Venturi Scrubber: Working Principle, Construction, Efficiency, Advantages, and Disadvantages Explained

Author: Michael Klepik, Chief Executive Officer

• Expanding Section: After passing through the throat, the stream enters the expanding section, where its velocity decreases, allowing the spray that captures the contaminants to settle.
• Liquid Injection System: This includes pumps, pipelines, and nozzles.
• Droplet Separator: Located after the expanding section, this component is designed to separate the contaminant-capturing droplets from the cleaned air.
• Drainage Hopper: This serves to collect and remove the contaminated liquid.
• Outlet Nozzle: The purified stream exits through this nozzle.

The operation of a Venturi scrubber is based on the principle that, as the stream accelerates in the throat, droplets collide with contaminant, capturing them. They then settle in the expanding section and are removed.

To ensure high-quality cleaning of emissions, we evaluate the performance of the Venturi scrubber mechanism at various stages of its operation. Efficiency depends on many factors, including air flow speed, particle size and concentration in the stream, droplet size and speed, and the geometry of the configuration itself.

How does a venturi scrubber work? Device designed as a pipe with a smooth constriction at the inlet (converging section) and a smooth expansion at the outlet (diverging section). The narrowest part of the Venturi tube is known as the throat. Liquid is introduced into the converging section at a designated distance from this area through nozzles. The dust-laden stream passes through the tube at high speed and enters the diverging section. As the flow passes through the tube, there is close contact between the gas and the fluid. This purification process in the device, based on the Venturi scrubber working principle, can be considered as filtration through a volumetric filter consisting of tiny droplets formed by the atomization of the fluid.

Design Variants Offered by Our Company:

• Low-pressure pipe with a larger diameter: Less resistance.
• High-pressure pipe with a smaller diameter: Higher flow resistance.
• Tube with adjustable settings: A special damper allows control of the airflow speed.

This type of equipment is highly effective in handling dusty contaminants since the tube does not get clogged. Additionally, it serves for air purification by removing harmful impurities, acid components, and more.

The efficiency of a Venturi wet scrubber with a packed bed is easy to calculate, and this is one of its key advantages. In laboratory conditions, experiments can be performed to assess the performance of a specific packing material. Typically, Pall rings and Tri-Pak are utilized. The hollow-type device with a cyclonic separator cannot be subjected to such calculations.

In this configuration, the tube separates large dust particles, while the packed column cleanses the gas components. For this version, a low-pressure tube is used because the packed column will provide high resistance. The basic configuration includes a mist eliminator that captures water in the cleaned air stream.

If you have a lot of dust, we recommend choosing the classic hollow principle of the Venturi scrubber. If you have numerous gaseous pollutants, especially those prone to condensation, you should opt for equipment with a packed column.

The main disadvantage of Venturi scrubbers is the abrasive wear on the walls, which occurs due to the high air velocities that can reach up to 267.19 mph in the throat. Solid particles or droplets, moving at such speeds and colliding with the walls, cause rapid erosion. Wear can be reduced by coating the inner walls of the throat with silicon carbide, making an inner sleeve of this material for convenience.

Wear can also occur in the elbow at the bottom of the device. To reduce wear here, the bottom of the elbow leading into the separator is filled with a layer of the same liquid used in the upper part of the system. Solid matter and liquid fragments fall into this layer, reducing the impact loads on the walls. Another drawback of this air purification method is the formation of large volumes of sludge.

Specific initial technical requirements for a system may vary depending on the particular project specifications, type of industry, and the contaminants that need to be removed. However, some general guidelines are outlined below:

• Efficiency: The percentage indicating how much of the contaminants are removed from the airflow.
• Capacity: The volume of air the equipment processes over a specified period.
• Materials: The materials used in the Venturi scrubber working should be chosen carefully, especially if the streams are corrosive or contain aggressive chemicals.
• Dimensions: The overall dimensions and weight of the equipment.
• Pressure Requirements: The maximum and minimum operating pressure in the system.
• Temperature: Acceptable operating temperatures for the air and fluid.
• Water Requirements: The quantity, quality, and parameters of the water employed for cleaning.
• Waste Disposal Guidelines: How to handle and dispose of fluid and solid waste generated after cleaning.
• Energy: The amount of electricity or other energy sources needed for device operation.
• Safety: Necessary safety measures, such as protective valves, alarms, emergency shutdown systems, etc.
• Maintenance: Frequency and type of required maintenance, availability of spare parts, ease of maintenance and repair.

These requirements may be supplemented or refined depending on the specific customer, application, and industry standards. If you have a particular project or task that requires a system, it is recommended to consult with our specialists for detailed specifications.

The efficiency of a Venturi scrubber can be calculated by determining the fraction of contaminants removed from the stream. This requires examining different factors such as air velocity, liquid volume rate, contaminant size, and operating conditions. Here's a step-by-step approach to calculating Venturi scrubber efficiency:

The relative velocity between the gas and droplets is crucial for effective collisions:

The collision efficiency is calculated using empirical correlations or theoretical models based on Stokes' law. One common approach is to use the following formula for spherical particles:

The overall collection performance of the equipment is expressed as:

The overall effectiveness for a range of particle sizes is assessed by integrating the collection performance across the particle size distribution:

This is only an approximate calculation of individual parameters. For more accurate information, please seek consultation.

These systems can operate across a wide range of temperatures, typically from ambient temperatures up to around 400°F (204°C). The materials used in the construction must be chosen to withstand the venturi scrubber operating temperature, with common materials including stainless steel, Hastelloy, and other high-temperature resistant alloys.

The performance of the cleaning system may be affected by the operating temperature, as higher temperatures may influence the viscosity and surface tension of the washing fluid, potentially impacting droplet formation and contact between the gas and liquid. In some cases, the gas stream may need to be cooled before entering the cleaning apparatus to ensure optimal performance and protect the materials, using heat exchangers or quenching methods. The design of the purifier must account for thermal expansion and contraction to prevent damage to the structure and ensure long-term reliability. High operating temperatures require careful consideration of safety features, such as pressure relief valves and temperature monitoring units, to prevent accidents and equipment failure.

When choosing a Venturi scrubber vendor, it is important to consider their experience, product quality, and customer support to ensure you get the most effective solution for your needs. For tailored advice and a high-quality product, please reach out to us directly.