Method for simultaneously recovering carbon dioxide and nitrogen from flue gas

Abstract

The invention provides a method for simultaneously recovering carbon dioxide and nitrogen from flue gas. The method comprises the following steps: 1) washing the flue gas with water and alkali; (2) flue gas compression and trapping; (3) compressing CO2 regenerated gas; 4) CO2 dehydration and drying; (5) refrigerating and liquefying CO2, and storing and loading; and 6) preparing nitrogen through membrane separation. Refined CO2 and N2 can be obtained from the flue gas at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of carbon dioxide capture, liquefaction and nitrogen refining, and in particular to a method for simultaneously recovering carbon dioxide and nitrogen from flue gas. Background Art

[0002] At present, the process of recovering carbon dioxide from flue gas mainly adopts chemical absorption method, which is based on the characteristics of absorbent absorbing at low temperature and low pressure and desorbing at high temperature, capturing CO2 from flue gas, and directly discharging the tail gas with high nitrogen content. The captured CO2 is compressed, dehydrated, liquefied, stored and loaded for utilization. The main problem of this process is high regeneration energy consumption. At the same time, due to the escape, oxidative degradation and thermal degradation of the absorbent, the loss is large, and it brings certain safety and environmental protection problems.

[0003] The technology of CO2 absorption under high pressure is relatively mature, but the N2 content in the raw gas is high, resulting in a waste of compression energy. If the nitrogen in the flue gas can be used, a new process needs to be adopted to fully utilize the energy of the system to produce nitrogen while recovering CO2. Summary of the invention

[0004] In view of this, the main purpose of the present invention is to provide a method for simultaneously recovering carbon dioxide and nitrogen from flue gas. The method is suitable for processing conditions where the CO2 content in the flue gas is low and the N2 content is high, and can achieve the simultaneous acquisition of refined CO2 and N2 from the flue gas.

[0005] In order to achieve the above object, the present invention provides a method for simultaneously recovering carbon dioxide and nitrogen from flue gas, comprising the following steps:

[0006] 1) Flue gas water washing and alkali washing: high-temperature flue gas is washed with water and alkali to reduce the consumption of decarbonization agents;

[0007] 2) Flue gas compression and capture: The flue gas after water washing and alkali washing is pressurized and decarbonized to obtain CO2 regeneration gas and high-N2 purified gas;

[0008] 3) CO2 regeneration gas compression: the CO2 regeneration gas obtained in step 2) is pressurized and then enters the CO2 solid adsorption dehydration device;

[0009] 4) CO2 dehydration and drying: dehydrating the CO2 obtained in step 3) to obtain dry CO2 regeneration gas;

[0010] 5) CO2 refrigeration, liquefaction, storage and loading: The dry CO2 regeneration gas obtained in step 4) enters the liquefier, and after refrigeration, the product CO2 is obtained, which enters the CO2 storage tank for storage, and finally is loaded into a truck for transportation through a loading pump;

[0011] 6) Nitrogen production by membrane separation: The purified gas with high N2 content obtained in step 2) is filtered and then enters a primary membrane separation unit, and N2 is obtained at one end after separation. The permeate gas at the other end is pressurized by a compressor and then enters a secondary membrane separation unit for secondary separation, and N2 is obtained at one end after separation. The permeate gas at the other end is pressurized by a compressor and then enters a tertiary membrane separation unit for separation, and N2 is obtained at one end after separation, and the other end is released gas; the product gases of the three units are combined to obtain a gas with N2 ≥ 99% (mol).

[0012] Furthermore, in step 1), the pH of the washing water is controlled between 6.7 and 7.2.

[0013] Furthermore, in step 1), the main components of the flue gas are N2 and CO2, wherein the concentration of CO2 is 5-15% (v / v).

[0014] Furthermore, in step 2), decarbonization is carried out in an absorption tower, and the operating pressure of the absorption tower is 2.0 to 2.5 MPa.

[0015] Furthermore, in step 2), the flue gas is decarbonized by an alcohol amine method, and the concentration of the amine solution is 40-50% (wt).

[0016] Furthermore, in step 2), the CO2 content in the CO2 regeneration gas is ≤1% (v / v).

[0017] Furthermore, in step 3), the CO2 regenerated gas obtained in step 2) is pressurized by a CO2 compressor, and the outlet pressure of the compressor is 2.5 to 3.0 MPa.

[0018] Furthermore, in step 3), the CO2 solid adsorption dehydration device is provided with an adsorbent, and the adsorbent is silica gel or molecular sieve.

[0019] Furthermore, in step 3), the calculation formula for the amount of the adsorbent is as follows:

[0020] Vw=1.3[(G1˙τ) / (24Xs˙ρ B )

[0021] Where:

[0022] G1-the amount of water dehydrated by the adsorbent, in kilograms per day (kg / d);

[0023] τ-selected adsorption cycle, in hours (h);

[0024] Xs-dynamic saturated adsorption capacity of the adsorbent, in kilograms of water per kilogram of adsorbent [kg(water) / kg(adsorbent)];

[0025] ρ B - Bulk density of the adsorbent in kilograms per cubic meter (kg / m 3 ).

[0026] Furthermore, in step 4), the CO2 obtained in step 3) is dehydrated by a three-tower isobaric regeneration dehydration process, and the operating pressure of the drying tower is 2.5 to 3.0 MPa; by controlling the water content in the outlet of the dry CO2 regeneration gas, the water dew point of the regeneration gas is made ≤-40°C.

[0027] Furthermore, the CO2 refrigeration liquefaction in step 5) specifically includes: the dry CO2 regeneration gas obtained in step 4) enters the liquefier, whose refrigerant medium is R507, and the product CO2 is obtained after refrigeration, enters the CO2 storage tank for storage, and finally is loaded into a truck for transportation through a loading pump.

[0028] Furthermore, in step 5), the outlet temperature of the liquefier is -20°C to -30°C.

[0029] Furthermore, the nitrogen production by membrane separation in step 6) specifically comprises: filtering the high-N2-containing purified gas obtained in step 2) through a two-stage filter, entering a primary membrane separation unit for separation, obtaining a gas with N2 ≥ 99% at one end after separation, and pressurizing the permeate gas at the other end to 2.0-3.0 MPa through a compressor, and then entering a secondary membrane separation unit for separation, obtaining a gas with N2 ≥ 99% at one end after separation, and pressurizing the permeate gas at the other end to 2.0-3.0 MPa through a compressor, and then entering a tertiary membrane separation unit for separation, obtaining a gas with N2 ≥ 99% at one end after separation, and releasing gas at the other end; the product gases of the three units are combined to obtain a gas with N2 ≥ 99% (mol).

[0030] Furthermore, in step 6), the primary membrane separation unit, the secondary membrane separation unit and the tertiary membrane separation unit are all hollow fiber membranes.

[0031] Furthermore, in step 6), the gas is provided with a gas temperature control and a constant temperature heater before entering the primary membrane separation unit, the secondary membrane separation unit or the tertiary membrane separation unit.

[0032] Furthermore, in step 6), the flow rate of the vented gas is ≤5% of the flow rate of the raw gas.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The invention can realize the simultaneous recovery of N2 and CO2 from flue gas to obtain refined CO2 and N2 at the same time. The invention can be used for oil field oil displacement, with an oil replacement rate of 0.2-0.3t / tCO2 and an increase in recovery rate of 10-15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention discloses a flow chart for simultaneously recovering carbon dioxide and nitrogen from flue gas. DETAILED DESCRIPTION

[0036] The present invention provides a method for simultaneously recovering carbon dioxide and nitrogen from flue gas. The specific implementation method is described below with specific examples. It should be understood that the specific examples described here are only used to explain the present invention and are not used to limit the present invention.

[0037] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. The following materials or reagents, unless otherwise specified, are commercially available.

[0038] Example 1

[0039] like Figure 1 As shown, the present invention provides a method for simultaneously recovering carbon dioxide and nitrogen from flue gas, comprising the following steps:

[0040] 1) Flue gas water washing and alkali washing: Cool the high-temperature flue gas to 40°C by water cooling, and at the same time, control the pH of the washing water to 7.0 by adding alkali solution. The main components of the flue gas are N2 and CO2, of which the concentration of CO2 is about 10% (v / v);

[0041] 2) Flue gas compression and decarbonization: The flue gas after water washing and alkali washing is compressed by a flue gas compression device, and the flue gas compression device uses a compressor to increase the pressure to 2.0 MPa. Then, the obtained flue gas is decarbonized by using a 45wt% MDEA solution (decarbonization is carried out in an absorption tower, and the operating pressure of the absorption tower is 2.0 MPa) to obtain CO2 regeneration gas (the content of CO2 is about 91% (v / v)) and high-N2 purified gas (the content of CO2 is about 1% (v / v);

[0042] 3) CO2 regeneration gas compression: The high CO2 regeneration gas (CO2 content ≥ 91% (v / v)) obtained in step 2) is pressurized to about 2.5MPa by a CO2 compressor and enters a silica gel adsorption dehydration device, wherein an adsorbent is provided in the silica gel adsorption dehydration device, and the adsorbent is silica gel, and the amount of the adsorbent is 60m 3 ;

[0043] 4) CO2 dehydration and drying: The CO2 obtained in step 3) is dehydrated by a three-tower isobaric regeneration dehydration process (the operating pressure of the drying tower is 2.5 MPa) to obtain dry gas (the water dew point is controlled to -40°C); the three-tower isobaric regeneration dehydration process is a prior art, and its operating parameters are not described here.

[0044] 5) CO2 refrigeration, liquefaction, storage and loading: The dry CO2 regeneration gas obtained in step 4) enters the liquefier (the outlet temperature of the liquefier is -25°C), and its refrigerant medium is R507. After refrigeration, the product CO2 is obtained and enters the CO2 storage tank for storage, and finally loaded into the truck for transportation through the loading pump.

[0045] 6) Nitrogen production by membrane separation: The purified gas with high N2 content obtained in step 2) passes through a two-stage filter and enters a primary hollow fiber membrane. A gas with N2 content of 99.2% (mol) is obtained at one end after separation. The permeate gas at the other end is pressurized to about 2.4 MPa by a compressor and then enters a secondary hollow fiber membrane for separation. A gas with N2 content of 99.2% (mol) is obtained at one end after separation. The permeate gas at the other end is pressurized to 2.4 MPa by a compressor and then enters a tertiary hollow fiber membrane for separation. A gas with N2 content of 99.2% (mol) is obtained at one end after separation, and the other end is released gas (4% of the raw gas flow rate); the product gases of the three units are combined to obtain a gas with N2 content of 99.2% (mol).

[0046] In order to verify the effect of the above-mentioned simultaneous recovery of CO2 and N2 from flue gas, we took the flue gas of a power plant as the object and analyzed it using the method described in the present invention.

[0047] Table 1 Composition of flue gas from power plants (mol%)

[0048]

[0049] HYSYS software is used to perform calculation and analysis on the flue gas components of power plants and the method described in the present invention.

[0050] Calculation conditions:

[0051] 1) Flue gas water washing and alkali washing: Cool the high-temperature flue gas (normal pressure, 150°C) from the third power plant to 40°C; at the same time, control the pH of the washing water at 7.0 by adding alkali solution. The main components of the flue gas are N2 and CO2, of which the concentration of CO2 is about 10% (v / v);

[0052] 2) Flue gas compression: The flue gas (normal pressure, 40°C) after water washing and alkali washing is pressurized to 2.0MPa by a compressor unit;

[0053] 3) Flue gas decarbonization: The pressurized (2.0 MPa) flue gas is decarbonized using a 45 wt% MDEA solution to obtain CO2 regeneration gas (CO2 content is 91% (v / v)) and purified gas (CO2 content is 1% (v / v); the purified gas after decarbonization enters the membrane separation nitrogen production device in step 6, and the CO2 regeneration gas enters the CO2 compressor for pressurization.

[0054] 4) CO2 regeneration gas compression, dehydration and drying: The high CO2 regeneration gas (CO2 content ≥ 91% (v / v)) obtained from the flue gas capture unit is pressurized to 2.5MPa by a CO2 compressor and then enters the CO2 silica gel adsorption dehydration device. The dehydrated dry gas (water dew point is controlled to -40°C) enters the refrigeration liquefaction device of step 5); the CO2 silica gel adsorption dehydration device is a prior art and will not be described here. The refrigeration liquefaction device is a conventional R507 refrigeration unit. The CO2 silica gel adsorption dehydration device is provided with an adsorbent, and the adsorbent is silica gel. The amount of the adsorbent is 60m 3 ;

[0055] 5) CO2 refrigeration, liquefaction, storage and loading: The dry CO2 (dehydrated dry gas) after dehydration in step 4) enters the liquefier (the outlet temperature of the liquefier is -25°C), and its refrigerant medium is R507. The obtained product CO2 (temperature is -20°C) enters the CO2 storage tank for storage, and the CO2 is loaded into the truck for transportation through the loading pump.

[0056] 6) Membrane separation for nitrogen production: The purified gas after decarburization obtained in step 2) is filtered and enters the primary hollow fiber membrane. One end after separation obtains gas with N2 of 99.2% (mol). The permeate gas at the other end is pressurized to 2.4MPa by a compressor and then enters the secondary hollow fiber membrane. One end after separation obtains gas with N2 of 99.2% (mol). The permeate gas at the other end is pressurized to 2.4MPa by a compressor and then enters the tertiary hollow fiber membrane for separation. One end after separation obtains gas with N2 of 99.2% (mol), and the other end is released gas (4% of the raw gas flow rate). The product gases of the three units are combined to obtain gas with N2 of 99.2% (mol).

[0057] Through the above example analysis, the present invention can realize the simultaneous recovery of CO2 and N2 in flue gas, which can be finally used for oil field oil displacement and production increase, with an oil exchange rate of 0.23t / tCO2 and a recovery rate of 13%.

[0058] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simultaneously recovering carbon dioxide and nitrogen from flue gas, characterized in that: The following steps are involved: 1) Flue gas water washing and alkali washing: Wash the high-temperature flue gas with water and alkali; 2) Flue gas compression and capture: The flue gas after water washing and alkali washing is pressurized and decarbonized to obtain CO2 regeneration gas and high-N2 purified gas; 3) CO2 regeneration gas compression: the CO2 regeneration gas obtained in step 2) is pressurized and then enters the CO2 solid adsorption dehydration device; 4) CO2 dehydration and drying: dehydrating the CO2 obtained in step 3) to obtain dry CO2 regeneration gas; 5) CO2 refrigeration, liquefaction, storage and loading: The dry CO2 regeneration gas obtained in step 4) enters the liquefier, and after refrigeration, the product CO2 is obtained, which enters the CO2 storage tank for storage, and finally is loaded into a truck for transportation through a loading pump; 6) Nitrogen production by membrane separation: The purified gas with high N2 content obtained in step 2) is filtered and then enters a primary membrane separation unit, and N2 is obtained at one end after separation. The permeate gas at the other end is pressurized by a compressor and then enters a secondary membrane separation unit for secondary separation, and N2 is obtained at one end after separation. The permeate gas at the other end is pressurized by a compressor and then enters a tertiary membrane separation unit for separation, and N2 is obtained at one end after separation, and the other end is released gas; the product gases of the three units are combined to obtain a gas with N2 ≥ 99% (mol).

2. The method according to claim 1, characterized in that In step 1), the pH of the washing water is controlled between 6.7 and 7.2; the main components of the flue gas are N2 and CO2, wherein the concentration of CO2 is 5 to 15% (v / v).

3. The method according to claim 1, characterized in that In step 2), decarbonization is carried out in an absorption tower, and the operating pressure of the absorption tower is 2.0-2.5 MPa; the flue gas is decarbonized by an alcohol amine method, and the concentration of the amine solution is 40-50% (wt); the CO2 content of the purified gas is ≤1% (v / v).

4. The method according to claim 1, characterized in that In step 3), the CO2 regenerated gas obtained in step 2) is pressurized by a CO2 compressor, and the outlet pressure of the compressor is 2.5-3.0 MPa.

5. The method according to claim 1, characterized in that In step 3), the CO2 solid adsorption dehydration device is provided with an adsorbent, and the adsorbent is silica gel or molecular sieve.

6. The method according to claim 1, characterized in that In step 4), the CO2 obtained in step 3) is dehydrated by a three-tower isobaric regeneration dehydration process, and the operating pressure of the drying tower is 2.5-3.0 MPa; by controlling the water content in the outlet of the dry CO2 regeneration gas, the water dew point of the regeneration gas is made ≤-40°C.

7. The method according to claim 1, characterized in that The dry CO2 regeneration gas obtained in step 4) enters the liquefier, whose refrigerant medium is R507, and the product CO2 is obtained after refrigeration, enters the CO2 storage tank for storage, and finally is loaded into a truck for transportation through a loading pump.

8. The method according to claim 7, characterized in that In step 5), the outlet temperature of the liquefier is -20°C to -30°C.

9. The method according to claim 1, characterized in that The nitrogen production by membrane separation in step 6) specifically comprises: filtering the high-N2-containing purified gas obtained in step 2) and entering the primary membrane separation unit, obtaining N2≥99% (mol) gas at one end after separation, pressurizing the permeate gas at the other end to 2.0-3.0 MPa by a compressor, and then entering the secondary membrane separation unit, obtaining N2≥99% (mol) gas at one end after separation, pressurizing the permeate gas at the other end to 2.0-3.0 MPa by a compressor, and then entering the tertiary membrane separation unit for separation, obtaining N2≥99% (mol) gas at one end after separation, and releasing gas at the other end; the product gases of the three units are combined to obtain N2≥99% (mol) gas.

10. The method according to claim 1, characterized in that In step 6), the primary membrane separation unit, the secondary membrane separation unit and the tertiary membrane separation unit are all hollow fiber membranes; the gas is provided with a gas temperature control and a constant temperature heater before entering the primary membrane separation unit, the secondary membrane separation unit or the tertiary membrane separation unit; the flow rate of the vented gas is ≤5% of the flow rate of the raw gas.

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