Implementation of biorefining technologies in Kraft mills: impact assessment and feasibility

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The Kraft process produces wood pulp for the manufacture of high quality printing papers, tissue papers and packaging material. It is an attractive candidate for partial conversion to biorefinery while maintaining the manufacturing of its traditional core products. The premise of the forest biorefinery is that some of the organic constituents of the wood which are by-products of the chemical pulping step dissolved in the spent liquor may be used for greater advantage than being burnt on-site to recover their beating value as is currently done; they could be used as feedstock for the manufacture of a broad variety of products which have a significant market value. However, the conversion of a Kraft mill to a biorefinery will profoundly modify its capacity for sustainable energy production. This project proposes to develop a methodology and criteria to evaluate the techno-economic feasibility of biorefinery options for Canadian Kraft mills. Starting from the base-case of highly integrated and energy efficient Kraft mills, we will apply state-of-the-art simulation techniques and systems engineering tools to examine the effects of key biorefinery technologies on the energy balance and operating cost of the process. They are, lignin precipitation, hemicelluloses extraction and biomass gasification. A new methodology for advanced energy efficiency analysis will be developed and applied to the study. It will take into account the factors that affect energy consumption individually and in conjunction: internal energy recovery, use of steam injection and mixing, water systems closure, heat and power production and the incorporation of energy upgrading technologies (co- and tri-generation, absorption heat pumps). Economic viability will be assessed by a new thermo-economic analysis method. The impacts of biorefining technologies on the process air emissions will be determined. The major outcome of this project will be guidelines that can be applied to examine the feasibility of proposed biorefinery concepts, guide investments in these technologies and help develop research strategies that address technical impediments. Models of biorefinery unit operations and a unique process simulation software for pulp mill-based biorefineries will be produced and validated.