Federico Bonzani

Multi-Objective Constrained Aero-Mechanical Optimization of an Axial Compressor Transonic Blade

This paper presents a flexible and effective optimization approach to design an axial compressor transonic blade for heavy duty gas turbines. The design goals are to improve design efficiency, choke margin and off-design performance while maintaining mass flow in design point as well as structural integrity. The new blade has to provide a wide operating range and to satisfy tight geometrical constraints.A database of aero-mechanical calculation results is obtained for three operating conditions. A number of 3D flow simulations are performed using a CFD solver with endwall boundary layer simplified model (thin layer) to reduce computational costs. The optimization process adopts a set of artificial neural networks (ANN) trained for each operating condition and a random walking search algorithm to determine the multi-objective Pareto Front. ANN enables speed up of the optimization process and allows high flexibility in choosing criteria for optimum member selection. Random walking algorithm gives a fast and effective method to predict the multi-dimensional Pareto Front.© 2012 ASME

Ansaldo Energia Gas Turbine Operating Experience With Low BTU Fuels

The Gas Turbine market for low BTU fuels has become very important in Italy in the last decade mainly due to the chance for the private utilities to sell power to the grid at higher rates according to a national law (CIP6/1992) specifically dealing with recovery fuel use for gas turbine power generation. Ansaldo Energia has been engaged in three low BTU fuel projects in Italy dealing respectively with IGCC technology and steel mill fuel gas. Each of these plants has its own features which all in all gives a wide range of experiences in development and operation of gas turbine fired with low BTU fuels. The first project is the ISAB Priolo IGCC plant, whereas two V94.2K manufactured by Ansaldo Energia are in operation burning syngas from residual refinery gasification since 1999. Since the presence of fuel impurities coming from the gasifier a new design phase and a test campaign has been necessary to re-design the syngas burner, originally developed by Siemens PG, in order to overcome this problems. The engines are now successfully operating. The second project is the Elettra Servola combined cycle plant whereas a V94.2K manufactured by Ansaldo Energia is in operation since 2000 burning a mixture of steel mill gas and natural gas. During the successfully operation some burner design optimisation has been required in order to meet the industrial process modification. The third project is the ENIPower Ferrera Erbognone IGCC plant is under realisation and the relevant first firing will be expected on next January 2004. The syngas burner test campaign carried out has shown very promising results that have to be confirmed on site. The paper is showing the combustion concept relevant to the combustion system and is giving an overview about the operating experience achieved by Ansaldo Energia in this field mainly focusing on how the main critical aspects have been faced and overcome.© 2004 ASME

Operating Experience of Ansaldo V94.2 K Gas Turbine Fed by Steelworks Gas

ANSALDO ENERGIA S.p.A. has been commissioned by ELETTRA GLT S.p.A, a company located in Trieste, Italy for the realisation of a combined cycle plant where all the main components (gas turbine, steam turbine, generator and heat recovery steam generator) are provided by ANSALDO ENERGIA. The total power output of the plant is 180 MW. The gas turbine is a V94.2 K model gas turbine dual fuel (natural gas and steelworks process gas), where the fuel used as main fuel is composed by a mixture of natural gas, blast furnace gas and coke oven gas in variable proportions according to the different working conditions of the steel work plant. The main features adopted to burn such a kind of variability of fuels are reported below: • fuel as by product of steel making factory gas (coke oven gas “COG”, blast furnace gas “BFG”) with natural gas integration; • modified compressor from standard V94.2, since no air extraction is foreseen; • dual fuel burner realised based on Siemens design. This paper describes the operating experience achieved on the gas turbine, focusing on the main critical aspect to be overcome and on to the test results during the commissioning and the early operating phase. The successful performances carried out have been showing a high flexibility in burning with stable combustion a very different fuel compositions with low emissions measured all operating conditions.Copyright

Numerical and Experimental Investigation of Thermo–Acoustic Combustion Instability in a Longitudinal Combustion Chamber: Influence of the Geometry of the Plenum

This paper concerns the study of self–sustained combustion instabilities that occur in a test rig characterized by a single longitudinal combustion chamber equipped with a full scale industrial burner and a longitudinal plenum. The length of both plenum and combustion chamber can be continuously varied. During tests, at a fixed value of the length of the combustion chamber, a sensibility of the amplitude of pressure oscillations to the length of the plenum has been registered, while the frequency remained constant. To investigate this behavior, a linear stability analysis has been performed evaluating the influence of the length of the plenum on the frequency and growth rate of the registered unstable mode. The analysis has been performed by means of a finite element method (FEM) code with a three–dimensional distribution of the n-τ Flame Transfer Function (FTF) computed by means of computational fluid dynamics (CFD) simulations. According to the Rayleigh criterion, the distribution of the local Rayleigh index has been computed in order to evaluate the acoustic energy production, while the scattering matrix of the entire system has been used to evaluate the acoustic energy losses. Numerical results show that the reduction of the plenum length induces an increase of acoustic energy losses while the energy production remains almost constant. This result is in agreement with the reduction of the pressure oscillations amplitude observed during tests.Copyright

Numerical Procedure for the Investigation of Combustion Dynamics in Industrial Gas Turbines: LES, RANS and Thermoacoustics

The necessity for a combustion system to work with premixed flames and its capability to cope with rapid load variations avoiding the occurrence of thermo-acoustic instabilities, has led to investigate the complex dynamic phenomena that occur during combustion. Thanks to numerical simulations it is possible to examine these complex mechanisms getting useful information to optimize the combustion system. The aim of this work is to describe a numerical procedure developed in Ansaldo Energia for the investigation of combustion dynamics occurring in Ansaldo Energia gas turbines.In this paper, firstly the experimental apparatus of a full scale atmospheric test rig equipped with Ansaldo Energia burner is described. Secondly, the flame behavior is studied by means of a Large Eddy Simulation (LES). Once the LES has reached a statistically stationary state, a forcing is added to the system to compute the Flame Transfer Function (FTF), in terms of amplitude n and delay time τ, related to initial phases of humming. Thirdly, the forced flame simulations are used as the input of an Helmholtz solver to analyze the acoustic behavior of the system, which is then compared to experimental data. Finally, to evaluate the feasibility of a less computationally intensive approach, a RANS simulation of the same configuration is described and the results are transferred to FEM (Finite Element Method) Helmholtz solver: a comparison between the LES approach and the RANS approach is carried out with reference to the experimental data.Copyright

Design Validation on Pressurized Test Rig of Upgraded VeLoNOx™ Combustion System for F-Class Engine

The design of future combustion system for F-class heavy duty gas turbine is driven by very low emission requirements, high reliability, long lifetime, fuel flexibility and combustion instability free operation. The present paper introduces the process of design validation, at test rig, of the new VeLoNOx ™ burner prototypes for the most recent upgrades of the AE94.3A engine families, equipped with 24 annular combustors. Full scale testing is usually a very costly process. At the first design stage it can be reduced on a single burner housed in a cylindrical flame tube, whose shape is representative of 1/24 of the real annular combustion chamber. Because the thermo acoustic behaviour of one single burner can be greatly different than on the real engine, the design validation process cannot rely only on emission levels but should take into account the assessment of some correlations relating both test rig and field behaviour. Tests are carried out on a pressurized test rig, covering all relevant conditions of the engine, starting from Full Speed No Load to 105% of the Base Load. Each prototype, and its relevant design process, is then assessed by applying a design validation procedure to the results of experimental test campaign on the rig. Particular attention is given to analyze the acoustic response of each system as function of air to fuel ratio, flame mode, emission levels, rangeability and thermal power output. From the acoustic point of view, each burner is accurately analysed both at steady state conditions and during ramps. This paper shows the results of different VeLoNOx ™ burner prototypes tested in order to identify the most promising solution to be fitted onto the AE94.3A engines.Copyright

Operating Experience of High Flexibility Syngas Burner for IGCC Power Plant

Ansaldo Energia Low BTU engines have been accumulating more than 150000 EOH (Equivalent Operating Hours) burning low Btu Fuels on two different projects such as Isab Priolo and Elettra Servola. More over a new unit Ferrera Erbognone 3 has started to be commissioned in March 2006 burning syngas from tar gasification. This latter will be the first real commercial power plant in Italy to be operated without taking into account the high benefits once available according to the national law (CIP6/1992) specifically dealing with recovery fuel usage (alternative to natural gas). The end of the first phase of commissioning of Ferrera Erbognone 3 will give the opportunity to present the results achieved and to validate the burner design process for this specific power plant. In the IGCC gasifier island of Ferrera 3 power plant, it will be possible to separate hydrogen in variable quantity from the syngas according to the demands of the refinery located nearby the power plant, thus giving a high composition variability as output fuel. Also, if the maximum quantity of hydrogen will be separated, an integration with natural gas will be performed in order to get the maximum power output of the power plant. As a consequence, the syngas burner has been designed taking into account all the fuel characteristics depending on the different composition carried out. According to these, the burner has been optimised in order to fit the various syngas blends to be fuelled when running the engine. The paper describes the experience achieved during the commissioning activity prior to the commercial operation started in September 2006 highlighting the main results achieved with respect to the plant requirement. Furthermore a description of the functional improvement of the engine in order to face the unexpected off design conditions will be reported.Copyright

Development of a Heavy Duty GT Syngas Burner for IGCC Power Plant in Order to Enlarge the GT Operating Conditions

In order to increase the fuel flexibility of the current design of the SynGas burner [4,5,6], Ansaldo Energia, since the growing requests of the market, performed a RD b) acceleration; c) loading at part load; d) change over from diffusion line to main SynGas line. To fulfill with new requirements, the standard V94.2K burners have been modified in order to operate from ignition up to the change over point with a SynGas mixture provided by the coal gasification process of a typical IGCC plant [7]. After the design phase, a experimental test campaign on the new design burner has been performed at atmospheric pressure. In order to validate the test results carried out at actual engine working conditions a further test campaign has been performed at the high pressure consistent with the test rig technical limitations [2.3]. The paper show the results carried out that are really promising to meet the customer requirements.Copyright

Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Rig for Testing Full Scale Burners

This paper concerns the acoustic analysis of self–sustained thermoacoustic pressure oscillations that occur in a test rig equipped with full scale lean premixed burner. The experimental work is conducted by Ansaldo Energia and CCA (Centro Combustione Ambiente) at the Ansaldo Caldaie facility in Gioia del Colle (Italy), in cooperation with Politecnico di Bari. The test rig is characterized by a longitudinal development with two acoustic volumes, plenum and combustion chamber, coupled by the burner. The length of both chambers can be varied with continuity in order to obtain instability at different frequencies. A previously developed three dimensional finite element code has been applied to carry out the linear stability analysis of the system, modelling the thermoacoustic combustion instabilities through the Helmholtz equation under the hypothesis of low Mach approximation. The heat release fluctuations are modelled according to the κ-τ approach. The burner, characterized by two conduits for primary and secondary air, is simulated by means of both a FEM analysis and a Burner Transfer Matrix (BTM) method in order to examine the influence of details of its actual geometry. Different operating conditions, in which self–sustained pressure oscillations have been observed, are examined. Frequencies and growth rates of unstable modes are identified, with good agreement with experimental data in terms of frequencies and acoustics pressure wave profiles.Copyright

Syngas Burner Optimization for Fuelling a Heavy Duty Gas Turbine With Various Syngas Blends

The IGCC power plant of Ferrera Erbognone will be the first real commercial power plant in Italy to be operated without taking into account the high benefits once available according to the national law (CIP6/1992) specifically dealing with recovery fuel usage alternative to natural gas. The syngas will be provided by the nearby refinery using tar as main feedstock. Furthermore, according to the demands of the refinery it will be possible in the gasifier island to separate hydrogen in variable quantity from the syngas thus giving a high variability composition as output fuel. Also, if the maximum quantity of hydrogen will be separated, an integration with natural gas will be performed in order to get the maximum power output of the power plant. As a consequence, the syngas burner has been designed taking into account all the fuel characteristics depending on the different composition carried out. According to these, the burner has been optimised in order to fit the various syngas blends to be fuelled when running the engine. In order to verify the modifications carried out the burner has been tested both at atmospheric and full engine conditions since the NOx requirements for this project are the more stringent experienced with respect to the past projects (NOx to be below 25 ppm). During these test the main aspect to be in investigated have been: a) Minimum load when feeding the gas turbine with syngas. b) NOx emission from 60% load up to base load. c) Change over from natural gas to syngas and vice versa. The tests have been performed successfully: commissioning on site will start on November 2005. The paper describe the design and the testing phase highlighting the main features of the burner and the fuel system with respect to the plant requirements.Copyright