Flue gas carbon dioxide trapping low-energy-consumption desorption process

Abstract

The invention discloses a low-energy-consumption desorption process for capturing carbon dioxide in flue gas. The process comprises the following steps: carrying out heat exchange on an absorbent rich solution and an absorbent barren solution after absorbing carbon dioxide in a heat exchanger; the absorbent rich solution after heat exchange enters a desorber for desorption; desorbing liquid discharged from the bottom of the desorber is subjected to pressure reduction and then is subjected to gas-liquid separation in a flash reboiler, an obtained gas phase is compressed by a flash compressor and then is circulated into the desorber, and an obtained absorbent barren solution is circulated to a heat exchanger for heat exchange; the heating mode of the flash reboiler is microwave heating; the temperature of the absorbent-rich solution after heat exchange is recorded as T1, the bubble point temperature of the absorbent-rich solution under the desorption pressure is recorded as T2, and T1-T2 =-2 DEG C to 2 DEG C. According to the invention, by controlling the temperature of the absorbent-rich solution entering the desorber, and combining the microwave heating flash reboiler, the flash compressor and the like, all process steps and parameters are matched with each other, so that the absorbent-rich solution with the determined loading capacity can be regenerated with lower energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide capture, and particularly to a low-energy consumption desorption process for flue gas carbon dioxide capture. Background Technique

[0002] The chemical absorption method for carbon dioxide capture is currently the most important technical route for low-concentration flue gas carbon dioxide capture. One of the main problems of this technology is high energy consumption, and the energy consumption is mainly concentrated in the regeneration step of the absorbent. The regeneration of the absorbent generally adopts the method of heating and desorption, and the energy consumption includes three parts: one is the sensible heat difference between the outlet and the inlet of the desorption unit; the second is the reaction heat for desorbing CO 2 ; the third is the latent heat carried away by the vaporization of part of the water during desorption. Among the above three parts of heat, the sensible heat is generally recovered by the rich and lean liquid heat exchanger, and the temperature difference between the cold and hot fluid streams of the heat exchanger has basically reached the limit in the current advanced process; the reaction heat depends on the chemical properties of the absorbent, and developing a new absorbent with low absorption heat is an important technical direction to reduce the energy consumption of CO 2 capture; when the heat exchanger is restricted and the absorbent formula is determined, reducing the latent heat consumption of water is one of the important ways to optimize and improve the various chemical absorption CO 2 capture technologies in terms of process flow.

[0003] In terms of the absorption-desorption process conditions, increasing the absorbent loading is beneficial to reducing the H 2 O / CO 2 ratio of the desorbed gas, but a higher loading will lead to a decrease in the absorption rate. Chinese patent documents CN116531918A, CN112870919B, etc. propose a middle section cooling scheme for the absorption tower, extracting and cooling the semi-rich liquid after the absorbent is heated due to absorbing CO 2 and then returning it to the absorption tower. By utilizing the characteristic that the absorption capacity increases after the temperature is reduced, the absorption loading can be improved to a certain extent. Middle section cooling is a common technical means to improve the efficiency of the absorption process, but a high loading will also reduce the absorption rate, and a balance needs to be found between the scale of the absorption tower and the loading.

[0004] In terms of the operating conditions of the desorption unit, the paper in the 1st issue of the "International Journal of Greenhouse Gas Control" in 2010 analyzed from the perspective of thermodynamic equilibrium and proposed that for most amine absorbents, higher temperature and pressure at the same loading are beneficial to reducing the water content of the desorbed gas. The GSP high-pressure desorption technology was reported at the US Department of Energy's Carbon Capture Conference in 2015. The operating pressure of the desorption tower was increased from the conventional 0.1 - 0.2 MPa to 0.5 - 6 MPa, preferably above 1 MPa, and the desorption energy consumption can be reduced by up to 1 MJ / kgCO 2. However, generally speaking, a higher temperature is not conducive to the stability of the absorbent. Therefore, the desorption temperature is restricted by the high-temperature resistance performance of the absorbent. According to the thermodynamic equilibrium, the H 2 O / CO 2 ratio is mainly affected by the process conditions at the top inlet of the rich liquid. Therefore, a segmented desorption scheme has emerged, that is, different temperatures and pressures are used for desorption respectively. The December 2007 issue of the *AICHE Journal* analyzed a two-stage desorption scheme. The rich liquid first enters the high-pressure desorption tower for desorption, and the semi-lean liquid at the bottom of the tower enters the low-pressure desorption tower for continuous desorption. The two desorbed gases are sent to different sections of the compressor to be pressurized into product gas. Chinese patent documents such as CN114632402A, CN111715033A, CN102895860A, and CN102274676A have disclosed the technical solutions of high-low pressure two-stage desorption towers, including the heat utilization scheme between the two desorption towers, which has a certain effect on reducing the desorption energy consumption. Segmented desorption essentially makes use of the characteristic that the water content in the desorbed gas is relatively low during high-pressure desorption. At the same time, in order to avoid too high a temperature at the bottom of the tower, a low-pressure desorption tower is used to obtain the desorption depth. However, the water content in the desorbed gas of the low-pressure desorption tower is still relatively high. If the desorbed gases of the two towers are connected in parallel to form a product, only part of the latent heat of vaporization of water can be reduced. A further technical solution is multi-stage desorption at different pressures and series connection of desorbed gases. For example, the multi-stage compression desorption disclosed in the December 2007 issue of the *AICHE Journal* and the August 2006 issue of *Ind&Eng Chem Res*. In the low-pressure desorption section, the desorbed gas needs to be pressurized by a compressor and sent to the high-pressure desorption section of the upper stage, thereby reducing the generation of high-water-content gas. However, this scheme requires adding multiple compressors.

[0005] Another energy-saving technical solution for the desorption unit is the segmented feeding of the rich absorbent liquid at different temperatures. The rich absorbent liquid is heat-exchanged to different temperatures and fed into different positions of the desorption tower, thereby reducing the energy consumption of the desorption tower. In Chinese patent documents such as CN103463955A and CN114522513A, the rich liquid is divided into two streams for feeding, and in CN103961979A and CN114669177A, the rich liquid is further divided into three streams. The splitting of the rich liquid can realize the optimized utilization of heat at different temperature levels. In essence, it condenses part of the water in the desorbed gas through the feeding of the relatively cold rich liquid, reducing the latent heat loss of water. However, from the overall heat of the desorption unit, the sensible heat of the lean absorbent liquid is sufficient to heat-exchange the rich liquid to a temperature exceeding the equilibrium temperature corresponding to its load. If part of the rich liquid is fed at a low temperature, the heat of the lean liquid is not fully utilized, and the overall energy consumption will instead increase. Therefore, the segmented feeding of the rich liquid is usually accompanied by other utilization schemes for the heat of the lean liquid. Since the heat supply of the desorption unit is the heating of the desorption tower bottom, where the temperature level is the highest, the lean liquid and other low-temperature heat in the system cannot be utilized by conventional heat-exchange processes. Chinese patent documents such as CN107754568A and CN114669177A disclose the scheme of returning the flash steam of the lean liquid to the desorption tower for heating after compression. After the temperature level of the flash steam is increased by the MVR compressor, it can be used for heating the desorption tower. Currently, the scheme of splitting the rich liquid and compressing the flash steam of the lean liquid has been a technical route actually adopted in many CO 2 capture projects.

[0006] The technical solution for further reducing the water content in the desorbed gas is heat pump technology. From the perspective of desorption equilibrium, after the absorbent load and the desorption temperature and pressure are determined, the H 2 O / CO 2 ratio in the desorbed gas can be optimized to an extreme value, but there is still a large amount of water vapor present. Chinese patent documents such as CN219518342U, CN103638780A, CN103977683A, and CN104941393A propose heat pump schemes for recovering heat after raising the temperature level of the desorbed gas. The recovered heat can be used for heating the desorption tower bottom or for heating the rich liquid feed, etc. Heat pump schemes include absorption heat pumps and compression heat pumps. The key lies in the heat recovery efficiency of the heat pump process adopted, and a balance needs to be struck between equipment investment and heat recovery efficiency.

[0007] Process intensification technology is also beneficial for reducing desorption energy consumption. Usually, CO 2The rate of the desorption reaction is not sufficient to reach the desorption equilibrium. Therefore, the water content ratio in the desorbed gas will be higher than the equilibrium value, and the lower the desorption rate, the farther away from the equilibrium. Chinese patent document CN112870919A discloses a supergravity desorption process, which uses a supergravity device to strengthen the desorption process and can reduce the desorption energy consumption. The paper in the 12th issue of 《International Journal of Greenhouse Gas Control》 in 2018 reported the effect of desorbing CO2 from MEA absorbent under microwave action. Microwave can achieve desorption at a lower temperature and greatly improve the desorption rate. The report in the 1st issue of 《Adsorption》 in 2014 showed that microwave also has an obvious effect on the desorption rate of the 2 system. Japanese patent document JP2008095741 discloses a method of using microwave to strengthen the desorption of 2 physical absorbent. Chinese patent document CN209348357U discloses a microwave-assisted desorption technical solution used for the desorption of 2 CO. CN114699883A discloses a technology of using catalyst plus microwave-assisted synergistic desorption of CO2. CN103638780A discloses a device and method of using ultrasonic wave to strengthen the desorption of 2 CO. Chinese patent document CN102274676A proposes a device and method of using a combination of microwave and vacuum to recover oil and gas in liquid in VOC treatment. The above technical solutions have announced the beneficial effects of process intensification technologies such as microwave in the desorption process. The microwave method is mainly manifested in that it can achieve a higher desorption rate at a lower temperature. However, the microwave process intensification technology has not been combined with the process of reducing energy consumption in the current chemical absorption method for 2 the desorption unit of CO. There is no complete technical solution to solve problems such as the desorption depth at low temperature and the higher equilibrium value of the water content ratio in the desorbed gas during low-temperature desorption. Summary of the Invention

[0008] In view of this, the present invention provides a low-energy-consumption desorption process for flue gas carbon dioxide capture to solve the problem of high energy consumption in the desorption unit in the existing chemical absorption method for 2 carbon dioxide capture process.

[0009] To achieve the above object, the present invention provides a low-energy-consumption desorption process for flue gas carbon dioxide capture, including the following steps:

[0010] S1: The rich liquid of the absorbent after absorbing carbon dioxide exchanges heat with the lean liquid of the absorbent in a heat exchanger;

[0011] S2: The rich liquid of the absorbent after heat exchange enters a desorber for desorption;

[0012] S3: After the desorbing liquid discharged from the bottom of the desorber is depressurized, gas-liquid separation is carried out in a flash reboiler. The obtained gas phase is compressed by a flash compressor and then recycled into the desorber, and the lean absorbent liquid (liquid phase) obtained is recycled to the heat exchanger for heat exchange;

[0013] Among them, the heating method of the flash reboiler is microwave heating;

[0014] Let the temperature of the rich absorbent liquid after heat exchange be T1, and the bubble point temperature of the rich absorbent liquid be T2, and T1 - T2 = -2 to 2 °C.

[0015] In the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the rich absorbent liquid after absorbing carbon dioxide is formed by the chemical absorbent contacting the flue gas countercurrently and absorbing the carbon dioxide in the flue gas, and this process can adopt the conventional method in the industry. For a fixed chemical absorbent, the greater the amount of carbon dioxide it absorbs, the more beneficial it is to reduce the subsequent desorption energy consumption; in other words, for a fixed chemical absorbent such as piperazine solution, as the amount of carbon dioxide it absorbs increases, the water content ratio in the desorbed gas is lower when the same desorption conditions are adopted in the subsequent desorption unit. Compared with the prior art, the technical solution of the present invention controls the temperature of the rich absorbent liquid entering the desorber on the premise of using the same chemical absorbent and the same carbon dioxide absorption amount, and separates the obtained desorbing liquid after depressurization in a flash reboiler with microwave heating function. The obtained gas phase is compressed by a flash compressor and then recycled into the desorber. Each process step and parameter cooperate with each other, so that the rich absorbent liquid with a determined loading amount can be regenerated with lower energy consumption.

[0016] The equilibrium temperature or bubble point temperature of the rich absorbent solution under the desorption pressure, which depends on the nature of the absorbent itself, the absorption loading, and the operating pressure of the desorber, is a thermodynamic property of the absorbent under determined conditions. The research of the present invention is carried out on the premise of determined absorbent properties and loading. Therefore, the improvement of specific absorbent formulations and performance, and how to maximize the absorption loading while meeting the requirements of the absorption rate are not within the scope of the research and optimization of the present invention. The temperature at which the rich absorbent solution enters the desorber as defined in the present invention is the equilibrium temperature corresponding to the rich absorbent solution under the desorption pressure, that is, the bubble point temperature. At this temperature, the minimum amount of water vaporization can be obtained in the desorbed gas. However, it should be noted that 1) the pressure of the rich absorbent solution in the rich / lean solution heat exchanger should be higher than that in the desorber; 2) the temperature of the rich absorbent solution after heat exchange should be lower than the bubble point temperature at this pressure and remain in the liquid phase; 3) measures such as head difference, regulating valve, or feed distributor are required to reduce the pressure so that the rich absorbent solution reaches a level equivalent to the pressure in the desorber after leaving the rich / lean solution heat exchanger. Generally, the operating pressure of the desorber is usually 0 - 250 kPa(g). For most absorbents, increasing the pressure is beneficial, but it will also cause the temperature in the desorber to increase accordingly, thus affecting the thermal stability of the absorbent. That is to say, the above three conditions should be optimized according to the nature of the absorbent. The present invention does not restrict the above conditions, but obtains a unique bubble point temperature value based on the three determined conditions. For example, taking 30% MEA solution (monoethanolamine) as the absorbent, when the absorption loading of the rich absorbent solution is 0.5 mol CO 2 / mol MEA and the operating pressure of desorption is 40 kPa(g), the bubble point temperature of the rich absorbent solution is 86 °C, while when the operating pressure of desorption is 0 kPa(g), the bubble point temperature of the rich absorbent solution is 80 °C. The deviation degree between the temperature at which the rich absorbent solution enters the desorber and its bubble point temperature can be represented by the difference between the feed temperature of the rich absorbent solution and the temperature at the feed position in the desorber during the operation process. When the feed temperature of the rich absorbent solution is equal to the bubble point temperature, the temperature at the feed position in the desorber is also the bubble point temperature. When the feed temperature of the rich absorbent solution is higher than the bubble point temperature, that is, in the superheated state, flashing will occur after entering the desorber, so the temperature at the feed position in the desorber is lower than the feed temperature, and the liquid phase loading is significantly lower than the feed loading. At this time, the H 2 O / CO 2 ratio in the desorbed gas will be higher than the equilibrium H 2 O / CO 2 ratio corresponding to the rich absorbent solution loading. In the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the preferred process condition is that the feed temperature of the rich absorbent solution is 0 - 2 °C higher than the bubble point temperature, that is, T1 - T2 = 0 - 2 °C; the further preferred range is 0 - 1 °C, that is, T1 - T2 = 0 - 1 °C.

[0017] Optionally, in the low - energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the temperature of the flash reboiler is denoted as T3; the heat exchange temperature difference between the lean absorbent and the rich absorbent is denoted as T4, that is, the difference between the inlet temperature of the lean absorbent and the outlet temperature of the rich absorbent in the heat exchanger is denoted as T4, and T3 - T1 = T4.

[0018] Optionally, in the low - energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, T4 = 5 - 10°C.

[0019] In general conventional desorption tower operations, in order to recover the heat of the lean liquid as much as possible, the temperature difference of the lean - rich liquid heat exchanger is gradually improved from above 20°C to 5 - 10°C. However, this will cause the temperature difference change in the desorption tower to be higher than that of the heat exchanger, so that the heat of the lean absorbent cannot be fully utilized. If all is used for heating the rich absorbent feed, the temperature of the rich absorbent will be higher than the equilibrium temperature, or vaporize in the heat exchanger, or flash when entering the desorption tower, ultimately resulting in an increase in the proportion of water in the desorbed gas; if it is not used for heating the rich absorbent, there will be an excess of heat in the lean absorbent. As described in the background art, the common technical solution for this problem in the prior art is to split the rich absorbent flow and use the flash compression scheme to recover the excess heat of the lean absorbent. In the low - energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, by directly reducing the temperature of the flash reboiler to be consistent with the conditions of the lean - rich liquid heat exchanger, the heat exchange process is shorter. For example, if the heat exchange temperature difference between the lean and rich liquids in the heat exchanger is limited to 5 - 10°C (i.e., the temperature difference between the rich absorbent after heat exchange and the lean absorbent before heat exchange), this condition can be achieved in existing heat exchangers currently; the temperature difference between the temperature of the flash reboiler and the temperature at which the rich absorbent enters the desorber is also 5 - 10°C; by further limiting these two temperature differences to be the same (the two temperature difference values take the same value within the range of 5 - 10°C), the energy consumption can be further reduced and the energy consumption utilization of the lean absorbent can be improved. Generally speaking, a lower reboiler temperature may lead to too low a desorption rate and not meet the desorption requirements. The present invention further combines microwave heating technology to achieve the purpose of rapid desorption at a lower temperature, while increasing the desorption rate and reducing the desorption energy consumption.

[0020] The temperature of the flash reboiler is determined according to the temperature at which the rich absorbent enters the desorber, and the temperature difference range between them is 5 - 10°C, that is, 5 - 10°C higher than the feed temperature of the rich absorbent. Specifically, the temperature of the flash reboiler is controlled by the pressure of the flash reboiler, and the pressure of the flash reboiler is adjusted by the gas delivery volume of the flash vapor compressor, so as to control its temperature to reach the limited temperature difference range. The function of the flash vapor compressor is to transport the flash vapor at a lower pressure back to the desorber. The pressure boost of the flash compressor only needs to be able to return the gas to the desorber, without specific limitations.

[0021] In the above-mentioned low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, microwave heating is adopted in the flash reboiler. Specifically, there is no limitation. Any existing microwave heating method can be used to heat the material in the flash reboiler to evaporate the low-boiling point material. Microwave heating is a method of converting electrical energy into microwave energy and using it to heat the material. Generally, a microwave heater includes a microwave cavity, a microwave generator, a microwave power supply, and a corresponding control system. The common microwave frequencies are 915 MHz or 2450 MHz. The microwave introduction method can be selected as the waveguide port feeding form, that is, using the internal cavity of the flash reboiler as the microwave cavity, and setting waveguide feeding ports at the liquid phase position in the flash reboiler to introduce microwaves into the flash reboiler to heat the absorbent; or the form of a microwave antenna can be selected, placing the microwave antenna in the flash reboiler, with the antenna body immersed in the liquid phase, and the internal cavity of the flash reboiler and the antenna together form a microwave resonance cavity. Other common forms in the technical field of the present invention can also be selected for the microwave heating method, as long as the overall uniform heating of the absorbent liquid phase in the flash reboiler can be achieved. To ensure uniform heating in the flash reboiler, the present invention recommends adopting the form of multiple microwave sources and multiple waveguide feeding ports, and using their different spatial distribution positions to achieve mode complementarity and vector superposition, so as to achieve the purpose of uniform microwave field distribution.

[0022] Specifically, the interior of the flash reboiler can be horizontally divided into an absorbent inlet area, a microwave area, and an absorbent outlet area in sequence, and the three areas are connected by gas. The absorbent flowing into the flash reboiler passes through the inlet area, the microwave area, and the outlet area in sequence. The microwave cavity is arranged in the microwave area of the flash reboiler, and microwaves are introduced into the microwave cavity in the form of a group of microwave antennas. The absorbent is heated and vaporized in the microwave cavity, and part of the absorbent spontaneously circulates due to the density difference caused by heating in the inlet area and the microwave area, thus forming an overall internal flow of the absorbent, which can improve the uniformity of microwave heating.

[0023] Optionally, in the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the chemical absorbent for absorbing carbon dioxide can be 2 any chemical absorbent commonly used in the field of carbon dioxide capture, specifically, it can be selected from amine compound solutions and / or alkanolamine compound solutions, etc.; such as at least one of monoethanolamine (MEA) solution, piperazine (PZ) solution, 2-amino-2-methyl-1-propanol (AMP) solution, and N-methyldiethanolamine (MDEA) solution.

[0024] Optionally, in the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, a heat exchange reboiler is provided between the bottom of the desorber and the flash reboiler;

[0025] The desorbed gas discharged from the top of the desorber is compressed and then exchanges heat with the desorbing liquid discharged from the bottom of the desorber in the heat exchange reboiler; the desorbing liquid after heat exchange is separated in the heat exchange reboiler to obtain desorbing liquid reboiler gas and desorbing liquid reboiler condensate, and the desorbing liquid reboiler gas is transported into the flash compressor; the desorbing liquid reboiler condensate is transported into the flash reboiler.

[0026] Optionally, in the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, saturated liquid water is introduced into the flash compressor.

[0027] Optionally, in the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the saturated liquid water comes from the liquid phase part obtained by gas-liquid separation of the desorbed gas after heat exchange.

[0028] Optionally, in the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the devices involved are not specifically limited, and existing devices can all meet the implementation of the technical solution of the present invention. For example, the desorber can adopt a conventional packed desorption tower or a supergravity packed tower in the industry (rotating wire mesh packing can be set inside according to the situation), and the flash reboiler can adopt a conventional microwave heating method in the industry for heating.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] Beneficial effect 1: In the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, by limiting the temperature of the rich absorbent liquid entering the desorber and combining with the microwave low-temperature desorption method (i.e., the flash reboiler uses microwave heating), on the one hand, the temperature difference between the feed temperature of the rich absorbent liquid and the discharge temperature of the lean absorbent liquid in the desorption unit is made consistent with the heat exchange temperature difference achieved by the current rich and lean liquid heat exchanger. This can not only make full use of the advantage of the high CO concentration of the desorbed gas in the rich absorbent liquid under high load, but also only requires the rich and lean liquid heat exchanger to fully utilize the high-quality heat of the lean liquid. On the other hand, the CO desorption process of the rich absorbent liquid is strengthened by microwave heating, which can reduce the desorption temperature and the residence time of the absorbent under high-temperature conditions, thereby reducing the performance degradation of the absorbent caused by high temperature. Microwave heating uses reduced pressure or vacuum conditions, and can achieve the same desorption depth as conventional conditions at a lower temperature, thus solving the problem that the microwave method has a limited desorption depth when used in the absorbent desorption process while improving the rate and reducing the temperature. 2 concentration advantage, but also only requires the rich and lean liquid heat exchanger to fully utilize the high-quality heat of the lean liquid. On the other hand, the CO 2 desorption process of the rich absorbent liquid is strengthened by microwave heating, which can reduce the desorption temperature and the residence time of the absorbent under high-temperature conditions, thereby reducing the performance degradation of the absorbent caused by high temperature. Microwave heating uses reduced pressure or vacuum conditions, and can achieve the same desorption depth as conventional conditions at a lower temperature, thus solving the problem that the microwave method has a limited desorption depth when used in the absorbent desorption process while improving the rate and reducing the temperature.

[0031] Beneficial effect 2: The low-energy desorption process for flue gas carbon dioxide capture provided by the present invention realizes the efficient regeneration of the absorbent rich liquid under a specified load through the combination of microwave low-temperature heating, overall regulation of the temperature distribution of the desorber and the temperature difference of the rich and lean liquid heat exchanger, the gas compression scheme of the reboiler, etc., achieving the effects of reducing the regeneration energy consumption and reducing the risk of high-temperature degradation of the absorbent. Brief Description of the Drawings

[0032] Figure 1 It is a schematic flow chart of a low-energy desorption process for flue gas carbon dioxide capture provided by the present invention;

[0033] Figure 2 It is a schematic flow chart of another low-energy desorption process for flue gas carbon dioxide capture provided by the present invention;

[0034] Figure 3 It is a schematic diagram of the material flow inside a flash reboiler with microwave heating provided by the present invention;

[0035] Figure 4 It is a graph of the bubble point temperature and gas phase composition of 30% MEA solution at different loads and desorption pressures provided by the present invention;

[0036] Figure 5 It is a schematic flow chart of the low-energy desorption process for flue gas carbon dioxide capture adopted in the comparative example of the present invention.

[0037] Among them, 1 - flue gas tail gas, 2 - absorber, 3 - flue gas, 4 - absorbent rich liquid, 5 - rich liquid pump, 6 - pressure reducing valve, 7 - rich and lean liquid heat exchanger, 8 - lean liquid after heat exchange, 9 - lean liquid cooler, 10 - absorbent, 11 - lean liquid pump, 12 - absorbent lean liquid, 13 - flash reboiler, 14 - microwave generation and introduction device, 15 - throttle valve, 16 - desorbed liquid, 17 - flash vapor, 18 - flash vapor compressor, 19 - reboiler, 20 - absorbent rich liquid, 21 - desorbed gas, 22 - desorber, 23 - desorbed gas compressor, 24 - compressed desorbed gas, 25 - heat exchange reboiler, 26 - desorbed gas after heat exchange, 27 - condensed desorbed gas, 28 - gas-liquid separation tank, 29 - condensed water, 30 - desorbed liquid reboiler condensate, 31 - desorbed liquid reboiler gas, 32 - microwave antenna, 33 - isolation baffle, 34 - inlet area, 35 - microwave area, 36 - outlet area, 37 - feed flash line, 38 - rich liquid line, 39 - bubble point temperature line, 40 - feed position state, 41 - lean liquid line, 42 - mole ratio line of water and carbon dioxide in the gas phase. Detailed Embodiments

[0038] The present invention will be specifically described below through embodiments. It is necessary to point out here that the following embodiments are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0039] For those embodiments in which specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0040] In the low-energy consumption desorption process for flue gas carbon dioxide capture provided by the present invention, the flash reboilers using the conventional microwave heating method can all meet the implementation of the technical solution of the present invention.

[0041] Figure 4 It is the bubble point temperature and gas phase composition diagram of the 30% MEA solution provided by the present invention at different loadings and desorption pressures. Specifically, the rich liquid feed temperature, the temperature and pressure of the flash reboiler can be determined according to Figure 4 the temperature equilibrium line, and the molar ratio of H 2 O / CO 2 in the desorbed gas can be estimated to obtain the latent heat of vaporization part of water in the desorption energy consumption composition. Similar curves can be drawn for other absorbents according to the analysis results. First, the designed loadings of the lean liquid and rich liquid of the absorbent are optimized according to the absorption process. Taking the lean liquid loading of 0.2 mol / mol and the rich liquid loading of 0.5 mol / mol as examples, they are the lean liquid line 41 and the rich liquid line 38 respectively. The intersection of the rich liquid line 38 and the bubble point temperature line 39 at the specified desorption pressure is the bubble point temperature of the rich liquid of the absorbent. Taking the desorption at 140 kPa(g) as an example, the intersection with the bubble point temperature line is about 100 °C, and the intersection with the molar ratio line 42 of water and carbon dioxide in the gas phase is the molar ratio of H 2 O / CO 2 in the theoretically desorbed gas, about 0.6. The intersection temperature of the lean liquid line 41 and the bubble point temperature line 39 at the same pressure is about 125 °C, which is the temperature of the reboiler. According to the rich liquid bubble point temperature and the heat exchange temperature difference between the rich and lean liquids, taking 10 °C as an example in the figure, the rich liquid feed temperature after sufficient heat exchange between the rich and lean liquids in the conventional technical solution can be obtained, about 116 °C. When the feed temperature exceeds the bubble point temperature, flashing occurs when entering the tower, and the state change is as shown by the feed flash line 37 in the attached drawing. After flashing, the liquid phase loading decreases, and the actual feed loading is the state line 40 at the feed position. The intersection of it and the molar ratio line 42 of water and carbon dioxide in the gas phase is the molar ratio of H 2 O / CO 2 in the desorbed gas, about 1. When the rich liquid feeds at the bubble point, that is, feeds according to the rich liquid line 38, the molar ratio of H 2 O / CO 2The vaporization amount of water during flash evaporation is reduced by 40% compared to the feed. Further, from Figure 4 it can be obtained that if the technical solution of the present invention is adopted, the temperature of the flash reboiler is 110 °C (the bubble point temperature is 100 °C, and the temperature difference is 10 °C). The pressure of the bubble point temperature line where the intersection of this temperature line and the lean liquid line is approximately 40 kPa, which is the design pressure of the flash reboiler, and the pressure boost of the flash compressor is approximately 100 kPa.

[0042] In the following examples and comparative examples, the flue gas used is simulated flue gas configured from standard gas, and the absorbent is configured from analytical pure chemical reagents and deionized water according to the composition requirements. In the composition analysis, the composition of the flue gas is measured by gas chromatography, using a dual-column switching of GDX-502 and 13X molecular sieves, a TCD detector, and hydrogen as the carrier; the concentration of desorbed gas CO 2 is detected by an on-line analyzer with an infrared sensor, the moisture is absorbed and measured by a drying tube, and the H 2 O / CO 2 ratio of the desorbed gas is calculated based on the gas flow; the CO 2 loading in the absorbent is measured according to the SY / T 6537 method. After all the CO 2 in the absorbent is desorbed, it is absorbed and precipitated by barium hydroxide solution, and the remaining barium hydroxide is titrated with potassium hydrogen phthalate. The CO 2 content in the absorbent is calculated based on the reagent consumption. The above methods are all common analysis methods in this technical field.

[0043] Comparative Example 1

[0044] This comparative example provides a low-energy consumption desorption process for carbon dioxide capture, as Figure 5 shown, which specifically includes the following steps:

[0045] S1: The flue gas 3 enters from the lower part of the absorber 2 and contacts countercurrently with the absorbent 10 entering from the upper part of the absorber 2. The flue gas tail gas 1 from which part of the carbon dioxide has been removed is discharged from the top of the absorber 2, and the absorbent rich liquid 4 formed by the absorbent that has absorbed carbon dioxide is discharged from the bottom of the absorber 2;

[0046] S2: The absorbent rich liquid 4 discharged from the bottom of the absorber 2 is input into the rich-lean liquid heat exchanger 7 by the rich liquid pump 5, and exchanges heat with the absorbent lean liquid 12 transported by the lean liquid pump 11 in the rich-lean liquid heat exchanger 7; the heated absorbent rich liquid 20 enters the upper part of the desorber 22 after being depressurized by the pressure reducing valve 6, and the heat-exchanged lean liquid 8 is further cooled by the lean liquid cooler 9 and then circulated as the absorbent 10 into the absorber 2;

[0047] S3: The heated lean absorbent solution 20 flows downward in the desorber 22, contacts the hot gas from the bottom of the desorber 22, and desorbs carbon dioxide. Meanwhile, part of the water in the desorbing solution 16 vaporizes, and the vaporized water combines with the desorbed carbon dioxide and leaves from the top of the desorber 22 as the desorbed gas 21. The desorbing solution 16 discharged from the bottom of the desorber 22 flows into the reboiler 19 heated by conventional electricity, where vaporization and further desorption of carbon dioxide occur under heating, obtaining the flash gas 17 and the lean absorbent solution 12 after desorption. After the flash gas 17 leaves the reboiler 19, it directly returns to the desorber 22 as the hot gas to contact the subsequent rich absorbent solution 20 for carbon dioxide desorption. The lean absorbent solution 12 after desorption is transported to the rich-lean solution heat exchanger 7 by the lean solution pump 11 for heat exchange.

[0048] Among them, the flue gas 3 is simulated flue gas. In terms of volume percentage, the dry-based composition of the simulated flue gas is 76% nitrogen, 2% oxygen, and 12% carbon dioxide. The flow rate of the simulated flue gas in the absorber 2 is 4.5 Nm 3 / h, CO 2 The product scale is 1 kg / h. The absorbent 10 uses an aqueous solution of 30 wt% monoethanolamine (MEA).

[0049] The absorber 2 uses an absorption tower with a diameter of filled with two sections of θ-ring packing The total height of the packing is 2 m.

[0050] The desorber 22 uses a desorption tower filled with packing. The diameter of this desorption tower is filled with the same packing as that in the absorption tower. There are 2 sections of packing inside the desorption tower, and the height of each section of packing is 500 mm. And 100 mm height of the same specification packing is installed at the top outlet position of the desorption tower for condensation water washing. Part of the desorbed gas 21 is condensed to 80 °C by the cooler and then returns to the top water washing section of the desorption tower. The reflux ratio of the return flow to the discharge amount of the desorbed gas is 0.2 mol / mol. This part of the reflux helps to recover the entrainment of the absorbent, and at the same time, due to the condensation effect, it will cause a slight increase in the energy consumption of the reboiler. All subsequent test conditions are controlled according to this reflux ratio and temperature.

[0051] The rich-lean solution heat exchanger 7 uses a plate heat exchanger, and the difference between the temperature of the lean absorbent solution entering the rich-lean solution heat exchanger 7 and the temperature of the absorbent solution flowing out of the rich-lean solution heat exchanger 7 after heat exchange is controlled to be 10 °C. In order to keep the rich absorbent solution in the plate heat exchanger in the liquid phase, a pressure reducing valve is used to reduce the pressure at the inlet of the rich absorbent solution to the desorption tower, so that the rich absorbent solution flashes after entering the desorption tower.

[0052] During the test operation, the operating conditions of the absorption tower were adjusted, and the temperature of absorbent 10 entering the absorption tower was controlled at 35 °C and the flow rate was 21 L / h. The carbon dioxide loading in the rich absorbent solution was obtained as 0.5 mol / mol, and the operating conditions of the desorption tower were compared based on the lean absorbent loading of 0.25 mol / mol.

[0053] According to Figure 4 the equilibrium line design, the top pressure of the desorption tower, the feed temperature of the rich absorbent solution, and the temperature of the flash reboiler were adjusted. The test results are shown in Table 1.

[0054] Table 1 Desorption parameters under different desorption pressures

[0055]

[0056] It can be seen from Table 1 that as the desorption pressure increases, the corresponding bottom temperature needs to be increased, and the heat load decreases accordingly. When the desorption pressure is increased from atmospheric pressure to 50 - 100 kPa, the heat load decreases significantly. When it is further increased to the range of 140 - 150 kPa, the effect gradually weakens. In addition, as the desorption pressure increases, the difference between the feed temperature of the rich absorbent solution and the feed position temperature of the desorption tower increases, indicating that the flash evaporation amount of the rich absorbent solution at the moment of entering the tower increases after the pressure increases.

[0057] Example 1

[0058] This example provides a low - energy - consumption desorption process for flue gas carbon dioxide capture. The specific process is as Figure 1 shown, and specifically includes the following steps:

[0059] S1: The flue gas 3 enters from the lower part of the absorber 2 and contacts counter - currently with the absorbent 10 entering from the upper part of the absorber 2. The flue gas tail gas 1 with partial carbon dioxide removed is discharged from the top of the absorber 2 out of the system, and the rich absorbent solution 4 formed by the absorbent absorbing carbon dioxide is discharged from the bottom of the absorber 2.

[0060] S2: The rich absorbent solution 4 discharged from the bottom of the absorber 2 is pumped into the rich - lean liquid heat exchanger 7 by the rich liquid pump 5, and exchanges heat with the lean absorbent solution 12 transported by the lean liquid pump 11 in the rich - lean liquid heat exchanger 7. The heated rich absorbent solution 20 enters the upper part of the desorber 22, and the heat - exchanged lean liquid 8 is further cooled by the lean liquid cooler 9 and then circulates as the absorbent 10 into the absorber 2.

[0061] S3: The heated rich absorbent liquid 20 flows downward in the desorber 22, contacts the hot gas from the bottom of the desorber 22 and desorbs carbon dioxide. Meanwhile, part of the water in the desorbed liquid 16 vaporizes, and the vaporized water combines with the desorbed carbon dioxide and leaves from the top of the desorber 22 as the desorbed gas 21. The desorbed liquid 16 discharged from the bottom of the desorber 22 flows into the flash reboiler 13 heated by microwave after the pressure is reduced by the throttle valve 15. The desorbed liquid 16 flashes due to the pressure reduction in the flash reboiler 13, and vaporization and further desorption of carbon dioxide occur under the combined action of pressure reduction and microwave heating in the flash reboiler 13 to obtain the flash gas 17 and the lean absorbent liquid 12 after desorption. After the flash gas 17 leaves the flash reboiler 13, it enters the flash gas compressor 18, and after the pressure is increased, it returns to the desorber 22 as the hot gas to contact the subsequent rich absorbent liquid 20 for carbon dioxide desorption. The lean absorbent liquid 12 after desorption is transported to the rich-lean liquid heat exchanger 7 by the lean liquid pump 11 for heat exchange.

[0062] Among them, the flash reboiler 13 is a vertical kettle. Three feed-in type microwave antennas are used in the microwave generation and introduction device, which are arranged in a triangle and inserted into the liquid phase in the vertical kettle parallel to the axis from the bottom, and are respectively connected to three independent microwave sources. The microwave power is controlled by measuring the liquid phase temperature in the flash reboiler 13.

[0063] The flue gas 3, absorbent, and control conditions are all the same as those in Comparative Example 1.

[0064] The absorber 2, desorber 22, rich-lean liquid heat exchanger 7, and control conditions are all the same as those in Comparative Example 1. In this embodiment, the top pressure of the desorption tower is controlled to be 1 kPa(g). According to Figure 4 the bubble point temperature of the rich liquid on the equilibrium line is 82 °C. The operating conditions are designed and adjusted to achieve stable operation. The results are as follows: The feed temperature of the rich absorbent liquid entering the desorption tower is 82 °C, the bottom temperature of the desorption tower is 102 °C, the ratio of H 2 O / CO 2 in the desorbed gas is 0.52, the temperature of the flash reboiler is 92 °C, the pressure is -30 kPa(g), the outlet temperature of the flash gas compressor is 137 °C, and the power of the microwave energy is 0.95 kW. It should be noted that the power of the microwave energy here is the energy power of the input microwave, rather than the power of the microwave power supply. The desorption energy consumption includes microwave energy consumption and compressor energy consumption. Among them, the shaft power of the compressor is calculated based on the material composition and isentropic compression theory value, rather than the actual power consumption of the compressor, because the energy utilization efficiency of small compressors is very low. Based on the above calculation basis, the total desorption power consumption is 1.0 kW, and the unit energy consumption of CO 2 product is 3.41 MJ / kg. Compared with the operating condition 1 in Comparative Example 1 with the same desorption pressure, the unit product energy consumption is reduced by 20%.

[0065] Example 2

[0066] This example is similar to Example 1, with the only difference being that in this example, the top pressure of the desorption tower is adjusted to 140 kPa(g), and the corresponding bubble point temperature of the rich liquid is 100 °C. During stable operation, the feed temperature of the absorbent rich liquid is 100 °C, the bottom temperature of the desorption tower is 122 °C, and the ratio of H 2 O / CO 2 in the desorbed gas is 0.31. The temperature of the flash reboiler is 110 °C, the pressure is 28 kPa(g), the outlet temperature of the flash gas compressor is 179 °C, and the power of the microwave energy is 0.867 kW. The total desorption energy consumption is 0.94 kW, and the energy consumption per unit of CO 2 product is 3.18 MJ / kg. Compared with Case 3 of Comparative Example 1 with the same desorption pressure, the energy consumption per unit product is reduced by 9.7%.

[0067] Example 3

[0068] This example is similar to Example 2, with the only difference being that in this example, hot water with a temperature of 95 °C and a flow rate of 86 ml / h is injected into the inlet of the flash gas compressor 18. Under stable operating conditions, the outlet temperature of the flash gas compressor 18 drops to 128 °C, and the other control parameters are basically the same as those in Example 2, and the calculated energy consumption is the same. Compared with Example 2, the addition of a small amount of hot water reduces the temperature during the flash gas compression process, reduces the probability of degradation of the trace absorbent component in the flash gas at high temperatures, and is beneficial to the service life of the absorbent.

[0069] Example 4

[0070] This example is similar to Example 1, with the only difference being that in this example, the top pressure of the desorption tower is 1 kPa(g), and the temperature difference control of the rich and lean liquid heat exchanger is 5 °C. The corresponding feed temperature of the absorbent rich liquid is 82 °C, the bottom temperature of the desorption tower is 102 °C, and the ratio of H 2 O / CO 2 in the desorbed gas is 0.52. The temperature of the flash reboiler is 87 °C, the pressure is -43 kPa(g), the outlet temperature of the flash gas compressor is 160 °C, and the power of the microwave energy is 0.83 kW. The total desorption energy consumption is 0.91 kW, and the energy consumption per unit of CO 2 product is 3.07 MJ / kg. The energy consumption is further reduced compared with Example 1.

[0071] Example 5

[0072] This example is similar to Example 3, with the only difference being that in this example, the top pressure of the desorption tower is 140 kPa(g), and the temperature difference control of the rich and lean liquid heat exchanger is 5 °C. The feed temperature of the absorbent rich liquid is 100 °C, the bottom temperature of the desorption tower is 124 °C, and the ratio of H 2 O / CO 2The ratio is 0.31. The temperature of the flash reboiler is 105 °C, and the pressure is 15 kPa(g). Hot water with a temperature of 105 °C and a pressure of 150 kPa(g) is injected into the inlet of the flash gas compressor at a flow rate of 120 ml / h. The temperature at the outlet of the flash gas compressor is 128 °C, and the power of the microwave energy is 0.741 kW. The total desorption energy consumption is 0.84 kW, and the unit CO 2 The product energy consumption is 2.85 MJ / kg. The energy consumption is further reduced compared with Example 3.

[0073] Example 6

[0074] This example provides a low-energy consumption desorption process for flue gas carbon dioxide capture. The specific process is as Figure 2 shown, and specifically includes the following steps:

[0075] S1: The flue gas 3 enters from the lower part of the absorber 2 and contacts countercurrently with the absorbent 10 entering from the upper part of the absorber 2. The flue gas tail gas 1 from which part of the carbon dioxide has been removed is discharged from the top of the absorber 2, and the absorbent rich liquid 4 formed by the absorbent that has absorbed carbon dioxide is discharged from the bottom of the absorber 2;

[0076] S2: The absorbent rich liquid 4 discharged from the bottom of the absorber 2 is input into the rich and lean liquid heat exchanger 7 by the rich liquid pump 5, and heat exchange is carried out with the absorbent lean liquid 12 transported by the lean liquid pump 11 in the rich and lean liquid heat exchanger 7; The heated absorbent rich liquid 20 enters the upper part of the desorber 22, and the heat-exchanged lean liquid 8 is further cooled by the lean liquid cooler 9 and then circulates as the absorbent 10 into the absorber 2;

[0077] S3: The absorbent rich liquid 20 after temperature rise flows downward in the desorber 22, contacts with the hot gas from the bottom of the desorber 22 and desorbs carbon dioxide. Meanwhile, part of the water in the desorbing liquid 16 vaporizes, and the vaporized water combines with the desorbed carbon dioxide and leaves from the top of the desorber 22 as the desorbed gas 21. The desorbed gas 21 is compressed and heated up by the desorbed gas compressor 23, and the compressed desorbed gas 24 enters the heat exchange reboiler 25 after compression. The desorbing liquid 16 discharged from the bottom of the desorber 22 is depressurized by the throttle valve 15 and then flows into the heat exchange reboiler 25 to exchange heat with the compressed desorbed gas 24. After heat exchange, the desorbed gas 26 forms a gas-liquid two-phase, which is separated in the gas-liquid separation tank 28. The condensed desorbed gas 27 (i.e., the high-pressure condensed desorbed gas) discharged from the top of the gas-liquid separation tank 28 leaves the system, and the liquid phase discharged from the bottom of the gas-liquid separation tank 28 is the condensed water 29. Part of the condensed water 29 is atomized through a nozzle and enters the inlet of the flash gas compressor 18 to reduce the outlet temperature of the flash gas compressor 18. The desorbing liquid 16 forms the desorbing liquid reboiler gas 31 and the desorbing liquid reboiler condensate 30 after heat exchange in the desorbing liquid reboiler 25. The desorbing liquid reboiler gas 31 is transported to the flash gas compressor 18, pressurized and then returned to the desorber 22. The desorbing liquid reboiler condensate 30 flows into the flash reboiler 13 and is further vaporized and desorbed by microwave heating. In the flash reboiler 13 using microwave heating, the desorbing liquid reboiler condensate 30 flashes due to the pressure reduction in the flash reboiler 13. Under the combined action of pressure reduction and microwave heating, the desorbing liquid reboiler condensate 30 vaporizes and further desorbs carbon dioxide, obtaining the flash gas 17 and the lean absorbent liquid 12 after desorption. The flash gas 17 leaves the flash reboiler 13 and enters the flash gas compressor 18, together with the desorbing liquid reboiler gas 31 and part of the condensed water 29. After the pressure is increased, it returns to the desorber 22 as the hot gas to contact with the subsequent absorbent rich liquid 20 for carbon dioxide desorption. The lean absorbent liquid 12 after desorption is transported to the rich-lean liquid heat exchanger 7 by the lean liquid pump 11 for heat exchange.

[0078] In this embodiment, the desorbing liquid reboiler 25 and the flash reboiler 13 are separately arranged, or they can be arranged in the same device and respectively utilize the heat exchange functional area and the microwave heating functional area.

[0079] The flash reboiler 13 in this embodiment adopts Figure 3 the flash reboiler with microwave heating function shown in the material flow. As shown in the appendix Figure 3As shown in the figure, the flash reboiler 13 is horizontal and is divided into three zones by two vertical isolation baffles 33 (the arrangement of the baffles is similar to the intermediate baffle and the lower baffle in a dividing wall distillation column) located inside the flash reboiler 13. According to the flow direction of the material, it is successively divided into an inlet zone 34, a microwave zone 35, and an outlet zone 36, where the microwave zone 35 is arranged in the middle. The upper and lower regions of the isolation baffle 33 between the inlet zone 34 and the microwave zone 35 allow the flow of gas and liquid respectively, and the upper part of the isolation baffle 33 between the microwave zone 35 and the outlet zone 36 allows the flow of gas and liquid. The microwave generation and introduction device 14 feeds microwaves into the microwave zone 35 through the microwave antenna 32. The microwave antenna 32 can be one or more, and is evenly arranged according to the spatial structure and liquid holdup of the microwave zone 35 to achieve the purpose of uniform heating. At the same time, the internal structure of the microwave zone 35 meets the requirements of microwave conduction and no local discharge and other phenomena will occur. After the desorbate 16 from the desorber enters the flash reboiler 13, it first enters the inlet zone 34 and then enters the microwave zone 35. Due to the microwave heating effect, part of the absorbent in the microwave zone 35 is vaporized and the density becomes smaller. A partial circulation of the liquid phase of the absorbent occurs between the inlet zone 34 and the microwave zone 35. The generated gas converges in the upper part of the flash reboiler 13 to form flash vapor 17 and leaves the flash reboiler 13 through the gas phase outlet. Part of the liquid phase (lean absorbent 12) flows into the outlet zone 36 and flows out through the liquid phase outlet.

[0080] The basic conditions of the flue gas and the absorbent are the same as those in Example 1. The flue gas flow rate is 45 Nm 3 / h, the absorbent circulation rate is about 220 kg / h, and the CO 2 product scale is about 100 tons / year.

[0081] The absorber 2 uses an absorption tower, and the diameter of the absorption tower is filled with two sections of θ-ring packing The total height of the packing is 2 m.

[0082] The desorber 22 uses a desorption tower filled with packing. The diameter of the desorption tower is filled with the same packing as that in the absorption tower. There are 2 sections of packing inside the desorption tower, and the height of each section of packing is 1 m.

[0083] The rich and lean liquid heat exchanger 7 uses a plate heat exchanger.

[0084] The pressure at the top of the desorption tower is 85 kPa(g), and the temperature difference control of the rich and lean liquid plate heat exchanger is 10°C. The results during stable operation are as follows: the bubble point temperature of the rich liquid is 93°C, the feed temperature of the rich liquid is 95°C, the bottom temperature of the desorption tower is 117°C, and the H 2 O / CO 2The ratio is 0.69. After being boosted in pressure to 400 kPa(g) by the desorbed gas compressor, the temperature reaches 210 °C. After compression, the desorbed gas exchanges heat with the absorbent that has been depressurized at the bottom of the desorption column, and the temperature drops to 110 °C. Part of the condensed water is introduced into the flash gas compressor, and the flow rate of the condensed water introduced into the flash gas compressor is 0.8 kg / h. The temperature of the flash reboiler is 105 °C, and the pressure is 14 kPa(g). The outlet temperature of the flash gas compressor is 119 °C. The power of the microwave energy is 8.15 kW. The sum of the microwave power consumption and the shaft work of the two compressors results in a total desorption energy consumption of 9.23 kW, and the specific energy consumption is 3.12 MJ / kg. Adopting the desorbed gas compression heat recovery scheme will increase a part of the power consumption for desorbed gas compression, but after compression and temperature increase, part of the condensation heat of water vapor can be recovered, reducing the comprehensive energy consumption. Compared with the working condition 2 of the reference ratio 1, under the same desorption pressure condition, the comprehensive desorption energy consumption is reduced by 15%. In addition, by using the desorbed gas compression heat recovery scheme, the rich liquid feed temperature range can be appropriately widened. In this embodiment, the feed temperature deviates from the bubble point temperature by 2 °C, and the increased water content in the desorbed gas relative to the bubble point feed can be recovered in the subsequent desorbed gas compression heat exchange process. Since the CO 2 The product needs to be compressed to a higher pressure in the subsequent process. This scheme can also reduce the subsequent compression power consumption. However, during the desorbed gas compression process, the temperature rises significantly, and it is necessary to perform a defoaming operation on the top of the desorption column to reduce the entrainment of the absorbent. If necessary, the treatment measures for flash gas compression in the technical solution of the present invention can be adopted to return a part of the condensed water to reduce the temperature rise. In this embodiment, the microwave heating uses the structure of the material flow shown in Figure 3 This structure is more suitable for large-scale heating processes. Through the density difference of the liquid after heating, internal flow is generated, adding a convective heat transfer process on the basis of a uniformly designed microwave field, and avoiding the problem of large local temperature differences that may occur in large-scale microwave heating.

[0085] Example 7

[0086] This example is similar to Example 6, with the only difference being that: in this example, a rotating packed bed desorption column is used as the desorption column, which is internally equipped with a rotating wire mesh packing. The rich absorbent liquid 4 is sprayed in the form of droplets from the central axis of the rotating packed bed desorption column through a nozzle onto the inner wall of the wire mesh packing, and then flies to the inner wall of the rotating packed bed desorption column along the radial direction under the action of the rotating packing, and flows down along the wall surface to the discharge port of the rotating packed bed desorption column. The gas from the flash gas compressor enters from the outer edge of the wire mesh packing and contacts the rich absorbent liquid countercurrently on the wire mesh packing. Under the action of the high gravity field, the gas-liquid mass transfer intensity is enhanced, and the desorption process approaches the gas-liquid equilibrium state. Under the same operating conditions as in Example 6, the microwave power is 7.76 kW, the total desorption power consumption is 8.88 kW, and the specific consumption is 3.12 MJ / kg. Due to the small scale of the device, the power consumption of the high gravity equipment itself is not included. When using a rotating packed bed desorption column for desorption operation, because the liquid phase residence time is short and the heat transfer intensity along the flow direction is low, it is more suitable for the operating conditions where the absorbent temperature changes little during the desorption process.

[0087] Comparative Example 2

[0088] This comparative example is similar to Comparative Example 1, with the only differences being that: 1) the absorbent is replaced with an aqueous solution of a mixture of PZ (piperazine) and MDEA (N-methyldiethanolamine), where the PZ content is 21.6 wt% and the MDEA content is 7.3 wt%. 2) The top reflux operation of the desorption column is cancelled in this comparative example, and the desorbed gas is directly discharged for composition analysis. 3) According to the absorption requirements, the absorbent loading in this comparative example is controlled as follows: the rich liquid loading is 0.55 mol / mol, and the lean liquid should be desorbed to a loading of 0.2 mol / mol. The pressure at the top of the desorption column is set at 50 kPa(g), the corresponding temperature at the bottom of the desorption column is 112 °C, the temperature difference of the plate heat exchanger is set at 10 °C, the rich liquid is heated to 102 °C for feeding, the temperature of the desorbed gas at the top of the column is 96 °C, and the temperature at the feeding position is also 96 °C. The H 2 O / CO 2 ratio is 1.21. The heating power of the reboiler at the bottom of the desorption column is 1.28 kW, and the calculated specific desorption energy consumption for the CO 2 product is 3.61 MJ / kg.

[0089] Example 8

[0090] This example is similar to Example 1, with the only differences being that: 1) the same absorbent as in Comparative Example 2 is used in this example. The absorbent loading control range is the same as in Comparative Example 2. 2) The desorbed gas is directly discharged for composition analysis in this example. The pressure at the top of the desorption column is set at 50 kPa(g), the bubble point temperature of the rich liquid is 90 °C, the rich liquid feeding temperature is controlled at 91 °C, and the temperature difference of the plate heat exchanger is set at 10 °C; under stable operating conditions, the temperature at the top of the desorption column is 90 °C, and the H 2 O / CO 2The ratio is 0.79; the bottom temperature of the desorption tower is 111°C, the pressure of the flash reboiler is 1 kPa(g), and the temperature is 101°C. The microwave energy power is 1.10 kW, and the total desorption energy consumption is 1.16 kW. Calculate the unit CO 2 The desorption energy consumption of the product is 3.26 MJ / kg. Compared with Comparative Example 2, the desorption energy consumption is reduced by 10%.

[0091] The method of the present invention is suitable for common amine or alkanolamine absorbents. According to this method, the main process parameters are determined, including the rich liquid feed temperature, the temperature and pressure of the flash reboiler for microwave heating, etc. Optimal process conditions can be obtained within the absorbent loading range required by the absorption index, and it has an obvious effect of reducing desorption energy consumption compared with the conventional technology.

[0092] Of course, the present invention may also have various other embodiments and their deformations. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A low - energy consumption desorption process for flue gas carbon dioxide capture, characterized in that, it comprises the following steps: S1: The rich absorbent solution after absorbing carbon dioxide exchanges heat with the lean absorbent solution in a heat exchanger; S2: The rich absorbent solution after heat exchange enters a desorber for desorption; S3: After the desorbed liquid discharged from the bottom of the desorber is depressurized, gas - liquid separation is carried out in a flash reboiler. The obtained gas phase is compressed by a flash compressor and recycled into the desorber, and the obtained lean absorbent solution is recycled to the heat exchanger for heat exchange; wherein, the heating method of the flash reboiler is microwave heating; Denote the temperature of the rich absorbent solution after heat exchange as T1, and the bubble - point temperature of the rich absorbent solution under the desorption pressure as T2, T1 - T2=-2 to 2 °C.

2. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 1, characterized in that, T1 - T2 = 0 to 2 °C.

3. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 1, characterized in that, Denote the temperature of the flash reboiler as T3; Denote the heat exchange temperature difference between the lean absorbent solution and the rich absorbent solution as T4, T3 - T1 = T4.

4. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 3, characterized in that, T4＝5～10℃。 5. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 1, characterized in that, The chemical absorbent for absorbing carbon dioxide is selected from amine compound solutions and / or alkanolamine compound solutions.

6. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 1, characterized in that, A heat exchange reboiler is provided between the bottom of the desorber and the flash reboiler; The desorbed gas discharged from the top of the desorber is compressed and then exchanges heat with the desorbed liquid discharged from the bottom of the desorber in the heat exchange reboiler; The desorbed liquid after heat exchange is separated in the heat exchange reboiler to obtain desorbed liquid reboiler gas and desorbed liquid reboiler condensate. The desorbed liquid reboiler gas is transported into the flash compressor; The desorbed liquid reboiler condensate is transported into the flash reboiler.

7. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 6, characterized in that, Saturated liquid water is introduced into the flash compressor.

8. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 7, characterized in that, The saturated liquid water comes from the liquid phase part obtained by gas - liquid separation of the desorbed gas after heat exchange.

9. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 1, characterized in that, The desorber is a packed desorption tower or a high - gravity packed tower.

10. The low - energy consumption desorption process for flue gas carbon dioxide capture according to claim 9, characterized in that, The high - gravity packed tower is internally provided with a rotating wire mesh packing.

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