Development Of A Multistage Gas-solid Reaction Analyzer And Experimental Studies On Char Reaction Kinetics

Particle gas-solid reaction kinetics is fundamental to explore new technologies in the fields of energy production,chemical engineering,metallurgy and other industries.In this thesis,a micro fluidized bed reaction analyzer for multistage gas-solid reactions(MFBRA-MR)was developed to determine particle reactivity under reaction rate controlled and rapid conditions.The MFBRA-MR was used to study the intrinsic combustion kinetics of chars prepared from high temperature flame.An in-situ decoupling analysis methodology for multistage gas-solid reaction was proposed to determine the intrinsic reactivity of hot and in-situ particle.The MFBRA–MR was also used to study intrinsic kinetics of steam gasification and rapid combustion of hot and in-situ chars.The design scheme of MFBRA-MR was studied.For the control of reaction conditions,a micro fluidized bed was adopted to provide a reaction condition with efficient heat transfer and mass transfer;the gas-solid reaction was initiated by switching reaction atmosphere fast and smoothly to ensure the accuracy of intrinsic and fast reaction conditions;weak reaction of particle at last stage was accelerated by adjusting reaction temperature quickly to convert reactants completely and ensure the reliability of absolute conversion rate.For the characterization of conversion rate,continuous and rapid detection of the concentration of gas released from a reaction was employed to obtain differential reaction process.Several key technologies have been broken through,including switching atmosphere fast and smoothly,fast adjusting reaction temperature,improving the accuracy of gas concentration detection signals,characterizing the detection distortion of gas concentration curves quantitatively.Several key components have been developed,including a micro fluidized bed quartz reactor with gas preheated in a narrow annulus passageway,a miniature infrared radiation heating furnace and a fast and smooth atmosphere switching device.The complete MFBRA–MR was then designed and ultimately manufactured.The signal stability of a process mass spectrometer was found affected by the temperature fluctuation of the sampling capillary.The mechanism was revealed through experiments.An effective method to improve the stability and repeatability of signals of the process mass spectrometer by using a precision temperature controller and a pressure-regulating device was then invented.The method improved the accuracy of the process mass spectrometer in measuring the rapid changes of gas concentration.This work provided an important guarantee for the MFBRA-MR to analyze the rapid gas-solid reaction process.A calibration theory for the rate measurement results of a fast isothermal and rate controlled gas-solid reaction was proposed.A theoretical and experimental method to quantitatively characterize the detection distortion of gas concentration curves was established.The experimental results of concentration wave response and char combustion showed that the pipe gas flow in the MFBRA-MR approximated plug flow;the concentration detection distortion could be neglected when measuring a reaction with a half-life longer than 3 s.The MFBRA-MR was proved to be excellent in characterizing the intrinsic fast isothermal gas-solid reaction process according to the calibration theory.MFBRA-MR was used to study kinetics of rapid and reaction rate controlled combustion of chars prepared from high temperature flame.The application showed a high operation efficiency and reliable measurement results.The char combustion process can be well described by the nth–order Arrhenius model.The reaction order n was found and proved increased with the increase of temperature and decreased with the increase of conversion rate.This result could explain the dispersive n in the literatures.The intrinsic transition temperature of the rate control region(Tin)was obtained.The Tin of Jincheng char was about 900 °C;The Tin of Datong char was related to oxygen concentration and conversion rate,generally located between 800–900 °C.The MFBRA-MR was used to study steam gasification kinetics of hot and in-situ chars.The results show the measured gas release process can directly characterize the gasification process when an MFBRA-MR equipped a water removal system was used to measure a slow reaction process.Char was not completely gasified at 800–950 °C.A lower temperature would derive a lower final carbon conversion rate and the steam concentration had no significant effect on the final carbon conversion rate.Gasification no longer accelerated with increasing steam concentration from 25%.The carbon conversion process was well described by both the shrinking core model and the random pore model.The kinetic parameters calculated from relative or absolute conversions differed from each other.Absolute conversion avoided mutation effects and should be used for kinetic study.The char activity was decreased significantly by cooling and reheating.The main reason was due to the change of chemical structure.Deactivation of highly reactive chars was more sensitive to cooling and reheating than that of less reactive chars.The MFBRA-MR was also used to study intrinsic and rapid reaction kinetics of hot and in-situ char combustion.The procedures showed the performances of atmosphere switching and temperature fast adjusting were both reliable;the reaction conditions and the measurement results were both accurate.The results show that Tin of Shenhua in-situ char combustion was about 700 °C.The activation energy under rapid and rate controlled reaction conditions was about 125 kJ/mol.The experimental results show that a lower rank of coal was more sensitive to the char deactivation caused by cooling and reheating.When conducting experiments on combustion or gasification kinetics of low rank fuels,such as high volatile bituminous coal,lignite or biomass,it is necessary to consider the effects of cooling and reheating of samples on test results.The typical application examples proved MFBRA–MR achieved excellent performances in the organization of multistage isothermal reaction process,determination of intrinsic and rapid gas-solid reaction rate,and reliable characterization of the intrinsic reactivity of hot and in-situ particle.The MFBRA-MR has broad application prospects in gas-solid reaction study.