Evaluation of Excess Heat Driven Carbon Capture Integrated at a Swedish Pulp Mill

Sammanfattning: As the atmospheric carbon dioxide keeps increasing, bioenergy with carbon capture and storage (BECCS) is getting increased attention as a measure to reduce the emissions of carbon dioxide. It is especially interesting in Sweden where the extensive paper and pulp industry constitutes point sources of biogenic carbon dioxide. As carbon capture requires energy, it is important to investigate the opportunity to use excess heat to cover the energy demand in order to avoid causing new emission which would counteract the purpose of implementing BECCS. In this thesis, integration of excess heat driven carbon capture was investigated on two flue gas streams at the Södra Cell Värö pulp mill in Sweden: the recovery boiler and lime kiln flue gases. Three different carbon capture technologies were investigated, which included the commercially available aqueous MEA (monoethanolamine) and HPC (hot potassium carbonate) as well as the novel technology of AMP (2-amino-2-methyl-1-propanol) in DMSO (dimethyl sulfoxide). Their energy demands were calculated through mass and energy balances. A mapping of sources of excess heat at the mill was also executed. The results showed that the lime kiln flue gases would be more reasonable to treat due to the smaller flue gas stream with a higher CO2 concentration. Partial carbon capture of the recovery boiler flue gases could also be an option worth considering. For the lime kiln flue gases, two components of the mill, the condensing turbine and the surface condenser, proved to be sources of excess heat that could cover the heat demand at the cost of some electrical power. The condensing turbine was more promising as it could cover the heat demand regardless of which technology is used while the surface condenser could only be used on the AMP in DMSO technology. In addition, a heat pump is required to make use of the heat from the surface condenser, making the electrical power demand higher for the surface condenser than for the condensing turbine. The MEA and AMP in DMSO technologies required much less energy supply than the HPC technology did but have higher cooling demands. Further studies are needed which include more detailed process designs, management of the captured CO2, and evaluations of economical feasibility. This thesis gives a good indication on what to focus on going forward.