Calculating molten-salt central-receiver lifetime under creep-fatigue damage

Assessment of the time resolution used to estimate the central solar receiver lifetime

“…It is based on the separation of the temperature profile as the addition of the circumferential and radial components, allowing the superimposition of the thermal stresses resulting from both gradients, and, opposite to previously existing methodologies, such as the ones employed in the work of Conroy et al [14] and Logie et al [46], it considers the temperature dependence of the material properties, which is critical for accurate lifetime calculations. For example, if temperature independent material properties are considered for the thermal stress analysis, the stress may be underestimated up to 20% at the tube crown [17]. That deviation translates into a considerable error in the creep rupture time: in the specific case of Haynes 230 material, it means a creep rupture time 77% lower than the predicted using temperature independent material properties [17].…”

“…For example, if temperature independent material properties are considered for the thermal stress analysis, the stress may be underestimated up to 20% at the tube crown [17]. That deviation translates into a considerable error in the creep rupture time: in the specific case of Haynes 230 material, it means a creep rupture time 77% lower than the predicted using temperature independent material properties [17]. On the other hand, the mechanical restrictions of the receiver tubes, set to avoid their excessive bending -which could cause collisions between adjacent tubes and the appearance of hot spots-, are also taken into account.…”

“…Subsequently, the analytical lifetime model employed, developed by González-Gómez et al [17], is based on these elastic stresses and strains to give out the elastic-plastic ones. This model also considers the stress relaxation phenomenon, which occurs during hold times under high temperatures and stresses and can develop during a certain stabilization time; this is so even with the characteristic cyclic operation of this kind of technology, suffering from daily start-ups and shutdowns, as long as the stress reset limit is not surpassed.…”

“…However, elastic stresses were considered for the creep damage, and the stress reset disregarded. More recently, González-Gómez et al [17] followed the ASME B&PV Section III: Subsection NH to study the lifetime of a molten salt SPT receiver considering 60-minute time intervals during the clean spring equinox design day. They regarded the plastic deformations of the tubes and the stress relaxation effect, paramount to avoid the underestimation of the receiver lifetime; yet, the aiming strategy of the heliostat field was not modified during the operation, which penalizes the receiver thermal production rates.…”

“…In this work, the AFD is set not only depending on the film temperature of the tubes, T film, in order to avoid an excessive corrosion, but a new parameter is regarded as well for that end: the stress reset limit [32], which determines if the global stress relaxation is achieved. In existing literature dealing with CSP lifetime analysis, the stress reset limit was not taken into account, either because the stress relaxation effects of the material, which are essential to avoid the receiver lifetime excessive underestimation [17], were disregarded (an issue present in the majority of the works), or because the aiming strategy selected was too conservative, assuring the receiver endurance but penalizing the power production since the receiver would operate with an intercepted heat flux way below the AFD [17]. The heliostat field and the receiver are two of the most expensive subsystems [33], which justifies the need of trying to maximize their profitability while ensuring their safe operation in the most accurate way.…”