Publications

Hydrogen offers a promising solution to reduce emissions in the energy sector with the growing need for decarbonisation. Despite its environmental benefits the use of hydrogen presents significant challenges in storage and transport. Many studies have focused on the different types of hydrogen production and analysed the pros and cons of each technique for different applications. This study focuses on techno-economic analysis of onsite hydrogen production through ammonia decomposition by utilising the heat from exhaust gas generated by hydrogen-fuelled gas turbines. Aspen Plus simulation software and its economic evaluation system are used. The Siemens Energy SGT-400 gas turbine’s parameters are used as the baseline for the hydrogen gas turbine in this study together with the economic parameters of the capital expenditure (CAPEX) and operating expenditure (OPEX) are considered. The levelised cost of hydrogen (LCOH) is found to be 5.64 USD/kg of hydrogen which is 10.6% lower than that of the conventional method where a furnace is used to increase the temperature of ammonia. A major contribution of the LCOH comes from the ammonia feed cost up to 99%. The price of ammonia is found to be the most sensitive parameter of the contribution to LCOH. The findings of this study show that the use of ammonia decomposition via heat recovery for onsite hydrogen production with ammonic recycling is economically viable and highlight the critical need to further reduce the prices of green ammonia and blue ammonia in the future.

Underground hydrogen storage in aquifers is a promising solution to address the imbalance between energy supply and demand yet its practical implementation requires optimized strategies to ensure high efficiency and economic viability. To improve the storage and production efficiency of hydrogen it is essential to select the appropriate cushion gas and to study the influence of reservoir and process parameters. Based on the conceptual model of aquifer with single-well injection and production three potential cushion gas (carbon dioxide nitrogen and methane) were studied and the changes in hydrogen recovery for each cushion gas were compared. The effects of temperature initial pressure porosity horizontal permeability vertical to horizontal permeability ratio permeability gradient hydrogen injection rate and hydrogen production rate on the purity of recovered hydrogen were investigated. Additionally the impact of different well pattern on the purity of recovered hydrogen was studied. The results indicate that methane is the most effective cushion gas for improving hydrogen recovery in UHS. Different well patterns have significant impacts on the purity of recovered hydrogen. The mole fractions of methane in the produced gas for the single-well line-drive pattern and five-spot pattern were 16.8% 5% and 3.05% respectively. Considering the economic constraints the five-spot well pattern is most suitable for hydrogen storage in aquifers. Reverse rhythm reservoirs with smaller permeability differences should be chosen to achieve relatively high hydrogen recovery and purity of recovered hydrogen. An increase in hydrogen production rate leads to a significant decrease in the purity of the recovered hydrogen. In contrast hydrogen injection rate has only a minor effect. These findings provide actionable guidance for the selection of cushion gas site selection and operational design of aquifer-based hydrogen storage systems contributing to the large-scale seasonal storage of hydrogen and the balance of energy supply and demand.

Propulsion systems in aircraft using reciprocating engines often face the challenge of managing thermal loads effectively. This problem is similar to the utilisation of polymer electrolyte membrane fuel cell systems which despite their high efficiency emit a high proportion of heat when converting chemical energy into electrical energy. Transfer of the rejected heat to the air is efficiently performed by heat exchangers. Since convective heat transfer is physically linked to fluid friction at the heat exchanger walls a pressure loss occurs. In a high-speed flow regime of the aircraft during cruise the integration of heat exchangers combined with a fan stage inside a nacelle (thus forming an impeller configuration) represents a promising approach for the dual benefit of dissipating excess heat and harnessing it for additional thrust generation through the ram jet effect. Striving for enhanced thrust performance of hydrogen electric commercial aircraft this paper presents the results of a parameter study based on a 1D-modelling approach. The focus is placed on the influence of design and operating parameters (ambient conditions fan pressure ratio diffusion ratio airside temperature difference) on performance and sizing of the proposed propulsion system. It is shown that the proposed system performs best at an altitude of 11 km and with increasing freestream Mach number. Furthermore the main challenges related to the combination of a thrust generation system with a heat exchanger in terms of sizing in particularly the required heat exchanger dimensions under different operating conditions are discussed.

Hydrogen plays a key role in decarbonising hard-to-abate sectors like aviation steel and shipping. However producing pure hydrogen requires significant energy to break chemical bonds from its sources such as gas and water. Ideally the energy used for this process should match the energy output from hydrogen but in reality energy losses occur at various stages of the hydrogen economy—production packaging delivery and use. This results in needing more energy to operate the hydrogen economy than it can ultimately provide. To address this passive power sources like latent thermal energy storage systems can help reduce costs and improve efficiency. These systems can enable passive cooling or electricity generation from waste heat cutting down on the extra energy needed for compression liquefaction and distribution. This study explores integrating latent thermal energy storage into all stages of the hydrogen economy offering a cost and sizing approach for such systems. The integration could reduce costs close the waste-heat recycling loop and support green hydrogen production for achieving NetZero by 2050.

The use of rare earth elements in hydrogen storage processes offers significant advantages in terms of increasing technological efficiency and ensuring system security. However this process also creates some serious problems in terms of environmental and economic sustainability. It is necessary to determine the most critical indicators affecting the sustainable use of these elements. Studies on this subject in the literature are quite limited and this may lead to wrong investment decisions. The main purpose of this study is to determine the most important indicators to increase the sustainable use of rare earth elements in hydrogen storage processes. An original decision-making model in which Siamese network logarithmic percentage-change driven objective weighting (LOPCOW) fractal fuzzy numbers and weighted influence super matrix with precedence (WISP) approaches are integrated in the study. This study provides an original contribution to the literature by identifying the most critical indicators affecting the sustainable use of rare earths in hydrogen storage processes by presenting an innovative model. Fractal structures such as Koch Snowflake Cantor Dust and Sierpinski Triangle can model complex uncertainties more successfully. Fractal structures are particularly effective in modeling linguistic fuzziness because their recursive nature closely mirrors the layered and imprecise way humans often express subjective judgments. Unlike linear fuzzy sets fractals can capture the patterns of ambiguity found in expert evaluations. Hydrogen storage capacity and government supports are determined as the most vital criteria affecting sustainability in rare earth use.

Hydrogen energy is key for the global green energy transition and biomass thermochemical has become an important option for green hydrogen production due to its carbon neutrality advantage. Pyrolysis is the initial step of thermochemical technologies. A systematic analysis of the mechanism of H2 production from biomass pyrolysis is significant for the subsequent optimal design of efficient biomass thermochemical H2 production technologies. Biomass is mainly composed of cellulose hemicellulose and lignin and differences in their physicochemical properties and structures directly affect the pyrolysis hydrogen production process. In this study thermogravimetry-mass spectrometry-Fourier transform infrared spectroscopy (TG-MS-FTIR) was employed and fixed-bed pyrolysis experiments were conducted to systematically investigate the pyrolysis of biomass component with focusing on hydrogen production. According to the results of TG-MS-FTIR experiments hemicellulose produced hydrogen through the breaking of C-H bonds in short chains and acetyl groups as well as secondary cracking of volatiles and condensation of aromatic rings at high temperatures. Cellulose produced hydrogen through the breaking of C-H bonds in volatiles generated from sugar ring cleavage along with char gasification and condensation of aromatic rings at high temperatures. Lignin produced hydrogen through ether bond cleavage breaking of methoxy groups as well as cleavage of phenylpropane side chains and condensation of aromatic rings at high temperatures. Results from fixed-bed pyrolysis experiments further showed that hemicellulose exhibited the strongest hydrogen production capacity with the maximum H2 production efficiency of 6.09 mmol/g the maximum H2 selectivity of 17.79% and the maximum H2 effectiveness of 59% at 800°C.

The global climate crisis necessitates the urgent implementation of sustainable practices and carbon emission reduction strategies across all sectors. Transport as a major contributor to greenhouse gas emissions requires transitional technologies to bridge the gap between fossil fuel dependency and renewable energy systems. Natural gas recognised as the cleanest fossil-derived fuel with approximately half the CO2 emissions of coal and 75% of oil presents a potential transitional solution through Natural Gas Vehicles (NGVs). This manuscript presents several distinctive contributions that advance the understanding of Natural Gas Vehicles within the contemporary energy transition landscape while synthesising updated emission performance data. Specifically the feasibility and sustainability of NGVs are investigated within the energy transition framework by systematically incorporating recent technological developments and environmental economic and infrastructure considerations in comparison to conventional vehicles (diesel and petrol) and unconventional alternatives (electric and hydrogen-fuelled). The analysis reveals that NGVs can reduce CO2 emissions by approximately 25% compared to petrol vehicles on a well-to-wheel basis with significant reductions in NOx and particulate matter. However these environmental benefits depend heavily on the source and type of natural gas used (CNG or LNG) while economic viability hinges largely on governmental policies and infrastructure development. The findings suggest that NGVs can serve as an effective transitional technology in the transport sector’s sustainability pathway particularly in regions with established natural gas infrastructure but require supportive policy frameworks to overcome implementation barriers.

Hydrogen storage is integral to reducing CO2 emissions particularly in the oil and gas industry. However a primary challenge involves the solubility of hydrogen in subsurface environments particularly saline aquifers. The dissolution of hydrogen in saline water can impact the efficiency and stability of storage reservoirs necessitating detailed studies of fluid dynamics in such settings. Beyond its role as a clean energy carrier and precursor for synthetic fuels and chemicals understanding hydrogen’s solubility in subsurface conditions can significantly enhance storage technologies. When hydrogen solubility is high it can reduce reservoir pressure and alter the chemical composition of the storage medium undermining process efficiency. Machine learning techniques have gained prominence in predicting physical and chemical properties across various systems. One of the most complex challenges in hydrogen storage is predicting its solubility in saline water influenced by factors such as pressure temperature and salinity. Machine learning models offer substantial promise in improving hydrogen storage by identifying intricate nonlinear relationships among these parameters. This study uses machine learning algorithms to predict hydrogen solubility in saline aquifers employing techniques such as Bayesian inference linear regression random forest artificial neural networks (ANN) support vector machines (SVM) and least squares boosting (LSBoost). Trained on experimental data and numerical simulations these models provide precise predictions of hydrogen solubility which is strongly influenced by pressure temperature and salinity under a wide range of thermodynamic conditions. Among these methods RF outperformed the others achieving an R2 of 0.9810 for test data and 0.9915 for training data with RMSE values of 0.048 and 0.032 respectively. These findings emphasize the potential of machine learning to significantly optimize hydrogen storage and reservoir management in saline aquifers.

The carbon emission reduction mission requires a multifaceted approach in which green hydrogen is expected to play a key role. The accelerated adoption of green hydrogen technologies is vital to this journey towards carbon neutrality by 2050. However the energy transition involving green hydrogen requires a data-driven approach to ensure that the benefits are realised. The introduction of testing sites for green hydrogen technologies will be crucial in enabling the performance testing of various components within the green hydrogen value chain. This study involves an areal assessment of a selected test site for the installation of a grid-tied solar PV-green hydrogen-battery storage microgrid system at a factory facility in South Africa. The evaluation includes a site energy audit to determine the consumption profile and an analysis of the location’s weather pattern to assess its impact on the envisaged microgrid. Lastly a design of the microgrid is conceptualised. A 39 kW photovoltaic system powers the microgrid which comprises a 22 kWh battery storage system 10 kW of electrolyser capacity an 8 kW fuel cell and an 800 L hydrogen storage capacity between 30 and 40 bars.

Green hydrogen offers a sustainable alternative source of fossil fuels to compensate for the increasing energy demand. This study addresses the increasing energy demand and the need for sustainable alternatives to fossil fuels by examining the production of green hydrogen in an existing Egyptian oil refinery. The primary objective is to evaluate the technical economic and environmental outcomes of integrating green hydrogen to increase the refinery’s hydro processing capacity. The methodology involves the use of water electrolysis powered exclusively by renewable electricity from a 60 MW solar installation with a panel surface area of 660000 m². A simulation model of alkaline electrolyzer skids was developed to assess the production of an additional 1260 kg/h of hydrogen representing a 15% increase over the existing Steam Methane Reforming (SMR) capacity. The environmental impact was quantified by calculating the reduction in CO₂ and equivalent emissions while an economic forecasting analysis was conducted to project the production costs of green versus grey hydrogen. The main results indicate that the integration is technically feasible and environmentally beneficial with a significant reduction in the refinery’s carbon footprint. Economically the study projects that by 2028 the production cost of green hydrogen will fall to 1.56 USD/kg H₂ becoming more cost-effective than grey hydrogen at 1.65 USD/kg H₂ largely due to the influence of carbon taxes and credits. This study underscores the transformative potential of green hydrogen in decarbonizing industrial processes offering a viable pathway for refineries to contribute to global climate change mitigation efforts.