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Comment by pfdietz | Hacker News Reader

I wonder if it would be possible to economically separate and store the CO2 from methanol combustion (on the ship), then deliver it back to a methanol production facility. Alternately, this could enable use of a fossil fuel, with the CO2 delivered to a facility for sequestration, or perhaps even pumped into deep water during an ocean crossing.

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Comments like this make be curious how many people understand the carbon cycle and it's relationship to global warming. CO2 isn't just a byproduct of combustion like sulfur or the particles in smoke, it's an essential part of the chemical release of energy that drives our society.

Plants take in sunlight (energy) + co2 + h2o, and chemically use the energy to break down the co2 and h2o in to complex hydrocarbons they use build their structure and store energy and release o2.

When you add o2 back to the hydrocarbons through combustion, you undo the process getting energy + co2 + h2o.

Hydrocarbons, from table sugar to crude oil, are really just solar batteries. They store energy captured by the sun, and then release this when combined with oxygen.

But as you can see co2 is a necessary part of the process and you cannot simply undo the process without taking more energy than you got in the first place (since nothing is 100% efficient). This is why "carbon capture" is a fundamentally tricky problem. In order for it to be successful you need more energy than you started with, and clearly cannot get that energy from fossil fuels (even indirectly) or you ultimately make the problem worse.

Taking your comment, it sounds like mechanical / industrial scale carbon capture is only viable if we have large amounts of cheap and renewable energy. That won't happen anytime soon either, any excess is bought up by datacenters, hydrogen production (which is used like a cheap electricity sink), or storage (batteries, water pumped up into a lake, etc).

But yeah, carbon emissions won't be solved until renewable energy production out-competes emitting energy production by a significant margin, and even then it will take a while due to market forces.

Carbon capture from combustion rather than from the air seems more practical, hence the suggestion to do that on the ship. Allam cycle systems have an overall efficiency similar to combined cycle systems (around 60% LHV) and deliver the CO2 of combustion in separated, compressed, liquefied form.

https://en.wikipedia.org/wiki/Allam_power_cycle

You can capture CO2 while still getting net energy out of the process, as long as you don't turn it back into (the same) hydrocarbons. The tricky part of carbon capture is not the capturing, but storing it in a way that ensures that it won't be released into the atmosphere anytime soon.

Is anyone (and certainly anyone with any power) actually having to be reminded of conservation of energy?

Co2 dissolved in water makes it acid, which is bad for plenty of sea life

Yes, but the deep ocean is where almost all the CO2 we've released is going to end up, eventually. This is just accelerating that process.

Why you might not want to accelerate that:

> Effects of Ocean Acidification on Marine Phytoplankton

https://cmi.princeton.edu/annual-meetings/annual-reports/yea...

> Regime shifts and ecological catastrophes in a model of plankton-oxygen dynamics under the climate change

https://pubmed.ncbi.nlm.nih.gov/28456463/

You're not going to see phytoplankton 15,000 feet deep. Not living ones, anyway.

Maybe I misunderstand the situation, but not all ocean acidification happens at great depths, does it?

This was about deliberate injection of CO2 into the deep ocean.

I don’t think fish like CO2. It makes the water more acidic.

The deep ocean is naturally acidic due to the natural carbon pump. Because of this, below a certain depth (typically around 15,000 feet), calcite and aragonite just dissolve (the "carbonate compensation depth") and there is no accumulation in the ooze. The carbon pump involves dead organic matter falling to depth, where it is consumed and oxidized, producing CO2 there.

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