Concentrated Solar Power plant piping optimization for gaseous Heat Transfer Fluid
CHALLENGE - Airlight Energy SA builds its CSP parabolic collectors by adopting huge fiber reinforced concrete troughs on which pneumatic mirrors are mounted and protected by ETFE foils. A physical model of a peripheral portion of a CSP plant based on this technology was developed, implementing temperature dependent properties for the gaseous HTF, namely air. However, air implies greater duct sections thus the piping insulation strategy should be carefully analyzed to limit structure weight without losing effectiveness.
SOLUTION - The original physical model was exploited in a first optimization approach by means of optimization software modeFRONTIER, which embedded a set of optimization algorithms. The multi-objective evolutionary algorithm MOGA was chosen, and the optimization was set defining a list of goals to be minimized at the same time: pressure drop, heat losses, energy required to warm up the plant from a black start and investment cost. In order to help the convergence, all indices were merged into a synthetic one, the total cost. This procedure led to a Pareto Front, with designs characterized by the same value of the objective function but in which with no further improvements were seen without a worsening of at least one of the other targets (i.e. heat losses and transient energy). A further step involved an annual simulation of the plant which included the solar power radiation variation and the thermal energy storage models. MOGA and MOPSO algorithms were employed to maximize the total revenues of the plant.
BENEFITS - Results show that the diameter reduction from the TES towards the feeding line and the cold branches, and conversely its increase from hot branches back to TES, is a common feature in all the best designs in both approaches. In addition, in the first optimum design the insulation of all the piping line is characterized by the lowest number of radiation shields combined with the largest air gaps yet in the second approach, the optimum insulating structure includes a higher number of shields, with air gaps large as in the previous solution.