62 ARTICLE / MAKALE Absorption cooling systems Absorption cooling systems are similar to the mechanical refrigeration systems. except that instead of using mechanical chillers, these systems use absorption chillers that require thermal energy (steam or hat water) as the primary source of energy, and require much less electrical energy than mechanical chillers. Absorption cooling systems can be used to cool the inlet air to about 10°C. These systems can be employed with or without chilled water TES systems. Absorption chillers can be single-effect or double-effect chillers. The single-effect absorption chillers use hat water from 100 kPa steam, while the double-effect chillers require less steam, but need the steam ata higher pressure (800 kPa). The advantage of this system is that it has a much lower parasitic load, and its major disadvantage is that its capital cost is much higher than even mechanical refrigeration systems. The primary successful applications of absorption chillers is in power plants where there is excess thermal energy available and the conversion of this energy to high-value electricity is profitable far the user. LNG vaporization systems Liquefied natural gas (LNG) vaporization systems are useful far power plants located near an LNG facility. in supplying natural gas far power plant or other applications. LNG must be vaporized by a heat source. Far applications in turbine air inlet cooling, the inlet air is used as a heat source. Hybrid systems Hybrid systems incorporate some combination of technologies, such as mechanical and absorption chillers. Such a system is optimized far a specific plant based on the power demand and electricity prices and the availability of thermal energy. ECONOMICS The economics of turbine air inlet cooling are best discussed using specific examples. The examples used here are of two fictional cogeneration plants located in Los Angeles. Califarnia. US. üne plant deploys an industrial gas turbine of 83.5 MW capacity, and the other uses an aeroderivative gas turbine of 42 MW capacity. a 86 3 846 82 '5 o.. 80 • '5 o 78 t 3: ~ 72 No Evap. cool iııg cooling When the ambient dry-bulb temperature is 31°C and the wetbulb temperature is 18°C. !he output of the uncooled turbines drops to about 75.3 MW and 32.1 MW respectively. Compared to the rated capacities of the two plants, !he reduced outputs represent a capacity loss of about 10% and 24% respectively. Three possible cooling technologies far these two plants were considered: wetted media, fagging, and electric chillers. The evaluation of the economic viability of these technologies depends in part upon the weather far the specific planı location. Output enhancement Assuming 90% and 98% in the difference between the dry-bulb and wet-bulb temperatures far the welted media and fagging technologies, these two technologies can cool the inlet air to 19°C and 18°C respectively. lf the electric ehiller system is designed to cool the inlet air to 7°C, such a system would require total cooling capacities of 2330 refrigeration tonnes (RT - the cooling effect of 1 tonne of ice at 0°C far 24 hours) and 1200 RT far the 83.5 MW and 42 MW gas turbines respectively. Assuming a typical electric ehiller power requirement of 0.65 kW /RT far chilled water, condenser water and cooling tower pumps, the total parasitic power needs far the ehiller capacities are 1.9 MW and 0.96 MW far !he larger and smaller gas turbines respectively. The results show !hat evaporative cooling and fagging can enhance !he capacities of !he larger uncooled system (75.3 MW) to 81.3 MW and 81.9 MW respectively - see Figure 4a. Therefare, these technologies can restore most of the 10% lost capacity, to within 3% of the rated capacity. The results far the aeroderivative gas turbine are similar, hut more pronounced !han those far the industrial gas turbine - see Figure 4b. The capacity of !his uncooled system rises from 34.1 MW to 39.9 MW and 40.4 MW by !he evaporative cooling and fagging technologies respectively, and thus restores most of the lost 24% capacity to within 4% of !he rated capacity. Even though the results of using evaporative cooling and fagging are very good, these technologies are not able to achieve !he full rated capacities. in addition, the extent of cooling achieved by these technologies depends on the ambient wet-bulb temperature. lf the wet-bulb temperature rises (i.e. the outside humidity rises), their effectiveness decreases. b 46 44 3 42 6 '5 40 B- :::, 38 o t 36 3: o cı.. 34 32 . 30 No Evap. cooling cooling Figııre 4. Net µower oııtpııt of cııı (cı) 83.5 MW cı11d (b) 42 MW gcıs turbiııe. e./Ject ofııırbine cıir inlet coo/i11g 1 ENERJj & KOJENERASYON DÜNYASI "Kojenerasyon: Yüksek Verim, Temiz Çevre, Ene~ide Yeniden Yapılanma"
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