Coal power supplies most of the electricity that we use here in America. It’s been that way for a long time. Because of coal’s popularity as a source of power, mines, both active and abandoned, lay scattered across the nation. And now, with coal’s popularity waning, the number of abandoned mines could increase. Since 2001 alone, 100 coal-fired plants have taken their turn in front of the firing squad.
And it doesn’t seem as though it’s over. If the trend of extinguishing coal-fired plants continues, more and more mines will be shut down, not to mention mines that simply up and quit. But what is to be done with the abandoned mines? It isn’t as though we can just dispose of them at some hi-tech facility. These mines will become useless scars.
Two engineers from the University of Oviedo have an idea, though. In their research, which is being published in the journal Renewable Energy, Rafael Rodríguez and his colleague María Belarmina Díaz claim that mine shafts on the point of being closed down could be used to provide geothermal energy to local towns.
“One way of making use of low-intensity geothermal energy is to convert mine shafts into geothermal boilers, which could provide heating and hot water for people living nearby,” said Rodríguez. However, different mines would have different geothermal capacities. What Rodríguez and Díaz have done is developed a “semi-empirical” method (meaning that it is part mathematical and part experimental) to calculate the amount of heat that could be produced by a mine tunnel that is due to be abandoned, based on studies carried out while it is still in use.
“When the mine is still active one can access the tunnels easily in order to gather data about ventilation and the properties of the rocks, as well as to take samples and design better circuits, and even programme the closure of some sections in order to use them for geothermal energy production.”
But what about mines that are already closed? Rodríguez says that, while closed mines can still be used in harvesting geothermal energy, “it is no longer possible by that stage to make any modifications, or to gather any useful data to evaluate and improve the system.”
The study looks into harvesting geothermal energy from a two-kilometre-long mine shaft. In the shaft, rock temperatures 500m below the surface is around 30º C. This is typical of many of the mining areas in Asturias (where the study was carried out), but harvesting geothermal energy could also be applied to other parts of the world. Water could be forced in through tubes at 7º C and return at 12º C, a big enough heat gain to be of benefit to towns located above the mines.
Rodríguez and Díaz highlight the fact that, aside from having predictable production levels, boilers built in mine shafts function practically as an open tube system “but without any risk of heat contamination of aquifers.”
Other benefits of harvesting geothermal energy from mines are that, unlike wind and solar, which are dependent on ambient conditions, geothermal energy is not dependent on any variables; these facilities make use of a country’s own resources; no new developments on large sites are required; and the boilers do not pollute the immediate environment.
Source: Science Daily
Photo Credit: sincretic via flickr under Creative Commons License