The Simulation And Experiment Study Based On Manganese Oxygen Carriers Of Coal-fueled Chemical Looping Gasification

The coal chemical looping gasification technology applies the theory of "flameless combustion" to the circulating fluidized bed,and realizes the clean conversion of coal by means of oxygen carrier to transfer the oxygen and heat needed in the coal gasification process.At present,the industrial application of coal chemical looping gasification technology is not mature,among which the self-heating operation of megawatt device,the large-scale preparation of oxygen carriers and the regulation of reaction performance still need to be solved.In order to solve the above problems,this paper first uses Aspen Plus software to analyze the thermodynamics of coal chemical looping gasification;through the preparation of manganese perovskite oxygen carrier,then studies the performance of manganese perovskite oxygen carrier/coal chemical looping gasification reaction and the evolution law of oxygen carrier structure in the process of cyclic reaction.The main research contents are as follows:(1)The process model of 1 MWth coal chemical looping gasification was established by Gibbs free energy minimization method.The influence of coal type(Ningxia coal,Xinjiang coal,Yunnan coal),oxygen carrier type(hematite,natural manganese ore),operating temperature in fuel reactor,O/C ratio,pressure,steam/coal ratio on the generation of syngas in the system and the conditions for realizing self-heat balance operation of the system are discussed.The results show that in the range of 700?1200?,with the increase of temperature,the syngas yield and cold gas efficiency of three kinds of coal increase first and then tend to be flat.When the steam/coal mass ratio increases in the range of 0.5?1.5 and the pressure increases in the range of 0.1?3.0 MPa,the yield of syngas will decrease.With the increase of O/C molar ratio in the range of 0.1?1.7,the yield of syngas decreased significantly,and the system changed from external heat supply to external heat release.When the system realizes self-heat balance operation,the O/C molar ratio of hematite and natural manganese ore is 1.1 and 1.5 respectively.Under the premise of ensuring reaction rate and economic cost,natural manganese ore is preferred as oxygen carrier.(2)Mn-based perovskite oxygen carrier(MnSFMCH)was prepared by using waste manganese sand filter material and calcium hydroxide.The waste manganese sand filter material was reused as a new manganese source.In addition,under the same experimental conditions,the perovskite oxygen carrier prepared by natural manganese ore combined with calcium hydroxide(MnCH)was compared.The thermogravimetry experiment shows that under the same O/C ratio,compared with the MnCH oxygen carrier,the reaction of MnSFMCH oxygen carrier with coal is more thorough,and it can release 1151 J/g more heat when reacting with coal.When the same mass of MnCH and MnSFMCH oxygen carrier react with H2 and CO respectively,the conversion of MnSFMCH oxygen carrier is significantly higher than that of MnCH oxygen carrier at the same time.The results of fluidized bed experiment show that the syngas yield,instantaneous gasification rate and carbon conversion using MnSFMCH oxygen carrier are higher than MnCH oxygen carrier.Both of them release gaseous oxygen in an inert atmosphere at 950?,but MnSFMCH oxygen carrier shows a higher release rate of gaseous oxygen.(3)In the thermogravimetric and fluidized bed,reaction performance,attrition performance of the manganese-based perovskite oxygen carrier during circulation were investigated,and then XRD,N2 adsorption/desorption and SEM were used to analyze the evolution of crystal structure,pore structure and morphology of oxygen carrier in the process of multiple cycles.The weight loss of MnSFMCH oxygen carrier is more stable in each reduction process.After 4 cycles,the actual oxygen carrying capacity of the oxygen carrier decreased from 17.5%to 16.78%,with a decrease of about 4.1%.And the actual oxygen carrying capacity of the MnCH oxygen carrier dropped from 10.5%to 9.0%,a decrease of about 14.3%.In the 20-cycle experiment of the fluidized bed,when using MnSFMCH oxygen carrier,the gas fluctuations at each outlet during coal chemical looping gasification were smaller,and the synthesis gas yield was higher.The average attrition rates of MnCH and MnSFMCH oxygen carriers are 0.14%/h and 0.11%/h,respectively.XRD analysis showed that the crystal structure of MnSFMCH oxygen carrier was mainly CaMn0.7Fe0.3O2.845 during the cyclic experiments.SEM analysis shows that the MnSFMCH oxygen carrier particles have good appearance and no obvious sintering phenomenon.Considering the reaction performance,cycle stability and attrition resistance of two manganese perovskite oxygen carriers,MnSFMCH oxygen carrier is more suitable for large-scale application of coal chemical looping gasification process.