An analytical assessment on the impact of covers on the onset of air convection in mine wastes

Lu, Ning

doi:10.1002/nag.133

Cited by 8 publications

(8 citation statements)

References 16 publications

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“…It has been suggested that heat convection within the piping area may affect the performance of BTES systems in terms of both heat storage and the rate of heat transfer (McCartney et al, 2013). Lu (2001) found that the rate of heat transfer in a convective cell in an unsaturated soil layer may be up to 10 times faster than heat transfer by conduction. Previously, the influence of the soil intrinsic permeability on convective processes within a BTES system in saturated soil was shown.…”

Section: Sensitivity Resultsmentioning

confidence: 99%

Numerical Modeling of a Soil‐Borehole Thermal Energy Storage System

Catolico

McCartney

2016

Vadose Zone Journal

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Borehole thermal energy storage (BTES) in soils combined with solar thermal energy harvesting is a renewable energy system for the heating of buildings. The first community-scale BTES system in North America was installed in 2007 at the Drake Landing Solar Community (DLSC) in Okotoks, AB, Canada, and has since supplied >90% of the thermal energy for heating 52 homes. A challenge facing BTES system technology is the relatively low efficiency of heat extraction. To better understand the fluid flow and heat transport processes in soils and to improve BTES efficiency of heat extraction for future applications, a three-dimensional transient coupled fluid flow and heat transfer model was established using TOUGH2. Measured timedependent injection temperatures and fluid circulation rates at DLSC were used as model inputs. The simulations were calibrated using measured soil temperature time series. The simulated and measured temperatures agreed well with a subsurface having an intrinsic permeability of 1.5 ´ 10 −14 m 2 , thermal conductivity of 2.0 W m −1 °C −1 , and a volumetric heat capacity of 2.3 MJ m −3 °C −1 . The calibrated model served as the basis for a sensitivity analysis of soil thermal and hydrological parameters on BTES system heat extraction efficiency. Sensitivity analysis results suggest that: (i) BTES heat extraction efficiency increases with decreasing soil thermal conductivity; (ii) BTES efficiency decreases with background groundwater flow; (iii) BTES heat extraction efficiency decreases with convective heat losses associated with high soil permeability values; and (iv) unsaturated soils show higher overall heat extraction efficiency due to convection onset at higher intrinsic permeability values.Abbreviations: BTES, borehole thermal energy storage; DLSC, Drake Landing Solar Community.Growing concerns about greenhouse gas emissions and fossil fuel consumption have motivated the increased development of renewable energy systems including solar thermal energy harvesting technologies for the heating and cooling of buildings. In recent decades, borehole thermal energy storage (BTES) systems with heat derived from solar technology are rapidly gaining attention and use worldwide (Claesson and Hellstrom 1981;Dalenbäck and Jilar, 1985;Nordell and Hellström, 2000;Sanner and Knoblich, 1999;Sanner et al., 2003;Morofsky, 2007;Sibbitt et al., 2007Sibbitt et al., , 2011Sibbitt et al., , 2012Wang et al., 2010;Dehkordi and Schincariol, 2014a;Acuna and Palm, 2013;Başer and McCartney, 2015). In BTES systems, a series of U-tube pipes placed in closely spaced (1.5-2.5 m) vertical boreholes are connected to form a closed-loop heat exchanger (Fig. 1). Heat exchange is achieved by circulation of a heat carrier fluid through the closed-loop U-tube pipes. Many BTES systems store heat collected from solar thermal panels in the summer months until it can be extracted for use during the winter months. These thermal energy storage systems present a potentially economical and environmentally sustainable alternative to traditional...

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Section: Sensitivity Resultsmentioning

confidence: 99%

Numerical Modeling of a Soil‐Borehole Thermal Energy Storage System

Catolico

McCartney

2016

Vadose Zone Journal

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“…This process is referred to as a convection cell. Lu (2001) found that the rate of heat transfer in a convective cell in an unsaturated soil layer may be up to 10 times faster than assuming that heat conduction is the only means of heat transfer. Traore (2013) evaluated the behavior of SBTES systems in the vadose zone using a series of tank-scale physical modeling tests, and observed that a convection cell formed in a borehole array with a spacing of 300 mm, leading to an increase in the apparent thermal conductivity by about 7%, along with a slight increase in specific heat capacity of 4%.…”

Section: Introductionmentioning

confidence: 94%

Development of a Full-Scale Soil-Borehole Thermal Energy Storage System

Başer

McCartney

2015

Ifcee 2015

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This study involves an evaluation of the design and construction process for a soil-borehole thermal energy storage (SBTES) system installed in a sandy-silt deposit. A series of simplified numerical simulations were performed to understand the role of different variables on the heat storage in the SBTES system. The results indicate that soils with lower thermal conductivity have less lateral heat loss, and that arrays with smaller borehole spacings permit more concentrated storage of heat at higher temperatures.

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“…Density dependent convective airflow is a well-documented process, and has been observed in waste rock piles (Lu 2001). Convective airflow is initiated when a temperature induced density gradient exists between air within waste rock piles and ambient conditions.…”

Section: Convective Airflow Modellingmentioning

confidence: 99%

Progressive rehabilitation — Martabe Gold Mine as a case study

Pearce¹,

Orr²,

Grohs³

et al. 2016

Proceedings of the International Conference on Mine Closure

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Progressive rehabilitation has been recognised by the mining industry as a key strategy for minimising mine closure costs and environmental risk, with the rehabilitation of potentially acid-forming waste rock being of particular interest due to the very large liabilities associated with sites where this risk has not been properly addressed. When properly implemented as an engineered solution, progressive rehabilitation of potentially acid-forming waste rock can provide an inherently more robust and lower risk rehabilitation strategy compared with the commonly-implemented alternative of an end-of-life waste dump covers. A case study is presented herein where progressive rehabilitation of potentially acid-forming waste rock has been successfully integrated with ongoing construction of the embankment of a tailings storage facility (TSF). The mine site in question, the Martabe Gold Mine in Indonesia, is thought to be unique in that construction of the TSF embankment at the site will require utilisation of almost all of the waste rock to be produced life-of-mine. The TSF embankment is therefore a fully integrated and engineered structure addressing both tailings and waste rock disposal requirements for the site. This approach offers a number of key benefits, including minimisation of both waste rock rehabilitation and tailings storage costs, and minimising the risk of long-term acid mine drainage. The progressive mine waste rehabilitation strategy adopted by G-Resources at the Martabe Gold Mine was designed taking into account the inherent properties of the waste rock materials, the run-of-mine waste rock schedule, and the engineering constraints required in order to construct a TSF embankment to exacting geotechnical standards. The strategy has required systematic implementation of outcomes reflective of industry leading practice, including:  Detailed waste characterisation studies.  Development of waste characterisation criteria.  Production of a life-of-mine waste schedule.  Selection of a waste sealing specification based on oxidation modelling.  Progressive implementation of selective waste placement and sealing.  Performance measurement to validate design and implementation. All key technical teams at the Martabe Gold Mine, including exploration, mine geology, mine planning, TSF construction and environment, have played an integral role in the implementation of this strategy, which can be described as an integrated waste management solution in which minimisation of mine closure risk is process that is carried out across the life of the mine.

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An analytical assessment on the impact of covers on the onset of air convection in mine wastes

Cited by 8 publications

References 16 publications

Numerical Modeling of a Soil‐Borehole Thermal Energy Storage System

Numerical Modeling of a Soil‐Borehole Thermal Energy Storage System

Development of a Full-Scale Soil-Borehole Thermal Energy Storage System

Progressive rehabilitation — Martabe Gold Mine as a case study

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