Dry Low NOx Gas Turbine Research Articles

Experimental and Numerical Investigations of Novel Natural Gas Low NOx Burners for Heavy Duty Gas Turbine

A novel dry low-NOx gas turbine technology requires well-balanced assessments since the early development phases. The weak knowledge of often conflicting aspects, such as operability and manufacturability, make any roadmap difficult to be drawn. Introduction of innovative manufacturing technologies such as the direct metal laser sintering (DMLS) process allows rapid manufacturing of components and test them in dedicated facilities to support real-time development of new products. The use of such a manufacturing process allows the adoption of designed experiment-based development strategies, which are still uncommon at industrial level, due to the reduced time from drawings to test.The paper describes a reactive test campaign performed by BHGE in cooperation with University of Florence, aimed at the exploration of capabilities of different innovative burners in terms of pollutant emissions containment and blow-out margin. In particular, the test campaign has been conceived to provide a robust estimate of the effects of key geometrical parameters on principal burner performances. The flame stabilization mechanism of the investigated burners is based on the swirling flow generated by different setup of two internal channels: corotating and counter-rotating radial and axial swirlers. The effect of both the shape and the size of the internal air passages, as well as of the swirler characteristics, has been matter of investigation. Burners were tested in a single-cup test rig operated at moderate pressure conditions (up to 6 bar), with two levels of preheated air temperature (300 °C and 400 °C). Each burner was equipped with two natural gas feeding lines representing the diffusion (pilot) and premixed (main) fuel supplies: both lines were regulated during tests to assess the effect of fuel split on emissions and to identify a stable low-NOx operating window, within which a lean blow-out test was performed. Dynamic pressure probes were used to evaluate the onset of combustion instabilities. The burner development was supported by computational fluid dynamics (CFD) investigations with the purpose to have a detailed understating of the flow-field and flame structure and to perform a preliminary screening to select the most promising solutions for the testing phase. The post process of the experimental results has allowed to correlate the main design parameters to burner performance variables discovering possible twofold optimizations in terms of emissions and operability.

Development of Dry Low-NOx Gas-Turbine Combustors Equipped with Multi-Hole Co-Axial Jet Burners for IGCC

Development of Dry Low-NOx Gas-Turbine Combustors Equipped with Multi-Hole Co-Axial Jet Burners for IGCC

Effects of CO2 dilution on combustion instabilities in dual premixed flames

There has been a rapid increase in the demand for biogas applications in recent years, and dry low NOx and dry low emission gas turbine combustors are promising platforms for such applications. Combustion instability is the most important drawback in dry low NOx gas turbine combustors and has, therefore, attracted considerable research interest lately. As a fundamental study towards the use of biogas in dry low NOx and dry low emission gas turbine combustors, this article investigates the influence of CO2 in surrogate biogas on combustion instability. Tests were conducted using a dry low NOx type, a dual lean premixed gas turbine combustor. For a dual flame with dual swirl, the pilot fuel mass fraction affects the flame structure, and the flame structure, in turn, determines the temperature distribution in the combustion chamber and the combustion instability. The effects of the pilot fuel mass fraction, which is an important parameter of the combustor, and the CO2 dilution rate, which is a major contributor of biogas combustion, on the combustion characteristics and instability are investigated through dynamic pressure signal and phase-resolved OH* images. Combustion instability decreases for higher CO2 dilution rates, whose effects depend on the pilot fuel mass fraction. The instability reaches its maximum at a pilot fuel mass fraction of 0.3. Tests confirm that combustion instability diminishes with CO2 dilution, as it reduces the perturbation in the heat emission, and the flame speed decreases resulting in a greater flame surface or volume. Further, investigation of the Rayleigh Index, which represents the coupling strength of the heat release fluctuation and the natural frequency, shows that CO2 dilution weakens the coupling strength, resulting in less combustion instability.

Combustion instability mechanism of a lean premixed gas turbine combustor

Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations.

Performance of a Dry Low-NOx Gas Turbine Combustor Designed With a New Fuel Supply Concept

This paper describes the performance of a dry low-NOx gas turbine combustor designed with a new fuel supply concept. This concept uses automatic fuel distribution achieved by an interaction between the fuel jet and the airflow. At high loads, most of the fuel is supplied to the lean premixed combustion region for low-NOx, while at low loads, it is supplied to the pilot combustion region for stable combustion. A numerical simulation was carried out to estimate the equivalence ratio in the fuel supply unit. Next, through the pressurized combustion experiments on the combustor with this fuel supply unit using natural gas as fuel, it was confirmed that NOx emissions were reduced and stable combustion was achieved over a wide equivalence ratio range.