90 MAKALE / ARTICLE Cooling The inlet Air Another approach for higher efficiencies is inlet air cooling. The market for cooling technology has grown rapidly i n recent years. The besi applications are found in areas with a dry and hol cli mate. inlet air cooling is actually a technology for power augmentation but with it follows an i mprovement in efficiency. The efficiency i mprovement comes with the lowering of the Tmin temperature in the Carnot efficiency equation. The power boost achieved at a typical ly hol and dry site can be as much as 1 5%. The amount of work the compressor consumes depends on ambient conditions such as air pressure, temperature and humidity. Gas turbines operate at a constant vol ume of air, but the power generated depends upon the mass flow of air. Warm air is less dense than cold air and so results i n lower power output. in addition, warm air is much harder to compress than cold air, leaving less net available shaft energy. i nlet air cooli ng is sensiti ve to ambient conditions at site. Choosing the correct inlet air cooling system is very site-specific. Table 1 shows four power augmentation technologies and their pros and cons. Keeping The Compressor Clean Gas turbi nes engines consume large quantities of air. Air contains foreign particles, i n the form of aerosols, which enler the gas turbine compressor with the airstream. The purpose of the inlet air filler is to block these particles, but no filters are 100% effective. The majority of foreign particles that manage to pass the filters will follow the gas path and exit the engine with the exhaust gases. However, there are particles with properties that cause them to stick onto the compressor blades and vanes. This is known as compressor foul i ng. The deposits result in an increase of the surface roughness on the otherwise well polished and smooth blades. The i ncrease in surface roughness results in a thickening of the boundary layer airstream. The thicker boundary layer results in a reduced mass flow through the engine. This reduced mass flow is the most profound effect of compressor foul i ng. Further, the thicker boundary layer results i n a reduced compression pressure gain which, in turn, results in the engine operating at a reduced pressure ratio. The reduced pressure gain is the second most important effect from compressor foul i ng. Compressor foul ing not only reduces the mass flow and pressure gai n but also reduces the compressor isentropic efficiency. Reduced compressor efficiency means !hat the compressor requires more power for compressing the same amount of air. Washing restores engine efficiency that would otherwise be lost by fouling - � . .. ' . . Table 1. inlet air cooling technologies • limited possibility to reach wet-bulb temperature • high pressure drop loss • small parasitic load • mid-range installation cost • limited to ambient conditions • water-quality dependent • size restricted by media velocity • Works best when it is hottest Fogging -water in the form ofa fıne spray evaporates upstream of the compressor • closest approach to wet-bulb temperature • low pressure drop loss • minimal parasitic load • low installation cost • easily retrofıttable • low maintenance (single-pump system) • limited by ambient conditions • need to use demineralized water (or trace elements will enler compressor) • downstream material may have to be upgraded (corrosion may occur) • works best when hottest Refrigeration cooling - a stand-alone refrigeration unit cools the inlet air • achieves temperatures well below dew point • high pressure drop loss • highest power production • consistent leading air temperature year-around • high parasitic load • higher installed cost than others • large footprint compared to others • advantageous when water is scarce Overspray cooling - droplets are allowed to evaporate inside the compressor • as for fogging, butwith excess ofwater. Also known as 'wet compression' • cooling is beyond wet-bulb temperature (cooling continues inside compressor) • low pressure drop loss • low parasitic loss • risk of erosion damage • limited by ambient conditions • need to use demineralized water (or trace elements will foul • low installation cost
RkJQdWJsaXNoZXIy MTcyMTY=