Black Liquor Gasification-Based Biorefineries – Determining Factors for Economic Performance and CO2 Emission Balances

Doktorsavhandling, 2011

Biorefineries constitute an attractive future development option for the pulp and paper industry, allowing mills to produce not only pulp or paper but also other value-added products. Black liquor gasification (BLG) is currently being developed as an alternative technology for energy and chemical recovery in kraft pulp and paper mills. The technology enables the mill to increase the internal electricity generation or produce chemicals such as motor fuels. This thesis investigates the influence of different factors, including choice of product, type of mill, alternative investments, opportunities for carbon capture and storage (CCS) and future energy market conditions, on the economic performance and CO2 emission balances for BLG-based biorefinery concepts. Implementation of biorefinery concepts such as BLG with electricity production in future market pulp mills can be achieved without making the mill dependent on external wood fuel. However, implementation in integrated pulp and paper mills requires external wood fuel and reduces the amount of wood fuel available for other applications, thereby increasing the CO2 emissions from those applications. The results show that BLG with motor fuel production could be profitable for both market and integrated mills, whereas BLG with electricity generation is primarily an attractive option for market mills. For mills that operate with conventional recovery boiler technology, potentially profitable biorefinery concepts include lignin extraction or motor fuel production from gasified wood fuel. Few of the biorefinery concepts investigated in this work achieve a significant reduction of CO2 emissions, especially for integrated mills. However, if commercially available, CCS could contribute to significant CO2 emissions reduction and enhanced profitability for future energy market conditions characterized by a high CO2 emissions charge, for both combustion- and gasification-based biorefinery concepts. Steam-saving measures could also significantly improve the economic performance as well as the CO2 emission balances, especially for biorefinery concepts that use external wood fuel. The results also show that even if the recovery boiler has not reached the end of its technical lifetime, it could nevertheless be attractive for mills to consider investment in a smaller BLG plant.