This research forms part of a programme of work at the University of Canterbury investigating the production of liquid fuels from biomass. The drivers for this research are the plentiful supply of woody biomass in New Zealand as well as the necessity for a reduction in the use of fossil fuels. Fischer-Tropsch synthesis has been chosen as the base conversion method for syngas to liquid fuels. While Fischer-Tropsch plants are traditionally very large, the low geographical density of the biomass feedstock necessitates a shift from a traditional economies of scale approach. In this research a sawmill integrated polygeneration scenario is proposed that recognises the synergy between the heat and electrical requirements of a mill and the Fischer-Tropsch process that can supply both as well as liquid fuels. Techno-economic modelling of variations to this polygeneration arrangement were performed using a traditional Fischer-Tropsch slurry reactor as the basis. The breakeven price of syncrude produced in the process based on a 30 year plant life and 10% discount factor was as low as $US 167 per barrel. This arrangement is coupled with development of and experimentation with a microchannel reactor in a further attempt to overcome economies of scale disadvantages. The lab scale microchannel reactor consisted of a shim with 50 channels of 37mm length with 0.2mm height and 0.3mm width. The microchannel reactor was tested with shorter run periods to compare different catalyst washcoats consisting of neat cobalt, cobalt on titania and a combustion synthesis method over a temperature range of 210-240°C at 20 bar. Comparison was also made to a lab scale fixed bed reactor with a powdered cobalt on titania catalyst. The neat cobalt washcoat proved to have the best performance per unit mass of catalyst of the three washcoats. The performance of the microchannel reactor was 32-40 times better per unit catalyst mass than the fixed bed reactor. From data based on the shorter runs the neat cobalt washcoat and the cobalt on titania washcoat were selected for further analysis over longer runs at a range of pressures from 2-20 bar and temperatures from 210-240°C. These runs were each approximately 70 hours long and provided a better analysis of the narrowed catalyst choice. The productivity results of the catalysts were fitted to established kinetic equations from literature with an excellent correlation. More accurate Anderson-Schultz-Flory selectivity values were also obtained ranging between 0.72 to 0.82. This is certainly an area that would warrant further attention as a higher selectivity has a very positive affect on plant economics. Establishment of the kinetic equations for the catalyst performance allowed modelling of reactors with greater volume along with investigation of mass transfer limitations to assist in scale up of the technology. It was found that under 4-5mm hydraulic diameter channel dimensions the mass transfer limitation from the bulk gas phase to the catalyst interface is negligible. A scaled up microchannel reactor concept design is proposed utilising stainless steel mesh folded into 2mm channels to increase catalyst surface area compared to straight shim. A costing correlation was produced per unit of reactor volume to allow a full scale cost of the microchannel reactor to be estimated for inclusion into the techno-economic model. The revised techno-economic model was optimised through pressure variation to give a breakeven syncrude value of $US118 per barrel at Fischer-Tropsch reaction conditions of 10 bar and 240°C. This brings the value well within historical crude price trends.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21753号 / 工博第4570号 / 新制||工||1712(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 西脇 眞二, 教授 松原 厚, 教授 黒瀬 良一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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 (<10 Pa mm-1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to low-power fuel cell systems. In Chapter 4, hydrogen production from the Ni-Pt-washcoated ammonia-fuelled microchannel reactor was mathematically simulated in a three-dimensional (3D) CFD model implemented via Comsol Multiphysics™. The objective was to obtain an understanding of reaction-coupled transport phenomena as well as a fundamental explanation of the observed microchannel reactor performance. The transport processes and reactor performance were elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case was first investigated to comprehend the behavior of the microchannel reactor, then microstructural design and operating parameters were methodically altered around the baseline conditions to explore the optimum values (case-study optimization). The modelling results revealed that an optimum NH3 space velocity (GHSV) of 65.2 Nl 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 was also shown that a 40-μm-thick porous washcoat was most desirable at these conditions. Finally, a low channel hydraulic diameter (225 μm) was observed to contribute to high NH3 conversion. Most importantly, mass transport limitations in the porouswashcoat and gas-phase were found to be negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor produced 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 was observed, so the integrated experimental-modeling approach used here may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformers. In Chapter 5, the prospect of producing H2 via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Cs-promoted Ru/Al2O3 catalyst (ACTA Hypermec 10010). 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 Ru-based microchannel reactor outperformed other NH3 microstructured reformers reported in literature including the Ni-based system used in Chapter 3. Furthermore, the microchannel reactor showed a superior performance against a fixed-bed tubular microreactor with the same Ru-based catalyst. Overall, the high H2 throughput exhibited may promote widespread use of the Ru-based micro-reaction system in high-power applications. Four peer-reviewed journal publications and six conference publications resulted from this work. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

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 (<10 Pa mm-1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to low-power fuel cell systems. In Chapter 4, hydrogen production from the Ni-Pt-washcoated ammonia-fuelled microchannel reactor was mathematically simulated in a three-dimensional (3D) CFD model implemented via Comsol Multiphysics™. The objective was to obtain an understanding of reaction-coupled transport phenomena as well as a fundamental explanation of the observed microchannel reactor performance. The transport processes and reactor performance were elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case was first investigated to comprehend the behavior of the microchannel reactor, then microstructural design and operating parameters were methodically altered around the baseline conditions to explore the optimum values (case-study optimization). The modelling results revealed that an optimum NH3 space velocity (GHSV) of 65.2 Nl 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 was also shown that a 40-μm-thick porous washcoat was most desirable at these conditions. Finally, a low channel hydraulic diameter (225 μm) was observed to contribute to high NH3 conversion. Most importantly, mass transport limitations in the porouswashcoat and gas-phase were found to be negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor produced 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 was observed, so the integrated experimental-modeling approach used here may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformers. In Chapter 5, the prospect of producing H2 via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Cs-promoted Ru/Al2O3 catalyst (ACTA Hypermec 10010). 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 Ru-based microchannel reactor outperformed other NH3 microstructured reformers reported in literature including the Ni-based system used in Chapter 3. Furthermore, the microchannel reactor showed a superior performance against a fixed-bed tubular microreactor with the same Ru-based catalyst. Overall, the high H2 throughput exhibited may promote widespread use of the Ru-based micro-reaction system in high-power applications. Four peer-reviewed journal publications and six conference publications resulted from this work. / PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2015