4 SUPERCRITICAL CO₂ While the steam cycle has dominated power generation for modern history, CO2 in a supercritical state, has advantageous physical properties that make it behave close to a liquid – allowing the compressor to act closer to a pump – but has the characteristics of a gas in terms of its thermodynamics offering advantages over steam. The benefits of sCO2 power systems include higher efficiencies, reduced emissions from less fuel use, compact turbomachinery, reduced plant size, rapid response to load transients, reduced water use, heat source application flexibility, and overall better potential economics. Given these potential benefits, the use of supercritical carbon dioxide was recognised and first explored in the 1950s. However, limitations in materials and equipment, including the shell and tube heat exchangers in use at the time, curbed the thermal performance and stalled its development. Decades later in 1985, the printed circuit heat exchanger (PCHE) was developed which enabled compact, efficient, and cost-effective heat transfer at the higher temperatures and pressures associated with sCO2 cycles. PCHE’s consist of flat metal plates in which fluid flow channels are chemically etched. The etched plates are stacked with plates of alternating hot and cold flow channels and are diffusion bonded together to make a strong heat exchanger block with a large heat transfer surface area. Initially, while PCHE’s had helped to enable the use of supercritical carbon dioxide in power conversion cycles experiments, it was still limited to a relatively small scale ranging from a few kilowatts to a few hundred of kilowatts. For targeted industrial-scale applications, something on the megawatt scale was required, and when the PCHE technology became available and proven at commercial scales in Oil and Gas it supported cost effective sCO2-based power plants and contributed to the decision to proceed with the 10 MWe STEP Demo project. Image 2 – The Heatric “HTR” (High Temperature Recuperator) PCHE at the Heatric manufacturing facility in Poole, UK before shipment. Image 3 – The Heatric “LTR” (Low Temperature Recuperator) PCHE awaiting installation at the 10 MWe STEP Demo project in San Antonio, Texas.
RkJQdWJsaXNoZXIy MTQ4NTgyMQ==