In-flight melting of granulated powders by 12-phase AC arc discharge for glass production

Current glass melting technology, based on the Siemens furnace developed in 1860s, has evolved in response to manufacturing requirement. However few revolutionary changes to the basic technology have occurred. Glass production is still one of the most energy intensive industries, because the conventional method used for glass melting is air-fuel firing, which is inefficient, energy-intensive and time-consuming. With increased energy issue and global warming, it is urgent to develop a new technology to save energy and reduce emissions for glassmaking. In view of high temperatures of thermal plasmas, an innovative in-flight glass melting technology with an induction plasma, a multiphase AC arc, and an oxygen burner was developed. In this study, characteristics of the treated powders by a 12-phase AC arc during their flight time were investigated. The reagents for alkali-free glass was mixed and prepared into granulated powders with the grain size of 20-80 mum by spray dry method. The granulated powders were injected into a 12-phase AC arc for the in-flight treatment. The stable 12- phase AC arc discharge with 100 mm in diameter was obtained at the power of 46 kW. The vitrification, morphology, size distribution, and composition of the treated powders were characterized to evaluate the melting characteristics. Results show that the melted particles are spherical with a smooth surface and compact structure. Higher vitrification and decomposition degrees of raw material as well as higher volatilization of B₂O₃ are attributed to larger heat transferred to per particle under smaller flow rate of carrier gas and lower feed rate of granulated powders. The properties of glass powders were strongly dependent on the feed rate and the carrier gas flow rate. The high decomposition and vitrification degrees, which are achieved in milliseconds, shorten the melting and fining times of glass considerably. Our results indicate that the proposed in-flight melting technology is a promising method for use in the glass industry.