Development of a Compact Direct Air to Carbon Dioxide Heat Exchanger

Supercritical carbon dioxide (sCO2) power cycles offer breakthrough advantages in thermal to electric power conversion, including higher thermodynamic efficiency, lower capital, operation and maintenance cost and reduced system footprints when compared against both traditional and advanced steam Rankine cycles. The closed loop nature of these cycles requires heat rejection of low-grade heat. Historically, locally available water sources or cooling towers were the most common medium for heat rejection, as they represent a high capacity, low temperature heat sink that provides favorable thermodynamic performance. However economic and environmental concerns have limited the use of water cooling in new power plants. Because of this, air cooling can offer distinct advantages over water cooled systems. Current state-of-the-art technology for air cooled heat exchangers consist of two primary methods of construction, both circulating CO2 directly to several banks of fin-fan heat exchangers. These banks consist of multiple rows of finned tubes with air forced across the tube banks by electrically driven fans. The tube banks can be either flat or V-shaped. Because air has much lower density and heat capacity than water, these heat exchangers tend to take up a large amount of real estate and require large parasitic loads to operate the fans. Effective, small footprint, low-fan power air cooled heat exchangers have the potential to accelerate the adoption of sCO2 power cycles. In this program, Echogen will work with Pacific Northwest National Laboratory (PNNL) to baseline performance and cost targets for advanced air cooled heat exchangers, provide conceptual designs based on the MHx technology developed by PNNL, design the test configuration and hardware required for air cooled heat exchanger evaluation and conduct testing on conventional air coolers to provide baseline performance data to be used in Phase II to evaluate a prototype MHx. This proposal presents a vital advancement to state-of-the-art sCO2 cycles via “dry cooling” using advanced air-cooled heat exchanger technology. This advancement will increase sCO2 cycle flexibility, minimizing impact on water usage and local ecosystems, and maximizing the potential for improving energy usage across numerous U.S. industry markets.