Chemical looping electricity storage systems

Objective

This research assesses the feasibility of using using chemical looping as a grid-scale electricity storage system. Produced metal particles can be stored, transported, and traded to be utilized at a desired rate, time, and location by simply burning them with air and converting the reproduced thermal energy into electricity using conventional power conversion cycles. In principle, the produced metal can replace fossil fuels in thermal power plants as the main source of thermal input. Noting that combusting reduced metals/metal-oxides does not involve any carbon dioxide emission, zero carbon power generation can be achieved in case of using renewable energy sources for its production.

 

Background

An immediate transition to low-carbon energy infrastructure to mitigate climate change is evident; however, large scale implementation of renewable energy sources has been hindered by the intermittency (variation in supply) issues and inability to provide immediate response to changes in demand.  The most practical solution to the aforementioned difficulties is to utilize energy storage systems. Energy storage can provide an effective path in dealing with renewable energy intermittency and unpredictability by storing the surplus during high generation instances to be used during high demand periods.

Thermal energy storage (TES), which refers to the technique of storing thermal energy, can be applied to a wide range of applications from residential cooling/heating to large scale power generation. Furthermore, TES can be utilized to store electricity by using the available electricity to run a heat pump or electrical heater and generate thermal energy (converting electricity to heat).  Therefore, TES can be applied to all types of renewable energy sources from those with thermal output such as solar thermal collectors to those with electrical output such as solar cells and wind turbines. There are three major approaches for storing thermal energy including sensible heat storage, latent heat storage, and thermochemical storage. In this project, a thermochemical storage system is proposed by using metals/metal oxides as the storing medium. Metal/metal oxide is a promising recyclable and zero carbon energy carrier/storage medium that reacts energetically with air and forms nontoxic and stable reaction products. Furthermore, there are several metals with a higher volumetric energy density than that of most fossil fuels such as aluminum, magnesium, iron, and silicon. In addition, the aforementioned metals are inexpensive and available in abundance with satisfactory specific energies.       

Storing thermal energy in metal carriers involves two cyclic reactions of reduction (recycle/charging) and oxidation (use/discharging). Reducing the utilized metal-oxide to its reduced form is an endothermic process, thereof, the available thermal energy either provided by renewable sources directly or converted using heat pump/electrical heater is employed for the metal recycle stage.  In other words, the available thermal energy is stored both chemically and sensibly and it can be easily used during high demand periods. Furthermore, the produced metal can replace the commonly used fossil fuels in stationary power plants as a zero-carbon source of thermal energy (if it is produced with renewable sources of energy), it can be simply transported from areas with high accessibility to renewable sources of energy or traded as a commodity between countries. Surprisingly, metal energy carrier/storage has been largely overlooked for thermal energy storage even with all the aforementioned advantages.

 

Technology

The technology concept of the project involves the combination of renewable energy sources, packed bed reactor, metal energy carriers/storage, and thermochemical storage cycle. In combination, this technology will be able to increase the share of renewable energy power generation. To be more specific, renewable sources of energy are utilized to provide the thermal input required for the reduction stage. In case of storing electrical energy, a heat pump or electrical heater is utilized to convert electricity into thermal energy. Next, the provided thermal energy is stored within the reduced metal particles both sensibly and chemically.

© 2015 by Mohammad Saghafifar

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