Air pollution - types and control devices

Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.

Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases and are important sources of morbidity and mortality.

WHO data show that almost all of the global population (99%) breathe air that exceeds WHO guideline limits and contains high levels of pollutants, with low- and middle-income countries suffering from the highest exposures.

Air quality is closely linked to the earth’s climate and ecosystems globally. Many of the drivers of air pollution (i.e. combustion of fossil fuels) are also sources of greenhouse gas emissions. Policies to reduce air pollution, therefore, offer a win-win strategy for both climate and health, lowering the burden of disease attributable to air pollution, as well as contributing to the near- and long-term mitigation of climate change.

1. Air Pollution Prof. Mrs. D. A. Latthe Dr. J. J. Magdum College of Engineering , Jaysingpur

2. Definition , Sources and classification of pollutants, Effects . Control of industrial air pollution- Settling chamber , Bag filter, Cyclone separator, Scrubbers , Electrostatic precipitators. Air quality standards

3. What is Air Pollution? Air pollution refers to any physical, chemical or biological change in the air. It is the contamination of air by harmful gases, dust and smoke which affects plants, animals and humans drastically. There is a certain percentage of gases present in the atmosphere. An increase or decrease in the composition of these gases is harmful to survival. This imbalance in the gaseous composition has resulted in an increase in earth’s temperature, which is known as global warming.

4. Types of Air Pollutants There are two types of air pollutants: Primary Pollutants The pollutants that directly cause air pollution are known as primary pollutants. Sulphur -dioxide emitted from factories is a primary pollutant. Secondary Pollutants The pollutants formed by the intermingling and reaction of primary pollutants are known as secondary pollutants. Smog, formed by the intermingling of smoke and fog, is a secondary pollutant.

5. Causes of Air Pollution Burning of Fossil Fuels The combustion of  fossil fuels  emits a large amount of sulphur dioxide. Carbon monoxide released by incomplete combustion of fossil fuels also results in air pollution. Automobiles The gases emitted from vehicles such as jeeps, trucks, cars, buses, etc. pollute the environment. These are the major sources of greenhouse gases and also result in diseases among individuals. Agricultural Activities Ammonia is one of the most hazardous gases emitted during agricultural activities. The insecticides, pesticides and fertilisers emit harmful chemicals in the atmosphere and contaminate it.

6. Factories and Industries Factories and industries are the main source of carbon monoxide, organic compounds, hydrocarbons and chemicals. These are released into the air, degrading its quality. Mining Activities In the mining process, the minerals below the earth are extracted using large pieces of equipment. The dust and chemicals released during the process not only pollute the air, but also deteriorate the health of the workers and people living in the nearby areas. Domestic Sources The household cleaning products and paints contain toxic chemicals that are released in the air. The smell from the newly painted walls is the smell of the chemicals present in the paints. It not only pollutes the air but also affects breathing.

7. Effects of Air Pollution Diseases Air pollution has resulted in several respiratory disorders and heart diseases among humans. The cases of lung cancer have increased in the last few decades . Children living near polluted areas are more prone to pneumonia and asthma. Many people die every year due to the direct or indirect effects of air pollution. Global Warming Due to the emission of greenhouse gases, there is an imbalance in the gaseous composition of the air. This has led to an increase in the temperature of the earth. This increase in earth’s temperature is known as  global warming . This has resulted in the melting of glaciers and an increase in sea levels. Many areas are submerged underwater. Acid Rain The burning of fossil fuels releases harmful gases such as nitrogen oxides and sulphur oxides in the air. The water droplets combine with these pollutants, become acidic and fall as acid rain which damages human, animal and plant life.

8. Ozone Layer Depletion The release of chlorofluorocarbons, halons , and hydrochlorofluorocarbons in the atmosphere is the major cause of depletion of the ozone layer. The depleting ozone layer does not prevent the harmful ultraviolet rays coming from the sun and causes skin diseases and eye problems among individuals. Effect on Animals The air pollutants suspend in the water bodies and affect aquatic life. Pollution also compels the animals to leave their habitat and shift to a new place. This renders them stray and has also led to the extinction of a large number of animal species.

9. Settling chamber A settling chamber is a device that uses gravity to remove large particles from a gas stream. It's a simple, low-cost, and effective mechanical collector that's often used to pre-clean gas. 

10. How it works The gas stream enters the chamber at one end  The gas velocity is reduced to allow the particles to settle out of the gas stream  The settled particles collect at the bottom of the chamber  The settled material is collected using hoppers, drag scrapers, or screw conveyers 

11. Settling chamber design Settling chambers are usually long, horizontal, and rectangular  They have an inlet at one end and an exit at the side or top of the opposite end  Flow straighteners are often used at the inlet to ensure uniform flow 

12. Advantages of Settling Chambers: 1. Low capital cost 2. Very low energy cost 3. No moving parts, therefore, few maintenance requirements and low operating costs 4. Excellent reliability 5. Low pressure drop through device 6. Device not subject to abrasion due to low gas velocity 7. Provide incidental cooling of gas stream 8. Temperature and pressure limitations are only dependent on the materials of construction 9. Dry collection and disposal.

13. Disadvantages of Settling Chambers: 1. Relatively low particulate matter collection efficiencies, particularly for particulate matter less than 50 µm in size. 2. Unable to handle sticky or tacky materials. 3. Large physical size; and 4. Trays in multiple-tray settling chamber may warp during high-temperature operations.

14. Cyclone Separator The main body of a cyclone separator is a cylinder and a cone, which is divided into a liquid collection area, a separation area, and a purification room. The gas inlet can be set at the upper, middle, or lower part. When there is a lot of water in the gas that needs to be purified, we use lower intake air; On the contrary, when the gas moisture is low, the upper or middle intake is used. The advantage of the upper intake is uniform gas distribution, but it requires a larger diameter and height of the equipment, which will increase the cost. The middle intake does not require a very high height, which is relatively low in cost.

15. Cyclone Separator Applications The cyclone separator has a simple structure and uses the principle of centrifugal sedimentation to separate particles from the airflow. It can separate solid particles and liquid mist below 5 microns and is a commonly used equipment in mining, cement, chemical and other industries. Industrial Production : In many industrial production processes, cyclone separators are used to remove particles from gases or liquids. For example, in the mining and metallurgical industries, cyclone separators are used for solid-liquid separation in mineral processing and refining processes. Environmental Protectio n: Cyclones are also used in the field of environmental protection. For example, it is used to remove pollutants and dust from the emitted gases.

16. Medical and Pharmaceutical : In the medical and pharmaceutical fields, cyclone separators are used to separate solid drugs and liquid formulations. Food Processing : In the food processing industry, cyclone separators are used to remove solid particles from liquids or gases, such as the separation of flour and coke.

17. Characteristics of Cyclone Separators Long service life of cyclone separator. The cyclone separator has good separation effect. Various types of cyclone separators. The management and maintenance of cyclone separators are relatively simple, requiring only regular inspection and cleaning of the ash discharge port. The manufacturing cost and price of cyclone separators are relatively low

18. Fabric Filter – Baghouse What Industries Use Baghouse Filter? Baghouses , also known as fabric dust collectors or fabric filters, are gas  pollution control  devices designed to remove particulate matter from industrial exhaust gases . They function by drawing dirty stream into the device, passing it through fabric filters that capture and hold the airborne particles, and then returning the cleaned gas to the atmosphere

19. Parts of a Fabric Dust Collector • Inlet: Contaminated flow is introduced into the system. • Filtering Chamber: A space where the pockets are located. • Filter Pockets: Fabric bags that trap particles, allowing clean medium to pass through. • Cages: Metal structures inside the pockets that prevent them from collapsing as stream passes through. • Cleaning System: Mechanisms, such as reverse stream pulses or mechanical vibrators, that periodically clean the pockets. • Outlet: Cleaned air exits the system. •  Dust Hopper : A section or container where the collected particulate is stored for subsequent disposal or removal. • Fan: A device that creates a draft to move contaminated substance through the system and expel cleaned air out.

20. Working Principle The industrial bag house dust collector operates on the principle of using fabric filters to trap pollutants from the incoming air, ensuring that only purified air is discharged from the system. The operating principle involves 2 main stages : Intake of dusty stream into the cleaning channel . The process of gas filtration. Fine particles settle on the fabric of the bags, and the clean gas is vented out through the exhaust pipe . An additional important stage can be identified — the regeneration of filters. During continuous stream cleaning, a layer of fine particles accumulates on the fabric, which can slow down operation. Therefore, it is essential to regularly clean the equipment. There are different cleaning methods, and baghouses are classified based on them.

21. What are the Advantages of Bag house Filters? Higher efficiency, i.e., the degree of gas purification. The ability to clean at any stream pressure, at any concentration of suspended particles, and at high temperatures. Chemically resistant materials are used. Full process automation is possible.

22. Electrostatic Precipitator (ESP) An electrostatic precipitator (ESP) is a device that uses electricity to remove particles from a gas stream. ESPs are used in power generation and industrial applications to remove dust and smoke from the air. 

23. An  electrostatic precipitator  ( ESP ) is a filter less device that removes fine particles, such as dust and smoke, from a flowing gas using the force of an induced  electrostatic charge  minimally impeding the flow of gases through the unit.

24. Working Principle of Electrostatic Precipitator The working principle of the electrostatic precipitator is moderately simple. It consists of two sets of electrodes: positive and negative . The negative electrodes are in the form of a wire mesh, and the positive electrodes are plates. These electrodes are vertically placed and are alternate to each other.

25. Types of Electrostatic Precipitator There are different electrostatic types, and here, we will study each one of them in detail. Following are the three types of ESPs: Plate precipitator:  This is the most basic precipitator type that consists of rows of thin vertical wires and stack of vertically arranged large flat metal plates that are placed at a distance of 1cm to 18cm apart. The air stream is passed horizontally through the vertical plates and then through the large stack of plates. In order to ionize the particles, a negative voltage is applied between the wire and the plate. These ionized particles are then diverted towards the grounded plates using electrostatic force. As the particles get collected on the collection plate, they are removed from the air stream.

26. Dry electrostatic precipitator:  This precipitator is used to collect pollutants like ash or cement in a dry state. It consists of electrodes through which the ionized particles are made to flow through and a hopper through which the collected particles are extracted out. The dust particles are collected from a stream of air by hammering the electrodes. Wet electrostatic precipitator:  This precipitator is used to remove resin, oil, tar, paint that are wet in nature. It consists of collectors that are continuously sprayed with water making the collection of ionized particles from the sludge. They are more efficient than dry ESPs.

27. Tubular precipitator:  This precipitator is a single-stage unit consisting of tubes with high voltage electrodes that are arranged parallel to each other such that they are running on their axis. The arrangement of the tubes could either be circular or square or hexagonal honeycomb with gas either flowing upwards or downwards. The gas is made to pass through all the tubes. They find applications where sticky particles are to be removed.

28. Advantages of electrostatic precipitator: The durability of the ESP is high. It can be used for the collection of both dry and wet impurities. It has low operating costs. The collection efficiency of the device is high even for small particles. It can handle large gas volumes and heavy dust loads at low pressures.

29. Disadvantages of electrostatic precipitator: Can’t be used for gaseous emissions. Space requirement is more. Capital investment is high. Not adaptable to change in operating conditions.

30. Electrostatic Precipitator Applications A few noteworthy electrostatic precipitator applications are listed below: Two-stage plate ESPs are used in the engine rooms of shipboard as the gearbox produces explosive oil mist. The collected oil is reused in a gear lubricating system. Dry ESPs are used in thermal plants to clean the air in ventilation and air conditioning systems. They find applications in the medical field for the removal of bacteria and fungus. They are used in zirconium sand for detaching the rutile in plants. They are used in metallurgical industries to clean the blast.

31. Scrubbers Scrubbers are devices that remove pollutants from air by using liquids or solids to absorb or neutralize contaminants. They are a key technology for reducing air pollution from industrial sources. 

32. How scrubbers work Wet scrubbers : Use liquids to remove pollutants from gas streams. The gas stream passes through a packed bed and downward-flowing liquid sprays. Pollutants are collected in the liquid droplets.  Dry scrubbers : Use solids to remove pollutants from gas streams. 

33. Benefits of scrubbers  Can remove acid gases, particulate matter, and odors Can handle high-temperature, high-humidity gas streams Can reduce the temperature and volume of exhaust streams Can be retro-fitted into existing systems

34. Air quality standards

35. National Clean Air Programme (NCAP) The Central Government has launched the National Clean Air Programme (NCAP) to reduce particulate matter (PM) pollution. NCAP is the first ever effort in the country to frame a national framework for air quality management with a time-bound reduction target. India has an overall target to reduce hazardous PM levels by 20-30% by 2024 from their 2017 levels in 122 cities under the NCAP which was launched in 2019. NAAQS sets limits for SO₂, NO₂, particulate matter (PM2.5 and PM10), Ozone, Lead, Carbon Monoxide, Ammonia, Benzene, Benzo Pyrene , Arsenic, Nickel. Central Pollution Control Board (CPCB) will execute this nation-wide programme in consonance with the section 162 (b) of the Air (Prevention and Control of Pollution) Act, 1986 .

36. The Ministry of Environment, Forest and Climate Change ( MoEFCC ), as a nodal central and apex agency, will have to flex its authority to ensure all NCAP indicators are integrated with multi-sector and inter-ministerial programmes to align with the air quality target and objectives. The plan includes 102 non-attainment cities, across 23 states and Union territories, which were identified by Central Pollution Control Board (CPCB) on the basis of their ambient air quality data between 2011 and 2015. Non-attainment cities are those which have been consistently showing poorer air quality than the National Ambient Air Quality Standards. These include Delhi, Varanasi, Bhopal, Kolkata, Noida , Muzaffarpur , and Mumbai. As part of the programme , the Centre also plans to scale up the air quality monitoring network across India. Approach of NCAP: Collaborative, Multi-scale and Cross- Sectoral Coordination between relevant Central Ministries, State Government and local bodies. Focus on no Regret Measures, Participatory and Disciplined approach.

37. Thank You!