A procedure to predict solar receiver damage during transient conditions

Abstract

The successful deployment of solar-power-towers lies in the reliable design of solar receivers, assuring the lifetime under high heat flux and cloud passages. Two main damage mechanisms appear during central-receiver operation: creep, during hold times at high temperatures and stresses, and fatigue, caused by transient operation. This work aims to determine the extent of each damage on a Haynes 230 receiver. It is analyzed using transient DNI of a whole year, controlling the operation to guarantee the receiver preheat and minimize the start-ups. The molten-salt flow-rate during cloud passages or hazy days remains as the clear-sky scheduled one, to avoid tube overheat, preventing salt degradation and stress reset, when the clouds cleared.The results show that creep dominates, with a minimum share of 73.8% for the transient case. High creep is motivated by the long operating (6 h per day on average), mostly at high DNI, while the low number of average start-ups per day (1.4) do not increase much the fatigue, barely affected by small transients. The use of clear-sky, instead of the transient DNI, constitutes a conservative estimation, with the creep greatly increasing, showing a minimum share of 82%. Consequently, the predicted lifetime is lower, going from 45 years to 27.8. Intermediate mass-flow control modes fall in-between them. Clustering the days according to their DNI features shows that the high-energy days, with high creep, are the most common, highlighting the creep interest and that the fatigue can be estimated taking only the strain range produced by the start-up.