Giovanni Riccio

Pressurised Oxy-Coal Combustion Rankine-Cycle for Future Zero Emission Power Plants: Technological Issues

Among possible options to capture carbon dioxide, pressurised oxy-fuel combustion is a promising one. Accordingly, Enel teamed with Itea and Enea to develop a pressurised oxy-combustion technology. Currently, extensive tests have been carried out at 4 bar on a 5 MWt facility based in Gioia del Colle (Southern Italy). By starting from the know-how gained on that scale, Enel planned to build by 2010 an experimental 48 MWt demo-plant, based on the same pressurised combustion process introduced above. This will be the necessary intermediate step for the further scale-up towards a zero emission plant of industrial scale. This paper is the prosecution of a previous publication presenting the process design and energy analysis of a power cycle integrating the developed pressurised oxy-coal combustion technology with a Rankine cycle including carbon capture. After having briefly presented the pressurised oxycombustion project carried out at Enel, the paper focuses on technology issues related to the proposed cycle and the related process integration, with respect to main components.Copyright

Study of an External Fired Gas Turbine Power Plant Fed by Solid Fuel

The study of a gas turbine plant fed by solid fuel is discussed in this paper. The plant presented is a small one, 3 MWel, externally fired by the combustion of solid biomass. The aim of the technical discussion is to find both the energetic optimisation and the actual feasibility of the plant through available industrial components (gas turbine, heat exchanger, biomass combustor). The final optimal configuration found in the present study allows for a mix of internal (gas) and external (solid fuel) combustion. In this way higher maximum cycle temperature than in standard biomasss combustors are reached through a small addition of gaseous or liquid fuel. The technical study is based on an optimum size and configuration of the power plant, previously defined, with respect to the performance and the complexity of the plant, and in comparison with other energy conversion processes of biomass such as pyrolysis or gasification. A sensitivity analysis permits the determination an optimal gas turbine in terms of pressure ratio and TIT for the current application and indicates the most important parameters that affect the power plant performance, i.e. the components on which the performance of the plant may depend. Economic data show that the direct external combustion of solid fuel has a more favourable trade-off than the configuration of the plant with gasifier.© 2000 ASME

Evaluation of a Micro Gas Turbine Fed by Blends of Biomass Producer Gas and Natural Gas

Small scale gasification is a promising technology for bioenergy generation. Reciprocating engines are usually combined with downdraft gasifiers, nevertheless this approach is associated with high emissions, in particular CO and NOx and with a limited co-generation potential. MGT technology, rapidly improved during the last years, offers the possibility to reduce the levels of pollutants in the exhaust. Moreover they offer some other advantages in the small size range, such as a higher exhaust gas flow at higher temperatures, while maintaining a similar net electric efficiency. Evaluating the possibility to couple a MGT with a gasifier, the quality of the producer gas is also a relevant issue. In this work an overview of the typical gas quality produced by existing small scale gasifiers is carried out; moreover, a review regarding the syngas combustion in GT is realized, considering GT requirements related to gas composition. Co-firing with natural gas is considered, in order to reduce the modification needed to the engine. An evaluation of the proper range of mixing is then carried out. The performances of a commercial 100 kWel MGT are then simulated by means of an “in-house” developed code named AMOS (Advanced MGT system Operation Simulator). This tool allows to perform a steady-state matching analysis based on the characteristic lines of each component, when using a low calorific gas in a MGT. Producer gas and natural gas mixtures are considered and a parametric study is carried out. Performances were computed considering MGT full-load operation.Copyright

Preliminary Design and Economic Analysis of a Biomass Fed Micro-Gas Turbine Plant for Decentralised Energy Generation in Tuscany

Biomass is a significant renewable energy source in Tuscany. A GIS-based software model, jointly developed by the Energetics Department of the University of Florence (DEF), the Agriculture and Forestry Economic Department of the University of Florence (DEEAF) and Energia Trasporti Agricoltura (ETA) in the framework of a LIFE supported project (BIOSIT) has been used to estimate the available resources in the Tuscany region. In this context, a gas turbine cycle based on a dual combustion system has been considered (DCGT, Dual Combustion Gas Turbine). The size of the plant (∼100 kWe) targets small decentralised power generation. The DCGT system aims at achieving a great flexibility through both internal and external firing. In fact, the adoption of an external combustion chamber makes possible to adapt the plant to various types of solid biomass without affecting significantly the thermodynamic cycle and therefore the performances. The technical analysis of available industrial components (gas turbine, heat exchanger, biomass combustor) has been carried out. The computation of the thermodynamic performances was carried out by a dedicate in-house developed software. The economic analysis was performed for the proposed system, and a sensitivity analysis on the critical parameters elaborated. The use of natural gas and bioethanol was also compared in the dual combustion mode.Copyright

Experimental and Numerical Characterization of Lean Hydrogen Combustion in a Premix Burner Prototype

The use of hydrogen as derived fuel for low emission gas turbine is a crucial issue of clean coal technology power plant based on IGCC (Integrated Gasification Combined Cycle) technology. Control of NOx emissions in gas turbines supplied by natural gas is effectively achieved by lean premixed combustion technology; conversely, its application to NOx emission reduction in high hydrogen content fuels is not a reliable practice yet. Since the hydrogen premixed flame is featured by considerably higher flame speed than natural gas, very high air velocity values are required to prevent flash-back phenomena, with obvious negative repercussions on combustor pressure drop. In this context, the characterization of hydrogen lean premixed combustion via experimental and modeling analysis has a special interest for the development of hydrogen low NOx combustors. This paper describes the experimental and numerical investigations carried-out on a lean premixed burner prototype supplied by methane-hydrogen mixture with an hydrogen content up to 100%. The experimental activities were performed with the aim to collect practical data about the effect of the hydrogen content in the fuel on combustion parameters as: air velocity flash-back limit, heat release distribution, NOx emissions. This preliminary data set represents the starting point for a more ambitious project which foresees the upgrading of the hydrogen gas turbine combustor installed by ENEL in Fusina (Italy). The same data will be used also for building a computational fluid dynamic (CFD) model usable for assisting the design of the upgraded combustor. Starting from an existing heavy-duty gas turbine burner, a burner prototype was designed by means of CFD modeling and hot-wire measurements. The geometry of the new premixer was defined in order to control turbulent phenomena that could promote the flame moving-back into the duct, to increase the premixer outlet velocity and to produce a stable central recirculation zone in front of the burner. The burner prototype was then investigated during a test campaign performed at the ENEL’s TAO test facility in Livorno (Italy) which allows combustion test at atmospheric pressure with application of optical diagnostic techniques. In-flame temperature profiles, pollutant emissions and OH* chemiluminescence were measured over a wide range of the main operating parameters for three fuels with different hydrogen content (0, 75% and 100% by vol.). Flame control on burner prototype fired by pure hydrogen was achieved by managing both the premixing degree and the air discharge velocity, affecting the NOx emissions and combustor pressure losses respectively. A CFD model of the above-mentioned combustion test rig was developed with the aim to validate the model prediction capabilities and to help the experimental data analysis. Detailed simulations, performed by a CFD 3-D RANS commercial code, were focused on air/fuel mixing process, temperature field, flame position and NOx emission estimation.Copyright

Scaling From Atmospheric Pressure Rig to Full-Scale Pressure for the Emission Measurements From a Gas Turbine Combustor

Investigating the pressure scalability of pollutant emissions from a heavy-duty diffusion flame type, natural gas fuelled gas turbine combustor a two steps approach is presented in the current paper. First a theoretical viewpoint is established using similitude theory to characterize the operation conditions chosen for atmospheric tests in relation to the real gas turbine pressurized conditions. Then the corresponding experimental tests are presented for the full-scale gas turbine combustor in the original version both under atmospheric and pressurized gas turbine conditions at the ENEL test facilities.The results from the theoretical study indicate, that similitude cannot be maintained rigorously between the atmospheric and pressurized tests. However the experimentally determined NOx-emissions obtained under the reduced similarity test conditions provide a pressure scaling relation that can be maintained between the original and the retrofitted version of the combustor.© 2001 ASME

Numerical Re-Design of a Heavy Duty Gas Turbine Hydrogen-Fired Combustion Chamber

The present work describes the numerical methodology followed to characterize and study modifications to a silo-type diffusive combustion chamber installed on a GE10, a 10 MW class heavy-duty gas turbine manufactured by GE Oil & Gas. The goal of the work was to investigate modifications to the combustion chamber to allow operation with 100% hydrogen fuel at reduced NOx production in dry conditions. The investigation focused mainly on the burner; the liner was not substantially changed. The swirler and the fuel injection holes were redesigned to achieve better fuel-air mixing and a higher airflow rate in the primary zone of the combustor, maintaining a diffusion flame scheme. The proposed modifications were analyzed using a 3D CFD RANS reactive procedure based on commercial codes. The method was previously validated by comparison with the experimental data from the full scale tests performed at the Enel Facility at Sesta, Italy. In-house codes were developed for the post-processing of the results. The numerical analysis has shown that the modified version can provide a NOx reduction up to 40%. The results are discussed focusing on the effect of fuel injection scheme on mixing quality and NOx emission containment.Copyright

Analysis of the Fuel Injection in Gas Turbine Premixing Systems by Experimental Correlations and Numerical Simulations

This paper presents the aerodynamic study of two premixing systems for gas turbine combustion chamber based on detailed CFD 3-D simulations. The work was carried out with the aim to describe the aerodynamic and the mixing process in two different premixing system schemes, typical for DLE gas turbine combustion chamber. Results from different numerical tools (CFD 3-D and 0/1-D) for the estimation of the fuel jet pathway were compared. Both the premixer configurations analysed are related to the cross-flow injection scheme. The first one considers the fuel injection orthogonal to a low swirled air stream while the second one considers the fuel injection directly from hole rows drilled on the suction and pressure side of the swirler blades. The aerodynamic analysis of the premixing devices was focused on the fuel injection in terms of the jets pathway and air/fuel mixing in steady-state conditions. The aerodynamic investigations were performed by CFD 3-D “full Navier-Stokes” codes. Calculations were repeated, on the same mesh, by an in-house developed code (HybFlow) and by commercial codes also. Some previous experimental results were exploited to tune and validate the calculations. Results of the simulation were post-processed in order to allow a quantitative evaluation of the air/fuel mixing. Moreover the calculations were used to verify the accuracy of 0/1-D models, taken from the literature, for the estimation of the maximum penetration and the trajectory for the cross-flow of gaseous fuel jet, considering typical working conditions for gas turbine premixing system. Finally, preliminary considerations related to the fuel injection schemes and to the influence of the main injection conditions on the mixing were carried out.© 2006 ASME

Improvement of Gas Turbine Injection Systems by Combined Experimental/Numerical Approach

An aerodynamic study for the premixing device of an industrial turbine gas combustor is discussed. The present work is based on a joint application of numerical CFD and experimental investigation tools in order to verify and optimize the combustor gaseous fuel injection system. The objective is the retrofit of an old generation gas turbine combustion chamber that is carried out considering new targets of NOx emission keeping the same CO and combustion stability performances. CFD has been used to compare different premixing duct configurations for improved mixing features. Experimental test has been carried out in order to assess the pollutant emissions, flame stability and pattern factor characteristics of the full combustion chamber retrofitted with the modified injection system.Copyright

Development and Experimental Testing of a Pilot Burner for DLN Combustors

Different geometrical modifications have been investigated and experimentally tested to improve a pilot burner for low emission industrial gas turbine combustors. Results of the ongoing collaboration between the DE of Florence and the Italian electric company ENEL are reported. The activity is dedicated to the improvement of the pilot burner to extend the operable margin of the engine and to reduce, at the same time, the emissions. The study has been performed mainly by means of experimental investigations both on isothermal flow as on combustion test rig. Results of the activity were employed both to obtain design information about the swirler and injection fuel holes for the pilot burner under investigation. Moreover the post-processing of the experimental data permitted the improvement of the correlation implemented into the 1-D model for the prediction of the injected fuel path. These results were implemented in the routine DoFHIS (Design of Fuel Holes Injection Systems) developed for the analysis/design of injection fuel systems.Copyright