Studies On Pressurized Fluidization Characteristic Of Wet\Dry Geldart-D Particles

Oxy-fuel pressurized combustion is regarded as the most expected carbon capture technique and shows great potential in retreating municipal solid waste and biomass particles.Pressurized fluidization blow tank has good stability and conveying rate,and is the core equipment in oxy-fuel pressurized combustion.The study on pressurized fluidization characteristics of particles is of great meaning in design,optimization of the pressurized fluidization blow tank,so as the stable and safe operation of the industrial process.The pressurized fluidization characteristics of Geldart-D wet\dry particles are studied in the current work by experimental and simulated approaches.Firstly,the pressurized fluidized bed experimental system was built up,which includes a quasi-2D fluidized bed（150mm×30mm×500mm）that used for observing the flow pattern and bed pressure drop,and a 3D fluidized bed（150mm in inner diameter,800mm in height）that used for measuring the minimum fluidization velocities of particles.Experimental study was carried out to investigate the pressurized fluidization characteristics of dry Geldart-D particle,the effect of operating pressure P,fluidization gas velocity U_f and fluidization number U_mf/U_fon the flow pattern,bed pressure drop and minimum fluidization velocity was studied.Results indicated that:under the same fluidization gas velocity U_f,as raising the operating pressure P,the particle motion and bubble behavior became more intense,both the standard deviation of the pressure drop and the power density of the main frequency increased;Under the same fluidization number U_mf/U_f,with the increase of operating pressure P,the fluidization of dry Geldart-D particles became smoother and the bubble size decreased,both the standard deviation and power density of dominant frequency of the pressure drop signal decreased,the fluidization behavior of Geldart-D particles would transition to that of Geldart-B particles;The minimum fluidization velocity U_mf of dry Geldart-D particle deceases with the increase of the operating pressure P.An empirical equation specifically for calculating the minimum fluidization velocity U_mf of dry Geldart-D particles at elevated operating pressures P was proposed,which provides a relative error of less than 20%compared with the experimental measurement results of the minimum fluidization velocity U_mf in the current study.Experimental study was also conducted to study the fluidization characteristics of wet Geldart-D particles at elevated pressure,the effect of operating pressure,liquid saturation and fluidization gas velocity U_f on the flow pattern,bed pressure drop and minimum fluidization velocity U_mf of wet Geldart-D particle were studied.Experimental results showed that:wet particles were easily agglomerating in the process of pressurized fluidization,elevating the operating pressure could effectively destroying particle agglomeration and promoting the fluidization quality of wet particle;the minimum fluidization velocity U_mf of wet Geldart-D particle is higher than that of dry particle and decreased as the increase of operating pressure P;the minimum fluidization velocity U_mf of wet particle increased as rising the liquid saturation S at the range of S=0～0.1,and kept almost constant as further increasing the liquid saturation S.An empirical equation specifically for calculating the minimum fluidization velocity U_mf of wet Geldart-D particles at elevated operating pressures P was proposed,which provides a relative error of less than 20%compared with the experimental measurement results of the minimum fluidization velocity U_mf in the current study.Numerical simulation studies were carried out using calculational fluid dynamics-discrete element method（CFD-DEM）to investigate the fluidization characteristics of dry Geldart-D particles at the range of P=0.1-1.2MPa,the influence of operating pressure P on the particle velocity,flow pattern and minimum fluidization velocity U_mfwere studied.Results indicated that:With the increase of operating pressure,the mean particle velocity increased;at range of P=0.1-0.8MPa,increasing the operating pressure P would lead to a more intense flow pattern and a sharp decrease in minimum fluidization velocity U_mf of Geldart-D particle;while at range of P=0.8-1.2MPa,increasing the operating pressure had little influence on the flow pattern and minimum fluidization U_mf of Geldart-D particle.