Efficiency, tray 700 Subject

The problem we have just discussed—poor fractionation efficiency due to inadequate vapor and liquid initial distribution—is rather similar to tray deck dumping in trayed fractionators. And, just like trays, packed towers are also subject to flooding. 

Input the liquid viscosity in centipoise. The liquid here is that on the subject tray. This is an important factor in determining tray efficiency. The value should be entered accurately and derived from reliable data sources, such as a reliable computer program for tray-to-tray fractionation calculations. Values greater than the normal range may occur, causing lower tray efficiencies. 

Most theoretical models incorporate the effects of vapor and liquid nonuniformity into the relationship between the Murphree and the point efficiency. Developing models for vapor-liquid contact on trays has been a fertile research area in the last couple of decades, with literally hundreds, maybe thousands of papers published on the subject. A thorough review is given by Lockett (12). 

In the Coastal Refinery in Aruba, we used sieve trays with one-half-inch holes, which seemed to work fine. Avoid packed towers. They are subject to vapor-liquid channeling and poor fractionation efficiency due to sloppy installation, fouling, or poor liquid feed distribution. When calculating the required hole area for the trays, don t forget that the vapor loads and hence the required tray hole area will substantially diminish as the vapor flows up the column from the reboiler to the feed tray. This will normally require a reduction in the tray deck hole area in proportion to the reduced vapor flow rate. 

---