Method of shipping green methanol and backhauling carbon dioxide

Abstract

The present invention is broadly directed to a method of shipping green methanol and backhauling carbon dioxide (CO2) comprising the steps of: (a) shipping green methanol at (10) via a dual-cargo carrier ship (12) from a methanol production region at (14) to a methanol consumption region at (16); (b) consuming the green methanol at (18) at the methanol consumption region (16); (c) backhauling CO2 emissions at (20) from the methanol consumption region (16) to the methanol production region (14) via the dual-cargo carrier ship (12).

Description

METHOD OF SHIPPING GREEN METHANOL AND BACKHAULING CARBON DIOXIDETechnical Field

[0001] The present invention is broadly directed to a method of shipping green methanol and backhauling carbon dioxide (CO2). The invention is also broadly directed to a method of purging residual gas from a dual-cargo carrier ship. In corresponding aspects, the invention is directed to a dual-cargo transportation and infrastructure system, and an in situ nitrogen purge gas assembly of a dual-cargo carrier ship.Summary of Invention

[0002] According to a first aspect of the present invention there is provided a method of shipping green methanol and backhauling carbon dioxide (CO2), said method comprising:(a) shipping green methanol via a dual-cargo carrier ship from a methanol production region to a methanol consumption region being remote from the methanol production region;(b) consuming the green methanol at the methanol consumption region;(c) backhauling CO2 emissions from the methanol consumption region to or near the methanol production region via the dual-cargo carrier ship.

[0003] Preferably the method involves repeating steps (a) to (c) for multiple shipping roundtrips between the methanol production region and the methanol consumption region.

[0004] Preferably the step of shipping green methanol involves exporting the green methanol via the dual-cargo carrier ship from the methanol production region to the methanol consumption region. More preferably the step of backhauling CO2 emissions involves importing the CO2 emissions to or near the methanol production region via the dual-cargo carrier ship.

[0005] Preferably the step of consuming the green methanol involves generation of electricity utilising the green methanol as fuel wherein combustion of the green methanol emits the CO2 emissions. More preferably the step of backhauling CO2 emissions involves backhauling of the CO2 emissions emitted from the generation of electricity via the green methanol fuel.

[0006] Alternatively the step of backhauling CO2 emissions involves backhauling CO2 emissions produced independent of the step of consuming the green methanol. In this variation the CO2 emissions are obtained from CO2 stores located at the methanol consumption region, said CO2 stores obtained from any one or more of the following CO2 sources: industrial processes producing or emitting CO2, or CO2 emissions captured onboard ships including methanol-fuelled ships.

[0007] Preferably the method also comprises production of green methanol at the methanol production region, said production involving a reaction between hydrogen (H2) and carbon dioxide (CO2) wherein said CO2 is at least in part obtained from CO2 emissions backhauled from the consumption region. More preferably said production also involves obtaining the H2 from electrolysis of water. Still more preferably said electrolysis of water is powered via green electricity derived from solar power, wind turbines, hydro power or other located at or near the methanol production region.

[0008] Alternatively the method also comprises production of green methanol at the methanol production region independent of CO2 emissions backhauled from the methanol consumption region. In this variation the production of green methanol in the reaction between H2 and CO2 involves obtaining the CO2 from either a sustainable biomass, direct air capture of CO2 from atmosphere, or initially sourcing CO2 from a fossil source such as a carbon capture storage (CCS) facility. The production of methanol via the reaction may be supplemented with methanol derived from biomass. In this embodiment CO2 emissions backhauled from the methanol consumption region are geosequestrated or otherwise stored at or near the methanol production region.

[0009] Preferably the method further comprises liquefying the CO2 emissions at the methanol consumption region. More preferably the method also comprises storing the liquefied CO2 emissions at said consumption region in preparation for the step of backhauling CO2 emissions via the dual-cargo carrier ship.

[0010] Preferably the method further comprises unloading of the green methanol from storage vessels of the dual-cargo carrier ship at the methanol consumption region in preparation for the step of consuming the green methanol. More preferably the method also comprises loading of the CO2 emission into the storage vessels of the dual-cargo carrier ship docked at a port or terminal at the methanol consumption region.

[0011] In a first embodiment the method further comprises purging of the storage vessels of said carrier ship at the methanol consumption region of residual green gaseous methanol following unloading of the green liquid methanol and prior to loading of the CO2 emissions at said consumption region. In the first embodiment the method also comprises purging of said storage vessels at the methanol production region of residual backhauled gaseous CO2 emissions following unloading of the backhauled liquid CO2 emissions and prior to the loading of the liquid green methanol at the methanol production region.

[0012] In a second embodiment the method comprises inerting of green methanol loaded in storage vessels of the dual-cargo carrier ship at the methanol production region. In this second embodiment the backhauled CO2 emissions are unloaded from the storage vessels at the methanol production region leaving CO2 gas within said vessels which functions as inerting gas for said green methanol subsequently loaded in said storage vessels. In this second embodiment the CO2 inerting gas pressure is determined by the interaction between the storage vessels of the dual cargo carrier ship and the CO2 liquid storage tanks at the methanol production region. This interaction will determine the inerting gas pressure at which the storage vessels are maintained for shipping of the green methanol from the methanol production region to the methanol consumption region.

[0013] In the second embodiment the method also comprises, following unloading of the green methanol, pressurising of the storage vessels at the green methanol consumption region via gaseous CO2 emissions in a predominantly gas phase prior to loading of the CO2 emissions in a predominantly liquid phase at the methanol consumption region. In this second embodiment the method further comprises controlled interaction between the storage vessels of the dual cargo carrier ship and the CO2 liquid storage tanks at the methanol consumption region thereby maintaining the required relatively high pressure of the CO2 emissions within the storage vessels for backhauling of the CO2 emissions in the liquid phase.

[0014] According to a second aspect of the invention there is provided a dualcargo transportation and infrastructure system comprising: a dual-cargo carrier ship adapted to ship green methanol from a methanol production region to a methanol consumption region; a green methanol consumption facility located at the methanol consumption region, said consumption facility adapted for consuming the green methanol; the dual cargo carrier ship adapted to backhaul CO2 emissions from the methanol consumption region to or near the methanol production region.

[0015] According to a third aspect of the invention there is provided a method of purging residual gas from a dual-cargo carrier ship, said method comprising: in situ capturing of nitrogen (N2) from atmosphere, said capturing being effected onboard the dual-cargo carrier ship; purging of residual gas remaining in storage vessels onboard said carrier ship, said purging being effected onboard said carrier ship using the captured N2.

[0016] Preferably the method also comprises in situ storing of the captured N2 onboard the dual-cargo carrier ship, said storing being effected prior to purging of residual gas. More preferably the steps of in situ capturing and storing of N2 occur whilst the dual-cargo carrier ship sails between its port of origin and port of designation and thus the captured N2 progressively accumulates onboard. Evenmore preferably the captured N2 accumulates in a plurality of high pressure storage tanks located on deck the dual-cargo carrier ship.

[0017] Preferably the method further comprises compression of the captured N2 prior to its storage thereby increasing the onboard accumulation of the captured N2. More preferably the onboard N2 storage capacity of the dual-cargo carrier ship exceeds onboard storage capacity of the storage vessels.

[0018] Preferably the step of purging involves selectively introducing the captured N2 either below or above the residual gas thereby purging a storage vessel within which the gas is contained onboard the dual-cargo carrier ship. More preferably said selective purging of the residual gas via the captured N2 is enabled by piping and associated valves connected between the N2 storage tanks and the gas storage vessel at its bottom and top for purging of the residual gas from outlets at respective of the top and bottom of said storage vessel.

[0019] Preferably the step of in situ capturing of N2 involves direct capture of N2 from atmosphere via one or more membrane nitrogen generators or pressure swing adsorption (PSA) generators. Alternatively said capture of nitrogen is effected onboard via an air separation plant.

[0020] According to a fourth aspect of the invention there is provided an in situ nitrogen (N2) purge gas assembly of a dual-cargo carrier ship, said assembly comprising: one or more air capture modules located onboard said carrier ship for in situ capturing of N2 from atmosphere; a purging sub-assembly located onboard said vessel and associated with said air capture modules, said purging sub-assembly arranged for purging of residual gas remaining in storage vessels onboard the dual-cargo carrier ship, said purging effected onboard said ship via the purging sub-assembly using the captured N2.Brief Description of Drawings

[0021] In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a method of shipping green methanol andbackhauling carbon dioxide (CO2) together with other aspects of the technology will now be described, by way of example only, with reference to the accompanying illustrations in which:Figure 1 is a schematic illustration of a method of shipping green methanol and backhauling CO2, as well as a dual-cargo transportation and infrastructure system of first embodiments according to first and second aspects of the invention;Figure 2 is a schematic illustration of a method of shipping green methanol and backhauling CO2, as well as a dual-cargo transportation and infrastructure system of second embodiments according to first and second aspects of the invention;Figure 3 is a schematic illustration of a method of purging residual gas from a dualcargo carrier ship, as well as an in situ nitrogen (N2) purge assembly of a dual-cargo carrier ship of embodiments according to third and fourth aspects of the invention.Detailed Description

[0022] Figure 1 schematically depicts a first embodiment of a method of shipping green methanol and backhauling carbon dioxide (CO2) according to the first aspect of the technology. The method of this example in the context of the first aspect of the invention broadly comprises the steps of:(a) shipping green methanol at 10 via a dual-cargo carrier ship 12 from a methanol production region at 14 to a methanol consumption region at 16;(b) consuming the green methanol at 18 at the methanol consumption region 16;(c) backhauling CO2 emissions at 20 from the methanol consumption region 16 to the methanol production region 14 via the dual-cargo carrier ship 12.

[0023] In this first embodiment the method also comprises the step of producing green methanol at 22 at the methanol production region 14. This production involves a reaction between hydrogen (H2) and CO2 which is at least in part obtained from emissions or “recycled CC at 24 backhauled from the consumption region 16. The recycled CO2 24 may be supplemented or topped up with non-fossil fuel CO2 or “Biomass to CC>2“ at 26 such as that derived from sustainable biomass at 28. In thisembodiment the production of green methanol also involves obtaining the H2 from electrolysis of water (not shown). This electrolysis of water is powered via green electricity derived from solar panel, wind turbines, or hydropower located at or near the methanol production region 14. It is to be understood that green methanol in the context of this patent specification is methanol produced from sustainable or nonfossil sources of H2 and CO2.

[0024] In this first embodiment the step of consuming the green methanol 18 involves generation of electricity utilising the green methanol as a fuel wherein combustion of the green methanol emits the backhauled CO2 emissions. The CO2 emissions obtained directly from the generation of electricity are liquefied at 30 at the methanol consumption region 16. The liquefied CO2 emissions are stored at the consumption region 16 in preparation for backhauling of the CO2 emissions 20 via the dual-cargo carrier ship 12. In an alternative construct, the step of backhauling CO2 emissions involves backhauling CO2 emissions produced independent of the step of consuming the green methanol at 18. In this variation the CO2 emissions may be obtained from CO2 stores located at the methanol consumption region 16. The CO2 stores may be obtained from any one or more of the following CO2 sources: geosequestrated CO2, industrial processes producing or emitting CO2, or methanol- fuelled ships capturing CO2 emissions onboard.

[0025] It is be understood that the method of shipping green methanol and backhauling CO2 is performed in multiple shipping round trips between the methanol production region 14 and the methanol consumption region 16. In this first embodiment the step of shipping green methanol at 10 involves exporting the green methanol via the dual-cargo carrier ship 12 from the methanol production region 14 to the methanol consumption region 16. The step of backhauling CO2 emissions involves importing the CO2 emissions 20 to the methanol production region 14 via the dual-cargo carrier ship 12. In one implementation of this technology the green methanol is exported from Australia to Singapore via a dual-cargo carrier ship where it is consumed, and CO2 emissions imported from Singapore to Australia via the same dual-cargo ship.

[0026] In this first embodiment the method further comprises unloading of the green methanol from storage vessels (not shown) of the dual-cargo carrier ship 12 at the methanol consumption region 16. In this example the unloaded green methanol is thereafter consumed as fuel in the generation of electricity at 18. In this scenario the method also comprises loading of CO2 emissions, resulting from consumption of the green methanol in the generation of electricity, into the same storage vessels of the same dual-cargo carrier ship 12. Generally, the CO2 emissions are liquefied and stored at 30 prior to loading into these storage vessels of the dual-cargo carrier ship 12 docked at a point or terminal at the methanol consumption region 16.

[0027] In this first embodiment the method further comprises purging of the storage vessels of the dual-cargo carrier ship 12. This purging is typically performed using nitrogen (N2) gas at either or both:1) the methanol consumption region 16 where residual green methanol is purged following unloading of the green methanol and prior to loading of the CO2 emissions;2) at the methanol production region 14 where residual backhauled CO2 emissions are purged following unloading of the backhauled CO2 emissions and prior to the loading of the green methanol at the methanol production region 14.

[0028] In this first embodiment the storage vessels of the dual-cargo carrier ship 12 have a total or combined storage capacity of up to around 60,000 m3It will be understood that the storage vessels are capable of storing (i) liquid methanol at ambient conditions at a density of around .8 tonne I m3, and (ii) liquefied CO2 at 7 to 10 Bar and down to around -50 degree Celsius at a density of around 1.1 tonne / m3. This means the storage vessels of the dual-cargo carrier ship are pressure rated up to around 16 Bar and constructed of a material compatible with both liquid methanol and liquid CO2.

[0029] Remaining with figure 1, there is schematically depicted a dual-cargo transportation and infrastructure system designated generally at 50 of a first embodiment of the second aspect of the invention. The system 50 of this firstembodiment in the context of the second aspect of the invention broadly comprises:1) a dual-carrier cargo ship 12 adapted to ship green methanol from a methanol production region 14 to a methanol consumption region 16;2) a green methanol consumption facility 18 located at the methanol consumption region 16, said consumption facility 18 adapted for consuming the green methanol;3) the dual-cargo carrier ship 12 adapted to backhaul CO2 emissions from the methanol consumption region 16 to the methanol production region 14.

[0030] Figure 2 schematically depicts a second embodiment of the first and second aspects of the invention. The second embodiment is fundamentally similar to the first embodiment except there is no requirement for purging of residual gas from the dual-cargo carrier ship. For ease of reference and in order to avoid repetition, like components of the second embodiment are referenced with an additional “0”. For example, the dual-cargo carrier ship of the second embodiment is designated as 120.

[0031] In the second embodiment the method comprises inerting of green methanol loaded in storage vessels such as 130 of the dual-cargo carrier ship 120 at the methanol production region 140. It is to be understood that backhauled CO2 emissions unloaded from the storage vessel 130 at the methanol production region 140 leaves CO2 gas within said vessel 130. The remaining CO2 gas within said vessel 130 functions as the inerting gas for green methanol subsequently loaded in the storage vessels such as 130. In this second embodiment, during loading of the green methanol, the CO2 inerting gas pressure is determined by the interaction between the storage vessels such as 130 and the CO2 liquid storage tanks such as 240, at the methanol production region 140thereby determining the inerting gas pressure at which the storage vessels such as 130 are maintained for shipping of the green methanol from the methanol production region 140 to the methanol consumption region 160 via the dual-cargo carrier ship 120.

[0032] In this second embodiment the CO2 emissions are unloaded from the storage vessels such as 130 by pumping into CO2 liquid storage tanks such as 240 at the methanol production region 140. The vessel 130 when empty of CO2 in its liquid form remain full of CO2 gas at above atmospheric pressure. In this example, the liquid methanol is pumped from methanol tank such as 230 into the bottom of the storage vessels 130 of the dual-cargo carrier ship 120 forcing the remaining CO2 gas into the gas space above the methanol liquid. The gas pressure within the storage vessel 130 is above atmospheric pressure for shipping of the green methanol at 100 via the dual-cargo carrier ship 120 from the methanol production region at 140 to the methanol consumption region at 160. The liquid methanol is thus above atmospheric pressure and ambient temperature wherein it is shipped to the methanol consumption region 160 in the liquid form with no refrigeration being required at 100.

[0033] In this second embodiment the method also comprises pressurising of the storage vessels such as 130 at the green methanol consumption region 160 following unloading of the green methanol. In this example, CO2 emissions in a predominantly gas phase are used for this pressurising prior to loading of the CO2 emissions in a predominantly liquid phase. The CO2 gas emissions are obtained from either an Allam cycle power station at 250 or captured from methanol combustion at 270.

[0034] In this second embodiment it will be understood that either the Allam cycle power station at 250 or methanol combustion at 270 is fuelled from liquid methanol shipped to methanol consumption region 160 and stored at a green methanol tank 290. The CO2 gas emissions are stored at the methanol consumption region 160 at CO2 liquid storage tanks 300 in a liquid form under pressure generally between 7 and 15 Bar absolute and at a temperature generally between minus 48°C and minus 30°C. In this second embodiment CO2 gas from the storage tank 300 is fed into the storage vessels such as 130 of the dual-cargo carrier ship 120 prior to any CO2 liquid being pumped into the storage vessel such as 130 from the CO2 tank 300. The liquid CO2 emissions are thus backhauled to the methanol production region 140 at the required relatively high pressure and low temperatures to ensure the CO2 is maintained in its liquid form. It is expected that by the storage vessels 130 beinginsulated and thereby limiting any pressure increase on the backhauling journey 200 none or limited refrigeration will be required.

[0035] Figure 3 schematically depicts embodiments of a method of purging residual gas from a dual-cargo carrier ship, as well as an in situ nitrogen (N2) purge gas assembly of a dual-cargo carrier ship according to third and fourth aspect of the technology. It will be understood that these third and fourth aspects are an alternative to the CO2 inerting of the first and second aspects of the second embodiment of the invention as depicted in figures 1 and 2.

[0036] The method of this embodiment in the context of the third aspect of the invention broadly comprises the steps of:(a) in situ capturing of N2 from the atmosphere at 11a and 11b, said capturing being effected onboard a dual-cargo carrier ship;(b) purging of residual gas remaining in storage vessels at 13 onboard said carrier ship, said purging being effected onboard said carrier ship using the captured N2

[0037] In this embodiment the method also comprises in situ storing of the captured N2 onboard the dual-cargo carrier ship, said storing being effected prior to purging of residual gas. It is to be understood that the steps of in situ capturing and storing of N2 occur whilst the dual-cargo carrier ship sails between its port of origin and port of destination. This means the captured N2 progressively accumulates onboard, in this example in a plurality of high pressure storage tanks 15a to 15f located on deck of the dual-cargo carrier ship.

[0038] In this embodiment the method further comprises compression of the captured N2 prior to its storage thereby increasing the onboard accumulation of the captured N2. This compression of the captured N2 is effected at one or more N2 compressors such as 17 located between the “Nitrogen Generator” such as 11a / b and the high pressure storage tanks such as 15a to 15f. In this example the liquid N2 is compressed and stored at around up to 130 Bar. The high pressure storage tanks such as 15a are in this case rated up to around 150 Bar and otherwise of a conventional construction such as a 20 foot ISO tank. It is to be understood that theonboard N2 storage capacity of the dual-cargo carrier ship exceeds onboard storage capacity of the storage vessels.

[0039] In the scenario where dual-cargo carrier ship accommodates storage vessels of up to around 50,000 m3, the onboard N2 storage capacity should at least equal this volume. Where the in situ capture of N2 generates at around 500 m3 / hr, it will be understood that 60,000 m3of N2 is generated over a 5 day (120 hours) period. This example is intended to provide an indication of the volume of N2 captured in situ whilst the dual-cargo carrier ship sails between its port of origin and port of destination, such as between Australia and Singapore. It is also possible that large scale onboard generation of N2 removes the need for any onboard storage of the captured N2. In this departure from the onboard generation and storage of N2, the captured N2 is used for direct purging of the residual gas at the port of origin or port of destination.

[0040] In this embodiment the step of purging of residual gas involves selectively introducing the captured N2 either below or above the residual gas thereby purging a storage vessel within which the gas is contained onboard the dual-cargo carrier ship. This selective purging of the residual gas via the captured N2 is enabled by piping 19a and 19b and associated valves (not shown) connected between the N2 storage tanks 15a to 15f and the gas storage vessel 13. In this example the residual:1 . methanol remaining from methanol stores within the onboard storage vessel 13 is purged at 21a by the introduction of the captured N2 at the bottom of the vessel 13 via the pipe 19b;2. CO2 remaining from CO2 stores within the onboard storage vessel 13 is purged at 21b by the introduction of the captured N2 at the top of the vessel 13 via the pipe 19a.

[0041] It is to be understood that the residual gas purged from the onboard storage vessels 13 is predominantly in the gas phase with virtually all of the liquid phase having already been pumped out or otherwise unloaded from the dual-cargocarrier ship such as 12. The purged gas may however include trace or very small amounts of the residual gas in the liquid phase and this component is known as heel.

[0042] It is to be understood that the in situ capture of N2 involves direct capture of N2 from atmosphere via one or more membrane nitrogen generators or pressure swing air adsorption (PSA) generators such as 11a and 11b. In an alternative arrangement the capture of N2 is effected by an air separation plant (not shown) also located onboard the dual-cargo carrier ship. In each of these scenarios it is to be understood that N2 generators are powered from the vessels auxiliary power supply systems.

[0043] It should be appreciated that purging of the residual gas via the captured N2 may be limited to the green methanol stores at the consumption region and as such may not apply to purging of residual CO2 emissions at the production region. This is on the understanding that methanol being a hydrocarbon is more sensitive to storage and handling requirements as compared with CO2 where, unlike methanol, potential ignition of flammable materials is not expected. In purging of the green methanol via the captured N2 there may be a requirement to detect or sense concentrations of methanol in the purged gas stream such as 21a where purging is continued until methanol concentrations are detected at relatively low or ppm levels. This may be important where methanol is understood to mix with other fluids whereas CO2 inherently laminates well for effective separation, CO2 being roughly double the density of N2.

[0044] Now that several embodiments of the various aspects of the invention have been described it will be apparent to those skilled in the art that the method of shipping green methanol and backhauling carbon dioxide as well as the method of purging the residual gas from a dual-cargo carrier ship and related aspects have at least the following advantages:1. the method of shipping and backhauling utilise the same dual-cargo carrier ship thus providing an economical solution compared with a two ship model dedicated to methanol for one journey and CO2 for a return journey with each of the dedicated ships being empty on their respective return journeys;2. the method and system greatly increase the amount of green methanol which can be produced unlike current practices where the production of green methanol is constrained by the supply of sustainable biomass, this method and system effectively multiplies the volume of green methanol which can be produced from a given volume of sustainable biomass;3. the exemplary recycling of non-fossil CO2 obtained from utilising green methanol as the fuel source in generating electricity presents a carbon neutral solution;4. the inerting of CO2 over methanol potentially removes any requirement for separate purging of methanol via an inert gas (typically N2) at the methanol consumption region before backhauling CO2 thereby eliminating delays due to purging;5. the shipping of methanol as a fuel means no refrigeration is required during the voyage from the methanol production region to the methanol consumption region, because methanol remains as a liquid at ambient conditions;6. CO2 gas use for pressurisation of the storage vessels on the backhaul of CO2 emissions from the consumption to the production regions means none or limited onboard refrigeration is required to maintain the CO2 emissions in the liquid phase and within the pressure limits of the onboard storage vessels;7. the alternative in situ capture of N2 onboard a dual-cargo carrier ship means the generation and purging functions are largely self-contained increasing the number of potential destinations for deployment of this technology;8. the alternative in situ capture of N2 improves the viability of dual-cargo carrier ships in enabling “self-cleaning” of storage vessels dedicated in this example to either green methanol or CO2 emissions.

[0045] Those skilled in the art will appreciate that the invention as described herein is susceptible to variations and modifications other than those specifically described. For example, the green methanol consumption may be achieved via arange of different engines and combustion devices including processes such as the Allam cycle. The backhauled CO2 may be obtained independent of the green methanol consumption and in some instances may extend to CO2 derived from a fossil source. In this variation backhauled CO2 emissions may be shipped to a site for geosequestration at or near the methanol production region. The backhauled CO2 may be sourced from bulk cargo ships or container ships powered by methanol with onboard carbon capture and storage or in a variation on this theme may extend to ships powered by methanol fuel cells. The initial source of non-fossil CO2 may exclude backhauled CO2 in which case sustainable biomass or direct air capture (DAC) of CO2 provide the CO2 required for the production of green methanol, where the DAC units are renewably powered. It is also possible that methanol production may initially source CO2 from a fossil source, such as an industrial carbon capture and storage plant, provided the CO2 emissions produced at the consumption region are continuously recycled ensuring that this resulting CO2 does not escape into atmosphere.

[0046] All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

Claims

Claims1. A method of shipping green methanol and backhauling carbon dioxide (CO2), said method comprising:(a) shipping green methanol via a dual-cargo carrier ship from a methanol production region to a methanol consumption region being remote from the methanol production region;(b) consuming the green methanol at the methanol consumption region;(c) backhauling CO2 emissions from the methanol consumption region to or near the methanol production region via the dual-cargo carrier ship.

2. A method as claimed in claim 1 involving repeating steps (a) to (c) for multiple shipping roundtrips between the methanol production region and the methanol consumption region.

3. A method as claimed in either of claims 1 or 2 wherein the step of shipping green methanol involves exporting the green methanol via the dual-cargo carrier ship from the methanol production region to the methanol consumption region.

4. A method as claimed in any one of claims 1 to 3 wherein the step of backhauling CO2 emissions involves importing the CO2 emissions to or near the methanol production region via the dual-cargo carrier ship.

5. A method as claimed in any one of the preceding claims wherein the step of consuming the green methanol involves generation of electricity utilising the green methanol as fuel wherein combustion of the green methanol emits the CO2 emissions.

6. A method as claimed in claim 5 wherein the step of backhauling CO2 emissions involves backhauling of the CO2 emissions emitted from the generation of electricity via the green methanol fuel.

7. A method as claimed in any one of claims 1 to 4 wherein the step of backhauling CO2 emissions involves backhauling CO2 emissions produced independent of the step of consuming the green methanol.

8. A method as claimed in claim 7 wherein the backhauled CO2 emissions are obtained from CO2 stores located at the methanol consumption region, said CO2 stores obtained from any one or more of the following CO2 sources: industrial processes producing or emitting CO2, or CO2 emissions captured onboard ships including methanol-fuelled ships.

9. A method as claimed in any one of the preceding claims also comprising production of green methanol at the methanol production region, said production involving a reaction between hydrogen (H2) and carbon dioxide (CO2)10. A method as claimed in claim 9 wherein said CO2 from the reaction is at least in part obtained from CO2 emissions backhauled from the consumption region.

11. A method as claimed in either of claims 9 or 10 wherein said production also involves obtaining the H2 from electrolysis of water.

12. A method as claimed in claim 11 wherein said electrolysis of water is powered via green electricity derived from solar power, wind turbines, hydro power, or other renewable energy utilities located at or near the methanol production region.

13. A method as claimed in claim 9 also comprising production of green methanol at the methanol production region independent of CO2 emissions backhauled from the methanol consumption region.

14. A method as claimed in claim 10 wherein the production of green methanol in the reaction between H2 and CO2 involves obtaining at least in part the CO2 from either a sustainable biomass, direct air capture of CO2 from atmosphere, or initially sourcing CO2 from a fossil source such as a carbon capture storage (CCS) facility.

15. A method as claimed in claim 13 wherein the production of methanol via the reaction may be supplemented with methanol derived from biomass.

16. A method as claimed in any one of claims 13 to 15 wherein CO2 emissions backhauled from the methanol consumption region are geosequestrated or otherwise stored at or near the methanol production region.

17. A method as claimed in any one of the preceding claims further comprising liquefying the CO2 emissions at the methanol consumption region.

18. A method as claimed in claim 17 also comprising storing the liquefied CO2 emissions at said consumption region in preparation for the step of backhauling CO2 emissions via the dual-cargo carrier ship.

19. A method as claimed in any one of the preceding claims further comprising unloading of the green methanol from storage vessels of the dual-cargo carrier ship at the methanol consumption region in preparation for the step of consuming the green methanol.

20. A method as claimed in any one of the preceding claims also comprising loading of the CO2 emission into the storage vessels of the dual-cargo carrier ship docked at a port or terminal at the methanol consumption region.

21. A method as claimed in either of claims 19 or 20 further comprising purging of the storage vessels of said carrier ship at the methanol consumption region of residual green gaseous methanol following unloading of the green liquid methanol and prior to loading of the CO2 emissions at said consumption region.

22. A method as claimed in claim 21 also comprising purging of said storage vessels at the methanol production region of residual backhauled gaseous CO2 emissions following unloading of the backhauled liquid CO2 emissions and prior to the loading of the liquid green methanol at the methanol production region.

23. A method as claimed in any one of claims 1 to 18 comprising inerting of green methanol loaded in storage vessels of the dual-cargo carrier ship at the methanol production region.

24. A method as claimed in claim 23 wherein the backhauled CO2 emissions are unloaded from the storage vessels at the methanol production region leaving CO2 gas within said vessels which functions as inerting gas for said green methanol subsequently loaded in said storage vessels.

25. A method as claimed in either of claims 23 or 24 wherein the CO2 inerting gas pressure is determined by interaction between the storage vessels of the dual cargo carrier ship and the CO2 liquid storage tanks at the methanol production region thereby determining the inerting gas pressure at which the storage vessels are maintained for shipping of the green methanol from the methanol production region to the methanol consumption region.

26. A method as claimed in claim 19 also comprising, following unloading of the green methanol, pressurising of the storage vessels at the green methanol consumption region via gaseous CO2 emissions prior to loading of the CO2 emissions in a predominantly liquid phase at the methanol consumption region.

27. A method as claimed in claim 26 further comprising controlled interaction between the storage vessels of the dual cargo carrier ship and the CO2 liquid storage tanks at the methanol consumption region thereby maintaining the required relatively high pressure of the CO2 emissions within the storage vessels for backhauling of the CO2 emissions in the liquid phase.

28. A dual-cargo transportation and infrastructure system comprising: a dual-cargo carrier ship adapted to ship green methanol from a methanol production region to a methanol consumption region; a green methanol consumption facility located at the methanol consumption region, said consumption facility adapted for consuming the green methanol; the dual cargo carrier ship adapted to backhaul CO2 emissions from the methanol consumption region to or near the methanol production region.

29. A method of purging residual gas from a dual-cargo carrier ship, said method comprising: in situ capturing of nitrogen (N2) from atmosphere, said capturing being effected onboard the dual-cargo carrier ship; purging of residual gas remaining in storage vessels onboard said carrier ship, said purging being effected onboard said carrier ship using the captured N2.

30. A method as claimed in claim 29 also comprising in situ storing of the captured N2 onboard the dual-cargo carrier ship, said storing being effected prior to purging of residual gas.

31. A method as claimed in claim 30 wherein the steps of in situ capturing and storing of N2 occur whilst the dual-cargo carrier ship sails between its port of origin and port of designation and thus the captured N2 progressively accumulates onboard.

32. A method as claimed in claim 31 wherein the captured N2 accumulates in a plurality of high pressure storage tanks located on deck the dual-cargo carrier ship.

33. A method as claimed in any one of claims 29 to 32 further comprising compression of the captured N2 prior to its storage thereby increasing the onboard accumulation of the captured N2.

34. A method as claimed in claim 33 wherein the onboard N2 storage capacity of the dual-cargo carrier ship exceeds onboard storage capacity for the storage vessels.

35. A method as claimed in any one of claims 29 to 34 wherein the step of purging involves selectively introducing the captured N2 either below or above the residual gas thereby purging a storage vessel within which the gas is contained onboard the dual-cargo carrier ship.

36. A method as claimed in claim 35 wherein said selective purging of the residual gas via the captured N2 is enabled by piping and associated valves connected between the N2 storage tanks and the gas storage vessel at its bottom and top for purging of the residual gas from outlets at respective of the top and bottom of said storage vessel.

37. A method as claimed in any one of claims 29 to 35 wherein the step of in situ capturing of N2 involves direct capture of N2 from atmosphere via one or more membrane nitrogen generators or pressure swing adsorption (PSA) generators.

38. A method as claimed in any one of claims 29 to 36 wherein said capture of nitrogen is effected onboard via an air separation plant.

39. An in situ nitrogen (N2) purge gas assembly of a dual-cargo carrier ship, said assembly comprising: one or more air capture modules located onboard said carrier ship for in situ capturing of N2 from atmosphere; a purging sub-assembly located onboard said vessel and associated with said air capture modules, said purging sub-assembly arranged for purging of residual gas remaining in storage vessels onboard the dual-cargo carrier ship, said purging effected onboard said ship via the purging sub-assembly using the captured N2.

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