Thermo-economic design of a load-flexible steam generator for solar power towers

The large-scale commercialization of solar power tower (SPT) plants is limited by high capital costs and reliability challenges, particularly in the steam generator system (SGS), where failures can cause extended outages and substantial economic losses. Enhancing SGS operational flexibility is also critical as power systems increasingly rely on dispatchable generation to complement variable renewables. This study presents the first comprehensive thermo-economic design of a coil-wound once-through steam generator (CWOTSG) for SPTs. Coil-wound heat exchangers (CWHEs) are well-suited for once-through operation, potentially allowing faster thermal ramp rates than conventional recirculating systems, and therefore enabling quicker start-ups and load transitions. CWHEs can incorporate multiple tubesheets, which reduce thermal stress and allow the heat exchanger to operate as a variable-area system by modulating active tubesheets, potentially allowing once-through operation at low minimum loads. The framework couples a finite-difference model of the evaporation process with a multi-stream analysis to assess flow maldistribution, while ensuring that the mechanical design adheres to TEMA and ASME standards. Optimal configurations are identified through total annual cost minimization via full-factorial enumeration. Results demonstrate low flow maldistribution, enabling accurate reduced-order 1D modelling. The TAC of conventional TEMA E/F forced-circulation designs is 37% below that of the proposed CWOTSG. However, including four tubesheets potentially improves structural reliability by reducing the tubesheet diameter by up to 80%, while turbulent once-through operation can be maintained down to 10% load by closing three tubesheets. These findings identify the CWOTSG as a promising reliable solution for enhancing operational flexibility in SPT plants.