Biomass Gasification-Based Biorefineries in Pulp and Paper Mills – Greenhouse Gas Emission Implications and Economic Performance
Sammanfattning: The pulp and paper industry has a great opportunity to take advantage of the experience about forestry and wood handling for production of renewable fuels, chemicals and materials. Residues from forestry, i.e., tops, branches and stubs, have great potential to become a raw material that can replace crude oil or natural gas in many applications. By constructing a gasification-based production facility close to a pulp and paper mill, heat from the gasification process can be utilised in the mill, which replaces fuel for the boiler. The overall aim of this thesis has been to demonstrate how the pulp and paper industry can help cut global greenhouse gas (GHG) emissions and increase revenues by efficient use of biomass via gasification. In this thesis, the impact of different end products and biomass pretreatment measures connected to integrated gasification processes were evaluated regarding efficiency, GHG emissions and economic performance. The selection of end product from a gasification-based process (methanol, Fischer-Tropsch crude, synthetic natural gas or electricity, in this thesis) was demonstrated to significantly influence the required biomass input, if the sizing constraint was to replace heat production in the bark boiler. The size varied between approximately 200 MWbiomass and 600 MWbiomass. The selection of dryer type was shown to significantly impact the economic performance of a process despite its relatively low capital cost in relation to the total capital cost of 100 to 140 million Euros. With the preconditions in this study, thermal pretreatment (torrefaction or pyrolysis) of biomass may be beneficial with biomass-to-biofuel efficiencies reaching 68%. Assumptions regarding the electricity production sector influence whether an integrated gasification process is better than a stand-alone unit and whether onsite co-generation of electricity should be prioritised in favour of increased yield of biofuels. Sequestration of separated CO2 has been shown to improve the climatic performance of a system and increase its competitiveness against, e.g., co-firing biomass in a coal power plant, by increasing the potential from approximately 300 kgCO2,eq./MWhbiomass to 700 kgCO2,eq./MWhbiomass. Global GHG emission consequences are greatly affected by the assumed electricity production sector and selected end product.
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