Carbon capture system coupled with steel process waste heat

Abstract

The utility model discloses a carbon capture system coupled with steel process waste heat. The system comprises a heat pump, an absorption tower and a desorption tower, a flue gas inlet of the absorption tower is communicated with a raw flue gas conveying pipeline, a liquid outlet of the absorption tower is communicated with a liquid inlet of the desorption tower through a first absorbent circulating pipeline, and a liquid outlet of the desorption tower is communicated with a liquid inlet of the absorption tower through a second absorbent circulating pipeline. And a first heat exchanger is also arranged on the first absorbent circulating pipeline. The first absorbent circulating pipeline is connected with a hot working medium circulating pipeline of the heat pump through the first heat exchanger. And a cold working medium circulating pipeline of the heat pump is connected with the raw flue gas conveying pipeline through the second heat exchanger. According to the system, through phase change circulation of a working medium in the heat pump, double effects are achieved, the flue gas temperature is reduced, the pretreatment cost of flue gas before the flue gas enters the absorption tower is reduced, meanwhile, flue gas waste heat is recycled, rich liquid is preheated, and the overall energy consumption of the system is reduced.

Description

Technical Field

[0001] This utility model relates to a carbon capture system, specifically a carbon capture system coupled with waste heat from steelmaking processes, and belongs to the field of carbon capture technology. Background Technology

[0002] The steel industry is a major carbon emitter, ranking highest among manufacturing sectors. Steelmakers bear primary responsibility for emissions reduction. For steelmaking processes reliant on fossil fuels, end-of-pipe carbon emissions monitoring (CCUS) is an indispensable part of emissions reduction.

[0003] CO2 emissions from the iron and steel metallurgical process are concentrated in the ironmaking and pre-ironmaking stages, where flue gas temperatures range from 130-200℃, making waste heat recovery economically unfeasible. Steel plants typically release the emissions directly after pollution reduction treatment. However, for a CCUS (Carbon Capture System), the flue gas temperature needs to be reduced to around 40℃ to ensure efficient CO2 adsorption or absorption. This usually requires additional pretreatment methods like spraying to lower the temperature, increasing carbon capture costs. Heat pump technology is the preferred technology for achieving both flue gas cooling and waste heat recovery. It reduces pretreatment costs through heat transfer while providing heat for subsequent carbon capture and separation. The iron and steel process itself also contains a large amount of surplus low-grade waste heat resources, which are inefficient for power generation. This waste heat can be transferred to the carbon capture system to reduce capture energy consumption.

[0004] Among domestic and international carbon capture technologies, the most mature and commercially widely used is the chemical absorption method, represented by organic amine absorption. However, it still suffers from high desorption energy consumption and high operating costs, which greatly limits its engineering application and promotion. The iron and steel metallurgical process has abundant waste heat resources; therefore, coupling carbon capture systems with low-grade waste heat from steelmaking is a preferred strategy for low-cost carbon reduction in the steel industry.

[0005] Existing technical solutions such as Figure 2 After pretreatment such as front-end desulfurization and cooling, the flue gas temperature is reduced to about 40℃ before entering the absorption tower. The absorption tower is a packed spray type, where the flue gas and absorbent liquid come into countercurrent contact. CO2 in the flue gas is selectively absorbed and separated. The decarbonized flue gas is discharged from the top of the absorption tower, while the carbon-rich absorbent liquid is discharged from the bottom. The carbon-rich liquid is pumped by a rich liquid pump to exchange heat with the high-temperature carbon-lean liquid at the bottom of the tower, and then enters the top of the desorption tower. Inside the desorption tower, the carbon-rich liquid is heated by a reboiler, desorbing CO2 gas. After complete desorption, it enters the bottom of the tower and is pumped back to the absorption tower for circulation by a lean liquid pump. The overall energy consumption level of this scheme is 3.5-3.9 GJ / t CO2, and the capture cost reaches 250-500 yuan / t CO2, which is relatively high.

[0006] In existing technologies, the overall energy consumption level is not considered from a system perspective, and the effect during actual operation is uncertain. When recovering and utilizing waste heat steam, the waste heat utilization efficiency is low, and the recovered waste heat steam does not achieve the maximum economic benefits. Utility Model Content

[0007] To address the problems of low waste heat utilization efficiency, high system operating costs, and failure to maximize the economic benefits of recovered waste heat steam in existing technologies, this invention proposes a carbon capture system coupled with waste heat from steel processes. The system uses a heat pump to absorb the heat from the high-temperature flue gas in front of the absorption tower, reducing the flue gas temperature and transferring the heat to the subsequent desorption section, thereby reducing pretreatment costs and system heat consumption.

[0008] According to the embodiments of this utility model, a carbon capture system coupled with waste heat from steelmaking processes is provided.

[0009] A carbon capture system coupled with waste heat from a steelmaking process includes a heat pump, an absorption tower, and a desorption tower. The flue gas inlet of the absorption tower is connected to the original flue gas delivery pipeline. The liquid outlet of the absorption tower is connected to the liquid inlet of the desorption tower via a first absorbent circulation pipeline, and the liquid outlet of the desorption tower is connected to the liquid inlet of the absorption tower via a second absorbent circulation pipeline. A first heat exchanger is also installed on the first absorbent circulation pipeline. The first absorbent circulation pipeline is connected to the hot working fluid circulation pipeline of the heat pump via the first heat exchanger. The cold working fluid circulation pipeline of the heat pump is connected to the original flue gas delivery pipeline via the second heat exchanger.

[0010] Preferably, a third heat exchanger is also installed on the first absorbent circulation pipe upstream of the first heat exchanger, according to the flow direction of the liquid. The first absorbent circulation pipe is connected to the second absorbent circulation pipe through the third heat exchanger. The third heat exchanger is an indirect heat exchanger.

[0011] Preferably, the heat pump further includes a compressor and an expansion valve. The working fluid outlet of the compressor is connected to the working fluid inlet of the expansion valve via a hot working fluid circulation pipe. The working fluid outlet of the expansion valve is connected to the working fluid inlet of the compressor via a cold working fluid circulation pipe.

[0012] Preferably, the first heat exchanger and / or the second heat exchanger are indirect heat exchangers.

[0013] Preferably, the second heat exchanger is a shell-and-tube heat exchanger or a wall-and-tube heat exchanger.

[0014] Preferably, the first heat exchanger is a coil-type gas-liquid heat exchanger.

[0015] Preferably, the system also includes a reboiler. The reboiler exchanges heat with the desorption tower via steam heat exchange pipes inside the desorption tower. The steam inlet of the reboiler is connected to a steam source.

[0016] Preferably, the steam inlet of the reboiler is equipped with a steam temperature detection device and a steam flow detection device.

[0017] Preferably, the original flue gas conveying pipeline and / or the first absorbent circulation pipeline and / or the second absorbent circulation pipeline are equipped with a temperature detection device and a flow detection device.

[0018] Preferably, the system further includes a flue gas treatment device, and the flue gas outlet of the desorption tower is connected to the flue gas treatment device through a flue gas exhaust pipe.

[0019] Preferably, the system also includes a chimney. The flue gas treatment device is connected to the chimney via a flue gas emission duct.

[0020] Preferably, a rich liquid transfer pump is installed on the first absorbent circulation pipeline.

[0021] Preferably, a lean solution delivery pump is installed on the second absorbent circulation pipeline.

[0022] In this invention, since the flue gas temperature in key steelmaking processes is concentrated between 130 and 200°C, it needs to be cooled to around 40°C before entering the absorption tower to meet the operating requirements of the absorbent. This system places a second heat exchanger on the original flue gas conveying pipeline. The flue gas cools down after exchanging heat with the working fluid before entering the absorption tower, while the heated working fluid is sent to the first heat exchanger to heat the rich liquid discharged from the absorption tower. This reduces the temperature of the flue gas in the process to meet the temperature requirements for carbon capture, and also allows the recovered waste heat to be used for preheating the rich liquid, improving waste heat utilization and reducing heat loss. Preferably, based on the reverse Carnot cycle principle, the unit is driven by a small amount of electricity. The working fluid in the heat pump undergoes a phase change cycle, absorbing, compressing, and heating low-grade heat energy for utilization. The second heat exchanger contains a low-temperature, low-pressure working fluid, while the external environment contains process flue gas. Driven by the temperature difference, heat exchange occurs. The working fluid absorbs sensible heat from the flue gas and undergoes a phase change, carrying away heat and lowering its temperature to the absorbent's collection temperature. The working fluid, having recovered heat and undergone a phase change, is drawn into the compressor. The compressor's work transforms the working fluid into a high-temperature, high-pressure medium. This high-temperature, high-pressure medium enters the first heat exchanger, heating the rich liquid. Then, after passing through a throttling device (expansion valve, etc.), it becomes a low-temperature, low-pressure working fluid again, returning to the second heat exchanger for the next cycle. The working fluid is a liquid that can evaporate before absorbing heat and liquefy before releasing heat, such as supercritical CO2 or fluoroalkane. This invention employs a reverse Carnot cycle, fully utilizing the large temperature difference between the heat source and cold source, resulting in high efficiency and facilitating the full utilization of waste heat from the flue gas.

[0023] In this invention, since the desorption temperature of CO2 in the desorption tower is higher than 110℃, the temperature of the CO2-free absorbent (i.e., lean liquid) discharged from the desorption tower is also relatively high. A third heat exchange device is installed on the first absorbent circulation pipeline to preheat the rich liquid using the lean liquid discharged from the desorption tower. Because the temperature of the lean liquid is relatively low, and the temperature of the working fluid in the first heat exchanger can be changed by controlling the work done by the heat pump, the third heat exchanger is located upstream of the first heat exchanger on the first absorbent circulation pipeline for primary preheating, while the first heat exchanger performs secondary preheating of the rich liquid.

[0024] In this invention, low-grade waste heat (flue gas at <300℃, low-quality steam generated from high-temperature slag) generated by processes such as steel production is transported to the reboiler to provide heat for raising the temperature of the rich liquid in the desorption tower.

[0025] In this invention, a flow detection device and a temperature detection device are provided. By detecting the temperature and flow rate of the rich liquid in the first absorbent circulation pipe, and then based on the temperature and flow rate of the lean liquid in the original flue gas conveying pipe and the second absorbent circulation pipe, the flow rate of the high-temperature medium in the reboiler and the power of the heat pump compressor are controlled to achieve precise control of the rich liquid temperature and efficient utilization of waste heat. Preferably, the heating ratio of the rich liquid by the heat pump compressor power and the gas flow rate in the reboiler is further controlled by calculating the thermal efficiency of heating the rich liquid. The optimal process temperature point for system thermal efficiency is sought based on the power consumption per unit temperature change. Combined with the type and price of input energy, the optimal process temperature point for system cost is obtained.

[0026] In this invention, the rich liquor undergoes multiple preheating processes before entering the desorption tower, in the following order: the rich liquor is preheated for the first time using the lean liquor discharged from the desorption tower, preheated for the second time using a heat pump, and finally heated for the third time using a reboiler, so that the temperature of the rich liquor meets the desorption requirements.

[0027] In this invention, low-grade waste heat (flue gas waste heat with a flue gas temperature <300℃ or difficult-to-recover sensible heat waste heat) is recovered through waste heat boilers, vaporization cooling, etc., to form low-grade waste heat steam (saturated steam with a pressure less than 5kg, which has low efficiency for power generation but can be used for desorption heating in carbon capture systems). This steam is then added to the reboiler of the desorption tower in the carbon capture system, reducing carbon capture energy consumption. Part of the steam in the reboiler comes from low-grade waste heat steam from the main steelmaking processes, such as waste heat steam from converters, circuits, and rolling mill heating furnaces.

[0028] In this invention, the first heat exchanger is a coil-type gas-liquid heat exchanger, with a high-temperature and high-pressure working fluid inside and an absorbent-rich liquid outside. The waste heat from the flue gas recovered by the heat pump is directly used to heat the absorbent-rich liquid, rather than indirectly through steam, thereby improving thermal efficiency.

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

[0030] 1. The present invention provides a carbon capture system coupled with waste heat from steelmaking processes. Through the phase change circulation of the working fluid in the heat pump, it achieves a dual effect: reducing the flue gas temperature, thereby reducing the pretreatment cost of the flue gas before it enters the absorption tower; and simultaneously recovering the waste heat from the flue gas and preheating the rich liquid, thereby reducing the overall energy consumption of the system.

[0031] 2. The present invention provides a carbon capture system coupled with waste heat from steelmaking processes, which utilizes lean liquor and CO2 discharged from the desorption tower and transports low-grade waste heat generated by steelmaking and other processes to the reboiler, thereby achieving efficient utilization of various waste heat resources.

[0032] 3. The present invention provides a carbon capture system for coupled steelmaking process waste heat. When multiple waste heat utilization methods are used in combination in the system, the system optimizes the overall thermal efficiency of the system or reduces the overall cost of the system by comprehensively calculating the thermal efficiency of each heating method and controlling the heating ratio of the heat pump and reboiler to the rich liquid. Attached Figure Description

[0033] Figure 1 This utility model provides a structural schematic diagram of a carbon capture system that couples waste heat from a steelmaking process.

[0034] Figure 2 This is a schematic diagram of the structure of an existing carbon capture system.

[0035] Figure 3 A schematic diagram of the structure of a heat pump in a carbon capture system that couples waste heat from a steelmaking process, provided by this utility model.

[0036] Reference numerals: 1: Heat pump; 101: Compressor; 102: Expansion valve; 2: Absorber tower; 3: Desorption tower; 4: First heat exchanger; 5: Second heat exchanger; 6: Third heat exchanger; 7: Reboiler; 8: Flue gas treatment device; 9: Chimney; 10: Rich liquor transfer pump; 11: Lean liquor transfer pump; G: Raw flue gas transfer pipeline; G1: First absorbent circulation pipeline; G2: Second absorbent circulation pipeline; G3: Hot working medium circulation pipeline; G4: Cold working medium circulation pipeline; G5: Flue gas exhaust pipeline; G6: Flue gas emission pipeline. Detailed Implementation

[0037] The technical solution of this utility model is illustrated below. The scope of protection of this utility model includes, but is not limited to, the following embodiments.

[0038] According to the embodiments of this utility model, a carbon capture system coupled with waste heat from steelmaking processes is provided.

[0039] A carbon capture system coupled with waste heat from a steelmaking process includes a heat pump 1, an absorption tower 2, and a desorption tower 3. The flue gas inlet of the absorption tower 2 is connected to the original flue gas conveying pipeline G. The liquid outlet of the absorption tower 2 is connected to the liquid inlet of the desorption tower 3 via a first absorbent circulation pipeline G1. The liquid outlet of the desorption tower 3 is connected to the liquid inlet of the absorption tower 2 via a second absorbent circulation pipeline G2. A first heat exchanger 4 is also installed on the first absorbent circulation pipeline G1. The first absorbent circulation pipeline G1 is connected to the hot working fluid circulation pipeline G3 of the heat pump 1 via the first heat exchanger 4. The cold working fluid circulation pipeline G4 of the heat pump 1 is connected to the original flue gas conveying pipeline G via a second heat exchanger 5.

[0040] Preferably, a third heat exchanger 6 is also provided on the first absorbent circulation pipe G1 located upstream of the first heat exchanger 4, according to the flow direction of the liquid. The first absorbent circulation pipe G1 is connected to the second absorbent circulation pipe G2 through the third heat exchanger 6. The third heat exchanger 6 is an indirect heat exchanger.

[0041] Preferably, the heat pump 1 further includes a compressor 101 and an expansion valve 102. The working fluid outlet of the compressor 101 is connected to the working fluid inlet of the expansion valve 102 via a hot working fluid circulation pipe G3. The working fluid outlet of the expansion valve 102 is connected to the working fluid inlet of the compressor 101 via a cold working fluid circulation pipe G4.

[0042] Preferably, the first heat exchanger 4 and / or the second heat exchanger 5 are indirect heat exchangers.

[0043] Preferably, the second heat exchanger 5 is a shell-and-tube heat exchanger.

[0044] Preferably, the first heat exchanger 4 is a coil-type gas-liquid heat exchanger.

[0045] Preferably, the system also includes a reboiler 7. The reboiler 7 exchanges heat with the desorption tower 3 through a steam heat exchange pipe inside the desorption tower 3. The steam inlet of the reboiler 7 is connected to a steam source.

[0046] Preferably, the steam inlet of the reboiler 7 is equipped with a steam temperature detection device and a steam flow detection device.

[0047] Preferably, the original flue gas conveying pipeline G and / or the first absorbent circulation pipeline G1 and / or the second absorbent circulation pipeline G2 are equipped with a temperature detection device and a flow detection device.

[0048] Preferably, the system further includes a flue gas treatment device 8, and the flue gas outlet of the desorption tower 3 is connected to the flue gas treatment device 8 through a flue gas exhaust pipe G5.

[0049] Preferably, the system also includes a chimney 9. The flue gas treatment device 8 is connected to the chimney 9 via a flue gas emission pipe G6.

[0050] Preferably, a rich liquid transfer pump 10 is provided on the first absorbent circulation pipeline G1.

[0051] Preferably, a lean liquid transfer pump 11 is provided on the second absorbent circulation pipeline G2. Example 1

[0052] A carbon capture system coupled with waste heat from a steelmaking process includes a heat pump 1, an absorption tower 2, and a desorption tower 3. The flue gas inlet of the absorption tower 2 is connected to the original flue gas conveying pipeline G. The liquid outlet of the absorption tower 2 is connected to the liquid inlet of the desorption tower 3 via a first absorbent circulation pipeline G1. The liquid outlet of the desorption tower 3 is connected to the liquid inlet of the absorption tower 2 via a second absorbent circulation pipeline G2. A first heat exchanger 4 is also installed on the first absorbent circulation pipeline G1. The first absorbent circulation pipeline G1 is connected to the hot working fluid circulation pipeline G3 of the heat pump 1 via the first heat exchanger 4. The cold working fluid circulation pipeline G4 of the heat pump 1 is connected to the original flue gas conveying pipeline G via a second heat exchanger 5. Example 2

[0053] The embodiment 1 is repeated, except that, according to the flow direction of the liquid, a third heat exchanger 6 is also provided on the first absorbent circulation pipe G1 located upstream of the first heat exchanger 4. The first absorbent circulation pipe G1 is connected to the second absorbent circulation pipe G2 through the third heat exchanger 6. The third heat exchanger 6 is an indirect heat exchanger. Example 3

[0054] The embodiment 2 is repeated, except that the heat pump 1 further includes a compressor 101 and an expansion valve 102. The working fluid outlet of the compressor 101 is connected to the working fluid inlet of the expansion valve 102 through a hot working fluid circulation pipe G3. The working fluid outlet of the expansion valve 102 is connected to the working fluid inlet of the compressor 101 through a cold working fluid circulation pipe G4. Example 4

[0055] Example 3 is repeated, except that the second heat exchanger 5 is a partition wall heat exchanger, and the first heat exchanger 4 is a coil-type gas-liquid heat exchanger. Example 5

[0056] The system repeats Example 4, except that it also includes a reboiler 7. The reboiler 7 exchanges heat with the desorption tower 3 through a steam heat exchange pipe inside the desorption tower 3. The steam inlet of the reboiler 7 is connected to a steam source. Example 6

[0057] Example 5 is repeated, except that the steam inlet of the reboiler 7 is equipped with a steam temperature detection device and a steam flow detection device. Example 7

[0058] Example 6 is repeated, except that the original flue gas conveying pipeline G, the first absorbent circulation pipeline G1, and the second absorbent circulation pipeline G2 are equipped with temperature detection devices and flow detection devices. Example 8

[0059] The same as Embodiment 7 is repeated, except that the system also includes a flue gas treatment device 8, and the flue gas outlet of the desorption tower 3 is connected to the flue gas treatment device 8 through a flue gas exhaust pipe G5. Example 9

[0060] The system is a repeat of embodiment 8, except that it also includes a chimney 9. The flue gas treatment device 8 is connected to the chimney 9 via a flue gas emission pipe G6. Example 10

[0061] Example 9 is repeated, except that a rich solution transfer pump 10 is installed on the first absorbent circulation pipeline G1, and a lean solution transfer pump 11 is installed on the second absorbent circulation pipeline G2.

[0062] The method for heating rich liquor using the carbon capture system coupled with waste heat from the steelmaking process described in this utility model is as follows: Flue gas is transported in the original flue gas conveying pipeline G, and after heat exchange with the cold working medium in the second heat exchanger 5, it enters the absorption tower 2. The CO2 in the flue gas is absorbed by the collector and becomes rich liquor. The rich liquor is discharged from the liquid outlet of the absorption tower 2, and after passing through the first absorbent circulation pipeline G1, it enters the desorption tower 3, where CO2 is desorbed and discharged to obtain lean liquor. The lean liquor enters the adsorption tower 2 through the second absorbent circulation pipeline G2.

[0063] The rich liquor undergoes two heating processes in the first absorbent circulation pipeline G1. The first heating occurs in the third heat exchanger 6, where it exchanges heat with the lean liquor discharged from the desorber 3. The second heating occurs when the cold working fluid, having absorbed heat from the flue gas, is compressed to become a hot working fluid. This hot working fluid is then transported through the hot working fluid circulation pipeline G3 to the first heat exchanger 4 for heat exchange with the rich liquor. After heat exchange, the working fluid is transported through the cold working fluid circulation pipeline G4 and passes through the expansion valve 102 to become a cold working fluid. This cold working fluid then re-enters the second heat exchanger for heat exchange with the flue gas. Furthermore, the rich liquor undergoes a third heating process in the desorber 3, specifically by introducing low-grade waste heat through the reboiler 7 to heat the rich liquor in the desorber 3.

Claims

1. A carbon capture system coupled to steel process waste heat, characterized by: The system comprises a heat pump (1), an absorption tower (2) and a desorption tower (3); the flue gas inlet of the absorption tower (2) is communicated with the original flue gas conveying pipeline (G), the liquid outlet of the absorption tower (2) is communicated with the liquid inlet of the desorption tower (3) through a first absorbent circulating pipeline (G1), the liquid outlet of the desorption tower (3) is communicated with the liquid inlet of the absorption tower (2) through a second absorbent circulating pipeline (G2); a first heat exchanger (4) is further arranged on the first absorbent circulating pipeline (G1); the first absorbent circulating pipeline (G1) is communicated with the heat working medium circulating pipeline (G3) of the heat pump (1) through the first heat exchanger (4); the cold working medium circulating pipeline (G4) of the heat pump (1) is communicated with the original flue gas conveying pipeline (G) through a second heat exchanger (5).

2. The system of claim 1, wherein: According to the flow direction of the liquid, a third heat exchanger (6) is further arranged on the first absorbent circulating pipeline (G1) upstream of the first heat exchanger (4); the first absorbent circulating pipeline (G1) is communicated with the second absorbent circulating pipeline (G2) through the third heat exchanger (6); wherein the third heat exchanger (6) is an indirect heat exchanger.

3. The system of claim 1, wherein: The heat pump (1) further comprises a compressor (101) and an expansion valve (102); the working medium outlet of the compressor (101) is connected with the working medium inlet of the expansion valve (102) through the heat working medium circulating pipeline (G3); the working medium outlet of the expansion valve (102) is connected with the working medium inlet of the compressor (101) through the cold working medium circulating pipeline (G4).

4. The system of claim 1, wherein: The first heat exchanger (4) and / or the second heat exchanger (5) is an indirect heat exchanger.

5. The system of claim 4, wherein: The second heat exchanger (5) is a partition wall type or a tube shell type heat exchanger.

6. The system of claim 4, wherein: The first heat exchanger (4) is a coil type gas-liquid heat exchanger.

7. The system of any one of claims 1-6, wherein: The system further comprises a reboiler (7); the reboiler (7) exchanges heat with the desorption tower (3) through a steam heat exchange pipeline inside the desorption tower (3); the steam inlet of the reboiler (7) is communicated with a steam source.

8. The system of claim 7, wherein: The steam inlet of the reboiler (7) is provided with a steam temperature detection device and a steam flow detection device.

9. The system of any one of claims 1-6, wherein: The original flue gas conveying pipeline (G) and / or the first absorbent circulating pipeline (G1) and / or the second absorbent circulating pipeline (G2) are provided with a temperature detection device and a flow detection device.

10. The system of any one of claims 1-6, wherein: The system further comprises a flue gas treatment device (8); the flue gas outlet of the desorption tower (3) is communicated with the flue gas treatment device (8) through a flue gas exhaust pipeline (G5).

11. The system of claim 10, wherein: The system further comprises a chimney (9); the flue gas treatment device (8) is communicated with the chimney (9) through a flue gas exhaust pipeline (G6).

12. The system of any one of claims 1-6, wherein: The first absorbent circulating pipeline (G1) is provided with a rich liquid conveying pump (10); and / or The second absorbent circulating pipeline (G2) is provided with a lean liquid conveying pump (11).

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