| Carbon peaking and carbon neutrality provide excellent opportunity for the development of chemical looping combustion(CLC),which is known as a low-cost in-situ CO2 capture technology.Technical routes for CLC reactors that have potential for industrial application include dual circulating fluidized bed and parallel packed bed reactors,the former being suitable for solid fuels such as coal and the latter being fit for gas fuels like syngas.However,due to the significantly different operating principles of different types of reactors,as well as the involved extremely complex gas-solid reaction/flow and heat/mass transfer processes,the existing semi-empirical reactor design methods are inadequate for the engineering design and scale-up of CLC devices.To address this issue,focusing on the two technical routes of the coal-fueled dual circulating fluidized bed CLC reactor and the syngas-fueled parallel packed bed CLC reactor,this paper carefully clarifies the operating principles of these reactors,and establishes a two-step complementary design procedure based on the 0-dimensional phenomenological model and the 1-dimensional macroscopic model for each reactor.Eventually,a design and optimization framework,which effectively describes the "transport-reaction" phenomena in the CLC reactor,is formed.Specifically,this paper has carried out the following works:Firstly,based on the computational particle fluid dynamics method,a 3-dimensional full bed simulation of 50 k Wth dual circulating fluidized bed reactor for i G-CLC of coal is carried out.In this part,the gas-solid two-phase flow pattern,operation stability,parameters regulation characteristics,gas-solid conversion are successively studied.Through these investigations,the basic operation and regulation principles of the reactor are elucidated,providing a theoretical foundation for subsequent establishment of the design method for the coal-fueled dual circulating fluidized bed CLC reactor on MWth level.Secondly,to address the key issue of char slip from the fuel reactor to the air reactor in the coal-fueled dual circulating fluidized bed CLC reactor,which can lead to low carbon capture efficiency,a compact carbon stripper coupled within the loopseal is proposed.Using the numerical design method,the structure and operating parameters of the carbon stripper are optimized,and its operational characteristics are thoroughly investigated.Furthermore,the performance of the carbon stripper strategy is compared with other strategies aimed at promoting char gasification.Results show that the carbon stripper can achieve a carbon capture efficiency of over 97%,providing an effective technical foundation for improving the carbon capture efficiency of MWth-level reactors.Then,based on the aforementioned investigations,a design method for the coal-fueled dual circulating fluidized bed i G-CLC reactor is established using a phenomenological model as the first part of the two-step design procedure for this type of reactor.This method reasonably describes the fundamental operational laws of the reactor under steady state,taking into account aspects such as mass/energy conservation,gas-solid reaction process,and fluidization characteristics in the reactor.Using this method,the regulation characteristics of bed material circulation and distribution,as well as heat/mass transfer in the reactor,are carefully analyzed,and the influences of the main design parameters on the reactor performance are explored.Ultimately,a preliminary design scheme for the 5 MWth reactor is determined.Further,a numerical design method for the dual circulating fluidized bed i G-CLC reactor of coal is established as the second step of the two-step design procedure for this type of reactor.This method is based on the one-dimensional steady-state macroscopic model that describes the principles of gas-solid reaction flow and heat/mass transfer in a more detailed and reliable manner.Using this method,the preliminary design scheme of the5 MWth reactor is simulated and validated,while the gas-solid hydrodynamics,conversion status,and auto-thermal operational status of the fuel reactor and air reactor are thoroughly analyzed.Based on these results,the preliminary design scheme of the 5 MWth reactor is further optimized.On the other hand,for the packed bed reactor,a comprehensive phenomenological model is constructed to describe the macroscopic propagation laws of the heat front and reaction front in the bed.The mass/energy conservation in the bed and the dynamic characteristics of the gas-solid conversion are revealed from the instantaneous and global perspectives.Based on this phenomenological model,a design method for the parallel packed bed CLC reactor of syngas is established as the first step of the two-step design procedure for this type of reactor.The study investigates the relationships between reactor size and design/operation parameters,identifies the reasonable range of reactor size,and explores the effects of design parameters on reactor performance.Consequently,a preliminary design scheme for the 1.5 MWth parallel packed bed CLC reactor is proposed.Finally,a one-dimensional dynamic macroscopic model of the parallel packed bed CLC reactor of syngas is constructed to effectively and reliably describe the dynamic evolution process of reaction,flow,and heat/mass transfer along the reactor’s axial direction.Subsequently,a numerical design method for the reactor based on order-reduced simulation is developed as the second step of the two-step design procedure for the parallel packed bed reactor.This method is used to analyze the dynamic characteristics and operational stability of the parallel reactors during alternate switching and continuous operation.Furthermore,the study proposes heat and mass regulation strategies for the reactor to optimize its design and improve the quality of energy output.Ultimately,the preliminary design scheme for the1.5 MWth reactor is optimized to enhance the performance of the reactor. |
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