Gas turbines are widely used in industrial and power generation operations. A typical gas turbine includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (e.g., air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
It is widely known that the thermodynamic efficiency of a gas turbine increases as the operating temperature, namely the combustion gas temperature, increases. However, if the fuel and air are not evenly mixed prior to combustion, localized hot spots may exist in the combustor near the nozzle exits. The localized hot spots increase the chance for flame flash back and flame holding to occur which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher reactivity and wider flammability range. The localized hot spots may also increase the generation of oxides of nitrogen, carbon monoxide, and unburned hydrocarbons, all of which are undesirable exhaust emissions.
A variety of techniques exist to allow higher operating temperatures while minimizing localized hot spots and undesirable emissions. For example, various nozzles have been developed to more uniformly mix higher reactivity fuel with the working fluid prior to combustion. Oftentimes, however, the higher reactivity fuel nozzles include multiple mixing tubes that result in a larger differential pressure across the nozzles. In addition, the higher reactivity fuel nozzles often do not include mixing tubes in the center portion of the nozzles. The absence of tubes from the center portion increases the need for higher differential pressure to meet the required mass flow rate. In addition, the absence of tubes from the center portion may create recirculation zones of combustion gases in the vicinity of the center portion that increase the local temperature of the center portion and adjacent mixing tubes. The increased local temperatures may result in increased maintenance and repair costs associated with the nozzle. As a result, continued improvements in nozzle designs that can support increasingly higher combustion temperatures and higher reactive fuels would be useful.