Soudan MN Mine Opportunity 
 

The Soudan MN community has a tremendous opportunity to utilize the Soudan mine for producing heat and electricity.  The mines’ close proximity to the town, coupled with its geothermal capabilities, offer promising heating and air conditioning resources.

A study by Maria B. Diaz and Rafael Rodriguez concludes that geothermal energy may be created by converting mine shafts into geothermal boilers.  Reference:  Rafael Rodriguez, Maria B. Diaz.  “Analysis of the utilization of mine galleries as geothermal heat exchangers by means a semi-empirical prediction method.”  Renewable Energy 34 (7):  1716, 2009.

While research is being done in abandoned coalmines, many of which are flooded, no one is currently looking at the tremendous opportunity of the Soudan mine.  I first recommended a look at the mine for energy purposes on October 2, 2009 to representatives, the IRRRB, and mine staffers.  The IRRRB said staffers of the mine, owned, operated, and managed by the DNR would have to pursue the recommendation.

Sources of Mine Energy


While geothermal systems offer an excellent heat transfer system, the lesser-known Air Source heat system work well too. 

Air, at any temperature above absolute zero (–459.67° F) contains some heat.  An air-source heat pump (ASHP) transfers some of this heat from one place to another, such as between the outside and inside of a building.  This can provide space heating and/or hot water.  A single system can be designed to transfer heat in either direction, to heat or cool the interior of the building in winter and summer respectively.

The technology is similar to a refrigerator or freezer or air conditioning unit: the different effect is due to the physical location of the different system components.  Just as the pipes on the back of a refrigerator become warm as the interior cools, so an ASHP warms the inside of a building while cooling the outside air. 

Air-source heat pump have two main components:  1) An outdoor heat exchanger coil, which extracts heat from ambient air and 2) An indoor heat exchanger coil, which transfers the heat into hot air ducts, an indoor heating system such as water-filled radiators or under floor circuits and/or a domestic hot water tank.

Air source heat pumps can provide low cost space heating.  A high efficiency heat pump can provide up to four times as much heat as an electric heater using the same energy.  In comparison to gas as a primary heat source, however, the lifetime cost of an air source heat pump may be affected by the price of electricity compared to gas.  Of course, gas prices also fluctuate according to demand, regulations, transportation, and drilling costs.

Energy Capacity and Paybacks


The capacity of the Soudan mine is so large that there would not be any disruption to current tours.  In fact, as a model for other former and current mine cities/towns it would attract a whole new spectrum of tourists and visitors.  They might include engineers, city planners, green energy enthusiasts, and officials of other mining areas.

The savings to the community would be immense as geothermal systems are 300-600% efficient.  Given the depth of the Soudan mine (2,341 feet) and its steady 50° F temperatures all year long, the potential is great and promises higher than normal (300%) efficiencies.  ASHP's perform best at temperatures above 23° F (-5° C).

Ground source Heat Pumps (GHPs) also reduce electricity use by 30–60% compared with traditional heating and cooling systems, because the electricity which powers them is used only to collect, concentrate, and deliver heat, not to produce it.
The Soudan mine consists of more than 54 miles of drifts, adits, and raises.  The potential energy from this mine is tremendous.  This is a rare structurally sound mine that already pumps its water out daily (86,400 gallons/day).

Definitions
 

Adit:  This is the first thing that most people would call a tunnel. You could think of it as half a tunnel. If you walk into a mountain and come out again the same way, you entered via an adit.

Drift:  A horizontal opening that runs along the vein.  Typically, there are many ore chutes from stopes above, and the drift will wander to follow the vein.

Raise:  A raise is like a shaft that starts underground and goes upwards.  Typically, a ladder next to an ore chute along a drift goes up a raise and gives access to a stope above.

The heating/cooling savings would result in bills about 1/3 to ¼ of what is currently paid.  This savings would be a wonderful incentive to living in Soudan and may attract additional residents while retaining a higher percentage of current residents.

Conclusion


Mechanical engineers could design two systems to fully utilize the mine openings.  One would be used to heat and cool homes and businesses in the city.  The second would be for generating electricity.

This project would bring more jobs, while reducing costs for everyone in the area.  Excess electricity could be fed back to the grid, and earn money.
Crazy idea?  Maybe, but definitely worth a closer look by professionals.