| The ferroalloy smelting process has been widely adopted in various energy-intensive industries.Nonetheless,it suffers from several drawbacks such as high energy consumption,large amount of pollution and emissions.Currently,a number of smelting methodologies are commonly adopted for producing the ferroalloy including blast furnace process,electric furnace and outside furnace process.The preheating reduction-electric furnace process(i.e.reducing electric furnace)has the characteristics of a great potential in energy saving,strong adaptability of raw materials,high grade of ferronickel alloy,less harmful elements and high production efficiency.It is therefore widerly used in production of ferroalloy.The preheating reduction-electric furnace process not only involoves heat and mass transfer and phase transformation physical processes,but also incorporates many chemical reactions such as dissociation,reduction,replacement reactions and so on.The process is obviously a complex system with the material and energy flows coordinated operations.The exisiting challenge for engineers/researchers is to enhance performance and efficiency of such coordinated operation,such as recycling rate of by-product energy and re-resourcization rate of solid waste.To promote the quality of ferroalloy products and maximize the potential energy saving opportunity,it is therefore a pressing need to grasp a full understanding of the material and energy flows coordinated operation in the whole process and establish the evaluation indices for providing a guideline for optimizing the operating process and designing a novel smelting process with high performance.In this work,a multidisciplinary synergy research method was applied to investigate the preheating reduction-electric furnace process.The aim of this work is to reveal the running rules of the material and energy flows coordinated operation in the preheating reduction-electric furnace process.The analysis methods of energy and exergy were used for quantitatively analyzing the energy flow from both quantity and quality aspects respectively.The synergy analysis was used for quantitatively evaluating the order degrees of material and energy flows,as well as the synergy degree.The numerical analysis was used to study the co-combustion of pulverized coal and flue gas and the multi-phase flow of gas,pulverized coal and particle in rotary kiln.The temperature distribution under magnetical-thermal coupled action has also been studied to reveal the characteristics of multi-physical fields undergo a high temperature smelting in electric furnace.A summary of the main achievements of this work are listed as follows:A XRD,X ray fluorescence analysis and flame atomic absorption spectrometry were used to analyze the chemical compositions and element contents of the ores,product and slag.The real-time monitoring equipment was used to measure the key parameters of material and energy flows,such as flow rate,pressure,temperature.The measurement data were used to further research.Through analyzing the running rules of material and energy flows in preheating reduction-electric furnace process,based on the fundamental mass conservation and energy conservation,a material and energy flows analysis model with internal cycling of material and energy has been developed for the preheating reduction-electric furnace process.The energy analysis method has identified and quantified the available energy of system,and be used to establish the evaluation indices of energy efficiency.Through assessing the performance of several energy saving technological options,such as recycling the waste gas of rotary kiln and electric furnace,this study found that the bituminous coal consumption could be reduced by about 45.94%and 38.00%,respectively.By recycling the residual heat of rotary dryer flue gas and electric furnace slag,the energy efficiency of system could be increased by 2.97%and 24.6%,respectively.Using mold flux for avoiding heat dissipation of alloy,the energy flow discharge rate of electric furnace could be reduced by 4.74%.The synergy relationship of material and energy flows was established by synergetic theory in the preheating reduction-electric furnace process.By introducing the evaluation indices of order parameters,the order degrees,coordination ability and mismatching degree of material and energy flows was then clearly defined and quantativelly evaluated.The evaluation method of synergy degree between material flow and energy flow was established.Using the running rules of material and energy flows to formulate the production index,then the order degrees of material flow and energy flow could be improved.It was found that the synergy degree of test 1(alloy containing 12 mass%Ni)was 9.51%higher than that of test 2(alloy containing 14 mass%Ni).Recycling rotary dryer flue gas and electric furnace slag could increase the material flow indices,such as recirculation rate of waste and re-resourcization rate of solid waste,and improve energy flow indices,such as energy efficiency,recycling rate of residual heat and energy,as well as discharge rate of energy flow.The synergy degree between material flow and energy flow could then be increased by 24.93%.An exergy analysis model of the whole process has also been established in this work.The assessment indices provide an effective mean to measure the exergy efficiency of the process.The results have showed that:the exergy destruction of rotary dryer,rotary kiln and electric furnace were of 38.159GJ/h,118.511GJ/h and 9.766GJ/h,respectively;the exterior exergy loss of rotary dryer,rotary kiln and electric furnace were of 30.530GJ/h,22.857GJ/h and 89.229GJ/h,respectively.Based on the analysis of the exergy flow,some measures were identified to reduce exterior exergy loss due to heat dissipation,such as reducing outlet temperature of output flows,improving the thermal insulation property of furnace and conveying equipment,and recycling residual heat of high temperature output flows.A model of co-combustion of pulverized coal and furnace gas has also been developed for the rotary kiln.The finite-rate/eddy-dissipation model was employed to model the gas phase turbulence-chemical reaction.The released of volatiles was expressed using the single kinetic rate devolatilization model while the surface combustion was modeled by the multiple-surface-reaction model.The effects of co-combustion on the combustion rate of pulverized coal and flame characteristics were analyzed.The influences of solid-gas fuel co-combustion on the calcination zone,temperature of kiln and flue gas composition were investigated.The finding showed that recycling the furnace gas not only increases the recycling rate of residual heat and energy but also increases the exergy efficiency of rotary kiln which in term improves the synergy degree between material flow and energy flow.The Andre-Mukulihski method was also applied to calculate the geometrical parameters of electric furnace.An electrical/magnetic/thermal muti-physics field coupling model for high temperature smelting process of electric furnace was developed.The magnetic vector potential method was used to resolve the current,magnetic induction and joule heat.The load vector method was coupled with the joule heat to capture the temperature distribution under magnetical-thermal coupled action.The effect of electrode diameter size,pitch circle diameter size and furnace height on temperature distribution was analyzed,while the influence factors of temperature distribution were revealed in electric furnace.The analysis showed that when the electrode diameter,pitch circle diameter size and furnace height size are of 1.4m,4.27m and 4.2m respectively,it could result in a more reasonable temperature distribution within the electric furnace.Therefore,optimizating the geometry parameters of electric furnace not only increases the utilization rate of electricity but also reduces the exergy destruction as well as improving the order degree of material and energy flows. |
PDF Full Text Request