Packed Tower – Working Principle and Advantages in Industrial Filtering

Packed tower, filled with large quantities of tower packings and tower internals, is an widely used and important gas-liquid mass transfer equipment. It was used in the industries from the mid-nineteenth century. With the development of packed tower, it is divided into plate tower and packed tower. Now, we will introduce the packed tower, which has simple structure, high filtering performance.

The packed tower is composed of tower body, pedestal, padding supporting part, liquid distributor, liquid redistributor, tower packings, packing hold-down grid, etc.

Working principle of packed tower

Liquid enters from tower top and is evenly distributed onto tower packings through liquid distributors and then flow down along the packing surface. The gas enters from tower bottom and distributed evenly through gas distributor device. The gas raises up against the liquid path through void of tower packing. The gas and liquid will contact on the packing surface for mass transfer.

The packed tower is a continuous contact type gas-liquid mass transfer equipment, which makes the two-phase composition change continuously along the tower height. In the normal condition, the gas phase presents continuous phase while the liquid phase presents dispersed phase.

When the liquid flow down along the packings, it has a tend to flow to the tower wall, which make the tower wall liquid quantity increase rapidly. This phenomenon is called wall flow, which may cause the nonuniform distribution of gas and liquid. To avoid it, liquid redistributors are placed in the middle of tower body when the packing layer is too high.

A packed tower and its internal structure drawing on the blue background.

PT-01: Packed tower is composed of tower body, tower packings and interns.

A drawing shows liquid and gas distribution and mass transfer process.

PT-02: Plate tower working principle.

A drawing shows the mass transfer principle of gas and liquid.

PT-03: Packed tower working principle.

Components of packed tower

  • Tower body.
  • Tower packings.
    • Structured packings.
    • Random packings.
    • Demister pads.
  • Tower internals.
    • Liquid distributor.
    • Packing supporting grid.
    • Packing hold-down grid.
    • Liquid redistributor.
    • Gas distributor.
A piece of perforated plate structured packing on the gray background.

PT-04: Perforated plate structured packing.

Several random packings in different materials, types and sizes on the gray background.

PT-05: Plastic and metallic random packings.

A piece of through type liquid distributor on the gray background.

PT-06: Through type liquid distributor.

A piece of tower packing support grid on the gray background.

PT-07: Tower packing support grid.

Features of packed tower

  • Large production capacity. The working principle of plate tower and packed tower is different. The rising gas in the plate tower passing though the liquid layer to achieve the mass transfer. The open area on the tower plate is 7% to 10%. In the packed tower, the rising gas and flowing down liquid contacts and achieve the mass transfer. The open area of tower packing is above 50% and the voidage is above 90%. So the production capacity of packed tower is far more superior than the plate tower in the unit sectional area.
  • High separating efficiency. As we all know, most of the filtering operation in the tower is under atmospheric pressure and vacuum pressure. In these condition, the filtering efficiency of packed tower is much higher than the plate tower.
  • Low pressure drop. The packed tower has higher voidage, so the pressure drop is lower than the plate tower. In the normal condition, the pressure drop of plate tower is about 0.4–1.1 kPa per unit theoretical stage while the packed tower is about 0.01–0.27 kPa. The low pressure drop can not only save the operating cost, but also save energy. It is very suitable for the heat sensitive material separating.
  • Low liquid hold-up quantity. Liquid hold-up quantity refers to the liquid quantity on the packing surface, internals and plates. The liquid hold-up quantity of packed tower is less than 6% while the plate tower is higher to 8-12%. Though the higher liquid hold-up quantity can ensure the stable structure of materials and tower, but it needs long operating hours, long operating period and expensive operating costs, which is bad for the distillation process.
  • High operation flexibility. Operation flexibility refers to the adaptation of tower to the load. In the packed tower, the operation flexibility is decided for the internal designs, especially the liquid distributor. Each components including tower packings and tower inters has high operation flexibility. So the operation flexibility can be adjusted according to different applications. The operation flexibility of plate tower is limited by the liquid flood, liquid entrainment and downcomer capacity.

Applications of packed tower

Packed tower is widely used in the industrial filtering: such as pharmacy, coal mine, petroleum, chemical engineering.

  • Separating.
  • Filtering.
  • Vacuum distillation.
  • Purifying.
A packed tower and we can see the column internals, demister pads and random/structured packing clearly.