Slag formation plays a decisive role in all steelmaking processes. In top-blowing Basic Oxygen Steelmaking (BOS) i.e., in the LD process, an emulsion consisting of liquid slag, dispersed metal droplets, undissolved particles and solid precipitates will, together with process gases, form an expanding foam. Extensive research has defined the parameters that govern the foaming characteristics of BOS slag-metal emulsions. It is a well-known fact that certain process conditions in the Basic Oxygen Furnace (BOF) will lead to excessive foam growth, forcing foam out through the vessel opening (mouth). This process event is commonly known as slopping. Slopping results in loss of valuable metal, equipment damage, lost production time, unsafe work environment and pollution. A literature survey covering the slopping phenomena has been carried out, as well as a deeper investigation into the causes behind slopping on the BOF type LD/LBE at SSAB Europe, Luleå, equipped with an automatic system for slopping registration using image analysis Good slag formation and foam-growth control in order to avoid slopping is primarily accomplished by taking preventive “static” measures. The most common pre-blowing operational conditions favouring foam growth and, hence, slopping were found to be linked to oxygen lance positioning, hot metal Si and Mn contents, scrap quality and large additions of iron oxide bearing materials. Improved slopping control may be achieved by developing oxygen lance control schemes with automatic adjustment of the distance between the lance tip and the metal bath (i.e., the lance gap) according to scrap quality and ore additions. If “static” measures cannot be effectuated, a set of in-blow slopping preventive measures is needed. For such “dynamic” measures to be effective, it is necessary to have a system for slopping prediction. Trials with vessel vibration measurements for indirect foam height estimation in industrial scale BOFs, type LD/LBE, have been carried out. FFT spectrum analysis was applied in order to find the frequency band with best correlation to an estimated foam height. The results show that there is a correlation between vessel vibration and foam height which can be used for dynamic foam level and slopping control, and this during the entire blow. The vessel vibration results have been tested against what is the perhaps most commonly implemented technique for dynamic foam height estimation and slopping control, the audiometric system. Parallel vibration and audio measurements have been carried out on 130-tonne as well as on 300-tonne BOFs. The results show that during stable process conditions there is good agreement between the two methods in regard to foam height estimation and that combining the two methods will provide a powerful slopping prediction and control system. A feasibility study has been carried out with the aim to describe the possibilities and limitations of multivariate data analysis, including batch analysis, for dynamic BOS process control, mainly in regard to slopping prevention. Two principal modelling approaches were tested.A central part of this PhD work is the performed emulsion characterisation and the subsequent investigation into the influence of emulsion mineralogy and morphology on slopping in the LD process. The results are based on the study of emulsion samples from trial heats conducted in a 6-tonne pilot plant LD vessel. The main emulsion slag phase mineral species identified were di-calcium silicate, monoxides (mainly FeO, MnO and MgO), calcium ferrites and late-appearing tri-calcium silicate. The study also show that the iron oxidation state has a large influence on the emulsion mineralogy and morphology, as a higher Fe3+ content facilitates the precipitation of calcium ferrites, raising the emulsion apparent viscosity and, hence, the foam index. The same effect is caused by higher MgO contents (i.e., at saturation), resulting in the precipitation of monoxide phase. However, large volume fractions of emulsion precipitates will not always lead to slopping in the LD process. A second “requirement” for excessive foam growth is a simultaneously high gas generation rate. Vice versa; an LD heat may very well slop at low volume fractions of 2ndphase particles in the emulsion if the gas generation rate is sufficiently high. It is an indisputable fact that excessive foaming is one of the main features of the LD process, due to the practice of top-lance oxygen blowing, creating a highly oxidised slag, and heavy batch additions of basic slag formers, causing an initial formation of large quantities of precipitates. Therefore, preventing slopping is primarily a matter of tight process control, most importantly, control of the oxygen lance gap in order to reach a state of sufficiently high liquid MeO phase to minimise the emulsion apparent viscosity, but low enough to avoid over-oxidising and a high gas generation rate.

Vanadium in raw materials used in iron- and steelmaking, a particular challenge for Nordic steel producers, affects the composition of the generated slag from the steelmaking vessel, i.e. the basic oxygen furnace (BOF) adversely and reduces the potential for recycling and external utilisation. A process concept under development aims to enrich and extract the vanadium content of slag from the BOF, making use of the vanadium in the slag and also increasing the overall slag use potential. Applications of this concept affect slag compositions and internal material flows in the iron and steel production system, especially when recycling BOF slags as flux in the blast furnace (BF). This paper will present a case study, based on a Process Integration (PI) approach, using a designated system model to simulate the steel production system and the implementation of the process concept, thereby analysing how to obtain maximum usage of metallurgical slags without compromising the quality of the main product, i.e. liquid steel. Different approaches were studied to improve the environmental sustainability in the production system by maximising the material efficiency through vanadium recovery (as FeV alloy) and the use of slags, thereby minimising the stored/deposited slag amounts.

Some elements in the raw materials used in iron- and steelmaking make it difficult to maintain or further improve the steel quality, but also adversely affect the composition of generated slags and other materials, thereby reducing their potential for internal recycling and/or other utilisation.A Process Integration (PI) approach was taken to analyse the dependence of the properties of a specific metallurgical slag on individual processes as well as on the interaction between processes. Analyses were made of how to obtain maximum usage of metallurgical slags without compromising the quality of the main product, i.e. crude steel. Based on a real case scenario, a number of approaches were studied with regard to the quality demands for maximised use of slags. The effects of changes in raw materials on blast furnace (BF) and basic oxygen furnace (BOF) processes were investigated. Altered composition of the raw materials affects material and BF reductant rate, generated slag amounts, slag recycling and material compositions, etc. In this study special attention was directed towards the magnesium oxide (MgO) contents in BF and BOF slags and, subsequently, the effects on phosphorus (P) refining in the BOF.The analysis of system effects of changed quality of lime raw material, i.e. limestone and consequently on-site produced burnt lime, show that an increased MgO content raises the MgO level, exceeding the set maximum permissible MgO content in both the BF and the BOF slag. The increased MgO content in burnt lime charged to the BOF will have a strong negative effect on the P refining capacity of the slag; therefore, burnt lime with an increased MgO content cannot be used without taking further measures if maximum P refining is required.Based on the results of the analysis, a number of approaches were further investigated in order to identify methods to preserve or decrease current MgO levels in generated slags and maintain, or further improve, slag utilisation potential without compromising the liquid steel (LS) quality. Analysed strategies were: diluting the MgO content in the BF slag by increased slag rate, decreased BOF slag recycling to the BF, increased P tolerance in BF produced hot metal (HM), lower MgO content in pellet mix or decreased use of dolomitic lime in the BOF. The most efficient approach to markedly increase the BOF slag recycling rate and simultaneously maintain the prerequisite MgO content in BF slag and LS quality is by increasing the tolerance of P in hot metal while at the same time excluding dolomitic lime in the BOF.

In the BOS process liquid slag together with dispersed metal droplets, solid particles and process gases form an expanding foam. Certain process conditions may lead to excessive foam growth, forcing foam out through the vessel mouth, an event commonly known as 'slopping'. Slopping results in loss of valuable metal, equipment damage and lost production time. In the early 1980s a system for foam level and slopping control was installed at SSAB's steel plant in Lulea, a system based on the correlation between BOS vessel vibration in a narrow low frequency band and foam development. The technique, in this case with an accelerometer mounted on the trunnion bearing housing, soon showed its usefulness, for example when adapting existing lance patterns to a change in oxygen lance design from a 3-hole to a 4-hole nozzle. Estimating the actual foam height in the BOS vessel was of great importance in the recently completed RFCS funded research project "IMPHOS" (Improving Phosphorus Refining). Based on the earlier positive experiences, it was decided to further develop the vessel vibration measurement technique. Trials on an industrial size BOS vessel type LD/LBE have been carried out, this time with a tri-axial accelerometer mounted on the vessel trunnion. FFT spectrum analysis has been used in order to find the frequency band with best correlation to the foam level development. The results show that there is a correlation between vessel vibration and foam height that can be used for dynamic foam level and slopping control

Excess slag foam growth is a frequent problem in the BOS process. In the worst case, foam is forced out of the vessel and this phenomenon, commonly called slopping, not only results in loss of valuable metal yield but also in equipment damage and lost production time. In order to minimize slopping, accurate estimation of the foam level inside the vessel is an important part of BOS process control. In the top blown BOS vessel, slopping control is achieved using both static and dynamic measures. The most common implemented technique for dynamic foam height estimation and slopping control is the audiometer system. An alternative method, vessel vibration monitoring, has been investigated as part of the work in a RFCS funded research project called IMPHOS. In order to judge the usefulness of this method, parallel vibration and audio measurements have been carried out on 130 tonne as well as on 300 tonne BOS vessels. The results show that during stable process conditions there is good agreement between the two methods with regard to foam height estimation and, as vessel vibration and audiometry are largely independent of each other, a combination of the two is likely to increase significantly the accuracy of slopping prediction.

Slag formation plays a decisive role in all steelmaking processes. In top-blowing Basic Oxygen Steelmaking (BOS), i.e. in the LD process, an emulsion consisting of liquid slag, dispersed metal droplets and solid particles will, together with process gases, form an expanding foam. Extensive research has defined the parameters that govern the foaming characteristics of BOS slag emulsions. It is a well known fact that certain process conditions will lead to an excessive foam growth, forcing the foam out through the vessel opening (mouth). This process event is commonly known as slopping. Slopping results in loss of valuable metal, equipment damage, lost production time and pollution. A literature survey covering the slopping phenomena has been carried out, as well as a deeper investigation into the causes behind slopping on the BOS vessels, type LD/LBE, at SSAB EMEA Metallurgy Luleå, equipped with an automatic system for slopping registration using image analysis. Good slag formation and foam-growth control in order to avoid slopping is primarily accomplished by taking preventive "static" measures. Improved slopping control has been achieved by developing a new oxygen lance control scheme, featuring adjustment of the distance between the lance tip and the metal bath according to scrap quality and ore additions. If "static" measures cannot be effectuated, in-blow control measures are needed. For such "dynamic" measures to be effective, it is necessary to have a system for slopping prediction. In the early-1980s a system for foam level and slopping control, based on BOS vessel vibration, was temporarily installed and tested on one of the vessels in Luleå. Based on the experiences from these tests it was decided to re-investigate the vessel vibration measurement technique. Trials on industrial scale BOS vessels of type LD/LBE have been carried out. FFT spectrum analysis has been applied in order to find the frequency band with best correlation to an estimated foam height. The results show that there is a correlation between vessel vibration and foam height which can be used for dynamic foam level and slopping control. The vessel vibration results have been tested against perhaps the most common implemented technique for dynamic foam height estimation and slopping control, the audiometric system. Parallel vibration and audio measurements have been carried out on a 130-tonne as well as on 300-tonne BOS vessels. The results show that during stable process conditions there is good agreement between the two methods with regard to foam height estimation and that combining the two methods will provide a powerful slopping prediction and control system.

Extreme BOS processing conditions may sometimes lead to excessive slag foaming and slopping, resulting in considerable amounts of metallic losses, equipment damage and un-necessary production disturbances. Control of slag formation without slopping is primarily accomplished by taking preventive measures. If static control measures are not effective then in-blow control measures are required and for these to be successful, it is necessary to employ a method for predicting slopping events. Such a system, utilizing BOS vessel vibration measurement, is presently being re-introduced at SSAB's BOS plant in Luleå, Sweden. A deep study into the causes of slopping has been carried out for a 114 tonne LD/LBE vessel, equipped with an automatic system for slopping registration using image analysis. Improved slopping control was achieved by developing a novel lance control scheme, with a new approach to the adjustment of lance position according to scrap quality and ore additions

SSAB EMEA's BOS plant in Luleå, Sweden installed a new system in April 2009 for slopping registration in order to raise the level of metallurgical process control. An excellent and well-documented tool for investigating the causes behind slopping is image analysis. The system scans each received camera image (25 per second) and counts the number of light pixels above a set threshold within a designated area of the camera frame. The scanning output is a 1-second number called the slopping value (in %). A 2-second average value is stored for a period of up to 14 days. Data for a complete year of production on BOS vessel LDI (over 11,000 heats) were collected and scrutinized. The multivariate analysis showed that main static causes behind slopping are the large additions of scrap of lower quality, mainly recycled large-size skulls and pig iron, but also purchased scrap, high ratio of dolomitic fluxes and high Si content in hot metal in the case of HS blowing regime.

Detta är dokumentation för en Matlab-implementation av ett program som läser in vibrations- och/eller ljudmätningar från exempelvis en LD-ugn samt räknar ut och plottar RMS-data som beskriver hur frekvensinnehållet i mätdata varierar med tiden.