In-line sampling of basic oxygen steelmaking dust Tobias Heinrich Anthony Griffiths Martyn Griffiths Andrew Hopkins Julian Steer
Contents Background Basic oxygen steelmaking (BOS) process Dust characteristics Dust extraction Sampling location and requirements Vertical particle distribution in slurry Sampling design and installation Sample preparation and results Conclusion
BOS process
Dust characteristics Quantity: 15 20 kg per tonne of liquid steel Particle size: 90% with diameter less than 100 microns Composition: Fe 50-80%, Zn 1.7-6.5 %, Ca 3.0-8.8 %
Dust extraction BOS converter during blow period BOS dust extraction system
Sampling location and requirements Sampling location: 15 metres above ground Solids : 0.3 50 g/litre Flow velocity: 2.7 3.0 m/sec CO gas hazard Requirements: Representative sample to be directed to ground level Quick installation 10 litre samples Sampling every 30 sec
Rouse number Measurement of vertical particle distribution Ratio between fall velocity and upwards velocity Rouse number definition: (1) Shear velocity: (2) Bed shear stress: (3) Fall velocity: (4) Submerged specific gravity: (5)
Vertical particle distribution in slurry Bed load Suspended load Wash load Total sediment load Transport Rouse number Bed load > 2.5 Suspended load: 50 % > 1.2, < 2.5 Suspended load: 100 % > 0.8, < 1.2 Wash load < 0.8
Vertical particle distribution in slurry Particles under 200 microns transported as wash load 200-600 micron particles transported as suspended load No bed load since all BOS dust particles are under 600 microns Sampling over complete cross section of pipe
Sampling design Three inlets to sample over wide cross section Inner diameter of the three sampling pipes much larger than diameter of the largest particles System was initially primed with vacuum cleaner Flow velocity in three sampling pipes: 2.8 m/sec
Sampling installation Sampler and flow meter installed in slurry pipe Three way valve on ground level for extraction of slurry
Sample preparation Samples weighed and left for particle settlement Wet vacuum cleaner used to reduce majority of waste water Samples dried, weighed and ground with a ring mill Inductively coupled plasma mass spectrometry for analysing chemical composition Laser diffraction particle size analyser and sieves for analysing particle size
Sampling results Generic dust mass and particle size profile during a BOS heat Mass flow profiles Composition profiles Particle size profiles Giving insight into how dust varies during each heat Allowing correlations between process changes and dust generation to be identified Research into treatment and recycling possibilities
Conclusion The in line sampling design allowed samples representative of the process to be taken at regular intervals. Difficulties due to the sampling location including the height and gas hazard were overcome by moving the actual sampling activity down to ground level in a safe area. Prior to the sampling process the particles and the flow characteristics were analysed, allowing a suitable sampling system to be designed. To ensure a representative sample was generated, the slurry was extracted at three different slurry depths under close to isokinetic conditions. This work has shown how to overcome various sampling difficulties by the use of practical, technical solutions.
Acknowledgments The authors wish to express their gratitude to Tata Steel UK for the financial support and ongoing assistance in this study and the practical assistance and guidance provided by: Fiona Abbott Claire Grainger Kevin Linsley
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References European commission (2001) Best Available Techniques Reference Document on the Production of Iron and Steel, Integrated pollution prevention and control p.233, European commission, Joint research centre, Institute for prospective technological studies. Ferguson, R. & Church, M. (2004) A simple universal equation for grain settling velocity, Journal of Sedimentary Research, Vol. 74, No. 6, November 2004, p. 933-937, Society of Sedimentary Geology. Flowline Manufacturing Ltd (n.d.) Flo-Dar Open Channel Flowmeter for sewer, drain and part full pipe measurement, viewed 13 July 2011, <http://flowline.co.uk/products/product/moredetails/flo-dar.id69.html#download>. Pictures: http://resources.schoolscience.co.uk/corus/14-16/steel/msch4pg2.html Gordon, N., et al. (2004) Stream hydrology: an introduction for ecologists, 2nd edition, ISBN 0-470- 84357-8, John Wiley & Sons Ltd., West Sussex, England.