Abstract:

To store low-temperature heat below 120℃, novel expanded vermiculite/CaCl₂ composite sorbents with four different salt contents were developed by impregnation methods. Morphologies records, sorption kinetics measurements, simultaneous thermal analyses (STA) and theoretical calculations of energy storage density were implemented on EV/CaCl₂ sorbents, with EV and CaCl₂·H₂O as reference. Scanning electron microscope (SEM) imagines indicate that EV has huge pore volume with numerous layers, which contributes to relative high salt content without the worry issue of solution leakage. Simulative sorption experiment was conducted to identify threshold salt content that composite sorbents can hold without solution leakage. The sorption kinetics and equilibrium sorption capacity were obtained utilizing a constant temperature and humidity chamber, and the influence of salt content and relative humidity on sorption performance was analyzed. The quantitative analysis of total water uptake demonstrates that their sorption process consists of three different phases:physical adsorption, chemical adsorption and liquid-gas absorption of CaCl₂ solution. Furthermore, water uptake, sorption heat and reaction temperature of each sorption process were obtained by analyzing the STA measurements. In general, EV/CaCl₂ composite sorbent with salt content of 47.9% was selected as the optimal sorbent, whose water uptake,mass energy storage density and volumetric energy storage density can reach as high as 1.12 g·g^-1, 1.25 kW·h^-1·kg^-1, 213.56 kW·h·m^-3, respectively.

Key words: sorbents, expanded vermiculite, calcium chloride, sorption characteristics, reaction kinetics, thermal storage density, solar energy

摘要：

为了储存120℃以下的热能，提出了以水为介质的热化学吸附储热方法。配制了一种以膨胀蛭石为多孔基质、氯化钙为反应盐的新型复合吸附剂，并对其进行了微观形貌表征、吸附性能测试、同步热分析测试和储热密度的理论计算。扫描电子显微镜（SEM）观测显示膨胀蛭石特有的片层状的大孔结构产生了相对巨大的孔体积；利用恒温恒湿箱实验排除有溶液泄漏问题的含盐量；通过恒温恒湿箱对30℃、3种相对湿度下的动态吸附过程进行测试，分析了含盐量和相对湿度对吸附特性的影响，证实了该复合吸附剂具有3个不同的吸水阶段，包括物理吸附、化学吸附和溶液的气-液吸收过程；利用同步热分析测试（STA）和数值计算进一步对上述3个吸附过程的吸水量、吸附热和反应温度进行分析。最终优选出含盐量47.9%（质量分数）的复合吸附剂，其吸水量高达1.24 g·g^-1，质量和体积储热密度分别高达1.25 kW·h·kg^-1和213.56 kW·h·m^-3。

关键词: 吸附剂, 蛭石, 氯化钙, 吸附性能, 反应动力学, 储热密度, 太阳能