Numerical Simulation Of Gas/oil Co-combustion Process And NOx Formation

Owing to Relying on only oil fuel for the operation of thermal power plants could pose problems in the times of fuel market instabilities. To decrease an exposure on fuel supply uncertainties and price oscillations, and to ensure continuous and most economic power production, it is desirable to have more options. Nearly all old oil-fueled boilers in industry are now retrofitted to allow possibility to use two different kinds of fuel, namely heavy fuel oil and natural gas. On the other hand, with the expanding of manufacture of petrochemical factories, gas, a by-product, is more and more. Same oil-fired and coal-fired boilers are converted to burn this gas, and have got good result of saving energy and protecting environment.However, fuel diversification might lead to redistribution of temperature, wall heat flux as well as boiler efficiency, or may lead to dangerous accident at worst. To ensure adaptability of fuel diversification, it is desirable to have a further investigation to combustion and dynamic process of furnace. As it is very difficult and expensive to collect data from in-situ experiment, numerical simulation is now widely used in engineering science and plays an important role.The other aspect of dual firing is ecological. Combustion of fuel of high caloric value like oil and natural gas, has an large amount emission of NOx due to its higher temperature in combustion area. Based on the literature search, it is clear that the problem of NOx formation in industrial boilers although received much attention in regard to coal-fired boilers, a limited portion of research work was focused on gas-fired or oil-fired boilers. In this paper only thermal mechanism NOx was taken into account for the formation of thermal NOx requires temperature above 1800K to produce a significant amount of NOx. The other two types of NOx were neglected because the prompt NOx forms insignificant contribution to the total amount and the fuel NOx is weakly dependent on temperature.This paper presents full-scale numerical simulation of flow and combustion process in the furnace of co-combustion of oil/gas boiler of Y-130/39-1, which is now retrofitted from oil-fired boiler. The prediction presents the flow filed, temperature filed, average wall heat flux, and NOx concentration distribution in the furnace under the various conditions. The results demonstrate that excess air coefficient and swirl intensity of air flow has significantly influenced temperature field, average wall heat flux, flame length and NOx formation. In particular, the simulation provided more insight on the correlation between the maximum furnace temperature and the thermal NOx concentration. Based on the analysis of influence of the different conditions, we investigated some cases in which we try to maintain the best performance of combustion and to reduce the NOx formation.