A steel slag sensible heat recovery and carbon sequestration modification process

Abstract

The application discloses a steel slag sensible heat recovery and carbon fixation modification process, which comprises the following steps: a steel slag melt is cast into a block through a block casting device, the high-temperature steel slag block shell is solid, and the inner core is liquid; the steel slag block enters a vertical reactor from an upper feeding port of the vertical reactor, metallurgical flue gas is introduced from a gas inlet pipeline at the bottom of the vertical reactor, heat exchange is performed between the metallurgical flue gas and the high-temperature steel slag block in the flowing process, high-temperature flue gas is formed, meanwhile, the high-temperature steel slag block reacts with CO2 in the flue gas, the steel slag block is modified by carbon fixation, carbon fixation modified steel slag blocks are formed, and the high-temperature flue gas is discharged through a pipeline at the top of the vertical reactor; S3: the high-temperature flue gas after dust removal enters a heat exchanger to perform heat exchange, and the flue gas is discharged from a chimney after heat exchange; the carbon fixation modified steel slag blocks are classified and utilized after crushing and separation, and steel slag high-value-added products are prepared. The steel slag sensible heat recovery and carbon fixation can be simultaneously performed.

Description

Technical Field

[0001] This invention relates to the field of sensible heat recovery and carbon fixation technology of steel slag, and in particular to a process for sensible heat recovery and carbon fixation modification of steel slag. Background Technology

[0002] With the development and progress of human industrialization, CO2 emissions have continued to increase, leading to increasingly serious global warming problems. How to reduce carbon emissions and curb global warming has become a hot issue of concern for humanity.

[0003] The discharge temperature of steel slag is as high as 1400-1600℃, and its specific heat capacity in the molten state is about 1.2 kJ / (kg·℃). Based on an initial temperature of 1400℃ and a final temperature of 500℃, one ton of steel slag can recover approximately 1.2 GJ of sensible heat, equivalent to the heat generated by the complete combustion of 41 kg of standard coal. For currently developed steel slag sensible heat recovery technologies, slag crushing is an indispensable step. Based on the crushing mechanism, three commonly used physical methods have been promoted: mechanical crushing, air quenching, and centrifugal granulation.

[0004] Mechanical crushing methods include solid particle impact, mechanical stirring, and drum crushing, which mainly use mechanical force to decompose molten steel slag into steel slag particles. For example, Chinese patent application No. 201811004273.8 discloses a mechanical thermal crushing and waste heat recovery device for steel slag. This application involves pouring hot steel slag into a hopper, spraying cooling water, and then mechanically crushing it. Finally, the high-temperature steam generated is recovered. However, because the steel slag particles produced by mechanical crushing are of uneven size, they are difficult to meet industrial needs. At the same time, the temperature of the cooled steel slag is still relatively high (500-900℃), which greatly reduces the efficiency of sensible heat recovery.

[0005] The air quenching method uses high-speed, high-pressure gas to impact a stream of molten steel slag, causing the slag to decompose into small particles as it rapidly cools. For example, Chinese patent application No. 201210387654.5 discloses a device and method for air quenching steel slag and recovering waste heat. This application uses low-temperature nitrogen to quench liquid steel slag into uniform particles, and then recovers waste heat through pneumatic conveying. Although this method can recover the sensible heat of the steel slag, the sensible heat recovery efficiency is low and the cost is high.

[0006] Centrifugal granulation utilizes centrifugal force to granulate molten slag, creating conditions for sensible heat recovery. For example, Chinese patent application No. 201710117736.0 discloses a method for recycling high-temperature slag. This application involves rapidly cooling high-temperature liquid molten slag and then feeding it into a centrifugal granulator for granulation. The resulting particles are then subjected to forced heat exchange with water, and the heat is recovered. However, the sensible heat recovery efficiency of this method is relatively low, and the molten slag particles after heat exchange are difficult to process.

[0007] Steel slag, a typical solid waste from the metallurgical industry, is mainly used to produce cement, road materials, and steel slag bricks. However, due to problems such as poor stability of free calcium oxide and low cementitious activity, the comprehensive utilization rate of steel slag is less than 30%, and the stockpiled amount exceeds 1 billion tons, causing problems such as land encroachment and environmental pollution. However, steel slag is rich in calcium and magnesium, typically containing 40%-60% CaO and 2%-10% MgO, exhibiting significant carbonation activity. Carbonation of steel slag can not only absorb CO2 but also replace natural ores in capturing and storing CO2, reducing carbon emissions. Currently, steel slag carbon fixation can be divided into indirect carbon fixation by leaching and direct carbon fixation by heat. Indirect carbon fixation by leaching generally occurs at temperatures below 200℃, utilizing a solution to remove CaO from the steel slag. 2+ It dissolves, and then reacts with CO3 in the solution. 2- The reaction produces CaCO3, thus achieving indirect carbon fixation. For example, Chinese patent application No. 202223494217.1 discloses a device for efficiently capturing carbon dioxide from activated steel slag. This application first crushes the steel slag, then removes the CaCO3 through acid leaching. 2+ The steel slag is leached in a solution, and then the liquid enters a CO2 absorption tower to absorb CO2. However, the efficiency of indirect carbon fixation through steel slag leaching is limited by the amount of Ca in the steel slag. 2+ The leaching rate is affected, and the treatment method consumes a lot of water and causes serious environmental pollution. Hot direct carbonization is a carbonization treatment performed on steel slag at high temperature, which can achieve the dual purpose of carbonization and sensible heat utilization. At the same time, the high temperature improves the carbonization efficiency of steel slag and generates carbonate products, which helps to enhance the density and compressive strength of steel slag structure, thereby improving the cementing activity of steel slag. It can also reduce the content of f-CaO and f-MgO, improve the stability of steel slag, and enhance the resource utilization value of steel slag.

[0008] However, existing steel slag carbonization technologies neglect the recovery of sensible heat from the steel slag, resulting in significant resource waste. For example, Chinese patent application No. 202211142705.8 discloses a steel slag carbonization device and its usage method. This application involves adding steel slag powder to a loading box and then throwing the slag out through a throwing disc, allowing the steel slag powder to react with CO2 to generate carbonates for carbonization. However, it does not recover the sensible heat of the steel slag during carbonization. Another example is Chinese patent application No. 202210599827.3, which discloses a method and application for wet grinding of steel slag in steel plants to reduce emissions through carbonization. This application involves water quenching and rapidly cooling molten steel slag produced by steel plants, followed by crushing, iron removal, and drying to obtain steel slag powder. The steel slag powder is then prepared into a steel slag slurry, which is finally used for carbonization. However, this application directly water quenches and rapidly cools the molten steel slag produced by steel plants, resulting in a waste of the sensible heat of the steel slag.

[0009] Because steel slag produced by steel plants is in a molten liquid state with a high temperature (above 1500℃), it is difficult to recover the sensible heat of the steel slag through gas-liquid heat exchange. While gas-solid heat exchange is the most efficient, casting the steel slag completely into a solid state would result in the loss of most of its sensible heat, leading to resource waste. Reducing CO2 emissions, recovering the sensible heat of steel slag, and utilizing steel slag as a resource have become urgent problems to be solved in the metallurgical industry. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a process for sensible heat recovery and carbon fixation modification of steel slag, thereby achieving the goal of simultaneously recovering sensible heat and fixing carbon in steel slag and improving resource utilization.

[0011] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0012] The steel slag sensible heat recovery and carbon fixation modification process includes the following steps:

[0013] S1: The molten steel slag is cast into blocks using a casting device. The resulting high-temperature steel slag block has a solid outer shell and a liquid inner core.

[0014] S2: Steel slag castings enter the vertical reactor through the feed inlet at the top of the vertical reactor via a feeding device. At the same time, metallurgical flue gas is introduced from the air inlet pipe at the bottom of the vertical reactor. The metallurgical flue gas flows from bottom to top in the vertical reactor. During the flow, the metallurgical flue gas exchanges heat with the high-temperature steel slag castings to form high-temperature flue gas. At the same time, the high-temperature steel slag castings react with CO2 in the flue gas to perform carbon fixation modification on the steel slag castings, forming carbon-fixed modified steel slag blocks. The high-temperature flue gas is discharged through the pipe at the top of the vertical reactor.

[0015] S3: After the flue gas is discharged from the vertical reactor, it enters the gravity dust collector for dust removal. The high-temperature flue gas after dust removal enters the heat exchanger for heat exchange. After heat exchange, the flue gas is discharged from the chimney. The carbon-modified steel slag blocks are crushed, separated and graded for utilization to prepare high-value-added steel slag products.

[0016] in,

[0017] The temperature range of the molten steel slag is 1500-1700℃.

[0018] The temperature range of the cast high-temperature steel slag ingot is 900-1300℃.

[0019] The gas and solid phases in the vertical reactor flow in opposite directions.

[0020] The feed inlet of the vertical reactor is located on the upper side, the air inlet pipe is located on the lower side, the bottom is an inverted trapezoidal discharge outlet, and the top center is provided with an air outlet pipe.

[0021] The flue gas temperature range of the pipe at the top of the vertical reactor is 700-1100℃.

[0022] The heat exchanger is a vertical heat exchanger.

[0023] The outer shell temperature of the high-temperature steel slag casting is 850-900℃, and the inner core temperature is 1250-1300℃.

[0024] There are two air intake pipes, which are symmetrically arranged on both sides of the lower part of the vertical reactor.

[0025] The vertical reactor is equipped with a conveying mechanism at the bottom corresponding to the discharge port, and a crushing device and a separation device are arranged in sequence behind the conveying mechanism.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The design of this steel slag sensible heat recovery and carbon fixation modification process is reasonable. It can simultaneously carry out steel slag sensible heat recovery and steel slag carbon fixation, overcoming the difficulty of simultaneously carrying out steel slag sensible heat recovery and steel slag carbon fixation in existing technologies. It can improve resource utilization, reduce enterprise operating costs, and effectively alleviate the environmental pollution caused by steel slag. It is of great significance to the high-quality development of the metallurgical industry. Attached Figure Description

[0028] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0029] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and through the description of the examples.

[0031] This steel slag sensible heat recovery and carbon fixation modification process first involves casting the steel slag into blocks with a "chocolate-filled" structure—a low-temperature solid outer shell and a high-temperature liquid inner shell. This structure maximizes the recovery of sensible heat from the steel slag. Then, the steel slag blocks are transported to a vertical reactor for heat exchange with metallurgical flue gas. Simultaneously, the steel slag blocks react with carbon dioxide in the flue gas to perform carbon fixation modification on the steel slag. Finally, the carbon-modified steel slag is utilized as a resource.

[0032] This process can simultaneously recover sensible heat from steel slag and fix carbon in steel slag, overcoming the difficulty of doing so simultaneously in existing technologies. It improves resource utilization, reduces enterprise operating costs, and can also effectively alleviate environmental pollution caused by steel slag, which is of great significance to the high-quality development of the metallurgical industry.

[0033] like Figure 1 The preferred specific example shown is:

[0034] The sensible heat recovery and carbon fixation modification process for steel slag based on molten slag ingots includes the following steps:

[0035] S1: The molten steel slag produced by the steel plant is cast into blocks through a casting device. The resulting high-temperature steel slag blocks have a solid outer shell and a liquid inner core.

[0036] S2: High-temperature steel slag castings enter the vertical reactor through the feed inlet at the top of the vertical reactor via a feeding device. At the same time, metallurgical flue gas is introduced from the air inlet pipe at the bottom of the vertical reactor. The metallurgical flue gas flows from bottom to top in the vertical reactor and flows in the opposite direction to the high-temperature steel slag castings. During the flow, the metallurgical flue gas exchanges heat with the high-temperature steel slag castings to form high-temperature flue gas. At the same time, the high-temperature steel slag castings react with CO2 in the flue gas to perform carbon fixation modification on the steel slag castings, forming carbon-modified steel slag blocks. The high-temperature flue gas is discharged through the pipe at the top of the vertical reactor.

[0037] S3: After being discharged from the vertical reactor, the high-temperature flue gas enters a gravity dust collector for dust removal. The dust-removed high-temperature flue gas then enters a heat exchanger for heat exchange, and is discharged from the chimney after heat exchange. The carbon-modified steel slag blocks are crushed, separated, and graded for utilization to prepare high-value-added steel slag products.

[0038] in,

[0039] The temperature range of the molten steel slag is 1500-1700℃; the temperature range of the cast high-temperature steel slag ingot is 900-1300℃. Specifically, the shape of the high-temperature steel slag ingot can be a cube, cuboid, cube with curved edges, or column. Its outer shell temperature is 850-900℃, and its inner core temperature is 1250-1300℃.

[0040] The feed inlet at the top of the vertical reactor is located on one side of the reactor. There are two air inlet pipes at the bottom, which are symmetrically located on the left and right sides respectively. The bottom is an inverted trapezoid with a discharge port, and there is an air outlet pipe at the center of the top. The temperature range of the flue gas discharged from the pipe at the top of the vertical reactor is 700-1100℃.

[0041] The heat exchanger is a vertical heat exchanger; the vertical reactor, gravity dust collector, heat exchanger, and chimney are all connected by pipes. A conveying mechanism is installed below the vertical reactor corresponding to the discharge port, and crushing and separating equipment are installed in sequence behind the conveying mechanism. Existing equipment can be used for the crushing and separating equipment.

[0042] Because steel slag produced by steel plants is in a molten liquid state with a high temperature (above 1500℃), it is difficult to recover the sensible heat of the steel slag through gas-liquid heat exchange. While gas-solid heat exchange is the most efficient, casting the steel slag completely into a solid state results in the loss of most of its sensible heat, leading to resource waste. To address this issue, the applicant has innovatively proposed a high-temperature steel slag casting with the structural characteristics of a chocolate-filled liqueur. The outer shell of the steel slag casting is a low-temperature solid state, while the inner core is a high-temperature liquid state. This structure not only maximizes the retention of the sensible heat of the steel slag but also ensures the heat exchange rate, enabling the maximum recovery of the sensible heat from the steel slag.

[0043] The applicant conducted a systematic study on the carbon fixation characteristics of steel slag and metallurgical flue gas from steel plants, finding that reaction temperature significantly affects the direct carbon fixation of steel slag. At 500℃, the carbon fixation reaction essentially did not occur. At temperatures above or equal to 650℃, a significant carbon fixation reaction occurred, but at 950℃, the CO2 concentration began to increase with prolonged time, indicating that carbonates underwent a decomposition reaction. To address this issue, the applicant proposed a vertical reactor design. This design employs counter-current gas-solid flow, allowing the carbon fixation reaction to occur fully in the low-temperature zone, avoiding carbonate decomposition in the high-temperature zone, and ensuring a more complete carbon fixation reaction for the high-temperature steel slag castings within the vertical reactor.

[0044] This invention conducted industrial experiments on the sensible heat recovery and carbon fixation of converter steel slag; specific embodiments are as follows:

[0045] The temperature of the converter slag melt used is 1550℃, the outer shell temperature of the cast high-temperature slag ingot is 870℃, and the inner core temperature is 1280℃. The residence time of the slag ingot in the vertical reactor is 1.8h. After carbon fixation and heat exchange, the temperature of the carbon-modified slag is 58℃, and the carbon fixation conversion rate is as high as 92%. The temperature of the high-temperature flue gas input to the vertical reactor is 960℃, and the sensible heat recovery rate of the slag is as high as 75%. It can simultaneously carry out sensible heat recovery and carbon fixation of slag, overcoming the problem that it is difficult to carry out sensible heat recovery and carbon fixation of slag simultaneously in the existing technology.

[0046] The present invention has the following advantages:

[0047] 1. By casting molten steel slag into blocks with a low-temperature solid outer shell and a high-temperature liquid outer shell, this structure enables both solid-state slag transport and liquid-state heat exchange between the solid and liquid steel slag, significantly improving the sensible heat recovery rate of the steel slag. 2. A vertical reactor design is proposed, in which the gas and solid phases flow in opposite directions, allowing the carbon fixation reaction to occur fully in the low-temperature zone, avoiding the decomposition of carbonates in the high-temperature zone, and greatly improving the direct carbon fixation efficiency of the steel slag. 3. This design enables the ultimate recovery of the sensible heat of the molten slag, direct solidification of CO2 from metallurgical flue gas, and modification of the steel slag through carbonation, allowing for high-value-added utilization of the modified steel slag.

[0048] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the concept and technical solution of the present invention, or the direct application of the concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A process for recovering sensible heat and modifying carbon in steel slag, characterized in that: The process includes the following steps: S1: The molten steel slag is cast into blocks using a casting device. The resulting high-temperature steel slag block has a solid outer shell and a liquid inner core. S2: Steel slag castings enter the vertical reactor through the feed inlet at the top of the vertical reactor via a feeding device. At the same time, metallurgical flue gas is introduced from the air inlet pipe at the bottom of the vertical reactor. The metallurgical flue gas flows from bottom to top in the vertical reactor. During the flow, the metallurgical flue gas exchanges heat with the high-temperature steel slag castings to form high-temperature flue gas. At the same time, the high-temperature steel slag castings react with CO2 in the flue gas to perform carbon fixation modification on the steel slag castings, forming carbon-fixed modified steel slag blocks. The high-temperature flue gas is discharged through the pipe at the top of the vertical reactor. S3: After the flue gas is discharged from the vertical reactor, it enters the gravity dust collector for dust removal. The high-temperature flue gas after dust removal enters the heat exchanger for heat exchange. After heat exchange, the flue gas is discharged from the chimney. Carbon-modified steel slag blocks are crushed, separated, and graded for use in the preparation of steel slag products.

2. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The temperature range of the molten steel slag is 1500-1700 ℃.

3. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The temperature range of the cast high-temperature steel slag ingot is 900-1300℃.

4. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The gas and solid phases in the vertical reactor flow in opposite directions.

5. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The feed inlet of the vertical reactor is located on the upper side, the air inlet pipe is located on the lower side, the bottom is an inverted trapezoidal discharge outlet, and the top center is provided with an air outlet pipe.

6. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The flue gas temperature range of the pipe at the top of the vertical reactor is 700-1100℃.

7. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 1, characterized in that: The heat exchanger is a vertical heat exchanger.

8. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 3, characterized in that: The outer shell temperature of the high-temperature steel slag casting is 850-900℃, and the inner core temperature is 1250-1300℃.

9. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 5, characterized in that: There are two air intake pipes, which are symmetrically arranged on both sides of the lower part of the vertical reactor.

10. The steel slag sensible heat recovery and carbon fixation modification process as described in claim 5, characterized in that: The bottom of the vertical reactor is equipped with a conveying mechanism corresponding to the discharge port, and crushing equipment and separation equipment are arranged in sequence behind the conveying mechanism.

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