Simulation And Experimental Study On Pneumatic Drying And Burning Characteristics Of Biomass Fuel

As a kind of renewable energy,how to clean and utilize it effectively has a vital role in alleviating the energy problem and improving the ecological environment.The industrial chain of biomass drying and combustion is increasingly becoming the focus of attention.In this study,two-dimensional mathematical model for the drying of sawdust particles in a pneumatic dryer was developed and contrasted with experiments.The twodimensional modeling was done with computational fluid dynamics(CFD),in which the gas phase is modeled as a continuum using the Euler approach,and the particle phase is modeled by a discrete phase model with a Lagrange approach.The experiments were performed on the self-built pneumatic dryer.The comparison between the simulated values and the experimental values shows that the effect of input quantity on the fluid velocity in the pipe is not obvious,but the water vapor content of gas increase,and the fluid temperature in a pipe and drying rate decrease with the increase of input quantity.The heat and mass transfer coefficients and the temperature difference driving force increase as the inlet gas temperature increases and the drying rate increases as a result.As the drying process progresses,the evaporation rate decreases and the heat of evaporation is worse than the convective heat transfer,the higher the inlet temperature,the greater the convective heat transfer.The simulation results are in good agreement with the experimental values.The model can be used to predict the change of moisture content of sawdust under different drying conditions.This paper applies sawdust to obtain various drying product on the self-design rotary dryer,via changing different parameters to get diverse combination of different conditions.With moisture content of drying base and the thermal efficiency of rotary dryer as evaluation standard,the following conclusions can be elicited: the sawdust residence time and rotary dryer thermal efficiency will get lower with the increasing rotational speed between 5.9 rpm and 9.5 rpm,meanwhile,the moisture content of drying base at the outlet will get to the opposite.At the same speed range,the moisture content of drying base at the outlet and rotary drier thermal efficiency will gradually increase with the increasing input quantity.The optimum condition can be found: 5.9 rpm as rotational speed and 3651 kg/h as sawdust input quantity.Effects of particle sizes on releasing characteristics of chlorine,alkali and alkaline earth metals(AAEMs)in the rice straw and corn straw combustion process of a fixed bed reactor at different temperatures have been investigated.It is found that the particle size has a great influence on the releasing of potassium.Besides,the amount of potassium releasing increases with the decrease of the particle size.The content of K2 O in rice straw ashes and corn straw ashes decrease in 44.8% and 57.5%,respectively.Moreover,as for a certain biomass,the changing regularity of contents of MgO and CaO are similar in ashes at a certain temperature.The range of contents change in 1.5%.Furthermore the particle size has an impact on the releasing of chlorine.Actually,chlorine completely releases when the temperature is above 800 ?.AAEMs have different physical and chemical reactions with different particle sizes under high temperature,which leads to different kinds of reaction products.