| The clean coal utilization technology has great significance to the national strategic goal of "carbon peak and carbon neutrality".The gas-solid reactor is the core of clean coal utilization technology and is widely used in the coal chemical industry.Reactor modeling is important to reactor design,operation,and optimization.Thus,the mathematical model of reactor must be able to describe the actual characteristics of transport phenomena and reactions more accurately.The particles present behavior characteristics in the the gas-solid reactors of the coal chemical industry,including the form variation caused by physical property change(such as fragmentation,agglomeration,and fusion),and the flow phenomena caused by the reactor operation and particle distribution(auch as gas channeling,and circulation).Furthermore,the behavior characteristics of particles have influence to the fluid distribution,transfer and reaction rates.Thus,the gas-solid reactors of the coal chemical industry present complex internal transport and reaction phenomena.Unfortunately,the influence of particle behavior characteristics is rarely considered in most mathematical models of the reactor.Therefore,the effect of particle behavior characteristics on fluid distribution,transport and reaction rates were considered in the proposed model and the model was applied to the gas-solid reactors of the coal chemical industry in this work.Moreover,simulation results of the reactor model were analyzed to provide guidance for the design and operation of the reactor.The content of this paper was as follows:Chapter 2 was the literature review of the heat transfer model and particle behavior characteristics in the gas-solid reactor.The heat transfer models and the behavior characteristics of solid particles in typical reactors,including fixed bed,moving bed,fluidized bed,and entrained-flow bed,were introduced.The heat transfer model of fixed bed and moving bed included gas-solid heat transfer model,bed-wall heat transfer model,and radiation model.The heat transfer model of fluidized bed mainly included interphase heat transfer and bed-wall heat transfer models.The heat transfer model in the entrained-flow bed was mainly divided into fluid-wall heat transfer and radiation models.The behavior characteristics of solid particles presented diversity in different types of reactors.The particle behavior characteristics in the moving bed gasifier included fragmentation,agglomeration,and the gas channeling due to the nonuniformity distribution of particles.There were entrainment,elutriation,and circulation of particles in the fluidized bed,and particle agglomeration occurred in the fluidized bed gasifier at high temperature.The interaction between particles and wall was prominent in the entrained-flow gasifier under the influence of flow field and high temperature,such as collision,adhesion,and separation.Chapter 3 was the modeling of molten ash slagging moving bed gasifier.In this chapter,a two-phase model of molten ash slagging moving bed gasifier was proposed.In the proposed model,the effects of particle behavior characteristics on the bed were considered,including:(ⅰ)particle fragmentation and agglomeration change particle size and bed voidage;(ⅱ)the gas channeling caused by non-uniformity distribution of particles weakens the efficiency of two-phase heat transfer,and gas-phase temperature change;(ⅲ)the molten ash covering part of the particle surface reduces the gas-solid chemical reaction rate under the high temperature in the combustion and gasification zones.Industrial data were used for model validation,and the simulation results of the model were consistent with the industrial data.Then,the operating and model parameters analyses were carried out.According to the simulation results with different operating pressures(2.5 MPa(G),4.0 MPa(G),6.0 MPa(G)),oxygen coal ratio(2.5,0.33,0.40),and steam coal ratio(0.20,0.32,0.40),the steam coal ratio had the greatest influence on the outlet gas composition.The mole fraction of CO decreased significantly(decreased from 63.98%to 54.68%)when the steam coal ratio changed from 0.20 to 0.40.On the contrary,the mole fraction of H2 and CO2 increased.The mole fraction change of CO,H2,and CO2 was caused by the water gas shift reaction.On the other hand,the effects of the factors of gas channeling(fch and fchg)on the two-phase temperature in the countercurrent section were analyzed in the model parameter analysis.The temperature equation of the proposed model at the initial boundary of the countercurrent section showed high nonlinearity due to the influence of the strong coupling of the chemical reaction and gas-solid heat transfer.Therefore,the change of fch and fchg had an obvious effect on the temperature at the initial boundary of the countercurrent section,and the effect of fch was more significant.Chapter 4 was the modeling for bubbling fluidized bed CO-methanation reactor.A two-phase model of bubbling fluidized bed CO-methanation reactor was proposed.In the proposed model,the fluidized bed was divided into bubbling region and freeboard.The bubbling region consisted of bubble and emulsion phases,and the fluid in the freeboard was regarded as a quasi-homogeneous phase.Based on the particle behavior characteristics in the bed,the effect of the particle and circulation flows was introduced to the model:(ⅰ)The motion of the particle flow in the bubbling region and freeboard has a great contribution to the reaction heat removal.(ⅱ)The particle circulation leads to the generation of circulation flow;the interface of bubble and emulsion phases is easily penetrated and more gas from the bubble phase flows to the emulsion phase with the effect of circulation flow.The proposed model and the classical Kunii-Levenspiel model were used in the simulation for the lab-scale fluidized bed COmethanation reactor.By comparison between the simulation results and experimental data,the simulation results of the proposed model had better agreement with the experimental data,and the proposed model was validated.Finally,sensitivity analyses for particle and circulation flows,bubble size,and bed-wall heat transfer coefficient were carried out.The results indicated that:particle flow had more significance than circulation flow in the proposed model;the effect of bubble size was limited within the bubbling region and bed-wall heat transfer had an obvious influence on the temperature in the freeboard.In brief,the mathematical modeling for molten ash slagging moving bed gasifier and bubbling fluidized bed CO-methanation reactor was carried out in this work.The transport and reaction phenomena in the reactor were more comprehensively described by the mathematical model based on the consideration of the effect of the particle behavior characteristics.Furthermore,the simulation results showed a good agreement with the industrial and experimental data.In addition,this work provided an approach for modeling the gas-solid reactor in the coal chemical industry by(ⅰ)considering the effect of particle behavior characteristics on the fluid distribution,transport,and reaction rates,and(ⅱ)combining the mathematical expression of the effect of particle behavior characteristics with the mass and energy equations. |
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