Impact of the Integrated Pulp Mill/Biorefinery on the Chemical Recovery Cycle, 2008 Engineering, Pulping and Environmental Conference

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Integrated pre-extraction of hemi-cellulose in pulp mills will impact both the loading on the chemical recovery cycle and the black liquor chemistry. This paper uses the modeling results from the excel spreadsheet model BioRefinOPT^TM to estimate the impacts on the chemical recovery cycle. This work is meant to compliment the pulping work and economic assessments being done for hemi-cellulose pre-extraction. For this study, pulp production was kept constant. Because pre-extracted chips are delignified more rapidly, it is possible to use lower EA:wood charges. For this paper we considered an EA:wood charge of 16% as the base case and modeled also 14% and 13%. Evaporation load will increase due to the saturation of the wood after pre-extraction and also due to cellulose decomposition. The black liquor chemistry will also change slightly, affecting the solubility limits of inorganic salts, viscosity, boiling point rise and heating value which will additionally impact both the evaporators and recovery boiler. The load on recausticizing will increase for an EA:wood charge of 16% because of the decreased yield due to cellulose decomposition and hemicellulose pre-extraction. However, reducing the EA:wood charge will reduce the load on recausticizing to below the level used for pulping wood chips at an EA:wood charge of 16 %.