lmproved predictability of power output Some turbine air inlet cooling technologies allow gas turbines to the operate at any desired temperature, potentially as low as 6°C. independent of the weather conditions. These technologies temperature potentially as low as 6 °C, independent of the weather conditions. These technologies make it easier to predict the power output, and eliminate weather as a variable in predicting power output of power plants using gas turbines. TECHNOLOGIES Several technologies are commercially available for turbine air inlet cooling. These technologies can be divided into the following major categories: O Evaporative - wetted media, fogging, and wet compression/oversprav, O Chillers - mechanical and absorption chillers with or without thermal energy storage, O LNG vaporization, O Hybrid systems. Wetted media This was the first technology to be used for turbine air inlet cooling. Wetted media is an evaporative cooling technology in which cooling is achieved by the evaluation of water added to the gas turbine inlet air. in this technology, inlet air is exposed to a film of water in a welted media. A honeycomb-like medium is one of the most commonly used. The water used for welting the medium may require treatment, depending upon the quality of water and the medium manufacturer's specificatious. Welled media can cool the inlet to within 85%-95% of the difference between the ambient dry-bulb and wet-bulb temperature. it is one of the lowest capital and operating cost options. lts main disadvantage is that the extent of cooling is limited by the wet-bulb temperature and it is therefore dependent on the weather. in addition, it also requires careful control of the chemistry of the recirculating water that absorbs contaminants and monitoring of the degradation of the media. it works most efficiently during dry and dry weather, and is less effective when ambient humidity is high. it also consumes large amounts of water. Nevertheless, wetted media is the most widely used technology. Fogging Fogging is another form of evaporative cooling technology, which works by adding water to the inlet air in the form of a spray of very fıne droplets. Fogging systems can be designed to produce droplets of variable size, depending on the desired evaporation time and ambient conditions. The water droplet size is generally less than 40 um and, on average, is about 20 um. The water used for fogging typically requires demineralization. Fogging systems can cool the inlet air by 95%-98% of the difference between ambient dry-bulb and wet-bulb temperature. it is therefore slightly more effective than the "Kojenerasyon: Yüksek Verim, Temiz Çevre, Enerjide Yeniden Yapılanma" ARTICLE / MAKALE wetted media method. The capital cost of fogging is similar to that for wetted media, and fogging systems also have similar limitations and disadvantages to those for welted media. Fogging is the second most frequently applied technology for turbine air inlet cooling. Some gas turbine manufacturers do not allow fogging systems to be applied to their equipment due to compressor degradation and failures associated with fogging. Overspraying/wet compression This is another evaporative cooling technology in which more fog is added to the inlet air than can he evaporated under the conditions of the ambient air. The air stream carries the excess fog into the compressor section of the gas turbine, where it further evaporates, cools the compressed air and creates extra mass for boosting the gas turbine output beyond that possible with the evaporative cooling technologies. However, the maintenance costs of !his method are higher due to the impingement characteristics and quality of the water ingested. Mechanical ehiller systems Mechanical ehiller systems can cool the inlet air to much lower temperatures than those possible with evaporative cooling, and they can maintain any desired inlet air temperature down to as low as 6°C. independent of the ambient wet-bulb temperature. The mechanical chillers used in these systems could be driven by electric motors or steam turbines. inlet air is drawn across cooling coils, in which either chilled water or refrigerant is circulated, which cool it to the desired temperature. The chilled water can be supplied directly from a ehiller or from a thermal energy storage (TES) tank that stores ice or chilled water. A TES is typically used when there are only a limited number of hours required for inlet air-cooling. TES can reduce overall capital costs because it reduces ehiller capacity requirements compared to !hat required to match the instantaneous on-peak demand for cooling. Net power planı on-peak capacity is greater, as less or no electrical energy is required to operate the chillers as they charge the TES system the night before using lower-cost off-peak electricity. Somewhat offsetting these benefits, a system with TES requires a larger site footprint for the TES tank. in summary, the advantages ofa mechanical refrigeration system are that it can maintain the inlet air at much lower temperatures than those possible by other technologies, and achieves the desired temperatures independent of weather or elimale conditions. The primary disadvantage of this system is that it is capital cost-intensive, and it also has higher parasitic loads that lead to higher overall heat rates - and hence lower efficiencies - than those for the evaporative cooling technologies. ENERJi & KOJENERASYON DÜNYASI 1 61
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