A method for recovering waste heat from an alcohol amine method co2 capture system based on a high-temperature heat pump

Abstract

The present application belongs to the field of carbon capture and energy saving technology, solves the problem of low comprehensive thermal efficiency and large steam consumption of the existing alcohol amine solution absorption method, and discloses a waste heat recovery and utilization method of an alcohol amine method CO2 capture system based on a high-temperature heat pump, wherein a heat exchanger is used to preheat the rich liquid discharged from an absorption tower, and the heat source of the heat exchanger is the lean liquid discharged from a desorption tower; after the lean liquid flows through the heat exchanger, it is sent to a heat pump evaporation unit for secondary extraction of heat, and then returned to the absorption tower; after the rich liquid flows through the heat exchanger, it is sent to the desorption tower for heating, and the heat pump evaporation unit provides the heat required for heating the desorption tower. The present application greatly reduces external steam consumption, uses the heat pump evaporation unit to improve the waste heat of the lean liquid to a temperature that can be directly used for desorption, replaces traditional steam heating, and reduces the unit CO2 regeneration heat consumption by 40% to 50%; realizes energy closed loop in the system, reduces cooling water consumption and has low implementation difficulty.

Description

Technical Field

[0001] This invention belongs to the field of carbon capture and energy-saving technology, specifically relating to a waste heat recovery and utilization method for an alcohol amine method CO2 capture system based on a high-temperature heat pump. Background Technology

[0002] Alkylamine solution absorption is one of the most mature technologies for CO2 capture in industry, and it is widely used in flue gas treatment processes in coal-fired power plants, cement plants, steel plants, etc.

[0003] In this process, the rich liquor (referring to the amine solution after absorbing CO2, which absorbs CO2 in the absorption tower) needs to be heated to 100–130°C in the desorption tower to achieve CO2 regeneration (the rich liquor releases CO2 upon heating in the desorption tower, regenerating into a lean liquor, i.e., the amine solution). Traditionally, high-temperature steam (>150°C) is used as the heat source. Meanwhile, the lean liquor discharged from the bottom of the desorption tower still retains a residual heat temperature of 80–95°C. Therefore, directly discharging the lean liquor would result in a significant waste of low-grade heat energy.

[0004] In summary, the existing technology for CO2 capture using alkanolamine solution absorption has the following shortcomings: 1. The overall thermal efficiency of the capture system is low, and steam consumption accounts for more than 60% of the operating cost; 2. There is a lack of efficient and stable waste heat upgrading and coupled utilization schemes. Summary of the Invention

[0005] In view of the problems of low overall thermal efficiency and high steam consumption in existing technologies, the purpose of this invention is to provide a waste heat recovery and utilization method for an alcohol amine CO2 capture system based on a high-temperature heat pump, so as to improve the overall thermal efficiency of the alcohol amine CO2 capture system and replace or partially replace traditional steam heating, significantly reduce the external energy consumption of the CO2 desorption process, and make the operation of the entire CO2 capture system more energy-efficient and environmentally friendly.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for waste heat recovery and utilization in an alcohol amine method CO2 capture system based on a high-temperature heat pump includes the following: (1) A heat exchanger is used to preheat the rich liquid discharged from the absorption tower. The heat source used in the heat exchanger is the lean liquid discharged from the desorption tower. (2) After the lean liquid flows through the heat exchanger, it is sent to the heat pump evaporation unit for secondary heat extraction, and then returned to the absorption tower; (3) After the rich liquid flows through the heat exchanger, it is sent to the desorption tower for heating. The heat pump evaporation unit provides the heat required for heating the desorption tower.

[0007] In this invention, the lean liquid absorbs CO2 in the absorption tower and is converted into a rich liquid. The rich liquid discharged from the absorption tower is preheated by a heat exchanger and then enters the desorption tower to be heated to 100-130°C to release the CO2. The temperature of the lean liquid discharged from the desorption tower is 80-95°C. To avoid wasting the heat from the lean solution, before sending it to the absorption tower for CO2 reabsorption, First, the lean liquid flows through a heat exchanger to preheat the rich liquid discharged from the absorption tower; Secondly, the lean liquor enters the heat pump evaporation unit for secondary heat extraction. The heat extracted by the heat pump evaporation unit is used to heat the desorption tower. After heat extraction, the temperature of the lean liquor drops to 50-65℃. In this way, by recycling the residual heat, the amount of steam used can be greatly reduced, and the energy saving rate can reach 40% to 50%. Moreover, this method is highly adaptable. In the existing amine solution absorption method, only the addition of a heat pump evaporation unit and the adjustment of the pipeline are required. The heat pump evaporation unit can be driven by green electricity, which can further reduce the net emissions of CO2 capture.

[0008] As a preferred technical solution of the present invention, the heat pump evaporation unit The heat from the lean liquor is extracted through the evaporator, and the working medium is heated and vaporized. The working medium is compressed by a compressor to pressurize and heat it. The heat of the working medium is transferred to the desorption tower through the condenser, which serves as the heat for heating the rich liquid. The pressure and temperature of the working medium are reduced by the expansion valve, and the working medium is released by the expansion valve and then flows back to the evaporator.

[0009] This invention transfers heat from the lean liquor to the working medium via an evaporator, causing the working medium to heat up and vaporize. The vaporized working medium is then compressed by a compressor, further heating and pressurizing it. The temperature of the compressed working medium can reach over 120°C, meeting the temperature requirements of the desorption tower for heating the rich liquor. The condenser is connected to the reboiler or heating coil inlet at the bottom of the desorption tower to achieve heat transfer. After heat transfer, the working medium is released through an expansion valve, depressurized and cooled, and returns to the evaporator to await the next cycle.

[0010] In some optional instances, the working medium is R1336mzz(Z), R1224yd(Z), or R600.

[0011] As a preferred technical solution of the present invention, electric heating and / or steam heating are used when the system is started up or when the heat pump evaporation unit is insufficient to provide heat.

[0012] The beneficial effects of this invention are: 1. Significantly reduces external steam consumption by using a heat pump evaporation unit to raise the waste heat of the originally discarded lean liquor to a temperature that can be directly used for desorption, replacing traditional steam heating, and reducing the unit CO2 regeneration heat consumption by 40%-50%; 2. Achieve closed-loop energy circulation within the system: lean liquid waste heat – heat exchanger, heat pump evaporation unit – desorption heat source, forming a heat self-circulation and reducing cooling water consumption; 3. The heat pump evaporation unit can be driven by green electricity, further reducing net CO2 emissions from CO2 capture; 4. The implementation is simple; it only requires adding a heat pump evaporation unit and adjusting the pipeline in the existing amine solution absorption method. Attached Figure Description

[0013] The present invention can be further illustrated by the non-limiting embodiments given in the accompanying drawings; Figure 1 This is a schematic diagram illustrating the principle of an embodiment of the present invention. Detailed Implementation

[0014] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein. Example

[0015] like Figure 1 As shown, this embodiment provides a method for waste heat recovery and utilization in an alcohol amine method CO2 capture system based on a high-temperature heat pump. Steam heating is used to supply the start-up heat for the CO2 capture system; The rich liquor discharged from the absorption tower is preheated by a heat exchanger and then enters the desorption tower. After being heated to release CO2, it is regenerated into lean liquor. The lean liquid at the bottom of the desorption tower is 85°C. It flows through the heat exchanger and the heat pump evaporation unit in sequence. After two cooling processes, the temperature drops to 55°C and returns to the absorption tower to wait for CO2 to be reabsorbed. The evaporator absorbs the waste heat of the lean liquid, and the R1336mzz(Z) working medium is heated and vaporized. It is then pressurized and heated to 130°C by the compressor, and the heat is released in the condenser to heat the desorption tower. Finally, the heat is released through the expansion valve, the temperature and pressure are reduced, and it flows back to the evaporator to wait for the next cycle.

[0016] This embodiment utilizes a heat pump evaporation unit to raise the waste heat of the originally discarded lean liquor to a temperature that can be directly used for desorption, significantly reducing external steam consumption and reducing the unit CO2 regeneration heat consumption by 40% to 50%. Throughout the process, the energy loop within the system is achieved, with the waste heat from the lean liquid flowing into the heat exchanger and heat pump evaporation unit, which then desorbs the heat source, forming a self-circulating heat system and reducing the consumption of cooling water (which is needed to provide steam). The entire method is easy to implement; it only requires adding a heat pump evaporation unit and adjusting the pipeline in the existing amine solution absorption method.

[0017] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for waste heat recovery and utilization in an alcohol amine CO2 capture system based on a high-temperature heat pump, characterized in that: Includes the following: (1) A heat exchanger is used to preheat the rich liquid discharged from the absorption tower. The heat source used in the heat exchanger is the lean liquid discharged from the desorption tower. (2) After the lean liquid flows through the heat exchanger, it is sent to the heat pump evaporation unit for secondary heat extraction, and then returned to the absorption tower; (3) After the rich liquid flows through the heat exchanger, it is sent to the desorption tower for heating. The heat pump evaporation unit provides the heat required for heating the desorption tower.

2. The waste heat recovery and utilization method of an alcohol amine method CO2 capture system based on a high-temperature heat pump according to claim 1, characterized in that: The heat pump evaporation unit The heat from the lean liquor is extracted through the evaporator, and the working medium is heated and vaporized. The working medium is compressed by a compressor to pressurize and heat it. The heat of the working medium is transferred to the desorption tower through the condenser, which serves as the heat for heating the rich liquid. The pressure and temperature of the working medium are reduced by the expansion valve, and the working medium is released by the expansion valve and then flows back to the evaporator.

3. The waste heat recovery and utilization method of an alcohol amine method CO2 capture system based on a high-temperature heat pump according to claim 2, characterized in that: The working medium is compressed by the compressor and its temperature is above 120℃.

4. The waste heat recovery and utilization method of an alcohol amine method CO2 capture system based on a high-temperature heat pump according to claim 1, characterized in that: When the system starts up and the heat pump evaporator unit provides insufficient heat, Electric heating and / or steam heating are used.

5. A CO2 generation method based on a high-temperature heat pump using an alcohol amine process according to claim 1 The method for recovering and utilizing waste heat from a heat capture system is characterized by: The temperature of the lean liquor discharged from the desorption tower is between 80 and 95°C; after the lean liquor undergoes secondary heat extraction by the heat pump evaporation unit, the temperature is between 50 and 65°C.

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