Model-based evaluation of the integration of solid oxide fuel cells and electrolysis cells for high purity oxygen production
File(s)
Author(s)
Taher, Mohamed Asaad Asaad
Type
Thesis
Abstract
Oxygen is used for a wide range of applications, with a globally projected production
capacity of 1.8 million tonne per day in 2020. Depending on the economic range and
the required purity, various methods are used to extract oxygen. Conventionally,
cryogenic air separation is used for the large to medium production scale,
characterised by high purity oxygen and relatively low energy consumption, whilst
pressure swing adsorption (PSA) is widely used for the small-scale production, with
lower oxygen purity and higher energy consumption. A high-efficiency system for
high purity oxygen production based on the integration of solid oxide- fuel and
electrolysis cells (SOFC and SOEC) was first proposed by Iora and Chiesa in 2009.
However, the lack of a detailed methodology and the novelty of such a system
necessitated a system-level energy analysis with an emphasis on the SOFC and SOEC
to understand the nature of thermal and electrical coupling between them. Here, the
initial feasibility of the system has been evaluated considering the lumped-parameter
modelling of the SOFC, SOEC and balance of plant. A system energy consumption
that is significantly less than that of PSA systems was predicted, and a significant
contribution of the stack energy consumption to the overall system energy
consumption was observed, suggesting the need for a thorough examination of the
electrochemical models. Therefore, the parameter estimation technique has been
implemented to validate the electrochemical models based on a 5-cell stack and a
single repeating unit SOEC experimental data. A good agreement was obtained
between the experimental and model-predicted cell potential across all operating
conditions, and key electrochemical parameters were estimated with confidence. The
validated electrochemical model has then been integrated into a newly-developed onedimensional
model of a planar SOFC-SOEC stack to further improve the predictions
of the stack and system performance. Significant contributions of experimental
validation and distributed modelling on enhancing the predictions of the stack model
were observed. The advantages of the system over PSA systems in terms of energy
efficiency and oxygen purity were confirmed. A potential design point of the system
was selected via a techno-economic study, revealing an extremely low contribution
of the electricity cost to the total cost of production. An adequate thermal integration
at both the stack and system levels were demonstrated at the design point.
capacity of 1.8 million tonne per day in 2020. Depending on the economic range and
the required purity, various methods are used to extract oxygen. Conventionally,
cryogenic air separation is used for the large to medium production scale,
characterised by high purity oxygen and relatively low energy consumption, whilst
pressure swing adsorption (PSA) is widely used for the small-scale production, with
lower oxygen purity and higher energy consumption. A high-efficiency system for
high purity oxygen production based on the integration of solid oxide- fuel and
electrolysis cells (SOFC and SOEC) was first proposed by Iora and Chiesa in 2009.
However, the lack of a detailed methodology and the novelty of such a system
necessitated a system-level energy analysis with an emphasis on the SOFC and SOEC
to understand the nature of thermal and electrical coupling between them. Here, the
initial feasibility of the system has been evaluated considering the lumped-parameter
modelling of the SOFC, SOEC and balance of plant. A system energy consumption
that is significantly less than that of PSA systems was predicted, and a significant
contribution of the stack energy consumption to the overall system energy
consumption was observed, suggesting the need for a thorough examination of the
electrochemical models. Therefore, the parameter estimation technique has been
implemented to validate the electrochemical models based on a 5-cell stack and a
single repeating unit SOEC experimental data. A good agreement was obtained
between the experimental and model-predicted cell potential across all operating
conditions, and key electrochemical parameters were estimated with confidence. The
validated electrochemical model has then been integrated into a newly-developed onedimensional
model of a planar SOFC-SOEC stack to further improve the predictions
of the stack and system performance. Significant contributions of experimental
validation and distributed modelling on enhancing the predictions of the stack model
were observed. The advantages of the system over PSA systems in terms of energy
efficiency and oxygen purity were confirmed. A potential design point of the system
was selected via a techno-economic study, revealing an extremely low contribution
of the electricity cost to the total cost of production. An adequate thermal integration
at both the stack and system levels were demonstrated at the design point.
Version
Open Access
Date Issued
2017-04
Date Awarded
2017-10
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Brandon, Nigel
Sponsor
Masdar Institute of Science and Technology
Publisher Department
Earth Science and Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)