Lifetime analysis of the steam generator of a solar tower plant

Abstract

Solar tower plants are pushed to operate with fast start-ups and/or load changes to increase their dispatchability and competitiveness. However, this operation mode decreases the lifetime on components like the steam generator due to fatigue damage. Moreover, the high operating temperatures typical of solar tower plants also lead to creep damage, which it is combined with fatigue. Both damage mechanisms may lead to a dramatic reduction of the steam generator lifetime, compromising the power plant economic viability.In this work the lifetime of the steam generator of a solar tower plant is investigated. For that purpose, an elastic-plastic approach is used to consider the material cyclic hardening. The results show that the steam generator formed by shell-and-tube heat exchangers can operate during 25 years with temperature change rates up to 150 °C/h, assuming 300 start-ups per year. The most critical point is the superheater head-nozzle junction for both intermittent and continuous operation regimes. An optimization of the superheater head thickness is performed to maximize its lifetime in both regimes. Finally, it can be concluded that temperature change rates higher than 150 °C/h may require a different design of the superheater head and/or a material with better creep-fatigue properties.