No 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.

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Addition of hydrogen (H2) to gas turbine fuel has recently become a topic of interest facing the global challenges of CO2 free combustion. As a drawback, Nitrogen oxide (NOx) emissions are likely to increase in hydrogen-rich fuel combustion which in return limits the use of the technology. In the course of this development, a model-based quantification of NOx emission increase by fuel flexibility may identify possible operation ranges of this technology. This paper evaluates the effect of an increased hydrogen fraction in the fuel on the NOx emissions of a non-premixed 10 MWth gas turbine combustor. A simple reactor network model has been set up using a perfectly stirred reactor (PSR) to simulate the flame zone and a plug flow reactor (PFR) to simulate the post flame zone. The change of residence time in the flame zone is accounted for by an empirical expression. The model is validated against data from high-pressure test rig experiments of an industrial non-premixed gas turbine combustor. The model results are in good agreement with the experimental data. Based on the model results, a fundamental correlation of the effect of hydrogen on the NOx emissions is formulated.

This paper describes a model to predict the nitric oxides (NOx) emissions for a dry non-premixed flame gas turbine combustor at full operation conditions. The NOx correlation considered the combustor pressure, the combustor outlet temperature and the fuel composition from natural gas (NG) to pure hydrogen (H2) fuel. The test data for parametrizing the model was acquired with a high pressure combustion test rig for industrial 10 MWth reverse-flow gas turbine combustors. The experimental results confirm the typical dependencies of NOx emissions. As expected, higher NOx emissions occur with increasing combustor pressure, combustor outlet temperature and hydrogen content of the fuel. The reference NOx model has been derived on the basis of physical approaches for the pressure and temperature effects. The substitution of natural gas with hydrogen is taken into account by a variable pressure exponent and a variable factor in the exponent of the exponential temperature correlation. As a result, the pressure exponent increases with increasing hydrogen. The temperature exponent factor decreases with increasing hydrogen. The model can describe the data set with limitations at high pressure and high hydrogen content fuel operation conditions.