- The following devices are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.
- Settling chamber
- Cyclone separator
- Bag filter
- Electrostatic precipitator
- Catalytic converter
- Ventary scrubber
- These are used to enrich the quality of air by arresting the impurities present in the dust air.
- The central pollution control board recommanded a limiting value for each particulate matter.
Category SPM SO2 NOx CO
Industrial 500 120 120 5000
Residential 200 80 80 2000
Sensitive area 100 30 30 1000
Note : Limiting value measured in Ug/ Nm3.
1. Settling chamber :
- The settling chamber is the simplest type of equipment used for collecting of solid particulates.
- It consists of a chamber in which the gas has to flow from the inlet and descend from the outlet. Among this process velocity of gas is reduced so the particulate matter of gas is reduced so the particulate matter are allow to settle down in the hopper due to gravity and form there the PMs are removed.
Advantages :
- Low initial cost
- Simple construction
- Low maintenance cost
- Low pressure drop
- Dry and continuous disposal of solid particles.
Disadvantages :
- Large space requirement
- Comparatively large particles can be collected only.
2. Cyclonic separator :
- Cyclonic separator utilizes a centrifugal force which is generated by spinning gas stream in the chamber. This process separates the particulate matters from the carrier gas and the carrier gas flow upward in the chamber whereas the particulate matters go down in the hopper due to gravitational force action.
- This process are more effective to remove small size particulate matters than the settling chamber.
- These chambers are shaped like an upside-down cone to promote the collectively of these particulate matters at bottom and cleaned gas escapes from the top of the chamber.
Advantages :
- Low initial cost
- Simple construction
- Low pressure drop
- Low maintenance
- Continuous disposal of solid particles
- Small particulate matters can be collect
Disadvantages :
- Low collection efficiency
- Equipment is subjected to abrasive deterioration.
3. Bag filter/ Fabric filter :
- The bag filter is also known as bag house filter. This system typically comprises a tubular bag which suspended or mounted in a chamber. The structure in which the bags hung is known as bag house.
- Generally dirty gases enters in the bag house and the air is passing through the fabric tubular bag which collect the particulate matters and run the clean air upward where it is escape from the chamber whereas the particulate matters collect by the tubular bag which is further shaking at the fixed intervals of time. While shaking the bag, the PM are fall downward and collected in hopper.
Advantages :
- Very high efficiency
- Retention of fine particles.
- Collection of solid fine particles in dry form.
- Relatively low pressure drop
- Small and fine particles can be collected
Disadvantages:
- Requirement of large space for process
- High construction cost
- Operation below 285 C of the carrier gas.
4. Electrostatic Precipitator :
- Electrostatic precipitator can be defined as a type of air cleaner or filter that utilizes electric energy for removing the impurities, dust particles from the air.
- It consists vertical wire which is placed in between parallel plates. A strong electric field is created between the wires and the plates by impressing a high negative voltage on the wires. The negatively changed electrode generates free electrons which move towards the plate and on the way it attach some particulate matters. The particles now carry a charge which cause them to move under the influence of the electric field to the surface of the plates. Eventually, they are removed by the gravitational action or by the flashing the collecting plates with liquid.
Advantages :
- Less power consumption
- Economical and easy to operate
- Highly efficiency obtained
- Very fine particles can be collect
Disadvantages :
- High initiate cost
- Large space required
- Required skill person for operating due to high voltage operations.
5. Catalytic converter :
- Catalytic ocnverter is the most modern car equipped with three way converter. The three way refers to that the device converts three harmful compounds in car exhaust into the harmless compounds.
- These harmful compounds are carbon monoxide, Volatile organic carbon and oxides of the nitrogen.
- To convert these compounds into harmless compound it uses two different type of catalysts namely, reduction catalyst and oxidation catalyst.
- Usually platinum, rhodium and palladium are used as catalysts.
- In the catalytic converter, three steps are used.
- Reduction
- Oxidation
- Control system
1. Reduction :
In this step, the platinum and rhodium are used as catalystis. In this step, oxides of nitrogen are converted into harmless nitrogen molecule as follows.
2NO ----- N2 + O2
2NO2 ----- N2 + 2O2
2. Oxidation :
In this step,the plantinum and palladium are used as catalyst. In this step, carbon monoxide and volatile organic carbon are converted into carbon dioxide as per the following reactions.
2CO + O2 -------- 2CO2
4HC + 5O2 ------- 4CO2+2H2o
3. Control system :
The third step of catalyst converter is control stage. In which, air to fuel ratio is controlled eith the help of oxygen sensor. This sensor is placed upper in the catalyst converter. It manages the oxygen and follows the increase and decrease of oxygen as per requirement.
Advantages :
3. Control system :
The third step of catalyst converter is control stage. In which, air to fuel ratio is controlled eith the help of oxygen sensor. This sensor is placed upper in the catalyst converter. It manages the oxygen and follows the increase and decrease of oxygen as per requirement.
Advantages :
- Reduction of harmful gases emitted into atmosphere.
- Small size and easy mechanism inside the car.
Disadvantages :
High initial cost- High maintenance
- Require high temperature for proper functioning.
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