Learn ferrosilicon furnace characteristics and treatment methods of flue gas

Submerged arc furnace for ferrochrome production introduction

Ferrosilicon furnace, also known as electric arc furnace or resistance furnace, is an industrial electric furnace with huge power consumption. It mainly consists of furnace shell, furnace cover, furnace lining, short net, water cooling system, smoke exhaust system, dust removal system, electrode shell, electrode pressing and lifting system, loading and unloading system, holder, burn-through device, hydraulic system, submerged arc furnace transformer and various electrical equipment and other components.

It is mainly used for reducing smelting ores, carbonaceous reducing agents and solvents and other raw materials main production, like ferrosilicon, ferromanganese, ferrochromium, ferrotungsten, silicon-manganese alloy, ferroalloy and chemical raw materials such as stone.

Its working characteristic is to use carbonaceous or magnesia refractory material as furnace lining and use self-cultivation electrode electricity. The pole is inserted into the charge for arc management, and the energy and current of the arc are used to pass through the charge.

The resistance of the charge produces energy to smelt the metal, feeding continuously, intermittently tapping the slag, continuously an industrial electric furnace for continuous operation.

Submerged electric arc furnace's flue gas characteristics

During the smelting and production process of the ferrosilicon furnace, a large amount of high-temperature flue gas with fine dust particles is generated. Since the air excess coefficient is very large, it is basically close to the air composition.

The soot in the flue gas is mainly composed of two parts, one part is the mechanical blowout of the charge, mainly coke powder and coal powder; the other part is the gaseous Sio formed by the reduction of Sio2 in the silica. These Sio should continue to be reduced to silicon, Ferrosilicon is formed, but in fact a part of it escapes from the material surface and is oxidized into SiO2 in the air to form amorphous very fine particles, which are brought out of the furnace by the flue gas. The former accounts for about 10% to 20% of the two parts of the smoke. , the latter accounts for about 80% to 90%, and the amount of ferrosilicon soot depends on the recovery rate of silicon in the smelting process.

To sum up, the characteristics of the flue gas and dust of the ferrosilicon electric furnace are:

1. The amount of flue gas is large. In order to reduce the amount of flue gas, the temperature of the flue gas must be increased, so there must be a cooling method before dust removal.

2. The heat content of flue gas is large, and the heat content in 1 ton of 75% ferrosilicon flue gas is equivalent to the input electricity.

3. Fine dust and high specific resistance. A high-efficiency dust collector must be used to achieve the purpose of dust removal.

Ferrosilicon furnace flue gas treatment method

Generally, the temperature of ferrosilicon flue gas is between 375-600 °C, mostly around 450 °C, and the content of smoke (powder) dust in the flue gas is 5~8g/m3. Generally, there are two treatment methods, wet purification and dry purification.

The wet purification equipment is generally a scrubber or a Venturi scrubber. Although the equipment is simple and the investment is low, there is a large power consumption (about 3 to 6 times that of the bag filter), and the water treatment system is very complicated, and the processing The dust cannot be used and so on.

Dry purification generally uses electrostatic precipitator and bag dust collector. The main problem of electrostatic precipitator is that the specific resistance of Hui silicon dust is high, and water must be added to the flue gas to increase the humidity, so that the specific resistance can be lowered to achieve the dust removal effect. In addition to the problems of acid corrosion and water treatment, and the investment is expensive: almost all the peripherals use filter bag dust removal technology.

Therefore, the flue gas of the ferrosilicon furnace is generally treated by air cooling + cyclone dust collector + bag filter. When the flue gas purification system of the ferrosilicon furnace is running, the dust-laden flue gas is led to the natural air cooler from the low hood through the air duct, and the flue gas temperature is cooled from 450 ℃ to below 250 ℃, and then enters the cyclone dust collector to remove the dust in the flue gas. Large particles of dust and carbon particles with sparks are removed to prevent burning of the cloth bag and improve the grade of silicon powder, and then enter the bag filter for filtration. In order to ensure the safe operation of the bag filter, an automatic air mixing valve is generally installed on the pipeline in front of the fan inlet. This valve is connected to the temperature measuring point at the inlet of the dust collector. When the temperature is greater than 250 °C, the valve is automatically opened, and cold air is mixed to reduce the temperature of the flue gas. , to ensure the safe operation of the dust collector.

The flue gas treatment system of the ferrosilicon furnace is also divided into positive pressure type and negative pressure type. The positive pressure type means that the main fan of the system is installed in front of the bag filter, and the flue gas is directly discharged from the top of the bag house of the bag filter after treatment. The negative pressure dust removal method means that the fan is installed after the bag filter, and the flue gas is finally discharged through the chimney. Both dust removal methods have advantages and disadvantages. Among them, the positive pressure dust collector system has low resistance, relatively low air leakage rate, and good collection efficiency of ferrosilicon furnace flue gas. During the production of ferrosilicon furnace, the emission of unorganized dust in the workshop is relatively small. However, the treated flue gas is directly discharged through the top of the bag house of the bag filter, which is not conducive to the monitoring and management of pollution sources; the negative pressure dust removal method is adopted, and the flue gas is discharged through the chimney after treatment, which is conducive to the standardized management of pollution sources and the control of waste gas. However, the system has large operating resistance and high operating power consumption, which is not conducive to energy saving. In short, both treatment methods have advantages and disadvantages, but the treated flue gas can be discharged up to the standard. At present, the positive pressure dust removal method is widely used.