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Feasibility study for the four pilot locations
This publication has been produced with the �inancial assistanceof the European Union under the ENPI CBC Mediterranean Sea Basin Programme
DisclaimerThis document has been produced with the �inancial assistance of the European Union under the ENPI CBC Mediterranean Sea Basin Programme. The contents of this document are under the sole responsibility of STS-Med Consortium and can under no circumstances be regarded as re�lecting the position of the European Union or of the Programme’s management structures.The total budget of STS-Med project is 4.953.513 Euro and it is �inanced for an amount of 4.458.162 Euro by the European Union through the ENPI CBC Mediterranean Sea Basin Programme (www.enpicbcmed.eu).
The ProgrammeThe 2007-2013 ENPI CBC Mediterranean Sea Basin Programme is a multilateral Cross-Border Cooperation initiative funded by the European Neighbourhood and Partnership Instrument (ENPI). The Programme objective is to promote the sustainable and harmonious cooperation process at the Mediterranean Basin level by dealing with the common challenges and enhancing its endogenous potential. It �inances cooperation projects as a contribution to the economic, social, environmental and cultural development of the Mediterranean region. The following 14 countries participate in the Programme: Cyprus, Egypt, France, Greece, Israel, Italy, Jordan, Lebanon, Malta, Palestinian Authority, Portugal, Spain, Syria, Tunisia. The Joint Managing Authority (JMA) is the Autonomous Region of Sardinia (Italy). Of�icial Programme languages are Arabic, English, French and Greek.Launched in May 2011, the strategic call focused six topics chosen by the Joint Monitoring Committee based on their potential for the development of cooperation in the Mediterranean area. These are: agro-food industry, sustainable tourism, integrated coastal zone management, water management, waste treatment and recycling, solar energy. Out of 300 proposals presented, 19 projects were approved for funding. Total value of these operations is € 82.5 million (€ 74.1 million ENPI contribution).
The European UnionThe European Union is made up of 28 Member States who have decided to gradually link together their know-how, resources and destinies. Together, during a period of enlargement of 50 years, they have built a zone of stability, democracy and sustainable development whilst maintaining cultural diversity, tolerance and individual freedoms. The European Union is committed to sharing its achievements and its values with countries and peoples beyond its borders.
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STS-Med Small scale thermal solar district units for Mediterranean communities Ref. I-A/2.3/174
Feasibility study for the four pilot locations issued by ENEA - Italian National Agency for New technologies, Energy and Sustainable Economic Development December 2015
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Contact person for this report
Dr. Alberto Giaconia, Ph.D.
ENEA – Casaccia Research Center Energy Technologies Department (DTE) Solar Thermal and Thermodynamic Division (STT)
Email: [email protected]
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ACRONYMS and NOMENCLATURE CPV: Concentrating Photo-Voltaic CS: Concentrating Solar CSP: Concentrating Solar Power HTF: Heat Transfer Fluid MS: Molten Salts ORC: Organic Rankine Cycle PV: Photo-Voltaic RE: Renewable EnergyR&D: Research and Development RD&D: Research, Development and Demonstration SME: Small-Medium Enterprise TES: Thermal Energy (heat) Storage TRL: Technology Readiness Level WP: Work Package
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Table of contents 1. INTRODUCTION ....................................................................................................................................... 5 2. FEASIBILITY STUDIES ............................................................................................................................ 5
2.1 Site selection ..................................................................................................................................... 5 2.2 Description of the plants .................................................................................................................... 6
2.2.1 Pilot plant in Cyprus ...................................................................................................................... 6 2.2.2 Pilot plant in Egypt ........................................................................................................................ 7 2.2.3 Pilot plant in Jordan ....................................................................................................................... 7 2.2.4 Pilot plant in Italy ........................................................................................................................... 8
2.3 Technical feasibility ......................................................................................................................... 10 3. SUMMARY AND CONCLUSIONS .......................................................................................................... 11
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1. INTRODUCTION The main objective of work package 5 (WP5) of the STS-Med project is to develop reliable, low-cost, and flexible small/medium multi-generative CS power plants to satisfy the energy demand of buildings in the Mediterranean area. This technical objective is achieved combining and optimizing innovative subsystems for the efficient capture and conversion of solar energy to essential energy products and services for building: electrical power, air conditioning and water treatment (e.g. desalination or sterilization). The primary solar energy sources can feed this conversion process either alone or in combination with backups (e.g. gas or biomass). In a first phase of the development, the basic elements to be integrated have been identified, according to the technological demand and specifications of the process (i.e. the capture, conversion and delivery of solar energy). This work is reported in Deliverable D5.1, representing an extensive overview of the different unit options for the plant components. Then, the way to combine the above mentioned components has been determined in optimization studies aimed at obtaining reliable, low-cost, and flexible small/medium multi-generative CS plants to satisfy the energy needs of buildings in the Mediterranean area. The optimization studies and the proposed methodology to analyse the systems have been reported in Deliverables D5.2 and D5.3. Finally, work package 5 (Task 5.4) involves feasibility studies for the multi-generative CS plants developed in STS-Med project, considering different aspects for the reliable design and operation of the plants. This Deliverable (D5.4) reports the results of this feasibility study with specific focus on the four plants basic designs developed in STS-Med project (executive designs are developed in WP6).
2. FEASIBILITY STUDIES
2.1 Site selection During the first year of STS-Med project, partners identified the locations for the four pilot plants to be installed in their countries (Cyprus, Egypt, Jordan, Italy), including the building integration scenarios. These proposals have been evaluated and accepted by the partnership at the end of 2013. The choice of the sites for four pilot units has been primarily based on an opportunity analysis considering representativeness, logistic issues, opportunities for future development, social and scientific impact, etc. Moreover, the architectural integration potentials into buildings have been considered. Hence, different integration scenarios have been finally considered for the pilot pants:
• rooftop of a research center, the Novel Technologies Laboratory (STS-Med plant in Nicosia, Cyprus)
• ground field close to a medical center (STS-Med plant in Sekem, Egypt)
• rooftop of an educational building (STS-Med plant in Irbid, Jordan) • ground field between an university campus and a city park, in the framework of a
broad requalification action concerning the same area characterized by archeological interests and related building constraints (STS-Med plant in Palermo, Italy)
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2.2 Description of the plants After the identification of the site, during the first project year partners proposed possible layouts for the demonstration plants to be installed. These layouts have been reviewed and widely discussed within the partnership, considering the feasibility, potential impacts and budget constraints. Suitability of the components and best-fit opportunities in the integrated system have been considered in the designs (following the advices provided in Deliverable D5.2). Scaling process has been applied in the frame of work package 6.
2.2.1 Pilot plant in Cyprus The STS-Med plant in Cyprus is located nearby the Cyprus Institute. This CS multi-generative plant will provide cooling and heating to the Novel Technologies Laboratory (NTL), in view of is conversion to a “near to zero” energy building. The plant is shown in Figure 1. It is based on linear Fresnel collectors about 70 kW thermal power, installed on the 352 m2 roof of the KEPA School, close to NTL. The collector has an aperture area of 184 m2 and uses thermal oil at 180°C as a heat transfer fluid (HTF). The heat is exchanged with pressurized water, then stored in a tank allowing 2 hours self-sufficiency. A LiBr single-effect absorption chiller of 35 kW cooling capacity uses this heat to cool the NTL in summer. The chiller is by-passed in winter to directly produce heat. This platform is a pilot demonstration case in Cyprus, as it provides cooling thanks to solar concentration in urban environment. Technical details about this plant and its feasibility are reported in Annex 1 of this report.
Figure 1. STS-Med linear Fresnel solar field built on the rooftop of the Novel Technologies
Laboratory in Nicosia (Cyprus).
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2.2.2 Pilot plant in Egypt The STS-Med plant in Egypt is located in an area close to the Sekem medical centre (Figure 2), about 100 km north of Cairo. The plant is based on linear Fresnel collectors with a thermal power of 120 kW, installed on land and connected with a ORC system for the production of 5 kWe and a single-stage LiBr chiller to generate 35 kW of cold.
This plant will show the feasibility of multi-generation of three different forms of energy (heating, cooling and electricity) serving such a typical Mediterranean public building.
Technical details about this plant and its feasibility are reported in Annex 2 of this report.
Figure 2. The Sekem medical centre in Egypt, location of the STS-Med multi-generative CS plant.
2.2.3 Pilot plant in Jordan The STS-Med plant in Jordan is installed in on the rooftop of an educational building in Irbid (Figure 3). This multi-generative CS plant consists of concentrated in a parabolic tough collectors using oil as heat transfer fluid (HTF) up to 240°C. The plant will generate electric power through steam micro-turbines, heat for the building cooling/heating, and hot and distilled water. More in detail, during the summer the thermal oil will drive an absorption chiller to provide space cooling. A steam generator is applied to generate superheated steam at 200°C to drive a steam turbine generating electricity (1.5 kW). The condensate from the turbine will be collected as distilled water in a tank. A oil/water heat exchanger is also applied to generate hot water to be both used for space heating and stored in a tank for later use. Technical details about this plant and its feasibility are reported in Annex 3 of this report.
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Figure 3. Localization of the STS-Med multi-generative CS plant in Irbid (Jordan).
2.2.4 Pilot plant in Italy The STS-Med plant in Italy, installed in an area between the university campus and a city park, is integrated within a broad requalification action of this area. The plant localization is shown in Figure 4. An area of about 3000 m2 for the solar field has been assigned by the University of Palermo as well as a protected place for the installation of equipment and controls. Specific solutions have been developed to minimize the impact on the area of archeological interest. Some components derive from R&D activities involving regional SMEs that have been participating into the supply chain.
Figure 4. Localization of the STS-Med multi-generative CS plant in Palermo (Italy).
The plant scheme is represented in Figure 5. The solar field consists of 3 linear Fresnel collectors (each consisting of 7 basic modules) with a compact focal distance, connected in parallel, with a total (active) surface of about 700 m2. High performance (evacuated) receiver tubes are used to maximize the solar radiation capture efficiency. The heat transfer fluid (HTF) is a bio-derived oil (Paratherm NF) with no environmental impact, with inlet/outlet temperatures in/from the solar field of 260°C/280°C, respectively. The HTF transfers its thermal energy to the innovative thermal energy storage (TES) system, based on the
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use of a single tank with a ternary molten salt mixture, integrated with two heat exchangers, specifically developed in the STS-Med project. This TES system is described in Deliverable D5.2 and its technological feasibility discussed in the following sections. The TES is connected to the heat loads: a 10 kW ORC unit (with 100 kW thermal load in the 160-180°C range) for electrical power production and a 23 kW LiBr chiller (thermal load in the 165-200°C range). Technical details about this plant and its feasibility are reported in Annex 4 of this report.
Figure 5. Scheme of the STS-Med multi-generative CS plant in Palermo (Italy).
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2.3 Technical feasibility Technical feasibility of the proposed plant layouts has been validated with the basic design and the available specifications of the integrated commercial units. Process flow sheets have been analysed in order to validate the performances the overall system, as detailed in the technical Annexes 1, 2, 3, and 4. In Deliverable D5.2 it is highlighted that some innovative components, not yet commercially available but still undergoing RD&D stage, have been considered. Specifically, in Deliverable D5.2 it is highlighted the importance of applying a Thermal Energy Storage (TES) system in small-medium CS multi-generative plants. Therefore, an innovative TES system has been developed to optimize the STS-Med plant design in Palermo. Before installation in the demonstration plant, an innovative Thermal Energy Storage (TES) prototype (see Deliverable D5.2) has been designed, built and installed at the ENEA-Casaccia research center (Rome) for proof.-of-concept. This prototype is sown in Figure 6. Additional details and technical feasibility study of this innovative system in the framework of the STS-Med project (WP5) is described in Annex 4.
Figure 6. Heat storage system prototype developed in STS-Med (ENEA-Casaccia center, Rome).
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3. SUMMARY AND CONCLUSIONS This report with its four Annexes (1, 2, 3, 4) represents the final Deliverable of the work carried out in the frame of work package 5 of STS-Med project. Initially, partners identified the locations for the four pilot plants to be installed in their own countries (Cyprus, Egypt, Jordan, Italy). The choice of the sites has been primarily based on an opportunity analysis and, interestingly, different integration scenarios have been considered for the pilot pants: the rooftops of a research center and a school (Cyprus and Jordan) and ground fields close to a medical center and an university campus (Egypt and Italy). After, partners proposed different technical layouts for the demonstration plants to be installed. These layouts have been widely discussed and evaluated within the STS-Med partnership. Particularly, the suitability of the components and best-fit opportunities in the integrated system have been considered in the basic designs. The general description of the four pilot plants (in Cyprus, Egypt, Jordan and Italy) is provided in this report, and the technical details. Detailed description of the plants, analysis and technical feasibility studies are reported in the four annexes of this report (Annexes 1, 2, 3, 4). Although most units are commercial, some innovative components not yet commercially available, but still undergoing RD&D stage, have been considered. As reported in Deliverable D5.2, an innovative Thermal Energy Storage (TES) has been developed specifically to optimize the STS-Med plant design. Hence, a prototype has been designed, built, installed and tested to prove the developed TES concept before installation in the STS-Med demonstration plant. Results are presented in Annex 4.
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STS-Med Small scale thermal solar district units for Mediterranean communities Ref. I-A/2.3/174
D5.4 - Annex 1 STS-Med pilot plant in Cyprus contribution from the Cyprus Institute December 2015
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Design tool The model of the toolbox at the Cyprus Institute relies on one hand on the technical specifications of the already installed absorption chiller (YAZAKI WFC –SC10) and on the other on the technical specifications of ordered components (Fresnel collector and thermal storage, Figure 1). The model is based on the TRNSYS software package and its extra TESS libraries.
Figure 1. Schematic diagram of solar cooling system and integration with existing HVAC system
The above schematic shows the integration of the Fresnel collector, the thermal storage and the absorption chiller (+ cooling tower) on the already implemented HVAC system. The system includes several loops with heat-exchangers stages in order to meet the temperature requirement to fire the absorption chiller at 88°C. The characteristics of the main components, i.e. Fresnel collector, absorption chiller and thermal storage are detailed in Table 1. The simulation model only includes the part of the integration on the implemented HVAC components. In summer the heat produced will fire the absorption chiller and in winter the heat is recovered at the level of the heat exchanger HX3.1. The cooling and heating capacity of the system is lower than the requirements of the building. Since the Novel Technologies Laboratory is a professional dedicated facility, heating and air-conditioning are just required during weekdays. The heat recovery system and the absorption chiller are turned off on weekends but the Fresnel collector remains on to store heat in the thermal storage. The Absorption chiller is also scheduled to be working between 8:00 AM and 8:00 PM on working days. All the components for control are listed in Table2.Components forcontrol Table 2. The global system of Simulation Studio is shown in Figure 2.
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Component Main characteristics Subcomponent - TRNSYS Type
Solar collector : LFR
• Aperture area : 184.32 m2
• nominal outlet temperature of the receiver : 180°C
• Specific Fluid Heat capacity (thermal oil) : 2.12 kJ.kg-1.K-1
• Fluid density : 900 kg.m-3
Type 1288 (TESS): “Linear Fresnel Collector using the EN12975-2 Efficiency Approach”
External file : “Bi-Axial IAMs\Typical_EvacTube_IAM.dat”
Absorption chiller • Thermal cooling capacity 35 kW • COP = 0.7 • Nominal heat medium temperature (hot
water): 88°C inlet and 83°C outlet temperature
• Nominal chilled water temperature: 12°C inlet and 7°C outlet temperature
Type 107 (TESS) : “Hot Water-Fired Single-Effect Absorption Chiller”
External file : “Type107-HotWaterFiredAbsorptionChiller.dat”
Thermal storage : Pressurized water : 100 kWh thermal
• Volume : 3 m3 • Up to 100 kWh of thermal storage, able to
secure 2 hours of autonomy to the absorption chiller
Type 534 (TESS) : Cylindrical Storage Tank with Immersed Heat Exchangers
Table 1. Components for the toolbox in TRNSYS.
Component Main characteristics Subcomponent - TRNSYS Type
Controls (pump)
• Regulates the flowrate in the loops according to the needs of the building
• Regulates according to the temperatures of the state of charge of the various tanks and buffer
Equation
Valves system
• By-pass on the Fresnel collector and heat-exchangers in order to regulate the temperatures for the tanks
• Regulates the flow of heat medium according to the season (Heat recovery or absorption chiller)
Type 11h: “Tee Piece”
Type 11f: “Controlled flow diverter”
Type 953 (TESS): “Controller for Tempering Valves”
Heating/cooling season
• Regulates the gross season for heating and cooling (summer or winter)
• Regulates heating and cooling according to the day of the week
• Regulates heating and cooling according to the hour of the day
Type 579 (TESS): “N-Level Forcing Function”
Weather data
• Data for the outside temperature • Direct Normal Irradiance
Type 15 (TESS): “Weather Data Processor; Combines data reading, radiation processing and sky temperature calculations”
External file : “Europe\CY-Nicosia-hour.tm2”
Table 2. Components for control.
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Figure 2. Simulation Studio model.
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Localization and scaling to the demonstration unit As defined in the previous section, the simulation support on TRNSYS/Simulation Studio allows us to predict the performance of each subcomponent of the toolbox (Errore. L'origine riferimento non è stata trovata.). This report details these predictions.
Figure 3. Simulation Studio model.
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Thermal oil loop The thermal oil loop includes the Fresnel collector, on the roof of the KEPA School, one small buffer of thermal oil, one circulator, one heat-exchanger with the pressurized water loop and the valve by-pass control. The by-pass controls the temperature inlet for the buffer. This temperature is set to 180°C, and was not chosen to higher level in order to be able to store in pressurized water but at low level of pressure. One electric heater will be included in the real platform to improve the pumping ability of the thermal oil at the beginning of the day at low temperatures. Figure shows the annual evolution of:
• the temperature outlet after the bypass,
• the average temperature of the buffer of oil, • the thermal power of the Fresnel collector.
The collector is working all day long although the facilities are not in use during the weekend, thus heat is stored in the buffer oil. According to prediction, the control permits to stabilize the temperature outlet of the receiver at 180°C when the DNI is high enough. The temperature decreases during the nights, under cloudy conditions and when the pump P2.2 is in use. The power of the Fresnel collector oscillates according to the days of the year (up to 150 kW), but mainly stays between 40 kW and 80 kW in normal operating conditions.
Figure 4. Thermal oil loop.
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Pressurized water loop This loop stores the heat produced by the Fresnel collector to shift it for the absorption chiller. Figure shows the annual evolution of:
• the average temperature of the pressured water tank,
• the outlet temperature of the valve after the heat exchanger,
• the thermal power received by the water at the heat-exchanger. The power is only exchanged during week days. The average temperature of the tank oscillates between 90°C and 140°C, depending on the heat/cooling needs of the building. The control valve forces the outlet temperature of the return after heat-exchanger to be at 140°C. When the thermal production at the level of the Fresnel collector is not sufficient this return temperature is lower (generally in winter and nights). This occurs also when the absorption chiller is working and uses the heat of the tank. The loop of heat medium (and PABSCH) works if the average temperature of the pressurized water in the tank is higher than the average temperature of the heat-medium tank.
Figure 5. Pressurized water loop.
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Heat medium loop This loop permits to fire the absorption chiller in the summer and to produce heat for heat recovery purposes in the winter. Figure shows the annual evolution of:
• The average temperature of the water tank,
• The outlet temperature of the valve after the heat exchanger,
• The thermal power received by the water at the heat-exchanger. The water is stored at 55°C in winter for the heat coils of air handling units and fan coil units. In the summer, the water is stored at 95°C to fire the absorption chiller.
Figure 6. Heat-medium loop.
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Absorption cooling The absorption chiller only works in the summer, so heat is removed only during the weekdays of the cooling season (around 35 kW). The inlet temperature of the chilled water is 12°C and the desired outlet at 7°C. These results are shown in Figure . The absorption chiller will not be sufficient to provide enough cooling to the building. So it will support the already implemented chillers and the heat-pump. But the use of the absorption chiller will be the priority.
Figure 7. Absorption chiller.
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Heat recovery In the winter, the water of heat coils are heated up to 55°C. Since the absorption chiller is not working (no heating option), the heat produced will be directly used to support the heating system. Figure 3 shows the results of the heat recovery loop. In the summer no heat is recovered.
Figure 3. Heat recovery.
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STS-Med Small scale thermal solar district units for Mediterranean communities Ref. I-A/2.3/174
D5.4 - Annex 2 STS-Med pilot plant in Egypt contribution from ASRT December 2015
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Plant Description The plant shall be installed at SEKEM medical center near Belbis city which lies in the north of Egypt at latitude 31° and longitude 30°. The total surface area of the building is about 963 m2. Classification of the building electric loads in kW are mainly to supply cooling during summer (63% of electric load), winter heating (50%), equipment electric loads (17%) , and water pumping for irrigating the landscape (20%). The solar plant is designed to mainly provide chilled water to cover about 35 kwth (about 10 TR) peak of building cooling load during summer. The extra power output from the solar field shall be used to generate electricity. In winter, the plant shall be mainly used to provide electric power of about 4.3 kWe peak. The extra power output from the solar field shall be used to produce hot water for heating purposes. A thermal energy storage system shall work in conjunction with the solar field, power block, and chiller. A schematic layout of the CSP plant is shown in Figure 1. The heat transfer fluid, Therminol 66, is pumped through the solar field (LFR) where it gets heated up to the nominal temperature of 140-160°C. The fluid is then sent to the storage system. The heat transfer fluid is pumped to the ORC and TDC using separate pump for each component. A three-way thermostatic mixing valve is installed at the inlet of ORC unit evaporator and the absorption chiller generator in order to control the hot fluid supply temperature to each of them. The power unit integrated in the solar power plant is a 4-8 kWe non-recuperative Rankine cycle using HFC-245fa as working fluid. The thermally driven chiller (TDC) is single stage with 35 kW cooling capacity and 48 kW heating capacity.
Figure 1. Schematic diagram of the solar power plant.
CT
CT
ORC
AbsorptionChiller
TES
LFC
PP
P
S.T
Rooms
fC fC
+-
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Plant Model Description
The tool box for simulating the thermal performance of the total components of the plant was built using the Engineering Equation Solver EES. The model for each component is described in the following sections.
Linear Fresnel collectors
The rate of energy incident to the receiver tube can be calculated from the following equation:
ELF)(IAMDNIAq p,otpnetinput ∗∗∗∗= θη! (1)
The incidence angle modifier IAM (θi) is approximated by multiplying the incidence angle modifier in the longitudinal direction IAML (θi) with the incidence angle modifier in transversal direction IAMT (θT)
)(IAM*)(IAM)(IAM TTiL θθθ = (2)
The End Losses Factor (ELF)
Ltan/F1ELF iθ−= (3)
The model of the evacuated receiver tube which consists of the absorber tube and the glass cover and the HTF flow through it as shown in Figure 2.
Tf
!̇f
Tst
Tg
!̇conv ,g_a
!̇rad ,g_a
!̇rad ,st _g
Glasscover
Absorbertube
! ̇_abs
Figure 2. Energy flow of the receiver tube. The energy balance equations per unit length for a small segment of length dx for the heat transfer fluid, steel tube and the glass cover are as follow: The energy balance for the heat transfer fluid:
( )t
TCpm qq dxDTTh f
ffoii,stmsi,sfst,c ∂
∂=+−−− π (4)
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The energy balance for the absorber tube:
( )t
TCpmdxD* TTh dxD)qq( stststi,stfi,stfst,co,stgst,rabs ∂
∂=−−− −− ππ (5)
The energy balance for the glass cover:
( ) ( )t
TCpmdxqqdxrrqdxDq g
ggskyg,rag,c2
i,g2
o,gg,abso,sgst,r ∂
∂=+−−+ −−− ππ (6)
By solving the previous equations simultaneously using the Engineering Equation Solver (EES), the glass temperature Tg, absorber tube temperature Tst and the fluid temperature Tf can be obtained. The outlet temperature of the oil fluid, which represents the HTF, is calculated from the following equation:
infout TT*2T −= (7)
The power output from the receiver tube that is transferred to the synthetic oil can be calculated from the following equation:
)TT(*Cp*mq inoutout −= !! (8)
Thermal loss for the receiver tube q! loss is the difference between the input radiation power to the receiver tube and the thermal power gained by the oil q! out.
Storage tank
The storage tank was modelled as a transient one dimensional stratified tank with interior heat convection and conduction between tank nodes. The thermal losses from the tank surface as well as mixing at the tank inlet and outlet boundaries were considered in the model. The tank is divided into N equal horizontal segments with equal height. Transmission of the thermal energy to or from the tank layers (node) is accompanying with or without mass flow. The thermal energy flows indicated by the solid arrows, as shown in Figure 3, represent energy transfer associated with mass flow, and the dashed arrows represent the energy transfer without mass flow.
Figure 3. Energy flow in a node. Taking all the energy flows for one segment into account and by arranging the coefficients of Ti-1, Ti and Ti+1, the node energy balance take the following equation:
0dTcTbTa i1iiii1ii =+++ +− (9)
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Where Ti-1, Ti and Ti+1 are the temperature (°C) of the nodes. The coefficients a, b, c and d are computed from the heat and mass transfer equations among the nodes-
Organic Rankin Cycle (ORC)
Modelling of the ORC is based on modelling of all components forming the cycle as shown in Figure 4. The evaporator and the condenser were treated as a heat exchanger. The turbine and plume were simulated with isentropic process. For design and performance calculations, the effectiveness-Number of Heat transfer Unit (NTU) method was used without iteration. For each zone the inlet temperature for the hot and the cold fluid stream are Th,i and Tc,i, respectively and the outlet temperature for hot and cold streams are Th,o and Tc,o, respectively. The outlet fluids temperatures were calculated from the following equations:
maxQ=Q !! ε (10)
)T-(TCp m)T-(TCp m=Q ic,oc,ccoh,ih,hh !!! = (11)
where:
Q! : actual heat transfer rate (KW)
Q! max : maximum possible heat transfer rate (KW). ε :effectiveness.
hm! : mass flow rates of the hot fluid (kg/s).
cm! : mass flow rates of the cold fluid (kg/s).
The effectiveness ε for single and the two phase zones are calculated using the following equations:
))C-(-NTU(1C-)))/(1 C-exp(-NTU(1-(1 = rrrε (12)
exp(-NTU)-1 = tpε (13)
Figure 4. A schematic diagram of the storage tank with segments.
Condenser
Evaporator
TurbinePump
1
2 3
4
G
Oilin Oilout
WaterinWaterout
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The heat transfer rate from the evaporator eQ ! into the working fluid is given by:
) h-h ( m=Q 23fe !! (14)
The power output from the tW ! turbine is given by:
) h-h ( m=W 43ft !! (15)
The heat rate removed by the condenser cQ ! can be expressed as:
) h-h (m=Q 14 fc !! (16)
The pump power Wp can be expressed as:
) h-h (m= W 12 fp ! (17)
User Interface
The model is developed using EES software. A user friendly graphical interface is developed for the analysis of plant operation, see Figure 5 and Figure 6. This interface allows the user to change design and operating parameters in the plant and analyze the results. This is very useful tool for training purposes.
Figure 5. A screen photo of the main interface window for the tool box.
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Figure 6. A screen photo of sub interface window for the absorption chiller.
Technical Details of Plant Components Technical details and design data of the plant are reported in Table 1. Detailed technical specifications of the solar collector are reported in Table 2.
Solar field(LFR)
Aperture area (m2) 296 Peak power (kW) 120 Heat transfer fluid Therminol- 66 Outlet temperature (˚C) 160 Mass flow rate (kg/s) Function of control strategy and minimum Reynolds number in collector receiver pipe ORC unit Electrical output (kW) 4-8 Heat medium (therminoil) Heat input (kW) 53-95
Inlet temperature (ºC) 125-150 Outlet temperature (ºC) 115-130
Cooling water Heat rejection (kW) 45-85 Inlet temperature (ºC) 31 Outlet temperature (ºC) 35
Absorption Chiller Cooling mode Heating mode Capacity (kW) 35 48 Chilled/Hot Water Inlet temperature ( C) 12.5 47.4
Outlet temperature (C) 7 55 Flow (L/s) 1.52
Heat Medium (therminol- 66) Heat input (kW) 50 Inlet temperature (C) 88 Outlet temperature (C) 83
Cooling Water Heat rejection (kW) 85
Table 1. Technical data for CSP plant components.
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ITEM SPECIFICATIONS Collector net collecting surface [sqm] 14 module x 22 m2mirror area for each Peak power/collector [kWth] 120kWthat 850 DNI No. of collectors 1 Working temperature Up to 280 °C Heat transfer fluid Thermal oil Nominal Inlet/outlet temperature. °C 120/140 Characteristics of LFC module Net mirror surface 22 m2 Tracking system Single axis Dimension 4 x 8.7 m Materials Mirrors Ultraclean glass with silver coating Reflectivity > 95% Absorber Vacuum glass/steel pipe CERMET coated Structure Galvanized Further features - Completely automatic
- Monitoring and diagnosing system - Bad weather automatic stowing procedure - Web based remote control - Safety system against overheating - Complete tracking system
Table 2. Technical specification of LFR solar field. Other plant components include oil storage tank, oil pumps, chilled water pumps, condenser water pumps, fan coil units and cooling towers. oil storage tank is fabricated from galvanized steel with circular shape and thickness of 6 mm thickness. The diameter and the height of the tank is 1.4 m and 1.8 m, respectively. The total tank capacity is 2.8 m3. The storage tank include steel base, frame, shut-off valves, vent valves, drain valves, level indicator, controller valves, thermometers temperature and pressure solenoid valve. LFR system oil pumps are variable speed 14 m3/h (3.85 L/s, 61 gpm) flow rate. ORC and TDC oil pumps are also variable speed pumps (2.2 L/s, 35 gpm) flow rate. The cooling towers are 50 TR cooling capacity for condenser cooling of ORC and TDC.
Plant Operation The plant operation is determined by the control facilities available in the ORC and TDC as provided by the manufacturers. For the selected ORC unit, the nominal hot fluid supply temperature is 125 ˚C with heat input of 53 kW and electric power output of 4.3 kW. For the TDC, the nominal hot fluid supply temperature is 88 ˚C with heat input of 50 kW and cooling capacity of 35 kW. Different independent control variables can be operated to regulate the power plant. The speed of the solar loop pump controls the HTF mass flow rate circulating in the solar collectors and the exit temperature from the solar field. Regulation of the ORC three way mixing valve controls the HTF temperature entering into the ORC evaporator and ultimately changes the mass flow rate of oil taken from the storage tank. The thermal power input to the chiller generator is controlled by adjusting the variable pump speed at generator inlet and inlet fluid temperature by using the three way mixing valve. The climatic conditions determine the solar field performance, which defines the temperature level of the thermal storage tank. The temperature level of the tank determines the performance of the
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ORC and TDC. The building calls for cooling in summer (chiller works in cooling mode) and heating in winter (chiller works in cooling mode). The ORC electric output is directly injected into the building local electric grid. Both the ORC and TDC are supplied by thermal power from the storage tank. The TDC and ORC are switched off when the oil temperature in the storage tank is lower than the required nominal input temperature, 88 C for the TDC and 125 C for the ORC
Performance Predictions
Solar field performance predictions LFR solar filed performance predictions are analysed for summer and winter months. These results are shown in figures below. It can be observed that the peak power output from the solar field reaches about 100 kW in June and 40 kW in December. The daily energy gain in June and December reaches about 1200 kWh and 600 kWh, respectively. These results are based on the EES model developed for the purpose of the toolbox, as described in the previous sections.
Figure 7. The rate of output energy gained from the LFC at December, March and June.
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Figure 8. The daily energy gained and the energy incident on the collector.
Plant performance predictions The storage tank energy feed withdraw and storage in June during the cooling mode is shown in Figure 9. Prediction of plant efficiency for four operating modes in May is shown in Figure 10.
Figure 9. The tank energy feed, withdraw and stored during the cooling mode.
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Figure 10. The plant efficiency at the four operating modes through a day in May. Analysis of plant cooling and electricity production shows that plant operation in combined electricity and cooling mode using LFR can produce about to 9443 KWh of cooling and 791 kWh of electricity in summer months of May, June, and July. In winter mode operation, when the plant is used for generating electricity only, the plant produces a minimum of 264 kWh of electricity in January.
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STS-Med Small scale thermal solar district units for Mediterranean communities Ref. I-A/2.3/174
D5.4 - Annex 3 STS-Med pilot plant in Jordan contribution from Millennium Energy Industries December 2015
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Introduction This document provides a comprehensive description of the solar multi-generation plant (demonstration plant) that will be installed in Balqa University College in Irbid/Jordan. The plant is part of the STS-Med project which aims at promoting and implementing innovative technologies and know-how transfer in the field of solar energy.
Plant location
The plant will be installed on the rooftop of an educational building shown in the figures below (Figure 1, Figure 2 and Figure 3) in Irbid city located in the north of Jordan. The geographic location of the plant is:
- Latitude: 32.487 N.
- Longitude: 35.89 E.
- Elevation: 648 m.
Figure 1. Google earth image for the building.
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Figure 2. Building elevation.
Figure 3. Building rooftop.
Plant description The plant will generate electric power, cooling/heating, hot water and distilled water from a single source of energy (solar energy). A schematic diagram of the plant is provided in Figure 4. Solar energy will be collected and concentrated in two parabolic tough collectors (PTC-1) connected in series. The concentrated solar radiation will heat the heat transfer fluid (HTF) which thermal oil to a temperature of 240°C. The heated oil will be stored in a break tank (TOT-1) to provide a stabilized operation for the heat consuming equipment. In summer, the hot thermal oil will drive an absorption chiller (CHLR-1) to provide space cooling through two Fan-Coil units (FCU-1) in one of the classrooms. The oil will also be utilized to generate superheated steam through saturated steam generator (STG-1) and super-heater (SH-1). The super-heated steam will drive a 1.2 kW steam turbo-generator (ST-1) to generate electricity, the turbine will be fed with soft water from a water softener. The steam will exit the turbine in a liquid phase (condensate) which will be collected in a tank (DWT-1) and used as distilled water. If
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the available solar energy exceeds the cooling and electricity generation demands, the excess heat will be delivered to hot water network through shell and tube heat exchanger (HEX-1) and the hot water will be stored in a tank (HWT-1). If the excess heat exceeds the storage capacity, it will be dissipated in a dry cooler (DC-2). In winter, the operation will be similar to summer operation with space cooling replaced by space heating which will be provided by the hot water stored in HWT-1 through the fan-coil units (FCU-1).
Figure 4. Schematic plant layout.
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STS-Med Small scale thermal solar district units for Mediterranean communities Ref. I-A/2.3/174
D5.4 - Annex 4 STS-Med pilot plant in Italy contribution from ENEA and Consorzio Arca December 2015
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Introduction The STS-Med plant in Italy, installed in an area between the university campus and a city park, is integrated within a broad requalification action of this area. The plant localization is shown in Figure 1. An area of about 3000 m2 for the solar field has been assigned by the University of Palermo as well as a protected place for the installation of equipment and controls. Specific solutions have been developed to minimize the impact on the area of archeological interest. Some components derive from R&D activities involving regional SMEs that have been participating into the supply chain.
Figure 1. Localization of the STS-Med multi-generative CS plant in Palermo (Italy).
The plant scheme is represented in Figure 2. The solar field consists of 3 linear Fresnel collectors (each consisting of 7 basic modules) with a compact focal distance, connected in parallel, with a total (active) surface of about 700 m2. High performance (evacuated) receiver tubes are used to maximize the solar radiation capture efficiency. The heat transfer fluid (HTF) is a bio-derived oil (Paratherm NF) with no environmental impact, with inlet/outlet temperatures in/from the solar field of 260°C/280°C, respectively. The HTF transfers its thermal energy to the innovative thermal energy storage (TES) system, based on the use of a single tank with a ternary molten salt mixture, integrated with two heat exchangers, specifically developed in the STS-Med project. This TES system is described in Deliverable D5.2 and its technological feasibility discussed in the following sections. The TES is connected to the heat loads: a 10 kW ORC unit (with 100 kW thermal load in the 160-180°C range) for electrical power production and a 23 kW LiBr chiller (thermal load in the 165-200°C range).
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Figure 5. Scheme of the STS-Med multi-generative CS plant in Palermo (Italy).
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Technical feasibility Technical feasibility of the proposed layout was validated by the basic design and the available specifications of the integrated commercial units. Process flow sheets have been analysed in order to validate the performances the overall system. In Deliverable D5.2 it is highlighted that some innovative components, not yet commercially available but still undergoing RD&D stage, have been considered. Specifically, in Deliverable D5.2 it is highlighted the importance of applying a Thermal Energy Storage (TES) system in small-medium CS multi-generative plants. Therefore, an innovative TES system has been developed to optimize the STS-Med plant design in Palermo. Before installation in the demonstration plant, this innovative component needed to be proved in laboratory by ENEA. The following sections provide the technical feasibility study of this innovative system in the framework of the STS-Med project.
Thermal Energy Storage (TES) system A prototype of the innovative Thermal Energy Storage (TES) system (see Deliverable D5.2) has been designed, built and installed at the ENEA-Casaccia research center (Rome) for proof.-of-concept. The general view of the prototype is shown in Figure 5. It consists of a 900 litres tank filled with a molten salt mixture, specifically the nitrate ternary mixture Ca(NO3)2/NaNO3/KNO3 (42/15/42 %w).
Figure 5. Heat storage system prototype developed in STS-Med (ENEA-Casaccia center, Rome).
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This system is by itself characterized by a number of positive features. Since this fluid has negligible vapor pressure and no interaction with air, the tank is neither pressurized or air tight, even up to 450°C. Moreover, the salt is nontoxic, stable, and with low cost (< 1 €/kg). Additional details of the prototype are shown in Figure 6. Two helicoidally shaped heat exchangers are placed on the top and bottom of the tank, immersed in the molten salt. Note that this system with integrated heat exchangers is highly compact and does not require molten salts pumping and piping external to the tank. The heat exchangers are integrated within two corresponding oil loops, designed to remove and supply the heat in the temperature range of 150-400°C. As described in Deliverable D5.2, the working principle is based on the thermal stratification of the molten salt resulting from the heat exchange in the two coils during the charge and/or discharge phases. Depending on the temperature gradients of the molten salt, this prototype is characterized by a heat storage capacity in the range of 50-170 kWh.
Figure 6. Some details of the heat storage system prototype developed in STS-Med (ENEA-Casaccia center, Rome): general drawing (left), top view with the four flanges connecting with the oil loops (top right), and the bottom heat exchanger shell with downcomers (bottom right).
A synthetic organic oil (Dowtherm Q) has been used as heat transfer fluid (HTF) in the oil loops. In Figure 7 is shown the process diagram of the two oil loops. The “charging loop” (represented in “red” in Figure 7) connects the bottom heat exchanger with electrical heaters to heat up the oil stream up to 310°C, in order to simulate the solar field. Differently, the “discharging loop” (represented in “blue” in Figure 7) connects the top heat exchanger with an air fan to cool down the oil stream, in order to simulate the heat load. The inlet temperatures and the flow rates of the two oil loops can be controlled independently.
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Figure 7. Oil loops integrated with the prototype developed in STS-Med (ENEA-Casaccia center,
Rome). The heating and cooling loops are red and blue coloured, respectively. A specific procedure has been developed for the salts loading, mixing, and melting. Particular concern has been addressed to the hydration of the salt, since the commercial Ca(NO3)2/KNO3 mixture contained a relevant amount of water that is removed during the melting phase. In total, more than 2 tons of the salt mixture with the selected composition (Ca(NO3)2/NaNO3/KNO3 = 42/15/42 %w) have been loaded in the TES prototype. It is noteworthy that the salts melting has been achieved using only the charging heat exchanger in order to prove the possibility to avoid equipping the TES with external heaters only to manage this initial melting stage. After the experimental campaign, in order to simulate accidental conditions which may occur during the plant lifetime, the possibility of complete freezing and re-melting of the salts loaded in the tank has been studied and validated too.
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During the experimental campaign, a number of tests have been carried out to prove the typical charge and discharge phases, also simultaneously, under representative conditions for the pilot plants. As shown in Figure 8, a total number of 20 thermocouples (A1 to A10, B1 to B10) have been placed in the tank in order to determine the temperature profiles during the different working phases.
Figure 8. Positioning of the temperature sensors in the TES tank to monitor and validate the
working principles. Experimental results have been extensively reported in an internal report available at the ENEA (ref. DTE-STT/2015/001). In the following paragraphs the most relevant results are presented and summarized. Figure 9 shows the trend of the temperature profile during a typical TES discharge phase. At the beginning of the discharge run, the TES is fully loaded with the molten salts temperature nearly homogeneous, close to the maximum temperature TS-high (e.g. 280°C as in the STS-Med plant in Palermo). When the heat starts to be released, a stratification occurs, this the lower tank section at the lower temperature (TS-low), and a thin thermocline section appears in between the “hot” and the colder sections. This thermocline zone proceeds towards the top of the tank during the discharge, as hot molten salts are moved from the top to the colder section. In Figure 10 are shown the oil inlet and outlet temperatures and the determined molten salts flow rate in the heat exchanger: note that the TES operation is rather stable. Exactly opposite trends have been observed during the charging phase, with a roughly homogeneous temperature profile close to TS-low at the beginning, and the thermocline section moving from the top to the bottom during the charging run. Additional experimental tests have been carried out to validate the simultaneous charge and discharge of the TES, as representative condition of a “daily” working.
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Figure 9. Temperature profiles obtained experimentally in the TES prototype during a typical
discharge phase.
Figure 10. Oil inlet and outlet temperatures and molten salts (MS) flow rates through the top heat
exchanger during a typical discharge phase.
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In conclusion, the experimental tests carried out on the STS-Med TES prototype proved the concept, with the expected performance with respect to the thermal stratification, the molten salts fluid dynamics (by natural convection), the effectiveness of the heat transfer to the thermal oil (HTF) and the stability of the system. The experimental results and concept validation with the prototype enhanced the design of an up-scaled TES for the demonstration plant in Palermo. In order to select suitable materials corrosion tests on the TES materials with the molten salt mixtures under representative conditions have been carried out. Additionally, the interaction of the molten salts with the thermal oil (HTF) used in the plant in Palermo has been studied in laboratory under representative conditions. The objective of this experimental study was to identify potential safety issues which may arise during the plant management: in case of a potential leakage from one immersed heat exchanger in the molten salt bath the oil can interact with the oxidizing molten salts with consequent exothermic reactions leading to gas formation. Experimental results carried out at the ENEA-Casaccia chemical laboratories demonstrated that, under representative conditions of the TES, there is no occurrence of such strong interaction between the components in event of failure.
Partnership
• The Cyprus Institute (Cyprus)• Cyprus Chamber of Commerce and Industry (Cyprus)• Academy for Scienti�ic Research and Technology (Egypt)• New and Renewable Energy Authority (Egypt)• Elsewedy Electric (Egypt)• French Alternative Energies and Atomic Energy Commission (France)• CEEI Provence - Innovation business support (France)• University of Athens, Institute of Accelerating Systems and Application (Greece)• Al Balqa Applied University (Jordan)• Ministry of Energy and Mineral Resources (Jordan)• Millenium Energy Industries (Jordan)• Sicily Region - Department of Production Activities (Italy)• ENEA - National Agency for New Technologies, Energy and Sustainable Economic Development (Italy)
Project coordinator
Consorzio ARCA (Italy)
Consorzio ARCAViale delle Scienze
Edif. 16 - 90128 Palermo (Italy)
Project LeaderFabio Maria Montagnino +39 091 661 56 54
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