Application And Fundamental Study Of Granulated Copper Slag Waste Heat Recovery And Carbon-based Direct Reduction

Copper smelting industry is an energy and resource intensive enterprise.Improving the new technology of energy saving in copper smelting industry is an important way to realize the goal of energy saving and emission reduction in China.Copper slag is a by-product of copper smelting process with high yield and high recovery value of waste heat and iron.In order to solve the recovery problem of waste heat and metal in copper slag by traditional water quenched method,this paper presents the technology of copper slag granulation,waste heat recovery and direct reduction within carbon(TER-DR).By experimental demonstration and theoretical analysis,basic research data was provided for the implementation of this method.Besides,the research is to solve global problem to recover copper slag waste heat and valuable metal efficiently and green recycle.The researches were carried out as follow.(1)In order to recover the waste heat and iron from molten copper slag,TER-DR technology system was proposed based on the granulation technology and direct reduction technology.The feasibility analysis of the technology was carried out by using thermal compass method.Exergy efficiency and thermal efficiency of different recovery method were systematicly analyzed.Four kinds of typical endothermic chemistry reactions were studied.Compared with physical method,exergy efficiency and exergy value was improved greatly.As the optimal waste heat recovery model,biomass gasification-pyrolysis strengthen system can prepare syngas,biochar and recover waste heat of copper slag.(2)Copper slag granulation is an important step to realize the recovery of waste heat.To verify the feasibility of the granulation technology of copper slag,the melting point,chemical composition,phase composition and viscosity were tested at first.Then,rotor cup granulation experiments were carried out.Copper slag particles with uniform particle size distribution were prepared.With the increase of rotating speed,diameter of copper slag particle increases.(3)Using granulated copper slag particle as heat carrier,biomass pyrolysis experiments were carried out.The effects of biomass type,temperature and heating rate on biomass pyrolysis weight loss and weight loss rate were investigated.The composition of biomass pyrolysis gas,phase composition and surface morphology of biochar were investigated.It was found that copper slag had catalysis function of biomass pyrolysis process and it improve the production of hydrogen.(4)In order to find out the conversion rule of slag concentration in the reduction process of copper slag,calculation model of CaO-FeO-Fe2O3-SiO2 action concentration slag system was established.Simplified mechanism thermodynamics calculation was carried out by four main ingredients of copper slag.In order to find out the equilibrium composition change rule of slag and gas in copper slag reduction process,phase equilibrium calculation model was established.As four kinds of elemental typical reducer,the reduction of C,CO,H2 and CH4 was studied.The variation rule of equlibrium composition,reduction degree under influence of temperature,C/O and Ca/Si was studied.When concentration of reducer improves,reduction degree of Fe3O4 increases.However,reducer concentration can not change phase conversion temperature.CaO can participate separation process of Si from copper slag and improves reduction rate.By indirect reduction index,variation law with C and CO co-existence conditions was found out.Direct reduction verification experiment by biochar,veracity of phase equilibrium calculation model was verified.(5)In order to study the effects of direct reduction kenetics,the direct reduction thermogravimetry experiment of copper slag was carried out using biochar and coal as reducer.The effects of C/O and Ca/Si on weight loss rate,peak temperature and activation energy were investigated.It is found that the addition of CaO can improve the reduction weight loss rate of per mass of copper slag(RML),promote the peak temperature of the direct reduction interval to the low temperature area,improve the reduction rate and reduce the reaction activation energy.When Ca/Si is 1.0,the effect works best,which also verifies the correctness of action concentration calculation model and phase equilibrium model calculation above.When C/O increases,RML,reduction rate increases and reaction activation energy decreases,however the peak temperature remains unchanged.In the early stage of the reduction reaction of copper slag,reduction process is controlled by the diffusion of C and O(D4 model),in the stage of later stage of reduction,reaction is controlled by interface chemical reaction(C2 model).When Ca/Si and C/O change,the restrictive process link of reduction reaction remains unchanged.(7)The preparation experiments of carbon based copper slag pellets were carried out with biomass as binder,coal and biochar as reducer.With increase of biomass addition ratio,the compressive strength of carbon based copper slag pellets has been greatly improved.The direct reduction of carbon based copper slag pellets was carried out with biomass and coal as reducer.The effects of reaction temperature,reaction time,C/O and Ca/Si on RML,and phase compositions were investigated.The thermodynamic calculation results were verified.The transport process of Fe and Cu from copper slag particles was studied based on SEM-EDS.Combined with the results of thermodynamic calculation,dynamic experiment and reduction experiment,direct reduction mechanism of copper slag within carbon pellets was established.