With nearly 87.8 per cent of the total industrial water being used in thermal power plants (TPPs) for power generation, concerns of India becoming a water-stressed country are growing. Water plays a significant role in power generation and is required for process cooling in condensers, ash disposal, the removal of heat generated in plant auxiliaries, and various other plant consumptive uses. The requirement of water for other plant consumptive uses is met by an alternative source or by installing a desalination plant.
Given the significant dependence of the power generation segment on water, measures are needed for reducing the stress in the segment. The government has been pushing for a reduction in water consumption in TPPs through various policy interventions.
Water consumption trends
India, once a water-surplus country with per capita water availability of around 4,100 cubic metres (cum) per capita per year (as per 1960 data), recorded a per capita water availability of just 1,545 cum per capita per year as per the 2011 census. As per international norms, countries with per capita water availability of less than 1,700 cum per year are categorised as water stressed. Studies estimate the per capita water availability to come down to 1,401 cum and 1,191 cum by 2025 and 2050 respectively, with India eventually becoming a water-scarce country.
The estimated water use in TPPs is 35,157.4 million cubic metres (mcm) annually. This can be broadly classified into various types depending upon the quality of water and end-use considerations such as cooling tower water, that is, water used in cooling towers; make-up water, which is used for compensating the loss due to evaporation of water in cooling towers; demineralised (DM) water, which is used in boilers for generating steam (DM water costs more than cooling tower water and its use is limited); ash handling water, which is used for handling the ash generated during the combustion process; service water, which is used for coal dust suppression, firefighting measures, plantation, toilets and other civic amenities; and potable water.
Policy norms and progress in implementation
The 2015 notification by the Ministry of Environment, Forest and Climate Change (MoEF&CC) brought in four changes for reducing water consumption:
- All TPPs with once-through cooling (OTC) have to install cooling towers.
- All existing plants with cooling towers have to achieve a maximum specific water consumption (SWC) of 3.5 cum per MWh.
- Plants installed after January 1, 2017 have to meet an SWC of 3 cum per MWh and also achieve zero wastewater discharge.
Power plants have been asked to submit compliance reports on a quarterly basis since October 2018. As per CPCB data on compliance for the April-June 2019 period, of the 183 power stations with SWC limits specified, only 93 stations have achieved compliance. This forms about 51 per cent of the total.
Directions have also been issued to plants with OTC to switch to cooling towers (CTs) by 2022. State Pollution Control Boards (SPCBs) have been asked to take the necessary action against TPPs not complying with the SWC limit based on quarterly SWC monitoring data.
As an alternative to fresh water, the government has mandated that all coal power plants located within a 50 km radius of a sewage treatment plant must use treated wastewater in their operations.
Issues and concerns
Water shortage is one of the key concerns facing the thermal power generation segment. Excess water consumption leads to excess auxiliary power consumption because water and energy are dependent on each other; therefore, an increase in the consumption of auxiliary power results in a reduction in the efficiency of the power plant. Thus, efficient and optimal use of water should be made mandatory for the benefit of both the environment and power plants.
While various old plants meet the 3.5 cum per MWh norm, others face layout constraints and retrofitting issues in installing additional treatment systems. This poses a challenge for TPPs. Further, high capital cost is required to be incurred by plants for the adoption of dry cooling systems. Also, higher amount of chemical treatment is required to increase the cycles of concentration (COC) for lowering CT make-up water. Another issue is that additional water is required to operate FGDs. The handling of wastewater from FGD units thus becomes a problem for TPPs.
The way forward
Although power production by burning coal is a water-intensive process, it can be optimised by conducting water audits. The domestic water requirement of the plant is unavoidable hence sewage (domestic wastewater) should be treated in the sewage treatment plant itself and repurposed within the plant for other needs. This will help reduce domestic water consumption. Also, the wastewater generated in one system could be reused for other systems/applications. For new plants, pretreatment should be designed to handle secondary treated sewage water.
Water consumption can be reduced by modifying the existing facility and selecting an alternative wastewater treatment technology. Also, a customised tertiary treatment plant to treat secondary treated sewage to be used as feed for TPPs can have a significant impact on the social water cycle.
In sum, it is important that authorities adopt stringent measures to ensure compliance with norms, rules and guidelines that govern water consumption, and make the process efficient. The water situation in India will be grim and also lead to, among other things, power outages, thus impacting the economy of the country. Industry and the government should join hands with the public to conserve and consume water efficiently.