A self-decomposing metallurgical lime and a method for producing the same

Abstract

The present application relates to a kind of self-decomposing metallurgical lime and its preparation method, raw material used in the present application is limestone.The technical scheme is that screened limestone is transported to rotary kiln preheater bin, preheated by kiln tail hot gas through discharging chute, the limestone is uniformly pushed to transfer chute by push head on preheater and enters rotary kiln for calcination, rotary kiln temperature is lower than 1200 DEG C.Due to the rotary kiln cylinder has certain inclination angle and self-rotation, material rolls forward in kiln, and the calcined material is cooled in vertical cooler from kiln head, to obtain self-decomposing metallurgical lime.The self-decomposing metallurgical lime has low production cost, small kiln head powder rate, and is not easy to pulverize in transportation and screening process, has long storage time;it can utilize high-temperature metallurgical kiln waste heat decomposition, has high P and S removal efficiency, and reduces the use amount of fluorite etc slagging agent.

Description

Technical Field

[0001] This invention relates to the field of metallurgical lime, and more particularly to a self-decomposing metallurgical lime and its preparation method. Background Technology

[0002] The metallurgical lime used by Shanxi Taigang Stainless Steel Co., Ltd. in smelting carbon steel and stainless steel is ordinary metallurgical lime grade II, as specified in YB / T 042 "Metallurgical Lime". The lime transported to the plant is in the form of mixed lumps, which needs to be screened to obtain lime lumps before being sent to the steelmaking plant for smelting. Due to the vibration during the screening and conveying process, the powder content of the metallurgical lime used for smelting increases (9.7-30.5%). The lime powder is sucked away by environmental protection equipment during use, resulting in low dephosphorization and desulfurization efficiency in the smelting process and an increase in the amount of lime used.

[0003] Currently, research on the preparation of metallurgical lime includes: Patent "A method for producing metallurgical lime using highly pulverized limestone (CN202310482180.X)", which effectively utilizes limestone resources, but because no measures are taken to improve the strength of the metallurgical lime after the limestone is calcined in a rotary kiln, the powder content at the kiln head cannot be reduced, and the lime powder content still increases during screening and transportation. Another example is patent "A method for producing active metallurgical lime (CN202310252080.9)", which requires crushing and pulverizing the limestone, adding a combustion aid, and filtration. Furthermore, it uses a fluidized bed kiln, which is costly and complex. The use of a combustion aid can easily lead to increased powder content and over-burning, and can also cause segregation in the batching process and make the calcination process control difficult.

[0004] The present invention aims to overcome the defects of the prior art and provides a self-decomposing metallurgical lime and its preparation method. The self-decomposing metallurgical lime prepared has low production cost, low kiln head powder rate, is not easily pulverized during transportation and screening, and has a long storage time. It can utilize the waste heat of high-temperature metallurgical kiln for decomposition, has high P and S removal efficiency, and reduces the amount of slag-forming agents such as fluorite used. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a self-decomposing metallurgical lime and its preparation method.

[0006] The objective of this invention is achieved as follows: a self-decomposing metallurgical lime and its preparation method, comprising the following steps: Step 1: The raw material used is limestone. The limestone raw material is subjected to chemical and particle size testing to ensure that the chemical properties of the limestone are qualified; Step 2: The qualified limestone is unloaded into a hopper and conveyed to a screening system via a conveyor belt. The limestone is screened into particles of 10-50mm. Limestone larger than 50mm is crushed and re-screened, while limestone smaller than 10mm is transported to a slag bin; Step 3: The screened limestone is further processed... The limestone is transported to the preheater hopper of the rotary kiln and preheated to 900±50℃ by the hot air at the kiln tail. Some of the limestone has begun to decompose. The limestone is pushed evenly by the pusher on the preheater to the transfer chute and enters the rotary kiln for calcination. The temperature inside the rotary kiln is 1000-1200℃, the rotation speed of the rotary kiln is 0.4-5r / min, and the negative pressure at the kiln head is set to 0 to -15Pa. Step 4: The limestone after being calcined in the rotary kiln enters the vertical cooler from the kiln head and is cooled to below 200℃, thus obtaining autodecomposition metallurgical limestone.

[0007] The qualified chemical indicators of the limestone raw material are: CaO≥52%, MgO≤3.0%, SiO2≤2.2%, S≤0.040%; particle size: 10-50mm.

[0008] The outer wall temperature of the preheater shell is 40-70℃, and the internal flue gas temperature is 800-1050℃; the wear resistance of the refractory material used in the preheater is 1-7cm. 3 .

[0009] The outer wall temperature of the vertical cooler shell is 40-80℃, and the kiln tail hot gas temperature is 950-1100℃; the wear resistance of the refractory material used is 1-8cm. 3 .

[0010] The beneficial effects of this invention are: this invention controls the quality of limestone from the source, ensuring that the S content, MgO content and SiO2 content in limestone will not have an adverse effect on steelmaking, while ensuring the stability of lime quality, thereby ensuring the stability of steelmaking.

[0011] The key to self-decomposing metallurgical lime lies in controlling the degree of decomposition of CaCO3 in limestone. By controlling the temperature of the rotary kiln, most of the CaCO3 is decomposed, but a small amount of CaCO3 is retained, forming a microstructure in which CaO and CaCO3 are interwoven. Compared to normal loose and porous metallurgical lime, the presence of a small amount of CaCO3 interspersed within CaO not only improves the strength and abrasion resistance of self-decomposing metallurgical lime and reduces the kiln head dust rate, significantly minimizing dust increase during transportation and screening, but also greatly extends its storage time due to the interspersed and encapsulated CaCO3 within CaO. Because CaCO3 and CaO have different cleavage planes, even if the self-decomposing metallurgical lime breaks along the CaCO3 cleavage planes during drum tests, the particle size of the broken self-decomposing lime remains larger than 6.3 mm, not affecting normal use. Furthermore, the interspersed structure of CaCO3 and CaO, along with the cleavage of CaCO3, easily forms a CaCO3-encapsulated CaO structure, which does not affect the hydration resistance or storage time of the self-decomposing metallurgical lime, nor does it increase the dust rate during transportation and screening.

[0012] Metallurgical lime is used in AOD furnaces, electric furnaces, converters, medium-frequency furnaces, LF furnaces, etc., all of which are high-temperature environments. During the process of self-decomposing lime being added to a high-temperature kiln, the residual heat of the molten steel in the kiln heats the self-decomposing lime. CaCO3 first breaks down into small pieces and then decomposes into CaO. This not only reduces the adsorption of lime by environmental protection equipment but also increases the content of active lime. At the same time, the melting rate of lime also increases, and the amount of solvents such as fluorite is reduced accordingly. Since the self-decomposing lime has already decomposed into highly active CaO when it comes into contact with molten steel, the desulfurization efficiency, the one-time reduction rate of sulfur, the desulfurization efficiency, and the adsorption capacity of inclusions are all improved.

[0013] Rotary kilns use injected fuel to heat the kiln, and the highest temperature inside the kiln generally exceeds 1300℃. However, since complete decomposition of limestone is not required, only the decomposition of most of the limestone is needed, the firing temperature can be reduced to below 1200℃, which greatly saves fuel costs.

[0014] The self-decomposing metallurgical lime prepared by this invention has been tested and found to have the following characteristics: kiln head powder rate reduced from 15-40% to 7-25%, fuel consumption reduced by 15-25%, CaCO3 content in lime reduced to 8-20%, slag-reducing agent usage reduced by 5-10%, AOD one-time reduction S rate increased from 70-90% to 85-98%, and O content in steel reduced by 5-30 ppm compared to ordinary metallurgical lime.

[0015] Therefore, the self-decomposing metallurgical lime prepared by this invention has low production cost, low kiln head powder rate, is not easily pulverized during transportation and screening, and has a long storage time; it can utilize the waste heat of high-temperature metallurgical kilns for decomposition, has high P and S removal efficiency, and reduces the amount of slag-forming agents such as fluorite used. Implementation

[0016] This invention controls the quality of limestone, the raw material for metallurgical lime, from the source, eliminating its impact on steelmaking; by controlling the degree of decomposition of CaCO3 in limestone, it reduces the powder rate while increasing the storage time of metallurgical lime; when used in AOD and LF steelmaking processes, the undecomposed CaCO3 will decompose to obtain highly active CaO, thereby improving the desulfurization efficiency, one-time S reduction rate, P removal efficiency, and adsorption capacity of inclusions.

[0017] The technical solution adopted in this invention is: the self-decomposing metallurgical lime and its preparation method, characterized in that the preparation method comprises the following steps: Step 1: The raw material used is limestone, and the incoming limestone is subjected to chemical and particle size testing to ensure that the chemical properties of the limestone are qualified.

[0018] Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into 10-50mm pieces. Limestone larger than 50mm is crushed and re-screened. Limestone smaller than 10mm is transported to the slag hopper (for other uses).

[0019] Step 3: The screened limestone is conveyed to the preheater hopper of the rotary kiln, where it is preheated to approximately 900°C by the hot air from the kiln tail. Some of the limestone has already begun to decompose. The limestone is then pushed evenly by multiple pushers on the preheater into the transfer chute and into the rotary kiln for calcination. The temperature inside the rotary kiln is 1000-1200°C, the rotation speed is 0.4-5 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa.

[0020] Step 4: Due to the tilt angle and rotation of the cylinder, the material tumbles and moves forward inside the kiln. The calcined lime (limestone can be heated in the rotary kiln to obtain lime, so the calcined limestone becomes lime, i.e., calcined lime) enters the vertical cooler from the kiln head and is cooled to below 200°C, thus obtaining self-decomposing lime.

[0021] The incoming limestone must undergo chemical and particle size testing before it can enter the silo. Chemical indicators: CaO≥52%, MgO≤3.0%, SiO2≤2.2%, S≤0.040%; Particle size: 10-50mm (YB / T 5279-2016 requirements).

[0022] The rotary kiln mainly consists of a cylinder, tire, support rollers, thrust rollers, transmission device, and sealing device. The cylinder is mounted obliquely on the support device via a tire fitted onto it, and is then driven to rotate by gears of varying sizes. The inner diameter of the cylinder ranges from 1.6 to 7.0 meters, the rotational speed is 0.3 to 7.0 r / min, and the inclination (sine) of the cylinder is 1-5%. (The rotary kiln is an existing device; the national standard for rotary kilns is JB / T 8916-2017. Models conforming to JB / T 8916 are acceptable. Generally, rotary kilns are designed by Class A metallurgical design units and constructed by qualified metallurgical construction units. The cylinder is mounted obliquely on the support device via a tire fitted onto it, and is then driven to rotate by gears of varying sizes. The above information is entirely derived from JB / T 8916-2017.)

[0023] The inner and outer surfaces of the silos, slag silos, and preheater silos should be flat and smooth, and no obvious rust or pits are allowed.

[0024] The screening capacity of the screening system is matched with the production capacity of the rotary kiln.

[0025] The preheater and its associated preheater pusher are auxiliary facilities of the rotary kiln. Under operating conditions, the outer wall temperature of the preheater shell is 40-70℃, and the internal flue gas temperature is 800-1050℃; the abrasion resistance of the refractory material used in the preheater is ≤7cm. 3 .

[0026] The vertical cooler is an auxiliary facility for the rotary kiln. Under operating conditions, the outer wall temperature of the vertical cooler shell is 40-80℃, and the internal flue gas temperature is ≤1100℃; the wear resistance of the refractory material used is ≤8cm. 3 .

[0027] The self-decomposing metallurgical lime is prepared according to the preparation method of self-decomposing metallurgical lime described above.

[0028] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the scope of protection thereof.

[0029] To avoid repetition, the equipment and materials involved in the specific implementation are described in a unified manner as follows, and will not be repeated in the examples: The limestone material must undergo chemical testing and particle size testing before it can enter the silo; Chemical indicators: CaO≥52%, MgO≤3.0%, SiO2≤2.2%, S≤0.040%; Particle size: 10-50mm.

[0030] The rotary kiln mainly consists of a cylinder, tire, support rollers, thrust rollers, transmission device, and sealing device. The cylinder is mounted at an angle on the support device via a tire sleeved on the cylinder, and then rotated by gears of varying sizes. The inner diameter of the cylinder ranges from 1.6 to 7.0 meters, the rotational speed of the cylinder is 0.3 to 7.0 r / min, and the inclination (sine) of the cylinder is 1-5%.

[0031] The inner and outer surfaces of the silos, slag silos, and preheater silos should be flat and smooth, and no obvious rust or pits are allowed.

[0032] The screening capacity of the screening system is matched with the production capacity of the rotary kiln.

[0033] The preheater and its associated preheater pusher are auxiliary facilities of the rotary kiln. Under operating conditions, the outer wall temperature of the preheater shell is 40-70℃, and the internal flue gas temperature is 800-1050℃; the abrasion resistance of the refractory material used in the preheater is ≤7cm. 3 .

[0034] The vertical cooler is an auxiliary facility for the rotary kiln. Under operating conditions, the outer wall temperature of the vertical cooler shell is 40-80℃, and the internal flue gas temperature is ≤1100℃; the wear resistance of the refractory material used is ≤8cm. 3 . Example

[0035] A self-decomposing metallurgical lime and its preparation method. The steps of the preparation method described in this embodiment are as follows: Step 1: The raw material used is limestone. The incoming limestone is subjected to chemical and particle size tests to ensure that the chemical properties of the limestone are qualified.

[0036] Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into 10-50mm pieces. Limestone larger than 50mm is crushed and re-screened. Limestone smaller than 10mm is transported to the slag hopper (for other uses).

[0037] Step 3: The screened limestone is conveyed to the preheater hopper of the rotary kiln, where it is preheated to 900±50℃ by the hot air from the kiln tail, and some of the limestone begins to decompose. The limestone is then pushed evenly by multiple pushers on the preheater into the transfer chute and into the rotary kiln for calcination. The temperature inside the rotary kiln is 1050℃, the rotation speed is 1.2 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa.

[0038] Step 4: Due to the tilt angle and rotation of the cylinder, the material tumbles and moves forward inside the kiln. The calcined lime enters the vertical cooler from the kiln head and is cooled to below 200°C, thus obtaining self-decomposing lime.

[0039] The self-decomposing metallurgical lime prepared in this embodiment was tested and found to have the following characteristics: kiln head powder rate decreased from 15-40% to 11%, fuel consumption decreased by 24%, CaCO3 content in lime was 19%, slag-reducing agent usage such as fluorite decreased by 9.1%, AOD one-time reduction S rate increased from 70-90% to 87%, and O content in steel before LF refining was reduced by 14 ppm compared to ordinary metallurgical lime. Example

[0040] A self-decomposing metallurgical lime and its preparation method. The steps of the preparation method described in this embodiment are as follows: Step 1: The raw material used is limestone. The incoming limestone is subjected to chemical and particle size tests to ensure that the chemical properties of the limestone are qualified.

[0041] Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into 10-50mm pieces. Limestone larger than 50mm is crushed and re-screened. Limestone smaller than 10mm is transported to the slag hopper (for other uses).

[0042] Step 3: The screened limestone is conveyed to the preheater hopper of the rotary kiln, where it is preheated to 900±50℃ by the hot air from the kiln tail. Some of the limestone has already begun to decompose. The limestone is then pushed evenly by multiple pushers on the preheater into the transfer chute and into the rotary kiln for calcination. The temperature inside the rotary kiln is 1100℃, the rotation speed is 1.0 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa.

[0043] Step 4: Due to the tilt angle and rotation of the cylinder, the material tumbles and moves forward inside the kiln. The calcined lime enters the vertical cooler from the kiln head and is cooled to below 200°C, thus obtaining self-decomposing lime.

[0044] The self-decomposing metallurgical lime prepared in this embodiment was tested and found to have the following characteristics: kiln head powder rate reduced from 15-40% to 15%, fuel consumption reduced by 22%, CaCO3 content in lime reduced to 18%, slag-reducing agent usage reduced by 7.4%, AOD one-time reduction S rate increased from 70-90% to 90%, and O content in steel before LF refining was reduced by 19 ppm compared to ordinary metallurgical lime. Example

[0045] A self-decomposing metallurgical lime and its preparation method. The steps of the preparation method described in this embodiment are as follows: Step 1: The raw material used is limestone. The incoming limestone is subjected to chemical and particle size tests to ensure that the chemical properties of the limestone are qualified.

[0046] Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into 10-50mm pieces. Limestone larger than 50mm is crushed and re-screened. Limestone smaller than 10mm is transported to the slag hopper (for other uses).

[0047] Step 3: The screened limestone is conveyed to the preheater hopper of the rotary kiln, where it is preheated to 900±50℃ by the hot air from the kiln tail, and some of the limestone begins to decompose. The limestone is then pushed evenly by multiple pushers on the preheater into the transfer chute and into the rotary kiln for calcination. The temperature inside the rotary kiln is 1150℃, the rotation speed is 1.0 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa.

[0048] Step 4: Due to the tilt angle and rotation of the cylinder, the material tumbles and moves forward inside the kiln. The calcined lime enters the vertical cooler from the kiln head and is cooled to below 200°C, thus obtaining self-decomposing lime.

[0049] The self-decomposing metallurgical lime prepared in this embodiment was tested and found to have the following characteristics: kiln head powder rate reduced from 15-40% to 18%, fuel consumption reduced by 20%, CaCO3 content in lime reduced to 13%, slag-reducing agent usage reduced by 6.5%, AOD one-time reduction S rate increased from 70-90% to 92%, and O content in steel before LF refining reduced by 21 ppm compared to ordinary metallurgical lime. Example

[0050] A self-decomposing metallurgical lime and its preparation method. The steps of the preparation method described in this embodiment are as follows: Step 1: The raw material used is limestone. The incoming limestone is subjected to chemical and particle size tests to ensure that the chemical properties of the limestone are qualified.

[0051] Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into 10-50mm pieces. Limestone larger than 50mm is crushed and re-screened. Limestone smaller than 10mm is transported to the slag hopper (for other uses).

[0052] Step 3: The screened limestone is conveyed to the preheater hopper of the rotary kiln, where it is preheated to 900±50℃ by the hot air from the kiln tail, and some of the limestone has begun to decompose. The limestone is then pushed evenly by multiple pushers on the preheater into the transfer chute and into the rotary kiln for calcination. The temperature inside the rotary kiln is 1200℃, the rotation speed is 0.8 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa.

[0053] Step 4: Due to the tilt angle and rotation of the cylinder, the material tumbles and moves forward inside the kiln. The calcined lime enters the vertical cooler from the kiln head and is cooled to below 200°C, thus obtaining self-decomposing lime.

[0054] The self-decomposing metallurgical lime prepared in this embodiment was tested and found to have the following characteristics: kiln head powder rate decreased from 15-40% to 22%, fuel consumption decreased by 18%, CaCO3 content in lime was 9%, slag-reducing agent usage such as fluorite decreased by 5.3%, AOD one-time reduction S rate increased from 70-90% to 95%, and O content in steel after LF refining was reduced by 28 ppm compared to ordinary metallurgical lime.

[0055] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for preparing self-decomposing metallurgical lime, characterized in that: Includes the following steps: Step 1: The raw material used is limestone. Chemical and particle size tests are conducted on the limestone raw material to ensure that the chemical properties of the limestone are qualified. Step 2: Unload the qualified limestone into the feed hopper and convey it to the screening system via a conveyor belt. The limestone is screened into particles of 10-50mm. Limestone larger than 50mm is crushed and re-screened, while limestone smaller than 10mm is transported to the slag hopper. Step 3: The qualified limestone is transported to the preheater hopper of the rotary kiln and preheated to 900±50℃ by the hot air at the kiln tail. Some of the limestone has begun to decompose. The limestone is pushed evenly by the pusher on the preheater to the transfer chute and enters the rotary kiln for calcination. The temperature inside the rotary kiln is 1000-1200℃, the rotation speed of the rotary kiln is 0.4-5 r / min, and the negative pressure at the kiln head is set to 0 to -15 Pa. Step 4: After being calcined in the rotary kiln, the lime enters a vertical cooler from the kiln head and is cooled to below 200°C to obtain autodecomposition metallurgical lime. The qualified chemical properties of the limestone raw material are as follows: CaO ≥ 52%, MgO ≤ 3.0%, SiO2 ≤ 2.2%, S ≤ 0.040%; Particle size: 10-50mm; The outer wall temperature of the preheater shell is 40-70℃, and the internal flue gas temperature is 800-1050℃. The outer wall temperature of the vertical cooler shell is 40-80℃, and the internal flue gas temperature is 950-1100℃.