A method and system for smelting chromite

Abstract

The application discloses a method for smelting chromite, comprising the following steps: step 1) placing raw materials containing chromite, a reducing agent and a flux into a smelting device, spraying oxygen-rich air and fuel into the raw materials for combustion, smelting the raw materials, and obtaining a side-blown pre-reduction melt; and step 2) reducing and smelting the side-blown pre-reduction melt to obtain a chromite product. The raw materials are directly put into the furnace without pretreatment, thereby avoiding pollution caused by grinding and balling, and the environment-friendly electric furnace has low power consumption, which is only 300-400 kWh / t of iron, the steam power generation can completely supply the power consumption, external power supply is not needed, and the demand for electric energy in the production of the chromite product is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of chromite smelting technology, specifically to a chromite smelting method and system. Background Technology

[0002] Ferrochrome is an important alloying additive for stainless steel, and is generally obtained by smelting chromite ore in an electric furnace. Currently, there are four main processes used to produce ferrochrome: the conventional process, the Outokumpu process, the DC arc process, and the Premus process.

[0003] In traditional processes, a mixture of chromite, reducing agent, and flux is granulated and then directly fed into an open submerged arc furnace. This process has low investment and strong raw material adaptability, and many smelters in countries such as South Africa and Zimbabwe still use it. However, this process is not environmentally friendly, has low efficiency, and will eventually be phased out.

[0004] The Outokumpu process involves wet grinding of fine chromite, followed by pelletizing and sintering with binders such as bentonite, then air cooling and storage. The pellets are then heated with flux in a preheater above the furnace chamber before being fed into a closed submerged arc furnace. This process reduces specific energy consumption and improves chromium recovery, but it has a long process flow, high investment costs, and poor environmental impact.

[0005] The DC electric arc furnace route uses a single solid carbon electrode to generate a DC arc at the anode at the bottom of the furnace. The arc is typically open or semi-submerged. Raw materials can be charged directly into the furnace or hollow electrodes can be used. The main advantage of this process is that it can utilize any available raw material, including 100% chromite powder, with minimal or no pretreatment. Chromium recovery rates are very high using this process, but the method is energy-intensive.

[0006] The Premus process is currently the most advanced and common process. Its main process flow is: grinding - pelletizing - drying and preheating - rotary kiln pre-reduction - electric furnace smelting. However, the main disadvantages of this process are that it has a long process flow, high investment, high energy consumption, heavy pollution, and low recovery rate of valuable metals such as chromium. Summary of the Invention

[0007] To address the problems of long process times, high investment, high energy consumption, heavy pollution, and low recovery rates of valuable metals such as chromium in existing chromium smelting methods, this invention proposes a chromium smelting method and system. The above objective can be achieved through the following technical solutions:

[0008] A method for smelting chromite includes the following steps:

[0009] Step 1) Place the raw material containing chromite, reducing agent and flux in the smelting equipment, and inject oxygen-enriched air and fuel into the raw material for combustion to smelt the raw material and obtain the side-blown pre-reduced melt.

[0010] Step 2) The side-blown pre-reduced melt is reduced and smelted to obtain ferrochrome products.

[0011] Optionally, the flux in step 1) is silica or quartz.

[0012] Optionally, the amount of flux added in step 1) is 10-15% of the weight of chromite.

[0013] Optionally, the reducing agent in step 1) is a carbon-based reducing agent;

[0014] The carbon-based reducing agent is selected from at least one of pulverized coal, coke powder, activated carbon powder, and graphite.

[0015] Optionally, in step 1), the amount of reducing agent added is 20-35% of the weight of chromite.

[0016] Optionally, in step 1), the volume fraction of oxygen in the oxygen-enriched air is 50-100%; the pressure of the oxygen-enriched air and the fuel side-blown injection is 0.2MPa to 0.6MPa.

[0017] Optionally, the velocity of the oxygen-enriched air and fuel side-blown injection is 200-300 m / s;

[0018] Optionally, the fuel is one or more of pulverized coal, natural gas, heavy oil, and mineral oil.

[0019] Optionally, in step 1), the temperature for melting the raw materials is 1550-1700℃, and the melting time is 1-3 hours.

[0020] Optionally, the reduction melting temperature in step 2) is 1650-1750℃, and the melting time is 1-2h.

[0021] Optionally, the flue gas formed in steps 1) and 2) can be used for waste heat power generation after secondary combustion.

[0022] Optionally, the electricity generated from waste heat can be used for reduction smelting.

[0023] The present invention also proposes a chromite smelting system, comprising:

[0024] A side-blown molten pool furnace is used to melt raw materials to form a side-blown pre-reduced melt. The side-blown molten pool furnace is equipped with a spray gun, which is used to inject oxygen-enriched air and fuel into the raw materials inside the side-blown molten pool furnace. The bottom of the side-blown molten pool furnace is provided with a side-blown pre-reduced melt outlet. The side-blown molten pool furnace is also provided with a raw material inlet and a flue gas outlet.

[0025] An electric furnace is used to reduce and smelt a side-blown pre-reduced melt to form ferrochrome products. The electric furnace is equipped with a melt inlet, electrodes, a reducing agent inlet, and an electric furnace flue gas outlet. A slag outlet 202 is located in the middle of the electric furnace, and a ferrochrome product outlet is located at the bottom of the electric furnace.

[0026] A chute is used to transport side-blown pre-reduction melt from a side-blown molten pool furnace to an electric furnace.

[0027] Optionally, the system further includes a secondary combustion device and a waste heat power generation device. The secondary combustion device is used to perform secondary combustion on the flue gas discharged from the side-blown molten pool furnace and the electric furnace. The flue gas after secondary combustion enters the waste heat power generation device to generate electricity, and the electricity generated by the waste heat power generation device is used to power the furnace.

[0028] Optionally, the system further includes a dust collection device and a desulfurization device; the flue gas discharged from the side-blown molten pool furnace and the electric furnace passes through the dust collection device and the desulfurization device in sequence, and the resulting dust is input into the side-blown molten pool furnace from the raw material inlet.

[0029] The technical solution of this invention has the following advantages:

[0030] This invention utilizes side-blown pre-reduction combined with electric furnace reduction smelting, resulting in a short process flow and low investment. Raw materials are fed directly into the furnace without pretreatment, avoiding pollution from grinding and pelletizing processes, making it environmentally friendly. The electric furnace has low power consumption, only 300-400 kWh / t of iron, which can be fully supplied by steam power generation, eliminating the need for external power supply and significantly reducing the energy demand for ferrochrome production. Cr metal recovery rate is as high as 95%, achieving full recovery. It has strong fuel adaptability, allowing for the selection of appropriate fuels based on local resources, thus demonstrating strong process adaptability. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a process flow diagram from Embodiment 1 of the present invention;

[0033] Figure 2 This is a schematic diagram of the system structure in an embodiment of the present invention.

[0034] The reference numerals in the accompanying figures have the following meanings:

[0035] The attached diagram is labeled as follows: side-blown molten pool furnace 1, electric furnace 2, chute 3; wherein the side-blown furnace is equipped with raw material inlet 101, flue gas outlet 102, side-blown spray gun 103, melt outlet 104; the electric furnace is equipped with melt inlet 201, slag outlet 202, ferrochrome outlet 203, electric furnace flue gas outlet 204, electrode 205, reducing agent inlet 206. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0037] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] Example 1

[0041] Figure 1 The chromite smelting method includes the following steps:

[0042] Step 1) Place the raw material containing chromite, reducing agent and flux in the smelting equipment, and inject oxygen-enriched air and fuel into the raw material for combustion to smelt the raw material and obtain the side-blown pre-reduced melt.

[0043] Step 2) The side-blown pre-reduced melt is reduced and smelted to obtain ferrochrome products.

[0044] In step 1), the flux is silica or quartz, and the amount of flux added is 10-15%. The reducing agent is a carbon-based reducing agent, selected from at least one of pulverized coal, coke powder, activated carbon powder, and graphite. The amount of reducing agent added is 20-35%.

[0045] The oxygen-enriched air contains 50-100% oxygen. The fuel is one or more of pulverized coal, natural gas, heavy oil, and mineral oil. The pressure of the oxygen-enriched air and fuel injected from the side is 0.2MPa to 0.6MPa, and the velocity of the oxygen-enriched air and fuel injected from the side is 200-300m / s.

[0046] In step 1), the temperature for melting the raw materials is 1550-1700℃, and the melting time is 1-3 hours; the Fe reduction rate in the melt is >90%, and the Cr reduction rate is 60-70%.

[0047] In step 2), the reduction smelting temperature is 1650-1750℃, and the smelting time is 1-2 hours. The Cr recovery rate of the ferrochrome product is >95%, and the Fe recovery rate is >98%.

[0048] As shown in the figure, the flue gas formed in steps 1) and 2) is used for waste heat power generation after secondary combustion. The flue gas formed in steps 1) and 2) is treated with dust collection and desulfurization to obtain flue dust, which is then added to the raw materials in step 1) for reuse.

[0049] The system in this invention is as follows Figure 2 As shown, it includes:

[0050] A side-blown molten pool furnace 1 is used to melt raw materials to form a side-blown pre-reduced melt; the side-blown molten pool furnace is equipped with a spray gun 103, which is used to spray oxygen-enriched air and fuel into the raw materials in the side-blown molten pool furnace; the bottom is provided with a side-blown pre-reduced melt outlet 104; the side-blown molten pool furnace is also provided with a raw material inlet 101 and a flue gas outlet 102;

[0051] Electric furnace 2 is used to reduce and smelt side-blown pre-reduced melt to form ferrochrome products; the electric furnace 2 is provided with melt inlet 201, electrode 205, reducing agent inlet 206, and electric furnace flue gas outlet 204; the electric furnace is provided with slag outlet 202 in the middle and ferrochrome product outlet 203 at the bottom of the electric furnace.

[0052] Sluice 3 is used to transport the side-blown pre-reduction melt from the side-blown molten pool furnace to the electric furnace.

[0053] The system also includes a secondary combustion device and a waste heat power generation device. The secondary combustion device is used to perform secondary combustion on the flue gas discharged from the side-blown molten pool furnace and the electric furnace. The flue gas after secondary combustion enters the waste heat power generation device to generate electricity, and the electricity generated by the waste heat power generation device is used to power the furnace.

[0054] The system also includes dust collection equipment and desulfurization equipment; the flue gas discharged from the side-blown molten pool furnace and the electric furnace passes through the dust collection equipment and the desulfurization equipment in sequence, and the resulting dust is input into the side-blown molten pool furnace from the raw material inlet of the side-blown molten pool furnace.

[0055] Example 2

[0056] The system in Example 1 is used to process chromite with the composition shown in the table below.

[0057] content 28.5 41.6 21 27 0.21 ＜0.3 2.88 9.62 15.3 0.13 0.91

[0058] 1 million tons / year of chromite ore, 120,000 tons / year of quartz sand, and 260,000 tons / year of anthracite are batched and fed into a side-blown furnace. Pulverized coal and oxygen-enriched air are injected into the furnace at a pressure of 0.5 MPa through side-blown lances to provide energy. The side-blown pre-reduction temperature is controlled at 1600℃. After smelting for 1 hour, the high-temperature melt is sent to an electric arc furnace for reduction smelting via a chute. The electric arc furnace temperature is maintained at 1720℃, and the smelting time is 1.5 hours. The VCO / V(CO+CO2) ratio in the reduction zone is 80%, yielding 530,000 tons / year of ferrochrome, with an electricity consumption of 862 kWh / t per ton of iron. A secondary combustion device performs secondary combustion on the flue gas discharged from the side-blown smelting furnace and the electric arc furnace. The flue gas after secondary combustion enters a waste heat power generation device to generate electricity, which is used to power the furnace. The power generation capacity is 187 MW, equivalent to 2676 kWh / t of electricity generated per ton of iron. Cr recovery rate was 95.5%, and Fe recovery rate was 98.5%.

[0059] Example 3

[0060] 1 million tons / year of chromite ore, 130,000 tons / year of quartz sand, and 300,000 tons / year of anthracite are batched and fed into a side-blown furnace. Pulverized coal and oxygen-enriched air are introduced into the furnace through side-blown lances to provide energy. The side-blown pre-reduction temperature is controlled at 1700℃. After 1 hour of smelting, the high-temperature melt is fed into an electric arc furnace for reduction smelting via a chute. The electric arc furnace temperature is maintained at 1720℃, and the smelting time is 1.5 hours. The VCO / V(CO+CO2) ratio in the reduction zone is 80%, yielding 531,000 tons / year of ferrochrome, with an electricity consumption of 823 kWh / t per ton of iron. A secondary combustion device performs secondary combustion on the flue gas discharged from the side-blown smelting furnace and the electric arc furnace. The flue gas after secondary combustion enters a waste heat power generation device to generate electricity, which is used to power the furnace. The power generation capacity is 190 kW, equivalent to 2662 kWh / t of electricity generated per ton of iron. The Cr recovery rate is 96.5%, and the Fe recovery rate is 98.6%.

[0061] Example 4

[0062] 1 million tons / year of chromite ore, 110,000 tons / year of quartz sand, and 250,000 tons / year of anthracite are batched and fed into a side-blown furnace. Pulverized coal and oxygen-enriched air are injected into the furnace at a pressure of 0.5 MPa through side-blown lances to provide energy. The side-blown pre-reduction temperature is controlled at 1650℃. After smelting for 1 hour, the high-temperature melt is fed into an electric arc furnace for reduction smelting via a chute. The electric arc furnace temperature is maintained at 1720℃, and the smelting time is 1.5 hours. The VCO / V(CO+CO2) ratio in the reduction zone is 80%, yielding 529,000 tons / year of ferrochrome. The electricity consumption per ton of iron is 867 kWh / t. The power generation capacity is 180 kW, which translates to 2535 kWh / t of electricity generated per ton of iron. The Cr recovery rate is 95.5%, and the Fe recovery rate is 98.3%.

[0063] Comparative Example 1

[0064] As a comparison, the Premus process, which treats the aforementioned ore, involves dry grinding, pelletizing, and preheating of 1 million tons / year of chromite, 10,000 tons / year of bentonite, and 250,000 tons / year of reducing agent before being added to the rotary kiln. Partial pre-reduction of chromium and iron oxide then occurs in the rotary kiln. The metallized pellets are then hot-charged into a closed submerged arc furnace for smelting, with 110,000 tons / year of quartz sand added simultaneously, producing 500,000 tons / year of ferrochrome. The power consumption per ton of iron is approximately 2000 kWh / t, with a Cr recovery rate of 90%–92% and an Fe recovery rate of 98.0%.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for smelting chromite, characterized in that, Includes the following steps: Step 1) Place the raw material containing chromite, reducing agent and flux in the smelting equipment, and inject oxygen-enriched air and fuel into the raw material for combustion to smelt the raw material and obtain the side-blown pre-reduced melt. Raw materials are fed directly into the furnace without pretreatment, avoiding grinding and pelletizing. In step 1), the volume fraction of oxygen in the oxygen-enriched air is 50-100%; the pressure of the oxygen-enriched air and the fuel side-blown injection is 0.2 MPa to 0.6 MPa. Step 2) The side-blown pre-reduced melt is reduced and smelted to obtain ferrochrome products.

2. The chromite smelting method according to claim 1, characterized in that, In step 1), the flux is silica or quartz.

3. The chromite smelting method according to claim 2, characterized in that, In step 1), the amount of flux added is 10-15% of the weight of chromite.

4. The chromite smelting method according to claim 1, characterized in that, The reducing agent in step 1) is a carbon-based reducing agent; The carbon-based reducing agent is selected from at least one of pulverized coal, coke powder, activated carbon powder, and graphite.

5. The chromite smelting method according to claim 4, characterized in that, In step 1), the amount of reducing agent added is 20-35% of the weight of chromite.

6. The chromite smelting method according to claim 1, characterized in that, The fuel is one or more of pulverized coal, natural gas, heavy oil, and mineral oil.

7. The chromite smelting method according to claim 1, characterized in that, In step 1), the temperature for melting the raw materials is 1550-1700℃, and the melting time is 1-3 hours.

8. The chromite smelting method according to claim 7, characterized in that, In step 2), the reduction smelting temperature is 1650-1750℃ and the smelting time is 1-2h.

9. The chromite smelting method according to claim 1, characterized in that, The flue gas formed in steps 1) and 2) is used for waste heat power generation after secondary combustion.

10. The chromite smelting method according to claim 1, characterized in that, The flue gas formed in steps 1) and 2) is treated by dust collection and desulfurization, and the resulting flue dust is added to the raw materials in step 1) for reuse.

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