Matlab Simulation of 10 MW Molten Salt Solar Power Tower ... · Matlab Simulation of 10 MW Molten Salt Solar Power Tower Plant in Aswan ... system is presented. ... with Simulink®

Noble International Journal of Scientific Research Vol. 1, No. 1, pp: 34-43, 2017

Published by Noble Academic Publisher URL: http://napublisher.org/?ic=journals&id=2

Open Access

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Matlab Simulation of 10 MW Molten Salt Solar Power Tower

Plant in Aswan

M. Qenawy*

*Mechanical Power Engineering Department, Faculty of Energy Engineering,

Aswan University, Aswan, Egypt

Abstract: In this paper, a simulation of a similar solar power plant as PS10 plant with a modified storage system is presented. The simulation study of this modified plant is conducted for determining the viability of

installing this plant in Aswan. The presented study, building, results, and analysis of the model plant are conducted

with Simulink tools in MATLAB program. The simulation results are presented by the first day of each season

during the year. This model will show how system behaviour is affected during solar transients in arid zones taking

into account solar variability throughout the day.

Keywords: Modified PS10 Plant, Solar Power Tower, CSP, Thermal Energy Storage, Simulation of Thermal Energy Storage System.

1. Introduction The increasing instability of fossil fuel costs has led the world in a quest for exploiting the free and

naturally available energy from the Sun to produce electric power. Solar Power Tower SPT Plants

behaves like a conventional thermal power plant, but uses solar energy instead of a fossil fuel as a heat

source for producing steam, Duffe and Beckman [1]. The principle is to concentrate the solar irradiation

using a configuration of mirrors to produce high temperature heat, Dunn [2]. It is an environmentally

friendly way of producing power. It need to high solar density and flatting lands as in Egypt.

PS10 plant, the commercial plant built worldwide located in Seville, Spain, is used as a

demonstrative model in order to estimate the relative advantage of installing such kind of power plant in

Aswan, Solucar Report [3]. The plant is calculated and analysed using the simple equations and heat

transfer relation. PS10 heliostat field is composed by 624 heliostats. Each heliostat is a mobile 121 m2

curved reflective surface mirror that concentrates solar radiation on a receiver placed on top of a 115m

tower, Osuna [4]. The average field efficiency of PS10 plant in Aswan is 67.47 %, Mustafa [5].

Molten salts are the only commercial storage medium nowadays for storing energy during extended

periods of time. The molten salt chosen was a nitrate salt that is composed of 40% KNO3 and 60%NaNO3,

Kearney [6]. The desired characteristics for molten salts are low vapour pressure, high density, low

chemical reactivity, moderate specific heat and low cost, Sohal [7]. Among the benefits of the molten salt

is its stability up around 600OC that is suitable for working at high solar density in Aswan (23.5

O Latitude

33O longitude).

Figure 1. Schematic Diagram of Two Tanks Molten Salts SPT Plant.

Noble International Journal of Scientific Research

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SPT plant generate electric power from sunlight by focusing concentrated solar radiation on a

thermal receiver mounted at the top of a tower. The HTF at minimuim operating temperature is pumped

from a cold storage tank through the receiver where it is heated to its maximuim operating temperature

and then on to a hot storage tank. When power is needed from the plant, the HTF is pumped to a steam

generating system (Heat Exchanger) that produces superheated steam for a conventional Rankinecycle

turbine/generator system. From the steam generator, HTF is returned to the cold storage tank where it is

stored and eventually reheated in the receiver, Cardozo [8]. Fig.1. is a schematic diagram of a simple two

tanks molten salts SPT plant.

The Simulation study of 10MW Molten Salts Solar Power Tower Using Control on Receiver Flow

Rate is conducted for Aswan, with local solar data, for determining the viability of installing a similar

project. This study will show how system behaviour is affected during solar transients in arid zones taking

into account solar variability throughout the day. The simulation taking 21th March as a reference day for

plant operation and it present the results in the first day of each season during the year. For the presented

study, building, results, and analysis of the plant was conducted in Simulink tools in MATLAB

programme. The reference plant, PS10, parameters are taken from literature in or from manufacturers

data.

The study takes many steps in order to make the proposed simulation. In this section, more

knowledge about PS10 plant, Heat Transfer Fluid HTF of the plant, are presented. Section 2 displays the

description of the plant on Simulink program. It also discusses the mathematical equations that used in the

plant subsystems. In section 3, Results are discussed. The results are presented and discussed during each

season during the year.

2. Model Description 2.1. Tower Receiver Subsystem

The receiver used for receiving sunlight from the heliostat field to raise the temperature of the

working fluid to the desired temperature. The receiver design has been optimized to absorb a maximum

amount of solar energy while reducing the heat losses due to convection and radiation. The molten salts, is

pumping from the cold storage tank by using electrical pump. The molten salts then enters the tower

receiver to heated from minimum operating temperature to a maximum operating temperature.

The design of that receiver allows it to rapidly change temperature without being damaged. The

formula which describes the tower receiver operation can be expressed in Equation 1, Cardozo [8].

( )

Figure 2. is presented the detailed model of the tower receiver subsystem which provides the

modeling based in Equation 1.

Figure 2. Tower Receivers Subsystem Designed with Simulink.

2.2. Storage Subsystem The storage system is consisted of a two heat reservoirs which are called hot and cold storage tanks.

They are externally insulated and constructed of stainless steel and carbon steel for the hot and cold

storage tanks, respectively. The design of the storage system is done by using dynamic differential


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equation for the heat transfer between the HTF and each tank, with energy balances on each tank.

Equation 2 describes the calculation of the temperatures reached during the operation of the plant in the

hot and cold storage tanks, Cardozo [8].

where M is the mass of each tank, Tin is the inlet tank temperature, Tout is the outlet tank temperature

and Ta is the ambient temperature, U is the global coefficient of heat transfer, and A the area of each tank.

Equation 3 is used for determine the mass balance of the storage tanks as a function of the inlet

mass flow rate and the outlet mass flow rate

, where tmax is the upper limit saturation of storage

tank, tmin is the lower saturation limit of the storage tank, Cardozo [8].

[

]

Hot storage tank is the main storage tank used in the storage system. Working fluid at its maximum

operating temperature is flows from the tower receiver to this tank. Now, we need to model and define the

hot storage tank subsystem. For this purpose, previous equations are applied to the hot storage tank and

defined with another subsystem in Simulink. Figure 3. represents the math operations for obtaining the

outlet temperature of the hot storage tank.

Figure 3. Hot Storage Tank Subsystem Designed with Simulink.

Cold storage tank is the complementing storage tank used in the storage system. It is very similar to

the hot storage tank in its operations, equations, and Simulink model. Working fluid flows from the heat

exchanger to the cold storage tank. Now, we also need to model and define the equations of the cold

storage tank subsystem that will describe the outer temperature of the molten salts. It can clearly shown in

Fig.4.

Figure 4. Cold Storage Tank Subsystem Designed with Simulink.


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2.3. Power Block Subsystem After the working fluid outlet from the hot storage tank, a heat exchanger between the HTF and

water constructed. The steam generator, consist of a shell-and-tube heat exchanger. Equation 4 describes

the heat amount required in the heat exchanger, Cardozo [8].

Another equation was used in order to calculate the power output released by the turbine Pele. It is a

function of the steam generator power , and the Rankine cycle efficiency Rk , Equation 5. Note that

the vapor cycle, which includes the steam generation, is not included in the scope of this work, Cardozo

[8].

Equations 4, 5 are presented in Figure 5. as another Simulink model in order to build the power

block subsystem.

Figure 5. Power Block Subsystem Designed with Simulink.

2.4. Control System The model of SPT plant can be built using MATLAB software tool called Simulink, being the

general view of this model presented in Figure 6.

Figure 6. Simulink Model of the SPT Plant.

Initially two equal mass flows are defined and they are assumed to be constant values, namely

.The mass flow is the molten salts flow rate that goes out of the hot storage tank and

passes through the steam generator. It provide steam in order to produce electrical power in the steam

turbine. It then continues flowing to the cold storage tank from the steam generator. The mass flow is

the molten salts flow rate that goes out of the cold storage tank into the tower receiver for warming up and

then continues towards the hot storage tank.


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3. Results and Discussions This section describes the theoretical results of the plant. As mention in the introduction subtitle, the

referance day of plant operation is 21th March and consedering the first day in each season as an indication

of whole year. The temperature analysis is presented in Figures 7, 8. and the behaviour of the storage

tanks for each seasion are shown in the other Figures. The simulation results show that, each storage tank

of model designed to accommodate about 1000 tons of molten salts which mean store of about 534m3 of

molten salts.

In Figure 7, 8, during the day light, the control system on the flow rate of molten salts to the

receiver make the temperature of the molten salts at the tower receiver outlet reached around its desired

temperature 565OC in addition to the cold storage tank outlet temperature around its desired temperature

290OC. this achieved during every day in the year. But the first day of plant operation has a specific

temperature change.

Figure 7. Outlet Temperature of the Tower Receiver, during 21

th, 22

th, 23

th March.

Figure 8. Outlet Temperature of CST, during 21

th, 22

th, 23

th March.

In Figure 9, operation of the two tanks during 21th, 22

th , 23

th march, At the beginning of operation,

hot and cold storage tanks are filling to their middle level [500Ton].

Figure 9. Operation of Hot and Cold Storage Tanks during 21

th, 22

th, 23

th March.


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In Figure 10, plant power during 21th, 22

th , 23

th March, the solar irradiation equations are plotted

and discussed at the beginning plant operation. The electrical output power of the model related to

available solar radiation in each day during the year is around 10MW.that happend as a result of the lack

in hot storage tank operating temperature. Following, Figure 11 to Figure 18 Show the operation of the

plant during the first three days of each season over the year (March-June-September-December).

Figure 10. Plant Power during 21

th, 22

th, 23

th March.

March


th, 30

th, 31

th March.


th, 30

th, 31

th March.

June


40


th, 22

th, 23

th June.


th, 22

th, 23

th June.

September


th, 22

th, 23

th September.


th, 22

th, 23

th September.

December


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th, 22

th, 23

th December.


th, 22

th, 23

th December.

4. Whole year It is important to apply the model to operate in the whole year, Figure 19 show the operation of the

hot and cold storage tank. It is noted that the cold storage tank filled with the molten salt the most time of

the year while the hot storage tank is empty the most time of the year. Figure 20 shows also the operation

of the hot and cold storage tank outlet temperature during the year. In Figure 21, the plant collected

power, the heat added in the heat exchanger, and the output electrical power are plotted.

Figure 19. Operation of Hot and Cold Storage Tanks during the Year.

Figure 20. Operation of Hot and Cold Storage Tanks Outlet Temperature during the Year.


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Figure 21. Plant Power during the Year.

5. Conclusions This study is a simulation analysis of installing 10MW solar power tower plant. The goal of this

paper is to successfully model and simulate the plant storage system in Aswan. The simulation illustrate

successfully the operation of the control system to benefit as much as possible from the irradiation with

easy storage process. It helped also in identifying the properties of the plant when operated in Aswan. The

simulation showed the benefits of installing the plant as it produce about 47GWh annually.That means the

average daily energy production is close to 130MWh which equivalent to 200% of what was produced by

PS10 plant.The simulation results presented may not be very useful in its current form but the study

developed can be used for research and future plant analysis and development.

Nomenclature CSP : Concentrated Solar Power

CST : Cold Storage Tank

HTF : Heat Transfer Fluid (Molten Salts)

HST : Hot Storage Tank

SPT : Solar Power Tower

receiver : Receiver Efficiency [92%]

Rk : Rankine Cycle Efficiency [30.7%]

: Tower Received Power [kW]

: Heliostat Reflected Power [kW]

: Mass flow rate in the receiver [kg/s]

Cp : Specific Heat [2660 J/kg K at 400Oc]

: Temperature of Receiver Outlet [565OC]

: Temperature of Receiver Inlet [290OC]

M : Accumulated Mass in each Tank [kg]

: Rate of Temperature Change [OC/s] : Mass Flow Rate to each Tank [kg/s] : Molten Salts Density [kg/m

3]

Tin : Tank Inlet Temperature [OC]

Tout : Tank Outlet Temperature [OC]

U : Overall Heat Transfer Coefficient [W/m2 k]

A : Tank Total Area [m2]

Ta : Tank Ambient Temperature [OC]

: Rate of Accumulated Mass Change [kg/s] tmin : Tank Minimuim Level [m

3]

tmax : Tank Maximium Level [m3]

: Inlet Mass Flow Rate to Tower Receiver [kg/s]

: Inlet Mass Flow Rate to Steam Generator[kg/s]

: Steam Generations Heat Exchange [kW]

Pele : Electrical Output Power [kW]

T4 : Heat Exchanger Inlet Temperature [565OC]

T5 : Heat Exchanger Outlet Temperature [290OC]


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Mh : Mass Accumulated in the HST [m3]

MC : Mass Accumulated in the CST [m3]

References [1] J. A. Duffe and W. A. Beckman, Solar engineering of thermal processes, solar energy laboratory,

3rd

ed. vol. 2. University of Wisconsin: Joha Wiley & Sons Publisher.

[2] R. Dunn, "A global review of concentrated solar power storage," in 48th AuSES Annual

Conference, Australian Solar Energy Society, 2010, pp. 1-10.

[3] Solucar Report, "PS10: a 11.0-MWe solar tower power plant with saturated steam receiver," pp.

1-13, 2004.

[4] R. Osuna, "PS10, Construction of a 11 mw solar thermal tower plant in seville, Spain, Solar

PACES, Solcar R&D, Sevilla, Spain," pp. 1-8, 2006.

[5] M. A. Mustafa, "Analytical study of an innovated solar power tower (PS10) in Aswan,"

International Journal of Energy Engineering, vol. 2, pp. 273-278, 2012.

[6] D. Kearney, "Assessment of a molten salt heat transfer fluid in a parabolic trough solar field," in

Proceedings of 11th Solar Paces International Symposium on Concentrating Solar Power and

Chemical Energy Technologies, ASME Publisher, 2002, pp. 1-20.

[7] M. S. Sohal, "Conceptual design of forced convection molten salt heat transfer testing loop, Idaho

energy national laboratory," pp. 6-14, 2010.

[8] F. R. Cardozo, "Concentrating solar power technologies using molten salts for storage and

production of energy, Integrated Master in Environmental Engineering, Fundacio CTM Centre

Tecnologic, Spain," pp. 44-66, 2012.

Documents

Matlab Simulation of 10 MW Molten Salt Solar Power Tower ... · Matlab Simulation of 10 MW Molten Salt Solar Power Tower Plant in Aswan ... system is presented. ... with Simulink®