IMPROVEMENT OF THE ENERGY MANAGEMENT OF THE GAS GRID IN FUTURE ENERGY SCENARIOS

The thesis aims at improving the energy management of the natural gas grid as a whole, focusing on both i) the possible opportunities of energy recovery and ii) the utilization of the grid as storage capacity of renewable energies. The basic motivation is to exploit completely this infrastructure in the transition phase fossil-to-renewable energy conversion system. As regards energy recovery, the goal is to identify all possible solutions of energy recovery, both the more complex and costly ones based on expanders for power generation and the simpler and more inexpensive ones based on dissipation processes and aimed to avoid gas preheating. In the expander field, special focus is on micro-turbines where novel designs are proposed with the support of an original CFD analysis criterion and of an extended campaign of experiments. The new prototypes show a power output almost doubled in comparison with the current machines available in the market. On the other hand, novel solutions based on “smart throttling” are proposed, designed, and tested. Although these solutions dissipate the majority of the energy content of an expanding gas as the traditional throttling valves, they allow exploiting part of the available energy to avoid the preheating of natural gas or to produce small amounts of electricity. Considering Italy as a case of study, the study indicates that 90% of the energy consumptions for preheating can be avoided within acceptable return of investments even without financial incentives and with beneficial consequences for the environment. As regards the utilization of the gas grid for renewable energy storage, the main goal is to verify the capability of the grid to store and transport “green gas”, and the practical mode of utilization in this circumstance. The analysis is performed at increasing share of renewable penetration to simulate possible realistic scenarios in the next future. Results supply a reliable spectrum of RES systems to be progressively installed by the time new restrictions imposed by the regulation will appear. Overall, the thesis shows wide margins for improvement on the “energy recovery side”, where many solutions are available and economically feasible but mostly unexplored because of established technological “habits” and, perhaps, a scarce environmental sensitivity. On the “storage side”, the thesis traces interesting paths for the utilization of the gas network as conjunction node between RES generation and use. In spite of some necessary simplifying assumptions made at this step and the need to add all local constraints in the practical application of the proposed solutions, these paths have solid foundations and can be used to implement a general strategy for a faster transition to a renewable system. On the other hand, the utilization of the gas grid as storage capacity poses new challenges also on the energy recovery side, where the technologies must be adapted to the constantly evolving operation constraints.