Revamping of Random Packing

Random packing has been used for fractionation, absorption and stripping operations in gas, refinery and chemical plants for many years and the benefits are well established. Random packing is generally the preferred mass transfer device in towers operating at elevated pressure and/or high liquid rates. The performance of these towers can be improved by using modern random packing with increased capacity or efficiency.

Fig. 1 Random packing column

Working Principle of Random Packing

Random packing tower is with a packing support plate at the bottom and a packing platen at the top, and the packing is placed on the support plate in a random or complete manner. In most chemical separation processes, vapor is driven upward in the column by heat and pressure while liquid falls downward under the force of gravity. On the surface of the packing, the gas-liquid two phases are in close contact for mass transfer. The packed tower belongs to a continuous contact gas-liquid mass transfer device, and the two-phase composition continuously changes along the tower height. Under normal operating conditions, the gas phase is a continuous phase, and the liquid phase is a dispersed phase.

There are 3 primary components in the selection of a random packing, and they are capacity/pressure drop, efficiency and costs. The larger the random packing, the higher the capacity, but at a cost of lower efficiency.

Design Principle of Random Packing Column

Mass transfer between phases is promoted by their intimate contact through all the extent of the packed bed. The main factors involving the design of packed columns are mechanics and equipment efficiency. Among the mechanical factors one could mention liquid distributors, supports, pressure drop and capacity of the column. The factors related to column efficiency are liquid distribution and redistribution, in order to obtain the maximum area possible for liquid and vapor contact. The performance of random packing is driven by the effective area and the mass transfer coefficients.

There are some rules which should be followed when designing a random packing column:

• The column should operate in the loading region (40 to 80% flooding), which will assure the best surface area for the maximum mass transfer efficiency.
• The packing size (random) should not be greater than 1/8 the column diameter.
• The packing bed is limited to 6D (Raschig rings or sells) or 12D for Pall rings. It is not recommended bed sections greater than 10m.
• Liquid initial distribution and its redistribution at the top of each section are very important to correct liquid migration to the column walls.

Commonly, the design of a random packing column follows these steps: choose the proper packing, estimate the column diameter, determine the mass transfer coefficients, estimate the pressure drop, and then design the internals.

Why Choose Us

As with decades of experience in chemical products and technical service, Alfa Chemistry has become a trustable supplier in petroleum and chemical industry, food and beverage industry, pharmaceutical and bio-technology industry, etc. We can offer revamping of random packing services including equipment improvement and process optimization. Please feel free to contact us for a better solution to your several of columns.