Dry Low NOx Emissions Operability Enhancement of a Heavy-Duty Gas Turbine by Means of Fuel Burner Design Development and Testing

Abstract

This paper describes the development phases of an annular type combustor for heavy-duty gas turbine applications. High cycle efficiency and low emissions are required over a wide range of load conditions, with the consequence of reducing margin to thermo-acoustic instability onset and lean blow-out. In addition, in lean premixed combustors, the increased fuel air mixing times required to keep emissions low, may lead to undesired ignition or flashback into the fuel burner ducts. All these aspects are matter of this work and focus is on fuel burner design modifications which allowed dry emissions reduction while maintaining a sufficiently wide safe operation window. A synergic effort has been put in place, involving experimental campaigns and CFD simulations, with the purpose of assessing design changes initially and doing screening. In the meanwhile, numerical practices have taken benefits form the experience growth. Results of past work on similar components has been leveraged too. Test campaign involved different scale facilities, from single burner through full annular combustor up to full scale prototype engine. The progressive reduction of viable option for combustor components design changes, due to high impact of such modifications during the gas turbine late development phases, forced designers to concentrate efforts onto fuel burner optimization, looking for efficient ways to implement modifications and assess their effectiveness of combustion system performances. Emissions trends, blow-out and flashback margin for several burner designs are reported. Numerical analysis results are also shown, which revealed to be well aligned with the experimental outcomes, allowing burner optimized solution to be identified. Finally, characterization with respect to fuel gas composition is shown as well as sensitivity to different operating conditions.

Numerical Study of Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach

“…The premixer has a double counter-rotating swirler to enhance the mixing of the fuel injected through the premixed fuel line as well as the piloted fuel line [45]. The latter is responsible for the flame stabilization injecting the fuel in the primary zone of the combustor through co-axial holes [46].…”

Dry-Low Emission Gas Turbine Technology: Recent Trends and Challenges

“…This phenomenon is widely known as the LBO fault, which will be thoroughly discussed in the next section. In many cases, as reported in [79][80][81][82][83][84], LBO fault is considered the most common problem in DLE systems, which leads the gas turbine to trip. Other problems are observed before the blowout, such as auto-ignition, flashback, and combustion instability.…”

“…Controlling the air and fuel ratio to keep the gas turbine in its operating region [79][80][81][82][83][84] Auto-ignition…”

Experimental and Numerical Characterization of the Self-Excited Dynamics Behavior of a Technically Premixed Burner

“…So, the characterization of the performance of a design solution with respect to the thermo-acoustic instabilities is a step that needs to be anticipated quite early during its development phase [6][7][8]. At this purpose, several numerical methods have been proposed over the last decades, aiming also at reducing the extremely high experimental costs related to this kind of investigation [9].…”