| People are looking for renewable energy sources or increase the efficiency of energy utilization to fit the severe energy situation. Renewable energy sources which are mainly characterized by discontinuity of production periods and shift between energy supply and its use. Using heat storage method can cope with this problem, and it can also store the waste heat generated in industrial processes to improve energy utilization efficiency. There are mainly three types of TES systems, sensible storage systems, latent storage systems and thermochemical heat storage systems based on different energy storage principles. This paper discusses the use of chemical methods to store heat, introduce the material selection principle and state of the art on thermochemical energy storage domestic and overseas. As the magnesium hydride system has a high heat storage density at a temperature level between almost300and500℃is set free and has the advantage of long term heat storage without the need for the thermal insulation measures, this article will choose magnesium-magnesium hydride thermochemical heat storage system as research content.Based on the physical and chemical processes happened during the heat storage and exothermic process in magnesium-magnesium hydride thermochemical heat storage system, this article establish a two dimensional unsteady numerical model. By numerical calculation, the temperature, reaction rate, extent of reaction field, power output variation and other parameters can be obtained. We designed a magnesium-magnesium hydride thermochemical heat storage experiment station, and made a series of experiments, mutual authenticate with the mathematical model, some conclusions are obtained:The numerical simulation found that there is a narrow reaction front carried out from the wall to the core during the heat storage and exothermic process in magnesium-magnesium hydride thermochemical heat storage system.The numerical simulation found that there is an optimum reaction temperature exists which leads to a maximum discharging power for a given heat transfer coefficient. As the heat transfer coefficient increases, the maximum discharging power is also increased and ultimately approaches the maximum discharging power when the boundary condition is constant wall temperature. The power output will decrease with time when the boundary condition is constant wall temperature, for a system with a constant heat flux as it’s boundary condition, the reaction will suddenly stopped. In the experiment this article check the influence of the wall temperature on the reaction rate of the system, and find there is an optimum wall temperature which leads to the fastest reaction rate, and in all experiment this article did, the power output decrease with time, the result matches with the conclusion of the numerical simulation.In the numerical simulation the reaction rate become faster with the increase of hydrogen pressure, it is also confirmed in the experiment.For the charging process of the heat storage system, the result shows that the charging time decrease when the boundary temperature increase.The magnesium powder conversion rate reaches48%for this experiment system and heat storage density is1468/kgMg. According to the research experience on this system, at the end of this article pose some problem of the system, including the agglomeration and sintering of the reactants, low thermal conductivity, fast exothermic rate at the beginning and other issues. By the experiment and simulation of this article, there will be some help to the further study for the magnesium hydride thermochemical heat storage system. |
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