Published on January 19th, 2016 | by Michael Barnard76
Carbon Capture Is Expensive Because Physics
January 19th, 2016 by Michael Barnard
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 wholesale 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 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.
More 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.
Typically, sorbents are dropped into a hot liquid bath to release the captured CO2. Heating the water up requires energy, and heating water takes a lot of energy. There’s lots of waste heat in coal and gas plants because most of the energy from burning coal and gas is wasted as heat, so this isn’t as big a problem, but that heat has to be directed to the correct place in the right amounts. Once again, more duct work, more processing, more fans and more controls. More expense.
CO2 when captured is a gas. It’s very diffuse. In order to store it, it must be compressed or liquified. Compressing and liquifying via cooling are both highly energy-consuming processes. More expense.
CO2 must typically be stored onsite in preparation for shipping. Given that the weight of the CO2 is 1.87 time the weight of coal and that CO2 must be stored in compressed or liquified form, this requires very large pressure vessels or very large pressure and insulated vessels. By comparison, coal can be piled on the ground before use. This means that the effluent requires a much greater expense for storage and handing than the feedstock.
Air carbon capture ignores the source of carbon emissions, and like a plant works off of the ambient CO2 in the atmosphere, right now just over 400 parts per million. Air carbon capture avoids some of the issues, but adds others.
- By using air, concerns about temperature and contaminants causing inefficiencies in the sorbent are reduced substantially.
- 400 ppm is a much lower concentration of CO2 in the atmosphere than is found in coal or gas plant emissions. That means that a great deal more air must be forced through the sorbents and there is no ‘free’ auxiliary power to do this with, but must be purchased.
- Sorbents must still be put into heated liquid in order to release the CO2 and heating water is very expensive. That’s why Global Thermostat’s solution is to use waste industrial heat at sites which require CO2 as a feedstock, allowing the waste industrial heat to overcome one expense, and avoiding the distribution expense (to be explained later).
- CO2 must still be compressed or liquified.
- CO2 must still be stored in preparation for distribution or use.
How is CO2 Distributed?
As pointed out, CO2 produced by burning coal or methane is 1.87 times the mass of coal, 2.75 times the mass of methane, is a gas or a liquid and must be kept compressed or very cold. It is much more like methane than it is like coal. Distribution of it is much more challenging than coal.
While coal can be run in open hopper train cars, CO2 distributed by train requires pressure containers or pressure containers that are also maintained at a very low temperature. The total number of train cars required is much higher than the number of train cars which would deliver the coal, and this would be a substantially higher expense as a result. Coal is a cheap commodity and getting it from point A to point B is a large portion of its expense already, which is why many coal generation plants are built at coal mines.
When CO2 is distributed by pipeline, the pipeline has to deal with 2.75 times the mass of CO2 as of gas entering the facility, effectively requiring close to three times the infrastructure to remove the waste as the feedstock. Regardless of whether a coal or gas plant is considered, all of that pipeline must be built.
Very few CO2 pipelines exist in any country. Several do in the USA. They run mostly from geological formations which trapped CO2 over millions of years to enhanced oil recovery sites for the most part. More on that later. Extensive increases in capturing CO2 at source or from the air would require a very large network of new pipelines which would need to be constructed at great infrastructure expense.
Both trains and pipelines are businesses. They make money by moving commodities and goods through their networks from producers to consumers. Moving CO2 will cost more money than moving the coal or gas does, effectively doubling or tripling distribution costs for every coal and gas plant.
All of the above is why many places that require CO2 as an industrial feedstock use CO2 production facilities onsite instead of purchasing it. They burn gas or oil themselves to create the CO2 so that they don’t have to pay two to three times the cost to have it shipped to them.
CO2 is a commodity which is worth $17-$50 a ton. Coal ranges from about $40 to $140, depending on several factors although it has been in decline for a while. Methane is in the $2-$5 per million BTU range with about 35,000 BTU per cubic meter. Suffice it to say, coal and gas are worth more than CO2 as commodities, and the ratio of the expense of distribution to value of the commodity is very different, especially when you consider two to three times the mass needing to be distributed.
Coal and gas generation plants are placed close to population centers or coal beds, not close to places which require CO2 or where CO2 can be sequestered. Distribution is a very expensive component of the cost of CCS.
How is CO2 sequestered or used?
Especially if coal and methane continue to be burned for electricity, it is not enough to capture CO2, it must be stored securely for periods closer to how long the coal and methane were underground than to human lifetimes. The containment storage can’t leak significantly and must work passively. As CO2 is a gas in the range of temperatures in the atmosphere and below the surface of the earth, it by definition likes to leak.
By far the biggest consumption point for CO2 is enhanced oil recovery fields. CO2 is acidic. Pumping it into played out oil fields makes the remaining sludge flow more smoothly and increases pressures underground. This makes the oil flow toward the other end of the field where it can be pumped out.
In theory, the CO2 used in enhanced oil recovery remains underground, but in practice, it is being pumped into formations with dozens or even thousands of natural and man-created holes in the form of oil wells and natural faults. Enhanced oil recovery is not a sequestration technique, but a technique designed to get more carbon-based fuel out of the ground to be burned.
Enhanced oil recovery cannot be seriously considered as a sequestration technique if the CO2 merely leaks to the surface again and more carbon is extracted from fossil fuel beds and released into the atmosphere through burning. Significant amounts of effort have to be performed to keep the CO2 from leaking, and there is little value to the EOR operators in doing so, so it typically doesn’t get done.
Comparatively small amounts of CO2 are used by other industrial processes such as soft drinks, industrial scale greenhouses, some forms of cement, etc. There is no substantial market for CO2 which is not being met today, hence the reason why the commodity is cheap. About three-quarters of industrial CO2 is captured from underground concentrations of CO2, effectively like methane deposits. This CO2 is cheap compared to sequestering it after it is created, so captured CO2 has a higher cost base than mined CO2 and will not be competitive with it, especially without a carbon tax. As was already pointed out, the large majority of pipelines for CO2 are from mining points to major enhanced oil recovery sites, not from places it is created due to generation to industrial consumers.
Enhanced oil recovery used only 48 million metric tons of CO2 in 2008 in the USA, which would be the CO2 emissions from only 13 coal generation plants. The other consumers of CO2 are much smaller. In 2013, there were over 500 coal generation plants and over 1,700 methane generation plants in the USA alone. Capturing CO2 from all forms of coal and methane generation would swamp what market exists for CO2, collapsing its value and making it even less economically viable.
Other forms of sequestration have no fiscal value at all, but merely inject the CO2 into underground structures where it remains as a gas or bonds with other minerals underground to become calcium carbonate, a stable mineral. Injecting the CO2 requires large facilities, drilling, capping, pumping, monitoring etc. There is no revenue gained to offset this, so very little of this is done except as ‘pilots’, ‘test facilities’ and the like. While it has interesting challenges from an engineering perspective, it’s hard to imagine anyone with a good STEM background directly involved with it taking it seriously as a solution.
What does this all add up to?
Carbon capture and sequestration will never be economically viable compared to alternatives. The physical reality of the scale of CO2 production from generation requires a distribution infrastructure two to three times the scale of the existing fossil fuel distribution infrastructure and would result in electricity at four to five times the cost. Meanwhile, wind and solar generation are already directly cost competitive with and actually cheaper in many places than fossil fuel generation. This trend is clear. Fossil fuel generation without carbon capture and sequestration is trending to be or already is more expensive than renewable generation which emits no CO2 during operation and is getting cheaper.
Fossil fuels are nature’s form of carbon sequestration, and nature took millions of years of free and slow processes to do so. It’s not a rational choice for humanity to dig up the sequestered carbon, recapture it and resequester it at great expense when there are alternatives. Leaving the carbon that geological processes sequestered where it is is the rational choice.
* Natural gas is 89.5% to 92.5% methane which is a much more potent greenhouse gas than CO2 in the short term. When burned, by far the dominant use for it, it emits CO2 in significant amounts. Extraction, storage and distribution all have leaks from small to disastrous in scale and when used as intended it creates CO2. Calling it methane more accurately labels it and allows lay people to understand the implications of its use. Like ‘clean coal’, ‘natural gas’ has PR connotations which are undeserved.