Control of the washing zone in a continuous digester

Multivariable temperature and alkali control in the washing zone of a continuous digester is considered. A linear model is identified from a nonlinear digester model, which is obtained by applying the method of orthogonal collocation to a model in terms of partial differential equations. The linear model is used for control design employing the Smith predictor in combination with an H/sub /spl infin// robust stabilization procedure. Simulations using both the nominal and perturbed nonlinear models in combination with both a full and a reduced order controller are performed. Simulation studies show that the proposed control design approach is useful and may prove effective in digester control.<>