Process Instability

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    Why Your Ammonia Scrubber Is Not Working

    On paper, ammonia removal with a wet scrubber looks simple.
    Add acid. Control pH. Remove NH₃.

    In reality, many industrial scrubbers fail to remove ammonia consistently — even when all “parameters” seem correct.

    If your ammonia scrubber is not working, the problem is rarely a single variable.
    It is almost always a process issue, not a component issue.

    The Real Problem

    Ammonia absorption is not just a chemical reaction.
    It is a mass transfer process limited by:

    You don’t have “a pH”.

    Most scrubbers fail because they are designed as equipment, not as process systems.

    Why It Happens

    1. pH control is not enough

    Lowering pH shifts ammonia (NH₃) into ammonium (NH₄⁺), which is soluble.

    But:

    • local pH ≠ bulk pH
    • poor mixing creates zones where ammonia is not absorbed

    You don’t have “a single pH value”.
    You have a distribution of pH conditions inside the tower.

    2. L/G Ratio Is Too Low

    Ammonia absorption requires sufficient liquid flow.

    If the liquid-to-gas ratio (L/G) is too low:

    • contact area is reduced
    • absorption capacity is limited

    Typical failure:

    Scrubber sized on airflow only → insufficient liquid phase

    3. Poor Liquid Distribution

    Even with correct flow rate:

    • uneven spray
    • asymmetric piping
    • clogged nozzles

    create preferential paths.

    poor liquid distribution in wet scrubber nozzle spray pattern
    • Gas bypasses the liquid
    • Efficiency collapses

    This is one of the most underestimated causes of failure.

    4. Buffering Systems in the Liquid

    This is where most engineers get it wrong.

    In real systems:

    • carbonates
    • bicarbonates
    • ammonium salts

    create buffer systems

    Result:

    • pH does not drop as expected
    • acid consumption increases
    • ammonia removal becomes unstable

    The problem is not dosing.

    The problem is chemistry equilibrium.

    5. Insufficient Contact Time

    Short towers, high velocity, or undersized packing:

    • reduce residence time
    • limit absorption

    Ammonia removal is not instantaneous

    It requires time + interface

    6. Gas Conditions Are Ignored

    Temperature and saturation matter.

    • hot air reduces solubility
    • low humidity limits absorption
    • low humidity limits absorption

    A scrubber designed for “nominal conditions” will fail in real operation.

    What Most Engineers Get Wrong

    • Designing based only on airflow
    • Assuming pH = performance
    • Ignoring liquid distribution
    • Treating ammonia as a “simple pollutant”
    • Oversimplifying chemistry

    What Actually Works

    An ammonia scrubber works when:

    • L/G ratio is correctly sized
    • liquid distribution is uniform
    • pH is controlled considering buffering systems
    • contact time is sufficient
    • process variability is included in design

    This is not about adding more acid.
    It is about designing the system as a whole.

    When the System Cannot Work

    There are cases where:

    • tower is undersized
    • gas load is too high
    • variability exceeds design limits

    In these situations:

    • no adjustment will fix the problem
    • only a redesign or revamping will

    Can an Existing Scrubber Be Fixed?

    Sometimes, yes.

    Typical interventions:

    • increase liquid recirculation
    • redesign distribution system
    • introduce a second stage
    • modify chemical control strategy

    But:

    • not all systems are recoverable
    • and not all problems are “operational”

    Final Insight

    Ammonia removal is not difficult.

    But stable ammonia removal in real industrial conditions is.

    Is your ammonia scrubber underperforming?

    Contact us for a technical evaluation
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    Scrubber foam problem: root causes

    Scrubber foam problem: context

    In many industrial wet scrubbing systems, foam formation is often dismissed as a secondary or cosmetic issue. In reality, persistent foam is almost always the visible symptom of a deeper process inconsistency.
    This insight originates from real operational evidence: a recirculation tank completely filled with stable foam, generated during normal plant operation.

    What foam really indicates

    Foam inside a scrubber is not random. It is the result of a combination of physical and chemical conditions:

    • Presence of surfactants or organic compounds
    • High gas velocities and turbulence
    • Unstable liquid chemistry (pH, oxidation state, salinity)
    • Accumulation of reaction by-products

    When these factors align, foam transitions from transient to persistent.
    At that point, it stops being a nuisance and becomes a process variable.

    Why Foam Is a Problem

    The consequences are rarely limited to aesthetics:

    • Loss of effective liquid–gas contact
    • Carryover of droplets and contaminants
    • Unstable pressure drop
    • Reduced mass transfer efficiency
    • Risk of downstream fouling
    • Cavitation of recirculation pump

    In extreme cases, the scrubber continues to operate, but no longer performs its intended function.

    The Typical Reaction (and Why It Fails)

    The most common response is the addition of antifoam agents.
    This approach is appealing because it is immediate and simple.
    However, it rarely addresses the root cause.
    Antifoam acts on the symptom, not on the mechanism that generates foam. As a result:

    • Consumption increases over time
    • Performance becomes inconsistent
    • Operating costs rise without solving the instability

    Engineering Perspective: Treat the Cause, Not the Symptom

    Foam must be interpreted within the broader process context.
    The correct approach requires asking fundamental questions:

    • What compounds are actually present in the gas phase?
    • Is the chemical regime (acid/base/oxidative) coherent with those compounds?
    • Is the liquid recirculation accumulating by-products?
    • Is the hydraulic design promoting local imbalances?

    Only by reconnecting the scrubber to the upstream process can the issue be solved.

    Design Implications

    Persistent foam often reveals deeper design limitations:

    • Systems designed for steady-state conditions operating under variable loads
    • Lack of pollutant speciation during the design phase
    • Oversimplified assumptions about liquid chemistry
    • Inadequate purge and make-up strategies

    In other words, the problem is not the foam itself.
    The problem is that the system was never designed to handle the real process conditions.

    Key Takeway

    A scrubber does not fail when foam appears.

    It fails when foam is treated as an isolated issue.

    Understanding and controlling the origin of the emission is the only way to restore performance.

    Final note

    Visible phenomena in industrial systems are rarely superficial.
    They are signals.
    Ignoring them — or masking them with quick fixes — only delays the real engineering work.