MEV 015: Unit 09 - Air Pollution and Its Control

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Unit 9: Air Pollution and Its Control

9.1 Introduction

Air pollution is one of the most serious environmental problems faced by the modern world. It occurs when harmful gases, dust, smoke, or other particles are released into the atmosphere, making the air unsafe for living beings. Air pollution affects health, damages property, and harms ecosystems. This unit focuses on various methods used to control and reduce air pollution, especially from industries and vehicles.

9.2 Objectives

The main goals of this unit are to:

·         Explain different methods used to control particulate and gaseous air pollutants

·         Understand how each method works and where it is used

·         Learn about technologies to control harmful gases like sulphur dioxide and nitrogen oxides

·         Explore solutions for reducing volatile organic compounds (VOCs) in the air

9.3 Control Measures for Particulate Pollutants

Particulate pollutants are tiny solid or liquid particles suspended in the air. Common examples include dust, smoke, and ash. Various mechanical and technical methods are used to remove them:

Gravitational Settling

This method uses gravity to remove large and heavy particles from the air by slowing down the airflow, allowing particles to settle at the bottom.

Cyclonic Separation

In this method, air is made to spin rapidly in a circular chamber. The spinning force pushes heavier particles to the walls, where they fall down and are collected.

Filtration

Air is passed through filters made of cloth or other materials, which trap the solid particles while allowing clean air to pass through. This method is common in industries.

Wet Scrubbing

This method uses water or liquid sprays to trap and remove dust and pollutants from the air. The pollutants get captured in the water droplets and are removed as sludge.

Electrostatic Precipitation

This method uses electric charges to remove particles. Polluted air is passed through charged plates which attract and collect the particles. It is very effective for fine dust and smoke from power plants.

9.4 Control Measures for Volatile Organic Compounds (VOCs)

VOCs are gases released from chemicals, fuels, and industrial solvents. They can cause smog and health problems. Methods to control VOCs include:

Absorption in Suitable Liquids

Polluted air is passed through a liquid that absorbs the harmful gases. The liquid absorbs VOCs and prevents them from escaping into the air.

Condensation

In this method, the temperature of the gas is lowered so that the VOCs turn into liquid and can be collected. It is mainly used when the concentration of VOCs is high.

Adsorption

Polluted air is passed over solid materials (like activated carbon) that attract and hold the VOCs on their surface.

Incineration

VOCs are burned at high temperatures in special chambers. This converts the harmful gases into less harmful substances like carbon dioxide and water.

9.5 Control Measures for Gaseous Emissions

Industrial processes and vehicles emit harmful gases such as sulphur dioxide (SO₂) and nitrogen oxides (NOₓ). These gases cause acid rain, respiratory problems, and smog. Their control requires special techniques:

Control of Sulphur Dioxide (SO₂)

·         Flue Gas Desulphurization (FGD): This is a popular method where SO₂ is removed from exhaust gases using lime or limestone.

·         Use of low-sulphur fuels: Using fuels that contain less sulphur reduces SO₂ emissions.

·         Switching to cleaner energy sources like natural gas, solar, and wind also helps reduce SO₂ levels.

Control of Nitrogen Oxides (NOₓ)

·         Selective Catalytic Reduction (SCR): This method uses ammonia and a catalyst to convert NOₓ into nitrogen and water.

·         Low NOₓ burners: These are specially designed burners that reduce the formation of nitrogen oxides during combustion.

·         Exhaust Gas Recirculation (EGR): In this method, a part of the exhaust gas is returned to the engine cylinder to lower the combustion temperature and reduce NOₓ formation.

9.6 Let Us Sum Up

Air pollution can be controlled by using scientific and technical methods. Particulate matter can be removed through gravitational settling, cyclonic separation, filtration, wet scrubbing, and electrostatic precipitation. VOCs can be controlled using absorption, condensation, adsorption, and incineration. Harmful gases like SO₂ and NOₓ can also be reduced using advanced technologies. Effective air pollution control is essential for cleaner air, better health, and a safer environment.

 

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