Operation of Reheat Combustors With Secondary Air Flow (SAF) Control Valves

Abstract

GT26 reheat gas turbines have been continuously developed and upgraded to improve the engine performance and operational flexibility. In a standard SAF flow orifices configuration typically sized for the design point, the supply pressure ratios of secondary air flow systems for base-load operation vary over ambient temperatures. The adjustable secondary air flow control valves make the active control of the cooling air supply pressure ratios possible and could provide a customized cooling air consumption and adjust engine operation conditions. This control valve concept has been comprehensively tested and validated in Alstom test power plant and operated in customer engines. This paper focuses mainly on combustor cooling improvement with this secondary air flow control valves. G26 reheat combustors with the adjustable secondary air flow control valves have improved significantly sequential combustor cooling and combustor performance. The supply pressure ratios of secondary air flow system over wide part load range which are originally lower and critical with a standard orifice configuration have been raised and results in more cooling air flows to the combustor cooling system than original standard orifice configuration. This increased cooling air flow improves SEV combustor liner and SEV burner cooling over large range of part load operation. The metal temperatures of the SEV liners and SEV burners are reduced significantly over part load, while the highest metal temperatures are recorded over part load operation with previously installed standard orifices configuration. In addition, the supply pressure ratios in secondary air flow systems with fixed throttling element are lower during oil operation than the corresponding ratios for fuel gas operation. The cooling supply pressure ratios in cooling systems with SAF control valves are optimized to supply the required combustor cooling air flow for oil operation. The optimized cooling can also be achieved through adjustment of SAF control valves for high-fogging (HF) engines between dry operation and wet operation. In addition, pulsation reduction at oil operation can be achieved by fully opening of MBH30 control valve.