METHOD FOR SYNGAS SEPARATION AT HYDROGEN PRODUCING FACILITIES FOR CARBON CAPTURE AND STORAGE

Abstract

Methods and systems for gas separation of syngas applying differences in water solubilities of syngas components, the method including producing a product gas comprising hydrogen and carbon dioxide from a hydrocarbon fuel source; separating hydrogen from the product gas to create a hydrogen product stream and a byproduct stream by solubilizing components in water that are more soluble in water than hydrogen; injecting the byproduct stream into a reservoir containing mafic rock; and allowing components of the byproduct stream to react in situ with components of the mafic rock to precipitate and store components of the byproduct stream in the reservoir.

Claims

1. A system for gas separation of syngas applying differences in water solubilities of syngas components, the system comprising: a hydrogen production unit with a hydrocarbon fuel inlet operable to produce a product gas comprising hydrogen and carbon dioxide from hydrocarbon fuel; a hydrogen separation unit operable to separate hydrogen from the product gas to create a hydrogen product stream and a byproduct stream by solubilizing components in water that are more soluble in water than hydrogen; and an injection well operable to inject the byproduct stream into a reservoir containing mafic rock to allow components of the byproduct stream to react in situ with components of the mafic rock to precipitate and store components of the byproduct stream in the reservoir.

2. The system according to claim 1, where the hydrogen separation unit includes at least one vertical scrubbing tower with countercurrent flow of the product gas and water, the product gas flowing at about 20° C.

3. The system according to claim 2, where at least about 50% of CO.sub.2 and about 95% of H.sub.2S are removed from the product gas and separated from the hydrogen product stream by being solubilized in the countercurrent flow of water in a single pass through one scrubbing tower.

4. The system according to claim 1, where the hydrogen separation unit includes at least two vertical scrubbing towers in series with countercurrent flow of the product gas and water.

5. The system according to claim 1, where the mafic rock comprises basaltic rock.

6. The system according to claim 1, further comprising a byproduct treatment unit to treat the byproduct stream to separate and purify CO.sub.2 from other components and to increase CO.sub.2 concentration of the byproduct stream for injection into the reservoir.

7. The system according to claim 1, further comprising a compressor to liquefy CO.sub.2 in the byproduct stream for injection into the reservoir.

8. The system according to claim 1, further comprising a reaction unit to react the separated hydrogen with nitrogen to form compressed liquid ammonia.

9. The system according to claim 8, further comprising a transportation unit to transport the compressed liquid ammonia and return the compressed liquid ammonia to hydrogen and nitrogen via electrolysis for use of hydrogen as a hydrogen fuel source.

10. The system according to claim 1, where the hydrogen production unit includes a steam reformer or partial oxidation reactor.

11. The system according to claim 1, where components of the produced byproduct stream react in situ with components of the mafic rock to precipitate products selected from the group consisting of: calcium carbonates, magnesium carbonates, iron carbonates, and combinations thereof.

12. The system according to claim 1, where the reservoir is between about 250 m and about 2,200 m below the surface and is between about 30° C. and about 325° C.

13. The system according to claim 1, where the reservoir is between about 350 m and about 1,500 m below the surface and is less than about 325° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

[0023] FIG. 1 shows a schematic flow chart for an example embodiment of a system for simultaneous H.sub.2 production, H.sub.2 water-solubility-based separation, and CO.sub.2 sequestration for producing H.sub.2 from hydrocarbons with near zero greenhouse gas emissions.

DETAILED DESCRIPTION

[0024] So that the manner in which the features and advantages of the embodiments of systems and methods for efficient H.sub.2 separation from syngas during production of hydrogen from hydrocarbon fossil fuels, with little to no greenhouse gas emissions, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

[0025] The production of H.sub.2 from hydrocarbons using technologies such as steam-reforming or partial oxidation/gasification includes three steps. In steam reforming, hydrocarbons, for example methane, are heated in the presence of H.sub.2O (steam) and catalysts to release raw syngas consisting of hydrogen (H.sub.2), carbon monoxide (CO), small amounts of carbon dioxide (CO.sub.2), and/or other impurities as shown in Equations 1 and 2:

CH.sub.4+H.sub.2O.Math.CO+3H.sub.2  Eq. 1

and/or

C.sub.nH.sub.m+nH.sub.2O.Math.nCO+(n+0.5 m)H.sub.2  Eq. 2

[0026] The raw syngas is then treated to remove sulfur compounds and/or purified further. H.sub.2 yield is then maximized by reacting the raw syngas with H.sub.2O steam in the presence of catalyst to produce H.sub.2 and CO.sub.2 according to Equation 3:

CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2  Eq. 3

[0027] This is known as a water-gas shift reaction, hence the product is called “shifted” syngas. In partial oxidation, hydrocarbons are reacted with small (non-stoichiometric) amounts of oxygen (O.sub.2) to produce raw syngas consisting of H.sub.2 and CO according to Equation 4:

CH.sub.4+½O.sub.2.fwdarw.CO+2H.sub.2  Eq. 4

[0028] This raw syngas also contains minor amounts of CO.sub.2 and/or nitrogen (N.sub.2, if air was used instead of pure O.sub.2). The raw syngas is then purified, and its H.sub.2 content maximized by the reaction of Equation 3. The composition of an example shifted syngas produced by both processes (steam reforming and partial oxidation) is presented in Table 1:

TABLE-US-00001 TABLE 1 Example shifted syngas composition from steam reforming or partial oxidation. Component H.sub.2 CO CO.sub.2 N.sub.2 O.sub.2 Ar H.sub.2S H.sub.2O Other Mol. % 40.9 1 29.8 2.4 0 0.4 0.01 25.4 0.11

[0029] Following water-gas shift, H.sub.2 is conventionally purified by separation from CO.sub.2 and other impurities by processes that employ adsorption, absorption, and/or membrane filtration. Membrane technologies have been developed, but are not yet widely-used on an industrial scale. One example process is Pressure Swing Adsorption (“PSA”), which uses pressure-dependent selective adsorption properties of materials such as activated carbon, silica, and zeolites. Waste or byproduct CO.sub.2 and other impurities separated from H.sub.2 during PSA are then vented to the atmosphere. Unfortunately, if a conventional CCS scheme were to be used to sequester CO.sub.2, then the CO.sub.2 must be purified further and compressed to a liquid (supercritical) state for transportation and injection into a deep reservoir. Both steps, however, are avoided (or simplified significantly) here when CSB is applied instead.

[0030] PSA is energy intensive and increases the cost and complexity of obtaining a final substantially pure H.sub.2 product. In systems and methods of the present disclosure, PSA or other conventional H.sub.2-syngas separation systems can be reduced in size or replaced entirely with a surprisingly and unexpectedly efficient technology which employs significant differences in water solubility between H.sub.2 and CO.sub.2 (and/or other acid gases). In embodiments of the present disclosure, syngas produced after water-gas shift is cooled to about 20° C. and injected into the base of a vertical pressurized vessel, for example a scrubbing tower, where dispersed gas interacts with and intimately intermingles with a stream of water fed from the top of the vessel and dispersed throughout the vessel. To maximize contact between dispersed gas and water, the tower is packed with a filling or channels that create highly tortuous pathways. Consequently, CO.sub.2 (and/or other water soluble gases) dissolve in the water, whereas H.sub.2 (and/or other insoluble gases) accumulate at the top of the vessel for collection and/or further treatment/purification.

[0031] While conventional CCS relies predominantly on physical processes such as the injection and storage of single phase liquid CO.sub.2 in non-reactive rock reservoirs (e.g., sandstone, limestone), CSB relies on the naturally occurring chemical reactions between CO.sub.2 and mafic and ultramafic rocks to precipitate solid carbonates. Reactions include the following: first CO.sub.2 dissolves in and reacts with water (either or both water supplied with CO.sub.2 gas at the surface or water present in situ in a mafic reservoir) to form a week carbonic acid as shown in Equations 5-7:

CO.sub.2+H.sub.2O.Math.H.sub.2CO.sub.3(aq)  Eq. 5

H.sub.2CO.sub.3.Math.HCO.sub.3.sup.−+H.sup.+  Eq. 6

HCO.sub.3.sup.−.Math.CO.sub.3.sup.2−+H.sup.+  Eq. 7

[0032] Acidified water dissolves Ca, Fe, and Mg-rich silicate phases (minerals and/or volcanic glass) which results in the release of divalent metal ions in solution according to Equation 8:

(Mg,Fe,Ca).sub.2SiO.sub.4+4H.sup.+.fwdarw.2(Mg,Fe,Ca).sup.2++2H.sub.2O+SiO.sub.2(aq)  Eq. 8

[0033] CO.sub.3.sup.2− formed during the reaction shown in Equation 7 reacts with the divalent metal cations leading to the precipitation of carbonate minerals as shown in Equation 9:

(Ca,Mg,Fe).sup.2++CO.sub.3.sup.2−.fwdarw.(Ca,Mg,Fe)CO.sub.3  Eq. 9

[0034] Geochemical reaction-transport modeling demonstrates that mineral phases (for example calcite, siderite, and magnesite) will remain stable under prevailing subsurface conditions, hence safely removing CO.sub.2 from the atmosphere for hundreds of thousands to millions of years. Other carbonate minerals include ankerite Ca[Fe, Mg, Mn](CO.sub.3).sub.2. In addition, CSB has extreme tolerance for other water soluble acid gas impurities (e.g. H.sub.2S, which is also mineralized as sulphides). Such an advantageous quality not only simplifies the process further, eliminating the need to remove those impurities from a gas mixture exiting an H.sub.2 production process, but it also allows for simultaneous sequestering of all other H.sub.2O soluble gas contaminants capable of forming stable mineral phases by reacting with basalts/mafics.

[0035] CO.sub.2 dissolution in water for CSB can be achieved by either: a) separately injecting CO.sub.2 and water in the tubing and annular space of injector wells and allowing these to mix at or below about a 350 m depth in the wellbore prior to entering the reservoir; or b) dissolving CO.sub.2 and water at the surface in a pressurized vessel and then injecting the solution in a basalt/ultramafic reservoir. While the first method generally applies to pure CO.sub.2 and/or a mixture of CO.sub.2 and other water soluble acid gases, the latter method is used to effectively separate CO.sub.2 (and other water soluble gases) from insoluble or weekly soluble impurities, and can therefore be used to process complex flue gas mixtures (e.g. shifted syngas).

[0036] Due to certain thermodynamic constraints of CO.sub.2 dissolution in water, both methods require about 27 tons of H.sub.2O per 1 ton of CO.sub.2 sequestered. In areas where water is in short supply, CSB may be done by injecting supercritical (liquid) CO.sub.2 in basalts or ultramafics; however, this would increase energy demands due to the need for liquefying CO.sub.2 via compression.

[0037] With respect to the produced H.sub.2, conventionally H.sub.2 is stored and transported as a liquid at a temperature of about −253° C., which requires special double-walled isolated vessels and/or constant refrigeration. However, reversible chemical conversion of H.sub.2 into liquid ammonia (NH.sub.3) allows storage and transportation of H.sub.2 at low pressure and ambient temperatures, at greatly reduced volumes. The reversible H.sub.2 to NH.sub.3 storage and transport method is inherently safer and advantageous in particular where large volumes of H.sub.2 are to be stored and transported.

[0038] Due to high tolerance of CSB to impurities in the CO.sub.2 stream (such as H.sub.2S and other gases), CO.sub.2—rich tail gases from other sources such as refining, power production, and desalinization could, after limited treatment, be either added to the principal waste stream or independently injected into reactive lithologies for permanent immobilization and disposal.

[0039] Unexpected and surprising advantages of simultaneously producing H.sub.2 from hydrocarbons while using CSB for permanent CO.sub.2 immobilization in basalts and ultramafics include significantly lower predicted energy usage and cost due to: lower energy consumption and lower well costs because there is no requirement to compress and liquefy the CO.sub.2; lower complexity of operations due to high tolerance to impurities in the CO.sub.2 stream; simultaneous removal of H.sub.2S along with CO.sub.2 in the reservoirs via precipitation as solids; no need for a reservoir caprock; and no need for sophisticated long-term monitoring programs. There is no need to liquefy CO.sub.2 when it is dissolved in water either at the surface or in the wellbore, but it can be liquefied if directly injected in the subsurface as supercritical fluid.

[0040] FIG. 1 shows a schematic flow chart for an example embodiment of a system for simultaneous H.sub.2 production, H.sub.2 separation, and CO.sub.2 sequestration for producing H.sub.2 from hydrocarbons with near zero greenhouse gas emissions. In system 100, a hydrocarbon inlet 102 provides a hydrocarbon source, for example natural gas, to a hydrogen production system 104. Hydrogen production system 104 might include steam reforming or partial oxidation, and water-gas shift reactions, for example as described in Equations 1-4. Production gases exit via outlet 106 to a separation unit 108. Separation unit 108 is operable to separate hydrogen from CO.sub.2 and other byproducts, such as for example acid gases.

[0041] PSA is energy intensive and increases the cost and complexity of obtaining a final substantially pure H.sub.2 product. In systems and methods of the present disclosure, PSA or other conventional H.sub.2-syngas separation systems can be reduced in size or replaced entirely with a surprisingly and unexpectedly efficient technology which employs significant differences in water solubility between H.sub.2 and CO.sub.2 (and/or other acid gases). In FIG. 1, syngas produced after water-gas shift in hydrogen production system 104 is cooled to about 20° C. and injected into the base of separation unit 108 from outlet 106. Separation unit 108 includes at least one vertical pressurized vessel, for example a scrubbing tower, where dispersed gas interacts with and intimately intermingles with a stream of water fed from the top of the vessel at stream 107. To maximize contact between dispersed gas (including H.sub.2, CO.sub.2, and acid gases such as H.sub.2S) and water, the tower is packed with a filling or channels that create highly tortuous pathways. Consequently, CO.sub.2 (and/or other water soluble gases) dissolve in the water, whereas H.sub.2 (and/or other insoluble gases) accumulate at the top of separation unit 108 for collection and/or further treatment/purification at outlet stream 118.

[0042] One purpose of a scrubbing tower is to facilitate an efficient mass transfer of CO.sub.2 and other acid gases, such as H.sub.2S, from a gas phase to a liquid phase. This is carried out through a contact tower filled with high specific surface area media (such as Tri-Mer® Tri-Packs® or Lantec Lanpac® for example) and/or through a low profile tortuous path air bubbler design, optimized specifically for this purpose. Providing maximum surface contact between gas and the scrubbing liquid (water for example) by facilitating continuous formation of droplets throughout the packed bed results in high scrubbing efficiency, and minimizes packing depth.

[0043] A suitable residence time in a scrubbing tower can be between about 5 and about 120 seconds, depending on the syngas composition and flow patterns. Temperature can range from about 2° C. to about 55° C. under a pressure range of about 1 atm to about 6 atm. The obtained purity of H.sub.2 will range from about 50-99.9 mol. % depending on the operating conditions and the syngas composition. Embodiments of separation units including at least one scrubbing tower can function under all ranges of CO.sub.2 concentrations in gas phase, and one variable impacted and able to be adjusted is the quantity of water needed, which is also dependent on the operating pressure and temperature.

[0044] Water-soluble CO.sub.2 and additional water-soluble gases such as acid gases exit separation unit 108 via outlet 110 mixed with water from stream 107, and can optionally proceed to a further CO.sub.2 purification and liquidification unit 112, but need not to. Water can be supplied via a water supply well, and in some embodiments may be supplied via water in a basaltic reservoir to ultimately be recycled back to the same basaltic reservoir with CO.sub.2 and H.sub.2S dissolved components. In some embodiments using a single scrubbing tower, between about 40% and about 60%, or between about 50% and about 70% of the CO.sub.2 and between about 90% and 100% or between about 97% and about 100% of the H.sub.2S are recovered from the syngas in separation unit 108 and proceed via outlet 110 mixed with water from stream 107. Separation unit 108 in some embodiments can have 1 scrubbing tower, but in other embodiments can have more than 1 scrubbing tower operating in parallel or series.

[0045] In the case of further CO.sub.2 purification and liquidification unit 112, liquefied CO.sub.2 is injected into basaltic formation 116 via injection well 114 to form solid precipitated metal carbonates per Equations 5-9. Without optional further CO.sub.2 purification and liquidification unit 112, CO.sub.2 and additional gases such as acid gases exit separation unit 108 via outlet 110 and proceed directly into basaltic formation 116 via injection well 114 to form solid precipitated metal carbonates per Equations 5-9. CO.sub.2 can be mixed with water as a gas at the surface or in situ in basaltic formation 116, or both. Solid carbonate nodules form in vugs and veins in basalt around injection wells and extending outwardly from the injection wells.

[0046] Rates of basalt dissolution and mineral carbonation reactions can increase with increasing temperature, and thus higher temperature basaltic reservoirs may be advantageous, while deep reservoirs beyond about 850 m are not required because high pressures are not required to keep CO.sub.2 in a pressurized or liquid state. An example suitable reservoir temperature is about 185° C., or for example between about 150° C. and about 280° C., or less. As explained, injected CO.sub.2, either by itself or with other gases, creates an acidic environment with water near the injection well, such as injection well 114. Near injection well 114, the acidic fluids remain undersaturated with respect to basaltic minerals and volcanic glass.

[0047] Undersaturation and acidity leads to dissolution of host rock basalts in the vicinity of injection wells, such as injection well 114. Mineralization then mostly occurs at a distance away from the injection well (which allows continuous injection of CO.sub.2 in a reservoir such as basaltic formation 116), after heat exchange and sufficient dissolution of host basaltic rock neutralizes the acidic water and saturates the formation water with respect to carbonate and sulfur minerals.

[0048] Hydrogen exits separation unit 108 at outlet stream 118 to proceed to reaction unit 120 where hydrogen is reacted with nitrogen to form ammonia (NH.sub.3). In some embodiments, before H.sub.2 proceeds to a reaction unit such as reaction unit 120, other H.sub.2 purification techniques such as PSA, absorption, or membrane separation could be carried out as needed based on requirements of the H.sub.2 product. Ammonia exits reaction unit 120 at outlet 122 for reduced volume transport of H.sub.2 as NH.sub.3. Reaction unit 120 can include a pressurized multistage ammonia production system (PMAPS) to produce ammonia in a pressurized liquid phase. Pressurized liquid NH.sub.3 can be transported by a pressurized tanker truck, and using an NH.sub.3 electrolyzer, NH.sub.3 can be reversibly returned to N.sub.2 and H.sub.2 wherever hydrogen is required.

[0049] The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

[0050] The term “about” when used with respect to a value or range refers to values including plus and minus 5% of the given value or range.

[0051] In the drawings and specification, there have been disclosed embodiments of systems and methods for efficient H.sub.2 separation from syngas during production of hydrogen from hydrocarbon fossil fuels with little to no greenhouse gas emissions of the present disclosure, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.