MOLTEN GLASS CONDUIT STRUCTURE, AND DEVICE AND METHOD USING CONDUIT STRUCTURE

There are provided a conduit structure for molten glass, a vacuum degassing apparatus using the conduit structure, and a process for vacuum-degassing molten glass by use of the vacuum degassing apparatus, wherein without using a cooling system, solid thermal insulating materials constituting a backup for the conduit are prevented from being corroded by molten glass oozing out of a joint between adjacent fused cast refractories constituting the conduit, and wherein production cost is reduced. A conduit structure for molten glass, comprising a conduit and a backup disposed around the conduit; the conduit being a hollow pipe made of fused cast refractories disposed in longitudinal and circumferential directions thereof; the backup comprising a refractory layer outside the conduit, and a thermal insulating material layer disposed outside the refractory layer; the refractory layer including a refractory brick layer made by placing refractory bricks along the longitudinal and circumferential directions of the conduit, and a monolithic refractory layer formed by placing a monolithic refractory containing from 30 to 100% of Al 2 O 3 and from 0 to 70% of SiO 2 in percent by mass on an oxide basis and sintering the monolithic refractory; the thermal insulating material layer containing a solid thermal insulating material layer made of solid thermal insulating materials disposed along the longitudinal and circumferential directions of the conduit; the fused cast refractories constituting the conduit, the monolithic refractory forming the refractory brick layer and the refractory bricks constituting the refractory brick layer are selected such that the refractory layer contains a portion that has a temperature equal to the flow point of the molten glass when the molten glass passes through the conduit.