OptiBOF - Process Control Solution for BOF Steel making

OptiBOF

The stringent demands placed on high quality of steel in the primary steelmaking coupled with reduction in production cost has necessitated the implementation of high level automation systems. These Automation systems with an integrated approach and optimization models help steelmakers to achieve these objectives with substantial benefits in terms of quality achievements and cost control

 

Automation Division, TATA STEEL has implemented OptiBOF - a comprehensive higher Level-II automation in both it’ s steelmaking units i.e. .- LD #l and LD #2 shops. OptiBOF brings in standardization of operations, consistency in end blow chemistry and temperature and provides assistance in the planning of heats in the shop by integrating with Planning systems and other production units in the shop. Further the optimization models contribute significantly to the savings in raw materials and improvements in vessel life.

 

OptiBOF

The Level-II automation system comprises of the communication to other computer systems for data acquisition, tracking of heats and equipment and the man-machine interfaces to display online status of the shop. At the core of the system are process models to optimize the charge and also achieve end point conditions. These models provide guidance to operators at various stages of a heat. Further enhancements have also been done to integrate the process data with management information systems.

 

The Level-II system has the following major components which cater to specific functions of the process:

 

Communication and interfacing;

The Level II system interfaces with other systems installed in the shop to provide data in real time for the process models and for data logging for process analysis.

  1. Level - I: communication is developed to receive online process data from Level-I and transfer setpoints from Level-II using the standard communication protocols.
  2. Level-Ill: communication with level 3 system is developed on TCP/IP Ethernet protocol. Daily production schedules are downloaded from Level-III and the actual heat data (including material consumptions) are sent to Level-lll.
  3. Laboratory computer: The Level-II system interfaces with the Laboratory management computer and receives the analysis of hot metal, steel and slag in an online mode.
  4. Caster Level-II: Heat data is transferred at tapping to Caster Level-II and this communication is established using TCPIIP protocols.

The reliability of these communication modules is very important for the effective functioning of the Level-II system.

 

Scheduling:

This module handles all the Scheduling and Planning functions in the shop. The production schedules are prepared on Scheduling (Level-3) computer and downloaded to level-II. Each order in the schedule denotes the steel grade to be made, the tonnage, route to be followed and the expected time of arrival at caster.

Heat planning is done in the Vessel Control room based on this schedule.

 

Process Models:

At the core of the level-II system are the process models which aid the shop in achieving the desired end blow conditions by providing the calculations for the input charge materials. The Level-II system has a number of models which are run at different stages 01 a heat to cater to the entire steelmaking process. Though the models vary in terms of data sets used and algorithms, a few common functions have been incorporated in each model:

  • All the models are triggered automatically on an event or receipt of all the relevant data
  • The models can be rerun on operator request
  • The setpoints are downloaded only on operator acceptance of the results.

All the models have the following components

OptiBOF

Data interfaces for the process model

  • Message handling routines to receive activation messages from other system components.
  • Data reading routines to read heat database, master data and perform limit checks on input data.
  • Algorithms to perform calculations with defined iterations/exit criteria.
  • Data output routines to update data in heat database, display results on screens or flash alarms/errors in cases of failures.

 

The following are the major process models :

Static charge balance model : This model is a thermochemical model based on mass and heat balance calculations. It also has a set of empirical relationships to represent the individual shop practices. Based on the inputs to the vessel comprising the actual hot metal and scrap weights charged and the hot metal analysis and temperature the model predicts the quantity of fluxes and oxygen to be blown to achieve the aim steel specifications and temperature.

 

The slag-steel equilibrium relations are derived by empirical relationships based on the actual process data from the shop and filled by regression analysis or Adaptive Neural nets.
There are different sets of relationships evaluated for different blow profiles and bottom stirring profiles and thus cover various combinations of blowing practices.

 

Dynamic Model : The dynamic models executed at start of blow and runs cyclically in automatic mode. The model calculates the decarburization rate (dc/dt) based on the waste gas analysis, temperature and flow rate. To start with, the initial condition is the hot metal and as the blow progresses the last calculated steel condition is taken as the initial bath state for calculations.

 

The model also calculates the carbon in the bath and the temperature of the steel and displays these data during the blowing process graphically.

 

Alloying Model : The existing Ferro Alloy calculation model predicts Ferro alloys weight required during tapping from vessel based on burning equations and thermodynamic considerations coupled with linear cost optimization module (Simplex module). It selects combination of ferro-alloys for the calculation based on given priority for each element to achieve aim analysis of steel at optimal cost.

This model is activated at blowing end on receipt of turn down analysis

 

Process Tracking:

These set of modules are responsible for tracking all the data for a heat from the time hot metal is received at torpedo station upto tapping of the heat. The data received by the communication modules are either periodic or event based. These data are updated by the Tracker in data base after associating it with a heat. Subsequently this can be displayed or available as status information at all stations in the shop.

 

Data pertaining to various equipment in the shop such as hot metal torpedoes, hot metal ladles, steel ladles, and convertor are tracked by the system so that the status of these is readily available. This helps in better planning and coordination between the sections in the shop. The software is designed such that Tracker modules closely follow the heat in the shop as it progresses across the various units. Accordingly the Tracker modules perform the following functions at each stage of a heat cycle.

 

The software is designed such that Tracker modules closely follow the heat in the shop as it progresses across the various units. Accordingly the Tracker modules perform the following functions at each stage of a heat cycle.

  • Production Scheduling
  • Heat Planning
  • Hot metal preparation at torpedo station
  • Desulphurization station
  • Scrap preparation
  • Blowing process
  • After Main blow
  • Tapping process

 

Man-machine interfaces :

This module comprises of all the screen displays for all the terminal locations. It provides for data entry facilities and display of data relevant for the specific location. This is totally menu based with other features such as online help, fixed function keys performing similar functions at each terminal e.g. saving data, navigating through screens and message and alarm lines. The display screens are user friendly.

 

Benefits of OptiBOF

While the models directly lead to improvements in the process. The other modules of Level-II automation also contribute to the overall shop's performance enhancements.

 

The tracking modules along with the communication modules enables direct capturing and recording of the heat data right from torpedo station to tapping end. These data displayed to the shop through display and report modules enhance the data availability. Heat data or data for a given period can be seen at any location in the shop or analyzed easily to understand the process behavior. Further the status displays at various locations aid the operators in better planning from hot metal preparation to tapping. A fully customized and tuned Level-II system for BOF provides the following benefits:

  • Reduced reblows
  • Optimized charge balance
  • Standard operational practices
  • Effective process analysis