Apparatus and method

Abstract

An apparatus (100) comprises an inlet (102) configured to receive a gas from outside the apparatus and a fluid ejector device (110). The fluid ejector device (110) comprises a suction inlet (112) conf

Description

BACKGROUND There are many applications where it is desirable to convert a fluid from a gas to a liquid. 5 Compression of a gas to a liquid is achieved by increasing the pressure of the gas, which moves the individual particles of gas closer together inducing a change of state. This can be achieved by positive displacement devices such as reciprocating or screw compressors which reduce the volume that the gas occupies and hence increases the pressure. It can also be achieved by centrifugal blowers, compressors, or pumps which use impellers to 10 accelerate the gas and then then decelerate the gas converting the kinetic energy of the gas to pressure. Usually to achieve this, multiple stages of compression and cooling between these stages are required. This is due to the limitations of the maximum compression possible in a single stage. 15 The actual suction and volumetric flow rate and discharge pressure required for a process can heavily impact compressor selection. Generally, the short comings of these various devices in gas compression are: a requirement for multiple stages; a requirement for interstage cooling; complex control methodology; leakage of lubrication oil into a process gas; servicing requirements of moving parts. 20 A fluid ejector device can be used to condense a gas to a liquid. A fluid ejector device uses a flow of motive fluid through the device to draw (or entrain) a flow of gas into a suction inlet of the device. Typically, a fluid ejector device uses a motive fluid which is different to the gas which is entrained into the device. This requires a separation process to be performed at 25 some point downstream of the fluid ejector device to separate the motive fluid from the gas / liquid which was entrained. It is an aim of the present invention to address at least one disadvantage associated with the prior art. 30 SUMMARY OF THE INVENTION There is provided an apparatus according to claim 1. Ejector devices have an advantage over many conventional mechanical pumps in that they 35 can have substantially no moving parts, so may therefore provide a longer service life in many practical applications without intervention. 20 08 24 An advantage of using a recycled portion of the output fluid as a source of motive fluid is that in some embodiments there is no requirement to provide a separate source of motive fluid. 5 An advantage of using a single fluid (e.g. carbon dioxide) as the motive fluid and the entrained gas is that there is no requirement to separate the motive fluid and the entrained gas at some later stage. This avoids the need for a separation vessel or other separation apparatus. It also avoids issues with contamination of the processed gas. 10 Converting a process gas such as carbon dioxide (CO2) to liquid or supercritical fluid form has an advantage of simplifying transport and / or storage. For example, it is easier to transport carbon dioxide (CO2) in liquid or supercritical fluid form compared to gaseous form. A supercritical fluid has a higher density and can be conveyed at higher pressures than in the form of a gas as it will occupy a smaller volume. This can simplify transport of carbon 15 dioxide in a Carbon Capture and Storage (CCS) scheme. For example, a pipeline to transport carbon dioxide in liquid or supercritical form can have a significantly smaller diameter compared to a pipeline to transport carbon dioxide in gaseous form. This reduces cost and complexity of the pipeline and makes a CCS scheme more viable. Supercritical CO2 and other supercritical fluids could be repurposed at source for numerous applications. 20 Optionally, the apparatus comprises a heater or a source of heat configured to apply heat to the output flow path. Optionally, the apparatus comprises a heat exchanger configured to transfer heat from the 25 return flow path to the output flow path. Optionally, the heat exchanger comprises: a first heat exchanger part configured to receive heat from a portion of the return flow path downstream of the pump; and a second heat exchanger part configured to apply heat to the output flow path. 30 Optionally, the heat exchanger is configured to apply heat to the output flow path downstream of where the return flow path is tapped. Optionally, the return flow path comprises a fluid inlet for providing a source of the motive 35 fluid. Optionally, the apparatus comprises a valve for controlling flow of fluid from the fluid inlet. In some embodiments, the fluid inlet is provided for the purpose of providing the system with an initial charge of fluid, after which the inlet is closed, for example by means of the fluid inlet 5 valve. Motive fluid is then supplied to the return flow path from the apparatus output flow path connected to the outlet of the ejector as described above, a portion of the fluid passing through the output flow path being caused to follow the return flow path. In some embodiments, the fluid inlet in the return flow path may be used to provide a portion 10 of the motive fluid during operation of the system in addition to or instead of providing the system with an initial charge of motive fluid. Thus, in some embodiments the fluid inlet may provide motive fluid to supplement motive fluid supplied to the return flow path from the apparatus output flow path, during operation of the apparatus to compress gas from outside the apparatus that enters the suction inlet. In embodiments in which a fluid inlet valve is 15 provided in the return flow path, the fluid inlet valve may therefore remain open during Xl normal operation in order to allow the provision of supplementary motive fluid. In some C\J * embodiments the fluid inlet valve may be opened when it is required to provide CM supplementary motive fluid during operation of the apparatus and then closed when the 1 provision of supplementary motive fluid is not required during operation of the apparatus. C02O Optionally, the apparatus comprises a valve configured to control flow of gas into the suction inlet of the ejector. Optionally, the apparatus comprises an output flow path valve configured to control flow of 25 fluid from the output flow path. Optionally, the apparatus comprises a return flow path valve configured to control flow of fluid along the return flow path. The return flow path valve can be a non-return valve or any valve which restricts flow to a single direction of flow. 30 The motive fluid and the gas can be the same type (species) of fluid. The motive fluid and the gas can be one of: water (H2O); Methane (CH4); Ethane (C2H6); Propane (CaHs); Ethylene (C2H4); Propylene (CaHe); Methanol (CH3OH); Ethanol (C2H5OH); Acetone (CaH6O); Nitrous oxide (N2O). 35 There is also provided a method of converting a fluid according to claim 14. 20 08 24 The second (returned / recycled) portion of the output fluid can be smaller than the first portion of the output fluid which is output from the outlet. 5 Optionally, the method comprises applying heat to the output fluid in the output flow path. Optionally, the method comprises transferring heat from a portion of the return flow path downstream of where the pressure is increased to the output flow path. 10 Optionally, the method comprises providing motive fluid to the return flow path from an external source via a return flow path fluid inlet. Fluid may be provided to the return flow path via the return flow path fluid inlet for the purpose of providing an initial charge of motive fluid for the apparatus. Alternatively, or in addition, fluid may be provided to the return flow path via the return flow path fluid inlet during operation of the apparatus for the purpose of 15 supplementing fluid supplied to the return flow path from the apparatus output flow path during operation. There is also provided a method of converting a fluid according to claim 17. 20 Carbon dioxide is one example of a fluid that can be processed using the apparatus. Other examples of possible fluids are: water (H2O); Methane (CH4); Ethane (C2H6); Propane (CsHs); Ethylene (C2H4); Propylene (C3H6); Methanol (CH3OH); Ethanol (C2H5OH); Acetone (C3H6O); Nitrous oxide (N2O). 25 Embodiments of the invention may be understood with reference to the appended claims. Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and / or in the following description and drawings, may be 30 taken independently or in any combination. For example, features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. For the avoidance of doubt, it is to be understood that features described with respect to one 35 aspect of the invention may be included within any other aspect of the invention, alone or in appropriate combination with one or more other features. 20 08 24 BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which: 5 FIGURE 1 shows an apparatus for converting a fluid from a gas to a liquid or a supercritical fluid; FIGURE 2 shows the apparatus of FIGURE 1 during an initial start-up period of operation; FIGURE 3 shows the apparatus of FIGURE 1 with a heat exchanger; FIGURE 4 shows a pressure / temperature diagram for carbon dioxide; 10 FIGURE 5 shows an example of an ejector device which can be used in the apparatus; FIGURE 6 shows processing of carbon dioxide; FIGURE 7 shows a processing apparatus for controlling operation of apparatus. DETAILED DESCRIPTION 15 FIGURE 1 shows an example of an apparatus 100 for converting a fluid. The apparatus 100 comprises an inlet 102 and an outlet 119. The inlet 102 is configured to receive a gas from outside the apparatus 100. For example, the gas may be carbon dioxide received from an external source which generates carbon dioxide, such as a carbon capture apparatus. The outlet 119 is configured to output fluid from the apparatus 100. The outlet 119 outputs fluid 20 externally of the apparatus, such as to a pipeline, storage or some other source. The apparatus 100 can be used to convert a fluid from the form of a gas received via the inlet 102 to the form of a liquid or a supercritical fluid which is output from the outlet 119. A supercritical fluid is a compound which has been subjected to pressure and temperature higher than its critical point. The terms “form”, “state” and “phase” are used interchangeably 25 in this description to refer to the different states of matter. It will be understood that a fluid can take the form of a gas, a liquid or a supercritical fluid. The apparatus 100 comprises a fluid ejector device 110. The fluid ejector device 110 comprises a motive fluid (high pressure, HP) inlet 111, a suction (low pressure, LP) inlet 112 30 and an outlet 113. The motive fluid inlet 111 is configured to receive a motive fluid via inlet 102 and inlet line 104. The suction inlet 112 is configured to receive a gas from an input line 124. The outlet 113 is configured to output a flow of output fluid. The output fluid can be in the form of a liquid or a supercritical fluid. An output flow path 115 is connected between the outlet 113 of the ejector and an outlet 119 of the apparatus. The output flow path 115 can 35 be one or more pipes or conduits. 20 08 24 Operation of ejector devices 110 is based upon the venturi principle. Velocity of a relatively high pressure fluid (called the motive fluid) along a channel provides a suction effect on a relatively low pressure fluid (called the entrained fluid or suction fluid). The suction fluid is entrained into the main flow through the channel and ejected from the ejector device as a 5 discharge fluid. Examples of such ejector devices which use a motive liquid to pressurise a gas may be called a jet pump, a liquid jet compressor or a Venturi pump. A return flow path 116 is connected between the output flow path 115 and the motive fluid inlet 111 of the fluid ejector device 110. The return flow path 116 is configured to tap a 10 portion of the output flow along the output flow path 115. The return flow path 116 can be connected to the output flow path 115 by a T-piece 126 or any other suitable fitting. The return flow path 116 can be one or more pipes or conduits. The return flow path 116 may include a non-return valve 123. The non-return valve 123 15 permits flow in one direction, i.e. down in FIGURE 1, but blocks flow in the other direction. Valve 123 can prevent leakage of fluid, such as when fluid is added to the apparatus via inlet 117. Valve 123, or another valve in the return flow path 116, can provide a restriction on flow of fluid into the return flow path 116. The amount of restriction provided by the valve can be fixed, or variable. 20 The apparatus 100 comprises a pump 118 in the return flow path 116. Pump 118 is configured to pump motive fluid along the return flow path 116 to the motive fluid inlet 111 of the fluid ejector device 110. Pump 118 increases pressure of the motive fluid entering the motive fluid inlet 111 of the fluid ejector device 110. Another term for the pump 118 is a 25 compressor. In use, flow of high pressure liquid through the fluid ejector device 110 (from the motive inlet 111 to the outlet 113) entrains a flow of gas received from inlet 102 via the suction inlet 112. The fluid ejector device 110 causes the gas received via the suction inlet 112 to be 30 condensed to a liquid or a supercritical fluid. Fluid (in the form of a liquid or a supercritical fluid) is output from the ejector outlet 113 along the output flow path 115 to the outlet 119. A first portion of the fluid output from the ejector outlet 113 is output from outlet 119 of the apparatus. A second portion of the output liquid flow along the output flow path 115 is tapped to the return flow path 116 to provide a source of motive fluid for the fluid ejector 35 device 110. That is, a portion of the fluid output from the ejector outlet 113 is recycled. The return flow path 116 carries fluid to the pump 118. Pump 118 increases the pressure of the 20 08 24 liquid on the return flow path 116. This provides a flow of high pressure motive fluid to the motive inlet 111 of the fluid ejector device 110. Once established, the process is self-supporting. A tapped portion of the output fluid flow provides a source of motive fluid to the fluid ejector device 110 to generate an output fluid and a further tapped portion of the output fluid is returned, and so on. By using a tapped portion of the output flow as a source of motive fluid, there is no requirement to provide a separate source of motive fluid. By using a single fluid (e.g. carbon dioxide) as the motive fluid and the entrained gas, there is no requirement to separate the motive fluid and the entrained gas at some later stage. Within the fluid ejector device 110, temperature and pressure exerted on the gas by the motive fluid and the passage through the ejector causes the gas to be condensed to a liquid, or to a supercritical fluid. The output flow path 115 comprises a valve 121. The valve 121 can be an on / off valve. Valve 121 can control flow of fluid from the apparatus 100. It can be used to isolate the apparatus 100. Valve 121 can be a pressure control valve. This can bleed out air from the flow path 115 or release liquid (or supercritical fluid) condensed by the fluid ejector device 110. A valve 124 can be provided in the input line 124 to the ejector 110. Valve 124 can be used to selectively open or close the input line 124 to the suction inlet of the ejector 110. FIGURE 2 shows operation of the apparatus 100 during an initial start-up phase of operation. Initially, the flow paths 115, 116 may contain a quantity of air. The paths 115, 116 require a volume of fluid at pressure before they can begin to function. An initial supply of fluid can be provided to the return flow path 116. Fluid (in liquid form) is supplied via inlet 117 to the return flow path 116. The return flow path 116 carries the liquid to pump 118. Pump 118 increases the pressure of the liquid on the return flow path 116. This provides a flow of high pressure liquid to the motive inlet 111 of the fluid ejector device 110. During this period, valve 121 prevents passage of fluid. This allows the flow paths 115, 116 to fill with liquid and to displace any air remaining in the flow paths. Valve 121 (or another valve) allows air to escape from the flow paths. Valve 124 can be closed during this initial period. When a sufficient quantity of liquid is in the flow paths 115, 116, valve 117 can be closed. Valve 124 can be opened to admit gas to the suction inlet 112. Valve 121 can be opened to allow fluid to exit. 20 08 24 Once up and running, the process is self-supporting, with a (small) tapped portion of the output liquid flow providing an input to the ejector 111. A valve 122 is provided in the flow path from the inlet 117. Valve 122 can be opened to allow fluid to be added to the return 5 path 116. Once fluid has been added, valve 122 is closed. Apparatus 100 comprises a controller 140 to control operation of the apparatus. The controller 140 is connected to the pump 118 and one or more of the valves 121, 122, 123, 124. The controller outputs one or more control signals 142 to control devices. Full 10 connections between the controller 140 and devices have not been shown in FIGURE 1 to improve clarity. Apparatus 100 may also comprise one or more sensors to provide inputs to the controller 140. For example, sensors can monitor operating parameters of fluids in one or more of: the inlet line 104; the output flow path 115; the return flow path 116. The sensors can monitor temperature and / or pressure. The controller 140 is connected to the sensors 15 and receives input signals 142 from the sensors. Heat can be applied to the output flow path 115 by a heater 120. The applied heat can be used to cause the output fluid to transition to a supercritical state (e.g. liquid to supercritical fluid), or to remain in a supercritical form. For example, heat may be applied to the 20 supercritical fluid to ensure that it remains in a supercritical form during transport along a conduit, where there are likely to be heat losses from the conduit. The heater 120 can receive waste heat from an external process. For example, in the case of a power station, waste heat from the power station can be applied by the heater 120. The term “heater” is intended to include any device which applies heat. The heater may comprise part of a heat 25 exchanger. The heater may comprise an electrical heating element or combust fuel (e.g. gas) to provide heat. FIGURE 3 shows another example of the apparatus. A heat exchange 130 is provided between the return flow path 116 and the output flow path 115. A first part 131 of the heat 30 exchange is provided in the return flow path 116 at a position downstream of the pump 118. A second part 132 of the heat exchange is provided in the output flow path 115 at a position downstream of the tap point. The first part 131 of the heat exchanger is configured to receive heat from the return flow path 116. The second part 132 of the heat exchanger is configured to apply heat to the output flow path 115. Removing heat from the return flow 35 path improves efficiency of the fluid ejector device 110. 20 08 24 The higher temperature is present in the fluid due to the compression effect of the ejector on the fluid, and due to the compression effect of the pump and the pump’s internal inefficiencies 118 on liquid. The heat exchanger part 132 can be used as the heater 120 shown in FIGURE 1, or in addition to the heater 120. 5 One or more temperature / pressure booster units may be provided as part of apparatus 100, or downstream of the apparatus. Each booster may increase temperature and / or pressure of the fluid. For example, a pipeline which transports a fluid in supercritical form may require a booster unit at some point along the pipeline to maintain pressure and / or temperature 10 above the critical point for the type of fluid. FIGURE 4 shows a graph of pressure versus temperature for carbon dioxide. Boundary values are indicated for the various phases of carbon dioxide, i.e. solid, gas, liquid and supercritical fluid. The triple point is the boundary (in terms of temperature and pressure) 15 between solid, liquid and gas phases. It is a temperature of 216.6 K (-56.6 °C) and a pressure of 0.52 MPa. The critical point for the boundary between liquid / gas and supercritical fluid is a temperature of 304.1 K (30.1 °C) and a pressure of 7.38 MPa (73.8 bar). That is, when temperature is above 304.1 K and pressure is above 7.38 MPa, carbon dioxide will transition from a gas or a liquid to a supercritical fluid. 20 In the supercritical region, the fluid has properties which are intermediate between a liquid and a gas. A supercritical fluid has liquid-like densities and gas-like viscosities and diffusivities. By converting the gas to a liquid or a supercritical fluid the gas can be stored and / or transported more efficiently. 25 The graph of FIGURE 4 determines the operating points for the apparatus. For example, if a supercritical fluid is required at the output of the ejector 110, pressure and temperature of the fluid output from the ejector must both be above the critical point (i.e. temperature of 304.1 K and a pressure of 7.38 MPa). If a liquid is required at the output of the ejector 110, 30 pressure and temperature of the fluid output from the ejector should fall within the region shown in FIGURE 4. As described above, the apparatus can apply heat to the output flow path to increase temperature of the output fluid. Heat may be applied to cause the output fluid to transition to a supercritical fluid phase, if that is required. 35 FIGURE 5 shows an example of an ejector device which can be used as the ejector device 110 of FIGURES 1-3. This ejector device is described in WO 2012 / 059773 A2. The ejector 20 08 24 device in FIGURE 5 is a single channel device. It is also possible to use a multiple channel ejector device for increased flow rates. The ejector device 1 has a motive fluid inlet portion 10 through which a motive fluid can enter 5 the device 1. The motive fluid may for example be pumped by a pump (not shown) into and through the motive fluid inlet or injector portion 10. The velocity of the motive fluid increases as it passes through a conical nozzle portion 40 of the device 1 before being injected through an outlet aperture 44 of the nozzle portion 40 at an apex thereof into an inlet aperture 52 of a diffuser portion 50. The diffuser portion 50 provides a fluid conduit in the 10 form of a Venturi tube, in which, passing from the inlet aperture 52 of the diffuser portion 50 towards an outlet aperture 54 thereof, a diameter of the conduit initially decreases along a first length of the diffuser portion 50 to a diameter less than that of the inlet aperture 52, then remains at that reduced diameter for a short distance, and then along a second length of the diffuser portion 50 the diameter of the conduit increases towards the outlet aperture 54 of the 15 diffuser portion 50. The outlet aperture 44 of the nozzle portion 40 and the inlet aperture 52 of the diffuser portion 50 are in fluid communication with a suction fluid inlet portion 20 of the device 1. As a flow of motive fluid flows out from the outlet aperture 44 of the nozzle portion 40 and into 20 the diffuser portion 50, the motive and suction fluids are mixed, and this results in a transfer of momentum and thus kinetic energy from the motive fluid to the suction fluid. This is accompanied by a reduction in the flow velocity of the combined fluids and an increase in the pressure of the suction fluid phase. It is to be noted that this is a reverse process to that occurring in the nozzle portion 40 where an increase in motive fluid velocity occurs, thereby 25 reducing a pressure of the motive fluid as it exits the nozzle portion 40 through its outlet aperture 44. This table provides details of fluids which can be processed by the apparatus. Each fluid includes a respective critical temperature and a critical pressure. Solvent Molecular mass Critical temperature Critical pressure Critical density g / nwl K MPa (atm) g / cm3 Carbon dioxide (CO2) 44.01 304.1 7.38 (72.8) 0.469 Water (H2O)t 18.015 647.096 22.064 (217.755) 0.322 Methane (CH4) 16.04 190.4 4.60 (45.4) 0.162 Ethane (C2H6) 30.07 305.3 4.87(48.1) 0.203 Propane (C3H8) 44.09 369.8 4.25 (41.9) 0.217 Ethylene (C2H4) 28.05 282.4 5.04 (49.7) 0.215 Propylene (C3H6) 42.08 364.9 4.60 (45.4) 0.232 Methanol (CH3OH) 32.04 512.6 8.09 (79.8) 0.272 Ethanol (C2H5OH) 46.07 513.9 6.14 (60.6) 0.276 Acetone (C3H6O) 58.08 508.1 4.70 (46.4) 0.278 Nitrous oxide (N2O) 44.013 306.57 7.35 (72.5) 0.452 20 08 24 FIGURE 6 shows a flow diagram of an example of processing carbon dioxide. Carbon Dioxide (CO2) is a gas which occurs in vast quantities as a waste product of various processes, such as power stations which burn carbon-based fuels. There is considerable 5 interest in removing carbon dioxide from waste gas. Carbon Capture and Storage (CCS) schemes aim to capture (i.e. remove) carbon dioxide and then store the captured carbon dioxide in the form of a gas in underground geological formations. This typically requires transport of carbon dioxide in the form of a gas by pipelines or vessels. Carbon Capture and Utilization (CCU) schemes aim to capture carbon dioxide and then convert the captured 10 carbon dioxide into a form with another practical use. At block 301 carbon dioxide is generated. The carbon dioxide may be generated in gas form as a waste product of combustion in a power station, an industrial process (e.g. a cement works) or some other process. At block 302 carbon dioxide is captured. Carbon dioxide is 15 separated from other waste gases. At block 303 the carbon dioxide is converted from a gas to a liquid or a supercritical fluid. The apparatus 100 described above can perform this conversion. An output product of the conversion (block 303) is carbon dioxide in liquid or supercritical form. At block 304 the carbon dioxide (in liquid or supercritical form) is transported. For example, transport could be via a pipeline, by road / rail / sea or any other 20 08 24 suitable means. -At block 305 the carbon dioxide is stored or converted to another form for use. FIGURE 7 shows an example of a processing apparatus 500 which may implement the 5 controller 140 shown in FIGURE 1. Processing apparatus 500 comprises one or more processors 501 which may be any type of processor for executing instructions to control the operation of the device. The processor 501 is connected to other components of the device via one or more buses 506. Processor-executable instructions 512 may be provided using any data storage device or computer-readable media, such as memory 502. The processor-10 executable instructions 512 comprise instructions for implementing the functionality of the described methods. The memory 502 is of any suitable type such as non-volatile memory, a magnetic or optical storage device. The processing apparatus 500 comprises input / output (I / O) interfaces 507. The I / O interfaces 507 can receive signals from sensors in the apparatus and output control signals to control devices in the apparatus such as the pump 15 118 and valves 121, 122, 123, 124. The processing apparatus 500 connects to a user interface 508. Memory 502, or a separate memory, stores data 511 used by the processor. In some embodiments, the apparatus 100 may be configured such that, during operation of the apparatus 100 to compress gas entering suction inlet 112, motive fluid may be supplied 20 to the return flow path 116 via the liquid inlet 117 in order to supplement the portion of fluid tapped from the output flow path 115 to flow along the return flow path 116. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means 25 “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is 30 used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be 35 understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. 20 08 24

Claims

1. Apparatus for converting a fluid from a gas to a liquid or a supercritical fluid comprising:5 an inlet configured to receive a gas from outside the apparatus;a fluid ejector device comprising:a suction inlet configured to receive the gas;a motive fluid inlet configured to receive a motive fluid;an outlet configured to output an output fluid as a liquid or a supercritical fluid;10 an output flow path connected to the outlet of the fluid ejector device, the output flowpath having an outlet configured to output fluid from the apparatus as a liquid or a supercritical fluid;a return flow path connected between the output flow path and the motive fluid inlet of the fluid ejector device, the return flow path configured to tap a portion of the output flow15 as a source of the motive fluid;a pump in the return flow path,wherein the fluid ejector device is configured to increase a pressure of the gas received via the suction inlet to an operating point at which the gas is condensed to a liquid or a supercritical fluid.

202. Apparatus according to claim 1 comprising a heater or a source of heat configured to apply heat to the output flow path.

3. Apparatus according to claim 1 or 2 comprising a heat exchanger configured to 25 transfer heat from the return flow path to the output flow path.

4. Apparatus according to claim 4 wherein the heat exchanger comprises:a first heat exchanger part configured to receive heat from a portion of the return flow path downstream of the pump;30 a second heat exchanger part configured to apply heat to the output flow path.

5. Apparatus according to claim 3 or 4 wherein the heat exchanger is configured to apply heat to the output flow path downstream of where the return flow path is tapped.35 6. Apparatus according to any one of the preceding claims wherein the return flow pathcomprises a fluid inlet for providing a source of the motive fluid.20 08 247. Apparatus according to claim 6 comprising a valve for controlling flow of fluid from the fluid inlet.5 8. Apparatus according to any one of the preceding claims comprising a valveconfigured to control flow of gas into the suction inlet of the fluid ejector device.

9. Apparatus according to any one of the preceding claims comprising an output flow path valve configured to control flow of fluid from the output flow path.1010. Apparatus according to any one of the preceding claims comprising a return flow path valve configured to control flow of fluid along the return flow path.

11. Apparatus according to claim 10 wherein the return flow path valve is a non-return 15 valve.

12. Apparatus according to any one of the preceding claims wherein the motive fluid and the gas are the same type (species) of fluid.20 13. Apparatus according to any one of the preceding claims wherein the motive fluid andthe gas are one of: water (H2O); Methane (CH4); Ethane (C2H6); Propane (CaHs); Ethylene (C2H4); Propylene (C3H6); Methanol (CH3OH); Ethanol (C2H5OH); Acetone (CaH6O); Nitrous oxide (N2O).25 14. A method of converting a fluid from a gas to a liquid or a supercritical fluidcomprising:receiving a gas from an external process;applying a motive fluid to a motive fluid inlet of a fluid ejector device and causing the fluid ejector device to draw the gas into a suction inlet of the fluid ejector device;30 outputting an output fluid from the fluid ejector device along an output flow path,wherein the output fluid is a liquid or a supercritical fluid;outputting a first portion of the output fluid from an outlet as a liquid or a supercritical fluid;returning a second portion of the output fluid to the motive inlet of the fluid ejector 35 device along a return flow path to provide a source of the motive fluid;increasing pressure of the motive fluid in the return flow path;20 08 24wherein applying a motive fluid to the motive fluid inlet of the fluid ejector device increases a pressure of the gas to an operating point at which the gas is condensed to a liquid or a supercritical fluid.5 15. A method according to claim 14 comprising applying heat to the output fluid in theoutput flow path.

16. A method according to claim 14 or 15 comprising transferring heat from a portion of the return flow path downstream of where the pressure is increased to the output flow path.1017. A method of converting a fluid from a gas to a liquid or a supercritical fluid comprising:receiving a gas from an external process;applying a motive fluid to a motive fluid inlet of a fluid ejector device and causing the15 fluid ejector device to draw a gas into a suction inlet of the fluid ejector device;outputting an output fluid from the fluid ejector device as a liquid or a supercritical fluid;outputting at least a portion of the output fluid from an outlet as a liquid or a supercritical fluid;20 wherein applying a motive fluid to the motive fluid inlet of the fluid ejector device increases a pressure of the gas to an operating point at which the gas is condensed to a liquid or a supercritical fluid, andwherein the motive fluid and the gas are the same type of fluid.

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