The Water Fog Injection ( Wfi ) Concept

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The water fog injection (WFI) concept has been considered as early as 1950, when Wilcox and Trout [38] suggested that the compressor work and discharged temperature could be reduced by injecting a liquid into the gas to be compressed, thus increase the gas turbine net power output. The study indicated that the cooling effectiveness of evaporative cooling system depends on the ambient temperature and relative humidity. White et al. [39] showed that the output power of gas turbine theoretically increases up to 4.9 % by using a direct spray evaporative cooling at the design conditions of 32.2 °C and 60 % relative humidity. However, due to difficulties in producing the required 5-10 micron droplets size at high flow rates, the actual increases in the power is limited to only 3.8 % of the nominal power. Experimental work conducted by John Emory and Jack McGoarty of the Navy 's land-based LM2500 engine facility at Philadelphia is reported by Urbach, et al. [40]. It has been stated that the addition of 4.45 gpm of water to the inlet of the engine compressor reduces the NOx emissions by approximately 33 ppm over the engine operating range. The thermodynamic study by Urbach, et al. [40] reported that for an engine operation with airflow rate of 60.8 kg/sec, an increase in power output of nearly 34.5 % could be achieved when 24 gpm of water are injected to the inlet air [40]. The parametric analysis of gas turbines performance with inlet evaporative and overspray fogging was discussed by Bhargava and Meher-Homji [41]. The results showed that the gas turbine net output increases from 100.381 to 110.868 MW, because of the increase in air mass flow rate caused by the 13 °C temperature drop in the inlet air temperature. The effect of fogging... ... middle of paper ... ...n is based on the first law efficiency, the external social cost of air pollution for an operational system and energy cost. It was concluded that the optimization of the cooling system results in a great reduction in electricity price. Athari et al. [54] proposed and analyzed with energy, exergy and exergo-economic analyses of gas-turbine cycles utilizing both fogging for inlet air cooling and steam injection in biomass fired plants to improve understanding of the techno-economic behavior of such systems and assist improvement efforts. The results indicated the great impact of inserting the fogging cooling system during hot periods. Instead of injecting water, Perez-Blanco and Kim [55] injected ammonia as refrigerant fluid. However, it was concluded that injecting the ammonia does not introduce substantial improvements, in spite of its favorable evaporation rate.

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