WO2024221720A1

WO2024221720A1 - Device and method for treating chromite using fluidized suspension roasting electric furnace to smelt ferrochromium alloy

Info

Publication number: WO2024221720A1
Application number: PCT/CN2023/120558
Authority: WO
Inventors: 唐晓玲; 张剑廷
Original assignee: 上海逢石科技有限公司
Priority date: 2023-04-26
Filing date: 2023-09-22
Publication date: 2024-10-31
Also published as: CN116497210A

Abstract

A device and method for treating chromite using a fluidized suspension roasting electric furnace to smelt a ferrochromium alloy. The device comprises a fire coal combustion unit, a crushing and feeding unit, a heating and preheating unit, a suspension roasting unit, a desulfurization, denitrification and dust removal unit, a material-returning recovery unit, and an electric-furnace smelting unit. The method for smelting a ferrochromium alloy comprises: providing reaction heat for the suspension roasting system and the electric furnace by means of coal-based combustion, heating and preheating chromite ores in a suspension state, then reducing the chromite ores in a high-temperature environment by using a reducing agent coke, and recycling gas generated by regenerative reduction and cooling gas of the product.

Description

Fluidized suspension roasting electric furnace to treat chromite ore and smelt ferrochrome alloy device and method

Technical Field

The invention belongs to the technical field of suspended fluidized roasting in metallurgy and mineral processing, and in particular relates to a device and a method for treating chromite ore and smelting ferrochrome alloy in a fluidized suspended roasting electric furnace.

Background Art

Chromium in nature usually forms spinels with complex components such as iron, magnesium, and aluminum, collectively known as chromite. The world's chromium ore resources are relatively abundant, with proven reserves of about 7.5 billion tons and exploitable reserves of about 4.8 billion tons. The world's chromium ore reserves are mainly distributed in a few countries such as South Africa, Kazakhstan, Zimbabwe, India, Brazil, Finland, and Russia. In addition, there are relatively small reserves distributed in Turkey, Albania, Iran, Oman, Australia, and Vietnam. The global annual chromium ore mining volume is about 30 million tons, of which 90% is metallurgical grade chromium ore, mainly used to produce ferrochrome alloys. China's chromium ore resources are extremely scarce. At present, the total proven reserves of chromium ore in my country are about 10.78 million tons. my country has a small chromium ore reserve, poor ore quality, and remote geographical location, and high mining costs. Domestic chromium ore has basically relied on imports for a long time. According to customs statistics, my country imported 12.1 million tons of chromium ore and 1.839 million tons of ferrochrome alloys in 2013. Natural chromite ore mainly has two forms: lump and powder. Lump ore accounts for about 20% of the total, and the rest is powder. With the increase of chromite mining and the decrease of ore grade, the output rate of chromite powder will become higher and higher. Powder ore has a wide range of sources, high grade and low price.

More than 90% of the world's chromium resources are used to smelt stainless steel. my country's stainless steel production accounts for more than 50% of the world's total, and the demand for chromite is very large. Ferrochromium is the most important raw material for producing stainless steel. It is mainly used in the production of stainless steel, ball bearing steel, tool steel, nitriding steel, heat-resistant steel, quenched and tempered steel, carburizing steel and hydrogen-resistant steel. This is because chromium is the only element that determines the properties of stainless steel. Each stainless steel must contain a certain amount of chromium. Chromium is an important alloying element in steel. Chromium can significantly improve the mechanical properties of steel and give steel special physical and chemical properties. For example, chromium can increase the wear resistance of steel, improve the hardness, elasticity, antimagnetism, corrosion resistance, heat resistance, tensile strength, etc. Therefore, the use of chromite determines the output of stainless steel to a certain extent. Since chromium is the most used metal and ranks first among the "strategic metals", countries with chromium ore resources or countries lacking resources in the world today are stepping up research on chromium ore.

At present, the smelting of chromium ore in my country is mainly done by the electric furnace method in pyrometallurgy, which is further divided into the ore thermal method and the refining electric furnace method. The electric furnace method in pyrometallurgy uses carbon as a reducing agent, and uses chromium ore, coke, and silica as raw materials to produce high-carbon ferrochrome, or uses silica, coke, and high-carbon ferrochrome as raw materials to produce silicon-chromium alloy. At present, most of the domestic and foreign production processes of high-carbon ferrochrome use traditional pretreatment (chrome ore crushing, wet grinding, gravity separation/magnetic separation/flotation) + smelting methods (filtration, pelletizing, smelting) or non-pretreatment smelting methods (chrome ore crushing, wet grinding, filtration, pelletizing, preheating, pre-reduction, smelting process). These processes are characterized by long and complex processes, large plant area, many equipment, difficult operation, cumbersome management, large investment, high overall cost, Poor risk resistance, etc. At present, my country's electric furnace technology is backward, and most of them have not achieved electric furnace closure and gas recovery. The energy consumption of domestic high-carbon ferrochrome smelting process is still high. In the actual production of enterprises, the power consumption of high-carbon ferrochrome smelting per ton of benchmark ferrochrome is generally higher than 3400kwh, far from the national energy-saving design specification ≤2800kW·h/t. Therefore, the economic benefits of production enterprises are low and the market competitiveness is not strong. At present, the country will increase the implementation of tiered electricity prices or punitive electricity prices for high-energy-consuming industries, so energy conservation and consumption reduction have become a top priority for high-carbon ferrochrome smelting enterprises.

Summary of the invention

In view of the shortcomings of the existing process technology, the present invention proposes a device and method for treating chromite ore and smelting ferrochrome alloy using a fluidized suspension roasting electric furnace, and studies a process for treating chromite ore and smelting ferrochrome alloy using suspended fluidized roasting technology. The chromite ore is treated by the technology of "fluidized suspension roasting heating cracking thermal decomposition pre-oxidation-electric furnace heat storage reduction".

The fluidized suspension roasting electric furnace for treating chromite ore to smelt ferrochrome comprises a coal combustion unit, a crushing and feeding unit, a heating and preheating unit, a suspension roasting unit, a desulfurization, denitrification and dust removal unit, a return material recovery unit and an electric furnace smelting unit.

The coal-fired combustion unit includes a speed-regulating coal feeder and a coal-fired combustion furnace, and the speed-regulating coal feeder is connected to the coal-fired combustion furnace; the crushing and feeding unit includes an ore bin, a high-pressure roller mill, a storage bin, an electronic quantitative feeder, and a screw feeder. The ore bin is connected to the high-pressure roller mill, the high-pressure roller mill is connected to the storage bin, the storage bin is connected to the electronic quantitative feeder, and the electronic quantitative feeder is connected to the screw feeder; the heating and preheating unit includes a Venturi flash dryer, a cyclone preheating separator I, a cyclone preheating separator II, and a cyclone heater. The Venturi flash dryer is connected to the cyclone preheating separator I, the cyclone preheating separator I is connected to the cyclone heater, and the cyclone heater is connected to the cyclone preheating separator II; the suspension roasting unit includes a suspension roasting main furnace, a double-layer flap valve, a double-layer flap valve is arranged under the suspension roasting main furnace, and the cyclone preheating separator II is connected to the bottom of the suspension roasting main furnace. The bottom of the suspension roasting main furnace is connected to the coal-fired combustion furnace, and the upper part of the suspension roasting main furnace is connected to the cyclone heater; the desulfurization, denitrification and dust removal unit includes a denitrification reactor, a large bag dust collector, an induced draft fan, a desulfurization wet electrostatic precipitator, the denitrification reactor is connected to the large bag dust collector, the large bag dust collector is connected to the induced draft fan, the induced draft fan is connected to the desulfurization system, and the cyclone preheating separator I is connected to the denitrification reactor; the return material recovery unit includes a Roots blower, a powder feeder, and a small bag dust collector. The Roots blower is connected to the powder feeder, the powder feeder is connected to the small bag dust collector, and the small bag dust collector is connected to the cyclone heater; the electric furnace smelting unit includes an ore-fired furnace, coke, silica, a flue gas recovery pipeline, a preheating recovery pipeline, a cyclone heater is connected to the ore-fired furnace, the ore-fired furnace is connected to the bottom of the suspension roasting main furnace via the flue gas recovery pipeline, and the ore-fired furnace is connected to the bottom of the suspension roasting main furnace via the preheating recovery pipeline.

A method for treating chromite ore to smelt ferrochrome alloy by using a fluidized suspension roasting electric furnace, using the above-mentioned device, specifically comprising the following steps:

Step (1): crushing the chromite ore with a high pressure roller mill, and preheating and separating the obtained chromite powder mineral material through a Venturi flash dryer and a cyclone preheating separator I to obtain a powder material and flue gas;

Step (2): The flue gas separated by the cyclone preheating separator I in the above step (1) is transported to the denitration reactor to remove NO _x in the flue gas, and then transported to the large bag filter for dust removal. The flue gas separated by the large bag filter is passed through The induced draft fan transports the particles and pollutants to the desulfurization system for treatment to achieve standard or ultra-low emissions; the fine-grained materials separated by the large bag dust collector are transported to the small bag dust collector through the Roots blower and powder conveyor, and then returned to the cyclone heater;

Step (3): the powder material in the above step (1) is passed into the cyclone preheating separator II for cyclone separation under the action of the rising flue gas of the cyclone heater, and the separated flue gas is sent to the Venturi flash dryer, and the chromite is recycled; the material separated by the cyclone preheating separator II enters the suspension roasting main furnace for roasting;

Step (4): The high-temperature material after roasting is transported to a cyclone heater for separation. The separated high-temperature powder is sent to a submerged arc furnace for smelting, and a reducing agent and a solvent are added to obtain ferrochrome and chromium slag.

The chromite ore in step (1) has a Cr ₂ O ₃ mass content greater than 38%, and a Cr ₂ O ₃ /FeO mass ratio greater than 2.5; the moisture content in the chromite ore is not higher than 5%; the crushing is to crush the ore to a particle size not higher than 1.5 mm, and the mass content of the chromite powder mineral material with a particle size of -200 mesh is 10% to 20%; the drying temperature of the Qiuri flash dryer is 400 to 600° C., the temperature of the cyclone preheating separator I is not higher than 450° C., and the preheating time is 20s to 50s.

The preheating separation in step (1) converts all the iron oxides in the ferrochrome powder into α-Fe ₂ O ₃ and removes the crystal water in the ferrochrome powder. The structure and process design of the cyclone preheating separator are based on a separation efficiency of 80% to 90%.

In step (1), when the moisture content of the chromite ore is not less than 5%, without using a high pressure roller mill, an alternative crushing device is to set a powder closed-circuit dry grinding system between the feed end of the preheating section and the conveying end of the screw feeder for shearing, extrusion and crushing;

Part of the heat released in step (1) is used to preheat the pre-selected concentrate in the system, thereby reducing the energy consumption of the system;

In step (2), the wind pressure power of the system is supplied by the exhaust fan;

In step (2), the denitration reactor adopts a selective catalytic reduction (SCR) process, the inlet temperature of the denitration reactor is 320° C. to 420° C., and the reducing agent of the catalytic reduction (SCR) process is urea; the desulfurization process in the desulfurization system adopts limestone-gypsum wet desulfurization; the inlet temperature of the bag filter is not higher than 280° C.;

The standard or ultra-low emission in step (2) is: _NOx emission concentration ≤40mg/ ^Nm3 (dry basis, standard state, 16% _O2 ), _SO2 emission concentration ≤35mg/ _Nm3 (dry basis, standard state, 16% _O2 ), dust emission concentration ≤10mg/ ^Nm3 (dry basis, standard state, 16% _O2 );

The temperature of the cyclone heating separator in step (3) is 1000° C. to 1200° C., the temperature of the cyclone preheating separator is 700° C. to 900° C., and the temperature of the suspension roasting main furnace is 1100° C. to 1300° C.;

In step (4), the reducing agent is coke, and the solvent is silica; the temperature of the submerged arc furnace is 1100-1300° C.; the inlet temperature of the submerged arc furnace is 900° C.-1100° C.; the high-temperature exhaust gas generated by smelting in the submerged arc furnace is connected to the bottom combustion chamber of the suspension roasting main furnace, and the hot air after the high-temperature ferrochrome alloy and chromium slag are heat-exchanged with cold air is connected to the bottom combustion chamber of the suspension roasting main furnace, so as to provide combustion-supporting hot air for the suspension roasting main furnace;

The submerged arc furnace is a conventional open or semi-enclosed type, which is convenient for the use of powdered chromite; the temperature of the submerged arc furnace heat storage reduction reaction is less than 100-300°C, and the power supply is replenished by the submerged arc furnace itself;

The whole system provides heat for the suspension roasting unit, the desulfurization, denitrification and dust removal unit and the electric furnace smelting unit through the coal combustion unit; the coal used in the coal combustion unit is anthracite or bituminous coal with high volatility, low ash content, high calorific value and low sulfur; the coal is lump coal with a particle size not higher than 200mm; the lump coal treated by the speed-adjustable coal feeder has a content of not less than 60% of -200 mesh and coal particles not higher than 5mm; the heating is provided by natural gas or coal gas, and the coal gas includes one of producer gas, coke oven gas, blast furnace gas and gas producer gas;

The cooling method of the ferrochrome alloy and chromium slag is set to cold air cooling, and the device is a snake-type cooler. The cold air passes through the snake-type cooler to cool the high-temperature ferrochrome alloy and chromium slag by indirect heat exchange. The hot air after air cooling is connected to the bottom of the suspension roasting furnace as the combustion-supporting air of the system to achieve energy recycling;

The insufficient part of the heat storage reduction reaction temperature of the submerged arc furnace (in the range of 100-300℃) is supplied by the submerged arc furnace's own electricity consumption; the material is preheated and heated to crack through suspension roasting, which produces activated pores, cracks and interfaces that are beneficial to the reduction reaction of the particulate material in the submerged arc furnace, increasing its reaction activity; at a temperature of not less than 1150℃, the chromium-containing spinel phase participates in the reduction reaction, the spinel structure is destroyed, and the chromium element becomes the main element of the precipitated phase.

After being treated by the method of the present invention, the chromium recovery rate is above 95%.

During the process of producing high-carbon ferrochrome by smelting in a submerged arc furnace, a large amount of high-temperature flue gas is generated. The high-temperature flue gas is composed of elemental carbon and carbon monoxide combined with the skeleton oxygen in the spinel structure on the surface of the ore, forming carbon monoxide and carbon dioxide gases that leave the system, resulting in the destruction of part of the spinel structure. In open and semi-enclosed furnaces, due to the lower furnace pressure, the rising flue gas can easily pass through the charge. Therefore, open and semi-enclosed furnaces can use a large amount of powdered chromite, and the rising flue gas (mainly CO and _CO2 ) is connected to the bottom combustion chamber of the main suspension roasting furnace, so that secondary energy is effectively utilized and recycled.

Beneficial effects of the present invention:

The fluidized suspension roasting electric furnace for treating chromite to smelt ferrochrome alloy device and method of the present invention provides reaction heat for the suspension roasting system and the electric furnace through coal-based combustion, preheats the chromite ore in a suspended state, and then uses the reducing agent coke to reduce the chromite ore in a high temperature environment, and efficiently recycles the gas generated by the heat storage reduction and the product cooling gas.

Compared with the existing process, the characteristics and advantages of the present invention are:

(1) Compared with the traditional chromite treatment process, the process of treating chromite by combining suspension roasting with electric furnace smelting is short, occupies a small area, requires less equipment, has low investment cost, high chromium recovery rate, low power consumption, energy saving and environmental protection, is easy to operate and manage, has a wide application area (can be used in areas with water and electricity shortages), has low overall cost and significant benefits.

(2) The primary energy source, fossil coal, is directly burned to provide heat instead of the secondary energy source, electricity. The heat provided by the coal is recovered through multiple means such as suspended roasting, multi-stage preheating, and efficient recycling of waste heat from smelting furnaces. This has achieved efficient energy utilization and greatly reduced energy consumption. The total energy consumption of the process system is reduced by about 0.15 tce (equivalent standard coal) per ton of standard coal compared with the conventional process.

(3) The process of efficiently combining suspended roasting with electric furnace smelting to treat chromite ore makes up for the limitations and shortcomings of traditional processes. It provides a new direction for the efficient utilization of chromite resources to smelt ferrochrome alloys and improves the economic value of the development and utilization of such resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the flow structure of the method for smelting ferrochrome alloy by treating chromite with fluidized suspension roasting-electric furnace according to the present invention;

Figure numerals: 11. Speed-regulating coal feeder, 12. Coal-fired combustion furnace, 21. Ore bin, 22. High-pressure roller mill, 23. Storage bin, 24. Electronic quantitative feeder, 25. Screw feeder, 31. Venturi flash dryer, 32. Cyclone preheating separator I, 33. Cyclone preheating separator II, 34. Cyclone heater, 41. Suspension roasting main furnace, 42. Double-layer flap valve, 51. Denitrification reactor, 52. Large bag dust collector, 53. Induced draft fan, 54. Desulfurization system, 61. Roots blower, 62. Powder conveyor, 63. Small bag dust collector, 71. Submersible arc furnace, 72. Coke, 73. Silica, 74. Flue gas recovery pipeline, 75 Preheating recovery pipeline.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

The coal-fired combustion unit includes a speed-regulating coal feeder 11 and a coal-fired combustion furnace 12, wherein the speed-regulating coal feeder 11 is connected to the coal-fired combustion furnace 12; the crushing and feeding unit includes an ore bin 21, a high-pressure roller mill 22, a storage bin 23, an electronic quantitative feeder 24, and a screw feeder 25, wherein the ore bin 21 is connected to the high-pressure roller mill 22, the high-pressure roller mill 22 is connected to the storage bin 23, the storage bin 23 is connected to the electronic quantitative feeder 24, and the electronic quantitative feeder 24 is connected to the screw feeder 25; the heating and preheating unit includes a venturi flash dryer 31, a cyclone preheating separator I 32, a cyclone preheating separator II 33, and a cyclone heater 34, wherein the venturi flash dryer 31 is connected to the cyclone preheating separator I 32, the cyclone preheating separator I 32 is connected to the cyclone heater 34, and the cyclone heater 34 is connected to the cyclone preheating separator II 33; the suspension roasting unit includes a suspension roasting main furnace 41, a double-layer flap valve 42, a double-layer flap valve 42 is arranged below the suspension roasting main furnace 41, the cyclone preheating separator II 33 is connected to the bottom of the suspension roasting main furnace 41, the bottom of the suspension roasting main furnace 41 is connected to the coal-fired combustion furnace 12, and the upper part of the suspension roasting main furnace 41 is connected to the cyclone heater 34; the desulfurization and denitration dust removal unit includes a denitration reactor 51, a large bag dust collector 52, an induced draft fan 53, and a desulfurization system 54. The denitration reactor 51 is connected to the large bag dust collector 52, the large bag dust collector 52 is connected to the induced draft fan 53, the induced draft fan 53 is connected to the desulfurization system 54, and the cyclone preheating separator I 32 is connected to the denitration reactor 51; the return material recovery unit includes a Roots blower 61, an output A powder machine 62, a small bag dust collector 63, a Roots blower 61 is connected to the powder feeder 62, the powder feeder 62 is connected to the small bag dust collector 63, and the small bag dust collector 63 is connected to the cyclone heater 34; the electric furnace smelting unit includes an ore-fired furnace 71, coke 72, silica 73, a flue gas recovery pipe 74, a preheating recovery pipe 75, the cyclone heater 34 is connected to the ore-fired furnace 71, the ore-fired furnace 71 is connected to the bottom of the suspension roasting main furnace 41 via the flue gas recovery pipe 74, and the ore-fired furnace 71 is connected to the bottom of the suspension roasting main furnace 41 via the preheating recovery pipe 75.

The control steps of the fluidized suspension roasting electric furnace for treating chromite ore to smelt ferrochrome are as follows:

The raw ore bin 21 is connected to the ferrochrome raw ore feeding belt and the high-pressure roller mill 22. The qualified particle size product material crushed by the high-pressure roller mill is stored in the storage bin 23. The material is fed into the screw feeder 25 through the electronic quantitative feeder 24 below and then connected to the Venturi dryer 31. Under the action of negative pressure, the ferrochrome powder material is transported to the cyclone preheater I 32. The flue gas separated by the cyclone preheater I 32 is transported to the denitrification reactor 51 to remove NO _x and then to the large bag dust collector 52. The fine-grained materials separated by the large bag dust collector are transported to the small bag dust collector 63 through the Roots blower 61 and the powder conveyor 62, and then return to the cyclone heater 34 after separation; the large bag dust collector 52 is connected to the induced draft fan 53, and the flue gas after dust removal is transported to the desulfurization system 54 through the induced draft fan 53 for particulate matter and pollutant treatment to achieve standard or ultra-low emission; after separation in the cyclone preheater I 32, the powder material is passed into the cyclone preheater II 33 under the action of the rising flue gas of the cyclone heater 34 for cyclone separation, and the separated flue gas is sent to the Venturi flash dryer 31. The material separated by the cyclone preheater II 33 enters the suspension roasting main furnace 41 for high-temperature roasting. The bottom of the suspension roasting main furnace 41 is connected to the coal or gas system 12. The high-temperature material after roasting is transported to the cyclone heater 34 for separation under the action of negative pressure. The separated high-temperature powder enters the submerged arc furnace 71 for smelting, and the reducing agent 72 and the solvent 73 are added along the way. The high-temperature exhaust gas generated by the smelting in the submerged arc furnace 71 is connected to the bottom combustion chamber of the suspension roasting main furnace 41. The hot air after the high-temperature ferrochrome alloy and chromium slag are exchanged with cold air is connected to the bottom combustion chamber of the suspension roasting main furnace 41, providing the suspension roasting main furnace with combustion-supporting hot air.

Example

The process structure diagram of this embodiment is shown in Figure 1, which includes the following steps:

Step 1: Use high pressure roller mill 22 to crush the chromite ore with a moisture content of no more than 5% into a closed circuit to a particle size of no more than 1.5mm and a material particle size of -200 mesh content of 10% to 20%, and then feed it into the heating and preheating unit for preheating by the screw feeder 25 after weighing and metering by the electronic quantitative feeder 24; the preheating temperature is no more than 450°C and the preheating time is 20s to 50s; all the iron oxides in the chromite powder are oxidized, that is, the iron-containing substances in the siderite and limonite are converted into α-Fe ₂ O ₃ in the hematite, and the crystal water and other substances in the mineral are removed, so that the iron oxides in the chromite powder undergo decomposition and oxidation reactions and are converted into α-Fe ₂ O _3. At the same time, the cold ore can be preheated into high-temperature material;

Step 2: directly burning coal through lump coal combustion units 11, 12 and connecting to the bottom combustion chamber of the suspension roasting main furnace 41, providing heat required for the reaction for the suspension roasting, denitration system and electric furnace; the temperature of the suspension roasting main furnace 41 is 1100-1300°C; the temperature of the cyclone heating separator 34 is 1000-1200°C, the temperature of the cyclone preheating separator 33 is 700-900°C, the temperature at the Venturi flash dryer 31 is 400-600°C, and the temperature of the inlet of the electric furnace 71 is 900-1100°C;

Step 3: The lump coal combustion unit includes a speed-regulating coal feeder 11 and a coal-fired combustion furnace 12; the speed-regulating coal feeder 11 is composed of a coal storage bin, a hammer crusher, a screen, a feeder, a mixer, and a fan. Specifically, the lump coal with a particle size composition of less than 200 mm is fed from the coal storage bin into the hammer crusher for crushing, and the crushed product is sieved through a screen, the content of the product under the screen is not less than 60% of -200 mesh, and the coal particles are not more than 5 mm. The large particles on the screen are returned to the hammer crusher for further crushing, and the product under the screen is transported through the feeder, mixed with air in the mixer to ensure a certain air-to-coal ratio, and then transported to the coal-fired combustion furnace 12 by the fan. The coal-fired combustion furnace 12 is composed of a burner and a combustion chamber; the coal used in the lump coal combustion unit requires the lump coal to be anthracite or bituminous coal with high volatile matter, low ash content, high calorific value, and low sulfur;

Step 4: A small amount of solid fine-particle material separated by the cyclone preheating separator 32 is dedusted by the bag dust collector 52, and then conveyed by the powder conveyor 62 to the small bag 63 for dedusting, and then fed into the cyclone heating separator 35, so that the chromite is recycled; the temperature of the cyclone preheating separator 32 is not higher than 450°C, and the inlet temperature of the bag dust collector 52 is not higher than 280°C;

Step 5: The wind pressure power of the system is extracted and supplied by the exhaust fan 53, and the flue gas at the outlet of the cyclone preheating separator 32 is transported to the desulfurization system 54 through the exhaust fan 53 after denitration and dust removal; the denitration reactor 51 adopts a selective catalytic reduction (SCR) process, with an inlet temperature of 320°C to 420°C, urea as a reducing agent, and limestone-gypsum wet desulfurization as a desulfurization process;

Step 6: The material is preheated by the preheated flue gas and then fed into the suspension roasting main furnace 41 for roasting and heating. The material in the cone of the cyclone heating separator 34 is fed into the electric furnace through a flap valve. Coke is added as a reducing agent and silica is added as a solvent along the way. Due to the relatively small particle size of the ore and the large specific surface area, as well as the voids and cracks, the electric furnace 71 can quickly achieve deep reduction, and the reduction temperature is 1100-1300°C.

Step 7: The product of electric furnace smelting is ferrochrome, and the by-product is chromium slag. The cooling method of the ferrochrome alloy and the chromium slag is set to cold air cooling. The device is a snake-type cooler. The cold air passes through the snake-type cooler in an indirect heat exchange manner to cool the high-temperature ferrochrome alloy and chromium slag. The hot air after air cooling is connected to the bottom of the suspended roasting main furnace as the combustion-supporting air of the system to achieve energy recycling.

The chromium recovery rate of chromite ore smelting ferrochrome in this embodiment is above 95%, and the total energy consumption of the process system is reduced by about 0.15 tce (equivalent standard coal) compared with the conventional process.

Claims

Fluidized suspension roasting electric furnace to treat chromite ore to smelt ferrochrome alloy device, characterized by comprising a coal combustion unit, a crushing and feeding unit, a heating and preheating unit, a suspension roasting unit, a desulfurization, denitrification and dust removal unit, a return material recovery unit and an electric furnace smelting unit;

The coal combustion unit comprises a speed-regulating coal feeder (11) and a coal combustion furnace (12), wherein the speed-regulating coal feeder (11) is connected to the coal combustion furnace (12); the crushing and feeding unit comprises an ore bin (21), a high-pressure roller mill (22), a storage bin (23), an electronic quantitative feeder (24), and a screw feeder (25), wherein the ore bin (21) is connected to the high-pressure roller mill (22), the high-pressure roller mill (22) is connected to the storage bin (23), the storage bin (23) is connected to the electronic quantitative feeder (24), and the electronic quantitative feeder (24) is connected to the screw feeder (25); the heating and preheating unit comprises a Venturi flash The venturi flash dryer (31) comprises a cyclone preheating separator I (32), a cyclone preheating separator II (33), and a cyclone heater (34). The venturi flash dryer (31) is connected to the cyclone preheating separator I (32), the cyclone preheating separator I (32) is connected to the cyclone heater (34), and the cyclone heater (34) is connected to the cyclone preheating separator II (33). The suspension roasting unit comprises a suspension roasting main furnace (41), a double-layer flap valve (42), a double-layer flap valve (42) is arranged below the suspension roasting main furnace (41), the cyclone preheating separator II (33) is connected to the bottom of the suspension roasting main furnace (41), and the suspension roasting main furnace (41) is connected to the bottom of the suspension roasting main furnace (41). 1) The bottom is connected to the coal combustion furnace (12), and the upper part of the suspended roasting main furnace (41) is connected to the cyclone heater (34); the desulfurization and denitration dust removal unit includes a denitration reactor (51), a large bag dust collector (52), an induced draft fan (53), and a desulfurization wet electrostatic precipitator (54). The denitration reactor (51) is connected to the large bag dust collector (52), the large bag dust collector (52) is connected to the induced draft fan (53), the induced draft fan (53) is connected to the desulfurization system (54), and the cyclone preheating separator I (32) is connected to the denitration reactor (51); the return material recovery unit includes a Roots blower (61), a powder conveyor (62), a small bag The Roots blower (61) is connected to a powder conveyor (62), the powder conveyor (62) is connected to a small bag dust collector (63), and the small bag dust collector (63) is connected to a cyclone heater (34); the electric furnace smelting unit comprises an ore-heating furnace (71), coke (72), silica (73), a flue gas recovery pipeline (74), a preheating recovery pipeline (75), the cyclone heater (34) is connected to the ore-heating furnace (71), the ore-heating furnace (71) is connected to the bottom of a suspension roasting main furnace (41) via the flue gas recovery pipeline (74), and the ore-heating furnace (71) is connected to the bottom of the suspension roasting main furnace (41) via the preheating recovery pipeline (75).
A method for treating chromite ore to smelt ferrochrome alloy by using the fluidized suspension roasting electric furnace as claimed in claim 1, characterized in that it comprises the following steps:

Step (1): crushing the chromite ore with a high pressure roller mill (22), and preheating and separating the obtained chromite powder mineral material through a venturi flash dryer (31) and a cyclone preheating separator I (32) to obtain a powder material and flue gas;

Step (2): The flue gas separated by the cyclone preheating separator I (32) in the above step (1) is transported to the denitration reactor (51) to remove NO x in the flue gas, and then transported to the large bag filter (52) for dust removal. The flue gas separated by the large bag filter (52) is transported to the desulfurization system (54) through the induced draft fan (53) to treat the particulate matter and pollutants to achieve standard or ultra-low emission; the fine-grained material separated by the large bag filter (52) is sent to the desulfurization system (54) through the roots blower (61) and the conveyor The powder is transported from the powder machine (62) to a small bag filter (63) and then returned to the cyclone heater (34);

Step (3): the powder material in the above step (1) is passed into the cyclone preheating separator II (33) for cyclone separation under the action of the rising flue gas of the cyclone heater (34), and the separated flue gas is sent to the Venturi flash dryer (31), and the chromite is recycled; the material separated by the cyclone preheating separator II (33) enters the suspension roasting main furnace (41) for roasting;

Step (4): The high-temperature material after roasting is transported to the cyclone heater (34) for separation, and the separated high-temperature powder material enters the submerged arc furnace (71) for smelting, and a reducing agent (72) and a solvent (73) are added to obtain ferrochrome alloy and chromium slag.
The method for treating chromite ore and smelting ferrochrome alloy in a fluidized suspension roasting electric furnace according to claim 2, characterized in that the chromite ore in step (1) has a Cr2O3 mass content greater than 38%, and a Cr2O3 /FeO mass ratio greater than 2.5; the moisture content in the chromite ore is not higher than 5%; the crushing is to crush the ore to a particle size not higher than 1.5 mm, and the mass content of the ferrochrome powder mineral material with a particle size of -200 mesh is 10% to 20%; the drying temperature of the Chury flash dryer (31) is 400 to 600°C, the temperature of the cyclone preheating separator I (32) is not higher than 450°C, and the preheating time is 20s to 50s.
The method for treating chromite ore to smelt ferrochrome alloy by a fluidized suspension roasting electric furnace according to claim 2 is characterized in that the preheating separation in step (1) converts all iron oxides in the chromite powder ore into α- Fe2O3 and removes crystal water in the chromite powder ore ; and the structure and process design of the cyclone preheating separator are based on a separation efficiency of 80% to 90%.
The method for treating chromite ore in a fluidized suspension roasting electric furnace to smelt a ferrochrome alloy device according to claim 2 is characterized in that in step (1), when the moisture content of the chromite ore is not less than 5%, without using a high-pressure roller mill, an alternative crushing device is to set a powder closed-circuit dry grinding system between the feed end of the preheating section and the conveying end of the screw feeder for shearing, extrusion and crushing; part of the heat released during step (1) is used for preheating the pre-selected concentrate of the system, thereby reducing the energy consumption of the system.
The method for treating chromite ore and smelting ferrochrome alloy in a fluidized suspension roasting electric furnace according to claim 2, characterized in that the wind pressure power of the system in step (2) is extracted and supplied by an induced draft fan (53); the denitration reactor (51) adopts a selective catalytic reduction (SCR) process, the inlet temperature of the denitration reactor (51) is 320°C to 420°C, and the reducing agent of the catalytic reduction (SCR) process is urea; the desulfurization process in the desulfurization system (54) adopts limestone-gypsum wet desulfurization; the inlet temperature of the bag filter (52) is not higher than 280°C; the standard or ultra-low emission is: NOx emission concentration ≤40mg/ Nm3 (dry basis, standard state, 16% O2 ), SO2 emission concentration ≤35mg/ Nm3 (dry basis, standard state, 16% O2 ), dust emission concentration ≤10mg/ Nm3 (dry basis, standard state, 16% O2 ).
The method for treating chromite ore to smelt ferrochrome alloy by a fluidized suspension roasting electric furnace according to claim 2, characterized in that the temperature of the cyclone heating separator (34) described in step (3) is 1000°C to 1200°C, the temperature of the cyclone preheating separator (33) is 700°C to 900°C, and the temperature of the suspension roasting main furnace (41) is 1100°C to 1300°C.
The method for treating chromite ore to smelt ferrochrome alloy in a fluidized suspension roasting electric furnace according to claim 2, characterized in that the reducing agent in step (4) is coke, the solvent is silica; the temperature of the submerged arc furnace (71) is 1100-1300°C; the inlet temperature of the submerged arc furnace (71) is 900°C-1100°C; the smelting produced in the submerged arc furnace (71) The high-temperature exhaust gas is connected to the bottom combustion chamber of the suspension roasting main furnace (41), and the hot air after the high-temperature ferrochrome alloy and chromium slag are heat-exchanged with cold air is connected to the bottom combustion chamber of the suspension roasting main furnace (41), providing the suspension roasting main furnace with combustion-supporting hot air;

The submerged arc furnace (71) is a conventional open or semi-enclosed type, which is convenient for using powdered chromite. When the temperature of the submerged arc furnace (71) for heat storage reduction reaction is 100-300° C., the submerged arc furnace (71) consumes electricity to supply the electricity.

The material is preheated and heated to crack by suspension roasting, thereby generating activated holes, cracks and interfaces that are conducive to the reduction reaction of the particle material in the ore-fired furnace (71), thereby increasing its reaction activity; at a temperature not lower than 1150° C., the chromium-containing crystal phase in the ferrochrome alloy participates in the reduction reaction, the crystal phase structure is destroyed, and the chromium element becomes the main element of the precipitated phase.
The method for treating chromite with a fluidized suspension roasting electric furnace to smelt a ferrochrome alloy device according to claim 2 is characterized in that the entire system provides heat to the suspension roasting unit, the desulfurization, denitrification and dust removal unit and the electric furnace smelting unit through a coal combustion unit; the coal used in the coal combustion unit is anthracite or bituminous coal with high volatility, low ash content, high calorific value and low sulfur; the coal is a lump coal with a particle size not higher than 200 mm; the lump coal treated by a speed-regulating coal feeder (11) has a -200 mesh content of not less than 60%, and the coal particles are not higher than 5 mm; the heating is provided by natural gas or coal gas, and the coal gas includes one of producer gas, coke oven gas, blast furnace gas and gas producer gas.
According to the method of treating chromite ore and smelting ferrochrome alloy by a fluidized suspension roasting electric furnace as described in claim 2, it is characterized in that the cooling mode of the ferrochrome alloy and the chromium slag is set to cold air cooling, the device is a serpentine cooler, and the cold air passes through the serpentine cooler in an indirect heat exchange manner to perform heat exchange cooling on the high-temperature ferrochrome alloy and the chromium slag, and the hot air after air cooling heat exchange is connected to the bottom of the suspension roasting furnace as the combustion-supporting air of the system to realize the recycling of energy.