In recent years, the atmospheric environment in our country has been facing a severe situation. The emission control of the steel enterprises has always been the focus of our country's concern. Shaft furnace pellet production process will produce a large amount of dust, SO2 and other harmful substances, causing serious pollution to the environment. In order to reduce the emissions of SO2 and dust and other harmful substances in the shaft furnace pellet production process and meet the environmental protection requirements, the iron and steel plant installed a rotary atomizing semi-dry method (SDA) smoke at the outlet of the main exhaust fan flue of a shaft furnace pellet Gas desulfurization system. This paper analyzes the application of semi-dry desulphurization system in shaft furnace flue gas desulphurization project, and introduces its process characteristics and desulfurization effect. Summary of rotary spray semi - dry desulfurization process Currently, in the US desulfurization market, the total amount of desulfurization by rotary spray semi-dry desulfurization process accounts for 91% of the total desulfurization by dry (semi-dry) desulfurization process and the maximum flue gas treatment capacity by single tower reaches 2 million standard cubic meters per hour. Rotary spray semi-dry desulfurization system is mainly composed of the following components: desulfurization tower and ancillary equipment; bag filter and ancillary equipment; desulfurization agent storage, transportation and slurry preparation and supply system; desulfurization ash storage, drainage system; desulfurization system Auxiliary equipment, including the sink in the desulfurization area and ancillary facilities, desulfurization process water system, nitrogen system, steam system; instrumentation, communications, on-line monitoring, fire and control systems. Semi-dry desulfurization process to Ca (OH) 2 as absorbent through the desulfurization tower atomizer lime slurry atomized into 30μm ~ 80μm droplets, small droplets and flue gas desulfurization tower in contact with the rapid gas In the SO2 reaction, to purify the purpose of desulfurization. Lime slurry involved in the reaction from the quick-adding amount of quicklime digestion tank and add water preparation, lime slurry sieved through the shaker into the slurry tank, formulated into a qualified lime slurry. According to the concentration of SO2 in the flue gas, the slurry pump is used to quantitatively feed the lime slurry into the slurry top tank. The slurry in the top tank flows into the atomizer at the top of the desulfurization tower, atomized into atomized droplets by the atomizer, contacts the flue gas in the desulfurization tower, and quickly completes the reaction with SO2. Due to the very small size of lime slurry and the large specific surface area, the contact reaction with SO2 can be accelerated. The removal rate of SO2 in flue gas can reach 97%. The desulfurized and dried flue gas into the bag filter, its further purification. Due to the incomplete reaction of Ca (OH) 2, the dust collected by the bag filter is transported to the circulating ash system by the bucket elevator, and the collected dust is periodically transported by the outside.  Rotary spray semi-dry desulfurization process characteristics Rotary spray semi-dry flue gas desulfurization process has the advantages of simple system, high desulfurization efficiency, strong adaptability to working conditions, etc. In summary, there are mainly the following features: System is simple, running resistance, easy operation and maintenance. The SDA desulfurization tower has the advantages of simple structure, low energy consumption, low operation and maintenance cost. SDA flue gas desulfurization process does not require a large number of solid circulating ash circulating in the tower, desulfurized flue gas does not require reflux, tower solid desulfurization ash in the fluidized state, there is no collapse bed, dead bed or partial bed situation. SDA desulfurization tower resistance will not exceed 1000Pa. High desulfurization efficiency. The SDA process uses the same mechanism as the wet desulfurization process with a desulfurization efficiency between wet and dry processes. The SDA process atomizes the lime slurry into extremely fine droplets (average 50 μm), increasing the specific surface area of ​​the lime slurry in contact with the flue gas. Therefore, only need to spray less desulfurization agent can achieve higher desulfurization efficiency. In addition, the SDA process also has a nearly 100% removal rate for acidic substances such as HCL, HF and the like. Reasonable and uniform airflow distribution. The top of the SDA desulfurization tower and the center of the tower with a flue gas distribution device to ensure uniform tower flue gas flow distribution, the flue gas and atomized droplets fully mixed to improve the flue gas and droplet contact quality and heat transfer Efficiency, to achieve the best drying and reaction conditions; the same time, to ensure that the tower flue gas droplets have a reasonable contact time, get the maximum SO2 removal rate. Flexible adjustment of slurry volume, desulfurization efficiency is not affected. Because the SDA nebulizer uses the centrifugal force generated by high-speed rotation to atomize the slurry, the droplet size is only related to the diameter and speed of the atomizer wheel. Therefore, the slurry atomization effect has nothing to do with the slurry supply. When the slurry feed rate varies with the flue gas flow rate, temperature and SO2 concentration, the droplet size will not be affected, ensuring that the desulfurization efficiency is unaffected. Desulfurization agent using Ca (OH) 2 slurry. SDA process does not directly use quicklime, but first make quicklime and water react to produce Ca (OH) 2 slurry, and then inject the slurry into the desulphurization tower to avoid CaO in the desulfurization tower dust collector heat absorption and lead to bagging bag and Ash system plugging phenomenon occurred. Desulfurizer on the quality of less demanding. SDA process lime kiln can be finished product dust collection system as a desulfurizer powder, to meet the requirements of circular economy. Adaptable to the pellet conditions. As the pellet flue gas system load varies greatly, and its flow, temperature and SO2 and other changes are also large, SDA flue gas desulfurization system through the control valve to adjust the tower atomized slurry volume to adapt to changes in pellet conditions will not increase Dust collector load. System settings bypass, does not affect the normal production of pellets. The desulfurization system is arranged in parallel with the existing exhaust system of the pellet. The construction, operation and maintenance of the desulfurization system will not affect the normal production of the pellet process. After desulfurization, the flue gas temperature is greater than the dew point temperature. Duster outlet flue gas temperature control at a low level, but again above the dew point temperature (flue gas temperature greater than dew point above 15 ℃). Therefore, SDA flue gas desulfurization system can use carbon steel as a structural material, the whole desulfurization system does not require anti-corrosion treatment, do not need to install the heating system. SDA flue gas desulfurization process water consumption is low, does not produce wastewater. SDA flue gas desulfurization process can directly use low-quality water (such as alkaline wastewater, to achieve the purpose of waste treatment), and does not produce wastewater. Desulfurization by-products can be comprehensive utilization. Dry desulfurization ash can be used as a building material additive, but also can be used to produce unburned brick, with a variety of purposes, enabling the reuse of waste to meet the requirements of circular economy.  Application of Semi - dry FGD Process in Steel Plant  Domestic steel shaft furnace semi-dry desulfurization system since its establishment, the system is stable. The steel mill semi-dry desulfurization system for a month the operating parameters of the furnace as shown in the table above. It can be seen from the above table, semi-dry desulfurization system operation
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