Scrubbers pollutants removed

The principal technological developments in the control of air pollution by engineering during the nineteenth century were the stoker for mechanical firing of coal, the scrubber for removing acid gases from effluent gas streams, cyclone and bag house dust collectors, and the introduction of physical and chemical principles into process design. 

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. 

Packed-tower wet scrubber A gas scrubber that removes gases and vapors, by using either v/ater or a chemical liquid method. Efficient pollutant removal depends on the contact time between the entering gas stream and the wetted surface of the pack in the tower. This type of scrubber can be classified as... 

Another critical part of the incinerator design is the pollution control system.11 Pollution control systems directly influence the levels and kinds of pollutants that are released and that can potentially reach the public. Most modern hazardous waste incinerators are designed with extensive air pollution removal systems. For example, a common pollution control system might include a system that cools or quenches gases produced by burning waste, followed by a system that reduces acid gas emissions, and ultimately followed by a particulate removal system such as fabric filters (bag-houses), electrostatic precipitators, venturi scrubbers, and others.10... 

This type of technology is a part of the group of air pollution controls collectively referred to as wet scrubbers. The removal of air pollutants is achieved by the use of condensation to increase pollutant particle size, followed by inertial interception. Condensation scrubbers are typically intended to control fine PM with an aerodynamic diameter of between approximately 0.25 and 1.0 pm. 

Air from the atmosphere. The cooling tower functions like an air scrubber where around 500 to 1000 m of air circulates per cubic meter of water. Depending on the environment of the site, the pollution removed from the air can be made up of mineral and organic dust, sand, smoke, gases and microorganisms. 

There are two strategies to reduce air pollution processes that produce fewer pollutants and efficient clean-up processes. Although both approaches also involve noncatalytic technologies, for example, combustion modifications or better scrubbers for removal of SO2, environmental catalysis is contributing increasingly to both strategies. Two environmental catalytic processes are treated in Section 6.18,... 

It must be remembered that a fume scrubber merely removes a contaminant from a gas stream but does not destroy it. The scrubber liquid effluent will contain all of these scrubbed contaminants thus, it will present a water pollution potential [7]. Particulates can be settled, or filtered, out of this discharged liquid for recovery or sludge disposal. Chemical... 

Incineration is a common form of waste disposal. The incineration of plastic wastes has raised two important issues the production and emission of noxious air pollutants into the atmosphere, and the loss of valuable solid forms of carbon and nitrogen resources. Incineration of plastic wastes produces carbon dioxide, water and corrosive gases such as sulfur dioxide and nitrogen oxide. Inefficient processes produce hydrogen chloride, carbon monoxide and other particulate matters as well. The cost of efficient scrubbers to remove noxious gases and particulate matters before emission into the atmosphere has raised the cost of incineration to an often impractical level. 

Therefore the bulk of emissions reductions must come from pollution-control devices. These include "scrubbers" and more exotic technologies currently under development (see Chapter 6). Scrubbers can remove up to 90% of the SO2 from coal combustion, but they carry a price tag of at least 100 million dollars each. 

Scrubbers. Scrubbers are designed to contact a liquid with the particle-laden gas and entrain the particles with the liquid. They offer the obvious advantage that they can be used to remove gaseous as well as particulate pollutants. The gas stream may need to be cooled before entering the scrubber. Some of the more common types of scrubbers are shown in Fig. 11.2. 

Small solid particles, present in dust and grit emissions, have very low settling velocities (Table 4.4) The collection efficiencies of simple cyclones are tlierefore, as shown in Figure 17.3, relatively low. Fabric filters, electrostatic precipitators or wet scrubbers may be required to remove particles <5 pm in size with an acceptable efficiency. Therefore the cost of pollution control inevitably increases when dealing with particle size distributions skewed towards the lower end. 

Other Considerations In situations where waste gas contains both particulates and gases to be controlled, venturi scrubbers are sometimes used as a pretreatment device, removing PM to prevent clogging of a downstream device, such as a packed bed scrubber, which is designed to collect primarily gaseous pollutants. 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors 1) availability of suitable solvent 2) required removal efficiency 3) pollutant concentration in the inlet vapor 4) capacity required for handling waste gas and, 5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Packed-bed scrubbers are typically used in the chemical, aluminum, coke and ferro-alloy, food and agriculture, and chromium electroplating industries. 

As many emissions involve chlorinated compounds, corrosion is a major problem in many control methods. The corrosion of columns and surface condensers can be prevented or reduced by the correct material selection. However, corrosion remains a constant threat to the interior of incinerators. Additional pollution control equipment such as scrubbers may also be required to remove acidic compounds from treated gases before discharging into the atmosphere. 

Scrubbers and absorbers Wet systems used for the removal of aerosols and other gaseous pollutants from an airstream. 

Wet scrubbers have found widespread use in cleaning contaminated gas streams because of their ability to effeetively remove both particulate and gaseous pollutants. Specifically, wet scrubbing describes the technique of bringing a contaminated gas stream into intimate contact with a liquid. The types most widely used for particulate control are spray towers, packed-bed units, ionizing wet scrubbers, and venturi scrubbers. 

Wet scrubbers are air pollution control devices used to remove particulates and fumes from air by entraining the pollutants in a water spray. 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

S02 and NOx in flue gas from coal combustion contribute to smog and acid rain. Methods to remove these pollutants include alkaline wet scrubber systems that fix S02 to solid CaS04, and selective catalytic reduction by metal/metal oxide systems of NO/NOz to N2 and steam in the presence of ammonia. Particulate active carbons have also been used in flue gas decontamination, especially as they avoid costly scrubber processes and can operate at lower temperatures. The potential of active carbon fibers in this application has been explored by a... 

---