Simplified Automatic Nonlinear Grade Change Control for Paper Machines, 19PaperCon
The demands of the paper industry on a QCS (quality control system) are to enable the papermakers to produce optimum quality paper at the lowest cost and to maximize production. One method of maximizing production is to minimize production losses. A significant portion of production losses are during grade changes as papermakers try to minimize the duration of the grade change, avoid off specification production and avoid sheet breaks. To address the strict demands on the QCS, the system’s grade change package incorporates modern technologies such as: the ability to predict the whole MV (manipulated variable) and CV (controlled variable) trajectories, a first principles paper machine model to capture the nonlinearity of the grade change and the option to conduct a grade change with supervisory machine direction multivariable MPC (model predictive controls). Employment of these technologies comes with configuration complexity. The challenge is to have a grade change package with these latest technologies and have the papermakers easily configure, understand and use it. A simplified nonlinear multivariable grade change package is discussed in this paper. It incorporates all the technologies discussed above and it is easy to configure, understand and it is used by papermakers worldwide. Several grade changes are analyzed utilizing the simplified automatic grade change package and compared to the previous automatic grade change package at WestRock Paper in Longview, WA.
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