THE AUTONOMOUS MILL: UTILIZING DIGITAL TWINS TO OPTIMIZE THE PULP & PAPER MILL OF THE FUTURE

This paper will describe the Autonomous Mill of the future as a mill that benefits from the use of Digital Twins utilizing a Process Model coupled with a Control Model of the real-time Control System to allow the Autonomous Mill to "run itself" with little or no human intervention. This paper will then give an overview of the unit operations and equipment common to pulp and paper mills and conclude with several examples of specific opportunities where control systems optimization through Advanced Process Control (APC) and Model-Based Predictive Control (MPC) can increase production; reduce costs, and autonomously operate the mill of the future. The pulp and paper mill is often divided into six main "islands" of automation; raw material receiving and preparation (the woodyard), the pulp mill, the powerhouse, the paper mill, converting and finishing, and effluent treatment. Each of these islands presents their own, unique set of unit operations; but, perhaps not surprisingly, you can see similar unit operations in various industries besides pulp and paper. For example, the powerhouse equipment, besides the main difference being that the fuel is "black liquor", the equipment can be found in any other industrial power plant. In the paper machine "island", the use of cascaded variable-speed drives to control the paper sheet tension is also seen in the draw line of a steel, textile, or fiber mill. And, as a final example, the effluent treatment facility of the paper mill has many of the same equipment you will find in a municipal water/wastewater plant. Several examples of specific control systems optimization included for each of these "islands" include chemical savings in the lime kiln and causticizing, pulping, screening and refining, washing, and bleaching processes of the pulp mill; energy savings in recovery boiler sootblowing and the lime kiln, pulp stock preparation including cleaning and refining and the paper pressing and drying sections of the paper mill; and the environmental savings involved in effluent treatment and recycling water.