About 90% of the country’s power comes from thermoelectric power plants, natural gas, coal, oil and nuclear energy, all of which require cooling. The remaining percentage is sourced from other facilities like hydroelectric power plants. Renewable sources of energy such as solar, biomass and geothermal power plants can be classified as thermoelectric.
Why cool power plants?
In order to produce power, thermoelectric power plants boil water, which then spins turbines. The source of heat could be underground geothermal sources, sun or nuclear reactions. Before it can be reused and passed through the turbine in the turbine, the steam has to be cooled. Using cold water for this purpose is more effective, allowing efficient electricity generation. Allowing the heat to build-up can lead to acceleration of wear and tear of the turbines. It can also compromise the efficiency of the power plant productivity. A working cooling system is therefore important. There are different methods of cooling and the one chosen will depend on several factors.
Types of cooling
One of the main aspects that most peple don't realize is that in as much as all thermoelectric plants rely on water to generate electric power; they don’t all rely on water for cooling purposes. Generally, there are three methods of power plant cooling. These include wet-recirculation or closed-loop, once-through and dry cooling.
- Wet-recirculation or closed loop
For systems that use this cooling method, cooling water is reused during the second cycle. This is unlike most systems which discharge water to the original source. Cooling towers are used by wet-recirculation systems to expose water to ambient air. While some of it evaporates, most of the water is resent to the power plant’s condenser. Wet recirculation systems are only used to restore water that was lost during evaporation, they have less water withdrawals compared to their once-through counterparts. They, however, consume more water. Wet recirculation systems are the most popular power plant cooling systems in the country.
- Once-through cooling systems
These take water from surrounding sources including rivers, lakes and oceans and use it to cool power plants. From the water source, the water is passed through pipes and absorbs heat from steam in condensers. The warmer water is then discharged to the water source. Due to their low price, simplicity and the possibility to sit power plants in locations with plenty of water sources are a few of the reasons why these systems were so popular just a few decades ago. It’s still used widely nationwide, but newer plants are no longer utilizing them probably due their interruption of local eco-systems. It’s also becoming increasingly difficult to build power plants near water sources.
- Dry-cooling system
Rather than use water for cooling, dry-cooling systems use air to cool steam from turbines. As there’s no water used in cooling, dry-cooling systems can effectively reduce water consumption by nearly 95%. While this may seem like a good thing, it can lead to lower efficiency as well as higher costs. This includes negative environmental impact due to mining, fuel transport and processing. Air pollution could also increase. Unlike before, dry-cooling systems are just used in small power plants, particularly natural gas combined-cycle power plants.
The following are some of the electricity generation technologies that use cooling
Conventional electricity technologies such as:
- Natural gas
Renewable electricity technologies such as:
- Concentrating solar
Additional key issues
In as much as power plants rely on fresh water for cooling, there are several ways in which waste and salty water can affect the cooling process. Salty water is often the option, especially with power plants located in coastal areas. Such plants, however, face most of the challenges faced by plants in inland areas. This includes thermal pollution due to hot water discharge and damage to aquatic systems due to excess water withdrawal.
The sitting of a power plant has a huge impact on the availability of water, type of water used for cooling, cooling technology options as well as the impact on the environment. In the case of geothermal or solar power plants, the location has to have high geothermal energy and solar radiation respectively. Dry-cooling technology can be an option with the above power plants. All the choices made will play significant roles in the performance of power plants and the impact on the environment.