(517f) Novel Process for Energy Storage and Conversion: Combined Chemical Looping
AIChE Annual Meeting
2015
2015 AIChE Annual Meeting Proceedings
Innovations of Green Process Engineering for Sustainable Energy and Environment
Chemical Looping Processes II - Processes
Wednesday, November 11, 2015 - 2:35pm to 3:00pm
Novel process for energy storage and conversion: combined chemical looping
Vladimir V. Galvita, Hilde Poelman and Guy B. Marin
Laboratory for Chemical Technology, Ghent University, Technologiepark 914, B-9052 Ghent, Belgium, E-mail: Vladimir.Galvita@Ugent.be
The development of reliable and environmentally friendly approaches for energy conversion and storage is one of the key challenges that our society is facing [1, 2]. Energy can be stored in different forms: in an electric or magnetic field; as mechanical energy; or as chemical energy [3]. In a typical energy storage process, one type of energy is converted into another form which can easily be stored and converted for use when needed [4].
Chemical looping combustion (CLC) is an emerging combustion technology. In this process, fuel is oxidized by a reducible metal oxide and the reduced metal oxide is re-oxidized by air in a separate step [5, 6]. CLC hence produces a pure CO2 stream, not diluted by N2. By replacing air with H2O or CO2 as oxidizer, the chemical looping analogue to steam (CLSR) and dry reforming (CLDR) is obtained [6-8]. The latter converts CO2 to high-purity CO, providing an efficient path for CO2 conversion. The overall stoichiometry of this process indeed demonstrates that the oxidation step converts more CO2than was produced in the fuel combustion step.
The calcium looping technology is a promising new technique for high-temperature scouring of CO2 from flue gas and syngas. Calcium looping cycles have been intensively investigated in order to produce a concentrated CO2 stream from the utilization of fossil fuels and biomass. Efficient CO2 capture and storage using Ca-based sorbents can be achieved via the reversible reaction CaO + CO2 CaCO3 (ΔH298 K = −178kJ mol–1), the so-called Ca-looping cycle [9].
The present novel concept proposes energy storage and conversion based on a combination of chemical and calcium looping processes [10]. It uses a physical mixture of a CO2 sorbent and an oxygen storage material. CO2 serves as mediation gas to facilitate metal oxidation and carbon gasification into CO by means of chemical looping, while the calcium looping process ensures storage and release of CO2.
Combination of Fe3O4/Fe redox cycles with CaO/CaCO3 looping in this novel concept of “combined chemical looping” provides a number of important advantages. Where chemical looping dry reforming immediately oxidizes fuel to CO2, which is further converted to CO, the CO2 mediation gas is now stored to be used at will. The CaCO3 solid material acts both as CO2 reservoir and supplier, by cyclic CaO/CaCO3 calcination-carbonation. In addition, the adsorption of CO2gas from the stream during iron oxide reduction promotes faster material reduction and carbon formation.
The working principle of the “combined chemical looping” can be described as follows [10]. During the reduction step (“charge process”), CH4 + CO2 is fed into a mechanical mixture of Fe3O4 and CaO. Interaction of methane with Fe3O4 leads to formation of metallic iron and surface carbon as well as CO2, H2O and H2 (Eq. 1 and 2). The H2 (Eq. 2) obtained can be used for fuel cells. At the same time carbonation of calcium oxide occurs by interaction of CO2 with CaO (Eq. 3). CaO particles react with CO2 at typical high temperatures (600–700°C) to form CaCO3.
CH4 + Fe3O4 → 2H2O + CO2+ 3Fe (1)
CH4 → C + 2H2 (2)
CaO + CO2 → CaCO3 (3)
The material can be kept in this “charged” condition if storage is required or be put to immediate use. For the oxidation step (“discharge”), the temperature of the sample is increased by 50-150oC which leads to decomposition of calcium carbonate into CaO and CO2 (Eq. 4).
CaCO3 → CaO + CO2 (4)
At the same time, the interaction of CO2with metallic iron as well as with carbon produces CO via the following chemical reactions:
4CO2 + 3Fe → Fe3O4 + 4CO (5)
C + CO2 → 2CO (6)
The thus generated CO could for example be used in a solid oxide fuel cell (SOFC) where it is electrochemically oxidized,
CO + O2− = CO2 + 2e−, producing electricity and CO2.
The objective of the present study is the experimental validation of the proposed concept of combined chemical looping. The proof of concept was performed in two steps. In the first, a single NiO-Fe2O3/CeO2 material was used and CH4 was fed for iron oxide reduction and carbon formation. Interaction of this material with CO2 led to CO formation by iron and carbon oxidation by CO2. In the second step, the NiO-Fe2O3/CeO2 material was mixed with CaO to perform a complete combined chemical looping test with a feed of CH4+CO2. The amount of CO produced is higher than the theoretical amount for Fe3O4, because carbon deposits from CH4equally contribute to the CO yield. It was shown that this cycle of “charge-discharge” can be repeated with limited decrease of the rate of the involved reduction/oxidation steps. The proposed methodology offers a wide flexibility both in energy storage/release and fuel type. For charging, diluted gas streams can be applied, making it very attractive for present-day applications.
Acknowledgments
This work was supported by the “Long Term Structural Methusalem Funding by the Flemish Government”, the Fund for Scientific Research Flanders (FWO, project number 3G004613), and the Interuniversity Attraction Poles Programme, IAP7/5, Belgian State – Belgian Science Policy.
[1] A.M. Omer, Renew. Sust. Energ. Rev. 12 (2008) 2265-2300.
[2] A. Antonino Salvatore, P. Bruce, B. Scrosati, J.-M. Tarascon, W. van Schalkwijk, Nat Mater 4 (2005) 366-377.
[3] L. Schlapbach, A. Zuttel, Nature 414 (2001) 353-358.
[4] T. Kousksou, P. Bruel, A. Jamil, T. El Rhafiki, Y. Zeraouli, Energy storage: Applications and challenges, 2014, pp. 59-80.
[5] S. Bhavsar, M. Najera, R. Solunke, G. Veser, Catalysis Today 228 (2014) 96-105.
[6] L.-S. Fan, L. Zeng, S. Luo, AIChE Journal 61 (2015) 2-22.
[7] V.V. Galvita, H. Poelman, C. Detavernier, G.B. Marin, Applied Catalysis B: Environmental 164 (2015) 184-191.
[8] V.V. Galvita, H. Poelman, V. Bliznuk, C. Detavernier, G.B. Marin, Industrial & Engineering Chemistry Research 52 (2013) 8416-8426.
[9] E.J. Anthony, Greenhouse Gases: Science and Technology 1 (2011) 36-47.
[10] V.V. Galvita, H. Poelman, G.B. Marin, Journal of Power Sources 286 (2015) 362-370.