(78g) Improving Efficiency of Multiple Downcomer Tray Performance by Various Tray Structure Modifications

Promotions of multiple downcomer trays were studied and discussed. Directing baffles were added on tray deck to reduce the liquid back mixing, resulting in uniform liquid distribution. A bed of structured packing was hung under the tray deck to capture and reduce the entrainment. Fixed valves with downward inclined margins were employed as bubble units to reduce the entrainment and weeping and to increase the chance of gas-liquid contacting. The experimental results showed that when the F-factor increased to 2.0, the entrainment fraction of the tray with the packing was 0.003 kg water/kg air, obviously lower than that of the tray without the packing, 0.014 kg water/kg air. This indicated that the combined packing technology could reduce the entrainment significantly. The experimental results also showed that when fixed valves with downward inclined margins were employed as bubble units, the F0 factor of entrainment flooding point was larger than sieve tray and V1 valve tray. Anti-dumping units were applied to prevent the liquid from dumping through orifices. The experiment with ethanol/water system showed that the DJ-3 tray efficiency was 10%-15% higher than that of the conventional multiple downcomer tray. The experiment with cyclohexane/N-heptane system showed that the DJ-5 tray efficiency was 10%~ 20% higher than that of conventional multiple tray in all operating load and as large as V1 valve tray in middle and large operating load.