The Challenges Of Carbon Capture & Storage

Challenges Of Carbon Capture
Rendering of a Carbon Engineering Direct Capture Plant. Credit: AAA.

Carbon capture and storage (or CCS for short), involves capturing carbon emissions and burying them underground. There are two points at which this can be done:

  1. At the power plant before the CO2 is released into the atmosphere, and
  2. Later after the CO2 has entered the atmosphere.

Capturing CO2 at the Power Plant:

Most carbon capture today is being conducted by the fossil fuel industry at the power plant.  They do it in order to extract oil from depleted wells.  The technology is called enhanced oil recovery or EOR for short.  CO2 is pumped into tapped out oil wells so that the sludge liquefies and can be pumped out and sold. That oil then goes into products like gas and diesel fuel that are burned and emit more CO2.  This is not helpful when you are trying to reduce emissions.

Another problem is that the oil wells are not secure storage sites because the ground is porous so the CO2 can seep out into the atmosphere again. It is a sham to call this green technology when all it is doing is enabling the oil industry to sell more product that will generate even more emissions.

Capturing CO2 from the Air:

Carbon capture from the air is still in the experimental stage.  A leading company in this industry is Carbon Engineering located in British Columbia.  It is developing a process to convert the captured CO2 into fuel.  This would eliminate the storage problem and would provide a source of revenue to fund their carbon capture operations.

There are also many other products that could be made using CO2, but unfortunately the amount of CO2 in the atmosphere which needs to be removed dwarfs the potential market for it.  This means that most captured CO2 will have to be stored underground, and since there is no profit in doing this, CCS will have to be funded by the government.

Steps in Carbon Capture and Storage from the Air:

Carbon Capture and Storage from the air is not a simple or inexpensive process, and it requires a lot of energy.  There are four steps: Capturing the CO2, liquefying it, shipping it, and storing it (assuming that it is not used to make products).

  1. Capture: Capturing CO2 from the air is very difficult because it is only present in a trace amount.  Today it is about four molecules out of every million molecules of air.  To capture it you have to move a lot of air across an “air contactor” (a large air filter) that contains a substance that will bind to the CO2 (called a sorbent). Because the CO2 concentration is so low, you have to draw a lot of air across the air contactor, and the sorbent must form a very strong bond to reach out and capture the rare CO2 molecules that cross the air contactor.

But then the CO2 must be separated from the sorbent so it can be recirculated through the air contactor. It takes energy to move the air across the air contactor, but it takes much more energy to heat the sorbent in order to break its bond with the CO2 molecule. If the energy required comes from fossil fuel plants, the process becomes very inefficient because you must subtract the additional emissions you produce from the amount of CO2 removed from the atmosphere in order to get the net amount of CO2 reduction.  This is why capturing CO2 from the air must be powered by a green energy source.  This competition for green energy will reduce the amount available to reduce the CO2 concentration in the atmosphere.

  1. Shipping: The storage site for the CO2 may not be near the capture site, so it will have to be liquified and transported to the storage site.  Both the liquification process and the transportation will require expending even more energy.
  2. Storage: The liquified CO2 will need to be pumped underground.  This requires more energy.

For CCS to be practical it will have to be powered by a clean energy source.

The Problem of Scale: 

The biggest challenge that CCS faces is the immense size of the task.  Since 1880, humans have poured an extra 1.6 trillion metric tons of CO2 into the atmosphere.

Every cubic meter of air has .75 grams of CO2.  In order to remove one metric ton of CO2 you would need to pull 1,300,000 cubic meters of air across the air contactor.

A typical 48” industrial fan with a 524 cubic meter per minute rating and operating 24 hours a day 7 days a week at 75% efficiency (an allowance for the extra energy to force the air through the sorbent) could pull 3.44 million cubic meters of air across the air contactor and remove 2.58 metric tons of CO2.

A CO2 removal plant with 1,000 of these fans could move 3.44 cubic kilometers of air in a year.  This plant could remove 2,580 metric tons of CO2 in a year.

If you had 5,000 of these plants scattered across the world, they could pull 1,720 cubic kilometers of air across the air contactors in a year and remove 12.9 million metric tons of CO2.

We need to remove one half of the trillion tons of CO2 we have put into the atmosphere.  That’s 500 billion metric tons.  At 12.9 million metric tons per year, these 5,000 plants would have to operate for 39,000 years to remove 500 billion tons of CO2.  If we developed a revolutionary technology that improved the efficiency by a factor of 100, the job could be done in a mere 390 years.

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The scale of the excess CO2 problem is orders of magnitude larger than our ability to remove any meaningful amount of it from the atmosphere in any reasonable timeframe. We will have to live with the CO2 we have already emitted.  The only thing we can do now is to reduce our emissions in hopes of mitigating the scope of the damage that is coming our way.  Perhaps the future will bring a solution, but it isn’t on anyone’s radar screen.