Microwave drying of automotive industry paint sludge

Abstract

The moisture content of process sludges generated by industries is an important problem affecting the cost and convenience of sludge management. Sludge can be dried to decrease its volume and reduce most of the moisture. This research analyzes the microwave drying process of water-based paint sludge from the automotive industry by investigating the influence of dielectric constant, sludge form (raw or ground), drying method (microwave and conventional), drying period, and air curing, and by conducting numerical modeling. The drying period of sewage sludge is also analyzed for comparison. The moisture losses range between 8 and 12% and between 26 and 31% for 5 and 10min microwave drying periods, respectively. The moisture losses obtained with conventional heating range between 0.2 and 1.2% and between 0.7 and 2.9% for 5 and 10min drying, respectively. Air curing of the samples following microwave drying results in a 3% increase in the moisture losses. Numerical modeling results show that the dielectric characteristics of the paint sludge might change during the drying process inside the oven and different chemical compositions of the sludges might lead to temperature changes during the drying process. By modeling the microwave oven, it is possible to determine the regions that can dissipate more heat without measuring, which is confirmed with the dissipated power density maps and electric field distribution obtained.