Abstract

Concern for the environment and a need for more efficient energy generation have sparked a growing interest throughout the world in renewable fuels. In order to reduce emissions that negatively contribute to global warming, especially CO2, enormous efforts are being invested in technologies to reduce our impact on the environment. Biomass is an option that is considered CO2 friendly due to the consumption of CO2 upon growth. Co-firing biomass with coal offers economic advantages because of reduced capital costs as well as other positive impacts, such as NOx and SOx emission reductions. However, due to the large average particle size of biomass, issues arise such as poor flame stability and poor carbon burnout. Larger particles can also result in longer flames and different heat transfer characteristics. Oxygen enrichment is being investigated as a possible solution to mitigate these issues and enable co-firing in existing facilities. An Air Liquide designed burner was used in this work to explore the impact of oxygen enrichment on biomass flame characteristics, emissions, and burnout. Multiple biomass fuels were used (medium hardwood, fine hardwood, and straw) in conjunction with multiple burner configurations and operating conditions. Exhaust ash samples and exhaust NO were collected for various operating conditions and burner configurations. All operating parameters including O2 addition, swirl, and O2 location could be used to reduce LOI but whenever LOI was reduced, NO increased producing an NO-LOI trade-off. Starting with high LOI, various parameters such as O2 addition and increased swirl could be used to reduce LOI with only small increases of NO. As O2 or swirl increased further, small decreases in LOI were obtained only with large increases in NO. This behavior was captured through NO-LOI trade-off curves where a given configuration or operating condition was deemed better when the curve was shifted toward the origin. Global enrichment or O2 addition to the secondary stream and O2 addition to the primary stream produced better trade-off results than center O¬2 injection. Straw produced NO-LOI trade-off curves just as the wood particles but the curve was shifted further from the origin, likely due to the higher nitrogen content of the straw. Flame characterization results showed that small amounts of O2 in the center improved flame attachment and stability while increasing flame temperature and pyrolysis rates.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

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