Pedchenko A. Thermoelectric state of Castner graphitization furnaces

The dissertation deals with the important scientific task of creating the scientific basis for development and enhancement of furnace equipment and its operation instructions during the graphitization process of large-size electrode production in Castner's furnace. It allows to determine the rational technical solutions and increase the production quality using minimal material and labour resources, saving the energy in such a way. The physical model was developed and the usage of the mathematical model for the graphitization process of electrode production in Castner's furnace was considered taking the following factors into account: thermal effects of chemical gasification reactions in the carbon material, hydrogen and carbon oxide conversion in the thermal insulating material, mechanism of damp and vapour transfer, graphite sublimation, thermo-electrical and mechanical contact interaction between the furnace construction elements. The mathematical model of the directly fired furnace is based on the system of nonlinear differential equations of thermal and electrical conductivity and the balance of the mechanical motion in the incremental form with the usage of the mechanical model for the granular Drucker-Prager medium. The model describes the mechanical and thermo-electrical state of Castner's graphitization furnace taking into account the contact interaction of the thermo-electrical and mechanical nature of the boundary "granular material-solid body". The numerical methodology for the problem of the thermo-electrical and mechanical state was developed on the basis of the finite elements. The appropriate software was designed and it underwent testing. The numerical model of the mechanical and thermo-electrical state of the directly fired furnace was developed based on the dependence of the physical properties of carbon materials on the temperature and pressure. The numerical model enables to collect data from the physical fields and thermal expenditures under various guidelines of electrical power, thermal insulating material loads, granular materials moisture etc. It is required for improvement of the current and future furnace equipment and energy efficient guidelines of its operation. Based on the developed electrical artifacts load scheme, scheme of the experimental indicators installation, experimental research methodology, it was possible to conduct a research on the thermo-electrical state of Castner's furnace during the graphitization process of electrode artifacts with the diameter of 435 mm. It was experimentally proved that the gasification process of carbon material takes place in the form of vapour in the furnace operation areas during the electrode production heating. It leads to the heating velocity decrease of the electrode artifacts under the temperature 600-900 °С by 10-20 %. Based on the gained experimental data, the verification of the numerical model of the thermal and electrical state of the furnace was conducted. It was found out that the relative violation between the values of average temperatures, gained from the computer modelling and physical experiments, is up to 4 % within the temperature range up to 1600 °С. Based on the conducted numerical analyses of the influence of the technological instructions on the graphitization process of the carbon production in Castner's furnace, the technical solutions were developed in order to minimize the temperature fall in the terminal artifacts. It was determined that the usage of the special compensation conducting elements in the form of empty graphite cylinders filled with thermal high-resistant insulating material is the most efficient solution. The results of the theoretical and experimental researches are implemented into production for development of the rational constructions and technological instructions for Castner's furnace operation. The results are protected by useful model patents.