The internal principle of the design of the plate rectification tower: the liquid is discharged from the top plate to the bottom of the tower by gravity, and a flowing liquid layer is formed on the plate surface of each layer of the plate; the gas is driven by the pressure difference and passes upward from the bottom The openings evenly distributed on the tower plate spread each layer of the tower plate in turn and are discharged from the tower top.
The contact state of the gas-liquid two-phase on the plate is an important factor that determines the hydrodynamics of the two-phase flow on the plate and the law of mass and heat transfer. When the liquid flow rate is constant, as the gas velocity increases, the following contact states can occur:
1. Air velocity in bubbling contact state
When it is lower, the gas flows through the liquid layer in the form of bubbling. Due to the small number of bubbles, the gas-liquid mixture formed is basically liquid, and the surface area of the gas-liquid contact is not large, and the mass transferlow efficiency.
2. Honeycomb contact state
As the gas velocity increases, the number of bubbles continues to increase. When the bubble formation speed is greater than the bubble rise speed, the bubbles accumulate in the liquid layer. The bubbles collide with each other to form various polyhedral atmospheres bubble. Since the bubbles are not easy to burst and the surface cannot be renewed, this state is not conducive to heat and mass transfer.
3. Foam contact state
When the gas velocity continues to increase, the number of bubbles increases sharply, and the bubbles continue to collide and rupture. At this time, most of the liquid on the plate exists between the bubbles in the form of a liquid film, forming some dynamic bubbles with small diameters and very violent disturbances. The contact state has a large surface area and is constantly updated, which is a good contact state.
4. Spray contact state
When the gas velocity continues to increase, the liquid on the plate is sprayed upward into droplets of varying sizes. The droplets with a larger diameter fall back to the plate by gravity, and the droplets with a smaller diameter are taken away by the gas to form liquid droplets. Entrainment. The droplets return to the tray and are dispersed again. Such droplets are repeatedly formed and aggregated, increasing the mass transfer area and constantly renewing the surface, which is a better contact state.
The design editor of the plate rectification tower reminds everyone that because the gas velocity in the spray contact state is higher than the foam contact state, the spray contact state has a larger production capacity, but the spray state has more liquid foam entrainment, and if it is not well controlled, it will be destroyed During the mass transfer process, most towers are controlled to work in the foam contact state.