An analysis of the flow that depends on the fuel composition (natural gas) in the combustor–transition piece system, applying computational fluid dynamics, is presented. The study defines the velocity and temperature profiles at the exit of the transition piece and the hot streak along the system. The variation of the composition in the fuel depends of the amount of N2 contained in the fuel, and the hot track influences on the temperature distribution at the input of the first stage of vanes and blades of the gas turbine. The study takes place in a three-dimensional model in steady state using FLUENT® 6.3.26, applying the k-ε turbulence model and chemical equilibrium to the combustion process. The results show the influence of the transition piece geometry over the velocity and temperature profiles, principally, in the radial direction. The velocity profiles on the radial direction can be represented by six order polynomial and the temperature profile by third order polynomial. The temperature and velocity profiles keep a symmetry profile and they can be represented by six order polynomial at the circumferential direction. Knowing these profiles, it is possible to compute a more exact study of the heat transfer at vanes and blades of the first stage of the turbine to evaluate the performance and life of them. On the other hand, considering from 2% to 10% of N2 in the fuel composition, the maximum temperature is reduced in the combustion process and consequently the NOx emissions too.

Two older boilers were burning low grade heavy fuel oil (number 6) and emitting large amounts of unburned carbon particles. Owing to the short life remaining of the units and economic constrains, it was not possible to change to a better fuel or install new burners. To contribute to the solution of this problem, an experimental program was carried out by emulsifying water in the fuel oil. Tests were performed in a scale furnace (0.35MWth) and the emulsions that produced the best results were assessed in the two boilers, 28 and 34 MWe capacity with Y-jet atomizer type. The system to prepare the emulsion was very simple: water was added into the oil before the fuel oil pump, no chemical products were added and a static mixed was used to improve the water size distribution, which 90% ranged from 1 to 9 micron. In the pilot furnace the emulsions were prepared with 5 and 10% water and atomized with compressed air. Particle reductions of 43 and 67% were obtained compared with the net heavy fuel oil. In the boilers, the emulsions were prepared with the same amount of water, and were atomized with saturated steam. In the 28 MWe boiler, a similar particle reduction was obtained to that of the scale furnace. However, in the 34 MWe boiler there was no particle abatement. By using a commercial fluid dynamic computer code, it was found that the combustion air transferred heat to the steam raising its temperature. Thus, in the mixing chamber of the Y-jet atomizers, the steam was superheated and destroyed the water droplets of the emulsion. Compressed air and saturated steam as atomizing medium of the emulsions had similar effect on the unburned particle reduction. However, the effectiveness of the emulsions may be affected by the steam. Care should be taken to avoid the use of steam with a temperature higher than the saturated water temperature.