Control of CO-postcombustion inside EAF with the FTIR (Fourier transformed infrared) spectroscopy system (2004)

Feasibility of the FTIR-Spectroscopy in principle for high temperature gas measurement was tested at Physics Department, Reading University, UK. Spectrometer has shown during these experiments its feasibility for this temperature range in principle. For the test a burner rig was used, which reached nearly the temperature expected at the industrial scale electric arc furnace. Burner flame was free from dust. That is why spectrometer was tested in a hostile environment similar the EAF conditions in industry. FTIR-Spectroscopy system was tested at an experimental set-up at IEHK. Exhaust gas was determined; the FTIR-spectrometer has shown its feasibility. The driving of an industrial furnace was simulated. Different Measurements were done in an EAF aggregate in industrial scale. Amounts of CO and CO 2 as well as temperature were monitored nearly on-line and determined. All data were overlaid with power input and other furnace processes in order to understand and to model furnace off-gas-composition. Industrial tests took place at Stahlwerk Thuringen. Spectrometer was installed at a distance of 15 m from the gap in the elbow in the melting shop. Composition of the off-gas in the gap of the furnace elbow was measured; influence of entrained air through the gap was very low at this measuring point. Measurements gave spectra of CO 2 and CO. From these spectra composition and temperature of the exhaust gas can be calculated. In order to evaluate the results data were compared with a common measuring method basing on sampling constructed by Messer Griesheim. Problem is the compatibility of both methods because of different measuring volumes. FTIR-spectroscopy takes the average of the whole off-gas volume streaming through the gas line; methods basing on sampling analyze only small volumes. Both measurement methods were discussed and evaluated. Absolute values of the carbon monoxide and carbon dioxide content of the off gas were not comparable. Both methods have shown same tendencies. Common analyser by Messer Griesheim had purging periods to clean the probe lance. For these periods off gas could not be compared and discussed. The water cooled probe lance was developed and patented by Messer Griesheim. All data were overlaid with furnace power input to discuss the development of the off gas composition in dependence from the melting state and important process events. To evaluate the results of the measurements with help of the FTIR-spectroscopy off-gas situation of an EAF was modelled at the Institute of Ferrous Metallurgy. Model gave the off composition in dependence from furnace input parameters after for periods of 20 seconds. Results of modelling were compared with measured values of CO 2 and CO for the whole heat cycle. Therefore it was necessary to do a furnace input output analyse for all materials and energy. A Snaky diagram has shown the furnace input and output. The compared data are similar in tendencies. Absolute values are not exactly the same because of the high number of furnace processes which the model could not considerate. Project has shown the feasibility of FTIR spectroscopy for the detection of hot EAF-exhaust gas. Results of tests in laboratory scale have shown results of common measuring and FTIR-spectroscopy systems are comparable. System gave the content of carbon monoxide and carbon dioxide. It is not possible to detect oxygen with help of the FTIR-spectroscopy. In future a visible light spectrometer has to be tested for the detection of oxygen. Off-gas composition was modelled. FTIR-spectroscopy system has shown its feasibility in detecting very hot off-gas in hostile environment nearly on-line even in industrial scale. Off-gas measurements basing on FTIR-spectroscopy in the elbow of the EAF in Stahlwerk Thuringen were monitored and compared with results of a common analyse system.