Can Carbon Engineering's Plants Remove Enough CO2 To Solve Global Warming?

I know they aren't claiming they can, but I've seen this hyped a lot and wanted to run the numbers to get an idea of how feasible it is.

Carbon Engineering's process

The only detailed overview for their process that I can find is here. This implies that capturing 1 ton of CO2 requires either 8.81 GJ of natural gas, or 5.25 GJ of natural gas + 366 kWh of electricity. To convert both of those to effective amounts of electricity, we can use the fact that ~8000 BTUs (~8.4 MJ) of natural gas yields 1 kWh of electricity. That the translates into either ~1050 kWh (8.1 GJ of gas) or ~991 kWh (5.25 GJ of gas + 366 kWh). Just call this 1000 kWh.

Summarizing that...the Carbon Engineering process requires ~1000 kWh to remove one ton of CO2 from the atmosphere.

How much carbon needs to be removed?

There are a bunch of ways we can approximate how much carbon needs to be removed. An obvious one is to remove enough to offset current emissions. We emit somewhere around 40 billion tons of CO2 per year, so we can use that as an estimate. We'd need to remove 40 billion tons of CO2 per year with the above process.

A second much would we need to remove to lower atmospheric CO2 to a safe level? Let's say 350 ppm is the safe level. We'd need to drop by roughly 60 ppm which would mean that in addition to offsetting the 40 billion tons we emit per year, we'd need to remove an additional 900 billion tons or so. Let's give ourselves 50 years to do it. That means an additional 18 billion tons per year.

Summarizing that...we need to remove between 40 and 60 billion tons of CO2 per year. I'll use 50 billion tons in the calculation below.

Is this feasible?

Using the two numbers above, the amount of electricity needed is:

(1000 kWh/ton) * (50x10^9 tons/year) = 50x10^12 kWh/year

We can compare this with total electricity production around the world. It's ~25,000 TWh/year (p 46). Converting our number from above, 50x10^12 kWh/year is 50,000 TWh/year. If all of the world's electricity production were used to capture carbon with this process, it would remove about half as much as we need. In other words, to remove enough CO2 from the atmosphere, we would need to triple our current electricity production and devote 2/3 of it to this without emitting any additional CO2. This seems very unlikely to me. This is also an ideal case where we bury all CO2 we capture instead of burning it as new fuel and magically emit no new CO2 in the process of producing this extra power, burying the CO2, etc.

Just for fun...imagine we produced all this extra power with solar. How much additional CO2 would that add? Utility scale PV solar results in ~50 g of CO2 emitted per kWh produced (table A.III.2). We need 50,000 TWh/year. This means it would emit ~2.5x10^15 g, or ~2.5 billion tons of additional CO2/year.

Let me know in the comments if I screwed up the math somewhere.

Image taken from 
LeJean Hardin and Jamie Paynederivative work: Jarl Arntzen (talk) -, CC BY-SA 3.0, Link

No comments:

Post a Comment