Cleaning Technology For Fluorine-containing Flue Gas Control In Electrolytic Aluminum Process Based On Bag Filter

The bag filter is a highly efficient dedusting device consisting an ontology system?inlet and exhaust flue,guide structure,ash storage hopper,clean air box and other flow space with flue gas?,fiber filter dedusting unit,and dust cleaning device.The bag filter used in electrolytic aluminum industry does not only remove the particulates present in the smoke exhaust,but more importantly,it ensures the purification effect of the alumina particles on the harmful fluorine-containing flue gas.In the process of production of the electrolytic aluminum,the alumina powder serves not only a raw material of electrolytic aluminum,but also an adsorbent for purifying the flue gas generated during the electrolytic process.Furthermore,the fluorinated alumina after the adsorption process,is partially recycled in order to continue the purification of the fluorine-containing flue gas,and partially sent back to the electrolytic cell for the production of aluminum.The creation of good hydrodynamic conditions is necessary for the adsorption of hydrogen fluoride by alumina to ensure the purification effect of the system.An efficient separation between the fluorinated alumina and the flue gas needs to be implemented by the bag filter for electrolytic aluminum.It can be seen that the bag filter for electrolytic aluminum does not possess the limitation of the traditional bag filter that has only a single function of controlling dust emission.This makes the bag filter technology treat the gaseous pollutants-particulates cooperatively,and realizes the"single machine with multi functions"of purification-dedusting.Obviously,the design method,theoretical basis,research results and engineering experience of the traditional bag filter are not fully applicable to the research and engineering application of the bag filter technology for electrolytic aluminum.Currently,China's electrolytic aluminum production capacity has been ranked first in the world for many years,and the electrolytic aluminum industry requires the overall ultra-low emission transformation,hence,the electrolytic aluminum with fluorine-containing flue gas requires a deep treatment urgently.Therefore,by studying the flow field structure characteristics,gas-solid two-phase motion control and high-efficiency filtration technologies of the bag filter in the purification of the fluorine-containing flue gas during the electrolysis process,the fluorine-containing flue gas purification technology in the electrolytic aluminum process based on bag filter was developed,which has an practical application value for promoting the up gradation of fluorine-containing flue gas purification technology,realizing harmless treatment of flue gas pollution of electrolytic aluminum,implementing clean production of electrolytic aluminum and expanding the functions and application fields of the bag filter.Based on the above objectives,we carried out the following research:?1?In view of the problems in the technical background of the bag filter used in the purification of flue gas during electrolytic aluminum,the fluorine balance and fluorine migration during the electrolytic aluminum production process were studied,and the functional positioning,research focus and control objectives of the bag filter technology in the flue gas purification of electrolytic aluminum were analyzed and determined.Using the particle size distribution test for the particulate source-adsorbent alumina particles,we studied the effects of the number of cycles on the crushing of alumina powder and the change of PM_2.5 content in the purification system,so as to grasp the characteristics of particle size distribution and fluctuation in the alumina particles.This provided a basis for establishing a time model of the suspension movement of alumina particles based on the purification purposes in a bag filter.Furthermore,it assisted the study of the gas-solid two-phase motion law in a bag filter for electrolytic aluminum,as well as,the filter material filtration technology for electrolytic aluminum.On the basis of a comprehensive summary of the technical background,the concept of clean treatment for pollutants was proposed,and the characteristics of the cleaning technology of flue gas purification during electrolytic aluminum based on bag filter were analyzed.?2?In the purification of the bag filter for electrolytic aluminum,the structural characteristics of dedusting flow field,the flow field structure mechanism and the motion law of internal gas-solid two-phase of the bag filter for electrolytic aluminum were studied.Initially,through the analysis of the movement and force analysis of the aluminum particles in the bag filter,a calculation model of the suspension movement time and distance of alumina particles in the bag filter was established,and a method was designed for the flow field structure of the bag filter with the characteristics of the adsorbent itself.The above method and model were used to propose the basic configuration of the flow field of the bag filter,which was suitable for the purification of the flue gas during electrolytic aluminum.Subsequently,a numerical calculation model of the gas-solid two-phase flow in a bag filter was established,and numerical simulation method was used to study the back mixing,reflux and gas-solid separation of alumina particles in the above-mentioned bag filter for electrolytic aluminum.Furthermore,we studied the influence of the characteristics of alumina particles on the distribution of the suspension movement residence time?adsorption purification time?in the bag filter,and the deposition distribution law of the alumina particles on the filter bags,which provided a theoretical support in the study of the uniform control of the gas-solid two phases in the bag filter and improving the efficiency of purification-dedusting of the system.?3?In the gas-solid two-phase uniform distribution control consisting of a wide particle size distribution particle group of the bag filter for flue gas purification during electrolytic aluminum,the orthogonal test with multi indexes was established to analyze the influence of the structural parameters of the flow-equalizing device inside the hopper on the distribution uniformity of the flue gas velocity field and the particle concentration field.The difference significance tests and the comprehensive equilibrium analysis method at different levels among the different factors were used to determine the optimum combination of the structural parameters for the flow-equalizing device inside the hopper that influences the gas-solid two-phase uniform distribution in the bag filter.Based on this,a multiple flow guiding technology of"N-type flue pipe elbow diversion+flue outlet diversion+flow equalization inside the hopper"was established to implement the uniform control of gas-solid two phases.?4?A performance evaluation method was developed for the bag filter during the purification of the flue gas in electrolytic aluminum.The method implemented comprehensive evaluation of the residence time of the alumina particles in the bag filter?the time required to ensure the completion of the adsorption reaction?,and the uniformity of the gas-solid two-phase distribution?assuring the purification effect and improving the filtration efficiency?,and fluorine removal efficiency of the system?adsorbent selection and fluorine removal efficiency evaluation?.This can help providing a research and analysis method for the design optimization and performance evaluation of the bag filter in the electrolytic aluminum process.?5?Considering the requirements of flue gas purification-dedusting of electrolytic aluminum,we studied the filter material and filter bag technology using the testing method along the complete process route including characteristics of the filter fabric?construction?,the filter material forming and the filter bag making.Through the study on the above contents,we studied and analyzed the structural characteristics of the gas-solid two-phase flow field,design optimization,performance evaluation and special filter material of the bag filter for electrolytic aluminum,with the goal of achieving a high-efficiency flue gas purification-dust removal.The clean technology concept and technical characteristics of the pollutant treatment were proposed,and the new index of particle residence time distribution was introduced as the standard in the design,research and performance evaluation of the bag filter.Based on the requirements for the purification of fluorine-containing flue gas,a calculation model of the suspension movement time of alumina particles was established,providing a theoretical basis for the flow field design of the bag filter for electrolytic aluminum.The comprehensive performance evaluation method of bag filter for electrolytic aluminum was constructed,which provided a systematic research method for the design,optimization and evaluation of purification-dedusting bag filter.The research results of this project have been successfully implemented in the“863”project demonstration project,and achieved good environmental protection with comprehensive economic benefits.Certain research results and research methods of this project can be extended to the research and application of dry desulfurization,mercury removal of coal-fired boiler,dioxin removal of waste incineration and other projects,which make contributions to explore the collaborative treatment technology with multi-pollutants such as industrial flue gas,using bag filter as the core.