Can you take the heat? – Geothermal energy in mining

In 2013, there are less than 20 documented examples of operational geothermal systems on mine sites worldwide. This is surprising, since on remote mine sites, where fuels may have to be shipped in over great distances, heating and cooling from low-enthalpy geothermal sources may have a significant advantage in operational cost over conventional energy sources. A review of factors affecting the feasibility of geothermal systems on mining projects has been undertaken, and has identified the possible configurations of geothermal systems suitable for the exploration, operational and closure phases of mine development. The geothermal opportunities associated with abandoned or legacy mines are also discussed. The potential categories of heat reservoirs associated with mine sites are: natural ground; backfilled workings; mine waste; dewatering pumping; and flooded workings/pit lakes. The potentially lower operational costs for heating and cooling must be offset against the capital cost of a geothermal system. The focus for mine operators should therefore be on identifying at feasibility stage those projects where conditions are favourable for geothermal systems, the potential risks are understood, the economics are likely to be beneficial, and geothermal systems can be established while minimising additional capital costs

Studying the impact of construction dewatering discharges to the urban storm drainage network(s) of Doha city using infoworks integrated catchment modeling (ICM)

The discharge of construction dewatering flows to the storm drainage network for disposal is a common activity in Qatar. The Dupuit empirical approach was utilized to establish various hypothetical dewatering scenarios on the basis of site classifications, which were modeled on 4 Case Study Areas of Doha’s Existing Surface Drainage Network in order to study the impact of dewatering discharge against an established baseline. The simulations were undertaken using InfoWorks Integrated Catchment Modeling (ICM) software for critical and non-critical rainfall events. The results indicated significant localized flooding in excess of the baseline conditions for scenarios exceeding 0.5 m3/sec flows, while individual catchments demonstrated variations and sensitivities on the basis of catchment properties and rainfall events. It is evident that dewatering discharge under unpredictable rainfall events poses various levels of risk to the city’s infrastructure, which is further exacerbated due to the massive scale of construction activity in the country and the rising ground water table in Greater Doha Area basin

The design and evaluation of an open loop ground source heat pump operating in an ochre-rich coal mine water environment

Mine water from the abandoned coal mines is considered a good source of low enthalpy energy resource as the temperature of the mine water remains stable throughout the year and is suitable to be used for heating and cooling applications when implemented in conjunction with Ground Source Heat Pump (GSHP). The GSHP is considered to be a low carbon technology and its application for space heating and cooling is being actively investigated and developed by companies and local councils around the world. The open loop GSHP installations, in comparison to closed loop systems, are suitable and economical for large scale heating and cooling demands. This is because there is no time delay for heat transfer when compared with closed loop systems and because they use large volumes of coal mine water at a relatively constant temperatures. A few installations both large and small scale open loop mine water heating and cooling systems have been recently constructed throughout the world. However, coal mine water is associated with relatively poor water quality in some cases, often characterised by high salinity and pyrite oxidation. Despite the fact that mine water temperatures are favourably inclined for an efficient GSHP operations, concerns have been raised over the possibility of damage to the equipment due to poor water quality caused by clogging of the heat exchangers due to pyrite oxidation (ochre) in particular. Not much information is available on the impact of ochre has on the performance of an open loop GSHP when it is operated using the coal mine water rich in pyrite. This paper presents a novel design and implementation of an open loop system of GSHP operating in an ochre rich mine water environment. The results show that open loop systems, when combined with suitable heat pump and the associated design configurations of heat exchangers and maintenance procedures, could provide an efficient and reliable heating system at a lower cost

Water from abandoned mines as a heat source: practical experiences of open- and closed-loop strategies, United Kingdom

Pilot heat pump systems have been installed at two former collieries in Yorkshire/Derbyshire, England, to extract heat from mine water. The installations represent three fundamental configurations of heat exchanger. At Caphouse Colliery, mine water is pumped through a heat exchanger coupled to a heat pump and then discharged to waste (an open-loop heat exchange system). The system performs with high thermal efficiency, but the drawbacks are: (1) it can only be operated when mine water is being actively pumped from the colliery shaft for the purposes of regional water-level management, and (2) the fact that the water is partially oxygenated means that iron oxyhydroxide precipitation occurs, necessitating regular removal of filters for cleaning. At Markham Colliery, near Bolsover, a small amount of mine water is pumped from depth in a flooded shaft, circulated through a heat exchanger coupled to a heat pump and then returned to the same mine shaft at a slightly different depth (a standing column arrangement). This system’s fundamental thermal efficiency is negatively impacted by the electrical power required to run the shaft submersible pump, but clogging issues are not significant. In the third system, at Caphouse, a heat exchanger is submerged in a mine water treatment pond (a closed-loop system). This can be run at any time, irrespective of mine pumping regime, and being a closed-loop system, is not susceptible to clogging issues

Ground energy systems: from analysis to geotechnical design

Ground energy systems use the ground and groundwater beneath a site as a heat source or sink to reduce energy costs and improve the environmental performance of buildings. The design and performance of the ground element of these systems (boreholes and ground loops) are dominant factors in the capital and operating costs of the system, yet, at present, such systems are often specified with little geotechnical input. This paper reviews some of the existing design approaches from a geotechnical perspective, and identifies potential failure modes (short term, long term and regulatory related) for ground energy systems. Short-term failures may result from deficiencies in the capacity of the infrastructure forming the ground element and/or from poor connection between the infrastructure and the ground. Long-term failures may derive from misestimation of loads and/or ground parameters. Possible future directions in the design of ground energy systems are discussed, and the need for informed geotechnical input to ground energy system design is highlighted

Ground energy systems: delivering the potential

Ground energy systems are increasingly being considered as an alternative to traditional heating and cooling systems as a way to reduce carbon emissions, control energy costs and improve the environmental performance of buildings. These systems use the ground and groundwater beneath a site as a heat source or sink, interacting through boreholes or pipes that exchange heat with the ground. This paper reviews the principles underpinning the systems and describes the two main types of system (open loop and closed loop). Four potential barriers to wider scale application of ground energy systems are highlighted. These are thermal interference between neighbouring systems in densely developed urban areas, increasing environmental regulation of below-ground elements, capital cost and the need to ensure that systems are sustainable in the long term. If the full potential of ground energy systems is to be realised, it is important that input from geotechnical and geological specialists is used to ensure that the below-ground elements are designed using appropriate design tools and site-specific data. It is also important that appropriate post-occupancy monitoring is in place to provide feedback to designers on the long-term performance of these systems.<br/

Performance of ejectors in construction dewatering systems

Construction dewatering in fine soils can be difficult, becausewell yieldsare often low and it is usually necessary to apply a vacuum to assist drainage. Ejector systems are therefore ideally suited to groundwater control in fine soils and have been used increasingly in the UK in recent years. Although their efficiency is low, this is not usually an issue when the flow rate of groundwater is small...<br/