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Laser sensing in the iron-making blast furnace

The measurement of parameters such as distance and temperature in the Ironmaking Blast Furnace is crucial to the performance of the furnace. A series of instruments has been designed, built and tested by BHP which perform these tasks optically requiring no physical intrusion into the harsh environment of the furnace. The problem of coupling high peak power Nd:YAG and ultra violet laser radiation into environments consisting of very high water vapour level, acidic, high aerosol loading, and high temperature environments is considered. The performance of two systems enabling distance measurement with sub-pulse length range resolution under the above conditions is discussed in detail. The use of optical fibres to deliver the pulsed energy to and from the environment together with specific window design parameters are also described. A major problem in making time of flight range measurements in very high density aerosol conditions is the signal processing required to extract the target return pulse position from the complex aerosol return signal. Incoherent detection techniques used to achieve this discrimination where target temperatures can exceed 2000°C are discussed. The selection of operating laser wavelength and repetition rate were based on an analysis of the optical characteristics of gases and aerosol forming the measurement environment together with the dynamic behaviour of the high temperature target. The extension of laser radar techniques to optical fibres is discussed and a distributed temperature sensing system is described which measures temperatures up to 250°C with a spatial resolution better than O.Sm.