Danieli has established a new business called

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1 Danieli converter technology Danieli Linz Technology, in conjunction with Danieli Corus, offer full design, manufacturing, installation, process control, automation and commissioning of BOF converters. Examples of design principles, new products and the benefits obtained are described Authors: Dr Günther Staudinger, Dr Andreas Hackl, Peter Illecker, Alberto Passon, Edo Engel and Walter Vortrefflich Danieli Linz Technology and Danieli Corus Danieli has established a new business called Danieli Linz Technology, offering converter design and engineering from proven Austrian specialists. R&D researchers based in Italy support developments for the converter suspension system, tilting drive etc, and workshops based mainly in Italy and Thailand provide in-house manufacturing capability. This business is further complemented by specialists from Danieli Corus who have decades of experience in BOF process control and automation systems. CONVERTER DESIGN Vessel shell From a metallurgical point of view the converter has to provide a certain reaction volume, bath depth and surface area for efficient steelmaking to occur. In order to optimise the process, the reaction volume should be as high as possible, with an ideal value for the specific volume (ratio of inner volume to mass of liquid steel) of 1.0m 3 /t. In greenfield cases this value is easy to achieve, but restrictions reducing this ratio to 0.8m 3 /t or even less are not uncommon, particularly in the revamping business when, for instance, converter size is increased to increase output. The vessel shell acts as an enclosure for the lining and should have enough stiffness to cope with the weight of refractory and steel as well as the 360 tilting torques and dynamic loads during charging, blowing and tapping, etc. The vessel shape is mostly defined by the need to maximise the reaction volume. A typical shell has a top cone, barrel section, bottom cone, dished end and a flat lip-ring on top. Knuckle sections are not necessary, but might be applied for other reasons and, in order to minimise the relining time the converter may be equipped with a detachable bottom. Additionally, the shell is exposed to elevated temperatures of 500 C or more. For instance, during tapping, some parts of the shell are exposed to heat radiation from the liquid steel in the ladle and, during slopping, direct contact with liquid steel or slag is also possible. When too little lining remains inside the converter, hot spots may appear and, in the worst case, this can even result in a break-through of the vessel shell, most likely in the area of the trunnion pins underneath the trunnion ring. Thus, material selection for the vessel shell is important and has to be done carefully to serve the abovementioned requirements. Based on experience, the most common material used is a fine grain size unalloyed pressure vessel steel, such as P275NH, P355NH or A516 Gr.60. Such material has medium strength and high ductility and avoids progressive crack growth in cases of serious damage, but offers enough strength to accommodate the allowable stress level with a safety margin. Such material can be repaired relatively easily by welding. However, since refractory life has increased over the years, eg, by using Mg-C-bricks and use of slag-splashing or extended gunning, the temperature of the vessel shell under normal operations has increased. This increases the tendency of the material to creep over many years of operation. As the vessel shell enlarges it gets closer to the trunnion ring, reducing the natural cooling effect, so further increasing the temperature and consequently progressively stimulating the creep effect. Usually the lifetime of the vessel shell is reached either when its temperature gets too high to maintain structural integrity or, in the worst case, the vessel shell touches the trunnion ring. For higher creep resistance the steels used are P355GH, A 204 Gr.60, 16Mo3 or even higher grades like 13CrMo44, A 387 Gr.11. Some cases even require Cr-Mo-alloyed steel grades like A387 Gr.22 or 10CrMo9-10, but these are very difficult to weld and post-weld-heat-treatment has to be applied, which is very difficult in an in-situ weld repair. Suspension systems The suspension system plays a very important role. When the shell is exposed to high stresses and creep, any additional sources of stress should be avoided as much as possible. To this end, the suspension system has to be as flexible as possible yet stiff, and there are a number of different suspension systems in operation worldwide in an attempt to solve these issues: ` Bracket suspension system (compensation of thermal expansion by optimised angle of the wedges) ` Disk suspension system Isostatic system the converter is supported on two large disks and a link 44

2 STEELMAKING AND CASTING achieves and stabilises tilting the vessel ` Link suspension system Isostatic system the converter is supported by five links and a stabiliser ` Lamella type suspension system The converter is supported by eight elements underneath the trunnion ring. Each element consists of two relatively thin, high strength steel plates that act like spring elements. These are very flexible for radial deformation and stiff in the longitudinal and circumferential directions. The horizontal forces in the 90 position are controlled by horizontal elements. Danieli has developed a new suspension system based on tie-rods which are arranged at four locations around the vessel shell. Each location incorporates four vertical tie-rods which are flexible for radial deformation and stiff in the longitudinal and circumferential directions. Additionally, two horizontal supports are arranged underneath the trunnion pins in order to take most load of the converter in the 90 tilted position (see Figure 1). The first application of the tie rod suspension system will be applied on a 350t converter for ArcelorMittal, Poland, with startup scheduled for Danieli has also developed an alternative suspension system which is based on lamella type vertical elements and special horizontal support elements. It is called the Daniella suspension system and a patent has been issued (No.MI2013A00019). When the vessel shell gets to operating temperature (up to 500 C), the trunnion ring is at approximately 200 C. The stress so caused is compensated by elastic deformation in lamella-type plates arranged in the support brackets welded to the trunnion ring. The horizontal bracket welded to the vessel shell can expand and does not significantly increase the load on the support brackets due to elastic deformation. When the deformation from the thermal expansion is applied, the mechanical horizontal load of the converter deforms the lamellae further until solid contact to the centre bracket welded to the trunnion ring is reached, and the full load is transferred to the trunnion ring. The lamella plates are kept in place by holder elements, which means no welding or other mechanical equipment is involved to keep this plates in splace. Consequently these plates can be easily changed when needed. Also a change of the characteristic of the behaviour of the horizontal element is possible after a certain time of operation. The first application of this Daniella system is planned for a 170t converter for NTMK in Russia. r Fig 1 Finite element calculation of suspension elements (tie rods) r Fig 2 Danieli converter tilting drive (left). Example of drive system in workshop (right) r Fig 3 General arrangement of the Danieli lance design CONVERTER TILTING DRIVE SYSTEM The tilting drive has special requirements. The converter tilting torques are relatively large and vary during tilting from one side to the other. However, most of the time the a 45

3 converter is stationary and the tilting drives act only as a brake. Based on our substantial experience in the design of large gears (from rolling technology), a suitable tilting drive was developed. The drive is split into the bull gear and primary gears, varying from one to six primary gears per drive system and modern designs have two or four primary gears and motors (see Figure 2). Additionally, one or two additional pneumatic motors on the drive are provided so that in the case of power failure, the drive can be operated in order to empty the converter if necessary. The tilting drive rides on the trunnion ring axes in order to follow the elastic and dynamic deformation of the trunnion ring without creating any additional load. The suspension system, which acts as a torque support only, introduces vertical loads in the foundation. A large horizontal interconnection shaft acts like a spring and minimises any impact loads to the teeth of the large wheel during shock loads or shaking of the converter. The drive is manufactured in Italy. OXYGEN LANCE SYSTEM The design of the lance lifting device is based on our long experience in crane design and is equipped with an emergency drive for emergency use (see Figure 3). Cooling r Fig 4 3D fluid dynamic analysis of the water flow in the lance tip water and oxygen flow in the lance tip are analysed and optimised using fluid dynamics software (see Figure 4). PROJECT REALISATION AND QUALITY CONTROL Danieli provides the complete supply chain and hence is within the full Danieli quality control system. The core equipment is manufactured in-house, including: ` Shell ` Trunnion ring ` Suspension system ` Tilting drive ` Oxygen lance system Danieli has a number of production centres in Europe and Asia and employs highly qualified staff. This is a major advantage, particularly for the vessel shell and trunnion ring, as these areas are the most critical and have to be manufactured to the highest standards (see Figure 5). The engineering, manufacturing and site assembly of the vessel shell as well as the trunnion ring is carried out according to pressure vessel codes and rules. Danieli operates workshops that are certified according to ISO 9001:208, ISO 14000, ISO as well as ASME boiler and pressure vessel code (U2 and U for production of pressure vessels as well on site, PP for production of pressure piping and S for power boilers). Delivery time is minimised by careful workshop planning and optimisation of manufacturing in terms of engineering adapted to workshop capabilities. This minimises, for instance, the number of welding seams and weld sizes in order to reduce residual stress. All manufacturing steps can be done in-house such as the pressing of the bottom dish end or knuckle sections, stress relieving of complete trunnion rings, local stress relieving and developing special welding procedures. All non-destructive testing is performed inhouse with qualified personnel (Level 2 and 3). The quality control plan (QCP) is issued by the engineering department and directly implemented. Following manufacturing, preassembly and erection on site are also done by Danieli, and r Fig 5 Examples of large vessel shells manufactured within Danieli Thailand 46

4 STEELMAKING AND CASTING preparation can be optimised for customer requirements. With proprietary workshops, it is also possible to provide additional services such as stocks of spares for emergency cases like break-outs or other unforeseeable events. FROM PROCESS CONTROL TO AUTOMATIC STEELMAKING BOF steelmaking is a rapid process which requires stateof-the-art process control and, over many decades, many improvements have been made, such as the use of a sublance, waste gas analysis and slag control. All of these tools depend on a solid, well-tuned process model to be successful. The Automatic Steelmaking System developed by Danieli Corus integrates all available tools and combines them within the BOF static-dynamic process model. This model was first developed at the IJmuiden steel plant and further improved during implementation in other plants worldwide. It has been consistently successful with high hitting rates and substantially reduced tap-to-tap times. The Danieli Corus process control system consists of a set of hardware and software components that can be implemented individually or combined. After the initial installation, a system can be upgraded with additional modules. A comprehensive process model is at the core of the system. The system integrates operation and exchange of information with plant systems varying from raw material ordering to the plant s planning and manufacturing systems ( see Figure 6). The converters can be operated in full computer mode, but the system also accepts manual intervention. The system can be fine-tuned to any plant and optimised to follow existing operational procedures. A typical operator screen is shown in Figure 7. Sublance Danieli Corus is a market leader in this area, with more than 100 systems in operation. The sublance automatically takes the selected probe (for measuring temperature, oxygen, carbon and phosphorous) from a conditioned storage chamber and, after moving over the converter, is lowered into the steel bath through the entrance port on top of the hood. Measurement data is fed to the process model and the sublance is retracted. The probe is removed automatically and deposited in a collection chamber on the converter floor, making a sample available for analysis within seconds. r Fig 6 Danieli Corus process control system r Fig 7 Typical operator screen Waste gas analysis For additional on-line process control, a gas analysis system can be installed. This system is based on mass spectrometry to measure the levels of carbon monoxide, carbon dioxide, oxygen, hydrogen, nitrogen, water and argon in the waste gas. This provides valuable information on the decarburisation rate and a 47

5 bath. The system consists of a pressure reducing system and a flow control system, capable of controlling the flow for each individual line. This achieves the desired rate of agitation and prevents damage and clogging. Flow control is split over two parallel banks. One has a fixed flow controller which is always in operation for safety reasons; the second has an adjustable flow controller which will be switched on and off depending on the desired steel grade or process moment. A unique feature of the Danieli design is that the nozzles can be drilled, allowing for tuyere replacement during the converter campaign. r Fig 8 P content measured by the sublance system versus laboratory analysis of steel sample oxygen content in the slag and is used to generate information on the steel carbon content and helps update decision support information for oxygen blowing. Since the system provides on-line information on converter off-gas composition, it is invaluable in monitoring explosion risk, and either the operator will be informed or the system will interrupt the blowing process automatically. Advanced slag control (ASCON) In converter steelmaking, a dry slag leads to increased lining erosion, whereas a foamy slag induces a risk of slopping, and both can affect converter availability. This system is based on a number of measurement modules based on techniques such as ultrasonics and acoustics for on-line, real-time slag monitoring and control through closed-loop input into the oxygen lance control and bottom agitation system. This module offers automated lance height control for an optimum balance between slag foaming and process performance without slopping. Bottom agitation This offers a significant increase in oxygen blowing efficiency. It is applied to enhance the reaction between slag and liquid steel and to lower the oxygen content, and allows the steel maker to produce low carbon contents without excessive yield, alloy and refractory losses and a better control of end-point nitrogen is achieved. Slag will contain reduced amounts of ferrous elements. Nitrogen or argon is introduced at the bottom of the converter through special nozzles, so agitating the steel AUTOMATIC STEELMAKING CONCEPTS BOF process control and process automation have now reached such levels of sophistication that it has become possible to fully automate the process from charge to tap. Some aspects, however, may be more attractive to control semi-automatically with the information provided by a decision support system. This option is becoming increasingly attractive now that critical parameters with respect to liquid steel quality can be measured on-line that in the past could only be measured by taking a sample and waiting for lab analysis. Phosphorous measurement and safe tapping Controlling steel P levels, particularly with the increased use of high P iron ores, continues to be of interest because of its impact on steel quality. BOF slag is complex in nature and contains several oxides including CaO, SiO 2, P 2 O 5, MgO, MnO, and FeO. Towards the end of blow, the kinetics of the different reactions slow down such that the slag composition approaches a pseudo equilibrium with the steel, and application of thermodynamic models alone for direct estimation of P distribution does not yield sufficiently reliable information for deciding to start tapping, hence a delay is incurred awaiting the laboratory results of the turn down sample. Danieli Corus has successfully implemented P measurement into the Static Dynamic Model, so shortening tap-to-tap times. Measurements are taken with a dedicated, newly invented sublance TSOP (temperature, sulphur, oxygen and phosphorus) probe. Figure 8 shows the results from recent measurements at a steel plant in China comparing predicted P from the probe versus laboratory analysis of the solidified sample. It should be mentioned that no alterations were made to the converter operation to produce more favourable conditions for P measurement, and no precautions were taken with respect to converter addition material quality, quantities or other process control parameters. It was possible to limit the standard deviation of the measurement to 24.6ppm with a P content in the steel bath of <300ppm. 48

6 STEELMAKING AND CASTING q Fig 9 Safe Tapping probability graph A great benefit for the operator in the converter control room in deciding whether to start tapping the heat or not is the addition of a decision support system. Rather than showing the measured data on the operator screen and letting the operator interpret the data, process conditions are presented through a newly developed concept called Safe Tapping. This is a graphical information tool that informs the operator through a multi-colour graph whether or not it is safe (from the point of view of meeting the steel P specification) to start tapping the heat (see Figure 9). After each measurement, a marker is shown on the Safe Tapping operator screen. Although the Safe Tapping decision support system was built for P measurement, it can be customised to include any set of process parameters (such as carbon content and bath temperature windows) that are regarded essential for tapping. This gives the operator control of the BOF process at high levels of confidence. Operating the converter in full computer mode Modern BOF process control systems have reached a level of sophistication allowing for fully computerised operation. With our static dynamic process model, after the hot metal and scrap have been charged (in automatic mode) the operator can start the heat with one click of a mouse. Oxygen lance control, converter material additions systems and all process control equipment, then work together in computer mode until it is ready for tapping. This proprietary model has been constantly improved for over 40 years and can be fine-tuned to any BOF plant and, with this level of automation, energy consumption, tap-totap times and additives consumption are further reduced. More than 25 systems capable of running multiple converter plants have been installed so far. ENVIRONMENTAL TECHNOLOGY In cooperation with GEA Bischoff (Germany), Danieli has also full capabilities to handle the primary off-gases coming from the converter. GEA Bischoff has equipped more than 200 plants with wet (annular gap scrubber) and dry (electrostatic precipitator) systems, fulfilling the highest environmental standards. Danieli also cooperates with Oschatz (Germany) as the preferred sub supplier for primary cooling stack systems, giving additional convenience with respect to safe and reliable operation and maximised energy recovery via high sophisticated steam production. Regarding secondary fume emissions Danieli Environment, with more than 150 references for bag filter systems, provides sophisticated solutions tailor made to process and customer needs. SUMMARY Danieli now offers full design, manufacturing, installation, process control, automation and commissioning of BOF converters. We have established a new business called Danieli Linz Technology, offering converter design and engineering which is further complemented by Danieli Corus, who has decades of experience in BOF process control and automation systems. All core components are developed, engineered and manufactured within the Danieli quality control system, providing assurance from start to finish. MS Dr Günther Staudinger, Dr Andreas Hackl, Peter Illecker and Alberto Passon are with Danieli Linz Technology, Linz, Austria. Edo Engel and Walter Vortrefflich are with Danieli Corus, Ijmuiden, The Netherlands Contact: comms.office@danieli-corus.com 49