Performance investigation of the solar power tower driven combined cascade supercritical CO2 cycle and organic Rankine cycle using HFO fluids

ABSTRACT

Current study examined the effect of solar power tower (SPT) design parameters (solar emittance, concentration ratio and heat transfer fluid velocity, solar irradiation) on SPT-integrated combined cascade sCO₂ (CSCO₂) cycle and organic Rankine cycle (ORC) using ultra-low global warming potential (GWP) hydro fluoro olefins (HFO) fluids. Exergy efficiency, thermal efficiency and net output power were considered as performance parameters. A computational technique was used for the analysis. It was investigated that thermal and exergy efficiencies of the standalone (SPT+ CSCO₂) cycle improved by 2.36% and 2.41%, respectively, by the incorporation of the ORC as bottoming cycle. Highest exergy efficiency, thermal efficiency and net output power were increased with solar irradiation, concentration ratio, heat transfer fluid velocity while decreased with solar emittance. Highest performance were found with R1224yd(E) while lowest with R1234yf among other considered low GWP fluids at current input conditions.

KEYWORDS:

• Thermodynamic analysis
• solar power tower
• cascade sCO₂ cycle
• organic rankine cycle
• HFO and low GWP fluids

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability Statement

There is no raw data associated with this study.

Nomenclature

${\mathrm{A}}_{\mathrm{h}}$	=	Single heliostat area (m2)
Ė	=	Exergy rate (kW)
${\dot{\mathrm{Q}}}_{\mathrm{h}}$	=	Actual solar heat received by heliostat field (kW)
$\mathrm{E}\dot{\mathrm{D}}$	=	Exergy destruction rate (kW)
${\dot{\mathrm{Q}}}_{\mathrm{l}\mathrm{o}\mathrm{s}\mathrm{s},\mathrm{r}}$	=	Heat loss from the receiver (kW)
$\mathrm{E}\dot{\mathrm{D}}$	=	Solar exergy inlet to combined cycle (kW)
fview	=	Receiver view factor
Cp	=	Specific heat at constant pressure (kJ/kg-K)
DNI	=	Direct normal irradiation (W/m2)
h	=	Specific enthalpy (kJ/kg)
${\mathrm{h}}_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{v}}$	=	Convective heat loss coefficient (W/ m2-K)
$\dot{\mathrm{m}}$	=	Mass flow rate (kg/s)
${\mathrm{N}}_{\mathrm{h}}$	=	Number of heliostat
$\dot{\mathrm{Q}}$	=	Heat rate in (kW)
${\dot{\mathrm{Q}}}_{\mathrm{r}}$	=	Heat received by central receiver (kW)
${\dot{\mathrm{Q}}}_{\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{a}\mathrm{r}}$	=	Solar heat received by heliostat field (kW)
s	=	Specific entropy (kJ/kg-K)
sCO2	=	Supercritical carbon dioxide
${\mathrm{T}}_{\mathrm{R}}$	=	Surface temperature of receiver (K)
$\dot{\mathrm{W}}$	=	Power (kW)
T	=	Temperature (K)
${\eta }_{\mathrm{e}\mathrm{x}}$	=	Exergy efficiency
${\eta }_{\mathrm{h}}$	=	Heliostat efficiency
${\eta }_{\mathrm{r}}$	=	Receiver thermal efficiency
${\eta }_{\mathrm{t}\mathrm{h}}$	=	Thermal efficiency

Abbreviations

CFC	=	Chlorofluorocarbon
Comp	=	compressor
Cond	=	Condenser
CR	=	Concentration ratio
CSCO2	=	Cascade sCO2
GWP	=	Global warming potential
HFO	=	Hydro fluoro olefins
HFC	=	Hydro fluoro carbon
HEX2	=	Heat exchanger −2
HTR	=	High temperature recuperator
LTR	=	Low temperature recuperator
ORC	=	Organic Rankine cycle
HEX1	=	Heat exchanger −1
OT	=	ORC turbine
SPT	=	Solar power tower
Greek letters	=
δ	=	change in property
ζ	=	thermal emittance
η	=	efficiency
α	=	Solar absorbance
σ	=	Stephen Boltzmann constant (W/m)
ε	=	effectiveness
Subscripts	=
0	=	environmental conditions
b	=	boiling
c	=	critical
e	=	exit
h	=	heliostat
i	=	inlet
ms	=	molten salt
r	=	receiver

Additional information

Notes on contributors

Yunis Khan

Dr. Yunis Khan did his Ph.D in 2021 from Delhi Technological University India. His area of research is solar energy, trigeneration, cogeneration, refrigeration and waste heat recovery.

Radhey Shyam Mishra

Dr. Radhey Shyam Mishra is the professor in mechanical engineering department in Delhi Technological University India. His research area is solar energy, Thermal power plant, and refrigeration.