Development of Pig Iron and Molten Slag Level Measurement Technique for Blast Furnace

Abstract

Measurement of the pig iron and slag level in the blast furnace is essential to operate the furnace stably because an increase of these liquids level can cause fluctuations of the pressure in the furnace or the temperature of the furnace which are related to the furnace condition and may finally result in reduced productivity or serious trouble.The conventional method is the EMF (electromotive force) measurement correlated with the liquid level. It can be thought that a voltage generated electrochemically (as in a battery) by the reduction reaction of iron oxides. However some reports said that EMF sometimes loses correlation with the liquid level because of thermal influence.In this paper a new method is proposed using a quite small electrical resistance measurement of the hearth of a blast furnace which contains pig iron and molten slag. Accordingly the four point contact method was adopted and a pseudo random signal as a current pattern was fed to improve the S/N ratio.Measurements were done at plural positions along the circumference of the blast furnace. However when the current signal is independently fed at each position, spike noises are generated. These noises are originated in the induced voltage which is generated at neighbor positions when the polarity of the current changes. But finally this noise problem can be solved by feeding synchronized current and measuring the signal on the noiseless timing.The measurement results indicated that the level in the hearth is not necessary identical at all positions.KEY WORDS: blast furnace; pig iron; molten slag; level measurement; electrical resistance; pseudo random signal. BackgroundStability is extremely important in blast furnace operation, as the blast furnace is the first upstream process in steel production. Nevertheless, increase of the pig iron and molten slag level prevents stable operation. Pig iron descends, and then accumulates in the blast furnace hearth. And also, molten slag descends to the hearth. However, the molten slag accumulates over the pig iron because its density is lower than that of iron.Pig iron and molten slag are drained from one of plural tap holes (in the case of large blast furnaces) by turns at regular intervals. However, molten slag has poor drainage due to its relatively higher viscosity, and under special conditions when the temperature in the furnace is lower than usual, the viscosity of the molten slag increases, making tapping even more difficult. In the worst case, an excessive rise of the pig iron and molten slag level can cause serious trouble in which the molten slag melts the tuyeres. This type of trouble does not have only an adverse influence on operation over an extended time, but is also a problem for safety. Therefore, when the pig iron and molten slag level rises, pig iron and molten slag are drained from plural tap holes at the same time, enabling control of the productivity of pig iron and molten slag in order to keep the appropriate level and realize stable operation.The conventional method of measuring the...

Monitoring Liquid Level of Blast Furnace Hearth and Torpedo Ladle by Electromotive Force Signal

“…A relative EMF signals from the four heights is processed with Equation (4). ∆EMF = EMF base − EMF top,middle or bottom (4) where: base, top, middle and bottom are shown in Figure 3.…”

“…Then the liquid level recorded by the video is used to validate the evolution of EMF signals during tapping. (4) where: base, top, middle and bottom are shown in Figure 3.…”

“…The blast furnace is still the main section in an integrated steel company and its production and efficiency determines the costs and profits of the company. However, a blast furnace is a typical black box in which many phenomena cannot be directly observed and measured, such as the liquid level of hot metal and slag in hearth, the extent of lining erosion and location of dead man in hearth [1][2][3][4]. These phenomena not only influence a smooth operation of hot metal tapping practice but also determine stabilities of blast furnace productivity and a long time campaign [5].…”

“…Comparing with other hearth state monitoring methods, the EMF technique maintains its own characteristics in the development process, for example the signal of the EMF sensor, which is believed to originate from the thermal and chemical reactions occurring in the hearth [5][6][7], while the signal of the thermocouple originates from the thermoelectric effect; the above is the electromotive force generative mechanism difference between the EMF technique and the thermocouple. Comparing with the other methods reported in References [4,[11][12][13][14], the former concentrates on the generation of EMF noise and the solution of the noise, the latter are all mathematical models including CFD and (or) DEM to simulate the tapping procedure. Therefore, the EMF technique can obtain the liquid level information more quickly and actually.…”

Array Sensing Using Electromagnetic Method for Detection of Smelting in Submerged Arc Furnaces

“…The fluctuation of the furnace condition occurs frequently under the influence of many factors. Thus measurement technique and detection system for the furnace are necessary for operators to analyze the furnace condition accurately and take measures opportunely to guarantee the stable running of the furnace [10,11]. In practice, the furnace condition is observed through simple instruments, personal experiences or naked eyes, which are difficult to get the optimal smelting parameters and thus lower production efficiency [12].…”