Scholarly article on topic 'Characterization of Several Moroccan Rocks Used as Filler Material for Thermal Energy Storage in CSP Power Plants'

Characterization of Several Moroccan Rocks Used as Filler Material for Thermal Energy Storage in CSP Power Plants Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — H. Grirate, N. Zari, Iz. Elamrani, R. Couturier, A. Elmchaouri, et al.

Abstract This paper demonstrates the potential of the quartzite as an economic and efficient filler material in thermal oil direct thermocline storage system. This natural rock appears as a good candidate for thermal energy storage by sensible heat up to 350°C. In the present study, many experiences were conducted in order to choose the best rock among five varieties (quartzite, basalt, granite, hornfels and marble) which are found abundant in Morocco. The optimal rock was selected according to various criteria such as surface characteristics, porosity, density, calorific capacity, hardness, mechanical resistance. The chosen rock should also provide a thermal stability during energy exchange with the heat transfer fluid (HTF). It should be noted that choice of the rocks as a filler material may reduce the quantity of the HTF used for charging and discharging the thermal energy. Hence, the shrinkage of tank volume by thermocline sensible heat storage system using rocks as filler materials allows reducing the cost with an increase in the efficiency of the system.

Academic research paper on topic "Characterization of Several Moroccan Rocks Used as Filler Material for Thermal Energy Storage in CSP Power Plants"

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Energy Procedía 49 (2014) 810 - 819

SolarPACES 2013

Characterization of several Moroccan rocks used as filler material for thermal energy storage in CSP power plants

H. Griratea,d, N. Zaria*, Iz. Elamranib, R. Couturierc, A. Elmchaourid,

S. Belcadi , P. Tochon

a Moroccan foundation for Advanced Science Innovation and Research MAScIR, Avenue Mohamed El Jazouli,Rabat, Morocco b Scientific institute, Department of Earth Sciences, Team of geomaterials and geoenvironment, Avenue Ibn Batouta Rabat, Morocco c CEA LITEN, National Institute of Solar Energy, Solar Technologies Department, Thermal Systems Laboratory,Grenoble,France d Hassan II University, Faculty of Science and Technology, Department of Chemistry, BP 146, Mohammedia, Morocco

Abstract

This paper demonstrates the potential of the quartzite as an economic and efficient filler material in thermal oil direct thermocline storage system. This natural rock appears as a good candidate for thermal energy storage by sensible heat up to 350 °C. In the present study, many experiences were conducted in order to choose the best rock among five varieties (quartzite, basalt, granite, hornfels and marble) which are found abundant in Morocco. The optimal rock was selected according to various criteria such as surface characteristics, porosity, density, calorific capacity, hardness, mechanical resistance. The chosen rock should also provide a thermal stability during energy exchange with the heat transfer fluid (HTF). It should be noted that choice of the rocks as a filler material may reduce the quantity of the HTF used for charging and discharging the thermal energy. Hence, the shrinkage of tank volume by thermocline sensible heat storage system using rocks as filler materials allows reducing the cost with an increase in the efficiency of the system.

© 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selectionandpeerreviewbythescientificconference committeeofSolarPACES2013underresponsibilityof PSEAG. Final manuscript published as received without editorial corrections. Keywords: TES; CSP; materials storage; rocks; thermocline

1. Introduction

Solar thermal power plants are considered as a key technology for electricity generation from renewable energy resources [1]. In the last years, concentrated solar power (CSP) has drawn the attention of the energy utilities all over the world. Its operating principle is based on capturing energy from solar radiation, transforming it into heat

* Corresponding author. Tel.: + 212.661.83.18.06 E-mail address:n.zari@mascir.com

1876-6102 © 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons. org/licenses/by-nc-nd/ 3.0/).

Selection and peer review by the scientific conference committee of SolarPACES 2013 under responsibility of PSE AG.

Final manuscript published as received without editorial corrections.

doi:10.1016/j.egypro.2014.03.088

Nomenclature

CSP ConcentratedSolarPower TES ThermalEnergyStorage HTF HeatTransferFluid TGA ThermogravimetricAnalysis DSC DifferentialScanningCalorimetry XRS X-rayFluorescenceSpectrometer

and generating electricity by using steam turbines, gas turbines or Stirling engines. However, solar energy is known for its intermittent nature that may be quite predictable and not suitable for base load electricity generation without an energy backup system [2]. For this purpose, TES system is required to be attached to solar collectors in order to regulate the mismatch between energy supply and energy demand [3]. The period of heat production can be extended and exploited during night time or cloudy days. Thermal energy can be stored as sensible heat, latent heat or chemical energy [4]. In sensible heat storage, heat is exchanged without phase transition between two materials in an isolated system. Latent heat is stored in phase change materials. In case of thermo-chemical storage, this technique involves a chemical reaction [4].

Developing efficient and inexpensive installation of TES and increasing its reliability is the principal object of current research [5, 6]. There are different ways or techniques to store energy such as thermocline systems. This technique is efficient for heat exchange, because of the direct contact between the HTF and storage materials. It has been developed since the 80s, based on a single tank which separates the hot fluid and the cold fluid by a thermal gradient. Indeed, the energy stored in this case depends on the material used. The advantages of the thermocline system are: a decrease of the storage tanks cost (thermocline system is about 35 % cheaper than the two tank storage system according to Brosseau and al [7]), and a possibility to use inexpensive solid filler materials [8, 9]. Hasnain [10] reported that the available solid materials which can be used for low as well as high temperatures heat storage are metals, sand, bricks, rocks, concrete and ceramic. It's known that some materials such as concrete and ceramics are industrialized. Therefore, choosing natural rocks as filler material may reduce the cost and also the quantity of the HTF used for charging and discharging energy up to 80% in the tank [11]. Furthermore, rocks are non-toxic, non-flammable and act both as heat transfer surface and storage medium [12]. Concerning the properties that must be taken into account in assessing the storage material, Ismail and Stuginsky [13] conducted an analytical study on possible fixed bed models for phase change materials and sensible heat storage and presented a detailed report on the effects of various parameters on the performance. They report that the relevant thermophysical properties of storage material are thermal capacity, thermal conductivity and particle size. Another study of the effects of storage material properties on the thermal behavior of packed beds during charging realized by Aly and El-Sharkawy [14], showed that the specific heat of the storage material affects the thermal behavior of the packed bed in the same general manner as the density, where its increase causes a higher rate of charging and greater storage capacity. Hence, low cost, density, heat capacity and thermal conductivity are decisive criteria for choosing the best rocks that will store a significant amount of solar energy according to their importance.

On the other hand, the HTF also plays an important role in the profitability of TES system or thermocline. It must be operating to higher temperatures to improve power cycle efficiency. In fact, using molten salts as HTF may raise the solar field output temperature to 450-500 °C. The major challenge of this HTF is its high freezing point, leading to complications related to freeze protection in the solar field [15]. However, the thermal oil especially synthetic oil allows transferring a large amount of thermal energy because of its high specific capacity and conductivity. In addition thermal oil may reach a high temperature of about 393 °C [16] and has a low freezing point (< 25 °C). These properties will minimize the complication during operation of the solar plant. Since HTF will be in direct contact with the storage material, we must take into consideration the porosity of the rocks during the selection. Chosen Rock should have a low porosity to prevent the oil infiltration, which may cause its degradation. Therefore, mechanical resistance and hardness are measured in order to evaluate the internal cohesion of the rock and its strength to bear external mechanical stresses. Furthermore, rock chemical composition and mineralogy are also determined. This last point is especially important, as it could permit to prevent corrosion of the HTF by revealing

the precursor elements and the degradation of the rock caused by the destruction of hydrothermal minerals at high temperature. The determination of structure and texture allows assessing the rock surface and prevents possible cracking. The experimental results are discussed in this paper.

The most papers found in the literature discuss about testing rocks in system of storage solar energy using air as HTF [17-19].

2. Materials and methods

2.1. Description of material storage

Potential rocks for energy storage are selected according to their abundance in Morocco and their particular properties. The specifications of preferred rocks discussed in literature, are summarized in Table 1.

Table 1.Specification given in literature of chosen rocks [20-22].

Porosity

Density kg. m-3at 20°C

Uniaxial compressive strength MPa

Isobaric specific heat Capacity J kg"1 K"1 at 20°C

Conductivity W/m. K at 25°C

Thermal Capacity kJ m"3K_1

Granite (Grt) Basalt (Blt) Quartzite (Qtz) Marble (Mar) Hornfels (Hor)

igneous

1.02 - 2.87 0.22 - 22.1

igneous

metamorphic 0.40 - 0.65

metamorphic °.65 " °.81

metamorphic 0.8 " 2.3

2530 - 2620 2210 - 2770 2510 - 2860 2610 - 2670 2400 - 2800

100 - 300 100 - 350 150 - 300 50 - 200 100-200

600 -1200 800 -900 700 -1000 1470 700 -900

7. 7 3.2 1.5

1440 - 2880

1750 - 2500 3822

1680-2520 2560-2880

In the present study, samples of rocks were collected from different regions in Morocco. A detailed geological map has been prepared in order to describe the sample locations as shown in Figure 1.

Fig.1. Samples locations in the map of Morocco

2.2. Methods applied

Firstly, all samples of each type of rock defined previously were subjected to petrographic study (macroscopic and microscopic examination). The rocks were investigated macroscopically through the naked eye and a magnifying glass for their identification. The examination is made on the basis of visible criteria (shape, color, grain size, hardness and presence of carbonated elements detected by reaction to acid ...) and it was performed in the natural state of the rock as seen in Figure 2a, due to the weathering and sawing, which sometimes affect the surface of the rock and make it difficult to identify. In addition to the macroscopic description, samples were subjected to both tests in order to assess their hardness and reaction with hydrochloric acid (HCl). The hardness test is based on the Mohs scale which classifies minerals according to their hardness ranging from the softest (talc; N°1) to the hardest mineral (diamond, N°10). The test of hydrochloric acid (10 to 20% w/v) is performed to distinguish carbonate rocks of clay minerals, gypsum and siliceous.

Macroscopic characterization is followed later by thin section microscopy as shown in Figure 2b using a polarizing microscope. Major minerals and structure types (heteroblastic, homeoblastic or granoblastic) were determined.

The test of physical properties was performed on the saw-cut specimens as per ASTM C373-88 [23] (Figure 2c). Regarding a mechanical property, several cubes were prepared for determining the compressive strength of each rock using the compression pressure gauge.

Geochemical and thermal analyses were conducted using a fine powder of each sample. X-Ray Fluorescence spectrometry (XRS) was applied to determine geochemistry of samples. Thermogravimetric analysis (TGA instruments model Q 500) was used to determine their weight losses at high temperature and finally differential scanning calorimetry (DSC instrument model Q 100) was applied to measure the heat capacity of the selected rocks. These measurements were made by varying the temperature in the range from 25 °C to 400 °C under a N2 flow of 60 ml/min (O2 of 10 ml/min for TGA) and a heating rate at 10 °C/min. Samples mass was kept between 10 to 20 mg. All specimens were analyzed thrice in order to ensure measurements reproducibility. At a fixed temperature, the heat capacity of the sample was determined by the following equation [24]:

ExHx60 Cp =-

M: Sample weight (mg) H: Heat flux (mW) Hr: Scan rate (°C/min)

Fig.2. Samples preparation for the various studies: (a) specimens in the natural state, (b) specimen thin section, (c) saw-cut specimens

3. Results and discussions

3.1. Petrography and Geochemistry

Petrographic study is divided into two main parts: macroscopic and microscopic observations. Table 2 presents the main macroscopic features of the studied samples and Figure 3 shows their microscopic description according to their texture and constituent minerals (Appendix).

All rocks studied are from Morocco and they are distinguished by their diversity regarding color, structure, texture, minerals and hardness. Despite its compactness, marble is the only carbonated rock (calcite and dolomite) which presents a low to medium hardness. This feature may limit the lifetime of the rock causing its early degradation. Basalt presents a massive structure like all other studied rocks. However, it is composed of fine and dark grain which could affect the HTF causing its deterioration. On the basis of microscopic observation, it is noted that the granite and hornfels are composed of hydrothermal minerals (muscovite and biotite) which can deteriorate at high temperature, especially a granitic rock. This theory is proved by the thermogravimetric analysis afterward. Concerning the quartzite, this rock is very hard and distinguished by a cemented aspect, composed mostly of quartz. This mineral is known by its high thermal conductivity (7 W/m K) which is one of the important criteria for the storage of solar energy.

Table 2. Results of macroscopic examination of the varieties of rocks studied.

Rocks Macroscopic description Hardness Test HCl

Grt Massive rock with gray clear color and rough surface. Grains are joined and present an average size between 1 and 4 mm. high -

Blt Qtz Massive and homogeneous rock with a black to dark green color. This rock presents a few vacuoles, very fine grained and shiny and sometimes oriented. Massive rock, locally heterogeneous and microcracked. It has a light gray to yellow color, it presents also iron oxide and fine grain to invisible. medium to high very High -

Mar Massive and compact rock with pinkish gray color. Average grain size from 1 to 2 mm. It presents a meshed appearance and bright surface. low to medium +

Hor Massive and heterogeneous rock with green color and cornel appearance. Some visible crystals appear on a very fine-grained and glossy background. medium -

Fig.3. Microphotographs of the rocks studied (A: Granite, B: Basalt, C: Quartzite, D: Marble, E: Hornfels)

Geochemical characteristics study of the rocks provides information about the element that can affect the HTF (thermal oil) and may cause a possible nuisance of the storage unit. Table 3 reports the results obtained in percentage. The overall analysis of geochemical data presented in Table 3 reveals big contrast assessments where every variety of rocks is characterized by its own chemistry. The element iron is present with values quite marked in basalt (10.92 %). This result is confirmed in literature [25]. It should be noted that the iron can be combined to hydroxyl element, causing then the decay of the HTF. While the percentage of combustion elements is observed predominately in the marble (loss on ignition (L.I) = 43.05%). The abundance of carbon elements noted explains the effervescence occurred during the test of hydrochloric acid that was cited previously. On the other hand, carbonated element that contains the marble can produce the carbon dioxide (CO2) from the dissociation of CO3 under the rise of the temperature. This gas may create an increase in pressure of the storage unit leading to its burst if it is not connected to the safety valves. The granite and hornfels show a composition mostly of silica (69.74 and 63.40% respectively) with relatively high contents of alumina (14.30 and 21.70% respectively) and a minimal amount of alkali metals and iron. The quartzite is the rock that contains the highest quantity of silica of about 94.50 % with a few traces of other elements.

The geochemical data shows that the marble and basalt present unfavorable potentials in contact of the HTF and can lead to a serious consequences during operation of the solar system.

Table 3. Geochemistry of rocks studied given in percentage (%).

SiO2 TiO2 Al2Os Fe2O3 MnO MgO CaO Na2O K2O P2O5 L.I Total

Grt 69.74 0.62 14.30 4.05 0.06 0.82 1.71 3.18 4.74 0.13 0.87 100.25

Blt 47.27 2,12 17.46 10.92 0.28 1.83 13.39 3.08 1.02 0.25 0.37 98.99

Qtz 94.50 - 1.0 0.5 0.6 0.3 0.3 0.7 1.3 - 0.8 100.00

Mar 0.76 - 1.10 0.4 - - 54.75 - - - 43.05 100.06

Hor 63.40 1.13 21.70 6.0 - 1.59 0.12 0.30 3.36 0.11 2.29 100.00

3.2. Thermal and Physico-Mechanical Characterizations

• Physical and mechanical properties

Porosity can be classified into different types: total porosity, open porosity, and connected porosity [23]. The total porosity is simply the fractional volume of all void spaces inside a porous material. The connected porosity is the volume fraction of pore spaces that are fully interconnected between two opposite end faces and allowing the fluid to flow through the material. This porosity is classically quantified by permeability measurement. While the open porosity, considers only the proportion of voids that are communicated with the outside of the sample.

In this part, we measured the open porosity which is distributed and available at rock surface. In this case, open porosity can also report the cracks of the rock. This theory was proved by Chaki et al in a study of thermal damage of rocks revealing that open porosity increases with temperature, the microscopic examination showed some cracks appearing at the surface of the samples [26].

Regarding the mechanical properties, the uniaxial compressive strength (aC) is one of the important factors influencing rocks thermal conductivity. It should be noted that this property rises with increasing rocks uniaxial compressive strength; this study was carried out by Singh and al [27] to predict the thermal conductivity of rock through physico-mechanical properties. Further, thermal conductivity is one of the important criteria which define the optimal material storage as found by Ismail and Stuginsky [13].

Table 4 shows the result obtained. The rocks studied don't present notable difference in the physical properties. They generally have a low open porosity (between 0.2 and 1.17%), also a low water absorption (between 0.07 and 0.43%), and thus, the oil penetration is prevented. In addition, they present a high density (between 2.5 and 3 g/cm3) that will allow to increase the thermal capacity of energy storage according to the work of Aly and Sharkawy which aims to study the effects of storage media properties [14].

The quartzite and granite show the highest compressive resistance of about 150 to 170 MPa and 140 to 200 MPa respectively. The results of these tests are in good agreement with the hardness of the rocks which was estimated

during the pétrographie study through its constituent minerals and also with literature given in the first part of the storage material description.

Table 4. Physical and mechanical properties measurements.

Grt Bst Qzt Mar Hor

Porosity (%) 0.2 0.81 0.77 0.45 1.17

Density p (kg m-3) 2820 3020 2570 2680 2740

Water absorption (%) 0.07 0.27 0.30 0.17 0.43

ac (MPa) 150 - 170 70 - 90 140 - 200 70 - 100 60 - 80

• Thermal study - Thermogravimetric analysis (TGA)

Thermogravimetric analysis points out that only the granite and marble have lost weight at high temperature of about 3.3 and 2.9% respectively as seen in Figure 4. Based on petrographic examination, it can be noted that granite is composed of some minerals (biotite) containing hydroxyl bonds which broke at high temperature, leading to a weight loss later. Marble is composed predominantly of CaCO3 and its loss can be explained by the escape of CO2 during heating.

Fig.4. Thermogravimetric analysis curves

- Differential scanning calorimetry (DSC)

Heat capacity Cp at constant pressure was determined in the temperature range between 20- 400°C for each rock sample using a dynamic differential heat flow calorimeter (DSC). Table 5 shows the values of these measurements for different rocks that were studied at a temperature of about 300°C. The measured heat capacity ranges from 622 to 948 J kg-1K-1. The basalt and marble have relatively high capacities (948 and 931 J kg-1K-1), followed by the hornfels and quartzite (877 and 842 J kg-1K-1) and then the granite shows the lowest value (622 J kg-1K-1). These values appear consistent with the literature as shown in Table 1. It should be noted that the sample size influences the capacity of the rock according to the research of Ueli Scharli and Ladislaus Rybach [28] which was carried out to determine the specific heat capacity on rock fragments. Hence, the powdered samples should have a heat capacity much lower than the greater size. When heat capacity is related to unit volume rather than to unit mass or unit amount of substance it is referred to as volumetric heat capacity or thermal capacity. It can be calculated as the product of specific heat capacity c and density p as shown in Table 5 or as the ratio of thermal conductivity X and thermal diffusivity k [29]. Hence, the thermal capacity increases with the thermal conductivity.

Table 5. Thermal capacity of rocks at high temperature

Ort Bst Qzt Mar Hor

cp at 300°C (J kg-1 K-1) 620 950 840 930 880

P (kg m-3) 2820 3020 2570 2680 2740

Cp (kJ m-3 K-1) 1750 2870 2160 2490 2410

4. Conclusion

The physico-chemical and thermal properties are considered as a key for choosing the best material which will allow storage of solar energy with more efficiency and ensuring a long lifetime. Some criteria like porosity were listed according to the HTF chosen that should be operational and more profitable for the solar power plant.

The petrographic study was conducted to obtain information on the macroscopic and microscopic structural aspects of the rocks. This study showed the conformity of the quartzite which was proved by its compact structure formed of nested grain, as well as its mineralogical composition that is rich in quartz. It's noteworthy that this mineral presents a high thermal conductivity compared to other minerals (7W/m K) and this property presents one of the important criteria to ensure efficient heat transfer between the thermal oil and the rocks.

The analysis of physical properties of the tested rocks has demonstrated a high-density (2.5 to 3 g/ cm3). Therefore, their porosity is considered unsignificant. Thermogravimetric analysis showed mass losses of granite and marble which requires to be removed from the list of varieties studied in order to avoid any damages during storage unit operations. Differential scanning calorimetry showed that basalt has the highest heat capacity; nevertheless, it is composed of mafic1minerals in the form of very fine and dark grains, which can contaminate the thermal oil used as HTF, causing then its corrosion. The hardness evaluation turned out that the quartzite has a very high hardness compared to the hornfels and the other rocks.

Based on the results obtained, it seems that the quartzite satisfies the criteria listed previously and can be used in direct contact with thermal oil as the most suitable filler material for energy storage. This rock was identified also by Sandia National Laboratories (SNL) which demonstrates that the quartzite appears to be able to endure the molten salt environment quite well with no significant deterioration [30]. Some additional work is needed to conclude about the compatibility of the rock with thermal oil. Laboratory scale, equipments are installed for testing interaction between the materials chosen in order to validate this approach.

1 Rock rich in magnesium and iron

Acknowledgements

We express our thanks to all members of the laboratory team for their help to use the analytical techniques. Appendix

- Granite, grainy texture, Plagioclase (Pl) in polysynthetic twins- Feldspar (Fk) in subhedral crystals- Quartz (Qz) is anhedral in shape and is found in the interstices between crystals. Biotite (Bi) is present with a brown color, flaky and shreds outline containing some inclusions of zircon; Accessory minerals are found there such as apatite, zircon, ilmenite, hematite, chlorite...

- Basalt, Microlithic and porphyritic texture, Plagioclase (Pl) microlites in a background with calcic composition Plagioclase laths in porphyritic phase with polysynthetic macle and pyroxene crystals (Px) which present the tints of high polarization - Small amount of glass (non-crystalline material) and accessory minerals such as opaque (Op).

- Quartzite, Granoblastic texture, Quartz crystals are anhedral to extinction generally ondulente, present with an appearance very welded - besides quartz grains, few dominant plagioclases exist and some opaque grains (including iron oxides)

- Marble, Granoblastic texture, Calcite (Ct) and dolomite (Do) recrystallized in contiguous crystals - Some accessory minerals such as opaque (titanium or sulfides such as pyrite), diopside (pyroxene) or forsterite (magnesium peridot).

- Hornfels, Granoblastic texture. Quartz (Qz), Feldspar and Muscovite (Ms). Chlorite (Ch) green oriented in small bundle - Andalusite with clear appearance and a few spots of ovoid shape and whitish color of cordierite (Cd) -Some accessory minerals are also present such as oxides, zircon and apatite.

References

[1] Bauer. T et al, Overview of molten salt storage systems and material development for solar thermal power plants, Institute of Technical Thermodynamics, German Aerospace Center (DLR), Germany.

[2] Price H, Lupfert et al, Advances in parabolic trough solar power technology, Journal of Solar Energy Engineering 2002; 124:109.

[3] Ercan.O, Storage of thermal energy, Encyclopedia of Life Support Systems, Mechanical Engineering Department, Ankara.

[4] Atul Sharma et al, Review on thermal energy storage with phase change materials and applications, Department of Mechanical Engineering, Renewable and Sustainable Energy Reviews, Taiwan, 2009, 318-345.

[5] Gil A et al, State of the art on high temperature thermal energy storage for power generation, Renew Sustain Energy Rev 2010; 14:31-55.

[6] Medrano M, Gil A, Martorell I, Potau X, Cabeza LF. State of the art on high temperature thermal energy storage for power generation. Part 2, case studies. Renew Sustain Energy Rev 2010; 14:56-72.

[7] Brosseau D et al,Testing of thermocline filler materials and molten-salt heat transfer fluids for thermal energy storage systems in parabolic trough power plants. J Solar Energy Eng- Trans ASME 2005; 127: 109-16.

[8] Pacheco JE, Showalter SK, Kolb WJ. Development of a molten-salt thermocline thermal storage system for parabolic trough plants. In: Proceedings of ASME 2001, solar forum 2001, Washington, DC

[9] St Laurent SJ, Kolb WJ, Pacheco JE. Thermocline thermal storage tests for large scale solar thermal power plants. Sandia National Laboratories, Report SAND 2000-2059C; 2000.

[10] Hasnain SM. Review on sustainable thermal energy storage technologies. Part 1. Heat storage materials and techniques. Energy Convers Manage J 1998; 39 (11):1127-38.

[11] Nicolas Calvet et al, Compatibility of a post-industrial ceramic with nitrate molten salts for use as filler material in a thermocline storage system, Applied Energy, CIC Energigune, Spain, 2012.

[12] Harmeet Singh, A review on packed bed solar energy storage systems, Alternate Hydro Energy Centre, India, Renewable and Sustainable Energy Reviews, 2009.

[13] Ismail KAR et Stuginsky R, A parametric study on possible fixed bed models for PCM and sensible heat storage. Appl Thermal Eng 1999;19 (7):757-88.

[14] Aly SL et al, Effect of storage medium on thermal properties of packed bed, Heat Recovery Syst CHP 1990;10 (5/6):509-17.

[15] Kearney D, Herrmann U, Nava P, Kelly B, Mahoney R, Pacheco J, et al. Assessment of a molten salt heat transfer fluid in parabolic trough solar field.Trans ASME 2003;125:170-6.

[16] Pablo A, Antoni G, Joan R, Marc M et al, pilot plant for high temperature TES systems, GREA Innovacio Concurrent, Spain.

[17] Fricker. W, High-temperature heat storage using natural rock, North-Holland, Solar Energy Materials 24 (1991) 249-254.

[18] Waked AM. Solar energy storage in rocks, Mechanical Engineering Department, Kuwait University, Solar Wind Technolgy, Kuwait, 1986; 3(1):27-31.

[19] Audi. M, Experimental study of a solar space heating model using Jordonian rocks for storage, Energy Convers,1992, 33 (9) : 833-842.

[20] GOKHALE.B.V, Rotary drilling and blasting in large surface mines. CRC Press/Balkema, London, UK, 2011.

[21] Jaeger. C, Physical and mechanical properties of rock material, Cambridge University Press, 2010.

[22] Schumann. W, Der neue BLV Steine-und Mineralienfüher, Ed BLV, Munich, 1985.

[23] ASTM C373 - 88(2006) Standard Test Method for Water Absorption, Bulk Density, Apparent Porosity, and Apparent Specific Gravity of Fired Whiteware Products.

[24] Lesson, Differential Scanning Calorimetry (DSC), Theory and Experimental Conditions.

[25] GUEZAL. J et al, Le magmatisme jurassique-crétacé de Béni-Mellal (Haut-Atlas central, Maroc) : géochimie et signification géodynamique, Faculté des Sciences et Techniques, Béni Mellal, Maroc, 2011.

[26] Chaki. S et al, Influence of thermal damage on physical properties of a granite rock: Porosity, permeability and ultrasonic wave evolutions, Construction and Building Materials, France, 2007.

[27] Singh T.N et al, Prediction of thermal conductivity of rock through physico-mechanical properties, department of Earth Sciences, India,2005.

[28] Schärli Ueli, Ladislaus Rybach, Determination of specific heat capacity on rock fragments, Geothermics, 2001, 93-110.

[29] Clauser Christoph, Thermal storage and transport Properties of Rocks, I: Heat Capacity and Latent Heat, Encyclopedia of Solid Earth Geophysics, Harsh Gupta (ed.), E.ON Energy Research Center, Germany.

[30] Brosseau. D, Kelton JW, Ray D, Edgar M, Chisman K, Emms B. Testing of thermocline filler materials and molten-salt heat transfer fluids for thermal energy storage systems in parabolic trough power plants. J Solar Energy Eng-Trans ASME 2005;127: 109-16.