Because the thermal power industry understands the importance of water, a lot is being done to optimise its use and to conserve it. For one, it is trying to recycle non-potable sewage water for power plant operations. Complying with the Tariff Policy, 2016 provision that made it mandatory for thermal plants within 50 km of sewage treatment facilities to use treated sewage water, the country’s largest power producer, NTPC Limited, has started work on five power plants to make use of municipal wastewater. Other central and state gencos are expected to follow suit. According to industry estimates, the Tariff Policy provision could impact nearly 80 GW of projects.
Another area that is gaining significant importance is cooling tower technology with the environment ministry’s revised norms that require new thermal power plants to use at least 30 per cent less water than the existing ones, while the existing ones will have to reduce their water usage by at least 10 per cent. Different cooling systems consume different amounts of water. For example, wet cooling towers use only around 5 per cent of the water that once-through systems use, but consume at least 100 per cent more water than a once-through system, since the majority of the heat rejection for wet cooling towers is through water evaporation. Using dry cooling would virtually eliminate any water use for cooling.
Another way the industry is looking to save water is to replace wet bottom ash handling systems (such as ash sluicing) with semi-dry (where the ash is dewatered and the collected water is recycled) or completely dry systems (which use air to cool the ash). Also, flue-gas desulfurisation units that consume less water are becoming more important, given the large number of systems being installed to meet the new emission standards.
The vulnerability of power plants to water shortages is only expected to increase in the future. For an industry that consumes around 80 cubic metres of water per MW, as compared to 10 cubic metres per MW in developed countries, both reducing water usage and water consumption are important areas. While the use of treated sewage water will help industries reach the former goal, retrofits and new technologies in cooling systems and ash handling plants can be used to achieve the latter.
Power Line’s Infocus section on Water Management in thermal power plants takes a closer look at the current and future water needs and requirements of the thermal power industry and discusses the opportunities and areas for better water management.