A MOPSO-based design optimization on molten salt steam generator forced circulation system under off-design conditions

The concentrating solar power (CSP) technologies have been demonstrated their effectiveness in providing ancillary services for peak regulation in power systems with high penetration of renewable energy. Investigating control mechanisms of a forced circulation mode applied in the steam generator, which a shell-and-tube heat exchanger, in the CSP plant is imperative for swift adaptation to its off-design operating conditions. This study aims to develop a predictive model for the hydrodynamics of a molten salt steam generator in a forced circulation mode, integrating heat transfer and phase change through the lumped parameter method. Additionally, a solution approach is proposed based on multi-objective particle swarm optimization (MOPSO) to achieve thermal-economic optimization designs of the steam generator under varying off-design conditions. Optimization analyses are conducted separately for the constant load and the off-design conditions, considering variables such as molten salt flow rate, steam-water circulation flow rate, number of baffles, and tube diameter of the heat exchanger. The results reveal that during the prolonged operation at low evaporation rates, employing an evaporator with more baffles and a larger tube diameter of 20 mm leads to favorable outcomes. Conversely, meticulous design considerations are imperative when planning for sustained high evaporation rates due to the significant impact of the number of baffles on both efficiency and economic costs. At a load of 215 t/h, the adding of two baffles results in an approximate increase of $20 million in operational costs by nearly and an improvement in efficiency by 0.01. Additionally, a fitting formula is provided to offer recommendations on optimal mass flow rates that maximize effectiveness and minimize economic costs for varying evaporation demands under off-design conditions, thereby assisting engineers in optimizing peak regulation operations.