Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS
Zulkarnain ABBAS1, Yong LI2(), Ruzhu WANG1
1. Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China 2. College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China
This paper aims to explore an efficient, cost-effective, and water-saving seasonal cold energy storage technique based on borehole heat exchangers to cool the condenser water in a 10 MW solar thermal power plant. The proposed seasonal cooling mechanism is designed for the areas under typical weather conditions to utilize the low ambient temperature during the winter season and to store cold energy. The main objective of this paper is to utilize the storage unit in the peak summer months to cool the condenser water and to replace the dry cooling system. Using the simulation platform transient system simulation program (TRNSYS), the borehole thermal energy storage (BTES) system model has been developed and the dynamic capacity of the system in the charging and discharging mode of cold energy for one-year operation is studied. The typical meteorological year (TMY) data of Dunhuang, Gansu province, in north-western China, is utilized to determine the lowest ambient temperature and operation time of the system to store cold energy. The proposed seasonal cooling system is capable of enhancing the efficiency of a solar thermal power plant up to 1.54% and 2.74% in comparison with the water-cooled condenser system and air-cooled condenser system respectively. The techno-economic assessment of the proposed technique also supports its integration with the condenser unit in the solar thermal power plant. This technique has also a great potential to save the water in desert areas.
. [J]. Frontiers in Energy, 2021, 15(2): 328-344.
Zulkarnain ABBAS, Yong LI, Ruzhu WANG. Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS. Front. Energy, 2021, 15(2): 328-344.
Thermal conductivity of vertical layer/((kg·(h·m·K)–1))
4.32
16
Flow rate in U pipes/(m·s–1)
0.5
17
Pump power/kW
37
19
Overall pump efficiency
0.6
20
Fluid specific heat/(kJ·(kg·K)–1)
4.19
21
Rated flow rate/(kg·h–1)
900
22
Insulation height fraction/m
0.5
23
Insulation thickness/m
0.0254
24
Insulation thermal conductivity/(W·(m·K)–1)
0.043
25
Average airtemperature/°C
9.57
Tab.1
Fig.6
Fig.7
Fig.8
Month
Inlet fluid temperature/°C
Air temperature/°C
Oct
0
–2
Nov
–5
–7
Dec
–6
–11
Jan
–9
–13
Feb
–5
–8
Mar
–1
–3
Tab.2
Fig.9
Fig.10
Fig.11
Fig.12
Fig.13
Fig.14
Fig.15
Fig.16
Fig.17
Rated parameters
Value
Rated flow/(m3·h–1)
400
Rated head/m
20
Rated efficiency/%
70
Motor power/kW
37
Tab.3
Fig.18
Cooling technique
Total electrical power for cooling/MW
Per megawatt electrical power for cooling
Water-cooled condenser at 137 MW power plant
2.056
0.015
Air-cooled condenser at 137 MW power plant
3.355
0.024
BTES system at 10 MW power plant
0.037
0.0037
Tab.4
Cooling technique
Total water consumption/(g·min−1)
Per megawatt water consumption /(g·min−1)
Water-cooled condenser at 137 MW power plant
77930
568.8
Water-cooled condenser with seasonal cooling at 10 MW power plant
1656.84
165.68
Tab.5
Parameters
Cost/$
Equipment cost
1004200
Borehole field cost
1062000
Total capital cost
2066200
Annual operating cost
5000
Annual maintenance cost
20662
Total annual cost
25662
LCOH/($·GJ–1)
10
Payback period
20–25 years
Tab.6
Fig.19
TES
Thermal energy storage
Qf
Total fluid flow rate/(kg·h–1)
STES
Seasonal thermal energy storage
β
Damping factor
BTES
Borehole thermal energy storage
Lp
Pipe length/m
CF
Specific heat capacity of the fluid
Tf
Fluid temperature
GSHP
Ground source heat pump
QF
Fluid flow rate/(kg·h–1)
V
Storage volume/m3
ql
Regional heat conduction heat flow
Tg
Global heat conduction temperature
qsf
Steady-state heat flow
Tl
Regional heat conduction temperature
r
Radial distance of buried pipes
Vk
Volume of grid k
Average temperature in grid k
Correction factor
Temperature of the grid (i, j)
C
Volumetric heat capaci/(J·(m3·K)–1)
Nb
Number of boreholes
Heat transfer coefficient
COP
Coefficient of performance
Cp
Specific heat capacity//(J·(kg·K)–1)
co
Before cooling
ρ
Density/(kg·m–3)
Ta
Ground temperature
Q(t)
Rate of heat injection/extraction
ce
End of cooling
Tfin
Inlet fluid temperature/K
ATES
Aquifer thermal energy storage
Tfout
Outlet fluid temperature/K
ΔT
Temperature difference/ K
Vf
Volumetric flow rate of fluid
A
Pipe cross-sectional area/m2
Q
Flow rate through the pipe/(m3·s–1)
λ
Friction coefficient
ξ
Minor loss coefficient
Qc
Total cold energy stored
W
Pump work required by system
q
Flow capacity
h
Differential head/head losses,
g
Gravitational acceleration
Cc
Capital cost/$
Cmt
Maintenance cost in a year/$
Cot
Operational cost in a year/$
Et
Energy delivered in year t/GJ
r
Discount rate
Np
Payback period/a
Cs
Total cost of equipment/$
QL
Total heat load/GJ
if
Electricity inflammation rate
CF
Cost of input electrical energy
d
Down payment
F
Annual solar fraction/%
Rt
Net cash flow
N
Total number of periods
t
Time of cash flow
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