Study On Simulation And Optimization Of High-temperature Electric Heating Process

With the development of new material industry, the industrial electric heating equipment is widely applied. Controlling product quality, decreasing energy consumption, keeping production safety are the goals for the development of industrial electric heating equipment. This paper treated the Process System Engineering (PSE) Theory as guide, applied the Finite Element Method (FEM) to analyze the heating process of high-temperature resistance furnace for benefiting the high-temperature electric heating process research.This thesis reviewed the feature and development of PSE, FEM and Acheson resistance furnace. The open source FEM software-FEPG was introduced; this work discussed the development of high-temperature resistance furnace, analyzed the research trends of furnace type improvement, process improvement and simulation optimization of silicon carbide (SiC) furnace and graphitizing furnace at domestic and overseas. Based on the analysis of question of resistance furnace heating process, this work presented the research directions.Through the analysis of Acheson resistance furnace, the 2D nonlinear dynamic heat transfer FEM model was built by principle of virtual work. Through the analysis of process of reaction release the gas, the 2D thermal-seepage coupled FEM model was built. Considering the deformation and stress of furnace and equipment component, the 3D thermal-deformation-stress coupled FEM model was built. Because the charge material is built by a variety of particle, the mixed model was simplified to stratified homogeneous model and was described by modified heat percolation model. Based on the FEM calculation and comparison with existing literature, the results showed that the FEM model built by this work and the calculation method of effective heat conductivity of charge material are effective. By the FEM model, the production process was analyzed for Acheson SiC furnace (effective width and highness is 2.1m×1.9m, furnace core profile width and highness is 0.35m×0.6m, the unit volume load of furnace core is 8.5×10~5W/m~3):(1)The dynamic temperature field distributions, temperature gradient on one horizontal line at different moment, the heat flux change were analyzed. The yield and unit product energy consumption were investigated with the process of production trend. The results showed the yield linear increase dependence the time, and the unit product energy consumption have the trend from high to low, then steady, at last rising. The temperature of furnace core surface has the closely relation with energy consumption. the steady low energy consumption phase corresponds to the process of form some point of core surface reaching 2600℃to total over 2600℃.it is means the phase is the highest stage of thermal efficiency. it is the best moment for production shutdown when the temperature of core total over 2600℃. Through analysis the temperature gradient and heat flux, the maximum temperature gradient occur the zone synthesis SiC, and the heat flux of furnace surface is increasing dependence time.(2) The spouting of Acheson SiC furnace still is the problem not resolved. This thesis applied thermal-seepage coupled FEM, investigated the pressure and gas flux with normal production condition, increasing load of core, increasing charge material density with seepage coefficient become smaller. The spouting reasons were discovered: 1) Unsuitable charging mixture ratio lead to gas seepage coefficient become smaller. 2) The higher load causes the reaction too fast to release the gas.(3) The graphite electrode part in furnace and part out of furnace, and connect with high temperature charging and itself product heat with the production process. For investigating if the electrode will be damage, the thermal-deformation-stress coupled FEM was applied. The temperature distribution, deformation and main stress of electrode were acquired. The results showed that the outer electrode temperature blow 90℃and no oxidation reaction damage, the total temperature difference less than 20 and no deformation. So the electrode will be safe in normal production condition. For enforcing the electrode safety, the programs of thickness of electrode protective coating was put forward basing the calculation results. For solving the problem of high energy consumption and spouting of Acheson SiC furnace, this work applied thermal-seepage coupled FEM with PSE theory to simulate production process of SiC furnace(effective width and highness is 2.3m×2.1m, furnace core profile width and highness is 0.35m×0.6m, the unit volume load of furnace core is 8.8×10~5W/m~3). Author divided the production process into three phases: 1) The Pre-production, the heat is used to heat the charge material and the SiC synthesis reaction not yet start, this phase should be finished as soon as possible for saving energy. 2) The mid-production, it is the phase that form reaction start to temperature of core surface over 2600℃, this phase should be finished as soon as possible but spouting must be controlled. 3) The latter-production, the phase is form some points reach 2600℃to all the surface reach 2600℃of furnace core, the reaction should be controlled to keep product increasing and decrease SiC decomposition and heat loss of furnace surface. Based on analysis of three phases, this work built minimum energy consumption as objective function and simplified optimization strategy with spouting as main limiting condition, acquired optimized power curve. The calculation results showed that applying optimal power curve will avoid spouting, the optimal results can be got that are energy consumption decreasing 8% and output increasing 3%, output increasing 12% and energy consumption decreasing 5% by choosing different shutdown time.According to the references, the thermal efficiency of SiC furnace and graphitizing furnace is about 50% because of great heat loss. based on FEM analysis of two type furnace, the LWG graphitizing furnace vice-product SiC process was put forward and the example (above mentioned unit volume load of furnace core is 8.8×10~5W/m~3 ) was simulated. The results showed that the SiC energy consumption is half of Acheson SiC furnace and output is 54-68% of Acheson SiC furnace after deduction the graphite manufacture energy, and the new process reduce the total waste gas emission; For solving the Acheson furnace's problem of poor insulation, spouting, low product quality, high energy consumption and dust pollution, this paper put forward a new type SiC furnace with enforcing insulation, parallel, good ventilation. The new type furnace not only enforces the insulation but also avoid spouting, and the gas released as the insulation layer. The new type furnace also easy transports the gas to waste gas gathering unit. The new type furnace can be got by reform exiting Acheson SiC furnace and have 15-17% energy consumption saving after reform.