4 ms·

I’m curious, what is currently the most promising carbon capture methodology that’s actually scalable? Already in use or ready to use, so we can exclude researc

by RayVR 5y ago

I’m curious, what is currently the most promising carbon capture methodology that’s actually scalable? Already in use or ready to use, so we can exclude research projects with no path to mega-scale

chris_va 5y ago
There are only a few that are truly scalable and plausible. A lot of investment today is going into the low hanging fruit (afforestation, methane capture, etc). These are cheap (<$15/ton), but they cap out at a couple of Gt-CO2/yr equivalent. BECCS isn't really scalable past a certain point, either, which leaves direct air capture and enhanced weathering. Enhanced weathering is basically moving around alkalinity, which the CO2+water (carbonates) will neutralize. There are other ways of doing this besides dumping olivine rock into the sea (which gives you a very large surface area to absorb co2), though dumping rock is very inexpensive (probably less than $20/ton, modulo grind size and bio toxicity issues). If humans disappeared today, the CO2 would revert back to pre-industrial levels predominantly through the ocean. The ocean is a large sponge for CO2, and it will stay in equilibrium with the atmosphere. As it turns over (~5000 years), it brings the extra CO2 down to depth, where it reacts with sediment. Extra CO2 will initially raise the carbonate compensation depth, reacting slopes of marine snow with the extra CO2 (kind of like snow melting) fairly quickly (on a geologic timescale). If/when that is exhausted, the ocean floor (which in places is covered with basalt and other material that will neutralize CO2) will (very very) slowly eat the rest of the CO2. As the carbonates drop in the ocean, the ocean will start to absorb more CO2 from the atmosphere. The ppm will drop slowly, until it hits the biosphere equilibrium (marine cycle, etc) of ~280ppm. One scalable way (personal disclaimer, one of my research areas) to do carbon capture is to just speed up this process. There is no reason CO2 has to react with basalt, it can just as easily react with NaOH or some other source of alkalinity, which can be minutes instead of millennia. In fact, some direct air capture proposals (long ago) were just waterfalls of fine droplets with NaOH embedded as a sorbent. So, long story short, if you can create alkalinity, you can easily turn that into sequestered CO2. Literally throwing an antacid tablet into the ocean sequesters CO2. Depending on the method of creation (e.g. chloralkali process), you may also have to dispose of an equal amount of acid, but that can be injected underground (e.g. poured out onto a bunch of olivine). Doing it all on land is a little trickier, as the ocean has some nice surface area and mixing ... but a large pond with a vertical firehose of high PH solution may be effective, though it starts to bleed over into the definition of DAC at some point and eats more power.

by RayVR 5y ago

chris_va 5y ago

There are only a few that are truly scalable and plausible. A lot of investment today is going into the low hanging fruit (afforestation, methane capture, etc). These are cheap (<$15/ton), but they cap out at a couple of Gt-CO2/yr equivalent. BECCS isn't really scalable past a certain point, either, which leaves direct air capture and enhanced weathering. Enhanced weathering is basically moving around alkalinity, which the CO2+water (carbonates) will neutralize. There are other ways of doing this besides dumping olivine rock into the sea (which gives you a very large surface area to absorb co2), though dumping rock is very inexpensive (probably less than $20/ton, modulo grind size and bio toxicity issues). If humans disappeared today, the CO2 would revert back to pre-industrial levels predominantly through the ocean. The ocean is a large sponge for CO2, and it will stay in equilibrium with the atmosphere. As it turns over (~5000 years), it brings the extra CO2 down to depth, where it reacts with sediment. Extra CO2 will initially raise the carbonate compensation depth, reacting slopes of marine snow with the extra CO2 (kind of like snow melting) fairly quickly (on a geologic timescale). If/when that is exhausted, the ocean floor (which in places is covered with basalt and other material that will neutralize CO2) will (very very) slowly eat the rest of the CO2. As the carbonates drop in the ocean, the ocean will start to absorb more CO2 from the atmosphere. The ppm will drop slowly, until it hits the biosphere equilibrium (marine cycle, etc) of ~280ppm. One scalable way (personal disclaimer, one of my research areas) to do carbon capture is to just speed up this process. There is no reason CO2 has to react with basalt, it can just as easily react with NaOH or some other source of alkalinity, which can be minutes instead of millennia. In fact, some direct air capture proposals (long ago) were just waterfalls of fine droplets with NaOH embedded as a sorbent. So, long story short, if you can create alkalinity, you can easily turn that into sequestered CO2. Literally throwing an antacid tablet into the ocean sequesters CO2. Depending on the method of creation (e.g. chloralkali process), you may also have to dispose of an equal amount of acid, but that can be injected underground (e.g. poured out onto a bunch of olivine). Doing it all on land is a little trickier, as the ocean has some nice surface area and mixing ... but a large pond with a vertical firehose of high PH solution may be effective, though it starts to bleed over into the definition of DAC at some point and eats more power.