Gas Scrubber

What is a gas scrubber, chemical scrubber, or fume scrubber?


A gas scrubber (or fume scrubber) is an air pollution control device that is designed to remove specific gases, vapors, and fumes from an industrial exhaust air stream.

Also known as chemical scrubber, a gas scrubber typically sprays a scrubbing liquid into the exhaust air stream to absorb, dissolve, or chemically react with the gas-phase contaminants and pollutants.

In some cases, the gas scrubber could also be a dry scrubber type. This depends on the type of gases or chemicals that need to be absorbed or dissolved. Some vapors or fumes that aren't water-soluble could be good targets for a dry scrubber or dry sorbent injection (DSI) system. The most common type of dry scrubber is a limestone-based scrubber which uses limestone powder.

Most gas scrubber applications are best suited to use a liquid-based scrubber. Applications include gases such as:

  • Sulfur dioxide (SO2)
  • Sulfuric acid (H2S04)
  • Ammonia (NH3)
  • Chlorine (Cl)
  • Hydrochloric acid (HCl)
  • Hydrogen sulfide (H2S)
  • Other sulfur compounds

The scrubbing liquid is chosen specifically to neutralize the incoming contaminants. For example, if the incoming vapor pollutant is an acid gas, then an alkaline scrubbing solution will be used to neutralize the acid via a chemical reaction. Similarly, if the pollutant is ammonia gas, then diluted sulfuric acid will be used as the scrubbing liquid to react with and neutralize the ammonia gas.

Gas Scrubbers are typically in the form of a cylindrical tower, where the scrubbing liquid is sprayed into the top of the tower and travels downward, while the dirty air enters at the bottom of the tower and moves upwards through the liquid. The tower may contain a packing material to facilitate air-to-liquid mixing, these are called packed-bed gas scrubbers.

Gas Scrubbers can be used to capture several types of exhaust gases in a single stream, but they are typically not effective for capturing organic non-polar gases (this includes most VOCs and some organic non-polar odors). Gas/chemical scrubbers can be used to capture gases that are soluble in water, such as alcohols and other polar molecules. The names 'gas scrubber', 'fume scrubber', and 'chemical scrubber' may be used interchangeably.

Gas Scrubber effectiveness on:

Inorganic fumes, vapors, gases, and odors95
Polar, water-soluble gases95
Heavy metal gases*80

*Examples include: chromium (hexavalent chromium), arsenic, cadmium, mercury (mercury vapors), and lead.

Odors* (Organic-based)60

*A gas scrubber is effective at removing inorganic odor compounds, such as hydrogen sulfide (H2S) and ammonia (NH3).

Particulate matter50
Hazardous Air Pollutants (HAPs)30
Volatile Organic Compounds (VOCs)20

Components of a Gas Scrubber


Ductwork and fan/blower

Scrubbers may use a forced draft or induced draft fan system, depending on the exhaust air conditions: temperature, corrosiveness, and amount of particulate.

Scrubbing tower

The scrubbing tower contains the liquid spray nozzles, the packed bed (if applicable), and a liquid collection and drain at the bottom.

Depending on the corrosiveness of the contaminants, a variety of materials for the scrubbing vessel may be used: stainless steel, polypropylene, fiberglass, PVC, fiber-reinforced plastic, and more.

Mist Eliminators and Stack

After scrubbing, the exhaust air is typically near 100% relative humidity. At the top of the scrubber tower are mist eliminators to remove excess water particles before exhausting from the stack, to reduce the visible plume.

Liquid Circulation and Spray

The system includes pumps to circulate the scrubbing liquid. Sometimes the spent liquid can be treated and/or filtered and then recycled. If the liquid cannot be recycled, then a chemical pump with fresh RO/DI water will be included to maintain proper levels of scrubbing liquid in the tower.

A simple forced-draft gas scrubber with liquid pump, riser, and two sets of spray nozzles.


A hot gas scrubber with quench spray to cool incoming air stream.
Used for hot gases above ~220°F.

Gas Scrubber Design Considerations


CFM

The volume of process air to be treated is a key consideration. Scrubbers systems can be designed to handle any amount from 100 CFM to over 100,000 CFM.

Destruction or Removal Efficiency (DRE)

Factors that impact DRE:

  1. Type of contaminants
    • Solubility
    • Reactivity
  2. Concentration of contaminants
  3. Residence time
  4. Liquid-to-gas ratio
  5. Flow rates
  6. Gas temperature

Materials of Construction

Material options include:

  1. Stainless steel
  2. Fiberglass
  3. Fiber-reinforced plastic (FRP)
  4. Polypropylene
  5. PVC
  6. Non-reactive liners like Teflon available

Equipment Configuration & Layout

Key questions include:

  1. Are multiple control devices needed?
  2. Scrubbers available up to 60,000 CFM.
    • More than 60,000 CFM? -> Use 2 scrubbers in parallel
    • Are there multiple contaminants? -> equipment in series
      • Two scrubbers with different liquids
      • Scrubber + thermal oxidizer combo
  3. Fan location: induced draft or forced draft?
  4. Recirculation, treatment, and pump skids
  5. Inlet ductwork
  6. Outlet ductwork and exhaust stack
  7. Test ports & access platforms

Industries, Applications, & Case Studies


Specific chemistries and applications include:

  • Nitric Acid
  • Hydrochloric Acid
  • Hydrofluoric Acid
  • Sulfuric Acid
  • Phosphoric Acid
  • Acetic Acid
  • Hydrogen Sulfide
  • Chromium Compounds
  • Nickel Compounds
  • Ammonia
  • Chlorine
  • Formaldehyde
  • Cyanide Compounds
  • Bromine
  • Hydrogen Bromine
  • Isopropyl Alcohol (IPA)
  • NOx

Petroleum Refinery
  • Petrochemical refining, natural gas processing, and other oil & gas processes generate emissions contaminated with petrochemical fumes and vapors, toxic gases, or other petro-based contaminants. Gas scrubbers may be used to absorb or dissolve the harmful chemical vapors before releasing to atmosphere.

Chemical Production
  • Manufacturing chemicals or processing chemicals generates exhaust streams contaminated with toxic chemical vapors and gases. Gas scrubbers are often used to absorb, dissolve, neutralize, or otherwise remove chemical vapors before releasing to atmosphere. Often an acidic or basic scrubbing liquid is used to neutralize any reactive contaminants.

Acid Manufacturing
  • Gas scrubbers are a perfect choice for treating and removing acid gases, fumes, and vapors. A basic (alkaline) solution is injected into the scrubber and mixes with the acidic exhaust vapors. A chemical reaction occurs, combining the acidic vapors and basic scrubbing liquid to produce harmless salts and water. The acid-base reaction neutralizes the vapors.

Power Plants, Flue Gas
  • In the food-processing industry, a venturi water scrubber may be used to capture the microscopic grease mist, particulates, and smoke that forms during meat cooking. It will also work to capture the flour dust from baking and many other food-processing applications. In these cases, a wet scrubber is more effective than mechanical air filters.

Pharmaceutical
  • Tablet coating, fluid-bed processing, and tray drying in the Pharmaceutical industry offers unique air pollution control challenges as the ethanol, isopropyl alcohol (IPA), and other VOCs releases into process exhaust air stream. If the chemical vapors are all water-soluble, then a gas scrubber may be used as the air pollution control device.

Wastewater, Odor Control
  • Municipal waste, wastewater, and drinking water facilities often release large amounts of hydrogen sulfide and other malodorous compounds which may require capture and control, depending on your local regulations. Gas scrubbers are a perfect odor control device, employed for many odor capture applications when the odor chemicals are polar and water-soluable.

Metal Finishing
  • Metal finishing and surface finishing includes electroplating, anodizing, etching, galvanizing, phosphating, aluminizing, zinc plating, nickel plating, cadmium plating, chrome plating, and includes capturing off-gas chemicals such as ammonia, chromic acid, hydrofluoric acid, nitric acid, phosphoric acid, sodium hydroxide, and sulfuric acid.

Semiconductor
  • In the semiconductor industry, gas scrubbers are used to capture various Hazardous Air Pollutants (HAPs) and ozone-depleting GHGs, including Silane-, Tetrachloride-, and Siloxane-based contaminants. These compounds will hydrolyze and decompose once in contact with water. Any solid reaction products will end up in the scrubbing liquid and need to be filtered out.

The Best Gas Scrubber Manufacturers


CECO Environmental

CECO offers their HEE-Duall brand of gas scrubbers to treat chemical fumes, NOx, Odors, high-temp gases, particulates, and more. CECO builds scrubbers for the building products, manufacturing, oil & gas, chemical, and semiconductor industries.


CECO differentiators:

  • High quality materials
  • Expertly engineered
  • Many technology options
  • Higher cost

Gulf Coast Environmental

Gulf Coast Environmental Systems (GCES) offers both venturi and packed bed gas scrubbers for Ammonia, Chlorine, HCl Acid, Chlorinated Silanes, Sulfur Dioxide, Hydrogen Sulfide, Boron Trifluoride, and Amines. GCES supplies systems worldwide.


Gulf Coast differentiators:

  • Often lowest cost
  • Quality in-house construction
  • Responsive field service
  • Limited scrubber options

HEIL Engineered Equipment

HEIL builds gas scrubbers to remove odor-causing compounds, hazardous and corrosive chemicals, and soluble gases and vapors. HEIL services the Metal Finishing, Chemical Processing, Food/Bev, Pharmaceutical, Fertilizer, Glass/Optics, Pulp/Paper, Semiconductor, and Mining industries.


HEIL differentiators:

  • In-house manufacturing
  • High quality construction
  • In-house design and engineering
  • Focused on a few industries

Mech-Chem Fume Scrubber

Mech-Chem offers their fume scrubber, their flagship product, in several design options including Acid, NOx, Chrome, Ammonia, and more. Mech-Chem also offers turn-key systems, including: exhaust hood, duct/fan, fume scrubber, and acid recovery systems.


Mech-Chem differentiators:

  • Focused on fume scrubbers
  • Many design options
  • Full-service engineering
  • Limited to fume scrubbers

Hydro-Sonic Systems

Hydro-Sonic Systems offers wet scrubbers with a steam or tandem nozzle design. They supply scrubbers worldwide with a focus on Texas and the central U.S. They focus on the metals/steel, hazardous/radioactive waste, and chemical processing industries.


Hydro-Sonic Systems differentiators:

  • Optimized for sub-micron particles
  • Expert gas/fluid Engineering
  • Offers sonic-based technologies
  • Only offers wet scrubbers

KCH Engineered Systems

KCH offers air pollution control, odor control, and metal surface finishing equipment. They supply to the Aerospace, Automotive, Semiconductor, Municipal Wastewater, Metal Finishing, Food / Beverage, Pharmaceutical, and Energy Production industries.


KCH Systems differentiators:

  • High quality construction
  • Highest reliability
  • Many technology options
  • Focused on metal finishing

Other Types of Scrubbers


  • Scrubbers
Gas Scrubber
  • Chemical Scrubber
  • Fume Scrubber
Venturi Scrubber
  • Particulate Scrubber
  • Dust Scrubber
Ammonia Scrubber
  • Alkaline Scrubber
NOX Scrubber
  • Boiler Scrubber
Acid Scrubber
  • Sulfuric Acid Scrubber
  • H2S Scrubber
  • Chlorine Scrubber
Coal Scrubber
  • Sulfur Dioxide Scrubber
  • SO2 Scrubber
  • Flue Gas Desulfurization (FGD)
Smokestack Scrubber
  • Power Plant Scrubber

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The budget calculator is really helpful to get some ballpark figures, without having to deal with any sales people. It's also helpful to know that we have an accurate budget cost, so there's no surprises later.


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