L. Pelagalli

Micro Gas Turbines

Conventional gas turbines (GTs) range from a size of one or a few MWe to more than 350 MWe (GTW, 2009). Those at the small end of the range are commonly used in industrial applications, for mechanical or onsite electrical power production, while the larger ones are usually installed in large-scale electrical power plants, often in combined cycle plants, and are typically located far away from the consuming region. In the future distributed energy systems based on small local power plants are likely to spread; since they lie close to the final users, they reduce electrical transport losses, and make thermal energy recovery profitable both in energy-related and in economic terms (Papermans et al., 2005; IEA, 2002). These benefits explain the increasing interest in smallsize generation systems. Recently, gas turbines < 1 MWe, defined as micro gas turbines (MGTs), have appeared on the market. MGTs are different from large GTs and cannot therefore be considered merely as their smaller versions. Their advantages as distributed energy systems lie in their low environmental impact in terms of pollutants and in their competitive operation and maintenance (OM Zogg et al., 2007).

Micro Combined Plant With Gas Turbine and Organic Cycle

In this paper we discuss the usefulness of a bottoming cycle applied to a micro size gas turbine unit to enhance its electric performance. A commercial 100 kWe micro gas turbine is used as a topping system; a basic thermodynamic analysis is performed to define the principal characteristics of viable vapour bottoming cycles. The analysis points to a solution adopting an Organic Rankine Cycle (ORC) with R245fa as working fluid, due both to environmental constrains and to technical criteria.Copyright

PERFORMANCE ANALYSIS OF COGENERATIVE AND TRIGENERATIVE PLANT WITH MICROGAS-TURBINE

The paper reports on the performance analysis of cogenerative and trigenerative plants based on Micro Gas Turbines. The core of the system is a natural-gas-fuelled Turbec T100 operating on a regenerated open-air cycle. A code specifically developed by the authors to simulate the micro gas turbine in cogeneration plants, and already checked against experimental data, has been upgraded to simulate the units behavior when facing also a cooling demand (trigenerative case). For this purpose the model of a water-LiBr single-effect absorption chiller driven by hot water has been used. The analysis cover all the units application range and represent a start for its economic evaluation.

New Running Strategies of a STIG Power Plant for District Heating

We describe the running plan of a 5.5-MWe-STIG-plant. Located in a medium-sized town in the centre of Italy, the plant both produces electric power and partially satisfies the thermal load of a nearby city district. An account of the Italian energy market is provided and the impact of recent legislation on plant operation is analysed. The liberalization of the Italian energy market in 1999 has significantly affected the technical and economic scenario for both existing and future power plants. As an example, we analyse the effects of liberalization on the overall performances of the plant described herein as well as the main changes in its running-strategies. A better economic result is shown to be possible in the new scenario mainly thanks to plant flexibility when operating as CHP (Combined Heat and Power) unit. The pursuit of optimum economic performance however prevents the plant from working at its best energetic efficiency.Copyright

Experimental Results From a Two-Stroke Gasoline Direct-Injected Engine Prototype

Recently, research on internal combustion spark-ignited engines has focused increasingly on charge control by means of direct injection. The concepts proposed in this field involve in most cases high-cost systems which do not seem to be widely applicable, especially to small, low-cost engines. In this respect, the challenge is to avoid complicating the existing power systems that make of simplicity and low cost their better qualities. The paper reports on the design and realization of a two-stroke gasoline direct-injection engine prototype which employs a Water-Hammer effect injection system. The experimental data obtained with the prototype are presented showing how the system significantly reduces hydrocarbon emissions and specific fuel consumption.Copyright

Cogeneration Micro Turbine Fuelled by Solid Biomass: A Technical-Economic Study for Italy

The paper presents part of the results of two studies, the European “Radar” (Raising Awareness on renewable energy Developing Agro-eneRgetic chain models) Project and the “Energy and environmental plan for the consortium of the municipalities of the Esino-Frasassi mountain area”, conducted in an area in central Italy. The area is characterized by huge forestry biomass resources and by substantial amounts of agricultural residues. The work presents a technical-economic study of a cogeneration plant using a solid biomass-fuelled micro turbine as the prime mover. The energy conversion of solid biomass can be achieved with different technologies, e.g. organic Rankine cycles, micro turbines with an external combustion chamber, or Stirling engines. The choice of the conversion system depends mainly on biomass availability and on the level of user demand. Of the conversion technologies mentioned above, the micro turbine is suitable to meet the requirements of the cogeneration plant examined here, which is applied to a low thermal demand public building. The work describes a micro turbine based on a regenerative Brayton cycle endowed with an external combustion chamber. The inlet air, after being compressed, passes through a regenerator and then through an external furnace fuelled by solid biomass, where it is further heated, and finally expands through the turbine. The outlet air of the turbine, before being funnelled through the chimney, passes through the regenerator and subsequently through a dry kiln, thereby reducing the humidity of the solid biomass. The micro turbine studied produces 75 kWe and 300 kWt. The biomass is made up of olive tree prunings. After the technical analysis, an economic study stresses the critical role of incentives systems (herein provided by the Italian legislation) in making the technology appealing to investors in renewable energy solutions. The energy and economic analysis considers different combinations of three different amounts of annual operation hours, of two operating modes (with/without cogeneration) and three purchase prices of the solid biomass. The incentives mechanism considered is the Feed-In Tariff (FiT) granted by the Italian legislation for plants < 1 MWe. The economic analysis highlights some influential factors for solid biomass-fuelled systems: contract with fuel suppliers, biomass price, availability, transportation, storage, and processing, and plant location. In particular, the purchase price of solid biomass is substantially negotiated between the manager of the energy conversion plant and suppliers. The work demonstrates the crucial role of the incentives mechanisms for economic sustainability; the strong influence of biomass price on investment profitability; and the role of cogeneration in further shortening the payback period.Copyright

Analysis of Cavitating and Non-Cavitating Transient Flow in Pipelines Connected by Junctions

The paper deals with the development of experimental benches designed with the aim of producing test cases of transients flow through different types of junctions both in non-cavitating and cavitating conditions. The non-cavitating test cases consist in a rapid depressurization of a reservoir to which a pipe network containing the junction is connected while in the cavitating test cases the same pipe network is discharged towards an open-air reservoir by means of an ad hoc very rapid opening valve apparatus. First of all the experimental data allowed for a deeper insight on the subject from a phenomenological point of view. Then the recorded pressure time histories have been used to validate the numerical results of a code which solves the flow by means of a 1D model suitable to describe unsteady friction and cavitating phenomena. In the code the discrete gas-cavity model (DGCM) introduced by Provoost and Wylie is integrated in the method of characteristics and the junctions are modeled using a standard constant pressure approach improved with the gas cavity model.Copyright