How to Select an Industrial Scrubber for Chemical Fumes
Choosing the right industrial scrubber for chemical fumes is determined by the nature of the chemicals involved, concentration of the gas, air velocity, temperature and the efficiency at which emissions need to be controlled. An appropriate scrubber will aid in the control of corrosive gases, acidic fumes, and other water soluble pollutants created by industrial activities.
A chemical processing plant, pharmaceutical industry, laboratory, metal treatment facility, and wastewater treatment plant may all require scrubbers that are designed differently. Selecting equipment based on the size of the plant or air flow could mean inefficiency in emissions control, corrosion, pressure loss, or high costs.
This manual gives some of the important considerations in choosing an industrial scrubber for chemical fumes.
What Is an Industrial Scrubber?
An industrial scrubber is an air pollution control equipment that removes certain pollutants from the stream of exhaust gases before their emission via appropriate vents or stacks.
In wet scrubbers, the contaminated gases come into contact with the liquid that adsorbs or reacts with the targeted pollutants. The liquid can either be water or chemical solution, depending on the application.
Common applications of scrubbers include:
- Chemical factories
- Production of pharmaceuticals and APIs
- Areas where acid is stored or handled
- Electroplating processes and metal treatment processes
- Fertilizer industry and other chemical processes
- Laboratories and fume extraction systems
- Waste-water treatment plants
Scrubber selection is done based on the particular pollutant and process. It is not all scrubbers that will work for all fumes.
1. Identify the Type of Chemical Fumes
The first step is to identify exactly which pollutants the system must remove. Different gases have different solubilities, reactivities and corrosion characteristics.
| Type of fume or gas | Typical source | Selection consideration |
|---|---|---|
| Hydrochloric acid (HCl) fumes | Acid handling, pickling and chemical processing | Evaluate water or alkaline scrubbing, depending on concentration and process conditions |
| Sulphur dioxide (SO₂) | Certain chemical and combustion processes | Assess suitable alkaline reagents and gas-liquid contact requirements |
| Ammonia (NH₃) | Chemical processing and fertiliser operations | Evaluate water absorption or an appropriate acidic scrubbing solution |
| Chlorine (Cl₂) | Chemical manufacturing and handling | Requires a specifically engineered scrubbing system and compatible treatment chemistry |
| Acidic vapours and mists | Chemical tanks, reactors and transfer operations | Determine whether gas absorption, mist removal or both are required |
| Mixed chemical fumes | Multi-stage manufacturing processes | Assess each contaminant and potential interactions before selecting the treatment system |
Important: These are sample cases, not standard treatments for all cases. The correct reagent and design of the system have to be determined using the true chemical content, concentration, temperature, and safety criteria.
2. Calculate the Required Airflow Rate
Airflow is one of the key factors when dimensioning a scrubber for an industrial application. The scrubber should be capable of processing the exhaust flow created during the process and ensuring the necessary gas-liquid contact.
Airflow is usually measured in cubic meters per hour (m3/h) or cubic feet per minute (CFM).
Prior to choosing a scrubber, you need to calculate:
- Total exhaust airflow for the process
- Number of hoods, tanks or extraction points
- Continuous or discontinuous operation of the system
- Maximum exhaust volume at production or transfer of chemicals
- Dimension of the ductwork and pressure losses
- Operating parameters at the fan
Scrubber which is too small will fail to ensure the necessary removal efficiency. Oversized systems may cause an increase of the cost of construction, pumps and operation of the system.
Calculations of the airflow should include the whole extraction system, not just the scrubber.
3. Select the Appropriate Scrubber Type
Different scrubber designs suit different contaminants, gas loads and performance requirements.
Packed-bed wet scrubber
In the packed-bed scrubber, the contaminated gas is made to pass through a packed section, whereas the scrubbing liquid falls on top of this packed section.
The use of packing greatly enhances the surface area available for interaction between the gas and the liquid phase.
This is generally used for cases where suitable acid or base gases exist, whose absorption or chemical reaction leads to their removal.
Spray tower scrubber
The spray tower utilizes the use of spray nozzles to inject the scrubbing fluid into the gas stream. It could be that its straightforward design would make it applicable for some processes requiring gas-liquid contact.
It is dependent on the following factors: size of the droplets, rate of the liquid, velocity of the gas, and the contaminant to be removed.
Venturi scrubber
The Venturi scrubber works through the mechanism of creating liquid droplets at high velocity in order to provide intensive contact. The Venturi scrubber may be effective in some particulate/mist removal operations, although it normally experiences high pressure drops.
Multi-stage scrubber
Multi-stage systems might be necessary in situations where the exhaust gas stream has multiple pollutants, or the single stage can’t achieve the required performance.
The different stages need to be designed according to what pollutant they will deal with.
How do you decide? Well, based on pollutant properties and outlet concentration needed and then analyze the scrubber design with an expert in pollution-control system design. Do not choose a scrubber just because it is called so.
4. Choose the Right Construction Material
The reason why chemical compatibility is important is that the scrubber, pipes, and fan along with other parts can come into contact with corrosive gases, reagent liquids, and condensates.
Some of the most popular choices are FRP, PP, PVC, CPVC, and certain metals or alloys. However, there is no material that can resist all chemicals.
| Material | Important considerations |
|---|---|
| FRP (fibre-reinforced plastic) | Resin selection, temperature limits, chemical resistance and structural design are critical |
| PP (polypropylene) | Often considered for compatible chemical environments; verify temperature, chemical concentration and mechanical requirements |
| PVC | Can suit certain corrosive environments within its specified temperature and chemical limits |
| CPVC | May be considered where its particular temperature and chemical-resistance characteristics are suitable |
| Metal or specialised alloys | Selection depends on corrosion conditions, temperature, mechanical loads and process chemistry |
For instance, a scrubber for hydrochloric acid vapor might need a different material specification than a scrubber for hot oxidizing chemicals.
In assessing FRP equipment, make sure to check the resin formulation, laminate configuration, chemical resistance, and temperature ratings. For thermoplastic equipment, make sure you review the chemical resistance data.
Remember not to assume that all FRP and plastic scrubbers have the same chemical resistance.
5. Determine the Required Removal Efficiency
The scrubber needs to meet the performance of emissions control demanded for the process and relevant environmental conditions.
Key data includes the following:
- Inlet concentration of pollutants
- Desired concentration at the outlet
- Gas flow rate and temperature
- Solubility and reaction rate of pollutants
- Composition and flow rate of the scrubbing liquid
- Contact time and contact area of gas and liquid
- Depth of packing, if any
- Pressure loss and fan capacity
At the first stage, removal efficiency can be determined as follows:
Removal Efficiency (%) = [ (Inlet Concentration – Outlet Concentration) / Inlet Concentration ] × 100
For example, if the inlet concentration is 100 mg/m³ and the outlet concentration is 10 mg/m³, the removal efficiency is 90%.
Such calculation indicates concentration reduction; however, it doesn’t prove compliance with the regulation. The applicable emission limit and test conditions need to be taken into account.
The supplier should offer design basis and performance data for the target pollutants.
6. Evaluate the Blower and Ducting System
The scrubbing will not function properly if the exhaust system fails to create the desired air flow.
The blower must be chosen to accommodate the desired air flow under the total pressure drop in the system, consisting of losses in:
- Extraction hoods and collectors
- Ductwork, elbow fittings
- The scrubber and packing
- Mist eliminators and other accessories
- The discharge stack
The construction and positioning of the blower must also be appropriate for the gas stream. Corrosive or humid exhaust may necessitate an appropriate fan and installation.
The ductwork and hoods need to be installed so that the fumes are captured close to their origin. A good scrubber cannot overcome poor fume capture.
Explore industrial ducting and canopy hoods and discuss the required airflow and pressure conditions when planning the complete system.
7. Consider Scrubbing Liquid, Water Consumption and Wastewater
The wet scrubbers convert the collected pollutants into a liquid flow. This implies that the wastewater handling must be taken into account when designing the pollution control process.
Before completion of the process design, the following issues must be known:
- Scrubbing liquid and chemical reagent needed
- Flow rate and pumping needs for recirculation
- Process-control parameters (pH etc.)
- Make-up water needed
- Blowdown and wastewater generation
- Sludge generation or salt precipitation
- Handling and disposal
Some processes need continuous or periodic addition of a reagent. Others will need monitoring to ensure that the absorption or neutralisation is effective.
The wastewater might contain toxic chemicals or dissolved salts or reaction products. This has to be known and handled accordingly.
8. Plan for Maintenance and Safe Operation
The industrial scrubber requires regular checks for its effective operation and prevention of unexpected shutdowns.
A good maintenance schedule includes the following:
- Check-up of pumps, nozzles and distribution of liquid
- Blockage, scaling and any damage of the packing material
- Pressure drop and airflow
- pH, reagent concentration or other process indicator
- Check-up of blower, motor and duct connections
- Fouling of the mist eliminator
- Any leaks in the vessel, joints and liner
- Instrument, alarm and control systems check
Safe inspection and cleaning access should be provided. Chemicals exposure, energy storage and risks of opening process equipment should be considered while performing maintenance procedures.
If required, gas monitoring, interlocks and emergency provisions should be included into the system design.
9. What Information Should You Provide When Requesting a Scrubber Quotation?
A detailed enquiry helps the manufacturer assess the application and avoid an unsuitable equipment selection.
| Information required | Example or description |
|---|---|
| Industry and process | Chemical manufacturing, API production or acid handling |
| Pollutants | Chemical names and relevant mixtures |
| Gas flow rate | Design airflow in m³/h or CFM |
| Inlet concentration | Measured or estimated concentration with units |
| Required outlet performance | Applicable outlet concentration or emission requirement |
| Gas temperature | Normal and maximum operating temperature |
| Moisture and particulate load | Humidity, mist, droplets or solids in the exhaust |
| Scrubber material | Proposed material, subject to compatibility review |
| Available utilities | Water, power, compressed air and reagent supply |
| Installation conditions | Indoor or outdoor installation, available space and duct routing |
| Wastewater handling | Existing neutralisation or treatment arrangements |
If some information is unavailable, identify the unknowns clearly. The manufacturer or system designer may need to conduct a process assessment before confirming the design.
Why Consider Plastic Fabricators for Industrial Scrubber Requirements?
Plastic Fabricators supplies industrial products for chemical and related processing applications, including a published PP/FRP scrubber product range.
In looking at your scrubber, consider the chemistry, exhaust volume, operating temperature, expected scrubbing efficiency, and installation parameters including wastewater handling facilities.
If you want a more comprehensive evaluation of your scrubbing system needs, the related ducting, fume hood design, and blower requirements should also be taken into account along with the scrubber itself.
Ask for a technical conversation regarding your specific process requirements as opposed to just buying on a nominal size and cost basis.
Conclusion
Choosing an industrial scrubber to control chemical emissions necessitates proper knowledge of the pollutants, exhaust flow rate, efficiency needed for removal, material of construction, and the waste water management issues. The choice of the best type should also take into consideration the ductwork, blower capacity, pressure drop, maintenance and safety considerations.
Packed-bed scrubbers might be suitable for some gas absorption processes, while spray towers, Venturi scrubbers and other types of scrubbers might also be considered depending on the needs.
Plastic Fabricators offers a PP/FRP scrubber range for industrial applications. Share your process details and operating conditions to begin evaluating a suitable solution for your facility.