Primary methods of reduction of nitrogen oxides compared to secondary ones are definitely cheaper in construction and operation, therefore they are still being developed. They are the first step in the reduction of nitrogen oxides and the basis for the use of more advanced methods. The paper presents the innovative research results of the multivariate numerical calculations on the combustion process supported by zero-dimensional calculations of the novel ultra-supercritical boiler BP-680. The numerical model was verified based on the boiler design calculations, made using the advanced O-dimensional model of the whole boiler. The calculations were carried out in Ansys Fluent Workbench. On the basis of the obtained results, the effect of changing the configuration and the location of OFA nozzles on flue gas temperature, CO, O-2 and NOx content in the flue gas, the heat flux along the height of the furnace chamber, and the burnout in the slag hopper and fly ash were analysed. It is very important in the boiler design process the numerical analysis of the impact of the location and the configuration of OFA nozzles on the combustion process. The results of calculations included in this work will help the boiler designer to create a product that is environmentally friendly. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.