CARBON DIOXIDE CAPTURING STEAM METHANE REFORMER

Abstract

An integrated system for carbon dioxide capture includes a steam methane reformer and a CO.sub.2 pump that comprises an anode and a cathode. The cathode is configured to output a first exhaust stream including oxygen and carbon dioxide and the anode is configured to receive a reformed gas from the steam methane reformer and to output a second exhaust stream that includes greater than 95% hydrogen.

Claims

1. An integrated system for carbon dioxide capture comprising: a steam methane reformer; and a CO.sub.2 pump comprising an anode and a cathode; wherein the cathode is configured to output a first exhaust stream and the anode is configured to receive a reformed gas from the steam methane reformer and to output a second exhaust stream; wherein the first exhaust stream comprises oxygen and carbon dioxide; and wherein the second exhaust stream comprises greater than 95% hydrogen.

2. The integrated system of claim 1, wherein the CO.sub.2 pump comprises a reforming-electrolyzer-purifier system.

3. The integrated system of claim 1, wherein the reforming-electrolyzer-purifier system comprises a molten carbonate fuel cell running in reverse.

4. The integrated system of claim 1, wherein the reformed gas comprises a natural gas, hydrogen, carbon dioxide, carbon monoxide and water.

5. (canceled)

6. The integrated system of claim 1, wherein the CO.sub.2 pump is configured to convert the residual methane from the steam methane reformer to hydrogen and to convert the carbon monoxide to hydrogen and carbon dioxide.

7. The integrated system of claim 1, wherein the first exhaust stream comprises greater than about 95% of the feed carbon dioxide.

8. The integrated system of claim 1, wherein the cathode is configured to output a mixture of carbon dioxide and oxygen in a ratio of between approximately 1:1 and 4:1.

9. (canceled)

10. The integrated system of claim 8, wherein the system further includes a mechanism for transporting the carbon dioxide and oxygen back to the reformer.

11. The integrated system of claim 1, wherein the second exhaust stream further comprises residual carbon monoxide and carbon dioxide.

12. The integrated system of claim 11, further comprising a methanator that is configured to convert the residual carbon monoxide and a portion of the carbon dioxide from the second exhaust stream to a third exhaust stream comprising methane, hydrogen, and carbon dioxide.

13. The integrated system of claim 12, further comprising an electrochemical hydrogen compressor that is configured to receive the third exhaust stream from the methanator.

14. The integrated system of claim 13, wherein the electrochemical hydrogen compressor is configured to generate pure hydrogen at pressure and an off-gas stream with the residual methane and residual hydrogen.

15. The integrated system of claim 14, wherein the system is configured to recycle the off-gas stream to the steam methane reformer.

16. The integrated system of claim 12, further comprising a low temperature fuel cell that is configured to receive the third exhaust stream from the methanator and generate power.

17. A method for capturing carbon dioxide from a reformed gas comprising: supplying a reformed gas to CO.sub.2 pump; outputting, from the CO.sub.2 pump, a first exhaust stream comprising carbon dioxide and oxygen and a second exhaust stream comprising hydrogen; and transporting the carbon dioxide and oxygen back to the reformer to convert the reformer fuel comprising methane and hydrogen to reformer flue gas comprising carbon dioxide and water.

18. (canceled)

19. The method of claim 17, further comprising sequestering substantially all of the carbon dioxide from the reformer flue gas.

20. (canceled)

21. The method of claim 17, further comprising: optionally cooling the second exhaust stream, transporting the cooled second exhaust stream comprising mainly hydrogen to a methanator to generate a third exhaust stream, and transporting the third exhaust stream from the methanator to an electrochemical hydrogen compressor.

22. (canceled)

23. The method of claim 21, further comprising transporting the third exhaust stream from the methanator to an electrochemical hydrogen compressor, separating hydrogen from the residual methane in the electrochemical hydrogen compressor to produce a purified hydrogen stream and increasing the pressure of the purified hydrocarbon.

24. (canceled)

25. The method of claim 23, further comprising increasing the pressure of the purified hydrocarbon and outputting a pure hydrogen gas stream from the electrochemical hydrogen compressor.

26. The method of claim 25, wherein the pure hydrogen gas comprises greater than 98% hydrogen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a schematic view of a standard SMR configuration.

[0029] FIG. 2 shows a schematic view of a SMR system utilizing a CO.sub.2 pump (REP), in accordance with a representative embodiment.

[0030] FIG. 3 shows a detail schematic view of the SMR-CO.sub.2 capture system of FIG. 2 in accordance with a representative embodiment.

[0031] FIG. 4 shows a schematic view of the SMR-CO.sub.2 capture system, according to an exemplary embodiment.

DETAILED DESCRIPTION

[0032] Referring generally to the figures, disclosed herein is an enhanced SMR-CO.sub.2 capture system capable of producing a highly purified CO.sub.2 flue gas while co-producing a highly pure hydrogen syngas for additional energy needs that is both less costly and highly efficient in terms of energy production.

[0033] FIG. 1 shows a typical standard SMR configuration. Steam supplied by a steam supply line 110 and natural gas supplied by a natural gas supply line 120 and are mixed and fed to a reformer 100 for converting the methane to hydrogen CO.sub.2, and CO. The reformer effluent is transported through effluent line 140 to a shifting assembly 150, where the effluent is cooled and most of the CO is shifted to hydrogen. The shifted gas is then sent via shift gas line 160 to a PSA (pressure swing adsorption) system 170 where the hydrogen is separated from the residual methane and CO in the gas along with the CO.sub.2 produced from the reforming and shift reactions. The residual gases are recycled as fuel to the reformer 100 via the recycling line 180, where the gases are combusted with air supplied by an air supply line 130 to provide the heat needed for the endothermic reforming reaction. All of the CO.sub.2 generated in the production of the hydrogen is vented in the reformer flue gas as a mixture of N.sub.2, CO.sub.2, and H.sub.2O with some NOx. Typically the SMR is the largest CO.sub.2 emitter in a refinery.

[0034] FIG. 2 shows a SMR-CO.sub.2 capturing system which includes a CO.sub.2 pump (REP) 200 for capturing carbon dioxide and producing hydrogen. As shown in FIG. 2, steam supplied by a steam supply line 210 and natural gas supplied by a natural gas supply line 220 are mixed and fed to a reformer 200 for converting the methane to hydrogen and CO. This reformer operates at a lower temperature than a standard reformer since residual methane in the reformed gas is also converted to H.sub.2 in the CO.sub.2 pump (REP). This reduces the cost of the reformer substantially. The reformer effluent is transported through effluent line 240 and introduced in to a high temperature CO.sub.2 pump (REP) 250. In the embodiment shown in the Figures, the CO.sub.2 pump (REP) 250 comprises a molten carbonate fuel cell (MCFC) operating in reverse in electrolysis mode. In some embodiments, the CO.sub.2 pump (REP) 250 may further comprise a plurality of individual cells connected to form a fuel cell stack. During operation of the pump 250 as a reverse MCFC unit, the residual methane is converted to hydrogen and CO is converted to CO.sub.2 and pumped across the membrane as a CO.sub.3.sup.− ion where the third oxygen comes from the separation of water into H.sub.2 and O.sup.−. Since the CO.sub.2 is removed electrochemically at a high temperature, the equilibrium of the reforming reaction can be pushed close to completion.

[0035] In the pump, CO.sub.2 reacts with water to create CO.sub.3.sup.− according to the following reaction:

CO.sub.2+H.sub.2O.Math.CO.sub.3.sup.═⬆+H.sub.2

[0036] This reaction is driven forward by the electrochemical removal of the CO.sub.3.sup.− ion so that near pure {˜98%) hydrogen is generated. The MCFC unit which is used as the CO.sub.2 pump (REP) generates a cathode exhaust stream and an anode exhaust stream. The cathode exhaust stream, which substantially contains oxygen and carbon dioxide, is removed from the CO.sub.2 pump (REP) 250 and recycled through a cathode exhaust line 230 to the reformer system 200. At this point, the cathode exhaust stream may include about 66% of carbon dioxide and 34% O.sub.2. This stream can be used in place of air normally used in the combustor of the SMR. The absence of N.sub.2 in the stream means that the flue gas from the SMR is now only CO.sub.2 and water with traces of unreacted O.sub.2. If desired, the trace O.sub.2 can be minimized by catalytically reacting the O.sub.2 with a stoichiometric amount of fuel or H.sub.2. Thus CO.sub.2 and O.sub.2 recycled to the reformer produce a pure CO.sub.2 exhaust gas once the gas is cooled and the water condensed from the flue gas which is removed from the reformer along with water. The gas is then further cooled and compressed so that the CO.sub.2 is captured. Carbon dioxide is then removed from the reformer system where the CO.sub.2 may be stored for other purposes.

[0037] As further shown in FIG. 2, the effluent from the CO.sub.2 pump (REP), which is over 95% hydrogen, is cooled and passed through a methanator 260 where the residual CO and much of the CO.sub.2 are converted back into methane so that CO does not impact downstream processes. The effluent from the methanator (third exhaust stream) is transferred through an exhaust line 270 to a electrochemical hydrogen compressor (EHC) 280, where the hydrogen gas is purified and compressed. This allows the hydrogen to be stored at pressure and/or exported. Additional hydrogen is generated from the electrolysis reaction and added to the hydrogen from reforming methane. The value of the additional hydrogen generated offsets most or all of the cost of the power needed by the pump.

[0038] Alternately, mechanical compression and a small PSA could be used to increase the pressure of the H.sub.2 and purify the H.sub.2 (not shown). Since a PSA is not poisoned by CO, methanation is not required if a PSA is used.

[0039] The pure hydrogen gas generated using the present systems and methods may include greater than about 95% hydrogen. The pure hydrogen generated may include greater than about 96%, greater than about 86.5%, greater than about 97%, greater than about 97.5%, greater than about 98%, greater than about 98.5%, or greater than about 99% hydrogen. In an exemplary embodiment, the pure hydrogen gas includes greater than 98% hydrogen. In an exemplary embodiment, the pure hydrogen prior to purification (e.g., prior to feeding to EHC) may include greater than about 95% hydrogen, and after purification (e.g., output from EHC) may include greater than about 99.9% hydrogen.

[0040] The generated hydrogen could be used in a low-temperature fuel cell to load follow and produce peak power or it could be exported for use in fuel-cell vehicles or other industrial uses. The EHC not only removes the residual methane but also increases the pressure of the hydrogen. The exhaust stream from the EHS, comprising mainly of methane and hydrogen exits the EHS through a recycle line 290 where the exhaust stream is recycled back to the reformer 200. This recycled exhaust may be used as fuel for the reform or feed to the reformer. A blower may be needed to recycle the exhaust gas as feed to the reformer.

[0041] FIG. 3 is a detailed, close-up view of the embodiment of the SMR-CO.sub.2 capture system depicted in FIG. 2. As shown in FIG. 3, once the cathode exhaust stream comprising CO.sub.2 and O.sub.2 is transported back through a cathode exhaust line 330 to the reformer 300, the anode exhaust stream comprised mainly of hydrogen is cooled and then sent to a methanator 360. In the methanator, all of the residual CO and most of CO.sub.2 are converted back into methane. Removal of all CO in the gas helps to minimize the power requirement of the electrochemical hydrogen compressor. The CO.sub.2 pump (REP) 350 generates a mixture of two thirds carbon dioxide and one third oxygen by transferring electrochemically the CO.sub.3.sup.− ion across the high temperature membrane. This CO.sub.2 oxygen mixture can be used in place of air in the reformer. By replacing the air with CO.sub.2 and oxygen, essentially all of the methane and hydrogen used as fuel in the reformer are converted into CO.sub.2 and water. Thus the flue gas output from the reformer is essentially pure CO.sub.2 after it is cooled and the water is condensed out. All of the CO.sub.2 from the system can be sequestered by compressing this gas without the need for further purification. Since no nitrogen is present, there is the additional advantage that no in NOx is produced or emitted.

[0042] The SMR-CO.sub.2 capture system has several advantages over standard SMR, such as: [0043] CO.sub.2 is produced which is ready for capturing. [0044] No NOx emissions even if exhaust vented. [0045] The purified hydrogen produced is at pressure, preferably 3000 psig or greater. [0046] High conversion of the methane to hydrogen means that the system remains in heat balance with no excess heat that must be converted to steam or other byproducts. [0047] The system is scalable from a small home 1 kg/day system to 2,000+kg/day. [0048] The equipment used in the system is the same as currently used for MCFC fuel cells and thus is readily available. [0049] About 20% of the hydrogen produced is from the water-CO.sub.2 reaction, reducing the fuel consumption of the system. [0050] The system can be operated to load follow, if needed, to meet the hydrogen demand. It could also be used to load follow to help balance the power requirements of the area.

[0051] The cost of the power required to operate the CO.sub.2 pump (REP) and the electrochemical hydrogen separator is offset by the hydrogen produced from water which is extremely efficient at the high temperature of the CO.sub.2 pump (REP). Further, the high hydrogen pressure should eliminate or reduce downstream compression power.

Example 1

[0052] A detailed heat and material balance was performed on the SMR-CO.sub.2 capture system based on a 30 cell DFC stack. This system would be expected to produce 122 kg/day of H.sub.2 at 3000 psig with no moving parts. Raw H.sub.2 production efficiency (excluding compression power) is 70 to 93% depending on the how the power is included in the calculations and the voltage assumptions of the CO.sub.2 pump (REP) and the EHC. The efficiency of the pure, 3000 psig H.sub.2 is still 76% (excluding power production efficiency). If steam is used for the water source, the system is in heat balance when heat losses are included. If liquid water is used for the water source, an additional 3-5% of energy is needed. Steam based heat and material balance (HMB) balance is shown in FIG. 4 and Table 1.

TABLE-US-00001 TABLE 1 CO.sub.2 Pump w Stm Ref 8-8-13b.xlsm Stream No. 602 303 621 622 626 Name Natural Gas Water/Steam H2 to H2 from H2 Export Feed Feed Methanator Methanator Molar flow 1.40 4.00 6.69 6.68 5.60 lbmol/hr Mass flow 22.5 72.1 18.8 18.8 11.3 lb/hr Temp F. 100° 255° 500° 501° 176° Pres psia 20.00 30.00 19.98 19.98 3,000.00 lb- mole lb- mole lb- mole lb- mole lb- mole Components mole/hr % mole/hr % mole/hr % mole/hr % mole/hr % Hydrogen 0.00 0.00 0.00 0.00 6.34 94.83 6.34 94.82 5.60 100.00 Methane 1.40 100.00 0.00 0.00 0.11 1.72 0.12 1.73 0.00 0.00 Carbon 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 Monoxide Carbon 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Dioxide Water 0.00 0.00 4.00 100.00 0.23 3.44 0.23 3.45 0.00 0.00 Nitrogen 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Oxygen 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 1.40 100.00 4.00 100.00 6.69 100.00 6.68 100.00 5.60 100.00 ppm CO 50 ppm <1 ppm Stream No. 627 330 617 655 350 Name EHC Exh Gas to EHC Condensate CO2/O2 from Cooled CO2 for Cooled CO2 Reformer as fuel from Exh Gas CO2 Pump Export/Capture Condensate 0.01 gpm 0.04 gpm Molar flow 0.90 0.18 1.88 1.42 0.99 lbmol/hr Mass flow 4.2 3.3 75.7 62.0 17.9 lb/hr Temp F. 101° 101° 1100° 95° 95° Pres psia 19.00 19.00 19.98 50.00 50.00 lb- mole lb- mole lb- mole lb- mole lb- mole Components mole/hr % mole/hr % mole/hr % mole/hr % mole/hr % Hydrogen 0.74 81.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Methane 0.12 12.80 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Carbon 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Monoxide Carbon 0.00 0.00 0.00 0.00 1.28 68.16 1.40 98.37 0.00 0.03 Dioxide Water 0.05 5.23 0.18 100.00 0.00 0.00 0.02 1.63 0.99 99.97 Nitrogen 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Oxygen 0.00 0.00 0.00 0.00 0.60 31.84 0.00 0.00 0.00 0.00 Total 0.90 100.00 0.18 100.00 1.88 100.00 1.42 100.00 0.99 100.00

[0053] The SMR-CO.sub.2 capture system is modular in nature and may be sized for a given location. For example, a plurality of CO2 pump (REP) assemblies may be incorporated into the CO.sub.2 capture system depending on need. Moreover, when based on renewable feedstock, the CO.sub.2 capture system may be capable of producing a highly pure hydrogen gas or hydrogen containing feedstock with negative CO.sub.2 emissions. The result is a system that may realize a lower operating and capital cost, while producing a highly pure CO.sub.2 gas and hydrogen syngas for increased value.

[0054] As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

[0055] The terms “coupled,” “connected,” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

[0056] References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below,” etc.) are merely used to describe the orientation of various elements in the Figures. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

[0057] It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention. For example, the heat recovery heat exchangers may be further optimized.