Water is a key input in thermal power plants (TPPs) and finds a variety of uses, from cooling condensers to ash disposal. The physical and chemical properties of water as well as its relative abundance in the past made it an ideal cooling fluid for power plants. However, the growing shortage of water and increasing water consumption by the expanding fleet of TPPs in recent years have focused attention on the need for water management.
The loss of generation due to water shortage increased from 1,258 MUs in 2014-15 to 5,870 MUs in 2016-17 (up to February 2017). The number of thermal units shut down due to water shortage increased from 9 to 21 during this period (Source: Lok Sabha questions/answers).
To address these issues, the Ministry of Environment, Forest and Climate Change (MoEFCC) tightened the water consumption standards for TPPs in December 2015. As per the revised norms, the existing plants are required to achieve a specific water consumption of 3.5 cubic metres per MWh by December 2017. Further, plants deploying the once-through cooling mechanism are required to install a cooling tower. Meanwhile, all plants set up after January 2017 need to operate with a water consumption level of 2.5 cubic metres per MWh and achieve zero liquid discharge (ZLD).
Further, in January 2016, the government notified measures in the amended Tariff Policy, 2016, wherein all TPPs located within a 50 km radius of a sewage treatment plant were mandated to use treated sewage water and the associated cost was allowed to be passed through in the tariff. Currently, Pragati Power Corporation Limited (Delhi TPP), Rattan India Power Limited (Nashik TPP) and Maharashtra State Power Generation Company Limited (Koradi TPP) are using treated sewage water. Meanwhile, NTPC has identified five power stations – Solapur, Mouda, Meja, Dadri and the upcoming Patratu plant – for the use of sewage water to cater to the make-up water requirement of its TPPs.
Water management solutions
Cooling systems account for the maximum water usage in TPPs, making up over 80 per cent of the total input water requirement. These, therefore, offer scope for the maximum conservation of water through design and technological changes. As per the Central Electricity Authority (CEA), the consumptive water requirement for TPPs for closed cycle cooling water systems has reduced from about 7 cubic metres per MWh to about 3 cubic metres per MWh over the years, mainly owing to technological interventions.
One such intervention is operating the cooling tower at a higher cycle of concentration (CoC), which reduces the wastewater generated by the plant. CoC is the ratio of dissolved solids in the circulating water to that in the make-up water. Some amount of water is taken out of the cooling system as blowdown to reduce the salt concentration and fresh make-up water is added to take care of evaporation, drift and blowdown water loss. The higher the CoC, the lower is the make-up water and blowdown water requirement.
Other systems of a power plant also offer potential for saving water. For instance, the deployment of an ash water recirculation system helps recover water from the ash pond for further use in the ash handling plant (AHP). In plants using an ash water recirculation system, about 70 per cent of the ash pond water can be recovered and reused in the AHP. The installation of a dry fly ash handling system and a high concentration slurry disposal (HCSD) system help considerably in reducing the water required for disposing of ash from TPPs. The HCSD system helps minimise water consumption due to the high concentration of ash (60-70 per cent) as compared to lean concentration slurry disposal (15-25 per cent). Further, the installation of effluent treatment plants helps the TPP operator reuse the treated wastewater for low-grade applications like ash handling and coal dust suppression, thereby reducing the amount of make-up water to be procured from state water boards. Besides, it reduces wastewater discharge from the plant, thereby avoiding contamination of groundwater and surface water sources.
The use of ZLD systems is expected to pick up in the coming years with the MoEFCC’s notification mandating the same for new TPPs. ZLD systems ensure treating the wastewater produced in the plant with no discharge of water so as to reduce the consumptive water requirement of the power plant and prevent pollution. In addition, simple changes like alterations in the internal design of the centrifugal pumps, the use of efficient motors and the prevention of evaporation from raw water reservoirs can lower the power plant’s water requirement.
Going forward, prudent water management practices by operators will be vital for ensuring uninterrupted power generation from TPPs.