METHOD OF EXTRACTING ENERGY FROM A CAVITY CREATED BY MINING OPERATIONS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority on U.S. Provisional Application No. 61/601 ,733, now pending, filed on February 22, 2012, which is herein incorporated by reference.

FIELD OF THE INVENTION

[0002] The present relates to a method for the extraction of renewable energy from minefilled excavations of mines for the purposes of heating, cooling, power generation, mine ventilation and other applications.

BACKGROUND ART

[0003] Mining is known as one the most energy-consuming industries. The pending depletion of fossil fuels and their associated environmental concerns has required the mining industry to strive for new sources of renewable energy source. Considering the fact that deep excavations become available in mining techniques, geothermal energy will be one of the best choices of renewable energy for the mining industry. However, one of the main problems in extraction of geothermal energy from the earth by means of a closed-loop geothermal cycle is the cost of drilling and excavation. These excavation and drilling costs are necessary for installation of the ground-coupled heat exchanger tubes. Another problem in the application of closed-loop geothermal cycles is the low ground temperature which increases electricity consumption of the ground-coupled heat pump and lowers the feasibility of using the geothermal system. The present application solves both issues by implementing a novel technique for extraction of renewable geothermal energy from mine excavations. SUMMARY

[0004] In accordance with an aspect of the invention, there is provided a method for extracting energy from at least one cavity of a rock mass created by mining operations, the method comprising: placing a hydraulically connected network of geothermai pipes into the at least one cavity produced in the mining operations; covering the network of geothermai pipes with a minefill material such that the cavity is filled and the minefill material is in direct contact with the network of pipes and the rock mass; circulating a thermal fluid through the network of geothermai pipes, wherein the minefill material transfers energy between the rock mass surrounding the at least one cavity and the thermal fluid within the network of geothermai pipes; and extracting energy from the thermal fluid.

[0005] In accordance with another aspect of the invention, there is provided an energy-extracting mine ventilation system comprising: a ventilation unit for conditioning the intake air of a mine; a network of pipes installed in at least one cavity of the mine, the network of pipes comprising a geothermai fluid circulating therethrough wherein the network is in contact with a minefill material within the cavity and a rock mass; wherein the minefill material transfers energy between the rock mass surrounding the at least one cavity and the thermal fluid, the minefill; and a heat exchanger unit in fluid communication with the network of pipes and extracting the energy from the thermal fluid, the heat exchanger unit being configured to transfer extracted energy directly or indirectly to the ventilation unit in order to condition the intake air of the mine.

[0006] Also in accordance with the present invention, there is provided a method for extracting energy from at least one cavity of a rock mass created by mining operations, the method comprising:

[0007] - placing a hydraulically connected network of geothermai pipes into the at least one cavity produced in the mining operations;

[0008] - covering the network of geothermai pipes with a minefill material such that the cavity is filled and the minefill material is in direct contact with the network of pipes and the rock mass;

[00093 - circulating a thermal fluid through the network of geothermal pipes;

[0010] - wherein the minefill material transfers energy between the rock mass of the at least one cavity and the thermal fluid within the network of geothermal pipes; and

[0011] - extracting energy from the thermal fluid.

[0012] Further in accordance with the present invention, there is provided an energy extracting mine ventilation system comprising:

[0013] - a ventilation unit for conditioning an intake air of a mine;

[0014] - a network of pipes installed in at least one cavity of the mine, the network of pipes comprising a geothermal fluid circulating therethrough wherein the network is in contact with a minefill material within the cavity and a rock mass;

[0015] - wherein the minefill material transfers energy between the rock mass of the at least one cavity and the thermal fluid; and

[0016] - a heat exchanger unit in fluid communication with the network of pipes and extracting the energy from the thermal fluid, the heat exchanger unit being configured to transfer extracted energy directly or indirectly to the ventilation unit in order to condition the intake air of the mine.

[0017] Still further in accordance with the present invention, there is provided a method for extracting energy from at least one cavity of a rock mass, the method comprising: [0018] - placing a hydraulically connected network of geothermal pipes into the at least one cavity;

[0019] - covering at least part of the network of geothermal pipes with a minefill material such that the cavity is at least partly filled;

[0020] - circulating a thermal fluid through the network of geothermal pipes;

[0021] - wherein the minefill material transfers energy between the rock mass of the at least one cavity and the thermal fluid within the network of geothermal pipes; and

[0022] - extracting energy from the thermal fluid.

[0023] Still further in accordance with the present invention, there is provided an energy extracting mine ventilation system comprising:

[0024] - a ventilation unit for conditioning an intake air of a mine;

[0025] - a network of pipes adapted to be installed in at least one cavity of the mine, the network of pipes comprising a geothermal fluid circulating therethrough;

[0026] - minefill material adapted to be positioned in the cavity for transferring energy between a rock mass of the at least one cavity and the thermal fluid; and

[0027] - a heat exchanger unit adapted to extract energy from the thermal fluid, the heat exchanger unit being configured to transfer extracted energy directly or indirectly to the ventilation unit in order to condition the intake air of the mine. [0028] Still further in accordance with the present invention, there is provided a method for extracting energy from at least one cavity of a rock mass, the method comprising:

[0029] - providing a heat transfer system into the at least one cavity;

[0030] - covering at least part of the heat transfer system with a minefill material such that the cavity is at least partly filled;

[0031] - wherein the minefill material transfers energy between the rock mass of the at least one cavity and the heat transfer system; and

[0032] - extracting energy from the heat transfer system.

[0033] Still further in accordance with the present invention, there is provided an energy extracting mine ventilation system comprising:

[0034] - a ventilation unit for conditioning an intake air of a mine;

[0035] - a heat transfer system adapted to be installed in at least one cavity of the mine;

[0036] - minefill material adapted to be positioned in the cavity for transferring energy between a rock mass of the at least one cavity and the heat transfer system; and

[0037] - a heat exchanger unit adapted to extract energy from the heat transfer system, the heat exchanger unit being configured to transfer extracted energy directly or indirectly to the ventilation unit in order to condition the intake air of the mine.

[0038] Still further in accordance with the present invention, there is provided a system for extracting energy from a mine, comprising: [0039] - a heat transfer system adapted to be installed in at least one cavity of the mine;

[0040J - minefill material adapted to be positioned in the cavity for transferring energy between a rock mass of the at least one cavity and the heat transfer system; and

[0041] - a heat exchanger unit adapted to extract energy from the heat transfer system.

[0042] Still further in accordance with the present invention, there is provided a system for extracting energy from a mine, comprising:

[0043] - a heat transfer system adapted to be installed in at least one cavity of the mine;

[0044] - minefill material adapted to be positioned in the cavity for transferring energy between a rock mass of the at least one cavity and the heat transfer system; and

[0045] - an energy-extracting device adapted to extract energy from the heat transfer system.

[0046] Still further in accordance with the present invention, there is provided a system for extracting energy from a mine in combination with a cavity defined in the mine, the system comprising:

[0047] - a heat transfer system installed in the cavity of the mine;

[0048] - minefill material positioned in the cavity for transferring energy between a rock mass of the cavity and the heat transfer system; and

[0049] - an energy-extracting device adapted to extract energy from the heat transfer system. [0050] The term "Geothermal pipe" when used herein is understood to refer to a tube or pipe network installed in mining excavations or any other cavity created in mining operations. These pipes can be interconnected in series forming a branch. Each branch is connected to a main geothermal fluid pipe which brings the inlet fluid and another main tube which takes the outlet fluid out. Multiple geothermal pipe systems may be employed in parallel. The geometric arrangement and sizing of the geothermal pipe system depend on ground temperature, geometry of installation site(s), heating/cooling load demands, operational strategies of the mine and the thermo-physical properties of the minefill material and rock mass.

[0051] The term "minefill material" when used herein is understood to refer to at least one of soil (with or without water, with or without binder material (e.g. cement)); tailing material (with or without water, with or without binder material); minefill material which is a blend of soil or tailings, water and binder; any other material which could be formed by adding additive(s) (like pozzolanic material such as cement, grinded slag or color) to one; and a group of the above mentioned materials which is placed in mine cavities in order to secure the mining operation and prevent the occurrence of ground failure in mining operation.

[0052] The terms "Geothermal fluid" or "thermal fluid" are understood to be synonyms and when used herein are understood to refer to a fluid which flows in the geothermal pipe network. The thermal fluid can be water, brine or any other liquid capable of withstanding the thermal and chemical conditions inside the geothermal pipe.

[0053] The term "rock mass" is the large thermal reservoir of rock into which the mine or mining operation is found, and from which the energy is ultimately extracted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Reference will now be made to the accompanying drawings, showing by way of illustration an illustrative embodiment of the present invention, and in which:

[0055] Fig.1 is a schematic view of a system for the extraction of renewable energy from mine-filled excavations in accordance with one embodiment.

DESCRIPTION OF VARIOUS EMBODIMENTS

[0056] The present application reduces the aforesaid difficulties and disadvantages of closed loop geothermal cycles. The present application discloses a mine ventilation system and method for the extraction of geothermal energy from mine excavations for the purposes of heating, cooling and power generation. This idea is applicable in mining operations that employ minefill material to fill the mine cavities. By coupling the proposed system to the mine ventilation system, an enormous amount of energy will be saved, ventilation costs of mines will be cut considerably and the carbon footprint of the mines will be improved. This system and method are applicable in mining operations that employ the minefilling technique in which excavated mine stopes are filled with minefill material.

[0057] The mine ventilation system and method in accordance with the present disclosure comprises the installation of a network of heat exchange tubes, called geothermal pipes, in empty mine excavations, called stopes, followed by minefilling of the excavated space. The geothermal fluid is circulated in the geothermal pipe network, allowing for the heat transfer to take place between the minefill and the geothermal fluid. The minefill material serves as the medium that transfers heat between the rock mass and the geothermal pipes. If the inlet temperature of the geothermal fluid is less than the temperature of the rock mass, then heat or high temperature energy (higher than 60°C) is extracted and if the inlet temperature is higher, then cold or low temperature energy (lower than 60°C) is extracted. [0058] The mine ventilation system benefits from the renewable and clean source of heat (or cold) energy provided by the above system in different ways. One application is to use the heat (or cold) energy content of the fluid which is circulated in the pipe network to preheat the intake air of the mine. If the provided heat energy content or its temperature is enough for ventilation purposes then there is no need for further intake air ventilation. If not, other conventional heating or refrigeration systems may assist the ventilation system in conditioning the air to the required temperature. For example, in some Canadian mines, millions of dollars of natural gas are burned to condition the freezing intake air (between -1°C to -50°C) to just above 0°C. Employing the above system, the mine intake air ventilation costs are cut considerably and the CO2 production is substantially lowered. Another mine ventilation application of the above system is to use the geothermal pipe networks installed in the upper mine levels to provide cold energy for cooling the deeper levels of the mine. In this application, the provided geothermal fluid absorbs the heat of the deeper levels by passing through forced convective heat exchange surfaces (or condensers) in the deeper levels of the mine and conveys this heat to the upper levels of the mine which are considerably cooler. The temperature difference between the deeper and higher levels can vary from 5°C to 70°C in some cases. Usually, in deep underground mines the forced convective heat exchange surfaces (or condensers) installed in the deeper levels of the mine condition the temperature of the deep underground mine workshops to a tolerable temperature. For instance, in some South African gold mines, a mixture of ice and brine is pumped 5000 m deep underground to prevent the temperature of the underground workshops from exceeding 32°C. This operation is energy consuming and, therefore, costly. Hence, the above system reduces the energy and economic burdens of the mine ventilation system. Alternatively, the system can be used to convey the heat from deeper mine levels to the colder levels where heat energy is needed.

[0059] After the installation of geothermal pipes inside the emptied space of the mine, this area is filled with minefill material to cover the pipes. This allows for transfer of heat between the geothermal pipes and the surrounding rock mass and will prevent the risk of damage to the geothermal pipes due to falling rocks. These pipes will be placed at an appropriate distance from each other depending on the properties of the fill material, tube flow and the sizing of the tubes (1 to 5 meters apart from each other). Every few feet the geothermal pipes will be connected to each other and will be fed out to the main geothermal fluid distribution pipe(s). The inlet fluid will flow through the geothermal pipe and will be flowing out through the major pipes into the heat exchange surfaces or heat pump system.

[0060] From one aspect, there is provided a novel system that takes advantage of the minefill material as means of heat exchange media that results in a renewable energy extraction system which has little to no drilling or excavation cost. Also, this system is able to extract a considerable amount of energy due to having access to vast underground spaces with high and stable ground temperature. Advantageously, this system will convert an underground mine into a sustainable renewable energy generator which provides a considerable amount of inexpensive heat/cold energy efficiently, not only when the mine is active but also when the ore body of the mine is no longer operating.

[0061] The proposed system is economical for extraction of heat and/or cold energy from underground mines since there is little to no need for drilling or excavation.

[0062] In a preferred embodiment, the method further comprises extracting high or low temperature energy from the thermal fluid.

[0063] In another preferred embodiment, the method further comprises extracting high temperature energy from the thermal fluid; and converting the extracted high temperature energy into mechanical or electrical power.

[0064] In a yet further embodiment, the method further comprises transferring the extracted energy to a second network of geothermal pipes via a heat exchanger in contact with the first network of geothermal pipes, the second network comprising a second thermal fluid circulating therein.

[0065] In a further preferred embodiment, the method further comprises transferring the extracted energy to a ventilation unit in order to condition an intake air of the mining operations.

[0066] In a further embodiment, the method generates energy to be used in a variety of applications, including, but not limited to, district heating, acid leaching, and water heating.

[0067] Reference will now be made to the embodiment illustrated in the drawings and described herein. It is understood that no limitation of the scope of the disclosure is thereby intended.

[0068] Referring to Fig. 1 , the system for the extraction of renewable energy from minefilled excavations 10 in accordance with the invention is shown. The system 10 comprises at least one mine stope or cavity 12 in which a network of geothermal pipes 14 is installed. The at least one stope 12 is filled with minefill material (not shown) after the network of geothermal pipes 14 is installed. The at least one stope 12 is connected to the surface through a mine shaft 16 or any other opening through which the network of geothermal pipes 4 can reach the surface. A geothermal fluid is introduced with a pump 26 into the network of geothermal pipes 14 and circulated throughout the network of geothermal pipes 14. The placement of the pump 26 is illustrative and may be at any one of a variety of locations within the system. The minefill material which covers the network of geothermal pipes 14 allows for transfer of heat between a rock mass of the at least one stope 12 and the geothermal fluid within the network of geothermal pipes 14.

[0069] The geothermal fluid flows from the network of geothermal pipes 14 which is in fluid communication with a heat exchanger 20 for extracting the energy from the geothermal fluid. If needed, the energy extracted or the geothermal fluid flowing from the geothermal pipes 14 may be directed to a heat pump 22. Alternatively the heat exchanger 20 is configured for transferring directly or indirectly the extracted energy to the mine ventilation unit 22 in order to condition the intake air of the mine. The geothermal fluid is returned to the network of geothermal pipes 14. [0070] The extracted energy from the heat pump 22 or air leaving the mine ventilation system 22 is directed to a system 24 which consumes the provided energy. The system 24 can be either one of the following: a mine area which requires energy for conditioning its intake air; residential, commercial or industrial heating or cooling systems; a power generation cycle; or other mine operations such as acid leaching.

[0071] The function of each of the components of the system 10 is as follows:

[0072] Mine ventilation system: In order to provide comfortable working conditions in mine working areas, the fresh intake air of the mine is conditioned year round. The ventilation process includes heating and/or cooling mine intake air which bears considerable energy costs.

[0073] Geothermal pipe: Geothermal pipe is a pipe or tube network installed in mining excavations or any other cavity created in mining operations. These pipes can be interconnected in series forming a branch. Each branch will be connected to a main geothermal fluid pipe which brings in the inlet fluid and another main tube which takes the outlet fluid out. Multiple geothermal pipe systems may be employed in parallel and are hydraulically connected such that thermal fluid circulates therein. The geometric arrangement and sizing of the geothermal pipe system will depend on ground temperature, geometry of installation site(s), heating/cooling load demands, operational strategies of the mine and the thermo-physical properties of minefill material and rock mass. The network of geothermal pipes is in a closed loop, with some allowance for makeup of thermal fluid.

[0074] Minefill material: It is a blend of mine tailings, binder and water which is placed in mine cavities in order to secure the mining operation and prevent the occurrence of ground failure in a mining operation.

[0075] Geothermal fluid: Geothermal, or simply thermal, fluid is the fluid which flows in the geothermal pipe system. It can be water, brine or any other liquid capable of withstanding the thermal and chemical conditions inside the geothermal pipe. It is also possible to use more than one geothermal fluid in a system. For example, a special kind of brine can be used for capturing heat from the mine and then this heat can be conveyed to water to be transferred to end users.

[0076] Heat exchanger: If more than one type of geothermal fluid is used or if there is a need to have heat exchange between separate loops of geothermal fluid(s), then heat exchanger(s) will be used.

[0077] Pump: The pump is needed to circulate the geothermal fluid in the geothermal pipe system.

[0078] Heat pump: If the system is used to extract heat or cool energy from mine and if there is a need to increase the temperature of the heat energy extracted, heat pump(s) will be used. However, if the temperature of the provided geothermal fluid is hot or cold enough for direct usage or if the system is used for power (or electricity) generation, there is no need for heat pumps.

[0079] Power generation cycle: If the ground temperature is suitable for power (or electricity) generation, then the geothermal pipe system can be coupled to a power generation cycle to provide mechanical (or electric) power.

[0080] It should be appreciated that the invention is not limited to the particular embodiments described and illustrated herein but includes all modifications and variations falling within the scope of the invention.

[0081] The system can be installed in many mining operations, particularly the following:

[0082] In mining operations with stopes prior to minefill material placement (any type of minefill is applicable, and comprises tailings, sand or rocks with or without binders and with or without water). Here, the stope which is filled with minefill material may have any size (ranging from tens of cubic meters to thousands of cubic meters). Also, the stope can have a regular or irregular shape.

[0083] In the underground long wall coal mines, where the heat exchanger tubes are placed along the side of gate road ways (between the packs). The geothermal pipes will be placed horizontally on the floor or in vertical standing form and then the geothermal pipes will be covered by the minefill material so that the geothermal pipes are insulated and also prevented of being damaged from falling rocks.

[0084] In another application in underground long wall coal mines (both in the advance or retreat mining technique), where the geothermal pipe heat exchanger is placed on the floor of the gouge area behind the power supports followed by the minefill material placement which fills the entire area). The geothermal pipes are placed horizontally or vertically on the floor in the area (area behind the power supports).

[0085] In underground coal mines produced with the room and pillar mining technique, where the geothermal pipe heat exchanger is placed in the mined-out area followed by filling the entire area with minefill material.

[0086] In underground potash mines where the geothermal pipe heat exchanger is placed in the mined-out area followed by filling the entire area with minefill material.

[0087] In surface mines, such as a strip mining operation. As the ore is mined, the closed loop pipes are placed on the floor, followed by filling the entire area with minefill material, followed by waste material on top. The geothermal pipes will be placed prior to minefill material placement.

[0088] In surface mines under a tailings dam, where the closed loop geothermal pipe system could be placed in the tailings material. The geothermal pipes will be placed horizontally or vertically prior to the tailings being placed on top.

[0089] In accordance with an embodiment, the proposed system can operate in a wide range of ground temperatures which can be described as follows:

[0090] If the system is used for heat energy extraction, the ground temperature can be as low as 8°C to as high as 200°C. However, if the ground temperature is close to, or higher than, the boiling temperature of the fluid which flows in the geothermal pipes, another fluid should be used or the whole geothermal pipe line will be pressurized to prevent the boiling in the line. Also, in the case of cooling energy application of the system, the ground temperature can vary from -15°C to 30°C. If the ground temperature is lower than the freezing point of the fluid, a brine fluid should be used to prevent pipes from bursting or blockage due to freezing.

[0091] The filling material used to fill the cavities can be at least one of soil (with or without water, with or without binder material (e.g. cement)); tailings material (with or without water, with or without binder material); minefill material which is a blend of soil or tailings, water and binder; and any other material which could be formed by adding additive(s) (like pozzolanic material such as cement, grinded slag or color) to one or a group of the above mentioned materials. The filling material can have a porosity range of 0.3 to 0.5 and a thermal conductivity range of 0.4 (W/m-K) to 10 (W/m-K).

[0092] The configuration of the geothermal pipe heat exchanger for all mining operations may be vertical, horizontal, slinky (curtate cycloid) or slanting with different configuration sizes depending on the pipe diameter size and loop length. Any number of the tubes can be used in series (connected) in order to improve the heat transfer. Finned tubes can be used in order to improve the heat transfer. Either internal or external fins can be used.

[0093] Flexible pipe connectors can be used along the length of the tubes or between them in order to make it possible for the tube network to bear the shrinkage of the fill material. This shrinkage may happen in the fill material due to loss of water, consolidation, cementation or even earthquake or rock fall. [0094] Iron, cast iron, aluminum, copper, stainless steel, PVC, ABS or any other metallic or plastic pipe(s) can be used depending on the thermo- physical and chemical properties of the environment in which the pipes are installed.

[0095] The geothermal pipe size diameter can range between ¼ inch to 4 inches and its length is dependent on the space in which it is installed. However, different tube sizes may be used in a single tube network system.

[0096] In one embodiment, the proposed system and method can be used in any of the following scenarios:

[0097] The system can be employed as a means of mine ventilation. For instance, the system can be used to provide hot water for heating the intake air of the mine, or cold water for cooling it. The intake air can be contacted directly through the sprayed geothermal fluid or come into indirect contact with the geothermal fluid in a heat exchanger. In this special application, the renewable energy extracted from the stable temperature mine geothermal source will cut the costs of mine ventilation significantly and will save a considerable amount of fuel or electricity.

[0098] The system can be used for heating or cooling, and if the temperature of the geothermal fluid is not suitable for direct usage, a heat pump will be used. If more than one geothermal fluid is used for exchange of heat between the heat pump and the ground, then a heat exchanger will be used to make the heat exchange between the geothermal fluids possible. If the geothermal fluid loop is open and there is considerable elevation raise in the loop, a turbine will be implemented to recover part of the electric power needed for pumping.

[0099] If the temperature of the hot geothermal fluid provided is hot enough for power (or electricity) generation, then a power generation cycle will be employed to convert the extracted heat energy to mechanical, and possibly even electrical, power. This power generation cycle can be any mechanical or electrical equipment capable of converting the ground heat to mechanical (or electrical) power (e.g. Organic Rankine Cycle or Solid State Heat to Electricity Conversion Unit).

[00100] Whether the proposed system is used for heating or cooling or even power (or electricity) generation purposes, the system can exchange heat between the ground source and surface or between one level of the mine and another.

[00101] As indicated, the system can be implemented in mine stopes. It may be used only in one stope or cavity at time or can be integrated in all stopes/areas or a combination of stopes/areas in surface or underground mines. In the individual stope system, the geothermal pipes in each stope will be connected to a central station on each level and the pumping will be regulated at that station. Alternatively, all the stopes will be individually connected to the central station in one station either at the surface or in one of the underground levels. The pumping will be regulated at that station. In this system, if one of the geothermal pipes is damaged in one of the locations then that part of the system could be taken out of the network without affecting the whole system which would comprise the number of individual stopes. In the system of employing a combination of stopes, the geothermal pipes which are installed in each location are connected to the geothermal pipes of other zones either in series or parallel. The geothermal pipes are then brought to a central station at the surface or in a level underground. In these systems, the geothermal pipes are placed in the stopes either vertically, horizontally or in a slinky fashion. The geothermal pipes could be placed close to, or on the walls of, the rock stopes prior to minefill material placement.

[00102] There are other possible applications for the geothermal energy extracted from mine stopes, for instance, heap leaching. Heap leaching is an industrial mining process for extracting precious metals, copper, uranium, and other compounds from ore via a series of chemical reactions that absorb specific minerals and then re-separate them after their division from other earth materials. Comparable to in situ mining, heap leach mining differs in that a liner is provided for placing amounts of ore thereon, then the chemicals are added via drip systems to the ore, whereas in situ mining lacks these pads and pulls pregnant solution up to obtain the minerals. Geothermal heat extracted from mines stopes using the present system can be used to increase the leaching temperature in order to improve the efficiency of this reaction.

[00103] Other possible applications for the geothermal energy extracted from mine stopes include mine intake air ventilation (heating); heating the offices, buildings and workshops in the vicinity of the mine; district heating (if a community is close to the mine); etc.

[00104] Finally, although the present invention has been described hereinabove by way of embodiments thereof, it may be modified, without departing from the nature and teachings of the subject invention as described herein.