How does one revitalize the abandoned mines amidst the era of depleting mines and declining coal industry? A Chinese research team has recently proposed transforming these mines into hydro-pumped power plants, which would become a new type of power generation facility when being paired with solar and wind power generation equipment.
According to the analysis of Chongqing University and Shaanxi Investment, there are currently 3,868 suspended mines in China that can undergo such transformation, where the shaft of the coal mines can be further utilized into become a reciprocating reservoir for the hydro-pumped power plant.
The hydro-pumped water plant is divided into upper and lower levels, where the water would be transported from the lower section to the upper reservoir during low electricity demand or prices, and released into the lower level to actuate the turbine in transmitting electricity through the water level during high electricity demand or a period that requires additional power. The ideal height difference between the upper and lower reservoirs is 100m.
The team believes that the numerous shafts and channels in underground mines often require a prolonged periods of maintenance in water level and water treatment in order to avoid flooding or environmental pollution after the decommission, thus the water storage capacity, available volume, and fluid exchange must be taken into account when evaluating nearly 4,000 abandoned mines.
The team emphasizes that the capacity of water storage not only depends on the space of the mine, but has to also consider the porosity and permeability of the soil and rocks, since the higher the porosity the higher the water content, and the larger the permeability the easier fluidity of groundwater. The system design of the team also comprises of a ventilation shaft at 2m above the highest water level of the reservoir to allow better air flow during water pumping and filling.
As indicated by the model simulation, the reformation of abandoned mines into hydro-pumped power plants can ensure an average efficiency of 82.8% within a year, and a REPV expected at 2.82kWh/ m3.
Researchers believe that although the particular solution is feasible pertaining to technology, extra emphases must be placed on the environment of the mines in order to prevent acidic water from corroding plants and soil, which releases metal ions and heavy metals that would damage the underground structure and pollute surrounding water, while water quality inspection and purification are also indispensable.
(Cover photo source: pixabay)