Gas-liquid combined cooling steel slag waste heat recovery method and device

Abstract

This invention relates to the field of tubular heat exchange technology, specifically to a method and apparatus for recovering waste heat from steel slag through gas-liquid combined cooling. The apparatus includes a counter-current rotating body, whose interior is divided into a preheating zone, a main reaction zone, and a cooling zone from high to low. A gas circulation and waste heat recovery system includes a shell-and-tube heat exchanger, a gas preheater, and a mixer. The shell-side inlet of the shell-and-tube heat exchanger is connected to the high-end outlet of the counter-current rotating body via a pipeline, and its shell-side outlet is connected to the hot-side inlet of the gas preheater via a pipeline. The hot-side outlet of the gas preheater is sequentially connected to a processing component via a pipeline. The cold-side inlet of the gas preheater is connected to the outlet of the mixer via a cold-side inlet pipe, and its cold-side outlet is connected to a jet assembly located within the counter-current rotating body via a cold-side outlet pipe.

Description

Technical Field

[0001] This invention relates to the field of tubular heat exchange technology, specifically to a method and apparatus for recovering waste heat from steel slag through gas-liquid combined cooling. Background Technology

[0002] Steel slag is the main solid waste generated during the iron and steel smelting process, producing approximately 0.1-0.2 tons of steel slag for every ton of crude steel produced. Steel slag exits the furnace at temperatures as high as 1200-1400℃, containing a large amount of sensible heat and possessing extremely high waste heat recovery value. Simultaneously, steel slag contains free calcium oxide (f-CaO), free magnesium oxide (f-MgO), and various silicate minerals. These components not only affect the volume stability of steel slag, limiting its large-scale utilization in the building materials field, but also provide a natural alkaline reaction medium for CO2 mineralization and fixation.

[0003] For example, patent document CN118189683A discloses a method and device for recovering waste heat from steel slag using a combined gas-liquid cooling system. High-temperature steel slag is introduced into a spiral heat exchange tube within a heat exchanger and moves downwards. Low-temperature outside air is introduced into the spiral heat exchange tube by a blower, creating a counter-current heat exchange between the high-temperature steel slag and the low-temperature air. Simultaneously, cooling water inside the heat exchanger exchanges heat with the wall of the spiral heat exchange tube. After heat exchange, the temperature of the high-temperature steel slag drops below 500°C, and it falls from the spiral heat exchange tube into a storage tank outside the heat exchanger under gravity. This patent document uses a spiral heat exchange tube as the heat exchange pipeline to enhance heat transfer and utilizes a combined water-cooling and air-cooling technology to achieve rapid cooling of the high-temperature steel slag inside the tube. This avoids the disintegration of the glassy structure of the slag, preventing granulated steel slag gelation, and improving equipment safety and energy utilization efficiency.

[0004] Currently, the main methods for treating steel slag include hot pouring, water quenching, and air cooling. While hot pouring and water quenching offer rapid cooling, they suffer from significant drawbacks such as high water consumption, the generation of sulfur- and dust-laden steam that pollutes the environment, and ineffective waste heat recovery. Air cooling (dry cooling) involves direct contact between air or nitrogen and the high-temperature steel slag for heat exchange, allowing for partial waste heat recovery. However, its cooling efficiency is limited by the gas-solid contact area and the temperature difference during heat exchange, and the resulting gas temperature is relatively low, making it difficult to generate high-grade steam, thus limiting the value of waste heat utilization.

[0005] In recent years, the technology of CO2 mineralization and fixation using steel slag has attracted widespread attention. CaO and MgO in steel slag can react with CO2 to form stable carbonates, thereby achieving permanent CO2 sequestration. However, most existing CO2 mineralization processes are carried out at room temperature or low temperature (<100℃), resulting in slow reaction rates and requiring additional pretreatment steps such as grinding and stirring, leading to high energy consumption. Furthermore, these processes typically treat cooling and mineralization as separate steps, failing to fully utilize the reactivity and thermodynamic advantages of steel slag at high temperatures.

[0006] In terms of waste heat recovery, existing technologies mostly use a single heat exchanger to recover waste heat from high-temperature flue gas. For waste heat in the medium and low temperature sections (such as liquid cooling sections and atomization sections), it is often directly discharged, resulting in waste of thermal energy.

[0007] Therefore, this application proposes a method and apparatus for recovering waste heat from steel slag through gas-liquid combined cooling. Summary of the Invention

[0008] The purpose of this invention is to provide a method and apparatus for recovering waste heat from steel slag through gas-liquid combined cooling, so as to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for recovering waste heat from steel slag through gas-liquid combined cooling, comprising the following steps:

[0010] S1. After the high-temperature steel slag is crushed and screened, it is fed into the high end of the countercurrent rotating body, so that it flows through the preheating zone, main reaction zone and cooling zone of the countercurrent rotating body in sequence.

[0011] In the preheating zone, the high-temperature steel slag undergoes countercurrent heat exchange with the hot gas from the main reaction zone, which initially cools it down and evaporates moisture, forming a heat seal to prevent downstream CO2 from backflowing to the feed inlet.

[0012] In the main reaction zone, high-temperature steel slag is repeatedly thrown to form a material curtain, which reacts with high-concentration CO2 gas injected from independent gas nozzles in the direction of slag flow to undergo a carbonation reaction. The exothermic reaction and the sensible heat of the steel slag together rapidly heat the flowing gas to 800-1000℃.

[0013] In the cooling zone, the steel slag undergoes final heat exchange with the 300-500°C gas entering from the lower end of the countercurrent rotating body and completes the residual reaction, and is discharged after being cooled to 600-800°C.

[0014] S2. The 800-1000℃ high-temperature gas discharged from the high end of the countercurrent rotating body enters the shell-and-tube heat exchanger after dust removal, and exchanges heat with the boiler feedwater to generate 1.6-2.5MPa high-pressure steam, and the gas temperature drops to 350-500℃.

[0015] S3. The 350-500℃ gas flowing out of the shell and tube heat exchanger is divided into two paths. The first path enters the hot side of the gas preheater to preheat the circulating gas from the mixer; the second path is sent to the temperature-switching adsorption device for CO2 capture.

[0016] S4. The CO2-containing tail gas from the lime kiln or hot blast stove of the steel plant is purified and pressurized, and then mixed with the gas returned after being treated by the temperature-switching adsorption device in step S3, the supplemented air, and the circulating gas preheated by the gas preheater in the mixer to adjust the CO2 concentration to 5%-30%.

[0017] After the mixed gas is preheated to 300-500℃ by the gas preheater, it is divided into two parts: the first part enters from the lower end of the countercurrent rotating body as the main cooling gas, and the second part is injected into the main reaction zone through an independent gas nozzle facing the slag flow direction as a high-concentration CO2 reaction gas source, thus forming a gas circulation loop.

[0018] The present invention also provides a gas-liquid combined cooling steel slag waste heat recovery device, comprising:

[0019] The countercurrent rotating body has its internal cylinder divided into a preheating zone, a main reaction zone, and a cooling zone from high to low.

[0020] A gas circulation and waste heat recovery system, which includes a shell-and-tube heat exchanger, a gas preheater, and a mixer;

[0021] The shell-side inlet of the shell-and-tube heat exchanger is connected to the high-end outlet of the counter-current rotating body via a pipeline, and its shell-side outlet is connected to the hot-side inlet of the gas preheater via a pipeline.

[0022] The hot-side outlet of the gas preheater is connected to a processing component via a pipeline. The cold-side inlet of the gas preheater is connected to the outlet of the mixer via a cold-side inlet pipe of the preheater. Its cold-side outlet is connected to a jet assembly located in the countercurrent rotating body via a cold-side outlet pipe of the preheater.

[0023] Preferably, the preheating zone is provided with a large-pitch spiral guide plate, the main reaction zone is provided with a dense lifting plate, the cooling zone is provided with a small-pitch spiral guide plate, the countercurrent rotating body is provided with a sealing gas inlet at the high end and a discharge port at the low end, and is connected to a cooling unit through a chute, and the top of the countercurrent rotating body is connected to a sealing gas inlet.

[0024] Preferably, the cooling unit includes a spray cooling chamber with a spray header pipe at the top and a liquid collection ditch at the bottom. The liquid collection ditch is connected to a sedimentation tank via a pumping pipe. The sedimentation tank is connected to the spray header pipe via a return pump and a return spray header pipe, forming a liquid circulation loop.

[0025] Preferably, the cooling unit further includes an atomizing cooling chamber, which is equipped with a high-pressure atomizing nozzle array and a high-pressure plunger pump installed on the atomizing cooling chamber, the outlet of which is connected to the high-pressure atomizing nozzle array. A heat-resistant conveyor belt for conveying steel slag is installed inside the atomizing cooling chamber.

[0026] Preferably, the jet assembly includes a distributor connected to the cold side outlet pipe of the preheater. The distributor has two outlets, which are respectively connected to the gas inlet at the lower end of the countercurrent rotating body through a short gas outlet pipe, and extend to the main reaction zone of the countercurrent rotating body through an independent gas nozzle. The nozzle direction of the independent gas nozzle is set to face the slag flow direction.

[0027] Preferably, the gas circulation and waste heat recovery system further includes an exhaust fan connected to one end of the countercurrent rotating body. The output end of the exhaust fan is connected to a cyclone dust collector through a high-temperature gas pipe. The outlet end of the cyclone dust collector is connected to the shell-side inlet of the shell-and-tube heat exchanger through the heat exchanger inlet passage.

[0028] Preferably, the gas circulation and waste heat recovery system further includes a three-way regulating valve connected to the shell-side inlet of the shell-and-tube heat exchanger. The two ends of the three-way regulating valve are respectively connected to a three-way manifold and a preheater hot-side pipe. The preheater hot-side pipe is connected to the hot-side inlet of the gas preheater, and the gas preheater hot-side outlet is connected to the three-way manifold. The three-way manifold extends to the top of the spray cooling chamber and the atomizing cooling chamber for collecting waste heat gas.

[0029] Preferably, the processing component includes a gas distribution pipe connected to the three-way confluence pipe, a gas pump installed in the gas distribution pipe, and a temperature-switching adsorption device and a dust collector connected in sequence. The gas distribution pipe is connected to the temperature-switching adsorption device, and the outlet of the dust collector is connected to a circulating gas pipe that flows into the inlet of one end of the mixer. An induced draft fan and a three-way vent valve are respectively installed on the circulating gas pipe. The mixer is respectively connected to a tail gas inlet pipe and a makeup air pipe. The temperature-switching adsorption device is connected to the mixer through a CO2 pipe, and a selection valve is provided on the CO2 pipe.

[0030] Preferably, it also includes a gear ring assembly for driving the counter-current rotating body to rotate and a support roller for guiding the rotation of the counter-current rotating body.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] By introducing a carbonation reaction into the main reaction zone of the countercurrent rotating body, and utilizing the strong exothermic reaction between carbon dioxide and free calcium oxide in steel slag, the temperature of the circulating gas is increased from 600-700℃ in traditional processes to 800-1000℃. Combined with the efficient heat exchange of a shell-and-tube heat exchanger, high-grade steam of 1.6-2.5 MPa can be generated, representing a 50%-100% increase in steam grade compared to traditional steel slag waste heat recovery technologies (typically 0.8-1.2 MPa), significantly improving the economic value of energy recovery. Carbon dioxide is captured and recycled through a temperature-switching adsorption device, and supplemented by tail gas from the steel plant's lime kiln introduced through the tail gas inlet pipe, achieving efficient carbon dioxide recovery and recycling. Attached Figure Description

[0033] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0034] Figure 2 This is a schematic diagram of the internal structure of the countercurrent rotating body in this invention;

[0035] Figure 3 This is a schematic diagram of the chute structure in this invention;

[0036] Figure 4 This is a schematic diagram of the spray cooling chamber and the atomizing cooling chamber in this invention;

[0037] Figure 5 This is a schematic diagram of the connection structure of the shell-and-tube heat exchanger, gas preheater, and mixer in this invention.

[0038] Figure 6 This is a schematic diagram of the connection structure between the shell-and-tube heat exchanger and the gas preheater in this invention.

[0039] Figure 7 This is a schematic diagram of the gas preheater in this invention;

[0040] Figure 8 This is a schematic diagram of the mixer in this invention.

[0041] In the diagram: 100. Countercurrent rotating body; 101. Spray cooling chamber; 102. Atomizing cooling chamber; 103. Sealing gas inlet; 104. Support roller; 105. Gear ring assembly; 106. Chute; 107. Spray header; 108. Liquid collection ditch; 109. Liquid extraction pipe; 110. Sludge tank; 111. Return spray header; 112. Return liquid pump; 113. Heater; 114. Diverter plate; 115. Heat-resistant conveyor belt; 116. High-pressure plunger pump; 117. High-pressure atomizing nozzle array; 200. Exhaust fan; 201. High-temperature gas pipe; 202. Cyclone dust collector; 203. Heat exchanger inlet; 204. Shell-and-tube heat exchanger; 205. Three-way regulating valve ; 206. Three-way junction pipe; 207. Hot side pipe of preheater; 208. Gas preheater; 209. Cold side outlet pipe of preheater; 210. Distributor; 211. Short outlet pipe; 212. Independent air nozzle; 300. Mixer; 301. Tail gas inlet pipe; 302. Selector valve; 303. Make-up air pipe; 304. Circulating air pipe; 305. Gas distribution pipe; 306. Gas pump; 307. Variable temperature adsorption device; 308. CO2 pipe; 309. Dust collector; 310. Exhaust fan; 311. Three-way vent valve; 312. Cold side inlet pipe of preheater; 400. Large pitch spiral guide plate; 401. Dense material lifting plate; 402. Small pitch spiral guide plate. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1: Please refer to Figure 1 - Figure 8 The present invention provides a technical solution: a gas-liquid combined cooling steel slag waste heat recovery device, including a countercurrent rotating body 100, the body of which is divided into a preheating zone, a main reaction zone and a cooling zone from high end to low end.

[0044] The preheating zone is equipped with a large-pitch spiral guide plate 400 to quickly push the high-temperature steel slag falling into the zone forward, while simultaneously allowing the steel slag to dissipate heat and evaporate residual moisture. The main reaction zone is equipped with dense lifting plates 401 to repeatedly lift and scatter the steel slag, forming a uniform and dense material curtain to greatly increase the gas-solid contact area. The cooling zone is equipped with a small-pitch spiral guide plate 402 to slow down the movement speed of the steel slag and ensure sufficient reaction and cooling time.

[0045] The counter-current rotary body 100 has a sealing gas inlet 103 at its high end to form a gas seal during feeding, preventing internal gas from leaking out. The counter-current rotary body 100 has a discharge outlet at its low end, which is connected to a cooling unit via a chute 106. The counter-current rotary body 100 is also equipped with a gear ring assembly 105 and a support roller 104. The gear ring assembly 105 drives the counter-current rotary body 100 to rotate, while the support roller 104 supports and guides the counter-current rotary body 100 to rotate smoothly.

[0046] The cooling unit includes a spray cooling chamber 101 and an atomizing cooling chamber 102. The top of the spray cooling chamber 101 is equipped with a spray header pipe 107 for uniformly spraying coolant onto the surface of the steel slag; the bottom is equipped with a collection ditch 108 for collecting unevaporated spray liquid. The collection ditch 108 is connected to a slag settling tank 110 via a suction pipe 109. The slag settling tank 110 is used to settle solid particles in the liquid. The slag settling tank 110 is connected to the spray header pipe 107 via a return pump 112 and a return spray header pipe 111. A diverter plate 114 is installed between the return spray header pipe 111 and the spray header pipe 107 to divert the liquid, ensuring it evenly enters multiple spray header pipes 107, forming a liquid circulation loop and allowing the spray liquid to be reused.

[0047] The atomizing cooling chamber 102 is equipped with a high-pressure atomizing nozzle array 117, which atomizes cooling water into tiny droplets and sprays them onto the surface of the steel slag for rapid evaporative cooling. A high-pressure plunger pump 116 is installed on the atomizing cooling chamber 102, its outlet connected to the high-pressure atomizing nozzle array 117, providing it with a high-pressure water source of 2-5 MPa. A heat-resistant conveyor belt 115 is also installed inside the atomizing cooling chamber 102. As the steel slag moves on the belt, its surface is covered by high-pressure micro-mist, and the micro-droplets evaporate instantly, absorbing heat and rapidly reducing the steel slag temperature to below 200°C, completing the final cooling process.

[0048] The return spray header 111 is equipped with a heater 113 to regulate the temperature of the spray liquid and maintain it within the optimal range of 80-200℃. Within this chamber, the steel slag is sprayed and cooled to 300-400℃.

[0049] It also includes a gas circulation and waste heat recovery system, which is used to recover the high-grade heat energy generated during the reaction and cooling, and to construct a closed-loop, CO2-rich reaction gas circulation system. This system includes a shell-and-tube heat exchanger 204, a gas preheater 208, and a mixer 300. The shell-and-tube heat exchanger 204 is used to convert the high-grade heat in the 800-1000℃ gas into steam.

[0050] The shell-side inlet of the shell-and-tube heat exchanger 204 is connected to the high-end outlet of the counter-current rotating body 100 via a pipeline. This pipeline includes an exhaust fan 200 connected to one end of the counter-current rotating body 100. The output end of the exhaust fan 200 is connected to a cyclone dust collector 202 via a high-temperature gas pipe 201. The outlet end of the cyclone dust collector 202 is connected to the shell-side inlet of the shell-and-tube heat exchanger 204 via a heat exchanger inlet passage 203. The shell-side outlet is connected to the hot side of the gas preheater 208 via a pipeline. The inlet includes a three-way regulating valve 205 connected to the shell-side inlet of the shell-and-tube heat exchanger 204. The two ends of the three-way regulating valve 205 are respectively connected to a three-way manifold 206 and a preheater hot-side pipe 207. The preheater hot-side pipe 207 is connected to the hot-side inlet of the gas preheater 208, and the hot-side outlet of the gas preheater 208 is connected to the three-way manifold 206. The three-way manifold 206 extends to the top of the spray cooling chamber 101 and the atomizing cooling chamber 102 for collecting waste heat gas.

[0051] It is worth mentioning that the shell-side outlet of the shell-and-tube heat exchanger 204 is connected to a three-way regulating valve 205, which splits the 350-500℃ gas discharged from the heat exchanger into two parallel branches.

[0052] First route: One end of the three-way regulating valve 205 is connected to the hot-side pipe 207 of the preheater, which in turn connects to the hot-side inlet of the gas preheater 208. This gas at 350-500°C serves as a heat source, releasing heat in the gas preheater 208. After completing the preheating process, the gas exits from the hot-side outlet of the gas preheater 208 and merges with the three-way manifold 206 described below.

[0053] The second bypass branch: The other end of the three-way regulating valve 205 is directly connected to the three-way junction pipe 206, and directly enters the subsequent processing stage.

[0054] In addition, the three-way confluence pipe 206 extends to the top of the spray cooling chamber 101 and the atomizing cooling chamber 102, specifically for collecting steam-containing exhaust gas with a temperature of 100-250°C generated in the two chambers.

[0055] Thus, the three-way confluence pipe 206 achieves the complete convergence of three gas streams: the first gas after preheating and cooling, the second bypass gas without heat exchange, and the low-temperature exhaust gas from the cooling unit.

[0056] The hot-side outlet of the gas preheater 208 is connected to a processing component via a pipeline. The processing component includes a gas distribution pipe 305 connected to a three-way manifold 206, a gas pump 306 installed in the gas distribution pipe 305, and a temperature-switching adsorption device 307 and a dust collector 309 connected in sequence. The gas distribution pipe 305 is connected to the temperature-switching adsorption device 307. The outlet of the dust collector 309 is connected to a circulating gas pipe 304 that flows into one end of the mixer 300. An induced draft fan 310 and a three-way vent valve 311 are installed on the circulating gas pipe 304. The mixer 300 is connected to a tail gas inlet pipe 301 and a makeup air pipe 303. The makeup air pipe 303 is used to supplement fresh air or nitrogen to adjust the oxygen content and total gas volume balance in the system. The temperature-switching adsorption device 307 is connected to the mixer 300 via a CO2 pipe 308. A selector valve 302 is provided on the CO2 pipe 308.

[0057] Specifically, the combined gas first enters the temperature-switching adsorption device 307, whose main function is to selectively capture a portion of CO2 from the circulating gas. The captured CO2 is then transported back to the mixer 300 at the gas front end through the CO2 pipe 308 and the selector valve 302 thereon, for adjusting the CO2 concentration in the system or for enrichment and utilization.

[0058] The gas after CO2 capture enters the dust collector 309 for further removal of residual dust. The outlet of the dust collector 309 is connected to a recirculation pipe 304, which returns the purified gas to the system through one end of the recirculation pipe, where it enters the mixer 300. An induced draft fan 310 and a three-way vent valve 311 are installed sequentially on the recirculation pipe 304. The induced draft fan 310 provides the main power for the entire gas circulation, pressurizing the purified gas before sending it to the mixer 300. The three-way vent valve 311 is responsible for intermittently or continuously releasing a small amount (≤15%) of the gas to maintain system pressure stability and gas composition balance, and to discharge excess non-condensable gases.

[0059] The exhaust gas inlet pipe 301 is used to receive exhaust gas from the lime kiln or hot blast stove of the steel plant as a supplementary gas source for high-concentration CO2. This exhaust gas needs to be pre-extracted by an external induced draft fan to a water washing cooling tower for cooling and washing to remove dust and sulfides, then the liquid droplets are removed by a gas-liquid separator, and finally pressurized by a Roots booster blower. Only after being cleaned can it be sent into the exhaust gas inlet pipe 301.

[0060] The cold-side inlet of the gas preheater 208 is connected to the outlet of the mixer 300 through the cold-side inlet pipe 312 of the preheater, and its cold-side outlet is connected to the jet assembly located in the countercurrent rotating body 100 through the cold-side outlet pipe 209 of the preheater.

[0061] The jet assembly includes a distributor 210 connected to the cold side outlet pipe 209 of the preheater. The distributor 210 has two outlets, which are connected to the gas inlet at the lower end of the countercurrent rotating body 100 via a short outlet pipe 211, and extend to the main reaction zone of the countercurrent rotating body 100 via an independent nozzle 212. The nozzle direction of the independent nozzle 212 is set to face the slag flow direction.

[0062] Specifically, most of the gas is connected to the gas inlet at the low end of the counter-current rotating body 100 through the gas outlet short pipe 211, and enters the cooling zone as the mainstream cooling gas to exchange heat with the steel slag in a counter-current manner.

[0063] A small portion of the gas extends to the main reaction zone of the countercurrent rotating body 100 through the independent gas nozzle 212, and the nozzle direction of the independent gas nozzle 212 is set to face the slag flow direction, so as to accurately inject fresh, high-concentration CO2 gas into the material curtain of the reaction zone to enhance the carbonation reaction.

[0064] In summary, by introducing a carbonation reaction into the main reaction zone of the countercurrent rotating body 100, and utilizing the strong exothermic reaction between carbon dioxide and free calcium oxide in steel slag, the circulating gas temperature is increased from 600-700℃ in traditional processes to 800-1000℃. Combined with the efficient heat exchange of the shell-and-tube heat exchanger 204, high-grade steam at 1.6-2.5 MPa can be generated, representing a 50%-100% increase compared to the typical 0.8-1.2 MPa steam grade of traditional steel slag waste heat recovery technologies, significantly improving the economic value of energy recovery. Carbon dioxide is captured and recycled through the temperature-switching adsorption device 307, and supplemented by tail gas from the steel plant's lime kiln introduced through the tail gas inlet pipe 301, achieving efficient carbon dioxide recovery and recycling.

[0065] Example 2: Please refer to Figure 1 - Figure 8 The present invention also provides a technical solution, which differs from the technical solution of Embodiment 1 as follows: a method for recovering waste heat from steel slag through gas-liquid combined cooling, comprising the following steps:

[0066] S1. Within the countercurrent rotating body 100, the internal space of its cylinder is divided into a preheating zone, a main reaction zone, and a cooling zone from high to low, in order to achieve stepwise cooling and reaction of the steel slag.

[0067] High-temperature fine steel slag at 1200-1400℃ falls from the sealed gas inlet 103 into the high-end preheating zone of the countercurrent rotating body 100. Within this zone, a large-pitch spiral guide plate 400 rapidly pushes the slag towards the lower end. During this process, the slag quickly transfers its sensible heat to the surrounding gas and walls, achieving initial heat dissipation, reducing the temperature to approximately 700℃, and eliminating residual moisture. Simultaneously, this high-temperature zone forms a positive pressure "heat seal" from the inside out, effectively preventing the high-concentration CO2 in the downstream main reaction zone and cooling zone from backflowing and leaking back towards the inlet.

[0068] After initial cooling, the steel slag enters the main reaction zone, where it is repeatedly lifted and scattered by densely packed lifting plates 401, forming a uniform and dense "material curtain." The temperature of the steel slag in this zone is precisely maintained within the optimal window for the carbonation reaction, between 550-700℃. This temperature range is maintained through a dynamic balance between the sensible heat of the steel slag itself, the exothermic reaction of carbonation, and the heat carried away by gas convection.

[0069] After passing through the main reaction zone, the steel slag enters the cooling zone. In this zone, the steel slag comes into countercurrent contact with the still relatively cool CO2-rich gas that has just entered from the lower end, further completing the remaining carbonation reaction and cooling the slag. The internally installed small-pitch spiral guide plate 402 effectively slows down the axial movement speed of the steel slag, ensuring sufficient reaction completion time. Finally, the cooled and modified slag is discharged from the lower end of the cylinder at approximately 600°C, and enters the subsequent cooling unit via the receiving chute 106, where it is finally cooled to below 200°C through the spray cooling chamber 101 and the atomizing cooling chamber 102.

[0070] S2. The preheated mixed gas with a temperature of 400-550℃ from the gas preheater 208 is transported to the distributor 210 for diversion through the cold side outlet pipe 209 of the preheater.

[0071] The traffic splitting strategy and functions are as follows:

[0072] Mainstream cooling gas: Most of the gas enters from the lower end of the counter-current rotating body 100 through one outlet of the distributor 210 and the outlet short pipe 211. As the mainstream cooling medium, it passes through the cooling zone and the main reaction zone in the opposite direction of the slag flow, and exchanges heat extensively with the steel slag.

[0073] Enhanced reaction injection gas: A small portion of the gas enters the independent nozzle 212, which extends into the main reaction zone of the countercurrent rotating body 100, through another outlet of the distributor 210. The nozzle of the independent nozzle 212 faces the direction of the slag flow, directly and precisely injecting fresh, high-concentration CO2 gas onto the steel slag curtain thrown up by the lifting plate.

[0074] CO2 gas reacts violently and rapidly with free calcium oxide (f-CaO) and some silicate minerals on the surface of steel slag particles in the material curtain, resulting in an exothermic carbonation reaction: CaO + CO2 → CaCO3. The enormous chemical heat released by this reaction, combined with the original sensible heat of the steel slag, rapidly raises the temperature of the gas flowing through the main reaction zone to 800-1000℃.

[0075] S3. The high-temperature gas (800-1000℃) generated in step S2 is discharged from the high-end outlet under the pressure of the internal air pressure at the high end of the counter-current rotating body 100 and the suction action of the exhaust fan 200. After being guided by the exhaust fan 200, it enters the cyclone dust collector 202 through the high-temperature gas pipe 201 for efficient dust removal, separating out a portion of the carbonized steel slag powder carried out by the airflow.

[0076] The purified, high-temperature gas enters the shell side of the shell-and-tube heat exchanger 204 through the heat exchanger inlet passage 203. Here, the gas transfers high-grade heat to the boiler feedwater flowing in the tubes. Due to the superposition of exothermic carbonation reaction, the inlet gas temperature and average temperature are significantly higher than those of conventional processes without reaction. Therefore, this method can stably generate high-grade steam at 1.6-2.5 MPa for direct external supply.

[0077] S4. After heat exchange, the gas flows out of the shell-and-tube heat exchanger 204, still at a temperature of 350-500℃. Here, it is split into two branches by the three-way regulating valve 205:

[0078] Branch 1 Preheating Branch: This branch enters the hot side of the gas preheater 208 through the hot side pipe 207 of the preheater, serving as a heat source to indirectly preheat the cold mixed gas from the mixer 300 that is about to enter the cold side of the gas preheater 208. After releasing heat, the gas in this branch decreases in temperature and then flows out from the hot side outlet, connecting with the three-way confluence pipe 206.

[0079] Branch 2 bypass branch: directly connected to the third branch junction pipe 206, and merged with the outlet gas of branch 1.

[0080] Meanwhile, the steam-containing waste gas with a temperature of 100-250℃ generated during the operation of the spray cooling chamber 101 and the atomizing cooling chamber 102 is also collected and sent into the three-way confluence pipe 206. The gas from branch one after cooling, the gas from branch two without heat exchange, and the waste gas from the cooling unit are completely merged in the pipe to form a mixed gas with a uniform temperature.

[0081] The combined gases are connected to the gas distribution pipe 305 and, driven by the gas pump 306, enter the temperature-switching adsorption device 307. This device selectively captures a portion of the CO2 from the mixed gas. The captured CO2, according to system operating requirements, is returned to the upstream mixer 300 through the regulation of the CO2 pipe 308 and the selector valve 302 to maintain the system CO2 concentration.

[0082] The gas after CO2 capture enters the subsequent dust collector 309 for final fine dust removal. The clean gas after dust removal enters the recirculation pipe 304, is pressurized by the induced draft fan 310, and is sent to the mixer 300 as the main recirculation gas for a new round of gas distribution. A three-way vent valve 311 installed on the recirculation pipe 304 releases a small amount of gas (≤15% of which meets environmental standards) in a controlled manner, intermittently or continuously, to maintain the pressure stability and gas composition balance of the entire closed-loop system.

[0083] Among them, intelligent gas distribution is achieved in the mixer 300 through multiple gas sources:

[0084] The mixer 300 receives pre-treated CO2 exhaust gas from the lime kiln or hot blast stove of the steel plant through the exhaust gas inlet pipe 301. The gas is then drawn by an external induced draft fan to a water washing cooling tower for cooling and washing to remove dust and sulfides. After the liquid droplets are removed by the gas-liquid separator, the clean high-concentration CO2 exhaust gas is finally pressurized by the Roots booster blower and used as a supplementary carbon source.

[0085] The mixer 300 introduces supplementary air or nitrogen through the air supply pipe 303 to precisely regulate the oxygen content and total gas volume in the system, ensuring safety.

[0086] Mixer 300 receives captured CO2 returned through CO2 pipe 308 and selector valve 302.

[0087] The mixer 300 receives purified circulating gas delivered by the circulating gas pipe 304.

[0088] The various gases are uniformly mixed in the mixer 300, and the resulting cold mixed gas enters the cold side of the gas preheater 208 through the cold side inlet pipe 312 at the outlet of the mixer 300. Here, the mixed gas absorbs the heat from the 350-500°C gas flowing through the hot side in step S4 and is preheated to 400-550°C.

[0089] In summary, the high-density material curtain formed by the densely packed lifting plates 401 in the main reaction zone of the countercurrent rotating body 100, in full contact with the high-concentration carbon dioxide injected by the independent air nozzle 212, achieves deep carbonation and solidification of free calcium oxide in steel slag. This fundamentally solves the stability problem caused by the hydration and expansion of free calcium oxide in steel slag, allowing the treated steel slag to be directly used in cement admixtures, roadbed materials, and other high-efficiency applications.

[0090] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recovering waste heat from steel slag using a combined gas-liquid cooling system, characterized in that, Includes the following steps: S1. After the high-temperature steel slag is crushed and screened, it is sent to the high end of the countercurrent rotating body (100) so that it flows through the preheating zone, main reaction zone and cooling zone in the countercurrent rotating body (100) in sequence. In the preheating zone, the high-temperature steel slag undergoes countercurrent heat exchange with the hot gas from the main reaction zone, which initially cools it down and evaporates moisture, forming a heat seal to prevent downstream CO2 from backflowing to the feed inlet. In the main reaction zone, high-temperature steel slag is repeatedly thrown to form a material curtain, which reacts with high-concentration CO2 gas injected from the independent gas nozzle (212) in the direction of slag flow to undergo a carbonation reaction. The exothermic reaction and the sensible heat of the steel slag together rapidly heat the flowing gas to 800-1000℃. In the cooling zone, the steel slag undergoes final heat exchange with the 300-500°C gas entering from the lower end of the countercurrent rotating body (100) and completes the residual reaction, and is discharged after being cooled to 600-800°C. S2. The high-temperature gas of 800-1000℃ discharged from the high end of the counter-current rotating body (100) enters the shell-and-tube heat exchanger (204) after dust removal, and generates high-pressure steam of 1.6-2.5MPa by exchanging heat with the boiler feedwater, and the gas temperature drops to 350-500℃. S3. The 350-500℃ gas flowing out from the shell-and-tube heat exchanger (204) is divided into two paths. The first path enters the hot side of the gas preheater (208) to preheat the circulating gas from the mixer (300); the second path is sent to the temperature-switching adsorption device (307) for CO2 capture. S4. The CO2-containing tail gas from the lime kiln or hot blast stove of the steel plant is purified and pressurized, and then mixed with the gas returned after being treated by the temperature-switching adsorption device (307) in step S3, the supplemented air, and the circulating gas preheated by the gas preheater (208) in the mixer (300) to adjust the CO2 concentration to 5%-30%. After the mixed gas is preheated to 300-500℃ by the gas preheater (208), it is divided into two parts: the first part enters from the lower end of the countercurrent rotating body (100) as the main cooling gas, and the second part is injected into the main reaction zone through the independent gas nozzle (212) facing the slag flow direction as a high-concentration CO2 reaction gas source, thus forming a gas circulation loop.

2. A gas-liquid combined cooling steel slag waste heat recovery device for implementing the method of claim 1, characterized in that, include: The countercurrent rotating body (100) has its cylinder divided into a preheating zone, a main reaction zone and a cooling zone from high to low. A gas circulation and waste heat recovery system, comprising a shell-and-tube heat exchanger (204), a gas preheater (208), and a mixer (300). The shell-side inlet of the shell-and-tube heat exchanger (204) is connected to the high-end outlet of the counter-current rotating body (100) via a pipeline, and its shell-side outlet is connected to the hot-side inlet of the gas preheater (208) via a pipeline. The hot side outlet of the gas preheater (208) is connected to a processing component in sequence via a pipeline. The cold side inlet of the gas preheater (208) is connected to the outlet of the mixer (300) via the cold side inlet pipe (312) of the preheater. Its cold side outlet is connected to a jet assembly located in the countercurrent rotating body (100) via the cold side outlet pipe (209) of the preheater.

3. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 2, characterized in that: The preheating zone is equipped with a large-pitch spiral guide plate (400), the main reaction zone is equipped with a dense lifting plate (401), the cooling zone is equipped with a small-pitch spiral guide plate (402), the countercurrent rotary body (100) is equipped with a sealing gas inlet (103) at the high end and a discharge port at the low end, and is connected to a cooling unit through a chute (106). The high end of the countercurrent rotary body (100) is connected to the sealing gas inlet (103).

4. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 3, characterized in that: The cooling unit includes a spray cooling chamber (101), with a spray header pipe (107) at the top and a liquid collection ditch (108) at the bottom. The liquid collection ditch (108) is connected to a sedimentation tank (110) via a liquid extraction pipe (109). The sedimentation tank (110) is connected to the spray header pipe (107) via a return pump (112) and a return spray header pipe (111) to form a liquid circulation loop.

5. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 4, characterized in that: The cooling unit also includes an atomizing cooling chamber (102), which is equipped with a high-pressure atomizing nozzle array (117) and a high-pressure plunger pump (116) installed on the atomizing cooling chamber (102), the outlet of which is connected to the high-pressure atomizing nozzle array (117). A heat-resistant conveyor belt (115) for conveying steel slag is installed in the atomizing cooling chamber (102).

6. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 2, characterized in that: The jet assembly includes a distributor (210) connected to the cold side outlet pipe (209) of the preheater. The distributor (210) has two outlets, which are connected to the gas inlet at the lower end of the countercurrent rotating body (100) via a short outlet pipe (211) and extend to the main reaction zone of the countercurrent rotating body (100) via an independent nozzle (212). The nozzle direction of the independent nozzle (212) is set to face the slag flow direction.

7. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 2, characterized in that: The gas circulation and waste heat recovery system also includes an exhaust fan (200) connected to one end of the countercurrent rotating body (100). The output end of the exhaust fan (200) is connected to a cyclone dust collector (202) through a high-temperature gas pipe (201). The outlet end of the cyclone dust collector (202) is connected to the shell-side inlet of the shell-and-tube heat exchanger (204) through a heat exchanger inlet passage (203).

8. The gas-liquid combined cooling steel slag waste heat recovery device according to claim 5, characterized in that: The gas circulation and waste heat recovery system also includes a three-way regulating valve (205) connected to the shell-side inlet of the shell-and-tube heat exchanger (204). The two ends of the three-way regulating valve (205) are respectively connected to a three-way manifold (206) and a preheater hot-side pipe (207). The preheater hot-side pipe (207) is connected to the hot-side inlet of the gas preheater (208). The hot-side outlet of the gas preheater (208) is connected to the three-way manifold (206). The three-way manifold (206) extends to the top of the spray cooling chamber (101) and the atomizing cooling chamber (102) for collecting waste heat gas.

9. A gas-liquid combined cooling steel slag waste heat recovery device according to claim 8, characterized in that: The processing assembly includes a gas distribution pipe (305) connected to a three-way confluence pipe (206), a gas pump (306) installed in the gas distribution pipe (305), and a temperature-switching adsorption device (307) and a dust collector (309) connected in sequence. The gas distribution pipe (305) is connected to the temperature-switching adsorption device (307). The outlet of the dust collector (309) is connected to a circulating gas pipe (304) that flows into the inlet of one end of the mixer (300). An induced draft fan (310) and a three-way exhaust valve (311) are installed on the circulating gas pipe (304). The mixer (300) is connected to a tail gas inlet pipe (301) and a make-up air pipe (303). The temperature-switching adsorption device (307) is connected to the mixer (300) through a CO2 pipe (308). A selector valve (302) is provided on the CO2 pipe (308).

10. A gas-liquid combined cooling steel slag waste heat recovery device according to claim 1, characterized in that: It also includes a gear ring assembly (105) for driving the counter-current rotating body (100) to rotate and a support roller (104) for guiding the rotation of the counter-current rotating body (100).

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