Since the Federal Government, according to an internal paper, considers Carbon Capture and Storage (CCS) "on the megaton scale" to be necessary to achieve the climate goals, the debate about technology has been back. Among experts and large parts of society are indisputable that the emissions of carbon dioxide (CO2) have to be drastically reduced, but that should not be enough to keep the temperature rise below two degrees to Celsius. That is why many scenarios that the World Climate IPCC takes into account require to incorporate CO2 and save them permanently.
Already ten years ago there was a broad debate about the procedure in Germany. At that time, it was primarily a matter of making coal electricity "clean": the CO2, which is free during the combustion, should be separated and pressed underground so that it does not even come into the atmosphere. There was a lot of contradiction, which revolved around possible leaks and their consequences, about high costs and competition for the energy transition - after all, this form of CCS would fix coal as a long -term source of energy. The project appeared hopeless, the plans were stopped, CCS prohibited.
The current discussion is primarily about the CO2 sources of industry, for example from the areas of cement, glass, lime, waste and chemistry. In principle, the procedure can also be used for separated carbon dioxide from the combustion of biomass and for those that are removed with special systems from the ambient air. These options are not yet developed as far, but often contain in CCS scenarios, which sometimes makes the discussion difficult. This should be about whether CO2 can be separated from so -called sources of points in the industry - immediately in front of the chimney - and permanently locked away in deep layers.
Where to put the greenhouse gas?
The technology has been used in the Sleipner gas field off the Norwegian coast since 1996. Around one million tons of the greenhouse gas are brought to the bottom of the North Sea every year. There are now several other projects, including in Australia, Canada and Denmark.
Germany could participate in CCS projects of its neighbors and get rid of unwanted greenhouse gas there. "Norway has already indicated that it will take large quantities and store them under the North Sea," says Susanne Buiter, scientific director of the Helmholtz-Zentrum Potsdam – Deutsches Geoforschungszentrum (GFZ). However, it should be borne in mind that transport requires infrastructure and costs energy. "Why don't we store the resulting CO2 with us?", the researcher asks and makes it clear: From her point of view, this would be possible.
The Federal Institute for Geosciences and raw materials (BGR) analyzed which geological formations in Germany would be considered. In addition to exhausted oil and natural gas deposits, it is mainly water-leading sandstone layers at many hundred meters. These "salinars aquifer" are so far from the surface and so salty that they excrete for drinking water extraction. They can be found primarily in northern Germany, along the Upper Rhine Grab and in the Alpine foothills. The BGR estimates that a total of around nine billion tons of CO2 can be sunk under the mainland. In addition, it is currently being examined how big the potential is in the underground of the German North Sea. The results are expected for 2024. Experts already point to usage conflicts with offshore wind turbines that are to be massively expanded.
Such conflicts are also possible with potential storage horizons on land. "The geothermal energy near the surface, which uses geothermal energy up to a maximum of 400 meters deep, or caverns there is no competition," says Buiter. It could be different with mining and for future storage for "green" methane or hydrogen. "It would therefore be important that politics regulates the use, for example with spatial planning plans for the surface." So whether the estimated nine billion-ton potential is really usable in the end remains open. Especially since the underground is not equally well explored everywhere and the experts are still allowed to experience some surprises.
How carbon dioxide stays in the soil
Technically, the storage of the greenhouse gas is feasible and safe - this is the conclusion of a research project led by the GFZ. From 2008 to 2013, around 67,000 tons of CO2 were pressed near Ketzin, west of Berlin. The gas was brought up with tankers and pumped into a porous sandstone at a depth of around 630 meters, which used to serve as a gas storage facility and is therefore already well known geologically.
The CO2 dissolves down there in the salty water like in a bubble bottle, sometimes it also converts into solid minerals. How fast the processes take place in CCS horizons depends on the pressure and temperature conditions, as well as the chemical composition of the rocks. In Iceland, for example, researchers have pumped CO2 into basalt. Within two years, almost the entire amount has turned into minerals, reports the team led by Juerg Matter in the journal "Science".
This shows the limits of the term "storage" - the sense of the word includes the possibility of bringing back the carbon dioxide. Only who wanted to do that, get a greenhouse gas out of the earth with a lot of effort, where it is slightly available up here? Property of the CCS argue that at least the option should be obtained if the sunk CO2 is to be used as a raw material. Critics see another point: You can simply get a "memory" faster than a "landfill".
During the project in Ketzin, gas flows and other parameters were recorded at the surface and in monitoring wells. Result: nothing has escaped, as can be seen from the final report. The boreholes were professionally closed in 2017 and monitoring ceased. Too early, criticizes Karsten Smid, climate expert at Greenpeace. "Four years of observation is an extremely short period of time to conclude that a leak is supposed to have existed for more than 10,000 years.«
. It is important to have a scale comparison here: In our view, the four years of post-injection monitoring for the 67 kilotons are saved a reasonable time compared to the 40 years for industrial quantities in the megaton area. «
There is resistance to the technique
Here it is indicated which major steps would still be necessary to get an effective relief of the climate balance from a small project in "heretical format". According to the Federal Environment Agency, the overall German CO2 emissions in 2021 was 762 million tons. Around 120 million tons are eliminated - around two thirds of which come from large industrial plants, which would be fundamentally suitable as point sources for CCS. However, it should be borne in mind that the CO2 separation costs additional energy and requires further systems-up to transport to a geological depth bearing. So these can only absorb a fraction.
Environmental organizations such as Greenpeace or the Federal Government continue to oppose CCS. They warn of dangers to the environment due to leaks and induced earthquakes, and also criticize strains caused by the construction of pipelines and increased shipping traffic, at least in the case of offshore storage facilities. "The industry has saved itself a real decarbonization," says Kerstin Meyer, Head of Economics and Finance at the Federal Government. Large CO2 networks are already being planned, to which the major emitters such as cement, steel and chemical plants are joining in order to get rid of the climate gas. "Instead of avoiding and reducing emissions now, there will continue to be many emissions – this runs counter to the international climate protection architecture.«
It sounds similarly from politics. In Schleswig-Holstein, for example, all five parliamentary groups in the state parliament confirmed their no to CCS in summer. And even now, after the Federal Government's plans became known, there is no reason to say goodbye, explains Silke Backsen, deputy group leader of the Greens and spokeswoman for nature and environmental protection. "Instead of taking care of residual emissions in the middle of an energy and climate crisis, the view and political strength should be directed at how emissions can finally be reduced and avoided."
More questions than answers
The argument that the subsoil must be found as a CO2 landfill to relieve the atmosphere quickly replies critics with the »Rescue« study by the Federal Environmental Office of 2020. According to this, there can be a succeed in Germany, »by the natural sinks-such as forests - and sustainable wooden industry to bind so much carbon that CCS is not necessary for the achievement of greenhouse gas neutrality in Germany «.
After several years with drought, forest fires and massive damage caused by bark beetles, the question arises whether the local forests can still meet the great expectations. "I am skeptical," says Andreas Bolte, head of the Thünen Institute for Wald ecosystems in Eberswalde. The Federal Forest Inventory is currently underway for the critical years 2017 to 2022, a result will only be available in 2024. But it is already clear: the inventory has broken out to 400,000 hectares, especially due to beetle damage, and thus the storage capacity for four million tons of CO2 a year. Although it is being newly planted, it takes at least 20 years before trees are large enough to bind a lot of carbon. The bottom line is that, according to Bolte, "that the memory performance of the forests has decreased".
There are also a number of uncertainties in terms of CCS. The great expectations of climate protection will only begin to meet the global scale, write Joe Lane and Chris Greig from Princeton University and Andrew Garnett from the University of Queensland in Brisbane in the journal "Nature Climate Change". Previous attempts to stimulate industry remained behind expectations - the authors are also skeptical for the future. On the one hand, there is geology that only offers potential memory in certain regions. In addition, there would be a not always existing scientific and technical expertise, lack of acceptance in society, and the question of how the high costs should be financed. That brakes the development. The authors in Asia see particularly large delays. They demand that the problems mentioned should be addressed urgently to reduce the uncertainties at CCS. The procedure is absolutely necessary to avoid the emission budget in the sense of the Paris climate agreement.
