Pressure swing adsorption comprehensive utilization method for carbon dioxide in cement kiln flue gas

Abstract

The invention discloses a cement kiln flue gas carbon dioxide pressure swing adsorption comprehensive utilization method. The method comprises the following steps: 1) an adsorption process; 2) a pressure drop equalizing process; 3) a reverse release process; 4) a flue gas heat exchange desorption process; 5) a vacuumizing process; 6) a circulating water cooling process; (7) a pressure equalizing and rising process; and 8) a final boosting process, wherein the adsorbent needing desorption regeneration can be subjected to rapid heat exchange, the vacuumizing time is shortened, the waste heat is utilized, the efficiency of the whole carbon capture process flow is improved, and the capture power consumption is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide capture, and particularly relates to a method for comprehensive utilization of pressure swing adsorption of carbon dioxide in cement kiln flue gas. Background Art

[0002] In the process of implementing the present invention, the inventor found that the prior art has at least the following problems:

[0003] The pressure swing adsorption carbon capture technology realizes the adsorption and desorption of carbon dioxide by changing the gas pressure, so as to achieve the purpose of carbon capture. Specifically, under higher pressure conditions, the adsorbent can effectively adsorb carbon dioxide; when the pressure decreases, the adsorbent will desorb carbon dioxide. The temperature swing adsorption carbon capture technology controls the adsorption and desorption process of the adsorbent by means of temperature change to achieve carbon dioxide capture. Generally, the adsorbent has good adsorption performance for carbon dioxide in a low-temperature environment, and will desorb carbon dioxide in a high-temperature environment. At present, in industrial demonstration projects, the pressure swing adsorption carbon capture technology is widely used. This is because the temperature change rate of the temperature swing adsorption carbon capture technology is slow, there are certain limitations, and the flexibility is poor, which greatly limits its wide application. There are also patents that mention using the method of coupling electric heating with occasional pressure swing to carry out carbon capture. Although the time for vacuum pumping when the adsorbent desorbs carbon dioxide is reduced, the power consumption of electric heating is increased and the heating rate of electric heating is slow. At present, in the application of adsorption method carbon capture for carbon dioxide capture in cement kiln flue gas, based on the existing process, the flue gas has undergone wet desulfurization before emission, the SOx content reaches ultra-low emission, the carbon dioxide concentration is about 20%, and the temperature is 70-110°C. If only the pressure swing adsorption carbon capture technology is used, the energy consumption is high; if the waste heat of the flue gas is used to couple vacuum desorption for adsorbent regeneration, the temperature of 70-110°C is relatively low and the heat exchange effect is poor. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for comprehensive utilization of pressure swing adsorption of carbon dioxide in cement kiln flue gas,

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: A method for comprehensive utilization of pressure swing adsorption of carbon dioxide in cement kiln flue gas, comprising the following steps:

[0006] 1) Adsorption process; 2) Equal pressure drop process; 3) Reverse release process; 4) Flue gas heat exchange desorption process; 5) Vacuum pumping process; 6) Circulating water cooling process; 7) Equal pressure rise process; 8) Final pressure rise process.

[0007] In the above step 1), the high-temperature flue gas after heat exchange enters the adsorption tower from the bottom after being desulfurized and treated for water separation, and then is pressurized by a raw material compressor. The adsorbent selectively adsorbs the relevant components of CO2. The compression pressure is between 0.05 and 9 bar gauge pressure, preferably between 0.1 and 4 bar gauge pressure. Under the conditions of meeting the product purity and recovery rate, the lower the compression pressure, the better. Reducing the compression pressure can reduce equipment investment and operating energy consumption.

[0008] In the above step 1), the unadsorbed gas is discharged from the top of the tower and vented; when the mass transfer zone front of the adsorbed substance reaches the set position of the reserved section at the bed outlet, the adsorption is stopped and the regeneration process is started. The position of the mass transfer front of the adsorbate is controlled by the adsorption time. According to the commissioning test of the device, the appropriate adsorption time is determined. Through the adsorption time, usually 30 - 500 seconds, preferably 50 - 300 seconds, the mass transfer front of CO2 is dynamically regulated to the reserved section at the bed outlet to prevent CO2 breakthrough and reduce the product recovery rate.

[0009] In the above step 2), after the adsorption process in the adsorption tower is completed, the raw material gas inlet is stopped, and the high-pressure CO2 mixed gas in the tower is discharged along the adsorption direction into other low-pressure adsorption towers that have completed regeneration for pressure equalization. The pressure equalization process is, on the one hand, to boost the pressure of other adsorption towers, and on the other hand, to recover the carbon dioxide in the dead volume of the adsorption tower. The number of pressure equalization times is usually 2 - 4 times according to the adsorbent performance (such as specific surface area, pore volume, and CO2 recovery rate requirements), preferably 1 - 2 times of pressure equalization. This can not only recover about 30 - 40% of the CO2 in the dead volume of the adsorption tower, but also stepwise reduce the valve impact and extend the equipment life.

[0010] In the above step 3), after the pressure equalization is completed, the pressure of the adsorption tower is reduced to atmospheric pressure against the adsorption direction, and at this time, the CO2 desorbed from the adsorbent is recovered.

[0011] In the above step 4), the high-temperature flue gas is introduced into the tubes in the adsorption tower after the reverse release. At this time, CO2 continues to be desorbed from the adsorbent. When the temperature of the adsorbent rises, the carbon dioxide adsorption capacity decreases, and the adsorbent will further desorb carbon dioxide. The high-temperature flue gas before desulfurization (190 - 230 °C) is introduced into the adsorption tower tubes, and the heat exchange time is maintained for 10 - 30 minutes to increase the temperature of the adsorbent by 10 - 40 °C. Using the waste heat of the cement kiln to replace traditional electric heating can save 2 - 10 kWh / ton of CO2. The CO2 adsorption capacity of the adsorbent decreases at high temperatures, accelerating the desorption process.

[0012] In the above step 5), after the above-mentioned heat exchange time of the flue gas, the high-temperature flue gas continues to be introduced into the adsorption tower for 2 - 10 minutes; the vacuum pump evacuates the adsorption tower to reduce the CO2 partial pressure in the adsorbent, so that CO2 is further desorbed and the adsorption tower is regenerated. This step couples heating and vacuum pumping, reducing the vacuum pumping time and reducing the comprehensive regeneration energy consumption by 10% - 30%.

[0013] In step 6), after the vacuum regeneration process is completed, the high-temperature flue gas is cut into other adsorption towers that require high-temperature heat exchange. Circulating water is passed through the tubes in this tower to cool the adsorption tower in preparation for subsequent adsorption. Circulating water (temperature 20-35°C) is passed to cool the adsorbent to below 50°C for 10-20 minutes. The low-temperature environment restores the adsorption performance of the adsorbent. Preheated circulating water is used for other processes in the plant, such as tropical fish farming.

[0014] In the above step 7), after the circulating water cooling process is completed, the adsorption tower is pressurized with high-pressure gas from other adsorption towers. This process corresponds to the equalization pressure drop process.

[0015] In the above step 8), after the equalization pressure raising process is completed, in order to make the adsorption tower reach the pressure during adsorption, the pressure of the adsorption tower is raised to the adsorption pressure by the exhaust gas from other towers through the final pressure raising.

[0016] One of the above technical solutions has the following advantages or beneficial effects. It is the first to create a heat exchange process between the high-temperature flue gas (above 190°C) before desulfurization and the vacuum regeneration adsorption tower, coupling the cement kiln process with the carbon capture process. Specifically, the flue gas that has not been desulfurized is first heat exchanged with the adsorption tower in the adsorption tower to be vacuum desorbed and regenerated, and then desulfurized. After that, it can enter the adsorption tower for carbon dioxide adsorption and capture. In this process, the temperature of the flue gas before desulfurization can reach above 190°C. The first heat exchange process between the high-temperature flue gas (above 190°C) before desulfurization and the vacuum regeneration adsorption tower can quickly exchange heat with the adsorbent that needs to be desorbed and regenerated, reduce the time for vacuuming, use waste heat, improve the efficiency of the entire carbon capture process, and reduce the comprehensive regeneration energy consumption by 10%-30%. The process has multi-effect desorption synergy, and the temperature-vacuum coupled desorption makes the adsorbent regeneration rate reach more than 90%, which is more than 10% higher than the single method, and the purity of the CO2 product is increased by more than 5%. This process reduces compressor energy consumption by more than 10% through pressure equalization strategy and pressure recovery, and reduces the overall operating cost by 25-30 yuan / ton CO2.

[0017] The present invention is suitable for new dry-process cement kiln flue gas treatment. A single set of equipment can capture 10,000 to 500,000 tons of CO2 per year, and the capture cost is reduced by 30 to 60 yuan per ton of CO2 compared with the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the comprehensive utilization method of carbon dioxide pressure swing adsorption of cement kiln flue gas provided in an embodiment of the present invention; DETAILED DESCRIPTION

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Embodiment 1

[0021] The pressure swing adsorption comprehensive utilization system for carbon dioxide in cement kiln flue gas uses vacuum pumping in combination with high-temperature flue gas heat exchange for adsorbent regeneration and consists of multiple adsorption towers. Its technological process consists of steps such as adsorption, equal pressure drop, reverse release, flue gas heat exchange desorption, vacuum pumping, circulating water cooling, equal pressure rise, and final pressure boost.

[0022] The specific technological process is as follows:

[0023] 1. Adsorption process. The high-temperature flue gas after heat exchange, after desulfurization and water separation treatment, enters the raw material compressor for pressurization and then enters the adsorption tower from the bottom of the tower. The adsorbent selectively adsorbs the relevant components mainly CO2, and the unadsorbed gas is discharged from the top of the tower for venting. When the mass transfer zone front (referred to as the adsorption front) of the adsorbed substance reaches a certain position in the reserved section at the outlet of the bed layer, the adsorption stops and the regeneration process is entered.

[0024] 2. Equal pressure drop process. After the adsorption process in the adsorption tower ends, the raw material gas inlet is stopped, and the higher-pressure CO2 in the tower is released along the adsorption direction into other lower-pressure adsorption towers that have completed regeneration. On the one hand, it is a pressure reduction process, and on the other hand, the dead volume CO2 in the bed layer is recovered, improving the CO2 recovery rate.

[0025] 3. Reverse release process. After the equal pressure is completed, the pressure in the adsorption tower is reduced to near atmospheric pressure against the adsorption direction. At this time, CO2 begins to desorb from the adsorbent. On the one hand, part of the product gas CO2 is obtained, and on the other hand, the adsorbent is also preliminarily regenerated.

[0026] 4. Flue gas heat exchange desorption process. The high-temperature flue gas is introduced into the tubes in the adsorption tower after the reverse release ends. At this time, part of the CO2 desorbs from the adsorbent. On the one hand, part of the product gas CO2 is obtained, and on the other hand, the adsorbent is also partially regenerated.

[0027] 5. Vacuum pumping process. After the flue gas heat exchange for a period of time, the high-temperature flue gas continues to be introduced into the adsorption tower. In order to thoroughly regenerate the adsorbent, a vacuum pump is used to pump the adsorption tower to further reduce the CO2 partial pressure in the adsorbent, obtain the product CO2, and thoroughly regenerate the adsorption tower.

[0028] 6. Circulating water cooling process. After the vacuum regeneration process is completed, the high-temperature flue gas is cut into other adsorption towers that require high-temperature heat exchange. Circulating water is passed through the tubes in the tower to cool the adsorption tower, preparing for subsequent adsorption.

[0029] 7. Equal pressure increase process. After the circulating water cooling process is completed, the adsorption tower is pressurized with higher-pressure gas from other adsorption towers. This process corresponds to the equal pressure decrease process and can not only increase the pressure but also recover CO2 in the dead volume of other tower beds.

[0030] 8. Final pressure increase process. After the equal pressure increase process is completed, in order to make the pressure of the adsorption tower reach the adsorption pressure, final pressure increase is required, and the pressure of the adsorption tower is increased to the adsorption pressure with the exhaust gas from other towers.

[0031] In this process, through the coupling of the cement kiln process flow and pressure swing adsorption carbon capture, the wet desulfurization process is placed after the flue gas heat exchange, increasing the temperature of the outlet flue gas, which can effectively exchange heat with the adsorption tower to be regenerated; in addition, the addition of the flue gas heat exchange desorption process in process 4 and the circulating water cooling process in 6 shortens the vacuum pumping time in 5, reducing the power consumption of the entire process flow.

[0032] In the present invention, tubular heat exchange tubes are installed in the adsorption tower. First, the high-temperature flue gas (above 190°C) without desulfurization is passed into the adsorption tower to be regenerated for heat exchange, and then desulfurization and water treatment are carried out. After being pressurized by the raw material compressor, it enters the adsorption tower from the bottom, and the carbon dioxide capture begins. Its process consists of steps such as adsorption, equal pressure decrease, reverse release, flue gas heat exchange desorption, vacuum pumping, circulating water cooling, equal pressure increase, and final pressure increase. In the invention, after the reverse release process of the adsorption tower to be regenerated ends, the high-temperature flue gas is passed into the tubes in the adsorption tower. At this time, part of the CO2 is desorbed from the adsorbent due to heat exchange and temperature increase, enabling partial desorption of the adsorbent. In addition, in the next step, vacuum pumping is carried out at a higher temperature, reducing the vacuum pumping time and power consumption.

[0033] After adopting the above solution, the cement kiln process is coupled with the carbon capture process. Specifically, first, the flue gas without desulfurization treatment is heat-exchanged with the adsorption tower to be vacuum-desorbed and regenerated in the adsorption tower, then desulfurization treatment is carried out, and after direct simple water treatment, it can enter the adsorption tower for carbon dioxide adsorption and capture. In this process, the flue gas before desulfurization, with a temperature reaching above 190°C, can quickly exchange heat with the adsorbent to be desorbed and regenerated, reducing the vacuum pumping time, utilizing waste heat, improving the efficiency of the entire carbon capture process flow, and reducing the capture power consumption.

[0034] Embodiment 2

[0035] See Figure 1, A method for comprehensive utilization of carbon dioxide in cement kiln flue gas by pressure swing adsorption, comprising the following steps:

[0036] 1) Adsorption process; 2) Equal pressure reduction process; 3) Reverse release process; 4) Flue gas heat exchange desorption process; 5) Vacuum pumping process; 6) Circulating water cooling process; 7) Equal pressure increase process; 8) Final pressure increase process.

[0037] In the above step 1), the high-temperature flue gas after heat exchange, after desulfurization and water treatment, enters the raw material compressor for pressurization and then enters the adsorption tower from the bottom of the tower, and the adsorbent selectively adsorbs the relevant components of CO2.

[0038] In the above step 1), the unadsorbed gas is discharged from the top of the tower and vented; when the mass transfer zone front of the adsorbed substance reaches the set position of the reserved section at the outlet of the bed layer, the adsorption is stopped and the regeneration process is started.

[0039] In the above step 2), after the adsorption process in the adsorption tower is completed, the raw material gas inlet is stopped, and the high-pressure CO2 in the tower is discharged in the adsorption direction into other low-pressure adsorption towers that have completed regeneration.

[0040] In the above step 3), after the equal pressure process is completed, the pressure of the adsorption tower is reduced to atmospheric pressure against the adsorption direction, and at this time, CO2 begins to desorb from the adsorbent.

[0041] In the above step 4), the high-temperature flue gas is introduced into the tubes in the adsorption tower after the reverse release is completed, and at this time, CO2 desorbs from the adsorbent.

[0042] In the above step 5), after the flue gas heat exchange for the set time, the high-temperature flue gas continues to be introduced into the adsorption tower; the vacuum pump evacuates the adsorption tower to reduce the partial pressure of CO2 in the adsorbent, obtains CO2, and regenerates the adsorption tower.

[0043] In the above step 6), after the vacuum pumping regeneration process is completed, the high-temperature flue gas is switched to other adsorption towers that require high-temperature heat exchange, and circulating water is introduced into the tubes in this tower to cool the adsorption tower, preparing for subsequent adsorption.

[0044] In the above step 7), after the circulating water cooling process is completed, the adsorption tower is pressurized with high-pressure gas from other adsorption towers, and this process corresponds to the equal pressure reduction process.

[0045] In the above step 8), after the equal pressure increase process is completed, in order to make the adsorption tower reach the adsorption pressure, through the final pressure increase, the pressure of the adsorption tower is increased to the adsorption pressure with the exhaust gas from other towers.

[0046] After adopting the above - mentioned solution, the cement kiln process is coupled with the carbon capture process. Specifically, first, the flue gas without desulfurization treatment is heat - exchanged with the adsorption tower to be regenerated by vacuum desorption in the adsorption tower, then desulfurization treatment is carried out. After that, after simple water separation directly, it can enter the adsorption tower for carbon dioxide adsorption and capture. In this process, the flue gas before desulfurization, whose temperature can reach above 190 °C, can be used to quickly heat - exchange the adsorbent that needs to be regenerated by desorption, reducing the time of vacuum pumping, making use of waste heat, improving the efficiency of the entire carbon capture process flow, and reducing the power consumption for capture.

[0047] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by terms such as "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "front", "center", "both ends", etc. are based on the orientation or positional relationships shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention.

[0048] In the present invention, unless otherwise clearly specified and defined, terms such as "installed", "set", "connected", "fixed", "swiveling connection", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be the internal communication of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above - mentioned terms in the present invention can be understood according to specific situations.

[0049] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for comprehensive utilization of carbon dioxide from cement kiln flue gas by pressure swing adsorption, characterized in that: The steps include: 1) Adsorption process; 2) Pressure drop process; 3) Reversal process; 4) Flue gas heat exchange and desorption process; 5) Vacuuming process; 6) Circulating water cooling process; 7) Pressure increase process; 8) Final pressure increase process.

2. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas according to claim 1, characterized in that: In the above step 1), the high-temperature flue gas after heat exchange is desulfurized and separated, and then enters the raw material compressor for pressurization and then enters the adsorption tower from the bottom of the tower. The adsorbent selects the relevant components of CO2 for adsorption.

3. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 2, characterized in that: In the above step 1), the unadsorbed gas is discharged from the top of the tower to be vented; when the front edge of the mass transfer zone of the adsorbed substance reaches the set position of the reserved section at the bed outlet, the adsorption is stopped and the regeneration process is started.

4. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 3, characterized in that: In the above step 2), after the adsorption process of the adsorption tower is completed, the feed gas is stopped, and the high-pressure CO2 mixed gas in the tower is placed into other low-pressure adsorption towers that have completed regeneration along the adsorption direction for equal pressure drop.

5. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 4, characterized in that: In the above step 3), after the pressure equalization is completed, the pressure of the adsorption tower is reduced to normal pressure in the opposite direction of adsorption, and the CO2 desorbed from the adsorbent is recovered.

6. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 5, characterized in that: In the above step 4), the high-temperature flue gas before desulfurization is introduced into the tube array in the adsorption tower at the end of the inversion, and CO2 continues to be desorbed from the adsorbent.

7. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 6, characterized in that: In the above step 5), after the flue gas heat exchange setting time, the high-temperature flue gas continues to be introduced into the adsorption tower tube array; the adsorption tower is evacuated with a vacuum pump to reduce the CO2 partial pressure in the adsorbent, so that CO2 is further desorbed and the adsorption tower is regenerated.

8. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 7, characterized in that: In the above step 6), after the vacuum regeneration process is completed, the high-temperature flue gas is cut into other adsorption towers that require high-temperature heat exchange, and circulating water is passed through the tubes in this tower to cool the adsorption tower in preparation for subsequent adsorption.

9. The method for comprehensive utilization of carbon dioxide by pressure swing adsorption of cement kiln flue gas as claimed in claim 8, characterized in that: In the above step 7), after the circulating water cooling process is completed, the adsorption tower is evenly pressure-raised using high-pressure gas from other adsorption towers, and this process corresponds to the even pressure drop process.

10. The method for comprehensive utilization of carbon dioxide from cement kiln flue gas by pressure swing adsorption as claimed in claim 9, characterized in that: In the above step 8), after the equalization pressure raising process is completed, in order to make the adsorption tower reach the pressure during adsorption, the pressure of the adsorption tower is raised to the adsorption pressure by the exhaust gas from other towers through the final pressure raising.

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