIG. 1 illustrates a hybrid positive-displacement, near-isothermal compression system 100 for NGV at-home refueling. The system 100 includes a low part count and a compact design. Compression of natural gas from near atmospheric to higher pressure, as high as or higher than standard CNG pressure, about 3600 psig for example, is achieved through a two-stage positive displacement compression design, comprised of a first-stage rotary compressor 12 and a second-stage liquid piston compressor 18. The liquid piston compressor 18 is driven by a rotary hydraulic pump 14 and hydraulic system 102 (system 102 is shown in FIG. 2).

[0069] Through the use of liquid injection into a first-stage rotary compressor 12 and a second-stage liquid piston compressor 18, system 100 achieves near-isothermal compression up to and including the standard CNG pressure of about 3600 psig or higher, for example, according to various embodiments. By locating the rotary compressor 12 and hydraulic rotary pump 14 co-axially with an integrated electric drive motor 16 that drives both the compressor 12 and the pump 14, the system 100 efficiency can be increased while system size, weight and cost can be decreased.

[0070] As shown in FIGS. 15 and 16, the motor 16, compressor 12, and pump 14 are hermetically sealed within a shell 16b of the motor 16. A hydraulic rotary seal 16c separates the motor 16 from the pump 14 and surrounds the shaft(s) 16a and/or 14a. A gas and hydraulic rotary seal 14c separates the pump 14 from the compressor 12 and surrounds the shaft(s) 16a, 14a, and/or 12a. A gas rotary seal 12c separates the compressor 12 from the remainder of the inside of the shell 16b, and surrounds the shaft 16a and/or 12a. However, one or more of the seals 16c, 14c, 12c may be omitted without deviating from the scope of the present invention.

[0071] Positioning the hydraulic rotary pump 14 above the rotary compressor 12 allows for the hydraulic fluid to act as a seal against axial leakage from the rotary compressor 12 to the motor 16, further increasing efficiency and eliminating or reducing the need for a separate set of seals to prevent gas leakage into the motor 16. For example, the sealing function of the seal 14c is aided by the fact that the hydraulic fluid above is at a higher pressure than the gas below, thereby further discouraging gas from leaking from the compressor 12 into the pump 14.

Through these and/or other approaches, the system 100 may achieve the desired performance and cost targets to provide a cost-effective, small CNG at-home refueling technology.

[0072] The process flow for the system 100 is outlined in FIG. 2. An overview rendering of the system is shown in FIG. 4. The system 100 can be broken down into major subsystems and key components as seen in the bill of materials in FIG. 5, for example. The bill of materials shown in FIG. 5 should be considered a non-limiting example. The specifics of the bill of materials shown in FIG. 5 (e.g., use of a rotary vane style compressor and pump, specific line sizes, specific valve components, specific discharge components, etc.) represent just one potential embodiment of the system 100. In some embodiments, the system 100 may include some and/or none of the components listed in FIG. 5. In some embodiments, the system 100 may include components not listed in FIG. 5.

[0073] As shown in FIGS. 1 and 2, an output shaft 16a of the motor 16, and the drive shafts 12a, 14a of the compressor 12 and pump 14 are co-axially disposed and connected to each other for common rotation. The shafts 12a,14a,16a may be discrete structures that are operatively connected together for common rotation, or the shafts 12a, 14a, 16a may be integrally formed with each other. The co-axial arrangement may simplify the system 100 design and reduce cost. The hydraulic pump 14 may be located above the rotary gas compressor 12 (an example arrangement is shown in FIG. 1) so that hydraulic fluid that leaks out of the pump 14 will travel downwards by gravity into the gas compressor 12 to aid in sealing and cooling of the gas. The relative locations of the first-stage gas compressor and hydraulic pump may be reconfigured. For example, the compressor 12 may alternatively be disposed above the pump 14. [0074] Co-axial power is transmitted through direct-drive coupling of the motor 16 to the hydraulic pump 14 and rotary gas compressor 12. In some embodiments, the output shaft 16a of the motor 16 could be developed with the other rotating components such that all three components 12a, 14a, 16a would share a common shaft. Co-axial location may allow for reduced part counts and manufacturing costs. In addition, assembly may be simplified since shafts are integrally aligned and may avoid the use of expensive laser alignment systems for assembly.

[0075] Alternatively, the output shaft 16a could be located in a non-co-axial fashion relative to the drive shafts 12a, 14a, while power could be transmitted through gears, pulleys, or other power transmission methods.

[0076] The relative sizes and outputs of the compressor 12 and pump 14 may be optimized to balance the demand for first stage compressed gas from the compressor 12 and pressurized hydraulic liquid from the pump 14. The power of the motor 16 may, in turn, be optimized to meet the demand placed on the motor 16 by the compressor 12 and pump 14 during use of the system 100.

[0077] The illustrated motor 16 comprises an electric motor 16. Alternatively, any other type of motor 16 may be used (e.g., a natural gas engine, an internal combustion engine, etc.).

[0078] The first stage gas compressor 12 may be a rotary-type gas compressor. Rotary compression technology is described as the preferred embodiment, but any other rotary-type compression technology may alternatively be used, including, but not limited to, lobe, scroll, screw, liquid-ring, rotary piston and rolling piston technologies. According to various embodiments, the rotary gas compressor comprises a positive displacement rotary gas compressor. According to various embodiments, the first stage compressor 12 is similar or identical to any of the rotary compressors described in U.S. Application Serial No. 13/782,845, filed March 1, 2013, titled "COMPRESSOR WITH LIQUID INJECTION COOLING," the entire contents of which are incorporated herein by reference. The first-stage gas compressor 12 is used to increase the pressure of the natural gas entering the system from near atmospheric pressure, and/or other pressures to the first pressure. Alternatively, the compressor 12 may comprise a non-rotary-type compressor (e.g., piston compressor), and the motor 16 can be adapted to power such a compressor (e.g., linear motor, rotary motor with a linear motion converter, etc.).

[0079] In some embodiments, first stage gas compressor 12 increases the pressure from about 0.25 psig to about 220 psig, for example. However, inlet pressure can range from about 0.05 psig to about 200 psig or higher, for example, depending on the gas source. Residential gas supplies tend to be lower (e.g., between about 0.5 and 50 psig) and commercial/industrial gas supplies tend to be higher (e.g., between about 40 and 200 psig). The first-stage discharge pressure can range from about 50 psig to about 400 psig or higher, for example. In some embodiments, depending on the type of first stage compressor used, the first pressure level is (a) at least 50, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, and/or 2000 psig, (b) less than 2500, 2000, 1750, 1500, 1250, 1000, 750, 500, 400, 300, 200, and/or 100 psig, (c) between 50 and 2000 psig, and/or (d) between any ranges nested within such ranges. The rotary compressor 12 is driven by a rotary power source (e.g., motor 16, internal combustion (e.g., natural gas) engine, hydraulic motor, etc.) to achieve compression.

[0080] As shown in FIG. 2, cooling liquid is injected into the rotary compressor 12's chamber through the use of atomized liquid injectors (e.g., atomizing nozzles) 15 in order to reduce gas temperatures. In some embodiments, liquid can be injected into the compression chamber through the use of valves, other nozzles, ports, or other methods of injection.

Additionally, liquid may be injected, through any of the aforementioned injection methods, into the gas stream before suction or after discharge. In some embodiments, the liquid to be injected would be of the same composition as those used in the hydraulic system. Thus, the atomized liquid used for gas cooling may comprise atomized hydraulic liquid from a low pressure hydraulic reservoir 26. As shown in FIG. 2, the pressurized hydraulic liquid may be provided by the pump 14 to the nozzles 15 to provide atomized hydraulic fluid into the compression chamber of the compressor 12. The atomized liquid injected into the compressor 12 may flow along with the first stage compressed gas to the compressor 18 and then back to the reservoir 26 during the suction step (discussed below) during which hydraulic liquid in the compressor 18 is drained back into the reservoir 26. Additionally and/or alternatively, the compressor 12 may include a liquid drain and passageway (and optional pump) that directly drains the liquid back to the reservoir 26.

[0081] While the illustrated system 100 uses the hydraulic liquid from the pump 14 as the coolant,, other liquids may be used as the cooling liquid for heat transfer including, but not limited to, ionic liquids, oils, glycol-based coolants, and water. Alternatively, liquid cooling may be omitted without deviating from the scope of various alternative embodiments.

[0082] In some embodiments, the hydraulic pump 14 uses rotary pump technology. The hydraulic pump 14 type may be re-configured based on the technology application. In some embodiments, gear, rotor, screw, swashplate, radial piston, peristaltic pump, and/or other types of pumps may be used for this hydraulic pressurization stage. Pump 14 suctions liquid from a low-pressure reservoir 26 and pumps it to the liquid piston compressor 18, increasing the pressure of the liquid as needed to allow for compression of the gas in the liquid piston 18. Compressor and pump geometries may be re-configured for system optimization.

[0083] The second stage gas compressor 18 may be a liquid piston gas compressor. This compression technology uses a hydraulically-driven liquid to reduce the volume, and thereby increase the pressure, of the gas. The compressor 18 includes a vertical cylinder/piston with a hydraulic port on the lower portion of the cylinder and gas suction and discharge valves (e.g., valve(s) 30a, 30b, respectively) on the upper portion of the cylinder. The unit is powered through hydraulic liquid pumped by the hydraulic rotary pump 14. In some embodiments, the hydraulic fluid is an ionic liquid. In some embodiments, oils or hydraulic fluids may be used. In addition, additives may be included to prevent foaming of the liquid and increase the useful life of the liquid.

[0084] In some embodiments, depending on the type of second stage compressor 18 used, the output second pressure level of the second stage compressed gas is (a) at least 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, 2000, 2500, 3000, 3500, 4000, 4500, and/or 4900 psig, (b) less than 6000, 5100, 5000, 4500, 4000, 3700, 3500, 3000, 2500, 2000, 1750, 1500, 1250, 1000, and/or 750 psig, (c) between 1900 and 5100 psig, and/or (d) between any ranges nested within such ranges. According to various preferred embodiments, the second pressure level is about 2000, 3600, or 5000 psig.

[0085] During compression in the compressor 18, heat is removed from the gas through heat transfer between the gas and the hydraulic fluid within the compressor 18. In addition, liquid injection (e.g., atomized liquid coolant) may be used in the liquid piston 18 to further reduce gas temperatures in the same or similar manner as can be done in the compressor 12, as discussed above. As shown in FIG. 2, pressurized hydraulic liquid is provided from the pump 14 to atomized liquid injectors (e.g., atomizing nozzles, valves, ports, or other atomized liquid injectors) 19 to deliver atomized hydraulic liquid to the compression chamber of the compressor 18 so that the atomized liquid absorbs heat from the gas being compressed. The atomized liquid then joins the hydraulic liquid in the compressor 18 and returns to the reservoir 26 during the suction step (discussed below) Additionally, liquid may be injected, through any of the aforementioned injection methods, into the gas stream before suction or after discharge. In some embodiments, the liquid to be injected would be of the same composition as those used in the hydraulic system, but some embodiments may use other liquids for heat transfer including, but not limited to, ionic liquids, oils, glycol-based coolants, and water.

[0086] As shown in FIG. 2, a gas cooler 33 may be disposed downstream from the compressor 18 to further cool the gas, particularly in situations where low temperature compressed gas is desired. However, the hydraulic liquid cooler 29 is preferably effective enough that the gas cooler 33 may be omitted and a single hydraulic liquid cooler 29 used to cool the entire system 100. According to various embodiments, the gas cooler 33 may use fresh hydraulic liquid from the reservoir 26 (or downstream from the hydraulic liquid cooler 29) as the coolant so that the gas cooler 33 ultimately relies on the cooler 29 to remove heat from the gas.

[0087] Additionally and/or alternatively, the compressor 12 and/or compressor 18 may be lined with a cooling jacket with a coolant passage through which cooled coolant (e.g., the hydraulic liquid) flows to cool the compressor 12,18 and the gas therein.

[0088] According to various embodiments, the reservoir 26 may be sized and shaped to function as both a heat sink and a heat exchanger. During use of the system 100, heat is transferred to the hydraulic liquid and accumulates in the reservoir 26 filled with such heated hydraulic liquid. The reservoir 26 may be shaped to facilitate passive heat transfer from the hydraulic liquid to the ambient environment (e.g., via large reservoir exterior surface area and/or heat transfer fins (e.g., aluminum). A fan may be added to further boost such heat transfer to the ambient environment. In embodiments in which the system 100 is entirely hermetically sealed, the exterior of the reservoir 26 may be disposed outside of the hermetically sealed environment so as to facilitate heat transfer to the ambient environment.

[0089] As shown in FIG. 2, heat that is transferred to the hydraulic liquid from the gas in the compressor 12 and/or compressor 18 is then dumped to the ambient environment or other heat sink via a hydraulic liquid cooler/heat exchanger 29 that is disposed between the valve 28 and reservoir 26 or between the reservoir 26 and pump 14 (FIG. 2 illustrates both alternative options, though additional locations along the hydraulic liquid piping may alternatively be used). The hydraulic liquid cooler 29 may comprise any type of suitable active or passive cooler (e.g., a heat exchanger coupled to a refrigeration system, a vaned-heat sink over which air is blown by a fan to dump heat into the ambient environment, etc.). According to various embodiments, the use of the hydraulic fluid as a coolant facilitates the use of a single cooler/heat exchanger 29 to dump heat that is generated during gas compression in the compressor 12 and compressor 18. Thus, according to various embodiments, the hydraulic liquid cooler 29 is the only component of the system 100 that is configured to actively remove heat from the system 100. The remaining heat exchange components (e.g., the atomized liquid injectors 15, 19, the gas cooler 33) may be used to transfer heat from the gas into the liquid, with such heat then transferred out of the system by the cooler 29.

[0090] In some embodiments, the liquid piston compressor 18 may be replaced with a "power gas" compressor, which operates in a similar manner, but uses 2-stage boosted gas in place of hydraulic liquid. In this embodiment, a steeple piston would be used to boost the gas to up to about 3600 psig of gas pressure or above, for example. A steeple piston uses one large piston and one small piston with a gas or liquid filled volume separating them and their cylinders, each of different size. Lower pressure gas, from about 50 to about 300 psig for example, would force the large piston up in its cylinder. As the piston moved upwards, it would force the gas or liquid filling the intermediary volume to push the smaller piston upwards, compressing the "power gas" up to about 3600 psig or above. This power gas would be pumped into the main compression piston, which would boost the process gas from its intermediary pressure, as it came out from the first-stage rotary compressor 12, to up to about 3600 psig or above. This system may use a physical barrier between the process gas and the power gas, such as any combination of a piston, flat plate, disc, and piston skirt.

[0091] In some embodiments, gas is kept separate from hydraulic liquid in the compressor 18 through the use of ionic liquid as the hydraulic liquid, due to very low gas solubility. In some embodiments, gas may be isolated from the hydraulic liquid, ionic liquid or other liquids, through the use of a barrier whose outer profile matches the liquid piston chamber's shape. This barrier can be a solid thin disc, a perforated surface, a thicker curved surface that can be oriented to trap hydraulic fluid and/or gas, and/or other barriers. A piston skirt may be used to ensure alignment of the physical barrier during reciprocation, preventing jamming or clocking of the barrier. Additionally, a diaphragm can be used to isolate gas from hydraulic liquid.

[0092] Due to potential contamination of the process gas, a filter and dryer 20 is typically used at the discharge outlet of the compressor 18 to remove or reduce contaminants and liquids found in the stream before the gas is discharged from the home refueling system 100. In some embodiments, this filtration system 20 is designed to utilize a cartridge-type filter for easy maintenance. In some embodiments, the filter could be cleaned and re-used. The disposable dryer cartridge element, which could be composed of either absorbent and/or adsorbent materials, may also feature filtration mechanisms such as coalescing and interception. The disposable nature of this cartridge according to various embodiments may reduce upfront costs to the user by spreading those costs out over time, as an operating cost incurred by periodic maintenance. For normal operating conditions, moisture in the gas will be low after the second stage of compression. Therefore, a small dryer, or none at all, can be integrated into the filter unit 20 according to various embodiments. However, for extreme operating conditions, a full dryer system may be used to remove moisture from the gas before it is discharged from the home refueling system 100. To achieve low cost and flexibility, the unit 100 may be offered, for example, in two variations, for normal and extreme operating conditions. The filter/dryer units 20 may be designed to be interchangeable on a system level, dependent on the operating conditions expected for the unit 100.

[0093] As illustrated in FIGS.1 and 2, the home refueling system 100 may be designed as a turnkey system featuring just two process connection points. Gas enters the system through a suction connection 10 permanently attached to a gas line and discharges through a

standardized CNG connector 24 on the end of a flexible hose 22. A simple control system allows the user to monitor system performance, maintenance requirements, and operation of the unit. An encompassing housing enclosure 50 with mounted back-plate 52 may facilitate simple installation of the system 100 as a unit.

[0094] The gas suction line 10 leads from the exterior of system 100 into a tee connection within the unit. The tee branches out between the first-stage gas compressor 12's suction port and the gas recycle line from the outlet of the first-stage compressor 12. A backflow valve 60 (shown in FIG. 2) is used to control recycled flow from the first-stage compressor's discharge to inlet. Once the liquid piston 18 has finished its suction cycle, high-pressure gas from the first stage is no longer needed until the next liquid piston suction cycle. It is at this point that flow is recycled through opening of backflow valve 60 while the compressor 12 runs at lower load, saving energy. Once the liquid piston 18 has started to discharge, this backflow control valve 60 is closed again, allowing the first-stage gas compressor 12 to fill the liquid piston's suction line with high pressure gas for the next cycle.

[0095] After the gas has been compressed in the second-stage liquid piston 18, it passes through filter and dryer 20 to remove all, most, or some contamination and moisture. Then, it exits the enclosure 50 through a connection to external flexible hose 22. At the end of this hose 22, a break-away valve and NGV connector 24 are mounted. The break-away valve is included as a safety device that will break and stop flow in case the vehicle is driven away from the home refueling system 100 while still connected. The flexible hose 22 is used to allow a person to connect to their vehicle. [0096] As shown in FIG. 2, the hydraulic system 102 is anchored by a large low- pressure hydraulic reservoir 26 (also shown in FIG. 1) which is sized to hold a multiple of the volume of liquid required to fill the liquid piston compressor 18's chamber. Hydraulic reservoir 26 is vented to the inlet to ensure that its internal pressure remains at or below a predetermined threshold (e.g., at or below 20, 15, 10, and/or 5 psig). Since reservoir 26 does not have to hold relatively high pressure, it can be shaped in a convenient way to fit in the package and reduce overall system 100 size. Fins may be included on the hydraulic reservoir 26 to increase heat transfer from the liquid to the ambient environment. From the base of the reservoir 26, liquid is drawn into the suction side of the rotary hydraulic pump 14. It is then pumped into a multi-way valve 28 between the liquid piston 18 and the low pressure reservoir 26. In some embodiments, a four-way valve will be used, as seen in FIG. 2. During the compression and discharge steps, the valve 28 will connect the discharge of the hydraulic rotary pump 14 to the liquid piston 18 to fill the piston 18 with pressurized hydraulic liquid. Concurrently, the valve 28 will connect the hydraulic reservoir 26 to the inlet of the hydraulic rotary pump 14. During the suction stroke of the liquid piston 18, the valve 28 will switch to connect the liquid piston 18 to the hydraulic reservoir 26 to discharge the hydraulic fluid. Concurrently, the valve 28 will connect the hydraulic pump 14 discharge to the hydraulic pump 14 inlet, recycling the hydraulic fluid at low pressure, saving energy. In some embodiments, the position of the four-way valve 28 may be controlled electrically based on the signal of a float in the liquid piston 18 that triggers the system 100 to alternate between the suction and compression steps. In some embodiments, the four-way valve 28 could be actuated electrically based on the use of a flow transducer before the filter element. In some embodiments, a solenoid valve could be used at the inlet of the low pressure hydraulic reservoir 26, just past a tee connection between the liquid piston hydraulic port and the hydraulic pump discharge piping. Actuation of this solenoid valve may control the direction of flow during liquid piston 18 suction and discharge cycles.

[0097] The pumped liquid pressure is dependent on pressure in the liquid piston 18. The pump 14 will produce enough hydraulic pressure to overcome the pressure downstream.

Therefore, the hydraulic pump 14 may be sized so that it can achieve more than about 3600 psig or higher, for example, hydraulic pressure to allow for compression of the gas in the liquid piston compressor 18. During the liquid piston's compression cycle, the hydraulic pump 14 increases hydraulic pressure continually such that hydraulic pressure exceeds gas pressure and the liquid level in the liquid piston 18 rises. Once the gas has been fully compressed and subsequently discharged, the hydraulic fluid is forced out of the liquid piston 18 by the incoming gas pressure, where it goes back into the hydraulic reservoir 26. Throughout this process, the hydraulic pump 14 continues to pump the fluid through the system at very low energy cost, due to the lack of back-pressure to compress against.

[0098] System 100 is mounted onto a frame for simple installation in a residential environment. Part of the enclosure is hermetically sealed to eliminate the risk of harmful methane leakage into a residential environment. This hermetically-sealed chamber may be kept at very slight positive pressure, under 2 psig for example, to prevent air from the outside environment from entering the hermetically-sealed chamber. This hermetically-sealed chamber may be kept at very slight negative pressure to prevent methane from escaping into the outside environment from the hermetically-sealed chamber. Hydraulic pressure may be used to energize hermetic sealing of the chamber. In some embodiments, the hermetically-sealed chamber may be kept at atmospheric pressure, a slight vacuum (negative) pressure, and/or other pressures. The other part of the enclosure is vented to the environment to enable heat transfer from the compression systems. The compression systems generate heat that is preferably vented. To reduce or avoid the buildup of high temperatures, a lower explosive limit (LEL) sensor is used. If a temperature within the LEL limits is detected, the system 100 may automatically shut itself down to reduce the chance of catastrophic damage.

[0099] FIG. 6 is a schematic illustration of external surfaces of housing enclosure 50 of home refueling system 100 in accordance with various embodiments. FIG. 7 is a schematic illustration of the components (described herein) housed by a housing enclosure 50 of system 100 in accordance with various embodiments. FIG. 8 illustrates first stage gas compressor 12 and hydraulic pump 14 in accordance with various embodiments. FIG. 9 illustrates electric motor driver 16 for a co-axial gas compressor (e.g., first stage compressor 12) and hydraulic pump (e.g., hydraulic pump 14) in accordance with various embodiments. FIG. 10 illustrates second stage liquid piston compressor 18 in accordance with various embodiments. FIG. 11 illustrates integrated post-compression filter/dryer unit 20 in accordance with various embodiments. FIG. 12 illustrates a hermetically sealed mounting package (e.g., housing enclosure 50) in accordance with various embodiments.

[00100] Operation

[00101] Operation of the refueling system 100 is described with reference to FIG. 2.

[00102] First Stage Compression: At the bottom left of FIG. 2, natural gas enters the system from the residence's (or commercial site's) natural gas supply line via a gas inlet 10. Typically, this supply of natural gas is regulated down to a pressure of about 0.25 psig, but system 100 covers inlet gas pressure ranging from about 0.05 to about 50 psig or higher. Gas enters the first-stage rotary compressor 12, where it is compressed near-isothermally at high speed, allowing a high volumetric efficiency and a compact unit due to the high displacement per unit of volume and weight typical to a rotary device. Gas temperature rise, a result of compression, is mitigated through the use of atomized liquid injection for cooling purposes, for example as disclosed in U.S. Application Serial No. 13/782,845, filed March 1, 2013, titled "COMPRESSOR WITH LIQUID INJECTION COOLING," the entire contents of which are incorporated herein by reference. The atomized liquid may also coat the internal compressor surfaces to serve a second purpose as a lubricant to the compressor's components and bearings. Atomized liquid injection is used to increase the liquid surface area available for heat transfer from the compressed gas into the liquid. In addition, the atomized liquid can be injected in a turbulent pattern in order to increase heat transfer. Very rapid heat transfer may, especially in the rotary first stage, reduce temperature fast enough that it reflects in a reduction of the actual compression volume, thereby reducing the energy required to complete compression.

[00103] Second Stage Suction Step: During the first stage compression step, the first- stage compressed gas is piped from the compressor 12 to the second-stage liquid piston compressor 18. At the beginning of this suction step, the liquid piston compressor 18 is partially or substantially filled with hydraulic fluid (from the second stage compression step discussed below). As gas flows from the compressor 12 to the piston compressor 18, the liquid in the liquid piston 18 is forced out by the pressure of the gas entering the piston compressor 18.

[00104] During the second stage suction step, a control valve 28 (1) connects the bottom of the compressor 18 to the hydraulic reservoir to allow hydraulic fluid to drain from the compressor 18 to the reservoir 26, and (2) disconnects an outlet of the pump 14 from the compressor 18 so as to cause the pump 14 to recirculate hydraulic fluid back to itself and/or the reservoir 26. To ensure that the liquid does not discharge too quickly from the compressor 18 during the suction step, resulting in the inefficient expansion of the gas from the first-stage entering the liquid piston stage, the control valve 28 maintains synchronicity between the gas flowing into the piston compressor 18 and hydraulic fluid flowing out of the compressor 18 and into the low pressure hydraulic reservoir 26. For example, the valve 28 may be pressure- regulated (e.g., via a pressure-regulated valve, or through an active control system) so as to only allow fluid flow from the compressor 18 to the reservoir 26 when the liquid pressure in the compressor 18 exceeds a predetermined pressure (e.g., a pressure at or slightly lower than a designed outlet pressure of the first-stage compressed gas provided by the compressor 12). Hydraulic line pressure control may be designed so that the gas entering the compressor 18 can suction quickly enough that it does not get choked at the inlet, increasing back-pressure on the liquid piston.

[00105] The pressurized gas from the first stage helps to drive the hydraulic liquid from the cavity of the compressor 18 at a faster rate than gravity or other methods, increasing the velocity/rate of compression cycling, and in turn enabling a higher efficiency for the unit. For example, by increasing the speed of the compressor 12, the volume of gas compressed per unit time is increased such that a smaller machine at a higher speed may achieve the same flow rate as a larger machine at a lower speed.

[00106] The suctioning step is completed when the first stage compressed gas has filled or substantially filled the compressor 18, and the hydraulic fluid has been substantially drained from the compressor 18.

[00107] During the suction step, a compressor 18 inlet valve 30a is open, and a compressor 18 outlet valve 30b is closed. In addition to or in the alternative to the valves 30a, 30b comprising on/off valves, the valves 30a,30b may comprise check- valves such that the valve 30a only permits gas flow from the compressor 12 to the compressor 18, and valve 30b only permits gas flow from the compressor 18 to the user (e.g., via the filter and dryer 20).

[00108] Second Stage Compression Step: Once first stage compressed gas has

substantially or completely filled the liquid piston cylinder 18 during the suction step, hydraulic fluid from the pump 14 is pumped into the compressor 18, compressing the gas. During the compression stroke of the liquid piston compressor 18, this fluid is pumped into the liquid piston 18 through the 4-way valve 28, which is positioned to fluidly connect the outlet of the pump 14 to the compressor 18.

[00109] The liquid piston compressor 18 operates at a significantly lower speed than the rotary compressor 12 allowing for more time for heat transfer. This may be advantageous in one or more embodiments because this compression step, in some embodiments, features the highest compression ratio in the gas system 100. To prevent carryover, the atomization performed in the hydraulic stage may be of larger droplets which in turn separate and coalesce into the walls of the compressor 18 and the liquid surface. Most of the heat transfer may be performed by the turbulent pattern and the travel of the liquid droplets through the gas.

[00110] When the liquid piston 18 is compressing and/or discharging gas, a backflow valve 60 recycles the first stage compressed gas from the rotary compressor 12 back to its inlet. In another embodiment, the piping between the first-stage 12 and second-stage 18 compressors may be sized efficiently to eliminate the need for a back-pressure control valve (e.g., if the piping acts as a buffer tank, if a buffer tank is disposed in-line with the piping).

[00111] During the compression step, the valves 30a,30b are closed. If the valves 30a,30b are check-valves, the valve 30a is closed because the pressure in the compressor 18 is higher than the outlet pressure of the compressor 12, and the valve 30b is closed because the user pressure (e.g., CNG storage tank, CNG vehicle tank, etc.) is higher than the compressor 18 pressure.

[00112] As used herein, the term "user" is used to describe a thing that receives compressed gas from the system. The user may be a CNG vehicle tank, another type of gas tank, a device that consumes compressed gas, an industrial, commercial, or residential site, etc.

[00113] Compressed Gas Discharge Step; Once the liquid piston 18 has sufficiently increased the pressure of the gas to its final discharge pressure, up to and including about 3600 psig or higher, the compressed gas is discharged to the user (e.g., into a CNG vehicle's CNG tank) via a discharge passageway 21 and hose 22.

[00114] Once gas pressure in the compressor 18 has exceeded the desired discharge pressure, up to and including about 3600 psig for example, the discharge valve 30 opens (e.g., through differential pressure between the compressor 18 and the discharge passageway 21, for example, if the valve 30 is a check valve), allowing flow out of the liquid piston compressor 18. In some embodiments, ports and control valves may be used in place of valves operated by differential pressure.

[00115] Discharged compressed gas flows from the compressor 18 into an integrated filter and dryer 20. The filter is used to remove any particulates that may have been present in the residential natural gas supply line. Potential contaminants include, but are not limited to, hydrogen sulfide (H2S), oxygen, liquefiable hydrocarbons, entrained water, and the cooling liquid. These contaminants are usually present in small quantities. However, to improve safety, the system 100 may be designed to filter out potentially harmful contaminants, possibly with the exception of mercaptan, added as an odorant for safety purposes, or other purposeful additives. The removal of moisture through an integrated dryer may be beneficial in some circumstances; however, for the majority of residential applications, the ambient temperature is high enough to prevent or minimize water vapor condensation expected in low temperature environments, eliminating the need for a dryer according to various embodiments. System 100 may use two or more interchangeable filter-dryer sets, one for use under standard operating conditions and the other for extreme operating conditions. Moderate to high- temperature environments that do not have reason to worry about the condensation and freezing of water in natural gas may benefit from a lighter, less expensive dryer component.

[00116] Once the compressed gas has been filtered and dried sufficiently, it passes through a flexible tube (e.g., CNG hose 22 illustrated in FIG. 1) into a standard NGV dispensing nozzle (e.g., time fill nozzle 24 illustrated in FIG. 1). This nozzle features an in-line breakaway valve as a safety feature. These components are integrated to reduce cost and weight. If a person drives away from their residence while their CNG vehicle is still refueling, and/or still connected to the home refueling system, the dispensing line will break away to reduce the risk of damaging the compression system or causing a natural gas leak. In addition to the safety risks inherent to this type of accidental misuse, the economic costs may also be large to a consumer. Therefore, an in-line breakaway valve will be used in system 100 to provide a safe, easy to replace break point in the line.

[00117] After completion of the discharge step, the process immediately or quickly returns to the suction and first stage compression steps.

[00118] Controller And Sequential Operation Of One Or More Embodiments

[00119] FIG. 13 illustrates method 1300 for compressing gas using the above-discussed system 100. The operations of method 1300 presented below are intended to be illustrative. In some embodiments, method 1300 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method 1300 are illustrated in FIG. 13 and described below is not intended to be limiting.

[00120] In some embodiments, method 1300 and/or one or more operations of method 1300 (e.g., controlling valves) may be implemented in one or more controllers that include one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices executing some or all of the operations of method 1300 in response to instructions stored electronically on an electronic storage medium. In some embodiments, the one or more controllers and/or the one or more processing devices may control one or more components of system 100 based on output signals from one or more sensors that are part of system 100. For example, a float switch may generate output signals conveying information related to a fluid level in one or more components of system 100. A controller may be configured to control one or more valves to open and/or close based on the fluid level information. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method 1300.

[00121] FIG. 14 illustrates a controller 80 configured to control various components of system 100. In some embodiments, controller 80 may be configured to control a user interface 84, valve(s) 28, valve(s) 30,31,32,60, sensor(s) 86, hydraulic pump 14, motor 16, and/or other components of system 100 such that system 100 functions as described herein. In some embodiments, controller 80 may include one or more processors 82, and/or other components. Using the process flow described in FIG. 2 as an example, during a suction step, controller 80 may control suction valve(s) and discharge valve(s) 30 to be opened and closed respectively such that the flow of the gas from the first stage compressor 12 may enter and fill second stage compressor 18. During the suction step, the controller 80 may control valve(s) 28 to control the flow of the hydraulic fluid to flow from the hydraulic pump 14 and the second stage compressor 18 such that the hydraulic fluid from pump 14 is recycled and hydraulic fluid from compressor 18 flows into reservoir 26. Similarly, during compression and/or discharge steps, controller 80 may control valve(s) 30, 28 to open and/or close appropriately such that system 100 functions as described herein with respect to the compression and/or discharge steps.

[00122] Returning to FIG. 13, at an operation 1302, gas is compressed to a first pressure level and provided for a second stage compressor at the first pressure level. Operation 1302 may be performed by a first stage compressor that is the same as or similar to first stage compressor 12 (shown in FIG. 2 and described herein).

[00123] At an operation 1304, pressurized hydraulic fluid may be provided for the second stage compressor. Operation 1304 may be performed by a hydraulic pump the same as or similar to hydraulic pump 14 (shown in FIG. 2 and described herein).

[00124] At an operation 1306, the gas may be compressed from the first pressure level to a second pressure level. Operation 1306 may be performed by a second stage compressor the same as or similar to second stage compressor 18 (shown in FIG. 2 and described herein).

[00125] At an operation 1308, a flow of the gas and a flow of the hydraulic fluid may be controlled during a suction cycle such that the second stage compressor fills with the gas at the first pressure level. Operation 1308 may be performed by one or more valves the same as or similar to valve 28 (shown in FIG. 2 and described herein), valves 30 (shown in FIG. 2 and described herein), and/or valves 32 (shown in FIG. 3 and described herein). [00126] At an operation 1310, the flow of gas, the gas in the second stage compressor, and the flow of hydraulic fluid may be controlled during a compression cycle such that the second stage compressor fills with hydraulic fluid and compresses the gas in the second stage compressor. Operation 1310 may be performed by one or more valves the same as or similar to valve 28 (shown in FIG. 2 and described herein), valves 30 (shown in FIG. 2 and described herein), and/or valves 32 (shown in FIG. 3 and described herein).

[00127] At an operation 1312, the flow of gas, the gas in the second stage compressor, the flow of hydraulic fluid, and the hydraulic fluid in the second stage compressor may be controlled during a discharge cycle such that the gas in the second stage compressor is pushed by the hydraulic fluid out of the second stage compressor at the second pressure level for dispensing via a dispensing port. Operation 1312 may be performed by one or more valves the same as or similar to valve 28 (shown in FIG. 2 and described herein), valves 30 (shown in FIG. 2 and described herein), and/or valves 32 (shown in FIG. 3 and described herein).

[00128] Dual Piston Compressor Embodiments

[00129] FIG. 3 illustrates a compression system 100', which is generally similar to the system 100. Accordingly, a redundant description of similar or identical components is omitted, and common components are identified with common reference numbers. For example, the motor 16, compressor 12, valve 30a, atomizers/injectors 15, 19, coolers 29, 33, and filter/drying 20 are not illustrated in FIGS. 17-21, but are present in the system 100' and used in the same manner as described above with respect to the system 100. While the system 100 used a single second stage compressor 18, the system 100' uses dual liquid piston compressors 40.

[00130] The two second stage compressors 40a,40b are operated 180 degrees out of phase from each other such that when the compressor 40a is in its suction step, the compressor 40b is in the second stage compression or discharge steps, and vice versa. Three-way switching valves 30 and 32 control gas and hydraulic liquid flows, both in and out, to effect the switching of the compressors 40a,40b alternately between their different steps. By operating two liquid pistons 40 in this way, compression and pumping losses are mitigated because the hydraulic pump 14 is always pumping to fill one of the liquid pistons 40 during its compression stroke and the first- stage rotary gas compressor 12 is always compressing to fill the other liquid piston 40 during its suction stroke, eliminating recycling of gasses and fluids.

[00131] When the compressor 40a is in the suction step and compressor 40b is in the discharge step, (1) the valve 31b fluidly connects the outlet of the compressor 12 to the compressor 40a to pump first stage compressed gas into the compressor 40a, and fluidly disconnects the compressor 12 from the compressor 40b, and (2) the valve 31a fluidly disconnects the compressor 40a from the discharge passageway 21 , and fluidly connects the compressor 40b to the discharge passageway to permit discharge of the second stage compressed gas to the user via the passageway 21 and hose 22.

[00132] Because the compressor 12 is always or almost always pumping first stage compressed gas into one of the piston compressors 40a,40b, the backflow valve 60 and path may be omitted from the system 100' without deviating from the scope of the present invention.

[00133] When the compressor 40a is in the suction step and compressor 40b is in the compression or discharge step, the valves 32 are positioned such that the pump 14 pumps liquid from the compressor 40a to the compressor 40b. Conversely, when the compressor 40b is in the suction step and compressor 40a is in the compression or discharge step, the valves 32 are positioned such that the pump 14 pumps liquid from the compressor 40b to the compressor 40a.

[00134] According to an alternative embodiment, the compressors 40a,40b may include actual hydraulic fluid-driven pistons that are mechanically linked together (e.g., via a shared shaft or other linkage) to ensure that they operate 180 degrees out of phase with each other.

[00135] Because the pump 14 is always or almost always pumping liquid from one compressor 40a,40b to the other compressor 40a,40b, the low pressure hydraulic reservoir 26 may be kept and/or may be eliminated from the system 100'. For example, the hydraulic reservoir 26 is not shown in FIG. 3.

[00136] The controller 80 from the system 100 may be adapted to carry out the dual- compressor-40 operation discussed above by additionally controlling the valves 31a,3 lb,32 to effect the above-discussed process.

[00137] Pressure- Vessel Boosted Embodiments

[00138] FIGS. 17-21 illustrate a system 2000 according to alternative embodiments of the present invention. The system 2000 is generally similar to the system 100, except that three booster vessels 2010, 2020, 2030 and their associated pipes and valves are added. A redundant detailed description of structures and features that are common to both systems 100, 2000 is omitted. For example, the motor 16, compressor 12, valve 30a, atomizers/injectors 15, 19, coolers 29, 33, and filter/drying 20 are not illustrated in FIGS. 17-21, but are present in the system 2000 and used in the same manner as described above with respect to the system 100.

[00139] The system 2000 includes the same or similar motor 16, compressor 12, and associated piping and cooling as used in the system 100. The compressor 12 discharges first stage compressed gas to the compressor 18 in the same manner as discussed above with respect to the system 100.

[00140] As shown in FIG. 18, during non-boosted regular operation, first stage compressed gas (e.g., medium pressure gas) flows from the compressor 12 into the compressor 18 during the suction step, is compressed during the second stage compression step, and then flows out of the compressor 18 as second stage compressed gas (e.g., discharge pressure gas) to the discharge line 21, cooler 33, filter/dryer 20, and user (e.g., CNG tank of CNG vehicle) during the discharge step in the same or substantially similar manner as discussed above with respect to the system 100. As the compressor 18 suctions gas in and hydraulic liquid is exiting the compressor 18, the 3 -way valve 2005 is set to connect the compressor 18 to the hydraulic reservoir 26. The valve 2005 may include a pressure regulator that only permits hydraulic liquid to flow from the compressor 18 to the reservoir 26 to control the fiowrate of the liquid for cycle optimization purposes. According to various embodiments, the pressure regulator of the valve 2005 only permits hydraulic liquid to flow from the compressor 18 to the reservoir 26 when the pressure in the compressor 18 exceeds a predetermined value (e.g., a pressure at or slightly below the design first stage discharge pressure). Alternatively, additional pressure-regulating valve(s), orifices, or other structures may be provided in the passageway leading from the compressor 18 to the reservoir 26 to limit the flow rate of liquid out of the compressor 18 during the suction step to thereby avoid inefficiencies associated with depressurizing first stage gas that flows into the compressor 18. During a compressor 18 suction phase where gas is coining from the first-stage compressor 12 and not from the booster vessels 2010, 2020, 2030, hydraulic liquid coming from the discharge of hydraulic pump 14 may be recycled to the hydraulic reservoir 26 through the use of a solenoid-actuated bypass line 2006 and valve 2007. Liquid may also be recycled through this bypass line 2006 during a re-charge cycle, as seen in Figure 21

[00141] The booster vessels 2010, 2020, 2030 may be operated in several different discharge modes: a boosted suction discharge mode, and a direct boosted discharge mode.

However, either of these specific discharge modes may be omitted without deviating from the scope of the invention.

[00142] Boosted Suction Discharge Mode: As shown in FIG. 19, during a boosted suction discharge mode, the compressor 12 and compressor 18 work in the same manner as discussed above with respect to the suction step of the system 100. However, in the boosted suction discharge mode, additional compressed gas flows from one of the booster vessels 2010, 2020, 2030 through the associated valves 2080, 2090, 2100, through passageways 2045, 2046 and 3- way valve 2040 into the compressor 18 to supplement flow of first stage compressed gas from the compressor 12, and shorten the time required for each suction step. During the boosted suction discharge mode, the 3-way valve 2040, and associated valves 2080, 2090, 2100 of the selected booster vessel 2010, 2020, 2030 are each positioned to permit compressed gas flow from the selected booster vessel 2010, 2020, 2030 to the compressor 18 (or the passageway leading from the compressor 12 to the compressor 18) via the passageways 2045, 2046.

According to various embodiments, the valves 2080, 2090, 2100 may be pressure-regulated valves or simple on/off valves.

[00143] As shown in FIG. 19, hydraulic liquid hydraulic liquid is pumped from the pump 14 through a backfilling passageway 2125 and a corresponding pressure regulating valve 2130, 2140, 2150 into the selected booster vessel 2010, 2020, 2030 to make up for the volume of gas being discharged back to the compressor 18. The valves 2130, 2140, 2150 may be set to the desired pressures of the vessels 2010, 2020, 2030, respectively, so as to cause pressurized hydraulic liquid to flow into the vessels 2010, 2020, and/or 2030 when the vessel pressure falls below the set point. The valves 2130, 2140, 2150 may incorporate check valves that prevent backflow of liquid or gas from the vessel 2010, 2020, 2030 to the pump 14, reservoir 26, and/or compressor 18. Consequently, as compressed gas flows out of a booster vessel 2010, 2020, 2030, the vessel 2010, 2020, 2030 is backfilled with hydraulic liquid, thereby maintaining the vessel 2010, 2020, 2030 at about its desired pressure level. Such back flowing mitigates inefficiencies associated with vessel 2010, 2020, 2030 pressure drops that would otherwise occur when discharging compressed gas from the vessel 2010, 2020, 2030. According to various embodiments, the valves 2130, 2140, 2150 may be pressure-regulated valves or simple on/off valves.

[00144] The boosted suction discharge mode illustrated in FIG. 19 enables the system 2000 to deliver discharge pressure (e.g., 3,600 psi) gas to the user at a higher flow rate than if a booster vessel 2010, 2020, 2030 is not used to boost the suction step.

[00145] Direct Boosted Discharge Mode: FIG. 20 illustrates a direct boosted discharge mode, which is generally similar to the discharge step of the system 100, except that discharge pressure gas flow from the compressor 18 to the user via the discharge passageway 21 is augmented or replaced by direct flow of discharge pressure gas from a selected one of the booster vessels 2010, 2020, 2030, through an associated valve 2080, 2090, 2100, through the passageway 2045, through the valve 2040, tlirough the passageway 2047, through the valve 30b, and into the discharge passageway 21. The valve positions during boosted discharge are identical to the valve positions during boosted suction, except that the valve 2040 directs compressed gas from the selected booster vessel 2010, 2020, 2030 directly to the discharge passageway 21 via the passageway 2047, rather than to the inlet of the compressor 18 via passageway 2046 (as is done during a boosted suction step).

[00146] According to various alternative embodiments, the valve 2040 may be replaced with a simple T coupling, or eliminated altogether (if only one of the downstream branches 2046, 2047 is used). In such an embodiment, the selected vessel 2010, 2020, 2030 could provide boosted discharge when the vessel pressure exceeds a pressure of the downstream discharge passageway 21, and could provide boosted suction if the downstream user line is at a higher pressure. In such an alternative embodiment, the passageway 2046 or 2047 connecting the vessel 2010, 2020, 2030 to the compressor 18 would be disposed between the valves 30a,30b (see FIG. 2) to prevent gas flow in the wrong direction. One or more check valves could also be used to prevent gas flow from the compressor 18 to the vessel 2010, 2020, 2030 when the system 2000 is being used to deliver discharge pressure gas to the user.

[00147] As shown in FIG. 20, as with the boosted suction discharge mode, hydraulic liquid backfills into the gas-discharging vessel 2010, 2020, 2030 as gas is discharged. The pressure-regulated valves 2130, 2140, 2150 open as needed to provide sufficient flow to make up for gas being discharged and maintain the vessel 2010, 2020, 2030 at or around the desired pressure level.

[00148] In the illustrated embodiment, the valve 30b is disposed downstream from where the passageway 2047 from the vessels 2010, 2020, 2030 meets the discharge passageway.

However, according to alternative embodiments, the valve 30b may be disposed in the discharge passageway 21 between the compressor 18 and where the passageway 2047 meets the discharge passageway.

[00149] According to various alternative embodiments, discharge pressure gas is discharged to the user via the discharge passageway 21 from the vessels 2010, 2020, 2030 instead of (rather than in addition to) from the compressor 18. The direct discharge from the vessels 2010, 2020, 2030 may comprise discharge (a) from a selected one of the vessels 2010, 2020, 2030, (b) from sequential ones of the vessels 2010, 2020, 2030, and/or (c) from multiple of the vessels 2010, 2020, 2030 simultaneously. The controller 80 may be designed to automatically or selectively carry out the discharge in these different modes. In such an embodiment, the compressor 18 may be used solely to recharge the vessels 2010, 2020, 2030. Alternatively, discharge to the user via the discharge line 21 may sometimes be from the vessels 2010, 2020, 2030, and sometimes be from the combined discharge of the vessels 2010, 2020, 2030 and compressor 18 together.

[00150] According to various embodiments, the compressor 18 is not used during discharge pressure discharge of gas to the user from one or more of the vessels 2010, 2020, 2030. During such discharge, the pump 14 may be used solely to provide backfilling liquid to the vessel 2010, 2020, 2030 from which gas is being discharged. Such dedicated use of the pressurized hydraulic liquid from the pump 14 may accelerate the rate of gas discharge to the user, relative to the rate if some of the pressurized hydraulic liquid were being used to power the compressor 18.

[00151] According to various embodiments, the pump 14 is sized to provide sufficient pressurized liquid to simultaneously power both the compressor 18 and provide back flowing liquid into the vessel 2010, 2020, 2030 being discharged. Additionally and/or alternatively, the controller 80 may alternate between using the pressurized liquid to (1) compress gas in the compressor 18, and (2) backfill liquid into the vessel 2010, 2020, 2030 being discharged, so that the pump 14 may be of a smaller size.

[00152] According to various embodiments, the reservoir 26 and hydraulic liquid are of sufficient volume to completely fill all of the vessels 2010, 2020, 2030 (in case of complete discharge of all vessels 2010, 2020, 2030), the compressor 18, and the passageways and intermediate spaces (e.g., inside of the pump 14).

[00153] According to various embodiments, an internal volume of one or more of the vessels 2010, 2020, 2030 is at least 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 500, 750, 1,000, 2,000, 3,000, 4,000, 5,000, 7,500, 10,000, 15,000, 50,000, 100,000, and/or 200,000 times larger than an internal volume of the compressor 18. According to various embodiments, the internal volume of one or more of the vessels 2010, 2020, 2030 is also less than 1,000,000, 500,000, 400,000, 300,000, 200,000, 100,000, 75,000, 50,000, 40,000, 30,000, 25,000, 20,000, 15,000, 10,000, 7,500, 5,000, 4,000, 3,000, 2,000, 1,000, 750, 500, 400, 300, 200, 100, 90, 80, 70, 60, 50, 40, 30, 25, 20, 15, and/or 10 times larger than the internal volume of the compressor 18. According to various embodiments, the internal volume of one or more of the vessels 2010, 2020, 2030 is between 5 and 1,000,000 times larger than the internal volume of the compressor 18.

[00154] Booster Vessel Recharging Mode: When the system 2000 is not being used to deliver discharge pressure gas (e.g., when a vehicle's CNG tank is not being filled), the booster vessels 2010, 2020, 2030 may be recharged with high or relatively high pressure gas. The booster vessel recharging mode is substantially similar in operation to non-boosted regular operation (as discussed above with respect to FIG. 18), except that second stage compressed gas is discharged into a selected booster vessel 2010, 2020, 2030, rather than to the end user. To do so, a valve leading to the end user is closed, and a valve 2210, 2220, 2230 associated with a respective selected vessel 2010, 2020, 2030 is opened.

[00155] During the booster vessel recharging mode, the respective valve 2050, 2060, 2070 of the vessel 2010, 2020, 2030 being recharged fluidly connects the recharging vessel 2010, 2020, 2030 to the reservoir 26 to allow hydraulic liquid in the recharging vessel 2010, 2020, 2030 to drain out of the vessel and back into the reservoir 26. The valves 2050, 2060, 2070 and/or other structures in the hydraulic liquid drain passageway 2055 may be pressure regulated so as to only permit hydraulic liquid flow out of the recharging vessel 2010, 2020, 2030 when the vessel pressure exceeds a predetermined pressure (e.g., a desired pressure of the vessel 2010, 2020, 2030). As a result, second stage gas flow into the vessel 2010, 2020, 2030 is balanced with hydraulic liquid discharge from the vessel 2010, 2020, 2030, thereby maintaining the pressure within the vessel 2010, 2020, 2030 at about the desired vessel pressure.

[00156] As shown in FIGS. 20-21, in the illustrated embodiment, each vessel 2010, 2020, 2030 has a discrete (1) gas inlet port leading from the respective valve 2210, 2220, 2230, (2) gas outlet port leading to the respective valve 2080, 2090, 2100, (3) hydraulic liquid inlet port leading from the respective valve2130, 2140, 2150, and (4) hydraulic liquid outlet port leading from to the respective valve 2050, 2060, 2070. As shown, the gas inlet and outlet ports are disposed at the top of the vessels 2010, 2020, 2030 because that is where the lighter gas in these vessels 2010, 2020, 2030 is disposed. These gas port positions help to prevent liquid from flowing from the vessel 2010, 2020, 2030 to the user via the passageway 2045 and discharge line 21. Conversely, the liquid inlet and outlet ports are disposed at the bottom of the vessels 2010, 2020, 2030 because that is where the relatively heavier liquid is disposed in these vessels 2010, 2020, 2030. These liquid port positions help to prevent gas from flowing from the vessel 2010, 2020, 2030 to the reservoir 26.

[00157] According to various alternative embodiments, the gas inlet and outlet ports of each vessel 2010, 2020, 2030 can be merged. Thus, for example, a single gas port can lead from a top of the vessel 2010 and branch into two passageways that lead to the valves 2210, 2080, respectively.

[00158] Similarly, according to various alternative embodiments, the respective liquid inlet and outlet ports of each vessel can be merged. Thus, for example, a single liquid port can lead from a bottom of the vessel 2010 and branch into two passageways that lead to the valves 2130, 2050, respectively.

[00159] According to various embodiments, the valves 30b, 2005, 2007, 2040, 2050, 2060, 2070, 2080, 2090, 2100, 2130, 2140, 2150, 2170, 2180, 2190, 2100, 2210, 2220, 2230 and other equipment used to effect the various discharge and recharge modes of the vessels 2010, 2020, 2030 are operatively connected to and controlled by the controller 80. The controller 80 may automatically start and stop the discharge and recharge modes of the vessels 2010, 2020, 2030 to optimize the performance of the overall system 2000. For example, the controller 80 may be configured to operate a vessel 2010, 2020, 2030 in a boosted discharge mode when the system 2000 is connected to a user and supplying compressed gas to the user. Conversely, the controller 80 may be configured to operate a vessel 2010, 2020, 2030 in a recharge mode when the system 2000 is not being used to supply compressed gas to a user.

[00160] Sensors 2240, 2250, 2260 (e.g., liquid sensors (e.g., electric liquid detector (e.g., capacitive or resistive detector), float sensor), weight sensors, etc.) may be appropriately positioned (e.g., in the vessel or at its inlet and/or outlet ports) to sense the liquid level in each vessel 2010, 2020, 2030 and operatively connected to the controller 80. When the controller 80 determines that a particular vessel 2010, 2020, 2030 is emptied of compressed gas (e.g., when the vessel is filled with liquid as detected by the sensor 2240, 2250, 2260) during a boosted discharge mode for that vessel, the controller 80 is configured to automatically end the boosted discharge mode for that vessel, and may automatically initiate a boosted discharge mode for another of the vessels 2010, 2020, 2030.

[00161] Similarly, when the controller 80 determines that a particular vessel 2010, 2020, 2030 is full of compressed gas (e.g., when the vessel is emptied of hydraulic liquid as detected by the sensor 2240, 2250, 2260) during a recharge mode for that vessel, the controller 80 is configured to automatically end the recharge mode for that vessel, and may automatically initiate a recharge mode for another of the vessels 2010, 2020, 2030. Additionally and/or alternatively, the controller 80 may be configured to alternate between recharge modes for different vessels 2010, 2020, 2030 even before a particular vessel 2010, 2020, 2030 is completely filled with gas. Such alternating may result in more heat dissipation from the vessels 2010, 2020, 2030 to the ambient environment.

[00162] During the discharge and recharge modes of the vessels 2010, 2020, 2030, the use of backfilling liquid helps to keep the pressure within the vessels 2010, 2020, 2030 at or near the predetermined pressure set point for the particular vessel 2010. According to various embodiments, the system 2000 and its associated pressure-regulated valves 2050, 2060, 2070, 2130, 2140, 2150 and/or controller 80 controlled valves may be configured to maintain the pressure within the vessel 2010, 2020, 2030 to within 20%, 15%, 10%, 5%, 4%, 3%, 2%, and/or 1% of the psig set point for the vessel 2010, 2020, 2030 throughout the use of the booster vessel 2010, 2020, 2030 in its discharge and recharge modes. In such embodiments, the set point may be considered a range with a lower pressure threshold a predetermined percentage lower than a desired set point and an upper pressure threshold a predetermined percentage above the desired set point. Alternatively, the upper and lower pressure thresholds may be defined in absolute, rather than relative terms. For example, the lower threshold may be 1900 psig and the upper threshold may be 2100 psig. Thus, the pressure-regulated valves 2130, 2140, 2150 may be set to the lower threshold such that during the discharge mode, hydraulic liquid fills the vessel 2010, 2020, 2030 when the vessel pressure falls below the lower threshold. Conversely, the pressure- regulated valves 2050, 2060, 2070 may be set to the upper threshold during the recharge mode so that liquid drains from the vessel 2010, 2020, 2030 when the pressure in the vessel exceeds the upper pressure threshold. While the illustrated control system for maintaining the desired vessel 2010, 2020, 2030 pressure comprises one or more pressure-regulated valves 2050, 2060, 2070, 2130, 2140, 2150, any other suitable type of control system may be used to maintain the pressure in the vessels 2010, 2020, 2030 (e.g., an active feedback control system that includes the controller 80, pressure sensors in the vessel 2010, 2020, 2030 and controller-actuated valves to control the flow of hydraulic liquid and compressed gas into and out of the vessel 2010, 2020, 2030 in a manner that maintains the vessel pressure within a desired range).

[00163] According to various embodiments, the vessels 2010, 2020, 2030 may be maintained at different set points (e.g., 2000 psig for the vessel 2010, 3600 psig for the vessel 2020, and 5000 psig for the vessel 2030). The vessels 2010, 2020, 2030 may comprise respective materials that are tailored to their respective intended working pressures. For example, the vessel 2010 may be constructed of a less expensive material than the vessel 2030 if the vessel 2010 is kept at a lower pressure than the vessel 2030. A relatively low pressure one of the vessels 2010, 2020, 2030 may be used for boosted suction, while a relatively higher pressure one of the vessels 2010, 2020, 2030 may be used for boosted discharge.

[00164] The booster vessels 2010, 2020, 2030 may facilitate the use of a lower power motor 16, compressor 12, pump 14, and compressor 18 than might be desired if the vessels 2010, 2020, 2030 were not used. In particular, the system 2000 may compress gas continuously (or until the vessels 2010, 2020, 2030 are full of compressed gas at their desired pressures), even when there is not user demand for discharge pressure gas from the user. Thus while the power of the motor 16, compressors 12,18, and pump 14 may be insufficient to satisfy an instantaneous user demand, the system 2000 can nonetheless do so because the instantaneous user demand is intermittent and the system 2000 can operate continuously to recharge the booster vessels 2010, 2020, 2030.

[00165] According to various embodiments, the vessels 2010, 2020, 2030 have different volumes. For example, the highest pressure vessel 2030 may have the smallest volume.

[00166] In the illustrated system 2000, the system utilizes three vessels 2010, 2020, 2030 with cascaded pressures. However, greater or fewer booster vessels 2010, 2020, 2030 could be used without deviating from the scope of the present invention. For example, a single vessel 2010 could be used, and the vessels 2020, 2030 omitted.

[00167] While the system 2000 is illustrated as being used with a single compressor 18 like the system 100, the system 2000 may be modified to comprise a dual-compressor 40 system like the system 100' without deviating from the scope of the present invention. Even in a dual- compressor embodiment of the system 2000, the reservoir 26 is preferably retained to provide sufficient hydraulic liquid to displace the volumes in the vessels 2010, 2020, 2030 when desired (as explained above).

[00168] While the illustrated booster vessels 2010, 2020, 2030 are illustrated as being used in connection with a two-stage compressor system 2000, the vessels 2010, 2020, 2030 and the use of backfilling liquid to balance out gas flow into or out of the vessels 2010, 2020, 2030 may alternatively be used in any other suitable circumstance (e.g., along with single-stage compressors). For example, the vessels 2010, 2020, 2030 may be used in an environment in which (1) a compressor system is insufficient to satisfy an instantaneous demand such that augmented discharge from the vessel 2010, 2020, 2030 can be used to meet the instantaneous user demand , but (2) the instantaneous user demand is intermittent such that the compressor system may be used to recharge the vessel 2010, 2020, 2030 when user demand is non-existent or limited.

[00169] According to various embodiments, the overall compressive power of the system 100, 100', 2000 may be (a) at least 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, and/or 130 HP, (b) less than 500, 400, 300, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, and/or 50 HP, (c) between 5 and 500 HP, 10 and 250 HP, and/or 50 and 100 HP, and/or (d) between any ranges nested within such ranges. [00170] The description herein of compression of natural gas by the gas compression system is not intended to be limiting. The principles described in this application may be applied to compression of gasses other than natural gas.

[00171] Although one or more embodiments have been described in connection with a home refueling system, such embodiments may alternatively be used on non-home

environments (e.g., commercial or industrial environments, at well-heads, etc.) without deviating from the scope of the present invention. Moreover, various embodiments may be used in any situation where it is desired to provide gas from a low pressure source to a high-pressure demand.

[00172] Although the disclosure has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

Claims

What is claimed is:

1. A two-stage gas compression system configured to compress gas, the system comprising:

a rotary power source having an output shaft;

a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft;

a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and

a positive-displacement second stage compressor having

a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to a user,

wherein the second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump.

2. The system of claim 1, wherein:

the pump comprises a rotary hydraulic pump driven by a pump drive shaft that is driven by the output shaft;

the first stage rotary compressor comprises a compressor drive shaft that drives the compressor and is driven by the output shaft; and

the output shaft, pump drive shaft, and compressor drive shaft are co-axial with each other.

3. The system of claim 1, wherein the first stage rotary compressor and hydraulic pump are commonly disposed within a sealed shell.

4. The system of claim 3, wherein:

a shaft driven by the rotary power source extends between the first stage rotary compressor and pump;

a seal is disposed between the first stage rotary compressor and pump, the seal surrounding the shaft that extends between the first stage rotary compressor and pump; and during operation, pressurized liquid in the pump aids the seal in discouraging gas in the first stage rotary compressor from leaking into the pump.

5. The system of claim 3, wherein the hydraulic pump is disposed above the first stage rotary compressor.

6. The system of claim 3, wherein the second stage compressor is disposed within the sealed shell.

7. The system of claim 1, wherein:

the system is a home refueling system configured to compress natural gas from a residential natural gas supply and supply compressed natural gas to a compressed natural gas vehicle;

the system comprises a dispensing port operatively connected to the second stage gas outlet, the dispensing port being configured to connect to the compressed natural gas vehicle to provide second stage compressed gas to the vehicle; and

the first stage gas inlet is configured to receive gas at a base pressure level from a natural gas supply line of a residential natural gas supply.

8. The system of claim 1, wherein the first stage compressor and the second stage compressor are configured such that the gas compression is near-isothermal.

9. The system of claim 1, further comprising at least one atomized liquid injector connected to at least one of the compressors and configured to provide atomized liquid into the at least one of the compressors to cool the gas being compressed in the at least one of the compressors.

10. The system of claim 9, wherein the at least one atomized liquid injector is operatively connected to the liquid outlet of the pump such that during operation, pressurized hydraulic liquid is provided by the pump to the atomized liquid injector and injected as an atomized liquid into the at least one of the compressors.

11. The system of claim 10, further comprising:

a hydraulic liquid passage loop leading from the hydraulic liquid outlet of the pump, through the at least one atomized liquid injector, into the at least one of the compressors, and back to the hydraulic liquid inlet of the pump; and

a hydraulic liquid cooler disposed in the hydraulic liquid passage loop, the cooler being configured to cool hydraulic liquid in the loop and thereby remove heat that is transferred from gas to the liquid.

12. The system of claim 11, wherein the system does not include a separate gas cooler to cool the gas.

13. The system of claim 11 , wherein the hydraulic liquid cooler is the only component of the system that is configured to actively remove heat from the system.

14. The system of claim 9, wherein: the at least one of the compressors comprises the first stage compressor and the second stage compressor; and

the at least one atomized liquid injector comprises

at least one first stage atomized liquid injector connected to the first stage compressor and configured to provide atomized liquid into the first stage compressor, and

at least one second stage atomized liquid injector connected to the second stage compressor and configured to provide atomized liquid into the second stage compressor.

15. The system of claim 1 , wherein the hydraulic fluid is an ionic liquid.

16. The system of claim 1, wherein:

the second stage compressor comprises a first hydraulic piston compressor;

the system further comprises a second positive-displacement hydraulic piston compressor having

a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to the user;

the second hydraulic piston compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump; and

the system further comprises a controller that is configured to operate the first hydraulic piston compressor out of phase from the second hydraulic piston compressor.

17. The system of claim 1, further comprising a booster vessel operatively connected to the pump and second stage compressor, the booster vessel having a discharge mode and a recharge mode,

wherein the discharge mode comprises a mode in which

(a) compressed gas in the booster vessel is discharged to the user, and

(b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel; and

wherein the recharge mode comprises a mode in which

(a) second stage compressed gas flows from the second stage compressor to the booster vessel to refill the booster vessel with compressed gas, and

(b) hydraulic liquid drains out of the booster vessel.

18. The system of claim 17, further comprising a controller that is configured to control the flow of hydraulic liquid out of the booster vessel so as to control a pressure within the booster vessel during the recharge mode.

19. The system of claim 17, wherein the discharge of compressed gas from the booster vessel during the discharge mode comprises direct discharge from the booster vessel to the user.

20. The system of claim 17, wherein the discharge of compressed gas from the booster vessel during the discharge mode comprises discharge from the booster vessel through the compressor to the user.

21. The system of claim 17, wherein the discharge mode comprises a boosted discharge mode in which:

(a) compressed gas in the booster vessel is discharged to and combined with a flow of compressed gas provided by one of the compressors, and

(b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel.

22. The system of claim 17, further comprising a controller that is configured to control the flow of hydraulic liquid into the booster vessel so as to control a pressure within the booster vessel during the discharge mode.

23. The system of claim 17, further comprising a controller that is configured to maintain a pressure within the booster vessel between lower and upper pressure thresholds during the discharge and recharge modes.

24. The system of claim 17, wherein:

the booster vessel comprises a first booster vessel;

the discharge mode comprises a first discharge mode;

the recharge mode comprises a first recharge mode;

the system further comprises a second booster vessel having a second discharge mode and a second recharge mode;

the second discharge mode comprises a mode in which

(a) compressed gas in the second booster vessel is discharged to the user, and

(b) hydraulic liquid is pumped from the pump into the second booster vessel to take the place of compressed gas being discharged from the second booster vessel; and

the second recharge mode comprises a mode in which

(a) second stage compressed gas flows from the second stage compressor to the second booster vessel to refill the second booster vessel with compressed gas, and

(b) hydraulic liquid drains out of the second booster vessel.

25. A method of using a two-stage gas compression system to compress gas, the system comprising a rotary power source having an output shaft; a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft; a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and a positive-displacement second stage compressor having a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to a user, wherein the second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump, the method comprising:

receiving a gas at the first stage gas inlet;

operating the rotary power source, which causes the output shaft to drive the first stage compressor, thereby compressing the gas in the first stage compressor into first stage

compressed gas;

causing the first stage compressed gas to flow from the first stage gas outlet into the second stage compressor via the second stage gas inlet;

operating the rotary power source, which causes the output shaft to drive the pump and pump hydraulic liquid into the second stage compressor, thereby compressing the first stage compressed gas disposed within the second stage compressor into second stage compressed gas; and

discharging the second stage compressed gas from the second stage compressor to a user.

26. The method of claim 25, wherein the gas comprises natural gas.

27. The method of claim 25, further comprising injecting atomized liquid into at least one of the compressors while the at least one of the compressors is compressing gas.

28. The method of claim 27, wherein the injecting comprises transferring pressurized hydraulic liquid from the liquid outlet of the pump to an atomized liquid injector, and atomizing the pressurized liquid to create the atomized liquid.

29. The method of claim 27, wherein:

the system comprises a hydraulic liquid passage loop leading from the hydraulic liquid outlet of the pump, through the at least one atomized liquid injector, into the at least one of the compressors, and back to the hydraulic liquid inlet of the pump, and a hydraulic liquid cooler disposed in the hydraulic liquid passage loop; and the method further comprises using the cooler to cool hydraulic liquid in the loop.

30. The method of claim 25, wherein the method further comprises alternately operating a booster vessel in a discharge mode and a recharge mode,

wherein operating the booster vessel in the discharge mode comprises simultaneously

(a) discharging compressed gas from the booster vessel to the user during the discharging of the second stage compressed gas from the second stage compressor to the user, and

(b) pumping hydraulic liquid from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel; and

wherein operating the booster vessel in the recharge mode comprises simultaneously

(a) transferring second stage gas from the second stage compressor to the booster vessel to refill the booster vessel with compressed gas, and

(b) draining hydraulic liquid out of the booster vessel.

31. The system of claim 30, wherein:

the pumping of hydraulic liquid from the pump into the booster vessel maintains a pressure within the booster vessel above a predetermined lower threshold; and

the draining of hydraulic liquid out of the booster vessel maintains the pressure within the booster vessel below a predetermined upper threshold.

32. A compressed gas supply system comprising:

a compressed gas supply line configured to supply compressed gas to a user;

a hydraulic pump configured to provide pressurized hydraulic liquid; and

a booster vessel having a discharge mode and a recharge mode,

wherein the discharge mode comprises a mode in which

(a) compressed gas in the booster vessel is discharged to the user, and

(b) hydraulic liquid is pumped from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel, and

wherein the recharge mode comprises a mode in which

(a) compressed gas flows from the compressed gas supply line to the booster vessel to refill the booster vessel with compressed gas, and

(b) hydraulic liquid drains out of the booster vessel.

33. The system of claim 32, wherein the compressed gas supply line is part of a compressor system comprising at least one compressor.

34. The system of claim 32, wherein the discharge mode comprises a boosted discharge mode in which

(a) compressed gas in the booster vessel is discharged to and combined with a flow of compressed gas flowing through compressed gas supply line to increase a compressed gas flow rate provided by the system to the user, and

35. The system of claim 32, further comprising a controller that is configured to control the draining of hydraulic liquid out of the booster vessel so as to control a pressure within the booster vessel during the recharge mode.

36. The system of claim 32, further comprising a controller that is configured to control the pumping of hydraulic liquid into the booster vessel so as to control a pressure within the booster vessel during the discharge mode.

37. The system of claim 32, further comprising a controller that is configured to maintain a pressure within the booster vessel between lower and upper pressure thresholds.

38. A method of providing compressed gas to a user, the method comprising alternately operating a booster vessel in a discharge mode and a recharge mode,

wherein operating the booster vessel in the discharge mode comprises

(a) discharging compressed gas from the booster vessel to the user, and

(b) pumping hydraulic liquid from a pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel; and

wherein operating the booster vessel in the recharge mode comprises

(a) transferring compressed gas from the compressed gas supply line into the booster vessel to refill the booster vessel with compressed gas, and

(b) draining hydraulic liquid out of the booster vessel.

39. The method of claim 38, wherein:

40. The method of claim 38, wherein operating the booster vessel in the discharge mode comprises: (a) discharging compressed gas from the booster vessel to the user while discharging compressed gas from a compressed gas supply line to the user to increase a compressed gas flow rate provided to the user, and

(b) pumping hydraulic liquid from the pump into the booster vessel to take the place of compressed gas being discharged from the booster vessel.