Anaerobic Digestion (AD) is used worldwide for treating organic waste and wastewater. Biogas produced can be converted using conventional energy conversion devices to provide energy efficient, integrated waste solutions. Typically, the electrical conversion-efficiency of these devices is 30–40% and is lowered due to biogas utilization instead of high pure refined natural gas. The Solid Oxide Fuel Cell (SOFC) as an alternative device offers high (50–60%) electrical efficiency with low emissions (CO2, NOx) and high temperature residual heat. The high quality residual heat from SOFCs could be used to improve biogas production through thermal pre-treatment of the substrate for anaerobic digestion. This work discusses the advantages and challenges of integrated AD-SOFC systems against the most recent scientific and practical developments in the AD and SOFC domain. First, the biogas production process and its influence on the composition and level of contaminants in biogas are explained. Subsequently, the potential of various biogas cleaning techniques is discussed in order to remove contaminants that threaten stable and long-term SOFC operation. Since SOFCs utilize H2 and/or CO as fuel, possibilities for internal and external reforming are explained in detail. Special attention is given to biogas dry reforming in which CO2 naturally present in the biogas is utilized effectively in the reforming process. A detailed discussion on the choice of SOFC materials is presented, with a focus on biogas internal reforming. Various integrated SOFC system models with multiple configurations are also reviewed indicating the overall efficiencies. Some biogas SOFC pilot-plants are described and discussed to conclude with the techno-economic aspects of biogas SOFC systems.

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Increased climate change over past decades has resulted in an increase in the average temperature (also called global warming) of Earth’s climate system. At the recent Paris climate conference (COP21) in 2015, 195 countries in the world have agreed upon a stringent plan to limit global warming below 2oC. This demands a significant reduction in the industrial emission of greenhouse gases, predominantly carbon dioxide (CO2). Existing fossil fuel (coal, natural gas) fired power plants account for the majority share in global carbon dioxide (CO2) and other harmful (SOx , NOx) emissions. Therefore clean, efficient and flexible power plant concepts need to be developed towards upgrading existing power plants and to meet the strict CO2 emission targets. Combined cycle power plants like the integrated gasification combined cycle, IGCC (coal based) and integrated reforming combined cycle, IRCC (natural gas based) can be utilized to produce electricity using fossil fuels at relatively high efficiencies compared to conventional single cycle plants. Possible approaches to make IGCC/IRCC power plants cleaner, efficient and more flexible include biomass utilization (renewable energy source), application of CO2 capture technologies, retrofitting with highly efficient fuel conversion technologies like solid oxide fuel cells (SOFCs) and energy/fuel storage. This dissertation primarily aims to provide design concepts and thermodynamic system analysis for large scale IGCC and IRCC power plants with a focus on achieving high electrical efficiencies, low CO2 emissions and high operational flexibility. SOFCs have been explored as an efficiency augmenting technology and metal hydride based hydrogen storage as a flexibility option. Furthermore, future development of safe and optimally operating hydrocarbon (like natural gas (methane)) fuelled SOFC units on the basis of system and numerical models, requires reliable experimental data and understanding in the underlying reaction kinetics. Thereupon, an extended experimental study has been carried out in this work on methane steam reforming (MSR) kinetics in single operating SOFCs.@en

A summary of research activities and on-going multiple projects at Delft University of Technology aimed at the development of Solid Oxide Fuel Cells (SOFCs) integrated waste to energy systems are presented in this paper. A wide range of studies ranging from pattern cell impedance analysis to integrated system development is also presented. Cleaning the gas to match constraints of SOFCs requires complex approaches. A brief discussion on the achievable system efficiencies with SOFC integrated waste to energy systems is presented and novel concepts such as gasifier-Reversible SOFC integrated power production cum energy storage systems are discussed. Additionally, an overview of a wide range of national, European and international projects that helped or currently helping us to carry out the above mentioned research activities are presented.@en

Major operating challenges remain to safely operate methane fuelled solid oxide fuel cells due to undesirable temperature gradients across the porous anode and carbon deposition. This article presents an experimental study on methane steam reforming (MSR) global kinetics for single operating SOFCs with Ni-GDC (gadolinium doped ceria) anodes for low steam to carbon (S/C) ratios and moderate current densities. The study points out the hitherto insufficient research on MSR global and intrinsic kinetics for operating SOFCs with complete Ni-ceria anodes. Further, it emphasizes the need to develop readily applicable global kinetic models as a subsequent step from previously reported state-of-art and complex intrinsic models. Two rate expressions of the Power law (PL) and Langmuir-Hinshelwood (LH) type have been compared and based on the analysis, limitations of using previously proposed rate expressions for Ni catalytic beds to study MSR kinetics for complete cermet anodes have been identified. Firstly, it has been shown that methane reforming on metallic (Ni) current collectors may not be always negligible, contrary to literature reports. Both PL and LH kinetic models predict significantly different local MSR reaction rate and species partial pressure distributions along the normalized reactor length, indicating a strong need for further experimental verifications.

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This article presents a detailed thermodynamic case study based on the Willem-Alexander Centrale (WAC) power plant in the Netherlands towards retrofitting SOFCs in existing IGCC power plants with a focus on near future implementation. Two systems with high percentage (up to 70%) biomass co-gasification (based on previously validated steady state models) are discussed: (I) a SOFC retrofitted IGCC system with partial oxy-fuel combustion CO₂ capture (II) a redesigned highly efficient integrated gasification fuel cell (IGFC) system with full oxy-fuel CO₂ capture. It is concluded that existing IGCC power plants could be operated without major plant modifications and relatively high electrical efficiencies of more than 40% (LHV) by retrofitting SOFCs and partial oxy-combustion CO₂ capture. In order to apply full scale CO₂ capture, major process modification and redesign needs to be carried out, particularly in the gas turbine unit and heat recovery steam generator (HRSG). A detailed exergy analysis has also been presented for both the systems indicating significant efficiency improvement with the utilization of SOFCs. Additional discussions have also been presented on carbon deposition in SOFCs and biomass CO₂ neutrality. It is suggested that scaling up of the SOFC stack module be carried out gradually, synchronous with latest technology development. The thermodynamic analysis and results presented in this article are also helpful to further evaluate design challenges in retrofitted IGCC power plant systems for near future implementation, gas turbine part load behaviour, to devise appropriate engineering solutions and for techno-economic evaluations.

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Computational fluid dynamics (CFD) models can be used to optimize operational conditions for safe and stable operation of direct internal reforming solid oxide fuel cells (SOFCs), but require an appropriate description of the reforming kinetics on the anode. A CFD model, representing a single channel in a single cell test station is developed in this study. Data from previous methane steam reforming experiments on single cells is used to parameterize two kinetic models, one of the power law and one of the Langmuir-Hinshelwood type, using an ideal plug flow reactor model. Both rate equations are implemented in the CFD model and used to simulate the experimental conditions. Although the model shows good statistical agreement with the experimental data for both rate equations, different spatial distributions of reaction rates, species concentrations and temperature are predicted.@en

Natural gas combined cycle (NGCC) power plants with pre-combustion CO2 capture called, integrated reforming combined cycle (IRCC) power plants could be operated in a flexible and environment friendly manner by incorporating hydrogen storage. The current article presents a thermodynamic model evaluation of such a flexible large scale power plant system with co-production of hydrogen and subsequent hydrogen storage with metal hydrides (MH). A comparative analysis has been presented using steady state ASPEN Plus models for a Reference NGCC system, an IRCC system and a Flexible IRCC system with MH (MgH2) based hydrogen storage. In addition, a detailed exergy analysis indicating irreversibilities in the system has been presented. The system study indicates that such Flexible IRCC systems could be operated with a time based average (considering charging and discharging) electrical efficiency above 45% depending on the amount of hydrogen stored, appropriate heat integration and choice of the metal hydride. Exergy analysis indicates that such flexible systems could still be operated at a relatively high average net exergy efficiency (considering charging and discharging). Addition of MH based H2 storage in an IRCC system does not lead to significant electrical/exergy efficiency penalty. Carbon capture and storage is a larger source of efficiency penalty than the MH based H2 storage unit. The largest exergy destruction is observed in the gas turbine combustor and reformer units, providing additional scope for efficiency enhancement. With a larger share of renewable power in the total electrical power production expected in future, Flexible IRCC systems as presented in this article could be used as an efficient solution to address the large fluctuations in power supply and demand. Additional investigations are however encouraged further toward optimizing the choice of the metal hydride, detailed design of a single heat integrated system (including part load behavior) and economic assessments based on the heat and mass balances developed in this study.@en