| Thermochemical heat storage is a novel thermal energy storage technology.Compared with sensible heat storage and latent heat storage,it has a larger heat storage density and ability of long-term thermal energy storage without heat loss.CaO/Ca(OH)2 is a typical thermochemical heat storage material pair,which widely exists in nature and is easily available.It is especially suitable for medium and high temperature heat storage.Therefore,it has a broad application prospect in renewable energy utilization and industrial waste heat recovery.This research mainly focuses on three aspects:improving the heat storage reaction performance of CaO/Ca(OH)2 pair,strengthening the mechanical strength of the material and exploring the operation characteristics of direct thermochemical heat storage system.Firstly,the KNO3 doped Ca(OH)2 composite was prepared,which can improve the heat storage rate of Ca(OH)2 and expand its thermal storage temperature range.The optimal KNO3 doping ratio was determined.On this basis,the non-isothermal kinetic analysis of pure Ca(OH)2 and its composites was carried out,and their decomposition kinetic parameters and kinetic controlling equations were obtained,which provides a theoretical basis for the subsequent design of thermochemical heat storage system.The test results show that KNO3 doping can not only reduce the decomposition activation energy of Ca(OH)2,but also enhance the mass transfer in the decomposition process.In addition,the cyclic stability tests of pure Ca(OH)2 and its composites in different atmospheres were carried out,and the solutions to restrain the failure of the materials were proposed.Secondly,in order to solve the problem that the particles of CaO/Ca(OH)2in fluidized bed are easy to be broken,heavy tar was used as binder,KCl was used as catalyst to prepare the CaO based composite material with enhanced mechanical properties by high temperature calcination.The results show that the network carbon structure formed by pyrolysis of heavy tar at high temperature can support the CaO particles effectively.In addition,due to the small amount of graphitized carbon in the network carbon structure,the thermal conductivity of the composite has also been improved.After 30 cycles of stability test,the composite still has good mechanical and reactive properties.At last,the characteristics of heat storage and release process of CaO/Ca(OH)2 direct thermochemical heat storage system were investigated.It is found that in the process of heat storage,the endothermic decomposition of Ca(OH)2 will cause the temperature in the reactor to appear a concave section,and the concave section of the temperature in the upper part will last for a shorter time because the materials in this part can receive more heating power.In the process of heat release,the heat release intensity in the reactor can be improved by increasing the water vapor flow rate and nitrogen flow rate,respectively.The heat release strengthened region will also be expanded.However,the strengthening effect of increasing water vapor flow rate on the exothermic intensity of the material is more obvious. |
PDF Full Text Request