Author: Michael Klepik, Chief Executive Officer
One type of versatile equipment that demonstrates the highest efficiency in capturing chemical gaseous, aerosol, and vapor contaminants, as well as airborne particles, is the wet scrubber. It is a device used for cleaning in various chemical and technological processes.
Key Design Components
Despite the fact that dust scrubbers come in several types (which will be discussed shortly), let's consider the features that are inherent to all types of these devices.
Wet scrubbers, as the name suggests, use liquid to capture mechanical and gaseous pollutants. Therefore, an essential component of each unit is the liquid supply circuit to the working chamber and, of course, the setup for removing the spent liquid (known as sludge). Since the cleaning process occurs in a moist environment, setups are equipped with demisters to prevent the escape of droplets.
Externally, a wet scrubber dust control unit can take the form of either a vertical column (tower) or a horizontal module (horizontal configuration is typically chosen to enhance compactness).
Wet scrubbers, as the name suggests, use liquid to capture mechanical and gaseous pollutants. Therefore, an essential component of each unit is the liquid supply circuit to the working chamber and, of course, the setup for removing the spent liquid (known as sludge). Since the cleaning process occurs in a moist environment, setups are equipped with demisters to prevent the escape of droplets.
Externally, a wet scrubber dust control unit can take the form of either a vertical column (tower) or a horizontal module (horizontal configuration is typically chosen to enhance compactness).
Wet Scrubber Diagram
Other components of dust scrubber design include:
The dust scrubber fan is used to ensure circulation of the air flow through the device. This fan plays a crucial role in maintaining the necessary flow velocity for the effective operation in capturing pollutants.
- Inlet nozzle;
- Main body (cylindrical, rectangular, or complex shape) / support frame (frames can be combined into two-stage and multi-stage designs for parallel or sequential cleaning);
- Pre-cooling chamber (optionally included for high-temperature flows);
- Working chamber (hollow, with trays / pans, stationary or moving filler). The interior can also be lined with alkali-, acid-resistant, abrasive-resistant, or refractory coatings, and rarely with stationary or replaceable sleeves;
- Spraying system (typically a nozzle block);
- Separator for capturing residual amounts of absorbent;
- Outlet nozzle.
The dust scrubber fan is used to ensure circulation of the air flow through the device. This fan plays a crucial role in maintaining the necessary flow velocity for the effective operation in capturing pollutants.
Principle of Operation
The principle of operation of a scrubber in dust separation:
Dirty gas enters the housing through a duct, where it swirls due to aerodynamic forces. The filtration process involves using water supplied by a pump station, which passes through pipelines and nozzles to moisten the gas. Droplets capture contaminants, causing them to descend. The resulting sludge is drained into a settling tank or disposed of through cleaning processes.
Dirty gas enters the housing through a duct, where it swirls due to aerodynamic forces. The filtration process involves using water supplied by a pump station, which passes through pipelines and nozzles to moisten the gas. Droplets capture contaminants, causing them to descend. The resulting sludge is drained into a settling tank or disposed of through cleaning processes.
Spray Tower Scrubber
Types of Pollutant Capture
Wet scrubber dust collectors are effective at trapping a variety of contaminant types, including:
- Particulate Matter (PM): Coarse (PM10) and fine particles (PM2.5).
- Chemical contaminants encompass acid vapors, alkalis, solvents, and acid mist.
- Metallic pollutants include heavy metals (lead, arsenic, cadmium, mercury) and metal oxides (iron oxide, aluminum oxide).
- Organic biological particles such as mold spores, pollen, and bacteria.
- Combustion products include soot, ash, carbon dioxide, and other byproducts.
- Mineral particulates comprise silica, asbestos, and fibrous contaminants.
- Textile fibers.
- Paper and wood fibers
BOREAS
Primary Types for Capturing Solid Particles
Wet scrubber dust collector includes the following type:
- Hollow (spray tower) or nozzle types are widely used for cleaning from relatively large particles and for cooling. The apparatus is a column of circular or rectangular cross-section where contact occurs between the gases to be cleaned and liquid droplets sprayed by nozzles.
- Tray Tower (plate bubble, plate column) or foam dust scrubber systems are complex devices. These units can have sieve plates or overflow plates. The filter housing is usually modular. The operating principle involves plates (slotted or perforated) being wetted with liquid. The foam formed on them seizes contaminants, which are removed from the apparatus as sludge.
- Packed bed devices are columns filled with various-shaped baffles. These setups are recommended for capturing well-wettable particulates, especially when collection processes involve gas cooling or absorption.
- The principle of operation is based on the features of the Venturi tube, which in cross-section resembles an hourglass with a narrow middle section. Contaminated emissions are introduced into the upper cone, where the flow accelerates significantly in the middle section. Water breaks into tiny droplets and envelops solid particles. In the lower section (diffuser), the flow velocity decreases, allowing contaminants to agglomerate and settle into a dedicated sump. Clean air is discharged into the atmosphere from the Venturi.
Wet Scrubber vs. Dust Collector
The scrubber removing fine dust significantly improves air quality in industrial environments. By entrapping even the smallest particles, it reduces respiratory risks for workers and minimizes environmental pollution. This technology is essential for industries with stringent air quality regulations.
Characteristics
Technical specifications depend on the configuration. Manufacturers develop custom wet dust scrubbers for each customer. The defining characteristics are based on a detailed survey of production and emission characteristics. Each parameter can be adjusted according to customer requirements, production needs, and practical considerations.
When selecting a filter for production, attention should be paid to several characteristics:
When selecting a filter for production, attention should be paid to several characteristics:
- Performance. Selected based on production requirements, specific processes, or equipment. Filtration complexes may be used to increase performance.
- Efficiency. The cleanliness of the outgoing gas, ranging from 90% to 99.99%.
- Power of each fan.
- Capacity (pool) for water and solution circulation (absorbers).
Advantages and Disadvantages
The main drawback of this contaminant filtration method is the formation of large volumes of sludge. The action of the devices is based on entrapping particles with liquid, which carries them out of the devices as sludge. The process of capturing in wet scrubber dust collection is enhanced by the condensation effect — particles are enlarged due to the condensation of water vapor on them. The downsides of the setup include additional electricity consumption for compressors, as well as the need for fluid supply, along with frequent clogging of the nozzles.
Advantages:
When selecting a filter for production, attention should be paid to several characteristics:
Disadvantages:
When selecting a filter for production, attention should be paid to several characteristics:
Advantages:
When selecting a filter for production, attention should be paid to several characteristics:
- Venturi type units can be used for filtering fine particles and removing foreign gases as contaminants.
- The desired concentration of contaminants in the cleaned gas can be achieved by adjusting the operating parameters of the Venturi, such as the air velocity in the throat of the pipe and the liquid flow rate.
- The equipment is characterized by relatively low cost and higher dust scrubber efficiency in capturing suspended pollutants compared to dry mechanical setups.
- Some types of systems (turbulent) can be used for filtration of particulate matter as small as 0.1 microns.
- It can not only compete successfully with highly efficient collectors like baghouses but also be used in cases where bag filters are not applicable, such as with high-temperature and high-humidity gases, and in environments with fire and explosion hazards.
- It is capable of simultaneously capturing suspended particles, vapor, and airborne components.
Disadvantages:
When selecting a filter for production, attention should be paid to several characteristics:
- The main disadvantage of setups is that the water utilized in them also requires treatment, necessitating the construction of settling tanks, energy expenditure for slurry pumping, pipeline installation, and other related infrastructure.
- When cleaning aggressive components, equipment and pipelines need to be protected with corrosion-resistant materials.
- High water consumption: 1 gallon per 670 cubic feet of cleaned air. If the device's capacity is 50,000 cubic feet of air per minute, more than 4,478 gallons of water per hour are required for its operation.
- Products captured by devices are discharged as sludge, requiring wastewater treatment and thereby increasing the cost of the cleaning process.
- During the cooling of cleaned air to temperatures close to the dew point, and as a result of mechanical entrainment of liquid droplets from the cleaning setup, pollutants can deposit in gas pipelines, smokestacks, and flues.
Maintenance
Once a week, visual inspection through inspection hatches:
- Occurs without stopping the operation of the spraying and fluid circulation system.
- Is performed without stopping the operation of the slurry tank
- Testing the spraying and liquid circulation setup under different operating conditions.
- Checking the slurry tank for sludge buildup.
- Checking the automation setups for proper operation.
- Equipment shutdown and visual inspection of all components for wear, breakage, or imminent failure: spraying systems, liquid circulation setups, pumps, fans, and automation.
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Vladimir Nikulin
Vladimir Nikulin
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