A method and system for calcium looping capture of co2 driven by ammonia cracking

Abstract

This invention discloses a method and system for capturing CO2 using ammonia cracking-driven calcium cycle. The method includes the following steps: the flue gas to be treated reacts with a CaO adsorbent in a carbonation tower to remove CO2 and generate CaCO3; the CaCO3 product is fed into a calcining furnace, calcined to generate CaO, and then fed back into the carbonation tower for further CO2 removal; NH3 is pressurized and enters an ammonia cracking reactor to react, the heat of which is provided by the heat generated in the carbonation tower; the product from the ammonia cracking reactor enters a burner, mixes with pressurized air, and is burned, the heat released during combustion providing heat for the calcination reaction in the calcining furnace. Using this method, the energy penalty of the calcium cycle combustion-based CO2 capture process can be significantly reduced, effectively reducing the capture energy consumption of the calcium cycle combustion-based CO2 capture technology and improving energy efficiency.

Description

Technical Field

[0001] This invention relates to the field of CO2 capture technology, specifically to a method and system for capturing CO2 using ammonia cracking-driven calcium cycling. Background Technology

[0002] Carbon dioxide capture and storage (CO2 capture and storage) is expected to become key to mitigating CO2 emissions and reducing environmental impact. Among different CO2 capture technologies, post-combustion CO2 capture is the only end-of-pipe capture method that can reduce carbon emissions from stationary sources without altering industrial plants.

[0003] Calcium cycle post-combustion capture technology achieves decarbonization of flue gas after combustion by employing calcium-based adsorbents in a reversible carbonation / calcination reaction under medium-to-high temperature conditions. It has attracted considerable attention due to the wide availability and low cost of adsorbents. Efficiently recovering the sensible heat of the medium-to-high temperature flue gas and the heat released by the carbonation reaction during the calcium cycle post-combustion capture process through organized thermodynamic circulation is a crucial means of reducing the energy consumption of the calcium cycle post-combustion capture system. However, recovering the heat of carbonation and sensible heat of the flue gas by heating the working fluid will generate a large heat exchange temperature difference and a significant grade difference in the energy transfer process, resulting in substantial irreversible losses during the carbonation heat recovery process. Furthermore, since the calcination process requires the absorption of high-temperature heat, fossil fuel combustion is typically used to provide heat for the calcination process. To avoid additional CO2 emissions from the fuel, pure oxygen is usually produced by an air separation unit for oxygen-enriched combustion or chemical looping combustion is used to avoid dilution of the fuel's carbon composition. However, these technologies all introduce additional CO2 capture requirements due to the use of fossil fuels for energy. This invention addresses the issues of temperature gaps in carbonation heat recovery and additional CO2 capture requirements arising from fossil fuel energy supply during the calcination process in calcium cycle combustion capture technology. It proposes using zero-carbon fuel to provide energy for calcium cycle combustion capture and recovering the intermediate-temperature heat from the carbonation process through chemical reheating. This effectively avoids the additional CO2 capture requirements caused by energy supply and efficiently recovers the isothermal heat released during carbonation, preventing significant irreversible losses caused by large temperature difference heat exchange. Summary of the Invention

[0004] To address the temperature gap in heat recovery during the carbonation process of the calcium cycle in post-combustion capture technology and the additional CO2 capture demand caused by fossil fuel energy supply during the calcination process, this invention provides an ammonia cracking-driven calcium cycle CO2 capture method and system, which can effectively reduce the capture energy consumption of calcium cycle post-combustion capture technology and improve energy efficiency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of this invention provides a method for capturing CO2 using an ammonia cracking-driven calcium cycle, comprising the following steps:

[0007] (1) The flue gas to be treated reacts with CaO adsorbent in the carbonation tower to remove CO2 and generate CaCO3;

[0008] (2) The product CaCO3 is sent to a calcining furnace, calcined to produce CaO, and then sent to a carbonation tower for further CO2 removal.

[0009] (3) NH3 is pressurized and enters the ammonia cracking reactor to react. The heat of this reaction is provided by the heat generated in the carbonation tower. The products of the ammonia cracking reactor enter the burner and are mixed with pressurized air for combustion. The heat released during the combustion process provides heat for the calcination reaction in the calcining furnace.

[0010] Preferably, the reaction in the carbonation tower is carried out under normal pressure and the reaction temperature is 500-700℃; more preferably, the reaction temperature in the carbonation tower is 600-650℃; the main chemical reaction occurring in the carbonation tower is CaO + CO2 → CaCO3.

[0011] Preferably, the reaction in the calcining furnace is carried out under normal pressure and the reaction temperature is 800-950℃; more preferably, the reaction temperature in the calcining furnace is 900-950℃; the main chemical reaction occurring in the calcining furnace is CaCO3→CaO+CO2.

[0012] Preferably, the reaction pressure in the ammonia cracking reactor is 4–30 bar, and the reaction temperature is 300–750 °C; more preferably, the reaction pressure in the ammonia cracking reactor is 4–12 bar; the main chemical reaction occurring in the ammonia cracking reactor is NH3→N2+H2.

[0013] Preferably, the reaction pressure in the burner is 4–30 bar, and the reaction temperature is 900–1500 °C; more preferably, the reaction pressure in the burner is 4–12 bar; the main chemical reactions occurring in the burner are H2+O2→H2O and NH3+O2→N2+H2O.

[0014] Preferably, a portion of the gaseous products from the ammonia cracking reactor are sent to the power plant's combustion chamber to be co-fired with fuel for power generation.

[0015] Preferably, the hydrogen in the ammonia cracking reactor is separated and then sent to the power plant combustion chamber to be co-fired with fuel for power generation, thereby reducing the dilution of carbon components in the fuel products. The hydrogen recovery rate is set to meet the stability requirements of hydrogen co-firing combustion, typically in the range of 0-40%.

[0016] Preferably, the outlet gas of the burner is used to drive the gas turbine to do work.

[0017] More preferably, the gas exiting the calcining furnace and the gas exiting the gas turbine enter the waste heat boiler to heat the feedwater, generating high-temperature and high-pressure steam, which drives the steam turbine to generate electricity.

[0018] A second aspect of the present invention provides a system for capturing CO2 using the aforementioned ammonia cracking-driven calcium cycle method, comprising a carbonation tower, an ammonia cracking reactor, a burner, and a calcining furnace connected in sequence; the carbonation tower is connected to the calcining furnace.

[0019] Preferably, the system using the ammonia cracking-driven calcium cycle CO2 capture method further includes a gas turbine power generation unit and a waste heat recovery power generation unit; the gas turbine power generation unit is connected to a burner, and the burner outlet gas drives the gas turbine to do work; the waste heat recovery power generation unit is connected to the gas turbine power generation unit and a calcining furnace, and the calcining furnace outlet gas and the gas turbine power generation unit outlet gas enter the waste heat recovery power generation unit.

[0020] This system uses ammonia instead of fossil fuels to power the calcium cycle capture process, avoiding the additional CO2 capture requirements caused by fossil fuel power supply. Furthermore, compared to directly using the heat released from the carbonation reaction and the decarbonized flue gas from the carbonation tower outlet to heat feedwater, this system utilizes the heat of the carbonation reaction and the sensible heat in the middle temperature range of the decarbonized flue gas to provide heat for the ammonia cracking process. This method converts the medium-grade heat energy generated by the carbonation reaction into high-grade fuel chemical energy (H2) through chemical regeneration, achieving an improvement in energy grade, avoiding significant irreversible losses caused by large temperature difference heat exchange, and realizing the cascade utilization of the sensible heat of the decarbonized flue gas. In addition, this system also uses a combined cycle to recover energy from the burner outlet gas.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The method of this invention can significantly reduce the energy penalty of the capture process after calcium cycle combustion. This method has the following beneficial effects: (1) By using the chemical reheating method to convert the medium-grade thermal energy generated by the carbonation reaction into high-grade fuel chemical energy (H2), the energy grade is improved. Compared with direct heating of feedwater, it avoids the large irreversible loss caused by large temperature difference heat exchange; (2) The use of zero-carbon fuel ammonia to replace the fossil fuel originally used for energy supply avoids the additional carbon capture requirements (such as high-energy-consuming air separation) caused by fossil fuel energy supply; (3) Compared with direct combustion of ammonia for energy supply, the combustion of H2, the product of ammonia cracking reaction, for energy supply can release fuel chemical energy at a higher temperature to generate electrical energy or higher quality thermal energy. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the ammonia cracking-driven calcium cycle CO2 capture system of the present invention;

[0024] Figure 2 This is a schematic diagram of the reaction heat recovery type ammonia cracking driven calcium cycle CO2 capture system of Example 1;

[0025] Figure 3 This is a schematic diagram of the sensible heat regenerative ammonia cracking-driven calcium cycle CO2 capture system of Example 2;

[0026] Figure 4 This is a schematic diagram of the oxygen-enriched combustion calcium recycling process in Comparative Example 1. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0029] This invention provides a method for capturing CO2 using ammonia cracking-driven calcium cycling, the process flow of which is attached. Figure 1 As shown.

[0030] Power plant flue gas reacts with CaO adsorbent in a carbonation tower at medium-high temperatures (500–700°C) to remove CO2, resulting in clean flue gas and producing CaCO3. The CaCO3 product is fed into a calcining furnace, where it is reduced to CaO at 800–950°C. The CaO is then fed back into the carbonation tower to continue reacting with CO2 in the flue gas. The fuel, NH3, is pressurized to 4–30 bar by a compressor and then enters an ammonia cracking reactor to react at a temperature of 300–600°C. The heat for this reaction is provided by the medium-temperature heat generated by the carbonation reaction. The products from the ammonia cracking reactor, H2 / N2 / NH3, enter a burner and are mixed with air for combustion. The reaction pressure in the burner is 4–30 bar, and the reaction temperature is 900–1500°C. The heat released during combustion provides the high-temperature heat for the calcination reaction in the calcining furnace.

[0031] The main chemical reactions that occur in the ammonia cracking reactor are:

[0032] NH3→N2+H2

[0033] The main chemical reactions that occur in the burner are:

[0034] H₂ + O₂ → H₂O

[0035] NH3 + O2 → N2 + H2O

[0036] Example 1

[0037] This embodiment provides a reaction heat recovery type ammonia cracking driven calcium cycle CO2 capture system, as shown in the attached figure. Figure 2 As shown.

[0038] The reaction heat recovery type ammonia cracking driven calcium cycle CO2 capture system and its process parameters are as follows:

[0039] (1) Carbonation tower: The emission source flue gas (CO2 concentration in the flue gas is 3.2%, and the flue gas molar flow rate is 14716.1 kmol / h) reacts with CaO adsorbent at medium and high temperature (600℃) and normal pressure to remove CO2 from the flue gas and obtain clean flue gas, and generate product CaCO3.

[0040] (2) Calcining furnace: The product CaCO3 generated in the carbonation tower is sent into the calcining furnace and reduced to CaO at 900℃ and normal pressure. The CaO is then sent back into the carbonation tower to continue reacting with CO2 in the flue gas.

[0041] (3) Ammonia cracking reactor, in which NH3 pressurized to 12 bar by a compressor undergoes cracking reaction at 400°C, the medium and high temperature heat required for the reaction is provided by the heat released by the carbonation reaction in the carbonation tower;

[0042] (4) The products of the ammonia cracking reactor, including N2, H2 and unreacted NH3, are completely burned with air pressurized to 12 bar by a compressor at 1000°C. The high-temperature heat released by this reaction provides heat for the reaction in the calcining furnace.

[0043] (5) Flue gas preheating unit: Waste heat from the gas outlet of the carbonation tower is used to preheat the flue gas.

[0044] (6) Gas turbine power generation unit, the combustor outlet gas H2O / N2 is used to drive the gas turbine to do work, and the high temperature and high pressure energy of the gas is recovered; the operating conditions of the gas turbine combustion chamber are: temperature 1100℃, pressure 12bar;

[0045] (7) Waste heat recovery power generation unit: High-temperature CO2 gas from the calcining furnace outlet and gas from the gas turbine unit outlet enter the waste heat boiler to heat feedwater, generating high-temperature and high-pressure steam, which drives the steam turbine to generate electricity; The waste heat boiler power generation unit is a triple reheat unit with a steam pressure of 126 / 26 / 5.5 bar, a steam temperature of 566°C, and an entropy efficiency of 0.88 / 0.89 / 0.87.

[0046] (8) In the power generation unit of the power plant, a portion of the products from the ammonia cracking reactor are mixed with natural gas and burned to heat steam to drive the steam turbine to do work.

[0047] Example 2

[0048] This embodiment provides a sensible heat regenerative ammonia cracking-driven calcium cycle CO2 capture system, as shown in the attached figure. Figure 3 As shown.

[0049] The ammonia cracking-driven calcium cycle CO2 capture system and its process parameters in a natural gas power plant are as follows:

[0050] (1) Carbonation tower: Power plant flue gas reacts with CaO adsorbent at medium and high temperature (600-650℃) to remove CO2 from the flue gas and obtain clean flue gas, and generate CaCO3 as a product.

[0051] (2) Calcining furnace: The product CaCO3 generated in the carbonation tower is sent into the calcining furnace and reduced to produce CaO at a high temperature of 900-950℃. The CaO is then sent back into the carbonation tower to continue to react with CO2 in the flue gas.

[0052] (3) In the ammonia cracking reactor, NH3 pressurized to 12 bar by the compressor undergoes a cracking reaction at 400°C. The medium- and high-temperature heat required for this reaction is provided by the sensible heat of the medium-temperature section of the decarbonized flue gas at the outlet of the carbonation tower.

[0053] (4) The products of the ammonia cracking reactor, including N2, H2 and unreacted NH3, are completely burned with air pressurized to 12 bar by a compressor at 1000°C. The high-temperature heat released by this reaction provides heat for the reaction in the calcining furnace.

[0054] (5) Flue gas preheating unit: The sensible heat of the low-temperature section of the gas outlet gas of the carbonation tower is used to preheat the flue gas.

[0055] (6) Gas turbine power generation unit, the combustor outlet gas H2O / N2 is used to drive the gas turbine to do work, and the high temperature and high pressure energy of the gas is recovered;

[0056] (7) Waste heat recovery power generation unit: the high-temperature CO2 gas at the outlet of the calcining furnace and the gas at the outlet of the gas turbine unit enter the waste heat boiler to heat the feedwater, generate high-temperature and high-pressure steam, and drive the steam turbine to generate electricity.

[0057] (8) In the power generation unit of the power plant, a portion of the products from the ammonia cracking reactor are mixed with natural gas and burned to heat steam to drive the steam turbine to do work.

[0058] Comparative Example 1

[0059] This comparative example employs an oxygen-enriched combustion calcium ring combustion and subsequent collection process, as shown in the attached figure. Figure 4As shown, it consists of a carbonation tower, a calcining furnace, and an air separation unit. CO2 is removed from the power plant flue gas in the carbonation tower. The adsorbent, after CO2 adsorption, is sent to the calcining furnace for regeneration. The high-temperature heat required for the calcination process is provided by the combustion of fuel and pure oxygen. Waste heat from each process is used to drive the Rankine cycle. The specific process includes the following:

[0060] Flue gas from the power plant is fed into a carbonation tower to react with CaO, removing CO2 through adsorption and resulting in clean flue gas. The carbonation reaction occurs at 600–650°C. Subsequently, the reaction product, CaCO3, is sent to a calcination furnace for regeneration, where it decomposes at high temperature (900–950°C) to produce CO2 and CaO. The heat for the regeneration reaction is provided by pure oxygen combustion in a fuel-air separator. The CaO produced by calcination is returned to the carbonation tower for recycling. Because the adsorption capacity of the calcium-based adsorbent decreases during the recycling process, a small amount of fresh CaO needs to be added to the carbonation furnace to maintain the circulating CO2 adsorption capacity of the calcium-based adsorbent.

[0061] The main chemical reactions that occur in the carbonation tower are:

[0062] CaO + CO2 = CaCO3

[0063] The main chemical reactions occurring in the calcining furnace are:

[0064] CaCO3=CaO+CO2

[0065] CH x O y +O2=CO2+H2O

[0066] Table 1. Comparison between the ammonia cracking-driven calcium cycle CO2 capture system and the traditional oxygen-enriched combustion calcium ring CO2 capture system.

[0067]

[0068]

[0069] *Energy efficiency = Net power output / Energy input; Energy penalty = Energy efficiency without trapping system - Energy efficiency with trapping system

[0070] The performance of the examples and comparative cases is shown in Table 1. The results show that the performance of the ammonia cracking-driven calcium cycle CO2 capture system is significantly improved compared to the traditional oxy-fuel combustion calcium cycle. The efficiency of the new capture system increased from 42.1% in the traditional oxy-fuel combustion calcium cycle to 50.3% and 49.9%, respectively, and the energy penalty of the capture system decreased to 0.9 and 1.3 percentage points, respectively, a decrease of 7.8 percentage points compared to the traditional oxy-fuel combustion method. This is because, compared to the oxy-fuel combustion method, the new system avoids the additional natural gas input and the energy consumption required for the air separation unit to produce pure oxygen for capturing carbon elements in the input natural gas. On the other hand, the new system realizes the cascade utilization of the sensible heat of the flue gas at the carbonation tower outlet and adopts a combined cycle to recover the energy of the burner outlet gas, improving the system's waste heat recovery performance. Therefore, this method can provide a highly efficient CO2 capture scheme for power plant flue gas capture.

[0071] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for capturing CO2 using ammonia cracking-driven calcium cycling, characterized in that, Includes the following steps: (1) The flue gas to be treated reacts with CaO adsorbent in the carbonation tower to remove CO2 and generate CaCO3; (2) The product CaCO3 is sent to the calcining furnace, calcined to produce CaO, and then sent to the carbonation tower for further CO2 removal; (3) NH3 is pressurized and enters the ammonia cracking reactor to react. The heat of this reaction is provided by the heat generated in the carbonation tower. The products of the ammonia cracking reactor enter the burner and are mixed with pressurized air for combustion. The heat released during the combustion process provides heat for the calcination reaction in the calcining furnace. The reaction in the carbonation tower is carried out under normal pressure at a temperature of 500-700 °C. The main chemical reaction occurring in the carbonation tower is as follows: ; The reaction in the calcining furnace is carried out under normal pressure at a temperature of 800-950 °C. The main chemical reaction occurring in the calcining furnace is as follows: ; The ammonia cracking reactor operates at a reaction pressure of 4–30 bar and a reaction temperature of 300–750 °C. The main chemical reactions occurring in the ammonia cracking reactor are as follows: ; The reaction pressure in the burner is 4~30 bar, and the reaction temperature is 900~1500 ℃. The main chemical reaction occurring in the burner is... , .

2. The method for capturing CO2 by ammonia cracking-driven calcium cycling according to claim 1, characterized in that, A portion of the gaseous products from the ammonia cracking reactor are sent to the power plant's combustion chamber to be co-fired with fuel for power generation.

3. The method for capturing CO2 by ammonia cracking-driven calcium cycling according to claim 1, characterized in that, The outlet gas of the burner is used to drive the gas turbine to do work.

4. The method for capturing CO2 by ammonia cracking-driven calcium cycling according to claim 3, characterized in that, The gas exiting the calcining furnace and the gas exiting the gas turbine enter the waste heat boiler to heat the feedwater, generating high-temperature and high-pressure steam, which drives the steam turbine to generate electricity.

5. A system for capturing CO2 using the ammonia cracking-driven calcium cycle method according to any one of claims 1-4, characterized in that, It includes a carbonation tower, an ammonia cracking reactor, a burner, and a calcining furnace connected in sequence; the carbonation tower is connected to the calcining furnace.

6. The system according to claim 5, characterized in that, It also includes a gas turbine power generation unit and a waste heat recovery power generation unit; the gas turbine power generation unit is connected to the burner, and the gas outlet of the burner drives the gas turbine to do work; the waste heat recovery power generation unit is connected to the gas turbine power generation unit and the calcining furnace, and the gas outlet of the calcining furnace and the gas outlet of the gas turbine power generation unit enter the waste heat recovery power generation unit.

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