Abstract
Renewable sources and electric distribution network can produce or make available a surplus of electric and thermal energies. The Intermediate Temperature Solid Oxide Electrolyzer (IT-SOE) fed by CO2-steam mixtures can store these electric and thermal energies producing CO-H2 mixtures with high conversion efficiency. Inside the IT-SOE, the CO2-steam mixtures are converted into CO-H2 mixtures and O2 through cathodic and anodic electrochemical reactions and reverse water gas shift chemical reactions. In this article an IT-SOE stack fed by different types of steam mixtures was tested at different operating temperatures and the stack polarization and electric power curves were detected experimentally. At the highest hydrogen production operating temperature of the stack fed by steam mixtures, the experimental polarization and electric power curves of the stack fed by steam and CO2-steam mixtures were compared. A simulation model of the IT-SOE system (stack and furnace) fed by CO2-steam mixtures was formulated ad hoc and implemented in a MatLab environment and experimentally validated. At the highest hydrogen production stack operating temperature, the IT-SOE system thermal equilibrium current was evaluated through the simulation model. Moreover, the influence of this current on the IT-SOE system efficiency and the CO-H2 mixture degree of purity was highlighted.
Highlights
The increase in the use of renewable sources to replace fossil fuels, for energy production, aims to reduce greenhouse gas emissions and mitigate climate changes
Where Pth,lost,s is the thermal power generated by irreversibility, Ohm and contact overvoltage and polarization phenomena in the stack expressed in W; Pth,rwgs,s is the thermal power absorbed by the reverse water water gas gas shift shift (RWGS) chemical reaction in the stack expressed in W; FH2 O,b,s FCO2,b,s are the molar flows of steam and carbon dioxide electrochemically consumed in the stack expressed in mol·s−1 ; Tc and nc are the electrolytic cell operating temperature expressed in K and the number of electrolytic cells in the stack;
Ηel,re f ηth,re f where m H2 and mCO are the mass flows of hydrogen and carbon monoxide produced expresses in kg·s−1 ; LHVH2 and LHVCO are the lower heating values of hydrogen and carbon monoxide expressed in J kg−1 ; Pth,tot,sys is the total additional thermal power (>0) required by the solid oxide (SOE) system (SOE stack and furnace) expressed in W; Pth,ph,H2 O is the thermal power required to produce the steam at the stack inlet starting from water at a temperature equal to 25 ◦ C at the SOE system inlet expressed in
Summary
The increase in the use of renewable sources (sun, wind, water, etc.) to replace fossil fuels (petroleum, natural gas and coal), for energy production, aims to reduce greenhouse gas emissions and mitigate climate changes. The hydrogen produced can be adequately stored and converted into electric energy through fuel cells at times when the energy demand is high or can fuel “carbon free” and sustainable mobility systems [6,7,8,9,10] In this context, solid oxide electrolytic cells (SOEs) are able to convert steam and/or carbon dioxide and air into gas rich in hydrogen and/or carbon monoxide and oxygen-rich air with no environmental impact and with a lower electric energy consumption produced from RES. The authors have experimentally tested the SOE stack, which operated at intermediate temperatures (IT) ranging from 650 to 750 ◦ C and was fed by various gaseous mixtures of steam, carbon dioxide and hydrogen at the cathode inlet and by air at the anode inlet, for the detection of its polarization and electrical power curves.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
