A flue gas waste heat recovery device and method for simultaneously capturing carbon and sulfur

Abstract

The present invention belongs to the field of flue gas recovery, and specifically relates to a flue gas waste heat recovery device and method for simultaneously capturing carbon and sulfur, comprising a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a carbon dioxide desorption tower, a sulfur dioxide desorption tower and an absorption tower; the flue gas is successively cooled by heat exchange through the first heat exchanger, the second heat exchanger and the third heat exchanger, so that the temperature of the flue gas entering the absorption tower is controlled and the absorption amount of carbon dioxide and sulfur dioxide is increased; the return water of the heat network is successively heated by heat exchange through the fourth heat exchanger and the first heat exchanger, so that the heat utilization efficiency of the system is relatively high, and the water temperature of the heat network can eventually reach 100-130°C.

Description

Technical Field

[0001] The present invention belongs to the field of flue gas recovery, and in particular relates to a flue gas waste heat recovery device and method for simultaneously capturing carbon and sulfur. Background Art

[0002] Reducing greenhouse gas emissions such as carbon dioxide has become one of the severe challenges facing human society. Sulfur dioxide is an important precursor to acid rain and haze, and SO2 in coal flue gas has become the main cause of air pollution. Reducing SO2 pollution has become a top priority for today's atmospheric environmental governance. The development direction of carbon dioxide and sulfur dioxide capture technology is to reduce the operating energy consumption of the technology.

[0003] Carbon dioxide capture technology can be divided into post-combustion capture technology, pre-combustion capture technology, and oxygen-enriched combustion technology. Currently, post-combustion capture technology is more commonly used, that is, capturing carbon dioxide in the flue gas discharged after the combustion equipment; flue gas desulfurization is currently the most effective and widely used desulfurization technology for controlling the concentration and total amount of sulfur dioxide emissions in the atmosphere, but the existing technology lacks a method that can capture carbon dioxide and sulfur dioxide in flue gas and make full use of flue gas heat. Summary of the invention

[0004] The present invention provides a flue gas waste heat recovery device and method for simultaneously capturing carbon and sulfur, so as to solve the problem that the prior art does not involve the capture of carbon and sulfur and has a low heat recovery rate.

[0005] To solve the above problems, the present invention proposes the following technical solutions:

[0006] A flue gas waste heat recovery device for capturing carbon and sulfur simultaneously, comprising a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a carbon dioxide desorption tower, a sulfur dioxide desorption tower and an absorption tower;

[0007] The first heat exchanger is provided with a first heat exchanger smoke inlet, a first heat exchanger smoke outlet and a first heat exchanger hot network water inlet; the first heat exchanger smoke inlet is connected to the first heat exchanger smoke outlet;

[0008] The second heat exchanger is provided with a second heat exchanger smoke inlet, a second heat exchanger smoke outlet, a second heat exchanger ionic liquid inlet and a second heat exchanger ionic liquid outlet; the second heat exchanger smoke inlet is connected to the second heat exchanger smoke outlet, and the second heat exchanger ionic liquid inlet is connected to the second heat exchanger ionic liquid outlet;

[0009] The third heat exchanger is provided with a third heat exchanger smoke inlet, a third heat exchanger smoke outlet, a third heat exchanger ionic liquid inlet and a third heat exchanger ionic liquid outlet; the third heat exchanger smoke inlet is connected to the third heat exchanger smoke outlet, and the third heat exchanger ionic liquid inlet is connected to the third heat exchanger ionic liquid outlet;

[0010] The fourth heat exchanger is provided with a fourth heat exchanger hot network water inlet, a fourth heat exchanger hot network water outlet, a fourth heat exchanger ionic liquid inlet and a fourth heat exchanger ionic liquid outlet; the fourth heat exchanger hot network water inlet is connected to the fourth heat exchanger hot network water outlet, and the fourth heat exchanger ionic liquid inlet is connected to the fourth heat exchanger ionic liquid outlet;

[0011] The carbon dioxide desorption tower is provided with a carbon dioxide desorption tower ion liquid inlet and a carbon dioxide desorption tower ion liquid outlet;

[0012] The sulfur dioxide desorption tower is provided with a sulfur dioxide desorption tower ionic liquid inlet and a sulfur dioxide desorption tower ionic liquid outlet;

[0013] The absorption tower is provided with an absorption tower flue gas inlet, an absorption tower ionic liquid inlet and an absorption tower ionic liquid outlet;

[0014] The flue gas outlet of the first heat exchanger is connected to the flue gas inlet of the second heat exchanger, the flue gas outlet of the second heat exchanger is connected to the flue gas inlet of the third heat exchanger, the flue gas outlet of the third heat exchanger is connected to the flue gas inlet of the absorption tower, the ionic liquid outlet of the absorption tower is connected to the ionic liquid inlet of the third heat exchanger, the ionic liquid outlet of the third heat exchanger is connected to the ionic liquid inlet of the sulfur dioxide desorption tower, the ionic liquid outlet of the sulfur dioxide desorption tower is connected to the ionic liquid inlet of the second heat exchanger, the ionic liquid outlet of the second heat exchanger is connected to the ionic liquid inlet of the carbon dioxide desorption tower, the ionic liquid outlet of the carbon dioxide desorption tower is connected to the ionic liquid inlet of the fourth heat exchanger, and the ionic liquid outlet of the fourth heat exchanger is connected to the ionic liquid inlet of the absorption tower;

[0015] The hot network water outlet of the fourth heat exchanger is connected to the hot network water inlet of the first heat exchanger.

[0016] Preferably, the first heat exchanger is provided with a first heat exchanger hot network water outlet; the first heat exchanger hot network water inlet is connected to the first heat exchanger hot network water outlet; the first heat exchanger hot network water outlet is connected to the hot network.

[0017] Preferably, a carbon dioxide outlet is provided on the carbon dioxide desorption tower; the carbon dioxide outlet is connected to a carbon dioxide storage tank.

[0018] Preferably, a sulfur dioxide outlet is provided on the sulfur dioxide desorption tower, and the sulfur dioxide outlet is connected to a sulfur dioxide storage tank and a chimney.

[0019] Preferably, the absorption tower is provided with an absorption tower flue gas outlet;

[0020] Preferably, the ionic liquid outlet of the carbon dioxide desorption tower is located at the bottom of the carbon dioxide desorption tower, and the carbon dioxide outlet is located at the top of the carbon dioxide desorption tower;

[0021] Preferably, the ionic liquid outlet of the sulfur dioxide desorption tower is located at the bottom of the sulfur dioxide desorption tower, and the sulfur dioxide outlet is located at the top of the sulfur dioxide desorption tower;

[0022] Preferably, the ionic liquid outlet of the absorption tower is located at the bottom of the absorption tower, and the flue gas outlet of the absorption tower is located at the top of the absorption tower.

[0023] A flue gas waste heat recovery method for capturing carbon and sulfur at the same time, the flue gas enters the first heat exchanger, exchanges heat with the hot network water in the first heat exchanger, the hot network water is heated, and is discharged into the hot network through the hot network water outlet of the first heat exchanger, and the flue gas is cooled and enters the second heat exchanger;

[0024] The flue gas exchanges heat with the ionic liquid rich in carbon dioxide and poor in sulfur dioxide from the sulfur dioxide desorption tower in the second heat exchanger, and the ionic liquid enters the carbon dioxide desorption tower after the temperature is increased. The flue gas enters the third heat exchanger after the temperature is decreased. The flue gas exchanges heat with the ionic liquid from the absorption tower in the third heat exchanger, and the ionic liquid enters the sulfur dioxide desorption tower after the temperature is increased. The flue gas enters the absorption tower after the temperature is decreased.

[0025] The flue gas in the absorption tower contacts the ionic liquid to obtain the ionic liquid rich in carbon dioxide and sulfur dioxide and the flue gas poor in carbon dioxide and sulfur dioxide. The flue gas enters the chimney, the ionic liquid rich in carbon dioxide and sulfur dioxide enters the third heat exchanger, is heated in the third heat exchanger and enters the sulfur dioxide desorption tower, the ionic liquid rich in carbon dioxide and sulfur dioxide is desorbed in the sulfur dioxide desorption tower, the desorbed sulfur dioxide enters the sulfur dioxide storage tank, the remaining ionic liquid rich in carbon dioxide and poor in sulfur dioxide enters the second heat exchanger, is heated in the second heat exchanger and enters the carbon dioxide desorption tower, and is desorbed in the carbon dioxide desorption tower, the desorbed carbon dioxide is discharged through the carbon dioxide outlet and enters the carbon dioxide storage tank, the remaining ionic liquid poor in carbon dioxide and poor in sulfur dioxide enters the fourth heat exchanger;

[0026] The hot network water enters the fourth heat exchanger, in which the hot network water exchanges heat with the ionic liquid from the carbon dioxide desorption tower, the ionic liquid cools down and enters the absorption tower, and the hot network water heats up and enters the first heat exchanger.

[0027] Preferably, after the heating network water is heated in the first heat exchanger, the temperature is greater than 100 degrees Celsius and less than 130 degrees Celsius.

[0028] The present invention is beneficial in that:

[0029] Through multi-stage heat exchange between flue gas and ionic liquid, the flue gas is cooled in stages and the return water of the heat network is heated in stages, thus realizing the step-by-step utilization of flue gas waste heat and improving the heat utilization efficiency.

[0030] At the same time, carbon dioxide and sulfur dioxide in flue gas can be captured.

[0031] By recycling the waste heat in the flue gas, the heating income is increased and the economic benefits of the power plant are improved.

[0032] Capable of providing hot water at a maximum temperature of 130°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 A schematic diagram of a flue gas waste heat recovery device for simultaneously capturing carbon and sulfur;

[0035] In the figure, 1 is a first heat exchanger, 2 is a second heat exchanger, 3 is a third heat exchanger, 4 is a fourth heat exchanger, 5 is a carbon dioxide desorption tower, 6 is a sulfur dioxide desorption tower, and 7 is an absorption tower;

[0036] 11 is the smoke inlet of the first heat exchanger, 12 is the smoke outlet of the first heat exchanger, 13 is the water inlet of the hot network of the first heat exchanger, and 14 is the water outlet of the hot network of the first heat exchanger;

[0037] 21 is a flue gas inlet of the second heat exchanger, 22 is a flue gas outlet of the second heat exchanger, 23 is an ionic liquid inlet of the second heat exchanger, and 24 is an ionic liquid outlet of the second heat exchanger;

[0038] 31 is a flue gas inlet of the third heat exchanger, 32 is a flue gas outlet of the third heat exchanger, 33 is an ionic liquid inlet of the third heat exchanger, and 34 is an ionic liquid outlet of the third heat exchanger;

[0039] 41 is the water inlet of the fourth heat exchanger hot network, 42 ​​is the water outlet of the fourth heat exchanger hot network, 43 is the ionic liquid inlet of the fourth heat exchanger, and 44 is the ionic liquid outlet of the fourth heat exchanger;

[0040] 51 is the ionic liquid inlet of the carbon dioxide desorption tower, 52 is the ionic liquid outlet of the carbon dioxide desorption tower, and 53 is the carbon dioxide outlet;

[0041] 61 is the ionic liquid inlet of the sulfur dioxide desorption tower, 62 is the ionic liquid outlet of the sulfur dioxide desorption tower, and 63 is the sulfur dioxide outlet;

[0042] 71 is the flue gas inlet of the absorption tower, 72 is the flue gas outlet of the absorption tower, 73 is the ionic liquid inlet of the absorption tower, and 74 is the ionic liquid outlet of the absorption tower. DETAILED DESCRIPTION

[0043] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0044] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0045] Embodiment 1:

[0046] See also Figure 1 As shown, the present invention discloses a flue gas waste heat recovery device for capturing carbon and sulfur simultaneously, comprising: a first heat exchanger 1, a second heat exchanger 2, a third heat exchanger 3, a fourth heat exchanger 4, a carbon dioxide desorption tower 5, a sulfur dioxide desorption tower 6 and an absorption tower 7;

[0047] The first heat exchanger 1 is provided with a first heat exchanger smoke inlet 11, a first heat exchanger smoke outlet 12, a first heat exchanger hot network water inlet 13 and a first heat exchanger hot network water outlet 14; the first heat exchanger smoke inlet 11 is connected to the first heat exchanger smoke outlet 12, the first heat exchanger hot network water inlet 13 is connected to the first heat exchanger hot network water outlet 14; the first heat exchanger hot network water outlet 14 is connected to the hot network; the first heat exchanger smoke inlet 11 is connected to the smoke inlet;

[0048] The second heat exchanger 2 is provided with a second heat exchanger smoke inlet 21, a second heat exchanger smoke outlet 22, a second heat exchanger ionic liquid inlet 23 and a second heat exchanger ionic liquid outlet 24; the second heat exchanger smoke inlet 21 is connected to the second heat exchanger smoke outlet 22, and the second heat exchanger ionic liquid inlet 23 is connected to the second ionic liquid outlet 24;

[0049] The third heat exchanger 3 is provided with a third heat exchanger smoke inlet 31, a third heat exchanger smoke outlet 32, a third heat exchanger ionic liquid inlet 33 and a third heat exchanger ionic liquid outlet 34; the third heat exchanger smoke inlet 31 is connected to the third heat exchanger smoke outlet 32, and the third heat exchanger ionic liquid inlet 33 is connected to the third heat exchanger ionic liquid outlet 34;

[0050] The fourth heat exchanger 4 is provided with a fourth heat exchanger hot network water inlet 41, a fourth heat exchanger hot network water outlet 42, a fourth heat exchanger ionic liquid inlet 43 and a fourth heat exchanger ionic liquid outlet 44; the fourth heat exchanger hot network water inlet 41 is connected to the fourth heat exchanger hot network water outlet 42, and the fourth heat exchanger ionic liquid inlet 43 is connected to the fourth heat exchanger ionic liquid outlet 44; the fourth heat exchanger hot network water outlet 42 is connected to the first heat exchanger hot network water inlet 13;

[0051] The carbon dioxide desorption tower 5 is provided with a carbon dioxide desorption tower ion liquid inlet 51, a carbon dioxide desorption tower ion liquid outlet 52 and a carbon dioxide outlet 53; the carbon dioxide desorption tower ion liquid outlet 52 is located at the bottom of the carbon dioxide desorption tower 5, and the carbon dioxide outlet 53 is located at the top of the carbon dioxide desorption tower 5; the carbon dioxide outlet 53 is connected to the carbon dioxide storage tank.

[0052] The sulfur dioxide desorption tower 6 is provided with a sulfur dioxide desorption tower ionic liquid inlet 61, a sulfur dioxide desorption tower ionic liquid outlet 62 and a sulfur dioxide outlet 63; the sulfur dioxide desorption tower ionic liquid outlet 62 is located at the bottom of the sulfur dioxide desorption tower 6, and the sulfur dioxide outlet 63 is located at the top of the sulfur dioxide desorption tower 6; the sulfur dioxide outlet 63 is connected to the sulfur dioxide storage tank.

[0053] The absorption tower 7 is provided with an absorption tower flue gas inlet 71, an absorption tower flue gas outlet 72, an absorption tower ionic liquid inlet 73 and an absorption tower ionic liquid outlet 74; the absorption tower ionic liquid outlet 74 is located at the bottom of the absorption tower 7, and the absorption tower flue gas outlet 72 is located at the top of the absorption tower 7; the absorption tower flue gas outlet 72 is connected to the chimney.

[0054] The first heat exchanger flue gas outlet 12 is connected to the second heat exchanger flue gas inlet 21, the second heat exchanger flue gas outlet 22 is connected to the third heat exchanger flue gas inlet 31, the third heat exchanger flue gas outlet 32 ​​is connected to the absorption tower flue gas inlet 71, the absorption tower ionic liquid outlet 74 is connected to the third ionic liquid inlet 33, the third heat exchanger ionic liquid outlet 34 is connected to the sulfur dioxide desorption tower ionic liquid inlet 61, the sulfur dioxide desorption tower ionic liquid outlet 62 is connected to the second ionic liquid inlet 23, the second heat exchanger ionic liquid outlet 24 is connected to the carbon dioxide desorption tower ionic liquid inlet 51, the carbon dioxide desorption tower ionic liquid outlet 52 is connected to the fourth ionic liquid inlet 43, and the fourth heat exchanger ionic liquid outlet 44 is connected to the absorption tower ionic liquid inlet 73;

[0055] Embodiment 2:

[0056] This embodiment discloses a flue gas waste heat recovery method for simultaneously capturing carbon and sulfur, comprising the following steps:

[0057] The flue gas enters the first heat exchanger 1 through the first heat exchanger flue gas inlet 11, exchanges heat with the heating network water in the first heat exchanger 1, the heating network water is heated, and is discharged into the heating network through the first heat exchanger hot network water outlet 14, and the flue gas cools down and enters the second heat exchanger 2 through the first heat exchanger flue gas outlet 12 and the second heat exchanger flue gas inlet 21;

[0058] The flue gas exchanges heat with the carbon dioxide-rich and sulfur dioxide-poor ionic liquid from the sulfur dioxide desorption tower 6 in the second heat exchanger 2. The ionic liquid is heated up and enters the carbon dioxide desorption tower 5 through the second ionic liquid outlet 24 and the carbon dioxide desorption tower ionic liquid inlet 51. The flue gas is cooled down and enters the third heat exchanger 3 through the second heat exchanger flue gas outlet 22 and the third heat exchanger flue gas inlet 31. The flue gas exchanges heat with the ionic liquid from the absorption tower 7 in the third heat exchanger 3. The ionic liquid is heated up and enters the sulfur dioxide desorption tower 6 through the third heat exchanger ionic liquid outlet 34 and the sulfur dioxide desorption tower ionic liquid inlet 61. The flue gas is cooled down and enters the absorption tower 7 through the third heat exchanger flue gas outlet 32 ​​and the absorption tower flue gas inlet 71.

[0059] The flue gas in the absorption tower 7 contacts with the ionic liquid to obtain the ionic liquid rich in carbon dioxide and sulfur dioxide and the flue gas poor in carbon dioxide and sulfur dioxide. The flue gas is discharged into the chimney through the absorption tower flue gas outlet 72. The ionic liquid rich in carbon dioxide and sulfur dioxide enters the third heat exchanger 3 through the absorption tower ionic liquid outlet 74 and the third heat exchanger ionic liquid inlet 33. After being heated in the third heat exchanger 3, it enters the sulfur dioxide desorption tower 6. In the sulfur dioxide desorption tower 6, the ionic liquid rich in carbon dioxide and sulfur dioxide is desorbed. The desorbed sulfur dioxide enters the sulfur dioxide storage tank through the sulfur dioxide outlet 63. The remaining carbon dioxide-rich ionic liquid enters the sulfur dioxide storage tank through the sulfur dioxide outlet 64. The ionic liquid depleted in carbon dioxide and sulfur dioxide enters the second heat exchanger 2 through the ionic liquid outlet 62 of the sulfur dioxide desorption tower and the ionic liquid inlet 23 of the second heat exchanger, and after being heated in the second heat exchanger 2, enters the carbon dioxide desorption tower 5 through the second ionic liquid outlet 24 and the ionic liquid inlet 51 of the carbon dioxide desorption tower, and is desorbed in the carbon dioxide desorption tower 5. The desorbed carbon dioxide is discharged through the carbon dioxide outlet 53 and enters the carbon dioxide storage tank, and the remaining ionic liquid depleted in carbon dioxide and sulfur dioxide enters the fourth heat exchanger 4 through the ionic liquid outlet 52 of the carbon dioxide desorption tower and the ionic liquid inlet 43 of the fourth heat exchanger;

[0060] The hot network water enters the fourth heat exchanger 4 through the hot network water inlet 41 of the fourth heat exchanger. In the fourth heat exchanger 4, the hot network water exchanges heat with the ionic liquid from the carbon dioxide desorption tower 5. The ionic liquid cools down and enters the absorption tower 7 through the ionic liquid outlet 44 of the fourth heat exchanger and the ionic liquid inlet 73 of the absorption tower. The hot network water heats up and enters the first heat exchanger 1 through the hot network water outlet 42 of the fourth heat exchanger and the hot network water inlet 13 of the first heat exchanger.

[0061] After the water in the hot network is heated in the first heat exchanger 1, the temperature is greater than 100 degrees Celsius and less than 130 degrees Celsius.

[0062] The present invention utilizes the characteristics that the absorption of carbon dioxide and sulfur dioxide by ionic liquid decreases with increasing temperature, and the absorption of different gases decreases with increasing temperature in different degrees. It absorbs carbon dioxide and sulfur dioxide at low temperature, releases sulfur dioxide at medium temperature, and releases carbon dioxide at high temperature, thereby realizing the simultaneous capture of sulfur and carbon in flue gas. The heat in the flue gas is recycled and utilized in stages. The flue gas is successively cooled by heat exchange in the first heat exchanger 1, the second heat exchanger 2, and the third heat exchanger 3, the temperature of the flue gas entering the absorption tower 7 is controlled, and the absorption of carbon dioxide and sulfur dioxide is increased; the return water of the heat network is successively heated by the fourth heat exchanger 4 and the first heat exchanger 1, the system has a high heat utilization efficiency, and the water of the heat network can eventually reach 100-130°C. The value of the water of the heat network at this temperature is relatively high.

[0063] By using the return water from the heat network as a cold source, the use and consumption of circulating cooling water is reduced, achieving a certain water-saving effect. By designing desorption towers with different temperatures, carbon dioxide and sulfur dioxide are removed and captured separately. By using the step-by-step cooling of flue gas and the step-by-step heating of the return water from the heat network, the flue gas temperature entering the absorption tower is reduced, and the carbon dioxide absorption amount is increased; at the same time, the step-by-step utilization of flue gas waste heat is achieved, the heat utilization efficiency is improved, and the heating efficiency is improved.

[0064] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur, characterized in that: The invention is realized based on a flue gas waste heat recovery device for simultaneously capturing carbon and sulfur, the flue gas waste heat recovery device comprising a first heat exchanger (1), a second heat exchanger (2), a third heat exchanger (3), a fourth heat exchanger (4), a carbon dioxide desorption tower (5), a sulfur dioxide desorption tower (6) and an absorption tower (7); The first heat exchanger (1) is provided with a first heat exchanger smoke inlet (11), a first heat exchanger smoke outlet (12) and a first heat exchanger hot network water inlet (13); the first heat exchanger smoke inlet (11) is connected to the first heat exchanger smoke outlet (12); The second heat exchanger (2) is provided with a second heat exchanger smoke inlet (21), a second heat exchanger smoke outlet (22), a second heat exchanger ionic liquid inlet (23) and a second heat exchanger ionic liquid outlet (24); the second heat exchanger smoke inlet (21) is connected to the second heat exchanger smoke outlet (22), and the second heat exchanger ionic liquid inlet (23) is connected to the second heat exchanger ionic liquid outlet (24); The third heat exchanger (3) is provided with a third heat exchanger smoke inlet (31), a third heat exchanger smoke outlet (32), a third heat exchanger ionic liquid inlet (33) and a third heat exchanger ionic liquid outlet (34); the third heat exchanger smoke inlet (31) is connected to the third heat exchanger smoke outlet (32), and the third heat exchanger ionic liquid inlet (33) is connected to the third heat exchanger ionic liquid outlet (34); The fourth heat exchanger (4) is provided with a fourth heat exchanger hot network water inlet (41), a fourth heat exchanger hot network water outlet (42), a fourth heat exchanger ionic liquid inlet (43) and a fourth heat exchanger ionic liquid outlet (44); the fourth heat exchanger hot network water inlet (41) is connected to the fourth heat exchanger hot network water outlet (42), and the fourth heat exchanger ionic liquid inlet (43) is connected to the fourth heat exchanger ionic liquid outlet (44); The carbon dioxide desorption tower (5) is provided with a carbon dioxide desorption tower ion liquid inlet (51) and a carbon dioxide desorption tower ion liquid outlet (52); The sulfur dioxide desorption tower (6) is provided with a sulfur dioxide desorption tower ionic liquid inlet (61) and a sulfur dioxide desorption tower ionic liquid outlet (62); The absorption tower (7) is provided with an absorption tower flue gas inlet (71), an absorption tower ionic liquid inlet (73) and an absorption tower ionic liquid outlet (74); The first heat exchanger flue gas outlet (12) is connected to the second heat exchanger flue gas inlet (21), the second heat exchanger flue gas outlet (22) is connected to the third heat exchanger flue gas inlet (31), the third heat exchanger flue gas outlet (32) is connected to the absorption tower flue gas inlet (71), the absorption tower ionic liquid outlet (74) is connected to the third heat exchanger ionic liquid inlet (33), the third heat exchanger ionic liquid outlet (34) is connected to the sulfur dioxide desorption tower ionic liquid inlet (61), the sulfur dioxide desorption tower ionic liquid outlet (62) is connected to the second heat exchanger ionic liquid inlet (23), the second heat exchanger ionic liquid outlet (24) is connected to the carbon dioxide desorption tower ionic liquid inlet (51), the carbon dioxide desorption tower ionic liquid outlet (52) is connected to the fourth heat exchanger ionic liquid inlet (43), and the fourth heat exchanger ionic liquid outlet (44) is connected to the absorption tower ionic liquid inlet (73); The fourth heat exchanger hot network water outlet (42) is connected to the first heat exchanger hot network water inlet (13); The flue gas waste heat recovery method comprises the following steps: The flue gas enters the first heat exchanger (1), exchanges heat with the water in the heating network in the first heat exchanger (1), the water in the heating network is heated, and is discharged from the first heat exchanger (1) into the heating network, while the flue gas cools down and enters the second heat exchanger (2); The flue gas exchanges heat with the ionic liquid rich in carbon dioxide and poor in sulfur dioxide from the sulfur dioxide desorption tower (6) in the second heat exchanger (2); the ionic liquid enters the carbon dioxide desorption tower (5) after the temperature is increased; the flue gas enters the third heat exchanger (3) after the temperature is decreased; the flue gas exchanges heat with the ionic liquid from the absorption tower (7) in the third heat exchanger (3); the ionic liquid enters the sulfur dioxide desorption tower (6) after the temperature is increased; the flue gas enters the absorption tower (7) after the temperature is decreased; The flue gas in the absorption tower (7) contacts the ionic liquid to obtain the ionic liquid rich in carbon dioxide and sulfur dioxide and the flue gas poor in carbon dioxide and sulfur dioxide. The flue gas enters the chimney. The ionic liquid rich in carbon dioxide and sulfur dioxide enters the third heat exchanger (3). After being heated in the third heat exchanger (3), the ionic liquid enters the sulfur dioxide desorption tower (6). In the sulfur dioxide desorption tower (6), the ionic liquid rich in carbon dioxide and sulfur dioxide is desorbed. The desorbed sulfur dioxide enters the sulfur dioxide storage tank. The remaining ionic liquid rich in carbon dioxide and poor in sulfur dioxide enters the second heat exchanger (2). After being heated in the second heat exchanger (2), the ionic liquid enters the carbon dioxide desorption tower (5). The desorbed carbon dioxide is discharged through the carbon dioxide outlet (53) and enters the carbon dioxide storage tank. The remaining ionic liquid poor in carbon dioxide and poor in sulfur dioxide enters the fourth heat exchanger (4). The hot network water enters the fourth heat exchanger (4), in which the hot network water exchanges heat with the ionic liquid from the carbon dioxide desorption tower (5), the ionic liquid is cooled and enters the absorption tower (7), and the hot network water is heated and enters the first heat exchanger (1).

2. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 1, characterized in that: The first heat exchanger (1) is provided with a first heat exchanger hot network water outlet (14); the first heat exchanger hot network water inlet (13) is connected to the first heat exchanger hot network water outlet (14); and the first heat exchanger hot network water outlet (14) is connected to the hot network.

3. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 1, characterized in that: The carbon dioxide desorption tower (5) is provided with a carbon dioxide outlet (53); the carbon dioxide outlet (53) is connected to a carbon dioxide storage tank.

4. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 1, characterized in that: The sulfur dioxide desorption tower (6) is provided with a sulfur dioxide outlet (63), and the sulfur dioxide outlet (63) is connected to a sulfur dioxide storage tank.

5. The flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 1, characterized in that: The absorption tower (7) is provided with an absorption tower smoke outlet (72), and the absorption tower smoke outlet (72) is connected to a chimney.

6. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 3, characterized in that: The carbon dioxide desorption tower ionic liquid outlet (52) is located at the bottom of the carbon dioxide desorption tower (5), and the carbon dioxide outlet (53) is located at the top of the carbon dioxide desorption tower (5).

7. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 4, characterized in that: The sulfur dioxide desorption tower ionic liquid outlet (62) is located at the bottom of the sulfur dioxide desorption tower (6), and the sulfur dioxide outlet (63) is located at the top of the sulfur dioxide desorption tower (6).

8. A flue gas waste heat recovery method for simultaneously capturing carbon and sulfur as claimed in claim 5, characterized in that: The absorption tower ionic liquid outlet (74) is located at the bottom of the absorption tower (7), and the absorption tower flue gas outlet (72) is located at the top of the absorption tower (7).

9. The flue gas waste heat recovery method for simultaneously capturing carbon and sulfur according to claim 1, characterized in that: After the water in the hot network is heated in the first heat exchanger (1), the temperature is greater than 100 degrees Celsius and less than 130 degrees Celsius.

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