The Study Of Drying Characteristics In Pulsed Fluidized Bed

Fluidized bed has a wide range of applications in industry,and it also can achieve high-efficiency industrial applications.Compared with the traditional reactor and equipment,fluidized bed has the advantages of process easy controlled and high heat and mass transfer efficiency,and the advantages of bed temperature distribution more uniform,and it can improve efficiency of gas-solid two phase contact,so it has the advantages of enhancing heat transfer efficiency.Although the fluidized bed can achieve good drying effect,but when it deals with some special nature particles such as irregular shape and low bulk density or high moisture content particles has made particles fluidization quite problematic at some time it could lead to channeling,gas bypassing and eventually defluidization.So the fluidized bed dryer should be reformed.On the study of pulsated fluidized bed,the pulsed flow has already been shown to be effective in overcoming defluidization,reducing channeling and by-passing,improving the fluidization quality of coarse particles greatly.In the previous researches,the introduction of the pulsed gas to the fluidized bed can be divided into two kinds: one kind is only a pulsed gas flow.The other is a mixed air flow,which contains a steady air flow and an oscillating secondary flow.So this paper studied the effect of the ratio of continuous flow and pulsed flow on the particles fluidization and heat transfer at a certain total gas flow.Then the advantages of pulsed frequency under different ratios were analyzed.The pulsed gas flow fluctuation graph and gas enthalpy value curve were introduced to analyze the factors that affecting the drying rate.In this work a rectangle pulsed fluidized bed was used to investigate the hydrodynamic and drying characteristics.In this experiment,the gas flow contains two streams,one is the continuous flow and the other is pulsed flow.When the total gas flow rate is small,increasing the pulsed flow will strengthen the drying progress.When the total flow rate is larger,the continuous gas flow velocity should be stabilized close to the minimum fluidization velocity.The effects of gas flow rate,gas temperature,pulsation frequency on drying performances have been investigated.At low inlet pulsed gas velocity,moist particles could get a higher drying rate when the pulsed gas frequency is 0.25 Hz.However,when the pulsed gas velocity increased,the pulsation frequency should be increased to 3.3Hz.Pulsed gas flow fluctuation graph and gas enthalpy value curve interpretation method were also introduced to explain the relevant conclusions in this paper.And explains the phenomenons reasonable,which give us an new way to understand the characteristic of gas-solid two-phase flows.