Real-Time, Optical Measurement of Gas Temperature and Particle Emissivity in a Full-Scale Steelmaking Furnace
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TRODUCTION
DURING the decarburization phase of the basic oxygen furnace (BOF) process, oxygen is blown into the molten steel bath to reduce its carbon content from approximately 4 pct to 873 K). These thermometers have been used to measure exhaust gas temperatures of approximately 973 K in an incinerator. However, the principle of operation of these thermometers is not clearly stated and, to the best of our knowledge, they have not yet been successfully applied in steelmaking furnaces. The current proof-of-concept test at a full-scale BOF shows the potential of a recent emission spectroscopy technique[5] to measure gas temperature and particle emissivity in real time. The benefits of having real-time temperature data are twofold: (1) computational fluid dynamic (CFD) models of the exhaust-handling system for a BOF[6] usually resort to estimating off-gas temperature for their boundary condition and (2) dynamic temperature data, combined with off-gas concentration, would allow mass and energy balances around the converter that may serve as the basis for a model-based feedback-control strategy. This approach is currently being developed for an electric arc furnace[7] with the gas temperature and concentration at the fourth hole; the same principle may readily be applied to a BOF. Particle emissivity (ep) is a useful variable in CFD codes that include radiation heat-transfer submodels for calculating the radiative source term in the energy conservation equation for fluid flow. For simplicity, while CFD codes normally work with spectrally averaged particle emissivities,[8] the present technique yields spectral emissivity at 3.95 lm. However, for coal ash samples containing Fe2O3, MgO, CaO, SiO2, and SO3, and for single-component samples of FeO and Fe2O3, METALLURGICAL AND MATERIALS TRANSACTIONS B
Bohnes et al.[9] showed that the spectrally averaged particle emissivity and the emissivity at 3.95 lm are very similar for temperatures above 1200 K. All these components are also common to BOF particles.[1,10] The emissivity values of Bohnes et al. and Linka et al.[11] were taken from a layer of particles in a crucible, to characterize coal ash deposits on heat-transfer surfaces. Thus, they cannot be applied to individual particles entrained in a gas stream. One of the strengths of the current technique is that it measures ep for particles suspended in a high-temperature gas column. The emissivity measured by Bohnes et al. and Linka et al. is normally referred to as directional emissivity[12] or effective emissivity (eeff),[5] as in the present study, whereas the individual emissivity (ep) is simply called particle emissivity. Both are spectral quantities. The analytical relationship between eeff and ep for semiinfinite particle clouds has been developed by RegoBarcena et al.[5] A brief review of the methodology for the retrieval of off-gas temperature and particle emissivity is followed by a description of the experimental setup and the measuring campaign at a full-scale BOF. In the discussion, the temperature and emissivity values ar
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