Study On Drying Process In The Pulsed Fluidized Bed

Fluidized bed drying of pulsating airflow is a drying technology, inwhich the air velocity varies following some periodic law in the apparatus.Comparing with the conventional fluidized bed, a drying method of energysaving is provided for the slowdown drying process of granular material, using the fluidized bed drying of pulsating airflow. Pulsating temperaturedrying is a drying technology which the air temperature changes accordingto certain models, using alternating air temperature drying, the productionquality can be improved and the energy can be saved, which has beenwidely used in many areas. It is hoped that the pulsofluidized bed dryingwill have effect in the drying process, in witch the air velocity and (or) theair temperature will synchronously (separately) varies following someperiodic law in the apparatus.The drying process of spheral particular materials have been studied, according to the orthogonal and single factor experiment, in witch thediameter of particles were 3.3mm～5.7mm and the particle is produced byporous materials, while the experimental apparatus was a pulsofluidizedbed dryer with low frequency rectangular wave. Seven parametersincluding the diameter of particle, the inlet air temperature of hot blast, theair velocity of hot blast, the time of hot air blow, the inlet air temperature ofcoal blast, the air velocity of coal blast and the time of coal air blow have been studied the effect on the drying time and the energy expense when themoisture content of particle from 41% to 16%, using the orthogonalexperiment. Besides, another four parameters involving inlet airtemperature, the fluidizing flowrate, the time of a pulsate cycle and theon/off time proportion of air blow have been investigated the influence onthe drying rate, the unit energy expense, the bed temperature when the endof drying, the drying time, the total and unit energy expense when themoisture content of particle from 43% to 18% or 13%, depending on thesingle factor experiment. The experimental results as follow:1. Drying rates of the pulsofluidized bed drying which the air velocityvaries following low frequency can be increased in the process ofslowdown drying for the granular material, while the energy expense ofdrying and the temperature of material can be decreased in this system.2. Drying rate is increased with the inlet air temperature, the fluidizingflowrate and the on/off time proportion of air blow, the drying rate ofpulsofluidized bed drying is rapidly than the conventional fluidized bed inthe process of slowdown drying when the on/off time proportion is 3:1, thetotal time of on/off periods is 120s and 150s, in the experimental condition.3. The unit energy dissipation is decreased increasing with the inlet airtemperature, the total time of on/off periods and the on/off time proportionof air blow, while optimum air velocity is exist, in the experimentalcondition. The energy dissipation of pulsofluidized bed drying is 40% lessthan that of the conventional fluidized bed at the same air temperature andvelocity, when the air velocity is 4m/s, the inlet air temperature is 115℃, the total time of on/off periods is 150s, the on/off time proportion is 3:1.The mathematical model of drying has been modified, and a recursivemodel of bed temperature at the end of experiment has been established in the pulsed fluidized bed drying, as follows: In(-InMR)=k₁In(Int)+k₂ T_b=-7.42967+0.844891T₁+2.86v-0.02446T+2.951794§It proved that the change of moisture content of the material and thetemperature can be predicted exactly by the mathematical model in thedrying process according to the experimental results.