Flue gas purification system of iron ore suspension magnetization roasting furnace

Abstract

The invention discloses an iron ore suspension magnetization roasting furnace flue gas purification system, which comprises a roasting main furnace, roasting flue gas discharged from the roasting main furnace sequentially enters a main furnace cyclone and a secondary preheating cyclone, and then enters an SCR denitration tower, flue gas discharged from the SCR denitration tower enters a Venturi preheater, and flue gas discharged from the Venturi preheater enters a secondary preheating cyclone. The flue gas enters a Venturi preheater and exchanges heat with iron ore powder added into the Venturi preheater, then the flue gas subjected to heat exchange and cooling enters a first-stage preheating cyclone cylinder, the flue gas subjected to gas-solid separation enters a subsequent bag-type dust collector, a wet desulfurization tower and a wet electric dust collector, and then the purified flue gas is discharged into the atmosphere through a top chimney; compared with the prior art, investment cost and operation cost can be reduced, system operation is safer, arrangement is more compact, ultra-low emission can be achieved even under the condition that a wet-type electric dust remover is not arranged, and the investment cost, the occupied area and the operation cost of the whole device are obviously reduced.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas desulfurization, denitrification and dust removal, in particular to a flue gas desulfurization, denitrification and dust removal purification system for an iron ore suspension magnetization roasting furnace. Background Art

[0002] China's crude steel output has long maintained a proportion of more than 50% of the world's total output. In 2024, my country's crude steel output will exceed 1 billion tons, accounting for about 53% of the world's total. A large amount of iron ore needs to be imported; my country has rich resources of difficult-to-select iron oxide, which mainly have the characteristics of fine crystal size, complex composition, weak magnetism, etc. It is difficult to obtain ideal technical and economic indicators using conventional mineral processing technology, so a large amount of resources have been abandoned for a long time and cannot be effectively used.

[0003] In recent years, suspended magnetization roasting technology has begun to be applied and developed in the iron-making industry. It mainly changes the magnetic properties of the ore, thereby optimizing the subsequent magnetic separation efficiency, and increasing the iron recovery rate from 50-60% in traditional processes to 80-90%, which can produce better economic efficiency. Practice has proved that it is an effective utilization method that suits China's reality.

[0004] Since the iron ore is roasted in a suspended magnetized roasting furnace, a large amount of waste gas will be generated, and the negative pressure is relatively large, about -15000Pa. The waste gas composition varies according to the iron ore composition, SO 2 The concentration can reach more than 3000mg / Nm³, NOx is generally around 200-300mg / Nm³, the dust concentration in the flue gas at the denitrification inlet is very high, reaching about 100g / Nm³, and the total iron content in the ash is above 40%, with great abrasive turbidity; in addition, the oxygen content at the desulfurization inlet is relatively high, at about 16-18%.

[0005] At present, there are few suspended magnetized roasting furnace production lines for iron ore, and there is no mature exhaust gas purification technology for this working condition on the market. Basically, the exhaust gas treatment process of other roasting furnaces is still applied. It mainly has the following two technologies: one is an alumina roasting furnace flue gas zero emission system with the authorization announcement number CN210410140U, which adopts SNCR+SCR for denitrification, and SNCR spray guns are arranged at the inlet / outlet of the secondary preheating separator at the roasting furnace outlet. The core of the suspended magnetized roasting furnace iron ore lies in mineral reduction modification and magnetic enhancement. Generally, the maximum combustion temperature is controlled at about 900℃, and the furnace top outlet is controlled at 500-600℃. Therefore, no matter at the main furnace outlet or at the inlet and outlet of the secondary preheating cyclone, there is no condition to arrange SNCR spray guns, which can only A large amount of reducing agent is wasted, and the denitrification efficiency is very low. Of course, a spray gun can also be arranged at the throat of the main roasting furnace, but the reducing agent consumption is large and the economy is not high. In dust removal, the patent recommends the use of an electrostatic precipitator, mainly considering that the flue gas temperature coming out of the roasting furnace is relatively high. The use of bag dust collectors will burn the filter material, and the use of metal filter bags is too expensive. However, when an electrostatic precipitator is used, the outlet dust concentration is relatively high, generally reaching 30-50 mg / Nm³. To achieve ultra-clean emissions from the chimney, it is necessary to rely on the dust removal efficiency of desulfurization and subsequently add a wet electrostatic precipitator to reach 5-10 mg / Nm³; at the same time, the high dust concentration at the inlet of the induced draft fan will also wear the blades; in addition, due to the high smoke temperature, the patent requires a more reliable flue gas cooling device to be installed in front of the desulfurization tower, otherwise the equipment and materials in the tower will be burned.

[0006] The other is the patent "An industrial ore-fired furnace flue gas desulfurization and denitrification device" with authorization announcement number CN218307178 U. The SNCR technology used in its denitrification is also not suitable for the denitrification purification of suspended magnetized roasting furnace flue gas. Taking into account the high dust concentration and high abrasiveness at the denitrification inlet, which will wash the catalyst, it adopts the process of dust removal and desulfurization before denitrification; because of the temperature requirements of the denitrification catalyst, it adopts dry / semi-dry desulfurization to minimize the temperature drop during the desulfurization and dust removal process; however, the low-temperature catalyst needs to ensure that the inlet flue gas temperature is above 180 degrees. If the temperature is not enough, the flue gas needs to be heated, which wastes energy. Compared with the high-temperature catalyst, the low-temperature catalyst is more expensive and has a shorter lifespan, which increases the equipment investment and operating costs. In addition, since a bag dust collector is set after the dry method and the denitrification is arranged at the rear end, the risk of dust exceeding the standard is also relatively large. Summary of the invention

[0007] The purpose of the present invention is to solve the problems in the prior art and to propose a flue gas purification system for an iron ore suspended magnetization roasting furnace, which can reduce investment costs and operating costs, and the system operation is safer and the layout is more compact. Even in the absence of wet electrostatic precipitators, ultra-low emissions can be achieved, which significantly reduces the investment cost, floor space and operating costs of the entire device.

[0008] To achieve the above-mentioned purpose, the present invention proposes a flue gas purification system for an iron ore suspended magnetization roasting furnace, comprising a roasting main furnace, wherein the flue gas outlet of the roasting main furnace is sequentially connected to a main furnace cyclone, a secondary preheating cyclone, an SCR denitrification tower, a venturi preheater, a primary preheating cyclone, a bag filter, an induced draft fan and a wet desulfurization tower, and the roasting flue gas discharged from the roasting main furnace sequentially enters the main furnace cyclone, the secondary preheating cyclone, and then enters the SCR denitrification tower. The flue gas coming out of the SCR denitrification tower enters the Venturi preheater, exchanges heat with the iron ore powder added into the Venturi preheater, and then the flue gas after heat exchange and cooling enters the first-stage preheating cyclone. The flue gas coming out after gas-solid separation in the first-stage preheating cyclone enters the bag filter. The flue gas coming out after purification in the bag filter is pressurized by the induced draft fan and enters the wet desulfurization tower. The desulfurized flue gas is discharged into the atmosphere through the wet desulfurization tower, the wet electrostatic precipitator, and the top chimney.

[0009] Preferably, the inlet flue of the SCR denitrification tower and the inlet flue of the Venturi preheater are respectively provided with cold air valves.

[0010] Preferably, the filter material of the bag filter is PTFE or a blended structure of PTFE and other high-performance fibers.

[0011] Preferably, a wet electrostatic precipitator and a top chimney are arranged above the wet desulfurization tower to realize a three-tower arrangement.

[0012] Preferably, when the dust emission requirement at the chimney outlet is 5 mg / Nm³, a wet electrostatic precipitator may not be provided.

[0013] Preferably, the inlet flue of the wet desulfurization tower is provided with an emergency cooling device.

[0014] Preferably, denitration adopts SCR technology, the inlet flue gas temperature of the SCR denitration tower is 320-400°C, and a medium-high temperature conventional catalyst is used.

[0015] Preferably, the reducing agent supply of the SCR denitration tower adopts ammonia gasification, urea hydrolysis or pyrolysis process.

[0016] The beneficial effects of the present invention are as follows: considering the flue gas temperature distribution on the top of the suspended magnetized roasting furnace and the primary and secondary preheating cyclones, it is not suitable to adopt the conventional SNCR+SCR combined denitrification of the roasting furnace, but to adopt the medium and high temperature SCR technology, which can not only ensure the denitrification efficiency, but also greatly save the reducing agent consumption.

[0017] According to the flue gas characteristics of the suspended magnetized roasting furnace, a bag dust collector is used to improve the efficiency of mineral recovery, which not only saves investment but also ensures the subsequent desulfurization conditions, making it easy to achieve ultra-low emissions or even near-zero emissions of dust.

[0018] The three-tower (dual-tower) integration technology is adopted to significantly reduce the equipment layout space, while saving investment costs, operating power consumption, etc.

[0019] When using conventional wet desulfurization, it is only necessary to set up an emergency spray cooling device under fault conditions to ensure the safety of equipment in the desulfurization tower and that the desulfurization efficiency meets ultra-low emission requirements.

[0020] As bag dust collector is installed before desulfurization, the dust at the desulfurization tower inlet can be guaranteed to be below 5mg / Nm³. If wet electrostatic precipitator is installed, the dust concentration of chimney emissions can be less than 2mg / Nm³, truly achieving near-zero emissions.

[0021] Compared with the existing technology, it can reduce investment cost and operating cost, and the system operation is safer and the layout is more compact. Even without wet electrostatic precipitator, it can achieve ultra-low emissions, which significantly reduces the investment cost, floor space and operating expenses of the whole device.

[0022] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of a flue gas purification system for an iron ore suspension magnetization roasting furnace according to Example 1 of the present invention; Figure 2 This is a schematic structural diagram of a flue gas purification system for an iron ore suspended magnetization roasting furnace according to Example 2 of the present invention.

[0024] In the figure: 1-roasting main furnace, 2-main furnace cyclone, 3-first-stage preheating cyclone, 4-second-stage preheating cyclone, 5-SCR denitrification tower, 6-Venturi preheater, 7-cold air valve, 8-bag dust collector, 9-induced draft fan, 10-wet desulfurization tower, 11-wet electrostatic precipitator, 12-top chimney. DETAILED DESCRIPTION

[0025] Example 1 See also Figure 1The present invention discloses an iron ore suspension magnetization roasting furnace flue gas purification system, comprising a roasting main furnace 1, wherein the flue gas outlet of the roasting main furnace 1 is sequentially connected to a main furnace cyclone 2, a secondary preheating cyclone 4, an SCR denitration tower 5, a venturi preheater 6, a primary preheating cyclone 3, a bag filter 8, an induced draft fan 9 and a wet desulfurization tower 10, and the roasting flue gas discharged from the roasting main furnace 1 sequentially enters the main furnace cyclone 2, the secondary preheating cyclone 4, and then enters the SCR denitration tower 5, wherein the flue gas discharged from the roasting main furnace 1 sequentially enters the main furnace cyclone 2, the secondary preheating cyclone 4, and then enters the SCR denitration tower 5. The flue gas coming out of the SCR denitrification tower 5 enters the venturi preheater 6, exchanges heat with the iron ore powder added into the venturi preheater 6, and then the flue gas after heat exchange and cooling enters the primary preheating cyclone 3. The flue gas coming out after gas-solid separation in the primary preheating cyclone 3 enters the bag filter 8. The flue gas coming out after purification in the bag filter 8 is pressurized by the induced draft fan 9 and enters the wet desulfurization tower 10. The desulfurized flue gas is discharged into the atmosphere through the chimney 12 at the top of the wet desulfurization tower 10.

[0026] The inlet flue of the SCR denitration tower 5 and the inlet flue of the venturi preheater 6 are respectively provided with a cold air valve 7 .

[0027] The filter material of the bag filter 8 is PTFE or a blended structure of PTFE and other high-performance fibers.

[0028] A top chimney 12 is arranged above the wet desulfurization tower 10, and the two towers are arranged in one.

[0029] The inlet flue gas temperature of the SCR denitration tower 5 is 320-400° C., and the SCR denitration adopts a medium-high temperature conventional catalyst.

[0030] The reducing agent supply of the SCR denitration tower 5 adopts ammonia gasification, urea hydrolysis or pyrolysis process.

[0031] The inlet flue of the wet desulfurization tower 10 is provided with an emergency cooling device.

[0032] Example 2 See also Figure 2 The difference from Example 1 is that a wet electrostatic precipitator 11 is arranged above the wet desulfurization tower 10, so that the dust concentration emitted from the chimney can be less than 2 mg / Nm³, truly achieving near-zero emissions.

[0033] Working process of the present invention: In the working process of the iron ore suspension magnetization roasting furnace flue gas purification system of the present invention, the flue gas of the iron ore suspension magnetization roasting furnace is controlled at 500-600°C at the flue gas outlet of the roasting main furnace 1, and is generally controlled at 320-400°C at the outlet temperature of the secondary preheating cyclone 4, which just meets the temperature requirement of the medium and high temperature SCR denitration catalyst; after the flue gas enters the SCR denitration tower 5, NOx can be reduced to 50mg / Nm³ through the action of 2-3 catalysts, and the temperature of the flue gas after denitration flue gas fluctuates within the range of 130-230°C after passing through the Venturi preheater 6 and the primary preheating cyclone 3, so the use of PTFE filter material can meet the requirements, and the bag outlet can ensure that the dust concentration is 10mg / Nm³, and after the roasting furnace system operates normally, the flue gas temperature at the desulfurization inlet can be guaranteed to be stable below 150°C, meeting the temperature conditions for long-term operation of desulfurization; and then through the wet desulfurization tower 10, after 3-5 layers of spraying and multi-layer demisters, SO 2 It can be reduced to below 35mg / Nm³, and dust can be reduced to below 5mg / Nm³. After that, a wet electrostatic precipitator 11 is configured, and the outlet dust can be reduced to below 2mg / Nm³.

[0034] In addition, the inlet flue of the desulfurization tower should be equipped with a flue gas emergency cooling device to ensure the safe operation of the desulfurization tower under fault conditions.

[0035] When the entire roasting furnace system fails and the smoke temperature suddenly rises to exceed the catalyst temperature resistance value or the bag filter material temperature limit, the corresponding cold air valve 7 will automatically open to ensure that the inlet smoke temperature of the SCR denitrification tower 5 and the bag filter 8 does not exceed the set value.

[0036] In order to reduce the investment cost, floor space and operating power consumption of the entire purification system, the wet desulfurization tower 10, the wet electrostatic precipitator 11 and the top chimney 12 are integrated into one and arranged vertically.

[0037] The above embodiments are intended to illustrate the present invention, not to limit the present invention. Any solution that is a simple transformation of the present invention belongs to the protection scope of the present invention.

Claims

1. An iron ore suspension magnetization roasting furnace flue gas purification system, characterized in that: The invention comprises a main roasting furnace (1), wherein the flue gas outlet of the main roasting furnace (1) is connected in sequence to a main furnace cyclone (2), a secondary preheating cyclone (4), an SCR denitrification tower (5), a venturi preheater (6), a primary preheating cyclone (3), a bag filter (8), an induced draft fan (9) and a wet desulfurization tower (10); the roasting flue gas discharged from the main roasting furnace (1) enters in sequence the main furnace cyclone (2), the secondary preheating cyclone (4), and then enters the SCR denitrification tower (5); the flue gas discharged from the SCR denitrification tower (5) The flue gas enters the venturi preheater (6) and exchanges heat with the iron ore powder added to the venturi preheater (6). The flue gas after heat exchange and cooling enters the primary preheating cyclone (3). The flue gas after gas-solid separation in the primary preheating cyclone (3) enters the bag filter (8). The flue gas after purification in the bag filter (8) is pressurized by the induced draft fan (9) and enters the wet desulfurization tower (10). The desulfurized flue gas is discharged into the atmosphere through the wet desulfurization tower (10), the wet electrostatic precipitator (11), and the top chimney (12).

2. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 1, characterized in that: The inlet flue of the SCR denitration tower (5) and the inlet flue of the Venturi preheater (6) are respectively provided with a cold air valve (7).

3. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 1, characterized in that: The filter material of the bag filter (8) is PTFE or a blended structure of PTFE and other high-performance fibers.

4. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 1, characterized in that: A wet electrostatic precipitator (11) and a top chimney (12) are arranged above the wet desulfurization tower (10), adopting a three-tower arrangement.

5. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 4, characterized in that: When the dust emission requirement at the top chimney outlet is 5 mg / Nm³, a wet electrostatic precipitator (11) may not be installed.

6. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 1, characterized in that: The inlet flue of the wet desulfurization tower (10) is provided with an emergency cooling device.

7. The iron ore suspension magnetization roasting furnace flue gas purification system according to claim 1, characterized in that: Denitration adopts SCR technology, the inlet flue gas temperature of the SCR denitration tower (5) is 320-400°C, and a medium-high temperature conventional catalyst is used.

8. An iron ore suspension magnetization roasting furnace flue gas purification system according to any one of claims 1 to 7, characterized in that: The reducing agent supply of the SCR denitration tower (5) adopts ammonia gasification, urea hydrolysis or pyrolysis process.

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