How a pulp mill can transform waste and emissions into new products
By adding new process steps, a pulp mill can utilize both waste products and carbon dioxide emissions and transform them into new products. Researchers are now investigating what such a biorefinery could look like and how it affects the energy balance of the factory.
Currently, the majority of lignin from pulp production is used as fuel. This energy powers the factory, but it also generates flue gases containing carbon dioxide. In the study conducted under Mistra Digital Forest, a process chain is simulated that can reduce emissions from pulp mills by utilizing a significant amount of the lignin that is currently used for energy and capturing the carbon dioxide that the factory would otherwise release into the atmosphere.
– We are seeking solutions that can enable the pulp mill to achieve net-zero emissions while simultaneously utilizing the captured carbon dioxide in new biorefinery concepts, says Tomas Rydberg, Senior Researcher at IVL and also involved in the study.
– The study also aims to push the boundary of how much lignin can be extracted by simulating the impact on the energy balance of the mill when a larger amount of lignin, around 50%, is extracted compared to more common levels of 10-20%. The reduced availability of process energy due to a decreased amount of lignin for combustion needs to be compensated for in other ways.
"We strongly believe in this as a viable alternative for the climate and the wallet."
To capture the carbon dioxide present in the flue gases, various solutions are being studied. One of them involves utilizing the chemicals used to extract lignin from wood, which are also effective in absorbing carbon dioxide. These solutions are combined with replacing the recovery boiler, the final process step for chemical recovery, with an electric furnace that processes the carbon dioxide. The result is pure carbon dioxide that can be used, for example, to produce bio-derived electrofuels or other raw materials for the chemical industry.
– Now that we have a model in place, our ongoing work aims to further understand how the energy supply of the mill is impacted by this biorefinery configuration. We strongly believe in this as a viable alternative for the climate and the economy, says Tomas.