Study On The Drying Characteristics And Drying Models Of Dredged Sludge From Dian Lake

Dredged sludge has high utilization value because it is rich in beneficial ingredient and has large quantity. However, the rapid development of its resource utilization is limited by high moisture content. Therefore, it has become the focus of current research which is the most effective way to reduce the moisture content to a reasonable range.The drying behavior of dredged sludge from Dian Lake was experimentally investigated in drying process by convection, microwave, infrared and chemical regulation. The Modified Page-I was found to be most suitable for dredged sludge drying simulation by using drying models to carry on the numerical simulation. The kinetic parameters such as moisture diffusion coefficient were calculated by some equations. The main research results were as follows:(1) The results of convective drying showed that, the effective diffusion coefficient was calculated by applying Fick diffusion model. The values were positively correlated with temperature and thickness which were varied from5.283×10-9to7.337X10-9m2/s and2.497×10-9to9.955X10-8m2/s for different initial moisture content and different thickness. The relationship between temperature and effective diffusion coefficient was built by Arrhenius formula. The activation energy for the moisture evaporation of dredged sludge was found to be varied from9.87to16.73kJ/mol.(2) The results of microwave drying showed that, the splash phenomenon was obvious during drying process of high moisture content dredged sludge under high power and the surface of dredged sludge was honeycomb after drying. It could obviously shorten the drying time of dredged sludge for different thickness to improve the drying efficiency when power was exceeded280W. Through calculation, the values of unit energy consumption for each thickness were very low when the power was280W and the energy could be sufficient used. The trend of unit energy consumption was decreased when the power was reached700W and the energy utilization was gradually tended to rationalize at the moment.(3) The results of infrared drying showed that, the moisture content of dredged sludge was reduced slowly by infrared drying as the penetration of infrared ray had little effect on dredged sludge. The effective diffusion coefficient for different initial moisture content was positively correlated with temperature and negatively correlated with initial moisture content which was calculated by applying Fick diffusion model and the values were varied from3.504×10-9～6.908×10-9m2/s over the temperature120～160℃. The activation energy for the moisture evaporation of dredged sludge was found to be varied from8.82～16.41kJ/mol which was calculated by Arrhenius formula. The effective diffusion coefficient for different thickness was positively correlated with temperature and thickness which were varied from2.525×10-9-78.61X10-9m2/s at120～160℃. The activation energy for the moisture evaporation of dredged sludge was found to be varied from4.19～17.09kJ/mol.(4) It had water retention during infrared drying process of dredged sludge when separate addtion of LYG-1was varied from1%to4%and the water conservation effect was positively correlated with initial moisture content. But it was promoted to drying when addition was reached5%, and it had a high effective diffusion coefficient through calculated results. It had played the greatest role in drying effect which was added LYF-2individually during the experiments of adding compound medicament, meanwhile, it had a higher effective diffusion coefficient at different temperature. The activation energy for the moisture evaporation of dredged sludge was found to be varied from8.28～14.80kJ/mol which was dealt with different addition of medicament.