In an age of rapidly rising fuel bills the discovery of vast supplies of free hot water sounds too good to be true. But that is exactly what one Dutch city has found to run the radiators of hundreds of homes, shops and offices.

Heerlen, in the southern province of Limburg, has created the first geothermal power station in the world using water heated naturally in the deep shafts of old coalmines — which once provided the southern Netherlands with thousands of jobs but have been dormant since the 1970s.

http://www.timesonline.co.uk/tol/news/environment/article4887672.ece 

---

Isn't the thermal conductivity of rock the stumbling block in the first place.

Hence the thinking years ago that an underground nuclear explosion could fracture the rock enough to provide sufficient surface area.

Rather than "in the face of rising fuel bills" I'd say "In the face of the Hirsch Report" and suggest that people stop mucking about with toy energy and address the problem fair and square.

Interesting reading....

http://www.netl.doe.gov/publications/others/pdf/Oil_Peaking_NETL.pdf 

Summary here:-

http://en.wikipedia.org/wiki/Hirsch_report 

It would be interesting to see how the project fares and how the energy tails off.

To put into a mining context, if you look at the deep levels of Tresevean and United, there are figures quoted for air temps and rock temps, the difference between them being due to a cool skin of rock building up in short time.

After all, this factor is why the rocks are still hot!!!! 🙂

I thought the rocks were hot because the temperature below the earths surface steadily rises due to the temp of the earth's core.
Anyway this doesn't seem to be a conventional geothermal arrangement. Certainly not one one similar to the hard rocks trials which as you know were started near Stithians many years ago, and now continues at Soultz-sous-Forets with a consortium of countries.

http://ec.europa.eu/research/energy/nn/nn_rt/nn_rt_geo/article_1136_en.htm 

A bit more about the Dutch plant and an idea of future plans,

http://sxmislandtime.com/index.php?option=com_content&view=article&id=3363:first-mine-with-green-energy-&catid=31:general&Itemid=76 

---

Kensa Engineering are manufacturers of Ground source heat pumps and they are extracting heat from the main shaft at Mount Wellington Mine to heat thier factory assembly shops and doing a darn good job of it too.
There is water welling up from Roskear shaft at blood heat but there are no plans I'm aware of at present, to exploit this resource. Maybe if Crofty hit big in Dolcoath and decide to expand then we may see a move to that side of the site and the miners dry could be heated with it. 🙂

---

I believe your old mate Allen Buckley does a fair bit of work in this field. 😉 Apart from the miners dry, what about those wonderful new flats in Roskear :lol:

---

I would much prefer to see Cramp's bookbinders back there instead. Maybe the residents will end up eith cramps of their own ::)

---

Back on topic again :angel: The United Mines Hot Lode phenomenon has been atributed to several different causes.
There is the sulphide decomposition idea, which although plausible on a small and limited scale and mostly post mining, would not account for water temperatures over 100 Farenheit.
Decomposition of radioactive materials is another explanation but the levels of radioactivity in the mine and in the water do not seem to support this as the only factor.
heating due to a localised 'thin' section of crust (Earth's not Mother's Pride) seems the more likely. With the granite plutons having risen after the erosion of the mountain ranges, it is possible, I suppose, that joints between plutons may have allowed mantle material to 'spike up' in odd places producing localised heating beyond the normal range of the usual depth/temperature gradients, typical for that kind of geology.
But then...I'm not too sure it aint old Nick!!!! 😮

---

Renewables are something which interest me a lot. The sad thing is that they often lack the data to criticise/applaud their credibility. Since data is the tool of dissection, it would be nice to have some.

Ground source heat pumps are a beautiful piece of design and make total thermodynamic sense. The same principles allow a huge amount of heat to be stored and transferred.

The same principles are at work with geothermal, but several factors are different. Namely the specific heat capacity of the system.

For any system concerned with transferring heat, there are 2 simple equations with characters which you can estimate or calaculate according to how you want to model your proposal.

These are:-

Relating an amount of heat energy to mass of stuff and temperature rise, as well as how well it transfers heat

Q=mCp dT where

Q=total duty
m=mass of stuff to be heated
Cp=Specific heat capacity (how easy the stuff is to heat)
dT=Temperature change.

and

Q=UA LMTD where

U=related to the sum of heat transfer coefficients (how well heat makes it from where it is to where you want it)

A=Area (are required to transfer heat for the specific material)

LMTD= Log of mean temp difference (magic calculator stuff to do with difference between hot and cold stuff)

Essentially, in order to transfer a load of heat from here to there, you need to heat a fluid by so and so degrees and move it to so and so where the stuff can lose it's heat.

The heat transfer coefficients are bloody important, how the rocks in this case give up their heat, which isn't very well.

A given amount of rocks contain a given amount of heat, proportional to their depth. You need to circulate your working fluid (water) over a given area in order to abstract your required heat (Q) which is limited by the heat transfer coefficients of the material (how well it conducts it)

The snag is that given a large amount of time you can achieve a big resevoir of hot water (roskear) heated by a load of rocks over a long period. The poor thermal conductivity (related to U) means that the heat in the rocks is slow to dissipate into the water, when you cool the water. In order to do this more effectively, you need to have a bigger surface area, which is the bane of geothermal energy.

As a conservationist who seriously sees the importance of alternative energy, this is the falling point and the hurdle which has to be overcome. Fracturing the rock is sort of proportaional to depth, if you drill deeper, you have to fracture less. Snag is fracturing is more difficult at depth. The nuclear boys had problems with rock "glassifying" and the conventional explosives gang had a problem with getting the explosives where they were needed. These guys with their water technology are pissing in the wind. You aren't going to create the necessary surface area, of area for flow via water pressure. No amount of wishing will make it happen.

The snag is that in order for heat abstraction from the ground to take place (geothermal energy) you either need a massive working fluid (like mine water) for a little task, or a very large, hot, highly fractured piece of ground which you would gradually cool via a very slow circulating primary fluid and a secondary fluid (greater volume) in order to throttle the high heat duty.

Anything else doesn't add up.

These guys can calculate their required duty via do-able equations and scaling up isn't a problem, they can sample the temp at depth and calculate Q, from the rock properties, they know U, from tables, they know Cp, they know the dT available. The beast is getting the surface area.

The second beast is the fact that unlike a heat exchanger, the heat in the rocks is not replaced (ignoring radioactivity) and so the available dT and therefore Q is less. You either build a huge plant to power not very much and have it for long, ie:- water in amy shaft (loads) vs heat in Kensa offices (not much) or you run out of heat quickly. You then have to redo the plant again, which involves deep drilling and rock shattering, so I gather.

I'm a big fan of people's ideas actually working and ideas which work or are projected to work have data and that data speaks for itself. A lack of data might suggest the idea itself being flawed.

This most certainly includes the very data lacking wind turbines, which doesn't stand up to the fag packet maths test either.

Anyway, as you were 😉

and a reply to Roy's bit.

The earth should be solid now, if it's rate of cooling was proportional to the heat it had for the given (radio-dating) age of the earth. Since it isn't, that heat come from radioactive decay.

Radioactive decay doesn't actually release that much heat, but in a substance with a crap heat transfer rate, it hold onto it more than you'd think. In short, radioactive heat hangs around more than most.

The lodes are sat there in the rock, not being hot or anything like that but as soon as they are exposed to air, as soon as water percolates through them with air, a whole load of different reactions start happening, virtually all of which are exothermic. They include most reactions where "stuff gets to be with stuff that it would rather be with" eg Sulphites+O2==>Sulphates Sulphuric Acid+Carbonates===>Stuff Sulphate+CO2.

It all contributes to heat, bad air and acid, which the united mines are famed for.

Interesting stuff.

I would attribute the heat of Roskear shaft to the actual depth and residual heat (rather than chemical or radio) found in the deep mine.

To say you couldn't cool it down faster than it would be replaced would be foolhardy.

Anyway..... a good old yarn after a night at the pub!

Night folks!

Renewables are something which interest me a lot. The sad thing is that they often lack the data to criticise/applaud their credibility. Since data is the tool of dissection, it would be nice to have some.

Ground source heat pumps are a beautiful piece of design and make total thermodynamic sense. The same principles allow a huge amount of heat to be stored and transferred.

The same principles are at work with geothermal, but several factors are different. Namely the specific heat capacity of the system.

For any system concerned with transferring heat, there are 2 simple equations with characters which you can estimate or calaculate according to how you want to model your proposal.

These are:-

Relating an amount of heat energy to mass of stuff and temperature rise, as well as how well it transfers heat

Q=mCp dT where

Q=total duty
m=mass of stuff to be heated
Cp=Specific heat capacity (how easy the stuff is to heat)
dT=Temperature change.

and

Q=UA LMTD where

U=related to the sum of heat transfer coefficients (how well heat makes it from where it is to where you want it)

A=Area (are required to transfer heat for the specific material)

LMTD= Log of mean temp difference (magic calculator stuff to do with difference between hot and cold stuff)

Essentially, in order to transfer a load of heat from here to there, you need to heat a fluid by so and so degrees and move it to so and so where the stuff can lose it's heat.

The heat transfer coefficients are bloody important, how the rocks in this case give up their heat, which isn't very well.

A given amount of rocks contain a given amount of heat, proportional to their depth. You need to circulate your working fluid (water) over a given area in order to abstract your required heat (Q) which is limited by the heat transfer coefficients of the material (how well it conducts it)

The snag is that given a large amount of time you can achieve a big resevoir of hot water (roskear) heated by a load of rocks over a long period. The poor thermal conductivity (related to U) means that the heat in the rocks is slow to dissipate into the water, when you cool the water. In order to do this more effectively, you need to have a bigger surface area, which is the bane of geothermal energy.

As a conservationist who seriously sees the importance of alternative energy, this is the falling point and the hurdle which has to be overcome. Fracturing the rock is sort of proportaional to depth, if you drill deeper, you have to fracture less. Snag is fracturing is more difficult at depth. The nuclear boys had problems with rock "glassifying" and the conventional explosives gang had a problem with getting the explosives where they were needed. These guys with their water technology are pissing in the wind. You aren't going to create the necessary surface area, of area for flow via water pressure. No amount of wishing will make it happen.

The snag is that in order for heat abstraction from the ground to take place (geothermal energy) you either need a massive working fluid (like mine water) for a little task, or a very large, hot, highly fractured piece of ground which you would gradually cool via a very slow circulating primary fluid and a secondary fluid (greater volume) in order to throttle the high heat duty.

Anything else doesn't add up.

These guys can calculate their required duty via do-able equations and scaling up isn't a problem, they can sample the temp at depth and calculate Q, from the rock properties, they know U, from tables, they know Cp, they know the dT available. The beast is getting the surface area.

The second beast is the fact that unlike a heat exchanger, the heat in the rocks is not replaced (ignoring radioactivity) and so the available dT and therefore Q is less. You either build a huge plant to power not very much and have it for long, ie:- water in amy shaft (loads) vs heat in Kensa offices (not much) or you run out of heat quickly. You then have to redo the plant again, which involves deep drilling and rock shattering, so I gather.

I'm a big fan of people's ideas actually working and ideas which work or are projected to work have data and that data speaks for itself. A lack of data might suggest the idea itself being flawed.

This most certainly includes the very data lacking wind turbines, which doesn't stand up to the fag packet maths test either.

Anyway, as you were ;)

So why does the US have so many geothermal sites?

---

Wow Stu! Looking at it that way I can see why progress in these fields isn't storming ahead as you would think it ought.
I know the Hotrocks guys were experimenting with small pyro charges and opening the joints hydraulicly using a special gel, which by the way was apparently being munched by bacteria deep in the rock. I guess something like the wee beasties that produce the all too familiar 'Snottite' in sulphide mines.
I think it would be hard to really deplete a heat reservoir as large as say Wheal Jane (also quite warm) as the geology of that area is naturally fractured to hell in all directions for miles around. The phreatic waters circulating underground would be pulling in heat faster than say arock only reservoir could. I guess i may have to have a chat with Kensa and pick a few brains for their observations on the subject.

---

and a reply to Roy's bit.

The earth should be solid now, if it's rate of cooling was proportional to the heat it had for the given (radio-dating) age of the earth. Since it isn't, that heat come from radioactive decay.

Radioactive decay doesn't actually release that much heat, but in a substance with a crap heat transfer rate, it hold onto it more than you'd think. In short, radioactive heat hangs around more than most.

Night folks!

What exactly does that mean?

---

I think this discussion just goes to illustrate the terrific amount of expertise that there is available on this web site.

Really fascinating stuff.

After reading through this thread and the contemporary thread on the deepest coalmine shaft I was asking myself if deep coalmines with temperatures around 40C or Boulby Potash mine with a temp of 45C would not be suitable places for extracting heat. After reading the foregoing with Stuey's learned dissertation, I was not sure if water was captured after percolating through the rock or whether it would be piped through the mines to capture the heat in some sort of giant heat exchanger.

As the coal mines and Boulby work seams as opposed to veins or loades, would this make heat extraction easier as there are vast areas of exposed rock? Before the experts, who know Boulby, wade in, I know the roof sags and the floor heaves so hence major engineering problems.

I don't want to pour cold water on any Cornish ideas but you are a hell of a long way from any centre of population whereas the deep shaft in Lancashire is in the Greater Manchester conurbation and Boulby is only a kick off Teesside so heat would not have to be transferred for long distances.

Any of this make sence or is it just pie-in-the-sky. I'll leave it to the experts

🙂

---

Not sure about american gt, I'm assuming that their rocks are either allready fractured enough (fault breccia/etc) and are geologically recent--hot. The hot stuff is close to the surface.

If you go shizzling around near a volcano or active fault, it's going to be hot and fractured!

I think it was Lord Kelvin who originally was trying to calculate the age of the earth (probably to **** the jehova's witnesses off) and kept getting the wrong answer. It should have been solid long ago. Plate tectonics should have stopped and the whole thing ground to a halt. There was too much heat kicking around. If you go back up the curve a bit and go back say a billion years, there was a whole lot more radioactive stuff keeping things hot.

It's amazing that when you consider the age (bloody old) of the granite in the SW, it's still sodding hot.

Assuming they can crack the area problem (which for the SW is the big one) we will have it coming out of our ears.....

I wonder how hot the water is in the deep part of united mines. The snag being that it's also acidic..... stainless kit is considerably more pricey.

I really am not a naysayer of renewables but the maths really has to add up, it certainly does in places and there will always be places which it works and doesn't work. I should have clarified that further. Cornwall most certainly has the heat.

I remember talking to a couple of guys (engineers from Crofty) who were saying that the bottom levels of Crofty were hotter than you would think by a lot.

I would expect to see some pretty big convection currents and some warm water in shafts.......... can you?

Edit:- This would probably expain the pipes going down Amy shaft (wellington)..... I suppose it would be difficult for proper convection currents and flow patterns to be set up, but there would probably be a bit of it..... It would be interesting to measure the temps of both the shaft water and the stope water in wellington, my bet is there would be a difference...

Patch wrote

I think this discussion just goes to illustrate the terrific amount of expertise that there is available on this web site.

I came late to this thread, but it illustrates what's best about the forum. I've been interested in the posts, but I have to thank Carnkie and others for sending me off on another internet search and reminding me that I used to be a scientist!

Incidentally I used to visit Heerlen (and Brunsum) a lot in the early seventies, as I lived relatively close. It made me remember all the activity in the area, including lignite extraction to the south east, so more hours spent on line then.......

Not sure about american gt, I'm assuming that their rocks are either allready fractured enough (fault breccia/etc) and are geologically recent--hot. The hot stuff is close to the surface.

If you go shizzling around near a volcano or active fault, it's going to be hot and fractured!.....

.

I'm pretty sure stuey is right. Most of the 'hot rock phenomena' in the U.S. is geothermal in nature, heat being created due to friction of rock on rock in a subduction zone for example. Since the U.K isn't sitting on or near a tectonic plate we have to look to other causes for heat underground as spelled out in immaculate detail by stuey (just wish I felt I understood it all 😞 )

---

I'm not sure that tells the whole story in the US although I'm not disagreeing with Stuey. There is some interesting information here with a nifty little animation.

http://www1.eere.energy.gov/geothermal/ 

---

In my defense I did say "most of the hot rock" etc. After all the US is a big place and it's mostly the area west of the Rockies (the result of tectonic movement).

:angel:

---