【作者】 吴娟；

【导师】 龙新峰；

【作者基本信息】 华南理工大学 ， 化学工程， 2015， 硕士

【摘要】 聚光式太阳能热发电技术可以将太阳能转换成电能,故可以减少化石燃料的消耗以及缓解其燃烧产生CO2所带来的温室效应等问题。然而由于太阳能具有间歇性且容易受环境因素的影响,如何保证太阳能的持续供给成为太阳能热发电技术的关键。一种可行的方法是采用热能储存系统,在天气晴朗的时候储存太阳能,并在弱或无太阳光辐射的时候将所储存的能量释放出来。目前存在三种热能储存方法,显热储热、潜热储热以及化学储热,其中化学储热由于具有较高的储能密度、较小的热损失而引起了广泛探究。在可供选择的十几种热化学储热体系中,Ca(OH)2/Ca O体系由于较高的储能密度、较快的反应动力学、安全无毒且价格低等优点,已成为研究比较多的体系之一。本文探究了Ca(OH)2/Ca O系统吸热/放热反应过程中反应床内传质、传热性能及20次循环过程中反应物的循环可逆性。结果表明:脱水过程中,当反应床温度升高到400℃,脱水反应迅速发生,脱水180 min后,反应物的摩尔反应分数减小到0.06;随着脱水温度的升高,脱水反应进行得越快;水化反应过程中,反应床内各处温度迅速升高,然后又开始逐渐下降,且反应床内部温度要高于反应床外周温度;水化反应结束时反应物的摩尔反应分数为0.95;20次循环后反应物性能没有发生明显衰减。吸热反应过程中,随着脱水温度的升高,反应床储热容量逐渐增大;脱水90 min时的储热容量相当于整个脱水过程储热容量的33.6%;随着脱水温度的升高,相同时间下反应床的储热容量增大;放热过程中,水化30 min的总热输出量相当于整个放热过程总热输出量的91.7%;随着循环次数的增加,相同时间下的储热容量和总热输出量不断减小,但总体变化不大。文中采用多重速率扫描法来探究Ca(OH)2在氮气气氛、不同升温速率下的分解动力学参数,结果表明:Ca(OH)2分别在623.15~773.15 K和873.15~973.15 K出现两个热分解失重过程;所得动力学参数与反应转化率、升温速率以及选用的模型方法有关;当转化率等于0.2~0.8时,非模型法所求的表观活化能在115~140 k J/mol之间,指前因子ln(A/s-1)=12~19;实验条件下Ca(OH)2分解动力学模型为相边界反应中的收缩圆柱体模型,积分机理函数G(α)=1-(1-α)1/2;不同升温速率下所得的指前因子A的自然对数和活化能E之间都存在着线性关系。更多还原

【Abstract】 Solar energy can be converted into electricity by means of concentrating solar thermal power technology, which can not only reduce the consumption of fossil fuels but also ease greenhouse effect caused by CO2 problems. However, because the solar energy is intermittent and is easily affected by environmental factors, how to ensure the continuous supply of solar energy has become the key of solar thermal power generation technology. A feasible method is the development of thermal energy storage system, which will store heat during the sunshine periods and release it during the periods of weak or no solar irradiation.At present, three kinds of thermal energy storage methods exist: sensible heat storage, latent heat storage and chemical heat storage. Due to the high energy density and negligible heat loss, thermochemical energy storage method has attracted widespread researches. In several available thermochemical heat storage systems, the Ca(OH)2/Ca O system has become one of the most studied systems because of high energy storage density, faster reaction kinetics, safe, nontoxic and low price.The heat and mass transfer performance of reaction bed during the endothermic and exothermic reaction processes, as well as the cyclical stability of reactants after 20 cycles had been investigated in this paper. The results show that: when the reaction bed temperature rises to 400 ℃, the dehydration reaction occurs rapidly and the mole reacted fraction of the reactants reduces to 0.06 after dehydration 180 minutes; The dehydration reaction proceeds faster with the increase of dehydration temperature; During the hydration process, the temperatures within the reaction bed increase rapidly and then begin to decrease. Temperatures inside the reactor bed are higher than that of the outer periphery; Mole reacted fraction is 0.95 at the end of the hydration process and no significant performance decay is observed after 20 cycles.The reactor bed heat storage capacity gradually increases with increasing dehydration temperature during the endothermic reaction process; Heat storage capacity after dehydration 90 minutes is equivalent to 33.6% of that during the whole dehydration process; With the increase of dehydration temperature, heat storage capacity of reaction bed increases at the same time; During exothermic process, the gross heat output after hydration 30 minutes is equivalent to 91.7% of the total heat output throughout the exothermic process; the heat storage capacity and total heat output at the same time decrease with the increase of cycle number, however, little changes are found in overall.Multi-rate scanning method was used in this paper to explore the decomposition kinetics parameters of Ca(OH)2 in nitrogen atmosphere and different heating rates, the results show that two weight loss processes are observed during the thermal decomposition of Ca(OH)2 at a temperature range of 623.15~773.15 K and 873.15~973.15 K; The resulting kinetic parameters are related to the reaction conversion rate, the heating rate and the selection of model approach; When the conversion rate is equal to 0.2~0.8, the obtained apparent activation energy using non-model approach is 115~140 k J/mol and the pre-exponential factor ln(A/s-1) is between 12 and 19; The decomposition kinetics model of Ca(OH)2 under the experimental conditions is proved to be shrinking cylinder mechanism with surface reaction rate controlling, and the integral mechanism function is G(α) =1-(1-α)1/2; Besides, a linear relationship between the activation energy E and the natural logarithm of pre-exponential factor A is discovered under different heating rates.更多还原