Cost-based design optimization of the heat exchangers in a parabolic trough power plant

Abstract

This paper addresses two important concerns of the design of steam generators of parabolic trough power plants: cost minimization and component reliability. A thorough economic analysis of the heat exchangers of the steam generator and oil-to-salt heat exchangers of a 50 MWe parabolic trough power plant is presented. The heat exchanger design is realized following TEMA standards and optimized using a genetic algorithm. Two design strategies are compared: the minimization of the total heat transfer area and the minimization of the total annualized cost. It is seen that the second approach provides substantial savings over the lifetime of the plant.The economic analysis reveals a global optimum with an outlet temperature of the heat transfer fluid of 293 ºC and an evaporator pinch point of 4.85 ºC. The best design of the steam generator consists of a TEMA-H shell superheater and preheater and a TEMA-F shell reheater. The best design of the oil-to-salt heat exchangers includes six TEMA-F shell heat exchangers in series, with a log mean temperature difference of 7ºC and the molten salt on the shell-side. Lastly, a TEMA-X recirculation evaporator is proposed with a considerably reduced wall thickness when compared to a kettle evaporator.

Dynamic performance and stress analysis of the steam generator of parabolic trough solar power plants

“…The SG consists of two parallel trains each one formed by the superheater (SH), reheater (RH), and evaporator (EV) and preheater (PH), respectively. The thermal oil flows on the shell-side in SH, RH and PH whereas the high-pressure water/steam flows on the tube-side [12]. On the contrary, in the EV, the low pressure oil is situated on the tube-side and the water/steam flows on the shell-side [12].…”

“…The low-pressure turbine steam outlet is sent to the condenser where heat is rejected. This configuration attains a power block efficiency of 37.5% [12]. The SG consists of two parallel trains each one formed by the superheater (SH), reheater (RH), and evaporator (EV) and preheater (PH), respectively.…”

“…The thermal oil flows on the shell-side in SH, RH and PH whereas the high-pressure water/steam flows on the tube-side [12]. On the contrary, in the EV, the low pressure oil is situated on the tube-side and the water/steam flows on the shell-side [12]. The PH and SH consist of TEMA H shell type heat exchangers.…”

“…The kettle evaporator design was obtained for Ref. [12]. The dynamic model for kettle was developed using a simplified second-order model based on Equations 4, 5 and 6.…”

“…Normally the SG of CSP plants consists of shell-and-tube heat exchangers as was shown in Refs. [12,13]. Extensively used methods for the heat exchanger design are TEMA standards [14] and ASME Section VIII Div 1 [15], which consider continuous operation and do not consider fatigue due to cyclic operation [16].…”