Engineering Evaluation Case: A Venturi Pre-Scrubber Sends So Much Liquid Carryover into the Packed Tower That the Polishing Bed Floods
A Venturi scrubber can be highly effective at contacting gas with liquid and capturing particulate.
It can also generate a large quantity of droplets.
If the gas flows directly from the Venturi into a packed polishing tower without adequate phase separation, the packed bed may receive much more liquid than its own distributor supplies.
Project Situation
Consider a treatment train:
- Venturi scrubber;
- packed absorber;
- final demister.
The packed tower is designed using its recirculation flow.
During operation, pressure drop is much higher than predicted.
The bed appears heavily loaded even when its circulation pump is reduced.
Upstream Droplets Are Hidden Liquid Load
Liquid leaving the Venturi with the gas enters the packed tower from below.
The packed bed now handles:
- downward distributor liquid;
- upward-carried droplets.
This is not the hydraulic condition used in a normal countercurrent calculation.
The Packing Can Act as a Droplet Separator
Large droplets impact the first layers of packing.
Captured liquid drains downward.
The lower bed therefore experiences unusually high local holdup.
Slurry Makes the Problem Worse
Venturi stages are often used for particulate capture.
Their droplets may contain:
- dust;
- slurry;
- solids.
The lower packed bed then becomes both:
- separator;
- solids collector.
An Interstage Separator May Be Necessary
The treatment train may require bulk droplet removal between the Venturi and packed absorber.
The exact arrangement depends on:
- droplet size;
- solids;
- pressure-drop allowance.
More Open Packing Is Only Partial Mitigation
Open packing may tolerate the extra liquid better.
It does not eliminate the upstream carryover.
The correct system design should control the droplet load before the polishing bed.
Engineering Takeaway
A packed tower cannot be sized correctly if the upstream equipment sends an unquantified liquid stream into its gas inlet.