METALLURGICAL CONTROLLING METHOD

Abstract: The present invention relates to a method for monitoring and control of smeltmetallurgical processes, endothermic as well as exothermic ones, preferably pyrometallurgical processes, by means of optical spectrometry, whereby one first determines for each endothermic and exothermic smeltmetallurgical process and/or process step characteristic emissions or absorptions and identifies the atomic or molecular origin of the emissions/absorptions, that one during a running pro­ cess records changes in the characteristic emissions/absorptions and relates these changes to the condition of the process and with reference hereto controls the process.

Description: The present invention relates to a method for monitoring and control of endothermic and exothermic smeltmetallurgical processes, particularly pyrometallurgical processes, by means of optical spectrometry, whereby one first determines for each endothermic and exothermic smeltmetallurgical process and/or process step characteristic light emissions or absorptions simultaneously in one wave length interval and identifies the atomic or molecular origin of the emissions/absorptions, that one records momentarily changes in the characteristic emissions/absorptions during a running process. The object of the present invention is to obtain a possibility to control different smeltmetallurgical, endothermic and exothermic processes, particularly pyrometallurgical processes by spectrophotometry in a simple and rational way thus making it possible to improve the yield of the processes in a qualitative and quantitative way. Background of the invention In pyrometallurgy, such as copper production, lead production, and iron and steel production fire and flames are generally encountered. The visual observation of these flames has for a long time been used to judge if and when such a process is to be interrupted or the running mode to be changed in any other way. In doing so one has then more or less on a firm ground supposed, that the process has reached a certain stage, phase or temperature as the flames have changed their colour, or seemingly have changed their colour. In iron production certain quantitative methods of analysis are in use, whereas in the copper production on-line methods are not in use to the same extent. Particularly the copper converting process uses purely visual methods for process control. In particular during the slag blowing phase and the production of blister copper it is important that the process is interrupted at the correct moment. An incorrect blowing time leads to an impaired yield and difficulties during the continued process. An incorrect temperature leads to disturbances of the process possibly leading to a break down. One requirement is thus that the end point of e.g. the slag blowing stage has to be determined to within better than one minute. Depending on the composition of the melt the flame present above the converter will look different, and thus it can not easily be determined visually, if, and when, the process is to be interrupted. Thus there exists a considerably technical problem to be solved within the smeltmetallurgy, at endothermic and exothermic processes, and in that connection particularly within pyrometallurgy but also in plasma smelting and electric arc smelting. Framsteg inom Forskning och Teknik, (1986), IVA-meddelande 254, pages 57-58, discloses a method for monitoring and control of a pyrometallurgical process, viz, a copper blowing process, by means of optical spectrometry, where one first determines characteristic light emissions or absorptions simultaneously in one wave length interval and calculates a ratio between the emissions of two products at one wave length. Trans ISIJ 27 , (1987) B 185 discloses a method for measuring the emission from the hot spot in a molten iron bath in order to determine the manganese. Thereby atomic emission spectrometry was used at one wave length. The temperature of a smeltmetallurgical process is not always determined quite accurately, and it is obvious that the introduction of measuring lances into the melt as such is troublesome. However, using a determination of a ratio between two different wave lengths related to the temperature can easily form a basis for the determination of the temperature during a process. Description of the present invention It has now surprisingly been shown possible to solve the above mentioned technical problems by means of the present invention which is characterized in that one calculates the ratio between the intensities of at least two emitting products at at least two different wave lengths, and/or the intensities at, at least two different wave lengths, of an emitting product and relates the changes in the ratios to the condition of the process/process equipment, and with reference hereto and thereby determined limiting values controls the process. Further characteristics are evident from the accompanying claims. The invention will be described more in detail in the following with reference to the example below, which example is directed to a copper converting process, however, without restricting the invention thereto. Example Spectrophotometric measurements of a copper converter flame were carried out using a modern optical system capable of measuring either a complete spectrum or part of a spectrum with a high resolution in a very short time period, typically 10 ms. A Jarrel-Ash model 1233 spectrometer containing three interchangeable gratings was used to disperse the incoming light. The gratings covered the spectral range 3200Å, 800Å, and 200Å (and had 150, 600, and 2400 grooves per mm). The measurements were carried out in the wave length range 200 to 800 nm, and more particularly in the range 400 to 650 nm. The resulting spectra were recorded on a PARC model 1421 detector with 1024 diodes placed in a row in the exit plane of the spectrometer. The detector included an image intensifier. A PARC model 1460 OMA (Optical Multichannel Analyser) console was used to display the data, and spectra were stored on floppy discs for further processing and evaluation. The system was used both for emission measurements, when the light from the converter flame was focused on the entrance slit of the spectrometer, and for absorption measurements when light from a Xe-lamp after having passed the flame was fed through an optical fibre to the entrance slit. It turned out that emission spectra from the slag and copper making stages were quite different. On the other hand spectral characteristics were reproducible from one process cycle to another. Fig. 1 shows parts of the spectra emitted during slag and copper making stages. The spectra consist of a continous background caused by Planck radiation from particles in the flame and contributions from gaseous elements. It turned out that the dominating gaseous emitter during the slag phase was PbS while during copper making phase PbO dominated the emission spectrum. Close to the end of the slag phase one could observe that the emission spectrum started to change from a pure PbS spectrum to a mixture of a PbS and PbO spectra. A series of determinations were made in which the ratios between the intensity of certain PbO and PbS bands were recorded during the last minutes of the slag phase. Fig. 2 shows the end-point value of the ratio determined versus the copper content in the white metal (concentrated matte). When the ratio increases the copper content reaches an asymptotic value of 77.5 %. The Cu content of the white metal was determined using XRF (X-ray fluorescense) determinations on a sample taken after the interruption of the process. By means of the present measurements it could be determined that when PbO(g):PbS(g) approached 1 at the actual choice of wave lengths the slag blowing should be interrupted, however, preferably at a value of 0.2 to 0.5, whereat less amounts of metallic copper is formed. Due to the high load of particles during slag phase it was possible to carry out absorption measurements only during the copper making phase. Preliminary observations showed a strong absorption at wave lengths shorter than 350 nm, which was in good agreement with laboratory measurements of SO₂ at 1200°C. When the end point is reached the concentration of SO₂ decreases and the transmission of light down to 350 nm can gradually be observed. A calculation of the ratio of the intensities at 320 nm and 350 nm was hereby used to determine the end point of the copper making phase. Fig. 5 shows the intensity of the SO₂ absorption versus the wave length at some different instants before the end point. The theoretical composition of the gas phase in equilibrium with the matte and slag was calculated for comparison and as a guide in the analysis of the emission spectra recorded. In these calculations equilibrium conditions were assumed to be present during both slag and copper making phases. The assumption of equilibrium is not necessarily true for all elements but is likely to describe the major changes during the converting cycle. Necessary thermodynamic data were taken from a previous calculation of the copper converting process and assessment of slag data completed by data from thermodynamic tables. The calculation of the composition of the matte, white metal and slag phase in the converter process were carried out using the free energy minimizing programme SOLGASMIX. The metal-containing gaseous constituents which were considered in the calculations were PbS, Pb, PbO, Bi, Bi₂, BiS, Zn, ZnS, As, As₂, As₄, AsS, AsO, As₄S₄, As₄O₆, Sb, Sb₂, Sb₄, SbO, and SbS. Fig. 3 shows the calculated partial pressure exceeding 10⁻⁶ bar during the slag production phase versus the amount of air injected per ton matte and the copper content of the matte. The calculated variation of the partial pressures of PbO(g) and PbS(g) is in good agreement with spectrometric measurements, and show a greater increase in the ratio p(PbO,g):p(PbS,g) at matte concentrations exceeding 75% of Cu. Fig. 4 shows the calculated composition of the gas phase in the copper making stage versus the amount of air being injected per ton matte during the initial slag blowing stage. The white metal was supposed to contain 77.1% of Cu and 2% of the slag formed during the slag forming stage were supposed to be suspended in the white metal. From about 60 Nm³ air per ton of initial matte metallic copper starts to form and from that point the p(PbO,g):p(PbS,g) ratio remains unchanged during the whole process with a value of about 2.6 in a quantitative agreement with the optical observation. The calculated distribution in the gas phase is in good agreement with the values given in Table 1, below, with exceptions for Pb and Zn, for which the calculated values are lower than in practical operation. Consequently the partial pressures of lead and zinc compounds in the gas phase have to be higher than the values given in Fig. 3. The determination of the end point of the slag forming stage and copper making stage in the converting process is today mainly dependent on skilful operators. Computer programmes for the calculation of blowing time, addition of sand, and heat balances exist. However, the reliability of the calculated blowing time is dependent on the amount of Cu left in the converter from a previous cycle, the amount of slag in the matte added, the composition of scrap added and recirculated slag from different steps of the process, as well as the oxygen efficiency. All these parameters thus influence the process to a greater or lesser extent and thus have to be estimated by the operator. The calculated blowing time can thus be used as a coarse guide only to determine the end point and the final decision is today in the hands of the operator. However, as has been shown above the light emitted from the process can be used, after spectrometric determinations and analysis, to exactly determine the end point of the process steps, independent of the skil of the operators. The values given are in % by weight for the composition of matte, slag and white metal in the actual plant. The values for dust refer to the percentage of the total amount of the respective elements occurring as dust. By means of this new method the process can also be closed to a greater extent which leads to less emissions of sulphur dioxide through the ventilation system of the plant. The invention is thus based on a technique where, in this case, the end point of the slag producing phase of a copper process can be determined by measurements of the intensity ratios between the emitted light from PbO(g) and PbS(g) whereby variations in the background due to disturbances are restricted, and disturbances from variations in the total lead content are restricted as long as spectra from lead compounds can be identified. The lead content in the white metal formed in the slag phase varied in the actual plant between 0.5 to 2 % by weight and even at lower concentrations the emitted light was strong enough to be detected. The variations of the silicon content of the slag influences the oxygen partial pressure and thus also the PbO:PbS ratio in the gas phase. These differences dependent on variations of the silicon content are small compared with the rapid increase of the PbO:PbS ratio at the end of the slag producing phase. The utilization of the present method for an exact monitoring and control of the slag producing phase at a copper process leads to potentially great advantages as the number of over blows and to early interrupted slag blows are reduced to a minimum. Normally the copper content of the white metal is 76 to 77 % after the final blow. If this step is interrupted too early the blow has to be restarted after an analysis, which takes about 20 minutes to carry through. If on the other hand one drives the copper making stage with too low Cu content there exists a considerable risk for of the formation of magnetite and an increased risk of slag foaming with a great time loss as a consequence. The exact monitoring and control of the copper content is also essential to optimize the removal of impurities to the slag phase during the slag stage. Several impurities such as Ni and Sb show an improved distribution to the slag phase at higher copper concentrations but if the blow continues above 78% of copper in the white metal metallic copper starts to form as indicated above, and this counteracts the elimination of impurities to the slag as the distribution of impurities between slag and metallic copper is more unfavourable than between slag and white metal. It is not only the Cu concentrations which are of interest to control, but it is also possible to determine and control the release of halogenides which are known to form compounds with precious metals. The precious metals are a valuable constituent in the form of an impurity in the copper metal and these precious metals should not be evaporated in the form of gaseous molecules with a halogen. In the same way the temperature can easily be followed in a process by recording and comparing the intensities in different emission/absorption bands from one and the same molecule and/or the width of an emission/absorption band from one and the same molecule. For example one can record and compare the intensities of the PbO bands in a copper process, and in an iron steel process different atomic Fe lines can be compared with each other. Fig. 9 shows the changes in relative intensities of two emissions of one product of an iron/steel process, where the intensities are recorded from 1500°C (top), and to 1650°C (bottom). Thus there is a gap of approximately 35°C between each recording. As is evident from these recordings the temperature can be easily determined by re-cording and calculating the ratios between the two intensities. The use of the present invention means that open converter processes can easily be closed and thereby it is possible to radically improve the environment in and around a smelter. Further by closing the process gas collecting systems do not need to be dimensioned for the large gas volumes necessary to handle when using an open converter to remove hazardous gases leaking to the environment but can be adopted to the amount of gas which is really produced in the process. In producing iron and steel one can, in the way described above, record and compare the intensities of different carbon compounds (CO, CO₂, CN⁻) or work with different atomic states in for example Fe, Mn, K, Na, etc. in order to determine the condition of the process. The measurement is carried out in the interval 260 to 600 nm, more preferably in the interval 300 to 400 nm. FIG. 6 shows the emitted spectrum from a converter flame in a small resolution in the interval 200 to 700 nm, and FIG. 7 shows a spectrum of the hot spot in the wave length interval 200 to 300 nm, in which spectrum the majority of the discrete structures come from atomic iron, but also atomic manganese, sodium, and potassium have been identified. Strong iron and manganese lines have been marked in Fig. 7. The recordings show that the ratio Fe/Mn changes during the blow in a converter, as well as the K/Fe ratio varies considerably. During the production of alloy steel, stainless steel and other qualities, Ni, Cr, Mn, Mo, Al, MgO, CaO, are present in the smelt, and, in particular, FeSi is present during the reduction phase. Mn and Cr are present as compounds and can be easily determined. In the same way as described above the temperature in a smelter can be determined accurately, and the elementary composition of the melt can be determined in order to reach a correct alloy point. It is important in a steel making process to reach the correct concentration of carbon at the correct temperature of the melt. This can easily be achieved by means of the present invention. One can also use the method for measuring the composition of the alloying metals of the iron. The elementary composition can be used to control the addition of alloying metals which has become more important because of the increasing use of scrap metal, the total composition of which is very uncertain. It is also very important to be able to monitor the status of the lining of a melting furnace so that the lining is not worn out and a penetration of the converter/furnace takes place, which can cause very high costs. The quality of the lining layer can easily be determined by monitoring through the oxygen lance the K, Na, and Al presence in the hot spot. Particularly monitoring of the emission/absorption of Na makes it possible to check the lining. The determination hereby involves a study of the intensity and shape of the absorption and emission lines of Na and K, particularly at 600, and 400 nm, respectively. Compare Fig. 8 in which graph a) shows the sodium lines in absorption only, and graph b) the lines as self-reversed emission lines. At the production of lead the ratio PbO:PbS can of course be used as well as bands from imnpurities like Hg. As evident from above impurities, but also a product to be produced but present in a characteristic intermediary form can be utilized for these recordings and comparisons for process control. As indicated the method can use different measuring methods such as direct optical measurement using conventional optics, but also modern fibre optics whereby process control based on the conditions underneath a protecting and cooling slag layer is technically possible. A protecting and cooling slag layer may sometimes change the status of the atom or molecule on which a determination is based and thus it may be of utmost interest to follow the conditions at the actual reaction site. This situation is encountered for example, in a steel melt during oxygen blowing.

Claims: A method for monitoring and control of endothermic and exothermic smeltmetallurgical processes, particularly pyrometallurgical processes, by means of optical spectrometry, whereby one first determines for each endothermic and exothermic smeltmetallurgical process and/or process step characteristic light emissions or absorptions simultaneously in one wave length interval and identifies the atomic or molecular origin of the emissions/absorptions, that one records momentarily changes in the characteristic emissions/absorptions during a running process, characterized in that one calculates the ratio between the intensities of at least two emitting products at at least two different wave lengths, and/or the intensities at, at least two different wave lengths, of an emitting product and relates the changes in the ratios to the condition of the process/pro-cess equipment, and with reference hereto and thereby determined limiting values controls the process. A method according to claims 1, characterized in that one determines the ratio between emissions from PbO and PbS at more than one wave lengths in the wave length range 200 to 800 nm, preferably 400 to 650 nm, in a copper converting process during slag phase, and when the ratio PbO(g):PbS(g) reaches a predetermined value, set by the wave lengths, interrupts the slag production phase. A method according to claim 1, characterized in that one determines halogenides of precious metals present in the gas phase at a copper process. A method according to claim 1, characterized in that one determines the light absorption in SO₂ at two or more wave lengths in the interval 300 to 400 nm and with reference hereto controls the process at a copper converting process during the copper stage. A method according to claim 1, characterized in that one records and compares emitted light intensity of PbO:PbS at the lead production. A method according to claim 1, characterized in that one determines the ratio between the emitted intensity of an atom or a molecule at different wave lengths to monitor and control the temperature of a smeltmetallurgical process, particularly an iron-steel process. A method according to claim 1, characterized in that one records and compares the intensities of emitting carbon compounds and/or free atoms, such as Fe, Mn, K, and/or Na, preferably in the interval 200 to 800 nm, in iron and steel production. A method according to claims 1 and 7, characterized in that one determines the elementary composition of an iron melt, such as with regard to the alloying metals of the iron, for monitoring and controlling the addition of alloying metals and/or carbon. A method according to claim 1, characterized in that one determines the status of the smeltmetallurgical process plant by determining the intensities of absorptions/emissions of K, Na, and/or Al preferably at 770, and 600 nm, respectively. A method according to claim 1, characterized in that the measurement is made spectrophotometrically immediately above the melt. A method according to claim 1, characterized in that one measures spectro photometrically through a lance provided with fibre optics and introduced into the melt.

Inventors: ALDEN, LARS, ERIK, MARCUS, PERSSON, ERIK, WILLY, WENDT, ERIK, WILHELM
Applicants: SCANDINAVIAN EMISSION TECHNOLOGY AKTIEBOLAG
Application year: 1988
Main classification: C22B5
IPC codes: G01J3, C21C5, C22B13, C22B5, H01J37, G01N21, C22B15