AN EXPERIMENTAL STUDY ON THERMO CHEMICAL ENERGY STORAGE SYSTEM.JEFFY SCARIA ROLL NO 4, TFEGUIDED BY:Sri. SWARAJ KUMAR .B

OVERVIEWIntroduction

Review of papers

Conclusion

Scope for future work

INTRODUCTIONNEED FOR THERMAL ENERGY STORAGE SYSTEM (TES).

WHEN THERE IS A TIME PERIOD BETWEEN SUPPLY AND DEMAND OF THERMAL ENERGY.

SOLAR HEAT ENERGY VARIES SEASONALLY.

THE COLLECTED THERMAL ENERGY CAN BE USED LATER FOR WATER HEATING SPACE HEATING OR ABSORPTION REFRIGERATION

There are three main types of TES systems Sensible Latent Chemical

The main principle of thermo chemical TES is based on a reaction that can be reversed: CHARGING: C + heat A + B DISCHARGING: A + B C + heat

CHARGINGThe charging process is endothermic. Thermal energy is absorbed from an energy resource.

Which could be a renewable energy resource and/or conventional energy sources like fossil fuels.

This energy is used for dissociation of the thermochemical material, and is equivalent to the heat of reaction or enthalpy of formation.

After this process, two materials (A and B) with different properties are formed that can be stored.

Usually second material is water vapour, and is released to the atmosphere.

STORINGAfter the charging process, components A and B are separately stored with little or no energy losses.

The materials are usually stored at ambient temperatures, leading to no thermal losses.

Any other energy losses are due to degradation of the materials.

DISCHARGINGDuring this process, A and B are combined in an exothermic reaction.

The energy released from this reaction permits the stored energy to be recovered.

After discharging, component C is regenerated and can be used again in the cycle.

A + B C + heat

Temperature range of thermochemical systems The range possible for the purpose of heat storage using thermochemical reactions (charging and discharging) is very wide.

Starting from temperatures of around 70C for salt-hydrates and solutions.

Dissociation processes of hydroxides at around 200-350C.

ammonia dissociation at 400-700C.

These specifications refer to equilibrium reaction temperatures.

Storage densityThe amount of stored energy per unit volume is the key indicator for the quality of heat storage.

The energy density of sensible heat storage is limited by the maximum applicable temperature and the specific heat capacity of the storage material.

Water, for example, is able to absorb about 210 kJ per litre or 58 kWh/m3 while being heated from 40 to 90C.

Energy storage densities of thermal heat storage systems.

Sensible - 0.2 GJ/m3 latent - 0.3 - 0.5 GJ/m3 Thermochemical - 0.5 - 3 GJ/m3

Thermochemical Material selection

The selection of a TCM depends on the charging temperature, output temperature required , number of load cycles during lifetime etc.

common materials used are Salt solutions, salt hydrates, ammonia, hydroxides and carbonates .

Major factors to be considerd are

Cost Cycling behavior (reversibility and degradation over large numbers of cycles) Availability Toxicity and safety Corrosiveness Energy storage density Reaction temperature

ADVANTAGES COMPARED TO OTHER SYSTEMSNO LOSS.

LONGER STORAGE PERIOD ( MONTHS OR YEARS).

LATENT SENSIBLE HEAT STORAGE SYSTEM HAVE STORAGE TIME OF ONLY FEW DAYS.

HIGH ENERGY STORAGE DENSITY.

SO, SYSTEM WLL BE COMPACT.

EASY TO TRANSPORT.

REVIEW OF RESEARCH PAPERS A Critical Review of Thermochemical Energy Storage Systems by Ali H. Abedin and Marc A. Rosen, Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Ontario, 2011.

Reviews various types of heat storage systems.

Compares energy storage density of sensible, latent, and chemical systems.

And finds thermochemical system as the best but expensive.

It gives the factors to be considered for thermochemical material selection.

Low temperature chemical heat storage an investigation of hydration reactions by F. Bertsch, B. Mette, S. Asenbeck, H.Kerskes, H. Mller-Steinhagen , Institute for Thermodynamics and Thermal Engineering (ITW), University of Stuttgart, Germany.

Two different salt hydration reactions have been studied.

magnesium sulfate monohydrate and copper sulfate monohydrate, hydrated by a moist air flow .

The hydration experiments have shown that for both, magnesium- and copper-sulfate-monohydrate, a high water vapor pressure is needed for a sufficiently high reaction rate.

A water vapor pressure of more than 13 mbar cannot be provided easily from ambient air during the heating period.

Calcium sulphate hemihydrate hydration leading to gypsum crystallization by a) N.B. Singh, b) B. Middendorf . a) DDU Gorakhpur University, Chemistry Department, Gorakhpur, India ,b) University of Dortmund, Department of Building Materials, Germany.

In this paper hydration of calcium sulphate hemihydrate (CaSO4 0.5H2O) leading to the crystallization of calcium sulphate dihydrate (CaSO4 2H2O) has been investigated .

Depending on the process of production, hemihydrate occurs in two different forms (a- and b-forms).

Hydration reactions of both a- and b-hemihydrates are highly exothermic in nature .

But in regeneration process a- hemihydrate need low temperature(90- 100 o C ) and high partial pressure of water vapour.

And for b- hemihydrate high temperature (200 o C +) and very low pressure is needed

Application of MgCl26H2O for thermochemical seasonal solar heat storage by H.A. Zondag,V.M. van Essen,L.P.J. Bleijendaal, B.W.J. Kikkert, M. Bakker 5th International Renewable Energy Storage Conference IRES November 2010, Berlin, Germany.

This paper investigates the thermochemical properties of magnesium chloride.

During heating dehydration of the hexahydrate started at about 50C and the formation of monohydrate started at about 120C.

Subsequent hydration of this dry magnesium chloride using moist air at 12 mbar vapour pressure, gave good temperature difference to air (20C)

CONCLUSION Based on the reviewed papers, thermo chemical system is an efficient heat storage method.

Main part of the design is the selection of thermo chemical material, based on the output requirements.

The papers investigated various materials.

Among them, magnesium chloride (MgCl26H2O) was the the most suitable for household water heating applications ( working temperature range 100 130 C) .

SCOPE FOR FUTURE WORK Design a household water heater to heat 40 ltrs of water from ~ 25 C to 45 C.

Using thermochemical method.

Waste heat from engines or solar heat is stored thermochemically, that is dehydration of the chemical.

Then required heat is obtained by hydrating the chemical by moist air.

Heat required is 3,348.8 KJ. 4.7kg of mgcl2 will provide required heat.

ReferencesA Critical Review of Thermochemical Energy Storage Systems by Ali H. Abedin and Marc A. Rosen, Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Ontario, 2011.

Application of MgCl26H2O for thermochemical seasonal solar heat storage by H.A. Zondag,V.M. van Essen,L.P.J. Bleijendaal, B.W.J. Kikkert, M. Bakker 5th International Renewable Energy Storage Conference IRES November 2010, Berlin, Germany.

Low temperature chemical heat storage an investigation of hydration reactions by F. Bertsch, B. Mette, S. Asenbeck, H.Kerskes, H. Mller-Steinhagen , Institute for Thermodynamics and Thermal Engineering (ITW), University of Stuttgart, Germany.

Calcium sulphate hemihydrate hydration leading to gypsum crystallization by a) N.B. Singh, b) B. Middendorf . a) DDU Gorakhpur University, Chemistry Department, Gorakhpur, India ,b) University of Dortmund, Department of Building Materials, Germany.