Engineering Evaluation Case: A Kraft Mill Reduced-Sulfur Scrubber Receives Black-Liquor and Soap Carryover
Kraft pulp and recovery processes can generate reduced-sulfur odor streams.
A wet scrubber may be installed to treat gaseous sulfur compounds.
The exhaust can also contain entrained process liquids such as:
- black-liquor droplets;
- soap-like organics;
- condensate contaminants.
These materials can change packed-bed behavior substantially.
Project Situation
Consider a packed odor scrubber in a kraft or pulp process.
The tower is designed around gas-phase reduced-sulfur treatment.
After an upstream process upset, operators observe:
- dark liquid in the sump;
- stable foam;
- sticky deposits on packing;
- increasing carryover.
Gas chemistry alone does not explain the change.
Black-Liquor Carryover Adds Dissolved and Suspended Material
Process droplets can contain:
- organic material;
- inorganic salts.
Once captured, these components remain in the recirculating liquid.
Soap-Like Organics Can Promote Foam
Surface-active organics can stabilize bubbles inside the packed bed.
The tower may then experience:
- higher holdup;
- increased pressure drop;
- mist carryover.
This can occur without a major change in gas flow.
Sticky Material Can Alter Wetting
Organic deposits can coat packing and change how the aqueous scrubbing solution spreads.
The tower can therefore suffer both:
- foaming;
- loss of effective wetted surface.
Demister Fouling Can Follow
Dark or sticky droplets reaching the top separator can create:
- embedded deposits;
- drainage problems.
The demister becomes a secondary victim of the same upstream carryover.
Source Control Is Important
If black-liquor or soap carryover originates from an upstream separator upset, repeatedly cleaning the packed tower will not provide a durable fix.
Engineering Takeaway
An odor scrubber can become hydraulically unstable because of entrained process liquid even when the target gas concentration remains unchanged.