Ambra Giovannelli

High-temperature solar receiver integrated with a short-term storage system

Small-Scale Concentrated Solar Power Plants could have a potential market for off-grid applications in rural contexts with limited access to the electrical grid and favorable environmental characteristics. Some Small-Scale plants have already been developed, like the 25-30 kWe Dish-Stirling engine. Other ones are under development as, for example, plants based on Parabolic Trough Collectors coupled with Organic Rankine Cycles. Furthermore, the technological progress achieved in the development of new small high-temperature solar receiver, makes possible the development of interesting systems based on Micro Gas Turbines coupled with Dish collectors. Such systems could have several advantages in terms of costs, reliability and availability if compared with Dish-Stirling plants. In addition, Dish-Micro Gas Turbine systems are expected to have higher performance than Solar Organic Rankine Cycle plants.The present work focuses the attention on some challenging aspects related to the design of small high-temperature solar receivers for Dish-Micro Gas Turbine systems. Natural fluctuations in the solar radiation can reduce system performance and damage seriously the Micro Gas Turbine. To stabilize the system operation, the solar receiver has to assure a proper thermal inertia. Therefore, a solar receiver integrated with a short-term storage system based on high-temperature phase-change materials is proposed in this paper. Steady-state and transient analyses (for thermal storage charge and discharge phases) have been carried out using the commercial CFD code Ansys-Fluent. Results are presented and discussed.Small-Scale Concentrated Solar Power Plants could have a potential market for off-grid applications in rural contexts with limited access to the electrical grid and favorable environmental characteristics. Some Small-Scale plants have already been developed, like the 25-30 kWe Dish-Stirling engine. Other ones are under development as, for example, plants based on Parabolic Trough Collectors coupled with Organic Rankine Cycles. Furthermore, the technological progress achieved in the development of new small high-temperature solar receiver, makes possible the development of interesting systems based on Micro Gas Turbines coupled with Dish collectors. Such systems could have several advantages in terms of costs, reliability and availability if compared with Dish-Stirling plants. In addition, Dish-Micro Gas Turbine systems are expected to have higher performance than Solar Organic Rankine Cycle plants.The present work focuses the attention on some challenging aspects related to the design of small high-temper...

Expander Models for a Generic 300 MW F Class Gas Turbine for IGCC

Gas Turbines (GTs) for large IGCC plants need some modifications because, usually, they have been developed to be fed with Natural Gas (NG) while the Syngas from the IGCC has a lower Low Heating Value (LHV). As a consequence, the larger flow in the expander raises the compressor exit pressure, producing some instability risks.One of the possible options consists in the modification of the Expander Flow Functions to accommodate the input pressure in a safe range. The above option modifies also the hot surface blade wall temperature with no changes in cooling flows.In this paper flow path data, average blade temperatures, cooling flows and global performance for the Reference GT (RGT) fed with CH4 and for the modified GT fed with syngas (H2R-GT) are reported and compared.The changes in the stagger angles to accommodate the Expander Flow functions for stable GT conditions are presented and results widely discussed.Copyright

Dynamics of a Prescribed Mixing Ratio Variable Fuel Flow Valve

The production of emulsions on board of engines in real time with the fuel needs for the actual loading requires the development of a mixer that is capable to give the right volumetric ratio between the dispersed phase (water or ethanol) and the continuous phase (fuel). A Prescribed Mixing Device (PMD) has been developed to follow in real time the fuel request of a Gas Turbine or other engines. Previous investigations have demonstrated the stable steady state behavior at the various fuel flow rates ranging from idle to full load. Moreover, the influence of fuel viscosity variations (due to fuel temperature and quality changes) on the PMD response has been studied. This paper deals with the dynamic behavior of such a PMD. A physical model has been developed and accordingly, an amply series of tests have been carried on to check the PMD response to step and sinusoidal changes in the fuel request. A stable behavior has been evidenced thus the water content of the emulsion produced does not show significant drift in its value versus time.Copyright

OPTIMUM PLANNING OF ELECTRICITY PRODUCTION

The power production planning problem has been deeply investigated. Maintenance management and load allocation problems have been assumed as crucial aspects for achieving maximum plant profitability. Modelling of life consumption of hot section components has been considered as one of the key feature necessary to simulate the plant behaviour. The approach takes market scenarios, as well as actual status and performance of plant components into account. A supervisor algorithm provides the operating parameters needed to establish each plant loading. Economic implications related to maintenance strategies including postponement or anticipation of maintenance interventions are investigated and results obtained by the numerical simulation are presented and widely discussed.Copyright

Wind Turbine Installation for High Elevations

The strong drive to exploit wind energy has recently led to new types of location for wind turbine installations being considered, including mountain regions and, to be more specific, areas at elevations coming between 800 and 2,500 m asl. Authoritative sources, such as the European Wind Energy Association (EWEA), have estimated that 20–25% of the approximately 60,000 MW expected to be installed in Europe between now and 2010 will be situated in cold-climate areas, and a part of them will be on hills and mountains. The installation of wind farms in the mountains consequently demands an in-depth analysis, in the design of such plant, into both the methods for assessing the resource and the more or less direct transfer of procedures and technologies developed for conventional sites. For the time being, the IEC standards (originally developed to provide a reference picture relating to conventional sites) fail to provide recommendations on this type of site, where the structure of the flow field is substantially more complex in terms of its effect on the stresses involved. The present work outlines the main features of mountain wind farm sites and discusses the effects of some of said features on the structural assessment of the turbines destined for such installations in the light of the IEC standard requirements. The work illustrate that the installation of wind turbines in mountain sites must consider different site-related features from those used to develop the requirements of the IEC standards. The examples given here indicate that, based on the standards, these features influence both energy generation and the turbine’s working life. Only an adequate understanding of these features can lead to a cost-effective sizing of the turbines. This type of approach can lead to a site-specific design concept, and only certain components are structurally adequate for the stress characteristics of a given site. These procedures will then have to be transferred to the standards, overcoming the conflict between the minimum standard requirements specifying the fundamental elements to consider in the project and the set of parameters describing the external conditions that demand a turbine of equivalent sturdiness in comparable applications.Copyright