(463c) Process Systems Considerations in Forest Biorefineries with Thermochemical Processing of Wood Wastes

Integration of plants that produce syngas-derived fuels and chemicals with chemical pulp mills, the integrated Forest BioRefinery Concept, has the potential of reducing the overall cost of producing both pulp/paper and biomass-derived chemicals/fuel products. The savings are achieved by (a) reducing the capital cost for gasification of black liquor and wood wastes in an integrated biorefinery as compared with separate pulp mills and fuel/chemical plants, and (b) by increasing the yield of power and chemicals or fuels by integration of mass and heat exchange between the two parts of the integrated complex.

Another potential advantage, when black liquor is gasified, is increased pulp yield. During gasification, at least part of the sulfur in black liquor is converted to H₂S instead of Na₂S. The separation of sulfur from sodium before the pulping chemicals are regenerated makes it possible to produce polysulfide or other alternative pulping liquors for higher yield pulping.

Several other factors must be considered in the design of integrated forest biorefineries. One is the need for a carefully designed energy exchange network to minimize entropy generation. Another is the need to minimize the production of NaHCO₃ and the accompanying increase in lime demand for causticizing when regenerating pulping liquors. A third factor is the need and availability of technology for removing contaminants ? especially tar, alkali metals, and halides ? from the synthesis gas produced.