Carbon Capture Is Expensive Because Physics
Carbon capture and sequestration is expensive because it has three components, each with its own expensive challenges: capture, distribution, and sequestration. The mass of CO2 produced is 2-3 times the mass of coal or methane* burned and is more challenging per unit to ship than coal, so the cost of capture, distribution and sequestration is typically a multiple of the cost of doing the same with the coal or methane.
How expensive is it?
According to an organization which promotes carbon capture and sequestration, it will cost $120-$140 per ton of CO2. This will add from $168 to $196 to the cost of a MWh of coal generation. That’s 16.8 to 19.6 cents per KWh, which puts existing coal plants impossibly deep into unprofitable territory. Methane generation plants emit less CO2 per MWH, so would see 9.5 to about 11 cents per KWH added to their base cost, typically in the 5 to 7 cent range. Coal generation at 20 to 25 cents per KWH wholsale and methane generation at 15 to 18 cents per KWH wholesale wouldn’t be purchased by any utility.
How is Carbon Captured?
There are two general approaches to carbon capture, each of which have different challenges.
Carbon capture at source of emissions diverts exhaust emissions from coal and gas generation plants through a series of catalysts, sorbents and other technologies.
Coal plants in developed countries already have scrubbers for sulphur and filters for particulate matters. Retrofitting another step onto these two is another bolt-on.
Coal and methane generation flues originally were very simply designed, with the heat of the emissions overcoming gravity so that the fumes flowed upward and out. With each addition of filtration and scrubbing, that ability to void emissions with waste heat is reduced. Now electricity is used to operate fans that push the emissions through the various filtration points. That costs money, or rather is consider as auxiliary power load on the generation station, and every point of auxiliary power is money that they aren’t making.
Capturing CO2 typically uses sorbents, porous ceramic filters which capture the CO2 and let everything else through. They expect gases within a certain temperature range and set of components to operate effectively. Achieving these conditions may require cooling the emissions further or other processing. Both of these add costs.
Sorbents are effectively ceramic nano filters. Air must be forced through them. This requires larger fans and more electricity, once again increasing costs.
fotw519More CO2 is emitted than coal or gas is burned. CO2 is formed by a chemical reaction of the carbon in the fossil fuel with oxygen from the atmosphere. Oxygen has an atomic mass a hair under 16. Carbon has an atomic mass a hair over 12. Adding two heavier atoms to one lighter atom means that about 3.67 times the weight of carbon in the coal is emitted as CO2. Coal is about 51% carbon so the CO2 weights about 1.87 times the weight of coal. Burning methane (CH4) produces about 2.75 times the weight of CO2. What this means is that the mechanism for capturing and processing the CO2 is going to be potentially larger in scale than the mechanism for burning the coal and gas in the first place. The energy required to capture the very large amount of CO2 is non-trivial.
