Oxygen-enriched combustion for natural gas combined cycle operation

Abstract

Systems and methods for operating a combined cycle power plant while increasing the CO2 content in the flue gas produced by the power plant are provided. The CO2 content is increased by using a combination of exhaust gas recirculation and oxygen-enriched combustion. The oxygen-containing gas stream used to conduct the oxygen-enriched combustion can be produced by an integrated pressure swing adsorption process that allows the production of a commercial grade nitrogen gas stream (95 vol% or higher N2) while also providing an oxygen-containing gas stream with an oxygen content of between 25 vol% and 48 vol% as well as a higher O2 recovery.

Description

Technical Field

[0001] The present invention relates to a system and method for operating a combined cycle power plant using oxy-combustion to provide a flue gas having an elevated CO2 content. Background Art

[0002] Combined cycle power plants offer an efficient way to generate electricity by burning petroleum products or other carbon-based fuels. Combined cycle power plants can use the initial combustion reaction to power multiple turbines to generate electricity, thereby increasing power generation efficiency. However, conventional CO2 capture methods tend to reduce power generation efficiency because additional energy is required to capture and / or store the CO2.

[0003] One of the difficulties in capturing CO2 from flue gas for natural gas combined cycle (NGCC) power plants is the relatively low concentration of CO2 in the flue gas. For natural gas combustion using air as an oxygen source, the typical concentration of CO2 in the flue gas is between 4.0 vol% and 6.0 vol%. Partly due to the relatively low concentration of CO2, a large amount of additional energy is required to capture CO2 from the flue gas at an efficiency of 90% or more. In addition, because CO2 is dilute, a large amount of gas must be processed, resulting in higher capital equipment costs and / or a larger equipment footprint in order to effectively process the required amount of flue gas. It is desirable to have an improved method for capturing CO2 from flue gas while reducing or minimizing the power consumption and / or other costs required for CO2 capture.

[0004] US Patents 9,903,316 and 10,677,160 describe the operation of a natural gas combined cycle power plant with oxygen-enriched air as the oxygen source for combustion and pressurized exhaust gas recirculation. The flue gas produced is described as containing elevated amounts 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 performed on carbon molecular sieves to determine equilibrium and kinetic parameters.

[0006] Sircar et al. (Fractionation of Air by Zeolites), in: A., ed., Surface Science and Catalysis Research (Stud Surf Sci Catal: Elsevier; 1999, pp. 395-423) describes various pressure swing adsorption processes using zeolites to separate air. Some processes are described that can produce O2 streams and N2 streams with purities of 90% or more. In general, no process is described that produces a first stream containing 95 vol% or more N2 and a second stream containing 25 vol% to 48 vol% O2.

[0007] The journal article by Hassan et al. describes the production of a high purity N2 stream by separating air. (Chemical Engineering Science, Vol. 42, No. 8, p. 2037 (1987)) No information is provided regarding the O2 concentration in the second stream produced by the process. It should be noted that the process cycle described in the article achieves pressure balance by connecting the two ends of the adsorbent environment to each other.

[0008] The journal article by Shirley et al. describes the production of a high purity N2 stream by separating air. (Adsorption, Vol. 8, p. 147 (2002)) No information is provided regarding the O2 concentration 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 gas stream containing 95 vol% or more N2 and an oxygen-containing gas stream containing 25 vol% to 48 vol% O2. The method further includes burning a fuel with O2 from at least a portion of the oxygen-containing gas stream in the presence of a recycle stream in a combustion chamber of a turbine to form a flue gas. Optionally, the O2 from at least a portion of the oxygen-containing gas stream may correspond to 16 vol% to 35 vol% of the combined volume of the fuel, the at least a portion of the oxygen-containing gas stream, and the recycle stream. Optionally, the flue gas may contain 12 vol% or more CO2. The method further includes forming the recycle stream from one or more portions of the flue gas. In addition, the method includes post-combustion capture of at least a portion of the flue gas to form a CO2-containing product stream and one or more CO2-depleted flue gas streams. The one or more CO2-depleted flue gas streams may contain 30 vol% or less CO2 from at least a portion of the flue gas. Additionally or alternatively, the CO2-containing product stream may contain 70 vol% or more CO2 from the at least a portion of the flue gas.

[0010] In another aspect, a system for power generation is provided. The system includes a pressure swing adsorption stage corresponding to a plurality of pressure swing adsorption vessels containing an adsorbent having a kinetic selectivity for O2 relative to N2. The pressure swing adsorption stage may have an air inlet, a nitrogen-containing product outlet, and an oxygen-containing product outlet. The system further includes a turbine, which includes a compressor, a combustion chamber, an expander, and a shaft connecting the expander to the compressor. The combustion chamber may include a combustion outlet and one or more combustion inlets. The one or more combustion inlets may be in fluid communication with a fuel source and the oxygen-containing product outlet. Optionally, the system may further include a supplementary burner having a supplementary fuel inlet, a flue gas inlet in fluid communication with the combustion outlet, and a supplementary combustion outlet. The system may 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. In addition, the system may include a post-combustion capture stage. The post-combustion capture stage may 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 may include one or more amine scrubbers, one or more adsorbent environments containing solid adsorbents, one or more adsorbent environments containing liquid adsorbents, or a combination thereof. In other aspects, the post-combustion capture stage may include one or more membrane separators, one or more molten carbonate fuel cells, or a combination thereof. The one or more combustion inlets may 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

[0011] Figure 1 A portion of a process cycle using a dual bed system to separate air to form a nitrogen-containing gas stream and an oxygen-containing gas stream having target purity values ​​is shown.

[0012] Figure 2 Another portion of a process cycle is shown using a dual bed system to separate air to form a nitrogen-containing gas stream and an oxygen-containing gas stream having target purity values.

[0013] Figure 3 An example of a configuration of a combined cycle power plant using oxyfuel combustion and exhaust gas recirculation is shown.

[0014] Figure 4 An example of a configuration of a combined cycle power plant is shown, using oxy-combustion, selective exhaust gas recirculation and a membrane stage for separating CO 2 from the flue gases.

[0015] Figure 5 A model configuration of an amine scrubber is shown.

[0016] Figure 6The relationship between membrane size and compressor load for separation of CO2 from flue gas under a representative set of conditions is shown.

[0017] Figure 7 Another process cycle is shown that uses a dual bed system to separate air to form a nitrogen-containing gas stream and an oxygen-containing gas stream having target purity values. DETAILED DESCRIPTION

[0018] All numerical values ​​in the detailed description and claims herein are modified by the indication of "about" or "approximately", and take into account experimental error and variations that would be expected by a person of ordinary skill in the art.

[0019] Overview

[0020] In various aspects, a system and method for operating a combined cycle power plant while increasing the CO2 content in the flue gas produced by the power plant is provided. The CO2 content is increased by using a combination of exhaust gas recirculation and oxygen-enriched combustion. When operating a natural gas combined cycle power plant, this allows the formation of flue gas with a CO2 content between 12vol% and 30vol%, or between 15vol% and 30vol%, or between 20vol% and 30vol%. More generally, depending on the nature of the combustion reaction, a combination of exhaust gas recirculation and oxygen-enriched combustion can allow the formation of flue gas with a CO2 content of 12vol% or higher, or 15vol% or higher, or 20vol% or higher, or 25vol% or higher, or 30vol% or higher, such as up to 50vol% or possibly higher. The oxygen-containing gas stream for oxygen-enriched combustion can be produced by an integrated pressure swing adsorption process, which allows the production of a commercial grade nitrogen stream (95vol% or higher N2), while also providing an oxygen-containing gas stream with an oxygen content between 25vol% and 48vol% or between 30vol% and 48vol% and a higher O2 recovery rate. By increasing the CO2 content of the flue gas, all power generation stages of the combined cycle power plant can be maintained while still producing a flue gas with a sufficiently high CO2 content to enhance, improve and / or increase the efficiency of post-combustion CO2 capture.

[0021] Conventionally, one of the difficulties in post-combustion CO2 capture from flue gas produced by commercial-scale power plants is that the CO2 content in the flue gas is relatively low. For example, since the CO2 content in typical flue gas from natural gas power plants is only 4.0vol% to 6.0vol%, commercial-scale options for capturing this CO2 are limited. Currently, the main option for capturing CO2 from flue gas is to use an amine scrubber, in which the CO2 is adsorbed by an aqueous amine solution. While this method is effective, the cost of operating such an amine scrubber is high due to the large amount of flue gas that needs to be processed. These costs include capital equipment costs and operating costs for heating and managing the fluid streams involved in the amine scrubber.

[0022] There are several options for increasing the CO2 content in the flue gas from a power plant based on the combustion of hydrocarbon-containing fuels (e.g., a natural gas power plant). One option is to use exhaust gas recirculation to increase the CO2 concentration of the combustion process input stream. Another option is to reduce the nitrogen content of the oxygen-containing gas stream entering the combustion process.

[0023] Exhaust gas recirculation alone can increase the CO2 content of the flue gas produced by the combustion reaction. However, the amount of exhaust gas recirculation that can be performed is limited. For example, when air is used as the oxygen source for combustion, the initial O2 content in the air is close to 21 vol%. This O2 content is slightly diluted when the fuel is introduced into the combustion chamber. Increasing exhaust gas recirculation will further dilute the O2 concentration. In order to maintain flame speed and / or other desired combustion characteristics, it is desirable to maintain an O2 concentration of 16 vol% or higher in the combustion chamber. This limits the total amount of exhaust gas that can be recirculated while still maintaining a sufficient O2 concentration.

[0024] There is also a practical upper limit to the oxygen concentration in the combustion chamber. Specifically, as the oxygen concentration increases, the flame speed and / or other combustion characteristics may cause the temperature in the combustion chamber to increase. It is desirable to maintain the O2 concentration in the combustion chamber at 35 vol% or less. This keeps the combustion temperature low enough so that conventional metallurgy can be used, and thus the process can be used in power plants that have been built using such conventional metallurgy.

[0025] Based on the above limitations, it is expected that the oxygen concentration of the combustion environment is between 16vol% and 35vol%, while also increasing the CO2 content in the flue gas. In order to achieve this goal, it is expected that the oxygen content of the oxygen-containing gas stream used for combustion is 25vol% to 48vol%, or 30vol% to 48vol%, or 35vol% to 48vol%, or 40vol% to 48vol%, so that after being diluted by the fuel and the exhaust gas recirculation flow, a target oxygen concentration of 16vol% to 35vol% can be achieved. Unfortunately, it is costly and / or inefficient to use conventional methods to achieve such oxygen concentrations. Part of the reason is that it is difficult to produce a nitrogen byproduct with commercial value while producing an oxygen-containing gas stream with an oxygen content of 25vol% to 48vol%. For example, cryogenic air separation can simultaneously form a high-purity nitrogen stream and a high-purity oxygen stream. However, cryogenic separation systems require a large amount of additional costs and specialized equipment. In addition, the high-purity oxygen stream produced will need to be diluted to achieve an oxygen content of 25vol% to 48vol%.

[0026] In various aspects, systems and methods are provided that can allow the operation of a combustion-based power plant using both exhaust gas recirculation and oxyfuel combustion while reducing or minimizing efficiency losses and / or reducing or minimizing additional costs for equipment replacement for core power plant operations. This is achieved by integrating the power plant combustion process with an oxyfuel process that can produce a nitrogen stream with a purity greater than 95 vol% and an oxygen stream with a purity of 25 vol% to 48 vol%. By producing a nitrogen stream with a purity of 95 vol% or more and an oxygen stream containing 25 vol% to 48 vol% oxygen, both streams from the process of producing an oxygen-containing gas stream can be used for further processes. This is in contrast to conventional methods of producing a pure oxygen gas stream product and then diluting it to produce oxygen-enriched air containing 25 vol% to 48 vol% oxygen, which conventional methods involve: a) a large amount of additional cost and equipment for performing cryogenic air separation followed by dilution of the oxygen stream, or b) a large amount of additional cost and equipment for vacuum pressure swing air separation with cationic zeolites to produce an O2 product, wherein the nitrogen byproduct stream produced essentially corresponds to a waste stream due to insufficient purity. It should be noted that vacuum pressure swing air separation using cationic zeolites also requires an additional dehydration step to remove water so that the cationic zeolites can perform N2-O2 separation while both the thermodynamic and kinetic adsorption properties for air separation can function properly.

[0027] By operating a power plant that uses both exhaust gas recirculation and oxyfuel combustion, there may be additional options for post-combustion CO2 capture from the flue gas stream produced. In some aspects, the increase in CO2 concentration in the flue gas may allow the size of the amine scrubber to be reduced or minimized, thereby reducing equipment costs and operating costs. In other aspects, the increase in CO2 concentration in the flue gas may enable the use of other types of CO2 post-combustion capture technologies, such as separation using membrane separation, separation using a fuel cell (e.g., a molten carbonate fuel cell), or direct displacement.

[0028] For the use of amine scrubbers, the use of both exhaust gas recirculation and oxygen-enriched combustion can greatly reduce the total amount of flue gas treated by the amine plant. The reduction in flue gas volume is caused by a variety of factors. First, the amount of oxygen-containing gas delivered to the combustion reaction is selected based on the target ratio of fuel to O2 in the combustion chamber. In other words, the amount of oxygen-containing gas flow is selected using the flow rate of O2 entering the combustion chamber, rather than the total gas flow rate of the oxygen-containing gas flow. The higher the O2 content in the oxygen-containing gas, the less total gas flow can be delivered to the combustion chamber, while still providing the same O2 gas flow rate required to achieve the target ratio of fuel to O2. Increasing the O2 content of the oxygen-containing gas flow to between 25vol% and 48vol% is equivalent to increasing the O2 content of the oxygen-containing gas relative to air by about 1.5 to 2.5 times. Therefore, the amount of oxygen-containing gas delivered to the combustion chamber can be reduced by a similar multiple. The amount of N2 diluent in the oxygen-containing gas is also reduced. It should be noted that any reduction in N2 in the gas stream corresponds to a reduction in the amount of N2 that must be separated from CO2 for carbon capture. By using oxy-combustion, the amount of flue gas that must be treated by the carbon capture system can be reduced by 40 vol% to 70 vol% (or potentially more) relative to the amount of flue gas treated when using air as the oxygen-containing gas.

[0029] It should be noted that by increasing the oxygen content in the combustion zone, the flue gas produced may also have an increased oxygen concentration. In aspects using an amine scrubber as a post-combustion capture process, this increased oxygen concentration may result in increased degradation of the amines, since some types of amines are susceptible to oxidative degradation at sufficiently high temperatures in the presence of sufficient amounts of oxygen. In some aspects, the oxygen concentration of the flue gas may be reduced by using a duct burner. For example, a duct burner may be located before a heat recovery steam generator (HRSG) in a combined cycle power plant.

[0030] Another difficulty with amine scrubbers, as opposed to other options, is the relatively high energy cost per CO2 molecule captured. After CO2 capture with an amine scrubber, the aqueous amine solution must be regenerated, for example by using a thermal regeneration cycle. Increasing the CO2 concentration of the flue gas can reduce this cost by reducing the amount of aqueous amine solution required, but there is a thermodynamic limit to the amount of energy reduction that can be achieved while still regenerating the aqueous amine solution.

[0031] In the aspect that the CO2 content of flue gas / other gases for post-combustion capture is 12 vol% or higher, or 15 vol% or higher, or 20 vol% or higher, an alternative to using an aqueous amine solution may be to use a membrane separation method. Membrane systems are commercially available (e.g., polymer membranes) that can provide a separation factor of about 50 to separate CO2 from N2. Combined with the use of reduced pressure on the permeate side / pressurization on the retentate side to provide a driving force, such membranes can be used to separate flue gas with a CO2 content of 12 vol% or higher to produce a permeate flow. By using membrane separation for CO2 capture, the thermal cost of regenerating the adsorbent can be avoided, and replaced by the lower cost of maintaining the pressure difference on both sides of the membrane. In addition to direct cost savings by avoiding the need for heating and cooling, such thermal costs may include (but are not limited to) avoiding the need for a stripper / reboiler unit, avoiding the need for an additional heat exchanger, avoiding any emissions associated with the generation of heat, and avoiding losses generated when heating and cooling various fluids for heat exchange.

[0032] A membrane separator is an example of a post-combustion capture stage. More generally, there are a variety of post-combustion capture options that can be used to treat flue gas containing CO2, such as exhaust gas from a combustion chamber of a turbine. In various aspects, the post-combustion capture stage can separate the flue gas (or a portion thereof) to form one or more CO2-depleted streams and at least one CO2-containing stream. The CO2-containing stream may contain 70 vol% or more CO2, or 80 vol% or more, or 90 vol% or more, for example, up to substantially entirely composed of CO2. In some aspects, such a CO2-containing stream may correspond to 70 vol% or more, or 80 vol% or more, or 90 vol% or more (e.g., up to 100 vol% of the CO2 present in the combustion exhaust gas) of the CO2 present in the combustion exhaust gas. In addition or alternatively, the recovery of CO2 by the post-combustion process can also be characterized based on the relative amount of CO2 that leaves 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 flue gas. It should be noted that if there is a supplemental combustion device (e.g., a duct burner) located downstream of the combustion chamber to reduce the oxygen content of the flue gas, then the comparison of one or more CO2-depleted streams and / or CO2-containing streams to the flue gas can be made based on the composition of the combustion exhaust gas after passing through the supplemental combustion device. In some aspects, the CO2 content of one or more CO2-depleted streams can correspond to 30 vol% or less, or 20 vol% or less, or 10 vol% or less, or 5.0 vol% or less, or 2.0 vol% or less, or 1.0 vol% or less of the CO2 present in the exhaust gas from the combustion chamber (after any optional duct burners), for example, as low as 0.1 vol% (or possibly lower) of the CO2 present in the flue gas.

[0033] A CO2 content of 15 vol% or more, or 20 vol% or more, or 25 vol% or more in the flue gas can be achieved by using oxygen-enriched combustion, wherein the O2 content of the oxygen-containing gas is 35 vol% or more, or 40 vol% or more. Additionally or alternatively, such a CO2 content in the flue gas can be achieved by using selective exhaust gas recirculation, wherein the CO2 content of the exhaust gas recirculation stream is 70 vol% or more, or 80 vol% or more, or 90 vol% 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 capturing CO2 from the flue gas. Further additionally or alternatively, in some aspects, a supplementary combustion stage (e.g., a duct burner) can be used to reduce the O2 content of the flue gas and increase the CO2 content.

[0034] In this discussion, post-combustion capture is defined as one or more separation processes that separate an input gas stream containing CO2 (e.g., combustion exhaust) into one or more CO2-depleted streams and at least one CO2-containing product stream. A CO2-depleted stream is defined as an output stream having a volume percentage of CO2 that is lower than the CO2 content of the input gas stream containing CO2. A CO2-containing product stream is defined as an output stream having a volume percentage of CO2 that is higher than the CO2 content of the input gas stream containing CO2. It should be noted that some post-combustion capture processes, such as molten carbonate fuel cells, may have multiple input streams. For molten carbonate fuel cells, the total cathode input flow is used to determine whether the output stream corresponds to a CO2-depleted stream or a CO2-containing product stream.

[0035] As another benefit, it should be noted that since both the N2 stream and the O2 stream produced by the oxygen-enriched process can be used, most of the cost of carrying out the oxygen-enriched process can be offset. Traditionally, air separation units are designed to produce N2 streams or O2 streams, and any other stream from the process corresponds to a waste stream that is actually worthless. In contrast, for the oxygen-enriched process described herein integrated with a combustion-based power plant, the N2 stream also has sufficient purity (95 vol% or higher, or 98 vol% or higher) so that the N2 stream can be used for another co-located process and / or sold as a commercial product. It should also be noted that in some aspects, the N2 stream produced by the process is actually under high pressure, which means that integrating N2 with a co-located process operating under high pressure will reduce the energy cost of N2 compression.

[0036] Formation of O2-containing stream and high-purity N2 stream

[0037] In various aspects, the oxygen source for the combustion process in the power plant can be provided by an integrated separation process, which simultaneously produces a relatively high purity N2 stream (95 vol% or higher) and an oxygen-containing gas stream having an oxygen (O2) content of 25 vol% to 48 vol%. It has been found that such nitrogen-containing gas streams and oxygen-containing gas streams can be produced by kinetically separating air using a pressure swing adsorption process in combination with a suitable adsorbent material. 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 aspects, the generated oxygen-containing gas stream can be formed at a pressure of 100 kPa-a or less.

[0038] Conventionally, cryogenic air separation units can be used to produce large quantities of high purity nitrogen streams and high purity oxygen streams. While this is effective, the high pressure and low temperature separation involved in using air separation units means that the oxygen produced is very expensive to produce. This high purity oxygen can be diluted to reach a concentration of 25 vol% to 48 vol%, but this is a costly method and the concentration of the oxygen stream produced is only slightly increased relative to air. This method generally requires a large operating space and a long start-up time of about several days. In addition, as production increases, the efficiency of the air separation unit improves, but the cost is often too high for producing small amounts of gas.

[0039] Another option is to use a non-cryogenic adsorption process using a zeolite adsorbent that is selective for nitrogen adsorption and thus produces high purity oxygen as a product, for example in a pressure swing adsorption (PSA) process. An example of such a process is described in Sircar et al. (Separation of air with zeolites, in: A, ed., Surface Science and Catalysis Research: Elsevier; 1999, pp. 395-423). However, such processes are unable to simultaneously form a high purity nitrogen gas stream containing 95 vol% or more N2 and an oxygen-containing gas stream containing 25 vol% to 48 vol% O2.

[0040] It has been found that by using a suitable kinetic adsorbent and using an improved process cycle for kinetic separation, separation can be performed to simultaneously produce a stream containing 25vol% to 48vol% oxygen and a second stream containing 95vol% or more nitrogen. The O2 enrichment level can be adjusted according to the recovery rate and N2 purity and recovery rate. It should be noted that higher recovery rate requirements usually lead to lower purity; similarly, higher purity is usually accompanied by the sacrifice of recovery rate. The separation provided herein can use this compromise between recovery rate and purity to provide the flexibility of cyclic operation. For example, in some aspects, the O2 enrichment amount and / or the purity of the N2 product used for the combustion process can be adjusted by adjusting the process to reduce the recovery rate of N2 and / or O2. Compared with a cryogenic air separation unit, this provides more adjustable specifications for N2 products and rich O2 streams. In some aspects, a stream containing 25vol% to 48vol% O2 can also contain 50vol% or more N2.

[0041] One adsorbent used to perform this kinetic separation is a carbon molecular sieve, which is used in some commercial N2 generators. Another adsorbent that can be used is ITQ-55, which is a zeolite material. ITQ-55 is described in detail, for example, in U.S. Patent 9,695,056, U.S. Patent 9,738,539 and U.S. Patent 9,856,145. Still other types of adsorbents that can perform kinetic separations of N2 are also known, such as ETS-4. In general, any kinetic adsorbent that has sufficient kinetic selectivity for O2 relative to N2 can be used, which, when used in conjunction with the improved separation process described herein, allows the formation of an effluent corresponding to: a) a high purity nitrogen stream containing 95 vol% or more N2, and b) an oxygen-containing gas stream having an oxygen content of 30 vol% to 50 vol%. N2 corresponds to a stream of sufficiently high purity to be commercially valuable, while the oxygen-containing gas stream has a target oxygen concentration for oxy-enriched combustion. As used herein, the term "kinetic selectivity" is defined as the ratio of the single component diffusion coefficient D (in m) of two different substances. 2 These single-component diffusion coefficients are also called transport diffusion coefficients and are measured for a given adsorbent and a given pure gas component. Thus, for example, the kinetic selectivity of a particular adsorbent for component A relative to component B will be equal to D A / D BThe single component diffusion coefficient of a material can be determined by tests well known in the art of adsorbent materials. A preferred method for measuring the kinetic diffusion coefficient is to utilize the frequency response technique described by Reyes et al., "Frequency Modulation Methods for Diffusion and Adsorption Measurements in Porous Solids", J. Phys. Chem. B 101, pp. 614-622, 1997.

[0042] In addition to using a suitable adsorbent, the kinetic separation is performed using an improved separation process that helps to form a nitrogen-containing gas stream and an oxygen-containing gas stream with a target purity level. The improved kinetic separation process can involve having multiple adsorbent vessels. The improved process benefits from the integration of streams from different stages in the adsorption / desorption process. This integration of streams from different stages in the adsorption / desorption process enables the simultaneous recovery of an oxygen-containing gas stream having an oxygen content of 25 vol% to 48 vol% and a nitrogen-containing gas stream having a purity of 95 vol% or more.

[0043] In some aspects, the adsorption / desorption cycle can correspond to a pressure swing adsorption process that includes a total of eight steps. In this example, a process using a dual bed system is described, in which the adsorbent beds are of approximately equal size and the volumes of the containers that hold the adsorbent beds are approximately equal. In this example, the process for the dual bed system is symmetrical in time so that the steps occurring in the paired beds are synchronized. For the eight-step cycle, when step 1 occurs in one bed, step 5 occurs in the other bed. When step 2 occurs in one bed, step 6 occurs in the other bed. When step 3 occurs in one bed, step 7 occurs in the other bed. When step 4 occurs in one bed, step 8 occurs in the other bed. It should be noted that other synchronized process flows can be developed with more beds.

[0044] 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 vol% or more. Because the oxygen load on the adsorbent is driven by kinetics, a high percentage of oxygen can be removed from the stream, so that the purity of the nitrogen reaches 95 vol% or more, or 97 vol% or more, or 98 vol% or more, for example, up to substantially all adsorption effluents corresponding to nitrogen. This step is carried out at a high pressure between, for example, 200 kPa-a and 800 kPa-a. Various temperatures can be used. Temperatures close to room temperature can facilitate processing, but lower temperatures are likely to provide higher purity adsorption effluents. In some aspects, the temperature can be between -100 ° C and 40 ° C. The air velocity in the adsorption environment during the adsorption step can vary depending on the configuration of the adsorbent environment. In some aspects, the gas velocity during the adsorption step can be approximately between 0.01 m / s and 1.0 m / s. The resulting adsorption effluent having a N2 content of 95 vol% or more is produced at a pressure similar to the pressure during the adsorption step. In some aspects, any convenient source of air can be used as the input stream for steps 1 and 2. In some aspects, such as aspects where the separation is performed at a temperature between 0°C and 40°C, the air used 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, such as as low as substantially no water content (and thus effectively a relative humidity of 0%).

[0045] Step 3 corresponds to a pressure balance step, in which the first bed and the second bed are fluidly connected. The pressure in the first bed is balanced with the pressure in the second bed. In some aspects, this pressure balance is carried out by connecting the top of the first bed to the top of the second bed. Using only the flow from the top of the pressurized bed to pressurize can help improve the purity of the O2 stream produced by the separation process. This is in contrast to the pressure balance process, which uses the gas flow from both ends of the pressurized bed to balance the pressure. This balance step carried out from both ends of the pressurized bed can be used for the process in which the only product of interest is a high-purity N2 product. At the beginning of the pressure balance step, the first bed will be under a pressure between 200kPa-a and 800kPa-a, and the second bed will be under a pressure close to the environment (that is, about 100kPa-a). After balance, the pressure in the bed will roughly correspond to the average value of the initial pressure. Because this is a pressure balance step, the output flow from one bed is used as the input flow of another bed.

[0046] Step 4 corresponds to a discharge step to reduce the pressure in the first bed to about ambient pressure (about 100 kPa-a). Since the pressure is being released, the discharge step does not require an input stream. The discharge step produces a discharge exhaust gas. This discharge exhaust gas corresponds to a stream with a lower O2 content and a higher N2 content relative to air. In some aspects, the O2 content in the discharge exhaust gas can be between 5.0 vol% and 14 vol%, or between 5.0 vol% and 12 vol%, or between 8.0 vol% and 12 vol%.

[0047] Step 5 corresponds to a first countercurrent purge step. This purge step is referred to as "countercurrent" because the flow direction is opposite to the flow direction in step 1. In some aspects, the first countercurrent purge step is performed using a portion of the exhaust gas as an input stream. In this example, approximately half of the total exhaust gas is used as the purge gas for this countercurrent purge. This step is performed at approximately ambient pressure or approximately 100 kPa-a. This produces a first purge exhaust gas stream. This first purge exhaust gas stream is enriched in oxygen and corresponds to a stream containing 25 vol% to 34 vol% O2. It should be noted that higher O2 concentrations are also possible, but at the expense of reducing the amount of O2 recovered per volume of air processed in the system.

[0048] It should be noted that the use of exhaust gas as the input stream of the first purge input stream is an unexpected choice. The exhaust gas is rich in nitrogen and contains 5.0vol% to 14vol%, or 5.0vol% to 12vol%, or 8.0vol% to 12vol%. Therefore, by using air as the first purge input stream, a higher purity O2 effluent can be produced. However, because kinetic separation is being carried out, the use of air as the first purge input stream will result in too much O2 still being adsorbed on the adsorbent at the end of the first purge step. This will prevent the adsorption effluent from containing 95vol% or higher N2 in the adsorption step in the subsequent cycle. It should also be noted that the use of a portion of the exhaust gas as the input stream of step 5 greatly increases the recovery rate of N2 and O2 relative to the amount of gas processed in the system. If a separate N2 stream is used as the input of step 5, then this N2 stream will offset the benefit of producing a high purity N2 stream as a part of the product, thereby reducing the yield of high purity N2. For O2, the use of exhaust gas allows the recovery of a portion of O2 present in the exhaust gas.

[0049] Step 6 corresponds to a second countercurrent purge step. In the second countercurrent 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 gas. A high purity nitrogen stream (95 vol% or higher N2) needs to be used as the second purge input stream so that the adsorption effluent corresponds to a high purity nitrogen stream. Otherwise, after the purge, too much oxygen will still be adsorbed on the adsorbent. This will reduce the purity of N2 in the adsorption effluent produced in the next adsorption step. By using a 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, since a portion of the adsorption effluent is used for the second purge, the yield of high purity nitrogen is reduced. It should be noted that a high purity nitrogen stream from another source can be used in this step, for example, at the beginning of the process operation but when the adsorption effluent is not yet available.

[0050] Step 7 corresponds to another pressure equalization step. This time, the pressure of the first bed is lower (about 100 kPa-a) and the pressure of the second bed is higher. In other respects, this step is similar to step 3. It should be noted that the pressure equalization step increases the yield of N2 relative to the total amount of gas processed. The pressure equalization step also increases the O2 content in the exhaust gas.

[0051] Step 8 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 the next process cycle.

[0052] Table 1 shows an example of a process cycle based on the above 8 steps. As an example of the timing of the process cycle shown in Table 1, step 1 and step 2 can each last for 10 seconds. This is consistent with the duration of step 5 and step 6, which can also be 10 seconds each. Step 3 can last for 2 seconds, consistent with step 7. Step 4 can last for 0.5 seconds, consistent with step 8. In other aspects, any other convenient combination of process step durations can be used, as long as the appropriate bed can be used for the pressure equalization step at the same time.

[0053] Table 1 - Examples of adsorption / desorption process cycles

[0054]

[0055] Figure 1 and Figure 2 A graphical representation of the eight-step adsorption / desorption cycle shown in Table 1 is shown. Figure 1 The first four steps of the cycle of the first adsorbent environment are shown, and Figure 2 The last four steps of the cycle of the first adsorbent environment are shown. Thus, Figure 1 The last four steps of the cycle of the second adsorbent environment are also shown, and Figure 2 The first four steps of the cycle of the second sorbent environment are shown. Figure 1 and 2 The points in time at which the bed is in each step of the cycle are shown.

[0056] exist Figure 1 In , A corresponds to the first adsorption step (step 1) of bed 1 and the first purge step (step 5) of bed 2. During this period, input air stream 110 enters bed 1 to form adsorption effluent 115. During this period, a portion 137 of exhaust effluent 135 is used as the first purge input stream for bed 2 to form first purge waste gas 145. Figure 1 In FIG. 1 , B corresponds to the second adsorption step (step 2) of bed 1 and the second purge step (step 6) of bed 2. During this period, the input air stream 110 continues to pass through bed 1 to form adsorption effluent 115. During this period, a portion 117 of the adsorption effluent 115 is used as the input stream of bed 2 to form a second purge waste gas 155. Figure 1 In , C corresponds to the pressure equalization step, in which bed 1 is depressurized (step 3) by discharging stream 125, which is passed to bed 2 to be pressurized (step 7). Figure 1 In FIG. 1 , D corresponds to the discharge step (step 4) of bed 1, where the remaining pressure is vented from bed 1 to form discharge waste gas 135. D also corresponds to step 8 of bed 2, where bed 2 is pressurized using air stream 170.

[0057] Figure 2 and Figure 1 In parallel, but bed 1 performs steps 5 to 8, and bed 2 performs steps 1 to 4. Figure 2 In , E corresponds to step 5 of bed 1 and step 1 of bed 2. Figure 2 In , F corresponds to step 6 of bed 1 and step 2 of bed 2. Figure 2 In , G corresponds to another pressure equalization step, in which bed 2 is depressurized (step 7) by discharging stream 165, which is passed to bed 1 to be pressurized (step 3). Figure 2 , H corresponds to step 8 for bed 1 and step 4 for bed 2.

[0058] Increase O2 content via vacuum pressure swing adsorption

[0059] Table 1 and Figure 1 and 2The process shown in corresponds to a process in which all steps are carried out at about ambient pressure or higher pressure. In other aspects, by using a pressure lower than 100kPa-a to form an oxygen-containing gas stream, a higher O2 concentration can be achieved in the oxygen-containing gas stream while still maintaining a high-purity nitrogen stream. Therefore, in these other aspects, the adsorption / desorption process may correspond to a vacuum pressure swing adsorption process. The same type of adsorbent may be used for such a vacuum pressure swing adsorption process. By using vacuum pressure swing adsorption (VPSA), an oxygen-containing gas stream having an O2 content of 25vol% to 48vol%, or 30vol% to 48vol%, or 35vol% to 48vol%, or 40vol% to 48vol% can be produced. It should be noted that VPSA is a PSA process, and therefore, when referring to a pressure swing adsorption process without further explanation, it may refer to a process carried out at ambient pressure or higher pressure, or it may refer to a vacuum pressure swing adsorption process comprising at least one step carried out at a pressure lower than 100kPa-a.

[0060] An example of a vacuum pressure swing adsorption (VPSA) process that can form a nitrogen-containing gas stream having a N2 content of 95 vol% or more and an oxygen-containing gas stream having a N2 content of 30 vol% to 48 vol% O2 is a six-step process. To illustrate the process, the process can be described for a system having two adsorbent beds that are synchronized so that both beds are in a pressure equalization step at the same time. In this example of a VPSA process, the various steps can be performed at approximately ambient temperature, although lower temperatures can also be used.

[0061] In this example, step 1 of the VPSA process corresponds 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 vol% or more. Because the oxygen load on the adsorbent is driven by kinetics, a high percentage of oxygen can be removed from the stream, thereby making the purity of the nitrogen reach 95 vol% or more, or 97 vol% or more, or 98 vol% or more, for example, up to substantially all of the adsorption effluent corresponding to nitrogen. This step is carried out at a high pressure, for example, between 200 kPa-a and 800 kPa-a. The resulting adsorption effluent with a N2 content of 95 vol% 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 may be similar to the flow rate of step 1 or step 2 (adsorption step) of the process shown in Table 1.

[0062] Step 2 of the VPSA process corresponds to a pressure balancing step, in which the first bed is fluidly connected to the second bed. The pressure in the first bed is balanced with the pressure in the second bed. At the beginning of the pressure balancing step, the first bed will be at a pressure between 200 kPa-a and 800 kPa-a, while the second bed will be at a pressure of 50 kPa-a or less. After balancing, the pressure in the bed will roughly correspond to the average value of the initial pressure. Because this is a pressure balancing step, the output stream from one bed is used as the input stream of the other bed.

[0063] It should be noted that this pressure equalization step is valuable for improving recovery. Specifically, after the adsorption step is completed, the composition of the pressurized gas left in the first bed is similar to the composition of the adsorption effluent. By performing pressure equalization, this high N2 content gas is used to pressurize the second bed that has just completed the desorption step. By performing pressure equalization, the high N2 content gas from the first bed is used to provide most of the pressurization of the second bed. The use of a top equalization step is beneficial for producing high purity nitrogen and improving the recovery of oxygen and nitrogen.

[0064] 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, the blowdown step does not require an input stream. The blowdown step produces a blowdown waste gas.

[0065] Step 4 of the VPSA process corresponds to a vacuum desorption step. The pressure in the adsorbent environment is reduced to a pressure between 1.0 kPa-a and 50 kPa-a, or between 1.0 kPa-a and 20 kPa-a, or between 1.0 kPa-a and 10 kPa-a, or between 5.0 kPa-a and 50 kPa-a, or between 5.0 kPa-a and 20 kPa-a. This vacuum desorption step is called "countercurrent" because the end at which the output stream leaves the adsorbent environment is opposite to the end at which the adsorbed effluent leaves the adsorbent environment. The vacuum desorption off-gas is rich 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.

[0066] Step 5 corresponds to another pressure equalization step. This time, the pressure of the first bed is lower (1.0 kPa-a to 50 kPa-a), and the pressure of the second bed is higher. In other respects, this step is similar to step 2.

[0067] 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 for repeated cycles of the adsorbent environment.

[0068] Table 2 shows an example of the above VPSA cycle, in which the timing of each step is shown. As an example of the timing of the process cycle shown in Table 2, step 1 can be performed for 20 seconds, which can be consistent with the duration of step 4. Step 2 can be performed for 2 seconds, which is consistent with step 5. Step 3 can be performed for 0.5 seconds, which is consistent with step 6.

[0069] Table 2 - Example of VPSA process cycle

[0070] step bed 1 bed 2 1 Adsorption to produce adsorption effluent Vacuum countercurrent desorption 2 Depressurize from top of bed to equalize with bed 2 Pressurize the top of the bed again until it is balanced with bed 1 3 Discharge to atmospheric pressure Feed pressurization 4 Vacuum countercurrent desorption Adsorption to produce adsorption effluent 5 Pressurize the top of the bed again until it is balanced with bed 2 Depressurize from the top of the bed to equalize with bed 1 6 Feed pressurization Vent to atmospheric pressure

[0071] Figure 7 A schematic representation of the six-step adsorption / desorption cycle shown in Table 2 is shown. Figure 7 The points in time at which the bed is in each step of the cycle are shown.

[0072] exist Figure 7 In , "A" corresponds to the adsorption step (step 1) of bed 1 and the desorption step (step 4) of bed 2. During this period, the input air stream 710 enters bed 1 to form the adsorption effluent 715 (nitrogen-rich product). During this period, bed 2 is subjected to countercurrent desorption while reducing the pressure to a pressure between 1.0 kPa-a and 50 kPa-a. The output 745 from this step corresponds to the oxygen-rich product. Figure 7 In , B corresponds to the pressure equalization step, in which bed 1 is depressurized (step 2) by discharging stream 725, which is passed to bed 2 to be pressurized (step 5). Figure 1 , C corresponds to the blowdown step (step 3) of bed 1, where the remaining pressure is vented from bed 1 to form blowdown waste gas 735. C also corresponds to step 6 of bed 2, where bed 2 is pressurized using air stream 770. Steps D, E, and F are similar to steps A, B, and C, but with beds 1 and 2 having opposite effects.

[0073] Exhaust Gas Recirculation

[0074] In various aspects, exhaust gas recirculation (EGR) can be used to further increase the CO2 concentration in the flue gas from the combustion process. One option for exhaust gas recirculation is to recirculate a portion of the flue gas after power generation is completed. For example, the flue gas leaving the heat recovery generator system can be used as a source of recirculated exhaust gas. In this aspect, 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 of 16 vol% to 35 vol% in the combustion chamber.

[0075] If selective exhaust gas recycle (SEGR) is used, 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 a recycle stream. Thus, selective exhaust gas recycle uses a recycle stream containing 70 vol% or more, or 80 vol% or more, or 90 vol% or more CO2, for example up to a recycle stream consisting essentially entirely of CO2. It should be noted that the CO2 stream formed after capture may involve multiple recovery stages (e.g., multiple membranes or multiple pressure swing adsorption vessels in series) to achieve a final CO2 purity of 90 vol% or more. Thus, a recycle stream having a CO2 content of less than 90 vol% can be used in aspects where the final high purity CO2 stream has a CO2 content greater than 90 vol%.

[0076] In various aspects, the flow rate of the gas entering the combustion chamber can be characterized based on the relative volume percentage (at 20°C and 100kPa-a) of the gas stream 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 before entering the combustion chamber. For example, in some aspects, the exhaust gas recirculation stream and the oxygen-containing stream can be combined before entering the main compressor of the natural gas turbine, wherein the fuel stream is added to the combustion chamber separately. According to specific aspects, the exhaust gas recirculation stream can correspond to 25vol% to 60vol%, or 35vol% to 60vol%, or 45vol% to 60vol% of the combustion chamber input stream. It should be noted that when exhaust gas recirculation is performed with air as the oxygen-containing stream, the use of an exhaust gas recirculation higher than 20vol% will cause the oxygen content in the combustion chamber to drop to less than 16vol%.

[0077] In some aspects, the exhaust gas recirculation stream can 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 flow of the exhaust gas recirculation stream and the oxygen-containing gas stream can then be compressed (e.g., compressed in the main compressor of the natural gas turbine) before entering the combustor, where the combined flow is mixed with fuel for combustion. In other aspects, other configurations can be used to compress the various gas streams before entering the combustor.

[0078] As used herein, the term "stoichiometric combustion" refers to a combustion reaction having a volume of reactants including a fuel and an oxidant and a volume of products formed by burning 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 in which the molar ratio of the combustion fuel to the oxygen ranges from about plus or minus 10% of the oxygen required for the stoichiometric ratio or more preferably from 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). The stoichiometric ratio of fuel to oxygen for propane would be 1:5. Another way to measure substantially stoichiometric combustion is based on the ratio of oxygen supplied to oxygen required for stoichiometric combustion, for example, from about 0.9:1 to about 1.1:1, or more preferably from about 0.95:1 to about 1.05:1.

[0079] Post-combustion capture

[0080] There are a variety of options available for the post-combustion capture stage. In some aspects, a variety of different types of post-combustion capture devices may be used to create a CO2-containing stream that contains a target amount of CO2 produced in the combustion zone and / or any supplemental combustion devices.

[0081] One option for a post-combustion capture stage is to use one or more aqueous amine separators or amine scrubbers. By using a combination of oxyfuel combustion and exhaust gas recirculation, the size of the one or more amine scrubbers used for post-combustion capture can be significantly reduced. Optionally, in aspects where an amine scrubber is used as at least a portion of a post-combustion capture stage, the combustion zone can be operated under substantially stoichiometric conditions and / or a supplemental combustion stage can be used to reduce or minimize the amount of oxygen passed into the one or more amine scrubbers.

[0082] Another option for the post-combustion capture stage is to use a liquid phase capture device, which works by providing a high interfacial gas-liquid mass transfer surface area. The liquid in the device can include one or more components (such as amines) that perform CO2 adsorption. 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 centrifugal shearing of the liquid; devices that increase the surface area by producing small droplets that can be dispersed into the gas stream; and devices that increase the surface area by producing a thin film of liquid in contact with the gas stream. Optionally, in aspects where the liquid phase adsorbent is at least partially based on amines, the combustion zone can be operated under essentially stoichiometric conditions and / or a supplemental combustion stage can be used to reduce or minimize the amount of oxygen introduced into the post-combustion capture stage.

[0083] Another option for the post-combustion capture stage is to use a solid adsorbent. There are a variety of solid adsorbent systems available. The solid adsorbent may include an adsorbent supported on a carrier material, such as an adsorbent supported on a monolith or an adsorbent supported on particles in an adsorbent bed. Other types of solid adsorbents may be formed as a monolith, particles, or another convenient structure without the use of a carrier material. Examples of solid adsorbents may include, but are not limited to, zeolites, metal organic framework materials, and amino polymers. The method of recovering CO2 after adsorption on a solid adsorbent may vary depending on the properties of the adsorbent. In some aspects, a direct displacement method may be used. For example, after adsorption of CO2 by a solid adsorbent, CO2 may be replaced with low-pressure steam, and the adsorbent may be regenerated for further use. As another example, a temperature change may be used to change the adsorbent from a condition of adsorbing CO2 to a condition of desorbing CO2. Yet another example may be the use of an adsorbent in which a change in pressure causes the adsorbent to change from a condition of adsorbing CO2 to a condition of desorbing CO2. Yet another example may be the use of a combination of two or more of direct displacement, temperature swing, and pressure swing to transition the sorbent from conditions that adsorb CO to conditions that desorb CO. Optionally, in aspects where the solid sorbent is at least partially amine based, the combustion zone may be operated under substantially stoichiometric conditions and / or a supplemental combustion stage may be used to reduce or minimize the amount of oxygen passed into the post-combustion capture stage.

[0084] It should be noted that having higher CO2 concentrations in the combustion exhaust can provide additional benefits for solid sorbent based post-combustion capture stages. For many types of solid sorbents, the equilibrium adsorption capacity of the sorbent depends on the CO2 concentration available in the input gas stream of the sorbent environment. Therefore, the productivity (CO2 captured per unit time per mass of sorbent) of such sorbents increases when CO2 capture is performed on higher concentration streams.

[0085] Another option for the post-combustion capture stage is to use a molten carbonate fuel cell. The working principle of a molten carbonate fuel cell is to convert CO2 and O2 in the cathode into carbonate ions, which are then transported through the electrolyte in the fuel cell. The carbonate combines with the hydrogen in the anode to form CO2 and H2O, while also generating electricity. In order to use a molten carbonate fuel cell as a post-combustion capture device, the flue gas (combustion exhaust) from the combustion zone of the turbine is used as at least a portion of the cathode input stream of the fuel cell. It should be noted that O2 is also a reactant required for the cathode operation of a molten carbonate fuel cell. Therefore, the presence of additional oxygen in the combustion exhaust gas may be beneficial to improving the CO2 utilization in the cathode while maintaining stable operating conditions.

[0086] Because CO2 is used to form ions that are transported in the electrolyte, molten carbonate fuel cells provide an unusual property that allows CO2 to be transferred 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, it may be difficult to achieve capture of 80 vol% or more CO2 in the cathode input stream (i.e., 80 vol% or more CO2 utilization) when the CO2 concentration in the cathode input stream is about 5.0 vol% or less. However, by increasing the CO2 concentration in the combustion exhaust gas using oxygen-enriched combustion and / or exhaust gas recirculation, 80 vol% or more CO2 in the cathode input stream can be captured (via transfer to the anode exhaust gas), or 90 vol% or more CO2 can be captured while still having a cathode exhaust gas with a CO2 content of 1.0 vol% or more, or 1.5 vol% or more, or 2.0 vol% or more (e.g., up to 5.0 vol%). In some aspects, maintaining a CO2 concentration of 1.5 vol% or greater (or 2.0 vol% or greater) in the cathode exhaust gas can contribute to stable operation of a molten carbonate fuel cell because it increases the likelihood that a large amount of CO2 will be present throughout the cathode, rather than having some portion of the cathode be substantially depleted of CO2 during operation.

[0087] Yet another option for the post-combustion capture stage is to use a membrane separator. Membrane systems are commercially available (e.g., polymer membranes) that can provide a separation factor of approximately 50 to separate CO2 from N2. Combined with the use of reduced pressure on the permeate side / pressurization on the retentate side to provide the driving force, such membranes can be used to separate flue gases with a CO2 content of 12 vol% or more to produce a permeate stream. By using membrane separation for CO2 capture, the thermal cost of regenerating the adsorbent can be avoided and replaced by the lower cost of maintaining a pressure differential across the membrane. In addition to direct cost savings by avoiding the need for heating and cooling, such thermal costs may include (but are not limited to) 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 incurred when heating and cooling various fluids for heat exchange.

[0088] Another option 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 and / or increasing the pressure by a sufficient amount so that CO2 forms a condensed phase while the other components remain in the gas phase. It should be noted that combustion waste materials usually contain a large amount of water. This water is removed before exposing the stream to full cryogenic conditions, for example by condensing the water while the CO2 remains in the gas phase.

[0089] It should be noted that the post-combustion capture stage may optionally include multiple devices of a given type, and / or may include mixed types of post-combustion capture devices. For example, multiple membranes, solid adsorbents, and / or molten carbonate fuel cells may be arranged in series as needed to obtain a CO2-containing product stream having a target CO2 purity.

[0090] Combined Cycle Process - Configuration Example

[0091] In various aspects, systems and methods are provided for generating electricity while controlling and / or capturing emissions generated during power generation. One goal of power generation is to utilize input feed (e.g., fuel) as efficiently as possible so that power generation is increased for a given amount of fuel and / or a given amount of equipment. Based on conditions for efficient power generation, a goal of controlling and / or capturing emissions can be to provide efficient emissions capture while reducing or minimizing changes in power generation conditions.

[0092] In various aspects, the methods described herein can be used to generate electricity while substantially capturing the CO2 produced during the process, such as capturing 70 vol% or more, or 80 vol% or more, or 90 vol% or more CO2 in the exhaust flue gas from the combustion process (e.g., up to capturing substantially all CO2 in the combustion exhaust gas). In one or more aspects, a mixture of oxygen-enriched air and fuel can be burned. Before 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 gas so that the recirculation stream generally includes the products of the combustion reaction. Including CO2, H2O and diluent gases present in the combustion environment, such as N2. In other aspects, a selective exhaust gas recirculation stream with a CO2 content of 80 vol% or more, or 90 vol% or more can be used. Exhaust gas recirculation can be used as a diluent to control, adjust or otherwise regulate the combustion temperature and the exhaust gas entering the subsequent expander. In addition, exhaust gas recirculation can further increase the CO2 content of the resulting flue gas formed by combustion. The combined use of oxygen-enriched air and recirculated exhaust gas may allow the expander to operate at a higher expansion ratio at the same intake and exhaust temperatures, thereby producing increased electrical power.

[0093] In various aspects, any convenient oxygen to fuel ratio may be used. For example, when natural gas is used as the fuel, the molar ratio of O2 to fuel may be in the range of about 2.0:1 (substantially stoichiometric combustion) to 5.0:1, or possibly higher. As another example, the molar ratio of O2 to fuel may be in the range of about 2.0:1 to 3.5:1, or 2.0:1 to 3.0:1. It should be noted that if a fuel other than methane is used, then a lower O2 to fuel ratio value will correspond to substantially stoichiometric combustion, such as a ratio of about 1.5:1. In these aspects, the ratio of O2 to fuel may be in the range of about 1.5:1 to 3.5:1.

[0094] It should be noted that in commercial gas turbines, combustion at or substantially at stoichiometric conditions (e.g., "slightly rich" combustion) can prove advantageous in order to eliminate the cost of excess oxygen removal. This operation can also reduce the amount of N2 present in the combustion exhaust gas. By cooling the exhaust gas and condensing water out of the cooled exhaust stream, a relatively high CO2 content exhaust stream can be produced. While a portion of the recycled exhaust gas can be used for temperature regulation in a closed Brayton cycle, the remaining purge stream can be used for EOR applications and / or can be used in a process with little or no sulfur oxides (SO x ), nitrogen oxides (NO x ) and / or CO2 are discharged into the atmosphere. As a result of the process, electricity is generated and additional CO2 is produced in three independent cycles. In some aspects, performing stoichiometric combustion allows the production of an exhaust gas stream consisting essentially of CO2, H2O, and N2. An exhaust gas stream consisting essentially of CO2, H2O, and N2 is defined as an exhaust gas stream containing about 5 mol % or less of other gas molecules, such as about 2.5 mol % or less of other gas molecules, or about 1 mol % or less of other gas molecules.

[0095] In some aspects, such as in some aspects where substantially stoichiometric combustion is not performed, duct burners and / or other supplemental combustion stages can be used to reduce the oxygen content of the combustion exhaust gas. Such supplemental combustion stages can work by adding additional fuel to the combustion exhaust gas and then consuming most of the oxygen present in the combustion exhaust gas via the supplemental combustion reaction.

[0096] Figure 3 An example of an integrated system for power generation and CO2 capture using a combined cycle arrangement including oxyfuel combustion and exhaust gas recirculation is shown. Figure 3A natural gas combined cycle power plant is shown, but a combined cycle power plant based on any other convenient type of combustion may also be used, for example a power plant based on the combustion of propane, fuel oil, coal, kerosene.

[0097] In some aspects, the power generation system may include a gas turbine system characterized by a closed Brayton cycle for power generation. The gas turbine system may have a first or main compressor 304, which is coupled to an expander 306 via a shaft 308. The shaft 308 may be any mechanical, electrical or other power coupling, thereby allowing a portion of the mechanical energy generated by the expander 306 to drive the main compressor 304. In at least one aspect, the gas turbine system may be a standard gas turbine, wherein the main compressor 304 and the expander 306 form a compressor end and an expander end, respectively. In other aspects, the main compressor 304 and the expander 306 may be independent components.

[0098] In various aspects, the gas turbine system may also include an integrated pressure swing adsorption system 370. The pressure swing adsorption system may optionally correspond to a vacuum pressure swing adsorption system. Figure 3 In the example configuration shown in FIG. 3 , air 301 is compressed 303 and then enters a pressure swing adsorption system 370 to form a nitrogen-containing gas stream 372 having an N2 content of 95 vol% or more and an oxygen-containing gas stream 375 having an O2 content of 25 vol% to 48 vol%. The oxygen-containing gas stream 375 is then combined with the exhaust gas recycle 345 (after any optional compression), and the combined stream 377 is then passed to the main compressor 304.

[0099] The combustor 310 combusts the fuel 312 in a combined stream 377. In one or more aspects, the fuel 312 in the pipeline can include any suitable hydrocarbon gas or liquid, such as natural gas, methane, ethane, naphtha, butane, propane, syngas, diesel, kerosene, aviation fuel, coal-derived fuels, biofuels, oxygenated hydrocarbon feedstocks, or any combination thereof.

[0100] The exhaust gas 316 directed to the inlet of the expander 306 may be produced as a combustion product in the combustion chamber 310. When the exhaust gas 316 in the pipeline is expanded through the expander 306, it generates mechanical power to drive the main compressor 304, the generator and / or other facilities, and also generates a gaseous exhaust gas 322 with an increased CO2 content. In some aspects, the expander 306 may be adapted to generate additional mechanical power that can be used for other purposes.

[0101] The power generation system may also include a heat recovery steam generator (HRSG) 326 or similar device. The gaseous exhaust 322 may enter the HRSG 326 where it is used to generate steam. The HRSG 326 may be coupled to one or more steam turbines. Figure 3In the example shown in FIG. 3 , HRSG 326 is fluidly coupled to high pressure steam turbine 362 , intermediate pressure steam turbine 364 , and low pressure steam turbine 366 . In other aspects, any convenient number of steam turbines may be fluidly coupled to HRSG 326 .

[0102] Optionally, an optional duct burner 390 may be used to burn any remaining oxygen present in the gaseous exhaust gas 322 prior to passing the gaseous exhaust gas 322 into the HRSG 326. This is accomplished by adding additional fuel (not shown) to the duct burner to allow substantially all of the remaining oxygen in the gaseous exhaust gas 322 to be consumed by the combustion reaction. This produces additional heat and a duct burner exhaust gas stream 392 that contains 2.0 vol% or less, or 1.0 vol% or less, or 0.1 vol% or less O2, such as as low as substantially no O2 content. The additional heat generated by the combustion reaction in the optional duct burner 390 may also be recovered in the HRSG 326.

[0103] After passing through the HRSG 326, a portion of the resulting cooled exhaust gas 332 may be used as an exhaust gas recirculation stream 345. A blower 344 may be used to recover any pressure lost due to the pressure drop across the HRSG 326 before combining the exhaust gas recirculation stream 345 with the oxygen-containing gas stream 375. In some aspects, after optional compression, the pressure of the exhaust gas recirculation 345 may be between 95 kPa-a and 115 kPa-a.

[0104] The remaining portion 336 of the cooled flue gas 332 may enter one or more CO2 capture stages. In this example, CO2 capture is performed using one or more amine scrubber stages 350. Because the CO2 content of the cooled flue gas 332 is 12 vol% or higher, or 15 vol% or higher, or 20 vol% or higher, the size of the one or more amine scrubber stages is significantly smaller than the size required to capture the same amount of CO2 at a concentration between 4.0 vol% and 8.0 vol%. Optionally, before the portion 336 of the cooled flue gas 332 is passed into the one or more amine scrubbers 350, one or more temperature and / or pressure regulating stages 351 (e.g., compressors and heat exchangers) may be used to change the temperature and pressure of the portion 336. The amine scrubber produces a flue gas 359 with a reduced CO2 concentration and a high purity CO2 output stream 355, which contains 90 vol% or higher CO2 in the portion 336 of the cooled flue gas 332 that enters the one or more amine scrubbers 350. The CO2 concentration of flue gas 359 may be 3.0 vol% or less, or 2.0 vol% or less, or 1.0 vol% or less, such as as low as substantially no CO2 content (0.1 vol% or less). Figure 3 In the example configuration shown in , the CO2 output stream 355 may also contain water. This water can then be removed by cooling the CO2 output stream 355 (not shown). After removing the water, the CO2 output stream may contain 80 vol% or more, or 90 vol% or more CO2. The CO2 output stream may include 80 vol% or more, or 90 vol% or more CO2 in the gaseous waste gas 322.

[0105] Figure 4 Another combined cycle configuration is shown. Figure 4 In the example shown in , the pressure swing adsorption process corresponds to the vacuum pressure swing adsorption process. In addition, Figure 4 The exhaust gas recirculation in the configuration shown in corresponds to a selective exhaust gas recirculation, wherein the recirculation stream corresponds to a portion of the high-purity CO2 formed after separation from the flue gas. When using additional oxygen that can be provided by vacuum pressure swing adsorption and / or when using selective exhaust gas recirculation, the CO2 content of the flue gas from the combustion can be high enough to allow alternative separation methods, such as in Figure 4 The membrane system used in the example configuration shown in .

[0106] exist Figure 4 In the main compressor 304, air 401 is compressed 403 and then enters 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 recycle stream 445 before entering the main compressor 304. The combined mixture is then combusted 310 with the fuel 312. The selective exhaust gas recycle stream 445 corresponds to a CO2 stream containing 90 vol% or more CO2.

[0107] By using a higher O2 content oxygen-containing gas stream and / or a selective exhaust gas recirculation stream 445, a higher CO2 content exhaust gas 435 exits the HRSG 326. Based on the higher CO2 content, a membrane 480 can be used to produce a permeate stream 485 containing 90 vol% or more CO2. Additionally or alternately, the CO2 in the permeate can correspond to the 90 vol% or more CO2 originally produced by the combustion reaction in the combustor 310. The membrane separation also produces a retentate 489 corresponding to a low CO2 content flue gas.

[0108] Example 1 - Oxygen Enrichment via Pressure Swing Adsorption

[0109] A kinetic model was used to determine the separation performance of the two adsorbents in a pressure swing adsorption device. Table 3 shows the kinetic parameters used to simulate the performance of a carbon molecular sieve (CMS) adsorbent and an ITQ-55 based adsorbent. The parameters for CMS were obtained from Qinglin et al., "Revisiting Gas Transport in Carbon Molecular Sieve Micropores," Langmuir (2003) 19, 393-405. The parameters for ITQ-55 were derived based on diffusivity measurements obtained using a pressure swing frequency response device.

[0110] Table 3 - Kinetic parameters of adsorbents

[0111] Adsorbent Adsorbate <![CDATA[(D / r 2 ) 0,i (1 / s)]]> <![CDATA[ΔE D,i (J / mol)]]> ITQ-55 oxygen 19.61 25965 Nitrogen 9.88 15937 CMS oxygen 31.75 28971 Nitrogen 7.07 18500

[0112] Based on the kinetic parameters in Table 3, a pressure swing adsorption system was simulated for aerodynamic separation using ITQ-55 or CMS as the adsorbent. Figure 1 A dual-bed configuration of the example configuration discussed in Example 1 was used to simulate kinetic separation. The dimensions of a single adsorption bed were 1.5 m (diameter) x 2 m (length), the bed voidage was 0.4, and the adsorbent was formed into granules. For the separation in Example 1, the eight-step process described in association with Table 1 was used. Table 4 shows detailed information about the composition and flow rates in the simulated separation process. The goal of this simulated process is to produce an oxygen-containing gas stream with an O2 concentration of approximately 30 vol% and a high recovery rate, while also producing a high purity N2 stream. For the separation in Example 1, steps 1, 2, 5, and 6 are 10 seconds long; steps 3 and 7 are 2.0 seconds long; and steps 4 and 8 are 0.5 seconds long.

[0113] Table 4 - Flow of the Pressure Swing Adsorption Process

[0114]

[0115] In Table 4, the "Feed+Pressure" row corresponds to the input streams of Step 1 and Step 7 of the process. The "Raffinate" corresponds to the net adsorption effluent produced in Step 1 minus the portion of the adsorption effluent used in Step 5 (the second purge step). The "Extracted Product" corresponds to the first purge off-gas formed in Step 4. As shown in Table 4, both ITQ-55 and CMS are suitable as adsorbents for forming a nitrogen-containing product having an N2 concentration of 95 vol% or more and for forming an oxygen-containing product having an O2 concentration of about 30 vol%.

[0116] Table 5 shows more detailed information regarding purity, flow rate and productivity for the simulated process in Table 4.

[0117] Table 5 - Products of the Pressure Swing Adsorption Process

[0118]

[0119] As shown in Table 5, approximately 90 vol% or more of the O2 entering the adsorbent bed during the pressurization and adsorption steps was successfully recovered as part of the oxygen-containing gas. Nitrogen recovery was lower, corresponding to 35 vol% to 40 vol% N2 entering the bed during the pressurization and adsorption steps.

[0120] Example 2 - Oxygen Enrichment via Vacuum Pressure Swing Adsorption

[0121] The same kinetic model was used to simulate the vacuum pressure swing adsorption process, with the goal of producing an oxygen-containing gas stream with an O2 concentration of approximately 40 vol%. The process flow uses the six-step process described in association with Table 2. Table 6 shows detailed information about the composition and flow rates in the simulated VPSA process. The total cycle time is 45 seconds, with adsorption / desorption times of 20 seconds each; discharge / repressurization times of 0.5 seconds each; and equilibrium times of 2 seconds per equilibrium.

[0122] Table 6 - Flow of Vacuum Pressure Swing Adsorption Process

[0123]

[0124] In Table 6, the "Feed+Pressure" row corresponds to the input streams of Step 1 and Step 6 of the process. The "Raffinate Product" corresponds to the net adsorption effluent produced in Step 1. The "Purge Off-Gas" corresponds to the effluent during Step 3 of the process. The "Extract Product" corresponds to the vacuum purge off-gas formed in Step 4. In the simulated process shown in Table 6, the vacuum purge was performed by reducing the pressure in the adsorbent environment to 10 kPa-a. As shown in Table 6, both ITQ-55 and CMS are suitable as adsorbents for forming a nitrogen-containing gas product having an N2 concentration of 97 vol% or more and forming an oxygen-containing gas product having an O2 concentration of about 40 vol%.

[0125] Table 7 shows more detailed information regarding purity, flow rate and productivity for the simulated process in Table 6.

[0126] Table 7 - Products of Vacuum Pressure Swing Adsorption Process

[0127]

[0128] As shown in Table 7, approximately 90 vol% or more of the O2 entering the adsorbent bed during the pressurization and adsorption steps was successfully recovered as part of the oxygen-containing gas. Nitrogen recovery was lower, corresponding to approximately 40 vol% N2 entering the bed during the pressurization and adsorption steps.

[0129] Example 3 - Combined Cycle Operation with PSA and EGR

[0130] To demonstrate the benefits of operating with oxygen-rich combustion and exhaust gas recirculation on carbon capture, a commercially available software package (Aspen ) to simulate the operation of an amine scrubber for capturing CO2 from flue gas. The amine scrubber was simulated based on the use of monoethanolamine (MEA) as the adsorbent. Figure 5 The simulated configuration is shown.

[0131] A simulation configuration was used to study the capture of CO2 from three different types of simulated flue gases. The first flue gas corresponds to the flue gas produced using air as the oxygen-containing gas (about 21 vol% O2) and without exhaust gas recirculation. The CO2 concentration of the corresponding flue gas is only 4.0 vol%. The second flue gas corresponds to the flue gas produced using an oxygen-containing gas containing 30 vol% O2 and some exhaust gas recirculation (about 43 vol% flue gas leaving the HRSG). This flue gas was modeled to have a CO2 content of 13 vol%. The third flue gas was modeled to have a CO2 content of 16 vol%, based on a combination of exhaust gas recirculation (55 vol% flue gas leaving the HRSG) and the use of an oxygen-containing gas containing 40 vol% O2.

[0132] In the process model, flue gas 501 enters the absorber at 1.1 bar pressure (110 kPa-a) and 40°C temperature. Lean amine (28 wt% MEA in water) is also fed to the absorber 510. "Green flue gas" 515 leaves the absorber from the top, while CO2-rich amine 518 leaves the absorber 510 from the bottom. The CO2-rich amine then enters the lean / rich heat exchanger 520 where it is heated by the lean amine 538 leaving the stripper 530. The heated rich amine 528 is fed to the stripper 530 where high purity CO2 (>94%) 535 leaves from the top of the stripper. The stripper reboiler duty is provided by LP steam from the HRSG (not shown). By calculating the required steam flow rate, the power debit of the amine unit reboiler can be calculated.

[0133] Table 8 shows the simulation results for the baseline case (21% O2 content in the intake air and no EGR) and two cases using oxygen-rich combustion with exhaust gas recirculation. Due to the use of air with a higher O2 concentration and flue gas recirculation, the concentration of CO2 in the flue gas in the oxygen-rich combustion case is significantly higher than in the baseline case. Therefore, the total flow rate of the flue gas that needs to be sent to the capture unit is reduced. Compared with the baseline case, for the case where the O2 content in the oxygen-containing gas is 30 vol%, the total flue gas flow rate is reduced by 71%. For the case where the O2 content in the oxygen-containing gas is 40 vol%, the reduction increases to more than 75%. This can significantly save the load on the compressor and cooler. In addition, since the amine inventory required for the oxygen-rich combustion case is lower, the reboiler load and LP power consumption are lower. Therefore, for the oxygen-rich combustion case, the total power consumption of carbon capture is significantly lower. The efficiency loss of the oxygen-rich combustion case is only about 5%, while the efficiency loss of the baseline case is 11.5%. This means significant energy savings for NGCC power plants.

[0134] Another observation from Table 8 is that the number of absorber stages required to achieve 90% CO2 capture in the OEC case is reduced by 20% compared to the baseline case. For the baseline case, the required absorber size is 80m high and 20m diameter. For the case of 40 vol% O2 content in the oxygen-containing gas, the absorber is estimated to be 60m high and 10m diameter. This results in a significant increase in the strength of the capture unit.

[0135] Table 8 - Simulation results using Aspen Hysys for the baseline case and selected OEC cases for the amine unit

[0136]

[0137] Example 4 - CO2 Separation via Membrane

[0138] In aspects where the CO2 content of the flue gas increases to 15 vol% or more, a membrane system can be used instead of an amine scrubber while still producing a CO2-containing stream with a CO2 content of 90 vol% or more. Additionally, in these aspects, the membrane can allow capture of 90 vol% or more CO2 in the flue gas.

[0139] To illustrate the potential use of membranes for carbon capture, a polymer membrane with a CO2 permeability of 1000 GPU and a CO2 / N2 separation factor of 50 can be used as a model membrane. Polymer membranes with these properties are currently commercially available, such as some membranes available from Membrane Technology and Research in Newark, CA. Table 9 shows the effect of membrane feed CO2 concentration on permeate CO2 concentration when using membranes with these properties. As shown in Table 9, at a flue gas concentration of 16% CO2, membranes with the above-mentioned properties can be used to produce a permeate flow containing more than 90 vol% CO2. It should be noted that if higher purity is required, a second membrane stage can be used, or the membrane can be connected to another capture unit (such as a PSA).

[0140] Table 9 - Membrane properties

[0141] <![CDATA[Membrane feed CO2 concentration (mol%)]]> <![CDATA[CO2 concentration in the membrane permeate (mol%)]]> 10 84.7 16 90.5 25 94.3 40 97.1

[0142] To further illustrate the potential benefits of using membranes, an NGCC power plant with 354 MW net power and a MEA amine scrubber can be used as a baseline scenario. This corresponds to the same baseline scenario used in Example 3 above. For comparative calculations, membranes can be used for CO2 in an NGCC system that uses oxyfuel combustion and exhaust gas recirculation to form a flue gas containing 25 vol% CO2. Based on these assumptions, Figure 6 The effect of feed pressure on the required maximum membrane area and feed compressor load to achieve capture of 90 vol% of the CO2 in the flue gas as part of the permeate is shown. Figure 6 The arrows in the figure indicate the relevant vertical axis of each data graph. Figure 6 As shown in , there is a trade-off between membrane area and compressor load. It should be noted that Figure 6 The maximum membrane area required when all the flue gas from the power plant is sent to the membrane is shown - in practice, the required membrane area will be smaller. The exact amount of membrane area required depends on the amount of exhaust gas recirculation. Specifically, in the case of selective exhaust gas recirculation, a significantly smaller membrane area may be sufficient.

[0143] The use of membranes can help reduce or minimize the amount of energy consumption that occurs when performing CO2 capture. As shown in Example 3, the use of a combination of oxygen-enriched combustion and exhaust gas recirculation can reduce the amount of flue gas treated by 70% or more relative to the baseline case of using air as the oxygen-containing gas and no exhaust gas recirculation. Based on reducing the flue gas flow rate by 70%, the amount of energy required to separate CO2 using a membrane under representative conditions can be calculated. For example, when the flue gas flow rate is reduced by 70%, the membrane feed (i.e., flue gas) pressure is 150kPa-a, the membrane feed temperature is 50°C, and the membrane permeate side pressure is 10kPa-a, the energy loss of using a membrane for CO2 separation is about 13MW for the compressor and vacuum pump and 14.4MW for the flue gas cooler. The total energy consumption is 27.4MW, while the baseline case of using an amine scrubber to capture CO2 in a system without exhaust gas recirculation and using air as an oxygen source is 69.9MW. In fact, the energy consumption of the membrane is lower than that of Example 3 where the oxygen-containing gas contains 30 vol% O2 and exhaust gas recirculation is used together with the amine scrubber (31.1 MW).

[0144] The required membrane area is 141,900m 2 - Even assuming a plate and frame membrane with the lowest surface area to volume ratio (but also the lowest pressure drop), the volume of the membrane unit is about 2400m 3 Alternatively, spiral wound membranes would reduce the volume of the membrane unit by an order of magnitude. Based on previously performed calculations, the productivity of a commercial amine scrubber (e.g., the MHI process) is 7.7 kg CO2 / h / m 3 Without OEC and EGR, the volume requirement for the process would be 15,800m 3 , which is 6.6 times the volume occupied by the plate and frame membrane unit.

[0145] Example 5 - Additional Performance and Energy Evaluation

[0146] To evaluate the cost-effectiveness of using the vacuum pressure swing adsorption process in Table 2 for O2 enrichment, four scenarios were simulated for performance, capital, and energy estimation. Scenario I used conventional CMS adsorbent and 0.1 bar vacuum, while Scenario II, Scenario III, and Scenario IV used zeolite ITQ-55 and vacuum pressures of 0.1 bar, 0.2 bar, and 0.3 bar, respectively. Since CMS adsorbent cannot provide the required performance at low vacuums above 0.1 bar, only one scenario of CMS at 0.1 bar vacuum is shown. ITQ-55 showed good tunability at low vacuums and achieved the required separation performance.

[0147] A small-scale NGCC with a production capacity of 100kTA CO2 will require about 1000 tons / day of 40% oxygen enrichment to feed the gas turbine. The calculations are based on representative assumptions: the total flue gas flow rate of the 727MW NGCC is 138,406kmol / hr and the CO2 concentration is 4.08%. With a CO2 capture rate of 90% on a 100kTA basis, the NGCC power will be about 37MW. Based on the calculations in the example, a 350MW NGCC will require 10,000TPD (tons / day) of 40% O2-enriched air. Therefore, assuming linear scaling, a 37MW gas turbine will require about 1000TPD of 40% oxygen-enriched feed.

[0148] For the four cases, the main power consumption of the compressor and pump is estimated on an annual basis (assuming 300 days of operation per year). The details of the performance and energy consumption are summarized in Table 3. It should be noted that co-produced N2 with a purity of more than 97% is also formed, and the oxygen from the exhaust stream is enriched to 40%. The cycle is adjusted to have a higher oxygen recovery.

[0149] Table 3 - Comparison of vacuum transformer processes

[0150]

[0151] Additional Embodiments

[0152] Embodiment 1. A method for operating a power generation process, comprising: separating air using a pressure swing adsorption process to form a nitrogen-containing gas stream containing 95 vol% or more N2 and an oxygen-containing gas stream containing 25 vol% to 48 vol% O2; burning a fuel in the presence of a recirculation stream in the presence of O2 from at least a portion of the oxygen-containing gas stream in a combustion chamber of a turbine to form a flue gas, the O2 from the at least a portion of the oxygen-containing gas stream accounting for 16 vol% to 35 vol% of the combined volume of i) the fuel, ii) the at least a portion of the oxygen-containing gas stream and) the recirculation stream, the flue gas containing 12 vol% or more CO2; forming the recirculation stream from one or more portions of the flue gas; and performing post-combustion capture on at least a portion of the flue gas to form a CO2-containing product stream and one or more CO2-depleted flue gas streams, the one or more CO2-depleted flue gas streams containing 30 vol% or less CO2 from the at least a portion of the flue gas.

[0153] Embodiment 2. The method according to embodiment 1, wherein the pressure swing adsorption process comprises at least one process step carried out at a pressure of 90 kPa-a or less.

[0154] Embodiment 3. The method according to any of the above embodiments, wherein the oxygen-containing gas stream comprises 35 vol% or more O2, or wherein the oxygen-containing gas stream further comprises 50 vol% or more N2, or a combination thereof.

[0155] Embodiment 4. The method according to any of the above embodiments, wherein the pressure swing adsorption process comprises: exposing air to an adsorbent having kinetic selectivity for O2 relative to N2 in an adsorbent environment at a pressure of 200 kPa-a to 800 kPa-a to form an adsorption effluent comprising the nitrogen-containing gas stream; discharging a purge effluent from the adsorbent environment; purging the adsorbent environment with at least a portion of the purge effluent to form the oxygen-containing gas stream; and purging the adsorbent environment with a portion of the adsorption effluent, the adsorbent having kinetic selectivity for O2 relative to N2, optionally comprising at least one of a carbon molecular sieve and ITQ-55.

[0156] Embodiment 5. The method according to embodiment 4, wherein the exhaust effluent and the adsorption effluent are discharged from the same end of the adsorbent environment.

[0157] Embodiment 6. A method according to embodiment 4 or 5, wherein the pressure swing adsorption process is performed in multiple adsorbent environments, and the pressure swing adsorption process further comprises: balancing the pressure of a first adsorbent environment after exposing air to a first adsorbent with the pressure of the second adsorbent environment after purging the second adsorbent environment with a portion of the adsorption effluent.

[0158] Embodiment 7. A method according to any of the above embodiments, wherein the recycle stream is mixed with the oxygen-containing gas stream before entering the combustion chamber, or wherein the recycle stream is at a pressure of 90 kPa-a to 115 kPa-a when mixed with the oxygen-containing gas stream, or a combination thereof.

[0159] Embodiment 8. A method according to any one of the above embodiments, i) wherein the flue gas contains 16 vol% or higher CO2 content, ii) wherein the CO2-containing stream contains 90 vol% or higher CO2, iii) wherein the CO2-containing stream contains 80 vol% or higher CO2 from at least a portion of the flue gas; or iv) a combination of two or more of i), ii) and iii).

[0160] Embodiment 9. The method according to any of the above embodiments, wherein forming the recycle stream from one or more portions of the flue gas comprises forming the recycle stream from the CO 2 -containing stream.

[0161] Embodiment 10. A method according to any of the above embodiments, wherein post-combustion capture of at least a portion of the flue gas comprises separating at least a portion of the flue gas using: a membrane separator; an amine scrubber; a liquid phase adsorbent, wherein the liquid is at least partially in the form of droplets or a thin liquid film; or a combination thereof.

[0162] Embodiment 11. A method according to any one of embodiments 1 to 9, wherein post-combustion capture of at least a portion of the flue gas comprises: exposing at least a portion of the flue gas to a solid adsorbent to adsorb CO2 on the solid adsorbent; and desorbing at least a portion of the adsorbed CO2 by direct displacement, pressure swing, temperature swing, or a combination thereof.

[0163] Embodiment 12. A method according to any one of embodiments 1 to 9, wherein post-combustion capture of at least a portion of the flue gas comprises: forming a cathode input stream comprising at least a portion of the flue gas; passing the cathode input stream into a cathode of a molten carbonate fuel cell; and operating the molten carbonate fuel cell to generate electricity, an anode output stream, and a cathode output stream corresponding to the CO2-depleted stream.

[0164] Embodiment 13. A method according to any of the above embodiments, wherein the method further comprises passing the at least a portion of the flue gas through a heat recovery steam generator to generate electricity before separating the at least a portion of the flue gas; or wherein the method further comprises adding fuel to the at least a portion of the flue gas and supplementing combustion of the at least a portion of the flue gas before performing post-combustion capture on the at least a portion of the flue gas; or a combination thereof.

[0165] Embodiment 14. A system for power generation, comprising: a pressure swing adsorption stage, comprising a plurality of pressure swing adsorption vessels, the plurality of pressure swing adsorption vessels containing an adsorbent having kinetic selectivity for O2 relative to N2, the pressure 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 supplemental burner, comprising a supplemental fuel inlet, a nitrogen-containing product outlet, and a shaft coupling the expander to the compressor; a flue gas inlet and a supplementary combustion outlet; a heat recovery steam generator, which includes a heat recovery inlet and a heat recovery outlet fluidly connected to the supplementary combustion outlet; and a post-combustion capture stage, which includes a capture inlet fluidly connected to 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 amine scrubbers, one or more adsorbent environments containing solid adsorbents, one or more adsorbent environments containing liquid adsorbents, or a combination thereof, wherein the one or more combustion inlets are further fluidly connected to at least one of the heat recovery outlet and the CO2-containing product outlet.

[0166] Embodiment 15. A system for power generation, comprising: a pressure swing adsorption stage, comprising a plurality of pressure swing adsorption vessels, the plurality of pressure swing adsorption vessels containing an adsorbent having kinetic selectivity for O2 relative to N2, the pressure 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 connecting 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 fluidly connected to a fuel source and the oxygen-containing product outlet; a heat recovery steam generator, comprising a heat recovery inlet fluidly connected to the combustion outlet and a heat recovery outlet; and a post-combustion capture stage, comprising a capture inlet fluidly connected to 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 membrane separators, one or more molten carbonate fuel cells, or a combination thereof, wherein the one or more combustion inlets are further fluidly connected to at least one of the heat recovery outlet and the CO2-containing product outlet.

[0167] Additional Embodiments A. The method according to any one of embodiments 1 to 13, wherein the separating air using a pressure swing adsorption process comprises a kinetic separation process.

[0168] Additional Embodiment B. The method of any of Embodiments 1 to 13, wherein the fuel comprises natural gas.

[0169] Additional Embodiment C. The method of any of Embodiments 1 to 13, wherein the turbomachine comprises a compressor, the combustion chamber, an expander, and a shaft coupling the expander to the compressor.

[0170] While the present invention has been described and illustrated with reference to particular embodiments, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. Accordingly, reference should be made solely to the appended claims to determine 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 gas stream containing 95 vol% or more N2 and an oxygen-containing gas stream containing 25 vol% to 48 vol% O2; combusting a fuel in the presence of a recycle stream in the presence of O2 from at least a portion of the oxygen-containing gas stream in a combustion chamber of a turbine to form a flue gas, the O2 from the at least a portion of the oxygen-containing gas stream accounting for 16 vol% to 35 vol% of the combined volume of i) the fuel, ii) the at least a portion of the oxygen-containing gas stream and iii) the recycle stream, the flue gas containing 12 vol% or more CO2; forming the recycle stream from one or more portions of the flue gas; and performing post-combustion capture on at least a portion of the flue gas to form a CO2-containing product stream and one or more CO2-depleted flue gas streams, the one or more CO2-depleted flue gas streams containing 30 vol% or less CO2 from the at least a portion of the flue gas.

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

3. The process according to any one of the preceding claims, wherein the oxygen-containing gas stream comprises 35 vol% or more O2, or wherein the oxygen-containing gas stream further comprises 50 vol% or more N2, or a combination thereof.

4. The method of any of the preceding claims, wherein the pressure swing adsorption process comprises: exposing air to an adsorbent having kinetic selectivity for O2 relative to N2 in an adsorbent environment at a pressure of 200 kPa-a to 800 kPa-a to form an adsorption effluent comprising the nitrogen-containing gas stream; discharging a purge effluent from the adsorbent environment; purging the adsorbent environment with at least a portion of the purge effluent to form the oxygen-containing gas stream; and purging the adsorbent environment with a portion of the adsorption effluent, the adsorbent having kinetic selectivity for O2 relative to N2, optionally comprising at least one of a carbon molecular sieve and ITQ-55.

5. The method of claim 4, wherein the exhaust effluent and the adsorption effluent are discharged from the same end of the adsorbent environment.

6. The method of claim 4 or 5, wherein the pressure swing adsorption process is performed in a plurality of adsorbent environments, the pressure swing adsorption process further comprising: balancing 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.

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

8. A method according to any one of the preceding claims, i) wherein the flue gas contains a CO2 content of 16 vol% or more, ii) wherein the CO2-containing stream contains 90 vol% or more CO2, iii) wherein the CO2-containing stream contains 80 vol% or more CO2 from at least a portion of the flue gas; or iv) a combination of two or more of i), ii) and iii).

9. The method according to any of the preceding claims, wherein forming the recycle stream from one or more portions of the flue gas comprises forming the recycle stream from the CO2-containing stream.

10. The method of any of the preceding claims, wherein post-combustion capture of the at least a portion of the flue gas comprises separating the at least a portion of the flue gas using: a membrane separator; an amine scrubber; a liquid phase adsorbent, wherein the liquid is at least partially in the form of droplets or a thin liquid film; or a combination thereof.

11. The method according to any one of claims 1 to 9, wherein post-combustion capture of the at least a portion of the flue gas comprises: exposing the at least a portion of the flue gas to a solid adsorbent to adsorb CO2 on the solid adsorbent; and desorbing at least a portion of the adsorbed CO2 by direct displacement, pressure swing, temperature swing, or a combination thereof.

12. A method according to any one of claims 1 to 9, wherein post-combustion capture of at least a portion of the flue gas comprises: forming a cathode input stream comprising at least a portion of the flue gas; passing the cathode input stream into a cathode of a molten carbonate fuel cell; and operating the molten carbonate fuel cell to generate electricity, an anode output stream, and a cathode output stream corresponding to the CO2-depleted stream.

13. A method according to any of the above claims, wherein the method further comprises passing the at least a portion of the flue gas through a heat recovery steam generator to generate electricity before separating the at least a portion of the flue gas; or wherein the method further comprises adding fuel to the at least a portion of the flue gas and supplementing the at least a portion of the flue gas before performing post-combustion capture on the at least a portion of the flue gas; or a combination thereof.

14. A system for power generation, comprising: a pressure swing adsorption stage, comprising a plurality of pressure swing adsorption vessels, the plurality of pressure swing adsorption vessels containing an adsorbent having kinetic selectivity for O2 relative to N2, the pressure 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 supplemental burner, comprising a supplemental fuel inlet, a a flue gas inlet and a supplementary combustion outlet; a heat recovery steam generator comprising a heat recovery inlet and a heat recovery outlet fluidly connected to the supplementary combustion outlet; and a post-combustion capture stage comprising a capture inlet fluidly connected to 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 comprising solid adsorbents, one or more adsorbent environments comprising liquid adsorbents, or a combination thereof, wherein the one or more combustion inlets are further fluidly connected to at least one of the heat recovery outlet and the CO2-containing product outlet.

15. A system for power generation, comprising: a pressure swing adsorption stage, comprising a plurality of pressure swing adsorption vessels, the plurality of pressure swing adsorption vessels containing an adsorbent having a kinetic selectivity for O2 relative to N2, the pressure 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 connecting 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 fluidly connected to a fuel source and the oxygen-containing product outlet; a heat recovery steam generator, comprising a heat recovery inlet fluidly connected to the combustion outlet and a heat recovery outlet; and a post-combustion capture stage, comprising a capture inlet fluidly connected to 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 membrane separators, one or more molten carbonate fuel cells, or a combination thereof, wherein the one or more combustion inlets are further fluidly connected to at least one of the heat recovery outlet and the CO2-containing product outlet.

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