Experimental Study Of Lignite Low-temperature Drying

The high moisture lignite is getting more attention because of its huge reserves in theday with a growing energy crisis. Making ample use of the flue gas waste heat coal-firedpower plant to low-temperature drying lignite is one of the effective methods to expand theuse range of lignite and improve the market competitiveness. Based on this, the paper carriedout the low-temperature heat treatment experimental study of lignite, investigated the dryingcharacteristics of lignite, provided certain theoretical basis for using boiler flue gas to drylignite.Firstly, the thermo-gravimetric analyzer was applied to determine the dryingcharacteristics of lignite with different heating rate, proved that the drying of lignite at200℃is feasible; and then, the non-isothermal drying kinetics of lignite is analyzed. On the otherhand, this paper studied the drying characteristics of lignite under different conditions in afixed bed, discovered the drying rate increasing with the drying temperature rising and theparticle sizes decreasing. The drying rate under CO2atmosphere is slightly higher than thatof N2and air atmosphere. Midilli-Kucuk model was found can best predict the ligniteisothermal drying process with the use of the thin layer drying model theory. Then, used thetheory of thermal analysis kinetics, made the isothermal drying dynamics combined thekinetics of non-isothermal drying, discovered the random nucleation function is the mostsuitable to describe the process of lignite drying, and obtained the activation energy andpre-exponential factor.Then, the static solution method was used to determine the isothermal moistureabsorption curve of the lignite, discovered the Chung-Pfost model can best predict theequilibrium moisture content of lignite under different relative humidity at30℃. Humiditychamber was used to determine the moisture absorption characteristics of lignite underdifferent moisture conditions, discovered the equilibrium moisture content of lignitedecreasing with the drying temperature rising and the relative humidity decreasing. With the increasing of environment temperature, the equilibrium moisture content reducing after firstincreasing, and peaked at30℃.Finally, a microwave reactor was used to carried out the lignite drying experiment,discovered the microwave drying rate increasing with microwave power increasing and thebigger of the sample sizes and mass. At the same time, found Midilli-Kucuk model can bestdescribe the microwave drying process. Also found that compared with conventional dryingmicrowave drying more quickly and efficiently.