Gas turbine fouling: A comparison among one hundred heavy-duty frames

Over recent decades, the variability and high costs of thetraditional gas turbine fuels (e.g. natural gas), have pushedoperators to consider low-grade fuels for running heavy-dutyframes. Synfuels, obtained from coal, petroleum or biomassgasification, could represent valid alternatives in this sense.Although these alternatives match the reduction of costs and, inthe case of biomass sources, would potentially provide a CO2emission benefit (reduction of the CO2capture andsequestration costs), these low-grade fuels have a highercontent of contaminants. Synfuels are filtered before thecombustor stage, but the contaminants are not removedcompletely. This fact leads to a considerable amount ofdeposition on the nozzle vanes due to the high temperaturevalue. In addition to this, the continuous demand for increasinggas turbine efficiency, determines a higher combustor outlettemperature. Current advanced gas turbine engines operate at aturbine inlet temperature of (1400-1500) °C which is highenough to melt a high proportion of the contaminantsintroduced by low-grade fuels. Particle deposition can increasesurface roughness, modify the airfoil shape and clog the coolantpassages. At the same time, land based power units experiencecompressor fouling, due to the air contaminants able to passthrough the filtration barriers. Hot sections and compressorfouling work together to determine performance degradation.This paper proposes an analysis of the contaminantdeposition on hot gas turbine sections based on machinenameplate data. Hot section and compressor fouling areestimated using a fouling susceptibility criterion. Thecombination of gas turbine net power, efficiency and turbineinlet temperature (TIT) with different types of synfuelcontaminants highlights how each gas turbine is subjected toparticle deposition. The simulation of particle deposition on onehundred (100) gas turbines ranging from 1.2 MW to 420 MWwas conducted following the fouling susceptibility criterion.Using a simplified particle deposition calculation based on TITand contaminant viscosity estimation, the analysis shows howthe correlation between type of contaminant and gas turbineperformance plays a key role.The results allow the choice of the best heavy-duty frame asa function of the fuel. Low-efficiency frames (characterized bylower values of TIT) show the best compromise in order toreduce the effects of particle deposition in the presence of hightemperature melting contaminants. A high-efficiency frame issuitable when the contaminants are characterized by a lowmelting point thanks to their lower fuel consumption.