The present disclosure relates to a Steam Methane Reformer (SMR). In particular, the present disclosure relates to a SMR with enhanced CO2 capture.
Steam methane reformers (SMRs) are generally used to produce a syngas from a gas feedstock such as natural gas or refinery gas. The produced syngas can be further processed within the plant to yield various end products, including purified hydrogen, methanol, carbon monoxide and ammonia. However, the flue gas produced during the reforming process contains many contaminants, such as carbon dioxide. These contaminants are known to adversely affect the environment by contributing to overall climate change. SMR's are known to be one of the largest carbon dioxide (CO2) emitters in refinery systems. As such, in recent years, many government regulatory bodies have required the reduction in emissions of these contaminants, in particular carbon dioxide, into the atmosphere.
Given the recognition of the harmful effect of carbon dioxide release and recent restrictions on its emission, efforts have been made to efficiently remove carbon dioxide in a purified form from a flue gas produced by a reformer plant. By removing carbon dioxide from the flue gas, the carbon dioxide alternatively may be used for other, safer purposes, such as underground storage or oil production needs.
Current methods for CO2 capture from flue gas, such as for example, using an amine absorption stripper system or a molten carbonate fuel cell (MCFC) fuel cell running in fuel cell mode, are highly inefficient. This is due, in part, to the dilute concentration of carbon dioxide present in the flue gas, which can be as little as 5% in concentration. The amine systems are generally too energy intensive, and the MCFC fuel cell incurs a substantial voltage penalty due to the dilution of the cathode with the large quantity of nitrogen contained in flue gas lowering the efficiency and output of the fuel cell. As such, conventional systems designed to remove CO2 can be very costly and require a high input of energy to sufficiently remove or reduce the CO2, significantly reducing the production capabilities of the refinery itself.
Embodiments described herein provide a SMR-CO2 capture system that generates pure CO2, as well as pure H2, such that a higher output value may be realized, further offsetting the costs of capturing CO2 and increasing the overall efficiency of the power plant. The system also has zero NOx emissions, since combustion is done without the presence of N2.
In certain embodiments, a SMR-CO2 capture system includes a CO2 pump referred to as a Reforming-Electrolyzer-Purifier (REP) in a related patent application WO2015/116964 configured to receive a reformed gas from a SMR and output a first exhaust stream comprising oxygen and carbon dioxide and a second exhaust stream containing a high concentration of hydrogen which can be exported as a valuable by-product.
In certain embodiments, an integrated system for carbon dioxide capture is provided, which includes a steam methane reformer; and a CO2 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.
In certain embodiments, natural gas and steam are fed to a reformer and the outlet reformed gas from the reformer is fed to a high temperature CO2 pump (REP). In certain embodiments, the CO2 pump (REP) is a MCFC fuel cell running in reverse. In certain embodiments, the CO2 pump (REP) converts the residual methane (CH4) to hydrogen (H2) and the carbon monoxide (CO) to CO2. The CO2/oxygen mixture generated by the CO2 pump (REP) can be recycled back to the reformer to be used in place of air, and essentially all of the methane and hydrogen used as fuel to the reformer is converted into CO2 and water. In certain embodiments, the flue gas from the reformer is essentially pure CO2 which can be cooled and almost all water removed by condensation.
In certain embodiments, the CO2 pump (REP) anode effluent is cooled and transported to a methanator, where the residual CO and CO2 are converted back into methane. Without CO in the gas, the methanator outlet can be fed to Electrochemical Hydrogen Compressor (EHC) to generate pure H2 at pressure and an off-gas stream with the residual methane and residual H2. The off-gas stream generated from the EHC may be recycled as fuel to the SMR or recycled as feed to the SMR. If recycled as feed to the SMR, another fuel, such as methane, will be needed in the SMR to heat balance the system. The hydrogen generated in the CO2 capture system could be used in a low-temperature fuel cell to load follow and produce peak power, or could be exported for fuel-cell vehicles and other industrial uses. The hydrogen could be used in a low temperature fuel cell after methanation, but before purification if desired.
In certain embodiments, an integrated SMR-carbon dioxide capture system removes carbon dioxide from a reformer system. The carbon dioxide is delivered to the CO2 pump (REP) which generates an output of a first exhaust stream comprising oxygen and carbon dioxide and a second exhaust stream containing a high concentration of hydrogen from water.
In one aspect, which is combinable with the above embodiments and aspects, the CO2 pump (REP) is a molten carbonate fuel cell operating in reverse, and configured to receive reformed gas from a reformer to produce CO2. In another aspect, the CO2 gas source for the CO2 pump (REP) is a steam methane reformer.
In one aspect, which is combinable with the above embodiments and aspects, the SMR is operated at lower than typical temperature and higher than typical steam feed, allowing lower cost materials to be used in the SMR. Completion of the reforming reaction then occurs in the REP
In one aspect, which is combinable with the above embodiments and aspects, the CO2 pump (REP) is configured to produce a first exhaust stream comprising mainly CO2 and oxygen. The CO2 pump (REP) is also configured to produce a second exhaust stream comprising mainly hydrogen. In one aspect, which is combinable with the above embodiments and aspects, the first exhaust stream comprises greater than about 95% of the feed carbon dioxide.
In certain embodiments, a carbon dioxide capture system for removing carbon dioxide from a reformer includes a CO2 pump (REP) having an anode and a cathode. The anode is configured to receive a reformed natural gas and output an enriched hydrogen stream. The cathode is configured to output a mixture of CO2 and O2 in approximately a 2/1 ratio. In one aspect, the CO2 pump (REP) is a molten carbonate fuel cell operating in reverse as an electrolyzer.
In one aspect, which is combinable with the above embodiments and aspects, the hydrogen enriched anode exhaust stream is partially cooled and transported to a methanator that is configured to convert the residual CO and CO2 to methane. In another aspect, the third exhaust stream from the methanator is transported to a electrochemical hydrogen compressor that is configured to receive the exhaust stream. The third exhaust stream may include hydrogen and methane and CO2, but essentially no CO.
In certain embodiments, capturing carbon dioxide from a reformed gas is provided, which includes supplying a reformed gas to CO2 pump; and outputting, from the CO2 pump, a first exhaust stream comprising carbon dioxide and oxygen and a second exhaust stream comprising hydrogen.
In one aspect, which is combinable with the above embodiment, the method for capturing the carbon dioxide further includes transporting the CO2 and oxygen back to the reformer to convert the methane and hydrogen used as fuel to the reformer into CO2 and water.
In one aspect, which is combinable with the above embodiment, the method for capturing the carbon dioxide further includes sequestering substantially all of the carbon dioxide from the reformer flue gas.
In one aspect, which is combinable with the above embodiments and aspects, the method for capturing the carbon dioxide further includes supplying a natural gas and water to the reformer.
In one aspect, which is combinable with the above embodiments and aspects, the method for capturing the carbon dioxide further includes transporting a second exhaust stream comprising hydrogen with small amounts of CO, CO2 and CH4 to a methanator.
In one aspect, which is combinable with the above embodiments and aspects, the method for capturing the carbon dioxide further includes optionally cooling the second exhaust stream comprising mainly hydrogen prior to transporting it to a methanator to generate a third exhaust stream.
In one aspect, which is combinable with the above embodiments and aspects, the method includes transporting the third exhaust stream generated in the methanator to an electrochemical hydrogen compressor.
In one aspect, which is combinable with the above embodiments and aspects, the method further includes separating hydrogen from the residual methane in an electrochemical hydrogen compressor to produce a purified hydrogen stream.
In one aspect, which is combinable with the above embodiments and aspects, the method further includes separating hydrogen from the residual methane in an electrochemical hydrogen compressor and increasing the pressure of the purified hydrogen.
In one aspect, which is combinable with the above embodiments and aspects, the method for capturing the carbon dioxide further includes outputting a pure hydrogen gas stream from the electrochemical hydrogen compressor. In certain embodiments, the pure hydrogen gas includes greater than 98% hydrogen, typically greater than 99.9% hydrogen.
The foregoing is a summary of the disclosure and thus by necessity contains simplifications, generalizations, and omissions of detail. Consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes described herein, as defined by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings.
Referring generally to the figures, disclosed herein is an enhanced SMR-CO2 capture system capable of producing a highly purified CO2 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.
In the pump, CO2 reacts with water to create CO3− according to the following reaction:
CO2+H2O↔CO3═⬆+H2
This reaction is driven forward by the electrochemical removal of the CO3− ion so that near pure {˜98%) hydrogen is generated. The MCFC unit which is used as the CO2 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 CO2 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% O2. This stream can be used in place of air normally used in the combustor of the SMR. The absence of N2 in the stream means that the flue gas from the SMR is now only CO2 and water with traces of unreacted O2. If desired, the trace O2 can be minimized by catalytically reacting the O2 with a stoichiometric amount of fuel or H2. Thus CO2 and O2 recycled to the reformer produce a pure CO2 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 CO2 is captured. Carbon dioxide is then removed from the reformer system where the CO2 may be stored for other purposes.
As further shown in
Alternately, mechanical compression and a small PSA could be used to increase the pressure of the H2 and purify the H2 (not shown). Since a PSA is not poisoned by CO, methanation is not required if a PSA is used.
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.
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.
The SMR-CO2 capture system has several advantages over standard SMR, such as:
The cost of the power required to operate the CO2 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 CO2 pump (REP). Further, the high hydrogen pressure should eliminate or reduce downstream compression power.
A detailed heat and material balance was performed on the SMR-CO2 capture system based on a 30 cell DFC stack. This system would be expected to produce 122 kg/day of H2 at 3000 psig with no moving parts. Raw H2 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 CO2 pump (REP) and the EHC. The efficiency of the pure, 3000 psig H2 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
The SMR-CO2 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 CO2 capture system depending on need. Moreover, when based on renewable feedstock, the CO2 capture system may be capable of producing a highly pure hydrogen gas or hydrogen containing feedstock with negative CO2 emissions. The result is a system that may realize a lower operating and capital cost, while producing a highly pure CO2 gas and hydrogen syngas for increased value.
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.
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.
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.
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.
The present application claims priority to U.S. Provisional Application No. 62/329,707, filed on Apr. 29, 2016, which is hereby incorporated by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/US2017/030230 | 4/28/2017 | WO | 00 |
Number | Date | Country | |
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62329707 | Apr 2016 | US |