A method for hydrogen-based reduction roasting pretreatment of chromite pellets

Abstract

The present invention provides a method for hydrogen-based reduction roasting pretreatment of chromite pellets, belonging to the field of metallurgical technology. The method comprises the following steps: mixing chromite powder, a binder and water to form pellets, obtaining green chromite pellets; mixing H2 and CO to obtain a reducing gas; and carrying out reduction roasting on the green chromite pellets in the reducing gas. The reduction roasting of the present invention is carried out in an H2-CO atmosphere, completely without involving the use of primary energy solid carbon, and enables the chromite pellets to obtain sufficient strength and metal pre-reduction degree before entering the ore thermal furnace, which can greatly reduce the comprehensive energy consumption and emissions in the production of ferrochrome alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and particularly to a method for hydrogen-based reduction roasting pretreatment of chromite pellets. Background Art

[0002] Data shows that under the condition of extensive use of fine ore today, a reasonable pretreatment process is the key way to reduce the comprehensive energy consumption of submerged arc furnaces before chromite enters the furnaces. The relatively advanced SRC and DRC pretreatment processes have controlled the comprehensive energy consumption of producing ferrochrome alloys in submerged arc furnaces within the range of 1300 - 1500 kgce / t. Compared with the traditional cold briquette pretreatment process (the comprehensive energy consumption of ferrochrome alloys is about 2100 kgce / t), the comprehensive energy consumption of producing ferrochrome alloys in submerged arc furnaces has been reduced by about one-third. However, the basic principle of the SRC and DRC processes is to mix carbon (coke powder or coal powder) in green chromite pellets, and carry out carbon combustion in a rotary kiln or a rotary hearth furnace respectively, and there is limited room for further reducing energy consumption and emissions. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for hydrogen-based reduction roasting pretreatment of chromite pellets. The present invention conducts reduction roasting in an H2-CO atmosphere and does not involve the use of primary energy solid carbon at all.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a method for hydrogen-based reduction roasting pretreatment of chromite pellets, comprising the following steps:

[0006] Mix chromite powder, binder and water to make pellets, obtaining green chromite pellets;

[0007] Mix H2 and CO to obtain a reducing gas;

[0008] Conduct reduction roasting on the green chromite pellets in the reducing gas.

[0009] Preferably, the volume percentage of H2 in the reducing gas is 10% - 80%.

[0010] Preferably, the volume percentage of H2 in the reducing gas is 20% - 60%.

[0011] Preferably, the excess coefficient of the reducing gas is 1.00 - 3.00.

[0012] Preferably, the temperature of the reduction roasting is 1200 - 1400 °C, and the heat preservation time is 0.5 - 3 h.

[0013] Preferably, the particle size of the chromite powder is <74 μm.

[0014] Preferably, the chromite powder contains 32-48 wt% of Cr₂O₃, 20-35 wt% of Fe₂O₃, 1-5 wt% of FeO, 5-10 wt% of MgO, 5-15 wt% of Al₂O₃, and 1-10% of SiO₂.

[0015] Preferably, the binder includes bentonite.

[0016] Preferably, the mass of the binder is 1-7% of the mass of the chromite powder.

[0017] The present invention provides a method for hydrogen-based reduction roasting pretreatment of chromite pellets, comprising the following steps: mixing chromite powder, binder and water to form pellets to obtain green chromite pellets; mixing H₂ and CO to obtain a reducing gas; performing reduction roasting on the green chromite pellets in the reducing gas.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The present invention performs reduction roasting in an H₂-CO atmosphere, completely does not involve the use of primary energy solid carbon, and enables the chromite pellets to obtain sufficient strength and metal pre-reduction degree before entering the submerged arc furnace, which can greatly reduce the comprehensive energy consumption and emissions in the production of ferrochrome alloy.

[0020] Moreover, by adjusting the mixing ratio of H₂ and CO and the temperature and time of reduction roasting, the present invention enables the formation of a sufficient amount of low-melting point phases in the chromite pellets, and this phase serves as an effective binding phase. Thus, the compressive strength of the chromite pellets after reduction roasting can reach more than 1500 N, the green pellet drop strength is 2-7 times / 0.5 m, fully meeting the requirements for entering the submerged arc furnace. And the maximum pre-reduction degree of Fe is 80%, the maximum pre-reduction degree of Cr is 5%, and the maximum total pre-reduction degree of metals is 42.5%, which can be directly hot-charged into the submerged arc furnace for smelting. Compared with the existing pretreatment process, it can greatly reduce the comprehensive energy consumption and emissions in the production of ferrochrome alloy. Description of the Drawings

[0021] Figure 1 It is a bar chart of the iron and chromium metallization rates of the chromite pellets prepared in Examples 1-3;

[0022] Figure 2 It is a bar chart of the compressive strength of the chromite pellets prepared in Examples 1-3;

[0023] Figure 3 It is an SEM image of the chromite pellets prepared in Examples 1-3, where (a), (b), and (c) correspond to Examples 1, 2, and 3 respectively. Detailed Embodiments

[0024] The present invention provides a method for hydrogen-based reduction roasting pretreatment of chromite pellets, comprising the following steps:

[0025] Mix chromite powder, binder and water to form pellets, obtaining green chromite pellets;

[0026] Mix H2 and CO to obtain a reducing gas;

[0027] Carry out reduction roasting on the green chromite pellets in the reducing gas.

[0028] The present invention mixes chromite powder, binder and water to form pellets, obtaining green chromite pellets.

[0029] In the present invention, the particle size of the chromite powder is preferably <74 μm.

[0030] In the present invention, the content of Cr2O3 in the chromite powder is preferably 32-48 wt%, more preferably 38-45 wt%, the content of Fe2O3 is preferably 20-35 wt%, more preferably 28-30 wt%, the content of FeO is preferably 1-5 wt%, more preferably 2-3 wt%, the content of MgO is preferably 5-10 wt%, more preferably 6-9 wt%, the content of Al2O3 is preferably 5-15 wt%, more preferably 10-13 wt%, and the content of SiO2 is preferably 1-10%, more preferably 5-7 wt%. The present invention has no special limitation on the source of the chromite powder, and any source well-known to those skilled in the art can be used.

[0031] In the present invention, the mass of the binder is preferably 1-7% of the mass of the chromite powder, more preferably 2-3%.

[0032] In the present invention, the binder preferably includes bentonite.

[0033] The present invention has no special limitation on the specific manner of pelletizing, and any manner well-known to those skilled in the art can be used.

[0034] The present invention mixes H2 and CO to obtain a reducing gas.

[0035] In the present invention, the volume percentage of H2 in the reducing gas is preferably 10%-80%, more preferably 20%-60%.

[0036] In the present invention, the excess coefficient of the reducing gas is preferably 1.00-3.00, more preferably 1.50-2.80.

[0037] In the present invention, the source of H2 preferably includes green hydrogen obtained from various renewable energy sources, and also includes hydrogen obtained through other means, such as: hydrogen production by electrolysis of water, hydrogen production from fossil fuels, hydrogen production by water gas method, synthesis gas from thermal cracking of petroleum, hydrogen production from natural gas, hydrogen production by freezing coke oven gas, by-product hydrogen from electrolysis of brine, by-product hydrogen from brewing industry or hydrogen production by reaction of iron with steam.

[0038] In the present invention, the source of CO preferably includes: blast furnace gas, coke oven gas, submerged arc furnace gas or coal-fired industrial waste gas.

[0039] The present invention makes full use of CO in secondary energy sources such as secondary gas of submerged arc furnace, and combines it with green hydrogen obtained from renewable energy sources or other means. Without involving primary energy solid carbon at all, chromite pellets with strength meeting the requirements for furnace charging are obtained, which has great potential in reducing the comprehensive energy consumption of ferrochrome alloy and broad application prospects.

[0040] After obtaining chromite green pellets and reducing gas, the present invention reduces and roasts the chromite green pellets in the reducing gas.

[0041] In the present invention, the temperature of the reduction roasting is preferably 1200 - 1400 °C, and the holding time is preferably 0.5 - 3 h.

[0042] In the present invention, the reduction roasting is preferably carried out in a reactor capable of achieving sealing and precise control of gas composition, more preferably including a shaft furnace, a rotary kiln, a rotary hearth furnace or a strand pelletizer.

[0043] The present invention preferably introduces an inert gas into the reactor to remove impurity gases such as oxygen, nitrogen, carbon dioxide, etc., and then puts the chromite green pellets into the device, and when the temperature is raised to the temperature of the reduction roasting, the reducing gas is introduced.

[0044] In the present invention, the inert gas is preferably nitrogen or argon.

[0045] After the reduction roasting is completed, the present invention preferably loads the obtained chromite pellets with certain strength and metal pre-reduction degree into a submerged arc furnace for smelting, significantly reducing the comprehensive energy consumption and emissions of ferrochrome alloy.

[0046] In the present invention, preferably cooling is also included before loading into the submerged arc furnace for smelting. The present invention has no special limitation on the specific cooling method, and any method well-known to those skilled in the art can be adopted.

[0047] In order to further illustrate the present invention, the following describes in detail the method for hydrogen-based reduction roasting pretreatment of chromite pellets provided by the present invention with reference to examples, but they should not be construed as limiting the protection scope of the present invention. Examples

[0048] Contents of various substances in chromite powder: Cr2O3 40wt%, Fe2O3 28wt%, FeO 4wt%, MgO 6wt%, Al2O3 10wt%, SiO2 7%, and the balance is MnO and TiO2.

[0049] Prepare green balls by adding bentonite (with a mass of 2% of the mass of chromite powder) and an appropriate amount of water to chromite ore powder. Place the green balls in a corundum crucible and put it in a horizontal tube furnace. During the heating process, introduce argon gas. Heat up to 1200°C at a rate of 20°C / min, and then switch to a reducing gas with a volume ratio of H2:CO of 2:8. The excess coefficient of the reducing gas is 2, the flow rate is 0.2L / min, the reduction roasting time is 3h, and switch to argon gas during cooling; take it out after cooling to room temperature to obtain reduced chromite pellets. Example

[0050] The preparation method of Example 2 is basically the same as that of Example 1, except that the constant temperature "1200°C" is adjusted to "1300°C". Example

[0051] It is basically the same as the preparation method of Example 2, except that the reducing gas is adjusted to "a volume ratio of H2:CO of 4:6".

[0052] Test Example 1

[0053] The metallization rates of iron and chromium in the chromite pellets prepared in Examples 1, 2, and 3 are as Figure 1 shown.

[0054] From Figure 1 it can be seen that with the increase of the hydrogen ratio and roasting temperature, the metallization rate of iron in the chromite pellets shows an obvious upward trend, proving that hydrogen is more conducive to the reduction of metal oxides in chromite pellets than CO, but the oxides of Cr are difficult to be reduced under these process conditions.

[0055] Test Example 2

[0056] The compressive strengths of the chromite pellets prepared in Examples 1, 2, and 3 are as Figure 2 shown.

[0057] From Figure 2 it can be seen that the pellet strengths are all higher than 1500N, meeting the requirements of the furnace charging strength for subsequent smelting reduction in a submerged arc furnace.

[0058] Test Example 3

[0059] The microstructures of the chromite pellets prepared in Examples 1, 2, and 3 are as Figure 3 shown. Figure 3 Among them, (a), (b), and (c) are the SEM images of the chromite pellets prepared in Examples 1, 2, and 3 respectively.

[0060] It can be seen from Figure 3 that as the proportion of hydrogen increases, the white iron metal particles in the pellets gradually increase in number and size; the results show that hydrogen has a promoting effect on the reduction of chromite pellets; at the same time, the precipitated iron grains and the low-melting-point "FeO"-containing phase increase the adhesion of the fine particles in the chromite pellets and improve the pellet strength.

[0061] The above is only the preferred embodiment of the present invention and does not impose any formal limitation on the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for hydrogen-based reduction roasting pretreatment of chromite pellets, characterized in that, It includes the following steps: Mix chromite ore powder, binder and water to form pellets, obtaining green chromite ore pellets; Mix H2 and CO to obtain a reducing gas; Reduce and roast the green chromite ore pellets in the reducing gas; The volume percentage of H2 in the reducing gas is 20% - 60%; The mass of the binder is 2% of the mass of the chromite ore powder; The temperature of the reduction roasting is 1200 - 1400 °C, and the holding time is 0.5 - 3 h; The content of Cr2O3 in the chromite ore powder is 32 - 48 wt%, the content of Fe2O3 is 20 - 35 wt%, the content of FeO is 1 - 5 wt%, the content of MgO is 5 - 10 wt%, the content of Al2O3 is 5 - 15 wt%, and the content of SiO2 is 1 - 10%; The compressive strength of the chromite ore pellets after reduction roasting reaches more than 1500 N.

2. The method according to claim 1, wherein The excess coefficient of the reducing gas is 1.00 - 3.

00.

3. The method according to claim 1, wherein The particle size of the chromite ore powder is <74 μm.

4. The method according to claim 1, wherein The binder includes bentonite.

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