Steel smelting solid waste treatment method and treatment system

Abstract

The invention discloses a steel smelting solid waste treatment method and system, and the steel smelting solid waste treatment method provided by the invention comprises the following steps: mixing digested steelmaking LT ash and steelmaking sludge for pelletizing under the condition of not adding a binder. According to the method, composite pelletizing is achieved through the synergistic effect of the autohension of the steelmaking sludge and the gelling characteristic of calcium oxide (CaO) after digestion of the steelmaking LT ash, the pellets are prepared without adding a binder, solid waste value-added treatment can be effectively achieved, the solid waste can be reused for the metallurgical process, and the prepared pellets can be directly used for smelting of a rotary hearth furnace, a converter, an electric furnace and the like; and recovery of iron and zinc resources is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical solid waste treatment, and in particular to a method and system for treating steel smelting solid waste. Background Art

[0002] Steelmaking sludge is a secondary resource containing elements such as iron, calcium, zinc, and carbon. It is produced by wet dust removal in the converter during the steelmaking process, while steelmaking LT ash is produced by dry dust removal. Its composition is complex and steelmaking LT ash is prone to dust. Direct stacking or landfilling will cause environmental pollution.

[0003] In view of this, the present invention proposes a method and system for treating solid waste from steel smelting. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a method and system for treating solid waste from steel smelting.

[0005] The present invention solves the technical problem by adopting the following technical solutions.

[0006] The present invention provides a method for treating steel smelting solid waste, comprising: mixing and pelletizing the digested steelmaking LT ash and steelmaking sludge without adding a binder.

[0007] The present invention also provides a steel smelting solid waste treatment system, comprising: a receiving bin for receiving steelmaking LT ash, a biaxial humidifier, a batching bin 1# for storing plastic LT ash, a batching bin 2# for storing steelmaking sludge, a high-pressure mixer, a buffer bin, a pelletizer, a roller ball screen and a chain grate dryer, wherein: the discharge port of the receiving bin is connected to the feed port of the biaxial humidifier through a pipeline, the biaxial humidifier is connected to the batching bin 1# through a material conveying device, the plastic LT ash in the batching bin 1# and the steelmaking sludge in the batching bin 2# are conveyed to the high-pressure mixer through the material conveying device, the discharge port of the high-pressure mixer is connected to the feed port of the buffer bin through a pipeline, the pelletizer is arranged below the buffer bin to make the material in the buffer bin into pellets, the pellets in the pelletizer are conveyed to the roller ball screen through the material conveying device to remove the adhesive on the surface of the pellets, and the material on the roller ball screen is conveyed to the chain grate dryer through the material conveying device to be dried to obtain formed pellets.

[0008] The present invention has the following beneficial effects: The present invention provides a method and system for treating solid waste from steel smelting.

[0009] (1) Utilize the self-adhesiveness of steelmaking sludge and the decomposition and gelation of steelmaking LT ash to produce viscous pellets, which greatly reduces the cost of adding binders for pelletizing; (2) Through the heat-assisted drying of the steelmaking LT ash digestion reaction, the energy consumption of the pellet drying process is reduced by 10%; (3) Pellets can be directly used in rotary hearth furnaces, converters, electric furnaces, etc. to achieve iron and zinc resource recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0011] Figure 1 Schematic diagram of the steel smelting solid waste treatment system. DETAILED DESCRIPTION

[0012] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0013] The following is a detailed description of a steel smelting solid waste treatment method and treatment system provided by an embodiment of the present invention.

[0014] In a first aspect, an embodiment of the present invention provides a method for treating steel smelting solid waste, comprising: mixing digested steelmaking LT ash and steelmaking sludge to form pellets without adding a binder.

[0015] Typically, steelmaking LT ash has an iron content of over 55%, making it an excellent iron-containing raw material. It also has a high FeO content, over 10% CaO, small amounts of SiO2, MgO, and Al2O3, and a high zinc content. The dust is fine, making it a highly fine dry powder. The outlet temperature of dust removal is high, making it prone to spontaneous combustion when exposed to air during transportation.

[0016] Steelmaking sludge is the sludge obtained from the flue gas generated during the steelmaking process through wet dust removal and solid-liquid separation of the dust removal wastewater. Steelmaking sludge is a solid waste generated by steel mills and pollutes the environment. However, due to its high iron content, it is a valuable secondary resource for steel mills, and its comprehensive recycling and utilization is gaining increasing attention.

[0017] For the above-mentioned steelmaking LT ash and steelmaking sludge, traditional treatment methods include batching return sintering, wet zinc extraction, pelletizing or direct reduction, cold solidification pelletizing, etc., but there are the following problems: (1) Free CaO in steelmaking LT ash is digested with water to form Ca(OH)2, which expands in volume and causes sintering ore to pulverize; (2) The viscosity generated during the digestion of steelmaking LT ash is not effectively utilized, resulting in high energy consumption for subsequent treatment; (3) Steelmaking sludge needs to be dried during direct reduction, which has high energy consumption costs. (4) Steelmaking sludge and steelmaking LT ash contain iron oxides such as FeO and Fe2O3. The former has a high water content and unstable viscosity, while the latter needs to be completely digested before direct pelletization, which requires the addition of a large amount of binder (organic binder, bentonite), which is costly and reduces the iron grade, increasing costs.

[0018] Through extensive experience, the inventors have developed a method for treating steelmaking solid waste. This method involves mixing digested steelmaking LT ash and steelmaking sludge to form pellets without the addition of a binder. This method utilizes the self-adhesive nature of steelmaking sludge and the viscous pellets produced by digestion and gelation of steelmaking LT ash, achieving both solid waste treatment and reuse.

[0019] In some optional embodiments, the method includes the following steps: without adding a binder, water is added to the steelmaking LT ash to digest it to obtain plastic LT ash, and the plastic LT ash and steelmaking sludge are mixed to form pellets. The present invention utilizes the self-adhesiveness of steelmaking sludge and the viscosity spontaneously generated during the process of steelmaking LT ash digesting calcium oxide to achieve a self-adhesive pelletizing method without the need for an external binder. The prepared pellets can also be reused in rotary hearth furnaces, converters, electric furnaces, etc., to achieve the recycling and reuse of iron and zinc resources. It is worth noting that there is no limit on the ratio of plastic LT ash to steelmaking sludge during the pelletizing process, and it can be determined based on the processing volume of plastic LT ash and steelmaking sludge.

[0020] In some optional embodiments, the process further includes adding at least one of iron oxide scale, coarse particles, and carbon-containing material, representing 1% to 3% of the total mass of the steelmaking LT ash, to the pelletizing process. Adding iron oxide scale and coarse particles to the raw materials can enhance the toughness of the pellets, while adding carbon-containing material can increase the carbon content in the pellets, allowing them to serve as a reducing agent in a rotary hearth furnace.

[0021] In some optional embodiments, the plastic LT ash is prepared by the following method: mixing steelmaking LT ash with water, and then controlling the temperature and time to adjust the viscosity to a plastic state to obtain the plastic LT ash; Preferably, the water-cement ratio of steelmaking LT ash mixed with water is 5%-10%. Extensive practice has proven that controlling the water-cement ratio of steelmaking LT ash to water within this range is more appropriate. A water-cement ratio within this range can effectively convert alkaline oxides (such as calcium oxide) in the ash and avoid secondary pollution during conveyor belt transportation. If the water-cement ratio is lower than 5%, the LT ash will not reach a plastic state after digestion, which is not conducive to mixing with steelmaking sludge and is prone to cracking during the subsequent drying process. If the water-cement ratio is higher than 10%, the LT ash will become a material with sludge-like properties, affecting the pelletizing effect. In addition, if the water-cement ratio is too high, the LT ash will easily adhere to the belt during transportation.

[0022] Preferably, after steelmaking LT ash is mixed with water, the temperature is controlled to be 40-80° C. for 10-30 minutes to obtain plastic LT ash with a viscosity in the range of 500-2000 mPa·s.

[0023] In some optional embodiments, the water content of the steelmaking sludge is 8-10%. If the water content of the steelmaking sludge is too low, its properties are similar to dust, dust is easily generated during the mixing process, and more water needs to be added, making it difficult to accurately control the moisture content of the mixture. If the water content of the steelmaking sludge is too high, it is difficult to break up during the mixing process, and the particle size is too high, affecting the pelletizing effect.

[0024] In some optional embodiments, the mixing and pelletizing comprises the following steps: mixing the plastic LT ash and the steelmaking sludge, adding water again to mix the materials evenly, and then sending the mixed materials to a pelletizing machine for mixing and pelletizing to form wet balls with a particle size of 8-16 mm; Preferably, the moisture content of the mixed material is 10-12%; Preferably, the inclination angle of the pelletizing disk of the pelletizing machine is controlled to be 45-50° and the rotation speed is 10-15r / min.

[0025] A large amount of practice has proven that it is more appropriate to control the moisture content of the mixed material at 10-12%. If the moisture content is too low, the amount of water required during the pelletizing process will be too high, and the pelletizing process will require higher technical requirements. At the same time, during the pelletizing process, the calcium oxide in the steelmaking LT ash is completely digested after three water additions for the mixed material with the above moisture content (during the pelletizing process, the steelmaking LT ash undergoes the following changes: during the raw material processing, the addition of water triggers the digestion of part of the steelmaking LT ash, and then during the mixing process with steelmaking sludge, the addition of water further digests part of the steelmaking LT ash, and finally during the pelletizing process, it is completely digested under the action of water). During the dynamic pelletizing process, centrifugal force is used to firmly bond the particles through the sticky Ca(OH)2 film, and then drying is carried out. The pellets are less likely to crack or pulverize. In addition, during the pelletizing process, the inclination angle of the pelletizing disk of the pelletizing machine is controlled at 45-50°, the rotation speed is 10-15r / min, and the particle size is controlled by the water adding rule of "dripping water to form balls, mist water to grow, and waterless compaction" to obtain pellets with uniform particle size and good dispersion.

[0026] In some optional embodiments, the method further comprises: feeding the pellets in the pelletizing machine into a roller ball screen for material screening, and then feeding the screened material into a dryer for drying to obtain dry pellets; Preferably, the drying is carried out by a programmed temperature rising method, wherein: the temperature of the low temperature section is controlled at 80-120°C, and the temperature of the high temperature section is controlled at 120-250°C. The wet bulb undergoes two drying processes at low and high temperatures, which can slowly evaporate the moisture therein and avoid pulverization or cracking of the pellets. In addition, the drying in the high temperature section can also partially carbonize the Ca(OH)2 on the surface of the pellets into CaCO3, thereby improving the strength of the pellets.

[0027] In some optional embodiments, the pellets have a particle size of 8-12 mm and a compressive strength of 500 N / ball. The pellets produced using the solution provided by the present invention have uniform particle size and high compressive strength and can be directly used in rotary hearth furnaces, converters, electric furnaces, and other smelting processes, enabling the recovery of iron and zinc resources.

[0028] In the second aspect, an embodiment of the present invention provides a steel smelting solid waste treatment system, comprising: a receiving bin for receiving steelmaking LT ash, a biaxial humidifier, a batching bin 1# for storing plastic LT ash, a batching bin 2# for storing steelmaking sludge, a high-pressure mixer, a buffer bin, a pelletizer, a roller ball screen and a chain grate dryer, wherein: the discharge port of the receiving bin is connected to the feed port of the biaxial humidifier through a pipeline, the biaxial humidifier is connected to the batching bin 1# through a material conveying device, the plastic LT ash in the batching bin 1# and the steelmaking sludge in the batching bin 2# are conveyed to the high-pressure mixer through the material conveying device, the discharge port of the high-pressure mixer is connected to the feed port of the buffer bin through a pipeline, the pelletizer is arranged below the buffer bin, for making the material in the buffer bin into pellets, the pellets in the pelletizer are conveyed to the roller ball screen through the material conveying device to remove the adhesive on the surface of the pellets, and the material on the roller ball screen is conveyed to the chain grate dryer through the material conveying device to be dried to obtain formed pellets.

[0029] In some optional embodiments, the material conveying device is a belt or an adhesive tape.

[0030] The present invention will be further described below with reference to the embodiments.

[0031] A method for treating steel smelting solid waste comprises the following steps: 1. Pretreatment of steelmaking LT ash: Mix the steelmaking LT ash with a certain amount of water (water-ash ratio 5%-10%) to trigger the CaO digestion reaction: CaO+H2O→Ca(OH)2+heat The gel-like Ca(OH)2 generated by the reaction wraps around the particles to form a sticky matrix.

[0032] 2. Viscosity control: By controlling the reaction temperature (40-80°C) and time (10-30 minutes), the viscosity is adjusted to the plastic state (viscosity range 500-2000mPa·s).

[0033] 3. Ingredient mixing: After mixing the plastic LT ash and steelmaking sludge with a moisture content of 8-10%, add water again to mix the materials evenly to obtain a mixture with a moisture content of 10-12%.

[0034] 4. Dynamic ball making: The viscous mixture is fed into a high-speed rotating ball making machine, and the centrifugal force is used to combine the particles through the viscous Ca(OH)2 film to form wet balls with a particle size of 8-16mm.

[0035] 5. Curing and strengthening: The wet ball undergoes low-temperature drying (80-120℃) and high-temperature drying (120~250℃) to partially carbonize Ca(OH)2 into CaCO3, forming a dry ball with a particle size of 8-12mm, thereby improving the strength of the pellet (compression resistance ≥500N / ball).

[0036] Example 1 See also Figure 1 One ton of steelmaking LT ash (CaO content 8.3%) is transported by tanker truck to a receiving silo, where it is humidified and digested with 80kg of water spray in a dual-axis humidifier. The sludge is then conveyed by belt conveyor to batching silo #1, where it is stored at 60°C for 30 minutes. The steelmaking sludge is naturally dried to 8% moisture in the storage room, then transported by truck to batching silo #2, where it is loaded into a hopper by forklift or overhead crane for storage. The mixture is mixed in a ratio of 55% steelmaking sludge to 45% steelmaking LT ash. The mixture is then conveyed by belt conveyor to a high-performance mixer, where water is added to achieve a high-speed blending. Water is then added to bring the moisture content to 10%, and the mixture is then conveyed to a buffer silo and pelletized in a pelletizer (45° inclination, 10 rpm) to produce 8-12mm pellets. The material is screened by a rolling ball screen and dried in a chain grate dryer (80°C in the low-temperature range and 120°C in the high-temperature range). The compressive strength reaches 500N / ball, meeting metallurgical requirements.

[0037] Example 2 See also Figure 1 One ton of steelmaking LT ash (CaO content 8.3%) is transported by tanker truck to a receiving bin, where it is humidified and digested with 80kg of water spray in a dual-axis humidifier. The sludge is then conveyed by belt conveyor to batching bin #1, where it reacts and is stored at 60°C for 30 minutes. The steelmaking sludge is naturally dried in the storage room to a moisture content of 10%, then transported by truck to batching bin #2, where it is loaded into a hopper by a forklift or overhead crane for storage. The mixture is mixed in a ratio of 55% steelmaking sludge to 45% steelmaking LT ash. The mixture is then conveyed by belt conveyor to a high-speed mixer where water is added to achieve a high-speed blending. Water is then added to bring the moisture content to 12%, and the mixture is then conveyed to a buffer bin and pelletized in a pelletizer (50° inclination, 12 rpm) to produce 8-12mm pellets. The material is screened by a rolling ball screen and dried in a chain grate dryer (100°C for the low-temperature section and 200°C for the high-temperature section). The compressive strength reaches 500N / ball, meeting metallurgical requirements.

[0038] Example 3 See also Figure 1One ton of steelmaking LT ash (CaO content 8.3%) is transported by tanker truck to a receiving bin, where it is humidified and digested with 80kg of water spray in a dual-axis humidifier. The sludge is then conveyed by belt conveyor to batching bin #1, where it is stored at 60°C for 30 minutes. The steelmaking sludge is naturally dried to 10% moisture in the storage room, then transported by truck to batching bin #2, where it is loaded by forklift or overhead crane into a hopper for storage. The mixture is mixed in a ratio of 60% steelmaking sludge to 40% steelmaking LT ash. The mixture is then conveyed by belt conveyor to a high-performance mixer where water is added to achieve a high-speed blending. Water is then added to bring the moisture content to 12%. The mixture is then conveyed to a buffer bin and then to a pelletizer (50° inclination, 12 rpm) to produce 8-12mm pellets. The material is screened by a rolling ball screen and dried in a chain grate dryer (120°C in the low-temperature range and 220°C in the high-temperature range). The compressive strength reaches 500N / ball, meeting metallurgical requirements.

[0039] Example 4 See also Figure 1 One ton of steelmaking LT ash (CaO content 8.3%) is transported by tanker truck to a receiving bin, where it is humidified and digested with 80kg of water spray in a dual-axis humidifier. The sludge is then conveyed by belt conveyor to batching bin #1, where it is stored at 60°C for 30 minutes. The steelmaking sludge is naturally dried to 9% moisture in the storage room, then transported by truck to batching bin #2, where it is loaded by forklift or overhead crane into a hopper for storage. The mixture is mixed in a ratio of 65% steelmaking sludge to 35% steelmaking LT ash. The mixture is then conveyed by belt conveyor to a high-performance mixer where water is added to achieve a high-speed blending. Water is then added to bring the moisture content to 11%. The mixture is then conveyed to a buffer bin and pelletized in a pelletizer (50° inclination, 15 rpm) to produce 8-12mm pellets. The material is screened by a rolling ball screen and dried in a chain grate dryer (120°C in the low-temperature range and 250°C in the high-temperature range). The compressive strength reaches 500N / ball, meeting metallurgical requirements.

[0040] Comparative Example 1 The traditional method of pelletizing with bentonite or binder results in the use of large amounts of binder, which is costly and reduces the iron grade, thus increasing the cost.

[0041] Comparative Example 2 The steps are similar to those in Example 1, except that the steelmaking LT ash is not pre-treated and digested. As a result, the steelmaking LT ash generates a lot of dust during transportation and has severe cracking during the subsequent drying process.

[0042] Comparative Example 3 The steps are similar to those in Example 1, with the only difference being that the free calcium oxide is completely digested during the pretreatment of the steelmaking LT ash. As a result, a larger area is required for stacking, digestion and drying, and no plastic LT ash can be obtained, resulting in a lower pelletizing strength.

[0043] Comparative Example 4 The steps were similar to those in Example 1, except that the moisture content of the steelmaking sludge was 20%. As a result, during the mixing process with the steelmaking LT ash, some of the steelmaking sludge formed lumps, making it difficult to form a uniformly dispersed mixture. The resulting pellets had poor stability and poor performance.

[0044] Comparative Example 5 The steps were similar to those in Example 1, except that the temperature of the low-temperature section was controlled at 60°C and the temperature of the high-temperature section was controlled at 220°C during the wet-bulb drying process. As a result, the temperature of the low-temperature section was too low, resulting in less water volatilization. Subsequently, drying at a higher temperature caused cracks in some pellets, resulting in a decrease in the qualified rate of finished products.

[0045] From the above results, it can be seen that the method for treating steel smelting solid waste provided by the present invention utilizes the self-adhesiveness of steelmaking sludge and the decomposition and gelation of steelmaking LT ash to produce viscous pellets, which greatly reduces the cost of adding binders for pelletizing. The pellets can be directly used in rotary hearth furnaces, converters, electric furnaces, etc., to achieve iron and zinc resource recovery, which not only reduces the sludge to the environment but also can bring about better economic value.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for treating solid waste from steel smelting, characterized in that: include: Without adding any binder, the digested steelmaking LT ash and steelmaking sludge are mixed to form pellets.

2. The method for treating solid waste from steel smelting according to claim 1, characterized in that: The following steps are involved: Under the condition of not adding a binder, steelmaking LT ash is digested with water to obtain plastic LT ash, and the plastic LT ash and the steelmaking sludge are mixed to form pellets.

3. The method for treating solid waste from steel smelting according to claim 2, characterized in that: Also includes: At least one of iron oxide scale, coarse particles and carbon-containing substances accounting for 1% to 3% of the total mass of the steelmaking LT ash is added and mixed to form pellets.

4. The method for treating solid waste from steel smelting according to claim 2, wherein: The plastic LT ash is prepared by the following method: mixing the steelmaking LT ash with water, and then controlling the temperature and time to adjust the viscosity of the steelmaking LT ash to a plastic state, thereby obtaining the plastic LT ash; Preferably, the water-cement ratio of the steelmaking LT ash mixed with the water is 5%-10%; Preferably, after the steelmaking LT ash is mixed with water, the temperature is controlled to be 40-80° C. for 10-30 minutes to obtain plastic LT ash with a viscosity in the range of 500-2000 mPa·s.

5. The method for treating solid waste from steel smelting according to claim 2, characterized in that: The water content of the steelmaking sludge is controlled to be 8-10%.

6. The method for treating solid waste from steel smelting according to claim 2, characterized in that: The mixing and pelletizing comprises the following steps: mixing the plastic LT ash and the steelmaking sludge, adding water again to mix the materials evenly, and then sending the mixed materials to a pelletizing machine for mixing and pelletizing to form wet balls with a particle size of 8-16 mm; Preferably, the moisture content of the mixed material is 10-12%; Preferably, the inclination angle of the pelletizing disk of the pelletizing machine is controlled to be 45-50° and the rotation speed is 10-15r / min.

7. The method for treating solid waste from steel smelting according to claim 2, wherein: Also includes: The pellets in the pelletizing machine are sent to a roller ball screen for material screening, and the screened material is then sent to a dryer for drying to obtain dry balls; Preferably, the drying is performed in a programmed temperature rising manner, wherein the temperature of the low temperature section is controlled to be 80-120°C, and the temperature of the high temperature section is controlled to be 120-250°C.

8. The method for treating solid waste from steel smelting according to any one of claims 1 to 7, characterized in that: The pellets have a particle size of 8-12 mm and a compressive strength of 500 N / ball.

9. A steel smelting solid waste treatment system, characterized in that: include: A receiving bin for receiving steelmaking LT ash, a biaxial humidifier, a batching bin 1# for storing plastic LT ash, a batching bin 2# for storing steelmaking sludge, a high-pressure mixer, a buffer bin, a pelletizer, a roller ball screen and a chain grate dryer, wherein: the discharge port of the receiving bin is connected to the feed port of the biaxial humidifier through a pipeline, the biaxial humidifier is connected to the batching bin 1# through a material conveying device, the plastic LT ash in the batching bin 1# and the steelmaking sludge in the batching bin 2# are conveyed to the high-pressure mixer through the material conveying device, the discharge port of the high-pressure mixer is connected to the feed port of the buffer bin through a pipeline, the pelletizer is arranged below the buffer bin, for making the material in the buffer bin into pellets, the pellets in the pelletizer are conveyed to the roller ball screen through the material conveying device to remove the adhesive on the surface of the pellets, and the material on the roller ball screen is conveyed to the chain grate dryer through the material conveying device to be dried to obtain formed pellets.

10. The iron and steel smelting solid waste treatment system according to claim 9, characterized in that: The material conveying device is a belt or an adhesive tape.

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