Preparation And Properties Of The Composite Absorbent Used In Solar Energy Storage Technique

Solar energy is a widely used new energy resource, whose utilization has received great attention due to its huge storage and free of pollution. However, the radiation intensity of solar energy changes periodically between day and night and the seasons. It can also be influenced by the random weather which leads to a mismatch between supply and demand. The thermal energy storage technique can be used to store the abundant solar energy temporarily and supply the energy when it is needed. In this study, the absorbent thermal energy storage technique is researched for it has many merits as high-quality energy storage density, free of poison and pollution and can supply the heat and cooling energy directly. It has great application prospects compared with the other thermal energy storage techniques. The absorbent thermal energy storage technique includes chemical and physical absorption. The traditional simple chemical absorbent and physical absorbent have advantages and disadvantages separately.The experimental setup is based on the three phase equilibrium theory of solid liquid and gas and the humidity changes with the different relative humidity of different kinds of inorganic salts. It is designed to control the temperature and humidity separately. Quantities of experiments on the absorption capacity of single chemical energy storage inorganic salt and physical absorbent are first investigated. Results show that under the experimental environmental conditions of30℃and43%humidity, the CaCl2absorbent regarded as chemical absorbent has the largest absorption capacity. The largest equilibrium absorption capacity is0.326g·g-1and the initial absorption rate is0.008g·g-1·h-1. But it takes a long time to reach equilibrium and can easily become agglomeration during the absorption process which will terminate the absorption. Then the other physical absorbents such as13X molecular sieve are also studied. For example, the13X molecular sieve has the largest equilibrium absorption capacity among the physical absorbents tests. It is0.254g·g-1 which is much smaller than chemical absorbent. The physical absorbent has a high absorption speed and reaches the absorption equilibrium quickly but has a small absorption capacity and energy storage density.According to the results, the chemical inorganic salt with well absorption capacity and the optimized physical absorbent are combined through filling up the inorganic salt into pores of physical absorbent. The orthogonal experiment method is used to determine the preparing conditions of the composite absorbent. Results show that the property of the composite absorbent is influenced by the factors such as chosen physical absorbent, concentration of the inorganic salt solution, dipping time and drying temperature and time. The equilibrium absorption capacity of the composite absorbent increases with these factors but it increases a little when it reaches a constant. Then the preparing conditions influencing the absorbent property most can be found out. The composite absorbent is prepared by the optimal conditions as below. The13X molecular sieve is first immersed in the CaCl2solution with a concentration of40%for14hours and then the composite absorbent is dried at450℃for5hours.The property of the composite absorbent under different preparing conditions is investigated by controlling the temperature and humidity. The equilibrium absorption capacity of the composite absorbent combined by CaCl2and13X molecular sieve at30℃and43%humidity is0.305g·g-1which is between13X molecular sieve and CaCl2. The absorption rate is increased apparently and it is0.013g·g-1·h-1in the initial stage of absorption. It can also inhibit the agglomeration compared to CaCl2absorbent.The absorption rate and equilibrium capacity of the CaCl2-13X molecular sieve composite absorbent is investigated with the environmental humidity of11%,32%,43%and56%at30℃to meet the potential of practical application. The absorbent capacity and the initial absorption rates of the composite absorbent are0.306g·g-1/0.008g·g-1·h-1,0.306g·g-1/0.009g·g-1·h-1,0.308g·g-1/0.013g·g-1·h-1and0.302g·g-11/0.016g·g-1·h-1separately. The absorption rate increases with the environmental humidity but it has little influence on the equilibrium absorption capacity of the composite absorbent. The environmental humidity can be used to control the absorption rate of the composite absorbent.The cycling property of the optimized composite absorbent is also tested. The absorption capacity of the CaCl2-13X molecular sieve composite absorbent barely decreases after using8times.Based on theoretical analysis and experiments results, the chemical storage composite absorbent is studied. This will contribute to the increase of the capacity of the composite storage materials and provide some theoretical basis and technical guidance for practical applications. It is also very important in practical use of energy storage of solar energy and waste heat.