A method for separating carbon dioxide from a boiler flue gas

Abstract

This application belongs to the field of gas separation technology, specifically relating to a method for separating carbon dioxide from boiler flue gas. The method for separating carbon dioxide from boiler flue gas includes the following steps: (1) sequentially compressing, cooling, and dehydrating the flue gas, and then passing the dehydrated flue gas into a primary liquid-locking membrane separator for separation; (2) further compressing, cooling, and dehydrating the carbon dioxide gas passing through the primary liquid-locking membrane separator, and then passing the dehydrated flue gas into a secondary liquid-locking membrane separator for further separation. The advantages of this application include: the method for separating carbon dioxide from boiler flue gas described in this application uses a liquid-locking membrane separator to separate carbon dioxide from a mixed gas, which is simple to operate, has high separation efficiency, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, specifically relating to a method for separating carbon dioxide from boiler flue gas. Background Technology

[0002] Methods for separating carbon dioxide from boiler flue gas mainly include physical absorption, chemical absorption, pressure swing adsorption (PSA), and membrane separation. Physical absorption utilizes the high solubility of carbon dioxide in certain solvents to capture it. Under specific temperature and pressure conditions, carbon dioxide is absorbed by the solvent, and then released by changing the conditions. While this method is energy-efficient and simple to operate, it requires a highly efficient solvent recovery system. Chemical absorption separates carbon dioxide from flue gas through chemical reactions. Although its capture efficiency is relatively high, the regeneration process can consume significant energy. Membrane separation technology uses specific membrane materials that allow only carbon dioxide molecules to pass through, thus achieving separation. Membrane separation offers advantages such as high separation efficiency, low energy loss, and ease of operation, making it very popular in the field of CO2 separation. Summary of the Invention

[0003] This application provides a method for separating carbon dioxide from boiler flue gas, aiming to solve the problems of high cost and low efficiency in the existing method of separating carbon dioxide from boiler flue gas.

[0004] This application provides a method for separating carbon dioxide from boiler flue gas, comprising the following steps:

[0005] (1) The flue gas is sequentially compressed, cooled and dehydrated, and the dehydrated flue gas is then passed into a first-stage liquid-locking membrane separator for separation.

[0006] (2) The carbon dioxide gas that has passed through the first-stage liquid-locking membrane separator is compressed, cooled and dehydrated again, and then the dehydrated flue gas is passed into the second-stage liquid-locking membrane separator for separation.

[0007] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, the flue gas in step (1) is flue gas after desulfurization and denitrification.

[0008] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, in step (1), the compression is to compress the flue gas to 400-800 kPa.

[0009] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, in step (2), the compression is to compress the flue gas to 3000-4000 kPa.

[0010] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, the cooling in steps (1) and (2) each independently includes cooling the compressed flue gas to 20-25°C.

[0011] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, the cooling device is a raw gas heat exchanger.

[0012] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, the water removal equipment in steps (1) and (2) is a gas-liquid separator.

[0013] According to some embodiments of the method for separating carbon dioxide from boiler flue gas described in this application, the method further includes mixing the flue gas and flue gas retained by the secondary liquid-locking membrane separator for further separation. Detailed Implementation

[0014] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0015] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0016] This application provides a method for separating carbon dioxide from boiler flue gas, comprising the following steps:

[0017] (1) The flue gas is sequentially compressed, cooled and dehydrated, and the dehydrated flue gas is then passed into a first-stage liquid-locking membrane separator for separation.

[0018] (2) The carbon dioxide gas that has passed through the first-stage liquid-locking membrane separator is compressed, cooled and dehydrated again, and then the dehydrated flue gas is passed into the second-stage liquid-locking membrane separator for separation.

[0019] The method for separating carbon dioxide from boiler flue gas described in this application is simple to operate, low in cost, and has high carbon dioxide separation efficiency.

[0020] The primary and secondary liquid-locking membrane separators described in this application both employ a liquid-locking membrane device for gas separation, as specified in patent number CN118526938A. The liquid-locking membrane device for gas separation includes: a housing, an inlet, an outlet, end caps, an extraction port, and a liquid-locking membrane element. Both ends of the tubular housing are sealed with end caps, and an extraction port is provided at the end of each end cap. The housing has an inlet and an outlet at its two sides, respectively. The liquid-locking membrane element is installed inside the housing and is fixed within the housing by perforated plates inserted into both ends of the housing; the liquid-locking membrane element is sealed to the perforated plates.

[0021] The liquid-locking membrane separator can effectively load a liquid-locking membrane to prevent liquid leakage while achieving selective CO2 permeation. By setting a liquid-locking membrane that selectively permeates CO2 gas, CO2 can be selectively separated from a CO2-containing gas mixture.

[0022] In some embodiments of this application, the flue gas mentioned in step (1) is flue gas after desulfurization and denitrification. Flue gas refers to the gaseous substances that pollute the environment and are produced when fossil fuels such as coal are burned. It is usually discharged through flues or chimneys. Its main components include nitrogen, carbon dioxide, oxygen, water vapor, and sulfides.

[0023] In some embodiments of this application, in step (1), the compression is to compress the flue gas to 400-800 kPa, such as 400 kPa, 600 kPa, 650 kPa, 700 kPa, 760 kPa, 800 kPa, etc.

[0024] In some embodiments of this application, in step (2), the compression is to compress the flue gas to 3000-4000KPa, such as 3000KPa, 3200KPa, 3500KPa, 3800KPa, 4000KPa, etc.

[0025] In some embodiments of this application, the cooling described in steps (1) and (2) each independently includes cooling the compressed flue gas to 20-25°C, such as 20°C, 22°C, 23°C, 25°C, etc.

[0026] In some embodiments of this application, the cooling device is a raw gas heat exchanger.

[0027] In some embodiments of this application, the water removal device described in steps (1) and (2) is a gas-liquid separator.

[0028] In some embodiments of this application, the method further includes mixing the flue gas and flue gas trapped by the secondary liquid-locking membrane separator for further separation. The liquid-locking membrane separator of this application only allows selective permeation of carbon dioxide gas, achieving selective separation of carbon dioxide from the mixed gas containing carbon dioxide gas, while other gases are trapped, thus achieving efficient separation of carbon dioxide-containing gases.

[0029] The technical solution of this application will be further described below with reference to specific embodiments.

[0030] Example 1

[0031] A method for separating carbon dioxide from boiler flue gas includes the following steps:

[0032] First, the flue gas after simulated desulfurization and denitrification (CO2 volume concentration of 15%, flow rate of 20 L / min) is fed into the feed gas compressor and compressed to 0.4 MPa. Then, it enters the feed gas heat exchanger to be cooled to 25°C. After cooling, the gas is passed through a gas-liquid separator to remove water, and then introduced into a primary liquid-locking membrane separator (membrane area of ​​15 m²). 2 The first-stage intercepted flue gas from the first-stage liquid-locking membrane separator is sent to the high-purity N2 production process. The CO2-rich gas from the permeate side of the first-stage liquid-locking membrane separator is extracted by a vacuum pump (0.03 MPa). The extracted carbon dioxide gas is then compressed again to 4 MPa by a compressor. The compressed gas is then cooled to 25°C by a feed gas heat exchanger. After being dehydrated by a gas-liquid separator, the cooled gas is then fed into a second-stage liquid-locking membrane separator (membrane area 10 m²). 2 The secondary intercepted flue gas on the intercept side of the secondary liquid-locking membrane separator is sent back to the feed line of the primary liquid-locking membrane separator, while the CO2 gas on the permeate side of the secondary liquid-locking membrane separator is extracted by the secondary vacuum pump (0.03MPa) and sent out of the boundary area as product.

[0033] Example 2

[0034] A method for separating carbon dioxide from boiler flue gas includes the following steps:

[0035] First, the flue gas after simulated desulfurization and denitrification (CO2 volume concentration of 8%, flow rate of 20 L / min) is fed into the feed gas compressor and compressed to 0.6 MPa. Then, it enters the feed gas heat exchanger to be cooled to 25°C. After cooling, the gas is passed through a gas-liquid separator to remove water, and then introduced into a primary liquid-locking membrane separator (membrane area of ​​10 m²). 2The first-stage intercepted flue gas from the first-stage liquid-locking membrane separator is sent to the high-purity N2 production process. The CO2-rich gas from the permeate side of the first-stage liquid-locking membrane separator is extracted by a vacuum pump (0.03 MPa). The extracted carbon dioxide gas is then compressed again to 3 MPa by a compressor. The compressed gas is then cooled to 20°C by a feed gas heat exchanger. After being dehydrated by a gas-liquid separator, the cooled gas is then fed into a second-stage liquid-locking membrane separator (membrane area 15 m²). 2 The secondary intercepted flue gas on the intercept side of the secondary liquid-locking membrane separator is sent back to the feed line of the primary liquid-locking membrane separator, while the CO2 gas on the permeate side of the secondary liquid-locking membrane separator is extracted by the secondary vacuum pump (0.03MPa) and sent out of the boundary area as product.

[0036] Example 3

[0037] A method for separating carbon dioxide from boiler flue gas includes the following steps:

[0038] First, the flue gas after simulated desulfurization and denitrification (CO2 volume concentration of 10%, flow rate of 20 L / min) is fed into the feed gas compressor and compressed to 0.8 MPa. Then, it enters the feed gas heat exchanger to be cooled to 20°C. After cooling, the gas is passed through a gas-liquid separator to remove water, and then fed into a primary liquid-locking membrane separator (membrane area of ​​12 m²). 2 The first-stage intercepted flue gas from the first-stage liquid-locking membrane separator is sent to the high-purity N2 production process. The CO2-rich gas from the permeate side of the first-stage liquid-locking membrane separator is extracted by a vacuum pump (0.03 MPa). The extracted carbon dioxide gas is then compressed again to 4 MPa by a compressor. The compressed gas is then cooled to 25°C by a feed gas heat exchanger. After being dehydrated by a gas-liquid separator, the cooled gas is then fed into a second-stage liquid-locking membrane separator (membrane area 15 m²). 2 The secondary intercepted flue gas on the intercept side of the secondary liquid-locking membrane separator is sent back to the feed line of the primary liquid-locking membrane separator, while the CO2 gas on the permeate side of the secondary liquid-locking membrane separator is extracted by the secondary vacuum pump (0.03MPa) and sent out of the boundary area as product.

[0039] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for separating carbon dioxide from boiler flue gas, characterized in that, Includes the following steps: (1) The flue gas is sequentially compressed, cooled and dehydrated, and the dehydrated flue gas is then passed into a first-stage liquid-locking membrane separator for separation. (2) The carbon dioxide gas that has passed through the first-stage liquid-locking membrane separator is compressed, cooled and dehydrated again, and then the dehydrated flue gas is passed into the second-stage liquid-locking membrane separator for separation.

2. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, The flue gas mentioned in step (1) is the flue gas after desulfurization and denitrification.

3. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, In step (1), the compression is to compress the flue gas to 400-800 kPa.

4. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, In step (2), the compression is to compress the flue gas to 3000-4000 kPa.

5. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, The cooling described in steps (1) and (2) each independently includes cooling the compressed flue gas to 20-25°C.

6. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, The cooling device is a raw gas heat exchanger.

7. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, The equipment for removing water in steps (1) and (2) is a gas-liquid separator.

8. The method for separating carbon dioxide from boiler flue gas according to claim 1, characterized in that, The method also includes mixing the flue gas and flue gas trapped by the secondary liquid-locking membrane separator and then separating them again.