Compared to combustion in a recovery boiler, gasification of black liquor with downstream synthesis to biofuels in Kraft pulp mills shows ad­vantages regarding energy efficiency and economic performance. The good performance is partly due to the strong catalytic effect of the black liquor that enhances gasification reactions. Experimental research has shown that the reactivity can be kept even if the black liquor is significantly diluted with a secondary feedstock. Therefore, as a way to increase the operation flexibility as well as the biofuel production capacity of a mill integrated gasifier, a secondary biomass feedstock could be blended into the black liquor and co-gasified.

In a newly finished project within the Swedish Energy Agency and f3 collaborative research program Renewable transportation fuels and systems, the main aim has been to evaluate the techno-economic and greenhouse gas (GHG) per­formances of co-gasification of black liquor with various blends of pyrolysis liquid, crude glycerol and fermentation residues for production of biomethanol of two different qualities, grade AA and crude. Material and energy balances to evaluate the systems’ techno-economic and greenhouse gas performances were obtained via process modelling, with input data mainly from pilot and lab-scale experiments.

The general conclusions were that blending a secondary feedstock with black liquor for co-gasification was an energy efficient and cost effective pathway to convert the feedstock to metha­nol. The produced methanol, in all considered cases, fulfilled the currently required 60 % GHG emissions reduction target as compared to a fossil fuel reference according to RED.

The project has been lead by Joakim Lundgren, Bio4Energy (Luleå University of Technology), with participants from Bio4Energy, Lund University and Perstorp Bioproducts AB. Read more on the project site: Methanol production via black liquor gasification with expanded raw material base.

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