Method for detecting content of active lime in metallurgical lime for AOD smelting

Abstract

The present application relates to a kind of AOD smelting with metallurgical lime active lime content detection method, the source of CaO in metallurgical lime mainly has three kinds: CaO in burning, CaO in overburning, CaO in active lime.AOD smelting with lime CaO and S are necessary inspection items, while detecting CaO can obtain MgO data, while detecting S can obtain C data, burning rate can be calculated according to C data, and burning overburning rate can be detected by digestion method;Linear fitting is carried out on the above data through big data, and the regression equation active lime=1.391 MgO+0.4396 burning rate+1.000 CaO-1.000 burning overburning rate is obtained.The active lime content detection method of AOD smelting with metallurgical lime described in the present application is simple to operate, and can be operated on site in steelmaking plant;Without using activity detection means, cost is saved;The obtained active lime content can guide AOD production, and improve one-time reduction S rate.

Description

Technical Field

[0001] This invention relates to the field of metallurgical lime, and more particularly to a method for detecting the content of active lime in metallurgical lime used in AOD smelting. Background Technology

[0002] The main equipment for stainless steel smelting at Shanxi Taiyuan Iron & Steel Stainless Steel Co., Ltd. is the AOD furnace. During the reduction period, metallurgical lime is used for desulphurization. The one-time desulphurization rate is the ratio of the number of furnaces in a day that can remove sulfur from stainless steel to below a specified level in a single operation to the total number of stainless steel furnaces smelted in a day. A higher one-time desulphurization rate results in shorter smelting time and less metallurgical lime consumption (metallurgical lime is also required for secondary desulphurization). Therefore, overall, a higher one-time desulphurization rate leads to relatively lower daily smelting costs, an increase in the number of furnaces smelted, and increased steel production, thus improving quality and efficiency while reducing costs.

[0003] Activity, as a core physical indicator of metallurgical lime, directly determines the amount of active lime, thus directly affecting the one-time desulfurization rate. However, in the AOD smelting of stainless steel, the amount of lime used is calculated based on the CaO content, not the activity. Therefore, activity is merely an objective indicator guiding the use of metallurgical lime, and cannot directly guide its actual application. Currently, the detection of metallurgical lime activity is supported by YB / T 015-2014 "Physical Testing Methods for Metallurgical Lime," which allows the calculation of the active lime content based on lime activity. However, activity detection is cumbersome, involves numerous batches, and has a long cycle, making it difficult to detect before the use of metallurgical lime. Other methods for detecting active lime content are not mentioned in relevant patent literature. Therefore, a simple method is needed to determine the active lime content in metallurgical lime, accurately guide the amount of metallurgical lime used in the AOD smelting of stainless steel, and improve the one-time desulfurization rate of stainless steel smelting.

[0004] This invention aims to overcome the shortcomings of existing technologies and provides a method for detecting the active lime content in metallurgical lime used in AOD smelting. The method is simple to operate and can be carried out on-site in steel plants. It eliminates the need for activity testing methods, thus saving costs. The obtained active lime content can guide AOD production and improve the one-time reduction rate of sulfur. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a method for detecting the content of active lime in metallurgical lime used in AOD smelting.

[0006] The objective of this invention is achieved as follows: A method for detecting the active lime content in metallurgical lime used in AOD smelting, comprising the following steps: Step 1: Sampling: Weigh 10±1 kg of metallurgical lime sample from the AOD high-level silo, sieve the metallurgical lime sample using a 10 mm standard sieve, and take the sample remaining on the sieve for chemical analysis and detection of underburning / overburning rate; Step 2: Determine the CaO and MgO content of the metallurgical lime using complexometric titration, determine the C and S content using an infrared carbon-sulfur analyzer, and determine the underburning / overburning rate using a digestion method; Step 3: Multiply the C content by 8.34 to obtain the underburning rate, then active lime = 1.391MgO + 0.4396 underburning rate + 1.000CaO - 1.000 underburning / overburning rate, and the calculated result is the active lime content.

[0007] The digestion method in step two is as follows: Weigh 1.0 kg of the sample on the sieve and place it in a sieve cylinder filled with water. The metallurgical lime reacts with the water. After the reaction stops, the metallurgical lime that cannot react with water is placed in an oven along with the sieve cylinder to dry the moisture. Weigh the mass of the metallurgical lime in the sieve cylinder after drying and calculate the proportion of dried metallurgical lime, which is the under-burning and over-burning rate.

[0008] The beneficial effects of this invention are: for metallurgical lime, CaO and S are key indicators that must be tested. Data on MgO can be obtained simultaneously with CaO testing, and data on C can be obtained simultaneously with S testing, without increasing the workload of the testing and analysis. The underburning rate can be obtained from the C content, and the overburning rate can be obtained by the digestion method. The digestion method is simple to operate and can be carried out in the control room of the steelmaking site.

[0009] Unlike the cumbersome activity testing method (YB / T 015-2014), this patented testing method can obtain relevant parameters in a timely manner without increasing the workload, and is suitable for stainless steel smelting in multiple batches and large quantities.

[0010] The activity test of metallurgical lime essentially involves hydrating the metallurgical lime and detecting the content of CaO and MgO in the fully hydrated metallurgical lime that can react with hydrochloric acid. The activity of the metallurgical lime is characterized by the amount of hydrochloric acid consumed. Therefore, active lime is defined as the content of CaO and MgO that can react with hydrochloric acid; lime that cannot react with hydrochloric acid is defined as underburned lime, and the corresponding content is the underburning / overburning rate. Overburned lime is low-activity lime, while underburned lime is undecomposed limestone. Therefore, the active lime content is calculated as: CaO content plus MgO content (which needs to be converted to CaO for calculation), minus the underburning / overburning content, plus the CO2 content from the underburned lime CaCO3. After large-scale linear regression analysis, we can obtain: Active lime = 1.391MgO + 0.4396 Underburning rate + 1.000 CaO - 1.000 Underburning / overburning rate.

[0011] The determination of the active lime content in metallurgical lime can accurately calculate the amount of metallurgical lime that needs to be added, thereby improving the desulfurization rate, reducing the sulfur content, and thus improving the one-time desulfurization rate.

[0012] Therefore, the method for detecting the active lime content in metallurgical lime for AOD smelting described in this invention is simple to operate and can be carried out on-site in steel plants; it eliminates the need for activity testing methods, saving costs; and the obtained active lime content can guide AOD production and improve the one-time reduction rate of S. Implementation

[0013] The technical solution adopted in this invention is: the method for detecting the active lime content in metallurgical lime used in AOD smelting, wherein the steps of the detection method are: sampling: weighing 10±1kg of metallurgical lime sample from the AOD high-level silo, sieving the metallurgical lime sample using a 10mm standard sieve, and taking the sample on the sieve for chemical analysis and detection of overburning rate.

[0014] The CaO and MgO content of metallurgical lime was determined by complexometric titration, with detailed technical requirements and operating procedures in accordance with GB / T 3286.1-2012. The C and S content was determined using an infrared carbon-sulfur analyzer, with detailed technical requirements and operating procedures in accordance with GB / T 6039-2022. The overburning rate was determined using a digestion method, with detailed technical requirements and operating procedures in accordance with GB / T 6039-2022: the sieve sample was crushed to below 0.125 mm to obtain a sample, which was then melted with a sodium carbonate-boric acid mixed flux and leached with dilute hydrochloric acid to obtain a test solution. Take a portion of the test solution, mask iron, aluminum, and manganese ions with triacetylamine, and titrate the amount of CaO in a strongly alkaline medium using calcium carboxylic acid (calcium indicator) as an indicator, with ethylenediaminetetraacetic acid (EDTA) or ethylene glycol diethyl ether diaminetetraacetic acid (EGTA) standard titration solution. Take another portion of the test solution, mask iron, aluminum, and manganese ions with triacetylamine, and titrate the combined amount of CaO and MgO in an ammoniacal buffer solution with pH 10 using a mixture of acid chrome blue K and chamomile green B as indicators, with EDTA standard titration solution (subtracting the amount of CaO gives the amount of MgO). Alternatively, mask calcium with a slightly excess of EGTA standard titration solution and titrate the amount of MgO with cyclohexanediaminetetraacetic acid (CyDTA) standard titration solution.

[0015] The content of C and S was determined using an infrared carbon-sulfur analyzer: The sample on the sieve was crushed to below 0.125 mm to obtain a sample. 0.10 g of the sample was weighed, and combined with other reagents, and analyzed according to the operating procedure of the infrared carbon-sulfur analyzer to obtain the content of C and S.

[0016] Determination of underburning rate: The underburning rate is obtained by multiplying the carbon content by 8.34.

[0017] The underburning / overburning rate was determined using the digestion method: 1.0 kg of the sample on the sieve was weighed and placed into a sieve cylinder filled with water. The metallurgical lime reacted with the water. After the reaction stopped, the metallurgical lime that could not react with the water was placed in an oven along with the sieve cylinder to dry the moisture. The mass of the metallurgical lime in the sieve cylinder after drying was weighed, and the proportion of dried metallurgical lime was calculated, which is the underburning / overburning rate.

[0018] Calculation of active lime content: Active lime = 1.391 MgO + 0.4396 Underburning rate + 1.000 CaO - 1.000 Overburning rate. The calculated result is the active lime content. All coefficients above are obtained from Minitab linear analysis and are all 100%; similar to the pitting corrosion resistance formula for austenitic stainless steel: PRENW = Cr + 3.3 × Mo + 16 × N + 1.15 × W.

[0019] The standard sieve shall conform to GB / T 6003.1-2022 "Technical Requirements and Inspection of Test Sieves - Part 1: Metal Wire Woven Mesh Test Sieves".

[0020] The determination of CaO and MgO content in metallurgical lime by complexometric titration shall be carried out in accordance with the relevant technical requirements and procedures of complexometric titration in GB / T 3286.1-2012 "Chemical Analysis Methods for Limestone and Dolomite Part 1: Determination of Calcium Oxide and Magnesium Oxide Content by Complexometric Titration and Flame Atomic Absorption Spectrometry".

[0021] The infrared carbon-sulfur meter has a measurement range of C of 0.0001%-10.0000% and a measurement range of S of 0.0001-2.000%, and its precision must meet the national metrological verification procedure JJG395-97 standard.

[0022] The determination of C and S content using an infrared carbon-sulfur analyzer should be performed in accordance with the relevant technical requirements and procedures in GB / T 6039-2022 "Methods for Determination of Raw and Overburned Lime in Metallurgy".

[0023] The determination of the raw and overburned rate by the digestion method shall be carried out in accordance with the relevant technical requirements and procedures in GB / T 6039-2022 "Determination of Raw and Overburned Rate of Metallurgical Lime".

[0024] The self-decomposing metallurgical lime is the active lime content detected by the method described above for detecting the active lime content in metallurgical lime used in AOD smelting.

[0025] 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.

[0026] 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 standard sieve shall conform to GB / T 6003.1-2022 "Technical Requirements and Inspection of Test Sieves Part 1: Metal Wire Woven Mesh Test Sieves" standard.

[0027] The determination of CaO and MgO content in metallurgical lime by complexometric titration shall be carried out in accordance with the relevant technical requirements and procedures of complexometric titration in GB / T 3286.1-2012 "Chemical Analysis Methods for Limestone and Dolomite Part 1: Determination of Calcium Oxide and Magnesium Oxide Content by Complexometric Titration and Flame Atomic Absorption Spectrometry".

[0028] The infrared carbon-sulfur meter has a measurement range of C of 0.0001%-10.0000% and a measurement range of S of 0.0001-2.000%, and its precision must meet the national metrological verification procedure JJG395-97 standard.

[0029] The determination of C and S content using an infrared carbon-sulfur analyzer should be performed in accordance with the relevant technical requirements and procedures in GB / T 6039-2022 "Methods for Determination of Raw and Overburned Lime in Metallurgy".

[0030] The determination of the raw and overburned rate by the digestion method shall be carried out in accordance with the relevant technical requirements and procedures in GB / T 6039-2022 "Determination of Raw and Overburned Rate of Metallurgical Lime". Example

[0031] A test method for the performance of stainless steel die-casting heating agents. The steps of the test method described in this embodiment are as follows: A method for detecting the active lime content in metallurgical lime used in AOD smelting. The steps of the test method described in this embodiment are as follows: Sampling: Weigh 10±1 kg of metallurgical lime sample from the AOD high-level silo, sieve the metallurgical lime sample using a 10 mm standard sieve, and take the sample remaining on the sieve for chemical analysis and over-burning rate detection.

[0032] The CaO and MgO contents of metallurgical lime were determined by complexometric titration, with detailed technical requirements and operating procedures in accordance with GB / T 3286.1-2012. The C and S contents were determined using an infrared carbon-sulfur analyzer, with detailed technical requirements and operating procedures in accordance with GB / T 6039-2022. The underburning and overburning rates were determined using a digestion method, with detailed technical requirements and operating procedures in accordance with GB / T 6039-2022.

[0033] Multiplying the C content by 8.34 gives the underburning rate. Therefore, the active lime content is calculated as follows: 1.391 MgO + 0.4396 Underburning rate + 1.000 CaO - 1.000 Overburning rate.

[0034] The calculation data for the active lime are shown in the table below. The single-pass reduction rate (%) remains the same except for the different lime usage due to the metallurgical lime calculation method (using two AOD furnaces, maintaining the same smelting process, and keeping the stainless steel grade consistent in the same furnace). It can be seen that the single-pass reduction rate of S is significantly improved after using active lime in the calculation.

[0035]

[0036] Note: Due to differences in smelting products, the one-time reduction rate of sulfur may fluctuate.

[0037] 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 detecting the content of active lime in metallurgical lime used in AOD smelting, characterized in that: Includes the following steps: Step 1: Sampling: Weigh 10±1kg of metallurgical lime sample from the AOD high-level silo, sieve the metallurgical lime sample using a 10mm standard sieve, and take the sample on the sieve for chemical analysis and raw / overburning rate detection. Step 2: Determine the CaO and MgO content of metallurgical lime using complexometric titration, determine the C and S content using an infrared carbon-sulfur analyzer, and determine the underburning / overburning rate using a digestion method. Step 3: Multiply the C content by 8.34 to get the underburning rate. Then, the active lime = 1.391MgO + 0.4396 underburning rate + 1.000CaO - 1.000 underburning / overburning rate. The calculated result is the active lime content. The digestion method in step two is as follows: Weigh 1.0 kg of the sample on the sieve and place it in a sieve cylinder filled with water. The metallurgical lime reacts with the water. After the reaction stops, the metallurgical lime that cannot react with water is placed in an oven along with the sieve cylinder to dry the moisture. Weigh the mass of the metallurgical lime in the sieve cylinder after drying and calculate the proportion of dried metallurgical lime, which is the under-burning and over-burning rate.

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