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Energy Analysis of a Kraft Pulp Mill: Potential for Energy Efficiency and Advanced Biomass Cogeneration
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Energy use at a Kraft pulp mill in the United States is analyzed in detail. Annual average process steam and electricity demands in the existing mill are 19.3 MMBtu per ADST and 687 kWh per ADST, respectively. This is relatively high by industry standards. The mill meets nearly all its electricity needs with a back-pressure steam turbine. Higher electricity to heat ratios is an industry wide trend and anticipated at the mill. The potential for self-sufficiency in energy using only black liquor and bark available on-site is assessed based on the analysis of the present energy situation and potential process changes. The analysis here suggests that steam and electricity demand could be reduced by 89% by operating consistently at high production rates. Process modifications and retrofits using commercially proven technologies could reduce steam and electricity demand to as low as 9.7 MMBtu per ADST, a 50% reduction, and 556 kWh per ADST, a 19% reduction, respectively. Electricity demand could increase to about 640 kWh per ADST due to closed-cycle operation of the bleach plant and other efforts to improve environmental performance. The retrofitted energy efficient mill with low environmental impact could be self-sufficient in steam and electricity using conventional technology, such as a back pressure steam turbine or a condensing extraction steam turbine. In addition to meeting mill energy demand, about 1,000 kWh per ADST would be available for export from the mill if gasification/combined cycle technology were used instead.
Subbiah, A.; Nilsson, L. J.; Larson, E. D. (1995). Energy Analysis of a Kraft Pulp Mill: Potential for Energy Efficiency and Advanced Biomass Cogeneration. Energy Systems Laboratory (http://esl.tamu.edu). Available electronically from