engleski

Modeling of Pollutants Formation in Gas Fired Furnaces

Natural gas is more and more proving to be the most efficient fuel in the production of electricity in thermal power plants, from the aspect of minimizing the pollution. Burning gas that usually carries negligible amounts of sulfur containing substances therefore results in low sulfur oxides pollution. Due to the fact that gas has negligible amount of particles, the production of soot will also be limited. Therefore, the main pollutants left are the nitrogen oxides and carbon monoxide. With different methods the concentrations of those pollutants can be minimized. In order to advise those methods, detailed chemistry of methane/ethane combustion in air has to be studied and all significant mechanisms isolated. The most important mechanisms of the production of NOx while burning natural gas in furnaces, which mainly occurs in oxygen rich (fuel lean - superstoichiometric) mixtures are thermal or Zeldovich mechanism and N2O mechanism. The carbon monoxide chemistry is a very important part of the combustion of any carbohydrates, since nearly all carbon atoms get first oxidized to carbon monoxide, and only then to carbon dioxide. But what is of utmost importance for the concentration of carbon monoxide that leave the furnace, and therefore cause the pollution, is the amount of free radicals containing oxygen. In order to model natural gas combustion with all the details necessary to calculate the rate of formation of pollutants, the reaction system consisting of 143 elementary chemical reactions was devised. The reaction model was linked to the three dimensional mathematical model of heat and mass transfer previously developed by the authors. The model was tested by comparing the experimental results obtained from the literature with results of calculation. The model was then applied to the utility steam generator furnace, and the results considering pollution formation where discussed with the respect to the national regulation.

mathematical model; furnace; nitrogen oxides; carbon monoxide

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