Bernardo Fortunato

A Modular Code for Real Time Dynamic Simulation of Gas Turbines in Simulink

A high-fidelity real-time simulation code based on a lumped, nonlinear representation of gas turbine components is presented. The code is a general-purpose simulation software environment useful for setting up and testing control equipments. The mathematical model and the numerical procedure are specially developed in order to efficiently solve the set of algebraic and ordinary differential equations that describe the dynamic behavior of gas turbine engines. For high-fidelity purposes, the mathematical model takes into account the actual composition of the working gases and the variation of the specific heats with the temperature, including a stage-by-stage model of the air-cooled expansion. The paper presents the model and the adopted solver procedure. The code, developed in Matlab-Simulink using an object-oriented approach, is flexible and can be easily adapted to any kind of plant configuration. Simulation tests of the transients after load rejection have been carried out for a single-shaft heavy-duty gas turbine and a double-shaft aero-derivative industrial engine. Time plots of the main variables that describe the gas turbine dynamic behavior are shown and the results regarding the computational time per time step are discussed.

Part Load Performance and Operating Strategies of a Natural Gas–Biomass Dual Fuelled Microturbine for CHP Generation

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative micro gas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with natural gas takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for pre-heating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant.Different biomass/natural gas energy input ratios are also modelled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD) and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average and mild climate conditions.Copyright

VGT turbocharger controlled by an adaptive technique

This paper provides an adaptive technique for the control of the variable geometry turbine in a turbocharged compression ignition engine. The adaptive control is based on a one-step-ahead (OSA) technique and a least-square parameter estimator algorithm. In order to test the performance of the proposed control technique, a numerical model of the engine has been developed, which employs a thermodynamic (zero-dimensional) approach. The paper will show that the OSA technique is able to improve dramatically the control performance with respect to that provided by a commonly applied proportional integral derivative control technique.

One step ahead adaptive control technique for wind systems

The control of a wind system considered as an isolated source of power and composed of a horizontal-axis wind-turbine connected to an induction generator is analyzed. Appropriate mathematical models for both the horizontal-axis wind-turbine and the induction generator are used. The one-step-ahead adaptive control technique is presented and used to regulate the wind system. A sensitivity analysis of the induction generator performances with respect to control and disturbance variables is presented in order to evaluate the control flexibility. The results of three control problems are finally shown in order to prove the reliability of the suggested control technique.

Performance of a mixed gas–steam cycle power plant obtained upgrading an aero-derivative gas turbine

Abstract The performance that can be achieved in a power plant obtained upgrading a typical aero-derivative gas turbine is analysed. The methodology is based on the off-design analysis of the gas generator (compressor and high pressure turbine) in the upgraded plant configuration and is applied to the design of a power plant based on the recuperative water injected cycle. The gas generator operating region and its boundary have been evaluated for the upgraded plant configuration; an optimization procedure has been established in order to show the maximum efficiency and power output that can be achieved.

Technical-economic optimization of a wind power plant by means of a stochastic analytical model

Stochastic analytical approaches are particularly suitable to design and study engineering systems based on aleatory information, as wind systems are. The present paper provides a stochastic analytical model to evaluate the performance of a wind power plant. The model has been applied to a small isolated wind system. The results obtained indicate a strong influence of wind speed stochastic variability on the minimum production costs turbine size. The results also point out the economic advantage in the use of a stochastic analytical approach in wind system design compared with a design procedure based on system average performances evaluated according to a determinist approach.

Design of a ducted wind turbine for offshore floating platforms

Within the Marine Energy Laboratory project, funded by the Italian Ministry for Education, University and Research, one of the first offshore wind plants on floating hulls, hosting ducted wind turbines, has been considered. The confinement of horizontal-axis wind turbines inside divergent ducts is reconsidered, in light of material innovation and direct drive coupling. Ducted wind turbines can take advantage of the flow rate increase due to the effect of the divergent shrouds. The conventional blade element momentum theory has been reformulated in order to deal with ducted turbines. Furthermore, computational fluid dynamics simulations have been carried out based on the solution of the steady two-dimensional Reynolds-averaged Navier–Stokes equations for axisymmetric swirling flows. In order to avoid any expensive mesh refinement near the actual rotor blades, the turbine effect on the flow field is taken into account by means of source terms for the momentum equations solved inside the domain swept by the rotor. This technique allowed us to optimize the geometry of the ducted wind turbine in an extremely effective way.

Externally Fired Micro Gas Turbine and ORC Bottoming Cycle: Optimal Biomass/Natural Gas CHP Configuration for Residential Energy Demand

Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly true when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key issue to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and is influenced by climatic conditions, in particular in the case of residential and tertiary end users. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale micro turbine for heat and power cogeneration, a bottoming ORC system can be coupled to the cycle, however this option reduces the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper presents the results of a thermo-economic analysis of small scale CHP plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC), serving a typical residential energy demand. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas (NG), 2) a dual fuel EFGT cycle, fuelled by biomass and natural gas (50% energy input) (DF) and 3) an externally fired gas turbine (EFGT) with direct combustion of biomass (B). The bottoming cycle is a simple saturated Rankine cycle with regeneration and no superheating. The ORC cycle and the fluid selection are optimized on the basis of the available exhaust gas temperature at the turbine exit. The research assesses the influence of the thermal energy demand typology (residential demand with cold, mild and hot climate conditions) and CHP plant operational strategies (baseload vs heat driven vs electricity driven operation mode) on the global energy efficiency and profitability of the following three configurations: A) MGT with cogeneration; B) MGT+ ORC without cogeneration; C) MGT+ORC with cogeneration. In all cases, a back-up boiler is assumed to match the heat demand of the load (fed by natural gas or biomass). The research explores the profitability of bottoming ORC in view of the following tradeoffs: (i) lower energy conversion efficiency and higher investment cost of high biomass input rate with respect to natural gas; (ii) higher efficiency but higher costs and reduced heat available for cogeneration in the bottoming ORC; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid.Copyright

Biomass Utilization in Dual Combustion Gas Turbines for Distributed Power Generation in Mediterranean Countries

In Mediterranean regions, such as Puglia in Italy, the supply chain constraints (i.e. local biomass availability, logistics of supply, storage and seasonality issues) limit the optimal size of a biomass fired power plant in a range of 5–15 MWe. In this scenario, innovative Dual Combustion Externally Fired Gas Turbine (DCGT) Power Plants cofired by natural gas and biomass are examined. For this purpose, biomass external firing is explored under two alternatives: direct combustion of solid biomass and atmospheric fixed bed biomass gasification with air. The proposed cycles are analyzed considering both the Net Overall Electric Efficiency and the Marginal Efficiency of biomass energy conversion, defined for the cofiring of biomass and natural gas. Since natural gas represents a quite expensive fossil fuel resource, a Marginal Efficiency higher than zero indicates the convenience to burn natural gas in this typology of power plant rather than in traditional Combined Cycle with higher efficiency. The energy analysis has been carried out by varying pressure ratio, turbine inlet temperature, heat exchanger efficiency and considering the further option of steam injection. The results of the thermodynamic assessment highlight that the gasification should be preferred to the direct combustion of biomass because of the higher marginal efficiency, although the net overall electric efficiencies of the two plants are almost the same (31%).Copyright

CFD Analysis of the Flow Through Tube Banks of HRSG

The prediction of the performance of HRSG (Heat Recovery Steam Generator) by means of CFD codes is of great interest, since HRSGs are crucial elements in gas turbine combined cycle power plants, and in CHP (combined heat and power) cycles. The determination of the thermo-fluid dynamic pattern in HRSGs is fundamental in order to improve the energy usage and limit the ineffectiveness due to non-homogeneous flow patterns. In order to reduce the complexity of the simulation of the fluid flow within the HRSG, it is useful modeling heat exchangers as porous media zones with properties estimated using pressure drop correlations for tube banks. Usually, air-side thermo-fluid dynamic characteristics of finned tube heat exchangers are determined from experimental data. The aim of this work is to develop a new procedure, capable to define the main porous-medium non-dimensional parameters (e.g., viscous and inertial loss coefficients; porosity; volumetric heat generation rate; etc...) starting from data obtained by means of accurate three-dimensional simulations of the flow through tube banks. Both finned and bare tube banks will be considered and results presented. The analysis is based on a commercial CFD code, Fluent v.6.2.16. In order to validate the proposed procedure, the simulation of an entire fired HRSG of the horizontal type developed by Ansaldo Caldaie for the ERG plant at Priolo (Italy) has been performed and results have been compared with their data.Copyright