Application of microwave installations for swelling of granular thermal insulation materials based on liquid glass
Abstract
The paper studies the process of obtaining swelled granular materials based on liquid glass under the action of microwave radiation and compares it with the process of obtaining these materials with traditional convective heating. It has been established that under the action of microwave radiation at the same temperatures with convective heating, swelling of granular material occurs twice as intensively. Thus, at a power of 650 W (T=115-120 °C), the swelling coefficient reaches its constant value of 2.86 already at the 6th minute of the process, while when grains swell during convective heating at the same temperature, the highest value of the swelling coefficient is 1.534, and it is reached after 11 minutes, which indicates the complexity of grain swelling under these conditions, due to the occurrence of competing processes of porization and dehydration. The acceleration of the swelling process and the possibility of carrying it out at lower temperatures are due to the fact that under the action of microwave radiation due to the excitation of ionic currents by the microwave field, diffusion processes of substances with ionic conductivity, which include liquid glass, are significantly intensified. The impossibility of carrying out the process at given temperatures during convective heating is explained by the fact that the main condition which ensures swelling during heat treatment is the coincidence in time of the pyroplastic state of the material with the most intense gas evolution. The pyroplastic properties of alkali soluble silicates are manifested in the temperature range of 120-250 °C, which corresponds to the maximum water removal, that is, at the temperatures of 115-120 °C, the process is just beginning. To confirm the effectiveness of the use of microwave installations, the energy consumption and efficiency ratio of the installations have been calculated and it is determined that the efficiency ratio of the microwave installation is almost twice the efficiency ratio of the drying installation. The paper also presents the types of industrial microwave installations in which it is possible to carry out the process of swelling of liquid glass grains
Keywords
granular materials; liquid glass; microwave radiation; convective heating; swelling coefficient; efficiency ratio
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