Simulation And Optimization Of New Baking Process In AOD Furnace For Stainless Steel-making

AOD (Argon and Oxygen Decarburization)furnace is one of the most important equipment for stainless steel-making. The baking quality of AOD furnace directly affects the product quality and energy consumption. At present, the exploration of advanced AOD baker and baking process are carried out in most of the stainless steel making plants at home and abroad to solve the outstanding problems such as high energy consumption, low efficiency and non-uniform baking temperature. Regenerative baking technique is developed on HTAC (high temperature air combustion) technique and is extensive applied to metallurgical equipment especially for the aspect of ladle and tundish baking, however it has not been applied to AOD baking process yet. The configuration of AOD furnace is relatively special because of its long-narrow type, so the application of the advanced combustion technology on AOD needs plenty of research work and innovative design. Therefore, it is very necessary to understand the baking process in AOD and to develop new baking technology.The current status of AOD baking technology, the development of HTAC technique and the feasibility of the application of HTAC technique on AOD, the method of numerical simulation of the AOD baking process were reviewed in this thesis. Combined with research work in steelworks, CFD was employed to simulate the present 120 ton AOD baking process and the application of HTAC in AOD. Main research work and results are described as follows.(1) The distribution of temperature of AOD furnace with present baking process was measured and the temperature uniformity and the distribution in the furnace were obtained. As well as, the composition of off gas was measured, thus the exhaust gas emission during the baking process with natural gas combustion in AOD was understood. All these have provided the important data for the validation of numerical simulation and laid the base for the further system energy saving of AOD.(2) By means of commercial software STAR-CD, the temperature distribution of AOD furnace lining during the present baking process and the combustion characteristics of the baker were investigated with numerical simulation, and the predicted results were validated by actual measurements. The results show that the maximum temperature of AOD furnace lining after baking can reach 1380K, and the biggest temperature difference in the same circle direction is 20K. The temperature at the side close to the outlet is relatively high. The biggest temperature difference in height direction is 56K, and the temperature in the lower-middle part is relatively high. The small flow rate and lower temperature of the off gas in AOD lead to the non-uniform temperature of the wall. The present baking effectiveness is not satisfactory. The predictions are in good agreement with the measured.(3) According to the characteristics of AOD structure and baking process, the new type regenerative AOD baker was designed in order to replace the original combustion system. Combined with the actual situation on site, the complete reform scheme of regenerative equipments was established.(4) In order to study the effect of the new regenerative baker on the baking process in AOD, numerical simulation of gas flow, combustion and heat transfer in AOD during the baking process has been carried out. The influences of air-fuel ratio, preheated air temperature and nature gas flux on the lining temperature and combustion temperature field and distribution of O2/NO in AOD after baking were quantitatively analyzed. The influences of components of various fuels on temperature distribution were presented to investigate the fuel adaptability of the AOD baker. The feasibility of replacing nature gas with mixed gas and other fuels were discussed.Results show that raising the flux of nature gas and preheated air temperature are effective measures to increase the lining temperature, while the influence of air-fuel ratio on the lining temperature is relatively small. Using the regenerative AOD baker, with the flux of nature gas of 380～420Nm3/h and preheated air temperature of about 1073K and air-fuel ration of 10:1～12:1, the lining temperature can reach the desired temperature 1373K, and the temperature difference can maintain lower than 50K, that shows a good uniformity for the temperature. Distribution of O2 in furnace is uniform, and NO concentration is some higher than original baking system. But because the baking time of new system will shorter than before, the total amount of NO is not large. The heating effect of baker using nature gas as fuel is relatively better than other fuels. The heating temperature of mixed gas can also match the requirement of AOD baking, so replacing nature gas is feasible. In addition, the optimal baking parameters for the actual performance were presented in this paper.