Numerical and Experimental Characterization of Low NOx Micromix Combustion Principle for Industrial Hydrogen Gas Turbine Applications

Abstract

The international effort to reduce the environmental impact of electricity generation, especially CO2-emissions requires considerations about alternative energy supply systems. An effective step towards low pollution power generation is the 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 use of hydrogen and hydrogen rich gases as a fuel for industrial applications and power generation combined with the control of polluted emissions, especially NOx, is a major key driver in the design of future gas turbine combustors. The micromix combustion principle allows a secure and low NOx combustion of hydrogen and air and achieves a significant reduction of NOx-emissions. The combustion principle is based on cross-flow mixing of air and gaseous pure hydrogen and burns in multiple miniaturized diffusion-type flames. For the characterization of the jet in cross-flow mixing process, the momentum flux ratio is used. The paper presents an experimental analysis of the momentum flux ratio’s impact on flame anchoring and on the resultant formation of the NOx-emissions. Therefore several prototype test burner with different momentum flux ratios are tested under preheated atmospheric conditions. The investigation shows that the resultant positioning and anchoring of the micro flames highly influences the NOx-formation. Besides the experimental investigations, numerical simulations have been performed by the application of a commercial CFD code. The cold flow simulation results show the mixing of the air and hydrogen after the injection, in particular in the Counter Rotating Vortices (CRV). Furthermore, the hydrogen jet interacts also with another vortex system resulting from a wake flow area behind the combustor geometry. Furthermore, reacting flow simulations have been performed by the application of a Hybrid Eddy Break-Up (EBU) combustion model. The combustion pressure has been varied from atmospheric conditions up to a pressure of 16 bar. The experimental and numerical results highlight further potential of the micromix combustion principle for low NOx-combustion of hydrogen in industrial gas turbine applications.

Frontiers in combustion techniques and burner designs for emissions control and CO2capture: A review

“…Lean Direct Injection (LDI) was found to drastically reduce the risk of flashback in H 2 combustors. 244 The combustion of high-H 2 fuels using air in MMs has been examined in past studies, [238][239][240] but never under oxycombustion conditions. Miniature-scale distributed premixer arrays, aka MMs, were developed and tested in several studies, in order to reduce NO x emissions safely with H 2 -rich fuel.…”

“…Some of the examined configurations were jetin-crossflow mixing, 242 co-flow mixing, 243 and swirlinduced mixing in miniature cups with axial and radial inflow. 244 The combustion of high-H 2 fuels using air in MMs has been examined in past studies, [238][239][240] but never under oxycombustion conditions. Hernandez et al 245 natural gas/air ones in MMs.…”

Development and Testing of a Low NOx Hydrogen Combustion System for Heavy-Duty Gas Turbines

“…These injectors are similar to LDI, but include a small premixing zone, and may approach the operability characteristics of LDI if designed carefully. Configurations in the literature include jet-in-crossflow mixing [8], coflow mixing in channels [9], and swirl-based mixing in small "cups" with radial and axial inflow [10]. The latter concept was incorporated into a 1.3 MW fuel injector array that was built with a macrolamination process and operated at pressures of 8 to 12 bar with fuels consisting of hydrogen, natural gas, nitrogen and/or carbon dioxide [11].…”

Development and integration of a scalable low NOx combustion chamber for a hydrogen-fueled aerogas turbine

“…From this follows that besides the jet in cross- §ow process, other §ow phenomena have an important in §uence on §ame stabilization and, consequently, on the resultant NOx formation, such as the wake formation of the recirculation zones, resultant from the burner geometry, impacts highly the positioning of the micro §ames. The further improvement of the combustion principle with regard to scalability and enhancement of the energy density is still part of the current research activities [9]. Figure 2c shows the latest manufactured combustion chamber, based on the micromix principle, for the integration into the APU GTCP 36-300.…”

“…Figure 6b demonstrates this correlation. The ¦gure shows the impact of air mass §ow variations on the burner£s burning e©ciency at di¨erent λ-values [9], done with a prototype test burner at the university£s atmospheric combustion chamber test rig. On the vertical axis, the burning e©-ciency and on the horizontal axis, the λ-values are plotted.…”