Charge Scheduling:

Charge scheduling is a database of important information concerning each part (billet/slab/ingot) arranged in a queue structure. Scheduling information is comprised of dimension (length, width and thickness), steel grade, charge temperature, aim mill production rate, aim dropout temperature and aim rougher exit temperature. The information is either entered by the operator or received from Mill Automation Computer or an ERP system. Whenever a part is charged inside the furnace, the product scheduling system passes information concerning each part to the tracking sub-system.

Product Tracking:

The primary function of the furnace tracking is to maintain a map of the physical locations and identities of all the parts (billet/slab/ingot) in the furnace. With the arrival of a part inside the furnace, the information associated with the part is transferred from scheduling module to the tracking module. With every walk, push or rotation (in case of rotary furnace) tracking updates the position of each part by the amount of walk, push or rotation. The furnace tracking therefore knows when the part reaches the discharge position. On part extraction from the furnace the part is removed from the tracking system. The historical record is compiled for each piece for a production report.

Zone Setpoint Management:

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 - 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.

Delay Management - Scheduled:

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 tempearture 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 Tempeartures, Charge Postions inside the Furnace, Furnace Profile, and Product Tempeartures at the last step.

Communication:

Tracking information should come from the tracking computer to our FurnXpert Level 2 system. The level 2 system calculates the setpoints and sends them to the supervisory system or PLC. The process variables come from the supervisory system or PLC to our Level 2 system. Level 2 System can reside on the same computer as the supervisory system or could be a different computer. In the same computer data passing will be relatively simpler.

Simulator:

The purpose of the Level 1 simulator is to generate Level I signals just as one would see in an actual furnace control system. The signals could be the billet/slab/ingot walk rate or push rate, temperatures in each zones and from other thermocouples, air and fuel flow rates and any other parameters that are captured by the Level 1 system. These data are used by the Level 2 system to comtrol the furnace.