Abstract : In view of the fact that most converters in China still use wet dedusting method to recover converter gas, the dust removal mechanism is analyzed, and an improvement plan for embedding a wet electrostatic precipitator in an existing wet dedusting system is proposed. The wet dedusting system further improves the contradiction between dust removal efficiency and energy consumption, and realizes super clean discharge of the primary flue gas of the converter.
I. Introduction
Since the development of iron and steel enterprises in the first decade of this century, a huge scale of about 1 billion tons of steel has been formed. According to preliminary statistics, there are 765 converters (14 years of statistics) for key large and medium-sized iron and steel enterprises in the country. The 2/3 amount of primary dedusting of the converter adopts the wet method (OG method) for dust removal, and most of them cannot meet the new emission requirements and are facing renovation.
Dry method (LT system) purification and recovery system is a new generation of dust removal technology, which has been accepted by steel companies for its advantages of water saving, energy saving, land saving, large amount of gas recovery, and high dust removal efficiency; The project basically adopts the dry dust removal process; despite the fact that the wet dust removal system has changed the dry method and has great technical advantages, there is a problem that the space for the internal reconstruction of the factory is limited and the area outside the factory is insufficient due to the built factory building in the implementation process. , making it difficult for the wet system to change the dry method. In order to solve the above problems, a wet electrostatic precipitator for purifying a converter flue gas was born. Converter wet flue gas with a wet electrostatic precipitator can be integrated into the existing wet dedusting system to maximize the use of existing systems, optimize system configuration, improve dust removal efficiency, and achieve super clean emission of converter flue gas.
Second, the converter with a wet smoke electrostatic precipitator process configuration
Common wet ODF system dust removal, mostly using coarse dust (overflow venturi tube, scrubber), fine dust removal (adjustable throat venturi, RSW ring seam) and dehydrator series operation. The high-temperature dusty flue gas produced during the blowing process of the converter is initially cooled by the vaporized cooling flue, and then it is cooled and dusted by the wet method dust removal system. The saturated flue gas after cooling enters the gas blower, and the gas recovery condition is satisfied by the three-way valve. The detailed flow chart of the reclaimed gas that has been recycled and used without satisfying the recycling conditions is shown in Figure 1.
III. Dust removal mechanism and energy consumption analysis of converter wet dedusting system
As mentioned above, the old OG system of converter wet dust removal mainly uses dual venturi dust removal, ie overflow Venturi tube and adjustable diameter Venturi tube. Venturi Venturi pipes with a certain diameter of throat are mainly used for cooling and coarse dedusting. By vaporizing and cooling the flue, the flue gas is cooled to 800-1000°C, rapidly cooled to 70-80°C when overflowing the Venturi tube, and the dust is condensed, and the coarse dust in the flue gas is removed through the expansion section and the dehydrator. The dust removal efficiency is 90%-95%. When the throat speed is 40-60m/s and the outlet flue gas velocity is 15-20m/s, the resistance loss is 3-5kPa. The venturi venturi is equipped with an adjustment mechanism at the throat, which is mainly used for fine dust removal. During the blowing process, the amount of flue gas changes greatly. To maintain the constant speed of the throat flue gas to stabilize the dust removal efficiency, it is necessary to increase or decrease the area of ​​the throat section in accordance with the change in the amount of flue gas and maintain the smoke velocity at the throat. It is also possible to control the differential pressure at the furnace port by adjusting the suction volume of the fan to ensure the quality of the recovered gas. The velocity of the inlet flue gas in the contraction section of the Venturi tube is 15 to 20/s; the resistance in the text is generally 10 to 12 kPa. Due to technical limitations, the double-dust removal structure has the problems of large resistance and high emission concentration. Relatively speaking, the tower text structure of the high-efficiency washing tower and the vent joint venturi tube has low system resistance; the adjustment range of the annular venturi venturi tube is large, the water distribution is uniform, and the purification effect is good; the emission concentration can be reduced to 50 mg/m3; However, when it is necessary to further improve the dust removal efficiency of the tower structure, it is very difficult to implement both the dual text structure and the tower text structure. According to the analysis of the existing converter dust particle size, about 30% of the dust particle size is below 5um. If a single-stage venturi tube is used to remove these dusts, extremely high energy consumption is required. Figure 2 shows the relationship between dust particle removal efficiency and venturi pressure loss below 5um. It can be seen that when the dust removal efficiency is greater than 99%, the corresponding resistance of the single-stage annular venturi is close to 15kPa and the energy consumption is equivalent. Big.
IV. The Wet Electrostatic Precipitator Scheme for the Reformation of a Primary Flue Gas Wet dedusting System in the Converter
In recent years, the energy-saving and emission-reduction indicators of the steel industry have been greatly improved. However, due to the large scale, the total energy consumption is high and the total amount of pollutants discharged is large. In particular, some of the main steel production capacity areas have exceeded the environmental carrying capacity. It is foreseeable that in these areas, it is necessary to advance the reform of advanced clean production technologies and further increase the level of energy conservation and emission reduction.
As mentioned above, the use of venturi fine dust removal to achieve ultra-clean emission of smoke, high energy consumption, if you want to further improve dust removal efficiency, single-stage venturi pressure loss needs to be increased to 20kPa or more, excessive energy consumption . Therefore, in the transformation of the primary flue gas wet dedusting system, a series of primary wet electrostatic precipitators can be used on the existing wet process system to remove the small particle dust using the electrostatic adsorption principle. The process flow chart is shown in Figure 3 .
Similar to conventional high-pressure electrostatic precipitators, the wet electrostatic precipitator used in the conversion of primary flue gas from the converter consumes less energy and has a high dust removal efficiency. It is suitable for the removal of 0.01-50 μm dust. Due to the use of flushing and cleaning, dry electrostatic dust removal can be avoided. The secondary dust phenomenon in the dust cleaning greatly improves the dust removal efficiency and the stability of the dust removal. By embedding a wet electrostatic precipitator into an existing wet process system, super clean exhaust gas (10mg/m3) of the converter can be achieved without changing the original system, while the equipment itself occupies less land and the investment cost Low, the combination of equipment is flexible and convenient, and it is one of the choices for the conversion of converter wet dust removal systems. In terms of operating costs, according to the configuration, the cost is 0.5~1 yuan/ton steel.
5 Conclusion
As the country's emission requirements for steel enterprises are further raised, the role of wet electrostatic precipitators in flue gasification will become more apparent. In addition to the possibility of embedding wet electrostatic precipitators in existing wet dedusting systems, a complete flue gas reform of converters can also be implemented. New OG + wet electricity and LT + wet electricity models are used to achieve ultra-clean emission of the primary flue gas from the converter.
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