Thermochemical energy storage utilising the material system CaO/Ca(OH)2 is currently investigated using fluidised bed technology. Overall goal is to develop large-scale heat storage for industrial applications at 400 °C to 600 °C. Two crucial challenges must be faced in the development of the process. First, low thermal conductivity of the material results in heat transfer limitation of the reaction rate limiting the power in- and output of the system. Second, increasing particle breakage with increasing number of storage cycles may limit the overall number of storage cycles since it can lead to a rising share of fines in the fluidised bed and therefore its defluidisation eventually.
For examining these material and process characteristics in scale-up relevant size, a new, unique setup is commissioned. It is specifically designed to enable time efficient, high throughput experiments on long-term cyclisation of CaO/Ca(OH)2 and its production reaction from CaCO3 at precisely adjustable reaction conditions over the whole cyclisation process.
The cylindrical fluidised bed reactor has a fluidised bed volume of 1.8 L (9.5 L total volume) and a height to diameter ratio of up to 4. This enables batch sizes of up to 1 kg Ca(OH)2, equal to 0.5 kWh in storage capacity. As fluidising medium nitrogen or steam are used, enabling fluidisation velocities of up to 0.3 m/s. Thereby process conditions of up to 800 °C and 4 bar are possible in the reaction zone. To extend the range of analytics on the setup, a system for measuring the differential pressures between windbox – reaction zone – freeboard – reactor exit and numerous temperature measurements in the reactor are installed. A blowback filter system is equipped in the freeboard. This prevents the pressure in the reaction zone from increasing due to the formation of a filtration cake of fines at the reactor exit during long-term cyclisation.
First experimental investigations using CaCO3 of 250 μm - 400 μm particle size as initial material show promising results in terms of performing the calcination reaction at 700 °C to 750 °C and successive cyclisation of the produced CaO in pure steam atmosphere. Up to 20.5 storage cycles were achieved up to now with no detectable loss in fluidisation quality.
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Thermochemical energy storage utilising the material system CaO/Ca(OH)2 is currently investigated using fluidised bed technology. Overall goal is to develop large-scale heat storage for industrial applications at 400 °C to 600 °C. Two crucial challenges must be faced in the development of the process. First, low thermal conductivity of the material results in heat transfer limitation of the reaction rate limiting the power in- and output of the system. Second, increasing particle breakage with i...
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