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Show ) IFRF Doc. No. K 70/a/12 August 1989 - 7 - Mathematical Modelling of Pulverised Coal Flames surfaces with a temperature of 400 K and an absorption coefficient of 0.6. The furnace walls are regarded as adiabatic. At the inlet to the burner the axial and tangential velocities and their fluctuating components were measured during calibration of the swirler. These measurements provide precise inlet conditions for the computations. The inlet value of turbulent energy dissipation was estimated [6]. 4. fLAME PREDICTIONS For both flames, the predicted flame shape, length, and overall flow pattern in the furnace agree very well with those identified from both in-flame measurements of flow direction and flame photography. The predicted flow patterns inside and just downstream of the burner quarl are shown in Figure 4. The impact of the fuel gun insertion on the flow is dramatic. In Flame 3 the primary air is rapidly entrained into the secondary air. In Flame 4 however, the primary air is jnjected into the reverse flow. Consequently, in Flame 3, the coal particles are rapidly entrained into the secondary air where they devolatilise in an oxygen rich environment. In Flame 4, the coal is injected into the oxygen lean zone and it gives off the volatiles in an oxygen deficient environment (particle trajectories can be found in Reference 10). These distinct flow patterns generate different near burner zone chemistries which either promote or inhibit the NOx formation. ,~ ,~ I ,, -.......::;T~~.~~.~.~.,. ... ._-. .- -- I ...... _____ _ , .. -- - --- .. - low NOx flqme ,-,. ,,~, I . .. i ... ... ---- -- ... .,, <II . .: ... ! ----- --..... . .-:. ! ----- --~- -- ;....-.'. ...... ; -- .... - - ,,""",,"'., .. ~.~...,./ /~ -: ::~~ ~ ~ ~~~0;'~' "JoJ'.Jlr.....#"'" " ~ ~, , ,.. • ... ~~~%;I'/" ~" •• II • ~~~~\.l" :;:,.. i~~~~~-a:/~~~ ~ : = : :: . ... . l: /'~ ~ ~ : = : :: • .,' , /"" . .. . . ." . . . . ;:;::~~:;.-"i~:f;: ; J I ! ! iii i Hi! i ~ ~ 'J ,-:;-~:.:' .: : : : ; : : : :: . ... .. .. - - \ ..... _-- ....... .... ............... ... , .... _______ ••••••• I •• ____ _ ....... ____ •• __ •• II' •••• __ ... _ -hIgh NOx flome Fig. 4. Aerodynamics of low alld high NOx flames A comparison of predicted temperatures and oxygen concentrations with those measured in the quarl zone is presented in Figures 5 and 6. Except in the very close vicinity of the gun, a very good agreement between measurements and predictions is obtained. Inside the quarl, temperature gradients of 200 K/cm were predicted, with respect to these values, the differences between measured and predicted temperatures inside the quarl may be regarded as acceptable. The carbon dioxide concentrations were again |