NTPC, India’s largest energy conglomerate and its largest coal generator, in March commissioned the country’s first supercritical coal-fired plant equipped with an air-cooled condenser (ACC). The effort responds to concerted efforts by the company and the Indian government—which holds 51.1% of the company—to forge new pathways for coal power that will proactively address water sustainability issues.

1. NTPC’s newly opened 2-GW North Kanapura plant in the vicinity of Tandwa town in Jharkhand state is equipped with three coal-fired units and has a total capacity of 1,980 MW. The pit-head and supercritical project is the first in India to include an air-cooled condenser. Courtesy: NTPC

The pioneering ACC was installed in Jharkhand state at NTPC’s 2-GW North Kanapura plant, which comprises three supercritical units of 660 MW each (Figure 1). When conceived by the Indian government in 1990 as a pit-head thermal power plant (owing mainly to ample coal availability from the nearby Tandwa block coal fields), the plant’s original design called for a closed-cycle conventional condenser that would have required 55 million cubic meters (MCM) of water annually. Initial plans called for the construction of a 22.5-meter (m)-high dam across the nearby Garhi River, a tributary of the Damodar River, to ensure a permanent source of water to meet the water requirements through the plant’s lifetime.

Building the dam, however, would have required acquiring an estimated 5,000 acres. The dam would have also required submerging fertile or forest land and rehabilitating 10 villages. In 2014, the Indian government reviewed its plans and considered an ACC, which could potentially reduce the annual water requirement by nearly a third to 20 MCM.

NTPC ultimately worked out an integrated water management scheme that included the incorporation of ACCs, a low-height barrage within the river regime, and a raw water reservoir within the plant boundary. The new scheme promised to halve costs. On March 1, nine years after construction was kicked off at the plant, the effort became a reality as the North Kanapura project was commissioned, marking a first for India. It presents a “true example of sustainable development,” the company said.

A Notable First for Coal-Heavy India

However, the development is also notable because while ACC technology utilization is fairly common around the world, it marks a potential new paradigm for Indian coal generation.

An ACC is a heat exchanger, in which steam is condensed inside air-cooled finned tubes. It is a direct dry cooling system. “The cool ambient air flow outside the finned tubes is what removes heat and defines the functionality of an ACC,” explains solutions firm SPG Dry Cooling. “In thermal power plants, the steam from the turbine exhaust flows into the ACC where condensation occurs. Then the condensate returns to the boiler in a closed loop. Since the steam coming from the turbine is at low pressure, the ACC works at a pressure close to a vacuum, and non-condensable gases are removed continuously by an air evacuation unit.”

According to the U.S.-based ACC Users’ Group, the first direct ACC generating plant in North America, the 21.7-MW coal-fired Neil Simpson plant in Gillette, Wyoming, came online in 1969. By 2008, dry cooling had become standard practice at many thermal power plants in the U.S., Europe, and China, even in places that are not water-stressed.

But while India relied on 179 coal power plants—a combined 204 GW—for nearly 50% of its total generation as of January 2023, it has so far shunned the uptake of ACCs, owing to its high capital costs, use of auxiliary energy, and a relatively low reduction of water footprints when compared to wet cooling.

“Although ACC is used to save the water footprint of power plants, the adverse impact of such devices on the thermal efficiency of power plants is a matter of concern,” Ravi Prakash, a professor of mechanical engineering at Motilal Nehru National Institute of Technology in Uttar Pradesh, told POWER. Another reason India has avoided ACC installations is that ACCs and integral ACC components—including tube bundles, gearboxes, and vacuum pumps—would typically need to be imported, which hinders cost competitiveness.

However, recent events highlighting regional vulnerabilities to water scarcity paired with sustainability initiatives have prompted energy conglomerates like NTPC to re-examine the feasibility and constraints of ACCs. The effort falls under NTPC’s environmental, social, and governance (ESG) strategy, which envisions a more sustainable outcome for the company’s 70-GW fleet, which includes 26 coal-fired power plants with a combined capacity of 51 GW.

Under NTPC’s ESG initiative, the company is, for example, pursuing a massive effort to diversify its fuel by growing its renewables portfolio from 10 GW to 60 GW by 2032. Along with plans to decommission 1.4 GW of its coal capacity, it plans to blend up to 10% of biomass at its existing coal plants; explore carbon capture, utilization, and storage at two coal plants; and reduce its air pollutant emissions from its overall fleet.

The company has also notably committed to leading India’s energy efforts on water conservation. Along with furnishing new plants with ACCs, efforts include adopting higher cycles of concentration in circulating water systems, zero-liquid discharge, high concentrations of slurry disposal, and seawater desalination, including from flue gas–based systems.

Expert: High Water Stress a Growing Concern for India’s Coal Power Fleet

Now that the North Karanpura project is online, NTPC will focus on completing its second ACC installation at the 2.4-GW Patratu Super Thermal Power Project, which is under construction in Jharkhand. India’s giant equipment maker BHEL has an engineering, procurement, and construction contract for that project.

According to Prakash, however, India will need much wider efforts to reduce its thermal power water withdrawals and consumption. An estimated 40% of India’s thermal power plants are located in regions with high water stress, Prakash and five other authors note in a recently published paper, “Energy-Water Nexus for Thermal Power Generation in India: Challenges and Opportunities.” If the current level of water use by thermal power plants continues and existing water-related regulations remain unchanged, water withdrawal could grow 4.3 times and consumption would increase 3.2 times by 2050, they suggest.

The authors studied several approaches to applying ACCs. One possibility entails an ACC that reduces the temperature of air before entering into the condenser, using vapor absorption chillers. The paper illustrated its analyses based on the technology’s hypothetical use at a 300-MW JSW Vijayanagar Power Station unit. JSW is a thermal power plant located in Toranagallu village in Karnataka state, in south India. “The temperature and relative humidity of the ambient air have a significant impact on an ACC’s auxiliary power consumption,” it notes.

However, the paper concludes that the use of an ACC was “not feasible due to the high cooling loads in the thermal power plants.” For now, a better alternative may be to use seawater for cooling thermal power generation, it suggests.

One approach the researchers described entails drawing deep seawater of about 6C and then pumping it (at 3 bar pressure) to plant premises. “First, this cool sea water is used to produce [a] cooling effect in air conditioning plant by passing through [a] heat exchanger where it cools the supply chilled water to 10C. The cool sea water temperature rises from 6C to 14C; and provides a cooling effect of 2,515 kW (nearly 716 tonnes of refrigeration).” The condenser cooling water, available at a lower temperature than in-land plants, could lead to a reduction in the condensing pressure, the researchers suggest. “Thus, turbine exhaust pressure can be reduced to 0.05 bar and more power output can be obtained as compared to [an] in-land plant.”After passing through the condenser, the temperature of the condenser cooling water would fall to about 26C, readying it for desalination to provide fresh water and salt as a byproduct, they said.

While the approach is location-constrained—limited to plants in coastal areas—“India has [a] vast coastal boundary,” the researchers noted. “When compared to conventional inland plants, the electrical equivalent efficiency of the proposed system with deep sea water cooling increased by 27.7%. This clearly demonstrates the multiple advantages of the proposed system,” they said.

Sonal Patel is a POWER senior associate editor (@sonalcpatel@POWERmagazine).