Preparation and performance study of incinerated slag based shape-stable phase change composites

doi:10.11949/0438-1157.20211680

Abstract

Abstract:

Massive accumulation and landfill of municipal sludge will damage the local ecological environment around the city. Incineration can realize the harmlessness of municipal sludge, however, the heavy metals inside the incinerated slag are difficult to be effectively fixed. In order to effectively fix the heavy metals inside the incinerated slag and recycle the slag to produce low-cost shape-stable phase change composites, this work proposed the sludge incinerated slag as skeleton material, and five slag-based shape-stable phase change composites were prepared with sodium nitrate as phase change material with different mass ratio of incinerated slag to sodium nitrate by cold-compression & hot-sintering method. Then, the thermal performance, micromorphology, mechanical performance and chemical compatibility between the slag components and the sodium nitrate were investigated. Results shows that the shape-stable phase change composite with the mass ratio 5∶5 of slag to sodium nitrate, namely the sample SS3 possesses the best heat transfer and thermal energy storage performance as well as excellent high-temperature thermal stability, which fixed the heavy metals inside properly. Moreover, a good chemical compatibility between the slag components and the sodium nitrate is observed and the sample SS3 achieves the thermal energy storage density of 409.25 J/g and the maximum thermal conductivity of 0.955 W/(m·K) in the range of 100—400℃ and the mechanical strength of 139.65 MPa. In addition, the sample SS3 possesses excellent heat transfer and thermal energy storage performance after 500 heating/cooling cycles, which indicates that sludge incinerated slag is suitable for preparing low-cost shape-stable phase change composites as skeleton materials.

Key words: municipal sludge, skeleton materials, thermal energy storage, stability, chemical compatibility, phase change, preparation

摘要：

市政污泥的大量堆积或填埋会破坏局部生态环境，而焚烧可实现污泥的无害化处理，但污泥炉渣中的重金属难以有效固定。为有效固定污泥炉渣中的重金属，资源化利用污泥焚烧炉渣制备低成本复合相变储热材料，提出市政污泥焚烧炉渣作为骨架材料，硝酸钠为相变储热材料，采用冷压-烧结法制备了5种不同质量比的污泥焚烧炉渣基定型复合相变储热材料，并对其传热储热性能、微观形貌、抗压性能以及化学相容性进行研究。结果表明，在100～400℃范围内，焚烧炉渣与硝酸钠质量比为5∶5（样品SS3）时定型复合相变储热材料具有最佳的传热储热性能和良好的高温热稳定性，可实现对重金属的有效固定；炉渣组分与硝酸钠间具有良好的化学相容性，样品SS3的储热密度高达409.25 J/g，热导率最高达0.955 W/（m·K），抗压强度为139.65 MPa。经历500次加热/冷却循环后，样品SS3仍然具有良好的传热储热性能，表明污泥焚烧炉渣适合作为制备定型复合相变储热材料的骨架材料。

关键词: 市政污泥, 骨架材料, 储热, 稳定性, 化学相容性, 相变, 制备

CLC Number:

TK 02

Chaoyu SONG, Yaxuan XIONG, Jinhua ZHANG, Yuhe JIN, Chenhua YAO, Huixiang WANG, Yulong DING. Preparation and performance study of incinerated slag based shape-stable phase change composites[J]. CIESC Journal, 2022, 73(5): 2279-2287.

宋超宇, 熊亚选, 张金花, 金宇贺, 药晨华, 王辉祥, 丁玉龙. 污泥焚烧炉渣基定型复合相变储热材料的制备和性能[J]. 化工学报, 2022, 73(5): 2279-2287.

Figures/Tables 13

Table 1 Chemical compositions of the incinerated slag of municipal sludge

Al₂O₃	SiO₂	P₂O₅	CaO	Fe₂O₃	MgO	Others
37%	24.9%	17.3%	7.7%	5.7%	2.6%	4.8%

Fig.1 Fabrication process of shape-stable phase change composites

Table 2 Composition and appearance of shape-stable phase change composites

样品编号	污泥炉渣/ %(质量)	硝酸钠/ %(质量)
SS0	0	100
SS1	60	40
SS2	55	45
SS3	50	50
SS4	45	55
SS5	40	60

Fig.2 Specific heat of samples SS0, SS2, SS3 and SS4 over temperature

Fig.3 Specific heat curves of sample SS3 before and after cycles

Table 3 Change of thermal performance and mass of sample SS3 before and after cycling

项目	熔点(熔化起始温度)/°C	熔化终止温度/°C	潜热/（J/g）	质量/mg
500次加热/冷却循环前	303.7	316.2	60.33	1000
500次加热/冷却循环后	303.8	318.1	55.61	960

Fig.4 Thermal energy storage capacity of sample SS3 before and after cycles

Fig.5 Thermal diffusivity and thermal conductivity of sample SS3 before and after cycles

Fig.6 Micromorphology of sample SS3 before and after cycles

Fig.7 Element mapping of sample SS3 before and after cycles

Fig.8 Chemical compatibility between the slag components and NaNO3

Fig.9 Mechanical strength of samples SS2, SS3 and SS4

Fig.10 Mechanical strength of sample SS3 before and after cycles

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