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:
TDA Research will develop a water recovery system that extracts and condenses 64% of the water vapor produced by the gas turbine in a natural gas combined cycle’s (NGCC) power plant and stores this water for use in evaporative cooling. The system will provide supplemental cooling to NGCC power plants in which the combustion process – burning the natural gas to produce heat – produces a significant quantity of water vapor that is typically discharged to the atmosphere. First, a direct-contact condensation cycle will recover 27% of water vapor from the flue gas. To increase the amount of water recovered, a desiccant, which is a substance that attracts water, will be used to absorb an additional 37% of the water vapor. TDA’s desiccant cycle utilizes the waste heat in the exhaust to regenerate the desiccant for reuse. This water recovery cycle would occur during cooler months when the water from combustion is easier to capture. Much of the water collected during this period will then be stored in an adjacent lake and saved for use during hotter summer months when evaporative cooling offers the maximum benefit to improve power plant efficiency. The project team estimates that its technology can reduce the performance penalty of a dry-cooling system by 30% compared to wet cooling. Moreover, the team is designing the system to use low-cost materials, which reduces capital costs.
If successful, TDA and its team members will develop a novel water recovery system that reduces water consumption for power plant cooling by capturing flue gas condensate and storing this water for use in evaporative cooling.
Power plants can maintain energy efficiency by using the team’s technology, instead of using separate water sources for cooling when water use is restricted.
The team’s system could reduce water usage for evaporative cooling on hot days, which helps conserve water for other uses.
TDA will use low-cost materials for its system, helping to reduce the cost of dry cooling.