Capturing CO2 emissions into the atmosphere, a technology that has always been too expensive, could begin to be common thing thanks to a bill signed last February by Donald Trump. We have interviewed Yolanda Moratilla, director of the Rafael Mariño Chair of New Energy Technologies of Comillas ICAI, regarding this technology.
Q- What is the CO2 capture and what are the methods used by this technology?
A- These are procedures to remove CO2 from a gas stream. There are basically three: post-combustion, pre-combustion and oxy-combustion. The “post” is the simplest and applies to existing plants. It consists of a chemical capture with a substance called amine. The problem is that CO2 is very diluted in the current (around 14%), which hinders efficiency.
In the “oxy” case the idea is to burn with oxygen instead of air, so that the concentration of CO2 in the gases increases greatly and the capture is facilitated. The problem is that very high combustion temperatures are reached, which requires recirculating part of the CO2. It is used in new plants that have the boiler adapted for this type of combustion.
Finally there is the “pre” that is carried out under the integrated gasification mode in combined cycle (GICC). It consists of gasifying the coal prior to combustion, so that the coal becomes a mixture of CO and H2. Subsequently the CO is turned into CO2 by the addition of steam, producing more hydrogen. In that current the CO2 has high concentration and it separates. H2 can be burned in the gas turbine of the combined cycle, normally diluted with nitrogen, or sold as an energy product (for fuel cells, for example). This method has the advantage of opening the doors to the H2 economy. There are other methods based on thermochemical cycles, but they are less widespread.
One technique that goes beyond capture and on which work is being undertaken is the so-called P2G (power to gas), which consists of producing hydrogen by electrolysis with wind surpluses to turn the H2 into CH4, similar to natural gas, which would be fed into the gas pipeline network.
Q- Are you working on any project related to this in ICAI?
A- Some time ago we carried out a study comparing the introduction of these techniques in the electricity generation mix, versus advanced nuclear energy. The idea was to assess how the cost of generation varied depending on what technology was applied, taking into account its contribution to the network stability and the CO2 storage restrictions.
Q- Could these CO2 capture technologies be extended to Europe?
A- Without a doubt. There are several international projects. At the technical level, it can be applied to any country provided it has the capacity to store the CO2 captured. To reduce transport costs it is desirable that the storage intended for the CO2 housing be close to the plant, less than 200 km away. In Spain the largest storage capacity is estimated to be in deep salty aquifers with a capacity in the range of 500 to 15,000 million tons of CO2.
In terms of prices, since the technology is not yet commercial, prices are expensive today, in the order of 75 dollars per ton of CO2, while they are expected to fall to 50 dollars a ton once the technology has matured. This means that it will not be a competitive technology until the market price of emission rights increases significantly. The current price in this market is 7.5 euros per ton, and it started at around 30 euros per ton. The implementation of capture technology in coal plants represents an increase in costs of 60% today and expected to decrease by around 20% in the future.
Despite the cost increase, it is a technology that does not have to be discarded since it allows to really remove the CO2 from the atmosphere and on the other hand it enables the use of coal, which has a crucial role in the stability of the electric network. The reason behind it is that this type of power plants operate with steam turbines that contribute a lot of inertia to the system, necessary to regulate the frequency and voltage of the network. If coal is not used, such role should be left to nuclear energy. You cannot dispose of both generation systems. The point is that both are CO2 free: nuclear because it does not use fossil fuel and coal because it can be made sustainable by making use of capture and storage.
Q- What is cheaper / most profitable, stop emitting or capturing carbon?
A-It is not about valuing only the profitability, but the benefits it brings to the system. Today network stability and safety of supply. If coal is suppressed, that role could only be represented by nuclear.
Q- Would this technology reduce emissions? Would it contribute to the fight against climate change?
A- It eliminates the CO2. In terms of acid (NOx) and particulate emissions, there other techniques to control them which are already being applied. Regarding climate change, this technology would undoubtedly contribute, since it removes the CO2 formed in the combustion (or even before it is formed, in the pre-combustion technique).
Q- What uses does the captured CO2 have? In what applications is it used?
A- It is normal to store it in diverse geological structures (deep saline aquifers, non-mineable coal layers, or natural gas depleted deposits). That CO2 stored is not intended for later exploitation. In fact, with the passage of time, a series of physical and chemical mechanisms are produced that lead to a geological entrapment. There are other techniques, such as that of the P2G discussed before, allowing CO2 along with H2 to be turned into CH4, which is similar to natural gas.
It is also possible to use CO2 in industrial processes, and it is usually done, for example for carbonated drinks, as an inert gas, as a cooling fluid, as a growth stimulator in greenhouses …
Q- Are there any geological risks stemming from this practice?
R- The injection of CO2 into depleted oil and natural gas fields has been used for many years to extract oil and gas that does not come out by itself. It is what is known as EOR and EGR. Therefore, experience already exists in a certain type of storage. In isolated cases micro-earthquakes can be produced but it is not usual. As for CO2 leaks, the storage itself prevents them over time, and in any case, CO2 is not toxic. The hypothetical leak would be very gradual. There have been experiences in some African lake of massive and brutish releases of CO2 (stored there naturally, not by human action), which have caused the death of people by asphyxia (abrupt displacement of oxygen), but that sudden leak could not occur in a geological CO2 storage site.