Abstract

Increasing concern for energy sustainability has created motivation for the combustion of renewable, CO2 neutral fuels. Biomass co-firing with coal provides a means of utilizing the scaled efficiencies of coal with the lower supply availability of biomass. One of the challenges of co-firing is the burnout of biomass particles which are typically larger than coal but must be oxidized in the same residence time. Larger biomass particles also can increase the length of the radiative region and alter heat flux profiles. As a result, oxygen injection is being investigated as a means of improving biomass combustion performance.An Air Liquide designed burner was used to investigate the impact of oxygen enrichment on biomass combustion using two size distributions of ground wood pellets (fine grind 220 µm and medium grind 500 µm mass mean diameter). Flame images were obtained with a calibrated RGB digital camera allowing a calculation of visible radiative heat flux. Ash samples and exhaust NO were collected for a matrix of operating conditions with varying injection strategies. The results showed that oxygen can be both beneficial and detrimental to the flame length depending on the momentum of the oxygen jet. Oxygen injection was found to improve carbon burnout, particularly in the larger wood particles. Low flow rates of oxygen enrichment (2 to 6 kg/hr) also produced a modest increase in NO formation up to 30%. The results showed medium grind ~500 µm mass mean diameter particle combustion could improve LOI from 30% to 15% with an oxygen flow rate of 8 kg/hr. Flame images showed low flow rates of O2 (2 kg/hr) in the center of the burner with the fine particles produced a dual flame, one flame surrounding the center oxygen jet and a second flame between the volatiles and secondary air. The flame surrounding the center oxygen jet produced a very high intensity and temperature (2100 K). This center flame can be used to help stabilize the flame, increase devolatilization rates, and potentially improve the trade-off between NO and burnout.

Degree

MS

College and Department

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

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2013-12-01

Document Type

Thesis

Handle

http://hdl.lib.byu.edu//1877/etd7469

Keywords

biomass combustion, hardwood biomass, oxygen injection, oxygen enriched, neat oxygen combustion, NO, burnout, flame intensity, flame emissive power, flame temperature, cofire

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