Multi-state coupling heat storage steel-making electric furnace flue gas waste heat deep utilization system

Abstract

The utility model discloses a multi-state coupling heat storage steel-making electric furnace flue gas waste heat deep utilization system which comprises a flue gas system, a low-pressure steam system, a fused salt heat exchange and storage system, a high-pressure steam system and a power generation system. A front flue heat accumulator is additionally arranged in a front flue of a settling chamber, a settling chamber heat accumulator is additionally arranged in a combustion settling chamber, and a high-pressure water storage tank is additionally arranged on a connecting pipeline between an outlet of a high-pressure economizer and a water inlet of a high-pressure preheater. Through the arrangement of the front flue heat accumulator, the settling chamber heat accumulator and the high-pressure water storage tank, the large fluctuation of the flue gas temperature of the electric furnace can be better stabilized, the control of fused salt and feed water flow in a high-pressure steam system is simplified, the stable output of high-pressure steam is maintained, the stability and the safety of the system are improved, and the energy consumption is reduced. And the electric furnace flue gas waste heat recovery technology is further improved.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas waste heat utilization, in particular to a system for deeply utilizing the waste heat of the flue gas of a polymorphic coupling regenerative steelmaking electric furnace. Background Technique

[0002] Compared with the traditional converter steelmaking with a long process, electric furnace steelmaking has outstanding advantages such as short process, low investment, fast construction, good energy conservation and emission reduction effects.

[0003] In order to meet the requirements of the dust removal system, the flue gas of the electric furnace needs to be cooled to below 180°C. According to statistics, the heat carried away by cooling water, flue gas and dust during the electric furnace smelting period accounts for more than 10% of the total input heat of the electric furnace, and can even approach 30% when the amount of hot metal added is large.

[0004] After the electric furnace is powered on, the primary flue gas is extracted from the fourth hole through the furnace cover, and is successively cooled through a water-cooled elbow, a water-cooled sliding sleeve, a water-cooled sedimentation chamber and a water-cooled flue, and then cooled to about 200°C through an air cooler or a spray cooling tower, and then fully mixed with the secondary waste gas at about 45°C collected by the environmental dust removal hood. Finally, after being dust-removed by a bag filter, it is discharged to the atmosphere by a dust removal fan. The water-cooling and air-cooling hybrid mode can effectively reduce the flue gas temperature and efficiently capture flue gas dust, but it needs to be equipped with a large cooling system, consumes a large amount of cooling water and electricity, has a high operating cost, and a large amount of high-quality heat contained in the high-temperature flue gas is not recycled. Some steel enterprises also adopt forms such as preheating scrap steel, vaporizing flue, heat pipe waste heat boiler and water pipe waste heat boiler to recover the waste heat in the flue gas, but there are problems such as incomplete waste heat recovery in each temperature section, low waste heat recovery rate, and low recovery steam parameters.

[0005] The utility model ZL202322630661.X discloses a system for deep utilization of waste heat from the flue gas of an electric steelmaking furnace. By setting up a low-pressure steam system, a high-pressure steam system, and a molten salt heat exchange and energy storage system, it can largely suppress the fluctuations in flue gas temperature and flow rate, creating conditions for recovering the waste heat of the electric furnace flue gas in the full temperature range. However, the large fluctuations in flue gas temperature and flow rate have always objectively existed. Although the fluctuating flue gas heat can be stored in the molten salt through the molten salt heat exchange and energy storage system and then continuously and stably output in the high-pressure steam system, restricted by the fluctuations in the heat absorbed by the tail high-pressure economizer, the feed water flow rate and temperature entering the high-pressure steam system from the high-pressure economizer fluctuate greatly, and it is difficult to match well with the molten salt temperature and flow rate in the high-pressure steam system in real time. In extreme cases, overheating or undercooling may occur in the heating surface of the high-pressure steam system, which is not conducive to the stable generation of high-pressure steam and the safe operation of the heating surface and the system. Therefore, further suppressing the large fluctuations in the electric furnace flue gas temperature and flow rate, maintaining stable molten salt and feed water flow rates in the high-pressure steam system, thereby ensuring the stable generation of high-parameter steam that meets the requirements in the high-pressure steam system, and ensuring the safe and stable operation of the entire system are of great significance for promoting the electric furnace flue gas waste heat utilization system, reducing the cost of electric furnace steelmaking, and improving the energy conservation and carbon reduction level of iron and steel enterprises. Summary of the Utility Model

[0006] To solve the above technical problems, the utility model designs a system for deep utilization of waste heat from the flue gas of a multi-state coupled heat storage electric steelmaking furnace.

[0007] The utility model adopts the following technical solutions:

[0008] A system for deep utilization of waste heat from the flue gas of a multi-state coupled heat storage electric steelmaking furnace, including a flue gas system, a low-pressure steam system, a molten salt heat exchange and energy storage system, a high-pressure steam system, and a power generation system;

[0009] The flue gas system includes an electric furnace, a flue before the settling chamber, a combustion settling chamber, a flue after the settling chamber, a fan, and a dust removal connection flue connected in sequence;

[0010] The low-pressure steam system includes a deaerator, a heat accumulator, an external supply steam superheater, a low-pressure steam drum, a flue gas vaporization heat exchanger, a settling chamber vaporization heat exchanger, a low-pressure evaporator, a low-pressure economizer, and corresponding connecting pipes;

[0011] The molten salt heat exchange and energy storage system includes a high-temperature molten salt tank, a medium-temperature molten salt tank, a low-temperature molten salt tank, a high-temperature molten salt heat exchanger, a medium-temperature molten salt heat exchanger, and corresponding connecting pipes;

[0012] The high-pressure steam system includes a high-pressure preheater, a high-pressure evaporator, a high-pressure steam drum, a high-pressure superheater, a high-pressure economizer, and corresponding connecting pipes;

[0013] In the low-pressure steam system, the inlet of the deaerator is connected to the feed water, and the outlet of the deaerator is respectively connected to the inlet of the low-pressure economizer and the inlet of the high-pressure economizer. The outlet of the low-pressure economizer is connected to the water inlet of the low-pressure steam drum. The water outlet of the low-pressure steam drum is respectively connected to the inlet of the flue gas vaporization heat exchanger, the inlet of the settling chamber vaporization heat exchanger, and the inlet of the low-pressure evaporator. The outlets of the flue gas vaporization heat exchanger, the settling chamber vaporization heat exchanger, and the low-pressure evaporator are connected to the steam-water mixture inlet of the low-pressure steam drum. The steam outlet of the low-pressure steam drum is connected to the inlet of the heat accumulator; the outlet of the heat accumulator is connected to the inlet of the externally supplied steam superheater;

[0014] In the high-pressure steam system, the outlet of the high-pressure economizer is connected to the water inlet of the high-pressure preheater. The water outlet of the high-pressure preheater is connected to the water inlet of the high-pressure steam drum. The water outlet of the high-pressure steam drum is connected to the water inlet of the high-pressure evaporator. The outlet of the high-pressure evaporator is connected to the steam-water mixture inlet of the high-pressure steam drum. The steam outlet of the high-pressure steam drum is connected to the steam inlet of the high-pressure superheater. The steam outlet of the high-pressure superheater is connected to the power generation system;

[0015] In the molten salt heat exchange and heat storage system, the outlet of the high-temperature molten salt tank is connected to the molten salt inlet of the high-pressure superheater. The molten salt outlet of the high-pressure superheater is connected to the molten salt inlet of the high-pressure evaporator. The molten salt outlet of the high-pressure evaporator is connected to the molten salt inlet of the high-pressure preheater. The molten salt outlet of the high-pressure preheater is connected to the molten salt inlet of the low-temperature molten salt tank. The molten salt outlet of the low-temperature molten salt tank is connected to the inlet of the medium-temperature molten salt heat exchanger. The outlet of the medium-temperature molten salt heat exchanger is connected to the inlet of the medium-temperature molten salt tank. The outlet of the medium-temperature molten salt tank is connected to the inlet of the high-temperature molten salt heat exchanger. The outlet of the high-temperature molten salt heat exchanger is connected to the inlet of the high-temperature molten salt tank;

[0016] A pre-flue gas heat accumulator is arranged in the pre-flue gas of the settling chamber, and a settling chamber heat accumulator is arranged in the combustion settling chamber. A high-pressure water storage tank is connected to the connecting pipe between the outlet of the high-pressure economizer and the water inlet of the high-pressure preheater.

[0017] Preferably, the pre-flue gas heat accumulator and the settling chamber heat accumulator are made of high heat capacity and high temperature resistant materials such as porous magnesia bricks, porous ceramics or porous precast concrete.

[0018] Preferably, the flue gas vaporization heat exchanger is installed in the pre-flue gas of the settling chamber, and the settling chamber vaporization heat exchanger is installed in the combustion settling chamber.

[0019] Preferably, the high-temperature molten salt heat exchanger, the medium-temperature molten salt heat exchanger, the low-pressure evaporator, the high-pressure economizer, and the low-pressure economizer are sequentially installed in the post-flue gas of the settling chamber from front to back.

[0020] Preferably, the externally supplied steam superheater is installed in the low-pressure steam drum.

[0021] Preferably, a low-pressure feed water pump is connected between the outlet of the deaerator and the inlet of the low-pressure economizer, and a high-pressure feed water pump is connected between the outlet of the deaerator and the inlet of the high-pressure economizer.

[0022] Preferably, the high-pressure steam system further includes a high-temperature molten salt pump, a low-temperature molten salt pump, and a medium-temperature molten salt pump. The outlet of the high-temperature molten salt tank is connected to the molten salt inlet of the high-pressure superheater through the high-temperature molten salt pump. The molten salt outlet of the low-temperature molten salt tank is connected to the inlet of the medium-temperature molten salt heat exchanger through the low-temperature molten salt pump. The outlet of the medium-temperature molten salt tank is connected to the inlet of the high-temperature molten salt heat exchanger through the medium-temperature molten salt pump.

[0023] Preferably, the outlet of the high-temperature molten salt heat exchanger is connected to the inlet of the medium-temperature molten salt tank through a bypass.

[0024] Preferably, the power generation system includes a back-pressure steam turbine and a generator, and the back-pressure steam turbine is connected to the generator; the steam outlet of the high-pressure superheater is connected to the inlet of the back-pressure steam turbine, and the steam outlet of the back-pressure steam turbine is connected to a heat user.

[0025] Preferably, the outlet of the externally supplied steam superheater is connected to a heat user.

[0026] In the present utility model, the low-pressure steam system absorbs part of the heat of the high-temperature flue gas at the front end and the heat of the low-temperature flue gas at the back end to generate low-pressure steam, which can be used for other processes in steelmaking or supplied to heat users. At the same time, the molten salt heat exchange and heat storage system absorbs the heat of the high-temperature flue gas and stores it in the high-temperature molten salt tank. The high-temperature molten salt in the high-temperature molten salt tank releases heat through the high-pressure superheater, high-pressure evaporator, and high-pressure preheater of the high-pressure steam system to stably produce high-temperature and high-pressure superheated steam for power generation by the back-pressure steam turbine. The low-pressure steam discharged after power generation can be used for other processes in steelmaking or supplied to heat users. A total of 3 molten salt tanks are set in the system. Among them, the low-temperature molten salt tank is used to store the cold salt (such as 280 °C) that leaves after heat exchange with the high-pressure steam system, providing an endothermic medium for the waste heat recovery of the medium-temperature flue gas; the medium-temperature molten salt tank is used to store the molten salt within a certain temperature range (such as 350 °C to 510 °C), providing an endothermic medium for the waste heat recovery of the high-temperature flue gas. When the flue gas temperature is not higher than the set temperature (such as 540 °C), the medium-temperature molten salt circulates between the medium-temperature molten salt tank and the high-temperature molten salt heat exchanger through a bypass to exchange heat with the flue gas (being heated by the flue gas or heating the flue gas) to suppress the temperature fluctuation of the flue gas; the high-temperature molten salt tank is used to store the high-temperature molten salt reaching a certain temperature (such as 510 °C), providing a stable heat source for the high-pressure steam system. When the flue gas temperature is higher than the set temperature (such as 540 °C), the medium-temperature molten salt is pumped from the medium-temperature molten salt tank to the high-temperature molten salt heat exchanger, absorbs the high-temperature waste heat of the flue gas and is heated to the set temperature (such as 510 °C) and then sent to the high-temperature molten salt tank for storage, so as to keep the temperature of the molten salt in the high-temperature molten salt tank stable.

[0027] Compared with the utility model ZL 2023 2 2630661.X, in the present utility model, a pre-flue gas heat accumulator and a settling chamber heat accumulator are respectively added in the pre-flue of the settling chamber and the combustion settling chamber, and a high-pressure water storage tank is added between the high-pressure economizer and the high-pressure preheater.

[0028] The functions of setting the pre-flue gas heat accumulator and the settling chamber heat accumulator are as follows: when the flue gas temperature is high, the heat accumulator absorbs the heat in the flue gas and heats up, stores part of the heat of the high-temperature flue gas in the heat accumulator and reduces the flue gas temperature; when the flue gas temperature is low, the heat accumulator releases heat to the flue gas and cools down, increasing the flue gas temperature.

[0029] The function of setting the high-pressure water storage tank is as follows: during the smelting cycle of the electric furnace, due to the large fluctuations in the temperature and flow rate of the flue gas flowing through the high-pressure economizer, the heat absorbed by the high-pressure feed water in the high-pressure economizer also fluctuates greatly. In order to ensure that the feed water entering the high-pressure preheater and the high-pressure evaporator has a suitable temperature to guarantee the safety of the heating surface, it is usually necessary to adjust the feed water flow rate according to the heat absorption, which causes the feed water flow rate to fluctuate greatly following the flue gas temperature and flow rate, and does not match the stable molten salt flow rate in the high-pressure preheater, the high-pressure evaporator, and the high-pressure superheater. In extreme cases, there may be insufficient cooling of the heat transfer surface or molten salt solidification. After adding a high-pressure water storage tank between the high-pressure economizer and the high-pressure preheater, the inlet high-pressure feed water flow rate of the water storage tank is adjusted according to the fluctuations in the flue gas temperature and flow rate to make the feed water temperature appropriate, and the outlet flow rate of the water storage tank can be kept stable, matching the stable molten salt flow rate in the high-pressure preheater, the high-pressure evaporator, and the high-pressure superheater.

[0030] Compared with the existing electric furnace flue gas waste heat utilization technology, the beneficial effects of the present utility model are: (1) By setting the pre-flue gas heat accumulator and the settling chamber heat accumulator, the large fluctuations in the flue gas temperature are suppressed to a certain extent, and part of the dust in the flue gas is separated, improving the working conditions of subsequent heating surfaces at all levels; (2) By setting the high-pressure water storage tank, the system can achieve a stable matching of the feed water and molten salt flow rates in the high-pressure steam system, simplify the flow control of the molten salt, ensure the stable production of high-pressure steam, and at the same time avoid overheating and overcooling phenomena in the heat transfer surface caused by water flow fluctuations, eliminating the risks of dry burning of the heating surface and molten salt solidification, and further ensuring the safe and stable operation of the entire system; (3) Through reasonable settings, the present system converts the fluctuating heat of the electric furnace flue gas into different forms such as sensible heat of the heat accumulator, sensible heat of the molten salt, sensible heat of low-pressure steam, and sensible heat of high-pressure feed water and accumulates them, and then converts them into a stable output of low-pressure steam and high-pressure steam. Not only is the waste heat at each temperature section recovered more completely, improving the waste heat utilization efficiency, but also the influence of large fluctuations in the flue gas temperature on the quality of the recovered waste heat is eliminated, improving the quality of waste heat utilization. Description of the Drawings

[0031] Figure 1It is a schematic structural diagram of the present utility model;

[0032] In the figure: 1, feed water; 2, low-pressure feed water pump; 3, high-pressure feed water pump; 4, heat user; 100, flue gas system; 101, electric furnace; 102, flue before sedimentation chamber; 103, combustion sedimentation chamber; 104, flue after sedimentation chamber; 105, fan; 106, dust removal connecting flue; 107, heat storage body in the front flue; 108, heat storage body in the sedimentation chamber; 200, low-pressure steam system; 201, deaerator; 202, heat accumulator; 203, external supply steam superheater; 204, low-pressure steam drum; 205, flue gas vaporization heat exchanger; 206, sedimentation chamber vaporization heat exchanger; 207, low-pressure evaporator; 208, low-pressure economizer; 300, molten salt heat exchange and heat storage system; 301, high-temperature molten salt tank; 302, high-temperature molten salt pump; 303, medium-temperature molten salt tank; 304, low-temperature molten salt tank; 305, low-temperature molten salt pump; 306, medium-temperature molten salt pump; 307, high-temperature molten salt heat exchanger; 308, medium-temperature molten salt heat exchanger; 400, high-pressure steam system; 401, high-pressure preheater; 402, high-pressure evaporator; 403, high-pressure steam drum; 404, high-pressure superheater; 405, high-pressure economizer; 406, high-pressure water storage tank; 500, power generation system; 501, back-pressure steam turbine; 502, generator. Specific embodiments

[0033] The technical solution of the present utility model will be further specifically described below through specific embodiments and in conjunction with the accompanying drawings:

[0034] Embodiment: As Figure 1 shown, a multi-state coupling heat storage and deep utilization system for the waste heat of the flue gas of an electric steelmaking furnace includes a flue gas system 100, a low-pressure steam system 200, a molten salt heat exchange and heat storage system 300, a high-pressure steam system 400, and a power generation system 500.

[0035] The flue gas system 100 includes an electric furnace 101, a flue before the sedimentation chamber 102, a heat storage body 107 in the front flue, a combustion sedimentation chamber 103, a heat storage body 108 in the sedimentation chamber, a flue after the sedimentation chamber 104, a fan 105, and a dust removal connecting flue 106. The electric furnace 101, the flue before the sedimentation chamber 102, the combustion sedimentation chamber 103, the flue after the sedimentation chamber 104, the fan 105, and the dust removal connecting flue 106 are connected in sequence. The heat storage body 107 in the front flue is arranged in the flue before the sedimentation chamber 102, and the heat storage body 108 in the sedimentation chamber is arranged in the combustion sedimentation chamber 103. The heat storage body 107 in the front flue and the heat storage body 108 in the sedimentation chamber are high heat capacity and high temperature resistant materials such as porous magnesia bricks, porous ceramics, or porous precast concrete.

[0036] The low-pressure steam system 200 includes a deaerator 201, a heat accumulator 202, an external supply steam superheater 203, a low-pressure steam drum 204, a flue gas vaporization heat exchanger 205, a sedimentation chamber vaporization heat exchanger 206, a low-pressure evaporator 207, a low-pressure economizer 208, and corresponding connecting pipelines.

[0037] The molten salt heat exchange and storage system 300 includes a high-temperature molten salt tank 301, a high-temperature molten salt pump 302, a medium-temperature molten salt tank 303, a low-temperature molten salt tank 304, a low-temperature molten salt pump 305, a medium-temperature molten salt pump 306, a high-temperature molten salt heat exchanger 307, a medium-temperature molten salt heat exchanger 308, and corresponding connecting pipelines.

[0038] The high-pressure steam system 400 includes a high-pressure preheater 401, a high-pressure evaporator 402, a high-pressure steam drum 403, a high-pressure superheater 404, a high-pressure economizer 405, a high-pressure water storage tank 406, and corresponding connecting pipelines.

[0039] The power generation system 500 includes a back-pressure steam turbine 501 and a generator 502.

[0040] Correspondingly, the flue gas vaporization heat exchanger 205 is installed in the front flue 102 of the sedimentation chamber, the sedimentation chamber vaporization heat exchanger 206 is installed in the combustion sedimentation chamber 103, and the high-temperature molten salt heat exchanger 307, the medium-temperature molten salt heat exchanger 308, the low-pressure evaporator 207, the high-pressure economizer 405, and the low-pressure economizer 208 are installed in the rear flue 104 of the sedimentation chamber in sequence from front to back. The external supply steam superheater 203 is installed in the low-pressure steam drum 204.

[0041] In the low-pressure steam system 200, the outlet of the deaerator 201 is respectively connected to the inlet of the low-pressure feed water pump 2 and the inlet of the high-pressure feed water pump 3. The outlet of the low-pressure feed water pump 2 is connected to the inlet of the low-pressure economizer 208, and the outlet of the low-pressure economizer 208 is connected to the water inlet of the low-pressure steam drum 204. The water outlet of the low-pressure steam drum 204 is respectively connected to the inlet of the flue gas vaporization heat exchanger 205, the inlet of the sedimentation chamber vaporization heat exchanger 206, and the inlet of the low-pressure evaporator 207. The outlet of the flue gas vaporization heat exchanger 205, the outlet of the sedimentation chamber vaporization heat exchanger 206, and the outlet of the low-pressure evaporator 207 are connected to the steam-water mixture inlet of the low-pressure steam drum 204. The steam outlet of the low-pressure steam drum 204 is connected to the inlet of the heat accumulator 202. The outlet of the heat accumulator 202 is connected to the inlet of the external supply steam superheater 203, and the outlet of the external supply steam superheater 203 is connected to the heat user 4.

[0042] In the high-pressure steam system 400, the outlet of the high-pressure feed water pump 3 is connected to the inlet of the high-pressure economizer 405, the outlet of the high-pressure economizer 405 is connected to the inlet of the high-pressure accumulator tank 406, the outlet of the high-pressure accumulator tank 406 is connected to the water inlet of the high-pressure preheater 401, the water outlet of the high-pressure preheater 401 is connected to the water inlet of the high-pressure steam drum 403, the water outlet of the high-pressure steam drum 403 is connected to the water inlet of the high-pressure evaporator 402, the outlet of the high-pressure evaporator 402 is connected to the steam-water mixture inlet of the high-pressure steam drum 403, the steam outlet of the high-pressure steam drum 403 is connected to the steam inlet of the high-pressure superheater 404, the steam outlet of the high-pressure superheater 404 is connected to the inlet of the back-pressure steam turbine 501, and the steam outlet of the back-pressure steam turbine 501 is connected to the heat user 4.

[0043] In the molten salt heat exchange and energy storage system 300, the outlet of the high-temperature molten salt tank 301 is connected to the molten salt inlet of the high-pressure superheater 404 through the high-temperature molten salt pump 302, the molten salt outlet of the high-pressure superheater 404 is connected to the molten salt inlet of the high-pressure evaporator 402, the molten salt outlet of the high-pressure evaporator 402 is connected to the molten salt inlet of the high-pressure preheater 401, the molten salt outlet of the high-pressure preheater 401 is connected to the molten salt inlet of the low-temperature molten salt tank 304, the molten salt outlet of the low-temperature molten salt tank 304 is connected to the inlet of the medium-temperature molten salt heat exchanger 308 through the low-temperature molten salt pump 305, the outlet of the medium-temperature molten salt heat exchanger 308 is connected to the inlet of the medium-temperature molten salt tank 303, the outlet of the medium-temperature molten salt tank 303 is connected to the inlet of the high-temperature molten salt heat exchanger 307 through the medium-temperature molten salt pump, the outlet of the high-temperature molten salt heat exchanger 307 is connected to the inlet of the high-temperature molten salt tank 301, and at the same time, the outlet of the high-temperature molten salt heat exchanger 307 is connected to the inlet of the medium-temperature molten salt tank 303 through a bypass.

[0044] A brief description of the waste heat recovery process of the electric furnace flue gas based on the present utility model is as follows.

[0045] During the steelmaking process, flue gas continuously discharges from the fourth hole of the electric furnace 101, flows through the front flue of the sedimentation chamber 102, the combustion sedimentation chamber 103, and the rear flue of the sedimentation chamber 104 in sequence, and then is drawn by the fan 105 to the dust removal connection flue 106 and goes to the dust removal system. In the front flue of the sedimentation chamber 102 and the combustion sedimentation chamber 103, CO in the flue gas is mixed with the inhaled air and burned, and most of the dust is settled and separated in the combustion sedimentation chamber 103. During the process of the flue gas flowing from front to back, it exchanges heat with the front flue regenerator 107, the flue gas vaporization heat exchanger 205, the sedimentation chamber regenerator 108, the sedimentation chamber vaporization heat exchanger 206, the high-temperature molten salt heat exchanger 307, the medium-temperature molten salt heat exchanger 308, the low-pressure evaporator 207, the high-pressure economizer 405, and the low-pressure economizer 208 in sequence. The temperature of the flue gas is cooled to below 180 °C, and then it enters the dust removal system to complete dust removal.

[0046] The externally supplied feed water 1 enters the deaerator 201, where deaeration is carried out. The deaerated water passes through the low-pressure feed water pump 2 and enters the low-pressure economizer 208, and also passes through the high-pressure feed water pump and enters the high-pressure economizer 405.

[0047] The deaerated water entering the low-pressure economizer 208 exchanges heat with the flue gas therein and then enters the low-pressure steam drum 204 through the water inlet of the low-pressure steam drum 204. The saturated water in the low-pressure steam drum 204 enters the flue gas vaporization heat exchanger 205, the settling chamber vaporization heat exchanger 206, and the low-pressure evaporator 207 respectively through the water outlet, vaporizes after absorbing the heat of the flue gas, and enters the low-pressure steam drum 204 in the form of a steam-water mixture through the steam-water mixture inlet. The steam in the low-pressure steam drum 204 enters the heat accumulator 202 through the steam outlet after steam-water separation. When steam needs to be supplied externally, the steam in the heat accumulator 202 enters the external supply steam superheater 203 installed in the low-pressure steam drum 204 through the outlet. Since the pressure of the heat accumulator 202 is lower than that of the low-pressure steam drum 203, the saturated steam temperature in the heat accumulator 202 is lower than the saturated steam temperature of the low-pressure steam drum 203. The saturated steam from the heat accumulator 202 absorbs heat in the external supply steam superheater 203 and becomes low-pressure superheated steam, which is then supplied to the heat user 4. In this embodiment, the pressure of the low-pressure superheated steam is 1.35 MPa and the temperature is 205 °C.

[0048] To prevent the water temperature entering the high-pressure steam drum from being too low, a high-pressure preheater is provided between the high-pressure economizer 405 and the high-pressure steam drum 403. The deaerated water from the high-pressure feed water pump 3 enters the high-pressure economizer 405, exchanges heat with the flue gas therein, enters the high-pressure water storage tank, and then enters the high-pressure preheater 401 from the outlet of the high-pressure water storage tank 406 at a stable flow rate, exchanges heat with the molten salt therein, is heated to an appropriate temperature, and then enters the high-pressure steam drum 403. The saturated water in the high-pressure steam drum 403 enters the high-pressure evaporator 402 through the water outlet, exchanges heat with the molten salt in the high-pressure evaporator 402 and vaporizes and evaporates, enters the high-pressure steam drum 403 in the form of a steam-water mixture through the steam-water mixture inlet. The steam in the high-pressure steam drum 403 enters the high-pressure superheater 404 through the steam outlet after steam-water separation, exchanges heat with the high-temperature molten salt in the high-pressure superheater 404 and becomes high-temperature and high-pressure superheated steam. The superheated steam is led out from the steam outlet of the high-pressure superheater 404 and enters the back-pressure steam turbine 501, driving the back-pressure steam turbine 501 to rotate. The back-pressure steam turbine 501 then drives the generator 502 to generate electricity. The low-pressure superheated steam after power generation is discharged from the back-pressure steam turbine 501 and sent to the heat user 4. In this embodiment, the pressure of the high-temperature and high-pressure superheated steam used for power generation is 9.8 MPa and the temperature is 480 °C; the pressure of the low-pressure superheated steam is 1.35 MPa and the temperature is 205 °C.

[0049] To stabilize the production of high-temperature and high-pressure superheated steam for power generation, a molten salt heat exchange and energy storage system 300 including three molten salt tanks is provided. In this embodiment, the high-temperature molten salt tank 301 is used to store high-temperature molten salt with a temperature higher than the set temperature (510°C in this embodiment) and provide a stable heat source for the high-pressure steam system 400; the low-temperature molten salt tank 304 is used to store the cold salt (280°C in this embodiment) that leaves after heat exchange with the high-pressure steam system 400 and provide an endothermic medium for the waste heat recovery of medium-temperature flue gas; the medium-temperature molten salt tank 303 is used to store molten salt within a certain temperature range (350°C to 510°C in this embodiment) and provide an endothermic medium for the waste heat recovery of high-temperature flue gas. When high-temperature and high-pressure steam needs to be generated for the power generation system 500 to generate electricity, the high-temperature molten salt in the high-temperature molten salt tank 301 is pumped into the high-pressure superheater 404 through the high-temperature molten salt pump 302, superheats the saturated steam coming from the high-pressure steam drum 403 in the high-pressure superheater 404, then enters the high-pressure evaporator 402, heats and vaporizes the saturated water coming from the high-pressure steam drum 403 in the high-pressure evaporator 402, and then enters the high-pressure preheater 401. In the high-pressure preheater 401, the unsaturated water coming from the high-pressure economizer 405 is heated to an appropriate temperature to facilitate its entry into the high-pressure steam drum 403. The molten salt with a temperature of about 280°C after releasing heat flows out of the high-pressure preheater 401 and enters the low-temperature molten salt tank 304. The molten salt in the low-temperature molten salt tank 304 is pumped into the medium-temperature molten salt heat exchanger 308 through the low-temperature molten salt pump 305, absorbs the waste heat of the flue gas in the medium-temperature molten salt heat exchanger 308, and then enters the medium-temperature molten salt tank 303. According to the different flue gas temperatures at the inlet of the high-temperature molten salt heat exchanger 307, the molten salt in the medium-temperature molten salt tank 303 has two operating modes: when the flue gas temperature at the inlet of the high-temperature molten salt heat exchanger 307 is higher than the set temperature (540°C in this embodiment), the medium-temperature molten salt is pumped from the medium-temperature molten salt tank 303 to the high-temperature molten salt heat exchanger 307 through the medium-temperature molten salt pump 306, absorbs the high-temperature waste heat of the flue gas and is heated to above the set temperature (510°C in this embodiment), and then is sent to the high-temperature molten salt tank 301 for storage; when the flue gas temperature at the inlet of the high-temperature molten salt heat exchanger 307 is not higher than the set temperature (540°C in this embodiment), the medium-temperature molten salt is pumped from the medium-temperature molten salt tank 303 to the high-temperature molten salt heat exchanger 307 through the medium-temperature molten salt pump 306, exchanges heat with the flue gas (is heated by the flue gas or heats the flue gas), and then is sent back to the medium-temperature molten salt tank 303 through a bypass.In this way, when the temperature of the flue gas passing through the high-temperature molten salt heat exchanger 307 is not high enough to heat the medium-temperature molten salt to the required temperature (510°C in this embodiment), the medium-temperature molten salt flowing from the medium-temperature molten salt tank 303 does not enter the high-temperature molten salt tank 301 after passing through the high-temperature molten salt heat exchanger 307. Instead, it circulates between the medium-temperature molten salt tank 303 and the high-temperature molten salt heat exchanger 307 through a bypass. On the one hand, it avoids feeding molten salt below the set temperature (510°C in this embodiment) into the high-temperature molten salt tank 301, thus ensuring the stable temperature of the molten salt in the high-temperature molten salt tank 301. On the other hand, through the circulation of the medium-temperature molten salt between the medium-temperature molten salt tank 303 and the high-temperature molten salt heat exchanger 307, the purpose of suppressing the fluctuation of the flue gas temperature is achieved, which is beneficial to the stable heat exchange of the subsequent heat exchange surfaces.

[0050] In order to better suppress the large fluctuations in the flue gas temperature in the high-temperature section, a pre-flue gas regenerator 107 is provided in the pre-flue 102 of the settling chamber, and a settling chamber regenerator 108 is provided in the combustion settling chamber 103. The pre-flue gas regenerator 107 and the settling chamber regenerator 108 are made of high-heat-capacity and high-temperature-resistant materials such as porous magnesia bricks, porous ceramics, and porous precast concrete. When the flue gas temperature is high, the regenerator absorbs the heat in the flue gas and heats up, storing part of the heat of the high-temperature flue gas in the regenerator and reducing the flue gas temperature. When the flue gas temperature is low, the regenerator releases heat to the flue gas and cools down, increasing the flue gas temperature. The setting of the regenerator reduces the fluctuation range of the flue gas temperature, improves the heat exchange conditions of each heating surface, and reduces the design difficulty and manufacturing cost of each heating surface. At the same time, the porous structure of the regenerator can separate part of the dust in the flue gas, reducing the wear of the subsequent heating surfaces by the dust and improving the operation stability and safety of the entire system.

[0051] A high-pressure water storage tank 406 is provided between the high-pressure economizer 406 and the high-pressure preheater 401. After adding the high-pressure water storage tank 406, the inlet high-pressure feed water flow of the high-pressure water storage tank 406 is adjusted according to the fluctuations of the flue gas temperature and flow rate. When the flue gas temperature is high and the flow rate is large, the high-pressure feed water flow is increased by control. When the flue gas temperature is low and the flow rate is small, the high-pressure feed water flow is reduced by control. In this way, the water temperature entering the high-pressure preheater 401 can be controlled at an appropriate temperature, which is beneficial to the safety of the subsequent high-pressure evaporation and superheating processes. Due to the storage effect of the high-pressure water storage tank 406, the outlet flow can be stably output at a value close to the average value of the entire smelting cycle, matching the stable molten salt flow in the high-pressure preheater, high-pressure evaporator, and high-pressure superheater. The presence of the high-pressure water storage tank 406 enables the feed water / steam flow and molten salt flow in the high-pressure preheater 401, high-pressure evaporator 402, and high-pressure superheater 404 in the high-pressure steam system 400 to achieve stable input and output, ensuring the stable production of high-pressure steam. At the same time, it also greatly simplifies the control of the molten salt and feed water flow in the high-pressure steam system 400.

[0052] By setting the pre-flue gas regenerator 107, the settling chamber regenerator 108 and the high-pressure water storage tank 406, the utility model can better suppress the large fluctuations in the temperature of the electric furnace flue gas, simplify the control of the molten salt and feed water flow rates in the high-pressure steam system 400 and maintain the stable output of high-pressure steam, increase the stability and safety of the system, and further improve the electric furnace flue gas waste heat recovery technology.

[0053] The above-described embodiments are only a preferred solution of the utility model, and do not impose any form of limitation on the utility model. There are other variations and modifications without exceeding the technical solutions described in the claims.

Claims

1. A multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system, including a flue gas system, a low-pressure steam system, a molten salt heat exchange and heat storage system, a high-pressure steam system and a power generation system; The flue gas system includes an electric furnace, a flue before a settling chamber, a combustion settling chamber, a flue after a settling chamber, a fan and a dust removal connecting flue which are connected in sequence; The low-pressure steam system includes a deaerator, a heat accumulator, an external steam superheater, a low-pressure steam drum, a flue gasification heat exchanger, a settling chamber gasification heat exchanger, a low-pressure evaporator, a low-pressure economizer and corresponding connecting pipelines; The molten salt heat exchange and heat storage system includes a high-temperature molten salt tank, a medium-temperature molten salt tank, a low-temperature molten salt tank, a high-temperature molten salt heat exchanger, a medium-temperature molten salt heat exchanger and corresponding connecting pipes; The high-pressure steam system includes a high-pressure preheater, a high-pressure evaporator, a high-pressure steam drum, a high-pressure superheater, a high-pressure economizer and corresponding connecting pipelines; In the low-pressure steam system, the deaerator inlet is connected to the feed water, the deaerator outlet is respectively connected to the low-pressure economizer inlet and the high-pressure economizer inlet, the low-pressure economizer outlet is connected to the water inlet of the low-pressure drum, the water outlet of the low-pressure drum is respectively connected to the flue gasification heat exchanger inlet, the settling chamber gasification heat exchanger inlet, and the low-pressure evaporator inlet, the flue gasification heat exchanger outlet, the settling chamber gasification heat exchanger outlet, and the low-pressure evaporator outlet are connected to the steam-water mixture inlet of the low-pressure drum, the steam outlet of the low-pressure drum is connected to the inlet of the heat accumulator; the outlet of the heat accumulator is connected to the inlet of the external steam superheater; In the high-pressure steam system, the outlet of the high-pressure economizer is connected to the water inlet of the high-pressure preheater, the water outlet of the high-pressure preheater is connected to the water inlet of the high-pressure drum, the water outlet of the high-pressure drum is connected to the water inlet of the high-pressure evaporator, the outlet of the high-pressure evaporator is connected to the steam-water mixture inlet of the high-pressure drum, the steam outlet of the high-pressure drum is connected to the steam inlet of the high-pressure superheater, and the steam outlet of the high-pressure superheater is connected to the power generation system; In the molten salt heat exchange and heat storage system, the outlet of the high-temperature molten salt tank is connected to the molten salt inlet of the high-pressure superheater, the molten salt outlet of the high-pressure superheater is connected to the molten salt inlet of the high-pressure evaporator, the molten salt outlet of the high-pressure evaporator is connected to the molten salt inlet of the high-pressure preheater, the molten salt outlet of the high-pressure preheater is connected to the molten salt inlet of the low-temperature molten salt tank, the molten salt outlet of the low-temperature molten salt tank is connected to the inlet of the medium-temperature molten salt heat exchanger, the outlet of the medium-temperature molten salt heat exchanger is connected to the inlet of the medium-temperature molten salt tank, the outlet of the medium-temperature molten salt tank is connected to the inlet of the high-temperature molten salt heat exchanger, and the outlet of the high-temperature molten salt heat exchanger is connected to the inlet of the high-temperature molten salt tank; Its characteristics are: A front flue heat storage body is arranged in the front flue of the settling chamber, a settling chamber heat storage body is arranged in the combustion settling chamber, and a high-pressure water storage tank is connected to the connecting pipe between the outlet of the high-pressure economizer and the water inlet of the high-pressure preheater.

2. According to claim 1, a multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system is characterized in that: The front flue heat storage body and the settling chamber heat storage body are porous magnesium bricks, porous ceramics or porous precast concrete.

3. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The flue gasification heat exchanger is installed in the flue before the settling chamber, and the settling chamber gasification heat exchanger is installed in the combustion settling chamber.

4. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The high-temperature molten salt heat exchanger, the medium-temperature molten salt heat exchanger, the low-pressure evaporator, the high-pressure economizer, and the low-pressure economizer are installed in the rear flue of the settling chamber in sequence from front to back.

5. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The external steam superheater is installed in the low-pressure steam drum.

6. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: A low-pressure feed water pump is connected between the outlet of the deaerator and the inlet of the low-pressure economizer, and a high-pressure feed water pump is connected between the outlet of the deaerator and the inlet of the high-pressure economizer.

7. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The high-pressure steam system also includes a high-temperature molten salt pump, a low-temperature molten salt pump and a medium-temperature molten salt pump. The outlet of the high-temperature molten salt tank is connected to the molten salt inlet of the high-pressure superheater through the high-temperature molten salt pump, the molten salt outlet of the low-temperature molten salt tank is connected to the inlet of the medium-temperature molten salt heat exchanger through the low-temperature molten salt pump, and the outlet of the medium-temperature molten salt tank is connected to the inlet of the high-temperature molten salt heat exchanger through the medium-temperature molten salt pump.

8. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The outlet of the high-temperature molten salt heat exchanger is connected to the inlet of the medium-temperature molten salt tank through a bypass.

9. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The power generation system comprises a back-pressure steam turbine and a generator, wherein the back-pressure steam turbine is connected to the generator; the steam outlet of the high-pressure superheater is connected to the inlet of the back-pressure steam turbine, and the steam outlet of the back-pressure steam turbine is connected to a heat user.

10. The multi-state coupling heat storage steelmaking electric furnace flue gas waste heat deep utilization system according to claim 1 is characterized in that: The outlet of the external steam superheater is connected to a heat user.

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