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, forsterite, calcium magnesium rhodonite, dicalcium ferrate, free calcium oxide, free magnesium oxide, etc. Among them, the mass fraction of iron is about 10%~20%, and after recovering iron, it can be used as raw materials such as steel slag powder, steel slag block bricks, and subgrade water-stabilized layer, which has high recycling value.

　　At present, most iron and steel enterprises at home and abroad are processing hot steel slag after various cooling treatments, extracting the metal and then using it. On the basis of analyzing the steel slag treatment methods at home and abroad, Beijing Bopeng Zhongke Environmental Protection Technology Co., Ltd. conducted an in-depth study on the characteristics of the flue gas generated in the steel slag treatment process, and optimized the flue gas purification process to achieve ultra-low emission of particulate matter.

　　1. Analysis of common flue gas purification process

　　1. Water bath dust removal process

　　It is mainly used in the flue gas treated by the hot boiling method steel slag, in the hot boiling process, the hot boiling 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 discharge chimney through the fan and discharges. The advantages of this process are low investment and simple process. Its disadvantages are low purification efficiency and substandard discharge; Ventilation ducts are often blocked, resulting in smoke that cannot be extracted; It can only deal with the flue gas when it is boiled, and cannot deal with the flue gas generated when the slag is stirred, stirred and slag is discharged.

　　2. The combined process of cyclone spray dust removal and self-excited dust collector

　　It is mainly used in the drum steel slag treatment system, and the pollution control technology scheme of the exhaust air system of the liquid steel slag water quenching process is as follows:

　　A spinning device is added at the entrance of the main flue gas pipeline, so that the flue gas rotates forward in the pipeline, an atomization spray device is added at the front end of the rotating flow pipeline, and the atomized water droplets become the condensation nucleus of the smoke and dust, so that the smoke and dust collide with the droplets to become large particles, and a chute is arranged at the bottom of the pipeline, so that the dusty water removed in the pipeline is discharged through the chute; After rough dust removal, the flue gas enters the self-excited wet dust collector to purify the flue gas again, and after purification, it is connected to the chimney through the fan for high-altitude discharge.

　　Its advantage is that the operation is stable, and the disadvantage is 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 cannot meet the requirements of 10mg/m3 of ultra-low emission.

　　3. Scrubber humidification electrostatic precipitator

　　The process flow is as follows: the flue gas generated when the liquid slag is cooled→ the smoke and dust collection hood→ the flue gas collection branch pipe→ electric switching valve→ flue gas collection main pipe→ spray scrubber → wet electrostatic precipitator→ fan → release chimney.

　　The advantage of this scheme is that it can reach the standard of ultra-low emission, and the disadvantage is that the investment is large, and after a period of operation, the water hardness of the steel slag dust will lead to the fouling of the electrostatic precipitator plate and pole line, which will affect the discharge effect, thereby affecting the purification effect; Maintenance is difficult, and it is necessary to replace the pole wire and clean the 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 less investment in research and development, stable operation and particulate matter emission concentration to meet the requirements of ultra-low emission.

　　2. New process characteristics and applications to achieve ultra-low emissions

　　1. New dust removal process and characteristics

　　Dust hood capture + purification device technology is a common method in the metallurgical industry to prevent dust from flying. In this method, all dust points are sealed by a closed cover, and then a dust collection hood (dust collection pipeline inlet) is set at the place where the dust is generated. After the dust is sucked out, the dusty air flow is reduced by the purification device, and then discharged into the system through the negative pressure fan, so as to achieve the purpose of treatment.

　　The pollutants produced by the hot slag treatment process are water vapor mixed with dust, and the conventional bag filter cannot be used, so the wet dust removal process is preferentially adopted in the purification, and the dust contained in the flue gas is purified through the scrubber first, and then dehydrated to ensure the purification effect and the exhaust flue gas does not contain mechanical water.

　　In order to meet the ultra-low emission standards required by the state, the following processes are adopted: trap hood→ pipeline→ spray scrubber→ high-efficiency dust collector (AWDA + cyclone dehydrator), → fan → release chimney.

　　The specific features of the process are as follows:

　　(1) It can stably and reliably ensure that the emission concentration ≤10mg/m3.

　　(2) Two-stage dust removal to ensure the purification effect, the system adopts the form of washing tower + high-efficiency dust collector, and the washing tower plays the role of cooling and rough dust removal.

　　(3) The high-efficiency dust collector adopts an all-in-one machine composed of AWDA + cyclone dehydrator, and AWDA is a sonic dust collector. The high-efficiency dust collector is placed in the scrubber tower, mainly used for fine dust removal, and is equipped with a fine spray device inside, and the particle size of the atomized particles sprayed into it is not more than 200μm, and the fine dust is collected by using extremely small and fast atomized water droplets, and large dusty water droplets are formed after collision, and the dusty water droplets settle by their own gravity to achieve the purpose of dust removal. In order to improve the dust removal efficiency, a sonic agglomeration high-efficiency fog trap device is added in the high-efficiency dust collector, and the dust removal device uses the acoustic wave agglomeration fog trapping device to impact the dust fine particles, so that the dust fine particles after impact collide with the atomized water droplets sprayed by the fine spray device, condense into larger dust-containing droplets, and remove a part of the smoke and dust by gravity in the high-efficiency dust collector, and the remaining smoke and dust enter the upper dehydrator for further removal. Its dust removal efficiency can reach about 99.9%.

　　(4) The automatic control system adopts the proprietary technology of Beijing Bopeng Zhongke Environmental Protection Technology Co., Ltd. "STW flue gas purification intelligent control system V1.0", which can set different flue gas treatment models according to the slag treatment process, so as to better control the dust collection and release effect.

　　(5) The compressed air system adds a quick shut-off valve, and the compressed air can be used according to the specific situation, and the automatic shut-off can be adopted according to the situation when it is not needed.

　　(6) The structure is simple, the maintenance is convenient, and there is no need to enter the equipment for internal maintenance, and at the same time the equipment failure rate and the labor intensity of workers are reduced.

　　2. Efficient dust removal equipment configuration

　　One is a high-efficiency spray scrubber. The high-efficiency spray scrubber system is composed of several parts: the scrubber body, the drainage water seal, and the atomization system.

　　The high-efficiency spray scrubber uses the atomization spray gun nozzle to directly spray atomized water and mix it with the dusty air stream, and uses the contact between the gas and the water to transfer the pollutants in the gas to the water, and then separates the clean gas from the polluted water to achieve the purpose of purifying the flue gas. The flue gas is treated by gas-liquid reverse through the high-efficiency spray scrubber, that is, the flue gas flows downward from the top of the tower, and the water is sprayed upwards in the form of mist (or small droplets) to achieve the purpose of gas-liquid contact, and then the dusty water droplets are discharged through the lower drainage pipe, and the flue gas enters the follow-up dust removal equipment to achieve the purpose of dust removal again.

　　The second is a high-efficiency dust collector. The high-efficiency dust collector (AWDA+ cyclone dehydrator) system is composed of the dust collector body, drainage water seal, seed system (fine spray device), high-efficiency fog trapping device (sound wave generation device), recovering assembly, swirl assembly, water baffle and automatic control system.

　　The principle of the high-efficiency dust collector is as follows: the use of extremely small and fast atomized water droplets to collect fine dust, after the collision to form large dust-containing water droplets, in the lower part of the scrubber, after the gas flow rate slows down, the dusty water droplets rely on their own gravity to settle, to achieve the purpose of dust removal.

　　In order to improve the dust removal efficiency of the dust collector, a sonic agglomeration fog trap gun is added to the high-efficiency dust collector, and the sound wave agglomeration fog trap gun is used to impact the dust fine particles, so that the dust particles after impact collide with the atomized water droplets sprayed by the fine spray device to form large dust-containing droplets, and the condensed fog droplets are removed by gravity in the high-efficiency dust collector.

　　A high-efficiency fog trap device is added to the high-efficiency dust collector, so that there are still small particles in the flue gas after rough dust removal (scrubber), and they are pretreated under the action of sound waves to collide and condense, so as to facilitate more efficient removal in the cyclone dehydrator.

　　In order to improve the effect of agglomeration, the atomized water droplets are sprayed into the atomized water droplets as seeds by the fine spray device in the high-efficiency dust collector, so that the agglomeration can be changed into agglomeration, so that the fine dust after agglomeration becomes dusty water droplets, and the dusty water droplets continue to agglomerate and collide with each other, and condense into larger dusty water droplets to be removed by gravity, so as to achieve the purpose of dust removal.

　　The high-efficiency dust collector adopts a three-stage dehydration method, which relies on gravity for first-stage dehydration at the lower part of the cylinder, followed by the second-stage dehydration of the restop, and a cyclone dehydration device for three-stage dehydration in the middle and upper parts. When the water-containing gas enters the dust collector, the airflow velocity drops to below 5m/s, which plays the role of gravity dehydration, and the baffle plate and the swirl dehydration device play the role of centrifugal dehydration. When the air flow mixed with water droplets enters the recovery and swirl dehydration device, the fine water droplets are impacted and gathered on the swirl plate to form large particles of water droplets, and driven by the air flow, the water droplets are thrown along the blades to the inner wall of the dehydrator in the centrifugal direction and flow down, and at the same time, part of the water droplets entrained in the gas are also separated due to the rotation of the air flow. It removes 99% of the mechanical water in the flue gas over a large area.

　　The process has been successfully applied, and iron and steel enterprises in Jiangsu, Shanxi, Hebei and other provinces have achieved good purification effects; In particular, this year, the two sets of dust removal systems put into operation in the relevant iron and steel enterprises in Hebei Province have achieved ultra-low emissions, and the particulate matter emission concentration is far less than 10mg/m3, and the particulate matter emission concentration is below 5mg/m3 for many times, and the process is simple and the operation is stable.

　　——Source: China Metallurgical News