Robust estimation of Base Sheet Ash during a Wet End Break, scanner warm up and initialization

During a Wet End break, the loss of paper feed through the paper machine causes the two main scanners to go offline and the remaining parts of the process are operated in open-loop. This causes the stock composition in the Headbox to deviate substantially from the nominal specifications, causing paper quality (after start up) and paper machine runability issues. In this work, the Base Sheet Ash measurement of the scanner is estimated using a Least Absolute Value (LAV) model which can then be used for control of the chalk valve during the breaks to keep the Headbox Ash within specified limits. The model is developed around key Wet End variables which have been identified using PCA and sensitivity analysis. Modeling is performed on plantwide data obtained from actual running of a paper machine in the UK.