New way to produce geothermal energy while storing CO2

Article rédigé le 11/05/2016

The project “CO2-DISSOLVED” - directed by Prof. Christophe Kervevan - main aims were to develop a new and innovative approach combining Carbon Capture and Storage (process called CCS) and geothermal heat recovery process.
The main results of this project were presented on March 30, 2016 in Orléans (France), at a conference of the ATEE (Association Technique Energie Environnement).

Background of CCS and geothermal energy recovery

Combining CCS and geothermal energy is of great concern. The main known process joining CO2 storage and geothermal energy recovery - developed by Prof. Kevin Brown (University of Canterbury New Zealand) and then studied by Prof. Karsten Pruess (University of Texas, USA) - uses supercritical CO2 as a working fluid in an Enhanced Geothermal System (EGS). This process is more of an energy recovery way to produce electricity than a way to combine energy production and CO2 storage. Furthermore, this process has only been investigated theoretically.

Details of CO2-DISSOLVED project

The CO2-DISSOLVED project was granted by the French National Research Agency (ANR) for 36 months and began in January 2013. This project is led by a French research team and directed by Prof. Christophe Kervevan, senior researcher in Geochemistry, Hydrogeology at the French Geological Survey (also called BRGM - BUREAU DE RECHERCHES GEOLOGIQUES ET MINIERES), Orléans (France).
It involves different institutes : BGR (Bundesanstalt für Geowissenschaften und Rohstoffe [Federal Institute for Geosciences and Natural Resources] Germany), CFG Services (engineering and services company, BRGM subsidiary, France), Geogreen (an engineering service created by IFPEN and BRGM, France), GeoRessources (a multidisciplinary laboratory -UMR 7359- devoted to the field of Applied Geology, from Sections 35, 36 and 60 of the CNU and Sections 18 and 30 of the CNRS. This laboratory is hosted by the University of Lorraine, and has three supervising institutions : the University of Lorraine, INSU CNRS and CREGU, and a secondary attachment to INSIS CNRS, France), “Université d’Orléans” (LEO, France), Partnering in Innovation, Inc. (USA) and the “Université de Lorraine” (France).

The CO2-DISSOLVED project main goals were to assess the technical-economic feasibility of a new industrial CCS concept integrating geothermal energy recovery, aqueous dissolution of CO2 and injection via a doublet system, and an innovative post-combustion CO2 capture technology.

The approach uses different processes as follow :

1) CO2 capture and separation using a patented aqueous technology.
2) Extraction of brine aquifer through a doublet specially created for heat extraction and using a heat surface exchanger system (this process is similar to those used in common low energy geothermal processes) .
3) Re-injection of the cooled brine in the injection well of the doublet equipped with a patented CO2 capture system created to separate and dissolve the CO2.

The innovative process of this low cost CCS method deals also with many objectives as renewable energy production and greenhouse gas reduction.

Conclusion

This new project offers substantial benefits in terms of storage safety. Indeed - compared to the usual use of a supercritical phase - this project using dissolved CO2 allows lower brine displacement risks, lower CO2 escape risks, and the potential for more rapid mineralization.

There are some disadvantages and limiting factors.

The major inconvenient of this new approach is that the amount of CO2 injection is physically limited by the solubility of CO2 in brine. Nevertheless, the project shows that the implementation of this technology is relevant in the immediate vicinity of low industrial emitters (10.000 to 150.000 tons of CO2 per year). Based on the usual characteristics of a low temperature geothermal doublet situated in the Paris Basin (at a rate of 200-350 m3/h and a temperature of 60 to 90°C) and on the CO2 solubility data in these conditions - a single doublet is able to dissolve a maximum of 150.000 tCO2/year.
Also, this solution can only be implemented locally and for small scale. But thanks to this and if the local underground geology is favorable, the costs related to CO2 transport would then be dramatically reduced.

More than 650 sites with these characteristics (industries emitting less than 150.000 tCO2/year and located close to a right geothermal resources) have been identified in France alone, the equivalent of almost 20% of French national industrial CO2 emissions (17% of French national industrial CO2 emissions in 2011) .

CO2-DISSOLVED project shows economic viability of the operation in the case of a "medium" scenario and with a wide range of variability of the assumed cost per ton of CO2 (5 to 50 €).

This project shows both the energetic and economical potentials coupled to geothermal heat recovery. This interesting way of valorization of CO2 injection operations demonstrates the viability of a synergy between geothermal heat process and CO2 storage.

Follow-ups

The next phase of the project will be experimental. This second phase will complement the knowledge and select an industrial site for future implementation of a demonstration pilot. This project will be financed by “Géodénergies” a French Scientific Interest Group for carbon-free energy.

To complement the study, a next step will try to adapt the process to the scale of bigger emitters (several million tons of CO2 per year).

Rédacteur :
Julie METTA, Chargée de mission scientifique - Hong Kong