Dry Low NOx (DLN) Combustion System Operability Considerations

Abstract Modern gas turbines employ dry low NOx (DLN) combustion systems to reduce air pollution and meet stringent environmental regulations. Gas turbine DLN combustion systems operate in lean premix mode near the extinction limit. In this region, the quantity of fuel in the air/fuel mix at the burner is barely sufficient to sustain combustion at low flame temperatures. Safe and reliable operation of modern combustors near the flame extinction limit requires a number of vital elements: 1) an in-depth understanding of mechanisms that promote combustion stability at these extremely low fuel equivalence ratios, 2) precise manufacturing and repair of key combustion components with narrow design tolerances, 3) a reliable monitoring system to detect onset of instabilities in individual combustors, and, 4) protective measures that can implement corrective actions such as changes in fuel splits. Given these elements, operators often need to act proactively in preventing onset of excessive pressure oscillations and combustion-induced vibrations and flame instabilities. The purpose of this paper is to educate plant engineers on gas turbine combustion systems for operational flexibility of modern gas turbine low-NOx combustion systems. The paper will describe technologies for monitoring, control, and methods for adjusting and optimizing system performance on natural gas fuels. This paper is directed at plant engineers. It presents several applications, with supporting data and photographs, to help this audience understand the core working principles of modern DLN combustion systems.