IQGradeChange - The first truly automatic grade change application, which runs the grade changes with the quality controls on.

Traditionally, Automatic Grade Change (AGC) has suspended normal quality controls and ramped the manipulated variables to pre-calculated setpoints without actually utilizing quality measurements. This old type of AGC consists of many ramps, delays and grade change models, making it hard to tune and even harder to maintain. Not surprisingly, most installations have fallen quickly into disuse. With IQGradeChange, it is possible to perform grade change that is fully automatic, i.e. with the quality controls on all the time. The advanced control algorithm calculates the new control actions throughout the grade change, so all the quality variables are controlled smoothly to their new targets. IQGradeChange does not need the ramps, delays and grade change models required by traditional AGC packages. The same models which are used during normal production are used also for grade change. IQGradeChange is fast to commission and easy to maintain guaranteeing smooth, fast and reliable performance.

Description

IQGradeChange adjusts paper machine production from one grade to another while minimizing off-quality paper and lost time. When the next grade to be run is selected, the computer proposes setpoints taken from grade tables stored in the memory. These values may be grade standards or historical values from the last time that particular grade was run. All targets are listed on IQGradeChange displays with their active setpoints, measurements and control status.

Operators are free to modify the targets proposed by the system to accommodate the current machine and furnish conditions. They are also presented with some calculated information to assist their decision-making, such as production rate and expected grade change duration. Once the operators are satisfied, they initiate the actual grade change.

When the grade change starts, the quality control application (IQWetendMD) controls the quality variables during the grade change. Instead of ramping the setpoints of the manipulated variables, IQGradeChange ramps the setpoints of the controlled variables to their new grade specific targets. Speed change is included in the grade change application, so the effect of the speed change on the quality variables is handled automatically. During the ramping the control algorithms adjust the manipulated variables so that the measurements follow the setpoint trajectories. IQGradeChange can also control variables other than measurements, e.g. slice lip opening or stock component ratios. It ramps these variables to the new setpoints automatically at the appropriate time as the grade change proceeds.

IQGradeChange handles both fast and smooth grade changes. In fast grade changes the grades are widely separated and the grade change time is critical. The goal in this type of grade change is to minimize off spec production. In smooth grade changes, grade limits are overlapping - thus grade change time is not as critical. In this type of grade change, the quality variables must be on target all the time so that no broke is produced.

Progress of the change can be monitored on dedicated trend pages of key variables. Once complete, these trends are frozen for later analysis and further tuning. Dedicated tuning displays and a simple, flexible and modular structure facilitate tuning and modification by mill maintenance personnel for continued good performance.



Benefits for the papermaker

• Smooth and fast grade changes for minimum production loss.
• Reliable grade changes, because the quality controls are on during the grade change.
• Easy to maintain because no grade specific tuning is needed. The grade change application utilizes the same models during grade changes as during normal steady-state production runs.

Technical features

• Utilizes multivariable MPC (model predictive control) during the grade change. The quality variables are constantly controlled during the grade change.
• Setpoint ramping time is selectable by the operators. It is usually determined by the machine speed ramping time.
• Any process variable can be added to the grade change application with coordinated ramping function.
• The grade change can be completed in the bottom of the new reel, or in the top of the old reel or grade change ramp can be divided equally between the old and the new reels.
• Utilizes the system recipe features. Either grade standards or historical values are stored in grade tables.
• When the next grade is selected, targets from that grade table are proposed by the system.
• The operator can adjust the proposed targets before starting the grade change.
• The time required for the grade change and the limiting loop are displayed.
• Operator decision support calculations, such as production rate, are available.
• Monitoring display features:
  • Provides progress information during a grade change.
  • Stores results for later analysis.

Engineering support features

• Comprehensive set of tools for tuning, maintenance and troubleshooting.
• All operations are performed with dedicated task-oriented tuning displays.
• Runs on the metsoDNA platform and is confi gured by standard metsoDNA tools.