- Large pressure drops
- Signs of erosion when scrubbing abrasive mediums
Welcome to our Drizgas Company!
Drizgas Tech is specialists in all types of wet scrubber system. We are the leading manufacturer of wet scrubber in India for various industrial application.
If you are a plant manager, a process engineer, or Environmental Health and Safety (EHS) Engineer who works in manufacturing industries or wastewater treatment industry, then you may be looking for a solution to remove harmful chemicals, pollutants and odors from your process exhaust streams before they are released into the atmosphere and contaminate the outside air. One technology worth to consider strongly is the industrial scrubber. Industrial scrubber is an air pollution control systems that utilize solids in dry scrubbers, or water or other liquids in wet scrubbers to remove gas pollutants and odors from exhaust streams.
In general, the main advantages of industrial wet scrubbers to clean gas exhaust streams include:
Industrial scrubbers are categorized as either dry or wet scrubber. Dry scrubbers remove pollutants by “Adsorption” principle using dry solid media/activated carbon or adsorbent without utilizing water or solvent. Dry scrubbers are well suited for applications in facilities that lack the infrastructure to properly handle produced wastewater. Dry scrubbers remove pollutants from exhaust gases without the use of liquids. Instead, they utilize a dry reaction material known as sorbent, such as alkaline slurry, and they are primarily implemented for removal of acid from gas by moving the gas through the sorbent to maximize binding.
In contrast to dry scrubbers, wet scrubbers remove contaminated gas through liquid that is designed to remove pollutants. Wet scrubbers constitute a versatile and cost-effective pollution control technology that can eliminate up to 99% of gaseous pollutants and particulate matter.
| Dry Scrubber | Wet Scrubber |
|---|---|
| Removes pollutants using “Adsorption” principle | Removes pollutants using “Absorption” principle |
| Uses dry solid media to capture pollutants | Uses water or chemical solvent to capture pollutants |
| Does not produce waste water | It produces waste water or slurry |
| Suitable for pollutants, which can be trapped by activated carbon/dry media | Suitable for water soluble pollutants |
| Suitable for low pollutant load (less than 5000 ppm) | Suitable for high pollutant load (more than 5000 ppm) |
| Efficiency can be achieved up to 99.9% | Efficiency can be achieved up to 99% |
Water is the most common solvent used to remove inorganic contaminants. In the most basic form of wet scrubbers, water is encapsulated in a metal or composite container, contaminated gas is moved through the water, the water then absorbs the contaminates, and clean gas exits the scrubber.
Aside from water, other liquids can be used as absorbing solutions to effectively remove varied contaminates. Manipulating the chemical composition of the absorbing solutions changes the overall charge, which can be highly positively charged, negatively charged, or non-charged. Because pollutants differ in their charge, wet scrubbers are packed with the liquid that will bind most effectively to remove the contaminants from the gas. Caustic solution (sodium hydroxide, NaOH) is the most common scrubbing liquid used for acid-gas control (e.g., HCl, SO2, or both), though sodium carbonate (Na2CO3), calcium hydroxide (slaked lime, Ca[OH]2), Potassium Hydroxide (KOH) are also used.
Wet scrubbers can remove particulate matter by capturing them in liquid droplets. The droplets are then collected, with the liquid dissolving or absorbing the pollutant gases. Any droplets that are in the scrubber inlet gas must be separated from the outlet gas stream using a mist eliminator. Also, the resultant scrubbing liquid must be treated prior to any ultimate discharge or being reused in the plant.
A wet scrubber’s ability to collect particulate matter is often directly proportional to the power input into the scrubber. Additionally, a properly designed and operated mist eliminator is important to achieve high removal efficiencies.
If the gas stream contains both particulate matter and gases, wet scrubbers are generally the only single air pollution control device that can remove both gaseous pollutants and particulate matter.
Wet scrubbers that remove gaseous pollutants are referred to as absorbers. Gas-to-Liquid contact is essential to obtain high removal efficiencies in absorbers. Various wet scrubber designs are used to remove gaseous pollutants, with one of the most popular sub categories of wet scrubber known as Packed bed, Packed tower scrubber.
Although they can also collect solid particulate matter, packed bed scrubbers are generally used more for the treatment of gas. Packed bed scrubbers are typically used in the chemical, aluminum, coke and ferroalloy, food and agriculture, and chromium electroplating industries, in acid plants, fertilizer plants, steel mills, and asphalt plants.
Packed bed wet scrubbers are used to control:
Inorganic fumes, vapors, and gases (e.g., chromic acid, hydrogen sulfide, ammonia, chlorides, fluorides, and SO2) - Inorganic fumes, vapors and gases are the primary pollutants controlled by Packed-Bed wet scrubbers. They typically achieve removal efficiencies in the range of 95 to 99%.
Volatile Organic Compounds (VOC) - Wet scrubbers are occasionally used to control volatile organic compounds (VOCs). Removal efficiencies for gas absorbers vary for each pollutant-solvent system and with the type of absorber used. Most absorbers have removal efficiencies in excess of 90%, and packed tower absorbers may achieve efficiencies greater than 99% for some pollutant-solvent systems. The typical collection efficiency range is from 70% to greater than 99%.
Particulate Matter (PM) and Hazardous Air Pollutants (HAP) in particulate form (PMHAP) - Packed-bed wet scrubbers are limited to applications in which dust loading is low, and collection efficiencies range from 50-95 %, depending upon the application.
Packed bed scrubbers remove air pollutants through inertial or diffusional impaction, reaction with a sorbent or reagent slurry, or absorption into liquid solvent.
Packed bed scrubbers consist of a chamber containing layers of variously shaped packing material (e.g.,Pall rings, Intalox saddle) that provides a large surface area for liquid-gas contact. The packing's shape, weight, surface area and cost all influence the efficiency of the low gas-phase pressure drop and high gas-liquid contact. The packing is held in place by wire mesh retainers, and is supported by a plate near the bottom of the scrubber.
Waste gas is forced into the bottom of the scrubber's chamber and flows vertically or horizontally through the packing while scrubbing liquid is simultaneously and evenly introduced above the packing and flows down through the bed to coat the packing and establish a thin film. In vertical designs (packed towers), the gas stream flows up the chamber (“counter-current” to the liquid). However, some packed beds are designed horizontally for gas flow across the packing (“cross-current”).
The cleaned gas is then passed through a mist eliminator built into the top of the structure, and the waste slurry drops to the bottom of the chamber.
Another popular type of wet scrubber is the Venturi scrubber. Venturis can be used to collect both particulate and gaseous pollutants, but they are more effective in removing particles than gaseous pollutants. With Venturi scrubbers, the dirty gas entering a scrubber is forced at high velocity through a Venturi where it collides with scrubbing water. The tiny water droplets capture particles through impaction and diffusion. The mist eliminator for a Venturi scrubber is often a separate device called a cyclonic separator. The dirty water is then removed in the cyclonic separator and discharged into a recycle tank. Some of the liquid is continuously purged to limit the solids concentration and allow recirculation back to the Venturi section.
A Venturi scrubber typically consists of three sections:
Converging section - Inlet gas stream enters the converging section and, as the area decreases, gas velocity increases. Liquid is introduced either at the throat or at the entrance to the converging section.
Throat section - In the small throat section, the inlet gas is forced to move at extremely high velocities in the small throat section, and shears the liquid from its walls, producing an enormous number of very tiny droplets.
Diverging section - in the diverging section, particle and gas removal occurs as the inlet gas stream mixes with the fog of tiny liquid droplets. The inlet stream then exits through the diverging section, where it is forced to slow down.
Eductor Venturi Scrubbers
Eductor scrubbers are designed to remove soluble gases and particulate by inducing a gas flow using high pressure liquid focused into a Venturi throat, which eliminates the need for a separate exhaust fan or blower to transport the contaminated gas stream to the filtration device.
Design incorporates a high pressure spray for maximum entrainment and scrubbing efficiency, and is the optimal choice where high temperatures, heavy contaminant loads, and corrosive conditions are present.
Maximum efficiency - up to 99% removal efficiency of mists 3 microns or larger
Spray towers are very simple, low-energy wet scrubbers. In these scrubbers, the particulate-laden gas stream is introduced into a chamber where it comes into contact with liquid droplets generated by multiple spray zones. These scrubbers are also known as pre-formed spray scrubbers, since the liquid is formed into droplets prior to contact with the gas stream. The size of the droplets generated by the spray nozzles is controlled to maximize liquid-particle contact and, consequently, scrubber collection efficiency.
Spray towers are cylindrical or rectangular chambers that can be installed vertically or horizontally. In vertical spray towers, the gas stream flows up through the chamber and encounters several sets of spray nozzles producing liquid droplets. A de-mister at the top of the spray tower removes liquid droplets and wetted PM from the exiting gas stream. Scrubbing liquid and wetted PM also drain from the bottom of the tower in the form of slurry. Horizontal spray chambers operate in the same manner, except for the fact that the gas flows horizontally through the device.