Carbon Capture Suggestion

[mistermack]

2 hours ago, exchemist said:

On the density of seawater he seem to me to be substantially right. At 4000m depth it is typically 1.046: https://www.britannica.com/science/seawater/Density-of-seawater-and-pressure , due to the compression effect he referred to.   

This is from the UK's Open University on density : 

They clearly state a range from 1024 to 1028. 

And you've ignored, as he did, what I pointed out about compression due to pressure, and that is that as the water rises up the tube, it will expand as the pressure drops, and it's compression at any point will be identical to the water outside the tube, so the effect of compression for pumping purposes will be nil. 

That's an example of what I meant, when I said that he ignored specifics. The way is open to you to correct me, if that point is wrong, or to agree if it's right. But ignoring it is not great for a supposedly scientific debate. 

The people who ARE pumping water daily from the depths, at the experimental OTEC plant in Hawaii don't cite water density as a main problem. They don't even mention it. It's more a trade off between pumping velocity against heat gain in the pipes. Thinner pipes at higher velocity gain less heat but incur more friction. 

But they quote costs per unit generated at about 20c, which used to be much higher than fossil fuel costs, but after the latest rises, the gap must have closed quite a lot.  Although of course, they are now paying more for their own grid power too. 

I would like to see some sort of breakdown of their figures. Basically, how much electricity they generate, against how much they use for pumping. They say that they are feeding power into the grid, which doesn't seem very logical, if they are taking power from the grid for the pumps. But maybe there's an engineering reason for that.

They say that much bigger units are planned, so the economics can't be too awful. 

https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php   

Edited May 4, 2023 by mistermack

[exchemist]

26 minutes ago, mistermack said:

This is from the UK's Open University on density : 

They clearly state a range from 1024 to 1028. 

And you've ignored, as he did, what I pointed out about compression due to pressure, and that is that as the water rises up the tube, it will expand as the pressure drops, and it's compression at any point will be identical to the water outside the tube, so the effect of compression for pumping purposes will be nil. 

That's an example of what I meant, when I said that he ignored specifics. The way is open to you to correct me, if that point is wrong, or to agree if it's right. But ignoring it is not great for a supposedly scientific debate. 

The people who ARE pumping water daily from the depths, at the experimental OTEC plant in Hawaii don't cite water density as a main problem. They don't even mention it. It's more a trade off between pumping velocity against heat gain in the pipes. Thinner pipes at higher velocity gain less heat but incur more friction. 

But they quote costs per unit generated at about 20c, which used to be much higher than fossil fuel costs, but after the latest rises, the gap must have closed quite a lot.  Although of course, they are now paying more for their own grid power too. 

I would like to see some sort of breakdown of their figures. Basically, how much electricity they generate, against how much they use for pumping. They say that they are feeding power into the grid, which doesn't seem very logical, if they are taking power from the grid for the pumps. But maybe there's an engineering reason for that.

They say that much bigger units are planned, so the economics can't be too awful. 

https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php   

Yes, you must be right about the expansion, I think. I had difficulty seeing why that would have an effect. 

[mistermack]

If you remove the compression effect, then the relevant difference in density is just caused by the difference in temperature, from surface to ocean floor. (assuming equal salinity). The density of seawater at different temperatures is easily measured and widely known. 

"Seawater density increases from 1.0240 g/cm³ at 20°C to 1.0273 g/cm³ at 0°C at a constant salinity."        https://w3.ric.edu/faculty/PSCI103/Seawater/Seawater_notes.htm#:~:text=Seawater density increases from 1.0240,surface to bottom of ocean.     

Even if you ignore compression, and just do an evelope style calculation, the effect of greater density in the tube doesn't look like a game changer. 

If you take the figures from the Open University, of 1024 to 1028 range, then the average extra density in the tube is 2kg per m³  over the whole length of the tube. 

If you take a tube of 1 sq meter cross section, then 1 meter weighs 2kg more on average than the surrounding water. So for a tube 1,000 metres long, the extra weight of water in it when pumping  would be 2,000 kg. Or two metric tons. So your propeller would need to provide 2 tonnes of thrust, on top of what it takes to overcome friction, for a tube of that size.  A little bit less, using the 1.0273  figure above. 

While it's not insignificant, I don't think that's a game changer. It's obviously not for the Hawaii experiment. And as stated, that cold water can be used at the surface to generate electricity, maybe a significant proportion of what's needed to power the pump.    

[sethoflagos]

52 minutes ago, mistermack said:

While it's not insignificant, I don't think that's a game changer.

The game changer appears to be arbitrarily reducing the seawater flowrate by a factor of 10⁶ and moving the seawater intake from the abyssal plains to 3 parts of the way up the continental rise.

Are we done with the original thread?

 

[CharonY]

I think it should be acknowledged that artificial upwelling is at least technically feasible. The big unknown is whether it allows long-term carbon sequestration and whether that offsets all the negatives (including cost, energy consumption, release of CO2 due to upwelling of inorganic and organic carbon, temperature effects, local disruption of sedimentation and so on).

Research on that matters does indeed show rather low effectiveness even under optimal conditions for carbon capture. In one paper the biggest effect seems to be caused by cooling rather than biomass production in the ocean, eliminating even the benefits of the best case scenario:

Quote

When upwelling is stopped for whatever reasons, both surface temperatures and atmospheric CO₂ levels rise to levels even somewhat higher than in a world that had never engaged in artificial upwelling. This is because artificial upwelling is expected to further increase the imbalance of the planetary radiation budget. It may thereby limit the options for action of future generations.

See Oschlies et al. https://doi.org/10.1029/2009GL041961

As mentioned above, in many areas upwelling would cause a net release of CO2 (as are natural upwells).

[sethoflagos]

3 hours ago, CharonY said:

See Oschlies et al. https://doi.org/10.1029/2009GL041961

An interesting paper.

The technical feasibility and volumetric scale factor of the scenario is defined by the following:

Quote

 In areas that contain simulated pipes, water is transferred adiabatically from the grid box at the lower end of the pipe to the surface grid box at a rate of 1 cm/day. For a rough estimate of the required number of pipes, we use a manufacturer's estimate of 1 m diameter pipes pumping up 13 × 10³ m³/day [Kithil, 2006]. About one of such pipes would have to be deployed per square kilometer in order to achieve an areal-mean artificial upwelling rate of 1 cm/day. An artificial upwelling rate of 1 Sv (= 10⁶ m³/s) would then require about 7 million pipes.

 The Kithil reference was rather difficult to locate but I eventually found it here. 

Quote

A device to control sea surface temperature and effects on hurricane intensity

Philip W. Kithil, Atmocean, Inc., Santa Fe, NM

Of the known variables affecting hurricane intensity, sea surface temperature (SST) is perhaps the most controllable. A device has been prototyped which pumps 1 km deep ocean water to the surface to reduce the SST during hurricane season. The device can be disabled when not needed. Large numbers of these devices can be economically deployed in a region such as the Gulf of Mexico. The prototype device consists of a buoy, and a 1 meter diameter x 1000 meter long polyethylene tube and heavy rigid base with controllable valve. Upon deployment the heavy rigid base sinks and the tube fills with seawater entering through the open valve in the rigid base. Once deployed, the buoy provides pumping action from passing waves. On wave down-slopes the buoy allows the tube and heavy base to drop and the valve opens, capturing 1 km-deep seawater in the base. On wave up-slopes the valve closes, pumping the deep seawater toward the surface where it is ejected just below the buoy. Assuming one-meter wave height and five-second wave period, at 60% efficiency the device can pump approximately 13,000 cubic meters of cold seawater to the surface over 24 hours. One complete cycle would take about 140 minutes. Further assuming a temperature difference of 18 ⁰C between the surface and 1000 m and 25% conductive loss during each cycle, we predict the surface water can be cooled up to -6.75 ⁰C. extending outward and downward tens of meters from the buoy. Preliminary temperature data employing a smaller prototype (0.25 m diameter x 60 m length) were used to create a model predicting the ability to reduce hurricane intensity when devices are spaced 100 meters apart. Tethering adjacent devices would provide a "sea-anchor" effect to counteract movement from surface and sub-surface currents. A command can be sent to put the valve in an "open" state thereby disabling pumping by some or all devices, allowing precise control over SST.   Recorded presentation

Session 3B, Tropical Cyclone Intensity I
Monday, 24 April 2006, 1:30 PM-3:00 PM, Regency Grand BR 1-3

So the pumping principle is essentially that of a wave-powered shaduf (no disrespect - it's just a mental picture). 

Perhaps we should note that wave height and period given here are roughly in tune with a consistent 20 knot wind which implies installation in the 'roaring forties' for example..

[sethoflagos]

2 hours ago, sethoflagos said:

Assuming one-meter wave height and five-second wave period, at 60% efficiency the device can pump approximately 13,000 cubic meters of cold seawater to the surface over 24 hours.

Actually looking at this a little more closely, if the 1 metre diameter pipe (say 0.785 m² cross-section) were to oscillate the full one metre wave height (crest to trough I assume) and back every 5 seconds then 0.785 / 5 x 3600 x 24 = 13,572 m³/d at 100% efficiency doesn't it? So how does the quoted 13,000 m³/d amount to 60% efficient operation?

Now I'm a little suspicious.

The pipe is tracing a displacement ca. h = 0.5 sin (1.26 t) m       where 0.5 - wave height / 2, 1.26 = 2 x pi / wave period

Hence pipe velocity dh/dt = 0.628 cos (1.26 t) m/s

Pipe acceleration d²h/dt² = - 0.792 sin (1.26 t) m/s²

Mass of pipe contents ~ 0.785 x 1,025 x 1,000 = 804,625 kg

Maximum upward force exerted by buoy = 0.792 x 804,625 = 637,007 N = 64,954 kgf    neglecting friction

So the buoy must be capable of developing a lift of 64,954 kgf with >> 1 m displacement from the ocean surface. Clearly some displacement is required so let's take 0.1 m

Buoy cross-section >= 64,954 / 1,025 / 0.1 = 634 m²    hence buoy diameter >= 28.4 m

That's pretty big even by single buoy mooring standards but I guess it can't be ruled out as a concept. For a moment I thought we were looking at a supertanker hull.

Edited May 5, 2023 by sethoflagos

[sethoflagos]

PS: I was going to say something about whether polyethylene was up to handling the considerable tensile forces involved, but perhaps we can save that for later.

And for >>1m in the previous post please read <<1m. I really must get my eyes checked.

 

Edited May 5, 2023 by sethoflagos
Brevity

[mistermack]

One surpising fact that I've read, after starting this thread, is that human consumption of aquaculture products is now getting close to equal with wild-caught fish etc. https://www.fao.org/3/ca9229en/online/ca9229en.html#chapter-1_1

I did wonder what the Chinese and Norwegians etc were doing with the Krill that they were catching in the South Atlantic. The explanation seems to be that they are mainly using it as fish food. The trend is for more and more aquaculture, and smaller and smaller wild fish. I like mackerel, one of my favourites, but I won't buy small ones, but that seems to be all there is these days. I haven't seen a decent size mackerel on a supermarket slab for years.

I think we're heading for a time when wild fish will be very rare, and all you can buy will be farmed stuff. That's part of the reason that ocean fertilization appeals to me. It would take the pressure off wild stocks, and indeed, it would add to wild stocks, because the increased production would tend to migrate, whatever was not caught by onsite fisheries.

Maybe stationing the aquaculture in stategic spots in ocean deserts would have a beneficial effect. All of the waste products could slowly spread into non-productive seas, causing blooms. 

[Ken Fabian]

On 5/4/2023 at 12:01 PM, sethoflagos said:

One pumping method that may be worth considering is Gas Lift. By sparging compressed air perhaps 200 - 300 m below the top of the pipe via an array of nozzles, the density of the mixed fluid above is substantially reduced generating the pressure difference necessary for the desired flowrate. 

That would create suction below that level, so either rigid walls or else pumping the air in at the base.

11 hours ago, sethoflagos said:

PS: I was going to say something about whether polyethylene was up to handling the considerable tensile forces involved, but perhaps we can save that for later.

Yes, I'd had that thought - wind and wave pushing the surface installation, tides and currents at different depths pushing the pipe, would make a lot of tension. Interesting as a thought experiment - as a first look, to identify the issues.

@mistermack - good point about the density differences from compression being in balance with surrounds - the effective weight of the column would be less than my rough estimate.  I've learned things in this discussion.

Data on how much nutrient and plankton and subsequent fish stocks from ocean overturning may exist (or be derivable) in journals about marine science and provide some idea of how much deep water overturning for how much benefit and avoid the need for expensive experiments. Someone more interested in it and more optimistic about it than me would have to do that.  I expect - strongly suspect that is - the volumes will have to be extremely large - but am open to being shown incorrect.

Of course I still think it is a non-starter for marine fisheries enhancement as well as for carbon capture. It can still be worth putting some numbers to, if that can be done, to be sure.

 

.

 

[mistermack]

Is there any chilling effect when you reduce the pressure on a liquid? I've never heard of it, but you would think that there must be some, even if it's tiny. I'm not suggesting it would be a relevant amount, but I just wondered if there is any effect at all. ( I did have a quick google, but didn't see anything relevant )

[sethoflagos]

2 hours ago, Ken Fabian said:

That would create suction below that level, so either rigid walls or else pumping the air in at the base.

Introducing the air at the base would require much more compression, and since the expansion occurs overwhelmingly in the top couple of hundred metres, that's where the suction will be generated in any case. 

There are such animals as flexible submarine hoses (eg here), but these are highly complex composite builds that have other issues to address. I would have thought that rigid wall piping was mandatory whatever the pumping method. 

2 hours ago, Ken Fabian said:

Yes, I'd had that thought - wind and wave pushing the surface installation, tides and currents at different depths pushing the pipe, would make a lot of tension. Interesting as a thought experiment - as a first look, to identify the issues.

I'm not clear on what sort of flowrate we are supposed to be considering now. For the Mm³/s range, a somewhat buoyant cylindrical honeycomb structure a couple of km in diameter held in place by a suitable spread of anchor chains strikes me as potentially feasible. It could conceivably be constructed predominantly from a couple of km³ of reprocessed plastic waste which would be one approach to carbon sequestration.

Whether appropriate or not for the climate, as a technical challenge, this topic has some very interesting aspects. 

43 minutes ago, mistermack said:

Is there any chilling effect when you reduce the pressure on a liquid? I've never heard of it, but you would think that there must be some, even if it's tiny. I'm not suggesting it would be a relevant amount, but I just wondered if there is any effect at all. ( I did have a quick google, but didn't see anything relevant )

It's still performed some PdV work on its surroundings, so yes, there will be a corresponding if small adiabatic temperature drop. 

[Airbrush]

That sounds like a good idea for capturing carbon.  I had thought there could be a way to make desalinization economical enough that we can convert desert into lush rain forests to accelerate carbon capture.  But these natural methods seem too SLOW.  So, is there a way, after energy becomes dirt cheap thru fusion reactors, to simply build a large number of machines that can pull the carbon out of the air faster than nature can?  The only limit is energy and the materials to build carbon capture machines.

When you say "carbon capture" does that mean separating the CO2 into carbon and O2?  Or does it mean pulling CO2 out of the atmosphere and storing it under ground?  Will the day come when earth vegetation gets so accustomed to high CO2 in the air that when we finally, thru technology, pull huge amounts of CO2 out of the air, that plants will suffer because they had evolved and adapted to high CO2 atmosphere?

[TheVat]

20 minutes ago, Airbrush said:

after energy becomes dirt cheap thru fusion reactors,

It may help to read the thread.  Things moved on from the OP.  And if energy is dirt cheap and carbon neutral then the need for your suggested air extraction would seem less pressing.  As a practical matter, the air extraction systems I've seen all seem to be Drop in the Bucket solutions.  

27 minutes ago, Airbrush said:

When you say "carbon capture" does that mean

It's a general term for removing atmospheric co2 and keeping it in some relatively stable form, out of the airshed.

[mistermack]

Back to the original OP idea of fertilizing sterile desert ocean waters with nutrients from the ocean floor, it seems that Sperm Whales have been doing that for thousands of years. They dive very deep to the floor, hunting for squid, but they only poop at the surface, so they are constantly moving nutrients from the deep to the surface, as I was suggesting we should be doing. And according to the article, their poop nutrients hang around on the surface for very long periods, and cause algal blooms where there would otherwise be clear sterile ocean waters. 

So maybe by killing most of the deep diving whales, we've been causing the planet to warm somewhat, and by copying the whales by pumping up nutrients, we could do what they've been doing, causing algal blooms which could support a huge new fishery and fix some CO2 at the same time. 

Anyway, here's the link :  Caribbean island creates world’s first area for sperm whales – and their poop could save the planet (msn.com) 

Saving the planet is a bit overhyped, but it's an interesting story.