| Ladle is an indispensable equipment in the process of steel smelting.In the process of ladle transfer,high temperature molten steel will produce heat loss and cause the temperature of molten steel to drop.Molten steel temperature is a key index to measure the energy consumption in steelmaking.Every time the molten steel discharge temperature decreases by 1 K,the cost of per ton of steel decreases by 0.5-2 yuan.The temperature of molten steel is generally 10 K higher than that of foreign countries.Reducing the temperature of molten steel and the temperature drop during transfer is the main means of saving energy and reducing consumption.The preheating of ladle baking can effectively reduce the heat loss during the transfer of molten steel,thus reducing the temperature of molten steel.At present,ladle baking is faced with such problems as low efficiency,large heat loss,difficult to control air-combustion ratio and large consumption of refractory materials.In the face of these problems,a new type of ladle baking process for natural gas with Oxy-fuel combustion was developed,considering the high combustion temperature of Oxy-fuel combustion theory and low heat loss of flue gas.In this paper,the combustion field,energy saving,economy and so on are studied by establishing the combustion,heat transfer and three-dimensional unsteady state mathematical models for the baking process of Oxy-fuel combustion ladle.The flow in the baking area is turbulent during the baking process of the Oxy-fuel combustion aid ladle.The flow in the baking area was turbulent and the standard k-εmodel was used.The finite rate reaction model is adopted for combustion of non-premix gas,and the reaction rate is controlled by the vorticity dissipation model.The heat transfer process in baking area includes three basic heat transfer modes,among which the dominant mode is radiation heat transfer process,which is described by P-1 radiation model.Due to the combustion mode of natural gas with pure oxygen,its combustion products are mainly H2O and CO2,which have a strong enhancement effect on the radiation heat transfer of gas.However,the traditional WSGGM model used to calculate the radiation absorption coefficient of gas in the radiation model cannot accurately describe this process,so this paper modifies the traditional WSGGM model and coupling it with the radiation model.The influence of inlet conditions on the structure and temperature distribution of Oxy-fuel combustion flame was studied.The distribution of temperature,flow and combustion products in the baking area during the ladle baking process of Oxy-fuel combustion was analyzed,and the comparison with the ladle baking method of air combustion was made.Based on the comparison results,the baking process of Oxy-fuel combustion ladle was optimized,and the combined baking method of Oxy-fuel combustion in the first stage a was put forwardCompared with the traditional WSGGM model,the modified WSGGM model refined the partial pressure ratio of H2O and CO2,improved sensitivity and accuracy,and expanded the scope of application.The numerical simulation results show that the modified WSGGM model has a fast response to the temperature at the initial baking stage with an obvious change trend.After the whole baking process enters a stable state,the simulated temperature corresponding to the modified model is 12-14 K higher than that of the original model.The comparison between the simulation results of Oxy-fuel combustion and air combustion ladle shows that the Oxy-fuel combustion fume volume is only one third of that of air combustion,and the corresponding heat dissipation loss of flue gas is small.The Oxy-fuel combustion has short baking time and high baking efficiency.The final temperature of Oxy-fuel combustion assisted baking is 1551 K,and the final temperature of air combustion assisted baking is 1200 K.For ladle in this paper,Oxy-fuel combustion baking can save fuel 41.68%compared with air combustion assisted baking.After adopting the optimized combined baking method,although the first stage baking time was extended from 4 h to 5 h to optimize the ladle baking process,namely,the first stage adopted the air combustion,the last two stages adopted the Oxy-fuel combustion,which can give full play to the high combustion temperature characteristic of Oxy-fuel combustion assisted theory.Compared with the whole stage air combustion,the combined baking method can save 124.8 m3 of oxygen and 39.6%of fuel.The study on flame length shows that when the gas speed is 11.2 m/s,the longest flame length is 1.81 m and the highest temperature is 2900.41 K.When the gas speed is 6.30 m/s,the shortest flame length is 1.06 m and the lowest temperature is 2387.25 K.When the auxiliary gas speed is 4.09 m/s,the longest flame length is 1.22 m and the lowest temperature is 2249.35 K.When the gas speed is 1.47 m/s,the shortest flame length is 0.69 m,and the overall maximum temperature increases as the gas speed decreases.It is recommended that the optimal ladle baking gas speed is between 6.3-4.03 m/s,and the auxiliary gas speed is between 2.3-1.47 m/s,while taking into account the coordination between the two.In summary,a three-dimensional unsteady mathematical model of combustion,heat transfer and flow in Oxy-fuel combustion ladle baking process was established in this study.The distribution law of temperature,flow field and concentration of combustion products during the ladle baking of Oxy-fuel combustion was studied,the influence of inlet conditions on the temperature distribution was analyzed,and the optimizationscheme for the baking process was put forward.The research results provided theoretical basis for the improvement and practical application of the Oxy-fuel combustion ladle baking process. |
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