Method for activating coal gangue by steel slag waste heat and in-situ carbon sequestration

Abstract

The application discloses a method for activating coal gangue by using steel slag waste heat and in-situ carbon fixation, which utilizes the waste heat of high-temperature molten steel slag, activates coal gangue by means of a steel slag heat sweating device system, so that the coal gangue obtains higher pozzolanic activity, meanwhile, the steel slag reacts with CO2 to generate stable carbonate, captures CO2 released in the heat activation process, and realizes permanent carbon sequestration. The application effectively utilizes the heat of hot steel slag discharged from a steel smelting furnace, activates coal gangue, and at the same time, the steel slag generates a carbonation reaction, thereby improving the heat recovery rate in the steel slag cooling process; through the coupling effect of heat activation and carbonation, the steel slag is used to capture CO2 generated in the coal gangue activation process, thereby realizing the synergistic effect of coal gangue-steel slag activation and carbon fixation, providing a new idea for the utilization of coal-based solid waste; the coal gangue is used to prepare high pozzolanic activity materials, and the stability of the steel slag is improved, so that the steel slag is convenient for subsequent building material utilization, and the resource utilization rate of the steel slag is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for heat-activating coal gangue and in-situ carbon sequestration using steel slag waste heat, belonging to the technical field of comprehensive utilization of solid waste and energy saving and emission reduction. BACKGROUND

[0002] Coal gangue is a kind of mining solid waste produced in the process of coal mining and washing and processing in coal preparation plants, and its main chemical composition is SiO2 (51%~65%) and Al2O3 (16%~36%), and it also contains a small amount of Fe2O3, CaO, MgO, TiO2, P2O3, K2O, Na2O, V2O3. However, after heat activation, the stable mineral crystal structure contained in the coal gangue can be effectively decomposed, and at the same time, the residual coal content is reduced and the activity is improved. Yuan Mei-juan et al. (Yuan Mei-juan, Fan Panpan, Bao Weiren, et al. Influence of calcination temperature and atmosphere on the pozzolanic activity and carbon sequestration performance of flotation tailings [J]. Journal of Coal, 2023, 48(S1): 314-324.) found that the activity of coal gangue heat-activated at 650~750°C in air and different concentrations of CO2 atmosphere was the best, meeting the requirements of GB / T2847 "Pozzolanic admixtures for use in cement", and it could be directly mixed with cement and used as building materials. However, during the heat activation process, the residual coal in the coal gangue is converted into CO2 and released into the atmosphere. How to improve the activity of coal gangue while reducing or even not producing carbon emissions is an important prerequisite for the resource utilization of coal gangue.

[0003] Steel slag is an inevitable product of the steelmaking process, and its output is about 10%~15% of the crude steel output. With the steady growth of steel output, by 2021, the steel slag output in China reached 164 million tons. Zhang Shufan et al. (Zhang Shufan, Cheng Xingxing, Wang Luyuan, et al. Research on carbon sequestration path of steel slag under the background of carbon neutrality [J]. Huadian Technology, 2021, 43(6): 86-91.) disclosed the ways of cold-state steel slag direct carbon sequestration, cold-state steel slag indirect carbon sequestration, and hot-state steel slag direct carbon sequestration, and pointed out that: "The hot-state steel slag direct carbon sequestration technology has a high application prospect, which can utilize the high-temperature waste heat of about 1500°C of the steel slag when it is discharged, accelerate the carbon sequestration reaction, and at the same time, the waste heat of the steel slag can be recycled, further saving energy. Coupling the steel slag gas quenching technology with the steel slag carbon sequestration technology can realize steel slag carbon sequestration and waste heat recovery at the same time." However, at present, most of the high-temperature molten steel slag discharged in the steelmaking process of steel enterprises has a temperature of 1450°C~1650°C, and the waste heat of the molten steel slag when it is cooled to room temperature is not reasonably utilized by using cooling processes such as hot sweating, hot splashing, and water quenching, which is worth our high attention. However, there is currently a lack of practical experience in utilizing the waste heat of the steel slag during the cooling process, and how to effectively utilize this part of heat and take the road of high-quality energy development is still a topic that we need to pay close attention to.

[0004] On the other hand, the steel slag heat treatment makes the unstable factors of free calcium oxide (f-CaO) and free magnesium oxide (f-MgO) in the steel slag be eliminated, eliminates the expansibility of the steel slag, and improves the volume stability of the steel slag, thereby facilitating the subsequent building material utilization of the steel slag. Furthermore, the steel slag contains a large amount of calcium-based compounds, has good CO2 capture and storage capacity, and utilizes the steel slag to capture CO2 by carbonation, which can convert waste into useful products, realize resource recycling and reuse, improve the comprehensive utilization efficiency of waste, and reduce the dependence on natural resources; on the other hand, it can reduce CO2 emissions and alleviate the impact of greenhouse effect.

[0005] In summary, the present application provides a method for heat activation of coal gangue and in-situ carbon fixation by using steel slag waste heat, which can effectively utilize the heat of high-temperature steel slag to activate coal gangue, reduce additional heat input, realize energy saving, utilize steel slag to capture CO2 generated in the process of coal gangue heat activation, reduce carbon emissions, and form an environmentally friendly resource utilization. SUMMARY

[0006] The present application aims to provide a method for heat activation of coal gangue and in-situ carbon fixation by using steel slag waste heat, which utilizes the waste heat of high-temperature molten steel slag to realize heat activation of coal gangue in a specific device through heat activation-carbonation coupling, and realizes in-situ capture of CO2 generated in the process of coal gangue heat activation by steel slag.

[0007] The present application puts coal gangue into a self-made steel slag heat treatment device, utilizes the waste heat in the cooling process of high-temperature molten steel slag to heat activate coal gangue and stimulate its pozzolanic activity, and improves the resource utilization rate of coal gangue; at the same time, a part of CO2 is generated in the process of coal gangue heat activation, which is fixed by calcium-containing substances in the steel slag, thereby reducing carbon emissions in the activation process, and the volume stability of the heat-treated steel slag is improved, which is beneficial to the subsequent building material utilization of the steel slag.

[0008] The present application provides a method for heat activation of coal gangue and in-situ carbon fixation by using steel slag waste heat, which utilizes the waste heat of high-temperature molten steel slag to heat activate coal gangue in a self-made steel slag heat treatment device, so that the coal gangue obtains higher pozzolanic activity, and at the same time, the steel slag reacts with CO2 to generate stable carbonate, so as to achieve the purpose of capturing CO2 released in the heat activation process, thereby realizing permanent storage of carbon.

[0009] The method for heat activation of coal gangue and in-situ carbon fixation by using steel slag waste heat specifically includes the following steps:

[0010] Step 1: high-temperature liquid steel slag is transferred from a converter to a heat treatment device by a slag tank car, and a crane is used to pour the liquid slag in the steel slag heat treatment device in batches;

[0011] Step two: crushing and grinding the coal gangue raw material, and loading the crushed and ground coal gangue into a hanging device;

[0012] Step three: placing the hanging device loaded with coal gangue of a certain particle size into a hot leaching device, covering the hot leaching cover, and performing a hot leaching process at a temperature of 500-850 ℃ and a pressure of 0.3-0.4 MPa, and spraying water to perform slag leaching treatment by means of an automatic spraying device, and the reaction time is 2-3 h, and the coal gangue is subjected to a hot activation reaction, and at the same time, the steel slag and CO2 are subjected to a carbonation reaction to capture CO2 generated in the activation process of the coal gangue;

[0013] Step four: after the hot leaching process is completed, the active material is taken out, and the cooled and crushed steel slag is excavated from the hot leaching device by means of an excavator and is sent to a subsequent iron and slag separation system.

[0014] In the above step one, the steel slag hot leaching device is a self-made hot leaching device, and the device has no requirement on the flowability of the steel slag and is suitable for solid, semi-solid and liquid steel slag. The self-made steel slag hot leaching device is a cylindrical tank structure, a hot leaching cover is arranged at the top, a hanging device is arranged in the middle, and a drainage hole is arranged at the bottom; a wall, a high-temperature refractory layer and a baffle are sequentially arranged from the outside to the inside of the side wall and the bottom of the tank, the wall is made of reinforced concrete, the high-temperature refractory layer is made of refractory bricks, and the baffle is made of steel plate. The bottom baffle is designed to be inclined to facilitate the discharge of wastewater, and the inclination angle is 5-20°; a ring of bosses is arranged above the side wall baffle, and the hanging device is placed on the bosses.

[0015] Further, the inner center of the hanging device is a semicircular groove made of reinforced concrete, 8 support rods are uniformly connected along the circumferential direction at the outer edge of the semicircular groove, the outer end of the support rod is connected with a circular ring-shaped support, the circular ring-shaped support is placed above the bosses, the end of the hanging device is about 80 cm away from the upper edge of the hot leaching tank, and the diameter of the semicircular groove in the hanging device is 100 cm.

[0016] Further, the hot leaching cover is provided with an automatic spraying device, a gas release device, a safety valve and an explosion-proof device, the spraying device can automatically spray water, the temperature in the device is sensed by a sensor, the controller judges whether to start spraying, and the spraying device sprays water mist; the gas release device can discharge easily explosive gases such as H2 and CO with smaller density generated in the slag leaching process; the safety valve ensures the steam pressure in the tank and releases the steam pressure when necessary, and when the pressure in the device rises above 0.4 MPa, the medium is discharged to the outside of the system to prevent the medium pressure in the device from exceeding the specified value.

[0017] Further, when the crane pours the steel slag into the hot smelting device, after pouring a part of the steel slag, the excavator is used to flip and break the large pieces of slag, while the appropriate amount of water is manually sprayed for cooling. After the slag surface solidifies, the above operation is repeated until the distance from the internal boss of the hot smelting device is 45-50 cm and the temperature of the steel slag is about 850-900 ℃, and then the slag pouring is stopped.

[0018] In the above step two, the treatment method of the coal gangue raw material is as follows: the coal gangue is broken by a jaw crusher and then ground by a ball mill, and then sieved by a screen with a pore size of 0.18 mm. The particle size of the broken and ground coal gangue should be below 0.2 mm.

[0019] Further, the sieved coal gangue is loaded into a suspension device which is connected and fixed with the upper boss of the hot smelting device, so that the coal gangue can be suspended on the upper part of the hot smelting device. The heat in the hot smelting device system is used to activate the coal gangue and stimulate its pozzolanic activity.

[0020] In the above step three, when the high-temperature liquid steel slag meets cold water, due to the different expansion coefficients of steel and slag, uneven shrinkage occurs to crush the large pieces of steel slag. In addition, the hydration reaction between free calcium oxide (f-CaO) and free magnesium oxide (f-MgO) in the steel slag leads to volume expansion, which causes the steel slag to further break, and eliminates the instability of the steel slag, facilitating the subsequent comprehensive utilization of the steel slag. The chemical reaction formula is as follows:

[0021]

[0022] Further, during the process of heat activation of the coal gangue in an air atmosphere, kaolinite is dehydroxylated into metakaolin (Al2O3•2SiO2), and the metakaolin is further decomposed into amorphous SiO2 and Al2O3. These amorphous SiO2 and Al2O3 are key factors determining the activity of the coal gangue. The chemical reaction formula is as follows:

[0023]

[0024] Further, the calcium compounds in the steel slag generate CaCO3 through carbonation reaction, fixing the CO2 generated during the activation of the coal gangue into carbonate, and part of the calcium existing in the form of silicate generates active SiO2 through carbonation reaction. The chemical reaction formula is as follows:

[0025]

[0026] Further, the water spraying system of the automatic spraying device during hot smelting is as follows: spraying for 0.5 h, stopping spraying for 1 h, continuing spraying for 0.5 h, and stopping spraying for 1.5 h. The water pressure is 0.25-0.35 MPa, and the flow rate is 15-30 m 3 / h.

[0027] In the fourth step, the f-CaO in the treated steel slag is less than 3%, and the content of the treated steel slag with a particle size of less than 20 mm can reach more than 60%.

[0028] The beneficial effects of the present application are:

[0029] (1) The heat of the hot steel slag discharged from the steelmaking furnace is effectively utilized, the coal gangue is activated, the carbonation reaction of the steel slag is generated, the heat recovery rate in the cooling process of the steel slag is improved, the energy saving is further strengthened, the energy efficiency is improved, and a new idea is provided for breaking the resource and environmental bottleneck constraints and promoting high-quality development;

[0030] (2) Through the coupling effect of thermal activation-carbonation, the CO2 generated in the coal gangue activation process is captured by the steel slag, the synergistic effect of coal gangue-steel slag activation and carbon sequestration is realized, and a new idea is provided for the utilization of coal-based solid waste;

[0031] (3) The coal gangue is used to prepare a high-pozzolanic activity material, and the stability of the steel slag is improved, which is convenient for subsequent building material utilization of the steel slag, increases the resource utilization rate of the steel slag, realizes the green resource utilization target, and improves the resource utilization way of such solid waste;

[0032] (4) The amount of cooling water used in the steel slag cooling process is saved, because the carbonation reaction of the steel slag will absorb the heat of the surrounding environment, causing the temperature of the heat sweating device system to drop rapidly, so the amount of water used in the steel slag cooling link is relatively reduced, and the purpose of saving resources is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The process flowchart of the present application is shown in the figure;

[0034] Figure 2 The self-made heat sweating device schematic diagram of the present application is shown in the figure;

[0035] Figure 3 The figure is Figure 2 The section view along line A-A in the figure;

[0036] Figure 4 The compressive strength of the hot activated coal gangue and cement stone body (a) is shown in the figure;

[0037] Figure 5 The compressive strength of the hot activated coal gangue and cement stone body (b) is shown in the figure;

[0038] Figure 6 The TG-DTG graph of the steel slag sample after carbon sequestration (a) is shown in the figure

[0039] Figure 7 The TG-DTG graph of the steel slag sample after carbon sequestration (b) is shown in the figure;

[0040] Figure 8 is the XRD spectrum of coal gangue after thermal activation at different temperatures in air atmosphere;

[0041] Figure 9 is the FTIR spectrum of coal gangue after thermal activation at different temperatures in air atmosphere;

[0042] In the figure: 1 - wall; 2 - high-temperature refractory layer; 3 - baffle; 4 - boss; 5 - explosion-proof device; 6 - safety valve; 7 - air release device; 8 - hot steaming cover; 9 - spraying device; 10 - water seal groove; 11 - suspension device; 12 - drainage hole. DETAILED DESCRIPTION

[0043] The present application is further illustrated by the following examples, but is not limited to the following examples.

[0044] The present application provides a method for thermal activation of coal gangue and in-situ carbon sequestration using steel slag waste heat, which utilizes the waste heat of high-temperature molten steel slag, uses a self-made steel slag hot steaming device, and activates coal gangue by means of the temperature of the steel slag hot steaming device system, so that the coal gangue obtains a higher pozzolanic activity. At the same time, the steel slag reacts with CO2 to form stable carbonate, achieving the purpose of capturing CO2 released in the thermal activation process, thereby realizing permanent sequestration of carbon.

[0045] The method for thermal activation of coal gangue and in-situ carbon sequestration using steel slag waste heat described above specifically comprises the following steps:

[0046] Step one: high-temperature liquid steel slag is transferred from the converter to the hot steaming device by the slag tank car, and the liquid slag is poured into the steel slag hot steaming device in batches using a crane;

[0047] Step two: the coal gangue raw material is crushed and ground, and the crushed and ground coal gangue is loaded into the suspension device;

[0048] Step three: the suspension device loaded with coal gangue of a certain particle size is placed in the hot steaming device, and the hot steaming cover is covered, the reaction temperature is 500-850 ℃, the pressure is 0.3-0.4 MPa, the spraying device automatically sprays water for steaming slag treatment, the reaction time is 2-3 h, the coal gangue is subjected to thermal activation reaction, at the same time, the steel slag and CO2 undergo carbonation reaction, capturing CO2 generated in the coal gangue activation process;

[0049] Step four: after the hot steaming process is completed, the active material is taken out, the crushed and cooled steel slag is excavated from the hot steaming device using an excavator, and is sent to a subsequent iron and slag separation system.

[0050] The steel slag hot steaming device provided by the present application is a self-made hot steaming device, such as Figure 2 and 3As shown, the sidewall and the bottom of the device are composed of wall body 1, high-temperature refractory layer 2 and baffle 3 from outside to inside, and the device has no requirement on the flowability of steel slag and is suitable for solid, semi-solid and liquid steel slag. The wall body is reinforced concrete, the high-temperature refractory layer is refractory brick, and the baffle is steel plate.

[0051] Further, the self-made steel slag hot stripping device is a cylindrical tank structure, the top is provided with a hot stripping cover 8, the middle is provided with a suspension device 11, and the bottom is provided with a drainage hole 12; the sidewall and the bottom of the tank body are sequentially provided with a wall body 1, a high-temperature refractory layer 2 and a baffle 3 from outside to inside, the bottom baffle is designed to be inclined to facilitate the discharge of wastewater, and the inclination angle is 5-20°; a ring of bosses 4 is arranged above the sidewall baffle, and the suspension device 11 can be placed on the bosses 4.

[0052] Further, the inner center of the suspension device 11 is a semicircular groove made of reinforced concrete, eight support rods are uniformly connected along the circumferential direction at the outer edge of the semicircular groove, the outer end of the support rod is connected with a circular ring-shaped support, the circular ring-shaped support is placed above the bosses 4, the end of the suspension device is about 80 cm away from the upper edge of the hot stripping tank, and the diameter of the semicircular groove in the suspension device is 100 cm.

[0053] Further, the hot stripping cover is provided with an automatic spraying device 9, a degassing device 7, a safety valve 6 and an explosion-proof device 5, the spraying device 9 can realize automatic water spraying of the device, the temperature in the device is sensed by an inductor, the controller judges whether to start spraying, and the spraying device sprays water mist; the degassing device 7 can discharge easily explosive gases such as H2 and CO with smaller density generated in the process of slag stripping; the safety valve 6 ensures the steam pressure in the tank body and releases the steam pressure when necessary, so as to prevent the medium pressure in the device from exceeding the specified value by discharging the medium outside the system when the pressure in the device rises to more than 0.4 MPa.

[0054] The specific implementation process of the present application for hot activation of coal gangue and in-situ carbon fixation by using steel slag waste heat will be described below through specific examples: Example 1

[0055] The coal gangue of a coal preparation plant and the converter steel slag of a steel plant are selected, and the main chemical components of the two materials are analyzed by X-ray fluorescence spectroscopy (XRF) as shown in Table 1.

[0056] Table 1 Main chemical components (wt.%) of two raw materials in Example 1

[0057]

[0058] Liquid steel slag is transported from a converter of a steel plant to a hot disintegration device, then the liquid steel slag is poured into the hot disintegration device in batches using a crane, water is manually sprayed after each pouring of the steel slag, the excavator is used to flip up and down after the surface of the steel slag solidifies and a large number of cracks appear, and the above operation is repeated until the distance from the internal boss of the device is 48 cm and the temperature of the steel slag is about 879 ℃.

[0059] The coal gangue raw material is crushed by a jaw crusher and then ground by a ball mill, and the crushed and ground coal gangue with a particle size of less than 0.2 mm is sieved through a screen with a pore size of 0.18 mm and placed in the suspension device.

[0060] The sieved coal gangue is placed on the upper part of the hot disintegration tank by means of the suspension device, the hot disintegration cover is covered, the hot disintegration device is started, the reaction temperature is 500-850 ℃, the pressure in the device is 0.38 MPa, the reaction time is 2 h, the automatic spraying device on the hot disintegration cover sprays water at regular intervals, sprays for 0.5 h, stops for 1 h, continues to spray for 0.5 h, and stops for 1.5 h. After the hot disintegration is completed, the activated coal gangue is taken out, and the steel slag after crushing and cooling in the hot disintegration device is grabbed out by the excavator.

[0061] After the cooling treatment, the f-CaO in the steel slag is less than 3%, and the content of the steel slag with a particle size of less than 20 mm after the treatment is more than 60%. The cooled and cooled steel slag is sent to a matching iron and slag separation system to recover elemental iron in the steel slag. The steel slag powder after cooling, crushing and magnetic separation can be used as a concrete admixture in the field of construction engineering.

[0062] The mass loss of CO2 in the steel slag after high-temperature carbon sequestration is measured by using a thermogravimetric analyzer, as shown in Figure 6 According to the DTG curve, it can be seen that the decomposition temperature of CaCO3 in the hot activated coal gangue in the thermal analyzer is about 600-822 ℃, and the weight loss rate of the steel slag sample after carbon sequestration in this interval is 9.48 wt.%, and the carbon sequestration efficiency is 10.43 wt.%.

[0063] The activated coal gangue is prepared into a stone body with cement, and the strength of the stone body is used as an index of the pozzolanic activity. The mechanical property cement mortar strength test is carried out according to GB / T17671-2021, the cement clinker accounts for 70% of the solid materials, the hot activated coal gangue accounts for 30%, the water-cement ratio is 0.5, and the prepared neat paste stone body is tested for compressive strength. As shown in Figure 4 The 28 d strength of the stone body of the hot activated coal gangue sample is 25.4 MPa, which is 6 MPa higher than that of the stone body of the unactivated coal gangue sample, and the pozzolanic activity reaches the requirement.

[0064] Figure 8 and Figure 9The XRD spectrum and FTIR spectrum of the coal gangue after heat activation at different temperatures in air atmosphere obtained in the embodiment are shown respectively. Figure 8 It can be seen from the XRD spectrum that the kaolinite diffraction peaks at 2θ=12° and 24° basically disappear, indicating that the crystalline kaolinite (Al2O3•2SiO2•2H2O) in the coal gangue is converted into amorphous metakaolin (Al2O3•2SiO2), and the active Al2O3 and SiO2 obviously increase. Figure 9 It can be seen from the FTIR spectrum that the absorption bands of the coal gangue after heat activation at 3695 cm -1 , 3650 cm -1 , and 3620 cm -1 are obviously reduced, which is that the crystal kaolinite (Al2O3•2SiO2•2H2O) is converted into a transition phase-metakaolin (Al2O3•2SiO2) with poor crystallinity, and the layered structure is converted into a porous and disordered amorphous structure; the absorption bands at 914 cm -1 and 540 cm -1 of the coal gangue after heat activation are greatly weakened, which respectively corresponds to the destruction of Al-OH and Si-O-Al; accompanied by the disappearance of the absorption bands at 1099 cm -1 , 1031 cm -1 , and 1010 cm -1 , a new broadened absorption band appears, which is caused by the depolymerization of the silicon-oxygen tetrahedral layer of kaolinite to generate amorphous silicon during the heat activation process; the absorption bands at 756 cm -1 , 696 cm -1 , and 468 cm -1 are all weakened to different degrees, which are all the characteristics of the formation of amorphous silicon-aluminum compounds due to the structural changes of kaolinite. Example 2

[0065] The coal gangue of a coal preparation plant and the electric furnace slag of a steel plant were selected, and the main chemical components of the two materials were analyzed by X-ray fluorescence spectroscopy (XRF), as shown in Table 2.

[0066] Table 2 Main chemical components (wt.%) of the two raw materials in Example 2

[0067]

[0068] The liquid steel slag was transported from the converter of a steel plant to a hot smelting device, and then the liquid steel slag was poured into the hot smelting device in batches using a crane, and water was manually sprayed after each pouring of the steel slag. After the surface of the steel slag solidified and a large number of cracks appeared, the excavator was used to flip up and down, and the above operation was repeated until the distance from the device inside the boss was 50 cm, and the temperature of the steel slag was about 893 ℃.

[0069] The coal gangue raw material is crushed by a jaw crusher and then ground by a ball mill. It is then sieved through a 0.18 mm sieve, and the coal gangue with a particle size of less than 0.2 mm after crushing and grinding is placed into a suspension device.

[0070] Using a suspension device, the screened coal gangue is placed on top of the hot-quenching tank, the hot-quenching cover is closed, and the hot-quenching device is started. The reaction temperature is 500-850℃, the pressure inside the device is 0.35 MPa, and the reaction time is 3 hours. An automatic sprinkler system on the hot-quenching cover sprays water at regular intervals: spraying for 0.5 hours, stopping for 1 hour, then continuing for 0.5 hours and stopping for 1.5 hours. After the hot-quenching is completed, the activated coal gangue is removed, and the crushed and cooled steel slag in the hot-quenching device is removed using an excavator.

[0071] After cooling, the f-CaO content in the steel slag is less than 3%, and the content of particles smaller than 20mm in the treated steel slag can reach over 60%. The cooled steel slag is sent to a supporting iron and slag separation system to recover elemental iron from the steel slag. The cooled, crushed, and magnetically separated steel slag powder can be used as a concrete admixture in construction projects and other fields.

[0072] The mass loss of CO2 in steel slag after high-temperature carburization was measured using a thermogravimetric analyzer, see [reference needed]. Figure 7 As shown in the figure, the decomposition temperature of CaCO3 in thermally activated coal gangue in the enthalpy tester is approximately 604~815 ℃. After carbon fixation, the weight loss rate of the steel slag sample in this range is 9.95 wt.%, and the carbon fixation efficiency is 11.01 wt.%.

[0073] Activated coal gangue was mixed with cement to prepare a stone-like body, and the strength exhibited by the stone-like body was used as an indicator of pozzolanic activity. The mechanical properties of the cement mortar were tested according to GB / T17671-2021, with cement clinker accounting for 70% of the solid materials, thermally activated coal gangue accounting for 30%, and a water-cement ratio of 0.5. The compressive strength of the prepared neat cement paste stone-like body was then tested. See [link / details]. Figure 5 As shown, the 28-day strength of the aggregate in the thermally activated coal gangue sample was 26.1 MPa, which was 7.4 MPa higher than that of the aggregate in the unactivated coal gangue sample, indicating that the pozzolanic activity met the requirements.

Claims

1. A method for thermally activating coal gangue and in-situ carbon fixation using waste heat from steel slag, characterized in that: By utilizing the residual heat of high-temperature molten steel slag, coal gangue is activated in the steel slag hot quenching device system to obtain high pozzolanic activity. At the same time, the steel slag reacts with CO2 to generate stable carbonates, capturing the CO2 released during the thermal activation process and achieving permanent carbon sequestration. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat from steel slag includes the following steps: Step 1: High-temperature liquid steel slag is transported from the converter to the hot quenching device by slag tank trucks, and the liquid slag is poured into the steel slag hot quenching device in batches by crane; The steel slag hot quenching device is a cylindrical tank structure with a hot quenching cover on the top, a suspension device in the middle, and a drainage hole at the bottom. The tank sidewall and bottom are provided with a wall, a high-temperature refractory layer, and a baffle from the outside to the inside. The bottom baffle is designed to be inclined to facilitate the discharge of wastewater, and the inclination angle is 5~20°. A ring of protrusions is provided above the sidewall baffles, and the suspension device is placed on the protrusions. Step 2: Crush and grind the coal gangue raw material, and load the crushed and ground coal gangue into the suspension device; Step 3: Place the suspension device containing coal gangue into the hot quenching device, cover it with the hot quenching cover, the reaction temperature is 500~850℃, the pressure is 0.3~0.4 MPa, the spraying device automatically sprays water to treat the slag, the reaction time is 2~3 hours, the coal gangue undergoes thermal activation reaction, at the same time the steel slag and CO2 undergo carbonation reaction, capturing the CO2 generated during the activation of coal gangue; Step 4: After the hot quenching process is completed, the active material is removed, and the crushed and cooled steel slag is shoveled out of the hot quenching device by an excavator and sent to the subsequent iron and slag separation system.

2. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The internal center of the suspension device is a semi-circular groove made of reinforced concrete. Eight support rods are evenly connected along the circumference of the outer edge of the semi-circular groove. The outer ends of the support rods are connected to a circular support member, which is placed on top of the boss. The end of the suspension device is about 80 cm away from the upper edge of the hot sealing tank. The diameter of the semi-circular groove in the suspension device is 100 cm.

3. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The wall is made of reinforced concrete, the high-temperature refractory layer is made of refractory bricks, and the baffle is made of steel plate.

4. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The hot slag quenching cover is equipped with an automatic spraying device, a venting device, a safety valve, and an explosion-proof device. The spraying device can automatically spray water. The temperature inside the device is detected by a sensor, and the controller determines whether to start the spraying. The spraying device sprays water mist. The venting device discharges the less dense and explosive gases generated during the slag quenching process. The safety valve ensures the steam pressure inside the tank. When the pressure inside the device rises above 0.4 MPa, the medium is discharged to the outside of the system to prevent the pressure of the medium inside the device from exceeding the specified value.

5. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: When the steel slag is poured into the hot quenching device by the crane, after each portion of steel slag is poured in, the excavator is used to turn it up and down to break up the large pieces of slag. At the same time, an appropriate amount of water is manually sprayed in to cool it. After the slag surface solidifies, the above operation is repeated until the distance from the inside of the hot quenching device to the protrusion is 45~50cm and the temperature of the steel slag is 850~900℃, at which point the slag distribution is stopped.

6. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The processing method for coal gangue raw materials is as follows: after crushing with a jaw crusher, it is ground with a ball mill and sieved through a 0.18mm sieve. The particle size of the coal gangue after crushing and grinding should be below 0.2mm. The sieved coal gangue is then loaded into a suspension device, which is connected and fixed to the upper boss of the hot quenching device, so that the coal gangue can be suspended on the upper part of the hot quenching device. The heat in the hot quenching device system is used to activate the coal gangue and stimulate its pozzolanic activity.

7. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The automatic sprinkler system operates on the following schedule during hot and humid conditions: spray for 0.5 hours, stop for 1 hour, then continue spraying for 0.5 hours, stop for 1.5 hours. The spray pressure is 0.25~0.35MPa, and the flow rate is 15~30m³ / h. 3 / h.

8. The method for thermally activating coal gangue and in-situ carbon fixation using waste heat of steel slag according to claim 1, characterized in that: The treated steel slag contains less than 3% f-CaO and more than 60% of particles smaller than 20mm.

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