The effect of combined radiation and convection on hot dip galvanizing kettle wear

Hot dip galvanizing furnaces are designed to maintain a quantity of molten zinc at 450 °C in a kettle to allow steelwork to be galvanized. The most common heating medium for such furnaces both in the UK and abroad is natural gas. The alloying reaction between the zinc and the steel kettle wall is temperature dependent. Above a certain rate of heat transfer this forms a non-adherent alloy, which allows molten zinc to erode away the kettle wall, limiting the life span of the kettle and the production rate for the furnace. In order to investigate the causes of high levels of localised wear on kettle walls a model of a hot dip galvanizing furnace has been built using CFD software. This model is compared with measurements taken from an actual furnace in operation and also from wear data of the kettle walls after the serviceable life. In contrast to received wisdom, which is that the high wear is a result of direct flame impingement onto the kettle wall, the modelling suggests that radiation and convection exchange from the flame causes the wear rather than direct contact between the flame and kettle wall.