I. Introduction of converter and mixed iron furnace
The mixed iron furnace emits a lot of smoke and dust when mixing the molten iron and molten iron. In order to improve the working conditions and protect the environment, a dust removal system needs to be installed. The dust removal system of the mixed iron furnace includes the exhaust hood, pipes, dust collectors, fans, chimney hoods, and the determination of the exhaust air volume at the mouth of the hood is the determinant of the smoke collection efficiency of the hood.
Second, the characteristics of converter flue gas
2.1 Secondary soot parameters of the converter
The secondary dust of the converter is mainly harmful substances such as iron oxide and graphite, which are generated in the process of mixing molten iron, adding scrap steel, adding bulk materials, tapping, and slag, etc.Its characteristics are: large amount of flue gas and scattered dust sources. Severely polluted the workshop interior and the factory atmosphere.
In the secondary flue gas of the converter, the most amount of smoke is generated when the molten iron is mixed. 40% to 66% of the soot are iron oxides, and the rest are graphite powder and oxides of silicon, calcium, and magnesium. The particle size distribution is: 10 to 40um, 11%; 40 to 60um, 13%;> 60um balance.
Flue gas composition: CO2%, CO8 ～ 10%, O2 ～ 8%
Flue gas temperature: ～ 150 ℃ (center 800 ℃)
Soot concentration: 3 ～ 5g / Nm3
Soot composition: iron oxide 45%, graphite 30%, other 25%
Soot particle size: <100um
2.2 Flue gas parameters of mixed iron furnace
Concentration of dust in the flue gas of iron-mixing furnace: 2 ～ 5g / Nm3 for a long time when mixed with molten iron, about 1g / Nm3 when molten iron is produced.
Soot composition: C30% ～ 45%; TFe40% ～ 50%; others 3% ～ 12%.
Smoke density: 113kg / Nm3.
Flue gas temperature (along the vertical center of the molten iron port): the center of the molten iron port ~ 1200 ℃, the upper part of the molten iron port 2 ~ 3m 300 ~ 500 ℃, the upper part of the tapped iron port 160 ~ 200 ℃.
Particle size of soot: From the dust discharged from the iron mixing furnace, more than 80% of the dust with a particle size of more than 20um and less than 20% of the dust with a particle size of less than 20um. The soot particle size composition is listed in the following table.
Third, the secondary flue gas dust removal of the converter
3.1 Dust removal process
The secondary flue gas dust removal uses a dry dust removal process. The process is: smoke-containing gas → exhaust hood before and after the furnace → dust removal pipe → bag dust collector → dust removal fan → muffler → chimney → atmosphere.
3.2 Exhaust Hood
The secondary flue gas exhaust hood of the converter is divided into a front exhaust hood and a rear exhaust hood. The smoke exhaust hood in front of the furnace is set in the smoke prevention chamber in front of the furnace, and the smoke exhaust hood in front of the furnace is set on the smoke prevention chamber side of the furnace. Adopt pipeline connection as a whole.
The smoke trap in front of the furnace is a square pipe, which is set in the smoke-proof chamber in the upper part of the converter, and captures the flue gas in the opening below the position of the converter inlet, which is divided into left and right parts. The trap becomes a circular duct outside the smoke chamber. The smoke trap in front of the furnace is made of heat-resistant material and lined with refractory material.
Behind the furnace, the dust collector is made of carbon steel and is set outside the converter smoke prevention chamber. The operation door is opened only after the steel and slag are discharged.
3.3 Air volume of secondary dust removal system of converter
There is no mature calculation method for the amount of exhaust gas from the secondary dust removal in converters in China. In design, it is determined by referring to domestic statistical data. Calculating the rising speed of smoke and the cross-sectional area of the smoke column, the average speed of the hood is 10m / s, and the effect is obvious after production, and the capture rate is above 95%. The flue gas volume of the two dust removal systems of the two converters is 60 × 104m3 / h.
3.4 Dust collector and fan
The converter's secondary flue gas dry dust removal mainly uses a long-bag off-line pulse dust collector, with a dust removal efficiency of more than 99%. There are a total of 2 × 10 cabinets. A vibrator and an electric ash discharge valve are provided at the bottom of each ash box. There are two cut-out scrapers. Filtering area: 8800m2, maximum filtering wind speed: 1114m / min.
Maximum air flow of the fan: 60 × 104m3 / h, wind pressure: 4500Pa, flue gas inlet temperature: <100 ℃, motor power: 1600kW.
Dust removal from mixed iron furnace flue gas
4.1 Dust removal process
The dust removal of the iron mixing furnace adopts a dry dust removal process. The process is: smoke-containing gas → side exhaust iron flue hood and iron outlet fume hood → dust removal pipe → bag dust collector → dust removal fan → muffler → chimney → atmosphere.
4.2 Exhaust Hood
The mixed iron furnace fume hood mainly includes the upper fume exhaust hood and the iron outlet fume hood. The flue-exhaust hood of the ironing nozzle adopts a side vertical type, and the inside of the hood has a layer of refractory spraying material, and the outside is reinforced by flat steel, and is fixed on the operating platform by a diagonal support bracket. The upper part of the fume hood adopts a movable shielding baffle.
A semi-closed fixed hood is used at the tap outlet, which is arranged on the operating platform and is equipped with observation holes. The exterior of the fume hood is reinforced with flat steel. The fume hood has sufficient rigidity to prevent deformation of the hood wall after high temperature radiation. The lower part of the fume hood adopts a movable shielding baffle.
4.3 Air volume of dust removal system of mixed iron furnace
The average speed of the air outlet of the ironed water hood is 10m / s, and the average speed of the semi-closed iron outlet hood is 5m / s. The dust volume of the dust removal system is 35 × 104m3 / h.
4.4 Dust collector and fan
Using long bag offline pulse dust collector, the dust removal efficiency reaches more than 99%. There are 2 × 10 boxes in total. Each ash box is equipped with a vibrator and electric ash discharge valve, and two cut-out scrapers. Filtering area: 5600m2, maximum filtering wind speed: 1104m / min.
Maximum fan capacity: 35 × 104m3 / h, wind pressure: 4500Pa, flue gas inlet temperature: 100 ℃, motor 800kW.
V. Fan room and chimney
The dust removal fan room is a steel structure, and a converter secondary dust removal fan and a mixed iron furnace dust removal fan are set inside. The converter's secondary dust removal system is configured according to the two furnaces and one machine, and spares are not considered. The system sets up a high-voltage inverter. The low-pressure pulse bag filter is arranged in the open air. The fan inlet is provided with an air volume regulating valve, and the fan outlet is provided with a muffler. An LD-A electric single-girder crane is provided for the convenience of maintenance, with a lifting capacity of 10 t and a fan maintenance span.
The two sets of dust collectors share a diffusing chimney. The chimney exit diameter is <4500mm and the height is 30m.
Six, automatic control
In order to ensure the normal operation of the operation and stable compliance, the dust and dust removal system of the converter and the mixed iron furnace is tested online. The fan uses a high-voltage frequency converter to regulate the speed. Adjust the output of the inverter (that is, the working speed of the dust removal fan) according to the number (number) of electric valve opening and closing. Regardless of whether the electric valve is manually controlled or automatically controlled, the opening and closing signals of each electric valve will be automatically fed back to the dust removal fan speed control system.The dust removal fan speed control system will automatically adjust the dust removal according to the number of valves opened and closed. The working speed of the fan.
The secondary dust removal fan of the converter is set to three gears of high speed, medium speed and low speed. The dust-removal fan of the mixed-iron furnace is set to two gears, high speed and low speed.
The fan receives a speed increase signal from low speed to medium speed, while receiving a second speed increase signal from medium speed to high speed; receives two speed increase signals, that is, the fan directly increases from low speed to medium speed; the fan receives To the speed-down signal, if the fan is in the high-speed gear and reduced to the medium speed, the fan is in the medium-speed gear and reduced to the secondary medium-speed, and the fan in the secondary-medium-speed gear is reduced to the low speed.
Goals achieved after implementation
7.1 Purified captured dust is mainly composed of iron oxides, and the rest is lime powder and graphite carbon flakes. After humidification, it is transported by the car to the sintering workshop for batching and utilization.
7.2 The secondary dust removal system of the converter and the iron dust removal system of the mixed furnace are normally put into operation. After the flue gas is processed by the dry purification dust removal system, the dust content is <30mg / m3, and the emissions are up to the standard. After the dust removal treatment, the dust content of the operation table of the converter and the iron mixing furnace is <10mg / m3, which meets the national health standards.
7.3 All joints of pipes and equipment are provided with flexible joints, flexible joints are installed at the inlet of the fan, and a muffler is installed at the exit of the plant.
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