Making molten steel pouring more accurate
26 April 2011
TATA Steel in Scunthorpe produces a range of steel slab, billets, structural sections, rail and wire rod the focus at the plant is always on efficiencies, with close attention being paid to process improvement strategies in all areas of production.
Once the iron is manufactured in the Blast Furnaces, it is transported in a rail mounted ‘torpedo’ vessel to the Basic Oxygen Steelmaking (BOS) plant for conversion to steel. It is discharged into large 300 ton capacity ladles used for both charging the converters and receiving the finished steel once the process is complete. The level in a steel-pouring ladle is referred to as ‘freeboard’, (freeboard is a nautical term: the level between the sea and the ‘freeboard’ deck of a ship) in a steel works, this is the difference between the top edge of the ladle and the surface of molten metal level inside. This parameter in a steelmaking plants is very difficult to determine accurately and repeatably, especially while the steel is being ‘tapped’ from the converter. After it is filled, it is often also mixed with an argon lance to prevent stratification and homogenise any additives, if the steel level is too high, the turbulence could cause dangerous spills. However, ensuring the capacity of the ladles is also maximised for every fill plays a key part in efficiency on the plant, where a few centimetres represents tonnes of steel.
So, there are challenges, even for experienced operators, with the high radiated temperatures, glare, molten steel and sparks during a tapping operation. Usually, operators pick a point on the ladle and watch it carefully as the molten steel fills to the required ‘freeboard’ this can lead to consistency issues, as it is prone to variation from one operator to another. However, if the freeboard measurement could be augmented to be more reliable and consistent then, with the increased productivity and safer handling of the product over the thousands of fills per year, the potential for efficiencies are huge.
TATA turned to non-contact VEGAPULS radars to assist with this application. The radars use low power microwave pulses which are reflected from the surface to measure the level; in this case, the molten metal in the ladle, they are also largely unaffected by temperature, pressure, dust or vapours. The technical manager of VEGA attended site to do a test with a temporary set-up system, the results were very encouraging and as a result of the report provided, Tata ordered a permanent system.
For this application VEGA supplied units fitted with an extended, right angled wave guide tube to keep the electronics away from the hot area where the antenna is mounted. A purging system is also installed should build-up of dust occur in the antenna over time, it can also be used for cooling on some applications, however to date neither function has been required on this application.
The VEGAPULS radar is mounted approximately 8m above the low level point, but still capable of measuring the level to a repeatability of 2mm. With a narrow focussed beam and accomplished signal processing software, it reads the level real-time, even during filling. By enabling a safer, more accurate measured fill each time, Tata is achieving an average of just 100mm extra level in each vessel which equates to an extra 10 tonnes per ladle -this improvement on all three transfer stations, will contribute towards £12million efficiencies on the plant every year.
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