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.