| Solar thermal power generation technology is an important technology to alleviate the energy crisis and improve the ecological environment,however,solar energy has some problems such as low density,instability and intermittence,so it needs large-scale energy storage to balance the load.Thermal energy can be stored in three different ways:sensible energy storage,latent energy storage and thermochemical energy storage.Thermochemical energy storage has the obvious advantages of high energy storage density,high energy quality and long-term storage without heat loss,which is very suitable for coupling with solar thermal power generation system to solve the instability of solar energy.Among the main thermochemical energy storage systems,Ca（OH）2/Ca O system has been widely studied and concerned in the field of thermochemical energy storage due to its high energy storage density,safety,non-toxicity,low price and simple operation.This paper builds an indirect heating fixed bed reactor,changes the vapor pressure in the reaction bed,prepares composite materials,and explores the reaction performance in the process of dehydration and hydration.During dehydration,the temperature of the area around the reaction bed is higher than that at the center of the bed.The temperature at the center of the strain bed is characterized by a rapid rise,followed by a temperature plateau,after which the temperature rises again until it stabilizes at the maximum temperature.When the steam pressure increases,the platform temperature at the center of the reaction bed increases,and there is no platform temperature at5.6k Pa.When the bed temperature rises above 400℃,the dehydration reaction occurs rapidly.When the water temperature/water vapor pressure is higher than 20℃/2.3k Pa,the heat storage capacity of the reaction bed does not change significantly.During the hydration process,the internal temperature of the reaction bed is higher than that of the area around the reaction bed.As the water vapor pressure decreases,the maximum temperature of the bed decreases.When the water vapor pressure is 20k Pa,the bed temperature remains above 200℃for a long time.In the process of hydration reaction before 25 min,the hydration rate is very fast.With the decrease of water vapor pressure,the hydration rate slows down,and the end time of the reaction is delayed.When the water vapor pressure is 20k Pa,the reaction is still not finished after 60 min.With the decrease of water vapor pressure,the total heat output of the reactor decreases.In the dehydration process,the peak temperature of the bed increases,the duration of the platform temperature decreases,and the heat storage capacity of the reaction bed increases with the increase of the doping proportion of expandable graphite.In the first 40 min of the dehydration process,the heat storage capacity of the composite with the doping ratio of 0.25 is100.7k J/kg,which is about twice that of pure Ca（OH）2.The heat storage capacity of the composite material is much higher than that of pure Ca（OH）2 within 40～90 min.During the hydration process,the peak temperature of the bed decreases slightly,the reaction rate accelerates,and the total heat output of the bed increases,but the overall increase is not large.In the first 10 min of hydration reaction,when the doping ratio is less than 0.5,the total heat output increases with the increase of the doping ratio.When the doping ratio is higher than 0.5,the total heat output is less affected by the doping ratio.The results of the cyclic stability of the composites with different doping ratios show that the molar reaction fraction of pure Ca（OH）2and the composites does not change much during the dehydration process.During the hydration process,the molar reaction fraction of pure Ca（OH）2 decreases slightly,while that of the composites does not change much.The dehydration and hydration processes of both the composite and pure Ca（OH）2 were incomplete during the cycling process,and the conversion rate of the composite increased slightly with the increase of the doping amount of expandable graphite. |
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