Manage, MN; (2014) An investigation into the feasibility of integrating intermediate-temperature solid oxide electrolysers with power plants. Doctoral thesis , UCL (University College London).

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Abstract

The detrimental effect of increasing global emissions of CO2 on the environment has prompted action to be taken to improve the environmental impact of hydrocarbon-based processes and fuel use. Therefore, producing hydrogen as an alternative fuel for vehicles fitted with fuel cells through solid oxide electrolyser cells (SOECs) has been considered. Coal fired power plants are major energy providers and are operational all day. Introducing SOECs into the plant to utilise hot steam and electricity during times of low energy demand may provide a step to large scale hydrogen production. Through modelling and experimentation of power plants and SOECs, this project aims to evaluate the feasibility of an integrated system based on the thermodynamic, techno-economic and SOEC performance analyses. Results show that SOECs, which operate between 600 and 1000 °C, take advantage of the heat of the steam, which increases electrolyser efficiency. Steam from before the intermediate pressure turbine at 560 °C and 46 atm was located from a simulation of a coal fired power plant. The intermediate-temperature steam of the plant was applicable to less used Gd-doped CeO2 (CGO) than yttria stabilised zirconia (YSZ) electrolyte that performs best at 900 °C, as shown experimentally. Modelling showed SOEC efficiency was improved by 25.2 % through an integrated system rather than traditional methods of heating water to steam, due to reduced energy requirements. Furthermore, the thermoneutral point of 4,644 A m -2 (1.31 V) formed a guide for the design and operation of SOECs. Analysis on the integrated system showed that 250 MW (7500 kg hr-1) and 290 MW (8700 kg hr-1) H2 can be produced with SOECs sized at 43,300 and 50,100 m -2, respectively, for scenarios of 7% steam extraction and a purely H2 production plant, at a cost of 3.76 $ kg H2-1. Although an integrated system shows promise for large scale hydrogen production, further development for suitable electrolytes and hydrogen storage and infrastructure is required.

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