OBSERVATIONS OF THE BUBBLE DYNAMICS IN A PULP SUSPENSION USING FLASH X-RAY RADIOGRAPHY

A better understanding of bubble dynamics in an air/water/fiber suspen sion is important to many paper processing areas, including flotation deinking and gaseous bleaching. However, using conventional visualizat ion techniques to view gas bubbles in pulp suspensions is nearly impos sible because these systems are opaque at consistencies relevant to th e paper industry. Therefore, alternative tools and techniques must be developed to characterize bubble behavior in these complex systems. In this study, flash X-ray radiography (FXR) is used to visualize air fl ows in a suspension of unprinted old newspaper (ONP) at various consis tencies and air injection rates. FXR provides stop-motion images of ai r bubbles rising through the opaque ONP suspension. The technique is e ffective because air has a significantly different X-ray attenuation c oefficient than water or wood pulp, which have similar attenuation coe fficients. Qualitative observations of these air/water/fiber flow cond itions are reported and compared with those obtained in a simple air/w ater system. The radiographic images reveal that agas flow characteris tics are substantially altered in the presence of fibers. The results demonstrate that gas flows in a simple air/water system are not the sa me as those in an air/water/fiber system.