- Email: [email protected]
Industrial Heating application of a Salinity gradient solar pond for salt production
ScienceDirect Energy Procedia 00 (2018) 000–000 ScienceDirect
Available online at www.sciencedirect.com
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2019) 000–000 231–238 EnergyProcedia Procedia160 00 (2017) www.elsevier.com/locate/procedia 2nd International Conference on Energy and Power, ICEP2018, 13–15 December 2018, Sydney, Australia 2nd International Conference on Energy and Power, ICEP2018, 13–15 December 2018, Sydney, Australia
Industrial Heating application of a Salinity gradient solar pond for salt production Industrial Heating application of a Salinity The 15th International Symposium on District gradient Heating and solar Coolingpond for a& b a& c a salt production Mohammed Bawahab , Hosam Faqeha , Quoc Line Ve , Ahmadreza Faghihd, Assessing theAbhijit feasibility of using the heat demand-outdoor a a Date , and Aliakbar Akbarzadaha * a& b a& c d Mohammed Bawahab , Hosam Faqeha , Quoc Line3083, Ve , Ahmadreza Faghih , temperature function for a long-term district heat demand forecast School of Engineering, RMIT University, Melbourne, Victoria, Australia. a a a
Abhijit DateDepartment, , and Aliakbar Akbarzadah Engineering Jeddah university, Jeddah, Saudi * Arabia. *, A.dMechanical Pina , P.Engineering FerrãoDepartment, , J. Fournier ., B. Lacarrière , O. Le Correc b Yazd University, Yazd, Iran bMechanical
cMechanical aSchool of a,b,c a a Umm AL-Qura bVictoria, c Engineering Department, University, Makkah, Saudi Arabia. Engineering, RMIT University, Melbourne, 3083, Australia.
I. Andrić
Mechanical Engineering Department, Jeddah university, Jeddah, Saudi Arabia. cMechanical Engineering Department, Umm AL-Qura University, Makkah, Saudi Arabia. IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Mechanical Department, Yazd University, Yazd, Iran Veolia dRecherche & Engineering Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Abstract Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France a
This research is investigating the possibility of using heat stored in solar ponds for salt drying. At present, Pyramid Salts, a salt Abstract producing company located in the north of Victoria, Australia, use electric heaters to heat ambient air from around 20 °C to Abstract around 70 °C in their salt crystallizers for saltofdrying. Thisstored research paperponds aims to a solar drivenPyramid heat pump coupled This research is investigating the possibility using heat in solar fordevelop salt drying. AtPV present, Salts, a salt with a solarcompany pond to located supply necessary hot of air.Victoria, According to the collected dataheaters solar pond performance in Pyramid Hill 20 indicates producing in the north Australia, use electric to heat ambient air from around °C to District heating networks addressed in theresearch literature oftothe most solutions for decreasing the that heat70will available atare thecommonly bottomforofsalt thedrying. pond between 35 °C paper to as 50 one °C (winter to summer). Coupling salinity gradient around °C be in their salt crystallizers This aims develop aeffective solar PV driventhe heat pump coupled greenhouse gas emissions from the systems require high investments which areinreturned the heat solar the heat pump is building the of These this to research paper. The heat pump’s evaporation booststhrough from ambient with apond solar with pond to supply necessary hotnovelty air.sector. According the collected data solar pond performance Pyramid Hill indicates sales. tobeavailable the changed climate conditions and building policies, heat demand inamount the future could gradient decrease, temperature solar pond heat andbetween above 24/7 around. result, theCoupling of electrical energy that heatDue willto available at the bottom of(40 the°C) pond 35renovation °Calltoyear 50 °C (winterAs toasummer). the salinity prolonging the investment return period. saving in thiswith project estimated be about GWh per year. In this preliminary data onboosts the developments of solar pond the has heatbeen pump is the to novelty of 1this research paper. Thework, heatthe pump’s evaporation from ambient The main scope of this ispond to profiles assess the of using temperature function for heat demand salinity, temperature, andpaper turbidity willfeasibility be considered andthe discussed. temperature to available solar heat (40 °C) and above 24/7 allheat yeardemand around.– outdoor As a result, the amount of electrical energy forecast. Theproject districthas of been Alvalade, located Lisbon (Portugal), was as a the casepreliminary study. Thedata district is developments consisted of 665 saving in this estimated to beinabout 1 GWh per year. In used this work, on the of buildings that vary in construction typology. weather scenarios (low, medium, high) and three district salinity, temperature, andboth turbidity profiles period will beand considered andThree discussed. scenariosPublished were developed (shallow, ©renovation 2018 The Authors. by Elsevier Ltd. intermediate, deep). To estimate the error, obtained heat demand values were © 2019 The Authors. Published by Elsevier Ltd. compared with results from aunder dynamic heatBY-NC-ND demand model, previously developed and validated by the authors. This is an open access article the CC license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This isresults an open accessthat article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) The showed when weather change considered, the margin of error be acceptable for some applications Selection andAuthors. peer-review underonly responsibility of theis scientific committee of the 2nd could International Conference on Energy and © 2018 The Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and (the iserror in annual was lower 20% for all weather scenarios considered). However, after introducing renovation Power, ICEP2018. This an open accessdemand article under the CCthan BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Power, ICEP2018. scenarios,and thepeer-review error value under increased up to 59.5% oncommittee the weather scenarios combination considered). Selection responsibility of (depending the scientific of and the renovation 2nd International Conference on Energy and Keywords: Solar Solar Pond;increased Salinity Gradient Solar Pond; Heat Heat Waste The value of Energy; slope coefficient on average within thepump; range of generation; 3.8% up to 8%heat perrecovery; decade, that corresponds to the Power, ICEP2018. decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios On the other Solar hand,Pond; function 7.8-12.7% per decade (depending on the Keywords: Solar Energy; considered). Solar Pond; Salinity Gradient Heat intercept pump; Heatincreased generation;for Waste heat recovery; coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. by Elsevier Ltd. * Corresponding author.Published Tel.: +6-144-991-3036. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and E-mail address: [email protected] Cooling. * Corresponding author. Tel.: +6-144-991-3036.
1876-6102 © 2018 The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. committee of the 2nd International Conference on Energy and Power, ICEP2018. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and Power, ICEP2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and Power, ICEP2018. 10.1016/j.egypro.2019.02.141
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
232
2
1. Introduction A solar pond is a body of saline water in which the salt solution increase from top to bottom at or near the saturation brine. Solar heat can be stored in a solar pond more effectively compared to a thin body of water with the same size because the salinity gradient which prevent convection current. The Salinity Gradient Solar Pond (SGSP) It is a type of solar collector that can simultaneously collect solar irradiance and store it for a long time as thermal energy. The storage of thermal energy can be suitable for sourcing heat during the year. In case of solar radiation falls onto a surface of an ordinarily freshwater pond, part of this radiation reflected away from the surface, and the rest penetrated and absorbed into a freshwater pond. The thermal absorbed energy is quickly dissipated to the atmosphere due to the natural convection heat transfer. Therefore, freshwater pond temperature keep following the pathway of average ambient temperature and heat never rises in such pond. In the case of SGSP, the natural convection is suppressed which allow the heat to be penetrated, collected and trapped for a longer time. SGSP generally divided into three zones as shown in figure 1. The upper convective zone (UCZ) is a thin homogenous layer of fresh water or low salinity water. Its temperature follows the average ambient temperature of the region. The non-convective zone (NCZ) is the middle layer in SGSP where the saline concentration increases progressively with depth. As the salinity concentration increases, the density of the solution increases. Consequently, brine water in one layer cannot rise to the next upper layer in NCZ as the next layer has a higher density than the previous one. This suppresses heat transfer by convection due to the density gradient and the only losses of heat due to conduction in this layer. The lower convective zone (LCZ) is the bottom layer of the pond that has a uniform high salinity concentration of salinity, near saturation or saturation brine. The LCZ is the heat storage layer in the form of thermal energy [1, 2].
Fig. 1. Salinity Gradient solar Pond; Height in (Y axis) vs. Temperature and Density in (X axis)
As stated, solar radiation penetrates the surface of SGSP to be collected and stored as heat in the lower layer LCZ. This heating temperature can reach up to 90 °C to be available on a 24-hour basis for all applications requiring lowgrade heat. The heat stored in the bottom layer of the pond can be used directly for heating applications such as industrial process heating or converted into electricity using an appropriate heat engine to drive an electrical generator. This research is investigating the possibility of applying heat stored in solar ponds for salt drying. Nomenclature COPh LCZ NCZ NTUs SGSP
Coefeicent of Performance heat Lower Convective Zone Non-Convective Zone Nephelometric Turbidity Unit Salinity Gradient Solar Pond
UCZ TL Cp ∆T ṁ ρ
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
233 3
Upper Convective Zone Heat Pump Low Temperature Specific heat of fluid measured in [J/Kg°C] Temperature deference measured in [°C] mass flow rate measured in [Kg/s] density [kg/m3 ]
1.1. Pyramid Hill Solar Pond The salinity gradient solar pond has been built on Pyramid Salt Pty Ltd in the north of Victoria, Australia and is approximately 200 km north of Melbourne in the Pyramid Hill. This solar pond called the Pyramid Hill solar pond. It was constructed in 2001. The Pyramid Hill solar pond illustrated in figure 2. It has a rectangular constriction shape. This pond is 3000 m2 in an area, and 3 meters in deep. The base and walls of the pond were lined with a 1 mm thick high-density polyethylene Nylex Millennium. The water depth is fixed at 2.2 m from the bottom using an overflow system.
Fig. 2. SGSP in Pyramid Salt Pty Ltd taken from Google map
2. Current status Solar pond profiles have been measured using different instruments by collecting samples using sampling tube on April 2018 and on August 2018. The reading was collecting every 10 cm segments starting from the surface to the bottom of SGSP. 2.1. Temperature profile The temperature profile was measured by using HT-9815 Digital K type Thermocouple Thermometer. Thermocouple wire was fixed on the sampling tube which allows temperature reading to be taken from the same level as the taken sample simultaneously. Solar pond’s temperature profile is shown in figure 3. As seen it has its maximum recorded temperature at the bottom and decreases with height. At present (winter) is 29 °C. It is anticipated that the temperature at the bottom will get to higher than 50 °C as the warmer months approach.
234
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
4
Fig. 3. Pyramid Salt Solar Temperature profile on April & August 2018
2.2. Density profile Density profile was measured by using Anton Paar DMA 35 V4 portable Density Meter. The current density profile is shown in figure 4. The maximum density is 1275kg/m3 which is the density of saturated brine (≈30%). The density decreases with height. At the moment the pond has a thick top convective layer and almost no storage zone. By injecting concentrated brine at the bottom of the pond LCZ layer will be created.
Fig. 4. Pyramid Salt Solar Pond Density profile on April & August 2018
2.3. Transparency of SGSP Turbidity profile was measured by using Hach 2100Q Portable Turbidimeter. The profile is presented in figure 5 where the turbidity less than one has been achieved for most of the upper parts of the pond where high transparency is desired. The efficiency of the solar pond reduces dramatically with increasing the turbidity. According to [3], it is recommended to keep turbidity less or equal 0.5 NTUs for a salinity gradient solar pond. Transparency of solar pond can be achieved by two methods. Chemical treatment is one of the methods, such as lowering PH level using chloride acid. The natural method can clarify solar pond water using brine shrimp. This method is employed in Pyramid Hill solar pond to control the population of algae which are one of the main sources of solar pond turbidity. As a result, clarification and low turbidity are achieved [4].
Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000 Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238
5 235
Fig. 5. Pyramid Salt Solar Pond Density profile on April & August 2018
2.4. Heat extraction from Pyramid Hill solar pond. Extracting heat from solar pond can be divided into two methods. First, extracting the brine from the layer below the interface of NCZ and LCZ via a diffuser and then the hot brine flow via an external heat exchanger. After that, the cooled brine returned to the LCZ via another diffuser. Using the diffuser prevents excessive velocity between brine layers. Second, this method involves a heat exchanger submerged in the LCZ of the pond. Fluid such as fresh water will be pumped to the external heat exchanger. This will deliver heat only by natural convection in the brine and to the application area. The brine at LCZ level is saturated or near saturated brine. Thus, corrosion can be avoided in such a harsh environment by using non-metallic material and may make this option more cost-effective. The second method is established in the pyramid Hill solar pond as shown in figure 6. There are 50 parallel lines submerged into the solar pond as a heat exchanger. Each line with 60 m in length is crossing the LCZ of the pond and connected tightly to two perpendiculars, parallel pipes (inlet and outlet) at the sides of the ponds. Fresh water will be pumped by 2kW water pump to the CO2 heat pump. The heat extraction rate can be calculated using the following formula [5, 6]: 𝑄𝑄𝑄𝑄̇ = 𝑚𝑚𝑚𝑚̇ ∗ 𝐶𝐶𝐶𝐶𝑝𝑝𝑝𝑝 ∗ ∆𝑇𝑇𝑇𝑇
Fig. 6. Solar pond's parallel submerge and side perpendicular pipes
236
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
6
3. PV driven heat pump system coupled with Pyramid Hill solar pond The solar pond project is a collaborative venture between RMIT University, Pyramid Salt Pty Ltd and Mayekawa Australia Pty Ltd to demonstrate and commercialise hot air supply systems for heating by coupling PV with the heat pump. Recently, numbers of large-scale PV systems are grown in Australia such as the PV panels installed in Pyramid Salt Pty Ltd. PV panels are ground-mounted in rows and columns using Aluminum beams. They are located in front of the Pyramid Salt manufacture in a flat area. The system capacity can produce 300 kW. According to the forecast power generation of this system, it can produce 21.5 MWh in July where the actual data shows 27.5 MWh was generated in July 2018. 4. Theoretical performance for CO2 Heat Pump hot air supply “Eco Sirocco”: Ecosirocco (CO2 Heat Pump) is one of MAYEKAWA Australia Pty Ltd products. It is a compact and light design heat pump that has no combustion process in use. According to the company website, the air can be heated up to 120 °C, and the theoretical energy saving can reach up to 56% with a reduction in CO2 emission up to 68% compared with a conventional boiler. This makes this product attractive to replace the current use of the conventional electrical heater. 5. Conventional heating system The current heating system in RMIT University-industry partner (Pyramid Salt Pty Ltd) requires approximately 175 KWh of electrical energy per month that is consumed for the heating system to raise the air temperature from around 20 °C to 70 °C for the salt drying process. Figure 7 represents a schematic drawing of the current conventional hating system. Ambient air heated up by an electric heater and then pass salt dryer. As the hot air entering the salt tray, it will absorb moisture from the salt crystals and take it to the atmosphere outside the salt tray. In this stage, the air temperature will be around 40 °C with relative humidity of 90%.
Fig. 7. Electrical heating system for salt drying
6. Project description This project proposes to use solar energy and heat pumps to provide heating for industrial processes. The success of the proposed project will reduce the electrical energy consumption by 1GWh per year, and renewable energy source will replace this. PV panels installed in Pyramid Salt Pty Ltd by March 2018, that can produce up to 300 KWh. A pilot scale 100 kW solar pond-heat pump system will be designed, fabricated and installed to boost the temperature of the heat generated from a 3000 m² solar pond to be constructed next to the industrial mineral/salt dryer. The solar pond will be used to boost the CO2 heat pump efficiency to heat the air from ambient temperature to some 40 °C in summer and winter time. Data will be collected and stored throughout the last year of the project on the performance of the system. By analysing the data, the saving energy of the solar pond coupled with air heating system using the heat pump will be calculated.
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
237 7
6.1. Coupling solar pond with Ecosirocco Currently, Pyramid Salt Pty Ltd is using an electrical heater for rising ambient air temperature (about 20 ℃) to 70 ℃. The difference in temperature is 50 ℃. This heat is required for the process of salt drying. The average consumption of electricity during the year 2018 is 180 KWh/month where the majority of this consumption spent on the electrical heat system. To reduce the power consumption of the current heater a “CO2 Heat Pump” will be integrated with the current air heater system. Consequently, the inlet air temperature of the current electrical heater will increase as shown in figure 8. The CO2 heat pump will preheat the ambient temperature air from 20 ℃ to 70 ℃ via the heat pump’s condenser. To boost the system and reduce its consumption, SGSP will be integrated into the CO2 Heat Pump. This can be achieved by circulating fresh water through submerged pipes in LCZ and the evaporator of the CO2 Heat Pump. Therefore, the TL will be increased to near LCZ temperature via the heat exchanger. As a result, the required work consumption of heat pump will be reduced eventually. Mayekawa Australia Pty Ltd provides Table 1 which is a theoretical calculation. Air inlet temperature column represents the ambient air temperature entering the heater. Air outlet temperature column represents the required output air temperature after the heater for the heating process. Air inlet flow rate column represents the flow rate of air from the atmosphere to the salt dryer via heaters. Hot water temperature from SGSP column represents the temperature of the circulated fresh water entering the evaporation of the heat pump. Hot water temperature to SGSP column represents the temperature of circulated fresh water exiting the evaporation of the heat pump. Water flow rate of heat source column represents the flow rate of circulated fresh water between the submerged pipes in LCZ of SGSP and the evaporation of the heat pump. As shown in table 1, in case of the first row, the ambient temperature is assumed 10 ℃, circulated fresh water interring the heat pump is 35 ℃, and then exiting the heat pump with 29.9℃, and the air inlet flow rate is 6092 m3 /h, the maximum heating capacity is equal to 126.7 KW. The heating coefficient of performance for the heat pump increases with heat capacity increases. According to the theoretical calculation, the heat pump with a coefficient of performance close to 5 COP can reduce the consumption to 90 KWh/ month.
Table 1. Theoretical Performance Hot water Temp. from SGSP
Hot water Temp. to SGSP
Water flow rate of heat source
Heating capacity
cooling capacity
Power consumption
COPh
℃
kW
kW
kW
-
35
℃
L/min
6092
29.9
300
126.7
107.8
24.3
5.2
15
6717.1
35
29.9
300
125.6
106.1
24.8
5.1
70
25
8264.4
40
35
287.8
121.7
100.4
25.1
4.8
70
28
8740.7
40
35
277.4
118.6
96.8
25.4
4.7
Air outlet Temp.
Air inlet Temp.
Air inlet flow rate
℃
m3/h
70
℃
10
70
238
Mohammed 00 (2018) 000–000 MohammedBawahab/ BawahabEnergy et al. / Procedia Energy Procedia 160 (2019) 231–238
8
Fig. 8. A schematic drawing of SGSP and solar PV integrated with a heat pump to boost its efficiency
7. Conclusion CO2 Heat Pump can supply hot air from ambient temperature up to 120 °C. The theoretical result for the heat pump can be boost by coupling it with solar pond. The salinity gradient solar pond store energy at the lower convective zone will be used by a submerged heat exchanger. The LCZ temperature of the solar pond varies between 35 °C to 50 °C throughout the year. The Proposed project between RMIT University, Pyramid Salt Pty Ltd, and Mayekawa Australia Pty Ltd has investigated the possibility of PV driven heat pump coupled with the solar pond to provide heating for salt crystallizers to dry salt. The estimated reduction of electrical energy for this project in Pyramid Hill Company is about 1 GWh/year. References
[1] Singh R, Tundee S, Akbarzadeh A. Electric power generation from solar pond using combined thermosyphon and thermoelectric modules. Solar Energy. 2011;85(2):371-8. [2] Faqeha H, Bawahab M, Vermont D, Date A, Akbarzadeh A. Setting up salinity gradient in an experimental solar pond (SGSP). 2018. [3] Wang Y, Akbarzadeh A. A study on the transient behaviour of solar ponds. Energy. 1982;7(12):1005-17. [4] Hull JR. Maintenance of brine transparency in salinity gradient solar ponds. Journal of Solar Energy Engineering. 1990;112(2):65-9. [5] Leblanc J, Akbarzadeh A, Andrews J, Lu H, Golding P. Heat extraction methods from salinity-gradient solar ponds and introduction of a novel system of heat extraction for improved efficiency. Solar Energy. 2011;85(12):3103-42. [6] El-Sebaii A, Ramadan M, Aboul-Enein S, Khallaf A. History of the solar ponds: a review study. Renewable and Sustainable Energy Reviews. 2011;15(6):3319-25.
Available online at www.sciencedirect.com
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2019) 000–000 231–238 EnergyProcedia Procedia160 00 (2017) www.elsevier.com/locate/procedia 2nd International Conference on Energy and Power, ICEP2018, 13–15 December 2018, Sydney, Australia 2nd International Conference on Energy and Power, ICEP2018, 13–15 December 2018, Sydney, Australia
Industrial Heating application of a Salinity gradient solar pond for salt production Industrial Heating application of a Salinity The 15th International Symposium on District gradient Heating and solar Coolingpond for a& b a& c a salt production Mohammed Bawahab , Hosam Faqeha , Quoc Line Ve , Ahmadreza Faghihd, Assessing theAbhijit feasibility of using the heat demand-outdoor a a Date , and Aliakbar Akbarzadaha * a& b a& c d Mohammed Bawahab , Hosam Faqeha , Quoc Line3083, Ve , Ahmadreza Faghih , temperature function for a long-term district heat demand forecast School of Engineering, RMIT University, Melbourne, Victoria, Australia. a a a
Abhijit DateDepartment, , and Aliakbar Akbarzadah Engineering Jeddah university, Jeddah, Saudi * Arabia. *, A.dMechanical Pina , P.Engineering FerrãoDepartment, , J. Fournier ., B. Lacarrière , O. Le Correc b Yazd University, Yazd, Iran bMechanical
cMechanical aSchool of a,b,c a a Umm AL-Qura bVictoria, c Engineering Department, University, Makkah, Saudi Arabia. Engineering, RMIT University, Melbourne, 3083, Australia.
I. Andrić
Mechanical Engineering Department, Jeddah university, Jeddah, Saudi Arabia. cMechanical Engineering Department, Umm AL-Qura University, Makkah, Saudi Arabia. IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Mechanical Department, Yazd University, Yazd, Iran Veolia dRecherche & Engineering Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Abstract Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France a
This research is investigating the possibility of using heat stored in solar ponds for salt drying. At present, Pyramid Salts, a salt Abstract producing company located in the north of Victoria, Australia, use electric heaters to heat ambient air from around 20 °C to Abstract around 70 °C in their salt crystallizers for saltofdrying. Thisstored research paperponds aims to a solar drivenPyramid heat pump coupled This research is investigating the possibility using heat in solar fordevelop salt drying. AtPV present, Salts, a salt with a solarcompany pond to located supply necessary hot of air.Victoria, According to the collected dataheaters solar pond performance in Pyramid Hill 20 indicates producing in the north Australia, use electric to heat ambient air from around °C to District heating networks addressed in theresearch literature oftothe most solutions for decreasing the that heat70will available atare thecommonly bottomforofsalt thedrying. pond between 35 °C paper to as 50 one °C (winter to summer). Coupling salinity gradient around °C be in their salt crystallizers This aims develop aeffective solar PV driventhe heat pump coupled greenhouse gas emissions from the systems require high investments which areinreturned the heat solar the heat pump is building the of These this to research paper. The heat pump’s evaporation booststhrough from ambient with apond solar with pond to supply necessary hotnovelty air.sector. According the collected data solar pond performance Pyramid Hill indicates sales. tobeavailable the changed climate conditions and building policies, heat demand inamount the future could gradient decrease, temperature solar pond heat andbetween above 24/7 around. result, theCoupling of electrical energy that heatDue willto available at the bottom of(40 the°C) pond 35renovation °Calltoyear 50 °C (winterAs toasummer). the salinity prolonging the investment return period. saving in thiswith project estimated be about GWh per year. In this preliminary data onboosts the developments of solar pond the has heatbeen pump is the to novelty of 1this research paper. Thework, heatthe pump’s evaporation from ambient The main scope of this ispond to profiles assess the of using temperature function for heat demand salinity, temperature, andpaper turbidity willfeasibility be considered andthe discussed. temperature to available solar heat (40 °C) and above 24/7 allheat yeardemand around.– outdoor As a result, the amount of electrical energy forecast. Theproject districthas of been Alvalade, located Lisbon (Portugal), was as a the casepreliminary study. Thedata district is developments consisted of 665 saving in this estimated to beinabout 1 GWh per year. In used this work, on the of buildings that vary in construction typology. weather scenarios (low, medium, high) and three district salinity, temperature, andboth turbidity profiles period will beand considered andThree discussed. scenariosPublished were developed (shallow, ©renovation 2018 The Authors. by Elsevier Ltd. intermediate, deep). To estimate the error, obtained heat demand values were © 2019 The Authors. Published by Elsevier Ltd. compared with results from aunder dynamic heatBY-NC-ND demand model, previously developed and validated by the authors. This is an open access article the CC license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This isresults an open accessthat article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) The showed when weather change considered, the margin of error be acceptable for some applications Selection andAuthors. peer-review underonly responsibility of theis scientific committee of the 2nd could International Conference on Energy and © 2018 The Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and (the iserror in annual was lower 20% for all weather scenarios considered). However, after introducing renovation Power, ICEP2018. This an open accessdemand article under the CCthan BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Power, ICEP2018. scenarios,and thepeer-review error value under increased up to 59.5% oncommittee the weather scenarios combination considered). Selection responsibility of (depending the scientific of and the renovation 2nd International Conference on Energy and Keywords: Solar Solar Pond;increased Salinity Gradient Solar Pond; Heat Heat Waste The value of Energy; slope coefficient on average within thepump; range of generation; 3.8% up to 8%heat perrecovery; decade, that corresponds to the Power, ICEP2018. decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios On the other Solar hand,Pond; function 7.8-12.7% per decade (depending on the Keywords: Solar Energy; considered). Solar Pond; Salinity Gradient Heat intercept pump; Heatincreased generation;for Waste heat recovery; coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. by Elsevier Ltd. * Corresponding author.Published Tel.: +6-144-991-3036. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and E-mail address: [email protected] Cooling. * Corresponding author. Tel.: +6-144-991-3036.
1876-6102 © 2018 The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. committee of the 2nd International Conference on Energy and Power, ICEP2018. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and Power, ICEP2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Energy and Power, ICEP2018. 10.1016/j.egypro.2019.02.141
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
232
2
1. Introduction A solar pond is a body of saline water in which the salt solution increase from top to bottom at or near the saturation brine. Solar heat can be stored in a solar pond more effectively compared to a thin body of water with the same size because the salinity gradient which prevent convection current. The Salinity Gradient Solar Pond (SGSP) It is a type of solar collector that can simultaneously collect solar irradiance and store it for a long time as thermal energy. The storage of thermal energy can be suitable for sourcing heat during the year. In case of solar radiation falls onto a surface of an ordinarily freshwater pond, part of this radiation reflected away from the surface, and the rest penetrated and absorbed into a freshwater pond. The thermal absorbed energy is quickly dissipated to the atmosphere due to the natural convection heat transfer. Therefore, freshwater pond temperature keep following the pathway of average ambient temperature and heat never rises in such pond. In the case of SGSP, the natural convection is suppressed which allow the heat to be penetrated, collected and trapped for a longer time. SGSP generally divided into three zones as shown in figure 1. The upper convective zone (UCZ) is a thin homogenous layer of fresh water or low salinity water. Its temperature follows the average ambient temperature of the region. The non-convective zone (NCZ) is the middle layer in SGSP where the saline concentration increases progressively with depth. As the salinity concentration increases, the density of the solution increases. Consequently, brine water in one layer cannot rise to the next upper layer in NCZ as the next layer has a higher density than the previous one. This suppresses heat transfer by convection due to the density gradient and the only losses of heat due to conduction in this layer. The lower convective zone (LCZ) is the bottom layer of the pond that has a uniform high salinity concentration of salinity, near saturation or saturation brine. The LCZ is the heat storage layer in the form of thermal energy [1, 2].
Fig. 1. Salinity Gradient solar Pond; Height in (Y axis) vs. Temperature and Density in (X axis)
As stated, solar radiation penetrates the surface of SGSP to be collected and stored as heat in the lower layer LCZ. This heating temperature can reach up to 90 °C to be available on a 24-hour basis for all applications requiring lowgrade heat. The heat stored in the bottom layer of the pond can be used directly for heating applications such as industrial process heating or converted into electricity using an appropriate heat engine to drive an electrical generator. This research is investigating the possibility of applying heat stored in solar ponds for salt drying. Nomenclature COPh LCZ NCZ NTUs SGSP
Coefeicent of Performance heat Lower Convective Zone Non-Convective Zone Nephelometric Turbidity Unit Salinity Gradient Solar Pond
UCZ TL Cp ∆T ṁ ρ
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
233 3
Upper Convective Zone Heat Pump Low Temperature Specific heat of fluid measured in [J/Kg°C] Temperature deference measured in [°C] mass flow rate measured in [Kg/s] density [kg/m3 ]
1.1. Pyramid Hill Solar Pond The salinity gradient solar pond has been built on Pyramid Salt Pty Ltd in the north of Victoria, Australia and is approximately 200 km north of Melbourne in the Pyramid Hill. This solar pond called the Pyramid Hill solar pond. It was constructed in 2001. The Pyramid Hill solar pond illustrated in figure 2. It has a rectangular constriction shape. This pond is 3000 m2 in an area, and 3 meters in deep. The base and walls of the pond were lined with a 1 mm thick high-density polyethylene Nylex Millennium. The water depth is fixed at 2.2 m from the bottom using an overflow system.
Fig. 2. SGSP in Pyramid Salt Pty Ltd taken from Google map
2. Current status Solar pond profiles have been measured using different instruments by collecting samples using sampling tube on April 2018 and on August 2018. The reading was collecting every 10 cm segments starting from the surface to the bottom of SGSP. 2.1. Temperature profile The temperature profile was measured by using HT-9815 Digital K type Thermocouple Thermometer. Thermocouple wire was fixed on the sampling tube which allows temperature reading to be taken from the same level as the taken sample simultaneously. Solar pond’s temperature profile is shown in figure 3. As seen it has its maximum recorded temperature at the bottom and decreases with height. At present (winter) is 29 °C. It is anticipated that the temperature at the bottom will get to higher than 50 °C as the warmer months approach.
234
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
4
Fig. 3. Pyramid Salt Solar Temperature profile on April & August 2018
2.2. Density profile Density profile was measured by using Anton Paar DMA 35 V4 portable Density Meter. The current density profile is shown in figure 4. The maximum density is 1275kg/m3 which is the density of saturated brine (≈30%). The density decreases with height. At the moment the pond has a thick top convective layer and almost no storage zone. By injecting concentrated brine at the bottom of the pond LCZ layer will be created.
Fig. 4. Pyramid Salt Solar Pond Density profile on April & August 2018
2.3. Transparency of SGSP Turbidity profile was measured by using Hach 2100Q Portable Turbidimeter. The profile is presented in figure 5 where the turbidity less than one has been achieved for most of the upper parts of the pond where high transparency is desired. The efficiency of the solar pond reduces dramatically with increasing the turbidity. According to [3], it is recommended to keep turbidity less or equal 0.5 NTUs for a salinity gradient solar pond. Transparency of solar pond can be achieved by two methods. Chemical treatment is one of the methods, such as lowering PH level using chloride acid. The natural method can clarify solar pond water using brine shrimp. This method is employed in Pyramid Hill solar pond to control the population of algae which are one of the main sources of solar pond turbidity. As a result, clarification and low turbidity are achieved [4].
Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000 Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238
5 235
Fig. 5. Pyramid Salt Solar Pond Density profile on April & August 2018
2.4. Heat extraction from Pyramid Hill solar pond. Extracting heat from solar pond can be divided into two methods. First, extracting the brine from the layer below the interface of NCZ and LCZ via a diffuser and then the hot brine flow via an external heat exchanger. After that, the cooled brine returned to the LCZ via another diffuser. Using the diffuser prevents excessive velocity between brine layers. Second, this method involves a heat exchanger submerged in the LCZ of the pond. Fluid such as fresh water will be pumped to the external heat exchanger. This will deliver heat only by natural convection in the brine and to the application area. The brine at LCZ level is saturated or near saturated brine. Thus, corrosion can be avoided in such a harsh environment by using non-metallic material and may make this option more cost-effective. The second method is established in the pyramid Hill solar pond as shown in figure 6. There are 50 parallel lines submerged into the solar pond as a heat exchanger. Each line with 60 m in length is crossing the LCZ of the pond and connected tightly to two perpendiculars, parallel pipes (inlet and outlet) at the sides of the ponds. Fresh water will be pumped by 2kW water pump to the CO2 heat pump. The heat extraction rate can be calculated using the following formula [5, 6]: 𝑄𝑄𝑄𝑄̇ = 𝑚𝑚𝑚𝑚̇ ∗ 𝐶𝐶𝐶𝐶𝑝𝑝𝑝𝑝 ∗ ∆𝑇𝑇𝑇𝑇
Fig. 6. Solar pond's parallel submerge and side perpendicular pipes
236
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
6
3. PV driven heat pump system coupled with Pyramid Hill solar pond The solar pond project is a collaborative venture between RMIT University, Pyramid Salt Pty Ltd and Mayekawa Australia Pty Ltd to demonstrate and commercialise hot air supply systems for heating by coupling PV with the heat pump. Recently, numbers of large-scale PV systems are grown in Australia such as the PV panels installed in Pyramid Salt Pty Ltd. PV panels are ground-mounted in rows and columns using Aluminum beams. They are located in front of the Pyramid Salt manufacture in a flat area. The system capacity can produce 300 kW. According to the forecast power generation of this system, it can produce 21.5 MWh in July where the actual data shows 27.5 MWh was generated in July 2018. 4. Theoretical performance for CO2 Heat Pump hot air supply “Eco Sirocco”: Ecosirocco (CO2 Heat Pump) is one of MAYEKAWA Australia Pty Ltd products. It is a compact and light design heat pump that has no combustion process in use. According to the company website, the air can be heated up to 120 °C, and the theoretical energy saving can reach up to 56% with a reduction in CO2 emission up to 68% compared with a conventional boiler. This makes this product attractive to replace the current use of the conventional electrical heater. 5. Conventional heating system The current heating system in RMIT University-industry partner (Pyramid Salt Pty Ltd) requires approximately 175 KWh of electrical energy per month that is consumed for the heating system to raise the air temperature from around 20 °C to 70 °C for the salt drying process. Figure 7 represents a schematic drawing of the current conventional hating system. Ambient air heated up by an electric heater and then pass salt dryer. As the hot air entering the salt tray, it will absorb moisture from the salt crystals and take it to the atmosphere outside the salt tray. In this stage, the air temperature will be around 40 °C with relative humidity of 90%.
Fig. 7. Electrical heating system for salt drying
6. Project description This project proposes to use solar energy and heat pumps to provide heating for industrial processes. The success of the proposed project will reduce the electrical energy consumption by 1GWh per year, and renewable energy source will replace this. PV panels installed in Pyramid Salt Pty Ltd by March 2018, that can produce up to 300 KWh. A pilot scale 100 kW solar pond-heat pump system will be designed, fabricated and installed to boost the temperature of the heat generated from a 3000 m² solar pond to be constructed next to the industrial mineral/salt dryer. The solar pond will be used to boost the CO2 heat pump efficiency to heat the air from ambient temperature to some 40 °C in summer and winter time. Data will be collected and stored throughout the last year of the project on the performance of the system. By analysing the data, the saving energy of the solar pond coupled with air heating system using the heat pump will be calculated.
Mohammed Bawahab et al. / Energy Procedia 160 (2019) 231–238 Mohammed Bawahab/ Energy Procedia 00 (2018) 000–000
237 7
6.1. Coupling solar pond with Ecosirocco Currently, Pyramid Salt Pty Ltd is using an electrical heater for rising ambient air temperature (about 20 ℃) to 70 ℃. The difference in temperature is 50 ℃. This heat is required for the process of salt drying. The average consumption of electricity during the year 2018 is 180 KWh/month where the majority of this consumption spent on the electrical heat system. To reduce the power consumption of the current heater a “CO2 Heat Pump” will be integrated with the current air heater system. Consequently, the inlet air temperature of the current electrical heater will increase as shown in figure 8. The CO2 heat pump will preheat the ambient temperature air from 20 ℃ to 70 ℃ via the heat pump’s condenser. To boost the system and reduce its consumption, SGSP will be integrated into the CO2 Heat Pump. This can be achieved by circulating fresh water through submerged pipes in LCZ and the evaporator of the CO2 Heat Pump. Therefore, the TL will be increased to near LCZ temperature via the heat exchanger. As a result, the required work consumption of heat pump will be reduced eventually. Mayekawa Australia Pty Ltd provides Table 1 which is a theoretical calculation. Air inlet temperature column represents the ambient air temperature entering the heater. Air outlet temperature column represents the required output air temperature after the heater for the heating process. Air inlet flow rate column represents the flow rate of air from the atmosphere to the salt dryer via heaters. Hot water temperature from SGSP column represents the temperature of the circulated fresh water entering the evaporation of the heat pump. Hot water temperature to SGSP column represents the temperature of circulated fresh water exiting the evaporation of the heat pump. Water flow rate of heat source column represents the flow rate of circulated fresh water between the submerged pipes in LCZ of SGSP and the evaporation of the heat pump. As shown in table 1, in case of the first row, the ambient temperature is assumed 10 ℃, circulated fresh water interring the heat pump is 35 ℃, and then exiting the heat pump with 29.9℃, and the air inlet flow rate is 6092 m3 /h, the maximum heating capacity is equal to 126.7 KW. The heating coefficient of performance for the heat pump increases with heat capacity increases. According to the theoretical calculation, the heat pump with a coefficient of performance close to 5 COP can reduce the consumption to 90 KWh/ month.
Table 1. Theoretical Performance Hot water Temp. from SGSP
Hot water Temp. to SGSP
Water flow rate of heat source
Heating capacity
cooling capacity
Power consumption
COPh
℃
kW
kW
kW
-
35
℃
L/min
6092
29.9
300
126.7
107.8
24.3
5.2
15
6717.1
35
29.9
300
125.6
106.1
24.8
5.1
70
25
8264.4
40
35
287.8
121.7
100.4
25.1
4.8
70
28
8740.7
40
35
277.4
118.6
96.8
25.4
4.7
Air outlet Temp.
Air inlet Temp.
Air inlet flow rate
℃
m3/h
70
℃
10
70
238
Mohammed 00 (2018) 000–000 MohammedBawahab/ BawahabEnergy et al. / Procedia Energy Procedia 160 (2019) 231–238
8
Fig. 8. A schematic drawing of SGSP and solar PV integrated with a heat pump to boost its efficiency
7. Conclusion CO2 Heat Pump can supply hot air from ambient temperature up to 120 °C. The theoretical result for the heat pump can be boost by coupling it with solar pond. The salinity gradient solar pond store energy at the lower convective zone will be used by a submerged heat exchanger. The LCZ temperature of the solar pond varies between 35 °C to 50 °C throughout the year. The Proposed project between RMIT University, Pyramid Salt Pty Ltd, and Mayekawa Australia Pty Ltd has investigated the possibility of PV driven heat pump coupled with the solar pond to provide heating for salt crystallizers to dry salt. The estimated reduction of electrical energy for this project in Pyramid Hill Company is about 1 GWh/year. References
[1] Singh R, Tundee S, Akbarzadeh A. Electric power generation from solar pond using combined thermosyphon and thermoelectric modules. Solar Energy. 2011;85(2):371-8. [2] Faqeha H, Bawahab M, Vermont D, Date A, Akbarzadeh A. Setting up salinity gradient in an experimental solar pond (SGSP). 2018. [3] Wang Y, Akbarzadeh A. A study on the transient behaviour of solar ponds. Energy. 1982;7(12):1005-17. [4] Hull JR. Maintenance of brine transparency in salinity gradient solar ponds. Journal of Solar Energy Engineering. 1990;112(2):65-9. [5] Leblanc J, Akbarzadeh A, Andrews J, Lu H, Golding P. Heat extraction methods from salinity-gradient solar ponds and introduction of a novel system of heat extraction for improved efficiency. Solar Energy. 2011;85(12):3103-42. [6] El-Sebaii A, Ramadan M, Aboul-Enein S, Khallaf A. History of the solar ponds: a review study. Renewable and Sustainable Energy Reviews. 2011;15(6):3319-25.