scholarly journals Improvement of operation of steam cushion system for sensible thermal energy storage

2019 ◽  
Vol 116 ◽  
pp. 00107
Author(s):  
Ryszard Zwierzchowski
Keyword(s):  
Heat Flux ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Energy Savings ◽  
Operating Conditions ◽  
Production Costs ◽  
Technical Solution ◽  
Atmospheric Air ◽  
Suction Pipe

The paper contains a method for improvement of operation of steam cushion system including its energy savings analyses, for a Thermal Energy Storage (TES) tank. Energy savings analyses were performed using operational data from selected Combined Heat and Power plants, which supply heat to large cities in Poland and are furnished with the TES. The role of the steam cushion system in the TES tank is to prevent the stored water against absorbing oxygen from atmospheric air. In the TES tank, which is a non-pressure tank, oxygen from atmospheric air could penetrate to the network water through the surge chamber and safety valves. The steam pressure under the roof is generated from technological steam injected under the roof. Energy savings in the steam cushion system are generated by using an appropriate technical solution for the upper orifice and suction pipe for circulation water, i.e., to make it movable through the use of pontoons. An isolating buffer layer is created at the top of the tank with very small convective and turbulent heat transport, which causes limited heat transfer from steam bed to the stored water in the tank. This results in heat flux of approximately 10% of the heat flux that occurs in the typical technical solution of the upper orifice and suction pipe for circulation water in the TES tank. This technology offers great opportunities to improve the operating conditions of District Heating System, cutting energy production costs and emissions of pollutants to the atmosphere.

Thermal Energy Storage Through Melting of a Commercial Phase Change Material in an Annulus with Radially Divergent Longitudinal Fins

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Tonny Tabassum Mainul Hasan ◽  
Latifa Begum
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Operating Conditions ◽  
Melting Time ◽  
Bottom Part ◽  
Change Material

This study reports on the unsteady two-dimensional numerical investigations of melting of a paraffin wax (phase change material, PCM) which melts over a temperature range of 8.7oC. The PCM is placed inside a circular concentric horizontal-finned annulus for the storage of thermal energy. The inner tube is fitted with three radially diverging longitudinal fins strategically placed near the bottom part of the annulus to accelerate the melting process there. The developed CFD code used in Tabassum et al., 2018 is extended to incorporate the presence of fins. The numerical results show that the average Nusselt number over the inner tube surface, the total melt fraction, the total stored energy all increased at every time instant in the finned annulus compared to the annulus without fins. This is due to the fact that in the finned annulus, the fins at the lower part of the annulus promotes buoyancy-driven convection as opposed to the slow conduction melting that prevails at the bottom part of the plain annulus. Fins with two different heights have been considered. It is found that by extending the height of the fin to 50% of the annular gap about 33.05% more energy could be stored compared to the bare annulus at the melting time of 82.37 min for the identical operating conditions. The effects of fins with different heights on the temperature and streamfunction distributions are found to be different. The present study can provide some useful guidelines for achieving a better thermal energy storage system.

scholarly journals Nucleation Triggering of Highly Undercooled Xylitol Using an Air Lift Reactor for Seasonal Thermal Energy Storage

2018 ◽  
Author(s):  
Marie DUQUESNE ◽  
Elena PALOMO DEL BARRIO ◽  
Alexandre GODIN
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Energy ◽  
Operating Conditions ◽  
High Energy Density ◽  
Bubble Generation ◽  
Spontaneous Nucleation ◽  
Air Lift Reactor ◽  
Air Lift

Xylitol is an organic, non-toxic, biosourced phase change material with high potential for seasonal thermal energy storage material. It has a high energy density, a high and stable undercooling allowing storing solar energy at ambient temperature thus, reducing thermal losses and the risk of spontaneous nucleation (i.e., the risk of losing the stored energy). When the energy is needed, the discharge triggering of the storage system (i.e., Nucleation triggering of highly viscous undercooled Xylitol) is very difficult as well as reaching a sufficient power delivery (i.e., the control of the subsequent crystal growth rates). Both are the mains locks for the use of Xylitol in seasonal energy storage. Different techniques to crystallize highly undercooled Xylitol have hence been considered. It has been proven that nucleation triggering of highly undercooled Xylitol using an air lift reactor would allow reaching performances matching with building applications (i.e., at medium temperatures, below 100 °C). The advantages of this technique compared to other existing techniques to activate the crystallization are discussed. The mechanisms triggering the nucleation are investigated. The air bubble generation, transportation of nucleation sites and subsequent crystallization are discussed to improve the air injection operating conditions.

Near Optimal Receding Horizon Control of Thermal Energy Storage

2021 ◽  
pp. 1-13
Author(s):  
Omer Ahmed Qureshi ◽  
Peter R. Armstrong
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Energy Savings ◽  
Search Algorithm ◽  
Cost Savings ◽  
Weather Conditions ◽  
Receding Horizon Control ◽  
Receding Horizon ◽  
Favorable Weather

Abstract Efficient plant operation can be achieved by properly loading and sequencing available chillers to charge and discharge a thermal energy storage (TES) reservoir at optimal rates and times. TES charging sequences are often determined by heuristic rules that typically aim to reduce utility costs under time of use rates. However, such rules of thumb may result in significantly sub optimal performance on somedays. Rigorous optimization, on the other hand, is computationally expensive and can be unreliable as well if not carefully implemented. Receding Horizon Control (RHC) using the novel finite search algorithm is reliable and can reach ~80% of achievable energy efficiency and/or peak shifting capacity has been our target. A novel algorithm is developed to reliably achieve near optimal control for charging the stratified sensible cool storage reservoir of a chiller plant. The algorithm provides a constant COP (or cost per ton-hour) for 24-hr dispatch plan under which chillers operate during most favorable weather conditions. Analysis of four hot climates, ranging from humid to dry, indicates 2.4~2.6% energy savings under a flat electricity rate relative to the same plant operating without TES. Annual cost savings from 6% to 9% was found for electricity billed under a simple (10am-10pm) time-of-use rate with no demand charge and no ratchet component.

scholarly journals Nucleation Triggering of Highly Undercooled Xylitol Using an Air Lift Reactor for Seasonal Thermal Energy Storage

2019 ◽  
Vol 9 (2) ◽  
pp. 267 ◽  
Author(s):  
Marie Duquesne ◽  
Elena Palomo Del Barrio ◽  
Alexandre Godin
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Energy ◽  
Operating Conditions ◽  
High Energy Density ◽  
Bubble Generation ◽  
Spontaneous Nucleation ◽  
Air Lift Reactor ◽  
Air Lift

Bio-based glass-forming materials are now considered for thermal energy storage in building applications. Among them, Xylitol appears as a biosourced seasonal thermal energy storage material with high potential. It has a high energy density and a high and stable undercooling, thus allowing storing solar energy at ambient temperature and reducing thermal losses and the risk of spontaneous nucleation (i.e., the risk of losing the stored energy). Generally when the energy is needed, the discharge triggering of the storage system is very difficult as well as reaching a sufficient power delivery. Both are indeed the main obstacles for the use of pure Xylitol in seasonal energy storage. Different techniques have been hence considered to crystallize highly undercooled Xylitol. Nucleation triggering of highly undercooled pure Xylitol by using an air lift reactor has been proven here. This method should allow reaching performances matching with building applications (i.e., at medium temperatures, below 100 °C). The advantages of this technique compared to other existing techniques to activate the crystallization are discussed. The mechanisms triggering the nucleation are investigated. The air bubble generation, transportation of nucleation sites and subsequent crystallization are discussed to improve the air injection operating conditions.

Optimization of a Packed Bed Thermal Energy Storage Unit

1987 ◽  
Vol 109 (3) ◽  
pp. 170-175 ◽  
Author(s):  
H. Torab ◽  
D. E. Beasley
Keyword(s):  
Energy Storage ◽  
Cross Section ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Relative Size ◽  
Packed Bed ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Storage Unit ◽  
Energy Storage Unit

The optimization of the design of a packed-bed thermal energy storage unit is presented. A one-dimensional, transient, two-phase model is chosen for the packed bed which assumes uniformity at each cross section within the packing. The governing equations for the time dependent temperature distributions in both the solid and fluid phases are solved using a fully implicit formulation. The accuracy of the numerical method is demonstrated by comparison with experimental measurements of temperature distribution in a randomly packed bed of uniform spheres. The goal of the optimization is to achieve maximum utilization of the thermal energy storage and recovery capabilities of the storage medium for a given set of operating conditions. The optimum combination of bed length, size of the packing particles, and relative size of the bed cross section to the particle diameter is determined, subject to constraints on the maximum allowable pressure drop across the packing, the maximum outlet fluid temperature, and the total amount of supplied energy. The thermodynamic availability is examined as the measure of storage utilization. The monotinicity method is utilized for the optimization process. This method identifies a global optimum without any special computations, and prevents acceptance of false optimum solutions, as could be generated by numerical techniques. The results of the study provide guidelines for choosing the size of the packing and the packing particle subject to the constraints for a practical operating system.

Heat Transfer in a High-Temperature Packed Bed Thermal Energy Storage System—Roles of Radiation and Intraparticle Conduction

1996 ◽  
Vol 118 (1) ◽  
pp. 50-57 ◽  
Author(s):  
A. A. Jalalzadeh-Azar ◽  
W. G. Steele ◽  
G. A. Adebiyi
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Packed Bed ◽  
Energy Storage System ◽  
Operating Conditions ◽  
Thermal Energy Storage System

A model is developed and experimentally verified to study the heat transfer in a high-temperature packed bed thermal energy storage system utilizing zirconium oxide pellets. The packed bed receives flue gas at elevated temperatures varying with time during the storage process and utilizes air for the recovery process. Both convection and radiation are included in the model of the total heat transfer between the gas and the pellets. It is found that thermal radiation and intraparticle conduction do not play a major role in the overall heat transfer in the packed bed under the specified operating conditions. An uncertainty analysis is performed to investigate the propagation of the uncertainties in the variables to the overall uncertainty in the model predictions and the experimental results.

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