Inline non-targeted component removal

Abstract

An improved method for the removal of non-targeted components from a non-targeted component containing gas stream, the method includes the steps of: (i) contacting the non-targeted component containing gas stream with a fluid solvent stream; (ii) passing the product of step i) through a co-current phase separation step to produce both a non-targeted component containing solvent stream and a partially purified gas stream; (iii) passing the partially purified gas stream product of step ii) through a mass transfer step to produce a wet gas product; and (iv) passing the wet gas product of step iii) through a final co-current phase separation step to produce a purified gas stream, wherein the method is performed in a subsea location.

Claims

1. A method for the removal of non-targeted components from a non-targeted component containing gas stream, the method comprising the steps of: i) contacting the non-targeted component containing gas stream with a fluid solvent stream obtained from a subsea source and producing a contacted non-targeted component containing gas stream; ii) passing the contacted non-targeted component containing gas stream of step i) through a co-current phase separation step to produce both a non-targeted component containing solvent stream and a partially purified gas stream; iii) passing the partially purified gas stream of step ii) through an inline mass transfer step to produce a wet gas product, said mass transfer step comprising passing the partially purified gas stream through an inline mass transfer apparatus, in which it is contacted with a fine spray of additional fluid solvent; and iv) passing the wet gas product of step iii) through a final co-current phase separation step to produce a purified gas stream, wherein the method is performed in a subsea location.

2. The method according to claim 1, wherein the wet gas product of step iii) is passed through at least one further combination of a co-current phase separation step and an inline mass transfer step before proceeding to step iv).

3. The method according to claim 1, wherein the non-targeted components are carbon dioxide, hydrogen sulphide and/or other greenhouse gases.

4. The method according to claim 1, wherein the liquid solvent is water which has a pressure higher than atmospheric pressure.

5. The method according to claim 1, further comprising introducing fresh fluid solvent during each of steps ii), iii) and iv).

6. The method according to claim 1, wherein the partially purified gas stream of step (iii) is contacted with an alkylamine.

7. The method according to claim 1, wherein the non-targeted component containing solvent stream is injected into a natural or surface reservoir for sequestration purposes and/or enhanced oil and/or gas production purposes.

8. The method according to claim 1, wherein the fluid solvent stream is passed through one or more inline separation devices to remove solid non-targeted components from the fluid solvent stream prior to being contacted with the non-targeted component containing gas stream.

9. The method according to claim 1, wherein the non-targeted component containing solvent stream is injected into a methane hydrate reserve to produce methane and a hydrate.

10. The method according to claim 1, wherein the method further comprises the step of: Separating the non-targeted component containing gas stream from a fluid stream by way of an initial co-current phase separation step in order to separate residual liquids and solids, prior to the step of: Contacting the non-targeted component containing gas stream with a fluid solvent stream.

11. The method according to claim 10, wherein the separated residual liquids and solids undergo further phase separation to separate targeted liquids from produced water and/or sand before the targeted liquids are sent downstream for further processing and/or collection.

12. The method according to claim 1, wherein the co-current phase separation step and the final co-current phase separation step are all inline processes.

13. The method according to claim 12, wherein the inline co-current phase separation step ii) comprises passing the contacted non-targeted component containing gas stream through an inline co-current phase separation apparatus to separate the partially purified gas stream from the non-target component containing fluid solvent.

14. The method according to claim 1, wherein the non-targeted component containing solvent stream is released in deep water areas, so that the non-targeted components may be sequestered.

15. The method according to claim 14, wherein the non-targeted component containing solvent stream is progressively released over a length of pipeline.

16. A method for the removal of non-targeted components comprising greenhouse gases from a non-targeted component containing gas stream in an offshore subsea installation, the method comprising: producing a contacted non-targeted component containing gas stream by combining the non-targeted component containing gas stream with a fluid solvent stream obtained from a subsea source; after the producing, passing the contacted non-targeted component containing gas stream through a co-current phase separation to produce both a non-targeted component containing solvent stream and a partially purified gas stream; after the passing, producing a wet gas product by passing the partially purified gas stream and a fine spray of fluid solvent through an inline mass transfer apparatus; after the wet gas product is produced, passing the wet gas product through a final co-current phase separation to produce a purified gas stream; and pumping the purified gas stream to a storage location.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic representation of a flow sheet depicting a method for the removal of non-targeted components from a gas stream in accordance with the present invention;

(3) FIG. 2 is a cross sectional view of an inline co-current phase separation apparatus in accordance with the method of FIG. 1; and

(4) FIG. 3 is a cross sectional view of an inline mass transfer apparatus in accordance with the method of FIG. 1.

DESCRIPTION OF EMBODIMENTS

(5) In FIG. 1 there is shown a method 10 for the removal of non-targeted components from a fluid stream, for example either atmospheric or non-atmospheric gas streams. In general terms, the method 10 utilises a high pressure, low temperature open water source as a solvent in order to remove greenhouse gases from a gas stream.

(6) A gas or multi-phase fluid stream 12 may be combined with one or more other gas or multi-phase fluid streams 14 to produce a combined multi-phase fluid stream 16. The combined multi-phase stream 16 is then directed to a first co-current phase separation apparatus, for example an inline co-current phase separation apparatus 18, wherein the combined multi-phase stream 16 is separated into a predominantly gas stream 20 and a predominantly liquid stream 22. The predominantly gas stream 20 is then directed to a first mass transfer apparatus, for example an inline mass transfer apparatus 24, where it is spray contacted with a solvent stream 26 to produce a mixed phase stream 28.

(7) The mixed phase stream 28 is then directed to a second co-current phase separation apparatus, for example an inline co-current phase separation apparatus 30, wherein the mixed phase stream 28 is separated into a gas stream 32 and a solvent stream 34.

(8) The gas stream 32 is then directed to a second mass transfer apparatus, for example an inline mass transfer apparatus 36, where it is spray contacted with solvent stream 38 to produce a mixed phase stream 40.

(9) The mixed phase stream 40 is then directed to a final co-current phase separation apparatus, for example an inline co-current phase separation apparatus 44, wherein the mixed phase stream 40 is separated into a purified gas stream 46 and a solvent stream 48. The purified gas stream 46 then can be piped or otherwise transported for storage and/or further processing.

(10) The predominantly liquid stream 22 is then directed for downstream transportation which can include for injection into a reservoir or piping for storage and/or further processing and this may be facilitated by pump means 50 as required.

(11) If the solvent is to be regenerated rather than released or sequestered Solvent streams 34 and 48 may be passed to regeneration means 52 which may involve de-pressurization with release of non-targeted components to produce a regenerated solvent stream 54. The regenerated solvent stream 54 is directed for use at inline mass transfer apparatuses 24 and 36 by way of pumping means 56.

(12) The method 10 of the present invention as hereinbefore described is a two stage method. It is envisaged that the number of phase separation/mass transfer steps may be increased or decreased to one mass transfer step and one phase separation depending on the composition of the flow streams and the level of separation required.

(13) It is further envisaged that whilst highly applicable to natural gas and also oil and/or condensate and natural gas streams, the method of the present invention may be used for the removal of carbon dioxide and other greenhouse gases from the coal seam gas streams, biogas streams, steel works, power station flue gases and other gas or fluid streams, including from the atmosphere, where these gas or fluid streams contain undesirable levels of non-targeted components and where a suitable solvent, such as a high pressure, low temperature water source, is available in sufficient quantities.

(14) It is further envisaged that the method of the present invention may be used for the removal of any targeted component from any fluid containing the targeted component where there is a suitable solvent for the targeted component.

(15) In FIG. 2 there is shown an inline phase separating apparatus 100 for use in a method for the removal of non-targeted components from a gas stream, for example atmospheric or non-atmospheric gas streams. The inline phase separating apparatus 100 utilises cyclonic separation to generate high G-forces in order to separate liquid from a gas stream.

(16) The inline phase separating apparatus 100 comprises a main separation section 102 in which the liquid is extracted from the wet gas stream entering at the wet gas inlet 104 to produce a predominantly single phase gas stream at the dry gas outlet 106. The separated liquid is directed to a liquid outlet stream 108 by way of liquid drains 110, 112, 114. Therefore the unit is fully capable of producing two predominantly single phase outlet streams from one multiphase inlet stream. Upon entering the main section 102, the wet gases velocity is decreased due to the increase in the pipe's cross section. This allows large liquid particles to drop to the bottom of the vessel due to gravitational effects and such may be drained from the unit by way of liquid drain 110. The remaining gas, which contains a fine mist of liquid particles, then proceeds through a cyclonic spinner 116. This forces the gas to spin, which will act to agglomerate the smaller liquid droplets and force them to the outer edge of the flow stream due to their increased mass over the gas particles. This allows the droplets to be caught radially and drained from the vessel by way of liquid drains 112 and 114. The remaining dry gas then exits the separator by way of dry gas outlet 106.

(17) The inline phase separating apparatus 100 may be manufactured from suitable materials including any material used in offshore applications and is also suitable for subsea installation. If sand is expected, erosion can be prevented by applying a coating such as tungsten carbide.

(18) The inline phase separating apparatus 100 may accommodate both thin and thick liquid films through the use of a gas recycle loop (not shown). Thin liquid films are on the wall of the cyclone are generated by low liquid loadings and as a result of the friction with the cyclone' wall they have a low momentum.

(19) As the gas approaches the gas outlet cone of the cyclone it has to constrict and as a consequence a local negative pressure field is set up in addition to a gas recirculation. This in combination with the low liquid film momentum leads to an accumulation of the liquid, which subsequently leads to increased liquid carryover from the cyclone. By adding the recycle the negative pressure fields and gas recirculation zones are not formed as the gas is allowed to flow in the annulus between the gas outlet and the wall of the cyclone.

(20) The use of the gas recycle loop is not required for higher liquid loading as the thin film effect will not be as problematic. Due to the increased quantities of the liquid required for the mass transfer process of the present invention it is envisaged that the liquid loadings will be typically high and that the gas recycle loop will not be required during normal operation.

(21) In FIG. 3 there is shown an inline mass transfer apparatus 200 for use in a method for the removal of non-targeted components from a gas stream, for example atmospheric or non-atmospheric gas streams. The inline mass transfer apparatus 200 introduces a smaller liquid phase 202 into a gas stream 204 through a liquid injector pipe 206 that discharges a fine spray of the liquid phase 202 by way of a liquid spray nozzle 208. This ensures the uniform introduction of the liquid phase 202 into the gas stream 204. The liquid and gas phases are contacted by static mixing elements 210. Fine liquid stream 202 droplets are developed by the high velocity gas/liquid streams resulting in a greater amount of liquid phase 202 surface area exposed to the gas phase stream 204. The static mixing elements 210 produce a mixed phase output stream 212.

(22) The use of static mixer elements 210 provides increased mass transfer between the liquid phase 202 and the gas stream 204. The pressure drop is also minimized due to parallel paths offered to the static mixing elements 210. The decreased pressure drop lowers the required horsepower, average requirements and therefore utility costs. It is envisaged that the mixing elements 210 may be removed and through the use of fine droplets, similar mass transfer efficiencies may be achieved.

(23) It is further envisaged that the removed non-targeted components may be sequestered in deep water areas, where solubility is higher than at sea level. The non-targeted components may further be sequestered as a gas hydrate in deep water, by injecting the non-targeted component gas into methane hydrate reserves. In doing so the non-targeted component gas molecules, for example CO.sub.2 with or without additional non-targeted components will exchange with the methane in the hydrates, forming for example a CO.sub.2 hydrate, and thereby releasing methane from the methane hydrate reserves.

(24) The process of the present invention may be implemented in a variety of locations in the overall process of an upstream oil and/or gas production facility. However, it is envisaged that there are two main locations where this technology is most likely to be employed, being subsea and/or on a topsides facility such as a platform or floating production vessel.

(25) System Configurations

(26) It is envisaged that the method and apparatus of the present invention may be implemented in a number of advantageous configurations. These include:

(27) Transmission Pipelines

(28) In such a configuration the method and apparatus of the present invention is implemented in the form of transmission line which may supplement already established pipeline used to transport gas streams. Such a configuration provides a pipeline that has multiple injection point by which fresh or lean fluid solvent streams may contact the non-targeted component rich gas stream. Downstream from such injection points there are provided separation/extraction points for the non-targeted component rich solvent stream. Given that such transmission pipelines extend across large distances, the contact time of the non-targeted component containing gas stream and the fluid solvent stream is extended, thus substantially improving the absorption of the non-targeted components into the fluid solvent.

(29) Modular Systems

(30) In such a configuration the method and apparatus of the present invention are configured in the form of a compact modular multi-stage inline pipe based system. In such a configuration it is envisaged that the apparatus would comprise vertical orientation stages, followed by subsequent separation/extraction stages. In such a configuration, the apparatus of the present invention may be implemented in environments where space is limited, such as an offshore oil rig. The modular design of apparatus may be inserted in line with existing equipment on site.

(31) The method of the present invention may implemented in a number of locations on an existing topsides facility, the following location is provided by way of example:

(32) Immediately Upstream or Downstream of the Topsides Chokes

(33) The benefit of this location is to reduce the gas loading to the downstream processes. For example, one of these processes could be gas drying through the use of MEG or TEG. Alternatively, in the case of an existing facility the total production throughput of the platform may be increased.

(34) High Pressure Solvent

(35) The performance of the system is greatly improved when the pressure of the fluid solvent is increased, the temperature is lowered and the the concentration of the component to be absorbed is low. Thus to improve the efficiency of the process it is envisaged that the inclusion of an apparatus, such as a pump, to increase the pressure of the fluid solvent may be included. When operating in subsea environments, the fluid solvent is preferably obtained from deep water sources. Such deep sources, such as deep ocean water, are high pressure, low temperature and have a low carbon dioxide concentration.

(36) If implemented subsea, it is expected this will be between the wellhead and the topside facility chokes. Ideally it would be located as close to the well head as possible to minimise slugging flow entering the initial stage of separation. This will provide additional benefits of improved liquid from gas separation and a reduced line pressure drop.

(37) When locating the unit subsea, except where seawater is utilised as a solvent, it is likely that the regeneration of the solvent/reactant that is selected may need to be handled on a topside or onshore facility.

(38) The process and associated apparatus of the present invention has a number of advantages over the prior art. Importantly, the pipelines are able to be fabricated to operate safely at pressures of over 200 bar and as such, can be deployed below depths of 1000 m below sea level. Accordingly, the aforementioned advantages of utilising high pressure deep ocean water can be achieved. Typically the absorbed gas may also be sequestered directly into seawater at deep sea levels or injected in storage reservoirs, thus preventing their release into the atmosphere.

(39) As the method of the present invention is an inline process, it is far less limited by gas velocity than counter-current systems. Advantageously, the inline process may not require the regeneration of the solvent. As opposed to conventional systems incorporating large pressure vessels the compact inline systems utilised in the present co-current process are characterised by:

(40) light weight

(41) lower fabrication costs

(42) small footprints

(43) small inventory (reduced holding cost and improved safety)

(44) overall improved safety; and

(45) a low inspection and regulation regime in comparison with pressure vessels.

(46) Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.