The experimental study on thermal conductivity of backfill material of ground source heat pump based on iron tailings

• Published in: Energy and buildings Vol. 174; pp. 1 - 12
• Main Authors: Wan, Rong, Kong, Dequan, Kang, Jiayuan, Yin, Tianyu, Ning, Jiangfeng, Ma, Jianping
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.09.2018; Elsevier BV
• Subjects: Backfill; Backfill material; Concentrates (ores); Energy conservation; Engineering research; Formulas (mathematics); Functional equations; Geothermal energy; Ground source heat pump; Heat conductivity; Heat exchangers; Heat pumps; Iron; Iron ores; Iron tailings; Loess; Mine tailings; Mineral processing; Moisture content; Pumps; Solid wastes; Tailings; Thermal conductivity; Thermodynamic efficiency; Waste disposal; Waste materials; Water content; China; Loess; Thermal conductivity; Backfill material; Iron tailings; Ground source heat pump
• DOI: 10.1016/j.enbuild.2018.06.010
• ISSN: 0378-7788

•The thermal conductivity of iron tailings is higher than that of loess at same condition.•Mixtures of tailings and loess present higher thermal conductivity than single use of loess and iron tailings.•When loess and tailings are mixed with the mass ratio of 3:7, the thermal conductivities are higher than that of the others.•The thermal conductivity of backfill materials shows great relationship with saturation.•A empirical equation of thermal conductivity of backfill material was proposed. Iron tailings are the remains of solid waste after iron ore concentrates are selected by mineral processing technology. For a long time, iron tailings are disposed through accumulation and burial, which not only occupy large space but also increase the cost of treatment. Ground source heat pump (GSHP) system is a kind of environmental-friendly, energy-saving system by using geothermal energy. This is getting more and more wide use in China. The main problem of using GSHP is the low thermal property of backfill materials in the loess region of Northwest China, which affects the thermal efficiency of GSHP system. Improving the thermal conductivity of backfill materials is necessary and urgent for energy conservation. The authors hypothesized that thermal efficiency increases as the rate of tailings addition increases. To test this hypothesis, the authors applied iron tailings to the backfill material. Experiments were conducted to measure the thermal conductivity of the loess and iron tailings, determined under the conditions of different dry density, water content, and mixing ratio. Then, the changes of thermal conductivity were analyzed as tailings' mix proportion varies. The optimum mix ratio was determined and the reason was discussed. The results showed that the thermal conductivity of backfill material is a formula of saturation and rate of tailings addition. A series of functional equation was given in the end. The calculated value of the formulae matched well with the experimental data. The research concluded that the iron tailings as backfill material of GSHP is feasible and the result can be used as a reference for related engineering research.