Thermal and mechanical analysis of a sodium-cooled solar receiver operating under a novel heliostat aiming point strategy

Abstract

The nature in which a solar receiver in a concentrated solar power plant interacts with an accompanying heliostat field plays a significant role in plant performance and economics. An appropriate heat flux distribution should help deliver maximum receiver thermal performance, while minimising mechanical damage – thereby maximising power production and reducing costs. The current work presents an investigation into the thermal performance and mechanical reliability of a sodium-cooled solar receiver operating under heat flux profiles generated by a novel heliostat aiming strategy. A modification of the HFLCAL model is used to generate heat flux profiles for individual heliostats in a representative plant, and simulated annealing optimisation techniques are used to produce a novel heliostat aiming strategy. The importance of giving consideration to receiver limitations under non-uniform thermal boundary conditions in the development of a heliostat aiming strategy is demonstrated in this study, with mathematical optical, thermal, and mechanical models used to complete the analysis. An investigation has been conducted for a point-in-time resulting in maximum thermal loading conditions, with theoretical modelling techniques used to calculate receiver tube temperatures for aiming strategy yielded heat flux profiles, thereby allowing for the determination of heat losses and mechanical reliability through creep-fatigue damage. Results show that the simulated annealing algorithm can significantly improve heat flux homogeneity on the receiver, potentially reducing peak heat flux to less than 10% that of a single aiming point strategy, given an appropriate spillage allowance and aiming point grid size. A satisfactory configuration of spillage allowance and aiming grid size exists so as to supply maximum power to the receiver, while uniformly distributing the incident heat flux in order to meet mechanical reliability requirements. Based on the receiver design and conditions simulated in the analysis, a grid constructed of more than 81 aiming points (receiver area coverage of 32.7%), and an additional spillage allowance of 10% allows the receiver to deliver maximum power output while retaining mechanical durability through a 30 year plant life cycle.