Cooling Systems Explained
An explanation of the difference between an air cooled condenser system and a water cooling system for an Energy Recovery Facility (ERF).
In order for an ERF to produce power, water is boiled to create steam which spins a turbine, generating electricity. A cooling system is required to condense the wet steam back into water. This water is then pumped back into the system so that it may be reused in the power generation process.
Two cooling systems options have been proposed: 1) an air cooled system; and 2) a water cooling system. An air cooled system uses a fan blowing cold air to condense steam back into water whereas a water cooling system uses cold water.
The type of cooling system chosen will have an impact on the amount of energy produced by the ERF. A water cooling system has a higher energy generation potential along with lower capital and operating costs but results in a large visible water vapour plume on cold days.
Why is a condenser needed?
In order for an Energy Recovery Facility (ERF) to produce power, water is boiled to create steam which spins a turbine to generate electricity. Once the steam has passed through the turbine it must be cooled back into water so that it may be reused in the power generation process.
An essential component of the new facility will be the cooling system to condense the steam back into water. There is a choice between two main types of systems:
1. An air cooled condenser; or
2. A water cooling system.
Air Cooled Condenser
An air cooled condenser uses circulating air to cool the hot steam from the power generation process. An air cooled condenser system is made up of several large low speed fans blowing cold air over a series of thin tubes containing the wet exhaust steam. The air lowers the temperature of the steam condensing it back into water. The water can then be pumped back to the boiler to be used again in the power generation process.
Water Cooling System
A water cooling system condenses the steam from the turbine back into water through the natural process of evaporation. Cold water which is drawn from an adjacent watercourse is sprayed onto cooling pipes. This causes the remaining heat from the steam to be transferred to the water spray, creating a large cloud of warm water vapour (plume) which is visible on cold days. The water which is evaporated is continuously replenished from the adjacent watercourse.
How do they compare?
The type of cooling system used has a direct impact on the amount of energy produced by an ERF. A water cooling system results in a greater amount of energy being generated by the system. When comparing the energy performance of the systems (i.e. all inputs are identical),
a water cooled system produces around an additional 1MWe which is enough energy to power around 1,200 homes. Therefore, a water cooled system will enable the proposed ERF to produce a greater amount of energy.
A water cooling system also has lower capital and operating costs than the air cooled condenser system. Therefore, the purchasing, construction and installation of the water cooling tower would cost significantly less than the air cooled condenser system. These cost assumptions are based on a nearby free source of water for the cooling system and high electricity prices. If in the future an industrial supply cost has to be paid for the water, then the operating cost of this system would increase.
As part of the functioning of the water cooling system it would be necessary to extract water from the adjacent watercourse in order to cool the hot steam. This would be the same arrangement as the existing Energy from Waste facility which draws cooling water from the adjacent watercourse, and would require a similar volume of water.
However, unlike the water cooling system, an air cooled condenser system produces no visible plume. This is because an air cooled condenser system is an enclosed system and therefore no moisture is lost to the surrounding atmosphere. A large plume from the water cooling system will be visible on certain days resulting in a visual impact.
Cooling water is pre-treated to ensure it is suitable for use in the cooling system. This can lead to higher maintenance requirements for cleaning water, and a potential knock-on impact of a plume generated by a water cooling system is often the deterioration of adjacent steel structures.
The amount of space required to accommodate the condenser unit varies significantly. An air cooled condenser system requires 2-3 times more space than a water cooled system. The area required for an air cooled condenser would be 1,225 m2 for the new ERF (slightly larger than the area of an Olympic-sized swimming pool). The area required for a water cooling system is smaller - just about one-third the area of the air cooled condenser system. In addition, the air cooled condenser unit would be slightly taller than the water cooled system.
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