1. Recuperator pinch point
GIT
Dual Loop Line-Focusing Solar Power Plants with Supercritical Brayton Power cycles Luis Coco Enríquez, Javier Muñoz-Antón, José M. Martínez-Val Grupo de Investigaciones Termoenergéticas (GIT), ETSII-UPM
Concentrated Solar Power plants (CSP) with Dual Loop Solar Field (SF) are being studied since 2012 [1] for gaining the synergies between thermal oils and molten salt properties as Heat Transfer Fluids (HTF). The primary loop with thermal oil (Dowtherm A), for heating the Balance Of Plant working fluid from ~300ºC up to ~400ºC, and a secondary loop with Solar Salt (60% NaNO3, 40% KNO3) as HTF, for boosting the working fluid temperature from ~400ºC up to 550ºC. The CSP Dual Loop state of the art technology includes Rankine power cycles [2, 3, 4] . The integration between a Dual Loop SF, with linear solar collectors, Parabolic Troughs (PTC) or Linear Fresnel (LF) and a Brayton power cycles is the main innovation in this paper for increasing gross energy efficiency up to 44.4%. In comparison with 41.8% gross efficiency in the state of the art Dual Loop solar power plants with Rankine cycles.
As a secondary conclusion deducted we confirmed the Single loop SF with Dowtherm A as HTF, and a s-CO2 Brayton power cycle is the most cost competitive technical solution due to low cost material and not required heat tracing for the thermal oil.
Configuration 1: Line-Focusing solar power plant with a Simple Brayton power cycle with ReHeating and two Single-Loop SF with Solar Salt (Reference) or Dowtherm A as HTF.
Configuration 2: Line-Focusing solar power plant with a Simple Brayton power cycle with ReHeating and a Dual Loop Main SF with Dowtherm A and Solar Salt as HTF, and a Single Loop ReHeating SF with Solar Salt as HTF.
Configuration 3: Line-Focusing solar power plant with a Simple Brayton power cycle with ReHeating and a Dual Loop Main and Dual Loop ReHeating SF with Dowtherm A and Solar Salt as HTF.
Simulations Results, Recuperator fixed UA = 5000 kW/K
s-CO2 Simple Brayton with Recuperation and Reheating
Without ∆P in HXs
With ∆P in HXs
Config. SF
TIT (ºC)
Main
SF HTF
ReHeating SF HTF
Net Effic. (%)
Recuperator pinch point
(ºC)
Net Effic.
(%) 1
400
Solar Salt
36.05
3.7
35.48
4.089
DowTherm A
3.683
35.35
4.127 3
450
DowTherm A Solar Salt
38.67
3.073
37.94
3.585 2
38.7
38.15
3.436
38.75
38.22
3.394
500
41.17
2.621
40.59
3.037
41.2
2.618
40.67
2.949
550
43.42
2.314
42.84
2.688
43.44
42.93
2.613
References:
[1] Lang C, Cuthbert J. Evaluation of dual loop design for parabolic trough. 18th SolarPaces Conference, Marrakech, Morocco; 2012.
[2] Joseph R. Shinners. Analysis of Dual Loop Parabolic Trough Concentrating Solar Power Plants. University of Wisconsin-Madison (2014).
[3] A.K. Vogel, H. Reilinga, T.P. Fluria W.J. Platzera. High temperatures in line focusing systems: Dual loop cycle efficiency and heat losses. Energy Procedia 69 (2015) 1461 – 1470.
[4] Qibin Liu, Zhang Bai, Jie Sun a, Yuejun Yan, Zhichao Gao, Hongguang Jin. Thermodynamics investigation of a solar power system integrated oil and molten salt as heat transfer fluids. Applied Thermal Engineering 93 (2016) 967–977.