Lime kiln flue gas recovery system and flue gas recycling method in iron and steel smelting

Abstract

The invention discloses a lime kiln flue gas recovery system and a flue gas recycling method in iron and steel smelting, and belongs to the technical field of iron and steel smelting resource recycling. The system comprises a lime production system, a fly ash utilization system and a preheated flue gas utilization system, the lime production system communicates with the fly ash utilization system and the preheated flue gas utilization system, the lime production system conveys fly ash flue gas to the fly ash utilization system, and the lime production system conveys preheated flue gas to the preheated flue gas utilization system; and the preheated flue gas utilization system conveys fuel to the lime production system through the fly ash utilization system. According to the invention, flue gas and substances and energy derived in the flue gas recycling process are fully utilized by adopting abundant flue gas recycling means, so that the emission of available substances and energy is reduced to the greatest extent, and the flue gas generated in the lime production process and the substances and energy derived in the flue gas recycling process have higher utilization rate; the energy consumption is obviously reduced, the waste is reduced, and the flue gas pollution is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of resource recycling in steel smelting, and relates to a lime kiln fume recovery system and a fume recycling method in steel smelting. Background Art

[0002] In the process of steel smelting, especially in electric furnace steelmaking, the addition of lime can adjust the temperature in the furnace and neutralize the acidic oxides in the furnace to form stable calcium silicate and other silicate substances, thereby promoting the formation of slag, reducing the content of impurities and oxides in the furnace, and improving the quality of molten steel. The establishment of lime kilns in steel plants to produce lime has played a great role in improving the energy efficiency and economic benefits of the steel smelting process. However, in the process of lime kiln calcination to produce lime, a large amount of high-temperature flue gas will be generated. The temperature of high-temperature flue gas can reach about 1150℃. The high-temperature flue gas not only contains a lot of heat, but also carries dust, sulfur dioxide and other substances, which are polluting to the environment. Therefore, the high-temperature flue gas cannot be discharged directly, and the high heat of the high-temperature flue gas and the pollutants contained therein can be reused as resources. On the one hand, it can not only save energy consumption, but also reduce the pollution of high-temperature flue gas. Therefore, it is of great significance to improve the utilization rate of high-temperature flue gas generated in the lime production process.

[0003] Therefore, it is necessary to provide a lime kiln flue gas recovery system and a flue gas recovery and utilization method in steel smelting, so that the high-temperature flue gas generated in the lime production process can be efficiently utilized. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention designs a lime kiln flue gas recovery system in steel smelting combined with a flue gas recovery method, so that high-temperature flue gas can be used more efficiently in the lime production process, thereby achieving the purpose of saving energy and reducing flue gas pollution.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] On the one hand, the present invention proposes a lime kiln flue gas recovery system in steel smelting, the system comprising a lime production system, a fly ash utilization system, and a preheating flue gas utilization system, the lime production system is connected to the fly ash utilization system and the preheating flue gas utilization system, the lime production system transports fly ash flue gas to the fly ash utilization system, the lime production system transports preheating flue gas to the preheating flue gas utilization system, and the preheating flue gas utilization system transports fuel to the lime production system through the fly ash utilization system.

[0007] Preferably, the lime production system includes a limestone preheater 100, a lime kiln 110, and a lime collector 190, the flue gas outlet of the lime kiln 110 is connected to the flue gas inlet of the limestone preheater 100, the fly ash outlet of the lime kiln 110 is connected to the fly ash utilization system, the lime outlet of the lime kiln 110 is connected to the lime collector 190, and a filter is installed in the pipeline connecting the flue gas outlet of the lime kiln 110 and the flue gas inlet of the limestone preheater 100.

[0008] Preferably, the preheated flue gas utilization system includes a blower 210, a three-stage heat exchanger 220, a hot blast furnace 230, and a blast furnace 240. The flue gas inlet of the three-stage heat exchanger 220 is connected to the flue gas outlet of the limestone preheater 100. The blower 210 blows cold air into the three-stage heat exchanger 220 through the air inlet of the three-stage heat exchanger 220. The air outlet of the three-stage heat exchanger 220 is connected to the air inlet of the hot blast furnace 230. The air outlet of the hot blast furnace 230 is connected to the heat source inlet of the blast furnace 240. The flue gas outlet of the three-stage heat exchanger 220 is connected to the fly ash utilization system to provide raw materials for the fly ash utilization system.

[0009] Preferably, the fly ash utilization system includes a digestion chamber 120, a desulfurization reaction chamber 130, and a gypsum collector 200. The material inlet of the digestion chamber 120 is connected to the fly ash outlet of the lime kiln 110, and the digestion chamber 120 is connected to a water source, which transports water into the digestion chamber 120. The material inlet of the desulfurization reaction chamber 130 is respectively connected to the material outlet of the digestion chamber 120 and the material outlet of the tertiary heat exchanger 220, and the material outlet of the desulfurization reaction chamber 130 is connected to the gypsum collector 200. The gypsum collector 200 is a solid-liquid separation device, and the liquid material outlet of the gypsum collector 200 is connected to the water inlet of the digestion chamber 120.

[0010] Preferably, the fly ash utilization system also includes a primary heat exchanger 150, a secondary heat exchanger 160, and a gas bin 170. The heat exchange medium inlet of the primary heat exchanger 150 is connected to the steam outlet of the digestion chamber 120, the material inlet of the primary heat exchanger 150 is connected to the material outlet of the gas bin 170, the material inlet of the gas bin 170 is connected to the gas outlet of the blast furnace 240, the material outlet of the primary heat exchanger 150 is connected to the fuel inlet of the lime kiln 110, the steam outlet of the primary heat exchanger 150 is connected to the material inlet of the secondary heat exchanger 160, and the material outlet of the secondary heat exchanger 160 is connected to the material inlet of the digestion chamber 120.

[0011] Preferably, the heat exchange medium inlet of the secondary heat exchanger 160 is connected to the boiler feed water source, and the heat exchange medium outlet of the secondary heat exchanger 160 is connected to the boiler feed water tank 180 .

[0012] Preferably, the fly ash utilization system further includes a dust collector 140 , and a material inlet of the dust collector 140 is connected to a fly ash outlet of the desulfurization reaction chamber 130 .

[0013] Another aspect of the present invention provides a method for recovering and utilizing flue gas from the above system, the method comprising the following steps:

[0014] (1) Limestone produced by steel smelting is added to the limestone preheater 100 for preheating.

[0015] (2) In step 1, the limestone is preheated and then transported to the lime kiln 110. The limestone is calcined in the lime kiln 110 to obtain lime, which is then stored in the lime collector 190. The flue gas generated by the lime kiln 110 is divided into two parts, which are transported to the limestone preheater 100 and the digestion chamber 120, respectively. The flue gas transported to the limestone preheater 100 serves as a heat source for preheating the limestone. The flue gas transported to the digestion chamber 120 contains CaO. Water is introduced into the digestion chamber 120, and the CaO in the flue gas reacts with water in the digestion chamber 120 to generate Ca(OH)2.

[0016] (3) The Ca(OH)2 generated in step 2 is transported to the desulfurization reaction chamber 130. At the same time, the flue gas generated by the limestone preheater 110 is divided into two parts after heat exchange and cooling in the three-stage heat exchanger 220, and is transported to the hot blast furnace 230 and the desulfurization reaction chamber 130 respectively. The flue gas transported to the hot blast furnace 230 is heated and then transported to the blast furnace 240 as a heat source. The flue gas transported to the desulfurization reaction chamber 130 contains SO2, which reacts with the Ca(OH)2 entering the desulfurization reaction chamber 130 to generate CaSO3. The CaSO3 is transported to the gypsum collector 200 for solid-liquid separation. The separated solid matter is collected and stored. The separated liquid material is transported to the digestion chamber 120 to react with CaO again to generate Ca(OH)2.

[0017] (4) In step 3, the coal gas generated by the operation of the blast furnace 240 is transported to the coal gas bin 170 for storage, and the coal gas stored in the coal gas bin 170 is transported to the primary heat exchanger 150. Meanwhile, in the digestion chamber 120, the reaction between CaO and water is an exothermic reaction, which heats the water in the digestion chamber 120 into steam, and the steam is transported to the primary heat exchanger 150. The coal gas transported to the primary heat exchanger 150 is preheated by the steam, and the preheated coal gas is transported to the lime kiln 110 as fuel;

[0018] (5) In step 4, steam enters the primary heat exchanger 150 to heat the coal gas, forming a mixture of steam and liquid water. The mixture is transported to the secondary heat exchanger 160. The secondary heat exchanger 160 exchanges heat and cools the steam in the mixture, converting the steam into liquid water. All the liquid water in the secondary heat exchanger 160 is transported to the digestion chamber 120 to react with CaO.

[0019] Beneficial effects of the present invention:

[0020] The present invention adopts relatively abundant flue gas recovery and utilization means, combines the recycling of multiple energies among the lime production system, the fly ash utilization system and the preheating flue gas utilization system, fully utilizes the flue gas and the substances and energy derived from the flue gas recovery and utilization process, minimizes the emission of available substances and energy, thereby making the flue gas generated in the lime production process and the substances and energy derived from the flue gas recovery and utilization process have a high utilization rate, significantly reduces energy consumption, reduces waste, and reduces the pollution of flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the flue gas recovery and utilization system of the present invention.

[0022] In the figure, 100-limestone preheater, 110-lime kiln, 120-digestion chamber, 130-desulfurization reaction chamber, 140-dust collector, 150-primary heat exchanger, 160-secondary heat exchanger, 170-gas bin, 180-boiler feed water tank, 190-lime collector, 200-gypsum collector, 210-blower, 220-third-stage heat exchanger, 230-hot blast furnace, 240-blast furnace. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the described contents.

[0024] like Figure 1 As shown, the system includes a lime production system, a fly ash utilization system, and a preheated flue gas utilization system. The lime production system is connected to the fly ash utilization system and the preheated flue gas utilization system, respectively. The lime production system transports fly ash flue gas to the fly ash utilization system, and the lime production system transports preheated flue gas to the preheated flue gas utilization system.

[0025] The lime production system generates high-temperature flue gas during the production of quicklime. The high-temperature flue gas is respectively sent to the preheating flue gas utilization system and the fly ash utilization system. The preheating flue gas utilization system mainly recycles and reuses the heat of the flue gas, and the fly ash utilization system mainly reuses the fly ash and other substances contained in the flue gas. During the operation of the preheating flue gas utilization system and the fly ash utilization system, both the preheating flue gas utilization system and the fly ash utilization system will generate derivative substances and energy. After the derivative energy generated by the fly ash utilization system acts on the derivative substances generated in the preheating flue gas utilization system, the derivative substances generated by the preheating flue gas utilization system can be returned to the lime production system for reuse. At the same time, the derivative substances generated in the fly ash utilization system can be reused within the system, so that the high-temperature flue gas generated in the lime production process of the present invention and the derivative substances and energy for treating the high-temperature flue gas are fully utilized, which significantly reduces energy consumption, reduces waste, and reduces flue gas pollution.

[0026] The lime production system includes a limestone preheater 100, a lime kiln 110, and a lime collector 190. The flue gas outlet of the lime kiln 110 is connected to the flue gas inlet of the limestone preheater 100, the fly ash outlet of the lime kiln 110 is connected to the fly ash utilization system, the lime outlet of the lime kiln 110 is connected to the lime collector 190, and a filter is installed in the pipeline connecting the flue gas outlet of the lime kiln 110 and the flue gas inlet of the limestone preheater 100.

[0027] When lime is produced, limestone is first added to the limestone preheater 100 for preheating. The preheated limestone enters the lime kiln 110 to be calcined to obtain quicklime. The chemical reaction formula is: CaCO3=CaO+CO2. During the operation of the lime kiln 110, high-temperature flue gas is generated. The quicklime calcined in the lime kiln 110 directly enters the lime collector 190 for collection and storage, and the high-temperature flue gas is discharged from the lime kiln 110 through the flue gas outlet of the lime kiln 110, and enters the limestone preheater through the flue gas inlet of the limestone preheater 100. Since the high-temperature flue gas has a high temperature and contains more heat, the high-temperature flue gas can preheat the limestone after entering the limestone preheater 100, thereby playing a role of replacing heating and reducing the energy consumption in the limestone preheating process. A filter is installed in the flue gas channel to filter the fly ash and other dust brought out during the high-temperature flue gas transportation process, thereby preventing a large amount of solid matter such as dust from entering the limestone preheater 100.

[0028] The high-temperature flue gas flow rate can be controlled by installing valves on the flue gas passages between the lime kiln 110 and the limestone preheater 100, thereby adjusting the speed and amount of the high-temperature flue gas entering the limestone preheater 100 according to specific production conditions.

[0029] The preheated flue gas utilization system includes a blower 210, a three-stage heat exchanger 220, a hot blast furnace 230, and a blast furnace 240. The flue gas inlet of the three-stage heat exchanger 220 is connected to the flue gas outlet of the limestone preheater 100. The blower 210 blows cold air into the three-stage heat exchanger 220 through the air inlet of the three-stage heat exchanger 220. The air outlet of the three-stage heat exchanger 220 is connected to the air inlet of the hot blast furnace 230. The air outlet of the hot blast furnace 230 is connected to the heat source inlet of the blast furnace 240. The flue gas outlet of the three-stage heat exchanger 220 is connected to the fly ash utilization system to provide raw materials for the fly ash utilization system.

[0030] The hot blast furnace 230 is one of the main supporting equipment for the blast furnace in the iron and steel plant. The hot blast furnace continuously provides high-temperature hot air of more than 1000°C for the blast furnace during operation. The hot blast furnace 230 usually uses coal gas as fuel to heat the cold air, and then supplies high-temperature hot air to the blast furnace 240. The blower 210 blows cold air into the tertiary heat exchanger 220. At the same time, the flue gas in the limestone preheater 100 also enters the tertiary heat exchanger 220. Since the flue gas from the limestone preheater 100 to the tertiary heat exchanger 220 still has a certain temperature, the flue gas and the cold air are heat exchanged in the tertiary heat exchanger 220. The cold air is heated to a certain extent, which can reduce the heating burden of the hot blast furnace 230 on the cold air, thereby saving the energy consumption of the hot blast furnace 230 and the use of coal gas. The flue gas entering the fly ash utilization system as a raw material has basically no temperature restriction. Therefore, the reduction in flue gas temperature does not affect its entry into the fly ash utilization system as a raw material.

[0031] The fly ash utilization system includes a digestion chamber 120, a desulfurization reaction chamber 130, and a gypsum collector 200. The material inlet of the digestion chamber 120 is connected to the fly ash outlet of the lime kiln 110, and the digestion chamber 120 is connected to a water source, which transports water into the digestion chamber 120. The material inlet of the desulfurization reaction chamber 130 is respectively connected to the material outlet of the digestion chamber 120 and the material outlet of the tertiary heat exchanger 220, and the material outlet of the desulfurization reaction chamber 130 is connected to the gypsum collector 200. The gypsum collector 200 is a solid-liquid separation device, and the liquid material outlet of the gypsum collector 200 is connected to the water inlet of the digestion chamber 120.

[0032] Since CaO is generated by calcination in the lime kiln 110, the high-temperature flue gas will carry fly ash during transportation. The main component of fly ash is CaO. Therefore, the fly ash is carried into the digestion chamber 120 by conveying the high-temperature flue gas, and then water is introduced into the digestion chamber 120, so that CaO and water react to generate Ca(OH)2. The chemical reaction chamber is: CaO+H2O=Ca(OH)2. Ca(OH)2 enters the desulfurization reaction chamber 130 along the connecting channel between the digestion chamber 120 and the desulfurization reaction chamber 130. During the operation of the lime kiln 110, fuel combustion is usually used to obtain heat, and fuel combustion will produce SO2. Therefore, SO2 is contained in the high-temperature flue gas. When the high-temperature flue gas enters the limestone preheater 100, it only preheats the limestone. At the same time, after heat exchange in the tertiary heat exchanger 220, the flue gas is only a temperature difference. In addition, at this time, the flue gas also contains SO2. When the flue gas containing SO2 is passed into the desulfurization reaction chamber 130, Ca(OH)2 and SO2 react to generate CaSO3. The chemical reaction formula is: Ca(OH)2+SO2=CaSO3+H2O. CaSO3 is gypsum. The gypsum generated by the reaction enters the gypsum collector 200 for solid-liquid separation. The gypsum collector 200 can use equipment such as a filter press to separate the gypsum generated by the reaction into solid and liquid. The solid matter obtained is gypsum. The solid matter in the gypsum collector 200 is uniformly collected and stored. The liquid obtained by solid-liquid separation is mainly H2O. The water is sent back to the digestion chamber 120 and can react with CaO to generate Ca(OH)2, thereby reducing the amount of water supplied to the digestion chamber 120 through the water source, thereby achieving the purpose of saving resource consumption. At the same time, the desulfurization of high-temperature flue gas is realized, thereby reducing the pollution of flue gas.

[0033] Valves may be installed on the connecting pipes between the digestion chamber 120 and the lime kiln 110, the digestion chamber and the desulfurization reaction chamber 130, etc. to control the flow rate and amount of material conveyance.

[0034] The fly ash utilization system also includes a primary heat exchanger 150, a secondary heat exchanger 160, and a gas bin 170. The heat exchange medium inlet of the primary heat exchanger 150 is connected to the steam outlet of the digestion chamber 120, the material inlet of the primary heat exchanger 150 is connected to the material outlet of the gas bin 170, the material inlet of the gas bin 170 is connected to the gas outlet of the blast furnace 240, the material outlet of the primary heat exchanger 150 is connected to the fuel inlet of the lime kiln 110, the steam outlet of the primary heat exchanger 150 is connected to the material inlet of the secondary heat exchanger 160, and the material outlet of the secondary heat exchanger 160 is connected to the material inlet of the digestion chamber 120.

[0035] Blast furnace gas is a combustible gas produced as a byproduct in the blast furnace ironmaking process, which can be used as fuel in the operation of the lime kiln 110. Therefore, the gas produced by the blast furnace 240 is transported to the gas bin 170 for storage, and the gas is transported to the primary heat exchanger 150. In the digestion chamber 120, the process of calcium oxide and water reacting to form calcium hydroxide is an exothermic reaction. A large amount of heat is released during the reaction, which vaporizes the water in the digestion chamber 120 and converts it into a steam state. The steam is transported to the primary heat exchanger 150, which can exchange heat with the gas on the one hand, thereby improving the efficiency of the reaction. The gas temperature is increased, thereby enhancing the gas combustion efficiency and reducing energy consumption. On the other hand, the steam loses heat and turns back into liquid water. The liquid water flows from the steam outlet to the secondary heat exchanger 160. Since the liquid water entering the secondary heat exchanger 160 may carry part of the steam, in order for the steam to enter the secondary heat exchanger 160 for cooling and heat exchange, it is converted into liquid water. Then, it flows from the secondary heat exchanger 160 into the digestion chamber 120 in the form of liquid water and reacts with CaO as a raw material, which can once again reduce the supply of water to the digestion chamber 120.

[0036] The heat exchange medium inlet of the secondary heat exchanger 160 is connected to the boiler feed water source, and the heat exchange medium outlet of the secondary heat exchanger 160 is connected to the boiler feed water tank 180 .

[0037] The boiler feed water needs to be preheated before being supplied to the boiler, and the secondary heat exchanger 160 needs to cool the steam. Therefore, in the secondary heat exchanger 160, steam is used to preheat the boiler feed water. On the one hand, the boiler feed water is preheated, and on the other hand, the steam is cooled and converted into liquid water. There is no need to use additional cooling medium, which is beneficial to saving energy.

[0038] The fly ash utilization system further includes a dust collector 140 , and a material inlet of the dust collector 140 is connected to a fly ash outlet of the desulfurization reaction chamber 130 .

[0039] After gypsum is generated by the reaction in the desulfurization reaction chamber 130, a certain amount of desulfurization ash will be produced. In order to avoid pollution caused by the discharge of desulfurization ash, the desulfurization ash is collected in the dust collector 140 for dust removal, which is also convenient for other utilization and treatment of the desulfurization ash.

[0040] The flue gas recovery and utilization method of the system of the present invention is carried out according to the following steps:

[0041] (1) Limestone produced by steel smelting is added to the limestone preheater 100 for preheating.

[0042] (2) In step 1, the limestone is preheated and then transported to the lime kiln 110. The limestone is calcined in the lime kiln 110 to obtain lime, which is then stored in the lime collector 190. The flue gas generated by the lime kiln 110 is divided into two parts, which are transported to the limestone preheater 100 and the digestion chamber 120, respectively. The flue gas transported to the limestone preheater 100 serves as a heat source for preheating the limestone. The flue gas transported to the digestion chamber 120 contains CaO. Water is introduced into the digestion chamber 120, and the CaO in the flue gas reacts with water in the digestion chamber 120 to generate Ca(OH)2.

[0043] (3) The Ca(OH)2 generated in step 2 is transported to the desulfurization reaction chamber 130. At the same time, the flue gas generated by the limestone preheater 110 is divided into two parts after heat exchange and cooling in the three-stage heat exchanger 220, and is transported to the hot blast furnace 230 and the desulfurization reaction chamber 130 respectively. The flue gas transported to the hot blast furnace 230 is heated and then transported to the blast furnace 240 as a heat source. The flue gas transported to the desulfurization reaction chamber 130 contains SO2, which reacts with the Ca(OH)2 entering the desulfurization reaction chamber 130 to generate CaSO3. The CaSO3 is transported to the gypsum collector 200 for solid-liquid separation. The separated solid matter is collected and stored. The separated liquid material is transported to the digestion chamber 120 to react with CaO again to generate Ca(OH)2.

[0044] (4) In step 3, the coal gas generated by the operation of the blast furnace 240 is transported to the coal gas bin 170 for storage, and the coal gas stored in the coal gas bin 170 is transported to the primary heat exchanger 150. Meanwhile, in the digestion chamber 120, the reaction between CaO and water is an exothermic reaction, which heats the water in the digestion chamber 120 into steam, and the steam is transported to the primary heat exchanger 150. The coal gas transported to the primary heat exchanger 150 is preheated by the steam, and the preheated coal gas is transported to the lime kiln 110 as fuel;

[0045] (5) In step 4, steam enters the primary heat exchanger 150 to heat the coal gas, forming a mixture of steam and liquid water. The mixture is transported to the secondary heat exchanger 160. The secondary heat exchanger 160 exchanges heat and cools the steam in the mixture, converting the steam into liquid water. All the liquid water in the secondary heat exchanger 160 is transported to the digestion chamber 120 to react with CaO.

[0046] The present invention can achieve the purpose of controlling the material flow speed and the material inflow and outflow by installing a valve on the material circulation pipeline. The material flow speed can be adjusted with different valve openings, and the material inflow and outflow can be controlled by closing or opening the valve.

[0047] Finally, it should be noted that the above preferred 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 through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A lime kiln fume recovery system in steel smelting, characterized by: The system includes a lime production system, a fly ash utilization system, and a preheating flue gas utilization system. The lime production system is connected to the fly ash utilization system and the preheating flue gas utilization system, respectively. The lime production system transports fly ash flue gas to the fly ash utilization system, and the lime production system transports preheating flue gas to the preheating flue gas utilization system. The preheating flue gas utilization system transports fuel to the lime production system through the fly ash utilization system.

2. A lime kiln fume recovery system in steel smelting according to claim 1, characterized in that: The lime production system comprises a limestone preheater (100), a lime kiln (110), and a lime collector (190); the flue gas outlet of the lime kiln (110) is connected to the flue gas inlet of the limestone preheater (100); the fly ash outlet of the lime kiln (110) is connected to a fly ash utilization system; the lime outlet of the lime kiln (110) is connected to the lime collector (190); and a filter is installed in a pipeline connecting the flue gas outlet of the lime kiln (110) and the flue gas inlet of the limestone preheater (100).

3. A lime kiln fume recovery system in steel smelting according to claim 2, characterized in that: The preheated flue gas utilization system comprises a blower (210), a three-stage heat exchanger (220), a hot blast furnace (230), and a blast furnace (240); the flue gas inlet of the three-stage heat exchanger (220) is connected to the flue gas outlet of the limestone preheater (100); the blower (210) blows cold air into the three-stage heat exchanger (220) through the air inlet of the three-stage heat exchanger (220); the air outlet of the three-stage heat exchanger (220) is connected to the air inlet of the hot blast furnace (230); the air outlet of the hot blast furnace (230) is connected to the heat source inlet of the blast furnace (240); the flue gas outlet of the three-stage heat exchanger (220) is connected to the fly ash utilization system to provide raw materials for the fly ash utilization system.

4. A lime kiln fume recovery system in steel smelting according to claim 3, characterized in that: The fly ash utilization system comprises a digestion chamber (120), a desulfurization reaction chamber (130), and a gypsum collector (200). The material inlet of the digestion chamber (120) is connected to the fly ash outlet of the lime kiln (110), and the digestion chamber (120) is connected to a water source, which transports water into the digestion chamber (120). The material inlet of the desulfurization reaction chamber (130) is respectively connected to the material outlet of the digestion chamber (120) and the material outlet of the tertiary heat exchanger (220). The material outlet of the desulfurization reaction chamber (130) is connected to the gypsum collector (200). The gypsum collector (200) is a solid-liquid separation device. The liquid material outlet of the gypsum collector (200) is connected to the water inlet of the digestion chamber (120).

5. A lime kiln fume recovery system in steel smelting according to claim 4, characterized in that: The fly ash utilization system also includes a primary heat exchanger (150), a secondary heat exchanger (160), and a gas bin (170); the heat exchange medium inlet of the primary heat exchanger (150) is connected to the steam outlet of the digestion chamber (120); the material inlet of the primary heat exchanger (150) is connected to the material outlet of the gas bin (170); the material inlet of the gas bin (170) is connected to the gas outlet of the blast furnace (240); the material outlet of the primary heat exchanger (150) is connected to the fuel inlet of the lime kiln (110); the steam outlet of the primary heat exchanger (150) is connected to the material inlet of the secondary heat exchanger (160); and the material outlet of the secondary heat exchanger (160) is connected to the material inlet of the digestion chamber (120).

6. A lime kiln fume recovery system in steel smelting according to claim 4, characterized in that: The heat exchange medium inlet of the secondary heat exchanger (160) is connected to the boiler feed water source, and the heat exchange medium outlet of the secondary heat exchanger (160) is connected to the boiler feed water tank (180).

7. A lime kiln fume recovery system in steel smelting according to claim 4, characterized in that: The fly ash utilization system further comprises a dust collector (140), wherein a material inlet of the dust collector (140) is connected to a fly ash outlet of the desulfurization reaction chamber (130).

8. The method for recycling flue gas of a lime kiln flue gas recovery system in steel smelting according to claim 5, characterized in that: The method comprises the following steps: (1) adding limestone produced by steel smelting into a limestone preheater (100) for preheating; (2) After the limestone is preheated in step (1), it is transported to the lime kiln (110), the limestone is calcined in the lime kiln (110) to obtain lime, and the lime enters the lime collector (190) for storage. The flue gas generated by the lime kiln (110) is divided into two parts, which are transported to the limestone preheater (100) and the digestion chamber (120) respectively. The flue gas transported to the limestone preheater (100) serves as a heat source for preheating the limestone, and the flue gas transported to the digestion chamber (120) contains CaO. Water is introduced into the digestion chamber (120), and the CaO in the flue gas reacts with the water in the digestion chamber (120) to generate Ca(OH)2; (3) The Ca(OH)2 generated in step (2) is transported to the desulfurization reaction chamber (130). At the same time, the flue gas generated by the limestone preheater (110) is divided into two parts after heat exchange and cooling in the three-stage heat exchanger (220), and is transported to the hot blast furnace (230) and the desulfurization reaction chamber (130) respectively. The flue gas transported to the hot blast furnace (230) is heated and then transported to the blast furnace (240) as a heat source. The flue gas transported to the desulfurization reaction chamber (130) contains SO2, which reacts with the Ca(OH)2 entering the desulfurization reaction chamber (130) to generate CaSO3. The CaSO3 is transported to the gypsum collector (200) for solid-liquid separation. The separated solid matter is collected and stored. The separated liquid material is transported to the digestion chamber (120) to react with CaO again to generate Ca(OH)2. (4) In the step (3), the coal gas generated by the operation of the blast furnace (240) is transported to the coal gas bin (170) for storage, and the coal gas stored in the coal gas bin (170) is transported to the primary heat exchanger (150). At the same time, in the digestion chamber (120), the reaction between CaO and water is an exothermic reaction, which heats the water in the digestion chamber (120) to become steam, and the steam is transported to the primary heat exchanger (150). The coal gas transported to the primary heat exchanger (150) is preheated by the steam, and the preheated coal gas is transported to the lime kiln (110) as fuel; (5) In step (4), steam enters the primary heat exchanger (150) to heat the coal gas, thereby forming a mixture of steam and liquid water. The mixture is then transported to the secondary heat exchanger (160). The secondary heat exchanger (160) cools the steam in the mixture by heat exchange, and the steam is converted into liquid water. All the liquid water in the secondary heat exchanger (160) is transported to the digestion chamber (120) to react with CaO.

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