【作者】 徐艳；

【导师】 龙新峰；

【作者基本信息】 华南理工大学 ， 化学工程， 2020， 硕士

【摘要】 热能储存技术能有效提高可再生能源的利用效率,解决太阳能间歇不稳定的缺陷,减少化石原料燃烧带来的环境问题,为热能的存储和持续稳定供应提供了方法。热能能以三种方式存储:显热储能、潜热储能、热化学储能。热化学储能体系的储能密度大、存储时间长等优点,可广泛应用到废热回收、能量传输等体系。几十种热化学储能体系中,Ca（OH）₂/CaO体系原材料廉价易得、安全无毒、储能密度等优点,是目前具有发展潜力的中高温热化学储能体系之一。本文通过搭建固定床反应器,制备复合材料CE和CEL,探究复合材料在脱水和水合过程中的反应性能。在Ca（OH）₂中掺杂膨胀石墨制备复合材料CE。探究复合材料CE吸热/放热反应过程中的床层温度、反应摩尔分数、能量存储变化以及不同脱水温度和水合压力对其反应影响。在吸热反应过程中,床层温度先增加后趋于稳定。随着膨胀石墨质量混合比的增加,反应速率增加,w=0.25的复合材料CE在脱水进行75 min,床层温度趋于稳定;而纯氢氧化钙在反应140 min后床层温度在494℃保持稳定。另外,复合材料CE的储热容量比纯Ca（OH）₂要高,纯氢氧化钙在脱水过程中吸收了801.1 k J/kg的热能,而w=0.25的复合材料CE吸收能量为983.8 k J/kg。在放热过程中,水蒸气进入反应床与氧化钙发生反应,床层温度迅速上升。随着EG质量混合比的增加,床层温度的最高值增加,水合反应速率增加。当w=0和0.25时,释热容量分别占纯Ca（OH）₂/CaO理论焓变所对应的最大储能容量的80.8%、85.8%。在复合材料CE中掺杂LiBr制备复合材料CEL。观察复合材料CEL在脱水-水合-脱水循环反应过程的传质传热性能和循环稳定性。结果表明:在复合材料CE中添加LiBr对吸热反应过程中反应床层温度和摩尔反应分数没有很大的影响。在水合反应过程中,随着LiBr摩尔混合比的增加,水合摩尔分数增加,释能容量增加。n=0.100的CEL水合结束时的摩尔反应分数比纯Ca（OH）₂高0.1118。纯Ca（OH）₂、CE、LiBr摩尔混合比为0.100的CEL的释热容量分别为1132.8 k J/kg、1191.8 k J/kg、1298.6 k J/kg。不论是纯Ca（OH）₂、CE复合材料还是CEL复合材料,在脱水过程中,随着脱水温度的增加,反应速率增加;在水合过程中,随着水合压力的增加,水合反应速率增加;随着循环次数的增加,反应物的粒径增加,但是摩尔反应分数在小范围内波动,具有良好的循环稳定性。在数值模拟方面,采用Gambit软件建立间接传热反应床模型,导入FLUENT软件中进行数值计算,分别探究Ca（OH）₂的脱水性能和CaO的水合性能。研究表明:在脱水过程中数值模拟与实验结果相差不大。但是在水合过程中,数值模拟中增加了间接传热流体,随着HTF流速的增加,水合反应速率增加。水蒸气的分压影响着水合反应速率,随着水合压力的增大,床层温度的最大值越大。反应床孔隙率越低,水合反应时间越长,储能密度越大。更多还原

【Abstract】 Thermal energy storage technology can effectively improve the utilization efficiency of renewable energy,solve the defects of intermittent and unstable solar energy,reduce the environmental problems caused by the burning of fossil raw materials,and provide a method for the storage and continuous stable supply of thermal energy.There are three ways to store thermal energy:sensible heat storage,latent heat storage,and thermochemical energy storage.Due to the advantages of large energy storage density and long storage time,the thermochemical energy storage system can be widely used in waste heat recovery and energy transmission systems.Among the dozens of thermochemical energy storage systems,Ca（OH）₂/CaO system has the advantages of cheap and easily available raw materials,safety and non-toxicity,and energy storage density.It is one of the current high-temperature thermochemical energy storage systems with development potential.This paper builds a fixed-bed reactor,prepares composite materials CE and CEL,and explores the reaction performance of composite materials in the process of dehydration and hydration.The composite material CE is prepared by doping expanded graphite in Ca（OH）₂.The effects of bed temperature,reaction mole fraction,energy storage changes,and different dehydration temperatures and hydration pressures on the endothermic/exothermic process of composite materials CE were investigated.During the endothermic reaction,the bed temperature first increased and then stabilized.As the mass mixing ratio of the expanded graphite increases,the reaction rate increases.The composite material CE with w=0.25undergoes dehydration for 75 minutes,and the bed temperature tends to be stable;while the pure calcium hydroxide remains stable at 494℃after 140 minutes of reaction.In addition,the thermal storage capacity of the composite material CE is higher than that of pure Ca（OH）₂.Pure calcium hydroxide absorbs 801.1 k J/kg of thermal energy during the dehydration process,while the composite material CE of w=0.25 absorbs 983.8 k J/kg.During the exothermic process,water vapor enters the reaction bed and reacts quickly with calcium oxide,and the bed temperature rises rapidly.With the increase of the EG mass mixing ratio,the maximum value of the bed temperature increases,and the hydration reaction rate increases.When w=0and 0.25,the heat release capacity accounts for 80.8%and 85.8%of the maximum energy storage capacity corresponding to the theoretical enthalpy change of pure Ca（OH）₂/CaO,respectively.The composite material CEL is prepared by doping LiBr in the composite material CE.Observe the mass and heat transfer performance and cycle stability of the composite material CEL during the dehydration-hydration-dehydration cycle reaction process.The results show that the addition of LiBr to the composite material CE has no significant effect on the reaction bed temperature and molar reaction fraction during the endothermic reaction.During the hydration reaction,as the LiBr molar mixing ratio increases,the hydration molar fraction increases and the release energy capacity increases.The molar reaction fraction at the end of hydration of CEL with n=0.100 is 0.1118 higher than that of pure Ca（OH）₂.The heat release capacities of CEL with pure Ca（OH）₂,CE and LiBr molar mixing ratio of 0.100 are 1132.8k J/kg,1191.8 k J/kg and 1298.6 k J/kg,respectively.Whether it is pure Ca（OH）₂,CE composite or CEL composite,during the dehydration process,as the dehydration temperature increases,the reaction rate increases;during the hydration process,as the hydration pressure increases,the hydration reaction rate increases;As the number of cycles increases,the particle size of the reactants increases,but the molar reaction fraction fluctuates within a small range and has good cycle stability.In terms of numerical simulation,Gambit software was used to establish an indirect heat transfer reaction bed model,which was imported into FLUENT software for numerical calculation to explore the dehydration performance of Ca（OH）₂and the hydration performance of CaO,respectively.The research shows that the numerical simulation is not much different from the experimental results during the dehydration process.However,during the hydration process,indirect heat transfer fluids were added to the numerical simulation,and as the HTF flow rate increased,the hydration reaction rate increased.The partial pressure of water vapor affects the rate of hydration reaction.With the increase of hydration pressure,the maximum value of the bed temperature increases.The lower the porosity of the reaction bed,the longer the hydration reaction time and the greater the energy storage density.更多还原