Model Research And Experimental Study On The Gas-Solid Flow In The Circulating Fluidized Bed Boiler

The gas-solid fluid dynamic characteristics mainly including voidage distribution, pressure distribution, gas velocity and particle velocity, have deep influence upon combustion, heat transfer, pollutant formation and control in the Circulating Fluidized Bed (CFB) boiler and they also affect the stability and economy of the equipment performance. Therefore, the study of the CFB hydrodynamic characteristics is of great significance.The fluid dynamic characteristics of the gas-solid flow for the CFB boiler were studied in two ways: the theoretical model research and the experimental study.The main features of the CFB gas-solid flow performance are the structures of local inhomogeneous and overall inhomogeneous, so the inhomogeneity is studied as the task of the gas-solid flow model. The detailed derivation and introduction of the theoretical model is given in the second chapter. The basis for the theoretical model is a substantially assumed core-annulus approach with both gas and solids ascending in the core and descending in the annulus. There are two boundaries in the model presented in this dissertation. The boundary between the core and annulus is the first one and is demarcated by the radial location at which the solids mass flux is zero. The axial location at which the core radius is a minimum specifies the second boundary that divides the bed into lower and upper zones and represents the axial location where the center-line mass flux is at a maximum and the wall mass flux and solids velocity are at a minimum. The calculation of the model is based on constitutive equations and the calculation of pressure drop includes contributions from the static head and particle acceleration throughout the length of the bed which is better than other models. The model can predict the axially varying core radius and pressure, the axially and radially varying solids mass flux and velocity and voidage given the bed geometry, inlet temperature, and inlet solids mass flux, and physical properties of the gas and solids.The third chapter establishes a two-dimensional cold state CFB test-bed. In order to measure the axial static pressure correctly, the traditional method of measuring pressure is improved and a special static pressure measuring instrument is invented, which can measure the center-line static pressure. The axial voidage profile is obtained indirectly by measuring pressure differentials along the length of the bed and equating them with the static head of solids. The experiment adopts two solids that are Silica Gel Resin and Quartz Sand and is measured in ten different experimental conditions.The comparison between experimental data and model predictive valve is presented in the fourth chapter. The results show that the axial pressure profile and voidage profile are uneven. The pressure distribution and voidage distribution in the lower dense-phase region have large change and in the upper dilute-phase region have small change and the overall distributions present exponential function distribution. The impact factors on the pressure distribution and voidage distribution are also obtained. Compared with the experiments, the theoretical model agrees well, especially in the upper dilute-phase region. Therefore the validity of theoretical models has been tested.