Environ Earth Sci DOI 10.1007/s12665-015-4285-y
THEMATIC ISSUE
Geothermal heat recovery from abandoned mines: a systematic review of projects implemented worldwide and a methodology for screening new projects Esmeralda Peralta Ramos1 • Katrin Breede1 • Gioia Falcone1
Received: 9 October 2014 / Accepted: 8 March 2015 Springer-Verlag Berlin Heidelberg 2015
Abstract Due to the increasing energy demand worldwide and the resulting rising costs of conventional fuels, alternative energy sources could play a significant role towards global energy sustainability. Geothermal nearsurface systems based on heat pumps have already proved to be a feasible option for the heating and cooling of buildings, while offering low CO2 footprint. In this study, the concept of using abandoned mines for geothermal heat recovery with either closed- or open-loop configurations is systematically reviewed based on 18 projects worldwide. Key engineering parameters such as temperature on depth, circulation flow rate, mine water quality, and end-users’ location and demand have been used to characterize and classify the different projects. The study shows that the projects significantly differ from one another, thus highlighting the attractive versatility of this geothermal concept. A key outcome of this work is the development of a systematic procedure to evaluate future projects, followed by an example of a preliminary system design for a synthetic case scenario in the Harz region in Germany. After China’s energy administration’s recent announcement that the country will close 1,725 small-scale coal mines over the course of 2014 and considering the alarming levels of air pollution in the country, the concept of geothermal heat recovery from abandoned mines could become even more significant in the near future.
& Esmeralda Peralta Ramos
[email protected] 1
Institute of Petroleum Engineering, Clausthal, Clausthal University of Technology, Agricolastr. 10, 38678 Clausthal-Zellerfeld, Germany
Keywords Waste heat Geothermal energy Abandoned mines District heating
Introduction As the environmental protection consciousness and idea of sustainability grows, the interest in renewable energy sources increases. At present, the most common energy source for space heating and cooling are fossil fuels having a high environmental impact and being in addition exhaustible. An alternative is a heat pump utilizing geothermal energy being an economical and sustainable energy source. As a result of the distribution of mineral resources all over the world, mining activity is found in almost every country. Over the operational period of the mines, encroaching ground water must be controlled so that the mining activity can be performed safely and efficiently. Once the excavation process is stopped, so is the dewatering process, which leads to the mines flooding. Hence, abandoned mines around the world represent a potential for geothermal energy. The best known geothermal project using water from an abandoned mine as a heat source was installed in Spring Hill, Canada, in 1989 (Jessop et al. 1995). The flooded water of abandoned mines can act as a heat source for heat pumps. The mines can provide heating and cooling for a single household or for district heating, depending on the total capacity of the individual site. This concept with its efficiency, cost-effectiveness, and environmental advantages has been implemented in many countries worldwide, including Germany. A well-known German mining area is located in the Upper Harz region, where copper, silver, lead and zinc
123
Environ Earth Sci
were mined (Ließmann 2010). Nowadays, most of the abandoned underground structures in this region are flooded and thus present, especially due to the interconnectivity of the different mines, a large potential for the installation of this sustainable system to capture the heat of the mine water via heat pumps. This study presents a systematic review of the implemented systems worldwide, which harness the heat potential of the flooded water from abandoned mines. Various parameters are collected for each project, to characterize and classify them. These parameters are then used to determine the minimum requirements for a heat pump implementation for an abandoned mine in the Upper Harz region as a precursor for a feasibility study aimed at an upscaling project to provide geothermal energy to the Campus of the Clausthal University of Technology using the large abandoned mine situated underneath the town of Clausthal-Zellerfeld.
Materials and methods Heat pumps are designed to take the heat from a colder source and transfer it to a hotter source. These devices capture the heat through evaporation of a refrigerant, increasing the refrigerants temperature by compression, releasing the heat in a heat exchanger, and reducing the temperature of the refrigerant with a valve. The process can be reversed to provide air-conditioning. The efficiency of heat pumps is quantified by the coefficient of performance (COP), which is the rate of heat produced by work supplied. The smaller the difference between the inlet and the delivered temperature, the higher the pump efficiency, meaning that less energy is needed to achieve the heating or cooling requirements. Different types, designs, and configurations are available for heat pumps, which enables them to meet either the total heating requirement of a building, part of the load, or to cover the basic requirement while a conventional system supplies the peaks. There are two configurations to transfer the heat of the mine water to the heat pumps: open-loop or closed-loop systems. The open-loop configuration extracts the mine water and discharges it after capturing heat (heating mode) or releasing it (cooling mode). This system is more common and simpler than the closed-loop system, which requires additional material such as pipes circulating a working fluid to capture the heat from the mine water. The working fluid itself is never in contact with the mine water and thus the closed-loop configuration is used for mines with contamination issues or not enough water volume being available.
123
Description of implemented systems This section describes the systems that have already been implemented to harness geothermal energy using heat pumps for space heating and cooling. The database presented in this paper should not be considered to be exhaustive, as it is based primarily on information available in the public domain. A total of 18 projects around the world were reviewed and a comparative study of the parameters such as depth, temperature, and flow rate was performed. The goal is to understand the implementation procedures and analyze the relation between the source parameters as offered by the mines and the system design. The parameters for the respective projects are presented in detail in the next section and will be compared later. Canada In addition to the project in Spring Hill, a second one has been implemented as an open-loop system that utilizes the mine water from the Goyer Quarry, which is located in Quebec. The Goyer Quarry has a total volume of flooded mine water of 8,064,000 m3 and is used to supply heating and cooling to 36 apartments using heat pumps. The project is designed as a decentralized system, with heat pumps located at each customer site. The installed heat pumps have capacities in the range of 3.6–5.3 kW (Raymond et al. 2008). Germany Numerous geothermal mine water projects have been implemented in Germany. Alsdorf, North Rhine Westphalia The ‘‘GrEEn-Projekt’’, in the Alsdorf municipality of the state of North Rhine Westphalia, aims to implement a sustainable geothermal system for heating one or two buildings belonging to the Energeticon Company. A closed-loop system would be used to harness the heat energy from the water flooding the abandoned Anna coal mine, which is at a temperature of 26 C. The planned access to the mine water is via the Eduard Shaft, which has a depth of about 890 m (Energeticon 2013). Bad Schlema, Saxony In Bad Schlema, a mine water geothermal system was planned to be installed for an old school building, which was built in 1907. In July 2009, the renovation work began on 5,685 m2 of the school building. The annual energy
Environ Earth Sci
requirement before installing the geothermal system was 504.7 kWh/m2 and could be reduced to 175.3 kWh/m2 after the implementation. The total costs incurred for the renovation are about 2,693,163 €; this includes exchange of windows (isolation glass windows replaced the simple ones), external walls (insulation), and isolation of pipes among others (Just 2013). Ehrenfriedersdorf, Saxony In the old mining town of Ehrenfriedersdorf, where predominantly tin was mined for about 700 years, two different geothermal projects have been implemented. These projects utilize the mine water from different sections of the abandoned mine. A two-stage heat pump system has been in operation at the Sauberger Haupt- and Richtschacht mining areas. The system consists of a plate heat exchanger in the shaft at a depth of 110 m, which takes the heat from the mine water, warms up clean water in the secondary loop, and transports it to a heat pump on the surface. The heat is transferred from the latter heating loop and the water of the secondary loop, now cooled down by 5 C, is transported back to the heat exchanger (Krassmann 2014). Freiberg, Saxony Freiberg has two geothermal projects that have been presented in the literature. One has been implemented for a castle and the museum it houses, while the second one was implemented to supply heat to buildings belonging to the Freiberg University of Mining and Technology. The geothermal system installed at the Castle Freudenstein supplies the base requirements of the infrastructure while a conventional system covers the peak load and the special air conditioning requirements. The low-enthalpy is harnessed from the water flowing in the Alter Tiefer Fu¨rstenstollen gallery which is located at a depth of 60 m. Mine water, at a constant 10.2 C, is accumulated in this gallery using a dam (Kranz and Dillenardt 2010). Two submersible rotary pumps with a combined capacity of 21.6 m3/h raise the water to a height of 50 m to the shaft head, where a heat exchanger is placed, and then the water is returned to the gallery. The heat exchanger captures the heat and transfers it to a secondary loop (DT of 5 C), which at the same time transfers the heat to a twostage heat pump located 230 m away from the shaft at a building behind the castle. The heat pump has a maximum heat capacity of 130 kW with a net consumption of 29.24 kW. According to the manufacturer, the COP values are 2.4–4.3 in operational mode. In heating mode, the heat pump delivers temperatures up to 42 C. This hot water is then stored in a buffer. Another pump is used to transport
the hot water from the buffer to two mixed water distributors that supply the heating system at the desired inlet temperature. Floor heating is used in some parts of the castle building (Bu¨ttner et al. 2010). The ReicheZeche mine was abandoned in 1913, later the TU Bergakademie Freiberg endeavored to turn the ReicheZeche area into a research project and, since 1992, it is also used as a mining museum (Grab et al. 2010). An openloop system was implemented in which, according to the mode (heating or cooling), mine water is extracted either from the Rothscho¨nberger gallery or the flooded ReicheZeche shaft. The outflow water has a temperature of 4 C lower than the intake water. Four pumps raise the water to the four 168 kW capacity plate heat exchangers installed at the third level. Closed-loop systems are connected in series to the heat pumps to supply heat to individual customers on the campus of TU Bergakademie Freiberg (Baukonzept-Dresden 2014). The planned first phase of the heating mode is to recover about 260 kW (approximately 155 kW for cooling use) and in the final stage it is planned to withdraw up to 670 kW (500 kW cooling case) of mine water. The heating and cooling performance of the first stage of development is planned to supply a newly constructed Institute building of the University. In the heating mode, mine water with a temperature of 18 C is pumped from the flooded shaft system to the heat exchanger. By means of two heat pumps, the temperature is raised to about 55 C. An electrical power output of 50 kW is planned for the heat pumps, with a COP of 4 (Grab et al. 2010). Marienberg, Saxony In 2006 in the city of Marienberg, a geothermal low-enthalpy project was implemented using ‘shaft 302’ which accesses the 107 m deep ‘‘Weibtaubener’’ mine (Matthes and Schreyer 2007). An open-loop system harnesses the constant mine water temperature of 12.4 C by extracting the water using three submersible pumps with a maximum combined flow rate of 120 m3/h and a total consumption of 120 kW. A stainless steel plate heat exchanger has been installed on a platform at a depth of 105 m. Plastic pipes are used between the pumps and the heat exchanger. In the latter, the mine water is cooled down by 5 C to heat up clean water in a secondary closed-loop, which is flowing at a maximum flow rate of 120 m3/h. The cooled mine water is then discharged into a drainage tunnel (Stadtwerke Marienberg GmbH 2013). Two sections can be distinguished in the closed-loop: one vertical and one horizontal, which are made of different materials that reflect their service. The pipes in the vertical section are made of galvanized steel. Water flows via these pipes from the pump station at the surface to the
123
Environ Earth Sci
underground heat exchanger and back. The horizontal section transports the water from the pumping station to the end-users heat pumps by means of buried plastic pipes. The temperature difference between the delivered and returned water ranges from 4 to 5 C. Neither the horizontal, nor the vertical section is isolated (Stadtwerke Marienberg GmbH 2013). The potential heating capacity of the system is estimated to be 690 kW (Matthes and Schreyer 2007). The geothermal system started to operate at the end of 2007 and is supplying heat to the adventure pool, Aqua Marien, a tennis hall, and some supermarkets. Wettelrode, Saxony-Anhalt A feasibility study revealed the Ro¨hrig shaft, located in Wettelrode, as one of the potential sites for the implementation of the geothermal mine water concept. A project was started with the goal of implementing a geothermal pilot system for the Wettelrode Ro¨hrigschacht mining museum, to provide heat and hot water to the building. The system started successful operation in September 2013 (Koch and Hoffmann 2013). The Ro¨hrig shaft is connected to the water discharge in the Segen-Gottes gallery, at a depth of 163 m and to the first level at a depth of 283 m, which is its deepest point. An open-loop configuration was installed in the Ro¨hrig shaft to extract mine water from a depth of 283 m and transport it to a plate heat exchanger, which has been placed in the Segen-Gottes gallery. Three rotary pumps have been placed in the same loop at the first level; one is working constantly, the second one is used to cover requirement peaks, and the third one is a backup pump (Hartung 2014). The mine water arrives at the heat exchanger at a constant temperature of 13 C and it is reduced by 5 C to warm clean water by up to 13 C. The mine water is then discharged in the Segen-Gottes gallery. The warmed clean water is circulated in a closed-loop and transferred to the heat pump, which is located 45 m away from the shaft in a heating room. Steel has been used for both loops; however, only the horizontal section (from the shaft to the heating room) has been isolated and buried 1 m below surface to reduce thermal losses. In the heating room, the clean water arrives at a temperature of 13 C, while the heat pump supplies 50 C to the heating system of the building (Hartung 2014). The renovation of the building’s museum was carried out from July 2012 to September 2013. During this time, the existing building was renewed and the restaurant was expanded, making a total area of 400 m2. Floor heating and isolation were installed to reduce the building’s heating load. The heating requirement of the entire building is
123
47 kW, including the supply of warm water (Hartung 2014). The Netherlands The full scale Mine Water Project in Heerlen, located in the province of Limburg, Netherlands, is one of the world’s largest geothermal district heating systems sourced by mine water. The idea of the geothermal concept started in 2000. The projects’ evolution is characterised by two stages with the first one being the Mine Water 1.0, running from 2003 to 2008. Its aim was to determine, by means of a pilot system, how the low-enthalpy stored in the flooding water of the abandoned Oranje Nassau mine could be harnessed for buildings’ heating and air-conditioning (Verhoeven et al. 2013). The second stage, Mine Water 2.0, is still under development with the primary objective of redefining the system to a full scale smart grid (Verhoeven et al. 2013). For the assessment of the pilot project, detailed studies (geological, mechanical, hydraulic, thermal and chemical) and pumping tests were carried out. Numerical simulation was used to study the mine water in detail on the basis of the tests information and old maps. Based on the chemical analysis of the water, it was determined to use titanium in the heat exchanger and high-grade polypropylene for the piping system (Minewater Good Practice Guide 2013). The pilot project is an open-loop configuration, which extracts the warm mine water at a temperature of 28 C from a depth of about 700 m through two wells. In addition, cold water (16 C) was supplied from a depth of 250 m using two wells, called HLN-1 and HLN-2 (Op ‘t Veld et al. 2010). Each working well has a submersible pump located at a depth of 130 m and to avoid thermal losses, the pipe transporting warm water has been isolated with Armaflex (Verhoeven 2013). Every building has its own energy station consisting of a titanium heat exchanger, heat pumps, and gas fired high-efficiency boilers. After leaving the energy stations, the mine water is re-injected into the abandoned mine at a depth of 350 m. The pilot system started successful operations in 2008. The second stage of the project, Mine Water 2.0, aims to develop the concept of the pilot system to a sustainable full scale smart grid. Warm and cold mine water are extracted from the wells HH-1 and HLN-1, respectively. However, in this second stage of the project, the mine water is no longer the only source for heat pumps, as waste heat and waste cold from the connected buildings is additionally used through local cluster grids. To assure the sustainability of the system, the mine water is heated up to 28 C or cooled down to 16 C in the energy stations before being re-injected into the corresponding wells, HH-2 and HLN-2. The extraction capacity will be increased so that a maximum of
Environ Earth Sci
120 m3/h of hot mine water and 230 m3/h of cold mine water can be produced (Verhoeven et al. 2013). The number of heat pumps, along with their capacities, has been individually determined according to the requirements of each customer. The geothermal system works completely automatically, based on a demand/supply concept (Rene´ Verhoeven, personal communication 2013). The system is currently servicing 125,000 m2, with 200,000 m2 as of contract; however, the objective is to go up to 500,000 m2 by the end of 2016 with a total of 700,000 m2 by contract (Verhoeven 2015). Norway A mine water heat pump system was installed in October 1998 at the ‘‘Folldal Gamle Gruver’’ mining museum, located in Folldal, Norway. The system operated for 10 years, until the heat pump broke down. Due to a 50 m vertical section of the pipe being surrounded by air instead of mine water, the efficiency of the system was reduced and therefore the operator decided to replace the water-toair heat pump (the system) with an air-to-air heat pump (Kristoffersen 2014). The flooded mine water has a temperature of 6 C. The heat of the mine water was harnessed through a closed-loop system to heat the Wormshall chamber which is 125 m underground. This configuration was selected because the mine water is heavily polluted with sulphides. A mixture of water and anti-freezing agent was circulated in the loop to capture the heat of the mine water and transport it to a water–air heat pump (Kristoffersen 2014). The heat pump was providing a temperature of 22 C and a heat capacity of 18 kW with an electrical consumption of 4.6 kW (Banks et al. 2004). In Kongsberg, Norway, a closed-loop system similar to the one installed in Folldal was planned (Kristoffersen 2014). Russia In the town of Novoshakhtinsk in the Rostov region, a project was implemented to substitute fossil fuels as a heating source with renewable energy sources. The project ensured heating distribution in three districts through the installation of three heat pump stations (HPS), a small hydroelectric plant (SHEP), and the required renovation of the existing distribution system. This region, close to the border with Ukraine, has numerous abandoned coal mines, which are flooded with water that can reach temperatures between 12 and 13 C. The mine water is extracted by a submersible pump via boreholes about 50–150 m deep. At each HPS, an openloop configuration has been installed and the mine water
enters the heat pump at a temperature of 12–13 C, cooled down to 5–7 C, and then returned to the underground structure at a different level. The heat pumps’ COP has been estimated to be 3.5. The three installed HPS provide a total heating capacity of 40 MW. HPS-1 was started to be built in June 2006. Both, the end-users and the boreholes are within a radius of 500 m of the HPS. The system provides heat to a hospital, a school, a vocational school, a kindergarten, administrative offices, and industrial sites. An advantage of the implementation of the project is a decrease in CO2 emission. A reduction of 16,700 tons of CO2 emission per year from fossil fuels has been forecasted (Joint Implementation Project 2006). Spain In the city of Asturias, Spain, a geothermal system has been successfully implemented for two buildings on the campus ´ lvarez Buylla of the University of Oviedo and for the new A hospital. It has been estimated that the heat source, which is a nearby abandoned coal mine, contains about 5.8 million m3 of water. The temperature of the flooding water ranges from 17 to 23 C (Jardo´n et al. 2013). A research center and a residence of the University of Oviedo currently use the mine water for heating and cooling. The shaft, which is used to extract the mine water, is close to the buildings, some 250 m away. The mine water is used to warm clean water circulating in a polypropylene closed-loop (Garzo´n 2011). Afterwards, the clean water enters the heat pumps at 14 C, where it is cooled down to 7 C (Jardo´n et al. 2013). ´ lvarez Buylla hospital, an For the system at the A open-loop configuration has been installed to capture the temperature of the mine water. The fluid is pumped to the surface at a rate of 400 m3/h. In heating mode, the mine water decreases from a temperature of 23–13.9 C during its passage through the heat exchanger before it is discarded. Using the heat exchanger, clean water, which has to be transported to the end user about 2 km away, was warmed up from 12–19 C. The pipes made of propylene are buried to reduce thermal losses to 0.15 C. A heating system with heat pumps, chillers and boilers has been designed for the hospital. At the heating station, the clean water releases the heat to water-to-water heat pumps, which provide temperatures of 46 C (Garzo´n 2011). An estimation was conducted for the university buildings showing a total annual energy saving of 73 % (1,112,050 kWh/year), a reduction of CO2 emissions of up to 39 % per year, and monetary savings of 15 % for the student residence and up to 20 % for the research facility (Garzo´n 2011).
123
Environ Earth Sci
United Kingdom Shettleston, Glasgow, Scotland The Shettleston Colliery was producing coal from 1872 until its abandonment in 1923. Since 1999, a geothermal project for space heating using mine water from abandoned coal mines is working. The mine water with a temperature of 12 C is extracted at a depth of 100 m using a well specifically drilled for this purpose. Heat pumps use the mine water to increase the temperature of water that is collected in tanks to store the heat. A total of 16 houses are supplied with heat from this system (John Gilbert Architects 2014). Thermostats are used to switch from space heating, once the desired temperatures have been reached in the living spaces, to water heating. Thus, the energy conservation by reducing energy losses in rooms ensures more free hot water (Architecture and Design Scotland 2013). Lumphinnans, Fife, Scotland The same concept as used in Shettleston has been implemented in Lumphinnans. A 170 m deep extraction well delivers mine water at a temperature of 14.5 C. Using the low enthalpy of the mine water, the heat pump provides clean water on the surface with a temperature between 45 and 53 C for space heating purposes. Meanwhile, the mine water temperature is reduced to 3 C and returned to the abandoned mine via a re-injection well, which is above a permeable layer. As the heat pump only works for 18 h each day, the clean water is stored before its distribution to the connected houses. Annual savings of 80 % on heating costs have been estimated (Watzlaf and Ackman 2006).
The mine water is extracted through a PVC pipe using a submersible pump with a capacity of 20.5 m3/h. At surface, a flat plate heat exchanger has been installed. The temperature of the mine water is reduced from 16.1–11.9 C. A heat pump uses the heat of the warmed water to increase the temperature of the building’s heating system from 32–50 C. During summer, the system can be reversed to provide air-conditioning (Schubert and McDaniel 1982). Park Hills, Missouri Mine water has being used for heating and air-conditioning of the municipal building in Park Hills since 1995. The source is the flood water from the abandoned mines located 10 to 133 m underneath the town, which have about 265 million m3 of water at a constant temperature of 13.9 C (Geothermal Heat Pump Consortium 1997). An open-loop configuration has been installed to extract mine water from a 122 m deep well by means of a submersible pump having a maximum capacity of 17 m3/h. At the surface, a plate and frame heat exchanger transfers heat from the mine water to clean water, which circulates in a closed-loop. The mine water is then returned via a second 122 m deep well. Both return and extraction pipes have a diameter of about 6 cm. The closed-loop transports the heat to nine water-to-air heat pumps, which are located directly in the rooms. The installed capacity of each heat pump ranges from 5.3 to 17.6 kW generating a combined capacity of 112.5 kW. As the largest rooms have a precondition for the supply of outside air, two air-to-air heat pumps were additionally installed. The temperature delivered during winter is up to 22 C, while in summer, the temperature for air-conditioning is 24 C (Geothermal Heat Pump Consortium 1997).
United States of America Scranton, Pennsylvania Kingston, Pennsylvania Way back in 1981, a geothermal heating and cooling system based on heat pumps sourced by mine water was implemented in Kingston, Pennsylvania, for a 1,580 m2 recreation center. With the exception of some reparations, this system has been working without complications to this day (Korb 2012). The heat source is the flood water from an abandoned coal mine, whose shallowest point can be found at a depth of 58 m (Schubert and McDaniel 1982). An open-loop configuration has been implemented, with the mine water being returned to avoid precipitation produced by the iron in the water and the oxygen being released due to pressure change in the mine water (Korb 2012). The extraction well is located 76 m away from the building, while the reinjection well is situated 27 m from the extraction well.
123
In 2010 in Scranton, a mine water geothermal system was installed to cool the Center for Architectural Studies of the Marywood University. The project’s objective was the implementation of a cost-effective system that can be used for both building and process cooling. The US Department of Energy financed the geothermal project through the Pennsylvania Department of Environmental Protection. The water level in the Marvine Colliery is settled by the dewatering tunnel known as the Old Forge Borehole. Two wells were drilled and tested to determine the flow rate and the water chemistry. Based on the results, an openloop system has been installed. Mine water is extracted with a submersible pump from a 122 m deep well. At surface, a heat exchanger increases the temperature of the mine water from 13.9 to 16.1 C and decreases the temperature of clean water from 15.6 to 12.8 C. The mine
Environ Earth Sci Table 1 Reservoir properties of the implemented systems
Flow rate (m3/h)
Country
Projects location
Canada
Quebec
Germany
Alsdorf
Germany
Bad Schlema
Germany
Ehrenfriedersdorf
Germany
Freiberg (Castle)
Germany
Freiberg (University)
Germany
Marienberg
124–2000
12.4
Germany
Wettelrode
90–150
12–13
Netherlands
Heerlen
Norway
Folldal
Russia Spain
Rostov Asturias (University and hospital)
UK
Shettleston
UK
Lumphinnans
USA
Kingston
USA
Park Hills
USA
Scranton
water is returned to the abandoned mine while the clean water flows into a passive chilled beam in a closed-loop system. A monitoring system measures the mine water temperature (produced and returned), together with the energy transferred. Sample ports were incorporated for water sampling so that the chemical composition of the mine water can be monitored (Korb 2012).
Comparative study In this section the world wide implemented systems, presented in the previous section are compared. An analysis of the reservoir and end user parameters is performed to better understand the implementation requirements of such systems. Table 1 compares important reservoir parameters for the implemented geothermal systems. In some cases the information available to estimate the reservoir volume is the total flooded volume of water and for others the water flow rate. The variation of both of these parameters highlights that the implementation of the system is possible, irrespective of the size of the reservoir. In addition, the water temperature in the reservoir is presented in the table showing that different systems work with a wide range of the mine water temperatures, ranging from as low as 6 C in case of Folldal, Norway to a maximum of 32 C in Heerlen, Netherlands. The reservoir capacity is based on these parameters and, thus, the heating requirement it can fulfill. The diverse end users for the presented systems are listed in Table 2. The size and type of these end users differ from each
Available volume (million m3)
Temperature (C)
8 15–26 1.75 10.8
495
10.2
2.5
10–11
27–32 6
5.8
12–13 17–23 13.9
265
13.9 16.1
other. Moreover, as they are also located in different environmental conditions, such as different water temperature, they have different heating and cooling requirements, so the system needs to be designed specifically for each location. In all the cases, the source and costumer are closely linked together, and a heat pump system needs to be selected in such a way that it can supply the end user requirements while keeping the system sustainable so that it does not change the source parameters to an irreversible point. Most of the systems presented here use floor heating as a method of heat distribution, which is the most effective way especially for lowenthalpy sources. In some cases water-to-air heat pumps are used to provide the required air conditioning. Mine water geothermal systems include various components such as heat exchanger, heat pump, piping, valves and buffers. Depending on the reservoir properties and the end user location, the position and type of these components may vary. The selection of the capacity and model of the heat exchanger and heat pumps strongly depends on the heating requirements and the capacity of the heat source. By relating the reservoir’s properties with the end-user’s heating and cooling requirements, the most suitable design can be developed, and the number, type, and size of heat pumps can be chosen accordingly. In Freiberg, for example, a dam was constructed to accumulate the required volume of water based on a study of the rock properties. In Folldal, a closed-loop was considered to be more appropriate due to the highly contaminated mine water. Table 3 presents the available information on the heat pumps for the implemented projects. The open-loop system can be complemented by a heat exchanger (HE), to prevent
123
Environ Earth Sci Table 2 End-users of the implemented systems
Projects location
End-user
Heating area (m2)
Quebec
Appartment building
6039
Alsdorf
Office buildings
Bad Schlema
School
Ehrenfridersdorf (Museum)
Mining and mineralogical museum
Freiberg (Castle)
Castle and mineralogical museum
Freiberg (University)
University building
Marienberg
Two commercial installations, tennis hall and adventure pool
Wettelrode
Mining museum
Heerlen
Offices buildings and university
125,000
Folldal
Wormshall (Cavern)
1599 m3a
Rostov Asturias (University)
Different building of 3 areas Research center and student residence
57,393b
Asturias (Hospital)
Hospital
28,000
Shettleston
Building (16 houses)
Lumphinnans
Houses (18)
Kingston
Recreation venter
1580
Park Hills
Municipal building
753
Scranton
University building
a
For this project, only the volume was stated
b
Area corresponding to the research center
corrosion or scaling damage that the mine water could cause if put in direct contact with the heat pumps. The HE can be installed either in the mine, or on the surface. In Marienberg, the HE was installed in the gallery, as it was determined that the environmental conditions in the abandoned mine were unlikely to damage the equipment. For the project in Freiberg, which supplies heat to the Freudenstein castle, the equipment was installed on the surface, although subsurface access to the mine was available. To try and capture the efficiency of the various geothermal systems, the COP, mine water temperature and delivered temperature of selected projects have been plotted in Fig. 1. As expected from the COP definition, the graph shows a trend of increasing COP with increasing mine water temperature. The majority of the cases are lowtemperature heat distribution systems, as they better suit heat pumps. Thus, it can also be observed that the delivered temperatures vary between 40 and 55 C, with Rostov being an outlier. This is because, in Rostov, at each heat station, a gas-engine cogeneration has been installed to boost the temperature up to 95 C. The extraction depth of the mine water varies across the projects, with the greatest depths encountered where dedicated wells were drilled, e.g., the 700 m wells in Heerlen. An important component of a heating system is the pumping module; thus, the extraction depth must be appropriately selected considering both the inlet mine water temperature and financial aspects (drilling costs,
123
5685
400
shaft remediation, pumping system). In Table 3, it can be observed that the depth of the HE does not exceed 163 m. The extent of the heated area also varies considerably across the projects, from single buildings to urban areas of over 125,000 m2. In most of the case studies, additional equipment was used either to boost or to store the heat (e.g., chiller and boilers in the hospital in Asturias). The 400 m2 mining museum in Wettelrode is an exception as such additional equipment was not implemented. Design of geothermal mine water system for the Harz region Several abandoned mines are located in the Upper Harz region. A screening process was carried out and highlighted the Kaiser Wilhelm II shaft in Clausthal-Zellerfeld as one of the locations with high potential for the implementation of the geothermal mine water concept. Parameter determination To be able to design a heat pump configuration at the selected location, further analysis of the source and possible customers is required. The approach to assess the heat capacity of the system is presented in Fig. 2. Given the lack of information of the mine water in the region, the design parameters have been assumed based on the case studies presented.
Environ Earth Sci Table 3 Description of the heat pump systems for the implemented projects Project location
HP location
HP type
Quebec
In each apartment
Number of HP
Heating capacity (kW)
Delivered temperature (C)
Loop configuration
HE depth (m)
3.6–5.3
Open-loop
0
138
Open-loop
110
Alsdorf* Bad Schlema
0
Ehrenfridersdorf (Museum) Freiberg (Castle)
w/w Building behind castle
Freiberg (University)
w/w
1
130
42 and 19
Open-loop
0
w/w
2
260
55
Open-loop
216
w/w w/w
1
310 47
50
Open-loop Open-loop
105 163
45
Open-loop
0
1
18
22
Closed-loop
NA
Marienberg Wettelrode
In building In building
Heerlen
In buildings
w/w
Folldal
Underground, at the Wormshall
w/a
Rostov
Pump station
w/w
9 (3 per station)
40,000
95
Open-loop
0
Asturias (University)
In buildings
w/w
2
1000
50 and 7
Open-loop
0
Asturias (Hospital)
In building
w/w
4
3600
46 and 7
Shettleston
w/w
Lumphinnans
w/w
Kingston
w/w
1
w/a
9
Park Hills
In each room
Scranton
Open-loop
0
Open-loop
NA
45–53 112.5
w/a
50
Open-loop
0
22 and 24
Open-loop
0
12.8
Open-loop
0
w/w water-to-water heat pumps, w/a water-to-air heat pumps, NA no heat exchanger * Project under development
Fig. 1 Effect of mine water temperature on delivered temperature and COP for selected projects
COP 100
6
Delivered temperature Mine water temperature
5 4
60 3
COP
Temperature [°C]
80
40 2 20
1
0
0 Freiberg (Castle)
In the Upper Harz, most of the shafts were abandoned in the 1930s; therefore, it is assumed that during this time the solids might have precipitated and would not be suspended in the mine water. In addition, in most of the case studies, the mine water was used in open-loops implementing monitoring systems, maintenance programs, and accessories such as filters, degassing tanks, and pH controllers to avoid the equipment from being damaged; for instance, in Freiberg and Heerlen. For these reasons, the mine water
Rostov
Asturias (University)
Freiberg (University)
Asturias (Hospital)
Heerlen
quality is assumed to be good enough to implement an open-loop system also for the Kaiser Wilhelm II shaft. To establish the more likely values of the source parameters, such as mine water temperature and extraction flow rate, the influence of outliers was removed with statistical procedure. The standard deviation of the values reported in the case studies was calculated to fix limit values (mean plus and minus one standard deviation). Then the average was assessed with the values lying inside the
123
Environ Earth Sci
limits. This procedure was followed to determine the mine water temperature and the extraction flow rate, 13 C and 20 m3/h, respectively. The change in temperature of the mine water induced by the heat exchanger was assumed to be 5 C, which was common for the studied cases. End-user selection The selected shaft is located near different types and sizes of buildings that can be considered as potential end-users of the system. In Fig. 3, a map showing the location of the shaft (red point) and potential end-users at different distances is presented. Most of the buildings within a radius of 150 m belong to the Clausthal University of Technology. The university utilizes an underground piping system that could also be considered to supply heat to all the connected buildings by means of the geothermal system. Among the buildings connected to this network is the computer center (marked in orange), which could be a potential end-user for heat pump air-conditioning. However, to reduce heat loss by transportation via pipes, the workshop of the mining institute has been selected (marked in yellow) to determine the technical feasibility of the concept in the area. System description An open-loop configuration has been selected, assuming that the chemical composition of the mine water would not damage the equipment. A control system is incorporated to detect possible damages, and a maintenance program is followed to avoid future problems. Assumptions and considerations for the design of the components: • •
Pumps The selection of a pump and the number depends on the required power to pump the fluid. Pipes The friction losses and heat loss depend on the properties of the piping material. The assessment of the heat loss is useful to determine if the use of insulation is required or not and to calculate the temperature at which the fluid will arrive to the heat pump. The friction losses are considered in the pump design.
Determine heat recovery from mine water
Determine building heat requirement
Heang capacity of the system
Fig. 2 Workflow to assess heating capacity of the system
123
• •
Heat exchanger The heat transfer is assumed to be 5 C in an ideal process. Heat pump The selection of the heat pump is based on the heating requirements of the building and the reservoir’s capacity (maximum heat load that can be extracted from the reservoir without depletion).
Figure 4 represents a schematic of the proposed system to harness mine water via an open-loop configuration. To determine the dimension of the heat pump, the technical data provided by the manufacturer have to be used. Therefore, six heat pumps from the Viessmann Company (Viessmann 2007) have been implemented for this project. The heating requirement of the potential end-user was determined using the following simplified equation: Qreq ¼ V Tdesign Ta Kbuilding With V being the building volume of 3,345.18 m3; Tdesign being the designed room temperature of 25 C; Ta being the ambient air temperature 0 C (based on the average lowest and average highest during winter season); Kbuilding describing the insulation level of the building being 1 according to moderate insulation. For the calculated heating requirement of the selected end-user being 97 kWt, the installation requires 7 heat pumps in total, an input flow rate of 11.3 m3/h, and an electrical consumption of 26 kWe. This gives an overall COP for the system equal to 3.7. On the other hand, the mine water has to supply 71 kWt to the system.
Discussions and conclusions The water flooding the underground mines is a sustainable resource that can be harnessed via heat pumps to heat and cool spaces. Heat pumps can be implemented using closedloop or open-loop systems. The selection and design, however, are based on factors of each location, such as the temperature and quality of the mine water. In this study several geothermal case studies using mine water were analyzed. The temperature of the mine water used as heating source varies in a wide range from 6 to 28 C. The extraction of the mine water can be as shallow as 50 m or as deep as 700 m. The heat load supplied by the system can cover requirements of individual buildings, such as museums, up to complete districts, such as industrial parks or University Campuses. The versatility and efficiency of these geothermal systems has been demonstrated through several case studies and indicates that the geothermal mine water concept can be implemented worldwide independent of reservoir size and resource type. Thus, this concept provides a large
Environ Earth Sci Fig. 3 Potential end-users for the geothermal system at different radii. (Google Maps)
Fig. 4 Schematic of the proposed system to harness mine water via an open-loop configuration
potential for heating and cooling using a renewable energy source having a low CO2 footprint and providing heat or air-conditioning independent of weather or climate aspects. Therefore, it is especially interesting for countries that have a large quantity of abandoned mines, such as Germany or China, to switch from high-emission conventional fossil fuels to low-emission geothermal energy. Another aspect that results from the analysis of the case studies is the system configuration. Most of the implemented systems opted for the open-loop configuration. This choice is based on site parameters and should involve a risk assessment. In the case of open-loop systems, the possible
variations are based on drilling wells or using shafts. In the latter, the location of the heat exchanger can be at surface or in a gallery of the shaft. In addition, fundamental enquiries need to be carried out into the legal requirements for re-opening and using a shaft. If such operations are prohibited, it has to be determined if boreholes can be drilled instead to extract and re-inject the mine water. Hydraulic, chemical and petrophysical investigations need to be performed to design a sustainable and economical system. Based on the test results, different configurations can be compared based not only on the technical aspects, but also economic considerations and a risk assessment. Hence, the economic advantage of the designed geothermal system for the Upper Harz compared to the existing heating system can also be determined. In the Upper Harz, abandoned mines offer a great potential as geothermal reservoirs. The mines, with numerous underground tunnels and shafts, which are mostly interconnected and thus result in a large geothermal reservoir, lie beneath the towns and therefore there are numerous buildings available as potential end-users. However, tests must be performed to gain accurate information of the reservoirs situation to design a sustainable and efficient geothermal system. The presented design procedure is based on statistically determined assumptions for the parameters required to assess the implementation of the heat pumps. The parameters for the selected mine water source have been fixed in this manner. The heating requirements of the end-user considered were obtained from the consumption data for previous years. A mathematical formula was used to determine the heat requirements for the customers for whom this information was not available. An
123
Environ Earth Sci
assumption was made in this case for the insulation factor, which would depend among others on the construction of the building. Comparisons were made between the selected end-user (mining institute of TU Clausthal) with the case studies involving projects of similar dimensions, such as those installed for the hospital in Asturias and the university buildings in Freiberg and in Asturias. However, when considering the distance from the extraction well or shaft to the building, from these three projects, the hospital case should be discarded as the 2 km distance is much larger than for the mining institute of TU Clausthal. In Clausthal-Zellerfeld, the available volume of the mine water is large enough so that a dam, such as it is the case in Freiberg, would not be required. On the other hand, the surface configuration, including the measurement equipment, is of great interest. An additional aspect to be taken into account is that none of the buildings of TU Clausthal, including the selected end-user, has low-temperature heating systems. Thus, one should consider providing temperatures as high as the ones currently being used to the heating system or to change the radiators to floor heating. A major disadvantage in the Upper Harz region is the lack of information about the mine water properties such as temperature and quality. In addition, the mine water level of the abandoned mines in the study region is much deeper than other implemented projects, resulting in significantly increased pumping expenditures. The deepest extraction well depth is in Heerlen (700 m depth), which is supplying heat to an area of 125,000 m2; however, the mine water temperature is also extraordinary high at 28 C, which is much hotter than the abandoned mines in the Upper Harz region. To upscale the heating requirements from the selected single end-user (mining institute) to the whole campus of the TU Clausthal, Heerlen and Rostov should be considered as similar case studies due to their large heating area. In Rostov, several buildings in the proximity of the extraction well are benefiting from the implemented geothermal system. Moreover, the system is delivering temperatures as high as the ones currently obtained in the heating plant of TU Clausthal. In case of designing a similar installation, which is based on gas-engine cogeneration, the existing underground transportation system and radiators in the buildings could be used. Another possibility would be a scenario similar to Heerlen, that of installing heat pumps in each single building to cover the specific heating requirements. Warm water circulation in the existing underground transportation system could be used for the heat pump system, which at the same time could be heated at the heating plant via heat pumps sourced, indirectly, by mine water. However, this approach is likely to
123
be more expensive, as the entire existing heating system in each building would have to be exchanged. Taking into account this scenario, the closest shaft to the heating plant can be found at about 700 m distance. This shaft could be used to access the mine water or a well could be drilled to reach a gallery. For both cases, it would be required to install a HE, to capture the heat of the mine water, in close vicinity to the well and transport the heat to the heating plant by means of clean water.
References Architecture and Design Scotland (2013) Glenalmond Street Housing Shettleston, Glasgow-Case Banks D, Skarphagen H, Wiltshire R, Jessop C (2004) Heat pumps as a tool for energy recovery from mining wastes. Geol Soc 236:499–513 Bu¨ttner R, Kupka M, Werner S (2010) Wa¨rmepumpentechnik bei Einsatz von Grubenwasser am Beispiel ‘‘Schloss Freudenstein’’. Thesis at Institut fu¨r Wa¨rmetechnik und Thermodynamik, TU Bergakademie Freiberg Baukonzept-Dresden (2014) Project: Geothermische Grubenwassernutzung in Freiberg. Retrieved from www.bauconzept-dresden. de/portfolio/geothermische-grubenwassernutzung-in-freiberg/. Last accessed Apr 2014 Energeticon (2013) Grubenwasserenergie fu¨r das ENERGETICON (GrEEn). Retrieved from http://www.energeticon.de/index.php/ ort/die-aussenanlagen/das-green-projekt. Last accessed Sep 2013 Garzo´n B (2011) Grupo HUNOSA: Servicios Energe´ticos. In: Ca´tedra Hunosa. Presentation retrieved from http://www.unioviedo.es/ catedrahunosa/archivos/. Last accessed Mar 2014 Geothermal Heat Pump Consortium (1997) Municipal Building Park Hills, Missouri. Geoexchange. Retrieved from http://www. geoexchange.org/pdf/cs-064.pdf. Last accessed Sep 2013 Grab Th, Storch Th, Kleutges J, Gro¨tzsch S, Grob U (2010) Geothermieanlage zur Grubenwassernutzung fu¨r Heizung (200–670 kW) und Ku¨hlung (155–500 kW). Der Geothermiekongress Karlsruhe Hartung E (2014) Personal communication a visit in Wettelrode. ´ lvarez R, Cienfuegos P, Loredo J (2013) Mine Jardo´n S, Ordo´n˜ez A, A water for energy and water supply in the Central Basin of Asturias (Spain). Mine Water Environ 32(2):139–151 Jessop AM, MacDonald JK, Spence H (1995) Clean energy from abandoned mines at Springhill, Nova Scotia. Energy Sour 17:93–106 John Gilbert Architects (2014) Glenalmond Street, Shettleston. Retrieved from http://www.johngilbert.co.uk/files/JGA_Glenal mondSt_v2.pdf. Last accessed Apr 2014 Joint Implementation Project (2006) Joint Implementation Project Design Documents Form-Version 01 Retrieved from http://www. netinform.net/KE/files/pdf/Novoshakhtinsk_PDD_ver01_Det.pdf. Last accessed Mar 2014 Just R (2013) Friedrich-Schiller-Schule, Bad Schlema. Bundesamt fu¨r Bauwesen und Raumordnung. Retrieved from http://www. bbr.bund.de/nn_486326/StBauF/DE/Investitionspakt/Praxis/Mass nahmen/BadSchlema/badschlema__inhalt.html. Last accessed Sep 2013 Koch L and Hoffmann M (2013) Geothermal Wettelrode -Presentation of mining session at Doctoral School Energy and Geotechnology. Retrieved from http://de.scribd.com/doc/121983233/ Geothermal-Wettelrode. Last accessed Oct 2014
Environ Earth Sci Korb M C (2012) Minepool Geothermal in Pennsylvania. 2012 Pennsylvania AML Conference: New Frontiers in Reclamation. Retrieved from https://www.portal.state.pa.us/portal/server.pt/ gateway/PTARGS_0_2_1391321_0_0_18/Mine_Pool_Geother mal_in_PA-2012.pdf. Last accessed Feb 2014 Kranz K and Dillenardt J (2010) Mine water utilization for geothermal purpose in Freiberg, Germany: determination of hydrological and thermophysical rock parameters. Mine Water Environ. Springer. 9(1): 68–76 Krassmann T (2014) Geothermische Energieausehemaligen Bergbauanlagen. Retrieved from www.untertage.com/publikationen/ 22-interessantes/5-geothermische-energie-aus-ehemaligen-berg bauanlagen.html. Last accessed Apr 2014 ˚ (2014) Personal communication via e-mail Kristoffersen A Matthes R and Schreyer J (2007) Remediation of the old WismutShaft 302 in Marienberg and installation of a Technical Plant for Geothermic mine water use (Ore Mountains, Germany). IMWA Symposium 2007: Water in Mining Environment. Retrieved from https://imwa.info/docs/imwa_2007/IMWA_2007_Matthes. pdf. Last accessed Sep 2013 Ließmann W (2010) Historischer Bergbau im Harz. Springer, Berlin Minewater Good Practice Guide (2013) Mine water as a Renewable Energy Resource: An information guide based on the Minewater Project and the experiences at pilot locations in Midlothian and Heerlen. Retrieved from http://skrconline.net/content/images/ stories/documents/mine_water_renewable_energy_guide.pdf. Last accessed Feb 2013 Op ‘t Veld P, Malolepszy Z, Bojadgieva K, Vetrsek J (2010) Geothermal development of low temperature resources in European coal mining fields, The EC REMINING—Lowex project. Proceedings World Geothermal Congress, pp 1–8
Raymond J, Therrien R, and Hassani F (2008) Overview of Geothermal Energy Resources in Que´bec (Canada) Mining Environments. International Mine Water Association. Retrieved from http://www.imwa.info/docs/imwa_2008/IMWA2008_039_ Raymond.pdf. Last accessed Jan 2014 Schubert JP and McDaniel M J (1982) Using Mine Waters for Heating and Cooling. Proceedings, 1st International Mine Water Congress. Pp 63–82. Budapest, Hungary. Retrieved from https:// imwa.info/docs/imwa_1982/IMWA1982_Schubert_063.pdf. Last accessed Feb 2014 Stadtwerke Marienberg GmbH (2013) Geothermie. Retrived from http://www.stadtwerke-marienberg.de/geothermie/ausgangssitua tion.html. Last accessed Nov 2013 Verhoeven R (2013) Personal communication via e-mail and a visit in Heerlen Verhoeven R (2015) Personal communication via e-mail Verhoeven R, Willems E, Harcoue¨t-Menou V, De Boever E, Hiddes L, Op’t Veld P, and Demaollin E (2013) The EC-REMINING— Lowex project in Heerlen the Netherlands: transformation from a geothermal mine water pilot project into a full scale hybrid sustainable energy infrastructure Mine Water 2.0. In: 8th International Renewable Energy Storage Conference and Exhibition 2013 Viessmann (2007) VITOCAL 300/350 Datasheet. Retrieved fom http://www.viessmann.co.uk/content/dam/internet_uk/attachments/ datasheets_technical/heat_pumps/vitocal_300_350_datasheet.pdf. Last accessed June 2014 Watzlaf G, Ackman T (2006) Underground mine water for heating and cooling using geothermal heat pump systems. Mine Water Environ 25:1–14
123