Particulate matter scrubbers

Dry aerosols, or particulate matter, differ so much from the carrying gas stream that their removal should present no major difficulties. The aerosol is different physically, chemically, and electrically. It has vastly different inertial properties than the carrying gas stream and can be subjected to an electric charge. It may be soluble in a specific liquid. With such a variety of removal mechanisms that can be applied, it is not surprising that particulate matter, such as mineral dust, can be removed by a filter, wet scrubber, or electrostatic precipitator with equally satisfactory results. 

ESPs), and some of the previously discussed novel devices. Series combinations of control devices may be necessary to achieve the required level of particulate matter emission. A commonly used system is a multiple cyclone followed by a fine-particle control system, such as a baghouse, scrubber, or ESP. 

Figure 30-lA presents the integrated environmental control potential for maximum control of particulate matter and SO2. Cooling tower water blowdown and treatment by-products may be used to satisfy scrubber makeup requirements. Fly ash and scrubber sludge will be produced separately. If the catalytic NO, process is required, the integration issues will be increased significantly. 

Figure 30-lE includes a hot ESP for fly ash collection prior to a catalytic NO , unit. Having a hot ESP dictates the use of a conventional wet scrubber and perhaps the need for a second particulate matter control device at the end of the system. Fly ash and scrubber sludge would be separate byproducts, but sludge could be contaminated with NH4 from the catalytic NO process. 

Air pollution control systems using wet scrubbers will remove some water-soluble gases, but the removal of particulate matter is the primary concern for a control system. The air pollution control system, therefore, is usually a single device such as a wet scrubber, small-diameter multiple cyclones, fabric filters, or ESPs. The multicyclones are the least expensive system and the ESPs the most expensive. 

Calcium oxide (lime) Rotary kilns, vertical and shaft kilns, fluidized bed furnaces Particulate matter Cyclones plus secondary collectors (baghouse, ESP, wet scrubbers, granular bed filters, wet cyclones)... 

Sodium carbonate (soda ash) Solvay (ammonia-soda) Particulate matter Wet scrubbers... 

Triple superphosphate, granular SiF, HF, particulate matter Venturi or packed scrubber... 

Sinter machine discharge Particulate matter Multiple cyclones, baghouse, or low-energy wet scrubber... 

The electric arc furnace process accounted for about 25% of the 1982 U.S. steelmaking capacity (14). Most of the raw material used for the process is steel scrap. Pollutants generated by the electric furnace process are primarily particulate matter and CO. The furnaces are hooded, and the gas stream containing the particulate matter is collected, cooled, and passed to a bag-house for cleaning. Venturi scrubbers and ESPs are used as control devices at some mills. Charging and tapping emissions are also collected by hoods and ducted to the particulate matter control device. 

Blast furnace exhaust gases Particulate matter Multiple cyclone plus wet scrubber or wet ESP, two-stage wet scrubber... 

Chargine and tapping Particulate matter Baghouse or venturi scrubber... 

Furnace waste gases Particulate matter (7-30 kg per metric ton of steel) ESP or venturi scrubber... 

Cupolas Particulate matter Baghouses, wet scrubbers, and ESPs... 

Sand conditioning. Particulate matter Medium-energy wet scrubbers. 

Urea Plants - In urea plants, wet scrubbers or fabrie filters are used to control fugitive emissions from prilling towers fabric filters are used to eontrol dust emissions from bagging operations. These equipment are an integral part of the operations, to retain product. New urea plants should achieve levels of particulate matter in air emissions of less than 0.5 kg/t of product for both urea and ammonia. 

Baghouses are preferred over venturi scrubbers for controlling particulate matter emissions from loading and pushing operations because of the higher removal efficiencies. ESPs are effective for final tar removal from coke oven gas. Stack air emissions should be monitored continuously for particulate matter. Alternatively, opacity measurements of stack gases can suffice. Fugitive emissions should be monitored annually for VOCs. 

Venmri scrubbers are primarily used to control particulate matter (PM), including PM less than or equal to 10 micrometers ( m) in aerodynamic diameter (PM,o), and PM less than or equal to 2.5 fim in aerodynamic diameter (PMj 5). Though capable of some incidental control of volatile organic compounds (VOC), generally venturi scrubbers are limited to control PM and high solubility gases (EPA, 1992 EPA, 1996). 

Orifice scrubbers are primarily used to control particulate matter (PM), including particulate matter less than or equal to 10 micrometers (fim) in aerodynamic... 

Foam scrubber A cleaning device that uses foam as a collecting medium for particulate matter in a gas stream. 

Gas scrubber A device for the removal of particulate matter from a gas stream by scrubbing the gas with a liquid. 

Wet and dry scrubbers Dry scrubbers are generally preferred today. Scrubbers can be used for the removal of both particulate matter and toxic sulfur gases (dry scrubber or spray dryer desulfurizers). 

Fiber-bed scrubbers are used to collect fine or soluble particulate matter or as mist eliminators to collect liquid aerosols, including inorganic (e.g., sulfuric acid mist) and volatile organic compounds. Insoluble or coarse PM will clog the fiber bed with time, and VOCs that are difficult to condense will not be collected efficiently. 

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