Power plant cooling system

Power plant cooling system is used to provide heat transfer media for steam turbine, in wihch exhaust steam is cooled down to condensate water, and then goes back to water-steam cycle in boiler.

Cooling system types

 

By cooling medium, cooling system could be categorized into: air cooling system and water cooling system.

 

Direct air cooling system consists of steam pipeline with large diameter, air cooled condenser, axial flow fan and condensate pump, etc. Exhaust steam is delivered to condenser in outdoor through pipeline, axial flow fan drives ambient air to pass through condenser. Direct air cooling system is featured with no cooling water needed, less equipment, simpler diagram. It is normally used in areas lacking water resource.

 

 

 

Water cooling system is classified into: once-through cooling system, open circuit water cooling system, closed circuit water cooling system.

 

Once-through cooling system takes water from natural resources like lake, river and sea. Cooling water passes through condenser and takes away waste heat, then goes back to natural environment. So, it is also called single pass cooling system. This way is often adopted in coastal power plants.

 

Open circuit water cooling system mainly consists of water circulation pipeline, circulating water pump, cooling tower, side stream filter, makeup water system, water treatment system, etc. Circulating water gets pumped to steam condenser, and takes heat away from exhaust steam. Then it goes to cooling tower and gets exposed to ambient air. Evaporation happens on the surface of water. The evaporation of 1kg cooling water (at 35℃) will absorb about 24094J heat, which could bring the temperature of 576kg cooling water 1℃ lower.

 

For a closed circuit cooling water system, there is no contact between circulating water and ambient air. Actually, this system could be seen as indirect air cooling system. It has two variations: Heller type and Hamon type.

 

Heller system consists of a jet condenser, radiator and cooling tower. Cooling water enters jet condenser and mixes with exhaust steam. Steam turns into condensate, part of which will go to radiator located in cooling tower, and the other part will go back to water-steam cycle. As Heller system is difficult to control feedwater quality, it is not used on large capacity boiler.

 

Hamon system consists of a surface condenser, circulating water pump, radiator and cooling tower. Cooling water and steam circulates in two different routes. Cooling water catches heat from shell and tube type condenser, and releases in cooling tower.

Cooling tower types

 

Cooling tower is basically classified into natural draft type and mechanical draft type.

 

Inside natural draft cooling tower, air flow is driven by differential pressure between warm, moisture air (lower density) and ambient, dry air (higher density). It consists of reinforced concrete shell, water distribution system, drift eliminator, fill, basin, etc.

 

 

Mechanical draft cooling tower is equipped with fan to provide forced draft. This could decrease the size and height of cooling tower. But it consumes power and lots of maintenance work is required by the fan, it is usually used for small power plants.

 

 

Construction

 

Cooling tower framework built with reinforced concrete is featured with rigid structure and long service life. It could withstand the vibration during operation. Column with small section could reduce system resistance and improve cooling performance obviously.

 

 

Cooling tower built with FRP material is getting more popular due to its excellent mechanical strength and anti-corrosion ability. FRP cooling tower is featured with stable framework, light weight, easy installation, anti-corrosion, and widely used in chemical, metallurgy, power generation, especially for the case where corrosive chemical water, seawater is used as circulating water.

 

 

Cooling tower built with structure steel adopts rigid girder system. All the components are connected with bolts. Beam and column are joint together by web component. Steel cooling tower has good rigidity and reasonable internal force distribution. It could bear point load, non-symmetric load, earthquake, strong wind. It is a better design to reduce vibration of cooling tower.