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In this thesis, ammonia (NH3) decomposition was assessed as a fuel processing technology for producing on-demand hydrogen (H2) for portable and distributed fuel cell applications. This study was motivated by the present lack of infrastructure to generate H2 for proton exchange membrane (PEM) fuel cells. An overview of past and recent worldwide research activities in the development of reactor technologies for portable and distributed hydrogen generation via NH3 decomposition was presented in Chapter 2. The objective was to uncover the principal challenges relating to the state-of-the-art in reactor technology and obtain a basis for future improvements. Several important aspects such as reactor design, operability, power generation capacity and efficiency (conversion and energy) were appraised for innovative reactor technologies vis-à-vis microreactors, monolithic reactors, membrane reactors, and electrochemical reactors (electrolyzers). It was observed that substantial research effort is required to progress the innovative reactors to commercialization on a wide basis. The use of integrated experimental-mathematical modelling approach (useful in attaining accurately optimized designs) was notably non-existent for all reactors throughout the surveyed openliterature. Microchannel reactors were however identified as a transformative reactor technology for producing on-demand H2 for PEM cell applications. Against this background, miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reactor (reformer) washcoated with a commercial Ni-Pt/Al2O3 catalyst (ActiSorb® O6) was demonstrated successfully in Chapter 3. The reformer performance was evaluated by investigating the effect of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6 520–32 600 Nml gcat -1 h-1) on key performance parameters including NH3 conversion, residual NH3 concentration, H2 production rate, and pressure drop. Particular attention was devoted to defining operating conditions that minimised residual NH3 in reformate gas, while producing H2 at a satisfactory rate. The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32 600 Nml gcat -1 h-1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L-1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (

The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed to global warming due to the huge CO2 emissions of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the limited lifespan of coal reserves. These simultaneous challenges of environmental sustainability and energy security associated with CTL facilities have been defined in earlier studies. To reduce the environmental impact and improve the carbon conversion of existing CTL facilities, this paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS) plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL plant. A synthesis gas (syngas) plant mass–analysis model described in this paper demonstrates that the water–gas shift (WGS) and combustion reactions occurring in hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The nuclear–assisted CTL plant concept that we have developed is entirely based on the elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75% reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas output. In addition, we have developed a financial model for use as a strategic decision analysis (SDA) tool that compares the relative syngas manufacturing costs for conventional and nuclear–assisted syngas plants. Our model predicts that syngas manufactured in the nuclear–assisted CTL plant would cost 21% more than that produced in the conventional CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model works out to below this threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear–assisted CTL plant. Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

MEng (Chemical Engineering), North-West University, Potchefstroom Campus This dissertation evaluates the performance of a microchannel reactor for the decomposition of vaporised formic acid as a promising technology for the production of hydrogen for proton exchange membrane fuel cell applications. Accordingly, a combined experimental and modelling approach was used to evaluate the microchannel reactor coated with a gold supported on alumina (1.15 wt. % Au/Al2O3) catalyst. For the experimental evaluation, two phase of experiments were carried out where pure formic acid (99.99 %) and dilute formic acid (50 vol. %) were taken as the feed to the reactor respectively. The first phase of the experimental evaluation involved measuring key performance parameters such as, formic acid conversion, formic acid residual concentration, selectivity to hydrogen and hydrogen yield at different temperatures of 250 – 350°C and formic acid (99.99 %) vapour flowrates of 12 – 48ml/min. Overall, the reactor performed well in decomposing pure formic acid (99.99 %), achieving conversions (98 to 99 %) close to equilibrium at 350 oC and all studied vapour formic acid flowrates of 12 – 48 ml/min. At all studied temperatures however, both dehydrogenation (HCOOH → H2 +CO2) and dehydration (HCOOH → H2O+CO) reactions occurred and the dehydrogenation reaction was found to be dominant. The dehydration reaction was mostly favoured at high temperatures and carbon monoxide concentrations ranged between 4 – 15 % while the corresponding selectivity towards H2 production ranged between 0.7 and 0.88. Effort was made to improve the H2 yields in the second phase of the experiments through decomposing a mixture of formic acid and water (50/50 vol. %) thereby promoting the occurrence of the forward water gas shift reaction. Under these conditions, carbon monoxide concentrations decreased to a range of 2 – 7 % while selectivity towards hydrogen production increased to a range of 0.84 – 0.94. Overall, for both pure FA (99.99 %) and dilute FA (50 vol.%), the best microchannel reactor performance was achieved at a reactor operating temperature of 350 oC and FA vapour flowrate of 48 ml/min (17.1 Nml.gcat-1.h-1). At these conditions, H2 production rate (11.8 NL.gcat-1.h-1) was maximised with pure FA (99.99 %) while selectivity (0.81) and H2 yield (80) were maximised with dilute FA (50 vol.%). Overall, the reactor was found stable at a continuous period of 144 hours after running for approximately 1 200 hours. A computational fluid dynamic model was developed for concentrated formic acid (99.99 %) experiments aimed at describing reaction-coupled transport phenomena relating to velocity, mass and temperature profiles within the microchannel reactor. Kinetic rate expressions that best described the experimental results were successfully estimated using a model-based parameter optimisation and refinement on Comsol Multiphysics™ 4.3b. Validation of the model against the experimental results showed that the developed model was an acceptable fit to the experimental conversions and hydrogen yields especially at temperatures higher than 250 oC. Overall, this dissertation highlights the first steps in the development and use of microchannel reactors in promoting formic acid as a future hydrogen storage medium for portable and distributed fuel cell applications. Masters

In this work, an integrated experimental and CFD modelling technique was used to evaluate a microchannel reactor producing hydrogen from ammonia decomposition using a commercial Ru/Al2O3 catalyst. The microchannel reactor performance was first assessed in a series of experiments varying the reaction temperature (723–873 K) and ammonia flow rates (100–500 Nml min−1) at atmospheric pressure. A global rate expression based on Temkin-Pyzhev kinetics that accurately predicts the entire experimental operating space was established using a model-based technique with parameter refinement and estimation. The kinetic model provided the reaction source term for subsequent CFD simulations aiming to obtain a more fundamental understanding of the reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance were discussed in detail using velocity, temperature, and species concentration profiles. Finally, the influence of mass transport limitations within the various regions of the microchannel reactor was evaluated and discussed by means of dimensionless numbers vis-a-vis Damkohler and Fourier numbers. Overall, results presented in this paper provide valuable data for the efficient design of ammonia-fuelled microchannel reactors for hydrogen generation aimed at portable and distributed fuel cell applications.

The methanation of carbon dioxide (CO 2 ) via the Sabatier process is increasingly gaining interest for power-to-gas application. In this investigation, a microchannel reactor was evaluated for CO 2 methanation at different operational pressures (atmospheric, 5 bar, and 10 bar), reaction temperatures (250–400 °C) and space velocities (32.6–97.8 L.g cat −1 .h −1 ). The recommended operation point was identified at reactor conditions corresponding to 5 bar, 400 °C, and 97.8 L.g cat −1 .h −1 . At this condition, the microchannel reactor yielded good CO 2 conversion (83.4%) and high methane (CH 4 ) productivity (16.9 L.g cat −1 .h −1 ). The microchannel reactor also demonstrated good long-term performance at demanding operation conditions relating to high space velocity and high temperature. Subsequently, a CFD model was developed to describe the reaction-coupled transport phenomena within the microchannel reactor. Kinetic rate expressions were developed and validated for all reaction conditions to provide reaction source terms for the CFD modelling. Velocity and concentration profiles were discussed at different reaction conditions to interpret experimental results and provide insight into reactor operation. Overall, the results reported in this paper could give fundamental design and operational insight to the further development of microchannel reactors for CO 2 methanation in power-to-gas applications.

Hydrogen production from an ammonia-fuelled microchannel reactor is simulated in a three-dimensional (3D) model implemented via Comsol Multiphysics™. The work described in this paper endeavours to obtain a mathematical framework that provides an understanding of reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance are elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case is first investigated to comprehend the behaviour of the microchannel reactor, then microstructural design and operating parameters are methodically altered around the baseline conditions to explore the optimum values. The simulation results show that an optimum NH3 space velocity (GHSV) of 65,000 Nml gcat−1 h−1 yields 99.1% NH3 conversion and a power density of 32 kWe L−1 at the highest operating temperature of 973 K. It is also shown that a 40-μm-thick porous washcoat is most desirable at these optimum conditions. Finally, a low channel hydraulic diameter (225 μm) is observed to contribute to high NH3 conversion. Mass transport limitations in the porous-washcoat and gas-phase are negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor yields 98.2% NH3 conversion and a power density of 30.8 kWe L−1 when tested at the optimum operating conditions established by the model. Good agreement with experimental data is observed, so the integrated experimental-modelling approach developed in this paper may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformers http://www.journals.elsevier.com/international-journal-of-hydrogen-energy/ http://dx.doi.org/10.1016/j.ijhydene.2014.05.146 Hydrogen Infrastructure Centre of Competence, Department of Science and Technology of the Republic of South Africa (Grant numbers; KP4-I05 and IFR13022017531), and the North-West University

The production of synthetic fuels (synfuels) in Coal-to-Liquid (CTL) facilities has contributed to global warming due to the enormous carbon dioxide (CO2) emission footprint of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the severe consequences concomitantly posed by global warming and the rapid depletion of coal reserves. This paper seeks to address these simultaneous challenges of environmental and energy sustainability associated with CTL facilities. To reduce the environmental impact and improve the carbon conversion of CTL facilities, we propose and apply the concept of a nuclear-assisted synthesis gas (syngas) plant to a reference syngas plant in a CTL facility consisting of 36 dry fixed-bed gasifiers. In this kind of plant, a Hybrid Sulphur (HyS) plant powered by 10 high-temperature nuclear reactors (HTR's) splits water to produce nuclear hydrogen and oxygen. The nuclear hydrogen supplements the hydrogen-poor syngas from the Rectisol and the oxygen becomes part of the gasifier feed. The nuclear-assisted syngas plant concept that we have developed is entirely based on the premise that the water-gas shift (WGS) reaction is minimised by operating a dry fixed-bed gasifier under steam-lean conditions. A mass-analysis model of the syngas plant described in this paper demonstrates that the WGS reaction contributes 68% to the CO2 emission output. The consequent benefits of eliminating the WGS reaction include reductions in the CO2 emissions and gasification coal requirement of 75% and 40%, respectively, all to achieve the same syngas output as the conventional syngas plant. In addition, we have developed an economic model for use as a strategic decision analysis tool that compares the relative syngas manufacturing costs for conventional and nuclear-assisted syngas plants. Our model predicts that syngas manufactured in the nuclear-assisted CTL plant would cost 21% more to produce when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided, which at the average hydrogen cost is $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of $2/kg H2 or at a delivered coal cost of $128/t coal. The economic advantages of the nuclear-assisted syngas plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model is below the threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear-assisted CTL plant.

In this work, the prospect of producing hydrogen (H2) via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Ruthenium-based catalyst. The reactor performance was investigated under atmospheric pressure as a function of reaction temperature (723–873 K) and gas-hourly-space-velocity (65.2–326.1 Nl gcat−1 h−1). Ammonia conversion of 99.8% was demonstrated at 326.1 Nl gcat−1 h−1 and 873 K. The H2 produced at this operating condition was sufficient to yield an estimated fuel cell power output of 60 We and power density of 164 kWe L−1. Overall, the microchannel reactor considered here outperformed the Ni-based microstructured system used in our previous work DST Hydrogen Infrastructure Centre of Competence, and the North-West University (under the following Grant numbers: KP5-I05-Chemical Hydrogen Production Technologies; KP4-Hydrogen Fuelling Options; NRF grant 85309)

Microchannel reactors appear attractive as integral parts of fuel processors to generate hydrogen (H2) for portable and distributed fuel cell applications. The work described in this paper evaluates, characterizes, and demonstrates miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reformer. The performance of the microchannel reformer is investigated as a function of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6520–32,600 Nml gcat−1 h−1). The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32,600 Nml gcat−1 h−1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L−1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (

Hydrogen (H2) fuel obtained via thermo-catalytic ammonia (NH3) decomposition is rapidly attracting considerable interest for portable and distributed power generation systems. Consequently, a variety of reactor technologies are being developed in view of the current lack of infrastructure to generate H2 for proton exchange membrane (PEM) fuel cells. This paper provides an extensive review of the state-of-the-art reactor technology (also referred to as reactor infrastructure) for pure NH3 decomposition. The review strategy is to survey the open literature and present reactor technology developments in a chronological order. The primary objective of this paper is to provide a condensed viewpoint and basis for future advances in reactor technology for generating H2 via NH3 decomposition. Also, this review highlights the prominent issues and prevailing challenges that are yet to be overcome for possible market entry and subsequent commercialization of various reactor technologies. To our knowledge, this work presents for the first time a review of reactor infrastructure for distributed H2 generation via NH3 decomposition. Despite commendable research and development progress, substantial effort is still required if commercialization of NH3 decomposition reactor infrastructure is to be realized. http://www.journals.elsevier.com/international-journal-of-hydrogen-energy/

The Department of Science and Technology of South Africa developed the National Hydrogen and Fuel Cells Technologies (HFCT) Research, Development and Innovation Strategy. The National Strategy was branded Hydrogen South Africa (HySA). HySA has been established consisting of three Competency Centres - HySA Infrastructure, HySA Catalyst and HySA Systems. The scope of the Hydrogen Infrastructure Competency Centre (HySA Infrastructure CoC, [1]) is to develop applications and solutions for small- and medium-scale hydrogen production and storage through innovative research and development. The aim of this paper is to present an overview of the HySA Infrastructure CoC projects related to renewable hydrogen and fuel cell applications. The presentation will discuss how the HySA Infrastructure could assist telecommunication industry with providing a potential strategic platform for developing and testing various hydrogen generating solutions for fuel cell applications specific to African conditions. More specifically, the following enablers will be discussed: existing active projects for hydrogen production: solar-to-hydrogen demonstrations based on PEM electrolysis, ammonia-to-hydrogen projects for telecom, advanced PEM electrolysis concepts (high-current density operation), hydrogen storage, safety and codes, as well as close proximity of HySA Infrastructure to Gauteng, an economical hub of South Africa, commercialization road map, activities towards establishing “Platinum Valley” SEZ (special economic zone for Pt-related activities)