Testing of Thermocline Filler Materials and Molten-Salt Heat Transfer Fluids for Thermal Energy Storage Systems in Parabolic Trough Power Plants

Solar Energy ◽  
2004 ◽  
Author(s):  
Doug Brosseau ◽  
Mike Edgar ◽  
John W. Kelton ◽  
Kye Chisman ◽  
Daniel Ray ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Systems ◽  
Silica Sand ◽  
Filler Materials ◽  
Parabolic Trough ◽  
Concentrated Solar Energy

Parabolic trough power systems that utilize concentrated solar energy to generate electricity are a proven technology. Industry and laboratory research efforts are now focusing on integration of thermal energy storage as a viable means to enhance dispatchability of concentrated solar energy. One option to significantly reduce costs is to use thermocline storage systems, low-cost filler materials as the primary thermal storage medium, and molten nitrate salts as the direct heat transfer fluid. Prior thermocline evaluations and thermal cycling tests at the Sandia National Laboratories’ National Solar Thermal Test Facility identified quartzite rock and silica sand as potential filler materials. An expanded series of isothermal and thermal cycling experiments were planned and implemented to extend those studies in order to demonstrate the durability of these filler materials in molten nitrate salts over a range of operating temperatures for extended timeframes. Upon test completion, careful analyses of filler material samples, as well as the molten salt, were conducted to assess long-term durability and degradation mechanisms in these test conditions. Analysis results demonstrate that the quartzite rock and silica sand appear able to withstand the molten salt environment quite well. No significant deterioration that would impact the performance or operability of a thermocline thermal energy storage system was evident. Therefore, additional studies of the thermocline concept can continue armed with confidence that appropriate filler materials have been identified for the intended application.

Testing of Thermocline Filler Materials and Molten-Salt Heat Transfer Fluids for Thermal Energy Storage Systems in Parabolic Trough Power Plants

2005 ◽  
Vol 127 (1) ◽  
pp. 109-116 ◽  
Author(s):  
Doug Brosseau ◽  
John W. Kelton ◽  
Daniel Ray ◽  
Mike Edgar ◽  
Kye Chisman ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Systems ◽  
Silica Sand ◽  
Filler Materials ◽  
Parabolic Trough ◽  
Concentrated Solar Energy

Parabolic trough power systems that utilize concentrated solar energy to generate electricity are a proven technology. Industry and laboratory research efforts are now focusing on integration of thermal energy storage as a viable means to enhance dispatchability of concentrated solar energy. One option to significantly reduce costs is to use thermocline storage systems, low-cost filler materials as the primary thermal storage medium, and molten nitrate salts as the direct heat transfer fluid. Prior thermocline evaluations and thermal cycling tests at the Sandia National Laboratories’ National Solar Thermal Test Facility identified quartzite rock and silica sand as potential filler materials. An expanded series of isothermal and thermal cycling experiments were planned and implemented to extend those studies in order to demonstrate the durability of these filler materials in molten nitrate salts over a range of operating temperatures for extended time frames. Upon test completion, careful analyses of filler material samples, as well as the molten salt, were conducted to assess long-term durability and degradation mechanisms in these test conditions. Analysis results demonstrate that the quartzite rock and silica sand appear able to withstand the molten salt environment quite well. No significant deterioration that would impact the performance or operability of a thermocline thermal energy storage system was evident. Therefore, additional studies of the thermocline concept can continue armed with confidence that appropriate filler materials have been identified for the intended application.

scholarly journals Molten Nitrate Salt Development for Thermal Energy Storage in Parabolic Trough Solar Power Systems

2008 ◽  
Author(s):  
Robert W. Bradshaw ◽  
Nathan P. Siegel
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Power Plants ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Parabolic Trough ◽  
Heat Transfer Fluids

Thermal energy storage can enhance the utility of parabolic trough solar power plants by providing the ability to match electrical output to peak demand periods. An important component of thermal energy storage system optimization is selecting the working fluid used as the storage media and/or heat transfer fluid. Large quantities of the working fluid are required for power plants at the scale of 100-MW, so maximizing heat transfer fluid performance while minimizing material cost is important. This paper reports recent developments of multi-component molten salt formulations consisting of common alkali nitrate and alkaline earth nitrate salts that have advantageous properties for applications as heat transfer fluids in parabolic trough systems. A primary disadvantage of molten salt heat transfer fluids is relatively high freeze-onset temperature compared to organic heat transfer oil. Experimental results are reported for formulations of inorganic molten salt mixtures that display freeze-onset temperatures below 100°C. In addition to phase-change behavior, several properties of these molten salts that significantly affect their suitability as thermal energy storage fluids were evaluated, including chemical stability and viscosity. These alternative molten salts have demonstrated chemical stability in the presence of air up to approximately 500°C in laboratory testing and display chemical equilibrium behavior similar to Solar Salt. The capability to operate at temperatures up to 500°C may allow an increase in maximum temperature operating capability vs. organic fluids in existing trough systems and will enable increased power cycle efficiency. Experimental measurements of viscosity were performed from near the freeze-onset temperature to about 200°C. Viscosities can exceed 100 cP at the lowest temperature but are less than 10 cP in the primary temperature range at which the mixtures would be used in a thermal energy storage system. Quantitative cost figures of constituent salts and blends are not currently available, although, these molten salt mixtures are expected to be inexpensive compared to synthetic organic heat transfer fluids. Experiments are in progress to confirm that the corrosion behavior of readily available alloys is satisfactory for long-term use.

Effect of High Temperatures and Heating Rates on High Strength Concrete for Use as Thermal Energy Storage

2010 ◽  
Author(s):  
Emerson E. John ◽  
W. Micah Hale ◽  
R. Panneer Selvam
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
High Temperatures ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Heat Transfer Fluid ◽  
Heating Rates ◽  
Storage Media ◽  
Concrete Mixtures

In recent years due to rising energy costs as well as an increased interest in the reduction of greenhouse gas emissions, there is great interest in developing alternative sources of energy. One of the most viable alternative energy resources is solar energy. Concentrating solar power (CSP) technologies have been identified as an option for meeting utility needs in the U.S. Southwest. Areas where CSP technologies can be improved are improved heat transfer fluid (HTF) and improved methods of thermal energy storage (TES). One viable option for TES storage media is concrete. The material costs of concrete can be very inexpensive and the costs/ kWhthermal, which is based on the operating temperature, are reported to be approximately $1. Researchers using concrete as a TES storage media have achieved maximum operating temperatures of 400°C. However, there are concerns for using concrete as the TES medium, and these concerns center on the effects and the limitations that the high temperatures may have on the concrete. As the concrete temperature increases, decomposition of the calcium hydroxide (CH) occurs at 500°C, and there is significant strength loss due to degeneration of the calcium silicate hydrates (C-S-H). Additionally concrete exposed to high temperatures has a propensity to spall explosively. This proposed paper examines the effect of heating rates on high performance concrete mixtures. Concrete mixtures with water to cementitious material ratios (w/cm) of 0.15 to 0.30 and compressive strengths of up to 180 MPa (26 ksi) were cast and subjected to heating rates of 3, 5, 7, and 9° C/min. These concrete mixtures are to be used in tests modules where molten salt is used as the heat transfer fluid. Molten salt becomes liquid at temperatures exceeding 220°C and therefore the concrete will be exposed to high initial temperatures and subsequently at controlled heating rates up to desired operating temperatures. Preliminary results consistently show that concrete mixtures without polypropylene fibres (PP) cannot resist temperatures beyond 500° C, regardless of the heating rate employed. These mixtures spall at higher temperatures when heated at a faster rate (7° C/min). Additionally, mixtures which incorporate PP fibres can withstand temperatures up to 600° C without spalling irrespective of the heating rate.

Convective Heat Transfer in Porous Media

1979 ◽  
Vol 101 (3) ◽  
pp. 507-510 ◽  
Author(s):  
Ali Montakhab
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Energy Storage ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Systems ◽  
Energy Storage Systems ◽  
Thermal Energy Storage Systems

Convective heating or cooling of granular solids or porous media is of interest in the design of thermal energy storage systems. The solutions to the energy initial boundary value problems governing convective heat transfer between a fixed bed of granular solids and a steady flow of heating or cooling fluid are presented. The storage system is considered to be initially in thermal equilibrium at a uniform temperature, a step change in the inlet temperature of the working fluid is imposed, and the thermal response of the system predicted. The results are valid for gases and liquids when the temperature gradient in the solid material is small and axial conduction effect is negligible in comparison with the convective heat transfer. Unlike the previously available solutions to this problem, the results presented are in closed form. This greatly simplifies evaluation and design of thermal energy storage systems of this general type.

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