Background fOl] Compressed gas is useful in a number of different applications. For example, compressed natural gas vehicles include a tank for storing compressed natural gas used for propulsion. The tank stores the gas at a high pressure for use by an engine of the vehicle. Currently, approaches used to compress gas from a low pressure source (e.g., a residential line) to a high pressure tank (e.g., a vehicle storage tank) include using direct mechanical compression. These direct mechanical compression approaches use a reciprocating piston movable within a cylinder to compress the gas. In use, these systems can be expensive as well as difficult to repair and/or maintain.

Summary

[02] One aspect of concepts presented herein includes a method of compressing gas. The method includes maintaining a volume of gas at a first pressure within a first chamber. Pressurized liquid is forced into the first chamber. The pressurized liquid compresses the volume of gas to a second pressure greater than the first pressure. The liquid is separated from the gas in a second chamber while maintaining the gas at the second pressure to provide compressed, dry gas.

(03] Another aspect includes a system for compressing gas. The system includes a liquid tank storing a liquid therein and a compression chamber fluidly coupled to the liquid tank and configured to compress a volume of gas. A separation assembly is fluidly coupled to the compression chamber and configured to separate liquid from the volume of gas. A pump assembly is fluidly coupled to the liquid tank, the compression chamber and the separation assembly. The pump assembly, during operation, is configured to provide pressurized liquid from the liquid tank to the compression chamber to compress the volume of gas from a first pressure to a second pressure. The pump assembly further transfers the volume of gas at the second pressure to the separation assembly and injects the volume of gas at the second pressure to the separation assembly to separate liquid from the volume of gas to produce compressed, dry gas.

Brief Description of the Drawings

[04] Fig. 1 is a schematic view of a system for compressing gas using a liquid.

[05] Fig. 2 is a schematic sectional view of a compression chamber used in the system of Fig. 1.

[06] Fig. 3 is a schematic, partial sectional view of a nozzle for delivering liquid to the compression chamber illustrated in Fig. 2.

[07] Fig. 4 is a schematic view of a separation assembly used in the system of Fig.

1.

[08] Fig. 5 is a schematic sectional view of a portion of the separation assembly of

Fig. 4.

Detailed Description

[09] Fig. 1 is a schematic view of a system 10 capable of implementing a process using a pressurized liquid (e.g., water, gasoline, diescl fuel) to compress a gas (e.g., natural gas, hydrogen, inert gases). It will be appreciated that system 10 can include components such as valves and the like to facilitate transfer of fluid within the system. As illustrated, the system 10 includes a first, low pressure (LP) compression chamber 1 1 , a second, high pressure (HP) compression chamber 12, a transfer valve 13, a pump assembly 14, a separation assembly 15 and a liquid tank 16. Details of these components in system 10 are provided below. In general, however, the system 10 utilizes two stages of liquid compression (a first stage within the LP chamber 1 1 and a second stage within the HP chamber 12) coupled with a technique for cooling the gas during compression. During compression, a liquid piston is formed within a respective chamber and operates to compress gas within the chamber as well as provide a suitable medium for heat transfer from the compressed gas. In an alternative embodiment, system 10 can include only a single compression chamber. The single compression chamber in this embodiment would operate in a similar manner to the chambers 1 1 and 12 discussed herein.

[10] In one example method for compression, gas enters the system 10 from a source 18 (e.g., a residential natural gas line) at a low pressure (e.g., not greater than 25 bar, approximately 0.5 bar or less). In a first stage of compression, the gas is compressed to a higher, intermediate pressure (e.g., approximately 20-22 bar) in the LP chamber 1 1 by liquid provided from the tank 16 using pump assembly 14. In one embodiment, the LP chamber 1 1 can have a fixed internal volume (e.g., about 20 liters). Subsequently, in a second stage of compression, the gas is compressed to yet a higher, storage pressure (e.g., at least 200 bar, approximately 400 bar) in the HP chamber 12 also by liquid provided from the tank 16 using the pump assembly 14. In one embodiment, the HP chamber 12 also has a fixed internal volume (e.g., about 2 liters).

[11 ] Once the gas is compressed in the LP chamber 1 1 to the intermediate pressure, transfer valve 13 is used to transfer gas to the HP chamber 12. Pump assembly 14, in one embodiment, includes at least two pumps used to introduce the liquid to chambers 1 1 and 12 such that the gas is compressed to a desired exiting gas pressure. In one example, the pump assembly 14 includes a first pump designed to achieve high flow/low pressure of fluid within system 10 and a second pump designed to achieve high pressure/low flow of fluid within system 10. Regardless of configuration of pump assembly 14, gas exiting HP chamber 12 is then filtered to remove impurities in the separation assembly 15 prior to being delivered to a storage tank (e.g., located on a vehicle). (12] The liquid used for compression is continuously recirculated and stored in the tank 16. In one embodiment, the liquid is pressurized with compressed gas from the compressed gas source 18. In one embodiment, the source 18 includes one or more valves to control entry of gas into the tank 16. Transfer valve 13 can control entry of gas from the tank 16 to chamber 1 1 as well as entry of gas from LP chamber 1 1 to HP chamber 12. Pump assembly 14 is configured to provide liquid from tank 16 to LP chamber 1 1 , HP chamber 12 and receive liquid from the separation assembly 15. If desired, the tank 16 can include one or more cooling features (e.g., external cooling fins) to dissipate residual heat in the liquid.

[13] The LP chamber 1 1 and HP chamber 12 operate identical in principle and, for sake of brevity, only the LP chamber 1 1 is discussed in detail below. Principles explained with respect to LP chamber 1 1 are applicable to the structure and operation of HP chamber 12. As discussed in more detail below, each of the chambers include a liquid piston operable to compress gas utilizing a Coanda nozzle having a curved profile that operates to inject a liquid into a respective chamber. In general, a volume of gas is introduced into the chamber. Liquid is subsequently injected into the chamber through the nozzle and, according to the Coanda effect, entrains the gas as the liquid flows along the nozzle. As liquid level rises in the chamber a liquid piston is formed. In addition, the Coanda nozzle and compression chamber are designed to enhance the circulation of the gas while the gas is being compressed within the chamber. Due to the liquid within the chamber, the liquid can cool the gas as it is compressed at a high rate of heat transfer and approaching isothermal compression (i.e., a minimal change of temperature within the chamber during gas compression).

[14] Figure 2 shows a cross section of the LP chamber 1 1 where gas introduced into the chamber 1 1 via a ags inlet 30 is compressed using a liquid introduced through a liquid inlet 32. Inlet 32 is fluidly coupled to a nozzle 34 that divides the chamber 1 1 between an upper portion 36 and a lower portion 38. A volume of gas 39 is positioned in the upper portion 36 and lower portion 38 for compression. Nozzle 34 operates according to the Coanda effect to entrain gas 39 in the chamber due to introduction of liquid into the nozzle 34. In particular, due to the Coanda effect, as the liquid flows at a high rate over a curved surface (i.e., nozzle 34), a high flow of the gas (i.e., gas 39 from upper portion 36) surrounding the nozzle 34 will also be entrained. The nozzle 34 also acts as a transfer pump using the liquid to entrain the gas and circulate a liquid/gas mixture through the chamber 1 1. As the liquid level rises, the gas in the chamber 1 1 is compressed.

115) The nozzle 34 can take many forms. In the embodiment illustrated, the nozzle

34 converges along an entry portion 40 to a throat portion 42. In one embodiment, the liquid is injected into the nozzle 34 with high velocity (e.g., at least 10 m/s) from inlet 32 using pump assembly 14 and exits at throat portion 42 to form a liquid cone 44 extending from the nozzle 34. Liquid introduced to the nozzle 34 flows along the entry portion 40 as indicated by an arrow 46 in a cyclonic manner. Once exiting throat portion 42, the liquid continues to flow in the cyclonic manner to form the liquid cone 44. In the embodiment illustrated, the entry portion 40 is axi-symmetric around a longitudinal axis of the nozzle 34. In one embodiment, the curved entry portion 40 can define a parabolic profile that includes one or more structural features (e.g., slots) to create desired turbulence in flow of liquid along the entry portion 40. During the flow of liquid, the Coanda effect will keep liquid jets formed within the features attached to the entry portion 40 so as to create an area 48 of low pressure and high turbulence. Due to the low pressure and high turbulence created in area 48, gas entrainment in the liquid jets is maximized from the upper portion 36, bringing the gas to the lower portion 38.

[16] The nozzle 34 further includes a bell-shaped portion 50 disposed within the chamber along a longitudinal axis of the nozzle 34 in relation to throat portion 42. By changing a vertical position of the portion 50, a minimum cross section 52 of the throat portion 42 can be varied. In principle, a larger minimum cross section 52 will allow for a higher gas flow from the entry portion 40 to the cone 44. However, a smaller minimum cross section 52 will cause a direct increase in gas speed and enhance a turbulence level of a mixture of gas and liquid within chamber 1 1. Based on experimentation, a desired maximum heat transfer can be determined by adjusting flow, speed and turbulence of fluid within the chamber 1 1.

[17] After liquid passes through the throat portion 42, the liquid forms the cone 44 with assistance from the bell-shaped profile 50. In one embodiment, an angle defined by the entry portion 40 and cone 44 is greater than 90 degrees. Additionally, or independently, a swirl component can be introduced in the entry portion 40 to create a cyclonic flow about the nozzle 34. In relation to the bell-shaped portion 50, the cone 44 can define a greater angle with respect to the entry portion 40 than a corresponding angle between the bell-shaped portion 50 and the entry portion 40. In this configuration, flow between the bell-shaped portion 50 and the cone 44 will have a diffuser effect with a slight increase of gas pressure at the end of the bell- shaped portion 50 at a zone 54 in relation to an average gas pressure within the chamber 1 1. This diffusing process can also increase turbulence within chamber 1 1. As a result of this configuration, gas will tend to escape at a bottom of the cone 44, either by passing through the cone 44 and/or through a liquid piston 56 formed in the chamber 1 1. As more liquid enters chamber 1 1 , liquid piston 56 increases in volume to compress gas within the chamber 1 1.

[18] Ultimately, gas escapes from the cone 44 as depicted by arrows 58. Once exited from the cone 44, gas is drawn to the upper portion 36 following arrow 60 via recirculation channels 64 positioned about the nozzle 34. In one embodiment, due to the configuration of the nozzle 34, gas within chamber 1 1 will circulate at least twenty times for each compression cycle. For the HP chamber 12, a small low head recirculation pump can be used to achieve a higher number of recirculation cycles to counteract reduced heat exchange surface of the HP chamber 12.

[19J Fig- 3 illustrates a partial sectional view of the nozzle 34. In one embodiment, as illustrated, the entry portion 40 is formed of a single unitary body. One embodiment includes the flow profile 40 having a geometry described (in a simplified form) by a parabola with an inclined axis of approximately 30-45 degrees and a D/a ratio of 2.5 to 4. In one embodiment, the entry portion 40 can be formed as described in US Patent No. 3,337,121.

[20] From inlet 32, liquid flow is provided through a retaining plate 66 and cover plate 68. In an alternative embodiment, plates 66 and 68 can be formed of a single plate. The liquid is then provided to a delivery manifold formed by a first plate 70 and a second plate 72. The first plate 70 defines a central channel 74 for flow of liquid to apertures 76 provided in the second plate 72. Liquid provided through the apertures 76 is provided to a jet plate 78 fluidly coupled to the entry portion 40. The jet plate 78 defines a plurality of slots 80. Upon entry of liquid into the slots 80, liquid jets are formed and provided to the entry portion 40. Additionally, the slots 80 are formed proximate the recirculation channels 64 to enhance liquid and gas mixing.

[21J In the illustrated embodiment, the slots 80 are oriented at a 30 degree angle

(relative to a tangent line of an outer circumference of the chamber 1 1) in order to produce a clockwise swirling motion of liquid entering the slots 80. Although different configurations can be utilized, each of the slots 80 in the illustrated embodiment converge from an entry point and then diverge to a general confluence of each of the slots 80 upon entering entry portion 40. Variations of the jet plate 78 can include parametric variations of the swirl angle for slots 80, a confluence distance for each slot 80, plate thickness, exit area for slot 80 and exit angle of slot 80. In one embodiment, the jet plate 78 can be made of a suitable metal alloy such as 6061 aluminum or stainless steel.

[22J Figure 4 schematically illustrates the separation assembly 15, which receives high pressure compressed gas from HP chamber 12. The compressed gas is mixed with water in a liquid/gas mixture due to the compression taken place within the LP chamber 1 1 and the HP chamber 12. The separation assembly 15 includes a cyclonic separator 82 forming a chamber and optionally a rotor blade 84 that is utilized to separate gas from the liquid and produce compressed, dry gas. The compressed gas from HP chamber 12 is first delivered to an inlet 86 of the cyclonic separator 82 from operation of pump assembly 14. The cyclonic separator 82 illustratively includes an outer tube 88 and an inner tube 90 positioned within the outer tube 88. In one embodiment, both the outer tube 88 and inner tube 90 are metallic (e.g., cast iron, stainless steel). Gas is introduced to the outer tube 88 through the inlet 86 at a slight downward angle and tangential to an inner wall 92 of the outer tube 88 in order to produce a swirl. Centrifugal forces within the swirl operate to separate liquid from the gas. In particular, the liquid is forced against the inner wall 92 and travels along the wall 92 toward a bottom of the separator 82. After the swirl rotation diminishes, gas is transferred by the inner tube 90 to the rotor blade 84. In particular, gas turns 180 degrees into the inner tube 90 as the liquid, due to its high inertia, has the tendency to collect at the bottom of the outer tube 88.

Fig. 5 illustrates a portion of the rotor blade 84 that receives compressed gas from the inner tube 90 through an inlet 94. In one embodiment, the rotor blade 84 is formed from a plastic material and positioned within a housing 95. The rotor blade 84 can be supported by lubrication free, high chemical resistance rolling bearings. The rotor blade 84 is driven by energy from flow of the gas from inner tube 90. After passing through inlet 94, the gas is accelerated using at least one nozzle 96 (two of which are illustrated) at a high speed (e.g., a speed of approximately 50 m/s) and delivered at a shallow angle to a turbine 98 that includes a plurality of circumferentially spaced curved blades. The turbine 98 is a built as part of the rotor blade 84 and is located at the bottom of the rotor blade 84. The nozzles 96 are carved in a bearing carrier 100 positioned to receive flow from the inlet 94. It will be appreciated that different configurations for the nozzles 96 (e.g., number of nozzles, entry and exit angles for the nozzles) can be utilized.

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.