| OCR Text |
Show 11 5.1 The objective of the study Last summer, there were observations made of hot temperature corrosion on the sidewalls of the Meri-Pori furnace. This was due to the low-NOx burners and the over fire air system, which produce reducing conditions in the lower part of the furnace. By adjusting the burner operating parameters, it was possible to reduce the concentration of C O and H2S-spieces near the walls remarkably, which indicates that the corrosion rate will be decreased. However, the NOx-values were increased at the same time. In order to reduce the N O x emission values to the previous level, at least, the A R D E M U S single burner simulation was carried out to optimise the existing low-NOx burner at Meri-Pori. Also, the model was used to optimise the flame stability, which will be a problem, if there is a future need to reduce the boiler load from the existing 5 0 % load to lower loads. In addition to lowering the N O x emissions and the boiler load, the flame shape and flame width must be checked from the simulations to be sure that the flame is not too wide, otherwise the corrosion rate will increase. 5.2 ARDEMUS modelling The optimisation of the burner performance was carried out by ARDEMUS single burner simulations in order to get enough information about the flow and the temperature fields near the burner zone. The computational domain of the Meri-Pori burner included the burner itself and the 5-meter-area from the burner to the furnace. The geometry of the burner allowed the computation to be restricted to only the 1/8 of the burner, and the domain consisted of the 113000 number of control volumes with a refinement in the burner outlet area. The flame stability and the flame shape were estimated on the basis of the computed temperature and flow fields. N O x values were not calculated by A R D E M U S , but the relative values of N O x were possible to evaluate on the basis of the temperature, flow and 0 2 fields. The simulations began with the calculation of the existing low-NOx burner. After that, many different burner configurations were studied. In this report, only the best solution and the existing burner are presented and compared to each other. 5.3 Simulation results The flow, temperature and oxygen fields of the existing burner and the new construction are presented in Appendices 8-13. The existing burner and the new burner differ from each other by the different secondary and tertiary air guide sleeves, different secondary and tertiary air velocities and different kinds of flame stabilisers. Flow fields By changing the angle and the length of the combustion air sleeves and the velocities of the air streams, it is possible to affect the dimensions of the internal recirculation areas of the |
