GAS POWER SYSTEMS CATALOG I Heat Rejection Considerations


HEAT REJECTION CONSIDERATIONS OVERVIEW AND COMPARISON


The heat rejection system is an important factor in the engineering of a combined cycle power plant and has a significant impact on overall plant efficiency. Site characteristics determine what type of condenser and heat rejection system are employed. Condensers are heat exchangers that operate at sub-atmospheric pressures (vacuum) to condense steam turbine exhaust into feedwater for the HRSG. A colder cooling fluid creates a better vacuum that allows more steam expansion through the turbine, leading to increased power output. Condensers can be water- or air-cooled. Water-cooled condensers are divided into two categories: those served directly with once-through water (sea, river, or lake), and those cooled with water in mechanical or natural draft cooling towers.


Once-Through Applications Advantages


Coastal or waterside locations without access restrictions


• Highest plant efficiency possible


• Lowest condenser pressures possible


• Smallest footprint • Lowest cost


Disadvantages • Stringent siting requirements (direct access to a body of water)


• Highest regulatory burdens


Cooling Tower


Locations where sufficient make-up water is available


• Enhanced plant site locations (not limited to waterside areas)


• Better performance than air-cooled units


• Lower cost than air-cooled


• Significant make-up water requirements


• Large footprint


Air-Cooled


Locations where water access is prohibited or uneconomical


• Fewer water-related complications (use of air eliminates issues related to water corrosion, filtration, treatment and more)


• Fewest siting and regulatory restrictions


• Least efficient


• Impacted by ambient conditions (size and effectiveness)


• Largest footprint • Highest cost


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