Thermochemical energy storage uses reversible chemical reactions to store and release heat. This method offers high , making it great for long-term storage. It's like a chemical battery for heat, charging up with endothermic reactions and discharging with exothermic ones.
and are key techniques in thermochemical storage. These systems can upgrade low-grade heat to higher temperatures, making them useful for heating, cooling, and industrial applications. It's a game-changer for efficient energy use.
Thermochemical Reactions
Reversibility and Energy Transfer
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are reversible chemical reactions that involve the transfer of between the system and surroundings
Endothermic reactions absorb heat from the surroundings during the forward reaction (dehydration of , decomposition of )
Exothermic reactions release heat to the surroundings during the reverse reaction (hydration of anhydrous salts, synthesis of metal hydroxides from metal oxides)
The direction of the reaction depends on the temperature and pressure conditions
Thermal energy is stored during the and released during the , allowing for energy storage and release
Reaction Kinetics and Catalysis
describe the rate at which thermochemical reactions proceed and the factors that influence the rate
Temperature, pressure, concentration of reactants, and presence of catalysts affect the reaction rate
Higher temperatures generally increase the reaction rate by providing more kinetic energy for reactant molecules to overcome the activation energy barrier
Catalysts lower the activation energy of the reaction, increasing the rate without being consumed in the process (, )
Proper catalyst selection and optimization are crucial for efficient thermochemical energy storage systems
Thermochemical Storage Processes
Sorption Processes
Sorption processes involve the binding of a gas or liquid (sorbate) to a solid material (sorbent) through physical or chemical interactions
Adsorption is a surface phenomenon where the sorbate adheres to the surface of the sorbent (zeolites, , )
Absorption involves the incorporation of the sorbate into the bulk of the sorbent material (salt hydrates, metal hydroxides)
Sorption processes are used for thermal energy storage by exploiting the or absorption during the binding process and the during the release of the sorbate
Chemical Heat Pumps
Chemical heat pumps utilize thermochemical reactions to upgrade low-grade thermal energy to higher temperatures
The system consists of a reactor, condenser, and evaporator that operate in a closed-loop cycle
During the charging phase, heat is supplied to the reactor, driving an endothermic reaction that stores thermal energy in the chemical bonds of the reaction products
In the discharging phase, the reverse exothermic reaction occurs, releasing the stored thermal energy at a higher temperature than the input heat
Chemical heat pumps can be used for space heating, cooling, and industrial process heat applications (, )
Energy Density and Storage Capacity
Thermochemical energy storage systems offer high energy densities compared to sensible and latent heat storage methods
Energy density refers to the amount of thermal energy stored per unit mass or volume of the storage material
The energy density depends on the specific thermochemical reaction, the storage materials used, and the operating conditions
Higher energy densities enable more compact storage systems and reduce the required storage volume
The theoretical energy density of thermochemical storage can reach several GJ/m³, making it attractive for long-term and seasonal thermal energy storage applications