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Analysis of Ultra-Low Emission Technology of Converter Gas Dry Bag Dedusting System

浏览 Author Admin Browse Published 19/09/04

Analysis of Ultra-Low Emission Technology of Converter Gas Dry Bag Dedusting System

1 Overview At present, there are mainly three types of purification and recovery systems for converter steelmaking flue gas: ① wet dust removal system (OG method). The high-temperature flue gas produced by the converter is cooled to 800 ~ 1 000 ℃ through the vaporization cooling flue, and then the majority of dust in the system is removed by the action of a venturi tube and a dehydrator. ② Dry dust removal system. By adopting an organic combination of an evaporative cooler and an electrostatic precipitator, the evaporative cooler captures large particles of dust, and the electrostatic precipitator captures fine particles of dust. ③Semi-dry method dust removal system. Combining some of the advantages of the dry system and the wet system, it adopts the structure of "evaporative cooler + ring seam Venturi tube". The system contains both dry ash captured by cold evaporation and sludge collected by ring seams. Each of the three technical routes has its own characteristics, but the advantages of the dry system are more obvious from the perspectives of energy saving, consumption reduction, and emissions. Therefore, the converter gas dry dedusting system is the third item in the "National Key Energy-Saving and Low-Carbon Technology Promotion Catalog (2017 Edition, Energy Conservation Part)" compiled by the National Development and Reform Commission, and it is also the "Three Dry, Three Uses" Key technologies. 2 Converter dry dust removal system process Figure 1 shows the process flow of the converter gas dry dust removal system.

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The high-temperature flue gas (1 400 ~ 1 600 ℃) generated in the converter during smelting is cooled by the vaporized cooling flue, the temperature is reduced to 800 ~ 1 000 ℃, and then the cooling is continued through the evaporative cooler, and the flue gas temperature is reduced to about 250 ℃ At the same time of cooling, the flue gas was quenched and tempered, so that the specific resistance of the dust in the flue gas is more conducive to the capture of the electrostatic precipitator. 30% to 40% of the coarse dust in the flue gas is captured by the evaporative cooler. The quenched and tempered flue gas is naturally cooled by the waste gas pipe, the flue gas temperature drops to about 150 ℃, enters the circular electric precipitator, and the dust content after purification by the electric precipitator can reach below 15 mg / Nm3. The captured dust is dry and can be transported by car and sent to a sintering plant for recycling. The fan adopts inverter frequency conversion speed regulation, which can realize flow tracking adjustment to ensure the quantity and quality of gas recovery, save electricity and reduce consumption. The gas switching station consists of 2 hydraulically driven cup valves. When the flue gas meets the recovery conditions, the recovery cup valve opens and the bleed cup valve closes. The flue gas enters the gas cooler through the recovery cup valve, and the temperature is reduced from 150 ℃ to below 70 ℃ into the gas cabinet by spray cooling. When the flue gas does not meet the recovery conditions, the bleed cup valve is opened, the bleed cup valve is closed, and the flue gas is ignited by the bleed chimney through the bleed cup valve. 3 Status of Emissions from Converter Dry Dedusting System The average value of the dust concentration of the newly-converted dry-dust converter is below 15 mg / Nm3. However, the country currently has higher requirements for emissions in some areas. The General Office of the State Council also issued the "Notice on Printing and Distributing Measures for the Implementation of the Air Pollution Prevention and Control Action Plan," and imposed compulsory regulations on various types of air pollution in various places. Therefore, many iron and steel enterprises have put forward higher requirements for the emission-the average value of the dust concentration in the emission is ≤10 mg / Nm3. However, the electrostatic precipitator itself is limited by the technical bottlenecks inherent in electrostatic precipitators, such as back corona caused by high specific resistance dust, secondary dust caused by vibration, and insufficient charging of fine dust. It is difficult to achieve stable outlet emission concentration ≤10mg / Nm3. Under this background, the research on the ultra-low emission technology route of the converter gas dry dust removal system is proposed. 4 Terminal fine dust removal route 4.1 Add wet electrostatic precipitator after dry electric precipitator Add wet cylindrical electric precipitator after the cup valve of the original dry dedusting system and before the chimney. After the flue gas has been purified by the converter gas dry electrostatic precipitator, the dust content is below 15 mg / Nm3. And then through wet electrostatic precipitator for further fine dust removal, the flue gas emission concentration can be far below 10 mg / Nm3, and even below 5 mg / Nm3. This type of wet electrostatic precipitator must use a cylindrical type to ensure the plunger-like flow of smoke in the wet electricity. There is no dead angle in the equipment, which can reduce the possibility of explosion. The cylindrical wet electricity can be designed into a vertical type. And horizontal. Vertical wet electricity generally uses a honeycomb type, and the relative electric field wind speed can be larger than horizontal wet electricity. However, due to the vertical structure, the dust collector can only produce one electric field. Therefore, if there is a problem with the electric field, the entire dust collector will be unusable and smelting must be stopped. Horizontal wet electricity generally adopts plate wire type. Two or more electric fields can be set to ensure the stability of the system. When an electric field fails, it will not affect the stable operation of the system and will not cause production shutdown. But compared with vertical wet electricity, its investment cost is much higher. No matter it adopts horizontal wet electricity or vertical wet electricity, it will increase the possibility of explosion to the entire system, and it has higher requirements on the stability and reliability of the system. The disadvantages of increasing wet electrostatic precipitators are as follows: ① The amount of circulating water and energy consumption increase. Increasing the wet electricity after the dry electrostatic precipitator also needs to solve one problem, which is to spray water to cool down and saturate the flue gas. Before entering the wet electricity, the temperature of the flue gas should be reduced to below 60 ℃ through spray cooling to saturate the flue gas and ensure the dust removal efficiency of the wet electrostatic precipitator. ② The smoke is saturated after spraying water to cool down, and the “white plume” phenomenon will appear at the chimney outlet. In some areas, it is clear that "de-whitening" governance is required, and the investment and operation and maintenance costs are very high. ③ A set of water treatment and sludge treatment equipment must be added, and the cost increase basically accounts for 15% to 25% of the entire system cost. ④ The technical route of increasing wet electricity at the end introduces the possibility of explosion. Therefore, it is not recommended to use a technical route that adds a wet electrostatic precipitator at the end to ensure emissions.

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