Drying And Characteristics Changes Of Shengli Lignite By Microwave Fluidized Bed

The lignite from Inner Mongolia east region is characterized by high moisture, low calorific value, easy weathering and self-ignition, so it’s bad for long distance transportation as well as clean and efficient use. Microwave fluidized bed drying technology can dry lignite effectively as it combines the advantages of microwave with conventional fluidized bed drying technology. The technology was used to dry Shengli lignite and effects of process conditions on the drying characteristics and physic-chemical characteristics of coal were studied in this paper.The experimental results show that drying effect got better with enhancing microwave and flow conditions, but the effect of particle size on the drying effect is relatively small. After drying, lignite particle size distribution changed and the calorific value increased, but the other evaluations didn’t change significantly. The model of MR=exp(a+bt) can well describe the drying kinetics. Intensifying drying conditions can make coal moisture absorption rate increased, but the balance of moisture tended to decrease. Exp Assoc model of moisture absorption has better fitting results.When dry conditions strengthened, surface oxygen-containing functional groups of coal decreased firstly and then increased, but still lower than that of raw coal finally. Coal particle surface cracked more or less and internal holes of coal got larger after drying. When continued drying lignite at lower moisture, microwave had a tendency to make internal particles become flat. Coal particle surface cracks and broken rate increased with the air temperature and fluidization velocity increasing. Specific surface area decreased, but total pore volume and average pore diameter increased with the increasing of wind temperature and fluidization velocity. There exists a turning point about the influence of drying time and microwave power on the pore structure existed.The apparent activation energies of dehydrated lignite increased firstly and then decreased slightly with the increase of drying time and microwave power. The spontaneous combustion tendency of lignite decreased after drying. The release amount of aromatic hydrocarbons phenol and 2-methyl phenol increased from lignite pyrolysis increased, especially more obvious after microwave drying. However, the other component contents decreased, the reason probable be associated with the structure and the change of reactive group of coal.