Holmen Details Thermo-Mechanical Pulping Process for Paper Production

Holmen, a Swedish forest industry company, has provided a detailed explanation of its Thermo-Mechanical Pulping (TMP) process used in paper manufacturing. The company highlights the method's efficiency in material utilization and energy recovery.

The TMP process is characterized by a high yield of approximately 97%, meaning almost all input wood chips become usable paper fibers. While the process requires substantial electrical energy for fiber separation, the majority of this energy is captured as heat. This recovered thermal energy is then reused multiple times for preheating wood chips, drying paper on the paper machine, and heating ambient air in production facilities and offices.

Paper production begins with pulpwood logs sourced from sustainable forests, typically within a 150 km radius of Holmen's mills. This proximity reduces transport distances and associated fuel emissions. The logs are debarked, with the bark utilized as biofuel. Cleaned logs are then chipped into approximately 22 mm pieces, screened, and stored before the pulping stage.

In the TMP process, wood chips undergo washing and steaming to soften the lignin that binds wood fibers. They are then fed into a TMP refiner. This refiner uses two rotating, grooved metal plates that shred the chips into long, straight fibers. The objective is to produce fibers that allow for the creation of paper with high bulk, strength, and brightness properties.