A biogas carbon capture system based on heat pump preheating rich liquid and a method for operating the same

Abstract

The application discloses a biogas carbon capture system based on heat pump preheating of rich liquid and an operation method thereof, and belongs to the field of absorption carbon capture and waste heat utilization. The system comprises an absorption carbon capture unit, a heat pump unit and a heat supply water circulation flow channel. The absorption carbon capture unit is used for purifying and refining anaerobic fermentation biogas of kitchen waste, removing impurities such as CO2 and H2S, and realizing the simultaneous capture of CO2 while producing bio-natural gas. The heat pump unit is used for recovering high-temperature waste heat of flue gas of a waste incineration power plant and external low-temperature waste heat, and outputting medium-temperature waste heat to a rich liquid preheater. The heat supply water circulation flow channel is used for transmitting heat output by the heat pump unit to the rich liquid preheater. The application uses a double-effect incremental absorption heat pump and lean liquid flash evaporation recompression technology, utilizes high-temperature waste heat of flue gas and external low-temperature waste heat to generate a medium-temperature heat source, and supplies the medium-temperature heat source to rich liquid at an inlet of a desorption tower, so that the temperature at the top of the desorption tower is increased.

Description

Technical Field

[0001] This invention belongs to the field of carbon capture and waste heat utilization, specifically relating to a biogas carbon capture system based on heat pump preheating of rich liquid and its operation method. Background Technology

[0002] Biogas, an important renewable energy source, is mainly produced by the anaerobic fermentation of organic waste such as kitchen waste, and its main component is methane. However, untreated crude biogas typically contains 5%-40% carbon dioxide (CO2) and 1000-5000 ppm hydrogen sulfide (H2S) and other impurities, resulting in low calorific value and high corrosiveness, making it unsuitable for direct integration into natural gas pipelines or efficient utilization. Therefore, purifying biogas to remove CO2 and H2S to produce high-purity biomethane is a crucial step in realizing the resource utilization of waste and reducing greenhouse gas emissions.

[0003] Currently, commonly used biogas purification technologies in industry mainly include pressure swing adsorption (PSA), membrane separation, and chemical absorption. Among them, chemical absorption has attracted much attention due to its high selectivity for acidic gases, good treatment effect, and ability to achieve synergistic removal of CO2 and H2S. The enriched gas obtained after removal can undergo further desulfurization treatment to achieve high-purity CO2 capture and resource utilization. However, the widespread application of this technology is severely restricted by high energy consumption, which is mainly concentrated in the thermal regeneration process of the absorbent in the desorption tower. Traditional regeneration methods require the introduction of a large amount of medium-temperature steam (usually above 100°C) from the outside to supply the reboiler. Especially when integrated into waste-to-energy plants, steam extraction leads to a significant loss in power generation efficiency. Existing technologies still struggle to control this efficiency loss to within 7%. At the same time, the flue gas exiting waste-to-energy plants still has a high temperature, and recovering and utilizing the waste heat from the flue gas is an effective way to reduce the energy consumption of carbon capture systems. Traditional absorption carbon capture systems suffer from high reboiler temperatures at the primary heat-consuming end, resulting in limited usable flue gas waste heat and restricting energy-saving effects. Heat pump technology can recover and utilize flue gas waste heat, providing higher-temperature heat to the carbon capture system. However, existing combinations of heat pumps and absorption carbon capture systems have several limitations. Traditional compression heat pumps suffer from excessive power consumption, temperature-increasing absorption heat pumps have low heat conversion efficiency, and incremental absorption heat pumps struggle to meet the reboiler's output temperature requirements. Therefore, the application of heat pumps combined with carbon capture systems in biogas purification at waste-to-energy plants urgently needs further exploration and development. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art, solve the problems of limited available flue gas waste heat in waste incineration power plants and the high efficiency of power plant power generation due to carbon capture systems, and provide a biogas carbon capture system based on heat pump preheating of rich liquid and its operation method.

[0005] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a biogas carbon capture system based on heat pump preheating of rich liquid, including a carbon capture unit, a heat pump unit and a hot water circulation channel. The carbon capture unit is used to consume heat from the heat pump unit and the steam channel, and absorb and enrich carbon dioxide and hydrogen sulfide in the biogas in the biogas channel; the heat pump unit is used to recover the waste heat from the high-temperature heat source of the flue gas from the waste incineration power plant and the external low-temperature heat source, and output medium-temperature waste heat to the rich liquid preheater; the circulating water in the hot water circulation channel is used to absorb the heat output by the heat pump unit and enter the rich liquid preheater to exchange heat with the rich liquid inside.

[0006] Preferably, the carbon capture unit includes an absorption tower, a lean-rich liquid heat exchanger, a rich liquid preheater, a desorption tower, a desulfurization reactor, and a flash tank. The biogas inlet at the bottom of the absorption tower is connected to the biogas flow channel, and the biogas outlet at the top is connected to the biogas emission channel. The rich liquid outlet at the bottom is connected to the cold-side fluid channel inlet of the lean-rich liquid heat exchanger via a rich liquid pump. The cold-side fluid channel outlet of the lean-rich liquid heat exchanger is connected to the cold-side fluid channel inlet of the rich liquid preheater, and the cold-side fluid channel outlet of the rich liquid preheater is connected to the rich liquid inlet of the desorption tower. The gas phase outlet at the top of the desorption tower is connected to the heat source inlet of the regenerated gas condenser, and the liquid phase outlet at the bottom of the tower is connected to the cold-side fluid channel inlet of the reboiler. The cold-side fluid channel inlet and cold-side fluid channel of the regenerated gas condenser are both connected to the first cold source and form a loop. The condensate outlet is connected to the condensate inlet at the top of the desorption tower, and the gas phase outlet is connected to the gas phase inlet of the desulfurization reactor. The carbon dioxide-rich gas phase outlet of the desulfurization reactor is connected to the carbon dioxide-rich flow channel. The reboiler's gaseous outlet is connected to the hydrogen sulfide-rich flow channel; the reboiler's gaseous product outlet is connected to the gaseous inlet at the bottom of the desorption tower; both the hot-side fluid channel inlet and outlet are connected to the steam flow channel and form a loop; the liquid product outlet is connected to the lean liquid inlet of the flash tank; the flash tank's top steam outlet is connected to the compressor inlet; the bottom lean liquid outlet is connected to the lean liquid pump inlet; the compressor outlet is connected to the gaseous inlet at the bottom of the desorption tower; the lean liquid pump outlet is connected to the hot-side fluid channel inlet of the lean-rich liquid heat exchanger; the lean-rich liquid heat exchanger's hot-side fluid channel outlet is connected to the lean liquid cooler inlet; the lean liquid cooler inlet is also connected to the absorbent replenishment flow channel; both the cold-side fluid channel inlet and outlet are connected to the second cold source and form a loop; and the outlet is connected to the lean liquid inlet at the top of the absorption tower.

[0007] Preferably, the heat pump unit includes a high-pressure generator, a low-pressure generator, a condenser, an absorber, an evaporator, a high-temperature solution heat exchanger, and a low-temperature solution heat exchanger. The high-pressure generator's hot-side fluid channel inlet is connected to a high-temperature heat source in the flue gas, its hot-side fluid channel outlet is connected to the outside, its solution outlet is connected to the hot-side fluid channel inlet of a high-temperature solution heat exchanger, and its steam outlet is connected to the steam inlet of a low-pressure generator; the low-pressure generator's solution outlet is connected to the hot-side fluid channel inlet of a low-temperature solution heat exchanger, its steam outlet is connected to the hot-side fluid channel inlet of a condenser, and its condensate outlet is connected to the hot-side fluid channel inlet of the condenser via a first water throttling valve; the high-temperature solution heat exchanger's hot-side fluid channel outlet is connected to the solution inlet of an absorber via a first solution throttling valve, and its cold-side fluid outlet is connected to the solution inlet of the high-pressure generator; The hot-side fluid channel outlet of the low-temperature solution heat exchanger is connected to the solution inlet of the absorber via a second solution throttling valve, and the cold-side fluid outlet is connected to the solution inlet of the low-pressure generator. The solution outlet of the absorber is divided into two paths: one path is connected to the cold-side fluid channel inlet of the high-temperature solution heat exchanger via a first solution pump, and the other path is connected to the cold-side fluid channel inlet of the low-temperature solution heat exchanger via a second solution pump. The hot-side fluid channel outlet of the condenser is connected to the cold-side fluid channel inlet of the evaporator via a second water throttling valve. The cold-side fluid channel outlet of the evaporator is connected to the steam inlet of the absorber, the hot-side fluid channel inlet is connected to an external low-temperature heat source, and the hot-side fluid channel outlet is connected to the outside.

[0008] Preferably, the hot water circulation channel passes sequentially through the cold-side fluid channel of the absorber, the cold-side fluid channel of the condenser, and the hot-side fluid channel of the rich liquid preheater, and then returns to the cold-side fluid channel of the absorber, forming a closed loop.

[0009] Preferably, the steam source for the steam flow channel is exhaust gas from a power plant turbine.

[0010] Preferably, both the absorption tower and the desorption tower are packed distillation towers, and the internal packing is one of Raschig rings, Pall rings, stepped rings, arc saddle packing, rectangular saddle packing, corrugated packing, corrugated mesh packing or metal saddle ring packing.

[0011] Preferably, the absorbent in the internal circulation path of the carbon capture unit is an inorganic alkaline solution or an organic amine solution.

[0012] Preferably, the lean-rich liquid heat exchanger, the rich liquid preheater, the condenser, the evaporator, the high-temperature solution heat exchanger, and the low-temperature solution heat exchanger are all indirect-wall heat exchangers.

[0013] Preferably, the working fluid pair of the heat pump unit is lithium bromide aqueous solution-water.

[0014] Secondly, the present invention provides an operation method for the biogas carbon capture system based on heat pump preheating of rich liquid as described in the first aspect, as follows: S1: The operation method of the carbon capture unit is as follows: The lean liquid, after being cooled by the lean liquid cooler, enters the absorption tower through the lean liquid inlet at the top. Inside the absorption tower, it undergoes heat and mass exchange with the biogas to be treated, which enters through the biogas flow channel. During this process, the lean liquid absorbs carbon dioxide and hydrogen sulfide from the biogas, resulting in a rich liquid and treated biogas. The treated biogas is discharged through the biogas discharge channel. The rich liquid, after absorbing carbon dioxide and hydrogen sulfide, is connected to the inlet of the rich liquid pump via a pipeline and, driven by the rich liquid pump, enters the lean-rich liquid heat exchanger through the cold-side fluid channel inlet. The heat exchanger exchanges heat with the lean liquid from the flash tank's lean liquid outlet, transforming it into a high-temperature rich liquid. This high-temperature rich liquid enters the rich liquid preheater, absorbing heat from the hot water circulation channel for further heating. It then enters the desorption tower through the rich liquid inlet, where it is purged by high-temperature steam entering through the desorption tower's gas phase inlet, desorbing carbon dioxide and hydrogen sulfide. The desorbed carbon dioxide and hydrogen sulfide, along with the purging steam, are discharged through the gas phase outlet at the top of the desorption tower and enter the regenerated gas condenser, where the absorbent components in the gas phase are cooled and liquefied. The condensate is discharged through the condensate outlet and returned to the desorption tower. The remaining gas components are discharged through the gas phase outlet of the regeneration gas condenser and enter the desulfurization reactor through the gas phase inlet of the desulfurization reactor. After removing hydrogen sulfide, the solutions are collected through the carbon dioxide-rich gas phase outlet of the desulfurization reactor via the carbon dioxide-rich flow channel. The hydrogen sulfide-rich solutions are collected through the hydrogen sulfide-rich gas phase outlet of the desulfurization reactor via the hydrogen sulfide-rich flow channel. The desorbed absorbent solution is discharged from the liquid phase outlet at the bottom of the desorption tower and enters the reboiler. The high-temperature steam generated in the reboiler is discharged from the gas phase inlet at the bottom of the desorption tower. The remaining lean liquid from the reboiler is returned to the desorption tower for purging; the remaining lean liquid from the reboiler enters the flash tank for flash evaporation, and the generated flash steam enters the compressor through the steam outlet at the top of the flash tank. After being compressed, it enters the desorption tower through the gas phase inlet at the bottom for purging. The remaining lean liquid from the flash tank is discharged through the lean liquid outlet at the bottom and is pumped into the hot-side fluid channel inlet of the lean-rich liquid heat exchanger to heat the rich liquid from the rich liquid outlet at the bottom of the absorption tower. After heat exchange, the lean liquid is mixed with the absorbent solution replenished by the absorbent replenishment channel and then enters the lean liquid cooler to complete the cycle. S2: The operation method of the heat pump unit is as follows: The dilute solution from the absorber flows out in two streams. The first stream, pressurized by a first solution pump, enters the solution inlet of the high-pressure generator from the cold-side fluid channel of the high-temperature solution heat exchanger. Inside the high-pressure generator, it exchanges heat with the high-temperature heat source of the flue gas in the hot-side fluid channel, generating high-pressure steam and a high-pressure concentrated solution. The second stream, pressurized by a second solution pump, enters the solution inlet of the low-pressure generator from the cold-side fluid channel of the low-temperature solution heat exchanger. The high-pressure steam enters the hot-side fluid channel of the low-pressure generator through the steam outlet of the high-pressure generator, where it exchanges heat with the dilute solution from the cold-side fluid channel. The solution undergoes heat exchange, with high-pressure steam condensing into high-pressure condensate, and the dilute solution generating medium-pressure steam and a medium-pressure concentrated solution. The high-pressure condensate, through the condensate outlet of the low-pressure generator, is throttled and depressurized by a first water throttling valve, and together with the medium-pressure steam through the steam outlet of the low-pressure generator, enters the hot-side fluid channel of the condenser. In the condenser, hot water is circulated and released into the cold-side fluid channel, forming medium-pressure condensate. The medium-pressure condensate enters the second water throttling valve, expands into low-pressure water, and then enters the cold-side fluid channel of the evaporator, where it exchanges heat with an external low-temperature heat source in the hot-side fluid channel, evaporating into low-pressure water. High-pressure steam; the low-pressure steam enters the steam inlet of the absorber to complete the water working fluid circulation; the high-pressure concentrated solution enters the hot-side fluid channel of the high-temperature solution heat exchanger through the solution outlet of the high-pressure generator, exchanges heat with the dilute solution in the cold-side fluid channel, and then enters the solution inlet of the absorber through the first solution throttling valve; the medium-pressure concentrated solution enters the hot-side fluid channel of the low-temperature solution heat exchanger through the solution outlet of the low-pressure generator, exchanges heat with the dilute solution in the cold-side fluid channel, and then enters the solution inlet of the absorber through the second solution throttling valve; the high-pressure concentrated solution and the low-pressure concentrated solution from the two channels mix and are absorbed... The absorber absorbs low-pressure steam from the steam inlet and simultaneously exchanges heat with the heating circulating water in the cold-side fluid channel to generate a dilute solution. The solution then flows out in two streams through the absorber's solution outlet. The first stream of solution enters the cold-side fluid channel of the high-temperature solution heat exchanger via the first solution pump, exchanges heat with the high-pressure concentrated solution in the hot-side fluid channel, and then enters the solution inlet of the high-pressure generator. The second stream of solution enters the cold-side fluid channel of the low-temperature solution heat exchanger via the second solution pump, exchanges heat with the medium-pressure concentrated solution in the hot-side fluid channel, and then enters the solution inlet of the low-pressure generator, completing the working fluid circulation. S3: The operation method of the hot water circulation channel is as follows: Low-temperature hot water enters the absorber through the cold-side fluid channel, absorbing the heat generated when the concentrated solution absorbs low-pressure steam, becoming medium-temperature hot water. The medium-temperature hot water enters the condenser through the cold-side fluid channel, absorbing the condensation heat of the high-pressure steam, becoming high-temperature hot water. The high-temperature hot water enters the rich liquid preheater through the hot-side fluid channel, exchanging heat with the rich liquid to become low-temperature hot water, and then enters the cold-side fluid channel of the absorber through the hot-side fluid channel outlet, completing the cycle.

[0015] Compared with the prior art, the present invention has the following advantages: This invention combines dual-effect incremental heat pump technology, solution flash evaporation and recompression technology, and rich liquid preheating technology with a carbon capture system. This enables efficient recovery of high-temperature waste heat from flue gas and low-temperature waste heat from external sources in waste-to-energy plants, increasing the temperature at the top of the desorption tower, enhancing CO2 and H2S desorption, and thus reducing the amount of gas extracted from the turbine. This minimizes the impact of the carbon capture system's operation on the power plant's power generation efficiency. Compared to existing technologies combining compression heat pumps with carbon capture systems, this invention provides a system with lower power consumption, solving the problem of high power consumption. Compared to existing technologies combining heating-type heat pumps or single-effect incremental heat pumps with carbon capture systems, this invention offers higher efficiency in recovering low-temperature waste heat, solving the problem of low utilization rate of flue gas waste heat. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a preferred structure of the system of the present invention.

[0017] In the diagram: Carbon capture unit 101; Heat pump unit 102; Absorber tower 1; Lean liquor cooler 2; Rich liquor pump 3; Lean-rich liquor heat exchanger 4; Rich liquor preheater 5; Desorption tower 6; Regenerated gas condenser 7; Reboiler 8; Desulfurization reactor 9; Flash tank 10; Compressor 11; Lean liquor pump 12; High-pressure generator 13; Low-pressure generator 14; Condenser 15; Absorber 16; Evaporator 17; High-temperature solution heat exchanger 18; Low-temperature solution heat exchanger 19 9; First water throttling valve 20; First solution throttling valve 21; Second solution throttling valve 22; First solution pump 23; Second solution pump 24; Second water throttling valve 25; Biogas flow channel 26; Biogas discharge channel 27; First cold source 28; Carbon dioxide rich channel 29; Hydrogen sulfide rich channel 30; Steam channel 31; Absorbent replenishment channel 32; Second cold source 33; High-temperature heat source for flue gas 34; External low-temperature heat source 35; Hot water circulation channel 36. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0019] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0020] In the description of this invention, it should be understood that the terms "first," "second," etc., are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include at least one of those features.

[0021] In the description of this invention, it should be understood that the terms "high pressure" and "low pressure" in the components "high pressure generator 13; low pressure generator 14" are used only for distinguishing purposes and should not be construed as indicating or implying relative importance or implicitly specifying the pressure limitation of the indicated technical features.

[0022] In the description of this invention, it should be understood that the terms "high temperature" and "low temperature" in the components "high temperature solution heat exchanger 18; low temperature solution heat exchanger 19; flue gas high temperature heat source 34; external low temperature heat source 35" are used only for distinguishing descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the temperature limitation of the indicated technical features.

[0023] This invention provides a biogas carbon capture system based on heat pump preheating of rich liquid. The system can be divided into three parts: a carbon capture unit 101, a heat pump unit 102, and a hot water circulation channel 36, as detailed below. Figure 1 As shown. The carbon capture unit 101 is used to consume heat from the heat pump unit 102 and the steam channel 31, absorbing and enriching CO2 and H2S in the biogas channel 26; the heat pump unit 102 is used to recover waste heat from the high-temperature heat source 34 and the external low-temperature heat source 35 of the waste incineration power plant flue gas, and outputs medium-temperature waste heat to the rich liquid preheater 5 to increase the top temperature of the desorption tower 6; the circulating water in the hot water circulation channel 36 is used to absorb the heat output by the heat pump unit 102 and enters the rich liquid preheater 5 to exchange heat with the rich liquid, that is, to transfer the heat output by the heat pump unit 102 to the rich liquid preheater 5.

[0024] The structure and connection method of each unit will be explained in detail below.

[0025] In a preferred embodiment of the present invention, the carbon capture unit 101 mainly includes an absorption tower 1, a lean liquid cooler 2, a rich liquid pump 3, a lean and rich liquid heat exchanger 4, a rich liquid preheater 5, a desorption tower 6, a regeneration gas condenser 7, a reboiler 8, a desulfurization reactor 9, a flash tank 10, a compressor 11, a lean liquid pump 12, a biogas flow channel 26, a biogas emission channel 27, a first cold source 28, a carbon dioxide rich channel 29, a hydrogen sulfide rich channel 30, a steam channel 31, an absorbent replenishment channel 32, and a second cold source 33.

[0026] It should be noted that the absorbent refers to a liquid that has different solubilities for the components of a gas mixture and can selectively absorb one or more of them, including physical absorbents and chemical absorbents. The carbon capture unit 101 is filled with an absorbent solution for absorbing and desorbing CO2 and H2S, specifically an inorganic alkaline solution or an organic amine solution, such as ammonia, carbonates, monoethanolamine, methyldiethanolamine, etc.

[0027] In addition, the lean liquid cooler 2, the lean and rich liquid heat exchanger 4, the rich liquid preheater 5, the regenerated gas condenser 7, and the reboiler 8 each have a cold-side fluid channel and a hot-side fluid channel that can form a heat exchange.

[0028] like Figure 1 As shown, the bottom of the absorption tower 1 is provided with a biogas inlet connected to the biogas flow channel 26 for introducing biogas to be treated. The top of the absorption tower 1 is provided with a biogas discharge outlet connected to the biogas discharge channel 27 for discharging the treated biogas.

[0029] The bottom of the absorption tower 1 is also equipped with a rich liquid outlet, which is connected to the inlet of the rich liquid pump 3 via a pipeline. The outlet of the rich liquid pump 3 is connected to the inlet of the cold-side fluid channel of the lean-rich liquid heat exchanger 4 via a pipeline. The outlet of the cold-side fluid channel of the lean-rich liquid heat exchanger 4 is connected to the inlet of the cold-side fluid channel of the rich liquid preheater 5 via a pipeline. The outlet of the cold-side fluid channel of the rich liquid preheater 5 is connected to the rich liquid inlet of the desorption tower 6 via a pipeline.

[0030] The gas phase outlet at the top of desorption tower 6 is connected to the hot-side fluid channel inlet of regeneration gas condenser 7 via a pipeline. The cold-side fluid channel inlet of regeneration gas condenser 7 is connected to the first cold source 28 via a pipeline, and the cold-side fluid channel outlet returns to the first cold source 28 via a pipeline. The condensate outlet of regeneration gas condenser 7 is connected to the condensate inlet at the top of desorption tower 6 via a pipeline. The gas phase outlet of regeneration gas condenser 7 is connected to the gas phase inlet of desulfurization reactor 9 via a pipeline. The carbon dioxide-rich gas phase outlet of desulfurization reactor 9 is connected to the carbon dioxide-rich flow channel 29 via a pipeline. The hydrogen sulfide-rich gas phase outlet of desulfurization reactor 9 is connected to the hydrogen sulfide-rich flow channel 30 via a pipeline.

[0031] The liquid outlet at the bottom of desorption tower 6 is connected to the cold-side fluid channel inlet of reboiler 8 via a pipeline. The gaseous product outlet of reboiler 8 is connected to the gaseous inlet at the bottom of desorption tower 6 via a pipeline. The hot-side fluid channel inlet of reboiler 8 is connected to steam channel 31 via a pipeline, and the hot-side fluid channel outlet returns to steam channel 31 via a pipeline. The liquid product outlet of reboiler 8 is connected to the lean liquid inlet of flash tank 10 via a pipeline.

[0032] In this embodiment, the steam source for the steam flow channel 31 is preferably an extraction steam turbine from a power plant. An extraction steam turbine is an industrial device that extracts a portion of steam from the intermediate stage of a steam turbine to supply heat energy to users, while also generating electricity. In this way, the extraction steam turbine meets both the electrical load demand and provides heat energy, improving the unit's thermal efficiency and economy.

[0033] In this embodiment, the regenerated gas condenser 7 and the reboiler 8 have gas-liquid separation functions. The regenerated gas condenser 7 condenses the distillate gas from the gas phase outlet of the desorption tower 6 to obtain condensate and a mixture of CO2 and H2S. The condensate is returned to the desorption tower 6 through the condensate outlet of the regenerated gas condenser 7. The mixed gas enters the desulfurization reactor 9 through the gas phase outlet of the regenerated gas condenser 7 for desulfurization, resulting in CO2-rich gas and H2S-rich gas. The CO2-rich gas is discharged through the CO2-rich gas phase outlet of the desulfurization reactor 9 and collected through the CO2-rich flow channel 29, while the H2S-rich gas is discharged through the hydrogen sulfide-rich gas phase outlet of the desulfurization reactor 9 and discharged through the hydrogen sulfide-rich flow channel 30. The reboiler 8 separates the rich liquid from the liquid phase outlet of the desorption tower 6 into purge steam and lean liquid. Among them, the purging steam enters the desorption tower 6 through the gas phase product outlet of the reboiler 8 for purging, and the lean liquor flows through the liquid phase product outlet of the reboiler 8 to the lean and rich liquor heat exchanger 4 via the flash tank 10 and the lean liquor pump 12.

[0034] The top steam outlet of flash tank 10 is connected to the inlet of compressor 11 via a pipe. The outlet of compressor 11 is connected to the gas phase inlet at the bottom of desorption tower 6 via a pipe.

[0035] The lean liquid outlet at the bottom of flash tank 10 is connected to the inlet of lean liquid pump 12 via a pipe. The outlet of lean liquid pump 11 is connected to the hot-side fluid channel inlet of lean-rich liquid heat exchanger 4 via a pipe. The hot-side fluid channel outlet of lean-rich liquid heat exchanger 4 is connected to the inlet of lean liquid cooler 2 via a pipe. The inlet of lean liquid cooler 2 is also connected to absorbent replenishment channel 32 for replenishing absorbent solution. The cold-side fluid channel inlet of lean liquid cooler 2 is connected to the second cold source 33 via a pipe, and the cold-side fluid channel outlet returns to the second cold source 33 via a pipe. The outlet of lean liquid cooler 2 is connected to the lean liquid inlet at the top of absorption tower 1 via a pipe.

[0036] In this embodiment, the absorption tower 1 and desorption tower 6 are preferably packed distillation towers. Selectable packing types include Raschig rings, Pall rings, stepped rings, arc saddle packing, rectangular saddle packing, corrugated packing, corrugated mesh packing, and metal saddle ring packing. In practical applications, different packing types can be selected based on temperature, pressure, material properties, equipment structure, and the requirements of the processed products to optimize the operating efficiency within the tower and improve separation efficiency.

[0037] It should be noted that the first cold source 28 and the second cold source 33 can be provided by natural cold sources (such as water, air, etc.) or by refrigeration units.

[0038] In a preferred embodiment of the present invention, the heat pump unit 102 mainly includes a high-pressure generator 13, a low-pressure generator 14, a condenser 15, an absorber 16, an evaporator 17, a high-temperature solution heat exchanger 18, a low-temperature solution heat exchanger 19, a first water throttling valve 20, a first solution throttling valve 21, a second solution throttling valve 22, a first solution pump 23, a second solution pump 24, a second water throttling valve 25, a flue gas high-temperature heat source 34, and an external low-temperature heat source 35.

[0039] It should be noted that the working fluid pair in an absorption heat pump refers to the two different substances used in the absorption heat pump system, typically including an absorbent and a working fluid. This working fluid pair works together to achieve cooling or heating functions by absorbing and releasing heat. The heat pump unit 102 is filled with a solution-water working fluid pair for absorbing and releasing heat, specifically a lithium bromide aqueous solution-water mixture.

[0040] In addition, the high-pressure generator 13, the low-pressure generator 14, the condenser 15, the absorber 16, the evaporator 17, the high-temperature solution heat exchanger 18, and the low-temperature solution heat exchanger 19 each have a cold-side fluid channel and a hot-side fluid channel that can form a heat exchange.

[0041] The hot-side fluid channel inlet of the high-pressure generator 13 is connected to the high-temperature heat source 34 of the flue gas via a pipeline, and the hot-side fluid channel outlet is connected to the outside via a pipeline. The solution outlet of the high-pressure generator 13 is connected to the hot-side fluid channel inlet of the high-temperature solution heat exchanger 18 via a pipeline. The hot-side fluid channel outlet of the high-temperature solution heat exchanger 18 is connected to the inlet of the first solution throttling valve 21 via a pipeline. The outlet of the first solution throttling valve 21 is connected to the solution inlet of the absorber 16 via a pipeline. The solution outlet of the low-pressure generator 14 is connected to the hot-side fluid channel inlet of the low-temperature solution heat exchanger 19 via a pipeline. The hot-side fluid channel outlet of the low-temperature solution heat exchanger 19 is connected to the inlet of the second solution throttling valve 22 via a pipeline. The outlet of the second solution throttling valve 22 is connected to the solution inlet of the absorber 16 via a pipeline. The solution outlet of the absorber 16 is connected to the inlet of the first solution pump 23 and the inlet of the second solution pump 24 via pipelines respectively. The outlet of the first solution pump 23 is connected to the cold-side fluid channel inlet of the high-temperature solution heat exchanger 18 via a pipeline. The cold-side fluid channel outlet of the high-temperature solution heat exchanger 18 is connected to the solution inlet of the high-pressure generator 13 via a pipe. The outlet of the second solution pump 24 is connected to the cold-side fluid channel inlet of the low-temperature solution heat exchanger 19 via a pipe. The cold-side fluid channel outlet of the low-temperature solution heat exchanger 19 is connected to the solution inlet of the low-pressure generator 14 via a pipe.

[0042] The steam outlet of the high-pressure generator 13 is connected to the hot-side fluid channel inlet of the low-pressure generator 14 via a pipe. The steam outlet of the low-pressure generator 14 is connected to the hot-side fluid channel inlet of the condenser 15 via a pipe. The condensate outlet of the low-pressure generator 14 is connected to the inlet of the first water throttling valve 20 via a pipe. The outlet of the first water throttling valve 20 is connected to the hot-side fluid channel inlet of the condenser 15 via a pipe. The hot-side fluid channel outlet of the condenser 15 is connected to the inlet of the second water throttling valve 25 via a pipe. The outlet of the second water throttling valve 25 is connected to the cold-side fluid channel inlet of the evaporator 17 via a pipe. The cold-side fluid channel outlet of the evaporator 17 is connected to the steam inlet of the absorber 16 via a pipe. The hot-side fluid channel inlet of the evaporator 17 is connected to an external low-temperature heat source 35 via a pipe.

[0043] The hot water circulation channel 36 passes through the cold side fluid channel of the absorber 16, the cold side fluid channel of the condenser 15, and the hot side fluid channel of the rich liquid preheater 5 in sequence, and then returns to the cold side fluid channel of the absorber 16, forming a closed loop.

[0044] In this embodiment, the lean and rich liquid heat exchanger 4 and the rich liquid preheater 5 installed in the carbon capture unit 101, and the condenser 15, evaporator 17, high-temperature solution heat exchanger 18 and low-temperature solution heat exchanger 19 installed in the heat pump unit 102, are preferably indirect heat exchangers. Indirect heat exchangers can be classified into shell-and-tube heat exchangers, tube-and-shell heat exchangers, plate heat exchangers, and spray heat exchangers, depending on the form of the heat exchange surface. In practical applications, one type can be selected according to the requirements.

[0045] Utilizing the above-mentioned biogas carbon capture system based on heat pump preheating of rich liquid, the present invention also provides an operating method, as follows: The system achieves low-energy carbon capture through the combined operation of carbon capture unit 101 and heat pump unit 102. Carbon capture unit 101 consumes heat from heat pump unit 102 and steam channel 31, absorbing and enriching CO2 and H2S in biogas. Heat pump unit 102 absorbs high-temperature waste heat from flue gas and low-temperature waste heat from the outside, outputting medium-temperature waste heat. Circulating water in hot water circulation channel 36 absorbs the heat output from the heat pump and enters the rich liquid preheater 5 to exchange heat with the rich liquid. Due to the decrease in flash evaporation temperature of the lean liquid in the lean-rich liquid heat exchanger 4, the outlet rich liquid temperature also decreases, thus the rich liquid can absorb the medium-temperature waste heat from the circulating water in the rich liquid preheater 5.

[0046] S1: The working process of carbon capture unit 101 is as follows: The lean liquid, after being cooled by the lean liquid cooler 2, enters from the lean liquid inlet at the top of the absorption tower 1. Inside the absorption tower 1, it undergoes heat and mass exchange with the biogas to be treated, which enters the absorption tower 1 through the biogas flow channel 26. The lean liquid absorbs CO2 and H2S from the biogas, resulting in rich liquid and treated biogas.

[0047] After treatment, the biogas is discharged through the biogas discharge channel 27. The rich liquor after absorbing CO2 and H2S is connected to the inlet of the rich liquor pump 3 through a pipeline, and driven by the rich liquor pump 3, it enters the lean-rich liquor heat exchanger 4 through the cold side fluid channel inlet. In the lean-rich liquor heat exchanger 4, it exchanges heat with the lean liquor from the lean liquor outlet of the flash tank 10, becoming a high-temperature rich liquor. The high-temperature rich liquor enters the rich liquor preheater 5, absorbs heat from the hot water circulation channel 36 to further increase its temperature, and then enters the desorption tower 6 through the rich liquor inlet. Under the purging of high-temperature steam entering through the gas phase inlet of the desorption tower 6, CO2 and H2S are desorbed. The desorbed CO2 and H2S and the purging steam are discharged through the gas phase outlet at the top of the desorption tower 6 and enter the regeneration gas condenser 7. The absorbent components in the gas phase are cooled and liquefied in the regeneration gas condenser 7, and discharged through the condensate outlet and returned to the desorption tower 6. The remaining gas components are discharged through the gas phase outlet of the regenerated gas condenser 7, enter the desulfurization reactor 9 through the gas phase inlet to remove H2S, and are collected through the carbon dioxide-rich gas phase outlet of the desulfurization reactor 9 via the carbon dioxide-rich flow channel 29. The rich H2S is collected through the hydrogen sulfide-rich gas phase outlet of the desulfurization reactor 9 via the hydrogen sulfide-rich flow channel 30. The desorbed absorbent solution is discharged from the liquid phase outlet at the bottom of the desorption tower 6 and enters the reboiler 8. The generated high-temperature steam enters the desorption tower 6 through the gas phase inlet at the bottom of the desorption tower 6 for purging. The remaining lean liquid enters the flash tank 10 for flash evaporation. The generated flash steam enters the compressor 11 through the steam outlet above the flash tank 10. After being compressed, it enters the desorption tower 6 through the gas phase inlet at the bottom of the desorption tower 6 for purging. The remaining lean liquid is discharged through the lean liquid outlet at the bottom of the flash tank 10 and is pumped by the lean liquid pump 12 into the hot side fluid channel inlet of the lean-rich liquid heat exchanger 4 to heat the rich liquid from the rich liquid outlet at the bottom of the absorption tower 1. After heat exchange, the lean solution is mixed with the absorbent solution replenished in absorbent replenishment channel 32 and then enters the lean solution cooler 2 to complete the cycle.

[0048] It should be noted that during operation, absorbent solution can be added to the system through absorbent replenishment channel 32 to ensure a stable absorbent solution concentration in the system and balance the circulation loss.

[0049] S2: The working process of the heat pump unit is as follows: The dilute solution is divided into two streams. One stream, pressurized by the first solution pump 23, enters the solution inlet of the high-pressure generator 13 through the cold-side fluid channel of the high-temperature solution heat exchanger 18. Inside the high-pressure generator 13, it exchanges heat with the high-temperature heat source 34 of the flue gas in the hot-side fluid channel, generating high-pressure steam and a high-pressure concentrated solution. The other stream, pressurized by the second solution pump 24, enters the solution inlet of the low-pressure generator 14 through the cold-side fluid channel of the low-temperature solution heat exchanger 19. The high-pressure steam enters the hot-side fluid channel of the low-pressure generator 14 through the steam outlet of the high-pressure generator 13. Inside the low-pressure generator 14, it exchanges heat with the dilute solution in the cold-side fluid channel, condensing the high-pressure steam into high-pressure condensate, and generating medium-pressure steam and a medium-pressure concentrated solution from the dilute solution. High-pressure condensate, throttled and depressurized by the first water throttling valve 20 through the condensate outlet of the low-pressure generator 14, enters the hot-side fluid channel of the condenser 15 together with medium-pressure steam through the steam outlet of the low-pressure generator 14. In the condenser 15, hot water is supplied to the cold-side fluid channel, releasing heat and forming medium-pressure condensate. The medium-pressure condensate enters the second water throttling valve 25, expands into low-pressure water, and then enters the cold-side fluid channel of the evaporator 17. There, it exchanges heat with the external low-temperature heat source 35 in the hot-side fluid channel, evaporating into low-pressure steam. The low-pressure steam enters the steam inlet of the absorber 16, completing the water circulation process.

[0050] The high-pressure concentrated solution enters the hot-side fluid channel of the high-temperature solution heat exchanger 18 through the solution outlet of the high-pressure generator 13. After exchanging heat with the dilute solution in the cold-side fluid channel, it enters the solution inlet of the absorber 16 through the first solution throttling valve 21. The medium-pressure concentrated solution enters the hot-side fluid channel of the low-temperature solution heat exchanger 19 through the solution outlet of the low-pressure generator 14. After exchanging heat with the dilute solution in the cold-side fluid channel, it enters the solution inlet of the absorber 16 through the second solution throttling valve 22. The concentrated solutions from the two sources are mixed and absorb low-pressure steam from the steam inlet in the absorber 16. At the same time, they exchange heat with the heating circulating water in the cold-side fluid channel to generate a dilute solution. The solution is split into two streams through the solution outlet of the absorber 16. One stream enters the cold-side fluid channel of the high-temperature solution heat exchanger 18 via the first solution pump 23. After exchanging heat with the high-pressure concentrated solution in the hot-side fluid channel, it enters the solution inlet of the high-pressure generator 13. The other stream enters the cold-side fluid channel of the low-temperature solution heat exchanger 19 via the second solution pump 24. After exchanging heat with the medium-pressure concentrated solution in the hot-side fluid channel, it enters the solution inlet of the low-pressure generator 14, completing the working fluid circulation.

[0051] S3: The working process of the hot water circulation channel 36 is as follows: Low-temperature hot water enters the cold-side fluid channel of absorber 16, absorbing heat from the concentrated solution and low-pressure steam to become medium-temperature hot water. The medium-temperature hot water then enters the cold-side fluid channel of condenser 15, absorbing the condensation heat of high-pressure steam to become high-temperature hot water. The high-temperature hot water then enters the hot-side fluid channel of rich liquid preheater 5, exchanging heat with the rich liquid to become low-temperature hot water, which then enters the cold-side fluid channel of absorber 16 through the hot-side fluid channel outlet, completing the cycle.

[0052] In summary, this invention provides a biogas carbon capture system based on heat pump preheating of rich liquor. It utilizes a dual-effect incremental heat pump to recover high-temperature waste heat from flue gas and low-temperature waste heat from the outside, increasing the temperature at the top of the desorption tower and enhancing the desorption of CO2 and H2S at the top of the absorption tower. This reduces the steam demand for the carbon capture system, thereby mitigating its impact on power plant efficiency. The system achieves low-energy carbon capture through the combined operation of the carbon capture unit and the heat pump unit. The carbon capture unit incorporates a lean liquor flash evaporation and recompression process, utilizing the latent heat of the lean liquor to generate additional steam while simultaneously reducing the temperature of the lean liquor and the temperature of the rich liquor at the outlet of the lean-rich liquor heat exchanger. The heat pump unit uses a generator driven by high-temperature waste heat from the flue gas, recovers low-temperature waste heat from the outside through an evaporator, and outputs medium-temperature waste heat through a condenser and absorber to heat the rich liquor at the outlet of the lean-rich liquor heat exchanger, increasing the temperature at the top of the desorption tower. Heat exchange between the carbon capture unit and the heat pump unit is achieved through circulating hot water supply.

[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A biogas carbon capture system based on heat pump preheating of rich liquid, characterized in that, The system includes a carbon capture unit, a heat pump unit, and a hot water circulation channel. The carbon capture unit comprises an absorption tower, a lean-rich liquid heat exchanger, a rich liquid preheater, a desorption tower, a desulfurization reactor, and a flash tank. The biogas inlet at the bottom of the absorption tower is connected to the biogas flow channel, and the biogas outlet at the top is connected to the biogas discharge channel. The rich liquid outlet at the bottom is connected to the cold-side fluid channel inlet of the lean-rich liquid heat exchanger via a rich liquid pump. The cold-side fluid channel outlet of the lean-rich liquid heat exchanger is connected to the cold-side fluid channel inlet of the rich liquid preheater, and the cold-side fluid channel outlet of the rich liquid preheater is connected to the rich liquid inlet of the desorption tower. The liquid phase outlet at the bottom of the desorption tower is connected to the cold-side fluid channel inlet of the reboiler, and both the hot-side fluid channel inlet and outlet of the reboiler are connected to the steam channel and form a loop. The heat pump unit includes a high-pressure generator, a low-pressure generator, a condenser, an absorber, an evaporator, a high-temperature solution heat exchanger, and a low-temperature solution heat exchanger. The inlet of the hot-side fluid channel of the high-pressure generator is connected to a high-temperature heat source in the flue gas; the outlet of the hot-side fluid channel is connected to the outside; the solution outlet is connected to the inlet of the hot-side fluid channel of the high-temperature solution heat exchanger; and the steam outlet is connected to the steam inlet of the low-pressure generator. The solution outlet of the low-pressure generator is connected to the inlet of the hot-side fluid channel of the low-temperature solution heat exchanger; the steam outlet is connected to the inlet of the hot-side fluid channel of the condenser; and the condensate outlet is connected to the inlet of the hot-side fluid channel of the condenser via a first water throttling valve. The outlet of the hot-side fluid channel of the high-temperature solution heat exchanger is connected to the solution inlet of the absorber via a first solution throttling valve. The cold-side fluid outlet of the condenser is connected to the solution inlet of the high-pressure generator; the hot-side fluid channel outlet of the low-temperature solution heat exchanger is connected to the solution inlet of the absorber via a second solution throttling valve, and the cold-side fluid outlet is connected to the solution inlet of the low-pressure generator; the solution outlet of the absorber is divided into two paths, one connected to the cold-side fluid channel inlet of the high-temperature solution heat exchanger via a first solution pump, and the other connected to the cold-side fluid channel inlet of the low-temperature solution heat exchanger via a second solution pump; the hot-side fluid channel outlet of the condenser is connected to the cold-side fluid channel inlet of the evaporator via a second water throttling valve; the cold-side fluid channel outlet of the evaporator is connected to the steam inlet of the absorber, the hot-side fluid channel inlet is connected to an external low-temperature heat source, and the hot-side fluid channel outlet is connected to the outside; The carbon capture unit is used to consume heat from the heat pump unit and the steam channel, and absorb and enrich carbon dioxide and hydrogen sulfide in the biogas in the biogas channel; the heat pump unit is used to recover the waste heat from the high-temperature heat source of the flue gas from the waste incineration power plant and the external low-temperature heat source, and output medium-temperature waste heat to the rich liquid preheater; the circulating water in the hot water circulation channel is used to absorb the heat output by the heat pump unit and enter the rich liquid preheater to exchange heat with the rich liquid inside.

2. The biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 1, characterized in that, The gas phase outlet at the top of the desorption tower is connected to the heat source inlet of the regenerated gas condenser; the inlet and outlet of the cold-side fluid channel of the regenerated gas condenser are both connected to the first cold source and form a loop; the condensate outlet is connected to the condensate inlet at the top of the desorption tower; and the gas phase outlet is connected to the gas phase inlet of the desulfurization reactor. The carbon dioxide-rich gas phase outlet of the desulfurization reactor is connected to the carbon dioxide-rich flow channel, and the hydrogen sulfide-rich gas phase outlet is connected to the hydrogen sulfide-rich flow channel. The gas phase product outlet of the reboiler is connected to the gas phase inlet at the bottom of the desorption tower, and the liquid phase product outlet is connected to the lean phase outlet of the flash tank. The liquid inlet is connected; the top steam outlet of the flash tank is connected to the compressor inlet, and the bottom lean liquid outlet is connected to the lean liquid pump inlet; the compressor outlet is connected to the gas phase inlet at the bottom of the desorption tower; the lean liquid pump outlet is connected to the hot-side fluid channel inlet of the lean-rich liquid heat exchanger, and the hot-side fluid channel outlet of the lean-rich liquid heat exchanger is connected to the lean liquid cooler inlet; the lean liquid cooler inlet is also connected to the absorbent replenishment channel, and both the cold-side fluid channel inlet and outlet are connected to the second cold source and form a loop, with the outlet connected to the lean liquid inlet at the top of the absorption tower.

3. A biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 2, characterized in that, The hot water circulation channel passes sequentially through the cold-side fluid channel of the absorber, the cold-side fluid channel of the condenser, and the hot-side fluid channel of the rich liquid preheater, before returning to the cold-side fluid channel of the absorber, forming a closed loop.

4. A biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 1, characterized in that, The steam source for the steam flow channel is the exhaust gas from the power plant's steam turbine.

5. A biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 1, characterized in that, Both the absorption tower and the desorption tower are packed distillation towers, and the internal packing is one of Raschig rings, Pall rings, stepped rings, arc saddle packing, rectangular saddle packing, corrugated packing, corrugated mesh packing or metal saddle ring packing.

6. A biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 1, characterized in that, The absorbent in the internal circulation path of the carbon capture unit is an inorganic alkaline solution or an organic amine solution.

7. A biogas carbon capture system based on heat pump preheating of rich liquid according to claim 1, characterized in that, The lean and rich liquid heat exchangers, rich liquid preheaters, condensers, evaporators, high-temperature solution heat exchangers, and low-temperature solution heat exchangers are all indirect wall heat exchangers.

8. A biogas carbon capture system based on heat pump preheating of rich liquid according to claim 1, characterized in that, The working fluid pair of the heat pump unit is lithium bromide aqueous solution-water.

9. A method for operating a biogas carbon capture system based on heat pump preheating of rich liquid as described in claim 3, characterized in that, Specifically as follows: S1: The operation method of the carbon capture unit is as follows: After being cooled by the lean liquid cooler, the lean liquid enters from the lean liquid inlet at the top of the absorption tower. Inside the absorption tower, it undergoes heat and mass exchange with the biogas to be treated, which enters the absorption tower through the biogas flow channel. During this process, the lean liquid absorbs carbon dioxide and hydrogen sulfide from the biogas, resulting in a rich liquid and treated biogas. The treated biogas is then discharged through the biogas discharge channel. The rich liquor, after absorbing carbon dioxide and hydrogen sulfide, is connected to the inlet of the rich liquor pump via a pipeline. Driven by the rich liquor pump, it enters the lean-rich liquor heat exchanger through the cold-side fluid channel inlet. Inside the heat exchanger, it exchanges heat with the lean liquor from the flash tank outlet, becoming a high-temperature rich liquor. This high-temperature rich liquor enters the rich liquor preheater, absorbing heat from the hot water circulation channel for further heating. It then enters the desorption tower through the rich liquor inlet, where it is purged by high-temperature steam entering through the desorption tower's gas phase inlet, desorbing carbon dioxide and hydrogen sulfide. The desorbed carbon dioxide and hydrogen sulfide, along with the purging steam, are discharged through the gas phase outlet at the top of the desorption tower and enter the regeneration gas condenser. The absorbent components in the gas phase are cooled and liquefied in the regeneration gas condenser and discharged through the condensate outlet, flowing back into the desorption tower. The remaining gas components are discharged through the gas phase outlet of the regeneration gas condenser and enter the desulfurization reactor through the gas phase inlet. After hydrogen sulfide is removed from the desulfurization reactor, the absorbent solution is collected through the carbon dioxide-rich gas phase outlet of the desulfurization reactor via the carbon dioxide-rich flow channel, while the hydrogen sulfide-rich solution is collected through the hydrogen sulfide-rich gas phase outlet of the desulfurization reactor via the hydrogen sulfide-rich flow channel. The desorbed absorbent solution is discharged from the liquid phase outlet at the bottom of the desorption tower and enters the reboiler. The high-temperature steam generated in the reboiler returns to the desorption tower from the gas phase inlet at the bottom of the desorption tower for purging. The remaining lean liquid in the reboiler enters the flash tank for flash evaporation. The generated flash steam enters the compressor through the steam outlet at the top of the flash tank. After being compressed, it enters the desorption tower from the gas phase inlet at the bottom of the desorption tower for purging. The remaining lean liquid in the flash tank is discharged through the lean liquid outlet at the bottom and pumped into the hot-side fluid channel inlet of the lean-rich liquid heat exchanger to heat the rich liquid from the rich liquid outlet at the bottom of the absorption tower. The heat-exchanged lean liquid is mixed with the absorbent solution replenished by the absorbent replenishment flow channel and then enters the lean liquid cooler to complete the cycle. S2: The operation method of the heat pump unit is as follows: The dilute solution in the absorber flows out in two streams. The first stream of dilute solution is pressurized by the first solution pump and enters the solution inlet of the high-pressure generator from the cold side fluid channel of the high-temperature solution heat exchanger. In the high-pressure generator, it exchanges heat with the high-temperature heat source of the flue gas in the hot side fluid channel to generate high-pressure steam and high-pressure concentrated solution. The second dilute solution, pressurized by the second solution pump, enters the solution inlet of the low-pressure generator from the cold-side fluid channel of the low-temperature solution heat exchanger. The high-pressure steam enters the hot-side fluid channel of the low-pressure generator through the steam outlet of the high-pressure generator, where it exchanges heat with the dilute solution in the cold-side fluid channel. The high-pressure steam condenses into high-pressure condensate, and the dilute solution generates medium-pressure steam and a medium-pressure concentrated solution. The high-pressure condensate, through the condensate outlet of the low-pressure generator, is throttled and depressurized by the first water throttling valve, and enters the hot-side fluid channel of the condenser along with the medium-pressure steam through the steam outlet of the low-pressure generator. In the condenser, it releases heat by supplying hot water to the circulating cold-side fluid channel, forming medium-pressure condensate. The medium-pressure condensate enters the second water throttling valve, expands into low-pressure water, and then enters the cold-side fluid channel of the evaporator, where it interacts with the solution in the hot-side fluid channel. An external low-temperature heat source undergoes heat exchange, evaporating into low-pressure steam. The low-pressure steam enters the steam inlet of the absorber, completing the water working fluid circulation. The high-pressure concentrated solution enters the hot-side fluid channel of the high-temperature solution heat exchanger through the solution outlet of the high-pressure generator, exchanges heat with the dilute solution in the cold-side fluid channel, and then enters the solution inlet of the absorber through the first solution throttling valve. The medium-pressure concentrated solution enters the hot-side fluid channel of the low-temperature solution heat exchanger through the solution outlet of the low-pressure generator, exchanges heat with the dilute solution in the cold-side fluid channel, and then enters the solution inlet of the absorber through the second solution throttling valve. The high-pressure and low-pressure concentrated solutions from the two paths mix, absorb the low-pressure steam from the steam inlet in the absorber, and simultaneously exchange heat with the heating circulating water in the cold-side fluid channel to generate a dilute solution, which flows out in two paths through the solution outlet of the absorber. The first solution enters the cold-side fluid channel of the high-temperature solution heat exchanger via the first solution pump. After exchanging heat with the high-pressure concentrated solution in the hot-side fluid channel, it enters the solution inlet of the high-pressure generator. The second solution enters the cold-side fluid channel of the low-temperature solution heat exchanger via the second solution pump. After exchanging heat with the medium-pressure concentrated solution in the hot-side fluid channel, it enters the solution inlet of the low-pressure generator to complete the working fluid circulation. S3: The operation method of the hot water circulation channel is as follows: Low-temperature hot water enters the absorber through the cold-side fluid channel, absorbing the heat generated when the concentrated solution absorbs low-pressure steam, becoming medium-temperature hot water. The medium-temperature hot water enters the condenser through the cold-side fluid channel, absorbing the condensation heat of the high-pressure steam, becoming high-temperature hot water. The high-temperature hot water enters the rich liquid preheater through the hot-side fluid channel, exchanging heat with the rich liquid to become low-temperature hot water, and then enters the cold-side fluid channel of the absorber through the hot-side fluid channel outlet, completing the cycle.

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