Modelling of combustion and nitrogen oxide formation in gas turbines using methane and methane-hydrogen blend fuels

The investigations on use of the blend fuel of the hydrogen/hydrocarbon in the gas turbinesapplications have been recently made the attractive formed area. The reasons of this interestare explained as the demand for fuels of wide range heat value in terms of the reductionpotential of CO, NO and CO2 emissions and properties of stabile combustion in the fuel leanmixture condition. As the cost of hydrogen production decareases and awareness related toglobal warming increases, the studies about this subject have been more crucial. Utilization ofthe blend fuel should be determind as a transition strategy for a carbon-free energy system andthe use of these blend fuels in the related combustion systems should be investigated.Therefore, in this study, combustion process of the methane and methane/hydrogen blendfuels was investigated experimentally in the small scale gas turbine with the cylindricalcombustion chamber. Combustion process in the combustor was modeled usingComputational Fluid Dynamics method. In the study, methane as pure fuel andmethane/hydrogen mixtures as the blend fuels (including 10%, 20%, 30% hydrogen byvolumetric basis) have been used. The flame in the combustor of the gas turbine has beenobtained under the no-load circumstances for different turbine inlet temperatures.In this study, firstly, combustion process of pure methane has been modeled in the burner ofthe thermal power of 10 kW. NO emission and the temperature distributions in the combustorhave been investigated for diffrenet equivalence ratios from 0.6 to 1. Secondly, in theconsidered gas turbine, CH4 and CH4?H2 blend fuels has been burnt in the experimentalcircumstances. In the experimental study, the emission values have been obtained by using ofthe measurement method based on prob. Later, 3 D numerical model for the combustor hasbeen developed in the CFD Code by taken into experimental circumstances. The segment of60o of the combustor has been considered in terms of the calculation effort. In the combustionmodel, two steps for methane and one step for hydrogen have been taken into account. In thenumarical studies, Eddy Dissipation Model has been used. The model constant of A has beenchanged with diffrent values and its effect on the combustion flow has been determined.Standart k-? and RNG k-? turbulance models have been used as turbulance model and theresults of these models have been compared. The relation between velocity and pressure in thenumerical solution has been solved by using SIMPLE algorithm. The calculation of pressureand velocity distributions has been solved by means of PRESTO method. With the aim of theinvestigation of the effect of grid denisty on numerical solution, three diffrent cell cases havebeen tested, and as a result of these tests, 51811 cells have been selected in the model.In this study, the modelling of NO emission has been carried out by using the post-precessorin the CFD code. Both thermal NO and prompt NO mechanisms have been considered in themodelling. It can be seen from both experimental and numerical studies that as turbine inlettemperature increases, NO emission formed increases. In addition, we can observe that whenhydrogen ratio in the blend fuel increases, CO and CO2 emission decrease and H2O amountincreases. Furthermore, it has been shown that the predicted liner wall temperature is belowthe allowable temperature of the liner material. The predicted turbine inlet temperatures areconsistent with measured temperature values. Generally, both the temperature and NOemission values are in good agrement with the numerical solution values.Keywords: Gas turbine, NO emission, Blend fuel, Computational Fluid Dynamics