Liquid distributors are an important component of column internals. They provide adequate distribution of the liquid onto the packed bed and structured packing. To achieve an intensive mass transfer between the phases, the liquid should be distributed equally across the packed column area. It serves to overcome maldistribution and, poor initial distribution can only be compensated to a limited degree by a larger bed height
An ideal liquid distributor will perform with the following characteristics:
- Uniform liquid distribution
- Proper operation through its turndown range
- Low vapor phase pressure drop
- Resistance to plugging or fouling
- Minimum liquid resistance time
- Mixing capability for redistribution to the next bed
The liquid distributors in packed columns can be further classified as pressure fed distributors or gravity fed distributors.
Pressure Distributors: These liquid distributor types provide more passage for vapor flow and are comparatively less expensive than gravity distributors. Also, they require smaller lead-up piping than the latter. However, its operating cost is high and more likely to experience corrosion and plugging. Therefore, the quality of distribution is less compared to the gravity type. The spray nozzle and ladder type distributors are examples of pressure type distributors
Gravity Distributors: They can handle large liquid flow rates. The weir type (trough-type) distributors prove to be the least troublesome distributors with a high turndown ratio. However, it contains a limited number of drip points and is sensitive to internal liquid hydraulics.
The following table shows the range of liquid load that each type of distributor can handle.
| Distributor-Type | Liquid Load (m3/m2h) |
|---|---|
| Spray type | 0.5 to 120 |
| Ladder type | 4 to 25 |
| Trough type | 5 to 100 |
It is obviously difficult to distribute small than large amounts of liquid. The main design criteria for any liquid distributor is to determine the number of drip points in relation to the column area (irrigation density).
A crucial parameter in the design of a distributor is the liquid load uL required for the separation process. Together with the head ho, it allows the flow velocity at an outlet uo and thus the number of outlets required, to be determined in distributors with liquid discharge or overflow. The usual equation for flow through orifices is
Since the cross-sectional area of the outlet is known for the basic shape distributors or can be determined with the help of equations and correlation reported in other literature, the volumetric flow rate l can be obtained from
Once, l is known, the number Z of distributor outlets per square meter of column cross-section that is required to cope with a liquid load uL in m3/m2h can be obtained from
Without a proper liquid distributor installed in the tower, an efficient mass transfer fails to occur on the packing. MACH Engineering offers different types of liquid distributors to suit the need of chemical process in place. With our expertise in AutoCAD drawing, we can design and fabricate liquid distributors according to customers’ requirements. For more information regarding liquid distributors or column internals, contact us.