| dc.description.abstract | Human activities caused significant greenhouse gas emissions since industrial revolution which contributes to the global warming. To limit the emissions, the global energy system shall transform from a fossil-based energy system to an efficient and renewable-based low-carbon energy system. However, the intermittency of renewable energy sources provides unstable outputs and may not comply with the energy demands on all time frames, and the network faces periodic surplus and shortage of energy.
Therefore, hybrid energy systems which integrate renewable energy generation technologies with dispatchable energy generation technologies can be the ultimate solution. Currently, the commonly used dispatchable technologies are operating with fossil fuels which contributes to CO2 emissions. On the other hand, CCS and CCU are costly and cannot be applied for small scales. Hence, a dispatchable energy generation technology that can utilize clean and renewable based alternative fuels such hydrogen to maintain the grid flexibility and stability become attractive.
Micro gas turbines are considered as promising technologies to be applied in the carbon-free hybrid energy system. They can have overall efficiency of about 80% in combined heat and power applications. They have low maintenance requirement, high reliability, and fuel flexibility. In this context, an initiative to investigate different challenges and ultimately corresponding solutions from a small-scale perceptive using a micro gas turbine’s (MGT) system is under development at UiS. The research project indeed aims at performing an energy system analysis using a MGT running on hydrogen as an alternative carbon-free fuel to natural gas.
The present work aims to study the Turbec T100 micro gas turbines’ fuel flexibility in hydrogen application, which is the baseline technology for ongoing hydrogen conversion related experimental activities at UiS. To this end, this study focuses on the performance evaluation of MGT using a dynamic model developed based on Turbec T100 MGT. The modelling is done using UniSim software which is a process simulation tool. The model is validated against the available experimental data from the existing MGT at UiS. The validation results show an acceptable accuracy especially on the loads higher than 60%.
Using the validated model, the thesis presents the results of the simulation model with regards to fuel flexibility and performance of the MGT in hydrogen applications. Various fraction of hydrogen in natural gas (NG) is applied, to analyze the performance and efficiency of the gas turbine at different loads. Additionally, the effect of ambient temperature at constant load is studied. The results shows that higher hydrogen fractions in the fuel leads to lower fuel consumptions (mass) and higher electrical efficiencies but slight reduction in surge margin. The results from the effect of ambient temperature, at constant power output, confirms lower electrical efficiency and higher fuel consumption at higher air temperature but slightly higher surge margin.
As the main result, it can be suggested that converting the existing NG-based MGT to hydrogen based MGT not only worsens the overall performance of the gas turbine but also some improvements could potentially be achieved. And there is no need to modify/re-bundle the existing compressor or the turbine. On the other hand, combustion module, ventilation system, control valves, control system, safety systems such hydrogen detection and inert gas purge system, metering and gas composition monitoring requires upgrade to use the turbine for 0 to 100% hydrogen in natural gas.
A preliminary dynamic case study is also carried out for a hypothetical scenario to illustrate the capabilities of the simulation on the study of the MGT dynamic behavior in a future distributed energy system. According to the results, some challenges such as those concerning how quickly MGT can react on load changes, load profile, fuel availability and optimum operation exist, which however needs to be addressed in detail before drawing any conclusion. This has already been planned as a part of the future work. Solutions such as MGT integration to a storage system e.g., batteries for low power shortages, using predictive analysis to better plan the MGT start-up/ramping and overcome fast load changes as well as optimizing the control philosophy to minimize frequent start-up and shutdown of the MGT, can be among the improvement opportunities in the system. | |