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Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/11251

Title: A Passive Mid-infrared Sensor to Measure Real-time Particle Emissivity and Gas Temperature in Coal-fired Boilers and Steelmaking Furnaces
Authors: Rego Barcena, Salvador
Advisor: Thomson, Murray J.
Department: Mechanical and Industrial Engineering
Keywords: spectral particle emissivity
off-gas temperature
combustion diagnostics
mid-infrared emission spectroscopy
pyroelectric detector
optically thick assumption
gas-particle medium
coal-fired boiler
embedded invariance
particle scattering
Basic Oxygen Furnace (BOF)
oxygen lance end-point
steel composition and temperature
first turndown properties
remote sensing
asymptotic approximation of the Radiative Transfer Equation
Issue Date: 1-Aug-2008
Abstract: A novel technique for measuring gas temperature and spectral particle emissivity in high-temperature gas-particle streams is presented. The main application of this optical sensor is to improve the process control of batch unit operations, such as steelmaking furnaces. The spectral emission profile of CO and CO2 and the continuous particle emission in the 3.5 to 5 μm wavelength region was recorded and analyzed in real time with a low-resolution passive sensor. The sensor consisted of light collecting optics, a dispersion element (grating spectrometer) and a 64-pixel pyroelectric array. Wavelength and radiance calibrations were performed. The temperature of the gas-particle medium (Tg+p) followed from the least-squares minimization of the difference between the measured radiance in the 4.56-4.7 μm region –which saturates due to the large CO2 concentrations and path lengths in industrial furnaces– and the corresponding blackbody radiance. Particle emissivity (εp) was calculated at 3.95 μm from an asymptotic approximation of the Radiative Transfer Equation that yields the emerging radiance from a semi-infinite particle cloud. The major source of error in the magnitude of Tg+p and εp could come from particle scattering. Through the method of embedded invariance an expression was developed to estimate the lowering effect of particle size and volume fraction on the saturation of the 4.56-4.7 μm CO2 emission region. An iterative procedure for correcting the values of the gas-particle temperature and particle emissivity was applied to the datasets from the two industrial tests. Results from the measurement campaigns with the infrared sensor prototype at two full-scale furnaces are presented. A proof-of-concept test at a coal-fired boiler for electricity production was followed by more extensive measurements at a Basic Oxygen Furnace (BOF) for steelmaking. The second test provided temperature and particle emissivity profiles for eight heats, which highlighted the simplicity of the technique in obtaining in-situ measurements for modeling studies. Through the analysis of the particle emissivity profile in the BOF and the definition of a new variable –the minimum carbon time– a novel end-point strategy to stop the injection of high-purity oxygen during low-carbon heats in BOF converters was proposed.
URI: http://hdl.handle.net/1807/11251
Appears in Collections:Doctoral
Department of Mechanical & Industrial Engineering - Doctoral theses

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