In thermoelectric power generation, only about 40% of the energy in the fuel is converted into electricity. In other words, the power plant operates at about 40% efficiency. The remainder of the energy is converted to low-grade waste heat that must be removed to maintain the power plant’s efficiency. Most power plants use water from nearby rivers, lakes, or the ocean for cooling. The water may pass directly over tubes containing the plant’s heated condenser water, and then be returned, warmer, to the original source, or it may be evaporated to carry off the heat in water vapor. In areas with limited water or under drought conditions, dry-cooling systems use air to remove heat from the plant’s condenser water. However, present dry-cooling technology reduces the power plant’s efficiency and requires costly equipment. With water supplies becoming increasingly strained in many areas, economical dry-cooling approaches that do not reduce the efficiency of power plans are critically needed. Innovative methods to allow cooling below the daytime ambient air temperature and improve heat exchange between air and the plant’s recirculating condenser water will provide the keys to ensuring the continued efficiency of power generation while decreasing the burden on water supplies.
Project Innovation + Advantages:
The Electric Power Research Institute (EPRI) and its partners will design, fabricate, and demonstrate an indirect dry-cooling system that features a rotating mesh heat exchanger with encapsulated phase-change materials (PCMs) such as paraffin, which can absorb and reject heat efficiently. The novel system can be used downstream from a water-cooled steam surface condenser to cool water to a temperature near ambient air temperature, eliminating the need for a cooling tower. The team’s design capitalizes on the high latent heat of the solid-to-liquid transition in the PCMs to provide an extremely effective way to lower the temperature of hot water exiting the condenser. The encapsulated PCMs are embedded in polymer tubes that form a porous, mesh-like structure. These modules are then mounted on a rotating system that continuously circulates the encapsulated PCMs from the hot water – where they absorb heat – into a dry section where ambient air passes by the encapsulated PCMs, causing the PCMs to solidify and reject heat to the atmosphere. The multidisciplinary team includes leading industry and academic partners that will provide technical and market assistance, and help build and test a 50 kWth prototype to demonstrate the technology’s commercial viability.
If successful, EPRI and its partners will develop an improved heat exchanger with up to four times the air-side heat transfer coefficient of conventional air-cooled condensers, enabling more efficient, cost-effective dry cooling at power plants.
Enhanced dry-cooling heat exchangers could enable power plants to maintain energy efficiency when water use is restricted.
The team’s system results in negligible net water use, and therefore eliminates the large need for local water resources for cooling and conserves water for other uses.
ERPI estimates that the cost and footprint of its system will be 50% less than air-cooled condensers on the market today.