Finding a use for the lignin other than a boiler fuel

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Finding a use for the lignin other than a boiler fuel would enhance the economics of this process. Converting the lignin to a higher-value co-product like a fuel or chemical is envisioned. To be beneficial, the value of the lignin-derived co-product must be enough to cover the costs of the upgrade process and still supply revenue to the plant to offset the ethanol production costs. VI.2.6 Carbon Dioxide As in the starch process, the fermentation of lignocellulose into ethanol generates CO 2 . NREL has yet to investigate the possible market value of carbon dioxide from a robust lignocellulose-to-ethanol industry, so it is not included as a co-product. VI.2.7 Capital Costs The capital costs are listed by process area in Table 7. The complexity of the process is evident from the projected $136MM total capital investment. The boiler/turbogenerator area is the most expensive, followed by the pretreatment and conditioning area, and enzyme production area. Alternate process designs using a natural gas-fired boiler, which is cheaper, lowers the capital cost but incurs substantial landfill costs for the lignin residue as well as for the cost of the boiler fuel. Research to better understand the pretreatment process is aimed at reducing the reactor cost and eliminating the need for conditioning the hydrolyzate. The feedstock handling area costed here is preliminary for stover. A design for stover handling is being developed with an engineering firm. The
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22 equipment and labor costs may change from the estimate presented here. The total plant installed cost was developed in the same way as the starch process. Table 7. Capital Costs by Process Area (1999$) Feedstock Handling $5,400,000 Pretreatment/Detoxification $29,800,000 Simultaneous Saccharification/Co-fermentation $14,400,000 Cellulase Production $18,100,000 Distillation $5,100,000 Solid/Syrup Separation $9,200,000 Wastewater Treatment $9,000,000 Storage $2,100,000 Boiler/Turbogenerator $37,500,000 Utilities $5,500,000 Total Capital Investment $136,100,000 It should be noted that utilities such as steam, chilled water, and cooling tower water are treated as equipment in this cost model, contributing to the capital cost of the plant rather than the variable operating cost as in the starch model. When the two processes are combined in a co-location scenario, this equipment will provide service to both processes. For now, converting the capital costs for these utilities in the lignocellulose model to dollars per pound of service allows for a direct comparison. Table 8 shows the lignocellulose utilities as dollars per pound of steam and cooling medium for comparison with the starch model. A comparison of the two steam costs shows that for the starch process, the cost is a combination of natural gas fuel and a gas-fired boiler. The FBC, which is used in the lignocellulose process to burn the lignin residue, has higher capital, but no cost is assumed for the lignin, because it is a byproduct of the process that must be disposed of in some way. The cooling water capital costs were from different sources and will be evaluated more closely in the co-location scenario.
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