TABLE OF CONTENTS Tray efficiency is important for meeting product specifications. Even if all products are on spec, we should still be concerned about maximizing tray fractionation efficiency so as to minimize reflux rates. The more efficient the trays, the less reflux we require to produce an acceptable degree of fractionation. Since the reflux originates in the reboiler, reducing reflux also reduces reboiler energy requirements. As energy is our biggest operating cost, tray efficiency is a major component in minimizing operating costs.
The fractionation tray efficiency is largely a function of the vapor-liquid mixing efficiency. The more intimate the contact between the rising vapor and the descending liquid, the better the tray efficiency. The better the tray efficiency, the less fuel we need to run the process.
As I discussed in the previous chapters, tray contacting efficiency is mainly a function of two factors:
Tray deck levelness
Weir levelness
For smaller diameter towers a visual check of tray deck levelness is sufficient. For two-pass trays, a small diameter tower is less than 8 ft. For single-pass trays, a diameter of less than 6 ft is small.
For towers of 10 ft or more in diameter, check for out-of-levelness of a tray check using a carpenter s laser level, available in hardware stores for about $40. Purchase a level that has short tripod legs. Use the bubble to level up the legs. Set the level on one end of the tower, and check the height of the red beam at...
