Concerns about environmental pollution are of central importance as they influence technical applications and research in the field of combustion. Scaling methodology, applied to the transfer of results from laboratory to industrial scale, has often led to erroneous design solutions. The aim of this study is to obtain engineering guidelines for scaling of natural-gas-fired burners. To this end, both the experimental data generated within the Scaling 400 Project and additional CFD simulations have accompanied the recent data of ENEA. The work has been oriented to establish the dependence of NOX emissions on the furnace thermal input.
In the original Scaling-400 Project, five furnaces spanning the thermal input range from 30 kW to 12 MW were investigated. The constant velocity scaling principle, combined with the geometrical and the thermal similarities (partial scaling) were applied while designing burners for the Scaling-400 experiments. The present study used an alternative concept of partial scaling, which derives the generic burner design using the constant residence time criterion. With the use of all existing experimental data for baseline flames (constant velocity scaling criterion) and the CFD calculations (Fluent-IFRF Code) the necessary curves for scaling of flame properties have been generated.
A number of observations have been made. First of all, the laboratory scale experiments do not produce experimental results applicable to industrial furnaces. A second important observation deals with the scaling approaches used. It has been concluded that none of these approaches is superior as far as scaling of NOX emissions is concerned, in particular when the experiments are carried out at thermal inputs larger than 1.5 MW. For small-scale flames, a strong dependence of the NOX on thermal input has been observed.
The amount of the energy extracted from the flames has been identified as one of the main NOX scaling parameters.