Paper Machine Grade Change Control Trajectories
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Solution Overview
Problem
Paper machine grade changes often result in production losses due to undesirable characteristics in the sheets produced during the transition, leading to waste and revenue loss, as existing systems struggle to smoothly transition between different paper grades without shutting down.
Innovation Solution
A method and apparatus that identify target values for controlled and manipulated variables, such as dry weight, ash content, and machine speed, to generate trajectories for transitioning from one paper grade to another, using iterative processes and process models to minimize deviations and optimize the production process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the paper machine transitions from one grade to another in a continuous fashion, then the machine does not need to be shut down and restarted, but the sheet produced during the grade change has undesirable characteristics resulting in production losses
Solution Approach 1:
The control system performs preliminary actions by calculating optimal trajectories for manipulated variables (stock flow, filler flow, steam pressure, machine speed) before the grade change occurs. These pre-calculated trajectories guide the controlled variables (dry weight, ash content, moisture content) through the transition period, ensuring sheet characteristics remain within acceptable ranges throughout the grade change process.
Solution Approach 2:
The system dynamically adjusts multiple process parameters simultaneously during the grade change transition. Rather than static control, the system continuously modifies stock flow, filler flow, steam pressure, and machine speed according to calculated trajectories, enabling smooth transitions while maintaining product quality specifications.
2Adaptability or versatility
If the production process is altered to change the grade of the sheet being produced, then the grade transition is achieved, but the sheet has one or more undesirable characteristics causing waste of material and loss of revenue
Solution Approach 1:
The control system uses feedback mechanisms to monitor controlled variables (dry weight, ash content, moisture content) during the grade change process and compares them against target values. The system continuously adjusts manipulated variables based on the deviation between actual and target values, ensuring sheet characteristics remain within specifications and minimizing material waste.
Solution Approach 2:
The system changes multiple process parameters (stock flow rate, filler flow rate, steam pressure, machine speed) in a coordinated manner according to pre-calculated trajectories. This multi-parameter adjustment approach enables smooth grade transitions while maintaining sheet quality, preventing undesirable characteristics that would lead to material waste.
3Device complexity
If traditional control systems are used for grade changes, then the system is simpler to implement, but the transition results in unmarketable product and production losses
Solution Approach 1:
The system introduces an intermediary control layer that calculates optimal trajectories for manipulated variables based on desired grade transitions. This intermediary control system acts as a mediator between the operator's grade change request and the actual process adjustments, coordinating multiple process parameters to achieve smooth transitions while maintaining product quality and maximizing effective yield.
Data Source
AI summary
A paper machine includes equipment for processing or producing a product in a continuous manner, such as a paper sheet. A grade change occurs when the equipment transitions from producing or processing a product having a first grade to producing or processing a product having a second grade. To support the grade change, a target for at least one controlled variable and a target for at least one manipulated variable are identified. The at least one manipulated variable and the at least one controlled variable are associated with the production of the product. A trajectory for the at least one manipulated variable and a corresponding trajectory for the at least one controlled variable are identified using the targets. The grade change is implemented using the trajectories so as to transition from production of the product having the first grade to production of the product having the second grade.