Chapter 2 Air Pollution PDF

[email protected]  Course Outcome Distinguish and illustrate the source, impact and control infrastructure related to air, noise, water pollution and solid waste. Learning Outcome At the end of this lecture, student should be able to discuss: To de...

[email protected]  Course Outcome Distinguish and illustrate the source, impact and control infrastructure related to air, noise, water pollution and solid waste. Learning Outcome At the end of this lecture, student should be able to discuss: To describe the types, sources and effect of air pollution. To explain the impact of air pollutants on human & environment. To determine the measurement tools of air pollutants. To discuss the limit of air pollutants exposure. To discuss the control infrastructure of air pollution. [email protected]  Outline 2.1 Types of air pollution (gases & particulates) 2.2 Sources of air pollution (indoor & outdoor air pollution) 2.3 Dispersion of air pollution 2.4 Effects of air pollution (human health, vegetation & material) 2.5 Measurements of air pollution (high volume sampler: particulate) (glass bubbler/diffuser: gases) 2.6 Emission Standards and Air Quality Index 2.7 Control infrastructure (particulate pollutants: centrifugal collector, bag filter, settling chambers, electrostatic precipitators) (gaseous pollutants: absorber, adsorber, incinerator, condenser) [email protected]  WHAT IS AIR POLLUTION? Is the presence in the outdoor atmosphere of one or more air contaminants (dust, fumes, gas, mist, odor, smoke, or vapor) in sufficient quantities, of such characteristics, and of such duration as to be or to threaten to be injurious to human, plant or animal life or to property, or which reasonably interferes with the comfortable enjoyment of life or property. [email protected]  Hi everyone [email protected] 2.1 Types of air pollution (gases & particulates) AIR POLLUTANTS GASEOUS PARTICULATE (GASEOUS & CHEMICAL (SOLID & LIQUID STATE) VAPOUR STATE) SETTLEABLE - larger particles - 10µm diameter SUSPENDABLE - Smaller particles [email protected] 2.1 Types of air pollution (gases & particulates) GASEOUS (GASEOUS & CHEMICAL VAPOUR STATE) Gaseous pollutants such as SO2, Cl2, NOx, mercury or organic vapour are miscible with air in all proportions. Some of the gaseous pollutants are generated during combustion and others from process industries. Most of the gaseous pollutants containing sulphur, nitrogen and carbon. [email protected] 2.1 Types of air pollution (gases & particulates) Gaseous Carbon Oxides Pollutants Carbon Monoxide is a dangerous, poisonous pollutant that harms our environment in many ways. The major source of CO is incomplete combustion of fossil fuels like coal, wood, charcoal etc. Even exhaust from cars contains small amounts of Carbon Monoxide. Carbon Dioxide is actually an essential element for human survival because plants need it to perform photosynthesis. However it is currently present in our atmosphere and our surroundings, in extremely large quantities, and this is harmful to humans. Carbon Dioxide is mainly released due to the burning of fossil fuels. From manufacturing activities to running our cars to launching rockets they all need to burn fossil fuels. This is why it is so hard to control the emissions of CO2. [email protected] 2.1 Types of air pollution (gases & particulates) Gaseous Carbon Oxides Pollutants SOURCE [email protected] 2.1 Types of air pollution (gases & particulates) Gaseous Sulphur Oxides Pollutants Major source for Sulphur Dioxide (SO2) is the combustion of coal and petroleum products that contain sulphur. One natural source of Sulphur oxides is volcanic eruptions and hot springs. Other sources are thermal power station, oil refineries and copper industries. This may also get oxidized and turn to Sulphur Trioxide (SO3). And then when reacted with moisture or water it becomes Sulphuric Acid (H2SO4) and precipitates on Earth as Acid Rain. Sulphur Dioxide (SO2) in particular is a nasty pollutant that is very dangerous in high concentration. In fact, these pollutants can cause respiratory distress and lung diseases in humans. [email protected] 2.1 Types of air pollution (gases & particulates) Gaseous Nitrous Oxides Pollutants Nitrogen the most abundant gas in our atmosphere. (78% composition in air). However, oxides of nitrogen are a major pollutant of atmospheric pollution. Nitrous oxides (N2O) are majorly released by vehicle emissions. Other natural activity that produces nitrogen oxides is lightning. When lightning strikes dioxygen and dinitrogen combine at very high temperatures. Common products containing oxides of nitrogen include nitrate fertilisers. Cigarette smoke and other fuel burning activities, such as wood burning heaters, can be sources of oxides of nitrogen. Nitrogen Dioxide (NO2) is one of the most dangerous pollutants there is. It has a red-brown color that one often sees over traffic jams and in fumes coming out of factories. To humans, it is particularly harmful as it directly attacks our respiratory systems. It is toxic to plants too and slows down their photosynthesis rate. [email protected] 2.1 Types of air pollution (gases & particulates) Gaseous Volatile Organic Compounds (VOCs) Pollutants Organic chemicals that have a high vapor pressure at ordinary room temperature. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are released from burning fuel such as gasoline, wood, coal, or natural gas. They are also released from many consumer products: Paints and Hobby and Cigarettes Solvents Adhesives thinners craft supplies Dry cleaning Wood Cleaners and Moth Glues repellants fluids preservatives disinfectants Building Copy Air fresheners materials and machines and Pesticide furnishings printers [email protected] 2.1 Types of air pollution (gases & particulates) PARTICULATE (SOLID & LIQUID STATE) Particulate matter is the sum of all solid and liquid particles suspended in air many of which are hazardous. This complex mixture includes both organic and inorganic particles, such as dust, pollen, soot, smoke, and liquid droplets. These particles vary greatly in size, composition, and origin. Can only be detected using an electron microscope. [email protected]  2.1 Types of air pollution (gases & particulates) Coarse particles The coarse fraction contains the larger Particulate particles with a size ranging from 2.5 to 10 µm Pollutants (PM10 - PM2.5). Produced by the mechanical break-up of larger solid particles. The coarse fraction can include dust from roads, agricultural processes, uncovered soil or mining operations, as well as non-combustible materials released when burning fossil fuels. Fine particles The fine fraction contains the smaller ones with a size up to 2.5 µm (PM2.5). The particles in the fine fraction which are smaller than 0.1 µm are called ultrafine particles. Ultrafine particles (up to 0.1 µm) are formed by nucleation, which is the initial stage in which gas becomes a particle. These particles can grow up to a size of 1 µm either through condensation, when additional gas condensates on the particles, or through coagulation, when two or more particles combine to form a larger particle. [email protected] 2.1 Types of air pollution (gases & particulates) Particulate Pollutants [email protected] 2.1 Types of air pollution (gases & particulates) CLASSIFICATION OF AIR POLLUTANT air pollutant emitted directly Primary pollutant from a source. forms when other pollutants Secondary pollutant (primary pollutants) react in the atmosphere. [email protected] Photochemical Smog Formation [email protected]  Photochemical Smog Formation Primary pollutants – The two major primary pollutants, nitrogen oxides and VOCs, combine to change in sunlight in a series of chemical reactions, outlined below, to create what are known as secondary pollutants. Secondary pollutants – The secondary pollutant that causes the most concern is the ozone that forms at ground level. While ozone is produced naturally in the upper atmosphere, it is a dangerous substance when found at ground level. Many other hazardous substances are also formed, such as peroxyacetyl nitrate (PAN). Major Sources of Photochemical Smog – While nitrogen oxides and VOCs are produced biogenically (in nature), there are also major anthropogenic (man-made) emissions of both. [email protected]  Photochemical Smog Harmful Effects – Photochemical smog can have an effect on the environment, on people’s health and even on various materials. The main visible effect is the brown haze that can be seen above many cities. The brown tinge is caused by very small liquid and solid particles scattering the light. Plants – Chemicals such as nitrogen oxides, ozone and peroxyacetyl nitrate (PAN) can have harmful effects on plants. These substances can reduce or even stop growth in plants by reducing photosynthesis. Ozone, even in small quantities, can achieve this, but PAN is even more toxic to plants than ozone. Materials – Ozone can damage various compounds. It can cause the cracking of rubber, the reduction in tensile strength of textiles, fading of dyed fibres and cracking of paint. Ozone’s potential to damage artworks and books is of cultural importance, and some museums and libraries have taken steps to minimize this effect. [email protected] Photochemical Smog Human Health [email protected] 2.1 Types of air pollution (gases & particulates) CLASSIFICATION OF AIR POLLUTANT [email protected] 2.2 Sources of air pollution (indoor & outdoor air pollution) SOURCE OF AIR POLLUTION NATURAL ANTHROPOGENIC Volcanic eruption Mobile sources Lightning Forest fire - cars, buses, planes, trucks, and Dust storm trains Stationary sources - power plants, oil refineries, industrial facilities, and factories [email protected]  2.2 Sources of air pollution (indoor & outdoor air pollution) Indoor air pollution, also known as household pollution, refers to the chemical, biological, and physical contamination of indoor air. It includes smoke generated from your stove, paint smelling, pet dander and hair, secondhand smoke, dust and fumes of Gasoline from your garage etc. Indoor Pollution [email protected]  2.2 Sources of air pollution (indoor & outdoor air pollution) Indoor Pollution [email protected] 2.2 Sources of air pollution (indoor & outdoor air pollution) Here are some tips and best practices that you can implement to fix indoor air pollution problem. [email protected]  2.3 Dispersion of air pollution Air pollution dispersion – distribution of air pollution into the atmosphere. Sunshine, rain, air temperature and wind can affect the amount of air pollution present: Higher air temperatures - speed up chemical reactions in the air. Wind speed, atmospheric turbulence/stability, and mixing depth - affect the dispersal and dilution of pollutants. Dispersion refers to what happens to the pollution during and after its introduction; understanding this may help in identifying and controlling it. Unstable conditions - level pollution is readily dispersed thereby reducing ground level concentrations. Elevated emissions, however, such as those released from a chimney, are returned more readily to ground level, leading to higher ground level concentrations. Stable conditions - less atmospheric mixing and therefore higher concentrations around ground level sources, but better dispersal rates, and therefore lower ground level concentrations, for elevated plumes. [email protected]  2.3 Dispersion of air pollution Factors Physical nature of effluents that determine Chemical nature of effluents Dispersion Meteorology Location of the stack Nature of terrain downwind from the stack [email protected]  2.3 Dispersion of air pollution Primary factors affecting transport and dispersion of pollutants Atmospheric Wind direction stability - the natural horizontal motion of the atmosphere - caused by differences in pressure in the atmosphere - refers to the vertical motion of the - air moves from high pressure areas to low pressure atmosphere areas - unstable atmospheric conditions result in a - the higher the wind speed, the lower the pollutant concentration vertical mixing, thereby promoting dispersal of polluted air - wind dilutes pollutants and rapidly disperses them throughout the immediate area [email protected]  2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY is the rate at which an atmospheric variable, LAPSE RATE normally temperature in Earth's atmosphere, changes with altitude. Environmental Lapse Rate (ELR) LAPSE RATE TYPES Dry Adiabatic Lapse Rate (DALR) Saturated / Wet Adiabatic Lapse Rate (SALR) Atmospheric stability determines whether or not air will rise and cause storms, sink and cause clear skies, or essentially do nothing. Stability is dependent upon the Dry and Saturated Adiabatic Lapse Rates and the Environmental Lapse Rate. [email protected]  2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY STABILITY Tendency of an air parcel to move vertically following an initial dislocation (up or down). To determine stability, vertical motions of air parcels are assumed to be adiabatic processes. Rising parcels expand and cool, sinking parcels are compressed and warm. An Unsaturated (Dry) parcel will always rise and sink at 9.8˚C/km – known as Dry Adiabatic Lapse Rate. When parcels rise and cool, they will become saturated (Wet). As they continue to rise, the water vapor will condense into liquid water (cloud). So instead of cooling usually around 6˚C /km it is known as Wet Adiabatic Lapse Rate. Ambient Or Environment Lapse Rate: The actual atmospheric temperature change with altitude; not only does water content modify lapse rates, but wind, sunlight on the Earth’s surface, and geographical features change actual lapse rates. [email protected] 2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY STABILITY [email protected]  2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY STABILITY Superadiabatic: ELR > DALR. It indicates unstable atmosphere. Vertical motion and mixing processes are enhanced. Dispersion of pollution plume is enhanced. Tending to rise. Subadiabatic: ELR < DALR. It indicates stable atmosphere, vertical motion, and mixing are suppressed. Dispersion is suppressed, and contamination is trapped. Tending to sink. [email protected] 2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY [email protected]  2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY SUBADIABATIC: ELR < DALR Stable atmosphere Vertical motion, and mixing are suppressed. Dispersion is suppressed, and contamination is trapped. [email protected] 2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY [email protected]  2.3 Dispersion of air pollution LAPSE RATES AND ATMOSPHERIC STABILITY SUPER ADIABATIC: ELR > DALR Unstable atmosphere. Vertical motion and mixing processes are enhanced. Dispersion of pollution plume is enhanced. [email protected]  2.3 Dispersion of air pollution Air pollution emission plume: Flow of pollutant in the form of vapor or smoke released into the air. Plumes are of considerable importance in the atmospheric dispersion modelling of air pollution. Shapes of plumes depends upon atmospheric stability conditions. [email protected]  2.3 Dispersion of air pollution CHIMNEY PLUME DISPERSION In the stable atmosphere case (producing a fanning plume), there is horizontal dispersion at a right angle to the wind due to turbulence and diffusion. In the vertical, dispersion is suppressed by the stability of the atmosphere, so pollution does not spread toward the ground. This results in very low pollution concentrations at the ground. In unstable air, the plume will whip up and down as the atmosphere mixes around (whenever an air parcel goes up, there must be air going down someplace else to maintain continuity, and the plume follows these air currents). This gives the plume the appearance that it is looping around. An inversion a loft will trap pollutants underneath it, since the stable inversion prevents vertical dispersion. Pollution released underneath the inversion layer will fumigate the mixed layer. Note that if the smokestack was high enough to release the pollution within the inversion layer, the plume would fan because the plume occurs within stable air. [email protected] 2.3 Dispersion of air pollution CHIMNEY PLUME DISPERSION [email protected] 2.3 Dispersion of air pollution CHIMNEY PLUME DISPERSION [email protected] 2.3 Dispersion of air pollution CHIMNEY PLUME DISPERSION [email protected]  2.3 Dispersion of air pollution DISPERSION MODEL What is an atmospheric dispersion model? mathematical simulation of means of estimating the physics and chemistry downwind air pollution governing the transport, concentrations, given dispersion and transformation information about the of pollutants in the pollutant emissions and atmosphere nature of the atmosphere. [email protected] 2.3 Dispersion of air pollution DISPERSION MODEL [email protected] 2.3 Dispersion of air pollution [email protected] 2.3 Dispersion of air pollution [email protected] 2.3 Dispersion of air pollution [email protected] 2.3 Dispersion of air pollution DISPERSION COEFFICIENT [email protected] 2.3 Dispersion of air pollution PASQUILL STABILITY TYPES [email protected] 2.3 Dispersion of air pollution EXAMPLE 1 [email protected]  2.3 Dispersion of air pollution ³ S = 32 O + O = 16+16 = 32 SO2 = 32+32 = 64 EXAMPLE 1 [email protected] [email protected] 2.3 Dispersion of air pollution EXAMPLE 1 [email protected] 2.3 Dispersion of air pollution EXAMPLE 1 [email protected]  2.3 Dispersion of air pollution 1 At 3 km EXAMPLE 1 [email protected] 2.3 Dispersion of air pollution 75 EXAMPLE 1 [email protected]  2.3 Dispersion of air pollution STACK DESIGN Variations in stack height and pollutant exhaust velocity are considered to assess their influence on the distribution of pollutant concentrations in the neighbourhood of the emitting building. [email protected] 2.3 Dispersion of air pollution [email protected] 2.3 Dispersion of air pollution [email protected] 2.3 Dispersion of air pollution EXAMPLE 2 [email protected] 2.3 Dispersion of air pollution EXAMPLE 2 [email protected] 2.3 Dispersion of air pollution EXAMPLE 2 [email protected] 2.3 Dispersion of air pollution [email protected]  2.4 Effects of air pollution GLOBAL ISSUES ozone AGRICULTURAL & depletion ECOSYSTEM greenhouse crop losses effect eutrophication biodiversity soil global acidification warming & dimming HEALTH respiratory system nervous system cardiovascular allergy [email protected]  2.4 Effects of air pollution Global warming is a phenomenon of climate change characterized by a general increase in average temperatures of the Earth, which modifies the weather balances and ecosystems for a long time. [email protected]  2.4 Effects of air pollution Global dimming is defined as the decrease in the amounts of solar radiation reaching the surface of the Earth. The by- product of fossil fuels is tiny particles or pollutants which absorb solar energy and reflect back sunlight into space. [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected] 2.4 Effects of air pollution [email protected]  2.4 Effects of air pollution Pollutants can affect cardiovascular health by hardening the arteries and increase the risk of heart attack and strokes, and there is even HUMAN HEALTH emerging evidence that air pollution may be linked to mental health conditions and degenerative brain diseases such as Alzheimer's disease, Parkinson's disease and schizophrenia. Acid rain is a major cause of damage to vegetation, air pollutants which can also be harmful directly. These include sulphur dioxide and ozone. VEGETATION Sulphur dioxide, one of the main components of acid rain, has direct effects on vegetation. MATERIAL The effect of air pollution on materials may be seen in terms of discoloration, material loss, structural failing and soiling. [email protected]  2.5 Measurements of air pollution Units of measurement. Air quality measurement are commonly reported in terms of: micrograms per cubic meter (µg/m³) or parts per million (ppm). High Volume Air Samplers [email protected] 2.5 Measurements of air pollution High Volume Air Samplers [email protected]  2.5 Measurements of air pollution EXAMPLE A clean filter is found to weigh 10.00g. After 24 hours in a hi-vol, the filter plus dust weighs 10.10g. The air flow at the start and end of the test is 60 and 40 ft³/min, respectively. What is the particulate concentration? [email protected] 2.5 Measurements of air pollution [email protected] 2.5 Measurements of air pollution EXAMPLE [email protected]  2.5 Measurements of air pollution Glass Bubbler Gas is literally bubbled through the liquid, which either reacts chemically with the gas of interest or into which the gas is dissolved. Wet chemical techniques are then used to measure the concentration of the gas. [email protected]  2.5 Measurements of air pollution Dark smoke is partially burned particles of fuel, the result of incomplete combustion. It can be dangerous because small particles are absorbed into the lungs. White smoke is mainly tiny water droplets, generated when vapour released during combustion condenses in cool air. Generally, dark smoke is clearly visible against a light sky but difficult to see at night or against a dark background, white smoke is visible in darkness when illuminated but will be more difficult to see against a light sky background. [email protected]  2.5 Measurements of air pollution Ringlemann scale The darker the smoke – the more pollution Not necessarily true – some regulations still written on the basis of smoke density. Ringlemann scale – running from 0 for white or transparent smoke to 5 for totally opaque smoke. The darker the smoke – the more pollution Not necessarily true – some regulations still written on the basis of smoke density. Ringlemann scale – running from 0 for white or transparent smoke to 5 for totally opaque smoke. [email protected]  2.6 Emission Standards and Air Quality Index Air Quality Index An air quality index (AQI) is used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects. The air quality in Malaysia is reported as the API (Air Pollutant Index) Four of the index's pollutant components (i.e., carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide) are reported in ppmv but PM10 particulate matter is reported in μg/m3. [email protected] 2.6 Emission Standards and Air Quality Index Air Pollutant Index of Malaysia [email protected]  2.6 Emission Standards and Air Quality Index Emission Standards Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. They are generally designed to achieve air quality standards and to protect human life. [email protected] 2.6 Emission Standards and Air Quality Index Emission Standards [email protected] 2.6 Emission Standards and Air Quality Index Emission Standards [email protected] 2.6 Emission Standards and Air Quality Index Emission Standards [email protected] week 3. Tuesday 2/4/2014 2.7 Control infrastructure The techniques employed to reduce or eliminate the emission into the atmosphere of substances that can harm the environment or human health. AIR POLLUTION CONTROL SYSTEM INDIVIDUAL AND PUBLIC COMMITMENTS AWARENESS PROGRAMS AND CAMPAIGNS [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants Gaseous Pollutants centrifugal absorber collector bag filter adsorber settling incinerator chambers electrostatic condenser precipitators [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants centrifugal collector Cyclones are best at removing relatively coarse particulates. They can routinely achieve efficiencies of 90 percent for particles larger than about 20 micrometres (μm; 20 millionths of a metre). By themselves, however, cyclones are not sufficient to meet stringent air quality standards. They are typically used as pre-cleaners and are followed by more efficient air-cleaning equipment [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants centrifugal collector [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants bag filter One of the most efficient devices for removing suspended particulates is an assembly of fabric- filter bags, commonly called a baghouse. A typical baghouse comprises an array of long, narrow bags—each about 25 cm (10 inches) in diameter—that are suspended upside down in a large enclosure. A fabric-filter dust collector can remove very nearly 100 percent of particles as small as 1 μm and a significant fraction of particles as small as 0.01 μm. Fabric filters, however, offer relatively high resistance to airflow, which leads to substantial energy usage for the fan system. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants bag filter Operating Priciple: Bag filters use fabric bags to remove particles from dust-laden gas. They can achieve high efficiencies for fine particles because of the build-up of particles on either the inside or outside surface of the bag depending on the design. As dust builds up, the pressure across the bag increases, so the filters need regular cleaning. Usually bag filters work in tandem—one filter is working while the other filter is being cleaned. Mechanical shaking, using a reverse airflow or a pulse of compressed air are used to dislodge the dust from the fabric surface, which then falls by gravity into a collection system. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants settling chambers Simple particulate collection device using the principle of gravity to settle the particulate matter in a gas stream passing through its long chamber. The primary requirement of such a device would be a chamber in which the carrier gas velocity is reduced so as to allow the particulate matter to settle out of the moving gas stream under the action of gravity. This particulate matter is then collected at the bottom of the chamber. The chamber is cleaned manually to dispose the waste. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Particulate Pollutants electrostatic precipitators is a filtration device that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit. Electrostatic precipitators are important tools in the process of cleaning up flue gases. They are highly effective at reducing particle pollution, including those particles whose sizes approximate 1 micron (0.00004 inch) in diameter, and some precipitators can remove particles of 0.01 micron in diameter. In addition, they can handle large volumes of gas at various temperatures and flow rates, removing either solid particles or liquid droplets. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants absorber Absorption involves the transfer of a gaseous pollutant from the air into a contacting liquid, such as water. The liquid must be able either to serve as a solvent for the pollutant or to capture it by means of a chemical reaction. The absorption scrubbers are mostly equipped with a packed bed section, using different types of packing materials for the transfer of the gaseous components from the gaseous phase into the liquid phase, or multiple layer spraying sections using spray nozzles for mass transfer. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants absorber [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants adsorber Adsorption is a mass transfer process in which a porous solid comes in contact with a liquid or gaseous stream to selectively remove pollutants or contaminates by depositing (adsorbing) them onto the solid. The contaminates being removed are referred to as the adsorbate, and the solid doing the adsorbing is called the adsorbent. The most common adsorbents used in industry are activated carbon, silica gel, activated alumina (alumina oxide), and zeolite. Gas adsorption methods are used for odour control at various types of chemical- manufacturing and food-processing facilities, in the recovery of a number of volatile solvents (e.g., benzene), and in the control of VOCs at industrial facilities. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants adsorber Operating Priciple: Adsorption systems are configured either as stationary bed units or as moving bed units. In stationary bed adsorbers, the polluted airstream enters from the top, passes through a layer, or bed, of activated carbon, and exits at the bottom. In moving bed adsorbers, the activated carbon moves slowly down through channels by gravity as the air to be cleaned passes through in a cross-flow current. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants incinerator The process called incineration or combustion— chemically, rapid oxidation—can be used to convert VOCs and other gaseous hydrocarbon pollutants to carbon dioxide and water. Incineration of VOCs and hydrocarbon fumes usually is accomplished in a special incinerator called an afterburner. To achieve complete combustion, the afterburner must provide the proper amount of turbulence and burning time, and it must maintain a sufficiently high temperature. Sufficient turbulence, or mixing, is a key factor in combustion because it reduces the required burning time and temperature. A process called direct flame incineration can be used when the waste gas is itself a combustible mixture and does not need the addition of air or fuel. [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants condenser Is a process used heavily throughout industry to convert a gas or vapor to liquid. Any gas can be reduced to a liquid by sufficiently lowering the temperature (or increasing the pressure). Common examples can include distillation of various hydrocarbons in refining operations and drying of air. Condensation can be used to remove a pollutant from a gas stream if the dew point of the pollutant is higher than the carrier gas (or non-pollutant gas). [email protected]  2.7 Control infrastructure AIR POLLUTION CONTROL SYSTEM Gaseous Pollutants condenser Condensers work when the warmer vapor stream contacts a cooling medium. The heat from the warm gases is transferred to the cooler medium. Then, as the warm gas stream begins to cool, the kinetic energy of the gas is reduced. Condensation occurs because the pollutant molecules are slowed and crowded so close together that the attractive forces between the molecules cause them to condense into a liquid. This phenomenon is known as the van der Waals forces. [email protected] [email protected] [email protected]