New life for coal mines ?

[Bugtownboy]

https://www.bbc.co.uk/news/articles/c0l867k70p8o

[dan_b]

Very good

[Mart]

That's very interesting. And the mine water already has to be managed, back when I worked in Environment in the Welsh Office / Welsh Assembly Gov, my colleagues were heavily involved in 'pollution from flooded coal mines'. I organised a trip once to several venues, one of them to see the orange run off polluting some rivers from the iron in the water leaking out.

Mines used to pump out the water, to stay operational, but when they closed, the mines filled, then orange water started leaking out of the hillsides.

What a great idea / potential, I really hope it has legs and is viable.

[Moxi]

It’s not really a pollutant tho is it - it’s a naturally occurring chemical reaction that occurs in springs and water courses and just happens to also occur in abandoned mines where water finds its path of least resistance to the surface.

I can’t imaging that this has much scope depending on how much treatment the water needs before it’s passed across the heat exchanger, after that what do they do with the water ? They cannot put it back in the mine because its chemistry has been changed and it’s now at waste product ? If they did win the argument to put it back in the ground it will leach out more soluble minerals and eventually could lead to adit, gallery and shaft collapse as it’s a form of solution mining. High process costs for low grade heat doesn’t seem like a winner to me, arguably a distraction from better alternatives currently in roll out ?

Sorry for the negative Ned view on this one.

Moxi (Ned)

[AE-NMidlands]

Mine drainage is quite noxious though.
In the bedrock iron pyrites (FeS) is locked into the stone - coal - and layers like the seat-earth (clay the coal forests grew in) make groundwater movement minimal.

When you mine it there is tons of crushed coal and other debris left underground, packed in behind the advancing face but dry and in air, sitting there behaving itself... When the abandoned mine floods there is lots of water contact with the FeS allowing oxidation and movement of water eventually carries the acidic sulphur compounds out of the mine. If the low pH doesn't kill what lives in the streams, then the ochre deposits which drop out when the water meets the air will blanket out most life in the stream instead.

Wikipedia has a good article on it https://en.wikipedia.org/wiki/Acid_mine_drainage which points out that there are other heavy metals involved too.

[Moxi]

Oh I agree it’s very noxious but the actual mechanism is one that exists naturally in other geological water bodies - flooded mine workings are just another route to the surface for the water and its solutions. To use this cocktail it needs to be cleaned which creates a toxic concentrate that needs disposal, refreshes the universal solvent (water) to go and dissolve more nasties from the rock strata within the mine. All for some low grade thermal energy ?? For me it ranks up there with using hydrogen to charge military vehicles via fuel cells etc at best it’s a distraction at worst it’s a waste of tax payers contributions. Arguably you would get better thermal collection from a row of vacuum tubes equal to the footprint of all the process plant required to handle the mine water and for a lot less cost.

Moxi

[Oliver90owner]

GSHP?

[Mart]

As I mentioned, pollution from abandoned mines was a major issue for the team dealing with water quality, due to the pollution of rivers. This was back in the 90's and early 2,000's. And as I understand it, it hasn't improved much. If you drill lots of holes and tunnels through a hill/mountain, then you create many/new routes and surface area for water to easily flush out minerals.

Metal mine water pollution

Over 500 tonnes of metals like zinc, lead, cadmium and iron enter Welsh rivers from abandoned mines every year; causing 6% of them, nearly 700km, to fail to achieve good chemical or ecological status. The pollution harms the river ecology; reducing fish populations and the diversity of invertebrate life.

Apologies, didn't intend to make this a Welsh issue, as it's a problem across the UK, good report here:

Environment Agency - Abandoned mines and the water environment

[Moxi]

The geology and style of Welsh collieries means it’s more of an issue there than say the Yorkshire and Nottinghamshire coal fields where the surrounding strata is much less rich in metal ores. The low land coal fields also tend to close up after time so less surface area and smaller void volumes. My dad used to work in the Yorkshire coal field for a time and he used to tell me that the average pit prop would sink around two inches a month and need freeing with hydraulic props, re packing and setting again.

The main issue for the deep mines in those regions was the radon gas which collects in the fault planes of the collapsed galleries and seeps up to the surface where people have nice new homes built- heck there’s even been a few cases where nice new houses had been built right over the main shaft seal plug ! But I digress.

Moxi

[dan_b]

GSHP?

That was my thought - and could be done at a street/district level rather than individual buildings