Electric furnace deep waste heat recovery self-deoxidizing device

Abstract

A self-deoxidizing device for deep waste heat recovery of an electric furnace comprises a softened water tank (1), a deaerator (3), a water-cooling flue (8) and a water supply preheater (6), and is characterized in that the softened water tank is connected with the water supply preheater (6) and the water-cooling flue (8) through a softened water pump, the deaerator (3) is arranged on a top platform of a boiler, a water supply preheating downcomer connector is arranged at the bottom of the deaerator water tank, and a water supply preheating downcomer connector is arranged at the bottom of the deaerator water tank. The water cooling flue is connected with an electric furnace flue gas outlet and a flue gas settling chamber, the water cooling flue is connected with the water supply preheater in parallel, the water supply preheater is arranged in a waste heat boiler flue, and the water supply preheater is arranged between a coal economizer and a boiler outlet and used for reducing the boiler exhaust gas temperature and achieving deep waste heat recovery. The electric furnace deep waste heat recovery self-deoxygenization device has the advantages that the water supply preheater is additionally arranged, so that the smoke temperature is reduced, the heat recovery efficiency is improved, the use of deoxygenization steam is reduced, the heat recovery rate is improved, and the use amount of circulating cooling water is avoided.

Description

Technical Field

[0001] This utility model relates to a deoxygenation device, specifically, a self-deoxygenation device for deep waste heat recovery of electric furnaces. Background Technology

[0002] Currently, the waste heat recovery system for electric arc furnaces mainly includes a water-cooled flue, a settling chamber, and a waste heat boiler. The high-temperature primary flue gas from the electric arc furnace outlet passes sequentially through the water-cooled flue and settling chamber before entering the waste heat boiler. After heat exchange in the boiler, the high-temperature primary flue gas is cooled to approximately 220°C, and then sent through the boiler outlet flue to the dust removal system for purification before being discharged. The boiler system's feedwater, consisting of ambient temperature soft water, is sent to the thermal deaerator, heated to approximately 104°C saturated water by externally supplied steam, and after boiling and deaeration, is pumped to the waste heat boiler. After being heated by the economizer, it is sent to the steam drum. Through a natural circulation process consisting of the steam drum, downcomer, evaporator, and riser, it is heated into a steam-water mixture. The steam drum then separates the steam and water, generating steam for external distribution.

[0003] The settling chamber inlet flue is located near the high-temperature flue gas outlet of the electric furnace. The temperature of this flue gas is generally no lower than 800℃, and due to fluctuations in production conditions, it can reach over 1000℃ for short periods. Currently, water-cooled flues are generally used as the settling chamber inlet flues, using 30-50℃ net circulating cooling water to cool the flue and ensure it does not overheat and operates safely. However, this also results in the high-quality, high-temperature flue gas heat being carried away by the circulating cooling water, losing some of the heat energy that could have been recovered. Furthermore, due to the high flue gas temperature and large circulating water volume, the power consumption of the circulating water system and the water consumption of the evaporative cooling tower are both high, resulting in additional energy consumption.

[0004] Existing electric furnace waste heat recovery systems generally employ thermal deaerators. During normal operation, room-temperature soft water is directly sent to the deaerator for heating and deoxygenation. There are generally two types of heat sources for the deaerator: one is external steam sent to the deaerator to heat the room-temperature soft water to saturation temperature to complete deoxygenation; the other is that the deaerator and the boiler's heating surfaces form a natural or forced circulation system, where the final-stage flue gas directly heats the nearly saturated deoxygenated water to saturation temperature through the boiler's heating surfaces to complete deoxygenation. Under this process, because the water exchanging heat with the final-stage flue gas is high-temperature water, the temperature difference between the flue gas and water is small, and the waste heat boiler exhaust temperature is generally around 220℃, making it difficult to further reduce.

[0005] The high-temperature primary flue gas produced by electric arc furnace smelting exhibits drastic fluctuations in both temperature and flow rate. Under low-temperature flue gas conditions, since the steam drum does not produce steam, once the set liquid level is reached, there is no need to replenish water to the steam drum via the economizer. At this time, the water in the economizer is stagnant. Under continuous heating by the low-temperature flue gas, some of the feedwater in the economizer vaporizes, generating bubbles that are trapped within the economizer. This not only easily leads to excessive boiler outlet flue gas temperature, but also causes the bubbles to condense abruptly upon contact with the cooler feedwater when the boiler starts its next water supply cycle, creating a partial vacuum and resulting in water hammer. In severe cases, this can damage the economizer.

[0006] Therefore, the thermal deaerators in known electric furnace waste heat recovery systems have the aforementioned inconveniences and problems. Summary of the Invention

[0007] The purpose of this invention is to propose a safe and reliable deep waste heat recovery and self-deoxygenation device for electric furnaces.

[0008] To achieve the above objectives, the technical solution of this utility model is:

[0009] A deep waste heat recovery and self-deaeration device for electric furnaces includes a soft water tank, a deaerator, a water-cooled flue, and a feedwater preheater.

[0010] The soft water tank is connected to the water preheater and the water-cooled flue via a soft water pump. The outlet pipe of the water preheater and the outlet pipe of the water-cooled flue are combined and then connected to the deaerator.

[0011] The deaerator is installed on the top platform of the boiler. The bottom of the deaerator water tank is equipped with a feedwater preheating downcomer interface, and the deaerator head is equipped with a riser interface. The deaerated water from the deaerator outlet is connected to the economizer via a feedwater pump. The economizer outlet pipe is connected to the steam drum. One economizer inlet pipe is connected to the feedwater pump, and the other is connected to the downcomer interface of the steam drum. The steam drum is connected to the economizer via the riser and downcomer.

[0012] The water-cooled flue connects the electric furnace flue gas outlet and the flue gas settling chamber. The water-cooled flue is connected in parallel with the feed water preheater, which heats the room temperature soft water and then connects it to the deaerator.

[0013] The feedwater preheater is built into the flue of the waste heat boiler and is located between the economizer and the boiler outlet. It is used to reduce the boiler exhaust temperature and achieve deep waste heat recovery.

[0014] The electric furnace deep waste heat recovery and self-deoxygenation device of this utility model can also be further realized by the following technical measures.

[0015] The aforementioned electric furnace deep waste heat recovery self-deaerator device, wherein the deaerator is designed to have a pressure of ≥0.5 MPa.

[0016] The aforementioned electric furnace deep waste heat recovery and deoxygenation device, wherein the preheater adopts a serpentine tube bundle, and the material is ND steel or an anti-corrosion coating is sprayed on the surface of the heat exchange tube bundle.

[0017] After adopting the above technical solution, the electric furnace deep waste heat recovery and self-deoxygenation device of this utility model has the following advantages:

[0018] 1. Improve system operational safety. In traditional electric furnace waste heat recovery systems, when the furnace is not powered on, the flue gas temperature is low (approximately 300-400℃), and evaporation is high. To reduce or even stop external steam supply and to regulate the steam drum level, the feedwater flow through the economizer is correspondingly low or even zero. This not only makes the economizer prone to damage but also causes the exhaust gas temperature to exceed 250℃, affecting the safe operation of the subsequent dust removal system. Under this condition, the feedwater pump stops supplying water, and the economizer and steam drum switch to natural circulation mode. This not only absorbs heat from the flue gas to reduce the exhaust gas temperature but also ensures a continuous water flow through the economizer even when the steam drum is not replenished with water, protecting the economizer.

[0019] 2. Improved Waste Heat Recovery Efficiency. Compared with traditional waste heat recovery systems, this system can increase waste heat recovery efficiency in the following three aspects: First, ambient temperature soft water is pumped into the water-cooled flue gas duct, using the heat from the high-temperature flue gas that would otherwise be carried away by the circulating cooling water to heat the soft water, reducing heat loss. Second, under high-temperature flue gas conditions, the steam drum continuously generates steam, and deoxygenated water is replenished to the steam drum through the economizer. Correspondingly, ambient temperature soft water is heated by the feedwater preheater and then replenished to the deaerator. The final-stage low-temperature flue gas exchanges heat with ambient temperature water in the feedwater preheater. The gas-water heat exchange temperature difference is higher than that between the final-stage low-temperature flue gas and the deoxygenated water, which can increase the heat exchange capacity and further reduce the exhaust gas temperature. Third, under low-temperature flue gas conditions, the steam drum does not generate steam, and steam drum water replenishment stops. The heat of medium-temperature flue gas with a temperature above 200℃ is absorbed and stored in the steam drum through natural circulation between the steam drum and the economizer, and the heat of low-temperature flue gas with a temperature below 200℃ is absorbed and stored in the deaerator through natural circulation between the feedwater preheater, water-cooled flue, and deaerator, thus realizing the stepwise recovery of flue gas temperature.

[0020] 3. Increase system operational reliability. Under low-temperature flue gas conditions, this system adopts natural circulation of the feedwater preheater, water-cooled flue, and deaerator. Compared with forced circulation, this not only reduces the operating time of the feedwater pump, but also, due to the characteristics of natural circulation, the circulation flow rate is proportional to the flue gas temperature and flow rate, making it more adaptable to fluctuating flue gas conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the electric furnace deep waste heat recovery and self-deoxygenation device according to an embodiment of this utility model.

[0022] In the diagram: 1. Soft water tank, 2. Soft water pump, 3. Deaerator, 4. Feed water pump, 5. Economizer, 6. Feed water preheater, 7. Steam drum, 8. Water-cooled flue. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0024] Example 1

[0025] The electric furnace deep waste heat recovery and self-deaeration device of this utility model includes a soft water tank 1, a deaerator 3, a water-cooled flue 8, and a feedwater preheater 6.

[0026] Please see now Figure 1 , Figure 1 This is a schematic diagram of the electric furnace deep waste heat recovery and self-deaeration device according to an embodiment of this utility model. Soft water at room temperature is pressurized from the soft water tank 1 by the soft water pump 2 and sent to the feedwater preheater 6 and the water-cooled flue 8. The outlet pipes of the feedwater preheater 6 and the water-cooled flue 8 are combined and then connected to the deaerator 3. The deaerator 3 is connected to the feedwater preheater 6 and the water-cooled flue 8 through riser pipes and downcomer pipes, forming a natural steam-water circulation mode between them.

[0027] The deoxygenated water from the outlet of deaerator 3 is pressurized by feedwater pump 4 and sent to economizer 5. Steam drum 7 is connected to economizer 5 through riser and downcomer pipes, forming a natural steam-water circulation mode between the two.

[0028] Under steam drum production conditions, the flue gas at the electric furnace outlet is high-temperature flue gas. Soft water at ambient temperature is heated by the feedwater preheater 6 and water-cooled flue duct 8 before being sent to the deaerator. It is then replenished with deaerated steam and heated to saturation temperature to complete deaeration. The deaerated water is then heated by the economizer 5 to become saturated water before being sent to the steam drum. The ambient-temperature soft water is sequentially heated through the feedwater preheater 6 and water-cooled flue duct 8, deaerator 3, and economizer 5, fully absorbing the heat from the low-temperature flue gas in the final stage of the boiler.

[0029] When the steam drum is not producing steam, the electric furnace outlet produces medium-temperature flue gas. Since the steam drum 7 does not require water replenishment, it and the economizer 5 switch to natural circulation mode. At this time, the economizer 5 functions the same as other evaporators in the boiler. The deaerator 3, in principle, also does not require water replenishment when the steam drum is not replenished. In this case, the deaerator 3, along with the feedwater preheater 6 and the water-cooled flue duct 8, switches to natural circulation mode. By absorbing heat from the low-temperature flue gas, it circulates and heats the water inside the deaerator 3 to saturation temperature, achieving self-deaeration without the need for deaeration steam.

[0030] The main equipment used in practical applications of this utility model is as follows:

[0031] Deaerator: A thermal deaerator is used, equipped with a large-capacity deaerator water tank, which also functions as a low-pressure steam drum. Under normal high-temperature flue gas conditions, a small amount of steam is added to heat the soft water, which has undergone heat exchange in the feedwater preheater, to its saturation temperature, thus completing thermal deaeration. Under medium-temperature flue gas conditions, natural circulation absorbs heat from the flue gas, replacing the deaerator steam for heating, achieving self-deaeration.

[0032] Economizer: It adopts a serpentine tube structure and is arranged in the boiler flue after the evaporator. It exchanges heat with the flue gas to heat the feedwater and send it to the steam drum to participate in the steam-water circulation.

[0033] Feedwater preheater: Utilizing a serpentine tube structure, the tube bundles are horizontally arranged in the boiler flue after the economizer, further cooling the flue gas cooled by the economizer and achieving deep waste heat recovery. The material is ND steel resistant to low-temperature flue gas corrosion or an anti-corrosion coating is sprayed onto the surface of the heat exchange tube bundles.

[0034] Water-cooled flue: It adopts a densely packed pipe structure and is generally used to connect the flue gas outlet of the electric furnace to the inlet of the settling chamber, or the outlet of the settling chamber to the boiler inlet.

[0035] This utility model possesses substantial features and significant technological advancements. The electric furnace deep waste heat recovery and self-deaeration device of this utility model incorporates a feedwater preheater, using ambient temperature water for heat exchange. This further reduces flue gas temperature, improves heat recovery efficiency, and reduces the use of deaeration steam. The feedwater preheater, deaerator, and water-cooled flue form a natural circulation system, as do the economizer and steam drum. This dual natural circulation system ensures stable flue gas temperature and safe operation of the economizer under conditions of medium-temperature flue gas in the electric furnace and no steam production in the boiler. Simultaneously, it efficiently absorbs heat from medium- and low-temperature flue gas, replacing deaeration steam for heating and achieving self-deaeration. By heating ambient temperature soft water through the water-cooled flue, the heat originally carried away by the circulating water from the high-temperature flue gas is effectively utilized, thus improving the heat recovery rate and eliminating the need for circulating cooling water.

[0036] The above embodiments are for illustrative purposes only and are not intended to limit the scope of this utility model. Those skilled in the art can make various modifications and variations without departing from the spirit and scope of this utility model. Therefore, all equivalent technical solutions should also fall within the scope of this utility model and should be defined by the claims.

Claims

1. An electric furnace deep waste heat recovery self-deoxidation device, comprising a soft water tank (1), a deaerator (3), a water-cooled flue (8), and a feed water preheater (6), characterized in that: The soft water tank (1) is connected to the feed water preheater (6) and the water-cooled flue (8) via a soft water pump (2); the outlet pipe of the feed water preheater (6) and the outlet pipe of the water-cooled flue (8) are connected to the deaerator (3) after being combined; The deaerator (3) is arranged on the top platform of the boiler, a feed water preheating downcomer interface is provided at the bottom of the deaerator water tank, a riser interface is provided at the deaerator head, the deoxygenated water at the outlet of the deaerator (3) is connected to the economizer (5) via the feed water pump (4), the economizer outlet pipeline is connected to the steam drum (7), one path of the economizer inlet pipeline is connected to the feed water pump (4), and the other path is connected to the downcomer interface of the steam drum (7); the steam drum (7) is connected to the economizer (5) via the riser and the downcomer; The water-cooled flue (8) connects the flue gas outlet of the electric furnace and the flue gas settling chamber, and the water-cooled flue (8) is connected in parallel with the feed water preheater (6), and is connected to the deaerator (3) after heating the soft water at room temperature; The feed water preheater (6) is built into the flue of the waste heat boiler. The feed water preheater (6) is arranged between the economizer and the boiler outlet to reduce the boiler exhaust temperature and achieve deep waste heat recovery.

2. The electric furnace deep waste heat recovery self-deoxidation device according to claim 1, characterized in that: The deaerator design pressure is ≥0.5Mpa.

3. The electric furnace deep waste heat recovery self-deoxidation device according to claim 1, characterized in that: The preheater adopts a serpentine light tube bundle, the material of which is ND steel or an anti-corrosion coating is sprayed on the surface of the heat exchange tube bundle.

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