Image: A coal power plant. Credit: VileGecko (CC-BY SA 3.0).
Capturing CO2 from the smokestacks of power stations with the intention of storing it in underground reservoirs, oceans, rocks, consumer products, chemicals or fuels has gained a lot of credibility recently. Many experts believe that we will burn the world’s remaining fossil fuels anyway, and we should therefore try to lower the impact if we are to prevent a catastrophic climate change. Yet capturing, transporting and storing carbon dioxide raises energy consumption considerably and brings with it serious health and environmental problems. The benefits, on the other hand, are shadowed in doubt.
Capturing technology raises the energy consumption of a coal plant by an average of 32 percent
Earlier this month leading science and energy institutes advocated strongly for the development of carbon capture and storage technology. The science academies of the world’s 13 major economic powers called the implementation of carbon sequestration a “top priority”. Around the same time, the International Energy Association (IEA) argued for an energy technology revolution, of which carbon capture and storage forms a vital component. Meanwhile, many spin-offs and start-ups are presenting all kinds of “innovative” ideas that seem to differ substantially from the traditional approach of storing CO2 in underground reservoirs.
The idea of carbon capture and storage (CCS) – first introduced in the 1970s - is attractive at first sight. To begin with, it is a natural occurrence. There are many natural reservoirs of CO2, which have kept this gas contained for many millions of years.
Secondly, the potential for storage is significant. The available storage space in underground reservoirs (depleted oil and gas reserves, coal formations and especially saline formations) is probably large enough to store all the carbon dioxide still contained in earth’s remaining fossil fuel reserves. It will take more research to find out which reservoirs are suited to this and which ones are not, but finding the actual storage space does not seem to be a fundamental obstacle. To add to this, the technology for capture, transport and storage of CO2 is available.
Technology is available
Capturing CO2 from smokestacks has been a common practice for many years, for the purification of natural gas or at ammonia production facilities for instance. Injection and storage of carbon dioxide is already happening in the North Sea, in Algeria and in Texas. In these cases, CO2 is injected into oil and gas reservoirs in order to extract more fossil fuels than would otherwise be possible, a process called Enhanced Oil Recovery (EOR). For some of these applications, carbon dioxide is transported by pipeline or by ship.
A complete CCS infrastructure has not been demonstrated yet (all CO2 used for enhanced oil recovery is commercially produced or originates from other sources than power plants, and present capture techniques do not capture CO2 for storage but emit the gas in the atmosphere). Yet, since all the individual parts exist, this does not seem to be an obstacle either.
The problem at hand is that the process of capturing, transporting and storing carbon dioxide requires a vast amount of energy. If this energy were to be derived directly from fossil fuels the benefits of the CO2-savings by capture and storage will be offset by the very same energy intensive process. If the energy were to come from renewable sources the technology is rendered unnecessary as it would be much more efficient to generate electricity directly from the renewable source.
Capturing CO2 from smokestacks is the most energy-intensive part of the process. According to the International Panel of Climate Change (IPCC), which devoted a comprehensive study on the technology 3 years ago, capturing technology (including compression for further transport and storage) raises the energy consumption of a coal plant by an average of 32 percent.
A coal plant equipped with CO2-capture technology would thus need 32 percent more coal and other resources like water, chemicals and reagents to produce the same amount of electricity than the same power plant without this technology. Carbon capture technology forms a symbiosis with coal as a fuel (“clean coal”), since burning coal emits twice as much greenhouse gasses than burning gas. Capturing CO2 from a gas power plant requires less energy but is of not much use.
This 32 percent does not include the energy needed to mine, process and transport the many thousands of tonnes of extra coal, and it does not include the energy needed for the construction of the capture, transportation, storing and monitoring infrastructure either.
It is insufficient to simply place the smokestacks of a coal plant upside down as suitable underground reservoirs do not necessarily lie beneath the world’s power stations. A carbon capture and storage infrastructure requires a transport infrastructure consisting of pipelines (and tankers) that rivals the existing oil and gas network.
Manufacturing and installing these thousands of kilometres of stainless steel pipes will require a substantial amount of energy. Also, the transport by ship or pipeline itself requires energy, and so does the injection of the CO2 in underground reservoirs and the monitoring of the whole transport network (today’s pipelines are patrolled by plane every two weeks). Everything taken together, CCS will probably raise energy consumption by as much as 50 percent (this is an estimate as to my knowledge nobody seems to have investigated this yet). Even if all of the CO2 is eventually stored, a 50 percent increase in energy consumption is the last thing that the world needs.
In addition, it is impossible to store all of the carbon dioxide. Capturing technology can only capture 80 to 90 percent of CO2 from smokestacks. Taking into account an additional energy use of 50 percent this comes down to a reduction in CO2 emissions of only 70 to 85 percent compared to a coal plant without carbon capture technology (and only if all emissions coming from the additional energy use are captured as well).
Carbon capture and storage requires a transport infrastructure that rivals the existing oil and gas pipeline network.
There are losses during transport, too. According to the IPCC these are 1 to 2 percent per 1,000 kilometres of pipeline transport and 3 to 4 percent per 1,000 kilometres of ship transport (the ship’s fuel use included). Carbon dioxide is also not the only harmful effect of power generation. Burning coal brings with it serious air pollution and produces waste, both of which will also rise by at least 30 percent. The same goes for the ecological damage of coal mining, which is devastating. Storing the CO2 can never prevent this.
Because of all these disadvantages, researchers and entrepreneurs try to invent all kinds of other ways to keep carbon dioxide out of the atmosphere, like storing CO2 in consumer products, converting it to fuel or fixing it in rocks. Yet until now, all these proposals face – at best – a similar energy penalty.
That is mostly because the first step of the process is always the same: capturing CO2 from the smokestacks of a coal plant will raise fuel consumption by about 30 percent. The only alternative to this capture technology – sucking carbon dioxide out of ambient air by means of “artificial trees”– consumes even more energy because the concentration of CO2 in ambient air is much lower than the concentration of CO2 in smokestacks.
Turning CO2 in plastics
Besides, the storage potential of most of these alternative proposals is very limited compared to that of the traditional CCS-concept. A strategy that is getting a lot of attention these days is to store CO2 into consumer products based on polymers like plastic bottles or DVD’s, or in chemicals like those used in fertilizers, refrigeration or food packaging.
The idea is that it is better to do “something useful” with captured CO2 instead of just storing it underground. However, even though the amount of chemicals and plastics we produce is enormous, as a carbon sink they are all but meaningless.
If all polycarbonates and polyurethane would be produced by means of CO2 this would only store the emissions of 3 coal power plants.
According to the IPCC, producing all polycarbonates and polyurethane by means of carbon dioxide would store 3.3 million tons of CO2 – comparable to the annual emissions of just 3 coal power plants. China is building one coal plant per week (in large part to produce cheap goods for us to buy) and there are more than 100 coal plants on the drawing board in the US.
What makes this approach even more useless is that these consumer products and chemicals have a relatively short lifespan, from a few months for fertilizers to a few decades for plastic products. When the fertilizers are used, or when the DVD’s end up in the incinerator, the CO2 goes back into the atmosphere.
Using CO2 as a feeding stock for algae and then turning it into biofuel - another idea that is hyped these days - faces the same problem. It only delays CO2-emissions for a very short time. The carbon dioxide is converted into fuel which is subsequently burned in a car engine. It is impossible to capture CO2 from car engines since the gas is too heavy (your car would gain serious weight while driving, and it would have to pull a trailer to store the large volume of carbon dioxide).
One could argue that at least the CO2 is recycled and that we are using the by-product of electricity generation to make fuel – which means that we don’t have to dig up more fossil fuels to make gasoline. However, this argument does not take into account the fact that much energy (and water) is lost in the conversion process.
Firstly, there is again the energy penalty of CO2 capture from the smokestacks, on average 30 percent. Next, you have to build a huge infrastructure to produce algae (since their energy efficiency is 100 times smaller than that of solar panels) and furthermore there is the energy that gets lost during the process of turning algae to fuel. If there is net energy gain in the end, it will be small.
Turning CO2 into algae could be an interesting strategy if we bury the algae instead of burning them in our car engines. However, that’s not on anyone’s mind.
Turning CO2 into algae could be an interesting strategy to reduce CO2-emissions if we store the algae underground instead of burning them in our car engines (thus avoiding the energy-intensive process of converting them into fuel). However, that’s not on anyone’s mind.
Fixing CO2 in rocks
The only alternative approach that really could store a significant amount of CO2 is mineral carbonation: fixing carbon dioxide in rocks (limestone). This method is also based on a natural process. Under the influence of weathering, the surface of rocks combines with carbon dioxide. Earth has no shortage of rocks, so the potential of this method is large enough to store all possible future CO2-emissions.
But if we want the strategy to be useful for us, this natural chemical reaction has to be accelerated considerably and that is again a very energy-intensive process (rocks have to be crushed to powder in order to provide more rock surface, and then treated with chemicals and heated). According to the IPCC this method would raise energy consumption by 60 to 180 percent.
Capturing carbon dioxide in rocks would also require a mining and transport infrastructure that is comparable (and which would supplement) today’s coal industry. To fix a tonne of CO2, you need 1.6 to 3.7 tonnes of rock. These rocks have to be mined and transported to coal plants (some industrial wastes and mining tailings can also be used, for example fuel ash from coal plants or de-inking ash from the paper industry, but their total amounts are way too small to substantially reduce CO2-emissions). The process also generates large amounts of waste materials (apart from the carbonised rocks themselves). For every tonne of carbon dioxide stored in rock, you are left with 2.6 to 4.7 tonnes of disposable materials.
Atomic waste, meet your rival
Carbon capture technology is expected to become more energy-efficient in the future. But that would hardly make the whole scheme more attractive. Storing carbon dioxide in underground reservoirs (the only realistic option) is risky, not unlike the storing of atomic waste.
CO2 can escape. High concentrations of the gas are lethal to plants, animals and humans. Eventually the gas thins in the atmosphere but during escape concentrations can build up fast, especially since CO2 is denser than air. At concentrations above 2 percent in ambient air, carbon dioxide has a strong effect on respiration (the normal concentration in fresh air is 0.033 percent). At concentrations from 7 to 10 percent, it kills.
If CO2 escapes from storage reservoirs, the whole energy-intensive operation of capturing, transporting and storing it was all for nothing.
Small impurities in the gas make it lethal at even lower concentrations. Similar amounts in the soil kill vegetation and make groundwater unsuitable for drinking or irrigation. And of course, if CO2 escapes from storage reservoirs, the whole operation of capturing, transporting and storing it was all for nothing. The result is a considerable rise in emissions, because of the energy penalty involved (the energy use of the whole process can go down, but it will never come close to zero).
Storing CO2 in essence resembles storing a gas in a stone pot. When an underground reservoir is filled up, all injection wells are closed by a cement “cork”. This cork has to keep the gas inside for thousands of years. Now zoom out and you are looking at a planet with thousands of holes, each one sealed with a cork to keep inside a potentially deadly (and climate warming) gas. Reassuring, no? Yet, this is considered a high-tech solution. You also have a network of thousands of kilometres of pipelines, transporting the same gas and connecting power plants with these reservoirs.
How big is the chance that leaks or sudden bursts will cause damage? According to the IPCC, the risk is low, at least if all pipelines and storage sites are monitored closely. Leaks will occur, they also occur through cracks in natural CO2-reservoirs (sometimes killing vegetation, animals and people), but if watched closely (by means of sensors and computers) they could be stopped in time. Earthquakes or accidental drilling operations in a former storage site could release large clouds of the gas in a short time, but that should be prevented by using carefully chosen locations and painstaking indexing of storage sites.
All these risks might be manageable in the short term, but storing CO2 is – just like storing atomic waste – a very irresponsible thing to do in respect to future generations. Will people in 2178 still know where CO2 was stored? Will the corks hold until that date? Risk analysis does not seem to look too far ahead. Carbon capture will also bury a part of our oxygen supply, by the way. After all, we would not only store the C but also the O2. Oxygen is abundant in the atmosphere compared to carbon, so this might not be a big problem, but again, nobody seems to have investigated this yet.
Real solutions, please
Why introduce yet another expensive, energy-intensive and risky technology if there are so many other and better ways to solve the energy crisis? Why not channel the huge amounts of money needed for the development of CCS to countries with tropical rainforests, so that they have a very good reason to protect them fiercely? Stopping deforestation, especially in tropical forests, would contribute more to the fight against global warming than carbon capture technology could ever do. Tropical forests store enormous amounts of carbon and they are not prone to natural forest fires.
Halting deforestation in tropical forests would contribute more to the fight against global warming than capture technology could ever do.
Why not stop constructing any more power plants that burn non-renewable energy sources? There is already an enormous energy capacity in the world, why don’t we chose to do it with the power plants that we already have? This would at last make energy efficiency useful (because progress in energy efficiency is now always negated by new and more energy hungry products and services). Still want more energy? Build a solar plant or plant a windmill.
These are just some ideas that would be effective without the need to adapt our lifestyle (which is, of course, also the attraction of “clean coal”). They would not solve everything, but at least they would be very welcome steps into the right direction, towards a real solution. All high-tech carbon storage strategies described in this article are no solutions, they are just attempts to limit the problem. Let’s hope that the next appeal of the International Energy Association and of the Science Academies of the world (an awful lot of brains there) will contain a trace of innovative thinking.