In essence, there are two types of dry cooling system, these can be classified as either direct or indirect systems. Cooling towers are usually built where water supply is lacking and their purpose is to reject waste heat into the atmosphere.
A dry cooling system uses around 95% less water than a wet cooling system and cooling systems are one of the largest uses of water in any power plant. There is always a compromise to make with cost and efficiency versus ecological choices. Wet towers tend to produce runoff into the soil of heavy metals like zinc and lead which you do not get with an ACC. Power savings can be made within this type of dry cooling system by selecting high-efficiency components. This set-up also offers a high degree of recyclability.
An example of an indirect dry cooling system is the Heller system which is a type of natural draft system. Water is still required for this type of system but it is recirculated within the system and never comes into contact with the outside. The water does not need to be replenished making it one of the most cost effective systems to run. Other advantages include lower noise, lower ground level pollution and high operational availability.
Using the right type of fin tube bundle can affect both the cost and efficiency of any dry cooling system. Fin tube bundles can vary by the surface areas they require, the material they are made from and the configuration. All of these factors should be taken into account when deciding which system is best for a project. A single row bundle makes for easy access and clean-ability. When it comes to materials, carbon steel, stainless steel, copper and copper alloys are all options which can be beneficial depending on the system required and the amount of heat transfer. Hanson has been using single row aluminium finned tube since 1990 when the standard was multi-row round or oval tubes. A single row aluminium tube is now widely used for the following reasons: increased thermal efficiency, no dead zones, higher resistance to corrosion, lower pressure drop on both the air side and steam side, lower weight per surface area and lower sound levels.
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