Within the metallurgical industry as well as the underground mine industry, there is a need for on-line level detection in the different production processes and their material feeding systems. Microwave technology is a versatile, non-invasive measurement technique, which has a number of advantages compared with penetrating probes, laser and radar technology, and echo sound technique. In its extension, it could also be used for qualitative and quantitative analysis of waste gases due to the presence of specific molecules. This contribution describes the introduction of microwave technology in different metallurgical as well as underground mine production processes with the emphasis on EAF's.

Microwave technology has for decades been a tool for astronomers in their work to map and understand the complexities of the universe due to composition and extent. The technology is also frequently used on laboratory scale to examine properties of atomic and molecular compounds. Combining the knowledge gained in those these fields of research and transferring it to the environment of the Steel and metal industry, a project to investigate microwave spectroscopy for on-line process control has been launched. Due to the fact that the dynamic in most metallurgical processes as well as combustion processes is very fast and the response time for conventional extractive gas analysers is long, off-gas analysis for on-line process control is not expedient with this technology. On the other hand, by exploiting microwave technology, its short response time and high sensitivity for gas analysis, disadvantages such as long response time could be eliminated, and thus improve the process efficiency. With this approach a process control on-line in “real time” is possible. On- line gas analysis entails an improved process control, which for metallurgical and combustion processes implies energy savings, reduced emissions of green house gases and improved productivity. In this novel work we will present a series of trials in which a high tempered gas flow is spectroscopically analysed in a frequency band ranging from 110 to 120 GHz. The objective is to stimulate compounds sensitive to radiation in this frequency band to make a transition from one energy level to another and in doing so giving up energy that can be detected by the measuring system. Of interest for the steel and metal industry are molecular compounds such as CO, CO₂ (isotope), O₂, NO, NO₂, H₂O, OH and SO₂.

Microwave technology has for decades been a tool for astronomers in their work to map and understand the complexities of the universe in terms of composition and extent but it is also used at laboratory scale by spectroscopists to examine the properties of atomic and molecular compounds. This paper discusses the use of microwave technology for the investigation of liquid slag structures. Preliminary results indicate that alteration of slag composition could be correlated to the measured microwave refractive index. Investigations have been performed on Al2 O3 -CaO-SiO2.

By using a Tunable Diode Laser spectrometer the oxygen concentration and the temperature in the off-gases of an electric arc furnace, EAF, have simultaneously been monitored during operation. The spectrometer operates at a group of absorptoin lines lines in the near infrared wavelength region to measure the oxygen concentration and the temperature. The O₂ absotion line parameters used were determined in a controlled pilot experiment using a heated measurement path. The temperature is measured using the relative intensity of the absoption lines and thereafter concentration is calculated from the temperature compensated absorption. The measurements were performed in-situ with a specially designed high temperature sensor mounted on the furnace wall. Optical fibers were used to carry the probing light between the TDL spectrometer and the measurement point. This novel work shows the potential of using TDL spectrometer to measure O₂ and temperature in-situ in a steel making process.

Increased demands on quality control, reduced production-time, energy savings and reduction of green-house-gas emission in various metallurgical processes have created an interest for new methods to monitor and control the processes. By using Tunable Diode Laser spectrometers the gas temperature as well as the concentration of 0 2, CO and C02 have been monitored. Laboratory experiments were carried out in a specially designed high-temperature furnace at MEFOS to determine a set of absorption lines suitable for simultaneous 02ffemperature and CO/COz measurements. Field trials were carried out in an Electric Arc Furnace and a reheating furnace. 

Increased demands on energy savings and quality control in metallurgical processes have created incentives for new methods to monitor and control the process. In this paper we will present a field trial that shows the potential of tunable diode-laser spectroscopy (TDLS) for simultaneous contact free measuring and monitoring of the oxygen concentration as well as the gas temperature in a reheating furnaceduring production. The field trials were carried out at an oil-fueled reheating furnace during 7 weeks of production. The tunable diode-laserspectrometer was measuring in situ across the preheating zone and the soaking zone in the furnace. During the campaign the oxygenconcentration and the gas temperature in the furnace environment were simultaneously monitored and instantaneous variations in these parameters could easily be recorded and subsequently correlated to actual changes in the process. Furthermore, the much shorter response-time of the TDLS technique compared with conventional measurement methods such as thermocouples and extractive gas analyzers was also demonstrated during the trials. The results show the potential for the TDLS technique to be used for energy savings as well as product quality improvements by controlling the burners in the reheating furnace. The results show that it would be possible to control and optimize the oxygenconcentration with TDLS in the control loop of the reheating furnace. © 2002 Elsevier Science B.V. All rights reserved.

Tunable diode laser absorption spectroscopy (TDLAS) is a recent development in process instrumentation. A commercial TDLAS instrument has been tested both in an industrial steel reheating furnace and in a pilot furnace at MEFOS for continuous oxygen analysis of the furnace combustion gases. Automatic control of the air-to-fuel ratio (AFR) was proven using a time-averaged oxygen concentration signal with a TDC2000 furnace controller at MEFOS. The oxygen concentrations measured by the TDLAS instrument compared well with local measurements of the oxygen concentration using a conventional zirconia probe in both furnaces. The diode laser has the advantages of high reliability for average gas concentration measurements in the path of the beam, when compared to point gas analysis with conventional zirconia instrumentation. Reliable gas analysis offers the benefits of improved process control, which for steel reheating furnaces include energy savings, reduced emissions and improved productivity.