Assessment of a Rich-Burn, Quick-Mix, Lean-Burn–Based Supplemental Burner System in a Vitiated Air Stream

ABSTRACT

In an effort to increase overall efficiency of distributed power generation systems, strategies to optimize the combination of cooling or heating with power (CCHP) are desired. One significant issue in implementing a CCHP system is that electrical loads and heating/cooling loads are rarely synchronized. Duct burners are frequently used in large systems to provide additional heat when the waste heat available from the prime mover does not meet the needs of the heat recovery device. Duct burners must operate on vitiated oxidizer streams, which can result in poor stability, elevated emissions, or both. Rich-burn, quick-mix, lean-burn (RQL) style combustors have been shown to provide low emission and high stability in lean burn gas turbine applications, but have not been considered for duct burner applications. To this point, the current work carries out an experimental investigation to assess the merits of using an RQL style combustor in a duct burner application. A systematic evaluation of several RQL burner configurations revealed that a lean-zone-to-rich-zone air mass ratio of 2.5 produced the lowest emissions of NOx and CO at a fixed fuel-to-air ratio. However, this reduction in emissions was accompanied with a decrease in the stability range of the burner. Furthermore, decreasing the amount of swirl in the rich zone was found to decrease NOx emissions. It was observed that oxygen concentration of the oxidizer had a more significant effect on the emission of CO than any configuration of the burner.

KEYWORDS:

• CO
• Combination of cooling or heating with power (CCHP)
• NOx
• Rich-burn, quick-mix, lean-burn (RQL)
• Vitiated combustion

Notes

¹ Swirl number is defined as the ratio of the angular momentum to the axial momentum of the flow. Swirl number was calculated as: . D_Hub and D_SW are the swirler outer and inner diameter, and θ is the swirl vane angle.

Additional information

Funding

The authors gratefully acknowledge the California Energy Commission for financial assistance under contract PIR-09-015 (Rizaldo Aldas, program manager).