Key Words & Abbreviations

ROI	:	Region of interest
CCD	:	Charge Coupled Device
LD	:	LINZ DONAWITZ
PC	:	Personal Computer
H/W	:	Hardware
IR	:	Infra Red
NO/NC	:	Normally Open / Normally Close
SMDS	:	Slag monitoring & detection system
Pixel	:	One raster point in the image
VI	:	Virtual Instrument
SMS	:	Slag Monitoring System
PLC	:	Programmable Logic controller

Abstract

Detecting the presence of liquid slag in the pouring or tapping stream of a basic oxygen furnace after steel making offers a chance to aid the process by maximizing the amount of steel removed from the vessel while minimizing the amount of slag carried over to the ladle.

Steel making in modern integrated steel plants is performed in large-scale refractory-lined vessels known as Basic Oxygen Furnaces or simply BOFs. During the processing, a layer of heterogeneous liquid, non-metallic material called slag is produced. Being lighter than the liquid steel, it floats over steel.

Steel is removed from the vessel through a side opening, known as the tap hole. The liquid steel is poured into a transfer vessel (ladle). Some slag is inevitably carried over into the ladle. The increasing business pressure to be more productive while maintaining high quality in steel products results in the need to minimize the amount of slag carried over while maximizing the amount of steel extracted from the BOF.

An operator manually controls the entire pouring. Judgment about the slag content in the tap stream is based on visual observation. The steel stream is very bright because its temperature is about 1650 deg C. (~3000 deg F). It is nearly impossible for an observer to directly observe any details, let alone brightness variations of the stream. Even using a furnace glass filter in the scene, visual contrast is quite small and it requires considerable training for an observer to distinguish slag from steel by their brightness differences; slag being brighter than steel, because it has a higher emissivity. Routine observations have been made and found that the

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