Canada’s Carbon Capture Ambitions Have Hit A Roadblock

[Meredith Poor + 884]

Any time CO2 is stored under pressure in any volume that contains water, or is water, some fraction of the CO2 gets converted to methane over time. This has been the experience with CO2 injection in Louisiana salt formations, and occurs routinely in Lake Kivu in Africa. The addition of heat speeds this up but may or may not be a prerequisite. Usually this occurs because of microbial action, but it might also be geochemical. One microbe (archaea) in particular is Geobacter Sulfurreducens, but various 'methanogens' do this using different pathways.

This makes CO2/Methane a 'renewable' energy source, basically extracting the energy geothermally or geochemically.

[Rob Plant + 2,635]

On 9/5/2023 at 6:29 PM, Meredith Poor said:

This makes CO2/Methane a 'renewable' energy source, basically extracting the energy geothermally or geochemically.

Technically youre right it does, but there are much more economic forms of renewables, so its a moot point.

[Meredith Poor + 884]

6 hours ago, Rob Plant said:

Technically youre right it does, but there are much more economic forms of renewables, so its a moot point.

If one is injecting the CO2 to get methane, you are correct it most likely isn't viable. If the CO2 injection is simply to sequester the gas, then it is necessary to deal with this possible side effect.

[Rob Plant + 2,635]

My question on Co2 is this, if its so bad and we need to capture it (which im not convinced it is) then why are we trying to sequester it with CCS? Why not use the Co2 to power supercritical Co2 turbines to create more powergen??

https://energy.wisc.edu/industry/technology-highlights/supercritical-co2-gas-turbines

https://www.ansaldoenergia.com/offering/equipment/turbomachinery/co2-turbines

These are made by major players like Siemens, Toshiba, Ansaldo to name a few.

Can someone explain to me why every coal or gas station doesnt capture the Co2 and have a bolt on Co2 turbine in a plant next door to the steam or gas turbine hall?

ETCC plants do this but they're few and far between.

https://www.ansaldoenergia.com/offering/solutions-for-the-transition/energy-storage/energy-transition-combined-cycle

Is it cost prohibitive??? 

Maybe @turbguy is best placed to answer this???

Edited September 12, 2023 by Rob Plant

[turbguy + 1,405]

17 hours ago, Rob Plant said:

My question on Co2 is this, if its so bad and we need to capture it (which im not convinced it is) then why are we trying to sequester it with CCS? Why not use the Co2 to power supercritical Co2 turbines to create more powergen??

https://energy.wisc.edu/industry/technology-highlights/supercritical-co2-gas-turbines

https://www.ansaldoenergia.com/offering/equipment/turbomachinery/co2-turbines

These are made by major players like Siemens, Toshiba, Ansaldo to name a few.

Can someone explain to me why every coal or gas station doesnt capture the Co2 and have a bolt on Co2 turbine in a plant next door to the steam or gas turbine hall?

ETCC plants do this but they're few and far between.

https://www.ansaldoenergia.com/offering/solutions-for-the-transition/energy-storage/energy-transition-combined-cycle

Is it cost prohibitive??? 

Maybe @turbguy is best placed to answer this???

The quantity of "working fluid" used in these CO2 cycles is limited (with a quite small make-up CO2 flow for inevitable leakage from at least the shaft seals, unless they use a separate generator hermetically sealed with the CO2 Turbine and Compressor) but we will ignore that issue.

So the amount of CO2 required is limited, say to about 20 tons (actually a wild-ass guess on my part) for a reasonably sized CO2 turbine capable of absorbing the available waste heat from a reasonably sized CT.   Once that captured CO2 quantity is reached and stored for use in the cycle, that's the end of the storage capability of the unit, and the rest, resulting from wherever the unit sources CO2 from, must then be disposed of.

20 tons of pure CO2 at 60 degrees F at atmospheric pressure will require about 350,000 cubic feet of spherical "dome", or about a half spherical dome of at least 900 feet in diameter.   It would be smaller if my "wild-ass guess" is too large.

That said, there are some attractive thermodynamic advantages to a supercritical CO2 cycle.  And the fluid used is fairly benign. Pure water used in a steam Rankin cycle is NOT benign.

As for capital cost, I would expect it to be on-par with a steam bottoming cycle once the turbomachinery becomes "mature" (except for that dome).

Edited September 13, 2023 by turbguy

[turbguy + 1,405]

18 hours ago, Rob Plant said:

\

Can someone explain to me why every coal or gas station doesn't capture the Co2 and have a bolt on Co2 turbine in a plant next door to the steam or gas turbine hall

 

The waste heat available from a condensing steam turbine exhaust is at too low a temperature (say, only 100 degrees F for a really bad condensing steam turbine with relativity warm cooling water, typically it's even cooler)  for capture in a supercritical CO2 cycle.  There's a LOT of heat rejected in a steam Rankin cycle, but it's "low quality" heat.  I don;t want to get into the messy discussions of enthalpy and Mollier diagrams, but the non-condensing portions of a Steam Turbine can be about 90% efficient.  Same for a CO2 turbine, but the "condensing" part wastes less heat that a steam turbine, due to the different properties of CO2 vs H2O.

With a CT (Brandon cycle),the waste heat is the CT exhaust, which can easily reach about 800 (+/-) degrees F.   Now you're cookin'!

Hope that helps?

Edited September 13, 2023 by turbguy

[Rob Plant + 2,635]

6 hours ago, turbguy said:

The waste heat available from a condensing steam turbine exhaust is at too low a temperature (say, only 100 degrees F for a really bad condensing steam turbine with relativity warm cooling water, typically it's even cooler)  for capture in a supercritical CO2 cycle.  There's a LOT of heat rejected in a steam Rankin cycle, but it's "low quality" heat.  I don;t want to get into the messy discussions of enthalpy and Mollier diagrams, but the non-condensing portions of a Steam Turbine can be about 90% efficient.  Same for a CO2 turbine, but the "condensing" part wastes less heat that a steam turbine, due to the different properties of CO2 vs H2O.

With a CT (Brandon cycle),the waste heat is the CT exhaust, which can easily reach about 800 (+/-) degrees F.   Now you're cookin'!

Hope that helps?

Thanks Turbguy, knew you were the man to ask!

[footeab@yahoo.com + 2,135]

On 9/12/2023 at 7:08 PM, turbguy said:

The waste heat available from a condensing steam turbine exhaust is at too low a temperature (say, only 100 degrees F for a really bad condensing steam turbine with relativity warm cooling water, typically it's even cooler)  for capture in a supercritical CO2 cycle.  There's a LOT of heat rejected in a steam Rankin cycle, but it's "low quality" heat.  I don;t want to get into the messy discussions of enthalpy and Mollier diagrams, but the non-condensing portions of a Steam Turbine can be about 90% efficient.  Same for a CO2 turbine, but the "condensing" part wastes less heat that a steam turbine, due to the different properties of CO2 vs H2O.

With a CT (Brandon cycle),the waste heat is the CT exhaust, which can easily reach about 800 (+/-) degrees F.   Now you're cookin'!

Hope that helps?

Blatant NO. 

CO2 has higher efficiency due to the simple fact you can use higher temperatures at lower pressures allowing even HIGHER temperatures. 

H2O steam turbines are limited by their PRESSURES not their temperatures. 

Efficiency is driven by Delta T(Thot-Tcold).  CO2 has a HIGHER condensing temperature than H2O making it LESS efficient if one limits yourself to same Thot as the deltaT if equal to that of a steam turbine is less.

Economically speaking CO2 is FAR MORE viable as it allows 3 HUGE major things with one critical drawback other than the obvious seals issue which which in part is tied up with its MAJOR issue.

#1 Since CO2 steam turbine is NOT limited by its pressures, it therefore becomes limited by temperature just as the case with an Brayton open cycle Gas Turbine increasing the Thot FAR HIGHER than the increase in Tcold.  Main reason coal power plants are not operating at 60+% efficiency like their NG counterparts.

#2 Due to Power density of CO2 working fluid, CO2 allows smaller HOT turbine blades for same power output making them FAR cheaper to make and more importantly, last much longer if one so desires as creep/wear are the critical problems.  Or you can go for more power and less life. 

#3 CO2 condensor allows it to be built MUCH cheaper(AKA SMALLER) due to its higher final condensing stage temperature and ease of pulling the heat out to ambient sinks and become 100% condensed without incurring droplet formation inducing wear on the turbine blades whereas the H2O requires some inputted work to become 100% condensed.  To do this with H2O you have to take the condensor as close to a vacuum as one can get in a closed cycle system and it still does not achieve it.  Likewise the quality(temperature) of the waste heat from a 100% condensed CO2 final stage turbine is FAR closer to useful for say garment industry etc and technically you could still use a different working fluid for the last stage and obtain a better Tcold temp differential instead of CO2.  Instead of gargantuan cooling ponds and evaporating gobs of water, one can now use ambient air. 

### There is one Major major disadvantage.  When Admiral Murphy shows up, and he ALWAYS does, H20 while dangerous when hot, is NOT a danger to the surroundings where humans live/work.  CO2 when its pressure vessels fail due to Admiral Murphy, kills everything around it by asphyxiation and in a large power turbine there is an ENORMOUS quantity of it.  To stop from killing everyone in the vicinity, one would have to build a nuclear poweresque pressure dome over the working turbines. 

Why most likely one will NEVER see CO2 turbines on a ship for instance...  On land we will see them, it is only a matter of time.   But probably not in yours or my lifetime as the main reason for them would be for the Coal or Nuclear power industry and not the NG industry and with the gargantuan amount of DIRT CHEAP NG for the entire world for next several hundred/thousand years... yea this will not happen as NG and CO2 turbines would not be beneficial. 

School is hereby at recess