Pressure Effect on NOx and CO Emissions in Industrial Gas Turbines

Abstract

In order to determine the effect of pressure on emissions and stability limit, an experimental and modeling study has been performed jointly by UTRC and DOE-FETC. Experiments have been performed at lean conditions in 100–400 psi range with two different nozzles. Measured NOx and CO concentrations have been modeled with a PSR Network using detailed chemistry. Good agreement between the data and model predictions over a wide range of conditions indicate the consistency and reliability of the measured data and validity of the modeling approach. Experiments were conducted at the DOE-FETC facility in Morgantown. A simple refractory combustor liner with a fuel-air-premixing nozzle was used to map stability margins, emission levels of NOx, CO and combustion efficiency. Each experimental nozzle had a centerbody and wall pilot for flame stabilization. Data was collected at four different pressures of 100, 200, 300 and 400 psi, and at different diffusion pilot and moisture levels. The premixing nozzle hardware could be easily lit and operated over a broad range of flame temperatures with minimal combustion generated noise. Two different nozzles designed at UTRC were used to determine pressure and nozzle effects. Computations were made for comparison with the experiments. GRI Mech 2.11 kinetics and thermodynamic database was used for modeling the flame chemistry. A Perfectly Stirred Reactor (PSR) network code developed internally at UTRC was used to create a network of PSRs to simulate the flame and combustor. A total of 10 to 15 reactors were used in the network. Residence time varied with the flow rates (air was fixed while fuel flow rate was varied in order to obtain the required equivalence ratio, ϕ). Good agreement between the measured and modeled NOx (5–10%) was obtained, but the agreement for CO (model predictions are higher by 30–50%) was not as good as for NOx. The experimental data and the modeling predictions indicate that the NOx emission functionality with pressure is dependent on both equivalence ratio and absolute pressure. The CO levels tend to go down with increase in pressure as P−0.5, at different equivalence ratios, consistent with an equilibrium analysis.