Oxygen-enriched combustion for natural gas combined cycle operation

Abstract

A system and method are provided for operating a combined cycle power plant while enhancing the CO2 content of the combustion exhaust gas generated by the power plant. The CO2 content is enhanced by using a combination of exhaust gas recirculation and oxygen-enriched combustion. An oxygen-containing stream for performing oxygen-enriched combustion can be generated by an integrated pressure swing adsorption process, which provides an oxygen-containing stream having an oxygen content of 25% to 48% by volume with high O2 recovery and also enables the production of a commercial grade nitrogen stream (95% or more N2 by volume).

Description

Technical Field

[0001] The present invention relates to a system and method for operating a combined cycle power plant using oxygen-enriched combustion to provide a combustion exhaust gas having a high CO2 content.

Background Art

[0002] Combined cycle power plants provide an efficient way to generate electricity from the combustion of petroleum products or other carbon-based fuels. A combined cycle power plant can utilize an initial combustion reaction to power multiple turbines for the generation of electricity, which results in more efficient power generation. However, conventional methods for capturing carbon dioxide tend to reduce the efficiency of power generation due to the additional energy required to capture and / or sequester carbon dioxide.

[0003] For natural gas combined cycle (NGCC) plants, one of the difficulties in capturing CO2 from combustion exhaust gas is that the CO2 concentration in the combustion exhaust gas is relatively low. For natural gas combustion using air as the oxygen source, the typical CO2 concentration in the combustion exhaust gas is 4.0 to 6.0 volume %. Due in part to the relatively low CO2 concentration, a significant amount of additional energy is required to capture CO2 from the combustion exhaust gas with an efficiency of 90% or more. Additionally, since the CO2 is dilute, a significant volume of gas needs to be processed, which results in large capital equipment costs and / or a large equipment footprint to effectively handle the required volume of combustion exhaust gas. It would be desirable to have an improved method for capturing CO2 from combustion exhaust gas while reducing or minimizing the power consumption and / or other costs required to perform the CO2 capture.

[0004] U.S. Patent Nos. 9,903,316 and 10,677,160 describe the operation of a natural gas combined cycle plant with enriched air as an oxygen source for combustion and pressurized exhaust gas recirculation. The resulting combustion exhaust gas is described as containing a high amount of CO2.

[0005] The journal article by Qinglin et al. (“Revisiting Transport of Gases in the Micropores of Carbon Molecular Sieves” Langmuir (2003) 19, 393 - 405) describes measurements in carbon molecular sieves to determine equilibrium and kinetic parameters.

[0006] The paper by Sircar et al (Dabrowski A, editor. Fractionation of Air by Zeolites in Stud Surf Sci Catal: Elsevier; 1999. p. 395 - 423.) describes various pressure swing adsorption processes for the separation of air using zeolites. Several processes are described that can generate both O2 and N2 streams with purities greater than 90%. Generally, processes that generate a second stream containing 25 vol% - 48 vol% O2 while also generating a first stream containing 95 vol% or more N2 are not described.

[0007] The journal article by Hassan et al. describes generating a high - purity N2 stream by separating air. (Chemical Engineering Science, Vol. 42, No. 8, pg 2037 (1987)) No information is provided regarding the concentration of O2 in the second stream generated by the process. Note that the process cycle described in the paper performs pressure equalization by connecting both ends of the adsorbent environment to each other.

[0008] The journal article by Shirley et al. describes generating a high-purity N2 stream by separating air. (Adsorption, Vol. 8, No. pg 147 (2002)) No information is provided regarding the concentration of O2 in the second stream produced by the process.

Summary of the Invention

[0009] In one aspect, a method for operating a power generation process is provided. The method includes separating air using a pressure swing adsorption process to form a nitrogen-containing stream containing 95 volume % or more of N2 and an oxygen-containing stream containing 25 volume % to 48 volume % of O2. The method further includes combusting a fuel in a combustion chamber of a turbine in the presence of a recirculation stream with O2 from at least a portion of the oxygen-containing stream to form combustion exhaust gas. Optionally, the O2 from at least a portion of the oxygen-containing stream can correspond to 16 volume % to 35 volume % of the combined volume of the fuel, at least a portion of the oxygen-containing stream, and the recirculation stream. Optionally, the combustion exhaust gas can contain 12 volume % or more of CO2. The method further includes forming a recirculation stream from one or more portions of the combustion exhaust gas. Additionally, the method includes performing post-combustion capture on at least a portion of the combustion exhaust gas to form a CO2-containing product stream and one or more CO2-depleted combustion exhaust gas streams. The one or more CO2-depleted combustion exhaust gas streams can contain CO2 from at least a portion of the combustion exhaust gas at 30 volume % or less. Additionally or alternatively, the CO2-containing product stream can contain CO2 from at least a portion of the combustion exhaust gas at 70 volume % or more.

[0010] In another aspect, a system for generating power is provided. The system includes a swing adsorption stage corresponding to a plurality of swing adsorption vessels containing an adsorbent having a kinetic selectivity for O2 over N2. The swing adsorption stage can have an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet. The system further includes a compressor, a combustion chamber, an expander, and a turbine having a shaft coupling the expander to the compressor. The combustion chamber can include a combustion outlet and one or more combustion inlets. The one or more combustion inlets can be in fluid communication with a fuel source and the oxygen-containing product outlet. Optionally, the system can further include a supplementary combustor having a supplementary fuel inlet, a combustion exhaust gas inlet in fluid communication with the combustion outlet, and a supplementary combustion outlet. The system can further include a heat recovery steam generator having a heat recovery inlet in fluid communication with the combustion outlet and / or the supplementary combustion outlet, and a heat recovery outlet. Additionally, the system can include a post-combustion capture stage. The post-combustion capture stage can have a capture inlet in fluid communication with the heat recovery outlet, a CO2-containing product outlet, and one or more CO2-depleted stream outlets. In some aspects, the post-combustion capture stage can include one or more amine scrubbers, one or more adsorbent environments containing a solid adsorbent, one or more adsorbent environments containing a liquid adsorbent, or combinations thereof. In other aspects, the post-combustion capture stage can include one or more membrane separators, one or more molten carbonate fuel cells, or combinations thereof. The one or more combustion inlets can also be in fluid communication with at least one of the heat recovery outlet and the CO2-containing product outlet.

Brief Description of the Drawings

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[0012] All numerical values within the detailed description and claims of this specification are modified by the values indicated as "about" or "approximately" and take into account experimental errors and variations expected by those skilled in the art.

[0013] Summary In various aspects, a system and method are provided for operating a combined cycle power plant while enhancing the CO2 content of the combustion exhaust gas generated by the power plant. The CO2 content is enhanced by using a combination of exhaust gas recirculation and oxygen-enriched combustion. When operating a natural gas combined cycle power plant, this enables the formation of combustion exhaust gas having a CO2 content of 12 vol% to 30 vol%, or 15 vol% to 30 vol%, or 20 vol% to 30 vol%. Further, generally depending on the nature of the combustion reaction, the combination of exhaust gas recirculation and oxygen-enriched combustion can enable the formation of combustion exhaust gas having a CO2 content of 12 vol% or more, or 15 vol% or more, or 20 vol% or more, or 25 vol% or more, or 30 vol% or more, for example, up to 50 vol%, or perhaps even higher CO2 content. The oxygen-containing stream for performing oxygen-enriched combustion can be generated by an integrated pressure swing adsorption process, which provides an oxygen-containing stream having an oxygen content of 25 vol% to 48 vol% or 30 vol% to 48 vol% with high O2 recovery and also enables the production of a commercial grade nitrogen stream (95 vol% or more N2). By enhancing the CO2 content of the combustion exhaust gas, all of the power generation stages of the combined cycle power plant can still be maintained while still generating combustion exhaust gas having a CO2 content high enough to enable enhanced, improved, and / or more efficient post-combustion capture of CO2.

[0014] Conventionally, one of the difficulties in post-combustion capture of CO2 from combustion exhaust gases generated by commercial-scale power plants is the relatively low CO2 content of the combustion exhaust gases. For example, typical combustion exhaust gases from natural gas power plants have only a CO2 content of 4.0 to 6.0 volume percent, so the commercial-scale options for capturing such CO2 are limited. Currently, the main option for capturing CO2 from combustion exhaust gases is to use an amine scrubber, in which CO2 is adsorbed by an aqueous amine. This is effective, but the cost of operating such an amine scrubber is high due to the large volume of combustion exhaust gases that need to be processed. These costs include both capital equipment costs and operating costs for heating and managing the fluid streams involved in the amine scrubber.

[0015] Several options are available for increasing the CO2 content of combustion exhaust gases from power plants based on the combustion of hydrocarbon fuels (e.g., natural gas power plants). One option is to use exhaust gas recirculation to increase the CO2 concentration of the input stream to the combustion process. Another option is to reduce the nitrogen content of the oxygen-containing stream passed through the combustion process.

[0016] Exhaust gas recirculation alone can increase the CO2 content of the combustion exhaust gases produced from the combustion reaction. However, there are limits to the amount of exhaust gas recirculation that can be carried out. For example, when air is used as the oxygen source for combustion, air starts with an O2 content close to 21 volume percent. This is slightly diluted by the introduction of fuel into the combustion chamber. Adding exhaust gas recirculation further dilutes the concentration of O2. To maintain a flame speed and / or other desirable combustion characteristics, it is desirable to maintain an O2 concentration of 16 volume percent or more in the combustion chamber. This limits the total volume of exhaust gas that can be recirculated while still maintaining a sufficient O2 concentration.

[0017] Also, there is a practical upper limit to the oxygen concentration in the combustion chamber. In particular, as the oxygen concentration increases, the flame speed and / or other combustion characteristics can result in a higher temperature in the combustion chamber. It is desirable to maintain the O2 concentration in the combustion chamber at 35 vol% or less. This allows the combustion temperature to still be low enough that conventional metallurgy can be used, and thus the process can be used in power plants already constructed using such conventional metallurgy.

[0018] Based on the above limitations, it is desirable to increase the CO2 content of the combustion exhaust gas while also having a combustion environment with an oxygen concentration of 16 vol% to 35 vol%. To achieve this, it is desirable to have an oxygen-containing stream for combustion having an oxygen content of 25 vol% to 48 vol%, or 30 vol% to 48 vol%, or 35 vol% to 48 vol%, or 40 vol% to 48 vol%, such that a target oxygen concentration of 16 vol% to 35 vol% can be achieved after dilution with the fuel and the exhaust gas recirculation stream. Unfortunately, achieving such oxygen concentrations using conventional methods is costly and / or inefficient. This is partially due to the difficulty in generating an oxygen-containing stream having an oxygen content of 25 vol% to 48 vol% while still producing commercially viable nitrogen co-products. For example, cryogenic air separation can form both a high-purity nitrogen stream and a high-purity oxygen stream. However, cryogenic separation systems require significant additional expense and specialized equipment. Additionally, the resulting high-purity oxygen stream then needs to be diluted to achieve an oxygen content of 25 vol% to 48 vol%.

[0019] In various aspects, a system and method are provided that enable the operation of a combustion-based power plant that uses both exhaust gas recirculation and oxygen-enriched combustion while reducing or minimizing losses in efficiency and / or reducing or minimizing additional costs for equipment modifications for core power plant operation. This is achieved by integrating the power plant combustion process with an oxygen enrichment process, which can produce both a nitrogen stream having a purity greater than 95 volume percent and an oxygen stream having a purity of 25 volume percent to 48 volume percent. By producing a nitrogen stream having a purity of 95 volume percent or greater along with an oxygen stream containing 25 volume percent to 48 volume percent oxygen, both streams from the process for generating the oxygen-containing stream can be used in a further process. This is in contrast to conventional methods that produce a pure oxygen stream product and then dilute it to produce oxygen-enriched air containing 25 volume percent to 48 volume percent oxygen, which involve either a) cryogenic air separation followed by significant additional costs and equipment for performing dilution of the oxygen stream, or b) pressure swing air separation with a cationic zeolite to produce the O2 product, which involves either significant additional costs and equipment, and the resulting nitrogen co-product stream corresponds to a waste stream due to essentially not having sufficient purity. It should be noted that pressure swing air separation with a cationic zeolite also requires an additional dehydration step to remove water to enable the cationic zeolite to function properly for both the thermodynamic and kinetic adsorption characteristics for air separation while performing N2-O2 separation.

[0020] By operating a power plant that uses both exhaust gas recirculation and oxygen-enriched combustion, additional options become available for post-combustion capture of CO2 from the resulting combustion exhaust gas stream. In some embodiments, the enhancement in the CO2 concentration in the combustion exhaust gas can enable a smaller-sized amine scrubber, thus reducing both capital and operating costs. In other embodiments, the enhancement in the CO2 concentration in the combustion exhaust gas can enable the use of other types of post-combustion CO2 capture technologies, such as membrane separation, separation using a fuel cell (e.g., molten carbonate fuel cell), or the use of direct displacement.

[0021] With respect to the use of an amine scrubber, using both exhaust gas recirculation and oxygen-enriched combustion can substantially reduce the total volume of combustion exhaust gas processed by the amine plant. The reduction in the combustion exhaust gas volume is due to several factors. First, the volume of oxygen-containing gas delivered to the combustion reaction is selected based on the target fuel-to-O2 ratio in the combustion chamber. In other words, the flow rate of O2 into the combustion chamber is used to select the amount of oxygen-containing gas flow, rather than the total gas flow for the oxygen-containing gas stream. A higher O2 content in the oxygen-containing gas means that a smaller total gas flow can be delivered to the combustion chamber while still providing the same O2 gas flow rate required to achieve the target fuel-to-O2 ratio. Increasing the O2 content of the oxygen-containing stream to 25% to 48% by volume corresponds to increasing the O2 content of the oxygen-containing gas by approximately 1.5 to 2.5 times that of air. Thus, the amount of oxygen-containing gas delivered to the combustion chamber can be reduced by similar factors. Also, the amount of N2 diluent in the oxygen-containing gas is reduced. Note that any reduction in N2 in the gas stream corresponds to a reduction in the amount of N2 that needs to be subsequently separated from CO2 to perform carbon capture. By using oxygen-enriched combustion, the volume of combustion exhaust gas that needs to be processed by the carbon capture system can be reduced by 40% to 70% (or perhaps even higher) relative to the volume of combustion exhaust gas processed when using air as the oxygen-containing gas.

[0022] It should be noted that by increasing the oxygen content in the combustion zone, the resulting combustion exhaust gas can also have an increased oxygen concentration. In the mode where an amine scrubber is used as a post-combustion capture process, some types of amines are sensitive to oxidative decomposition at a sufficiently high temperature in the presence of a sufficient amount of oxygen, so this increased oxygen concentration can potentially lead to increased amine decomposition. In some embodiments, the oxygen concentration of the combustion exhaust gas can be reduced by using a duct burner. The duct burner can be located, for example, in front of the heat recovery steam generator (HRSG) of a combined cycle power plant.

[0023] Regarding other options, another difficulty in amine scrubbers is the relatively high energy cost per CO2 molecule captured. After performing CO2 capture with an amine scrubber, the aqueous amine needs to be regenerated, for example, by using a thermal regeneration cycle. Increasing the CO2 concentration of the combustion exhaust gas can reduce this cost by reducing the volume of aqueous amine required, but there are thermodynamic limits on how much energy reduction can be achieved while still regenerating the aqueous amine.

[0024] In embodiments where the CO2 content of the combustion exhaust gas / other gas for post-combustion capture is 12 volume % or more, or 15 volume % or more, or 20 volume % or more, an alternative to the use of aqueous amines can be the use of a membrane separation method. Membrane systems are commercially available (e.g., polymeric membranes) and can provide a separation factor of approximately 50 for the separation of CO2 from N2. In combination with the use of a reduced pressure on the permeate side / increased pressure on the residue side to provide a driving force, such membranes can be used to perform the separation in a combustion exhaust gas having a CO2 content of 12 volume % or more to produce a permeate stream. By using membrane separation for CO2 capture, the thermal costs for regenerating the adsorbent can be avoided and replaced with the lower cost of maintaining a pressure differential across the membrane. In addition to the direct cost savings by avoiding the need for heating and cooling, such thermal costs can include avoiding the need for a stripper / reboiler unit, avoiding the need for additional heat exchangers, avoiding any emissions associated with generating heat, and avoiding losses that occur when heating and cooling various fluids to perform heat exchange, but are not limited thereto.

[0025] The membrane separator is an example of a type of post - combustion capture stage. Further, generally, various post - combustion capture options are available for the treatment of CO2 - containing combustion exhaust gases, such as the exhaust gas from the combustion chamber of a turbine. In various embodiments, the post - combustion capture stage can separate the combustion exhaust gas (or a portion thereof) to form one or more CO2 - depleted streams and at least one CO2 - containing stream. The CO2 - containing stream can contain 70 volume % or more, or 80 volume % or more, or 90 volume % or more of CO2, and for example, at most, substantially the whole can be composed of CO2. In some embodiments, such a CO2 - containing stream can correspond to 70 volume % or more, or 80 volume % or more, or 90 volume % or more (e.g., up to 100 volume % of the CO2 present in the combustion exhaust) of the CO2 that was present in the combustion exhaust. Additionally or alternatively, the recovery of CO2 by the post - combustion process can also be characterized based on the relative amount of CO2 exiting the system via one or more CO2 - depleted streams. In other words, the post - combustion process can be characterized based on the amount of CO2 present in one or more CO2 - depleted streams relative to the amount of CO2 present in the combustion exhaust gas. If a supplementary combustion device (e.g., a duct burner) is located downstream of the combustion chamber to reduce the oxygen content of the combustion exhaust gas, it should be noted that the comparison of the one or more CO2 - depleted streams and / or the CO2 - containing stream with the combustion exhaust gas can be performed based on the composition of the combustion exhaust after passing through the supplementary combustion device. In some embodiments, the CO2 content of the one or more CO2 - depleted streams can correspond to 30 volume % or less, or 20 volume % or less, or 10 volume % or less, or 5.0 volume % or less, or 2.0 volume % or less, or 1.0 volume % or less of the CO2 present in the exhaust gas from the combustion chamber (after any optional duct burner), and for example, can correspond to a minimum of 0.1 volume % (or perhaps even lower) of the CO2 present in the combustion exhaust gas.

[0026] A CO2 content in the combustion exhaust gas of 15% by volume or more, or 20% by volume or more, or 25% by volume or more can be achieved by using oxygen-enriched combustion, whereby the oxygen-containing gas has an O2 content of 35% by volume or more or 40% by volume or more. Additionally or alternatively, such a CO2 content in the combustion exhaust gas can be achieved by using selective exhaust gas recirculation, in which the exhaust gas recirculation stream has a CO2 content of 70% by volume or more, or 80% by volume or more, or 90% by volume or more. Such a selective exhaust gas recirculation stream can be formed, for example, by using a portion of a high-purity CO2 stream produced after capture of CO2 from the combustion exhaust gas. Further, additionally or alternatively, in some embodiments, a supplementary combustion stage (e.g., a duct burner) can be used for both reducing the O2 content and increasing the CO2 content of the combustion exhaust gas.

[0027] In this context, post-combustion capture is defined as one or more separation processes that separate a CO2-containing input gas stream (e.g., combustion exhaust) into one or more CO2-lean streams and at least one CO2-containing product stream. A CO2-lean stream is defined as an output stream that contains a lower volume % of CO2 than the CO2 content of the CO2-containing input gas stream. A CO2-containing product stream is defined as an output stream that contains a higher volume % of CO2 than the CO2 content of the CO2-containing input gas stream. Note that some post-combustion capture processes, e.g., molten carbonate fuel cells, can have multiple input streams. For molten carbonate fuel cells, the total cathode input stream is used to determine whether the output stream corresponds to a CO2-lean stream or a CO2-containing product stream.

[0028] As a further benefit, it should be noted that a significant portion of the cost of running the oxygen enrichment process can be offset by the fact that both the N2 stream and the O2 stream generated by the process can be used. Conventionally, air separation units are designed to generate either an N2 stream or an O2 stream, and any other streams from the process correspond to essentially worthless waste streams. In contrast, for the oxygen enrichment process described herein that is integrated with a combustion-based power plant, the N2 stream also has a sufficient purity (95% by volume or greater or 98% by volume or greater), such that the N2 stream can be used in another co-existing process and / or sold as a commercial product. In some embodiments, the N2 stream generated by the process is actually at high pressure, which further notes that the integration of the N2 with a co-existing process operating at high pressure has a reduced energy cost for the compression of the N2.

[0029] Formation of an O2-containing stream and a high-purity N2 stream In various embodiments, the source of oxygen for the combustion process in a power plant can be provided by an integrated separation process that produces both a higher purity N2 stream (95% by volume or greater) and an oxygen-containing stream having an oxygen (O2) content of 25% to 48% by volume. It has been discovered that such nitrogen-containing and oxygen-containing streams can be generated by performing a kinetic separation using a pressure swing adsorption process in combination with a suitable adsorbent material in air. Optionally, the pressure swing adsorption process can include one or more desorption steps performed at a pressure of 100 kPa-a or less. In such optional embodiments, the resulting oxygen-containing stream can be formed at a pressure of 100 kPa-a or less.

[0030] Conventionally, cryogenic air separation units can be used to generate large quantities of both high-purity nitrogen streams and high-purity oxygen streams. This is effective, but high-pressure and cryogenic separation, including the use of air separation units, means that the oxygen obtained is costly to produce. Such high-purity oxygen can be diluted to achieve concentrations of 25% to 48% by volume, but this is a costly way to generate a slightly enriched oxygen stream relative to air. This approach typically requires a large space for operation and a start-up time of several days. Additionally, air separation units have improved efficiency as throughput increases, but tend to be overly costly for the production of small volumes of gas.

[0031] Another option is to use a zeolite adsorbent that is selective for nitrogen adsorption and thus use a non-cryogenic adsorption process that produces high-purity oxygen as a product, such as in a pressure swing adsorption (PSA) process. Examples of such processes are described in the paper by Sircar et al. (Dabrowski A, editor. Fractionation of Air by Zeolites in Stud Surf Sci Catal: Elsevier; 1999. p. 395-423). However, such processes do not allow for the formation of both high-purity nitrogen streams containing 95% or more N2 and oxygen-containing streams containing 25% to 48% O2.

[0032] Separation can be performed such that it generates both a stream containing 25 to 48 volume % oxygen and a second stream containing 95 volume % or more nitrogen by performing kinetic separation using a suitable kinetic adsorbent and an improved process cycle. The level of O2 enrichment can be adjusted for recovery, as well as for N2 purity and recovery. It should be noted that higher recovery requirements typically result in lower purity, and similarly, higher purity typically comes at the expense of recovery. The separation provided herein can use this trade-off between recovery and purity to provide flexibility in cycle operation. For example, in some embodiments, the amount of O2 enrichment for a combustion process and / or the purity of the N2 product can be adjusted by adjusting the process to reduce the recovery of N2 and / or O2. This provides more adjustable specifications for both the N2 product and the O2 enriched stream compared to a cryogenic air separation unit. In some embodiments, the stream containing 25 to 48 volume % O2 can also contain 50 volume % or more N2.

[0033] One type of adsorbent for performing such kinetic separations is the carbon molecular sieve used in some commercial N2 generators. Another type of adsorbent that can be used is the zeolite material ITQ-55. ITQ-55 is described in detail, for example, in U.S. Patent No. 9,695,056, U.S. Patent No. 9,738,539, and U.S. Patent No. 9,856,145. Also, other types of adsorbents capable of performing kinetic separations of N2, such as ETS-4, are known. Generally, any kinetic adsorbent that provides sufficient kinetic selectivity for O2 over N2 and enables the formation of an effluent corresponding to a) a high-purity nitrogen stream containing 95 vol% or more N2 and b) an oxygen-containing stream having an oxygen content of 30 vol% to 50 vol% can be used when employed with the improved separation process described herein. The N2 corresponds to a stream of sufficiently high purity to be commercially valuable, and the oxygen-containing stream has a target oxygen concentration for use in oxy-fuel combustion. As used herein, the term "kinetic selectivity" is defined as the ratio of the single-component diffusion coefficients D(m 2 / s) for two different species. These single-component diffusion coefficients are also known as the transport diffusion coefficients measured for a given adsorbent for a given pure gas component. Thus, for example, the kinetic selectivity of component A over component B for a particular adsorbent is D A / D B . The single-component diffusion coefficients for a material can be determined by tests well known in the field of adsorption materials. A preferred manner for measuring the kinetic diffusion coefficient is that of the frequency response technique described by Reyes et al. in "Frequency Modulation Methods for Diffusion and Adsorption Measurements in Porous Solids", J. Phys. Chem. B. 101, pages 614-622, 1997.

[0034] In addition to using a suitable adsorbent, the kinetic separation is carried out using an improved separation process that facilitates the formation of both a nitrogen-containing stream and an oxygen-containing stream having a target purity level. The improved kinetic separation process can include having a plurality of adsorbent vessels. The improved process benefits from integrating the streams from different stages in the adsorption / desorption process. This integration of the streams from different stages in the adsorption / desorption process enables the recovery of both an oxygen-containing stream having an oxygen content of 25% to 48% by volume and a nitrogen-containing stream having a purity of 95% or more.

[0035] In some embodiments, the adsorption / desorption cycle can correspond to a pressure swing adsorption process that includes a total of eight steps. In this example, the process is described using a two-bed system, where the adsorbent beds are approximately the same size and the vessels containing the adsorbent beds are approximately the same volume. The process in this example for the two-bed system is symmetric in time, such that the steps performed in the paired beds are synchronized. For the eight-step cycle, when step 1 is being performed in one bed, step 5 is being performed in the other bed. When step 2 is being performed in one bed, step 6 is being performed in the other bed. When step 3 is being performed in one bed, step 7 is being performed in the other bed. When step 4 is being performed in one bed, step 8 is being performed in the other bed. Note that other synchronized process flows can be developed with more beds.

[0036] In this example, both step 1 and step 2 correspond to an adsorption step, in which the adsorbent is exposed to an air stream. This produces an adsorbent with an increased oxygen load and an adsorption effluent with a nitrogen content of 95% by volume or more. Since the loading of oxygen onto the adsorbent is driven by kinetics, a high percentage of oxygen can be removed from the stream, which enables a nitrogen purity of 95% by volume or more, or 97% by volume or more, or 98% by volume or more, and for example, allows substantially all of the adsorption effluent to correspond to nitrogen at most. This step is carried out at a high pressure, for example, 200 kPa-a to 800 kPa-a. Various temperatures can be used. A temperature close to room temperature can be convenient for the process, but lower temperatures can potentially provide a higher purity adsorption effluent. In some embodiments, the temperature can be from -100 °C to 40 °C. The velocity of the air in the adsorption environment during the adsorption step can vary depending on the configuration of the adsorbent environment. In some embodiments, the gas velocity during the adsorption step can be approximately 0.01 m / s to 1.0 m / s. The resulting adsorption effluent having a N2 content of 95% by volume or more is produced at a pressure similar to the pressure during the adsorption step. In some embodiments, any convenient air supply source can be used as the input stream for steps 1 and 2. In some embodiments, for example, in embodiments where the separation is carried out at a temperature of 0 °C to 40 °C, the air for use as the input stream for steps 1 and / or 2 can have a relative humidity of 60% or less, or 50% or less, or 40% or less, and for example, at a minimum, have substantially no water content (and thus, effectively 0% relative humidity).

[0037] Step 3 corresponds to the pressure equalization step, in which the first bed and the second bed are arranged in fluid communication. The pressure from the first bed can be equalized with the pressure in the second bed. In some embodiments, this pressure equalization is performed by connecting the top of the first bed to the top of the second bed. Using the flow only from the top of the pressurized bed to pressurize can help improve the purity of the O2 flow generated by the separation process. This is in contrast to the pressure equalization process, in which pressure equalization is performed using the gas flow from both ends of the pressurized bed. Such an equalization step from both ends of the pressurized bed can be used in a process where the only desired product is a high-purity N2 product. At the start of the pressure equalization step, the first bed is at a pressure of 200 kPa-a to 800 kPa-a, and the second bed is at a pressure close to ambient (i.e., approximately 100 kPa-a). After equalization, the pressure in the bed corresponds approximately to the average of the initial pressures. Since this is a pressure equalization step, the output flow from one bed functions as the input flow to the other bed.

[0038] Step 4 corresponds to a blowdown step for reducing the pressure in the first bed to approximately ambient pressure (approximately 100 kPa-a). Since the pressure is being released, an input flow is not required for the blowdown step. The blowdown step generates a blowdown exhaust. This blowdown exhaust corresponds to a flow having a low O2 content and a high N2 content relative to air. In some embodiments, the O2 content in the blowdown exhaust can be 5.0 volume% to 14 volume%, or 5.0 volume% to 12 volume%, or 8.0 volume% to 12 volume%.

[0039] Step 5 corresponds to the first reverse purge step. This purge step is referred to as "reverse flow" because the flow is in the opposite direction to the flow in Step 1. In some embodiments, the first reverse purge step is performed using a portion of the blowdown exhaust as the input flow. In this example, approximately half of the total blowdown exhaust is used as the purge gas for this reverse purge. This step is performed at approximately ambient pressure or approximately 100 kPa-a. This generates a first purge exhaust flow. This first purge exhaust flow is enriched in oxygen and corresponds to a flow containing 25 vol% to 34 vol% O2. Note that higher O2 concentrations may be possible, but at the expense of reducing the amount of O2 recovered per volume of air processed in the system.

[0040] Note that using the blowdown exhaust as the input flow for the first purge input flow is an unexpected choice. The blowdown exhaust is enriched in nitrogen and contains 5.0 vol% to 14 vol%, or 5.0 vol% to 12 vol%, or 8.0 vol% to 12 vol%. Thus, a higher purity O2 effluent can be generated by using air as the first purge input flow. However, because the kinetic separation is being performed, using air as the first purge input flow leaves excessive O2 still adsorbed on the adsorbent at the end of the first purge step. This prevents the adsorption effluent from containing 95 vol% or more N2 in the adsorption step in subsequent cycles. Further note that using a portion of the blowdown exhaust as the input flow for Step 5 substantially increases the recovery of both N2 and O2 relative to the volume of gas processed in the system. If a separate N2 flow were used as the input for Step 5, such an N2 flow would offset the benefit of generating a high purity N2 flow as part of the product and thus reduce the yield of high purity N2. With respect to O2, using the blowdown exhaust enables the recovery of a portion of the O2 present in the blowdown exhaust.

[0041] Step 6 corresponds to the second reverse purge step. In the second reverse purge step, the input stream for the second purge is a portion of the adsorption effluent from Step 1. The output stream corresponds to the second purge exhaust. Using a high-purity nitrogen stream (95 vol% or more N2) as the second purge input stream is necessary because the adsorption effluent corresponds to the high-purity nitrogen stream. Otherwise, excessive oxygen remains adsorbed to the adsorbent after the purge. This reduces the purity of N2 in the adsorption effluent generated in the next adsorption step. By using the high-purity adsorption effluent as the second purge input stream, the high purity of the adsorption effluent can be maintained in subsequent process cycles. However, using a portion of the adsorption effluent for the second purge reduces the yield of high-purity nitrogen. Note that a high-purity nitrogen stream from another source can be used in this step, for example, at the start of process execution when the adsorption effluent is still not available.

[0042] Step 7 corresponds to another pressure equalization step. This time, the first bed is at a lower pressure (approximately 100 kPa-a) and the second bed is at a higher pressure. Otherwise, this step is the same as Step 3. Note that the pressure equalization step increases the yield of N2 with respect to the total volume of gas being processed. The pressure equalization step also increases the O2 content in the blowdown exhaust.

[0043] Step 8 corresponds to the feed pressurization step. During pressurization, air is passed through the adsorbent environment to reach the target pressure for the adsorption step, for example, a pressure of 200 kPa-a to 800 kPa-a. This prepares the adsorbent environment for the next process cycle.

[0044] Table 1 shows an example of a process cycle based on the eight steps described above. As an example of the timing for the process cycle shown in Table 1, Steps 1 and 2 can each last for 10 seconds. This is consistent with the lengths of Steps 5 and 6, which can also each be 10 seconds. Step 3 can last for 2 seconds, which is consistent with Step 7. Step 4 can last for 0.5 seconds, which is consistent with Step 8. In other embodiments, any other convenient combination of process step lengths can be used as long as a suitable bed is available at the same time for the pressure equalization step.

Table 1

[0045] Figures 1 and 2 show the display of an eight-step adsorption / desorption cycle shown in Table 1. Figure 1 shows the first four steps of the cycle for the first adsorbent environment, and Figure 2 shows the last four steps of the cycle for the first adsorbent environment. Thus, Figure 1 also shows the last four steps of the cycle for the second adsorbent environment, and Figure 2 shows the first four steps of the cycle for the second adsorbent environment. Figures 1 and 2 represent the points in time when the bed is at each of the steps of the cycle.

[0046] In FIG. 1, A corresponds to the first adsorption step (step 1) for bed 1 and the first purge step (step 5) for bed 2. During this time, the input air stream 110 is passed through bed 1, resulting in the formation of adsorption effluent 115. During this time, a portion 137 of the blowdown effluent 135 is used as the first purge input stream for bed 2, resulting in the formation of the first purge exhaust 145. In FIG. 1, B corresponds to the second adsorption step (step 2) for bed 1 and the second purge step (step 6) for bed 2. During this time, the input air stream 110 continues through bed 1, forming adsorption effluent 115. During this time, a portion 117 of the adsorption effluent 115 is used as the input stream for bed 2, resulting in the formation of the second purge exhaust 155. In FIG. 1, C corresponds to the pressure equalization step, in which bed 1 is depressurized (step 3) by discharging stream 125, and stream 125 is passed into bed 2 for pressurization (step 7). In FIG. 1, D corresponds to the blowdown step (step 4) for bed 1, in which the remaining pressure is discharged from bed 1 to form the blowdown exhaust 135. D also corresponds to step 8 for bed 2, in which bed 2 is pressurized using air stream 170.

[0047] FIG. 2 is parallel to FIG. 1, but bed 1 performs steps 5 - 8 and bed 2 performs steps 1 - 4. In FIG. 2, E corresponds to step 5 for bed 1 and step 1 for bed 2. In FIG. 2, F corresponds to step 6 for bed 1 and step 2 for bed 2. In FIG. 2, G corresponds to another pressure equalization step, in which bed 2 is depressurized (step 7) by discharging stream 165, and stream 165 is passed into bed 1 for pressurization (step 3). In FIG. 2, H corresponds to step 8 for bed 1 and step 4 for bed 2.

[0048] Higher O2 content via vacuum pressure swing adsorption The processes shown in Table 1, and FIGS. 1 and 2, correspond to processes where all steps are carried out at approximately ambient pressure or above. In other embodiments, pressures below 100 kPa-a can be used to form an oxygen-containing stream, such that a higher O2 concentration can be achieved in the oxygen-containing stream while still maintaining a high purity nitrogen stream. Thus, in such other embodiments, the adsorption / desorption process can correspond to a vacuum pressure swing adsorption process. The same type of adsorbent can be used for such a vacuum pressure swing adsorption process. By using vacuum pressure swing adsorption (VPSA), the oxygen-containing stream can be generated with an O2 content of 25 vol% to 48 vol%, or 30 vol% to 48 vol%, or 35 vol% to 48 vol%, or 40 vol% to 48 vol%. VPSA is a type of PSA process, and thus it should be noted that a reference to a pressure swing adsorption process without further specifications can refer to either a process carried out at ambient pressure or above, or a vacuum pressure swing adsorption process including at least one step carried out at a pressure below 100 kPa-a.

[0049] An example of a vacuum pressure swing adsorption (VPSA) process that can form a nitrogen-containing stream having an N2 content of 95 vol% or more and an oxygen-containing stream containing 30 vol% to 48 vol% of O2 is a 6-step process. For purposes of process description, the process can be described for a system having two adsorbent beds, the two adsorbent beds being synchronized such that both beds are in a pressure equalization step at the same time. In this example of the VPSA process, the various steps can be carried out at approximately ambient temperature, although lower temperatures can also be used.

[0050] In this example, step 1 of the VPSA process corresponds to the adsorption step, in which the adsorbent is exposed to an air stream. This produces an adsorbent with an increased oxygen load and an adsorption effluent with a nitrogen content of 95% by volume or more. Since the loading of oxygen onto the adsorbent is driven by kinetics, a high percentage of oxygen can be removed from the stream, which enables a nitrogen purity of 95% by volume or more, or 97% by volume or more, or 98% by volume or more, and for example, allows for substantially all of the adsorption effluent to correspond to nitrogen at most. This step is carried out at a high pressure, for example, 200 kPa-a to 800 kPa-a. The resulting adsorption effluent with a nitrogen content of 95% by volume or more is produced at a pressure similar to the pressure during the adsorption step. The input flow rate during step 1 of the VPSA process can be similar to the flow rate for step 1 or step 2 (adsorption step) of the process shown in Table 1.

[0051] Step 2 of the VPSA process corresponds to the pressure equalization step, in which the first bed and the second bed are arranged in fluid communication. The pressure from the first bed can be equalized with the pressure in the second bed. At the start of the pressure equalization step, the first bed is at a pressure of 200 kPa-a to 800 kPa-a, and the second bed is at a pressure of 50 kPa-a or less. After equalization, the pressure in the bed corresponds approximately to the average of the initial pressures. Since this is the pressure equalization step, the output flow from one bed functions as the input flow to the other bed.

[0052] It should be noted that this pressure equalization step is valuable for increasing recovery. In particular, after the end of the adsorption step, the pressurized gas remaining in the first bed has a composition similar to that of the adsorption effluent. By performing pressure equalization, this high N2 content gas is used to pressurize the second bed that has just ended the desorption step. By performing pressure equalization, the high N2 content gas from the first bed is used to provide a significant portion of the pressurization of the second bed. The step of using equalization from the top is beneficial for producing high purity nitrogen with improved recovery for both oxygen and nitrogen.

[0053] Step 3 of the VPSA process corresponds to a blowdown step to reduce the pressure in the first bed to approximately ambient pressure (approximately 100 kPa-a). Since the pressure is being released, an input stream is not required for the blowdown step. The blowdown step generates blowdown exhaust.

[0054] Step 4 of the VPSA process corresponds to a vacuum desorption step. The pressure in the adsorbent environment is reduced to a pressure of 1.0 kPa-a to 50 kPa-a, or 1.0 kPa-a to 20 kPa-a, or 1.0 kPa-a to 10 kPa-a, or 5.0 kPa-a to 50 kPa-a, or 5.0 kPa-a to 20 kPa-a. This vacuum desorption step is referred to as "countercurrent" because the output stream exits from the adsorbent environment at the end opposite to the end from which the adsorption effluent exits the adsorbent environment. The vacuum desorption exhaust is enriched in oxygen and corresponds to a stream containing 25 vol% to 48 vol%, or 30 vol% to 48 vol%, or 35 vol% to 48 vol%, or 40 vol% to 48 vol%, or 35 vol% to 44 vol% O2.

[0055] Step 5 corresponds to another pressure equalization step. This time, the first bed is at a lower pressure (1.0 kPa-a to 50 kPa-a) and the second bed is at a higher pressure. Otherwise, this step is similar to step 2.

[0056] Step 6 corresponds to the feed pressurization step. During pressurization, air is passed into the adsorbent environment to reach the target pressure for the adsorption step, for example, a pressure of 200 kPa-a to 800 kPa-a. This prepares the adsorbent environment for repeating the cycle.

[0057] Table 2 shows an example of the above VPSA cycle having timings for various steps. As an example of the timings for the process cycle shown in Table 2, step 1 can be carried out for 20 seconds, which can match the length of step 4. Step 2 can be carried out for 2 seconds, which matches step 5. Step 3 can be carried out for 0.5 seconds, which matches step 6.

Table 2

[0058] Figure 7 shows a display of the 6-step adsorption / desorption cycle shown in Table 2. Figure 7 represents the time points when the bed is at each of the steps of the cycle.

[0059] In FIG. 7, “A” corresponds to the adsorption step (step 1) for bed 1 and the desorption step (step 4) for bed 2. During this time, the input air stream 710 is passed through bed 1, resulting in the formation of adsorption effluent 715 (nitrogen-enriched product). During this time, countercurrent desorption is performed on bed 2 while reducing the pressure to a pressure of 1.0 kPa-a to 50 kPa-a. The output 745 from this step corresponds to the oxygen-enriched product. In FIG. 7, B corresponds to the pressure equalization step, and in the pressure equalization step, bed 1 is depressurized (step 2) by discharging stream 725, and stream 725 is passed into bed 2 for pressurization (step 5). In FIG. 1, C corresponds to the blowdown step (step 3) for bed 1, and in the blowdown step, the remaining pressure is discharged from bed 1 to form blowdown exhaust 735. C also corresponds to step 6 for bed 2, and in step 6, bed 2 is pressurized using air stream 770. Steps D, E, and F are the same as steps A, B, and C, but beds 1 and 2 have opposite roles.

[0060] Exhaust gas recirculation In various embodiments, exhaust gas recirculation (EGR) can be used to further increase the CO2 concentration in the combustion exhaust from the combustion process. One option for exhaust gas recirculation is to recirculate a portion of the combustion exhaust after completion of power generation. For example, the combustion exhaust exiting a heat recovery generator system can be used as a source of exhaust gas for recirculation. In this type of embodiment, the recirculated exhaust gas can contain various components, including CO2, N2, water formed during combustion, and any O2 and / or fuel that did not react during the combustion process. By using oxygen-enriched combustion, the amount of exhaust gas that can be recirculated can be increased while still maintaining an O2 concentration in the combustion chamber of 16 vol% to 35 vol%.

[0061] In the case of selective exhaust gas recirculation (SEGR), a further increase in the amount of exhaust gas recirculation can be achieved. Selective exhaust gas recirculation uses a portion of the high-purity CO2 stream formed during and / or after post-combustion capture as the recirculation stream. As a result, selective exhaust gas recirculation uses a recirculation stream containing 70% by volume or more, or 80% by volume or more, or 90% by volume or more of CO2, for example, a recirculation stream that is at most substantially entirely composed of CO2. It should be noted that the CO2 stream formed after capture may include multiple recovery stages (e.g., multiple membranes or multiple series swing adsorption vessels) to achieve a final CO2 purity of 90% by volume or more. Thus, a recirculation stream having a CO2 content of less than 90% by volume may be usable in embodiments where the final high-purity CO2 stream has a CO2 content of more than 90% by volume.

[0062] In various embodiments, the flow rate of gas into the combustion chamber can be characterized based on the relative volume percentage (at 20 °C and 100 kPa-a) of the gas streams entering the combustion chamber. These gas streams correspond to an oxygen-containing gas stream, a recirculated exhaust gas, and a fuel stream. It should be noted that these streams can be combined and then enter the combustion chamber. For example, in some embodiments, the exhaust gas recirculation stream and the oxygen-containing stream can be combined and then enter the main compressor for a natural gas turbine, and the fuel stream is added separately to the combustion chamber. Depending on the embodiment, the exhaust gas recirculation stream can correspond to 25% to 60% by volume, or 35% to 60% by volume, or 45% to 60% by volume of the input stream to the combustion chamber. It should be noted that when performing exhaust gas recirculation with air as the oxygen-containing stream, using more than 20% by volume of exhaust gas recirculation causes the oxygen content in the combustion chamber to drop below 16% by volume.

[0063] In some embodiments, the exhaust gas recirculation stream may be combined with the oxygen-containing gas stream at a pressure of 95 kPa-a to 115 kPa-a or 100 kPa-a to 115 kPa-a. The combined stream of exhaust gas recirculation and oxygen-containing gas stream may then be compressed (e.g., in the main compressor for a natural gas turbine), and then enter a combustion chamber where it is mixed with fuel for combustion. In other embodiments, other configurations may be used to compress the various gas streams before they enter the combustion chamber.

[0064] As used herein, the term "stoichiometric combustion" refers to a combustion reaction having a volume of reactants including fuel and oxidizer and a volume of products formed by combusting the reactants, wherein the entire volume of the reactants is used to form the products. As used herein, the term "substantially stoichiometric combustion" refers to a combustion reaction having a molar ratio of combustion fuel to oxygen in the range of about plus or minus 10% of the oxygen required for the stoichiometric ratio, or more preferably, about plus or minus 5% of the oxygen required for the stoichiometric ratio. For example, the stoichiometric ratio of fuel to oxygen for methane is 1:2 (CH4 + 2O2 > CO2 + 2H2O). Propane has a stoichiometric ratio of fuel to oxygen of 1:5. Another way to measure substantially stoichiometric combustion is as the ratio of the oxygen supplied to the oxygen required for stoichiometric combustion, e.g., about 0.9:1 to about 1.1:1, or more preferably, about 0.95:1 to about 1.05:1.

[0065] Post-combustion capture stage Various options are available for the post-combustion capture stage. In some embodiments, multiple different types of post-combustion capture devices may be used to form a CO2-containing stream containing a targeted amount of CO2 generated in the combustion zone and / or any supplementary combustion devices.

[0066] One option for the post-combustion capture stage is to use one or more aqueous amine separators or amine scrubbers. By using a combination of oxygen-enriched combustion and exhaust gas recirculation, the size of the amine scrubber used for post-combustion capture can be substantially reduced. Optionally, in embodiments where the amine scrubber is used as at least a portion of the post-combustion capture stage, the combustion zone can be operated under substantially stoichiometric conditions and / or a supplementary combustion stage can be used to reduce or minimize the amount of oxygen passed into the amine scrubber.

[0067] Another option for the post-combustion capture stage is to use a liquid-phase capture device, which is operated by providing a high interfacial gas-liquid mass transfer surface area. The liquid in the device can include one or more components (e.g., amines) that perform the adsorption of CO2. Examples of devices that can provide a high interfacial gas-liquid mass transfer surface area in the post-combustion capture stage include, but are not limited to, devices that increase the surface area based on the centrifugal shearing of the liquid, devices that increase the surface area by generating small liquid droplets that can be dispersed in the gas flow, and devices that increase the surface area by generating a thin film of liquid that contacts the gas flow. Optionally, in embodiments where the liquid-phase adsorbent is at least partially amine-based, the combustion zone can be operated under substantially stoichiometric conditions and / or a supplementary combustion stage can be used to reduce or minimize the amount of oxygen passed into the post-combustion capture stage.

[0068] Another alternative for the post - combustion capture stage is to use a solid adsorbent. A variety of solid adsorbent systems are available. The solid adsorbent can include an adsorbent supported on a support material, for example, an adsorbent supported on a monolith, or an adsorbent supported on particles in an adsorbent bed. Other types of solid adsorbents can be formed into a monolith, particles, or another convenient structure without using a support material. Examples of solid adsorbents can include, but are not limited to, zeotypes, metal - organic framework materials, and amino polymers. The method for recovering CO2 after adsorption onto the solid adsorbent can vary depending on the nature of the adsorbent. In some embodiments, a direct displacement method can be used. For example, after the adsorption of CO2 by the solid adsorbent, low - pressure steam can be used for the displacement of CO2 and the regeneration of the adsorbent for further use. As another example, a temperature swing can be used to enable the transition of the adsorbent from the conditions for CO2 adsorption to the conditions for CO2 desorption. Another example can be the use of the adsorbent when a pressure swing enables the transition of the adsorbent from the conditions for CO2 adsorption to the conditions for CO2 desorption. Yet another example can be the use of a combination of two or more of direct displacement, temperature swing, and pressure swing to enable the transition of the adsorbent from the conditions for CO2 adsorption to the conditions for CO2 desorption. Optionally, in embodiments where the solid adsorbent is at least partially amine - based, the combustion zone can be operated at substantially stoichiometric conditions and / or a supplementary combustion stage can be used to reduce or minimize the amount of oxygen passed into the post - combustion capture stage.

[0069] It should be noted that having a higher CO2 concentration in the combustion exhaust can provide an additional benefit for the post - combustion capture stage based on solid adsorbents. For many types of solid adsorbents, the equilibrium adsorption capacity of the adsorbent depends on the available CO2 concentration in the input gas stream to the adsorbent environment. Thus, the productivity of such an adsorbent (the amount of CO2 captured per unit time per unit mass of the adsorbent) increases when CO2 capture is performed in a higher - concentration stream.

[0070] Yet another option for the post - combustion capture stage is to use a molten carbonate fuel cell. Molten carbonate fuel cells are operated by using the conversion of CO2 and O2 at the cathode into carbonate ions for transport across the electrolyte in the fuel cell. The carbonate combines with hydrogen at the anode to generate power while also forming CO2 and H2O. To use a molten carbonate fuel cell as a post - combustion capture device, the combustion exhaust (flue gas) from the combustion zone of the turbine is used as at least a portion of the cathode input stream to the fuel cell. Note that O2 is also a reactant required for the operation of the cathode of the molten carbonate fuel cell. Thus, the presence of additional oxygen in the combustion exhaust is potentially beneficial for increasing CO2 utilization at the cathode while maintaining stable operating conditions.

[0071] Since CO2 is used to form the ions transported across the electrolyte, molten carbonate fuel cells offer the rare property of allowing CO2 to move from a lower - concentration cathode stream to a higher - concentration anode stream. Due to the nature of the electrochemical reactions in molten carbonate fuel cells, achieving capture of 80 volume % or more of the CO2 in the cathode input stream (i.e., utilization of 80 volume % or more of the CO2) can be difficult when the CO2 concentration in the cathode input stream is approximately 5.0 volume % or less. However, by using oxygen - enriched combustion and / or exhaust gas recirculation to increase the CO2 concentration in the combustion exhaust, 80 volume % or more of the CO2 in the cathode input stream can be captured (i.e., via movement to the anode exhaust) or 90 volume % or more can be captured while still having a cathode exhaust with a CO2 content of 1.0 volume % or more, or 1.5 volume % or more, or 2.0 volume % or more, for example, up to a maximum of 5.0 volume %. In some embodiments, maintaining a CO2 concentration of 1.5 volume % or more (or 2.0 volume % or more) in the cathode exhaust can assist in the stable operation of the molten carbonate fuel cell because it increases the likelihood that a significant amount of CO2 is present throughout the cathode as opposed to having a portion of the cathode where CO2 is substantially depleted during operation.

[0072] Another alternative for the post-combustion capture stage is to use a membrane separator. Membrane systems are commercially available (e.g., polymeric membranes) and can provide a separation factor of approximately 50 for the separation of CO2 from N2. In combination with the use of a reduced pressure on the permeate side / increased pressure on the residue side to provide a driving force, such membranes can be used to perform the separation in flue gas having a CO2 content of 12 volume % or more to produce a permeate stream. By using membrane separation for CO2 capture, the thermal costs for regenerating the adsorbent can be avoided and replaced with the lower cost of maintaining the pressure differential across the membrane. In addition to the direct cost savings by avoiding the need for heating and cooling, such thermal costs can include avoiding the need for a stripper / reboiler unit, avoiding the need for additional heat exchangers, avoiding any emissions associated with generating heat, and avoiding losses that occur when heating and cooling various fluids to perform heat exchange, but are not limited thereto.

[0073] Yet another alternative for post-combustion capture is to use cryogenic separation. During cryogenic separation, CO2 is separated from gases, such as N2 or O2, by reducing the temperature by a sufficient amount and / or increasing the pressure by a sufficient amount, whereby the CO2 forms a condensed phase and the other components remain in the gas phase. It should be noted that flue gas typically contains a significant amount of water. Such water is removed, for example, by condensing the water under conditions where the CO2 remains in the gas phase, and then the stream is exposed to full cryogenic conditions.

[0074] It should be noted that the post-combustion capture stage can optionally include a plurality of devices of a given type and / or can include a mixture of types of post-combustion capture devices. For example, if desired, multiple membranes, solid adsorbents, and / or molten carbonate fuel cells can be arranged in series to achieve a CO2-containing product stream having a target purity of CO2.

[0075] Composite Cycle Process - Configuration Example In various aspects, systems and methods are provided for generating power while controlling and / or capturing emissions generated during power generation. One goal of power generation is to use an input feed (e.g., fuel) as efficiently as possible, thereby increasing power generation for a given amount of fuel and / or a given amount of equipment. Based on the conditions for effective power generation, the goal for emissions control and / or capture can be to provide effective capture of emissions while reducing or minimizing changes to the conditions for power generation.

[0076] In various aspects, the processes described herein can be used to generate power while substantially capturing CO2 generated during the process, e.g., capturing 70 volume % or more, or 80 volume % or more, or 90 volume % or more of the CO2 in the exhaust combustion flue gas from a combustion process (e.g., up to substantially all of the CO2 in the combustion exhaust). In one or more aspects, a mixture of enriched air and fuel can be combusted. Prior to and / or during combustion, a recycled portion of the exhaust gas can be added to the mixture. In some aspects, the exhaust gas recirculation can correspond to a portion of the total exhaust, whereby the recirculation flow generally includes the products of the combustion reaction. This includes CO2, H2O, and diluent gases present in the combustion environment, e.g., N2. In other aspects, a selective exhaust gas recirculation flow can be used, which has a CO2 content of 80 volume % or more or 90 volume % or more. Exhaust gas recirculation can be used as a diluent to control, regulate, or otherwise moderate the temperature of the combustion and the exhaust entering the subsequent expander. Additionally, exhaust gas recirculation can further increase the CO2 content of the resulting combustion flue gas formed by the combustion. The combination of the use of enriched air and recycled exhaust gas can enable the expander to be operated at a higher expansion ratio for the same inlet and discharge temperatures, thereby generating increased power.

[0077] In various embodiments, any convenient ratio of oxygen to fuel may be used. For example, when using natural gas as fuel, the molar ratio of O2 to fuel may range from approximately 2.0:1 (substantially stoichiometric combustion) to 5.0:1, or perhaps even higher. As another example, the molar ratio of O2 to fuel can range from approximately 2.0:1 to 3.5:1 or 2.0:1 to 3.0:1. It should be noted that when fuels other than methane are used, lower values of O2 to fuel correspond to substantially stoichiometric combustion, for example, corresponding to a ratio of approximately 1.5:1. In such embodiments, the ratio of O2 to fuel can range from approximately 1.5:1 to 3.5:1.

[0078] Note that combustion under stoichiometric or substantially stoichiometric conditions (e.g., "slightly rich" combustion) in commercial gas turbines can be shown to be advantageous in order to eliminate the cost of excess oxygen removal. Such operation can also reduce the amount of N2 present in the combustion exhaust. By cooling the exhaust and condensing water from the cooled exhaust stream, an exhaust stream with a relatively high content of CO2 can be produced. A portion of the recirculated exhaust gas can be used for temperature moderation in a closed Brayton cycle, the remaining purge stream can be used for EOR applications, and / or the power can be generated with sulfur oxides (SO x ) nitrogen oxides (NO x ), and / or CO2 being produced with little or no release to the atmosphere. The result of this process is the generation of power in three separate cycles and the production of additional CO2. In some embodiments, performing stoichiometric combustion enables the generation of an exhaust stream consisting substantially of CO2, H2O, and N2. An exhaust stream consisting substantially of CO2, H2O, and N2 is defined as an exhaust stream containing other gas molecules at about 5 mole% or less, for example, other gas molecules at about 2.5 mole% or less or other gas molecules at about 1 mole% or less.

[0079] In some embodiments, for example, in some embodiments where substantially stoichiometric combustion is not performed, a duct burner and / or other supplementary combustion stage may be used to reduce the oxygen content of the combustion exhaust. Such a supplementary combustion stage can be operated by adding additional fuel to the combustion exhaust and then consuming a substantial portion of the oxygen present in the combustion exhaust via a supplementary combustion reaction.

[0080] Figure 3 shows an example of an integrated system for power generation and CO2 capture using a combined cycle apparatus that includes oxygen-enhanced combustion and exhaust gas recirculation. Figure 3 shows a natural gas combined cycle plant, but any other convenient type of combustion-based combined cycle power generation plant, for example, a power generation plant based on the combustion of propane, fuel oil, coal, or kerosene, may be used.

[0081] In some embodiments, the power generation system can include a gas turbine system characterized as a power generation closed Brayton cycle. The gas turbine system can have a first or main compressor 304 coupled to an expander 306 via a shaft 308. The shaft 308 can be any mechanical, electrical, or other power coupling, thereby enabling a portion of the mechanical energy generated by the expander 306 to drive the main compressor 304. In at least one embodiment, the gas turbine system can be a standard gas turbine, in which the main compressor 304 and the expander 306 each form a compressor and expander end, respectively, in the gas turbine system. In other embodiments, the main compressor 304 and the expander 306 can be individualized components.

[0082] In various aspects, the gas turbine system can also include an integrated pressure swing adsorption system 370. The pressure swing adsorption system can optionally correspond to a vacuum pressure swing adsorption system. In the exemplary configuration shown in FIG. 3, air 301 is compressed 303 and then passed into the pressure swing adsorption system 370 to form a nitrogen-containing stream 372 having an N2 content of 95% by volume or more and an oxygen-containing stream 375 having an O2 content of 25% to 48% by volume. The oxygen-containing stream 375 is then combined with the exhaust gas recirculation 345 (after any optional compression of either), and then the combined stream 377 is passed into the main compressor 304.

[0083] The combustion chamber 310 combusts fuel 312 together with the combined stream 377. In one or more aspects, the fuel in line 312 can include any suitable hydrocarbon gas or liquid, such as natural gas, methane, ethane, naphtha, butane, propane, syngas, diesel, kerosene, aviation fuel, coal-derived fuel, biofuel, oxygenated hydrocarbon feedstock, or any combination thereof.

[0084] The exhaust gas 316 directed towards the inlet of the expander 306 can be generated as a product of combustion in the combustion chamber 310. The exhaust gas in line 316, when expanded through the expander 306, generates mechanical power to drive the main compressor 304, the electric generator, and / or other equipment, and also produces a gas exhaust 322 having an increased CO2 content. In some aspects, the expander 306 can be adapted to generate additional mechanical power for other purposes.

[0085] The power generation system can also include a heat recovery steam generator (HRSG) 326 or a similar device. The gas exhaust 322 can be passed through the HRSG 326, where the gas exhaust is used to generate steam. The HRSG 326 can be coupled to one or more steam turbines. In the example shown in FIG. 3, the HRSG 326 is fluidly coupled to a high-pressure steam turbine 362, an intermediate-pressure steam turbine 364, and a low-pressure steam turbine 366. In other embodiments, any convenient number of steam turbines can be fluidly coupled to the HRSG 326.

[0086] Optionally, before passing the gas exhaust 322 through the HRSG 326, an optional duct burner 390 can be used to combust any remaining oxygen present in the gas exhaust 322. This is achieved by adding additional fuel (not shown) to the duct burner such that substantially all of the remaining oxygen in the gas exhaust 322 is consumed by the combustion reaction. This generates additional heat along with the duct burner exhaust stream 392, which contains 2.0 volume % or less, or 1.0 volume % or less, or 0.1 volume % or less O2, and for example, at a minimum, has substantially no O2 content. The additional heat generated by the combustion reaction in the optional duct burner 390 can also be recovered in the HRSG 326.

[0087] After passing through the HRSG 326, a portion of the resulting cooled exhaust gas 332 can be used as an exhaust gas recirculation stream 345. A blower 344 can be used to recover any pressure losses due to the pressure drop across the HRSG 326, after which the exhaust gas recirculation stream 345 is combined with an oxygen-containing stream 375. In some embodiments, after optional compression, the exhaust gas recirculation 345 can have a pressure of 95 kPa-a to 115 kPa-a.

[0088] The remaining portion 336 of the cooled exhaust gas 332 can be passed through one or more stages for CO2 capture. In this example, CO2 capture is performed using one or more amine scrubber stages 350. Since the CO2 content of the cooled exhaust gas 332 is 12 vol% or more, or 15 vol% or more, or 20 vol% or more, the size of the amine scrubber stage is substantially smaller than that required to capture the same amount of CO2 at a concentration of 4.0 vol% to 8.0 vol%. Optionally, one or more temperature and / or pressure adjustment stages 351 (e.g., compressors and heat exchangers) can be used to modify the temperature and pressure of the portion 336 of the cooled exhaust gas 332, after which the portion 336 is passed into the amine scrubber 350. The amine scrubber produces a combustion exhaust gas 359 with a reduced CO2 concentration and a high-purity CO2 output stream 355, and the high-purity CO2 output stream 355 contains CO2 from the portion 336 of the cooled exhaust gas 332 passed through the amine scrubber 350 at 90 vol% or more. The combustion exhaust gas 359 can have a CO2 concentration of 3.0 vol% or less, or 2.0 vol% or less, or 1.0 vol% or less, and for example, at a minimum, has substantially no CO2 content (0.1 vol% or less). Since the amine scrubber is used in the exemplary configuration shown in FIG. 3, the CO2 output stream 355 can also contain water. Thereafter, such water can be removed by cooling the CO2 output stream 355 (not shown). After water removal, the CO2 output stream can contain 80 vol% or more or 90 vol% or more of CO2. The CO2 output stream can contain 80 vol% or more or 90 vol% or more of the CO2 in the gas exhaust 322.

[0089] Figure 4 shows another composite cycle configuration. In the example shown in Figure 4, the pressure swing adsorption process corresponds to a vacuum pressure swing adsorption process. Additionally, the exhaust gas recirculation in the configuration shown in Figure 4 corresponds to selective exhaust gas recirculation, and in selective exhaust gas recirculation, the recirculation flow corresponds to a portion of high-purity CO2 formed after separation from the combustion exhaust gas. When using additional oxygen provided by vacuum pressure swing adsorption and / or when using selective exhaust gas recirculation, the CO2 content of the combustion exhaust gas from combustion can be high enough to enable alternative separation methods, such as the membrane system used in the exemplary configuration shown in Figure 4.

[0090] In Figure 4, air 401 is compressed 403 and then passed into a vacuum pressure swing adsorption stage 470. This produces a high-purity nitrogen stream 472 and an oxygen-containing stream 475 containing 30 vol% to 48 vol% or 35 vol% to 48 vol% O2. The oxygen-containing stream 475 is combined with a selective exhaust gas recirculation stream 445 and then passed into a main compressor 304. The combined mixture then burns 310 with fuel 312. The selective exhaust gas recirculation stream 445 corresponds to a CO2 stream containing 90 vol% or more CO2.

[0091] By using an oxygen-containing stream with a higher O2 content and / or a selective exhaust gas recirculation stream 445, an exhaust gas 435 with a higher CO2 content exits the HRSG 326. Based on the higher CO2 content, a membrane 480 can be used to generate a permeate stream 485 containing 90 vol% or more CO2. Additionally or alternatively, the CO2 in the permeate can correspond to 90 vol% or more of the CO2 originally generated by the combustion reaction in the combustion chamber 310. The membrane separation also generates a residue 489 corresponding to the combustion exhaust gas with a low CO2 content.

[0092] Example 1 - Oxygen Enrichment via Pressure Swing Adsorption Using kinetic models, the separation performance for two types of adsorbents in a pressure swing adsorption apparatus was determined. Table 3 shows the kinetic parameters used to model the performance of carbon molecular sieve (CMS) adsorbents and adsorbents based on ITQ-55. The parameters for CMS were obtained from Qinglin et al., “Revisiting Transport of Gases in the Micropores of Carbon Molecular Sieves” Langmuir (2003) 19, 393 - 405. The parameters for ITQ-55 were derived based on diffusivity measurements obtained using a pressure swing frequency response apparatus.

Table 3

[0093] Based on the kinetic parameters in Table 3, a pressure swing adsorption system was modeled for the kinetic separation of air using either ITQ-55 or CMS as the adsorbent. Kinetic separation was modeled using a two-bed configuration similar to the exemplary configuration considered in Figure 1. A single adsorption bed has dimensions of 1.5 meters (diameter) × 2 meters (length) and a bed porosity of 0.4 for the adsorbent formed of pellets. For the separation in Example 1, the 8-step process described in relation to Table 1 was used. Table 4 shows the details regarding the composition and flow rates in the modeled separation process. The goal for this modeled process was to generate a high-purity N2 stream while also generating an oxygen-containing stream with an approximate O2 concentration of 30 volume% with high recovery. For the separation in Example 1, Steps 1, 2, 5, and 6 were 10 seconds in length, Steps 3 and 7 were 2.0 seconds in length, and Steps 4 and 8 were 0.5 seconds in length.

Table 4

[0094] In Table 4, the "Feed + Pressurization" row corresponds to the input streams for process Steps 1 and 7. The "Raffinate Product" corresponds to the net adsorption effluent generated in Step 1 after subtracting the portion of the adsorption effluent used in Step 5 (the second purge step). The "Extract Product" corresponds to the first purge exhaust formed in Step 4. As shown in Table 4, both ITQ-55 and CMS were suitable as adsorbents for forming nitrogen-containing products having an N2 concentration of 95 vol% or more and for forming oxygen-containing products having an O2 concentration of approximately 30 vol%.

[0095] Table 5 shows additional details related to the purity, flow rate, and productivity for the modeled process in Table 4.

Table 5

[0096] As shown in Table 5, it is successful to recover approximately 90 vol% or more of the O2 passed through the adsorbent bed during the pressurization and adsorption steps as part of the oxygen-containing gas. The nitrogen recovery is lower, corresponding to 35 vol% - 40 vol% of the N2 passed through the bed during the pressurization and adsorption steps.

[0097] Example 2 - Oxygen Enrichment via Vacuum Pressure Swing Adsorption Using the same kinetic model, a vacuum pressure swing adsorption process aimed at generating an oxygen-containing stream having an O2 concentration of approximately 40 vol% was modeled. The 6-step process described in relation to Table 2 was used for the process flow. Table 6 shows details regarding the composition and flow rate in the modeled VPSA process. The total cycle time is 45 seconds, the adsorption / desorption times are each 20 seconds, the blowdown / re-pressurization times are each 0.5 seconds, and the equalization time is 2 seconds per equalization.

Table 6

[0098] In Table 6, the "Feed + Pressurization" row corresponds to the input streams for process steps 1 and 6. The "Raffinate Product" corresponds to the net adsorption effluent generated in step 1. The "Blowdown Exhaust" corresponds to the effluent during process step 3. The "Withdrawal Product" corresponds to the vacuum purge exhaust formed in step 4. In the model process shown by Table 6, the vacuum purge was carried out by reducing the pressure in the adsorbent environment to 10 kPa-a. As shown in Table 6, both ITQ-55 and CMS were suitable as adsorbents for forming nitrogen-containing products having an N2 concentration of 97 vol% or more and for forming oxygen-containing products having an O2 concentration of approximately 40 vol%.

[0099] Table 7 shows additional details related to purity, flow rate, and productivity for the modeled process in Table 6.

Table 7

[0100] As shown in Table 7, it is successful to recover approximately 90 vol% or more of the O2 passed through the adsorbent bed during the pressurization and adsorption steps as part of the oxygen-containing gas. The nitrogen recovery is lower, corresponding to approximately 40 vol% of the N2 passed through the bed during the pressurization and adsorption steps.

[0101] Example 3 - Composite Cycle Operation Example with PSA and EGR To explain the benefits of carbon capture from operation with oxygen-enriched combustion and exhaust gas recirculation, the operation of an amine scrubber for capturing CO2 from combustion exhaust gas was modeled using a commercially available software package (Aspen HYSYS®). The amine scrubber was modeled based on the use of monoethanolamine (MEA) as the adsorbent. Figure 5 shows the modeled configuration.

[0102] Using the modeled configurations, the capture of CO2 from three different types of modeled combustion exhaust gases was investigated. The first combustion exhaust gas corresponded to the combustion exhaust gas generated without exhaust gas recirculation using air as the oxygen-containing gas (about 21 vol% O2). The corresponding combustion exhaust gas had a CO2 concentration of only 4.0 vol%. The second combustion exhaust gas corresponded to the combustion exhaust gas generated with a certain degree of exhaust gas recirculation (approximately 43 vol% of the combustion exhaust gas exiting the HRSG) using an oxygen-containing gas containing 30 vol% O2. This combustion exhaust gas was modeled as having a CO2 content of 13 vol%. The third combustion exhaust gas was modeled as having a CO2 content of 16 vol% based on a combination of exhaust gas recirculation (55 vol% of the combustion exhaust gas exiting the HRSG) and the use of an oxygen-containing gas containing 40 vol% O2.

[0103] In the process model, the combustion exhaust gas 501 enters the absorber at a pressure of 1.1 bar (110 kPa-a) and a temperature of 40°C. Also, lean amine (28 wt% MEA in water) is fed to the absorber 510. The "green combustion exhaust gas" 515 exits at the top of the absorber, and the CO2-rich amine 518 exits the absorber 510 from the bottom. The CO2-rich amine 518 then proceeds to the lean / rich heat exchanger 520, where it is heated by the lean amine 538 exiting the stripper 530. The heated rich amine 528 is fed to the stripper 530, where high-purity CO2 (over 94%) 535 exits at the top of the stripper. The stripper reboiler duty is provided by the LP steam from the HRSG (not shown). By calculating the required steam flow rate, the power debit for the amine unit reboiler can be calculated.

[0104] The simulation results for the base case (21% O2 in the inlet air and no EGR) and two cases using oxygen-enriched combustion with exhaust gas recirculation are shown in Table 8. Due to the use of higher O2 concentration air and combustion exhaust gas recirculation, the concentration of CO2 in the combustion exhaust gas is significantly higher for the oxygen-enriched combustion cases compared to the base case. As a result, there is a reduction in the total flow rate of combustion exhaust gas that needs to be sent to the capture unit. For the case using 30 vol% O2 in the oxygen-containing gas, there is a 71% reduction in the total combustion exhaust gas flow rate compared to the base case. This increases to over 75% reduction for the case containing 40 vol% O2 in the oxygen-containing gas. This results in significant savings in compressor and cooler duty. In addition, due to the smaller amount of amine supply required for the oxygen-enhanced combustion cases, the reboiler duty, and thus the LP power debit, is lower. Therefore, the total power debit for carbon capture is significantly lower for the oxygen-enhanced combustion cases. The efficiency debit for the oxygen-enhanced combustion cases is only about 5%, while for the base case, the efficiency debit is 11.5%. This represents significant energy savings for NGCC power plants.

[0105] Another observation from Table 8 is that in the OEC cases, there is a 20% reduction in the number of absorber stages required to achieve 90% CO2 capture compared to the base case. For the base case, the absorber size required is 80 m in height and 20 m in diameter. For the case using 40 vol% O2 in the oxygen-containing gas, the absorber is estimated to be 60 m in height and 10 m in diameter. This enables significant intensification of the capture unit.

Table 8

[0106] Example 4 - CO2 Separation through Membranes In embodiments where the CO2 content of the combustion exhaust gas increases to 15% by volume or more, the membrane system can be used instead of an amine scrubber while still producing a CO2-containing stream having a CO2 content of 90% by volume or more. Additionally, in such embodiments, the membrane can enable the capture of 90% by volume or more of the CO2 in the combustion exhaust gas.

[0107] To illustrate the potential use of membranes for carbon capture, a polymer membrane having a CO2 permeability of 1000 GPU and a CO2 / N2 separation factor of 50 can be used as a model membrane. Polymer membranes having such characteristics are currently commercially available. For example, several membranes are available from Membrane Technology and Research of Newark, CA. Table 9 shows the effect of the membrane feed CO2 concentration on the permeate CO2 concentration when using membranes having these characteristics. As shown in Table 9, at a combustion exhaust gas concentration of 16% CO2, a permeate stream containing more than 90% by volume of CO2 can be generated using a membrane having the above characteristics. It should be noted that if higher purity is required, a second membrane stage may be used, or the membrane may be combined with another capture unit, such as a PSA.

Table 9

[0108] To further illustrate the potential benefits of using membranes, an NGCC power plant with 354 MW of net power and an MEA amine scrubber can be used as a base case. This corresponds to the same base case used in Example 3 above. To enable comparative calculations, membranes can be used for CO2 in an NGCC system that uses oxygen enhanced combustion and flue gas recirculation to form combustion flue gas containing 25 volume % CO2. Based on these assumptions, Figure 6 shows the maximum membrane area required and the effect of feed pressure on the feed compressor duty to achieve capture of 90 volume % of the CO2 in the combustion flue gas as part of the permeate. (The arrows in Figure 6 indicate the relevant vertical axis for each data plot.) As shown in Figure 6, there is a trade-off between membrane area and compressor duty. Figure 6 shows the maximum membrane area required if all of the combustion flue gas from the power plant is sent to the membrane and it should be noted that in practice a lower membrane area is required. The exact amount of membrane area required depends on the amount of flue gas recirculation. In particular, with selective flue gas recirculation, a substantially lower membrane area may be sufficient.

[0109] Using membranes can be advantageous for reducing or minimizing the amount of energy debit that occurs in the implementation of CO2 capture. As shown in Example 3, using a combination of oxygen-enriched combustion and exhaust gas recirculation can reduce the amount of combustion exhaust gas for treatment by more than 70% compared to a base case that has air as the oxygen-containing gas and no exhaust gas recirculation. Based on reducing the combustion exhaust gas flow rate by 70%, the amount of energy required to separate CO2 using a membrane can be calculated under representative conditions. For example, for a combustion exhaust gas flow rate reduced by 70%, a membrane feed (i.e., combustion exhaust gas) pressure of 150 kPa-a, a membrane feed temperature of 50 °C, and a pressure of 10 kPa-a on the permeate side of the membrane, the energy penalty for performing CO2 separation using the membrane is about 13 MW for the compressor and vacuum pump, and 14.4 MW for the combustion exhaust gas cooler. This is a total energy debit of 27.4 MW compared to 69.9 MW for the base case of using an amine scrubber for CO2 capture in a system that has no exhaust gas recirculation and uses air as the oxygen source. In fact, the energy debit for the membrane is lower than the energy debit (31.1 MW) from the case in Example 3 where the oxygen-containing gas contains 30 vol% O2 and exhaust gas recirculation is used together with an amine scrubber.

[0110] The membrane area required is 141,900 m 2 and even assuming a plate-and-frame membrane with the lowest surface area to volume ratio (and also the lowest pressure drop), the volume of the membrane unit is about 2400 m 3 . Alternatively, spiral-wound membranes reduce the volume of the membrane unit by an order of magnitude. Based on previous calculations, a commercial amine scrubber (e.g., MHI process) has a productivity of 7.7 kg of CO2 / h / m 3 . If OEC and EGR are not performed, the volume requirements for this process are 15,800 m 3 which is 6.6 times the volume footprint of the plate-and-frame membrane unit.

[0111] Example 5 - Additional Performance and Energy Evaluation To evaluate the cost - effectiveness in O2 enrichment using the vacuum pressure swing adsorption process in Table 2, four cases were simulated for performance, capital, and energy estimation. Case I uses a conventional CMS adsorbent and has a vacuum of 0.1 bar. Cases II, III, and IV use zeolite ITQ - 55 and have vacuum pressures of 0.1 bar, 0.2 bar, and 0.3 bar, respectively. Since the CMS adsorbent cannot provide the required performance at a low vacuum above 0.1 bar, CMS is shown for only one case with a vacuum of 0.1 bar. ITQ - 55 shows good tunability at low vacuum and achieves the required separation performance.

[0112] The throughput was set for a small - scale NGCC of 100 kTA of CO2, which requires that approximately 1000 tons / day of 40% oxygen - enriched gas be fed to the gas turbine. The calculations are based on typical assumptions that for a 727 MW NGCC, the total combustion exhaust gas flow rate is 138,406 kmol / h and the CO2 concentration is 4.08%. For 90% CO2 capture on a 100 kTA basis, the NGCC power is approximately 37 MW. Based on the calculations in the examples, a 350 MW NGCC requires 10,000 TPD (tons per day) of 40% O2 - enriched air. Thus, a 37 MW gas turbine requires an oxygen - enriched feed at approximately 40% of 1000 TPD assuming a linear scale.

[0113] For these four cases, the main power consumption for compressors and pumps was estimated on an annual basis (assuming 300 days / year of operation). Details of performance and energy consumption are summarized in Table 3. Note that co - produced N2 with a purity of over 97% is also formed and oxygen is enriched to 40% from the blow - down stream. The cycle was adjusted to have a high oxygen recovery.

Table 10

[0114] Additional Embodiments Embodiment 1. A method for operating a power generation process, comprising separating air using a pressure swing adsorption process to form a nitrogen-containing stream comprising at least 95% by volume of N2 and an oxygen-containing stream comprising 25% to 48% by volume of O2; combusting a fuel in a combustion chamber of a turbine in the presence of a recycle stream with O2 from at least a portion of the oxygen-containing stream to form combustion exhaust gas, wherein the O2 from at least a portion of the oxygen-containing stream constitutes 16% to 35% by volume of the combined volume of i) the fuel, ii) at least a portion of the oxygen-containing stream, and iii) the recycle stream, and the combustion exhaust gas contains at least 12% by volume of CO2; forming a recycle stream from one or more portions of the combustion exhaust gas; performing post-combustion capture on at least a portion of the combustion exhaust gas to form a CO2-containing product stream and one or more CO2-depleted combustion exhaust gas streams, wherein the one or more CO2-depleted combustion exhaust gas streams contain CO2 from at least a portion of the combustion exhaust gas at 30% by volume or less.

[0115] Embodiment 2. The method according to Embodiment 1, wherein the pressure swing adsorption process comprises at least one process step performed at a pressure of 90 kPa-a or less.

[0116] Embodiment 3. The method according to any of the above embodiments, wherein the oxygen-containing stream contains at least 35% by volume of O2, or the oxygen-containing stream further contains at least 50% by volume of N2, or a combination thereof.

[0117] Embodiment 4. The pressure swing adsorption process exposes air to an adsorbent including the kinetic selectivity for O2 over N2 at a pressure of 200 kPa-a to 800 kPa-a in an adsorbent environment to form an adsorption effluent including a nitrogen-containing stream, discharges the blowdown effluent from the adsorbent environment, purges the adsorbent environment with at least a portion of the blowdown effluent to form an oxygen-containing stream, and purges the adsorbent environment with a portion of the adsorption effluent, wherein the adsorbent having the kinetic selectivity for O2 over N2 optionally includes at least one of a carbon molecular sieve and ITQ-55. The method according to any one of the above embodiments.

[0118] Embodiment 5. The method according to Embodiment 4, wherein the blowdown effluent is discharged from the same end of the adsorbent environment as the adsorption effluent.

[0119] Embodiment 6. The pressure swing adsorption process is performed in a plurality of adsorbent environments, and the pressure swing adsorption process further includes equalizing the pressure of the first adsorbent environment after exposing air to the first adsorbent with the pressure of the second adsorbent environment after purging the second adsorbent environment with a portion of the adsorption effluent. The method according to Embodiment 4 or 5.

[0120] Embodiment 7. The method according to any one of the above embodiments, wherein the recycle stream is mixed with the oxygen-containing stream and then enters a combustion chamber, or the recycle stream is at a pressure of 90 kPa-a to 115 kPa-a when mixed with the oxygen-containing stream, or a combination thereof.

[0121] Embodiment 8. (i) The combustion exhaust gas includes a CO2 content of 16% by volume or more, (ii) the CO2-containing stream includes 90% by volume or more of CO2, (iii) the CO2-containing stream includes at least 80% by volume of CO2 from at least a portion of the combustion exhaust gas, or (iv) a combination of two or more of (i), (ii), and (iii). The method according to any one of the above embodiments.

[0122] Embodiment 9. The method according to any one of the above embodiments, wherein forming the recycle stream from one or more portions of the combustion exhaust gas includes forming the recycle stream from a CO2-containing stream.

[0123] Embodiment 10. The method according to any one of the above embodiments, wherein performing post-combustion capture on at least a portion of the combustion exhaust gas includes separating at least a portion of the combustion exhaust gas using a membrane separator, an amine scrubber, a liquid phase adsorbent in which the liquid is at least partially in the form of liquid droplets or a liquid thin film, or a combination thereof.

[0124] Embodiment 11. The method according to any one of Embodiments 1 to 9, wherein performing post-combustion capture on at least a portion of the combustion exhaust gas includes exposing at least a portion of the combustion exhaust gas to a solid adsorbent to adsorb CO2 onto the solid adsorbent, and desorbing at least a portion of the adsorbed CO2 by direct displacement, pressure swing, temperature swing, or a combination thereof.

[0125] Embodiment 12. The method according to any one of Embodiments 1 to 9, wherein performing post-combustion capture on at least a portion of the combustion exhaust gas includes forming a cathode input stream including at least a portion of the combustion exhaust gas, passing the cathode input stream into the cathode of a molten carbonate fuel cell, and operating the molten carbonate fuel cell to generate electric power, an anode output stream, and a cathode output stream corresponding to a CO2-depleted stream.

[0126] Embodiment 13. The method according to any one of the above embodiments, further comprising passing at least a portion of the combustion exhaust gas through a heat recovery steam generator to generate electric power and then separating at least a portion of the combustion exhaust gas, or the method further comprising adding fuel to at least a portion of the combustion exhaust gas, performing supplementary combustion on at least a portion of the combustion exhaust gas, and then performing post-combustion capture on at least a portion of the combustion exhaust gas, or a combination thereof.

[0127] Embodiment 14. A system for generating electricity, comprising: a swing adsorption stage including a plurality of swing adsorption vessels containing an adsorbent having a kinetic selectivity for O2 with respect to N2, the swing adsorption stage having an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet; a compressor, a combustion chamber, an expander, and a turbine having a shaft coupling the expander to the compressor, the combustion chamber having a combustion outlet and one or more combustion inlets, the one or more combustion inlets being in fluid communication with a fuel source and the oxygen-containing product outlet; a supplementary combustor having a supplementary fuel inlet, a combustion exhaust gas inlet in fluid communication with the combustion outlet, and a supplementary combustion outlet; a heat recovery steam generator having a heat recovery inlet in fluid communication with the supplementary combustion outlet and a heat recovery outlet; and a post-combustion capture stage having a capture inlet in fluid communication with the heat recovery outlet, a CO2-containing product outlet, and one or more CO2-depleted stream outlets, the post-combustion capture stage comprising one or more amine scrubbers, one or more adsorbent environments containing a solid adsorbent, one or more adsorbent environments containing a liquid adsorbent, or a combination thereof, the one or more combustion inlets being in further fluid communication with at least one of the heat recovery outlet and the CO2-containing product outlet.

[0128] Embodiment 15. A system for generating electricity, comprising a swing adsorption stage including a plurality of swing adsorption vessels containing an adsorbent having a kinetic selectivity for O2 with respect to N2, the swing adsorption stage having an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet; a turbine including a compressor, a combustion chamber, an expander, and a shaft coupling the expander to the compressor, the combustion chamber having a combustion outlet and one or more combustion inlets, the one or more combustion inlets being in fluid communication with a fuel source and the oxygen-containing product outlet; a heat recovery steam generator having a heat recovery inlet in fluid communication with the combustion outlet and a heat recovery outlet; and a post-combustion capture stage having a capture inlet in fluid communication with the heat recovery outlet, a CO2-containing product outlet, and one or more CO2-depleted stream outlets, the post-combustion capture stage including one or more membrane separators, one or more molten carbonate fuel cells, or a combination thereof, the one or more combustion inlets being in further fluid communication with at least one of the heat recovery outlet and the CO2-containing product outlet.

[0129] Additional Embodiment A. The method according to any one of Embodiments 1 to 13, wherein air is separated using a pressure swing adsorption process, the process including a kinetic separation process.

[0130] Additional Embodiment B. The method according to any one of Embodiments 1 to 13, wherein the fuel includes natural gas.

[0131] Additional Embodiment C. The method according to any one of Embodiments 1 to 13, wherein the turbine includes a compressor, a combustion chamber, an expander, and a shaft coupling the expander to the compressor.

[0132] The present invention has been described and illustrated with reference to specific embodiments, but it will be understood by those skilled in the art that the present invention may be subject to variations not necessarily described herein. For this reason, only the appended claims should be referred to for the purpose of determining the true scope of the present invention.

Claims

1. A method for operating a power generation process, comprising separating air using a pressure swing adsorption process to form a nitrogen-containing stream comprising 95% by volume or more of N ２ and an oxygen-containing stream comprising 25% to 48% by volume of O ２ combusting a fuel in a combustion chamber of a turbine in the presence of a recirculation stream with O ２ from at least a portion of the oxygen-containing stream to form combustion exhaust gas, wherein the O ２ from at least a portion of the oxygen-containing stream constitutes 16% to 35% by volume of the combined volume of i) the fuel, ii) at least a portion of the oxygen-containing stream, and iii) the recirculation stream, and the combustion exhaust gas comprises 12% by volume or more of CO ２ forming the recirculation stream from one or more portions of the combustion exhaust gas; performing post-combustion capture on at least a portion of the combustion exhaust gas to form a CO ２ -containing product stream and one or more CO ２ -depleted combustion exhaust gas streams, wherein the one or more CO ２ -depleted combustion exhaust gas streams contain CO ２ from at least a portion of the combustion exhaust gas at 30% by volume or less. A method comprising the above steps.

2. The method according to claim 1, wherein the pressure swing adsorption process comprises at least one process step carried out at a pressure of 90 kPa-a or less.

3. wherein the oxygen-containing stream contains 35% by volume or more of O ２ or the oxygen-containing stream further contains 50% by volume or more of N ２ or a combination thereof, the method according to any one of the preceding claims.

4. wherein the pressure swing adsorption process exposes air to an adsorbent comprising kinetic selectivity for O with respect to N at a pressure of 200 kPa-a to 800 kPa-a in an adsorbent environment to form an adsorption effluent comprising the nitrogen-containing stream, discharging a blowdown effluent from the adsorbent environment, purging the adsorbent environment with at least a portion of the blowdown effluent to form the oxygen-containing stream, and purging the adsorbent environment with a portion of the adsorption effluent, wherein the adsorbent having kinetic selectivity for O with respect to N optionally comprises at least one of a carbon molecular sieve and ITQ-55. ２ for O ２ with respect to N, and the method according to any one of the preceding claims, comprising: ２ for O ２ with respect to N, and purging, wherein the adsorbent having kinetic selectivity for O with respect to N optionally comprises at least one of a carbon molecular sieve and ITQ-55.

5. The method according to claim 4, wherein the blowdown effluent is discharged from the same end of the adsorbent environment as the adsorption effluent.

6. The pressure swing adsorption process is carried out in a plurality of adsorbent environments, and the pressure swing adsorption process further comprises equalizing the pressure of a first adsorbent environment after exposing air to a first adsorbent with the pressure of a second adsorbent environment after purging the second adsorbent environment with a portion of the adsorption effluent. The method according to claim 4 or 5.

7. The method according to any one of the preceding claims, wherein the recycle stream is mixed with the oxygen-containing stream and then enters the combustion chamber, or the recycle stream is at a pressure of 90 kPa-a to 115 kPa-a when mixed with the oxygen-containing stream, or a combination thereof.

8. i) the combustion exhaust gas contains a CO content of 16% by volume or more, or ii) the CO-containing stream contains 90% by volume or more of CO, or iii) the CO-containing stream contains 80% by volume or more of the CO from at least a portion of the combustion exhaust gas, or iv) is a combination of two or more of i), ii), and iii), the method according to any one of the preceding claims. ２ contains, or ii) the CO ２ containing stream contains 90% by volume or more of CO ２ or iii) the CO ２ containing stream contains 80% by volume or more of the CO from at least a portion of the combustion exhaust gas, or ２ is a combination of two or more of i), ii), and iii), the method according to any one of the preceding claims.

9. Forming the recirculation flow from one or more portions of the combustion exhaust gas, the recirculation flow being the CO ２ The method according to any one of the preceding claims, including forming from the containing flow.

10. Performing post-combustion capture on at least a portion of the combustion exhaust gas comprises separating at least a portion of the combustion exhaust gas using a membrane separator, an amine scrubber, a liquid-phase adsorbent in which the liquid is at least partially in the form of liquid droplets or a liquid thin film, or a combination thereof. The method according to any one of the preceding claims.

11. Performing post-combustion capture on at least a portion of the combustion exhaust gas includes exposing at least a portion of the combustion exhaust gas to a solid adsorbent to adsorb CO ２ onto the solid adsorbent, and desorbing at least a portion of the adsorbed CO ２ by direct displacement, pressure swing, temperature swing, or a combination thereof, according to any one of claims 1 to 9.

12. Performing post-combustion capture on at least a portion of the combustion exhaust gas includes forming a cathode input stream including at least a portion of the combustion exhaust gas, passing the cathode input stream into a cathode of a molten carbonate fuel cell, operating the molten carbonate fuel cell to generate power, an anode output stream, and CO ２ generating a cathode output stream corresponding to the depleted stream, and the method according to any one of claims 1 to 9.

13. The method further comprises passing at least a portion of the combustion exhaust gas through a heat recovery steam generator to generate power and then separating at least a portion of the combustion exhaust gas, or the method further comprises adding fuel to at least a portion of the combustion exhaust gas and performing supplementary combustion on at least a portion of the combustion exhaust gas and then performing post-combustion capture on at least a portion of the combustion exhaust gas, or a combination thereof. The method according to any one of the preceding claims.

14. A system for generating electricity, comprising N ２ An adsorption swing stage comprising a plurality of adsorption swing containers containing an adsorbent having kinetic selectivity for O with respect to N ２ The adsorption swing stage has an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet; a turbine comprising a compressor, a combustion chamber, an expander, and a shaft coupling the expander to the compressor, wherein the combustion chamber has a combustion outlet and one or more combustion inlets, and the one or more combustion inlets are in fluid communication with a fuel source and the oxygen-containing product outlet; a supplementary combustor having a supplementary fuel inlet, a combustion exhaust gas inlet in fluid communication with the combustion outlet, and a supplementary combustion outlet; a heat recovery steam generator having a heat recovery inlet in fluid communication with the supplementary combustion outlet and a heat recovery outlet; and a post-combustion capture stage having a capture inlet in fluid communication with the heat recovery outlet, a CO ２ -containing product outlet, and one or more CO ２ exhaust flow outlets, wherein the post-combustion capture stage comprises one or more amine scrubbers, one or more adsorbent environments containing a solid adsorbent, one or more adsorbent environments containing a liquid adsorbent, or combinations thereof, and the one or more combustion inlets are further in fluid communication with at least one of the heat recovery outlet and the CO ２ -containing product outlet; a system.

15. A system for generating electrical power comprising: ２ O ２ a swing adsorption stage comprising a plurality of swing adsorption vessels containing an adsorbent having a kinetic selectivity for CO, the swing adsorption stage comprising an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet; a turbine comprising a compressor, a combustion chamber, an expander, and a shaft coupling the expander to the compressor, the combustion chamber comprising a combustion outlet and one or more combustion inlets, the one or more combustion inlets being in fluid communication with a fuel source and the oxygen-containing product outlet; a heat recovery steam generator comprising a heat recovery inlet in fluid communication with the combustion outlet, and a heat recovery outlet; a capture inlet in fluid communication with the heat recovery outlet; ２ a product outlet, and one or more CO ２ a post-combustion capture stage comprising one or more membrane separators, one or more molten carbonate fuel cells, or a combination thereof, the one or more combustion inlets being connected to the heat recovery outlet and the CO ２ a post-combustion capture stage further in fluid communication with at least one of the contained product outlets.

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