The article presents a numerical-experimental approach for designing the primary air nozzles working with a large-scale Circulating Fluidized Bed (CFB) boiler. An analysis of the criteria that must be satisfied by CFB air grids has been made and it has been demonstrated that the existing correlations which are used in designing air grids are not possible to be utilized for determining the optimal nozzle design. On the example of a prototype nozzle design, based on the proposed design algorithm, the results of both numerical simulations and laboratory tests, whose aim was to determine the optimal geometry of a nozzle operating with a 235 WMe asymmetric-design CFB boiler, are presented. (C) 2011 Elsevier B.V. All rights reserved.