Comparison of Shell and Tube Heat Exchangers for CO2 and CO2+SiCl4 Mixtures Transcritical Cycles

Abstract

Concentrated solar power (CSP) plants have great potential for clean energy production, but their electricity cost is higher than that of noncontrollable renewable energy sources. The main ways to lower the electricity cost are equipment cost reduction and plant efficiency increase. Looking at the power unit, the closed supercritical CO₂ (sCO₂) cycles offer the efficiency advantage over both the steam Rankine and helium Brayton cycles at high turbine inlet temperatures. Further improvement could be achieved by increasing the critical temperatures using mixtures, allowing condensation at temperatures typical for air-cooled condensers. The sCO₂ and CO₂ mixture cycles are significantly affected by the performance of the recuperative system and require high pressures (comparable to steam cycles). An increase in efficiency compensates for higher complexity in the design and construction of the plant, according to the authors. High thermal power together with high pressures and temperatures demand customized CO₂ heat exchanger designs, which makes them a major part of power cycle specific cost. This paper provides a robust technological solution for the implementation of the above cycles in an industrial setup based on shell-and-tube heat exchangers. Based on the thermohydraulic and mechanical design of EMbaffle® Technology, heat exchangers weight reduction can be quantified in the range of 30 to 60% depending on the application, with additional advantages in terms of logistics and installation (footprint, foundations, etc…). Using the CO₂+SiCl₄ mixture instead of pure sCO₂ leads to a lower weight of primary and high-temperature heat exchangers, while the weight of low-temperature heat exchanger increases.