CN110787596A

CN110787596A - Low-temperature and membrane-coupled flue gas separation method

Info

Publication number: CN110787596A
Application number: CN201910946377.9A
Authority: CN
Inventors: 宋春风; 范智超; 李润; 邱依婷
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2019-10-04
Filing date: 2019-10-04
Publication date: 2020-02-14

Abstract

The invention provides a novel low-temperature and membrane-coupled flue gas separation method. Compared with the traditional membrane-low temperature mixing process, the performance of the membrane is improved in a low temperature environment. Meanwhile, the cold energy of the liquefied natural gas is adopted to maintain the low temperature and cryogenic conditions. The method adopts a three-section structure: the first part is a low-temperature unit used for cooling the feed gas; the second part is a membrane separation unit, and CO in the raw material gas is separated by a membrane separator₂And N₂Carrying out separation; the third part is a cryogenic unit which enriches CO₂CO in gas₂The anti-sublimation phase is changed into dry ice. Simulation results show that the process for coupling low temperature, membrane separation and cryogenic cooling provided by the method can effectively improve CO₂The recovery rate and the purity of the product are improved, and the energy consumption can be effectively reduced.

Description

Low-temperature and membrane-coupled flue gas separation method

Technical Field

The invention relates to the technical field of flue gas separation, in particular to a low-temperature and membrane separation coupled flue gas separation method.

Background

CO₂Capture, utilization and storage (CCUS) is important to mitigate climate change and slow down climate warmingStrategy. Various COs have been studied over the past decades₂Trapping techniques such as chemical absorption, physical adsorption, membrane separation, and cryogenic phase transition. Among them, chemical absorption (e.g., monoethanolamine, MEA) is considered the most mature technology, but one of its existing disadvantages is the energy intensive (about 2.5-3.5 MJ/kgCO) of solvent regeneration₂) Approximately 80% of the total energy consumption, and the proposed goal of the European Union is 2MJ/kgCO₂(including both trapping and compression). Besides energy consumption, the corrosion of chemical solvent to installation equipment, high capital cost of membrane separation materials, harsh cryogenic phase change conditions and high installation investment are also key problems to be solved.

One of the potential alternatives to overcome this problem is to couple different COs₂Trapping method, such as membrane-chemical absorption coupling method, membrane-cryogenic coupling process, etc. Despite coupling of CO₂The trapping process has led to extensive research and scrutiny, but there are several challenges to overcome. Amine absorption-membrane coupled processes generally have higher absorption rates, but their carbon dioxide separation costs outweigh the amine absorption process alone. In contrast, the membrane-low temperature coupling process is competitive with existing separation techniques. Recent findings indicate that CO is coupled₂The low-temperature environment applied in the trapping set can further improve the process efficiency of the membrane separation.

The invention designs a novel low-temperature and membrane separation coupled flue gas separation method. The flue gas is treated by a low-temperature unit at first, which is beneficial to improving the permeability of the membrane. The concentrated carbon dioxide is then captured by anti-sublimation in the cryogenic section.

Disclosure of Invention

The invention aims to solve the defects in the prior art, and provides a low-temperature and membrane-coupled flue gas separation method to overcome the defects in the prior art.

The technical scheme of the invention is a low-temperature and membrane-coupled flue gas separation method, which comprises the following steps:

s1, pressurizing a flue gas raw material gas through a compressor 1, cooling the gas through a refrigerator, and sending the gas into a membrane separation unit;

s2. lowerThe warmed flue gas is selectively enriched in a membrane separator 3, and enriched in CO through permeation measurement₂Gas, the retentate side being N₂And the like. N of redundant side₂Pumping into heat exchanger HX-1 for recovering cold energy, and permeating CO-rich gas at outlet₂The gas continues to the cryogenic unit;

s3, rich in CO₂CO in gas₂Is subjected to cryogenic phase change to solid CO in a flash tank 5₂The other impurity gases are sent to a heat exchanger HX-2 without phase change, and cold energy is recovered;

s4. phase-changed CO₂Recovered as gaseous CO by heat exchanger HX-3₂Storing and recovering cold energy.

In the step S2, the liquefied natural gas is used to cool the membrane separation unit, so as to improve the gas separation effect of the membrane separator.

In step S3, the cryogenic temperature of the flash tank is obtained by vaporizing the liquefied natural gas.

And the steps S2 and S4 both comprise heat exchangers for recovering impurity gases, thereby recovering cold energy and reducing energy consumption.

In the step S4, the flash tank temperature is controlled to only enable CO₂The phase change occurs, and other impurity gases are kept unchanged in gas state.

Compared with the prior art, the low-temperature and membrane-coupled flue gas separation method provided by the invention has the following advantages:

1. the product obtained in the invention has low temperature, and is easy to carry out subsequent treatment, thereby further reducing the cost.

2. The invention organically combines low temperature with the membrane, and improves the gas separation effect of the membrane separator through low temperature.

3. The coupling process provided by the invention can effectively improve CO₂The recovery rate and the purity of the product are improved, and the energy consumption of the process can be effectively reduced.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 shows the results of the test performance of the present invention.

The symbols in fig. 1 mean: 1-compressor, 2-refrigerator, 3-membrane separator, 4-pump, 5-flash tank, HX1, HX-2, HX 3-

heat exchangers

1, 2, 3, C1, C2-liquefied natural gas heat exchangers.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Example 1

Test with mixed gas, CO₂And N₂Concentrations of 15% and 85%:

pressurizing raw material gas to 303kPa by a compressor 1, introducing the raw material gas into a membrane separation unit through a low-temperature unit at the temperature of minus 20 ℃ at the flow rate of 600kg/s, selectively enriching by a membrane separator 3 in the membrane separation unit, and permeating the N side₂The impurity gas is recycled to a heat exchanger HX-1 through a pump 4 to recycle cold energy and is rich in CO₂The gas passes through the permeation side stream to a flash tank 5 in a cryogenic unit, where the CO is₂The residual impurity gas is recycled to a heat exchanger HX-2 to recycle cold energy and phase-changed CO₂The cold energy is recovered by the heat exchanger HX-3 and is phase-changed into gas state for storage.

Under the conditions of example 1, the material of the membrane separator used in the process of the invention was

5218 polyimide material, CO₂/N₂The selectivity is 100, the effective membrane area of the membrane separator is 90m²And is an isothermal separation, i.e. the upstream and downstream temperatures are unchanged.

In example 1, the adiabatic efficiency of the compressor and the pump was 85%.

From this example, the conclusion can be drawn that: compared with the traditional three-stage membrane separation flue gas treatment process, the purity of the captured CO2 is close to 100%, and the CO is collected₂The recovery rate is 93.5%, and better CO is obtained₂Purity and recovery (three-stage membrane separation process CO)₂Purity of 95% CO₂The recovery rate is 83 percent), and in addition, the process energy consumption is also reduced to 2MJ/kg CO₂The minimum can reach 1.7MJ/kg CO₂Is lower than the tradition3MJ/kg CO of membrane separation process₂。

Compared with the traditional membrane separation process, the method has better CO content₂The trapping and recovery effect is achieved, the energy consumption is lower, and the advantages are obvious.

Claims

1. A low-temperature and membrane-coupled flue gas separation method is characterized by comprising the following steps of: the whole process consists of a low-temperature unit, a membrane separation unit and a deep cooling unit;

introducing the flue gas into a cryogenic unit first, the feed gas being cooled and then sent to a membrane separation unit to promote gas permeation, creating a high pressure on the upstream flow side of the membrane and resulting in a relatively low pressure on the permeate side, thereby forming a gas permeation through the membrane;

after being treated by the membrane separation unit, the exhaust gas is conveyed to a heat exchanger through a pump to cool the subsequent flue gas, and meanwhile, the permeated CO 2-rich gas is conveyed to a cryogenic unit through a pump;

in cryogenic units, CO2 may be anti-sublimated into solid form (dry ice) and the residual gas (N2) will pass through without undergoing a phase change, thereby achieving enrichment and storage of CO 2.

2. The method of claim 1, wherein the flue gas separation process comprises the steps of: the cold energy required for the cryogenic and cryogenic units is provided by the liquefied natural gas.

3. The method of claim 1, wherein the flue gas separation process comprises the steps of: the cold energy of the two gas streams separated by the cryogenic unit (residual gas and carbon dioxide product) is recovered separately by two other heat exchangers to cool the subsequent incoming gas.

4. The method of claim 1, wherein the flue gas separation process comprises the steps of: the low temperature unit temperature was set to-20 ℃.

5. A low temperature and membrane coupling as claimed in claim 1The flue gas separation method is characterized in that: the temperature of the cryogenic unit is set to-120 ℃ to enable CO₂And (5) phase transition.