Role of Fuel assisted Solid oxide Electrolysis in the Renewable Energy Scenario: A Feasibility Study

Abstract

Fuel assisted electrolysis has the advantage of reducing the power demand of hydrogen production by solid oxide electrolysis with the help of assisting fuel. This thesis presents a feasibility study on the use of biogas fuelled solid oxide fuel assisted electrolysis (SOFEC) for hydrogen production on an industrial scale. The biogas is supplied as a source of hydrogen to the anode of the solid oxide electrolyser where hydrogen gets oxidised and provides electrons for the steam splitting taking place at the cathode. This results in upgrading of biogas to hydrogen and reduction in the electrical power demand. However, steam reforming of biogas (methane) is an endothermic reaction and hence,
heat has to be supplied externally.
The SOFEC system is modelled in Cycle Tempo and the modelling results are used to perform the feasibility study based on technical, economic and social aspects. Further, to corroborate the results from the study, a case study scenario of integration of SOFEC in a steelmill is presented.
With regard to technical aspects, the SOFEC cathode and electrolyte materialswere found to be in practice commercially, adequate biogas supply could be ensured by biogas production at waste water treatment plants and heat supply from high temperature waste heat sources was proposed to meet heat demand of methane reforming. Based on these conditions, the SOFEC system has high prospect of being technically feasible.
Further, for economic analysis, the net production cost of SOFEC was estimated to be less than 4.5 Eur/kg H2 which is lower than that of low temperature (7.32 Eur/kg H2) and high temperature electrolysis (5.54Eur/kg H2). Considering high temperature heat, recovered from molten slags in steel mills, being used as heat supply followed by a predicted drop in electrolyser capital costs, the SOFEC is able to compete with lower production costs of steam methane reforming (3 Eur/kg H2). Thus, low electrolyser capital costs and availability of low cost waste heat supply are the main driving factors for SOFEC to be economical.
In social aspects, the operational safety and social acceptance of SOFEC were investigated. It was concluded that for hydrogen storage challenges, existing commercial hydrogen storage solutions can work and with hydrogen fuel cells being socially accepted, the SOFEC was assumed to be accepted the same. Also the SOFEC was shown to have low CO2 (2 kg CO2 equivalent / kg H2) and low SO2 emissions provided sufficient desulfurisation of biogas is done. Therefore, it is concluded that the SOFEC has high potential to be socially feasible.
Although, the SOFEC has been presented to be a feasible technology, uncertainties
such as degradation in performance due to interruptions in biogas supply, absence of anode materials which can withstand reducing environments, absence of low cost high temperature heat and high costs of electrolyser systems are obstacles which have to be resolved.