The Electrolysis–Methanation–Oxy-fuel (EMO) concept is designed to bring a closed-loop solution able to absorb renewable electricity surplus and recover it later, via the transient storage of O2, CO2 and CH4 in salt caverns.
Since most renewable energies (wind, solar) are intermittent, it is necessary to find solutions to store the energy produced and to return it when needed. The massive storage of energy is therefore one of the components of the energy transition. When stored in fluid form, it requires the availability of large volumes that underground caverns can offer depending on the geology. The main objectives of the FluidSTORY project are to study the operability, the safety and the integrity of O2 and CO2 storage in salt caverns as well as to investigate the medium to long term (2030-2050) requirements for reaching the energy efficiency and economic profitability of the EMO concept in France.
One of the most promising ideas consists in using fluids to store energy. The concept Electrolysis-Methanation-Oxycombustion (EMO) consists in transforming the surplus electricity into methane and then burn this methane to produce electricity. The operation takes place in two stages: production of hydrogen and oxygen by water electrolysis and then methane production through combination of hydrogen with CO2. The oxygen generated by the electrolysis burns the produced methane in an oxy-fuel power generator to produce electricity again. Due to its relative purity, the emitted CO2 can be easily captured and reused in methane production. The process implies the temporary storage of large amount of fluids. Solution-mined caverns dug in deep salt layers same as those used today for the storage of hydrocarbons (strategic reserves, seasonal storage), can be used for massive and reversible storage of O2 and CO2. Fluidstory carries out a methodical inventory of salt formations capable of accommodating such caverns as well as existing caverns. The team studies the theoretical, numerical and experimental aspects of the thermodynamic and thermomechanical behavior of the storage caverns as well as the geochemical equilibria during storage. The project also includes a systematic study of operational risks as well as an economic component aimed at estimating storage requirements and the profitability of the concept by 2030-2050. Should each fluid be stored in separate cavities or in the same volume? What equilibrium will these gases find with respect to the residual water in these caverns? What are the risks to anticipate, during the exploitation phase or after site closure? Here are some technical and environmental issues raised by such storage, to which the project tries to provide answers.
- The inventory of the French potential for gas storage in salt caverns shows that saliferous formations of triassic or tertiary age are present in the six main French sedimentary basins. The Paris basin salt series could meet the constraints of small-scale storage, while those in the Apt-Forcalquier, Valence, Bresse or Mulhouse tertiary basins may be attractive targets for massive storage.
- A thermodynamic model was developed to represent the phase diagram of the CO2 / CH4 / O2 mixture. The parameters of the model were adjusted to data from the literature (steam equilibrium). This model makes it possible to predict the pressure diagram as a function of the molar volume of the CO2 + O2 system (for three compositions).
- The EMO unit was modeled in steady state to define the nominal operating conditions of the surface installations with respect to the storage conditions.
- Several economic scenarios for energy demand were analyzed. As a result, the EMO process could compete with other power-to-gas options on inter-seasonal energy demand. Depending on the economic competitiveness of the EMO compared to other options and the availability of storage capacity, between 1 and 5 EMO projects can be envisaged in 2050.
- The study of storage safety allowed identifying all the adverse events likely to affect new cavities of CO2 and O2. Based on the full list of scenarios to be considered, recommendations were made to provide an assessment of each event prior to the final project recommendations.
Complete the theoretical and experimental studies planned in the Fluidstory project to demonstrate the feasibility of the project. Launch a pilot project on a real scale with the participation of industrial players.
10 articles have been produced to date, including two in international peer-reviewed journals (Int. J. Rock Mech., Sci. and Int. J. of Hydrogen Energy). The others are for presentations at international conferences with proceedings. In addition, several popular articles have been published in the press and online newspapers (Rtflash, Petrole et Gas, Hydrogen today, Power 2d, etc.).
In the context of energy transition in France, massive energy storage is a key issue for the integration of renewable sources into the energy mix. One of the most promising ideas consists in using fluids to store energy. The Electrolysis–Methanation–Oxy-fuel (EMO) concept is designed to bring a closed-loop solution able to absorb electricity surplus, due in particular to renewable sources integration, and to recover it later, via the transient storage of O2, CO2 and CH4. The EMO addresses two major concerns of the “Power to methane” electric energy storage systems: i) the massive supply of CO2 to feed the methanation and ii) the release of CO2 into the atmosphere after methane combustion. In this concept, the oxygen generated by the electrolysis is used to burn the stored methane produced through combination of hydrogen and CO2, in an oxy-fuel power generator. Due to its relative purity, the emitted CO2 is then easily captured and reused in methane production. The process implies the temporary storage of large amount of fluids (O2, CO2 and CH4). Solution-mined caverns are studied as massive and reversible storage of fluids. The main objectives of the FluidSTORY project are to study the operability, the safety and the integrity of O2 and CO2 storage in salt caverns as well as to investigate the medium to long term (2030-2050) requirements for reaching the energy efficiency and economic profitability of the EMO concept in France. In order to achieve this goal, several electricity production scenarios for 2030-2050 will be developed in a techno-economic task. Economic environment and storage capacity needs for optimal use of EMO technology will be assessed as well as the profitability of the concept. In parallel, availability of storage volumes required by EMO development will be investigated through systematic inventory of the existing salt caverns and geological study of suitable salt formations for building new ones. In order to understand physico-chemical, thermo-dynamical and geochemical phenomena and processes which occur in salt caverns and resulting behavior, a large part of the project is dedicated to address scientific barriers brought by underground storage of O2 and CO2. Two options will be considered: i) each fluid is stored in a separate cavern, or ii) O2 and CO2 are stored together in the same cavern. Theoretical, numerical and experimental works will be carried out on geochemical equilibrium of stored fluids as well as on thermo-dynamical and thermo-mechanical behavior of the cavern. In comparison to the former FluidSTORY proposal submitted in 2014, this new version is enriched with the study of key surface elements and their interactions with the storage caverns. It provides knowledge on the global process and its operational needs. To meet regulatory requirements, the project also includes an analysis of potential risks induced by the storage operation and after cavern abandonment. An operational synthesis of this work, including a guideline for risk management, will be produced to support further development stages of EMO. In order to benefit from industry’s operational experience and to favor future dissemination of the concept, an external advisory board, already including GDF Suez and Air Liquide, is associated to the project. The board will give insight into industrial operability and will help to choose the adequate options at the main steps of the project. The preparation of two PhD theses will feed scientific developments inside the project, one addressing the geochemical behavior of stored fluids, the other one related to the geo-mechanical behavior of the salt caverns.
Monsieur behrooz bazargan sabet (BRGM)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LMS Ecole Polytechnique Laboratoire de mécanique du solide
BROUARD S.A.S BROUARD CONSULTING
CNRS DR ILE DE FRANCE SUD
Help of the ANR 890,053 euros
Beginning and duration of the scientific project: December 2015 - 48 Months