Evaluation of the use of microwave energy on green floor/wall tile drying process

Drying green ceramic tiles is necessary before the decoration and sintering processes and constitutes an important input in terms of energy consumption in the production step. Nowadays, natural gas-fueled vertical dryers are used to dry green ceramic tiles. However, alternative energy-efficient and environmentally friendly technologies are being investigated and used in many drying applications, such as microwave energy. In this study, the effects of magnetron power and drying rate on moisture, surface temperature, and dried bending strength of green ceramic tiles were experimentally examined. First, floor and wall tiles with a wet-based moisture content of 6% were shaped with an industrial hydraulic press with the specific pressures of 320 kg/cm² and 300 kg/cm² at the sizes of 33 × 33 cm and 25 × 40 cm, respectively. The shaped green floor and wall tiles were dried separately with a horizontal pilot-based microwave dryer at 20, 35, and 50 kW magnetron powers and 0.5, 1.0, 1.5, and 2.0 m/min belt speeds, and then the changes in moisture, surface temperature, and bending strength values were measured. The minimum and maximum 51 °C/143 °C and 50 °C/138 °C surface temperature values were obtained for the floor and wall tiles, respectively, after the microwave drying. The moisture values changed in direct proportion to the magnetron power and inversely to the belt speed. The moisture values were reduced from 6% to a minimum of 0.1% under the conditions of 35, 50 kW of magnetron powers with 0.5 m/min of belt speed for floor tile and 50 kW of magnetron power with 0.5 m/min of belt speed for wall tile. In addition, the corner moisture values of microwave-dried tiles were lower than those in the center on the surface. The bending strength increased as the belt speed and magnetron power decreased within the working conditions. The maximum bending strength values for the floor and wall tiles were obtained as 29.2 kg/cm² and 31.2 kg/cm² at 20 kW magnetron power and 0.5 m/min belt speed, respectively. Of 52.4% and 42.6% energy savings in economic terms, 1000% and 837.5% increase in drying capacity, and 50.0% and 42.1% of environmental gain were calculated for the drying of floor and wall tiles with microwave energy compared to the natural gas, respectively. This study indicates that microwave energy can be used as a more energy efficient and capacity booster environmentally friendly process than natural gas-fueled vertical dryers in green ceramic drying.<br>