The efficiency of operation of perforated trays in a cyclic mode depends on the accepted hydrodynamic modes, which determine the limits of stable operation of mass-exchange column apparatus. There are no general methods of calculating the boundaries of the hydrodynamic modes of perforated trays operate in the cyclic mode. On this basis, the authors were tasked to determine the hydrodynamic modes of operation of mass-exchange column apparatus equipped with perforated trays, the action of which occurs in the mode of controlled cycles of fluid retention on the plates and the overflow of fluid through all holes or slits. Sieve and scaly trays with arched-type scales without overflow devices were selected for study.
The aim of the work was to determine the hydrodynamic modes of operation of the sieve and scaly trays without overflow devices in a cyclic mode of retention and overflow of liquid, determination of lower and upper critical velocity of the vapor in the holes of the sieve and scaly trays, the linear velocity of the vapor in the free cross section of the mass-exchange column apparatus and the relative magnitude of the liquid splash to the upper trays. Liquid flow was monitored using a flowmeter RM, air velocity in the free section of the column was monitored using an anemometer MC-13.
It was determined that the lower critical air velocity in the bubbling holes was 5.4 m/s; linear air velocity in free column cross section was 0.25 m/s. The velocity of the air in the holes at which the fluid splashes onto the upper plates begins was 8 m/s; thus linear air velocity in free column cross section was equal to 0.7 m/s.
Hydrodynamic modes of scaly trays and corresponding values of air velocity in the free section of the column were established. In bubbling mode it was 0.5…0.9 m/s, in the transitional mode it was 0.9…1.3 m/s and in the jet mode, it was 1.3…2.0 m/s. It was determined that the lower critical air velocity in the holes of the trays, below which the drain of liquid is occurs, was 6.5…7.0 m/s. The upper critical air velocity in the holes of the trays above which the liquid splash on the upper trays is observed was 16 m/s.
The air velocity in the free cross section of the column was 1.3…1.5 m/s. the relative magnitude of the liquid splash in the mode of steady operation of scaly trays in the bubbling mode does not exceed 0.1 kg/kg of air, in the jet mode, does not exceed 0.2 kg/kg of air.
It is proved that intense overflow of liquid through bubbling holes of the perforated trays occurs at air velocities less than the lower critical. For sieve and scaly trays, this velocity should not exceed 1.5-1 m/s.
A slight spillage of liquid through the holes of the trays occurs in the range of values of air velocity in the holes of sieve trays of 1.5-5.3 m/s, in the holes of scaly trays of 1,5-6,4 m/s.
Analysis of dual-flow plates with a large free section
