Steel slag is the inevitable product of converter steelmaking, accounting for about 10% ~ 15% of crude steel output. The main mineral composition of steel slag is dicalcium silicate, tricalcium silicate, calcium magnesium olivine, calcium magnesium rosaxene, dicalcium ferrite, free calcium oxide, free magnesium oxide, etc. Among them, the mass fraction of iron is about 10% ~ 20%. After recovering iron, it can be used as raw materials such as steel slag powder, steel slag block brick and subgrade water stable layer, which has high recycling value.
At present, most iron and steel enterprises at home and abroad process the hot steel slag after various cooling treatments, extract the metal and then reuse it. Based on the analysis of steel slag treatment methods at home and abroad, Beijing bopeng Zhongke Environmental Protection Technology Co., Ltd. deeply studied the characteristics of flue gas generated in the process of steel slag treatment, optimized the flue gas purification process, and realized ultra-low emission of particles.
1、 Analysis of common flue gas purification processes
1. Water bath dedusting process
The flue gas is mainly used for the treatment of steel slag by the hot stewing method. During the hot stewing process, the hot stewing pool is covered, the flue gas enters the water bath through the ventilation pipe on the side of the pool, and the washed flue gas enters the dispersion chimney through the fan for discharge. The advantages of this process are less investment and simple process. Its disadvantage is that the purification efficiency is low and the discharge does not meet the standard; The ventilation duct is often blocked, so that the flue gas cannot be pumped away; It can only deal with the flue gas during hot stewing, but can not deal with the flue gas generated during slag, mixing and slag discharge.
2. Combined process of swirling spray dedusting and self excited dust remover.
It is mainly used in drum steel slag treatment system. The pollution control technical scheme of exhaust system of liquid steel slag water quenching process is as follows:
A spinning device is added at the inlet of the main flue gas pipeline to make the flue gas rotate and move forward in the pipeline. An atomization spray device is added at the front end of the rotating flow pipeline. The atomized water droplets become the condensation nodule of smoke and dust, so that the smoke and liquid droplets collide into large particles. A chute is set at the bottom of the pipeline to discharge the dusty water removed from the pipeline through the chute; The flue gas after coarse dust removal enters the self-excited wet dust collector to purify the flue gas again. After purification, it is connected to the dispersion chimney through the fan for high-altitude discharge.
Its advantages are stable operation, but its disadvantages are that the equipment is relatively large (the average wind speed of the pipeline section is 5m / s) and the emission concentration can reach 50mg / m3, but it can not meet the requirements of ultra-low emission of 10mg / m3.
3. Scrubber humidifying electrostatic precipitator
The technological process is: flue gas generated when liquid slag is cooled, smoke collecting hood, flue gas collecting branch pipe, electric switching valve, flue gas collecting main pipe, spray washing tower, wet electrostatic precipitator, fan and discharging chimney.
The advantage of this scheme is that it can meet the ultra-low emission standard, but the disadvantage is that the investment is large. After running for a period of time, the hydraulic hardness of steel slag dust will lead to the scaling of electrode plate and electrode line of electrostatic precipitator, affecting the discharge effect and thus the purification effect; It is difficult to maintain, so it is necessary to replace the polar wire and clean the polar plate regularly, and the maintenance cost is relatively large.
Based on the advantages and disadvantages of the above dust removal methods, it is urgent to develop a new process with low investment, stable operation and ultra-low particle emission concentration. Therefore, Beijing bopeng Zhongke Environmental Protection Technology Co., Ltd. has developed a dust removal process with acoustic agglomeration technology as the core, which meets the requirements of ultra-low emission and solves the problem of unstable operation.
2、 Characteristics and application of new process to realize ultra-low emission
1. New dust removal process and characteristics
Dust cover capture + purification device technology is a general method to prevent dust flying in metallurgical industry. In this method, the dust points are sealed by a closed cover, and then a dust suction cover (dust suction pipeline inlet) is set at the place where the dust is generated. The sucked dusty gas flows through the purification device for dust reduction and is discharged from the system through the negative pressure fan, so as to achieve the purpose of treatment.
The pollutant produced by the hot slag treatment process is the water vapor mixed with dust, so the conventional bag filter cannot be used. During purification, the wet dust removal process is preferred. The dust contained in the flue gas is purified through the washing tower, and then dehydrated to ensure the purification effect and that the discharged flue gas does not contain mechanical water.
In order to meet the national requirements of ultra-low emission standards, the following processes are adopted: capture cover, pipe to spray scrubber, high efficiency dust collector (AWDA+ swirl dehydrator), fan to chimney.
The specific characteristics of the process are as follows:
(1) It can stably and reliably ensure that the emission concentration is ≤ 10mg / m3.
(2) Two stage dust removal ensures the purification effect. The system adopts the form of washing tower + high-efficiency dust collector. The washing tower plays the role of cooling and coarse dust removal.
(3) The high-efficiency dust collector adopts an integrated machine composed of AwDA + cyclone dehydrator, and AwDA is an acoustic dust collector. After being put on the washing tower, the high efficiency dust collector is mainly used for fine dust removal, and the interior is equipped with a fine spray device. The particle size of the atomized spray is less than 200. μ m. Tiny and fast atomized water droplets are used to collect fine dust, and large dust containing water droplets are formed after collision. The dust containing water droplets settle by their own gravity to achieve the purpose of dust removal. In order to improve the efficiency of dust removal, an acoustic agglomeration high efficiency mist trap is added to the high efficiency dust collector. The dust removal device uses acoustic agglomeration mist collecting device to impacting the fine particles of dust, so that the impacted dust particles will collide with the atomized water droplets sprayed by the fine spray device and coalesce into larger dust droplets, and a part of the smoke and dust can be removed by gravity in the high efficiency dust remover. The remaining soot enters the upper dehydrator for further removal. The dust removal efficiency can reach about 99.9%.
(4) The automatic control system adopts the proprietary technology STW flue gas purification intelligent control system V1.0 of Beijing bopeng Zhongke Environmental Protection Technology Co., Ltd., and different flue gas treatment models can be set according to the slag treatment process, so as to better control the dust collection and dispersion effect.
(5) A quick shut-off valve is added to the compressed air system. The compressed air can be used according to the specific situation. When it is not needed, it can be cut off automatically according to the situation.
(6) The utility model has the advantages of simple structure and convenient maintenance, does not need to enter the equipment for internal maintenance, and reduces the equipment failure rate and workers' labor intensity.
2. Efficient dust removal equipment configuration
The first is efficient spray scrubber. The high efficiency spray scrubber system consists of washing tower body, drainage water seal and atomization system.
The high efficiency spray scrubber uses atomizing spray nozzle to directly spray out atomized water to mix with dusty airflow, and uses gas to contact with water to transport the pollutants in the water to the water, then the clean gas is separated from the polluted water to achieve the purpose of purifying the flue gas. The flue gas is treated by the high efficiency spray scrubber, which is treated by reverse flow of gas and liquid, that is, the flue gas flows downwards from the top of the tower, and the water sprays upward with mist (or small droplets) to achieve the purpose of gas-liquid contact. Then, the dust containing water drops are discharged through the lower drain pipe, and the flue gas enters the subsequent dust removal equipment to achieve the goal of dust removal once again.
The second is high-efficiency dust collector. The high efficiency dust collector (AWDA+ cyclone dehydrator) system consists of a dust collector body, a drainage water seal, a seed system (fine spray device), an efficient fog catching device (sound generating device), a complex block assembly, a swirl assembly, a water retaining plate and an automatic control system.
The principle of the high-efficiency dust collector is as follows: the very small and fast atomized water droplets are used to collect fine dust, and large dust containing water droplets are formed after collision. At the lower part of the washing tower, after the gas flow rate slows down, the dust containing water droplets settle by their own gravity to achieve the purpose of dust removal.
In order to improve the dedusting efficiency of dust catcher, an acoustic agglomeration mist trap gun is added to the high efficiency dust collector, and the dust particles are impacted by the acoustic agglomeration mist catching gun, which makes the impacted dust particles collide with the atomized water droplets sprayed by the fine spray device, forming larger dust droplets, and removing the condensed droplets by gravity in the high efficiency dust remover.
A high-efficiency fog catching device is added in the high-efficiency dust collector. In order to make the small particles still exist in the flue gas (scrubber) after coarse dust removal, they collide and agglomerate under the action of sound wave for pretreatment, which is convenient for more efficient removal in the cyclone dehydrator.
In order to improve the effect of agglomeration, the atomized water droplets are sprayed into the fine dust sprayer as seeds, so that they can become agglomerated to form condensation, and the fine particles of agglomeration can be turned into dust containing water droplets. Dust droplets will continue to reunite and collide together, and the larger dust droplets can be gathered to remove gravity, so as to achieve the purpose of dust removal.
The high-efficiency dust collector adopts the three-stage dehydration mode. The lower part of the cylinder is dewatered by gravity, followed by the second stage of re blocking, and the middle and upper part is also provided with a cyclone dehydration device for three-stage dehydration. When the water containing gas enters the dust collector, the air velocity drops below 5m / s, which plays the role of gravity dehydration, and the double baffle and cyclone dehydration device play the role of centrifugal dehydration. When the air flow mixed with water droplets enters the re blocking and cyclone dehydration device, small water droplets collide and gather on the cyclone plate to form large particle water droplets. Driven by the air flow, the water droplets are thrown to the inner wall of the dehydrator along the blade in the centrifugal direction and flow down. At the same time, some water droplets entrained in the gas are also separated due to the rotation of the air flow. It can remove 99% mechanical water in flue gas in a large range.
The process has been successfully applied and achieved good purification effect in iron and steel enterprises in Jiangsu, Shanxi, Hebei and other provinces; In particular, the two sets of dust removal systems put into operation in relevant iron and steel enterprises in Hebei Province this year have achieved ultra-low emission. The particle emission concentration is far less than 10mg / m3. The particle emission concentration has been detected below 5mg / m3 for many times, with simple process and stable operation.
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