Evaluation of the thermal energy storage performance of calcium-magnesium binary composite salt hydrates

doi:10.16085/j.issn.1000-6613.2023-0648

Abstract

Abstract:

Salt hydrate as a type of thermochemical energy storage materials involves reversible chemical reactions for the storage and release of heat during the processes of adsorption and desorption. It has high thermal energy storage density and is suitable for long-term thermal energy storage. Moreover, it can be combined with solar energy utilization, which can reduce the dependence on fossil energy. In this study, effect of different porous matrix, microporous molecular sieve(13X) and mesoporous diatomaceous earth(WSS) on the thermal energy storage performance of calcium-magnesium binary composite salt hydrates was investigated based on MgCl₂ and CaCl₂ with a molar ratio of 1∶2. Firstly, the pore structure, sorption isotherm and cycle stability of the developed two types of calcium-magnesium binary composite salt hydrates were compared. A two-dimensional model of a honeycomb thermal energy storage unit was used to analyze the storage/release performances of the developed two composites. Results showed that the 13X had smaller pore volume, larger specific surface area than WSS. Due to the impregnation of MgCl₂/2CaCl₂, the pore volume, specific surface area and porosity of calcium-magnesium binary composite salt hydrates had been reduced compared to those of corresponding porous matrix. Both MgCl₂/2CaCl₂ composites showed higher sorption capacity than that of the porous matrix. Moreover, the Polanyi adsorption potential theory could describe the sorption isotherm of the calcium-magnesium binary composite salt hydrates well. Furthermore, the simulation results showed that the thermal energy storage density of the WSS20 was 371.94MJ/m³, which was higher than that of 13X17, as well as the energy released power and recovery efficiency. The WSS20 could be used for storing/releasing thermal energy more than 47 times, while the 13X17 showed bad stability even within 10 cycles. Therefore, considering both thermal energy storage density and cycle stability, WSS20 was more suitable for storing thermal energy.

Key words: thermochemical energy storage, calcium-magnesium binary salt, wakkanai siliceous shale, cyclic stability, thermal energy storage density

摘要：

水合盐热化学储热利用可逆的化学反应，能够在吸附与脱附过程中实现热量的释放与储存，其具有储热密度高、适合长期跨季节储热等优点，与太阳能相结合可以减少对化石能源的依赖。为探究两种不同多孔基底对钙镁二元盐复合热化学储热材料储热性能的影响，基于摩尔比为1∶2的MgCl₂与CaCl₂两种水合盐，本文对以微孔分子筛（13X）为多孔基底的MgCl₂/2CaCl₂复合材料和以介孔硅藻土（WSS）为多孔基底的MgCl₂/2CaCl₂复合材料的孔结构、平衡吸附量和循环稳定性等进行实验对比分析。采用蜂窝状储热单元的二维模型，对两种MgCl₂/2CaCl₂复合热化学储热单元的储/放热过程进行模拟对比分析。结果表明，与WSS相比，13X的孔隙更小、比表面积更大、平衡吸附量更高。由于MgCl₂/2CaCl₂的填充，两种复合材料的孔体积、比表面积、孔隙率较多孔基底均有所下降。受MgCl₂/2CaCl₂与多孔基底协同作用的影响，MgCl₂/2CaCl₂复合材料的平衡吸附量在整个相对湿度区间均有明显提升，Polanyi 吸附势理论可以很好地描述MgCl₂/2CaCl₂复合材料的等温吸附线。WSS20储热单元的储热密度为371.94MJ/m³，可以持续输出20℃温升以上的空气198min，其放热功率和热回收效率均高于13X17储热单元。WSS20在循环47次后仍然保持完整的结构和良好的吸附量，而13X17在循环10次后发生破裂。综合储热密度和循环稳定性，WSS20更适合作为储热材料使用。

关键词: 热化学储热, 钙镁二元盐, 硅藻土, 循环稳定性, 储热密度

CLC Number:

TK11

LIU Han, QU Minglu, YE Zhendong, YANG Fan, HUANG Beijia, ZHANG Yaning, LIU Hongzhi. Evaluation of the thermal energy storage performance of calcium-magnesium binary composite salt hydrates[J]. Chemical Industry and Engineering Progress, 2024, 43(4): 1764-1773.

刘涵, 曲明璐, 叶振东, 杨帆, 黄蓓佳, 张亚宁, 刘洪芝. 钙镁二元盐复合材料的储热性能[J]. 化工进展, 2024, 43(4): 1764-1773.

Figures/Tables 17

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材料名称	MgCl₂/2CaCl₂质量分数/%
WSS	0
WSS7	7.37
WSS20	20.38
13X	0
13X7	7.24
13X17	17.90

材料名称	MgCl₂/2CaCl₂质量分数/%
WSS	0
WSS7	7.37
WSS20	20.38
13X	0
13X7	7.24
13X17	17.90

测点位置	储放热过程	计算百分比偏差δ/%						平均总和误差/%
测点位置	储放热过程	0~100min	101~200min	201~300min	301~400min	401~500min	501~600min	平均总和误差/%
进口	放热过程	1.9	1.9	0.9	0.4	0.1	0.2	0.8
	储热过程	10.9	0.3	0.2	1.6	—	—	6.2
120mm	放热过程	5.6	4.9	3.1	2.5	3.2	2.1	2.1
	储热过程	14	11	9.4	2.5	—	—	7.1
出口	放热过程	31.3	12.6	8.6	8.3	6.7	3.2	16.9
	储热过程	10.2	5.2	9.4	14.1	—	—	8.4

测点位置	储放热过程	计算百分比偏差δ/%						平均总和误差/%
测点位置	储放热过程	0~100min	101~200min	201~300min	301~400min	401~500min	501~600min	平均总和误差/%
进口	放热过程	1.9	1.9	0.9	0.4	0.1	0.2	0.8
	储热过程	10.9	0.3	0.2	1.6	—	—	6.2
120mm	放热过程	5.6	4.9	3.1	2.5	3.2	2.1	2.1
	储热过程	14	11	9.4	2.5	—	—	7.1
出口	放热过程	31.3	12.6	8.6	8.3	6.7	3.2	16.9
	储热过程	10.2	5.2	9.4	14.1	—	—	8.4

基底材料	材料名称	比表面积/m²·g^-1	孔体积/cm³·g^-1	孔隙率/%	孔径范围/nm	平均孔径/nm
13X	13X	594.18	0.36	51	0.8~1.6	0.86
	13X7	468.73	0.32	48	0.8~1.6	0.82
	13X17	363.01	0.26	42	0.8~1.6	0.84
WSS^[11]	WSS	136.66	0.36	60	4.3~17.4	9.71
	WSS7	94.75	0.31	57	5.6~17.4	10.60
	WSS20	57.26	0.19	52	5.6~17.4	10.50