A method for integrated carbon dioxide capture and processing of flue gas from a natural gas boiler

Abstract

The present application belongs to the field of carbon dioxide resource utilization, and discloses a kind of carbon dioxide capture processing integration method of natural gas boiler emission flue gas, comprising: gas in flue is after desulfurization, alkali washing enters absorption tower, and rich liquid is obtained by using absorbent absorption, the absorbent used in absorption tower is MEA-PEHA solution with concentration ratio of 5:5;Rich liquid enters carbon dioxide subsequent collection procedure or enters carbon dioxide capture hydrogenation integrated reaction procedure;Collection procedure: after regeneration in regeneration tower, lean liquid is obtained into absorption tower, and rich liquid and lean liquid are heat exchanged;Integrated reaction procedure: after heat exchanger, after desorption in desorption hydrogenation integrated tower, after separation by gas-liquid separator, liquid is heat exchanged with the absorbent that has absorbed carbon dioxide in absorption tower after flowing out, and then enters absorption tower for absorption;Separated gas is mixed with hydrogen and then enters desorption hydrogenation integrated tower and hydrogenation reaction tower.The device of the present application has the advantages of high degree of systematization and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide resource utilization, specifically relating to an integrated method for capturing and processing carbon dioxide from flue gas emitted by a natural gas boiler. Background Technology

[0002] The description of the background art in this invention pertains to related technologies and is used merely for illustration and to facilitate understanding of the invention. It should not be construed as the applicant explicitly believing or presuming that the invention was prior art on the filing date of the first application.

[0003] The capture and resource utilization of carbon dioxide in flue gas has always been a hot topic of social concern. Since the concentration of carbon dioxide in flue gas is relatively low, one current method for carbon dioxide resource utilization is to absorb carbon dioxide with absorbents and simultaneously mix high-concentration carbon dioxide with hydrogen to produce methane. However, current resource utilization methods generally suffer from high production costs and high system energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated method for capturing and processing carbon dioxide in flue gas emitted from natural gas boilers. The device of this invention has the advantages of high system integration and low energy consumption.

[0005] The objective of this invention is achieved through the following technical solutions:

[0006] An integrated method for capturing and processing carbon dioxide from flue gas emitted by a natural gas boiler includes:

[0007] The gas from the flue enters the absorption tower after desulfurization and alkali washing, and is absorbed by an absorbent to obtain a rich solution. The absorbent used in the absorption tower is a MEA-PEHA solution with a concentration ratio of 5:5.

[0008] The rich liquid is either entered into a subsequent carbon dioxide collection process or into an integrated carbon dioxide capture, hydrogenation, and methane production reaction process.

[0009] The subsequent carbon dioxide collection procedure includes the following steps:

[0010] The rich liquid is regenerated in the regeneration tower to obtain a lean liquid, which then enters the absorption tower. The rich liquid and the lean liquid exchange heat. The gas discharged from the regeneration tower is separated into gas and liquid to obtain carbon dioxide gas. The carbon dioxide gas is collected after precooling, compression, adsorption, drying, condensation and purification.

[0011] The integrated process for carbon dioxide capture, hydrogenation, and methane production includes the following steps:

[0012] After passing through a heat exchanger, the rich liquid is desorbed in the integrated desorption and hydrogenation tower. After being separated by a gas-liquid separator, the liquid exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower and then re-enters the absorption tower for carbon dioxide absorption.

[0013] The gas separated in the gas-liquid separator is mixed with hydrogen and then enters the desorption-hydrogenation integrated tower and the hydrogenation reaction tower.

[0014] The inlet of the hydrogenation reaction tower is connected to a pressure regulating valve.

[0015] Furthermore, the integrated carbon dioxide capture and hydrogenation to methane reaction process is completed using an integrated carbon dioxide capture and hydrogenation to methane reaction unit, which includes an absorption tower, a desorption and hydrogenation integrated tower, and a hydrogenation reaction tower.

[0016] The absorbent that has absorbed carbon dioxide in the absorption tower passes through a heat exchanger and is then desorbed in the integrated desorption and hydrogenation tower. After being separated by a gas-liquid separator, the liquid passes through a heat exchanger and exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower before re-entering the absorption tower for carbon dioxide absorption.

[0017] The gas separated in the gas-liquid separator is mixed with hydrogen and then enters the desorption-hydrogenation integrated tower and the hydrogenation reaction tower.

[0018] The inlet of the hydrogenation reaction tower is connected to a pressure regulating valve.

[0019] Furthermore, the absorption tower is equipped with a spraying device for absorbing the solvent.

[0020] The liquid outlet of the absorption tower is connected in series with the cold side inlet of the heat exchanger via a pipeline, and the cold side outlet of the heat exchanger is connected to the liquid inlet of the desorption and hydrogenation integrated tower via a pipeline.

[0021] The liquid outlet of the desorption and hydrogenation integrated tower is connected to the gas-liquid separator. The liquid outlet of the gas-liquid separator and the hot side inlet of the heat exchanger are connected in series through a pipeline. The hot side outlet of the heat exchanger is connected to the liquid inlet of the absorption tower through a pipeline.

[0022] The outlet of the gas-liquid separator is connected to the gas mixing tank via a pipeline; the outlet of the gas mixing tank is connected to the compressor via a pipeline; the compressor is connected in parallel with the inlet of the desorption-hydrogenation integrated tower and the inlet of the hydrogenation reaction tower via pipelines; the desorption-hydrogenation integrated tower is a shell-and-tube type, with carbon dioxide and hydrogen introduced into the tube side and rich liquid introduced into the shell side, and the flow heat exchange mode can be countercurrent or cocurrent; the heat exchange tube bundle of the desorption-hydrogenation integrated tower is filled with at least one carbon dioxide hydrogenation catalyst; the heat exchange tube bundle of the desorption-hydrogenation integrated tower is in the form of a bare tube or an internally finned tube.

[0023] Furthermore, the integrated desorption and hydrogenation tower is equipped with at least one hydrogenation reaction tower. The inlets of the integrated desorption and hydrogenation tower and the hydrogenation reaction tower are connected to a gas mixing tank via pipelines, and the inlet reactant flow rates of the two towers are distributed by a pressure regulating valve.

[0024] Furthermore, thermometers are installed on both the tube side and the shell side of the integrated desorption and hydrogenation tower.

[0025] Furthermore, the lean liquor after desorption in the integrated desorption and hydrogenation tower transfers heat to the rich liquor after CO absorption in the absorption tower via a heat exchanger.

[0026] Furthermore, a CH concentration measuring instrument is installed at the outlet of the integrated desorption and hydrogenation tower. A flow meter 9 is installed on the pipeline connecting the outlet of the gas-liquid separator to the gas mixing tank to obtain the CO2 flow rate, thereby controlling the H2 flow rate entering the gas mixing tank 6.

[0027] Furthermore, the subsequent carbon dioxide collection process is completed using a carbon dioxide capture and absorption device suitable for natural gas boiler flue gas emissions. The carbon dioxide capture and absorption device suitable for natural gas boiler flue gas emissions includes a desulfurization device, an alkaline scrubbing tower, an absorption tower, and a regeneration tower connected in sequence; the front end of the desulfurization device is connected to the flue.

[0028] The rich liquid outlet of the absorption tower is connected to the liquid inlet of the regeneration tower through a first pipe; the liquid outlet of the regeneration tower is connected to the lean liquid inlet of the absorption tower through a second pipe; the first pipe and the second pipe exchange heat through a lean-rich liquid heat exchanger; and the gas outlet of the regeneration tower is connected to a gas-liquid separator.

[0029] Furthermore, the absorption tower is equipped with a gas outlet, which is connected to the flue; the second pipeline is equipped with a lean liquid cooler; the subsequent carbon dioxide collection process employs a carbon dioxide capture and absorption device suitable for natural gas boiler emissions, which also includes a solution reboiler, and the solution reboiler is connected to the regeneration tower via a circulation pipeline; the subsequent carbon dioxide collection process employs a carbon dioxide capture and absorption device suitable for natural gas boiler emissions, which also includes a carbon dioxide treatment device, which is connected to the outlet of the gas-liquid separator; the carbon dioxide treatment device includes a precooling device, a compression device, an adsorption device, a drying device, a condensation device, and a purification device connected in sequence.

[0030] Furthermore, the outlet of the gas-liquid separator is connected to the regeneration tower.

[0031] The embodiments of the present invention have the following beneficial effects:

[0032] This invention rationally couples CO2 capture with hydrogenation to methane, using the heat of hydrogenation reaction in an integrated unit for rich-liquid desorption, significantly reducing system cost and energy consumption. It also includes a hydrogenation reaction tower, with reactant flow rates from both towers distributed via pressure regulating valves. This allows for precise control of the desorption and hydrogenation reaction temperatures in the integrated tower, ensuring a high reaction rate and methane selectivity.

[0033] The integrated carbon dioxide capture and hydrogenation to methane unit features strong adaptability and high heat exchange efficiency. By controlling the feed flow rate of the matching hydrogenation reaction tower, the desorption and reaction temperatures can be accurately controlled, maintaining high desorption rates, reaction rates, and CH4 selectivity. In the integrated unit, the heat of CO2 hydrogenation methanation reaction is used for rich liquid desorption, reducing system energy consumption. The system has high integration and reduced costs, meeting the needs of carbon dioxide resource utilization.

[0034] The rich liquor enters the regeneration tower from the top and middle sections, where some CO2 is desorbed by stripping. It then enters the reboiler for further CO2 desorption. The lean liquor (105°C) after CO2 desorption flows out from the bottom of the regeneration tower. Part of the steam is flashed in a flash tank, pressurized, and returned to the desorption tower for heat recovery. The lean liquor exiting the flash tank is cooled to 60°C after heat recovery in a lean-rich liquor heat exchanger. It is then pumped to a lean liquor cooler, cooled to 40°C, and enters the absorption tower. This solvent circulation constitutes a continuous CO2 absorption and desorption process, achieving a CO2 capture rate of over 90%.

[0035] The gas source for the compression and distillation purification unit is CO2 regenerated gas from the CO2 capture unit. The main impurities are sulfur-containing substances and other trace impurities, which are mainly removed by adsorption in the adsorber using high-quality activated carbon. This ensures that the product indicators meet food-grade quality standards. There is no large amount of wastewater or waste liquid discharged during the production process, and the exhaust gas basically does not contain harmful substances, fully meeting emission requirements. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of an integrated carbon dioxide capture and hydrogenation to methane reaction device according to an embodiment of the present invention;

[0037] Figure 2 The curves showing the change in absorption amount of different formulation solvent solutions over time are shown in the embodiments of the present invention.

[0038] Figure 3 The figures show the absorption rate of different solvent solutions as a function of time in the embodiments of the present invention.

[0039] Figure 4 The figures show the desorption rate of different solvent formulations over time in the embodiments of the present invention.

[0040] Figure 5This is a bar chart showing the solution desorption rate in an embodiment of the present invention. Detailed Implementation

[0041] The present application will be further described below with reference to the embodiments.

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, in the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Different embodiments can be substituted or combined, and for those skilled in the art, other implementation methods can be obtained based on these embodiments without creative effort.

[0043] Combined with appendix Figure 1-5 An integrated method for capturing and processing carbon dioxide from flue gas emitted by a natural gas boiler, comprising:

[0044] The gas from the flue enters the absorption tower after desulfurization and alkali washing, and is absorbed by an absorbent to obtain a rich solution. The absorbent used in the absorption tower is a MEA-PEHA solution with a concentration ratio of 5:5.

[0045] The rich liquid is either entered into a subsequent carbon dioxide collection process or into an integrated carbon dioxide capture, hydrogenation, and methane production reaction process.

[0046] The subsequent carbon dioxide collection procedure includes the following steps:

[0047] The rich liquid is regenerated in the regeneration tower to obtain a lean liquid, which then enters the absorption tower. The rich liquid and the lean liquid exchange heat. The gas discharged from the regeneration tower is separated into gas and liquid to obtain carbon dioxide gas. The carbon dioxide gas is collected after precooling, compression, adsorption, drying, condensation and purification.

[0048] The integrated process for carbon dioxide capture, hydrogenation, and methane production includes the following steps:

[0049] After passing through a heat exchanger, the rich liquid is desorbed in the desorption and hydrogenation integrated tower (2), separated by a gas-liquid separator (5), and then the liquid exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower (1) before re-entering the absorption tower for carbon dioxide absorption.

[0050] The gas separated in the gas-liquid separator (5) is mixed with hydrogen and then enters the desorption and hydrogenation integrated tower (2) and the hydrogenation reaction tower (3);

[0051] The inlet of the hydrogenation reaction tower (3) is connected to a pressure regulating valve.

[0052] In some embodiments of the present invention, an integrated carbon dioxide capture and hydrogenation to methane reaction device is provided, the integrated carbon dioxide capture and hydrogenation to methane reaction device comprising an absorption tower 1, a desorption and hydrogenation integrated tower 2, and a hydrogenation reaction tower 3.

[0053] The absorbent that has absorbed carbon dioxide in the absorption tower 1 passes through a heat exchanger and is then desorbed in the desorption and hydrogenation integrated tower 2. After being separated by a gas-liquid separator 5, the liquid passes through a heat exchanger and exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower 1 before re-entering the absorption tower for carbon dioxide absorption.

[0054] The gas separated in gas-liquid separator 5 is mixed with hydrogen and then enters desorption-hydrogenation integrated tower 2 and hydrogenation reaction tower 3;

[0055] The inlet of the hydrogenation reaction tower 3 is connected to a pressure regulating valve.

[0056] In some embodiments of the present invention, the absorption tower 1 is provided with a spraying device for spraying and absorbing solvent.

[0057] The liquid outlet 21 of the absorption tower 1 is connected in series with the cold side inlet of the heat exchanger 4 through a pipeline, and the cold side outlet of the heat exchanger 4 is connected to the liquid inlet 23 of the desorption and hydrogenation integrated tower 2 through a pipeline.

[0058] The liquid outlet 24 of the desorption and hydrogenation integrated tower 2 is connected to the gas-liquid separator 5. The liquid outlet of the gas-liquid separator and the hot side inlet of the heat exchanger 4 are connected in series through a pipeline. The hot side outlet of the heat exchanger 4 is connected to the liquid inlet 22 of the absorption tower 1 through a pipeline.

[0059] The outlet of the gas-liquid separator 5 is connected to the gas mixing tank 6 via a pipeline; the outlet of the gas mixing tank 6 is connected to the compressor 7 via a pipeline; the compressor 7 is connected in parallel with the inlet 25 of the desorption-hydrogenation integrated tower 2 and the inlet 27 of the hydrogenation reaction tower 3 via pipelines; the desorption-hydrogenation integrated tower 2 is a shell-and-tube type, with carbon dioxide and hydrogen introduced into the tube side and rich liquid introduced into the shell side, and the flow heat exchange mode can be countercurrent or cocurrent; the heat exchange tube bundle 18 of the desorption-hydrogenation integrated tower 2 is filled with at least one carbon dioxide hydrogenation catalyst; the heat exchange tube bundle 18 of the desorption-hydrogenation integrated tower 2 is in the form of a bare tube or an internally finned tube.

[0060] In some embodiments of the present invention, the desorption-hydrogenation integrated tower 2 is equipped with at least one hydrogenation reaction tower 3, and the inlets of the desorption-hydrogenation integrated tower 2 and the hydrogenation reaction tower 3 are connected to a gas mixing tank 6 through pipelines, and the inlet reactant flow rates of the two towers are distributed through a pressure regulating valve.

[0061] In some embodiments of the present invention, thermometers 12 and 13 are installed on the tube side and shell side of the integrated desorption and hydrogenation tower 2.

[0062] In some embodiments of the present invention, the lean liquid after desorption in the integrated desorption and hydrogenation tower 2 transfers heat to the rich liquid after CO2 absorption in the absorption tower 1 via the heat exchanger 4.

[0063] In some embodiments of the present invention, a CH4 concentration measuring instrument is installed on the gas outlet 26 of the integrated desorption and hydrogenation tower 2.

[0064] In some embodiments of the present invention, a flow meter 9 is installed on the pipeline connecting the outlet of the gas-liquid separator 5 and the gas mixing tank 6 to obtain the CO2 flow rate, so as to control the H2 flow rate entering the gas mixing tank 6.

[0065] The liquid outlet 21 of the absorption tower 1 is connected in series with the circulating pump 16 and the cold side inlet of the heat exchanger 4 via a pipeline; the liquid inlet 23 of the integrated desorption and hydrogenation tower 2 is connected to the cold side outlet of the heat exchanger 4 via a pipeline; the liquid outlet 24 of the integrated desorption and hydrogenation tower 2 is connected in series with the gas-liquid separator 5, the circulating pump 15, and the hot side inlet of the heat exchanger 4 via a pipeline; the liquid inlet 22 of the absorption tower 1 is connected to the hot side outlet of the heat exchanger 4 via a pipeline; the gas outlet of the gas-liquid separator 5 is connected to the gas mixing tank 6 via a pipeline; the gas outlet of the gas mixing tank 6 is connected to the compressor 7 via a pipeline; the compressor 7 is connected in parallel with the gas inlet 25 of the integrated desorption and hydrogenation tower 2 and the gas inlet 27 of the hydrogenation reaction tower 3 via a pipeline.

[0066] The absorption tower 1 is equipped with an air inlet 19, an air outlet 20 and a spray device 17. The flue gas entering from the air inlet 19 is absorbed by the CO2 by the absorbent solvent droplets sprayed by the spray device 17, and then leaves from the air outlet 20.

[0067] A flow meter 9 is installed on the pipeline connecting the outlet of the gas-liquid separator 5 and the gas mixing tank 6 to obtain the CO2 flow rate, so as to control the H2 flow rate entering the gas mixing tank 6.

[0068] Flow meters 10 and 11 are installed on the connecting pipes of the compressor 7 to the desorption and hydrogenation integrated tower 2 and the hydrogenation reaction tower 3 to obtain the flow rate of the reactants in the branch.

[0069] The compressor 7 is connected to the hydrogenation reactor 3 via a pipeline equipped with Pressure regulating valve 11 .

[0070] A thermometer 12 is installed inside the heat exchange tube bundle 18 of the integrated desorption and hydrogenation tower 2 to obtain the hydrogenation reaction temperature.

[0071] A thermometer 13 is installed on the shell side of the integrated desorption and hydrogenation tower 2 to obtain the desorption reaction temperature.

[0072] A CH4 concentration measuring instrument is installed on the gas outlet 26 of the integrated desorption and hydrogenation tower 2.

[0073] Cooling medium is introduced into the inlet 29 of the hydrogenation reaction tower 3, and after heat exchange, it leaves from the outlet 30.

[0074] The receiving tower has an inlet and an outlet at the bottom, and an outlet, an inlet, and a spray device at the top. The desorption-hydrogenation integrated tower has an inlet and an outlet at the top, and internally has a heat exchange tube bundle and a shell plate. The hydrogenation reaction tower has an inlet and an outlet at the top, and internally has a heat exchange tube bundle and a shell plate. The absorber's inlet is connected to the lean liquid inlet of the heat exchanger via a pipe, and its outlet is connected to the rich liquid inlet of the heat exchanger via a pipe and a circulating pump. The tube bundles of the desorption-hydrogenation integrated tower and the hydrogenation reaction tower are filled with carbon dioxide hydrogenation catalyst. The shell-side inlet of the desorption-hydrogenation integrated tower is connected to the rich liquid outlet of the heat exchanger via a pipe, and the shell-side outlet is connected to the lean liquid inlet of the heat exchanger via a pipe, a gas-liquid separator, and a circulating pump.

[0075] According to an embodiment of the present invention, the measuring points of the temperature detector are located inside the tube bundle and on the shell side of the integrated desorption and hydrogenation tower and the hydrogenation reaction tower.

[0076] According to an embodiment of the present invention, a gas concentration detector is installed at the outlet of the integrated desorption and hydrogenation tower and the hydrogenation reaction tower.

[0077] According to an embodiment of the present invention, a CO2 concentration detector is installed at the outlet of the absorption tower and the gas-liquid separator.

[0078] According to an embodiment of the present invention, the tube bundles of the desorption-hydrogenation integrated tower and the hydrogenation reaction tower use internally finned tubes to improve the heat transfer coefficient on the tube side.

[0079] According to an embodiment of the present invention, the rich liquid at the outlet of the absorption tower recovers heat from the lean liquid at the outlet of the integrated desorption and hydrogenation tower via a heat exchanger.

[0080] According to an embodiment of the present invention, the inlet of the integrated desorption and hydrogenation tower and the hydrogenation reaction tower are connected to a gas mixing tank via a compressor and a pipeline.

[0081] According to an embodiment of the present invention, the reactant flow rates at the inlet of the integrated desorption and hydrogenation tower and the hydrogenation reaction tower are controlled by a pressure regulating valve.

[0082] According to an embodiment of the present invention, the gas outlet of the gas-liquid separator is connected to the inlet of a gas mixing tank via a pipeline, and is mixed with hydrogen in a certain proportion.

[0083] According to an embodiment of the present invention, the inlet of the absorption tower is connected to the flue to recover carbon dioxide from the flue gas.

[0084] The flue gas has a low concentration of carbon dioxide, which is absorbed by an absorbent. At the same time, the high concentration of carbon dioxide is mixed with hydrogen to produce methane.

[0085] The reaction of carbon dioxide hydrogenation to produce methane is exothermic, but using this heat for carbon dioxide capture in flue gas can reduce the overall energy consumption of the system and lower the cost of methane production.

[0086] By combining it with the hydrogen source for new energy water electrolysis, green methane can be produced.

[0087] This technology enables integrated production of carbon dioxide capture and hydrogenation to produce methane, reducing system energy consumption and costs.

[0088] The absorption reaction of organic amines occurs at 40℃ and is exothermic, while the desorption temperature is 102–103.5℃ and is endothermic. MEA concentration is 80–100 KJ / mol.

[0089] The reaction temperature for the hydrogenation of carbon dioxide to produce methane is 300℃, and the heat of reaction is -165kJ / mol.

[0090] In some embodiments of the present invention, a carbon dioxide capture and absorption device suitable for flue gas emissions from natural gas boilers is used. The carbon dioxide capture and absorption device suitable for flue gas emissions from natural gas boilers includes a desulfurization device, an alkaline scrubbing tower, an absorption tower 1, and a regeneration tower 32 connected in sequence; the front end of the desulfurization device is connected to the flue.

[0091] The rich liquid outlet of the absorption tower 1 is connected to the liquid inlet of the regeneration tower 32 through a first pipe; the liquid outlet of the regeneration tower 32 is connected to the lean liquid inlet of the absorption tower 1 through a second pipe; the first pipe and the second pipe exchange heat through a lean-rich liquid heat exchanger 34; and the gas outlet of the regeneration tower 32 is connected to a gas-liquid separator 33.

[0092] In some embodiments of the present invention, the absorption tower 1 is provided with a gas outlet, which is connected to a flue.

[0093] In some embodiments of the present invention, the second pipe is provided with a lean liquid cooler.

[0094] In some embodiments of the present invention, a solution reboiler 35 is also included, which is connected to the regeneration tower 32 via a circulation pipeline.

[0095] In some embodiments of the present invention, a carbon dioxide treatment device is also included, which is connected to the outlet of the gas-liquid separator 33.

[0096] In some embodiments of the present invention, the carbon dioxide treatment apparatus includes a precooling device, a compression device, an adsorption device, a drying device, a condensation device, and a purification device connected in sequence.

[0097] In some embodiments of the present invention, the outlet of the gas-liquid separator 33 is connected to the regeneration tower 32.

[0098] To improve the absorption effect, the applicant independently developed a carbon dioxide capture and absorption agent suitable for flue gas emissions from natural gas boilers, and based on this, designed a carbon dioxide capture process for gas-fired boilers.

[0099] The applicant, through extensive research, determined the optimal concentration ratios of the absorbents: MEA-DETA solution 5:5, MEA-TETA compound solution 6:4, MEA-TEPA compound solution 6:4, and MEA-PEHA compound solution 5:5. By comparing the absorption and desorption properties of the four compound solutions, the optimal solvent formulation was determined.

[0100] The curves showing the change in CO2 absorption as a function of time for the four solvent formulations in the absorption experiment are shown below. Figure 2 .

[0101] Analysis of the curves reveals that the absorption rate of the MEA-PEHA solution over time is significantly higher than the other three curves, while the absorption rate of the MEA-DETA solution is the lowest. The order of carbon dioxide absorption rates for the four solutions is: MEA-PEHA solution > MEA-TEPA solution > MEA-TETA solution > MEA-DETA solution.

[0102] The absorption rate of CO2 by the four solvent formulations as a function of time in the absorption experiment are shown in the figure. Figure 3 .

[0103] As can be seen from the figure, the absorption rate curve of MEA-PEHA solution is significantly higher than the other curves, and its variation pattern is consistent with the variation pattern of absorption amount over time.

[0104] The relationship between the desorption rate of CO2 and time in the desorption experiments of the four solvent formulations and their rich solutions is shown in the figure. Figure 4 .

[0105] As mentioned earlier, the desorption rate curves of the four formulation solvent solutions over time show a high degree of overlap. Their variation patterns are all characterized by a rapid increase in desorption rate at the beginning of the experiment, followed by a gradual decrease. The desorption rates of the four formulation solvents are basically the same.

[0106] A comparison of the desorption rates of the four formulation solvents is shown below. Figure 5 Analysis of the data in the graph shows that the MEA-DETA solution has the highest desorption rate, while the MEA-PEHA solution has the lowest desorption rate.

[0107] The results of the desorption experiments for the four solvent formulations are shown in Table 1. The table shows that the MEA-PEHA solution had the lowest desorption temperature (68℃) and the lowest azeotropic temperature (102℃).

[0108] Table 1. Desorption experimental results of different absorbent solutions

[0109]

[0110] Based on the results of the small-scale experiment, considering the absorption and desorption effects of each solution as well as the desorption energy consumption, the optimal concentration ratio of the MEA-PEHA compound solution was 5:5, resulting in the best experimental performance. Therefore, the optimal binary compound solvent under the small-scale experimental conditions is a MEA-PEHA solution with a concentration ratio of 5:5.

[0111] Analysis of the sulfur and nitrification resistance of the composite solution

[0112] Study on the influence of SO2 in flue gas on capture performance

[0113] Test conditions: Raw material gas SO2 ~1000ppm, CO2 ~12%, raw material gas ~3.5Nm 3 / h.

[0114] Table 2 Desorption Experiment Results of Different Absorbent Solutions

[0115]

[0116] The composite amine solution showed a near 100% absorption rate for SO2. The CO2 absorption rate decreased with increasing total sulfur content in the solution. The SO2 content in the regenerated gas remained below 1 ppm, indicating that SO2 is difficult to regenerate under the experimental conditions.

[0117] NO in flue gas x Study on the impact on trapping performance

[0118] Test conditions: Raw material gas CO2 ~12%, raw material gas ~3.5Nm 3 / h.

[0119] Table 3. Desorption test results of different absorbent solutions

[0120]

[0121] To verify NO x The effect of accumulation in the solvent on carbon absorption was investigated by conducting enhanced absorption experiments with high concentrations of nitrogen oxides to study their impact on CO2 absorption performance.

[0122] Table 4. Desorption Experiment Results of Different Absorbent Solutions

[0123]

[0124] The following conclusions can be drawn from the small-scale CO2 capture experiment:

[0125] Whether it is a single-component absorbent solution or a binary compound absorbent solution, the absorption amount will increase rapidly in the early stage of the experiment, and then the increase will gradually decrease. The absorption rate and desorption rate both show a change pattern of first increasing and then decreasing.

[0126] Based on the results of the combined absorption and desorption experiments, the optimal concentration ratios of the binary compound absorbent solutions can be determined as follows: the optimal concentration ratio of MEA-DETA solution is 5:5, the optimal concentration ratio of MEA-TETA compound solution is 6:4, the optimal concentration ratio of MEA-TEPA compound solution is 6:4, and the optimal concentration ratio of MEA-PEHA compound solution is 5:5.

[0127] From the perspective of experimental results alone, the optimal reagent formulation is determined to be a MEA-PEHA solution with a concentration ratio of 5:5, based on a comparison of four binary compound absorbent solutions.

[0128] The main reason for severe equipment corrosion caused by the organic amine process is the carbamate formed by the reaction of organic amines with CO2 and the chemical degradation products of organic amines. Extensive research has been conducted both domestically and internationally. While some progress has been made in the development of corrosion inhibitors, a complete solution has not yet been found to reduce equipment corrosion by minimizing organic amine degradation. Through extensive experimental research, antioxidants and active amines were first added to address the chemical degradation of organic amines. Based on the aforementioned absorption system, a set of corrosion inhibitors was developed and incorporated into the composite amine solution, reducing the corrosion rate of the solution on equipment to less than 0.076 mm / a, fundamentally solving the technical problem of severe equipment corrosion caused by the organic amine process.

[0129] Process Overview

[0130] Flue gas (65℃, atmospheric pressure) from the outlet of desulfurization absorption tower 1 is pretreated with alkali and then cooled to 40℃ before entering the collection and purification unit for decarbonization. An organic amine composite absorbent is used to absorb CO2 from the flue gas. The flue gas enters absorption tower 1 from the bottom and comes into counter-current contact with the absorbent liquid. Interstage cooling is used to reduce the heat of reaction and improve absorption efficiency. The rich liquid after CO2 absorption is pumped from the bottom of the tower to the lean-rich liquid heat exchanger 34 to recover heat before being sent to regeneration tower 32. The desorbed CO2, along with water vapor, is separated to remove moisture, yielding product CO2 gas with a purity of 99.5% (dry basis) or higher, which then enters the subsequent compression process. The condensate separated from the regeneration gas is returned to the underground tank and periodically replenished to regeneration tower 32 using a replenishment pump.

[0131] The rich liquor enters from the upper and middle sections of regeneration tower 32, where some CO2 is desorbed by stripping. It then enters reboiler 35 for further CO2 desorption. The lean liquor (105°C) after CO2 desorption flows out from the bottom of regeneration tower 32. Part of the steam is flashed in a flash tank, pressurized, and returned to the desorption tower for heat recovery. The lean liquor exiting the flash tank is cooled to 60°C after heat recovery in the lean-rich liquor heat exchanger 34. It is then pumped to a lean liquor cooler, cooled to 40°C, and enters absorption tower 1. This solvent circulation constitutes a continuous CO2 absorption and desorption process, with a CO2 capture rate exceeding 90%.

[0132] The regeneration energy consumption of the 30wt% compound amine absorbent should be ≤3.0GJ / t CO2, and the circulating absorption load should be ≥23LCO2 / L solution.

[0133] The gas source for the compression and distillation purification unit is CO2 regenerated gas from the CO2 capture unit. The main impurities are sulfur-containing substances and other trace impurities, which are mainly removed by adsorption in the adsorber using high-quality activated carbon. This ensures that the product indicators meet food-grade quality standards. There is no large amount of wastewater or waste liquid discharged during the production process, and the exhaust gas basically does not contain harmful substances, fully meeting emission requirements.

[0134] This project adopts a combination of precooling, adsorption, drying and low-temperature distillation processes.

[0135] (1) Pre-cooling: Use a pre-cooler to lower the temperature of carbon dioxide so that the outlet temperature is around 15℃.

[0136] (2) Compression: This unit uses the medium-pressure method to produce liquid carbon dioxide. According to the thermodynamic conditions of the carbon dioxide phase diagram, pure carbon dioxide can be produced as long as it can be maintained at 2.1 MPa and -20℃ in the carbon dioxide liquefaction zone. Since the purity of the carbon dioxide in the feed gas entering this unit is above 99% (dry basis), and the rest are non-condensable gases, in order to reduce the loss of carbon dioxide during the purification process, the carbon dioxide in the feed gas needs to be compressed to a final pressure of 2.5 MPa through a three-stage compression without oil lubrication. The compressed carbon dioxide gas is then evaporated with R22 at -28 to -31℃, and indirectly cooled to -25℃ to liquefy it.

[0137] (3) Adsorption: The adsorber is filled with activated carbon to adsorb sulfur-containing impurities in the raw gas and oil-containing impurities that may be brought in by the compressor.

[0138] (4) Drying: The dryer is filled with molecular sieves, mainly to meet the following requirements: ① The moisture content of the liquid carbon dioxide product must be ≤20ppm; ② To ensure that during the liquefaction and purification process of carbon dioxide, the saturated moisture in the carbon dioxide source does not freeze at low temperatures, clogging pipes and equipment and disrupting production; the molecular sieve adsorbent removes trace amounts of water from the gas, ensuring that the moisture content of the pre-cooled and dried carbon dioxide raw material gas is ≤20ppm. The molecular sieves are regenerated by heating after adsorption saturation and reused. The drying tower operates on a one-on-one standby configuration.

[0139] (5) Condensation and liquefaction: The exhaust gas containing 99% carbon dioxide, after being purified through compression, precooling, adsorption, and drying processes, enters the condenser for condensation and liquefaction. Liquid R22 is evaporated at -25 to -30°C to indirectly cool the compressed carbon dioxide gas, thereby condensing and liquefying the carbon dioxide gas into liquid carbon dioxide.

[0140] (6) Purification: The liquefied liquid carbon dioxide needs to be purified. A composite distillation purification tower is used. Based on the different boiling points of carbon dioxide and impurity components, the principle of low temperature distillation is used to separate the impurities under specific conditions, which not only improves the purity of carbon dioxide and obtains qualified liquid carbon dioxide products, but also reduces the gas consumption of the products.

[0141] (7) Auxiliary facilities:

[0142] R507 Condensation System: This process unit uses the medium-pressure method to produce liquid carbon dioxide. The cooling and liquefaction of the carbon dioxide gas, as well as the cooling of the vented air from the purification tower, are all handled by a refrigeration unit. Using R507 as the refrigerant, the low-temperature evaporation of R507 transfers cooling energy to the carbon dioxide, causing it to liquefy. Then, the gaseous R507 is compressed by the refrigeration unit and condensed in the evaporator condenser, turning the gaseous R507 into liquid R507. This liquid R507 then evaporates again in the condenser, absorbing heat and completing the refrigeration cycle.

[0143] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integrated carbon dioxide capture and processing of flue gas emitted from a natural gas boiler, characterized in that, include: The gas from the flue enters the absorption tower after desulfurization and alkali washing, and is absorbed by an absorbent to obtain a rich solution. The absorbent used in the absorption tower is a MEA-PEHA solution with a concentration ratio of 5:

5. The rich liquid is then introduced into an integrated reaction process for carbon dioxide capture, hydrogenation, and methane production. The integrated process for carbon dioxide capture, hydrogenation, and methane production includes the following steps: After passing through a heat exchanger, the rich liquid is desorbed in the desorption-hydrogenation integrated tower, separated by a gas-liquid separator, and then the liquid exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower before re-entering the absorption tower for carbon dioxide absorption. The gas separated in the gas-liquid separator is mixed with hydrogen and then enters the desorption-hydrogenation integrated tower and the hydrogenation reaction tower. The inlet of the hydrogenation reaction tower is connected to a pressure regulating valve.

2. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 1, characterized in that, The integrated carbon dioxide capture and hydrogenation to methane reaction process is completed using an integrated carbon dioxide capture and hydrogenation to methane reaction unit, which includes an absorption tower, a desorption and hydrogenation integrated tower, and a hydrogenation reaction tower. The absorbent that has absorbed carbon dioxide in the absorption tower passes through a heat exchanger and is then desorbed in the integrated desorption and hydrogenation tower. After being separated by a gas-liquid separator, the liquid passes through a heat exchanger and exchanges heat with the absorbent that has absorbed carbon dioxide flowing out of the absorption tower before re-entering the absorption tower for carbon dioxide absorption. The gas separated in the gas-liquid separator is mixed with hydrogen and then enters the desorption-hydrogenation integrated tower and the hydrogenation reaction tower. The inlet of the hydrogenation reaction tower is connected to a pressure regulating valve.

3. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 2, characterized in that, The absorption tower is equipped with a spraying device for spraying the absorbent. The liquid outlet of the absorption tower is connected in series with the cold side inlet of the heat exchanger via a pipeline, and the cold side outlet of the heat exchanger is connected to the liquid inlet of the desorption and hydrogenation integrated tower via a pipeline. The liquid outlet of the desorption and hydrogenation integrated tower is connected to the gas-liquid separator. The liquid outlet of the gas-liquid separator and the hot side inlet of the heat exchanger are connected in series through a pipeline. The hot side outlet of the heat exchanger is connected to the liquid inlet of the absorption tower through a pipeline. The outlet of the gas-liquid separator is connected to the gas mixing tank via a pipeline; the outlet of the gas mixing tank is connected to the compressor via a pipeline; the compressor is connected in parallel with the inlet of the desorption-hydrogenation integrated tower and the inlet of the hydrogenation reaction tower via pipelines; the desorption-hydrogenation integrated tower is a shell-and-tube type, with carbon dioxide and hydrogen introduced into the tube side and rich liquid introduced into the shell side, and the flow heat exchange mode can be countercurrent or cocurrent; the heat exchange tube bundle of the desorption-hydrogenation integrated tower is filled with at least one carbon dioxide hydrogenation catalyst; the heat exchange tube bundle of the desorption-hydrogenation integrated tower is in the form of a bare tube or an internally finned tube.

4. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 3, characterized in that, The desorption-hydrogenation integrated tower is equipped with at least one hydrogenation reaction tower. The inlets of the desorption-hydrogenation integrated tower and the hydrogenation reaction tower are connected to a gas mixing tank through pipelines, and the inlet reactant flow rates of the two towers are distributed through a pressure regulating valve.

5. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 4, characterized in that, The tube side and shell side of the desorption and hydrogenation integrated tower are equipped with thermometers.

6. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 5, characterized in that, The lean liquor after desorption in the integrated desorption and hydrogenation tower transfers heat to the rich liquor after CO2 absorption in the absorption tower via a heat exchanger.

7. The integrated method for carbon dioxide capture and processing of flue gas from a natural gas boiler according to claim 6, characterized in that, A CH4 concentration measuring instrument is installed at the outlet of the desorption and hydrogenation integrated tower; a flow meter is installed on the pipeline connecting the outlet of the gas-liquid separator and the gas mixing tank to obtain the CO2 flow rate, so as to control the H2 flow rate entering the gas mixing tank.

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