As India grapples with water quality and availability issues, water available for industrial use has become a cause for concern. Amongst industries, the power sector consumes a sizeable share of water, coal-fired plants being responsible for 70 per cent of the total freshwater withdrawal. As per IEA estimates, India’s power sector withdraws nearly 30 billion cubic metres of water and India’s coal fleet takes up 80 per cent of the water withdrawn by the sector. Plants located in arid regions are prone to longer downtime and even shutdowns due to lack of resources. Thus, water management and optimisation of resource consumption has been one of the key focus areas for the thermal power generation segment.
Water consumption norms
With a view to regulate water usage, water consumption norms were first issued by the Ministry of Environment, Forest and Climate Change (MoEFCC) in 2015 to be adopted by December 2017. In December 2015, the MoEFCC instructed pre-established thermal power plants (TPPs) to limit their specific water consumption (SWC) to 3.5 m3 per hour per MW by December 2017 and for plants installed after January 1, 2017 to meet a limit of 2.5 m3 per MWh along with zero liquid discharge. The norms were revised in 2018 and as per the amended norms, the SWC limit was revised upwards to 3 m3 per hour per MW for plants installed after January 1, 2017. Further, all freshwater-based once-through cooling plants were required to install cooling towers and meet the above specifications of 3.5 m3 per hour per MW. The seawater-based plants were exempted from the above-stated norms. However, there is insufficient data for SWC compliance so far. For many plants, the only data available pertains to demineralised plant water consumption and process water consumption per unit of product. There is also a lack of uniformity in the format of data reporting.
Technologies and solutions for water management
The industry is witnessing the adoption of several new technologies to meet the norms and address water consumption concerns. Public power major NTPC and its research unit NETRA are working on several projects to reduce its freshwater consumption and effluent discharge. NTPC has successfully implemented a water policy and a rainwater harvesting policy, and ensured zero liquid discharge (ZLD) at all its stations. It has ensured the maintenance of freshwater quality in and around the plant premises. It has also installed air-cooled condensers, which can save 75 per cent water, along with cycles of concentration technology to reduce freshwater consumption.
An ongoing project by NETRA is the activated filter media-based tertiary treatment of existing sewage treatment plant (STP) water to help control the quality of effluent discharge. NTPC has adopted this technology for the Talcher K and Dadri stations. The project has advantages such as better filtration of discharge, efficient usage of filtered effluents, reduction in the need for backwash water by nearly 50 per cent, and 15 per cent energy savings. This project is expected to help in the compliance of green tribunal norms for STPs. Another project being undertaken by NETRA is the electro-dialysis reversal (EDR) technology. NETRA is developing a pilot 1,000 LPH system at an NTPC station to study system efficiency in terms of water recovery and ion removal capacity. EDR is an advanced water treatment process based on electrically charged membranes. In EDR, ion exchange membranes are used to separate ionic impurities from water under the influence of the DC electric field through flowing water.
ZLD for power plants is gaining momentum due to its potential to control pollution and reduce SWC. Water from power plants contains contaminants that are hard to dispose of, which is one of the prime reasons that ZLD is prioritised. Processes at work in cooling towers, bottom ash quenching and flue gas scrubbing are water heavy. ZLD reduces a plant’s dependence on freshwater sources for its daily operations. Apart from this, the Budge Budge power plant in Kolkata, operated by CESC Limited, has achieved ZLD status and has also been rated as one of the most water efficient plants. Similarly, the Torangallu power plant located in Bellary, Karnataka, and operated by JSW Energy Limited, has achieved ZLD status along with the most water efficient plant status.
The Central Pollution Control Board (CPCB) has also recommended certain technological changes to aid water management. Minimising boiler blowdowns by establishing CPU along with a good boiler can help save water. Using the demineralised process or RO process can yield the same result. CPCB also recommends using closed cycle cooling systems in place of once-through cooling systems. The cooling water obtained from the processes can be used for plantations or suppression of coal dust. Further, the dry cooling system for condensers can reduce water consumption and is highly recommended. Dry ash collection is another way for power plants to reduce their water consumption and effluent discharge.
Conclusion
Apart from these technology measures, there are non-technological measures that can be adopted to improve the compliance of TPPs. These include stricter penalties for defaulters, third-party verification of reporting formats and water audits. Also, water-scarce regions should be pushed for quicker compliance to prevent future plant shutdown. Overall, these measures coupled with technological solutions can help TPPs improve their water management.