Sunday, May 3, 2009
3-30
Ammonia recovery in AFEX biomass pretreatment systems
Ammonia Fiber Expansion (AFEX) is an effective and promising pretreatment process for the conversion of cellulosic biomass to ethanol and other useful products. In the AFEX process, ammonia is allowed to contact moist biomass and then absorb into biomass fibers at a moderately elevated temperature and pressure. After contacting for an adequate time period, pressure is released, and ammonia is partially removed as flashed vapor. It is envisioned that in commercial AFEX plants, the ammonia should be recovered and re-used to reduce material costs. Energy and capital costs for ammonia recovery should also be minimized, as they will contribute to overall operating and capital costs of commercial AFEX plants. In this study, we investigate the energy requirements and vaporization rates for recovery of ammonia remaining in the pretreated biomass after the initial flash. Vaporization rates of ammonia from selected biomass feedstocks are measured and used in a proposed model of an ammonia recovery operation for a commercial AFEX plant. The calculated heat and mass transfer coefficients for ammonia in moist biomass will be presented. Different approaches for minimizing ammonia recovery costs will also be discussed.
Web Page: www.mbi.org
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