Reheating furnaces are used in steel mills for heating steel pieces (Billets, blooms, slabs or ingots) to temperatures of around 2200 F or 1200 C, making them suitable for Hot Rolling. There are different types of continuous reheat furnaces. The most common types are Pusher, Walking Beam, Walking Hearth, Rotary Hearth and Roller Hearth. We have more than 50 years of combined experience in Continuous Reheat Furnaces. Over the years we have developed simulation software to size, analyze and design furnaces, Set point management software to determine optimal setpoints and on-line, and Level 2 software for complete automation. We also do Reheat Furnace Study and Data Analysis for energy efficiency, performance increase, and quality enhancement.

HeatXpert On-Line Level 2 Supervisory Software

HeatXpert Level 2 software system is very unique in a way that it comes packaged and requires very minimal customization, thereby reducing the total development cost to the end user. The HeatXpert Level 2 software can be connected to a Level 1 SCADA system easily. It can completely reside on the back ground and display the results on a Level 1 HMI screens or if required HeatXpert comes with its own set of HMI screens. The primary modules in our Level 2 system are as follows:

Setpoint Management (Determination of Optimum Furnace Temperature): In our on-line setpoint management module the furnace temperature in each zone is determined by real time heat transfer calculations. The setpoint calculation is a reverse transient computation to determine furnace profile from actual (computed) and target temperature profile of the billets and billet movement rate in order to achieve desired discharge temperature with minimum fuel consumption and scale formation. The algorithm takes into account delayed heating in order to optimize energy and minimize scale and decarburization formation. The on-line system has the capability of storing and modifying different heat curves for different grades of steel. Each curve has its own target billet temperature, zone setpoint limits as a function of charge temperature and production rate.

Delay Management (Scheduled and Unscheduled): Scheduled delays are planned and usually occur after a specific billet has been discharged. The delays usually take place due to maintenance work such as roll change or suspending mill production for a period of time. Unscheduled delays occur due to a problem that has caused the furnace to halt, stopping billet processing. These problems generally occur due to a furnace breakdown or a snag in the Hot Rolling process. The delay setpoint is directly proportional to the length of the delay. Longer the delay duration, more the temperature setpoint is reduced. However, a check is made to ensure that the zone setpoint is never reduced below a preset, minimum zone setpoint value or average temperature of the hottest billet inside the zone. The zones automatically ramp up whenever the drop in the zone temperatures divided by the ramp rate is greater than the time left for the delay to end. This ensures that the furnace is ready when the delay is over. Unscheduled delays are unexpected delays. Since the delays are unexpected, the end time is usually not known in advance. When such delays are encountered, the zone setpoints are reduced to force the burner to reduce the firing rate. As the furnace temperature goes down, the setpoints are further reduced until either minimum zone setpoint is reached or hottest billet temperature in the zone is reached.

Mathematical Model: The mathematical model consists of a finite difference heat transfer algorithm, which calculates temperatures throughout the thickness of billets at different positions along the length of the furnace. These temperatures are obtained by solving the system of heat transfer equations. The mathematical model executes at a predetermined time interval or steps. At each calculation step, the model determines the amount of heat that has diffused inside the billets since the previous calculation step. The Heat Transfer calculations take into account Steel Grades, Product Dimensions, Charge Temperatures, Charge Postions inside the Furnace, Furnace Profile, and Product Temperatures at the last step.

Tracking: Push or Walk information is passed on from the Level 1 system to our HeatXpert system. HeatXpert system tracks the parts inside the furnace and calculates their temperatures as they move along the furnace length.

Communication: Setpoints calculated by HeatXpert are sent to the Level 1 system. The process variables come from the Level 1 system to the HeatXpert system. HeatXpert System can reside on the same computer as the Level 1 system or could be on a different computer. The data can be passed back and forth either through the database or TCP/IP using socket.