CaO/CaCO₃ Thermochemical Heat Storage Performance Of Ca-based Honeycombs

High temperature thermochemical heat storage technology based on CaO/CaCO3 cycles is the most potential in concentrated solar power plants,which has the advantages of high heat storage density,low energy loss and low raw material price.However,it is limited by the problems of natural Ca-based materials’ activity reduction and breakage and wear after multiple heat storage cycles,which makes the research and development of Ca-based materials with heat storage performance and mechanical properties attract much attention.In this work,Ca-based honeycomb materials were prepared by extrusion-molding method,and the heat storage performance and mechanical properties of Ca-based honeycombs were studied based on macroscopic experiments and microscopic analysis,revealing the strengthening mechanism on its heat storage performance by different modification methods.In order to improve the mechanical properties of Ca-based materials,CaO honeycombs were prepared by extrusion molding,and the effects of carbonation pressure and temperature,calcination time and temperature,binder addition,different honeycomb cell densities and heat storage cycles on the heat storage performance of CaO honeycombs were studied in a dual fixed-bed reactor,and the optimal heat storage conditions were obtained.Proper increase of carbonation pressure can significantly improve the heat storage performance of CaO honeycombs.When the carbonation pressure is 0.2 MPa,the effective heat storage conversion and heat storage density of CaO honeycomb after 10 cycles are 0.65 and 2066 kJ/kg respectively,which are 2.3 and 1.8 times higher than those under 0.1 and 1.0 MPa,respectively.In addition,the compressive strength of CaO honeycomb prepared by extrusion molding method is significantly improved with increasing the heat storage cycles.The compressive strength of CaO honeycomb reaches 0.663 MPa after 20 cycles.In order to improve the heat storage performance and cycle stability of Ca-based honeycombs,a method of modifying it by adding inert support MgO and pore-forming agent waste plastics was proposed.The effects of MgO and waste plastics addition,carbonation pressure and heat storage cycles on the heat storage performance of CaO honeycomb composites were studied.The addition of MgO and waste plastics can effectively improve the heat storage performance of Ca-based honeycomb materials,and make CaO honeycombs have more porous structure and larger specific surface area and pore volume.When the content of MgO and waste plastics is 10 wt%and 5 wt%respectively,the effective conversion and heat storage density of Ca/Mg honeycomb composite after 15 cycles are 0.638 and 2028 kJ/kg respectively,which is 19%higher than that of CaO honeycomb.In order to further optimize the cyclic heat storage performance and mechanical properties of Ca/Mg honeycomb composites,a Ca/Mg/Zn honeycomb composite was prepared.The results show that when ZnO is 3 wt%,Ca/Mg/Zn honeycomb composite has the best heat storage performance and cycle stability.After 25 cycles,its effective conversion and heat storage density are 0.6 and 1900 kJ/kg,which are 1.1 and 1.4 times higher than those of Ca/Mg honeycomb composite and CaO honeycomb,respectively.The addition of ZnO can significantly improve the carbonation reaction of CaO.Although the thermal stability of Ca/Zn honeycomb composite becomes poor after many cycles,the addition of MgO inhibits the decrease of ZnO activity.Therefore,the co-doped MgO and ZnO not only promotes the heat storage reaction of Ca-based honeycomb,but also significantly improves the anti-sintering performance of CaO,thus making it have excellent heat storage performance and cycle stability.In addition,the addition of ZnO significantly improved the compressive strength of Ca-based hon eycomb,and the compressive strength of Ca/Mg/Zn honeycomb composite reached 0.8 MPa after 20 cycles.Therefore,Ca/Mg/Zn honeycomb composite has good application potential.