Jaan Hellat

25Years of BBC/ABB/Alstom Lean Premix Combustion Technologies

The paper will show the development of lean premix combustion technologies in BBC, ABB, and Alstom gas turbines. Different technologies have been developed and applied in Brown Boveri Company (BBC) before 1990. Considerable improvements with respect to NOx emissions as compared to gas turbines with a single combustor and a single diffusion burner for liquid and gaseous fuel have been achieved with burners with extended premixing sections and with multi-injection burners for annular combustors. Between 1990 and 2005, burners with short but effective premixing zones (EV burners: environmentally friendly V-shaped burners) have been implemented in all new gas turbines of the ABB (and later Alstom) fleet with NOx levels well below 25 vppmd (@15% O2). In addition to this, three variants of premix technologies have been successfully developed and deployed into Alstom GT engines: the sequential EV burners—a technology that allows premixing of natural gas and oil into a hot exhaust stream to reheat the exhaust gases of a first high-pressure turbine; the MBtu EV burners that are used to burn syngas in a premix flame with low NOx emissions; and the advanced EV burners (AEV) that are capable to prevaporize and premix liquid fuel prior to combustion and burn it with very low NOx emissions without water injection. The paper will give an overview of these technologies and their usage in Alstom gas turbines over the last 25years.

The Reheat Concept: The Proven Pathway to Ultralow Emissions and High Efficiency and Flexibility

Reheat combustion has been proven now in over 80 units to be a robust and highly flexible gas turbine concept for power generation. This paper covers three key topics to explain the intrinsic advantage of reheat combustion to achieve ultralow emission levels. First, the fundamental kinetic and thermodynamic emission advantage of reheat combustion is discussed, analyzing in detail the emission levels of the first and second combustor stages, optimal firing temperatures for minimal emission levels, as well as benchmarking against single-stage combustion concepts. Second, the generic operational and fuel flexibility of the reheat system is emphasized, which is based on the presence of two fundamentally different flame stabilization mechanisms, namely, flame propagation in the first combustor stage and autoignition in the second combustor stage. This is shown using simple reasoning on generic kinetic models. Finally, the present fleet status is reported by highlighting the latest combustor hardware upgrade and its emission performance.

THE REHEAT CONCEPT: THE PROVEN PATHWAY TO ULTRA-LOW EMISSIONS AND HIGH EFFICIENCY AND FLEXIBILITY

Reheat combustion has proven now in over 80 units to be a robust, and highly flexible gas turbine concept for power generation. This paper covers three key topics to explain the intrinsic advantage of reheat combustion to achieve ultra-low emission levels. First, the fundamental kinetic and thermodynamic emission advantage of reheat combustion is discussed analyzing in detail the emission levels of the first and second combustor stages, optimal firing temperatures for minimal emission levels, as well as benchmarking against single-stage combustion concepts. Secondly, the generic operational and fuel flexibility of the reheat system is emphasized, which is based on the presence of two fundamentally different flame stabilization mechanisms, namely flame propagation in the first combustor stage and auto-ignition in the second combustor stage. Finally, the present fleet status is reported by highlighting the latest combustor hardware upgrade and its emission performance.

Combustor Design for Low Emissions and Long Lifetime Requirements

Advanced combustor design for gas turbines in power generation is driven by reliability, lifetime and emission requirements, by needs for fuel flexible operation, and minimization of cost of electricity. The present paper explains in detail the basic design principles of the annular combustors, as implemented in the most recent upgrades of the GT13E2 and GT24/GT26 engine families. One fundamental principle is the choice of a premix burner system with low pressure drop, allowing serial combination of a convective cooling scheme by fuel-air premixing with almost all available air. This allows operating at the lowest possible flame temperature, for a given hot gas temperature, thus assuring the minimum NOx emissions. Introduction of advanced seals reduce the leakage of air, helping further to reduce the flame temperature and improve burnout and stability. A second distinct feature of annular combustors is the possibility of single- and multiple-row burner arrangements for optimized operational flexibility. Burner arrangements are further optimized to yield the best stability with low heat loads to combustor walls and more uniform exit temperature distribution over the entire engine load range. Another feature of the modular combustion chambers is the separation of cold load-carrying structures and hot heat-shielding elements, which allows for easy maintenance and minimization of air leakages. Examples for the most recent component upgrades will be given in the full paper, with a focus on the reheat (SEV) combustor improvements for increased robustness and life-time, whilst maintaining combustion performance and minimizing cost. Field-feedback has proven to be an important element to understand and exploit the full lifetime potential of this design concept. A comprehensive account of field data from both EV and SEV combustors are presented, accounting more than one and a half decade long operation experience with annular combustors.© 2009 ASME

Brennstoff, Brennstoffsystem und Fahrkonzept

Das Brennstoffsystem stellt die Verbindung her zwischen dem Brennstoffreservoir (i.d.R. eine Erdgaspipeline oder ein Heizoltank) und dem Brennstoffverbraucher, den Brennern bzw. der Brennkammer der Gasturbine. Aufgabe des Brennstoffsystems ist es, den Brennern in jeder Betriebssituation die erforderliche Brennstoffmenge in der richtigen Qualitat und Quantitat zur Verfugung zu stellen.

25 Years of BBC/ABB/Alstom Lean Premix Combustion Technologies

The paper will show the development of lean premix combustion technologies in BBC, ABB and Alstom gas turbines. Different technologies have been developed and applied in Brown Boveri Company (BBC) before 1990. Considerable improvements with respect to NOx emissions as compared to gas turbines with a single combustor and a single diffusion burner for liquid and gaseous fuel have been achieved with burners with extended premixing sections and with multi injection burners for annular combustors. Between 1990 and 2005 burners with short but effective premixing zones (EV burners: environmental friendly V-shaped burners) have been implemented in all new gas turbines of the ABB (and later Alstom) fleet with NOx levels well below 25 vppmd (@15%O2). In addition to this, three variants of premix technologies have been successfully developed and deployed into Alstom GT engines: the sequential EV burners — a technology that allows premixing of natural gas and oil into a hot exhaust stream to reheat the exhaust gases of a first high pressure turbine; the MBtu EV burners that are used to burn syngas in a premix flame with low NOx emissions; and the advanced EV burners (AEV) that are capable to prevaporize and premix liquid fuel prior to combustion and burn it with very low NOx emissions without water injection. The paper will give an overview of these technologies and their usage in Alstom gas turbines over the last 25 years.Copyright

Development of an Oil Injection System Optimised to the ABB Double Cone Burner

Present day land-based gas turbine combustors, operating on oil, must meet strict requirements for emissions (CO, unburned hydrocarbons, particulates, smoke and NOx) and burn stabily without pulsations over a wide range of operating conditions. In addition many engines, such as those produced by ABB, operate with both oil and natural gas fuels either together or independently. This paper concentrates on the development of an oil injection system which is optimised for ABB’s double cone burner (Figure 1) and which does not affect the operation of this burner on natural gas. The development procedure, which involved a coupling of numerical and experimental techniques, is described. The results of the application of this procedure indicate that a simple plain jet atomiser in conjunction with a small quantity of unswirling air admitted at the head of the burner is the best option for this burner.Copyright

Vergasung fester und flüssiger Brennstoffe

Gasturbinen werden bis heute noch fast ausschlieslich zur Verstromung von Erdgas oder Heizol eingesetzt. Die Vorschaltung einer Vergasungsanlage ermoglicht auch die Nutzung von festen oder flussigen Brennstoffen wie Kohle oder Raffinerieruckstanden, die sonst nicht direkt in einer Gasturbine bzw. GuD-Anlagemit hohem Wirkungsgrad umgesetzt werden konnten. Diese Kopplung aus Vergasungsanlage mit nachgeschalteter Gasreinigung und anschliesender Nutzung des gereinigten Synthesegases (Syngas) in einer GuD-Anlage wird als IGCC-Kraftwerk (IGCC = Integrated Gasification Combined Cycle) bezeichnet.

Besonderheiten des Betriebs mit Schweröl, Naphtha und Kondensaten

Brennstoffe, deren Einsatz in Gasturbinen eine Anpassung von Hilfsanlagen, Brenner oder zusatzliche Aufbereitungsmasnahmen gegenuber der Anwendung von Standard-Flussigbrennstoff bedeuten, werden als Sonderbrennstoffe bezeichnet. Sonderbrennstoffe dienen in der fossilen Energieerzeugung im Gasturbinen- wie auch im kombinierten Gas- und Dampfturbinen (GuD) Kraftwerk in vielen Fallen als Ausweichbrennstoffe zu den konventionellen Brennstoffen Erdgas und Heizol und werden mit Schwerpunkt dann eingesetzt, wenn als Folge lokaler Preispolitik solche Sonderbrennstoffe wirtschaftlich sind und den Zusatzaufwand rechtfertigen, der fur Brennstoffaufbereitung, Systeme und Verbrennung damit in der Regel verbunden ist. Eine Alternative zum Standard-Flussigbrennstoff Leichtes Heizol (siehe Kap. 11.2.2) bilden die Produkte der Verarbeitung von Rohol in Raffinerien (siehe Abb. 13-1).

Kohle- und Teervergasung

Gasturbinen werden bis heute fast ausschlieslich zur Verstromung von Erdgas oder Heizol eingesetzt. Die Einbindung eines Vergasungsverfahrens ermoglicht auch den Einsatz von festen oder flussigen Brennstoffen wie Kohle oder Raffinerieruckstande in dem thermodynamisch sehr vorteilhaften Gas- und Dampfturbinenprozess. Ein zusatzlicher, insbesondere bei der Verbrennung von Ruckstanden sehr wichtiger Vorteil sind die im Vergleich zu anderen Kraft-werkstechnologien sehr niedrigen Emissionen [11.5, 11.6].