Optimising Water Use

Strategies for TPPs to reduce consumption and improve efficiency

The power sector is one of the largest consumers of water in the country. Power generation is expected to account for nearly 9 per cent of the country’s water consumption by 2050 (in a business-as-usual scenario) – growing from 1.4 per cent in 2025 (Central Water Commission, 2015), and this figure is likely to vary significantly from region to region. There is a mismatch between water demand and supply when usable surface water capacity and “replenishable” groundwater levels are considered. Water stress is particularly acute in naturally arid regions and areas where water is also needed for other uses such as irrigation. Confronted with the growing risks to water and energy security, the power sector needs to adopt a long-term approach to reduce its dependence on fresh water while also meeting other environmental objectives such as reducing air, water and soil pollution.

For existing plants, interventions such as phasing out once-through cooling technologies, while restricting their installation at new thermal plants, through the enforcement of the announced regulatory water use standards, will substantially reduce water withdrawal. In addition, other water management strategies such as installation of wastewater treatment and zero liquid discharge (ZLD) systems can provide a range of benefits for power plant operators and gencos.

Energy and water interlinkages

The energy sector is expected to account for a steadily increasing share of the available water resources. The sector’s relative water consumption is projected to grow from 1.4 per cent to 9 per cent between 2025 and 2050 (from 15 billion cubic metres [bcm] to 130 bcm annually) (Central Water Commission, 2015).

In 2050, the total water demand is forecast to reach 1,400 bcm. The comparable annual figure for usable surface water capacity is around 690 bcm and the potentially replaceable annual groundwater capacity amounts to 433 bcm (Central Water Commission, 2015). The mismatch between demand and supply could affect the availability of water for different end-uses and increase the risk of competition, particularly in water-constrained areas. Further, as demand increases, water will need to be pumped from sources further away or deeper underground, thus increasing energy demand.

In the power sector, water availability directly impacts all plants. World Resources Institute (WRI) analysis shows that shutdowns owing to water shortages in 2016 resulted in the loss of nearly 14 TWh of thermal electricity generation – equivalent to the annual power use in the north-eastern region (Central Electricity Authority, 2017).

Water use in power generation

Water is used for many purposes in a power plant such as in the cooling tower, condensers, demineralisation plants, fire-fighting, coal handling, ash handling and service water, and to fulfil drinking water needs.

There is no comprehensive information available in the public domain regarding the water consumption of power plants in India. However, in a short-term study (see figure) of the break-up of specific water consumption of a coal-based thermal power plant (TPP), it can be seen that cooling towers and ash handling are the major water-consuming areas and account for about 70 per cent of water use in the plant.

The Energy and Resources Institute (TERI) published a policy brief discussing the challenges of water availability and scope to improve water-use efficiency in industries, especially in TPPs. The findings indicate that there is significant scope for saving water in wastewater discharge, cooling towers, ash handling systems and local township water supply. Interventions like recycling wastewater, curbing leakages, increasing cycles of concentration (CoCs) in cooling towers, using dry ash handling, etc. can significantly reduce the specific water consumption in power plants. The brief also highlights the need for mandatory water audits to understand the current water use and losses as well as identify opportunities for water conservation, reduction in specific water consumption, and an overall improvement in water-use efficiency in industries.

Specific recommendations for power plants:

  • A once-through system of water usage in cooling systems should be changed to closed-cycle systems. CoCs in cooling towers should be increased through interventions such as chemical treatment (anti-sludging, anti-sepsis, acidification, etc.) and periodic maintenance of cooling towers. The possibility of using dry or hybrid cooling technologies to replace traditional wet cooling towers should be explored in order to reduce water consumption in a few specific cases.
  • Overflows should be recycled, leakages plugged and wastewater reduced. An estimate suggests that for every 1 per cent of reduction in the ash-water ratio, there is a potential saving of 60 cubic metres per hour of water. Recycled ash-water could be utilised for gardening, firefighting and dust suppression in the coal-stacking yard. In addition, wet ash handling through slurry should be shifted to dry ash handling by use of “hydro bins”, where water is separated from the ash slurry in the plant and the dry lumps conveyed to ash dykes through conveyer belts. This would significantly reduce the amount of water consumed in ash handling units.
  • Firefighting water must not be used for any other purpose. It should be retained under pressure in fire hydrants and pipelines for emergencies.
  • Wastewater should be treated and recycled to achieve ZLD and save on fresh water intake. Township STP discharge water should be reused, ensuring adherence to ZLD.
  • Regular water audits should be conducted as a matter of corporate policy. To start with, a periodic annual water audit can be initiated.
  • Automation should be introduced in water quality and flow monitoring with a centralised control system and management information system.

Policy recommendations

One of the key policy developments for promoting water management in TPPs was the tightening of the water consumption standards by the Ministry of Environment, Forests and Climate Change in December 2015. The revised norms require all existing plants to achieve a specific water consumption of 3.5 cubic metres per MWh by December 2017. Further, plants with once-through cooling are required to install cooling towers. Meanwhile, all plants to be set up after January 2017 need to operate at a water consumption level of 2.5 cubic metres per MWh and achieve ZLD.

The use of treated sewage water for cooling was recently mandated for TPPs within 50 km of treatment plants (Ministry of Power, 2016). However, this is marginal at present, and insufficient data is available to assess its future use.

Water-use efficiency essentially should lie within the purview of the Ministry of Water Resources. However, since the functioning of power plants in India is under the Ministry of Power (MoP), the task of ensuring water audits and improving water-use efficiency in power plants could be initially with the MoP. Drawing on experiences from the Bureau of Energy Efficiency, in order to improve water-use efficiency in the entire water sector (agriculture, domestic and industrial), one of the key reforms would be to set up a central monitoring agency – Bureau of Water Efficiency, to train and certify water auditors to carry out performance assessment of water-use efficiency in all sectors, and place the reports and findings in the public domain.

Once benchmarks for water use in the TPP industry are established, third-party water audits should be made mandatory for all TPPs to ensure compliance with the set water use standards. Interventions identified through water audits will require capital investments. However, in most cases, such investments will result in considerable savings in the cost of procurement of fresh water with short payback periods.

Conclusion

The current water withdrawal intensity of India’s power sector (excluding hydropower) is largely driven by TPPs using once-through cooling systems. Withdrawal intensity could be reduced by upgrading plant cooling technology. From the industry perspective, in order to establish technically feasible benchmarks, the current scenario of water use in TPPs needs to be studied on a priority basis.

The various water saving and wastewater treatment alternatives proposed, should be studied through a detailed cost-benefit analysis. Comprehensive water use benchmarks must also consider social viability. For example, TPPs must provide adequate effluent treatment to protect their environment and neighbouring population, and ensure the provision of safe drinking water for workers.

Given the grim water scarcity scenario in India, water-intensive industries such as TPPs must focus on reducing water consumption and improving water-use efficiency. Continuous policy and regulatory support is required to achieve both water and carbon benefits. On both counts, dedicated policies and mandates have already been introduced including time-bound targets. However, their effective implementation and enforcement will be crucial for meeting the targets.

Anita Khuller with inputs from IRENA, WRI and TERI

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