Effect of Syngas Composition and CO₂-Diluted Oxygen on Performance of a Premixed Swirl-Stabilized Combustor

Abstract

Future energy systems based on gasification of coal or biomass for co-production of electrical power and fuels may require gas turbine operation on unusual gaseous fuel mixtures. In addition, global climate change concerns may dictate the generation of a CO₂ product stream for end-use or sequestration, with potential impacts on the oxidizer used in the gas turbine. In this study the operation at atmospheric pressure of a small, optically accessible swirl-stabilized premixed combustor, burning fuels ranging from pure methane to conventional and H₂-rich and H₂-lean syngas mixtures is investigated. Both air and CO₂-diluted oxygen are used as oxidizers. CO and NO_x emissions for these flames have been determined from the lean blowout limit to slightly rich conditions (ϕ ∼ 1.03). In practice, CO₂-diluted oxygen systems will likely be operated close to stoichiometric conditions to minimize oxygen consumption while achieving acceptable NO_x performance. The presence of hydrogen in the syngas fuel mixtures results in more compact, higher temperature flames, resulting in increased flame stability and higher NO_x emissions. Consistent with previous experience, the stoichiometry of lean blowout decreases with increasing H₂ content in the syngas. Similarly, the lean stoichiometry at which CO emissions become significant decreases with increasing H₂ content. For the mixtures investigated, CO emissions near the stoichiometric point do not become significant until ϕ > 0.95. At this stoichiometric limit, CO emissions rise more rapidly for combustion in O₂–CO₂ mixtures than for combustion in air.

Keywords:

• Carbon dioxide
• Carbon monoxide
• NO_x
• Premixed combustion
• Swirl
• Syngas

Acknowledgments

This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences Division and by a Laboratory Directed Research and Development project at Sandia National Labs. Sandia is operated by the Sandia Corporation, a Lockheed Martin Company under contract DE-AC04-94-AL85000.

Notes

*Units of mega-joules per normal cubic meter, with normal conditions defined to be 1 atm pressure and 298 K.

*Calculated using the NASA-Glenn Chemical Equilibrium Program (NASA, 2006).