Ways to Reduce Water use in Cooling at Power Plants
The most common form of thermal power plants that are operating today is coal-based plants that consume enormous quantities of water for various operations. One of the most important sources of water consumption is the cooling process in such plants which typically uses evaporative cooling towers.
Power plants in most developing countries, when compared to that of developed nations, consume almost twice the amount of water in operating their power plants. The amount of water consumed at a power plant is determined by a number of factors such as:
- The nature of cooling used
- The quality of coal
- Reutilization of ash
- Ash disposal systems
- Wastewater management
Cooling systems used in Thermal Power Plants
Currently, there are three kinds of condenser cooling system which are used in power plants. They are- open circuit cooling, evaporative cooling through towers and air condensers.
Open circuit cooling system, also known as once-through cooling is the cheapest form of condenser cooling system, but it is also the one which uses the maximum amount of water and has serious environmental impacts. Added to this, there are also high pumping costs associated with this process making it unpopular in our current times.
The evaporative technique which uses cooling towers is the traditional and most popular form of condenser cooling system. In such towers, hot water is made to come in contact with a draft of air. Heat is exchanged producing air saturation and consequent cooling of the water droplets. This processes uses significantly lower quantities of water for cooling and require small areas for installation. Despite its numerous advantages, the current industrial standards make cooling towers more disadvantageous from the perspective of water consumption and environmental impacts. Cooling towers require a lot of water and additional investments for controlling the discharge.
The third process of cooling with air condensers was developed for operating in areas with limited availability of water. This system of refrigeration has been especially popular with thermal power plants which are typically set up in areas with high abundance of sunlight and low water concentrations. In these condensers, air is passed through a turbine which brings it in contact with the steam through finned tubes. Heat is exchanged - and cooling takes place without the use of additional feed-water. In certain practices of this method, relatively low quality of water sources are tapped into either via on-spot drilling or from nearby sources.
Air condensers are by far the best solution to this issue from the environmental perspective. It doesn't use excessive water and occupy very less space. The only disadvantage here is that in cases where water is required, due to the poor quality separate water treatment processes may need to be implemented.
In order to balance the energy consumption of systems and the consumption of water, several hybrid technologies have been developed which combines the idea of air condensers with the above mentioned cooling systems. These systems are designed to strike a middle ground between systems efficiency and water consumption.