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Can we sweep our CO2 emissions under the rug?

CO2 capture to limit climate change: dream or reality?

Didier Dalmazzone, Professor of Chemistry and Processes at ENSTA Paris (IP Paris)
On January 11th, 2023 |
4 min reading time
Ddidier Dalmazzone
Didier Dalmazzone
Professor of Chemistry and Processes at ENSTA Paris (IP Paris)
Key takeaways
  • The IPCC considers that CO2 capture and storage are mitigation strategies that can help limit global warming.
  • To do so, it would be necessary to capture 7.6 Gt CO2/year by 2050, which currently seems unattainable: the sector has yet to be developed.
  • There are many obstacles preventing widespread adoption of CO2 capture technology becoming widespread, such as the cost or the quantities of water and energy required.
  • To store CO2, old hydrocarbon reservoirs seem more stable than deep saline aquifers.
  • Making use of captured CO2 on an industrial scale could avoid the drawbacks of storage.

#1 We have the ability to capture enough CO2 to meet the goals of the Paris Agreement.

True about statement #1…

The var­i­ous cli­mate change mit­i­ga­tion sce­nar­ios incor­po­rate CO2 cap­ture, stor­age and util­i­sa­tion (CCUS) technologies.

In its 2050 car­bon neu­tral­i­ty sce­nario1 projects that 7.6 Gt of CO2 will be cap­tured each year by 2050. As for the Inter­gov­ern­men­tal Pan­el on Cli­mate Change (IPCC), in its sixth report pub­lished in April 20222, it empha­sizes: « Mit­i­ga­tion strate­gies to lim­it warm­ing to 1.5°C or 2°C include the tran­si­tion to fos­sil fuels asso­ci­at­ed with CO2 cap­ture and stor­age […], and the deploy­ment of CO2 cap­ture meth­ods [edi­tor’s note: such as direct atmos­pher­ic cap­ture] to off­set resid­ual emis­sions. »

How­ev­er, it must be kept in mind that CO2 cap­ture is only part of the solu­tion: 37.1 Gt of fos­sil CO2 were emit­ted in 20213. A range of mea­sures must be imple­ment­ed to mit­i­gate cli­mate change: agri­cul­ture, forestry and the oceans all play, in their own way, a very impor­tant role in the glob­al car­bon balance.

False about statement #1…

The tar­gets are well above cur­rent CO2 cap­ture and recov­ery capacities.

The IEA esti­mates that 4 Gt of CO2/year must be cap­tured by 2035 and 7.6 Gt by 2050. To date, only 35 com­mer­cial facil­i­ties are using CCUS. These are pilot projects and their cap­ture capac­i­ties are extreme­ly small: less than 0.05 Gt of CO2 per year4.

The IEA esti­mates that 4 Gt of CO2/year must be cap­tured by 2035 and 7.6 Gt by 2050.

The indus­try has yet to be devel­oped, and the IEA’s tar­gets are out of reach due to the invest­ments required, par­tic­u­lar­ly in high-emit­ting coun­tries like Chi­na, India and the Unit­ed States. The ramp-up will require the instal­la­tion of new facil­i­ties, as well as the very cost­ly ren­o­va­tion of exist­ing units (retro­fitting).

Uncertain about statement #1…

The amount of water and ener­gy required for CCUS could lim­it the process.

Let’s look at the impact of installing a CO2 cap­ture unit on an exist­ing coal plant5. Assum­ing an elec­tri­cal effi­cien­cy of 46% for a pro­duc­tion capac­i­ty of 500 MWe, the effi­cien­cy loss in the ide­al case would be at least 3.8%. In real­i­ty, this loss is more like 10%, or an effi­cien­cy after cap­ture of 36%. Two-thirds of the ener­gy con­sumed is for cap­ture, and the remain­ing third for com­pres­sion of the CO2. To this must be added the ener­gy required for trans­port and injec­tion: keep­ing the CO2 in a super­crit­i­cal or liq­ue­fied state requires a lot of energy.

As for water, cur­rent process­es gen­er­ate a lot of heat. The water need­ed to cool the instal­la­tion will increase the con­sump­tion of this resource.

#2 It is already possible to capture and recycle CO2 emitted by human activities.

True about statement #2…

Many sec­tors are already using CCUS technologies.

CO2 cap­ture tech­nolo­gies have been around since the 1970s and are used for enhanced oil recov­ery and nat­ur­al gas pro­cess­ing. How­ev­er, in this con­text, the CO2 is not recov­ered but released into the atmos­phere. 35 com­mer­cial indus­tri­al facil­i­ties use CCSUs to cap­ture and recov­er CO2, for exam­ple by treat­ing flue gas­es with amine chemistry.

False about statement #2…

The recov­ery or stor­age chan­nels have yet to be developed.

To date, of the 440 Mt of CO2 cap­tured each year, 230 Mt of CO2 are used main­ly for the pro­duc­tion of urea for fer­til­iza­tion (130 mil­lion tons) and enhanced oil recov­ery (80 mil­lion tons)6. We can­not imag­ine recov­er­ing bil­lions of tons of CO2 in this way.

Regard­ing stor­age, some pilot projects are already exper­i­ment­ing with injec­tion into for­mer gas fields. But the devel­op­ment of this sec­tor will have to deal with ques­tions of social accept­abil­i­ty. It is impor­tant to store as close as pos­si­ble to the cap­ture site to lim­it costs: for exam­ple, in France, in the Paris Basin east of Paris or in the vicin­i­ty of Pau.

Uncertain about statement #2…

The val­ue of direct air cap­ture (DAC), a process that cov­ers dif­fuse emis­sions (heat­ing, cars, etc.), remains a sub­ject of debate.

There are cur­rent­ly 18 DAC facil­i­ties in the world (Europe, USA and Cana­da) cap­tur­ing almost 0.01 Mt of CO2 each year. These small facil­i­ties cap­ture CO2 for direct use, such as in the man­u­fac­ture of soft drinks. Only two of them store CO2 in geo­log­i­cal for­ma­tions7.

The glob­al con­cen­tra­tion of CO2 in the atmos­phere has increased from 277 ppm before the indus­tri­al era to 417 ppm in 20228. With DAC, we would have to treat gigan­tic vol­umes of air to reach pre-indus­tri­al era con­cen­tra­tions! I believe that the nec­es­sary invest­ments, oper­at­ing costs and ener­gy required make DAC a fin­ish­ing option: the pri­or­i­ty is to cap­ture CO2 from the most emit­ting industries.

#3 Long-term CO2 storage is risky.

True about statement #3…

The long-term per­me­abil­i­ty of deep saline aquifers is unknown.

Deep saline aquifers are spe­cialised reser­voirs for CO2: they are even­ly dis­trib­uted over the sur­face of the globe and there­fore lim­it the trans­port of CO2. More­over, they offer a very large stor­age poten­tial, rang­ing from 400 to 10,000 Gt9. In these reser­voirs, the CO2 would be dis­solved in water for stor­age, but uncer­tain­ties remain as to the sta­bil­i­ty of the reser­voir, par­tic­u­lar­ly in terms of geo­chem­i­cal risks. Indeed, the addi­tion of CO2 will acid­i­fy the water, which could cause chem­i­cal reac­tions with the host rock and weak­en the reservoir.

False about statement #3…

Old­er hydro­car­bon reser­voirs appear to be more sta­ble over time.

Old­er hydro­car­bon reser­voirs are among the oth­er reser­voirs being stud­ied for CO2 stor­age. While they have the dis­ad­van­tage of hav­ing a less inter­est­ing geo­graph­i­cal dis­tri­b­u­tion, they have been proven to be water­tight for mil­lions of years as hydro­car­bon reser­voirs (gas, coal, or oil). The geo­me­chan­i­cal and geo­chem­i­cal risks asso­ci­at­ed with CO2 injec­tion must nev­er­the­less be bet­ter under­stood: this is cur­rent­ly the sub­ject of demon­stra­tors in the Unit­ed States, Cana­da, Alge­ria and Norway.

Uncertain about statement #3…

New ways of recov­ery could make it pos­si­ble to do away with CO2 stor­age in part.

As we have already men­tioned, it is also pos­si­ble to recov­er cap­tured CO2. But the chan­nels remain lim­it­ed today: it is cer­tain that we can­not increase fer­tilis­er pro­duc­tion indef­i­nite­ly! How­ev­er, many well-known process­es could enable CO2 to be recov­ered in oth­er ways, some of which have already been devel­oped on an indus­tri­al scale in the past. For exam­ple, thanks to a reac­tion between hydro­gen and CO2, many syn­thet­ic fuels can be pro­duced. CO2 can also be used to pro­duce plas­tics or min­er­al car­bon­ates for build­ing mate­ri­als. The prob­lem is that these process­es are, at this stage, more expen­sive than those based on fos­sil mate­ri­als such as oil.

Anaïs Marechal
1IEA (2021), Net Zero by 2050, IEA, Paris https://​www​.iea​.org/​r​e​p​o​r​t​s​/​n​e​t​-​z​e​r​o​-​b​y​-2050, License: CC BY 4.0, the Inter­na­tion­al Ener­gy Agency (IEA)
2IPCC, 2022: Cli­mate Change 2022: Mit­i­ga­tion of Cli­mate Change. Con­tri­bu­tion of Work­ing Group III to the Sixth Assess­ment Report of the Inter­gov­ern­men­tal Pan­el on Cli­mate Change [P.R. Shuk­la, J. Skea, R. Slade, A. Al Khour­da­jie, R. van Diemen, D. McCol­lum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belka­ce­mi, A. Hasi­ja, G. Lis­boa, S. Luz, J. Mal­ley, (eds.)]. Cam­bridge Uni­ver­si­ty Press, Cam­bridge, UK and New York, NY, USA. doi: 10.1017/9781009157926
3Friedling­stein, P., et al.: Glob­al Car­bon Bud­get 2022, Earth Syst. Sci. Data, 14, 4811–4900, https://doi.org/10.5194/essd-14–4811-2022, 2022
4IEA (2022), CO2 Cap­ture and Util­i­sa­tion, IEA, Paris https://​www​.iea​.org/​r​e​p​o​r​t​s​/​c​o​2​-​c​a​p​t​u​r​e​-​a​n​d​-​u​t​i​l​i​s​ation, License: CC BY 4.0
5Pp. 31 & 53 in D. Stolten & V. Scher­er Ed., Car­bon Cap­ture for Coal Pow­er Plants, 2011, Wiley-VCH GmbH & Co. ISBN 978–3‑527–33002‑7
6IEA (2022), CO2 Cap­ture and Util­i­sa­tion, IEA, Paris https://​www​.iea​.org/​r​e​p​o​r​t​s​/​c​o​2​-​c​a​p​t​u​r​e​-​a​n​d​-​u​t​i​l​i​s​ation, License: CC BY 4.0
7IEA (2022), Direct Air Cap­ture, IEA, Paris https://​www​.iea​.org/​r​e​p​o​r​t​s​/​d​i​r​e​c​t​-​a​i​r​-​c​a​pture, License: CC BY 4.0
8Friedling­stein, P., et al.: Glob­al Car­bon Bud­get 2022, Earth Syst. Sci. Data, 14,4811–4900, https://doi.org/10.5194/essd-14–4811-2022, 2022
9Site con­sulté le 23/11/2022 : https://​www​.ifpen​ergies​nou​velles​.fr/​e​n​j​e​u​x​-​e​t​-​p​r​o​s​p​e​c​t​i​v​e​/​d​e​c​r​y​p​t​a​g​e​s​/​c​l​i​m​a​t​-​e​n​v​i​r​o​n​n​e​m​e​n​t​-​e​t​-​e​c​o​n​o​m​i​e​-​c​i​r​c​u​l​a​i​r​e​/​r​e​d​u​i​r​e​-​l​e​s​-​e​m​i​s​s​i​o​n​s​-​i​n​d​u​s​t​r​i​e​l​l​e​s​-​c​o​2​-​c​a​p​t​a​g​e​-​e​t​-​s​t​o​c​k​a​g​e​-​d​u-co2

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