Where Do Industrial Fumes Come From?

Industrial fumes can come from chemical storage, manufacturing and treatment processes. Their composition varies depending on the chemicals being handled, process temperature, moisture and operating conditions.

Common sources include:

• Chemical storage and process tanks.
• Reactors and mixing vessels.
• Pickling and metal-treatment lines.
• Chemical transfer and dosing points.
• Wastewater treatment processes.
• Fertilizer and chemical manufacturing operations.
• Combustion and thermal processes.

The exhaust stream may contain gases, vapours, acid mist, moisture, particles or a combination of these.

Some gases can also form corrosive condensate as they cool inside the exhaust system.

This is why system design cannot be based on airflow alone. Engineers first need to understand what is being released, how much is being released and under what process conditions.

Step 1: Capture Hoods Collect Fumes at the Source

The first job of an industrial fume control system is to capture contaminants before they spread through the surrounding work area.

A capture hood or enclosure is positioned close to the emission source. The hood draws contaminated air into the exhaust system before the fumes disperse.

Its effectiveness depends on factors such as:

• The location and size of the emission source.
• The direction in which the contaminant naturally travels.
• The velocity of the escaping fumes.
• Cross-drafts and surrounding air movement.
• Required exhaust airflow.
• Operator access around the process.

Hood design also affects the rest of the system.

If the hood requires higher airflow, the ducting, scrubber, mist eliminator, fan and stack must be able to handle that airflow.

A poorly positioned hood cannot usually be corrected simply by installing a larger scrubber farther downstream.

Once the contaminant enters the hood, the ducting becomes responsible for carrying it toward the treatment equipment.

Step 2: FRP Ducting Carries Corrosive Fumes to the Scrubber

The ductwork between the emission source and scrubber can be exposed to untreated contaminants, moisture and corrosive condensate.

This is why Fiberglass Reinforced Plastic, or FRP, is commonly considered for corrosive industrial exhaust applications.

Busubait manufactures FRP ducting systems in round, rectangular and custom configurations for chemical and industrial applications.

However, selecting FRP is only one part of duct design.

Engineers also need to consider:

• Duct diameter and required airflow.
• Air velocity.
• Straight sections, bends and transitions.
• Branch connections.
• Supports and structural loads.
• Vibration.
• Positive or negative pressure.
• Condensation.
• Chemical compatibility.
• Pressure loss through the complete route.

Every bend, transition and fitting creates resistance.

An undersized duct can increase air velocity and pressure loss. Poorly balanced branches can also result in some capture points receiving less extraction than required.

Condensation Inside FRP Ducting Also Matters

The chemical conditions inside a duct can change when the exhaust gas cools.

Moisture may condense on the internal surface and create a liquid chemical environment that is different from the original gas-phase conditions.

For example, a gas stream that appears relatively manageable in dry conditions may become much more corrosive once moisture and chemical vapours form condensate.

Material selection should therefore consider:

• Gas composition.
• Moisture content.
• Operating temperature.
• Possible temperature changes.
• Condensate chemistry.
• Chemical concentration.

The practical lesson is simple. Airflow design and corrosion resistance need to be considered together.

Step 3: The Wet Scrubber Treats the Contaminated Exhaust

After travelling through the ducting, the contaminated exhaust reaches the pollution-control equipment.

For many soluble industrial gases, treatment may involve a wet packed-bed scrubber.

Inside a packed-bed scrubber, contaminated gas moves through packing that provides a large wetted surface area. Scrubbing liquid flows across this packing, allowing targeted pollutants to transfer from the gas stream into the liquid.

Depending on the contaminant, chemicals may also be added to the scrubbing liquid to support neutralisation or absorption.

The exact scrubber configuration should always depend on the process conditions.

Busubait supplies FRP scrubber systems for industrial applications where corrosion-resistant construction is required.

What Affects Industrial Scrubber Performance?

A scrubber should not be selected based only on vessel diameter or airflow.

Important design inputs include:

• Exhaust airflow.
• Type of contaminant.
• Contaminant concentration.
• Gas temperature.
• Moisture content.
• Required outlet conditions.
• Scrubbing-liquid chemistry.
• Packing arrangement.
• Gas velocity.
• Pressure drop.
• Solids or particulate loading.

High particulate loading can also affect the suitability of a packed-bed configuration because excessive solids may cause fouling or plugging.

This is why one scrubber design cannot automatically be applied to every exhaust stream.

For a deeper explanation of this equipment, see why FRP scrubber systems are used in chemical fume control.

Step 4: The Mist Eliminator Controls Liquid Carryover

Wet scrubbing brings contaminated gas into direct contact with liquid.

Once the treatment process is complete, small liquid droplets may remain suspended in the outgoing gas stream.

These droplets can contain:

• Scrubbing chemicals.
• Absorbed contaminants.
• Dissolved solids.
• Moisture.

Allowing excessive liquid carryover into downstream equipment can contribute to corrosion, deposits and maintenance problems.

This is where the mist eliminator, also known as a demister, becomes important.

A mist eliminator separates entrained liquid droplets from the outgoing gas before it travels farther through the exhaust system.

Common arrangements may use mesh or vane-type separation depending on the droplet size, gas velocity and process conditions.

A Mist Eliminator Is Not the Same as a Scrubber

The two components perform different jobs.

The scrubber is designed to remove or react with targeted contaminants in the exhaust.

The mist eliminator primarily removes liquid droplets carried out of the wet treatment section.

Understanding this difference is important when diagnosing visible moisture, liquid carryover or downstream corrosion.

Step 5: The Exhaust Fan Keeps the Entire System Moving

The fan or blower creates the airflow that moves contaminated air through the exhaust system.

Its job is not simply to move air through one length of duct.

The fan may need to overcome resistance through the entire route:

Each component introduces some pressure resistance.

This means fan selection should consider the total system pressure drop at the required airflow.

For example, if the scrubber creates more resistance than expected, airflow available at the capture hood may decrease.

Similarly, changing the duct routing or adding additional fittings after fan selection can change the system operating point.

Fan material selection also matters.

Depending on its position in the system, the fan may be exposed to:

• Untreated corrosive fumes.
• Moist treated gas.
• Chemical mist.
• Condensate.
• Elevated temperatures.

The fan therefore needs to be considered as part of both the airflow design and the chemical environment.

Step 6: Why Is an FRP Stack Needed After the Scrubber?

Once the exhaust has been treated and liquid carryover has been controlled, it still needs a defined discharge route.

That is the job of the exhaust stack.

A stack carries the treated exhaust away from the equipment and releases it at an engineered discharge point.

The stack may also need to resist moisture, chemical traces and outdoor environmental exposure. FRP can therefore be considered where corrosion resistance is important.

But there is an important distinction.

The stack does not neutralise chemicals or remove contaminants in the way a scrubber does. Its role comes after treatment.

Stack design may need to consider:

• Required discharge height.
• Exhaust volume.
• Outlet velocity.
• Wind and structural loads.
• Temperature.
• Chemical environment.
• Stack supports.
• Access requirements.
• Pressure loss.

Stack height and outlet configuration should be determined for the individual project and applicable environmental requirements rather than copied from another installation.

How the Complete Industrial Fume Control System Works

The easiest way to understand the system is to follow the airflow.

Each stage influences the next.

For example, increasing extraction airflow at the hood also increases the air volume passing through the ducting and scrubber.

That can affect:

• Duct velocity.
• Pressure drop.
• Scrubber gas velocity.
• Mist eliminator loading.
• Fan duty.
• Stack discharge conditions.

Changing the scrubber configuration may alter system resistance. Changing duct routing can affect fan requirements. Changing the process chemistry may affect material selection throughout the system.

This is why fume-control equipment should be considered as one connected system instead of purchasing individual components first and trying to connect them later.

Busubait manufactures a range of FRP air pollution control equipment, including scrubbers, corrosion-resistant ducting, stacks, hoods and related exhaust-system components.

What Should Be Checked Before Designing the System?

Reliable system design starts with accurate process information.

Before selecting equipment, engineers should normally establish the main operating conditions.

Airflow

The expected exhaust volume should be identified for each capture point.

Multiple hoods or branches also need to be considered together so that the complete duct network can be properly balanced.

Contaminant

The system designer needs to understand which gases, vapours, particles or chemical mixtures will enter the exhaust.

The concentration may also vary between normal operation, start-up and upset conditions.

Temperature

Both normal and maximum temperatures matter.

Temperature changes may affect FRP material selection and can also cause condensation inside the ducting.

Moisture and Condensation

The amount of moisture inside the gas stream should be considered together with the possibility of condensation.

Condensate may create a chemical environment that differs from the original exhaust gas.

Particulate Loading

Particles or solids can influence scrubber selection and maintenance requirements.

High solids loading may also contribute to deposits or plugging.

Pressure Drop

Pressure resistance through each part of the system should be considered when determining fan duty.

This includes the hood, ducting, bends, scrubber, mist eliminator, fan connections and stack.

Chemical Compatibility

The materials used throughout the system should be suitable for the actual chemicals, concentrations and temperatures involved.

Maintenance Access

Engineers should also consider how components will be inspected, cleaned and maintained after installation.

Good access is particularly important around scrubbers, mist eliminators, fans and duct sections where deposits or condensate may collect.

Chemical Compatibility and FRP Resin Selection

FRP is not one single material formulation.

Its performance depends on the resin system, corrosion barrier, reinforcement and, in some cases, an additional thermoplastic liner.

This means material selection should follow the actual chemical environment.

Important questions include:

What Chemicals Are Present?

A mixture of chemicals can create different exposure conditions from a single chemical.

What Are the Concentrations?

Chemical compatibility may change significantly with concentration.

What Temperature Will the FRP Experience?

Normal process temperature is important, but start-up conditions and possible temperature excursions should also be considered.

Could Condensation Occur?

Condensate can expose the internal laminate to a different chemical environment from the gas itself.

Are Oxidising Chemicals Present?

Oxidising service may place different demands on the resin or liner system.

What Cleaning or Scrubbing Chemicals Will Be Used?

Materials should also be checked against chemicals used during washing, dosing and maintenance.

For more aggressive applications, Busubait's FRP ducting systems can also incorporate dual-laminate construction using suitable thermoplastic liners for specific service conditions.

The key point is straightforward.

Busubait Project Example: Bee’ah Thermal Capacity Expansion Project

Busubait's Bee’ah project in Jubail provides a practical example of scrubber, ducting and stack equipment being used as part of one exhaust system.

The published project information identifies the service as flue gases and lists:

• Scrubber.
• Ducting.
• Stack.

The project information also specifies a 3 mm vinyl ester liner with a polyester structural laminate.

Published equipment dimensions include:

The importance of the example is not simply the size of the equipment.

It shows how the scrubber, connecting ductwork and stack can form related parts of the same industrial exhaust project.

The published project information does not state a pollutant-removal efficiency or final emissions result, so no performance figure should be assumed from the equipment details alone.

You can view the Bee’ah Thermal Capacity Expansion Project for additional project information.

Why the Whole System Needs to Be Designed Together

Industrial fume control is more than selecting a scrubber.

The capture hood first needs to collect the fumes effectively. The FRP ducting needs to transport them without unacceptable pressure loss or material degradation. The scrubber has to match the contaminant and operating conditions.

After treatment, the mist eliminator needs to control liquid carryover. The fan has to maintain the required airflow through the resistance of the complete system. Finally, the FRP stack provides the engineered discharge route.

When these components are considered together, designers can work from one set of project conditions covering:

• Airflow.
• Pressure drop.
• Chemical compatibility.
• Temperature.
• Moisture.
• Treatment requirements.
• Material selection.
• Final discharge conditions.

This reduces the risk of treating each component as an isolated item.

If you are planning a corrosive industrial exhaust or fume-control project, Busubait can review your process conditions, drawings and specifications to help determine suitable FRP fabrication requirements.

Discuss your FRP air pollution control requirements with Busubait.

Frequently Asked Questions