[HN Gopher] Closed-loop geothermal energy recovery from deep hig...
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Closed-loop geothermal energy recovery from deep high enthalpy
systems
Author : blacksqr
Score : 39 points
Date : 2021-12-28 15:50 UTC (7 hours ago)
(HTM) web link (www.sciencedirect.com)
(TXT) w3m dump (www.sciencedirect.com)
| ganzuul wrote:
| Although expensive we have the materials to go much deeper. If we
| could get to 1400C we could make concrete almost for free.
| Gravityloss wrote:
| In Otaniemi they drilled to 6.4 km and got 125C rock.
| https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/437325
|
| Current deepest hole is 12 km. Temperature goes up 18 C per km.
| I think the hole would get quite technical if we tried to go to
| 70 km deep...
| Animats wrote:
| _Closed-loop technology applies thousands of meters long
| horizontal wellbores in the target thermal reservoir that are
| connected by two vertical wells, one inlet well, and one
| production well (Fig. 2). A low temperature working fluid is
| injected from the inlet, heated mostly through the horizontal
| interval in a geothermal reservoir with proper thermal
| properties, and the heat energy is harvested at the outlet for
| heating and power generation purposes._
|
| That's reasonable enough. It's an underground heat exchanger. How
| hard is that to drill? Can you get the horizontal and vertical
| wells to meet up?
|
| Output temperatures shown on the graph are in the 30C-50C range,
| so this is for heating buildings, not power generation.
| ganzuul wrote:
| > A reservoir rock at 200 degC will produce over 120 degC
| fluids, while a 100 degC reservoir can only produce fluids
| around 78 degC after 30 years of operation.
| beembeem wrote:
| Horizontal drilling is very expensive.
| blacksqr wrote:
| "this closed-loop system can provide a relatively stable energy
| production with fluids temperature over 100 C on a 30 year
| lifespan."
| Animats wrote:
| That paragraph is a little better, but 100C is not enough for
| a power plant. No steam, just hot water. Nuclear power plants
| typically produce 300C steam, and that's thermodyanamicaly
| inefficient. Naval steam boilers hit the 600C - 800C range.
| sigmaprimus wrote:
| Operating at such deep levels and high temperatures presents many
| challenges that can be avoided with lower overall temperatures
| and shallow wells.
|
| Eg: My residential well is at least +32F whilst the ambient
| outside temperature is -40F. I know this through observation of
| water flowing out of my tap and an outdoor thermometer. This
| provides a temperature difference of >72F which can be extracted
| through simple heat converters and then multiplied by compression
| to achieve temperatures sufficient for steam production. By
| exploiting the physical properties of steam condensation vast
| amounts of energy can be produced during this state change.
|
| I understand this report is directed towards large scale energy
| production with 30 year+ timelines but believe smaller
| decentralized solutions have many benefits over these large
| projects.
|
| I also do not understand why "Closed-loop" terminology is
| implying that this system is something new or distinct as all
| geothermal systems to my knowledge use closed loop systems to
| prevent environmental damage.(Other than possibly a water wheel
| at Yellowstone?)
| mojomark wrote:
| I had the same reaction about the "closed loop" highlight in
| the title. An open loop system seems very wasteful and hard to
| maintain.
|
| Your comment on decentralized application caught my attention.
| I agree with you. While there are clear merits to gaining
| economies of scale, there are often diseconomies of scale that
| go overlooked - which would make smaller decentralized
| applications more attractive.
|
| The trade largely comes down to lowering require capital
| expenditure ($/resource generated, e.g. $/kW) in order to gain
| operating flexibility (which can lower overall operating costs
| - though those savings are normally excluded from the published
| $/resource value, hence overlooked). Think of the merits of
| everyone having a car instead of trying to move people to-and-
| fro using trains. Sure, you pay less $/mile traveled,
| cumulative carbon emissions/mile are generally lower, and you
| avoid wear and tear on your car. BUT, you have to pay for taxis
| or rental car when you arrive at your destination, so you pay
| an inflated amout to restore flexibility. The cost for 'last
| mile' transit certainly isn't reflected in your train ticket
| cost.
|
| As a side study I've been wrestling with this problem in my
| industry (commercial ship design) for the past decade. One
| challenge is that it's hard for a corporation investing in the
| infrastructure to sell these decentralized units to achieve a
| profit margin competitive with a large-centralized product.
|
| The solution, I believe, is to figure out how to evalutate and
| factor in the cost of loss of flexibility in the $/resource
| calculation. That hasn't been an easy nut to crack.
| blacksqr wrote:
| >I also do not understand why "Closed-loop" terminology is
| implying that this system is something new or distinct as all
| geothermal systems to my knowledge use closed loop systems to
| prevent environmental damage
|
| Large-scale geothermal systems attempted up to now have
| generally been of the the type where you frack deep underground
| rock, then dig two wells into the fracked rock field, pump cool
| water into one and let it heat as it percolates through, then
| pump it back out the other.
|
| This as you mention carries the potential for environmental
| damage, but has been seen as necessary to overcome the problem
| of rock's slow thermal recharge rate.
|
| The linked paper suggests the rock thermal recharge problem can
| be overcome by digging not one but several horizontal pipes
| connecting the two deep vertical wells.
| mojomark wrote:
| I also was not aware of that open loop scheme. Seems like a
| simple and lower cost, albeit inefficient, solution. Thanks
| for sharing.
| sigmaprimus wrote:
| I was not aware they used such methods, I assumed they would
| use a glycol type solution to achieve better heat transfer
| and enable the transfer of heated media within a closed loop
| system of piping or well jackets. I find it shocking that
| they have been employing the tactics You described above,
| especially under the guise of a renewable alternative energy
| that is good for the environment.
| [deleted]
| seanwoods wrote:
| Not all geothermal systems are closed loop. I have an open-loop
| geothermal system at my house on Cape Cod, MA. It uses the same
| water pump I use for my domestic water, runs it through the
| heat pump, and discharges back to the aquifer via another well
| drilled exclusively for this purpose.
| sigmaprimus wrote:
| Interesting, do you also take advantage of the excess amount
| of water being pumped through your system with a reverse
| osmosis system?
|
| I would imagine this would be of great benefit if You are
| already moving the water to heat and cool your home.
| noveltyaccount wrote:
| "By exploiting the physical properties of steam condensation
| vast amounts of energy can be produced during this state
| change."
|
| Can you expand on this, or provide a reference?
| sigmaprimus wrote:
| https://en.wikipedia.org/wiki/History_of_the_steam_engine#:~.
| ...
| pfdietz wrote:
| One very interesting thing about closed-loop geothermal is that
| it isn't actually a baseload source. It has storage-like
| characteristics. One can draw more heat from it for a limited
| time, at a lower overall cost than a system that would be
| designed to draw that same level of heat constantly. This is due
| to the finite thermal conductivity of rock around the closed
| loop. After a "surge" that rock recharges by conduction of heat
| from further away.
| aaron695 wrote:
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