Method and system for capturing carbon dioxide and generating energy

Abstract

Disclosed are a method and a system for capturing carbon dioxide and generating energy. The method comprises passing atmospheric air through a CO₂ adsorbent to form a CO₂-free stream, and heating the adsorbent to capture CO₂ while producing a recovered waste heat stream. The CO₂-free stream produces energy through a turbine and generator after being compressed and heated, and produces a turbine waste heat stream. The recovered waste heat and the turbine waste heat are recycled to preheat the compressed stream step-by-step through heat exchange, and a portion of the turbine waste heat is also used for adsorbent regeneration heating.

Description

Carbon dioxide capture and energy generation method and system

[0001] The present invention relates to a method and system for carbon dioxide capture and energy generation, and more specifically, to a sector combination of a technology for directly capturing carbon dioxide from the atmosphere and a technology for converting heat generated from nuclear or concentrated solar power generation into electricity using air as a working fluid.

[0002] The present invention is the result of the external open call project (K-Cloud) of Korea Hydro & Nuclear Power, "A feasibility study of the OABC-DAC system for SMR secondary system application (Project No.: 24-Regeneration-19)".

[0003] Direct Air Capture (DAC) refers to the process of directly capturing carbon dioxide present in the atmosphere at a level of approximately 400 ppm. Among existing carbon capture technologies, DAC is the only technology capable of achieving net negative CO₂ emissions throughout the entire process, and it is attracting attention as a key carbon reduction technology for achieving carbon neutrality goals.

[0004] Despite possessing the promising technological capability to significantly reduce atmospheric CO₂ concentrations, current DAC technology suffers from low technological maturity and is utilized only on a very limited scale. According to the International Energy Agency (IEA)'s 2022 report on DAC, approximately 15 DAC projects are currently operating globally, capturing about 9,000 tons of carbon annually. This indicates that the level of commercialization remains low.

[0005] The main obstacles to the commercialization of DAC technology are low energy efficiency and a lack of economic profitability. Compared to post-combustion capture technology, which captures CO₂ from flue gas, DAC consumes more energy because it must capture carbon from air at CO₂ concentrations hundreds of times lower (approximately 400 ppm). According to Goldman Sachs and the IEA, the cost of capturing one ton of CO₂ using DAC technology currently ranges from $125 to $350, which is significantly higher than the cost of post-combustion capture technology ($50–$100).

[0006] Technically, DAC is based on principles similar to conventional carbon capture processes. In particular, adsorption-based capture technologies are widely discussed in DAC applications, with temperature swing adsorption (TSA) playing a significant role. Adsorption is a process of selectively capturing a target gas (e.g., CO₂) using a porous adsorbent; CO₂ is adsorbed using adsorbents such as zeolites or activated carbon, and then desorbed by applying vacuum or heat. This process is performed repeatedly, and the CO₂ adsorption capacity of the adsorbent varies with temperature and pressure.

[0007] Adsorption processes such as pressure swing adsorption (PSA), vacuum swing adsorption (VSA), and temperature swing adsorption (TSA) use pressure, vacuum, and temperature, respectively, as the primary variables. Although DAC technology is conceptually similar to afterburner capture technology, it requires significantly more energy because it must capture carbon from air with low CO₂ concentrations (approximately 400 ppm). The DAC process demands more heat and electricity, and requires large fans to handle large volumes of air. This results in additional energy consumption and leads to increased capital expenditure (CAPEX) and operating expenditure (OPEX).

[0008] To alleviate bottlenecks in DAC technology and strengthen its influence, innovations that reduce energy consumption are necessary. Sector coupling is being discussed as a promising alternative to reduce energy consumption and improve the economic profitability of DAC technology. Sector coupling is a concept that enhances efficiency by combining two or more systems, and in DAC technology, it is implemented through integration with combined heat and electricity systems (e.g., concentrated solar power (CSP)), thermal energy storage, or geothermal systems. However, these heat-centric sector coupling technologies face limitations in efficiency improvement due to the fundamental problem of handling the large volume of intake air required by DAC technology.

[0009] Accordingly, the present invention proposes an innovative approach to integrating an Open-Air Brayton Cycle (OABC) system into sector combinations of DAC technology. OABC systems have been discussed on a small scale since the mid-2010s and primarily use air as a working fluid to convert heat generated from nuclear power or CSP into electricity. This system produces electricity by collecting, compressing, heating, and then expanding air, and the efficiency of the overall system can be increased by adding a heat recovery system after the turbine.

[0010] Although OABC systems are in the early stages of development and have low technical maturity, they do not require a precooling phase because they use ambient air. Consequently, they do not require cooling towers or additional cooling water, making them suitable for power systems in desert or isolated regions where water resources are scarce. Accordingly, the potential for using OABC systems in small-scale next-generation reactors or CSP systems in desert regions is being discussed.

[0011] The OABC system requires a large volume of air intake as the working fluid, and this characteristic is closely related to the requirements of the DAC system. Integrating the two systems has the potential to transfer the costs associated with the large volume of air intake required by the DAC system to the power generation system.

[0012] In addition, the air working fluid used in OABC systems spans a wide temperature range from ambient temperature (15-25°C) to high temperature (over 500°C). This characteristic allows a significant portion of the energy required for heat regeneration in adsorption-based DAC systems to be utilized, and combining the two systems has the potential to significantly improve the energy efficiency of the DAC system.

[0013] Conceptually, sector combining and integrating the OABC system and the DAC system can be a promising approach to dramatically improve the energy efficiency of the DAC system and reduce costs.

[0014] To date, no research has been conducted on sector combination of DAC and OABC systems, and this remains an unexplored field despite its potential benefits. Therefore, the present invention aims to select components of a system combining DAC and OABC systems and to examine its feasibility through preliminary energy cost evaluation.

[0015] To this end, the integration of DAC technology and OABC systems is analyzed to explore ways to optimize overall system efficiency and reduce energy consumption. Furthermore, the present invention aims to provide the potential as a sustainable and economically viable solution for carbon capture and energy generation by evaluating the potential energy effects of the integrated system through thermodynamic evaluation.

[0016] This invention aims to address the issues of high energy consumption and low economic profitability associated with existing Direct Air Capture (DAC) technology for capturing low concentrations of CO₂ in the atmosphere. In particular, it seeks to overcome the difficulties in commercialization caused by the thermal energy consumption required to process large volumes of air and regenerate adsorbents in the DAC process. Furthermore, it aims to maximize thermal energy utilization through efficient integration with Open Air Brayton Cycle (OABC) technology and to resolve the lack of specific design and implementation methods to address the existing high costs and low efficiency associated with thermal integration. Through this, the invention seeks to optimize the system's energy efficiency and overcome technical and economic limitations by combining DAC and OABC.

[0017] In one aspect, the present invention provides a method for carbon dioxide capture and energy generation. The method comprises: (a) drawing in air containing carbon dioxide from the atmosphere; (b) passing the air through a CO2 adsorbent to form a CO2-free stream; (c) heating the CO2 adsorbent to regenerate the CO2 adsorbent, capture desorbed carbon dioxide, and form a regenerated waste heat stream; (d) compressing the CO2-free stream to form a compressed stream; (e) heating the compressed stream to form a heated stream; and (f) producing energy from the fluid energy of the heated stream through a turbine and a generator to form a turbine waste heat stream. and (g) a step of preheating by heat exchange and discharging to the atmosphere prior to the heating of step (e), wherein the heat of the regenerated waste heat stream is recovered and the compressed stream is preheated with the recovered heat to form a first preheating stream, and the regenerated waste heat stream in which heat exchange is performed is discharged to the atmosphere, and the heat of the turbine waste heat stream is recovered and the first preheating stream is preheated with part of the recovered heat to form a second preheating stream, and the remaining part is used to heat the CO2 adsorbent; comprising a step of preheating and discharging to the atmosphere.

[0018] Direct air capture (DAC) technology is a method of directly capturing trace amounts of carbon dioxide contained in the air by separating and capturing the carbon dioxide using methods such as absorption or adsorption. However, commercialization of this technology is difficult due to the excessive consumption of energy required to inhale large amounts of air and thermal energy for the regeneration of adsorbents / absorbents. Accordingly, the present invention aims to combine DAC technology with open air Brayton cycle (OABC) technology, which uses air as a working fluid to convert heat generated from a heat source into electricity.

[0019] The Open Air Brayton Cycle (OABC) is a type of Brayton cycle that utilizes air as the working fluid. It is a system that draws in a large volume of air, compresses it, heats it using a heat source, and generates power through a turbine. In this process, the system is designed to increase efficiency by reducing heat consumption through the recuperation of the compressor outlet using the high-temperature waste heat from the turbine outlet.

[0020] In particular, the present invention derived an optimal configuration by analyzing the configuration of an OABC system and a temperature swing adsorption (TSA)-based DAC system. In addition to simultaneously utilizing a large amount of air drawn from the atmosphere, the invention is configured to utilize high-temperature waste heat from the turbine downstream through multiple heat exchangers for DAC regeneration and reheating from the compressor downstream, and also utilize waste heat from the regeneration downstream for reheating from the compressor downstream.

[0021] The present invention contributes to achieving strategic thermal integration through sector combination of both systems and can improve the overall system utilization by simultaneously utilizing inhaled ambient air. In other words, it proposes a method for optimizing energy efficiency and enabling complementary roles between systems through the integration of DAC and OABC.

[0022] The carbon dioxide capture and energy generation method of the present invention is characterized in that the CO2 adsorbent is maintained in a plurality of separate swing zones, air comes into contact with the adsorbent in at least one swing zone, and is heated in another at least one swing zone to capture carbon dioxide and regenerate the adsorbent.

[0023] The CO2 adsorbent of the present invention is an adsorbent based on temperature swing adsorption (TSA), and may be an amine-functionalized adsorbent as a non-limiting example. To maintain continuous operation of the TSA process, two or more adsorption towers may be included. While adsorption is being performed in one tower, the other tower may be performing desorption or cooling. This allows the DAC system to continuously capture CO2 without process interruption.

[0024] The carbon dioxide capture and energy generation method of the present invention is characterized by further including a step of removing water vapor from the air of step (a). The inhaled air can be dried to meet the dew point that the DAC system can withstand.

[0025] In the carbon dioxide capture and energy generation method of the present invention, the carbon dioxide captured in step (b) can be compressed and stored or transported.

[0026] In the carbon dioxide capture and energy generation method of the present invention, heating in step (e) may be heating by heat released from nuclear or solar power generation.

[0027] In another aspect, the present invention provides a carbon dioxide capture and energy generation system. The system comprises: an air intake unit including an air intake device for drawing in air containing carbon dioxide from the atmosphere; a carbon dioxide capture unit into which the air containing carbon dioxide is introduced and which includes a CO2 adsorbent, which passes the introduced air through the CO2 adsorbent to discharge a CO2-free stream, which heats the CO2 adsorbent to capture desorbed carbon dioxide, and which discharges a regenerated waste heat stream; an air compression unit into which the CO2-free stream is introduced and which includes a compressor for compressing the introduced CO2-free stream and which discharges the compressed stream; a preheating unit into which the compressed stream is introduced and which includes a plurality of heat exchangers, which preheats the introduced compressed stream by heat recovered through the heat exchangers and discharges the preheated stream; and a heating unit into which the preheated stream is introduced and which includes a heat source, which heats the introduced preheated stream by the heat source and discharges the heated stream. The present invention comprises: a power generation unit into which the heated stream is introduced and which includes a turbine and a generator, and which produces energy from the fluid energy of the heated stream through the turbine and the generator and discharges a turbine waste heat stream; and an air discharge unit that discharges a stream in which heat recovery has been performed through a heat exchanger of the preheating unit to the atmosphere; wherein the regenerated waste heat stream and the compressed stream are introduced into at least one of the plurality of heat exchangers, the heat of the regenerated waste heat stream is recovered, and the compressed stream is preheated with the recovered heat to discharge a first preheating stream, and the regenerated waste heat stream in which heat recovery has been performed is discharged to the air discharge unit, and the turbine waste heat stream and the first preheating stream are introduced into at least one other heat exchanger, the heat of the turbine waste heat stream is recovered, the CO2 adsorbent is heated with part of the recovered heat, and the first preheating stream is preheated with the remaining heat to discharge a second preheating stream.

[0028] In the carbon dioxide capture and energy generation system of the present invention, the CO2 adsorbent is maintained in a plurality of separate swing zones, and in at least one swing zone, air comes into contact with the adsorbent, and in at least one other swing zone, the adsorbent is heated to capture CO2 and regenerate the adsorbent.

[0029] In the carbon dioxide capture and energy generation system of the present invention, the air intake unit is characterized by further including a dryer for drying the air.

[0030] In the carbon dioxide capture and energy generation system of the present invention, the carbon dioxide capture unit is characterized by further including a device for storing or transporting the captured carbon dioxide.

[0031] In the carbon dioxide capture and energy generation system of the present invention, the heat source is characterized as being nuclear or solar power generation.

[0032] Direct Air Capture (DAC) technology is essential for achieving carbon neutrality, as it enables net-negative CO2 emissions. However, the commercialization of this technology faces a significant challenge due to high energy requirements. Although various thermal integration attempts have been made to address this issue, the high cost of extracting large quantities of low-concentration CO2 from the atmosphere remains unresolved. This invention proposes a method to improve overall system utilization by integrating an Open-Air Brayton Cycle (OABC) to simultaneously utilize large quantities of atmospheric air. The configuration of a Temperature Swing Adsorption (TSA)-based DAC system combined with various OABCs was analyzed, and an optimal configuration was derived by considering different regeneration temperatures. As a result of the analysis, an optimal system configuration was identified that can significantly reduce the energy cost per unit of CO2 captured while achieving high purity and a high recovery rate. The present invention combines the equilibrium short-cut model of TSA with process simulation methodologies to present the concept of "energy cost," which represents the amount of captured CO2 relative to the energy penalty incurred in a DAC system combined with an OABC system. In the present invention, it was confirmed that the integration of OABC and DAC systems creates synergy in terms of energy consumption through strategic thermal management and the use of high-performance adsorbents, and that high-purity and high-recovery CO2 can be effectively captured.

[0033] The present invention integrates a DAC and an OABC system to efficiently utilize turbine waste heat and adsorbent regeneration waste heat during the regeneration process, thereby reducing energy consumption for CO₂ capture and improving economic feasibility. This enables the achievement of high purity (over 95%) and a high recovery rate (approximately 50%), while maximizing overall system efficiency through thermal integration and transferring air treatment costs to the power generation system, thereby increasing the commercialization potential of the DAC. Furthermore, by utilizing eco-friendly heat sources such as nuclear or solar power generation, energy can be generated without carbon emissions, contributing to the achievement of sustainable carbon neutrality goals. Additionally, the system is designed to be applicable across various heat sources and scales, ensuring both scalability and economic feasibility.

[0034] Figure 1 is a schematic diagram of the OABC system.

[0035] Figure 2 shows the flowsheet, sensitivity analysis results, and characteristics at optimal efficiency of a specific OABC system.

[0036] Figure 3 is a conceptual diagram of the swing adsorption process.

[0037] Figure 4 is a schematic diagram of possible cases of an OABC-DAC system.

[0038] Figure 5 is a schematic diagram of the 3-stage TSA process.

[0039] Figure 6 is a graph verifying the code implementation through comparison with reference (Jiajun et al. (2023)).

[0040] Figure 7 is a graph of the temperature-dependent isotherm fitting of mmen-Mg2(dobpdc) for CO2 and N2.

[0041] Figure 8 is a graph showing the results of the DAC design analysis in Case 1.

[0042] Figure 9 is a graph showing the results of the DAC design analysis in Case 1.

[0043] Figure 10 is a graph of purity and recovery rate for Case 3 and Case 4 at the regeneration temperature.

[0044] Figure 11 is a graph showing the results of the Case 3 DAC design analysis at a playback temperature of 600 K.

[0045] Figure 12 is a schematic diagram showing the additional boundary conditions of the OABC-DAC system due to the addition of a DAC.

[0046] Figure 13 is a graph of the efficiency and energy cost of an OABC-DAC system according to compression ratio and DAC regeneration temperature drop (α).

[0047] Figure 14 is a graph of energy cost as a function of α at the optimal compression ratio of the OABC-DAC system.

[0048] FIG. 15 is a representative drawing according to one embodiment of the present invention.

[0049] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Since the present invention is susceptible to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention. Similar reference numerals have been used for similar components in the description of each drawing. In the attached drawings, the dimensions of the structures are shown enlarged compared to the actual dimensions for the clarity of the present invention.

[0050] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention.

[0051] In addition, the description of one aspect of the present invention may be applied identically or similarly to the description of other aspects for identical or similar configurations or terms.

[0052] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0053] The embodiments of the present invention are described below. However, the embodiments described below are merely partial embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments.

[0054] Experimental method

[0055] OABC-DAC System Description

[0056] Figure 1 is a schematic diagram of an OABC system. Before discussing the sector coupling of the DAC and the OABC system, the general configuration of the OABC system must first be reviewed. In this invention, the OABC system design elements proposed by Bahman et al. (2014) were adopted for preliminary research purposes. Table 1 shows the design parameters of the OABC system components presented in that study. Additionally, the air was assumed to be dry, and its composition was set as shown in Table 2.

[0057] Heat recovered OABC reference modelTurbine inlet temperature933 KTurbine polytropic efficiency90%Compressor polytropic efficiency90%Compressor pressure ratioCalculatedMain heater pressure ratio0.99Recuperator effectiveness0.95Pressure ratio of the hot side of the recuperator0.99Atmospheric pressure1 atmAtmospheric temperature288 KRatio of exhaust pressure to atmospheric pressure0.98

[0058] Components of dry air: Nitrogen Balance, Oxygen 20.95%, Argon 0.93%, CO 20.04%

[0059] Figure 2 shows the optimal compression ratio and temperature / pressure conditions determined using DWSIM17. The fluid properties were determined using the CoolProp18 package for the equation of state. The power generation efficiency of this system was found to be 43.97%, which was used as a reference value in subsequent analyses. According to the analysis results of the OABC system shown in Figure 2, the OABC system generates waste air at a relatively high temperature of approximately 400K, which exhibits characteristics suitable for TSA from the perspective of the adsorption process. TSA is a process that utilizes the properties of substances that are easily adsorbed at low temperature and high pressure and easily desorbed at high temperature and low pressure to separate a desired gaseous substance from a mixed gas. Figure 3 conceptually illustrates this adsorption swing process. Depending on the temperature and pressure conditions under which adsorption and desorption occur, swing adsorption processes can be classified into PSA, TSA, temperature-PSA (TPSA), and temperature-VSA (TVSA).

[0060] The integration of the OABC system and the DAC system can be designed to maximize the utilization of heat generated from high-temperature exhaust gas. This integration can be conceptualized into four specific cases, and Figure 4 shows a schematic diagram of the OABC-DAC system corresponding to each case.

[0061] Case 1: The DAC system utilizes a TSA process designed not to compromise the optimal operating point of the OABC system. Adsorption is performed before the compressor stage, and air from the hot-side outlet of the recuperator is used for desorption. This method utilizes available thermal energy without affecting the efficiency of the OABC system.

[0062] Case 2: The DAC system is configured to use the TPSA process, adsorption is performed after the compressor stage (node ​​2), and desorption is performed using air from the hot side outlet of the heat recovery unit. This configuration utilizes a smaller temperature difference than Case 1, but has the advantage of being able to utilize an additional pressure difference.

[0063] Case 3: Adsorption is performed before the compressor stage, and only a portion of the heat recovered after the turbine stage is initially used in the DAC process. The remaining heat is utilized for heat recovery in the OABC system. This method aims to improve the efficiency of the OABC system by using some thermal energy preferentially in the DAC process and then using the remaining heat.

[0064] Case 4: Adsorption is performed after the compressor stage (node ​​2), and similar to Case 3, a portion of the heat recovered after the turbine stage is initially used for the DAC process. The remaining heat is then utilized for heat recovery in the OABC system. This approach differs from Case 3 at the adsorption point and offers another possibility for balancing the benefits of temperature and pressure.

[0065] TSA model for DAC

[0066] Figure 5 shows a schematic diagram of a DAC system utilizing temperature (and pressure) swing adsorption. In the initial stage, the target component, CO₂, is adsorbed as it passes through an adsorption tower. In the TSA process, this stage is carried out under low temperature and high pressure conditions and continues for a sufficiently long time until the adsorbent is saturated with the component.

[0067] Once the adsorbent is sufficiently saturated with the components, the adsorption tower is heated to collect the desorbed gas. This collected gas contains a high concentration of CO₂ and must be further controlled to achieve the purity required for CCS. Finally, the adsorption tower is cooled to a temperature suitable for resuming the adsorption process.

[0068] This constitutes a basic 3-stage TSA process, but modified methods may also exist, such as the addition of a vacuum process between heating and cooling. In the present invention, the compatibility of this basic 3-stage TSA process with the OABC process was evaluated.

[0069] There are two main methods for simulating swing adsorption processes. The first method involves modeling a fixed column bed in one dimension and solving the mass, energy, and momentum conservation equations over time during the adsorption / desorption process. This method is generally used to simulate PSA processes and is suitable when adsorption times are short and the process is completed before a breakthrough. This method requires relatively detailed information regarding the column bed geometry and processing times, and demands significant computational resources to solve the differential equations. Therefore, this method is primarily used to optimize process time during the initial screening stage, provided that the adsorbent type and process information (capacity, size, etc.) are determined in great detail.

[0070] The second method is known as the equilibrium-based short-cut model, which solves the process under the assumption that each step operates until it reaches an equilibrium state. This method has the advantage of not requiring column geometry information or operational data, and allows for the fundamental evaluation of key performance indicators such as purity and recovery rate by utilizing the adsorbent isotherm. Therefore, it is suitable for the preliminary analysis of the TSA process, where the adsorption or desorption steps proceed for a relatively long period. Considering these points, the present invention aims to analyze the TSA process using the equilibrium-based short-cut model.

[0071] The equilibrium-based uniaxial model simulates the TSA process by simplifying it based on the following assumptions:

[0072] Since the adsorption column maintains a mixed state during the heating and cooling processes, there are no axial or radial temperature and concentration gradients.

[0073] - The adsorption phase proceeds until a complete breakthrough is reached.

[0074] - The pressure drop inside the adsorption column is ignored.

[0075] - The thermal resistance and heat capacity of the adsorption column are neglected, and it is assumed that each stage reaches equilibrium before proceeding to the next stage.

[0076] It has been reported that these assumptions provide reasonable computational speed and acceptable accuracy in long-term TSA system simulations. However, the recovery rate tends to be overestimated when compared to relatively accurate purity results. Therefore, the recovery rate evaluated in this invention will be considered only as a reference for trends. Based on the above assumptions, each step of the TSA process can be simply modeled as follows.

[0077] Adsorption step

[0078] Under the assumptions mentioned above, the adsorption step proceeds until the adsorption level reaches a value defined by the adsorption isotherm. Taking this into account, the amount of component i (q) adsorbed by the adsorbent i The mole fraction (y) of the outlet stream at the end of the adsorption step is determined using equations (1) and (2):

[0079] , (1)

[0080] . (2)

[0081] Playback stage

[0082] After the adsorption step, CO₂ trapped inside the adsorbent is separated during the heating step, and the adsorbent is regenerated. The regeneration step involves a process in which the internal temperature of the adsorbent changes and proceeds for a relatively short period of time. If the same ideal assumptions as in the adsorption step are applied and only the final state is used in the calculation, a large error may occur. Therefore, it is appropriate to model this step by dividing the process into several sub-steps and assuming that each sub-step proceeds until equilibrium is reached. Accordingly, Equations (3) and (4) can be used to calculate the conditions of the k+1th sub-step based on the equilibrium result of the kth sub-step. Equation (3) represents the adsorption isotherm, and Equation (4) represents the concentration of component i in the k+1th sub-step determined by the reduced adsorption amount (i.e., the released adsorption amount) in the previous sub-step.

[0083] , (3)

[0084] . (4)

[0085] In particular, designated under conditions and Iterative calculation is required to calculate . This is because each parameter is determined by other parameters. Such iterative calculation can be performed using the bisection method or the secant method, and in the present invention, the calculation was performed using the secant method.

[0086] Cooling stage

[0087] In this step, the adsorption bed inlet is opened and the top product outlet is closed, and then the bed temperature is cooled to the supply temperature using a cooling fluid. In this step, the bed pressure is equal to the adsorption pressure (i.e., the supply pressure), and the inlet mole fraction is equal to the mole fraction of the supply air. Similar to the heating step, this cooling step is also modeled as the sum of equilibrated sub-steps using ideal assumptions. Equations (5) and (6) are identical to the numerical representations used in the heating step:

[0088] , (5)

[0089] . (6)

[0090] Performance metrics

[0091] TSA is a process that generates process gas by repeating cycles of adsorption, heating, and cooling. Although various performance indicators exist for this process, this invention focuses on analyzing the most fundamental output indicators: the purity and recovery rate of the captured and separated CO₂.

[0092] Purity is defined as the ratio of CO₂ to the gas collected during the regeneration process, and in the present invention, it can be defined as the ratio of CO₂ to the total gas generated during the heating step. This can be calculated based on the amount of gas captured by the adsorbent in the previous adsorption step and the amount of gas collected at the end of the heating step, and is expressed by Equation (7).

[0093] . (7)

[0094] The recovery rate represents the ratio of CO₂ recovered during the heating process to the total amount of CO₂ introduced into the adsorption bed during the adsorption and cooling processes. This can be calculated using Equation (8). The amount of CO₂ that passes through the adsorption bed without being adsorbed during the adsorption and cooling steps is It is indicated as such, and the total amount of gas introduced can be estimated by recalculating the gas mole fraction and partial pressure at the end of each stage. This is expressed by Equation (9).

[0095] , (8)

[0096] . (9)

[0097] Finally, the heat of regeneration can be calculated by multiplying the heat of adsorption by the difference in adsorption amount before and after regeneration, which is expressed by Equation (10).

[0098] . (10)

[0099] These equations can be used to quantitatively evaluate the feasibility and efficiency of the TSA process in DAC applications in terms of the quality (purity), quantity (recovery rate), and cost (regeneration heat) of CO₂ capture.

[0100] TSA Model Verification

[0101] To validate the developed model, a comparison was performed based on the model presented in the study by Wang et al. The results of the validation are shown in Figure 6. In this comparison, a four-stage pressure-temperature swing adsorption (PTSA) process was used, and the key process data used in the simulation were directly adopted from the values ​​presented in the paper.

[0102] Since this model is based on simple equilibrium assumptions, it is reasonable to expect that the results will be in perfect agreement. This indicates that the model adopted in this invention was accurately simulated without computational problems. These results demonstrate the reliability of the model in reproducing the PTSA process described in detail in reference studies and show that it can be utilized as a verified model for further analysis in this invention.

[0103] OABC-DAC Layout Study

[0104] DAC performance based on the OABC-DAC layout

[0105] The performance of the DAC system was analyzed according to the layout (Cases 1-4) presented in Fig. 4. The analysis considered the influence of temperature on purity and recovery rate, particularly because the regeneration temperature in Cases 3 and 4 can be considered a variable that can be changed during the design process. Prior to the analysis, it is necessary to select an adsorbent suitable for the example model of the DAC system.

[0106] Adsorbent Selection and Isotherm Model

[0107] Adsorbents for DAC must possess high selectivity even at low CO₂ concentrations, which limits the range of suitable candidates. Conventional physical adsorbents, such as zeolites and activated carbon, are not suitable for DAC due to their low equilibrium constant for CO₂ (<1.0 mmol / g) under air conditions with high nitrogen concentrations. Candidates for selective CO₂ adsorption include metal-organic frameworks (MOFs) and amine-functionalized adsorbents; however, according to Leonzio et al., amine-functionalized adsorbents are expected to be more useful than MOFs in DAC applications. Furthermore, previous studies have identified mmen-Mg₂(dobpdc) as an attractive adsorbent for DAC through material characterization and simulation. This adsorbent has also been considered as a candidate in research on the development of DAC systems utilizing building waste heat. Therefore, although the concept differs, mmen-Mg₂(dobpdc) was selected as a candidate adsorbent for the DAC system in this invention. According to previous studies, gases other than N₂ and CO₂ (such as O₂ and argon) exhibit much lower selectivity than N₂. Therefore, for conservative calculations, all other gases in this study were considered as N₂. The Langmuir-Henry isotherms (Equations (11)–(14)) were adopted for CO₂ adsorption isotherms, and the Langmuir isotherm (Equation (15)) was used for N₂ adsorption isotherms. Table 3 lists the parameters of the isotherm model, and Figure 7 shows the trend of the isotherm model.

[0108] , (11)

[0109] , (12)

[0110] , (13)

[0111] , (14)

[0112] . (15)

[0113] Isotherm Model ParametersValueParametersValueParametersValue 313.15 K 18,000 J / mol 0.036 51 Pa 74290 J / mol 0 28.25 mol / kg 70740 J / mol 0.53 3.5 mol / kg 1351 J / mol 2.5 x 10 -17 Pa -1 5.33 x 10 -9 mol / kg 67720 J / mol 2.58 x 10 -8 Pa -1 0.154 mol / kg 18670 J / mol 2.4 x 10 -13 Pa -1 8.314 J / mol / K 71,000 J / mol 18,000 J / mol 31

[0114] DAC Performance Analysis

[0115] The potential performance of the DAC system was analyzed when the DAC system was configured as in Cases 1-4, based on the design points of the optimized OABC system presented in Fig. 2. To simulate the DAC using a uniaxial equilibrium model, information on the adsorption pressure, desorption pressure, adsorption temperature, and desorption temperature is required. Table 4 lists the conditions for each case.

[0116] Design conditions T of a DAC using the OABC-DAC system ads T heat P ads P heat Case 1288 K395.91 K1 atm1 atmCase 2375.10 K395.91 K2.325 atm1 atmCase 3288 KVariable1 atm1 atmCase 4375.10 KVariable2.325 atm1 atm

[0117] In Cases 1 and 2, waste heat generated at the high-temperature end of the heat recovery unit is used directly in the regeneration process. This has the advantage of not affecting cycle efficiency because the heat used for regeneration does not impact the power generation system. However, it has the disadvantage that the temperature of the heat source available for regeneration is limited. Figures 8 and 9 show the results of analyzing these two cases using an equilibrium-based uniaxial approach. The analysis results showed that the layouts that do not sacrifice thermal energy (Cases 1 and 2) exhibited purity of 27.78% and 0.126%, respectively. These values ​​are significantly lower than the minimum purity (95%) required for Carbon Capture and Storage (CCS). Furthermore, when air after compression is utilized for adsorption, it was observed that the loss in adsorption capacity outweighs the benefits gained from compression due to the temperature rise occurring during the compression process. Although additional cooling after compression must be performed to mitigate this, it is expected to have a significant impact on the overall system efficiency.

[0118] The low purity issue can be improved by allocating some thermal energy to raise the regeneration temperature. Figure 10 shows the purity and recovery rate of the DAC system when some thermal energy is allocated from the heat recovery unit to raise the temperature to a specific level. Increasing the regeneration temperature resulted in a monotonic increase in both the purity and recovery rate of the DAC system.

[0119] In addition, when air after compression is utilized for adsorption as in Case 2 (Case 4), it was found that the temperature rise occurring after compression had a very negative impact on purity and recovery rate. On the other hand, the system in Case 3 achieved a purity of over 95% and a relatively high recovery rate of about 50%. It is noteworthy that when a certain temperature (about 550-600K) is exceeded, the effect on purity and recovery rate reaches a near-saturation point, and even if the temperature is further increased, the impact on system performance is minimal.

[0120] According to theoretical calculations, this DAC system is expected to achieve 96.30% purity and 49.67% recovery rate under playback conditions of 600K. Figure 11 shows the analysis results for the DAC design at this point.

[0121] Table 5 shows the CO₂ capture purity and recovery rate of the DAC system in four layouts, Cases 1-4. According to the results, Case 3, which captures CO₂ upstream of the compressor and utilizes part of the turbine exhaust heat for regeneration, demonstrated superior performance in both purity and recovery rate. All other cases were found to have issues with purity, recovery rate, or both.

[0122] OABC-DAC System Design Results According to Each Configuration PurityRecoveryCase 127.78%14.86%Case 20.126%1.848%Case 396.30%49.67%Case 43.383%49.72%

[0123] From the perspective of the energy cost estimation cycle through cycle analysis, two major effects that may affect the OABC system and the DAC system integrated with it can be considered.

[0124] First, additional heating or cooling may occur due to the exothermic nature of the adsorption process and the endothermic nature of the desorption process. Since the adsorption process is an exothermic reaction, the gas after adsorption is supplied to the compressor in a partially heated state, which reduces the heat supplied from the heat source and has a positive effect on the OABC system. Conversely, this has a negative effect on Case 3, which is the most attractive option for separating CO₂ with appropriate purity in the OABC-DAC system layout, due to heat recovery losses in the system. In this invention, only the desorption effect was considered for conservative assumptions.

[0125] Second, a pressure drop may occur due to the addition of adsorption towers and other valves. However, this generally does not have a significant impact. In the initial calculations of the present invention, the pressure drop through the DAC system was assumed to be 1%, which is the same as the pressure drop through the heat exchanger (see Table 3).

[0126] Cycle analysis was performed on a DAC system where playback takes place at 600K. Additional system boundary conditions resulting from the addition of the DAC system are shown in Fig. 12. Other system design data were directly adopted from the conditions presented in Table 1.

[0127] Based on the results presented in the previous chapter, the power loss of the system required to capture CO₂ in units when the DAC system is applied to the OABC system can be simply calculated. This calculation can be used to concisely derive the energy cost. The amount of heat required to capture a unit of CO₂ can be calculated using Equation (16). Under the design conditions presented in Fig. 11 (Case 3), the heat required for the corresponding DAC system was calculated to be 1.63 MJ / kgCO₂.

[0128] . (16)

[0129] The total energy cost resulting from the addition of the DAC system can be calculated in comparison to an OABC system without a DAC system. For the convenience of calculation, it is assumed that there is a temperature decrease of αK from the DAC regeneration side inlet temperature (600K) due to the heat consumed for the regeneration of the DAC system. In this case, the total flow rate of the OABC system Let it be denoted as, and the heat capacity under specific conditions is C p If so, the total heat used for regeneration is The amount of CO₂ that can be captured in a DAC system designed using this heat is expressed by Equation (17):

[0130] . (17)

[0131] The energy cost of the OABC-DAC system can be calculated using Equation (18):

[0132] , (18)

[0133] Here, β represents the power generation loss that occurs compared to a standalone OABC system due to the heat used for DAC system playback, and α is a function of the compressor's compression ratio and α in steady-state cycle calculations. Therefore, the change in energy cost due to changes in these two variables can be calculated through cycle analysis.

[0134] Figure 13 shows the efficiency and carbon capture energy cost of the OABC-DAC system as a function of α and the compression ratio. The results provide two main implications. First, α does not affect the optimal compression ratio that optimizes the power generation efficiency of the OABC system. Nevertheless, as intuitively expected, system efficiency tends to decrease as the temperature drop for DAC regeneration increases. Second, the energy cost of the DAC tends to decrease as the compression ratio and α increase. This indicates that energy costs can be reduced even if heat is extracted from the midpoint of the heat recovery unit for regeneration, as the impact on the efficiency of the power generation system is small. Figure 14 graphs the change in energy cost according to α at the optimal point of the system. According to the results, the capture cost tends to decrease very rapidly as α increases.

[0135] FIG. 15 is a representative drawing according to one embodiment of the present invention.

[0136] Discussion and Future Research Tasks

[0137] The present invention proposed and evaluated the integration of a DAC system and an OABC system to achieve high purity and low energy costs for CO₂ capture. The layout of the DAC system shown in Fig. 4 (Case 1-4) was analyzed, and the regeneration temperature was considered as a design modification variable. The main objective was to evaluate potential performance improvements and identify the configuration with the highest energy efficiency.

[0138] To analyze the TSA-type DAC system, the proposed layout was evaluated using an equilibrium-based single-line model. Initial results revealed that when thermal energy was not redistributed, the CO₂ purity levels in the DAC systems of Cases 1 and 2 fell far short of the CCS readiness criteria. Subsequent analysis confirmed that when some heat from the heat recovery unit was strategically distributed for DAC regeneration (Cases 3 and 4), both purity and recovery rates were significantly improved. In particular, Case 3 demonstrated the potential to maintain a recovery rate of approximately 50% while achieving a CO₂ purity of over 95%, highlighting the effectiveness of the system in terms of thermal management.

[0139] Additionally, the concept of energy costs was introduced to quantitatively evaluate the proposed layout. Since the proposed OABC-DAC system is not entirely dedicated to DAC operations, there were limitations in directly calculating the energy costs required for CO₂ capture, as is done in conventional DAC systems. Accordingly, the system's power generation capacity was calculated based on the optimal output of a standalone OABC system. The energy penalty resulting from pressure and heat losses due to the integration of the DAC system was considered as the carbon capture cost. The analysis confirmed that the energy cost can be represented as a monotonically decreasing function of the temperature drop (α) incurred for DAC system regeneration. When this temperature drop exceeds 10K, the energy cost is 1 MJ e It decreased to below / kgCO₂. This corresponds to existing DAC systems being at least 5-6 MJ th Compared to the thermal energy of / kgCO₂ and the additional hundreds of kilowatt-hours (kWh) of electricity required, it is considered a highly innovative solution.

[0140] Since this invention assumes an ideal TSA system for DAC and focuses on a simplified model system, further research is required to develop the system design in greater detail. To enhance the completeness of the design, it is necessary to consider the applicability of various adsorbents or to conduct more detailed simulations of the TSA system. As this invention utilizes a simplified uniaxial equilibrium model, comparative analysis must be performed with experimental studies on the adsorption and desorption processes of an actual DAC system, taking into account the time required for cooling and heating. Through this, the impact on purity and recovery rate can be verified by comparing with simulation results.

[0141] While the present invention has evaluated energy consumption, an actual cost analysis is also necessary to assess the economic feasibility of the system. Additional economic feasibility studies must be conducted to properly evaluate the proposed layout. This economic analysis must include key equipment excluded from the current layout study, which may reduce the analyzed energy efficiency. For example, additional data is required regarding the dew point that the DAC system can withstand, and an air dryer may be added to meet this requirement. Furthermore, scale factors not considered in the current analysis must also be incorporated. Once the actual power output and CO₂ capture capacity are determined, factors such as site area must be considered, and the design may be adjusted to include multiple compressors / turbines depending on the scale. Consequently, CO₂ capture costs and energy efficiency may vary depending on the system capacity. Upon completion of this analysis, the optimal capacity that minimizes the CO₂ capture cost of the proposed layout will be determined, and at this stage, the strengths and weaknesses of the proposed system can be evaluated through quantitative comparison with similar systems.

[0142] Despite these limitations, the present invention conceptually demonstrated that the integration of a DAC system and an OABC system can produce synergistic effects and enable an environmentally friendly process. Furthermore, unlike a standalone DAC system, this system was shown to significantly reduce energy consumption while minimizing efficiency losses in the OABC system. This suggests a promising direction for developing efficient and cost-effective carbon capture solutions by leveraging the advantages of DAC and OABC technologies.

[0143] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. (a) A step of inhaling air containing carbon dioxide from the atmosphere; (b) a step of passing the air through a CO2 adsorbent to form a CO2-free stream; (c) a step of regenerating the CO2 adsorbent and capturing desorbed carbon dioxide and forming a regeneration waste heat stream by heating the CO2 adsorbent; (d) a step of compressing the above CO2-free stream to form a compressed stream; (e) a step of heating the compressed stream to form a heated stream; (f) a step of producing energy from the fluid energy of the heated stream through a turbine and a generator and forming a turbine waste heat stream; and (g) a step of preheating by heat exchange and discharging to the atmosphere prior to the heating of step (e) above, wherein the heat of the regenerated waste heat stream is recovered and the compressed stream is preheated with the recovered heat to form a first preheating stream, and the regenerated waste heat stream in which heat exchange is performed is discharged to the atmosphere, and the heat of the turbine waste heat stream is recovered and the first preheating stream is preheated with part of the recovered heat to form a second preheating stream, and the remaining part is used to heat the CO2 adsorbent; comprising Carbon dioxide capture and energy generation method.

2. In Paragraph 1, The above CO2 adsorbent is maintained in a plurality of separate swing zones, in at least one swing zone the air comes into contact with the adsorbent, and in at least one other swing zone the adsorbent is heated to capture carbon dioxide and regenerate the adsorbent. Carbon dioxide capture and energy generation method.

3. In Paragraph 1, (a) further comprising a step of removing water vapor from the air of step, Carbon dioxide capture and energy generation method.

4. In Paragraph 1, (b) The carbon dioxide captured in step (b) can be compressed for storage or transported, Carbon dioxide capture and energy generation method.

5. In Paragraph 1, (e) In step, heating may be heating by heat released from nuclear or solar power generation, Carbon dioxide capture and energy generation method.

6. An air intake unit including an air intake device for inhaling air containing carbon dioxide from the atmosphere; A carbon dioxide capture unit that receives air containing the above-mentioned carbon dioxide and includes a CO2 adsorbent, passes the received air through the CO2 adsorbent to discharge a CO2-free stream, heats the CO2 adsorbent to capture desorbed carbon dioxide, and discharges a regenerated waste heat stream; The above CO2-free stream is introduced, and the air compression unit includes a compressor that compresses the introduced CO2-free stream and discharges the compressed stream; A preheating unit that receives the above-mentioned compressed stream and includes a plurality of heat exchangers, preheats the incoming compressed stream by heat recovered through the heat exchangers, and discharges the preheated stream; A heating unit that receives the above-mentioned preheated stream, includes a heat source, heats the incoming preheated stream by the heat source, and discharges the heated stream; A power generation unit into which the above-mentioned heated stream is introduced and which includes a turbine and a generator, and which produces energy from the fluid energy of the above-mentioned heated stream through the turbine and the generator and discharges a turbine waste heat stream; and It includes an air discharge unit that discharges the stream, through which heat recovery has been performed via the heat exchanger of the preheating unit, into the atmosphere; The regenerated waste heat stream and the compressed stream are introduced into at least one of the plurality of heat exchangers, heat of the regenerated waste heat stream is recovered, the compressed stream is preheated with the recovered heat to produce a first preheating stream, and the regenerated waste heat stream with recovered heat is discharged to the air discharge section; the turbine waste heat stream and the first preheating stream are introduced into at least one other heat exchanger, heat of the turbine waste heat stream is recovered, the CO2 adsorbent is heated with a portion of the recovered heat, and the first preheating stream is preheated with the remaining heat to produce a second preheating stream. Carbon dioxide capture and energy generation system.

7. In Paragraph 6, The above CO2 adsorbent is maintained in a plurality of separate swing zones, in at least one swing zone the air comes into contact with the adsorbent, and in at least one other swing zone the adsorbent is heated to capture CO2 and regenerate the adsorbent. Carbon dioxide capture and energy generation system.

8. In Paragraph 6, The above air intake unit further includes a dryer for drying the air, Carbon dioxide capture and energy generation system.

9. In Paragraph 6, The above carbon dioxide capture unit further includes a device for storing or transporting the captured carbon dioxide. Carbon dioxide capture and energy generation system.

10. In Paragraph 6, The above heat source is characterized as being nuclear or solar power generation, Carbon dioxide capture and energy generation system.

Images