CN104862440A - Low-grade iron ore direct reduction method - Google Patents
Low-grade iron ore direct reduction method Download PDFInfo
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 409
- 229910052742 iron Inorganic materials 0.000 title claims abstract description 190
- 230000009467 reduction Effects 0.000 title claims abstract description 77
- 238000000034 method Methods 0.000 title claims abstract description 56
- 239000003245 coal Substances 0.000 claims abstract description 187
- 239000008188 pellet Substances 0.000 claims abstract description 102
- 239000002245 particle Substances 0.000 claims abstract description 75
- 238000002156 mixing Methods 0.000 claims abstract description 48
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 48
- 229910001868 water Inorganic materials 0.000 claims abstract description 48
- 239000000843 powder Substances 0.000 claims abstract description 44
- 239000012141 concentrate Substances 0.000 claims abstract description 43
- 238000007885 magnetic separation Methods 0.000 claims abstract description 42
- 238000000227 grinding Methods 0.000 claims abstract description 40
- 239000000654 additive Substances 0.000 claims abstract description 29
- 230000000996 additive effect Effects 0.000 claims abstract description 29
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 21
- 238000011282 treatment Methods 0.000 claims abstract description 21
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 19
- 239000000463 material Substances 0.000 claims abstract description 18
- 238000001035 drying Methods 0.000 claims abstract description 13
- 239000011230 binding agent Substances 0.000 claims abstract description 8
- 238000001816 cooling Methods 0.000 claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims abstract description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical group [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 68
- 239000011780 sodium chloride Substances 0.000 claims description 34
- 239000000440 bentonite Substances 0.000 claims description 31
- 229910000278 bentonite Inorganic materials 0.000 claims description 31
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 claims description 31
- 230000009471 action Effects 0.000 claims description 17
- 238000001465 metallisation Methods 0.000 claims description 16
- 239000012466 permeate Substances 0.000 claims description 13
- 239000000203 mixture Substances 0.000 claims description 8
- 239000002994 raw material Substances 0.000 claims description 8
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 claims description 3
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 3
- 239000001110 calcium chloride Substances 0.000 claims description 3
- 229910001628 calcium chloride Inorganic materials 0.000 claims description 3
- 239000002817 coal dust Substances 0.000 claims description 3
- RHZUVFJBSILHOK-UHFFFAOYSA-N anthracen-1-ylmethanolate Chemical compound C1=CC=C2C=C3C(C[O-])=CC=CC3=CC2=C1 RHZUVFJBSILHOK-UHFFFAOYSA-N 0.000 claims description 2
- 239000003830 anthracite Substances 0.000 claims description 2
- 239000002131 composite material Substances 0.000 claims description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 2
- 238000002955 isolation Methods 0.000 claims description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 2
- 238000005507 spraying Methods 0.000 claims description 2
- 239000002028 Biomass Substances 0.000 claims 1
- 239000003077 lignite Substances 0.000 claims 1
- 238000009736 wetting Methods 0.000 abstract description 2
- 239000008187 granular material Substances 0.000 abstract 1
- 238000006722 reduction reaction Methods 0.000 description 54
- 238000005469 granulation Methods 0.000 description 26
- 230000003179 granulation Effects 0.000 description 26
- 238000010298 pulverizing process Methods 0.000 description 22
- 238000011084 recovery Methods 0.000 description 19
- 238000000498 ball milling Methods 0.000 description 17
- 230000008569 process Effects 0.000 description 9
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 6
- 238000011161 development Methods 0.000 description 6
- 238000011946 reduction process Methods 0.000 description 6
- 229910000831 Steel Inorganic materials 0.000 description 5
- 229910052500 inorganic mineral Inorganic materials 0.000 description 5
- 235000013980 iron oxide Nutrition 0.000 description 5
- 238000011068 loading method Methods 0.000 description 5
- 238000003801 milling Methods 0.000 description 5
- 239000011707 mineral Substances 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 238000005303 weighing Methods 0.000 description 5
- 238000005265 energy consumption Methods 0.000 description 4
- 230000008676 import Effects 0.000 description 4
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 229910052595 hematite Inorganic materials 0.000 description 3
- 239000011019 hematite Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 2
- 238000004939 coking Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000007363 ring formation reaction Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000002802 bituminous coal Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 229910052840 fayalite Inorganic materials 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
- 238000005550 wet granulation Methods 0.000 description 1
- 238000001238 wet grinding Methods 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Manufacture And Refinement Of Metals (AREA)
Abstract
The invention relates to a low-grade iron ore direct reduction method, which comprises: calculating and taking a certain amount of coal powder, an additive, a binder and water by adopting the dry basis mass of iron ore to be treated as reference; uniformly mixing the taken components, and completely wetting to obtain an internal matching coal; uniformly mixing the internal matching coal and iron ore particles to be treated, and granulating to obtain granulated pellets; directly conveying the obtained granulated pellets into a rotary kiln, carrying out drying, pre-heating, and reduction roasting to carry out coal base direct reduction so as to obtain a reduced material, cooling the reduced material in the absence of air, and carrying out dry magnetic separation to obtain the reduced roasting pellets and the residual carbon; and carrying out treatments such as ore grinding and magnetic separation on the reduced roasting pellets to obtain iron concentrate, or carrying out re-grinding and re-magnetic separation to obtain the reduced iron powder, wherein the obtained residual carbon can be recycled. With the method of the present invention, the low-grade iron ore can be effectively treated, the internal matching coal and the additive are used to granulate, the wet pellets enter the kiln, the coal base direct reduction is performed, the magnetic separation is performed to obtain the high-grade iron concentrate or the directly-reduced iron powder, and the method has characteristics of energy saving, high efficiency, and rapidness.
Description
Technical Field
The invention relates to a direct reduction method of low-grade iron ore, in particular to a coal-based direct reduction-magnetic separation method of low-grade iron ore internal coal blending and additive granulation wet-pellet entering a kiln.
Background
With the rapid development of the steel industry, the steel yield of China rises year by year, the problem of insufficient supply of domestic high-quality iron ores is increasingly serious, mineral resources become a bottleneck restricting the development of the steel industry of China, the demand of the iron ores in China is increased sharply, the quantity of imported iron ores in China from 2009 to 2009 increases 21.8% every year, the import quantity is increased continuously, the import dependence of the iron ores in China is improved continuously, and the import dependence of the iron ores in China in 2012 is increasedAbout 63%, and the dependence on foreign import rose again to 78.5% in 2014. Meanwhile, the development of the iron-making industry is severely restricted by the huge pressure faced by coke resources. The quality difference of coal resources in China is large, the proportion of bituminous coal and anthracite is large, coking coal only accounts for about 27 percent of the coal reserves, and the coking coal is not uniformly distributed, so that the development of blast furnace ironmaking production is very unfavorable. The coal-based direct reduction process takes coal as a main energy source and takes a rotary kiln as main equipment, the direct reduction technology of the rotary kiln is mature, and the production capacity, the scale, the operation rate, the automation level and the equipment operation capacity are greatly developed[1-4]. However, the rotary kiln process has the problems of long process, large investment, high overall energy consumption, long pellet retention time in the kiln, easy low-temperature reduction pulverization, low kiln capacity utilization coefficient, large powder amount in the kiln, easy ring formation of the rotary kiln and the like, and still needs to be further improved.
The Chinese iron ore is rich but not rich, 97% of the reserves (fourth in the world) of 581 hundred million t is lean ore, the average grade is 33%, 11% lower than the average grade of the world iron ore, the rich ore with the iron grade of more than 50% only accounts for 2.7% (about 15 hundred million t), and most of the iron ore can be smelted in a furnace after being enriched by mineral separation. The mineral separation technology of complex refractory iron oxide ores with the particle size embedded fine and the gangue mainly including quartz and iron silicate-containing hematite, low-grade limonite and the like accounting for more than 25 percent of the total reserves still has no breakthrough progress. The direct reduction-magnetic separation method for treating low-grade ores is the direction of the current key research, and the low-grade ores are reduced for 90-120 min at the reduction temperature of 1100-1200 ℃, so that concentrate with the iron grade and the recovery rate of more than 90 percent can be obtained[5-7]Can effectively treat the micro-fine particle embedded hematite. However, since low grade iron ore contains a large amount of gangue minerals (e.g., SiO)2Etc.) at 1100-1200 deg.C, which can generate a large amount of fayalite liquid phase, and has serious influence on the direct reduction, high energy consumption and long reduction time, and the method still stays in the laboratory stage at present. The invention can effectively utilize low-grade iron ore, adopts internal coal blending centralized reinforcement pretreatment granulation wet balls to enter a kiln for coal-based direct reduction, and obtains high-grade iron ore concentrate or straight iron ore by magnetic separationThe iron powder is connected, so that the method has the characteristics of energy conservation, high efficiency and high speed.
Reference documents:
[1]Schnabel W，Schlebusch D，Elsenheimer G.SL/RN coal-based direct reduction-the state of theart[J].Ironmaking Proc.,Metall.Soc.AIME，1983，42(1):163-170.
[2] born man c.j. south africa SL/RN sponge iron production nine years experience [ J ] sintered pellets, 1994, (2): 42-43.
[3] Zhao Jianhong, Lu Zhenhua, domestic coal-based rotary kiln direct reduction process and apparatus statement (J) Shanxi Metallurgical, 2002, 86 (2): 1-4.
[4] The present development status and prospect of coal-based direct reduced iron [ J ] of China, seventh China Steel Association proceedings, 2009.316-320.
[5] Zhudeqing, Deng Xiulan, Chun iron force, etc. some fine embedded lean hematite direct reduction-low intensity magnetic separation test [ J ] metal mine, 2012(2):60-62, 66.
[6] Influence of coal blending amount on direct reduction roasting of refractory iron ore briquettes [ J ]. school news of Zhongnan university (Nature science edition), 2013.44(4): 1305-.
[7] The research on the coal-based direct reduction of low-grade iron ore is carried out, namely [ J ] comprehensive utilization of ore products, 2001(06):20-24.
Disclosure of Invention
The invention aims to develop a method for directly reducing low-grade iron ore, which can effectively solve the problems that the low-grade iron ore is difficult to effectively utilize, the reduction temperature is high, the reduction time is long, the ring is easy to form, the cost is high and the like in a coal-based direct reduction process, thereby effectively reducing the production cost of enterprises, effectively relieving the situation of shortage of high-quality iron ore resources and promoting the development of the iron and steel industry in China.
The invention relates to a method for directly reducing low-grade iron ore, which comprises the following steps:
step one
Calculating and blending coal powder, an additive, a binder and water as internal coal blending pretreatment raw materials by taking the dry basis mass of the low-grade iron ore to be treated as a reference;
wherein,
the coal powder is prepared according to the mass ratio of C/Fe of 0.2-0.4; in the coal particles, the dry basis weight of the coal powder with the granularity less than 0.074mm accounts for more than 45 percent of the total dry basis weight of the coal powder;
the additive to be treated is prepared according to the mass of 2.0-5.0 percent of the dry base of the low-grade iron ore, and the additive is selected from NaCl and CaCl2、FeCl3、Na2CO3Preferably NaCl, CaCl2、FeCl3At least one of (1), more preferably NaCl;
the binder is prepared according to 0.5-2.0% of the dry basis weight of the low-grade iron ore to be treated, and is selected from at least one of bentonite and composite bentonite, and the bentonite is further preferred;
water is prepared according to 6.0 to 7.0 percent of the dry basis weight of the low-grade iron ore to be treated;
step two
Mixing the coal dust, the additive, the binder and the water which are taken as the pretreatment raw materials of the internal blending coal in the step one until coal dust particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain the pretreated internal blending coal;
step three
Uniformly mixing the pretreated internal coal blend obtained in the step two with low-grade iron ore particles to be treated, and granulating by adopting a disc or a cylinder to obtain a granulated pellet with the diameter of 3-8 mm; the mass percentage of water in the small granulated balls is 8-12%; in the low-grade iron ore particles to be treated, the dry basis weight of the particles with the granularity smaller than 0.074mm accounts for more than 70 percent of the total dry basis weight of the low-grade iron ore to be treated;
step four
Directly feeding the granulated pellets obtained in the step three into a rotary kiln, drying, preheating, and performing direct reduction roasting treatment on the coal base to obtain a reduction material, cooling the reduction material under the condition of air isolation, and performing dry magnetic separation to obtain reduction roasted pellets and residual carbon; the temperature of the coal-based direct reduction roasting treatment is 920-980 ℃;
step five
Grinding and magnetically separating the reduction roasting pellets obtained in the step four to obtain iron ore concentrate;
or
And D, grinding the reduction roasting pellets obtained in the step four, carrying out magnetic separation treatment, regrinding and recleaning to obtain the reduced iron powder.
The invention relates to a method for directly reducing low-grade iron ore, which comprises the following steps that in the first step, the volatile matter of coal powder is more than or equal to 25 percent; the fixed carbon content is greater than or equal to 45 percent.
The invention relates to a method for directly reducing low-grade iron ore.
According to the method for directly reducing the low-grade iron ore, the mass percentage of iron in the low-grade iron ore to be treated is more than or equal to 28%.
The invention relates to a method for directly reducing low-grade iron ore, which comprises the third step that low-grade iron ore particles to be treated are obtained by ore grinding treatment, wherein the ore grinding treatment is selected from one of wet grinding, high-pressure roller grinding and thunder grinding.
The invention relates to a method for directly reducing low-grade iron ore.
The invention relates to a method for directly reducing low-grade iron ore, wherein the pulverization rate of the pelletized pellets obtained in the third step is less than or equal to 5 percent after high-temperature drying and preheating of the pelletized pellets. The powdering ratio was measured by subjecting 500g of the pellets to wet granulation in N2Drying at 800 ℃ in a protected muffle furnace, dropping the obtained dried pellets from the position with the height of 0.5m, repeating the drying for 3 times, weighing Ag as the powder with the particle size of less than or equal to 1.0mm, and obtaining the pulverization rate of A/500.
The invention relates to a method for directly reducing low-grade iron ore, which comprises the fourth step that the time for reducing and roasting treatment is 20-45 min.
In order to achieve better implementation effect, the operation of step four may preferably be: feeding the granulated pellets obtained in the step three into a rotary kiln, and drying, heating and preheating the pellets under the action of high-temperature gas at the tail of the rotary kiln at the temperature of 500-920 ℃, wherein the temperature is increased from normal temperature to 920 ℃ for 60-90 min; then, directly reducing and roasting the coal base at 920-980 ℃ for 20-45 min to prepare a reducing material; the reducing material is isolated from air by a cooling cylinder spraying water from the outside and cooled to 90-110 ℃, and after cooling, the reducing material is separated by adopting dry magnetic separation to obtain reducing roasting pellets and residual carbon. And the magnetic field intensity during dry magnetic separation is 1.0-1.2 KA/m.
According to the method for directly reducing the low-grade iron ore, the residual carbon obtained in the fourth step can be used as a coal powder raw material for the first step.
The invention relates to a method for directly reducing low-grade iron ore, wherein the metallization rate of reduction roasting pellets obtained in the fourth step is 60-85%. Compared with the metallization rate of 30-40 in the prior art, the metallization rate is improved by 1.5-2.8 times. The prior art is typically a method for upgrading low-grade iron ore (application or patent No. 201410200461).
The invention relates to a method for directly reducing low-grade iron ore, which comprises the following steps: and D, grinding the reduction roasting pellets obtained in the step four until the mass percentage content of the reduction roasting pellets with the granularity of less than or equal to 0.074mm is more than 95% of the total mass of the reduction roasting pellets, and performing magnetic separation, wherein the magnetic field intensity during the magnetic separation is 1.4-2.0 KA/m. In order to improve the ore grinding efficiency, in the fifth step, the ore grinding time is generally controlled to be 10min to 20 min.
In the fifth step of the method for directly reducing the low-grade iron ore, the grade of the iron ore concentrate is greater than or equal to 70.95%, preferably greater than or equal to 74.33%, more preferably greater than or equal to 80.19%, and even more preferably greater than or equal to 83%.
Principles and advantages
The inventor finds out through repeated groping that the centralized strengthening pretreatment of the internal coal blending is a key technical means of the invention, not only strengthens the direct reduction reaction process of the iron oxide and the fixed carbon, but also is a key technical measure of the wet-ball kiln-entering coal-based direct reduction process. In the centralized strengthening pretreatment process of the internal blended coal, the coal and the NaCl additive are soaked and permeated into cracks and pores of the coal under the full action of moisture, and in the subsequent direct reduction roasting process of the coal base, the rapid reduction reaction of the fixed carbon and the iron oxide is strengthened, and the growth of metal iron grains is effectively strengthened; part of fixed carbon is consumed and residual carbon is generated in the process of reducing roasting at 920-980 ℃ for 20-45 min in a rotary kiln, and the residual carbon has developed pores and good reaction activity, so that the whole reduction reaction is carried out at low temperature and quickly. In addition, the produced carbon residue can be returned and utilized as a reducing agent after being intensively reinforced by an additive and water. Meanwhile, water and micromolecular hydrocarbon are removed from residual carbon (basically, the residual carbon does not participate in the reduction reaction in the reduction process), so that the pellet strength of the granulated pellets in the drying and heating processes is improved, and the cracking phenomenon is reduced. The addition of the binder changes the surface performance of coal under the reinforcing action of a proper amount of additive and a proper amount of water, so that the surface and internal cracks of coal particles are changed from hydrophobic to hydrophilic, the balling performance of the mixture is improved, the thermal stability of the coal is improved in the heating reduction process, the violent decrepitation phenomenon generated in the coal cracking or gasification process is effectively reduced, and the thermal stability of wet pellets of the internal coal blending granulation pellets is obviously improved. Because the components of the internal coal blending are reasonably arranged and the internal coal blending and the iron ore are properly matched, the small granulated balls (wet balls) can directly enter the kiln and can bear the high-temperature drying of 500-800 ℃ without generating powder, thereby ensuring the smooth direct reduction of the rotary kiln.
The method comprises the steps of effectively controlling the mass percentage of iron ore and coal with the granularity smaller than 0.074mm, determining the mass ratio of C/Fe by 0.2-0.4 through proportioning calculation, determining the content of NaCl serving as an additive by 2.0-5.0% and the using amount of a binder and wetting water, mixing and granulating the internally blended coal and the iron ore into granulated pellets by 3-8 mm through pretreatment, and under the comprehensive synergistic effect of the factors, remarkably improving the balling property, the thermal stability and the reducibility of the internally blended coal in the low-grade iron ore, wherein the obtained granulated pellets can realize that wet pellets can be directly fed into a kiln to be quickly and directly reduced at a low reducing temperature in a coal base at a medium temperature, so that the problems of long reduction time of lump ore, ring formation of a rotary kiln, poor reduction uniformity of the center and the edge of pellets and the like are effectively; the problems that the permeability of the fine ore during reduction is poor, dust flies with hot waste gas to affect the smooth operation of equipment and cause iron ore loss and the like can be effectively avoided; meanwhile, the invention eliminates a cylinder dryer, shortens the process flow and improves the heat efficiency. Through the effective cooperation and efficient control of all factors, the invention can realize medium-temperature rapid reduction of coal blending in low-grade iron ore and additive granulation coal base in a rotary kiln, only needs the temperature of 920-980 ℃, the reduction time is 20-45 min, thereby leading most iron oxides in the iron ore, particularly hematite part less than 0.010mm, to be rapidly reduced into metallic iron and to be rapidly gathered and grown under the action of the additive, other gangue minerals basically do not change or mineralize to form low-melting-point substances without obstructing the reduction of the iron oxides, being beneficial to the migration and growth of the metallic iron, obtaining high-grade iron ore concentrate or directly reduced iron powder after magnetic separation, and having the characteristics of energy saving, high efficiency and rapidness.
By adopting the method, the energy consumption standard coal for combustion is less than 120kg/t iron ore during the reduction of the rotary kiln, and is far lower than the energy consumption index of the conventional coal-based direct reduction rotary kiln. For theThe iron grade of the raw material is 28.81 percent and SiO2The percentage content of fixed carbon of 43.52% low-grade iron ore and reducing coal is 55.83%, the percentage content of volatile matter is 36.03%, the metallization rate of the obtained reduction roasting pellet ore can reach more than 80%, and iron ore concentrate can be obtained after magnetic separation or reduced iron powder can be obtained after regrinding. The grade of iron in the iron powder obtained by the method is more than or equal to 83 percent, and the recovery rate of the iron is more than 70 percent.
Drawings
FIG. 1 is a process flow diagram of the present invention.
Detailed Description
The invention is further illustrated by the following figures and examples. Wherein the raw materials comprise 28.81 percent of iron grade and SiO2The fixed carbon content of the low-grade iron ore and the reduced coal with the content of 43.52 percent is 58.38 percent, and the volatile component content of the low-grade iron ore and the reduced coal is 34.63 percent.
Comparative example 1
Weighing 350g of low-grade iron ore with the granularity of 12-16 mm, preparing coal powder according to the mass ratio of C to Fe of 0.8, uniformly mixing the iron ore and the coal powder, loading the mixture into a rotary tube furnace, raising the temperature from normal temperature to 950 ℃, wherein the time of raising the temperature is 60min, and carrying out coal-based direct reduction roasting for 35min after raising the temperature to 950 ℃; ball milling the reduced roasted ore for 20min, wherein the ore milling concentration is 50%, and magnetic separation is carried out under the magnetic field intensity of 1.2 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 62.53%, and the concentrate grade is 46.52%.
Comparative example 2
Weighing 350g of low-grade iron ore with the granularity of 1-3 mm, preparing coal powder according to the mass ratio of C to Fe of 0.5, uniformly mixing the iron ore and the coal powder, then loading the mixture into a rotary tube furnace, raising the temperature from normal temperature to 950 ℃, wherein the time of raising the temperature is 60min, and carrying out coal-based direct reduction roasting for 35min after raising the temperature to 950 ℃; ball milling the reduced roasted ore for 20min, wherein the ore milling concentration is 50%, and magnetic separation is carried out under the magnetic field intensity of 1.4 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 64.78%, and the concentrate grade is 49.38%.
Comparative example 3
Weighing 350g of low-grade iron ore with the granularity of less than 1mm, preparing coal powder according to the mass ratio of C to Fe of 0.5, uniformly mixing the iron ore and the coal powder, loading the mixture into a rotary tube furnace, raising the temperature from normal temperature to 950 ℃ for 60min, then lowering the temperature to 920 ℃, and carrying out reduction roasting at 920 ℃ for 35 min; ball milling the reduced roasted ore for 20min, wherein the ore milling concentration is 50%, and magnetic separation is carried out under the magnetic field intensity of 1.4 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 75.75%, and the concentrate grade is 50.05%.
Comparative example 4
Adding NaCl with the particle size of less than 1mm to the low-grade iron ore with the total mass of 3% of the iron ore, then briquetting the iron ore into 10mm briquettes, drying the briquettes, weighing 350g of the briquettes, then preparing coal powder according to the C/Fe mass ratio of 0.4, loading the coal powder and the iron ore briquettes with the NaCl into a rotary tube furnace, raising the temperature from the normal temperature to 950 ℃, wherein the temperature rise time is 60min, and performing coal-based direct reduction roasting for 35min after raising the temperature to 950 ℃; ball milling the reduced roasted ore for 20min, wherein the ore milling concentration is 50%, and magnetic separation is carried out under the magnetic field intensity of 1.4 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 59.78%, and the concentrate grade is 63.35%.
Comparative example 5
After crushing and grinding the low-grade iron ore and the coal, the mass percentages of the low-grade iron ore and the coal which are smaller than 0.074mm are respectively 80.45% and 47.38%, the coal is prepared according to the mass ratio of C to Fe of 0.3, NaCl is prepared according to 3.0% of the total mass of the iron ore dry basis, bentonite is prepared according to 1.5% of the total mass of the iron ore dry basis, then the iron ore powder, the coal, the NaCl and the bentonite are uniformly mixed, and then the mixture is pelletized into small balls with the diameter of 3-8 mm by a disc; drying the granulated pellets, loading the dried granulated pellets into a rotary tube furnace, raising the temperature from normal temperature to 950 ℃, wherein the temperature is raised for 60min, and carrying out coal-based direct reduction roasting for 35min after raising the temperature to 950 ℃; ball milling the reduced roasted ore for 20min, wherein the ore milling concentration is 50%, and magnetic separation is carried out under the magnetic field intensity of 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 68.89%, and the concentrate grade is 71.84%.
Comparative example 6
After crushing and grinding the low-grade iron ore and the coal, the mass percentages of the low-grade iron ore and the coal which are smaller than 0.074mm are respectively 80.45% and 47.38%, the coal is prepared according to the mass ratio of C to Fe of 0.3, the NaCl is prepared according to 3.0% of the total mass of the iron ore dry basis, the bentonite is prepared according to 1.5% of the total mass of the iron ore dry basis, then the iron ore powder, the coal, the NaCl and the bentonite are uniformly mixed, and then the mixture is pelletized into small balls (the mass content of water is 11.62%) with the diameter of 3-8 mm by a disc; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out at 950 ℃ for 35min, and the pulverization rate of the reduced pellets smaller than 1mm is 28.58%; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 65.89%, and the concentrate grade is 68.83%.
Example 1:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.50%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 81.10 percent and the pulverization rate of the reduced pellets is 4.56 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 71.55%, and the concentrate grade is 83.90%.
Example 2:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.2; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.58%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 73.61 percent and the pulverization rate of the reduced pellets smaller than 1mm is 3.92 percent; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 73.88%, and the concentrate grade is 80.19%.
Example 3:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.4; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.48%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 82.01 percent and the pulverization rate of the reduced pellets is 4.95 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 70.18%, and the concentrate grade is 83.79%.
Example 4:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 2.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.69%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 65.18 percent and the pulverization rate of the reduced pellets is 7.58 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 67.59%, and the grade of the concentrate is 70.95%.
Example 5:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 5.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.23%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 83.18 percent and the pulverization rate of the reduced pellets smaller than 1mm is 4.59 percent; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 70.59%, and the concentrate grade is 84.98%.
Example 6:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 0.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.98%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 80.28 percent, and the pulverization rate of the reduced pellets smaller than 1mm is 7.95 percent; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 73.61%, and the concentrate grade is 80.28%.
Example 7:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 2.0 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.88%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 80.08 percent, and the pulverization rate of the reduced pellets is 3.68 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 73.69%, and the concentrate grade is 80.38%.
Example 8:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.78%) with the diameter of 3-8 mm; after the wet pellets are granulated and put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 950 ℃ for 90min, coal-based direct reduction roasting is carried out for 35min at 950 ℃, the metallization rate of the reduced pellets is 81.08 percent, and the pulverization rate of the reduced pellets is 4.86 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 72.65%, and the concentrate grade is 81.35%.
Example 9:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.33%) with the diameter of 3-8 mm; after the wet pellets of the granulated pellets are put into a kiln, the temperature of the furnace burden in a rotary tube furnace is raised from normal temperature to 950 ℃ for 60min, coal-based direct reduction roasting is carried out for 45min at 950 ℃, the metallization rate of the reduced pellets is 82.05 percent and the pulverization rate of the reduced pellets is 5.87 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 70.53%, and the concentrate grade is 83.35%.
Example 10:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then, uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.65%) with the diameter of 3-8 mm; after the wet pellets are granulated and put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 920 ℃ for 60min, coal-based direct reduction roasting is carried out at 920 ℃ for 35min, the metallization rate of the reduced pellets is 76.25 percent, and the pulverization rate of the reduced pellets is 4.78 percent, wherein the pulverization rate is less than 1 mm; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 73.58 percent, and the concentrate grade is 74.33 percent.
Example 11:
after crushing and grinding treatment, the low-grade iron ore and the coal are respectively 80.45 percent and 47.38 percent in mass percentage of less than 0.074mm, and coal particles are prepared according to the mass ratio of C/Fe of 0.3; preparing NaCl according to 3.0 percent of the total mass of the iron ore dry basis, preparing bentonite according to 1.5 percent of the total mass of the iron ore dry basis, and preparing water according to 6.0 percent of the total mass of the iron ore dry basis; then uniformly mixing the prepared coal particles, NaCl, bentonite and water until the coal powder particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal coal; then uniformly mixing the internal coal and iron ore particles, and carrying out disc granulation to obtain a granulation pellet (the mass percentage of water is 11.57%) with the diameter of 3-8 mm; after the wet pellets are granulated and put into a kiln, the temperature of the charging material in a rotary tube furnace is raised from normal temperature to 980 ℃ for 60min, coal-based direct reduction roasting is carried out for 35min at 980 ℃, the metallization rate of the reduced pellets is 82.28 percent, and the pulverization rate of less than 1mm is 4.58 percent; ball milling the reduced small balls for 20min, wherein the ore grinding concentration is 50%, and the magnetic field intensity is 1.7 KA/m; the recovery rate of the obtained magnetic separation iron concentrate is 74.48%, and the concentrate grade is 83.38%.
Claims (10)
1. A method for directly reducing low-grade iron ore; the method is characterized by comprising the following steps:
step one
Calculating and blending coal powder, an additive, a binder and water as internal coal blending pretreatment raw materials by taking the dry basis mass of the low-grade iron ore to be treated as a reference;
wherein,
the coal powder is prepared according to the mass ratio of C/Fe of 0.2-0.4; in the coal particles, the dry basis weight of the coal powder with the granularity less than 0.074mm accounts for more than 45 percent of the total dry basis weight of the coal powder;
the additive is prepared according to the mass of 2.0-5.0% of the dry basis of the low-grade iron ore, and the additive is selected from NaCl and CaCl2、FeCl3、Na2CO3At least one of;
the binder is prepared according to 0.5 to 2.0 percent of the dry basis weight of the low-grade iron ore, and is selected from at least one of bentonite and composite bentonite;
water is prepared according to 6.0 to 7.0 percent of the dry basis weight of the low-grade iron ore;
step two
Mixing the internal blending coal pretreatment raw material prepared in the step one until coal dust particles are fully wetted and the additive permeates into holes and cracks of the coal particles under the action of moisture to obtain pretreated internal blending coal;
step three
Uniformly mixing the pretreated internal coal blend obtained in the step two with the low-grade iron ore to be treated, and granulating by adopting a disc or a cylinder to obtain a granulated pellet with the diameter of 3-8 mm; the mass percentage of water in the small granulated balls is 8-12%; in the low-grade iron ore particles to be treated, the dry basis weight of the particles with the granularity smaller than 0.074mm accounts for more than 70 percent of the total dry basis weight of the low-grade iron ore to be treated;
step four
Directly feeding the granulated pellets obtained in the step three into a rotary kiln, drying, preheating, and performing direct reduction roasting treatment on the coal base to obtain a reduction material, cooling the reduction material under the condition of air isolation, and performing dry magnetic separation to obtain reduction roasted pellets and residual carbon; the temperature of the coal-based direct reduction is 920-980 ℃;
step five
Grinding and magnetically separating the reduction roasting pellets obtained in the step four to obtain iron ore concentrate;
or
And D, grinding the reduction roasting small balls obtained in the step four, carrying out magnetic separation treatment, regrinding and recleaning to obtain the reduced iron powder.
2. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: in the first step, the volatile matter of the coal powder is more than or equal to 25 percent; the fixed carbon content is greater than or equal to 45 percent.
3. A method for direct reduction of low-grade iron ore according to claim 2; the method is characterized in that: in the first step, the pulverized coal is at least one selected from lignite, anthracite and biomass carbon.
4. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: the mass percentage of iron in the low-grade iron ore to be treated is more than or equal to 28 percent.
5. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: in the third step, the granulated pellet is subjected to N2Drying in a protected muffle furnace at 800 ℃ to obtain dried granulated pellets; taking 0.5Kg of dried granulated pellets, allowing them to fall from a height of 0.5m, repeating for 3 times, and making the mass of the powder with a particle size of 1.0mm or less to be 25g or less.
6. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: in the fourth step, the time of the coal-based direct reduction roasting treatment is 20min to 45 min.
7. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that the fourth step is as follows:
feeding the granulated pellets obtained in the step three into a rotary kiln, and drying, heating and preheating the pellets under the action of high-temperature gas at the tail of the rotary kiln at the temperature of 500-920 ℃, wherein the temperature is increased from normal temperature to 920 ℃ for 60-90 min; then carrying out coal-based direct reduction roasting at 920-980 ℃ for 20-45 min to prepare a reduction material; the reducing material is isolated from air by a cooling cylinder spraying water from the outside and cooled to 90-110 ℃, and after cooling, the reducing material is separated by adopting dry magnetic separation to obtain reducing roasting pellets and residual carbon.
8. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: the carbon residue obtained in the fourth step can be used as a coal powder raw material for the first step.
9. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that: the metallization rate of the reduction roasting pellets obtained in the fourth step is 60-85%.
10. A method for direct reduction of low-grade iron ore according to claim 1; the method is characterized in that the fifth step is as follows: and D, grinding the reduction roasting pellets obtained in the step four until the dry mass percentage content of the particles with the particle size of less than or equal to 0.074mm is more than 95% of the total mass of the reduction roasting pellets, and then carrying out magnetic separation, wherein the magnetic field intensity during the magnetic separation is 1.4-2.0 KA/m.
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| CN106591572A (en) * | 2017-01-06 | 2017-04-26 | 中南大学 | Method for reinforcing preparation and reduction of carbon-containing pellets in iron ore |
| CN108690909A (en) * | 2017-04-05 | 2018-10-23 | 祁东县顺达矿业有限公司 | The method that kiln is tied in preventing rotary kiln from producing |
| CN107177732A (en) * | 2017-05-19 | 2017-09-19 | 安徽工业大学 | It is a kind of to prepare high strength bainite agglomerate and gas iron co-production as bonding carrier with biomass |
| CN107177732B (en) * | 2017-05-19 | 2019-05-17 | 安徽工业大学 | It is a kind of that biomass is used to prepare high strength bainite agglomerate and gas iron co-production as bonding carrier |
| CN108676951A (en) * | 2018-06-15 | 2018-10-19 | 甘肃酒钢集团宏兴钢铁股份有限公司 | A kind of hydrocarbon joint direct-reduction technique of iron ore concentrate |
| CN111334633A (en) * | 2020-04-29 | 2020-06-26 | 王安新 | External heating type vertical rotary kiln |
| CN112588201A (en) * | 2020-12-30 | 2021-04-02 | 重庆长江造型材料（集团）股份有限公司 | Consolidation granulation method of slurry |
| CN113684337A (en) * | 2021-07-29 | 2021-11-23 | 张雷 | Method and device for optimizing iron ore by gas coal double-base direct reduction and magnetic separation |
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