The Multi-scale Mechanism Of Cylindrical Particle Fluidization In Fluidized Bed

With the environmental and social problems caused by solid waste have become increasingly severe,the energy recovery of biomass and combustible solid waste(or CSW)has become a hotspot across the world.Performing thermochemical treatment,such as pyrolysis,combustion and gasification,of biomass and CSW in fluidized bed can realize waste reduction and obtain heating or electric energy at the same time,thus became a common means of biomass and CSW energy recovery.Biomass and CSW are usually in the form of cylindrical particle and experiencing co-fluidization with inert media like sand in the fluidized bed,so basically it is a non-uniform density/shape multi-component particles fluidization process with complex multi-scale flow structure causing inhomogeneous distribution of temperature,which can jeopardize the continuity and reliability of the production process.These problems can only be solved by the optimization method based on multi-scale flow theory,but most of the existing researches focus on the macro-scale fluidization characteristic of cylindrical particle,and the generalization of these characteristics are limited.The understanding of meso-scale and micro-scale mechanism,and the coupling and transfer mechanism between scales are also lacking,which cannot meet the needs of industrial applications.On the other hand,the lack of measuring methods also restricts the research of multi-scale gas-solid flow characteristics of cylindrical particles,especially the measurement of micro-scale motion under dense gas solid flow.In this paper,a dense gas solid flow measurement system based on X-ray is built,and multi-scale gas solid flow properties of cylindrical particles is investigated,and a multi-scale mechanism model of key parameter is established.The main contents and conclusions are as follows:Single/dual vision X-ray imaging software and hardware system are constructed as,based on which the X-ray fluidized bed voidage measurement method,single vision X-ray particle tracking measurement method,dual X optical particle tracking measurement method and dual vision X-ray bubble measurement method are proposed.Investigation on the key technology and the error evaluation of the system are performed.The three-dimensional location,velocity and orientation of cylindrical particles,as well as the size and velocity of bubbles,have been successfully measured under the dense gas solid flow conditions.In the aspect of the micro-scale characteristics,the phenomenon of cylindrical particle rotation is reported and its mechanism is explained;The effects of particle properties and macro operating parameters on the position distribution,velocity and orientation of cylindrical particles are investigated,which lays the foundation for the cylindrical particles precise motion regulation in the process of fluidization;In the aspect of the micro-scale characteristics,The effects of particle properties and macro operating parameters on bubble properties are discussed,revealing the mechanism of bubble formation and development in cylindrical particles fluidization;In the aspect of the macro-scale characteristics,flow regime definition method characterizing a wider range of operating conditions is established,and different flow regime transition route is discovered and its variation properties are discussed.The flow regime diagram of cylindrical particle is obtained.Two kinds of unsteady flow patterns are found and their mechanism was explained.A meso-scale mechanism model describing the one-dimensional interaction between the ideal uniform inert fluidization particle cloud and cylindrical particle is proposed.The model predicts the occurrence of unsteady flow and other macro-scale flow phenomena successfully.A correlation predicting the cylindrical particles fluidization initiation(termination)velocity under partial fluidization(P)flow regime is proposed and evaluated.The successfully carrying out the direct measurement of the interaction process between cylindrical particles and bubbles and 3D reconstruction of the process is performed as well;The influence of particle properties and operating parameters for the interaction between bubbles and cylindrical particles is investigated;The mechanism of cylindrical particles various motion patterns are clarified and the understanding of cylindrical particle multi-cale gas-solid flow mechanism is promoted.