The air cooled condenser is a low water use option used for steam power plant water cooling, but at a cost and performance penalty. Adding a small evaporative cooling component to make it hybrid wet and dry cooling, can eliminate most of the performance penalty with only slightly more water use.
The air cooled condenser (also called a dry cooling tower) is seeing increased use for steam power plant condenser cooling because of increasing concern about the extent of power plant water usage for condenser cooling. Use of an air cooled condenser drastically reduces the rate of power plant water usage, but at the expense of increased capital cost, increased operating cost and a reduction in power production efficiency, especially in hot weather. An air cooled condenser with an added evaporative cooling component has come to be called a hybrid wet and dry cooling system. This combination provides the possibility of eliminating most of the efficiency penalty with only a small increase in power plant water usage.
Hybrid Wet and Dry Cooling Objectives
Both wet and dry components (evaporative cooling and an air cooled condenser) are included in a hybrid wet and dry steam power plant condenser cooling system. The evaporative cooling and air cooled condenser components may be used separately or they may be combined in one unit.
Plume abatement was the objective for the first hybrid wet and dry power plant water cooling systems put into operation. Plume abatement can be accomplished by using a small amount of dry cooling with an evaporative cooling tower, for use during cold, high humidity periods.
More recently hybrid wet and dry cooling systems are being developed with water conservation and reduction of the performance penalty of an air cooled condenser (dry cooling) system. Several way of combining evaporative cooling with an air cooled condenser are being developed to meet these objectives.
Hybrid Wet and Dry Cooling for Plume Abatement
Plume abatement, wet and dry systems are essentially a wet cooling tower that uses a small amount of dry cooling to dry out the cooling tower when the plume is most likely to be visible during cold, high-humidity days. This type of hybrid power plant water cooling system will reduce water consumption to some extent from the amount used by a strictly wet cooling tower, but the primary objective is plume abatement. The diagram at the left shows a system with a small air cooled condenser at the top of a wet cooling tower. The air cooled condenser would only be used during cold, high-humidity periods.
Hybrid Wet and Dry Cooling for Water Conservation
There are several configurations possible for a hybrid wet and dry cooling system that is intended for water conservation. There could be a single tower or separate wet and dry towers, using series or parallel airflow and series or parallel cooling water flow. The diagram at the left shows a hybrid cooling system with an evaporative cooling tower and an air cooled condenser as separate structures. The air cooled condenser would handle all of the cooling load except for the hottest periods, when part of the cooling load would be handled by the wet cooling tower.
Another option using a single tower with supplementary wet cooling available to be used as needed for hot weather is shown at the right. Some of the low capital cost alternatives include spraying water into the air cooled condenser or deluging the air cooled surface with water for short periods.
Hybrid wet and dry cooling systems can reduce steam power plant water usage to 5% to 80% of that needed for a wet cooling tower, and still achieve substantial hot weather efficiency and capacity improvements over a steam power plant with a completely dry cooling system.
Comparison of Alternate Cooling Technologies for California Power Plants:Economic, Environmental and Other Tradeoffs, EPRI, Palo Alto, CA, and California Energy Commission. 500-02-079F, February 2002.
Running Dry at the Power Plant, EPRI Journal, pp 28-35, Summer 2007
The images were adapted from some in the above two references.
About the Author
Dr. Harlan Bengtson is a registered professional engineer with 30 years of university teaching experience in engineering science and civil engineering. He holds a PhD in Chemical Engineering.