An outer-magnesium and inner-calcium composite flux type pellet and a preparation method thereof

Abstract

The application discloses a preparation method of an outer-magnesium and inner-calcium composite flux type pellet, and belongs to the technical field of sintering pellets. According to the distribution of materials in the inner and outer layers of the pellet according to the comprehensive basicity and magnesium content requirements, directional distribution of the flux in the green pellet is realized by controlling the raw material composition. After pelletizing and oxidizing roasting, the obtained pellet has radial basicity gradient distribution, the outer layer forms a bonding phase mainly composed of magnesium-based flux, and the inner layer forms a skeleton phase mainly composed of calcium-based flux. Through the synergistic effect of the double-layer pelletizing process and the component design, the compression strength and the reduction swelling performance of the pellet are improved, and the technical problem that the magnesium-based and calcium-based flux type pellets are difficult to balance the strength and the reducibility is solved.

Description

Technical Field

[0001] This invention belongs to the field of sintering pellet technology, specifically relating to an external magnesium and internal calcium composite flux pellet and its preparation method. Background Technology

[0002] In the blast furnace-converter long-process ironmaking process, the pollution and energy consumption generated during the production of iron-containing raw materials are enormous, accounting for nearly 70% of the total process. Therefore, developing high-quality, green, and low-cost iron-containing raw materials is an important direction for ironmaking production.

[0003] Traditionally, blast furnace burdens in my country consist mainly of high-basicity sinter and acidic pellets. However, the sintering process results in significant pollutant emissions and energy consumption. Therefore, domestic steel companies have extensively developed and applied another type of basic burden—flux-type pellets.

[0004] Flux-type pellets generally include two types: magnesium-based flux-type pellets and calcium-based flux-type pellets. Each type has its own advantages and disadvantages. Magnesium-based flux-type pellets have better reduction expansion indices; however, the magnesium olivine and magnesium ferrite phases generated during oxidative roasting significantly hinder hematite recrystallization, affecting the pellet's compressive strength. Calcium-based flux-type pellets improve reducibility by generating calcium ferrite and accelerating liquid phase formation; however, this increased basicity leads to abnormal reduction expansion, affecting the further increase of the proportion of basic pellets inside the blast furnace.

[0005] Therefore, under the technological background of simplifying blast furnace charge and increasing the proportion of pellets, it is particularly important to develop a new type of flux pellet that combines the properties of magnesium-based flux pellets and calcium-based flux pellets. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as insufficient compressive strength in magnesium-based flux pellets due to the formation of forsterite and magnesium ferrite hindering hematite recrystallization, and abnormal reducing expansion caused by increased alkalinity in calcium-based flux pellets, both of which suffer from the difficulty of balancing strength and reducibility, this invention aims to provide a novel composite flux pellet with an outer magnesium and inner calcium structure and its preparation method. This invention avoids the disadvantages of traditional calcium-based flux pellets, magnesium-based flux pellets, and pellets prepared by simply mixing calcium and magnesium raw materials, and develops a new type of composite flux pellet with superior overall performance, providing more operational flexibility for using high-proportion flux pellets in blast furnaces.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing magnesium-inner calcium composite flux pellets, comprising the following steps: S1: High-calcium iron-containing material A is prepared by mixing iron concentrate powder, calcium flux and binder according to the alkalinity requirements of the finished pellets; S2: First, the high-calcium iron-containing material A is used as the inner layer and pre-wetted in the disc pelletizer with a moisture content of 4.5%~5.5%. It is then continuously rolled and watered at a speed of 36~45 r / min to generate a homogeneous pellet core with a diameter of 6~8 mm, which is then sieved and removed. S3: Iron concentrate powder, magnesium flux and binder are mixed and formulated into high magnesium iron content material B according to the basicity requirements of the finished pellets; S4: Place the pellet core in another pelletizing tray, and spray the high magnesium iron-containing material B evenly onto the surface of the pellet core through a pressure atomizing nozzle. The material is then coated layer by layer by centrifugal force gradient until the target diameter of the pellet is 12~14 mm. The total pelletizing time is 16~20 min, and composite green pellets with a moisture content of 8%~9% are obtained. S5: The composite green pellets are dried, calcined, and cooled to obtain magnesium-inner calcium composite flux pellets.

[0009] Based on the above technical solution, further, the amount of iron concentrate powder added in S1 is 75~85 wt% of the high-calcium iron-containing material A; the amount of TFe in the iron concentrate powder is ≥65 wt%.

[0010] Based on the above technical solution, the calcium flux is limestone or hydrated lime, and the amount added is 8 to 30 wt% of the high calcium iron-containing material A, ensuring that the inner layer contributes 80% to 100% of the total global CaO.

[0011] Based on the above technical solution, further, the binder mentioned in S1 is sodium-based bentonite or organic composite binder, and the addition amount is 0.6~1.5 wt%.

[0012] Based on the above technical solution, the local alkalinity CaO / SiO2 of the pellet core further reaches 0.8~2.0.

[0013] Based on the above technical solution, further, the amount of iron concentrate powder added in S3 is 95~98 wt% of the high magnesium iron-containing material B; the amount of TFe in the iron concentrate powder is ≥65 wt%.

[0014] Based on the above technical solution, further, the magnesium flux in S3 is light-burned magnesite powder or finely ground dolomite, and the amount added is 1~3.8 wt% of the high magnesium iron-containing material B, so that the outer layer contributes 70%~100% of the total MgO content of the pellets; the MgO in the light-burned magnesite powder is ≥85%; the proportion of the finely ground dolomite -0.074 mm is >90%.

[0015] Based on the above technical solution, further, the binder mentioned in S3 is sodium-based bentonite or organic composite binder, and the addition amount is 0.8~1.3 wt%.

[0016] Based on the above technical solution, further, in S5, the green pellets are dried by raising the temperature from room temperature to 250-300℃ at a rate of 15-20℃ / min for 5-8 min; preheated by raising the temperature to 850-930℃ at a rate of 8-12℃ / min and holding for 10-20 min; oxidatively roasted by raising the temperature to 1220-1270℃ at a rate of 3-5℃ / min and holding for 18-24 min; and cooled to 300-400℃ at a rate of 10-15℃ / min and then air-cooled.

[0017] Secondly, the present invention provides a composite flux-type pellet prepared by the aforementioned preparation method.

[0018] Based on the above technical solution, further, the MgO content of the composite flux pellet is 0.8~2.5 wt%; the basicity is 0.6~1.6.

[0019] Based on the above technical solution, the composite flux-type pellets further exhibit a compressive strength of 2600~2900 N; a reducibility of 60%~75%; a reduction expansion rate of 5%~14%; and a low-temperature reduction pulverization rate (RDI). +3.15 mm It ranges from 85% to 92%.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) By designing materials for inner and outer layers and configuring targeted fluxes, this invention effectively maintains the magnesium content required for global pellets while constructing a high-calcium-alkalinity core zone inside. This significantly optimizes the mineral composition and consolidation behavior of the pellets during the roasting process, avoids the mutual inhibition of different fluxes in the mixed system, and thus improves the metallurgical performance and structural uniformity of alkaline pellets.

[0021] (2) By synergistically regulating the contribution ratio of inner and outer fluxes and global pellet composition, this invention has stably achieved the production of composite pellets with both moderate MgO content and high controllable alkalinity, providing a pellet raw material selection with excellent metallurgical performance and more flexible slag adjustment capability for blast furnace applications. Detailed Implementation

[0022] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0023] Example 1 (1) Prepare iron concentrate, binder and flux according to the set alkalinity scheme, and distribute the inner and outer layers of pellets under the conditions of comprehensive alkalinity of 0.9 and magnesium content of 2.0%.

[0024] The inner layer (calcium-rich material) is made by mixing iron concentrate powder, calcium flux, and binder to form high-calcium iron-containing material A. High-calcium iron-containing material A contains 78.9% iron concentrate powder (TFe 65.0%), 20.3% limestone, and 0.8% bentonite. At this time, the local basicity CaO / SiO2 of the pellet core reaches 1.85. The outer layer (magnesium-rich material) is made by mixing iron concentrate powder, magnesium flux, and binder to form high-magnesium iron-containing material B. High-magnesium iron-containing material B contains 95% iron concentrate powder, 3.8% light-burned magnesite powder, and 1.2% bentonite.

[0025] (2) Pelletizing is carried out by a double-layer pelletizing process. First, the inner layer mixture A is pre-wetted in a disc pelletizer (moisture content 5.0%), and water is continuously pumped and rolled at a speed of 40 r / min to generate a homogeneous core with a diameter of 6.5 mm. The pellets are then sieved and removed. The removed pellets are then placed in another pelletizing disc, and the outer layer mixture B is evenly sprayed onto the core surface through a pressure atomizing nozzle. The core is then coated layer by layer with centrifugal force gradient to the target diameter of 13 mm. The total pelletizing time is 19 min, and composite green pellets with a moisture content of 8.6% are obtained.

[0026] (3) The composite green pellets are roasted under the following temperature regime: The green pellets were dried by heating from room temperature to 280℃ at 15℃ / min for 5 min; preheated by heating to 890℃ at 10℃ / min and holding for 12 min; oxidatively roasted by heating to 1235℃ at 4℃ / min and holding for 20 min; then cooled to 300℃ at 12℃ / min and air-cooled to obtain magnesium-inner calcium composite flux pellets.

[0027] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0028] In this embodiment, the pellets have a compressive strength of 2280 N, a reduceability of 69.5%, a reduction expansion rate of 11.3%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 90.2%.

[0029] Comparative Example 1 (1) The homogeneous mixture was prepared under the conditions of a comprehensive alkalinity of 0.9 and a magnesium content of 2.0%. The homogeneous mixture consisted of iron concentrate powder, magnesium additives, calcium additives and binders. Among them, iron concentrate powder accounted for 87.2%, light-burned magnesite 3.5%, limestone 7.9% and bentonite 1.4%.

[0030] (2) The above homogeneous mixture is pelletized. The homogeneous mixture is placed in a pelletizing pan and pelletized at a rotation speed of 40 r / min for 18 min to obtain green pellets with a moisture content of 8.8% and a diameter of 13 mm.

[0031] (3) The raw pellets are roasted at the same temperature as step (3) in Example 1 to obtain pellets.

[0032] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0033] The pellets obtained in this comparative example have a compressive strength of 2580 N, a reducibility of 70.2%, a reduction expansion rate of 18.6%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 88.4%.

[0034] Example 2 (1) Prepare iron concentrate, binder and flux according to the set alkalinity scheme, and distribute the inner and outer layers of pellets under the conditions of comprehensive alkalinity of 1.2 and magnesium content of 2.5%.

[0035] The inner layer (calcium-rich material) is made by mixing iron concentrate powder, calcium flux, and binder to form high-calcium iron-containing material A. High-calcium iron-containing material A contains 76.6% iron concentrate powder (TFe 65.0%), 22.5% limestone, and 0.9% bentonite. At this time, the local basicity CaO / SiO2 of the pellet core reaches 2.0. The outer layer (magnesium-rich material) is made by mixing iron concentrate powder, magnesium flux, and binder to form high-magnesium iron-containing material B. High-magnesium iron-containing material B contains 95.1% iron concentrate powder, 3.8% light-burned magnesite powder, and 1.1% bentonite.

[0036] (2) Pelletizing is carried out by a double-layer pelletizing process. First, the inner layer mixture is pre-wetted in a disc pelletizer (moisture content 5.0%), and water is continuously pumped and rolled at a speed of 38 r / min to generate a homogeneous core with a diameter of 7 mm. The pellets are then sieved and removed. The removed pellets are then placed in another pelletizing disc, and the outer layer mixture is evenly sprayed onto the core surface through a pressure atomizing nozzle. The core is then coated layer by layer with centrifugal force gradient to the target diameter of 12.5 mm. The total pelletizing time is 18 min, and composite green pellets with a moisture content of 8.8% are obtained.

[0037] (3) The composite green pellets are roasted under the following temperature regime: The green pellets were dried by heating from room temperature to 280℃ at 15℃ / min for 5 min; preheated by heating to 910℃ at 12℃ / min and holding for 15 min; oxidatively roasted by heating to 1260℃ at 5℃ / min and holding for 20 min; then cooled to 300℃ at 12℃ / min and air-cooled to obtain magnesium-inner calcium composite flux pellets.

[0038] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0039] In this embodiment, the pellets have a compressive strength of 2470 N, a reduceability of 73.6%, a reduction expansion rate of 8.7%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 87.8%.

[0040] Comparative Example 2 (1) The homogeneous mixture was prepared under the conditions of a comprehensive alkalinity of 1.2 and a magnesium content of 2.5%. The homogeneous mixture consisted of iron concentrate powder, magnesium additives, calcium additives and binders. Among them, iron concentrate powder accounted for 82%, lightly calcined magnesite 3.3%, limestone 13.7% and bentonite 1.0%.

[0041] (2) Pelletize the homogeneous mixture. Place the homogeneous mixture in a pelletizing pan and pelletize at a rotation speed of 45 r / min for 17.5 min to obtain green pellets with a moisture content of 8.8% and a diameter of 12.5 mm.

[0042] (3) The raw pellets are roasted at the same temperature as in step (3) of Example 2 to obtain pellets.

[0043] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0044] The pellets prepared in this comparative example have a compressive strength of 2880 N, a reducibility of 74.3%, a reduction expansion rate of 13.3%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 85.5%.

[0045] Example 3 (1) Prepare iron concentrate, binder and flux according to the set alkalinity scheme, and distribute the inner and outer layers of pellets under the conditions of comprehensive alkalinity of 0.8 and magnesium content of 0.8%.

[0046] The inner layer (calcium-rich material) is made by mixing iron concentrate powder, limestone and binder to form iron-containing material A, which contains 82.4% iron concentrate powder (TFe 65.0%), 16.1% limestone and 1.5% bentonite. At this time, the local basicity CaO / SiO2 of the pellet core reaches 1.45. The outer layer (magnesium-rich material) is made by mixing iron concentrate powder, light-burned magnesite (MgO 88%) and binder to form iron-containing material B, which contains 97.7% iron concentrate powder, 1.3% light-burned magnesite and 1.0% bentonite.

[0047] (2) Pelletizing is carried out by a double-layer pelletizing process. First, the inner layer mixture is pre-wetted in a disc pelletizer (moisture content 5.0%), and water is continuously pumped and rolled at a speed of 40 r / min to generate a homogeneous core with a diameter of 7.5 mm. The pellets are then sieved and removed. The removed pellets are then placed in another pelletizing disc, and the outer layer mixture is evenly sprayed onto the core surface through a pressure atomizing nozzle. The core is then coated layer by layer with centrifugal force gradient to the target diameter of 13.5 mm. The total pelletizing time is 19.5 min, and composite green pellets with a moisture content of 9.1% are obtained.

[0048] (3) The composite green pellets are roasted under the following temperature regime: The green pellets were dried by heating from room temperature to 250℃ at 15℃ / min for 5 min; preheated by heating to 930℃ at 8℃ / min and holding for 17 min; oxidatively roasted by heating to 1270℃ at 5℃ / min and holding for 18 min; then cooled to 300℃ at 15℃ / min and air-cooled to obtain magnesium-inner calcium composite flux pellets.

[0049] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0050] In this embodiment, the pellets have a compressive strength of 2610 N, a reduceability of 63.9%, a reduction expansion rate of 6.5%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 91.0%.

[0051] Comparative Example 3 (1) The homogeneous mixture was prepared under the conditions of a comprehensive alkalinity of 0.8 and a magnesium content of 0.8%. The homogeneous mixture consisted of iron concentrate powder, magnesium additives, calcium additives and binders. Among them, iron concentrate powder accounted for 91.3%, light-burned magnesite 0.9%, limestone 6.5% and bentonite 1.3%.

[0052] (2) Pelletize the homogeneous mixture. Place the homogeneous mixture in a pelletizing pan and pelletize at a rotation speed of 42 r / min for 16.5 min to obtain green pellets with a moisture content of 9.0% and a diameter of 13.5 mm.

[0053] (3) The raw pellets are roasted at the same temperature as in step (3) of Example 3 to obtain pellets.

[0054] (4) The compressive strength, reduction expansion rate, low-temperature reduction pulverization rate and reducing properties of the prepared pellets were determined under the national standard.

[0055] The pellets obtained in this comparative example have a compressive strength of 2690 N, a reducibility of 64.1%, a reduction expansion rate of 14.1%, and a low-temperature reduction pulverization rate (RDI). +3.15 mm It is 89.3%.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an external magnesium and internal calcium composite flux pellet, characterized in that, The preparation method includes the following steps: S1: High-calcium iron-containing material A is prepared by mixing iron concentrate powder, calcium flux and binder according to the alkalinity requirements of the finished pellets; S2: First, the high-calcium iron-containing material A is used as the inner layer and pre-wetted in the disc pelletizer with a moisture content of 4.5%~5.5%. It is then continuously rolled and watered at a speed of 36~45 r / min to generate a homogeneous pellet core with a diameter of 6~8 mm, which is then sieved and removed. S3: Iron concentrate powder, magnesium flux and binder are mixed and formulated into high magnesium iron content material B according to the basicity requirements of the finished pellets; S4: Place the pellet core in another pelletizing tray, and spray the high magnesium iron-containing material B evenly onto the surface of the pellet core through a pressure atomizing nozzle. The material is then coated layer by layer by centrifugal force gradient until the target diameter of the pellet is 12~14 mm. The total pelletizing time is 16~20 min, and composite green pellets with a moisture content of 8%~9% are obtained. S5: The composite green pellets are dried, calcined, and cooled to obtain magnesium-inner calcium composite flux pellets.

2. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The amount of iron concentrate powder added in S1 is 75~85 wt% of the high-calcium iron-containing material A; the amount of TFe in the iron concentrate powder is ≥65 wt%.

3. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The calcium flux is limestone or hydrated lime, and the amount added is 8-30 wt% of the high-calcium iron-containing material A, ensuring that the inner layer contributes 80%-100% of the total global CaO.

4. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The binder in S1 is sodium-based bentonite or an organic composite binder, and the addition amount is 0.6~1.5 wt%.

5. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The local alkalinity CaO / SiO2 in the core of the pellet reaches 0.8~2.

0.

6. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The amount of iron concentrate powder added in S3 is 95~98 wt% of the high magnesium iron-containing material B; the amount of TFe in the iron concentrate powder is ≥65 wt%.

7. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The magnesium flux mentioned in S3 is light-burned magnesite powder or finely ground dolomite, and the amount added is 1~3.8 wt% of the high magnesium and iron content material B, so that the outer layer contributes 70%~100% of the total MgO content of the pellets; the MgO in the light-burned magnesite powder is ≥85%; the proportion of the finely ground dolomite -0.074 mm is >90%.

8. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, The binder mentioned in S3 is sodium-based bentonite or an organic composite binder, with an addition amount of 0.8~1.3 wt%.

9. The method for preparing an external magnesium and internal calcium composite flux pellet according to claim 1, characterized in that, In step S5, the green pellets are dried by heating from room temperature to 250-300℃ at a rate of 15-20℃ / min for 5-8 min; preheated by heating to 850-930℃ at a rate of 8-12℃ / min and holding for 10-20 min; oxidatively roasted by heating to 1220-1270℃ at a rate of 3-5℃ / min and holding for 18-24 min; and cooled to 300-400℃ at a rate of 10-15℃ / min and then air-cooled.

10. A composite flux pellet prepared by the method for preparing composite flux pellets with an outer magnesium and inner calcium structure according to any one of claims 1 to 9, characterized in that, The composite flux pellets have an MgO content of 0.8–2.5 wt%; a basicity of 0.6–1.6; a compressive strength of 2600–2900 N; a reducing power of 60%–75%; a reduction expansion rate of 5%–14%; and a low-temperature reduction pulverization rate (RDI). +3.15 mm It ranges from 85% to 92%.