D

FIG. 14-28 Baffle tray variations. (a) Segmental. (b) Disk and doughnut. (c) Multipass. (d) Angle irons.

that can plug up, the baffle trays are perhaps the most fouling-resis-tant device in the industry, and their main application is in extremely fouling services. To be effective in these services, their liquid rate needs to exceed 20 m3/hm (2 gpm/in) of outlet weir and dead spots formed due to poor support design (Kister, Distillation Troubleshooting, Wiley, 2006) eliminated.

There are several geometric variations. The disk and doughnut trays (Fig. 14-28b) replace the half-circle segmental plates by alternate plates shaped as disks and doughnuts, each occupying about 50 percent of the tower cross-sectional area. In large towers, multipass baffle trays (Fig. 14-28c) are common. Another variation uses angle irons, with one layer oriented at 90° to the one below (Fig. 14-28d). Multipass baffle trays, as well as angle irons, require good liquid (and to a lesser extent, also good gas) distribution, as has been demonstrated from field heat-transfer measurements [Kister and Schwartz, Oil & Gas J., p. 50 (May 20, 2002)]. Excellent overviews of the fundamentals and design of baffle trays were given by Fair and Lemieux [Fair, Hydro. Proc., p. 75 (May 1993); Lemieux, Hydroc. Proc., p. 106 (September 1983)]. Mass-transfer efficiency data with baffle trays by Fractionation Research Inc. (FRI) have been released and presented together with their correlation (Fair, Paper presented at the AIChE Annual Meeting, San Francisco, November 2003).

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