CO2 emission balances for different black liquor gasification biorefinery concepts for production of electricity or second generation liquid biofuels

Paper i proceeding, 2008

Black liquor gasification (BLG) is currently being developed as an alternative technology for energy and chemical recovery at chemical pulp mills. In the gasification process the black liquor is converted to a syngas, which can be used for e.g. production of renewable motor fuels or electricity generation. This study examines how different assumptions regarding systems surrounding the pulpmill, for example the electricity generation system, affect the CO2 emission balances for different BLG concepts. Different final products are considered, including DME, methanol, FT-diesel and electricity. Both a market pulp mill and an integrated pulp and paper mill are considered as host mill for the BLG plant to investigate how the mill influences the CO2 balances. Furthermore, the consequences of limited availability of biomass are shown, i.e. biomass is not necessarily considered as CO2-neutral. The results show that the potential to reduce CO2 emissions by introducing BLG is generally much higher for a market pulp mill than for an integrated pulp and paper mill. Electricity generation from the syngas is favoured when assuming high grid electricity CO2 emissions where as motor fuel production is favoured when assuming low grid electricity CO2 emissions. When considering the consequences of limited availability of biomass, the CO2 emission balances are strongly affected, in some cases changing the results from a decrease to an increase of the CO2 emissions.