Research On Chlorination Process Of High Aluminum Fly Ash

Fly ash is a kind of solid waste which is formed in the process of power generation or coal-fired heating.With an annual emissiom of up to 320 million tons,a series of pollution was caused by fly ash,such as soil,air and water and affecting human health.The alumina content in high-alumina fly ash is usually up to about 30～50%,which have the same equivalent to low-grade bauxite in China.For this reason the high alumina fly ash can be used as an alumina resource.At present,the high alumina fly ash to extract alumina mainly contain limestone sintering method,soda lime sintering method and acid method,but these methods all have the shortcomings such as high cost,high energy consumption,lower alumina leaching rate,complex process,and emissions of air and water.In this paper,aiming at the problem of alumina extraction from high-alumina fly ash,a method for preparing aluminum chloride by high-fly ash chlorination was proposed.The thermodynamic conditions of the chlorination process were studied to provide a theoretical basis for the chlorination reaction The chlorination process of single factor and orthogonal experiment to determine the appropriate conditions,analysis of high-aluminum fly ash in the chlorination process of alumina and silica dynamics,the relevant content and results are as follows:(1)The standard Gibbs free energies of chloride oxidation in fly ash are all negative in the temperature range from 273.15K to 1273.15K,which indicates that the above reactions are all positive in this temperature range.When the temperature higher than 900K,the order of chlorination reaction is K2O>Na2O>Fe2O3>CaO>Al2O3>TiO2>MgO>SiO2.The main components of fly ash are silica and alumina.It can be seen from the thermodynamic data that the standard Gibbs free energy of the chlorination reaction of silica is higher.Therefore,alumina is first chlorinated during the process.From the phase diagram of gas phase equilibrium,it can be seen that the main components of high-aluminum fly ash can produce the corresponding chlorides in the chlorination reaction and the chlorination reaction is relatively complete.The residual carbon in the high-alumina fly ash has no effect on the reaction.The results of chlorination process showed that both AlCl3 and SiCl4 could be stable at different temperatures.The increase of CO partial pressure was beneficial to the existence of chloride.With the increase of partial pressure of CO2,AlCl3 and SiCl4 were opposite to Al2O3 and Al6Si2O13 phase transition.(2)Single-factor experiment of chlorination of high-aluminum fly ash was carried out.The results show that the reaction temperature is 1000℃,the time is 40min,the carbon ratio is 4.5:1,the diameter of the pellet is 8mm,the flow rate of chlorine gas is 0.38 L/min,the aluminum oxide The chlorination rate reached 84%,and the silica chlorination rate reached 70%.(3)According to the results of single factor experiment,the orthogonal experiment was carried out on the five factors of chlorination temperature,chlorination time,carbon ratio,pellet diameter and chlorine flow rate.The experiment determined the influence of five factors on the experiment:time>ratio of carbon>temperature>flow rate of chlorine>diameter of pellet.It can be seen from orthogonal experiment analysis of variance that time factor is highly influenced on chlorination experiment.The carbon ratio and temperature have a significant impact on the experiment,and the flow rate of chlorine and the diameter of the pellet less impact on the reaction.(4)The experimental results of chlorination kinetics of high-aluminum fly ash show that the chlorination temperature and the carbon ratio have great influence on the experiment,which accords with the unreacted nuclear model without solid product layer.Kinetic equation of chlorination reaction.The apparent activation energy of the reaction of alumina at different temperature is 161.03 kJ/mol,the kinetic equation is:#12The kinetic equation of alumina under different carbon ratio is lnk=0.43637lnR-5.22652Under different temperature conditions,the apparent activation energy of the reaction of silica is 56.89 kJ/mol,the kinetic equation is:#12The kinetic equation of silica at different carbon ratio is lnk=0.39631nR-5.88708...