Benefits of Implementing Advance Process Control Technology Using MACS in Pulp & Paper Making Processes

<p>An optimum process control requires manipulation of multiple MV’s （manipulated variables）, FF’s （Feed Forward variables） and constraints matrix to achieve multiple CV （control variables） to remain in desired operating limits. It is extremely challenging to optimize each of the controlled variables to maintain the process close to required quality targets. While it is of utmost importance to have the field instruments, sensors and regulatory controls functioning accurately it is practically impossible for operators to manually optimize the process. For example, in a bleach plant, it is challenging to achieve final pulp brightness at minimal cost continuously using regulatory controls due to the complex multivariant nature of the process and the lengthy time delays introduced by dead times from Bleach towers. To overcome this challenge, Multivariable Advanced Control System （MACS）, a proven advanced nonlinear control platform, has successfully been implemented resulting in large savings to mills. MACS uses dynamic process models to account for the effect of process disturbances on downstream pulp or paper properties and manipulates the chemical charges for instance to compensate for these disturbances. MACS corrects for unmeasured disturbances via feedback control, and accounts for varying process delays and non-linear process response curves via real time model adaptation.</p><p>Utilizing a model predictive control solution coupled with an optimizer allows for optimization of the individual unit operations as well as a coordinated optimization between different departments. This is especially critical when considering the changing objectives from a facility which can range from production maximization requiring the minimization of bottlenecks to an objective of minimizing overall production costs. In most facilities there will be a balance between these two objectives that will continuously be changing based on the current market demands and operational costs.</p><p>We are now seeing the adaptation of these solutions by the P&P industry as single unit optimizations as well as entire process optimizations. MACS can be implemented in all unit operations from wood handling through to paper finishing as well as the utility areas.</p><p>This paper highlights some industrial case studies of implementing MACS solution to key unit operations in a Kraft process―Digester, Bleach Plant, Evaporators, Recovery Boiler, Recaust and Lime Kiln. The objective and the control strategies could be different for different unit operations, but the basic concept of developing mathematical correlations between MV’s, CV’s, FF’s and constraints are developed to predict the future behavior of the process. MACS Models provide new process setpoints to remain within target process conditions. MACS can manage 100’s of variables at the same time respecting all the operating targets while maintaining the process at the lowest cost point.</p>