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

Abstract

Listen

Translate article

One of the major uncertainties in the design of molten-salt solar receivers is the estimation of the lifetime because solar receivers have to withstand high temperature, thermal stress and corrosive-media in addition to daily star-up and shutdown. The first step to estimate the receiver damage and therefore, to monitor and manage the receiver life cycle, is to obtain properly the tube stresses under daily operating conditions. Whit this aim, we propose a straightforward low-computational cost procedure to determine the stresses under elastic-plastic regime. In addition, the stress relaxation due to visco-elastic behavior of the material, is also calculated. The analytical thermo-elastic, elastic-plastic and relaxation stress models for the high-nickel alloy Haynes 230 were verified against finite element simulations showing a good accuracy with a low-computational cost.For exemplification purposes, a reference operation day of a molten-salt solar receiver like Gemasolar is investigated. A receiver creep-fatigue damage assessment was developed for a flat aiming strategy. The results showed that the fatigue damage is 0.03% of the total damage. The average-field-receiver efficiency was 42.18% with a predicted lifetime higher than the expected. On the contrary, the receiver lifetime increases unnecessarily and the field-receiver efficiency drops to 26.25% when the receiver is operated limiting the stress as one third of the ultimate tensile strength (UTS/3). This limit results in a loss of revenues of around 250,000€ per month. Hence, the excessive level of conservatism produced by stress limit methods are not suitable for solar receivers due to the resulting economic penalties.