Preliminary Analysis of a New Methodology for Flameless Combustion in Gas Turbine Combustors

Abstract

Flameless combustion is one of the most promising technologies that can meet the stringent demands of reduced pollution and increased reliability in future gas turbine engines. Although this new combustion technology has been successfully applied to industrial furnaces, there are inherent problems that prevent application of this promising technology in a gas turbine combustor. One of the main problems is the need for recirculating large amount of burnt gases with low oxygen content, within limited volume, and over a wide range of operating conditions. In the present paper, thermodynamic analysis of a novel combustion methodology operating in the flameless combustion regime for a gas turbine combustor is carried out from the first principles, with an objective to reduce oxygen concentration and temperature in the primary combustion zone. The present analysis shows that unlike in the conventional gas turbine combustor, transferring heat from primary combustion zone to secondary (annulus) cooling air can substantially reduce oxygen concentration in reactants and the combustion temperature, thus reducing NOx formation by a large margin. In addition, to reduce the peak temperature, the proposed methodology is conceptualised / designed such that energy from fuel is released in two steps, hence reducing the peak flame temperature substantially. The new proposed methodology with internal conjugate heat transfer is compared vis-a`-vis to other existing schemes and the benefits are brought out explicitly. It is found that transferring heat from the combustion zone reduces oxygen concentration and increases carbon-dioxide concentration in the combustor, thus creating an environment conducive for flameless combustion. In addition, a schematic of a practical engineering design working on the new proposed methodology is presented. This new methodology, which calls for transfer of heat from the primary combustion zone to alternative air streams, is expected to change the way gas turbine combustors will be designed in the future.

An Experimental and Numerical Investigation of the Aerodynamic Characteristics of a Flameless Combustor

“…General problems to overcome are stability issues, establishing the auto-ignition temperature and adequate recirculation ratios and mixing of the flue gases, since these are all important requirements for flameless combustion operation. All this should be achieved in a limited volume and over a wide range of operations [11].…”

“…Others use one of the three design approaches but use different names than have been presented here [48]. Next to experimental setups computer models are also intensively used to try describing the working ways of flameless combustion and test the influence of the different variables [10,11]. Many others write about doing both [9,12,26,30,32,37,38,42,43,45,47,49].…”

“…Increasing residence times increases emisisons and increasing mass flows increases mixing but decreases residence times, increasing emisisons. Inside a gas turbine combustion chamber, flameless combustion is only determined by internal aerodynamic and thermodynamic processes making it hard to control the regime and ensure low emisisons [11].…”

Experimental Investigation of the Influence of Combustor Cooling on the Characteristics of a FLOX©-Based Micro Gas Turbine Combustor

“…An important influence factor for this behaviour is the exhaust gas recirculation rate which is enhanced by higher jet velocities and higher air numbers [11], respectively. Increasing recirculation serves to enhance the dilution of the fresh gas jets by hot flue gases [23] reducing the chemical reaction rates [24]. Simultaneously, rising jet velocity decreases the fluid dynamic time scale.…”

Numerical Simulation of Liquid Bio-Fuel Combustion in an EGR Equipped Micro Gas Turbine

“…As well known, activating an exhaust recirculation at the compressor inlet (Camporeale and Fortunato, 2007) allows the combustion chamber to be entered by an air-gas mixture with a relevant oxygen defect. Such a condition, together with the high temperature level induced by the recuperated cycles, leads the combustion development to situations close to the so called MILD (Cavaliere and de Joannon, 2004) or flameless (Panne et al, 2009;Duwig et al, 2006;Levy et al, 2007a;Li et al, 2006) regime. The authors have highlighted the advantages that arise from the adoption of an external EGR system, together a number of limitations, say:…”