Abstract: Thermomechanical pulp is an important process for producing fibrous mass used in papermaking. A two-level control strategy that stabilizes and optimizes the refining process has been developed. The Stabilization layer consists of a multivariable model predicative range controller that regulates the refiner line operations. The Quality Optimization layer provides the pulp quality control as measured by an online pulp quality (freeness, fibre length) sensor. This control startegy leverages the natural decoupling in the process. The modular design technique is able to handle multiple refiner lines that empty into a common latency chest. A global optimizer is also used to integrate and coordinate the two layers for enhanced constraint handling.