Experimental and Numerical Characterization of the Dry Low NOx Micromix Hydrogen Combustion Principle at Increased Energy Density for Industrial Hydrogen Gas Turbine Applications

Abstract

In the future low pollution power generation can be achieved by application of hydrogen as a possible alternative gas turbine fuel if the hydrogen is produced by renewable energy sources such as wind energy or biomass. The utilization of existing IGCC power plant technology with the combination of low cost coal as a bridge to renewable energy sources such as biomass can support the international effort to reduce the environmental impact of electricity generation. Against this background the dry low NOx Micromix combustion principle for hydrogen is developed for years to significantly reduce NOx emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen and burns in multiple miniaturized diffusion-type flames. The two advantages of this principle are the inherent safety against flash-back and the low NOx concentrations due to a very short residence time of reactants in the flame region of the micro-flames. The paper presents experimental results showing the significant reduction of NOx emissions at high equivalence ratios and at simultaneously increased energy density under preheated atmospheric conditions. Furthermore the paper presents the feasibility of enlarged Micromix hydrogen injectors reducing the number of required injectors of a full-scale Micromix combustion chamber while maintaining the thermal energy output with significantly low NOx formation. The experimental investigations are accompanied by 3D numerical reacting flow simulations based on a simplified hydrogen combustion model. Comparison with experimental results shows good agreement with respect to flame structure, shape and anchoring position. Thus, the experimental and numerical results highlight further potential of the Micromix combustion principle for low NOx combustion of hydrogen in industrial gas turbine applications.

Development and Testing of a Low NOx Micromix Combustion Chamber for Industrial Gas Turbines

“…For instance, the temperature level inside the outer recirculation zone of burner 1 is clearly higher compared to burner 7. This can be explained by a redirection of the cold flow from the inner to the outer recirculation zone due to an increase of the lateral distance between injections for enlarged injectors (this phenomena has been proven and described in detail in [18]) and due to increased blockage by the thicker flames in front of the air guiding panel.…”

“…Within the joint research of Kawasaki, B&B-AGEMA and AcUAS, [18] and [19] have proven that the low NO x Micromix characteristics can be maintained, even when the principle is adapted to increased energy densities and increased thermal energy output per fuel nozzle by sophisticatedly adjusting the key design parameters. The numerical analysis from [19] shows the progress towards high energy injection nozzles with enlarged diameters.…”

“…To study the interaction of scaling laws and key design drivers, the aerodynamic stabilization of the miniaturized flamelets and the resulting flow field, flame structure and NO x formation are analysed and validated by experimental atmospheric testing of representative combustor test segments. Early studies have focused on hydrogen nozzle diameters of 0.30 mm to 0.45 mm to keep the proven micro-scale of flames at high thermal power output [15], [18]. To reduce manufacturing complexity, to optimize gas turbine integration and to decrease the sensitivity for fuel contamination and blockage in industrial gas turbine (GT) environments, subsequent research has led to the definition of scaling laws for nozzle sizes up to 1.00 mm for optimized GT energy densities with high power and NO x emissions in a single digit ppm range [19].…”

Numerical Investigation Into the Impact of Injector Geometrical Design Parameters on Hydrogen Micromix Combustion Characteristics

“…The concept of hydrogen Micromix combustion for aero engines was first studied Aachen University [7,8], the concept utilises an array incorporating a large number of hydrogen flames at very lean conditions to limit flame temperature, hence the production of NOx. The concept is shown in Figure 1: hydrogen is injected via a circular orifice into accelerated air exiting the air gate, as jets in cross flow.…”

Numerical Investigation of Potential Cause of Instabilities in a Hydrogen Micromix Injector Array

“…Micromix combustion technology for aero engines was first studied by Aachen University [6,7]. The concept utilises an array incorporating a large number of hydrogen flames.…”