Scrubber systems are air pollution control devices that use liquid droplets to remove airborne pollutants like particulate matter, acid rain precursors and hazardous air pollutants from industrial exhaust streams and flue gases. There are different types of scrubbers designed to capture specific pollutants depending on the process they are treating.
Wet Scrubbers
Wet scrubbers use a reagent scrubbing liquid, usually water, to capture pollutants from flue gases as they pass through an absorption tower or spray chamber. The four main types are:
Packed-bed scrubbers employ closely spaced components like mesh pads or saddles that allow for intimate contact between gases and liquid. Pollutants are dissolved, neutralized or captured. They are effective for removal of particulate matter, sulfur dioxide and some hazardous air pollutants.
Venturi Scrubber System use a constriction in the ductwork to accelerate flue gases, creating a pressure differential. Reagent is injected upstream and atomized, allowing pollutants to adhere to droplets. They are suited for removal of particulate, SO2 and HCl.
Spray towers push flue gases up through a chamber counter-currently to a downward spray of reagent. Pollutants adhere to droplets, which collect at the bottom for disposal or further treatment. Effective for particulate removal including fly ash.
Bubble-cap scrubbers inject liquid reagent through caps within a vertical tower that passes exhaust gases. Intimate contact strips particulates, sulfur oxides and other acid gases from streams. Commonly used for wet desulfurization of flue gases.
Dry Scrubbers
When wet systems are not viable due to process incompatibility, dry scrubbers use dry reagents instead of liquid to remove air pollutants. Common types are:
Spray dryer absorbers mix sulfur dioxide-laden flue gas with an alkaline slurry to neutralize SO2. Water evaporates as the mixture leaves the absorber tower, leaving a dry powder suitable for landfill. Uses minimal water.
Dry injection systems force powdered sorbent like trona, lime or activated carbon into the flue gas duct downstream of particulate control. Pollutants react and adhere to the particles, which are then collected by fabric filters or electrostatic precipitators.
Dry sodium scrubbers use a rotating cylindrical absorber with sodium powder to capture SO3, SO2, HF and HCl. High removal rates but periodic replacement of the scrubbing medium is required.
Scrubber Systems in Industries
Power Plants
Coal and oil-fired power plants employ wet lime/limestone FGD scrubbers or spray dry scrubbers to remove over 90% of SO2 in compliance with acid rain regulations. Wet scrubbers also remove other pollutants including mercury.
Cement Manufacturing
Cement kilns produce dust, NOx, SOx and other regulated pollutants. Wet and dry scrubbers, particulate collectors and SCR systems ensure plant emissions meet standards. Scrubbers neutralize hydrochloric and sulfuric acid gases.
Refineries & Chemical Plants
These industries emit pollutants from fuel combustion as well as process vent streams. Wet scrubbers treat acid gases, VOCs, particulates and mercury from fluid catalytic cracking units, sulfur recovery plants and other sources.
Incinerators & Waste Combustors
Wet scrubbers control acid gases and particulate emissions from municipal and medical waste combustion, complying with strict air quality rules for these sources. Some use dry scrubbing or a combination of wet and dry systems.
Benefits of Scrubber Systems
Scrubbers provide major air quality benefits by allowing industries to comply with stringent emission limits and reducing health and environmental impacts. They allow facilities to continue operating fossil fuel power plants and manufacturing processes under increasingly tight clean air standards. Scrubber technology enhances sustainability efforts through pollution reduction. Proper design, operation and maintenance of scrubber systems ensure long-term compliance at low cost compared to alternatives like process modification. Advanced controls also maximize removal efficiency and minimize reagent use. As emissions standards continue to strengthen globally, scrubber systems will remain essential for industrial emission control.
Scrubber technology plays an important ongoing role in industrial air pollution control systems. Various scrubber types effectively remove a wide range of air pollutants from diverse industrial processes. Their proper application according to source conditions allows many facilities to comply with air quality regulations while maintaining operations. Advanced scrubber designs lower costs and improve environmental performance over time.
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