Off-design performance analysis of combined CSP power and direct oxy-combustion supercritical carbon dioxide cycles

Abstract

The solar power tower (SPT) has the potential to achieve high efficiency and large-scale power production due to its high achievable temperatures. However, thermal energy storage (TES) is required to solve the intermittency problem of the solar energy and to provide a dispatchable power production according to the power demand profile. Critical technical problems still exist in the TES systems including the high-temperature corrosion, expensive materials, temperature swing, and large size. Therefore, newly improvement approach is proposed by integrating the SPT system with direct oxy-combusted (DOC) sCO2 power cycle to enhance the overall efficiency and eliminate the need for the TES. In this paper, the off-design performance of two novel power cycle configurations that integrate SPT and DOC systems is investigated. The SPT system works as a preheater for the DOC system in the first configuration (S3) while works as a reheater in the second one (S4). The off-design analysis approach first verified and validated against published results and the results shows good agreement with error less than 1%. Also, the off-design analysis of these cycles is performed based on real ambient conditions and power demand profiles for two typical days in Qatar. The results show that the efficiency of S4 is considerably higher than S3, but S3 show better flexibility with the variation of the power demand profile. At 76% of the full load, the cycle efficiency is reduced by 5.64% in S4 and by 4.35% in S3. Moreover, at the design point conditions, the increase of the CIT reduces the cycle efficiency (by 8%) but also reduces the amount of the consumed fuel (by 15.8%). On the other hand, the increase of the TIT improves the cycle efficiency (by 8.6%) but also increases the consumed fuel by (57%).