| OCR Text |
Show the corresponding oxygen concentration should be the optimal one. The optimal combination of the preheated air temperature and the oxygen concentration will be different in the different cases of fuels, diluents and furnaces, and can be predicted by numerical simulation. A s an example in the regenerative furnace simulated here with L P G as fuel and diluted air with flue gas, the optimal combination of the preheated air temperature and the oxygen concentration was predicted, and the result is shown in Fig 17. The permitted N O x emission at the furnace exit was taken as 50 ppmv. The curve in the figure represents the optimal combination. In the zone under the curve, the N O x emission can be kept lower than the permitted value. If the combination of the preheated air temperature and the oxygen concentration tends to be far from this curve, the furnace temperature will decrease a lot even though the N O x emission has a certain decrease. While in the zone above the curve, the N O x emission will be over the permitted value even though the furnace temperature can have a certain increase. 4. CONCLUSIONS The combustion characteristics and the NOx emission in the gas diffusion flame with the highly preheated and diluted air have been numerically investigated. It has been found that the flame temperature increases as the preheated air temperature increasing, while the temperature distribution tends to be more uniform and the N O x emission decreases when the oxygen concentration in the preheated air is low. The temperature and N O x emission levels appear a difference when the air is mixed with different diluents. For a certain diluent, there exist optimal combinations of the preheated air temperature and the oxygen concentration which could provide the possible highest level of temperature while the N O x emission is lower than the permitted value. In principle, the highly preheated air temperature should combine with the low oxygen concentration. ACKNOWLEDGEMENTS This work has been financially supported by Japan Technical Information Service on the i |
