WO2014070568A1

WO2014070568A1 - Improved air handling and cooling in a mine

Info

Publication number: WO2014070568A1
Application number: PCT/US2013/066546
Authority: WO
Inventors: Neeraj Saxena; Harald Ranke; Joseph NAUMOVITZ
Original assignee: Linde Aktiengesellschaft
Priority date: 2012-11-01
Filing date: 2013-10-24
Publication date: 2014-05-08
Also published as: CA2898845A1; AU2013338268A1; ZA201503413B

Abstract

A method and system for supplying power to a mine, particularly during periods of high peak-power electrical power rates or low power grid availability, is achieved by liquefying air and storing it in a storage vessel. The liquefied air is fed to a series of heat exchangers where it will be warmed, becoming gaseous air at higher pressure. This gaseous air is fed to a turbo expander where cold air and power are produced. The cold air can be fed to an appropriate storage unit, or directly fed to the mine shafts to provide cooling of personnel and reduce direct means of cooling such as crushed ice and indirect means such as chilled air from a traditional over-ground ammonia chilled air refrigeration system. The power generated by the turbo expander will be recovered and used to provide power to the mine.

Description

IMPROVED AIR HANDLING AND COOLING IN A MINE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US provisional application serial number 81/721 ,127 filed November 1 , 2012.

BACKGROUND OF THE INVENTION

[0002] In underground mines used to recover precious metals, a complex system of vertical, horizontal and slanted shafts are created underground for the miners to blast and excavate rocks using electric and pneumatic rock drills to recover mineral ores. Vertical shafts for gold mines for example can be 3 to 5 kilometers deep, while platinum group metals mines have in general, lower depths on the order of 0.3 to 1 kilometers deep.

[0003] Air management systems in such mines are designed to provide air for ventilation for the miners, shaft wall surface cooling as well as compressed air for powering the pneumatic rock drills. Ventilation systems include electrically powered exhaust fans, as well as forced draft air using

compressors supplying air at 1 to 3 bar. In addition, compressed air is provided at 5 to 8 bar pressure in air ducts running deep into the mines to power the pneumatic rock drills. Multiple large compressors ranging from 2 to10 at 1000 to 3000 KVA each are installed above ground into a common ductwork, which runs off a common header with multiple leads and ducts providing the air needs underground. Power to these compressors is typically provided by grid power. Grid power rates can vary with time of use, and often peak power rates can be 5 to 10 times the unit power rate on a per KWH basis compared to rates for off-peak. Each large mine typically has long term contracts with utility companies where these variations are spelt out, including incentives for adopting energy conservation and peak-shaving methods adopted by the mines. [0004] For instance in South Africa where Eskorn is the national power utility and supplier of power to large mines such as the Anglo-American Group, utilities are unable to provide all the power required at the mine.

Mining companies concurrently use generators using fuel oil, diesel and gasoline and large diesel or other liquid fuels to supplement the power requirement to keep the mines operational. Take for instance the Anglo- Platinum Corporate Environmental Report for 201 1 that mine operations consumed over 200 MW of grid power in approximately 10 mining operations, in addition to 70 MW of power generated at a much higher price through the use of liquid fuels. It can be inferred that at 7 MW of liquid fuel based local generation of power in each mine, Anglo-Platinum consumed approximately 1.8 million liters of diesel costing them at 19M Rand per year per mine to a figure of 3.9 Rand KWH or 0.45 US Dollars/KWH.

[0005] Depending upon the mine, electrical power to provide air

management can be approximately 30 to 50% of the power requirement in a mine. To keep the air cool in such mines so as to allow the miners to work, cooling and chilling systems are also provided above ground, from where refrigerated air or crushed ice are forced down into the mine. These techniques also require large amounts of electrical power.

[0008] With energy shortage in the grid in many countries, increasing power prices and implementation of time-of-use tariff charges including peak and off-peak periods in a day, mining companies are keen to adopt ways to minimize use of more expensive fossil fuel and to minimize their cost of power without compromising miner safety.

SUMMARY OF THE INVENTION

[0007] To address these issues, the invention provide for a method of providing more energy efficient air and cooling management systems in a mine complex. [0008] In one embodiment of the invention, there is disclosed a method for producing power for use in a mine for mining operations wherein power from an electric grid is not being fed to the mining operations comprising the steps: a) liquefying air; b) feeding said liquefied air to a storage unit; c) feeding said liquefied air from said storage unit to a heat exchanger; d) feeding gaseous air from said heat exchanger to a turbo expander; and e) delivering power and if needed - cooling from said turbo expander to said mine.

[0003] The mine is typically an ore producing mine such as a gold or platinum mine. The mine contains a main shaft for the transportation of mine workers and needed supplies. The ventilation shaft provides air and cooling to the miners as well as an exhaust from the mine. The power that is delivered by the invention is electrical power which is generated by the turbo expander and fed to the power grid.

[0010J The storage unit is a cryogenic storage tank and the liquefied air will remain in this storage when the power consuming devices in the mining operations are drawing power from the power grid. When the mine stops drawing or reduces power from the electrical grid based on the operators parameters, the electrical power that is generated in step e) is fed to the mine through the electrical power grid.

[0011] For purposes of the present invention, reducing power from the electrical grid is defined to include the state of reducing power draw but also the state where there is no power drawn from the electrical grid. [0012] The heat exchanger can, for example, can draw heat from fuel exhaust or hot mine water and use this in exchanging heat with the liquefied air fed from the storage unit.

[0013] This step will cause the liquefied air to become gaseous and be fed to the turbo expander at a pressure of 20 to 70 Bar.

[0014] The cold expanded air exhausted from the turbo expander after if has generated electrical power and can be fed to a cold store and

regenerator. The cold expanded air can further be fed to the air liquefier to assist in providing cooling the air being liquefied. In addition, ambient air may be fed to the coid store and regenerator. The cold expanded air may also be fed into the ventilation shaft of the mine as a means to provide dry cooling to the mine without introducing additional moisture to the environment, such as when ice is employed.

[0015] a different embodiment there is disclosed a method for providing power to a mine comprising the steps; a) liquefying air; b) feeding said liquefied air to a storage unit; c) stopping or reducing feed of electricity from a power grid to the mine; d) feeding said liquefied air from said storage unit to a heat exchanger; e) feeding gaseous air from said heat exchanger to a turbo expander; and f) delivering power from said turbo expander to said mine.

As discussed earlier, the state of reducing the feed of electricity from the power grid to the mine will include the state where there is no electricity being fed from the power grid to the mine,

[0017] There is also disclosed a system for providing power to a mine comprising: a) an air liquefier; b) a liquid air storage unit; c) a heat exchanger; d) a turbo expander; and e) means for providing power from said turbo expander to said mine.

[0018] An appropriately sized Liquid Air Energy Storage (LAES) system comprising an (i) air liquefier system; (ii) cryogenic storage; (iii) insulated energy recuperation vessel including thermal/cryogenic fluids or packed bed of ceramic rocks providing low pressure drop; and (iv) associated pumps, compressors, pipes, heat exchangers and operating equipment are installed above ground in a mine complex.

[0019] The LAES is connected (a) electrically to the electrical power grid utility power lines at a mine; (b) mechanically into the main mine compressed air header that exists above ground; and (c) mechanically and thermally integrated with the mine cooling system that supplies the underground shaft network with cold air and ice,

[0020] The LAES is operated in a manner that allows using low cost power, available at low-power rate times, or when excess renewable power such as wind and solar is available to chill and liquefy air and store it as a liquid in a cryogenic vessel. At these times, normal mine operations such as compressed air generation, electrical drilling and lighting or chilling/ice~making operations continue without change.

[0021] During times of need, such as when grid or utility power is expensive or available in less quantities than the demand, or to substitute for more expensive fuel-power generated power from locally installed generators, stored liquid air is in full or in part: (i) compressed to higher pressures greater than 50 Bar using a cryogenic pump; (ii) followed by vaporization or heating of air in a supercritical state and exchange of heat from ambient air, mine water, steam heat recovery units from local power generators, or other waste heat source from mining operations; (iii) de-pressurized to a pressure of 4 to 8 Bar through one or more turbo-expanders whereby power is generated in single or multiple stages; (iv) the de-pressurized air at 4 to 6 Bar is in part or total fed into the main compressed air header in the mine; (v) this air reduces the power required for mine air compression system during such time partially or completely; (vi) a part of the liquid air or in combination with vaporized chilled air is directly dropped into the mines to reduce the chilling requirements of the mine; and/or (vii) a part of the liquid air or in combination with vaporized chilled air, exchanges energy with the mine refrigeration and chiller systems, thereby lowering the chilling/refrigeration requirements of the mine.

[0022] Alternatively, the embodiment may include (i) extracting a portion of the 4 to 8 Bar air; (ii) further heating this stream by exchange of heat from ambient air, mine water, heat recovery units from local power generators or other waste heat source from mining operations; (iii) depressurizing this heated air stream to 1 to 3 Bar pressure through one or more turbo-expander operations; and (iv) introducing this depressurized 1 to 3 Bar air stream into the mine ventilation system.

[0023] A further alternative embodiment may include diverting a portion of the stored liquid air directly into the mine to provide the cooling required

8 underground in the shafts for the miners while fulfilling the air requirement needs for health and safety.

[0024] The advantages realized by the invention include the reuse of compressed air and its cold for improved energy efficiency compared to the conventional LAES system where power is generated by air evaporation and air released back to ambient without the air being reused,

[0025] The use of vaporized chilled air utilized at slightly elevated pressure after the power generation step within the mining operation further reduces the peak power demand of a mine, since the power for compression is one of the main costs of operation a mine. The use of liquid air or chilled compressed air in the mines reduces the need for chilling/refrigeration in the mine. When crushed ice is dropped into a gold mine for instance, an equivalent amount of warm water has to be pumped out of a mine to ensure there is no excess water build up in the mine, Instead dry liquid air can reduce or eliminate in extreme cases the need to pump in ice or pump out warm water from the mine. Being dry, the air also results in slight evaporation of wafer in the mines, increasing the comfort level of air in the mine for the mine operators.

[0026] The use of the cold liquid air provides additional benefits to being used to produce electric power. The cold energy present in the liquid air can be used to off-set the need for and requirements of cold in a mine. For example, during the vaporization phase, or as a separate step, the cold energy extracted from the liquid air can be used to provide cool air to miners to breathe underground directly, or by exchanging the heat of the mine shaft to vaporize and pressurize the liquid or cold air through either direct or indirect heat exchange means,

[0027] In mine complexes where ice is created above ground from water and dropped down mine shafts to provide the cooling necessary for miners to be able to operate in deep shafts where rock surface temperatures can exceed 50°C, using the vaporized liquid air can heip minimize or eiiminate this practice. Minimizing water present in the mine has several advantages particularly in arid locations where access to water is limited or expensive or both.

[0028] The round trip efficiency of an LAES system can further be improved by using the thermal recuperator which consists of an insulated bed of ceramic rocks or thermal fluids and organic Rankine cycle, which recovers and stores the cold energy from vaporized air and uses it at a later time to reduce the overall energy needs of the entire LAES.

[0029] There are also areas within the mine that can have flammability concerns. As such, the oxygen in the form of liquid air that is used to provide power can be substituted for by using nitrogen or air with reduced oxygen content.

[0030] The invention may be used in operations beyond mining where industrial or commerciai operations use compressed air or chilling in large amounts such as providing power to a residential mining township (air conditioning and peak shaving in summer), metal making (metal

cooling/cleaning using compressed air) or other such applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic of a liquid air storage system per the invention when off-peak power rates and high grid power availability are applicable.

[0032] Figure 2 is a schematic of a liquid air storage system per the invention when peak power rates or low grid power availability are applicable. [0033] Figure 3 is a iabie detailing some assumptions in calculating power savings,

[0034] Figure 4 is a table detailing approximate power tariff rates for South Africa.

[0035] Figure 5 is a table detailing the savings realized by the instant invention,

[0036] Figure 6 is a table detailing tariff charts for the use of energy at various times of the day and week.

[0037] Figure 7 is a table showing the savings realized by the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Turning to the figures. Figure 1 is a schematic of a liquid air storage system operation when off-peak power rates are low and there is high grid power availability. The mine power requirements in this example are consistent with a mid-size mine and are 20 to 25 MW. Power for air ventilation and compressors for rock drills is about 10 to 15 MW and power for other uses is about 10 to 15 MW. The pressure requirement for shaft ventilation is 1 to 3 Bar and the pressure requirement for pneumatic rock drills is 5 to 6 Bar. Cooling requirements for the mine workers inside of the mine are 10 to 15 MW.

[0039] A schematic of the mine is represented in the lower left hand corner of Figure 1 showing the main shaft 101 and ventilations shaft 106 as well as shafts 1 13 that connect the main shaft 101 to the ore body itself 1 12. The main shaft 101 is connected to the surface by a headframe AA that contains the elevator assembly and related components (not shown) for transporting mine personnel and supplies underground. The ventilation shaft 106 is connected to the surface by a compressor and ventilator B and is responsible for providing air/oxygen underground. Ice and chilled water is also sent or fed into the mine through line 7 to assist in cooling off the temperatures under ground.

[0040] The main shaft 101 connects at the bottom with a stop 102 where the elevator would settle. Below this stop 102 is the sump 103 which is fluidly connected to the ore bin 105 and crusher 104. Water from the surface or ice added to the mine would gather in the sump 103. The shafts designated 1 13 are connected to the ore body 1 12. The main levels are connected by ore passes 104, 108 and 109 which allow for the passage of ore between the levels.

[0041] Exploration drilling occurs in shaft 1 10 where it connects to where diamond drilling 1 14 is occurring. The top main levels will contact the ore body 1 12 and the majority of the drilling operation will be occurring at the slope 1 1 1.

[0042] The grid power is represented by the top line 1 and this connects with the various components that require power during operation of a mine. So, for example, the headframe AA and components contained therein (not shown) will draw power from the grid power. The compressors and ventilators B will draw power as does the chiller and icemaker BB and the air Siquefier C.

[0043] During this period in which those power consuming devices are drawing power from the grid through line 1 , the inventive system is operating to liquefy air that can be stored for use when peak-power rates are applicable or when there is less grid power available. So for example, line 2 will supply power to the air liquefier C, line 3 will provide power to the chiller and icemaker BB; line 4 provides power to the compressors and ventilators B and line 5 will provide power for other uses within the mine installation,

[0044] Ambient air is fed through line 8 to the compressors and ventilators B and this ambient air can be fed into the ventilation shaft of the mine through the compressors and ventilators B. Line 6 will also deliver ambient air to a main air compressor CC which will compress the air and feed through line 8A to a drier DD. The dried and compressed air will leave drier DD through line 8B and be fed to the cold store and regenerator J which will coo! the dried and compressed air and feed it to the air liquefier C through line 20.

[0045] The air liquefier C wi!l draw power from the grid through Sine 1 during this period. Air will be drawn into the air liquefier device C such as a cryogenic distillation column where the air will be divided into its component constituents and liquefied. This liquefied air is fed through an appropriate line 8 to a liquid air storage unit D which may be any number of cryogenic storage tanks or other devices that will contain liquid air while maintaining its temperature. Any heat loss will be vented through the top of the liquid air storage unit and vented as air to the atmosphere through line 9. During this period when the power availability is high and rates low, the operation stops at this stage and the liquid air continues to remain in storage.

[0046] The remaining components shown in Figure 1 are not active when the mining operations are drawing power from the grid. The liquid air storage unit D is f!uidfy connected via Sine 10 and 1 1 to a liquid air pump F which in turn is fluidly connected to a regenerator J through Line 1 1 and then a heat exchanger G through line 12. Line 12 allows for the transfer of liquefied air to the cold store and regenerator J where the liquefied air will be warmed up and passed through a heat exchanger present in the cold store and regenerator J. This warmer air is passed through line 12A to a second heat exchanger G. The heat exchanger G may also be one or more heat exchangers. E and S are valves or circuit breakers which are active during this stage of operation. These valves or circuit breakers can be either off or on. For instance, at this stage, I indicates there is no power generated by the inventive system and therefor fed to the grid. E represents that all fluid flow in line 10 stops during this stage.

[0047] The heat exchanger G will use sources of heat such as fuel exhaust or hot mine water through line 14 to warm the liquid air as well as increase its pressure and will vent through line 13. The air now in the gaseous state will pass from the heat exchanger G through line 15 at a pressure of 20 to 70 Bar and be fed to a turbo expander H which will expand the high pressure air passing through and produce energy which can be fed into the power grid through line 18. The cold expanded air is then fed through line 17 to a cold store and regenerator J such as rocks or other organic compounds which can then be fed back to the air fiquefier C as cooied air through line 20. ! represents a "stoppage" of power supply into the grid from the evaporated air expansion - basically the evaporation of air is stopped during this stage so that no more power is generated and fed into the grid. Ambient air may be fed through line 18 to the cold store and regenerator J to take advantage of the cooling provided therein. Further, the cold store and regenerator J may feed cooled air to the ambient air via line 6 being fed from the surface into the ventilation shaft through line 19.

[0048] Figure 2 represents the situation when some of the mining operation stops drawing power from the grid line 1 , such as when peak power rates are present or there is low grid power available. Power through line 2, 3 and 4 will stop being drawn. At this point in time, sufficient amounts of air has been liquefied and stored. Like designations are employed in figure 2 as are employed in figure 1. In this situation power from the grid is reduced or completely stopped to the air iiquefier unit C, the chiller and icemaker BB and most to the power compressors and ventilators A. The mine power requirements remain ostensibly the same as in the situation described in Figure 1. Power continues to flow from the grid through line 1 and line 5 for the uses associated with the headframe AA connecting the main shaft 101 to the above ground.

[0049] As noted above in describing Figure 1 , E and S are valves or circuit breakers that can be turned on or off and reflect the current power state as to whether the mine is drawing electrical power from the grid or not. in Figure 2, K, L and also represent a stoppage of power. When power is stopped under condition K, the air !iquefier C is not operating to liquefy air. Likewise, when power stoppage represented by L occurs, there Is no power being directed to the chiller and icemaker BB so no cold energy is being produced for feeding into the mine. When power stoppage represented by occurs, no power is being fed to the ventilators and compressors B.

[0050] A schematic of the mine is represented in the lower left hand corner of the Figure 2 showing the main shaft 101 and ventilations shaft 108 as well as shafts 1 13 that connect the main shaft 101 to the ore body itself 1 12. The main shaft 101 is connected to the surface by a headframe AA that contains the elevator assembly and related components (not shown) for transporting mine personnel and supplies underground. The ventilation shaft 108 is connected to the surface by a compressor and ventilator B and is responsible for providing air/oxygen underground through line 8. Ice and chilled water is also inputted into the mine through line 7 to assist in cooling off the

temperatures under ground.

[0051] The main shaft 101 connects at the bottom with a stop 102 where the elevator wo u id settle. Below this stop 102 is the sump 103 which is fluidiy connected to the ore bin 105 and crusher 104. Water from the surface or ice added to the mine would gather in the sump 103. The shafts designated 1 13 are connected to the ore body 112. The main levels are connected by ore passes 104, 108 and 109 which allow for the passage of ore between the levels. [0052] Exploration driiling occurs in shaft 110 where it connects to where diamond drit!ing 1 14 is occurring. The top main levels will contact the ore body 1 12 and the majority of the drilling operation will be occurring at the slope 1 1 1.

[0053] With power draw stopped through line 2 to the air liquefier C, there is neither air being fed through line 8 to the liquid air storage unit D nor much heat loss occurring through vent 9.

[0054] The air liquefier C is not operating during this stage so no more liquid air is being produced and fed through line 8 to liquid air storage D. Instead, liquid air from the storage unit D is being fiuidly fed through line 10 to a liquid air pump F at 1 to 3 Bar pressure is fed through line 12 through cold store and regenerator J and to a heat exchanger G. Line 12 allows for the transfer of liquefied air to the cold store and regenerator J where the liquefied air will be warmed up and passed through a heat exchanger present in the cold store and regenerator J. This warmer air is passed through line 12A to a second heat exchanger G. Any heat loss would be accommodated by venting air to the atmosphere from the liquid air storage unit through line 9. The heat exchangers G and that present in the cold store and regenerator J will utilize sources of heat available at the mine such as fuel exhaust or hot mine water to warm the liquid air through line 14 and will be evacuated through line 3. This will change the liquid air to a gas and increases its pressure to 20 to 70 Bar where it will be fed through line 15 to the turbo expander H which will expand the gaseous air and produce power which can be fed into the grid 1 through line 16 or otherwise made available to the power drawing components necessary for mining operations.

[0055] The cold expanded air will then be fed through line 17 to the cold store and regenerator J which will supply cooled air back to the air liquefier C through line 20 but also to the compressors and ventilators for feeding into the ventilation shaft of the mine by way of line 19 to line 6. Additional ambient air may be fed through line 18 to the cold store and regenerator J.

[0058] Consequently, the amount of power that is used from the grid reflected in line 1 is greatly reduced and substituted for by the power that is generated using the liquid air scheme of the invention.

[0057] The tables embodied in Figures 3, 4 and 5 provide calculations assuming certain power rates, power usage and related information to project the savings using the inventive system. For the numbers generated in Table 3 (Figure 5), certain assumptions were made. For example, it was assumed that peak power rates were applicable 9 hours a day. This allows for a power savings of twenty three million dollars over 5 years. If a 15 year term is employed, the savings generated by the inventive system were sixty nine million dollars. These savings of course will be reduced after taking into consideration the cost of installing and operating the inventive LAES system, but it is anticipated that a net savings would result.

[0058] To achieve 40% roundtrip efficiency, design and optimization of the energy storage and utilization system requires first the availability of sufficiently high temperature fluid (T greater than 150°C) which can be used for warming the re-evaporated air to allow for more power recovery during depressurtzation and expansion, and second, the intermediate warm and cool streams for more efficient recovery of heat co!d from the liquid and

compressed air cycling. The actual efficiency will change based on the detailed plant design for generating the alternative power supply.

[0059] In a further hypothetical, certain assumptions were again made with respect to power, time employed and various economic rates such as tariff amounts. Time of use based power rates and hours of usage were taken from the published Eskom tariff booklet for 2012-2013. [0060] In this example, peak power was oniy available for a shorter time of 3 to 4 hours per day and only for 3 months of a year. Offsetting this peak power at the variable rate of 0.96 Rands/KWH with power generated from the LAES system of the invention may not result in sufficient savings. However, if a portion of the power generated from liquid fuel costing approximately 4 Rand/KWH is offset from the inventive system's generated power, savings are improved sufficiently to generate a net positive improvement.

[0081] In this hypothetical, no change is explored using standard power rates, only off-setting the peak and the off-peak power are explored. The example shows a power savings of seventeen million dollars over 5 years. Extrapolating to a 15 year term, all else being equal results in a fifty one million dollars in savings generated.

[0062] The tariff structure as shown in Table 4 in Figure 6 is based on assumptions. They may not be valid if a mine company contracts for a longer term that may or may not follow the same rates and schedules. It is known that the trend in South Africa is for power rates to increase more for industrial users than for residential users and that the large energy demands from mines, in excess of 20 to 30 MVA, do put considerable strain on the state utility (Eskom) grid network. As such, the opportunity cost for a mine-wide energy storage per the invention may yield higher numbers than shown in the example in Figures 6 and 7.

[0083] While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and

modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the invention.

Claims

Having thus described the invention, what we claim is:

1. A method for producing power for use in a mine for mining operations when power from an electric grid is reduced to the mining operations comprising the steps: a) liquefying air; b) feeding said liquefied air to a storage unit; c) feeding said liquefied air from said storage unit to a heat exchanger d) feeding gaseous air from said heat exchanger to a turbo expander; and e) delivering power from said turbo expander to said mine.

2. The method as claimed in claim 1 wherein said mine is selected from the group consisting of gold and platinum mines.

3. The method as claimed in claim 1 wherein said heat exchanger is one or more heat exchangers.

4. The method as claimed in claim 1 wherein said mine contains a main shaft and a ventilation shaft.

5. The method as claimed in claim 4 wherein said main shaft and said ventilation shaft may be more than one main shaft and ventilation shaft.

6. The method as claimed in claim 1 wherein said power is electrical power.

7. The method as claimed in claim 1 wherein said liquefying air is by a cryogenic distillation column.

8. The method as claimed in claim 1 wherein said storage unit is a cryogenic storage tank.

9. The method as claimed in claim 1 wherein said liquefied air remains in storage when power consuming devices are drawing power from a power grid.

10. The method as claimed in claim 1 wherein said heat exchanger draws heat from fuel exhaust or hot mine water.

1 1 . The method as claimed in claim 1 wherein said gaseous air is fed to said turbo expander at a pressure of 20 to 70 Bar.

12. The method as claimed in claim 1 wherein cold expanded air is fed from said turbo expander to a cold store and regenerator.

13. The method as claimed in claim 1 wherein said cold expanded air is further fed to the air liquefier.

14. The method as claimed in claim 1 further comprising feeding ambient air to said cold store and regenerator.

15. The method as claimed in claim 1 wherein cooled air is fed into the ventilation shaft of said mine.

18. The method as claimed in claim 1 wherein said power of step e) is delivered to said mine when said mine stops drawing power from the electric grid.

17. A method for providing power to a mine comprising the steps: a) liquefying air; b) feeding said liquefied air to a storage unit; c) reducing feed of electricity from a power grid to the mine; d) feeding said liquefied air from said storage unit to a heat exchanger; e) feeding gaseous air from said heat exchanger to a turbo expander; and f) delivering power from said turbo expander to said mine.

18. The method as claimed in claim 17 wherein said mine is selected from the group consisting of gold and platinum mines,

19. The method as claimed in claim 17 wherein said mine contains a main shaft and a ventilation shaft.

20. The method as claimed in claim 19 wherein said main shaft and said ventilation shaft may be more than one main shaft and ventilation shaft.

21. The method as claimed in claim 17 wherein said power is electrical power.

22. The method as claimed in claim 17 wherein said liquefying air is by a cryogenic distillation column.

23. The method as claimed in claim 17 wherein said storage unit is a cryogenic storage tank,

24. The method as claimed in claim 17 wherein said liquefied air remains in storage when power consuming devices are drawing power from a power grid.

25. The method as claimed in claim 17 wherein said heat exchanger draws heat from fuel exhaust or hot mine water.

26. The method as claimed in claim 17 wherein said gaseous air is fed to said turbo expander at a pressure of 20 to 70 Bar.

27. The method as claimed in claim 15 wherein cold expanded air is fed from said turbo expander to a cold store and regenerator.

28. The method as claimed in claim 17 wherein said cold expanded air is further fed to the air Siquefier.

29. The method as claimed in claim 17 further comprising feeding ambient air to said cold store and regenerator.

30. The method as claimed in claim 17 wherein cooled air is fed into the ventilation shaft of said mine.

31. A system for providing power to a mine comprising: a) an air liquefier; b) a liquid air storage unit; c) a heat exchanger; d) a turbo expander; and e} means for providing power from said turbo expander to said mine.

32. The system as claimed in claim 31 wherein said mine is selected from the group consisting of gold and platinum mines.

33. The system as claimed in claim 31 wherein said mine coniains a main shaft and a ventilation shaft.

34. The system as claimed in claim 31 wherein said power is electrical power.

35. The system as claimed in claim 31 wherein said air liquefier is a cryogenic distillation column.

36. The system as claimed in claim 31 wherein said storage unit is a cryogenic storage tank.

37. The system as claimed in claim 31 wherein said heat exchanger draws heat from fuel exhaust or hot mine water.

38. The system as claimed in claim 31 wherein said power of step e) is delivered to said mine when said mine stops drawing power from the electric grid.

39. The system as claimed in claim 31 wherein liquid air is fed directly into the mine.

40. The system as claimed in claim 31 further comprising nitrogen or oxygen reduced air is used for power in place of liquid air.