Design And Optimization Of A Continuous Flow Microwave Reactor

The preparation of biodiesel by microwave enhanced esterification is a very efficient technology,but most of the microwave reactors are batch reactors,which can only be produced intermittently.In order to realize continuous microwave heating and eliminate the problem of weak microwave penetration,it is necessary to design continuous microwave reactor by combining microwave heating with continuous flow chemistry.In order to achieve continuous microwave heating and better heating effect of the heated material,a multi-mode continuous rectangular microwave reactor with special shape pipe was designed.The electromagnetic field,flow field and temperature field were coupled by numerical simulation method.The distribution of electric field,temperature field and flow field in continuous flow microwave reactor under different conditions were studied by changing the height of pipe,height of waveguide,frequency of microwave source and dielectric properties of material,respectively.Response surface analysis and fitting curve method were used to investigate the internal relationship between microwave electromagnetic field and reactor size,material dielectric properties and other factors.According to the comprehensive analysis results,the optimal structure parameters of reactor and the relationship between process parameters and material temperature rise ratio and residence time were obtained.The specific research contents and conclusions are as follows:(1)Optimization of heating characteristics and structural parameters in the reactor.A continuous rectangular microwave reactor for continuous production was designed.The microwave heating characteristics in the reactor were analyzed by coupling the electromagnetic field,flow field and temperature field of the reactor.The effects of the structure parameters such as the height of waveguide,the height of pipe,the size of pipe diameter and the difference of pipe type on the heating effect and heating uniformity were also analyzed.Finally,taking the heating effect and heating uniformity as indexes,the optimal reactor structure was obtained by response surface analysis method as h_w=0.716,h_c=0.616.(2)The influence of reactor process parameters on heating effect and heating uniformity was analyzed.The effects of microwave frequency,microwave power,material flow rate,material dielectric properties and other process parameters on the heating effect and heating uniformity of the reactor were investigated by using multi physical field coupling method.It was found that the higher the microwave power,the lower the material flow rate,the higher the material temperature rise and the worse the heating uniformity.Then,on the basis of the structural parameters of the highest temperature rise,the fitting equations of the target temperature rise ratio,the residence time of the material after reaching the target temperature rise ratio,the material flow rate and the microwave power were established by fitting curve method.(3)The influence of mode stirring method on reactor efficiency and heating uniformity was analyzed.In order to further optimize the reactor,a mode stirrer was added in the chamber on the basis of the structure of the reactor reaching the highest temperature rise.The electromagnetic field in the cavity is changed by discrete method and coupled with the flow field to form a new temperature field.The reactor efficiency and heating uniformity were investigated by changing the size and height of agitator.Finally,taking the reactor efficiency as the index,the response surface analysis method was used to get the optimal parameters of mode agitator as?_D=0.159,?_C=0.719.At this time,the reactor efficiency reached the highest70.37%,compared with the continuous reactor without mode agitator,the efficiency increased by 8.23%,and the heating uniformity was better improved.