Author Topic: CO2 power generators using phase/volume change and latent martian heat at depth.  (Read 2376 times)

Offline go4mars

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Along this line, I was thinking about the use of areothermal power on mars by circulating water in a closed loop system then using the geysering effect to bring heat and energy the surface (taking power using hydraulic ram). 

But the challenges of insulating drill-pipe on earth make steaming oil reservoirs much below 500 meters uneconomic (implies technologically uncompetitive for now).  On Mars the added complications would be far worse.  Water freezes too easily. 

I was also thinking of a system taking advantage of the variable solubility and fugacity of CO2 in water with temperature, and how outgassing from water could drive the geysering effect under different pressure and temperature conditions.  This got me thinking about liquid CO2 injection, where an internal tubule pumped liquid CO2 down within a larger one that was pumping a low-freezing point brine.  At depth, they combine, and again, in a closed or variably-closed system, geyser to surface in the second well-bore under the geysering lift of CO2 expansion (excess energy supplied by areothermal heat).  Fluids drive a hydraulic ram, torque up a pressure-bladder, or otherwise store energy for surface use. 

But that has complications too, though it might work alright. 

Then I got to thinking that CO2 alone might be a much better (simpler) way to do this (at temperatures/depths that are more likely to be easily drilled by early colonists):  Atmospheric compression to make liquified CO2 (I don't think the impurites would matter much but if so, could be centrifuged out).  Then the liquid CO2 is pumped down to a deep chamber (formed explosively, or within a natural porosity system, or tunneled out by side-wall coring devices, rasps, or any of many options) and the CO2 is allowed to slowly heat at depth.  Pressure builds.  A valve at the bottom of secondary borehole into the chamber (reservoir) is opened, and the pressure release causes CO2 to rapidly expand (to 1500 times the volume) and goes up to the surface through the second wellbore with tremendous force.  The force is mechanically captured (spin-up flywheels, hydraulic ram, pressure-bladder fill, or what have-you) and latent heat is captured (it would likely be a closed-loop system), and the process begins again. 

The key is that CO2 is easier to compress to liquid form when it is colder (little energy). 

The temperature/pressure bands make this favourable to water/saline water systems. 

Thoughts/feedback/questions?   


Also, does any one know if the 'condensation induced water hammer' effect works with CO2?  There might be some clever way to use that to advantage as well if so. 

« Last Edit: 11/13/2011 03:29 AM by go4mars »
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Online A_M_Swallow

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Along this line, I was thinking about the use of areothermal power on mars by circulating water in a closed loop system then using the geysering effect to bring heat and energy the surface (taking power using hydraulic ram). 

But the challenges of insulating drill-pipe on earth make steaming oil reservoirs much below 500 meters uneconomic (implies technologically uncompetitive for now).  On Mars the added complications would be far worse.  Water freezes too easily. 

{snip}

You do not have to use water, alcohol freezes at −114 C, 159 K, -173 F and methanol at −98--97 C, 175-176 K, -144--143 F.

Offline douglas100

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The important thing is not the working fluid or the phase changes involved but the amount of heat available in the Martian crust. Until this is known it is impossible to say if useful power could be generated.
Douglas Clark

Offline kkattula

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Where's the math?

Unless you have some plausible numbers for the heat transfer, and the amount of mass required on Mars to produce a specific power level, it seems a bit pointless.

More than likely, solar cells and batteries (for night time) would produce more continuous kW per kg.

Offline grr

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Where's the math?

Unless you have some plausible numbers for the heat transfer, and the amount of mass required on Mars to produce a specific power level, it seems a bit pointless.

More than likely, solar cells and batteries (for night time) would produce more continuous kW per kg.

But solar cells can be denied access to the sunlight for months on end.
Basically, that is a real weakness of depending on a single source for energy.
If there is enough heat to do geo-thermal, then you have base energy.

Offline peter-b

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We do know that modern Mars exhibits very little or no vulcanism or tectonic activity, from which we can infer that geothermal heat will be much less accessible than on Earth. Deep core drilling rigs are extremely heavy and bulky equipment, and require complicated metallurgy that precludes their manufacture without significant pre-existent industrial infrastructure.

Warning: possibly off-topic stuff follows!

Since about 2007 I've been interested in the possible application of the Sabatier reaction as an energy storage method rather than for in-situ fuel manufacture. We know that it's possible to obtain H2O and CO2 on Mars, but that CO2 is significantly more abundant and easier to obtain than water. The hydrogen is very important to preserve as far as possible, but H2 is very difficult to store losslessly.

The concept is as follows. When solar energy is abundant (i.e. during the day / during the local summer), excess energy is used to electrolyse H2O.

2H20 ⇄ 2H2 + O2

The hydrogen is then used in a Sabatier reactor to generate methane.

2H2 + CO2 ⇄ CH4 + O2

The methane would be stored for use as an energy source when solar power is insufficient. The excess oxygen could be stored for use in life support systems or for fuelling purposes. Since both methane and oxygen are liquid at around the same temperature, they could easily be stored in a single cryogenic vessel, with oxygen boil-off used to maintain temperature.

As a practical note, the gaseous output from the Sabatier reactor would be very hot, so it should be passed through a heat exchanger to heat the input gases.

During nights / winters, a methane fuel cell would be used to burn the stored methane for power, producing water (to be stored) and CO2 (to be vented).

This arrangement would have many benefits: as well as providing an energy storage solution for the base, it could be used to recycle life support waste, and to produce fuel for vehicles (ground/air/space).

It could also be used in conjunction with a nuclear reactor instead of solar power. Nuclear reactors "like" to produce constant power, but base power needs would vary depending on the time of day or the operations taking place. Coupling a nuclear reactor with methane storage would permit even large variations in power consumption to be "smoothed out".
Research Scientist (Sensors), Sharp Laboratories of Europe, UK

Offline go4mars

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The important thing is not the working fluid or the phase changes involved but the amount of heat available in the Martian crust. Until this is known it is impossible to say if useful power could be generated.

CO2 is everywhere on Mars.  That's why it is important.  It's thermodynamic properties are also important, with respect to temp and pressure conditions on Mars.

There are some papers out there with rough calculations of geothermal gradient. 

As to deep drilling rigs, I'll try to comment on that one when I have more time.
« Last Edit: 11/16/2011 01:57 PM by go4mars »
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.

Offline douglas100

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I stand by my point. Theoretical estimates of the thermal gradient within the Martian crust are good and fine, but until it is actually measured this form of power generation is not a given.

If it turns out that there is sufficient energy available then the use of CO2 as a working fluid becomes an important consideration.
« Last Edit: 11/16/2011 08:13 AM by douglas100 »
Douglas Clark

Online kevin-rf

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What are you using as a drilling fluid and how will you get it to mars?
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Offline go4mars

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Air drilling like is used commonly in the San Juan basin.  No drill fluid per se.  This also avoids low temp clathrate formation and other problems historically associated with arctic drilling.  A colony effort ( or even a respectable effort for a large base) will assume a 10 m PLF and ability to land 50 tonnes at a time.  Given those constraints, there are a lot of places that already manufacture cheap 9 meter drill pipe sections.  Would probably need to run a batch at higher moly and vandy concentrations. A single pipe stand conventional air-drill rig should do the trick.  It's very well established tech that would need a few tweaks for Mars.  Build a tracked rig.  Tada. 

As to CO2, part of the reason to chose it is so you don't have to drill as deep based on it's thermodynamic properties.  The only place CO2 seems to stay solid on the surface is the poles in winter IIRC.  Living near the equator is much more likely for many reasons (seasonal light continuance being primary) so there isn't a risk of CO2 freezing in the well.  At the same time, CO2 can be easily compressed into a liquid at almost any temp (you can buy truck-loads of liquid CO2 for oil reservoir stimulation for cheap on earth for example).  At lower temps, it takes even less energy to compress (cold CO2 = almost all Martian air).  So it would be easy to fill your relatively shallow injection wellbore and reservoir with Liquid CO2.  Since CO2 is obviously a gas a nearly all temps on Mars (pressure is a big factor), when you open up the valve in the second reservoir, the CO2 (which only needed a modest temp boost from latent mars heat) will rapidly expand and surge to the surface.  The amount of additional heat energy absorbed will be the theoretical gain over the energy you used to compress it.  Heat exchangers can warm your big subterranean green-houses or ice-dome farms.  Excess mechanical energy from the geysering effect can provide electricity.
« Last Edit: 11/16/2011 01:55 PM by go4mars »
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.

Offline go4mars

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Theoretical estimates of the thermal gradient within the Martian crust are good and fine, but until it is actually measured this form of power generation is not a given.
On Mars, there is definitely latent heat and a geothermal gradient.  There wouldn't be volcanoes otherwise, and yes the dynamo stopped a long time ago, but part of that is due to lower gravity, part due to volume to surface area ratio (decay energy leaves the system faster, partly due to giant impact in early history, and perhaps partly due to rock chemistry (less radioactivity) when compared to Earth. 

Of course the exact nature of thermal gradient is unknown.  In this context, it's a question of reading the bottom-hole temperature from time to time to determine when to stop drilling. 

Revisiting the drill fluid issue: KISS suggests air drilling, but science suggests to keep continuous cores.  If coring is the secondary goal, liquid CO2 could once again be of use.  Circulate it down the wellbore and through bit jets to cool.  Much slower rate of penetration, but having deep wireline cores in a continous record might be worth it. 
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.

Offline go4mars

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Back to air-drilling:  Compressing the CO2 sufficiently for air drilling would make it a liquid.  It's expansion in the annulus would make this an even better choice than what we use (atmosphere) here on Earth. 

If any concerns arose from using CO2, like insurmountable pressure-related refrigeration effects, then argon could be stripped out of the atmosphere and used instead.
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.