Pollutant Emissions and Lean Blowoff Limits of Fuel Flexible Burners Operating on Gaseous Renewable and Fossil Fuels
This study provides an experimental and numerical examination of pollutant emissions and stability of gaseous fueled reactions stabilized with two premixed-fuel-flexible and ultra-low NOx burner technologies. Both burners feature lean combustion technology to control the formation of nitrogen oxides (NOx). The first fuel–flexible burner is the low-swirl burner (LSB), which features aerodynamic stabilization of the reactions with a divergent flow-field; the second burner is the surface stabilized combustion burner (SSCB), which features the stabilization of the reactions on surface patterns.
For combustion applications the most commonly studied species are: NOx, carbon monoxide (CO), and unburned hydrocarbons (UHC). However these are not the only pollutants emitted when burning fossil fuels; other species such as nitrous oxide (N2O), ammonia (NH3) and formaldehyde (CH2O) can be directly emitted from the oxidation reactions. Yet the conditions that favor the emission of these pollutants are not completely understood and require further insight.
The results of this dissertation close the gap existing regarding the relations between emission of pollutants species and stability when burning variable gaseous fuels. The results of this study are applicable to current issues such as:
1. Current combustion systems operating at low temperatures to control formation of NOx.
2. Increased use of alternative fuels such as hydrogen, synthetic gas and biogas.
3. Increasing recognition of the need/desire to operate combustion systems in a transient manner to follow load and to offset the intermittency of renewable power.
4. The recent advances in measurement methods allow us to quantify other pollutants, such as N2O, NH3 and CH2O.
Hence in this study, these pollutant species are assessed when burning natural gas (NG) and its binary mixtures with other gaseous fuels such as hydrogen (H2), carbon dioxide (CO2), ethane (C2H6) and propane (C3H8) at variable operation modes including: ignition; lean blowoff; and variable air to fuel ratio. Some remarkable results of this dissertation include:
• At a fixed fire rate (117kW) the addition of hydrogen to NG raises the emission of NOx for the reactions stabilized with the LSB. Under the same conditions, the addition of H2 to NG will reduce the emission levels of the reactions stabilized with the SSCB.
• It was found experimentally that nitrous oxide (N2O) is emitted during ignition and blowoff events.
• Ammonia (NH3) is also emitted during ignition and blowoff events.
• It was found experimentally that at high concentrations of hydrogen in NG (H2>70%), reactions aerodynamically stabilized with the LSB will emit significant amounts of N2O.