P

Figure 8. Gas flow holdup (u) vs. flowing volumetric concentration (b). The different zones in the plane u-b identify the two-phase flow. Adapted from Merchuk and Berzin (77).

A number of authors (71,76,78,79) have measured the local holdup profile along the riser of an external-loop ALR. In general, it was found that the holdup increases with height. This finding concurs with the expected expansion of gas bubbles as regions of lower pressure are reached. Common sense indicates that this situation must be limited to a certain range; an increase in bubble size will enhance turbulence and result in an increase in bubble encounters, leading eventually to bubble coalescence. The larger bubbles will rise much faster, resulting in a decrease in holdup. Such a scenario was indeed observed by Merchuk and Stein (71), as is illustrated in Figure 9. Merchuk and Stein (71) reported a maximum in the holdup profile for the case of a single-orifice gas distributor. For a multiple-orifice sparger, producing a more homogeneous bubble size distribution, a maximum was not observed within the studied length of the riser, which was 4 m.

Literature data from different sources for gas holdup in the riser under conditions of little or no carryover of gas from the separator into the downcomer for different Ad/Ar and top clearance Ct may be represented by the simple exponential:

Figure 9. Dependence of the riser gas holdup in a 4-m high external-loop ALR with a multiple-orifice sparger (solidlines) and a single-orifice sparger (broken lines). Adapted from Merchuk and

Figure 9. Dependence of the riser gas holdup in a 4-m high external-loop ALR with a multiple-orifice sparger (solidlines) and a single-orifice sparger (broken lines). Adapted from Merchuk and

Brew Your Own Beer

Brew Your Own Beer

Discover How To Become Your Own Brew Master, With Brew Your Own Beer. It takes more than a recipe to make a great beer. Just using the right ingredients doesn't mean your beer will taste like it was meant to. Most of the time it’s the way a beer is made and served that makes it either an exceptional beer or one that gets dumped into the nearest flower pot.

Get My Free Ebook


Post a comment