Effect of Mode of Operation on Gas Turbine Combustor Performance

Abstract

The primary goal of this study is to quantify the differences in combustor performance under different modes of operation as a function of the combustor exit temperature. The main focus is the effect on liner heat loading since liner durability is strongly dependent on the metal peak temperature as well as temperature gradients. The study also includes the effect on emissions and acoustics. Three modes of operation are discussed: non premixed natural gas operation, dry liquid fuel operation and wet liquid fuel. Limited, premixed, natural gas data are also discussed when appropriate. Experiments are conducted on a Single Nozzle Rig (SNR) at conditions representative of different power levels of F class gas turbines. The results are analyzed to show the natural gas vs. dry liquid fuel performance, followed by the effect of water injection and effect of load variation. The results show that heat loading impact is amplified in the head end region since this is where the flame stabilizes. The combustor head end average temperature is 55.6 K (100 F) higher for dry fuel oil when compared to natural gas. However, the tail section of the liner is 25.3 K (50 F) lower for fuel oil. The difference is mainly attributed to the change in flame shape and flame radiation. CO emissions were roughly 80 ppm lower for natural gas. NOx is higher for liquid fuel (35–80% depending on flame temperature). Emissions profiles at the combustor exit are similar for both fuels with a variability of 40% indicating [the profile] is controlled by flow-flame interaction. Acoustics are lower in amplitude for non-premixed natural gas, but peak frequency is similar. Liquid fuel wet mode of operation results in significant reduction in the head end temperature due to the water impingement on the liner 166.8 K (∼300F). However, the maximum temperature over the tail section is 25.3 K (50F) higher than dry operation. Yet, the average tail temperature is similar under both modes of operation with higher variability under wet operation (70%). This strong temperature variability can influence the liner life. More than 80% reduction in NOx emissions is achieved with water injection. Water injection impact on CO is dictated by CO generation mode (quenching vs. dissociation). More important is the significant improvement in emissions profile at the combustor exit with water injection (60% reduction in variability). At higher load, the maximum liner temperature is 44.5–83.5 K (80–150 F) higher than part load. This is mainly attributed to the increase in air inlet temperature and increase in radiation heat flux which is dependent on both flame temperature and pressure. More investigations are required to determine the impact on complicated engine configurations as well as to isolate the effect of flame shape.