Rémi Guillet
Direction de la Recherche - Gaz de France

Si l’eau a été longtemps utilisée pour améliorer la combustion de combustibles réputés difficiles, comme agent antidétonant, voire comme "booster" de moteurs en aéronautique, puis, plus récemment, comme agent diminuant la formation des oxydes d’azotes, elle apparaît aussi comme élément additionnel capable d’améliorer de façon substantielle les performances des turbines à gaz terrestres.
De son côté, le concept de "pompe à vapeur d’eau", initialement développé pour élargir le domaine d’application des générateurs à condensation offre des perspectives de performances énergétiques et écologiques remarquables notamment lors de l’utilisation de gaz naturel [1,2].
Alors, la mise en œuvre de ces différentes approches de la "combustion par voie humide", séparément ou combinées, offre de nouvelles possibilités notamment dans le contexte des applications de "cogénération". Cette présentation fait le point des développements et perspectives.

For many years, water has been used as an "additive" component to improve combustion efficiency, to boost power, even as an anti-knock agent, as technique to reduce NOx formation. Today, the challenge is to find new ways to promote energy conservation and to minimize global environmental impact. Using a "wet combustion" technique, gas turbine efficiency can be increased substantially...
On an other hand, water vapor pumps, which perform combustion with a humidified combustion agent, offer outstanding energy efficiency and environmental performance, particularly in case of natural gas utilization [1,2].
In cogeneration context we can often benefit of all of the advantages offered by the wet combustion technique. The proposed presentation will concern achievements, actual developments and perspectives.

F. Strub, J.P. Bédécarrats
Laboratoire de Thermodynamique et Energétique
Université de Pau et des Pays de l’Adour, av. de l’université 64000 Pau, France.

Gas turbine inlet air cooling improves its performance. Inlet air cooling process including a phase-change refrigeration storage is studied. The Modelling of a plant is carried out and tested for a hot and wet climate (New Delhi in August). It makes it possible to design each component and to quantify the benefit of the use of a refrigeration storage.

Serge Boudigues, Georges Descombes, Pierre Neveu et Laurent Prévond
Conservatoire national des arts et métiers
292, rue Saint-Martin 75141 Paris cedex 03

Le contexte énergétique et environnemental de ce début de 21^ème siècle impose à l'ingénieur énergéticien d'optimiser sans relâche les rendements des moteurs et machines thermiques en réduisant de manière drastique leurs sources de nuisances.
L'application du concept de valorisation des rejets thermiques est illustré par quelques exemples représentatifs de cogénération par turbine à gaz et moteur Diesel. On présente ensuite les résultats détaillés d'une modélisation de cycles thermodynamiques combinés en vue de maximiser l'efficacité thermodynamique de la conversion d'énergie.
Le calcul montre que ces cycles a priori réalisables industriellement peuvent générer une amélioration potentielle de l'ordre de 10 à 20% de l'efficacité énergétique. Ils engendrent évidemment une complexité technologique et un surcoût complémentaire qui reste à chiffrer. On insiste enfin sur l'intérêt de renforcer la synergie qui existe entre les turbomachines thermiques et les moteurs alternatifs.

J. Kaikko and L. Hunyadi
Department of Energy Technology, Royal Institute of Technology, SE-10044 Stockholm, Sweden

Air Bottoming Cycle (ABC) is an economical concept to increase power generating efficiency of small and medium-scale gas turbines. ABC is a Brayton cycle that utilises the exhaust heat from the topping gas turbine via a heat exchanger. As output, power is yielded, as well as heat from optional intercooling and in the form of exhausted hot air. In this paper, a thermodynamic analysis is presented for a cogenerative system where a fraction of the compressed air in an intercooled ABC will be taken to a Reversed Brayton Cycle (RBC) to provide cold airflow. System optimisation procedure is discussed and potential configurations to implement this system have been investigated. For the selected configuration, characteristics are presented for power, heat and cooling output. For ABC and RBC, sensitivity of the performance is presented against primary cycle parameters.

J. Kaikko¹, L. Hunyadi¹, A. Reunanen² and J. Larjola^2
1 Department of Energy Technology, Royal Institute of Technology, SE-10044 Stockholm, Sweden
² Department of Energy Technology, Lappeenranta University of Technology, FIN-53851 Lappeenranta, Finland

Two bottoming cycles are analysed in this paper, Air Bottoming Cycle (ABC) and Organic Rankine Cycle (ORC). A comparison of thermodynamic performance between the cycles is given. Special attention is paid to choose the component specifications on a realistic basis and the configurations so that an economic optimum for the cycles can be anticipated. Two cases for topping engines have been investigated : a small-scale (7.8 MW_e) gas turbine with an exhaust temperature of 534° C, and a large-scale (16.8 MW_e) Diesel engine with 400° C exhaust temperature. For all cases, two applications are considered : power generation only, and cogeneration of heat and power. Sensitivity of the performance against primary cycle parameters is also presented for both cycles. Considerations of applying high speed technology to both cycles are given. Hereby, the term high speed technology refers to a design where the turbomachine(s) and the electric machine (generator in this case) have a common shaft that is rotating at an optimum speed determined by the turbomachine(s).

Gheorghe Dumitrascu¹, Ovidiu Marin², Olivier Charon², Bogdan Horbaniuc^1
1 Engineering Thermodynamics Dept., "Gh. Asachi" Tech. University, Bd. D. Mangeron, 59–61, 6600 Iasi, Romania
² American Air Liquide, Chicago Research Center, 5230 S. East Ave., Countryside, IL 60525, USA

The power generated by a gas turbine is notably influenced by the temperature of the ambient air that enters the compressor. This major drawback could be diminished by the following measures :
 - a cooling by adiabatic humidification of the air in the intake flow section and between the compression stages,
 - a steam injection into the compressed air in the outlet flow section of the compressor’s diffuser and/or in the outlet flow section of the combustor.
The paper includes a sensitivity analysis of these possible operating schemes for a given gas turbine engine, additionally taking into consideration the variation of the intake air temperature. The first part of the article establishes the influences of both the intake air temperature in the compressor and the inlet volumetric ratio of steam and the temperature of the water-vapor mixture – combustion air in the gas turbine upon the composition and the enthalpy of the flue gases. The calculus considers the combustion with dissociation. The second part of the paper performs an analysis of the irreversible compression of the humid air and of the expansion of the flue gases that allows the estimation of the power and the first law efficiency of this kind of engine. We impose, in this analysis, constant cross flow section areas, constant revolution per minute, constant isentropic efficiency for both adiabatic irreversible processes. In this analysis, the engine work transfers were calculated as a sum of the work transfers of all the components of the humid air and of the flue gases, considering the dependencies of the adiabatic exponent as function of the temperature. The third part analyzes the opportunity of using oxygen-enriched air in the combustion process in order to obtain an increase of the generated power or to reduce the drawback of the increase of the ambient air temperature. Thus we once more perform the previous parts but considering in addition the volumetric ratio of the oxygen in the combustion air as being larger than the usual one.