1.Foreword A large number of flue gas is generated when the converter of a steel plant is mixed with molten iron, added waste steel, tilted tapping, and slag is discharged. During the converter blowing, part of the flue gas also escapes from the cover skirt and the furnace mouth. Converter secondary flue gas. In order to prevent secondary flue gas from polluting the environment, a secondary flue gas dust removal system is set up. According to the existence of the secondary flue gas dust removal system of the converter in the same industry, there are converter secondary flue gas dust removal systems. After time, the resistance increases and the dust removal efficiency decreases; the secondary flue gas temperature of the converter is high, which sometimes causes the dust removal bag to be damaged, resulting in the emission concentration of _over_standard; the fan speed of the bag dust removal system is constant. When the converter is in a non-hot metal state, the fan Full-speed operation causes waste of electrical energy; these defects directly affect the dust removal effect and the operating cost is also high.
In response to these problems, the company adopted the following measures when designing a secondary flue gas bag dust removal system for the steel plant:
(1) The converter's secondary flue bag dust collector uses a long-bag low-pressure pulse dust collector.
(2) The air volume of the converter dust removal system is directly added to the secondary flue gas bag dust removal system of the converter to achieve a cooling effect, so that the flue gas temperature at the inlet of the bag dust collector is lower than 120 ° C.
(3) In order to save energy and reduce consumption, the fan design uses a variable frequency motor to adjust the fan speed according to changes in the smelting conditions.
2. System design
2.1. Determination of the dust collector scheme The dust extraction hood of the secondary flue gas precipitator of the converter of the steel plant is to completely seal the surroundings of the converter above the operating layer of the converter, and set a dust extraction hood in front of the furnace. The dust extraction hood is a type of air suction on both sides, which is composed of the dust extraction hood main body and the movable curtain.Due to the high temperature of the flue gas at the mouth of the dust extraction hood, in order to prevent the dust extraction hood from being burned and deformed by the strong heat radiation for a long time, The inside of the fume hood is lined with refractory material under strong heat radiation. The secondary flue gas of the dust collection hood in front of the furnace enters the bag dust collector through the pipeline. The purified flue gas is discharged through the fan and the chimney, and the emission concentration is controlled at 50mg / m3.
2.2. Determination of air volume of bag dust removal system
2.2.1. The air volume of the secondary flue gas dust removal system of the converter is _ when it is mixed with the molten iron, and the secondary flue gas volume of the converter is as follows:
1) The flue gas volume of molten iron is 270,000m3 / h; working temperature: 220 ℃;
2), the volume of blowing flue gas is 210000m3 / h; working temperature: 80 ℃;
3) The smoke volume of the dismantling furnace is 120,000m3 / h; working temperature: 80 ℃;
4) Oxygen lance maintenance flue gas volume is 30000m3 / h; working temperature: 80 ℃;
2.2.2. In order to avoid the high cost of the dust bag of the bag filter due to the high temperature of the flue gas, the flue gas temperature is cooled below 120 ° C. The design adds the dust removal air volume of the converter charging system to the secondary flue gas dust removal system of the converter, which directly reduces the flue gas temperature of the system on the one hand, and also solves the dust removal problem of the converter charging system on the other.
Using the dust removal air volume of the converter feeding system as cold air, direct air cooling means directly entering the cold air in the high temperature flue gas to cool it into the bag filter, and calculating according to the thermal balance method, reducing the secondary flue gas temperature of the converter from 220 ° C to 120 ℃, need to infiltrate the cold air of 227803m3 / h, namely the dust removal air volume of the converter feeding system. The total air volume of the system includes the original air volume and the amount of direct infiltration of cold air (the dust removal air volume of the converter feeding system), which totals 497,803 m3 / h, which is 7.17 × 105 m3 / h when converted to a flue gas temperature of 120 ° C.
2.3. Resistance of converter bag dust removal system Resistance of converter bag dust removal system includes equipment resistance and total pressure loss of air duct. The resistance of the equipment includes the resistance of the bag filter and muffler.The total pressure loss of the air duct includes local pressure loss and pressure loss along the way.It is determined that the wind speed in the tube is 30m / s when it is molten with molten iron, and 25m / s when it is blown.The remaining working conditions are 17m / s, it is calculated that the total pressure loss of the duct is 3210Pa.
2.4. Selection of fan According to the operating experience of bag dust collectors in other steel plants, the air volume of the fan should be added to the system air volume by 20%, and the total pressure is the total pressure loss of the system: the total pressure loss of the air duct is 3010Pa, and the resistance of the dust collector 1500Pa, muffler resistance 150Pa, wind motor pressure loss 50Pa, the sum of 4 items is 5110Pa, taking the reserve factor of 1.15, the total pressure of the fan is 5877Pa, and the motor shaft power is 2032kW. When selecting a fan, the fan's intermediate support (F-type) transmission method should be used to balance operation. Especially the fan, because the impeller wear and dust will affect the balance of the rotor, and it is easy to cause the fan to vibrate. Since the working conditions of the converter are changed, if the necessary adjustment of the fan speed is not carried out, a large amount of power will be wasted. Therefore, the fan speed should be adjusted according to the required air volume of the converter. This design uses a variable frequency motor.
2.5.Selection of dust collectorIn order to make the resistance of the equipment lower, the converter's secondary flue gas dust removal uses a long-bag low-pressure large-scale pulse bag dust collector suitable for the secondary flue gas treatment of the converter.Its main features are:
1), converter low-pressure pulse dust collector is mainly composed of box, ash hopper, air inlet equalizing pipe, outlet air pipe, bracket, filter bag and blowing device, ash discharge device, etc. It adopts thin-plate type poppet valve to realize offline three-state, dust removal technology, and reliable work.
2). The reasonable design of the air inlet equalizing pipe and the ash bucket diversion technology of the converter bag filter removes the uneven air flow in each compartment of the general bag filter.
3). The bag structure of the converter low-pressure pulse dust collector has various structures (octagonal, circular, etc.) according to different working conditions. Changing the filter bag is quick and easy.
4) The upper end of the filter bag of the converter bag filter adopts spring expansion ring, which is well sealed; the standard length of the bag cage for maintenance and replacement is 6m, and it can be increased by 1-2m as required.
5) The service life of the consumable diaphragm of the electromagnetic pulse valve of the converter bag filter is greater than 1 million times. Dust collector control can adopt _ program controller with differential pressure, timing, and manual control methods to achieve comprehensive system control of the off-line network of the dust collector, pulse valve, and ash discharge room.
6) Strong cleaning ability. During dust removal, the acceleration of the filter bag wall is 60 to 200 times the acceleration of gravity g (back blower bag filter can only reach 3 to 5 g ), so the resistance of the equipment is low. Even for the fumes of various furnaces (such as steelmaking electric arc furnaces), the normal equipment resistance (less than 1600Pa) can be maintained.
7) Low injection pressure, the pressure required to reach the above-mentioned cleaning strength is 0 · 15 ~ 0 · 2MPa. This is due to the use of a straight-through fast pulse valve with small pressure loss and rapid opening and closing, and a reasonably designed injection pipe, which can deliver sufficient dust cleaning air to the filter bag in a short time, so it can be used at low pressure and the same Compressed air consumption achieves ash removal effect. Due to the low injection pressure, the pressure of the pipe network can be used, and no special air compressor is required.
8). Dust collector control can adopt _ program controller, which has three control methods: pressure difference, timing, and manual. It realizes comprehensive system control of off-line valve, pulse valve, ash discharge valve, etc. of the dust collector. The dust removal system is unattended.
Technical parameters of long bag low pressure large pulse bag filter:
Dust filter area: 15000m2;
Dust filter wind speed: 0.7-0.8m / min
Number of dust removal filter bags: 50,400 number of pulse valves: 3,600 sets of off-line valves: 360 conclusions The secondary flue gas dust collector of the steel plant uses a long-bag low-pressure pulse dust collector, and the fan uses an electric frequency motor. The company design will add converter dust removal The system air volume is directly combined with the converter's secondary flue gas dust removal system into a bag filter. After the bag dust removal system was put into operation, the flue gas emission concentration was 32mg / m3, and the flue gas temperature was below 110 ° C. Practice has proved that the pulse bag dust removal system has the characteristics of energy saving, high capture rate, low emission concentration and high degree of automation.