Energy 2030

Organizing Committee

Final Program

Poster Exhibition Venue 2006 Proceedings


Proceedings of the Second International Energy 2030 Conference,
November 4-5, 2008, Abu Dhabi, U.A.E.

Agitated Fluidized Bed Thermochemical Energy Storage for Industrial Waste Heat Recovery System

Jo Darkwa

Nottingham Trent University, UK

Optimum utilization of residual heat is often hampered by economic and technical boundary conditions. It is also affected by the mismatch between supply and demand with regard to quality, quantity, time, and location. It is estimated that about 10% of current total UK energy consumption is discharged into the atmosphere as waste [1-2]. With an appropriate technology a large proportion of this waste heat could potentially be recovered for useful applications and thus minimize energy consumption and CO2 emissions.

In recent years, thermal energy storage has emerged as a significant means by which residual heat may be recovered for later utilization. However, thermal energy stores do not in their own right save energy, in fact energy and thermodynamic availability is always lost in a storage process. In this regard various methods of storing energy form an important set of “enabling” technologies which increase both the cost effectiveness and energy conservation potential of storage systems. Close review of various storage methods has shown that thermochemical energy storage process in inorganic oxides has the potential to become probably the most effective and economic method of storing and utilizing waste heat. There are however technical and scientific problems such as inadequate heat and mass transfers associated with thermochemical energy reactors, which remain to be overcome. Various related studies have in the past been carried out. For instance Fuji et al. [3] experimented on an integrated metal foam reaction bed as supplement to retaining shape of reactant during reaction process, and ultimately to enhance the storage performance. Goetz et al. [4] evaluated the impregnation of reactants in consolidated blocks of natural graphite and observed dynamic limitations of heat transfer in the grains and in the bed. Groll [5] reviewed the operational characteristics of different types of fixed reaction beds and found their performances to be affected by unequal diffusivity of the chemical species and inadequate heat and mass transfers through the reaction beds. Darkwa et al. [6-10] have also carried out analytical and experimental evaluation of an integrated fixed bed thermochemical energy reactor but yet to overcome the associated problems. Fluidized beds are considered to be favorable for rapid exothermal reactions due to the large specific surface area available for reaction and short residences times for gas or solids. However, factors such as minimum fluidization velocity (umf), i.e. the velocity at which fluidization begins, and the velocity at which pneumatic transport begins (i.e. terminal velocity) do influence the performances of fluidized bed. There is also the problem of bubbles associated with umf, which tend to affect the combined heat transfer coefficient and thus the mode of heat and mass transfers in fluidized beds. Such parameters would therefore have to be considered and incorporated into the system. To this end, a double-acting agitated fluidized bed thermochemical energy storage system is proposed for an analytical investigation.


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