How to Select a Liquid Distributor for Fouling or Slurry Service
A distributor designed for clean water may fail rapidly when the process liquid contains suspended solids, scale, crystals, polymers or biological material.
For fouling service, the best distributor is not necessarily the one with the highest nominal drip-point density. Long-term passage size, drainage and cleaning access may be more important.
What Causes Distributor Fouling?
Common sources include:
- Suspended solids
- Corrosion products
- Crystallizing salts
- Polymer deposits
- Biological growth
- Catalyst particles
- Dust captured by scrubber liquid
- Fibers
- Oil or sticky organic material
Deposits may form inside holes, along trough bottoms, around nozzles or in stagnant sections.
Why Partial Plugging Is Especially Harmful
Uniform plugging would reduce total flow, but real fouling is normally uneven.
When only some outlets plug:
- Remaining outlets carry more liquid
- Dry zones develop below blocked areas
- Local flooding can occur elsewhere
- Distributor head rises
- Overflow becomes possible
- Packing efficiency declines
The pump flow may appear normal while internal distribution deteriorates.
Orifice-Pan Distributor
An orifice pan can provide many accurately located outlets for clean service.
Its disadvantages in dirty liquid may include:
- Small holes
- Solids settling on the pan
- Difficult underside inspection
- Non-uniform plugging
- Limited cleaning access
It should not be selected only because it provides high point density.
Trough or Weir Distributor
Trough and weir designs may offer:
- Larger flow passages
- Accessible openings
- Better tolerance of solids
- Easier visual inspection
- Improved cleaning access
However, they still require sufficient levelness, vapor area and hydraulic head.
Pipe Distributor
Pipe distributors can protect the liquid from open-tray contamination, but small holes or spray nozzles remain vulnerable to plugging.
The design should include practical access for:
- Flushing
- Branch cleaning
- Nozzle removal
- Inspection
- Complete drainage
Features Worth Evaluating
For fouling service, consider:
- Larger minimum passage size
- Side outlets rather than sediment-prone bottom holes
- Sloped or drainable surfaces
- Flush connections
- Removable covers
- Cleanout ports
- Accessible troughs
- Reduced dead zones
- Strainers where practical
- Segment removal through the manway
Do Not Ignore Shutdown Conditions
Some liquids crystallize or polymerize when:
- Temperature falls
- Flow stops
- Concentration increases
- Solvent evaporates
- The distributor cannot drain completely
A distributor that operates acceptably during continuous service may plug during shutdown and fail at restart.
Supplier Data Required
Provide:
- Solid-particle size range
- Solids concentration
- Deposit type
- Sticky or abrasive behavior
- Crystallization temperature
- Operating and shutdown temperature
- Cleaning liquid
- Flushing frequency
- Allowable passage size
- Maintenance interval
- Minimum, normal and maximum liquid flow
“Dirty liquid” alone is not enough for design.