Wet scrubber

Types of wet scrubbers

A wet scrubber is an air pollution control device used to remove harmful gases and particulate matter from industrial exhaust streams. It does this by using a liquid absorbent to wash the pollutants from the gas stream. There are numerous types of wet scrubbers, some of which are outlined below:

• Deep column scrubber

  The wet deep column scrubber functions like a packed or plate column. The deep column scrubber design is ideally suited for working with large gas volumes that have low pollutant concentrations.

• Venturi scrubber

  The Venturi scrubber is one of the most popular types in use today. Through the use of high speed and pressure drop within a Venturi throat, liquid is atomized into fine droplets. The gas stream is then redirected, allowing proper separation before discharge, making this device very efficient for removing particulate matter from gases.

• Wet electrostatic precipitator

  A wet electrostatic precipitator is a particle removal device that uses electrostatic attraction to collect particles. It works similarly to a dry electrostatic precipitator, but instead of dry demisters, it has cylindrical stainless steel rods that contain water films. These water films cool the particles and cause them to lose their charges, which are then neutralized by the grounded collection plates. The particles are washed off the plates by the water film, which carries them to a sludge pond. Wet electrostatic precipitators are efficient at removing fine particles in the 0.1 to 5 micron range, including lead, zinc, and copper.

• Multi-clones

  Multi-clones are a type of cyclone separator. They are efficient at separating particulate matter from gases by using a two-stage separation process. In the first stage, a vortex is induced in the gas stream which causes heavier particles to migrate to the rim of the container. In the second stage, water is introduced which helps separate lighter particles from the gas stream.

• Orifice scrubber

  The orifice scrubber is a device that removes particulates and solubilizes gaseous pollutants by spraying liquid through a series of orifices. It works in a similar way to Venturi scrubbers but handles lower gas quantities and higher pollutant concentrations. This type of scrubber is usually placed after cyclone dust collectors to capture remaining dust.

Specifications & maintenance of wet scrubbers

The efficiency and performance of wet scrubbers depend upon their specifications. Therefore, it becomes crucial to understand the specifications of wet scrubbers so that industries can select the right kind of scrubber as per their requirements.

Some of the key wet scrubber specifications with their maintenance requirements are given in the table below:

• Flow Rate

  Maintenance Requirement: Regular checks of the components such as pumps, fans, and valves to ensure there is no flow. If there is a deviation in the flow rate, the components are functioning properly. If there is a deviation in the normal flow rate, it can lead to over or under the scrubber's functioning. Analyse the reasons for any deviation in the normal flow rate and take corrective action. Monitor the flow controller and calibrate as required. Keep a log of the flow rate reading, and take necessary action if any pattern indicates a potential issue.

• Particle Size Removal

  Maintenance Requirement: Regular monitoring of the particle sizes removed by the scrubber. If there is a trend indicating that the scrubber is not removing a specific particle size, investigate the reason. It could be due to a malfunctioning pump, incorrect chemical concentration, or a monitoring system failure. Analyse the filtration of the particles, and adjust scrubber settings to ensure the correct removal of particle sizes. Maintain documentation of the monitored particle size removal data and take necessary action if there is a deviation from the standard.

• Droplet Size

  Maintenance Requirement: Monitor the droplet size generated by the scrubber. If there is a trend indicating a different droplet size than the normal one, investigate the reason. It could be due to a change in chemical properties, pump malfunction, or changes in airflow. Adjust the scrubber settings to ensure the proper generation of droplet size. Maintain the droplet size monitoring data, and if necessary, review the chemical properties and change them per the requirement. Document any changes and maintain records.

• Spray Nozzle

  Maintenance Requirement: Regular inspection of the spray nozzle conditions. Make sure there is no clogging or leakage in the nozzle. Clean the spray nozzle on a regular basis and ensure the effective spraying of liquid in the scrubber. Monitor the spray coverage area, and if there are any complaints regarding the coverage, investigate the issues. Look for the damages or wear and replace them if required.

• Pressure Drop

  Maintenance Requirement: Regular monitoring of pressure drops across the scrubber system. Investigate the scrubbing if there is a trend of high or low pressure drop. Analyse the reasons such as filter blockage, fan malfunction, duct leak, etc., and take corrective action. Document and maintain the pressure drop record. Analyse the trend to ensure the scrubber is operating in an efficient manner.

Industry scenarios wet scrubber

• Chemical manufacturing:

  Organic wet scrubbers are widely used in chemical manufacturing facilities to control volatile organic compounds (VOCs), solvent fumes, and other gaseous pollutants generated during production processes. By capturing these harmful substances, organic wet scrubbers protect both workers and the environment.

• Power plants:

  Power plants, particularly coal-fired ones, face the challenge of removing sulfur dioxide (SO2) from their flue gases to minimize acid rain and air pollution. Alkaline wet scrubbers have proven effective in this regard. By employing alkaline solutions, such as sodium hydroxide or limestone slurry, these scrubbers neutralize sulfur dioxide, preventing its release into the atmosphere and contributing to cleaner energy production.

• Steel manufacturing:

  Cyclone wet scrubbers find significant application in steel manufacturing industries. During various processes, substantial amounts of particulate matter and dust are generated, which can pose health risks and environmental concerns. By utilizing cyclone wet scrubbers, steel manufacturers can effectively remove dust and particulate matter from the air streams, thereby improving air quality and safeguarding the well-being of workers and nearby communities.

• Semiconductor manufacturing:

  The semiconductor manufacturing industry is highly sensitive to air quality, as even the slightest contaminants can compromise product integrity. Chemical wet scrubbers play a vital role in this industry by removing toxic gases and chemical vapors. By employing these scrubbers, semiconductor manufacturers can ensure clean and uncontaminated air within their facilities, minimizing the risk of defects in their delicate production processes.

How to choose a wet scrubber

Several factors need to be reviewed to ensure that the appropriate wet scrubber is selected to provide the desired functions and benefits.

• Type of pollutant

  It should be ensured that the chemical and physical characteristics of the pollutant are compatible with the wet scrubber being used. Some hazards may need to be considered, such as whether the gas contains corrosive substances or particulate matter that may clog the equipment.

• Scrubbing liquid

  The choice of scrubbing liquid can affect the effectiveness and economic benefits of gas treatment. Water is usually the most common scrubbing liquid, but other liquids, such as organic solvents or chemical solutions, may be more effective for certain types of pollutants.

• Treatment efficiency

  Different types of wet scrubbers have different handling efficiencies for different types of pollutants. It should be ensured that the selected scrubber is able to meet the treatment requirements for the specific type of pollutant.

• Flow rate

  It should be ensured that the handling capacity of the selected scrubber can meet or exceed the required value corresponding to the flow rate of the inlet gas.

• Operating conditions

  The operating conditions, such as temperature and pressure, are likely to have a significant impact on the choice of the wet scrubber. Some types of wet scrubbers are only suitable for certain temperature and pressure ranges.

• Footprint

  The footprint of the wet scrubber should be ensured to comply with the spatial layout of the relevant facilities.

• Cost

  Both the initial investment cost and the operating and maintenance costs during the life cycle should be considered.

Wet scrubber FAQ

Q1: What is a wet scrubber used for?

A1: Wet scrubbers are designed to reduce harmful pollutants in the air. They are often used in industrial settings to control gas emissions and prevent air pollution.

Q2: What is the difference between a wet and dry scrubber?

A2: Wet scrubbers use liquid, typically water, to absorb or react with pollutants. Dry scrubbers, on the other hand, use a powdery reagent or ꞌabsorberꞌ to capture gaseous pollutants. Both types of scrubbers are designed to control air pollution but operate on different principles.

Q3: Are wet scrubbers effective?

A3: Yes, wet scrubbers are often more effective at removing finer particles and gases than dry scrubbers because the liquid can capture particles that airborne ones might not. However, their effectiveness can depend on the design of the scrubber, the type of pollutant, and the quality of the water used.