Study On The Compatibility Between Heat Storage Concrete And Nitrate Salt

Owing to its superior advantages of easy to form, steady performance and low cost, heat storage concrete has great potential in many fields, such as solar thermal electric power generation, solar air condition and thermal energy storage concrete pile. Molten nitrate is an ideal candidate material in solar thermal electric power generation and solar thermal application, due to its small viscosity low corrosion and good thermal stability. Previous researchers usually designed thermal storage system, which use concrete as main thermal energy storage material, install alloy pipes in the concrete, and use molten nitrate or heat condition oil as heat transfer medium. Because of the high price of alloy pipes, the cost to construct the thermal energy storage system is expensive. Comprehensive utilization of the advantages of concrete and molten nitrate, we designed a new thermal storage system, in which concrete severed as main heat storage material to construct the storage unit with a heat transfer path, and molten nitrate served as transfer medium. In order to verify the feasibility of the system, we should study the compatibility between concrete and molten nitrate.In order to study the compatibility between concrete and molten nitrate, we choose the six main components of concrete mixing with solar salt, and then put them in the muffle with the temperature of600℃. According to the XRD analysis and thermodynamic calculation results, we can reach the conclusion that the two kinds of materials have a good chemical compatibility after soaking for8hours.Aim at studying the compatibility between aggregates (basalt and copper slag) and molten nitrate, we select some powdered, granular with the size of5-20mm basalt and copper slag respectively. Then soak the four kinds of materials into molten solar salt. At last, the materials were investigated on ore phase, thermo-physical properties, surface topography, weight, micro-morphology and nitrate distribution on sample cross section. The results show that:the erosion of molten solar nitrate darkened basalt sample from celadon to taupe. The weight of aggregates both increased with the erosion-cycle times prolongation, but the increasing rate rose firstly, and then reduced. After60erosion-cycle times, the weight increasing rate of basalt and copper slag were4.39%and1.04%, respectively. There were no corrosion layers in the interface between aggregates and molten solar salt, which have good chemical compatibility. After60times erosion circulations, the penetration depth of nitrate salts were between350μm and450μm.In order to research the effect of erosion-cycle temperature and times on concrete, the concrete samples were investigated on surface topography, porosity, micro-morphology and nitrate distribution on sample cross section, the weight of concrete and the attrition ratio of solar salt were also discussed. The results reveal that, after3times erosion circulations with the six different temperatures, the concrete samples did not appear severe disruption. But after60times erosion circulations at450℃, the surface of concrete appeared abscising and peeling. The increase of erosion temperature and erosion-cycle times both could promote serpentines transformed to olivine and Iron ion oxidizing. The pore size and porosity were increased, especially the harmful pores with size between100-1000nm. The weight of concrete and the mass lose of solar salt were also increased. After60times erosion circulations at450℃, the porosity of concrete rose from7.96%to21.09%, the weight of concrete was up to12.13%and the mass lose ratio of solar salt were67.40%. The nitrate content was decrease with the increase of depth, and the simulation result by EMPA using one dimensional diffusion model was similar to experimental data.In this paper, molten nitrate have good chemical compatibility with the main components and aggregates of concrete. But the compatibility between molten nitrate and concrete were poor, so as to the concrete can not satisfied with the requirement of composite thermal storage system. In order to ensure the reliability of the system, the porosity and anti-permeability of concrete must be improved.