A transient simulation and dynamic spray cooling control model for continuous steel casting
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A Transient Simulation and Dynamic Spray Cooling Control Model for Continuous Steel Casting RICHARD A. HARDIN, KAI LIU, ATUL KAPOOR, and CHRISTOPH BECKERMANN A two-dimensional heat-transfer model for transient simulation and control of a continuous steel slab caster is presented. Slab temperature and solidification are computed by the model as a function of timevarying casting speed, secondary spray cooling water flow rates and temperature, slab thickness, steel chemistry, and pouring and ambient temperatures. Typically, the solidification path, temperature-solid fraction relationship, is prescribed. However, if these data are not available, a microsegregation solidification model that approximates the effects of steel chemistry and cooling rate is incorporated in the caster model. Measured slab surface temperatures recorded from an operating caster are compared with predictions from the transient model. These demonstrate that the model typically can predict the temperature response at the slab surface within 30 °C. Results of several simulations are given to demonstrate the effects of changing casting conditions on the slab thermal profile, end of liquid pool, and solidification end point. A control methodology and algorithm suitable for online control of a continuous casting machine is described, and the ability to control the surface temperature profile by dynamically adjusting secondary spray cooling flow rates is demonstrated by simulation. Results from a preliminary version of the model that is capable of running in real time are presented and are compared with the slower, but more realistic, version of the model.
I. INTRODUCTION
IN order to remain competitive in the worldwide market for continuously cast steel, steel producers are finding it increasingly important to implement process control improvements. Through superior production process monitoring and control, producers are improving steel quality and are meeting customers’ requirements for steel size, grade, quantity, and properties at the lowest cost. Computer models used for real-time/online prediction and control of continuous steel casters are fundamental tools in this effort. Accurate online prediction and control allows for flexibility in caster operation. It gives operators the capability to vary casting speeds while keeping process parameters such as slab surface temperatures and solidification end point within desired ranges. Such control capability results in more uniform cast material throughout an entire casting sequence. Leaving aside the benefits of online/real-time control models, offline transient modeling gives insight into the time-varying behavior of process variables and parameters, and a more thorough understanding of the casting process. The simplest method of caster spray cooling control is to deliver a prescribed amount of water flow that is proportional to the casting speed. Different proportions of flow to casting speed are delivered to the casting machine’s spray cooling water flow loops. These flow loops supply water to ba
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