On-line combustion monitoring on dry low NOxindustrial gas turbines

Abstract

To reduce the NOxemissions levels produced by industrial gas turbines most manufacturers haveadopted a lean premixed approach to combustion. Such combustion systems aresusceptible to combustion-driven oscillations, and much of the installed moderngas turbines continue to suffer from reduced reliability due to instability-relatedproblems.The market conditions which now exist under the New ElectricityTrading Arrangements provide a strong driver for power producers to improve thereliability and availability of their generating units. With respect to low-emissiongas turbines, such improvements can best be achieved through a combination ofsophisticated monitoring, combustion optimization and, where appropriate,plant modifications to reduce component failure rates. On-line combustionmonitoring (OLCM) provides a vital contribution to each of these byproviding the operator with increased confidence in the health of thecombustion system and also by warning of the onset of combustion componentdeterioration which could cause significant downstream damage.The OLCMsystems installed on Powergen’s combined cycle gas turbine plant utilizehigh-temperature dynamic pressure transducers mounted close to thecombustor to enable measurement of the fluctuating pressures experiencedwithin the combustion system. Following overhaul, a reference data set isdetermined over a range of operating conditions. Real-time averaged frequencyspectra are then compared to the reference data set to enable identificationof abnormalities. Variations in the signal may occur due to changes inambient conditions, fuel composition, operating conditions, and the onset ofcomponent damage. The systems on Powergen’s plant have been usedsuccessfully to detect each of the above, examples of which are presented here.