Method for purifying molten steel by promoting rapid aggregation and growth of inclusions in steel

Abstract

The present application provides a method for purifying molten steel by promoting the rapid polymerization and growth of inclusions in steel, comprising the following steps: blowing the molten iron in a converter and decarburizing in an RH refining furnace to obtain decarburized molten steel, wherein the oxygen content in the decarburized molten steel is 400 to 800 ppm; adding aluminum to the decarburized molten steel to complete deoxidation and alloying to obtain alloyed molten steel; and causing the alloyed molten steel to circulate purely in an RH refining furnace to promote the polymerization and growth of the inclusions so that they can be removed. The present application starts with the polymerization and growth of inclusions, and focuses on studying the key parameters of the oxygen concentration after decarburization that affect the polymerization and growth of inclusions. It breaks the traditional idea of ​​requiring low oxygen throughout the smelting process to reduce the source of inclusions in previous IF steel research, and greatly accelerates the polymerization and growth of inclusions by increasing the base number of inclusions, thereby achieving efficient removal of inclusions, improving the cleanliness of molten steel, and providing a reference for high-quality production of IF steel.

Description

Technical Field

[0001] The present application belongs to the field of steel, and in particular relates to a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in the steel. Background Art

[0002] In the smelting process of ultra-low carbon steel, after decarburization in the vacuum refining furnace, the molten steel needs to be deoxidized and alloyed. Deoxidation is mostly completed by adding aluminum. After adding aluminum to deoxidize at the end of decarburization, a large amount of aluminum oxide inclusions are generated in the molten steel. In order to ensure the surface quality and stamping performance of automobile plates, the aluminum oxide inclusions in the steel must be reduced as much as possible, that is, while reducing the number of large particle inclusions (≥50μm) in the steel, reduce the total amount of inclusions in the steel.

[0003] How to reduce the number of inclusions in steel has always been a hot topic in steelmaking, especially in ultra-low carbon steelmaking. Summary of the invention

[0004] The embodiment of the present application provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in the steel, which can promote the rapid aggregation and growth of inclusions, improve the efficiency of inclusion removal, and improve the cleanliness of the molten steel.

[0005] The method for promoting the rapid polymerization and growth of inclusions in steel provided in an embodiment of the present application comprises the following steps: converter smelting: the molten iron is blown in a converter and decarburized in an RH refining furnace to obtain decarburized molten steel, wherein the oxygen content in the decarburized molten steel is 400 to 800 ppm; aluminum is added to the decarburized molten steel to complete deoxidation and alloying to obtain alloyed molten steel; the alloyed molten steel is subjected to pure circulation in the RH refining furnace to promote the polymerization and growth of inclusions so as to be removed.

[0006] According to the embodiments of the present application, the amount of aluminum added to the decarburized molten steel, mA1, satisfies mA1=(9 / 8*oxygen content after decarburization+Al content required for finished product)*molten steel amount / Al yield.

[0007] According to the embodiments of the present application, the circulation flow rate of the pure circulation is 100-300 t / min, and the time of the pure circulation is 5-15 min.

[0008] Compared with the prior art, the embodiments of the present application have at least the following beneficial effects:

[0009] The method for purifying molten steel by promoting the rapid polymerization and growth of inclusions in steel in the embodiment of the present application starts from the polymerization and growth of inclusions, and focuses on studying the key parameters of oxygen concentration after decarburization that affect the polymerization and growth of inclusions. It breaks the traditional idea of ​​requiring low oxygen throughout the smelting process to reduce the source of inclusions in previous IF steel research, and greatly accelerates the polymerization and growth of inclusions by increasing the base number of inclusions, thereby achieving efficient removal of inclusions, improving the cleanliness of molten steel, and providing a reference for high-quality production of IF steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical effects of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

[0011] Figure 1 This is a schematic flow chart of a method for purifying molten steel by promoting rapid aggregation and growth of inclusions in steel according to an embodiment of the present application. DETAILED DESCRIPTION

[0012] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0013] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0014] There are two main ways to remove inclusions in steel: one is to float to the slag interface and be absorbed by the top slag, and the other is to adhere to the refractory material of the furnace lining. Floating removal is the main removal method, accounting for more than 90% of the total inclusion removal. The floating removal of inclusions requires that the inclusions have a certain volume, because the floating speed of small particles is very slow, and they are easily dragged by the kinetic energy of the molten steel flow, and it is difficult to float to the slag interface. Therefore, the efficiency and degree of inclusion aggregation and growth are important factors that restrict the efficiency of inclusion removal and the cleanliness of molten steel.

[0015] The current control strategy for inclusions in IF steel focuses on controlling the source of inclusion formation, that is, it requires strict control of the oxygen content in molten steel throughout the entire smelting process of IF steel, including the end oxygen of the converter (250-650ppm), the end oxygen of RH decarburization (200-350ppm) and the total oxygen in the tundish (≤30ppm), striving to achieve the goal of low oxygen throughout the process. Few studies have been conducted from the perspective of facilitating the polymerization and growth of inclusions, and there are fewer studies on the effects on the polymerization, growth and removal efficiency of inclusions in molten steel. Therefore, a method for promoting the rapid polymerization and growth of inclusions is urgently needed to meet the needs of clean steel production.

[0016] In view of the above problems, the inventors of the present application provide a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, which can promote the rapid aggregation and growth of inclusions, improve the efficiency of inclusion removal, and improve the cleanliness of molten steel.

[0017] The embodiment of the present application provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in the steel. Figure 1 The process of purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel is shown in FIG. Figure 1 , the method provided in this application comprises the following steps:

[0018] S1: After the molten iron is blown in a converter and decarburized in a refining furnace, decarburized molten steel is obtained, and the oxygen content in the decarburized molten steel is 400-800ppm;

[0019] S2: adding aluminum to the decarburized molten steel to complete deoxidation and alloying to obtain alloyed molten steel;

[0020] S3: The alloyed molten steel is circulated purely in the refining furnace to promote the aggregation and growth of inclusions so that they can be removed.

[0021] The method for purifying molten steel by promoting the rapid polymerization and growth of inclusions in steel in the embodiment of the present application starts from the polymerization and growth of inclusions, and focuses on studying the key parameters of oxygen concentration after decarburization that affect the polymerization and growth of inclusions. It breaks the traditional idea of ​​requiring low oxygen throughout the smelting process to reduce the source of inclusions in previous IF steel research, and greatly accelerates the polymerization and growth of inclusions by increasing the base number of inclusions, thereby achieving efficient removal of inclusions, improving the cleanliness of molten steel, and providing a reference for high-quality production of IF steel.

[0022] In the embodiment of the present application, the refining furnace may be a RH refining furnace.

[0023] In step S1, considering that the oxygen content in the molten steel after decarburization is low, the base number of inclusions is too small, and the inclusions cannot quickly aggregate and grow in a short time, which will make it difficult for the inclusions to float up, the inventors of the present application controlled the oxygen content in the decarburized molten steel after decarburization to 400-800 ppm after multiple experiments. When the oxygen content in the decarburized molten steel is in this range, it is conducive to the rapid aggregation and growth of inclusions in a short time.

[0024] Without being bound by any theory, when the oxygen content in the molten steel after decarburization in the RH refining furnace is too high, although the inclusion polymerization rate is fast, the excessively high oxygen content in the molten steel will also increase the oxygen potential in the slag, and continue to transfer oxygen to the molten steel during the subsequent pure circulation of the molten steel, polluting the molten steel. In addition, when the oxygen content is too high, the subsequent aluminum deoxidation cost will increase significantly.

[0025] Exemplarily, the oxygen content in the decarburized molten steel is 400ppm, 420ppm, 440pm, 450pm, 460ppm, 480ppm, 500ppm, 520ppm, 540ppm, 550ppm, 560ppm, 580ppm, 600ppm, 620ppm, 640ppm, 650ppm, 660ppm, 680ppm, 700ppm, 720ppm, 740ppm, 750ppm, 760ppm, 780ppm, 800ppm or an interval range consisting of any two of the above values.

[0026] In step S2, the aluminum content mA1 added to the molten steel is (9 / 8*oxygen content after decarburization + required Al content of finished product)*molten steel volume / Al yield. If it is known that the oxygen content after decarburization is 400ppm, the required Al content of the finished product is 350ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%, then the aluminum content to be added is (9 / 8*400+350)*10-6*200*1000kg / 95%=168.4kg.

[0027] In step S2 of the present application, aluminum is used for deoxidation. The oxygen content after decarburization determines the number of initial inclusions in the steel. The higher the aluminum content in the steel, the lower the [O] content in the steel in balance with it, and the purer the molten steel. However, correspondingly, the Al in the steel is more susceptible to secondary oxidation during continuous casting. Therefore, the present application controls the Al content to 0.02% to 0.06% to achieve better results.

[0028] In step S3, the inventors of the present application have noticed in actual production that the circulation flow rate and pure circulation time of the pure circulation in the RH refining furnace will also affect the rate of polymerization and growth of inclusions in the steel. When the circulation flow rate is 100-300 t / min and the pure circulation time is 5-15 min, the rapid polymerization and growth of inclusions in the steel can be promoted.

[0029] When the circulation flow rate is low, the uniform efficiency of molten steel composition and temperature is slow, the flow is inactive, and the frequency of turbulent collision of inclusions is low; when the circulation flow rate is too high, the flow velocity at the steel-slag interface increases, the slag-steel reaction is violent, and the cleanliness of the molten steel is affected. Similarly, when the pure circulation time is short, the inclusions have insufficient time to aggregate and float, and the inclusion removal rate is low; when the pure circulation time is too long, the production rhythm is affected, and the continuous long-term reaction between slag and steel will endanger the purity of the molten steel.

[0030] Exemplarily, the circulation flow rate is 100 t / min, 120 t / min, 130 t / min, 140 t / min, 150 t / min, 160 t / min, 170 t / min, 180 t / min, 190 t / min, 200 t / min, 210 t / min, 220 t / min, 230 t / min, 240 t / min, 250 t / min, 260 t / min, 270 t / min, 280 t / min, 290 t / min, 300 t / min or an interval range consisting of any two of the above values.

[0031] Exemplarily, the cycle time is 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min or an interval range consisting of any two of the above values.

[0032] The method for purifying molten steel by promoting the rapid polymerization and growth of inclusions in steel in the embodiment of the present application starts from the polymerization and growth of inclusions, and focuses on studying the key parameters that affect the polymerization and growth of inclusions, such as oxygen concentration after decarburization, turbulent kinetic energy of molten steel, circulation flow rate and circulation time. It breaks the traditional idea of ​​requiring low oxygen throughout the smelting process to reduce the source of inclusions in previous IF steel research, and greatly accelerates the polymerization and growth of inclusions by increasing the base number of inclusions, thereby achieving efficient removal of inclusions, improving the cleanliness of molten steel, and providing a reference for high-quality production of IF steel.

[0033] Example

[0034] The following examples describe the disclosure of the present application in more detail, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0035] Example 1

[0036] This embodiment provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, comprising the following steps:

[0037] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 400ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0038] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*400+400)*10 -6 *200*1000kg / 95%=178.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*400ppm=850ppm;

[0039] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0040] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 6min. Sampling and analysis show that the total oxygen T.[O]=22ppm, the total amount of inclusions is about 47ppm, and the inclusion removal efficiency is about (850-47) / 850*100%=94.5% after 6min.

[0041] Example 2

[0042] This embodiment provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, comprising the following steps:

[0043] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 400ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0044] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*400+400)*10 -6 *200*1000kg / 95%=178.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*400ppm=850ppm;

[0045] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0046] The circulation flow rate of molten steel in the RH furnace is 100t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 6min. Sampling and analysis show that the total oxygen T.[O]=30ppm, the total amount of inclusions is about 64ppm, and the inclusion removal efficiency is about (850-64) / 850*100%=92.4% after 6min.

[0047] Example 3

[0048] This embodiment provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, comprising the following steps:

[0049] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 600ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0050] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*600+400)*10 -6 *200*1000kg / 95%=226.3kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*600ppm=1275ppm;

[0051] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0052] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 6min. Sampling and analysis show that the total oxygen T.[O]=16ppm, the total amount of inclusions is about 34ppm, and the inclusion removal efficiency is about (1275-34) / 1275*100%=97.3% after 6min.

[0053] Example 4

[0054] This embodiment provides a method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, comprising the following steps:

[0055] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 600ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0056] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*600+400)*10 -6 *200*1000kg / 95%=226.3kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*600ppm=1275ppm;

[0057] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0058] The circulation flow rate of molten steel in the RH furnace is 100t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 6min. Sampling and analysis show that the total oxygen T.[O]=21ppm, the total amount of inclusions is about 45ppm, and the inclusion removal efficiency is about (1275-45) / 1275*100%=96.5% after 6min.

[0059] Comparative Example 1

[0060] A method for purifying molten steel provided in this comparative example comprises the following steps:

[0061] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 100ppm; S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying;

[0062] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*100+400)*10 -6 *200*1000kg / 95%=107.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*100ppm=212.5ppm;

[0063] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0064] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 6min. Sampling and analysis show that the total oxygen T.[O]=72ppm, the total amount of inclusions is about 153ppm, and the inclusion removal efficiency is about (212.5-153) / 212.5*100%=28% after 6min.

[0065] Comparative Example 3

[0066] A method for purifying molten steel provided in this comparative example comprises the following steps:

[0067] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 900ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0068] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*400+400)*10 -6 *200*1000kg / 95%=178.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*400ppm=850ppm;

[0069] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0070] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 4min. Sampling and analysis show that the total oxygen T.[O]=85ppm, the total amount of inclusions is about 180ppm, and the inclusion removal efficiency is about (850-140) / 850*100%=78.8% after 4min.

[0071] Comparative Example 2

[0072] A method for purifying molten steel provided in this comparative example comprises the following steps:

[0073] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 400ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0074] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*400+400)*10 -6 *200*1000kg / 95%=178.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*400ppm=850ppm;

[0075] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0076] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 4min. Sampling and analysis show that the total oxygen T.[O]=85ppm, the total amount of inclusions is about 180ppm, and the inclusion removal efficiency is about (850-140) / 850*100%=78.8% after 4min.

[0077] Comparative Example 4

[0078] This comparative example provides a method for promoting rapid polymerization and growth of inclusions, comprising the following steps:

[0079] S1 molten steel is blown in a converter and decarburized in an RH furnace. The oxygen content of the molten steel after decarburization is 400ppm. S2 adds aluminum to the molten steel after decarburization to complete deoxidation and alloying.

[0080] In step S2, it is known that the Al content required for the finished product is 400ppm, the amount of molten steel is 200 tons, and the aluminum yield is 95%. The aluminum content to be added = (9 / 8*400+400)*10 -6 *200*1000kg / 95%=178.9kg, the total amount of aluminum oxide inclusions generated by deoxidation is 102 / 48*400ppm=850ppm;

[0081] After S3 deoxidation and alloying, the molten steel undergoes pure circulation in the RH, and the inclusions aggregate and grow and are removed from the molten steel.

[0082] The circulation flow rate of molten steel in the RH furnace is 150t / min. After deoxidation and alloying, the molten steel circulates in the RH furnace for 4min. Sampling and analysis show that the total oxygen T.[O]=85ppm, the total amount of inclusions is about 180ppm, and the inclusion removal efficiency is about (850-140) / 850*100%=78.8% after 4min.

[0083] In summary, the method for promoting the rapid polymerization and growth of inclusions in steel in the embodiment of the present application starts from the polymerization and growth of inclusions, focuses on the key parameters of oxygen concentration after decarburization that affect the polymerization and growth of inclusions, breaks the traditional idea of ​​requiring low oxygen throughout the smelting process to reduce the source of inclusions in previous IF steel research, and greatly accelerates the polymerization and growth of inclusions by increasing the base number of inclusions, controlling the oxygen content in the decarburized molten steel to 400-800ppm, and the amount of aluminum added mAl satisfies mAl=(9 / 8*oxygen content after decarburization+Al content required by the finished product)*molten steel volume / Al yield. The circulation flow rate of the pure cycle is 100-300t / min, and the time of the pure cycle is 5-15min, so as to achieve efficient removal of inclusions and improve the cleanliness of the molten steel. When the oxygen content in molten steel is high after decarburization, the oxygen content in the slag in equilibrium with the molten steel also increases. After the oxygen in the molten steel is removed by aluminum, the oxygen in the slag will continue to transmit oxygen to the molten steel in the subsequent period of time, forming inclusions again. These inclusions are more difficult to remove, resulting in reduced inclusion removal efficiency.

[0084] The above is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A method for purifying molten steel by promoting the rapid aggregation and growth of inclusions in steel, characterized in that: The steps include: The molten iron is blown in a converter and decarburized in an RH refining furnace to obtain decarburized molten steel, wherein the oxygen content in the decarburized molten steel is 400-800 ppm; adding aluminum to the decarburized molten steel to complete deoxidation and alloying to obtain alloyed molten steel; The alloyed molten steel is made to circulate purely in the RH refining furnace to promote the aggregation and growth of the inclusions so as to be removed.

2. The method according to claim 1, characterized in that The amount of aluminum added in the decarburized molten steel, mA1, satisfies mA1=(9 / 8*oxygen content after decarburization+Al content required in finished product)*amount of molten steel / Al yield.

3. The method according to claim 1, characterized in that The circulation flow rate of the pure circulation is 100-300 t / min, and the time of the pure circulation is 5-15 min.

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