Study On The Characteristics Of Oxy-fuel Combustion Of Bituminous Coal Char Particles In A Fluidized Bed

Coal is the dominant energy in China,and coal-fired power plants are the main body of coal consumption.CO2 capture in coal-fired power plants is conducive to achieving national carbon emission reduction targets.Oxy-fuel combustion in fluidized beds has the advantages of clean combustion and low-cost CO2 capture in fluidized beds.It is a promising technology for CO2 capture.Further study on this technology will contribute to the development and the promotion of commercialization process.In this paper,experimental and numerical methods are used to study the reaction characteristics of bituminous coal char in Oxy-fuel atmosphere,extract chemical reaction kinetic parameters and macro-combustion characteristics,and establish combustion model to reveal the combustion mechanism of bituminous coal char particles in oxy-fuel atmosphere.The main contents and achievements of this paper are as follows:(1)The reaction characteristics of bituminous coal char at 900? under the mixed atmosphere of O2?CO2?H2O were systematically investigated in a self-made high-precision thermogravimetric experimental device.The kinetic parameters of the reaction of bituminous coal char with O2?CO2 and H2O were calculated by the L angmuir-Hinshelwood(L-H)mechanism model based on the principle of adsorption and desorption.The interaction mechanism between Char-O2,Char-CO2 and Char-H2O under the atmosphere of O2/CO2,O2/H2O and CO2/H2O was analyzed by using two hypotheses of single active site and competitive active site.It was revealed that H2O molecule adsorbed on the surface of bituminous coal char preferentially,followed by O2 molecule,while CO2 molecule lagged behind relatively.The reactions of Char-O2,Char-CO2 and char-H2O in the atmosphere of O2/CO2/H2O show some competitive active sites.The traditional assumption of single active site and competitive active site can not accurately describe the reaction rate characteristics.Based on the principle of H2O molecule priority and O2 molecule sub-priority adsorption,the kinetic equation of coal char reaction rate L-H was established in the mixed atmosphere of O2 n CO2 and H2O.The calculated results of the equation were in great agreement with the experimental values.(2)The combustion characteristics of bituminous coal char after O2/CO2 replacing O2/N2 were investigated,and a simplified combustion model of coal char was established on a small fluidized bed experimental platform.The influence mechanism of CO2 replacing N2 on the combustion process of coal char was quantitatively analyzed.The results show that the reaction rate of coal char increases with the increase of bed temperature,the increase of O2 concentration and the decrease of particle size in the atmosphere of O2/CO2;the combustion reaction of coal char is controlled by the diffusion of O2,and the gasification reaction is controlled by reaction kinetics;the effect of gasification reaction on the overall reaction rate of bituminous coal char increases with the increase of bed temperature,and the consumption of carbon in gasification reaction accounts for about 7%of total carbon consumption at high bed temperature(?900?).(3)The combustion characteristics of typical coal particles in the atmosphere of O2/CO2/H2O were investigated on a small fluidized bed experimental platform.A particle-scale combustion model was established to quantitatively reveal the combustion mechanism of bituminous coal char particles in the atmosphere of O2/CO2/H2O.The results of experiments and numerical simulation show that the reaction of Char-CO2 and Char-H2O in the atmosphere of O2/CO2/H2O decreases the combustion temperature while increasing the reaction rate.The burnout time and peak temperature of coal char decrease with the increase of the concentration of H2O and CO2.The influence of H2O on combustion characteristics is more significant than that of CO2.The influence of gasification reaction on particle combustion process increases with the increase of H2O concentration.When the concentration of H2O is 40%,the carbon consumption of Char-H2O reaches 18.9%of the particulate carbon content which keeps unchanged,while the carbon consumption of Char-CO2 reaction is relatively small.