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Blast furnace level 2 monitoring and control system: giving the operators the tools to become the experts of the future A Level 2 system is a production supervisory system. However, when coupled with an intelligent selection of instrumentation and a proficient operating crew, it can also be an invaluable tool for continuous improvement, condition monitoring and campaign extension activities. It is not to be seen as a replacement for the operator, but a tool to assist them to increase their expertise at their craft, and the modular approach of this system focuses on the individual areas comprising a modern blast furnace, with intuitive navigation and clear visualisation techniques being of maximum benefit to the operator. Authors: Jennifer Wise, Rob Mijnen, Geert-Jan Gravemaker and Jim Plooij Danieli Corus bv The modern blast furnace is a different animal to that of only a few decades ago. It has gone from a wild, unpredictable monster to a rather domesticated creature but one which you would still not want to leave alone with your children. The taming of this particular beast has been accomplished largely by improved instrumentation and measurement control. This has allowed the process to be studied online and to be brought back within the control limits where it is known to behave in a predictable fashion. The increased predictability and repeatability of the process has, in turn, allowed the process to be further optimised, with productivity reaching new highs and campaign lifetimes growing longer. This improvement is a necessity for remaining competitive in the modern iron and steel industry. The contribution that process control can make is the subject of this article. A Level 2 system can be defined in many ways, however, the definition within the process control industry is that it is a production supervisory system. In simple terms the BF Level 2 system supervises the production process. But that is only part of what the typical Level 2 system is capable of. When coupled with an intelligent selection of instrumentation and a proficient operating crew, the Level 2 system can also be an invaluable tool for continuous improvement, condition monitoring and campaign extension activities. And, through learning how best to use this tool, the operator improves their understanding of the cause and effect nature of the blast furnace process. This self-learning in turn allows operators to concentrate on how to improve the process yet further, with the efficient functionality of the Level 2 system giving the r Fig 1 Schematic of the blast furnace area with related Level 2 modules operator time during a normal working shift to work on managed continuous improvement projects. The Danieli Corus solution to the Level 2 system is a modular approach with dedicated modules individually designed to be of optimum benefit to operations in that specific area. Each module has been designed with the operator in mind, using the experience of current and previous operators to capture relevant information and present it in the most useful format. Although the modules are area-specific, there is an overlap. Where this occurs the information is shared as much as possible. The main modules and their area of coverage are shown in Figure 1. System Architecture The systems are a set of applications that show the state of a blast furnace and are composed of several modules a 23

r Fig 2 State-of-the-art blast furnace control room r Fig 3 Sub-systems of the operator advisory and control system r Fig 4 Typical configuration of a BF Level 2 system that can be standalone, though they need to interact with each other to release the full potential of the system. Prime users can enter or modify data in the specific modules and submit changes to the server. Figure 2 shows a typical modern BF control room. The modules are not standalone but, where it is useful, such as in the burden calculation or heat and mass balance, some have the functionality to run in standalone mode. This is useful for predictive analysis or what-if? scenarios where an insight into what is likely to happen would be beneficial. In a full production environment the Level 2 system communicates via a gateway PLC with the Level 1 system, giving the client complete autonomy to arrange and maintain the Level 1 system as it suits them. The Level 2 system also provides interfaces for communicating with a Level 3 system, if required. The system consists of three sub-systems, as shown in Figure 3. The client-server system is used by operators, process engineers and managers. It is a rich-client application so software must be installed prior to use that shows the current and past state of the blast furnace. The calculation system is a set of windows services that has no interaction with users. Its purpose is to perform (near real time) calculations on data received from Level 1 or on data generated by users on the client-server system. The Level 2 system needs to be fed by the Level 1 system. The gateway system is a windows service that provides communication from Level 1 to Level 2 and vice versa. The modules that comprise the Level 2 system are assemblies running on the client and/or server. The server acts as an application and a database server. The application server hosts the application modules where the database maintains the state of the furnace as seen by the Level 2 system. The Level 2 presentation framework is run on the client, showing users the state of the furnace. Depending on the selected module a user can view the state of a process in the BF, perform calculations and carry out all tasks required. Each module has four layers (or tiers): persistence (or database), business, service and presentation. A layer partitions the system vertically whereas a module partitions it horizontally. The central module in the system is the Shared Service Module (SSM) through which the modules can communicate with each other (see Figure 4). Supervisory Modules The supervisory modules are designed to cover all aspects of blast furnace operation and control necessary to meet the needs of a modern furnace with the capability to operate at high productivity and realise an extended campaign life of up to 20 years. The key module for day-to-day operation is the Process 24

r Fig 6 Operator data entry screen tapping module r Fig 5 Some of the main process parameters that are calculated and monitored by the process support module Support Module (PSM). This calculates and displays the main process parameters in the furnace such as those shown in Figure 5. The system is designed to facilitate plots to be easily displayed over long-term trends. The grouping of plots and data is structured in such a way to make the analysis of long-term and short-term process operations as efficient as possible, thus maximising the time available to take appropriate actions when required. This functionality is specifically designed to provide the operator with the information to quickly assess the process state. In a smooth-running furnace this means it takes only one or two minutes to go through all the required process checks, leaving time to work on developmental or process improvement projects. The Tapping Module (TPM) combines the manually recorded tapping data with the automatically transferred data from Level 1 to deliver a comprehensive tracking and reporting system for all aspects of good liquid management. The manual entry part of the module requires the operator to enter the start and stop times per cast, as well as other critical events such as the time liquids are cast, are under the skimmer, and when slag is over the slag dam. Where instrumentation exists that is sufficiently reliable to replace this manual function, that can also be easily incorporated. Important details of the cast, such as drill diameter and taphole length, as well as the hot metal and slag analysis, are also recorded. The data retained by the system is used to produce data visualisation screens that encapsulate the tapping information in user-friendly format (see Figure 6). The hot metal and slag casting are presented as tapping sequences (known as trains) per taphole, as well as for the furnace as a whole. These trains are plotted with key furnace parameters to display at a glance what the status of the furnace was at the time of casting. Trains are also presented for the time from the furnace being ready to cast to the time the taphole is actually open, and then again from that moment to when the hot metal is under the skimmer block. These intervals assist greatly in the management of the casthouse operations as they indicate where time is being lost in the taphole opening procedure. The tapping module also has the functionality to display the real-time continuous indication of the depth of the liquids contained in the hearth (iron and slag). A reporting function presents the daily tapping history in overview format, containing all the relevant information that may be discussed during morning management meetings. The Heat Flux System (HFS) calculates the heat losses per panel in the stack cooling system, the tuyeres and the hearth. Raw data for water flows and temperatures and the resultant heat loadings for each area are calculated and presented (see Figure 7). The calculations include correction factors for deviations in the thermocouples, which are calibrated before blow-in of the furnace. Overview screens allow a rapid appraisal of current status in terms of heat losses, with more detailed analysis possible by zooming in to separate layers, such as bosh, belly or the different stack elevations. Trends are instantly presented as data points that can be sensibly compared on pre-set time frames, typically 1hr, 8hrs, day, week or month. These graphs allow all relevant aspects of the cooling losses to be assessed by the operator. This is an invaluable tool for monitoring and controlling gas flow in the furnace and the possible build-up and removal of a 25

actions may be taken to verify the inputs, or the results can be used for process assessment. The model allows the user to modify parameters to assess the influence on the process. The balance can either be run to determine the required hot blast rate for a specified production, or the resulting production from a specified hot blast rate. Using these functions the user can predict the influence of operational changes and control actions, and analyses numerous parameters, including those shown below: r Fig 7 Example of the visualisation displays of the heat flux information (visualisation made using test data to demonstrate full range of values) scabs on the furnace lining. The aim of the Silicon Prediction Model (SPM) is to give the blast furnace operators an early indication of changes to the thermal level of the furnace. This can then be used as a basis to make corrective changes to the blast furnace parameters such as coal injection, blast temperature and steam addition to maintain the thermal level and hot metal silicon within desired limits. An option also exists to use the predicted silicon online in Level 1 to correct the calculated production rate and coal injection rate to minimise fluctuations in the furnace thermal level. The prediction is done using the results of a steady state mass and energy balance on the furnace using actual operational data to determine the heat factor in the lower furnace. The heat factor represents changes in the excess or shortage of heat in the lower furnace. The coke and slag rate at the tuyeres are entered in the mass and energy balance based on the online burden tracking module, described later. This is an example of where the individual models also have links to one another to ensure that the information required for the calculation is always up to date and real-time. The Mass and Heat Balance Model (MHB) was developed over a number of years and encapsulates a huge amount of technical know-how. It is a two-stage model with the furnace split into an upper and a lower part. Over both parts the heat and mass balances are performed using some empirically tested assumptions. The aim of the model is to allow accurate assessment of the blast furnace operation taking into account all of the operational parameters. The actual process parameters for the current operation are displayed and can be selected as a data set to perform a mass and energy balance. Once calculated the results are compared to the actual operation data. Depending on the magnitude of the difference, ` Furnace efficiency ` Burden pressure drop ` Coke rate ` Coal injection type, composition and rate ` Slag rate ` Direct reduction ` Hot blast temperature ` Oxygen enrichment rate ` Steam addition ` Top temperature ` Top gas rate, temperature and calorific value ` Top pressure ` RAFT ` Cooling losses ` Hot metal chemistry Each run of the model can be saved with a short description of the basis of each calculation. Each series of calculation runs can be saved or printed and used as an analysis and decision tool, so that the learning process is preserved with every run that is carried out. The Burden Calculation Model (BCM) uses the weights and compositions of the charged materials to calculate the quantity and composition of hot metal and slag produced at an aim silicon level in the hot metal. The aim is to allow the operator to calculate the burden characteristics based on a charge and determine the charge for the optimum operation parameters, such as slag basicity and alumina percentage. Input values for calculations are manual inputs where the engineer can select from several material groups like ore bearing materials, additives and fuels. For comparison purposes the charged materials are presented as actual set point values based on readings from the Level 1 system. These materials can be chosen from an overall material list managed in the Level 2 system. Users can add, delete and update materials along with chemical compositions and give used materials unique names so that the material database can be kept up to date with all the materials that the furnace may use over its campaign life. Results can be stored in the database for future use and for report generation and each calculation can be 26

repeated to give insight information about the effect that changing the input materials have on the hot metal and slag composition of the blast furnace. The Burden Tracking Module (BTM) calculates the position of each charge in the furnace. This is based on a volume balance using the actual charged volumes together with the stockline level. For each charged volume the coke rate and slag rate are calculated with a burden balance. This allows the actual characteristics of each charge set to be examined. These are displayed graphically and in tables on the interface. This allows the operator to follow each charge in the furnace and make a judgement on when each charge reaches the melting zone. The tool is used to make correct changes to the blast conditions and coal injection rate based on the actual burden being melted in the melting zone. The Burden Distribution Model (BDM) s purpose is to visualise the distribution of the coke and ore in the throat/upper stack of the BF. The loading of the furnace will be characterised by the filling scheme: a sequence of dumps of coke, ore or mixture with the settings of the top charging system. This filling scheme is entered by the operator as a table containing material, weights and material types and charging position. The calculations consists of the addition of material after each dump at the stockline, considering the angle of repose of the material after it impacts to the stockline surface. The calculations mathematically determine if some material is laying at too steep an angle and will iterate through several calculations as long as no material in that layer exceeds the given angle, thus forming a stable layer. An example of an output is shown in Figure 8. The horizontal axis represents half of the throat diameter and the vertical axis the height in the throat of the blast furnace. With the output, the ore to coke ratio across the throat diameter can also be calculated and displayed. The visual display shows the formation of layers of coke (black) and ore (red) of a complete filling scheme on top of the previous base layer (white). This model is a very useful tool for predictive analysis purposes, particularly when trying to improve the process parameters through burden distribution. Interacting with this model on a regular basis gives the user an excellent insight into the capabilities of the burden distribution apparatus and, by studying the results of changes that have been made after using this model, the effect on the furnace performance can be further studied. The Hearth Monitoring System (HMS) is designed to visually present the temperature values that the thermocouples in the hearth pad, sidewall and taphole measure. As the hearth life will determine the campaign life of the furnace, the number of thermocouples in this area is the most of anywhere in the furnace. To keep track r Fig 8 Layer build-up from centre to wall r Fig 9 Overview of thermocouples in the pad of these thermocouple values, visualisation screens are presented to the operator in the HMS. The thermocouples are arranged in such a way as to allow heat flux calculations to be made through the refractory. These heat flux values are displayed in both the vertical and horizontal directions and are in turn used for calculation of the isotherm lines in the hearth. These are also presented to the operator in the form of crosssectional views of the hearth sidewall and pad, with the isotherms in colour coded lines. Figure 9 shows an overview of thermocouples in the pad. The alarm status is shown by the colour of the thermocouple and its temperature value beside it. Test data has been used to demonstrate the range of values and possible alarms, which are expected to become increasingly useful towards the end of a 15 20 year campaign when high temperature may be measured. The alarm values for the thermocouple temperature values are programmed in the system, and the colour of the thermocouple position indicating icon will reflect the alarm status. A traffic light system is used to colour code the alarm levels. The colours change depending on the alarm status. The system is intuitive to the analysis requirement of a 27

r Fig 10 One of the screens from the stove optimisation model 28 the operator and will pre-select the thermocouples to be displayed for comparison purposes with a thermocouple that is selected from previous analysis. A maintenance screen allows the alarm levels to be changed, to reflect the different stages in the campaign that the hearth is expected to undergo. This system has minimal interaction with the other modules and is a very useful standalone tool to secure longer campaign lives without the need for the entire Operator Advisory and Control System. The under-tuyere thermocouples are displayed in a series of short- and long-term trends. This tool allows the operators to observe temperature changes that can indicate water leakages in the furnace. Such leakages must be detected as early as possible to prevent any damage to the furnace lining. The data is also analysed statistically online for the fluctuations that can indicate water leakage. This is displayed graphically for easy analysis by the user. The Stack Lining Monitoring (SLM) system gives the operator the tools required to properly assess the thermal status of the stack lining. This is of great importance in analysing any conditions that can reduce the lining life, and take corrective actions, and is a necessity for any furnace hoping to extend campaign life beyond 15 years. The Danieli Corus furnace design incorporates refractory and cooling element thermocouples distributed through the stack. This data is displayed in graphs of typically 8 hours, 1 day, and longer. The data is also analysed online for statistics such as: maximum daily value, maximum daily fluctuation, average daily value and number of fluctuations above a specified level per time. These are plotted over the total campaign to allow a proper historical examination. A colour-coded system alerts the operator to unusual temperature levels. The Stove Optimisation Model (SOM) as a supplement to, at least a semi-automatic stove control system, will improve the operating efficiency of the stoves and render them fully automatic, which means that the decision on the changeover of the stoves will depend entirely on the control system and the required operating set points, and not on the decision of the stove tender or furnace operators. For special situations, such as maintenance or control checks, the system has manual overrides, but in normal operation the objective of the control and optimisation package is to optimise the efficiency of the stove system. Figure 10 shows one of the screens from the stove optimisation model with an overview of all three stoves in this system. The SOM provides reliable delivery of the desired hot blast to the furnace without continuous attention by operating personnel. Further, the control package will respond rapidly to changes in the blast furnace operation, thereby eliminating any manually retained safety margin. The model can also be run in an offline mode whereby calculated information can be verified. This gives a good idea about the results and assessments of the model in combination with the real measurements and special operational situations. A three-stove hot blast system is also designed to operate a two-stove cyclic operation in the event of a stove malfunction. The main feature is effective control of the heat balance of the stoves. This means that when operating parameters of the stoves change, by design or otherwise, the control system will automatically restore the stove system to stability either at the new parameters or at the original parameters before the variation(s) occurred. Optimum thermal efficiency has been demonstrated with this system where an improvement of 2% is commonly achieved by the addition of the control optimisation package over that which can be achieved by manual control. In a number of cases, a higher improvement in thermal efficiency of up to 4% has been realised. Of course, an important aspect of the control philosophy is optimum economic efficiency. In modern stove systems, dome temperature and hence flame temperature are controlled by varying the amount of enrichment gas added to the blast furnace gas. In most cases, the cost of the enrichment gas is well above that for the blast furnace gas. By minimising the use of the enrichment fuel, the control optimisation package will reach an optimum between thermal efficiency and economic efficiency that can be achieved by the relevant stove system. The traditional manual method of stove operation, even with automatic stove changing, is to maintain more heat in a stove than actually required, thus to cope with any emergency. However, to keep the waste gas temperature below the maximum design limits, the gas volume in type of operation should be lowered through the gassing period. It is possible to overheat the centre section of the stove

chequer column, which can cause excessive movement of the chequers and even collapse by crushing due to loss of strength through overheating. A good way of preventing such a catastrophe is to fire the stove with a constant gas volume throughout the gassing period. In this way, the temperature distribution over the total height of the chequer column will be a straight line from top to bottom. The benefit is that the waste gas temperature will give a realistic impression of the heat content of the stove at any time. This means that the waste gas temperature can be used for stove thermal monitoring. Danieli Corus is continuously developing its Level 2 models and continuously improving its Operator Advisory and Control System (OACS) for the BF. The OACS is an integrated part of the complete Danieli Corus Level 2 system and is capable of identifying process deviations at a very early stage. It is also designed to compare historical and calculated data in order to avoid major and costly incidents. The system advises and gives guidance to operators and process operators to help in taking the correct actions to keep the furnace operating in the most optimum and economic way. The OACS continuously collects actual data via the Level 1 system and checks the continuity of the process. The collected and calculated data will be continuously analysed and, in the case of any irregular or unexpected data, will give explanations and possible solutions. The OACS is based on years of experience from Corus BFs. Since these furnaces are running at very high production rates and long campaigns, the OACS is a reliable and helpful tool to increase stability and production. By using the OACS, system users will automatically receive training due to the detailed explanations. As the operator is key in closing the loop in the system, he will also retain ownership of the process. Overall Functionality It is recognised that the management and supervision of the overall material flow is essential for delay-free operation. For this reason each of the individual modules will include the functionality required for data gathering and management. Production reports will be generated on a daily, weekly and monthly basis within the relevant module, along with the other essential process and operational data required for maintaining consistent operational performance. Complementary to area-specific modules, the overall system includes communication to satellite areas such as the laboratory, casthouse or any other work area that is not serviced by the central control room. The maintenance screen within the Supervision Module will be available for maintenance personnel to enter the work carried out per equipment item or area. A database system will record the relevant parameters and will have a search and ordering function to allow selection or ordering by, for example, date, person, area or equipment code. The BF Level 2 system is configured such that it can be linked to the plant-wide system and communicate easily with any Level 3 system installed at site. In the development of the OACS, Danieli Corus has been very conscious of the fact that this system will be viewed continuously throughout the lifetime of the blast furnace on a 24/7 basis. For this reason great care and attention has been given to the graphics and displays in the system. Features such as black background have been retained from the Level 1 system both for reasons of viewing comfort and of energy efficiency. A black screen requires less backlighting and so is easier on the eyes and needs less power than a similar graphic on a white background. OUTLOOK The future development for the Danieli Corus OACS is to add a Material Tracking Module and a Ladle Tracking Module to the suite of models. The goal of these two additions is to fully account for the material stream through the blast furnace unit, from where the raw materials enter the stockhouse bunkers to where the hot metal arrives at the end destination. This will then allow the Level 2 systems for the internal supply chain throughout the plant to communicate with one another, realising a fully integrated steel plant in both practical and process control terms. CONCLUSIONS The continued development of additional functionality in the Danieli Corus Level 2 supervision and control systems of the blast furnace are not a replacement for operators, rather a tool to help them increase their expertise. Taming the blast furnace requires complete and absolute control over the inputs and operating parameters. This needs the instrumentation and control systems to be in place. The modular approach of this system focuses absolutely on the individual areas that comprise a modern blast furnace, with intuitive navigation and clear visualisation techniques being of maximum benefit to the operator. This promotes an efficient method of working whereby the operator can spend the minimum time monitoring a smooth running operation, and the maximum time developing ways to realise improvements for the future. MS Jennifer Wise, Rob Mijnen, Geert-Jan Gravemaker and Jim Plooij are all with Danieli Corus bv, Ijmuiden, The Netherlands. CONTACT: Jennifer.Wise@danieli-corus.com 29