A new study shows that paper mills in the United States can significantly reduce their emissions through three interrelated pathways: electrification of steam and process heat, more efficient dewatering before drying, and replacing natural gas with biogenic waste streams. According to the authors, net zero becomes a reality once the power mix becomes cleaner and mills better coordinate their processes.
Researchers at North Carolina State University modeled entire factories instead of a single production line. They compared four common configurations: factories using fresh fibers and factories using recycled fibers, each in an integrated and non-integrated version. This allows for a more realistic mapping of energy flows and emission sources, including their interdependencies. The Journal of Cleaner Production published the article in August.
The largest reduction comes from electrically powered boilers. Switching from gas to electric boilers can reduce emissions by up to 61 percent. In scenarios with a more sustainable electricity mix, factories move towards net zero. The researchers emphasize that the effect is related to the origin of the electricity. A greener grid increases the benefits of electrification.
Biomass as a link in the energy system
In integrated factories, biogenic residual flows already account for the majority of their own energy needs, often between 80 and 90 percent. Additional replacement of fossil fuels with waste wood or other biogenic flows reduces emissions by 24 to 48 percent, depending on the factory configuration and the extent of replacement. This doesn't always achieve the same reduction as full electrification, but it does increase energy security and reduce reliance on gas.
Drying is the most energy-intensive process step. Removing more water from the paper web before thermal drying immediately saves energy. The rule of thumb from the study, each percentage point of additional water removal before the drying cylinders, results in approximately three percent overall energy efficiency. This can, however, affect the factory's balance, as reduced steam production also means less on-site generation via turbines.
An integrated fresh fiber mill has a relatively high direct emissions rate, including through boilers and the lime kiln. A non-integrated tissue mill, on the other hand, relies more heavily on purchased electricity. These differences determine which measure yields the most. The study calculates the impact of electrification, more efficient dewatering, and fuel switching on emissions and the mill's energy balance for each configuration.
The pulp and paper sector consumes approximately six percent of industrial energy in the United States. Practical roadmaps that combine processes and energy sources are therefore relevant, even outside the US. European factories are pursuing similar measures, focusing on less gas, increased electrification, and improved drying. The bottom line remains: the cleaner the grid and the better the process coordination, the faster the decline in emissions.
Source:
Study, Advancing sustainability in the US pulp and paper industry, Decarbonization through energy efficiency, electrification, low carbon fuels, and the social cost of emissions. Journal of Cleaner Production.
