Approximate Modelling of Nitrogen Oxide Production from Solid Fuel Combustion
Abstract
The mathematical model of nitrogen oxides production described in the paper is developed on the basis of dimensional analysis. The theory of dimensional analysis is used when a mathematical description of a phenomenon is lacking. The aim of using this method was to find out what is the relationship between the parameters of an operating hard coal combustion plant (boiler output, fuel calorific value, quantity and temperature of combustion air, negative pressure in the boiler and flue gas temperature) and the nitrogen oxides produced. The results obtained from the developed model are compared with the values measured on a real device.
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Introduction
The production of nitrogen oxides during the combustion of fossil fuels in large boilers is influenced by a number of operating parameters. The dependence between the amount of nitrogen oxides produced and the individual parameters can also be expressed by means of dimensional analysis. The NOx generation model described in the paper was developed based on the results of measurements on a specific boiler. The information obtained from a given boiler can then be transferred to any other boiler that is physically similar to the analysed model.
Conclusion
The difference between the measured and calculated values according to relation (18) can be justified by the fact that, when choosing the relevant quantities, all the influences on which NOx depends on the combustion of fossil fuels were certainly not taken into account. For a more relevant description of the combustion process it would be necessary to include flame temperature among the selected variables. Because its measurement in online operation of the boiler is a problem, it was not included in the basic model of the boiler. Another variable that could be considered is the mass flow of the coal burned. In addition, the presented results are from a relatively small sample of measurements (only 24). With a large enough sample of data (on the order of 102 ), the results would be more accurate [10].
When using a method for determining NOx production based on dimensional analysis, it is irrelevant to know the details of the combustion device itself, regarding its construction, combustion air distribution system, location of burners, etc. It is also irrelevant to investigate what happens if it changes during combustion, e.g. fuel moisture. All these influences are reflected in the model in the measured values of the quantities that make up the model itself.