| OCR Text |
Show Furnace Flow Distribution and Heat Release Pattern Furnace Flow Field Besides the radiation terms, the total energy balance of each vo lume zone includes contributions from convective t .ransport and from heat release due the flame reactions. AS mentioned above, the advective transport of sensible heat is based on predetermined zonal mass flux distributions. There are several means to obtain such distributions ranging from simple engineering guesses to sophisticated 3-D fluid dynamics calculations. In the present study, suitable furnace flow distributions were determined from a mixed-type approach, combining enclosed jet theory, educated guesses and computer routines for continuity considerations and for direct graphical display of mass flux density vectors. The jet theory was in particular applied to estimate the flow for the 02 firing configuration. It was assumed that the forward flows of the high momentum 02-jets which fired from opposite furnace sides in a staggered manner, were not interacting. The flow fields associated with each burner were constructed as follows. The multi-jet outlet of an 02 burner was replaced by an equivalent nozzle diameter taking flame expansion into account. Forward flow profiles and local entrainment rates were calculated with the assumption that the jet entrains fluid halfway the distance between jet origin and impingement of the jet envelope at surrounding walls. The backflow necessary tc s~ ~, ~ort the entrainment rates was empirically distributed over the furnace wi~h he~p of profile factors. In a final step, the flow fields derived for the individual burners were arithmetically superimposed. Also superimposed are pairs of turbulent mass flux vectors with prescribed strength, in order to simulate large scale turbulent exchange over zone boundaries. The simple approach described above is currently validated by 3-D fluid dynamics modeling. Entrainment rates of the 02-flames were also validated with results of comprehensive 2-D modeling previously carried out for pilot-scale 02-burner trials (Ref. 10). Combustion Model The calculation of zonal heat release is based on the furnace flow obtained from above model and on an empirical function, which accounts for the mixing controlled p~ogress of burn-out. In this model, the gaseous fuel is represented by fuel lumps, which 5 |
