VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD
Dynamic Modelling and Simulation of Linear Fresnel Solar Field based on Molten Salt Heat Transfer Fluid SolarPACES 2015 Cape Town, South Africa, 14th October 2015 Elina Hakkarainen, Matti Tähtinen
Content VTT Technical Research Centre of Finland Ltd. Background The scope of the work APROS Dynamic Simulation Software
Basic concept modelled and simulated Methodology Model setup in APROS
Results Simulation cases First results of selected cases
Conclusions and future work
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VTT Technical Research Centre of Finland Ltd. Largest multi-technological applied research organization in Northern Europe Applied research for needs arising from industry Customers are Finnish and international companies as well as public sector organizations Total staff over 2300 High focus in future low carbon energy systems
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Background Molten salts gaining much interest as viable HTF option Several advantageous features Already demonstrated HTF with line-focusing technologies
The scope of the work is to... Configure initial model for linear Fresnel solar field with molten salt as HTF in APROS;
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easy to scale, easy to connect
Check the proper functionality of the model and new HTF properties Check the critical points and define needs for new APROS components and features Demonstrate the feasibility of APROS to study dynamic behavior of CSP applications 19/10/2015
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Background: APROS Dynamic Simulation Software APROS is a software package for modelling and dynamic simulation Applied in the wide range of processes
Nuclear power plants Combustion power plants Pulp & Paper mills General heating and cooling processes Smart grids Large-scale solar power
Developed since 1986 by VTT and Fortum Users in 27 countries
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APROS features: Accurate process modelling with a set of predefined process components; one-to-one analogous with concrete devices and properly validated Sophisticated automation & instrumentation system modelling Electrical system modelling Where can be APROS used?
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Basic concept: Linear Fresnel solar field with molten salt as HTF Collector row composed of 9 collector components total length ~ 400 metres Vacuum tube receivers
Direct connection to two-tank storage system Operated at 510 ˚C and 280 ˚C
HTF: nitrate salt mixture Hitec 53% KNO3 + 40% NaNO2 + 7% NaNO3 Freezing point 142 ˚C Upper temperature limit 535 ˚C
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Steam generator required Superheated steam at 450 ˚C and 90 bar
Solar field over sized in order to produce constant power round the clock Simple PI-controller based control system Freeze protection an important issue 19/10/2015
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Methodology: Model setup in APROS Subsystems modelled:
Solar components: irradiation data Solar field Thermal energy storage system Steam generator Control system
Fluids properties of Hitec imported to the code by defining polynomial functions for properties as a function of temperature Homogeneous i.e. 3-equation flow model Phase change not possible 19/10/2015
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Methodology: Model setup in APROS Solar Components Solar Radiation module Calculates the solar position and further both the beam and diffusive irradiation on a horizontal surface at each time step
coordinates, current standard time, Linke turbidity factor, clear-sky index
solar position, beam and diff. irradiation on hor. surface
Solar Irradiation Processor module Calculates the angle at which the beam irradiation enters the tracking surface and further the total amount of dir. and diff. irradiation on the surface
tracking mode, orientation, collector tilt angle
dir. and diff. irradiation on tilted surface
Alternatively, real measured and forecasted data can be fed to solar field model COLLECTOR 19/10/2015
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Methodology: Model setup in APROS Solar field Collectors configured as User Components Includes calculation of both optical and thermal behavior Calculations carried out by analog components and signals Mass and heat flows simulated with normal process components Dimensioning as for any process component Simplifications: Only one collector row modelled → multiplication coefficients Homogeneous heat flux around the receiver tube 19/10/2015
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Methodology: Model setup in APROS Two-tank thermal energy storage Hot and cold storage tanks; 510 ˚C and 280 ˚C Specific energy capacity over storage 74.4 kWh/tsalt Simple model for two tanks configured Current APROS version unable to handle interface of own liquid fluid and gas Calculation based on mass- and energy balances Constant pressure Heat losses neglected Moderated temperature in the tank (at each calculation time step) Stored energy Storage inventory 19/10/2015
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Methodology: Model setup in APROS Steam generator i.e. heat exchanger (HE) train Thermal power of 17 MWth Superheated steam at 450 ˚C and 90 bar Consist of three separate heat exchangers Preheating, evaporation and superheating parts
Simple dimensioning according to general heat exchanger designing methods Standard counter-current heat exchangers from APROS Process Model Library used 19/10/2015
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Results: Simulation cases Simulation location: Aldiere, Granada, Spain 37°13′ 50.83″ North and 3°4′ 14.08″ West (Andasol 1)
Selected simulation cases: June 21st i.e. summer solstice March 21st i.e. spring equinox Full 24-hours i.e. one operational cycle
Assumptions: Clear-sky conditions Monthly mean TL factor and day time temperature North-South orientation
June 21st
March 21st
TL factor *
3.4
2.4
Ambient temperature [˚C] *
23.3
12.5
Number of collector rows
19
30
Field nominal thermal power [MWth]
45.2
47.7
* Ref. SoDa; JRC
Varying size of the solar field between cases → to produce constant power round the clock → optimum size for solar field and TES system not considered in this work 19/10/2015
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Results: Solar field Alternatively measured data can be fed to the model.
Direct horizontal irradiance (yellow) and theoretical DNI on tracking surface (red) on June (solid line) and March (dashed line).
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Molten salt outlet temperature on June (solid line) and March (dashed line).
Solar field thermal power on June (solid line) and March (dashed line).
June 21st
March 21st
Nominal thermal power [MW th]
45.2
47.7
Daily production [MWh]
403.3
408.4
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Results: TES system and steam generator
Daily variation in hot TES temperature and cold TES temperature on June (solid line) and March (dashed line).
Superheated steam temperature (red) and steam generator thermal power (green) on June (solid line) and March (dashed line).
Control system improvements and optimization. 19/10/2015
Hot tank salt mass (red) and cold tank salt mass (blue) on June (solid line) and March (dashed line).
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Conclusions and future work APROS is a very capable tool to handle highly dynamic processes such as solar field operations To study dynamic behavior Improve and optimize control systems Study and improve operation strategy
APROS could be applied in the field of O&M and trouble shooting as well Control system development; Model Predictive Control (MPC) New components can be developed according to user/customer needs in-house (e.g. thermal storage components) Easy connection (OPC) to other simulation/programming tools (e.g. Aspen, Simulink) 19/10/2015
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Acknowledgements This work was carried out in the project funded by the European Regional Development Fund and in the ComboCFB (Combination of Concentrated Solar Power with Circulating Fluidized Bed Power Plants) research project coordinated by VTT with funding from the Finnish Agency for Technology and
Innovation, Tekes.
Thank you for your attention!
Poster Session 2: F-02 “Comparison of Measured and Simulated Irradiation Data in Dynamic Process Simulations” By VTT & Vaisala
Elina Hakkarainen
[email protected] +358 406 486 799
VTT Technical Research Centre of Finland Ltd. www.vttresearch.com
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