Study On Temperature Optimization And Reaction Kinetics Based On Biomass Microwave Pyrolysis System

The compositions of biomass are complex,it is difficult to describe the reaction process of pyrolysis from the microscopic,but the process law will still be presented in the form of apparent phenomena.In the process of biomass microwave pyrolysis,the error caused by temperature data measurement and the time-varying and time-delay of temperature during the control process will have a critical influence on the study of the reaction kinetic and reaction mechanism.Therefore,in this study,the biomass pyrolysis system was modeled,and the fuzzy PID control algorithm was used to improve the temperature control precision of the biomass microwave pyrolysis process.The temperature-optimized biomass microwave pyrolysis reaction kinetics was studied and kinetic parameters were analyzed.This study is expected to provide a theoretical basis for the application field of biomass microwave pyrolysis via comparative analysis with experimental data obtained from conventional pyrolysis.The main conclusions obtained in this paper are as follows:(1)corn stover was selected as feedstock during microwave pyrolysis,the model of the heating process of microwave pyrolysis was built according to the Cohen-Kun formula,the PID control algorithm,the Predictive control algorithm and the fuzzy PID control algorithm were used to control the model.The simulation results showed that: The heating process of corn stalk was used as the transfer function established by the first-order plus pure lag model.After the selected control algorithm was simulated by MATLAB,the PID control algorithm had the largest overshoot(about 19%),and the steady state took 38 s.In the predictive control,the established model transfer function was identified using the least squares method.According to the actual output of the system and the predicted output and the trend of the prediction error curve,it can be seen that the error gradually increased with the increase of the samples number,and the predictive control algorithm was able to reduce the overshoot of the controlled system,but the response speed was slower and the response time increased to 54 s.The control effect of the fuzzy PID was the best,the response time was reduced to 4s,there was no overshoots and the stability is the best.(2)Corn stove lignin,lignin and cellulose were used as raw materials for microwave pyrolysis,the PID control algorithm and fuzzy PID control algorithm were used to optimize the microwave pyrolysis system.The experimental results showed that the heating process of microwave pyrolysis of different raw materials was quite different.The temperature rise curve of lignin in the early pyrolysis was small.The temperature rise effect of fuzzy PID control was better than PID control after one minute,and the time taken for corn stalk to use the fuzzy PID control algorithm to reached the stable temperature value takings about six minutes,which was longer than PID.The control algorithm used less time,the pyrolysis temperature rise curve of cellulose was smoother than that of lignin and corn stover,and the temperature at the end of stabilization was higher than that of PID control,about 520?,and the temperature when the PID control reached stability was 460?,therefore,fuzzy PID control biomass microwave pyrolysis,its response speed was faster,the target set time was shorter,the control effect was better than the traditional PID control.(3)Pyrolysis experiments on lignin,corn stover and cellulose were carried out using a conventional heated thermogravimetric analyzer and a microwave-heated thermogravimetric analyzer.In comparision with ordinary thermogravimetric analysis and microwave pyrolysis of three raw materials,the experimental results showed that the reaction order changed and the apparent activation energy of the reaction significantly decreased.The apparent activation energy for lignin changed from a tertiary reaction to a first-order reaction,and the reaction became simple.Corn stalk changed from a secondary reaction to a first-order reaction,and pyrolysis reaction of cellulose changes from the secondary reaction to the tertiary reaction,the reaction process becomes complicated.(4)The reaction kinetics of microwave pyrolysis biomass were analyzed by PID algorithm and fuzzy PID algorithm.The analysis results indicated that the optimization of temperature using fuzzy PID control algorithm had not changed the chemical process of biomass pyrolysis,and the reaction order had no change.However,the apparent activation energy E of the reaction decreased,the apparentactivation energy E for lignin decreased from 20.13 KJ/mol to 16.65 KJ/mol,corn stover changed from 58.01 KJ/mol to 49.22 KJ/mol,and cellulose decreased from116.02 KJ/mol.Up to 92.97 KJ/mol,so it can be seen that more precise temperature control can reduce the error of the experiment.