Carbon dioxide recovery method and application

Abstract

The invention relates to the technical field of carbon dioxide recovery, in particular to a carbon dioxide recovery method and application. According to the system, part of CO2 product gas is recovered, a second tower is a carbon dioxide desorption tower, and CO2 is desorbed and sent to a carbon dioxide compressor pressure increasing and gas feeding section to serve as conveying gas and shielding gas; the CO2 gas is recovered, so that the temperature of an outlet of the conversion water cooler can be reduced, the thermal load entering a low-A system can be reduced, the barren liquor circulation amount is reduced, the system temperature is reduced, the barren liquor quality is improved, the thermal load of circulating water can be reduced, the return water temperature of the circulating water is reduced, the circulating water amount is reduced, the current of a circulating water pump is reduced, and the energy-saving effect is obvious. Meanwhile, low-pressure nitrogen is replaced by desorbed CO2 gas, the low-pressure nitrogen can be saved by about 5000 cubic meters per hour, liquid carbon dioxide is byproduct from surplus CO2 gas, and the product benefit is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide recovery, in particular to a carbon dioxide recovery method and application. BACKGROUND

[0002] The low temperature methanol washing system mainly removes CO2, H2S and COS impurities in the shift gas from the upstream shift process, and removes the saturated water brought in the shift gas, to obtain CO2: 3-4% (mol), total sulfur <0.1 ppm qualified purified gas sent to the synthesis device. The system recovers part of the CO2 product gas (CO2≥99%, total sulfur <2 ppmv); the second tower is a carbon dioxide stripping tower, the CO2 is sent to the carbon dioxide compressor after stripping to increase the pressure of the gasification section as conveying gas and protective gas; the third tower is a hydrogen sulfide concentration tower, which is divided into ABC three sections, and uses nitrogen stripping, which can further reduce the CO2 partial pressure dissolved in methanol, and can make CO2 desorption more thorough, equivalent to negative pressure (close to vacuum) operation, the more stripping nitrogen is introduced, the more CO2 partial pressure is reduced, and the more thorough desorption is, and the CO2 recovered after cooling is discharged to the atmosphere after passing through the tail gas washing tower.

[0003] In the prior art, the carbon dioxide recovery system cannot recover and utilize carbon dioxide gas, and cannot convert the excess CO2 gas into liquid carbon dioxide. Therefore, the present application provides a carbon dioxide recovery method and application to solve the above problems. SUMMARY

[0004] The present application aims to provide a carbon dioxide recovery method and application to solve the problems raised in the background art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a carbon dioxide recovery method, specifically comprising the following steps:

[0006] The shift gas is sent into the system;

[0007] The system recovers part of the CO2 product gas, wherein the second tower is a carbon dioxide stripping tower, and the CO2 is sent to the carbon dioxide compressor after stripping to increase the pressure of the gasification section as conveying gas and protective gas;

[0008] The third tower is a hydrogen sulfide concentration tower, which is divided into ABC three sections, and uses nitrogen stripping, which can further reduce the CO2 partial pressure dissolved in methanol, and can make CO2 desorption more thorough, the more thorough desorption is, and the CO2 recovered after cooling is discharged to the atmosphere after passing through the tail gas washing tower;

[0009] The CO2 gas in the third tower C section is stripped to act as a cold source and exchange heat with the shift water cooler, and the gas is sent to the gasification coal mill after heat exchange to replace low-pressure nitrogen, and the excess CO2 gas produces liquid CO2.

[0010] Preferably, the three-tower C section resolves CO2 gas flow 10000 standard cubic meters per hour, pressure 0.07 MPa, temperature -53 degrees Celsius, CO2 gas content about 99.5%, and after heat exchange with E2201, the temperature is 26 degrees Celsius.

[0011] Preferably, the three-tower C section resolves CO2 gas flow into two routes, one route increases DN200 pipeline after opening at the six-tower external delivery valve, sets hand valve, cut-off valve and liquid CO2 regulating valve, and the other route increases DN300 pipeline before opening at the six-tower external delivery valve, and adds a frequency conversion fan to pressurize the gas to 0.4 MPa before sending it to the shift water cooler to replace the circulating water.

[0012] Preferably, a bypass pipeline with a regulating valve is arranged on the pipeline, which can realize online switching operation of the water cooler circulating water and CO2 gas.

[0013] Preferably, the CO2 gas outlet pipeline of the water cooler after heat exchange is provided with a steam-water separator.

[0014] Preferably, the three-tower C section resolves CO2 gas heat exchange temperature to 26 degrees Celsius, and the temperature of the shift water cooler after heat exchange rises to 30 degrees Celsius, which can be adjusted in real time by adjusting the auxiliary line regulating valve of the shift water cooler, and the shift gas temperature drops to 32 degrees Celsius and is sent to the low methanol section.

[0015] Preferably, the CO2 after heat exchange enters the steam-water separator and is sent to the coal mill through a pressure regulating valve, and the flow and pressure entering the coal mill can be increased or decreased by increasing the frequency converter of the fan to meet the requirements of the coal mill.

[0016] Preferably, when the frequency conversion fan fails to start or the pressure difference between the low-pressure nitrogen and the circulating gas is low, the interlocked mill opens the low-pressure nitrogen cut-off valve, closes the CO2 cut-off valve into the mill, adjusts the valve to 0, closes the fan inlet cut-off valve, adjusts the six-tower vent gas flow and liquid CO2 flow according to the CO2 desorption gas pressure, ensures the stability of the three-tower pressure, interlocks the opening of the fan outlet and the steam-water separator outlet vent valve, interlocks the closing of the shift water cooler cut-off valve and the opening of the auxiliary line regulating valve, and interlocks the opening of the circulating water regulating valve to the shift water cooler to ensure the temperature of the shift cooler.

[0017] Preferably, when the coal mill is stopped due to failure and needs to be switched to low-pressure nitrogen gas, the low-pressure nitrogen gas shutoff valve of the mill is opened manually, the nitrogen gas shutoff valve opening signal interlocks the fan to stop, the CO2 shutoff valve into the mill is closed, the regulating valve is automatically closed to 0 position, the fan inlet shutoff valve is closed, the CO2 desorption gas pressure is adjusted to regulate the flow of the six-tower vent gas and the flow of liquid CO2, the three-tower pressure is ensured to be stable, the fan outlet and the steam-water separator outlet vent valves are opened interlockingly, the shutoff valve into the shift water cooler is closed interlockingly, the secondary line regulating valve is opened interlockingly, and the circulating water regulating valve into the shift water cooler is opened interlockingly to ensure the temperature of the shift cooler.

[0018] The application of a carbon dioxide recovery method in carbon dioxide recovery.

[0019] Compared with the prior art, the application has the beneficial effects that:

[0020] The application can reduce the outlet temperature of the shift water cooler, reduce the heat load into the low-methane system, reduce the circulating amount of lean liquid, reduce the system temperature, improve the quality of the lean liquid, reduce the heat load of the circulating water, reduce the temperature of the circulating water return, reduce the amount of circulating water, reduce the current of the circulating water pump, and save electricity obviously. The desorbed CO2 gas can replace low-pressure nitrogen gas, and about 5000 square meters of low-pressure nitrogen gas can be saved per hour, the surplus CO2 gas can produce liquid carbon dioxide, and the product benefit is increased. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the process structure of the application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in combination with the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application. Therefore, the following detailed description of the embodiments of the application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application.

[0023] Please refer to Figure 1 The application provides a technical scheme: a carbon dioxide recovery method, specifically including the following steps:

[0024] The low section methanol washing worker is mainly to remove CO2, H2S and COS impurities in the shift gas from the upstream shift process, and to remove the saturated water brought in the shift gas, to obtain a qualified shift gas with CO2 content of 3%~4%(mol) and total sulfur <0.1ppm, and to send the shift gas to the system; the system recovers part of the CO2 product gas (CO2≥99%, total sulfur <2ppmv), wherein the second tower is a carbon dioxide stripping tower, and the CO2 is sent to a carbon dioxide compressor after being stripped to increase the pressure and send it to the gasification section as conveying gas and protective gas;

[0025] The third tower is a hydrogen sulfide concentration tower, which is divided into three sections ABC, and uses nitrogen stripping, which can further reduce the CO2 partial pressure dissolved in methanol, and can make CO2 desorption more complete, equivalent to near vacuum operation. The more stripping nitrogen is introduced, the more CO2 partial pressure is reduced, and the more complete the desorption is. The stripped CO2 is recovered after cooling, and then discharged to the atmosphere after washing in the tail gas washing tower;

[0026] The CO2 gas from the third tower C section is pressurized as a cold source and exchanged with the shift water cooler. After heat exchange, the gas is sent to the gasification coal mill instead of low-pressure nitrogen. At the same time, the surplus CO2 gas produces liquid CO2. The CO2 gas flow from the third tower C section is 10000 standard cubic meters / hour, the pressure is 0.07 MPa, and the temperature is -53 degrees Celsius. The CO2 content is about 99.5%. After heat exchange with E2201, the temperature is 26 degrees Celsius. The CO2 gas flow from the third tower C section is divided into two paths. One path increases a DN200 pipeline after the opening of the six-tower external delivery valve. A hand valve, a shut-off valve, and an adjusting valve are set to send liquid carbon dioxide. The other path increases a DN300 pipeline before the opening of the six-tower external delivery valve. A hand valve, a shut-off valve, an adjusting valve, a thermometer, and a pressure gauge are set. A variable frequency fan is added to pressurize the gas to 0.4 MPa, and then send it to the shift water cooler instead of circulating water. A vent valve, a pressure gauge, and a flowmeter are set on the pipeline. Hand valves and adjusting valves are set at the inlet and outlet of the shift water cooler. At the same time, a bypass pipeline is added to realize online switching between the circulating water of the water cooler and the CO2 gas.

[0027] After heat exchange, the CO2 gas goes to the opening of the low-pressure nitrogen cut-off valve at the inlet of the gasification mill. A steam-water separator is set on the outlet pipeline of the water cooler after heat exchange to separate water from the gas. A hand valve is set at the inlet and outlet of the steam-water separator, and a safety valve is set in the body. A vent valve, a shut-off valve, an adjusting valve, a check valve, a thermometer, a pressure gauge, and a flowmeter are set on the outlet pipeline. The temperature of the CO2 gas after heat exchange in the third tower C section is 26 degrees Celsius, and the temperature after heat exchange with the shift water cooler rises to 30 degrees Celsius. The temperature can be adjusted in real time by adjusting the auxiliary valve of the shift water cooler. The shift gas temperature decreases to 32 degrees Celsius and is sent to the low methanol section.

[0028] The CO2 after heat exchange treatment will enter the steam-water separator, and after completing the related process of steam-water separation, it will be transported to the coal mill for use through the pressure regulating valve, and the flow and pressure of the CO2 entering the coal mill can be adjusted by corresponding operation of the fan frequency converter. By increasing the related parameters of the fan frequency converter, the CO2 flow entering the coal mill can be increased or reduced, thereby accurately meeting the use requirements of the coal mill in actual operation.

[0029] When the frequency conversion fan fails and the car jumps, or the pressure difference between the low-pressure nitrogen gas and the circulating gas reaches the low low set value, the system will trigger the interlocking mechanism to operate the mill related equipment; at this time, the interlocking will control the mill to open the low-pressure nitrogen gas cut-off valve, while closing the CO2 cut-off valve into the mill; at the same time, the regulating valve will automatically adjust until its opening is closed to 0 position, and the frequency conversion fan inlet cut-off valve will also be closed; according to the pressure condition of the CO2 desorption gas, the vent gas flow to the six towers and the flow to the liquid CO2 are accurately adjusted to ensure that the pressure of the three towers remains stable; the interlocking also opens the vent valves of the fan outlet and the steam-water separator outlet; at the same time, the interlocking also closes the cut-off valve into the shift water cooler, and opens the auxiliary line regulating valve. And the interlocking opens the circulating water regulating valve to the shift water cooler to ensure that the temperature of the shift cooler is in the appropriate range.

[0030] When the coal mill fails and stops running, if CO2 gas needs to be switched to low-pressure nitrogen gas, the operator needs to manually open the mill low-pressure nitrogen gas cut-off valve, and when the nitrogen cut-off valve is opened, its opening signal will trigger the interlocking mechanism to stop the fan running, at the same time, the CO2 cut-off valve into the mill is closed, at this time the regulating valve will automatically adjust until it is closed to 0 position; then, the fan inlet cut-off valve is closed; then, according to the pressure condition of the CO2 desorption gas, the vent gas flow to the six towers and the flow to the liquid CO2 are adjusted to ensure that the pressure of the three towers remains stable; after completing the above operation, the interlocking system will automatically open the vent valves of the frequency conversion fan outlet and the steam-water separator outlet; and the interlocking system will also close the cut-off valve into the shift water cooler, while opening the auxiliary line regulating valve; in addition, the interlocking system also opens the circulating water regulating valve to the shift water cooler, so as to ensure that the temperature of the shift cooler is in the normal range.

[0031] The low-temperature methanol washing two-tower tail gas resolving tower is divided into four sections, wherein the ABC section is sulfur-containing methanol, the D section is sulfur-free methanol, the CO2 gas is resolved and discharged to the atmosphere after being exchanged with the process gas from the shift in the E2201 heat exchanger and then being washed in the six-tower tail gas washing tower. The D section rich methanol liquid of the two-tower CO2 resolving tower is discharged to the C section of the three-tower hydrogen sulfide concentration tower through a liquid level regulating valve, the pressure is reduced from 0.2 MPa to 0.07 MPa, and the CO2 in the methanol is continuously resolved, the C section resolved CO2 gas is discharged to the atmosphere after being exchanged with the process gas from the shift in the E2201 heat exchanger and then being washed in the six-tower tail gas washing tower, and the BC section methanol of the two-tower is sent to the AB section of the three-tower to continuously resolve CO2 through a liquid level regulating valve, and the resolved CO2 gas enters the E2222 heat exchanger to be exchanged and cooled with the lean methanol, is exchanged with the process gas from the shift in the E2201 heat exchanger, and is then discharged to the atmosphere after being washed in the six-tower tail gas washing tower.

[0032] The C section of the three-tower resolves CO2 gas with a flow rate of 10000 standard cubic meters / hour, a pressure of 0.07 MPa, and a temperature of-53 degrees Celsius, and the CO2 gas contains about 99.5%, which is exchanged with the E2201 heat exchanger to have a temperature of 26 degrees Celsius, and is then discharged to the atmosphere after being washed in the six-tower washing tower through a regulating valve.

[0033] The C section of the three-tower resolves CO2 gas with a flow rate of 10000 standard cubic meters / hour, a pressure of 0.07 MPa, and a temperature of-53 degrees Celsius, and the CO2 gas contains about 99.5%, which is exchanged with the E2201 heat exchanger to have a temperature of 26 degrees Celsius, and is then discharged to the atmosphere after being washed in the six-tower washing tower through a regulating valve.

[0034] A carbon dioxide recovery method is applied to carbon dioxide recovery.

[0035] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

[0036] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Claims

1. A method for recovering carbon dioxide, characterized in that: Specifically, the steps include the following: The shift gas is introduced into this system; The system recovers a portion of the CO2 product gas, with the second tower being a carbon dioxide stripping tower. After CO2 stripping, the gas is sent to the carbon dioxide compressor for pressurization and delivery to the chemical section as transport gas and protective gas. The three towers are hydrogen sulfide concentration towers, which are divided into three sections: A, B, and C. They use nitrogen stripping, which can further reduce the partial pressure of CO2 dissolved in methanol and make CO2 desorption more thorough. The more thorough the desorption, the more the CO2 is recovered and cooled before being discharged into the atmosphere through the tail gas scrubbing tower. The CO2 gas in section C of the three towers is pressurized and used as a cold source for heat exchange with the shift water cooler. After heat exchange, the gas is sent to the gasification coal mill to replace the low-pressure nitrogen gas. At the same time, the excess CO2 gas is used to produce liquid CO2.

2. The carbon dioxide recovery method according to claim 1, characterized in that: The CO2 gas flow rate of the C section of the three towers is 10,000 standard cubic meters per hour, the pressure is 0.07 MPa, the temperature is -53 degrees Celsius, the CO2 gas content is about 99.5%, and the temperature after heat exchange with E2201 is 26 degrees Celsius.

3. The carbon dioxide recovery method according to claim 1, characterized in that: The CO2 gas flow in section C of the three towers is divided into two paths. One path adds a DN200 pipeline after the external control valve to the sixth tower, and is equipped with a manual valve, a shut-off valve and a regulating valve to deliver liquid carbon dioxide. The other path adds a DN300 pipeline before the external control valve to the sixth tower, and adds a variable frequency fan to pressurize the gas to 0.4 MPa before sending it to the changeover water cooler to replace the circulating water.

4. The carbon dioxide recovery method according to claim 3, characterized in that: A bypass pipeline is installed on the pipeline, and a regulating valve is installed on the bypass pipeline to enable online switching operation of the circulating water and CO2 gas in the water cooler.

5. A carbon dioxide recovery method according to claim 4, characterized in that: The CO2 heat exchanger is connected to the inlet low-pressure nitrogen shut-off valve of the gasification mill, and a steam-water separator is installed on the CO2 gas outlet pipeline after the water cooler heat exchanger.

6. The carbon dioxide recovery method according to claim 1, characterized in that: The temperature of the CO2 gas after heat exchange in the C section of the three towers is 26 degrees Celsius. After heat exchange with the shift water cooler, the temperature rises to 30 degrees Celsius. The temperature can be adjusted in real time by adjusting the control valve of the shift water cooler. After the temperature of the shift gas drops to 32 degrees Celsius, it is sent to the low-temperature section A.

7. A carbon dioxide recovery method according to claim 6, characterized in that: After heat exchange, the CO2 enters the steam-water separator and is then sent to the coal mill via a pressure regulating valve. The flow rate and pressure entering the coal mill can be adjusted by adding a fan frequency converter to meet the requirements of the coal mill.

8. The carbon dioxide recovery method according to claim 1, characterized in that: When the variable frequency fan malfunctions and trips, or when the pressure difference between low-pressure nitrogen and circulating gas is low, the interlocking mill opens the low-pressure nitrogen shut-off valve, closes the CO2 shut-off valve at the mill inlet, automatically closes the regulating valve to the 0 position, closes the fan inlet shut-off valve, and adjusts the air flow rate to the sixth tower and the liquid CO2 flow rate according to the CO2 desorption pressure to ensure stable pressure in the three towers. The interlocking mill opens the vent valves at the fan outlet and the steam-water separator outlet, interlocks closes the shut-off valve at the converter water cooler inlet and opens the bypass regulating valve, and interlocks open the circulating water regulating valve at the converter water cooler inlet to ensure the converter cooler temperature.

9. A carbon dioxide recovery method according to claim 1, characterized in that: When the coal mill malfunctions and stops, requiring the CO2 gas to be switched to low-pressure nitrogen, the low-pressure nitrogen shut-off valve of the mill is manually opened. The opening signal of the nitrogen shut-off valve stops the blower, the CO2 shut-off valve at the mill inlet is closed, the regulating valve automatically closes to the 0 position, the blower inlet shut-off valve is closed, and the air flow rate to the sixth tower and the liquid CO2 flow rate are adjusted according to the CO2 desorption gas pressure to ensure the pressure of the three towers is stable. The blower outlet and steam-water separator outlet vent valves are interlocked open, the shut-off valve at the converter water cooler is interlocked closed, the auxiliary line regulating valve is opened, and the circulating water regulating valve at the converter water cooler is interlocked open to ensure the converter cooler temperature.

10. The application of the carbon dioxide recovery method as described in any one of claims 1 to 9 in carbon dioxide recovery.

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