(Aktu Btech) Air and Noise Pollution Control Important Unit-3 Air Pollution Control

We’re here to look at the most essential Air and Noise Pollution Control important, repeated questions and notes that may appear in your upcoming exams, such as Btech and others. Unit-3 Air Pollution Control

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Important Questions For Air and Noise Pollution Control:
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Q1. What are the objectives of stack sampling at origin of pollution ? 

Ans. Objectives of Stack Sampling:

• 1. Gathering samples of petrol emission at the source is the most crucial task. The term “stack sampling at the source of pollutants” also applies to this gathering of samples.
• 2. To obtain comprehensive statistics on the air pollution emission in a certain area, emission inventories data are carefully gathered. 
• 3. The main objects of the sampling at source are:
  • i. To gauge the level and output of pollutants according to their source.
  • ii. To assess the effectiveness and quality of control devices under diverse circumstances.
  • iii. To calculate the emission as a result of modifications to the industry’s processes and raw materials.
  • iv. To implement a local control system at the location.
  • v. To gather information from a single pollutant source or several pollutant sources.
  • vi. To understand the type of pollutant source.
  • vii. To ascertain the impact on the polluting source’s emission in various climatic conditions.
  • viii. To ascertain the impact of emissions in various regions/zones of the nation.

Q2. Write the steps of procedure for particular matter sampling.

Ans. Procedure for Particular Matter Sampling: The NEERI (N ational Environmental Engineering Research Institute) has given the procedure for the collection of particulate matter sampling: 

• 1. Rectify the moisture content and determine the petrol composition.
• 2. Get the velocity and temperature at each traversal point.
• 3. Establish the weight thimble’s empty value (W1).
• 4. On the probe, indicate the traverse points. By using asbestos thread when typing, the marks are permanently fixed.
• 5. Inspect for leakages at every site.
• 6. Calculate the sample flow rate under isokinetic conditions.
• 7. Place the probe right next to the stack, at traversal point 1. Launch the pump, then modify the flow so that the rotameter displays the desired value.
• 8. At the conclusion of the sample period, turn off the pump.
• 9. Check the temperature and hoover at the dry gas metre (DGM).
• 10. Repeat steps 5 through 8 to move the probe to the following traverse sites.
• 11. Remove the probe and let it cool after the sample collection is finished.
• 12. Carefully remove the thimble. A portion of the dust would stick to the nozzle. Tap them off and then transfer them to the thimble.
• 13. Weigh the sample-filled thimble. The dust is given by the weight difference.
• 14. The volume of the sample that was collected, as determined by a dry gas metre or by a rotameter, multiplied by the sampling duration. 
• 15. Hence from (12) and (13) the emission rate can be calculated. This will give DGM conditions. This is to be corrected for temperature and pressure so as to obtain for standard conditions. 

Q3. Explain in detail “Cyclones Equipments” which is used to control air pollutants.

Ans. Cyclones Equipments:

• 1. It consists of a cylinder with a bottom-facing inverted cone.
• 2. The petrol particles tangentially enter the cylinder from the top.
• 3. After that, vertex separators are used. Gravity and the rotating effect are employed to separate mixtures of solids and liquids.
• 4. In commercial and industrial kitchens, a cyclone is used to separate grease from exhaust air and rotates the particles at a very high speed. 

• 5. In order to remove particles, a cyclone generates a high-speed spiral air flow. The particles experience a centrifugal force as a result of this spiral motion.
• 6. The particles are pushed to the cyclone’s outer walls by their own inertia, where they fall to the ground and are collected.
• 7. Particle removal is influenced by the cyclone’s width and airflow speed. The removal of particles is more effective the smaller the diameter.
• 8. A better removal of tiny particles is achieved because to the conical portion at the cyclone’s base, which gradually reduces the diameter of the spinning gas stream.
• 9. However, in practice, reducing the diameter increases the pressure drop across the cyclone. Combining several units together as a ‘multi-cyclone’ can prevent this.  
• 10. Its efficiency depends on the generated centrifugal force (F_c), which in turn, depends on mass of the particles (M_p), inlet gas velocity (v_i) and radius of cyclone (R), and is given by. 

• 11. A dynamic precipitator is 11th. Fig. imparts centrifugal force to the entering gas with the help of revolving vanes, and is, thus, about 7 times more effective than a standard ceylon.
• 12. This type of equipment can function as both an exhaust fan and a dust collector.
• 13. They are frequently used in ceramics, culinary and pharmaceutical sectors, and woodworking.
• 14. They are unable to manage moist fibrous debris that tends to build on the moving vanes.

Q4. What are the advantages and disadvantages of scrubber equipments ? 

Ans. A. Advantages of Scrubbers: Following are the advantages of scrubbers: 

• 1. Separating dirt from ambient air is a pretty efficient technique.
• 2. It can safely manage combustible and explosive dusts.
• 3. It combines gas absorption and dust collecting in one device.
• 4. It provides cooling by the use of hot gases.
• 5. It can neutralise corrosive and dusting agents.

B. Disadvantages of Scrubbers: Following are the disadvantages of scrubbers: 

• 1. There is a high risk of rusting.
• 2. Waste sludge disposal might be quite costly.
• 3. Collected particle may be polluted and unsuitable for recycling.
• 4. Make-up water is required to replace purged liquid and discarded sludge. 

Q5. Explain the bag house or fabric filters, used to control air pollution. 

Ans. Bag House or Fabric Filters:

• 1. In this system, the flue gas is permitted to pass through a woven or felted cloth, which filters out particulate matter while still allowing the gas to pass.
• 2. Tiny particles are trapped on the fabric, first through interception and electrostatic attraction, and then, when a dust mat forms, the cloth begins to gather particles more efficiently.
• 3. A bag house filter unit, shown in Fig. 3, is housed in an ordinary industrial room and contains numerous vertically hanging fabric cylinder bags (1.8 to 9 m long); the upper ends of the bags are closed, and the lower ends are coupled to a hopper, which also houses the flue gas input. 

• 4. The upwardly flowing gas deposits particulate matter in these bags, which settles into the hopper, while cleaner gas exits via the fabric filters.
• 5. The framework that houses the hanging bags has an automatic shaking system that cleans the bags of dust.
• 6. Bag houses, as compared to other types of air pollution control equipment, are extremely versatile and can be constructed for practically any dust producing application by modifying size and bag types.  
• 7. They are incredibly efficient when properly maintained, and they are also tough enough to withstand demanding applications.
• 8. However, they often necessitate a lot of upkeep and a relatively dry climate to function properly.
• 9. Its application is likewise restricted to specific operating temperatures and chemical conditions.

Q6. What are the equipments used to control air pollution in industries ? Describe any one of them.  

Ans. Air Pollution Controlling Equipments: 

Following are the equipments used to control air pollution in industries: 

• 1. Gravity settling chamber.
• 2. Scrubbers.
• 3. Cyclones.
• 4. Bag house filters. 
• 5. Electrostatic precipitator. 

Electrostatic Precipitator Equipment: 

• 1. The electrostatic precipitator uses an electrostatic charge to remove particles and smoke from a gas stream.
• 2. Electrostatic precipitators are often big, low-velocity dust collectors.
• 3. With this transformer, extremely high voltage is generated between charging electrodes and collecting plates.
• 4. Electrostatic precipitators are divided into two sections: charging and collecting.
• 5. In the charging section, incoming smoke, grease, mist, and other particulates pass through ioniser wires, which give these contaminants a positive electrical charge.
• 6. The positively charged pollutants are subsequently dragged into the collection section, which includes a secondary electrical field made up of negatively charged aluminium plates. 
• 7. Since opposing charges attract, positively charged impurities gather on negatively charged aluminium plates; the collected dust is periodically lifted off the collecting plates by a hammer device and dropped into a bottom hopper for removal.
• 8. ESP removal efficiencies vary greatly; however, for very small particles alone, the removal efficiency is approximately 99 percent.
• 9. ESPs are utilised in boilers, furnaces, and a variety of other units in thermal power plants, cement plants, steel plants, and so on.

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