Vanadia (V_2O_5) Attack of Refractories in Glass-Melting Furnace Regenerators

摘要

Glass-melting furnaces include a regenerator for recovering the heat from the exhaust gas. The heat exchange efficiency of the regenerator, which is constructed of checker brick, is based on the checker bricks absorbing heat from the exhaust gas and transferring it to the combustion air. The heat exchange efficiency has a big effect on the unit consumption of fuel, so it is necessary for the checker bricks to have sufficient durability, and to remain in good condition, to allow unobstructed air flow during the whole campaign of a glass-melting furnace. The suitable materials are installed in 4 partitioned zones of regenerators. 98 mass% magnesia bricks are installed in the top zone of regenerators. 95 mass% magnesia bricks are insalled in the 2nd zone, and magnesia-chrome bricks or magnesia-spinel bricks or magnesia-zircon bricks are used in the 3rd zone which is the sulfate-liquidization-solidification zone. Dense fired clay bricks are installed in the bottom zone (see Fig. 1). There are many reports on the development of bricks for the sulfate-liquidization-solidification zone and their field performance, because bricks in the 3rd zone are attacked by alkalis and sulfides and are exposed to temperature cycles, causing thermal fatigue, which determine the life of the regenerator. Furthermore, there are other factors, such as vanadia (V_2O_5) attack in the 2nd zone of the regenerator, which reduce the life of checker bricks. The degradation of bricks by vanadia attack involves the penetration/permeation of vanadium pentoxide (V_2O_5) which originates in heavy fuel oil. It is considered that the formation of calcium vanadate (a low-melting phase - about 778 deg C) results when V_2O_5 reacts with CaO in MgO bricks, leading to the collapse of the MgO bricks. But only a few reports have been written which discuss the details of this phenomenon.