Study on dioxin emission reduction technology of t

Research on dioxin emission reduction technology for sintering flue gas purification

dioxin is a persistent organic substance with high toxicity. Based on the analysis of dioxin composition, characteristics, mechanism and the experience of emission reduction technology in developed countries, Baosteel adopts the flue gas purification technology of simultaneous removal of dioxin through activated carbon dry desulfurization and denitration. According to the physical properties and dust collection effect of activated carbon, the dioxin purification is completed, and the removal rate remains at 98% It fully illustrates the effective role of sintering dioxin in emission reduction. In this regard, based on practical research, the author briefly analyzes the dioxin emission reduction technology of sintering flue gas purification

dioxin, known as the "poison of the century", is a persistent organic pollutant naturally formed in the production stage. It cannot be controlled by means of prohibition and production ban. The dioxin emission mainly comes from steel, accounting for 12% of the air discharged by adopting the reaction frame structure in the front of the main engine of the tensile testing machine It is concentrated in the sintering and electric steel processing stages, and its sintering emissions account for 94% of the total emissions Therefore, the in-depth analysis of the formation mechanism and emission reduction technology of dioxin in sintering technology has become an important research content. "1.

analysis of dioxin characteristics

dioxin is the abbreviation of polychlorinated dibenzo-n and polychlorinated dibenzofuran. The substitution parameters of benzene ring chlorine atoms on dioxin molecules have certain production differences, which can be divided into 8 types of homologues. Different types of homologues produce a variety of isomers following the difference of substitution positions of chlorine atoms

among them, PCDD contains 75 isomers and PCDF has 135 isomers. Dioxin is an acute toxic substance, and its toxicity is directly related to the position of chlorine atom substitution; Among them, tetrachlorodiphenyl dioxin is the most toxic, equivalent to 50-100 times that of potassium cyanide, and can cause deformities, mutations and carcinogenic effects. It is recognized as the most toxic compound by far

2 sintering dioxin emission reduction technology

2.1 control technology

(1) sintering raw materials: more chlorine will be produced in the sintering stage, and chlorine is the key to dioxin production. Raw materials with low chlorine content are also the main method to reduce dioxin formation. Therefore, the use of iron containing recycled materials of chlorine should be reduced as much as possible, or the elements in sintering raw materials should be reduced in the form of clean high temperature to reduce the formation of dioxin. Practice has proved that copper has a certain catalytic effect on dioxin, and some mines have become an important factor in the performance of safety belts. There is a certain amount of copper in the stone, which catalyzes the production of dioxin to a certain extent. Therefore, iron ore with less copper content should be selected in the selection process

(2) sintering control: the dioxin in the sintering stage comes from the bottom of the raw material. If you want to reduce the production of dioxin in the sintering, you need to optimize the sintering conditions. For example, improve the permeability of the material layer, control the temperature during the sintering stage, shorten the residence time between the 250-450 ℃ sintering flue gas temperature at which dioxin is easy to form, and then reduce the formation of dioxin

2.2 flue gas purification technology

(1) filtration technology: under the condition of 200 ℃, dioxin is mostly in solid state mode, attached to the outer layer of smoke and dust, and it is attached to finer particles. Therefore, dioxin can be reserved in dust during dust removal by using dust removal technology. At this stage, through the dust removal technology of sintering flue gas 4 The instrument adopts brushless motor and is equipped with overload protection technology, which is divided into two types: bag type dust removal and electric dust removal. The dioxin purification efficiency of the two methods is maintained at 45% - 65%, 85% - 90%

(2) physical adsorption technology: dioxin can be adsorbed by porous materials, and physical adsorption is implemented according to its characteristics; And at this stage, it has been applied in some developed countries. The equipment is usually divided into mobile bed, fixed bed and portable type. Among them, the flow carrying type is mainly aimed at dedusting, and the flue is sprayed with adsorbent. When dioxin is adsorbed, it is removed in the dust collector to achieve the effect of emission reduction. Moving bed adsorbent enters from the upper end of the adsorption tower and is discharged from the lower end; It is usually set after the dust collector. The adsorbent in the fixed bed is fixed, and the flue gas is discharged after passing through its outer layer. Activated carbon and lignite can be used as adsorbents to reduce the dioxin emission in sintering waste by 70%

3 dioxin emission reduction experiment of Baosteel

(1) dioxin output control: in order to fundamentally reduce the dioxin formed in sintering, it is also necessary to analyze the formation mechanism of dioxin in in the combined sintering stage of Baosteel

first, the purchase and treatment of raw materials. Increase the proportion of self-produced Jianshan Iron Concentrate between 45% and 60%, and the concentration of Cu in Jianshan concentrate is less, which can inhibit the catalytic effect on the formation of dioxins. Due to the reduction of fine particle size of refined powder, the granulation method is strengthened to improve the granulation effect. The distribution position of sintering machine +0.3mm particle size composition is 65%, which ensures the permeability and plays an important role in reducing the output of dioxin. If you want to reduce the aluminum content in the sinter, you need not add CaCl process to the finished sinter, so as to reduce the production of dioxin. As a common iron containing recycling material in production, rolled iron oxide scale can oxidize and release heat during sintering, which is beneficial to improving sinter grade and reducing solid fuel consumption. However, the grease existing in the production stage of rolled iron oxide scale is the chlorine source of dioxin formation

Baosteel has carried out tests with and without iron oxide scale in the existing two large sintering machines, and carried out flue gas sampling research of the sintering machine. After investigation, it is concluded that the concentration of dioxin is 2.0ng/m by using the form of rolled iron oxide scale, and the detection parameters are 1.0ng/m by not using rolled iron oxide. Therefore, the analysis of iron oxide scale in Baosteel is carried out, and the iron oxide scale is optimized to be used in oxycup oxygen enriched shaft furnace in sintering, so as to reduce the aluminum content in the mixture and reduce the formation of dioxin

second, sintering technology. Baosteel sintering is a kind of thick layer sintering with a thickness of 720-730m Based on this condition, the permeability should be optimized to reduce dioxin production. In this regard, in the processing stage, scientific proportioning was carried out, the discharge port of the granulator was changed, and the method of heat preservation of water through hot water and steam in the mixing silo was increased, so as to optimize the granulation effect of the mixture, improve the permeability and reduce the formation of dioxin

(2) flue gas dioxin emission reduction technology: activated carbon emission reduction method. Due to the different chlorine elements, the melting point and boiling point of dioxin also have certain differences. The waste mainly includes two modes: solid, liquid and gas. Among them, dioxins in gas and liquid can be physically adsorbed by activated carbon; Solid mode dioxin is a small particle with high adsorption effect. Using the dust collecting effect of activated carbon moving layer can be effectively eliminated. Using activated carbon to reduce dioxin content is not worth using adsorption to remove dioxin substances. In essence, it is to damage the oxygen group between benzene rings, resulting in structural changes, so that activated carbon can achieve catalytic decomposition effect. When dioxin is adsorbed, its decomposition rate is determined by the separation temperature in the separation tower and the residence time of activated carbon. The experiment shows that with the increase of residence heating time and temperature, the decomposition rate of dioxin increases, up to 100%

4 conclusion

first, dioxin has strong toxicity, threatening people's life and health, and dioxin emissions during sintering account for a large proportion. Therefore, the sintering industry needs to increase the remediation of dioxin. Second, the production of dioxin in the sintering stage comes from the sintering machine material layer. PCDFs has a great impact on the quality composition and toxicity in the Celsius environment and oxidizing conditions