Semtech OPC

Technology

In the control of both ferrous and non-ferrous converting processes material and energy balance models play a fundamental role. Often occasional analysis data from sub-lances or expendable sensors are used to control and improve on the theoretical models. As a consequence of increasing process intensity, quality demands, environmental constraints, fluctuations in the quality of raw materials etc, metallurgical processes have a tendency to get more and more complex and thereby more difficult to operate and optimize. This has resulted in an accelerating demand for equipment that can provide continuous, real-time information on the progress of the processes to allow for dynamic process control. The hostile environment inside metallurgical furnaces has hampered the development and the application of sensors for in-process use. However, during the last 15 – 20 years remote-sensing technologies based on optics and spectroscopy have proven to be efficient tools for on-line production control of various smelt-metallurgical processes.
The use of the human eye as an optical-spectroscopic instrument for monitoring light emitting metallurgical processes has a history as long as metallurgy itself. The first attempts to develop objective optical-spectroscopic techniques for on-line control of metallurgical processes dates back to the mid of the nineteenth century. In particular efforts to monitor by spectroscopic means the Bessemer and the Linz-Donawitz (LD) processes were reported. Various types of optical pyrometers have been in practical use for a long time.  The continued interest in spectroscopic methods to control smelt metallurgical processes is triggered by a number of attractive features inherent in optical measurements:

-  Remote sensing, i.e., without introducing any physical sensor into the furnace;
-  On-line capability, i.e., sampling is not a prerequisite for the measurement;
-  Detection of short-lived constituents like radicals;
-  Provides continuous real-time information;
-  Insensitive to electronic noise.
 
The basic idea behind the Semtech OPC technology is the following. The light spontaneously emitted by the off-gas flames of a converter is composed of heat radiation from particles and droplets and discrete radiation from atoms and molecules in the vapor phase. When analyzed by a spectrometer the latter will show up at well-defined wave-lengths, which are characteristic for each atom or molecule (a “name tag”) and with intensities which depend on the gas phase concentration (that is, the vapor pressure) of the light-emitting atom or molecule. On the other hand, the presence and concentration of a specific atom or molecule in the off-gases is determined by the thermodynamics inside the converter, e.g., by metal and slag composition and temperature. Thus, by analyzing spectroscopically the light emitted by the off-gases it is possible to obtain information on the status inside the converter.