INVESTIGATION OF THE EFFECT OF SWIRL ON MIXING WITHIN A KRAFT RECOVERY BOILER

摘要

An experimental study is performed to investigate themixing characteristics of the flow within a Kraft recoveryboiler. The focus is on a comparison of the degree of mixingbetween a boiler operating under conditions of balanced flowwhich exhibit grossly unsteady flow and one operating withturbulent flows which exhibit a more definite flow pattern, aswhen modest swirl is introduced into the flow. Such a study ispertinent for actual boiler operations where the air ports canclog, leading to changes in the boiler flow. The determinationof operating conditions which can increase mixing can lead toincreased operational efficiency for the recovery boiler.The experiments are performed on a 1/28 geometricalscale water model using laser Doppler velocimetry to measurethe flow field and particle tracking to investigate mixing. Inthe latter case, neutrally buoyant tracer particles are injectedthrough specific ports in the boiler models. These particles areilluminated by means of a laser sheet shone horizontally acrossa boiler cross section. The activity of the particles in the laserplane are recorded with a S-VHS camera and the pictures aredigitized for analysis.The results show that the flow patterns in the boiler aresignificantly different for the two cases investigated; namelythe balanced unsteady flow and the swirling flow. The rmsvelocityvalues for the balanced unsteady flow are greater thanthose for the swirling flow. Mixing, as quantified by aparameter involving the flux of particles, is more complete forthe swirling flow. This contrasts with the usual assumptionthat greater unsteadiness provides greater mixing.Comparisons of experimental results with computationalresults show good agreement in values and trends. Suchagreement provides confidence for future computationalinvestigation of mixing.